An electrode assembly and a secondary battery thereof

Abstract

The application provides an electrode assembly and a secondary battery thereof, the electrode assembly comprising a positive electrode sheet and a negative electrode sheet, one side of the positive electrode current collector is provided with a first empty foil area, a first tab slot is formed by surrounding the first empty foil area and the positive active material layer around the first empty foil area; a first tab is arranged in the first tab slot; the first tab is provided with a first solder printing area, and a plurality of first solder prints are formed in the first solder printing area; one side of the negative electrode current collector is provided with a second empty foil area, a second tab slot is formed by surrounding the second empty foil area and the negative active material layer around the second empty foil area; a second tab is arranged in the second tab slot; the second tab is provided with a second solder printing area, and a plurality of second solder prints are formed in the second solder printing area; the area of the first solder print satisfies formula 1: 2<=<=4.7; the area of the second solder print satisfies formula 2: 2<=<=4.7; the electrode assembly provided by the application can reduce the internal resistance of the battery and improve the rate performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to an electrode assembly and its secondary battery. Background Technology

[0002] To facilitate the welding of tabs and foil and improve welding stability, most mature technologies in the electrode design of existing lithium-ion batteries and other electrochemical energy storage cells adopt a scheme of setting up double-sided empty foil areas at the corresponding slots of the tabs. That is, both the front and back sides of the electrode sheet have reserved areas of metal foil (such as copper foil or aluminum foil) that do not contain active materials at the corresponding welding positions of the tabs. This design can achieve better welding results, but it also reduces the energy density of the battery.

[0003] To improve the energy density of batteries, a method of setting single-sided tab grooves on the electrode sheets for tab welding has been proposed. However, the welding effect of single-sided tab grooves may have the following problems compared with double-sided welding: weak welding, insufficient weld strength, deterioration of welding effect, slow current transmission rate, increased battery internal resistance, reduced rate performance, and even tab detachment. Summary of the Invention

[0004] To address the issues of weak welding, deteriorated welding effect, slow current transmission rate, reduced rate performance, and increased internal resistance caused by setting a single-sided tab groove on the electrode sheet for tab welding, this application provides an electrode assembly and its secondary battery.

[0005] To address the aforementioned technical problems, in a first aspect, this application provides an electrode assembly, including a positive electrode sheet and a negative electrode sheet. The positive electrode sheet includes a positive current collector and a positive active material layer. The positive active material layer is disposed on both sides of the positive current collector. The positive active material layer includes a positive active material. A first empty foil area is provided on one side of the positive current collector. A first tab groove is formed around the first empty foil area and the positive active material layer therearound. A first tab is provided in the first tab groove. A first soldering area is provided on the first tab. The first tab is connected to the first empty foil area through the first soldering area, and a plurality of first solder marks are formed in the first soldering area. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is disposed on both sides of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material. A second empty foil area is provided on one side of the negative electrode current collector. The second empty foil area and the negative electrode active material layer surrounding it form a second electrode tab groove. A second electrode tab is provided in the second electrode tab groove. A second soldering area is provided on the second electrode tab. The second electrode tab is connected to the second empty foil area through the second soldering area, and multiple second solder marks are formed in the second soldering area. The area of ​​the first solder mark satisfies the following equation 1: 2≤ ≤4.7 Equation 1; The area of ​​the second solder mark satisfies the following equation 2: 2≤ ≤4.7 Equation 2; Where L1 is the width of the first electrode tab, in mm; L2 is the width of the second electrode tab, in mm; P1 is the areal density of the negative electrode active material layer located on one side of the negative electrode current collector, in g / m³. 2 ; A1 is the compaction density of the negative electrode active material layer, in g / cm³. 3 ; B represents the D50 particle size of the negative electrode active material, in μm. S1 represents the total area of ​​all the first solder marks within the first solder mark area, in mm. 2 ; S2 represents the total area of ​​all second solder marks within the second solder mark area, in mm. 2 .

[0006] Preferably, the first tab groove is disposed on one side of the positive current collector, and the positive current collector is provided with the positive active material layer on the side opposite to the first tab groove; The second electrode groove is disposed on one side of the negative electrode current collector, and the negative electrode active material layer is disposed on the side of the negative electrode current collector opposite to the second electrode groove.

[0007] Preferably, the width L1 of the first electrode tab is 3~10mm.

[0008] And / or, the width L2 of the second electrode tab is 3~10mm.

[0009] Preferably, the areal density P1 of the negative electrode active material layer located on one side of the negative electrode current collector is 70 g / m³. 2 ~99g / m 2 .

[0010] Preferably, the compaction density A1 of the negative electrode active material layer is 1.6 g / m³. 3 ~1.8g / m 3 .

[0011] Preferably, the D50 particle size B of the negative electrode active material is 10 μm to 20 μm.

[0012] Preferably, the width of the first solder area is 20% to 80% of the width of the first tab, and the length of the first solder area is 15% to 75% of the length of the first tab groove; And / or, the width of the second solder area is 20%-80% of the width of the second tab, and the length of the second solder area is 15%-75% of the length of the second tab groove.

[0013] Preferably, the electrode assembly further includes a first insulating adhesive layer and a second insulating adhesive layer. The first insulating adhesive layer is disposed on the side of the first electrode tab opposite to the first electrode tab groove and covers the first solder area. The second insulating adhesive layer is disposed on the side of the second electrode tab opposite to the second electrode tab groove and covers the second solder area.

[0014] Preferably, the electrode assembly further includes a third insulating layer, a fourth insulating layer, and a sixth insulating layer; The sixth insulating adhesive layer is disposed on the side of the first empty foil area away from the first electrode tab groove, or the sixth insulating adhesive layer is disposed on the positive electrode active material layer on the side of the first empty foil area away from the first electrode tab groove. The projection of the sixth insulating adhesive layer on the first empty foil area is greater than the projection of the first soldering area on the first empty foil area; A third insulating adhesive layer is provided on the positive electrode sheet, the third insulating adhesive layer is disposed opposite to the second insulating adhesive layer, and the projection of the third insulating adhesive layer on the negative electrode sheet covers the second insulating adhesive layer; A fourth insulating adhesive layer is provided on the negative electrode sheet. The fourth insulating adhesive layer is disposed opposite to the first insulating adhesive layer, and the projection of the first insulating adhesive layer on the negative electrode sheet covers the fourth insulating adhesive layer.

[0015] Preferably, the electrode assembly further includes a fifth insulating adhesive layer; the positive electrode sheet is also provided with a fifth insulating adhesive layer, and the projection of the fifth insulating adhesive layer on the second empty foil area covers the projection of the second soldering area on the second empty foil area.

[0016] Preferably, the electrode assembly further includes a first balancing groove and a second balancing groove, the first balancing groove is disposed on the positive electrode active material layer, the first balancing groove and the second electrode groove are disposed opposite to each other, and the third insulating adhesive layer is disposed at the bottom of the first balancing groove; The negative electrode active material layer is provided with a second balancing groove, which is disposed opposite to the first electrode tab groove, and the fourth insulating adhesive layer is disposed at the bottom of the second balancing groove.

[0017] Preferably, the electrode assembly further includes a third tab groove, a third empty foil area is provided on one side of the positive current collector, the third empty foil area is disposed on the side of the positive current collector away from the first empty foil area, the third empty foil area and the positive active material layer surrounding it form the third tab groove, the sixth insulating adhesive layer is disposed in the third tab groove, and the width of the sixth insulating adhesive layer is greater than the width of the first tab. Alternatively, the electrode assembly may further include a fourth tab groove, a fourth empty foil area is provided on one side of the negative electrode current collector, the fourth empty foil area is located on the side of the negative electrode current collector away from the second empty foil area, the fourth empty foil area and the surrounding negative electrode active material layer surround to form the fourth tab groove; a seventh insulating adhesive layer is provided in the fourth tab groove; the width of the seventh insulating adhesive layer is greater than the width of the second tab.

[0018] Secondly, this application provides a secondary battery, including the electrode assembly described above.

[0019] The electrode assembly provided in this application has a first solder mark area that satisfies Equation 1 and a second solder mark area that satisfies Equation 2. Both are calculated by taking the width of the tab, the areal density of the negative electrode active material layer on one side of the negative electrode current collector, the compaction density of the negative electrode active material layer, and the D50 particle size parameter of the negative electrode active material to obtain a reasonable range of the first solder mark area and the second solder mark area. This ensures the welding effect of the first and second tabs, strengthens the welding of the tabs and the tab groove, increases the weld strength, improves the welding tensile strength, optimizes the welding effect, improves the current transmission rate, reduces the battery internal resistance, improves the battery rate performance, and prevents the tabs from falling off. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the electrode assembly – positive electrode and negative electrode – provided in this application; Figure 2 This is a schematic diagram of the first structure of the electrode assembly provided in this application, which has a single-sided groove welded electrode tab and contains a balance groove; Figure 3 This is a schematic diagram of the electrode assembly provided in this application - the electrode sheet with a single-sided groove welded tab without a balance groove structure; Figure 4 This is a schematic diagram of the second structure of the electrode assembly provided in this application, which has a single-sided groove welded electrode tab and contains a balance groove; Figure 5 This is a schematic diagram of the structure of the electrode assembly provided in this application - the positive electrode sheet with a single-sided slot welded tab and the negative electrode sheet with a double-sided slot welded tab; Figure 6 This is a schematic diagram of the structure of the electrode assembly provided in this application – a single-sided slot welded tab for the negative electrode and a double-sided slot welded tab for the positive electrode.

[0021] The reference numerals in the attached figures are explained as follows: 1. Positive electrode sheet; 10. First tab; 101. First soldering area; 102. First soldering mark; 111. First tab groove; 121. First insulating adhesive layer; 113. Third tab groove; 11. Positive active material layer; 2. Negative electrode sheet; 20. Second tab; 201. Second soldering area; 202. Second soldering mark; 211. Second tab groove; 221. Second insulating adhesive layer; 223. Seventh insulating adhesive layer; 213. Fourth tab groove; 21. Negative electrode active material layer; 122. Third insulating adhesive layer; 222. Fourth insulating adhesive layer; 112. First balancing groove; 212. Second balancing groove; 123. Fifth insulating adhesive layer; 124. Sixth insulating adhesive layer. Detailed Implementation

[0022] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] like Figures 1-6 As shown, this application provides an electrode assembly including a positive electrode 1 and a negative electrode 2. The positive electrode 1 includes a positive current collector and a positive active material layer 11. The positive active material layer 11 is disposed on both sides of the positive current collector. The positive active material layer 11 includes a positive active material. A first empty foil area is provided on one side of the positive current collector. A first tab groove 111 is formed around the first empty foil area and the positive active material layer 11 therearound. A first tab 10 is provided in the first tab groove 111. A first solder area 101 is provided on the first tab 10. The first tab 10 is connected to the first empty foil area through the first solder area 101, and a plurality of first solder marks 102 are formed in the first solder area 101. The negative electrode sheet 2 includes a negative electrode current collector and a negative electrode active material layer 21. The negative electrode active material layer 21 is disposed on both sides of the negative electrode current collector. The negative electrode active material layer 21 includes a negative electrode active material. A second empty foil area is provided on one side of the negative electrode current collector. A second electrode tab groove 211 is formed around the second empty foil area and the negative electrode active material layer 21 therearound. A second electrode tab 20 is provided in the second electrode tab groove 211. A second soldering area 201 is provided on the second electrode tab 20. The second electrode tab 20 is connected to the second empty foil area through the second soldering area 201, and a plurality of second soldering marks 202 are formed in the second soldering area 201. The area of ​​the first solder mark 102 satisfies the following equation 1: 2≤ ≤4.7 Equation 1; The area of ​​the second solder mark 202 satisfies the following equation 2: 2≤ ≤4.7 Equation 2; Where L1 is the width of the first electrode tab 10, in mm; L2 is the width of the second electrode tab 20, in mm; P1 is the areal density of the negative electrode active material layer 21 located on one side of the negative electrode current collector, in g / m³. 2 ; A1 is the compaction density of the negative electrode active material layer 21, in g / cm³. 3 ; B represents the D50 particle size of the negative electrode active material, in μm. S1 represents the total area of ​​all the first solder marks 102 within the first solder mark area 101, in mm. 2 ; S2 is the total area of ​​all the second solder marks 202 within the second solder mark area 201, in mm. 2 .

[0024] Specifically, the first tab 10 and the second tab 20 have opposite polarities. During the electrode assembly fabrication process, the first tab 10 is placed in the first tab groove 111, and then welded into the first tab groove 111. A first solder area 101 is provided on the first tab 10, and multiple first solder marks 102 are formed in the first solder area 101. The first tab 10 is connected to the first tab groove 111 through the multiple first solder marks 102 in the first solder area 101. It should be noted that multiple first solder marks 102 means that the number of first solder marks 102 in the first solder area 101 is greater than or equal to two.

[0025] Similarly, the second electrode tab 20 is placed in the second electrode tab groove 211, and then the second electrode tab 20 is welded into the second electrode tab groove 211 by welding. The second electrode tab 20 is provided with a second solder area 201, and a plurality of second solder marks 202 are formed in the second solder area 201. The second electrode tab 20 is connected to the second electrode tab groove 211 through the plurality of second solder marks 202 in the second solder area 201.

[0026] The total area of ​​the soldering marks is related to the welding effect between the tab and the foil in the tab groove, and affects the welding pull, the internal resistance of the cell and the rate performance of the battery.

[0027] The electrode assembly provided in this application satisfies Equation 1 for the total area S1, A1, P1, B, L1 of the first solder mark 102 and Equation 2 for the total area S2, A1, P1, B, L2 of the second solder mark 202. By substituting the areal density, compaction density, D50 particle size parameter of the negative electrode active material layer 21 on one side of the negative electrode current collector, the corresponding tab width, and the total area of ​​the solder marks into the calculation, Equations 1 and 2 are satisfied. This ensures the welding effect of the first tab 10 and the second tab 20, the strong welding of the first tab 10 and the first tab groove 111, and the strong welding of the second tab 20 and the second tab groove 211. The weld strength is increased, the welding tensile force is improved, the welding effect is optimized, the current transmission rate is increased, the battery internal resistance is reduced, the battery rate performance is improved, and the tab detachment is prevented.

[0028] The total area of ​​the first solder mark 102 in the positive electrode 1, S1, A1, P1, B, L1, satisfies Equation 1, and the total area of ​​the second solder mark 202 in the negative electrode 2, S2, A1, P1, B, L2, satisfies Equation 2. The design rationale behind Equations 1 and 2 is as follows: The tabs are mainly used for current transmission between the battery and the external circuit. The current carrying capacity of the tabs is highly related to their size and welding quality (tab width, solder mark area, etc.). The design of the negative electrode active material layer 21, such as its compaction density, areal density, and D50 particle size, can affect the battery rate and capacity, thereby affecting the charging / discharging current. Therefore, the tab width and solder mark area must be combined with the design of the negative electrode active material to avoid deterioration of rate performance, increased internal resistance, or even localized heating that could affect battery safety due to unreasonable solder joint design.

[0029] If the total area of ​​the first solder mark 102, S1, A1, P1, B, L1, does not satisfy Equation 1, and the total area of ​​the second solder mark 202, S2, A1, P1, B, L2, does not satisfy Equation 2, and if the value obtained by substituting S1, A1, P1, B, L1 into Equation 1 is less than 2, and / or the value obtained by substituting S2, A1, P1, B, L2 into Equation 2 is less than 2, it will not only affect production efficiency, but also easily cause over-soldering and increase the internal resistance of the battery; if the value obtained by substituting S1, A1, P1, B, L1 into Equation 1 is greater than 4.7, and / or the value obtained by substituting S2, A1, P1, B, L2 into Equation 2 is greater than 4.7, it will not only result in weak welding and increased impedance, but also limit the current transmission speed and deteriorate the rate performance of the battery.

[0030] In some embodiments, the positive electrode current collector is provided with the positive electrode active material layer 11 on the side opposite to the first electrode tab groove 111; The negative electrode current collector has a negative electrode active material layer 21 disposed on the side opposite to the second electrode groove 211.

[0031] Specifically, a first tab groove 111 is provided on one side of the positive current collector, and no first tab groove 111 is provided on the other side of the positive current collector. The total area of ​​the first solder mark 102, S1, A1, P1, B, L1, satisfies Equation 1. While improving the energy density of the battery, it can also ensure the welding strength between the first tab 10 and the first tab groove 111, ensure the welding effect, improve the welding pull of the first tab 10 and the first tab groove 111, reduce the internal resistance of the cell, improve the current transmission rate, and improve the rate performance of the battery.

[0032] A second tab groove 211 is provided on one side of the negative electrode current collector, and no second tab groove 211 is provided on the other side of the negative electrode current collector. The total area of ​​the second solder mark 202, S2, A1, P1, B, L2, satisfies Equation 2. While improving the energy density of the battery, it can also ensure the welding strength between the second tab 20 and the second tab groove 211, ensure the welding effect, improve the welding pull of the second tab 20 and the second tab groove 211, reduce the internal resistance of the cell, improve the current transmission rate, and improve the rate performance of the battery.

[0033] In some embodiments, the width L1 of the first electrode tab 10 is 3mm to 10mm. And / or, the width L2 of the second electrode 20 is 3mm to 10mm.

[0034] Specifically, the width L1 of the first tab 10 is in the range of 3mm to 10mm, and the width L2 of the second tab 20 is in the range of 3mm to 10mm. The current density is controlled within a reasonable range. The resistance of the first tab 10 and the second tab 20 are both small, and the area is small. The current can be evenly conducted through the first tab 10 and the second tab 20. The heat dissipation area is appropriate, which can dissipate heat quickly, improve the thermal stability of the battery, and improve the rate performance of the battery.

[0035] If the width of the first tab 10 and the second tab 20 is too low, the welding area will be too small, resulting in low welding strength between the tabs and the tab groove, low heat dissipation area, affecting the battery's heat dissipation performance, reducing battery thermal stability, and lowering battery rate performance. If the width of the first tab 10 and the second tab 20 is too high, the tab area will be too large, increasing internal resistance, lowering current transmission rate, increasing battery internal resistance, and lowering battery rate performance.

[0036] In a specific embodiment, the width L1 of the second electrode 20 can be 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm or within any two of the above ranges.

[0037] In some embodiments, the areal density P1 of the negative electrode active material layer 21 located on one side of the negative electrode current collector is 70 g / m³. 2 ~99g / m 2 .

[0038] Specifically, the areal density of the negative electrode active material layer 21 affects the battery rate performance and battery capacity, thereby affecting the charging and discharging current of the battery. Therefore, the area of ​​the first solder area 101 and the area of ​​the second solder area 201 are related to the areal density of the negative electrode active material layer 21. The areal density P1 of the negative electrode active material layer 21 located on one side of the negative electrode current collector is 70 g / m³. 2 ~99g / m 2 Within the specified range, while ensuring battery capacity, the current is evenly distributed within the negative electrode active material layer 21, resulting in a fast current carrying rate and improved battery rate performance.

[0039] If the areal density P1 of the negative electrode active material layer 21 is too low, the battery capacity and energy density will be reduced; if the areal density P1 of the negative electrode active material layer 21 is too high, the thickness of the active material layer will be larger, the electrolyte will be difficult to wet, the lithium ion insertion / extraction path in the solid phase will be increased, the current distribution will be uneven, and the battery rate performance will be reduced.

[0040] In a specific embodiment, the areal density P1 of the negative electrode active material layer 21 can be 70 g / m². 2 72g / m 2 75g / m 2 77g / m 2 80g / m 2 82g / m 2 84g / m 2 86g / m 2 88g / m 2 89g / m 2 90g / m 2 92g / m 2 93g / m 2 95g / m 2 97g / m 2 99g / m 2 Or within any two of the above.

[0041] In some embodiments, the compaction density A1 of the negative electrode active material layer 21 is 1.6 g / m³. 3 ~1.8g / m 3 .

[0042] Specifically, the compaction density of the negative electrode active material layer 21 affects the battery's rate performance and capacity, thus influencing the charge and discharge current. Therefore, the total area S1 of the first solder mark 102 and the total area S2 of the second solder mark 202 are related to the compaction density of the negative electrode active material layer 21. The compaction density A1 of the negative electrode active material layer 21 is 1.6 g / m³. 3 ~1.8g / m 3Within this range, the negative electrode contains a large amount of active material per unit volume, resulting in a dense conductive network, fast electron transport rate, low internal resistance, and high rate performance.

[0043] If the compaction density of the negative electrode active material layer 21 is too low, the particle spacing is large, the resistance to resistance transmission is high, the internal resistance of the battery is high, and the rate performance is low. If the compaction density of the negative electrode active material layer 21 is too high, the porosity of the electrode sheet is too low, the electrolyte wetting is difficult, the battery polarization increases, the battery rate performance decreases, and the internal resistance increases.

[0044] In a specific embodiment, the compaction density A1 of the negative electrode active material layer 21 can be 1.6 g / m³. 3 1.62g / m 3 1.65g / m 3 1.67g / m 3 1.7g / m 3 1.73g / m 3 1.75g / m 3 1.78g / m 3 1.8g / m 3 Or within any two of the above.

[0045] In some embodiments, the D50 particle size B of the negative electrode active material is 10 μm to 20 μm.

[0046] Specifically, the D50 particle size of the negative electrode active material affects the battery's rate performance and capacity, thus influencing the charge and discharge current. Therefore, the total area S1 of the first solder mark 102 and the total area S2 of the second solder mark 202 are related to the D50 particle size of the negative electrode active material layer 21. A D50 particle size B of 10μm to 20μm in the negative electrode active material results in a large specific surface area, ensuring effective contact between the active material and the electrolyte, a dense conductive network, a fast electron transport rate, low internal resistance, and high rate performance.

[0047] If the D50 particle size of the negative electrode active material is too small, the particles are prone to agglomeration, reducing internal porosity, decreasing electrode compaction density, increasing internal resistance, and reducing rate performance. If the D50 particle size of the negative electrode active material is too large, the specific surface area is small, resulting in insufficient contact with the electrolyte, a longer lithium-ion diffusion path, increased internal resistance, and reduced rate performance.

[0048] In a specific embodiment, the D50 particle size B of the negative electrode active material can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or within any two of the above ranges.

[0049] In some embodiments, the width of the first solder area 101 is 20% to 80% of the width of the first tab 10, and the length of the first solder area 101 is 15% to 75% of the length of the first tab groove 111; And / or, the width of the second solder area 201 is 20%-80% of the width of the second tab 20, and the length of the second solder area 201 is 15%-75% of the length of the second tab groove 211.

[0050] Specifically, the width and length of the first soldering area 101 and the width and length of the second soldering area 201 satisfy the above conditions. The total area of ​​the first soldering 102 is calculated using Equation 1, and the total area of ​​the second soldering 202 is calculated using Equation 2. Multiple first soldering 102 are set within the first soldering area 101, and multiple second soldering 202 are set within the second soldering area 201. Neither the first soldering 102 nor the second soldering 202 exceeds the electrode tab, which ensures that the welding energy is concentrated on the effective contact surface between the electrode tab and the electrode tab groove, avoids the welding range from exceeding the electrode tab size, helps to reduce contact resistance, ensures the uniformity of current transmission, and ensures the connection strength between the electrode tab and the electrode tab groove.

[0051] In some embodiments, the electrode assembly further includes a first insulating adhesive layer 121 and a second insulating adhesive layer 221. The first insulating adhesive layer 121 is disposed on the side of the first tab 10 opposite to the first tab groove 111 and covers the first solder area 101. The second insulating adhesive layer 221 is disposed on the side of the second tab 20 opposite to the second tab groove 211 and covers the second solder area 201.

[0052] Specifically, the first insulating adhesive layer 121 is disposed on the side of the first electrode tab 10 opposite to the first electrode tab groove 111, and the second insulating adhesive layer 221 is disposed on the side of the second electrode tab 20 opposite to the second electrode tab groove 211, covering the exposed metal part of the electrode tab to form an insulating barrier and prevent the metal electrode tab from contacting other conductive components.

[0053] The first insulating adhesive layer 121 covers the first soldering area 101, and the second insulating adhesive layer 221 covers the second soldering area 201, which can prevent burrs or protrusions in the soldering area from puncturing the separator and causing a short circuit in the battery.

[0054] The first insulating adhesive layer 121 and the second insulating adhesive layer 221 also have a heat insulation function.

[0055] In some embodiments, a first empty foil area is provided on one side of the positive electrode current collector. The first empty foil area and the surrounding positive electrode active material layer 11 form a first electrode tab groove 111. A first electrode tab 10 is disposed in the first electrode tab groove 111 and is connected to the first electrode tab groove 111 by welding. A first solder mark area 101 is provided on the first electrode tab 10, and a plurality of first solder marks 102 are formed on the first solder mark area 101. The first electrode tab 10 is electrically connected to the first electrode tab groove 111 through the first solder marks 102. A first insulating adhesive layer 121 is provided on the side of the first electrode tab 10 away from the first electrode tab groove 111, and the first insulating adhesive layer 121 covers the first solder mark area 101. The area of ​​the first insulating adhesive layer 121 is larger than that of the first solder mark area 101, thereby achieving complete coverage of the first solder mark area 101 by the first insulating adhesive layer 121. The area of ​​the first insulating adhesive layer 121 may be greater than the area of ​​the first electrode groove 111, or the area of ​​the first insulating adhesive layer 121 may be less than or equal to the area of ​​the first electrode groove 111. This application does not impose any limitation on this.

[0056] like Figure 1 As shown, a second empty foil area is provided on one side of the negative electrode current collector. The second empty foil area and the surrounding negative electrode active material layer 21 form a second electrode tab groove 211. The second electrode tab 20 is disposed in the second electrode tab groove 211 and is connected to the second electrode tab groove 211 by welding. A second solder area 201 is provided on the second electrode tab 20, and multiple second solder marks 202 are formed on the second solder area 201. The second electrode tab 20 is electrically connected to the second electrode tab groove 211 through the second solder marks 202. A second insulating adhesive layer 221 is provided on the side of the second electrode tab 20 away from the second electrode tab groove 211, and the second insulating adhesive layer 221 covers the second solder area 201. The area of ​​the second insulating adhesive layer 221 is larger than that of the second solder area 201, thereby achieving complete coverage of the second solder area 201 by the second insulating adhesive layer 221. The area of ​​the second insulating adhesive layer 221 may be greater than the area of ​​the second electrode slot 211, or the area of ​​the second insulating adhesive layer 221 may be less than or equal to the area of ​​the second electrode slot 211. This application does not impose any limitation on this.

[0057] In some embodiments, the width of the first insulating adhesive layer 121 is greater than the width of the first tab 10, and the length of the first insulating layer is greater than the length of the first solder area 101.

[0058] In some embodiments, the width of the second insulating adhesive layer 221 is greater than the width of the second tab 20, and the length of the second insulating layer is greater than the length of the second solder area 201.

[0059] In some embodiments, the electrode assembly further includes a third insulating adhesive layer 122, a fourth insulating adhesive layer 222, and a sixth insulating adhesive layer 124; The sixth insulating adhesive layer 124 is disposed on the side of the first empty foil area away from the first electrode groove 111, or the sixth insulating adhesive layer 124 is disposed on the positive electrode active material layer 11 on the side of the first empty foil area away from the first electrode groove 111. The projection of the sixth insulating adhesive layer 124 on the first empty foil area is greater than the projection of the first soldering area 101 on the first empty foil area; A third insulating adhesive layer 122 is provided on the positive electrode 1. The third insulating adhesive layer 122 is disposed opposite to the second insulating adhesive layer 221, and the projection of the third insulating adhesive layer 122 on the negative electrode 2 covers the second insulating adhesive layer 221. A fourth insulating adhesive layer 222 is provided on the negative electrode sheet 2. The fourth insulating adhesive layer 222 is disposed opposite to the first insulating adhesive layer 121, and the projection of the first insulating adhesive layer 121 on the negative electrode sheet 2 covers the fourth insulating adhesive layer 222.

[0060] Specifically, such as Figure 2 , 3 As shown in Figures 4, 5, and 6, the positive electrode 1 includes a positive current collector, a first positive active material layer, and a second positive active material layer. The first positive active material layer is disposed on one side of the positive current collector, and the second positive active material layer is disposed on the other side of the positive current collector. Similarly, the negative electrode 2 includes a negative current collector, a first negative active material layer, and a second negative active material layer. The first negative active material layer is disposed on one side of the negative current collector, and the second negative active material layer is disposed on the other side of the negative current collector.

[0061] A third insulating adhesive layer 122 is provided on the positive electrode 1. The third insulating adhesive layer 122 is disposed opposite to the second insulating adhesive layer 221. The projection of the third insulating adhesive layer 122 on the negative electrode 2 covers the second insulating adhesive layer 221. That is, the width of the third insulating adhesive layer 122 is greater than the width of the second insulating adhesive layer 221, and the length of the third insulating adhesive layer 122 is greater than the length of the second insulating adhesive layer 221.

[0062] The third insulating adhesive layer 122 is provided on the positive electrode 1 because the second tab 20 is provided in the second tab groove 211, and there is no negative electrode active material in the corresponding second tab groove 211. The third insulating adhesive layer 122 is provided on the positive electrode 1 opposite to the second tab groove 211, and the width of the third insulating adhesive layer 122 is greater than the width of the second insulating adhesive layer 221, and the length of the third insulating adhesive layer 122 is greater than the length of the second insulating adhesive layer 221. This prevents lithium ions in the corresponding positive electrode active material layer 11 from migrating to the position of the second insulating adhesive layer 221, prevents lithium deposition at the second insulating adhesive layer 221, and improves the battery safety performance.

[0063] The fourth insulating adhesive layer 222 is disposed on the negative electrode 2. The fourth insulating adhesive layer 222 is disposed opposite to the first insulating adhesive layer 121, and the projection of the first insulating adhesive layer 121 on the negative electrode 2 covers the fourth insulating adhesive layer 222, that is, the width of the first insulating adhesive layer 121 is greater than the width of the fourth insulating adhesive layer 222. Because the first tab 10 is disposed in the first tab groove 111, there is no positive electrode active material in the corresponding first tab groove 111. The fourth insulating adhesive layer 222 is disposed on the negative electrode 2 opposite to the first tab groove 111, and the width of the first insulating adhesive layer 121 is greater than the width of the fourth insulating adhesive layer 222, which can prevent lithium deposition at the negative electrode 2 corresponding to the first tab groove 111 and improve the battery safety performance.

[0064] like Figure 6 When the positive electrode 1 has two tab slots, and only one of the tab slots has a tab, the corresponding sixth insulating adhesive layer 124 is disposed on the side of the first empty foil area away from the first tab slot 111; for example Figure 2-5 As shown, when only one tab groove is provided in the positive electrode 1, the corresponding sixth insulating adhesive layer 124 is provided on the positive electrode active material layer 11 on the side of the first empty foil area away from the first tab groove 111.

[0065] The projection of the sixth insulating adhesive layer 124 on the first empty foil area is greater than the projection of the first soldering area 101 on the first empty foil area, that is, the area of ​​the sixth insulating adhesive layer 124 is greater than the area of ​​the first soldering area 101. This structure is designed to prevent dust from puncturing the diaphragm and causing a short circuit between the positive and negative electrodes, since dust may fall off during the welding process of the first electrode lug 111.

[0066] In some embodiments, the electrode assembly further includes a fifth insulating adhesive layer 123; the positive electrode 1 is also provided with a fifth insulating adhesive layer 123, and the projection of the fifth insulating adhesive layer 123 on the second empty foil area covers the projection of the second soldering area 201 on the second empty foil area.

[0067] Specifically, the second electrode groove 211 is disposed on the first negative electrode active material layer; or, the second electrode groove 211 is disposed on the second negative electrode active material layer; that is, the second electrode groove 211 can be disposed on the first negative electrode active material layer, or the second electrode groove 211 is disposed on the second negative electrode active material layer.

[0068] The negative electrode active material layer 21 includes a first negative electrode active material layer and a second negative electrode active material layer, and the negative electrode current collector is disposed between the first negative electrode active material layer and the second negative electrode active material layer. Figure 6 For example, Figure 6 As shown, a second empty foil is provided on one side of the negative electrode current collector, and the second empty foil and the surrounding first negative electrode active material layer form a second electrode groove 211. A non-reactive region is provided in the second negative electrode active material layer. The non-reactive region is the coating of the negative electrode current collector away from the area of ​​the second empty foil, and the fifth insulating adhesive layer 123 is provided opposite to the non-reactive region.

[0069] like Figure 2-6 As shown, the fifth insulating adhesive layer 123 is disposed on the positive electrode sheet 1. The projection of the fifth insulating adhesive layer 123 on the second empty foil area covers the projection of the second soldering area 201 on the second empty foil area, that is, the area of ​​the fifth insulating adhesive layer 123 is larger than the area of ​​the second soldering area 201. This structure is designed to prevent lithium deposition at the negative electrode active material layer 21 on the side of the second empty foil area away from the second electrode groove 211 during the welding process of the second electrode groove 211, thus improving the battery safety performance.

[0070] In some embodiments, the electrode assembly further includes a first balancing groove 112 and a second balancing groove 212. The first balancing groove 112 is disposed on the positive electrode active material layer 11. The first balancing groove 112 and the second electrode groove 211 are disposed opposite to each other. The third insulating adhesive layer 122 is disposed at the bottom of the first balancing groove 112. The negative electrode active material layer 21 is provided with a second balance groove 212, which is disposed opposite to the first electrode tab groove 111, and the fourth insulating adhesive layer 222 is disposed at the bottom of the second balance groove 212.

[0071] Specifically, the first balancing groove 112 and the second balancing groove 212 not only serve to accommodate the first electrode tab 10 and the second electrode tab 20, but also do not increase the overall thickness of the electrode assembly or reduce the volumetric energy density. For example... Figure 2 , 4 As shown, there is also a partial active material coating between the first balancing tank 112 and the second balancing tank 212 and the current collector.

[0072] In some embodiments, the electrode assembly further includes a third tab groove 113, a third empty foil area is provided on one side of the positive current collector, the third empty foil area is disposed on the side of the positive current collector away from the first empty foil area, the third empty foil area and the positive active material layer 11 surrounding it form the third tab groove 113, the sixth insulating adhesive layer 124 is disposed in the third tab groove 113, and the width of the sixth insulating adhesive layer 124 is greater than the width of the first tab 10; Alternatively, the electrode assembly may further include a fourth tab groove 213, a fourth empty foil area is provided on one side of the negative electrode current collector, the fourth empty foil area is located on the side of the negative electrode current collector away from the second empty foil area, the fourth empty foil area and the negative electrode active material layer 21 surrounding it form the fourth tab groove 213; a seventh insulating adhesive layer 223 is provided in the fourth tab groove 213; the width of the seventh insulating adhesive layer 223 is greater than the width of the second tab 20.

[0073] Specifically, the fourth electrode slot 213 not only serves to accommodate the seventh insulating layer 223 without increasing the overall thickness of the electrode assembly, but also prevents the negative electrode active material layer 21 from shedding powder due to welding, thus avoiding a short circuit caused by dust. The third electrode slot 113 serves to accommodate the sixth insulating layer 124 without increasing the overall thickness of the electrode assembly; it also prevents the positive electrode active material layer 11 from shedding powder due to welding, thus avoiding a short circuit caused by dust.

[0074] The width of the seventh insulating adhesive layer 223 is greater than the width of the second electrode tab 20 to prevent burrs from piercing the diaphragm and causing a short circuit.

[0075] The width of the sixth insulating adhesive layer 124 is greater than the width of the first tab 10 to prevent burrs from piercing the diaphragm and causing a short circuit.

[0076] The electrode assembly of this application, such as Figure 2-4 The diagram shows a structure where a tab groove is provided on one side of both the positive electrode 1 and the negative electrode 2, and tabs are welded into the tab groove; for example... Figure 5 Alternatively, the positive electrode 1 may have a single-sided tab groove with a welded tab, while the negative electrode 2 may have tab grooves on both sides with a welded tab in one of the grooves; for example... Figure 6 The diagram shows a structure where the negative electrode 2 has a tab groove on one side and a tab welded to it, and the positive electrode 1 has a tab groove on both sides and a tab welded to one of the grooves. The aforementioned single-sided tab groove refers to a tab groove being set on the active material layer on one side of the current collector; the double-sided tab groove refers to a tab groove being set on the active material layer on both sides of the current collector.

[0077] In some embodiments, the width of the third insulating adhesive layer 122 is greater than the width of the second insulating adhesive layer 221, and the length of the third insulating adhesive layer 122 is greater than the length of the second insulating adhesive layer 221.

[0078] The width of the third insulating adhesive layer 122 is greater than the width of the second insulating adhesive layer 221, and the length of the third insulating adhesive layer 122 is greater than the length of the second insulating adhesive layer 221, which has the function of preventing lithium deposition on the negative electrode sheet 2.

[0079] In some embodiments, the width of the third insulating adhesive layer 122 is greater than the width of the second tab groove 211.

[0080] The width of the third insulating adhesive layer 122 is greater than the width of the second electrode groove 211, which serves to prevent lithium deposition on the negative electrode 2.

[0081] In some embodiments, the width of the first insulating adhesive layer 121 is greater than the width of the fourth insulating adhesive layer 222.

[0082] The width of the first insulating adhesive layer 121 is greater than the width of the fourth insulating adhesive layer 222, which serves to prevent lithium deposition on the negative electrode 2.

[0083] In some embodiments, the width of the second insulating adhesive layer 221 is greater than the width of the second tab groove 211.

[0084] The width of the second insulating adhesive layer 221 is greater than the width of the second tab groove 211, which serves to protect the welding burrs and prevent the battery from short-circuiting.

[0085] In some embodiments, the width of the first insulating adhesive layer 121 is greater than the width of the first tab groove 111.

[0086] The width of the first insulating adhesive layer 121 is greater than the width of the first tab groove 111, which serves to protect the welding burrs and prevent the battery from short-circuiting.

[0087] In some embodiments, the width of the first balancing groove 112 is greater than the width of the second insulating adhesive layer 221.

[0088] The width of the first balancing groove 112 is greater than the width of the second insulating adhesive layer 221, which serves to prevent lithium deposition on the negative electrode 2.

[0089] In some embodiments, the width of the first insulating adhesive layer 121 is greater than the width of the first tab 10.

[0090] The width of the first insulating adhesive layer 121 is limited to be greater than the width of the first tab 10, so as to ensure that the first insulating adhesive layer 121 covers the edge of the first tab 10 and avoids short circuits caused by burrs piercing the diaphragm when the edge of the first tab 10 is cut.

[0091] In some embodiments, the width of the second insulating adhesive layer 221 is greater than the width of the second tab 20.

[0092] The width of the second insulating adhesive layer 221 is limited to be greater than the width of the second tab 20, so as to ensure that the second insulating adhesive layer 221 covers the edge of the second tab 20 and avoids short circuits caused by burrs piercing the diaphragm when the edge of the second tab 20 is cut.

[0093] In some embodiments, the area of ​​the fifth insulating adhesive layer 123 is greater than or equal to the area of ​​the second solder area 201. Limiting the area of ​​the fifth insulating adhesive layer 123 to be greater than or equal to the area of ​​the second solder area 201 serves to prevent lithium deposition on the negative electrode 2.

[0094] In some embodiments, the area of ​​the sixth insulating adhesive layer 124 is greater than or equal to the area of ​​the first solder area 101. Limiting the area of ​​the sixth insulating adhesive layer 124 to be greater than or equal to the area of ​​the first solder area 101 serves to prevent lithium deposition on the negative electrode 2.

[0095] It should be noted that the size of the tab groove can be adjusted according to the width of the tab and the size of the solder area, and this application does not limit it.

[0096] The negative electrode active material layer 21 includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder; the negative electrode active material includes at least one of carbon materials and silicon-carbon materials. Carbon materials and silicon-carbon materials are existing technologies. For example, carbon materials include graphite, hard carbon, and soft carbon. Silicon-carbon materials include silicon-carbon composite materials.

[0097] The negative electrode conductive agent includes one or more of carbon nanotubes, conductive carbon black, graphene, and carbon fiber. The negative electrode binder includes at least one of styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), polyacrylic acid, and polyacrylate.

[0098] The positive electrode active material layer 11 includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.

[0099] The positive electrode active material includes at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium manganese oxide, nickel-rich ternary materials, manganese-rich ternary materials, lithium nickel manganese oxide, and lithium vanadium phosphate.

[0100] Positive conductive agents include one or more of carbon nanotubes, conductive carbon black, graphene, and carbon fiber.

[0101] The positive electrode binder includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylic acid, polyacrylate, and polyimide.

[0102] Secondly, this application provides a secondary battery, including the electrode assembly described above.

[0103] The secondary battery provided in this application has high production efficiency and can guarantee the welding effect of the single-sided tab slot. The welding of the single-sided tab slot improves the energy density, increases the welding tensile strength, reduces the internal resistance of the battery, and improves the rate performance of the battery, based on the double-sided welding.

[0104] The specific embodiments of the present invention will be further explained and illustrated below through examples, but this does not mean that the scope of protection of the present invention is limited to the scope described in the examples.

[0105] Example 1 S1: Preparation of positive electrode 1 Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed thoroughly in an N-methylpyrrolidone organic solvent at a mass ratio of 97:1.5:1.5 to obtain a positive electrode slurry. The positive electrode slurry was coated on both sides of an aluminum foil current collector and dried to obtain a positive electrode sheet 1. The prepared positive electrode sheet 1 includes a first positive electrode active material layer and a second positive electrode active material layer. The first positive electrode active material layer is disposed on one side of the aluminum foil, and the second positive electrode active material layer is disposed on the other side of the aluminum foil.

[0106] S2: Preparation of negative electrode 2 Graphite (negative electrode active material), conductive carbon black (conductive agent), sodium carboxymethyl cellulose (binder), and styrene-butadiene rubber (binder) were thoroughly mixed in deionized water at a mass ratio of 97.8:0.4:0.8:1.0 to form a uniform negative electrode slurry. This slurry was then coated onto both sides of a copper foil current collector and dried to obtain negative electrode sheet 2. The prepared negative electrode sheet 2 comprises a first negative electrode active material layer and a second negative electrode active material layer. The first negative electrode active material layer is disposed on one side of the copper foil, and the second negative electrode active material layer is disposed on the other side of the copper foil. The areal density of both the first and second negative electrode active material layers is 78 g / m³. 2 P1=78g / m 2 The compaction density A1 of the negative electrode active material layer 21 is 1.6 g / m³. 3 The D50 particle size B of the negative electrode active material graphite is 13 μm.

[0107] S3: Electrode welding The positive electrode sheet 1 includes a positive current collector and a positive active material layer 11. The positive active material layer 11 is disposed on both sides of the positive current collector. A first empty foil area is provided on one side of the positive current collector. The first empty foil area and the positive active material layer 11 surrounding it form a first tab groove 111. A first tab 10 is placed in the first tab groove 111 and welded to it within the first tab groove 111, thereby forming a first solder area 101 on the first tab 10. Multiple first solder marks 102 are formed in the first solder area 101. The first tab 10 is connected to the first tab groove 111 through the first solder area 101. A first insulating adhesive layer 121 is attached to the side of the first tab 10 facing away from the first tab groove 111, and the first insulating adhesive layer 121 covers the first solder area 101. The width of the first insulating adhesive layer 121 is greater than the width of the first tab groove 111.

[0108] The negative electrode sheet 2 includes a negative electrode current collector and a negative electrode active material layer 21. The negative electrode active material layer 21 is disposed on both sides of the negative electrode current collector. The negative electrode active material layer 21 includes negative electrode active material. A second empty foil area is provided on one side of the negative electrode current collector. The second empty foil area and the surrounding negative electrode active material layer 21 form a second electrode tab groove 211. The second electrode tab 20 is placed in the second electrode tab groove 211 and connected to the second electrode tab groove 211 by welding, thereby forming a second solder area 201 on the second electrode tab 20. Multiple second solder marks 202 are formed in the second solder area 201. The second electrode tab 20 is connected to the second electrode tab groove 211 through the second solder area 201. A second insulating adhesive layer 221 is attached to the surface of the second electrode tab 20 away from the second electrode tab groove 211. At the same time, the second insulating adhesive layer 221 covers the second solder area 201. The width of the second insulating adhesive layer 221 is greater than the width of the second electrode tab groove 211.

[0109] The width L1 of the first electrode 10 is 3mm. The width L2 of the second electrode 20 is 3mm. The specific values ​​of the total area S1 of all first solder marks 102 and the total area S2 of all second solder marks 202 are shown in Table 1.

[0110] The width of the first solder area 101 is 50% of the width of the first tab 10, and the length of the first solder area 101 is 55% of the length of the first tab groove 111; the width of the second solder area 201 is 50% of the width of the second tab 20, and the length of the second solder area 201 is within 45% of the length of the second tab groove 211.

[0111] S4: Battery Manufacturing The positive electrode 1, separator, and negative electrode 2 are wound together to obtain an electrode assembly. The electrode assembly is then packaged in an aluminum-plastic film and subjected to conventional lithium battery manufacturing processes such as baking, electrolyte injection, and hot pressing to obtain the battery.

[0112] In the electrode assembly, the first positive electrode active material layer and the second negative electrode active material layer are arranged opposite to each other. The first positive electrode active material layer includes a first adhesive region, a second adhesive region, and a third adhesive region. The third adhesive region is disposed opposite to the second electrode groove 211. A third insulating adhesive layer 122 is disposed within the third adhesive region, and the width of the third insulating adhesive layer 122 is greater than the width of the second insulating adhesive layer 221. The second negative electrode active material layer includes a fourth adhesive region, which is disposed opposite to the first electrode groove 111. A fourth insulating adhesive layer 222 is disposed within the fourth adhesive region, and the width of the first insulating adhesive layer 121 is greater than the width of the fourth insulating adhesive layer 222. A first region is disposed on the side of the second negative electrode active material layer away from the second electrode groove 211, which is disposed opposite to the first adhesive region. A fifth insulating adhesive layer 123 is disposed within the first adhesive region, and the area of ​​the fifth insulating adhesive layer 123 is greater than the area of ​​the second soldering area 201. A second adhesive region is disposed on the side of the second positive electrode active material layer away from the first electrode groove 111, and a sixth insulating adhesive layer 124 is disposed within the second adhesive region, and the area of ​​the sixth insulating adhesive layer 124 is greater than the area of ​​the first soldering area 101.

[0113] Examples 2-11 and Comparative Examples 1-4 Examples 2-11, Comparative Examples 1-4 and Example 1 are mostly the same in terms of steps, except that the specific values ​​of L1, L2, S1, S2, A1, P1 and B are different, as shown in Table 1.

[0114] Example 12 Most of the steps in Example 12 are the same as those in Example 2, with the following differences: Figure 5 As shown, a fourth empty foil area is provided on one side of the negative electrode current collector. The fourth empty foil area is located on the side of the negative electrode current collector away from the second empty foil area. The fourth empty foil area and the surrounding negative electrode active material layer 21 form a fourth electrode tab groove 213. A seventh insulating adhesive layer 223 is provided in the fourth electrode tab groove 213. The width of the seventh insulating adhesive layer 223 is greater than the width of the second electrode tab 20. The second electrode tab 20 is still welded in the second electrode tab groove 211.

[0115] Example 13 Most of the steps in Example 13 are the same as those in Example 2, with the following differences: Figure 6 As shown, a third empty foil area is provided on one side of the positive current collector. The third empty foil area is located on the side of the positive current collector away from the first empty foil area. The third empty foil area and the positive active material layer 11 surrounding it form a third tab groove 113. A sixth insulating adhesive layer 124 is provided in the third tab groove 113. The width of the sixth insulating adhesive layer 124 is greater than the width of the first tab 10. The first tab 10 is still welded in the first tab groove 111.

[0116] Table 1 Performance testing: The electrode assemblies and batteries obtained from the above embodiments and comparative examples were subjected to the following performance tests.

[0117] 1) Test welding tensile strength The welding strength of the first tab 10 and the welding strength of the second tab 20 were tested using a tensile testing machine. The tensile rate of the tensile testing machine was 35 mm / min. The test results are shown in Table 2.

[0118] 2) Ratio performance At 25°C, the battery was initially charged to 4.4V at a constant current of 0.5C, with a cutoff current of 0.02C, and the charging capacity was recorded. Then, it was discharged to 3.0V at a constant current of 1.5C, and the discharge capacity was recorded. The rate performance of the battery was measured by the ratio of discharge capacity to charge capacity.

[0119] 3) Battery internal resistance At 25°C, the battery was first charged to 4.4V at a constant current of 1.0C with a cutoff current of 0.02C. After the battery was fully charged, the ohmic internal resistance of the battery was tested.

[0120] 4) Energy density Before aging, the battery was charged at a constant current of 0.2C to 4.4V, cut off at 0.02C, and left to stand for 10 minutes. Then, it was discharged at a constant current of 0.2C to 3.0V, and the discharge energy was recorded. The cell thickness was measured using a PPG thickness gauge.

[0121] Energy density = The test results are recorded in Table 2.

[0122] Table 2 As shown in Tables 1 and 2, comparing Examples 1-6 with Comparative Examples 1-4, substituting S1, S2, L1, L2, A1, P1, and B from Comparative Example 2 into Equation 1... Substitution 2 The obtained value is less than 2, indicating low welding tensile strength of the tabs, poor rate performance, and high internal resistance of the battery. Substituting S1, S2, L1, L2, A1, P1, and B into Equation 1 in Comparative Example 1... Substitution 2 The obtained value is greater than 4.7, indicating low welding pull of the tabs, poor rate performance, and high battery internal resistance. The L2, S2, A1, P1, and B values ​​on the positive electrode side of Comparative Example 3 are substituted into equation 2. The obtained value is greater than 4.7, indicating low welding tensile strength of the positive electrode tab, poor rate performance of the battery, and high internal resistance; Substituting L1, S1, A1, P1, and B on the negative electrode side of Comparative Example 4 into Equation 1... The obtained value is greater than 4.7, indicating that the welding pull of the negative electrode tab is low, the rate performance of the battery is poor, and the internal resistance is high. This means that the total area of ​​the first weld mark 102 on the positive electrode side, S1, A1, P1, B, L1, satisfies Equation 1, and the total area of ​​the second weld mark 202 on the negative electrode side, S2, A1, P1, B, L2, satisfies Equation 2. This can ensure the welding effect of the first electrode tab 10 and the second electrode tab 20, the welding of the electrode tab and the electrode tab groove is firm, the weld strength is increased, the welding pull is improved, the welding effect is optimized, the current transmission rate is improved, the battery internal resistance is reduced, the battery rate performance is improved, and the electrode tab is prevented from falling off.

[0123] Comparing Examples 1-6 and Example 7, the compaction density A1 of the negative electrode active material layer 21 in Example 7 is less than 1.6 g / m³. 3 ~1.8g / m 3 The compaction density of the negative electrode active material layer 21 is too low, resulting in large particle spacing and low battery energy density. This indicates that the compaction density A1 of the negative electrode active material layer 21 is 1.6 g / m³. 3 ~1.8g / m 3 The battery has a wide range of applications, low internal resistance, and good rate performance.

[0124] It should be noted that the low welding pull of the first tab 10 in Example 4 is because the welding area of ​​the tab with a width of 10mm is only 7mm. 2 The solder area is relatively low, therefore the welding pull force is lower compared to Examples 1-3 and 5-6. However, this welding pull force can meet production and current carrying requirements and has little impact on electrical performance. The rate performance of Example 6 is slightly lower, mainly because the designed compaction density and the particle size of the negative electrode active material both reach their upper limits. The rate performance is more affected by the material, and the performance results caused by the material are irreversible.

[0125] The low compaction density of Example 7 affects electrical performance. However, compared to Example 6, which has a higher D50 particle size and compaction density of the negative electrode active material, Comparative Example 6 has a greater impact on electrical performance, especially rate performance. Therefore, the rate performance of Example 7 is worse than that of Examples 1-4, but better than that of Example 6.

[0126] Comparing Examples 1-6 and Examples 8-9, the areal density P1 of the first negative electrode active material layer is less than 70 g / m². 2 ~99g / m 2 The coating density is low, resulting in good rate performance but low battery energy density; the areal density P1 of the first negative electrode active material layer exceeds 70 g / m². 2 ~99g / m 2 The range of electrolyte wetting difficulties leads to increased internal resistance and poor rate performance of the battery; this indicates that the areal density P1 of the negative electrode active material layer 21 located on one side of the negative electrode current collector is 70 g / m². 2~99g / m 2 Within this range, the battery exhibits higher rate performance, energy density, and lower internal resistance.

[0127] Comparing Examples 1-6 with Examples 10-12, the battery exhibits poor rate performance when the D50 particle size B of the negative electrode active material is below 10μm to 20μm, and higher internal resistance when the D50 particle size B of the negative electrode active material is above 10μm to 20μm. This indicates that when the D50 particle size B of the negative electrode active material is in the range of 10μm to 20μm, the battery has higher rate performance and lower internal resistance.

[0128] Comparative explanation of Examples 1-6 and Examples 12-13: A tab groove is provided on one side surface of the positive electrode 1 or the negative electrode 2, or a groove is provided on both sides surface of the positive electrode 1 or the negative electrode 2, and the grooves on both sides are located on the upper and lower surfaces of the current collector. As long as the tabs satisfy Formula 1 and Formula 2, the tabs and tab grooves are firmly welded, the welding pull of the tabs is large, the internal resistance of the battery is low, and the rate performance is good.

[0129] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electrode assembly, characterized in that, The device includes a positive electrode (1) and a negative electrode (2). The positive electrode (1) includes a positive current collector and a positive active material layer (11). The positive active material layer (11) is disposed on both sides of the positive current collector. The positive active material layer (11) includes a positive active material. A first empty foil area is provided on one side of the positive current collector. The first empty foil area and the positive active material layer (11) around it form a first tab groove (111). A first tab (10) is provided in the first tab groove (111). A first soldering area (101) is provided on the first tab (10). The first tab (10) is connected to the first empty foil area through the first soldering area (101), and a plurality of first soldering marks (102) are formed in the first soldering area (101). The negative electrode sheet (2) includes a negative electrode current collector and a negative electrode active material layer (21). The negative electrode active material layer (21) is disposed on both sides of the negative electrode current collector. The negative electrode active material layer (21) includes a negative electrode active material. A second empty foil area is provided on one side of the negative electrode current collector. The second empty foil area and the negative electrode active material layer (21) surrounding it form a second electrode tab groove (211). A second electrode tab (20) is provided in the second electrode tab groove (211). A second soldering area (201) is provided in the second electrode tab (20). The second electrode tab (20) is connected to the second empty foil area through the second soldering area (201), and a plurality of second soldering marks (202) are formed in the second soldering area (201). The area of ​​the first solder mark (102) satisfies the following equation 1: 2≤ ≤4.7 Equation 1; The area of ​​the second solder mark (202) satisfies the following equation 2: 2≤ ≤4.7 Equation 2; Where L1 is the width of the first electrode tab (10), in mm; L2 is the width of the second electrode tab (20), in mm; P1 is the areal density of the negative electrode active material layer (21) located on one side of the negative electrode current collector, in g / m³. 2 ; A1 is the compaction density of the negative electrode active material layer (21), in g / cm³. 3 ; B represents the D50 particle size of the negative electrode active material, in μm. S1 is the total area of ​​all the first solder marks (102) within the first solder mark area (101), in mm. 2 ; S2 is the total area of ​​all the second solder marks (202) within the second solder mark area (201), in mm. 2 .

2. The electrode assembly according to claim 1, characterized in that, The positive electrode current collector is provided with the positive electrode active material layer (11) on the side opposite to the first electrode groove (111). The negative electrode current collector has a negative electrode active material layer (21) on the side opposite to the second electrode groove (211).

3. The electrode assembly according to claim 1, characterized in that, The width L1 of the first electrode tab (10) is 3~10mm; And / or, the width L2 of the second electrode (20) is 3~10mm.

4. The electrode assembly according to claim 1, characterized in that, The areal density P1 of the negative electrode active material layer (21) located on one side of the negative electrode current collector is 70 g / m². 2 ~99g / m 2 .

5. The electrode assembly according to claim 1, characterized in that, The compaction density A1 of the negative electrode active material layer (21) is 1.6 g / m³. 3 ~1.8g / m 3 .

6. The electrode assembly according to claim 1, characterized in that, The D50 particle size B of the negative electrode active material is 10 μm to 20 μm.

7. The electrode assembly according to claim 1, characterized in that, The width of the first solder area (101) is 20% to 80% of the width of the first tab (10), and the length of the first solder area (101) is 15% to 75% of the length of the first tab groove (111). And / or, the width of the second solder area (201) is 20%-80% of the width of the second tab (20), and the length of the second solder area (201) is 15%-75% of the length of the second tab groove (211).

8. The electrode assembly according to claim 1, characterized in that, The electrode assembly further includes a first insulating adhesive layer (121) and a second insulating adhesive layer (221). The first insulating adhesive layer (121) is disposed on the side of the first tab (10) away from the first tab groove (111) and covers the first solder area (101). The second insulating adhesive layer (221) is disposed on the side of the second tab (20) away from the second tab groove (211) and covers the second solder area (201).

9. The electrode assembly according to claim 8, characterized in that, The electrode assembly further includes a third insulating adhesive layer (122), a fourth insulating adhesive layer (222), and a sixth insulating adhesive layer (124). The sixth insulating adhesive layer (124) is disposed on the side of the first empty foil area away from the first electrode groove 111, or the sixth insulating adhesive layer (124) is disposed on the positive electrode active material layer (11) on the side of the first empty foil area away from the first electrode groove 111. The projection of the sixth insulating adhesive layer (124) on the first empty foil area is greater than the projection of the first solder area (101) on the first empty foil area; A third insulating adhesive layer (122) is provided on the positive electrode (1). The third insulating adhesive layer (122) is disposed opposite to the second insulating adhesive layer (221), and the projection of the third insulating adhesive layer (122) on the negative electrode (2) covers the second insulating adhesive layer (221). A fourth insulating adhesive layer (222) is provided on the negative electrode sheet (2). The fourth insulating adhesive layer (222) is disposed opposite to the first insulating adhesive layer (121), and the projection of the first insulating adhesive layer (121) on the negative electrode sheet (2) covers the fourth insulating adhesive layer (222).

10. The electrode assembly according to claim 9, characterized in that, The electrode assembly further includes a fifth insulating adhesive layer (123); the positive electrode sheet (1) is also provided with a fifth insulating adhesive layer (123), and the projection of the fifth insulating adhesive layer (123) on the second empty foil area covers the projection of the second soldering area (201) on the second empty foil area.

11. The electrode assembly according to claim 10, characterized in that, The electrode assembly further includes a first balancing groove (112) and a second balancing groove (212). The first balancing groove (112) is disposed on the positive electrode active material layer (11). The first balancing groove (112) and the second electrode groove (211) are disposed opposite to each other. The third insulating adhesive layer (122) is disposed at the bottom of the first balancing groove (112). The negative electrode active material layer (21) is provided with a second balance groove (212), the second balance groove (212) and the first electrode tab groove (111) are arranged opposite to each other, and the fourth insulating adhesive layer (222) is provided at the bottom of the second balance groove (212).

12. The electrode assembly according to claim 10, characterized in that, The electrode assembly further includes a third tab groove (113), a third empty foil area is provided on one side of the positive current collector, the third empty foil area is located on the side of the positive current collector away from the first empty foil area, the third empty foil area and the positive active material layer (11) surrounding it form the third tab groove (113), the sixth insulating adhesive layer (124) is disposed in the third tab groove (113), and the width of the sixth insulating adhesive layer (124) is greater than the width of the first tab (10); Alternatively, the electrode assembly may further include a fourth tab groove (213), a fourth empty foil area is provided on one side of the negative electrode current collector, the fourth empty foil area is located on the side of the negative electrode current collector away from the second empty foil area, the fourth empty foil area and the negative electrode active material layer (21) surrounding it form the fourth tab groove (213); a seventh insulating adhesive layer (223) is provided in the fourth tab groove (213); the width of the seventh insulating adhesive layer (223) is greater than the width of the second tab (20).

13. A secondary battery, characterized in that, Includes the electrode assembly as described in any one of claims 1-12.

Images