Electrode sheet and lithium-ion battery

Abstract

The present invention provides an electrode sheet and a lithium-ion battery. The electrode sheet provided in a first aspect of the present invention includes a current collector and a first active layer and a second active layer stacked in order on the surface of the current collector, where a first groove is formed in the first active layer and a second groove is formed in the second active layer, the vertical projection of the second groove onto the current collector covers the vertical projection of the first groove onto the current collector, and a tab is provided in the first groove and electrically connected to the current collector. The electrode sheet provided in the present invention effectively reduces charging risk at the tab connection position and improves the cycle retention rate of the lithium-ion battery under conditions of maintaining high-speed charging.

Description

[Technical Field]

[0001] The present invention relates to an electrode sheet and a lithium ion battery, and to the field of lithium ion battery technology. [Background technology]

[0002] With the continuous development of the 5G era, lithium-ion batteries are becoming increasingly important, which is also driving the development of lithium-ion batteries in the direction of higher energy density and faster charging rates.Currently, by adjusting the tab connection position on the electrode sheet from the edge to the center of the side, the impedance of the lithium-ion battery can be reduced and the charging speed of the lithium-ion battery can be improved.

[0003] However, if the tab position is changed, the current density around the tab increases, and as the lithium ions are cycled, they precipitate, deteriorating the cycle performance of the lithium ion battery. Therefore, how to improve the cycle performance of lithium ion batteries while maintaining high-speed charging has attracted increasing attention. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides an electrode sheet for improving the cycling performance of lithium ion batteries under fast charging. [Means for solving the problem]

[0005] The electrode sheet provided in a first aspect of the present invention includes a current collector, and a first active layer and a second active layer laminated in this order on a surface of the current collector, wherein a first groove is provided in the first active layer, a second groove is provided in the second active layer, and a vertical projection of the second groove onto the current collector covers a vertical projection of the first groove onto the current collector; A tab is provided in the first groove and is electrically connected to the current collector.

[0006] Furthermore, the length of the second groove is greater than the length of the first groove.

[0007] Furthermore, the width of the second groove is the same as the width of the current collector.

[0008] Furthermore, the difference between the length of the second groove and the length of the first groove is 500 mm or less.

[0009] Furthermore, the electrode sheet is a negative electrode sheet, and the negative electrode active material in the second active layer has an average particle size of 10 to 18 μm and a graphitization degree of 86 to 94%.

[0010] Furthermore, the average particle size and degree of graphitization of the negative electrode active material in the first active layer are larger than the average particle size and degree of graphitization of the negative electrode active material in the second active layer.

[0011] Furthermore, the area of ​​the vertical projection of the first groove onto the current collector is greater than the area of ​​the tab connection region on the current collector.

[0012] Furthermore, the width of the first groove is 1 to 2 times the width of the tab connection region.

[0013] Furthermore, the length of the first groove is 1 to 2 times the length of the tab connection region.

[0014] A lithium ion battery provided in a second aspect of the present invention includes the electrode sheet according to any one of the above aspects. [Effects of the Invention]

[0015] The implementation of the present invention has at least the following advantages:

[0016] 1. The present invention provides an electrode sheet that reduces the thickness of the active layer around the tab, thereby effectively reducing the charging risk at the tab connection position and improving the cycle retention rate of lithium-ion batteries under the condition of maintaining high-speed charging.

[0017] 2. The lithium-ion battery provided by the present invention has excellent cycle performance during fast charging. [Brief explanation of the drawings]

[0018] In order to more clearly describe the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces drawings necessary for the description of the embodiments or prior art. The drawings in the following description are some embodiments of the present invention, and it is obvious that a person skilled in the art can obtain other drawings based on these drawings without any creative efforts. [Figure 1a] FIG. 2 is a front view of an electrode sheet provided in one embodiment of the present invention. [Figure 1b] FIG. 2 is a plan view of an electrode sheet provided in one embodiment of the present invention. [Figure 1c] FIG. 2 is a left side view of an electrode sheet provided in one embodiment of the present invention. [Figure 2a] FIG. 10 is a front view of an electrode sheet provided in another embodiment of the present invention. [Figure 2b] FIG. 2 is a plan view of an electrode sheet provided in another embodiment of the present invention. [Figure 3] FIG. 10 is a plan view of an electrode sheet provided in a further embodiment of the present invention. Modes for carrying out the invention

[0019] In order to clarify the objectives, technical solutions and advantages of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the embodiments of the present invention, but it is clear that the described embodiments are only some of the embodiments of the present invention and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without any creative efforts fall within the protection scope of the present invention.

[0020] The electrode sheet provided in a first aspect of the present invention includes a current collector, and a first active layer and a second active layer laminated in this order on a surface of the current collector, wherein a first groove is provided in the first active layer, a second groove is provided in the second active layer, and a vertical projection of the second groove onto the current collector covers a vertical projection of the first groove onto the current collector; A tab is provided in the first groove and is electrically connected to the current collector.

[0021] In the conventional electrode sheet design, grooves are provided on the side surfaces of the first and second active layers, connecting the upper surface of the second active layer with the upper surface of the current collector, so that tabs are provided in the grooves and electrically connected to the current collector exposed in the grooves. The electrode sheet provided in the present application mainly reduces the thickness of the active layer around the tabs to improve the charging risk at the tab connection position. Specifically, FIG. 1a is a front view of an electrode sheet provided in one embodiment of the present invention, and FIG. 1b is a front view of the electrode sheet provided in this embodiment. 1a to 1c are plan views of an electrode sheet provided in one embodiment of the present invention, and FIG. 1c is a left side view of the electrode sheet provided in one embodiment of the present invention. As shown in FIGS. 1a to 1c, the electrode sheet includes a current collector 1, a first active layer 2 provided on the upper surface of the current collector 1, and a second active layer 3 provided on the upper surface of the first active layer 2 away from the current collector 1. A first groove is provided at the center position of the side surface of the first active layer 2, and a second groove is provided in the second active layer 3. A tab 4 is provided between the first groove and the second active layer 3. The electrode sheet is provided in the groove and electrically connected to the current collector 1 (the vertical projection of the tab onto the current collector 1 overlaps with the vertical projection of the first groove onto the current collector 1), and the vertical projection of the second groove onto the current collector covers the vertical projection of the first groove onto the current collector, such that the thickness of the active layer in the area around the tab is lower than the thickness of the active layer away from the tab area. Here, the length of the electrode sheet is the same as the definition of the length of an electrode sheet in the art, i.e., the longest side of the electrode sheet is the length of the electrode sheet, the shortest side is the height of the electrode sheet, and the side between the longest and shortest sides is the width of the electrode sheet. That is, in FIG. 1a, the long side is the length of the electrode sheet, the short side is the height of the electrode sheet, and in FIG. 1b, the short side is the width of the electrode sheet, the value of the long side is the length of the electrode sheet, the value of the high side is the thickness of the electrode sheet, and the value of the width is the width of the electrode sheet, and the first groove and the second groove are the same in the length, width, and thickness directions of the electrode sheet. The electrode sheet provided by the present invention reduces the thickness of the active layer around the tab, thereby effectively reducing the charging risk at the tab connection position and improving the cycle retention rate of lithium-ion batteries under conditions of maintaining high-speed charging.

[0022] In the electrode sheet structure shown in Figures 1a to 1c, a second groove is provided in the second active layer, and therefore, in the actual manufacturing process, blank coating must be performed at the location of the second groove. However, this coating method cannot be directly achieved with conventional coating equipment and coating processes. Therefore, in order to improve the manufacturing efficiency of the second active layer, the width of the second groove can be made wider and the same as the width of the current collector. In this way, a second active layer provided with a second groove can be obtained by skip coating using conventional coating equipment.

[0023] FIG. 2a is a front view of an electrode sheet provided in another embodiment of the present invention, and FIG. 2b is a plan view of the electrode sheet provided in another embodiment of the present invention. As shown in FIGS. 2a-2b, the electrode sheet includes a current collector 1, and a first active layer 2 and a second active layer 3 disposed in that order on the surface of the current collector 1. A first groove is provided at the center of the side of the first active layer 2, and the first groove is connected to a tab 4 in a corresponding region of the current collector 1. A second groove is provided in the second active layer 3, and the width of the second groove is the same as the width of the current collector 1. That is, the second groove divides the second active layer into two independent parts, left and right.

[0024] In order to further improve the cycle performance of the lithium ion battery, the length of the second groove is greater than the length of the first groove. Research into the lengths of the first and second grooves has revealed that as the length of the second groove increases, the cycle performance of the lithium ion battery gradually improves. In order to achieve both the energy density and cycle performance of the lithium ion battery, the difference between the length of the second groove and the length of the first groove is 500 mm or less.

[0025] The length and width of the first groove are specifically determined according to the tab, and those skilled in the art can determine the length and width of the first groove according to the design and needs of the actual electrode sheet.

[0026] When the electrode sheet is a negative electrode sheet, the average particle size of the negative electrode active material in the second active layer is 10 to 18 μm, and the graphitization degree is 86 to 94%, in order to provide the lithium ion battery with rapid charging performance.

[0027] Furthermore, since the compaction density of fast-charging graphite is limited, this can lead to a decrease in the energy density of the lithium-ion battery. In order to achieve both the energy density and fast-charging performance of the lithium-ion battery, general graphite is selected as the negative electrode active material in the first active layer. Specifically, the average particle size and graphitization degree of the negative electrode active material in the first active layer are larger than those of the negative electrode active material in the second active layer. For example, when the average particle size and graphitization degree of the negative electrode active material in the second active layer are 10 to 18 μm and 86 to 94%, the average particle size and graphitization degree of the negative electrode active material in the first active layer are 12 to 30 μm and 90 to 98%.

[0028] According to the structure of the electrode sheet, in the process of manufacturing the negative electrode sheet, the negative electrode active material can be combined with an adhesive, a conductive agent, and a thickener to prepare a first negative electrode active layer slurry, which can be applied to the surface of the current collector to obtain the first active layer; then, a second negative electrode active layer slurry can be prepared, and the second negative electrode active material can be applied to the surface of the first active layer far from the current collector; during the application process, a blank application needs to be performed in the area corresponding to the second groove to obtain the second active layer including the second groove; finally, the central area of ​​the side of the first active layer is washed to obtain the first groove, and a tab is placed in the first groove to obtain the negative electrode sheet, where the negative electrode active material can be selected from the group consisting of artificial graphite, natural graphite, and modified graphite. The adhesive may include at least one of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, and styrene-butadiene rubber (SBR), the conductive agent may include at least one of conductive carbon black, carbon nanotubes, conductive graphite, and graphene, and the thickener may include sodium carboxymethyl cellulose.

[0029] The electrode sheet provided in the present invention can also be applied to a positive electrode sheet, and specific manufacturing methods can be referenced for the negative electrode sheet. The difference lies in the materials used. Specifically, the current collector may be aluminum foil, and the positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium-rich manganese-based material, and lithium nickel cobalt aluminate.

[0030] In actual manufacturing, the area of ​​the vertical projection of the first groove onto the current collector can be made larger than the area of ​​the tab connection region on the current collector to facilitate connection between the tab and the current collector.

[0031] Here, the tab connection area of ​​the current collector refers to the vertical projection area of ​​the tab onto the current collector. FIG. 3 is a plan view of an electrode sheet provided in a further embodiment of the present invention. As shown in FIG. 3, the vertical projection area of ​​the first groove onto the current collector is greater than the area of ​​the tab connection area on the current collector.

[0032] Furthermore, the width of the first groove is 1 to 2 times the width of the tab connection region.

[0033] Furthermore, the length of the first groove is 1 to 2 times the length of the tab connection region.

[0034] As described above, the present invention provides an electrode sheet that reduces the thickness of the active layer around the tab, thereby effectively reducing the charging risk at the tab connection position and improving the cycle retention rate of lithium-ion batteries under conditions of maintaining high-speed charging.

[0035] A second aspect of the present invention provides a lithium ion battery including any one of the above electrode sheets.

[0036] The present invention provides a lithium ion battery, and those skilled in the art can manufacture a lithium ion battery based on the electrode sheet provided by the present invention in conjunction with conventional techniques. The lithium ion battery provided by the present invention has excellent cycle performance in high-speed charging.

[0037] The following description will be given in connection with specific examples. Example 1

[0038] The front view of the electrode sheet provided in this example is shown in FIG. 2a, the plan view is shown in FIG. 3, and the left side view is shown in FIG. 1c, where: The current collector is copper foil and has a width of 81 mm. The first groove has a width of 25 mm and a length of 10 mm; The second groove is 81 mm wide and 30 mm long.

[0039] When the electrode sheet is a positive electrode sheet, the first active layer and the second active layer contain, in mass percentages, 97 parts by mass of lithium cobalt oxide, 1.5 parts by mass of PVDF, and 1.5 parts by mass of a carbon black conductive agent; When the electrode sheet is a negative electrode sheet, the first active layer and the second active layer each contain 97 parts by mass of graphite, 0.7 parts by mass of carbon black, 1.3 parts by mass of styrene butadiene rubber, and 1 part by mass of sodium carboxymethyl cellulose, where the negative electrode active material in the first active layer has an average particle size of 18 μm and a graphitization degree of 96%, and the negative electrode active material in the second active layer has an average particle size of 15 μm and a graphitization degree of 92%. Example 2

[0040] The front view of the electrode sheet provided in this example is shown in FIG. 2a, the plan view is shown in FIG. 3, and the left side view is shown in FIG. 1c, where: The current collector is copper foil and has a width of 81 mm. The first groove has a width of 25 mm and a length of 10 mm; The second groove is 81 mm wide and 40 mm long.

[0041] When the electrode sheet is a positive electrode sheet or a negative electrode sheet, the materials of the first active layer and the second active layer are the same as those in Example 1. Example 3

[0042] The front view of the electrode sheet provided in this example is shown in FIG. 2a, the plan view is shown in FIG. 3, and the left side view is shown in FIG. 1c, where: The current collector is copper foil and has a width of 81 mm. The first groove has a width of 25 mm and a length of 10 mm; The second groove is 81 mm wide and 50 mm long.

[0043] When the electrode sheet is a positive electrode sheet or a negative electrode sheet, the materials of the first active layer and the second active layer are the same as those in Example 1. Example 4

[0044] The front view of the electrode sheet provided in this example is shown in FIG. 2a, the plan view is shown in FIG. 3, and the left side view is shown in FIG. 1c, where: The current collector is copper foil and has a width of 81 mm. The first groove has a width of 25 mm and a length of 10 mm; The second groove is 81 mm wide and 60 mm long.

[0045] When the electrode sheet is a positive electrode sheet or a negative electrode sheet, the materials of the first active layer and the second active layer are the same as those in Example 1. Example 5

[0046] The front view of the electrode sheet provided in this example is shown in FIG. 2a, the plan view is shown in FIG. 3, and the left side view is shown in FIG. 1c, where: The current collector is copper foil and has a width of 81 mm. The first groove has a width of 25 mm and a length of 10 mm; The second groove is 81 mm wide and 70 mm long.

[0047] When the electrode sheet is a positive electrode sheet or a negative electrode sheet, the materials of the first active layer and the second active layer are the same as those in Example 1. Example 6

[0048] The front view of the electrode sheet provided in this example is shown in FIG. 2a, the plan view is shown in FIG. 3, and the left side view is shown in FIG. 1c, where: The current collector is copper foil and has a width of 81 mm. The first groove has a width of 25 mm and a length of 10 mm; The second groove is 81 mm wide and 30 mm long.

[0049] When the electrode sheet is a positive electrode sheet or a negative electrode sheet, the materials of the first active layer and the second active layer can refer to Example 1, except that the average particle size of the negative electrode active material in the second active layer is 15 μm and the graphitization degree is 94%. Example 7

[0050] The front view of the electrode sheet provided in this example is shown in FIG. 2a, the plan view is shown in FIG. 3, and the left side view is shown in FIG. 1c, where: The current collector is copper foil and has a width of 81 mm. The first groove has a width of 25 mm and a length of 10 mm; The second groove is 81 mm wide and 30 mm long.

[0051] When the electrode sheet is a positive electrode sheet or a negative electrode sheet, the materials of the first active layer and the second active layer can refer to Example 1, except that the average particle size of the negative electrode active material in the second active layer is 15 μm and the graphitization degree is 90%. Example 8

[0052] The front view of the electrode sheet provided in this example is shown in FIG. 2a, the plan view is shown in FIG. 3, and the left side view is shown in FIG. 1c, where: The current collector is copper foil and has a width of 81 mm. The first groove has a width of 25 mm and a length of 10 mm; The second groove is 81 mm wide and 30 mm long.

[0053] When the electrode sheet is a positive electrode sheet or a negative electrode sheet, the materials of the first active layer and the second active layer can refer to Example 1, except that the average particle size of the negative electrode active material in the second active layer is 10 μm and the graphitization degree is 90%. Comparative Example 1

[0054] The electrode sheet provided in this comparative example includes a current collector, a first active layer, and a second active layer, and a recessed groove is provided at the center of the side surface of the first active layer and the second active layer, wherein: The current collector is copper foil and has a width of 81 mm. The groove is 25 mm wide and 10 mm long.

[0055] When the electrode sheet is a positive electrode sheet or a negative electrode sheet, the materials of the first active layer and the second active layer are the same as those in Example 1.

[0056] The positive electrode sheets and negative electrode sheets provided in Examples 1 to 8 and Comparative Example 1 of the present invention were combined with separators and electrolytes to manufacture lithium ion batteries, and the cycle capacity retention rates of the lithium ion batteries were measured.

[0057] Here, the positive electrode active material was purchased from Xiamen Xiamen Tungsten New Energy Materials Co., Ltd., the negative electrode active material was purchased from Shanghai Shanshan Technology Co., Ltd., the separator was purchased from Dongguan Zhuogao Electronics Technology Co., Ltd., and the electrolyte was purchased from Shenzhen Capchem Technology (Shenzhen New Space Technology Co., Ltd.).

[0058] The performance measurement method for lithium-ion batteries is as follows. For the lithium ion batteries provided in Examples 1 to 8 and Comparative Example 1, 500 charge / discharge cycle measurements were performed at 2C / 0.7C under conditions of 25°C, and then the cycle retention rate (%) was calculated. The measurement results are shown in Table 1.

[0059] [Table 1]

[0060] As can be seen from Table 1, the lithium ion batteries provided in Examples 1 to 8 all have excellent cycle capacity retention, and as can be seen from the data provided in Examples 1 to 5, as the length of the second grooves increases, the cycle performance of the lithium ion battery improves accordingly, and as can be seen from the data provided in Examples 6 to 8, as the graphitization degree and average particle size of the active material in the second active layer decrease, the cycle retention of the lithium ion battery improves. As can be seen from the above, the lithium ion batteries provided by the present invention have excellent cycle performance during fast charging.

[0061] Finally, the above embodiments are only used to explain the technical solutions of the present invention, and are not intended to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art will understand that they can still modify the technical solutions described in the above embodiments, or equivalently replace some or all of the technical features therein, and these modifications or replacements will not cause the essence of the corresponding technical solutions to depart from the scope of the technical solutions of the embodiments of the present invention.

[0062] This application claims priority to a Chinese patent application filed with the China Patent Office on December 30, 2020, bearing application number 202011631163.1 and entitled "Electrode Sheet and Lithium-Ion Battery," the entire contents of which are incorporated herein by reference. [Explanation of symbols]

[0063] 1. Current collector 2. First active layer 3. Second active layer 4. Tab

Claims

1. An electrode sheet including a current collector and a first active layer and a second active layer laminated in this order on a surface of the current collector, the second active layer is provided on a side of the first active layer farther from the top surface of the current collector, wherein a first groove is provided in the first active layer, a second groove is provided in the second active layer, a vertical projection of the second groove onto the current collector covers a vertical projection of the first groove onto the current collector, a length of the second groove is longer than a length of the first groove, and a difference between the lengths of the second groove and the first groove is 500 mm or less; a tab disposed in the first groove and electrically connected to the current collector; the electrode sheet is a negative electrode sheet, and the average particle size and graphitization degree of the negative electrode active material in the first active layer are larger than the average particle size and graphitization degree of the negative electrode active material in the second active layer; An electrode sheet for a lithium ion battery.

2. The width of the second groove is the same as the width of the current collector.

2. The electrode sheet for a lithium ion battery according to claim 1 .

3. the average particle size of the negative electrode active material in the second active layer is 10 to 18 μm and the degree of graphitization is 86 to 94%; 3. The electrode sheet for a lithium ion battery according to claim 1 or 2.

4. an area of ​​the first groove vertically projected onto the current collector is greater than an area of ​​the tab connection region on the current collector; The electrode sheet for a lithium ion battery according to any one of claims 1 to 3.

5. The width of the first groove is 1 to 2 times the width of the tab connection area; 5. The electrode sheet for a lithium ion battery according to claim 4.

6. The length of the first groove is 1 to 2 times the length of the tab connection area; 5. The electrode sheet for a lithium ion battery according to claim 4.

7. The lithium ion battery electrode sheet according to any one of claims 1 to 6 is included. A lithium-ion battery characterized by:

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