JP7600254B2 - Electrodes, batteries and battery packs - Google Patents

Description

Embodiments of the present invention relate to electrodes, batteries and battery packs.

It has been reported that using active materials with different particle sizes can improve electrode density and produce nonaqueous electrolyte batteries with excellent input/output characteristics. However, no attention has been paid to the distribution of large and small particle sizes in the thickness direction within the electrode.

Japanese Patent Application Publication No. 2019-067541 Japanese Patent Application Publication No. 2009-117241 Japanese Patent Application Publication No. 2016-55254 Japan Special Table No. 2013-504168 Japan Special Table No. 2015-528181

The objective is to provide electrodes, batteries, and battery packs that have high capacity and excellent life characteristics.

According to an embodiment, an electrode is provided that includes a current collector and a mixture layer that is formed on at least one surface of the current collector and includes an active material. The active material includes first particles of a lithium-containing metal oxide and second particles of a lithium-containing metal oxide having an average particle size _D2 smaller than the average particle size _D1 of the first particles. The existence ratio of the first particles and the second particles represented by the following formula (1) is 60% or more and 90% or less.

{A1/(A1+A2)}×100 (1)
When the distance from the first surface of the mixture layer that contacts the current collector to the second surface that does not contact the current collector is T, A1 is the first distance on the surface of the mixture layer that has the length of the distance T. A1 is the sum of the areas of the first particles on the surface of the mixture layer having the distance T in length, and A2 is the sum of the areas of the second particles on the surface of the mixture layer having the distance T in length.

The first particles are unevenly distributed within a range of a distance 2D ₁ /T from the first surface toward the second surface at a ratio that satisfies the following formula (2).

(A3/A1)≧2D ₁ /T×1.05 (2)
Here, A3 is the total area of the first particles present within a range of a distance 2D ₁ /T from the first surface toward the second surface on the surface of the mixture layer having a length of the distance T. .
The particle size of the first particles is within a range of 8 μm to 25 μm, and the average particle size is the average particle size D1 _. The particle size of the second particles is within a range of 1 μm to 6 μm, and the particle size of the first particles is the average particle size D2. The average particle size is the average particle size D2 _.

According to another embodiment, a battery is provided that includes a positive electrode formed of the electrode according to the above embodiment and a negative electrode.

According to another embodiment, a battery pack is provided that includes a battery according to the above embodiment.

FIG. 2 is a schematic diagram showing an example of a cross section of a mixture layer of an electrode according to an embodiment. FIG. 2 is a plan view showing an outline of a sample obtained from the electrode of the embodiment. FIG. 4 is a plan view showing an example of an electrode group. FIG. 11 is a plan view showing another example of an electrode group. FIG. 2 is a partially cutaway perspective view showing an example of a battery according to an embodiment. FIG. 6 is an enlarged cross-sectional view of a portion A of the battery shown in FIG. 5 . FIG. 4 is a partially cutaway perspective view showing another example of a battery according to an embodiment. FIG. 13 is a partially cutaway perspective view showing still another example of a battery according to an embodiment. FIG. 9 is an enlarged cross-sectional view of part B of the battery shown in FIG. 8 . FIG. 2 is an exploded perspective view showing an example of a battery pack according to an embodiment. FIG. 11 is a block diagram showing an example of an electrical circuit of the battery pack shown in FIG. 10 .

(First embodiment)
Hereinafter, the embodiments will be described with reference to the drawings. In the following description, components that perform the same or similar functions are given the same reference numerals throughout the drawings, and duplicated descriptions will be omitted. Note that each figure is a schematic diagram for explaining the embodiment and facilitating understanding thereof, and the shapes, dimensions, ratios, etc. may differ from the actual device, but these can be appropriately modified in design by taking into consideration the following description and known techniques.
Patent Document 1 discloses that by setting the average particle size of the granules contained in the positive electrode mixture layer to 0.9 μm or more and 2 μm or less, and setting the particle size of 90% or more of the granules to 0.25 μm or more and 3.5 μm or less, it is possible to reduce the interface resistance between the current collector and the positive electrode mixture layer and improve the lithium ion conduction rate within the granules even if the pressure of the electrode is increased. Patent Document 2 discloses that by filling a lithium nickel manganese cobalt-based composite oxide powder having voids on the surface and inside of the secondary particles with fine particles smaller than the void size, it is possible to obtain a positive electrode active material powder with improved output characteristics by further filling the lithium nickel manganese cobalt-based composite oxide powder having voids on the surface and inside of the secondary particles with fine particles smaller than the void size.
However, all of the technologies to date have problems with life performance.

The inventors have determined that when the ratio of small particle active material inside the electrode mixture layer is high, the amount of gas generated increases, and the active material slides out from inside the electrode mixture layer during high-temperature storage, leading to a decrease in capacity. They have found that an electrode having the following configuration suppresses the amount of gas generated at high temperatures and improves life performance.

That is, the electrode according to the embodiment includes a current collector and a mixture layer formed on at least one surface of the current collector and including an active material, the active material including first particles of a lithium-containing metal oxide and second particles of a lithium-containing metal oxide having an average particle size _D2 smaller than the average particle size _D1 of the first particles. The existence ratio of the first particles and the second particles represented by the following formula (1) is 60% or more and 90% or less.

{A1/(A1+A2)}×100 (1)
When the distance from the first surface of the mixture layer that is in contact with the current collector to the second surface that is not in contact with the current collector is T, A1 is the surface of the mixture layer having a length of the distance T (hereinafter , the measurement surface), and A2 is the sum of the areas of the first particles in the measurement surface.

The first particles are unevenly distributed in a range from the first surface toward the second surface by a distance 2D ₁ /T (hereinafter, 2D ₁ /T region) at a ratio that satisfies the following formula (2).

(A3/A1)≧2D ₁ /T×1.05 (2)
Here, A3 is the total area of the first particles present in the 2D ₁ /T region of the measurement surface.

First, the reason why the abundance ratio represented by formula (1) is set in the range of 60% or more and 90% or less will be explained. If the abundance ratio is set to less than 60%, the abundance ratio of the second particles becomes relatively high, and the surface area of the active material becomes large. As a result, the side reaction between the active material and the electrolyte becomes large, and the amount of gas generated increases. On the other hand, if the abundance ratio exceeds 90%, the particle diameter of the active material becomes uniform, and the packing density of the active material decreases. For the above reasons, the abundance ratio is preferably in the above range. A more preferable range of the abundance ratio is 70% or more and 85% or less.

Next, formula (2) will be described. FIG. 1 is a schematic diagram of an example of a cross section of an electrode of the embodiment cut in the lamination direction. The electrode E is, for example, a positive electrode, and includes a layered positive electrode current collector C and a positive electrode mixture layer M formed on each of both sides of the positive electrode current collector C. The positive electrode mixture layer M includes a first particle P of a lithium-containing metal oxide and a second particle Q of a lithium-containing metal oxide having an average particle diameter D ₂ smaller than the average particle diameter D ₁ of the first particle. The surface of the positive electrode mixture layer M that contacts the positive electrode current collector C is the first surface S1, and the surface that does not contact the positive electrode current collector C is the second surface S2. The distance from the second surface S2 to the first surface S1 is T. In the above-mentioned measurement surface, the first particles P are unevenly distributed in a region ( _{2D 1 /} T region) defined by the length from the first surface S1 to the second surface S2 at a ratio that satisfies formula (2). The ratio of the area A3 of the first particles P present in the 2D ₁ /T region to the area A1 of the entire first particles P is represented by (A3/A1). When the abundance ratio represented by formula (1) is 60% or more and 90% or less, if the ratio of (A3/A1) is less than the value represented by 2D ₁ /T×1.05, the gas escape property from the mixture layer is reduced, and the mixture layer slides off during the charge and discharge cycle. As a result, the capacity reduction due to gas generation at high temperatures increases, and the charge and discharge cycle performance, especially the charge and discharge cycle performance at high temperatures, is reduced. By setting the abundance ratio represented by formula (1) to 60% or more and 90% or less, and setting the ratio of (A3/A1) to a value equal to or greater than the value represented by 2D ₁ /T×1.05, the gas escape property from the mixture layer is improved, and the slide off of the mixture layer during the charge and discharge cycle can be suppressed. As a result, the capacity reduction due to gas generation at high temperatures can be suppressed, and the charge and discharge cycle performance, especially the charge and discharge cycle performance at high temperatures, can be improved. In addition, the packing density of the active material can be increased, resulting in a high capacity, and thus an electrode capable of realizing a battery having a high capacity and excellent charge/discharge cycle performance can be provided.

The measurement methods for D ₁ and D ₂ are as follows.

The distance T, i.e., the thickness of the mixture layer, is measured as follows. It can be obtained by observing a cross section of the electrode cut along its lamination direction, for example, the cross section shown in FIG. 1, with a scanning electron microscope (SEM). As shown in FIG. 2, 5 cm of the electrode E is selected in an arbitrary direction (hereinafter, X direction), and divided into 5 in a direction perpendicular to the X direction (hereinafter, Y direction) to obtain 5 samples. Sample Z located at the center in the X direction among the obtained 5 samples is used as the measurement sample. The width of sample Z in the Y direction is divided into 2 to obtain two cross sections. An example of a cross section is shown in FIG. 1. An arbitrary cross section of the two obtained cross sections is observed with an SEM, and the distance between the contact point of the mixture layer and the current collector and the surface of the mixture layer that is not in contact with the current collector is measured at 4 positions (for example, shown by the dashed line in FIG. 1) that divide the range observed at a magnification of 1000 times into 5 equal parts, and the average value of the measured values obtained at the 4 points is taken as the thickness T of the mixture layer.

The method for measuring _D1 and _D2 is as follows. The same cross section used in measuring T is observed with SEM-EDX at a magnification of 1000 times and an acceleration voltage of 5 kV to 15 kV, and the longest dimension D of the particles is measured. Particles with a diameter of D of 8 μm or more are regarded as first particles, and their average diameter is _D1 . Particles with a diameter of D of less than 8 μm are regarded as second particles, and their average diameter is _D2 . The composition of each particle can be confirmed by elemental mapping using EDX.

A1 and A2 are determined as follows: In SEM-EDX observation performed under the same conditions as the measurements of _D1 and _D2 above, A1 is the sum of the areas of particles (first particles) having a particle size D of 8 μm or more, and A2 is the sum of the areas of particles (second particles) having a particle size D of less than 8 μm.

A3 is the total area of particles (first particles) with a particle size D of 8 μm or more that are present in the 2D ₁ /T region in SEM-EDX observation performed under the same conditions as the measurements of D ₁ and D ₂ above. However, when a mixture layer is formed on both sides of the current collector, A3 is obtained for each of a surface having a length equal to the distance T of the mixture layer formed on one side of the current collector, and a surface having a length equal to the distance T of the mixture layer formed on the other side of the current collector. The average value of the obtained A3 is used.

The electrodes of the embodiment are further described below.

The electrode includes a current collector and a mixture layer formed on at least one surface of the current collector. The mixture layer includes an active material and may optionally include a binder and a conductive agent.

The electrode can be applied to a positive or negative electrode. Below, an example of application to a positive electrode is described.

The positive electrode active material includes first particles of a lithium-containing metal oxide and second particles of a lithium-containing metal oxide having an average particle size _D2 smaller than the average particle size _D1 of the first particles. Examples of lithium-containing metal oxides include lithium-containing nickel-cobalt-manganese composite oxides, lithium-containing nickel-manganese composite oxides (e.g., Li _x Co _1-y-z Mn _y Ni _z O ₂ , 0<x≦1, 0<y≦1, 0<z≦1, 0≦1-y-z≦1), lithium-containing manganese composite oxides (e.g., Li _x Mn ₂ O ₄ or Li _x MnO ₂ , 0<x≦1), lithium-containing cobalt composite oxides (Li _x CoO ₂ , 0<x≦1), lithium-containing manganese-cobalt composite oxides (LixMn _2-y Co _y O ₄ , 0<x≦1, 0<y<2), and lithium iron composite oxides (e.g., Li _x FePO ₄ , Li _x Fe _1-y Mn _y PO ₄ , 0<x≦1, 0≦y<1). The type of lithium-containing metal oxide can be one or more kinds. The composition of the first particles and the composition of the second particles may be the same or different. In addition, positive electrode active material particles other than the first particles and the second particles may be included. In this case, the ratio of the total weight of the first particles and the second particles in the positive electrode active material is preferably 80% by weight or more and 90% by weight or less.

The lithium-containing metal oxide is preferably a lithium-containing nickel-cobalt-manganese composite oxide. The lithium-containing nickel-cobalt-manganese composite oxide is represented, for example, by Li _a Ni _(1-xy) Co _x Mn _y O ₂ (0.9≦a≦1.2, 0<x≦0.5, 0<y≦0.5, x≧y, 0.6≦1-x-y≦0.9). The positive electrode active material desirably contains a first particle of a lithium-containing nickel-cobalt-manganese composite oxide and a second particle of a lithium-containing nickel-cobalt-manganese composite oxide. More preferably, the positive electrode active material contains a first particle of a lithium-containing nickel-cobalt-manganese composite oxide, a second particle of a lithium-containing nickel-cobalt-manganese composite oxide, and a particle of a lithium-containing cobalt composite oxide.
Other preferred examples of lithium-containing metal oxides include lithium-containing nickel manganese composite oxides and lithium-containing manganese composite oxides. By using lithium-containing nickel manganese composite oxides, lithium-containing manganese composite oxides, or a mixture thereof as the lithium-containing metal oxide, the life performance of the electrode and the battery can be improved. More preferred is a positive electrode active material that contains a lithium-containing metal oxide and a lithium-containing cobalt composite oxide.
Further, a more preferred example of the positive electrode active material includes at least one lithium-containing metal oxide selected from the group consisting of lithium-containing nickel-cobalt-manganese composite oxide, lithium-containing nickel-manganese composite oxide, and lithium-containing manganese composite oxide. This can improve the life performance of the electrode and the battery. It is desirable that this positive electrode active material further contains a lithium-containing cobalt composite oxide in addition to the lithium-containing metal oxide.

The positive electrode active material may be primary particles or secondary particles formed by agglomeration of primary particles.

It is preferable that the particle size of the first particles is in the range of 8 μm to 25 μm, and the particle size of the second particles is in the range of 0.5 μm to 7 μm and smaller than the particle size of the first particles. This can enhance the effect of suppressing the active material from falling off from the positive electrode due to gas generation. It is more preferable that the particle size of the second particles is in the range of 1 μm to 6 μm. The positive electrode may contain a conductive agent in the form of secondary particles as a conductive agent. It is preferable that this positive electrode satisfies the following formula (3).
T2S>2×T1S (3)
Here, T1S is the total area (μm2) of the conductive agent contained in the region from the first surface to the second surface at a distance T/2 on the surface (measurement surface) of the mixture layer having a length of distance T. T2S is the total area ( ^μm2 ) of the conductive agent contained in the region from the second surface to the first surface at a distance T/ ² on the aforementioned measurement surface.

T1S and T2S are measured by the following method. In SEM-EDX observation performed under the same conditions as the measurements of _D1 and _D2 , the total area (μm ² ) of the conductive agent contained in the region defined by the distance T/2 from the first surface S1 toward the second surface S2, as shown in FIG. 1, is defined as T1S. Also, the total area (μm ² ) of the conductive agent contained in the region defined by the distance T/2 from the second surface S2 toward the first surface S1 is defined as T2S. However, when a mixture layer is formed on both sides of the current collector, T1S and T2S are obtained for each surface having a length equal to the distance T of the mixture layer formed on one side of the current collector and for each surface having a length equal to the distance T of the mixture layer formed on the other side of the current collector, and T1S and T2S are compared.
By satisfying the above formula (3), it is possible to suppress the occurrence of bias in the current distribution on the second surface that is not in contact with the current collector and is separated from the current collector and in its vicinity, and therefore it is possible to suppress the deterioration of the positive electrode active material in the vicinity of the second surface of the mixture layer, thereby improving the life performance of the electrode of the embodiment and thereby improving the life performance of the battery.

Any binder that is normally used in non-aqueous electrolyte batteries can be used. For example, electrochemically stable polyvinylidene fluoride (PVdF) or polytetrafluoroethylene can be used. The type of binder can be one or more types.

The conductive agent can be any material that has suitable conductivity. For example, carbon black such as acetylene black, or carbon such as graphite can be used. The conductive agent can be of one type or of two or more types. An example of a conductive agent in secondary particle form includes acetylene black.

The positive electrode current collector can be a conductive thin film with a positive electrode mixture layer on one or both sides. The positive electrode current collector can be a non-perforated metal foil, a punched metal with many holes, a metal mesh formed from thin metal wires, or the like. The positive electrode current collector can be, for example, a metal foil or an alloy foil. Examples of metal foils include aluminum foil, copper foil, and nickel foil. Examples of alloys include aluminum alloys, copper alloys, and nickel alloys.

The material of the positive electrode current collector is not particularly limited as long as it does not dissolve in the battery usage environment. For example, metals such as Al and Ti, or alloys containing the above metals as the main component and one or more elements selected from the group consisting of Zn, Mn, Fe, Cu, and Si, can be used. In particular, aluminum alloy foils containing Al as the main component are preferably thin films that are flexible and have excellent formability. The thickness of the positive electrode current collector is typically preferably 5 μm or more and 20 μm or less.

The mixed weight ratio of the positive electrode active material, the conductive agent and the binder is preferably 80% or more and 96% or less of the positive electrode active material, 3% or more and 15% or less of the conductive agent, and 0.5% or more and 5% or less of the binder. By making the amount of the conductive agent 3% or more, the current collection performance of the positive electrode mixture layer can be improved. In addition, by making the amount of the binder 0.5% or more, the binding property between the positive electrode mixture layer and the negative electrode current collector can be improved, and excellent cycle characteristics can be expected. On the other hand, it is preferable to make the total amount of the conductive agent and the binder 20% by weight or less in order to achieve high capacity.
The positive electrode density (positive electrode packing density) is preferably 2.8 g/cc or more and 3.6 g/cc or less from the viewpoints of increasing capacity, input/output characteristics, and gas escape from the mixture layer.

The portion of the positive electrode current collector where the positive electrode mixture layer is not formed can become a positive electrode current collecting tab.

The positive electrode can be obtained, for example, by the following method. A positive electrode active material including first and second particles and a conductive agent are dry mixed. A first solvent is added to the obtained mixed powder and binder, and the mixture is kneaded (solid kneaded) to prepare a first slurry. Next, a second solvent is added to the first slurry and stirred to prepare a second slurry. The second slurry is applied to at least one surface of a current collector, dried, and pressed to obtain a positive electrode. Cutting is performed as necessary. According to this method for producing a positive electrode, the solid content ratio of the second slurry is in a range suitable for coating the current collector, and the solid content ratio of the first slurry is higher than the solid content ratio of the second slurry. Therefore, the first slurry has a higher viscosity than the second slurry, and it becomes easier to disintegrate the aggregates (for example, aggregates of the conductive agent in the form of secondary particles) contained in the first slurry by kneading (solid kneading). As a result, the active material and the conductive agent can be uniformly dispersed in the first slurry. Then, the second solvent is added to the first slurry and stirred to prepare a second slurry in which the active material and the conductive agent are uniformly dispersed. When the second slurry is applied to at least one surface of the current collector, the active material particles having a large particle size settle to the current collector side due to their large specific gravity, and the conductive agent having a smaller specific gravity than the active material particles is dispersed on the surface of the layer formed by application. By drying and pressing this, a positive electrode of the embodiment, particularly a positive electrode that also satisfies the formula (3), is obtained. In addition, since the active material and the conductive agent are uniformly dispersed in the second slurry, when the layered product obtained is pressed after drying the second slurry applied to the current collector, the packing density can be easily increased, and a high-density electrode can be obtained.

The first solvent and the second solvent may be the same or different. Examples of the first solvent and the second solvent include organic solvents such as N-methylpyrrolidone (NMP) and water.

<Measurement of active material composition>
The composition of the active material contained in the electrode can be determined as follows.

The active material-containing layer is peeled off from the electrode to be measured using, for example, a spatula to obtain a powdered sample.

The crystal structure of the active material is identified by powder X-ray diffraction (XRD) measurement of the powdered sample. The measurement is performed using CuKα radiation as the radiation source, with 2θ ranging from 10° to 90°. This measurement makes it possible to obtain the X-ray diffraction pattern of the compound contained in the selected particles.

As an apparatus for powder X-ray diffraction measurement, for example, SmartLab manufactured by Rigaku Co., Ltd. is used. The measurement conditions are as follows:
X-ray source: Cu target Output: 45 kV, 200 mA
Soller slit: 5° for both incidence and reception
Step width: 0.02 deg
Scan speed: 20 deg/min Semiconductor detector: D/teX Ultra 250
Sample plate holder: Flat glass sample plate holder (thickness 0.5 mm)
Measurement range: 10°≦2θ≦90°.

When using other equipment, measurements should be performed using standard Si powder for powder X-ray diffraction to obtain measurement results equivalent to those above, and the conditions should be adjusted so that the peak intensity and peak top position match those of the above equipment.

Next, the sample containing the active material is observed using a scanning electron microscope (SEM). Even during SEM observation, it is desirable to prevent the sample from coming into contact with the air and to perform the observation in an inert atmosphere such as argon or nitrogen.

For example, several particles having the form of primary particles or secondary particles that can be confirmed within the field of view in a 3000x SEM observation image are selected. In this case, the selected particles are selected so that the particle size distribution is as wide as possible. The type and composition of the constituent elements of the active material are identified by EDX analysis of the observed active material particles. This makes it possible to identify the type and amount of elements other than Li contained in each of the selected particles. The same operation is performed on each of the multiple active material particles to determine the mixed state of the active material particles.

Next, the powdered sample collected from the active material-containing layer as described above is washed with acetone and dried. The resulting powder is dissolved in hydrochloric acid, the conductive agent is removed by filtration, and then the measurement sample is prepared by diluting with ion-exchanged water. The metal content ratio in the measurement sample is calculated by inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis.

When there are multiple types of active materials, the weight ratio is estimated from the content ratio of elements specific to each active material. The ratio of the weight of the specific elements to the active material is determined from the composition of the constituent elements obtained by EDX analysis. For example, the measurement sample obtained from the active material-containing layer may contain a lithium-containing nickel-cobalt-manganese composite oxide as the first active material and a lithium-containing cobalt composite oxide as the second active material. In this case, the chemical formula and formula weight of each of the first and second active materials are calculated from the metal ratio obtained, and the weight ratio of the first and second active materials contained in a predetermined weight of the collected active material-containing layer is obtained.

According to the electrode of the first embodiment described above, the active material includes first particles of a lithium-containing metal oxide and second particles of a lithium-containing metal oxide having an average particle diameter _D2 smaller than the average particle diameter _D1 of the first particles. The abundance ratio of the first particles is greater than that of the second particles. In addition, when the distance from the first surface of the mixture layer that contacts the current collector to the second surface that does not contact the current collector is T, the first particles are unevenly distributed within a range of a distance _2D1 /T from the first surface toward the second surface. With such an electrode, a battery with high capacity and excellent charge/discharge cycle performance can be realized.
Second Embodiment
The second embodiment relates to a battery. The battery of the embodiment includes a positive electrode formed of the electrode of the first embodiment, a negative electrode, and a non-aqueous electrolyte. The battery of the embodiment may further include a separator. The battery of the embodiment may also include an electrode group including a positive electrode, a negative electrode, and a separator. In this case, the non-aqueous electrolyte may be held in the electrode group.

The negative electrode, the non-aqueous electrolyte, and the separator will now be described.
(Negative electrode)
The negative electrode includes a negative electrode mixture layer containing a negative electrode active material, a conductive agent, and a binder, and a negative electrode current collector. A form in which the negative electrode mixture layer is present on one side or both sides of the negative electrode current collector is preferred, and a form in which the negative electrode mixture layer is present on both sides of the negative electrode current collector is more preferred. The negative electrode mixture layer is a layer in which the negative electrode active material, the conductive agent, and the binder are dispersed, and is provided on the negative electrode current collector.

Examples of negative electrode active materials include metal composite oxides, carbonaceous materials, metal compounds, etc. The type of negative electrode active material can be one or more types.

Examples of the metal composite oxide include spinel-type lithium titanate represented by Li4 _{+ xTi5O12} (x varies within the range of -1≦x≦3 depending on the charge/discharge reaction), _ramstellide -type _{Li2 + xTi3O7} (x varies within the range of -1≦x≦3 depending on the charge/discharge reaction), and metal composite oxides containing Ti and at least one element selected from the group consisting of P, V, Sn, Cu, Ni, and Fe. Examples of metal composite oxides containing Ti and at least one element selected from the group consisting of P, V, Sn, Cu, Ni, and Fe include TiO ₂ -P ₂ O ₅ , TiO ₂ -V ₂ O ₅ , TiO ₂ -P ₂ O ₅ -SnO ₂ , and TiO ₂ -P ₂ O ₅ -MO (M is at least one element selected from the group consisting of Cu, Ni, and Fe). Other examples include niobium titanium composite oxides such as TiNb ₂ O ₇ and Ti ₂ Nb ₁₀ O _19. These metal composite oxides are changed into lithium titanium composite oxides by insertion of lithium during charging.

Examples of the carbonaceous material include natural graphite, artificial graphite, coke, vapor-grown carbon fiber, mesophase pitch-based carbon fiber, spherical carbon, and resin-calcined carbon. More preferred carbonaceous materials include vapor-grown carbon fiber, mesophase pitch-based carbon fiber, and spherical carbon. The carbonaceous material preferably has a plane spacing d ₀₀₂ of 0.34 nm or less in terms of the (002) plane as determined by X-ray diffraction.

The metal compound may be a metal sulfide or a metal nitride. The metal sulfide may be, for example, titanium sulfide such as _TiS2 , molybdenum sulfide such as _MoS2 , or iron sulfide such as FeS, _FeS2 , or LixFeS2. The metal nitride may be, for example, lithium _cobalt nitride (for example, _LisCotN , 0<s< ₄ , 0<t<0.5).

The conductive agent can be any material that has suitable conductivity. For example, carbon black such as acetylene black, or carbon such as graphite can be used. The conductive agent can be of one type or two or more types.

Any binder that is commonly used in non-aqueous electrolyte batteries can be used. It is preferable to use electrochemically stable materials such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene, carboxymethyl cellulose, styrene butadiene rubber, and mixtures thereof. The type of binder can be one or more types.

The negative electrode current collector is a conductive thin film with a negative electrode mixture layer on one or both sides. The negative electrode current collector can be made of the same material as the positive electrode current collector.

The negative electrode is prepared, for example, by suspending the negative electrode active material, the conductive agent, and the binder in a suitable solvent, applying the prepared slurry to the negative electrode current collector, drying, and rolling. The negative electrode is a negative electrode current collector tab in the portion where the negative electrode mixture layer is not formed on the surface of the negative electrode current collector. It is desirable that the weight ratio of the negative electrode active material, the conductive agent, and the binder is 80% or more and 96% or less of the negative electrode active material, 2% or more and 18% or less of the conductive agent, and 1% or more and 5% or less of the binder. By setting the amount of the conductive agent to 2% or more, the current collection performance of the negative electrode mixture layer can be improved. In addition, by setting the amount of the binder to 1% or more, the binding property between the negative electrode mixture layer and the negative electrode current collector can be increased, and excellent cycle characteristics can be expected. On the other hand, it is preferable to set the total amount of the conductive agent and the binder to 20% or less in order to achieve high capacity. The negative electrode density (negative electrode packing density) is desirably 2.0 g/cc or more and 2.8 g/cc or less from the viewpoints of increasing capacity, input/output characteristics, and gas escape from the mixture layer. When the negative electrode satisfies at least one of these physical properties, the nonaqueous electrolyte battery of the embodiment suppresses side reactions with the electrolytic solution and enhances gas escape from the mixture layer during gas generation, thereby improving the life characteristics.
(Non-aqueous electrolyte)
The non-aqueous electrolyte may be, for example, a non-aqueous electrolyte solution, a gel electrolyte, a solid electrolyte, etc. The non-aqueous electrolyte solution is a solution containing an electrolyte salt and a non-aqueous solvent. Examples of the electrolyte salt include LiPF ₆ , LiBF ₄ , Li(CF ₃ SO ₂ ) ₂ N (lithium bistrifluoromethanesulfonylamide; commonly known as LiTFSI), LiCF ₃ SO ₃ (commonly known as LiTFS), Li(C ₂ F ₅ SO ₂ ) ₂ N (lithium bispentafluoroethanesulfonylamide; commonly known as LiBETI), LiClO ₄ , LiAsF ₆ , LiSbF ₆ , lithium bisoxalatoborate {LiB(C ₂ O ₄ ) ₂ , commonly known as LiBOB}, lithium difluoro(trifluoro-2-oxido-2-trifluoro-methylpropionato(2-)-0,0)borate {LiBF ₂ OCOOC(CF ₃ ) ₂ Lithium salts such as LiBF ₂ (HHIB), commonly known as LiBF 2 (HHIB), can be used. These electrolyte salts may be used alone or in combination of two or more.

The electrolyte salt concentration is preferably in the range of 0.5 mol/L to 3 mol/L, and more preferably in the range of 1 mol/L to 2 mol/L. By specifying the electrolyte concentration in this way, it is possible to further improve performance when a high load current is passed while suppressing the effect of increased viscosity due to an increase in the electrolyte salt concentration.

The non-aqueous solvent is not particularly limited, but examples thereof include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and dipropyl carbonate (DPC), 1,2-dimethoxyethane (DME), γ-butyrolactone (GBL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeHF), 1,3-dioxolane, sulfolane, and acetonitrile (AN). These solvents may be used alone or in combination of two or more. Non-aqueous solvents containing cyclic carbonates and/or chain carbonates are preferred.
(Separator)
The separator is used to avoid electrical contact between the positive and negative electrodes. It is also used to avoid an increase in resistance and volume due to the distance between the electrodes. The separator is made of a material having a porous structure and capable of permeating ions. A film-formed material is preferably used. For example, polyethylene, polypropylene, or cellulose is preferable. One side of the separator is preferably in physical contact with the entire surface of the positive electrode mixture layer, and the other side is preferably in physical contact with the entire surface of the negative electrode mixture layer. From the viewpoint of the permeability of the gas generated on the electrode surface and the safety of the battery, it is preferable that the air permeability of the separator measured by the method described in JIS 8117 (2009) is 10 sec/100 cc or more and 100 sec/100 cc or less. By setting the air permeability of the separator within this range, it is possible to suppress short-circuiting between the positive and negative electrodes, while making it easier for the gas generated on the electrode surface to escape outside the separator without being retained in the electrode group, thereby suppressing an increase in resistance.

Next, the electrode group will be described. The electrode group includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The electrode group may be a wound electrode group in which the positive electrode and the negative electrode are wound in a flat or cylindrical shape with a separator between them, or a stacked electrode group in which the positive electrode and the negative electrode are stacked with a separator between them.

It is desirable for the electrode group to have an aspect ratio in the range of 1 to 1.8. By setting the aspect ratio of the electrode group in this range, gas generated near the center of the electrode group can more easily escape to the outside of the electrode group. A more preferable range is 1.1 to 1.8.

The definition of the aspect ratio will be explained with reference to Figures 3 and 4. The electrode group 200 shown in Figure 3 is a flat shape in which a positive electrode, a separator 201, and a negative electrode are wound along the winding direction. The outermost periphery of the electrode group 200 is composed of the separator 201. On one side of the winding axis direction, the positive electrode current collector 202 protrudes from the separator 201, and on the other side, the negative electrode current collector 203 protrudes from the separator 201. On the surface with the largest area of the electrode group 200, the intersection point where two diagonals of the outermost separator 201 intersect is O. When the length passing through the intersection point O and perpendicular to the winding axis is A, and the length passing through O and parallel to the winding axis is B, the aspect ratio is expressed as B/A. Since gas diffuses in a direction parallel to the winding axis, by setting the aspect ratio (B/A) to be 1 or more and 1.8 or less, gas generated near the center of the electrode group can more easily escape to the outside of the electrode group.

The electrode group 200 shown in FIG. 4 is a flat shape in which a positive electrode, a separator 201, and a negative electrode are wound along the winding direction. The outermost periphery of the electrode group 200 is composed of the separator 201. The positive electrode current collector 202 and the negative electrode current collector 203 protrude from the separator 201 on one side of the winding axis direction. In the largest area surface of the electrode group 200, the intersection point where two diagonal lines of the outermost separator 201 intersect is O. When the length passing through the intersection point O and perpendicular to the winding axis is A, and the length passing through the intersection point O and parallel to the winding axis is B, the aspect ratio is expressed as B/A. Since gas diffuses in the direction parallel to the winding axis, by setting the aspect ratio (B/A) to 1 or more and 1.8 or less, gas generated near the center of the electrode group is more likely to escape to the outside of the electrode group.

The aspect ratio is measured in the following manner. The exterior material of the battery is dismantled without damaging the internal electrode group, and the electrode group is removed. The above dimensions A and B are measured with digital calipers so as to pass through the center of the part of the removed electrode group covered with the separator (excluding the part exposed from the separator), and B/A is the aspect ratio of the electrode group.

A wound electrode group is a laminate in which a strip-shaped positive electrode and a strip-shaped negative electrode are laminated with a separator between them, and the laminate is then further wound. The area on the positive electrode current collector where the positive electrode mixture layer is provided is the positive electrode coated part, and the area on the positive electrode current collector where the positive electrode mixture layer is not provided is the positive electrode uncoated part. The positive electrode uncoated part becomes a positive electrode current collector tab. The area on the negative electrode current collector where the negative electrode mixture layer is provided is the negative electrode coated part, and the area on the negative electrode current collector where the negative electrode mixture layer is not provided is the negative electrode uncoated part. The negative electrode uncoated part becomes a negative electrode current collector tab. The positive electrode, positive electrode current collector, positive electrode mixture layer, negative electrode, negative electrode current collector, and negative electrode mixture layer may all be in the form of a strip.

The positive and negative electrodes extend in a first direction (I) through the separator and have a band shape having a width in a second direction (II) perpendicular to the first direction. The wound electrode group is preferably housed in an exterior member so as to be oriented perpendicular to the winding axis.

After the positive and negative electrodes are produced, they are stacked and wound to produce a wound electrode group. It is desirable to wind the electrodes while adjusting their positions so that the surface of the positive electrode mixture layer faces the surface of the negative electrode mixture layer, i.e., so that no non-facing portions are created on the positive electrode. The outermost layer of the wound electrode group is preferably fixed with insulating tape.

The battery of the embodiment may further include any of an exterior member, a positive electrode lead, a negative electrode lead, a lid, a positive electrode terminal, a negative electrode terminal, a positive electrode backup lead, a negative electrode backup lead, a positive electrode insulating cover, a negative electrode insulating cover, a positive electrode gasket, a negative electrode gasket, a safety valve, and an electrolyte injection port. The battery of the embodiment may be, for example, a secondary battery that can be charged and discharged. In the figure, a square nonaqueous electrolyte battery is shown, but the battery is not limited to a square shape.

Examples of exterior components include containers made of laminated film and metal containers.

The laminate film may be a multi-layer film with a metal layer interposed between resin films. The metal layer is preferably aluminum foil or aluminum alloy foil to reduce weight. The resin film may be made of a polymeric material such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate (PET). The laminate film can be sealed by heat fusion and molded into the shape of the exterior component. The thickness of the laminate film is preferably, for example, 0.2 mm or less.

The metal container may be made of aluminum, an aluminum alloy, iron, stainless steel, etc. The lid may be made of aluminum, an aluminum alloy, iron, stainless steel, etc. It is desirable that the lid and the exterior member are made of the same type of metal. The thickness of the metal container is preferably, for example, 0.5 mm or less.

The positive electrode current collecting tab may be bundled with a positive electrode backup lead and electrically connected to the positive electrode terminal via the positive electrode lead. The negative electrode current collecting tab may be bundled with a negative electrode backup lead and electrically connected to the negative electrode terminal via the negative electrode lead.

The positive electrode lead is a conductive member that physically connects the positive electrode terminal and the positive electrode backup lead. The positive electrode lead is a conductive member such as aluminum or an aluminum alloy. The positive electrode lead and the positive electrode backup lead are preferably joined by, for example, laser welding.

The negative electrode lead is a conductive member that physically connects the negative electrode terminal and the negative electrode backup lead. The negative electrode lead is a conductive member such as aluminum or an aluminum alloy. The negative electrode lead and the negative electrode backup lead are preferably joined by, for example, laser welding.

The lid is a lid for an exterior member that houses a wound electrode group, and has a positive electrode terminal and a negative electrode terminal. The lid is equipped with a positive electrode terminal, a negative electrode terminal, a negative electrode insulating cover, a positive electrode gasket, a negative electrode gasket, a safety valve, and an electrolyte injection port. The lid is a molded member made of a metal or alloy such as aluminum, an aluminum alloy, iron, or stainless steel. The lid and the exterior member are preferably laser welded or bonded with a sealing material such as an adhesive resin.

The positive electrode terminal is an electrode terminal for the positive electrode of the secondary battery provided on the lid. The positive electrode terminal is made of a conductive material such as aluminum or an aluminum alloy. The positive electrode terminal is fixed to the lid via an insulating positive electrode gasket. The positive electrode terminal is electrically connected to the positive electrode via a positive electrode lead and a positive electrode backup lead.

The negative electrode terminal is an electrode terminal for the negative electrode of the secondary battery provided on the lid. The negative electrode terminal is made of a conductive material such as aluminum or an aluminum alloy. The negative electrode terminal is fixed to the lid via an insulating negative electrode gasket. The negative electrode terminal is electrically connected to the negative electrode via the negative electrode lead and the negative electrode backup lead.

The positive electrode backup lead is a conductive member that bundles the positive electrode current collecting tabs and is fixed to the positive electrode lead. It is preferable that the positive electrode backup lead and the positive electrode current collecting tab are joined by ultrasonic bonding.

The negative electrode backup lead is a conductive member that bundles the negative electrode current collector tabs and is fixed to the negative electrode lead. It is preferable that the negative electrode backup lead and the negative electrode current collector tab are joined by ultrasonic bonding.

The positive electrode insulating cover is an insulating member that covers the positive electrode lead and the positive electrode backup lead. The positive electrode insulating cover is joined to one end of the wound electrode group, including the positive electrode current collecting tab. The positive electrode insulating cover is preferably an insulating and heat-resistant member. As the positive electrode insulating cover, a resin molded body, a molded body of a material mainly made of paper, or a member in which a molded body of a material mainly made of paper is coated with resin is preferable. As the resin, polyethylene resin or fluororesin is preferably used. The shape of the positive electrode insulating cover is such that the positive electrode lead and the positive electrode backup lead are in contact with the exterior member. By using the positive electrode insulating cover, the positive electrode and the exterior member are insulated, and the current collecting tab area (current collecting tab, lead, backup lead) can be protected from external impact.

The negative electrode insulating cover is an insulating member that covers the negative electrode lead and the negative electrode backup lead. The negative electrode insulating cover is fitted to one end of the wound electrode group, including the negative electrode current collecting tab. The material, shape, etc. of the negative electrode insulating cover are the same as those of the positive electrode insulating cover. Explanations of what is common between the positive electrode insulating cover and the negative electrode insulating cover will be omitted.

The positive electrode gasket is a member that insulates the positive electrode terminal from the exterior member. The positive electrode gasket is preferably a resin molded body that is solvent-resistant and flame-retardant. For example, polyethylene resin or fluororesin is used for the positive electrode gasket.

The negative electrode gasket is a member that insulates the negative electrode terminal from the exterior member. The negative electrode gasket is preferably a solvent-resistant, flame-retardant resin molded body. For example, polyethylene resin or fluororesin is used for the negative electrode gasket.

The safety valve is a component provided in the lid that functions as a pressure reducing valve to reduce the pressure inside the exterior member when the internal pressure inside the exterior member increases. Although it is preferable to provide a safety valve, it can be omitted depending on the conditions of the battery protection mechanism, electrode material, etc.

The electrolyte injection port is a hole for injecting electrolyte. After the electrolyte is injected, it is preferable that the hole is sealed with resin or the like.

Although omitted in the figure, it is preferable that each component be fixed or connected using insulating adhesive tape.

Next, specific examples of batteries according to embodiments will be described with reference to the drawings.

First, with reference to Figures 5 and 6, we will explain a first example of a nonaqueous electrolyte battery according to an embodiment.

Figure 5 is a partially cutaway perspective view of an example of a nonaqueous electrolyte battery according to an embodiment. Figure 6 is an enlarged cross-sectional view of part A of the nonaqueous electrolyte battery shown in Figure 5.

The nonaqueous electrolyte battery 100 shown in Figures 5 and 6 includes a flat electrode group 1 and an exterior member 7 made of a laminate film. The flat electrode group 1 includes a negative electrode 2, a positive electrode 3, and a separator 4. The flat electrode group 1 is formed by winding the negative electrode 2 and the positive electrode 3 in a flat shape with the separator 4 between them.

As shown in FIG. 6, the negative electrode 2 comprises a negative electrode collector 2a and a negative electrode active material-containing layer 2b supported on the negative electrode collector 2a. As shown in FIG. 6, in the outermost portion of the negative electrode 2, the negative electrode active material-containing layer 2b is not supported on the main surface of the two main surfaces of the negative electrode collector 2a that does not face the positive electrode 3. In the other portions of the negative electrode 2, the negative electrode active material-containing layer 2b is supported on both main surfaces of the negative electrode collector. As shown in FIG. 6, the positive electrode 3 comprises a positive electrode collector 3a and a positive electrode active material-containing layer 3b supported on the two main surfaces of the positive electrode collector 3a.

A strip-shaped negative electrode terminal 5 is electrically connected to the negative electrode 2. A strip-shaped positive electrode terminal 6 is electrically connected to the positive electrode 3.

The electrode group 1 is housed in an exterior member 7 made of a laminate film with the ends of the negative electrode terminal 5 and the positive electrode terminal 6 extending from the exterior member 7. A non-aqueous electrolyte (not shown) is housed in the exterior member 7 made of a laminate film. The non-aqueous electrolyte is impregnated into the electrode group 1. The exterior member 7 made of a laminate film is sealed by heat fusing one end of the exterior member 7, with the negative electrode terminal 5 and the positive electrode terminal 6 sandwiched therebetween, and the end and two ends perpendicular to the end being sealed.

Next, another example of a battery according to an embodiment will be described in detail with reference to Fig. 7. Fig. 7 is a partially cutaway perspective view showing another example of a battery according to an embodiment.

The battery 100 shown in Figure 7 differs from the battery 100 shown in Figures 5 and 6 in that the exterior member is composed of a metal container 17a and a sealing plate 17b.

The flat electrode group 1 includes a negative electrode, a positive electrode, and a separator, similar to the electrode group 1 in the battery 100 shown in Figures 5 and 6. The electrode group 1 has a similar structure between Figures 5 and 7. However, in Figure 7, instead of the negative electrode terminal 5 and the positive electrode terminal 6, a negative electrode lead 15a and a positive electrode lead 16a are electrically connected to the negative electrode and the positive electrode, respectively, as described below.

In the battery 100 shown in FIG. 7, such an electrode group 1 is housed in a metal container 17a. The metal container 17a further houses an electrolyte (not shown). The metal container 17a is sealed by a metal sealing plate 17b. The metal container 17a and the sealing plate 17b constitute, for example, an exterior can as an exterior member.

One end of the negative electrode lead 15a is electrically connected to the negative electrode collector, and the other end is electrically connected to the negative electrode terminal 15. One end of the positive electrode lead 16a is electrically connected to the positive electrode collector, and the other end is electrically connected to the positive electrode terminal 16 fixed to the sealing plate 17b. The positive electrode terminal 16 is fixed to the sealing plate 17b via an insulating member 17c. The positive electrode terminal 16 and the sealing plate 17b are electrically insulated by the insulating member 17c.

8 and 9 show a battery including a stacked electrode group as yet another example of a battery. FIG. 8 is a partially cutaway perspective view showing yet another example of a battery according to an embodiment. FIG. 9 is an enlarged cross-sectional view of part B of the battery shown in FIG. 8.

The example battery 100 shown in Figures 8 and 9 comprises an electrode group 1 shown in Figures 8 and 9, an outer container 7 shown in Figures 8 and 9, a positive electrode terminal 6 shown in Figures 8 and 9, and a negative electrode terminal 5 shown in Figure 8.

The electrode group 1 shown in Figures 8 and 9 comprises a plurality of positive electrodes 3, a plurality of negative electrodes 2, and one separator 4.

As shown in Figure 9, each positive electrode 3 comprises a positive electrode collector 3a and a positive electrode active material-containing layer 3b formed on both sides of the positive electrode collector 3a. Also, as shown in Figure 9, the positive electrode collector 3a includes a portion on its surface where the positive electrode active material-containing layer 3b is not formed. This portion serves as a positive electrode collector tab 3c.

Each negative electrode 2 comprises a negative electrode current collector 2a and a negative electrode active material-containing layer 2b formed on both sides of the negative electrode current collector 2a. The negative electrode current collector 2a also includes a portion on its surface where the negative electrode active material-containing layer 2b is not formed (not shown). This portion acts as a negative electrode current collector tab.

As shown in part in Figure 9, the separator 4 is zigzag folded. A positive electrode 3 or a negative electrode 2 is disposed in the space defined by the opposing faces of the zigzag folded separator 4. As a result, the positive electrode 3 and the negative electrode 2 are stacked such that the positive electrode active material-containing layer 3b and the negative electrode active material-containing layer 2b face each other with the separator 4 interposed therebetween, as shown in Figure 9. In this way, an electrode group 1 is formed.

As shown in FIG. 9, the positive electrode current collector tab 3c of the electrode group 1 extends beyond the ends of the positive electrode active material-containing layer 3b and the negative electrode active material-containing layer 2b. As shown in FIG. 9, these positive electrode current collector tabs 3c are joined together and connected to the positive electrode terminal 6. Although not shown, the negative electrode current collector tab of the electrode group 1 also extends beyond the other ends of the positive electrode active material-containing layer 3b and the negative electrode active material-containing layer 2b. Although not shown, these negative electrode current collector tabs are joined together and connected to the negative electrode terminal 5 shown in FIG. 8.

Such an electrode group 1 is housed in an outer casing member consisting of an outer container 7 made of a laminated film, as shown in Figures 8 and 9.

The outer container 7 is formed of an aluminum-containing laminate film consisting of an aluminum foil 71 and resin films 72 and 73 formed on both sides of the aluminum foil. The aluminum-containing laminate film forming the outer container 7 is folded at the folding portion 7d so that the resin film 72 faces inward, and contains the electrode group 1. As shown in Figures 8 and 9, at the peripheral portion 7b of the outer container 7, the facing portions of the resin film 72 sandwich the positive electrode terminal 6 therebetween. Similarly, at the peripheral portion 7c of the outer container 7, the facing portions of the resin film 72 sandwich the negative electrode terminal 5 therebetween. The positive electrode terminal 6 and the negative electrode terminal 5 extend from the outer container 7 in opposite directions.

At the peripheral portions 7a, 7b and 7c of the outer container 7, except for the portions sandwiching the positive terminal 6 and the negative terminal 5, the opposing portions of the resin film 72 are heat-sealed.

In addition, in the battery 100, in order to improve the bonding strength between the positive terminal 6 and the resin film 72, as shown in FIG. 9, an insulating film 9 is provided between the positive terminal 6 and the resin film 72. In addition, in the peripheral portion 7b, the positive terminal 6 and the insulating film 9 are heat-sealed, and the resin film 72 and the insulating film 9 are heat-sealed. Similarly, although not shown, an insulating film 9 is provided between the negative terminal 5 and the resin film 72. In addition, in the peripheral portion 7c, the negative terminal 5 and the insulating film 9 are heat-sealed, and the resin film 72 and the insulating film 9 are heat-sealed. That is, in the battery 100 shown in FIG. 8, all of the peripheral portions 7a, 7b, and 7c of the outer container 7 are heat-sealed.

The outer container 7 further contains an electrolyte (not shown). The electrolyte is impregnated into the electrode group 1.

8 and 9, as shown in Fig. 9, multiple positive electrode current collecting tabs 3c are grouped together in the lowest layer of the electrode group 1. Similarly, although not shown, multiple negative electrode current collecting tabs are grouped together in the lowest layer of the electrode group 1. However, for example, multiple positive electrode current collecting tabs 3c and multiple negative electrode current collecting tabs can be grouped together near the middle of the electrode group 1 and connected to the positive electrode terminal 6 and the negative electrode terminal 5, respectively.

According to the second embodiment battery described above, since it includes the electrode of the first embodiment, it is possible to realize a battery with high capacity and excellent charge/discharge cycle performance.

Third Embodiment
According to a third embodiment, a battery pack is provided, the battery pack including the battery according to the second embodiment.

The battery pack according to the embodiment may also include a plurality of batteries. The plurality of batteries may be electrically connected in series or in parallel. Alternatively, the plurality of batteries may be electrically connected in a combination of series and parallel. That is, the battery pack according to the embodiment may include an assembled battery. There may be more than one assembled battery. The plurality of assembled batteries may be electrically connected in series, in parallel, or in a combination of series and parallel.

An example of a battery pack according to an embodiment will be described below with reference to Figs. 10 and 11. Fig. 10 is an exploded perspective view showing an example of a battery pack according to an embodiment. Fig. 11 is a block diagram showing an example of an electrical circuit of the battery pack shown in Fig. 10.

The battery pack 20 shown in Figures 10 and 11 includes a plurality of cells 21. The cells 21 may be, for example, a flat-type battery 100 according to an embodiment described with reference to Figure 5.

The multiple single cells 21 are stacked so that the negative electrode terminals 5 and positive electrode terminals 6 extending outward are aligned in the same direction, and are fastened together with adhesive tape 22 to form a battery pack 23. These single cells 21 are electrically connected in series with each other as shown in FIG.

The printed wiring board 24 is disposed so as to face the side from which the negative terminal 5 and positive terminal 6 of the battery 21 extend. The printed wiring board 24 is mounted with a thermistor 25, a protection circuit 26, and a terminal 27 for supplying current to an external device, as shown in FIG. 11. An insulating plate (not shown) is attached to the surface of the printed wiring board 24 facing the battery pack 23 to avoid unnecessary connection with the wiring of the battery pack 23.

The positive electrode lead 28 is connected to the positive electrode terminal 6 located on the bottom layer of the battery pack 23, and its tip is inserted into and electrically connected to the positive electrode connector 29 of the printed wiring board 24. The negative electrode lead 30 is connected to the negative electrode terminal 5 located on the top layer of the battery pack 23, and its tip is inserted into and electrically connected to the negative electrode connector 31 of the printed wiring board 24. These connectors 29 and 31 are connected to the protection circuit 26 through wiring 32 and 33 formed on the printed wiring board 24.

The thermistor 25 detects the temperature of the cell 21, and the detection signal is sent to the protection circuit 26. The protection circuit 26 can cut off the positive side wiring 34a and the negative side wiring 34b between the protection circuit 26 and the terminal 27 for supplying current to the external device under a predetermined condition. An example of the predetermined condition is when the temperature detected by the thermistor 25 becomes equal to or higher than a predetermined temperature. Another example of the predetermined condition is when overcharging, overdischarging, or overcurrent of the cell 21 is detected. This detection of overcharging, etc. is performed for each cell 21 or the entire battery pack 23. When detecting each cell 21, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 21. In the battery pack 20 of FIG. 10 and FIG. 11, wiring 35 for voltage detection is connected to each cell 21. A detection signal is transmitted to the protection circuit 26 through these wirings 35.

Protective sheets 36 made of rubber or resin are arranged on each of the three sides of the battery pack 23, except for the sides from which the positive terminal 6 and the negative terminal 5 protrude.

The battery pack 23 is housed in a container 37 together with each protective sheet 36 and the printed wiring board 24. That is, protective sheets 36 are arranged on both inner surfaces along the long side direction and the inner surface along the short side direction of the container 37, and the printed wiring board 24 is arranged on the inner surface along the other short side direction on the opposite side across from the battery pack 23. The battery pack 23 is located in a space surrounded by the protective sheets 36 and the printed wiring board 24. A lid 38 is attached to the top surface of the container 37.

It should be noted that heat shrink tape may be used to secure the battery pack 23 in place of the adhesive tape 22. In this case, protective sheets are placed on both sides of the battery pack, the heat shrink tape is wrapped around it, and then the heat shrink tape is thermally shrunk to bind the battery pack.

10 and 11 show the cells 21 electrically connected in series, but they may be electrically connected in parallel to increase the battery capacity. Furthermore, the assembled battery pack may be electrically connected in series and/or parallel.

The aspects of the battery pack according to the embodiment may be modified as appropriate depending on the application. The battery pack according to the embodiment is preferably used in applications where cycle performance in large current charging and discharging is desired. Specific applications include use as a power source for digital cameras, and in-vehicle applications such as two- to four-wheel hybrid electric vehicles, two- to four-wheel electric vehicles, and power-assisted bicycles. In-vehicle applications are particularly suitable for the battery pack according to the embodiment.

The battery pack according to the third embodiment includes the battery according to the second embodiment, and therefore has a high capacity and an excellent life performance.
[Example]
The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the examples listed below as long as it does not depart from the gist of the invention.

Example 1
1. Fabrication of Non-Aqueous Electrolyte Battery In Example 1, a square non-aqueous electrolyte battery was fabricated as follows.
[Preparation of Positive Electrode]
As the positive electrode active material, lithium nickel cobalt manganese composite oxide particles (first particles) having an average particle size D ₁ of 20 μm and represented by LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , lithium nickel cobalt manganese composite oxide particles (second particles) having an average particle size D ₂ of 5 μm and represented by LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , and lithium cobalt composite oxide particles having an average particle size D ₂ of 7 μm and represented by LiCoO ₂ were prepared. The particle size of the first particles was in the range of 8 μm to 25 μm. The particle size of the second particles was in the range of 2 μm to 6 μm. The particle size of the lithium cobalt composite oxide particles was in the range of 3 μm to 13 μm.

93% by weight of a positive electrode active material consisting of 69% by weight of first particles, 11% by weight of second particles, and 20% by weight of lithium-cobalt composite oxide particles was dry-mixed with 3% by weight of acetylene black as a conductive agent and 2% by weight of graphite. The resulting mixed powder and 2% by weight of polyvinylidene fluoride (PVdF) as a binder were suspended in N-methylpyrrolidone (NMP) to a solid content ratio of 82.3% by weight, and then kneaded to prepare a first slurry.

A second slurry with a solids content of 67.0% by weight was prepared by adding N-methylpyrrolidone to the first slurry and diluting it with stirring.

An aluminum foil having a thickness of 12 μm was prepared as a positive electrode current collector. The positive electrode current collector had a band shape extending in a first direction (I) and having a width in a second direction (II) perpendicular to the first direction. The positive electrode second slurry prepared by the above procedure was applied to both sides of the positive electrode current collector so that the thickness of the positive electrode mixture layer was 100 μm, and dried to obtain a positive electrode mixture layer. When applying the positive electrode second slurry, a band-shaped slurry uncoated portion extending in the first direction (I) was left 10 mm on a part of the surface of the positive electrode current collector to form a positive electrode current collector tab. After drying, the positive electrode mixture layer was cut to have a width of 90 mm. After cutting, the electrode was rolled with a constant load to prepare a positive electrode.
[Preparation of negative electrode]
A slurry for preparing a negative electrode was obtained by suspending spinel-type lithium titanate Li ₄ Ti ₅ O ₁₂ as a negative electrode active material, PVdF as a binder, and graphite as a conductive agent in N-methylpyrrolidone. The mixing ratios of lithium titanate, PVdF, and graphite added to N-methylpyrrolidone were 95% by weight, 2% by weight, and 3% by weight, respectively.

An aluminum foil having a thickness of 12 μm was prepared as the negative electrode current collector. The negative electrode current collector had a band shape extending in a first direction (I) and having a width in a second direction (II) perpendicular to the first direction. The negative electrode slurry prepared by the above procedure was applied to both sides and dried. When applying the negative electrode slurry, a band-shaped slurry uncoated portion extending in the first direction (I) was left 10 mm on a part of the surface of the negative electrode current collector to form a negative electrode current collector tab. After drying, the active material layer on the negative electrode current collector was cut to a width of 95 mm. After cutting, the electrode was rolled with a constant load to prepare a negative electrode.
[Preparation of wound electrode group]
As the separator, a cellulose nonwoven fabric having a thickness of 10 μm and an air permeability of 60 sec/100 cc measured by the method described in JIS 8117 (2009) was prepared. The positive electrode and negative electrode thus obtained were wound around an axis extending in the width direction of the positive electrode and negative electrode through the separator. At this time, 40 turns of the positive electrode and 41 turns of the negative electrode were wound while adjusting the position so that the positive electrode mixture layer and the negative electrode mixture layer do not protrude from the separator, that is, so that the surface of the positive electrode mixture layer faces the surface of the negative electrode mixture layer, that is, so that the surface of the positive electrode mixture layer does not protrude from the surface of the negative electrode mixture layer. An insulating tape having a thickness of 50 μm was attached to the surface of the negative electrode mixture layer at the outermost periphery of the electrode group to fix the electrode group. The electrode group prepared by winding as described above was pressed to obtain a flat wound electrode group. The positive electrode current collector tabs were ultrasonically welded to bundle the positive electrode current collector tabs, and the negative electrode current collector tabs were ultrasonically welded to bundle the negative electrode current collector tabs. The obtained electrode group had the structure shown in FIG. 4 and had an aspect ratio represented by B/A of 1.1.
[Battery Assembly]
The flat wound electrode group and the nonaqueous electrolyte thus obtained were housed in an aluminum rectangular container with a bottom having an opening. At this time, the positive electrode current collecting tab and the negative electrode current collecting tab were made to extend from the end face of the electrode group facing the opening. Next, an aluminum rectangular sealing plate was prepared. The sealing plate was provided with three openings (not shown). A rectangular positive electrode terminal was fitted and fixed in one of the three openings. A rectangular negative electrode terminal was fitted and fixed in the other of the three openings via an insulating gasket. The remaining one of the three openings was an injection port for injecting the electrolyte. Next, one end of the positive electrode terminal and the positive electrode current collecting tab of the electrode group were electrically connected by laser welding. Similarly, one end of the negative electrode terminal and the negative electrode current collecting tab of the electrode group were electrically connected by laser welding. Next, the peripheral portion of the sealing plate was welded to the container so as to close the opening of the container.

Next, a non-aqueous electrolyte solution was prepared by dissolving lithium hexafluorophosphate LiPF 6 at a concentration of 1.2 mol/L in a non-aqueous solvent prepared by mixing propylene carbonate (PC) and diethyl carbonate (DEC ₎ in a volume ratio of 1:1.

Next, the non-aqueous electrolyte prepared as described above was poured into the container through the electrolyte injection port provided in the sealing plate, and a sealing lid was welded to the periphery of the electrolyte injection port to assemble the battery.
Example 2
A battery was assembled in the same manner as in Example 1, except that the following positive electrode was used.

As the positive electrode active material, lithium nickel cobalt manganese composite oxide particles (first particles) having an average particle size D ₁ of 14 μm and represented by LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , lithium nickel cobalt manganese composite oxide particles (second particles) having an average particle size D ₂ of 5 μm and represented by LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , and lithium cobalt composite oxide particles represented by LiCoO ₂ were prepared. The particle size of the first particles was in the range of 8 μm to 20 μm. The particle size of the second particles was in the range of 2 μm to 6 μm. The particle size of the lithium cobalt composite oxide particles was in the range of 3 μm to 13 μm.

93% by weight of a positive electrode active material consisting of 65% by weight of first particles, 15% by weight of second particles, and 20% by weight of lithium-cobalt composite oxide particles was dry-mixed with 3% by weight of acetylene black as a conductive agent and 2% by weight of graphite. The resulting mixed powder was suspended in N-methylpyrrolidone (NMP) with 2% by weight of polyvinylidene fluoride (PVdF) as a binder so that the solid content ratio was 82.3% by weight, and the mixture was kneaded to prepare a first slurry.

A second slurry with a solids content of 67.0% by weight was prepared by adding N-methylpyrrolidone to the first slurry and diluting it with stirring.

An aluminum foil having a thickness of 12 μm was prepared as a positive electrode current collector. The positive electrode current collector had a band shape extending in a first direction (I) and having a width in a second direction (II) perpendicular to the first direction. The positive electrode second slurry prepared by the above procedure was applied to both sides of the positive electrode current collector so that the thickness of the positive electrode mixture layer was 40 μm, and dried to obtain a positive electrode mixture layer. When applying the positive electrode second slurry, a band-shaped slurry uncoated portion extending in the first direction (I) was left 10 mm on a part of the surface of the positive electrode current collector to form a positive electrode current collector tab. After drying, the positive electrode mixture layer was cut to have a width of 90 mm. After cutting, the electrode was rolled with a constant load to prepare a positive electrode.
Example 3
A battery was assembled in the same manner as in Example 1, except that the following positive electrode was used.

As the positive electrode active material, lithium nickel cobalt manganese composite oxide particles (first particles) having an average particle size D ₁ of 20 μm and represented by LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , lithium nickel cobalt manganese composite oxide particles (second particles) having an average particle size D ₂ of 5 μm and represented by LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , and lithium cobalt composite oxide particles represented by LiCoO ₂ were prepared. The particle size of the first particles was in the range of 8 μm to 25 μm. The particle size of the second particles was in the range of 2 μm to 6 μm. The particle size of the lithium cobalt composite oxide particles was in the range of 3 μm to 13 μm.

93% by weight of a positive electrode active material consisting of 78% by weight of first particles, 2% by weight of second particles, and 20% by weight of lithium-cobalt composite oxide particles was dry-mixed with 3% by weight of acetylene black as a conductive agent and 2% by weight of graphite. The resulting mixed powder was suspended in N-methylpyrrolidone (NMP) with 2% by weight of polyvinylidene fluoride (PVdF) as a binder so that the solid content ratio was 82.3% by weight, and the mixture was kneaded to prepare a first slurry.

A second slurry with a solids content of 67.0% by weight was prepared by adding N-methylpyrrolidone to the first slurry and diluting it with stirring.

An aluminum foil having a thickness of 12 μm was prepared as a positive electrode current collector. The positive electrode current collector had a band shape extending in a first direction (I) and having a width in a second direction (II) perpendicular to the first direction. The positive electrode second slurry prepared by the above procedure was applied to both sides of the positive electrode current collector so that the thickness of the positive electrode mixture layer was 100 μm, and dried to obtain a positive electrode mixture layer. When applying the positive electrode second slurry, a band-shaped slurry uncoated portion extending in the first direction (I) was left 10 mm on a part of the surface of the positive electrode current collector to form a positive electrode current collector tab. After drying, the positive electrode mixture layer was cut to have a width of 90 mm. After cutting, the electrode was rolled with a constant load to prepare a positive electrode.
Example 4
A battery was assembled in the same manner as in Example 1, except that the following positive electrode was used.

As the positive electrode active material, lithium nickel cobalt manganese composite oxide particles (first particles) having an average particle size D ₁ of 14 μm and represented by LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , lithium nickel cobalt manganese composite oxide particles (second particles) having an average particle size D ₂ of 1 μm and represented by LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , and lithium cobalt composite oxide particles represented by LiCoO ₂ were prepared. The particle size of the first particles was in the range of 8 μm to 20 μm. The particle size of the second particles was in the range of 0.5 μm to 1.4 μm. The particle size of the lithium cobalt composite oxide particles was in the range of 3 μm to 13 μm.

93% by weight of a positive electrode active material consisting of 78% by weight of first particles, 2% by weight of second particles, and 20% by weight of lithium-cobalt composite oxide particles was dry-mixed with 3% by weight of acetylene black as a conductive agent and 2% by weight of graphite. The resulting mixed powder was suspended in N-methylpyrrolidone (NMP) with 2% by weight of polyvinylidene fluoride (PVdF) as a binder so that the solid content ratio was 82.3% by weight, and the mixture was kneaded to prepare a first slurry.

A second slurry with a solids content of 67.0% by weight was prepared by adding N-methylpyrrolidone to the first slurry and diluting it with stirring.

An aluminum foil having a thickness of 12 μm was prepared as a positive electrode current collector. The positive electrode current collector had a band shape extending in a first direction (I) and having a width in a second direction (II) perpendicular to the first direction. The positive electrode second slurry prepared by the above procedure was applied to both sides of the positive electrode current collector so that the thickness of the positive electrode mixture layer was 100 μm, and dried to obtain a positive electrode mixture layer. When applying the positive electrode second slurry, a band-shaped slurry uncoated portion extending in the first direction (I) was left 10 mm on a part of the surface of the positive electrode current collector to form a positive electrode current collector tab. After drying, the positive electrode mixture layer was cut to have a width of 90 mm. After cutting, the electrode was rolled with a constant load to prepare a positive electrode.
Example 5
A battery was assembled in the same manner as in Example 1, except that the following positive electrode was used.

As the positive electrode active material, lithium nickel cobalt manganese composite oxide particles (first particles) having an average particle size D ₁ of 14 μm and represented by LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , lithium nickel cobalt manganese composite oxide particles (second particles) having an average particle size D ₂ of 6 μm and represented by LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , and lithium cobalt composite oxide particles represented by LiCoO ₂ were prepared. The particle size of the first particles was in the range of 8 μm to 20 μm. The particle size of the second particles was in the range of 4.5 μm to 7 μm. The particle size of the lithium cobalt composite oxide particles was in the range of 3 μm to 13 μm.

93% by weight of a positive electrode active material consisting of 73% by weight of first particles, 7% by weight of second particles, and 20% by weight of lithium-cobalt composite oxide particles was dry-mixed with 3% by weight of acetylene black as a conductive agent and 2% by weight of graphite. The resulting mixed powder was suspended in N-methylpyrrolidone (NMP) with 2% by weight of polyvinylidene fluoride (PVdF) as a binder so that the solid content ratio was 82.3% by weight, and the mixture was kneaded to prepare a first slurry.

A second slurry with a solids content of 67.0% by weight was prepared by adding N-methylpyrrolidone to the first slurry and diluting it with stirring.

An aluminum foil having a thickness of 12 μm was prepared as a positive electrode current collector. The positive electrode current collector had a band shape extending in a first direction (I) and having a width in a second direction (II) perpendicular to the first direction. The positive electrode second slurry prepared by the above procedure was applied to both sides of the positive electrode current collector so that the thickness of the positive electrode mixture layer was 100 μm, and dried to obtain a positive electrode mixture layer. When applying the positive electrode second slurry, a band-shaped slurry uncoated portion extending in the first direction (I) was left 10 mm on a part of the surface of the positive electrode current collector to form a positive electrode current collector tab. After drying, the positive electrode mixture layer was cut to have a width of 90 mm. After cutting, the electrode was rolled with a constant load to prepare a positive electrode.
Example 6
A battery was assembled in the same manner as in Example 1, except that the following positive electrode was used.

As the positive electrode active material, lithium nickel cobalt manganese composite oxide particles (first particles) having an average particle size _D1 of 19 μm and represented by LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , lithium nickel cobalt manganese composite oxide particles (second particles) having an average particle size _D2 of 5 μm and represented by LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , and lithium cobalt composite oxide particles represented by LiCoO ₂ were prepared. The particle size of the first particles was in the range of 8 μm to 23 μm. The particle size of the second particles was in the range of 2 μm to 6 μm. The particle size of the lithium cobalt composite oxide particles was in the range of 3 μm to 13 μm.

93% by weight of a positive electrode active material consisting of 75% by weight of first particles, 5% by weight of second particles, and 20% by weight of lithium-cobalt composite oxide particles was dry-mixed with 3% by weight of acetylene black as a conductive agent and 2% by weight of graphite. The resulting mixed powder was suspended in N-methylpyrrolidone (NMP) with 2% by weight of polyvinylidene fluoride (PVdF) as a binder so that the solid content ratio was 82.3% by weight, and the mixture was kneaded to prepare a first slurry.

A second slurry with a solids content of 65.0% by weight was prepared by adding N-methylpyrrolidone to the first slurry and diluting it with stirring.

An aluminum foil having a thickness of 12 μm was prepared as a positive electrode current collector. The positive electrode current collector had a band shape extending in a first direction (I) and having a width in a second direction (II) perpendicular to the first direction. The positive electrode second slurry prepared by the above procedure was applied to both sides of the positive electrode current collector so that the thickness of the positive electrode mixture layer was 120 μm, and dried to obtain a positive electrode mixture layer. When applying the positive electrode second slurry, a band-shaped slurry uncoated portion extending in the first direction (I) was left 10 mm on a part of the surface of the positive electrode current collector to form a positive electrode current collector tab. After drying, the positive electrode mixture layer was cut to have a width of 90 mm. After cutting, the electrode was rolled with a constant load to prepare a positive electrode.
(Example 7)
A battery was assembled in the same manner as in Example 1, except that the following positive electrode was used.

As the positive electrode active material, lithium manganese composite oxide particles (first particles) having an average particle size _D1 of 13 μm and represented by LiMn ₂ O ₄ , lithium manganese composite oxide particles (second particles) having an average particle size _D2 of 3 μm and represented by LiMn ₂ O ₄ , and lithium cobalt composite oxide particles represented by LiCoO ₂ were prepared. The particle size of the first particles was in the range of 8 μm to 18 μm. The particle size of the second particles was in the range of 1.5 μm to 5 μm. The particle size of the lithium cobalt composite oxide particles was in the range of 3 μm to 13 μm.

93% by weight of a positive electrode active material consisting of 74% by weight of first particles, 6% by weight of second particles, and 20% by weight of lithium-cobalt composite oxide particles was dry-mixed with 3% by weight of acetylene black as a conductive agent and 2% by weight of graphite. The resulting mixed powder was suspended in N-methylpyrrolidone (NMP) with 2% by weight of polyvinylidene fluoride (PVdF) as a binder so that the solid content ratio was 82.3% by weight, and the mixture was kneaded to prepare a first slurry.

A second slurry with a solids content of 65.0% by weight was prepared by adding N-methylpyrrolidone to the first slurry and diluting it with stirring.

An aluminum foil having a thickness of 12 μm was prepared as a positive electrode current collector. The positive electrode current collector had a band shape extending in a first direction (I) and having a width in a second direction (II) perpendicular to the first direction. The positive electrode second slurry prepared by the above procedure was applied to both sides of the positive electrode current collector so that the thickness of the positive electrode mixture layer was 150 μm, and dried to obtain a positive electrode mixture layer. When applying the positive electrode second slurry, a band-shaped slurry uncoated portion extending in the first direction (I) was left 10 mm on a part of the surface of the positive electrode current collector to form a positive electrode current collector tab. After drying, the positive electrode mixture layer was cut to have a width of 90 mm. After cutting, the electrode was rolled with a constant load to prepare a positive electrode.
(Example 8)

A battery was assembled in the same manner as in Example 1, except that the positive electrode mixture layer was cut to a width of 82 mm, the active material layer on the negative electrode current collector was cut to a width of 87 mm, and the electrode group was wound so that the aspect ratio was the value shown in Table 1.
(Example 9)

A battery was assembled in the same manner as in Example 1, except that the positive electrode mixture layer was cut to a width of 162 mm, the active material layer on the negative electrode current collector was cut to a width of 171 mm, and the electrode group was wound so that the aspect ratio was the value shown in Table 1.
(Example 10)

A battery was assembled in the same manner as in Example 1, except that a separator with an air permeability of 20 sec/100 cc was used.
Example 11

A battery was assembled in the same manner as in Example 1, except that a separator with an air permeability of 100 sec/100 cc was used.
(Comparative Example 1)
A battery was assembled in the same manner as in Example 1, except that the following positive electrode was used.

As the positive electrode active material, lithium nickel cobalt manganese composite oxide particles (first particles) having an average particle size D ₁ of 12 μm and represented by LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , lithium nickel cobalt manganese composite oxide particles (second particles) having an average particle size D ₂ of 5 μm and represented by LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , and lithium cobalt composite oxide particles represented by LiCoO ₂ were prepared. The particle size of the first particles was in the range of 8 μm to 12 μm. The particle size of the second particles was in the range of 2 μm to 6 μm. The particle size of the lithium cobalt composite oxide particles was in the range of 3 μm to 13 μm.

93% by weight of a positive electrode active material consisting of 36% by weight of first particles, 44% by weight of second particles, and 20% by weight of lithium-cobalt composite oxide particles was dry-mixed with 3% by weight of acetylene black as a conductive agent and 2% by weight of graphite. 2% by weight of polyvinylidene fluoride (PVdF) as a binder was suspended in N-methylpyrrolidone (NMP) to a solids ratio of 82.3% by weight in the resulting mixed powder to prepare a slurry.

An aluminum foil having a thickness of 12 μm was prepared as a positive electrode current collector. The positive electrode current collector had a band shape extending in a first direction (I) and having a width in a second direction (II) perpendicular to the first direction. The positive electrode second slurry prepared by the above procedure was applied to both sides of the positive electrode current collector so that the thickness of the positive electrode mixture layer was 40 μm, and dried to obtain a positive electrode mixture layer. When applying the positive electrode second slurry, a band-shaped slurry uncoated portion extending in the first direction (I) was left 10 mm on a part of the surface of the positive electrode current collector to form a positive electrode current collector tab. After drying, the positive electrode mixture layer was cut to have a width of 90 mm. After cutting, the electrode was rolled with a constant load to prepare a positive electrode.
(Comparative Example 2)

As the positive electrode active material, lithium nickel cobalt manganese composite oxide particles (first particles) having an average particle size D ₁ of 10 μm and represented by LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , lithium nickel cobalt manganese composite oxide particles (second particles) having an average particle size D ₂ of 5 μm and represented by LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , and lithium cobalt composite oxide particles represented by LiCoO ₂ were prepared. The particle size of the first particles was in the range of 8 μm to 12 μm. The particle size of the second particles was in the range of 2 μm to 6 μm. The particle size of the lithium cobalt composite oxide particles was in the range of 3 μm to 13 μm.

A slurry was prepared by suspending 93% by weight of positive electrode active material consisting of 72% by weight of first particles, 8% by weight of second particles, and 20% by weight of lithium-cobalt composite oxide particles, 3% by weight of acetylene black and 2% by weight of graphite as conductive agents, and 2% by weight of polyvinylidene fluoride (PVdF) as a binder in N-methylpyrrolidone (NMP) to a solids ratio of 82.3% by weight.

A battery was fabricated in the same manner as in Example 1, except that the positive electrode slurry was applied to both sides of the positive electrode current collector so that the thickness of the positive electrode mixture layer became 105 μm.
(Comparative Example 3)

As the positive electrode active material, lithium nickel cobalt manganese composite oxide particles (first particles) having an average particle size D ₁ of 25 μm and represented by LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , lithium nickel cobalt manganese composite oxide particles (second particles) having an average particle size D ₂ of 5 μm and represented by LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , and lithium cobalt composite oxide particles represented by LiCoO ₂ were prepared. The particle size of the first particles was in the range of 8 μm to 25 μm. The particle size of the second particles was in the range of 2 μm to 6 μm. The particle size of the lithium cobalt composite oxide particles was in the range of 3 μm to 13 μm.

A slurry was prepared by suspending 93% by weight of positive electrode active material consisting of 69% by weight of first particles, 11% by weight of second particles, and 20% by weight of lithium-cobalt composite oxide particles, 3% by weight of acetylene black and 2% by weight of graphite as conductive agents, and 2% by weight of polyvinylidene fluoride (PVdF) as a binder in N-methylpyrrolidone (NMP) to a solids ratio of 75.5% by weight.

A battery was fabricated using the same procedure as in Example 1, except that the positive electrode slurry was applied to both sides of the positive electrode current collector so that the thickness of the positive electrode mixture layer was 90 μm.

For the obtained battery, the abundance ratio (%) represented by the formula (1) as the abundance ratio of the first particle, the thickness T (μm) of the positive electrode mixture layer, the value of 2D ₁ /T that defines the range of the first particle uneven distribution region, 2D ₁ /T × 1.05, A3/A1, T/ ² (μm), T1S (μm 2 ), and T2S (μm ^{2 ) were measured by the above-mentioned method. T2S/T1S was calculated from T1S (μm 2 ) and T2S (μm 2 ) .} T2S/T1S, the abundance ratio (%), the thickness T (μm) of the positive electrode mixture layer, 2D ₁ /T, 2D _{1 /} T × 1.05, A3/A1, and T/2 (μm) are shown in Tables 1 and 2 below.
[Measurement of Discharge Capacity 1]
The battery thus produced was charged at a constant current of 1 C to 2.7 V in a 25° C. environment, then charged at a constant voltage until the current value reached 0.1 C, and after a 30-minute pause, discharged at a constant current of 0.5 C until the voltage reached 1.5 V. The discharge capacity at this time was taken as 1.
[Cycle test]
The battery for which discharge capacity 1 was measured was charged at a constant current of 2 C to 2.7 V in a 45° C. environment, then charged at a constant voltage until the current value reached 0.1 C, and then rested for 10 minutes, after which it was discharged at a constant current of 2 C until the voltage reached 1.5 V, and then rested for 10 minutes. This cycle of charge, rest, discharge, and rest was counted as one cycle, and the cycle was repeated 1000 times.
[Measurement of Discharge Capacity 2, Discharge Capacity Rate]
After the cycle test, the battery was cooled in a 25° C. environment for 3 hours, and then charged at a constant current of 1 C to 2.7 V in a 25° C. environment, and then charged at a constant voltage until the current value reached 0.1 C. After a 30-minute pause, the battery was discharged at a constant current of 0.5 C until the voltage reached 1.5 V. This was taken as discharge capacity 2. The discharge capacity rate was calculated as discharge capacity rate [%]=[discharge capacity 2]/[discharge capacity 1]×100.
[Measurement of capacity per unit volume of positive electrode]
One side of the positive electrode prepared by the above procedure was peeled off with NMP, cut into 2 cm x 2 cm, and then the thickness and weight of the positive electrode were measured. Separately, both sides of the positive electrode were peeled off with NMP, cut into 2 cm x 2 cm, and then the thickness and weight of the current collector foil were measured. From these results, the weight of the active material in the sample and the density of the active material layer of the sample were obtained. Drying was performed at 95 ° C. and -100 kPa for 12 hours. A three-electrode glass cell was prepared by dissolving lithium hexafluorophosphate LiPF ₆ at a concentration of 1.0 mol / L in a non-aqueous solvent prepared by mixing metal lithium as the counter electrode and reference electrode, glass filter paper as the separator, and ethylene carbonate (EC) and diethyl carbonate (DEC) as the electrolyte in a volume ratio of 1: 2.

The prepared glass cell was subjected to an initial charge-discharge test at 25° C. in a potential range of 3.0-4.25 V (vs. Li/Li ⁺ ) at a current of 0.2 C. It was charged at a constant current up to 4.25 V, and constant voltage charging was continued for 10 hours, after which it was paused for 10 minutes and then discharged at a constant current of 0.2 C down to 3.0 V.

At this time, the obtained discharge capacity was divided by the weight of the active material, and then further divided by the electrode density to obtain the capacity per unit volume of the positive electrode. The capacity per unit volume of the positive electrode in Example 1 was set to 1, and the values of the other examples are shown.

In Examples 1 to 11, high capacity and good charge/discharge cycle characteristics were obtained. The moderate ratio of large and small particles resulted in a high-capacity electrode with high packing density. Furthermore, the presence of a large number of large particles with a small specific surface area on the collector foil side exposed to a large current resulted in a small surface area of the active material present on the collector foil side, suppressing side reactions with the electrolyte, and good gas escape from the mixture layer during gas generation, suppressing slippage of the mixture layer. In Examples 1 to 11, T2S/T1S was greater than 2, satisfying the formula T2S>2×T1S (3). Therefore, the conductive agent was distributed in large amounts on the second surface (S2) side, which has a large electron conduction distance from the collector foil, suppressing the current density distribution and increasing the discharge capacity rate after cycling.

Example 6, in which _{LiNi0.5Co0.2Mn0.3O2} was used as the positive _electrode active material, and Example 7, in which _LiMn2O4 was used as the positive _electrode active material, both had high unit capacity and high discharge capacity retention. Therefore, by using a lithium _{- containing} metal oxide as the positive electrode active material, a battery with high _{capacity and} excellent charge/discharge cycle performance can be provided. In particular, the discharge capacity retention of Example 6 was as high as 93%, which was the same as the discharge capacity retention of Example ₁ , in which _{LiNi0.8Co0.1Mn0.1O2} was used as the positive electrode active material. Therefore, by using a lithium-containing nickel manganese composite oxide represented by the general formula Li _x Co _1-y-z Mn _y Ni _z O ₂ (0<x≦1, 0<y≦1, 0<z≦1, 0≦1-y-z≦1) as a positive electrode active material, a battery with particularly excellent charge-discharge cycle performance can be provided.

Example 8, which has an aspect ratio of 1, and Example 9, which has an aspect ratio of 1.8, both had excellent capacity per unit and discharge capacity retention. Therefore, when the aspect ratio of the electrode group is in the range of 1 to 1.8, a battery with high capacity and excellent charge/discharge cycle performance can be provided.

Example 10, which used a separator with an air permeability of 20 sec/100 ml, and Example 11, which used a separator with an air permeability of 100 sec/100 ml, both had excellent capacity per unit and discharge capacity retention. Therefore, if the separator has an air permeability of 20 sec/100 ml or more and 100 sec/100 ml or less, a battery with high capacity and excellent charge/discharge cycle performance can be provided.

In Comparative Example 1, the particle diameter of the active material in the electrode mixture layer was uniform, so the packing density was low and the capacity per unit volume was low. Furthermore, the proportion of small particles was high, so the surface area of the active material was large, which increased the side reaction with the electrolyte, increased the amount of gas generation, and poor gas escape from the mixture layer. As a result, the mixture layer slid off during charge-discharge cycles, resulting in a low discharge capacity rate after cycling.
In Comparative Example 2, the particle diameter of the active material present in the electrode mixture layer was uniform, so that the packing density was low and the capacity per unit volume was low.
In Comparative Example 3, the proportion of large particles unevenly distributed in the electrode mixture layer on the current collecting foil side was low, and therefore the surface area of the active material present on the current collecting foil side was large, causing a large side reaction with the electrolyte, and poor gas escape from the mixture layer, resulting in the mixture layer sliding off during charge/discharge cycles.

The active material contained in the electrode according to at least one of the embodiments and examples described above includes first particles of a lithium-containing metal oxide and second particles of a lithium-containing metal oxide having an average particle diameter _D2 smaller than the average particle diameter _D1 of the first particles. The abundance ratio of the first particles is greater than that of the second particles. In addition, the first particles are unevenly distributed in the electrode. With such an electrode, a battery with high capacity and excellent charge/discharge cycle performance can be realized.

Although some 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 can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and spirit of the invention.
The invention as originally claimed in the present application is set forth below.
[1] An electrode comprising a current collector and a mixture layer containing an active material formed on at least one surface of the current collector,
The active material includes first particles of a lithium-containing metal oxide and second particles of a lithium-containing metal oxide having an average particle size _D2 smaller than an average particle size _D1 of the first particles ,
an existence ratio of the first particles and the second particles represented by the following formula (1) is 60% or more and 90% or less,
{A1/(A1+A2)}×100 (1)
When a distance from a first surface of the mixture layer that is in contact with the current collector to a second surface that is not in contact with the current collector is defined as T, A1 is a total area of the first particles on a surface of the mixture layer having a length of the distance T, and A2 is a total area of the second particles on the surface of the mixture layer,
the first particles are unevenly distributed within a range of a distance 2D ₁ /T from the first surface toward the second surface at a ratio that satisfies the following formula (2):
(A3/A1)≧2D ₁ /T×1.05 (2)
Here, A3 is the total area of the first particles present in the range of the surface of the mixture layer.
[2] The electrode according to [1], wherein the particle size of the first particles is in the range of 8 μm or more and 25 μm or less, and the particle size of the second particles is in the range of 0.5 μm or more and 7 μm or less and is smaller than the particle size of the first particles.
[3] The electrode according to [1], wherein the particle size of the first particles is in the range of 8 μm or more and 25 μm or less, and the particle size of the second particles is in the range of 1 μm or more and 6 μm or less and is smaller than the particle size of the first particles.
[4] The mixture layer further contains a conductive agent in the form of secondary particles, and when a total area of the conductive agent included in a range from the first surface toward the second surface at a distance T/2 on the surface of the mixture layer is T1S (μm ² ), and a total area of the conductive agent included in a range from the second surface toward the first surface at a distance T/2 is T2S (μm ² ), the following formula (3) is satisfied:
T2S>2×T1S (3)
The electrode according to any one of [1] to [3].
[5] The lithium-containing metal oxide is at least one selected from the group consisting of a lithium-containing nickel-cobalt-manganese composite oxide, a lithium-containing nickel-manganese composite oxide, and a lithium-containing manganese composite oxide. The electrode according to any one of [1] to [4].
[6] The electrode according to any one of [1] to [4], wherein the lithium-containing metal oxide is at least one selected from the group consisting of Li _a Ni _{(1-xy) Co x Mn y O 2 (0.9≦a≦1.2, 0<x≦0.5, 0<y≦0.5, x≧y, 0.6≦1-x-y≦0.9), Li x Co 1-y-z} Mn _y Ni _z O _{2 (} 0 <x≦1, 0<y≦1, 0<z≦1, 0≦1-y-z≦1 ₎ , and _Li x _Mn 2 _O 4 (0<x ≦ ₁ ) _.
[7] The electrode according to any one of [5] or [6], wherein the active material further contains particles of a lithium-containing cobalt composite oxide.
[8] A positive electrode comprising the electrode according to any one of [1] to [7];
Negative electrode and
Including batteries.
[9] The battery according to [8], further comprising a separator having an air permeability of 20 sec/100 ml to 100 sec/100 ml.
[10] The battery according to [9], comprising an electrode group in which the positive electrode, the negative electrode, and the separator disposed between the positive electrode and the negative electrode are wound, and the electrode group has an aspect ratio of 1 or more and 1.8 or less.
[11] A battery pack comprising the battery according to any one of [8] to [10].

DESCRIPTION OF SYMBOLS 1...electrode group, 2...negative electrode, 2a...negative electrode current collector, 2b...negative electrode active material-containing layer, 3...positive electrode, 3a...positive electrode current collector, 3b...positive electrode active material-containing layer, 3c...positive electrode current collecting tab, 4...separator, 5...negative electrode terminal, 6...positive electrode terminal, 7...exterior member, 15...negative electrode terminal, 15a...negative electrode lead, 16...positive electrode terminal, 16a...positive electrode lead, 17a...metallic container, 17b...sealing plate, 17c...insulating member, 20...battery pack, 23...assembled battery, 24...printed wiring board, 25...thermistor, 26...protective circuit, 27...current-carrying terminal, 28...positive electrode side lead, 30...negative electrode side lead, 36...protective sheet, 37...container, 38...lid.

Claims (10)

An electrode including a current collector and a mixture layer formed on at least one surface of the current collector and including an active material,
The active material includes first particles of a lithium-containing metal oxide and second particles of a lithium-containing metal oxide having an average particle size _D2 smaller than an average particle size _D1 of the first particles,
an existence ratio of the first particles and the second particles represented by the following formula (1) is 60% or more and 90% or less,
{A1/(A1+A2)}×100 (1)
When a distance from a first surface of the mixture layer that is in contact with the current collector to a second surface that is not in contact with the current collector is defined as T, A1 is a total area of the first particles on a surface of the mixture layer having a length of the distance T, and A2 is a total area of the second particles on the surface of the mixture layer,
the first particles are unevenly distributed within a range of a distance 2D ₁ /T from the first surface toward the second surface at a ratio that satisfies the following formula (2):
(A3/A1)≧2D ₁ /T×1.05 (2)
Here, A3 is the total area of the first particles present in the range on the surface of the mixture layer,
An electrode, wherein the particle size of the first particles is within a range of 8 μm or more and 25 μm or less, the average particle size being the average particle size D1, and _the particle size of the second particles is within a range of 1 μm or more and 6 μm or less and is smaller than the particle size of the first particles, the average particle size being the average particle size D2 _.
The mixture layer further contains a conductive agent in the form of secondary particles, and when a total area of the conductive agent included in a range from the first surface toward the second surface at a distance T/2 on the surface of the mixture layer is T1S (μm ² ), and a total area of the conductive agent included in a range from the second surface toward the first surface at a distance T/2 is T2S (μm ² ), the following formula (3) is satisfied:
T2S>2×T1S (3)
2. The electrode of claim 1 . The electrode according to any one of claims 1 to 2 , wherein the lithium-containing metal oxide is at least one selected from the group consisting of a lithium-containing nickel-cobalt-manganese composite oxide, a lithium-containing nickel-manganese composite oxide, and a lithium-containing manganese composite oxide. The electrode according to any one of claims _{1 to 2, wherein the lithium-containing metal oxide is at least one selected from the group consisting of LiaNi(1-xy) CoxMnyO2 ( 0.9 ≦ a ≦ 1.2} , 0<x≦0.5, 0<y≦0.5, x≧y, 0.6≦1-x-y≦0.9), _LixCo1 -y- _zMnyNizO2 (0<x _≦ 1, ₀ <y≦1, 0<z≦ 1 , 0≦1-y-z≦1), and _LixMn2O4 (0<x≦1). 5. The electrode according to claim 3 , wherein the active material further comprises particles of a lithium-containing cobalt composite oxide. The electrode according to any one of claims 1 to 2, wherein the lithium-containing metal oxide of the first particles and the lithium-containing metal oxide of the second particles are each a lithium-containing nickel-cobalt-manganese composite oxide . A positive electrode comprising the electrode according to any one of claims 1 to 6 ;
a negative electrode. The battery according to claim 7 , further comprising a separator having an air permeability of 20 sec/100 ml to 100 sec/100 ml. 9. The battery according to claim 8, comprising an electrode group in which the positive electrode, the negative electrode, and the separator disposed between the positive electrode and the negative electrode are wound, and the electrode group has an aspect ratio of 1 or more and 1.8 or less. A battery pack comprising the battery according to any one of claims 7 to 9 .

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