A negative electrode sheet, a secondary battery, and an electric device

Abstract

The application relates to a negative electrode sheet, a secondary battery and a power utilization device, and belongs to the technical field of batteries. The negative electrode sheet comprises a current collector and a coating arranged on at least one side surface of the current collector; the coating comprises a silicon coating and an active material coating, the silicon coating is arranged between the current collector and the active material coating; the silicon coating comprises a carboxyl polymer, silicon-containing active particles and a conductive agent; the carboxyl polymer contains -COOM, wherein M is at least one of H, Li, Na and K; and the active material coating comprises a negative electrode active material, a conductive agent and a binder. The negative electrode sheet has a low expansion rate in the charging and discharging process, and can make the battery have excellent cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a negative electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] Currently, commercial lithium-ion batteries mainly consist of carbon-based anodes and lithium transition metal oxide cathodes. However, the theoretical capacity of carbon-based anodes is limited (e.g., the theoretical capacity of graphite anodes is 372 mAh / g), making it difficult to meet the demands of high-energy-density batteries. Compared to carbon-based anodes, silicon-based anodes have a theoretical capacity of up to 4212 mAh / g, making them one of the most promising anode materials and capable of significantly improving battery energy density. However, silicon-based anodes undergo anisotropic expansion and contraction during lithium insertion and extraction, with a volume change rate as high as 300%. The enormous internal stress caused by this volume change pushes the silicon material to its mechanical limits, eventually leading to breakage and detachment, thus affecting the integrity of the electrode. Simultaneously, interfacial stress causes a loss of good contact between the active material, conductive agent, and current collector, resulting in poor battery cycle performance. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a negative electrode sheet, a secondary battery, and an electrical device.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] In a first aspect, the present invention provides a negative electrode sheet, comprising a current collector and a coating disposed on at least one surface of the current collector; the coating comprises a silicon coating and an active material coating, wherein the silicon coating is located between the current collector and the active material coating;

[0006] The silicon coating comprises a carboxyl polymer, silicon-containing active particles, and a conductive agent;

[0007] The carboxyl polymer contains -COOM, wherein M is at least one of H, Li, Na, and K;

[0008] The active material coating includes a negative electrode active material, a conductive agent, and a binder.

[0009] As an embodiment of the present invention, the mass percentage of carboxyl polymer in the silicon coating is 1% to 10%.

[0010] As an embodiment of the present invention, the molar percentage of -COOM in the carboxyl polymer is 50% to 70%.

[0011] As an embodiment of the present invention, the chemical structural formula of the carboxyl polymer is:

[0012]

[0013] Wherein, M is at least one of H, Li, Na, and K;

[0014] R1, R2, and R3 are each independently selected from at least one of H, C1-C3 straight-chain or branched alkyl groups;

[0015] m1, m2, and m3 satisfy the following condition: 50% ≤ m1 / (m1+m2+m3) ≤ 70%.

[0016] As an embodiment of the present invention, the silicon-containing active particles include at least one of nano-silicon, silicon oxide, and silicon carbon.

[0017] In one embodiment of the present invention, the mass percentage of silicon coating in the coating is 2% to 5%.

[0018] As an embodiment of the present invention, the negative electrode active material includes graphite, or a mixture of at least one of nano-silicon, silicon oxide, and silicon carbon with graphite.

[0019] As an embodiment of the present invention, the average thickness of the coating is 25 to 40 μm.

[0020] Secondly, the present invention provides a secondary battery comprising the aforementioned negative electrode plate.

[0021] Thirdly, the present invention provides an electrical device comprising the aforementioned secondary battery, wherein the secondary battery serves as the power supply for the electrical device.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] This invention involves depositing a silicon coating, primarily composed of carboxyl polymers, silicon-containing active particles, and a conductive agent, between the current collector and the active material layer in the negative electrode sheet. This ensures that the silicon is uniformly arranged and aligned in the same direction throughout the negative electrode sheet, resulting in more uniform overall expansion of the negative electrode sheet during charging and discharging, thus reducing the expansion of the negative electrode sheet. Furthermore, the carboxyl groups on the molecular chains of the carboxyl polymer in the silicon coating can undergo condensation reactions with the hydroxyl groups on the oxide layer of the silicon-containing active particles, forming hydrogen bonds and ion-dipole interactions. This enables the negative electrode sheet to achieve a self-healing effect during expansion and contraction. Simultaneously, the side chain groups in the carboxyl polymer can make multidimensional contact with the silicon-containing active particles, thereby preventing molecular chain slippage and effectively limiting the movement of the silicon-containing active particles. This significantly enhances the adhesion between the silicon-containing active particles and the current collector, reduces adhesion failure between the silicon-containing active particles and the current collector, and endows the battery with excellent cycle performance. Attached Figure Description

[0024] Figure 1This is a schematic diagram of the negative electrode sheet in Example 1. Detailed Implementation

[0025] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments and comparative examples. The purpose of this description is to provide a detailed understanding of the invention, not to limit its scope. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention. Unless otherwise specified, the experimental reagents and instruments involved in the implementation of this invention are commonly used reagents and instruments.

[0026] According to a first aspect of the present invention, a negative electrode sheet is provided, comprising a current collector and a coating disposed on at least one surface of the current collector; the coating comprises a silicon coating and an active material coating, the silicon coating being located between the current collector and the active material layer;

[0027] The silicon coating comprises a carboxyl polymer, silicon-containing active particles, and a conductive agent;

[0028] The carboxyl polymer contains -COOM, wherein M is at least one of H, Li, Na, and K;

[0029] The active material coating includes a negative electrode active material, a conductive agent, and a binder.

[0030] This invention involves depositing a silicon coating, primarily composed of carboxyl polymers, silicon-containing active particles, and a conductive agent, between the current collector and the active material layer in the negative electrode sheet. This ensures that the silicon is uniformly arranged and aligned in the same direction throughout the negative electrode sheet, resulting in more uniform overall expansion of the negative electrode sheet during charging and discharging, thus reducing the expansion of the negative electrode sheet. Furthermore, the carboxyl groups on the molecular chains of the carboxyl polymer in the silicon coating can undergo condensation reactions with the hydroxyl groups on the oxide layer of the silicon-containing active particles, forming hydrogen bonds and ion-dipole interactions. This enables the negative electrode sheet to achieve a self-healing effect during expansion and contraction. Simultaneously, the side chain groups in the carboxyl polymer can make multidimensional contact with the silicon-containing active particles, thereby preventing molecular chain slippage and effectively limiting the movement of the silicon-containing active particles. This significantly enhances the adhesion between the silicon-containing active particles and the current collector, reduces adhesion failure between the silicon-containing active particles and the current collector, and endows the battery with excellent cycle performance.

[0031] Optionally, the carboxyl polymer is polymerized from acrylic monomers, acrylamide monomers, and acrylonitrile monomers.

[0032] Optionally, the conductive agent in the silicon coating includes, but is not limited to, at least one of graphite, acetylene black, carbon black, carbon nanotubes, and carbon fibers.

[0033] Optionally, the conductive agent in the active material coating includes, but is not limited to, at least one of graphite, acetylene black, carbon black, carbon nanotubes, and carbon fibers; the binder includes, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyurethane (PU), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0034] As an embodiment of the present invention, the mass percentage of the carboxyl polymer in the silicon coating is 1% to 10%. Optionally, the mass percentage of the carboxyl polymer in the silicon coating can be any or both of the following: 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, and 10%. Studies have found that the carboxyl polymer at the above-mentioned mass percentages not only provides excellent adhesion to effectively prevent the silicon coating from peeling off from the current collector, but also maintains low impedance, thereby significantly improving the cycle performance of the battery.

[0035] As an embodiment of the present invention, the molar percentage of -COOM in the carboxyl polymer is 50% to 70%. Optionally, the molar percentage of -COOM in the carboxyl polymer can specifically be any one or a combination of 50%, 55%, 60%, 65%, and 70%. Studies have found that carboxyl polymers containing the above-mentioned molar percentages of -COOM can provide suitable intermolecular forces to ensure excellent adhesion performance, thereby improving the cycle performance of the battery.

[0036] As an embodiment of the present invention, the chemical structural formula of the carboxyl polymer is:

[0037]

[0038] Wherein, M is at least one of H, Li, Na, and K;

[0039] R1, R2, and R3 are each independently selected from at least one of H, C1-C3 straight-chain or branched alkyl groups;

[0040] m1, m2, and m3 satisfy the following condition: 50% ≤ m1 / (m1+m2+m3) ≤ 70%.

[0041] In the M1 block compound, the carboxyl group can undergo a condensation reaction with the hydroxyl group on the oxide layer of the silicon-containing active particles to form hydrogen bonds and ion-dipole interactions, thereby enabling the negative electrode to achieve a self-healing effect during expansion and contraction.

[0042] M2 block compounds can make multidimensional contact with silicon-containing active particles, thereby preventing molecular chain slippage and effectively limiting the movement of silicon-containing active particles, thus greatly enhancing the adhesion between silicon-containing active particles and current collectors.

[0043] The nitrile groups in the M3 block compounds can enhance the ionic conductivity of the binder, thereby improving its electrochemical performance.

[0044] As an embodiment of the present invention, the silicon-containing active particles include at least one of nano-silicon, silicon oxide, and silicon carbon.

[0045] As an embodiment of the present invention, the mass percentage of the silicon coating in the coating is 2% to 5%. Optionally, the mass percentage of the silicon coating in the coating can be any one or a combination of 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%. Studies have found that a silicon coating mass percentage of 2% to 5% not only facilitates coating to form a uniform silicon coating, but also allows the carboxyl polymer to better bind the silicon coating, preventing excessive expansion and delamination of the silicon coating, thereby resulting in better cycle performance of the battery.

[0046] As an embodiment of the present invention, the negative electrode active material includes graphite, or a mixture of graphite with at least one of nano-silicon, silicon oxide, and silicon carbon. Preferably, the mass percentage of graphite in the negative electrode active material is ≥50%, more preferably 90% to 100%; specifically, it can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc.

[0047] As an embodiment of the present invention, the average thickness of the coating is 25–40 μm. Optionally, the average thickness of the coating can specifically be any or both of the following: 25 μm, 27 μm, 30 μm, 33 μm, 35 μm, 38 μm, and 40 μm.

[0048] Secondly, the present invention provides a secondary battery comprising the aforementioned negative electrode plate.

[0049] Thirdly, the present invention provides an electrical device comprising the aforementioned secondary battery, wherein the secondary battery serves as the power supply for the electrical device.

[0050] To clearly understand the technical solution of the present invention, the present invention will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed by the present invention.

[0051] AMN polymer (chemical structure shown in formula (I), where M, R1, R2 and R3 are all H) is obtained by free radical polymerization of acrylic acid monomer, acrylamide monomer and acrylonitrile monomer. The molar percentage of carboxyl groups in AMN polymer is controlled by adjusting the amount of acrylic acid monomer.

[0052]

[0053] Example 1

[0054] This embodiment provides a negative electrode sheet, the preparation method of which includes the following steps:

[0055] S1. Mix the carboxyl polymer (AMN polymer, wherein the molar percentage of carboxyl groups is 60% (i.e., m1 / (m1+m2+m3)=60%, m1:m2:m3=6:2:2)), silicon-containing active particles (silicon carbon), conductive agent (CNT), and solvent (deionized water) evenly to obtain coating slurry 1 (where the mass ratio of silicon-containing active particles, carboxyl polymer, and conductive agent is 90:5:5).

[0056] The negative electrode active material (graphite), thickener (CMC), conductive agent (Super-P), binder (SBR) and solvent (deionized water) are mixed evenly to obtain coating slurry 2 (where the mass ratio of negative electrode active material, thickener, conductive agent and binder is 95:2:2:1).

[0057] S2. Coating slurry 1 from S1 is applied to both sides of the copper foil and dried to form a silicon coating. Then, coating slurry 2 from S1 is applied to the surface of the silicon coating and dried to form an active material layer, thus obtaining a negative electrode sheet (wherein the mass percentage of the silicon coating in the coating (i.e., silicon coating + active material layer) is 2%).

[0058] The average thickness of the coating in the negative electrode sheet was measured to be 30 μm.

[0059] Example 2

[0060] This embodiment provides a negative electrode sheet, the preparation method of which is basically the same as that of Embodiment 1, except that the mass ratio of silicon coating in the coating of the negative electrode sheet in step S2 is 3%.

[0061] Example 3

[0062] This embodiment provides a negative electrode sheet, the preparation method of which is basically the same as that of Embodiment 1, except that the mass ratio of silicon coating in the coating of the negative electrode sheet in step S2 is 4%.

[0063] Example 4

[0064] This embodiment provides a negative electrode sheet, the preparation method of which is basically the same as that of Embodiment 1, except that the mass ratio of silicon coating in the coating of the negative electrode sheet in step S2 is 5%.

[0065] Example 5

[0066] This embodiment provides a negative electrode sheet, the preparation method of which is basically the same as that of Example 1, except that: in step S1, the mass ratio of silicon active particles, carboxyl polymer and conductive agent in coating slurry 1 is 94:1:5.

[0067] Example 6

[0068] This embodiment provides a negative electrode sheet, the preparation method of which is basically the same as that of Example 1, except that: in step S1, the mass ratio of silicon active particles, carboxyl polymer and conductive agent in coating slurry 1 is 85:10:5.

[0069] Example 7

[0070] This embodiment provides a negative electrode sheet, the preparation method of which is basically the same as that of Example 1, except that: the carboxyl polymer in the coating slurry 1 in step S1 is an AMN polymer, wherein the molar percentage of carboxyl groups is 50% (i.e., m1 / (m1+m2+m3)=50%, m1:m2:m3=5:2:3).

[0071] Example 8

[0072] This embodiment provides a negative electrode sheet, the preparation method of which is basically the same as that of Example 1. The difference is that the carboxyl polymer in the coating slurry 1 in step S1 is an AMN polymer, wherein the molar percentage of carboxyl groups is 70% (i.e., m1 / (m1+m2+m3)=70%, m1:m2:m3=7:1:2).

[0073] Example 9

[0074] This embodiment provides a negative electrode sheet, the preparation method of which is basically the same as that of Embodiment 1, except that the silicon-containing active particles in the coating slurry 1 in step S1 are silicon oxide.

[0075] Example 10

[0076] This embodiment provides a negative electrode sheet, the preparation method of which is basically the same as that of Example 1, except that: in step S1, the negative electrode active material in the coating slurry 2 is composed of graphite and silicon carbon in a mass ratio of 90:10.

[0077] Comparative Example 1

[0078] This comparative example provides a negative electrode sheet, the preparation method of which is basically the same as that in Example 1, except that step S2 is as follows:

[0079] S2. Mix coating slurry 1 and coating slurry 2 in S1 evenly (satisfying a / (a+b)=2%, where a is the total mass of carboxyl polymer, silicon-containing active particles and conductive agent in coating slurry 1, and b is the total mass of negative electrode active material, thickener, conductive agent and binder in coating slurry 2) to obtain a mixed slurry; then coat the mixed slurry on both sides of the copper foil and dry it to form a coating to obtain a negative electrode sheet.

[0080] Comparative Example 2

[0081] This comparative example provides a negative electrode sheet, the preparation method of which is basically the same as that of Example 1, except that: in step S1, the molar percentage content of carboxyl groups in the carboxyl polymer AMN polymer in the coating slurry 1 is 100%, and the chemical structural formula of the carboxyl polymer is:

[0082]

[0083] Comparative Example 3

[0084] This comparative example provides a negative electrode sheet, the preparation method of which is basically the same as that of Example 1, except that: the carboxyl polymer AMN polymer in the coating slurry 1 in step S1 does not contain carboxyl groups, wherein m2:m3=1:1, and the chemical structural formula of the carboxyl polymer is:

[0085]

[0086] Comparative Example 4

[0087] This comparative example provides a negative electrode sheet, the preparation method of which is as follows:

[0088] S1. Mix the carboxyl polymer (AMN polymer, wherein the molar percentage of carboxyl groups is 60% (i.e., m1 / (m1+m2+m3)=60%, m1:m2:m3=6:2:2)), silicon-containing active particles (silicon-carbon), negative electrode active material (graphite), conductive agent (CNT), and solvent (deionized water) uniformly to obtain a coating slurry (wherein the mass ratio of silicon-containing active particles, negative electrode active material graphite, carboxyl polymer, and conductive agent is 1.8:93.1:2:3.1, wherein the proportion of silicon-containing active particles and negative electrode active material graphite is the same as in Example 1);

[0089] S2. The coating slurry in S1 is coated on both sides of the copper foil and dried to form an active material layer, thus obtaining the negative electrode sheet.

[0090] Performance testing

[0091] The negative electrode sheet from each embodiment and comparative example is stacked sequentially with the positive electrode sheet and separator, with the separator (PE film) positioned between the positive and negative electrode sheets. After welding, winding, and hot pressing, a bare cell is obtained. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±5℃ for 24 hours. Electrolyte is injected into the dried battery, and the battery is allowed to stand, form, and be capacity tested to obtain a lithium-ion soft-pack battery.

[0092] The preparation of the above-mentioned positive electrode sheet includes the following steps: the positive electrode active material lithium cobalt oxide, the conductive agent acetylene black, the conductive agent CNT and the binder PVDF are mixed in a mass ratio of 98:0.5:0.7:0.8 and then added to N-methylpyrrolidone (NMP) and stirred thoroughly to form a positive electrode slurry with a solid content of 76%. The positive electrode slurry is then coated on aluminum foil, dried, rolled and cut to obtain the positive electrode sheet.

[0093] The electrolyte is a 1 mol / L LiPF6 solution, wherein the solvent is composed of EP:EC:DEC in a volume ratio of 4:3:3.

[0094] The performance of the above-mentioned lithium-ion pouch batteries was tested, and the specific test methods are as follows:

[0095] 1) Capacity Retention Rate: The lithium-ion battery was repeatedly charged and discharged using the following steps, and the cycle capacity retention rate was calculated. First, a first charge and discharge cycle was performed at 25°C. Constant current and constant voltage charging was conducted at a charging current of 0.1C (the current value required to completely discharge the theoretical capacity within 10 hours) until the upper limit voltage reached 4.53V. Then, constant current discharging was performed at a discharging current of 1C until the final voltage reached 3V. The discharge capacity of the first cycle was recorded. Subsequently, 200 charge and discharge cycles were performed, and the discharge capacity of the 200th cycle was recorded. Cycle capacity retention rate = (Discharge capacity of the 200th cycle / Discharge capacity of the first cycle) × 100%.

[0096] 2) Volume Expansion Rate: The lithium-ion secondary battery was repeatedly charged and discharged using the following steps to calculate the cycle expansion rate. First, the initial thickness of the battery was measured at room temperature. Then, in an environment of 25°C, the battery was subjected to 200 constant current charge-discharge cycles at a discharge current of 1C (i.e., the current value that completely discharges the theoretical capacity within 1 hour). After that, the battery was fully charged to 4.53V, and the battery thickness was measured after the 200th cycle. Cycle expansion rate = (Battery thickness after 200 cycles - Initial thickness before cycling) / Initial thickness before cycling × 100%.

[0097] Table 1 shows the performance of the lithium-ion pouch batteries assembled with the negative electrode sheets in each embodiment and comparative example.

[0098] serial number Capacity retention rate / % Volume expansion rate / % Example 1 95.4％ 8.9％ Example 2 94.8％ 10.1％ Example 3 93.1％ 12.5％ Example 4 89.7％ 14.6％ Example 5 90.7％ 13.6％ Example 6 91.9％ 12.3％ Example 7 91.4％ 13.4％ Example 8 90.2％ 12.9％ Example 9 89.6％ 14.3％ Example 10 86.8％ 15.1％ Comparative Example 1 70.7％ 21.9％ Comparative Example 2 79.5％ 17.4％ Comparative Example 3 72.7％ 20.3％ Comparative Example 4 68.7％ 23.6％

[0099] According to the data in Table 1, the capacity retention rate of the lithium-ion soft-pack batteries in Examples 1 to 10 after 200 cycles is all above 85%, and the volume expansion rate is all ≤16%, indicating that the negative electrode sheet of the present invention has a low expansion rate, which enables the battery to have excellent cycle performance.

[0100] By comparing Example 1 and Comparative Example 1, it can be seen that the double coating method of pure silicon base coating and active material layer can significantly improve the capacity retention rate and cycle expansion rate. Placing silicon between the current collector and the active material layer can make the silicon uniformly arranged in the entire negative electrode and located in the same direction, thereby making the overall expansion of the negative electrode more uniform during the charging and discharging process, thus reducing the expansion of the negative electrode.

[0101] By comparing Examples 1-10 with Comparative Example 4, it was found that conventional Si-C negative electrodes easily cause uneven distribution of silicon in the electrode sheet, resulting in excessive local expansion of the cell, deformation of the battery, and ultimately, increased cyclic expansion.

[0102] Comparing Examples 1, 7, and 8 with Comparative Examples 2 and 3, it is evident that the performance is best when the carboxyl group content is between 50% and 70%. If there are more carboxyl groups and fewer other groups, the multidimensional contact between silicon-containing active particles will decrease, and the anti-slip effect of other groups on the silicon-containing active particles will be weakened. Without carboxyl groups, the formation of hydrogen bonds between molecules will decrease, leading to poor adhesion between the silicon-containing active particles and the current collector, ultimately resulting in deteriorated battery performance.

[0103] By comparing Examples 1 to 4, it was found that the higher the proportion of silicon undercoat, the greater the cyclic expansion. This is mainly because the higher the proportion of silicon undercoat, the higher the overall silicon content, and the cumulative effect formed in the expansion direction will cause the cell to expand more.

[0104] By comparing Examples 1, 5, and 6, the best performance was achieved when the mass ratio of silicon-containing active particles, carboxyl polymer, and conductive agent was 90:5:5. When the proportion of carboxyl polymer was low, its binding effect on the silicon-containing active particles was weakened; when the proportion of carboxyl polymer was high, local lithium plating in the battery would occur, and the cycle expansion would be greater.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A negative electrode sheet, characterized by, The coating layer comprises a silicon coating layer and an active material coating layer, the silicon coating layer is located between the current collector and the active material coating layer; The silicon coating layer comprises a carboxyl polymer, silicon-containing active particles and a conductive agent; The carboxyl polymer comprises -COOM, wherein M is H; The active material coating layer comprises a negative electrode active material, a conductive agent and a binder; The chemical structural formula of the carboxyl polymer is: M is H; R1, R2 and R3 are independently selected from at least one of H, C1-C3 linear or branched alkyl; m1, m2 and m3 satisfy: 50%≤m1 / (m1+m2+m3)≤70%; The mole percentage of -COOM in the carboxyl polymer is 50%-70%.

2. The negative electrode sheet according to claim 1, wherein The mass percentage of the carboxyl polymer in the silicon coating layer is 1%-10%.

3. The negative electrode sheet according to claim 1, wherein The silicon-containing active particles comprise at least one of nano-silicon, silicon oxide and silicon carbon.

4. The negative electrode sheet according to claim 1, wherein The mass percentage of the silicon coating layer in the coating layer is 2%-5%.

5. The negative electrode sheet according to claim 1, wherein The negative electrode active material comprises graphite or a mixture of at least one of nano-silicon, silicon oxide and silicon carbon and graphite.

6. The negative electrode sheet according to claim 1, wherein The average thickness of the coating layer is 25-40 μm.

7. A secondary battery characterized by comprising: The negative electrode plate comprises the negative electrode plate according to any one of claims 1-6.

8. An electrical device, characterized by The secondary battery comprises the secondary battery according to claim 7, and the secondary battery serves as a power supply for the power utilization device.

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