A negative electrode material of a lithium ion battery, a preparation method thereof, and a battery

Abstract

This application provides a negative electrode material for a lithium-ion battery, a method for preparing the same, and the battery itself. The negative electrode material includes graphite and a carbon layer located on at least a portion of the surface of the graphite. Raman spectroscopy is used to test the particle surface and cross-section of the negative electrode material at a depth of 1300 cm⁻¹. ‑1 ~1350cm ‑1 The peak area of ​​the D characteristic peak within the range and located at 1500 cm⁻¹ ‑1 ~1580cm ‑1 The peak area ratio of the G characteristic peak within the range is I D / I G The I on the surface of the particles of the negative electrode material was measured. D / I G The ratio is A, and the I of the particle cross-section of the negative electrode material is... D / I G The ratio is B, where 1.22 < A - B ≤ 2.10. The particle surface of the negative electrode material was tested using atomic force microscopy. Random 1μm test areas were selected on the particle surface of the negative electrode material, and the arithmetic mean of the absolute values ​​of the height deviations relative to the reference plane within the test area was S nm, where 15 nm ≤ S ≤ 60 nm. The negative electrode material provided in this application can comprehensively improve lithium-ion transport kinetics, initial coulombic efficiency, and cycle performance.

Description

[0001] The present application is a divisional application of the Chinese Patent Application No. 202411381906.2, titled "A negative electrode material, a preparation method thereof and a battery". TECHNICAL FIELD

[0002] The present application relates to the technical field of negative electrode materials, in particular to a negative electrode material of a lithium ion battery, a preparation method thereof and a battery. BACKGROUND

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

[0004] At present, the industry mainly uses surface coating to modify graphite, reduce the direct contact between electrolyte and natural graphite, and reduce the occurrence of side reactions. However, the surface and interface structure of graphite materials has a significant impact on capacity, lithium ion transport kinetics and other properties. The existing coating process cannot accurately control the surface and internal interface properties of graphite materials, resulting in poor lithium ion transport dynamics, low capacity and low initial efficiency. SUMMARY

[0005] Therefore, the present application provides a negative electrode material of a lithium ion battery, a preparation method thereof and a battery. The negative electrode material can comprehensively improve the lithium ion transport kinetics, the initial coulomb efficiency and the cycle performance.

[0006] In a first aspect, the present application provides a negative electrode material of a lithium ion battery, which comprises graphite and a carbon layer located on at least part of the surface of the graphite.

[0007] The particle surface and the particle section of the negative electrode material are tested by Raman spectroscopy. The peak area ratio of the D characteristic peak located in the range of 1300cm -1 ~1350cm -1 to the G characteristic peak located in the range of 1500cm -1 ~1580cm -1 is I D / I G , the I D / I G of the particle surface of the negative electrode material is measured.A, the ratio of I of the particle cross section of the negative electrode material D / I G B, 1.22 < A - B ≤ 2.10;

[0008] The particle surface of the negative electrode material is tested by using an atomic force microscope, 1 μm 1 μm test area, the arithmetic mean of the absolute value of the height deviation of the test area relative to the reference surface is S nm, 15 nm ≤ S ≤ 60 nm, wherein S = , n ≥ 5, and Z is the height deviation value of any test point in the test area relative to the reference surface.

[0009] In some embodiments, 1.70 ≤ A ≤ 3.00, and 0.4 ≤ B ≤ 0.8.

[0010] In some embodiments, the graphite includes at least one of artificial graphite, natural graphite, and microcrystalline graphite.

[0011] In some embodiments, the fixed carbon content of the graphite is ≥ 95%.

[0012] In some embodiments, the thickness of the carbon layer is 15 nm to 250 nm.

[0013] In some embodiments, the carbon layer includes amorphous carbon.

[0014] In some embodiments, the median particle size of the negative electrode material is 4 μm to 25 μm.

[0015] In some embodiments, the specific surface area of the negative electrode material is ≤ 6 m 2 / g.

[0016] In some embodiments, the tap density of the negative electrode material is 0.75 g / cm 3 ~ 1.3 g / cm 3 .

[0017] In some embodiments, the oil absorption value of the negative electrode material is 38 mL / 100 g to 48 mL / 100 g.

[0018] The application also provides a preparation method of a negative electrode material of a lithium ion battery, which includes the following steps:

[0019] The coating agent with active groups and the reaction regulator are dispersed in an aqueous solution to perform a prepolymerization reaction to obtain a prepolymerization solution, wherein the polymerization degree of the polymer in the prepolymerization solution is 3 to 30;

[0020] Graphite is added to the prepolymerization solution for liquid-phase coating, and the precursor is obtained by solid-liquid separation. The solid-liquid ratio of the graphite to the prepolymerization solution is 1:(1.3~3.5), and the mass ratio of the graphite to the coating agent is 100:(4~30).

[0021] The precursor is carbonized to obtain the negative electrode material.

[0022] In some embodiments, the active group includes at least one of a carbon-carbon double bond, a carboxyl group, a hydroxyl group, and an amino group.

[0023] In some embodiments, the reaction modifier includes at least one of a redox agent and a pH adjuster.

[0024] In some embodiments, the reaction modifier includes a redox agent, wherein the mass ratio of the redox agent to the coating agent is 1:(0.7 to 2.0).

[0025] In some embodiments, the prepolymerization reaction time is controlled to be 1 h to 4 h.

[0026] In some embodiments, the liquid phase coating time is 4h to 24h.

[0027] In some embodiments, the coating agent having active groups 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, ethyl acrylamide, phenyl acrylamide, maleic acid, maleic anhydride, diamine maleate, citric acid, succinic acid, itaconic acid, itaconic anhydride, aminosulfonic acid, ammonium aminosulfonate, benzoic acid, ammonium benzoate, and p-fluorobenzoic acid.

[0028] In some embodiments, the carbonization temperature is 1000°C to 2300°C.

[0029] In some embodiments, the holding time for the carbonization treatment is 0.5h to 6h.

[0030] In some embodiments, the carbonization process is carried out under a protective atmosphere. Thirdly, this application provides a battery comprising the above-described negative electrode material or a negative electrode material prepared according to the above-described preparation method.

[0031] The technical solution of this application has at least the following beneficial effects:

[0032] In the negative electrode material for lithium-ion batteries provided in this 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 particles can be used to characterize the degree of crystallinity and quality of graphite. During the research process, the inventors of this application discovered that when AB is too small, the Raman ratios of the particle surface and the interior of the negative electrode material 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, resulting in insufficient disorder of the carbon layer or insufficient crystallinity of the graphite. This will cause poor rate performance and low capacity of the negative electrode material. 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, resulting in a large difference in the kinetic transport performance of the interface between graphite and the carbon layer, increasing the impedance of the negative electrode material, and deteriorating its rate performance.

[0033] Furthermore, the inventors discovered during their research that the microstructure of the anode material particle surface is closely related to the material's capacity, first-efficiency, and other performance characteristics. Using atomic force microscopy, the arithmetic mean of the absolute values ​​of the height deviation relative to a reference surface within the scanning area was measured as S nm. When the anode material satisfies 15 ≤ S ≤ 60 nm, it exhibits high capacity, high first-efficiency, and low interfacial impedance. The inventors found that controlling S within the 15 nm to 60 nm range ensures that the coating layer on the anode material surface is uniformly distributed on the graphite particle surface, and the roughness of the coating layer is also within a suitable range, which helps with electrolyte wetting and reducing interfacial impedance. When S < 15 nm, the anode material surface is too smooth and flat, which is not conducive to electrolyte wetting, leading to a decrease in the anode material's capacity. When S > 60 nm, the surface roughness of the anode material is too high, enhancing electrolyte wetting, but due to the reduced uniformity of the coating layer, interfacial side reactions increase, leading to increased irreversible consumption of active lithium ions and a decrease in the first-efficiency of the anode material.

[0034] By controlling AB and S within the aforementioned ranges, this application ensures that the difference in Raman ratio between the surface and interior of the negative electrode material particles, as well as the smoothness of the surface coating layer, are within suitable ranges. This guarantees both the regularity of the internal graphite structure and the high disorder of the external coating layer structure, while also ensuring the uniform distribution and suitable morphological smoothness of the graphite surface coating layer. Therefore, the negative electrode material provided by this patent can effectively improve electrolyte wettability and enhance the interfacial transport dynamics of the negative electrode material, resulting in excellent performance characteristics such as high capacity, low impedance, high rate capability, and high initial efficiency.

[0035] This application provides a method for preparing a lithium-ion battery. A coating agent with active groups is pre-polymerized, resulting in a pre-polymerized solution with a polymer degree of polymerization ranging from 3 to 30. The polymer is primarily oligomers with small molecular chains, allowing for uniform dispersion in the pre-polymerized solution. Graphite is then added to the pre-polymerized solution for liquid-phase coating. During this coating process, the polymer, uniformly dispersed in the pre-polymerized solution, deposits onto the surface of the graphite particles, forming a uniform polymer coating layer. Simultaneously, the solid-liquid ratio of graphite to the pre-polymerized solution is controlled at 1:(1.3–3.5), ensuring the thickness of the uniformly adhered polymer coating layer on the graphite surface is within a suitable range. This improves both the capacity and lithium-ion interfacial transport efficiency of the negative electrode material. Finally, through carbonization, the polymer coating layer is fully carbonized to form a carbon layer. The carbon material in the carbon layer exhibits high disorder, and the difference in Raman ratio between the surface and interior of the negative electrode particles remains within a suitable range. Furthermore, the smoothness of the coating layer on the material surface is also within a suitable range. The above preparation method not only ensures the regularity of the graphite structure within the negative electrode material particles and provides better transport dynamics at the interface between the graphite and the carbon layer, but also improves the wettability of the interface between the negative electrode material surface and the electrolyte. The negative electrode material prepared by the method of this application can possess excellent lithium-ion transport dynamics, capacity, initial coulombic efficiency, and cycle performance. Attached Figure Description

[0036] Figure 1 A process flow diagram of the method for preparing the negative electrode material provided in this application;

[0037] Figure 2 A schematic diagram of the discharge state of a battery provided in an embodiment of this application;

[0038] Figure 3a and Figure 3b These are electron microscope images of the negative electrode material prepared in Example 1 of this application at different magnifications;

[0039] Figure 3c This is a cross-sectional electron microscope image of the negative electrode material prepared in Example 1 of this application;

[0040] Figure 4a 4b shows the Raman spectrum of the material particles prepared in Example 1 of this application; 4b shows the Raman spectrum of the cross-section of the material prepared in Example 1 of this application.

[0041] Figure 5 This is an atomic force microscope image of the material surface prepared in Example 1 of this application;

[0042] Figure 6 This is a comparison diagram of the electrochemical impedance of the negative electrode materials prepared in Example 1 and Comparative Example 4 of this application. Detailed Implementation

[0043] To better illustrate this application and facilitate understanding of its technical solutions, the following detailed description is provided. However, the following embodiments are merely simplified examples and do not represent or limit the scope of protection of this application. The scope of protection of this application is determined by the claims.

[0044] Based on this, in a first aspect, this 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;

[0045] Raman spectroscopy was used to test the particle surface and particle cross-section of the negative electrode material at a depth of 1300 cm⁻¹. -1 ~1350cm -1 The peak area of ​​the D characteristic peak within the range and the peak area located at 1500 cm⁻¹ -1 ~1580cm -1 The peak area ratio of the G characteristic peak within the range is I D / I G The I on the surface of the particles of the negative electrode material was measured. D / I G The ratio is A, and the I of the particle cross-section of the negative electrode material is... D / I G The ratio is B, and 1.22 < AB ≤ 2.10;

[0046] The particle surface of the negative electrode material was tested using atomic force microscopy. Random 1 μm samples were selected from the particle surface of the negative electrode material. The test area is 1 μm, and the arithmetic mean of the absolute values ​​of the height deviations relative to the reference plane within the test area is S nm, where 15 nm ≤ S ≤ 60 nm, and S = Where n≥5, and Z is the height deviation of any test point within the test area relative to the reference plane. In the negative electrode material provided in this application, the Raman ratio A of the particle surface can be used to characterize the disorder of the carbon layer, and the Raman ratio B of the cross-section of the negative electrode material particles can be used to characterize the crystallinity and quality of graphite. During the research process, the inventors of this application discovered that when AB is too small, the Raman ratios of the particle surface and the particle interior of the negative electrode material 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, resulting in insufficient disorder of the carbon layer or insufficient crystallinity of the graphite. This will cause poor rate performance and low capacity of the negative electrode material. When AB is too large, the difference in Raman ratios between the particle surface and the particle interior of the negative electrode material is too large, resulting in a large difference in the kinetic transport performance of the interface between graphite and the carbon layer, increasing the impedance of the negative electrode material, and deteriorating its rate performance.

[0047] Furthermore, the inventors discovered during their research that the surface area of ​​material particles is closely related to the material's capacity, first-efficiency, and other performance characteristics. Using an atomic force microscope, the arithmetic mean of the absolute values ​​of the height deviation relative to a reference surface within the scanning area is measured as S nm. S can specifically be 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or 60 nm, or other values ​​within the aforementioned range, without limitation. When the negative electrode material satisfies 15 nm ≤ S ≤ 60 nm, it exhibits high capacity, high first-efficiency, and low interfacial impedance. The inventors found that controlling S within the 15 nm to 60 nm range ensures that the coating layer on the negative electrode material is uniformly distributed on the graphite particle surface, and the roughness of the coating layer is also within a suitable range, which helps with electrolyte wetting and reduces interfacial impedance. When S < 15 nm, the surface of the negative electrode material is very smooth and flat, which is not conducive to electrolyte wetting and leads to a decrease in the capacity of the negative electrode material. When S > 60 nm, the surface roughness of the negative electrode material is too high, the electrolyte wettability is enhanced, but due to the reduced 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 first-efficiency of the negative electrode material decreases. This application controls AB and S within the above range, so that the difference in Raman ratio between the surface and the interior of the negative electrode material particles and the surface coating layer flatness are within a suitable range. This ensures both the regularity of the internal graphite structure and the high disorder of the external coating layer structure, as well as the uniform distribution and suitable morphological flatness of the graphite surface coating layer. The former helps to improve the rate performance and capacity of the negative electrode material, while 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 electrolyte wettability, improve the interfacial transport dynamics of the negative electrode material, and enable the negative electrode material to have high capacity, low impedance, high rate performance, and high first-efficiency performance.

[0048] In some embodiments, 1.70 ≤ A ≤ 3.00, specifically it can be 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, it can also be other values ​​within the above range, which are not limited here. In this application, the value of A is controlled within the above range, the carbon layer has a high degree of structural disorder, which can improve the wettability of the contact interface between the negative electrode material surface 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 transport power, reduce the interfacial impedance of the contact interface, and improve the initial coulombic efficiency and electrochemical performance of the negative electrode material.

[0049] 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, without limitation. This application controls the B value within the above range, resulting in a suitable degree of graphitization of graphite, good structural regularity of graphite, and the ability to control the interfacial impedance at the graphite-carbon layer interface within a suitable range, which is beneficial for improving the capacity and initial coulombic efficiency of the anode material.

[0050] In some implementations, the specific value of AB can be 1.26, 1.3, 1.5, 1.6, 1.8, 1.9, 2.0, 2.05 or 2.1, etc., or other values ​​within the above range, which are not limited here.

[0051] In some embodiments, graphite includes at least one of artificial graphite, natural graphite, and microcrystalline graphite. Natural graphite is flake graphite, a natural crystalline graphite with a fish-scale-like shape, belonging to the hexagonal crystal system, and exhibiting a layered structure. It possesses excellent properties such as high-temperature resistance, electrical conductivity, thermal conductivity, lubrication, 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 treatment.

[0052] In some embodiments, the graphite includes spherical graphite, which is natural graphite.

[0053] In some embodiments, the carbon content in the graphite is ≥95% by mass, specifically 95%, 96%, 97%, 97.5%, 98.3%, 98.8%, or 99%, but not limited to the listed values; other unlisted values ​​within this range are also applicable. Preferably, the carbon content in the graphite is ≥99% by mass.

[0054] In some embodiments, the thickness of the carbon layer is 15nm to 250nm, specifically 15nm, 20nm, 30nm, 40nm, 50nm, 80nm, 100nm, 150nm, 200nm, 220nm, or 250nm, but not limited to the listed values; other unlisted values ​​within this range are also applicable. Controlling the carbon layer thickness within the above range is beneficial for improving the lithium-ion transport power of the negative electrode material, reducing side reactions between the negative electrode material and the electrolyte, and improving the initial coulombic efficiency.

[0055] In some embodiments, the carbon layer includes amorphous carbon and graphitized carbon. The carbon layer has good compatibility with the electrolyte, ensuring the stability of the electrical performance of the negative electrode material during charging and discharging.

[0056] In some embodiments, the specific surface area of ​​the negative electrode material is ≤6m². 2 / g; specifically, it can be 1.0m2 / g, 1.8m 2 / g, 2.6m 2 / g, 3.5m 2 / g, 5.0m 2 / g or 6.0m 2 / g, of course, can also be other numbers within the above range, and 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 from the negative electrode material.

[0057] In some embodiments, the median particle size of the negative electrode material is 4μm to 25μm; more specifically, it can be 4μm, 6μm, 8μm, 9μm, 10μm, 12μm, 14μm, 15μm, 17μm, 20μm, 22μm or 25μm, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0058] In some embodiments, the tap density of the negative electrode material is 0.75 g / cm³. 3 ~1.3g / cm 3 Specifically, it could be 0.75 g / cm³. 3 0.8g / cm 3 0.85g / cm 3 0.9g / cm 3 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 1.3g / cm 3 Of course, other numbers within the above range are also possible, and no limitation is made here. Controlling the tap density of the negative electrode material within the above range in this application is beneficial for improving the energy density of lithium-ion batteries made from this negative electrode material.

[0059] In some embodiments, the oil absorption value of the negative electrode material is 38 mL / 100g to 48 mL / 100g, specifically 38 mL / 100g, 39 mL / 100g, 40 mL / 100g, 41 mL / 100g, 42 mL / 100g, 43 mL / 100g, 44 mL / 100g, 45 mL / 100g, or 48 mL / 100g, etc., and other values ​​within the above range are also possible, without limitation. The negative electrode material of this application, due to the high degree of structural disorder in the carbon layer, allows the oil absorption value of the negative electrode material to be controlled within the above range, which can improve the wettability of the contact interface between the negative electrode material surface and the electrolyte, enhance lithium-ion transport power, and reduce the interfacial impedance of the contact interface.

[0060] Secondly, this application provides a method for preparing a negative electrode material, such as... Figure 1 As shown, it includes the following steps:

[0061] Step S10: The coating agent and reaction regulator with active groups are dispersed in an aqueous solution and a prepolymerization reaction is carried out to obtain a prepolymerization solution, wherein the degree of polymerization of the polymer in the prepolymerization solution is 3 to 30.

[0062] Step S20: Graphite is added to the prepolymerization solution for liquid phase coating, and the precursor is obtained by solid-liquid separation. The solid-liquid ratio of graphite to prepolymerization solution is 1:(1.3~3.5), and the mass ratio of graphite to coating agent is 100:(4~30).

[0063] Step S30: The precursor is carbonized to obtain the negative electrode material.

[0064] In this application, a coating agent with active groups is prepolymerized to obtain a prepolymer solution in which the degree of polymerization of the polymer molecules is in the range of 3-30. The polymer is mainly an oligomer with small molecular chains, which can be uniformly dispersed in the prepolymer solution. Graphite is then added to the prepolymer solution for liquid-phase coating. During the coating process, the polymer uniformly dispersed in the prepolymer solution can deposit and adhere to the surface of the graphite particles, forming a uniform polymer coating layer. Simultaneously, the solid-liquid ratio of graphite to the prepolymer solution is controlled at 1:(1.3-3.5) to ensure that the thickness of the polymer coating layer uniformly attached to the graphite surface is within a suitable range, thereby improving both the capacity and lithium-ion interfacial transport efficiency of the anode 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 Raman ratio between the surface and interior of the anode material particles is also within a suitable range. In addition, the smoothness of the coating layer on the material surface is also within a suitable range. The above preparation method not only ensures the regularity of the graphite structure within the negative electrode material particles and provides better transport dynamics at the interface between the graphite and the carbon layer, but also improves the wettability of the interface between the negative electrode material surface and the electrolyte. The negative electrode material prepared by the method of this application can possess excellent lithium-ion transport dynamics, capacity, initial coulombic efficiency, and cycle performance.

[0065] The preparation method provided in this scheme is described in detail below:

[0066] Step S10: The coating agent and reaction regulator with active groups are dispersed in an aqueous solution and a prepolymerization reaction is carried out to obtain a prepolymerization solution, wherein the degree of polymerization of the polymer in the prepolymerization solution is 3 to 30.

[0067] In some embodiments, the degree of polymerization of the polymer in the prepolymerization solution is in the range of 3-30, and can be 3, 5, 10, 15, 20, 25, or 30, etc. When the degree of polymerization of the prepolymer is low, the utilization rate of the coating agent decreases, and the unpolymerized free coating agent deposited in the solid-liquid separation stage is directly wasted, increasing production costs. When the degree of polymerization of the prepolymer is high, the disorder of the final coating agent polymer deposition layer decreases, resulting in a decrease in the Raman value of the final negative electrode material, which is not conducive to improving kinetic performance.

[0068] In some embodiments, the active group includes at least one of a carbon-carbon double bond, a carboxyl group, a hydroxyl group, and an amino group.

[0069] In some embodiments, the coating agent having active groups 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, ethyl acrylamide, phenyl acrylamide, maleic acid, maleic anhydride, diamine maleate, citric acid, succinic acid, itaconic acid, itaconic anhydride, aminosulfonic acid, ammonium aminosulfonate, benzoic acid, ammonium benzoate, and p-fluorobenzoic acid.

[0070] In some embodiments, the reaction modifier includes at least one of a redox agent and a pH adjuster.

[0071] In some embodiments, the redox agent includes at least one selected from azobisisobutyronitrile, azobisisoheptanenitrile, hydrogen peroxide, ammonium persulfate, sodium persulfate, potassium persulfate, aluminum chloride, and ferric chloride.

[0072] In some embodiments, the pH adjuster includes at least one of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, and acetic acid.

[0073] In some embodiments, the coating agent includes a coating agent having an amino group, specifically at least one selected from aminostyrene, aniline, phenylenediamine, acrylamide, methacrylamide, ethylacrylamide, phenylacrylamide, diamine maleate, aminosulfonic acid, ammonium aminosulfonate, and ammonium benzoate.

[0074] In some embodiments, the coating agent includes a coating agent having an amine group, and the reaction regulator includes a pH regulator, which includes at least one of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, and acetic acid.

[0075] In some embodiments, the pH value of the prepolymerization reaction is controlled between 4 and 7, specifically 4, 4.5, 5, 5.5, 6, 6.5, or 7, or other values ​​within the above range, which are 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 lower degree of disorder in the polymer deposition layer on the graphite surface, ultimately affecting 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 remains free in the solution, and the polymer deposition layer on the graphite surface is insufficient.

[0076] In some embodiments, the coating agent comprises an amine-based coating agent, and the reaction regulator further comprises a redox agent, including at least one selected from 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.

[0077] In some embodiments, the coating agent includes a coating agent having carbon-carbon double bonds, specifically acrylic acid, methyl acrylate, ethyl acrylate, phenyl acrylate, methyl methacrylate, etc. The prepolymerization reaction temperature is 40℃~70℃, specifically 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, or 70℃, etc., and of course, other values ​​within the above range are also possible, and are not limited here. This application controls the prepolymerization reaction temperature within the above range so that the coating agent can fully prepolymerize. When the prepolymerization reaction temperature is too high, the degree of prepolymerization of the coating agent is too high, resulting in an uneven polymer coating layer on the graphite surface; when the prepolymerization reaction temperature is too low, the degree of prepolymerization of the coating agent is too low, and the oligomers are difficult to uniformly deposit and adhere to the graphite surface, resulting in waste of the coating agent.

[0078] In some embodiments, the mass ratio of oxidizing agent to 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., or other values ​​within the above range, which are not limited here. If the amount of oxidizing agent added is too low, it will affect the prepolymerization degree of the coating agent, resulting in a lower degree of disorder in the polymer deposition layer on the graphite surface, ultimately affecting the A value of the carbon layer of the negative electrode material. When the amount of oxidizing agent added is too high, the polymerization rate of the coating agent is too fast, resulting in the coating agent not being evenly distributed on the graphite surface, and excessive oxidizing agent will also increase production costs.

[0079] In some embodiments, the prepolymerization reaction time is controlled to be 1 to 4 hours, specifically 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours, or other values ​​within the above range, 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 incomplete. If the prepolymerization reaction time is too long, it leads to reduced production efficiency and is not conducive to industrial-scale preparation.

[0080] Step S20: Graphite is added to the prepolymerization solution for liquid phase coating, and solid-liquid separation is performed to obtain the precursor. The solid-liquid ratio of the graphite to the prepolymerization solution is 1:(1.3~3.5), and the mass ratio of the graphite to the coating agent is 100:(4~30).

[0081] In some embodiments, the graphite includes at least one of artificial graphite and natural graphite. Natural graphite is flake graphite or spherical graphite obtained by shaping flake graphite; it is a natural crystalline graphite, resembling fish scales in shape, belonging to the hexagonal crystal system, and exhibiting a layered structure. It possesses excellent properties such as high-temperature resistance, electrical conductivity, thermal conductivity, lubrication, plasticity, and acid and alkali resistance. Artificial graphite is a graphite material obtained by carbonizing organic matter and then undergoing high-temperature graphitization treatment.

[0082] In some embodiments, the graphite includes spherical graphite, which is natural graphite.

[0083] 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, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Multiple experiments have shown that controlling the median particle size of the graphite within the above range is beneficial for reducing the specific surface area of ​​the graphite, minimizing contact between the graphite and the electrolyte, and suppressing side reactions. Preferably, the median particle size of the graphite is 5 μm to 20 μm.

[0084] In some embodiments, the carbon content in the graphite is ≥95% by mass, specifically 95%, 96%, 97%, 97.5%, 98.3%, 98.8%, or 99%, but not limited to the listed values; other unlisted values ​​within this range are also applicable. Preferably, the carbon content in the graphite is ≥99% by mass.

[0085] In some embodiments, the solid-liquid ratio of graphite to the prepolymerization solution is 1:(1.3~3.5) g / mL, specifically 1:1.3 g / mL, 1:1.5 g / mL, 1:1.8 g / mL, 1:1.9 g / mL, 1:2.0 g / mL, 1:2.5 g / mL, 1:3.0 g / mL, 1:3.5 g / mL, etc., but not limited to the listed values; other unlisted values ​​within this range are also applicable. In this application, controlling the solid-liquid ratio of graphite to the prepolymerization solution within the above range allows control of the concentration of polymer molecules in the prepolymerization solution per unit volume, thereby ensuring that the thickness of the polymer coating layer uniformly attached to the graphite surface is within a suitable range. This improves both the capacity of the anode material and the lithium-ion interfacial transport efficiency of the anode material. When the solid-liquid ratio is too high, excessive graphite is added, resulting in insufficient polymer in the prepolymerization solution. This makes it difficult to ensure the formation of a uniformly thick polymer coating layer on the surface of the graphite particles, hindering interfacial transport of the anode material and affecting its capacity performance. When the solid-liquid ratio is too small, the amount of graphite added is too small, the polymer coating layer on the surface of the graphite particles is too thick, and the capacity of the negative electrode material decreases.

[0086] In some embodiments, the mass ratio of graphite to 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 other values ​​within the above range are also possible, without limitation. 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, which leads to the obstruction of interfacial transport of the negative electrode material and affects the capacity utilization of the negative electrode material.

[0087] In some embodiments, the liquid phase coating time is 4h to 24h, specifically 4h, 5h, 8h, 10h, 15h, 18h, 20h, 23h, 24h, etc. If the liquid phase coating time is insufficient, the polymer molecules in the prepolymerization solution are difficult to fully deposit and adhere 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 decreases, which is detrimental to industrial-scale preparation.

[0088] In some embodiments, the liquid-phase coating is carried out under stirring, and the polymer formed by the polymerization of the coating agent with active groups is deposited and attached to the surface of the graphite.

[0089] This application, by controlling the solid-liquid ratio, time, and amount of coating agent added during liquid-phase coating, can promote the uniform deposition and adhesion of polymers formed by coating agents with active groups onto the surface of graphite under stirring conditions.

[0090] In some embodiments, after liquid coating, the mixture is subjected to solid-liquid separation, and the obtained solid is dried to obtain the precursor.

[0091] In some embodiments, the solid-liquid separation includes at least one of vacuum filtration, centrifugation, and natural evaporation.

[0092] In some embodiments, the drying process includes at least one of blower drying, vacuum drying, freeze drying, and spray drying.

[0093] S30, the precursor is carbonized to obtain the negative electrode material.

[0094] In some embodiments, the carbonization temperature is 1000℃~2300℃, specifically, it can be 1000℃, 1300℃, 1500℃, 1800℃, 1900℃, 2000℃, 2200℃, 2300℃, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable. When the carbonization temperature is too low, the Raman value of the carbon layer of the negative electrode material is too high, that is, the disorder of the carbon layer is too high, leading to an aggravation of interfacial side reactions and a reduction in the first-efficiency of the negative electrode material; when the carbonization temperature is too high, the Raman value of the carbon layer of the negative electrode material is too low, that is, the disorder of the carbon layer is too low, leading to a deterioration of interfacial transport kinetics.

[0095] In some embodiments, the holding time for carbonization treatment is 0.5h to 6h. Specifically, it can be 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0096] In some embodiments, the carbonization process is carried out under a protective atmosphere, which includes at least one of nitrogen, helium, neon, argon, krypton, and xenon.

[0097] This invention also provides a battery. Figure 2 This is a schematic diagram of the discharge state of the battery provided in the embodiments of this application, such as... Figure 2 As shown, the battery includes a casing and an electrode assembly. The electrode assembly includes a positive electrode 1, a negative electrode 2, and a separator 3, with the separator 3 disposed between the positive electrode 1 and the negative electrode 2. The electrode assembly can be a stacked structure, formed by alternately stacking the positive electrode 1, the separator 3, and the negative electrode 2. In other embodiments, the electrode assembly can also be a wound structure, formed by sequentially stacking and winding the positive electrode, the separator, and the negative electrode.

[0098] In some embodiments, the positive electrode 1 includes a positive current collector 101 and a positive active layer 102 disposed on at least one surface of the positive current collector 101.

[0099] In some embodiments, the positive electrode current collector 101 may be made of aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil (aluminum foil or nickel foil, etc.) with a polymer substrate. The positive electrode active layer 102 contains a positive electrode active material, which includes compounds that can reversibly insert and deintercalate metal ions.

[0100] In some embodiments, the positive electrode active material may include lithium transition metal composite oxides, sodium transition metal composite oxides, etc. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

[0101] In some embodiments, the positive electrode active material may include, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), and lithium manganese oxide (LiMn2O3). 4) Lithium nickel manganese oxide (LiNi) 0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0102] In some embodiments, the negative electrode 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.

[0103] In some embodiments, the negative electrode current collector 201 may be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative electrode active material layer 202 includes a negative electrode material, which is the negative electrode material described in the first aspect or the negative electrode material prepared by the aforementioned preparation method.

[0104] The battery provided in this 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-state electrolyte battery, etc., and is not limited thereto.

[0105] The embodiments of the present invention will be further described below with reference to several examples. However, the embodiments of the present invention are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of the original claims.

[0106] The embodiments of this application will be further described below with reference to several examples. However, the embodiments of this application are not limited to the specific embodiments described below. Appropriate modifications and implementations can be made within the scope of protection.

[0107] Example 1

[0108] (1) Take 7 parts of phenylenediamine and an appropriate amount of pure water and mix them. Use 0.5 mol / L phosphoric acid solution to adjust the pH of the solution to 4. Add 7 parts of 1 mol / L ammonium persulfate solution to adjust the oxidative environment of the mixture. Stir continuously for 1 hour to produce a prepolymerization reaction and obtain a prepolymerization solution.

[0109] (2) The prepolymer solution, 100 parts of graphite (average particle size of 17 μm) and an appropriate amount of pure water are mixed at a solid-liquid ratio of 1:3 to form a uniform mixture. The mixture is then subjected to liquid phase coating treatment for 12 h under stirring. The polyphenylene diamine in the prepolymer solution is deposited and attached to the surface of the graphite particles. The mixture is then centrifuged, and the centrifuged product is then transferred to a drying oven at 120 °C for 36 h to obtain the precursor.

[0110] (3) Under a nitrogen atmosphere, the precursor was heated to 1250℃ for carbonization treatment for 4 hours and then cooled naturally to obtain the negative electrode material.

[0111] Example 2

[0112] Unlike Example 1:

[0113] (1) Take 7 parts of aminostyrene and an appropriate amount of pure water and mix them. Use 0.5 mol / L phosphoric acid solution to adjust the pH of the solution to 4. Add 7 parts of 1 mol / L ammonium persulfate solution to adjust the oxidative environment of the mixture. Stir continuously for 1 hour to carry out the prepolymerization reaction.

[0114] Example 3

[0115] Unlike Example 1:

[0116] (1) Take 7 parts of phenylenediamine and an appropriate amount of pure water and mix them. Use 0.5 mol / L phosphoric acid solution to adjust the pH of the solution to 5. Add 7 parts of 1 mol / L ammonium persulfate solution to adjust the oxidative environment of the mixture. Stir continuously for 1 hour to carry out the prepolymerization reaction.

[0117] Example 4

[0118] Unlike Example 1:

[0119] (1) Take 7 parts of phenylenediamine and an appropriate amount of pure water and mix them. Use 0.5 mol / L phosphoric acid solution to adjust the pH of the solution to 7. Add 7 parts of 1 mol / L ammonium persulfate solution to adjust the oxidative environment of the mixture. Stir continuously for 1 hour to carry out the prepolymerization reaction.

[0120] Example 5

[0121] Unlike Example 1:

[0122] (1) Take 7 parts of maleic anhydride and an appropriate amount of pure water, mix them, raise the solution temperature to 50°C and stir continuously for 2 hours to produce a prepolymerization reaction.

[0123] Example 6

[0124] The difference from Example 5 is:

[0125] (1) Take 7 parts of maleic anhydride and an appropriate amount of pure water, mix them, raise the solution temperature to 70°C and stir continuously for 2 hours to produce a prepolymerization reaction.

[0126] Example 7

[0127] The difference from Example 5 is:

[0128] (1) Take 7 parts of maleic anhydride and an appropriate amount of pure water, mix them, raise the solution temperature to 50°C and stir continuously for 4 hours to produce a prepolymerization reaction.

[0129] Example 8

[0130] Unlike Example 1:

[0131] (1) Take 7 parts of phenylenediamine and an appropriate amount of pure water and mix them. Use 0.5 mol / L phosphoric acid solution to adjust the pH of the solution to 4. Add 5 parts of 1 mol / L ammonium persulfate solution to adjust the oxidative environment of the mixture. Stir continuously for 1 hour to carry out the prepolymerization reaction.

[0132] Example 9

[0133] Unlike Example 1:

[0134] (1) Take 7 parts of phenylenediamine and an appropriate amount of pure water and mix them. Use 0.5 mol / L phosphoric acid solution to adjust the pH of the solution to 4. Add 12 parts of 1 mol / L ammonium persulfate solution to adjust the oxidative environment of the mixture. Stir continuously for 1 hour to carry out the prepolymerization reaction.

[0135] Example 10

[0136] Unlike Example 1:

[0137] (2) The prepolymer solution, 100 parts of graphite (average particle size of 17 μm) and an appropriate amount of pure water are mixed at a solid-liquid ratio of 1:1.5 to form a uniform mixture. The mixture is then subjected to liquid phase coating treatment for 12 h under stirring. The phenylenediamine in the mixture undergoes a polymerization reaction. The mixture is then centrifuged to separate the solid and liquid phases, and then transferred to a drying oven at 120 °C for 36 h to obtain the precursor.

[0138] Example 11

[0139] Unlike Example 1:

[0140] (1) Take 4 parts of phenylenediamine and an appropriate amount of pure water and 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. Stir continuously for 1 hour to carry out the prepolymerization reaction.

[0141] Example 12

[0142] Unlike Example 1:

[0143] (1) Take 25 parts of phenylenediamine and an appropriate amount of pure water and 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. Stir continuously for 1 hour to carry out the prepolymerization reaction.

[0144] Example 13

[0145] Unlike Example 1:

[0146] (3) Under a nitrogen atmosphere, the precursor was heated to 1600℃ for carbonization treatment for 4 hours and then cooled naturally to obtain the negative electrode material.

[0147] Example 14

[0148] Unlike Example 1:

[0149] (3) Under a nitrogen atmosphere, the precursor was heated to 2300℃ for carbonization treatment for 4 hours and then cooled naturally to obtain the negative electrode material.

[0150] Example 15

[0151] Unlike Example 1:

[0152] (2) The prepolymer solution, 100 parts of graphite (average particle size of 10 μm) and an appropriate amount of pure water are mixed at a solid-liquid ratio of 1:3 to form a uniform mixture. The mixture is then subjected to liquid phase coating treatment for 12 h under stirring. The phenylenediamine in the mixture undergoes a polymerization reaction. The mixture is then centrifuged to separate the solid and liquid phases, and then transferred to a drying oven at 120 °C for 36 h to obtain the precursor.

[0153] (3) Under a nitrogen atmosphere, the precursor is heated to 2300℃ and held for 4 hours, and then cooled naturally to obtain the negative electrode material.

[0154] Example 16

[0155] Unlike Example 1:

[0156] (2) The prepolymer solution, 100 parts of graphite (average particle size of 6 μm) and an appropriate amount of pure water are mixed at a solid-liquid ratio of 1:3 to form a uniform mixture. The mixture is then subjected to liquid phase coating treatment for 12 h under stirring. The phenylenediamine in the mixture undergoes a polymerization reaction. The mixture is then centrifuged to separate the solid and liquid phases, and then transferred to a drying oven at 120°C for 36 h to obtain the precursor.

[0157] (3) Under a nitrogen atmosphere, the precursor is heated to 2300℃ and held for 4 hours, and then cooled naturally to obtain the negative electrode material.

[0158] Example 17

[0159] Unlike Example 1:

[0160] (1) Take 7 parts of phenylenediamine and an appropriate amount of pure water and mix them. Use 0.5 mol / L phosphoric acid solution to adjust the pH of the solution to 4. Add 7 parts of 1 mol / L ammonium persulfate solution to adjust the oxidative environment of the mixture. Stir continuously for 3 hours to carry out the prepolymerization reaction and obtain the prepolymerization solution.

[0161] Comparative Example 1

[0162] Unlike Example 1:

[0163] (2) The prepolymer solution, 100 parts of graphite (average particle size of 17 μm) and an appropriate amount of pure water are mixed at a solid-liquid ratio of 1:1.1 to form a uniform mixture. The mixture is stirred and reacted for 12 hours. The phenylenediamine in the mixture undergoes a polymerization reaction. The mixture is then centrifuged to separate the solid and liquid components. Finally, it is dried in a drying oven at 120°C for 36 hours to obtain the precursor.

[0164] Comparative Example 2

[0165] Unlike Example 1:

[0166] (1) Take 0.8 parts of phenylenediamine and an appropriate amount of pure water and mix them. Use 0.5 mol / L phosphoric acid solution to adjust the pH of the mixture to 4. Add 0.8 parts of 1 mol / L ammonium persulfate solution to adjust the oxidation environment of the mixture. Stir continuously for 1 hour to carry out the prepolymerization reaction.

[0167] (2) The prepolymer solution, 100 parts of graphite (average particle size of 17 μm) and an appropriate amount of pure water are mixed at a solid-liquid ratio of 1:1.3 to form a uniform mixture. The mixture is stirred and reacted for 12 hours. The phenylenediamine in the mixture undergoes a polymerization reaction. The mixture is then centrifuged to separate the solid and liquid components. Finally, it is dried in a drying oven at 120°C for 36 hours to obtain the precursor.

[0168] Comparative Example 3

[0169] Unlike Example 1:

[0170] (3) Under a nitrogen atmosphere, the precursor of the coating material is heated to 700℃ and held at 4℃, and then cooled naturally to obtain a high-structure disordered carbon-coated graphite material.

[0171] Comparative Example 4

[0172] Unlike Example 1:

[0173] (1) Take 7 parts of phenylenediamine and an appropriate amount of pure water and mix them. Use 0.5 mol / L phosphoric acid solution to adjust the pH of the mixture to 10. Add 7 parts of 1 mol / L ammonium persulfate solution to adjust the oxidation environment of the mixture. Stir continuously for 1 hour to carry out the prepolymerization reaction.

[0174] Comparative Example 5

[0175] Unlike Example 1:

[0176] (1) Take 7 parts of phenylenediamine and an appropriate amount of pure water and mix them. Use 0.5 mol / L phosphoric acid solution to adjust the pH of the solution to 4. Add 7 parts of 1 mol / L ammonium persulfate solution to adjust the oxidative environment of the mixture. Stir continuously for 6 hours to carry out the prepolymerization reaction and obtain the prepolymerization solution.

[0177] Comparative Example 6

[0178] Unlike Example 1:

[0179] (1) Take 7 parts of phenylenediamine and an appropriate amount of pure water and mix them. Use 0.5 mol / L phosphoric acid solution to adjust the pH of the solution to 4. Add 7 parts of 1 mol / L ammonium persulfate solution to adjust the oxidation environment of the mixture. Do not perform prepolymerization reaction and proceed directly to the next step.

[0180] Comparative Example 7

[0181] Unlike Example 1:

[0182] (2) The prepolymer solution, 100 parts of graphite (average particle size of 17 μm) and an appropriate amount of pure water are mixed at a solid-liquid ratio of 1:3 to form a uniform mixture. The mixture is then subjected to liquid phase coating treatment for 2 hours under stirring. The polyphenylene diamine in the prepolymer solution is deposited and attached to the surface of the graphite particles. The mixture is then centrifuged, and the centrifuged product is then transferred to a drying oven at 120°C for 36 hours to obtain the precursor.

[0183] Test methods

[0184] (1) Test method for particle size distribution of negative electrode material: The particle size distribution range of negative electrode material was tested using a Malvern 3000 laser particle size analyzer. Dispersant (ethanol, pure water, and low-foaming surfactant) and the test sample were placed in a 50 mL beaker, followed by the addition of a certain amount of pure water. The mixture was stirred thoroughly with a glass rod to ensure uniform dispersion. The pump speed was set to 2400 r / min~2500 r / min, and the frequency was 19.5 Hz for particle size testing.

[0185] (2) Test method of tap density of negative electrode material: Place the negative electrode material in the sample chamber of the tap density meter, vibrate 1000 times and record the sample volume at this time. The tap density can be calculated according to the mass-volume ratio.

[0186] (3) Test method for specific surface area of ​​negative electrode material: The specific surface area of ​​the material was tested using a precision high-performance DX400 analyzer. The sample was loaded into a sample tube, and an isothermal jacket was used on the sample tube. The filler rod was placed into the bubble tube, and the retaining ring and O-ring were installed on the bubble tube. The assembled sample bubble tube was then placed into the corresponding analysis station for testing. Under constant temperature and low temperature, the amount of gas adsorbed on the solid surface at different relative pressures was measured. Based on the Brown-Nauer-Etter-Taylor adsorption theory and its formula (BET formula), the amount of monolayer adsorption of the sample was obtained, and the specific surface area of ​​the material was calculated.

[0187] (4) Oil absorption value test method of negative electrode material: The oil absorption value Q is tested by ASAHI S-500 oil absorption value tester of ASAHISOUKEN Japan. The oil absorption value Q is the amount of linseed oil added when the torque generated by the change of viscosity characteristics reaches 70% of the maximum torque, and the unit is mL / 100g.

[0188] (5) Test methods for surface morphology, cross-section, and coating of negative electrode material particles: The microstructure of the negative electrode material surface was observed using a HITACHI-S4800 scanning electron microscope. The steps are as follows: The conductive adhesive was attached to the sample cup, the sample was evenly coated on the conductive adhesive, and the sample that was not firmly fixed was blown away with a rubber bulb. The sample was then placed in the scanning electron microscope chamber for testing. The test steps for cross-section and coating are as follows: First, the graphite particles were polished using a HITACHI-E3500 ion milling machine. A small amount of carbon conductive adhesive was applied to the edge of the sample stage, and the graphite sample was evenly sprinkled on it. The sample was then gently pressed with a glass slide. After the conductive adhesive dried for 2 minutes, the excess sample was blown away with a rubber bulb. The sample stage was placed on the sample holder, the sample position was adjusted, and the airflow was adjusted to the maximum ion beam current. The polishing time was set for sample processing. After the process was completed, the cross-section and coating of the negative electrode material surface were observed using a HITACHI-S4800 scanning electron microscope.

[0189] (6) Raman testing method for negative electrode materials: Raman scattering spectra were measured using a HORIBA-XPLORA laser confocal Raman spectrometer with a laser wavelength of 532 nm. Data were collected at 30 points on the surface of the negative electrode material particles. The scattering spectra obtained at each point were then fitted with peaks to obtain the peaks at 1300 cm⁻¹. -1 ~1350cm -1 The peak area of ​​the D characteristic peak within the range and the peak area located at 1500 cm⁻¹ -1 ~1580cm -1 The peak area ratio of the G characteristic peak within the range is I D / I G I D / I GThe average value is A. After the negative electrode material particles were slicing, they were cut open using a HITACHI-E3500 ion milling machine, and the cut area was tested. Ten points were randomly selected within the particle cut area for Raman spectroscopy scanning, and the results were obtained at 1300 cm⁻¹. -1 ~1350cm -1 The peak area of ​​the D characteristic peak within the range and the peak area located at 1500 cm⁻¹ -1 ~1580cm -1 The peak area ratio of the G characteristic peak within the range is I D / I G I D / I G The average value is B.

[0190] (7) Polymer Degree of Polymerization Measurement Method: The degree of polymerization of polymers in the prepolymerization solution is tested using gel permeation chromatography (GPC), also known as size exclusion chromatography. GPC is a liquid chromatography method that uses a solvent as the mobile phase and flows through a porous packing material (such as porous silica gel or porous resin) as the separation medium. As the solvent elutes, molecules of different sizes are separated. Larger molecules are eluted first, and smaller molecules are eluted later. The molecular weight and distribution of the polymer are analyzed, and the obtained polymer molecular weight / monomer molecular weight is the degree of polymerization.

[0191] (8) Atomic Force Microscopy (AFM) Testing Method: The surface smoothness of graphite materials was tested using an atomic force microscope (AFM). A microcantilever, highly sensitive to minute forces, was fixed at one end, with a tiny needle tip at the other, gently touching the sample surface. Due to the extremely weak repulsive force between the atoms at the needle tip and those on the sample surface, the cantilever underwent a slight deflection. By detecting the amount of deflection and using feedback to control the constant repulsive force, the positional changes of the microcantilever at various points could be obtained, thus acquiring an image of the sample surface morphology. A 1μm sample was randomly selected from the image. The test area is 1 μm, and the arithmetic mean of the absolute values ​​of the height deviations relative to the reference plane within the test area is S nm, where 15 nm ≤ S ≤ 60 nm, and S = Where n≥5, and Z is the height deviation (i.e., ordinate value) of any test point within the test area relative to the reference plane. This application uses a tapping mode: the probe maintains a fixed frequency vibration along the Z-axis, contacting the sample when the vibration reaches its lowest point, resulting in minimal sample damage and high resolution. In this application, the reference plane of the atomic force microscope is an equipotential surface determined by detecting and analyzing the weak interactions between the probe tip and the atoms on the sample surface; it is the plane corresponding to the average height value of all test points.

[0192] (9) Electrochemical performance testing 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, carboxymethyl cellulose and styrene-butadiene rubber, respectively, with the solid content controlled at 50%. The solutions were coated onto copper foil current collectors, vacuum dried, and negative electrode sheets were obtained. A lithium metal sheet was used as the counter electrode, and the cells were assembled into coin cells in an argon-filled glove box. Charge and discharge tests were conducted at a current density of 0.1C, with a charge and discharge range of 0.01-1.5V. Cyclic charge and discharge were performed to obtain the first reversible specific capacity, the first charge capacity, and the first discharge capacity. The first coulombic efficiency = first discharge capacity / first charge capacity.

[0193] After completing the above tests, the charging current density was set to 0.2C, and discharge lithium intercalation tests were conducted at current densities of 0.2C, 0.5C, 1C, and 2C respectively. The 2C / 0.2C rate performance = 0.2C discharge lithium intercalation capacity / 2C discharge lithium intercalation capacity.

[0194] 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) obtained in this application are shown in Table 1 and Table 2 below.

[0195] Table 1. Preparation process parameters of negative electrode materials

[0196]

[0197] Table 2. Performance parameters of the negative electrode materials and their batteries prepared in each embodiment and comparative example.

[0198]

[0199] The negative electrode material prepared by the method provided in this application involves prepolymerizing a coating agent with active groups. The degree of polymerization of the polymer in the prepolymer solution is in the range of 3-30, and the polymer is mainly an oligomer with small molecular chains, which can be uniformly dispersed in the prepolymer solution. Graphite is then added to the prepolymer solution for liquid-phase coating. During the coating process, the polymer uniformly dispersed in the prepolymer solution can deposit and adhere to the surface of the graphite particles, forming a uniform polymer coating layer. Simultaneously, the solid-liquid ratio of graphite to prepolymer solution is controlled at 1:(1.3-3.5), and the mass ratio of graphite to coating agent is controlled at 100:(4-30), so that the thickness of the polymer coating layer uniformly attached to the graphite surface is within a suitable range. This improves both the capacity and lithium-ion interfacial transport efficiency of the negative electrode material.

[0200] Finally, through carbonization, 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 Raman ratio between the surface and interior of the negative electrode material particles is within a suitable range. In addition, the smoothness of the coating layer on the surface of the negative electrode material is also within a suitable range. The above preparation method not only ensures the regularity of the graphite structure inside the negative electrode material particles and the interface between graphite and carbon layer can have better transport dynamics, but also improves the wettability of the contact interface between the negative electrode material surface and the electrolyte. The negative electrode material prepared by the method of this application has AB greater than 1.22 and less than or equal to 2.10, indicating that the Raman ratio A of the carbon layer and the Raman value B (graphite) of the cross-section of the negative electrode material are both within a reasonable range. At this time, the negative electrode material can have both excellent lithium-ion transport dynamics and high capacity. S is in the range of 15nm~60nm, indicating that the coating layer on the surface of the material is uniformly distributed on the surface of the graphite particles, and the smoothness of the coating layer is also within a suitable range, which helps to wet the electrolyte and reduce the interfacial impedance. The graphite anode material provided by this patent not only ensures the regularity of the graphite structure inside the particles, enabling the interface between graphite and carbon layers to have better transport power, but also improves the wettability of the interface between the anode material surface and the electrolyte. The provided graphite anode material can have excellent lithium-ion transport power performance, capacity, first coulombic efficiency and cycle performance.

[0201] Figure 3a and Figure 3b These are electron microscope images of the negative electrode material prepared in Example 1 of this application at different magnifications; Figure 3a As shown, the carbon material in the carbon layer is uniformly distributed in a moss-like pattern on the surface of the graphite particles. Figure 3b As shown, the negative electrode material exhibits a potato-like particle distribution, with almost no highly disordered carbon material agglomerates between the particles, indicating that the graphite material obtained using the preparation method of this application is uniformly coated with highly disordered carbon material. Figure 3c As shown, when the negative electrode material is cut open, the exposed graphite sheet inside also reveals moss-like carbon material with a high degree of disorder, which is the same as the morphology of the outer surface of the negative electrode material. Figure 3a This indicates that the preparation method provided in this application can achieve uniform coating of highly disordered carbon materials on the outside of graphite particles. Figure 4a and Figure 4b The Raman spectra of the graphite anode material and its cross-section prepared in Example 1 of this application are shown 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 The image shows an atomic force microscope image of the graphite anode material prepared in Example 1, with an S value of 23.6 nm. The capacity, first-efficiency, and rate performance of the anode material prepared in Example 1 are significantly improved.

[0202] According to the test data of Examples 1-2 and Example 5, the A value and AB value of the prepared negative electrode materials do not change much when different coating agents with active groups are used. At the same time, the S value of the negative electrode materials are all in the range of 15nm~60nm. The specific capacity, first coulombic efficiency and rate performance of the negative electrode materials are good.

[0203] According to the test data of Examples 1 and 3-4, as the pH value increases, the A value of the prepared negative electrode material gradually decreases, and the corresponding AB value and S value also gradually decrease. This indicates that pH affects the degree of polymerization of the polymer in the prepolymerization solution, which in turn slightly reduces the disorder of the carbon material in the carbon layer, slightly increases the surface smoothness of the material, and decreases the capacity and initial coulombic efficiency of the negative electrode material, while the rate performance does not change much.

[0204] According to the test data of Examples 5-7, when the coating agent is a coating agent with carbon-carbon double bonds, the A value of the prepared negative electrode material decreases with the increase of the prepolymerization temperature; the A value of the prepared negative electrode material also decreases with the extension of the holding time. This is because the prepolymerization temperature and holding time affect the degree of polymerization of the polymer formed in the prepolymerization solution, the polymer molecular chain grows, and thus affects 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 this application, it helps to improve the capacity and first coulombic efficiency of the negative electrode material.

[0205] According to the test data of Examples 1, 8, and 9, as the amount of oxidizing and reducing agent added increases, the degree of polymerization of the polymer in the prepolymerization solution gradually increases, the disorder of the polymer deposited on the surface of the graphite particles gradually decreases, and the A value, AB value, and S value of the negative electrode material prepared after carbonization also decrease.

[0206] According to the test data from Examples 1 and 10, during the stirring reaction of graphite and prepolymer solution, controlling the solid-liquid ratio within a suitable range can control the concentration of polymer molecules in the prepolymer solution per unit volume. As the concentration decreases, the uniformity of polymer molecule deposition on the graphite particles decreases. With a decrease in the solid-liquid ratio, the A value of the negative electrode material gradually decreases, AB also decreases, and the S value increases significantly.

[0207] According to the test data of Examples 1 and 11-12, as the mass ratio of coating agent to graphite increases, the amount of 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 value also gradually increases, and the S value decreases significantly.

[0208] According to the test data of Examples 1 and 13-14, as the carbonization temperature increases, the disorder of the polymer carbonization layer deposited on the graphite surface gradually decreases, the A value of the obtained negative electrode material gradually decreases, the corresponding AB value also gradually decreases, and the S value does not change much.

[0209] According to the test data from Examples 14-16, as the particle size of the raw materials changes, the thickness of the polymer layer deposited on the graphite surface gradually increases, and the corresponding coating layer thickness also gradually increases. The A value and corresponding AB value of the carbonized material also gradually increase, while the S value remains relatively unchanged. This indicates that the preparation method of this application is applicable to the preparation of graphite materials with high surface disorder characteristics and different particle sizes.

[0210] According to the test data of Examples 1 and 17, as the prepolymerization time increases, the degree of polymerization of the polymer in the prepolymerization solution increases, the disorder of the polymer carbonization layer deposited on the graphite surface decreases, the A value of the obtained negative electrode material gradually decreases, the corresponding AB value also gradually decreases, and the S value decreases.

[0211] Compared with Example 1, in Comparative Example 1, the solid-liquid ratio of graphite and prepolymer solution was too high during the preparation process. The deposition reaction of polymer in prepolymer solution on graphite particles was uneven, and the polymer exhibited self-nucleation growth and agglomeration. The prepared anode material had Raman values ​​A > 3.00, AB > 2.10, and S > 60.0 nm. The specific surface area of ​​the anode material was too high, and the initial coulombic efficiency and rate capability were significantly reduced.

[0212] Compared with Example 1, in Comparative Example 2, the amount of coating agent added was too low during the preparation process, and the polymer concentration in the prepolymerization solution was also reduced. It was difficult for the polymer to be deposited on the graphite particles to form a uniform coating layer. The Raman value of the prepared negative electrode material was A < 1.70, AB < 1.22, and S > 60.0 nm. The specific surface area of ​​the negative electrode material increased, and the capacity, first efficiency, and rate of the negative electrode material also decreased.

[0213] Compared with Example 1, in Comparative Example 3, the carbonization temperature was too low during the preparation process, the disorder of the carbon layer coating the graphite particles was too high, and the defects inside the graphite particles also increased simultaneously. The Raman value A of the prepared high-structure disordered carbon-coated graphite material was greater than 3.00, but AB was in the range of 1.22~2.10. The S value was slightly higher than that of Example 1, the specific surface area of ​​the negative electrode material was higher, and the first efficiency was reduced.

[0214] Compared with Example 1, in Comparative Example 4, the pH value of the prepolymer solution was higher during the preparation process, and the degree of polymerization of the polymer in the prepolymer solution increased, which led to a decrease in the disorder of the carbon coating on the outside of the graphite particles. The Raman value of the prepared negative electrode material was A < 1.70, but AB was in the range of 1.22~2.10, S < 15nm, the specific surface area of ​​the negative electrode material was higher, and the first efficiency and rate performance were reduced.

[0215] Compared with Example 1, in Comparative Example 5, the prepolymerization stirring time was controlled to be too long during the preparation process, which increased the degree of polymerization of the polymer in the prepolymerization solution, resulting in a decrease in the disorder of the carbon coating on the outside of the graphite particles. The prepared anode material had a Raman value of A < 1.70, AB < 1.22, and an S value in the range of 15 nm to 60 nm. The capacity, first efficiency, and rate of the anode material were reduced.

[0216] Compared with Example 1, Comparative Example 6 did not undergo prepolymerization treatment during the preparation process, resulting in the coating agent not being completely deposited on the surface of the graphite particles. Under the same coating amount, the coating layer thickness was reduced, and the Raman value of the prepared negative electrode material was A < 1.70, AB < 1.22, and S > 60.0 nm. The specific surface area of ​​the negative electrode material increased, the side reaction between the negative electrode material and the electrolyte was aggravated, and the capacity, first efficiency, and rate of the negative electrode material decreased.

[0217] Compared with Example 1, in Comparative Example 7, the stirring time after adding graphite powder was too short during the preparation process, 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, and S > 60.0 nm. The specific surface area of ​​the negative electrode material increased, the side reaction between the negative electrode material and the electrolyte intensified, and the capacity, first efficiency, and rate of the negative electrode material decreased.

[0218] Although this application discloses preferred embodiments as described above, it is not intended to limit the claims. Any person skilled in the art can make several possible changes and modifications without departing from the concept of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims of this application.

Claims

1. A negative electrode material for a lithium-ion battery, 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, the carbon layer comprising amorphous carbon; Raman spectroscopy was used to test the particle surface and particle cross-section of the negative electrode material at a depth of 1300 cm⁻¹. -1 ~1350cm -1 The peak area of ​​the D characteristic peak within the range and the peak area located at 1500 cm⁻¹ -1 ~1580cm -1 The peak area ratio of the G characteristic peak within the range is I D / I G The I on the surface of the particles of the negative electrode material was measured. D / I G The ratio is A, and the I of the particle cross-section of the negative electrode material is... D / I G The ratio is B, 1.70≤A≤3.00, 0.4≤B≤0.8, 1.22<AB≤2.10; The particle surface of the negative electrode material was tested using atomic force microscopy. Random 1 μm samples were selected from the particle surface of the negative electrode material. The test area is 1 μm, and the arithmetic mean of the absolute values ​​of the height deviations relative to the reference plane within the test area is S nm, where 15 nm ≤ S ≤ 60 nm, and S = n≥5, Z is the height deviation of any test point in the test area relative to the reference plane; The oil absorption value of the negative electrode material is 38 mL / 100g to 48 mL / 100g.

2. The negative electrode material of the lithium-ion battery according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following characteristics: 1) The graphite includes at least one of artificial graphite, natural graphite, and microcrystalline graphite; 2) The fixed carbon content of the graphite is ≥95%.

3. The negative electrode material of the lithium-ion battery according to claim 1, characterized in that, The thickness of the carbon layer is 15nm~250nm.

4. The negative electrode material of the lithium-ion battery according to claim 1, characterized in that, The median particle size of the negative electrode material is 4μm~25μm.

5. The negative electrode material of the lithium-ion battery according to claim 1, characterized in that, The specific surface area of ​​the negative electrode material is ≤6m². 2 / g.

6. The negative electrode material of the lithium-ion battery according to claim 1, characterized in that, The tap density of the negative electrode material is 0.75 g / cm³. 3 ~1.3g / cm 3 .

7. A method for preparing a negative electrode material for a lithium-ion battery as described in any one of claims 1 to 6, characterized in that, The method includes the following steps: A coating agent with active groups and a reaction regulator are dispersed in an aqueous solution and subjected to a prepolymerization reaction to obtain a prepolymerization solution, wherein the degree of polymerization of the polymer in the prepolymerization solution is 3 to 30; the coating agent with active groups 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, ethyl acrylamide, phenyl acrylamide, maleic acid, maleic anhydride, diamine maleate, citric acid, succinic acid, itaconic acid, itaconic anhydride, aminosulfonic acid, ammonium aminosulfonate, benzoic acid, ammonium benzoate, and p-fluorobenzoic acid; Graphite is added to the prepolymerization solution for liquid-phase coating, and the precursor is obtained by solid-liquid separation. The median particle size of the graphite is 1 μm to 30 μm, the solid-liquid ratio of the graphite to the prepolymerization solution is 1:(1.3 to 3.5), and the mass ratio of the graphite to the coating agent is 100:(4 to 30). The precursor is subjected to carbonization treatment at a temperature of 1000℃ to 2300℃ and a holding time of 0.5h to 6h to obtain the negative electrode material.

8. The method for preparing the negative electrode material of the lithium-ion battery according to claim 7, characterized in that, The method satisfies at least one of the following characteristics: (1) The active group includes at least one of carbon-carbon double bonds, carboxyl groups, hydroxyl groups, and amino groups; (2) The reaction regulator includes at least one of an oxidizing agent and a pH regulator; (3) The reaction regulator includes an oxidizing agent, and the mass ratio of the oxidizing agent to the coating agent is 1:(0.7~2.0). (4) The time for the prepolymerization reaction is controlled to be 1h to 4h; (5) The liquid phase coating time is 4h to 24h.

9. The method for preparing the negative electrode material of the lithium-ion battery according to claim 7, characterized in that, The carbonization process is carried out under a protective atmosphere.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode material of the lithium-ion battery according to any one of claims 1 to 6 or the negative electrode material of the lithium-ion battery prepared by the preparation method according to any one of claims 7 to 9.

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