Electrode plate and secondary battery

Abstract

The utility model discloses an electrode plate and a secondary battery. The electrode plate comprises a current collector and an active material coating arranged on at least one surface of the current collector, the current collector comprises a first coating area and a second coating area which are connected with each other; the active material coating comprises a first preset length and a second preset length, and the second preset length is smaller than the first preset length; when the active material coating is in a first preset length state, the active material coating covers the first coating area and the second coating area; when the active material coating is in a second preset length state, the active material coating covers the second coating area, the length of the active material coating is equal to that of the second coating area, and the surface of the active material coating is of a flat structure. Compared with the prior art, the electrode plate provided by the utility model has the advantages that the thickness of the active material coating is uniform and consistent, the surface is smooth, and the problem of lithium precipitation caused by super-thick head and tail parts of the existing electrode plate is effectively solved.

Description

Technical Field

[0001] The utility model belongs to the technical field of batteries, and particularly relates to an electrode sheet and a secondary battery. Background Art

[0002] With the rapid development of modern technology, people's dependence on mobile devices and electric vehicles has increased day by day, which directly promotes the demand for high-performance battery technology. As an efficient energy storage solution, lithium-ion batteries are widely used in many fields such as smart phones, laptops and electric vehicles due to their high energy density and long life. However, with the continuous improvement of device performance and consumers' expectation of longer battery life, the existing lithium-ion battery technology faces the challenge of improving energy density. To meet these requirements, researchers and engineers have developed various methods to increase the total energy output of the battery, including the use of a multi-tab structure and a negative electrode double coating technology. The multi-tab structure can increase the current density of the battery, while the double coating technology allows two layers of active materials to be coated on the negative electrode simultaneously, thereby increasing the capacity of the battery.

[0003] However, there are still some important technical problems in the practical application of these technologies. When using the double coating process, especially in the manufacturing process of the negative electrode sheet, the surface and bottom active material slurries must be coated on the surface of the base-coated copper foil simultaneously. During this process, due to the surface tension and fluidity problems of the active material slurry, the coated electrode sheet often shows an over-thick phenomenon at the head and tail. This over-thickness will not only cause overpressure during the subsequent rolling process, but also may lead to insufficient electrolyte absorption, thereby affecting the forming quality and side parallelism of the battery cell. More seriously, this structural defect may induce lithium deposition during the long-term use of the battery, seriously affecting the cycle stability and safety of the battery.

[0004] In view of this, it is necessary to provide a technical solution to solve the above problems. Summary of the Utility Model

[0005] One of the utility model purposes of this application is: aiming at the deficiencies of the prior art, to provide an electrode sheet to solve the technical problems of uneven coating of the existing electrode sheet and lithium deposition caused by over-thickness at the head and tail of the electrode sheet.

[0006] To achieve the above purpose, the utility model adopts the following technical solutions:

[0007] An electrode sheet includes a current collector and an active material coating provided on at least one surface of the current collector; the current collector includes a first coating area and a second coating area connected to each other, and the first coating area is located on opposite sides of the second coating area; the active material coating includes a first preset length and a second preset length, and the second preset length is less than the first preset length; when the active material coating is in the first preset length state, the active material coating covers the first coating area and the second coating area; when the active material coating is in the second preset length state, the active material coating covers the second coating area, and the length of the active material coating is equal to the length of the second coating area, and the surface of the active material coating is a flat structure.

[0008] As an improvement to the electrode sheet of the present utility model, when the active material coating is in the second preset length state, the active material coating on the first coating area is removed by laser cleaning; and the laser power is 500 - 2000W, the laser spot diameter is 0.01 - 0.5mm, and the laser pulse frequency is 0.1 - 600Hz.

[0009] As an improvement to the electrode sheet of the present utility model, the length of the first coating area is 3 - 8mm.

[0010] As an improvement to the electrode sheet of the present utility model, the active material coatings are respectively provided on both surfaces of the current collector, and the length of the active material coating on one surface is greater than the length of the active material coating on the other surface.

[0011] As an improvement to the electrode sheet of the present utility model, the active material coating includes a first active material coating provided on the surface of the current collector and a second active material coating provided on the surface of the first active material coating, and the areal density of the first active material coating is greater than the areal density of the second active material coating.

[0012] As an improvement to the electrode sheet of the present utility model, the current collector is provided with one or more tabs.

[0013] As an improvement to the electrode sheet of the present utility model, the depth of laser cleaning is H, the thickness of the first active material coating is h1, the thickness of the second active material coating is h2, and the thickness of the current collector is h3, wherein H, h1, h2, and h3 satisfy the following relationship: h1 + h2 ≤ H < h1 + h2 + h3.

[0014] As an improvement to the electrode sheet of the present utility model, the thickness h1 of the first active material coating is 25μm - 100μm, the thickness h2 of the second active material coating is 5μm - 50μm, and the thickness h3 of the current collector is 4 - 7μm.

[0015] As an improvement to the electrode sheet of the present utility model, the current collector is a metal foil; and / or the current collector includes a metal foil and a conductive agent coating coated on the surface of the metal foil.

[0016] The second object of the utility model of this application is to provide a secondary battery, including the above-mentioned electrode sheet.

[0017] The beneficial effect of the present utility model lies in that: for the electrode sheet provided by the present utility model, its current collector includes a second coating area and first coating areas arranged on opposite sides of the second coating area. When the active material coating is in the first preset length state, the active material coating covers the first coating area and the second coating area, that is, the coating length of the active material coating is increased in advance; while in the second preset length state, the active material coating only covers the second coating area and matches the length of this coating area, that is, the active material coatings on both sides of the first coating area (the head and tail parts) are removed, thereby ensuring that the coating thickness of the pole piece is uniform and the surface is flat, and avoiding the problem of lithium precipitation caused by the excessive thickness at the head and tail of the pole piece. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide a further understanding of the present utility model and constitute a part of the present utility model. The schematic embodiments of the present utility model and their descriptions are used to explain the present utility model and do not constitute an improper limitation to the present utility model. In the drawings:

[0019] Figure 1 is a schematic structural diagram of the current collector in an embodiment of the present utility model;

[0020] Figure 2 is a top view of the electrode sheet in the first preset length state in an embodiment of the present utility model;

[0021] Figure 3 is a sectional view of the electrode sheet in the first preset length state in an embodiment of the present utility model;

[0022] Figure 4 is a top view of the electrode sheet in the second preset length state in an embodiment of the present utility model;

[0023] Figure 5 is a sectional view of the electrode sheet in the second preset length state in an embodiment of the present utility model;

[0024] Figure 6 is a comparison chart of the battery step-down cycle capacity retention rates of Embodiment 1 and Comparative Example 1 of the present utility model;

[0025] Figure 7This is a comparison chart of the thickness expansion rate during the battery step-down cycle for Embodiment 1 and Comparative Example 1 of the present utility model. Among them: 1 - current collector; 11 - first coating area; 12 - second coating area; 13 - empty foil area; D - tab

[0026] 2 - active material coating; 21 - first active material coating; 22 - second active material coating; L1 - first preset length; L11 - length of the active material coating on one side surface; L12 - length of the active material coating on the other side surface; L2 - second preset length; L21 - length of the active material coating on one side surface; L22 - length of the active material coating on the other side surface. Detailed implementation manners

[0027] Next, the technical solutions in the embodiments of the present application will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present application belongs. The terms used in the specification of the present application herein are only for the purpose of describing specific implementation manners and are not intended to limit the present application.

[0028] Although the present application is disclosed above with preferred embodiments, it is not used to limit the claims. Any person skilled in the art can make several possible changes and modifications without departing from the concept of the present application. Therefore, the protection scope of the present application should be determined by the scope defined by the claims of the present application.

[0029] Next, in combination with the specific implementation manners, the present utility model will be further described in detail, but the implementation manners of the present utility model are not limited thereto.

[0030] As Figure 1 shown, an electrode sheet provided by the present application includes a current collector 1 and an active material coating 2 provided on at least one surface of the current collector 1; the current collector 1 includes a connected empty foil area 13, a first coating area 11, and a second coating area 12, and the first coating area 11 is located on opposite sides of the second coating area 12; the active material coating 2 includes a first preset length L1 and a second preset length L2, and the second preset length L2 is less than the first preset length L1;

[0031] When the active material coating 2 is in the first preset length state, the active material coating 2 covers the first coating area 11 and the second coating area 12;

[0032] When the active material coating 2 is in the second preset length state, the active material coating 2 covers the second coating area 12, and the length of the active material coating 2 is equal to the length of the second coating area 12, and the surface of the active material coating 2 is a flat structure.

[0033] In a further embodiment of the present invention, the electrode sheet is a positive electrode sheet and / or a negative electrode sheet, preferably a negative electrode sheet.

[0034] In a further embodiment of the present invention, when the active material coating 2 is in the second preset length state, the active material coating 2 in the first coating area 11 is removed by laser cleaning; and the laser power is 500 - 2000W, the laser spot diameter is 0.01 - 0.5mm, and the laser pulse frequency is 0.1 - 600Hz.

[0035] Among them, the laser power can specifically be 500W, 600W, 700W, 800W, 900W, 1000W, 1100W, 1200W, 1300W, 1400W, 1500W, 1600W, 1700W, 1800W, 1900W, 2000W, and can include but are not limited to the above-listed laser power values, preferably 1000W. The laser spot diameter can specifically be 0.01mm, 0.02mm, 0.03mm, 0.04mm, 0.05mm, 0.06mm, 0.07mm, 0.08mm, 0.09mm, 0.1mm, 0.12mm, 0.13mm, 0.14mm, 0.15mm, 0.16mm, 0.17mm, 0.18mm, 0.19mm, 0.2mm, 0.21mm, 0.22mm, 0.23mm, 0.24mm, 0.25mm, 0.26mm, 0.27mm, 0.28mm, 0.29mm, 0.3mm, 0.31mm, 0.32mm, 0.33mm, 0.34mm, 0.35mm, 0.36mm, 0.37mm, 0.38mm, 0.39mm, 0.4mm, 0.41mm, 0.42mm, 0.43mm, 0.44mm, 0.45mm, 0.46mm, 0.47mm, 0.48mm, 0.49mm, 0.5mm, and can include but are not limited to the above-listed laser spot diameter values, preferably 0.02mm. The laser pulse frequency can specifically be 0.1Hz, 1Hz, 10Hz, 50Hz, 100Hz, 150Hz, 200Hz, 250Hz, 300Hz, 350Hz, 400Hz, 450Hz, 500Hz, 550Hz, 600Hz, and can include but are not limited to the above-listed laser pulse frequency values, preferably 300Hz.

[0036] In a further embodiment of the present utility model, the length of the first coating area 11 is 3 - 8 mm. Specifically, the length of the first coating area 11 may be 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, including but not limited to the lengths of the first coating area listed above, and preferably 5 mm.

[0037] In a further embodiment of the present utility model, the active material coatings 2 are respectively disposed on both side surfaces of the current collector 1, and the length L1 of the active material coating on one side surface is greater than the length L2 of the active material coating on the other side surface.

[0038] In a further embodiment of the present utility model, the active material coating 2 includes a first active material coating 21 disposed on the surface of the current collector 1 and a second active material coating 22 disposed on the surface of the first active material coating 21. The areal density of the first active material coating 21 is greater than that of the second active material coating 22. Preferably, in the negative electrode sheet, the active material coating 2 is double-layer coated. The first active material coating material 21 may be selected from large-particle high-compaction graphite or silicon-carbon active material, and the second active material coating 22 is selected from small-particle fast-charging graphite or silicon-carbon and other active materials; the second active material layer 22 uses small-particle fast-charging active substances, and the first active material layer 21 uses large-particle high-compaction active substances. Compared with the single-layer coating technology of the negative electrode, the double-layer coating can achieve hierarchical control of the porosity, reduce the surface overpotential, ensure the advantages of lithium-ion transport kinetics, further reduce the ohmic internal resistance and DCR (direct current internal resistance) of the battery and improve the battery discharge capacity, so as to achieve the purpose of improving the energy density of the battery. In the positive electrode sheet, the active material coating is single-layer coated, and the coated active material may be selected from one of LiCoO2, LiFePO4, and Li(NiCoMn)O2.

[0039] In a further embodiment of the present utility model, the current collector is provided with one or more tabs D. The electrode sheet of the present utility model adopts a multi-tab structure. Compared with the conventional single-tab structure battery cell, it can reduce the ohmic internal resistance of the battery, improve the battery discharge capacity, and at the same time weaken the electrochemical polarization effect, further greatly improving the high-current charge and discharge rate performance and charging window of the lithium battery.

[0040] In a further embodiment of the present utility model, when the current collector 1 is provided with a plurality of tabs, the number of the tabs is 20 - 25. The number of the tabs may specifically be 20, 21, 22, 23, 24, 25; among them, the number of the tabs on the positive electrode sheet in the present utility model is preferably 24, and the number of the tabs on the negative electrode sheet is preferably 25.

[0041] In a further embodiment of the present utility model, the depth of laser cleaning is H, the thickness of the first active material coating is h1, the thickness of the second active material coating is h2, and the thickness of the current collector is h3. Among them, H, h1, h2, and h3 satisfy the following relationship: h1 + h2 ≤ H < h1 + h2 + h3; controlling within the above range can prevent the laser cleaning from severely damaging the current collector foil, resulting in the phenomenon of broken belts in the electrode sheet, that is, the laser needs to completely clean the active material coating on the surface of the electrode sheet. In addition, the actual laser cleaning depth can be appropriately adjusted according to the cleaning effect of the active material coating on the surface of the electrode sheet.

[0042] In a further embodiment of the present utility model, the thickness h1 of the first active material coating is 25 μm to 100 μm, specifically it can be 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, and can include but not be limited to the values listed above; the thickness h2 of the second active material coating is 5 μm to 50 μm, specifically it can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, and can include but not be limited to the values listed above; the thickness h3 of the current collector is 4 to 7 μm, specifically it can be 4 μm, 5 μm, 6 μm, 7 μm, and can include but not be limited to the values listed above, and is preferably 5 μm.

[0043] In a further embodiment of the present utility model, the current collector 1 is a metal foil; and / or the current collector includes a metal foil and a conductive agent coating coated on the surface of the metal foil. Among them, the current collector is a metal foil, specifically it can be any one of copper foil, aluminum foil, nickel, and stainless steel. The positive current collector is preferably aluminum foil, and the negative current collector is preferably copper foil; the conductive agent in the conductive agent coating coated on the surface of the metal foil can specifically be at least one of conductive carbon, carbon nanotubes, acetylene black, and Ketjen black.

[0044] In a further embodiment of the present utility model, the total length of the electrode sheet is 1700 to 1800 mm, and the width of the electrode sheet is 75 to 80 mm.

[0045] The electrode sheet is prepared in combination with the actual situation as follows to obtain the following examples and comparative examples:

[0046] Example 1

[0047] Preparation of positive electrode sheet and negative electrode sheet:

[0048] Step 1: Conductive carbon nanotubes are double-sided coated on a bright copper foil with a negative electrode thickness of 5 μm and a length of 1778.5 mm, and the coating areal density is 2 g / m 2 , thus obtaining the conductive carbon nanotube bottom-coated copper foil 1;

[0049] Step 2: Small particle fast-charging graphite and large particle high-compaction graphite are respectively used as the second active material layer and the first active material layer of the negative electrode, and are double-sided coated on the conductive carbon nanotube bottom-coated copper foil 1 obtained in Step 1. Among them, the coating areal density of the first active material layer is 50.7 g / m 2 , and the coating areal density of the second active material layer is 14.3 g / m 2 ; thus obtaining the coated negative electrode sheet;

[0050] Step 3: The coated negative electrode sheet obtained in Step 2 is roll-pressed and slit to obtain the negative electrode sheet before laser pretreatment;

[0051] Step 4: A laser etching machine with a laser power of 1000 W, a pulse frequency of 300 HZ, and a laser spot diameter of 0.02 mm is used to continuously clean the negative electrode sheet obtained in Step 3. Among them, the length of the first coating area for laser cleaning is 5 mm and the width is 79.1 mm (the cleaning width is equal to the width of the negative electrode sheet). The laser-cleaned negative electrode sheet is cut by die-cutting to obtain a wound negative electrode sheet (the die-cutting parameters of the negative electrode tab are shown in Table 2);

[0052] Step 5: LiCoO2 active material is double-sided coated on a positive electrode aluminum foil with a thickness of 9 μm and a length of 1746 mm, and the coating areal density is 118 g / m 2 , thus obtaining the coated positive electrode sheet;

[0053] Step 6: After the positive electrode sheet obtained in Step 5 is roll-pressed, slit, and processed into a sheet, a wound positive electrode sheet is obtained (the die-cutting parameters of the positive electrode tab are shown in Table 3).

[0054] Preparation of the battery:

[0055] The positive electrode sheet, negative electrode sheet, and separator prepared above are wound to obtain a bare battery cell. After the wound bare battery cell is encapsulated, baked, injected with electrolyte, formed, secondarily sealed, and capacity-divided, the described wound battery is obtained.

[0056] Comparative Example 1

[0057] Preparation of the positive electrode sheet and negative electrode sheet:

[0058] Step 1: Conductive carbon nanotubes are double-sided coated on a bright copper foil with a negative electrode thickness of 5 μm and a length of 1778.5 mm, and the coating areal density is 2 g / m 2 , thus obtaining the conductive carbon nanotube bottom-coated copper foil 1;

[0059] Step 2: Use small particle fast charging graphite and large particle high compaction graphite as the second active material layer and the first active material layer of the negative electrode respectively, and coat them double-sided on the conductive carbon nanotube bottom-coated copper foil obtained in Step 1. The surface density of the first active material layer coated is 50.7 g / m 2 , and the surface density of the second active material layer coated is 14.3 g / m 2 ; thus, the coated negative electrode sheet can be obtained;

[0060] Step 3: Subject the coated negative electrode sheet obtained in Step 2 to rolling, slitting, sheet making, and die cutting to obtain a wound negative electrode sheet (the die cutting parameters of the negative electrode tab are shown in Table 2);

[0061] Step 4: Double-sidedly coat the LiCoO2 active material on the positive electrode aluminum foil with a thickness of 9 μm and a length of 1746 mm. The surface density of the coating is 118 g / m 2 , thus obtaining the coated positive electrode sheet;

[0062] Step 5: Subject the positive electrode sheet obtained in Step 4 to rolling, slitting, and sheet making to obtain a wound positive electrode sheet (the die cutting parameters of the positive electrode tab are shown in Table 3).

[0063] Preparation of the battery:

[0064] Wind the above-prepared positive electrode sheet, negative electrode sheet, and separator to obtain a bare battery cell. After the wound bare battery cell is encapsulated, baked, injected with electrolyte, formed, secondarily sealed, and capacity graded, the described wound battery is obtained.

[0065] Arrange the preparation parameters of the negative electrode sheets in the above Example 1 and Comparative Example 1 in the following Table 1.

[0066] Perform room temperature step-down cycle tests on the batteries prepared in Example 1 and Comparative Example 1 respectively. The specific test data are as shown in Table 4 below and Figures 6 - 7 as follows.

[0067] 1. Capacity retention rate test method: Under the condition of room temperature 25 ± 3°C, for 1 - 100 cycles, the charging regime is: 4.7C CC to 4.15V, 3.5C CC to 4.25V CV to 3C, 3C CC to 4.48V CV to 2C, 2C CC to 4.55V CV to 0.60C;

[0068] For 100 - 800 cycles, the charging regime is: 4.7C CC to 4.12V, 3.5C CC to 4.22V CV to 3C, 3C CC to 4.48V CV to 2C, 2C CC to 4.53V, CV to 0.60C; where CC represents constant current charging and CV represents constant voltage charging;

[0069] 1 - 800 - cycle discharge regime: 0.7C DC to 3.0V; where DC represents constant - current discharge;

[0070] Capacity retention rate = weekly discharge capacity / initial discharge capacity * 100%.

[0071] 2. Thickness expansion rate test method:

[0072] After every 100 cycles of the battery cell, it is charged at a constant current and constant voltage of 0.5C to 4.5V with a cut - off rate of 0.02C for full charge, and thickness measurement is carried out using a 600g PPG thickness gauge;

[0073] Thickness expansion rate = full - charge thickness every 100 cycles / initial full - charge thickness * 100%.

[0074] Table 1

[0075]

[0076] Table 2

[0077] Tab tab number Tab tab positioning distance mm Tab tab number Tab tab positioning distance mm D1 44.7 D14 33.9 D2 30.5 D15 92.5 D3 89.1 D16 34.4 D4 31.5 D17 93.1 D5 89.6 D18 34.9 D6 32.0 D19 93.7 D7 90.2 D20 35.4 D8 32.5 D21 94.3 D9 90.8 D22 35.9 D10 33.0 D23 94.8 D11 91.4 D24 36.4 D12 33.4 D25 95.4 D13 91.9

[0078] Table 3

[0079] Tab tab number Tab tab positioning distance mm Tab tab number Tab tab positioning distance mm d1 102.9 d13 93.2 d2 29.4 d14 32.7 d3 90.4 d15 93.7 d4 30.2 d16 33.2 d5 91.0 d17 94.3 d6 30.7 d18 33.8 d7 91.5 d19 94.8 d8 31.2 d20 34.3 d9 92.1 d21 95.4 d10 31.7 d22 34.8 d11 92.6 d23 95.9 d12 32.2 d24 35.3

[0080] Table 4

[0081]

[0082] From the test results of the above Table 4 and Figures 4 - 5 it can be seen that compared with Comparative Example 1, Example 1 has one more step in the process of preparing the electrode sheet, that is, laser cleaning to remove the additional active material layer (i.e., laser cleaning removes the above - mentioned first coating area). By laser cleaning, the slurry at the head and tail of the electrode sheet during coating is too thick, which causes the side of the subsequent formed battery cell to be too thick and deformed, affecting the parallelism. At the same time, the part where lithium deposition is likely to occur on the side of the battery cell is removed. The thickness of the prepared electrode sheet after laser cleaning is more uniform. The prepared lithium - ion battery has a higher cycle capacity retention rate and a smaller thickness expansion rate. After 100 - 800 cycles, the change rate of Example 1 is smaller, and the performance of the lithium - ion battery is more stable.

[0083] In summary, for the electrode sheet provided by the present utility model, a first coating area and a second coating area are provided in the active material coating layer. When the active material coating layer is in the second preset length state, the active material coating layer covers the second coating area, and the length of the active material coating layer is equal to the length of the second coating area. The surface of the active material coating layer is a flat structure. When the length of the active material layer is equal to the length of the second coating area, the thickness of the electrode sheet is more uniform, the flatness of the surface of the battery cell in the subsequent process is improved, and the probability of lithium deposition on the side is reduced at the same time, thereby improving the long-term cycle stability of the battery cell.

[0084] Based on the disclosure and teachings of the above specification, those skilled in the art to which the present utility model pertains are also able to make changes and modifications to the above embodiments. Therefore, the present utility model is not limited to the above specific embodiments, and any obvious improvements, substitutions or variations made by those skilled in the art on the basis of the present utility model fall within the protection scope of the present utility model. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not impose any limitation on the present utility model.

Claims

1. An electrode sheet, characterized in that: It includes a current collector and an active material coating provided on at least one surface of the current collector; The current collector includes a first coating area and a second coating area connected to each other, and the first coating area is located on opposite sides of the second coating area; The active material coating includes a first preset length and a second preset length, and the second preset length is less than the first preset length; When the active material coating is in the first preset length state, the active material coating covers the first coating area and the second coating area; When the active material coating is in the second preset length state, the active material coating covers the second coating area, and the length of the active material coating is equal to the length of the second coating area, and the surface of the active material coating is a flat structure.

2. The electrode sheet according to claim 1, wherein: The length of the first coating area is 3-8 mm.

3. The electrode sheet according to claim 1, wherein: The active material coatings are respectively provided on both surfaces of the current collector, and the length of the active material coating on one surface is greater than the length of the active material coating on the other surface.

4. The electrode sheet according to claim 1, wherein: The active material coating includes a first active material coating provided on the surface of the current collector and a second active material coating provided on the surface of the first active material coating, and the areal density of the first active material coating is greater than the areal density of the second active material coating.

5. The electrode sheet according to claim 1, characterized in that: One or more tabs are provided on the current collector.

6. The electrode sheet according to claim 4, wherein: The depth of laser cleaning is H, the thickness of the first active material coating is h1, the thickness of the second active material coating is h2, and the thickness of the current collector is h3. Among them, H, h1, h2, and h3 satisfy the following relationship: h1 + h2 ≤ H < h1 + h2 + h3.

7. The electrode sheet according to claim 6, wherein: The thickness h1 of the first active material coating is 25 μm to 100 μm, the thickness h2 of the second active material coating is 5 μm to 50 μm, and the thickness h3 of the current collector is 4 to 7 μm.

8. The electrode sheet according to claim 1, characterized in that: The current collector is a metal foil; and / or the current collector includes a metal foil and a conductive agent coating coated on the surface of the metal foil.

9. A secondary battery, characterized in that: It includes the electrode sheet according to any one of claims 1 to 8.

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