Negative pole piece, battery monomer and secondary battery

Abstract

The invention provides a negative pole piece, a battery cell and a secondary battery, and relates to the technical field of secondary batteries. The negative pole piece comprises a negative current collector, a B active coating positioned on at least one surface of the negative current collector, and an A active coating positioned on the surface of the B active coating. Wherein the mass ratio B1 of the binder B in the active coating B is greater than the mass ratio A1 of the binder A in the active coating A. The conductive agent B in the active coating B comprises a dotted conductive agent B, and the conductive agent A in the active coating A comprises a linear conductive agent A. The battery containing the negative pole piece is relatively good in fast charging performance and cycle performance.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a negative electrode plate, a battery cell and a secondary battery. Background Art

[0002] With the rapid development of electronic devices and new energy vehicles, the performance requirements for lithium-ion batteries are getting higher and higher, especially the need for fast charging capabilities to shorten charging time. The traditional single-layer coating technology has limited the improvement of battery performance to a certain extent, and it is difficult to improve the fast charging performance. Double-layer coating technology is a key means to solve the aforementioned industry pain points. By coating two slurries of different properties on the current collector respectively, a double-layer structure electrode is formed, and the different layers of the electrode can be targeted and optimized according to different needs. The leading battery cell manufacturers in the industry have all carried out electrode gradient layering design, and related technologies have been reflected in specific products. For example, the "Shenxing" 4C super-charged battery released by CATL, the key technical means is the multi-gradient layering design, so as to achieve the fast charging performance of the battery.

[0003] However, the current method makes it difficult to take into account both the fast charging performance and the cycle performance of the battery. Summary of the Invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode plate, a battery cell and a secondary battery, aiming to take into account both the fast charging performance and the cycle performance of the battery.

[0005] In a first aspect, the present application provides a negative electrode sheet comprising: a negative electrode current collector, an active coating layer B disposed on at least one surface of the negative electrode current collector, and an active coating layer A disposed on the surface of the active coating layer B. The mass proportion B1 of the binder B in the active coating layer B is greater than the mass proportion A1 of the binder A in the active coating layer A. The conductive agent B in the active coating layer B comprises a point-shaped conductive agent B, and the conductive agent A in the active coating layer A comprises a linear conductive agent A.

[0006] In the above technical solution, the content of binder B in the active coating layer B close to the negative electrode current collector is higher, which can make the bonding strength between the negative electrode current collector and the active coating layer higher, and it is not easy for the active coating layer and the negative electrode current collector to peel off, thereby making the mechanical stability of the negative electrode plate higher, so as to increase the cycle performance of the battery; the content of binder A in the active coating layer A far away from the negative electrode current collector is lower, which can make more ion transmission channels and increase the transmission rate of active ions, so as to make the fast charging performance of the battery better. In addition, the point-shaped conductive agent B in the active coating layer B and the linear conductive agent A in the active coating layer A can make the conductivity of the negative electrode plate better and meet the transmission of electrons, and the linear conductive agent A in the active coating layer A can better form a conductive network, which can improve the electrochemical stability while meeting the fast charging performance, so that the cycle performance of the battery is better. The present application plays a synergistic role by controlling the conductive agent and the binder in the double-layer coating, while improving the cycle performance and fast charging performance of the battery.

[0007] In some embodiments, 0.3%≤B1-A1≤1%.

[0008] The above technical solution can meet the bonding performance of different coatings while taking into account the cycle performance and fast charging performance of the battery.

[0009] In some embodiments, B1 is 2.5% to 3.5%; A1 is 2% to 3%.

[0010] The above technical solution can meet the bonding performance of different coatings while taking into account the cycle performance and fast charging performance of the battery.

[0011] In some embodiments, the binder B and the binder A are each independently selected from at least one of polyvinylidene fluoride, polyacrylic acid, polyacrylamide, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0012] In the above technical solutions, these binders can all be selected as better binders for negative electrode sheets to meet the bonding performance of different coatings of different negative electrode sheets.

[0013] In some embodiments, the conductive agent A in the active coating A further includes a dot-shaped conductive agent A.

[0014] In the above technical solution, the conductive agent A in the active coating A includes linear conductive agent A and point-shaped conductive agent A, which can form a better conductive network. The addition of point-shaped conductive agent A can also reduce the cost of the negative electrode sheet.

[0015] In some embodiments, the mass proportion of the dot-shaped conductive agent B in the B active coating layer is 0.5% to 1.5%.

[0016] In the above technical solution, the conductivity of the B active coating can be improved to meet the electron transmission requirements of the B active coating.

[0017] In some embodiments, the mass proportion of the linear conductive agent A in the active coating A is 0.05% to 0.3%, and the mass proportion of the dot-shaped conductive agent A in the active coating A is 0% to 1%.

[0018] In the above technical solution, the active coating A can form a better conductive network, and the addition of the point-shaped conductive agent A within the above range can also reduce the cost of the negative electrode sheet.

[0019] In some embodiments, the dot-shaped conductive agent B and the dot-shaped conductive agent A are each independently selected from at least one of acetylene black, Ketjen black, and conductive carbon black.

[0020] In the above technical solution, these conductive agents are all good point-shaped conductive agents and can be added to the negative electrode plate.

[0021] In some embodiments, the linear conductive agent A is selected from at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

[0022] In the above technical solution, these conductive agents are all better linear conductive agents, which are convenient for forming a better conductive network in the A active coating.

[0023] In some embodiments, the ratio of the thickness of the B active coating to the thickness of the A active coating is (0.5-1.5):1.

[0024] In the above technical solution, the thickness of the two coating layers is controlled within the above range to better meet the fast charging performance of the battery.

[0025] In some embodiments, the active material B in the B active coating layer and the active material A in the A active coating layer are each independently selected from at least one of hard carbon, soft carbon, artificial graphite, and natural graphite.

[0026] In a second aspect, the present application provides a battery cell comprising the above-mentioned negative electrode plate.

[0027] In a third aspect, the present application provides a secondary battery comprising the above-mentioned battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic structural diagram of a negative electrode plate provided in an embodiment of the present application.

[0029] 100-negative electrode sheet; 110-negative electrode current collector; 121-B active coating; 122-A active coating. DETAILED DESCRIPTION

[0030] Below, the embodiments of the negative electrode sheet, battery cell and secondary battery of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0031] As used herein, "ranges" are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit, the selected lower and upper limits defining the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive and may be combined arbitrarily, i.e., any lower limit may be combined with any upper limit to form a range.

[0032] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution. Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution. Unless otherwise specified, all steps of the present application can be performed sequentially or randomly, but are preferably performed sequentially.

[0033] The present application provides a secondary battery, which includes a battery cell, which includes an electrode assembly and a battery shell. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator located between the positive electrode sheet and the negative electrode sheet. The electrode assembly can be a wound battery or a laminated battery. The electrode assembly is placed in the battery shell, and then the electrolyte is injected to form a battery cell after formation.

[0034] Figure 1 This is a schematic diagram of the structure of a negative electrode sheet 100 provided in an embodiment of the present application. Figure 1 The negative electrode sheet 100 includes a negative electrode current collector 110, a B active coating layer 121 located on at least one surface of the negative electrode current collector 110, and an A active coating layer 122 located on the surface of the B active coating layer 121. The mass proportion B1 of the binder B in the B active coating layer 121 is greater than the mass proportion A1 of the binder A in the A active coating layer 122. The conductive agent B in the B active coating layer 121 includes a dot-shaped conductive agent B, and the conductive agent A in the A active coating layer 122 includes a linear conductive agent A.

[0035] In the above technical solution, the content of binder B in the B active coating 121 close to the negative electrode current collector 110 is higher, which can make the bonding strength between the negative electrode current collector 110 and the active coating higher, and it is not easy for the active coating and the negative electrode current collector 110 to peel off, thereby making the mechanical stability of the negative electrode plate 100 higher, so as to increase the cycle performance of the battery; the content of binder A in the A active coating 122 away from the negative electrode current collector 110 is lower, which can make more ion transmission channels and increase the transmission rate of active ions, so as to make the fast charging performance of the battery better. In addition, the point-shaped conductive agent B in the B active coating 121 and the linear conductive agent A in the A active coating 122 can make the conductivity of the negative electrode plate 100 better and meet the transmission of electrons, and the linear conductive agent A in the A active coating 122 can better form a conductive network, which can improve the electrochemical stability while meeting the fast charging performance, so that the cycle performance of the battery is better. The present application plays a synergistic role by controlling the conductive agent and the binder in the double-layer coating, while improving the cycle performance and fast charging performance of the battery.

[0036] in, Figure 1 In the embodiment, both surfaces of the negative electrode current collector 110 have the B active coating 121 and the A active coating 122 ; alternatively, only one surface of the negative electrode current collector 110 may have the B active coating 121 and the A active coating 122 , which is not limited in this application.

[0037] In some embodiments, 0.3%≤B1-A1≤1%, which can meet the bonding performance of different coatings while taking into account the cycle performance and fast charging performance of the battery.

[0038] As an example, the value of B1-A1 is 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1.0%; in other embodiments, the value of B1-A1 can also be 0.2%, 0.1%, 1.1%, 1.2%, etc.

[0039] In some embodiments, B1 is 2.5% to 3.5% and A1 is 2% to 3%, which can meet the bonding performance of different coatings while taking into account the cycle performance and fast charging performance of the battery.

[0040] As an example, the value of B1 is 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4% or 3.5%; the value of A1 is 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9% or 3%; and B1>A1.

[0041] In some embodiments, binder B and binder A are each independently selected from at least one of polyvinylidene fluoride, polyacrylic acid, polyacrylamide, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR). These binders can be used as preferred binders for the negative electrode sheet 100 to meet the bonding requirements of different coatings on different negative electrode sheets 100.

[0042] The adhesive B and the adhesive A may be the same or different. The adhesive B may be a single adhesive or a mixed adhesive. The adhesive A may be a single adhesive or a mixed adhesive.

[0043] In some embodiments, the conductive agent A in the A active coating 122 further includes a dot-shaped conductive agent A. The conductive agent in the A active coating 122 includes both linear conductive agent A and dot-shaped conductive agent A, which can form a better conductive network. The addition of the dot-shaped conductive agent A can also reduce the cost of the negative electrode sheet 100.

[0044] In some embodiments, the mass proportion of the dot-shaped conductive agent B in the B active coating 121 is 0.5% to 1.5%, which can improve the conductivity of the B active coating 121 and meet the requirements of electron transmission in the B active coating 121.

[0045] As an example, the mass proportion of the dot-shaped conductive agent B in the B active coating layer 121 is 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4% or 1.5%.

[0046] The conductive agent B may not contain any linear conductive agent, or may contain a small amount of linear conductive agent B, which is not limited in this application, as long as the content of the linear conductive agent B is less than that of the linear conductive agent A in the conductive agent A.

[0047] In some embodiments, the mass proportion of the linear conductive agent A in the A active coating layer 122 is 0.05% to 0.3%, and the mass proportion of the dot-shaped conductive agent A in the A active coating layer 122 is 0% to 1%. This can form a better conductive network in the A active coating layer 122. Furthermore, the addition of the dot-shaped conductive agent A within the above range can also reduce the cost of the negative electrode sheet 100.

[0048] As an example, the mass proportion of the linear conductive agent A in the A active coating 122 is 0.05%, 0.1%, 0.15%, 0.2%, 0.25% or 0.3%, and the mass proportion of the point-shaped conductive agent A in the A active coating 122 is 0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%.

[0049] In some embodiments, the dot-shaped conductive agent B and the dot-shaped conductive agent A are each independently selected from at least one of acetylene black, Ketjen black, and conductive carbon black. These conductive agents are all good dot-shaped conductive agents and can be added to the negative electrode sheet 100.

[0050] Among them, the selection of point-shaped conductive agent B and point-shaped conductive agent A can be the same or different. Point-shaped conductive agent B can be a single point-shaped conductive agent or a mixed point-shaped conductive agent; point-shaped conductive agent A can also be a single point-shaped conductive agent or a mixed point-shaped conductive agent.

[0051] In some embodiments, the linear conductive agent A is selected from at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers. These conductive agents are all good linear conductive agents, which facilitate forming a better conductive network in the active coating A 122 .

[0052] In some embodiments, the ratio of the thickness of the B active coating 121 to the thickness of the A active coating 122 is (0.5-1.5):1. The thickness of the two coating layers is controlled within the above range to better meet the fast charging performance of the battery.

[0053] As an example, the ratio of the thickness of the B active coating layer 121 to the thickness of the A active coating layer 122 is 0.5:1, 0.7:1, 0.9:1.1, 1.3:1, or 1.5:1.

[0054] In some embodiments, the active material B in the B active coating layer 121 and the active material A in the A active coating layer 122 are each independently selected from at least one of hard carbon, soft carbon, artificial graphite, and natural graphite.

[0055] The active material B and the active material A may be the same or different. The active material B may be a single active material or a mixture of active materials. The active material A may also be a single active material or a mixture of active materials.

[0056] After introducing the structure of the negative electrode sheet 100 above, the preparation method of the negative electrode sheet 100 will be specifically introduced below.

[0057] The preparation method of the negative electrode sheet 100 includes: The active slurry B is prepared, including: mixing the active material B, the binder B and the conductive agent B in deionized water according to a certain ratio to form the active slurry B.

[0058] The active slurry A is prepared, including: mixing the active material A, the binder A and the conductive agent A in deionized water according to a certain ratio to form the active slurry A.

[0059] Active slurry B is coated on the surface of the negative electrode current collector 110 and dried to obtain a B active coating 121 ; active slurry A is then coated on the surface of the B active coating 121 and dried to form an A active coating 122 to obtain the negative electrode sheet 100 .

[0060] Example Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0061] Example 1 This embodiment provides a method for preparing a battery cell, comprising the following steps: (1) Preparation of negative electrode sheet 100: Artificial graphite, carbon black SP (point-shaped conductive agent), binder SBR and binder CMC were mixed in deionized water at a mass ratio of 96:0.8:1.8:1.4 to form an active slurry B with a solid content of 60%.

[0062] Artificial graphite, carbon nanotubes (CNT, linear conductive agent), carbon black SP (point-shaped conductive agent), binder SBR and binder CMC were mixed in deionized water in a mass ratio of 96.7:0.1:0.4:1.4:1.4 to form an active slurry A with a solid content of 60%.

[0063] Active slurry B is coated on the surface of 6μm copper foil, dried and cold pressed to obtain B active coating 121 with a thickness of 80μm; then active slurry A is coated on the surface of B active coating 121, dried and cold pressed to obtain A active coating 122 with a thickness of 80μm, and cut to obtain negative electrode sheet 100.

[0064] (2) Preparation of positive electrode sheet: Lithium manganese iron phosphate material, acetylene black, and polyvinylidene fluoride are mixed in N-methylpyrrolidone in a mass ratio of 96:2:2 to form a positive electrode active slurry with a solid content of 60%.

[0065] The positive electrode active slurry was coated on the surface of 9 μm aluminum foil, dried and cold pressed to obtain a positive electrode active coating with a thickness of 200 μm, and then cut to obtain a positive electrode sheet.

[0066] (3) Preparation of electrode assembly: The separator is made of PP (polypropylene) and has a thickness of 20 μm. The negative electrode sheet 100, the separator, the positive electrode sheet, and the separator are stacked and wound to form an electrode assembly.

[0067] (4) Preparation of battery cells: The electrode assembly is placed in the shell and injected with electrolyte (the electrolyte is composed of ethylene carbonate and diethyl carbonate mixed in a volume ratio of 1:1:1, and LiPF6 is dissolved in the above solvent. The concentration of LiPF6 is 1 mol / L). Then, after vacuum packaging, standing, formation, shaping and other processes, a battery cell is obtained.

[0068] Example 2 The difference between Example 2 and Example 1 is that: (1) Preparation of negative electrode sheet 100: Artificial graphite, carbon black SP (point-shaped conductive agent), binder SBR and binder CMC were mixed in deionized water at a mass ratio of 96:0.8:1.8:1.4 to form an active slurry B with a solid content of 60%.

[0069] Artificial graphite, carbon nanotubes (CNT, linear conductive agent), carbon black SP (point-shaped conductive agent), binder SBR and binder CMC were mixed in deionized water in a mass ratio of 97.1:0.1:0.4:1.2:1.2 to form an active slurry A with a solid content of 60%.

[0070] Active slurry B is coated on the surface of 6μm copper foil, dried and cold pressed to obtain B active coating 121 with a thickness of 80μm; then active slurry A is coated on the surface of B active coating 121, dried and cold pressed to obtain A active coating 122 with a thickness of 80μm, and cut to obtain negative electrode sheet 100.

[0071] Example 3 The difference between Example 3 and Example 1 is that: (1) Preparation of negative electrode sheet 100: Artificial graphite, carbon black SP (point-shaped conductive agent), binder SBR and binder CMC were mixed in deionized water at a mass ratio of 96:0.8:1.8:1.4 to form an active slurry B with a solid content of 60%.

[0072] Artificial graphite, carbon nanotubes (CNT, linear conductive agent), binder SBR and binder CMC were mixed in deionized water at a mass ratio of 97:0.2:1.4:1.4 to form an active slurry A with a solid content of 60%.

[0073] Active slurry B is coated on the surface of 6μm copper foil, dried and cold pressed to obtain B active coating 121 with a thickness of 80μm; then active slurry A is coated on the surface of B active coating 121, dried and cold pressed to obtain A active coating 122 with a thickness of 80μm, and cut to obtain negative electrode sheet 100.

[0074] Example 4 The difference between Example 4 and Example 1 is that: (1) Preparation of negative electrode sheet 100: Artificial graphite, carbon black SP (point-shaped conductive agent), binder SBR and binder CMC were mixed in deionized water at a mass ratio of 96:0.8:1.8:1.4 to form an active slurry B with a solid content of 60%.

[0075] Artificial graphite, carbon nanotubes (CNT, linear conductive agent), binder SBR and binder CMC were mixed in deionized water at a mass ratio of 97.4:0.2:1.2:1.2 to form an active slurry A with a solid content of 60%.

[0076] Active slurry B is coated on the surface of 6μm copper foil, dried and cold pressed to obtain B active coating 121 with a thickness of 80μm; then active slurry A is coated on the surface of B active coating 121, dried and cold pressed to obtain A active coating 122 with a thickness of 80μm, and cut to obtain negative electrode sheet 100.

[0077] Comparative Example 1 The difference between Comparative Example 1 and Example 3 is: (1) Preparation of negative electrode sheet: Artificial graphite, carbon black SP (point-shaped conductive agent), binder SBR and binder CMC were mixed in deionized water in a mass ratio of 96:0.8:1.8:1.4 to form a negative electrode active slurry with a solid content of 60%.

[0078] The negative electrode active slurry was coated on the surface of a 6 μm copper foil, dried and cold pressed to obtain a negative electrode active coating with a thickness of 160 μm, and then cut to obtain a negative electrode sheet.

[0079] Comparative Example 2 The difference between Comparative Example 2 and Example 3 is: (1) Preparation of negative electrode sheet: Artificial graphite, carbon black SP (point-shaped conductive agent), binder SBR and binder CMC were mixed in deionized water at a mass ratio of 96:0.8:1.8:1.4 to form an active slurry B with a solid content of 60%.

[0080] Artificial graphite, carbon black SP (point-shaped conductive agent), binder SBR and binder CMC were mixed in deionized water at a mass ratio of 96.8:0.8:1.2:1.2 to form an active slurry A with a solid content of 60%.

[0081] Active slurry B was coated on the surface of 6μm copper foil, dried and cold pressed to obtain B active coating with a thickness of 80μm; then active slurry A was coated on the surface of B active coating, dried and cold pressed to obtain A active coating with a thickness of 80μm, and cut to obtain negative electrode sheets.

[0082] Some parameters of the battery cells in the above-mentioned Examples 1 to 4 and Comparative Examples 1 and 2 are shown in Table 1.

[0083] Test Example 1 Table 1 shows the performance tests of the battery cells in Examples 1 to 4 and Comparative Examples 1 and 2.

[0084] Cycling performance: In a constant temperature chamber set at 25°C, charge at a 3C fast charge strategy, let it rest for 0.5 hours, then discharge at a 1C current to a cutoff voltage of 2.5V. Let it rest for 0.5 hours before entering the next charge-discharge cycle. Repeat this cycle for a total of 500 charge-discharge cycles. Cycle capacity retention = (discharge capacity at the 500th cycle / initial discharge capacity) × 100%.

[0085] Fast charging performance: A portion of the electrode assembly prepared above was prepared into three electrodes, which were directly charged at 3C at 25°C. The negative electrode potential was then monitored until it reached 0V, and charging was terminated.

[0086] At 25 degrees Celsius and 3C charging, the lithium deposition cut-off SOC = charging cut-off time / 1200s.

[0087] Table 1 Some parameters of battery cells and battery performance in the examples and comparative examples

[0088] It can be seen from Table 1 that compared with Comparative Example 1, the fast charging performance and cycle performance of the batteries provided in Examples 1 to 4 are better.

[0089] From the comparison between Example 3 and Example 4 and Example 1 and Example 2, it can be seen that the selection of CNT as the conductive agent A in the active coating A can significantly improve the fast charging performance of the battery.

[0090] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode plate, characterized in that: include: A negative electrode current collector, an active coating layer B located on at least one surface of the negative electrode current collector, and an active coating layer A located on the surface of the active coating layer B; The mass proportion B1 of the binder B in the B active coating is greater than the mass proportion A1 of the binder A in the A active coating; The conductive agent B in the B active coating layer includes a point-shaped conductive agent B, and the conductive agent A in the A active coating layer includes a line-shaped conductive agent A.

2. The negative electrode sheet according to claim 1, wherein: 0.3%≤B1-A1≤1%; Or / and, the B1 is 2.5%~3.5%; the A1 is 2%~3%.

3. The negative electrode sheet according to claim 1, wherein: The binder B and the binder A are each independently selected from at least one of polyvinylidene fluoride, polyacrylic acid, polyacrylamide, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

4. The negative electrode sheet according to any one of claims 1 to 3, wherein: The conductive agent A in the active coating A also includes a dot-shaped conductive agent A.

5. The negative electrode sheet according to claim 4, wherein: The mass proportion of the dot-shaped conductive agent B in the B active coating is 0.5% to 1.5%; Or / and, the mass proportion of the linear conductive agent A in the active coating A is 0.05% to 0.3%, and the mass proportion of the dot-shaped conductive agent A in the active coating A is 0% to 1%.

6. The negative electrode sheet according to claim 4, wherein: The dot-shaped conductive agent B and the dot-shaped conductive agent A are each independently selected from at least one of acetylene black, Ketjen black and conductive carbon black; Or / and, the linear conductive agent A is at least one selected from single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

7. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The ratio of the thickness of the B active coating to the thickness of the A active coating is (0.5-1.5):

1.

8. The negative electrode sheet according to any one of claims 1 to 3, wherein: The active material B in the B active coating layer and the active material A in the A active coating layer are each independently selected from at least one of hard carbon, soft carbon, artificial graphite and natural graphite.

9. A battery cell, characterized in that: The negative electrode sheet according to any one of claims 1 to 8 is used.

10. A secondary battery, characterized in that: The invention comprises the battery cell described in claim 9.

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