A negative electrode material, a preparation method thereof, an electrochemical device, and an electronic device

Abstract

This application provides a negative electrode material and its preparation method, an electrochemical device, and an electronic device. The negative electrode material includes graphite and a coating located on at least a portion of the surface of the graphite. 13 The solid-state NMR spectrum of the C13 material exhibits characteristic peaks ranging from 150 ppm to 172 ppm; the anode material shows a peak at 1600 cm⁻¹ in the infrared spectrum. ‑1 Up to 1700cm ‑1 Characteristic peaks. Anode materials that meet these characteristics can improve the energy density and fast-charging performance of electrochemical devices.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, and in particular to a negative electrode material, a preparation method thereof, an electrochemical device, and an electronic device. BACKGROUND

[0002] Lithium ion batteries are widely used in notebook computers, mobile phones, new energy electric vehicles and other fields as a new type of high-energy green battery. However, as the penetration rate of lithium ion batteries is increasing, the endurance anxiety of various devices has been a bottleneck limiting the application of lithium ion batteries. Therefore, it is crucial to improve the energy density and fast charging capability of lithium ion batteries. Generally, improving the energy density often has a negative impact on the fast charging capability, and improving the fast charging capability also causes a loss of energy density, and the two are incompatible.

[0003] In order to solve the above problems, it is necessary to improve the specific capacity and rate performance of the negative electrode material (such as graphite) at the same time, but it is difficult to achieve the above results by conventional coating. Therefore, it is necessary to provide a coated negative electrode material that can simultaneously achieve high energy density and high fast charging performance for lithium ion batteries. SUMMARY

[0004] The purpose of the present application is to provide a negative electrode material, a preparation method thereof, an electrochemical device, and an electronic device to improve the energy density and fast charging performance of the electrochemical device. The specific technical solutions are as follows:

[0005] The first aspect of the present application provides a negative electrode material, which comprises graphite and a coating on at least a part of the surface of the graphite, and the negative electrode material has 13 a characteristic peak of 150 ppm to 172 ppm in a C solid-state nuclear magnetic spectrum; and a characteristic peak of 1600 cm -1 to 1700 cm -1 in an infrared spectrum. The negative electrode material comprises surface-coated graphite, the coating is derived from a supramolecular polymer polymerized in situ on the surface of the graphite, and then low-temperature carbonization is performed to obtain the surface-coated graphite. The above-mentioned surface-coated graphite can retain the nitrogen-doped carbon skeleton structure through low-temperature carbonization of the supramolecular polymer, effectively improving the electronic conductivity of the graphite surface; on the other hand, the existence of amide bonds and / or imine bonds on the surface of the graphite can improve the adsorption capacity of lithium ions, so that the surface-coated graphite has excellent properties such as high specific capacity and high rate performance. The above-mentioned surface-coated graphite is applied to an electrochemical device, which can improve the energy density and fast charging performance of the electrochemical device.

[0006] In an embodiment of the present application, the coating has carbon-oxygen double bonds, and at least part of the coating has carbon-nitrogen double bonds. The coating satisfies the above characteristics, and the surface-coated graphite obtained by low-temperature carbonization can retain the nitrogen-doped carbon skeleton structure thereof, further improving the electronic conductivity of the graphite surface; at the same time, the surface-coated graphite also has a high adsorption capacity for lithium ions, so that it has a high specific capacity and a high rate performance. When the above surface-coated graphite is applied to an electrochemical device, the energy density and fast-charging performance of the electrochemical device can be further improved.

[0007] In an embodiment of the present application, the coating includes at least one of the following structural formulas:

[0008] .

[0009] The coating includes the above structural formula, and the above structural formula includes carbon-oxygen double bonds and / or carbon-nitrogen double bonds. The surface-coated graphite obtained by low-temperature carbonization can retain the nitrogen-doped carbon skeleton structure thereof, further improving the electronic conductivity of the graphite surface; at the same time, the surface-coated graphite also has a high adsorption capacity for lithium ions, so that it has a high specific capacity and a high rate performance. When the above surface-coated graphite is applied to an electrochemical device, the energy density and fast-charging performance of the electrochemical device can be further improved.

[0010] In an embodiment of the present application, the precursor of the coating includes a carboxylic acid compound containing a benzene ring and a nitrogen-containing compound, the nitrogen-containing compound includes at least one of a cyclic nitrogen-containing heterocyclic compound or a linear nitrogen-containing compound, the carboxylic acid compound containing a benzene ring includes at least one of pyromellitic acid, trimesic acid, benzenehexacarboxylic acid, benzene-1,3-dicarboxylic acid, diphenic acid, or terephthalic acid, the cyclic nitrogen-containing heterocyclic compound includes at least one of melamine, imidazole, 2-methylimidazole, pyrrole, pyridine, or benzimidazole, and the linear nitrogen-containing compound includes at least one of diisocyanate, polyacrylonitrile, acrylonitrile, or urea. The mass percentage content of the coating in the negative electrode material is 0.5% to 2% based on the total mass of the graphite. The coating is derived from the mixed carbonization product of the precursor of the coating. The above precursor of the coating is selected, and the mass percentage content of the coating in the negative electrode material is regulated within the scope of the present application. The surface-coated graphite obtained by low-temperature carbonization can retain the nitrogen-doped carbon skeleton structure thereof, further improving the electronic conductivity of the graphite surface; at the same time, the presence of amide bonds and / or imine bonds on the surface of the graphite can further improve the adsorption capacity for lithium ions, so that the surface-coated graphite has a high specific capacity and a high rate performance. Furthermore, the coating in the negative electrode material has a suitable mass percentage content. When the above surface-coated graphite is applied to an electrochemical device, the energy density and fast-charging performance of the electrochemical device can be further improved.

[0011] In one embodiment of this application, the negative electrode material exhibits N2CH2 molecular fragments at temperatures between 500°C and 550°C in mass spectrometry analysis. The mass spectrometry analysis of the negative electrode material satisfies the above-mentioned characteristics, indicating that the negative electrode material contains the structural fragment of formula I-2; simultaneously, the negative electrode material possesses a nitrogen-doped carbon framework structure, which can further improve the electronic conductivity of the graphite surface; applying the above-mentioned negative electrode material to an electrochemical device can further improve the fast-charging performance of the electrochemical device.

[0012] In one embodiment of this application, the weight loss rate of the negative electrode material in an inert atmosphere from 35°C to 800°C is 0.1% to 0.3%. By controlling the weight loss rate of the negative electrode material in an inert atmosphere from 35°C to 800°C within the range of this application, the coating on the surface of the negative electrode material can be carbonized at a certain temperature to form a relatively stable and effective coating layer structure. Applying the above-mentioned negative electrode material to an electrochemical device can further improve the energy density and fast charging performance of the electrochemical device.

[0013] In one embodiment of this application, the graphitization degree of the negative electrode material is 93% to 95%. By controlling the graphitization degree of the negative electrode material within the scope of this application, the negative electrode material has a high graphitization degree, a high specific capacity, and a high lithium-ion diffusion coefficient. Applying the above-mentioned negative electrode material to an electrochemical device can further improve the energy density and fast-charging performance of the electrochemical device.

[0014] In one embodiment of this application, the negative electrode material satisfies at least one of the following conditions: (1) the specific surface area SSA of the negative electrode material is 1m². 2 / g to 3m 2 / g; (2) The Dv50 of the negative electrode material is 12μm to 16μm; (3) The tap density TD of the negative electrode material is 0.95g / cm³. 3 Up to 1.05 g / cm 3 .

[0015] In one embodiment of this application, the graphite includes at least one of artificial graphite or natural graphite. Using the aforementioned graphite, the graphite exhibits high electronic conductivity, lithium-ion transport rate, and specific capacity. Surface-coated graphite, obtained after surface coating, has even higher specific capacity and higher rate performance, which can further improve the energy density and fast-charging performance of the electrochemical device.

[0016] A second aspect of this application provides a method for preparing the negative electrode material in any of the foregoing embodiments, comprising the following steps:

[0017] (1) dissolving a precursor of the coating in a solution, and then mixing the precursor with graphite uniformly, so that the coating is at least on a part of the surface of the graphite, to obtain a slurry; the precursor of the coating comprises a carboxylic acid compound containing a benzene ring and a nitrogen-containing compound, the nitrogen-containing compound comprises at least one of a cyclic nitrogen-containing heterocyclic compound or a linear nitrogen-containing compound, the carboxylic acid compound containing a benzene ring comprises at least one of pyromellitic acid, trimesic acid, mellitic acid, benzene malonic acid, diphenic acid or terephthalic acid, the cyclic nitrogen-containing heterocyclic compound comprises at least one of melamine, imidazole, 2-methyl imidazole, pyrrole, pyridine or benzimidazole, and the linear nitrogen-containing compound comprises at least one of diisocyanate, polyacrylonitrile, acrylonitrile or urea;

[0018] (2) after the slurry is left to stand at 80-120℃ for 12-24h, performing suction filtration, water washing and drying to obtain a powder;

[0019] (3) performing heat treatment on the powder at 750-850℃ in an inert atmosphere, and keeping the temperature for 2-5h to obtain a negative electrode material, wherein the mass percentage of the coating in the negative electrode material is 0.5-2%.

[0020] The negative electrode material is prepared by the above method, and the precursor of the coating is selected from the precursors of the application. The coating is derived from a supramolecular polymer which is polymerized in situ on the surface of the graphite, and then is subjected to low-temperature carbonization to obtain the surface-coated graphite. The surface-coated graphite is subjected to low-temperature carbonization by the supramolecular polymer, so that the carbon skeleton structure doped with nitrogen can be retained, and the electronic conductivity of the surface of the graphite can be further improved. On the other hand, the existence of amide bonds and / or imine bonds on the surface of the graphite can improve the adsorption capacity of lithium ions, so that the surface-coated graphite has high specific capacity and high rate performance. When the surface-coated graphite is applied to an electrochemical device, the energy density and fast-charging performance of the electrochemical device can be further improved.

[0021] The third aspect of the application provides an electrochemical device comprising a negative electrode tab, wherein the negative electrode tab comprises a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector, and the negative electrode material layer comprises the negative electrode material in any one of the preceding embodiments or the negative electrode material prepared by the preparation method in any one of the preceding embodiments. Therefore, the electrochemical device provided by the application has good energy density and fast-charging performance.

[0022] The fourth aspect of the application provides an electronic device comprising the electrochemical device in any one of the preceding embodiments. Therefore, the electronic device provided by the application has good energy density and fast-charging performance.

[0023] The application has the following beneficial effects:

[0024] The application provides a negative electrode material and a preparation method thereof, an electrochemical device and an electronic device. The negative electrode material comprises graphite and a coating on at least part of the surface of the graphite, and the negative electrode material has 13 a characteristic peak of 150 ppm to 172 ppm in a C solid-state nuclear magnetic spectrum; and a characteristic peak of 1600 cm -1 to 1700 cm -1 in an infrared spectrum. The negative electrode material satisfies the above characteristics, and can improve the energy density and fast charging performance of the electrochemical device.

[0025] Of course, implementing any product or method of the application does not necessarily require achieving all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only constitute some embodiments of the application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0027] Figure 1 FIG. 1 is a scanning electron microscope (SEM) image of the negative electrode material of Embodiment 1 of the application;

[0028] Figure 2 FIG. 2 is a C solid-state nuclear magnetic spectrum of the negative electrode material of Embodiment 1 of the application; 13

[0029] Figure 3 FIG. 3 is an infrared spectrum of the negative electrode material of Embodiment 1 of the application. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments only constitute some of the embodiments of the application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the application also belong to the scope of protection of the application.

[0031] It should be noted that in the specific embodiments of the application, the lithium ion battery is taken as an example of the electrochemical device to explain the application, but the electrochemical device of the application is not limited to the lithium ion battery.

[0032] The first aspect of the application provides a negative electrode material comprising graphite and a coating on at least part of the surface of the graphite, and the negative electrode material has 13 ​C solid-state nuclear magnetic spectrum has a characteristic peak of 150 ppm to 172 ppm, indicating that there is an amide bond or an imine bond on the surface of the negative electrode material; the negative electrode material has a characteristic peak of 1600 cm -1 to 1700 cm -1 in the infrared spectrum, indicating that there is a C=N double bond stretching vibration peak or a C=O double bond stretching vibration peak on the surface of the negative electrode material. The above-mentioned "coating on at least part of the surface of graphite" means that the coating can be located on part of the surface of graphite, or can be located on the entire surface of graphite.

[0033] The inventors have found that the negative electrode material provided in the present application includes surface-coated graphite, the coating is derived from in-situ polymerization of supramolecular polymers on the surface of graphite, and then low-temperature carbonization is performed to obtain surface-coated graphite. The above-mentioned surface-coated graphite can retain its nitrogen-doped carbon skeleton structure through low-temperature carbonization of supramolecular polymers, effectively improving the electronic conductivity of the surface of graphite; on the other hand, the existence of amide bonds and / or imine bonds on the surface of graphite can improve the adsorption capacity of lithium ions, so that the surface-coated graphite has excellent properties such as high specific capacity and high rate performance. The application of the above-mentioned surface-coated graphite in electrochemical devices can improve the energy density and fast charging performance of the electrochemical devices.

[0034] In an embodiment of the present application, the coating has carbon-oxygen double bonds, and at least part of the coating has carbon-nitrogen double bonds. The coating satisfies the above-mentioned characteristics, and the surface-coated graphite obtained by low-temperature carbonization can retain its nitrogen-doped carbon skeleton structure, further improving the electronic conductivity of the surface of graphite; at the same time, the surface-coated graphite also has a high adsorption capacity of lithium ions, so that it has a high specific capacity and a high rate performance. The application of the above-mentioned surface-coated graphite in electrochemical devices can further improve the energy density and fast charging performance of the electrochemical devices.

[0035] In an embodiment of the present application, the coating includes at least one of the following structural formulas:

[0036] .

[0037] The coating includes the above-mentioned structural formula, and the above-mentioned structural formula includes carbon-oxygen double bonds and / or carbon-nitrogen double bonds. The surface-coated graphite obtained by low-temperature carbonization can retain its nitrogen-doped carbon skeleton structure, further improving the electronic conductivity of the surface of graphite; at the same time, the surface-coated graphite also has a high adsorption capacity of lithium ions, so that it has a high specific capacity and a high rate performance. The application of the above-mentioned surface-coated graphite in electrochemical devices can further improve the energy density and fast charging performance of the electrochemical devices.

[0038] In an embodiment of the present application, the precursor of the coating includes a carboxylic acid compound containing a benzene ring and a nitrogen-containing compound, the nitrogen-containing compound includes at least one of a cyclic nitrogen-containing heterocyclic compound or a linear nitrogen-containing compound, the carboxylic acid compound containing a benzene ring includes at least one of pyromellitic acid, trimesic acid, benzenehexacarboxylic acid, benzene-1,3-dicarboxylic acid, diphenic acid or terephthalic acid, the cyclic nitrogen-containing heterocyclic compound includes at least one of melamine, imidazole, 2-methylimidazole, pyrrole, pyridine or benzimidazole, and the linear nitrogen-containing compound includes at least one of diisocyanate, polyacrylonitrile, acrylonitrile or urea. The mass percentage content W1 of the coating in the negative electrode material is 0.5% to 2% based on the total mass of the graphite. Exemplarily, the value of W1 can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2% or a range between any two of the above values. The coating is derived from the mixed carbonization product of the precursor of the coating, and the precursor of the coating is selected as described above, and the mass percentage content of the coating in the negative electrode material is controlled within the scope of the present application, and the surface-coated graphite obtained by low-temperature carbonization can retain its nitrogen-doped carbon skeleton structure, further improving the electronic conductivity of the graphite surface; at the same time, the existence of amide bonds and / or imine bonds on the surface of the graphite can further improve the adsorption capacity of lithium ions, so that the surface-coated graphite has high specific capacity and high rate performance, and the coating in the negative electrode material has a suitable mass percentage content, and the application of the above surface-coated graphite in an electrochemical device can further improve the energy density and fast-charging performance of the electrochemical device.

[0039] In an embodiment of the present application, the negative electrode material has N2CH2 molecular fragments between 500°C and 550°C in mass spectrometric analysis. The mass spectrometric analysis of the negative electrode material meets the above characteristics, indicating that the negative electrode material contains the above structural fragment of formula I-2; at the same time, the negative electrode material has a nitrogen-doped carbon skeleton structure, which can further improve the electronic conductivity of the graphite surface; and the application of the above negative electrode material in an electrochemical device can further improve the fast-charging performance of the electrochemical device.

[0040] In an embodiment of the present application, the weight loss rate G of the negative electrode material in an inert atmosphere from 35°C to 800°C is 0.1% to 0.3%. Illustratively, the value of G can be 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.3%, or a range formed by any two of the above values. By adjusting the weight loss rate of the negative electrode material in an inert atmosphere from 35°C to 800°C within the range of the present application, the coating on the surface of the negative electrode material can form a relatively stable and effective coating layer structure after carbonization at a certain temperature. The use of the above negative electrode material in an electrochemical device can further improve the energy density and fast charging performance of the electrochemical device.

[0041] In an embodiment of the present application, the graphitization degree GD of the negative electrode material is 93% to 95%. Illustratively, the value of GD can be 93%, 93.1%, 93.3%, 93.5%, 93.7%, 93.9%, 94%, 94.1%, 94.3%, 94.5%, 94.7%, 94.9%, 95%, or a range formed by any two of the above values. By adjusting the graphitization degree of the negative electrode material within the range of the present application, the negative electrode material has a higher graphitization degree, a higher specific capacity, and a higher lithium ion diffusion coefficient. The use of the above negative electrode material in an electrochemical device can further improve the energy density and fast charging performance of the electrochemical device.

[0042] In an embodiment of the present application, the specific surface area SSA of the negative electrode material is 1 m 2 / g to 3 m 2 / g. Illustratively, the value of SSA can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, or a range formed by any two of the above values. By adjusting the specific surface area of the negative electrode material within the range of the present application, the negative electrode material can have a suitable specific surface area, which can shorten the transmission path of lithium ions and improve the fast charging performance of the negative electrode material, thereby further improving the fast charging performance of the electrochemical device.

[0043] In an embodiment of the present application, the Dv50 of the negative electrode material is 12 μm to 16 μm. Illustratively, the value of Dv50 can be 12, 12.3, 12.5, 12.7, 12.9, 13, 13.3, 13.5, 13.7, 13.9, 14, 14.3, 14.5, 14.7, 14.9, 15, 15.3, 15.5, 15.7, 15.9, 16 or a range between any two of the aforementioned values. By controlling the Dv50 of the negative electrode material within the range of the present application, the negative electrode material can have a suitable particle size, the transmission path of lithium ions can be shortened, the fast charging performance of the negative electrode material can be improved, and thus the fast charging performance of the electrochemical device can be further improved.

[0044] In the present application, Dv50 represents the particle size at which the volume accumulation is 50% in the particle size distribution of the material on a volume basis.

[0045] In an embodiment of the present application, the tap density TD of the negative electrode material is 0.95 g / cm3to 1.05 g / cm3. 3 3 Illustratively, the value of TD can be 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.01, 1.02, 1.03, 1.04, 1.05 or a range between any two of the aforementioned values. By controlling the tap density of the negative electrode material within the range of the present application, the negative electrode sheet can have a higher compaction density, and thus the electrochemical device can have a higher energy density on the basis of good fast charging performance.

[0046] In an embodiment of the present application, the graphite includes at least one of artificial graphite or natural graphite. By selecting the aforementioned graphite, the graphite has a higher electronic conductivity, a higher lithium ion transmission rate and a higher gram capacity, and the surface-coated graphite obtained after surface coating has a higher gram capacity and a higher rate performance, which can further improve the energy density and the fast charging performance of the electrochemical device.

[0047] The second aspect of the present application provides a preparation method of the negative electrode material in any of the aforementioned embodiments, which includes the following steps:

[0048] ​(1) dissolving a precursor of the coating in a solution, and then mixing the precursor of the coating with graphite uniformly, so that the coating is at least on a part of the surface of the graphite, to obtain a slurry; the precursor of the coating comprises a carboxylic acid compound containing a benzene ring and a nitrogen-containing compound, the nitrogen-containing compound comprises at least one of a cyclic nitrogen-containing heterocyclic compound or a linear nitrogen-containing compound, the carboxylic acid compound containing a benzene ring comprises at least one of pyromellitic acid, trimesic acid, benzene hexacarboxylic acid, benzene propanedioic acid, diphenyl dicarboxylic acid or terephthalic acid, the cyclic nitrogen-containing heterocyclic compound comprises at least one of melamine, imidazole, 2-methyl imidazole, pyrrole, pyridine or benzimidazole, and the linear nitrogen-containing compound comprises at least one of diisocyanate, polyacrylonitrile, acrylonitrile or urea;

[0049] (2) after the slurry is left to stand at T1 of 80-120°C for t1 of 12-24h, performing suction filtration, water washing and drying to obtain a powder;

[0050] (3) performing heat treatment on the powder in an inert atmosphere at T2 of 750-850°C for t2 of 2-5h to obtain a negative electrode material, and the mass percentage of the coating in the negative electrode material accounts for 0.5-2% of the graphite.

[0051] Exemplarily, T1 can be 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C, 100°C, 102°C, 104°C, 106°C, 108°C, 110°C, 112°C, 114°C, 116°C, 118°C, 120°C or a range formed by any two of the above values. t1 can be 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, 24h or a range formed by any two of the above values. T2 can be 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C, 850°C or a range formed by any two of the above values. t2 can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h or a range formed by any two of the above values. The mass percentage of the coating in the negative electrode material can account for 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2% or a range formed by any two of the above values of the graphite. In the present application, T2 is the carbonization temperature.

[0052] When the precursor of the coating comprises two or more than two, the present application does not particularly limit the molar ratio of the precursor of the coating, as long as the purpose of the present application can be achieved.

[0053] The mixing method is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the mixing can be performed by stirring.

[0054] The drying method is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the drying can be performed in an electric heating air drying oven. The drying temperature is not particularly limited in the present application, as long as the object of the present application can be achieved.

[0055] The inert atmosphere is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the inert atmosphere can be at least one of argon or helium.

[0056] The heat treatment method is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the heat treatment can be performed in a box-type atmosphere furnace.

[0057] The negative electrode material is prepared by the above method, and the precursor of the coating material is selected. The coating material is derived from a supramolecular polymer polymerized in situ on the surface of graphite, and then subjected to low-temperature carbonization to obtain surface-coated graphite. The above surface-coated graphite can retain the nitrogen-doped carbon skeleton structure through low-temperature carbonization of the supramolecular polymer, which can further improve the electronic conductivity of the graphite surface. On the other hand, the existence of amide bonds and / or imine bonds on the surface of the graphite can improve the adsorption capacity of lithium ions, so that the surface-coated graphite has high specific capacity and high rate performance. The application of the above surface-coated graphite in an electrochemical device can further improve the energy density and fast charging performance of the electrochemical device.

[0058] In the present application, the type of the coating material can be adjusted to adjust the molecular fragment type of the negative electrode material in the mass spectrum analysis. 13 The characteristic peak position in the C solid-state nuclear magnetic spectrum and the characteristic peak position in the infrared spectrum.

[0059] The adjustment method of the mass percentage content of the coating material in the negative electrode material is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the mass percentage content of the coating material can be adjusted by adjusting the mass ratio of the precursor of the coating material added to the graphite.

[0060] In the present application, the type of the coating material and the heat treatment temperature can be adjusted to adjust the molecular fragment type of the negative electrode material in the mass spectrum analysis.

[0061] The adjustment method of the weight loss rate of the negative electrode material is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the weight loss rate of the negative electrode material can be adjusted by adjusting the mass percentage content of the coating material. For example, when other conditions are unchanged, the mass percentage content of the coating material increases, and the weight loss rate of the negative electrode material increases; the mass percentage content of the coating material decreases, and the weight loss rate of the negative electrode material decreases.

[0062] The application does not have a particular limitation on the regulation method of the graphitization degree of the negative electrode material, as long as the application purpose can be achieved. For example, the graphitization degree of the negative electrode material can be regulated by regulating the carbonization temperature.

[0063] The application does not have a particular limitation on the regulation method of the specific surface area and Dv50 of the negative electrode material, as long as the application purpose can be achieved. Illustratively, the specific surface area and Dv50 of the negative electrode material can be regulated by grinding the negative electrode material. For example, the specific surface area and Dv50 of the negative electrode material can be regulated by regulating the grinding time and grinding speed. Illustratively, when other conditions are unchanged, the Dv50 of the negative electrode material decreases and the specific surface area of the negative electrode material increases as the grinding time is prolonged; the Dv50 of the negative electrode material increases and the specific surface area of the negative electrode material decreases as the grinding time is shortened. Illustratively, the specific surface area and Dv50 of the negative electrode material can be regulated by regulating the mass percentage content of the coating. For example, when other conditions are unchanged, the specific surface area of the negative electrode material increases and the Dv50 of the negative electrode material increases as the mass percentage content of the coating increases; the specific surface area of the negative electrode material decreases and the Dv50 of the negative electrode material decreases as the mass percentage content of the coating decreases.

[0064] The third aspect of the application provides an electrochemical device, which comprises a negative electrode tab, the negative electrode tab comprising a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector, the negative electrode material layer comprising the negative electrode material in any one of the preceding embodiments or the negative electrode material prepared by the preparation method in any one of the preceding embodiments. The "negative electrode material layer arranged on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be arranged on one surface of the negative electrode current collector along the thickness direction of the negative electrode current collector, or can be arranged on two surfaces of the negative electrode current collector along the thickness direction of the negative electrode current collector. It should be noted that the "surface" herein can be the entire region of the negative electrode current collector, or can be a partial region of the negative electrode current collector, and the application does not have a particular limitation, as long as the application purpose can be achieved.

[0065] The application does not have a particular limitation on the negative electrode current collector, as long as the application purpose can be achieved, for example, it can comprise a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam or a composite current collector (for example, a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.) and the like.

[0066] The negative electrode material layer of the present application includes a negative electrode active material, which includes the above-described negative electrode material. The negative electrode material layer of the present application also includes a binder and a thickening agent. The present application does not particularly limit the type of binder as long as the purpose of the present application can be achieved, for example, the binder can include at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene butadiene copolymer (SBR), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, lithium carboxymethyl cellulose, lithium polyacrylate, sodium hydroxymethyl cellulose, or potassium hydroxymethyl cellulose. The present application does not particularly limit the thickening agent as long as the purpose of the present application can be achieved, for example, the thickening agent can include sodium carboxymethyl cellulose (CMC-Na). The negative electrode material layer of the present application can also include a conductive agent. The present application does not particularly limit the type of conductive agent as long as the purpose of the present application can be achieved, for example, the conductive agent can include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials, or conductive polymers. The above-described conductive carbon black can include, but is not limited to, at least one of Super P, acetylene black, or Ketjen black. The above-described carbon nanotubes can include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-described carbon fibers can include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanocarbon fibers. The above-described metal materials can include, but are not limited to, metal powder and / or metal fibers, and specifically, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-described conductive polymers can include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. The present application does not particularly limit the mass ratio of the negative electrode active material, the binder, and the thickening agent in the negative electrode material layer, and a person skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0067] The present application does not particularly limit the thickness of the negative electrode current collector as long as the purpose of the present application can be achieved, for example, the thickness of the negative electrode current collector is 4 μm to 20 μm. The present application does not particularly limit the thickness of the negative electrode material layer as long as the purpose of the present application can be achieved, for example, the thickness of the single-sided negative electrode material layer is 30 μm to 250 μm.

[0068] Optionally, the negative electrode sheet can also include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. The present application does not particularly limit the composition of the conductive layer, which can be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and the binder in the conductive layer, which can be at least one of the above-described conductive agent and the above-described binder. The present application does not particularly limit the mass ratio of the conductive agent and the binder in the conductive layer, and a person skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0069] In the present application, the electrochemical device further includes a positive electrode tab. The positive electrode tab includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector in the thickness direction of the positive electrode current collector, or can be disposed on both surfaces of the positive electrode current collector in the thickness direction of the positive electrode current collector. It should be noted that the "surface" herein can be the entire area of the positive electrode current collector, or can be a partial area of the positive electrode current collector, and the present application does not have a particular limitation as long as the purpose of the present application can be achieved.

[0070] The present application does not have a particular limitation on the positive electrode current collector as long as the purpose of the present application can be achieved, for example, it can include an aluminum foil, an aluminum alloy foil, or a composite current collector (for example, an aluminum-carbon composite current collector), etc.

[0071] The positive electrode material layer of the present application includes a positive electrode active material, and the positive electrode active material includes a substance capable of reversibly intercalating and deintercalating active ions such as lithium ions. The positive electrode material layer can be one layer or multiple layers, and each layer of the multiple layers of the positive electrode material layer can include the same or different positive electrode active material. The present application does not have a particular limitation on the positive electrode active material as long as the purpose of the present application can be achieved, for example, the positive electrode active material can include but is not limited to at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. The above-mentioned lithium nickel cobalt manganese oxide can include LiNi 0.95 Co 0.03 Mn 0.02 O2(Ni95), LiNi 0.91 Co 0.03 Mn 0.06 O2(Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3at least one of the above-mentioned conductive agents. The positive electrode active material layer of the present application can further include a binder. The binder included in the positive electrode active material layer is not particularly limited as long as the object of the present application can be achieved. For example, the binder included in the positive electrode active material layer can include at least one of the above-mentioned binders. The mass ratio of the positive electrode active material, the conductive agent, and the binder included in the positive electrode active material layer is not particularly limited, and can be selected by a person skilled in the art according to the actual needs as long as the object of the present application can be achieved.

[0072] The thickness of the positive electrode current collector is not particularly limited as long as the object of the present application can be achieved, for example, the thickness of the positive electrode current collector is 6 μm to 16 μm. The thickness of the positive electrode material layer is not particularly limited as long as the object of the present application can be achieved, for example, the thickness of the single-sided positive electrode material layer is 25 μm to 250 μm.

[0073] Optionally, the positive electrode sheet can further include a conductive layer, and the conductive layer is located between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited, and can be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The conductive agent and the binder included in the conductive layer are not particularly limited, and can be at least one of the above-mentioned conductive agents and the above-mentioned binders. The mass ratio of the conductive agent and the binder included in the conductive layer is not particularly limited, and can be selected by a person skilled in the art according to the actual needs as long as the object of the present application can be achieved.

[0074] In the present application, the electrochemical device further includes an electrolyte. The electrolyte includes a lithium salt. The kind of the lithium salt is not particularly limited in the present application, and a lithium salt known in the art can be used. Illustratively, the lithium salt can include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2, LiTFSI), lithium bis(fluorosulfonyl)imide (Li(N(SO2F)2), LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate (LiB(C2O4)2, LiBOB), or lithium difluoro(oxalato)borate (LiBF2(C2O4), LiDFOB). The mass percentage content of the lithium salt in the electrolyte is not particularly limited in the present application, as long as the object of the present application can be achieved. The electrolyte further includes a non-aqueous organic solvent. The non-aqueous organic solvent is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the non-aqueous organic solvent can include at least one of a carbonate compound, a carboxylic acid ester compound, an ether compound, or other organic solvents. The carbonate compound described above can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluorinated carbonate compound. The chain carbonate compound described above can include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (EMC). The cyclic carbonate compound described above can include, but is not limited to, at least one of ethylene carbonate (EC), vinylene carbonate, propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound described above can include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, or trifluoromethyl ethylene carbonate. The carboxylic acid ester compound described above can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, or propyl propionate. The ether compound described above can include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyl tetrahydrofuran, or tetrahydrofuran. The other organic solvents described above can include, but is not limited to, at least one of 1,3-propanesultone, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphoric acid ester.The mass percentage content of the non-aqueous organic solvent in the electrolyte is not particularly limited in the present application, as long as the object of the present application can be achieved.

[0075] In the present application, the electrochemical device further includes a separator. The separator is used to separate the positive electrode sheet and the negative electrode sheet, prevent internal short circuit of the electrochemical device, allow electrolyte ions to pass freely, and not affect the electrochemical charging and discharging process. The separator is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) mainly including polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; and the type of the separator can include at least one of woven film, non-woven film, microporous film, composite film, calendered film, or spunlaced film.

[0076] In the present application, the separator can include a substrate and a surface treatment layer. The substrate can be a non-woven fabric or a composite film having a porous structure, and the material of the substrate can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a separator binder, and the inorganic particles are not particularly limited in the present application, and can include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The separator binder is not particularly limited in the present application, and can be at least one of the aforementioned binders. The polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or polyvinylidene fluoride-hexafluoropropylene copolymer.

[0077] The electrochemical device of the present application further includes a packaging bag for containing the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, and other components known in the art in the electrochemical device, which are not limited in the present application. The packaging bag is not particularly limited in the present application, and can be a packaging bag known in the art, as long as the object of the present application can be achieved.

[0078] The kind of the electrochemical device of the present application is not particularly limited, and it can include any device in which an electrochemical reaction occurs. In the present application, the electrochemical device can include, but is not limited to, a lithium metal electrochemical device, a lithium ion electrochemical device (lithium ion battery), a lithium polymer electrochemical device, or a lithium ion polymer electrochemical device (lithium ion polymer battery), etc. The type of the lithium ion electrochemical device of the present application is not particularly limited, for example, the lithium ion electrochemical device can be a soft pack battery, a square aluminum can battery, or a cylindrical aluminum can battery. The structure of the lithium ion electrochemical device of the present application is not particularly limited, for example, the structure of the lithium ion electrochemical device can be a jelly-roll structure, a stacked structure, or a multi-tab structure.

[0079] The preparation process of the electrochemical device of the present application is well known to those skilled in the art, and the present application is not particularly limited, for example, it can include, but is not limited to, the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, and winding, folding, etc. as needed to obtain an electrode assembly of a jelly-roll structure, placing the electrode assembly into a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain an electrochemical device; or stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, then fixing the four corners of the entire stacked structure with a tape to obtain an electrode assembly of a stacked structure, placing the electrode assembly into a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain an electrochemical device. In addition, a current protection element, a guide plate, etc. can also be placed in the packaging bag as needed to prevent the pressure inside the electrochemical device from rising and overcharging and discharging.

[0080] The fourth aspect of the present application provides an electronic device comprising the electrochemical device of any of the preceding embodiments. Therefore, the electronic device provided by the present application has good energy density and fast charging performance.

[0081] The kind of the electronic device of the present application is not particularly limited, and it can be any electronic device known in the art. In some embodiments, the electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0082] Embodiments

[0083] Hereinafter, examples and comparative examples are presented to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0084] Test methods and equipment:

[0085] Negative electrode material sampling method:

[0086] A lithium ion battery completely discharged (discharged to 3.0 V) was disassembled, and the negative electrode sheet was taken out, soaked in dimethyl carbonate (DMC) for 20 min, then washed with DMC and acetone in turn for one time each to remove the electrolyte and the surface solid electrolyte interface (SEI) film. Then, the negative electrode sheet was placed in an oven and baked at 80°C for 12 h to obtain a treated negative electrode sheet. The negative electrode material layer on the negative electrode sheet was scraped off with a scraper, and the powder of the scraped negative electrode material layer was heat treated at 400°C for 4 h in a tube furnace under argon protection to obtain a negative electrode material sample.

[0087] 13 C solid-state nuclear magnetic test:

[0088] Bruker AVANCE III 400 WB nuclear magnetic resonance spectrometer was used, the probe was 2.5 mm H / F / X triple resonance CP / MAS, and the negative electrode material sample was subjected to 13 C-solid-state nuclear magnetic scanning.

[0089] Infrared spectrum test:

[0090] Fourier transform infrared spectrum test was performed using a Thermo Nicolet iS20 FTIR spectrometer, the reference standard was GB / T 21186-2007 "Fourier transform infrared spectrometer" national standard, and the infrared spectrum test was performed using the potassium bromide tablet pressing method.

[0091] Mass spectrum analysis test:

[0092] Mass spectrum analysis of the negative electrode material was performed using a STA449F3-QMS403C thermal mass spectrometer, the reference standard was GB / T 6041-2020 "General method for mass spectrometric analysis", 99.99% nitrogen was used, the temperature rise rate was 10°C / min, and the cutoff temperature was 800°C.

[0093] Weight loss rate test:

[0094] The thermal weight loss of the substance was analyzed by a simultaneous thermal analyzer (model: NETZSCH STA 449 F3 Jupiter), and the reference standards were JY_T 0589.1-2020 / JY_T 0589.4-2020 / JY_T 0589.5-2020 General thermal analysis methods, 99.99% nitrogen was used, the heating rate was 10℃ / min, and the cutoff temperature was 800℃.

[0095] Graphitization degree test:

[0096] The negative electrode material was tested by an X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE), the target material was Cu Kα, the voltage and current were 40KV / 40mA, the scanning angle range was 5° to 80°, the scanning step was 0.00836°, and the time for each step was 0.3s. At the same time, 15% silicon powder by mass content was added to the negative electrode material, according to the principle of internal standard method, the peak position of the silicon standard was used to calibrate the instrument and test error, so as to accurately calculate the characteristic peak position of the negative electrode material, and the graphitization degree of the negative electrode material was obtained.

[0097] Specific surface area SSA test:

[0098] According to the national standard "Gas adsorption BET method for determining the specific surface area of solid substances" (GB / T 19587-2017), a specific surface area analyzer (model: Tristar II 3020M) was used to test the specific surface area of the negative electrode material by nitrogen adsorption method.

[0099] Particle size Dv50 test:

[0100] A Malvern particle size tester (model: MasterSizer 2000) was used to measure the particle size of the negative electrode material particles. 0.02g of negative electrode material particles was added to a 50mL clean beaker, 20mL of dispersant ethanol was added, and ultrasonic cleaning was performed in a 120W ultrasonic cleaner for 30min, so that the negative electrode material particles were completely dispersed in the ethanol to obtain a sample dispersion liquid. The above sample dispersion liquid was tested by using the Malvern particle size tester, and the particle size Dv50 of the negative electrode material particles was obtained.

[0101] Tap density TD test:

[0102] According to the national standard GB / T 24533-2019, a density analyzer (model: GeoPyc 1365) was used to test the tap density TD of the negative electrode material.

[0103] Negative electrode material 0.05C and 1C capacity test:

[0104] Reference national standard: GB / T 24533-2019 Lithium ion battery graphite negative electrode material, the negative electrode material is mixed, coated, rolled, punched, and dried to form a negative electrode sheet (the specific process is the same as the negative electrode sheet preparation method in Example 1), lithium sheet is used as a positive electrode sheet, and a button cell is assembled for testing. The button cell is kept at 25°C for 12h, discharged at 0.05C to 5.0mV, discharged at 50μA to 5.0mV, and discharged at 20μA to 5.0mV; charged at 0.1C to 2.0V, and the capacity of the button cell at this time is recorded as 0.05C gram capacity; then kept at 25°C for 2h, discharged at 1C to 5.0mV; charged at 0.1C capacity to 2.0V, and the capacity of the button cell at this time is recorded as 1C gram capacity.

[0105] Lithium ion battery energy density ratio test:

[0106] Take 5 of each group of lithium ion batteries using all the comparative examples and examples, and take the average. First, in a 25°C environment, perform the first charge and discharge, perform constant current charging (CC) at a charge current of 0.5C, charge to 4.48V, then convert to constant voltage charging (CV), stop charging when the charging current is lower than 0.02C, then perform constant current discharge at a discharge current of 0.2C, and the discharge cutoff voltage is 3V, record the energy density of the lithium ion battery during the discharge process, and calculate the energy density ratio of each example and comparative example relative to comparative example 1.

[0107] Energy density ratio (%) = energy density of lithium ion battery of each example and comparative example / energy density of lithium ion battery of comparative example 1 x 100%.

[0108] The higher the energy density ratio, the higher the energy density of the lithium ion battery.

[0109] Lithium ion battery charge rate performance test:

[0110] The lithium ion battery is repeatedly charged and discharged by the following steps, and the capacity of each stage of charging (average value) is counted to calculate the capacity ratio of the constant current charging (CC) segment. The specific steps are as follows: first, place the lithium ion battery in a 25℃ environment for 6 hours. The lithium ion battery is charged at a charge rate of 1C, and the constant current charging (CC) is converted to constant voltage charging (CV) when the voltage reaches 4.48V. The charging current is stopped when it is lower than 0.05C, and the battery is rested for 5 minutes. Then, the lithium ion battery is discharged at a constant current of 0.2C to 3V, and rested for 5 minutes to ensure the integrity of the subsequent charging and discharging process. Then, the lithium ion battery is fully charged at a charge rate of 3C according to the previous CC+CV charging mode, and the CC segment capacity ratio at 3C is calculated. The calculation formula is: CC segment capacity ratio at 3C (%) = [CC segment capacity / (CC+CV) total capacity] x 100%. Five lithium ion batteries are taken from each comparative example and example, and the average value is taken as the final result.

[0111] The higher the CC segment capacity ratio at 3C, the better the fast charging performance of the lithium ion battery.

[0112] Lithium ion battery 3C rate cycle capacity retention test:

[0113] In a 25℃ environment, the lithium ion battery is charged and discharged for the first time, and the constant current charging (CC) is carried out at a charging current of 3C. The constant voltage charging (CV) is converted when the voltage reaches 4.48V. The charging current is stopped when it is lower than 0.05C, and then the lithium ion battery is discharged at a constant current of 1C. The discharge cut-off voltage is 3V, and the discharge capacity of the lithium ion battery is measured as A. Then, the lithium ion battery is charged and discharged for 800 times according to the above steps in a 25℃ environment, and the discharge capacity of the lithium ion battery at the 800th time is measured as B. The cycle capacity retention rate of the lithium ion battery at 3C (%) = B / A x 100%. Five lithium ion batteries are taken from each comparative example and example, and the average value is taken as the final result.

[0114] Example 1

[0115] <Preparation of negative electrode material>

[0116] (1) The molar ratio of the precursor of the coating material to melamine is 3:4, and 300mL of water is added. Stir at room temperature for 12h, then transfer to an 80℃ oven and stand for 12h. After filtration, water washing and drying, the coating material raw material is obtained.

[0117] (2) The coating material raw material is tested for weight loss rate at 800℃ for 3h, and the weight loss rate x% of the coating material raw material at this temperature is 85%. The required mass of the coating material raw material m is calculated when the coating material content in the final negative electrode material is 0.5% by the following formula: 包覆物原料 , . Wherein, m 石墨 represents the mass of graphite added in step (3), m 石墨 is 50 g, m 包覆物原料 is 1.667 g.

[0118] (3) The m 包覆物原料 calculated above is weighed, wherein the molar ratio of pyromellitic acid and melamine is 3:4, 300 mL of water is added, and m 石墨 is 50 g of artificial graphite, stirring at room temperature for 12 h to obtain a slurry; then the slurry is transferred into an oven with T1 of 80℃ and is left to stand for t1 of 12 h, and then is subjected to suction filtration, water washing and drying to obtain a powder.

[0119] (4) The powder is transferred into a box-type atmosphere furnace for heat treatment, and is heated to T2 of 800℃ at a rate of 5℃ / min under an argon atmosphere, and is kept at T2 for t2 of 3 h to obtain a negative electrode material. The mass percentage of the coating in the negative electrode material is W1 of 0.5%.

[0120] <Preparation of a negative electrode sheet>

[0121] The above negative electrode material, thickening agent sodium carboxymethyl cellulose (CMC-Na) and binder styrene-butadiene rubber (SBR) are mixed according to a weight ratio of 95:2:3, and deionized water is added as a solvent, and then is stirred and mixed uniformly to obtain a negative electrode slurry, wherein the solid content of the negative electrode slurry is 75 wt%; the negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 12 μm, and is dried at 120℃ to obtain a negative electrode sheet with a negative electrode material layer coated on one surface, and the thickness of the coating layer is 120 μm. The above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a negative electrode material layer coated on both surfaces. After drying under vacuum at 120℃ for 1 h, the negative electrode sheet is subjected to cold pressing, cutting and slitting to obtain a negative electrode sheet with a size of 78 mm x 875 mm. The cold pressing process has a compaction density of 1.75 g / cm 3 .

[0122] <Preparation of a positive electrode sheet>

[0123] The positive active material lithium cobaltate (LiCoO2), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 96:2:2, N-methyl pyrrolidone (NMP) is added as a solvent, and the mixture is stirred and mixed uniformly to obtain a positive electrode slurry, wherein the solid content of the positive electrode slurry is 70 wt%. The positive electrode slurry is uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12 μm, and is subjected to drying treatment at 120°C for 1 h to obtain a positive electrode tab with a positive electrode material layer with a thickness of 100 μm coated on one surface. The above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode tab with a positive electrode material layer coated on both surfaces. After drying under vacuum at 120°C for 1 h, the positive electrode tab is subjected to cold pressing, cutting, and slitting to obtain a positive electrode tab with a size of 74 mm x 867 mm. In the cold pressing process, the compacted density is 4.2 g / cm3. 3 .

[0124] <Preparation of electrolyte>

[0125] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) are mixed in a weight ratio of 1:1:1 to obtain a base solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) is added and mixed uniformly to obtain an electrolyte. The mass percentage of lithium salt LiPF6 based on the mass of the electrolyte is 12.5%, and the balance is the base solvent.

[0126] <Preparation of separator>

[0127] A porous polyethylene film (provided by Celgard) with a thickness of 7 μm is used as a separator.

[0128] <Preparation of lithium ion battery>

[0129] The positive electrode tab, separator, negative electrode tab, and separator prepared above are stacked in order, with the separator between the positive electrode tab and the negative electrode tab to serve as a separation function, and are wound to obtain an electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte, and is subjected to vacuum packaging, standing, formation (formation upper limit voltage is 4.48 V, formation temperature is 70°C, and formation standing time is 2 h), degassing, and edge cutting processes to obtain a lithium ion battery.

[0130] Examples 2 to 5

[0131] Except that in step (2) of the <Preparation of negative electrode material> the required amount of coating material raw material is calculated so that the mass percentage of the coating material in the prepared negative electrode material is as shown in Table 1, the rest is the same as in Example 1.

[0132] Examples 6 to 9

[0133] Except that the heat treatment temperature is adjusted according to Table 1 in <Preparation of the negative electrode material>, and the temperature of the weight loss rate test in step (2) is adjusted synchronously, the rest is the same as Example 1.

[0134] Examples 10 to 12

[0135] Except that the heat treatment time is adjusted according to Table 1 in <Preparation of the negative electrode material>, and the time of the weight loss rate test in step (2) is adjusted synchronously, the rest is the same as Example 1.

[0136] Example 13

[0137] Except that the types of the precursors of the coating are pyromellitic acid and imidazole in <Preparation of the negative electrode material>, and the molar ratio of pyromellitic acid and imidazole is adjusted to 1:3, the rest is the same as Example 1.

[0138] Example 14

[0139] Except that the types of the precursors of the coating are terephthalic acid and diisocyanate in <Preparation of the negative electrode material>, and the molar ratio of terephthalic acid and diisocyanate is adjusted to 1:2, the rest is the same as Example 1.

[0140] Comparative Example 1

[0141] Except that untreated artificial graphite is used as the negative electrode material in <Preparation of the negative electrode sheet>, the rest is the same as Example 1.

[0142] Comparative Example 2

[0143] Except that only pyromellitic acid is added as the precursor of the coating in <Preparation of the negative electrode material>, and the heat treatment temperature is adjusted according to Table 1, and the temperature of the weight loss rate test in step (2) is adjusted synchronously, the rest is the same as Example 1.

[0144] Comparative Example 3

[0145] Except that the heat treatment temperature is adjusted according to Table 1 in <Preparation of the negative electrode material>, and the temperature of the weight loss rate test in step (2) is adjusted synchronously, the rest is the same as Example 1.

[0146] Comparative Example 4

[0147] Except that the negative electrode material is prepared according to the following method, the rest is the same as Example 1.

[0148] <Preparation of the negative electrode material>

[0149] (1) Polyacrylonitrile (PAN) is dissolved in a solvent N-dimethylformamide to obtain a solution containing PAN.

[0150] (2) The artificial graphite was added into the solution containing PAN, and stirred until mixed uniformly to obtain a slurry. The mass ratio of the artificial graphite to PAN was 200:1.

[0151] (3) The slurry was transferred into a spray drying device by a peristaltic pump, and dried at 190°C in a nitrogen atmosphere to obtain a dry powder. The rotation speed of the peristaltic pump was 20 rpm.

[0152] (4) The dry powder was heat-treated in a nitrogen atmosphere to obtain the negative electrode material. The heat-treatment temperature was 400°C, and the heat-treatment time was 4 h.

[0153] Comparative Example 5

[0154] Except that the negative electrode material was prepared according to the following method, the rest was the same as in Example 1.

[0155] <Preparation of the negative electrode material>

[0156] (1) Polyacrylonitrile (PAN) was dissolved in a solvent N-dimethylformamide to obtain a solution containing PAN.

[0157] (2) The artificial graphite was added into the solution containing PAN, and stirred until mixed uniformly to obtain a slurry. The mass ratio of the artificial graphite to PAN was 100:1.

[0158] (3) The slurry was transferred into a spray drying device by a peristaltic pump, and dried at 190°C in a nitrogen atmosphere to obtain a dry powder. The rotation speed of the peristaltic pump was 20 rpm.

[0159] (4) The dry powder was heat-treated in a nitrogen atmosphere to obtain the negative electrode material. The heat-treatment temperature was 300°C, and the heat-treatment time was 4 h.

[0160] The preparation parameters, material performance parameters and electrical performance parameters of each example and comparative example are shown in Tables 1-2.

[0161] Table 1

[0162]

[0163] (1) Note: " / " in Table 1 means that the corresponding substance or parameter does not exist; (2) In Table 1, the mass percentage content W1 of the coating material refers to the mass percentage content of the coating material in the graphite in the final negative electrode material prepared; (3) In Table 1, "C solid-state nuclear magnetic characteristic peak" refers to the characteristic peak at 150 ppm to 172 ppm in the C solid-state nuclear magnetic spectrum; "infrared spectrum characteristic peak" refers to the characteristic peak at 1600 cm 13 to 1700 cm 13 in the infrared spectrum. -1 -1 ​characteristic peaks of the infrared spectrum.

[0164] Table 2

[0165]

[0166] As can be seen from Examples 1 to 14 and Comparative Examples 1 to 5, when the negative electrode material is prepared by the preparation method of the present application and each preparation parameter is within the range of the present application, the 0.05C gram capacity and 1C gram capacity of the negative electrode material are high. When the lithium ion battery is prepared using the above negative electrode material, the lithium ion battery has a high energy density ratio, a high CC segment capacity ratio at 3C rate, and a high cycle capacity retention rate at 3C rate, thereby indicating that the negative electrode material prepared by the preparation method of the present application and each preparation parameter within the range of the present application, and the lithium ion battery has high energy density and fast charging performance when the above negative electrode material is applied to the lithium ion battery.

[0167] As can be seen from Examples 1 to 5 and Comparative Example 1, when the mass percentage content of the coating is within the range of the present application, the lithium ion battery has a high energy density ratio, a high cycle capacity retention rate at 3C rate, and a high energy density ratio, thereby indicating that the lithium ion battery has high energy density and fast charging performance. When the mass percentage content of the coating is high, for example, Example 5, the 0.05C gram capacity and 1C gram capacity of the negative electrode material are improved, the overall energy density ratio is slightly affected, and the initial efficiency and cycle stability of the lithium ion battery are also affected. As can be seen, a suitable content of the coating can form a nitrogen-doped carbon coating layer, which improves the electronic cross-linking conductivity on the surface of the graphite and between the particles, and improves the fast charging capability. At the same time, the retention of part of the amide bond and imine bond after low-temperature carbonization is beneficial to the capacity improvement of the negative electrode material and the overall energy density improvement of the lithium ion battery.

[0168] As can be seen from Examples 1, Examples 6 to 9, Comparative Example 2 and Comparative Example 3, the heat treatment temperature has a great influence on the coating effect of the coating. If the heat treatment temperature is too high, the nitrogen element will be completely decomposed and overflowed, for example, Comparative Example 3. The 13 No C solid-state nuclear magnetic characteristic peaks and infrared spectrum characteristic peaks were detected. If the heat treatment temperature is too low, the coating material cannot be completely carbonized, which will affect the conductivity of the negative electrode material and thus affect the overall performance of the lithium ion battery, for example, Comparative Example 2. The energy density ratio, CC segment capacity ratio at 3C rate, and cycle capacity retention rate at 3C rate of the lithium ion battery of Comparative Example 2 are all low, indicating that the overall performance of the lithium ion battery of Comparative Example 2 is poor. The heat treatment temperatures of Examples 1, Examples 6 to 9 are within the range of the present application, and the lithium ion battery has a high energy density ratio, a high CC segment capacity ratio at 3C rate, and a high cycle capacity retention rate at 3C rate, thereby indicating that the lithium ion battery has high energy density and fast charging performance.

[0169] As can be seen from Example 1, Example 10 to Example 12, when the heat treatment temperature is the same, the heat treatment time change brings slight structural changes of the negative electrode material. When the heat treatment time is within the scope of the present application, the lithium ion battery has a higher energy density ratio, a higher CC segment capacity ratio at 3C rate, and a higher cycle capacity retention rate at 3C rate, indicating that the lithium ion battery has higher energy density and fast charging performance.

[0170] As can be seen from Example 1, Example 13 to Example 14, when the precursor of the coating material of the present application is selected, the lithium ion battery has a higher energy density ratio, a higher CC segment capacity ratio at 3C rate, and a higher cycle capacity retention rate at 3C rate, indicating that the lithium ion battery has higher energy density and fast charging performance.

[0171] As can be seen from Example 1, Example 2, Comparative Example 4, and Comparative Example 5, the heat treatment temperature of Comparative Example 4 and Comparative Example 5 is lower, and the lithium ion battery prepared by the preparation method has lower energy density ratio, CC segment capacity ratio at 3C rate, and cycle capacity retention rate at 3C rate, indicating that the overall performance of the lithium ion battery of Comparative Example 4 and Comparative Example 5 is poor. However, when the negative electrode material prepared by the preparation method of the present application and within the scope of the present application is applied to the lithium ion battery, the lithium ion battery has higher energy density and fast charging performance.

[0172] As can be seen from Example 1, Example 2, Comparative Example 4, and Comparative Example 5, the heat treatment temperature of Comparative Example 4 and Comparative Example 5 is lower, and the lithium ion battery prepared by the preparation method has lower energy density ratio, CC segment capacity ratio at 3C rate, and cycle capacity retention rate at 3C rate, indicating that the overall performance of the lithium ion battery of Comparative Example 4 and Comparative Example 5 is poor. However, when the negative electrode material prepared by the preparation method of the present application and within the scope of the present application is applied to the lithium ion battery, the lithium ion battery has higher energy density and fast charging performance. Figure 1 As can be seen from the above, the negative electrode material of Example 1 is in irregular granular shape, and the surface of the graphite or at least part of the graphite particles contains flocculent coating.

[0173] As can be seen from the above, the negative electrode material of Example 1 is in irregular granular shape, and the surface of the graphite or at least part of the graphite particles contains flocculent coating. Figure 2 As can be seen from the above, the negative electrode material of Example 1 is in irregular granular shape, and the surface of the graphite or at least part of the graphite particles contains flocculent coating. 13 The characteristic peak of 150ppm to 172ppm in the C solid-state nuclear magnetic spectrum indicates that there is an amide bond or an imine bond on the surface of the negative electrode material.

[0174] As can be seen from the above, the negative electrode material of Example 1 is in irregular granular shape, and the surface of the graphite or at least part of the graphite particles contains flocculent coating. Figure 3 As can be seen from the above, the negative electrode material of Example 1 is in irregular granular shape, and the surface of the graphite or at least part of the graphite particles contains flocculent coating. -1 The characteristic peak of 150ppm to 172ppm in the C solid-state nuclear magnetic spectrum indicates that there is an amide bond or an imine bond on the surface of the negative electrode material. -1 The characteristic peak of 150ppm to 172ppm in the C solid-state nuclear magnetic spectrum indicates that there is an amide bond or an imine bond on the surface of the negative electrode material.

[0175] It should be noted that in this document, the term "comprise", "include" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method or article.

[0176] The various embodiments described in this specification are presented by way of example, and each embodiment is not mutually exclusive of the others. Each embodiment highlights a different aspect of the application.

Claims

1. A negative electrode material comprising graphite and a coating located on at least a portion of the surface of the graphite, the negative electrode material in... 13 The solid-state NMR spectrum of the anode material exhibits characteristic peaks ranging from 150 ppm to 172 ppm; the infrared spectrum of the anode material shows a peak at 1600 cm⁻¹. -1 Up to 1700cm -1 Characteristic peaks; the coating has carbon-oxygen double bonds and carbon-nitrogen double bonds.

2. The negative electrode material of claim 1, wherein, The coating comprises at least one of the following structural formulas: 。 3. The negative electrode material according to claim 1 or 2, wherein The negative electrode material has N2CH2 molecular fragments between 500℃ and 550℃ in mass spectrum analysis.

4. The negative electrode material according to claim 1 or 2, wherein The negative electrode material has a weight loss rate of 0.1% to 0.3% from 35℃ to 800℃ in an inert atmosphere.

5. The negative electrode material according to claim 1 or 2, wherein The negative electrode material satisfies at least one of the following conditions: (1) the specific surface area SSA of the negative electrode material is 1 m 2 / g to 3 m 2 / g; (2) The Dv50 of the negative electrode material is 12μm to 16μm; (3) the tap density TD of the negative electrode material is 0.95 g / cm3 3 to 1.05 g / cm3 3 ; (4) The graphitization degree of the negative electrode material is 93% to 95%; (5) The mass percentage of the coating in the negative electrode material is 0.5% to 2% based on the total mass of the graphite.

6. The negative electrode material according to claim 1 or 2, wherein The graphite comprises at least one of artificial graphite or natural graphite.

7. A preparation method of the negative electrode material according to any one of claims 1 to 6, comprising the following steps: (1) Dissolving a precursor of the coating in a solution, and then uniformly mixing with the graphite, so that the coating is at least on a part of the surface of the graphite, to obtain a slurry; the precursor of the coating comprises a carboxylic acid compound containing a benzene ring and a nitrogen-containing compound, the nitrogen-containing compound comprises at least one of a cyclic nitrogen-containing heterocyclic compound or a linear nitrogen-containing compound, the carboxylic acid compound containing a benzene ring comprises at least one of pyromellitic acid, trimesic acid, benzenehexacarboxylic acid, benzene malonic acid, diphenic acid or terephthalic acid, the cyclic nitrogen-containing heterocyclic compound comprises at least one of melamine, imidazole, 2-methyl imidazole, pyrrole, pyridine or benzimidazole, and the linear nitrogen-containing compound comprises at least one of diisocyanate, polyacrylonitrile, acrylonitrile or urea; (2) After the slurry is left to stand at 80℃ to 120℃ for 12h to 24h, the slurry is subjected to suction filtration, water washing and drying to obtain a powder; (3) The powder is subjected to heat treatment at 750℃ to 850℃ in an inert atmosphere, and is kept at the temperature for 2h to 5h to obtain the negative electrode material, and the mass percentage of the coating in the negative electrode material is 0.5% to 2%.

8. An electrochemical device comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector, the negative electrode material layer comprising the negative electrode material according to any one of claims 1 to 6 or prepared by the preparation method of claim 7.

9. An electronic device comprising the electrochemical device of claim 8.

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