JP7822984B2 - Active material, electrode, secondary battery, battery pack, and vehicle - Google Patents

Description

Embodiments of the present invention relate to active materials, electrodes, secondary batteries, battery packs, and vehicles.

In recent years, research and development of high-energy density secondary batteries, such as lithium-ion secondary batteries and non-aqueous electrolyte secondary batteries, has been actively pursued. Secondary batteries are expected to be used as power sources for vehicles such as hybrid and electric vehicles, as well as for uninterruptible power supplies in mobile phone base stations. Therefore, in addition to energy density, secondary batteries are also required to have excellent performance in other areas, such as rapid charge/discharge capability and long-term reliability.

Typical lithium-ion battery anodes include carbon-based anodes, which use carbonaceous materials such as graphite as the active material. Repeated rapid charge/discharge cycles of batteries using carbon-based anodes can lead to the formation of metallic lithium dendrites on the electrode, potentially resulting in internal short circuits and fires. Therefore, batteries with higher anode operating potentials have been developed by replacing carbonaceous materials with metal composite oxides. For example, batteries using spinel-type lithium-titanium composite oxide ( _{Li4Ti5O12 )} as anodes have a high average operating potential of 1.55 V (vs. Li _/ Li ⁺ ), which prevents the formation of lithium dendrites, enabling stable rapid charge/discharge. Furthermore _, they operate at potentials where electrolyte reduction side reactions are unlikely to occur, resulting in longer lifespans compared to batteries using carbon-based _anodes . However, batteries using _Li4Ti5O12 as anodes have a low theoretical capacity of 175 mAh/g, resulting in lower energy density compared to batteries with carbon-based anodes.

Therefore, monoclinic niobium titanium oxide TiNb ₂ O ₇ is being investigated. It is an active material that exhibits high capacity while having an operating potential of approximately 1 V (vs. Li/Li ⁺ ) based on the oxidation-reduction potential of lithium. Therefore, it is expected to achieve a volumetric energy density that exceeds that of carbon-based anodes. However, in order to fully popularize electric vehicles, it is desirable to further increase the energy density of lithium-ion secondary batteries from the perspective of improving driving range, and there is a need to develop even higher-capacity, fast-charging batteries.

JP 2012-99287 A Japanese Patent Application Laid-Open No. 2021-061223 International Publication No. 2019/234248

Nature, 559, 556-563(2018) J. Mater. Chem. A, 2019, 7, 6522-6532 International Tables for Crystallography (2006). 1st online ed. Chester: International Union of Crystallography. "Practice of Powder X-ray Analysis" First Edition (2002) Edited by the X-ray Analysis Research Forum of the Japan Society for Analytical Chemistry, edited by Izumi Nakai and Fujio Izumi (Asakura Shoten)

The purpose of the embodiments is to provide active materials and electrodes that can realize high-capacity secondary batteries, high-capacity secondary batteries and battery packs, and vehicles equipped with such battery packs.

According to an embodiment, an active material is provided that includes a composite oxide having a structure in which a plurality of rhenium oxide type blocks of different sizes are connected aperiodically at least by octahedral edge-sharing. The rhenium oxide type blocks include an octahedral structure composed of oxygen and a metal element, and are configured by corner-sharing of the octahedral structure. The composite oxide is represented by the general formula _LiaMbNbMocOd , where M _is any one _{or more} selected from the group consisting of Ti, V, Ta, Fe, Co, Mn, Ni, Bi, Sb, As, P, Cr, W, B, Na, K, Mg, Al, Ca, Y, and Si, and 0≦a≦b+2+3c, 0≦b≦1.5, 0≦c≦0.5, and 2.33≦d/(1+b+c)≦2.50.

According to another embodiment, an electrode containing the above-described active material is provided.

According to yet another embodiment, a secondary battery is provided comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode or the negative electrode is the electrode described above.

According to yet another embodiment, a battery pack including the above-described secondary battery is provided.

Furthermore, according to an embodiment, a vehicle equipped with the above-mentioned battery pack is provided.

2A and 2B are schematic diagrams showing examples of crystal structures that may be contained in a composite oxide contained in an active material according to an embodiment. 2 is a schematic diagram showing an example of a crystal structure contained in a composite oxide contained in an active material according to an embodiment. FIG. 1 is a cross-sectional view schematically illustrating an example of a secondary battery according to an embodiment. FIG. 4 is an enlarged cross-sectional view of a portion A of the secondary battery shown in FIG. 3 . FIG. 10 is a partially cutaway perspective view schematically showing another example of a secondary battery according to an embodiment. FIG. 6 is an enlarged cross-sectional view of part B of the secondary battery shown in FIG. 5 . FIG. 1 is a perspective view schematically illustrating an example of a battery pack according to an embodiment. FIG. 1 is an exploded perspective view schematically showing an example of a battery pack according to an embodiment. FIG. 9 is a block diagram showing an example of an electrical circuit of the battery pack shown in FIG. 8 . 1 is a partially see-through view schematically illustrating an example of a vehicle according to an embodiment. 1 is a diagram illustrating an example of a control system for an electrical system in a vehicle according to an embodiment; 2 is a graph showing a spectrum obtained by wide-angle X-ray scattering measurement of the composite oxide of the active material in Example 1. 1 is a graph showing a spectrum obtained by wide-angle X-ray scattering measurement of the composite oxide of the active material in Example 2. 1 is a graph showing a spectrum obtained by wide-angle X-ray scattering measurement of the composite oxide of the active material in Example 3. 1 is a graph showing a spectrum obtained by wide-angle X-ray scattering measurement of the composite oxide of the active material in Comparative Example 1. 1 is a graph showing enlarged spectra obtained by wide-angle X-ray scattering measurement of the composite oxides of the active materials in Examples 1 to 3 and Comparative Example 1. Graph showing initial charge-discharge curves in Examples 1-3 and Comparative Example 1.

To obtain a high-capacity material, it is desirable to select a material that has a large amount of charge compensation when carrier ions (e.g., lithium ions) are inserted. For this reason, a composite oxide containing molybdenum (Mo), a hexavalent element, can be used as an even higher-capacity compound. However, there have been no reports of molybdenum-niobium composite oxide materials with a high molybdenum content being used as battery materials.

Embodiments will be described below with reference to the drawings. In the following description, components that perform the same or similar functions will be given the same reference numerals throughout the drawings, and duplicate explanations will be omitted. Note that each figure is a schematic diagram intended to explain and facilitate understanding of the embodiments, and while the shapes, dimensions, ratios, etc. may differ from those of the actual device, these can be modified as appropriate in light of the following description and known technology.

(First embodiment)
According to a first embodiment, an active material is provided that includes a composite oxide having a structure including multiple rhenium oxide blocks of different sizes. The rhenium oxide blocks are connected aperiodically at least by octahedral edge-sharing. The rhenium oxide blocks include an octahedral structure composed of oxygen and a metal element. The octahedral structure is also configured by corner-sharing. The composite oxide is represented by the general _{formula LiaMbNbMocOd} . In the general formula, M is at least one selected from the group consisting of Ti, _V , Ta, Fe, Co, Mn, Ni, Bi, Sb, As, P, Cr, W, B, Na, K, Mg, _Al , Ca, Y, and Si. The subscripts in the formula satisfy the following conditions: 0≦a≦b+2+3c, 0≦b≦1.5, 0≦c≦0.5, and 2.33≦d/(1+b+c)≦2.50, respectively.
Furthermore, the subscript b may be in the range of 0≦b≦1.4.

The active material may be a battery active material. For example, the active material may be an electrode active material used in the electrodes of secondary batteries such as lithium-ion batteries and nonaqueous electrolyte batteries. More specifically, the active material may be, for example, a negative electrode active material used in the negative electrode of a secondary battery.

A high-capacity secondary battery can be realized by using a composite oxide represented by the general formula Li _a M _b NbMo _c O _d (the element M and each subscript are as described above; hereinafter omitted) and having a structure including the above-mentioned rhenium oxide-type block structure as an electrode active material.

<Crystal structure>
The composite oxide contained in the active material according to the first embodiment corresponds to a part of oxide materials having a Wadsley-Roth phase structure, which is a crystalline phase in oxide materials containing niobium. It has been reported that the Wadsley-Roth phase has a crystalline structure in the range of 2.33≦ _AO / _AM ≦2.65, where _AO and _AM are the number of oxygen atoms and the number of metal element atoms, respectively. For example, _TiNb2O7 has a crystalline structure on the reduction side _, where _AO / _AM = 2.33.

Here, "reduced" refers to a low proportion of oxygen within the structure. The Wadsley-Roth phase is a crystal structure in which the corner-sharing structures of oxygen-metal octahedra form rhenium oxide-type block structures, with the blocks sharing rhombohedrons or tetrahedrons interposing and sharing corners, resulting in two-dimensional connections between the rhenium oxide-type blocks ( _ReO3 -type blocks). The reduced crystal structure has small rhenium oxide-type blocks. Although the rhenium oxide-type crystal structure has voids that can accommodate large amounts of Li, its highly symmetric structure makes it difficult for the bond length between the metal and oxygen elements to change to resolve charge repulsion upon Li insertion. Therefore, the charge repulsion upon Li insertion restricts Li insertion. Here, the reduced crystal structure reduces the _A0 / _A0M ratio, thereby reducing the number of oxygen atoms in the structure and reducing the size of the rhenium oxide-type blocks. As a result, the crystal structure can expand in volume due to the change in bond length between the metal and oxygen elements upon Li insertion. For this reason, the inclusion of a rhenium oxide-type crystal structure allows for a large gap, but there are no restrictions on the structural changes that occur when Li is inserted, allowing for a large amount of Li insertion.

The composite oxide contained in the active material according to the first embodiment also has a reduced crystal structure like TiNb ₂ O ₇ , which allows more lithium (Li) to be inserted into the crystal structure, resulting in a crystal structure with a large reversible capacity. In other words, the crystal structure of this composite oxide is a reduced crystal structure belonging to the Wadsley-Roth phase consisting of three elements including niobium, molybdenum, and the metal element M.

_{Figure 1 shows a schematic diagram of an example of a crystal structure that a composite oxide represented by the general formula LiaMbNbMocOd may contain} . In this example, the ratio of the number of oxygen _O atoms, _A0 , to the number of metal element M _atoms , _{A1 ,} is 2.50. Figure 1 shows the crystal structure in a unit cell in the [001] direction as viewed along the c-axis. The space group notation for the crystal structure belongs to I ^- 4, and the space group number assigned is 82. The space group referred to here corresponds to the contents of the International Tables for Crystallography (Non-Patent Document 3), specifically, Vol. A: Space-group symmetry (Second Online Edition (2016); ISBN: 978-0-470-97423-0, doi: 10.1107/97809553602060000114). However, the space group can also be explained by assignment to a simple cubic lattice with a four-fold symmetry axis or four-fold anti-axis similar to I ^- ₄ (space group number 82), such as P4 (space group number 75), I4 (space group number 79), P ^- ₄ (space group number 81), P42 ^/ n (space group number 86), I4 ^/ m (space group number 87), P4nc (space group number 104), P-421c (space group number 114), or P-4n2 (space group number 118). This may change if the stoichiometric composition is deviated by adjusting the composition ratio or if the structure is distorted due to the presence of a different phase. Crystal structure 10 contains octahedra 10a and tetrahedra 10b, each composed of metal element 18 and oxygen element 19. The octahedra 10a are connected to each other by corner-sharing to form rhenium oxide-type blocks (ReO3 _- type blocks). The size of the block is 3 x 3 = 9 octahedra 10a. The nine-unit rhenium oxide block forms planes in the a-axis and b-axis directions by sharing the edges of the octahedra 10a or the vertices of the tetrahedra 10b. A crystal structure is formed by connecting multiple planes including these nine octahedra 10a on the c-axis side by octahedral edge sharing or tetrahedral vertex sharing.

Figure 2 shows a schematic diagram of another example of a crystal structure _that a composite oxide _represented by the general _{formula LiaMbNbMocOd} may contain. Figure 2 shows the structure viewed from the stacking direction of the _ReO3 blocks. The _ReO3 blocks enclosed by thick lines (e.g., block 15a) and the _ReO3 blocks indicated only by thin lines (e.g., block 15d) differ in the plane on which the metal elements 18 are arranged. This example is characterized by the absence of structural periodicity. Blocks of different sizes are connected according to the Wadsley-Roth phase arrangement. The smallest blocks have two sides, while the largest have six sides. For example, block 15a consists of 3 x 3 octahedrons 11a, block 15b consists of 2 x 3 octahedrons 11a, block 15c consists of 2 x 4 octahedrons 11a, block 15d consists of 2 x 2 octahedrons 11a, block 15e consists of 3 x 6 octahedrons 11a, block 15f consists of 5 x 3 octahedrons 11a, and block 15g consists of 4 x 4 octahedrons 11a. These sizes can be freely adjusted depending on the metal/oxygen ratio resulting from the mixed state of the elements M, Nb, and Mo, and are not limited thereto. The majority are connected by octahedral edge-sharing 17, but some may also include tetrahedral vertex-sharing by tetrahedra 11b. Compared to Figure 1, there are fewer tetrahedra, and as tetrahedral vertex connections are replaced by octahedral edge connections, the number of octahedral edge-sharing increases, resulting in increased octahedral lattice distortion. The large lattice distortion of the octahedron facilitates structural relaxation due to changes in bond length during Li insertion, making it possible to increase the amount of Li insertion. Furthermore, because the octahedral edge-sharing is included without a periodic structure, the asymmetry of the framework is maintained even when the amount of Li insertion is increased. Therefore, the crystal structure in Figure 2 has an even higher reversible capacity than the crystal structure in Figure 1. Therefore, by incorporating the crystal structure in Figure 2 into the active material, it is possible to improve the capacity.

In the crystal structure shown in Figure 2, the metal/oxygen ratio, which changes with the composition ratio, can be adjusted by changing the size of the _ReO3 -type block and the number of octahedral edge-sharing or tetrahedral vertex-sharing connections. Therefore, the oxygen/metal ratio can be changed by the composition ratio, and can be freely adjusted within _the composition range of _the general _{formula LiaMbNbMocOd} .

Molybdenum (Mo) can be incorporated into the crystal structure not only in a hexavalent state but also in a tetravalent or pentavalent state. The valence of Mo is determined by adjusting the charge balance depending on the amount of metal elements other than Mo and the amount of oxygen in the crystal structure shown in Figure 1 or Figure 2. With a hexavalent element, charge compensation during Li insertion with an M element such as Ti is a three-electron reaction, thereby increasing the theoretical capacity of Li that can be inserted. Elements in a tetravalent or pentavalent state are arranged in the crystal structure by supplying electrons to the d band of the Mo element. Therefore, the inclusion of a tetravalent or pentavalent Mo element can change the conductivity and improve battery performance. Wadsley-Roth phases containing molybdenum are known to have a higher operating potential (become noble). Comparing oxides containing titanium and niobium, for example, the titanium-niobium-molybdenum composite oxide, which is one aspect of the first embodiment, has a crystal structure containing a high concentration of molybdenum, thereby enabling a higher operating potential than _{TiNb2O7 .} As a result, the operating potential is in a potential range where there is little reduction side reaction of the electrolyte, and therefore a long life performance can be achieved.

The valence of Mo may be higher within the crystal structure than the valence estimated from the crystal structure in Figure 1 or Figure 2 and the balance between the amount of oxygen and the metal element. In this case, it is presumed that cation vacancies are formed within the crystal structure and included within the structure to adjust the charge balance. By including cation vacancies within the structure, the electronic conductivity of the active material is improved, thereby improving battery performance. On the other hand, because cation vacancies have the effect of locally capturing Li within the structure, excessive cation vacancies are undesirable from the perspective of inhibiting Li migration within the solid.

In addition, in such active materials, it is possible to create oxygen vacancies by reducing the amount of Mo element from the ideal composition. Creating oxygen vacancies improves the electronic conductivity of the active material, thereby improving battery performance. On the other hand, too many oxygen vacancies cause charge repulsion of Li. Therefore, too many oxygen vacancies are undesirable because they inhibit the mobility of Li.

In the general formula Li _a M _b NbMo _c O _d , the subscript d reflects the amount of cation vacancies and oxygen vacancies.

The structure shown in Figure 2 can be confirmed by observation using a scanning transmission electron microscope with a high-angle annular dark-field method, as described below. Furthermore, the compositional state of the crystalline structures contained in the complex oxides shown in Figures 1 and 2 can be estimated based on the diffraction pattern (diffraction spectrum) of powder X-ray diffraction using a Cu-Kα radiation source. In the diffraction spectrum of powder X-ray diffraction using a Cu-Kα radiation source, the intensity ratio between the peak intensity I1 of the most intense peak P1, which appears within the range of 2θ = 25.05 ± 0.25°, and the peak intensity I2 of the most intense peak P2, which appears within the range of 2θ = 24.00 ± 0.2°, indicates the degree to which the crystalline structure of Figure 1 and the crystalline structure of Figure 2 are mixed in the complex oxide.

The position of peak P2 does not change significantly between the crystal structures shown in Figures 1 and 2 because there is no significant difference in the length along the stacking axis. Because the peak positions overlap, it appears as if there is a single peak. Meanwhile, the main peak for the structure shown in Figure 1 appears at 2θ = 25.4 ± 0.10 and is assigned to the (420) plane. However, due to changes in the crystal structure, the main peak position, due to the apparent average period along the planar direction of the _ReO3 blocks, shifts toward lower angles in the structure shown in Figure 2. When I1/I2 ≦ 0.1, the crystal structure of the composite oxide is primarily composed of the structure shown in Figure 1. When I1/I2 > 0.1, at least a portion of the crystal structure has changed to the crystal structure shown in Figure 2. Furthermore, when I1/I2 ≧ 1, the structure shown in Figure 2 may occupy the majority of the crystal structure of the composite oxide.

A composite oxide represented by the general formula Li _a M _b NbMo _c O _d can contain, in addition to the metal elements Nb and Mo, a different element M. The structure shown in Figure 2 can maintain the oxygen/metal composition ratio due to charge compensation by changing the size of the ReO ₃ -type blocks and by varying the octahedral edge-sharing and tetrahedral corner-sharing at the connecting portions. The valence of Mo can be adjusted from tetravalent to hexavalent and incorporated into the structure. Furthermore, as mentioned above, such active materials can easily create oxygen vacancies and cation vacancies within the structure. This allows for a high degree of freedom in adjusting the charge balance within the structure, allowing for the free selection of element M. The element M can be at least one selected from the group consisting of Ti, V, Ta, Fe, Co, Mn, Ni, Bi, Sb, As, P, Cr, W, B, Na, K, Mg, Al, Ca, Y, Zr, and Si. In the above general formula, the subscript b can, for example, satisfy the condition 0<b.

The M element may be included in the crystal structure, for example, as a metal element constituting the tetrahedron or octahedron described above. The M element may also exist in the active material in a form that is not included in the crystal structure of the composite oxide.

For example, vanadium (V) and phosphorus (P) can be incorporated into the crystal structure as pentavalent elements. Titanium (Ti), zirconia (Zr), and silicon (Si) can be incorporated into the structure as tetravalent elements. Iron (Fe), chromium (Cr), aluminum (Al), bismuth (Bi), antimony (Sb), boron (B), arsenic (As), cobalt (Co), manganese (Mn), nickel (Ni), and yttrium (Y) can be incorporated into the crystal structure as trivalent elements. Magnesium (Mg) and calcium (Ca) can be incorporated into the crystal structure as divalent elements. Potassium (K) and sodium (Na) can be incorporated into the crystal structure as monovalent elements. Of these elements, tetravalent elements are preferred because they have a higher charge than elements with a valence of less than three, allowing for greater inclusion without decreasing the oxygen/metal ratio within the structure and increasing the Mo ratio within the structure. In particular, titanium (Ti) is the element that can be included in the largest amount within the structure, and because its ionic radius is similar to that of pentavalent Nb, it is easy to incorporate into the structure, making it the most preferable of the M elements.

Tantalum (Ta), as a pentavalent element, can replace Nb. Ta and Nb are in the same group on the periodic table, and therefore have similar physical and chemical properties. Therefore, equivalent battery performance can be achieved even when Nb is replaced with Ta.

Tungsten (W) is a hexavalent element that can partially replace Mo. Generally, Wadsley-Roth phases containing W are known to have high rate performance due to the fast Li diffusion rate within the solid. Therefore, the inclusion of W can further improve the rate performance of the active material.

<Active material particles>
The active material according to the first embodiment may be in the form of particles. That is, the active material may be composed of particles of a composite oxide represented by the general formula Li _a M _b Nb Mo _c O _d and having the above-described crystal structure. The active material may be a single primary particle, a secondary particle formed by agglomeration of a plurality of primary particles, or a mixture thereof.

The average primary particle diameter of such active material is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. When the average primary particle diameter of the active material is small, the diffusion distance of lithium ions within the primary particles is short, which tends to increase lithium ion diffusibility. Furthermore, when the average primary particle diameter of the active material is small, the reaction area increases, which increases the reactivity between the active material and lithium ions and tends to improve the lithium ion insertion/extraction reaction.

The average secondary particle diameter of such active material is preferably 1 μm or more and 50 μm or less. By keeping the average secondary particle diameter of the active material within this range, productivity during electrode production can be improved and batteries with good performance can be obtained. This average secondary particle diameter refers to the particle size at which the volume cumulative value is 50% in the particle size distribution determined using a laser diffraction particle size distribution analyzer.

The BET specific surface area of the active material is preferably 3.0 m ² /g or more and 120 m ² /g or less, and more preferably 4.0 m ² /g or more and 110 m ² /g or less. Using an active material with a high specific surface area can improve the discharge rate performance of the battery. Using an active material with a low specific surface area can improve the battery life performance and improve the coatability of a slurry containing the active material in the electrode manufacturing process described later in the second embodiment.

BET specific surface area refers to the specific surface area determined by the nitrogen BET (Brunauer, Emmet and Teller) method. The method for determining specific surface area based on this nitrogen BET method is described in detail below.

<Manufacturing method>
The active material according to the first embodiment can be produced as follows.

(liquid phase synthesis)
The method for producing the composite oxide is not particularly limited, but it can be synthesized by, for example, a solid-state reaction method, a sol-gel method, a hydrothermal synthesis method, etc. As an example, a method for producing a titanium-niobium-molybdenum composite oxide (i.e., element M=Ti) using the sol-gel method will be described.

The starting materials used are titanium compounds, niobium compounds, and molybdenum compounds. Examples of titanium compounds include titanium tetraisopropoxide, titanyl sulfate, titanium chloride, ammonium titanium oxalate and its hydrates, titanium hydroxide, and titanium oxide. Examples of niobium compounds include niobium chloride, ammonium niobium oxalate and its hydrates, niobium hydroxide, and niobium oxide. Examples of molybdenum compounds include molybdenum chloride, ammonium molybdate and its hydrates, molybdenum hydroxide, and molybdenum oxide. When an element other than Ti is selected as element M, or when another element is selected together with Ti, the titanium compound is appropriately replaced with or used in combination with a compound containing the selected element M.

It is preferable to dissolve the starting materials in pure water or acid beforehand to create a solution. By creating a solution, it is possible to obtain a dry gel in which each element is homogeneously mixed, thereby increasing reactivity. If the material cannot be dissolved in pure water, it is dissolved using acid.

Examples of acids used to dissolve the raw materials include citric acid and oxalic acid, but oxalic acid is preferred from the standpoint of solubility. For example, when using oxalic acid, it is preferable to use a concentration of 0.5M to 1M. When dissolving, it is preferable to use a temperature of 70°C or higher to shorten the reaction time.

If the raw materials are difficult to dissolve, the reaction can also be carried out as a dispersion. In this case, the average particle size of the raw materials contained in the dispersion should be 3 μm or less, and more preferably 1 μm. After preparing a solution (or dispersion) with the specified composition ratio for each compound, the solution is heated and stirred while being neutralized with an aqueous ammonia solution to adjust the pH. A gel solution is obtained by adjusting the pH. By setting the pH to between 5 and 8, it is possible to form a gel that uniformly contains each raw material, which allows for the production of a dry gel that has good reactivity when fired.

Next, the gel liquid is heated to near its boiling point to evaporate the water and promote gelation. After gelation, the water is further evaporated and the liquid is dried to obtain a dry gel. During gelation and drying, for example, the entire solution can be evaporated and concentrated to obtain a dry gel. The dried gel produced by evaporating and concentrating the entire solution is preferably crushed before firing to reduce the average particle size to 10 μm or less, more preferably 5 μm or less. This reduces the particle size after firing. The resulting dry gel is then fired.

It is more preferable to use a spray dryer in the process of evaporating the solvent to gel and obtain a dried gel. Spraying makes it possible to form tiny droplets of the sol solution. By drying in the form of tiny droplets, it is possible to prevent particle agglomeration that occurs during solvent drying, thereby reducing the particle size after drying and reducing the number of coarse particles. This increases the uniformity of the reaction during the precursor calcination and also suppresses particle agglomeration during calcination. The drying temperature during spray drying is preferably between 100°C and 200°C.

When baking the dried gel, it is pre-baked at a temperature of 200°C to 500°C for a baking time of 1 hour to 10 hours. This allows excess organic components to be burned off, thereby increasing reactivity during the main baking.

The firing temperature is preferably between 600°C and 800°C, and the firing time is preferably between 1 hour and 10 hours. By firing within this temperature range, it is possible to obtain the desired phase while suppressing the sublimation of molybdenum.

The powder after firing may form agglomerates, resulting in a high average particle size. In this case, it is preferable to adjust the specified average particle size by pulverizing.

After mechanical pulverization, the powder may have an amorphous surface. In this case, when used as a battery active material, overvoltage may be generated during Li insertion and desorption, potentially increasing side reactions. For this reason, it is preferable to perform an annealing treatment again. The annealing temperature should be below the main firing temperature, preferably between 500°C and 800°C.

<Various measurement methods>
The measurement methods for the active material will be described below. Specifically, the confirmation of the composite oxide, the measurement of the average particle size of the active material particles, and the measurement of the specific surface area of the active material will be described.

When using the active material contained in a battery electrode as a sample, the measurement sample is prepared by pre-treating it using the following method. First, the battery is fully discharged. Next, the battery is disassembled in a glove box under an argon atmosphere, and the electrodes are removed. The removed electrodes are then washed using a solvent such as ethyl methyl carbonate. Further processing is performed for each measurement to prepare a sample in the appropriate form.

(Confirmation of complex oxides)
Confirmation _{that the active material has the above-described crystal structure and contains a composite oxide represented by the general formula LiaMbNbMocOd can be} performed _by combining wide-angle X-ray diffraction (XRD), high-angle annular dark-field (HAADF), inductively coupled plasma (ICP) optical emission spectroscopy, and inert gas dissolution-infrared absorption spectroscopy. The crystal structure can be determined using wide-angle XRD and HAADF, and the elemental composition can be determined using ICP optical emission spectroscopy and inert gas dissolution-infrared absorption spectroscopy. Furthermore, the intensity ratio (I1/I2) of the above-described main peaks can be determined from the spectrum obtained by XRD measurement. The valence of elements can be measured, for example, by X-ray photoelectron spectroscopy (XPS) using characteristic X-rays.

XRD measurements are performed as follows. First, the active material particles are thoroughly pulverized to obtain a powdered sample. The average particle size of the powdered sample is preferably 20 μm or less. This average particle size can be determined using a laser diffraction particle size distribution analyzer.

Next, fill the holder portion of the glass sample plate with this powdered sample and smooth the surface. For example, a glass sample plate with a holder depth of 0.2 mm can be used.

Next, the glass sample plate is placed in a powder X-ray diffractometer, and an XRD spectrum is measured using Cu-Kα radiation. Specific measurement conditions are, for example, as follows:
X-ray diffraction equipment: Rigaku Corporation SmartLab
X-ray source: CuKα ray Output: 40 kV, 200 mA
Package measurement name: General purpose measurement (concentration method)
Incident parallel slit aperture angle: 5°
Length of entrance longitudinal limiting slit: 10 mm
Light receiving PSA: None Light receiving parallel slit aperture angle: 5°
Monochromatization method: Kβ filter method Measurement mode: Continuous Entrance slit width: 0.5°
Receiving slit width: 20 mm
Measurement range (2θ): 5 to 70°
Sampling width (2θ): 0.01°
Scan speed: 1° to 20°/min.

In this way, an XRD spectrum of the active material is obtained. In this XRD spectrum, the horizontal axis represents the angle of incidence (2θ) and the vertical axis represents the diffraction intensity (cps). The scan speed can be adjusted so that the count number of the main peak in the XRD spectrum is between 50,000 and 150,000.

When using the active material contained in a battery electrode as a sample, the electrode after cleaning, obtained by the pretreatment described above, is cut into a piece of glass sample plate with an area approximately the same as the holder area, and used as the measurement sample.

The resulting measurement sample is then attached directly to a glass holder and XRD measurement is performed.

Peak intensities in XRD spectra are derived using the following method. The ratio of peak height (Signal = S) to noise (Noise = N) on the spectrum (S/N ratio) should be large enough so as not to affect the calculation of peak intensities. After estimating and dividing the background using an appropriate function, the peak corresponding to the Kα2 line is estimated and divided. The background can be estimated using methods such as the Sonneveld-Visser method, spline function method, and background function method. The Kα2 line is removed using the Rachinger method or Ladell method. After identifying all peaks within the 2θ = 20° to 30° range for the processed spectrum, peak fitting using the least-squares method is performed. For example, the pseudo-Voigt function is used as the peak function. When calculating the peaks, care should be taken to eliminate any overlapping peaks from other battery components such as mixed active materials, conductive agents, and current collectors. For example, materials other than the active material that may be contained in the electrode, such as current collectors, conductive agents, and binders, are measured using XRD to determine the XRD patterns derived from these. Next, if there are peaks in the measured sample that are thought to be derived from the active material and peaks from other materials, the peaks from the materials other than the active material are separated. In this way, an XRD spectrum is obtained in which the main peak associated with the crystalline structure of the active material is separated. Peaks P1 and P2 are identified based on the peak top position of the main peak, and their peak intensity ratio I1/I2 is calculated.

To more precisely confirm whether the crystal structure of the measured sample corresponds to the tetragonal crystal structure shown in Figure 1, the Rietveld method is used. For example, an analysis program such as RIETAN-FP can be used to confirm that the reliability factor, R _wp , is at least 20% or less, preferably 15% or less. The presence of peaks containing impurities that overlap with the target phase can degrade the analytical accuracy. In this case, it is preferable to perform an analysis that excludes from the analysis area any areas that clearly overlap with peaks derived from impurities. However, this does not apply when the sample contains materials other than the active material according to the first embodiment, when the sample has a significantly high degree of orientation, or when coarse particles are present, as the intensity ratio will change. The structure can be confirmed by confirming that there are no inconsistencies in the positions and relative intensities of all peaks attributed to the crystal structure. Furthermore, when the spectral intensity and background intensity are low, the R _wp value may be small. The reliability factor does not have any significance in its absolute value, but rather in assessing the relative quality of the fit under certain measurement conditions.

Analysis methods using RIETAN-FP are explained in detail, for example, in Chapter 9, "Let's try using RIETAN-FP," of Non-Patent Document 4 ("Practical X-Ray Powder Analysis," First Edition (2002), edited by the X-Ray Analysis Research Forum of the Japan Society for Analytical Chemistry, edited by Izumi Nakai and Fujio Izumi (Asakura Shoten)).

RIETAN-FP is a Rietveld analysis program that is distributed free of charge (as of August 2022) on its developer's online webpage (http://fujioizumi.verse.jp/).

The structure shown in Figure 2 is difficult to analyze by XRD measurement because it lacks periodicity. To confirm the structure shown in Figure 2, direct observation of the microstructure is preferable. Observation can be performed using a scanning transmission electron microscope (STEM) with a high-angle annular dark-field (HAADF) technique. To improve measurement resolution, spherical aberration correction is preferable. The structure can be confirmed by acquiring an atomic image (10 nm × 10 nm) perpendicular to the ReO ₃ block and confirming the relative positions of the metal elements that make up the ReO ₃ block.

The content of each element in the active material particles contained in the sample can be confirmed using ICP atomic emission spectrometry for metal elements. Quantitative determination of the oxygen element can be performed using methods such as inert gas dissolution-infrared absorption spectroscopy, but precise quantitation is difficult.

After the pretreatment described above, the active material particles contained in the electrode are further subjected to the following treatment. After cleaning, the active material-containing component (e.g., the active material-containing layer described in the second embodiment) is peeled off, for example, from the electrode's current collector. The portion peeled off from the electrode is heated in air for a short period of time (approximately 1 hour at 500°C) to burn off unnecessary components such as binder components and carbon. The content of each element can then be quantified by ICP emission spectrometry or similar.

The valence of metal elements contained in a composite oxide can be measured using XPS as follows. It is preferable to use hard X-rays for the measurement, as they have a deep detection depth and can measure a state closer to the bulk. Spectroscopic techniques using hard X-rays are also called HAXPES. The valence can be determined by checking the binding energy position of each element's narrow spectrum. For example, for Ti, a tetravalent peak due to Ti2p3 _/2 is observed at 459.0±0.4 eV. For Mo, a hexavalent peak due to Mo3d5 _/2 is observed at 232.2±0.4 eV. For Nb, a pentavalent peak due to Nb3d5 _/2 is observed at 207.5±0.4 eV. Low-valence elements can be identified by detecting peaks at lower energy positions than the previous valences. In particular, Mo may contain valences of five or less.

Sample measurements are performed non-destructively to prevent changes in element valence. Therefore, when measuring complex oxides contained in electrodes, the electrode is used as the sample without material extraction. Measurements are performed carefully to ensure that charge-up during sample measurement does not affect the peak position. To prevent peak shifts due to charge-up, it is preferable to measure the electrode in a fully discharged state. Charging can be reduced if the electrode contains a conductive agent. Care must be taken, as prolonged X-ray irradiation can damage the sample and change element valence. Furthermore, when materials with different structures are mixed, peak shifts may occur due to changes in bonding state, so care must be taken not to confuse this with changes in valence. When elements with different valences are mixed, i.e., when the spectrum is a mixture of multiple peaks, the spectra can be separated using least-squares fitting, and the mixing ratio can be estimated from the area ratio of the separated peaks.

The Li content, represented by _{the subscript} a in the general formula _{LiaMbNbMocOd ,} varies depending on the state of charge of the electrode in which the composite oxide is used as the active material. For example, in the composite oxide contained in the negative electrode, Li is inserted as the battery is charged, increasing the subscript a, and Li is desorbed as the battery is discharged, decreasing the subscript a.

(Measurement of average particle size)
The average primary particle size of the active material can be determined by observation using a scanning electron microscope (SEM). Specifically, the average primary particle size determined by SEM observation can be calculated by the following method.

First, the length of the longest axis and the length of the shortest axis of the primary particles in the SEM image obtained by SEM observation are measured, and the arithmetic mean of these is taken as the primary particle diameter. This primary particle diameter measurement is performed on 100 randomly selected particles, and the average value of these measurements is taken as the average primary particle diameter.

The average secondary particle diameter of the active material can be determined from the particle size distribution measured using a laser diffraction particle size distribution analyzer. The sample used for this particle size distribution measurement is a dispersion diluted with N-methyl-2-pyrrolidone so that the active material concentration is 0.1% to 1% by mass. The particle size at which the volumetric cumulative value is 50% in the obtained particle size distribution is taken as the average secondary particle diameter.

(Measurement of BET specific surface area)
The BET specific surface area of the active material particles can be determined by the following method.

First, 4 g of active material is collected as a sample. Next, the evaluation cell of the measurement device is dried under reduced pressure at a temperature of 100°C or higher for 15 hours to perform a degassing treatment. For example, a 1/2-inch evaluation cell can be used. Next, the sample is placed in the measurement device. For example, a Shimadzu Micromeritics Tristar II 3020 can be used as the measurement device. Next, the nitrogen gas pressure P (mmHg) is gradually increased in nitrogen gas at 77 K (the boiling point of nitrogen), and the nitrogen gas adsorption amount (mL/g) of the sample is measured at each pressure P. Next, the pressure P (mmHg) is divided by the saturated vapor pressure P ₀ (mmHg) of nitrogen gas to obtain the relative pressure P/P _0. The nitrogen gas adsorption amount is plotted against each relative pressure P/P ₀ to obtain an adsorption isotherm. Next, a BET plot is calculated from this nitrogen adsorption isotherm and the BET equation, and the specific surface area is obtained using this BET plot. The BET plot is calculated using the BET multipoint method.

The active material according to the first embodiment includes a composite oxide having a structure including rhenium oxide blocks in _which an octahedral structure composed of oxygen and a metal element is configured by corner-sharing, and the composite _oxide is represented by the general formula _{LiaMbNbMocOd .} In the structure, multiple rhenium oxide blocks of different sizes are connected aperiodically at least by octahedral edge-sharing. In the general formula, M is at least one selected from the group consisting of Ti, V, Ta, Fe, Co, Mn, Ni, Bi, Sb, As, P, Cr, W, B, Na, K, Mg, Al, Ca, Y, and Si. The subscripts a, b, c, and d are numbers satisfying the following conditions: 0≦a≦b+2+3c, 0≦b≦1.5, 0≦c≦0.5, and 2.33≦d/(1+b+c)≦2.50. An electrode using the composite oxide as an electrode active material has a high capacity per volume. Furthermore, secondary batteries and battery packs using the composite oxide as an electrode active material have a high capacity per volume, i.e., the active material exhibits a high capacity.

Second Embodiment
According to a second embodiment, an electrode is provided.

The electrode according to the second embodiment includes the active material according to the first embodiment. This electrode may be a battery electrode that includes the active material according to the first embodiment as a battery active material. The electrode as a battery electrode may be, for example, a negative electrode that includes the active material according to the first embodiment as a negative electrode active material. Alternatively, the electrode may be a positive electrode that includes the active material according to the first embodiment as a positive electrode active material.

Such an electrode may include a current collector and an active material-containing layer. The active material-containing layer may be formed on one or both sides of the current collector. The active material-containing layer may include an active material and, optionally, a conductive agent and a binder.

The active material-containing layer may contain the active material according to the first embodiment alone, or may contain two or more types of active material according to the first embodiment. Furthermore, it may contain a mixture of one or more types of active material according to the first embodiment mixed with one or more types of other active materials. It is desirable that the content ratio of the active material according to the first embodiment relative to the total mass of the active material according to the first embodiment and the other active materials be 10% by mass or more and 100% by mass or less.

For example, when the active material according to the first embodiment is contained as a negative electrode active material, examples of other active materials include lithium titanate having a ramsdellite structure (e.g., Li2 _{+ xTi3O7} , 0 _≦ x≦3), lithium titanate having a spinel structure (e.g., Li4 _{+ xTi5O12} , 0≦x≦ ₃ ), titanium dioxide ( _TiO2 ), anatase titanium dioxide, rutile titanium dioxide, niobium pentoxide ( _Nb2O5 ), hollandite titanium composite oxide, orthorhombic titanium composite oxide, and monoclinic niobium titanium oxide, niobium oxide, niobium _titanium oxide, niobium molybdenum composite oxide, and niobium tungsten composite oxide.

An example of the orthorhombic titanium _- containing composite oxide is a compound represented by Li2 _+eMI2 ^- _{fTi6 -} ^gMIIhO14 _+σ . Here, MI is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb, and K. ^MI is at least one selected from the ^group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. The subscripts in the composition formula are 0≦e≦6, 0≦f<2, 0≦g<6, 0≦h< ₆ , and -0.5≦σ≦0.5. A specific example of the orthorhombic titanium-containing composite oxide is Li2 _{+eNa2Ti6O14 (} 0≦e≦ ₆ ).

An example of the monoclinic niobium titanium oxide is a compound represented by Li _x Ti _1-y M1 _y Nb _2-z M2 _z O _7+δ . Here, M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3. A specific example of the monoclinic niobium titanium oxide is Li _x Nb ₂ TiO ₇ (0≦x≦5).

Another example of monoclinic niobium titanium oxide is a compound represented by Li _x Ti _1-y M3 _y+z Nb _2-z O _7-δ , where M3 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3.

Conductive agents are added to improve current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents include carbonaceous materials such as vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, carbon nanotubes, and carbon nanofibers. One of these may be used as the conductive agent, or two or more may be used in combination. Alternatively, instead of using a conductive agent, the surfaces of the active material particles may be coated with carbon or an electronically conductive inorganic material. Furthermore, the current collection performance of the active material-containing layer can be improved by using a conductive agent and coating the active material surface with carbon or a conductive material.

Binders are added to fill the gaps between the dispersed active material and to bind the active material and current collector together. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and CMC salts. These may be used alone or in combination.

The blending ratios of the active material, conductive agent, and binder in the active material-containing layer can be adjusted appropriately depending on the application of the electrode. For example, when the electrode is used as the negative electrode of a secondary battery, the active material (negative electrode active material), conductive agent, and binder are preferably blended in proportions of 68% by mass or more and 96% by mass or less, 2% by mass or more and 30% by mass or less, and 2% by mass or more and 30% by mass or less, respectively. By using a conductive agent amount of 2% by mass or more, the current collection performance of the active material-containing layer can be improved. Furthermore, by using a binder amount of 2% by mass or more, sufficient binding between the active material-containing layer and the current collector can be achieved, and excellent cycle performance can be expected. On the other hand, it is preferable to use a conductive agent and binder amount of 30% by mass or less each in order to achieve high capacity.

When the surface of the active material is coated with carbon or a conductive material, the amount of coating material can be considered to be included in the amount of conductive agent. The amount of carbon or conductive material coated is preferably 0.5% by mass or more and 5% by mass or less. A coating amount within this range can improve current collection performance and electrode density.

The current collector is made of a material that is electrochemically stable at the potential at which lithium (Li) is inserted into and extracted from the active material. For example, when the active material is used as a negative electrode active material, the current collector is preferably made of copper, nickel, stainless steel, aluminum, or an aluminum alloy containing one or more elements selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 5 μm or more and 20 μm or less. A current collector with such a thickness can balance the strength and weight of the electrode.

The current collector may also include a portion on its surface where the active material-containing layer is not formed. This portion can function as a current collecting tab.

An electrode can be produced, for example, by the following method. First, an active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. This slurry is then applied to one or both sides of a current collector. The applied slurry is then dried to obtain a laminate of an active material-containing layer and a current collector. This laminate is then pressed. In this manner, an electrode is produced.

Alternatively, the electrode may be prepared by the following method. First, the active material, conductive agent, and binder are mixed to obtain a mixture. Next, this mixture is formed into pellets. These pellets are then placed on a current collector to obtain an electrode.

The electrode according to the second embodiment contains the active material according to the first embodiment. Therefore, the electrode according to the second embodiment can realize a secondary battery with a high capacity per volume.

(Third embodiment)
According to a third embodiment, a secondary battery is provided that includes a negative electrode, a positive electrode, and an electrolyte. This secondary battery includes the electrode according to the second embodiment as the negative electrode or the positive electrode. That is, the secondary battery according to the third embodiment includes, as a battery electrode, an electrode that includes the active material according to the first embodiment as a battery active material. A secondary battery of a desirable aspect includes, as a negative electrode, the electrode according to the second embodiment. That is, a secondary battery of a desirable aspect includes, as a negative electrode, an electrode that includes the active material according to the first embodiment as a battery active material. Desired aspects will be described below.

Such a secondary battery may further include a separator disposed between the positive electrode and the negative electrode. The negative electrode, positive electrode, and separator may constitute an electrode assembly. The electrolyte may be held in the electrode assembly.

Furthermore, such a secondary battery may further include an exterior member that houses the electrode group and electrolyte.

Furthermore, such a secondary battery may further include a negative electrode terminal electrically connected to the negative electrode and a positive electrode terminal electrically connected to the positive electrode.

The secondary battery according to the third embodiment may be, for example, a lithium secondary battery. The secondary battery also includes a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte.

The negative electrode, positive electrode, electrolyte, separator, exterior member, negative electrode terminal, and positive electrode terminal are described in detail below.

1) Negative Electrode The negative electrode may include a negative electrode current collector and a negative electrode active material-containing layer. The negative electrode current collector and the negative electrode active material-containing layer may be the current collector and the active material-containing layer, respectively, that can be included in the electrode according to the second embodiment. The negative electrode active material-containing layer contains the active material according to the first embodiment as the negative electrode active material.

Details of the negative electrode that overlap with those described in the second embodiment will be omitted.

The density of the negative electrode active material-containing layer (excluding the current collector) is preferably 1.8 g/cm ^or more and 2.8 g/cm or ^less . A negative electrode having a density of the negative electrode active material-containing layer within this range has excellent energy density and electrolyte retention. The density of the negative electrode active material-containing layer is more preferably 2.1 g/cm ^or more and 2.6 g/cm or ^less .

The negative electrode can be fabricated, for example, by a method similar to that used for the electrode according to the second embodiment.

2) Positive Electrode The positive electrode may include a positive electrode current collector and a positive electrode active material-containing layer. The positive electrode active material-containing layer may be formed on one or both sides of the positive electrode current collector. The positive electrode active material-containing layer may include a positive electrode active material, and optionally a conductive agent and a binder.

For example, oxides or sulfides can be used as the positive electrode active material. The positive electrode may contain one type of compound alone as the positive electrode active material, or may contain a combination of two or more types of compounds. Examples of oxides and sulfides include compounds that can insert and extract Li or Li ions.

Examples of such compounds include manganese dioxide (MnO ₂ ), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxides (e.g., Li _x Mn ₂ O ₄ or Li _x MnO ₂ ; 0<x≦1), lithium nickel composite oxides (e.g., Li _x NiO ₂ ; 0<x≦1), lithium cobalt composite oxides (e.g., Li _x CoO ₂ ; 0<x≦1), lithium nickel cobalt composite oxides (e.g., Li _x Ni _1-y Co _y O ₂ ; 0<x≦1, 0<y<1), lithium manganese cobalt composite oxides (e.g., Li _x Mn _y Co _1-y O ₂ ; 0<x≦1, 0<y<1), and lithium manganese nickel composite oxides having a spinel structure (e.g., Li _x Mn _2-y Ni _y O _{4 ;} 0<x≦1, 0<y<2), lithium phosphate oxides having an olivine _structure (e.g., _LixFePO4 ; 0<x≦1, _{LixFe1 - yMnyPO4} ; 0<x≦1, 0<y≦ ₁ , _LixCoPO4 ; 0<x≦1), iron sulfate ( _Fe2 ( _SO4 ) ₃ ), vanadium oxides (e.g., _V2O5 ), and lithium nickel cobalt manganese composite oxides ( _{LixNi1 - yzCoyMnzO2} ; 0<x≦1 _, 0<y<1 _{, 0} <z<1, y+z<1).

Among the above, examples of more preferred compounds as the positive electrode active material include lithium manganese composite oxides having a spinel structure (e.g., Li _x Mn ₂ O ₄ ; 0<x≦1), lithium nickel composite oxides (e.g., Li _x NiO ₂ ; 0<x≦1), lithium cobalt composite oxides (e.g., Li _x CoO ₂ ; 0<x≦1), lithium nickel cobalt composite oxides (e.g., Li _x Ni _1-y Co _y O ₂ ; 0<x≦1, 0<y<1), lithium manganese nickel composite oxides having a spinel structure (e.g., Li _x Mn _2-y Ni _y O ₄ ; 0<x≦1, 0<y<2), lithium manganese cobalt composite oxides (e.g., Li _x Mn _y Co _1-y O ₂ ; 0<x≦1, 0<y<1), and lithium iron phosphate (e.g., Li _x FePO ₄ ; 0<x≦1) and lithium nickel cobalt manganese composite oxide (Li _x Ni _1-yz Co _y Mn _z O ₂ ; 0<x≦1, 0<y<1, 0<z<1, y+z<1). When these compounds are used as the positive electrode active material, the positive electrode potential can be increased.

When a room-temperature molten salt is used as the battery electrolyte, it is preferable to use a positive electrode active material containing lithium iron phosphate, Li _x VPO ₄ F (0≦x≦1), lithium manganese composite oxide, lithium nickel composite oxide, lithium nickel cobalt composite oxide, or a mixture thereof. These compounds have low reactivity with room-temperature molten salts, and therefore can improve cycle life. Details of room-temperature molten salts will be described later.

The primary particle size of the positive electrode active material is preferably 100 nm or more and 1 μm or less. Positive electrode active materials with a primary particle size of 100 nm or more are easy to handle in industrial production. Positive electrode active materials with a primary particle size of 1 μm or less allow lithium ions to diffuse smoothly within the solid.

The specific surface area of the positive electrode active material is preferably 0.1 ^m /g or more and 10 ^m /g or less. A positive electrode active material having a specific surface area of ^{0.1 m} /g or more can ensure sufficient insertion and desorption sites for Li ions. A positive electrode active material having a specific surface area of ^{10 m} /g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

The binder is added to fill the gaps between the dispersed positive electrode active material and to bind the positive electrode active material to the positive electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and CMC salts. One of these may be used as the binder, or two or more may be used in combination as binders.

Conductive agents are added to improve current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as the conductive agent, or two or more may be used in combination. The conductive agent may also be omitted.

In the positive electrode active material-containing layer, the positive electrode active material and binder are preferably blended in proportions of 80% by mass or more and 98% by mass or less, and 2% by mass or more and 20% by mass or less, respectively.

By using a binder amount of 2% by mass or more, sufficient electrode strength can be achieved. The binder can also function as an insulator. Therefore, by using a binder amount of 20% by mass or less, the amount of insulator contained in the electrode is reduced, thereby reducing internal resistance.

When a conductive agent is added, the positive electrode active material, binder, and conductive agent are preferably blended in proportions of 77% by mass or more and 95% by mass or less, 2% by mass or more and 20% by mass or less, and 3% by mass or more and 15% by mass or less, respectively.

By setting the amount of conductive agent to 3% by mass or more, the above-mentioned effects can be achieved. Furthermore, by setting the amount of conductive agent to 15% by mass or less, the proportion of conductive agent that comes into contact with the electrolyte can be reduced. This low proportion can reduce electrolyte decomposition during high-temperature storage.

The positive electrode current collector is preferably aluminum foil or aluminum alloy foil containing one or more elements selected from the group consisting of Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si.

The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, and more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium contained in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

The positive electrode current collector may also include a portion on its surface where the positive electrode active material-containing layer is not formed. This portion can function as a positive electrode current collecting tab.

The positive electrode can be produced, for example, using a positive electrode active material in a manner similar to that used for the electrode according to the second embodiment.

3) Electrolyte The electrolyte may be, for example, a liquid nonaqueous electrolyte or a gel nonaqueous electrolyte. The liquid nonaqueous electrolyte is prepared by dissolving an electrolyte salt as a solute in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol/L or more and 2.5 mol/L or less.

Examples of electrolyte salts include lithium perchlorate ( _LiClO4 ), lithium hexafluorophosphate ( _LiPF6 ), lithium tetrafluoroborate (LiBF4), lithium hexafluoride ( _LiAsF6 ), lithium trifluoromethanesulfonate ( _LiCF3SO3 ), and lithium salts such as lithium bistrifluoromethylsulfonylimide (LiN( _CF3SO2 ) ₂ ) _and lithium bis( _{fluorosulfonyl} )imide (LiN( _SO2F ) ₂ ; LiFSI), and mixtures thereof. The electrolyte salt is preferably one that _is difficult to oxidize even at high potentials, and _LiPF6 is most preferred.

Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); linear carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); linear ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or as a mixed solvent.

Gel-type non-aqueous electrolytes are prepared by combining a liquid non-aqueous electrolyte with a polymer material. Examples of polymer materials include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or mixtures thereof.

Alternatively, in addition to liquid nonaqueous electrolytes and gel nonaqueous electrolytes, room-temperature molten salts containing lithium ions (ionic melts), polymer solid electrolytes, inorganic solid electrolytes, etc. may also be used as nonaqueous electrolytes.

A room-temperature molten salt (ionic melt) refers to an organic salt composed of a combination of organic cations and anions that can exist as a liquid at room temperature (15°C or higher and 25°C or lower). Room-temperature molten salts include room-temperature molten salts that exist as a liquid on their own, room-temperature molten salts that become liquid when mixed with an electrolyte salt, room-temperature molten salts that become liquid when dissolved in an organic solvent, and mixtures of these. Generally, the melting point of room-temperature molten salts used in secondary batteries is 25°C or lower. Furthermore, organic cations generally have a quaternary ammonium skeleton.

Polymer solid electrolytes are prepared by dissolving an electrolyte salt in a polymer material and solidifying it.

The inorganic solid electrolyte is a solid substance having Li ion conductivity. Here, "having Li ion conductivity" refers to exhibiting a lithium ion conductivity of 1×10 ⁻⁶ S/cm or more at 25°C. Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes. Specific examples of inorganic solid electrolytes are as follows:

As the oxide-based solid electrolyte, a lithium phosphate solid electrolyte having a NASICON (Sodium (Na) Super Ionic Conductor) structure and represented by the general formula Li1 _{+xMα2 ( PO4} ) ₃ is preferably used. In the general formula, Mα is, for example, one or more elements selected from the group consisting of titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), aluminum (Al), and calcium (Ca). The subscript x is within the range of 0≦x≦2.

Specific examples of lithium phosphate solid electrolytes having a NASICON structure include LATP compounds represented by Li1 _{+ xAlxTi2 -x} ( _PO4 ) ₃ where 0.1≦x≦0.5; compounds represented by Li1 _{+ xAlyMβ2 -y} ( _PO4 ) ₃ where Mβ is one or more selected from the group consisting of Ti, Ge, Sr, Zr, Sn, and Ca, and where 0≦x≦1 and 0≦y≦1; compounds represented by Li1 _{+ xAlxGe2 -x} ( _PO4 ) ₃ where 0≦x≦2; and compounds represented by Li1 _{+ xAlxZr2 -x ( PO4} ) ₃ where 0≦x≦ ₂ ; Li1 _{+x+ yAlxMγ2 -} xSiyP3-yO ₁₂ , where Mγ is 1 or more selected from the group consisting of Ti and Ge, and 0<x≦2, 0≦y<3; and a compound represented by Li _1+2x Zr _1-x Ca _x (PO ₄ ) ₃ , where 0≦x<1.

In addition to the lithium phosphate solid electrolyte, examples of oxide-based solid electrolytes include amorphous LIPON compounds (e.g., _{Li2.9PO3.3N0.46 )} represented by _LixPOyNz , where 2.6≦x≦3.5, _1.9 ≦y≦ _3.8 , and 0.1≦z≦ _1.3 ; garnet-type compounds represented by La5 _{+ xAxLa3 - xMδ2O12} , where A is 1 or _more selected from the group consisting of Ca, Sr, and Ba, Mδ is 1 or more selected from the group consisting of Nb and Ta, and 0≦x≦ _0.5 ; _{Li3Mδ2 - xL2O12} , where Mδ is 1 or more selected from the group consisting of Nb and Ta, and L may contain Zr, and 0≦ _x ≦ _0.5 ; and _{Li7-3xAlxLa3Zr} LLZ compounds (e.g., Li7La3Zr2O12) having a perovskite structure and represented by the formula _Li2 /3- _xLixTiO3 , where 0≦x≦ _0.7 ; _{Li5 + xLa3Mδ2 - xZrxO12} , where Mδ is at least one element selected from the group consisting of Nb _and Ta, and 0≦x≦ ₂ ; and compounds having a perovskite structure and represented by the formula La2 _{/3-xLixTiO3 , where} 0.3≦x≦ _0.7 .

One or more of the above compounds can be used as the solid electrolyte. Two or more of the above solid electrolytes may also be used.

Alternatively, instead of a nonaqueous electrolyte, a liquid aqueous electrolyte or a gelled aqueous electrolyte can be used as the electrolyte. A liquid aqueous electrolyte is prepared by dissolving, for example, the above-mentioned electrolyte salt as a solute in an aqueous solvent. A gelled aqueous electrolyte is prepared by combining a liquid aqueous electrolyte with the above-mentioned polymer material. A solution containing water can be used as the aqueous solvent. The solution containing water may be pure water or a mixed solvent of water and an organic solvent.

4) Separator The separator is formed from, for example, a porous film containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric. From the viewpoint of safety, it is preferable to use a porous film formed from polyethylene or polypropylene. This is because these porous films melt at a certain temperature and are capable of interrupting current.

5) Exterior Member As the exterior member, for example, a container made of a laminate film or a metal container can be used.

The thickness of the laminate film is, for example, 0.5 mm or less, and preferably 0.2 mm or less.

The laminate film used is a multilayer film containing multiple resin layers and metal layers sandwiched between these resin layers. The resin layers contain polymeric materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layers are preferably made of aluminum foil or aluminum alloy foil to reduce weight. The laminate film can be molded into the shape of the exterior component by sealing it with heat.

The wall thickness of the metal container is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

The metal container is made of, for example, aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc, and silicon. If the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content of these metals is preferably 1% by mass or less.

The shape of the exterior member is not particularly limited. The shape of the exterior member may be, for example, flat (thin), rectangular, cylindrical, coin-shaped, or button-shaped. The exterior member can be selected appropriately depending on the battery dimensions and intended use.

6) Negative Electrode Terminal The negative electrode terminal can be formed from a material that is electrochemically stable and conductive at the Li insertion/extraction potential of the above-described negative electrode active material. Specifically, the material for the negative electrode terminal can be copper, nickel, stainless steel, aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. Aluminum or an aluminum alloy is preferably used as the material for the negative electrode terminal. The negative electrode terminal is preferably made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

7) Positive Electrode Terminal The positive electrode terminal can be formed from a material that is electrically stable and conductive in a potential range of 3 V to 4.5 V relative to the redox potential of lithium (vs. Li/Li ⁺ ). Examples of materials for the positive electrode terminal include aluminum and aluminum alloys containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The positive electrode terminal is preferably formed from the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

Aspects including the electrode according to the second embodiment as the negative electrode have been described above. Among the aspects of the secondary battery according to the third embodiment, in aspects including the electrode according to the second embodiment as the positive electrode, the negative electrode, which is the counter electrode, can be, for example, the following counter electrodes. At least one electrode selected from lithium metal, lithium metal alloy, graphite, silicon, silicon oxide, tin oxide, silicon, tin, and other alloys can be used as the negative electrode. Materials that do not contain Li in the active material can be used as the negative electrode by pre-doping with Li element.

In the case of an embodiment in which the electrode according to the second embodiment is used as a positive electrode, details of the positive electrode overlap with those described in the second embodiment and are therefore omitted here.

Next, the secondary battery according to the third embodiment will be described in more detail with reference to the drawings.

Figure 3 is a cross-sectional view schematically showing an example of a secondary battery. Figure 4 is an enlarged cross-sectional view of part A of the secondary battery shown in Figure 3.

The secondary battery 100 shown in Figures 3 and 4 includes an electrode group 1 shown in Figure 3, a bag-shaped outer casing member 2 shown in Figures 3 and 4, and an electrolyte (not shown). The electrode group 1 and electrolyte are housed within the bag-shaped outer casing member 2. The electrolyte (not shown) is held in the electrode group 1.

The bag-shaped exterior member 2 is made of a laminate film containing two resin layers and a metal layer sandwiched between them.

As shown in Figure 3, the electrode group 1 is a flat, wound electrode group. As shown in Figure 4, the flat, wound electrode group 1 includes a negative electrode 3, a separator 4, and a positive electrode 5. The separator 4 is interposed between the negative electrode 3 and the positive electrode 5.

The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b. In the portion of the negative electrode 3 located at the outermost shell of the wound electrode group 1, the negative electrode active material-containing layer 3b is formed only on the inner surface of the negative electrode current collector 3a, as shown in Figure 4. In other portions of the negative electrode 3, the negative electrode active material-containing layer 3b is formed on both sides of the negative electrode current collector 3a.

The positive electrode 5 includes a positive electrode current collector 5a and a positive electrode active material-containing layer 5b formed on both sides of the positive electrode current collector 5a.

As shown in FIG. 3, the negative electrode terminal 6 and positive electrode terminal 7 are located near the outer peripheral edge of the wound electrode group 1. The negative electrode terminal 6 is connected to the outermost portion of the negative electrode current collector 3a. The positive electrode terminal 7 is connected to the outermost portion of the positive electrode current collector 5a. The negative electrode terminal 6 and positive electrode terminal 7 extend outward from the opening of the bag-shaped exterior member 2. A thermoplastic resin layer is provided on the inner surface of the bag-shaped exterior member 2, and the opening is closed by heat sealing this.

The secondary battery according to the embodiment is not limited to the secondary battery having the configuration shown in Figures 3 and 4, but may also be a battery having the configuration shown in Figures 5 and 6, for example.

Figure 5 is a partially cutaway perspective view schematically showing another example of a secondary battery. Figure 6 is an enlarged cross-sectional view of part B of the secondary battery shown in Figure 5.

The secondary battery 100 shown in Figures 5 and 6 includes an electrode group 1 shown in Figures 5 and 6, an exterior member 2 shown in Figure 5, and an electrolyte (not shown). The electrode group 1 and electrolyte are housed within the exterior member 2. The electrolyte is held in the electrode group 1.

The exterior member 2 consists of a laminate film containing two resin layers and a metal layer sandwiched between them.

As shown in Figure 6, the electrode group 1 is a laminated electrode group. The laminated electrode group 1 has a structure in which negative electrodes 3 and positive electrodes 5 are alternately stacked with separators 4 interposed between them.

The electrode group 1 includes a plurality of negative electrodes 3. Each of the plurality of negative electrodes 3 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b supported on both sides of the negative electrode current collector 3a. The electrode group 1 also includes a plurality of positive electrodes 5. Each of the plurality of positive electrodes 5 includes a positive electrode current collector 5a and a positive electrode active material-containing layer 5b supported on both sides of the positive electrode current collector 5a.

The negative electrode current collector 3a of each negative electrode 3 includes a portion on one side where the negative electrode active material-containing layer 3b is not supported on any surface. This portion functions as a negative electrode current collector tab 3c. As shown in FIG. 6, the negative electrode current collector tab 3c does not overlap with the positive electrode 5. Furthermore, the multiple negative electrode current collector tabs 3c are electrically connected to a strip-shaped negative electrode terminal 6. The tip of the strip-shaped negative electrode terminal 6 is extended outside the exterior member 2.

Although not shown, the positive electrode current collector 5a of each positive electrode 5 includes a portion on one side where the positive electrode active material-containing layer 5b is not supported on any surface. This portion functions as a positive electrode current collecting tab. Like the negative electrode current collecting tab 3c, the positive electrode current collecting tab does not overlap with the negative electrode 3. The positive electrode current collecting tab is located on the opposite side of the electrode group 1 from the negative electrode current collecting tab 3c. The positive electrode current collecting tab is electrically connected to a strip-shaped positive electrode terminal 7. The tip of the strip-shaped positive electrode terminal 7 is located on the opposite side from the negative electrode terminal 6 and is extended to the outside of the exterior member 2.

The secondary battery according to the third embodiment includes the electrode according to the second embodiment. In other words, the secondary battery according to the third embodiment includes an electrode containing the active material according to the first embodiment. Therefore, the secondary battery according to the third embodiment has a high capacity per volume.

(Fourth embodiment)
According to a fourth embodiment, there is provided a battery pack, which includes a plurality of secondary batteries according to the third embodiment.

In such a battery pack, the individual cells may be electrically connected in series or parallel, or may be connected in a combination of series and parallel.

Next, an example of a battery pack according to the fourth embodiment will be described with reference to the drawings.

Figure 7 is a perspective view showing a schematic example of a battery pack. The battery pack 200 shown in Figure 7 includes five cells 100a-100e, four bus bars 21, a positive electrode lead 22, and a negative electrode lead 23. Each of the five cells 100a-100e is a secondary battery according to the third embodiment.

The bus bar 21 connects, for example, the negative terminal 6 of one cell 100a to the positive terminal 7 of the adjacent cell 100b. In this way, the five cells 100 are connected in series by four bus bars 21. In other words, the battery pack 200 in Figure 7 is a five-series battery pack. Although an example is not shown, in a battery pack including multiple cells electrically connected in parallel, the multiple cells can be electrically connected, for example, by connecting multiple negative terminals together by a bus bar and connecting multiple positive terminals together by a bus bar.

The positive electrode terminal 7 of at least one of the five cells 100a-100e is electrically connected to a positive electrode lead 22 for external connection. The negative electrode terminal 6 of at least one of the five cells 100a-100e is electrically connected to a negative electrode lead 23 for external connection.

The battery pack according to the fourth embodiment includes the secondary battery according to the third embodiment. Therefore, the capacity per volume of such a battery pack is high.

Fifth Embodiment
According to a fifth embodiment, there is provided a battery pack. This battery pack includes the battery assembly according to the fourth embodiment. This battery pack may include a single secondary battery according to the third embodiment instead of the battery assembly according to the fourth embodiment.

Such a battery pack may further include a protection circuit. The protection circuit has the function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses the battery pack as a power source (e.g., electronic equipment, automobiles, etc.) may be used as the protection circuit for the battery pack.

The battery pack may also be equipped with external terminals for current flow. The external terminals for current flow are for outputting current from the secondary battery to the outside and/or inputting current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals for current flow. When charging the battery pack, charging current (including regenerative energy from the power of a vehicle, etc.) is supplied to the battery pack through the external terminals for current flow.

Next, an example of a battery pack according to an embodiment will be described with reference to the drawings.

Figure 8 is an exploded perspective view showing an example of a battery pack. Figure 9 is a block diagram showing an example of the electrical circuit of the battery pack shown in Figure 8.

The battery pack 300 shown in Figures 8 and 9 includes a container 31, a lid 32, a protective sheet 33, a battery pack 200, a printed wiring board 34, wiring 35, and an insulating plate (not shown).

The storage container 31 shown in Figure 8 is a bottomed, square container with a rectangular bottom. The storage container 31 is configured to be able to accommodate a protective sheet 33, a battery pack 200, a printed wiring board 34, and wiring 35. The lid 32 has a rectangular shape. The lid 32 covers the storage container 31 to accommodate the battery pack 200 and other components. Although not shown, the storage container 31 and the lid 32 are provided with openings or connection terminals for connecting to external devices, etc.

The battery pack 200 includes multiple cells 100, a positive electrode lead 22, a negative electrode lead 23, and adhesive tape 24.

At least one of the multiple cells 100 is a secondary battery according to the third embodiment. Each of the multiple cells 100 is electrically connected in series as shown in FIG. 9 . The multiple cells 100 may be electrically connected in parallel, or may be connected in a combination of series and parallel connections. Connecting multiple cells 100 in parallel increases battery capacity compared to connecting them in series.

Adhesive tape 24 fastens the multiple cells 100 together. Instead of adhesive tape 24, heat-shrinkable tape may be used to secure the multiple cells 100 together. In this case, protective sheets 33 are placed on both sides of the battery pack 200, heat-shrinkable tape is wrapped around the cells, and the heat-shrinkable tape is then thermally shrunk to bind the multiple cells 100 together.

One end of the positive electrode lead 22 is connected to the battery pack 200. One end of the positive electrode lead 22 is electrically connected to the positive electrode of one or more cells 100. One end of the negative electrode lead 23 is connected to the battery pack 200. One end of the negative electrode lead 23 is electrically connected to the negative electrode of one or more cells 100.

The printed wiring board 34 is installed along one of the shorter sides of the inner surface of the container 31. The printed wiring board 34 includes a positive connector 342, a negative connector 343, a thermistor 345, a protection circuit 346, wiring 342a and 343a, an external terminal 350 for supplying current, a positive wiring (positive wiring) 348a, and a negative wiring (negative wiring) 348b. One main surface of the printed wiring board 34 faces one side of the battery pack 200. An insulating plate (not shown) is interposed between the printed wiring board 34 and the battery pack 200.

The other end 22a of the positive electrode lead 22 is electrically connected to the positive electrode connector 342. The other end 23a of the negative electrode lead 23 is electrically connected to the negative electrode connector 343.

The thermistor 345 is fixed to one main surface of the printed wiring board 34. The thermistor 345 detects the temperature of each battery cell 100 and transmits the detection signal to the protection circuit 346.

The external terminals 350 for current flow are fixed to the other main surface of the printed wiring board 34. The external terminals 350 for current flow are electrically connected to devices external to the battery pack 300. The external terminals 350 for current flow include a positive terminal 352 and a negative terminal 353.

The protection circuit 346 is fixed to the other main surface of the printed wiring board 34. The protection circuit 346 is connected to the positive terminal 352 via the positive wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via the negative wiring 348b. The protection circuit 346 is also electrically connected to the positive connector 342 via wiring 342a. The protection circuit 346 is electrically connected to the negative connector 343 via wiring 343a. The protection circuit 346 is also electrically connected to each of the multiple cells 100 via wiring 35.

The protective sheet 33 is arranged on both inner surfaces of the long sides of the container 31 and on the inner surface of the short side that faces the printed wiring board 34 via the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

The protection circuit 346 controls the charging and discharging of the multiple cells 100. Furthermore, the protection circuit 346 cuts off the electrical connection between the protection circuit 346 and the external terminals 350 (positive terminal 352, negative terminal 353) for supplying electricity to external devices based on a detection signal transmitted from the thermistor 345 or a detection signal transmitted from an individual cell 100 or the battery pack 200.

Examples of detection signals transmitted from the thermistor 345 include signals detecting that the temperature of a cell 100 is equal to or higher than a predetermined temperature. Examples of detection signals transmitted from an individual cell 100 or the battery pack 200 include signals detecting overcharge, overdischarge, and overcurrent of a cell 100. When detecting overcharge, etc. for an individual cell 100, the battery voltage may be detected, or the positive electrode potential or negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 100.

The protection circuit 346 may also be a circuit included in a device (e.g., electronic equipment, automobile, etc.) that uses the battery pack 300 as a power source.

Furthermore, as described above, the battery pack 300 is equipped with the external terminal 350 for current flow. Therefore, the battery pack 300 can output current from the battery assembly 200 to an external device and input current from the external device to the battery assembly 200 via the external terminal 350 for current flow. In other words, when the battery pack 300 is used as a power source, current from the battery assembly 200 is supplied to the external device via the external terminal 350 for current flow. Furthermore, when charging the battery pack 300, charging current from the external device is supplied to the battery pack 300 via the external terminal 350 for current flow. When the battery pack 300 is used as an in-vehicle battery, regenerative energy from the vehicle's power can be used as charging current from the external device.

The battery pack 300 may include multiple battery assemblies 200. In this case, the multiple battery assemblies 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed wiring board 34 and wiring 35 may also be omitted. In this case, the positive electrode lead 22 and the negative electrode lead 23 may be used as the positive terminal 352 and the negative terminal 353, respectively, of the external terminal 350 for current supply.

Such battery packs are used in applications that require excellent cycle performance, for example, when drawing large currents. Specific examples of such battery packs include power sources for electronic devices, stationary batteries, and on-board batteries for various vehicles. Examples of electronic devices include digital cameras. This battery pack is particularly suitable for use as an on-board battery.

The battery pack according to the fifth embodiment includes the secondary battery according to the third embodiment or the battery pack according to the fourth embodiment. Therefore, the battery pack has a high capacity per volume.

Sixth Embodiment
According to a sixth embodiment, a vehicle is provided, which is equipped with the battery pack according to the fifth embodiment.

In such a vehicle, the battery pack, for example, recovers regenerative energy from the vehicle's motive power. The vehicle may also include a mechanism (regenerator) that converts the vehicle's kinetic energy into regenerative energy.

Examples of vehicles include two- to four-wheeled hybrid electric vehicles, two- to four-wheeled electric vehicles, power-assisted bicycles, and rail vehicles.

The location where the battery pack is installed in a vehicle is not particularly limited. For example, when the battery pack is installed in an automobile, the battery pack can be installed in the engine compartment, the rear of the vehicle, or under the seat.

A vehicle may be equipped with multiple battery packs. In this case, the batteries included in each battery pack may be electrically connected in series, in parallel, or a combination of series and parallel connections. For example, if each battery pack includes a battery assembly, the battery assembly may be electrically connected in series, in parallel, or a combination of series and parallel connections. Alternatively, if each battery pack includes a single battery, the batteries may be electrically connected in series, in parallel, or a combination of series and parallel connections.

Next, an example of a vehicle according to an embodiment will be described with reference to the drawings.

Figure 10 is a partially transparent view showing an example of a vehicle.

The vehicle 400 shown in Figure 10 includes a vehicle body 40 and a battery pack 300 according to the fifth embodiment. In the example shown in Figure 10, the vehicle 400 is a four-wheeled automobile.

The vehicle 400 may be equipped with multiple battery packs 300. In this case, the batteries (e.g., single cells or battery packs) included in the battery packs 300 may be connected in series, in parallel, or in a combination of series and parallel connections.

Figure 10 illustrates an example in which the battery pack 300 is mounted in an engine compartment located in the front of the vehicle body 40. As mentioned above, the battery pack 300 may also be mounted, for example, at the rear of the vehicle body 400 or under a seat. This battery pack 300 can be used as a power source for the vehicle 400. In addition, this battery pack 300 can recover regenerative energy for powering the vehicle 400.

Next, referring to Figure 11, we will explain the implementation of a vehicle according to an embodiment.

Figure 11 is a diagram that shows an example of a control system for an electrical system in a vehicle. The vehicle 400 shown in Figure 11 is an electric vehicle.

The vehicle 400 shown in Figure 11 includes a vehicle body 40, a vehicle power supply 41, a vehicle ECU (Electric Control Unit) 42 which is a higher-level control device for the vehicle power supply 41, an external terminal (terminal for connecting to an external power supply) 43, an inverter 44, and a drive motor 45.

The vehicle 400 is equipped with a vehicle power supply 41, for example, in the engine compartment, at the rear of the vehicle body, or under the seat. Note that the location of the vehicle power supply 41 in the vehicle 400 shown in Figure 11 is shown schematically.

The vehicle power supply 41 includes multiple (e.g., three) battery packs 300a, 300b, and 300c, a battery management unit (BMU) 411, and a communication bus 412.

Battery pack 300a includes battery pack 200a and battery pack monitoring device 301a (e.g., VTM: Voltage Temperature Monitoring). Battery pack 300b includes battery pack 200b and battery pack monitoring device 301b. Battery pack 300c includes battery pack 200c and battery pack monitoring device 301c. Battery packs 300a-300c are similar to battery pack 300 described above, and battery packs 200a-200c are similar to battery pack 200 described above. Battery packs 200a-200c are electrically connected in series. Battery packs 300a, 300b, and 300c can each be removed independently and replaced with another battery pack 300.

Each of the assembled batteries 200a to 200c includes a plurality of cells connected in series. At least one of the cells is a secondary battery according to the third embodiment. The assembled batteries 200a to 200c are charged and discharged via the positive terminal 413 and the negative terminal 414, respectively.

The battery management unit 411 communicates with the assembled battery monitoring units 301a-301c and collects information on the voltage, temperature, and other characteristics of each of the cells 100 contained in the assembled batteries 200a-200c included in the vehicle power supply 41. In this way, the battery management unit 411 collects information related to the maintenance of the vehicle power supply 41.

The battery management unit 411 and the assembled battery monitoring units 301a-301c are connected via a communication bus 412. In the communication bus 412, one set of communication lines is shared by multiple nodes (the battery management unit 411 and one or more assembled battery monitoring units 301a-301c). The communication bus 412 is a communication bus configured based on, for example, the CAN (Control Area Network) standard.

The battery pack monitoring devices 301a-301c measure the voltage and temperature of each cell that makes up the battery packs 200a-200c based on commands received via communication from the battery management device 411. However, the temperature can be measured at only a few locations per battery pack; it is not necessary to measure the temperature of all the cells.

The vehicle power supply 41 may also have an electromagnetic contactor (e.g., the switch device 415 shown in FIG. 11) that switches the electrical connection between the positive terminal 413 and the negative terminal 414. The switch device 415 includes a pre-charge switch (not shown) that turns on when the assembled batteries 200a-200c are being charged, and a main switch (not shown) that turns on when output from the assembled batteries 200a-200c is being supplied to a load. The pre-charge switch and the main switch each include a relay circuit (not shown) that is switched on or off by a signal supplied to a coil located near the switch element. Electromagnetic contactors such as the switch device 415 are controlled based on control signals from the battery management unit 411 or the vehicle ECU 42, which controls the operation of the entire vehicle 400.

The inverter 44 converts the input DC voltage into a three-phase alternating current (AC) high voltage for driving the motor. The three-phase output terminals of the inverter 44 are connected to the three-phase input terminals of the drive motor 45. The inverter 44 is controlled based on control signals from the battery management unit 411 or the vehicle ECU 42, which controls the operation of the entire vehicle. By controlling the inverter 44, the output voltage from the inverter 44 is adjusted.

The drive motor 45 rotates using power supplied from the inverter 44. The driving force generated by the rotation of the drive motor 45 is transmitted to the axles and drive wheels W, for example, via a differential gear unit.

Although not shown, the vehicle 400 is also equipped with a regenerative braking mechanism (regenerator). The regenerative braking mechanism rotates the drive motor 45 when the vehicle 400 is braked, converting kinetic energy into regenerative energy in the form of electrical energy. The regenerative energy recovered by the regenerative braking mechanism is input to the inverter 44 and converted into direct current. The converted direct current is input to the vehicle power supply 41.

One terminal of the connection line L1 is connected to the negative terminal 414 of the vehicle power supply 41. The other terminal of the connection line L1 is connected to the negative input terminal 417 of the inverter 44. A current detection unit (current detection circuit) 416 within the battery management device 411 is provided on the connection line L1 between the negative terminal 414 and the negative input terminal 417.

One terminal of the connection line L2 is connected to the positive terminal 413 of the vehicle power supply 41. The other terminal of the connection line L2 is connected to the positive input terminal 418 of the inverter 44. A switch device 415 is provided on the connection line L2 between the positive terminal 413 and the positive input terminal 418.

The external terminal 43 is connected to the battery management device 411. The external terminal 43 can be connected to, for example, an external power source.

In response to operational inputs from the driver and other devices, the vehicle ECU 42 coordinates control of the vehicle power supply 41, switch device 415, inverter 44, etc. together with other management and control devices, including the battery management device 411. Through coordinated control by the vehicle ECU 42 and other devices, the output of power from the vehicle power supply 41 and the charging of the vehicle power supply 41 are controlled, and the entire vehicle 400 is managed. Data related to the maintenance of the vehicle power supply 41, such as the remaining capacity of the vehicle power supply 41, is transferred via a communication line between the battery management device 411 and the vehicle ECU 42.

The vehicle according to the sixth embodiment is equipped with the battery pack according to the fifth embodiment. Because the battery pack has a high capacity per volume, there is a high degree of freedom in vehicle design. Therefore, it is possible to provide a wide variety of vehicles without compromising vehicle performance.

The above embodiment will be described in more detail below based on examples. However, the present invention is not limited to the examples listed below.

<Synthesis>
Example 1
A titanium-niobium-molybdenum composite oxide was synthesized as follows.

Niobium ammonium oxalate, ammonium molybdate, and titanium tetraisopropoxide were prepared as raw materials. These raw materials were weighed according to the specified composition ratio. Solution A was prepared by dissolving niobium ammonium oxalate and ammonium molybdate in pure water. Next, titanium tetraisopropoxide was added to a 1M aqueous oxalic acid solution and dissolved by heating and stirring to prepare Solution B. After mixing Solutions A and B, an ammonia solution was added while heating and stirring to adjust the pH to 7, yielding a sol. The sol was spray-dried at 180°C to evaporate the solvent, yielding a white precursor powder. The precursor powder was placed in an alumina crucible and fired in air at 600°C for 4 hours. The fired product was then dry-pulverized, and the pulverized product was classified to adjust the particle size. This process yielded an active material powder.

Example 2
A composite oxide was synthesized and an active material powder was obtained in the same manner as in Example 1, except that the temperature for firing the precursor was changed to 700°C.

Example 3
A composite oxide was synthesized and an active material powder was obtained in the same manner as in Example 1, except that the temperature for firing the precursor was changed to 800°C.

(Examples 4-7)
A composite oxide was synthesized in the same manner as in Example 1, except that the weighing ratio of the raw materials was adjusted, and an active material powder was obtained.

(Comparative Example 1)
A composite oxide was synthesized and an active material powder was obtained in the same manner as in Example 1, except that the temperature for firing the precursor powder was changed to 900°C.

<Measurement>
The powders obtained in the above Examples and Comparative Examples were observed using a scanning transmission electron microscope. Specifically, as described above, the microstructure was observed using a 10 nm x 10 nm image using a spherical aberration-corrected STEM-HAADF image. Wide-angle X-ray scattering measurements were also performed. The measurements were performed in accordance with the details described above. Crystal structure analysis was performed using the Rietveld method on the obtained spectra. Inductively Coupled Plasma (ICP) emission spectroscopy and HAXPES measurements were also performed.

Part of the obtained XRD spectra are shown in Figures 12 to 16. Figure 12 shows the spectrum for the composite oxide obtained in Example 1. Figure 13 shows the spectrum for the composite oxide obtained in Example 2. Figure 14 shows the spectrum for the composite oxide obtained in Example 3. Figure 15 shows the spectrum for the composite oxide obtained in Comparative Example 1. Figure 16 shows an enlarged spectrum of the range including peaks P1 and P2 of the crystal structure.

In the XRD spectrum of the composite oxide of Example 1, two main peaks, peaks P1 and P2, were observed at 2θ = 25.30° and 2θ = 23.88°, respectively. In contrast, in the XRD spectrum of the composite oxide of Comparative Example 1, the main peak observed together with peak P2 was located at 2θ = 25.40°, and was determined to be not peak P1 but peak _P420 derived from the (420) plane derived from the crystal structure of Figure 1. In Examples 2 and 3, the crystal structures of Figures 1 and 2 were mixed, but peaks _P420 and P1 derived from each overlapped, and a broad composite peak was confirmed, with peak P1 appearing as a shoulder on the low-angle side. Therefore, for Examples 2 and 3, simple fitting using a pseudo-Voigt function was further performed to separate the overlapping peaks (not shown).

For the composite oxide obtained in Example 1, observation of the microstructure using STEM-HAADF images revealed that the size of the _ReO3 blocks within the field of view varied, and that the crystal structure was non-periodic and connected by octahedral edge-sharing. Therefore, the crystal structure was identified as that shown in Figure 2. Connections involving tetrahedral corner-sharing were also confirmed in different fields of view.

The metal ratio of the composite oxide obtained in Example 1 was calculated by ICP analysis, resulting in a Ti:Nb:Mo = 0.23:1.00:0.23. The valence was evaluated by HAXPES measurement. Ti element was identified as tetravalent because a single peak derived from Ti2p3 _/2 was observed within the range of 459 ± 0.4 eV. Nb element was identified as pentavalent because a single peak derived from Nb5d3 _/2 was observed within the range of 207.5 ± eV. Mo element was identified as a mixed pentavalent and hexavalent peak because a peak derived from Mo3d5 _/2 derived from hexavalent was observed at 232.2 ± 0.3 eV, and a different peak was confirmed to be present at a value 1 eV smaller than that peak. Based on the peak mixture ratio, it was estimated that pentavalent and hexavalent elements were present in a 1:1 ratio, and the average valence was assumed to be 5.5. The composition formula calculated based on this assumption is Ti _0.23 NbMo _0.23 O _3.59 , where b = 0.23, c = 0.23, and d = 3.59.

It was confirmed that the composite oxide obtained in Example 2 contained a mixture of the crystal structures shown in Figures 1 and 2.

The metal ratio of the composite oxide obtained in Example 2 was calculated by ICP analysis, and was found to be Ti:Nb:Mo = 0.23:1.00:0.18. The valences were evaluated by HAXPES measurement using the same method as in Example 1, and Ti was identified as tetravalent, Nb as pentavalent, and the Mo valence _{as 5.3} . The composition formula calculated from the valences was _{Ti0.23NbMo0.18O3.47} . Therefore, b = 0.23, c = 0.18, and d = 3.47.

It was confirmed that the composite oxide obtained in Example 3 contained a mixture of the crystal structures shown in Figures 1 and 2.

The metal ratio of the composite oxide obtained in Example 3 was calculated by ICP analysis, and was found to be Ti:Nb:Mo = 0.23:1.00:0.18. The valences were evaluated by HAXPES measurement using the same method as in Example 1, and Ti was tetravalent, Nb was pentavalent, and the Mo valence was _5.6 . The composition formula calculated from the valences was _{Ti0.23NbMo0.18O3.49} . Therefore, b = 0.23, c = 0.18, and d = _3.49 .

The composite oxide obtained in Comparative Example 1 was confirmed to have the crystalline structure shown in Figure 1. Furthermore, structural analysis by XRD also confirmed the crystalline structure shown in Figure 1. Specifically, the estimated model was a crystalline structure assigned to space group I ^- 4 (space group number: 82), with 3 x 3 = 9 rhenium oxide-type block structures including tetrahedral corner-sharing structures, and a ratio of the number of oxygen atoms to the number of metal elements in the unit cell of _AO / _AM = 2.50. When this crystalline structure was used as the estimated model, fitting was performed to a Rietveld reliability factor R _wp value of 9.11% for all peaks excluding the heterophase appearing between 5° and 70°, and consistent peak positions and relative intensities were confirmed, confirming the above crystalline structure. The lattice constants were calculated as a = b = 15.703 Å, c = 3.803 Å, and 937.77 ^ų .

The main peak in the XRD spectrum of the composite oxide according to Comparative Example 1 shown in Figures 15 and 16 is determined to be peak _P420 , which originates from the (420) plane derived from the crystal structure of Figure 1, as described above. As described above, Comparative Example 1 is identified as having the crystal structure shown in Figure 1, and in this structure, the (420) plane appears prominently from the atomic positions, and peak P1 does not appear with a distinguishable intensity. Furthermore, since the lattice constant is large due to the large amount of tetrahedrons included, peak P1 does not appear in the range of 2θ = 25.05 ± 0.25°.

The metal ratio of the composite oxide obtained in Comparative Example 1 was calculated by ICP analysis, and was found to be Ti:Nb:Mo = 0.23:1.00: _0.15 . The composition formula calculated from the number of elements and crystal structure was _{Ti0.23NbMo0.15O3.45} . The valences were evaluated by _HAXPES measurement, and the Ti valence was found to be tetravalent, the Nb valence was pentavalent, and the Mo valence was _hexavalent . The composition formula calculated from the valences was found to be _{Ti0.23NbMo0.15O3.41} . Therefore, b = 0.23, c = _0.15 , and d = 3.41.

Table 1 below summarizes the results of structural analysis of the composite oxides synthesized in each example and comparative example. Specifically, it shows the composition formula derived by combining ICP analysis with HAXPES measurement, and the peak intensity ratio I1/I2 between peak P1 and peak P2 in the XRD spectrum.

As shown in Table 1, in both Examples 1-7 and Comparative Example 1, composite oxides having compositions represented by the general formula Li _a M _b NbMo _c O _d and containing rhenium oxide-type block structures composed of octahedral structures were synthesized. Furthermore, for Examples 1-7, STEM-HAADF observation confirmed that at least a portion of the crystal structure contained the structure shown in Figure 2. In particular, since the peak intensity ratio I1/I2 in the XRD spectra for Examples 1 and 4-6 was 1 or greater, it can be determined that the crystal structure shown in Figure 2 was the primary structure. In contrast, as described above, both the STEM-HAADF image and XRD spectrum for Comparative Example 1 were consistent with the crystal structure shown in Figure 1. Note that, as described above, the main peak in the spectrum of Comparative Example 1 is assigned to the (420) plane, and peak P1 does not appear in the spectrum. Therefore, in Comparative Example 1, peak intensity I1 was set to zero, which resulted in a peak intensity ratio I1/I2 of zero.

<Evaluation of battery performance>
Using the active material powders obtained in the above Examples and Comparative Examples, electrodes were fabricated as follows.

First, 100 parts by weight of active material, 6 parts by weight of conductive agent, and 4 parts by weight of binder were dispersed in a solvent to prepare a slurry. The composite material powders obtained using the method described above were used as the active materials. The conductive agent was a mixture of acetylene black, carbon nanotubes, and graphite. The binder was a mixture of carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR). Pure water was used as the solvent.

The resulting slurry was then applied to one side of a current collector, and the coating was dried to form an active material-containing layer. The current collector was an aluminum foil with a thickness of 12 μm. The current collector and the active material-containing layer were then pressed together to obtain an electrode. The electrode had a basis weight of 60 g/ ^m² .

A non-aqueous electrolyte was prepared as follows. An electrolyte salt was dissolved in an organic solvent to obtain a liquid non-aqueous electrolyte. _LiPF6 was used as the electrolyte salt. The molar concentration of _LiPF6 in the non-aqueous electrolyte was 1 mol/L. A mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) was used as the organic solvent. The volume ratio of EC to DEC was 1:2.

A three-electrode beaker cell was fabricated using the electrode obtained by the above-mentioned method as the working electrode, metal lithium foil as the counter electrode and reference electrode, and the nonaqueous electrolyte prepared by the above-mentioned method.

The initial charge/discharge performance of each fabricated cell was evaluated. Specifically, the cell was first charged at a temperature of 25°C with a charging current of 0.2 C until the battery voltage reached 0.7 V, and then subjected to constant voltage charging for 10 hours. The cell was then discharged with a discharge current of 0.2 C until the battery voltage reached 3.0 V. The charge/discharge capacity at this time was measured, and the capacity value per volume of the electrode active material-containing layer (excluding the current collector) was calculated for each charge and discharge. The charge/discharge efficiency during the initial charge/discharge was also calculated (initial charge/discharge efficiency = [(initial discharge capacity/initial charge capacity) × 100%]).

Figure 17 shows a graph showing the initial charge/discharge curves of some beaker cells. The charge curve is shown as the curve extending from the upper left to the lower right of the graph. The discharge curve is shown as the curve extending from the lower left to the upper right of the graph.

Table 2 below summarizes the performance of the composite oxides synthesized in each example and comparative example as active materials for batteries. Specifically, it shows the charge capacity and discharge capacity per volume, as well as the initial charge/discharge efficiency.

The composite oxide contained in the active material obtained in Example 1-7 was represented by the general formula Li _a M _b NbMo _c O _d described above and contained at least a portion of the crystal structure shown in FIG. 2, whereas the composite oxide obtained in Comparative Example 1 satisfied the general formula but had the main crystal structure shown in FIG. 1. As shown in Table 2, the active material of Example 1-7 exhibited higher charge capacity and discharge capacity than the composite oxide of Comparative Example 1. In addition, the initial charge/discharge efficiency obtained using the active material of Example 1-7 was comparable to that when Comparative Example 1 was used.

Therefore, it can be seen that a composite oxide having a crystal structure including the above-mentioned rhenium oxide-type block structure, represented by the above general formula Li _a M _b Nb Mo _{c O d} , and including the crystal structure shown in FIG. 2, exhibits good initial charge-discharge efficiency as an electrode active material and also has a high charge-discharge capacity per volume.

According to one or more of the above-described embodiments and examples, an active material containing a composite oxide is provided. The composite oxide includes rhenium oxide blocks in which an octahedral structure composed of oxygen and a metal element is formed by corner-sharing, and includes a structure in which multiple rhenium oxide blocks of different sizes are connected aperiodically by at least octahedral edge- _sharing . The composite oxide is represented by the general formula _LiaMbNbMocOd . Here, M in the _formula is any _one selected from the group consisting of Ti, V, Ta, Fe, Co, Mn, Ni, Bi, Sb, As, P, Cr, W, B, Na, K, Mg, Al, Ca, Y, and Si. The subscripts in the formula satisfy the relationships 0≦a≦b+2+3c, 0≦b≦1.5, 0≦c≦0.5, and 2.33≦d/(1+b+c)≦2.50, respectively. This active material can provide electrodes capable of realizing high-capacity secondary batteries, high-capacity secondary batteries and battery packs, and vehicles equipped with such battery packs.

The following describes several embodiments of the present invention.

[1] A structure including an octahedral structure composed of oxygen and a metal element, the octahedral structure including rhenium oxide type blocks configured by corner sharing, the octahedral structure including a plurality of rhenium oxide type blocks of different sizes, and the rhenium oxide type blocks including a structure in which the rhenium oxide type blocks are connected at least by octahedral edge sharing without periodicity,
An active material comprising a composite oxide represented by the general formula Li _a M _b NbMo _c O _d , where M is one or more selected from the group consisting of Ti, V, Ta, Fe, Co, Mn, Ni, Bi, Sb, As, P, Cr, W, B, Na, K, Mg, Al, Ca, Y and Si, and where 0≦a≦b+2+3c, 0≦b≦1.4, 0≦c≦0.5, and 2.33≦d/(1+b+c)≦2.50.
[2] A structure including an octahedral structure composed of oxygen and a metal element, the octahedral structure including rhenium oxide type blocks configured by corner sharing, the octahedral structure including a plurality of rhenium oxide type blocks of different sizes, and the rhenium oxide type blocks including a structure in which the rhenium oxide type blocks are connected at least aperiodically by octahedral edge sharing,
An active material comprising a composite oxide represented by the general formula Li _a M _b NbMo _c O _d , where M is one or more selected from the group consisting of Ti, V, Ta, Fe, Co, Mn, Ni, Bi, Sb, As, P, Cr, W, B, Na, K, Mg, Al, Ca, Y and Si, and where 0≦a≦b+2+3c, 0≦b≦1.5, 0≦c≦0.5, and 2.33≦d/(1+b+c)≦2.50.

[3] The active material according to [1] or [2], wherein in a diffraction spectrum of the composite oxide by powder X-ray diffraction using a Cu-Kα radiation source, the peak intensity I1 of peak P1 appearing within the range of 2θ = 25.05 ± 0.25° and the peak intensity I2 of peak P2 appearing within the range of 2θ = 24.00 ± 0.20° satisfy the relationship I1/I2 > 0.1.

[4] An electrode containing the active material described in any one of [1] to [3].

[5] The electrode described in [4], which includes an active material-containing layer containing the active material.

[6] a positive electrode;
a negative electrode;
and an electrolyte,
The secondary battery, wherein the positive electrode or the negative electrode is the electrode according to [4] or [5].

[7] A battery pack comprising the secondary battery described in [6].

[8] An external terminal for supplying current;
The battery pack according to [7], further comprising a protection circuit.

[9] A battery comprising a plurality of the secondary batteries,
The battery pack according to [7] or [8], wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.

[10] A vehicle equipped with the battery pack described in any one of [7] to [9].

[11] The vehicle described in [10], including a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

While several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be embodied in a variety of other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. These embodiments and their variations are within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

DESCRIPTION OF SYMBOLS 1... Electrode group, 2... Exterior member, 3... Negative electrode, 3a... Negative electrode current collector, 3b... Negative electrode active material containing layer, 4... Separator, 5... Positive electrode, 5a... Positive electrode current collector, 5b... Positive electrode active material containing layer, 6... Negative electrode terminal , 7... Positive electrode terminal, 10... Crystal structure, 10a... Octahedron, 10b... Tetrahedron, 11... Crystal structure, 11a... Octahedron, 11b... Tetrahedron, 18... Metal element, 19... Oxygen element, 21... Bus bar , 22...positive electrode side lead, 23...negative electrode side lead, 24...adhesive tape, 31...container, 32...lid, 33...protective sheet, 34...printed wiring board, 35...wiring, 40...vehicle body, 41...vehicle power supply, 42...electrical control device, 43...external terminal, 44...inverter, 45...drive motor, 100...secondary battery, 200...assembled battery, 200a...assembled battery, 200b...assembled battery, 200c...assembled battery, 300...battery pack, 300a...battery pack, 300b...battery pack, 300c...battery pack, 301a...assembled battery monitoring device, 301b...assembled battery monitoring device, 301c...assembled battery monitoring device, 342...positive electrode side connector, 343...negative electrode side connector, 345...thermistor, 346...protection circuit, 342a...wiring, 343a...wiring, 350...external terminal for supplying current terminal, 352...positive terminal, 353...negative terminal, 348a...positive wiring, 348b...negative wiring, 400...vehicle, 411...battery management device, 412...communication bus, 413...positive terminal, 414...negative terminal, 415...switch device, 416...current detection unit, 417...negative input terminal, 418...positive input terminal, L1...connection line, L2...connection line, W...drive wheel.

Claims (11)

The present invention relates to a structure comprising an octahedral structure composed of oxygen and a metal element, the octahedral structure comprising rhenium oxide type blocks formed by corner sharing, the octahedral structure comprising a plurality of rhenium oxide type blocks of different sizes, and the rhenium oxide type blocks being connected at least by octahedral edge sharing without periodicity,
An active material comprising a composite oxide represented by the general formula Li _a M _b NbMo _c O _d , where M is one or more selected from the group consisting of Ti, V, Ta, Fe, Co, Mn, Ni, Bi, Sb, As, P, Cr, W, B, Na, K, Mg, Al, Ca, Y and Si, and where 0≦a≦b+2+3c, 0≦b≦1.4, 0≦c≦0.5, and 2.33≦d/(1+b+c)≦2.50. The present invention relates to a structure comprising an octahedral structure composed of oxygen and a metal element, the octahedral structure comprising rhenium oxide type blocks formed by corner sharing, the octahedral structure comprising a plurality of rhenium oxide type blocks of different sizes, and the rhenium oxide type blocks being connected at least by octahedral edge sharing without periodicity,
An active material comprising a composite oxide represented by the general formula Li _a M _b NbMo _c O _d , where M is one or more selected from the group consisting of Ti, V, Ta, Fe, Co, Mn, Ni, Bi, Sb, As, P, Cr, W, B, Na, K, Mg, Al, Ca, Y and Si, and where 0≦a≦b+2+3c, 0≦b≦1.5, 0≦c≦0.5, and 2.33≦d/(1+b+c)≦2.50. The active material of claim 2, wherein in a diffraction spectrum of the composite oxide by powder X-ray diffraction using a Cu-Kα radiation source, the peak intensity I1 of peak P1 appearing within the range of 2θ = 25.05 ± 0.25° and the peak intensity I2 of peak P2 appearing within the range of 2θ = 24.00 ± 0.20° satisfy the relationship I1/I2 > 0.1. An electrode containing the active material described in claim 2 or 3. The electrode described in claim 4, comprising an active material-containing layer containing the active material. A positive electrode and
a negative electrode;
and an electrolyte,
The secondary battery, wherein the positive electrode or the negative electrode is the electrode according to claim 4 . A battery pack comprising the secondary battery described in claim 6. An external terminal for applying current;
8. The battery pack according to claim 7, further comprising a protection circuit. A battery includes a plurality of the secondary batteries,
The battery pack according to claim 7 , wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel. A vehicle equipped with the battery pack of claim 7. The vehicle of claim 10, further comprising a mechanism for converting kinetic energy of the vehicle into regenerative energy.