Battery

Abstract

A battery is provided with: an electrode body including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; the battery includes a positive electrode including a positive electrode mixed material layer and a positive electrode current collector, the positive electrode mixed material layer containing a positive electrode active material, and a negative electrode including a negative electrode mixed material layer containing a negative electrode active material, the positive electrode active material containing nickel as a transition metal, and a negative electrode current collector, the negative electrode current collector containing nickel as a transition metal. The ratio of nickel is 70 mol% or more of the total transition metal, the negative electrode active material contains graphite, the thickness of the negative electrode mixture layer is 150 [mu] m or more, and the confinement pressure of the battery is 300 kPa or less.

Description

Technical Field

[0001] The present invention relates to a battery. Background Art

[0002] A battery is known that includes an electrode body, which is a state in which a positive electrode current collector, a positive electrode mixed material layer containing a positive electrode active material, a separator, a negative electrode mixed material layer containing a negative electrode active material, and a negative electrode current collector are stacked in sequence. This battery is usually in a state in which pressure is applied in the thickness direction of the electrode body, the purpose of which is to suppress the volume change of the electrode body, maintain the electronic conductivity in the electrode body, etc.

[0003] From the viewpoint of increasing the capacity of the battery, a method of increasing the thickness of the negative electrode mixture layer in the electrode body (for example, to 150 μm or more) is being studied.

[0004] On the other hand, the volume change of the battery during charge and discharge of the negative electrode mixed material layer is large. Therefore, if the thickness of the negative electrode mixed material layer is increased, the space inside the electrode body to hold the electrolyte is easily compressed by the expansion of the negative electrode mixed material layer, so that the electrolyte is easily discharged to the outside. The increase in the amount of electrolyte discharged from the electrode body may become the cause of the reduction in battery performance.

[0005] As one of the means to suppress the increase in the amount of electrolyte discharged due to the increase in the thickness of the negative electrode mixed material layer, it is possible to consider reducing the constraint pressure of the battery. For example, Japanese Patent Application Publication No. 2018-125150 discloses a fully solid battery in which the pressure acting on the thickness direction of the single cell is set to about 100 kPa. Summary of the invention

[0006] The invention disclosed in Japanese Patent Application Laid-Open No. 2018-125150 relates to an all-solid-state battery that does not use an electrolyte, but the retention of the electrolyte and its effect on battery performance are not studied.

[0007] An object of the present invention is to provide a battery capable of achieving both an increase in the thickness of a negative electrode mixture layer and maintenance of good battery performance.

[0008] Means for solving the above-mentioned problems include the following embodiments.

[0009] <1> A battery comprising: an electrode body including a positive electrode, a negative electrode and a separator arranged between the positive electrode and the negative electrode; and an electrolyte, the positive electrode including a positive electrode mixed material layer and a positive electrode collector, the positive electrode mixed material layer containing a positive electrode active material, the negative electrode including a negative electrode mixed material layer and a negative electrode collector, the negative electrode mixed material layer containing a negative electrode active material, the positive electrode active material containing nickel as a transition metal, the ratio of nickel is 70 mol% or more of the total transition metal, the negative electrode active material contains graphite, the thickness of the negative electrode mixed material layer is 150 μm or more, and the restraint pressure of the battery is 300 kPa or less.

[0010] <2> The battery according to <1>, wherein the positive electrode mixture layer has a thickness of 80 μm or more.

[0011] <3> The battery according to <1> or <2>, wherein the negative electrode mixture layer has a porosity of 25% by volume or more.

[0012] <4> The battery according to any one of <1> to <3>, wherein the thickness of the negative electrode mixture layer is 400 μm or less.

[0013] <5> The battery according to any one of <1> to <4>, wherein the positive electrode active material has a layered structure.

[0014] According to one embodiment of the present invention, a battery is provided that is capable of achieving both an increase in the thickness of a negative electrode mixture layer and maintenance of good battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention are described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

[0016] Figure 1 This is a diagram schematically showing an example of the structure of a stacked body included in a battery. DETAILED DESCRIPTION

[0017] In the present invention, a numerical range expressed using "to" means a range including the numerical values ​​before and after "to" as the minimum value and the maximum value, respectively.

[0018] In the numerical ranges recorded in stages in the present invention, the upper limit or lower limit recorded in a certain numerical range can be replaced by the upper limit or lower limit of the numerical range recorded in other stages. In the numerical ranges recorded in the present invention, the upper limit or lower limit recorded in a certain numerical range can be replaced by the value shown in the embodiments.

[0019] In the present invention, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process can be achieved.

[0020] In the present invention, a more preferred embodiment is a combination of two or more preferred embodiments.

[0021] In the present invention, when there are plural substances corresponding to each component, the amount of each component means the total amount of the plural substances unless otherwise specified.

[0022] A battery of the present invention comprises: an electrode body, which includes a positive electrode, a negative electrode and a separator arranged between the positive electrode and the negative electrode; and an electrolyte, the positive electrode includes a positive electrode mixed material layer and a positive electrode collector, the positive electrode mixed material layer contains a positive electrode active material, the negative electrode includes a negative electrode mixed material layer and a negative electrode collector, the negative electrode mixed material layer contains a negative electrode active material, the positive electrode active material contains nickel as a transition metal, the ratio of nickel is more than 70 mol% of the total transition metal, the negative electrode active material contains graphite, the thickness of the negative electrode mixed material layer is more than 150 μm, and the constraint pressure of the battery is less than 300 kPa.

[0023] In the battery of the present invention, when the thickness of the negative electrode mixed material layer is 150 μm or more, good battery performance is also exhibited. The reason for this is speculated as follows, for example. However, the present invention is not limited to the following speculation.

[0024] In the battery of the present invention, the confinement pressure is set to a relatively low level of 300 kPa or less, so that compared with a battery with a confinement pressure exceeding 300 kPa, the discharge of electrolyte from the expanded negative electrode mixture layer during charging can be suppressed.

[0025] Moreover, as the positive electrode active material contained in the positive electrode mixed material layer, a positive electrode active material with a high nickel content is used. The positive electrode mixed material layer containing a positive electrode active material with a high nickel content shrinks more during battery charging (i.e., when the negative electrode mixed material layer expands) than the positive electrode mixed material layer containing a positive electrode active material with a low nickel content. Therefore, the compression of the negative electrode mixed material layer generated during battery charging is alleviated by reducing the volume of the positive electrode mixed material layer, thereby inhibiting the discharge of the electrolyte from the electrode body.

[0026] The battery of the present invention includes an electrode body including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode.

[0027] In the present invention, the electrode body refers to a structure including a laminated body, and the laminated body is composed of a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. An example of the structure of the laminated body included in the electrode body is schematically shown in Figure 1 middle.

[0028] Figure 1 The laminate 100 shown is composed of a positive electrode 10, a negative electrode 20, and a separator 30 disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10 is composed of a positive electrode mixture layer 10A and a positive electrode collector 10B. The negative electrode 20 is composed of a negative electrode mixture layer 20A and a negative electrode collector 20B.

[0029] Examples of the electrode body including a laminate composed of a positive electrode, a negative electrode, and a separator disposed therebetween include a state in which a plurality of laminates cut into a predetermined size are stacked, and a state in which a long laminate is wound.

[0030] In the present invention, the restraining pressure of the battery refers to the pressure constantly applied in the thickness direction of the electrode body included in the battery.

[0031] The means for applying the restraining pressure to the battery is not particularly limited, and generally used means can be used.

[0032] The restraint pressure of the battery may be 300 kPa or less, and from the viewpoint of suppressing discharge of the electrolyte from the electrode body, may be 250 kPa or less, 200 kPa or less, 150 kPa or less, or 100 kPa or less.

[0033] From the viewpoint of ensuring good electron conductivity, the confinement pressure of the battery may be 10 kPa or more, 20 kPa or more, or 30 kPa or more.

[0034] The restraint pressure of the battery can be measured, for example, by measuring the reaction force when the restraint pressure is released in a state where the battery to be measured is clamped by a universal tensile tester (Autograph).

[0035] Positive electrode mixed material layer

[0036] The positive electrode active material contained in the positive electrode mixed material layer contains nickel as a transition metal, and the ratio of nickel is not particularly limited as long as it is 70 mol % or more of the entire transition metal.

[0037] The ratio of nickel may be 75 mol % or more or 80 mol % or more of the total transition metal, and the ratio of nickel may be 90 mol % or less or 85 mol % or less of the total transition metal.

[0038] The positive electrode active material more preferably contains nickel and at least one selected from cobalt and manganese as transition metals, and further preferably contains nickel, cobalt and manganese (NCM, nickel cobalt manganese oxide).

[0039] The positive electrode active material may be composed only of lithium, oxygen, Ni, and a transition metal selected from Co and Mn, or may contain elements other than these (hereinafter also referred to as other elements).

[0040] When the positive electrode active material contains other elements, the ratio thereof may be 10 mol % or less, 5 mol % or less, or 1 mol % or less of the entire positive electrode active material.

[0041] When the positive electrode active material contains other elements, the ratio thereof may be 0.001 mol % or more, 0.01 mol % or more, or 0.1 mol % or more of the entire positive electrode active material.

[0042] The positive electrode active material is preferably a composite oxide containing lithium and one or more transition metals (lithium-transition metal composite oxide).

[0043] The positive electrode active material preferably has a layered structure. The layered structure may be, for example, a crystal structure in which transition metal layers having an octahedral structure composed of transition metal atoms and oxygen atoms and lithium layers are alternately arranged.

[0044] The positive electrode active material may be a compound having a composition represented by the following formula (1).

[0045] Li 1-a Ni x Me 1-x O2(1)

[0046] In formula (1), a satisfies the relationship -0.3≤a≤0.3,

[0047] x satisfies the relationship 0.7≤x≤1.0,

[0048] Me represents at least one selected from the group consisting of Co, Mn, Al, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Ti, Si, V, Cr and Ge.

[0049] The positive electrode active material may be in a particle form. The average particle size of the positive electrode active material in a particle form may be selected from a range of 5 μm to 30 μm, for example.

[0050] In the present invention, the average particle size of particles is defined as the particle size (D50) when the cumulative volume is 50% in the volume-based particle size distribution. The volume-based particle size distribution is obtained, for example, by a laser diffraction scattering method.

[0051] The positive electrode mixed material layer may be in a state of a mixture containing a positive electrode active material and components other than the positive electrode active material, such as a conductive auxiliary agent and a binder.

[0052] Specific examples of the conductive auxiliary agent include carbon materials such as carbon black (acetylene black, thermal black, furnace black, etc.), carbon nanotubes, and graphite.

[0053] The conductive material contained in the positive electrode material may be a single type or two or more types.

[0054] Specific examples of the binder include polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polyethylene terephthalate, cellulose, nitrocellulose, carboxymethyl cellulose, polyethylene oxide, polyepichlorohydrin, polyacrylonitrile, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), polyacrylate, and polymethacrylate.

[0055] The binder contained in the positive electrode material may be a single type or two or more types.

[0056] The positive electrode mixed material layer can be arranged on the positive electrode current collector. As the material constituting the positive electrode current collector, aluminum, aluminum alloy, nickel, titanium, stainless steel, etc. can be cited. As the shape of the positive electrode current collector, foil, mesh, etc. can be cited.

[0057] From the viewpoint of improving the retention capacity of the electrolyte, the porosity of the positive electrode mixture layer is preferably 15 volume % or more, more preferably 20 volume % or more, and even more preferably 25 volume % or more.

[0058] From the viewpoint of ensuring sufficient energy density, the porosity of the positive electrode mixture layer is preferably 40 volume % or less, more preferably 35 volume % or less, and even more preferably 30 volume % or less.

[0059] The positive electrode mixture layer is disposed on the positive electrode current collector by, for example, applying a slurry of the positive electrode mixture to one or both surfaces of the positive electrode current collector. If necessary, a pressurization treatment may be performed to adjust the density of the positive electrode mixture layer.

[0060] The thickness of the positive electrode mixture layer is not particularly limited, and can be set, for example, in consideration of the capacity ratio with the negative electrode mixture layer that faces the separator.

[0061] The thickness of the positive electrode mixture layer may be 80 μm or more, 90 μm or more, or 100 μm or more.

[0062] The thickness of the positive electrode mixture layer may be 300 μm or less, 250 μm or less, 200 μm or less, or 150 μm or less.

[0063] Negative electrode mixed material layer

[0064] The negative electrode active material contained in the negative electrode mixture layer contains graphite.

[0065] The negative electrode mixed material layer may contain only graphite as the negative electrode active material, or may contain negative electrode active materials other than graphite. Examples of negative electrode active materials other than graphite include carbon materials such as hard carbon, soft carbon, activated carbon, silicon, metallic lithium, lithium alloys, lithium titanate (LTO), and the like.

[0066] When the negative electrode mixed material layer contains a negative electrode active material other than graphite, the proportion of graphite is preferably 70 mass % or more, more preferably 80 mass % or more, and even more preferably 90 mass % or more of the entire negative electrode active material.

[0067] The negative electrode active material may be in a particle form. The average particle size of the negative electrode active material in a particle form may be selected from a range of 5 μm to 30 μm, for example.

[0068] The negative electrode mixed material layer may be in a state of a mixture containing a negative electrode active material and components other than the negative electrode active material, such as a conductive aid and a binder.

[0069] The conductive material and the binder can be selected from the materials that can be contained in the positive electrode mixed material layer mentioned above.

[0070] The negative electrode mixed material layer may be disposed above the negative electrode current collector. Materials constituting the negative electrode current collector include copper, copper alloys, nickel, titanium, stainless steel, etc. The shape of the negative electrode current collector includes foil, mesh, etc.

[0071] From the viewpoint of improving the retention capacity of the electrolyte, the porosity of the negative electrode mixture layer is preferably 25 volume % or more, more preferably 30 volume % or more, and even more preferably 35 volume % or more.

[0072] From the viewpoint of ensuring sufficient energy density, the porosity of the negative electrode mixture layer is preferably 55 volume % or less, more preferably 50 volume % or less, and even more preferably 45 volume % or less.

[0073] The negative electrode mixture layer is disposed on the negative electrode current collector by, for example, applying the negative electrode mixture in a slurry state to one or both surfaces of the negative electrode current collector. If necessary, a pressurization treatment may be performed to adjust the density of the negative electrode mixture layer.

[0074] The thickness of the negative electrode mixture material layer may be 150 μm or more, and may be 160 μm or more, 170 μm or more, or 180 μm or more.

[0075] The thickness of the negative electrode mixture material layer may be 400 μm or less, 300 μm or less, 250 μm or less, or 200 μm or less.

[0076] Partition

[0077] The type of separator disposed between the positive electrode and the negative electrode is not particularly limited, and a known separator can be used. Specific examples of the separator include nonwoven fabrics, fabrics, and microporous films containing polyolefins such as polyethylene and polypropylene as a main component.

[0078] The thickness of the separator is not particularly limited, and can be selected from the range of 5 μm to 50 μm, for example.

[0079] Electrolyte

[0080] The battery of the present invention comprises an electrode body and an electrolyte solution. That is, the battery of the present invention is a liquid battery using a liquid electrolyte.

[0081] As the electrolyte solution, an electrolyte solution obtained by dissolving a known electrolyte such as LiPF 6 in an organic solvent can be used without particular limitation.

[0082] As the organic solvent, specifically, cyclic or chain carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) can be mentioned. The solvent can be a mixture of two or more solvents, or a mixture comprising cyclic carbonates and chain carbonates.

[0083] The solvent may contain additives such as vinylene carbonate (VC).

[0084] Battery form

[0085] The form of the battery of the present invention is not particularly limited, and may be a known form.

[0086] The battery of the present invention may be in a state where the electrode body and the electrolyte are contained in an outer casing such as a metal can or a metal film. The shape of the battery is not particularly limited, and may be a rectangular parallelepiped, a cylinder, or the like.

[0087] The size of the battery is not particularly limited and can be selected according to the purpose of the battery and the like.

[0088] The battery of the present invention can effectively suppress the discharge of the electrolyte from the electrode body, so even if the area of ​​the main surface of the electrode body is large (for example, from 15000 cm 2 Up to 20000cm 2 ) and the battery performance can be well maintained even in a state where uneven electrolyte penetration is likely to occur.

[0089] Hereinafter, the present invention will be described in further detail based on Examples, but the present invention is not limited to these Examples.

[0090] Example 1

[0091] (1) Preparation of positive electrode

[0092] A layered lithium transition metal composite oxide (97.8 parts by mass) containing nickel (80 mol%), cobalt (10 mol%) and manganese (10 mol%) as transition metals, carbon nanotubes (0.8 parts by mass) and polyvinylidene fluoride (1.4 parts by mass) were mixed. The viscosity of the mixture was adjusted with a solvent to obtain a slurry of positive electrode mixed materials. The positive electrode mixed material was applied to an aluminum foil (thickness: 30 μm) with a scraper so that the single-side unit area weight was 34 mg / cm 2 The positive electrode material layer was formed by drying at 100°C for 10 minutes. Then, a pressing process was performed to make the density of the positive electrode material layer 3.3 g / cm 3 Table 1 shows the thickness and porosity of the positive electrode mixture layer.

[0093] (2) Preparation of negative electrode

[0094] Artificial graphite particles (96 parts by mass) with an average particle size of 22 μm, styrene-butadiene rubber (3 parts by mass) and carboxymethyl cellulose (1 part by mass) were mixed, and the viscosity was adjusted with a solvent to obtain a slurry of negative electrode mixed material. The negative electrode mixed material was applied to a copper foil (thickness: 15 μm) with a scraper to a single-side unit area weight of 23 mg / cm 2 The negative electrode mixture layer was formed by drying at 100°C for 10 minutes (i.e., the ratio of the positive electrode capacity to the negative electrode capacity was 1.1). Then, the negative electrode mixture layer was pressed to a density of 1.25 g / cm 3 Table 1 shows the thickness and porosity of the negative electrode mixture layer.

[0095] (3) Battery production

[0096] A separator (PP / PE / PP three-layer structure, thickness: 16μm) was sandwiched between the positive and negative electrodes produced in the above process, and the electrodes were stacked to produce an electrode body. A stacked battery was produced using the electrode body and the electrolyte. As the electrolyte, an electrolyte in which 1.1M LiPF6 was dissolved in a mixed solvent of EC (30% by volume), DMC (40% by volume) and EMC (30% by volume) was used. The restraint pressure of the battery was adjusted to 20kPa.

[0097] (4) Evaluation of battery performance

[0098] The battery activation treatment was carried out by the constant current-constant voltage method in the following steps.

[0099] Specifically, constant current charging was performed at a current value of 0.1 C to 4.25 V, then constant voltage charging was performed until the constant voltage charging time became 3 hours, and then constant current discharge was performed at a current value of 0.1 C to 3.0 V.

[0100] The activated battery was charged to 4.25V at a current value of 0.1C by constant current-constant voltage method, and then discharged to 3.0V by constant current method at a current value of 1C, and the discharge rate (1C discharge rate) relative to the theoretical rated capacity was calculated. The results are shown in Table 1.

[0101] (5) Measurement of resistance

[0102] The resistance of the electrode sheet was measured by the following method using an electrode resistance measuring instrument (KNH-0622, manufactured by Hioki Electric Co., Ltd.).

[0103] Apply current between two specific probes in contact with the surface of the electrode sheet to measure the potential distribution on the surface. Make a model of an electrode sheet consisting of a mixed material layer, a collector and the interface resistance therebetween. Assume that the volume resistivity of the mixed material layer and the collector and their interface resistance are uniform. The volume resistivity and interface resistance of the mixed material layer at this time are set as unknowns, and the thickness of the mixed material layer, the thickness of the collector and the volume resistivity of the collector are set as known values.

[0104] For the modeled electrode sheet, the equation in which the potential is set as an unknown function is solved by the finite volume method to obtain the potential corresponding to the actually measured potential, and output the volume resistivity and interface resistance of the mixed material layer.

[0105] Examples 2 to 10, Comparative Examples 1 to 3, Reference Examples 1 to 8

[0106] A battery having the positive electrode mixture layer characteristics, the negative electrode mixture layer characteristics and the battery restraint pressure values ​​shown in Table 1 was prepared in the same manner as in Example 1, and the 1C discharge rate was measured. The results are shown in Table 1.

[0107] [Table 1]

[0108]

[0109]

[0110] As shown in Table 1, in the batteries of Examples 1 to 5, the Ni ratio of the positive electrode active material is 70 mol% or more, and the thickness of the negative electrode mixed material layer is 150 μm or more. The 1C discharge rate of the batteries of Examples 1 to 5 is higher than that of the battery of Comparative Example 1, showing excellent battery performance. The conditions of the battery of Comparative Example 1 are the same as those of Examples 1 to 5 except that the restraining pressure exceeds 300 kPa.

[0111] Similarly, in the batteries of Examples 6 to 9, the Ni ratio of the positive electrode active material is 70 mol% or more, the thickness of the negative electrode mixed material layer is 150 μm or more, and the constraint pressure of the battery is 300 kPa or less. The 1C discharge rate of the batteries of Examples 6 to 9 is higher than that of the battery of Comparative Example 2, showing excellent battery performance. The conditions of the battery of Comparative Example 2 are the same as those of Examples 6 to 9 except that the constraint pressure exceeds 300 kPa.

[0112] In the battery of Example 10 in which the Ni ratio of the positive electrode active material is 70 mol%, the 1C discharge efficiency is high, showing excellent battery performance, compared with the battery of Comparative Example 3 which has the same conditions as Example 10 except that the Ni ratio of the positive electrode active material is 60 mol%.

[0113] As shown in the results of Reference Examples 1 to 4, for batteries having a negative electrode mixture layer thickness of less than 150 μm, the difference between the 1C discharge rate when the confinement pressure of the battery is 300 kPa or less and the 1C discharge rate when the confinement pressure exceeds 300 kPa is small.

[0114] As shown in the results of Reference Examples 5 to 8, for batteries in which the Ni ratio of the positive electrode active material contained in the positive electrode mixed material layer is less than 70 mol%, the difference between the 1C discharge rate when the constraint pressure of the battery is below 300 kPa and the 1C discharge rate when the constraint pressure exceeds 300 kPa is small.

[0115] The above results show that by setting the Ni ratio of the positive electrode active material contained in the positive electrode mixture layer to 70 mol % or more and the confinement pressure to 300 kPa or less, the effect of improving battery performance is significantly manifested when the thickness of the negative electrode mixture layer is 150 μm or more.

Claims

1. A battery, characterized in that: have: An electrode body, comprising a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode; and Electrolyte, The positive electrode comprises a positive electrode mixed material layer and a positive electrode current collector, wherein the positive electrode mixed material layer contains a positive electrode active material. The negative electrode comprises a negative electrode mixed material layer and a negative electrode current collector, wherein the negative electrode mixed material layer contains a negative electrode active material. The positive electrode active material contains nickel as a transition metal, and the ratio of nickel is 70 mol % or more of the entire transition metal. The negative electrode active material comprises graphite, The thickness of the negative electrode mixed material layer is greater than 150 μm. The restraint pressure of the battery is 300 kPa or less.

2. The battery according to claim 1, characterized in that The thickness of the positive electrode mixed material layer is greater than 80 μm.

3. The battery according to claim 1, characterized in that The porosity of the negative electrode mixed material layer is greater than 25 volume %.

4. The battery according to claim 1, characterized in that The thickness of the negative electrode mixed material layer is less than 400 μm.

5. The battery according to claim 1, characterized in that The positive electrode active material has a layered structure.

Images