Transition metal monatomic / nitrogen-doped carbon-coated lithium ion battery positive electrode material as well as preparation method and application thereof

Abstract

The invention provides a transition metal monatomic / nitrogen-doped carbon-coated lithium ion battery positive electrode material as well as a preparation method and application thereof, and belongs to the field of lithium ion battery positive electrode materials. Carbon dioxide thermal etching is adopted to treat a compound of carbonized dopamine coated silicon dioxide microspheres and a transition metal phthalocyanine complex, a large number of carbon defect sites are constructed in the carbon material, electron cloud arrangement and surface electronegativity in the carbon material are changed, and the electricity absorption effect of the carbon material is adjusted. The carbon material can effectively adjust the electronic structure of the positive electrode material of the lithium ion battery through the strong electron withdrawing effect of the carbon defect site and the pyrrole nitrogen structure and the synergistic effect of the transition metal-N-C annular carbon structure, promotes redistribution of charges in lattices of the positive electrode material of the lithium ion battery, provides an efficient electron / charge transfer path, and improves the performance of the lithium ion battery. The electronic conductivity and the ionic conductivity of the positive electrode material are powerfully improved, so that the compaction density, the discharge capacity and the rate capability of the material are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery cathode materials, and particularly relates to a transition metal single atom / nitrogen-doped carbon-coated lithium ion battery cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous improvement of the demand for battery performance, the market urgently needs the technological iteration of high-energy-density lithium ion battery products. The cathode material is a key factor determining the performance of lithium ion batteries. Common lithium ion battery cathode materials include lithium iron phosphate, lithium manganese phosphate, lithium manganate, lithium cobaltate, lithium nickel manganate, ternary cathode materials, and lithium-rich manganese-based cathode materials, etc. Cathode materials with high capacity, long cycle life, and high safety have become the focus of research and development in the new energy industry. Each researcher has started to modify the materials through diversified strategies such as carbon coating, cation doping, and nanosizing. Among them, carbon coating can effectively improve the conductivity of the materials, avoid direct contact between the lithium ion battery cathode material and the electrolyte, and at the same time inhibit the excessive growth of nanoparticles during the sintering process. However, the carbon coating content should be controlled within a suitable range. If the carbon content in the cathode material is too high, although it can improve the conductivity of the material, its low density itself causes the tap density of the material to decrease, and at the same time reduces the proportion of effective active substances, resulting in a decrease in the discharge specific capacity of the material; if the carbon content is too low, it cannot effectively improve the conductivity of the material. The traditional carbon coating method is to directly mix the carbon source into the grinding process, granulate, and sinter in one step. Through simple physical mixing, the carbon coating layer often shows a dot-like distribution or agglomeration, making it difficult to control the uniformity of carbon coating, resulting in poor improvement effects on electron conductivity, lithium ion diffusivity, and interfacial impedance. In addition, the carbon coating layer prepared by this method has a weak binding force with the active substances of the lithium ion battery cathode material, resulting in more losses in subsequent processes, the carbon coating effect is not as expected, and at the same time increases the preparation cost of the material.

[0003] CN 112864368 A discloses a preparation method of a composite-coated modified lithium iron phosphate cathode material, which uses the mutual promotion between the hydrolysis of the silicon source and the polymerization of dopamine to carry out the composite coating modification of lithium iron phosphate at room temperature, and then obtains a lithium ion battery cathode material with SiO2 and nitrogen-doped carbon co-coated lithium iron phosphate after calcination. However, this prior art uses silicon dioxide coating, and silicon dioxide will reduce the electrochemical activity and charge-discharge specific capacity of the electrode material, and its cycle capacity retention rate can be further improved. Summary of the Invention

[0004] In order to solve the problems existing in the above prior art, the primary object of the present invention is to provide a transition metal single atom / nitrogen-doped carbon material.

[0005] Another object of the present invention is to provide an application of the above transition metal single atom / nitrogen-doped carbon material.

[0006] Another object of the present invention is to provide a cathode material for a lithium-ion battery comprising the above-mentioned transition metal single-atom / nitrogen-doped carbon material.

[0007] Another object of the present invention is to provide a lithium-ion battery prepared from the above-mentioned cathode material for a lithium-ion battery.

[0008] To achieve the above objects, the present invention provides the following technical solutions:

[0009] A transition metal single-atom / nitrogen-doped carbon material is prepared by the following method:

[0010] S1. Mix the dopamine-coated silica microspheres with the transition metal phthalocyanine complex to obtain a first composite material;

[0011] S2. Carbonize the first composite material, thermally etch with carbon dioxide, and remove the silica to obtain the transition metal single-atom / nitrogen-doped carbon material;

[0012] The temperature of the carbon dioxide thermal etching is 600-950 °C.

[0013] The present invention uses carbon dioxide thermal etching to treat the composite of dopamine-coated silica microspheres and transition metal phthalocyanine complex after carbonization. Utilizing the weak oxidation ability of carbon dioxide for carbon, a large number of carbon defect sites are constructed in the carbon material, changing the electron cloud arrangement, surface electronegativity in the carbon material and adjusting the electron-withdrawing effect of the carbon material. At the same time, the transition metal phthalocyanine complex and dopamine are converted into a highly conductive carbon layer material with a transition metal-N-C cyclic coordination structure and a nitrogen-doped carbon structure (pyrrole nitrogen structure) in a carbon dioxide atmosphere. Using the transition metal single-atom / nitrogen-doped carbon material as the carbon source for the cathode material of a lithium-ion battery, through the synergistic effect among the carbon defect sites, the strong electron-withdrawing effect of the pyrrole nitrogen structure and the transition metal-N-C cyclic carbon structure, the electron structure of the cathode material of the lithium-ion battery can be effectively adjusted, promoting the redistribution of charges inside the lattice of the cathode material of the lithium-ion battery, providing an efficient electron / charge transfer path, and effectively improving the electron conductivity and ionic conductivity of the cathode material, thereby improving the compaction density, discharge capacity and rate performance of the material.

[0014] Specifically, the transition metal includes at least one of iron, manganese, zinc, cobalt, copper, chromium, and nickel.

[0015] Preferably, the transition metal is at least one of iron, nickel, and copper.

[0016] Specifically, the mass ratio of the dopamine-coated silica microspheres to the transition metal phthalocyanine complex is (0.1-10):1.

[0017] Preferably, the mass ratio of the dopamine-coated silica microspheres to the transition metal phthalocyanine complex is (4-6):1.

[0018] In the present invention, the preparation of the dopamine-coated silica microspheres can refer to the prior art.

[0019] Specifically, the preparation method of the dopamine-coated silica microspheres includes: mixing dopamine with a silicon source solution and aging to obtain the dopamine-coated silica microspheres.

[0020] More specifically, the silicon source is at least one of silica, tetraethoxysilane, methyl orthosilicate, methyltrimethoxysilane, ethyltrimethoxysilane, phenyltrimethoxysilane, vinyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-(methacryloyloxy)propyltrimethoxysilane, sodium silicate, and alkoxysilanes containing sulfhydryl or amino groups.

[0021] Preferably, the silicon source is tetraethoxysilane.

[0022] More preferably, the preparation method of the dopamine-coated silica microspheres includes: first preparing silica microspheres from tetraethoxysilane by the Stober method, then mixing with dopamine and aging to obtain the dopamine-coated silica microspheres.

[0023] Specifically, the molar ratio of dopamine to silica in the dopamine-coated silica microspheres is (0.01-0.1):(1-5).

[0024] Preferably, the molar ratio of dopamine to silica in the dopamine-coated silica microspheres is (0.04-0.06):(3-4).

[0025] More preferably, the molar ratio of dopamine to silica in the dopamine-coated silica microspheres is 0.052:3.61.

[0026] Specifically, there are 0-4 substituents on the benzene ring of the transition metal phthalocyanine complex.

[0027] More specifically, the substituents are at least one of halogen, carboxyl, nitro, sulfonic acid group, and amino group.

[0028] Preferably, the temperature of the carbon dioxide thermal etching is 800-850 °C.

[0029] Specifically, the time of the carbon dioxide thermal etching is 4-20 h.

[0030] Preferably, the time of the carbon dioxide thermal etching is 4-8 h.

[0031] Specifically, the heating rate of the carbon dioxide etching is 2 to 20 °C / min.

[0032] Preferably, the heating rate of the carbon dioxide etching is 2 to 5 °C / min.

[0033] Specifically, the temperature of the carbonization is 450 to 550 °C.

[0034] Preferably, the temperature of the carbonization is 450 to 500 °C.

[0035] Specifically, the time of the carbonization is 0.5 to 8 h.

[0036] Preferably, the time of the carbonization is 2 to 4 h.

[0037] Specifically, the method for removing silicon dioxide includes treatment with hydrofluoric acid.

[0038] The present invention uses hydrofluoric acid treatment to not only remove silicon dioxide in the composite material but also remove impurities such as metallic elements in the material.

[0039] The present invention also protects the application of the above-mentioned transition metal single-atom / nitrogen-doped carbon material in the preparation of a carbon-coated lithium-ion battery cathode material.

[0040] A carbon-coated lithium-ion battery cathode material, wherein the carbon source used for carbon coating includes the above-mentioned transition metal single-atom / nitrogen-doped carbon material.

[0041] Specifically, the lithium-ion battery cathode material is at least one of lithium iron phosphate manganese, lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate, lithium nickel phosphate, lithium vanadium phosphate, lithium manganate, lithium cobaltate, lithium nickelate, lithium nickel manganate, ternary cathode material, or lithium-rich manganese-based cathode material.

[0042] Preferably, the lithium-ion battery cathode material is lithium iron phosphate manganese or lithium iron phosphate.

[0043] Specifically, the mass of the transition metal single-atom / nitrogen-doped carbon material is 0.5 to 5 wt% of the mass of the lithium-ion battery cathode material not coated with carbon.

[0044] Preferably, the mass of the transition metal single-atom / nitrogen-doped carbon material is 1 to 2 wt% of the mass of the lithium-ion battery cathode material not coated with carbon.

[0045] The present invention also protects the application of the above-mentioned carbon-coated lithium-ion battery cathode material in the preparation of a lithium-ion battery.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] The present invention uses carbon dioxide thermal etching to construct a large number of carbon defect sites in transition metal single-atom / nitrogen-doped carbon materials, changing the electron cloud arrangement, surface electronegativity in the carbon materials, and adjusting the electron-withdrawing effect of the carbon materials. Transition metal phthalocyanine complexes and dopamine are converted into a highly conductive carbon layer material with a transition metal-N-C cyclic coordination structure and a nitrogen-doped carbon structure (pyrrole nitrogen structure) under a carbon dioxide atmosphere. When the transition metal single-atom / nitrogen-doped carbon material is used as the carbon source for the positive electrode material of a lithium-ion battery, through the synergistic effect of these three factors: the carbon defect sites, the strong electron-withdrawing effect of the pyrrole nitrogen structure, and the transition metal-N-C cyclic carbon structure, this carbon material can effectively regulate the electronic structure of the positive electrode material of the lithium-ion battery, promote the redistribution of charges inside the lattice of the positive electrode material of the lithium-ion battery, provide an efficient electron / charge transfer path, and effectively improve the electronic conductivity and ionic conductivity of the positive electrode material, thereby increasing the tap density, discharge capacity, and rate performance of the material. Description of the Drawings

[0048] Figure 1 It is a scanning electron microscope image of the lithium iron phosphate manganese positive electrode material coated with single-atom iron / nitrogen-doped carbon prepared in Example 1. Detailed Embodiments

[0049] The present invention will be further described below in conjunction with embodiments. These embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. For the experimental methods without specific conditions indicated in the following examples, they are generally carried out according to the conventional conditions in the art or according to the conditions recommended by the manufacturer; the raw materials, reagents, etc. used, unless otherwise specified, are all raw materials and reagents that can be obtained from commercial channels such as conventional markets. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention fall within the scope claimed by the present invention.

[0050] Example 1

[0051] S0. Measure 0.8 L of tetraethoxysilane and add it to a 1 L mixed solution composed of ammonia water, ethanol, and ultrapure water (the volume ratio of ammonia water, ethanol, and ultrapure water is 2:3:5) and stir for 1 h to prepare a mixed solution A. Weigh 8 g of dopamine and add it to a mixed solution composed of ethanol and ultrapure water (the volume ratio of ethanol and ultrapure water is 1:1) to prepare solution B. Slowly add solution B to mixed solution A and continuously stir for 1 h, then age for 6 h, and wash, filter by suction, and dry with ultrapure water to obtain dopamine-coated silica microsphere materials. The molar ratio of dopamine to silica in the dopamine-coated silica microspheres is 0.052:3.61.

[0052] S1. Weigh and add the dopamine-coated silica microsphere material and iron phthalocyanine into N,N-dimethylformamide according to the mass ratio of 5:1 to make a mixed solution C. After stirring the mixed solution C at room temperature for 12 h, wash it with N,N-dimethylformamide and dry it in a vacuum oven at 60 °C for 12 h to obtain the first composite material.

[0053] S2. Subsequently, place the first composite material in a box-type atmosphere furnace. In the atmosphere of carbon dioxide, first heat it to 450 °C at a heating rate of 2 °C / min and keep it warm for 2 h to carbonize the first composite material; then heat it to 800 °C at a heating rate of 2 °C / min and keep it warm for 6 h to perform carbon dioxide thermal etching on the carbonized first composite material. After naturally cooling to room temperature, wash the material taken out of the furnace with 1 mol / L HF solution and dry it in a vacuum oven at 60 °C for 12 h to obtain the metal iron single atom / nitrogen-doped carbon material.

[0054] S3. Weigh the corresponding lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate according to the stoichiometric ratio of the elements lithium:manganese:iron:phosphorus of 1.08:0.7:0.3:1.05 and disperse them in ultrapure water. Based on the mass of lithium iron manganese phosphate made from lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate, add 1.6 wt% of the above metal iron single atom / nitrogen-doped carbon material as a carbon source, and add ammonium metavanadate, ammonium oxalotitanate, and magnesium chloride as dopants in the dosages with a V doping amount of 1500 ppm, a Ti doping amount of 1500 ppm, and a Mg doping amount of 2000 ppm, and grind it in a vertical sand mill until the slurry D 50 is 0.36 μm. Subsequently, transfer the slurry to a spray granulation dryer for drying to obtain a spray powder. Under the protection of a nitrogen atmosphere, place the spray powder in an atmosphere box-type furnace for segmented heating and sintering. Among them, heat it to 500 °C at a heating rate of 5 °C / min and keep it at a constant temperature for 6 h, and then heat it to 720 °C and keep it at a constant temperature for 9 h. After naturally cooling to room temperature, after airflow pulverization and sieving treatment, obtain the metal iron single atom / nitrogen-doped carbon-coated lithium iron manganese phosphate cathode material.

[0055] Example 2

[0056] S0. Measure 0.8 L of tetraethoxysilane and add it to a 1 L mixed solution composed of ammonia water, ethanol, and ultrapure water (the volume ratio of ammonia water, ethanol, and ultrapure water is 2:3:5), and stir for 1 h to prepare a mixed solution A. Weigh 8 g of dopamine and add it to a mixed solution composed of ethanol and ultrapure water (the volume ratio of ethanol and ultrapure water is 1:1) to prepare solution B. Slowly add solution B to mixed solution A and continuously stir for 1 h, then age for 6 h, and wash, filter by suction, and dry with ultrapure water to obtain dopamine-coated silica microsphere materials. The molar ratio of dopamine to silica in the dopamine-coated silica microspheres is 0.052:3.61.

[0057] S1. Weigh and add dopamine-coated silica microsphere materials and nickel phthalocyanine in a mass ratio of 4:1 to N,N-dimethylformamide to prepare a mixed solution C. After stirring the mixed solution C at room temperature for 12 h, wash it with N,N-dimethylformamide and dry it in a vacuum oven at 60 °C for 12 h to obtain the first composite material.

[0058] S2. Subsequently, place the above composite material in a box-type atmosphere furnace. In a carbon dioxide atmosphere, first heat it at a heating rate of 3 °C / min to 500 °C and hold for 3 h to carbonize the first composite material; then continue to heat it at a heating rate of 3 °C / min to 850 °C and hold for 6 h to perform carbon dioxide thermal etching on the above composite material. After naturally cooling to room temperature, wash the material taken out of the furnace with 1 mol / L HF solution and dry it in a vacuum oven at 60 °C for 12 h to obtain metal nickel single-atom / nitrogen-doped carbon materials.

[0059] S3. Weigh the corresponding lithium carbonate, manganese tetraoxide, iron phosphate, and lithium dihydrogen phosphate according to the stoichiometric ratio of the elements lithium:manganese:iron:phosphorus of 1.03:0.6:0.4:1.01 and disperse them in ultrapure water. Based on the mass of lithium iron manganese phosphate made from lithium carbonate, manganese tetraoxide, iron phosphate, and lithium dihydrogen phosphate, add 1.7 wt% of the above metal nickel single-atom / nitrogen-doped carbon materials as a carbon source, and add ammonium metavanadate, ammonium oxalotitanate, and magnesium chloride as dopants in doses with a V doping amount of 1000 ppm, a Ti doping amount of 1000 ppm, and a Mg doping amount of 3000 ppm, and grind them in a vertical sand mill to obtain slurry D 50 to 0.35 μm. Subsequently, transfer the slurry to a spray granulation dryer for drying to obtain spray powder. Under the protection of a nitrogen atmosphere, place the spray powder in an atmosphere box-type furnace for segmented heating and sintering. Among them, heat it at a heating rate of 5 °C / min, first heat it to 500 °C and keep it constant for 6 h, and then heat it to 760 °C and keep it constant for 9 h. After naturally cooling to room temperature, after airflow pulverization and sieving treatment, obtain metal nickel single-atom / nitrogen-doped carbon-coated lithium iron manganese phosphate cathode materials.

[0060] Example 3

[0061] S0. Measure 0.8 L of tetraethoxysilane and add it to a 1 L mixed solution composed of ammonia water, ethanol, and ultrapure water (the volume ratio of ammonia water, ethanol, and ultrapure water is 2:3:5), and stir for 1 h to prepare a mixed solution A. Weigh 8 g of dopamine and add it to a mixed solution composed of ethanol and ultrapure water (the volume ratio of ethanol and ultrapure water is 1:1) to prepare solution B. Slowly add solution B to mixed solution A and continuously stir for 1 h, then age for 6 h, and wash, filter by suction, and dry with ultrapure water to obtain dopamine-coated silica microsphere materials. The molar ratio of dopamine to silica in the dopamine-coated silica microspheres is 0.052:3.61.

[0062] S1. Weigh and add dopamine-coated silica microsphere materials and copper phthalocyanine in a mass ratio of 6:1 to N,N-dimethylformamide to prepare a mixed solution C. After stirring the mixed solution C at room temperature for 12 h, wash it with N,N-dimethylformamide and place it in a vacuum oven at 60 °C to dry for 12 h to obtain the first composite material.

[0063] S2. Subsequently, place the above composite material in a box-type atmosphere furnace. In a carbon dioxide atmosphere, first heat it at a heating rate of 5 °C / min to 500 °C and hold for 4 h to carbonize the first composite material; then continue to heat it at a heating rate of 5 °C / min to 800 °C and hold for 6 h to perform carbon dioxide thermal etching on the above composite material. After naturally cooling to room temperature, wash the material taken out of the furnace with 1 mol / L HF solution and place it in a vacuum oven at 60 °C to dry for 12 h to obtain metal copper single atom / nitrogen-doped carbon materials.

[0064] S3. Weigh the corresponding lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate according to the stoichiometric ratio of the elements of lithium:manganese:iron:phosphorus of 1.05:0.8:0.2:1.02 and disperse them in ultrapure water. Based on the mass of lithium iron manganese phosphate made from lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate, add 1.6 wt% of the above metal copper single atom / nitrogen-doped carbon materials as a carbon source, and add ammonium oxalate titanate and magnesium chloride as dopants with a Ti doping amount of 1500 ppm and a Mg doping amount of 2500 ppm, and grind them in a vertical sand mill to a slurry D 50 with a particle size of 0.37 μm. Subsequently, transfer the slurry to a spray granulation dryer for drying to obtain a spray powder. Under the protection of a nitrogen atmosphere, place the spray powder in an atmosphere box-type furnace for segmented heating and sintering. Among them, heat it at a heating rate of 2 °C / min, first heat it to 550 °C and hold for 6 h, and then heat it to 750 °C and hold for 10 h. After naturally cooling to room temperature, obtain metal copper single atom / nitrogen-doped carbon-coated lithium iron manganese phosphate cathode materials after airflow pulverization and sieving treatment.

[0065] Example 4

[0066] S0. Measure 0.8 L of tetraethoxysilane and add it to 1 L of a mixed solution composed of ammonia water, ethanol, and ultrapure water (the volume ratio of ammonia water, ethanol, and ultrapure water is 2:3:5), and stir for 1 h to prepare a mixed solution A. Weigh 8 g of dopamine and add it to a mixed solution composed of ethanol and ultrapure water (the volume ratio of ethanol and ultrapure water is 1:1) to prepare solution B. Slowly add solution B to mixed solution A and continuously stir for 1 h, then age for 6 h, and wash, filter by suction, and dry with ultrapure water to obtain dopamine-coated silica microsphere materials. The molar ratio of dopamine to silica in the dopamine-coated silica microspheres is 0.052:3.61.

[0067] S1. Weigh and add dopamine-coated silica microsphere materials and iron phthalocyanine in a mass ratio of 5:1 to N,N-dimethylformamide to prepare a mixed solution C. After stirring the mixed solution C at room temperature for 12 h, wash it with N,N-dimethylformamide and place it in a vacuum oven at 60 °C for drying for 12 h to obtain the first composite material.

[0068] S2. Subsequently, place the first composite material in a box-type atmosphere furnace. In a carbon dioxide atmosphere, first heat it at a heating rate of 2 °C / min to 450 °C and hold for 2 h to carbonize the first composite material; then continue to heat it at a heating rate of 2 °C / min to 800 °C and hold for 6 h to perform carbon dioxide thermal etching on the above composite material. After naturally cooling to room temperature, wash the material taken out of the furnace with 1 mol / L HF solution and place it in a vacuum oven at 60 °C for drying for 12 h to obtain metal iron single-atom / nitrogen-doped carbon materials.

[0069] S3. Weigh the corresponding lithium carbonate, iron phosphate, and lithium dihydrogen phosphate according to the stoichiometric ratio of lithium:iron:phosphorus of 1.03:1:1.03 and disperse them in ultrapure water. Based on the mass of lithium iron phosphate made from lithium carbonate, iron phosphate, and lithium dihydrogen phosphate, add 1.6 wt% of the above metal iron single-atom / nitrogen-doped carbon materials as a carbon source, and add ammonium metavanadate, ammonium oxalotitanate, and magnesium chloride as dopants with a V doping amount of 1500 ppm, a Ti doping amount of 1500 ppm, and a Mg doping amount of 2000 ppm, and grind them in a vertical sand mill to obtain slurry D 50 to 0.36 μm. Subsequently, transfer the slurry to a spray granulation dryer for drying to obtain spray powder. Under the protection of a nitrogen atmosphere, place the spray powder in an atmosphere box-type furnace for staged heating and sintering. Among them, heat it at a heating rate of 5 °C / min, first heat it to 500 °C and hold for 6 h, and then heat it to 780 °C and hold for 10 h. After naturally cooling to room temperature, after airflow pulverization and sieving treatment, obtain metal iron single-atom / nitrogen-doped carbon-coated lithium iron phosphate cathode materials.

[0070] Comparative Example 1

[0071] The difference between this comparative example and Example 1 is that the composite material of iron phthalocyanine and dopamine-coated silica microspheres was not subjected to carbon dioxide thermal etching and HF treatment, and was directly used as a carbon source.

[0072] S0. Measure 0.8 L of tetraethoxysilane and add it to 1 L of a mixed solution composed of ammonia water, ethanol, and ultrapure water (the volume ratio of ammonia water, ethanol, and ultrapure water is 2:3:5), and stir for 1 h to prepare a mixed solution A. Weigh 8 g of dopamine and add it to a mixed solution composed of ethanol and ultrapure water (the volume ratio of ethanol and ultrapure water is 1:1) to prepare solution B. Slowly add solution B to mixed solution A, and continuously stir for 1 h, then age for 6 h, and wash, filter, and dry with ultrapure water to obtain dopamine-coated silica microsphere material. The molar ratio of dopamine to silica in the dopamine-coated silica microspheres is 0.052:3.61.

[0073] S1. Weigh and add the dopamine-coated silica microsphere material and iron phthalocyanine in a mass ratio of 5:1 to N,N-dimethylformamide to prepare a mixed solution C. After stirring the mixed solution C at room temperature for 12 h, wash it with N,N-dimethylformamide, and dry it in a vacuum oven at 60 °C for 12 h to obtain the first composite material.

[0074] S2. Weigh the corresponding lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate according to the stoichiometric ratio of the elements lithium:manganese:iron:phosphorus of 1.08:0.7:0.3:1.05 and disperse them in ultrapure water. Based on the mass of lithium iron manganese phosphate made from lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate, add 1.6 wt% of the above composite material of iron phthalocyanine and dopamine-coated silica microspheres as a carbon source, and add ammonium metavanadate, ammonium oxalotitanate, and magnesium chloride as dopants in doses with a V doping amount of 1500 ppm, a Ti doping amount of 1500 ppm, and a Mg doping amount of 2000 ppm, and grind to slurry D in a vertical sand mill 50 to 0.36 μm. Subsequently, transfer the slurry to a spray granulation dryer for drying to obtain a spray powder. Under the protection of a nitrogen atmosphere, place the spray powder in an atmosphere box furnace for segmented heating and sintering. Among them, with a heating rate of 5 °C / min, first heat up to 500 °C and keep it constant for 6 h, then heat up to 720 °C and keep it constant for 9 h. After naturally cooling to room temperature, obtain a lithium iron manganese phosphate cathode material with single-atom iron / nitrogen-doped carbon composite silica coating through air flow crushing and sieving treatment.

[0075] Comparative Example 2

[0076] The difference between this comparative example and Example 1 is that only the nitrogen-doped carbon material obtained by carbon dioxide thermal etching and HF treatment of dopamine-coated silica microsphere material is used as the carbon source, and iron phthalocyanine is not introduced.

[0077] S0. Measure 0.8 L of tetraethoxysilane and add it to 1 L of a mixed solution composed of ammonia water, ethanol, and ultrapure water (the volume ratio of ammonia water, ethanol, and ultrapure water is 2:3:5), and stir for 1 h to prepare a mixed solution A. Weigh 8 g of dopamine and add it to a mixed solution composed of ethanol and ultrapure water (the volume ratio of ethanol and ultrapure water is 1:1) to prepare solution B. Slowly add solution B to mixed solution A and continuously stir for 1 h, then age for 6 h, and wash, filter, and dry with ultrapure water to obtain dopamine-coated silica microsphere material. The molar ratio of dopamine to silica in the dopamine-coated silica microspheres is 0.052:3.61.

[0078] S1. Place the above dopamine-coated silica microsphere material in a box-type atmosphere furnace. In the atmosphere of carbon dioxide, first heat it at a heating rate of 2 °C / min to 450 °C and keep it warm for 2 h, then continue to heat it at a heating rate of 2 °C / min to 800 °C and keep it warm for 6 h. After naturally cooling to room temperature, wash the material taken out of the furnace with 1 mol / L HF solution and dry it in a 60 °C vacuum oven for 12 h to obtain nitrogen-doped carbon material.

[0079] S2. Weigh the corresponding lithium carbonate, manganese tetraoxide, iron phosphate, and lithium dihydrogen phosphate according to the stoichiometric ratio of lithium:manganese:iron:phosphorus of 1.08:0.7:0.3:1.05 and disperse them in ultrapure water. Based on the mass of lithium iron manganese phosphate made from lithium carbonate, manganese tetraoxide, iron phosphate, and lithium dihydrogen phosphate, add 1.6 wt% of the above nitrogen-doped carbon material as the carbon source, and add ammonium metavanadate, ammonium oxalotitanate, and magnesium chloride as dopants in doses with a V doping amount of 1500 ppm, a Ti doping amount of 1500 ppm, and a Mg doping amount of 2000 ppm, and grind it in a vertical sand mill to obtain slurry D 50 to 0.36 μm. Subsequently, transfer the slurry to a spray granulation dryer for drying to obtain spray powder. Under the protection of nitrogen atmosphere, place the spray powder in an atmosphere box-type furnace for staged heating and sintering. Among them, heat it at a heating rate of 5 °C / min, first heat it to 500 °C and keep it constant for 6 h, and then heat it to 720 °C and keep it constant for 9 h. After naturally cooling to room temperature, after airflow pulverization and sieving treatment, obtain nitrogen-doped carbon-coated lithium iron manganese phosphate cathode material.

[0080] Comparative Example 3

[0081] The difference between this comparative example and Example 1 is that the iron phthalocyanine and dopamine-coated silica microsphere composite material is not subjected to carbon dioxide thermal etching, and the carbon dioxide thermal etching is replaced by calcination under nitrogen.

[0082] S0. Measure 0.8 L of tetraethoxysilane and add it to 1 L of a mixed solution composed of ammonia water, ethanol, and ultrapure water (the volume ratio of ammonia water, ethanol, and ultrapure water is 2:3:5), and stir for 1 h to prepare a mixed solution A. Weigh 8 g of dopamine and add it to a mixed solution composed of ethanol and ultrapure water (the volume ratio of ethanol and ultrapure water is 1:1) to prepare solution B. Slowly add solution B to mixed solution A and continuously stir for 1 h, then age for 6 h, and wash, filter by suction, and dry with ultrapure water to obtain dopamine-coated silica microsphere materials. The molar ratio of dopamine to silica in the dopamine-coated silica microspheres is 0.052:3.61.

[0083] S1. Weigh and add dopamine-coated silica microsphere materials and iron phthalocyanine in a mass ratio of 5:1 to N,N-dimethylformamide to prepare a mixed solution C. After stirring the mixed solution C at room temperature for 12 h, wash it with N,N-dimethylformamide and place it in a vacuum oven at 60 °C for drying for 12 h to obtain the first composite material.

[0084] S2. Subsequently, place the first composite material in a box-type atmosphere furnace. In a nitrogen atmosphere, first heat it at a heating rate of 2 °C / min to 450 °C and hold for 2 h, and then continue to heat it at a heating rate of 2 °C / min to 800 °C and hold for 6 h. After naturally cooling to room temperature, wash the material taken out of the furnace with 1 mol / L HF solution and place it in a vacuum oven at 60 °C for drying for 12 h to obtain metal iron single-atom / nitrogen-doped carbon materials.

[0085] S3. Weigh the corresponding lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate according to the stoichiometric ratio of lithium:manganese:iron:phosphorus of 1.08:0.7:0.3:1.05 and disperse them in ultrapure water. Based on the mass of lithium iron manganese phosphate made from lithium carbonate, manganese tetroxide, iron phosphate, and lithium dihydrogen phosphate, add 1.6 wt% of the above-mentioned metal iron single-atom / nitrogen-doped carbon materials as a carbon source, and add ammonium metavanadate, ammonium oxalotitanate, and magnesium chloride as dopants in doses with a V doping amount of 1500 ppm, a Ti doping amount of 1500 ppm, and a Mg doping amount of 2000 ppm, and grind them in a vertical sand mill to obtain slurry D 50 to 0.36 μm. Subsequently, transfer the slurry to a spray granulation dryer for drying to obtain a spray powder. Under the protection of a nitrogen atmosphere, place the spray powder in an atmosphere box-type furnace for stepwise heating and sintering. Among them, at a heating rate of 5 °C / min, first heat it to 500 °C and keep it constant for 6 h, and then heat it to 720 °C and keep it constant for 9 h. After naturally cooling to room temperature, after airflow pulverization and sieving treatment, obtain metal iron single-atom / nitrogen-doped carbon-coated lithium iron manganese phosphate cathode materials.

[0086] Performance Test

[0087] Powder Compaction Density Test Method:

[0088] Use a battery powder compaction density tester to apply a specific pressure to the battery powder samples prepared in the examples and comparative examples, and measure the volume change of the system observation material based on high-precision pressure measurement and volume measurement techniques, and calculate and output the compaction density of the battery powder samples in the examples and comparative examples.

[0089] Powder Resistance Test Method:

[0090] Use an automatic powder resistivity tester to apply an excitation current to the battery powder samples prepared in the examples and comparative examples, measure the voltage, and obtain the surface resistivity and resistance data of the material.

[0091] Perform button cell electrochemical performance tests on the CR2032 type button cells assembled from the battery powder samples prepared in the examples and comparative examples.

[0092] CR2032 Type Button Cell Assembly Method:

[0093] Use the lithium-ion battery cathode materials obtained in the examples and comparative examples as the cathode active materials respectively, and perform slurry mixing and coating to prepare the cathode electrode sheets. Among them, disperse 5wt% carbon black conductive agent, 5wt% polyvinylidene fluoride binder and 90wt% active material in N-methylpyrrolidone dispersant to form a lithium-ion battery cathode material slurry, and then coat it on the surface of aluminum foil. After drying in a vacuum at 120°C for 12h, punch holes in the cathode material electrode sheet to obtain a circular electrode sheet, and weigh and record the mass. Use the above-prepared circular electrode sheet as the cathode, a lithium metal sheet as the anode, a polyethylene film as the separator, and 1mol / L LiPF6 dissolved in a mixed solution of dimethyl carbonate (DMC) and ethylene carbonate (EC) (the volume ratio of DMC to EC is 1:1) as the electrolyte, and assemble a CR2032 type button cell in a glove box with an atmosphere of O2≤0.01ppm and H2O≤0.01ppm, and perform electrochemical performance tests at room temperature after standing for 12h.

[0094] Button Cell Electrochemical Performance Test Method:

[0095] Perform charge and discharge tests on the CR2032 type button cells assembled from the battery powder samples prepared in the examples and comparative examples in the electrochemical window of 2 - 4.5V (for lithium iron manganese phosphate-based cathode) or 2 - 4.2V (for lithium iron phosphate-based cathode), and complete the charge and discharge tests at charge and discharge rates of 0.1C and 1C respectively. Among them, 1C = 170mAh / g.

[0096] Use a scanning electron microscope to perform microscopic morphology analysis on the lithium iron manganese phosphate cathode material coated with single-atom iron / nitrogen-doped carbon in Example 1.Figure 1 Scanning electron microscopy image of the lithium iron phosphate manganese cathode material coated with single-atom iron / nitrogen-doped carbon prepared in Example 1. As can be seen from the figure, the lithium iron phosphate manganese cathode material coated with single-atom iron / nitrogen-doped carbon is spherical-like nanoparticles, with good uniformity and dispersibility, and there is no free carbon layer on the particle surface.

[0097] The test data of the physical and chemical indexes of the lithium-ion battery cathode materials prepared in each example and comparative example of the present invention are shown in Table 1.

[0098] Table 1

[0099]

[0100] From the test results of Examples 1 to 3, it can be seen that after the axial compounding of the transition metal phthalocyanine complex and the dopamine carbon source, the transition metal single-atom / nitrogen-doped carbon-coated lithium iron phosphate manganese cathode material formed by carbon dioxide thermal etching and HF treatment can construct a large number of carbon defect sites in the carbon material. Based on the strong electron-withdrawing effect of carbon defects and pyrrole nitrogen, the electron cloud arrangement, surface electronegativity in the carbon material are changed, and the electron-withdrawing effect of the carbon material is adjusted. Cooperating with the transition metal-N-C cyclic carbon structure, the electron structure of the lithium iron phosphate manganese cathode material is effectively regulated, promoting the redistribution of charges and electron transfer inside the lithium iron phosphate manganese lattice, and improving the electron conductivity and ionic conductivity of the material. Therefore, the transition metal single-atom / nitrogen-doped carbon-coated lithium iron phosphate manganese cathode materials prepared in Examples 1 to 3 have excellent tap density, discharge capacity, rate performance and cycle performance.

[0101] From Example 1 and Comparative Example 1, it can be seen that since the transition metal single-atom / nitrogen-doped carbon material was not subjected to carbon dioxide thermal etching and HF treatment, there are fewer carbon defects in the carbon material synthesized in Comparative Example 1, resulting in less improvement in the electron cloud arrangement, surface electronegativity and electron-withdrawing effect of the lithium iron phosphate manganese composite material modified with the metal iron single-atom / nitrogen-doped carbon composite silica carbon coating layer than in Example 1. In addition, there are inactive silica substances in the carbon material prepared in Comparative Example 1, which reduces the mass ratio of the active substance in the overall electrode material, thereby affecting the discharge capacity of the cathode material; due to the insulating properties of silica, its coating effect on lithium iron phosphate manganese is poor, and the electron conductivity and ionic conductivity of the material are poor, thereby affecting the tap density, conductivity and lithium storage performance of the material.

[0102] As can be seen from Example 1 and Comparative Example 2, in Comparative Example 2, only the nitrogen-doped carbon material obtained by heat etching carbon dioxide and HF treatment of dopamine-coated silica microsphere material is used as the carbon coating layer to modify lithium iron phosphate manganese. The improvement effect of this conventional carbon material on the electron cloud arrangement, surface electronegativity and electron-withdrawing effect in the material is inferior to that of the transition metal iron single atom / nitrogen-doped carbon material. Due to the lack of the transition metal-N-C ring carbon structure, the electron conductivity of the material is poor, which in turn affects the conductivity and rate performance of the material. In addition, after the dopamine-coated silica microsphere material is heat-etched with carbon dioxide and treated with HF, the cavities left by the etching of a large amount of silica in the unit volume greatly reduce the tap density of the material; due to the hollow structure carbon material, the specific surface area of the material increases, so that a large number of lithium ions are embedded / adsorbed on the active sites of the carbon material during the charge and discharge process, thus consuming the active lithium, which in turn affects the lithium storage performance of the material.

[0103] As can be seen from Example 1 and Comparative Example 3, in Comparative Example 3, an inert gas nitrogen is used to replace carbon dioxide gas for the heat treatment of the composite material of iron phthalocyanine and dopamine-coated silica microspheres, and it fails to effectively construct rich defect sites in the composite carbon layer structure, so that the electron-withdrawing effect, electron cloud arrangement and surface electronegativity of the cathode material are inferior to those of the cathode material prepared in Example 1. This makes the conductivity, lithium storage capacity and rate performance of the lithium iron phosphate manganese modified by the metal iron single atom / nitrogen-doped carbon carbon coating prepared in Comparative Example 3 inferior to those of the metal iron single atom / nitrogen-doped carbon-coated lithium iron phosphate manganese cathode material in Example 1.

[0104] As can be seen from Example 4, the embodiments proposed in the present invention are also applicable to the cathode material of lithium iron phosphate lithium ion battery, and the prepared metal iron single atom / nitrogen-doped carbon-coated lithium iron phosphate cathode material performs excellently in terms of tap density, electron conductivity and lithium storage performance.

[0105] Obviously, the above embodiments of the present invention are merely examples for clearly explaining the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A transition metal single atom / nitrogen-doped carbon material, characterized in that, It is prepared by the following method: S1. Mix the dopamine-coated silica microspheres with the transition metal phthalocyanine complex to obtain a first composite material; S2. Carbonize the first composite material, thermally etch with carbon dioxide, and remove the silica to obtain the transition metal single atom / nitrogen-doped carbon material; The temperature of the carbon dioxide thermal etching is 600-950 °C.

2. The carbon material according to claim 1, characterized in that, The transition metal includes at least one of iron, manganese, zinc, cobalt, copper, chromium, and nickel.

3. The carbon material according to claim 1, characterized in that, The mass ratio of the dopamine-coated silica microspheres to the transition metal phthalocyanine complex is (0.1-10):

1.

4. The carbon material according to claim 1, wherein The molar ratio of dopamine to silica in the dopamine-coated silica microspheres is (0.01-0.1):(1-5).

5. The carbon material according to claim 1, characterized in that, The temperature of the carbon dioxide thermal etching is 800-850 °C.

6. The carbon material according to claim 1, wherein The time of the carbon dioxide thermal etching is 4-20 h.

7. Use of the carbon material according to any one of claims 1-6 in the preparation of a carbon-coated lithium-ion battery cathode material.

8. A carbon-coated cathode material for lithium-ion batteries, characterized in that, The carbon source used for the carbon coating includes the transition metal single atom / nitrogen-doped carbon material according to any one of claims 1-6.

9. The carbon-coated lithium ion battery cathode material according to claim 8, characterized in that, The mass of the transition metal single atom / nitrogen-doped carbon material is 0.5-5 wt% of the mass of the lithium-ion battery cathode material not coated with carbon.

10. A lithium-ion battery, characterized in that, It includes the carbon-coated lithium-ion battery cathode material according to claim 8 or 9.

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