Electrode tab and secondary battery

Abstract

This invention relates to an electrode sheet and a secondary battery. An electrode sheet includes a conductive substrate, a first material layer, and a second material layer. The first material layer is disposed on the surface of the conductive substrate, and the second material layer is disposed on the surface of the first material layer away from the conductive substrate. Both the first and second material layers extend along the length of the conductive substrate, and the width of the second material layer is smaller than the width of the first material layer. The smaller width of the second material layer compared to the first material layer allows for easier wetting of the portion of the first material layer not covered by the second material layer with electrolyte, increasing electrolyte retention. Simultaneously, the electrode sheet expands less during cycling, thus improving the cycle life of the battery cell. The smaller width of the second active layer saves material in the second active layer, reducing the cost of the electrode sheet.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to an electrode sheet and a secondary battery. Background Technology

[0002] With technological advancements, rechargeable batteries are widely used in electric vehicles, energy storage base stations, and 3C products. As various products demand increased energy density, the design and manufacturing of high-energy-density electrodes have become a research hotspot. To continuously improve the energy density of devices, the proportion of active material in the electrode also needs to be continuously increased. One method is to use a thick electrode with a double-layer structure. However, double-layer electrode structures have lower electrolyte retention, greater expansion, and higher cost. Summary of the Invention

[0003] Therefore, it is necessary to provide an electrode sheet that can improve electrolyte retention, reduce expansion, and lower costs.

[0004] In addition, a secondary battery is also provided.

[0005] An electrode sheet, comprising:

[0006] Conductive substrate;

[0007] A first material layer is disposed on the surface of a conductive substrate;

[0008] The first material layer is disposed on the side of the first material layer away from the conductive substrate. Both the second material layer and the first material layer extend along the length direction of the conductive substrate. The width of the second material layer is smaller than the width of the first material layer.

[0009] The width of the second material layer of the aforementioned electrode sheet is smaller than that of the first material layer, making it easier for the portion of the first material layer not covered by the second material layer to be wetted by the electrolyte, thereby increasing the electrolyte retention capacity. At the same time, the unequal width design of the first and second material layers allows for reserved space on the sides of the second material layer, enabling the expansion of the active materials in the first and second material layers to be well released through the reserved space, resulting in lower expansion of the electrode sheet during cycling and thus improving the cycle life of the battery cell. The smaller width of the second active layer saves material in the second active layer and reduces the cost of the electrode sheet.

[0010] In one embodiment, the width ratio of the second material layer to the width of the first material layer is 1:1.005 to 1:1.05.

[0011] In one embodiment, the difference between the width of the second material layer and the width of the first material layer is less than 6 mm.

[0012] In one embodiment, the first material layer has opposing first and second sides, and the second material layer has opposing third and fourth sides, wherein the line containing the first side is parallel to the line containing the third side, and the line containing the second side is parallel to the line containing the fourth side.

[0013] In one embodiment, the distance from the first side to the third side is equal to the distance from the second side to the fourth side.

[0014] In one embodiment, the distance from the first side to the third side is less than 3 mm.

[0015] In one embodiment, the width of the first material layer is equal to the width of the conductive substrate.

[0016] In one embodiment, the thickness of the first material layer is 25%-70% of the total thickness of the first material layer and the second material layer.

[0017] In one embodiment, there are two first material layers and two second material layers. The conductive substrate has two opposing surfaces. The two first material layers are respectively disposed on the two opposing surfaces of the conductive substrate, and the two second material layers are respectively disposed on the surfaces of the two first material layers away from the conductive substrate.

[0018] A secondary battery comprising the aforementioned electrode plates. Attached Figure Description

[0019] Figure 1 A schematic diagram of the structure of an electrode sheet according to one embodiment;

[0020] Figure 2 for Figure 1 A top view of the electrode plates shown;

[0021] Figure 3 This is a schematic diagram of the structure of an electrode sheet according to another embodiment. Detailed Implementation

[0022] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0024] Please see Figure 1 An electrode sheet 10 according to one embodiment includes a conductive substrate 110, a first material layer 120 and a second material layer 130.

[0025] The conductive substrate 110 has two opposing surfaces. Furthermore, the conductive substrate 110 has protrusions or grooves on its surface to increase the contact area between the conductive substrate 110 and the first material layer 120, thereby increasing the adhesion between the conductive substrate 110 and the first material layer 120.

[0026] The conductive substrate 110 extends along its length. Specifically, the conductive substrate 110 has a strip-shaped sheet structure. More specifically, the conductive substrate 110 has a rectangular sheet structure. Furthermore, the thickness of the conductive substrate 110 is 4 μm-18 μm.

[0027] Furthermore, the conductive substrate 110 may be formed of copper, aluminum, nickel, stainless steel, titanium and sintered carbon, or surface-treated copper, aluminum, stainless steel, or alloys of the above elements.

[0028] A first material layer 120 is disposed on the surface of the conductive substrate 110. Further, the first material layer 120 extends along the length of the conductive substrate 110. Specifically, the first material layer 120 is a strip-shaped structure. More specifically, the first material layer 120 is a strip-layered structure. Further, the first material layer 120 is a rectangular layered structure.

[0029] Please refer to the following: Figure 2 In one embodiment, the width of the first material layer 120 is equal to the width of the conductive substrate 110. Further, the first material layer 120 has opposing first sides 121 and second sides 122, which are respectively aligned with the long sides of the conductive substrate 110.

[0030] The first material layer 120 includes a first active substance, a first conductive agent, and a first adhesive.

[0031] In one embodiment, the electrode 10 is a positive electrode, and the first active material includes a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted by one or more transition metals; lithium iron phosphate (LiFe) 1-x M xPO4 (M = Co, Mn, Ni, Al, Zr, W, Cu, Zn, Mg, B or Ga and 0 ≤ x ≤ 1); lithium manganese oxides, such as Li 1+x Mn 2-x O4 (0≤x≤0.33), LiMn2O3 or LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides, such as LiV3O8, V2O5 or similar compounds; compounds with the chemical formula Li 1+x M 1-x O2 (where M = Co, Mn, Ni, Al, Zr, W, Cu, Zn, Fe, Mg, B or Ga, and 0 ≤ x ≤ 1) represents oxides. It should be noted that Li-site, metal-site substituted, or similar compounds of the above compounds are all within the scope of protection.

[0032] The first conductive agent is selected from at least one of conductive graphite, carbon black (SP), acetylene black, carbon nanotubes, carbon nanowires, carbon microspheres, carbon fibers, and graphene.

[0033] The first adhesive is selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), acrylonitrile copolymer, polybutyl acrylate, and polyacrylonitrile.

[0034] In another embodiment, electrode 10 is a negative electrode.

[0035] The first active material includes at least one of carbon materials, metal composite oxides, lithium metal, lithium alloys, silicon alloys, tin alloys, metal oxides, conductive polymers, titanium oxides, and lithium titanium oxides, or their analogues. For example, the metal composite oxide is Li. x Fe2O3 (0≤x≤1), Li x WO2 (0≤x≤1), etc.; conductive polymers include polyacetylene, etc.

[0036] The first conductive agent includes at least one of conductive graphite, carbon black, acetylene black, carbon nanotubes, carbon nanowires, carbon microspheres, carbon fibers, and graphene, but is not limited to these.

[0037] The first adhesive is selected from at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid (PAA), and polyacrylate.

[0038] The second material layer 130 is disposed on the surface of the first material layer 120 away from the conductive substrate 110. The second material layer 130 extends along the length of the conductive substrate 110, and its width is smaller than that of the first material layer 120. This unequal width design of the first and second material layers 120 allows for reserved space 133 on the side of the second material layer 130. Expansion of the active material in the first and second material layers 120 can be effectively released through this reserved space 133, resulting in lower expansion of the electrode plate 10 during cycling and thus improving the cycle life of the battery cell.

[0039] Furthermore, the ratio of the width of the second material layer 130 to the width of the first material layer 120 is 1:1.005 to 1:1.05, so as to reduce the impact on battery capacity while improving electrolyte retention, reducing expansion, and reducing costs. Even further, the difference between the width of the second material layer 130 and the width of the first material layer 120 is less than 6 mm.

[0040] Furthermore, the second material layer 130 has a third side 131 and a fourth side 132, with the straight line of the first side 121 being parallel to the straight line of the third side 131, and the straight line of the second side 122 being parallel to the straight line of the fourth side 132, so as to avoid short circuits in the electrode plate 10.

[0041] Furthermore, the distance from the first side 121 to the third side 131 is equal to the distance from the second side 122 to the fourth side 132. This equidistant design ensures more uniform force distribution on the electrode plates 10. Specifically, the distance from the first side 121 to the third side 131 is less than 3mm; the distance from the second side 122 to the fourth side 132 is less than 3mm, to ensure battery capacity.

[0042] The thickness of the first material layer 120 is 25%-70% of the total thickness of the first material layer 120 and the second material layer 130. If the first material layer 120 is too thin, the second material layer 130 will be too thick, making it easy to delaminate; if the first material layer 120 is too thick, the amount of adhesive used will be excessive, which is detrimental to cost and electronic conductivity. Furthermore, the total thickness of the first material layer 120 and the second material layer 130 is 20μm-200μm.

[0043] Specifically, the second material layer 130 has a strip-shaped structure. More specifically, the second material layer 130 has a strip-shaped layered structure. Further, the second material layer 130 has a rectangular layered structure.

[0044] Please see Figure 3In one embodiment, there are two first material layers 120 and two second material layers 130. The conductive substrate 110 has two opposing surfaces. The two first material layers 120 are respectively disposed on the two opposing surfaces of the conductive substrate 110, and the two second material layers 130 are respectively disposed on the surfaces of the two first material layers 120 away from the conductive substrate 110.

[0045] The second material layer 130 includes a second active substance, a second conductive agent, and a second adhesive.

[0046] In one embodiment, the electrode 10 is a positive electrode, and the second active material includes layered compounds such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or compounds substituted by one or more transition metals; lithium iron phosphate (LiFe) 1-x M x PO4 (M = Co, Mn, Ni, Al, Zr, W, Cu, Zn, Mg, B or Ga and 0 ≤ x ≤ 1); lithium manganese oxides, such as Li 1+x Mn 2-x O4 (0≤x≤0.33), LiMn2O3 or LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides, such as LiV3O8, V2O5 or similar compounds; compounds with the chemical formula Li 1+x M 1-x O2 (where M = Co, Mn, Ni, Al, Zr, W, Cu, Zn, Fe, Mg, B or Ga, and 0 ≤ x ≤ 1) represents oxides. It should be noted that Li-site, metal-site substituted, or similar compounds of the above compounds are all within the scope of protection.

[0047] The second conductive agent is selected from at least one of conductive graphite, carbon black, acetylene black, carbon nanotubes, carbon nanowires, carbon microspheres, carbon fibers, and graphene.

[0048] The second adhesive is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, acrylonitrile copolymer, polybutyl acrylate, and polyacrylonitrile.

[0049] In another embodiment, electrode 10 is a negative electrode.

[0050] The second active material includes at least one of carbon materials, metal composite oxides, lithium metal, lithium alloys, silicon alloys, tin alloys, metal oxides, conductive polymers, titanium oxides, and lithium titanium oxides, or their analogues. For example, the metal composite oxide is Li. x Fe2O3 (0≤x≤1), Li x WO2 (0≤x≤1), etc.; conductive polymers include polyacetylene, etc.

[0051] The second conductive agent includes at least one of conductive graphite, carbon black, acetylene black, carbon nanotubes, carbon nanowires, carbon microspheres, carbon fibers, and graphene, but is not limited to these.

[0052] The second adhesive is selected from at least one of sodium hydroxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid (PAA), and polyacrylate.

[0053] The electrode plate 10 described above has at least the following advantages:

[0054] The width of the second material layer 130 of the electrode 10 is smaller than that of the first material layer 120, making it easier for the portion of the first material layer 120 not covered by the second material layer 130 to be wetted by the electrolyte, thereby increasing the electrolyte retention capacity. At the same time, the unequal width design of the first material layer 120 and the second material layer 130 provides a reserved space 133 on the side of the second material layer 130. The expansion of the active material in the first material layer 120 and the second material layer 130 can be well released through the reserved space 133, resulting in lower expansion of the electrode 10 during cycling and thus improving the cycle life of the battery cell. The smaller width of the second active layer saves material for the second active layer and reduces the cost of the electrode 10.

[0055] A secondary battery includes the aforementioned electrode plates. At least one of the positive and negative electrode plates in the secondary battery is one of the aforementioned electrode plates. Specifically, the secondary battery is selected from lithium-ion batteries, sodium-ion batteries, magnesium-ion batteries, and aluminum-ion batteries. Further, the secondary battery is a battery analogue, such as a capacitor, supercapacitor, or pseudocapacitor, but is not limited thereto. This secondary battery has a high cycle life and a high energy density.

[0056] The following is a specific embodiment:

[0057] Example 1

[0058] The preparation steps of the electrode sheet in this embodiment are as follows:

[0059] 96.2 wt% lithium nickel cobalt manganese oxide (LiMn) 0.6 Ni 0.2 Co 0.2 O2 particles, 2 wt% SP, 0.9 wt% PVDF, and 0.9 wt% PTFE were added to a solvent and stirred to obtain a mixed slurry, forming a uniform and stable slurry 1. 97 wt% lithium nickel cobalt manganese oxide (LiMn) was then added. 0.6 Ni 0.2 Co 0.2O2 particles, 2 wt% SP, and 1 wt% PVDF are added to a solvent and stirred to obtain a mixed slurry, forming a uniform and stable slurry 2. Slurry 1 is coated onto the surface of an aluminum foil, and slurry 2 is coated onto the surface of slurry 1 away from the aluminum foil. The electrode is then dried and rolled to obtain an electrode sheet. The drying temperature is 110℃, the rolling pressure is 10 MPa, the rolling speed is 10 m / min, and the rolling temperature is room temperature. After drying and rolling, slurry 1 and slurry 2 form a first material layer and a second material layer, respectively. The width of the first material layer is 60 mm, and the width of the second material layer is 58 mm. The first material layer has opposing first and second sides, and the second material layer has opposing third and fourth sides. The distance from the first side to the third side is equal to the distance from the second side to the fourth side, both being 1 mm.

[0060] Example 2

[0061] The preparation steps of the electrode sheet in this embodiment are as follows:

[0062] 96.2 wt% lithium nickel cobalt manganese oxide (LiMn) 0.6 Ni 0.2 Co 0.2 O2 particles, 2 wt% SP, 0.9 wt% PVDF, and 0.9 wt% PTFE were added to a solvent and stirred to obtain a mixed slurry, forming a uniform and stable slurry 1. 97 wt% lithium nickel cobalt manganese oxide (LiMn) was then added. 0.6 Ni 0.2 Co 0.2 O2 particles, 2 wt% SP, and 1 wt% PVDF are added to a solvent and stirred to obtain a mixed slurry, forming a uniform and stable slurry 2. Slurry 1 is coated onto the surface of an aluminum foil, and slurry 2 is coated onto the surface of slurry 1 away from the current collector. The electrode is then dried and rolled to obtain an electrode sheet. The drying temperature is 110℃, the rolling pressure is 10 MPa, the rolling speed is 10 m / min, and the rolling temperature is room temperature. After drying and rolling, slurry 1 and slurry 2 form a first material layer and a second material layer, respectively. The width of the first material layer is 60 mm, and the width of the second material layer is 58 mm. The first material layer has opposing first and second sides, and the second material layer has opposing third and fourth sides. The distance between the first and third sides is 0.5 mm, and the distance between the second and fourth sides is 1.5 mm.

[0063] Example 3

[0064] The preparation steps of the electrode sheet in this embodiment are as follows:

[0065] 96.2 wt% lithium nickel cobalt manganese oxide (LiMn) 0.6 Ni 0.2 Co 0.2O2 particles, 2 wt% SP, 0.9 wt% PVDF, and 0.9 wt% PTFE were added to a solvent and stirred to obtain a mixed slurry, forming a uniform and stable slurry 1. 97 wt% lithium nickel cobalt manganese oxide (LiMn) was then added. 0.6 Ni 0.2 Co 0.2 O2 particles, 2 wt% SP, and 1 wt% PVDF are added to a solvent and stirred to obtain a mixed slurry, forming a uniform and stable slurry 2. Slurry 1 is coated onto the surface of an aluminum foil, and slurry 2 is coated onto the surface of slurry 1 away from the current collector. The electrode is then dried and rolled to obtain an electrode sheet. The drying temperature is 110℃, the rolling pressure is 10 MPa, the rolling speed is 10 m / min, and the rolling temperature is room temperature. After drying and rolling, slurry 1 and slurry 2 form a first material layer and a second material layer, respectively. The width of the first material layer is 60 mm, and the width of the second material layer is 58 mm. The first material layer has opposing first and second sides, and the second material layer has opposing third and fourth sides. The distance from the first side to the third side is 0 mm, and the distance from the second side to the fourth side is 2 mm.

[0066] Example 4

[0067] The preparation steps of the electrode sheet in this embodiment are as follows:

[0068] A mixed slurry was prepared by adding 92 wt% lithium iron phosphate particles, 4 wt% carbon nanotubes, 2 wt% PVDF, and 2 wt% polyacrylonitrile to a solvent and stirring. This resulted in a uniform and stable slurry 1. Another mixed slurry was prepared by adding 92 wt% lithium iron phosphate particles, 6 wt% carbon nanotubes, and 2 wt% PVDF to a solvent and stirring. This resulted in a uniform and stable slurry 2. Slurries 1 and 2 were simultaneously coated onto the surface of an aluminum foil, with slurry 1 applied as the bottom layer in direct contact with the current collector, and slurry 2 applied as the surface layer away from the current collector. The electrode sheets are then dried and rolled. The drying temperature is 95℃, the rolling pressure is 10MPa, the rolling speed is 10m / min, and the rolling temperature is room temperature. After drying and rolling, the coated slurry 1 and slurry 2 form the first material layer and the second material layer, respectively. The width of the first material layer is 60mm, and the width of the second material layer is 57.8mm. The first material layer has a first side and a second side, and the second material layer has a third side and a fourth side. The distance from the first side to the third side is 1.1mm, and the distance from the second side to the fourth side is 1.1mm.

[0069] Example 5

[0070] The preparation steps of the electrode sheet in this embodiment are as follows:

[0071] A mixed slurry, consisting of 92 wt% lithium iron phosphate particles, 4 wt% carbon nanotubes, 2 wt% PVDF, and 2 wt% polybutyl acrylate, was prepared by adding solvent and stirring. This resulted in a uniform and stable slurry 1. Similarly, a mixed slurry, consisting of 95 wt% lithium cobalt oxide particles, 3 wt% SP, and 2 wt% PVDF, was prepared by adding solvent and stirring. This resulted in a uniform and stable slurry 2. Slurries 1 and 2 were simultaneously coated onto the surface of an aluminum foil, with slurry 1 applied as the bottom layer in direct contact with the current collector, and slurry 2 applied as the surface layer away from the current collector. The electrode sheets are then dried and rolled. The drying temperature is 100℃, the rolling pressure is 10MPa, the rolling speed is 10m / min, and the rolling temperature is room temperature. After drying and rolling, the coated slurry 1 and slurry 2 form the first material layer and the second material layer, respectively. The width of the first material layer is 182mm, and the width of the second material layer is 180mm. The first material layer has a first side and a second side, and the second material layer has a third side and a fourth side. The distance from the first side to the third side is 0.8mm, and the distance from the second side to the fourth side is 1.2mm.

[0072] Example 6

[0073] The preparation steps of the electrode sheet in this embodiment are as follows:

[0074] A mixture of 95.3 wt% graphite particles, 1 wt% SP, 2.2 wt% SBR, and 1.5 wt% CMC was stirred in water to obtain a homogeneous and stable slurry 1. A mixture of 95.5 wt% silicon carbide particles, 1 wt% CNT, 2 wt% SBR, and 1.5 wt% CMC was stirred in water to obtain a homogeneous and stable slurry 2. Slurries 1 and 2 were simultaneously coated onto the surface of an aluminum foil, with slurry 1 on the bottom layer in direct contact with the current collector, and slurry 2 on the surface layer away from the current collector. The electrode sheets are then dried and rolled. The drying temperature is 85℃, the rolling pressure is 10MPa, the rolling speed is 5m / min, and the rolling temperature is room temperature. After drying and rolling, the coated slurry 1 and slurry 2 form the first material layer and the second material layer, respectively. The width of the first material layer is 93mm, and the width of the second material layer is 91.6mm. The first material layer has a first side and a second side, and the second material layer has a third side and a fourth side. The distance from the first side to the third side is 0.7mm, and the distance from the second side to the fourth side is 0.7mm.

[0075] Example 7

[0076] The preparation steps of the electrode sheet in this embodiment are as follows:

[0077] A mixture of 95 wt% graphite particles, 1 wt% SP, 2.5 wt% SBR, 1 wt% CMC, and 0.5% polyacrylic acid was stirred in water to obtain a homogeneous and stable slurry 1. A mixture of 95.7 wt% graphite particles, 1 wt% CNT, 1.8 wt% SBR, and 1.5 wt% CMC was stirred in water to obtain a homogeneous and stable slurry 2. Slurries 1 and 2 were simultaneously coated onto the surface of an aluminum foil, with slurry 1 on the bottom layer in direct contact with the current collector, and slurry 2 on the surface layer away from the current collector. The electrode sheets are then dried and rolled. The drying temperature is 90℃, the rolling pressure is 10MPa, the rolling speed is 5m / min, and the rolling temperature is room temperature. After drying and rolling, the coated slurry 1 and slurry 2 form the first material layer and the second material layer, respectively. The width of the first material layer is 63mm, and the width of the second material layer is 62mm. The first material layer has a first side and a second side, and the second material layer has a third side and a fourth side. The distance from the first side to the third side is 0mm, and the distance from the second side to the fourth side is 1mm.

[0078] Comparative Example 1

[0079] The preparation steps of the electrode sheet in this comparative example are roughly the same as those of the electrode sheet in Example 1. The difference is that the width of the first material layer and the second material layer of the electrode sheet in this comparative example are both 60 mm, and the distance from the first side to the third side is equal to the distance from the second side to the fourth side, which is 0 mm.

[0080] test:

[0081] 1) The electrode sheets prepared in Examples 1 to 7 and Comparative Example 1 were subjected to film resistance testing. The results are shown in Table 1. The specific testing methods are as follows.

[0082] Diaphragm resistance testing method: Five groups of 1540mm thick membranes were tested using a four-probe resistivity meter after rolling. 2 The resistance of the electrodes of different sizes is taken as the average value;

[0083] 2) The electrode sheets obtained in Examples 1 to 7 and Comparative Example 1 were made into pouch-type secondary batteries. Then, the cell liquid retention capacity, cell DC internal resistance, cell actual capacity, cell cycle life and BOM cost were tested. The results are shown in Table 1. The specific test methods are as follows.

[0084] Cell liquid retention test method: Measure the difference between the weight of five cells after liquid filling and the weight of the cells after secondary sealing, and take the average value.

[0085] Battery cell DC internal resistance test method: Take five battery cells, adjust the cells to 50% SOC state, test the internal resistance of 3C discharge for 10s, and take the average value;

[0086] Actual capacity testing method for battery cells: At room temperature, charge at a constant current of 1C to 4.2V, then charge at a constant voltage of 4.2V until the current drops to 0.15A. After resting for ten minutes, discharge at 1C to 2.8V. Repeat this charge-discharge cycle three times, and take the average discharge capacity of the three cycles as the actual capacity of a single battery cell. Test five batteries and take the average capacity of the five batteries.

[0087] Cell cycle life test method: Take two cells and cycle them for 500 cycles at room temperature under 1C / 1C charge and discharge conditions. Calculate the average value of the ratio of the discharge capacity of the two cells in the 500th cycle to the discharge capacity in the 1st cycle.

[0088] BOM cost calculation method: The ratio of the total raw material price of a single battery cell (based on the average market price) to the energy of a single battery cell.

[0089] Expansion test: The thickness of the electrode sheet 24 hours after rolling was measured with a digital micrometer and recorded as d0. After 500 cycles of the cell, the battery was disassembled, the electrode sheets were cleaned with DMC for 5 minutes and then dried at room temperature. The electrode sheet thickness d was measured with a digital micrometer. Electrode sheet expansion rate = (d - d0) / d0.

[0090] The preparation method of the soft-pack battery is as follows: 95.5 wt% artificial graphite particles, 1 wt% sp, 2 wt% SBR, and 1.5 wt% CMC are added to water and stirred to obtain a uniform and stable slurry; the slurry is uniformly coated on the surface of copper foil and then dried and rolled. The drying temperature is 80℃, the rolling pressure is 30 MPa, and the rolling speed is 3 m / min. The negative electrode sheet manufactured in the above manner is used as the negative electrode, and a PE material separator paper with a thickness of 20 micrometers is used as the separator. A liquid formed by dissolving 1M LiPF6 in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate is used as the electrolyte. Four sets of batteries with a capacity of 3.1 Ah were manufactured using the electrode sheets prepared in Examples 1-3 and Comparative Example 1 as the positive electrodes, and two sets of batteries with a capacity of 1.8 Ah were manufactured using the electrode sheets prepared in Examples 4-5 as the positive electrodes. 96.5 wt% LiMn 0.6 Ni 0.2 Co 0.2O2 particles, 2 wt% SP, and 1.5 wt% PVDF were added to NMP and stirred to obtain a uniform and stable slurry. The slurry was uniformly coated on the surface of aluminum foil and then dried and rolled. The drying temperature was 110°C, the rolling pressure was 10 MPa, and the rolling speed was 5 m / min. The positive electrode sheet manufactured in the above manner was used as the positive electrode, and a PE material separator paper with a thickness of 20 micrometers was used as the separator. The liquid formed by dissolving 1 M LiPF6 in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate was used as the electrolyte. Two sets of batteries with a capacity of 3.1 Ah were manufactured using the electrode sheets prepared in Examples 6 and 7 as the negative electrodes.

[0091] Table 1

[0092]

[0093] As can be seen from Table 1, compared with the electrode sheet prepared in Comparative Example 1, the secondary battery formed by using the electrode sheet prepared in Example 1 has a higher liquid retention capacity, a lower DC internal resistance, and a higher actual capacity, indicating that the electrode sheet of this application is beneficial to improving the energy density of the battery cell.

[0094] Compared to the electrode sheet prepared in Comparative Example 1, the secondary battery formed using the electrode sheet prepared in Example 1 exhibits a lower electrode expansion rate after cycling, indicating that the electrode sheet of this application has low expansion. Furthermore, the secondary battery formed in Example 1 has a higher 500-cycle capacity retention rate, demonstrating that the low-expansion electrode sheet improves cycle performance.

[0095] Compared with the electrode sheet prepared in Comparative Example 1, the secondary battery formed using the electrode sheet prepared in Example 1 has a lower cost, indicating that the electrode sheet of this application can make full use of the internal space of the cell and reduce the cost of the battery.

[0096] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0097] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An electrode tab, characterized by comprising: a conductive base; a first material layer disposed on a surface of the conductive base, the surface of the conductive base being provided with a protrusion or a groove, the first material layer and the conductive base having equal widths; and a second material layer disposed on a surface of the first material layer away from the conductive base, the second material layer and the first material layer both extending toward a length direction of the conductive base, the second material layer having a width smaller than that of the first material layer, so that a side edge of the second material layer has a reserved space through which expansion of an active material in the first material layer and the second material layer can be released; wherein the first material layer has a thickness of 25%-70% of a total thickness of the first material layer and the second material layer, a ratio of the width of the second material layer to the width of the first material layer is 1:1.005-1:1.05, a difference between the width of the second material layer and the width of the first material layer is 6 mm or less, and materials of the first material layer and the second material layer are at least partially different.

2. The electrode tab according to claim 1, characterized in that the first material layer has opposite first and second side edges, and the second material layer has opposite third and fourth side edges, a straight line on which the first side edge lies is parallel to a straight line on which the third side edge lies, and a straight line on which the second side edge lies is parallel to a straight line on which the fourth side edge lies.

3. The electrode tab according to claim 2, characterized in that a distance from the first side edge to the third side edge is equal to a distance from the second side edge to the fourth side edge.

4. The electrode tab according to claim 2, characterized in that the distance from the first side edge to the third side edge is 3 mm or less.

5. The electrode tab according to claim 1, characterized in that the first material layer and the second material layer are both two, the conductive base has opposite two surfaces, the two first material layers are respectively disposed on the opposite two surfaces of the conductive base, and the two second material layers are respectively disposed on surfaces of the two first material layers away from the conductive base.

6. A secondary battery, characterized by comprising the electrode tab according to any one of claims 1-5. ​ ​

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