Electrode and battery

Abstract

To provide an electrode and a battery that further improves the electrolyte impregnation ability of an active material layer.SOLUTION: An electrode 100 according to the present disclosure includes a current collector 200 and an active material layer 300 provided on a current collector 200, the active material layer 300 has a basis weight greater than 20 mg / cm2 and a coating area of 600 cm2 or more, with a high density portion 310 in the center where the active material has a high density, and a sloped portion 320 on the periphery where the active material density decreases from the center towards the edge.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an electrode and a battery.

Background Art

[0002] In a battery having an electrode provided with an active material layer on the surface of a current collector, it is required to enhance the electrolyte impregnation property with respect to the active material layer. For example, Patent Document 1 discloses a technique for reducing the density of an active material at the periphery of an active material layer in order to enhance the electrolyte impregnation property with respect to the active material layer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The inventors have found the following problems regarding the electrode and the battery. When the thickness and coating area of the active material layer are large, it is more difficult to sufficiently impregnate the electrolyte to the center of the active material layer than when the thickness and coating area of the active material layer are small. Therefore, there is room for improvement in the technique for enhancing the electrolyte impregnation property with respect to the active material layer.

[0005] The present disclosure has been made in view of such problems, and an object thereof is to provide an electrode and a battery that further enhance the electrolyte impregnation property with respect to the active material layer.

Means for Solving the Problems

[0006] One aspect for achieving the above object is an electrode including a current collector and an active material layer provided on the current collector, wherein the active material layer has a basis weight of more than 20 mg / cm 2 and a coating area of 600 cm 2As described above, a high-density portion with a high density of the active material is provided at the center, and an inclined portion where the density of the active material decreases from the center toward the edge is provided at the periphery.

[0007] One aspect for achieving the above object is a battery including the above-described electrode.

Effects of the Invention

[0008] According to the present disclosure, it is possible to provide an electrode and a battery that further enhance the electrolyte impregnation property with respect to the active material layer.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are denoted by the same reference numerals, and redundant descriptions are omitted as necessary for clarity of explanation. Also, for ease of understanding, the scales of the respective parts in the drawings may be different from the actual ones. In directions such as parallel, right angle, orthogonal, horizontal, vertical, up and down, left and right, a deviation to the extent that the effects of the embodiments are not impaired is allowed. Parallel, right angle, orthogonal, horizontal, and vertical may include substantially parallel, substantially right angle, substantially orthogonal, substantially horizontal, and substantially vertical. Further, in this specification, "substantially" means a state in which a person visually recognizes the same shape and the same dimensions.

[0011] (Embodiment 1) First, referring to FIG. 1, the configuration of the electrode 100 according to Embodiment 1 will be described. The electrode 100 is an electrode used in a battery. Specifically, the electrode 100 is an electrode of a lithium-ion secondary battery. The configuration of the battery having the electrode 100 is not particularly limited. The battery having the electrode 100 may be configured as, for example, a laminate-type battery or a square battery. In the following, the case where a laminate-type battery is configured as the battery having the electrode 100 will be described.

[0012] The laminate-type battery having the electrode 100 includes an electrode body, an electrolyte, an external terminal, and a laminate exterior body. The electrode body and the electrolyte function as a power generation element of the laminate-type battery. The electrode body and the electrolyte are sealed inside the laminate exterior body.

[0013] The configuration of the electrode body may be a known configuration and is not particularly limited. The electrode body is a laminated electrode body and includes one or more, typically a plurality of, sheet-like positive electrode bodies and negative electrode bodies. The positive electrode body and the negative electrode body are alternately laminated in a state of being insulated from each other.

[0014] The positive electrode body typically includes a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector. For example, aluminum is used as the positive electrode current collector. The positive electrode active material layer contains a positive electrode active material. The positive electrode active material is, for example, a lithium transition metal composite oxide such as lithium nickel cobalt manganese composite oxide.

[0015] The negative electrode body typically includes a negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector. For example, copper is used as the negative electrode current collector. The negative electrode active material layer contains a negative electrode active material. The negative electrode active material is, for example, a carbon material such as graphite.

[0016] A separator may be disposed between the positive electrode body and the negative electrode body. The separator insulates the positive electrode active material layer and the negative electrode active material layer. As the separator, for example, a resin sheet such as polyethylene (PE) or polypropylene (PP) is used.

[0017] The electrolyte composition may be a known composition and is not particularly limited. The electrolyte may be liquid, polymer (i.e., gel-like), or solid. As an example, the electrolyte may contain a non-aqueous solvent and a supporting salt such as a lithium salt that generates charge carriers.

[0018] The electrode body is provided with current collecting tabs. The current collecting tabs are a positive electrode current collecting tab and a negative electrode current collecting tab. Specifically, the positive electrode current collecting tab extends outward from the positive electrode current collector provided in the positive electrode body. The negative electrode current collecting tab extends outward from the negative electrode current collector provided in the negative electrode body. The current collecting tabs are exposed without including an active material layer. For example, the positive electrode current collecting tab and the negative electrode current collecting tab may extend from both sides of the short side.

[0019] The external terminals are formed in a plate shape. The external terminals are electrically connected to the current collecting tabs by being joined to the current collecting tabs. Specifically, the positive electrode external terminal extends further outward from the vicinity of the tip of the positive electrode current collecting tab and is exposed outside the laminate exterior body. The positive electrode external terminal is, for example, a thin aluminum plate. The negative electrode external terminal extends further outward from the vicinity of the tip of the negative electrode current collecting tab and is exposed outside the laminate exterior body. The negative electrode external terminal is, for example, a thin copper plate.

[0020] The positive electrode external terminal and the positive electrode current collecting tab are joined to each other at the joint. Also, the negative electrode external terminal and the negative electrode current collecting tab are joined to each other at the joint. The joining method of the joint may be, for example, resistance welding. Note that the joining method of the joint is not particularly limited and may be laser welding or ultrasonic joining, etc.

[0021] FIG. 1(a) shows a front view of an electrode 100 according to Embodiment 1. The electrode 100 is a positive electrode body or a negative electrode body constituting an electrode body. As shown in FIG. 1, the electrode 100 includes a current collector 200 and an active material layer 300. When the electrode 100 is a positive electrode body, the current collector 200 is a positive electrode current collector, and the active material layer 300 is a positive electrode active material layer. When the electrode 100 is a negative electrode body, the current collector 200 is a negative electrode current collector, and the active material layer 300 is a negative electrode active material layer. The current collector 200 is a rectangular metal foil. The active material layer 300 is formed by applying a slurry containing an active material and a binder to the current collector 200 and then pressing it. As shown in FIG. 1, the active material layer 300 is formed in a rectangular shape on the current collector 200. Note that the active material layer 300 has a basis weight of more than 20 mg / cm 2 and a coating area of 600 cm 2 or more.

[0022] A high-density portion 310 is provided at the center of the active material layer 300. The high-density portion 310 is a region where the density of the active material is higher compared to other regions. A sloped portion 320 is provided at the periphery of the active material layer 300, that is, in the portion other than the high-density portion 310. The sloped portion 320 is a portion where the density of the active material gradually decreases from the center toward the edge.

[0023] FIG. 1(c) is a graph schematically showing the density of the active material in the active material layer 300. As shown in FIG. 1(c), the active material layer 300 has a high density of the active material in the central portion, that is, the high-density portion 310, and the density of the active material gradually decreases from the center toward the edge in the peripheral portion, that is, the sloped portion 320.

[0024] Since the electrode 100 is provided with the sloped portion 320 in the active material layer 300, even when the basis weight and coating area of the active material layer 300 are large, the active material layer 300 can be sufficiently impregnated with the electrolyte throughout the layer. Therefore, in a battery having the electrode 100, a decrease in charge / discharge efficiency is suppressed, and generation of gas is suppressed. For this reason, in a battery having the electrode 100, an increase in resistance due to expansion between the electrodes is suppressed, and a decrease in durability performance due to Li deposition is suppressed.

[0025] (Embodiment 2) Next, referring to FIG. 2, the configuration of the electrode 500 according to Embodiment 2 will be described. FIG. 2(a) shows a front view of the electrode 500 according to Embodiment 2. The electrode 500 is different from the electrode 100 shown in FIG. 1 in that it includes an active material layer 600 instead of the active material layer 300. The active material layer 300 includes a high-density portion 610, an inclined portion 620, and a communication portion 630. Since the high-density portion 610 and the inclined portion 620 have the same configuration as the high-density portion 310 and the inclined portion 320 shown in FIG. 1, the description thereof will be omitted. As shown in FIG. 2, the communication portion 630 is provided so as to communicate from a part of one side of the active material layer 600 to a part of the opposing side. One communication portion 630 may be provided, or a plurality of communication portions 630 may be provided.

[0026] The communication portion 630 is any one of a low-density portion, a low-binder portion, and an alignment portion. The low-density portion is a portion where the density of the active material is lower than that of other regions of the active material layer 600. FIG. 2(b) is a graph showing the active material density of the active material layer 600 when the communication portion 630 is a low-density portion. By providing the low-density portion, the liquid retention property of the active material layer 600 can be further enhanced, and the gas generated at the center of the active material layer 600 can be easily discharged.

[0027] The low-binder portion is a portion where the content of the binder is less than that of other regions of the active material layer 600. The low-binder portion has more voids between the active materials than other regions. Therefore, by providing the low-binder portion, the same effect as in the case of providing the low-density portion can be obtained.

[0028] The alignment portion is a region where the active materials contained in the active material layer 600 are aligned in a predetermined direction. The cross-sectional area of the voids per active material particle is averaged in the alignment portion. Therefore, by providing the alignment portion, the same effect as in the case of providing the low-density portion or the low-binder portion can be obtained.

[0029] (Examples) Hereinafter, the present disclosure will be described in detail by way of examples. Note that the present disclosure is not limited thereto.

[0030] [Preparation of Samples] Samples according to the examples and comparative examples were prepared by the following method.

[0031] FIG. 3(a) is a schematic diagram showing the configuration of a coating device 700 used when preparing a sample of the negative electrode. The coating device 700 includes a squeegee 800 and a metal frame portion 1000. The coating device 700 is a screen printing device. Specifically, the coating device 700 is a device that coats a negative electrode slurry 900 on a copper foil 1100 by means of a squeegee 800. The arrow shown in FIG. 3(a) is the moving direction of the squeegee 800, that is, the coating direction of the negative electrode slurry. An inner frame 1010 is provided in the metal frame portion 1000. The inner frame 1010 constitutes the wall of a through hole having a size and shape corresponding to the size and shape of the area where the slurry is to be coated. In this example, the size of the inner frame was 30 cm × 50 cm. When performing screen printing, the copper foil 1100 was placed under the metal frame portion 1000 such that the inner frame 1010 was located in the negative electrode slurry coating area, and the negative electrode slurry 900 was coated.

[0032] FIG. 3(b) is a schematic diagram of the tip shape of the squeegee 800. As shown in FIG. 3(b), a squeegee 800 with both ends inclined was used, and a copper foil coated with a negative electrode slurry was obtained such that the central portion had a higher coating weight and the coating weights at both ends had an inclination. Next, the copper foil coated with the negative electrode slurry was pressed to produce a negative electrode. A laminated battery with a capacity of 10 Ah was produced using the produced negative electrode. The sample thus obtained was designated as Example 1.

[0033] FIG. 3(c) is a schematic diagram of another tip shape of the squeegee 800. As shown in FIG. 3(c), a squeegee 800 with both ends inclined and a recess in the central portion was used, and a copper foil coated with a negative electrode slurry was obtained such that the central portion had a higher coating weight, the coating weights at both ends had an inclination, and a part of the central portion had a lower coating weight. Next, the copper foil coated with the negative electrode slurry was pressed to produce a negative electrode. A laminated battery with a capacity of 10 Ah was produced using the produced negative electrode. The sample thus obtained was designated as Example 2.

[0034] A squeegee with no inclination at both ends, that is, a straight-tip squeegee, was used to obtain a copper foil coated with a negative electrode slurry so that the basis weight was constant in all regions. Next, a negative electrode was fabricated by pressing the copper foil coated with the negative electrode slurry. A laminated battery with a capacity of 10 Ah was fabricated using the fabricated negative electrode. The sample thus obtained was designated as Comparative Example 1.

[0035] A squeegee with recesses at both ends was used to obtain a copper foil coated with a negative electrode slurry such that both end portions had a low basis weight and the other portions had a high basis weight. Next, a negative electrode was fabricated by pressing the copper foil coated with the negative electrode slurry. A laminated battery with a capacity of 10 Ah was fabricated using the fabricated negative electrode. The sample thus obtained was designated as Comparative Example 2.

[0036] Figure 4(a) is a schematic diagram showing the negative electrodes of Examples 1-2 and Comparative Examples 1-2. The distribution of the basis weight during slurry coating for the samples of Examples 1-2 and Comparative Examples 1-2 is shown in Figure 4(b). a-i shown in Figure 4(b) correspond to the points a-i shown in Figure 4(a). As shown in Figure 4(b), in all of Examples 1-2 and Comparative Examples 1-2, the slurry was coated with a basis weight corresponding to the tip shape of the squeegee. The distribution of the negative electrode density after pressing for the samples of Examples 1-2 and Comparative Examples 1-2 is shown in Figure 4(c). a-i shown in Figure 4(c) correspond to the points a-i shown in Figure 4(a). As shown in Figure 4(c), in all of Examples 1-2 and Comparative Examples 1-2, the negative electrodes were fabricated with a negative electrode density corresponding to the basis weight of the slurry.

[0037] After performing screen printing using a metal frame portion provided with two inner frames of the same shape and adjacent to each other, a low binder slurry was applied to a groove portion provided at a position corresponding to the gap between the inner frames. Next, by pressing the copper foil coated with the slurry, a negative electrode provided with one communication portion in the active material layer was produced. The coating area of the active material layer provided in the produced negative electrode was the same as that in Examples 1 to 2. Further, the negative electrode slurry applied to a position corresponding to a portion other than the communication portion contained 3 wt% of SBR (styrene butadiene rubber). The negative electrode slurry applied to a position corresponding to the communication portion contained 1 wt% of SBR. A laminated battery having a capacity of 10 Ah was produced using the produced negative electrode. The sample thus obtained was designated as Example 3.

[0038] After applying a negative electrode slurry to a copper foil using a squeegee having the shape shown in FIG. 3(b), a magnetic field with a magnetic flux density of 0.3 T was applied for 60 seconds to the central portion of the negative electrode slurry, that is, the position corresponding to the communication portion of the active material layer. Next, by pressing the copper foil coated with the slurry, a negative electrode was produced. A laminated battery having a capacity of 10 Ah was produced using the produced negative electrode. The sample thus obtained was designated as Example 4.

[0039] [Evaluation of negative electrode liquid retention rate] Regarding the samples of Examples 1 to 4 and Comparative Examples 1 to 2, the cells in the initial state were disassembled, and the liquid retention rate of the negative electrode was evaluated. The evaluation results are shown in FIG. 5.

[0040] As shown in FIG. 5, at the end portion of the negative electrode, the liquid retention rate of all of Examples 1 to 4 and Comparative Examples 1 to 2 was at a level close to 100%. On the other hand, at the central portion of the negative electrode, Examples 1 to 4 had a higher liquid retention rate than Comparative Examples 1 to 2. In particular, in Examples 2 to 4, the liquid retention rate at the central portion of the negative electrode was at a level close to 100%. From this, it became clear that the liquid retention rate at the central portion of the active material layer can be improved by providing an inclined portion in the active material layer. Further, it became clear that the liquid retention rate at the central portion of the active material layer can be further improved by providing a communication portion in the active material layer.

[0041] [Evaluation of the Lithium Deposition Area Ratio] For the samples of Examples 1 to 4 and Comparative Examples 1 and 2, the lithium deposition area on the negative electrode was evaluated as an index of the amount of generated gas staying within the electrode coating area during the cycle. Specifically, each sample was charged until it reached SOC 100%, and then charged and discharged until it reached SOC 10% in a rectangular wave pattern with a discharge current of 1C. After repeating this operation 100 times, the cell was disassembled and the area of lithium deposited on the negative electrode was evaluated. The evaluation results are shown in Fig. 6.

[0042] As shown in Fig. 6, for Comparative Example 1, 10% of the negative electrode coating area was the lithium deposition area. For Comparative Example 2, the lithium deposition area decreased compared to Comparative Example 1 but did not reach a level close to 0%. For Examples 1 to 4, the lithium deposition area was approximately 0% in all cases. From this, it became clear that by providing an inclined portion in the active material layer, the gas generated within the active material layer during repeated charge and discharge can be discharged well.

[0043] Note that the present disclosure is not limited to the above-described embodiments and can be appropriately modified without departing from the gist.

Explanation of Reference Numerals

[0044] 100 Electrode 200 Current Collector 300 Active Material Layer 310 High-Density Portion 320 Inclined Portion 500 Electrode 600 Active Material Layer 610 High-Density Portion 620 Inclined Portion 630 Communication Portion 700 Coating Device 800 Squeegee 900 Negative Electrode Slurry 1000 Metal Frame Portion 1010 Inner Frame 1100 Copper Foil

Claims

1. An electrode comprising a current collector and an active material layer provided on the current collector, wherein the active material layer The basis weight is greater than 20 mg / cm ２ and the coating area is 600 cm ２ or more. has a high-density portion with a high density of the active material provided at the center and an inclined portion with a decreasing density of the active material from the center toward the edge provided at the periphery. Electrode.

2. The active material layer has at least one communication portion that communicates from one side to the opposite side of the active material layer in a part of the active material layer, and the communication portion is any one of a low-density portion with a low density of the active material, a low-binder portion with a low density of the binder, or an oriented portion with the active material oriented in a predetermined direction. The electrode according to claim 1.

3. The current collector is a negative electrode current collector, and the active material layer is a negative electrode active material layer. The electrode according to claim 1.

4. A battery having the electrode according to any one of claims 1 to 3.

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