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 a high-performance negative electrode material 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 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] In view of this, 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 1300 cm -1 ~1350cm -1 and the G characteristic peak located in the range of 1500 cm -1 ~1580cm -1 is I D / I G , the I D / I GA, 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] The graphite is added into the prepolymerization solution for liquid phase coating, and a precursor is obtained through solid-liquid separation, wherein 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 subjected to carbonization treatment to obtain the negative electrode material.

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

[0023] In some embodiments, the reaction regulator comprises at least one of an oxidation-reduction agent and a pH regulator.

[0024] In some embodiments, the reaction regulator comprises an oxidation-reduction agent, and the mass ratio of the oxidation-reduction agent to the coating agent is 1: (0.7-2.0).

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

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

[0027] In some embodiments, the coating agent with the active group comprises at least one of styrene, fluorostyrene, bromostyrene, aminostyrene, styrene acid, phenylpropionic acid, aniline, phenyldiamine, acrylic acid, methyl acrylate, ethyl acrylate, phenyl acrylate, benzyl acrylate, acrylamide, methyl acrylamide, ethyl acrylamide, phenyl acrylamide, maleic acid, maleic anhydride, maleic acid diamine, citric acid, mesaconic acid, itaconic acid, itaconic anhydride, sulfamic acid, ammonium sulfamate, benzoic acid, ammonium benzoate, p-fluorobenzoic acid.

[0028] In some embodiments, the temperature of the carbonization treatment is 1000℃-2300℃.

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

[0030] In some embodiments, the carbonization treatment is performed under a protective atmosphere. In a third aspect, the present application provides a battery comprising the negative electrode material described above or prepared according to the preparation method described above.

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

[0032] The application provides a negative electrode material of a lithium ion battery, wherein a Raman ratio A of a particle surface of the negative electrode material can be used to characterize the disorder degree of a carbon layer, and a Raman ratio B of a particle section of the negative electrode material can be used to characterize the crystallization degree and quality of graphite. The inventors of the application find in the research process that when A-B is too small, the Raman ratio of the particle surface of the negative electrode material is too close to that of the particle interior, which indicates that the Raman ratio A of the carbon layer is too small or the Raman ratio B of the particle section of the negative electrode material is too high, and the disorder degree of the carbon layer is insufficient or the crystallization degree of the graphite is insufficient, which results in poor rate performance and low capacity of the negative electrode material. When A-B is too large, the Raman ratio of the particle surface of the negative electrode material is too different from that of the particle interior, the kinetic transmission performance of the connection interface between the graphite and the carbon layer is greatly different, the impedance of the negative electrode material is increased, and the rate performance of the negative electrode material is deteriorated.

[0033] In addition, the inventors of the application find in the research process that the microstructure of the particle surface of the negative electrode material is closely related to the capacity and initial efficiency of the material, and the absolute value of the arithmetic mean of the height deviation of the scanning area relative to the reference surface measured by the atomic force microscope is S nm. When the negative electrode material satisfies 15≤S≤60, the negative electrode material has the characteristics of high capacity, high initial efficiency and low interface impedance. The inventors find that when S is controlled in the range of 15 nm to 60 nm, the coating layer on the surface of the negative electrode material is uniformly distributed on the surface of the graphite particle, and the roughness of the coating layer is also in a suitable range, which is helpful to the electrolyte infiltration and the reduction of the interface impedance. When S<15 nm, the surface of the negative electrode material is too smooth, which is not conducive to the electrolyte infiltration, resulting in 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 infiltration is enhanced, but the uniformity of the coating layer on the surface of the negative electrode material is reduced, resulting in an increase in the interface side reaction of the negative electrode material and an increase in the irreversible consumption of active lithium ions, which reduces the initial efficiency of the negative electrode material.

[0034] The application controls A-B and S in the above range, so that the difference between the Raman ratio of the particle surface of the negative electrode material and that of the particle interior and the flatness of the surface coating layer are in a suitable range, which can ensure the regularity of the internal graphite structure and the high disorder of the external coating layer structure, and can also ensure the uniform distribution and suitable flatness of the surface coating layer of the graphite. Therefore, the negative electrode material provided by the application can effectively improve the electrolyte infiltration and the interface transmission kinetics of the negative electrode material, so that the negative electrode material has excellent performance of high capacity, low impedance, high rate and high initial efficiency.

[0035] The application provides a preparation method of a lithium ion battery. The preparation method comprises the following steps: pre-polymerizing a coating agent with an active group to obtain a pre-polymerization solution, wherein the polymer molecules in the pre-polymerization solution have a polymerization degree in the range of 3-30, and the polymer is mainly an oligomer with a small molecular chain and can be uniformly dispersed in the pre-polymerization solution; and adding graphite into the pre-polymerization solution to perform liquid phase coating. In the coating process, the polymer uniformly dispersed in the pre-polymerization solution can be deposited and attached to the surface of the graphite particles to form a uniform polymer coating layer. Meanwhile, the solid-liquid ratio of the graphite and the pre-polymerization solution is controlled to be 1:(1.3-3.5), so that the thickness of the polymer coating layer uniformly attached to the surface of the graphite is in a suitable range, the lithium ion interface transmission efficiency of the negative electrode material is improved, and the capacity of the negative electrode material is improved. Finally, the polymer coating layer can be fully carbonized to form a carbon layer through carbonization treatment. The carbon material in the carbon layer has a high degree of disorder, the difference between the Raman ratios of the surface of the negative electrode material particles and the interior of the particles is also in a suitable range, and in addition, the flatness of the surface coating layer of the material is also in a suitable range. The above preparation method not only guarantees the structural regularity of the graphite located in the interior of the negative electrode material particles and the connection interface between the graphite and the carbon layer has 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 prepared by the preparation method of the application can have excellent lithium ion transmission power performance, capacity, first coulomb efficiency and cycle performance. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The process flow chart of the preparation method of the negative electrode material provided by the application is shown in the figure;

[0037] Figure 2 The discharge state schematic diagram of the battery provided by the embodiment of the application is shown in the figure;

[0038] Figure 3a The negative electrode material prepared by the embodiment 1 of the application is shown in the figures; Figure 3b The negative electrode material prepared by the embodiment 1 of the application is shown in the figures;

[0039] Figure 3c The section electron microscope graph of the negative electrode material prepared by the embodiment 1 of the application is shown in the figure;

[0040] Figure 4a The Raman test spectrum of the material prepared by the embodiment 1 of the application is shown in the figure, and the Raman test spectrum of the section of the material prepared by the embodiment 1 of the application is shown in the figure 4b;

[0041] Figure 5 The surface atomic force microscope graph of the material prepared by the embodiment 1 of the application is shown in the figure;

[0042] Figure 6 The electrochemical impedance comparison graph of the negative electrode material prepared by the embodiment 1 of the application and the comparative example 4 is shown in the figure. DETAILED DESCRIPTION

[0043] In order to better illustrate the present application, facilitate the understanding of the technical solutions of the present application, the present application is further described in detail below. However, the following examples are only simple examples of the present application, and do not represent or limit the protection scope of the present application. The protection scope of the present application is subject to the claims.

[0044] Based on this, in a first aspect, the present application provides a negative electrode material, which comprises graphite and a carbon layer on at least part of the surface of the graphite.

[0045] The particle surface and the particle section of the negative electrode material are tested by Raman spectroscopy, and the peak area of the D characteristic peak in the range of 1300 cm -1 ~1350cm -1 The peak area ratio of the D characteristic peak in the range of 1300 cm -1 ~1350cm -1 and the peak area of the G characteristic peak in the range of 1500 cm D ~1580cm G is I D / I G , the I D / I G ratio of the particle surface of the negative electrode material is A, the I D / I G ratio of the particle section of the negative electrode material is B, and 1.22

[0046] The particle surface of the negative electrode material is tested by atomic force microscopy, and 1 μm 1 μm test area is randomly selected on the particle surface of the negative electrode material, and 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. 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 particle section of the negative electrode material can be used to characterize the crystallization degree and quality of the graphite. The present inventors found in the research process that when A-B 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 negative electrode material section is too high, the disorder degree of the carbon layer is insufficient or the crystallization degree of the graphite is insufficient, which will cause poor rate performance and low capacity of the negative electrode material. When A-B is too large, the Raman ratios of the particle surface and the particle interior of the negative electrode material are too different, the dynamic transmission performance of the connection interface between the graphite and the carbon layer is greatly different, the impedance of the negative electrode material increases, and the rate performance of the negative electrode material deteriorates.

[0047] In addition, the inventors of the present application found in the research process that the surface of the material particles is closely related to the capacity, initial efficiency and other performances of the material. The absolute value of the arithmetic mean of the height deviation measured relative to the reference surface in the scanning area by atomic force microscope is S nm. S can be 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm or 60 nm, and of course can also be other values within the above range, which are not limited herein. When the negative electrode material satisfies 15 nm≤S≤60 nm, the negative electrode material has the characteristics of high capacity, high initial efficiency and low interface impedance. The inventors found that when S is controlled in the range of 15 nm to 60 nm, the coating layer on the surface of the negative electrode material is uniformly distributed on the surface of the graphite particles, and the roughness of the coating layer is also in a suitable range, which is helpful for electrolyte infiltration and interface impedance reduction. When S<15 nm, the surface of the negative electrode material is very smooth, which is not conducive to electrolyte infiltration, resulting in 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 infiltration is enhanced, but the uniformity of the coating layer on the surface of the negative electrode material is reduced, resulting in an increase in the interface side reaction of the negative electrode material, an increase in the irreversible consumption of active lithium ions, and a decrease in the initial efficiency of the negative electrode material. The present application controls A-B and S in the above range, so that the Raman ratio difference between the surface and the interior of the negative electrode material particle and the flatness of the surface coating layer are in a suitable range, which can ensure the regularity of the internal graphite structure and the high disorder of the external coating layer structure, and also can ensure the uniform distribution and suitable morphology flatness of the graphite surface coating layer. The former is helpful to improve the rate performance and capacity of the negative electrode material, and the latter is helpful to improve the initial efficiency and capacity of the negative electrode material. Therefore, the negative electrode material provided by the present patent can effectively improve the electrolyte infiltration, improve the interface transmission kinetics of the negative electrode material, and make the negative electrode material have high capacity, low impedance, high rate and high initial efficiency.

[0048] 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, and of course can also be other values within the above range, which are not limited herein. In the present application, A is controlled in the above range, the structure of the carbon layer has a high degree of disorder, which can improve the wettability of the contact interface between the surface of the negative electrode material and the electrolyte, reduce the occurrence of the interface side reaction of the negative electrode material, reduce the consumption of irreversible active lithium ions, improve the lithium ion transmission dynamics, reduce the interface 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, and the like, and of course, other values within the above range are also applicable, which are not limited herein. By controlling the value of B within the above range, the graphitization degree 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 conducive to improving the capacity and the first coulombic efficiency of the negative electrode material.

[0050] In some embodiments, the specific value of A-B can be 1.26, 1.3, 1.5, 1.6, 1.8, 1.9, 2.0, 2.05 or 2.1, and the like, and of course, other values within the above range are also applicable, which are not limited herein.

[0051] In some embodiments, the graphite includes at least one of artificial graphite, natural graphite and microcrystalline graphite. The natural graphite is flaky graphite, which is a natural allotropic graphite, and has a fish scale-like shape, belongs to hexagonal system, has a layered structure, and has good high-temperature resistance, electrical conductivity, thermal conductivity, lubricity, plasticity and acid and alkali resistance and the like. The artificial graphite is a graphite material obtained by carbonizing an organic matter and then performing graphitization high-temperature treatment.

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

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

[0054] In some embodiments, the thickness of the carbon layer is 15nm-250nm, specifically, 15nm, 20nm, 30nm, 40nm, 50nm, 80nm, 100nm, 150nm, 200nm, 220nm or 250nm, and the like, but is not limited to the listed values, and other values not listed within the value range are also applicable. By controlling the thickness of the carbon layer within the above range, the lithium ion transmission dynamics of the negative electrode material can be improved, and the occurrence of side reactions between the negative electrode material and the electrolyte can be reduced, thereby improving the first coulombic efficiency.

[0055] 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 properties of the negative electrode material in the charging and discharging process.

[0056] In some embodiments, the specific surface area of the negative electrode material is ≤6m 2 / g; specifically, 1.0m2 / g, 1.8 m 2 / g, 2.6 m 2 / g, 3.5 m 2 / g, 5.0 m 2 / g or 6.0 m 2 / g, of course, other numbers within the above range are also possible, which are not limited herein. Controlling the specific surface area of the negative electrode material within the above range is beneficial to improve the cycle performance of the battery made of the negative electrode material.

[0057] 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 values not listed within the range are also applicable.

[0058] In some embodiments, the tap density of the negative electrode material is 0.75 g / cm 3 ~1.3 g / cm 3 ; specifically, it can be 0.75 g / cm 3 , 0.8 g / cm 3 , 0.85 g / cm 3 , 0.9 g / cm 3 , 0.92 g / cm 3 , 1.0 g / cm 3 , 1.05 g / cm 3 , 1.1 g / cm 3 , 1.15 g / cm 3 , 1.2 g / cm 3 , 1.25 g / cm 3 or 1.3 g / cm 3 , of course, other numbers within the above range are also possible, which are not limited herein. Controlling the tap density of the negative electrode material within the above range in the present application is beneficial to improve the energy density of the lithium ion battery made of the negative electrode material.

[0059] In some embodiments, the oil absorption value of the negative electrode material is 38 mL / 100 g to 48 mL / 100 g, specifically can be 38 mL / 100 g, 39 mL / 100 g, 40 mL / 100 g, 41 mL / 100 g, 42 mL / 100 g, 43 mL / 100 g, 44 mL / 100 g, 45 mL / 100 g or 48 mL / 100 g, etc., and of course can also be other values within the above range, which are not limited herein. The negative electrode material of the present application can control the oil absorption value of the negative electrode material within the above range due to the high degree of structural disorder of the carbon layer, can improve the wettability of the contact interface between the surface of the negative electrode material and the electrolyte, improve the lithium ion transmission power, and reduce the interface impedance of the contact interface.

[0060] In a second aspect, the present application provides a preparation method of a negative electrode material, as shown in Figure 1 The preparation method comprises the following steps:

[0061] In step S10, the coating agent with active groups and the reaction regulator are dispersed in an aqueous solution to perform a prepolymerization reaction, and a prepolymerization solution is obtained, wherein the polymerization degree of the polymer in the prepolymerization solution is 3 to 30.

[0062] In step S20, graphite is added to the prepolymerization solution to perform liquid-phase coating, and a precursor is obtained by solid-liquid separation, wherein the solid-liquid ratio of graphite to the prepolymerization solution is 1: (1.3 to 3.5), and the mass ratio of graphite to the coating agent is 100: (4 to 30).

[0063] In step S30, the precursor is subjected to carbonization treatment to obtain the negative electrode material.

[0064] In the present application, by pre-polymerizing the coating agent with active groups, the polymer molecules in the obtained pre-polymerization solution have a polymerization degree in the range of 3-30, and the polymer is mainly an oligomer with a small molecular chain, which can be uniformly dispersed in the pre-polymerization solution. Then, graphite is added to the pre-polymerization solution for liquid phase coating. In the coating process, the polymer uniformly dispersed in the pre-polymerization 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 pre-polymerization solution is controlled to be 1:(1.3-3.5), so that the thickness of the polymer coating layer uniformly attached to the surface of the graphite is in a suitable range, which improves 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, the difference in Raman ratio between the surface of the negative electrode material particles and the interior of the particles can also be in a suitable range, and in addition, the flatness of the surface coating layer can also be in a suitable range. The above preparation method not only guarantees the structural regularity of the graphite located in the interior of the negative electrode material particles, but also improves the transmission dynamics of the connection interface between the graphite and the carbon layer, and improves the wettability of the contact interface between the surface of the negative electrode material and the electrolyte. The negative electrode material prepared by the preparation method of the present application can have excellent lithium ion transmission dynamic performance, capacity, first coulomb efficiency and cycle performance.

[0065] The preparation method provided by the present scheme is described in detail below.

[0066] In step S10, the coating agent with active groups and the reaction regulator are dispersed in an aqueous solution to perform a pre-polymerization reaction to obtain a pre-polymerization solution, wherein the polymerization degree of the polymer in the pre-polymerization solution is 3-30.

[0067] In some embodiments, the polymerization degree of the polymer in the pre-polymerization solution is in the range of 3-30, which can be 3, 5, 10, 15, 20, 25 or 30, etc. When the pre-polymerization molecule has a low polymerization degree, the utilization rate of the coating agent is reduced, the free coating agent that is not polymerized and deposited during the solid-liquid separation stage is directly wasted, and the production cost is increased. When the pre-polymerization molecule has a high polymerization degree, the disorder degree of the polymerization and deposition layer of the final coating agent is reduced, which reduces the Raman value of the final negative electrode material, and is not conducive to improving the 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 amine group.

[0069] In some embodiments, the coating agent with active groups includes at least one of styrene, fluorostyrene, bromostyrene, aminostyrene, styrene 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, maleic diamine, citric acid, mesaconic acid, itaconic acid, itaconic anhydride, sulfamic acid, ammonium sulfamate, benzoic acid, ammonium benzoate, p-fluorobenzoic acid.

[0070] In some embodiments, the reaction regulator includes at least one of an oxidation-reduction agent and a pH regulator.

[0071] In some embodiments, the oxidation-reduction agent includes at least one of azobisisobutyronitrile, azobisisoheptyl nitrile, hydrogen peroxide, ammonium persulfate, sodium persulfate, potassium persulfate, aluminum chloride, iron chloride.

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

[0073] In some embodiments, the coating agent includes a coating agent with an amine group, which can be at least one of aminostyrene, aniline, phenylenediamine, acrylamide, methacrylamide, ethyl acrylamide, phenyl acrylamide, maleic diamine, sulfamic acid, ammonium sulfamate, ammonium benzoate.

[0074] In some embodiments, the coating agent includes a coating agent with 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, acetic acid.

[0075] In some embodiments, the pH value of the prepolymerization reaction is controlled at 4-7, which can be 4, 4.5, 5, 5.5, 6, 6.5, or 7, and of course can be other values within the above range, which are not limited herein. 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 of the polymer deposition layer deposited on the surface of graphite, 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, and most of the coating agent is still free in the solution, and the polymer deposition layer deposited on the surface of graphite is insufficient.

[0076] In some embodiments, the coating agent comprises a coating agent with an amine group, and the reaction regulator further comprises a redox agent, and the redox agent comprises at least one of azobisisobutyronitrile, azobisisoheptyl nitrile, hydrogen peroxide, ammonium persulfate, sodium persulfate, potassium persulfate, aluminum chloride, and ferric chloride. The addition of the redox agent can promote the pre-polymerization of the coating agent containing active groups.

[0077] In some embodiments, the coating agent comprises a coating agent with a carbon-carbon double bond, and specifically can be acrylic acid, methyl acrylate, ethyl acrylate, phenyl acrylate, benzyl acrylate, etc., and the pre-polymerization temperature is 40-70℃, and specifically can be 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, or 70℃, etc., and of course can be other values within the above range, which are not limited herein. The application controls the pre-polymerization temperature within the above range, so that the coating agent can be fully pre-polymerized. When the pre-polymerization temperature is too high, the pre-polymerization degree of the coating agent is too high, causing the polymer coating layer on the surface of the graphite to be uneven; when the pre-polymerization temperature is too low, the pre-polymerization degree of the coating agent is too low, and the oligomer is difficult to uniformly deposit and adhere to the surface of the graphite, causing waste of the coating agent.

[0078] In some embodiments, the mass ratio of the redox agent to the coating agent is 1:(0.7-2.0), and specifically can be 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 can be other values within the above range, which are not limited herein. If the amount of the redox agent is too low, it will affect the pre-polymerization degree of the coating agent, resulting in a low degree of disorder of the polymer deposition layer deposited on the surface of the graphite, and ultimately affecting the A value of the carbon layer of the negative electrode material. When the amount of the redox agent is too high, the polymerization speed of the coating agent is too fast, causing the coating agent to be unable to uniformly distribute on the surface of the graphite, and too much redox agent will also increase the production cost.

[0079] In some embodiments, the pre-polymerization time is controlled to be 1-4h, and specifically can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, or 4h, etc., and of course can be other values within the above range, which are not limited herein. If the pre-polymerization time is too short, the content of the pre-polymerized polymer molecules in the pre-polymerization solution is low, and the pre-polymerization is insufficient. If the pre-polymerization time is too long, it will reduce the production efficiency and is not conducive to industrial production.

[0080] In step S20, the graphite is added to the pre-polymerization solution for liquid-phase coating, and a precursor is obtained by solid-liquid separation, wherein the solid-liquid ratio of the graphite to the pre-polymerization 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. The natural graphite is flake graphite or spherical graphite shaped from flake graphite, is a natural allotrope of carbon, has a fish scale-like appearance, belongs to hexagonal system, has a layered structure, and has good properties of high temperature resistance, electrical conductivity, thermal conductivity, lubrication, plasticity, and acid and alkali resistance. The artificial graphite is a graphite material obtained by carbonization of an organic substance and then high-temperature treatment.

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

[0083] In some embodiments, the graphite has a median particle size of 1 μm to 30 μm, and more particularly, 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, and other values not listed in the range are also applicable. It is found through repeated experiments that the graphite has a median particle size controlled in the above range, which is beneficial to reducing the specific surface area of the graphite, reducing the contact of the graphite with the electrolyte, and inhibiting the occurrence of side reactions. Preferably, the graphite has a median particle size of 5 μm to 20 μm.

[0084] In some embodiments, the graphite has a mass content of carbon of ≥95%, and more particularly, can be 95%, 96%, 97%, 97.5%, 98.3%, 98.8%, or 99%, but is not limited to the listed values, and other values not listed in the range are also applicable. Preferably, the graphite has a mass content of carbon of ≥99%.

[0085] In some embodiments, the graphite has a solid-liquid ratio of 1: (1.3-3.5) g / mL with the prepolymerization solution, and more particularly, can be 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, but is not limited to the listed values, and other values not listed in the range are also applicable. In the present application, the solid-liquid ratio of the graphite with the prepolymerization solution is controlled in the above range, which can control the concentration of polymer molecules in the prepolymerization solution in a unit volume, and then the thickness of the polymer coating layer uniformly attached to the surface of the graphite is in a suitable range, which improves the lithium ion interfacial transmission efficiency of the negative electrode material while improving the capacity of the negative electrode material. When the solid-liquid ratio is too large, the amount of graphite added is too much, and the polymer in the prepolymerization solution is insufficient, which makes it difficult to ensure the formation of a polymer coating layer with uniform thickness on the surface of the graphite particles, the interfacial transmission of the negative electrode material is hindered, and the capacity of the negative electrode material is affected. When the solid-liquid ratio is too small, the amount of graphite added is too small, and the polymer coating layer on the surface of the graphite particles is too thick, which reduces the capacity of the negative electrode material.

[0086] In some embodiments, the mass ratio of graphite to coating agent is 100:(4-30), which can be 100:4, 100:5, 100:8, 100:10, 100:15, 100:20, 100:25 or 100:30, and other values within the above range are also possible, which are not limited herein. When the amount of coating agent is too small, it is difficult to form a uniform polymer coating layer on the surface of graphite. When the amount of coating agent is too large, the thickness of the polymer coating layer deposited on the surface of graphite is too large, which hinders the interface transmission of the negative electrode material and affects the capacity of the negative electrode material.

[0087] In some embodiments, the liquid phase coating time is 4h-24h, which can be 4h, 5h, 8h, 10h, 15h, 18h, 20h, 23h, 24h, etc. When 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 graphite particles, and the coating layer on the surface of graphite is unevenly distributed. When the liquid phase coating time is too long, the production efficiency is reduced, which is not conducive to industrialized preparation.

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

[0089] By controlling the solid-liquid ratio, time and the amount of coating agent added in the liquid phase coating, the polymer formed by the coating agent with active groups can be uniformly deposited and adhered to the surface of the graphite under stirring.

[0090] In some embodiments, the mixture is subjected to solid-liquid separation after liquid phase coating to obtain a solid for drying to obtain a precursor.

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

[0092] In some embodiments, the drying treatment includes at least one of air blowing drying, vacuum drying, freeze drying and spray drying.

[0093] S30, the precursor is subjected to carbonization treatment to obtain a 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 active material can include, but is not limited to, at least one of lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganese oxide (LiMn2O4), lithium nickel manganese oxide (LiNiMnO4), or lithium iron phosphate (LiFePO4). 4) 0.5 Mn 1.5 O4) or lithium iron phosphate (LiFePO4).

[0102] In some embodiments, the negative electrode sheet 2 includes a negative current collector 201 and a negative active material layer 202 disposed on at least one surface of the negative current collector.

[0103] In some embodiments, the negative current collector 201 can use at least one of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, or a carbon-based current collector, and can also be 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 active material layer 202 includes a negative material, which is the negative material of the first aspect described above or the negative material obtained by the preparation method described above.

[0104] The battery provided by the embodiments of the present application has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low swelling. The battery can be a lithium ion battery, a sodium ion battery, a solid electrolyte battery, etc., without limitation.

[0105] The embodiments of the present application will be further described in the following embodiments. The embodiments of the present application are not limited to the following specific embodiments. Within the scope of the same rights, appropriate changes can be made.

[0106] The embodiments of the present application will be further described in the following embodiments. The embodiments of the present application are not limited to the following specific embodiments. Within the scope of the same rights, appropriate changes can be made.

[0107] Embodiment 1

[0108] (1) 7 parts of phenylenediamine and an appropriate amount of pure water were mixed, a 0.5 mol / L phosphoric acid solution was used to adjust the pH of the solution to 4, 7 parts of a 1 mol / L ammonium persulfate solution was added to adjust the oxidation environment of the mixed solution, and the reaction was continuously stirred for 1 h to occur a prepolymerization reaction, to obtain a prepolymerization solution.

[0109] (2) The prepolymerization solution, 100 parts of graphite (average particle size 17 μm) and an appropriate amount of pure water were stirred and mixed to form a uniform mixed solution at a solid-liquid ratio of 1:3, and liquid coating treatment was carried out under stirring for 12 h, the polyphenylenediamine in the prepolymerization solution was deposited and attached to the surface of the graphite particles, and then the mixed solution was centrifuged, and the centrifuged product was moved to a drying oven for drying at 120°C for 36 h, to obtain a precursor. ​

[0110] (3) Under the atmosphere of nitrogen, the precursor is carbonized at 1250℃ for 4h, and then naturally cooled to obtain the negative electrode material.

[0111] Example 2

[0112] Different from Example 1 is that:

[0113] (1) 7 parts of aminostyrene and appropriate amount of pure water are mixed, 0.5 mol / L phosphoric acid solution is used to adjust the pH of the solution to 4, 7 parts of ammonium persulfate solution with a concentration of 1 mol / L is added to adjust the oxidation environment of the mixed solution, and the pre-polymerization reaction is continuously stirred for 1h.

[0114] Example 3

[0115] Different from Example 1 is that:

[0116] (1) 7 parts of phenylenediamine and appropriate amount of pure water are mixed, 0.5 mol / L phosphoric acid solution is used to adjust the pH of the solution to 5, 7 parts of ammonium persulfate solution with a concentration of 1 mol / L is added to adjust the oxidation environment of the mixed solution, and the pre-polymerization reaction is continuously stirred for 1h.

[0117] Example 4

[0118] Different from Example 1 is that:

[0119] (1) 7 parts of phenylenediamine and appropriate amount of pure water are mixed, 0.5 mol / L phosphoric acid solution is used to adjust the pH of the solution to 7, 7 parts of ammonium persulfate solution with a concentration of 1 mol / L is added to adjust the oxidation environment of the mixed solution, and the pre-polymerization reaction is continuously stirred for 1h.

[0120] Example 5

[0121] Different from Example 1 is that:

[0122] (1) 7 parts of maleic anhydride and appropriate amount of pure water are mixed, the solution temperature is increased to 50℃ and continuously stirred for 2h to occur pre-polymerization reaction.

[0123] Example 6

[0124] Different from Example 5 is that:

[0125] (1) 7 parts of maleic anhydride and appropriate amount of pure water are mixed, the solution temperature is increased to 70℃ and continuously stirred for 2h to occur pre-polymerization reaction.

[0126] Example 7

[0127] Different from Example 5 is that:

[0128] (1) Take 7 parts of maleic anhydride and mix with appropriate amount of pure water, raise the solution temperature to 50°C and continue to stir for 4h to occur pre-polymerization reaction.

[0129] Example 8

[0130] Different from example 1 is:

[0131] (1) Take 7 parts of phenylenediamine and mix with appropriate amount of pure water, use 0.5 mol / L of 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 oxidation environment of the mixed solution, continue to stir for 1h to occur pre-polymerization reaction.

[0132] Example 9

[0133] Different from example 1 is:

[0134] (1) Take 7 parts of phenylenediamine and mix with appropriate amount of pure water, use 0.5 mol / L of 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 oxidation environment of the mixed solution, continue to stir for 1h to occur pre-polymerization reaction.

[0135] Example 10

[0136] Different from example 1 is:

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

[0138] Example 11

[0139] Different from example 1 is:

[0140] (1) Take 7 parts of maleic anhydride and mix with appropriate amount of pure water, raise the solution temperature to 50°C and continue to stir for 4h to occur pre-polymerization reaction.

[0141] Example 12

[0142] Different from example 1 is:

[0143] (1) 25 parts of phenylenediamine and appropriate amount of pure water are mixed, 0.5 mol / L phosphoric acid solution is used to adjust the pH of the solution to 4, 25 parts of ammonium persulfate solution with a concentration of 1 mol / L is added to adjust the oxidation environment of the mixed solution, and the pre-polymerization reaction is carried out for 1 h under continuous stirring.

[0144] Example 13

[0145] Different from example 1 is that:

[0146] (3) The precursor is carbonized at 1600℃ for 4 h under a nitrogen atmosphere, and the negative electrode material is obtained by natural cooling.

[0147] Example 14

[0148] Different from example 1 is that:

[0149] (3) The precursor is carbonized at 2300℃ for 4 h under a nitrogen atmosphere, and the negative electrode material is obtained by natural cooling.

[0150] Example 15

[0151] Different from example 1 is that:

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

[0153] (3) The precursor is carbonized at 2300℃ for 4 h under a nitrogen atmosphere, and the negative electrode material is obtained by natural cooling.

[0154] Example 16

[0155] Different from example 1 is that:

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

[0157] (3) The precursor is carbonized at 2300℃ for 4 h under a nitrogen atmosphere, and the negative electrode material is obtained by natural cooling.

[0158] Example 17

[0159] Different from example 1 is that:

[0160] (1) Take 7 parts of phenylenediamine and mix with appropriate amount of pure water, adjust the pH of the solution to 4 using 0.5 mol / L phosphoric acid solution, add 7 parts of ammonium persulfate solution with a concentration of 1 mol / L to adjust the oxidation environment of the mixed solution, continuously stir for 3h to occur pre-polymerization reaction, and obtain a pre-polymerization solution.

[0161] Comparative Example 1

[0162] Different from Example 1:

[0163] (2) The pre-polymerization solution, 100 parts of graphite (average particle size of 17 μm) and appropriate amount of pure water are stirred and mixed to form a uniform mixed solution with a solid-liquid ratio of 1:1.1, and continuously stirred for 12h, and the phenylenediamine in the mixed solution occurs polymerization reaction, and then the mixed solution is centrifuged to separate the solid and liquid, and then moved to a drying oven at 120℃ for drying for 36h to obtain a precursor.

[0164] Comparative Example 2

[0165] Different from Example 1:

[0166] (1) Take 0.8 parts of phenylenediamine and mix with appropriate amount of pure water, adjust the pH of the mixed solution to 4 using 0.5 mol / L phosphoric acid solution, add 0.8 parts of ammonium persulfate solution with a concentration of 1 mol / L to adjust the oxidation environment of the mixed solution, and continuously stir for 1h to occur pre-polymerization reaction.

[0167] (2) The pre-polymerization solution, 100 parts of graphite (average particle size of 17 μm) and appropriate amount of pure water are stirred and mixed to form a uniform mixed solution with a solid-liquid ratio of 1:1.3, and continuously stirred for 12h, and the phenylenediamine in the mixed solution occurs polymerization reaction, and then the mixed solution is centrifuged to separate the solid and liquid, and then moved to a drying oven at 120℃ for drying for 36h to obtain a precursor.

[0168] Comparative Example 3

[0169] Different from Example 1:

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

[0171] Comparative Example 4

[0172] Different from Example 1:

[0173] (1) Take 7 parts of phenylenediamine and mix with appropriate amount of pure water, adjust the pH of the mixed solution to 10 using 0.5 mol / L phosphoric acid solution, add 7 parts of ammonium persulfate solution with a concentration of 1 mol / L to adjust the oxidation environment of the mixed solution, and continuously stir for 1h to occur pre-polymerization reaction.

[0174] Comparative Example 5

[0175] Different from Example 1 is that:

[0176] (1) 7 parts of phenylenediamine and appropriate amount of pure water were mixed, 0.5 mol / L phosphoric acid solution was used to adjust the pH of the solution to 4, 7 parts of ammonium persulfate solution with a concentration of 1 mol / L was added to adjust the oxidation environment of the mixed solution, and the pre-polymerization reaction was carried out for 6 h under continuous stirring. The pre-polymerization solution was obtained.

[0177] Comparative Example 6

[0178] Different from Example 1 is that:

[0179] (1) 7 parts of phenylenediamine and appropriate amount of pure water were mixed, 0.5 mol / L phosphoric acid solution was used to adjust the pH of the solution to 4, 7 parts of ammonium persulfate solution with a concentration of 1 mol / L was added to adjust the oxidation environment of the mixed solution, and the pre-polymerization reaction was carried out for 6 h under continuous stirring. The pre-polymerization solution was obtained.

[0180] Comparative Example 7

[0181] Different from Example 1 is that:

[0182] (2) The pre-polymerization solution, 100 parts of graphite (average particle size of 17 μm) and appropriate amount of pure water were mixed to form a uniform mixed solution with a solid-liquid ratio of 1:3 under stirring, and the liquid phase coating treatment was carried out for 2 h under stirring. The polyphenylenediamine in the pre-polymerization solution was deposited and attached to the surface of the graphite particles. Then the mixed solution was centrifuged, and the centrifuged product was moved to a drying oven for drying at 120°C for 36 h to obtain the precursor.

[0183] Test method

[0184] (1) Test method for particle size distribution of negative electrode material: the particle size distribution range of the negative electrode material was tested by Malvern 3000 laser particle size analyzer. In a 50 mL beaker, a dispersant (ethanol, pure water and low foam surfactant) and a tested sample were placed, a certain amount of pure water was added, and a glass rod was used to stir thoroughly to make the sample uniformly dispersed. The particle size test was carried out at a pump speed of 2400 r / min-2500 r / min and a frequency of 19.5 Hz.

[0185] (2) Test method for tap density of negative electrode material: the negative electrode material was placed in the sample bin of the tap density instrument, and the sample volume was recorded after 1000 times of vibration, and the tap density was calculated according to the mass-volume ratio.

[0186] (3) Test method of specific surface area of negative electrode material: Use fine high-bo DX400 to test the specific surface of the material. Put the sample into the sample tube, use the isothermal jacket on the sample tube, put the filling rod into the bubble tube, put the snap ring and O-ring on the bubble tube, and then put the assembled sample bubble tube into the corresponding analysis station for testing. At a constant low temperature, the adsorption amount of gas on the surface of the solid is measured at different relative pressures, and then the monolayer adsorption amount of the sample is calculated based on the Brunauer-Emmett-Teller adsorption theory and its formula (BET formula), so as to calculate the specific surface area of the material.

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

[0188] (5) Test method of surface morphology, section and coating layer of negative electrode material particles: Use HITACHI-S4800 scanning electron microscope to observe the micro morphology of the surface of the negative electrode material. The steps are as follows: paste the conductive glue on the sample cup, evenly coat the sample on the conductive glue, blow away the sample that is not fixed firmly with ear cleaning ball, and put it into the scanning electron microscope room for testing. The steps of section and coating layer test are as follows: first, use HITACHI-E3500 ion milling machine to polish the graphite particles, coat a little carbon conductive glue on the edge of the sample table, and evenly sprinkle the graphite sample, press gently with a glass sheet, and after 2 min of conductive glue drying, blow away the excess sample with ear cleaning ball. Put the sample table on the sample seat, adjust the sample position, complete the adjustment, adjust the air flow to the maximum ion beam current, set the polishing time for sample processing. After completion, use HITACHI-S4800 scanning electron microscope to observe the section and coating layer of the surface of the negative electrode material.

[0189] (6) Raman test method of negative electrode material: Use HORIBA-XPLORA type laser confocal Raman spectrometer to test the Raman scattering spectrum, and the laser wavelength is 532 nm. Collect data from 30 points on the surface of the negative electrode material particles respectively, and then perform peak fitting on the scattering spectrum obtained from each point respectively to obtain the peak area ratio of the D characteristic peak in the range of 1300 cm -1 ~1350cm -1 and the G characteristic peak in the range of 1500 cm -1 ~1580cm -1 . D G D G ​​​The average value of A is B. After sectioning the negative electrode material particles, the particles are cut open using a HITACHI-E3500 ion milling machine, and the sectioned areas are tested. Ten points in the sectioned areas of the particles are randomly selected for Raman spectrum scanning, and the peak area ratio of the D characteristic peak in the range of 1300 cm -1 1350 cm -1 The average value of A is B. After sectioning the negative electrode material particles, the particles are cut open using a HITACHI-E3500 ion milling machine, and the sectioned areas are tested. Ten points in the sectioned areas of the particles are randomly selected for Raman spectrum scanning, and the peak area ratio of the D characteristic peak in the range of 1300 cm -1 1580 cm -1 The average value of A is B. After sectioning the negative electrode material particles, the particles are cut open using a HITACHI-E3500 ion milling machine, and the sectioned areas are tested. Ten points in the sectioned areas of the particles are randomly selected for Raman spectrum scanning, and the peak area ratio of the D characteristic peak in the range of 1300 cm D / I G / I D / I G The average value of A is B. After sectioning the negative electrode material particles, the particles are cut open using a HITACHI-E3500 ion milling machine, and the sectioned areas are tested. Ten points in the sectioned areas of the particles are randomly selected for Raman spectrum scanning, and the peak area ratio of the D characteristic peak in the range of 1300 cm

[0190] (7) Polymer degree of polymerization measurement method: The degree of polymerization of the polymer in the prepolymerization solution is tested using a gel chromatograph. Gel permeation chromatography (GPC) is also known as size exclusion chromatography. It is a liquid chromatography method in which a solvent is used as a mobile phase and a porous filler (such as porous silica gel or porous resin) is used as a separation medium. As the solvent is eluted, molecules of different sizes are separated. Larger molecules are eluted first, and smaller molecules are eluted later. The obtained polymer molecular weight and its distribution are analyzed, and the obtained polymer molecular weight / molecular weight of monomer is the degree of polymerization.

[0191] (8) Atomic force microscope test method: The surface flatness of the graphite material is tested using an atomic force microscope (AFM). One end of a microcantilever that is extremely sensitive to weak force is fixed, and the other end has a small needle tip, which is in light contact with the sample surface. Due to the extremely weak repulsive force between the atoms at the tip of the needle and the atoms on the sample surface, the microcantilever will deflect slightly. By detecting the deflection and applying feedback to control the constant repulsive force, the position changes of the microcantilever corresponding to each point can be obtained, and thus the image of the sample surface topography can be obtained. From the image, a 1 μm 1 μm test area is randomly selected, and the absolute value of the arithmetic mean of the height deviation of the test area relative to the reference plane is S nm, 15 nm≤S≤60 nm, wherein S= , n≥5, and 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. In this application, the tapping mode is used: the probe maintains a fixed frequency vibration in the Z axis, and when it reaches the bottom, it contacts the sample, causing little damage to the sample and having high resolution. In this application, the reference plane of the atomic force microscope is the equipotential surface determined by detecting and analyzing the weak interaction force between the needle tip and the atoms on the sample surface, which is the plane corresponding to the average value of the height values of all test points.

[0192] (9) Electrochemical performance test method: the negative electrode material prepared in the examples and the comparative examples is respectively dissolved in deionized water according to the mass ratio of 96.5:1.5:1 of the negative electrode material, carboxymethyl cellulose and butadiene rubber, the solid content is controlled to be 50%, and the negative electrode sheet is coated on the copper foil current collector, vacuum dried, and prepared. A coin cell is assembled in an argon-filled glove box with a lithium metal sheet as a counter electrode. The charge-discharge test is carried out at a current density of 0.1C and a charge-discharge interval of 0.01-1.5V. Cycle charge-discharge to obtain the first reversible specific capacity, the first charge capacity and the first discharge capacity. The first coulombic efficiency = the first discharge capacity / the first charge capacity.

[0193] After the above test is completed, the charging current density is set to 0.2C, and the lithium intercalation discharge test is carried out at a current density of 0.2C, 0.5C, 1C and 2C, respectively. The 2C / 0.2C rate performance = 0.2C lithium intercalation discharge capacity / 2C lithium intercalation discharge capacity.

[0194] The preparation process parameters and corresponding test results of the examples 1-17 (abbreviated as S1-S17) and the comparative examples 1-7 (abbreviated as D1-D7) prepared in the application are shown in Table 1 and Table 2.

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

[0196]

[0197] Table 2. Performance parameters of the negative electrode material and the battery prepared by each example and comparative example

[0198]

[0199] The negative electrode material prepared by the preparation method provided in the application is prepared by pre-polymerizing the coating agent with active groups, and the polymerization degree of the polymer in the pre-polymerization solution obtained is in the range of 3-30. The polymer is mainly an oligomer, and the molecular chain is small, which can be uniformly dispersed in the pre-polymerization solution. Then, the graphite is added to the pre-polymerization solution for liquid phase coating. In the coating process, the polymer uniformly dispersed in the pre-polymerization 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 pre-polymerization solution is controlled to be 1:(1.3-3.5), and the mass ratio of graphite to coating agent is 100:(4-30), so that the thickness of the polymer coating layer uniformly attached to the surface of the graphite is in a suitable range, which improves the capacity of the negative electrode material and the lithium ion interface transmission 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 embodiments 1-2 and 5, the A value and A-B value of the prepared negative electrode material do not change much with different coating agents with active groups, and the S value of the negative electrode material is in the range of 15-60 nm, and the specific capacity, the first coulombic efficiency and the rate performance of the negative electrode material are good.

[0203] According to the test data of embodiments 1 and 3-4, as the pH value increases, the A value of the prepared negative electrode material gradually decreases, and the corresponding A-B value also gradually decreases, and the S value also gradually decreases, indicating that the pH value can affect the polymerization degree of the polymer in the prepolymerization solution, and then the disorder degree of the carbon material in the carbon layer is slightly reduced, the material surface flatness is slightly increased, the capacity and the first coulombic efficiency of the negative electrode material are decreased, and the rate performance is not changed much.

[0204] According to the test data of embodiments 5-7, when the coating agent is a coating agent with carbon-carbon double bond, as the prepolymerization temperature increases, the A value of the prepared negative electrode material decreases; as the holding time is prolonged, the A value of the prepared negative electrode material also decreases; this is because the prepolymerization temperature and the holding time can affect the polymerization degree of the polymer formed in the prepolymerization solution, the polymer molecular chain grows, and then the disorder degree of the carbon layer on the surface of the negative electrode material is affected, and within the range of the prepolymerization temperature and the holding time in the present application, it is helpful to improve the capacity and the first coulombic efficiency of the negative electrode material.

[0205] According to the test data of embodiments 1 and 8, 9, as the amount of the redox agent increases, the polymerization degree of the polymer in the prepolymerization solution gradually increases, the disorder degree 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, A-B also decreases, and S also gradually decreases.

[0206] According to the test data of embodiments 1 and 10, during the stirring reaction of graphite and prepolymerization solution, controlling the solid-liquid ratio in a suitable range can control the concentration of polymer molecules in a unit volume of prepolymerization solution. As the concentration decreases, the uniformity of the polymer deposited on the graphite particles decreases. As the solid-liquid ratio decreases, the A value of the negative electrode material gradually decreases, the A-B value also decreases, and the S value significantly increases.

[0207] According to the test data of embodiments 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 surface of the graphite increases, the A value of the prepared negative electrode material gradually increases, the corresponding A-B value also gradually increases, and the S value significantly decreases.

[0208] According to the test data of Example 1 and Examples 13-14, as the carbonization temperature increases, the disorder degree of the polymer carbonized layer deposited on the surface of the graphite gradually decreases, the A value of the prepared negative electrode material gradually decreases, and the corresponding A-B also gradually decreases, and the S value changes little.

[0209] According to the test data of Examples 14-16, as the particle size of the raw material changes, the thickness of the polymer layer deposited on the surface of the graphite gradually increases, the corresponding coating layer thickness also gradually increases, the A value and the corresponding A-B of the carbonized material also gradually increase, and the S value changes little. It shows that the preparation method of the application is suitable for the preparation of graphite materials with different particle sizes and high surface disorder characteristics.

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

[0211] Compared with Example 1, in the preparation process of Comparative Example 1, the solid-liquid ratio of graphite and prepolymerization solution is too high, the deposition reaction of polymer in the prepolymerization solution on the graphite particles is not uniform, the polymer has self-nucleation growth and agglomeration phenomenon, the prepared negative electrode material has a Raman value A>3.00, A-B>2.10, S>60.0 nm, the specific surface area of the negative electrode material is high, and the first coulombic efficiency and the rate are obviously reduced.

[0212] Compared with Example 1, in the preparation process of Comparative Example 2, the amount of coating agent is too low, the concentration of polymer in the prepolymerization solution is also reduced, and the polymer is difficult to deposit on the graphite particles to form a uniform coating layer, the prepared negative electrode material has a Raman value A<1.70, A-B<1.22, S>60.0 nm, the specific surface area of the negative electrode material is increased, and the capacity, the first efficiency and the rate of the negative electrode material are also reduced.

[0213] Compared with Example 1, in the preparation process of Comparative Example 3, the carbonization temperature is too low, the disorder degree of the carbon layer coated on the outside of the graphite particles is high, and the defects in the inside of the graphite particles are also increased synchronously, the prepared high-structural-disorder carbon-coated graphite material has a Raman value A>3.00, but A-B is in the range of 1.22-2.10, and the S value is slightly higher than that of Example 1, the specific surface area of the negative electrode material is high, and the first efficiency is reduced.

[0214] Compared with Example 1, in the preparation process of Comparative Example 4, the pH value of the prepolymerization solution is too high, the polymerization degree of the polymer in the prepolymerization solution increases, which leads to the decrease of the disorder degree of the carbon layer coated on the outside of the graphite particles, the prepared negative electrode material has a Raman value A<1.70, but A-B is in the range of 1.22-2.10, and S<15 nm, the specific surface area of the negative electrode material is high, and the first efficiency and the rate are reduced.

[0215] Compared with Example 1, in the preparation process of Comparative Example 5, the stirring time of pre-polymerization is controlled to be too long, the polymerization degree of the polymer in the pre-polymerization solution is increased, the disorder degree of the carbon layer outside the graphite particles is reduced, the Raman value A of the prepared negative electrode material is less than 1.70, A-B is less than 1.22, the S value is in the range of 15nm-60nm, and the capacity, the initial efficiency and the rate of the negative electrode material are reduced.

[0216] Compared with Example 1, in the preparation process of Comparative Example 6, no pre-polymerization treatment is carried out, which leads to that the coating agent is not completely deposited on the surface of the graphite particles, the thickness of the coating layer is reduced under the same coating amount, the Raman value A of the prepared negative electrode material is less than 1.70, A-B is less than 1.22, S is greater than 60.0nm, the specific surface area of the negative electrode material is increased, the side reaction of the negative electrode material with the electrolyte is intensified, and the capacity, the initial efficiency and the rate of the negative electrode material are reduced.

[0217] Compared with Example 1, in the preparation process of Comparative Example 7, the stirring time after adding the graphite powder is too short, which leads to that the coating agent is not uniformly distributed on the surface of the graphite particles, the Raman value A of the prepared negative electrode material is greater than 3.00, A-B is greater than 2.10, S is greater than 60.0nm, the specific surface area of the negative electrode material is increased, the side reaction of the negative electrode material with the electrolyte is intensified, and the capacity, the initial efficiency and the rate of the negative electrode material are reduced.

[0218] Although the present application is disclosed with the preferred embodiments, 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 the present application, therefore the protection scope of the present application should be defined by the scope of the claims.

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 includes amorphous carbon, and the thickness of the carbon layer is 15 nm to 250 nm. 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 value of any test point in the test area relative to the reference plane.

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 median particle size of the negative electrode material is 4μm~25μm.

4. 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.

5. 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 .

6. A method for preparing a negative electrode material for a lithium-ion battery as described in any one of claims 1 to 5, 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; wherein 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 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). 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.

7. The method for preparing the negative electrode material of the lithium-ion battery according to claim 6, 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.

8. The method for preparing the negative electrode material of the lithium-ion battery according to claim 6, characterized in that, The carbonization process is carried out under a protective atmosphere.

9. 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 5 or the negative electrode material of the lithium-ion battery prepared by the preparation method according to any one of claims 6 to 8.

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