A single-atom-doped graphite negative electrode material for lithium-ion batteries and a preparation method thereof

Abstract

The present application relates to the technical field of preparation of negative electrode materials for lithium-ion batteries, in particular to a novel single-atom-doped graphite negative electrode material for lithium-ion batteries and a preparation method thereof. A novel single-atom-doped graphite negative electrode material for lithium-ion batteries comprises graphite as a carrier and transition metal single atoms doped on the graphite surface, wherein the graphite is natural graphite and / or artificial graphite; the content of transition metal doped in the graphite is 1-10wt%; and the transition metal single atoms include at least one of iron, cobalt, nickel, manganese, copper, zinc, tin, chromium, platinum, palladium, gold, ruthenium, rhodium, molybdenum, zirconium, silver, tungsten, iridium, and vanadium. Compared with commercial graphite negative electrodes, the novel single-atom-doped graphite negative electrode material in the present application can effectively increase the negative electrode lithium storage capacity and significantly improve the specific capacity, and its use in lithium-ion batteries can greatly improve the specific capacity, cycle stability, and fast charging performance of lithium batteries.

Description

Technical Field

[0001] The present application relates to the technical field of preparation of negative electrode materials for lithium-ion batteries, and in particular to a single-atom-doped graphite negative electrode material for lithium-ion batteries and a preparation method thereof. Background Art

[0002] Carbon-based materials have become important materials for lithium-ion battery negative electrode materials due to their high conductivity, high capacity ratio and high cost performance, and are widely used in various electronic devices, electric vehicles, aerospace and other fields. However, with the upgrading and transformation of industry and industrialization, as well as the problems of carbon-based materials in the charging and discharging process, such as capacity decay and poor cycle stability, their further development in commercial applications has been limited. Therefore, research on performance improvement of carbon-based negative electrode materials is of great significance. To this end, the present application provides a single-atom-doped graphite negative electrode material for lithium-ion batteries and a preparation method thereof, which solves the problems of low specific capacity, capacity decay, poor cycle stability and the like caused by insufficient electrochemical performance of existing commercial graphite negative electrode materials. Summary of the Invention

[0003] In order to solve the problems of low specific capacity, capacity decay, and poor cycle stability caused by the insufficient electrochemical performance of existing commercial graphite negative electrode materials, this application combines the theoretical research of single-atom catalysis, uses commercial graphite as a carrier, and systematically regulates the structure and properties of single-atom active sites by adjusting the types and ratios of transition metals and organic small molecule ligands to prepare carbon-based lithium-ion battery negative electrode materials containing single-atom active sites, thereby breaking through the capacity limit of existing commercial graphite negative electrodes and significantly improving the specific capacity, cycle stability and fast charging performance of lithium-ion batteries.

[0004] In a first aspect, the present application provides a single-atom-doped graphite negative electrode material for lithium-ion batteries, which adopts the following technical solution:

[0005] A single-atom-doped graphite negative electrode material for lithium-ion batteries comprises graphite as a carrier and transition metal single atoms doped on the graphite surface, wherein the graphite is natural graphite and / or artificial graphite; the content of the transition metal doped in the graphite is 1-10wt%; and the transition metal single atoms comprise at least one of iron, cobalt, nickel, manganese, copper, zinc, tin, chromium, platinum, palladium, gold, ruthenium, rhodium, molybdenum, zirconium, silver, tungsten, iridium, and vanadium.

[0006] This application uses graphite as a carrier and transition metal single atoms doped on the graphite surface as negative electrode materials, so that the discharge capacity of the negative electrode material is 450-650mAh / g, and the first-week Coulombic efficiency is ≥80%, effectively increasing the negative electrode lithium storage capacity and improving the specific capacity by ≥30%, breaking through the capacity limit of existing commercial graphite negative electrodes, and greatly improving the specific capacity, cycle stability, and fast charging performance of lithium-ion batteries.

[0007] Preferably, the discharge capacity of the natural graphite and / or artificial graphite is 340-365 mAh / g.

[0008] This application uses commercial graphite as a carrier, and systematically regulates the structure and properties of single-atom active sites by adjusting the types and ratios of transition metals and organic small molecule ligands to prepare carbon-based lithium-ion battery negative electrode materials containing single-atom active sites. The negative electrode material can effectively increase the lithium storage capacity of the negative electrode and improve the specific capacity by ≥30%, breaking through the capacity limit of existing commercial graphite negative electrodes and significantly improving the specific capacity, cycle stability, and fast charging performance of lithium-ion batteries.

[0009] Preferably, the content of transition metal doped in the graphite is 2-5 wt %.

[0010] This application

[0011] In a second aspect, the present application provides a method for preparing a single-atom-doped graphite negative electrode material for a lithium-ion battery, using the following technical solution:

[0012] Step 1: Dissolve the transition metal salt and the organic small molecule ligand in ethanol to form a transition metal salt ethanol solution and an organic small molecule ligand ethanol solution respectively, mix the prepared transition metal salt ethanol solution and the organic small molecule ligand ethanol solution, and stir them at 25-80° C. for 12-24 hours to form a stable precursor mixed solution;

[0013] Step 2: Graphite and ethanol are stirred and mixed to form a graphite-ethanol mixed solution. According to the content of transition metal doped in the graphite of 1-10wt%, the prepared graphite-ethanol mixed solution is added to the precursor mixed solution of step 1, stirred and ultrasonically mixed to obtain a mixed slurry, and then the obtained mixed slurry is heated and stirred at 60-80°C and evaporated to remove the solvent to obtain a dry powder;

[0014] Step three, the dry powder obtained in step two is ball-milled and then subjected to high-temperature pyrolysis treatment in an inert gas atmosphere, with an inert gas flow rate of 100-150 mL / min, a heating rate of 1-10°C / min, a heating time of 30-600 min to 200-1200°C, and a cooling rate of 1-5°C / min to room temperature to obtain a single-atom doped graphite negative electrode material.

[0015] This application prepares a single-atom precursor material by loading a transition metal salt and an organic small molecule ligand onto a graphite surface. The prepared single-atom precursor material is subjected to a high-temperature pyrolysis treatment. The organic small molecule ligand is carbonized by high-temperature pyrolysis and forms single-atom active sites with the transition metal in the transition metal salt, thereby forming a graphite negative electrode material doped with transition metal single atoms. After high-temperature pyrolysis of the organic small molecule ligand, non-metallic heteroatoms, nitrogen atoms, interact with the transition metal single atoms in the transition metal salt, resulting in a uniform distribution of the transition metal single atoms in the carbon layer formed by the carbonization of the organic small molecule ligand.

[0016] Preferably, the transition metal salt is at least one of a transition metal chloride, a transition metal nitrate, a transition metal sulfate, a transition metal phthalocyanine compound, and a transition metal acetylacetonate compound; and the organic small molecule ligand is at least one of 2-methylimidazole, urea, o-phenanthroline, melamine, pyrrole, dopamine, dicyandiamide, ethylenediaminetetraacetic acid, glycine, lysine, and phenylalanine.

[0017] Preferably, the transition metal salt is one of cobalt nitrate, cobalt chloride and cobalt sulfate; and the organic small molecule ligand is o-phenanthroline or ethylenediaminetetraacetic acid or a combination of o-phenanthroline and 2-methylimidazole.

[0018] The present application limits the types of the transition metal salt and the organic small molecule ligand to ensure that the non-metallic heteroatom nitrogen atom generated after high-temperature pyrolysis of the organic small molecule ligand interacts with the transition metal single atom in the transition metal salt, so that the transition metal single atom is evenly distributed in the carbon layer formed by the carbonization of the organic small molecule ligand.

[0019] Preferably, the molar ratio of the organic small molecule ligand to the transition metal single atom in the transition metal salt is 1:(1-20).

[0020] By limiting the ratio of organic small molecule ligands and transition metal salts, the present application can avoid the distribution of transition metal single atoms on the surface of small molecule ligands due to an excessively high ratio of transition metal, and can also avoid the inability to form good atomic doping due to a low content of transition metal single atoms due to an excessively low ratio of transition metal.

[0021] Preferably, the molar concentration of the transition metal salt in the transition metal salt ethanol solution in step one is 0.01-0.2 mol / L, and the molar concentration of the organic small molecule ligand in the organic small molecule ligand ethanol solution is 0.1-1.5 mol / L; the graphite content in the graphite ethanol mixed solution in step two is 2-50 g / L; and the volume ratio of the transition metal salt ethanol solution, the organic small molecule ligand ethanol solution, and the graphite ethanol mixed solution is 1:(1-10):(2-10).

[0022] The present application further limits the molar concentrations of the transition metal ethanol solution and the organic small molecule ligand ethanol solution to ensure that the solution contains sufficient amounts of transition metals and organic small molecule ligands, while also avoiding the situation where the transition metal ethanol solution and the organic small molecule ligand ethanol solution cannot be mixed and reacted well during use due to excessive content.

[0023] Preferably, in the stirring ultrasonic mixing treatment, the stirring speed is 500-600 r / min, the stirring time is 6-8 h, the ultrasonic time is 45-60 min, the ultrasonic frequency is 40 kHz, and the ultrasonic power is 600-800 W.

[0024] The present application can further ensure the uniformity of mixing by further defining various parameters of the ultrasonic mixing process.

[0025] Preferably, in the step three, the dry powder obtained in the step two is placed in a planetary ball mill for ball milling, the ball milling speed is 600-800 rpm, the ball milling time is 45-60 min, and the particle size of the pellets is between 30-50 μm. The pellets are subjected to high-temperature pyrolysis treatment under an inert gas atmosphere, the inert gas includes nitrogen and / or argon, the flow rate of the inert gas is 100-150 mL / min, the calcination temperature is 700 ° C, the heating rate is 5 ° C / min, the holding time is 120 min, and the pellets are cooled to room temperature at a cooling rate of 2 ° C / min to obtain a single-atom doped graphite negative electrode material.

[0026] The present application can ensure that the negative electrode material finally prepared has a good particle size by limiting the parameters of the ball milling process and the parameters of the inert gas, thereby avoiding the problem of poor mixing effect during use.

[0027] In summary, this application has the following beneficial effects:

[0028] 1. In this application, a carbon-based lithium-ion battery negative electrode material containing single-atom active sites is prepared, which can effectively increase the negative electrode lithium storage capacity and improve the specific capacity by ≥30%, breaking through the capacity limit of existing commercial graphite negative electrodes and significantly improving the specific capacity, cycle stability, and fast charging performance of lithium-ion batteries.

[0029] 2. The preparation method provided in the present invention is relatively simple and easy to achieve commercial mass production, which is conducive to the rapid commercialization and use of single-atom-doped graphite negative electrode materials, thereby accelerating the development of new energy storage industries such as lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a transmission electron microscope image of the 2 wt% single-atom cobalt-doped graphite negative electrode material in Example 1 of the present application;

[0031] Figure 2This is a transmission electron micrograph of the 5 wt% single-atom cobalt-doped graphite negative electrode material in Example 12 of the present application;

[0032] Figure 3 This is a transmission electron micrograph of the 2 wt% single-atom nickel-doped graphite negative electrode material in Example 15 of the present application;

[0033] Figure 4 This is a transmission electron micrograph of the 5 wt% single-atom nickel-doped graphite negative electrode material in Example 20 of the present application;

[0034] Figure 5 This is a transmission electron micrograph of the 2 wt% single-atom iron-doped graphite negative electrode material in Example 21 of the present application;

[0035] Figure 6 This is a transmission electron microscope image of the 2 wt% single-atom manganese-doped graphite negative electrode material in Example 23 of the present application;

[0036] Figure 7 This is a transmission electron microscope image of commercial graphite powder in Comparative Example 1;

[0037] Figure 8 This is a transmission electron microscope image of the cobalt nanoparticle-doped graphite negative electrode material in Comparative Example 2. DETAILED DESCRIPTION

[0038] The present application provides a single-atom-doped graphite negative electrode material for a lithium-ion battery, comprising graphite as a carrier and transition metal single atoms doped on the graphite surface, wherein the graphite is natural graphite and / or artificial graphite; the content of the transition metal doped in the graphite is 1-10wt%; the transition metal single atoms include at least one of iron, cobalt, nickel, manganese, copper, zinc, tin, chromium, platinum, palladium, gold, ruthenium, rhodium, molybdenum, zirconium, silver, tungsten, iridium, and vanadium.

[0039] In the present application, the graphite is artificial graphite, and the discharge capacity of the artificial natural graphite and / or artificial graphite is preferably 340-365 mAh / g; the discharge capacity of the single-atom doped graphite negative electrode material is preferably 450-650 mAh / g, and the first-cycle coulombic efficiency is preferably ≥80%.

[0040] In the present application, the transition metal single atom preferably includes at least one of iron, cobalt, nickel, manganese, copper, zinc, and silver; and the content of the transition metal doped in the graphite is preferably 2-5wt%.

[0041] In the present application, the transition metal single atom is preferably cobalt, iron or manganese, and the content of the transition metal doped in the graphite is preferably 2-5 wt%.

[0042] In the present application, the transition metal single atom is preferably cobalt, and the content of the transition metal doped in the graphite is preferably 5 wt %.

[0043] In the present application, the transition metal salt is preferably at least one of a transition metal chloride, a transition metal nitrate, a transition metal sulfate, a transition metal phthalocyanine compound, and a transition metal acetylacetonate compound; the organic small molecule ligand is preferably at least one of 2-methylimidazole, urea, o-phenanthroline, melamine, pyrrole, dopamine, dicyandiamide, ethylenediaminetetraacetic acid, glycine, lysine, and phenylalanine.

[0044] In the present application, the transition metal salt is preferably one of cobalt nitrate, cobalt chloride, and cobalt sulfate; the organic small molecule ligand is preferably a combination of o-phenanthroline or ethylenediaminetetraacetic acid or o-phenanthroline and 2-methylimidazole, and the content of transition metal cobalt doped in the graphite is preferably 2-5wt%.

[0045] In the present application, the transition metal salt is preferably cobalt nitrate; the organic small molecule ligand is preferably o-phenanthroline, and the content of transition metal cobalt doped in graphite is preferably 2-5wt%.

[0046] In the present application, the transition metal salt is preferably ferric nitrate nonahydrate or manganese nitrate, the organic small molecule ligand is preferably o-phenanthroline, and the content of transition metal iron or manganese doped in the graphite is preferably 2-5 wt%.

[0047] In the present application, the molar ratio of the organic small molecule ligand to the transition metal single atom in the transition metal salt is preferably 1:(1-20), and more preferably 1:(2-8).

[0048] In the present application, the graphite preferably contains any two transition metal atoms selected from iron, cobalt, nickel, manganese, copper, zinc, tin, chromium, platinum, palladium, gold, ruthenium, rhodium, molybdenum, zirconium, silver, tungsten, iridium, and vanadium, and the molar ratio of the two transition metal atoms is preferably 1:(1-10).

[0049] In the present application, the graphite preferably contains any two transition metal atoms selected from iron, cobalt, nickel, manganese, copper, zinc, tin, chromium, platinum, palladium, gold, ruthenium, rhodium, molybdenum, zirconium, silver, tungsten, iridium, and vanadium, and the molar ratio of the two transition metal atoms is preferably 1:(1-3).

[0050] In the present application, the graphite preferably contains any three transition metal atoms of iron, cobalt, nickel, manganese, copper, zinc, tin, chromium, platinum, palladium, gold, ruthenium, rhodium, molybdenum, zirconium, silver, tungsten, iridium, and vanadium, and the molar ratio of the three transition metal atoms is preferably 1:(1-10):(1-10).

[0051] In the present application, the graphite preferably contains any three transition metal atoms of iron, cobalt, nickel, manganese, copper, zinc, tin, chromium, platinum, palladium, gold, ruthenium, rhodium, molybdenum, zirconium, silver, tungsten, iridium, and vanadium, and the molar ratio of the three transition metal atoms is preferably 1:(1-2):(1-4).

[0052] The present invention also provides a method for preparing the aforementioned single-atom-doped graphite negative electrode material for lithium-ion batteries, comprising the following steps:

[0053] Step 1: Dissolve the transition metal salt and the organic small molecule ligand in ethanol to form a transition metal salt ethanol solution and an organic small molecule ligand ethanol solution respectively, mix the prepared transition metal salt ethanol solution and the organic small molecule ligand ethanol solution, and stir them at 25-80° C. for 12-24 hours to form a stable precursor mixed solution;

[0054] Step 2: Graphite and ethanol are stirred and mixed to form a graphite-ethanol mixed solution. According to the content of transition metal doped in graphite of 1-10wt%, the configured graphite-ethanol mixed solution is added to the precursor mixed solution of step 1, stirred and ultrasonically mixed to obtain a mixed slurry. The stirring speed in the ultrasonic mixing process is 300-600r / min, the stirring time is 2-8h, the ultrasonic time is 15-60min, the ultrasonic frequency is 28-80kHz, and the ultrasonic power is 500-2000W. The obtained mixed slurry is then placed at 60-80°C, heated, stirred, and evaporated to remove the solvent to obtain a dry powder;

[0055] Step three, the dry powder obtained in step two is ball-milled and then subjected to high-temperature pyrolysis treatment in an inert gas atmosphere, with an inert gas flow rate of 100-150 mL / min, a heating rate of 1-10°C / min, a temperature rise to 200-1200°C, a holding time of 30-600 min, and a cooling rate of 1-5°C / min to room temperature to obtain a single-atom doped graphite negative electrode material.

[0056] In the present application, the step one is preferably: fully dissolving the transition metal salt and the organic small molecule ligand in ethanol to form a transition metal salt ethanol solution and an organic small molecule ligand ethanol solution, respectively, mixing the configured transition metal salt ethanol solution and the organic small molecule ligand ethanol solution and then fully stirring them at 55-60°C for 12-14h to form a stable precursor mixed solution.

[0057] In the present application, the molar concentration of the transition metal salt in the transition metal salt ethanol solution in step one is preferably 0.01-0.2 mol / L, and the molar concentration of the organic small molecule ligand in the organic small molecule ligand ethanol solution is preferably 0.1-1.5 mol / L; the graphite content in the graphite ethanol mixed solution in step two is preferably 2-50 g / L; the volume ratio of the transition metal salt ethanol solution, the organic small molecule ligand ethanol solution, and the graphite ethanol mixed solution is preferably 1:(1-10):(2-10).

[0058] In the present application, the stirring speed in the stirring ultrasonic mixing treatment is preferably 500-600 r / min, the stirring time is preferably 6-8 h, the ultrasonic time is preferably 45-60 min, the ultrasonic frequency is preferably 40 kHz, and the ultrasonic power is preferably 600-800 W.

[0059] In the present application, the inert gas in step 3 preferably includes nitrogen and / or argon, the flow rate of the inert gas is preferably 100-150 mL / min, the calcination temperature is preferably 600-800°C, the heating rate is preferably 5-10°C / min, the holding time is preferably 100-150 min, and it is preferably cooled to room temperature at a cooling rate of 2-3°C / min.

[0060] In the present application, in the step three, the dry powder obtained in step two is preferably placed in a planetary ball mill for ball milling, the ball milling speed is preferably 600-800 rpm, the ball milling time is preferably 45-60 min, and the particle size of the pellets is preferably between 30-50 μm. It is subjected to high-temperature pyrolysis treatment under an inert gas atmosphere, and the inert gas preferably includes nitrogen and / or argon. The flow rate of the inert gas is preferably 100-150 mL / min, the calcination temperature is preferably 700 ° C, the heating rate is preferably 5 ° C / min, the holding time is preferably 120 min, and it is preferably cooled to room temperature at a cooling rate of 2 ° C / min to obtain a single atom doped graphite negative electrode material.

[0061] In order to further understand the present invention, preferred embodiments of the present invention are described below with reference to examples and comparative examples.

[0062] Example 1

[0063] A method for preparing a single-atom-doped graphite negative electrode material for a lithium-ion battery comprises the following steps:

[0064] Step 1: Prepare 0.5 mol / L cobalt nitrate ethanol solution: weigh cobalt nitrate hexahydrate, dissolve it in ethanol, and sonicate for 10 minutes to obtain 0.5 mol / L cobalt nitrate ethanol solution for later use;

[0065] Meanwhile, prepare a 1 mol / L organic small molecule solution: weigh 1-phenanthroline, dissolve it in ethanol, and sonicate for 10 min to obtain a 1 mol / L organic small molecule solution for later use;

[0066] A 0.5 mol / L cobalt nitrate ethanol solution and a 1 mol / L organic small molecule solution were stirred and mixed in a volume ratio of 1:1, and the mixture was fully reacted at 60°C for 12 hours to obtain a stable precursor mixed solution;

[0067] Step 2: Weigh artificial graphite with a discharge capacity of 365.37 mAh / g, the cobalt metal in the cobalt nitrate ethanol solution is 2wt% of the mass of the graphite powder, the graphite and ethanol are stirred and mixed to form a graphite ethanol mixed solution, and then the graphite ethanol mixed solution is added to the precursor mixed solution of step 1 at a dropwise rate of 1 L / h under stirring, and ultrasonically mixed to obtain a mixed slurry. During the stirring and ultrasonic mixing treatment, the stirring speed is 500 r / min, the stirring time is 8h, and the ultrasonic time is 45min; the ultrasonic frequency is 40kHz, and the ultrasonic power is 800W. The mixed slurry is then dried, heated and stirred at 80°C, and the solvent is removed by rotary evaporation to obtain a dry powder;

[0068] Step 3: The dry powder obtained in step 2 is ball-milled in a planetary ball mill at a ball milling speed of 600 rpm for 60 min until the particle size of the pellets is between 30 and 50 μm. The ball-milled powder is then transferred to a tube furnace for high-temperature pyrolysis treatment under a nitrogen atmosphere. The temperature is raised to 700°C at a rate of 5°C / min and kept for 120 min. After cooling to room temperature at a cooling rate of 2°C / min, the single-atom cobalt-doped graphite negative electrode material for lithium-ion batteries (cobalt metal loading is 2 wt%) is obtained. Figure 1 This is a transmission electron microscope image of the 2wt% single-atom cobalt-doped graphite negative electrode material in Example 1.

[0069] Example 2

[0070] The difference between Example 2 and Example 1 is that step 1 in Example 1 is replaced by "Step 1, prepare 0.5 mol / L cobalt nitrate solution: weigh cobalt nitrate hexahydrate, dissolve it in methanol, and ultrasonically dissolve it for 10 minutes to obtain a 0.5 mol / L cobalt nitrate solution for use; when preparing a 2 mol / L organic small molecule solution, weigh 2-methylimidazole, dissolve it in methanol, and ultrasonically dissolve it for 10 minutes; stir and mix the 2 mol / L 2-methylimidazole solution and the 0.5 mol / L cobalt nitrate solution, and fully react at 60°C for 12 hours to obtain a stable precursor mixed solution."

[0071] Example 3

[0072] The difference between Example 3 and Example 1 is that step 1 in Example 1 is replaced by "step 1, preparing a 0.5 mol / L cobalt nitrate solution: weighing cobalt nitrate hexahydrate, dissolving it in ethanol, and ultrasonically dissolving it for 10 minutes to obtain a 0.5 mol / L cobalt nitrate solution for use; when preparing a 3 mol / L organic small molecule solution, weighing dicyandiamide, dissolving it in ethanol, and ultrasonically dissolving it for 10 minutes; stirring and mixing the 3 mol / L dicyandiamide solution and the 0.5 mol / L cobalt nitrate solution, and fully reacting them at 80°C for 12 hours to obtain a stable precursor mixed solution."

[0073] Example 4

[0074] The difference between Example 4 and Example 1 is that step 1 in Example 1 is replaced by “step 1, preparing a 0.5 mol / L cobalt nitrate solution: weighing cobalt nitrate hexahydrate, dissolving it in ethanol, and ultrasonically dissolving it for 10 minutes, and setting aside; when preparing a 4 mol / L organic small molecule solution, weighing melamine, dissolving it in ethanol, and ultrasonically dissolving it at 80°C for 60 minutes; stirring and mixing the melamine solution and the cobalt nitrate solution, and fully reacting them at 80°C for 24 hours to obtain a stable precursor mixed solution”.

[0075] Example 5

[0076] The difference between Example 5 and Example 1 is that step three in Example 1 is replaced by "step three, ball milling the dry powder in step two in a planetary ball mill, the ball milling speed is 600 rpm, and the ball milling time is 60 min, then transferring the sample to a tubular furnace, and performing high-temperature pyrolysis treatment under a nitrogen gas atmosphere, raising the temperature to 600°C at a rate of 5°C / min, keeping warm for 120 min, and finally cooling to room temperature at a cooling rate of 2°C / min, taking out to obtain a single-atom cobalt-doped graphite negative electrode material for lithium-ion batteries."

[0077] Example 6

[0078] The difference between Example 6 and Example 1 is that step three in Example 1 is replaced by "step three, ball milling the dry powder in step two in a planetary ball mill, with a ball milling speed of 600 rpm and a ball milling time of 60 min, then transferring the sample to a tubular furnace, and performing high-temperature pyrolysis treatment in a nitrogen gas atmosphere, raising the temperature to 800°C at a rate of 5°C / min, keeping warm for 120 min, and finally cooling to room temperature at a cooling rate of 2°C / min, taking out to obtain a single-atom cobalt-doped graphite negative electrode material for lithium-ion batteries."

[0079] Example 7

[0080] The difference between Example 7 and Example 1 is that "weighing o-phenanthroline" in Example 1 is replaced by "ethylenediaminetetraacetic acid"; at the same time, step 1 in Example 1 is replaced by "step 1, preparing a 0.5 mol / L cobalt nitrate solution: weighing cobalt nitrate hexahydrate, dissolving it in ethanol, and ultrasonically dissolving it for 10 minutes, and setting aside; when preparing a 1 mol / L organic small molecule solution, weighing ethylenediaminetetraacetic acid, dissolving it in ethanol, and ultrasonically dissolving it for 10 minutes; stirring and mixing the ethylenediaminetetraacetic acid solution and the cobalt nitrate solution, and fully reacting them at 80°C for 24 hours to obtain a stable precursor mixed solution."

[0081] Example 8

[0082] The difference between Example 8 and Example 1 is that step 1 in Example 1 is replaced by “Step 1: prepare 0.5 mol / L cobalt chloride ethanol solution: weigh cobalt chloride, dissolve it in ethanol, ultrasonically dissolve it for 10 minutes, and set aside; when preparing 1 mol / L organic small molecule solution, weigh 1-phenanthroline, dissolve it in ethanol, and ultrasonically dissolve it for 10 minutes; stir and mix the 1-phenanthroline ethanol solution and the cobalt chloride ethanol solution, and fully react at 60°C for 12 hours to obtain a stable precursor mixed solution”.

[0083] Example 9

[0084] The difference between Example 9 and Example 1 is that step 1 in Example 1 is replaced by “Step 1: prepare 0.5 mol / L cobalt sulfate ethanol solution: weigh cobalt sulfate, dissolve it in ethanol, ultrasonically dissolve it for 10 minutes, and set aside; when preparing 1 mol / L organic small molecule solution, weigh 1-phenanthroline, dissolve it in ethanol, and ultrasonically dissolve it for 10 minutes; stir and mix the 1-phenanthroline ethanol solution and the cobalt sulfate ethanol solution, and fully react at 60°C for 12 hours to obtain a stable precursor mixed solution”.

[0085] Example 10

[0086] The difference between Example 10 and Example 1 is that step 1 in Example 1 is replaced by "step 1, preparing a 0.5 mol / L cobalt nitrate solution: weighing cobalt nitrate hexahydrate, dissolving it in ethanol, and ultrasonically dissolving it for 10 minutes for standby use; when preparing a 1 mol / L organic small molecule solution, weighing 1,0-phenanthroline, dissolving it in ethanol, and ultrasonically dissolving it for 10 minutes; when preparing a 2 mol / L organic small molecule solution, weighing 2-methylimidazole, dissolving it in ethanol, and ultrasonically dissolving it at 80°C for 60 minutes; stirring and mixing the 1,0-phenanthroline solution, 2-methylimidazole solution and cobalt nitrate solution, and fully reacting them at 80°C for 24 hours to obtain a stable precursor mixed solution."

[0087] Example 11

[0088] The difference between Example 11 and Example 1 is that step 1 in Example 1 is replaced by "step 1, preparing a 0.5 mol / L cobalt nitrate solution: weighing cobalt nitrate hexahydrate, dissolving it in ethanol, and ultrasonically dissolving it for 10 minutes, and setting aside; when preparing a 1 mol / L organic small molecule solution, weighing 1-phenanthroline, dissolving it in ethanol, and ultrasonically dissolving it for 10 minutes; when preparing a 4 mol / L organic small molecule solution, weighing melamine, dissolving it in ethanol, and ultrasonically dissolving it at 80°C for 60 minutes; stirring and mixing the 1-phenanthroline solution, melamine solution and cobalt nitrate solution, and fully reacting them at 80°C for 24 hours to obtain a stable precursor mixed solution."

[0089] Example 12

[0090] The difference between Example 12 and Example 1 is that step 2 in Example 1 is replaced by “step 2: weighing artificial graphite with a discharge capacity of 365.37 mAh / g, the cobalt metal in the cobalt nitrate ethanol solution is 5 wt% of the mass of the graphite powder, the graphite and ethanol are stirred and mixed to form a graphite-ethanol mixed solution, and then the graphite-ethanol mixed solution is slowly added to the precursor mixed solution of step 1 under stirring, and ultrasonically mixed to obtain a mixed slurry. During the stirring and ultrasonic mixing treatment, the stirring speed is 500 r / min, the stirring time is 8 h, and the ultrasonic time is 45 min; the ultrasonic frequency is 40 kHz, and the ultrasonic power is 800 W. The mixed slurry is then dried, heated at 80° C. and stirred by rotary evaporation to remove the solvent to obtain a dry powder.” Figure 2 This is a transmission electron microscope image of the 5wt% single-atom cobalt doped graphite negative electrode material in Example 12.

[0091] Example 13

[0092] The difference between Example 13 and Example 12 is that step 1 in Example 12 is replaced by "step 1, prepare 0.5 mol / L cobalt nitrate solution: weigh cobalt nitrate hexahydrate, dissolve it in ethanol, and dissolve it by ultrasonication for 10 minutes, and set aside; when preparing 1 mol / L organic small molecule solution, weigh 1-phenanthroline, dissolve it in ethanol, and dissolve it by ultrasonication for 10 minutes; when preparing 2 mol / L organic small molecule solution, weigh 2-methylimidazole, dissolve it in ethanol, and dissolve it by ultrasonication at 80°C for 60 minutes; stir and mix the 1-phenanthroline solution, 2-methylimidazole solution and cobalt nitrate solution, and fully react at 80°C for 24 hours to obtain a stable precursor mixed solution."

[0093] Example 14

[0094] The difference between Example 14 and Example 12 is that step three in Example 12 is replaced by "ball milling the dry powder obtained in step two in a planetary ball mill at a ball milling speed of 600 rpm and a ball milling time of 60 min until the particle size of the granules is between 30-50 μm, and then transferring the ball-milled powder to a tubular furnace and performing high-temperature pyrolysis treatment in a nitrogen gas atmosphere, heating the temperature to 600°C at a rate of 5°C / min and holding the temperature for 120 min, then cooling to room temperature at a cooling rate of 2°C / min, and taking out to obtain a single-atom cobalt-doped graphite negative electrode material for lithium-ion batteries."

[0095] Example 15

[0096] The difference between Example 15 and Example 1 is that step 1 in Example 1 is replaced by “Step 1: preparing a 0.5 mol / L nickel nitrate ethanol solution: weighing nickel nitrate hexahydrate, dissolving it in ethanol, and sonicating for 10 minutes to dissolve it, and setting aside; when preparing a 1.5 mol / L organic small molecule solution, weighing o-phenanthroline, dissolving it in ethanol, and sonicating for 10 minutes to dissolve it; stirring and mixing the o-phenanthroline ethanol solution and the nickel nitrate ethanol solution, and fully reacting them at 60° C. for 12 hours to obtain a stable precursor mixed solution”. Figure 3 This is a transmission electron microscope image of the 2wt% single-atom nickel-doped graphite negative electrode material in Example 15.

[0097] Example 16

[0098] The difference between Example 16 and Example 15 is that step one in Example 15 is replaced by "step one, prepare 0.5 mol / L nickel nitrate solution: weigh cobalt nitrate hexahydrate, dissolve it in ethanol, and dissolve it by ultrasonication for 10 minutes, and set aside; when preparing 1.5 mol / L organic small molecule solution, weigh o-phenanthroline, dissolve it in ethanol, and dissolve it by ultrasonication for 10 minutes; when preparing 3 mol / L organic small molecule solution, weigh 2-methylimidazole, dissolve it in ethanol, and dissolve it by ultrasonication at 80°C for 60 minutes; stir and mix the o-phenanthroline solution, 2-methylimidazole solution and nickel nitrate solution, and fully react at 80°C for 24 hours to obtain a stable precursor mixed solution."

[0099] Example 17

[0100] The difference between Example 17 and Example 15 is that step three in Example 12 is replaced by "Step three: ball-milling the dry powder obtained in step two in a planetary ball mill at a ball milling speed of 600 rpm and a ball milling time of 60 min until the particle size of the granules is between 30-50 μm, and then transferring the ball-milled powder to a tubular furnace and performing high-temperature pyrolysis treatment in a nitrogen gas atmosphere, heating the temperature to 600°C at a rate of 5°C / min and holding the temperature for 120 min, and then cooling to room temperature at a cooling rate of 2°C / min, taking out to obtain a single-atom cobalt-doped graphite negative electrode material for lithium-ion batteries."

[0101] Example 18

[0102] The difference between Example 18 and Example 12 is that step three in Example 12 is replaced by "Step three: ball-milling the dry powder obtained in step two in a planetary ball mill at a ball milling speed of 600 rpm and a ball milling time of 60 min until the particle size of the granules is between 30-50 μm, and then transferring the ball-milled powder to a tubular furnace and performing high-temperature pyrolysis treatment in a nitrogen gas atmosphere, heating the temperature to 800°C at a rate of 5°C / min and holding the temperature for 120 min, and then cooling to room temperature at a cooling rate of 2°C / min, taking out to obtain a single-atom cobalt-doped graphite negative electrode material for lithium-ion batteries."

[0103] Example 19

[0104] The difference between Example 19 and Example 15 is that step one in Example 15 is replaced by "Step one: prepare 0.5 mol / L nickel chloride ethanol solution: weigh nickel chloride, dissolve it in ethanol, and ultrasonically dissolve it for 10 minutes for use; when preparing 1.5 mol / L organic small molecule solution, weigh o-phenanthroline, dissolve it in ethanol, and ultrasonically dissolve it for 10 minutes; stir and mix the o-phenanthroline ethanol solution and the nickel chloride ethanol solution, and fully react at 60°C for 12 hours to obtain a stable precursor mixed solution."

[0105] Example 20

[0106] The difference between Example 20 and Example 15 is that step 2 in Example 15 is replaced by “step 2: weighing artificial graphite with a discharge capacity of 365.37 mAh / g, the nickel metal in the nickel nitrate ethanol solution is 5 wt% of the mass of the graphite powder, the graphite and ethanol are stirred and mixed to form a graphite-ethanol mixed solution, and then the graphite-ethanol mixed solution is slowly added to the precursor mixed solution of step 1 under stirring, and ultrasonically mixed to obtain a mixed slurry. During the stirring and ultrasonic mixing treatment, the stirring speed is 500 r / min, the stirring time is 8 h, and the ultrasonic time is 45 min; the ultrasonic frequency is 40 kHz, and the ultrasonic power is 800 W. The mixed slurry is then dried, heated at 80° C. and stirred by rotary evaporation to remove the solvent to obtain a dry powder.” Figure 4 This is a transmission electron microscope image of the 5wt% single-atom nickel-doped graphite negative electrode material in Example 20.

[0107] Example 21

[0108] The difference between Example 21 and Example 1 is that step 1 in Example 1 is replaced by “Step 1: preparing a 0.5 mol / L ferric nitrate ethanol solution: weighing ferric nitrate nonahydrate, dissolving it in ethanol, and sonicating for 10 minutes to dissolve it, and setting aside; when preparing a 1.5 mol / L organic small molecule solution, weighing 1,4-phenanthroline, dissolving it in ethanol, and sonicating for 10 minutes to dissolve it; stirring and mixing the 1,4-phenanthroline ethanol solution and the ferric nitrate ethanol solution, and fully reacting them at 60° C. for 12 hours to obtain a stable precursor mixed solution”. Figure 5 This is a transmission electron microscope image of the 2wt% single-atom iron-doped graphite negative electrode material in Example 21.

[0109] Example 22

[0110] The difference between Example 22 and Example 21 is that step three in Example 21 is replaced by "Step three: ball-milling the dry powder obtained in step two in a planetary ball mill at a ball milling speed of 600 rpm and a ball milling time of 60 min until the particle size of the granules is between 30-50 μm, and then transferring the ball-milled powder to a tubular furnace and performing high-temperature pyrolysis treatment in a nitrogen gas atmosphere, heating the temperature to 600°C at a rate of 5°C / min and keeping the temperature for 120 min, then cooling to room temperature at a cooling rate of 2°C / min, and taking out to obtain a single-atom cobalt-doped graphite negative electrode material for lithium-ion batteries."

[0111] Example 23

[0112] The difference between Example 23 and Example 1 is that step 1 in Example 1 is replaced by “Step 1: preparing a 0.5 mol / L manganese nitrate ethanol solution: weighing manganese nitrate, dissolving it in ethanol, and sonicating for 10 minutes to dissolve it, and setting aside; when preparing a 1 mol / L organic small molecule solution, weighing 1-phenanthroline, dissolving it in ethanol, and sonicating for 10 minutes to dissolve it; stirring and mixing the 1-phenanthroline ethanol solution and the manganese nitrate ethanol solution, and fully reacting them at 60° C. for 12 hours to obtain a stable precursor mixed solution”. Figure 6 This is a transmission electron microscope image of the 2wt% single-atom manganese-doped graphite negative electrode material in Example 23.

[0113] Example 24

[0114] The difference between Example 24 and Example 23 is that step three in Example 23 is replaced by "Step three: ball-milling the dry powder obtained in step two in a planetary ball mill at a ball milling speed of 600 rpm and a ball milling time of 60 min until the particle size of the granules is between 30-50 μm, and then transferring the ball-milled powder to a tubular furnace and performing high-temperature pyrolysis treatment in a nitrogen gas atmosphere, heating the temperature to 600°C at a rate of 5°C / min and keeping the temperature for 120 min, and then cooling to room temperature at a cooling rate of 2°C / min, taking out to obtain a single-atom cobalt-doped graphite negative electrode material for lithium-ion batteries."

[0115] Example 25

[0116] The difference between Example 25 and Example 1 is that step one in Example 1 is replaced by "Step one: prepare 0.5 mol / L copper nitrate ethanol solution: weigh copper nitrate trihydrate, dissolve it in ethanol, and ultrasonically dissolve it for 10 minutes, and set aside; when preparing 1.5 mol / L organic small molecule solution, weigh o-phenanthroline, dissolve it in ethanol, and ultrasonically dissolve it for 10 minutes; stir and mix the o-phenanthroline ethanol solution and the copper nitrate ethanol solution, and fully react at 60°C for 12 hours to obtain a stable precursor mixed solution."

[0117] Example 26

[0118] The difference between Example 26 and Example 1 is that step 1 in Example 1 is replaced by "Step 1: prepare 0.5 mol / L zinc nitrate ethanol solution: weigh zinc nitrate, dissolve it in ethanol, and ultrasonically dissolve it for 10 minutes, and set aside; when preparing 1.5 mol / L organic small molecule solution, weigh 1,0-phenanthroline, dissolve it in ethanol, and ultrasonically dissolve it for 10 minutes; stir and mix the 1,0-phenanthroline ethanol solution and the zinc nitrate ethanol solution, and fully react at 60°C for 12 hours to obtain a stable precursor mixed solution."

[0119] Example 27

[0120] The difference between Example 27 and Example 1 is that step 1 in Example 1 is replaced by "Step 1: prepare 0.5 mol / L silver nitrate ethanol solution: weigh silver nitrate, dissolve it in ethanol, and sonicate for 10 minutes to dissolve it, and set aside; when preparing 1.5 mol / L organic small molecule solution, weigh 1,0-phenanthroline, dissolve it in ethanol, and sonicate for 10 minutes to dissolve it; stir and mix the 1,0-phenanthroline ethanol solution and the silver nitrate ethanol solution, and fully react at 60°C for 12 hours to obtain a stable precursor mixed solution."

[0121] Example 28

[0122] The difference between Example 28 and Example 1 is that step 1 in Example 1 is replaced by "Step 1: prepare 0.5 mol / L cobalt nitrate ethanol solution: weigh cobalt nitrate hexahydrate, dissolve it in ethanol, and ultrasonically dissolve it for 10 minutes to obtain 0.5 mol / L cobalt nitrate ethanol solution, which is set aside; prepare 0.5 mol / L manganese nitrate ethanol solution: weigh manganese nitrate, dissolve it in ethanol, and ultrasonically dissolve it for 10 minutes to obtain 0.5 mol / L manganese nitrate ethanol solution, which is set aside; at the same time, prepare 1 mol / L organic small molecule solution: weigh o-phenanthroline, dissolve it in ethanol, and ultrasonically dissolve it for 10 minutes to obtain 1 mol / L organic small molecule solution, which is set aside; stir and mix the 0.5 mol / L cobalt nitrate ethanol solution, the 0.5 mol / L manganese nitrate ethanol solution and the 1 mol / L organic small molecule solution, and fully react at 60°C for 12 hours to obtain a stable precursor mixed solution."

[0123] Comparative Example 1

[0124] Commercial graphite powder was ground in a ball mill at 250 rpm for 30 min to obtain negative electrode material powder. Figure 7 This is the transmission electron microscope image of the commercial graphite powder in Comparative Example 1.

[0125] Comparative Example 2

[0126] The preparation method of nano-metal cluster doped graphite negative electrode material is as follows:

[0127] Step 1: Prepare 0.5 mol / L cobalt nitrate ethanol solution: weigh cobalt nitrate hexahydrate, dissolve it in ethanol, sonicate for 10 minutes, and set aside;

[0128] Step 2: Weigh commercial graphite powder, control the ratio of metal to graphite powder to be 5wt%, then slowly add the graphite powder to the precursor mixed solution of step 1 under stirring, and ultrasonically mix uniformly to obtain a mixed slurry. During the stirring and ultrasonic mixing treatment, the stirring speed is 500r / min, the stirring time is 8h, and the ultrasonic time is 45min; then the mixed slurry is dried, heated and stirred at 80°C and rotary evaporated to remove the solvent to obtain a dry powder;

[0129] Step 3: The dry powder was ball-milled in a planetary ball mill at a speed of 600 rpm for 60 min. The sample was then transferred to a tubular furnace for high-temperature pyrolysis in a nitrogen atmosphere. The temperature was raised to 700 °C at a rate of 5 °C / min and kept warm for 120 min. Finally, the sample was cooled to room temperature at a cooling rate of 2 °C / min to obtain a cobalt nanoparticle-doped graphite negative electrode material with a loading of 5 wt% of nano-metal cobalt clusters. Figure 8 This is a transmission electron microscope image of the cobalt nanoparticle-doped graphite negative electrode material in Comparative Example 2.

[0130] Performance testing: Discharge capacity and charge capacity are measured in accordance with GB / T 24533-2019. First-cycle coulombic efficiency is measured in accordance with GB / T 24533-2019.

[0131] Table 1 Test results of negative electrode materials in Examples 1-24 and Comparative Examples 1-2

[0132]

[0133] In combination with Examples 1-24 and Comparative Examples 1-2 and Table 1, it can be seen that the present application combines theoretical research on single-atom catalysis, uses commercial graphite as a carrier, and systematically regulates the structure and properties of single-atom active sites by adjusting the types and ratios of transition metals and organic small molecule ligands to prepare carbon-based lithium-ion battery negative electrode materials containing single-atom active sites. The negative electrode material can effectively increase the lithium storage capacity of the negative electrode and increase the specific capacity by ≥30%, breaking through the capacity limit of existing commercial graphite negative electrodes and greatly improving the specific capacity, cycle stability, and fast charging performance of lithium-ion batteries.

[0134] The above are all preferred embodiments of the present application, and are not intended to limit the scope of protection of the present application. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A method for preparing a single-atom-doped graphite negative electrode material for lithium-ion batteries, characterized in that: The following steps are involved: Step 1: Dissolve the transition metal salt and the organic small molecule ligand in ethanol to form a transition metal salt ethanol solution and an organic small molecule ligand ethanol solution respectively, mix the prepared transition metal salt ethanol solution and the organic small molecule ligand ethanol solution, and stir them at 25-80° C. for 12-24 hours to form a stable precursor mixed solution; Step 2: Graphite and ethanol are stirred and mixed to form a graphite-ethanol mixed solution. According to the content of transition metal doped in graphite of 1-10wt%, the configured graphite-ethanol mixed solution is added to the precursor mixed solution of step 1, stirred and ultrasonically mixed to obtain a mixed slurry, the stirring speed is 300-600r / min, the stirring time is 2-8h, the ultrasonic time is 15-60min, the ultrasonic frequency is 28-80kHz, and the ultrasonic power is 500-2000W. The obtained mixed slurry is then placed at 60-80°C, heated and stirred, and the solvent is removed by rotary evaporation to obtain a dry powder; Step 3: The dry powder obtained in step 2 is ball-milled and then subjected to high-temperature pyrolysis treatment under an inert gas atmosphere. The flow rate of the inert gas is 100-150 mL / min, the heating rate is 1-10°C / min, the temperature is raised to 600-800°C, the holding time is 120 min, and the temperature is cooled to room temperature at a cooling rate of 1-5°C / min to obtain a single-atom-doped graphite negative electrode material; The single-atom-doped graphite negative electrode material for lithium-ion batteries includes graphite as a carrier and transition metal single atoms doped on the graphite surface, wherein the graphite is natural graphite and / or artificial graphite; the discharge capacity of the natural graphite and / or artificial graphite is 340-365 mAh / g; the content of the transition metal doped in the graphite is 1-10 wt%; and the transition metal single atoms include at least one of iron, cobalt, nickel, manganese, copper, zinc, tin, chromium, platinum, palladium, gold, ruthenium, rhodium, molybdenum, zirconium, silver, tungsten, iridium, and vanadium.

2. The method for preparing a single-atom-doped graphite negative electrode material for a lithium-ion battery according to claim 1, wherein: The content of the transition metal doped in the graphite is 2-5wt%, and the transition metal single atom includes any one of iron, cobalt, nickel, and manganese.

3. The method for preparing a single-atom-doped graphite negative electrode material for a lithium-ion battery according to claim 1, wherein: The transition metal salt is at least one of a transition metal chloride, a transition metal nitrate, a transition metal sulfate, a transition metal phthalocyanine compound, and a transition metal acetylacetonate compound; the organic small molecule ligand is at least one of 2-methylimidazole, urea, o-phenanthroline, melamine, pyrrole, dopamine, dicyandiamide, ethylenediaminetetraacetic acid, glycine, lysine, and phenylalanine.

4. The method for preparing a single-atom-doped graphite negative electrode material for a lithium-ion battery according to claim 3, wherein: The transition metal salt is any one of cobalt nitrate, cobalt chloride and cobalt sulfate; the organic small molecule ligand is o-phenanthroline or a composition formed by o-phenanthroline and melamine or a composition formed by o-phenanthroline and 2-methylimidazole.

5. The method for preparing a single-atom-doped graphite negative electrode material for a lithium-ion battery according to claim 1, wherein: The molar ratio of the organic small molecule ligand to the transition metal single atom in the transition metal salt is (1-4):

1.

6. The method for preparing a single-atom-doped graphite negative electrode material for a lithium-ion battery according to claim 5, characterized in that: In the step 1, the molar concentration of the transition metal salt in the transition metal salt ethanol solution is 0.5 mol / L, and the molar concentration of the organic small molecule ligand in the organic small molecule ligand ethanol solution is 1-4 mol / L.

7. The method for preparing a single-atom-doped graphite negative electrode material for a lithium-ion battery according to claim 1, wherein: In the stirring and ultrasonic mixing treatment in step 2, the stirring speed is 500-600 r / min, the stirring time is 6-8 h, the ultrasonic time is 45-60 min, the ultrasonic frequency is 40 kHz, and the ultrasonic power is 600-800 W.

8. The method for preparing a single-atom-doped graphite negative electrode material for a lithium-ion battery according to claim 1, wherein: In the step three, the dry powder obtained in the step two is placed in a planetary ball mill for ball milling treatment, the ball milling speed is 600-800 rpm, the ball milling time is 45-60 min, and the particle size of the pellets is between 30-50 μm. The pellets are subjected to high-temperature pyrolysis treatment under an inert gas atmosphere, the inert gas includes nitrogen and / or argon, the inert gas flow rate is 100-150 mL / min, the calcination temperature is 700 ° C, the heating rate is 5 ° C / min, the holding time is 120 min, and the pellets are cooled to room temperature at a cooling rate of 2 ° C / min to obtain a single-atom doped graphite negative electrode material.

9. The method for preparing a single-atom-doped graphite negative electrode material for a lithium-ion battery according to claim 1, wherein: The following steps are involved: Step 1: Prepare 0.5 mol / L cobalt nitrate ethanol solution: weigh cobalt nitrate hexahydrate, dissolve it in ethanol, and sonicate for 10 minutes to obtain 0.5 mol / L cobalt nitrate ethanol solution for later use; Meanwhile, prepare a 1 mol / L organic small molecule solution: weigh 1-phenanthroline, dissolve it in ethanol, and sonicate for 10 min to obtain a 1 mol / L organic small molecule solution for later use; A 0.5 mol / L cobalt nitrate ethanol solution and a 1 mol / L organic small molecule solution were stirred and mixed in a volume ratio of 1:1, and the mixture was fully reacted at 60°C for 12 hours to obtain a stable precursor mixed solution; Step 2: Weigh artificial graphite with a discharge capacity of 365.37 mAh / g, the cobalt metal in the cobalt nitrate ethanol solution is 5wt% of the mass of the graphite powder, the graphite and ethanol are stirred and mixed to form a graphite ethanol mixed solution, and then the graphite ethanol mixed solution is slowly added to the precursor mixed solution of step 1 under stirring, and ultrasonically mixed to obtain a mixed slurry. During the stirring and ultrasonic mixing treatment, the stirring speed is 500 r / min, the stirring time is 8h, and the ultrasonic time is 45min; the ultrasonic frequency is 40kHz, and the ultrasonic power is 800W. The mixed slurry is then dried, heated at 80°C and stirred and evaporated to remove the solvent to obtain a dry powder; Step 3: The dry powder obtained in step 2 is ball-milled in a planetary ball mill at a ball-milling speed of 600 rpm for 60 min until the particle size of the pellets is between 30 and 50 μm. The ball-milled powder is then transferred to a tubular furnace and subjected to high-temperature pyrolysis treatment in a nitrogen atmosphere. The temperature is raised to 700°C at a rate of 5°C / min and kept for 120 min. After cooling to room temperature at a cooling rate of 2°C / min, the single-atom cobalt-doped graphite negative electrode material for lithium-ion batteries is obtained.

10. The method for preparing a single-atom-doped graphite negative electrode material for a lithium-ion battery according to claim 9, characterized in that: The single-atom cobalt-doped graphite negative electrode material has a discharge capacity of 627.62 mAh / g, a charge capacity of 505.08 mAh / g, and a first-cycle coulombic efficiency of 84.46%.

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