Electrode and battery

Abstract

The invention discloses an electrode and a battery. An electrode according to the present disclosure is provided with a current collector and an active material layer provided on the current collector, the active material layer having a weight per unit area of more than 20 mg / cm2, a coating area of 600 cm2 or more, a high-density portion in which the density of an active material is high being provided in the center, and an inclined portion in which the density of the active material decreases from the center toward an edge portion being provided on the periphery.

Description

Technical Field

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

[0002] In a battery having an electrode with an active material layer provided on the surface of a current collector, it is required to improve the electrolyte wettability with respect to the active material layer.

[0003] For example, in Japanese Unexamined Patent Application Publication No. 2019-169391, a technique is disclosed in which the density of the active material is reduced at the periphery of the active material layer in order to improve the electrolyte wettability with respect to the active material layer. Summary of the Invention

[0004] The inventors have found the following problems regarding the electrode and the battery.

[0005] When the thickness and coating area of the active material layer are large, it is more difficult to sufficiently infiltrate 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 techniques for improving the electrolyte wettability with respect to the active material layer.

[0006] 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 improve the electrolyte wettability with respect to the active material layer.

[0007] One aspect for achieving the above object is an electrode including: a current collector; and an active material layer provided on the current collector, with respect to the active material layer, the weight per unit area is greater than 20 mg / cm 2 and the coating area is 600 cm 2 or more, a high-density portion having a high density of the active material is provided at the center, and an inclined portion having a decreasing density of the active material from the center toward the edge is provided at the periphery.

[0008] One aspect for achieving the above object is a battery including the above electrode.

[0009] According to the present disclosure, it is possible to provide an electrode and a battery that further improve the electrolyte wettability with respect to the active material layer. Brief Description of the Drawings

[0010] Hereinafter, features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described with reference to the drawings, in which like reference numerals denote like elements, where: Figure 1 is a schematic view of the electrode according to Embodiment 1.

[0011] Figure 2 It is a schematic diagram of the electrode related to Embodiment 2.

[0012] Figure 3A It is a schematic diagram showing the structure of a coating device used when manufacturing a sample of a negative electrode.

[0013] Figure 3B It is a schematic diagram of other front-end shapes of a doctor blade.

[0014] Figure 4A It is a schematic diagram showing the negative electrodes of Examples 1 to 2 and Comparative Examples 1 to 2.

[0015] Figure 4B It is a graph showing the distribution of the weight per unit area during slurry coating for the samples of Examples 1 to 2 and Comparative Examples 1 to 2.

[0016] Figure 4C It is a graph showing the distribution of the negative electrode density after stamping for the samples of Examples 1 to 2 and Comparative Examples 1 to 2.

[0017] Figure 5 It is a chart showing the liquid retention rate of the negative electrode of each sample.

[0018] Figure 6 It is a chart showing the proportion of the Li precipitation area of each sample. Detailed Embodiments

[0019] 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 given the same reference numerals, and repeated descriptions are omitted as necessary to clarify the description. In addition, for ease of understanding, the scales of the respective parts in the drawings are sometimes different from the actual ones. In directions such as parallel, right-angled, orthogonal, horizontal, vertical, up and down, left and right, etc., offsets to the extent that do not impair the effects of the embodiments are allowed. In parallel, right-angled, orthogonal, horizontal, and vertical, it may also include substantially parallel, substantially right-angled, substantially orthogonal, substantially horizontal, and substantially vertical. In addition, in this specification, "substantially" means a state where the shapes and sizes are regarded as the same when observed by a person.

[0020] Embodiment 1 First, with reference to Figure 1 , the structure of the electrode 100 related to Embodiment 1 will be described. The electrode 100 is an electrode for a battery. Specifically, the electrode 100 is an electrode for a lithium-ion secondary battery. The structure of the battery having the electrode 100 is not particularly limited. The battery having the electrode 100 can be configured, for example, as a laminated battery or as a square battery. Hereinafter, the case where the battery having the electrode 100 is configured as a laminated battery will be described.

[0021] The laminated battery having the electrode 100 includes an electrode body, an electrolyte, external terminals, and a laminated exterior body. The electrode body and the electrolyte function as power generation elements of the laminated battery. The electrode body and the electrolyte are sealed inside the laminated exterior body.

[0022] The structure of the electrode body may be a known structure and is not particularly limited. The electrode body is a laminated electrode body, having one or more sheets of a sheet-like positive electrode body and negative electrode body, typically having a plurality of each. The positive electrode body and the negative electrode body are alternately laminated in a mutually insulated state.

[0023] Typically, the positive electrode body includes a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector. As the positive electrode current collector, for example, aluminum is used. 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.

[0024] Typically, the negative electrode body includes a negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector. As the negative electrode current collector, for example, copper is used. 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.

[0025] A separator may also 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.

[0026] The structure of the electrolyte may be a known structure and is not particularly limited. The electrolyte may be liquid, may be polymer-like i.e., gel-like, or may also be solid. As an example, the electrolyte may also contain a non-aqueous solvent and a supporting salt such as a lithium salt that generates charge carriers.

[0027] In the electrode body, current collector tabs are provided. The current collector tabs are a positive electrode current collector tab and a negative electrode current collector tab. Specifically, the positive electrode current collector tab extends outward from the positive electrode current collector included in the positive electrode body. The negative electrode current collector tab extends outward from the negative electrode current collector included in the negative electrode body. The current collector tabs are exposed without an active material layer. For example, the positive electrode current collector tab and the negative electrode current collector tab may also extend from both short sides of each other.

[0028] The external terminals are formed in a plate shape. The external terminals are electrically connected to the current collector tabs by being joined to the current collector tabs. Specifically, the positive electrode external terminal further extends outward from the vicinity of the front end of the positive electrode current collector tab and is exposed to the outside from the laminated exterior body. The positive electrode external terminal is, for example, a thin aluminum plate. The negative electrode external terminal further extends outward from the vicinity of the front end of the negative electrode current collector tab and is exposed to the outside from the laminated exterior body. The negative electrode external terminal is, for example, a thin copper plate.

[0029] The positive electrode external terminal and the positive electrode current collector tab are joined to each other at the joint portion. Further, the negative electrode external terminal and the negative electrode current collector tab are joined to each other at the joint portion. The joining method of the joint portion may be, for example, resistance welding. In addition, the joining method of the joint portion is not particularly limited, and may be laser welding or ultrasonic joining, etc.

[0030] Figure 1 The front view showing the electrode 100 according to Embodiment 1 is shown. The electrode 100 is a positive electrode body or a negative electrode body constituting the electrode body. As Figure 1 shown, 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 coating a slurry containing an active material and a binder onto the current collector 200 and then stamping. As Figure 1 shown, the active material layer 300 is formed in a rectangular shape on the current collector 200. In addition, the weight per unit area of the active material layer 300 is greater than 20 mg / cm 2 and the coating area is 600 cm 2 or more.

[0031] In the center of the active material layer 300, a high-density portion 310 is provided. The high-density portion 310 is a region where the density of the active material is greater than that of other regions. On the periphery of the active material layer 300, that is, in a portion other than the high-density portion 310, an inclined portion 320 is provided. The inclined portion 320 is a portion where the density of the active material gradually decreases from the center toward the edge portion.

[0032] Chart I is a chart schematically showing the density of the active material in the active material layer 300. As shown in Chart I, 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 portion in the peripheral portion, that is, the inclined portion 320.

[0033] Since the inclined portion 320 is provided in the active material layer 300 of the electrode 100, even when the weight per unit area and the coating area of the active material layer 300 are large, the electrolyte can be sufficiently infiltrated into the entire active material layer 300. Therefore, the battery having the electrode 100 suppresses a decrease in charge-discharge efficiency and suppresses gas generation. Therefore, the battery having the electrode 100 suppresses an increase in resistance caused by an expansion between the electrodes and suppresses a decrease in durability caused by Li precipitation.

[0034] Embodiment 2 Next, refer to Figure 2, describe the structure of the electrode 500 involved in Embodiment 2. Figure 2 A front view of the electrode 500 involved in Embodiment 2 is shown. The difference between the electrode 500 and Figure 1 the electrode 100 shown is that it has 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. The structures of the high-density portion 610 and the inclined portion 620 are the same as those of the high-density portion 310 and the inclined portion 320 shown, so the description thereof is omitted. As Figure 1 shown, the communication portion 630 is provided to communicate from a part of one side of the active material layer 600 to a part of the opposite side. The communication portion 630 may be provided with one or more. Figure 2

[0035] The communication portion 630 is any one of a low-density portion, a low-binder portion, and an orientation 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. Chart II is a chart 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 improved, and it is easy to discharge the gas generated in the center of the active material layer 600.

[0036] 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. In the low-binder portion, there are more voids between the active materials than in other regions. Therefore, by providing the low-binder portion, the same effects as in the case of providing the low-density portion are obtained.

[0037] The orientation portion is a region that orients the active material contained in the active material layer 600 in a predetermined direction. In the orientation portion, the cross-sectional area of the voids per particle of the active material is averaged. Therefore, by providing the orientation portion, the same effects as in the case of providing the low-density portion or the low-binder portion are obtained.

[0038] Hereinafter, the present disclosure will be described in detail based on examples. In addition, the present disclosure is not limited thereto.

[0039] Fabrication of Samples As samples involved in the examples and comparative examples, samples were fabricated by the following method.

[0040] Figure 3A is a schematic diagram showing the structure of a coating device 700 used when fabricating samples of the negative electrode. The coating device 700 includes a doctor blade 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 the negative electrode paste 900 placed on the metal frame portion 1000 onto the copper foil 1100 using the doctor blade 800.Figure 3A The arrow shown indicates the moving direction of the squeegee 800, which is the coating direction of the negative electrode paste. An inner frame 1010 is provided in the metal frame portion 1000. The inner frame 1010 forms the wall of a through-hole having a size and shape corresponding to the size and shape of the area where the paste is coated. In this embodiment, the size of the inner frame is 30 cm × 50 cm. When performing screen printing, the copper foil 1100 is arranged under the metal frame portion 1000 such that the inner frame 1010 is located in the negative electrode paste coating area, and the negative electrode paste 900 is coated.

[0041] Figure 3A The enlarged view of the lower part is a schematic diagram of the front-end shape of the squeegee 800. By using the squeegee 800 with both ends inclined as shown in the enlarged view, a copper foil is obtained on which the negative electrode paste is coated in such a way that the central part has a high unit area weight and the unit area weights at both ends are inclined. Next, a negative electrode is produced by stamping the copper foil coated with the negative electrode paste. A laminated battery with a capacity of 10 Ah is produced using the produced negative electrode. The sample thus obtained is taken as Example 1.

[0042] Figure 3B is a schematic diagram of another front-end shape of the squeegee 800. By using the squeegee 800 with both ends inclined and having a depression in the central part as shown in Figure 3B a copper foil is obtained on which the negative electrode paste is coated in such a way that the central part has a high unit area weight, the unit area weights at both ends are inclined, and a part of the central part has a low unit area weight. Next, a negative electrode is produced by stamping the copper foil coated with the negative electrode paste. A laminated battery with a capacity of 10 Ah is produced using the produced negative electrode. The sample thus obtained is taken as Example 2.

[0043] By using a squeegee with no inclination at both ends, i.e., a straight-line-shaped front end, a copper foil is obtained on which the negative electrode paste is coated in such a way that the unit area weight is constant in all areas. Next, a negative electrode is produced by stamping the copper foil coated with the negative electrode paste. A laminated battery with a capacity of 10 Ah is produced using the produced negative electrode. The sample thus obtained is taken as Comparative Example 1.

[0044] By using a squeegee with depressions at both ends, a copper foil is obtained on which the negative electrode paste is coated in such a way that both end parts have a low unit area weight and the other parts have a high unit area weight. Next, a negative electrode is produced by stamping the copper foil coated with the negative electrode paste. A laminated battery with a capacity of 10 Ah is produced using the produced negative electrode. The sample thus obtained is taken as Comparative Example 2.

[0045] Figure 4A is a schematic diagram showing the negative electrodes of Examples 1 to 2 and Comparative Examples 1 to 2. Figure 4BSamples of Examples 1 to 2 and Comparative Examples 1 to 2 show the distribution of the weight per unit area during slurry coating. Figure 4B The a to i shown correspond to Figure 4A the locations a to i shown. As Figure 4B shown, in any of Examples 1 to 2 and Comparative Examples 1 to 2, the slurry was coated with a weight per unit area corresponding to the front-end shape of the doctor blade. Figure 4C Samples of Examples 1 to 2 and Comparative Examples 1 to 2 show the distribution of the negative electrode density after stamping. Figure 4C The a to i shown correspond to Figure 4A the locations a to i shown. As Figure 4C shown, in any of Examples 1 to 2 and Comparative Examples 1 to 2, the negative electrode was made with a negative electrode density corresponding to the weight per unit area of the slurry.

[0046] After screen printing using a metal frame portion provided with two adjacent inner frames of the same shape, a low adhesive slurry was coated in a groove portion provided at a position corresponding to the gap between the inner frames. Next, by stamping the copper foil coated with the slurry, a negative electrode having one communication portion provided in the active material layer was fabricated. The fabricated negative electrode has the same coating area of the active material layer as that of Examples 1 to 2. In addition, the negative electrode slurry coated on the portion corresponding to the part other than the communication portion contains 3 wt% of SBR (styrene-butadiene rubber). The negative electrode slurry coated on the portion corresponding to the communication portion contains 1 wt% of SBR. A laminated battery with a capacity of 10 Ah was fabricated using the fabricated negative electrode. The sample thus obtained was taken as Example 3.

[0047] After coating a negative electrode slurry on a copper foil using a doctor blade having the shape shown in the lower enlarged view of Figure 3A , a magnetic field with a magnetic flux density of 0.3 T was applied for 60 seconds at the central portion of the negative electrode slurry, which corresponds to the communication portion of the active material layer. Next, a negative electrode was fabricated by stamping the copper foil coated with the slurry. A laminated battery with a capacity of 10 Ah was fabricated using the fabricated negative electrode. The sample thus obtained was taken as Example 4.

[0048] Evaluation of the negative electrode liquid retention rate For the samples of Examples 1 to 4 and Comparative Examples 1 to 2, the initial state unit was disassembled, and the liquid retention rate of the negative electrode was evaluated. Figure 5 The evaluation results are shown.

[0049] As Figure 5As shown, at the end of the negative electrode, in any of Examples 1 to 4 and Comparative Examples 1 to 2, the liquid retention rate is at a level close to 100%. On the other hand, in the central part of the negative electrode, the liquid retention rates of Examples 1 to 4 are higher than those of Comparative Examples 1 to 2. In particular, in Examples 2 to 4, the liquid retention rate in the central part of the negative electrode is at a level close to 100%. Thus, it was clarified that by providing an inclined portion in the active material layer, the liquid retention rate in the central part of the active material layer can be increased. In addition, it was clarified that by providing a communication portion in the active material layer, the liquid retention rate in the central part of the active material layer can be further increased.

[0050] Evaluation of Li precipitation area ratio Regarding the samples of Examples 1 to 4 and Comparative Examples 1 to 2, as an index of the amount of gas generated during cycling remaining within the electrode coating area, the Li precipitation area in the negative electrode was evaluated. Specifically, each sample was charged until it reached SOC 100%, and charge and discharge were performed with a rectangular wave pattern of a discharge current of 1C until it reached SOC 10%. After repeating this operation 100 times, the cell was disassembled, and the area of Li precipitated on the negative electrode was evaluated. Figure 6 The evaluation results are shown.

[0051] As Figure 6 shown, regarding Comparative Example 1, 10% of the negative electrode coating area is the Li precipitation area. Regarding Comparative Example 2, although the Li precipitation area decreased compared to Comparative Example 1, it did not reach a level close to 0%. Regarding Examples 1 to 4, the Li precipitation area was approximately 0%. Thus, it was clarified that by providing an inclined portion in the active material layer, the gas generated in the active material layer can be discharged well during repeated charge and discharge.

[0052] In addition, the present disclosure is not limited to the above-described embodiments, and can be appropriately changed without departing from the gist.

Claims

1. An electrode comprising: a current collector; and An active material layer is disposed on the current collector. Regarding the active material layer, Weight per unit area greater than 20 mg / cm 2 , and the coating area is 600cm 2 above, A high-density portion where the density of the active material is high 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.

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

3. The electrode according to claim 1, wherein The current collector is a negative electrode current collector, and the active material layer is a negative electrode active material layer. 4 . A battery comprising the electrode according to claim 1 .

Images