JP7749866B2 - Nonaqueous electrolyte battery and battery pack - Google Patents

Description

Embodiments of the present invention relate to non-aqueous electrolyte batteries and battery packs.

In recent years, the widespread use of electric vehicles (EVs) and electric buses (EV buses) has created a need for longer driving distances per charge. For the lithium-ion batteries that power these vehicles, there is a strong demand for high-energy-density lithium-ion batteries in order to increase the charging capacity per pack and reduce weight. One way to achieve this high energy density is to increase the battery's capacity. To increase the capacity of batteries, LNCM (lithium, nickel, manganese, cobalt) composite oxides, which have a high capacity per unit mass, are promising as positive electrode active materials.

In order to increase the capacity of a battery using this LNCM positive electrode active material, if it is used at a high positive electrode potential of 4.2 V or higher, which is the potential at which a large capacity can be extracted, a significant increase in resistance occurs due to gas generation caused by a side reaction between the surface of the positive electrode active material particles and the electrolyte. As a result, the positive electrode deteriorates significantly during charge/discharge cycles and storage.

Increasing the positive electrode density is one way to suppress side reactions between the surface of positive electrode active material particles and the electrolyte. However, conventional LNCM positive electrode active materials are generally polycrystalline, forming secondary particles formed by the aggregation of fine primary particles. When these active materials are filled into the positive electrode composite layer, they leave many voids. This makes it difficult to increase the positive electrode density.

When fabricating the positive electrode, it is possible to increase the density of the positive electrode by applying a large press load to the positive electrode composite layer. However, doing so not only reduces the electrolyte's ability to penetrate the positive electrode, but also creates issues such as a lack of electrolyte supporting salt in the voids in the positive electrode, which can lead to reduced discharge performance and greater reaction irregularities.

Japanese Patent Application Laid-Open No. 2021-153014 Japanese Patent Application Laid-Open No. 2021-52006 International Publication No. WO 2022/138451

To provide a non-aqueous electrolyte battery and battery pack in which gas generation and resistance increase during cycling at high potential are suppressed.

According to an embodiment, a nonaqueous electrolyte battery is provided, comprising a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and a nonaqueous electrolyte. The positive electrode includes a positive electrode active material-containing layer containing single particles of a positive electrode active material represented by the following formula (1) and having a first porosity of 10% to 25%. The nonaqueous electrolyte includes _LiPF6 and propylene carbonate. The mass ratio of _LiPF6 to propylene carbonate is 0.5 to 1.0. The ratio of the second porosity of the separator to the first porosity is 2.2 to 2.8.
Li _a Ni _(1-bcd) Co _b Mn _c M _d O ₂ (1)
Here, 1≦a≦1.2, 0< b≦0.4, 0< c≦0.4, 0≦d≦0.1, and M is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga, and V.

According to another embodiment, a battery pack is provided. The battery pack includes a nonaqueous electrolyte battery according to an embodiment.

FIG. 1 is an exploded perspective view of an example of a nonaqueous electrolyte battery according to an embodiment. FIG. 2 is a partially exploded perspective view of an example of an electrode group used in the nonaqueous electrolyte battery shown in FIG. FIG. 3 is a block diagram showing an example of an electric circuit of the battery pack according to the embodiment.

Embodiment

(First embodiment)
According to a first embodiment, a non-aqueous electrolyte battery is provided. The non-aqueous electrolyte battery includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte.

The positive electrode includes a positive electrode active material-containing layer. The positive electrode active material-containing layer contains, as a positive electrode active material, single particles of a lithium-containing metal oxide represented by the following formula (1). The positive electrode active material-containing layer has a first porosity of 10% or more and 25% or less.
Li _a Ni _(1-bcd) Co _b Mn _c M _d O ₂ (1)
Here, 1≦a≦1.2, 0≦b≦0.4, 0≦c≦0.4, 0≦d≦0.1, and M is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga, and V.

The lithium-containing metal oxide represented by the formula (1) has a large capacity per unit mass, and can obtain a large capacity by using it at a positive electrode potential of 4.2 V (vs. Li/Li ⁺ ) or higher. The molar ratio a in formula (1) can vary depending on the absorption and desorption of lithium ions by the positive electrode. A more preferred range is 1.05≦a≦1.15.

By setting the molar ratio b in formula (1) to 0<b≦0.4 and the molar ratio c to 0<c≦0.4, the lithium-containing metal oxide contains Co and Mn as transition metals in addition to Ni, thereby increasing the capacity per unit mass. The more preferred ranges for the molar ratios b and c are 0.05≦b≦0.2 and 0.05≦c≦0.2.

A more preferred range for the molar ratio d of element M in formula (1) is 0.01≦d≦0.05. The inclusion of element M provides the following advantages, for example: When M=Al, lattice distortion is reduced, improving Li-ion diffusivity. When M=Mg, bulk electronic conductivity is improved, improving apparent discharge capacity. Furthermore, cycle stability at high voltages is improved. When M=Zr, cycle performance is improved. When M=Ti, phase change mitigation during high-voltage charge/discharge improves cycle performance. When M=Ga, bulk electronic conductivity is improved, improving cycle performance.

The single particle of the active material represented by formula (1) does not contain crystal grain boundaries inside. Therefore, the single particle has a small specific surface area and is less likely to crack due to particle expansion and contraction.

The reason for setting the first porosity of the positive electrode active material-containing layer in the range of 10% to 25% is explained below. To prevent liquid drying up due to reaction consumption between the active material and the electrolyte, it is desirable to maintain a porosity of around 30%. However, if the porosity of the positive electrode containing the above-mentioned single particles exceeds 25%, the positive electrode density is low and sufficient contact between the particles cannot be ensured, resulting in a large increase in resistance. Furthermore, the expansion and contraction of the positive electrode active material-containing layer associated with the charge/discharge cycle of the battery tends to increase the area for side reactions between the active material-containing layer and the electrolyte, resulting in an increase in the amount of gas generated. On the other hand, if the first porosity is less than 10%, the positive electrode's ability to absorb the electrolyte decreases, resulting in a large increase in resistance.

The separator is disposed between the positive electrode and the negative electrode. The separator has a second porosity of 2.2 or more and 2.8 or less relative to the first porosity of the positive electrode active material-containing layer. That is, the separator can be formed, for example, from a porous material. A high porosity of the separator generally improves liquid retention, but if the second porosity of the separator is too high relative to the first porosity of the positive electrode, the supply of electrolyte to the positive electrode will be poor. As a result, the resistance will increase significantly. On the other hand, if the second porosity of the separator is too low compared to the first porosity, the electrolyte in the separator will dry up. Therefore, in this case as well, the resistance will increase significantly. Therefore, it is appropriate for the ratio of the first porosity to the second porosity to be within the above range.

The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte contains at least lithium hexafluorophosphate (LiPF6 ₎ as the electrolyte salt. The non-aqueous electrolyte contains at least propylene carbonate (PC) as the non-aqueous solvent.

The ratio of the mass of _LiPF6 to the mass of PC in the non-aqueous electrolyte (mass of _LiPF6 /mass of PC) is 0.5 or more and 1.0 or less. By keeping the mass ratio of _LiPF6 to PC within this range, gas generation can be suppressed. If the mass ratio is less than 0.5, the _LiPF6 in the positive electrode is consumed by reaction, resulting in a shortage, which increases reaction unevenness at the positive electrode. As a result, gas generation increases. If the mass ratio exceeds 1.0, the viscosity of the non-aqueous electrolyte increases significantly, reducing the transportability of _LiPF6 in the positive electrode and separator. This increases reaction unevenness within the battery and increases gas generation.

Next, the nonaqueous electrolyte battery according to the first embodiment will be described in detail. Such a nonaqueous electrolyte battery may include an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator positioned between the positive electrode and the negative electrode. The positive electrode may include a positive electrode current collector tab electrically connected to the electrode assembly. Furthermore, the negative electrode may include a negative electrode current collector tab electrically connected to the electrode assembly.

Such a nonaqueous electrolyte battery may further include an exterior member. The electrode group may be housed within this exterior member. The exterior member may house a nonaqueous electrolyte. The nonaqueous electrolyte may be impregnated into the electrode group housed within the exterior member. The nonaqueous electrolyte battery may further include a positive electrode terminal and a negative electrode terminal electrically connected to the exterior member. The positive electrode terminal may be electrically connected to the positive electrode current collector tab of the positive electrode. The negative electrode terminal may be electrically connected to the negative electrode current collector tab of the negative electrode.

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

Positive Electrode The positive electrode includes a positive electrode active material-containing layer. The positive electrode may further include a positive electrode current collector on which the positive electrode active material-containing layer is provided. When the positive electrode current collector has, for example, a sheet shape, the positive electrode active material-containing layer may be supported on at least one main surface of the positive electrode current collector. The positive electrode active material-containing layer includes single particles of the positive electrode active material represented by the above formula (1). The positive electrode active material-containing layer may include materials other than the positive electrode active material, such as a conductive agent or a binder.

The conductive agent can improve current collection performance and reduce contact resistance between the active material and the current collector. The conductive agent preferably contains a carbon material. Examples of carbon materials include acetylene black, ketjen black, furnace black, graphite, carbon nanotubes, and carbon nanofibers. The active material-containing layer can contain one or more of the above carbon materials.

The conductive agent may be in the form of particles or fibers, for example. The average particle size of the conductive agent particles is preferably 20 nm or more and 100 nm or less. The proportion of the conductive agent in the positive electrode active material-containing layer is preferably, for example, 3 mass % or more and 20 mass % or less.

Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine-based rubber. One or more types of binders may be used. The proportion of binder in the positive electrode active material-containing layer is preferably 1% by mass or more and 1.8% by mass or less.

The density of the positive electrode active material-containing layer is preferably 3.2 g/cm ³ or more and 3.8 g/cm ³ or less.

The positive electrode current collector can be, for example, a metal foil or alloy foil. Examples of metal foil include aluminum foil, stainless steel foil, and nickel foil. Examples of alloy foil include aluminum alloy, copper alloy, and nickel alloy.

The positive electrode is produced, for example, by the following method. A positive electrode active material, a conductive agent, and a binder are kneaded together with a solvent (e.g., N-methylpyrrolidone (NMP)) to prepare a slurry. The resulting slurry is applied to a positive electrode current collector, dried, and then pressed to obtain a positive electrode. The voids in the positive electrode active material-containing layer can be adjusted by pressing with a load appropriate for the composition of the positive electrode active material-containing layer. If necessary, a cutting process to a specified width may be performed before or after pressing.

The negative electrode includes, for example, a negative electrode current collector and a negative electrode active material-containing layer formed on the negative electrode current collector. The negative electrode active material-containing layer may include a conductive agent and a binder in addition to the negative electrode active material.

The negative electrode active material, conductive agent, binder, and negative electrode current collector are described below.

The negative electrode active material preferably contains a compound capable of inserting and extracting lithium ions at a potential of 0.4 V or more (vs. Li/Li ⁺ ) relative to the oxidation-reduction reaction potential of lithium. A nonaqueous electrolyte battery including such a negative electrode can suppress lithium deposition due to charge and discharge. Therefore, such a nonaqueous electrolyte battery has excellent rapid charge and discharge performance. Examples of the negative electrode active material that can be used include spinel-type lithium titanate represented by Li _4+x Ti ₅ O ₁₂ (x varies within the range of −1≦x≦3 depending on the charge-discharge reaction), ramsdellite-type lithium titanate represented by Li _2+x Ti ₃ O ₇ (x varies within the range of −1≦x≦3 depending on the charge-discharge reaction), monoclinic niobium-titanium composite oxide represented by Nb ₂ TiO ₇ , orthorhombic titanium-containing oxide represented by Li _2-x Ti ₆ O ₁₄ (x varies within the range of 0≦x≦6 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 TiO2 _{- P2O5} , TiO2- _V2O5 , TiO2 _{- P2O5 - SnO2} , _and TiO2 _{- P2O5 - MO} ( _wherein M is at least one element selected from the group consisting of Cu, Ni, and Fe). These metal composite oxides are converted into lithium-titanium composite oxides by intercalating lithium upon charging. Among the lithium-titanium composite oxides, spinel-type lithium titanate is preferred because it has excellent cycle performance.

It is more preferable that the negative electrode active material contains a titanium-containing oxide that exhibits a reaction potential for insertion and deintercalation of lithium ions at a potential of 0.5 V (vs. Li/Li ⁺ ) or more relative to the oxidation-reduction reaction potential of lithium. Examples of such titanium-containing oxides include spinel-type lithium titanate, ramsdellite-type lithium titanate, monoclinic niobium titanium composite oxide, and orthorhombic titanium-containing oxide, among the above-mentioned compounds.

The negative electrode active material may contain, for example, a carbonaceous material or a metal compound. Examples of the carbonaceous material include natural graphite, artificial graphite, coke, vapor-grown carbon fiber, mesophase pitch-based carbon fiber, spherical carbon, and resin-baked carbon. More preferred carbonaceous materials include vapor-grown carbon fiber, mesophase pitch-based carbon fiber, and spherical carbon. The carbonaceous material preferably has a (002) plane spacing d ₀₀₂ of 0.34 nm or less as determined by X-ray diffraction.

The metal compound may be a metal sulfide or a metal nitride. Examples of the metal sulfide include titanium sulfide such as _TiS2 , molybdenum sulfide such as _MoS2 , and iron sulfide such as FeS, _FeS2 , or _LixFeS2 (where 0≦x≦ ₂ ). Examples of the metal nitride include lithium _cobalt nitride (e.g., _LisCotN , 0<s<4, 0<t<0.5).
Examples of conductive agents include carbonaceous materials such as acetylene black, carbon black, and graphite.

Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, and styrene-butadiene rubber.

When the negative electrode active material is a material capable of absorbing and releasing lithium ions, the negative electrode current collector can be made of a material that is electrochemically stable at the lithium ion absorption and release potential of the negative electrode active material. The negative electrode current collector is preferably a metal foil made of at least one material selected from copper, nickel, stainless steel, and aluminum, or an alloy foil made of an aluminum alloy containing at least one element selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The shape of the negative electrode current collector can vary depending on the application of the battery.

A negative electrode can be produced, for example, by the following method. First, the negative electrode active material, binder, and, if necessary, conductive agent are suspended in a commonly used solvent, such as N-methylpyrrolidone, to prepare a slurry for producing the negative electrode. The resulting slurry is applied to a negative electrode current collector. The applied slurry is then dried, and the dried coating is pressed to obtain a negative electrode comprising a negative electrode current collector and a layer containing the negative electrode active material formed on the negative electrode current collector.

The separator is not particularly limited as long as it has insulating properties, but porous films or nonwoven fabrics made of polymers such as polyolefin, cellulose, polyethylene terephthalate, and vinylon can be used. The separator material may be one type, or two or more types may be used in combination.

The second porosity of the separator can be, for example, 55% or more and 70% or less.

The thickness of the separator can be between 5 μm and 20 μm.

The electrode group may have, for example, a wound structure in which a stack of positive electrodes, separators, and negative electrodes is wound, or a stack structure in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators interposed therebetween, or the electrode group may have another structure.

Nonaqueous Electrolyte The nonaqueous electrolyte includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. Examples of the nonaqueous electrolyte include a liquid nonaqueous electrolyte.

The non-aqueous electrolyte contains at least LiPF ₆ as an electrolyte salt. In addition to LiPF ₆ , the electrolyte salt may be, for example, LiBF ₄ (lithium tetrafluoroborate), Li(CF ₃ SO ₂ ) ₂ N (lithium bistrifluoromethanesulfonylamide; commonly known as LiTFSI), LiCF ₃ SO ₃ (lithium trifluoromethanesulfonate; commonly known as LiTFS), Li(C ₂ F ₅ SO ₂ ) ₂ N (lithium bispentafluoroethanesulfonylamide; commonly known as LiBETI), LiClO ₄ , LiAsF ₆ (lithium arsenic hexafluoride), LiSbF ₆ , or lithium bisoxalatoborate {LiB(C ₂ O ₄ ) _{2 N}.} , commonly known as LiBOB}, and lithium difluoro(trifluoro-2-oxido-2-trifluoro-methylpropionato(2-)-0,0)borate {LiBF ₂ OCOOC(CF ₃ ) ₂ , commonly known as LiBF ₂ (HHIB)}. These other electrolyte salts may be used alone or in combination of two or more. Of the electrolyte salts contained in the non-aqueous electrolyte, it is desirable that LiPF ₆ account for 80 mass % or more. The non-aqueous electrolyte may contain only LiPF ₆ as the electrolyte salt, in which case the content of LiPF ₆ in the electrolyte salt is 100 mass %.

The electrolyte salt concentration in the non-aqueous electrolyte is preferably in the range of 1 mol/L to 3 mol/L. When the electrolyte salt concentration is within this range, it is possible to further improve performance when a high load current is passed through the non-aqueous electrolyte while suppressing the effects of increased viscosity due to an increase in electrolyte salt concentration.

The non-aqueous solvent contains at least propylene carbonate (PC). In addition to PC, the non-aqueous solvent may further contain, for example, a cyclic carbonate (other than PC) such as ethylene carbonate (EC), a chain carbonate such as diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), or dipropyl carbonate (DPC), 1,2-dimethoxyethane (DME), γ-butyrolactone (GBL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeHF), 1,3-dioxolane, sulfolane, or acetonitrile (AN). These other solvents may be used alone or in combination.

The exterior member may be, for example, a laminate film or a metal container. The thickness of the laminate film and the metal container may each be 0.5 mm or less. Alternatively, the exterior member may be a resin container made of polyolefin resin, polyvinyl chloride resin, polystyrene resin, acrylic resin, phenolic resin, polyphenylene resin, fluorine resin, or the like.

The shape of the exterior member, i.e., the battery shape, can be flat (thin), rectangular, cylindrical, coin-shaped, button-shaped, etc. Furthermore, batteries can be used in both small applications, such as those installed in portable electronic devices, and large applications, such as those installed in two-wheeled or four-wheeled automobiles.

An example of a laminate film is a multilayer film containing a resin layer and a metal layer sandwiched between the resin layers. The metal layer is preferably aluminum foil or aluminum alloy foil for weight reduction. The resin layer can 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 metal container is made from aluminum or an aluminum alloy. Aluminum alloys containing elements such as magnesium, zinc, and silicon are preferred. If the alloy contains transition metals such as iron, copper, nickel, and chromium, the amount should preferably be 100 ppm or less.

Positive Electrode Terminal A portion of the positive electrode terminal is electrically connected to a portion of the positive electrode, thereby serving as a conductor for transferring electrons between the positive electrode and an external circuit. The positive electrode terminal can be connected, for example, to the positive electrode current collector, particularly the positive electrode current collector tab. Alternatively, the positive electrode terminal can be connected, for example, to the positive electrode current collector tab via a positive electrode lead.

The positive electrode terminal is preferably formed from a material that is electrically stable and conductive at a potential that is 3.0 V to 4.5 V (vs. Li/Li ⁺ ) higher than the Li oxidation-reduction reaction potential, for example. The positive electrode terminal is preferably formed from aluminum or an aluminum alloy containing one or more elements selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si.

The positive electrode terminal is preferably made of a highly electrically conductive material. When connected to the positive electrode current collector, the positive electrode terminal is preferably made of the same material as the current collector. Using the same material reduces the contact resistance between the positive electrode terminal and the positive electrode current collector. Similarly, the positive electrode lead is preferably made of the same material as the positive electrode terminal and the positive electrode current collector.

A portion of the negative electrode terminal is electrically connected to a portion of the negative electrode, thereby serving as a conductor for transferring electrons between the negative electrode and an external circuit. The negative electrode terminal can be connected, for example, to the negative electrode current collector, particularly the negative electrode current collector tab. Alternatively, the negative electrode terminal can be connected, for example, to the negative electrode current collector tab via a negative electrode lead.

The negative electrode terminal is preferably formed from a material that is electrically stable and conductive at a potential that is 0.5 V to 3.0 V (vs. Li/Li ⁺ ) higher than the Li oxidation-reduction reaction potential. The negative electrode terminal is preferably formed from aluminum or an aluminum alloy containing one or more elements selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si.

The negative electrode terminal is preferably made of a highly electrically conductive material. When connected to the negative electrode current collector, the negative electrode terminal is preferably made of the same material as the current collector. Using the same material reduces the contact resistance between the negative electrode terminal and the negative electrode current collector. Similarly, the negative electrode lead is preferably made of the same material as the negative electrode terminal and the negative electrode current collector.

Next, an example of such a nonaqueous electrolyte battery will be described in more detail with reference to the drawings.

Figure 1 is an exploded perspective view of an example of a nonaqueous electrolyte battery 100 according to an embodiment. The battery shown in Figure 1 is a sealed prismatic nonaqueous electrolyte battery. The illustrated nonaqueous electrolyte battery 100 comprises an outer can 1, a lid 2, a positive electrode external terminal 3, a negative electrode external terminal 4, and an electrode group 5. The outer can 1 and the lid 2 form an outer casing. The outer can 1 has a bottomed rectangular cylindrical shape and is formed from a metal such as aluminum, an aluminum alloy, iron, or stainless steel.

2 is a partially exploded perspective view of an electrode group used in the nonaqueous electrolyte battery 100 shown in FIG. 1. As shown in FIG. 2, the flat electrode group 5 is formed by winding a positive electrode 6 and a negative electrode 7 in a flat shape with a separator 8 interposed therebetween. The positive electrode 6 includes a strip-shaped positive electrode current collector made of, for example, metal foil, a positive electrode current collector tab 6a formed at one end parallel to the long side of the positive electrode current collector, and a positive electrode active material-containing layer 6b formed on the positive electrode current collector except for at least the portion of the positive electrode current collector tab 6a. Meanwhile, the negative electrode 7 includes a strip-shaped negative electrode current collector made of, for example, metal foil, a negative electrode current collector tab 7a formed at one end parallel to the long side of the negative electrode current collector, and a negative electrode active material-containing layer 7b formed on the negative electrode current collector except for at least the portion of the negative electrode current collector tab 7a.

The positive electrode 6, separator 8, and negative electrode 7 are wound with the positive electrode 6 and negative electrode 7 offset so that the positive electrode current collector tab 6a protrudes from the separator 8 in the direction of the winding axis of the electrode group, and the negative electrode current collector tab 7a protrudes from the separator 8 in the opposite direction. As a result of this winding, as shown in FIG. 2, the spirally wound positive electrode current collector tab 6a protrudes from one end face of the electrode group 5, and the spirally wound negative electrode current collector tab 7a protrudes from the other end face. A nonaqueous electrolyte (not shown) is impregnated into the electrode group 5.

As shown in Figure 1, the positive electrode current collector tabs 6a and the negative electrode current collector tabs 7a are each divided into two bundles, with the boundary near the winding center of the electrode group. The conductive clamping member 9 has first and second clamping portions 9a and 9b, each having a roughly U-shape, and a connecting portion 9c that electrically connects the first clamping portion 9a and the second clamping portion 9b. One bundle of the positive and negative electrode current collector tabs 6a and 7a is clamped by the first clamping portion 9a, and the other bundle is clamped by the second clamping portion 9b.

The positive electrode lead 10 has a substantially rectangular support plate 10a, a through hole 10b opened in the support plate 10a, and rectangular current collecting portions 10c and 10d that branch off from the support plate 10a and extend downward. The negative electrode lead 11 has a substantially rectangular support plate 11a, a through hole 11b opened in the support plate 11a, and rectangular current collecting portions 11c and 11d that branch off from the support plate 11a and extend downward.

The positive electrode lead 10 sandwiches the clamping member 9 between the current collecting portions 10c and 10d. The current collecting portion 10c is placed in the first clamping portion 9a of the clamping member 9. The current collecting portion 10d is placed in the second clamping portion 9b. The current collecting portions 10c and 10d, the first and second clamping portions 9a and 9b, and the positive electrode current collecting tab 6a are joined by, for example, ultrasonic welding. This electrically connects the positive electrode 6 of the electrode group 5 and the positive electrode lead 10 via the positive electrode current collecting tab 6a.

The negative electrode lead 11 sandwiches the clamping member 9 between the current collecting portions 11c and 11d. The current collecting portion 11c is positioned in the first clamping portion 9a of the clamping member 9. The current collecting portion 11d is positioned in the second clamping portion 9b. The current collecting portions 11c and 11d, the first and second clamping portions 9a and 9b, and the negative electrode current collecting tab 7a are joined by, for example, ultrasonic welding. This electrically connects the negative electrode 7 of the electrode group 5 and the negative electrode lead 11 via the negative electrode current collecting tab 7a.

The materials for the positive and negative electrode leads 10, 11 and the clamping member 9 are not particularly specified, but it is desirable that they be made of the same material as the positive and negative electrode external terminals 3, 4, respectively. The positive electrode external terminal 3 is made of, for example, aluminum or an aluminum alloy. The negative electrode external terminal 4 is made of, for example, aluminum, an aluminum alloy, copper, nickel, or nickel-plated iron. For example, if the external terminal is made of aluminum or an aluminum alloy, it is desirable that the lead be made of aluminum or an aluminum alloy. Furthermore, if the external terminal is made of copper, it is desirable that the lead be made of copper, etc.

The rectangular plate-shaped lid 2 is seam-welded to the opening of the outer can 1, for example, by laser. The lid 2 is made of a metal such as aluminum, aluminum alloy, iron, or stainless steel. It is desirable that the lid 2 and outer can 1 are made of the same type of metal. The positive electrode external terminal 3 is electrically connected to the support plate 10a of the positive electrode lead 10. The negative electrode external terminal 4 is electrically connected to the support plate 11a of the negative electrode lead 11. The insulating gasket 12 is disposed between the positive and negative electrode external terminals 3, 4 and the lid 2, and electrically insulates them from each other. It is desirable that the insulating gasket 12 is a resin molded product.

<Various measurement methods>
The methods for measuring the first porosity, the second porosity, the composition of the active material, and the composition of the non-aqueous electrolyte will be described below. First, a method for removing the electrodes from the battery will be described.

First, prepare the battery to be measured. The battery to be measured must have a discharge capacity of 80% or more of its rated capacity. In other words, batteries that have deteriorated excessively will not be measured.

Next, the prepared battery is discharged until the open circuit voltage reaches 2.0 V to 2.2 V. The discharged battery is then transferred to an argon-filled glove box with an internal atmosphere having a dew point of -70°C. The battery is opened in the glove box. The electrode group is removed from the cut-open battery. If the removed electrode group includes a positive electrode lead and a negative electrode lead, the positive electrode lead and the negative electrode lead are cut off, taking care not to short-circuit the positive and negative electrodes.

Next, the electrode group is disassembled into positive electrodes, negative electrodes, and separators. Each electrode obtained in this way is washed using diethyl carbonate as a solvent. During this washing, the disassembled components are completely immersed in the diethyl carbonate solvent and left in that state for 60 minutes.

After cleaning, the electrodes are subjected to vacuum drying. During vacuum drying, the pressure is reduced from atmospheric pressure to -97 kPa or higher in a 25°C environment, and this state is maintained for 10 minutes. The electrodes removed using this procedure are measured using the following method.

First Porosity The first porosity of the positive electrode active material-containing layer can be measured by mercury intrusion porosimetry.

Several strip-shaped measurement samples are cut from the positive electrode. The dimensions of the measurement samples are, for example, 1.25 cm x 2.50 cm. The mass of the cut measurement samples is then measured. 16 measurement samples are then placed in the cell of the measurement device. These measurement samples are measured under conditions of an initial pressure of approximately 10 kPa (approximately 1.5 psia, equivalent to a pore diameter of approximately 120 μm) and a maximum pressure of 414 MPa (approximately 59,986 psia, equivalent to a pore diameter of approximately 0.003 μm) to obtain a pore distribution curve for the positive electrode. For example, a Shimadzu Micromeritics Pore Distribution Measurement Device Autopore 9520 is used as the measurement device.

Next, the positive electrode active material-containing layer is peeled off from another measurement sample cut out from the same positive electrode, using, for example, a spatula, to obtain a current collector piece. The mass of this current collector piece is then measured. The mass of the current collector piece is then subtracted from the mass of the measurement sample to obtain the mass of the active material-containing layer contained in the measurement sample. The pore distribution curve of the positive electrode obtained by the above method is then recalculated and converted into the pore distribution curve of the positive electrode active material-containing layer. In this way, the pore distribution curve of the active material-containing layer is obtained. The pore volume per 1 g of the positive electrode active material-containing layer can be calculated from the pore distribution obtained in this manner and the mass of the positive electrode active material-containing layer. The first porosity is obtained by dividing the obtained pore volume (mL/g) by the volume per 1 g of the positive electrode active material-containing layer.

Second Porosity The second porosity of the separator can also be measured by mercury intrusion porosimetry. Details are as follows.

Several strip-shaped measurement samples are cut from the separator. The dimensions of the measurement samples are, for example, 1.25 cm x 2.50 cm. The mass of the cut measurement samples is then measured. Next, 16 measurement samples are placed in the cell of the measurement device. These measurement samples are measured under conditions of an initial pressure of approximately 10 kPa (approximately 1.5 psia, equivalent to a pore diameter of approximately 120 μm) and a maximum pressure of 414 MPa (approximately 59,986 psia, equivalent to a pore diameter of approximately 0.003 μm) to obtain a pore distribution curve for the separator. For example, a Shimadzu Micromeritics Autopore 9520 pore distribution measurement device is used. The pore volume per 1 g of separator can be calculated from the obtained pore distribution. The porosity is obtained by dividing the obtained pore volume (mL/g) by the volume per 1 g of separator.

Composition of the Active Material The composition of the active material can be obtained by measuring the surface of the electrode taken out of the battery by the above-mentioned method using X-ray fluorescence (XRF).

Composition of the non-aqueous electrolyte: The battery is discharged until the open circuit voltage reaches 2.0 V to 2.2 V. The discharged battery is then transferred to an argon-filled glove box with an internal atmosphere having a dew point of -70°C. The battery is then opened in the glove box. The electrode group is removed from the cut-open battery. The removed electrode group is squeezed to extract the electrolyte. If the amount extracted is small, the electrolyte is extracted using acetonitrile. The propylene carbonate (PC) content is determined by analyzing the obtained electrolyte using GC-MS (gas chromatography-mass spectrometry), and the _LiPF6 content is determined using capillary electrophoresis. The _LiPF6 /PC ratio is calculated from the respective contents obtained.

The nonaqueous electrolyte battery according to the first embodiment includes a positive electrode including a positive electrode active material-containing layer containing single particles of the positive electrode active material represented by formula (1) and having a first porosity of 10% to 25%, a separator having a second porosity with a ratio of 2.2 to 2.8 relative to the first porosity, and a nonaqueous electrolyte containing _LiPF6 and propylene carbonate (PC) in a mass ratio ( _LiPF6 /PC) of 0.5 to 1.0. Therefore, this battery can suppress gas generation and resistance increase even during cycles at high potential.

Second Embodiment
According to a second embodiment, a battery pack including a battery is provided. The battery is the nonaqueous electrolyte battery according to the first embodiment. The number of unit cells included in the battery pack can be one or more.

Multiple batteries can be electrically connected in series, parallel, or a combination of series and parallel to form a battery assembly. A battery pack may include multiple battery assemblies.

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

The battery pack may also be provided with external terminals for current flow. The external terminals for current flow are used to output current from the battery to the outside and to input current to the battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals for current flow. Furthermore, when the battery pack is charged, charging current (including regenerative energy from the vehicle's power) is supplied to the battery pack through the external terminals for current flow.

Next, an example of a battery pack according to the second embodiment will be described with reference to the drawings. Figure 3 is a block diagram showing an example of an electrical circuit of a battery pack according to the embodiment.

The battery pack shown in Figure 3 includes a plurality of flat-type cells 100 having the structure shown in Figures 1 and 2. These cells 100 are electrically connected in series with each other as shown in Figure 3.

In addition to the single battery 100, the battery pack is equipped with a thermistor 25, a protection circuit 26, and an external terminal 27 for supplying electricity.

At one end of the series connection, a positive electrode lead 28 is connected to the positive electrode external terminal of the cell 100. The positive electrode lead 28 is electrically connected to the protection circuit 26 via a positive electrode connector 29 and wiring 32. At the other end of the series connection, a negative electrode lead 30 is connected to the negative electrode external terminal of the cell 100. The negative electrode lead 30 is electrically connected to the protection circuit 26 via a negative electrode connector 31 and wiring 33.

The thermistor 25 detects the temperature of each cell 100 and transmits the detected temperature signal to the protection circuit 26. The protection circuit 26 can interrupt the positive wiring 34a and negative wiring 34b between the protection circuit 26 and the external terminal 27 for current supply under predetermined conditions. An example of a predetermined condition is when the thermistor 25 receives a signal indicating that the temperature of the cell 100 is above a predetermined temperature. Another example of a predetermined condition is when an overcharge, overdischarge, overcurrent, or other abnormality is detected in the cell 100. This overcharge detection is performed for each cell 100 or for all cells 100. When detecting an individual cell 100, the battery voltage or the positive or negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 100. In the battery pack shown in FIG. 3, each cell 100 is connected to a voltage detection wire 35, and a detection signal is transmitted to the protection circuit 26 via this wire 35.

The battery pack shown in the figure has a configuration in which multiple cells 100 are connected in series, but in such a battery pack, multiple cells 100 may be connected in parallel to increase battery capacity. Alternatively, the battery pack may include multiple cells 100 connected in a combination of series and parallel connections. The assembled battery pack may also be further connected in series or parallel.

Furthermore, although the illustrated battery pack includes multiple cells 100, the battery pack of the second embodiment may also include a single cell 100.

The battery pack configuration may be modified as appropriate depending on the intended use. Preferred battery pack applications require good cycle performance when drawing large current. Specific examples include power sources 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 preferred.

In a vehicle equipped with a battery pack according to this embodiment, the battery pack, for example, recovers regenerative energy from the vehicle's power.

The battery pack according to the second embodiment described above includes the nonaqueous electrolyte battery according to the first embodiment. Therefore, this battery pack can suppress gas generation and resistance increase even during cycles at high potentials.

<Fabrication of non-aqueous electrolyte battery>
Example 1
(Preparation of Positive Electrode)
A lithium _- containing nickel-cobalt-manganese composite oxide ( _{LiNi0.8Co0.1Mn0.1O2 )} formed as a single particle was prepared _as the active material. The average particle diameter ( _D50 ) of the prepared active material was 4 μm. Acetylene black was prepared as the conductive agent, and polyvinylidene fluoride was prepared as the binder. The active material, conductive agent, and binder were dissolved and mixed in N-methylpyrrolidone (NMP) in a mass ratio of 93:5:2 to prepare a paste.

The specific method for preparing the paste is described below. The active material and conductive agent were mixed using a Henschel mixer to form a composite (compound) of the active material and conductive agent. The resulting composite and binder were dispersed in NMP and kneaded using a planetary mixer with a capacity of 20 L. To avoid a sudden increase in viscosity, each material was added to the NMP little by little. Kneading was performed under high-pressure conditions with a solids concentration (non-volatile content; NV) of 78.5%. The kneaded mixture was then transferred to a bead mill with a capacity of 2 L and mixed at a bead rotation speed of 800 rpm to prepare a paste.

A paste-like dispersion liquid was used as the positive electrode coating liquid and uniformly applied to both the front and back surfaces of a strip-shaped current collector made of aluminum foil. The coating film of the positive electrode coating liquid was dried to form a positive electrode active material-containing layer. After drying, the strip was press-molded under the following conditions: a press roll made of hard chrome-plated steel with a press roll diameter of 350 mm was used, and the press load was set to approximately 8 kN/cm. A positive electrode with a first porosity of 24.6% was obtained by rolling. The rolled electrode was cut to the specified dimensions. A current collecting tab was welded to the cut electrode to obtain the positive electrode.

(Preparation of negative electrode)
A spinel-type lithium _{titanium oxide represented by Li4Ti5O12 was} prepared as the negative _electrode active material, graphite as the conductive agent, and polyvinylidene fluoride as the binder. These negative electrode active materials, conductive agent, and binder were dissolved and mixed in NMP in a mass ratio of 94:4:2 to prepare a paste. This paste was used as a negative electrode coating liquid and uniformly applied to both the front and back surfaces of a negative electrode current collector made of strip-shaped aluminum foil. The negative electrode coating liquid was dried to form a negative electrode active material-containing layer. The dried strip was press-molded and then cut to a predetermined size. The electrode thickness was adjusted to 130 μm. A current collecting tab was welded to the negative electrode to obtain a negative electrode.

(Preparation of electrode group)
Two nonwoven separators made of cellulose were prepared. Each separator had a thickness of 8 μm and a second porosity of 65%. Next, one separator, a positive electrode, the other separator, and a negative electrode were stacked in this order to form a laminate. The resulting laminate was wound so that the separator was positioned at the outermost periphery to obtain a wound body. The resulting wound body (coil) was then pressed while being heated. In this way, a wound electrode group was produced.

(Preparation of non-aqueous electrolyte)
A nonaqueous solvent was prepared by mixing propylene carbonate and diethyl carbonate in a volume ratio of 1:2. LiPF ₆ was dissolved in this mixed solvent as an electrolyte salt to a concentration of 1.5 mol/L to prepare a nonaqueous electrolyte. The resulting nonaqueous electrolyte had a LiPF ₆ mass/propylene carbonate (PC) mass ratio of 0.7.

(Battery assembly)
Electrode terminals were attached to the positive and negative electrodes of the wound electrode assembly obtained as described above. The electrode assembly was placed in an aluminum rectangular container. The nonaqueous electrolyte was poured into the container, and the container was sealed to obtain a nonaqueous electrolyte battery. The nonaqueous electrolyte battery was designed to have a nominal capacity of 26 Ah.

Example 2
The rolling conditions during the preparation of the positive electrode were changed so that the first porosity of the positive electrode was 19.6%, and the separator was changed to a cellulose nonwoven fabric separator having a second porosity of 55%. A nonaqueous electrolyte battery was prepared in the same manner as in Example 1, except for these changes.

Example 3
The rolling conditions during the preparation of the positive electrode were changed so that the first porosity of the positive electrode was 25%, and the separator was changed to a cellulose nonwoven fabric separator having a second porosity of 55%. A nonaqueous electrolyte battery was prepared in the same manner as in Example 1, except for these changes.

Example 4
The rolling conditions during positive electrode fabrication were changed so that the first porosity of the positive electrode was 25%, and the separator was changed to a cellulose nonwoven fabric separator having a second porosity of 55%. Furthermore, the _LiPF concentration was increased so that the _LiPF /PC mass ratio was 0.9. A nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except for these changes.

Example 5
The rolling conditions during the preparation of the positive electrode were changed so that the first porosity of the positive electrode was 16%, and the separator was changed to a cellulose nonwoven fabric separator having a second porosity of 44%. Aside from these changes, a nonaqueous electrolyte battery was prepared in the same manner as in Example 1.

Example 6
The rolling conditions during the preparation of the positive electrode were changed so that the first porosity of the positive electrode was 11%, and the separator was changed to a cellulose nonwoven fabric separator having a second porosity of 30%. Aside from these changes, a nonaqueous electrolyte battery was prepared in the same manner as in Example 1.

(Comparative Example 1)
A nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that a lithium-containing nickel-cobalt-manganese composite oxide LiNi _0.8 Co _0.1 Mn _0.1 O ₂ formed of secondary particles was used instead as the positive electrode active material.

(Comparative Examples 2 and 3)
A nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that the rolling conditions during fabrication of the positive electrode were changed so that the first porosity of the positive electrode would have the value shown in Table 1 below.

(Comparative Examples 4 and 5)
A nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that the concentration of LiPF ₆ was changed so that the LiPF ₆ /PC mass ratio was the value shown in Table 1 below.

(Comparative Examples 6 and 7)
A nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that the separator was changed to a cellulose nonwoven fabric separator having a second porosity shown in Table 1 below.

Each battery was charged at 2C from 0% SOC (state of charge) to 100% SOC in a 45°C environment, and then discharged at 2C from 100% SOC to 0% SOC for 1000 cycles. The amount of gas generated during 1000 cycles and the rate of resistance increase after 1000 cycles were measured. The results are shown in Table 1. For both the amount of gas generated and the rate of resistance increase during repeated charge-discharge cycles, the value measured in Example 1 was set to 100, and the measurement results for the other Examples and Comparative Examples are shown as relative values to this standard.

The amount of gas generated was measured and calculated as follows. It was calculated from the change in cell volume of the battery before and after a charge-discharge cycle. The cell volume was determined using Archimedes' principle by charging the battery at 1C in a 25°C environment until the state of charge (SOC) reached 50%, then submerging it in water.

The resistance increase rate was measured and calculated as follows. The resistance increase rate was calculated from the ratio of the discharge resistance values before and after the charge-discharge cycle. The discharge resistance was measured after charging at 1C in an environment of 25°C until the state of charge (SOC) reached 50%, and then discharging at 10C for 0.2 seconds.

Table 1 shows the particle shape of the positive electrode active material particles, the first porosity in the positive electrode, the second porosity of the separator, the ratio between the first and second porosities, the mass ratio of _LiPF6 to PC in the nonaqueous electrolyte, and the above measurement results. The particle shape of the positive electrode active material is indicated as either a single particle or containing secondary particles.

As shown in Table 1, in Example 1-X, both the amount of gas generated during cycling and the rate of increase in resistance were suppressed to the same extent. In contrast, in Comparative Examples 1 and 3, both the amount of gas generated and the rate of increase in resistance increased significantly. In Comparative Examples 2, 4, and 5, the amount of gas generated increased, and in Comparative Examples 6 and 7, the rate of increase in resistance was high.

From Comparative Example 1, it can be seen that when the positive electrode active material has the shape of secondary particles, the first porosity of the positive electrode active material-containing layer becomes higher, and the amount of gas generated and the rate of increase in resistance increase.

Comparative Examples 2 and 3 show that gas generation increases when the first porosity of the positive electrode active material-containing layer is too low or too high.

From Comparative Examples 4 and 5, it can be seen that if the ratio of _LiPF6 to PC in the electrolyte is too large or too small, the reaction becomes uneven and gas generation increases.

Comparative Examples 6 and 7 show that the increase in resistance is significant when the second porosity of the separator is too low or too high compared to the first porosity of the positive electrode active material.

According to at least one of the above-described embodiments and examples, a nonaqueous electrolyte battery is provided. The nonaqueous electrolyte battery includes a positive electrode, a negative electrode, a separator interposed therebetween, and a nonaqueous electrolyte. The positive electrode includes a positive electrode active material-containing layer including single particles of a positive electrode active material represented by the following formula (1). The active material-containing layer has a first porosity of 10% or more and 25% or less as measured by mercury porosimetry. The nonaqueous electrolyte includes _LiPF6 and propylene carbonate. The mass ratio of _LiPF6 to propylene carbonate in the nonaqueous electrolyte is 0.5 or more and 1.0 or less. The separator has a second porosity of 2.2 or more and 2.8 or less as a ratio to the first porosity of the active material-containing layer as measured by mercury porosimetry.
Li _a Ni _(1-bcd) Co _b Mn _c M _d O ₂ (1)
Here, 1≦a≦1.2, 0≦b≦0.4, 0≦c≦0.4, 0≦d≦0.1, and M is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga, and V.

The above-mentioned nonaqueous electrolyte battery can suppress gas generation and resistance increase even during charge-discharge cycles at high potentials.

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

Several embodiments of the present invention will be described below.
[1] A positive electrode including a positive electrode active material-containing layer that includes single particles of a positive electrode active material represented by the following formula (1) and has a first porosity of 10% or more and 25% or less;
a negative electrode;
a separator between the positive electrode and the negative electrode;
a non-aqueous electrolyte containing LiPF6 and propylene carbonate, wherein the mass ratio of the LiPF6 to the propylene carbonate is 0.5 or more and 1.0 or less;
A nonaqueous electrolyte battery, wherein the ratio of the second porosity of the separator to the first porosity is 2.2 or more and 2.8 or less:
Li _a Ni _(1-bcd) Co _b Mn _c M _d O ₂ (1)
Here, 1≦a≦1.2, 0≦b≦0.4, 0≦c≦0.4, 0≦d≦0.1, and M is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga, and V.
[2] The nonaqueous electrolyte battery according to [1], wherein the second porosity is 55% or more and 70% or less.
[3] The nonaqueous electrolyte battery according to [1] or [2], wherein the negative electrode contains a negative electrode active material that exhibits a reaction potential for insertion and deintercalation of lithium ions at a potential of 0.5 V (vs. Li/Li+) or more relative to the oxidation-reduction reaction potential of lithium.
[4] A battery pack including the nonaqueous electrolyte battery according to any one of [1] to [3].

1...Outer can, 2...Lid, 3...Positive electrode external terminal, 4...Negative electrode external terminal, 5...Electrode group, 6...Positive electrode, 6a...Positive electrode current collecting tab, 6b...Positive electrode active material containing layer, 7...Negative electrode, 7a...Negative electrode current collecting tab, 7b...Negative electrode active material containing layer, 8...Separator, 9...Cleaning member, 9a...First clamping portion, 9b...Second clamping portion, 9c...Connecting portion, 10...Positive electrode lead, 10a...Support plate, 10b...Through hole, 10c...Current collecting portion, 10d...Current collecting portion 11...negative electrode lead, 11a...support plate, 11b...through hole, 11c...current collecting portion, 11d...current collecting portion, 12...insulating gasket, 25...thermistor, 26...protective circuit, 27...external terminal for current supply, 28...positive electrode side lead, 29...positive electrode side connector, 30...negative electrode side lead, 31...negative electrode side connector, 32...wiring, 33...wiring, 34a...positive side wiring, 34b...negative side wiring, 35...wiring, 100...single cell

Claims (4)

a positive electrode including a positive electrode active material-containing layer that includes single particles of a positive electrode active material represented by the following formula (1) and has a first porosity of 10% or more and 25% or less;
a negative electrode;
a separator between the positive electrode and the negative electrode;
a non-aqueous electrolyte containing _LiPF6 and propylene carbonate, wherein the mass ratio of the _LiPF6 to the propylene carbonate is 0.5 or more and 1.0 or less;
A nonaqueous electrolyte battery, wherein the ratio of the second porosity of the separator to the first porosity is 2.2 or more and 2.8 or less:
Li _a Ni _(1-bcd) Co _b Mn _c M _d O ₂ (1)
Here, 1≦a≦1.2, 0< b≦0.4, 0< c≦0.4, 0≦d≦0.1, and M is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, Y, B, Mo, Nb, Zn, Sn, Zr, Ga, and V. The nonaqueous electrolyte battery described in claim 1, wherein the second porosity is 55% or more and 70% or less. 2. The nonaqueous electrolyte battery according to claim 1, wherein the negative electrode contains a negative electrode active material that exhibits a reaction potential for insertion and deintercalation of lithium ions at a potential of 0.5 V or more (vs. Li/Li ⁺ ) relative to the oxidation-reduction reaction potential of lithium. A battery pack including the nonaqueous electrolyte battery of claim 1.