Pole piece assembly and battery

Abstract

The utility model discloses a pole piece assembly and a battery. The pole piece assembly comprises an anode piece and a cathode piece, the anode piece comprises a first edge part, a second edge part and a first middle part, the first edge part and the second edge part are oppositely arranged on the two sides of the first middle part, the cathode piece comprises a third edge part, a fourth edge part and a second middle part, and the third edge part and the fourth edge part are oppositely arranged on the two sides of the second middle part. The surface density of the first edge part of the anode plate is greater than that of the first middle part, and the surface density of the third edge part of the cathode plate is smaller than that of the second middle part. According to the pole piece assembly, the surface density of the edge of the anode piece is high, and compared with the first middle part, the edge of the anode piece can provide more embedding points for lithium ions; the surface density of the edge of the cathode piece is low, compared with the second middle part, the number of lithium ions provided by the edge of the cathode piece is smaller, and the lithium separation risk in the charging and discharging process of the lithium ion battery is greatly reduced through cooperation of the anode piece and the cathode piece.

Description

Technical Field

[0001] The utility model relates to the technical field of batteries, in particular to a pole piece assembly and a battery. Background Art

[0002] As a new type of secondary battery, lithium-ion batteries have the advantages of high energy density and power density, high operating voltage, light weight, small size, long cycle life, good safety, and green environmental protection. Lithium-ion batteries have broad application prospects in portable appliances, power tools, large-scale energy storage, and electric transportation power sources. However, in the prior art, a uniform coating is generally provided on the pole piece, and there are kinetic differences between the cathode and anode pieces of lithium-ion batteries. During the long-term charge and discharge cycle of lithium-ion batteries, lithium deposition is very likely to occur at the edges of the cathode and anode pieces. Especially in the late stage of the cycle, lithium deposition is serious at the head and tail of the negative electrode of the lithium-ion battery, and the cycle attenuation is obvious. The lithium deposition problem of the pole piece will seriously affect the stability of the long-term cycle of the lithium-ion battery. Utility Model Content

[0003] The main purpose of the utility model is to provide a pole piece assembly and a battery, which can greatly reduce the risk of lithium plating of lithium-ion batteries.

[0004] To achieve the above-mentioned purpose, the utility model proposes a pole piece assembly, which includes an anode piece and a cathode piece. The anode piece includes a first current collector and a first active layer, the first active layer is coated on the first surface of the first current collector, the first active layer includes a first side portion, a second side portion and a first middle portion, the first side portion and the second side portion are relatively arranged on both sides of the first middle portion, and the first side portion is adjacent to the empty foil area of ​​the first current collector. The cathode piece includes a second current collector and a second active layer, the second active layer is coated on the second surface of the second current collector, the second active layer includes a third side portion, a fourth side portion and a second middle portion, the third side portion and the fourth side portion are relatively arranged on both sides of the second middle portion, and the third side portion is adjacent to the empty foil area of ​​the second current collector. Among them, the active material of the first side portion has a first surface density a, the active material of the first middle portion has a second surface density b, and the first surface density a and the second surface density b satisfy: a>b; the active material of the third side portion has a third surface density c, the active material of the second middle portion has a fourth surface density d, and the third surface density c and the fourth surface density d satisfy: c<d.

[0005] In some embodiments, the first surface density a and the second surface density b satisfy: 101%b≤a≤105%b.

[0006] In some embodiments, the third areal density c and the fourth areal density d satisfy: 97.5% d≤c≤99.5% d.

[0007] In some embodiments, along a direction perpendicular to the first surface, the first side portion has a first thickness e, the first middle portion has a second thickness f, and the first thickness e and the second thickness f satisfy: 0.5um≤ef≤2um.

[0008] In some embodiments, along a direction perpendicular to the second surface, the third side portion has a third thickness g, the second middle portion has a fourth thickness h, and the third thickness g and the fourth thickness h satisfy: 0.5um≤hg≤2um.

[0009] In some embodiments, the first side has a first thickness e along a direction perpendicular to the first surface, and the third side has a third thickness g along a direction perpendicular to the second surface. The first thickness e and the third thickness g satisfy: 1.2≤e / g≤2.

[0010] In some embodiments, the first side has a first width i along a direction parallel to the first surface, and the third side has a second width j along a direction parallel to the second surface. The first width i and the second width j satisfy: 1.2um≤ij≤1.5um.

[0011] In some embodiments, the active material on the second side has a fifth surface density m, the active material on the first middle portion has a second surface density b, and the fifth surface density m and the second surface density b satisfy: m>b; the active material on the fourth side has a sixth surface density n, the active material on the second middle portion has a fourth surface density d, and the sixth surface density n and the fourth surface density d satisfy: n<d.

[0012] In some embodiments, the first surface density a and the fifth surface density m satisfy: 0.9925≤a / m≤1.005.

[0013] In some embodiments, the third surface density c and the sixth surface density n satisfy: 0.9925≤c / n≤1.005.

[0014] On the other hand, the present application further provides a battery, which includes the pole piece assembly of any of the above embodiments.

[0015] Compared with the prior art, the beneficial effects of the utility model are:

[0016] In the technical solution of the present application, the pole piece assembly includes an anode piece and a cathode piece, the first side and the second side of the anode piece are relatively arranged on both sides of the first middle part, and the third side and the fourth side of the cathode piece are relatively arranged on both sides of the second middle part. The surface density of the first side of the anode piece is greater than the surface density of the first middle part, and the surface density of the third side of the cathode piece is less than the surface density of the second middle part. The edge surface density of the anode piece in the pole piece assembly is high, and compared with the first middle part, the edge of the anode piece can provide more embedding points for lithium ions; the edge surface density of the cathode piece is low, and compared with the second middle part, the edge of the cathode piece provides less lithium ions. The cooperation between the anode piece and the cathode piece can greatly improve the lithium plating problem of the lithium-ion battery, greatly reduce the risk of lithium plating, and greatly reduce the capacity loss of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0018] Figure 1 This is a schematic diagram of the structure of the anode sheet in one embodiment of the utility model;

[0019] Figure 2 for Figure 1 A partial cross-sectional schematic diagram at AA of FIG.

[0020] Figure 3 This is a schematic diagram of the structure of a cathode sheet in one embodiment of the utility model;

[0021] Figure 4 for Figure 3 A schematic partial cross-sectional view at BB of FIG.

[0022] Description of Figure Numbers:

[0023] Pole piece assembly 100;

[0024] Anode sheet 110; first current collector 111; first surface 112; first active layer 113; first side portion 1131; second side portion 1132; first middle portion 1133;

[0025] Cathode sheet 120; second current collector 121; second surface 122; second active layer 123; third side 1231; fourth side 1232; second middle part 1233;

[0026] first thickness e;

[0027] second thickness f;

[0028] The third thickness g;

[0029] fourth thickness h;

[0030] first width i;

[0031] The second width j.

[0032] The realization of the purpose, functional features and advantages of the utility model will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0034] As a new type of secondary battery, lithium-ion batteries have the advantages of high energy density and power density, high operating voltage, light weight, small size, long cycle life, good safety, and green environmental protection. Lithium-ion batteries have broad application prospects in portable appliances, power tools, large-scale energy storage, and electric transportation power sources. However, in the prior art, there are kinetic differences between the cathode and anode sheets of lithium-ion batteries. During the long-term charge and discharge cycle of lithium-ion batteries, lithium deposition is very likely to occur at the edges of the cathode and anode sheets. Especially in the late stage of the cycle, lithium deposition is serious at the head and tail of the negative electrode of the lithium-ion battery, and the cycle attenuation is obvious. The lithium deposition problem of the electrode sheet will seriously affect the stability of the long-term cycle of the lithium-ion battery.

[0035] To solve the above technical problems, Figures 1 to 4 As shown, the present application proposes a pole piece assembly 100 , which includes an anode piece 110 and a cathode piece 120 .

[0036] like Figure 1As shown, the anode sheet 110 includes a first current collector 111 and a first active layer 113. The first active layer 113 is coated on the first surface 112 of the first current collector 111. The first active layer 113 includes a first side portion 1131, a second side portion 1132 and a first middle portion 1133. The first side portion 1131 and the second side portion 1132 are relatively arranged on both sides of the first middle portion 1133, and the first side portion 1131 is adjacent to the empty foil area of ​​the first current collector 111. It can be understood that the first active layer 113 is coated on the surface of the first current collector 111. In order to connect with the pole tab, the first current collector 111 is generally provided with an empty foil area for connecting with the pole tab. Further, in the zebra-coated pole sheet structure, the pole sheet is composed of multiple empty foil areas and multiple independent active layer areas to achieve full utilization of materials. That is, the first side portion 1131 and the second side portion 1132 of the first active material layer may be adjacent to the empty foil area, and the first middle portion 1133 is disposed between the first side portion 1131 and the second side portion 1132 .

[0037] like Figure 3 As shown, the cathode sheet 120 includes a second current collector 121 and a second active layer 123, the second active layer 123 is coated on the second surface 122 of the second current collector 121, the second active layer 123 includes a third side portion 1231, a fourth side portion 1232 and a second middle portion 1233, the third side portion 1231 and the fourth side portion 1232 are relatively arranged on both sides of the second middle portion 1233, and the third side portion 1231 is adjacent to the empty foil area of ​​the second current collector 121. Similarly, in order to achieve connection with the tab, the second current collector 121 will be provided with an empty foil area not coated with an active material layer, the third side portion 1231 of the second active material layer can be adjacent to the empty foil area, and the second middle portion 1233 is arranged between the first side portion 1131 and the second side portion 1132.

[0038] Among them, the active material of the first side portion 1131 has a first surface density a, and the active material of the first middle portion 1133 has a second surface density b, and the first surface density a and the second surface density b satisfy: a>b. The active material of the third side portion 1231 has a third surface density c, and the active material of the second middle portion 1233 has a fourth surface density d, and the third surface density c and the fourth surface density d satisfy: c<d. The surface density of the active material refers to the mass of the active material per unit area, so the surface density of the first side portion 1131 is greater than the surface density of the first middle portion 1133, that is, the mass of the active material per unit area of ​​the first side portion 1131 is greater than the mass of the active material per unit area of ​​the first middle portion 1133. It should be noted that the body density of the first side portion 1131 and the first middle portion 1133 may be the same or different, and there is no limitation here. Similarly, the third side portion 1231 and the second middle portion 1233 can also be set in the same way, which will not be repeated here.

[0039] In the technical solution of the present application, the surface density of the first side portion 1131 of the anode sheet 110 is greater than the surface density of the first middle portion, and the surface density of the third side portion 1231 of the cathode sheet 120 is less than the surface density of the second middle portion 1233. In the pole sheet assembly 100 of the present application, the edge surface density of the anode sheet 110 is high, and compared with the first middle portion 1133, the edge of the anode sheet 110 can provide more embedding points for lithium ions; the edge surface density of the cathode sheet 120 is low, and compared with the second middle portion 1233, the edge of the cathode sheet 120 provides less lithium ions. The cooperation between the anode sheet 110 and the cathode sheet 120 can greatly improve the lithium plating problem of the lithium-ion battery, greatly reduce the risk of lithium plating, and greatly reduce the capacity loss of the battery cell.

[0040] In some embodiments, the surface density of the first active layer 113 can be set according to different usage requirements. Preferably, in this embodiment, the first surface density a and the second surface density b satisfy: 101%b≤a≤105%b. In other words, the first surface density a can be 1% to 5% higher than the second surface density b. Specifically, the first surface density a can be any suitable value such as 101%, 102%, 104%, 104.5% or 105% of the second surface density b, which is not limited here.

[0041] In some embodiments, the surface density of the second active layer 123 can be set according to different usage requirements. Preferably, in this embodiment, the third surface density c and the fourth surface density d satisfy: 97.5% d ≤ c ≤ 99.5% d. In other words, the third surface density c can be 0.5% to 2.5% lower than the fourth surface density d. Specifically, the third surface density c can be any suitable value such as 97.5%, 98%, 99%, 99.25% or 99.5% of the fourth surface density d, which is not limited here.

[0042] The first surface density a of the active material layer of the first side portion 1131 is greater than the second surface density b of the active material layer of the first middle portion 1133. In order to make the mass of the active material per unit area of ​​the first side portion 1131 greater than the mass of the active material per unit area of ​​the first middle portion 1133, the first side portion 1131 may be coated with multiple layers of active material compared to the first middle portion 1133, so that the first side portion 1131 has more active material per unit area. It is understandable that the volume density of the active material layer of the first side portion 1131 and the volume density of the active material layer of the first middle portion 1133 may be equal. At this time, when the first side portion 1131 is provided with multiple layers of active material, the thickness of the first side portion 1131 is greater than the thickness of the first middle portion 1133 along the direction perpendicular to the first surface 112. The density of the active material layer of the first side portion 1131 and the density of the active material layer of the first middle portion 1133 may also be different, and the thickness of the first side portion 1131 and the thickness of the first middle portion 1133 may also be different along the direction perpendicular to the first surface 112, which is not limited here. Figure 2 As shown, in this embodiment, along the direction perpendicular to the first surface 112, the first side portion 1131 has a first thickness e, and the first middle portion 1133 has a second thickness f, and the first thickness e and the second thickness f satisfy: 0.5um≤ef≤2um. That is, the first thickness e is greater than the second thickness f, and the first thickness e is 0.5um to 2um greater than the second thickness f. Specifically, the first thickness e can be 0.5um, 1um, 1.75um or 2um greater than the second thickness f. Any suitable value. Taking the first active layer 113 having a uniform body density as an example, the thickness of the first side portion 1131 is greater than the thickness of the first middle portion 1133. During charging and discharging, the first side portion 1131 can provide more lithium ion embedding sites compared to the first middle portion 1133, thereby effectively reducing the lithium deposition at the end of the pole piece. It should be noted that the thickness of each side portion in the present application can be uniformly set or unevenly set. The first thickness e, the second thickness f, and the fourth thickness h all refer to the maximum thickness of the corresponding portion, and the third thickness g refers to the minimum thickness of the corresponding portion.

[0043] Similarly, in order to make the third surface density c of the active material in the third side portion 1231 smaller than the fourth surface density d of the active material in the second middle portion 1233, when the second active layer 123 has a uniform volume density, the thickness of the active material layer coated on the third side portion 1231 can be smaller than the thickness of the active material layer in the second middle portion 1233. Figure 4As shown, in this embodiment, along the direction perpendicular to the second surface 122, the third side portion 1231 has a third thickness g, the second middle portion 1233 has a fourth thickness h, and the third thickness g and the fourth thickness h satisfy: 0.5um≤hg≤2um. In other words, the third thickness g is 0.5um to 2um smaller than the fourth thickness h. Specifically, the third thickness g can be any suitable value such as 0.5um, 1.5um, 1.75um or 2um smaller than the fourth thickness h. Compared with the second side portion 1132, the third side portion 1231 has a smaller thickness, that is, the amount of lithium ions that the third side portion 1231 can provide is less than the number of lithium ions that the second middle portion 1233 can provide, thereby effectively reducing the lithium deposition at the end of the electrode.

[0044] To further reduce lithium deposition at the end of the electrode, the total amount of active material on the first side 1131 of the anode sheet 110 may be greater than the total amount of active material on the third side 1231 of the cathode sheet 120. Figure 2 as well as Figure 4 As shown, in this embodiment, along the direction perpendicular to the first surface 112, the first side portion 1131 has a first thickness e, and along the direction perpendicular to the second surface 122, the third side portion 1231 has a third thickness g, and the first thickness e and the third thickness g satisfy: 1.2≤e / g≤2. In other words, the first thickness e of the first side portion 1131 can be 1.2 to 2 times the third thickness g of the third side portion 1231. Specifically, the first thickness e can be any suitable multiple of 1.2 times, 1.5 times, 1.8 times or 2 times the third thickness g. The thickness of the first side portion 1131 is greater than the thickness of the third side portion 1231, so that the number of lithium ion embedding sites in the first side portion 1131 is greater than the number of lithium ions in the third side portion 1231, so that the lithium deposition phenomenon at the end of the pole piece is greatly reduced during the charge and discharge process.

[0045] In order to further improve the ability of the anode sheet 110 to embed lithium ions and reduce the precipitation of lithium ions released by the cathode sheet 120 at the end of the electrode sheet, the coating width of the first side 1131 along the direction parallel to the first surface 112 is a first width i, and the coating width of the third side 1231 along the direction parallel to the second surface 122 is a second width j. The coating width of the first side 1131 can be greater than the coating width of the third side 1231. Figure 2 as well as Figure 4As shown, in this embodiment, along the direction parallel to the first surface 112, the first side portion 1131 has a first width i, and along the direction parallel to the second surface 122, the third side portion 1231 has a second width j, and the first width i and the second width j satisfy: 1.2um≤ij≤1.5um. In other words, the first width i is 1.2um to 1.5um larger than the second width j. Specifically, the first width i can be 1.2um, 1.25um, 1.3um or 1.5um larger than the second width j, and any other suitable vertical widths. It can be understood that when the anode sheet 110 and the cathode sheet 120 are wound or stacked, the first surface 112 is parallel to the second surface 122, and the first active layer 113 and the second active layer 123 are stacked in a direction perpendicular to the first surface 112. The projection of the first active layer 113 on the second surface 122 in a direction perpendicular to the second surface 122 is located within the projection of the second active layer 123 on the second surface 122 in a direction perpendicular to the second surface 122, that is, the width direction of the first side 1131 is in the same direction as the width direction of the third side 1231. The width of the first side 1131 is greater than the width of the third side 1231, thereby improving the ability of the active material layer of the first side 1131 to absorb lithium ions released by the third side 1231, and greatly reducing the lithium precipitation phenomenon at the end of the pole piece.

[0046] The first active layer 113 also has a second side portion 1132. The surface density of the first side portion 1131 is greater than the surface density of the first middle portion 1133, which can greatly reduce the lithium deposition of the electrode. Similarly, the surface density of the second side portion 1132 is greater than the surface density of the first middle portion 1133, which can also greatly reduce the lithium deposition of the electrode. Similarly, the surface density of the fourth side portion 1232 is lower than the surface density of the second middle portion 1233, which can also further reduce the lithium deposition of the electrode. Figure 2 as well as Figure 4As shown, in this embodiment, the active material of the second side portion 1132 has a fifth surface density m, the active material of the first middle portion 1133 has a second surface density b, and the fifth surface density m and the second surface density b satisfy: m>b. The active material of the fourth side portion 1232 has a sixth surface density n, the active material of the second middle portion 1233 has a fourth surface density d, and the sixth surface density n and the fourth surface density d satisfy: n<d. It can be understood that the thickness of the second side portion 1132 can be the same as the thickness of the first side portion 1131, or it can be different from the thickness of the first side portion 1131. The width of the second side portion 1132 can be the same as the width of the first side portion 1131, or it can be different from the width of the first side portion 1131. The width of the second side portion 1132 can also be greater than the width of the fourth side portion 1232, which is not limited here. Similarly, the thickness of the fourth side portion 1232 may be the same as the thickness of the third side portion 1231, and the width of the fourth side portion 1232 may be the same as the width of the third side portion 1231, which will not be repeated here. The surface density of the first side portion 1131 and the second side portion 1132 is greater than the surface density of the first middle portion 1133. The first side portion 1131 and the second side portion 1132 can provide more embedding sites for lithium ions compared to the first middle portion 1133. The surface density of the third side portion 1231 and the fourth side portion 1232 is less than the surface density of the second middle portion 1233, so that the third side portion 1231 and the fourth side portion 1232 can provide less lithium ions than the second middle portion 1233. The cooperation of the first side portion 1131, the second side portion 1132, the third side portion 1231 and the fourth side portion 1232 greatly reduces the risk of lithium deposition of the pole piece assembly 100.

[0047] Since the surface density excess value at the edge of the pole piece is smaller, the consistency of the pole piece is higher. In this embodiment, the first surface density a and the fifth surface density m satisfy: 0.9925≤a / m≤1.005, and the third surface density c and the sixth surface density n satisfy: 0.9925≤c / n≤1.005. Specifically, the ratio of the first surface density a to the fifth surface density can be any suitable value such as 0.9925, 0.995, 1 or 1.005. The ratio of the third surface density c to the sixth surface density n can be any suitable value such as 0.9925, 0.995, 1 or 1.005, and is not limited here.

[0048] To verify some of the above embodiments, the specific experimental data of this application are shown in Table 1. Among them, cls refers to the number of cycles of the battery cell at room temperature when the cycle retention rate is 80%, 500cls lithium deposition refers to the lithium deposition of the battery cell after 500 cycles when the cycle retention rate is 80% at room temperature, and 1000cls lithium deposition refers to the lithium deposition of the battery cell after 1000 cycles when the cycle retention rate is 80% at room temperature. Under the same cycle time, compared with the prior art, the degree of lithium deposition of the battery cell in the technical solution of this application is greatly reduced.

[0049] Table 1

[0050]

[0051] Specifically, in the prior art, taking Comparative Example 1 as an example, the first active layer 113 of the anode electrode of Comparative Example 1 has a uniform surface density, wherein the surface density of the first middle portion 1133 is 0.099 g / 1540.25 mm 2 The surface density of the first side 1131 and the second side 1132 is also 0.099g / 1540.25mm 2 The thickness of the anode electrode in the area coated with the first active layer 113 is 0.079 mm; the second active layer 123 of the cathode electrode of comparative example 1 has a uniform surface density, wherein the surface density of the second middle portion 1233 is 0.182 g / 1540.25 mm 2 The surface density of the third side 1231 and the fourth side 1232 is also 0.182g / 1540.25mm 2 The thickness of the cathode electrode in the area coated with the second active layer 123 is 0.064 mm. In the battery cell of comparative example 1, the first side 1131 and the second side 1132 have moderate lithium deposition in the cycle of 500 cls, and in the cycle of 1000 cls, the first side 1131 and the second side 1132 have severe lithium deposition.

[0052] In Example 1 of the present application, the surface density of the first middle portion 1133 is 0.099 g / 1540.25 mm 2 The thickness of the first middle portion 1133 is the same as the surface density of the first middle portion 1133 of Comparative Example 1; the surface density of the first side portion 1131 and the second side portion 1132 is 0.101g / 1540.25mm 2 The surface density of the first side portion 1131 and the second side portion 1132 is greater than the surface density of the side portion in Comparative Example 1; the surface density of the second middle portion 1233 is 0.182 g / 1540.25 mm 2The surface density of the second middle portion 1233 is the same as that of the second middle portion 1233 in comparative example 1; the surface density of the third side portion 1231 and the fourth side portion 1232 is 0.179 g / 1540.25 mm 2 , the surface density of the third side 1231 and the fourth side 1232 is less than the surface density of the first middle part 1133; the thickness of the area corresponding to the first middle part 1133 of the anode sheet 110 is 0.079mm, which is equal to the thickness corresponding to the first middle part 1133 of the anode plate in comparative example 1; the thickness corresponding to the first side 1131 and the second side 1132 of the anode sheet 110 is 0.085mm, which is greater than the thickness of the anode plate corresponding to the side in comparative example 1; the thickness of the second middle part 1233 of the cathode sheet 120 is 0.064mm, which is equal to the thickness corresponding to the second middle part 1233 of the cathode plate in comparative example 1; the thickness corresponding to the third side 1231 and the fourth side 1232 of the cathode sheet 120 is 0.058mm, which is less than the thickness corresponding to the side of the cathode plate in comparative example 1. In the battery cell of Example 1, in a cycle of 500cls, lithium is slightly deposited on the first side 1131 and the second side 1132. In a cycle of 1000cls, lithium is moderately deposited on the first side 1131 and the second side 1132. From the comparison of the experimental results, it can be seen that the technical solution of the present application can effectively reduce the risk of lithium deposition in the battery cell during the cycle process.

[0053] In Example 2 of the present application, the surface density of the first middle portion 1133 is 0.099 g / 1540.25 mm 2 The thickness of the first middle portion 1133 is the same as the surface density of the first middle portion 1133 of Comparative Example 1; the surface density of the first side portion 1131 and the second side portion 1132 is 0.101g / 1540.25mm 2 The surface density of the first side portion 1131 and the second side portion 1132 is greater than the surface density of the side portion in Comparative Example 1; the surface density of the second middle portion 1233 is 0.182 g / 1540.25 mm 2 The surface density of the second middle portion 1233 is the same as that of the second middle portion 1233 in comparative example 1; the surface density of the third side portion 1231 and the fourth side portion 1232 is 0.177 g / 1540.25 mm 2, the surface density of the third side 1231 and the fourth side 1232 is less than the surface density of the first middle part 1133; the thickness of the area corresponding to the first middle part 1133 of the anode sheet 110 is 0.079mm, which is equal to the thickness corresponding to the first middle part 1133 of the anode sheet in comparative example 1; the thickness corresponding to the first side 1131 and the second side 1132 of the anode sheet 110 is 0.085mm, which is greater than the thickness of the anode sheet corresponding to the side in comparative example 1; the thickness of the second middle part 1233 of the cathode sheet 120 is 0.064mm, which is equal to the thickness corresponding to the second middle part 1233 of the cathode sheet in comparative example 1; the thickness corresponding to the third side 1231 and the fourth side 1232 of the cathode sheet 120 is 0.053mm, which is less than the thickness corresponding to the side of the cathode sheet in comparative example 1. In the battery cell of Example 1, in a cycle of 500cls, both the first side 1131 and the second side 1132 no longer deposit lithium. In a cycle of 1000cls, both the first side 1131 and the second side 1132 no longer deposit lithium. From the comparison of the experimental results, it can be seen that the technical solution of the present application can greatly reduce the risk of lithium deposition in the battery cell during the cycle process.

[0054] In Examples 3 and 4 of the present application, compared with Example 2, the surface density corresponding to the first edge 1131 of Examples 3 and 4 is increased, and the thickness corresponding to the first edge 1131 and the second edge 1132 of the anode sheet 110 is increased. In a cycle of 500cls, the first edge 1131 and the second edge 1132 of Examples 3 and 4 no longer deposit lithium. In a cycle of 1000cls, the first edge 1131 and the second edge 1132 of Examples 3 and 4 no longer deposit lithium. From the comparison of the experimental results, it can be seen that the technical solution of the present application can greatly reduce the risk of lithium deposition of the battery cell during the cycle process, which will not be repeated here.

[0055] On the other hand, the present application also discloses a battery (not shown in the figure), which includes the pole piece assembly 100 of any of the above embodiments. Thanks to the improvement of the pole piece assembly 100, the battery of this embodiment (not shown in the figure) has the same technical effect as the pole piece assembly 100, which will not be described here.

[0056] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back...), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components in a certain specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0057] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the utility model, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of the features. In addition, if "and / or", "and / or" or "and / or" appears in the full text, its meaning includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the utility model.

[0058] The above are only preferred embodiments of the present invention, and do not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the utility model concept, or directly / indirectly used in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A pole piece assembly, characterized in that: include: An anode sheet, comprising a first current collector and a first active layer, wherein the first active layer is coated on a first surface of the first current collector, the first active layer comprises a first side portion, a second side portion and a first middle portion, the first side portion and the second side portion are arranged on both sides of the first middle portion, and the first side portion is adjacent to an empty foil area of ​​the first current collector; A cathode sheet, comprising a second current collector and a second active layer, wherein the second active layer is coated on a second surface of the second current collector, the second active layer comprises a third side portion, a fourth side portion and a second middle portion, the third side portion and the fourth side portion are arranged on both sides of the second middle portion, and the third side portion is adjacent to the empty foil area of ​​the second current collector; Among them, the active material in the first side portion has a first surface density a, the active material in the first middle portion has a second surface density b, and the first surface density a and the second surface density b satisfy: a>b; the active material in the third side portion has a third surface density c, the active material in the second middle portion has a fourth surface density d, and the third surface density c and the fourth surface density d satisfy: c<d.

2. The pole piece assembly according to claim 1, characterized in that: The first surface density a and the second surface density b satisfy: 101%b≤a≤105%b.

3. The pole piece assembly according to claim 1, characterized in that: The third surface density c and the fourth surface density d satisfy: 97.5% d≤c≤99.5% d.

4. The pole piece assembly according to claim 1, characterized in that: Along a direction perpendicular to the first surface, the first side portion has a first thickness e, the first middle portion has a second thickness f, and the first thickness e and the second thickness f satisfy: 0.5um≤ef≤2um.

5. The pole piece assembly according to claim 1, characterized in that: Along a direction perpendicular to the second surface, the third side portion has a third thickness g, the second middle portion has a fourth thickness h, and the third thickness g and the fourth thickness h satisfy: 0.5um≤hg≤2um.

6. The pole piece assembly according to claim 1, characterized in that: The first side has a first thickness e along a direction perpendicular to the first surface, and the third side has a third thickness g along a direction perpendicular to the second surface. The first thickness e and the third thickness g satisfy: 1.2≤e / g≤2.

7. The pole piece assembly according to claim 1, characterized in that: The first side portion has a first width i along a direction parallel to the first surface, and the third side portion has a second width j along a direction parallel to the second surface. The first width i and the second width j satisfy: 1.2um≤ij≤1.5um.

8. The pole piece assembly according to claim 1, characterized in that: The active material of the second side has a fifth surface density m, and the active material of the first middle part has a second surface density b, and the fifth surface density m and the second surface density b satisfy: m>b; the active material of the fourth side has a sixth surface density n, and the active material of the second middle part has a fourth surface density d, and the sixth surface density n and the fourth surface density d satisfy: n<d.

9. The pole piece assembly according to claim 8, characterized in that: The first surface density a and the fifth surface density m satisfy: 0.9925≤a / m≤1.005; and / or, The third surface density c and the sixth surface density n satisfy: 0.9925≤c / n≤1.

005.

10. A battery, characterized in that: A pole piece assembly comprising the pole piece assembly described in any one of claims 1 to 9.

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