Battery

Abstract

To provide a battery capable of achieving both the increased thickness of a negative electrode mixture layer and the maintenance of good battery performance.SOLUTION: A battery includes: an electrode body including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and an electrolyte. The positive electrode includes: a positive electrode mixture layer containing a positive electrode active material; and a positive electrode current collector. The negative electrode includes: a negative electrode mixture layer containing a negative electrode active material; and a negative electrode current collector. The positive electrode active material contains nickel as a transition metal, and the ratio of nickel is 70 mol% or more of whole transition metals. The negative electrode active material contains graphite. The negative electrode mixture layer has a thickness of 150 μm or more. The binding pressure of the battery is 300 kPa or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to batteries. [Background technology]

[0002] There is known a battery including an electrode assembly in which a positive electrode current collector, a positive electrode composite layer including a positive electrode active material, a separator, a negative electrode composite layer including a negative electrode active material, and a negative electrode current collector are laminated in this order. In such a battery, pressure is generally applied in the thickness direction of the electrode assembly for the purpose of suppressing volumetric fluctuation of the electrode assembly, maintaining electronic conductivity within the electrode assembly, and the like.

[0003] From the viewpoint of increasing the capacity of a battery, increasing the thickness of the negative electrode mixture layer in the electrode body (for example, to 150 μm or more) is being considered. On the other hand, the negative electrode mixture layer has a large volume change during charging and discharging of the battery. Therefore, if the thickness of the negative electrode mixture layer is increased, the space in which the electrolyte is held inside the electrode body is easily compressed by the expansion of the negative electrode mixture layer, and the electrolyte is easily discharged to the outside. An increase in the amount of electrolyte discharged from the electrode body may cause a decrease in battery performance. One of the means for suppressing the increase in the amount of electrolyte discharged due to the increase in the thickness of the negative electrode mixture layer is to reduce the restraining pressure of the battery. For example, Patent Document 1 describes an all-solid-state battery in which the pressure applied in the thickness direction of the unit cell is about 100 kPa. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-125150 A Summary of the Invention [Problem to be solved by the invention]

[0005] The invention described in Patent Document 1 relates to an all-solid-state battery that does not use an electrolyte, and the retention of the electrolyte or its effect on battery performance has not been considered. An object of the present disclosure is to provide a battery that can achieve both an increase in the thickness of the negative electrode mixture layer and the maintenance of good battery performance. [Means for solving the problem]

[0006] Means for solving the above problems include the following embodiments. <1> An electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and an electrolyte; The positive electrode includes a positive electrode mixture layer including a positive electrode active material and a positive electrode current collector, The negative electrode includes a negative electrode mixture layer including a negative electrode active material and a negative electrode current collector, The positive electrode active material contains nickel as a transition metal, and the ratio of nickel is 70 mol % or more of the total transition metals, The negative electrode active material includes graphite, The thickness of the negative electrode mixture layer is 150 μm or more, A battery having a confinement pressure of 300 kPa or less. <2> The thickness of the positive electrode mixture layer is 80 μm or more. <1> 2. The battery according to claim 1 . <3> The porosity of the negative electrode mixture layer is 25% by volume or more. <1> or <2> 2. The battery according to claim 1 . <4> The thickness of the negative electrode mixture layer is 400 μm or less. <1> ~ <3> 13. The battery according to any one of claims 1 to 12. <5> The positive electrode active material has a layered structure. <1> ~ <4> 13. The battery according to any one of claims 1 to 12. Effect of the Invention

[0007] According to one embodiment of the present disclosure, a battery is provided that can achieve both an increase in the thickness of the negative electrode mixture layer and the maintenance of good battery performance. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a diagram illustrating an example of a configuration of a laminate included in a battery. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] In the present disclosure, a numerical range indicated using "~" means a range that includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in the present disclosure. In the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples. In the present disclosure, the term "process" refers not only to an independent process, but also to a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. In the present disclosure, combinations of two or more preferred embodiments are more preferred embodiments. In the present disclosure, when there are multiple substances corresponding to each component, the amount of each component means the total amount of the multiple substances, unless otherwise specified.

[0010] The battery of the present disclosure comprises: An electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and an electrolyte; The positive electrode includes a positive electrode mixture layer including a positive electrode active material and a positive electrode current collector, The negative electrode includes a negative electrode mixture layer including a negative electrode active material and a negative electrode current collector, The positive electrode active material contains nickel as a transition metal, and the ratio of nickel is 70 mol % or more of the total transition metals, The negative electrode active material includes graphite, The thickness of the negative electrode mixture layer is 150 μm or more, The confining pressure is 300 kPa or less.

[0011] The battery of the present disclosure exhibits good battery performance even when the thickness of the negative electrode mixture layer is 150 μm or more. The reason for this is presumed to be as follows, for example. However, the present disclosure is not limited to the following presumption.

[0012] In the battery of the present disclosure, the confining pressure is set to a relatively low level of 300 kPa or less, which suppresses the discharge of electrolyte from the negative electrode mixture layer that expands during charging, compared to a battery with a confining pressure of more than 300 kPa. Furthermore, a positive electrode active material with a relatively high nickel content is used as the positive electrode active material contained in the positive electrode mixture layer. A positive electrode mixture layer containing a positive electrode active material with a high nickel content shrinks to a greater extent during charging of the battery (i.e., during expansion of the negative electrode mixture layer) than a positive electrode mixture layer containing a positive electrode active material with a low nickel content. Therefore, the pressure on the negative electrode mixture layer that occurs during charging of the battery is alleviated by the volume reduction of the positive electrode mixture layer, and the discharge of the electrolyte from the electrode body is suppressed.

[0013] The battery of the present disclosure includes an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. In the present disclosure, the electrode assembly refers to a structure including a laminate including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. An example of the configuration of the laminate included in the electrode assembly is shown in FIG. 1 comprises 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 comprises a positive electrode mixture layer 10A and a positive electrode current collector 10B. The negative electrode 20 comprises a negative electrode mixture layer 20A and a negative electrode current collector 20B.

[0014] Examples of the form of an electrode body including a laminate consisting of a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode include a state in which a plurality of laminates cut to a predetermined size are stacked, and a state in which a long laminate is wound.

[0015] In the present disclosure, the restraining pressure of a battery means a pressure that is constantly applied in the thickness direction of an electrode assembly included in the battery. There are no particular limitations on the means for applying restraining pressure to the battery, and any commonly used member may be used. The restraining pressure of the battery may be 300 kPa or less, and from the viewpoint of suppressing discharge of the electrolyte from the electrode assembly, it may be 250 kPa or less, 200 kPa or less, 150 kPa or less, or 100 kPa or less. From the viewpoint of ensuring good electronic conductivity, the restraining pressure of the battery may be 10 kPa or more, or 20 kPa or more, or 30 kPa or more.

[0016] The restraining pressure of the battery can be measured, for example, by clamping the battery to be measured with an autograph and measuring the reaction force when the restraining pressure is released.

[0017] (Positive electrode mixture layer) The positive electrode active material contained in the positive electrode mixture layer is not particularly limited as long as it contains nickel as a transition metal and the ratio of nickel to the total transition metals is 70 mol % or more. The proportion of nickel may be 75 mol % or more, or 80 mol % or more, of the total transition metals.The proportion of nickel may be 90 mol % or less, or 85 mol % or less, of the total transition metals.

[0018] The positive electrode active material more preferably contains nickel and at least one selected from cobalt and manganese as the transition metal, and further preferably contains nickel, cobalt and manganese (NCM, nickel cobalt manganese oxide).

[0019] The positive electrode active material may consist only of lithium, oxygen, and a transition metal selected from Ni, Co, and Mn, or may contain elements other than these (hereinafter also referred to as other elements). When the positive electrode active material contains other elements, the proportion thereof may be 10 mol % or less, 5 mol % or less, or 1 mol % or less of the entire positive electrode active material. When the positive electrode active material contains other elements, the proportion 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.

[0020] The positive electrode active material is preferably a composite oxide containing lithium and one or more transition metals (lithium transition metal composite oxide). The positive electrode active material preferably has a layered structure, which 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.

[0021] The positive electrode active material may be a compound having a composition represented by the following formula (1). Li 1-a Ni x Me 1-x O 2 (1) In formula (1), a satisfies the relationship of -0.3≦a≦0.3, x satisfies the relationship 0.7≦x≦1.0, 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.

[0022] The positive electrode active material may be in a particulate form. The average particle size of the particulate positive electrode active material can be selected, for example, within the range of 5 μm to 30 μm. In the present disclosure, the average particle size of particles is defined as the particle size (D50) at which the cumulative volume is 50% in the volume-based particle size distribution. The volume-based particle size distribution can be obtained, for example, by a laser diffraction / scattering method.

[0023] The positive electrode mixture layer may be in the state of a mixture containing, in addition to the positive electrode active material, components other than the positive electrode active material, such as a conductive assistant and a binder.

[0024] Specific examples of the conductive assistant include carbon materials such as carbon black (acetylene black, thermal black, furnace black, etc.), carbon nanotubes, and graphite. The conductive material contained in the positive electrode material may be of one type alone or of two or more types.

[0025] Specific examples of binders 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. The binder contained in the positive electrode material may be of one type alone or of two or more types.

[0026] The positive electrode mixture layer may be disposed on a positive electrode current collector. Examples of the material constituting the positive electrode current collector include aluminum, aluminum alloy, nickel, titanium, stainless steel, etc. Examples of the shape of the positive electrode current collector include foil, mesh, etc.

[0027] From the viewpoint of improving the electrolyte retention, the porosity of the positive electrode mixture layer is preferably 15 vol % or more, more preferably 20 vol % or more, and even more preferably 25 vol % or more. From the standpoint of ensuring sufficient energy density, the porosity of the negative electrode mixture layer is preferably 40 vol. % or less, more preferably 35 vol. % or less, and even more preferably 30 vol. % or less.

[0028] The positive electrode mixture layer is disposed on the positive electrode current collector by, for example, applying a positive electrode mixture slurry to one or both sides of the positive electrode current collector. If necessary, a pressure treatment may be performed to adjust the density of the positive electrode mixture layer. The thickness of the positive electrode mixture layer is not particularly limited, and can be set, for example, taking into consideration the capacity ratio to the negative electrode mixture layer facing it via a separator. The positive electrode mixture layer may have a thickness of 80 μm or more, 90 μm or more, or 100 μm or more. 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.

[0029] (Negative electrode composite layer) The negative electrode active material contained in the negative electrode mixture layer includes graphite. The negative electrode mixture layer may contain only graphite as the negative electrode active material, or may contain a negative electrode active material other than graphite, such as carbon materials such as hard carbon, soft carbon, and activated carbon, silicon, metallic lithium, lithium alloys, and lithium titanate (LTO). When the negative electrode mixture layer contains a negative electrode active material other than graphite, the proportion of graphite in the total negative electrode active material is preferably 70 mass % or more, more preferably 80 mass % or more, and even more preferably 90 mass % or more.

[0030] The negative electrode active material may be in a particulate form. The average particle size of the particulate negative electrode active material can be selected, for example, within the range of 5 μm to 30 μm.

[0031] The negative electrode mixture layer may be in the state of a mixture containing, in addition to the negative electrode active material, components other than the negative electrode active material, such as a conductive assistant and a binder. The conductive material and binder may be selected from the materials that may be included in the positive electrode mixture layer described above.

[0032] The negative electrode mixture layer may be disposed on a negative electrode current collector. Examples of materials constituting the negative electrode current collector include copper, copper alloy, nickel, titanium, stainless steel, etc. Examples of the shape of the negative electrode current collector include foil, mesh, etc.

[0033] From the viewpoint of improving the electrolyte retention, the porosity of the negative electrode mixture layer is preferably 25 vol % or more, more preferably 30 vol % or more, and even more preferably 35 vol % or more. From the standpoint of ensuring sufficient energy density, the porosity of the negative electrode mixture layer is preferably 55 vol % or less, more preferably 50 vol % or less, and even more preferably 45 vol % or less.

[0034] The negative electrode mixture layer is disposed on the negative electrode current collector by, for example, applying a slurry of the negative electrode mixture to one or both sides of the negative electrode current collector. If necessary, a pressure treatment may be performed to adjust the density of the negative electrode mixture layer. The thickness of the negative electrode mixture layer may be 150 μm or more, and may be 160 μm or more, 170 μm or more, or 180 μm or more. The thickness of the negative electrode mixture layer may be 400 μm or less, 300 μm or less, 250 μm or less, or 200 μm or less.

[0035] (Separator) The type of separator disposed between the positive electrode and the negative electrode is not particularly limited, and any known separator can be used. Specific examples of the separator include nonwoven fabrics, cloths, microporous films, etc., mainly composed of polyolefins such as polyethylene and polypropylene. The thickness of the separator is not particularly limited and may be selected from the range of, for example, 5 μm to 50 μm.

[0036] (electrolyte) The battery of the present disclosure includes an electrolyte together with an electrode assembly, that is, the battery of the present disclosure is a liquid-based battery that uses a liquid electrolyte.

[0037] The electrolyte is LiPF 6 Any known electrolyte dissolved in an organic solvent can be used without any particular limitation. Specific examples of the organic solvent include cyclic or chain carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. The solvent may be a mixture of two or more solvents, or may be a mixture containing a cyclic carbonate and a chain carbonate. The solvent may contain an additive such as vinylene carbonate (VC).

[0038] (Battery type) The form of the battery of the present disclosure is not particularly limited and may be any known form. The battery of the present disclosure may be in a state in which the electrode assembly and the electrolyte are housed in an exterior body such as a metal can, a metal film, etc. The shape of the battery is not particularly limited and may be a rectangular parallelepiped, a cylinder, etc.

[0039] The size of the battery is not particularly limited and can be selected depending on the application of the battery. In the battery of the present disclosure, the discharge of the electrolyte from the electrode assembly is effectively suppressed, and therefore the area of ​​the main surface of the electrode assembly is large (for example, 15,000 cm 2 ~20000cm 2 2) Even in a state where uneven electrolyte penetration is likely to occur, the battery performance is maintained at a good level. EXAMPLES

[0040] The present disclosure will be described in more detail below with reference to examples, but the invention of the present disclosure is not limited to these examples.

[0041] <Example 1> (1) Preparation of the positive electrode 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, and the viscosity was adjusted with a solvent to obtain a positive electrode mixture in a slurry state. The positive electrode mixture was placed on an aluminum foil (thickness: 30 μm) with a one-sided basis weight of 34 mg / cm. 2 The positive electrode mixture layer was then dried at 100° C. for 10 minutes to form a positive electrode mixture layer. After that, the density of the positive electrode mixture layer was 3.3 g / cm 3 The thickness and porosity of the positive electrode mixture layer are shown in Table 1.

[0042] (2) Preparation of the negative electrode 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-like negative electrode mixture. The negative electrode mixture was applied to a copper foil (thickness: 15 μm) so that the weight per surface area was 23 mg / cm2. 2(i.e., the ratio of the positive electrode capacity to the negative electrode capacity was 1.1) and then dried at 100°C for 10 minutes to form a negative electrode mixture layer. After that, the density of the negative electrode mixture layer was 1.25 g / cm 3 The pressing process was carried out so that the thickness and porosity of the negative electrode mixture layer were as follows: Table 1 shows the thickness and porosity of the negative electrode mixture layer.

[0043] (3) Battery construction The positive and negative electrodes prepared in the above steps were laminated with a separator (three-layer structure of PP / PE / PP, thickness: 16 μm) between them to prepare an electrode body. A laminate-type battery was prepared using this electrode body and an electrolyte. The electrolyte was 1.1 M LiPF 6 The above was dissolved in a mixed solvent of EC (30% by volume), DMC (40% by volume), and EMC (30% by volume) and the battery's restraining pressure was adjusted to 20 kPa.

[0044] (4) Battery performance evaluation The battery was activated using a constant current-constant voltage method according to the following procedure. Specifically, the battery was charged at a constant current of 0.1 C up to 4.25 V, then charged at a constant voltage for 3 hours, and then discharged at a current of 0.1 C down to 3.0 V by the constant current method. The activated battery was charged at a current of 0.1 C to 4.25 V using a constant current-constant voltage method, and then discharged at a current of 1 C to 3.0 V using a constant current method, and the discharge rate (1 C discharge rate) relative to the theoretical rated capacity was calculated. The results are shown in Table 1.

[0045] (5) Resistance measurement The resistance of the electrode sheet was measured using an electrode resistance measuring device (KNH-0622, Hioki Corporation) by the following method. The results are shown in Table 1. A current is applied between two specific probes that are in contact with the surface of the electrode sheet, and the potential distribution on the surface is measured. A model of the electrode sheet is created that is composed of a composite layer, a current collector, and the interface resistance between them. The volume resistivity of the composite layer and the current collector, as well as their interface resistance, are each assumed to be uniform. The volume resistivity and interface resistance of the composite layer at this time are unknown, while the thickness of the composite layer, the thickness of the current collector, and the volume resistivity of the current collector are assumed to be known values. For the modeled electrode sheet, an equation in which the potential is an unknown function is solved using the finite volume method to determine the potential corresponding to the actually measured potential, and the volume resistivity and interface resistance of the composite layer are output.

[0046] <Examples 2 to 10, Comparative Examples 1 to 3, Reference Examples 1 to 8> Batteries having the positive electrode mixture layer characteristics, the negative electrode mixture layer characteristics, and the battery restraining pressure shown in Table 1 were fabricated in the same manner as in Example 1, and the 1C discharge rate was measured. The results are shown in Table 1.

[0047] [Table 1]

[0048] As shown in Table 1, the batteries of Examples 1 to 5, in which the Ni ratio of the positive electrode active material is 70 mol % or more and the thickness of the negative electrode composite layer is 150 μm or more, have a higher 1C discharge rate and exhibit excellent battery performance than the battery of Comparative Example 1, which has the same conditions as Examples 1 to 5 except that the confining pressure exceeds 300 kPa. Similarly, the batteries of Examples 6 to 9, in which the Ni ratio of the positive electrode active material is 70 mol % or more, the thickness of the negative electrode composite layer is 150 μm or more, and the confining pressure is 300 kPa or less, have a higher 1C discharge rate and exhibit excellent battery performance than the battery of Comparative Example 2, which has the same conditions as Examples 6 to 9 except that the confining pressure exceeds 300 kPa.

[0049] The battery of Example 10, in which the Ni ratio of the positive electrode active material is 70 mol%, has a higher 1C discharge rate and exhibits excellent battery performance than the battery of Comparative Example 3, which is the same as Example 10 except that the Ni ratio of the positive electrode active material is 60 mol%.

[0050] As shown by the results of Reference Examples 1 to 4, in batteries having a negative electrode mixture layer thickness less than 150 μm, the difference between the 1C discharge rate when the confining pressure is 300 kPa or less and the 1C discharge rate when the confining pressure exceeds 300 kPa is small. As shown by the results of Reference Examples 5 to 8, in batteries in which the Ni ratio of the positive electrode active material contained in the positive electrode composite layer is less than 70 mol %, the difference between the 1C discharge rate when the confining pressure is 300 kPa or less and the 1C discharge rate when the confining pressure is more than 300 kPa is small. The above results show that the effect of improving battery performance by setting the Ni ratio of the positive electrode active material contained in the positive electrode composite layer to 70 mol % or more and the confining pressure to 300 kPa or less is significantly manifested when the thickness of the negative electrode composite layer is 150 μm or more. [Explanation of symbols]

[0051] 10: Positive electrode 10A: Positive electrode composite layer 10B: Positive electrode current collector 20: Negative electrode 20A: Negative electrode composite layer 20B: Negative electrode current collector 30: Separator 100: Laminate

Claims

1. An electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and an electrolyte; The positive electrode includes a positive electrode mixture layer including a positive electrode active material and a positive electrode current collector, The negative electrode includes a negative electrode mixture layer including a negative electrode active material and a negative electrode current collector, The positive electrode active material contains nickel as a transition metal, and the ratio of nickel is 70 mol % or more of the total transition metals, The negative electrode active material includes graphite, The thickness of the negative electrode mixture layer is 150 μm or more, A battery having a confinement pressure of 300 kPa or less.

2. The battery according to claim 1 , wherein the positive electrode mixture layer has a thickness of 80 μm or more.

3. The battery according to claim 1 , wherein the negative electrode mixture layer has a porosity of 25% by volume or more.

4. 2. The battery of claim 1, wherein the negative electrode mixture layer has a thickness of 400 μm or less.

5. 10. The battery of claim 1, wherein the positive electrode active material has a layered structure.

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