Battery and battery pack

Abstract

One embodiment of the present invention provides a battery that comprises: a positive electrode including a positive electrode mixture layer containing a lithium nickel cobalt manganese-containing oxide; a negative electrode; and an electrolyte. The battery satisfies the following formulas (1) and (2).　(1): 1.1≤MCo / MMn≤1.8 (2): 0.2≤R1 / R2≤0.5 In the formulas (1) and (2), MCo is the proportion (mol%) of cobalt in the total amount of nickel, cobalt, and manganese of the lithium nickel cobalt manganese-containing oxide, and MMn is the proportion (mol%) of manganese in the total amount of nickel, cobalt, and manganese of the lithium nickel cobalt manganese-containing oxide. R1 is the discharge resistance (Ω) of the battery at 25°C, and R2 is the discharge resistance (Ω) of the battery at -20°C.

Description

Batteries and battery packs

[0001] FIELD OF THE INVENTION Embodiments of the present invention relate to batteries and battery packs.

[0002] Lithium-ion secondary batteries, which are charged and discharged by the movement of lithium ions between the positive and negative electrodes, are being widely used in a wide range of applications, from small-scale applications such as portable electronic devices to large-scale applications such as electric vehicles and power supply and demand adjustment, taking advantage of their high energy density and high output.

[0003] Nickel-cobalt-manganese composite oxide, lithium iron phosphate, lithium manganese oxide, etc. are known as positive electrode active materials for lithium-ion batteries. Nickel-cobalt-manganese composite oxide is widely used because it can provide high battery capacity. In order to maximize the performance required for batteries, such as battery capacity, output performance, and life performance, various studies have been conducted on the active material, such as particle size, metal ratio, doping, and coating.

[0004] Japanese Patent Publication No. 2017-147194 International Publication No. WO2013-038939 International Publication No. WO2016-136803

[0005] The object is to provide a battery that has excellent low-temperature performance and in which an increase in resistance during storage is suppressed, and a battery pack including this battery.

[0006] According to an embodiment, there is provided a battery including a positive electrode including a positive electrode mixture layer containing a lithium-nickel-cobalt-manganese-containing oxide, a negative electrode, and an electrolyte. The battery satisfies the following formulas (1) and (2):

[0007] 1.1≦M Ｃｏ / M Ｍｎ ≦1.8 (1) 0.2≦R1 / R2≦0.5 (2) However, in equations (1) and (2), M Ｃｏ is the ratio (mol%) of cobalt to the total amount of nickel, cobalt, and manganese in the lithium nickel cobalt manganese-containing oxide, and M Ｍｎis the ratio (mol %) of manganese to the total amount of nickel, cobalt, and manganese in the lithium nickel cobalt manganese-containing oxide, R1 is the discharge resistance (Ω) of the battery at 25°C, and R2 is the discharge resistance (Ω) of the battery at -20°C.

[0008] According to another embodiment, there is provided a battery pack, the battery pack including the battery described above.

[0009] Fig. 1 is a plan view schematically showing an example of an electrode. Fig. 2 is a cross section of an example battery according to an embodiment cut in the thickness direction. Fig. 3 is an enlarged cross section of part E in Fig. 2. Fig. 4 is a partially cutaway perspective view of another example battery according to an embodiment. Fig. 5 is an exploded perspective view of an example battery pack according to an embodiment. Fig. 6 is a block diagram showing an electrical circuit of the battery pack shown in Fig. 5. Embodiment

[0010] Hereinafter, embodiments will be described with reference to the drawings. Note that common components throughout the embodiments will be denoted by the same reference numerals, and duplicated descriptions will be omitted.

[0011] Furthermore, each figure is a schematic diagram for explaining and understanding the embodiments, and the shapes, dimensions, ratios, etc. may differ from those of an actual device, but these can be appropriately modified in design by taking into consideration the following explanation and known techniques. (First Embodiment) The first embodiment relates to a battery.

[0012] Various improvements to active materials have been investigated. For example, reducing the particle size of the active material or increasing the specific surface area of ​​the active material by hollowing out the active material can improve the battery's output performance, especially at low temperatures. However, side reactions in the active material increase during battery charge / discharge or storage, resulting in trade-offs such as a higher rate of increase in the battery's resistance and a reduced battery life. Therefore, it is difficult to improve overall battery performance solely through improvements in the active material.

[0013] The present inventors have conducted extensive research to solve this problem, and as a result have found that a battery having a positive electrode containing a lithium nickel cobalt manganese-containing oxide and satisfying the following formulas (1) and (2) can improve output performance at low temperatures and suppress an increase in resistance during storage.

[0014] 1.1≦M Ｃｏ / M Ｍｎ ≦1.8 (1) 0.2≦R1 / R2≦0.5 (2) However, in equations (1) and (2), M Ｃｏ is the ratio (mol%) of cobalt to the total amount of nickel, cobalt, and manganese in the lithium nickel cobalt manganese-containing oxide, and M Ｍｎ is the ratio (mol %) of manganese to the total amount of nickel, cobalt, and manganese in the lithium nickel cobalt manganese-containing oxide, R1 is the discharge resistance (Ω) of the battery at 25°C, and R2 is the discharge resistance (Ω) of the battery at -20°C.

[0015] Although the mechanism by which the battery of the embodiment achieves the above-mentioned effects is not clear, it is presumed to be due to the following mechanism. The lithium nickel cobalt manganese-containing oxide has, for example, a layered crystal structure. A specific example of cation mixing is when lithium ions at the lithium sites of the lithium nickel cobalt manganese-containing oxide are replaced with transition metal ions such as nickel ions. When cation mixing occurs, the ionic conductivity of the lithium nickel cobalt manganese-containing oxide decreases. M Ｃｏ / M Ｍｎ By making the molar ratio represented by the formula (I) 1.1 or more, it is possible to reduce the mixing of cations such as lithium ions and nickel ions. As a result, it is possible to improve the diffusibility of lithium ions in the lithium nickel cobalt manganese-containing oxide, thereby suppressing an increase in resistance at low temperatures and improving low-temperature performance. Ｃｏ / M ＭｎBy setting the molar ratio represented by (R1 / R2) to 1.8 or less, it is possible to ensure a sufficient amount of manganese ions that stabilize the crystal structure of the oxide. By setting the discharge resistance ratio represented by (R1 / R2) to 0.2 or more and 0.5 or less, it is possible to make the reaction within the electrode, for example, the reaction within the electrode mixture layer, uniform, thereby suppressing local deterioration of the electrode. Furthermore, the effect of specifying the ratio of Co to Mn in the lithium nickel cobalt manganese-containing oxide using formula (1) can be fully obtained. As a result, storage performance, for example, high-temperature storage characteristics, can be further improved.

[0016] As a result, it is possible to improve the output performance at low temperatures and suppress an increase in resistance during storage.

[0017] In the battery of the embodiment, the value of R2 can be, for example, 1 mΩ or more and 3.5 mΩ or less. This can further improve the output performance at low temperatures and the storage performance at high temperatures. Next, the battery of the first embodiment will be described in more detail.

[0018] Examples of batteries according to the present invention include secondary batteries such as lithium-ion secondary batteries. Secondary batteries include nonaqueous electrolyte secondary batteries containing a nonaqueous electrolyte. The battery includes a positive electrode, a negative electrode, and an electrolyte. The battery may include a separator, an exterior member, or both. The positive electrode, the negative electrode, and the separator may constitute an electrode group. The electrolyte may be held in the electrode group. The battery may further include an exterior member that houses the electrode group and the electrolyte. The battery may further include a positive electrode terminal electrically connected to the positive electrode and a negative electrode terminal electrically connected to the negative electrode. At least a portion of the positive electrode terminal and at least a portion of the negative electrode terminal may extend outside the exterior member. (Positive Electrode) The positive electrode may include, for example, a positive electrode current collector and a positive electrode composite layer (a layer containing a positive electrode active material). The positive electrode current collector may have, for example, a first surface and a second surface opposite to the first surface. The positive electrode current collector may have, for example, a strip or sheet shape.

[0019] The positive electrode current collector is preferably an aluminum foil or an aluminum alloy foil containing aluminum and one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si.

[0020] For example, the positive electrode active material-containing layer may be formed on both the first and second surfaces of the positive electrode current collector. Alternatively, the positive electrode active material-containing layer may be formed on either the first or second surface of the positive electrode current collector. The positive electrode current collector may include a portion on neither the first surface nor the second surface that does not carry a positive electrode active material-containing layer. This portion may function as, for example, a positive electrode tab or a positive electrode lead.

[0021] The positive electrode active material-containing layer can include a positive electrode active material.

[0022] The positive electrode active material includes a lithium nickel cobalt manganese-containing oxide (also called a lithium nickel cobalt manganese composite oxide). The lithium nickel cobalt manganese-containing oxide may have a layered structure. The lithium nickel cobalt manganese-containing oxide may be, for example, Li ａ Ni ｘ Co ｙ Mn ｚ M ｂ O ２ In the above, it is preferable that 0<a≦1. Furthermore, M can be 1 or more selected from the group consisting of Mg, Al, Ti, Zr, and W. x, y, z, and b can each be in the ranges shown below. Note that x+y+z=1 can be satisfied.

[0023] By setting the range of x to 0<x≦0.7, the structural stability of the lithium nickel cobalt manganese-containing oxide can be improved.

[0024] By making 0<y≦0.4, it is possible to prevent the raw material cost of the lithium nickel cobalt manganese-containing oxide from becoming too high.

[0025] By making the range of z 0<z≦0.4, a high positive electrode capacity can be obtained.

[0026] By making the range 0≦b≦0.1, it is possible to achieve further structural stabilization and reduction of diffusion resistance without impairing the battery capacity.

[0027] The occupancy rate of the transition metal in the lithium sites of the lithium nickel cobalt manganese-containing oxide can be 2% or less. Here, the occupancy rate is the ratio of the number of transition metal atoms occupying the lithium sites to the number of lithium site atoms. By setting the occupancy rate of the transition metal in the lithium sites to 2% or less, the lithium ion diffusibility of the lithium nickel cobalt manganese-containing oxide can be increased. The lower limit of the occupancy rate can be 0%.

[0028] The positive electrode active material may contain a positive electrode active material other than the lithium nickel cobalt manganese-containing oxide. The proportion of the lithium nickel cobalt manganese-containing oxide in the positive electrode active material may be, for example, 70% by mass or more and 100% by mass or less. An example of the other positive electrode active material may be a lithium manganese composite oxide having a spinel-type crystal structure. The lithium manganese composite oxide having a spinel-type crystal structure is represented by the general formula Li e M1 f Mn 2-f It is preferable that the composition of the alloy is represented by the formula: O4, where 0<e≦1.2 and 0.2≦f≦0.7. M1 is at least one element selected from the group consisting of Mg, Ti, Cr, Fe, Co, Zn, Al, Li, and Ga. The element M1 is represented by the general formula: Li e It can be said that this element replaces part of the Mn in lithium manganese oxide having a composition represented by Mn2O4. More preferably, f is within the range of 0.22≦f≦0.7. The subscript e can vary within the range of 0<e≦1.2 depending on the state of charge of the lithium manganese composite oxide having a spinel-type crystal structure. Note that in lithium manganese composite oxides containing Li as the element M1, the amount of Li as the element M1 does not change depending on the state of charge of this composite oxide.

[0029] Still another example of the positive electrode active material is a lithium phosphate oxide having an olivine-type crystal structure (e.g., Li g FePO4, Lig MnPO4, Li g Mn 1-h Fe h PO4, Li g In the above, it is preferable that 0<g≦1 and 0≦h≦1.

[0030] As the positive electrode active material, one of the compounds listed above may be used alone, or a mixture of two or more of the compounds listed above may be used as the positive electrode active material.

[0031] The positive electrode active material-containing layer may further contain a conductive agent and a binder as necessary. The conductive agent that the positive electrode may contain may have the effect of improving current collection performance and reducing contact resistance between the positive electrode active material and the positive electrode current collector. Examples of the conductive agent include carbonaceous materials such as acetylene black, carbon black, graphite, carbon nanofibers, and carbon nanotubes. As the carbonaceous material, one of these may be used alone, or multiple carbonaceous materials may be used.

[0032] The binder can have the function of binding the positive electrode active material, the conductive agent, and the positive electrode current collector. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber, acrylic resin or a copolymer thereof, polyacrylic acid, and polyacrylonitrile.

[0033] The specific surface area of ​​the positive electrode measured by the BET method is 1.5 m 2 / g or more 2m 2 / g or less. 2 / g or more, the reactivity of the positive electrode mixture layer can be improved. 2 By making the specific surface area 1.5 m / g or less, it is possible to suppress side reactions in the positive electrode. 2 / g or more 2m 2 By making the specific surface area equal to or less than 1 / g, it is possible to achieve both an improvement in low-temperature output performance and suppression of an increase in resistance. The method for measuring the specific surface area by the BET method will be described later.

[0034] The positive electrode active material, conductive agent, and binder in the positive electrode mixture layer (positive electrode active material-containing layer) are preferably blended in proportions of 80% by mass or more and 95% by mass or less, 3% by mass or more and 18% by mass or less, and 2% by mass or more and 17% by mass or less, respectively. The conductive agent can exhibit the above-mentioned effects by being blended in an amount of 3% by mass or more. The conductive agent can be blended in an amount of 18% by mass or less to reduce electrolyte decomposition on the conductive agent surface during high-temperature storage. The binder can be blended in an amount of 2% by mass or more to obtain sufficient electrode strength. The binder can be blended in an amount of 17% by mass or less to reduce the blending amount of the binder, which is an insulating material in the positive electrode, and reduce internal resistance.

[0035] The positive electrode can be produced, for example, by the following method. First, a positive electrode active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. This slurry is applied to one or both surfaces of a positive electrode current collector, and the coating is dried. Next, the dried coating is subjected to pressing. In this way, a positive electrode can be obtained that includes a positive electrode current collector and a positive electrode mixture layer (positive electrode active material-containing layer) formed on one or both surfaces of the positive electrode current collector.

[0036] The density of the positive electrode is, for example, 3 g / cm 3 3.5g / cm or more 3 The weight per unit area of ​​the positive electrode (positive electrode weight) can be, for example, 60 g / m 2 110g / m or more 2 The preferred range is 60 g / m 2 80g / m or more 2 The following is the result.

[0037] The capacity per unit area of ​​the positive electrode is, for example, 6 Ah / m 2 More than 16Ah / m 2 The capacity per unit area of ​​the positive electrode can be reduced to 6 Ah / m or less. 2 More than 16Ah / m 2 By setting the lower limit of the capacity per unit area of ​​the positive electrode to 8 Ah / m, it is possible to enhance the improvement effects achieved by the above formulas (1) and (2) while ensuring a practical capacity. 2 The upper limit of the capacity per unit area of ​​the positive electrode is 12 Ah / m2 The capacity per unit area of ​​the positive electrode is preferably 8 Ah / m 2 More than 16Ah / m 2 A more preferable range is 8 Ah / m 2 More than 12Ah / m 2 The capacity per unit area of ​​the positive electrode can be adjusted by, for example, the thickness of the positive electrode composite layer, the positive electrode density, the weight per unit area of ​​the positive electrode (positive electrode basis weight), etc. For example, increasing the positive electrode basis weight can increase the capacity per unit area of ​​the positive electrode. Also, decreasing the positive electrode basis weight can decrease the capacity per unit area of ​​the positive electrode. The method for measuring the capacity per unit area of ​​the positive electrode will be described later.

[0038] Capacity per unit area of ​​the positive electrode (Ah / m 2 ) and the opposing area of ​​the positive electrode and the negative electrode (m 2 ) can be, for example, 17 Ah or more and 35 Ah or less. By setting the value of this product to 17 Ah or more and 35 Ah or less, the improvement effects achieved by the above formulas (1) and (2) can be enhanced. A more preferable range is 17 Ah or more and 30 Ah or less. For example, in the case of an electrode group having a wound structure, the opposing area between the positive electrode and the negative electrode can be adjusted by the number of windings. Specifically, increasing the number of windings can increase the opposing area. Reducing the number of windings can decrease the opposing area. Furthermore, in the case of an electrode group having a stacked structure, the opposing area can be adjusted by the number of stacks. Specifically, increasing the number of stacks can increase the opposing area. Reducing the number of stacks can decrease the opposing area. A method for measuring the opposing area between the positive electrode and the negative electrode will be described later. (Negative Electrode) The negative electrode may include a negative electrode current collector and a negative electrode composite layer (negative electrode active material-containing layer). The negative electrode mixture layer (negative electrode active material-containing layer) can be formed, for example, on one side or both sides of the current collector. The current collector has, for example, a strip or sheet shape. The negative electrode mixture layer (negative electrode active material-containing layer) can contain a negative electrode active material and, optionally, a conductive agent and a binder.

[0039] Examples of the negative electrode active material include metal oxides, carbonaceous materials, metal compounds, etc. The type of the negative electrode active material may be one or more.

[0040] 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 is preferably a material having a (002) plane spacing d ００２ is preferably 0.34 nm or less.

[0041] The metal compound may be a metal sulfide or a metal nitride. An example of the metal sulfide is TiS. ２ Titanium sulfides such as MoS ２ Molybdenum sulfides such as FeS, FeS ２ , Li ｘ FeS ２ As the metal nitride, for example, lithium cobalt nitride (e.g., Li ｓ Co ｔ N, 0<s<4, 0<t<0.5) can be used.

[0042] Examples of metal oxides include titanium-containing oxides. Examples of titanium-containing oxides include lithium titanium-containing oxides (lithium titanium composite oxides) and niobium titanium-containing oxides (niobium titanium composite oxides). The titanium-containing oxide preferably includes lithium titanium composite oxides. An electrode containing a titanium-containing oxide such as a lithium titanium composite oxide has a potential of 0.4 V (vs. Li / Li) relative to the oxidation-reduction potential of lithium. + ) or more, it is possible to prevent the deposition of metallic lithium on the electrode surface when a large current is repeatedly input and output. It is particularly preferable that the titanium-containing oxide contains a lithium-titanium composite oxide having a spinel-type crystal structure. Specific examples of such spinel-type lithium-titanium composite oxides include Li ４＋ａ Ti ５ O １２ The value of the subscript a varies within the range of 0≦a≦3 upon charge and discharge.

[0043] Examples of niobium titanium-containing oxides include niobium titanium-containing oxides having a monoclinic structure. Examples of niobium titanium-containing oxides having a monoclinic structure include Nb2TiO7, Nb2Ti2O9, and Nb 10 TiO 29 , Nb 14 TiO 37 , Nb 24 TiO 62 Includes:

[0044] The active material may be in the form of particles, fibers, or the like. The active material particles may be primary particles, secondary particles, or a mixture of primary and secondary particles. Examples of secondary particles include aggregates of primary particles.

[0045] The average particle size (average secondary particle size) of the secondary particles of the negative electrode active material is preferably 1 μm or more and 100 μm or less. When the average particle size of the secondary particles is within this range, the material is easy to handle in industrial production, and the mass and thickness of the coating film for producing the electrode can be made uniform. Furthermore, a decrease in the surface smoothness of the electrode can be prevented. The average particle size of the secondary particles is more preferably 2 μm or more and 30 μm or less.

[0046] The specific surface area of ​​the secondary particles measured by the BET method is 3 m ２ / g or more 50m ２ / g or less. ２ When the specific surface area is 50 m / g or more, it is possible to secure sufficient sites for occlusion and desorption of lithium ions. ２ More preferably, the secondary particles have a specific surface area of ​​5 m / g or less as measured by the BET method. ２ / g or more 50m ２ / g or less.

[0047] The active material may contain an active material other than the titanium-containing oxide. Here, for convenience, the active material containing the titanium-containing oxide is sometimes referred to as the "first active material," and the other active material is sometimes referred to as the "second active material." When the second active material is further contained in addition to the first active material, the second active material is used as the active material having a potential of 0.4 V (vs. Li / Li +When the second active material is contained, the mass ratio of the second active material to the first active material is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 30% by mass or less.

[0048] The conductive agent can improve current collection performance and reduce contact resistance between the active material and the current collector. Examples of the conductive agent include carbonaceous materials such as acetylene black, carbon black, graphite, carbon nanofibers, and carbon nanotubes. These carbonaceous materials may be used alone or in combination.

[0049] The binder can bind the active material, conductive agent, and current collector together. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing rubber, styrene-butadiene rubber, acrylic resin and its copolymer, polyacrylic acid, and polyacrylonitrile.

[0050] The compounding ratios of the active material, conductive agent, and binder are preferably in the ranges of 70% by mass or more and 97.5% by mass or less for the active material, 2% by mass or more and 20% by mass or less for the conductive agent, and 0.5% by mass or more and 10% by mass or less for the binder. By setting the amount of conductive agent to 2% by mass or more, the current collection performance of the composite layer (active material-containing layer) can be improved, and excellent high-current performance and low-temperature performance can be expected. Furthermore, by setting the amount of binder to 0.5% by mass or more, sufficient binding between the composite layer (active material-containing layer) and the current collector can be expected, and excellent high-temperature storage performance can be expected.

[0051] On the other hand, from the viewpoint of achieving high capacity, the conductive agent and binder are preferably 20% by mass or less and 10% by mass or less, respectively. A current collector suitable for the type of negative electrode active material can be used. The negative electrode current collector can contain, for example, at least one element selected from copper, nickel, and aluminum. The negative electrode current collector can be in the form of, for example, a foil or a porous body. When the negative electrode active material contains a titanium-containing oxide, the negative electrode current collector is preferably formed from aluminum foil or an aluminum alloy foil containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 20 μm or less, and more preferably 15 μm or less. (Separator) The separator can be disposed, for example, between the positive electrode and the negative electrode. The separator may include a portion that contacts or faces only one of the positive electrode and the negative electrode.

[0052] The separator is not particularly limited, and examples thereof include a microporous membrane, a woven fabric, a nonwoven fabric, or a laminate of the same or different materials among these. Examples of materials for forming the separator include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-butene copolymer, and cellulose. (Non-aqueous electrolyte) Examples of the electrolyte include non-aqueous electrolytes. Examples of the non-aqueous electrolyte include liquid non-aqueous electrolytes and gel non-aqueous electrolytes.

[0053] The liquid non-aqueous electrolyte can be prepared by dissolving an electrolyte in an organic solvent. The concentration of the electrolyte is preferably in the range of 0.5 to 3 mol / L. The gel non-aqueous electrolyte can be prepared by combining a liquid electrolyte with a polymer material.

[0054] Examples of electrolytes include lithium salts such as lithium perchlorate (LiClO), lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium hexafluoroarsenate (LiAsF), lithium trifluoromethanesulfonate (LiCFSO), and lithium bistrifluoromethylsulfonylimide [LiN(CFSO)]. One of these electrolytes may be used alone, or two or more electrolytes may be used in combination. The electrolyte preferably contains LiPF.

[0055] Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate; chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyltetrahydrofuran (2MeTHF), and dioxolane (DOX); chain ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); acetonitrile (AN), γ-butyrolactone (GBL), and sulfolane (SL). As the organic solvent, one of these solvents may be used alone, or two or more of them may be used in combination.

[0056] More preferred examples of organic solvents include mixed solvents of two or more selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC). By using such mixed solvents, a nonaqueous electrolyte battery with excellent charge-discharge cycle characteristics can be obtained. Additives can also be added to the nonaqueous electrolyte. (Exterior Component) The exterior component can be, for example, a bag-shaped container made of a laminated film or a metal container.

[0057] The shape is not particularly limited, but examples include flat, rectangular, cylindrical, coin, button, sheet, laminated, etc. Of course, the battery may be a small battery to be mounted in a portable electronic device or the like, or a large battery to be mounted in a two-wheeled or four-wheeled automobile or the like.

[0058] The laminate film may be, for example, a multilayer film in which a metal layer is sandwiched between resin films, or a multilayer film made of a metal layer and a resin layer covering the metal layer.

[0059] For the metal layer, aluminum foil or aluminum alloy foil is preferably used to reduce weight. Polymeric materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET) can be used for the resin film. 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 0.2 mm or less.

[0060] The metal container can be made of aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc, and silicon. On the other hand, the content of transition metals such as iron, copper, nickel, and chromium is preferably 100 ppm or less. This allows for dramatic improvements in long-term reliability and heat dissipation in high-temperature environments. The metal container preferably has a wall thickness of 0.5 mm or less, more preferably 0.2 mm or less. The metal container can also function as either a positive electrode terminal or a negative electrode terminal. (Positive Electrode Terminal) The positive electrode terminal is preferably made of a material that is electrically stable and conductive, for example, in a range of 3.0 V to 4.5 V relative to the redox potential of lithium. The positive electrode terminal is preferably made of aluminum or an aluminum alloy containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, and Si. The positive electrode terminal is preferably made of the same material as the positive electrode current collector to reduce contact resistance with the positive electrode current collector. The positive electrode terminal and the positive electrode current collector, e.g., a positive electrode lead, can also be connected via a positive electrode current collector tab. The positive electrode current collector tab is preferably formed from the same material as the positive electrode terminal and the negative electrode current collector. (Negative Electrode Terminal) The negative electrode terminal is preferably formed from a material that is electrically stable and conductive in a potential range of 0.8 V or more and 3.0 V or less relative to the redox potential of lithium. The negative electrode terminal is preferably formed from aluminum or an aluminum alloy containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, and Si. The negative electrode terminal is preferably formed from the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector. The negative electrode terminal and the negative electrode current collector, e.g., a negative electrode lead, can also be connected via a negative electrode current collector tab. The negative electrode current collector tab is preferably formed from the same material as the negative electrode terminal and the negative electrode current collector. <Measurement Method> Various measurement methods for batteries will be described. <Removal of electrodes> If the electrodes to be measured are incorporated into a battery, remove the electrodes as measurement samples from the battery as follows: Discharge the battery, disassemble it in a glove box under an argon atmosphere, and remove the electrodes.The electrode is washed with diethyl carbonate and then vacuum dried to obtain a measurement sample. <Confirmation of Lithium-Nickel-Cobalt-Manganese-Containing Oxide> The active material contained in the electrode is identified as follows, and the presence or absence of Lithium-Nickel-Cobalt-Manganese-Containing Oxide can be confirmed.

[0061] After washing and drying the electrodes removed from the battery as described above, attach the resulting electrodes to a glass sample plate. At this time, care should be taken to prevent the electrodes from peeling or floating, using double-sided tape or similar. If necessary, the electrodes can be cut to a size appropriate for attaching to the glass sample plate. In addition, a Si standard sample can be added to the electrodes to correct the peak position.

[0062] The glass plate with the electrodes attached is then placed in a powder X-ray diffraction (XRD) apparatus, and a diffraction pattern is obtained using Cu-Kα radiation. The X-ray diffraction pattern can be obtained by measuring with Cu-Kα radiation as the radiation source and varying 2θ within the measurement range of 5 to 90°.

[0063] The powder X-ray diffraction measurement device used is, for example, a SmartLab manufactured by Rigaku Co., Ltd. The measurement conditions are as follows: X-ray source: Cu target, Output: 45 kV, 200 mA, Soller slit: 5° for both incident and receiving, Step width: 0.02°, Scan rate: 20° / min, Semiconductor detector: D / teX Ultra 250, Sample plate holder: Flat glass sample plate holder (thickness: 0.5 mm), Measurement range: 5°≦2θ≦90°.

[0064] When using other equipment, measurements are carried out using standard Si powder for powder X-ray diffraction to obtain measurement results equivalent to those obtained by the above equipment, and conditions are found under which the peak intensities and peak top positions are equivalent to those obtained by the above equipment, and the sample is measured under those conditions.

[0065] When the active material to be measured contains a lithium-nickel-cobalt-manganese-containing oxide, it can be confirmed by X-ray diffraction measurement that an X-ray diffraction pattern belonging to the space group R3-m is obtained.

[0066] Next, the sample containing the active material is observed using a scanning electron microscope (SEM). It is desirable to prevent the sample from coming into contact with the air during SEM observation as well, and to perform the observation in an inert atmosphere such as argon or nitrogen.

[0067] In a 3000x SEM observation image, several particles having the form of primary particles or secondary particles that can be confirmed within the field of view are selected. The selected particles are selected so that the particle size distribution is as wide as possible. The observed active material particles are then subjected to energy dispersive X-ray spectroscopy (EDX) to identify the type and composition of the constituent elements of the active material. This allows the type and amount of elements other than Li contained in each selected particle to be identified. The same procedure is performed on each of the multiple active material particles to determine the mixed state of the active material particles.

[0068] Next, the composite layer (active material-containing layer) is separated from the current collector using, for example, a spatula, to obtain a powdered electrode composite sample containing the active material. The collected powdered sample is washed with acetone and dried. The obtained powder is dissolved in hydrochloric acid, the conductive agent is removed by filtration, and then the solution is diluted with ion-exchanged water to prepare a measurement sample. The metal content ratio in the measurement sample is calculated using inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0069] When multiple active materials are used, the mass ratio is estimated from the content ratio of elements specific to each active material. The mass ratio of the specific elements to the active material is determined from the composition of the constituent elements determined by energy dispersive X-ray spectroscopy.

[0070] Thus, the active material contained in the electrode can be identified. <Method for confirming occupancy> Rietveld analysis is performed using the X-ray diffraction pattern obtained from the above measurement to calculate the occupancy rate of the transition metal at the lithium site of the lithium-nickel-cobalt-manganese-containing oxide. Synchrotron radiation X-ray diffraction can be used for the Rietveld analysis. For example, RIETAN-FP can be used as the analysis program, and the extended pseudo-Voigt function can be used as the profile function. The initial values ​​used are ICSD (Inorganic Crystal Structure Database) No. 291340, space group: A-166, R-3m. <Measurement of the specific surface area of ​​the positive electrode by the BET method> A measurement sample electrode is obtained according to the method described in <Extracting the electrode>.

[0071] The specific surface area determined by the BET method is calculated by a nitrogen adsorption method. The analysis is carried out, for example, by the following method.

[0072] As described above, the electrode is removed from the battery, washed, and dried, and then cut to the size of a measurement cell to be used as a measurement sample. A 1 / 2-inch glass cell, for example, is used as the measurement cell. As a pretreatment method, the measurement cell is degassed by drying it under reduced pressure at a temperature of approximately 100°C or higher for 15 hours. A Quantasorb QS-20, manufactured by Quantachrome, for example, is used as the measurement device.

[0073] The cut electrodes used as the measurement sample are placed in a measurement cell and a mixed gas of 30% nitrogen and the balance helium is allowed to flow. While the gas is flowing, the glass cell is immersed in liquid nitrogen, allowing the nitrogen in the mixed gas to be adsorbed onto the sample surface. Once the adsorption is complete, the glass cell is returned to room temperature and the adsorbed nitrogen is desorbed. This increases the nitrogen concentration in the mixed gas, and the amount of increase is quantified. From this amount of nitrogen and the cross-sectional area of ​​the nitrogen molecule, the surface area of ​​the sample (m 2 ) and divide it by the sample weight (g) to obtain the specific surface area (m) of the positive electrode measured by the BET method. 2 / g) is calculated. <Measurement of discharge resistance> The battery resistance is evaluated as follows. The current value is changed appropriately depending on the battery capacity.

[0074] First, the battery is charged at a constant current of 1 C (e.g., 20 A) in a thermostatic chamber at 25°C until the battery voltage reaches 2.7 V. Then, the battery is charged at a constant voltage of 0.05 C (e.g., 1 A), followed by a 10-minute rest period. Next, the battery is discharged at a constant current of 0.2 C (e.g., 4 A) to 1.5 V, followed by a 10-minute rest period. This discharge capacity is used as the reference capacity.

[0075] Thereafter, the battery is similarly charged at a constant current and constant voltage to 2.7 V, followed by a 10-minute rest period. Next, 50% of the reference capacity is discharged at a constant current of 0.2 C (e.g., 4 A) to adjust the battery to an SOC of 50%, followed by a 1-hour rest period.

[0076] The battery is then discharged for 10 seconds at a constant current of 3 C (e.g., 60 A). The absolute value of the difference between the initial voltage and the voltage after 10 seconds is defined as ΔV1 (units: volts). The discharged capacity is then charged at a current value of 0.2 C (e.g., 4 A), adjusted to an SOC of 50% again, and then rested for one hour. The battery is then discharged for 10 seconds at a constant current of 6 C (e.g., 120 A). The absolute value of the difference between the initial voltage and the voltage after 10 seconds is defined as ΔV2. Similarly, ΔV3, ΔV4, and ΔV5 are calculated for current values ​​of 8 C (e.g., 160 A), 10 C (e.g., 200 A), and 12 C (e.g., 240 A). Five points of current are plotted on the horizontal axis and ΔV on the vertical axis. The resistance value R1 at 25°C can be calculated by calculating the slope.

[0077] Next, we will explain how to calculate the resistance value R2 at -20°C. Similarly, after adjusting the SOC to 50%, allow a one-hour rest period. After that, adjust the thermostatic chamber to -20°C and allow a three-hour rest period. All subsequent measurements will be performed at -20°C.

[0078] The battery is discharged for 10 seconds at a constant current of 1 C (e.g., 20 A). The absolute value of the difference between the initial voltage and the voltage after 10 seconds is ΔV6 (units: volts). Next, the discharged capacity is charged at a current value of 0.1 C (e.g., 2 A), adjusted again to an SOC of 50%, and then a one-hour rest period is allowed. The battery is then discharged for 10 seconds at a constant current of 2 C (e.g., 40 A). The absolute value of the difference between the initial voltage and the voltage after 10 seconds is ΔV7. Similarly, ΔV8, ΔV9, and ΔV10 are calculated for current values ​​of 3 C (e.g., 60 A), 4 C (e.g., 80 A), and 5 C (e.g., 100 A). Five points are then plotted, with the current value on the horizontal axis and ΔV on the vertical axis. The resistance value R2 at -20°C can be calculated by calculating the slope of the approximation curve. When calculating the slope of the approximation curve, if the correlation coefficient is less than 0.95, the measured current value can be appropriately adjusted so that it is 0.95 or greater. <Measurement of capacity per unit area of ​​positive electrode> First, a battery to be tested is prepared. The battery to be tested has a capacity of 80% or more of the rated capacity. The capacity retention rate of the battery is determined by the following method. First, the battery is charged to the upper operating voltage limit. The current value at this time is the current value corresponding to a 1C rate calculated from the rated capacity. After reaching the upper operating voltage limit, the voltage is maintained for 3 hours. After charging and maintaining the voltage, the battery is discharged to the lower operating voltage limit at a rate of 0.2C. The above charge / discharge cycle is performed for a total of 3 cycles, and the discharge capacity obtained during the third cycle discharge is recorded. The ratio of the obtained discharge capacity to the area of ​​the positive electrode is defined as the capacity per unit area of ​​the positive electrode. Note that the battery may be in any state of charge.

[0079] Next, to prevent the battery components from reacting with atmospheric components or moisture during disassembly, the battery is placed in an inert gas atmosphere, such as a glove box filled with argon gas. The battery is then opened in the glove box. For example, the heat-sealed portions around the positive and negative electrode current collector tabs can be cut to open the battery. The electrode assembly is removed from the opened battery. If the removed electrode assembly 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.

[0080] Next, the removed electrode group is disassembled into a positive electrode, a negative electrode, and a separator. Next, a portion of the positive electrode active material-containing layer that faced the negative electrode active material-containing layer is cut out to form a positive electrode piece. The positive electrode piece may include a positive electrode current collector supporting the cut-out portion of the positive electrode active material-containing layer. Similarly, a portion of the negative electrode active material-containing layer that faced the positive electrode active material-containing layer is cut out to form a negative electrode piece. The negative electrode piece may include a negative electrode current collector supporting the cut-out portion of the negative electrode active material-containing layer. The positive electrode piece and the negative electrode piece are then washed with a solvent. Examples of the solvent include chain carbonates (dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, etc.) and acetonitrile. After washing, the positive electrode piece and the negative electrode piece are transferred to a vacuum chamber filled with an inert gas atmosphere without exposure to the atmosphere, and the vacuum chamber is reduced in pressure. The positive electrode piece and the negative electrode piece are dried in the vacuum chamber. Drying can be performed, for example, at 50°C under vacuum for 10 hours. Next, the weights of the positive electrode piece and the negative electrode piece are measured. Then, a positive electrode sample including a positive electrode active material-containing layer, for example, 3 cm square, is cut from the positive electrode piece. Similarly, a negative electrode sample including a negative electrode active material-containing layer, for example, 3 cm square, is cut from the negative electrode piece.

[0081] Next, the weight of the cut positive electrode sample is measured. After the measurement, a two-electrode or three-electrode electrochemical measurement cell is fabricated using the positive electrode sample as the working electrode and lithium metal foil as the counter electrode and reference electrode. The fabricated electrochemical measurement cell is placed in a position where the potential of the working electrode is an upper limit potential of 4.25 V (vs. Li / Li + The current value at this time is 0.1 mA / cm 2 After charging and maintaining the voltage, the potential of the working electrode reaches the lower limit potential of 3.0 V (vs. Li / Li) at the same current value as during charging. + The above charge / discharge cycle is repeated three times in total, and the discharge capacity obtained in the third cycle is recorded. The obtained discharge capacity is multiplied by the area of ​​the positive electrode active material-containing layer incorporated in the electrochemical measurement cell, i.e., 9 cm2. 2 (= 3cm x 3cm) to get 1cm 2 Positive electrode capacity (single electrode capacity) per unit area [Ah / cm 2] is obtained. <Measurement of the opposing area between the positive electrode and the negative electrode> The opposing area between the positive electrode and the negative electrode is determined by comparing the total area of ​​the composite layer (active material-containing layer) of the positive electrode with the total area of ​​the composite layer (active material-containing layer) of the negative electrode, and using the smaller total area. If the two total areas are the same, either may be used. A method for calculating the area of ​​the composite layer (active material-containing layer) of an electrode will be described with reference to FIG. 1. The electrode 100 shown in FIG. 1 includes, for example, a strip-shaped current collector 101 and a composite layer (active material-containing layer) 102. In FIG. 1, the long side direction of the electrode 100 is indicated in the y-axis direction. The short side direction of the electrode 100 is indicated in the x-axis direction. The composite layer 102 is supported on a surface of the strip-shaped current collector 101 along the xy plane, except for one end in the short side direction (x-axis direction). The composite layer 102 may be supported on only one surface of the strip-shaped current collector 101, or on both surfaces. The portion of current collector 101 that does not carry composite material layer 102 can function as a current collecting tab or a lead. The area of ​​composite material layer 102 carried on one surface of current collector 101 is calculated from the product of length L1 of the long side along the y-axis direction and length L2 of the short side along the x-axis direction. When composite material layer 102 is carried on both surfaces of current collector 101, the total area to be calculated is the sum of the area of ​​composite material layer 102 carried on one surface of current collector 101 and the area of ​​composite material layer 102 carried on the other surface of current collector 101.

[0082] An example of a battery according to an embodiment will be described with reference to Figures 2 and 3. The flat-type battery shown in Figure 2 includes a flat wound electrode group 1, a housing member 2, a positive electrode terminal 7, a negative electrode terminal 6, and an electrolyte (not shown). The housing member 2 is a bag-shaped housing member made of a laminate film. The wound electrode group 1 is housed in the housing member 2. As shown in Figure 3, the wound electrode group 1 includes a positive electrode 3, a negative electrode 4, and a separator 5, and is formed by spirally winding a laminate obtained by stacking the negative electrode 4, separator 5, positive electrode 3, and separator 5 in this order from the outside in, and then press-molding the laminate.

[0083] The positive electrode 3 includes a positive electrode current collector 3a and a positive electrode active material-containing layer 3b. The positive electrode active material-containing layer 3b contains a positive electrode active material. The positive electrode active material-containing layer 3b is formed on both sides of the positive electrode current collector 3a. The negative electrode 4 includes a negative electrode current collector 4a and a negative electrode active material-containing layer 4b. The negative electrode active material-containing layer 4b contains a negative electrode active material. In the outermost portion of the negative electrode 4, the negative electrode active material-containing layer 4b is formed only on one side of the inner surface of the negative electrode current collector 4a. In the other portions of the negative electrode 4, the negative electrode active material-containing layer 4b is formed on both sides of the negative electrode current collector 4a.

[0084] 3 , a positive electrode terminal 7 is connected to the positive electrode 3 near the outer peripheral end of the wound electrode pack 1. Furthermore, a negative electrode terminal 6 is connected to the negative electrode 4 in the outermost layer portion. The positive electrode terminal 7 and the negative electrode terminal 6 extend to the outside through openings in the exterior member 2.

[0085] The battery is not limited to the configuration shown in FIGS. 2 and 3, but may have a configuration shown in FIG. 4, for example.

[0086] In the prismatic battery shown in Fig. 4, a wound electrode group 11 is housed in a metal rectangular cylindrical container 12 with a bottom, which serves as an exterior member. A rectangular lid 13 is welded to the opening of the container 12. The flat wound electrode group 11 may have a configuration similar to that of the wound electrode group 1 described with reference to Figs. 2 and 3, for example.

[0087] One end of the negative electrode tab 14 is electrically connected to the negative electrode current collector, and the other end is electrically connected to a negative electrode terminal 15. The negative electrode terminal 15 is fixed to the rectangular lid 13 by a hermetic seal with a glass material 16 interposed therebetween. One end of the positive electrode tab 17 is electrically connected to the positive electrode current collector, and the other end is electrically connected to a positive electrode terminal 18 fixed to the rectangular lid 13.

[0088] The negative electrode tab 14 is made of a material such as copper, nickel, aluminum, or an aluminum alloy containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, Si, etc. The negative electrode tab 14 is preferably made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

[0089] The positive electrode tab 17 is made of a material such as aluminum or an aluminum alloy containing elements such as Mg, Ti, Zn, Mn, Fe, Cu, Si, etc. The positive electrode tab 17 is preferably made of the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

[0090] Although the illustrated battery uses a wound electrode group in which a separator is wound together with a positive electrode and a negative electrode, the structure of the electrode group is not particularly limited. For example, a stacked electrode group in which a separator is folded zigzag and positive electrodes and negative electrodes are alternately arranged at the folded portions, or a stacked electrode group in which positive electrodes and negative electrodes are alternately arranged with a separator interposed therebetween may be used.

[0091] The battery according to the first embodiment includes a positive electrode containing a lithium-nickel-cobalt-manganese-containing oxide and satisfies the formulas (1) and (2). Therefore, it is possible to improve output performance at low temperatures and suppress an increase in resistance during storage.

[0092] 1.1≦M Ｃｏ / M Ｍｎ ≦1.8 (1) 0.2≦R1 / R2≦0.5 (2) However, in equations (1) and (2), M Ｃｏ is the ratio (mol%) of cobalt to the total amount of nickel, cobalt, and manganese in the lithium nickel cobalt manganese-containing oxide, and M Ｍｎ is the ratio (mol %) of manganese to the total amount of nickel, cobalt, and manganese in the lithium nickel cobalt manganese-containing oxide, R1 is the discharge resistance (Ω) of the battery at 25°C, and R2 is the discharge resistance (Ω) of the battery at -20°C.

[0093] Second Embodiment According to a second embodiment, a battery pack is provided, which includes a battery according to an embodiment.

[0094] The battery pack according to the embodiment may include one or more batteries (single cells) according to the embodiment described above. The batteries included in the battery pack may be electrically connected in series or parallel to each other to form a battery assembly. The battery pack may include a plurality of battery assemblies.

[0095] Next, an example of a battery pack according to an embodiment will be described with reference to the drawings.

[0096] Fig. 5 is an exploded perspective view of an example battery pack according to an embodiment, and Fig. 6 is a block diagram showing an electrical circuit of the battery pack of Fig. 5.

[0097] 5 and 6 includes a plurality of unit cells 21. The unit cells 21 may be flat batteries, an example of which is the embodiment described with reference to FIG.

[0098] The plurality of cells 21 are stacked so that the negative electrode terminals 51 and positive electrode terminals 61 extending outward are aligned in the same direction, and are fastened together with adhesive tape 22 to form a battery pack 23. These cells 21 are electrically connected in series with one another as shown in FIG.

[0099] The printed wiring board 24 is disposed opposite the side surface from which the negative electrode terminal 51 and the positive electrode terminal 61 of the cell 21 extend. As shown in Fig. 6, 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. An insulating plate (not shown) is attached to the surface of the printed wiring board 24 facing the assembled battery 23 to prevent unnecessary connection with the wiring of the assembled battery 23.

[0100] The positive electrode lead 28 is connected to a positive electrode terminal 61 located on the bottom layer of the battery pack 23, and its tip is inserted into and electrically connected to a positive electrode connector 29 on the printed wiring board 24. The negative electrode lead 30 is connected to a negative electrode terminal 51 located on the top layer of the battery pack 23, and its tip is inserted into and electrically connected to a negative electrode connector 31 on the printed wiring board 24. These connectors 29 and 31 are connected to the protection circuit 26 via wires 32 and 33 formed on the printed wiring board 24.

[0101] The thermistor 25 detects the temperature of the cell 21 and transmits the detection signal to the protection circuit 26. The protection circuit 26 can interrupt the positive wiring 34a and the negative wiring 34b between the protection circuit 26 and the power terminal 27 for connecting to the external device under predetermined conditions. An example of the predetermined condition is when the temperature detected by the thermistor 25 exceeds a predetermined temperature. Another example of the predetermined condition is when overcharge, overdischarge, overcurrent, or the like of a cell 21 is detected. This overcharge detection is performed for each cell 21 or the entire battery pack 23. When detecting an individual cell 21, the battery voltage may be detected, or the positive electrode potential or negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 21. In the battery pack 20 shown in FIGS. 5 and 6, each cell 21 is connected to wiring 35 for voltage detection. A detection signal is transmitted to the protection circuit 26 via these wirings 35.

[0102] Protective sheets 36 made of rubber or resin are disposed on the three sides of the battery pack 23 excluding the sides from which the positive electrode terminal 61 and the negative electrode terminal 51 protrude.

[0103] The battery pack 23 is housed in a storage container 37 together with the protective sheets 36 and the printed wiring board 24. That is, the protective sheets 36 are disposed on both inner surfaces along the long sides and the inner surface along the short sides of the storage container 37, and the printed wiring board 24 is disposed on the inner surface on the opposite side along the short sides. 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 storage container 37.

[0104] Heat-shrinkable tape may be used to secure the battery pack 23 instead of the adhesive tape 22. In this case, protective sheets are placed on both sides of the battery pack, and the heat-shrinkable tape is wrapped around the battery pack, and then the heat-shrinkable tape is thermally shrunk to bind the battery pack.

[0105] 5 and 6 show the cells 21 connected in series, they may be connected in parallel to increase the battery capacity. Furthermore, assembled battery packs may be connected in series and / or in parallel.

[0106] The configuration of the battery pack may be changed as appropriate depending on the application. The battery pack is preferably used in applications where good cycle performance is desired when a large current is drawn. Specific applications 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. The battery pack is particularly suitable for in-vehicle applications.

[0107] The battery pack according to the second embodiment includes the battery according to the first embodiment, and therefore the battery pack can improve output performance at low temperatures and suppress an increase in resistance during storage.

[0108] [Examples] Examples will be described below, but the present invention is not limited to the examples listed below as long as they do not depart from the gist of the present invention.

[0109] Example 1 In Example 1, a nonaqueous electrolyte battery of Example 1 was fabricated by the following procedure.

[0110] <Preparation of negative electrode> Li4Ti5O was used as the negative electrode active material. 12 A powder of lithium titanium composite oxide having the above composition and a spinel structure was prepared.

[0111] Graphite as a conductive agent was added to powder of spinel-type lithium-titanium composite oxide as the negative electrode active material, and the mixture was mixed in a Henschel mixer to obtain a mixture. Polyvinylidene fluoride (PVdF) as a binder and N-methylpyrrolidone (NMP) as a dispersion medium were added to this mixture and kneaded. Thus, a slurry (slurry for producing a negative electrode) was obtained.

[0112] In the above mixing, the amounts of graphite and PVdF added were adjusted so that the ratio of negative electrode active material:graphite:PVdF in the resulting slurry was 88 parts by mass:10 parts by mass:2 parts by mass.

[0113] This slurry was applied to both sides of a current collector made of aluminum foil with a thickness of 15 μm, and the coating film was dried. Next, the dried coating film was subjected to a roll press treatment. Further, vacuum drying was performed. Thus, the current collector and the electrode formed on both sides of this current collector and having an electrode density (excluding the current collector) of 2.1 g / cm were obtained. 3 The thickness of the negative electrode active material-containing layer formed on each surface of the current collector was 30 μm. <Preparation of Positive Electrode> First, a lithium nickel cobalt manganese composite oxide (LiNi) was used as the positive electrode active material. 0.52 Co 0.3 Mn 0.18 Powders of nickel, cobalt, and manganese were prepared. The mole percentages of nickel, cobalt, and manganese, respectively, when the total mole percentage of nickel, cobalt, and manganese was taken as 100 mole percent, are shown in Table 1. The mole percentages of M were calculated from the mole percentage of cobalt to the mole percentage of manganese. Ｃｏ / M Ｍｎ The values ​​are shown in Table 1.

[0114] 7 parts by mass of acetylene black as a conductive agent was added to 90 parts by mass of the positive electrode active material, and the mixture was mixed in a Henschel mixer to prepare a mixed positive electrode active material. Next, 3 parts by mass of PVdF and N-methylpyrrolidone (NMP) were added to this mixed positive electrode active material in a certain ratio, and the mixture was kneaded in a planetary mixer to prepare a slurry. This slurry was applied to both sides of a current collector made of aluminum foil with a thickness of 15 μm, and the coating was dried. The dried coating was then subjected to a roll press treatment. Thus, a current collector and an electrode formed on both sides of the current collector and having an electrode density (excluding the current collector) of 3.0 g / cm were obtained. 3 A positive electrode having a positive electrode active material-containing layer of the formula (I) was fabricated. <Fabrication of Electrode Assembly> A separator made of a 5 μm thick polyethylene porous film was prepared. Next, this separator and the previously fabricated positive electrode and negative electrode were spirally wound to fabricate a wound body. This was hot-pressed at 90° C. to fabricate a flat electrode assembly having a length of 96 mm, a width of 111 mm, and a thickness of 20 mm.

[0115] The obtained electrode group was placed in an outer can made of an aluminum alloy and vacuum dried at 100°C for 24 hours. <Preparation of liquid non-aqueous electrolyte> Propylene carbonate (PC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 1:2 to prepare a mixed solvent. LiPF6 (electrolyte) was dissolved in this mixed solvent at 1M (mol / L) to prepare a liquid non-aqueous electrolyte. <Manufacture of non-aqueous electrolyte secondary battery> The liquid non-aqueous electrolyte was poured into the outer can containing the electrode group. The pouring port was then sealed. Thus, a non-aqueous electrolyte secondary battery with a rated capacity of 20 Ah was manufactured.

[0116] Next, the fabricated nonaqueous electrolyte secondary battery was charged at a charge rate of 20 A (1 C) in an environment of 25° C. to adjust the SOC to 40%, and subjected to heat treatment for 24 hours at 70° C. Next, the battery was allowed to cool to room temperature, discharged at 1 A to 1.5 V in an environment of 25° C., and then charged at 20 A to adjust the SOC to 50%.

[0117] (Example 2) The capacity per unit area of ​​the positive electrode (Ah / m) was increased by reducing the weight of the positive electrode. 2 ) was changed to the value shown in Table 1. In addition, the number of windings of the electrodes in the electrode group was increased to increase the opposing area (m 2 ) was changed as shown in Table 1. As a result, the capacity per unit area of ​​the positive electrode (Ah / m 2 ) and opposing area (m 2 ) was changed as shown in Table 1. Except for this, non-aqueous electrolyte secondary batteries were produced in the same manner as in Example 1.

[0118] (Example 3) The capacity per unit area of ​​the positive electrode (Ah / m) was increased by increasing the weight of the positive electrode. 2 ) was changed to the value shown in Table 1. In addition, the number of windings of the electrodes in the electrode group was reduced to reduce the opposing area (m 2 ) was changed as shown in Table 1. As a result, the capacity per unit area of ​​the positive electrode (Ah / m 2 ) and opposing area (m 2 ) was changed as shown in Table 1. Except for this, non-aqueous electrolyte secondary batteries were produced in the same manner as in Example 1.

[0119] (Example 4) The composition of the lithium nickel cobalt manganese composite oxide was LiNi 0.45 Co 0.35 Mn 0.2 The mole percentages of nickel, cobalt, and manganese were changed to O2. Ｃｏ / M Ｍｎ The molar ratios represented by the formula are shown in Table 1. A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except for this.

[0120] (Comparative Examples 1 to 3) The composition of the lithium nickel cobalt manganese composite oxide was LiNi 0.50 Co 0.20 Mn 0.30 The mole percentages of nickel, cobalt, and manganese were changed to O2. Ｃｏ / M Ｍｎ The molar ratios expressed as follows are shown in Table 1. The capacity per unit area of ​​the positive electrode (Ah / m 2 ), the opposing area of ​​the positive electrode and the negative electrode (m 2 ) and the capacity per unit area of ​​the positive electrode (Ah / m 2 ) and opposing area (m 2 ) was set to the value shown in Table 1. Except for this, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

[0121] (Comparative Example 4) The composition of the lithium nickel cobalt manganese composite oxide was changed to LiNi 0.50 Co 0.30 Mn 0.20 The mole percentages of nickel, cobalt, and manganese were changed to O2. Ｃｏ / M Ｍｎ The molar ratios expressed as follows are shown in Table 1. The capacity per unit area of ​​the positive electrode (Ah / m 2 ), the opposing area of ​​the positive electrode and the negative electrode (m 2 ) and the capacity per unit area of ​​the positive electrode (Ah / m 2 ) and opposing area (m 2 ) was set to the value shown in Table 1. Except for this, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

[0122] (Comparative Example 5) Capacity per unit area of ​​positive electrode (Ah / m 2 ), the opposing area of ​​the positive electrode and the negative electrode (m 2) and the capacity per unit area of ​​the positive electrode (Ah / m 2 ) and opposing area (m 2 ) was set to the value shown in Table 1. Except for this, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

[0123] Comparative Example 6 The specific surface area of ​​the positive electrode measured by the BET method was set to the value shown in Table 1. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except for this.

[0124] (Comparative Example 7) The composition of the lithium nickel cobalt manganese composite oxide was changed to LiNi 0.48 Co 0.34 Mn 0.18 The mole percentages of nickel, cobalt, and manganese were changed to O2. Ｃｏ / M Ｍｎ The molar ratios represented by the formula are shown in Table 1. A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except for this.

[0125] For the batteries of the examples and comparative examples, the discharge resistance ratio R1 / R2, the discharge resistance R2 (Ω) at −20° C., and the specific surface area (m 2 / g), capacity per unit area of ​​the positive electrode (Ah / m 2 ), the opposing area of ​​the positive electrode and the negative electrode (m 2 ), the capacity per unit area of ​​the positive electrode (Ah / m 2 ) and opposing area (m 2) and the occupancy rate of the transition metal at the lithium site of the lithium-nickel-cobalt-manganese-containing oxide are shown in Tables 1 and 2. Note that each parameter was measured by the method described above. <Evaluation> Evaluation of the resistance increase rate was performed on the nonaqueous electrolyte batteries of the Examples and Comparative Examples. The results are shown in Table 2. <High-Temperature Storage Test> The batteries were charged to an SOC (state of charge) of 50%, and then stored in a thermostatic chamber set at 80°C for two weeks. The batteries were removed from the 80°C thermostatic chamber and left to stand in a room temperature environment until the temperature of the batteries reached room temperature. Thereafter, the resistance increase rate was measured by the following method. <Resistance Increase Rate> The resistance increase rate is the ratio (R3 / R2) of the discharge resistance value R3 measured after the high-temperature storage test to the discharge resistance R2 at -20°C. <Method for measuring discharge resistance value R3> First, the battery was charged at a constant current of 20 A (1 C) in a thermostatic chamber at 25°C until the battery voltage reached 2.7 V, and then charged at a constant voltage of 1 A (0.05 C) until the current value reached 1 A, followed by a 10-minute rest period. Next, the battery was discharged at a constant current of 4 A (0.5 C) to 1.5 V, followed by a 10-minute rest period. This charge-discharge cycle was repeated three times, and the discharge capacity at the third discharge was measured and used as the reference discharge capacity.

[0126] Next, the battery was charged at a constant current of 20 A (1 C) until the battery voltage reached 2.7 V, and then charged at a constant voltage until the current reached 1 A, after which it was discharged to 50% of the reference capacity.

[0127] The temperature of the thermostatic bath was then set to −20° C., and the battery was left to stand in the thermostatic bath for 3 hours. The battery was discharged for 10 seconds at a constant current of 20 A in the thermostatic bath at a low temperature (−20° C.), and the voltage change was measured.

[0128] Next, the temperature of the thermostatic chamber was set to 25°C, and the battery was discharged to 1.5 V at a constant current of 4 A (residual discharge), followed by a 10-minute rest period. The battery was charged at a constant current of 20 A (1 C) until the battery voltage reached 2.7 V, and then charged at a constant voltage until the current reached 1 A, followed by a 10-minute rest period. The battery was then discharged at a constant current of 4 A to 1.5 V, followed by a 10-minute rest period.

[0129] The SOC was adjusted again to 50% in the same manner as above, and the voltage change when discharged for 10 seconds at a constant current of 40 A was measured in a thermostatic chamber set at -20°C. A remaining discharge and one cycle were again performed. The discharge currents when discharging for 10 seconds at -20°C were set to 60 A, 75 A, and 90 A, and for a total of five points, including the 20 A and 40 A, the current value (A) was plotted on the horizontal axis and the voltage change (V) on the vertical axis. The slope of the approximate line was taken as the discharge resistance value R3 (Ω) after the high-temperature storage test.

[0130] The ratio of the discharge resistance R3 measured after storage to the discharge resistance R2 measured before storage was calculated as the resistance increase rate (%). The resistance increase rate (%) of Example 1 is set to 100, and the relative values ​​representing the resistance increase rates (%) of the other examples are shown in Table 2 as resistance increase rates.

[0131]

[0132]

[0133] As shown in Tables 1 and 2, the resistance increase rate of the batteries of Examples 1 to 4 is smaller than that of the batteries of Comparative Examples 1 to 7. From these results, it can be seen that the batteries of Examples 1 to 4 have a small increase in low-temperature resistance after storage at a high temperature of 80°C. In addition, the discharge resistance at a low temperature of -20°C does not increase significantly due to high-temperature storage, so it can be seen that the batteries of Examples 1 to 4 also have excellent low-temperature discharge performance. The batteries of Comparative Examples 1 to 7 have a low resistance increase rate of M Ｃｏ / M Ｍｎ This is because the molar ratio expressed by R1 / R2 is out of the range of formula (1), or the discharge resistance ratio expressed by R1 / R2 is out of the range of formula (2). 2 More than 12Ah / m 2 The batteries of Examples 1, 2 and 4 below had a smaller rate of increase in resistance after high-temperature storage than Example 3.

[0134] According to one or more of the embodiments and examples described above, a battery is provided that includes a positive electrode containing a lithium-nickel-cobalt-manganese-containing oxide and satisfies formulas (1) and (2). Such a battery can improve output performance at low temperatures and suppress an increase in resistance during storage.

[0135] 1.1≦M Ｃｏ / MＭｎ ≦1.8 (1) 0.2≦R1 / R2≦0.5 (2) However, in equations (1) and (2), M Ｃｏ is the ratio (mol%) of cobalt to the total amount of nickel, cobalt, and manganese in the lithium nickel cobalt manganese-containing oxide, and M Ｍｎ is the ratio (mol %) of manganese to the total amount of nickel, cobalt, and manganese in the lithium nickel cobalt manganese-containing oxide, R1 is the discharge resistance (Ω) of the battery at 25°C, and R2 is the discharge resistance (Ω) of the battery at -20°C.

[0136] The following describes embodiments of the invention. <1> A battery including a positive electrode including a positive electrode mixture layer containing a lithium-nickel-cobalt-manganese-containing oxide, a negative electrode, and an electrolyte, wherein the battery satisfies the following formulas (1) and (2):

[0137] 1.1≦M Ｃｏ / M Ｍｎ ≦1.8 (1) 0.2≦R1 / R2≦0.5 (2) However, in equations (1) and (2), M Ｃｏ is the ratio (mol%) of cobalt to the total amount of nickel, cobalt, and manganese in the oxide, and M Ｍｎ is the ratio (mol %) of manganese to the total amount, R1 is the discharge resistance (Ω) of the battery at 25°C, and R2 is the discharge resistance (Ω) of the battery at -20°C. <2> The capacity per unit area of ​​the positive electrode is 6 Ah / m 2 More than 16Ah / m 2 <3> The battery according to <1>, wherein the capacity per unit area of ​​the positive electrode is 8 Ah / m or less. 2 More than 12Ah / m 2 <4> The battery according to <1> or <2>, wherein the capacity per unit area of ​​the positive electrode (Ah / m 2 ) and the opposing area (m 2<5> The battery according to any one of <1> to <4>, wherein the product of R2 and R3 is 1 mΩ or more and 3.5 mΩ or less. <6> The battery according to any one of <1> to <4>, wherein the specific surface area of ​​the positive electrode measured by the BET method is 1.5 m 2 / g or more 2m 2 / g or less. <7> The battery according to any one of <1> to <6>, wherein the occupancy rate of the transition metal in the lithium sites of the lithium nickel cobalt manganese-containing oxide is 2% or less. <8> The battery according to any one of <1> to <7>, wherein the negative electrode contains a titanium-containing oxide. <9> A battery pack comprising the battery according to any one of <1> to <8>.

[0138] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied 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 intended to be included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims.

[0139] DESCRIPTION OF SYMBOLS 1...electrode group, 2...exterior member, 3...positive electrode, 3a...positive electrode current collector, 3b...positive electrode active material-containing layer, 4...negative electrode, 4a...negative electrode current collector, 4b...negative electrode active material-containing layer, 4c...negative electrode current collector tab, 5...separator, 6...negative electrode terminal, 7...positive electrode terminal, 11...electrode group, 12...container, 13...rectangular lid, 14...negative electrode tab, 16...glass material, 17...positive electrode tab, 18...positive electrode terminal, 20...battery pack, 21...single cell, 22...adhesive tape, 23...battery assembly, 24...print Wiring board, 25... thermistor, 26... protection circuit, 27... terminal for supplying current to external device, 28... positive electrode lead, 29... positive electrode connector, 30... negative electrode lead, 31... negative electrode connector, 32... wiring, 33... wiring, 34a... positive electrode wiring, 34b... negative electrode wiring, 35... wiring, 36... protective sheet, 37... storage container, 38... lid, 51... negative electrode terminal, 61... positive electrode terminal, 100... electrode, 101... current collector, 102... composite layer (active material containing layer).

Claims

1. A battery including a positive electrode including a positive electrode mixture layer containing a lithium-nickel-cobalt-manganese-containing oxide, a negative electrode, and an electrolyte, wherein the following formulas (1) and (2) are satisfied: 1.1≦M Ｃｏ / M Ｍｎ ≦1.8 (1) 0.2≦R1 / R2≦0.5 (2) However, in equations (1) and (2), M Ｃｏ is the ratio (mol%) of cobalt to the total amount of nickel, cobalt, and manganese in the oxide, and M Ｍｎ is the proportion (mol %) of manganese in the total amount, R1 is the discharge resistance (Ω) of the battery at 25°C, and R2 is the discharge resistance (Ω) of the battery at -20°C.

2. The capacity per unit area of ​​the positive electrode is 6 Ah / m 2 More than 16Ah / m 2 2. The battery of claim 1, wherein:

3. The capacity per unit area of ​​the positive electrode is 8 Ah / m 2 More than 12Ah / m 2 2. The battery of claim 1, wherein:

4. Capacity per unit area of ​​the positive electrode (Ah / m 2 ) and the opposing area (m 2 3. The battery according to claim 2, wherein the product of the capacity and the capacity of the battery is 17 Ah or more and 35 Ah or less.

5. The battery according to claim 1, wherein the value of R2 is 1 mΩ or more and 3.5 mΩ or less.

6. The specific surface area of ​​the positive electrode measured by the BET method is 1.5 m 2 / g or more 2m 2 10. The battery of claim 1, wherein the SiO2 content is 0.1 wt % or less.

7. The battery according to claim 1, wherein the occupancy rate of the transition metal in the lithium sites of the lithium nickel cobalt manganese-containing oxide is 2% or less.

8. The battery of claim 1, wherein the negative electrode comprises a titanium-containing oxide.

9. A battery pack comprising the battery according to any one of claims 1 to 8.

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