Negative plate, preparation method thereof and battery

Abstract

The embodiment of the invention discloses a negative electrode plate, a preparation method thereof and a battery, and belongs to the technical field of batteries, the negative electrode plate comprises a negative electrode active layer, the negative electrode active layer comprises a negative electrode active material, a first conductive agent, a second conductive agent and a binder, the conductivity of the first conductive agent is 500S / m to 2000S / m, and the conductivity of the second conductive agent is 105S / m to 108S / m. Wherein the mass percent of the first conductive agent in the negative electrode active layer is 10%-50%, and the mass percent of the second conductive agent in the negative electrode active layer is 0.3%-0.6%. According to the negative plate provided by the embodiment of the invention, a three-dimensional conductive network can be constructed through the synergistic effect of the first conductive agent and the second conductive agent, so that the electron transmission efficiency is remarkably improved, the capacity exertion rate is ensured, the cycling stability is improved, and the mechanical property can be improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a negative electrode sheet and its preparation method, and a battery. Background Technology

[0002] In the battery field, the negative electrode is a crucial component, and its performance directly impacts the overall battery performance. With the continuous expansion of battery applications and the increasing demands for battery performance, the thickness of the negative electrode is increasing, thereby contributing to improved battery capacity and energy density. However, during battery charging and discharging, ions need to be transported within the negative electrode to achieve charge transfer and storage. For thicker negative electrodes, the electron transport path becomes longer, leading to increased resistance during electron transport and a higher risk of mass transfer problems. This results in a lower capacity utilization rate of the negative electrode, severely hindering battery performance improvement. Summary of the Invention

[0003] This application provides a negative electrode sheet and its preparation method, as well as a battery, which can construct a three-dimensional conductive network through the synergistic effect of a first conductive agent and a second conductive agent, significantly improving electron transport efficiency, ensuring capacity utilization, and enhancing cycle stability.

[0004] In a first aspect, this application provides a negative electrode sheet, including a negative electrode active layer, wherein the material of the negative electrode active layer includes a negative electrode active material, a first conductive agent, a second conductive agent, and a binder; The conductivity of the first conductive agent is 500 S / m-2000 S / m, and the conductivity of the second conductive agent is 10. 5 S / m-10 8 S / m; The first conductive agent has a mass percentage of 10%-50% in the negative electrode active layer, and the second conductive agent has a mass percentage of 0.3%-0.6% in the negative electrode active layer.

[0005] By including a first conductive agent and a second conductive agent in the negative electrode active layer of the negative electrode sheet, a three-dimensional conductive network can be formed in conjunction with the negative electrode active material and binder, increasing electron transport channels. The first conductive agent has moderate conductivity and is added in a high proportion, allowing for sufficient contact with the negative electrode active material, reducing interfacial resistance, and exhibiting good dispersion performance. The second conductive agent has high conductivity, enabling the construction of conductive bridges across particles, forming a three-dimensional conductive network, significantly reducing the internal resistance of the negative electrode sheet, and improving capacity utilization. The combination of the first and second conductive agents forms a "short-range + long-range" synergistic conductive network, thereby optimizing electron transport. Furthermore, the first and second conductive agents can also form a framework in the negative electrode sheet, reducing pulverization of the negative electrode active material and improving the mechanical properties of the negative electrode sheet. In other words, the negative electrode sheet provided in this application embodiment can construct a three-dimensional conductive network through the synergistic effect of the first and second conductive agents, significantly improving electron transport efficiency, ensuring capacity utilization, improving cycle stability, and enhancing mechanical properties.

[0006] Optionally, the particle size of the first conductive agent is 30nm-5μm, and the particle size of the second conductive agent is 20nm-200nm.

[0007] By ensuring the particle sizes of the first and second conductive agents are within the aforementioned ranges, the first conductive agent can form a short-range conductive network between the negative electrode active materials, ensuring rapid electron transport between them. Furthermore, the second conductive agent constructs long-range conductive bridges within the gaps of the first conductive agent, shortening the electron transport path. In addition, the first conductive agent can encapsulate the negative electrode active material and leave gaps, alleviating the expansion stress of the negative electrode active material. The second conductive agent can support the gap structure, preventing structural collapse. Together, they improve the mechanical properties of the negative electrode sheet.

[0008] Optionally, the first conductive agent includes at least one of graphite, Super P, and acetylene black; And / or, the second conductive agent includes at least one of graphene, carbon nanotubes and carbon fibers.

[0009] The layered structure of graphite promotes lithium-ion insertion / extraction while providing mechanical support and mitigating volume expansion stress. The branched structure of Super P fills the gaps in the negative electrode active material, reducing contact resistance. The chain-like structure of acetylene black contributes to the formation of a good three-dimensional conductive network and exhibits high chemical stability. Graphene has a conductivity of 10⁻⁶. 6 With a strength of around S / m, it helps to construct long-range conductive channels, reduce the internal resistance of the negative electrode, and provide flexible support for the negative electrode active material, alleviating volume expansion stress. Carbon nanotubes have high electron mobility, enabling the construction of high-speed electron transport networks, and also have high mechanical strength. Carbon fibers can guide electron transport in a directional manner and have high porosity, promoting lithium-ion diffusion.

[0010] Optionally, the mass percentage of the first conductive agent in the negative electrode active layer is 40%-50%.

[0011] The first conductive agent can construct electron transport channels in the negative electrode active layer, reducing contact resistance. By making the first conductive agent account for 40%-50% of the mass percentage in the negative electrode active layer, the contact point density between the negative electrode active materials can be increased, forming a continuous conductive network. Combined with the second conductive agent, this accelerates electron mobility and lithium-ion migration, thereby improving charge-discharge efficiency. Furthermore, a higher proportion of the first conductive agent can also enhance the conductivity of the negative electrode, maintaining lower polarization during high-rate charge-discharge and reducing energy loss.

[0012] Optionally, the mass percentage of the negative electrode active material in the negative electrode active layer is 44.4%-58.7%; And / or, the mass percentage of the binder in the negative electrode active layer is 1%-5%.

[0013] By maintaining the mass percentage of the negative electrode active material within the aforementioned range in the negative electrode active layer, the battery's capacity and energy density can be guaranteed. This also helps maintain the mechanical integrity of the negative electrode sheet, reducing shedding and pulverization caused by volume expansion or contraction during charging and discharging, ensuring good structural stability, shortening the lithium-ion diffusion path, reducing polarization, improving charge-discharge efficiency, and enhancing cycle stability. Maintaining the mass percentage of the binder within the aforementioned range in the negative electrode active layer ensures effective bonding and improves the mechanical stability of the negative electrode active layer. Forming a thin and uniform coating layer on the surface of the negative electrode active material ensures effective bonding while reducing obstacles to lithium-ion transport and lowering electrode internal resistance.

[0014] Optionally, the negative electrode active material includes at least one of elemental silicon, silicon-carbon materials, silicon-oxygen materials, and silicon-based alloy materials; And / or, the adhesive includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, and polyacrylic acid.

[0015] Elemental silicon has a high theoretical specific capacity, significantly improving battery energy density. Silicon-carbon materials maintain high capacity while mitigating volume expansion. Silicon-oxygen materials form a buffer layer during the first charge-discharge cycle, exhibiting good cycle stability. Silicon-based alloys optimize expansion behavior through multi-element synergistic effects while ensuring high capacity. Polytetrafluoroethylene (PTFE) possesses excellent chemical properties; its fibrous structure forms a three-dimensional network, ensuring adhesion and mitigating volume expansion stress in the negative electrode active material. Polyvinylidene fluoride (PVDF) exhibits high adhesion, providing excellent bonding performance. Styrene-butadiene rubber (SBR) has a low elastic modulus, absorbing expansion stress in the negative electrode active material and reducing the risk of cracking. Polyacrylic acid contains carboxyl functional groups, enabling it to form strong chemical bonds with the surface of silicon-based negative electrode active materials, reducing material shedding.

[0016] Optionally, the thickness of the negative electrode active layer is 370μm-420μm.

[0017] By ensuring the thickness of the negative electrode active layer is within the aforementioned range, the loading of the negative electrode active material in the negative electrode active layer can be increased, thereby improving the energy density and capacity of the negative electrode sheet. Simultaneously, the negative electrode sheet provided in this application can also form a highly efficient electron transport channel within the negative electrode active layer through the synergistic effect of the first and second conductive agents, significantly improving electron transport efficiency, ensuring capacity utilization, and enhancing cycle stability.

[0018] Secondly, this application also provides a method for preparing a negative electrode sheet, comprising: It provides negative electrode active material, first conductive agent, second conductive agent and binder; The first conductive agent and the second conductive agent are mixed to obtain a composite conductive agent; The negative electrode active material and binder are mixed with the composite conductive agent to obtain a mixed dry material; The mixed dry materials are used to form a negative electrode active layer using a dry film-forming process to obtain a negative electrode sheet.

[0019] The method for preparing the negative electrode sheet provided in this application, by first mixing a first conductive agent and a second conductive agent, allows the second conductive agent, which is added in a lower proportion, to be dispersed in the first conductive agent, which is added in a higher proportion. This also allows the first conductive agent to be adsorbed onto the surface of the second conductive agent, preventing agglomeration of the second conductive agent due to van der Waals forces. This better leverages the synergistic conductivity mechanism, forming an excellent three-dimensional conductive network. Furthermore, the dry film-forming process, which uses the mixed dry materials to form the negative electrode active layer, improves the dispersion uniformity of the composite conductive agent. During calendering, the composite conductive agent forms an excellent interwoven network, mitigating conductive network breakage caused by volume expansion and improving capacity retention. The dry film-forming process also improves the mechanical properties and interfacial stability of the negative electrode active layer.

[0020] Optionally, the first conductive agent and the second conductive agent are mixed to obtain a composite conductive agent, comprising: A portion of the first conductive agent is mixed with a portion of the second conductive agent to obtain a first mixture; The remaining portion of the first conductive agent is mixed with the first mixture to obtain the second mixture; The remaining portion of the second conductive agent is mixed with the second mixture to obtain a composite conductive agent.

[0021] That is, in the process of mixing the first conductive agent and the second conductive agent, a multi-step mixing method is adopted, and the mixing is gradually increased to improve the dispersion effect.

[0022] Optionally, the mixed dry materials are used to form a negative electrode active layer using a dry film-forming process, including: The mixed dry materials are sheared to form sheared mixed dry materials; The sheared and mixed dry materials are pressed into a film at a temperature of 80℃-120℃ to form the negative electrode active layer.

[0023] By shearing the mixed dry materials, the binder can be fiberized. The fiberized binder can encapsulate the negative electrode active material, forming a three-dimensional network structure, which enhances mechanical strength and conductivity. Under temperature conditions of 80℃-120℃, the binder easily forms fibers, which can maintain good contact between the negative electrode active material and the first and second conductive agents, stabilize the structure of the negative electrode sheet, and ensure the structural integrity of the negative electrode sheet.

[0024] Thirdly, this application also provides a battery comprising the negative electrode sheet as described above, or comprising a negative electrode sheet prepared by the method described above.

[0025] The battery provided in this application has all the beneficial effects of the negative electrode sheet as described above, which will not be repeated here.

[0026] Optionally, the battery also includes a positive electrode, which comprises a positive electrode active material having the molecular formula Li. 1+x Co y Mn 2-(x+y) O4, 0<x≤0.33, 0<y≤0.1.

[0027] By using the molecular formula of the positive electrode active material as described above, the battery can meet the discharge capacity design requirements within a voltage range of 2.0V-3.3V. That is, the battery achieves a high capacity utilization rate within the 2.0V-3.3V range. Detailed Implementation

[0028] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] This application provides a negative electrode sheet, its preparation method, and a battery. These are described in detail below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to." Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0030] In a first aspect, this application provides a negative electrode sheet, including a negative electrode active layer. The material of the negative electrode active layer includes a negative electrode active material, a first conductive agent, a second conductive agent, and a binder. The conductivity of the first conductive agent is 500 S / m-2000 S / m, and the conductivity of the second conductive agent is 10 S / m. 5 S / m-10 8 S / m. The first conductive agent has a mass percentage of 10%-50% in the negative electrode active layer, and the second conductive agent has a mass percentage of 0.3%-0.6% in the negative electrode active layer.

[0031] By including a first conductive agent and a second conductive agent in the negative electrode active layer of the negative electrode sheet, a three-dimensional conductive network can be formed in conjunction with the negative electrode active material and binder, increasing electron transport channels. The first conductive agent has moderate conductivity and is added in a high proportion, allowing for sufficient contact with the negative electrode active material, reducing interfacial resistance, and exhibiting good dispersion performance. The second conductive agent has high conductivity, enabling the construction of conductive bridges across particles, forming a three-dimensional conductive network, significantly reducing the internal resistance of the negative electrode sheet, and improving capacity utilization. The combination of the first and second conductive agents forms a "short-range + long-range" synergistic conductive network, thereby optimizing electron transport. Furthermore, the first and second conductive agents can also form a framework in the negative electrode sheet, reducing pulverization of the negative electrode active material and improving the mechanical properties of the negative electrode sheet. In other words, the negative electrode sheet provided in this application embodiment can construct a three-dimensional conductive network through the synergistic effect of the first and second conductive agents, significantly improving electron transport efficiency, ensuring capacity utilization, improving cycle stability, and enhancing mechanical properties.

[0032] For example, the conductivity of the first conductive agent can be 500 S / m, 600 S / m, 700 S / m, 800 S / m, 900 S / m, 1000 S / m, 1100 S / m, 1200 S / m, 1300 S / m, 1400 S / m, 1500 S / m, 1600 S / m, 1700 S / m, 1800 S / m, 1900 S / m, or 2000 S / m, and the conductivity of the second conductive agent can be 10. 5 S / m, 10 6 S / m, 10 7 S / m or 10 8 S / m. The mass percentage of the first conductive agent in the negative electrode active layer is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, and the mass percentage of the second conductive agent in the negative electrode active layer can be 0.3%, 0.4%, 0.5%, or 0.6%.

[0033] In some embodiments, the particle size of the first conductive agent is 30 nm-5 μm, and the particle size of the second conductive agent is 20 nm-200 nm.

[0034] By ensuring the particle sizes of the first and second conductive agents are within the aforementioned ranges, the first conductive agent can form a short-range conductive network between the negative electrode active materials, ensuring rapid electron transport between them. Furthermore, the second conductive agent constructs long-range conductive bridges within the gaps of the first conductive agent, shortening the electron transport path. In addition, the first conductive agent can encapsulate the negative electrode active material and leave gaps, alleviating the expansion stress of the negative electrode active material. The second conductive agent can support the gap structure, preventing structural collapse. Together, they improve the mechanical properties of the negative electrode sheet.

[0035] For example, the particle size of the first conductive agent can be 30nm, 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1μm, 2μm, 3μm, 4μm or 5μm, and the particle size of the second conductive agent can be 20nm, 40nm, 50nm, 60nm, 80nm, 100nm, 120nm, 140nm, 150nm, 160nm, 180nm or 200nm.

[0036] In some embodiments, the first conductive agent includes at least one of graphite, Super P, and acetylene black.

[0037] The layered structure of graphite can promote lithium-ion insertion / extraction, while providing mechanical support and relieving volume expansion stress. The branched structure of Super P can fill the gaps in the negative electrode active material and reduce contact resistance. The chain structure of acetylene black helps to form a good three-dimensional conductive network and has high chemical stability.

[0038] In some embodiments, the second conductive agent includes at least one of graphene, carbon nanotubes, and carbon fibers.

[0039] Graphene has an electrical conductivity of 10. 6 With a strength of around S / m, it helps to construct long-range conductive channels, reduce the internal resistance of the negative electrode, and provide flexible support for the negative electrode active material, alleviating volume expansion stress. Carbon nanotubes have high electron mobility, enabling the construction of high-speed electron transport networks, and also have high mechanical strength. Carbon fibers can guide electron transport in a directional manner and have high porosity, promoting lithium-ion diffusion.

[0040] In some embodiments, the mass percentage of the first conductive agent in the negative electrode active layer is 40%-50%.

[0041] The first conductive agent can construct electron transport channels in the negative electrode active layer, reducing contact resistance. By making the first conductive agent account for 40%-50% of the mass percentage in the negative electrode active layer, the contact point density between the negative electrode active materials can be increased, forming a continuous conductive network. Combined with the second conductive agent, this accelerates electron mobility and lithium-ion migration, thereby improving charge-discharge efficiency. Furthermore, a higher proportion of the first conductive agent can also enhance the conductivity of the negative electrode, maintaining lower polarization during high-rate charge-discharge and reducing energy loss.

[0042] For example, the mass percentage of the first conductive agent in the negative electrode active layer can be 40%, 40.5%, 41%, 41.5%, 42%, 42.5%, 43%, 43.5%, 44%, 44.5%, 45%, 45.5%, 46%, 46.5%, 47%, 47.5%, 48%, 48.5%, 49%, 49.5%, or 50%.

[0043] In some embodiments, the mass percentage of the negative electrode active material in the negative electrode active layer is 44.4%-58.7%.

[0044] By ensuring that the mass percentage of the negative electrode active material in the negative electrode active layer is within the above range, the battery capacity and energy density can be guaranteed, and the mechanical integrity of the negative electrode sheet can be maintained. This reduces the shedding and pulverization caused by volume expansion or contraction during charging and discharging, ensures good structural stability, shortens the lithium-ion diffusion path, reduces polarization, improves charging and discharging efficiency, and enhances cycle stability.

[0045] For example, the mass percentage of the negative electrode active material in the negative electrode active layer can be 44.4%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 88.7%.

[0046] In some embodiments, the binder has a mass percentage of 1%-5% in the negative electrode active layer.

[0047] By maintaining the mass percentage of the binder in the negative electrode active layer within the aforementioned range, the bonding effect can be guaranteed, and the mechanical stability of the negative electrode active layer can be improved. Forming a thin and uniform coating layer on the surface of the negative electrode active material ensures the bonding effect while reducing obstacles to lithium-ion transport and lowering the electrode's internal resistance.

[0048] For example, the mass percentage of the binder in the negative electrode active layer can be 1%, 2%, 3%, 4% or 5%.

[0049] In some embodiments, the negative electrode active material includes at least one of elemental silicon, silicon-carbon materials, silicon-oxygen materials, and silicon-based alloy materials.

[0050] Elemental silicon has a high theoretical specific capacity, which can significantly improve the energy density of batteries. Silicon-carbon materials can maintain high capacity while mitigating volume expansion. Silicon-oxygen materials can form a buffer layer during the first charge and discharge cycle, resulting in good cycle stability. Silicon-based alloys can optimize expansion behavior and ensure high capacity characteristics through multi-element synergistic effects.

[0051] In some embodiments, the adhesive includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, and polyacrylic acid.

[0052] Polytetrafluoroethylene (PTFE) possesses excellent chemical properties; its fibrous structure forms a three-dimensional network, ensuring effective adhesion and mitigating the volume expansion stress of the negative electrode active material. Polyvinylidene fluoride (PVDF) exhibits high adhesion, providing excellent bonding performance. Styrene-butadiene rubber (SBR) has a low elastic modulus, enabling it to absorb the expansion stress of the negative electrode active material and reduce the risk of cracking. Polyacrylic acid contains carboxyl functional groups, which can form strong chemical bonds with the surface of silicon-based negative electrode active materials, reducing the shedding of the negative electrode active material.

[0053] In some embodiments, the thickness of the negative electrode active layer is 370 μm-420 μm.

[0054] By ensuring the thickness of the negative electrode active layer is within the aforementioned range, the loading of the negative electrode active material in the negative electrode active layer can be increased, thereby improving the energy density and capacity of the negative electrode sheet. Simultaneously, the negative electrode sheet provided in this application can also form a highly efficient electron transport channel within the negative electrode active layer through the synergistic effect of the first and second conductive agents, significantly improving electron transport efficiency, ensuring capacity utilization, and enhancing cycle stability.

[0055] For example, the thickness of the negative electrode active layer can be 370μm, 380μm, 390μm, 400μm, 410μm or 420μm.

[0056] It should be noted that in the negative electrode sheet provided in this application embodiment, the negative electrode active layer is directly used as the negative electrode sheet, and no negative electrode current collector is provided. The thickness of the negative electrode active layer is within the above range, which can ensure capacity and energy density, while also providing good mechanical properties.

[0057] Secondly, this application also provides a method for preparing a negative electrode sheet, comprising: It provides negative electrode active material, first conductive agent, second conductive agent and binder; The first conductive agent and the second conductive agent are mixed to obtain a composite conductive agent; The negative electrode active material and binder are mixed with the composite conductive agent to obtain a mixed dry material; The mixed dry materials are used to form a negative electrode active layer using a dry film-forming process to obtain a negative electrode sheet.

[0058] The method for preparing the negative electrode sheet provided in this application, by first mixing a first conductive agent and a second conductive agent, allows the second conductive agent, which is added in a lower proportion, to be dispersed in the first conductive agent, which is added in a higher proportion. This also allows the first conductive agent to be adsorbed onto the surface of the second conductive agent, preventing agglomeration of the second conductive agent due to van der Waals forces. This better leverages the synergistic conductivity mechanism, forming an excellent three-dimensional conductive network. Furthermore, the dry film-forming process, which uses the mixed dry materials to form the negative electrode active layer, improves the dispersion uniformity of the composite conductive agent. During calendering, the composite conductive agent forms an excellent interwoven network, mitigating conductive network breakage caused by volume expansion and improving capacity retention. The dry film-forming process also improves the mechanical properties and interfacial stability of the negative electrode active layer.

[0059] In some embodiments, a first conductive agent and a second conductive agent are mixed to obtain a composite conductive agent, comprising: A portion of the first conductive agent is mixed with a portion of the second conductive agent to obtain a first mixture; The remaining portion of the first conductive agent is mixed with the first mixture to obtain the second mixture; The remaining portion of the second conductive agent is mixed with the second mixture to obtain a composite conductive agent.

[0060] That is, in the process of mixing the first conductive agent and the second conductive agent, a multi-step mixing method is adopted, and the mixing is gradually increased to improve the dispersion effect.

[0061] In some embodiments, the mixed dry materials are used to form a negative electrode active layer using a dry film-forming process, including: The mixed dry materials are sheared to form sheared mixed dry materials; The sheared and mixed dry materials are pressed into a film at a temperature of 80℃-120℃ to form the negative electrode active layer.

[0062] By shearing the mixed dry materials, the binder can be fiberized. The fiberized binder can encapsulate the negative electrode active material, forming a three-dimensional network structure, which enhances mechanical strength and conductivity. Under temperature conditions of 80℃-120℃, the binder easily forms fibers, which can maintain good contact between the negative electrode active material and the first and second conductive agents, stabilize the structure of the negative electrode sheet, and ensure the structural integrity of the negative electrode sheet.

[0063] Thirdly, this application also provides a battery comprising the negative electrode sheet as described above, or comprising a negative electrode sheet prepared by the method described above.

[0064] The battery provided in this application has all the beneficial effects of the negative electrode sheet as described above, which will not be repeated here.

[0065] In some embodiments, the battery further includes a positive electrode sheet, which comprises a positive electrode active material having the molecular formula Li. 1+x Co y Mn 2-(x+y) O4, 0<x≤0.33, 0<y≤0.1.

[0066] By using the molecular formula of the positive electrode active material as described above, the battery can meet the discharge capacity design requirements within a voltage range of 2.0V-3.3V. That is, the battery achieves a high capacity utilization rate within the 2.0V-3.3V range.

[0067] The embodiments of this application are further illustrated below with reference to specific examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. Experimental methods in the following embodiments that do not specify specific conditions are generally performed according to the conditions recommended by the manufacturer.

[0068] Example 1 In this embodiment, the negative electrode active material layer includes a negative electrode active material, a first conductive agent, a second conductive agent, and a binder. The mass ratio of the negative electrode active material, the first conductive agent, the second conductive agent, and the binder is 55%:41.5%:0.5%:3%. The negative electrode active material is a pre-lithiated silicon-oxygen material, and the first conductive agent is graphite with a particle size of 3 μm and a conductivity of 10⁻⁶. 2 S / m-10 3 S / m, the second conductive agent is carbon nanotubes with a particle size of 45nm and a conductivity of 10. 6 S / m, the adhesive is polytetrafluoroethylene.

[0069] The preparation method of the negative electrode is as follows: (1) Stir and mix the first conductive agent and the second conductive agent for 30 minutes to obtain a composite conductive agent; (2) Stir and mix the negative electrode active material, binder and composite conductive agent for 30 min to obtain a mixed dry material; (3) The mixed dry materials are sheared using a twin-screw extruder to obtain a sheared mixture; (4) The shear mixture is extruded at a temperature of 100°C to form a negative electrode material layer with a thickness of 390 μm, thus obtaining a negative electrode sheet.

[0070] Example 2 In this embodiment, the negative electrode active material layer includes a negative electrode active material, a first conductive agent, a second conductive agent, and a binder. The mass ratio of the negative electrode active material, the first conductive agent, the second conductive agent, and the binder is 55%:41.5%:0.5%:3%. The negative electrode active material is a pre-lithiated silicon-oxygen material, and the first conductive agent is graphite with a particle size of 3 μm and a conductivity of 10⁻⁶. 2S / m-10 3 S / m, the second conductive agent is carbon nanotubes with a particle size of 45nm and a conductivity of 10. 6 S / m, the adhesive is polytetrafluoroethylene.

[0071] The preparation method of the negative electrode is as follows: (1) Mix 50% by weight of the first conductive agent and 50% by weight of the second conductive agent for 30 minutes to obtain the first mixture; (2) Stir and mix the remaining 50% by weight of the first conductive agent and the first mixture for 30 minutes to obtain the second mixture; (3) Stir and mix the remaining 50% by weight of the second conductive agent and the second mixture for 30 minutes to obtain the composite conductive agent; (4) Stir and mix the negative electrode active material, binder and composite conductive agent for 30 min to obtain a mixed dry material; (5) The mixed dry materials are sheared using a twin-screw extruder to obtain a sheared mixture; (6) The shear mixture is extruded at a temperature of 100°C to form a negative electrode material layer with a thickness of 390 μm, thus obtaining a negative electrode sheet.

[0072] Example 3 In this embodiment, the negative electrode active material layer includes a negative electrode active material, a first conductive agent, a second conductive agent, and a binder. The mass ratio of the negative electrode active material, the first conductive agent, the second conductive agent, and the binder is 86.5%:10%:0.5%:3%. The negative electrode active material is a pre-lithiated silicon-oxygen material, and the first conductive agent is graphite with a particle size of 3 μm and a conductivity of 10⁻⁶. 2 S / m-10 3 S / m, the second conductive agent is carbon nanotubes with a particle size of 45nm and a conductivity of 10. 6 S / m, the adhesive is polytetrafluoroethylene.

[0073] The preparation method of the negative electrode is as follows: (1) Stir and mix the first conductive agent and the second conductive agent for 30 minutes to obtain a composite conductive agent; (2) Stir and mix the negative electrode active material, binder and composite conductive agent for 30 min to obtain a mixed dry material; (3) The mixed dry materials are sheared using a twin-screw extruder to obtain a sheared mixture; (4) The shear mixture is extruded at a temperature of 100°C to form a negative electrode material layer with a thickness of 390 μm, thus obtaining a negative electrode sheet.

[0074] Example 4 In this embodiment, the negative electrode active material layer includes a negative electrode active material, a first conductive agent, a second conductive agent, and a binder. The mass ratio of the negative electrode active material, the first conductive agent, the second conductive agent, and the binder is 46.5%:50%:0.5%:3%. The negative electrode active material is a pre-lithiated silicon-oxygen material, and the first conductive agent is graphite with a particle size of 3 μm and a conductivity of 10⁻⁶. 2 S / m-10 3 S / m, the second conductive agent is carbon nanotubes with a particle size of 45nm and a conductivity of 10. 6 S / m, the adhesive is polytetrafluoroethylene.

[0075] The preparation method of the negative electrode is as follows: (1) Stir and mix the first conductive agent and the second conductive agent for 30 minutes to obtain a composite conductive agent; (2) Stir and mix the negative electrode active material, binder and composite conductive agent for 30 min to obtain a mixed dry material; (3) The mixed dry materials are sheared using a twin-screw extruder to obtain a sheared mixture; (4) The shear mixture is extruded at a temperature of 100°C to form a negative electrode material layer with a thickness of 390 μm, thus obtaining a negative electrode sheet.

[0076] Example 5 In this embodiment, the negative electrode active material layer includes a negative electrode active material, a first conductive agent, a second conductive agent, and a binder. The mass ratio of the negative electrode active material, the first conductive agent, the second conductive agent, and the binder is 55%:41.5%:0.5%:3%. The negative electrode active material is a pre-lithiated silicon-oxygen material, and the first conductive agent is graphite with a particle size of 3 μm and a conductivity of 10⁻⁶. 2 S / m-10 3 S / m, the second conductive agent is graphene with a particle size of 75nm and a conductivity of 10. 8 S / m, the adhesive is polytetrafluoroethylene.

[0077] The preparation method of the negative electrode is as follows: (1) Stir and mix the first conductive agent and the second conductive agent for 30 minutes to obtain a composite conductive agent; (2) Stir and mix the negative electrode active material, binder and composite conductive agent for 30 min to obtain a mixed dry material; (3) The mixed dry materials are sheared using a twin-screw extruder to obtain a sheared mixture; (4) The shear mixture is extruded at a temperature of 100°C to form a negative electrode material layer with a thickness of 390 μm, thus obtaining a negative electrode sheet.

[0078] Example 6 In this embodiment, the negative electrode active material layer includes a negative electrode active material, a first conductive agent, a second conductive agent, and a binder. The mass ratio of the negative electrode active material, the first conductive agent, the second conductive agent, and the binder is 55%:41.5%:0.5%:3%. The negative electrode active material is a pre-lithiated silicon-oxygen material, and the first conductive agent is graphite with a particle size of 3 μm and a conductivity of 10⁻⁶. 2 S / m-10 3 S / m, the second conductive agent is carbon fiber with a particle size of 150nm and an electrical conductivity of 10. 5 S / m, the adhesive is polytetrafluoroethylene.

[0079] The preparation method of the negative electrode is as follows: (1) Stir and mix the first conductive agent and the second conductive agent for 30 minutes to obtain a composite conductive agent; (2) Stir and mix the negative electrode active material, binder and composite conductive agent for 30 min to obtain a mixed dry material; (3) The mixed dry materials are sheared using a twin-screw extruder to obtain a sheared mixture; (4) The shear mixture is extruded at a temperature of 100°C to form a negative electrode material layer with a thickness of 390 μm, thus obtaining a negative electrode sheet.

[0080] Comparative Example 1 In this comparative example, the negative electrode active layer includes a negative electrode active material, a first conductive agent, and a binder. The mass ratio of the negative electrode active material, the first conductive agent, and the binder is 55%:42%:3%. The negative electrode active material is a pre-lithiated silicon-oxygen material, and the first conductive agent is graphite with a particle size of 3 μm and a conductivity of 10⁻⁶. 2 S / m-10 3 S / m, the adhesive is polytetrafluoroethylene.

[0081] The preparation method of the negative electrode is as follows: (1) Stir and mix the negative electrode active material, the first conductive agent and the binder for 30 minutes to obtain a mixed dry material; (2) The mixed dry materials are sheared using a twin-screw extruder to obtain a sheared mixture; (3) The shear mixture is extruded at a temperature of 100°C to form a negative electrode material layer with a thickness of 390 μm, thus obtaining a negative electrode sheet.

[0082] Comparative Example 2 In this comparative example, the negative electrode active material layer includes a negative electrode active material, a first conductive agent, a second conductive agent, and a binder. The mass ratio of the negative electrode active material, the first conductive agent, the second conductive agent, and the binder is 55%:41.9%:0.1%:3%. The negative electrode active material is a pre-lithiated silicon-oxygen material, and the first conductive agent is graphite with a particle size of 3 μm and a conductivity of 10⁻⁶. 2 S / m-10 3 S / m, the second conductive agent is carbon nanotubes with a particle size of 45nm and a conductivity of 10. 6 S / m, the adhesive is polytetrafluoroethylene.

[0083] The preparation method of the negative electrode is as follows: (1) Stir and mix the first conductive agent and the second conductive agent for 30 minutes to obtain a composite conductive agent; (2) Stir and mix the negative electrode active material, binder and composite conductive agent for 30 min to obtain a mixed dry material; (3) The mixed dry materials are sheared using a twin-screw extruder to obtain a sheared mixture; (4) The shear mixture is extruded at a temperature of 100°C to form a negative electrode material layer with a thickness of 390 μm, thus obtaining a negative electrode sheet.

[0084] Comparative Example 3 In this comparative example, the negative electrode active material layer includes a negative electrode active material, a first conductive agent, a second conductive agent, and a binder. The mass ratio of the negative electrode active material, the first conductive agent, the second conductive agent, and the binder is 55%:41%:1%:3%. The negative electrode active material is a pre-lithiated silicon-oxygen material, and the first conductive agent is graphite with a particle size of 3 μm and a conductivity of 10⁻⁶. 2 S / m-10 3 S / m, the second conductive agent is carbon nanotubes with a particle size of 45nm and a conductivity of 10. 6 S / m, the adhesive is polytetrafluoroethylene.

[0085] The preparation method of the negative electrode is as follows: (1) Stir and mix the first conductive agent and the second conductive agent for 30 minutes to obtain a composite conductive agent; (2) Stir and mix the negative electrode active material, binder and composite conductive agent for 30 min to obtain a mixed dry material; (3) The mixed dry materials are sheared using a twin-screw extruder to obtain a sheared mixture; (4) The shear mixture is extruded at a temperature of 100°C to form a negative electrode material layer with a thickness of 390 μm, thus obtaining a negative electrode sheet.

[0086] The negative electrode sheets from Examples 1-6 and Comparative Examples 1-3 were assembled with the positive electrode sheet and separator to form CR2016 batteries. The assembled batteries were subjected to charge-discharge performance evaluation and cycle performance testing. During the test, the charging was performed at 0.1C to 3.3V, and the discharging was performed at 0.1C to 2.0V. The capacity of the first discharge cycle was the capacity after one charge and one discharge, and the capacity after 100 cycles was the capacity after 100 charge and 100 discharge cycles. The test results are shown in Table 1.

[0087] The positive electrode sheet is prepared by a dry process using a mixture of positive electrode active material, graphite, and polytetrafluoroethylene in a mass ratio of 90:8:2. The molecular formula of the positive electrode active material is Li. 1.2 Co 0.01 Mn 0.79 O4. The diaphragm is made of 0.2mm thick glass fiber.

[0088] Table 1. Comparison of battery performance tests in different embodiments and comparative examples.

[0089] As can be seen from the comparison of Examples 1-2 and Comparative Examples 1-3 in Table 1, by incorporating a first conductive agent and a second conductive agent into the negative electrode active material, and ensuring that the ratio of the first conductive agent to the second conductive agent is within a reasonable range, the first-cycle discharge capacity and capacity retention rate can be improved. The comparison of Examples 1-2 shows that optimizing the mixing process during the preparation of the negative electrode sheet helps to improve the capacity retention rate and enhance cycle performance.

[0090] The comparison between Examples 1 and Examples 2-4 shows that the addition ratio of the first conductive agent and the second conductive agent affects the first-cycle discharge capacity and capacity retention. When the mass percentage of the first conductive agent in the negative electrode active layer is 40%-50% and the mass percentage of the second conductive agent in the negative electrode active layer is 0.3%-0.6%, it helps to improve the first-cycle discharge capacity and capacity retention.

[0091] A comparison of Examples 1 and 5-6 shows that, while meeting the requirements for the conductivity and addition ratio of the second conductive agent, adjusting the selection of the second conductive agent can still maintain excellent first-cycle discharge capacity and capacity retention.

[0092] In summary, the negative electrode provided in this application embodiment can construct a better three-dimensional conductive network through the synergistic effect of the first and second conductive agents, significantly improving electron transport efficiency, ensuring capacity utilization, and enhancing cycle stability.

[0093] The foregoing has provided a detailed description of a negative electrode sheet, its preparation method, and the battery provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A negative electrode sheet, characterized in that, It includes a negative electrode active layer, the material of which includes a negative electrode active material, a first conductive agent, a second conductive agent, and a binder; The conductivity of the first conductive agent is 500 S / m-2000 S / m, and the conductivity of the second conductive agent is 10. 5 S / m-10 8 S / m; The first conductive agent has a mass percentage of 10%-50% in the negative electrode active layer, and the second conductive agent has a mass percentage of 0.3%-0.6% in the negative electrode active layer.

2. The negative electrode sheet according to claim 1, characterized in that, The particle size of the first conductive agent is 30nm-5μm, and the particle size of the second conductive agent is 20nm-200nm.

3. The negative electrode sheet according to claim 1, characterized in that, The first conductive agent includes at least one of graphite, Super P, and acetylene black; And / or, the second conductive agent includes at least one of graphene, carbon nanotubes and carbon fibers.

4. The negative electrode sheet according to claim 1, characterized in that, The first conductive agent has a mass percentage of 40%-50% in the negative electrode active layer.

5. The negative electrode sheet according to claim 1, characterized in that, The negative electrode active material has a mass percentage of 44.4%-58.7% in the negative electrode active layer; And / or, the binder in the negative electrode active layer is 1%-5% by mass.

6. The negative electrode sheet according to claim 1, characterized in that, The negative electrode active material includes at least one of elemental silicon, silicon-carbon materials, silicon-oxygen materials, and silicon-based alloy materials; And / or, the adhesive includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, and polyacrylic acid.

7. The negative electrode sheet according to any one of claims 1-6, characterized in that, The thickness of the negative electrode active layer is 370μm-420μm.

8. A method for preparing a negative electrode sheet, characterized in that, include: It provides negative electrode active material, first conductive agent, second conductive agent and binder; The first conductive agent and the second conductive agent are mixed to obtain a composite conductive agent; The negative electrode active material and the binder are mixed with the composite conductive agent to obtain a mixed dry material; The mixed dry materials are used to form a negative electrode active layer using a dry film-forming process to obtain a negative electrode sheet.

9. The method for preparing the negative electrode sheet according to claim 8, characterized in that, The step of mixing the first conductive agent and the second conductive agent to obtain a composite conductive agent includes: A portion of the first conductive agent is mixed with a portion of the second conductive agent to obtain a first mixture; The remaining portion of the first conductive agent is mixed with the first mixture to obtain a second mixture; The remaining portion of the second conductive agent is mixed with the second mixture to obtain the composite conductive agent.

10. The method for preparing the negative electrode sheet according to claim 8, characterized in that, The step of forming a negative electrode active layer by using a dry film-forming process on the mixed dry materials includes: The mixed dry material is sheared to form a sheared mixed dry material; The shear-mixed dry material is pressed into a film at a temperature of 80℃-120℃ to form the negative electrode active layer.

11. A battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-7, or includes the negative electrode sheet prepared by the method described in any one of claims 8-10.

12. The battery according to claim 11, characterized in that, The battery further includes a positive electrode sheet, which comprises a positive electrode active material having the molecular formula Li. 1+x Co y Mn 2-(x+y) O4, 0<x≤0.33, 0<y≤0.1.

Images