CN109860539B - Composite lithium vanadium phosphate cathode material and preparation method and application thereof - Google Patents
Composite lithium vanadium phosphate cathode material and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to a composite lithium vanadium phosphate anode material and a preparation method and application thereof. The obtained composite lithium vanadium phosphate anode material has a mesoporous structure, the specific discharge capacity of the composite anode material is more than 150mAh/g at the 5C multiplying power, the capacity retention rate is more than 91% after the composite anode material is cycled for 1000 times, and the composite anode material has excellent specific capacity, multiplying power performance and cycling stability and is suitable for large-scale popularization and application.
Description
Technical Field
The invention belongs to the technical field of preparation of lithium ion battery anode materials, and particularly relates to a composite lithium vanadium phosphate anode material and a preparation method and application thereof.
Background
Li with monoclinic structure in lithium vanadium phosphate3V2(PO4)3The compound has good safety and higher Li+The ionic diffusion coefficient, higher discharge voltage and energy density, combine the advantages of lithium cobaltate and lithium vanadium phosphate and overcome the disadvantages of both, thus it is considered to be comparable to LiCoO2And a better anode material.
Lithium vanadium phosphate is of high interest to people due to its good conductivity, high theoretical specific capacity, high operating voltage plateau and good safety and stability. However, the lithium vanadium phosphate has poor internal electron transport capability, and inhibits the electrochemical performance of the lithium vanadium phosphate under high rate. In addition, lithium vanadium phosphate is used for Li extraction+The electrochemical performance of the electrolyte is influenced to a certain extent by the influence on the structural change of the electrolyte in the process and the side reaction between the active material and the electrolyte during the cyclic charge and discharge.
The common methods for modifying lithium vanadium phosphate at present comprise nanocrystallization, carbon coating, graphene or carbon fiber compounding and the like. For example, CN103985863A discloses a lithium ion battery cathode material with cerium oxide and carbon co-coated with lithium vanadium phosphate, and a preparation method thereof, wherein a sol-gel method for controlling pH value and a polyvinyl alcohol-assisted suspension mixing method are adopted to prepare CeO2The vanadium lithium phosphate is coated with carbon, so that the defect that the existing carbon-coated vanadium lithium phosphate anode material is poor in high-rate charge and discharge performance is overcome. CN103165889A discloses a three-dimensional conductive channel reinforced lithium vanadium phosphate nanosphere and a preparation method thereof, wherein the nanosphere is attached on a carbon net and has lithium vanadium phosphate nanospheres with uniform size, the lithium vanadium phosphate nanospheres are coated with a carbon layer, the carbon layer is linked with the carbon layer, and the diameter of the lithium vanadium phosphate nanospheres coated with the carbon layer is 60-70 nm. When the prepared lithium vanadium phosphate nanosphere electrode is used as a positive electrode material of a lithium ion battery, the lithium vanadium phosphate nanosphere electrode shows excellent multiplying power, higher specific capacity and good cycling stability. CN102332582A discloses a preparation method of a novel lithium vanadium phosphate/bamboo charcoal composite anode material, wherein a bamboo charcoal-coated lithium vanadium phosphate/bamboo charcoal composite material sample is prepared by sol-gel and microwave heating methods, and a conductive network connected with bamboo charcoal is formed, and the conductive network has higher capacity and higher multiplying power when being used as an anode material of a lithium ion power battery.
Although the electrochemical performance of lithium vanadium phosphate is improved to some extent by the above method, there is still room for further improvement in the performance.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide a composite lithium vanadium phosphate positive electrode material, and a preparation method and application thereof, so as to further improve the electrochemical performance of the lithium vanadium phosphate positive electrode material.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a preparation method of a composite lithium vanadium phosphate cathode material, which comprises the following steps:
(1) mixing a first carbon source, a vanadium source and a phosphorus source according to a proportion, then adding a template agent and oxalic acid into the mixed solution, and drying the materials after ultrasonic treatment to obtain a dry mixture; the first carbon source consists of sulfur-doped graphene and a conductive polymer in a mass ratio of 1 (4-6);
(2) roasting the dried mixture obtained in the step (1), and then adding an alkaline solution to remove the template agent to obtain mesoporous vanadium phosphate coated with a first carbon source in situ;
(3) mixing the mesoporous vanadium phosphate coated in situ by the first carbon source obtained in the step (2) with a lithium source, a nitrogen-doped oxygen-containing compound and a second carbon source, sanding, and performing spray drying after sanding to obtain a precursor of the cathode material; the second carbon source is a nitrogen and phosphorus co-doped carbon material;
(4) and (4) heating the precursor of the positive electrode material obtained in the step (3) to calcine, and cooling to obtain the composite lithium vanadium phosphate positive electrode material.
The composite lithium vanadium phosphate anode material is prepared by two steps of in-situ coating by adopting two different carbon sources. The adopted carbon coating method is obviously different from the traditional carbon coating method, on one hand, the method provided by the invention has more uniform coating and more excellent conductivity; on the other hand, the two carbon sources are different from the traditional carbon source in composition, in the two carbon sources, the first carbon source is composed of sulfur-doped graphene and a conducting polymer, the second carbon source is a nitrogen and phosphorus co-doped carbon material, and the two carbon sources are added to effectively inhibit the dissolution of active substances in electrolyte, prevent the structure collapse of the positive electrode material and further contribute to the improvement of the rate capability and the circulation stability of the positive electrode material.
In addition, the vanadium-lithium phosphate anode material is subjected to ion doping by adopting a nitrogen-doped oxygen-containing compound, and the introduction of nitrogen element can form a synergistic effect with P, S elements in a first carbon source and a second carbon source, so that various combined chemical bonds can be formed between five elements in the composite vanadium-lithium phosphate anode material and N, P, S, C, O on the surface of the composite vanadium-lithium phosphate anode material, for example, N-O, N-P, N-S, N-P-C, N-S-C, P-N-O, S-N-O, C-N-O and the like can be formed. The formation of the chemical bonds can well repair the lattice interface of the lithium vanadium phosphate anode material, effectively prevent the dissolution of transition metal ions in the electrolyte, enhance the cycle life and the cycle stability of the anode material and improve the electrochemical performance of the material.
According to the invention, the mass ratio of the sulfur-doped graphene to the conductive polymer in the first carbon source in the step (1) is 1 (3-7), which may be, for example, 1:3, 1:4, 1:5, 1:6 or 1:7, and the specific values between the above values are limited by space and for the sake of brevity, and the invention is not exhaustive.
The mass ratio of the sulfur-doped graphene to the conductive polymer in the first carbon source is preferably 1: 5.
According to the invention, the conductive polymer is at least one of polypyrrole, polyaniline, polythiophene or polyoxyethylene, or at least one of copolymers formed by at least two of polypyrrole monomers, polyaniline monomers, polythiophene monomers or polyoxyethylene monomers, or a composition of at least one of polypyrrole, polyaniline, polythiophene or polyoxyethylene and at least one of the copolymers.
According to the invention, the mass ratio of sulfur to graphene in the sulfur-doped graphene is (0.005-0.12):1, for example, 0.005:1, 0.01:1, 0.03:1, 0.05:1, 0.08:1, 0.1:1 or 0.12:1, and the specific values therebetween are limited to space and for the sake of brevity, and the invention is not exhaustive.
According to the invention, the vanadium source in step (1) is V2O5、V2O3、NH4VO3Or VOC2O4At least one of (1).
According to the invention, the phosphorus source in step (1) is at least one of sodium phosphate, potassium phosphate, triammonium phosphate, monoammonium phosphate, diammonium phosphate, monosodium phosphate, dipotassium phosphate, monopotassium phosphate, disodium phosphate, iron phosphate, manganese phosphate, lithium dihydrogen phosphate or phosphoric acid.
According to the invention, the template agent in the step (1) is at least one of SBA-15, KIT-6 or mesoporous carbon.
According to the invention, the molar ratio of the vanadium source, the oxalic acid and the template agent in the step (1) is 1 (2-8) to (0.1-12), and may be, for example, 1:2:0.1, 1:3:0.5, 1:4:1, 1:5:5, 1:7:1, 1:8:10, 1:3:6 or 1:8:12, etc., which is not exhaustive for the purpose of space and simplicity.
According to the present invention, the temperature of the ultrasonic treatment in step (1) is 25-100 ℃, for example, 25 ℃, 30 ℃, 40 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃, 90 ℃ or 100 ℃, and the specific values therebetween are limited by space and for the sake of brevity, and the present invention is not exhaustive.
According to the present invention, the power of the ultrasonic treatment in step (1) is 30-200W, such as 30W, 50W, 80W, 100W, 130W, 150W, 180W or 200W, and the specific values therebetween are limited for space and simplicity, and the present invention is not exhaustive.
According to the invention, the time of the ultrasonic treatment in the step (1) is 1-10h, for example, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, and the specific values between the above values are limited by space and for the sake of brevity, and the invention is not exhaustive.
According to the invention, the calcination of step (2) is carried out in a protective atmosphere, which is argon and/or nitrogen.
According to the present invention, the temperature of the calcination in step (2) is 150-650 ℃, such as 150 ℃, 200 ℃, 250 ℃, 300 ℃, 350 ℃, 400 ℃, 450 ℃, 500 ℃, 550 ℃, 600 ℃ or 650 ℃, and the specific values therebetween are not limited to space and for brevity, and the present invention is not exhaustive.
According to the invention, the roasting time in step (2) is 1-30h, for example 1h, 5h, 10h, 15h, 20h, 25h or 30h, and the specific values between the above values are limited by space and for the sake of brevity, and the invention is not exhaustive.
According to the invention, after the baking and sintering in the step (2), the template agent is removed by using an alkaline solution at 25-120 ℃, and the mesoporous vanadium phosphate coated with the first carbon source in situ is obtained after washing by deionized water and drying.
According to the invention, the lye solution in the step (2) is sodium hydroxide and/or potassium hydroxide.
According to the invention, the lithium source in step (3) is at least one of lithium chloride, lithium bromide, lithium phosphate, lithium dihydrogen phosphate, lithium sulfate, lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, lithium oxalate, lithium formate, lithium tert-butoxide, lithium benzoate or lithium citrate.
According to the invention, the oxygen-containing compound in the nitrogen-doped oxygen-containing compound in the step (3) is lithium-doped boron phosphate, or a combination of at least one of zinc oxide, copper oxide, cuprous oxide, magnesium oxide, vanadium oxide and metatitanic acid and lithium-doped boron phosphate.
According to the invention, the lithium-doped boron phosphate has the chemical formula LixB1-x/3PO4Wherein x is more than or equal to 0.01 and less than 0.15.
The above formula of the lithium-doped boron phosphate has a value of x in a range of 0.01 ≦ x < 0.15, which may be, for example, 0.01, 0.03, 0.05, 0.08, 0.1, 0.12, or 0.15, and specific values therebetween are not intended to be exhaustive for the sake of brevity and brevity.
According to the present invention, the mass fraction of nitrogen in the nitrogen-doped oxygen-containing compound in the step (3) is 0.01-0.5%, for example, 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, or 0.5%, and the specific values therebetween are not exhaustive for reasons of brevity and brevity.
According to the present invention, the mass fraction of nitrogen in the nitrogen and phosphorus co-doped carbon material of step (3) is 0.01-0.8%, for example, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7% or 0.8%, and the specific values therebetween are limited by space and for brevity, the present invention is not exhaustive.
According to the present invention, the mass fraction of phosphorus in the nitrogen and phosphorus co-doped carbon material in the step (3) is 0.01-1%, for example, 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.3%, 0.5%, 0.8% or 1%, and the specific values therebetween are not exhaustive for reasons of space and simplicity.
According to the present invention, the particle size of the slurry after the sanding in step (3) is 250-650nm, such as 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm or 650nm, and the specific values therebetween are not limited to space and for the sake of brevity, and the present invention is not exhaustive.
According to the invention, the sanding process in the step (3) is carried out in a solvent, and the solvent is at least one of water, isopropanol, ethylene glycol, acetone, tetrahydrofuran, diethyl ether, benzene, toluene or dimethylformamide.
According to the present invention, the temperature of the spray drying in step (3) is 25-220 ℃, for example, 25 ℃, 50 ℃, 80 ℃, 100 ℃, 130 ℃, 150 ℃, 180 ℃, 200 ℃ or 220 ℃, and the specific values therebetween are limited to space and for the sake of brevity, and the present invention is not exhaustive.
According to the present invention, the temperature of the calcination in step (4) is 500-1050 ℃, such as 500 ℃, 600 ℃, 700 ℃, 800 ℃, 900 ℃, 1000 ℃ or 1050 ℃, and the specific values therebetween are limited to the space and for brevity, and the present invention is not exhaustive.
According to the invention, the calcination time in step (4) is 1-24h, and may be, for example, 1h, 4h, 8h, 12h, 16h, 20h or 24h, and the specific values therebetween are limited by space and for the sake of brevity, and are not exhaustive.
According to the invention, the calcination of step (4) is carried out in a protective atmosphere, which is argon and/or nitrogen.
According to the invention, after the calcination in the step (4) is completed, the obtained product is naturally cooled and then is crushed and classified, so that the composite lithium vanadium phosphate anode material is obtained.
According to the invention, the vanadium source, the phosphorus source and the lithium source are added according to the proportion of each element in the following chemical formula in the preparation process, wherein the chemical formula is Li3V2(PO4)3。
According to the invention, the first carbon source, the nitrogen-doped oxygen-containing compound and the second carbon source are added in the following proportions:
the mass fraction of the first carbon source in the composite lithium vanadium phosphate cathode material is 0.1-10%, and may be, for example, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 3%, 5%, 8%, or 10%, and the specific values between the above values are limited by space and for brevity, the present invention is not exhaustive.
The mass fraction of the nitrogen-doped oxygen-containing compound in the composite lithium vanadium phosphate cathode material is 0.1-5%, and may be, for example, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, or 5%, and the specific values between the above values are limited by space and for simplicity, and the present invention is not exhaustive.
The mass fraction of the second carbon source in the composite lithium vanadium phosphate cathode material is 0.5-20%, and may be, for example, 0.5%, 1%, 3%, 5%, 8%, 10%, 13%, 15%, 18%, or 20%, and the specific values between the above values are limited to space and for brevity, and the present invention is not exhaustive.
In a second aspect, the present invention provides a composite lithium vanadium phosphate cathode material prepared by the method of the first aspect, wherein the composite lithium vanadium phosphate cathode material has a mesoporous structure.
In a third aspect, the invention provides the application of the composite lithium vanadium phosphate cathode material as described in the second aspect as a cathode material of a lithium ion battery.
Compared with the prior art, the invention has at least the following beneficial effects:
(1) the electrochemical performance of the lithium vanadium phosphate material is effectively improved, the prepared composite lithium vanadium phosphate anode material has high rate performance and good cycle stability, the specific discharge capacity of the composite anode material is more than 150mAh/g at the 5C rate, the capacity retention rate is more than 91% after the composite anode material is cycled for 1000 times, and the composite anode material has excellent specific capacity, rate performance and cycle stability and is suitable for large-scale popularization and application.
(2) The composite lithium vanadium phosphate anode material with the mesoporous structure is prepared, the whole process is simple and feasible, and large-scale popularization is facilitated.
Detailed Description
For the purpose of facilitating an understanding of the present invention, the present invention will now be described by way of examples. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
For the convenience of understanding, the technical solutions of the present invention will be further described by the following embodiments.
As a preferred technical scheme, the sulfur-doped graphene selected in each embodiment of the present invention is prepared according to the following method:
mixing a sulfur source and graphene according to a proportion, reacting for 1-36h under the conditions of 100-300 ℃ and 1-20MPa, cooling, washing and drying the obtained product to obtain a sulfur-doped graphene precursor, heating the obtained precursor to 500-1000 ℃ in an argon and/or nitrogen atmosphere for heat treatment for 1-30h, washing and drying to obtain the sulfur-doped graphene.
Preferably, the sulfur source is any one or a combination of at least two of sodium sulfide, sodium thiosulfate, thiourea, thiol, thiophenol, thioether, disulfide, polysulfide, cyclic sulfide, diallyl thiosulfonate, diallyl trisulfide or diallyl disulfide, preferably thiourea, or thiourea and at least one of thiol, thiophenol, thioether, disulfide, polysulfide, cyclic sulfide, diallyl thiosulfonate, diallyl trisulfide or diallyl disulfide.
Preferably, the mass ratio of sulfur to graphene in the sulfur-doped graphene is (0.005-0.12): 1.
As a preferred technical scheme, the nitrogen-doped oxygen-containing compound selected in each embodiment of the invention is prepared by the following method:
mixing an oxygen-containing compound and a nitrogen source according to a proportion, reacting for 1-72h under the conditions of 100-280 ℃ and 1-20MPa, cooling, washing and drying the obtained product after the reaction is finished, and then heating to 550-1100 ℃ in argon and/or nitrogen for heat treatment for 1-30h to obtain the nitrogen-doped oxygen-containing compound.
Preferably, the nitrogen source is at least one of thiourea, urea, an amino acid, acetamide, benzylamine, melamine, polyacrylonitrile or polypyrrole.
Preferably, the oxygen-containing compound in the nitrogen-doped oxygen-containing compound is lithium-doped boron phosphate, or a combination of at least one of zinc oxide, copper oxide, cuprous oxide, magnesium oxide, vanadium oxide, metatitanic acid and lithium-doped boron phosphate.
Preferably, the lithium-doped boron phosphate has the chemical formula LixB1-x/3PO4Wherein x is more than or equal to 0.01 and less than 0.15.
Preferably, the mass fraction of nitrogen in the nitrogen-doped oxygen-containing compound is 0.01-0.5%.
As a preferred technical scheme, the second carbon source (nitrogen and phosphorus co-doped carbon material) selected in each embodiment of the present invention is prepared according to the following method:
placing a carbon material in an ammonia atmosphere, heating to 700-950 ℃ at the speed of 1-10 ℃/min for nitridation treatment for 1-8h, grinding, sieving with a 200-mesh sieve, mixing with a phosphorus source, reacting for 1-24h under the conditions of 130-280 ℃ and 1-6MPa, cooling, washing and drying, heating the obtained product to 550-1050 ℃ for heat treatment for 1-30h, washing and drying to obtain the nitrogen-phosphorus co-doped carbon material;
preferably, the phosphorus source for preparing the second carbon source is one or a mixture of at least two of simple phosphorus, an organic phosphorus compound or an inorganic phosphorus compound, preferably an organic phosphorus compound, and more preferably at least one of phosphonitrilic trichloride, adenosine triphosphate, adenosine diphosphate, phosphoenone pyruvic acid, phosphate ester, tetrakis hydroxymethyl phosphonium chloride, dimethyl vinylphosphate, hexachlorocyclotriphosphazene, polydichlorophosphazene, polyalkoxyphosphazene, polyaryloxy phosphazene or polyfluorooxyphosphazene.
Preferably, the carbon material is at least one of polyvinyl alcohol, acetylene black, carbon fiber, graphene, polyethylene glycol, soluble starch, coal pitch, carbon black, dextrin, coke, citric acid, cellulose, glucose, single crystal/polycrystalline rock sugar, sucrose, fructose, or carbon nanotubes.
Preferably, the mass fraction of nitrogen in the nitrogen and phosphorus co-doped carbon material is 0.01-0.8%.
Preferably, the mass fraction of phosphorus in the nitrogen and phosphorus co-doped carbon material is 0.01-1%.
Typical but non-limiting examples of the invention are as follows:
example 1
In the embodiment, the mass ratio of sulfur to graphene in the sulfur-doped graphene is 0.05:1, and the mass ratio of the sulfur-doped graphene to polypyrrole in the first carbon source is 1: 6; the mass fraction of nitrogen in the nitrogen-doped oxygen-containing compound is 0.05 percent, and the chemical formula of the oxygen-containing compound is Li0.06B0.98PO4(ii) a The mass fraction of nitrogen in the second carbon source (nitrogen and phosphorus co-doped carbon material) is 0.1%, and the mass fraction of phosphorus is 0.3%.
Preparing the composite lithium vanadium phosphate cathode material according to the following method:
(1) a first carbon source, V2O5Potassium phosphate, a template agent SBA-15 and oxalic acid are mixed, and V is controlled2O5The mol ratio of the oxalic acid to the template agent is 1:3:1, and the mixture is dried for 1h after ultrasonic treatment at the temperature of 25 ℃ and the power of 200W to obtain a dry mixture;
(2) heating the dried mixture obtained in the step (1) to 650 ℃, roasting for 1h, and then adding a sodium hydroxide solution at 50 ℃ to remove a template agent to obtain mesoporous vanadium phosphate coated with a first carbon source in situ;
(3) mixing the mesoporous vanadium phosphate coated in situ by the first carbon source obtained in the step (2) with lithium nitrate, a nitrogen-doped oxygen-containing compound and a second carbon source, adding a proper amount of deionized water, sanding until the granularity of the slurry is 250-650nm, and spray-drying at 150 ℃ after sanding is finished to obtain a precursor of the positive electrode material;
(4) and (4) heating the precursor of the positive electrode material obtained in the step (3) to 950 ℃, calcining for 3h, and naturally cooling to obtain the composite lithium vanadium phosphate positive electrode material.
In the above preparation process, Li is represented by the chemical formula3V2(PO4)3The mass fractions of the first carbon source, the nitrogen-doped oxygen-containing compound and the second carbon source in the composite lithium vanadium phosphate anode material are respectively 2%, 5% and 5%.
Through detection, the specific discharge capacity of the composite lithium vanadium phosphate anode material obtained at the 5C rate is 151mAh/g, and the capacity retention rate is 93.8% after the composite lithium vanadium phosphate anode material is cycled for 1000 times.
Example 2
In the embodiment, the mass ratio of sulfur to graphene in the sulfur-doped graphene is 0.12:1, and the mass ratio of the sulfur-doped graphene to polyoxyethylene in the first carbon source is 1: 4; the mass fraction of nitrogen in the nitrogen-doped oxygen-containing compound is 0.3 percent, and the oxygen-containing compound is copper oxide and Li0.03B0.99PO4A mixture of (a); the mass fraction of nitrogen in the second carbon source (nitrogen and phosphorus co-doped carbon material) is 0.2%, and the mass fraction of phosphorus is 0.08%.
Preparing the composite lithium vanadium phosphate cathode material according to the following method:
(1) a first carbon source, NH4VO3Mixing sodium phosphate, a template agent KIT-6 and oxalic acid, and controlling NH4VO3The mol ratio of the oxalic acid to the template agent is 1:4.5:0.8, and the mixture is dried for 10 hours after ultrasonic treatment with the power of 30W at the temperature of 100 ℃ to obtain a dry mixture;
(2) heating the dried mixture obtained in the step (1) to 450 ℃, roasting for 16h, and then adding a sodium hydroxide solution at 80 ℃ to remove a template agent to obtain mesoporous vanadium phosphate coated with a first carbon source in situ;
(3) mixing the mesoporous vanadium phosphate coated in situ by the first carbon source obtained in the step (2) with lithium oxalate, a nitrogen-doped oxygen-containing compound and a second carbon source, adding a proper amount of ethylene glycol, sanding until the granularity of the slurry is 250-650nm, and spray-drying at 160 ℃ after sanding is finished to obtain a precursor of the positive electrode material;
(4) and (4) heating the precursor of the positive electrode material obtained in the step (3) to 800 ℃, calcining for 12h, and naturally cooling to obtain the composite lithium vanadium phosphate positive electrode material.
In the above preparation process, Li is represented by the chemical formula3V2(PO4)3The mass fractions of the first carbon source, the nitrogen-doped oxygen-containing compound and the second carbon source in the composite lithium vanadium phosphate anode material are respectively 0.7%, 1.5% and 8%.
Through detection, the specific discharge capacity of the composite lithium vanadium phosphate anode material obtained at the 5C rate is 153mAh/g, and the capacity retention rate is 91.8% after 1000 cycles.
Example 3
In the embodiment, the mass ratio of sulfur to graphene in the sulfur-doped graphene is 0.01:1, and the mass ratio of the sulfur-doped graphene to polythiophene in the first carbon source is 1: 6; the mass fraction of nitrogen in the nitrogen-doped oxygen-containing compound is 0.5 percent, and the chemical formula of the oxygen-containing compound is Li0.09B0.97PO4(ii) a The mass fraction of nitrogen in the second carbon source (nitrogen and phosphorus co-doped carbon material) is 0.8%, and the mass fraction of phosphorus is 0.5%.
Preparing the composite lithium vanadium phosphate cathode material according to the following method:
(1) a first carbon source, V2O3Mixing triammonium phosphate, template agent SBA-15 and oxalic acid, and controlling V2O3The mol ratio of the oxalic acid to the template agent is 1:5:3, and the mixture is dried after being treated by ultrasonic treatment for 5 hours at the temperature of 80 ℃ and with the power of 120W to obtain a dry mixture;
(2) heating the dried mixture obtained in the step (1) to 350 ℃, roasting for 14h, and then adding a potassium hydroxide solution at 100 ℃ to remove the template agent to obtain mesoporous vanadium phosphate coated with a first carbon source in situ;
(3) mixing the mesoporous vanadium phosphate coated in situ by the first carbon source obtained in the step (2) with lithium formate, a nitrogen-doped oxygen-containing compound and a second carbon source, adding a proper amount of deionized water, sanding until the granularity of the slurry is 250-650nm, and spray drying at 180 ℃ after sanding is finished to obtain a precursor of the positive electrode material;
(4) and (4) heating the precursor of the positive electrode material obtained in the step (3) to 1000 ℃, calcining for 2h, and naturally cooling to obtain the composite lithium vanadium phosphate positive electrode material.
In the above preparation process, Li is represented by the chemical formula3V2(PO4)3The mass fractions of the first carbon source, the nitrogen-doped oxygen-containing compound and the second carbon source in the composite lithium vanadium phosphate anode material are respectively 10%, 0.1% and 1%.
Through detection, the discharge specific capacity of the composite lithium vanadium phosphate anode material obtained at the 5C rate is 155.2mAh/g, and the capacity retention rate is 92.5% after 1000 cycles.
Example 4
In the embodiment, the mass ratio of sulfur to graphene in the sulfur-doped graphene is 0.1:1, and the mass ratio of the sulfur-doped graphene to polyoxyethylene in the first carbon source is 1: 5; the mass fraction of nitrogen in the nitrogen-doped oxygen-containing compound is 0.02 percent, and the oxygen-containing compound is vanadium oxide and Li0.12B0.96PO4A mixture of (a); the mass fraction of nitrogen in the second carbon source (nitrogen and phosphorus co-doped carbon material) is 0.03%, and the mass fraction of phosphorus is 0.05%.
Preparing the composite lithium vanadium phosphate cathode material according to the following method:
(1) a first carbon source, V2O5Potassium phosphate, template agent mesoporous carbon and oxalic acid, and controlling V2O5The mol ratio of the oxalic acid to the template agent is 1:2:5, and the mixture is dried for 3 hours after ultrasonic treatment at the temperature of 60 ℃ and the power of 150W to obtain a dry mixture;
(2) heating the dried mixture obtained in the step (1) to 500 ℃, roasting for 10h, and then adding a potassium hydroxide solution at 80 ℃ to remove the template agent to obtain the mesoporous vanadium phosphate coated with the first carbon source in situ;
(3) mixing the mesoporous vanadium phosphate coated in situ by the first carbon source obtained in the step (2) with lithium oxalate, a nitrogen-doped oxygen-containing compound and a second carbon source, adding a proper amount of ethylene glycol, sanding until the granularity of the slurry is 250-650nm, and spray-drying at 150 ℃ after sanding is finished to obtain a precursor of the positive electrode material;
(4) and (4) heating the precursor of the positive electrode material obtained in the step (3) to 650 ℃, calcining for 20h, and naturally cooling to obtain the composite lithium vanadium phosphate positive electrode material.
In the above preparation process, Li is represented by the chemical formula3V2(PO4)3The mass fractions of the first carbon source, the nitrogen-doped oxygen-containing compound and the second carbon source in the composite lithium vanadium phosphate anode material are respectively 0.5%, 3% and 10%.
Through detection, the specific discharge capacity of the composite lithium vanadium phosphate anode material obtained at the 5C rate is 154.1mAh/g, and the capacity retention rate is 94.1% after 1000 cycles.
Example 5
In the embodiment, the mass ratio of sulfur to graphene in the sulfur-doped graphene is 0.08:1, and the mass ratio of the sulfur-doped graphene to polypyrrole in the first carbon source is 1: 4; the mass fraction of nitrogen in the nitrogen-doped oxygen-containing compound is 0.1 percent, and the chemical formula of the oxygen-containing compound is Li0.06B0.98PO4(ii) a The mass fraction of nitrogen in the second carbon source (nitrogen and phosphorus co-doped carbon material) is 0.04%, and the mass fraction of phosphorus is 0.06%.
Preparing the composite lithium vanadium phosphate cathode material according to the following method:
(1) a first carbon source, VOC2O4Sodium phosphate, a template agent SBA-15 and oxalic acid are mixed to control VOC2O4The mol ratio of the oxalic acid to the template agent is 1:6:3, and the mixture is dried for 7 hours after ultrasonic treatment at the temperature of 50 ℃ and the power of 100W to obtain a dry mixture;
(2) heating the dried mixture obtained in the step (1) to 500 ℃, roasting for 7h, and then adding a sodium hydroxide solution at 100 ℃ to remove the template agent to obtain the mesoporous vanadium phosphate in which the first carbon source is coated in situ;
(3) mixing the mesoporous vanadium phosphate coated in situ by the first carbon source obtained in the step (2) with lithium hydroxide, a nitrogen-doped oxygen-containing compound and a second carbon source, adding a proper amount of deionized water, sanding until the granularity of the slurry is 250-650nm, and spray-drying at 180 ℃ after sanding to obtain a precursor of the positive electrode material;
(4) and (4) heating the precursor of the positive electrode material obtained in the step (3) to 1050 ℃, calcining for 1h, and naturally cooling to obtain the composite lithium vanadium phosphate positive electrode material.
In the above preparation process, Li is represented by the chemical formula3V2(PO4)3The mass fractions of the first carbon source, the nitrogen-doped oxygen-containing compound and the second carbon source in the composite lithium vanadium phosphate anode material are respectively 2%, 2% and 16%.
Through detection, the specific discharge capacity of the composite lithium vanadium phosphate anode material obtained at the 5C rate is 152.8mAh/g, and the capacity retention rate is 93.5% after 1000 cycles.
The applicant states that the present invention is illustrated by the above examples to show the detailed process equipment and process flow of the present invention, but the present invention is not limited to the above detailed process equipment and process flow, i.e. it does not mean that the present invention must rely on the above detailed process equipment and process flow to be implemented. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
Claims (32)
1. The preparation method of the composite lithium vanadium phosphate cathode material is characterized by comprising the following steps of:
(1) mixing a first carbon source, a vanadium source and a phosphorus source according to a proportion, then adding a template agent and oxalic acid into the mixed solution, and drying the materials after ultrasonic treatment to obtain a dry mixture; the first carbon source consists of sulfur-doped graphene and a conductive polymer;
(2) roasting the dried mixture obtained in the step (1), and then adding an alkaline solution to remove the template agent to obtain mesoporous vanadium phosphate coated with a first carbon source in situ;
(3) mixing the mesoporous vanadium phosphate coated in situ by the first carbon source obtained in the step (2) with a lithium source, a nitrogen-doped oxygen-containing compound and a second carbon source, sanding, and performing spray drying after sanding to obtain a precursor of the cathode material; the oxygen-containing compound in the nitrogen-doped oxygen-containing compound is lithium-doped boron phosphate, or the combination of at least one of zinc oxide, copper oxide, cuprous oxide, magnesium oxide, vanadium oxide and metatitanic acid and the lithium-doped boron phosphate; the second carbon source is a nitrogen and phosphorus co-doped carbon material;
(4) and (4) heating the precursor of the positive electrode material obtained in the step (3) to calcine, and cooling to obtain the composite lithium vanadium phosphate positive electrode material.
2. The method of claim 1, wherein the mass ratio of the sulfur-doped graphene to the conductive polymer in the first carbon source in the step (1) is 1 (3-7).
3. The method according to claim 1, wherein the conductive polymer is at least one of polypyrrole, polyaniline, polythiophene, or polyoxyethylene, or at least one of copolymers formed of at least two of polypyrrole, polyaniline, polythiophene, or polyoxyethylene monomers, or a combination of at least one of polypyrrole, polyaniline, polythiophene, or polyoxyethylene and at least one of the copolymers.
4. The method of claim 1, wherein the mass ratio of sulfur to graphene in the sulfur-doped graphene is (0.005-0.12): 1.
5. The method of claim 1, wherein the vanadium source of step (1) is V2O5、V2O3、NH4VO3Or VOC2O4At least one of (1).
6. The method of claim 1, wherein the source of phosphorus of step (1) is at least one of sodium phosphate, potassium phosphate, triammonium phosphate, monoammonium phosphate, diammonium phosphate, monosodium phosphate, dipotassium phosphate, monopotassium phosphate, disodium phosphate, ferric phosphate, manganese phosphate, lithium dihydrogen phosphate, or phosphoric acid.
7. The method of claim 1, wherein the template of step (1) is SBA-15 and/or KIT-6.
8. The method of claim 1, wherein the molar ratio of the vanadium source, oxalic acid and templating agent of step (1) is 1 (2-8) to (0.1-12).
9. The method of claim 1, wherein the temperature of the sonication in step (1) is from 25 ℃ to 100 ℃.
10. The method of claim 1, wherein the power of the sonication of step (1) is 30-200W.
11. The method of claim 1, wherein the sonication in step (1) is performed for a period of 1 to 10 hours.
12. The method of claim 1, wherein the firing of step (2) is performed in a protective atmosphere, the protective atmosphere being argon and/or nitrogen.
13. The method as claimed in claim 1, wherein the temperature of the calcination in the step (2) is 150-650 ℃.
14. The method of claim 1, wherein the calcination time in step (2) is 1-30 hours.
15. The method of claim 1, wherein after the baking and sintering in step (2), the template agent is removed by using an alkaline solution at 25-120 ℃, and the mesoporous vanadium phosphate coated with the first carbon source in situ is obtained after washing with deionized water and drying.
16. The method of claim 1, wherein the alkaline solution in step (2) is sodium hydroxide and/or potassium hydroxide.
17. The method of claim 1, wherein the lithium source of step (3) is at least one of lithium chloride, lithium bromide, lithium phosphate, lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium sulfate, lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, lithium oxalate, lithium formate, lithium tert-butoxide, lithium benzoate, or lithium citrate.
18. The method of claim 1, wherein the lithium-doped boron phosphate has a chemical formula of LixB1-x/ 3PO4Wherein x is more than or equal to 0.01 and less than 0.15.
19. The method of claim 1, wherein the mass fraction of nitrogen in the nitrogen-doped oxygen-containing compound of step (3) is 0.01 to 0.5%.
20. The method according to claim 1, wherein the mass fraction of nitrogen in the nitrogen and phosphorus co-doped carbon material in the step (3) is 0.01-0.8%.
21. The method according to claim 1, wherein the mass fraction of phosphorus in the nitrogen and phosphorus co-doped carbon material in the step (3) is 0.01-1%.
22. The method as claimed in claim 1, wherein the size of the slurry after the sanding in step (3) is 650 nm.
23. The method of claim 1, wherein the sanding process of step (3) is performed in a solvent, the solvent being at least one of water, isopropanol, ethylene glycol, acetone, tetrahydrofuran, diethyl ether, benzene, toluene, or dimethylformamide.
24. The method of claim 1, wherein the temperature of said spray drying of step (3) is from 25 ℃ to 220 ℃.
25. The method as claimed in claim 1, wherein the temperature of the calcination in step (4) is 500-1050 ℃.
26. The method of claim 1, wherein the calcination of step (4) is carried out for a time period of 1 to 24 hours.
27. The method of claim 1, wherein the calcining of step (4) is performed in a protective atmosphere, wherein the protective atmosphere is argon and/or nitrogen.
28. The method of claim 1, wherein after the calcination in the step (4), the obtained product is naturally cooled and then crushed and classified to obtain the composite lithium vanadium phosphate cathode material.
29. The method according to claim 1, wherein the vanadium source, the phosphorus source and the lithium source are added in the proportion of each element in the following chemical formula in the preparation process, and the chemical formula is Li3V2(PO4)3。
30. The method of claim 1, wherein the first carbon source, the nitrogen-doped oxygen-containing compound, and the second carbon source are added in the following ratios: the mass fraction of a first carbon source in the composite lithium vanadium phosphate anode material is 0.1-10%, the mass fraction of a nitrogen-doped oxide in the composite lithium vanadium phosphate anode material is 0.1-5%, and the mass fraction of a second carbon source in the composite lithium vanadium phosphate anode material is 0.5-20%.
31. The composite lithium vanadium phosphate cathode material prepared by the method of any one of claims 1 to 30, wherein the composite lithium vanadium phosphate cathode material has a mesoporous structure.
32. Use of the composite lithium vanadium phosphate positive electrode material according to claim 31 as a positive electrode material for a lithium ion battery.
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