Battery

Abstract

To improve discharge performance.SOLUTION: A battery comprising a positive electrode, a negative electrode, and a separator, wherein the negative electrode comprises a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer comprises a first region and a second region, and the first region is disposed between the negative electrode current collector and the second region, the first region has a higher concentration than the second region, the second region has a concentration of 1. 3g / cm3 or less, the negative electrode active material layer has a weight per unit area of 18mg / cm2 or more, a ratio of the weight per unit area of the second region to the weight per unit area of the negative electrode active material layer is 10% or more, and the separator includes a first surface facing the positive electrode and a second surface facing the negative electrode, and an adhesive layer is formed on the first surface and the second surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 (Japanese Patent Laid-Open Publication No. 10-116619) discloses a lithium ion secondary battery in which the packing density of graphite in the negative electrode plate is 1.2 to 2.0 g / cc. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-116619 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for even higher capacity batteries. To achieve this, efforts have been made to increase the weight and density of the electrodes. However, increasing capacity can lead to problems such as durability.

[0005] Separators with adhesive layers have been investigated as a solution to the above problems. Separators with adhesive layers are effective in improving durability because they can suppress the increase in interelectrode distance caused by volumetric changes in the active material. However, when such separators are used with electrodes with high basis weight or density, ion diffusion within the electrodes is hindered, leaving room for improvement in discharge performance.

[0006] The objective of the present disclosure is to improve discharge performance. [Means for solving the problem]

[0007] [1] A battery comprising a positive electrode, a negative electrode, and a separator, the negative electrode includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer includes a first region and a second region, the first region is disposed between the negative electrode current collector and the second region, the density of the first region is greater than the density of the second region; The density of the second region is 1.3 g / cm 3 is as follows: The negative electrode active material layer has a density of 18 mg / cm 2 With the above mentioned amount, a ratio of the basis weight of the second region to the basis weight of the negative electrode active material layer is 10% or more; the separator includes a first surface facing the positive electrode and a second surface facing the negative electrode, A battery having an adhesive layer formed on the first surface and the second surface.

[0008] Since the density of the second region is lower than that of the first region, ion diffusion within the electrode is improved. As a result, the basis weight of the negative electrode active material layer is 18 mg / cm 2 In the above-described electrode, even if an adhesive layer is present on the electrode surface, it is difficult to inhibit ion diffusion, thereby suppressing an increase in resistance. Furthermore, the presence of the adhesive layer makes it difficult for the distance between the electrodes to increase, thereby suppressing a decrease in discharge performance after a cycle test. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of the battery of this embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view showing an example of the negative electrode of this embodiment. [Figure 3] FIG. 3 is a table showing the experimental results. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present disclosure will be described, but the present disclosure is not limited thereto.

[0011] The battery of the present disclosure may be applied to any battery, such as a monopolar battery, a bipolar battery, a non-aqueous battery, or a lithium-ion battery.

[0012] <Battery> FIG. 1 is a schematic cross-sectional view showing an example of a battery according to this embodiment. The battery according to this embodiment includes an exterior body (not shown), an electrode assembly 50, and a non-aqueous electrolyte (not shown). The exterior body may be, for example, a pouch made of an aluminum laminate film. The electrode assembly 50 includes a positive electrode 10, a separator 30, and a negative electrode 20. The separator 30 includes a first surface facing the positive electrode 10 and a second surface facing the negative electrode 20. An adhesive layer 40 is formed on both the first surface and the second surface.

[0013] The electrode assembly 50 is, for example, a laminated type. The electrode assembly 50 is formed by laminating a positive electrode 10, a separator 30, and a negative electrode 20. The electrode assembly 50 may have any laminated structure as long as it includes at least one layer of each of the positive electrode 10, the separator 30, and the negative electrode 20. For example, the electrode assembly 50 may be formed by laminating the positive electrode 10, the separator 30, the negative electrode 20, the separator 30, and the positive electrode 10 in this order.

[0014] The positive electrode 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12. The positive electrode current collector 11 may be, for example, an aluminum (Al) foil or the like. The positive electrode current collector 11 may have a thickness of, for example, 10 μm or more and 30 μm or less.

[0015] The positive electrode active material layer 12 may have a thickness of, for example, 10 μm or more and 200 μm or less. The positive electrode active material layer 12 includes at least a positive electrode active material. The positive electrode active material layer 12 may further include, for example, a conductive material and a binder. The positive electrode active material may include, for example, a lithium composite oxide such as nickel cobalt manganese oxide lithium. The conductive material may include, for example, a carbon material such as acetylene black (AB). The binder may include, for example, polyvinylidene fluoride (PVdF).

[0016] 2 is a schematic cross-sectional view showing an example of the negative electrode of this embodiment. The negative electrode 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22. The negative electrode current collector 21 may be, for example, a copper (Cu) foil. The negative electrode current collector 21 may have a thickness of, for example, 5 μm or more and 30 μm or less.

[0017] The negative electrode active material layer 22 may have a thickness of, for example, 10 μm or more and 200 μm or less. The negative electrode active material layer 22 includes at least a negative electrode active material. The negative electrode active material layer 22 may further include, for example, a binder and a thickener. The negative electrode active material may include, for example, graphite (artificial graphite, natural graphite). The binder may include, for example, styrene butadiene rubber (SBR). The thickener may include, for example, carboxymethyl cellulose (CMC).

[0018] The negative electrode active material layer 22 includes a first region 1 and a second region 2. The first region 1 is disposed between the negative electrode current collector 21 and the second region 2. The thicknesses of the first region 1 and the second region 2 may be the same or different.

[0019] The density of the first region 1 is greater than the density of the second region 2. The density of the first region 1 is, for example, 1.4 g / cm 3 It may be 1.5 g / cm or more. 3 The density of the second region 2 may be 1.3 g / cm or more. 3 The following is the result.

[0020] The weight of the negative electrode active material layer 22 is 18 mg / cm 2 or more, 20 mg / cm 2 It may be 25 mg / cm or more. 2 It may be more than that.

[0021] The ratio of the weight of the second region 2 to the weight of the negative electrode active material layer 22 is 10% or more, or may be 20% or more, or may be 30% or more. The ratio of the weight of the second region 2 to the weight of the negative electrode active material layer 22 may be 50% or less.

[0022] (separator) The separator 30 is interposed between the positive electrode 10 and the negative electrode 20. The separator 30 is porous. The separator 30 may be made of, for example, polyolefin. The separator 30 may be made of, for example, a polyethylene (PE) layer. The separator 30 may have a thickness of, for example, 5 μm or more and 40 μm or less.

[0023] The separator 30 includes a first surface facing the positive electrode 10 and a second surface facing the negative electrode 20. An adhesive layer 40 is formed on both the first surface and the second surface. The adhesive layer 40 may have a thickness of, for example, 1 μm or more and 6 μm or less.

[0024] The adhesive layer 40 includes an adhesive resin. Examples of the adhesive resin include polyvinylidene fluoride. The adhesive layer 40 may further include, for example, inorganic particles. Examples of the inorganic particles include alumina. The adhesive resin and the inorganic particles may be mixed in a volume ratio of 50:50, for example.

[0025] (Non-aqueous electrolyte) The non-aqueous electrolyte contains a non-aqueous solvent and a supporting salt. For example, a non-aqueous solvent such as an organic solvent containing a supporting salt can be used. The non-aqueous solvent can be, for example, ethylene carbonate (EC), dimethyl carbonate (DMC), or ethyl methyl carbonate (EMC). One type of solvent can be used alone, or two or more types of solvents can be used in combination.

[0026] The supporting salt is dissolved in a non-aqueous solvent. The supporting salt may be, for example, a lithium salt (LiPF6, etc.). The supporting salt may have a molar concentration of, for example, 0.5 mol / L or more and 2 mol / L or less.

[0027] The non-aqueous electrolyte may contain any additive. Examples of the additive include vinylene carbonate (VC). The additive may be contained in an amount of 1.0 to 5.0 mass % based on the total mass of the mixed solvent. [Example]

[0028] The present embodiment will be described below using examples, but the present embodiment is not limited to these.

[0029] <Production of negative electrodes> (No. 1-6) Spheroidized artificial graphite (97% by mass) was used as the negative electrode active material, SBR (2.4% by mass) was used as the binder, CMC (0.6% by mass) was used as the thickener, and water was used as the dispersion medium, and these were mixed and dispersed to obtain a first slurry with a solid content of 54%. The first slurry was applied to a Cu foil (thickness: 15 μm) serving as a negative electrode current collector, thereby forming a first region. The first region was formed so that the basis weight after drying would be as shown in FIG. 3. The first region was dried to form a negative electrode active material layer. The negative electrode active material layer was compressed at a predetermined pressure to produce negative electrodes No. 1 to 6.

[0030] (No.7~17) A first region was formed in the same manner as Nos. 1 to 6. Next, a second slurry was obtained by using flake artificial graphite instead of spherical artificial graphite. The second slurry was applied on top of the first slurry to form a second region. The second region was formed so that the basis weight after drying would be the basis weight shown in FIG. 3. The first and second regions were dried to form a negative electrode active material layer. The negative electrode active material layer was compressed at a predetermined pressure to produce negative electrodes Nos. 7 to 17.

[0031] (density) Twenty cross-sectional SEM images of the cross sections of negative electrodes Nos. 1 to 17 were taken with a scanning electron microscope (SEM) in a field of view of 50 μm × 50 μm. Each cross-sectional SEM image was analyzed, and the density (g / cm) was calculated from the area ratio of the negative electrode active material to the voids in each region. 3 The results are shown in Figure 3. In Figure 3, the average density calculated from 20 cross-sectional SEM images was taken as the density of each region.

[0032] <Production of evaluation cells> LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 A slurry was obtained by mixing and dispersing O2 (96.1% by mass), AB (2.5% by mass) as a conductive material, PVdF (1.4% by mass) as a binder, and N-methyl-2-pyrrolidone as a dispersion medium. The slurry was uniformly applied to an Al foil (thickness: 30 μm) serving as a positive electrode current collector and dried to form a positive electrode active material layer. The positive electrode active material layer was compressed at a predetermined pressure to produce a positive electrode. The basis weight of the positive electrode was adjusted so that Y / X = 1.15, where X (mAh) is the charge capacity of the positive electrode and Y (mAh) is the charge capacity of the negative electrode.

[0033] PE (thickness: 16 μm) was prepared as a separator (separator A). In addition, a slurry (polyvinylidene fluoride:alumina=50:50 (volume %)) containing polyvinylidene fluoride and alumina was coated on both sides of separator A as an adhesive resin, and then dried to produce separator B having adhesive layers on both sides. The coating weight was 3.0 mg / cm on one side. 2 It was.

[0034] The outer packaging was a pouch made of aluminum laminate film. The electrolyte was prepared by mixing 1.1 mol / L LiPF as a supporting electrolyte, a non-aqueous solvent mixture of EC / EMC / DMC = 30 / 40 / 30 (volume ratio), and 2.0 mass% VC as an additive based on the total mass of the mixed solvent.

[0035] The positive electrode, the separator, and the negative electrode were stacked in this order to form an electrode assembly. The electrode assembly and the electrolyte were sealed in an outer package to produce evaluation cells Nos. 1 to 17.

[0036] <Evaluation> (activation) Each evaluation cell was charged and discharged using the constant current-constant voltage (CC-CV) method in a temperature environment of 25°C. The conditions are shown below. Note that "C" is the symbol representing the time rate of current. A current of 1C is defined as the design capacity of the evaluation cell being discharged in 1 hour.

[0037] [conditions] CC charging: Charging current = 0.1C, cutoff voltage = 4.25V CV charging: 3 hours CC discharge: Discharge current = 0.1C, cutoff voltage = 2.5V

[0038] (Initial discharge performance) The discharge capacity of each evaluation cell was measured at 0.1C and 1.5C. The ambient temperature during discharge was 25°C. The ratio of the capacity at 1.5C discharge (1.5C discharge capacity) to the capacity at 0.1C discharge (0.1C discharge capacity) was calculated (1.5C discharge capacity / 0.1C discharge capacity). This ratio was used as the initial discharge performance.

[0039] (Cycle test) The cells were subjected to 250 charge-discharge cycles using the CC method at a temperature of 40°C. One cycle is defined as a cycle of "charge → rest → discharge." The cells were then returned to room temperature, and the post-cycle discharge performance of each evaluation cell was measured.

[0040] [conditions] Charging: 0.2C, cutoff voltage = 4.25V Pause: 60 seconds Discharge: 0.3C, Cutoff voltage = 2.5V

[0041] <Result> In No. 1 to No. 6, the negative electrode weight was 18 mg / cm 2 When the adhesive layer was not present, the post-cycle discharge performance also decreased. 2Even at this density, the deterioration of the initial discharge performance was suppressed, and when an adhesive layer was provided, the deterioration of the discharge performance after cycling was also suppressed. 3 In No. 14, the initial discharge performance was reduced because the area weight ratio of the second region was 5%. On the other hand, in Nos. 15 to 17, the area weight ratio of the second region was 10% or more, so the reduction in the initial discharge performance and post-cycle discharge performance was suppressed.

[0042] The embodiments and examples disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0043] 1 first region, 2 second region, 10 positive electrode, 11 positive electrode current collector, 12 positive electrode active material layer, 20 negative electrode, 21 negative electrode current collector, 22 negative electrode active material layer, 30 separator, 40 adhesive layer, 50 electrode body.

Claims

[Claim 1] A battery comprising a positive electrode, a negative electrode, and a separator, the negative electrode includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer includes a first region and a second region, the first region is disposed between the negative electrode current collector and the second region, the density of the first region is greater than the density of the second region; The density of the second region is 1.3 g / cm ３ is as follows: The negative electrode active material layer has a thickness of 18 mg / cm ２ With the above mentioned amount, a ratio of a basis weight of the second region to a basis weight of the negative electrode active material layer is 10% or more; the separator includes a first surface facing the positive electrode and a second surface facing the negative electrode, An adhesive layer is formed on the first surface and the second surface.

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