Negative electrode sheet and preparation method thereof, battery and vehicle

Abstract

The present invention discloses a negative electrode plate and a preparation method thereof, a battery and a vehicle. The negative electrode plate comprises: a current collector and a negative electrode coating provided on at least one surface of the current collector, wherein the negative electrode coating comprises: a negative electrode active material and a fast charging aid, the negative electrode active material comprises graphite powder, the particle size of the graphite powder is not greater than 1 μm, and the fast charging aid comprises a carbon matrix and a nano-carbon particle layer deposited on the surface of the carbon matrix. The use of the negative electrode plate can not only reduce the concentration polarization of the electrolyte during charging, which is beneficial to improving the fast charging performance of the battery, but also increase the amount of negative electrode active material, which is helpful to improve the energy density of the battery cell.

Description

Technical Field

[0001] The present invention belongs to the field of batteries, and in particular, relates to a negative electrode plate and a preparation method thereof, a battery and a vehicle. Background Art

[0002] In recent years, in order to reduce the impact of environmental pollution, the widespread application of lithium-ion batteries in pure electric vehicles is accelerating. In order to meet consumers' growing demand for driving range, power battery manufacturers continue to improve the energy density of lithium-ion batteries, which has continuously improved the driving range of electric vehicles. However, the current charging facilities are not yet perfect, and the charging time is still difficult to meet consumers' requirements. The demand for fast charging of power batteries is constantly increasing. Therefore, it is still a great challenge to balance the improvement of battery energy density, charging time, and high safety performance. Summary of the invention

[0003] The present invention is mainly proposed based on the following problems and findings:

[0004] In graphite-based lithium-ion batteries with high energy density, the fast charging capability is mainly limited by the negative electrode. There is an obvious polarization effect in the high-rate charging process. Due to the polarization effect, the lithium ions that are rapidly released from the positive electrode are difficult to be embedded in the graphite negative electrode in time, resulting in lithium deposition on the negative electrode surface, which is prone to safety risks. The polarization effect in the graphite negative electrode is mainly attributed to the concentration polarization of lithium ions in the electrolyte.

[0005] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, one purpose of the present invention is to provide a negative electrode plate and a preparation method thereof, a battery and a vehicle, which can not only reduce the concentration polarization of the electrolyte during charging, which is beneficial to improving the fast charging performance of the battery, but also increase the amount of negative electrode active material, which is helpful to improve the energy density of the battery cell.

[0006] In one aspect of the present invention, the present invention provides a negative electrode plate. According to an embodiment of the present invention, the negative electrode plate comprises: a current collector and a negative electrode coating provided on at least one surface of the current collector, wherein the negative electrode coating comprises: a negative electrode active material and a fast charging aid, the negative electrode active material comprises graphite powder, the particle size of the graphite powder is not greater than 1 μm, and the fast charging aid comprises a carbon matrix and a nano-carbon particle layer deposited on the surface of the carbon matrix.

[0007] The negative electrode sheet according to the above embodiment of the present invention has at least the following beneficial effects: 1) By adding graphite powder and controlling the particle size of the graphite powder to be no more than 1 μm, the graphite powder can have good conductivity and can act as a conductive agent (such as conductive carbon black) to improve the electronic conductivity. When used as a negative electrode active material, the amount of other conductive agents added can be reduced while improving the electronic conductivity of the negative electrode sheet. Thus, the total amount of negative electrode active material can be increased while the total mass of the negative electrode sheet remains unchanged, thereby improving the energy density of the battery cell; 2) Since the graphite powder has a small particle size and a large specific surface area, it can effectively increase the contact with the electrolyte. The contact area can store more electrolyte, provide a medium for the migration of lithium ions, reduce the polarization effect produced during the charging process, especially when charging at a high rate, and improve the fast charging performance of the battery; 3) By adding a fast charging aid including a carbon matrix and a nano-carbon particle layer deposited on the surface of the carbon matrix, the specific surface area of ​​the carbon matrix can be significantly increased, and the storage capacity of its surface charge can be increased, so that more lithium ions can be adsorbed on the surface of the fast charging aid, reducing the concentration difference between the surface of the negative electrode and the electrolyte at the moment of high-rate charging, reducing negative electrode polarization, and reducing the risk of lithium precipitation on the negative electrode surface, which is beneficial to improving the fast charging performance of the battery and reducing safety hazards during fast charging. In summary, the use of the negative electrode plate of the above embodiment of the present invention is beneficial to taking into account the fast charging performance, energy density and safety performance of the battery, and has broad application prospects.

[0008] In addition, the negative electrode sheet according to the above embodiment of the present invention may also have the following additional technical features:

[0009] In some embodiments of the present invention, based on the total mass of the negative electrode active material, the graphite powder accounts for 0.5-1 wt %.

[0010] In some embodiments of the present invention, the particle size of the graphite powder is 0.5-1 μm.

[0011] In some embodiments of the present invention, the negative electrode active material further includes artificial graphite.

[0012] In some embodiments of the present invention, the artificial graphite is artificial graphite having a carbon coating layer.

[0013] In some embodiments of the present invention, based on the total mass of the negative electrode coating, the negative electrode active material accounts for 75-93 wt %.

[0014] In some embodiments of the present invention, the D50 particle size of the artificial graphite is 8 to 12 μm, and the D10 particle size is 3 to 6 μm.

[0015] In some embodiments of the present invention, based on the total mass of the negative electrode coating, the fast charging aid accounts for 5 to 20 wt %.

[0016] In some embodiments of the present invention, the D50 particle size of the fast-charging aid is 7 to 20 μm, and the D10 particle size is 3 to 14 μm.

[0017] In some embodiments of the present invention, the specific surface area of ​​the fast charging auxiliary agent is not less than 3m 2 / g.

[0018] In some embodiments of the present invention, the thickness of the nano-carbon particle layer is no more than 5 nm.

[0019] In some embodiments of the present invention, the nano-scale carbon particle layer is obtained by chemical vapor deposition, and the carbon source for forming the nano-scale carbon particle layer includes at least one of methane, ethylene, and acetylene.

[0020] In some embodiments of the present invention, the carbon matrix includes at least one of artificial graphite, natural graphite, and hard carbon.

[0021] In some embodiments of the present invention, the negative electrode coating further includes: a linear conductive agent.

[0022] In some embodiments of the present invention, based on the total mass of the negative electrode coating, the linear conductive agent accounts for 0.3-1.5 wt %.

[0023] In some embodiments of the present invention, the linear conductive agent includes conductive carbon nanotubes and / or conductive carbon fibers.

[0024] In some embodiments of the present invention, the negative electrode coating further includes: a thickener and / or a binder.

[0025] In some embodiments of the present invention, based on the total mass of the negative electrode coating, the thickener accounts for 1 to 1.8 wt %.

[0026] In some embodiments of the present invention, the thickener comprises sodium carboxymethyl cellulose.

[0027] In some embodiments of the present invention, based on the total mass of the negative electrode coating, the binder accounts for 0.6-2.5 wt %.

[0028] In some embodiments of the present invention, the binder includes at least one of styrene-butadiene rubber, acrylonitrile multipolymer, and acrylic resin.

[0029] In another aspect of the present invention, the present invention proposes a method for preparing the above-mentioned negative electrode plate. According to an embodiment of the present invention, the method includes: (1) depositing a negative electrode active slurry on at least one surface of a current collector; (2) drying the current collector on which the negative electrode active slurry is deposited and pressing it to obtain a negative electrode plate; wherein the negative electrode active slurry includes: a negative electrode active material and a fast charging aid, the negative electrode active material includes graphite powder, the particle size of the graphite powder is not greater than 1 μm, and the fast charging aid includes a carbon matrix and a carbon layer deposited on the surface of the carbon matrix. Compared with the prior art, this method not only has a simple preparation process, but also the prepared negative electrode plate can reduce the concentration polarization of the electrolyte during charging, and at the same time can increase the adsorption amount of the electrolyte, provide a medium for the migration of lithium ions, which is beneficial to take into account the energy density of the battery cell, the fast charging performance and the safety performance of the battery.

[0030] In some embodiments of the present invention, in step (1), the negative electrode active slurry further comprises: at least one of a thickener, a linear conductive agent, and a binder.

[0031] In some embodiments of the present invention, the surface density of the negative electrode active slurry deposited on one side of the current collector is 7 to 9 mg / cm 2 .

[0032] In some embodiments of the present invention, in step (2), the pressing includes a first pressing and a second pressing performed sequentially, and the thickness of the coating formed after the first pressing is 1.1 to 1.2 times the thickness of the coating formed after the second pressing.

[0033] In another aspect of the present invention, the present invention provides a battery. According to an embodiment of the present invention, the battery includes the above-mentioned negative electrode sheet and / or the negative electrode sheet prepared by the above-mentioned method. Compared with the prior art, the negative electrode sheet used in the battery is more conducive to having higher energy density, better fast charging performance and better safety performance.

[0034] In another aspect of the present invention, the present invention provides a vehicle. According to an embodiment of the present invention, the vehicle comprises the above-mentioned negative electrode sheet, and / or the negative electrode sheet prepared by the above-mentioned method, and / or the above-mentioned battery. Compared with the prior art, the vehicle can have a longer cruising range, a faster charging speed and better battery safety performance, and has a higher market satisfaction.

[0035] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0037] Figure 1 is a schematic diagram of the interaction between the components of the negative electrode coating according to one embodiment of the present invention;

[0038] Figure 2 It is a flow chart of a method for preparing a negative electrode sheet according to one embodiment of the present invention. DETAILED DESCRIPTION

[0039] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limitations on the present invention. In the description of the present invention, the terms "first" and "second" are used only for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0040] In one aspect of the present invention, the present invention proposes a negative electrode plate. According to an embodiment of the present invention, the negative electrode plate includes: a current collector and a negative electrode coating provided on at least one surface of the current collector, wherein the negative electrode coating includes: a negative electrode active substance and a fast charging aid, the negative electrode active substance includes graphite micropowder, the particle size of the graphite micropowder is not greater than 1 μm, and the fast charging aid includes a carbon matrix and a nano-carbon particle layer deposited on the surface of the carbon matrix.

[0041] The negative electrode sheet according to the above embodiment of the present invention has at least the following beneficial effects: 1) By adding graphite powder and controlling the particle size of the graphite powder to be no more than 1 μm, the graphite powder can have good conductivity and can act as a conductive agent (such as conductive carbon black) to improve the electronic conductivity. When used as a negative electrode active material, the amount of other conductive agents added can be reduced while improving the electronic conductivity of the negative electrode sheet. Thus, the total amount of negative electrode active material can be increased while the total mass of the negative electrode sheet remains unchanged, thereby improving the energy density of the battery cell; 2) Since the graphite powder has a small particle size and a large specific surface area, it can effectively increase the contact with the electrolyte. The contact area can store more electrolyte, provide a medium for the migration of lithium ions, reduce the polarization effect produced during the charging process, especially when charging at a high rate, and improve the fast charging performance of the battery; 3) By adding a fast charging aid including a carbon matrix and a nano-carbon particle layer deposited on the surface of the carbon matrix, the specific surface area of ​​the carbon matrix can be significantly increased, and the storage capacity of its surface charge can be increased, so that more lithium ions can be adsorbed on the surface of the fast charging aid, reducing the concentration difference between the surface of the negative electrode and the electrolyte at the moment of high-rate charging, reducing negative electrode polarization, and reducing the risk of lithium precipitation on the negative electrode surface, which is beneficial to improving the fast charging performance of the battery and reducing safety hazards during fast charging. In summary, the use of the negative electrode plate of the above embodiment of the present invention is beneficial to taking into account the fast charging performance, energy density and safety performance of the battery, and has broad application prospects.

[0042] Negative active material

[0043] According to an embodiment of the present invention, based on the total mass of the negative electrode active material, the proportion of graphite powder can be 0.5-1wt%, for example, it can be 0.6wt%, 0.7wt%, 0.8wt% or 0.9wt%, etc. The inventors found that in the negative electrode active material, if the amount of graphite powder is too much, it will affect the capacity of the graphite negative electrode; if the amount of graphite powder is too little, it is difficult to store more electrolyte, provide a medium for the migration of lithium ions, and it is difficult to give full play to its conductive properties. The present invention further helps to take into account the capacity of the graphite negative electrode, the fast charging performance and safety performance of the negative electrode sheet by controlling the amount of graphite powder in the negative electrode coating within the above range.

[0044] According to an embodiment of the present invention, the particle size of graphite powder can be 0.5-1 μm, for example, 0.6 μm, 0.7 μm, 0.8 μm or 0.9 μm, etc. The inventor found that if the particle size of graphite powder is too small, on the one hand, the processing cost increases, and on the other hand, the agglomeration between graphite powders is easily enhanced, which increases the difficulty of dispersion; if the particle size of graphite powder is too large, it will affect its conductivity, and also cause its specific surface area to decrease, weakening its improvement effect on polarization effect. The present invention controls the particle size of graphite powder within the above range, which is conducive to giving full play to the conductive effect of graphite powder while ensuring processing performance, effectively improving the energy density of the battery, and reducing the polarization effect generated during the charging process, especially when charging at a high rate, and improving the fast charging performance and safety performance of the battery.

[0045] According to an embodiment of the present invention, the negative electrode active material may further include artificial graphite. In the present invention, there is no particular restriction on the specific type of artificial graphite, and those skilled in the art may flexibly select according to actual conditions. For example, the artificial graphite may be at least one of artificial graphite without a carbon coating layer, artificial graphite doped with silicon, artificial graphite with a carbon coating layer, and artificial graphite doped with silicon with a carbon coating layer. In the present invention, there is no particular restriction on the specific type and amount of silicon material in the artificial graphite doped with silicon material. For example, the added silicon material may be at least one of silicon monoxide, silicon-carbon composite, and nano-silicon. The amount of silicon material added to the artificial graphite doped with silicon material may be 3 to 20 wt%. Silicon addition is beneficial to increasing the gram capacity of the negative electrode active material and improving the battery energy density. Further, according to some specific examples of the present invention, the D50 particle size of artificial graphite can be 8-12 μm, and the D10 particle size can be 3-6 μm. For example, the D50 particle size of artificial graphite can be 9 μm, 10 μm or 11 μm, and the D10 particle size can be 3 μm, 4 μm or 5 μm. The inventors found that if the particle size of artificial graphite is too small, it is easy to affect the processing performance and coating performance of the negative electrode active coating slurry; if the particle size of artificial graphite is too large, it may affect the rate performance and cycle performance of the battery. The present invention controls the particle size of artificial graphite within the above range, which is beneficial to taking into account both the processing performance of the electrode sheet and the electrochemical performance of the battery.

[0046] According to an embodiment of the present invention, based on the total mass of the negative electrode coating, the proportion of the negative electrode active material can be 75-93wt%, for example, 78wt%, 80wt%, 85wt%, 88wt%, 90wt% or 92wt%, etc. The inventors found that if the amount of the negative electrode active material is too little, the capacity of the battery will decrease; if the amount of the negative electrode active material is too much, the amount of other additives (such as fast charging aids) in the negative electrode coating will be compressed, affecting the comprehensive performance of the negative electrode sheet. The present invention controls the amount of the negative electrode active material in the negative electrode coating within the above range, which is conducive to obtaining a negative electrode sheet with both high energy density and good fast charging performance.

[0047] Fast charging additive

[0048] According to an embodiment of the present invention, based on the total mass of the negative electrode coating, the proportion of the fast charging aid can be 5 to 20wt%, for example, it can be 8wt%, 10wt%, 12wt%, 14wt%, 16wt% or 18wt%, etc. The inventors found that in the negative electrode coating, if the amount of the fast charging aid is too little, it is difficult to give full play to the fast charging aid to improve the fast charging performance of the negative electrode plate; if the amount of the fast charging aid is too much, it will compress the relative content of the negative electrode active material in the negative electrode coating, which is easy to affect the capacity of the negative electrode plate and reduce the energy density of the battery. The present invention controls the amount of the fast charging aid in the negative electrode coating within the above range, which is conducive to taking into account both the fast charging performance and the energy density of the battery.

[0049] According to an embodiment of the present invention, the specific surface area of ​​the fast charging auxiliary agent may be not less than 3m 2 / g, for example, 4m 2 / g, 5m 2 / g or 6m 2 / g, etc. The inventors found that if the specific surface area of ​​the fast charging aid is too small, it is difficult to store more electrolyte and provide a medium for the migration of lithium ions, and the effect of reducing the polarization effect generated during the charging process, especially during high-rate charging, is weakened. It should be noted that in the present invention, the purpose of increasing the specific surface area of ​​the fast charging aid is achieved by depositing a nano-carbon particle layer on the surface of the carbon matrix, and the nano-carbon particle layer has little effect on the particle size of the carbon matrix. Therefore, there is no special restriction on the particle size of the fast charging aid in the present invention. Those skilled in the art can flexibly choose according to actual conditions. For example, the particle size of the fast charging aid D50 can be 7-20 μm, and the particle size of D10 can be 3-14 μm. Specifically, the particle size of the fast charging aid D50 can be 8 μm, 10 μm, 14 μm, 16 μm or 18 μm, etc., and the particle size of D10 can be 5 μm, 7 μm, 9 μm, 11 μm or 13 μm, etc., thereby further improving the flatness and stability of the negative electrode coating.

[0050] According to an embodiment of the present invention, the nano-carbon particle layer can be obtained by chemical vapor deposition. For example, the carbon source can be deposited on the surface of the carbon matrix by chemical vapor deposition to obtain a carbon matrix and a nano-carbon particle layer formed on the surface of the carbon matrix. It should be noted that there is no particular restriction on the specific composition of the carbon matrix and the carbon source in the present invention. Those skilled in the art can flexibly choose according to actual conditions. For example, the carbon matrix can include at least one of artificial graphite, natural graphite, and hard carbon; the carbon source can include a small molecule organic carbon source, for example, it can include at least one of methane, ethylene, and acetylene. In addition, according to some specific examples of the present invention, the thickness of the obtained nano-carbon particle layer can be no more than 5nm, for example, it can be 2nm, 3nm or 4nm, etc. The inventors found that if the thickness of the nano-carbon particle layer is too large, not only the process cost will increase, but also the storage capacity of the fast charging aid for the electrolyte will be affected, and the improvement effect on the polarization effect will be weakened.

[0051] According to an embodiment of the present invention, the negative electrode coating may further include:

[0052] Conductive agent

[0053] According to the embodiments of the present invention, based on the current market requirements for the internal volume utilization of battery packs, long-sized cells have gradually become the mainstream trend in the industry. However, due to the longer electrode length, long-sized cells have a longer electron conduction path, which increases the internal resistance of the cell and increases the temperature rise of the cell during fast charging, which is likely to accelerate the attenuation of the cell capacity and limit the fast charging performance of the battery. Figure 1 It is understood that the present invention introduces a linear conductive agent into the negative electrode coating, so that the linear conductive agent cooperates with the negative electrode active material and the fast charging aid, which can effectively improve the long-range conductivity of the negative electrode sheet, thereby increasing the electronic conductivity of the long-size electrode sheet, which is beneficial to further improve the fast charging performance of the battery.

[0054] According to an embodiment of the present invention, based on the total mass of the negative electrode coating, the proportion of the linear conductive agent can be 0.3-1.5wt%, for example, 0.5wt%, 0.8wt%, 1.0wt%, 1.2wt% or 1.4wt%, etc. The inventors found that in the negative electrode coating, if the amount of the linear conductive agent is too small, it is difficult to produce sufficient synergy with the negative electrode active material and the fast charging aid, and it is difficult to effectively improve the long-range conductivity of the negative electrode sheet; if the amount of the linear conductive agent is too much, it will increase the difficulty of dispersing the negative electrode active slurry and affect the processing performance of the negative electrode sheet. The present invention controls the amount of the linear conductive agent in the negative electrode coating within the above range, which is beneficial to improving the conductive effect of the linear conductive agent while ensuring its processing and dispersion performance, and is particularly beneficial to improving the electronic conductivity of the long-size electrode sheet, thereby improving the fast charging performance of the battery. In addition, it should be noted that there is no particular limitation on the specific type of the linear conductive agent in the present invention, and those skilled in the art can flexibly select according to actual conditions. For example, the linear conductive agent may include conductive carbon nanotubes (CNTs) and / or conductive carbon fibers (VGCF), etc.

[0055] According to an embodiment of the present invention, the negative electrode coating may further include a thickener. There is no particular limitation on the specific type of the thickener in the present invention. Those skilled in the art may flexibly select the thickener according to actual conditions. For example, the thickener may include sodium carboxymethyl cellulose (CMC), etc. According to some specific examples of the present invention, based on the total mass of the negative electrode coating, the proportion of the thickener may be 1 to 1.8 wt%, for example, 1.2 wt%, 1.4 wt%, or 1.6 wt%, etc.

[0056] According to an embodiment of the present invention, the negative electrode coating may further include a binder. There is no particular limitation on the specific type of the binder in the present invention. Those skilled in the art may flexibly select the binder according to actual conditions. For example, the binder may include at least one of styrene-butadiene rubber, acrylonitrile multipolymer, and acrylic resin. According to some specific examples of the present invention, based on the total mass of the negative electrode coating, the proportion of the binder may be 0.6 to 1.5 wt%, for example, 0.7 wt%, 0.9 wt%, 1.1 wt%, or 1.3 wt%, etc.

[0057] According to an embodiment of the present invention, the surface density of the negative electrode coating on one side of the current collector may be 7 to 9 mg / cm 2 , for example, 7.5 mg / cm 2 , 8mg / cm 2 or 8.5 mg / cm 2The inventors found that if the surface density of the negative electrode coating on one side of the current collector is too small, the content of the negative electrode active material is reduced, affecting the energy density of the battery; if the surface density of the negative electrode coating on one side of the current collector is too large, it may affect the penetration of the electrolyte on the negative electrode sheet, thereby increasing the internal resistance of the battery. The present invention controls the surface density of the negative electrode coating within the above range, which is conducive to ensuring the wetting effect of the electrolyte on the electrode sheet and improving the energy density of the battery.

[0058] In another aspect of the present invention, the present invention provides a method for preparing the above-mentioned negative electrode sheet. Figure 2 It is understood that the method comprises:

[0059] S100: Depositing negative electrode active slurry on at least one surface of the current collector

[0060] According to an embodiment of the present invention, the negative electrode active slurry includes: a negative electrode active material and a fast charging aid, the negative electrode active material includes graphite powder, the particle size of the graphite powder is not greater than 1 μm, and the fast charging aid includes a carbon matrix and a carbon layer deposited on the surface of the carbon matrix. The specific characteristics and effects of adding the above-mentioned negative electrode active material and fast charging aid have been described in detail in the previous section and will not be repeated here. In addition, the negative electrode active slurry may also include at least one of a thickener, a linear conductive agent, and a binder, and those skilled in the art can flexibly select according to actual conditions.

[0061] According to an embodiment of the present invention, the specific steps of preparing the negative electrode active slurry may include:

[0062] (I) performing a first mixing process on a thickener and deionized water to obtain a thickener solution;

[0063] (II) performing a second mixing treatment on the negative electrode active material and the fast charging aid according to a ratio to obtain dispersed particles;

[0064] (III) performing a third mixing process on the thickener solution and the dispersed particles according to a ratio to obtain a first dispersion;

[0065] (IV) The first dispersion, the linear conductive agent and deionized water are mixed in a fourth manner according to a certain ratio, and impurities and / or large-sized particles are removed by filtration to obtain a negative electrode active slurry.

[0066] S200: drying the current collector on which the negative electrode active slurry is deposited and then pressing the current collector to obtain a negative electrode sheet

[0067] According to an embodiment of the present invention, the current collector deposited with the negative electrode active slurry can be dried and then subjected to a first pressing and a second pressing in sequence. The inventors have found that if only one pressing process is performed, it is easy to cause the active particles to break and affect the pore distribution of the pole piece. Performing a second pressing is beneficial to reduce the breakage of the active particles, improve the integrity of the negative electrode pole piece, and improve the pore distribution of the pole piece, making the distribution more uniform and enhancing the diffusion capacity of lithium ions. According to some specific examples of the present invention, the thickness of the coating formed after the first pressing can be 1.1 to 1.2 times the thickness of the coating formed after the second pressing. In addition, according to some specific examples of the present invention, the pressed negative electrode pole piece can also be cut and die-cut to obtain a negative electrode pole piece of a certain size.

[0068] Compared with the prior art, this method has all the characteristics and effects of the above-mentioned negative electrode sheet, which will not be described in detail here. In general, this method not only has a simple preparation process, but also the prepared negative electrode sheet can reduce the concentration polarization of the electrolyte during charging, and at the same time can increase the adsorption amount of the electrolyte, provide a medium for the migration of lithium ions, and is conducive to taking into account the energy density of the battery cell, the fast charging performance of the battery, and the safety performance.

[0069] In another aspect of the present invention, the present invention provides a battery. According to an embodiment of the present invention, the battery includes the above-mentioned negative electrode plate and / or the negative electrode plate prepared by the above-mentioned method. Compared with the prior art, the negative electrode plate used in the battery is more conducive to having higher energy density, better fast charging performance and better safety performance. It should be noted that there is no special restriction on the specific form of the battery in the invention, and those skilled in the art can flexibly choose according to actual conditions. For example, it can be a soft-pack battery, a square aluminum shell battery or a cylindrical battery, etc., or it can be a battery cell, a battery module or a battery pack, etc.

[0070] In another aspect of the present invention, the present invention proposes a vehicle. According to an embodiment of the present invention, the vehicle includes the above-mentioned negative electrode plate, and / or the negative electrode plate prepared by the above-mentioned method, and or the above-mentioned battery. Compared with the prior art, the vehicle can have a longer cruising range, a faster charging speed and better battery safety performance, and the market satisfaction is high. In addition, it should be noted that the specific form of the vehicle is not particularly limited in the present invention, and those skilled in the art can flexibly choose according to actual conditions. For example, it can be a pure electric vehicle, a hybrid vehicle, or an electric bicycle, an electric motorcycle, a battery tricycle, an electric car, an electric bus, an electric train, an electric balance car, etc.

[0071] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. If no specific techniques or conditions are specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0072] Example 1

[0073] Negative electrode active material: composed of carbon-coated artificial graphite and graphite powder, wherein the carbon-coated artificial graphite has a D50 particle size of 10.8 μm and a D10 particle size of 5 μm, and the particle size of the graphite powder is 500 nm to 800 nm. Based on the total mass of the negative electrode active material, the proportion of the graphite powder is 0.7 wt%. The negative electrode active material is recorded as C-1;

[0074] Fast charging aid: It is composed of natural graphite as the carbon matrix and a nano-carbon particle layer deposited on the surface of natural graphite. The D50 particle size of natural graphite is 9um, the D10 particle size is 5um, the thickness of the nano-carbon particle layer is 3-4nm, and the specific surface area of ​​the fast charging aid is 4.6m 2 / g. The fast charging aid is recorded as C-2;

[0075] The linear conductive agent is water-based CNTs; the thickener is CMC; and the binder is styrene-butadiene rubber (SBR).

[0076] The preparation method is as follows:

[0077] (1) The above C-1, C-2, CNTs, CMC, and SBR were mixed with deionized water in a ratio of 87wt%, 9.5wt%, 0.5wt%, 1.3wt%, and 1.7wt% to prepare a dispersion with a viscosity of 3000 to 5000mpas, and the dispersion was filtered through a 150-mesh sieve to obtain a negative electrode active slurry; the negative electrode active slurry was evenly coated on the upper and lower sides of the copper current collector with equal thickness, and the surface density of the double-sided coating was 17.5mg / cm 2 ;

[0078] (2) The copper current collector coated with the negative electrode active slurry is dried and then rolled twice, wherein the coating thickness formed after the first rolling is 1.1 times the coating thickness formed after the second rolling, and finally a negative electrode sheet is obtained.

[0079] Example 2

[0080] The difference from Example 1 is that in step (1), C-1, C-2, CNTs, CMC, and SBR are mixed in proportions of 91wt%, 5.5wt%, 0.5wt%, 1.3wt%, and 1.7wt% to prepare a negative electrode sheet.

[0081] Example 3

[0082] The difference from Example 1 is that in step (1), C-1, C-2, CNTs, CMC, and SBR are mixed in a ratio of 91.3wt%, 5.5wt%, 0.2wt%, 1.3wt%, and 1.7wt% to prepare a negative electrode sheet.

[0083] Example 4

[0084] The difference from Example 1 is that in step (1), C-1, C-2, CMC and SBR are mixed in a ratio of 87.5wt%, 9.5wt%, 1.3wt% and 1.7wt% to prepare a negative electrode sheet.

[0085] Comparative Example 1

[0086] The difference from Example 1 is that the negative electrode active material is only carbon-coated artificial graphite, and the negative electrode active material is recorded as C-11. In step (1), C-11, CMC, and SBR are mixed in a ratio of 97wt%, 1.3wt%, and 1.7wt% to prepare a negative electrode sheet.

[0087] Comparative Example 2

[0088] The difference from Comparative Example 1 is that C-11, C-2, CNTs, CMC, and SBR are mixed in proportions of 87wt%, 9.5wt%, 0.5wt%, 1.3wt%, and 1.7wt% to prepare a negative electrode sheet.

[0089] Comparative Example 3

[0090] The difference from Example 1 is that the fast charging aid C-2 is not added, and C-1, CNTs, CMC, and SBR are mixed in a ratio of 96.5%, 0.5%, 1.3%, and 1.7% to prepare a negative electrode sheet.

[0091] Comparative Example 4

[0092] The difference from Comparative Example 2 is that the fast charging aid C-2 is not added, and C-11, CNTs, CMC, and SBR are mixed in a ratio of 96.5%, 0.5%, 1.3%, and 1.7% to prepare a negative electrode sheet.

[0093] Testing and Characterization

[0094] Under the same conditions, the negative electrode sheets obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were tested for electronic resistivity and ion transfer impedance, and the test results are shown in Table 1. The test method is as follows:

[0095] Pole piece volume resistivity: The pole piece volume resistivity test is carried out using the HIOKI electrode resistance test system RM2610. Take 3 points at equal intervals on each side of the two long sides of the pole piece, and take 1 point at the center of the pole piece, and test the selected 7 positions. Specific test method: 1) Set the pole piece coating resistivity unit (Ω*cm), coating thickness, collector thickness, and test current 10uA in sequence; 2) Blow and suck the test bench and test probe clean; 3) Place the pole piece on the test bench, and place the 7 test points under the test probe in sequence. Put down the test probe and click the test to read the pole piece coating volume resistivity; 4) Calculate the average value of the 7 points to obtain the volume resistivity of the pole piece.

[0096] Ion transfer impedance: A symmetrical battery was used for EIS test, and the test curve was fitted with an equivalent circuit to calculate the electrode ion transfer impedance.

[0097] Symmetrical battery production: 1) Cut the electrode and diaphragm of a certain size, and stack the diaphragm-negative electrode-diaphragm-negative electrode-diaphragm; 2) Weld the electrode ears and bake; 3) Package and inject liquid; 4) Drain the liquid after immersion for 6 hours.

[0098] Symmetrical battery test: The symmetrical battery is subjected to voltage perturbation EIS test with a test frequency of 100KHz to 100mHz and an amplitude of 5mV. The test curve is fitted with an equivalent circuit to calculate the liquid phase ion transfer impedance.

[0099] Table 1 Comparison of negative electrode sheet resistivity and ion transfer impedance between the embodiment and the comparative example

[0100]

[0101] The negative electrode sheets obtained in the above-mentioned Examples 1 to 4 and Comparative Examples 1 to 4 are assembled into a laminated battery cell with a positive electrode sheet and a separator, which is then loaded into an aluminum shell, and a lithium-ion battery is prepared by liquid injection and negative pressure formation. Among them, the positive electrode sheet includes a positive electrode current collector and a positive electrode coating. The positive electrode coating contains a nickel-cobalt-manganese ternary material (NCM622), conductive carbon black (SP), oil-based conductive carbon nanotubes (CNTs), and a binder polyvinylidene fluoride (PVDF). NCM622: SP: CNTs: PVDF is fully mixed with nitrogen-methylpyrrolidone (NMP) in a mass ratio of 96.4%: 1.2%: 0.6%: 1.8%, and then coated on the upper and lower surfaces of the aluminum current collector. The double-sided coating surface density is 28.6 mg / cm 2 The evenly coated electrode is dried, rolled, slit and die-cut to produce a positive electrode of a certain size.

[0102] The lithium-ion batteries prepared in the above-mentioned embodiments 1 to 4 and comparative examples 1 to 4 were subjected to a 3C rate charging performance test at 25°C, and the constant current charging capacity ratio results are shown in Table 2; the lithium-ion batteries prepared in the above-mentioned embodiments 1 to 4 and comparative examples 1 to 4 were subjected to different rate step charging cycle tests at 0 to 80% SOC, and the battery cells were disassembled after 50 cycles to check the lithium deposition at the negative electrode interface, and the results are shown in Table 2; the battery cell energy density of the lithium-ion batteries prepared in the above-mentioned embodiments 1 to 4 and comparative examples 1 to 4 was tested, and the results are shown in Table 2. The specific test method for the 3C constant current charging capacity ratio at 25°C is as follows:

[0103] The battery cell is left at rest for 30 minutes at an ambient temperature of 25℃±2℃; discharged at a constant current of 1 / 3C to the specified discharge cut-off voltage, and left at rest for 30 minutes; charged at a constant current of 3C to the cut-off voltage at an ambient temperature of 25℃±2℃, and then switched to constant voltage charging until the charging current drops to 0.05C, and then stopped charging; left at rest for 30 minutes. The capacity of 3C constant current charging divided by the total capacity of 3C constant current and constant voltage charging is the 3C constant current charging capacity ratio of the battery cell.

[0104] Table 2 Comparison of rate charging performance and energy density of lithium ion batteries of Example and Comparative Example

[0105]

[0106] The lithium ion batteries prepared in the above Examples 1 to 4 and Comparative Examples 1 to 4 were subjected to a low temperature discharge performance test at -10°C, and the results are shown in Table 3. The -10°C low temperature discharge performance test method is as follows:

[0107] The battery cell was placed at an ambient temperature of 25℃±2℃ for 30 minutes, charged at a constant current of 1 / 3C to the cut-off voltage and then switched to constant voltage charging, and stopped charging when the charging current dropped to 0.05C, and then placed at an ambient temperature of 25℃±2℃ for 30 minutes, and then discharged at a constant current of 1 / 3C to the cut-off voltage, and then placed at an ambient temperature of 25℃±2℃ for 30 minutes, and then charged at a constant current of 1 / 3C to the cut-off voltage and then switched to constant voltage charging, and stopped charging when the charging current dropped to 0.05C, and then placed at an ambient temperature of -10±2℃ for 240 minutes, and then discharged at a constant current of 1 / 3C to the cut-off voltage, and then stopped charging when the charging current dropped to 0.05C, and then placed at an ambient temperature of -10±2℃ for 10 minutes, and then discharged at a constant current of 1 / 3C to the cut-off voltage, and then the -10℃ discharge capacity was obtained. Calculate the ratio of the discharge capacity at -10℃ to the discharge capacity at 25℃.

[0108] Table 3 Comparison of low temperature discharge performance of lithium ion batteries of the embodiment and the comparative example

[0109]

[0110]

[0111] Results and Discussion

[0112] As shown in Table 1, the negative electrode sheets prepared in Examples 1 to 4 have lower ion transfer impedance than the negative electrode sheets prepared in Comparative Examples 1 to 4. At the same time, compared with Comparative Example 1, the volume resistivity of the negative electrode sheet in Example 4 is also significantly reduced, indicating that the addition of graphite powder and fast charging aid is beneficial to reducing the volume resistivity and ion transfer impedance of the negative electrode sheet. Analysis shows that the graphite powder and fast charging aid have a large specific surface area, which can adsorb more electrolyte and lithium ions, which is beneficial to the transmission of lithium ions. Furthermore, compared with Example 4, the volume resistivity of the negative electrode sheet in Example 1 is further reduced, indicating that the long-range conductivity of the negative electrode sheet can be further improved and the sheet resistivity can be reduced by adding a linear conductive agent.

[0113] As shown in Table 2, the fast charging performance of the batteries prepared in Examples 1 to 4 is significantly improved compared with Comparative Examples 1 to 4. Specifically, compared with Comparative Example 2, Example 1 has an increased cell energy density and a higher constant current charging capacity ratio under the same charging conditions, indicating that by adding graphite powder as the negative electrode active material, the fast charging performance and energy density of the battery can be effectively improved; compared with Comparative Example 3, Example 2 has an increased cell energy density and also has a higher constant current charging capacity ratio under the same charging conditions, indicating that by adding a fast charging aid, it is also beneficial to improve the fast charging performance and energy density of the battery; compared with Example 2, Example 3 has a decreased constant current charging capacity ratio under the same conditions, and the cell energy density remains unchanged. The analysis shows that the amount of the linear conductive agent CNTs used is low, which reduces its conductive performance and affects the fast charging performance of the battery. Comparative Examples 1 and 4 did not add graphite powder and fast charging aids, and both showed poor charging capacity ratios and low cell energy densities. At the same time, it can be seen from Table 2 that when no fast charging aid was added, lithium deposition occurred to varying degrees on the negative electrode surface of the battery cell, while no lithium deposition occurred in the battery cell with the fast charging aid added.

[0114] It can be seen from Table 3 that the low-temperature performance of the batteries prepared in Examples 1 to 4 is significantly improved compared with that in Comparative Examples 1 to 4. Specifically, compared with Comparative Example 2, under the same discharge conditions, Example 1 has a higher discharge capacity ratio, indicating that the addition of graphite powder can effectively improve the low-temperature discharge performance of the battery; compared with Comparative Example 3, under the same discharge conditions, Example 2 has a higher discharge capacity ratio, indicating that the addition of fast charging aids can also effectively improve the low-temperature discharge performance of the battery. Analysis shows that this is because under low temperature conditions, the viscosity of the electrolyte increases and the migration rate of lithium ions decreases. The addition of fast charging functional aids and graphite powder can provide a higher lithium ion concentration and increase the number of lithium ion migrations, thereby improving the low-temperature performance of the battery cell to a certain extent.

[0115] In summary, the negative electrode plate of the above embodiment of the present invention can not only reduce the concentration polarization of the electrolyte during charging, which is beneficial to improving the fast charging performance of the battery, but also increase the amount of negative electrode active material, which helps to improve the energy density and low temperature performance of the battery cell.

[0116] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0117] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A negative electrode plate, characterized in that: include: A current collector and a negative electrode coating disposed on at least one surface of the current collector, wherein the negative electrode coating comprises: a negative electrode active material and a fast charging aid, the negative electrode active material comprises graphite powder, the particle size of the graphite powder is not greater than 1 μm, and the fast charging aid comprises a carbon matrix and a nano-carbon particle layer deposited on the surface of the carbon matrix; Based on the total mass of the negative electrode coating, the negative electrode active material accounts for 75-93wt%, and the fast charging aid accounts for 5-20wt%; Based on the total mass of the negative electrode active material, the graphite powder accounts for 0.5-1wt%.

2. The negative electrode sheet according to claim 1, characterized in that: The particle size of the graphite powder is 0.5 to 1 μm; Optionally, the negative electrode active material further comprises artificial graphite; Optionally, the artificial graphite is artificial graphite having a carbon coating layer; Optionally, the artificial graphite has a D50 particle size of 8 to 12 μm and a D10 particle size of 3 to 6 μm.

3. The negative electrode sheet according to claim 1, characterized in that: The D50 particle size of the fast-charging auxiliary agent is 7 to 20 μm, and the D10 particle size is 3 to 14 μm; Optionally, the specific surface area of ​​the fast-charging auxiliary agent is not less than 3m 2 / g; Optionally, the nano-sized carbon particle layer is obtained by chemical vapor deposition, and the carbon source for forming the nano-sized particle carbon layer includes at least one of methane, ethylene, and acetylene; Optionally, the thickness of the nano-carbon particle layer is no greater than 5 nm; Optionally, the carbon matrix includes at least one of artificial graphite, natural graphite, and hard carbon.

4. The negative electrode sheet according to claim 1 or 3, characterized in that: The negative electrode coating further comprises: a linear conductive agent, Based on the total mass of the negative electrode coating, the linear conductive agent accounts for 0.3-1.5wt%; Optionally, the linear conductive agent comprises conductive carbon nanotubes and / or conductive carbon fibers.

5. The negative electrode sheet according to claim 1, characterized in that: The negative electrode coating further comprises: a thickener and / or a binder; Optionally, based on the total mass of the negative electrode coating, the thickener accounts for 1 to 1.8 wt %; Optionally, the thickener comprises sodium carboxymethylcellulose; Optionally, based on the total mass of the negative electrode coating, the binder accounts for 0.6 to 2.5 wt %; Optionally, the binder includes at least one of styrene-butadiene rubber, acrylonitrile multipolymer, and acrylic resin.

6. A method for preparing the negative electrode sheet according to any one of claims 1 to 4, characterized in that: include: (1) depositing a negative electrode active slurry on at least one surface of a current collector; (2) drying the current collector on which the negative electrode active slurry is deposited and then pressing the current collector to obtain a negative electrode sheet; The negative electrode active slurry comprises: a negative electrode active material and a fast charging aid, the negative electrode active material comprises graphite powder, the particle size of the graphite powder is not greater than 1 μm, and the fast charging aid comprises a carbon matrix and a carbon layer deposited on the surface of the carbon matrix.

7. The method according to claim 6, characterized in that In step (1), the negative electrode active slurry further comprises: at least one of a thickener, a linear conductive agent, and a binder; Optionally, the surface density of the negative electrode active slurry deposited on one side of the current collector is 7 to 9 mg / cm 2 .

8. The method according to claim 6 or 7, characterized in that: In step (2), the pressing includes a first pressing and a second pressing performed sequentially, and the thickness of the coating formed after the first pressing is 1.1 to 1.2 times the thickness of the coating formed after the second pressing.

9. A battery, characterized in that: include: The negative electrode sheet according to any one of claims 1 to 4 and / or the negative electrode sheet prepared by the method according to any one of claims 6 to 8.

10. A vehicle, characterized in that: include: The negative electrode sheet according to any one of claims 1 to 4, and / or the negative electrode sheet prepared by the method according to any one of claims 6 to 8, and / or the battery according to claim 9.

Images