Negative electrode material and battery

Abstract

Provided in the present application are a negative electrode material and a battery. The negative electrode material comprises graphite and a carbon layer located on at least part of the surface of the graphite. The particle surface and the particle cross section of the negative electrode material are separately tested by means of Raman spectroscopy; the ratio of the peak area of a characteristic peak D within the range of 1300 cm-1 to 1350 cm-1 to the peak area of a characteristic peak G within the range of 1500 cm-1 to 1580 cm-1 is ID / IG; and the value of the ratio ID / IG of the particle surface of the negative electrode material is measured to be A, the value of the ratio ID / IG of the particle cross section of the negative electrode material is B, and 1.22<A-B≤2.10. The negative electrode material provided by the present application can comprehensively improve the lithium ion transport kinetics, initial coulombic efficiency and cycle performance.

Description

Anode materials and batteries

[0001] This application claims priority to the Chinese patent application number 202411381906.2, filed with the State Intellectual Property Office on September 30, 2024, entitled “A negative electrode material, a preparation method thereof, and a battery”, the contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the technical field of negative electrode materials, and in particular, to a negative electrode material and a battery. Background Art

[0003] The rapid development of lithium-ion batteries has brought about rapid changes in human life. As one of the core components of lithium-ion batteries, negative electrode materials have a significant impact on the electrochemical performance of lithium-ion batteries. Therefore, the development of cost-effective negative electrode materials is of great significance in lithium-ion battery research. Graphite materials are widely used as negative electrode materials for lithium-ion batteries. However, traditional graphite materials still have problems such as numerous surface defects and poor electrolyte compatibility, which lead to serious irreversible side reactions at the material interface during charging and discharging, resulting in low initial coulombic efficiency of the negative electrode material and continuous decay of the cycle capacity, which seriously hinders the further application of graphite negative electrode materials.

[0004] Currently, the industry primarily uses surface coating to modify graphite, reducing direct contact between the electrolyte and natural graphite and minimizing side reactions. However, the surface and interfacial structure of graphite significantly impacts performance, such as capacity and lithium-ion transport kinetics. Existing coating processes are unable to precisely control the interface characteristics between the graphite surface and the particles, leading to problems such as poor lithium-ion transport kinetics, low capacity, and low initial efficiency.

[0005] Application Contents

[0006] The present application provides a negative electrode material and a battery, wherein the negative electrode material has high capacity, low impedance, low expansion and excellent cycle performance.

[0007] The technical solution of this application is as follows:

[0008] In a first aspect, the present application provides a negative electrode material, the negative electrode material comprising graphite and a carbon layer located on at least a portion of the surface of the graphite;

[0009] Raman spectroscopy was used to test the particle surface and particle cross-section of the negative electrode material. - 1 ~1350cm -1 The peak area of ​​the characteristic peak D in the range of 1500 cm -1 ~1580cm -1 The peak area ratio of the G characteristic peak within the range is 1D / I G , the I on the surface of the particles of the negative electrode material is measured D / I G The ratio is A, the I D / I G The ratio is B, 1.22<AB≤2.10;

[0010] The particle surface of the negative electrode material is tested using an atomic force microscope. A 1 μm×1 μm test area is randomly selected on the particle surface of the negative electrode material. The arithmetic mean of the absolute value of the height deviation relative to the reference surface in the test area is S nm, 15 nm ≤ S ≤ 60 nm, where n≥5, Z is the height deviation of any test point in the test area relative to the reference plane.

[0011] In some embodiments, 1.70≤A≤3.00, 0.4≤B≤0.8.

[0012] In some embodiments, the graphite includes at least one of artificial graphite, natural graphite, and microcrystalline graphite.

[0013] In some embodiments, the fixed carbon content of the graphite is ≥ 95%.

[0014] In some embodiments, the carbon layer has a thickness of 15 nm to 250 nm.

[0015] In some embodiments, the carbon layer comprises amorphous carbon.

[0016] In some embodiments, the median particle size of the negative electrode material is 4 μm to 25 μm.

[0017] In some embodiments, the specific surface area of ​​the negative electrode material is ≤6m 2 / g.

[0018] In some embodiments, the tap density of the negative electrode material is 0.75 g / cm 3 ~1.3g / cm 3 .

[0019] In some embodiments, the oil absorption value of the negative electrode material is 38 mL / 100 g to 48 mL / 100 g.

[0020] In a second aspect, the present application provides a battery, comprising the above-mentioned negative electrode material or the negative electrode material prepared according to the above-mentioned preparation method.

[0021] The technical solution of this application has at least the following beneficial effects:

[0022] In the negative electrode material provided by the present application, the Raman ratio A of the particle surface of the negative electrode material can be used to characterize the degree of disorder of the carbon layer, and the Raman ratio B of the cross section of the negative electrode material particle can be used to characterize the degree of crystallization and quality of graphite. During the research process, the applicant of the present application found that when AB is too small, the Raman ratios of the particle surface of the negative electrode material and the interior of the particle are too close, indicating that the Raman ratio A of the carbon layer is too small or the Raman ratio B of the cross section of the negative electrode material is too high, the degree of disorder of the carbon layer is insufficient or the degree of crystallization of the graphite is insufficient, which will cause the rate performance of the negative electrode material to be poor and the capacity to be low. When AB is too large, the difference in Raman ratios between the particle surface and the interior of the negative electrode material is too large, the difference in kinetic transmission performance of the connection interface between graphite and carbon layer is large, the impedance of the negative electrode material increases, and the rate performance of the negative electrode material deteriorates. The present application controls AB within the above range, so that the difference in Raman ratio between the surface of the negative electrode material particles and the interior of the particles is within an appropriate range, which can ensure the regularity of the internal graphite structure and the high disorder of the external coating layer structure, effectively improve the electrolyte wettability of the negative electrode material, improve the interface transmission dynamics of the negative electrode material, and enable the negative electrode material to have high capacity, low impedance, high rate and high initial efficiency performance.

[0023] In addition, during the research process, the applicant of this application found that the microstructure of the surface of the negative electrode material particles is also closely related to the material capacity, first efficiency and other properties. The arithmetic mean of the absolute value of the height deviation measured relative to the reference plane in the scanning area using an atomic force microscope test is S nm. When the negative electrode material satisfies 15≤S≤60, the negative electrode material has the characteristics of high capacity, high first efficiency and low interface impedance. The applicant's research found that when S is controlled in the range of 15nm to 60nm, the surface coating of the negative electrode material is evenly distributed on the surface of the graphite particles, and the roughness of the coating is also in the appropriate range, which is conducive to electrolyte infiltration and interface impedance reduction. When S is less than 15nm, the surface of the negative electrode material is too flat and smooth, which is not conducive to electrolyte infiltration, resulting in a decrease in the capacity of the negative electrode material; when S is greater than 60nm, the surface roughness of the negative electrode material is too high, and the electrolyte wettability is enhanced. However, due to the decrease in the uniformity of the coating layer on the surface of the negative electrode material, the interface side reactions of the negative electrode material increase, the irreversible consumption of active lithium ions increases, and the first efficiency of the negative electrode material decreases.

[0024] Therefore, the present application simultaneously controls AB and S within the above range, which can make the Raman ratio difference between the surface and the interior of the negative electrode material particles and the surface coating flatness within an appropriate range, which can ensure the regularity of the internal graphite structure and the high disorder of the external coating structure, and can also ensure the uniform distribution and appropriate morphological flatness of the graphite surface coating. Therefore, the negative electrode material provided by this application can effectively improve the electrolyte wettability and improve the interface transmission dynamics of the negative electrode material, so that the negative electrode material has the excellent performance of high capacity, low impedance, high rate and high initial efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG1 is a process flow chart of a method for preparing a negative electrode material provided in this application;

[0026] FIG2 is a schematic diagram of a discharge state of a battery provided in an embodiment of the present application;

[0027] Figures 3a and 3b are electron microscope images of the negative electrode material prepared in Example 1 of the present application at different magnifications;

[0028] FIG3c is an electron micrograph of a cross-section of the negative electrode material prepared in Example 1 of the present application;

[0029] FIG4a is a Raman test spectrum of the material particles prepared in Example 1 of the present application;

[0030] FIG4 b is a Raman spectrum of a cross section of the material prepared in Example 1 of the present application;

[0031] FIG5 is an atomic force microscope image of the surface of the material prepared in Example 1 of the present application;

[0032] FIG6 is a comparison diagram of the electrochemical impedance of the negative electrode materials prepared in Example 1 and Comparative Example 4 of the present application. DETAILED DESCRIPTION

[0033] To better illustrate the present application and facilitate understanding of the technical solution of the present application, the present application is further described below. However, the following embodiments are merely simplified examples of the present application and do not represent or limit the scope of protection of the present application. The scope of protection of the present application shall be subject to the claims.

[0034] Based on this, in a first aspect, the present application provides a negative electrode material, the negative electrode material comprising graphite and a carbon layer located on at least a portion of the surface of the graphite;

[0035] Raman spectroscopy was used to test the particle surface and particle cross-section of the negative electrode material. - 1 ~1350cm -1 The peak area of ​​the characteristic peak D in the range of 1500 cm -1 ~1580cm -1 The peak area ratio of the G characteristic peak within the range is 1 D / I G , the I on the surface of the particles of the negative electrode material is measured D / I G The ratio is A, the I D / I G The ratio is B, 1.22<AB≤2.10;

[0036] The particle surface of the negative electrode material is tested using an atomic force microscope. A 1 μm×1 μm test area is randomly selected on the particle surface of the negative electrode material. The arithmetic mean of the absolute value of the height deviation relative to the reference surface in the test area is S nm, 15 nm ≤ S ≤ 60 nm, where n≥5, Z is the height deviation value of any test point in the test area relative to the reference plane. In the negative electrode material provided by the present application, the Raman ratio A of the particle surface of the negative electrode material can be used to characterize the disorder degree of the carbon layer, and the Raman ratio B of the cross section of the negative electrode material particle can be used to characterize the degree of crystallization and quality of graphite. During the research process, the applicant of the present application found that when AB is too small, the Raman ratios of the particle surface of the negative electrode material and the interior of the particle are too close, indicating that the Raman ratio A of the carbon layer is too small or the Raman ratio B of the cross section of the negative electrode material is too high, the disorder degree of the carbon layer is insufficient or the crystallization degree of the graphite is insufficient, which will cause the rate performance of the negative electrode material to be poor and the capacity to be low. When AB is too large, the difference in Raman ratios between the particle surface and the interior of the negative electrode material is too large, the difference in the kinetic transmission performance of the connection interface between graphite and carbon layer is large, the impedance of the negative electrode material increases, and the rate performance of the negative electrode material deteriorates.

[0037] The present application controls AB within the above range, so that the difference in Raman ratio between the surface of the negative electrode material particles and the interior of the particles is within an appropriate range, which can ensure the regularity of the internal graphite structure and the high disorder of the external coating layer structure, effectively improve the electrolyte wettability of the negative electrode material, improve the interface transmission dynamics of the negative electrode material, and enable the negative electrode material to have high capacity, low impedance, high rate and high initial efficiency performance.

[0038] In addition, the applicant of this application found in the research process that the surface of the material particles is closely related to the material capacity, first effect and other properties. The arithmetic mean of the absolute value of the height deviation measured relative to the reference plane in the scanning area using an atomic force microscope test is S nm, and S can specifically be 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm or 60nm, etc., of course, it can also be other values ​​within the above range, which is not limited here. When the negative electrode material satisfies 15nm≤S≤60nm, the negative electrode material has the characteristics of high capacity, high first efficiency and low interface impedance. The applicant's research found that when S is controlled in the range of 15nm to 60nm, the surface coating of the negative electrode material is evenly distributed on the surface of the graphite particles, and the roughness of the coating is also in a suitable range, which is conducive to electrolyte infiltration and reduction of interface impedance. When S is less than 15nm, the surface of the negative electrode material is very flat and smooth, which is not conducive to electrolyte infiltration, resulting in a decrease in the capacity of the negative electrode material; when S is greater than 60nm, the surface roughness of the negative electrode material is too high, and the electrolyte wettability is enhanced. However, due to the decrease in the uniformity of the coating layer on the surface of the negative electrode material, the interfacial side reactions of the negative electrode material increase, the irreversible consumption of active lithium ions increases, and the initial efficiency of the negative electrode material is reduced.

[0039] The present application controls AB and S within the above range, which can make the Raman ratio difference between the surface and the interior of the negative electrode material particles and the surface coating flatness within an appropriate range, which can ensure the regularity of the internal graphite structure and the high disorder of the external coating structure, and can also ensure the uniform distribution and appropriate morphological flatness of the graphite surface coating. The former helps to improve the rate performance and capacity of the negative electrode material, and the latter helps to improve the first efficiency and capacity of the negative electrode material. Therefore, the negative electrode material provided by this patent can effectively improve the electrolyte wettability, improve the interface transmission dynamics of the negative electrode material, and enable the negative electrode material to have high capacity, low impedance, high rate and high first efficiency performance.

[0040] In some embodiments, 1.70≤A≤3.00, specifically 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.5, 2.8 or 3.0, etc., and of course other values ​​within the above range can also be used, which is not limited here. In the present application, when the A value is controlled within the above range, the structural disorder of the carbon layer is high, which can improve the wettability of the contact interface between the surface of the negative electrode material and the electrolyte, reduce the occurrence of interfacial side reactions of the negative electrode material, reduce the consumption of irreversible active lithium ions, improve the lithium ion transmission power, reduce the interfacial impedance of the contact interface, and improve the first coulombic efficiency and electrochemical performance of the negative electrode material.

[0041] In some embodiments, 0.4≤B≤0.8, specifically 0.4, 0.5, 0.55, 0.58, 0.6, 0.7, 0.75, or 0.8, etc., and of course other values ​​within the above range are also possible, and are not limited here. In the present application, the B value is controlled within the above range, the degree of graphitization of the graphite is appropriate, the structural regularity of the graphite is good, and the interface impedance of the connection interface between the graphite and the carbon layer can be controlled within a suitable range, which is beneficial to improving the capacity and first coulombic efficiency of the negative electrode material.

[0042] In some embodiments, the specific value of AB may be 1.26, 1.3, 1.5, 1.6, 1.8, 1.9, 2.0, 2.05 or 2.1, etc. Of course, it may also be other values ​​within the above range, which is not limited here.

[0043] In some embodiments, the graphite comprises at least one of artificial graphite, natural graphite, and microcrystalline graphite. Natural graphite is flake graphite, a natural phaneritic graphite that resembles fish spores, belongs to the hexagonal crystal system, and has a layered structure. It exhibits excellent properties such as high temperature resistance, electrical and thermal conductivity, lubricity, plasticity, and acid and alkali resistance. Artificial graphite is a graphite material obtained by carbonizing organic matter and then subjecting it to high-temperature graphitization.

[0044] In some embodiments, the graphite includes spherical graphite, which is natural graphite.

[0045] In some embodiments, the carbon content of the graphite is ≥ 95% by mass, specifically 95%, 96%, 97%, 97.5%, 98.3%, 98.8%, or 99%, etc., but is not limited to the listed values. Other values ​​not listed within this range are also applicable. Preferably, the carbon content of the graphite is ≥ 99% by mass.

[0046] In some embodiments, the thickness of the carbon layer is between 15 nm and 250 nm, specifically 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 220 nm, or 250 nm, but is not limited to the values ​​listed above, and other values ​​not listed within this range are also applicable. Controlling the carbon layer thickness within the above range is beneficial for improving the lithium ion transmission power of the negative electrode material, reducing the occurrence of side reactions between the negative electrode material and the electrolyte, and improving the initial coulombic efficiency.

[0047] In some embodiments, the carbon layer includes amorphous carbon and graphitized carbon, and the carbon layer has good compatibility with the electrolyte, thereby ensuring the stability of the electrical performance of the negative electrode material during the charge and discharge process.

[0048] In some embodiments, the specific surface area of ​​the negative electrode material is ≤6m 2 / g; specifically, it can be 1.0m 2 / g, 1.8m 2 / g, 2.6m 2 / g, 3.5m 2 / g, 5.0m 2 / g or 6.0m 2 / g, of course, it can also be other numbers within the above range, which is not limited here. Controlling the specific surface area of ​​the negative electrode material within the above range is beneficial to improving the cycle performance of the battery made of the negative electrode material.

[0049] In some embodiments, the median particle size of the negative electrode material is 4 μm to 25 μm; more specifically, it can be 4 μm, 6 μm, 8 μm, 9 μm, 10 μm, 12 μm, 14 μm, 15 μm, 17 μm, 20 μm, 22 μm or 25 μm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0050] In some embodiments, the tap density of the negative electrode material is 0.75 g / cm 3 ~1.3g / cm 3 ; Specifically it can be 0.75g / cm 3 , 0.8g / cm 3 , 0.85g / cm 3 , 0.9g / cm3 , 0.92g / cm 3 , 1.0g / cm 3 , 1.05g / cm 3 , 1.1g / cm 3 , 1.15g / cm 3 , 1.2g / cm 3 , 1.25g / cm 3 or 1.3 g / cm 3 , of course, it can also be other numbers within the above range, which is not limited here. In this application, the tap density of the negative electrode material is controlled within the above range, which is conducive to improving the energy density of the lithium ion battery made of the negative electrode material.

[0051] In some embodiments, the oil absorption value of the negative electrode material is 38mL / 100g to 48mL / 100g, specifically 38mL / 100g, 39mL / 100g, 40mL / 100g, 41mL / 100g, 42mL / 100g, 43mL / 100g, 44mL / 100g, 45mL / 100g or 48mL / 100g, etc., and of course it can also be other values ​​within the above range, which is not limited here. The negative electrode material of the present application, due to the high degree of structural disorder of the carbon layer, the oil absorption value of the negative electrode material can be controlled within the above range, which can improve the wettability of the contact interface between the surface of the negative electrode material and the electrolyte, enhance the lithium ion transmission power, and reduce the interface impedance of the contact interface.

[0052] In a second aspect, the present application provides a method for preparing a negative electrode material, as shown in FIG1 , comprising the following steps:

[0053] Step S10: dispersing a capping agent having an active group and a reaction regulator in an aqueous solution, performing a prepolymerization reaction, and obtaining a prepolymerization solution, wherein the degree of polymerization of the polymer in the prepolymerization solution is 3 to 30.

[0054] Step S20, adding graphite to the prepolymer solution for liquid phase coating, and performing solid-liquid separation to obtain a precursor, wherein the solid-liquid ratio of graphite to the prepolymer solution is 1:(1.3-3.5), and the mass ratio of graphite to the coating agent is 100:(4-30).

[0055] Step S30: carbonizing the precursor to obtain a negative electrode material.

[0056] In the present application, a coating agent with an active group is prepolymerized to obtain a prepolymer solution having a degree of polymerization of polymer molecules in the range of 3-30. The polymer is mainly an oligomer with a small molecular chain and can be evenly dispersed in the prepolymer solution. Graphite is then added to the prepolymer solution for liquid-phase coating. During the coating process, the polymer evenly dispersed in the prepolymer solution can be deposited and attached to the surface of the graphite particles to form a uniform polymer coating layer. At the same time, the solid-liquid ratio of graphite to the prepolymer solution is controlled to be 1: (1.3 to 3.5), so that the thickness of the polymer coating layer evenly attached to the graphite surface is within a suitable range, thereby improving the capacity of the negative electrode material and the lithium ion interface transmission efficiency of the negative electrode material. Finally, through carbonization treatment, the polymer coating layer can be fully carbonized to form a carbon layer. The carbon material in the carbon layer has a high degree of disorder, and the difference in the Raman ratio between the surface of the negative electrode material particle and the interior of the particle can also be within a suitable range. In addition, the flatness of the coating layer on the surface of the material can also be within a suitable range. The above preparation method not only ensures the regularity of the graphite structure within the negative electrode material particles, but also ensures that the interface between the graphite and the carbon layer has better transmission power, and improves the wettability of the contact interface between the negative electrode material surface and the electrolyte. The negative electrode material prepared by the preparation method of the present application can combine excellent lithium ion transmission power performance, capacity, initial coulombic efficiency, and cycle performance.

[0057] The following is a detailed description of the preparation method provided in this scheme:

[0058] Step S10: dispersing a capping agent having an active group and a reaction regulator in an aqueous solution, performing a prepolymerization reaction, and obtaining a prepolymerization solution, wherein the degree of polymerization of the polymer in the prepolymerization solution is 3 to 30.

[0059] In some embodiments, the degree of polymerization of the polymer in the prepolymer solution is in the range of 3-30, and can be 3, 5, 10, 15, 20, 25, or 30. When the degree of polymerization of the prepolymer molecules is low, the utilization rate of the coating agent is reduced, and the free coating agent that is not polymerized and deposited during the solid-liquid separation stage is directly wasted, which increases the production cost. When the degree of polymerization of the prepolymer molecules is high, the disorder of the final coating agent polymer deposition layer is reduced, which reduces the Raman value of the final negative electrode material, which is not conducive to improving the kinetic performance.

[0060] In some embodiments, the active group includes at least one of a carbon-carbon double bond, a carboxyl group, a hydroxyl group, and an amine group.

[0061] In some embodiments, the capping agent having an active group includes at least one of styrene, fluorostyrene, bromostyrene, aminostyrene, styrenic acid, phenylpropionic acid, aniline, phenylenediamine, acrylic acid, methyl acrylate, ethyl acrylate, phenyl acrylate, benzyl acrylate, acrylamide, methacrylamide, ethylacrylamide, phenylacrylamide, maleic acid, maleic anhydride, maleic diamine, citric acid, mesaconic acid, itaconic acid, itaconic anhydride, sulfamic acid, ammonium sulfamate, benzoic acid, ammonium benzoate, and p-fluorobenzoic acid.

[0062] In some embodiments, the reaction moderator includes at least one of a redox agent and a pH adjuster.

[0063] In some embodiments, the redox agent includes at least one of azobisisobutyronitrile, azobisisoheptylnitrile, hydrogen peroxide, ammonium persulfate, sodium persulfate, potassium persulfate, aluminum chloride, and ferric chloride.

[0064] In some embodiments, the pH adjuster includes at least one of sodium hydroxide, potassium hydroxide, aqueous ammonia, sodium carbonate, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, and acetic acid.

[0065] In some embodiments, the coating agent includes a coating agent having an amine group, specifically at least one of aminostyrene, aniline, phenylenediamine, acrylamide, methacrylamide, ethylacrylamide, phenylacrylamide, maleic acid diamine, aminosulfonic acid, ammonium aminosulfonate, and ammonium benzoate.

[0066] In some embodiments, the coating agent includes a coating agent having an amine group, the reaction regulator includes a pH regulator, and the pH regulator includes at least one of sodium hydroxide, potassium hydroxide, ammonia water, sodium carbonate, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, and acetic acid.

[0067] In some embodiments, the pH value of the prepolymerization reaction is controlled at 4 to 7, specifically 4, 4.5, 5, 5.5, 6, 6.5 or 7, etc., and of course other values ​​within the above range can also be used, which is not limited here. When the pH value of the prepolymerization reaction is too high, it will affect the degree of prepolymerization of the coating agent, resulting in a low degree of disorder in the polymer deposition layer deposited on the graphite surface, which ultimately affects the A value of the negative electrode material. When the pH value of the prepolymerization reaction is too low, the prepolymerization reaction is insufficient, most of the coating agent is still free in the solution, and the polymer deposition layer deposited on the graphite surface is insufficient.

[0068] In some embodiments, the coating agent includes a coating agent having an amine group, and the reaction modifier further includes a redox agent, wherein the redox agent includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, hydrogen peroxide, ammonium persulfate, sodium persulfate, potassium persulfate, aluminum chloride, and ferric chloride. The addition of the redox agent can promote the prepolymerization reaction of the coating agent containing the active group.

[0069] In some embodiments, the coating agent includes a coating agent having a carbon-carbon double bond, which can be specifically acrylic acid, methyl acrylate, ethyl acrylate, phenyl acrylate, benzyl acrylate, etc. The temperature of the prepolymerization reaction is 40°C to 70°C, specifically 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C, etc., and of course it can be other values ​​within the above range, which is not limited here. The present application controls the temperature of the prepolymerization reaction within the above range so that the coating agent can fully prepolymerize. When the temperature of the prepolymerization reaction is too high, the prepolymerization degree of the coating agent is too high, resulting in an uneven polymer coating layer on the graphite surface; when the temperature of the prepolymerization reaction is too low, the prepolymerization degree of the coating agent is too low, and it is difficult for the oligomer to be uniformly deposited and attached to the graphite surface, resulting in a waste of the coating agent.

[0070] In some embodiments, the mass ratio of the redox agent to the coating agent is 1:(0.7-2.0), specifically 1:0.7, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.5, 1:1.7, 1:1.9 or 1:2.0, etc., and of course other values ​​within the above range, which are not limited here. If the amount of redox agent added is too low, it will affect the pre-polymerization degree of the coating agent, resulting in a low degree of disorder in the polymer deposition layer deposited on the graphite surface, which will ultimately affect the A value of the carbon layer of the negative electrode material. When the amount of redox agent added is too high, the coating agent polymerizes too quickly, resulting in the coating agent being unable to be evenly distributed on the graphite surface, and too much redox agent will also increase production costs.

[0071] In some embodiments, the prepolymerization reaction time is controlled to be 1 hour to 4 hours, specifically 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours or 4 hours, etc., and of course other values ​​within the above range can be used, which are not limited here. If the prepolymerization reaction time is too short, the content of prepolymerized polymer molecules in the prepolymerization solution is low, and the prepolymerization reaction is insufficient. If the prepolymerization reaction time is too long, the production efficiency is reduced, which is not conducive to industrial preparation.

[0072] Step S20, adding graphite to the prepolymer solution for liquid phase coating, and performing solid-liquid separation to obtain a precursor, wherein the solid-liquid ratio of the graphite to the prepolymer solution is 1: (1.3-3.5), and the mass ratio of the graphite to the coating agent is 100: (4-30).

[0073] In some embodiments, the graphite comprises at least one of artificial graphite and natural graphite. Natural graphite is flake graphite or spherical graphite formed from flake graphite. It is a natural phaneritic graphite with a fish-like shape, a hexagonal crystal system, and a layered structure. It has excellent properties such as high temperature resistance, electrical and thermal conductivity, lubricity, plasticity, and acid and alkali resistance. Artificial graphite is a graphite material obtained by carbonizing organic matter and then subjecting it to high-temperature graphitization.

[0074] In some embodiments, the graphite includes spherical graphite, which is natural graphite.

[0075] In some embodiments, the median particle size of the graphite is 1 μm to 30 μm, more specifically, it can be 1 μm, 5 μm, 8 μm, 10 μm, 11 μm, 13 μm, 16 μm, 18 μm, 20 μm, 23 μm, 26 μm or 30 μm, etc., but it is not limited to the listed values, and other values ​​not listed in this numerical range are also applicable. After many experiments, it was found that controlling the median particle size of graphite within the above range is beneficial to reducing the specific surface area of ​​graphite, reducing the contact between graphite and electrolyte, and inhibiting the occurrence of side reactions. Preferably, the median particle size of graphite is 5 μm to 20 μm.

[0076] In some embodiments, the carbon content of the graphite is ≥ 95% by mass, specifically 95%, 96%, 97%, 97.5%, 98.3%, 98.8%, or 99%, etc., but is not limited to the listed values. Other values ​​not listed within this range are also applicable. Preferably, the carbon content of the graphite is ≥ 99% by mass.

[0077] In some embodiments, the solid-liquid ratio of graphite to prepolymer solution is 1: (1.3 ~ 3.5) g / mL, specifically 1: 1.3g / mL, 1: 1.5g / mL, 1: 1.8g / mL, 1: 1.9g / mL, 1: 2.0g / mL, 1: 2.5g / mL, 1: 3.0g / mL, 1: 3.5g / mL, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. In the present application, the solid-liquid ratio of graphite to prepolymer solution is controlled within the above range, and the concentration of polymer molecules in the prepolymer solution per unit volume can be controlled, so that the thickness of the polymer coating layer uniformly attached to the graphite surface is within a suitable range, while improving the capacity of the negative electrode material, the lithium ion interface transmission efficiency of the negative electrode material is improved. When the solid-liquid ratio is too large, too much graphite is added, and the polymer in the prepolymer solution is insufficient, making it difficult to ensure that a polymer coating layer of uniform thickness is formed on the surface of the graphite particles, and the interface transmission of the negative electrode material is hindered, affecting the capacity of the negative electrode material. When the solid-liquid ratio is too small, the amount of graphite added is too little, the polymer coating layer on the surface of the graphite particles is too thick, and the capacity of the negative electrode material decreases.

[0078] In some embodiments, the mass ratio of graphite to the coating agent is 100:(4-30), specifically 100:4, 100:5, 100:8, 100:10, 100:15, 100:20, 100:25 or 100:30, etc., and of course other values ​​within the above range can also be used, which are not limited here. When the amount of coating agent added is too small, it is difficult to deposit a uniform polymer coating layer on the graphite surface. When the amount of coating agent added is too large, the thickness of the polymer coating layer deposited on the graphite surface is too large, resulting in obstruction of the interface transmission of the negative electrode material, affecting the capacity of the negative electrode material.

[0079] In some embodiments, the liquid-phase coating time is 4 to 24 hours, specifically 4 hours, 5 hours, 8 hours, 10 hours, 15 hours, 18 hours, 20 hours, 23 hours, 24 hours, etc. If the liquid-phase coating time is insufficient, the polymer molecules in the prepolymerization solution will not be sufficiently deposited and attached to the surface of the graphite particles, resulting in an uneven distribution of the coating layer on the graphite surface. If the liquid-phase coating time is too long, production efficiency will decrease, which is not conducive to industrial production.

[0080] In some embodiments, the liquid-phase coating is performed under stirring, and the polymer formed by polymerization of the coating agent having active groups is deposited and attached to the surface of the graphite.

[0081] The present application controls the solid-liquid ratio, time and amount of coating agent added during liquid phase coating, and can promote the uniform deposition and adhesion of the polymer formed by the coating agent having active groups on the surface of the graphite under stirring.

[0082] In some embodiments, after the liquid phase is coated, the mixed liquid is subjected to solid-liquid separation to obtain a solid which is then dried to obtain a precursor.

[0083] In some embodiments, the solid-liquid separation comprises at least one of suction filtration, centrifugation, and natural volatilization.

[0084] In some embodiments, the drying process comprises at least one of forced air drying, vacuum drying, freeze drying, and spray drying.

[0085] S30, carbonizing the precursor to obtain a negative electrode material.

[0086] In some embodiments, the temperature of the carbonization treatment is 1000°C to 2300°C, specifically, it can be 1000°C, 1300°C, 1500°C, 1800°C, 1900°C, 2000°C, 2200°C, 2300°C, etc., but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable. When the temperature of the carbonization treatment is low, the Raman value of the carbon layer of the negative electrode material is high, that is, the disorder of the carbon layer is high, resulting in aggravated interface side reactions and reduced first efficiency of the negative electrode material; when the temperature of the carbonization treatment is too high, the Raman value of the carbon layer of the negative electrode material is low, that is, the disorder of the carbon layer is low, resulting in poor interface transmission dynamics.

[0087] In some embodiments, the holding time of the carbonization treatment is 0.5h to 6h, specifically, it can be 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, etc., but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable.

[0088] In some embodiments, the carbonization treatment is performed under a protective atmosphere comprising at least one of nitrogen, helium, neon, argon, krypton, and xenon.

[0089] The present application also provides a battery. FIG2 is a schematic diagram of the discharge state of the battery provided in the present application. As shown in FIG2 , the battery includes a housing and an electrode assembly. The electrode assembly includes a positive electrode sheet 1, a negative electrode sheet 2, and a separator 3. The separator 3 is provided between the positive electrode sheet 1 and the negative electrode sheet 2. The electrode assembly can be a laminated structure, which is formed by alternatingly stacking the positive electrode sheet 1, the separator 3, and the negative electrode sheet 2. In other embodiments, the electrode assembly can also be a wound structure, which is formed by stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence and then winding them.

[0090] In some embodiments, the positive electrode sheet 1 includes a positive electrode current collector 101 and a positive electrode active layer 102 disposed on at least one surface of the positive electrode current collector 101 .

[0091] In some embodiments, the positive electrode current collector 101 may be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil (aluminum foil or nickel foil, etc.) and a polymer substrate. The positive electrode active layer 102 includes a positive electrode active material, which includes a compound that reversibly intercalates and deintercalates metal ions.

[0092] In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide, a sodium transition metal composite oxide, etc. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

[0093] In some embodiments, the positive electrode active material may include but is not limited to lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganese oxide (LiMn2O 4) 、Lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) or at least one of lithium iron phosphate (LiFePO4).

[0094] In some embodiments, the negative electrode sheet 2 includes a negative electrode current collector 201 and a negative electrode active material layer 202 disposed on at least one surface of the negative electrode current collector.

[0095] In some embodiments, the negative electrode current collector 201 can be made of at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or a carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil and a polymer substrate. The negative electrode active material layer 202 includes a negative electrode material, which can be the negative electrode material of the first aspect described above or a negative electrode material prepared by the above-described preparation method.

[0096] The battery provided in the embodiments of the present application has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion. The battery can be a lithium-ion battery, a sodium-ion battery, a solid electrolyte battery, etc., without limitation.

[0097] The following further illustrates the embodiments of the present application in multiple embodiments. The embodiments of the present application are not limited to the following specific embodiments. Within the scope of the unchanged main rights, appropriate changes can be made to the implementation.

[0098] The following further illustrates the embodiments of the present invention in multiple embodiments. The embodiments of the present invention are not limited to the following specific embodiments. Within the scope of protection, appropriate changes can be made to the implementation.

[0099] Example 1

[0100] (1) 7 parts of phenylenediamine and an appropriate amount of pure water were mixed, and the pH of the solution was adjusted to 4 using a 0.5 mol / L phosphoric acid solution. 7 parts of a 1 mol / L ammonium persulfate solution were added to adjust the oxidative environment of the mixed solution. The mixture was stirred for 1 hour to cause a prepolymerization reaction, thereby obtaining a prepolymerization solution.

[0101] (2) The prepolymer solution, 100 parts of graphite (average particle size of 17 μm) and an appropriate amount of pure water were stirred and mixed at a solid-liquid ratio of 1:3 to form a uniform mixed solution. The liquid phase coating treatment was carried out under stirring for 12 hours. The polyphenylenediamine in the prepolymer solution was deposited and attached to the surface of the graphite particles. The mixed solution was then centrifuged and the centrifuged product was moved to a drying oven at 120°C for drying for 36 hours to obtain a precursor.

[0102] (3) In a nitrogen atmosphere, the precursor was heated to 1250°C for carbonization treatment for 4 hours, and then naturally cooled to obtain the negative electrode material.

[0103] Example 2

[0104] The difference from Example 1 is that:

[0105] (1) 7 parts of aminostyrene and an appropriate amount of pure water were mixed, and the pH of the solution was adjusted to 4 using a 0.5 mol / L phosphoric acid solution. 7 parts of a 1 mol / L ammonium persulfate solution were added to adjust the oxidative environment of the mixture, and the mixture was stirred for 1 hour to cause a prepolymerization reaction.

[0106] Example 3

[0107] The difference from Example 1 is that:

[0108] (1) 7 parts of phenylenediamine and an appropriate amount of pure water were mixed, and the pH of the solution was adjusted to 5 using a 0.5 mol / L phosphoric acid solution. 7 parts of a 1 mol / L ammonium persulfate solution were added to adjust the oxidative environment of the mixture, and the mixture was stirred for 1 hour to cause a prepolymerization reaction.

[0109] Example 4

[0110] The difference from Example 1 is that:

[0111] (1) 7 parts of phenylenediamine and an appropriate amount of pure water were mixed, and the pH of the solution was adjusted to 7 using a 0.5 mol / L phosphoric acid solution. 7 parts of a 1 mol / L ammonium persulfate solution were added to adjust the oxidative environment of the mixture, and the mixture was stirred for 1 hour to cause a prepolymerization reaction.

[0112] Example 5

[0113] The difference from Example 1 is that:

[0114] (1) Mix 7 parts of maleic anhydride with an appropriate amount of pure water, raise the solution temperature to 50°C and continue stirring for 2 hours to cause a prepolymerization reaction.

[0115] Example 6

[0116] The difference from Example 5 is that:

[0117] (1) Mix 7 parts of maleic anhydride with an appropriate amount of pure water, raise the solution temperature to 70°C and continue stirring for 2 hours to cause a prepolymerization reaction.

[0118] Example 7

[0119] The difference from Example 5 is that:

[0120] (1) Mix 7 parts of maleic anhydride with an appropriate amount of pure water, raise the solution temperature to 50°C and continue stirring for 4 hours to cause a prepolymerization reaction.

[0121] Example 8

[0122] The difference from Example 1 is that:

[0123] (1) 7 parts of phenylenediamine and an appropriate amount of pure water were mixed, and the pH of the solution was adjusted to 4 using a 0.5 mol / L phosphoric acid solution. 5 parts of a 1 mol / L ammonium persulfate solution were added to adjust the oxidative environment of the mixture, and the mixture was stirred for 1 hour to cause a prepolymerization reaction.

[0124] Example 9

[0125] The difference from Example 1 is that:

[0126] (1) 7 parts of phenylenediamine and an appropriate amount of pure water were mixed, and the pH of the solution was adjusted to 4 using a 0.5 mol / L phosphoric acid solution. 12 parts of a 1 mol / L ammonium persulfate solution were added to adjust the oxidative environment of the mixture, and the mixture was stirred for 1 hour to cause a prepolymerization reaction.

[0127] Example 10

[0128] The difference from Example 1 is that:

[0129] (2) The prepolymer solution, 100 parts of graphite (average particle size of 17 μm) and an appropriate amount of pure water were stirred at a solid-liquid ratio of 1:1.5 to form a uniform mixed solution. The liquid phase coating treatment was carried out under stirring for 12 hours. The phenylenediamine in the mixed solution underwent polymerization reaction. The mixed solution was then centrifuged for solid-liquid separation and then moved to a drying oven for drying at 120 ° C for 36 hours to obtain a precursor.

[0130] Example 11

[0131] The difference from Example 1 is that:

[0132] (1) Take 4 parts of phenylenediamine and an appropriate amount of pure water, mix them, use 0.5 mol / L phosphoric acid solution to adjust the pH of the solution to 4, add 4 parts of 1 mol / L ammonium persulfate solution to adjust the oxidative environment of the mixture, and continue stirring the reaction for 1 hour to cause prepolymerization reaction.

[0133] Example 12

[0134] The difference from Example 1 is that:

[0135] (1) Take 25 parts of phenylenediamine and an appropriate amount of pure water, mix them, use 0.5 mol / L phosphoric acid solution to adjust the pH of the solution to 4, add 25 parts of 1 mol / L ammonium persulfate solution to adjust the oxidative environment of the mixture, and continue stirring the reaction for 1 hour to cause prepolymerization reaction.

[0136] Example 13

[0137] The difference from Example 1 is that:

[0138] (3) In a nitrogen atmosphere, the precursor was heated to 1600°C for carbonization treatment for 4 hours, and then naturally cooled to obtain the negative electrode material.

[0139] Example 14

[0140] The difference from Example 1 is that:

[0141] (3) In a nitrogen atmosphere, the precursor was heated to 2300°C for carbonization treatment for 4 hours, and then naturally cooled to obtain the negative electrode material.

[0142] Example 15

[0143] The difference from Example 1 is that:

[0144] (2) The prepolymer solution, 100 parts of graphite (average particle size of 10 μm) and an appropriate amount of pure water were stirred at a solid-liquid ratio of 1:3 to form a uniform mixed solution. The liquid phase coating treatment was carried out under stirring for 12 hours. The phenylenediamine in the mixed solution underwent polymerization reaction. The mixed solution was then centrifuged for solid-liquid separation and then moved to a drying oven for drying at 120 ° C for 36 hours to obtain a precursor.

[0145] (3) In a nitrogen atmosphere, the precursor was heated to 2300°C and kept at this temperature for 4 h, and then naturally cooled to obtain the negative electrode material.

[0146] Example 16

[0147] The difference from Example 1 is that:

[0148] (2) The prepolymer solution, 100 parts of graphite (average particle size of 6 μm) and an appropriate amount of pure water were stirred and mixed at a solid-liquid ratio of 1:3 to form a uniform mixed solution. The liquid phase coating treatment was carried out under stirring for 12 hours. The phenylenediamine in the mixed solution underwent polymerization reaction. The mixed solution was then centrifuged for solid-liquid separation and then moved to a drying oven for drying at 120 ° C for 36 hours to obtain a precursor.

[0149] (3) In a nitrogen atmosphere, the precursor was heated to 2300°C and kept at this temperature for 4 h, and then naturally cooled to obtain the negative electrode material.

[0150] Example 17

[0151] The difference from Example 1 is that:

[0152] (1) 7 parts of phenylenediamine and an appropriate amount of pure water were mixed, and the pH of the solution was adjusted to 4 using a 0.5 mol / L phosphoric acid solution. 7 parts of a 1 mol / L ammonium persulfate solution were added to adjust the oxidative environment of the mixed solution. The mixture was stirred for 3 hours to cause a prepolymerization reaction, thereby obtaining a prepolymerization solution.

[0153] Comparative Example 1

[0154] The difference from Example 1 is that:

[0155] (2) The prepolymer solution, 100 parts of graphite (average particle size of 17 μm) and an appropriate amount of pure water were stirred and mixed at a solid-liquid ratio of 1:1.1 to form a uniform mixed solution. The stirring reaction was continued for 12 hours. The phenylenediamine in the mixed solution was polymerized. The mixed solution was then centrifuged to separate the solid and liquid, and then moved to a drying oven at 120°C for drying for 36 hours to obtain a precursor.

[0156] Comparative Example 2

[0157] The difference from Example 1 is that:

[0158] (1) 0.8 parts of phenylenediamine and an appropriate amount of pure water were mixed, and the pH of the mixture was adjusted to 4 using 0.5 mol / L phosphoric acid solution. 0.8 parts of 1 mol / L ammonium persulfate solution was added to adjust the oxidative environment of the mixture, and the mixture was stirred for 1 hour to cause a prepolymerization reaction.

[0159] (2) The prepolymer solution, 100 parts of graphite (average particle size of 17 μm) and an appropriate amount of pure water were stirred and mixed at a solid-liquid ratio of 1:1.3 to form a uniform mixed solution. The stirring reaction was continued for 12 hours. The phenylenediamine in the mixed solution was polymerized. The mixed solution was then centrifuged to separate the solid and liquid, and then moved to a drying oven at 120°C for drying for 36 hours to obtain a precursor.

[0160] Comparative Example 3

[0161] The difference from Example 1 is that:

[0162] (3) In a nitrogen atmosphere, the coating material precursor is heated to 700°C and kept at 4°C, and then naturally cooled to obtain a highly structured disordered carbon-coated graphite material.

[0163] Comparative Example 4

[0164] The difference from Example 1 is that:

[0165] (1) 7 parts of phenylenediamine and an appropriate amount of pure water were mixed, and the pH of the mixture was adjusted to 10 using a 0.5 mol / L phosphoric acid solution. 7 parts of a 1 mol / L ammonium persulfate solution were added to adjust the oxidative environment of the mixture, and the mixture was stirred for 1 hour to cause a prepolymerization reaction.

[0166] Comparative Example 5

[0167] The difference from Example 1 is that:

[0168] (1) 7 parts of phenylenediamine and an appropriate amount of pure water were mixed, and the pH of the solution was adjusted to 4 using a 0.5 mol / L phosphoric acid solution. 7 parts of a 1 mol / L ammonium persulfate solution were added to adjust the oxidative environment of the mixed solution. The mixture was stirred and reacted for 6 hours to cause a prepolymerization reaction to obtain a prepolymer solution.

[0169] Comparative Example 6

[0170] The difference from Example 1 is that:

[0171] (1) 7 parts of phenylenediamine and an appropriate amount of pure water were mixed, the pH of the solution was adjusted to 4 using a 0.5 mol / L phosphoric acid solution, 7 parts of a 1 mol / L ammonium persulfate solution were added to adjust the oxidative environment of the mixed solution, and the next step was directly carried out without prepolymerization reaction.

[0172] Comparative Example 7

[0173] The difference from Example 1 is that:

[0174] (2) The prepolymer solution, 100 parts of graphite (average particle size of 17 μm) and an appropriate amount of pure water were stirred at a solid-liquid ratio of 1:3 to form a uniform mixed solution, and liquid phase coating treatment was performed for 2 hours under stirring. The polyphenylenediamine in the prepolymer solution was deposited and attached to the surface of the graphite particles. The mixed solution was then centrifuged, and the centrifuged product was moved to a drying oven at 120°C for 36 hours to obtain a precursor.

[0175] Test Method

[0176] (1) Test method for particle size distribution of negative electrode materials: The particle size distribution range of negative electrode materials was tested using a Malvern Panalytical Model 3000 laser particle size analyzer. Dispersant (ethanol, pure water, and low-foaming surfactant) and the test sample were placed in a 50 mL beaker. A certain amount of pure water was added and stirred thoroughly with a glass rod to ensure uniform dispersion of the sample. The equipment pump speed was set to 2400 r / min to 2500 r / min and the frequency was 19.5 Hz for particle size testing.

[0177] (2) Test method for the tap density of negative electrode materials: Place the negative electrode material in the sample chamber of a tap density meter (model: DAT-4-220) manufactured by Contacam Instrument Trading (Shanghai) Co., Ltd., USA. Vibrate the sample 1000 times and record the volume of the sample at this time. The tap density can be calculated according to the mass-to-volume ratio.

[0178] (3) Test method for the specific surface area of ​​the negative electrode material: The specific surface area of ​​the negative electrode material is tested using a DX400 specific surface area analyzer manufactured by Beijing Jingwei Gaobo Instrument Co., Ltd. The sample is placed in a sample tube, an isothermal jacket is placed on the sample tube, a filling rod is placed in the bubble tube, a retaining ring and an O-ring are installed on the bubble tube, and the assembled sample bubble tube is placed in the corresponding analysis station for testing. At a constant temperature and low temperature, the amount of gas adsorbed on the solid surface at different relative pressures is measured, and the sample monolayer adsorption amount is calculated based on the Brownauer-Ettel-Taylor adsorption theory and its formula (BET formula), thereby calculating the specific surface area of ​​the material.

[0179] (4) Oil absorption value test method of negative electrode material: The oil absorption value Q is tested using an ASAHI S-500 oil absorption value tester produced by Asahi Metal Industries, Ltd. of Japan. The oil absorption value Q is the amount of linseed oil added when the torque generated by the change in viscosity characteristics reaches 70% of the maximum torque, and the unit is mL / 100g.

[0180] (5) Test method for the surface morphology, cross-section and coating of negative electrode material particles: Use a HITACHI-S4800 scanning electron microscope to observe the microscopic morphology of the surface of the negative electrode material. The steps are as follows: stick the conductive glue on the sample cup, evenly apply the sample on the conductive glue, use an ear bulb to blow away the loose sample, and then place it in the scanning electron microscope room for testing. The cross-section and coating test steps are as follows: First, use a HITACHI-E3500 ion milling machine to polish the graphite particles, apply a small amount of carbon conductive glue on the edge of the sample stage, and evenly sprinkle the graphite sample, press lightly with a glass sheet, wait for 2 minutes for the conductive glue to dry, and blow away the excess sample with an ear bulb. Place the sample stage on the sample holder, adjust the sample position, and after completion, adjust the airflow to the maximum ion beam current, set the polishing time for sample processing. After completion, use a HITACHI-S4800 scanning electron microscope to observe the cross-section and coating of the negative electrode material surface.

[0181] (6) Raman test method for negative electrode materials: The Raman scattering spectrum was tested using a HORIBA-XPLORA laser confocal Raman spectrometer with a laser wavelength of 532 nm. Data was collected at 30 points on the surface of the negative electrode material particles. The scattering spectrum obtained at each point was then peak fitted to obtain the peak at 1300 cm -1 ~1350cm -1 The peak area of ​​the characteristic peak D in the range of 1500 cm -1 ~1580cm -1 The peak area ratio of the G characteristic peak within the range is 1 D / I G , I D / I GThe average value is A. After the negative electrode material particles are cut, the particles are cut using a HITACHI-E3500 ion milling machine, and the cut surface area is tested. The cut surface area refers to the graphite core area. 10 points are randomly selected in the particle cut surface area for Raman spectrum scanning, and the Raman spectrum at 1300 cm -1 ~1350cm -1 The peak area of ​​the characteristic peak D in the range of 1500 cm -1 ~1580cm -1 The peak area ratio of the G characteristic peak within the range is 1 D / I G , I D / I G The average value is B.

[0182] (7) Polymer degree of polymerization measurement method: The degree of polymerization of the polymer in the prepolymer solution is tested using a gel permeation chromatography instrument. Gel permeation chromatography (GPC), also known as size exclusion chromatography, is a liquid chromatography method that uses a solvent as the mobile phase and flows through a porous filler (such as porous silica gel or porous resin) as the separation medium. As the solvent elutes, molecules of different sizes are separated, with larger molecules eluting first and smaller molecules eluting later. The polymer molecular weight and its distribution are analyzed, and the obtained polymer molecular weight divided by the molecular weight of the molecular monomer is the degree of polymerization.

[0183] (8) Atomic force microscope test method: Use an atomic force microscope (AFM) to test the surface flatness of graphite materials. Fix one end of a micro-cantilever that is extremely sensitive to weak forces and have a tiny needle tip at the other end, so that it is gently in contact with the sample surface. Due to the extremely weak repulsive force between the atoms at the tip of the needle tip and the atoms on the sample surface, the cantilever will deflect slightly. By detecting the deflection amount and using feedback to control the constancy of its repulsive force, the position change of the micro-cantilever corresponding to each point can be obtained, thereby obtaining an image of the sample surface morphology. A 1μm×1μm test area is randomly selected from the image. The arithmetic mean of the absolute value of the height deviation relative to the reference surface in the test area is S nm, 15nm≤S≤60nm, where n≥5, Z is the height deviation value (i.e., the vertical coordinate value) of any test point in the test area relative to the reference plane. This application uses the tapping mode: the probe maintains a fixed frequency vibration on the Z axis, and contacts the sample when the vibration reaches the bottom, which causes little damage to the sample and has a higher resolution. In this application, the reference plane of the atomic force microscope is an equipotential surface determined by detecting and analyzing the weak force between the needle tip and the atoms on the sample surface. It is the plane corresponding to the average value of the height values ​​of all test points.

[0184] (9) Electrochemical performance test method: The negative electrode materials prepared in the examples and comparative examples were dissolved in deionized water at a mass ratio of 96.5:1.5:1 for the negative electrode material, carboxymethyl cellulose, and styrene-butadiene rubber, respectively, with the solid content controlled to 50%. The negative electrode sheets were coated on copper foil current collectors and vacuum dried to obtain negative electrode sheets. A metal lithium sheet was used as the counter electrode and assembled into button-type batteries in an argon-filled glove box. Charge and discharge tests were performed at a current density of 0.1C with a charge and discharge range of 0.01-1.5V. The first reversible specific capacity, first cycle charge capacity, and first cycle discharge capacity were obtained by cyclic charge and discharge. First coulombic efficiency = first cycle discharge capacity / first cycle charge capacity.

[0185] After completing the above tests, the charging current density was set to 0.2C, and discharge lithium insertion tests were performed at current densities of 0.2C, 0.5C, 1C, and 2C, respectively. The 2C / 0.2C rate performance = 0.2C discharge lithium insertion capacity / 2C discharge lithium insertion capacity.

[0186] The preparation process parameters and corresponding test results of Examples 1 to 17 (abbreviated as S1 to S17) and Comparative Examples 1 to 7 (abbreviated as D1 to D7) prepared in this application are shown in Tables 1 and 2 below.

[0187] Table 1. Preparation process parameters of negative electrode materials

[0188] Note: “-” in the table means no addition.

[0189] Table 2. Performance parameters of negative electrode materials and batteries prepared in various examples and comparative examples

[0190] The negative electrode material provided by the present application is prepared by pre-polymerizing a coating agent having an active group, and the degree of polymerization of the polymer in the obtained pre-polymer solution is in the range of 3-30. The polymer is mainly an oligomer with a small molecular chain and can be evenly dispersed in the pre-polymer solution. Graphite is then added to the pre-polymer solution for liquid phase coating. During the coating process, the polymer evenly dispersed in the pre-polymer solution can be deposited and attached to the surface of the graphite particles to form a uniform polymer coating layer. At the same time, the solid-liquid ratio of graphite to the pre-polymer solution is controlled to be 1: (1.3-3.5), and the mass ratio of graphite to the coating agent is 100: (4-30), so that the thickness of the polymer coating layer evenly attached to the graphite surface is within an appropriate range, while improving the capacity of the negative electrode material and the lithium ion interface transmission efficiency of the negative electrode material. Finally, through carbonization treatment, the polymer coating layer can be fully carbonized to form a carbon layer. The carbon material in the carbon layer has a high degree of disorder, and the difference in the Raman ratio between the surface and the interior of the negative electrode material particles can also be within an appropriate range. In addition, the flatness of the surface coating layer of the negative electrode material can also be within an appropriate range.

[0191] The regularity of the graphite structure inside the negative electrode material particles provided by the present application is improved, the connection interface between the graphite and the carbon layer can also have better transmission power, and the wettability of the contact interface between the surface of the negative electrode material and the electrolyte is improved. In the negative electrode material of the present application, AB is greater than 1.22 and less than or equal to 2.10. At this time, the negative electrode material can have both excellent lithium ion transmission power performance and high capacity. S is in the range of 15nm to 60nm, indicating that the surface coating layer of the material is evenly distributed on the surface of the graphite particles. At the same time, the flatness of the coating layer is also in the appropriate range, which is conducive to electrolyte infiltration and interface impedance reduction. The graphite negative electrode material provided by this patent not only ensures the regularity of the graphite structure inside the particles, so that the connection interface between the graphite and the carbon layer can also have better transmission power, but also improves the wettability of the contact interface between the surface of the negative electrode material and the electrolyte. The negative electrode material provided can have both excellent lithium ion transmission power performance, capacity, first coulomb efficiency and cycle performance.

[0192] Figures 3a and 3b are electron microscope images of the negative electrode material prepared in Example 1 of the present application at different magnifications, respectively; as shown in Figure 3a, the carbon material in the carbon layer is evenly distributed on the surface of the graphite particles in a moss-like shape. As shown in Figure 3b, the negative electrode material as a whole is distributed in potato-like particles, and there are almost no agglomerates of carbon material with a high degree of disorder between the negative electrode material particles, indicating that the surface of the graphite material obtained using the preparation method of the present application is evenly coated with carbon material with a high degree of disorder. As shown in Figure 3c, the negative electrode material is cut open, and moss-like carbon material with a high degree of disorder can also be observed on the surface of the exposed graphite sheet inside, which is the same as the morphology of the outer surface of the negative electrode material (Figure 3a), indicating that the preparation method provided by the present application can achieve uniform coating of carbon material with a high degree of disorder on the outside of the graphite particles. Figures 4a and 4b are the Raman spectra of the graphite negative electrode material and the cross-section prepared in Example 1 of this application, respectively. Combined with the data in Table 2, it can be found that the Raman ratio of the graphite material is 2.46, the Raman ratio of the cross-section is 0.55, and the corresponding AB value is 1.91, which is in the range of 1.22 to 2.10. Figure 5 is an atomic force microscopy image of the graphite negative electrode material prepared in Example 1, with a corresponding S value of 23.6nm. The capacity, first efficiency, and rate performance of the negative electrode material prepared in Example 1 are significantly improved.

[0193] According to the test data of Examples 1 to 2 and Example 5, the A value and AB value of the negative electrode materials prepared by using different coating agents with active groups do not change much. At the same time, the S value of the negative electrode materials is in the range of 15nm to 60nm, and the specific capacity, first coulombic efficiency and rate performance of the negative electrode materials are good.

[0194] According to the test data of Examples 1 and 3 to 4, it can be seen that as the pH value increases, the A value of the prepared negative electrode material gradually decreases, the corresponding AB value also gradually decreases, and the S value also gradually decreases, indicating that the pH will affect the degree of polymerization of the polymer in the pre-polymerization solution, thereby slightly reducing the disorder of the carbon material in the carbon layer, slightly increasing the surface flatness of the material, decreasing the capacity and first coulombic efficiency of the negative electrode material, and the rate performance does not change much.

[0195] According to the test data of Examples 5 to 7, it can be seen that when the coating agent is a coating agent with a carbon-carbon double bond, as the prepolymerization temperature increases, the A value of the prepared negative electrode material decreases; as the holding time increases, the A value of the prepared negative electrode material also decreases; this is because the prepolymerization temperature and holding time will affect the polymerization degree of the polymer formed by polymerization in the prepolymerization solution, the growth of the polymer molecular chain, and thus affect the degree of disorder of the carbon layer on the surface of the negative electrode material. Within the prepolymerization temperature range and holding time range of the present application, it is helpful to improve the capacity and first coulombic efficiency of the negative electrode material.

[0196] According to the test data of Examples 1, 8 and 9, as the amount of redox agent added increases, the degree of polymerization of the polymer in the prepolymerization solution gradually increases, the degree of disorder of the polymer deposited on the surface of the graphite particles gradually decreases, and the A value of the negative electrode material prepared after carbonization also decreases, AB also decreases, and S also gradually decreases.

[0197] According to the test data from Examples 1 and 10, during the stirring reaction between graphite and the prepolymer solution, regulating the solid-to-liquid ratio within an appropriate range can control the concentration of polymer molecules in the prepolymer solution per unit volume. As the concentration decreases, the uniformity of polymer deposition on the graphite particles decreases. As the solid-to-liquid ratio decreases, the A value of the negative electrode material gradually decreases, AB also decreases, and the S value significantly increases.

[0198] According to the test data of Examples 1 and 11 to 12, as the mass ratio of the coating agent to graphite increases, the amount of the coating agent added gradually increases, the thickness of the polymer coating layer deposited on the graphite surface increases, the A value of the obtained negative electrode material gradually increases, the corresponding AB also gradually increases, and the S value significantly decreases.

[0199] According to the test data of Examples 1 and 13-14, as the carbonization temperature increases, the disorder of the polymer carbonized layer deposited on the graphite surface gradually decreases, the A value of the obtained negative electrode material gradually decreases, the corresponding AB also gradually decreases, and the S value does not change much.

[0200] The test data from Examples 14-16 show that as the particle size of the raw material used changes, the thickness of the polymer layer deposited on the graphite surface gradually increases, the thickness of the corresponding coating layer also gradually increases, the A value and the corresponding AB value of the carbonized material also gradually increase, and the S value does not change much. This demonstrates that the preparation method of the present application is applicable to the preparation of graphite materials with high surface disorder characteristics of different particle sizes.

[0201] According to the test data of Example 1 and Example 17, it can be seen that as the prepolymerization time increases, the polymerization degree of the polymer in the prepolymerization solution increases, the disorder of the corresponding polymer carbonization layer deposited on the graphite surface decreases, the A value of the obtained negative electrode material gradually decreases, the corresponding AB also gradually decreases, and the S value decreases.

[0202] Compared with Example 1, in the preparation process of Comparative Example 1, the solid-liquid ratio of graphite and pre-polymerization solution is too high, the deposition reaction of the polymer in the pre-polymerization solution on the graphite particles is uneven, the polymer exhibits self-nucleation growth and agglomeration phenomena, the Raman value of the prepared negative electrode material is A>3.00, AB>2.10, S>60.0nm, the specific surface area corresponding to the negative electrode material is relatively high, and the first coulombic efficiency and rate are significantly reduced.

[0203] Compared with Example 1, in the preparation process of Comparative Example 2, the amount of coating agent added is too low, the polymer concentration in the prepolymerization solution is also reduced, the polymer is difficult to deposit on the graphite particles to form a uniform coating layer, and the Raman value of the prepared negative electrode material is A <1.70, AB <1.22, S >60.0nm. The specific surface area of ​​the negative electrode material is increased, and the capacity, first efficiency and rate of the negative electrode material are also reduced.

[0204] Compared with Example 1, during the preparation process of Comparative Example 3, the carbonization temperature is too low, the disorder of the carbon layer coating the outside of the graphite particles is relatively high, and the defects inside the graphite particles also increase synchronously. The Raman value A of the prepared high-structure disordered carbon-coated graphite material is greater than 3.00, and AB is 2.15, which exceeds the range. The S value is slightly higher than that of Example 1, the specific surface area of ​​the negative electrode material is relatively high, and the first efficiency is reduced.

[0205] Compared with Example 1, during the preparation process of Comparative Example 4, the pH value when the prepolymerization solution is formed is relatively high, and the degree of polymerization of the polymer in the prepolymerization solution increases, resulting in a decrease in the disorder of the carbon layer coating the outside of the graphite particles. The Raman value of the prepared negative electrode material is A<1.70, AB is 1.22, which exceeds the range, S<15nm, the specific surface area of ​​the negative electrode material is relatively high, and the first efficiency and rate are reduced.

[0206] Compared with Example 1, in the preparation process of Comparative Example 5, the pre-polymerization stirring time was controlled too long, and the degree of polymerization of the polymer in the pre-polymerization solution increased, resulting in a decrease in the disorder of the carbon layer coating the outside of the graphite particles. The Raman value of the prepared negative electrode material was A <1.70, AB <1.22, and the S value was in the range of 15nm to 60nm. The capacity, first efficiency and rate of the negative electrode material were reduced.

[0207] Compared with Example 1, Comparative Example 6 did not undergo pre-polymerization treatment during the preparation process, resulting in the coating agent not being completely deposited on the surface of the graphite particles. The thickness of the coating layer was reduced under the same coating amount, and the Raman value of the prepared negative electrode material was A <1.70, AB <1.22, S >60.0nm. The specific surface area of ​​the negative electrode material was increased, the side reaction between the negative electrode material and the electrolyte was intensified, and the capacity, first effect and rate of the negative electrode material were reduced.

[0208] Compared with Example 1, in the preparation process of Comparative Example 7, the stirring time after adding graphite powder was too short, resulting in the coating agent not being evenly distributed on the surface of the graphite particles. The Raman value of the prepared negative electrode material was A>3.00, AB>2.10, S>60.0nm, the specific surface area of ​​the negative electrode material increased, the side reaction between the negative electrode material and the electrolyte was intensified, and the capacity, first efficiency and rate of the negative electrode material were reduced.

[0209] Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the claims. Any person skilled in the art may make several possible changes and modifications without departing from the concept of the present application. Therefore, the scope of protection of the present application shall be based on the scope defined by the claims of the present application.

Claims

1. A negative electrode material, characterized in that The negative electrode material includes graphite and a carbon layer located on at least a portion of the surface of the graphite; Raman spectroscopy was used to test the particle surface and particle cross-section of the negative electrode material. - 1 ~1350cm -1 The peak area of ​​the characteristic peak D in the range of 1500 cm -1 ~1580cm -1 The peak area ratio of the G characteristic peak within the range is 1 D / I G , the I on the surface of the particles of the negative electrode material is measured D / I G The ratio is A, the I D / I G The ratio is B, 1.22<AB≤2.10; The particle surface of the negative electrode material is tested using an atomic force microscope. A 1 μm×1 μm test area is randomly selected on the particle surface of the negative electrode material. The arithmetic mean of the absolute value of the height deviation relative to the reference surface in the test area is S nm, 15≤S≤60, where Z is the height deviation of any test point in the test area relative to the reference plane.

2. The negative electrode material according to claim 1, characterized in that 1.70≤A≤3.00, 0.4≤B≤0.

8.

3. The negative electrode material according to claim 1, characterized in that The graphite includes at least one of artificial graphite, natural graphite and microcrystalline graphite.

4. The negative electrode material according to claim 3, characterized in that The fixed carbon content of the graphite is ≥95%.

5. The negative electrode material according to claim 1, characterized in that The thickness of the carbon layer is 15 nm to 250 nm.

6. The negative electrode material according to claim 1, characterized in that The carbon layer includes amorphous carbon.

7. The negative electrode material according to claim 1, characterized in that The median particle size of the negative electrode material is 4 μm to 25 μm.

8. The negative electrode material according to claim 1, characterized in that The specific surface area of ​​the negative electrode material is ≤6m 2 / g.

9. The negative electrode material according to claim 1, characterized in that The tap density of the negative electrode material is 0.75 g / cm 3 ~1.3g / cm 3 .

10. The negative electrode material according to claim 1, characterized in that The oil absorption value of the negative electrode material is 38 mL / 100 g to 48 mL / 100 g.

11. A battery, characterized in that: The battery comprises the negative electrode material according to any one of claims 1 to 10.

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