Negative electrode sheet, method for manufacturing the same, energy storage device, and electric device

Abstract

The application discloses a negative electrode sheet, a preparation method thereof, an energy storage device and an electric device. The negative electrode sheet comprises: a negative electrode current collector; and a conductive modification layer arranged on at least one side of the negative electrode current collector, wherein the porosity of the conductive modification layer is 25-65%, and the electrolyte contact angle of the conductive modification layer is not greater than 10°.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electrochemistry, and in particular, relates to a negative electrode sheet, a preparation method thereof, an energy storage device, and an electric device. BACKGROUND

[0002] A secondary battery, also known as a rechargeable battery or a storage battery, refers to a battery that can be activated by charging after discharging to continue use. The recyclable nature of the secondary battery makes it gradually become the main power source of electric devices. As the demand for secondary batteries gradually increases, people's requirements for their performance in all aspects are also getting higher and higher, for example, it is expected to obtain a battery with high energy density and good cycle performance. SUMMARY

[0003] The present application aims to at least partially solve one of the technical problems in the related art. To this end, one object of the present application is to provide a negative electrode sheet, a preparation method thereof, an energy storage device, and an electric device. The negative electrode sheet has good liquid affinity and liquid retention, which is beneficial to improve the deposition efficiency of ions, reduce the deposition overpotential, and improve the cycle performance of the battery.

[0004] In a first aspect of the present application, a negative electrode sheet is provided. The negative electrode sheet comprises:

[0005] a negative current collector;

[0006] a conductive modification layer, the conductive modification layer being provided on at least one side of the negative current collector, the porosity of the conductive modification layer being 25-65%, and the electrolyte contact angle of the conductive modification layer being not greater than 10°.

[0007] The negative electrode sheet of the above-mentioned embodiments of the present application has at least the following beneficial effects: the conductive modification layer has a porous structure and good wettability to the electrolyte, which not only provides an electronic path for the reaction of ions and electrons, but also facilitates the uniform and orderly deposition of metal, inhibits the generation and growth of metal dendrites, and the porous structure also provides good liquid storage capacity, so that the negative electrode sheet has good electrolyte wettability and liquid retention. The combination of the above can reduce the deposition overpotential of the metal and improve the cycle life. Therefore, the negative electrode sheet has good liquid affinity and liquid retention, which is beneficial to improve the deposition efficiency of ions, reduce the deposition overpotential, and improve the cycle performance of the battery.

[0008] In addition, the negative electrode sheet according to the above-mentioned embodiments of the present application can also have the following additional technical features:

[0009] In some embodiments of the present application, the negative current collector is a metal foil.

[0010] In some embodiments of the present application, the ion transport resistance of the negative electrode tab in the electrolyte environment is not greater than 500 mΩ.

[0011] In some embodiments of the present application, the conductive modification layer comprises a conductive agent and a binder, and the mass ratio of the conductive agent to the binder is (2.5-5):(1-4).

[0012] In some embodiments of the present application, the binder comprises one or more of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid.

[0013] In some embodiments of the present application, the conductive agent in the conductive modification layer comprises one-dimensional conductive agent and / or zero-dimensional conductive agent.

[0014] In some embodiments of the present application, the conductive agent comprises one-dimensional conductive agent and zero-dimensional conductive agent, and the mass ratio of the one-dimensional conductive agent to the zero-dimensional conductive agent is 1:(1-5).

[0015] In some embodiments of the present application, the one-dimensional conductive agent comprises carbon nanotubes and / or carbon fibers.

[0016] In some embodiments of the present application, the zero-dimensional conductive agent comprises conductive carbon black.

[0017] In some embodiments of the present application, the thickness of the conductive modification layer is 1-5 μm.

[0018] In a second aspect of the present application, a method for preparing a negative electrode tab is provided. The method comprises:

[0019] mixing a conductive agent and a binder with an organic solvent to obtain a conductive modification layer slurry;

[0020] coating the conductive modification layer slurry on at least one side of the negative electrode current collector, and performing desolvation treatment under constant temperature and humidity conditions to form a conductive modification layer,

[0021] wherein the temperature of the desolvation treatment is 70-120°C, the humidity is 70-100%, the porosity of the conductive modification layer is 25-65%, and the electrolyte contact angle of the conductive modification layer is not greater than 10°.

[0022] The method for preparing the negative pole piece of the above embodiments of the present application has at least the following beneficial effects: the method has good processability, and compared with the traditional drying process, the porous conductive modification layer formed by the method not only provides an electronic path and facilitates the reaction of ions and electrons, but also has good uniformity and order of the pore structure, which is conducive to the uniform and ordered deposition of the metal, and the porous structure can also provide good electrolyte infiltration capacity and liquid storage capacity, so that the negative pole piece has good electrolyte infiltration and liquid retention, and the combination of the above can reduce the deposition overpotential of the metal, improve the cycle life, and make the prepared negative pole piece have good liquid affinity and liquid retention, which is conducive to improving the deposition efficiency of ions and reducing the deposition overpotential and improving the cycle performance of the battery.

[0023] In some embodiments of the present application, the mass percentage of the conductive agent in the conductive modification layer slurry is 2.5-5wt%, and the mass percentage of the binder is 1-4wt%.

[0024] In some embodiments of the present application, the conductive agent includes one-dimensional conductive agent and / or zero-dimensional conductive agent.

[0025] In some embodiments of the present application, the binder includes one or more of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid.

[0026] In some embodiments of the present application, the organic solvent includes one or more of N-methylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide.

[0027] The thickness of the conductive modification layer is 1-5μm.

[0028] In some embodiments of the present application, the conductive agent includes one-dimensional conductive agent and zero-dimensional conductive agent, and the mass ratio of the one-dimensional conductive agent to the zero-dimensional conductive agent is 1:(1-5).

[0029] In some embodiments of the present application, the one-dimensional conductive agent includes carbon nanotubes and / or carbon fibers.

[0030] In some embodiments of the present application, the zero-dimensional conductive agent includes conductive carbon black.

[0031] In a third aspect of the present application, the present application provides a energy storage device. The energy storage device includes the above-mentioned negative pole piece and / or the negative pole piece prepared by the above-mentioned method for preparing the negative pole piece. The energy storage device has all the characteristics and effects described above in the negative pole piece and the method for preparing the negative pole piece, which will not be described here. In general, the energy storage device has a lower metal deposition overpotential and cycle performance.

[0032] In a fourth aspect, the present application provides a power consuming device. The power consuming device comprises the above-mentioned energy storage device. The power consuming device has all the features and effects described above for the energy storage device, which will not be repeated here.

[0033] Additional aspects and advantages of the present application will be made apparent from the following description of embodiments, which will be given by way of example only, and with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0034] The above and / or additional aspects and advantages of the present application will become apparent and be made clear to those skilled in the art from the following description of embodiments, which should be considered in conjunction with the accompanying drawings.

[0035] Figure 1 is a structural schematic diagram of a negative pole piece according to an embodiment of the present application.

[0036] Figure 2 is a structural schematic diagram of a negative pole piece according to another embodiment of the present application.

[0037] Figure 3 is a sectional structural schematic diagram of the distribution of one-dimensional conductive agent and zero-dimensional conductive agent in the conductive modification layer according to an embodiment of the present application.

[0038] Figure 4 is a porous structural schematic diagram of the conductive modification layer according to an embodiment of the present application.

[0039] Figure 5 is a porous structural schematic diagram of the conductive modification layer according to another embodiment of the present application.

[0040] Figure 6 is a top view schematic diagram of a negative pole piece according to an embodiment of the present application.

[0041] Figure 7 is a porous structural schematic diagram of the conductive modification layer according to yet another embodiment of the present application.

[0042] Figure 8 is a schematic diagram of an energy storage device according to an embodiment of the present application. DETAILED DESCRIPTION

[0043] Embodiments of the present application are described in detail below with reference to the accompanying drawings, in which like or similar elements are denoted by the same or similar reference signs, and examples of the embodiments are described. The embodiments described below are intended to be illustrative only, and should not be construed as limiting the present application.

[0044] The present application is mainly based on the following problems and findings: At present, in view of the use demand of high energy density batteries, there is a design scheme of using a negative electrode sheet without a negative electrode active material layer in the battery (i.e. a negative electrode-free battery), in which scheme, the characteristics of needing a negative electrode main material as a deintercalation accommodation in traditional ion batteries are abandoned, and the main structure of the negative electrode sheet is a negative electrode current collector, and the thickness of the sheet is small, thereby the energy density of the battery can be obviously improved. However, for the negative electrode-free technology, since the metal is directly deposited on the surface of the negative electrode sheet, the design of the negative electrode sheet is crucial, and the commonly used negative electrode sheets include ordinary metal foils and metal foils with carbon layers, which generally have the characteristics of smooth surface, few pores, no liquid affinity and liquid retention. If directly used, the deposition of the negative electrode metal is difficult and uneven, which is not conducive to the maintenance of long-term cycle life.

[0045] In a first aspect of the present application, the present application provides a negative electrode sheet. Referring to Figure 1 or 2, the negative electrode sheet comprises: a negative electrode current collector 10; and a conductive modification layer 20 provided on at least one side of the negative electrode current collector 10, the porosity of the conductive modification layer 20 is 25-65%, and the electrolyte contact angle of the conductive modification layer 20 is not greater than 10°.

[0046] For example, the porosity of the conductive modification layer 20 can be 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, etc., and the electrolyte contact angle of the conductive modification layer 20 can be 10°, 9°, 8°, 7°, 6°, 5°, 4°, 3°, 2°, 1°, etc.

[0047] The negative electrode sheet of the above-mentioned embodiments of the present application has at least the following beneficial effects: the conductive modification layer has a porous structure and good wettability to electrolyte, which not only provides an electronic path for the reaction of ions and electrons, but also facilitates the uniform and orderly deposition of metal, inhibits the generation and growth of metal dendrites, and the porous structure also provides good liquid storage capacity, so that the negative electrode sheet has good electrolyte wettability and liquid retention, and the combination of the above can reduce the deposition overpotential of the metal and improve the cycle life. Therefore, the negative electrode sheet has good liquid affinity and liquid retention, which is conducive to improving the deposition efficiency of ions, reducing the deposition overpotential, and improving the cycle performance of the battery.

[0048] In the embodiments of the present application, the porosity of the conductive modification layer can be measured by conventional methods in the art, such as calculating the porosity according to the true density and coating surface density of the materials added to the conductive modification layer, porosity = (CW / h-D) / (CW / h) x 100%, wherein D = 1 / (X1 / a+X2 / b+…+X n / n), X1, X2, ……Xn are the proportions of each material component in the conductive modification layer, a, b and n are the true densities of each material, CW is the coating density of the conductive modification layer, and h is the thickness of the conductive modification layer. In addition, when testing the electrolyte contact angle of the conductive modification layer 20, the electrolyte used can be a conventional electrolyte commonly used in batteries in the art. For example, an organic solvent can be prepared by mixing dioxolane (DOL) and ethylene glycol dimethyl ether (DME) in a volume ratio of 1:1, and dissolving an electrolyte salt (such as a lithium salt, as some specific examples, lithium bis(trifluoromethanesulfonyl)imide can be selected) in the organic solvent to obtain an electrolyte with a molar concentration of 1 mol / L. The prepared electrolyte is used to test the contact angle of the conductive modification layer.

[0049] Reference will now be made to Figures 1 to 3 The negative electrode sheet of the above-mentioned embodiments of the present application is described in detail.

[0050] In some embodiments of the present application, the negative current collector 10 can be a metal foil, which is more conducive to the design of the negative electrode sheet structure of the negative electrode-free battery. It should be noted that the specific type of metal foil in the present application is not particularly limited, and can be selected flexibly by those skilled in the art according to actual needs, for example, can include but is not limited to copper foil or aluminum foil, etc.

[0051] In some embodiments of the present application, the ion transport resistance of the negative electrode sheet in the electrolyte environment is not greater than 500 mΩ, for example, it can be 500 mΩ, 450 mΩ, 400 mΩ, 350 mΩ, 300 mΩ, 250 mΩ, 200 mΩ, 150 mΩ, 100 mΩ, 50 mΩ, etc. The ion transport resistance of the negative electrode sheet in the electrolyte environment is related to the electrolyte contact angle of the conductive modification layer 20. By further controlling the ion transport resistance of the negative electrode sheet in the electrolyte environment to meet the given conditions, the conductive modification layer can have a higher specific surface area and better wettability and liquid retention capacity, which is also conducive to further improving the deposition efficiency and deposition uniformity of ions, reducing the deposition overpotential, improving the cycle performance of the battery, promoting the ion and electron reaction, and improving the cycle performance of the battery.

[0052] In some embodiments of the present application, the conductive modification layer 20 can include a conductive agent and a binder, and the mass ratio of the conductive agent to the binder can be (2.5-5):(1-4). For example, the mass ratio of the conductive agent to the binder can be 2.5 / 4, 3 / 4, 2.5 / 3, 4 / 4, 5 / 4, 4 / 3, 3 / 2, 5 / 3, 4 / 2, 5 / 2, 3 / 1, 3.5 / 1, 4 / 1, 5 / 1, etc. Based on the amount of the conductive agent, increasing the amount of the binder is conducive to improving the adhesion strength between the conductive modification layer and the negative electrode current collector, and reducing the amount of the binder is conducive to reducing the risk of the pore diameter of the conductive modification layer being easily blocked to form closed pores or the pore forming efficiency being reduced. In the present application, controlling the mass ratio of the conductive agent to the binder to meet the above conditions not only enables the conductive modification layer and the negative electrode current collector to have a relatively high adhesion strength, but also is conducive to reducing the formation of closed pores, and takes into account the electronic conductivity of the conductive modification layer, thereby being conducive to improving the wettability and liquid retention capacity of the conductive modification layer, improving the deposition efficiency and deposition uniformity of ions, reducing the deposition overpotential, and improving the cycle performance of the battery.

[0053] In some embodiments of the present application, the type of the binder used in the conductive modification layer 20 is not particularly limited, and those skilled in the art can flexibly select according to actual needs. For example, the binder can include, but is not limited to, one or more of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid.

[0054] In some embodiments of the present application, the conductive agent in the conductive modification layer 20 can include one-dimensional conductive agents and / or zero-dimensional conductive agents. In some specific examples, the conductive agent can include one-dimensional conductive agents and zero-dimensional conductive agents, the one-dimensional conductive agents are in a linear shape, and the zero-dimensional conductive agents are in a point shape. Mixing the one-dimensional conductive agents and the zero-dimensional conductive agents can form a conductive network on the surface of the negative electrode current collector (see FIG. 2B). Figure 3 It is understood that, compared with the use of one of them alone, mixing the two can have a better conductive effect, thereby being conducive to further promoting the ion and electron reaction, improving the deposition efficiency and deposition uniformity of ions.

[0055] In some embodiments of the present application, the conductive agent can include one-dimensional conductive agents and / or zero-dimensional conductive agents, and the mass ratio of the one-dimensional conductive agents to the zero-dimensional conductive agents can be 1:(1-5). For example, the mass ratio of the one-dimensional conductive agents to the two-dimensional conductive agents can be 1 / 1, 1 / 2, 1 / 3, 1 / 4, 1 / 5, etc. Controlling the relative amount of the one-dimensional conductive agents and the zero-dimensional conductive agents to meet the given range is further conducive to forming an electronic path with good conductivity, thereby being conducive to further promoting the ion and electron reaction, improving the deposition efficiency and deposition uniformity of ions.

[0056] In some embodiments of the present application, the specific types of the one-dimensional conductive agent and the zero-dimensional conductive agent are not particularly limited, and a person skilled in the art can flexibly select according to actual needs. For example, in some specific examples, the one-dimensional conductive agent can include carbon nanotubes and / or carbon fibers. For another example, in some specific examples, the zero-dimensional conductive agent can include conductive carbon black. Optionally, the one-dimensional conductive agent can be selected as carbon nanotubes, and the zero-dimensional conductive agent can be selected as conductive carbon black, such as Super P. Both of the conductive agents are better, which is conducive to further improving the electrical conductivity of the formed electronic channel.

[0057] In some embodiments of the present application, the thickness of the conductive modification layer 20 can be 1-5 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc. Increasing the thickness of the conductive modification layer is conducive to improving its liquid storage capacity. Controlling the thickness of the conductive modification layer to meet the given conditions can not only make the conductive modification layer have good liquid retention, but also reduce the negative impact of the increase in the thickness of the conductive modification layer on its electronic conductivity, thereby being conducive to further taking into account the electrochemical reaction efficiency on the basis of reducing the battery deposition overpotential and improving the battery cycle performance.

[0058] Based on the same inventive concept, in the second aspect of the present application, a method for preparing a negative electrode sheet is provided.

[0059] The method comprises:

[0060] Mixing the conductive agent and the binder with the organic solvent to obtain a conductive modification layer slurry;

[0061] Coating the conductive modification layer slurry on at least one side of the negative electrode current collector and performing desolvation treatment under constant temperature and humidity conditions to form a conductive modification layer,

[0062] The temperature of the desolvation treatment is 70-120°C, the humidity is 70-100%, the porosity of the conductive modification layer is 25-65%, and the electrolyte contact angle of the conductive modification layer is not greater than 10°.

[0063] In the manufacturing process of the negative electrode sheet, the traditional coating and drying process is carried out under low humidity conditions, and the formed coating has disordered pores, which is easy to adversely affect the storage and transmission of ions in the pores. Based on the same inventive concept as the above-mentioned negative electrode sheet and the purpose of improving the pore structure of the conductive modification layer, the desolvation process after coating the conductive modification layer slurry can be carried out in a high humidity environment and at a high temperature, and the phase inversion method can be used to promote the removal of the solvent and improve the pore structure of the conductive modification layer. Among them, in a high humidity environment, the solvent will exchange with the water in the environment, and the water will enter the slurry and cooperate with the binder, which is conducive to improving the uniformity and orderliness of the pore structure.

[0064] The temperature of the desolvation treatment can be 70-120°C, for example, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 110°C, 120°C, etc. The humidity of the desolvation treatment can be 70-100%, for example, 70%, 75%, 80%, 85%, 90%, 95%, or 100%, etc. Under the condition of high humidity and high temperature, due to the diffusion effect, the solvent exchanges with the water in the environment, the solvent leaves the slurry, and the water enters the slurry, forming a polymer-rich phase (more binder, less solvent, and less water) and a polymer-lean phase (less binder, more solvent, and more water). After complete solidification, the rich phase forms the main structure, and the lean phase forms the pores, forming a porous network structure of the conductive modification layer. Increasing the temperature of the desolvation treatment is conducive to driving the exchange of solvent and water vapor, facilitating phase inversion and pore formation (see Figure 4 understanding); however, if the temperature is too high, the solvent volatilization rate can be too fast, which can cause the solvent to solidify directly without exchanging with the water vapor, affecting the pore formation effect (see Figure 5 understanding, the pore volume is reduced, and the structure of the conductive modification layer gradually becomes dense); in addition, the higher the humidity, the more conducive to promoting the entry of water vapor into the coated slurry, promoting the exchange of solvent and water for pore formation. In this application, by simultaneously controlling the temperature and humidity of the desolvation treatment to meet the given conditions, a high-humidity environment can be provided, and the phase inversion of the solvent and water vapor can be better driven, and the volatilization rate of the solvent can also be considered, improving the uniformity and order of the pore structure. In addition, by performing the desolvation treatment under constant temperature and humidity conditions, a stable solvent volatilization rate and phase inversion rate can be further obtained, which can further improve the uniformity and order of the pore size.

[0065] Therefore, the method for preparing the negative electrode sheet of the above-mentioned embodiments of the application has at least the following beneficial effects: the method has good processability, and compared with the traditional drying process, the porous conductive modification layer formed by the method not only provides an electronic path for the reaction of ions and electrons, but also has good uniformity and order of the pore structure, which is conducive to the uniform and ordered deposition of metal. In addition, the porous structure can also provide good electrolyte infiltration and storage capacity, so that the negative electrode sheet has good electrolyte infiltration and liquid retention, and the combination of the above can reduce the deposition overpotential of the metal, improve the cycle life, and make the prepared negative electrode sheet have good liquid affinity and liquid retention, which is conducive to improving the deposition efficiency of ions and reducing the deposition overpotential, and improving the cycle performance of the battery.

[0066] In some embodiments of the present application, the mass percentage of the conductive agent in the conductive modification layer slurry can be 2.5-5wt%, and the mass percentage of the binder can be 1-4wt%. For example, the mass percentage of the conductive agent can be 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, etc., and the mass percentage of the binder can be 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, etc. The concentration of the conductive agent and the binder in the slurry meets the given conditions, which is not only conducive to forming a porous conductive modification layer with the expected porosity, but also conducive to improving the adhesion strength of the conductive modification layer to the negative current collector and reducing the probability of forming a larger exposed area of the negative current collector in the conductive modification layer (see Figure 6 It is understood that when the metal foil is used as the negative current collector, too little amount of the conductive agent is easy to form a larger exposed area of the foil that is not covered by the conductive modification layer. In addition, it is also conducive to taking into account the efficiency of phase inversion and reducing the risk of reducing the pore-forming efficiency or blocking the pore size due to too much amount of the binder (see Figure 7 It is understood that too much amount of the binder is easy to cause the problem of blocking the pores.

[0067] In some embodiments of the present application, the conductive agent can include one-dimensional conductive agent and / or zero-dimensional conductive agent. Further, the conductive agent can simultaneously include one-dimensional conductive agent and zero-dimensional conductive agent, and the mass ratio of the one-dimensional conductive agent to the zero-dimensional conductive agent can be 1:(1-5). In some embodiments, the one-dimensional conductive agent can include carbon nanotubes and / or carbon fibers. In some embodiments, the zero-dimensional conductive agent includes conductive carbon black. The beneficial effects of the conductive agent meeting the given related conditions have been described in the foregoing part, which will not be repeated here.

[0068] In some embodiments of the present application, the binder can include one or more of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid.

[0069] In some embodiments of the present application, the organic solvent can include one or more of N-methylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide. The organic solvent is easy to volatilize under high temperature and high humidity conditions and to realize phase inversion with water.

[0070] In some embodiments of the present application, the thickness of the conductive modification layer can be 1-5μm. The beneficial effects of the thickness of the conductive modification layer meeting the given conditions have also been described in the foregoing part, which will not be repeated here.

[0071] It should be noted that the above-mentioned method for preparing the negative pole piece and the above-mentioned negative pole piece are based on the same inventive concept, and the features and effects described for the above-mentioned negative pole piece also apply to the method for preparing the negative pole piece of the present application, which will not be repeated here.

[0072] In a third aspect of the present application, the present application provides a energy storage device. The energy storage device comprises the negative electrode plate described above, and / or the negative electrode plate prepared by the method for preparing negative electrode plate described above. The energy storage device has all the characteristics and effects described above for the negative electrode plate and the method for preparing negative electrode plate, which will not be repeated here. In general, the energy storage device has both lower metal deposition overpotential and cycle performance.

[0073] It should be noted that the specific type of energy storage device in the present application is not particularly limited, and those skilled in the art can choose flexibly according to the actual situation, for example, refer to Figure 8 It is understood that the energy storage device can include a battery, which can include a positive electrode plate, a negative electrode plate, a separator and an electrolyte, and the negative electrode plate can be the negative electrode plate described above. The positive electrode plate can include a positive electrode current collector and a positive electrode active material layer provided on at least one side of the positive electrode current collector, and the positive electrode active material layer can include a positive electrode active material, a conductive agent, a binder, and optionally other conventional functional additives. The specific ratio and type of positive electrode active material, conductive agent and binder in the positive electrode plate, and the selection of the positive electrode current collector can be selected conventionally in the art, for example, the positive electrode active material can include but is not limited to multi-element layered oxide positive electrode active material, olivine-type positive electrode active material, etc., the conductive agent can use conductive carbon black, graphene, carbon nanotube, etc., the binder can use polyvinylidene fluoride, sodium carboxymethyl cellulose, etc., and the positive electrode current collector can include but is not limited to aluminum foil, etc. In addition, the specific composition of the separator and the electrolyte is not particularly limited in the present application, and can be selected conventionally in the art, for example, the separator can include at least one of polypropylene (PP), polyethylene (PE), ceramic separator; the electrolyte can include electrolyte salt and organic solvent, and the specific type and composition of the electrolyte salt and organic solvent are not particularly limited, and those skilled in the art can select according to the actual needs. In addition, the specific type of the battery in the present application is not particularly limited, and those skilled in the art can choose flexibly according to the actual situation, for example, the battery can be a square battery, a cylindrical battery, etc. For example, the battery can be a liquid battery, a semi-solid battery, etc. For example, the battery can be a lithium battery or a sodium battery, etc.

[0074] In a fourth aspect of the present application, the present application provides a power utilization device. The power utilization device comprises the energy storage device described above. The power utilization device has all the characteristics and effects described above for the energy storage device, which will not be repeated here. In general, the power utilization device has better performance. It should be noted that the specific type of power utilization device in the present application is not particularly limited, and those skilled in the art can choose flexibly according to the actual situation, for example, the power utilization device can include but is not limited to electronic equipment, vehicles, aircraft, household appliances, etc.

[0075] Embodiments of the present application are described in detail below. The embodiments described below are exemplary only, and are not to be taken in a limiting sense. Unless otherwise indicated, technical or scientific terms used in the embodiments have the same meaning as commonly understood by one of ordinary skill in the art to which the present application pertains. Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application pertains. The materials, methods, and examples provided are illustrative only and not intended to be limiting. Unless otherwise indicated, the materials described herein can be obtained through commercial means, or as otherwise described.

[0076] Example 1

[0077] Preparation of the negative electrode sheet:

[0078] The conductive agent, binder PVDF (polyvinylidene fluoride) and solvent NMP (N-methyl pyrrolidone) were mixed in a mass ratio of 5wt%, 1.5wt% respectively, and stirred to form a slurry. The conductive agent was composed of CNT (carbon nanotube) and SP (conductive carbon black) in a mass ratio of 1:1. The slurry was coated on the copper foil and transferred to a constant temperature & humidity environment (temperature 80℃, humidity 90%). After the slurry was fully phase-inverted and completely cured, punching was performed to obtain the negative electrode sheet. The conductive modification layer formed after curing had a thickness of 2μm.

[0079] Preparation of the positive electrode sheet:

[0080] The positive active material LiNi 0.8 Co 0.1 Mn 0.1 O2, super conductive carbon black (SP) and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 90:5:5 and dispersed in solvent NMP. After uniform stirring, they were uniformly coated on an aluminum foil, dried, rolled, and then punched to obtain the positive electrode sheet.

[0081] 3. Preparation of the electrolyte:

[0082] The electrolyte was composed of an organic solvent and an electrolyte salt. The organic solvent was composed of dioxolane (DOL) and dimethoxyethane (DME) in a volume ratio of 1:1. The electrolyte salt was lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and its concentration in the electrolyte was 1mol / L.

[0083] 4. Preparation of the separator:

[0084] A polyethylene composite separator coated with a ceramic coating on one side was selected as the separator.

[0085] 5. Assembly of the battery:

[0086] The above positive electrode sheet, separator and negative electrode sheet were stacked in order, with the separator between the positive and negative electrode sheets to play a separating role. The above electrolyte was added to assemble a button cell.

[0087] Examples 2-14 and Comparative Examples 1-2

[0088] The differences between Examples 2-14 and Comparative Examples 1-2 and Example 1 are shown in Table 1. Among them: Comparative Example 1 uses copper foil as the negative electrode tab, and does not contain a conductive coating layer; in Comparative Example 2, the conductive modification layer is cured in a low humidity environment.

[0089] The negative electrode tabs and batteries prepared in the above examples and comparative examples were tested, and the test results are shown in Table 1.

[0090] Among them:

[0091] 1) Pore size of conductive modification layer: The porosity of the conductive modification layer was characterized by scanning electron microscopy at 5 kV, and the scale was measured.

[0092] 2) Pore size of conductive modification layer: The porosity was calculated according to the true density of the materials added to the conductive modification layer and the coating surface density, and the porosity = (CW / h-D) / (CW / h) x 100%, wherein D = 1 / (X1 / a+X2 / b+…+X n / n), X1, X2, … Xn are the proportions of each material component in the conductive modification layer, a, b and n are the true densities of each material, CW is the coating surface density of the conductive modification layer, and h is the thickness of the conductive modification layer.

[0093] 3) Deposition overpotential: The prepared battery was cycled at room temperature at a charge-discharge current of 0.1C for 3 cycles, then cycled at 0.33C, with a voltage window of 4.2-2.5V, for 50 cycles. Based on the discharge capacity retention rate of the 50th week and the first week, the discharge capacity retention rate after the 50th cycle was calculated.

[0094] 4) Ion transport resistance R ion of the negative electrode tab in the electrolyte environment: The negative electrode was assembled into a symmetrical battery, and the ion transport resistance R ion of the tab pore liquid phase was obtained by EIS test (1Mhz-0.1hz).

[0095] Table 1 Differences and test results of Examples 1-14 and Comparative Examples 1-2

[0096]

[0097]

[0098] Note: In Table 1, " / " means "not present" or "not tested"; "~" means "about".

[0099] Results and conclusions:

[0100] It can be seen from the combination of Examples 1-14 and Comparative Examples 1-2 and the related test results that the electrolyte contact angle of the porous conductive modification layer formed by the desolvation treatment of the conductive modification layer slurry in a constant temperature and humidity high temperature and humidity environment is relatively small, indicating that the wettability of the porous modification layer formed is good, and the deposition overpotential of the negative electrode sheet used in the battery is relatively low, and the cycle capacity retention rate is good. Further, the relative amount of the conductive agent and the binder, the drying temperature and humidity during desolvation all have an effect on the pore structure of the conductive modification layer finally formed and the improvement effect on the battery performance: it can be seen from the combination of Examples 1, 5-8 and Comparative Example 2 that the drying temperature and humidity will affect the pore size and porosity of the conductive modification layer, and controlling the appropriate drying temperature is conducive to further improving the pore-forming effect and porosity of the conductive modification layer and the cycle performance of the battery; further, it can be seen from the combination of Examples 1 and 13-14 that under the same conditions, with the increase of the mass ratio of the conductive agent and the binder, the pore size of the porous conductive modification layer tends to increase, and the improvement effect on the cycle capacity retention rate of the battery tends to increase first and then decrease; by overall adjusting the drying temperature, humidity during desolvation, and the relative amount of the conductive agent and the binder, it is conducive to further improving the pore structure of the porous conductive modification layer and the improvement effect on the battery performance.

[0101] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, different embodiments or examples described in the present specification and the features of different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0102] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A negative electrode sheet, characterized by, The negative electrode tab includes: a negative electrode current collector; a conductive modification layer provided on at least one side of the negative electrode current collector, the conductive modification layer having a porosity of 25-65% and an electrolyte contact angle of no more than 10°; a method for preparing the negative electrode tab, including: mixing a conductive agent and a binder with an organic solvent to obtain a conductive modification layer slurry; applying the conductive modification layer slurry to at least one side of the negative electrode current collector and performing desolvation treatment under constant temperature and humidity conditions to form the conductive modification layer, wherein the desolvation treatment is performed at a temperature of 70-120°C and a humidity of 70-100%.

2. The negative electrode sheet according to claim 1, characterized by The negative electrode current collector is a metal foil; and / or the ion transport resistance of the negative electrode tab in an electrolyte environment is no more than 500 mΩ.

3. The negative electrode sheet according to claim 1 or 2, characterized by, The conductive modification layer includes a conductive agent and a binder, and the mass ratio of the conductive agent to the binder is (2.5-5):(1-4).

4. The negative electrode sheet according to claim 3, characterized by The binder includes one or more of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid.

5. The negative electrode sheet according to claim 1 or 4, wherein The conductive agent in the conductive modification layer includes one-dimensional conductive agents and / or zero-dimensional conductive agents.

6. The negative electrode sheet according to claim 5, characterized by At least one of the following conditions is met: The conductive agent includes one-dimensional conductive agents and zero-dimensional conductive agents, and the mass ratio of the one-dimensional conductive agents to the zero-dimensional conductive agents is 1:(1-5); The one-dimensional conductive agents include carbon nanotubes and / or carbon fibers; The zero-dimensional conductive agents include conductive carbon black.

7. The negative electrode sheet according to claim 1 or 6, wherein The thickness of the conductive modification layer is 1-5 μm.

8. The negative electrode plate of claim 1, wherein, At least one of the following conditions is met: In the conductive modification layer slurry, the mass fraction of the conductive agent is 2.5-5 wt%, and the mass fraction of the binder is 1-4 wt%; The conductive agent includes one-dimensional conductive agents and / or zero-dimensional conductive agents; The binder includes one or more of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid; The organic solvent includes one or more of N-methylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide; The thickness of the conductive modification layer is 1-5 μm.

9. The negative electrode sheet according to claim 1 or 8, wherein The conductive agent includes one-dimensional conductive agents and zero-dimensional conductive agents, and at least one of the following conditions is met: The mass ratio of the one-dimensional conductive agents to the zero-dimensional conductive agents is 1:(1-5); The one-dimensional conductive agents include carbon nanotubes and / or carbon fibers; The zero-dimensional conductive agents include conductive carbon black.

10. An energy storage device, characterized by, The negative electrode tab of any one of claims 1-9. The energy storage device of claim 10.

11. An electrical device, characterized by ​

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