CN109473674B - Graphene-loaded nano nickel phosphate lithium battery positive electrode material and preparation method thereof - Google Patents
Graphene-loaded nano nickel phosphate lithium battery positive electrode material and preparation method thereof Download PDFInfo
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Abstract
The invention relates to the technical field of lithium battery anode materials, and provides a graphene-loaded nano nickel phosphate lithium battery anode material and a preparation method thereof. According to the method, a hydrothermal method is adopted to prepare the nitrogen-sulfur doped graphene nanosheets, a nickel source is loaded on the surface and between sheets of the graphene nanosheets, a lithium source and a phosphorus source are added, hydrothermal reaction is carried out under the control of phenanthroline to generate a graphene-loaded nano rodlike nickel lithium phosphate precursor, then the precursor is dried to obtain a precursor xerogel, the xerogel is ground into powder and then sintered, and the graphene-loaded nano nickel lithium phosphate cathode material is prepared. Compared with the traditional method, the lithium nickel phosphate material prepared by the invention has the advantages that the ionic conductivity and the electronic conductivity are both obviously improved, and the stability and the charge and discharge performance under high rate are improved.
Description
Technical Field
The invention belongs to the technical field of lithium battery anode materials, and provides a graphene-loaded nano nickel phosphate lithium battery anode material and a preparation method thereof.
Background
The lithium battery is a new generation of green high-energy battery with excellent performance, and has become one of the key points of high and new technology development. The lithium battery has the following characteristics: high voltage, high capacity, low consumption, no memory effect, no public hazard, small volume, small internal resistance, less self-discharge and more cycle times. Because of the above characteristics, lithium ion batteries have been applied to various civil and military fields such as mobile phones, notebook computers, video cameras, digital cameras, and the like.
Lithium batteries are secondary battery systems in which two different lithium intercalation compounds capable of reversibly intercalating and deintercalating lithium ions are used as the positive and negative electrodes of the battery, respectively. During charging, lithium ions are extracted from crystal lattices of the anode material and inserted into crystal lattices of the cathode material after passing through the electrolyte, so that the cathode is rich in lithium and the anode is poor in lithium; during discharging, lithium ions are extracted from the crystal lattice of the negative electrode material and inserted into the crystal lattice of the positive electrode material after passing through the electrolyte, so that the positive electrode is rich in lithium and the negative electrode is poor in lithium. The main constituent materials of the lithium ion battery include electrolyte, isolating material, anode and cathode materials and the like. The anode material occupies a large proportion, the performance of the anode material directly influences the performance of the lithium ion battery, and the cost directly determines the cost of the battery.
Among the existing positive electrode materials, LiMPO4(M = Fe, Mn, Co, Ni) is considered as a positive electrode material used for next-generation batteries. Among them, lithium nickel phosphate (LiNiPO)4) Having an olivine structure belonging to the Pnma space group, Li+And N2+Occupies half of the octahedral vacancies, P5+Occupying tetrahedral vacancies1/8, the advantage of this structure is PO4 3-The P-O covalent bond in the battery is very strong, so that the battery plays a role in stabilizing during charging, prevents oxygen from being released under high voltage, and ensures the stability and safety of the battery; however, the method has the disadvantages of poor conductivity and slow lithium ion diffusion, so that the method for improving the conductivity of the nickel lithium phosphate is the focus of the current research.
The Chinese patent application No. 201410808851.9 discloses a preparation method of a silicon-based lithium nickel phosphate composite material, which comprises the steps of firstly mixing a manganese source compound, a doping compound and an ammonium phosphate compound (comprising ammonium dihydrogen phosphate, diammonium hydrogen phosphate and triammonium phosphate) in an ultrafine sanding mode to prepare a compound with a molecular formula of SiNi1-xMxPO4Wherein x is more than or equal to 0 and less than or equal to 0.2, M is selected from any one or more of Co, Fe, Mg and Ni, and the dispersant is an organic solvent; then SiNi is added1-xMxPO4And (2) uniformly mixing the precursor and a lithium salt compound, transferring the mixture into a hydrothermal kettle, reacting at a certain temperature for a proper time, drying to obtain a lithium manganese phosphate material, and finally preparing the silicon-based lithium nickel phosphate composite material by adopting a heat treatment in-situ carbon coating mode. However, the conductivity of the silicon-based lithium nickel phosphate composite material prepared by the method is still not ideal enough, and the rate capability of the silicon-based lithium nickel phosphate composite material is poor when the silicon-based lithium nickel phosphate composite material is used for a lithium battery.
Chinese patent application number 201310286222.X discloses a green synthesis method of a nickel lithium phosphate/carbon composite material for a lithium ion battery, wherein the size of particles and the tight combination degree among the particles are changed from the aspect of appearance through carbon coating, and Li is reduced+The diffusion path improves the conductivity of lithium ions, metal ion doping causes defects of material lattices, and improves the ionic conductivity of the material, but the improvement effect of the conductivity needs to be further enhanced so as to adapt to development and application of higher requirements of lithium batteries.
The Chinese invention patent application number 201810376622.2 discloses a lithium iron phosphate/nitrogen and sulfur co-doped graphene composite material and a preparation method thereof, wherein the composite material is prepared by the following method: (1) adding a lithium source aqueous solution and a phosphorus source into an iron source aqueous solution, and stirring to obtain a mixed solution; (2) adding graphene oxide into water, carrying out ultrasonic treatment, adding a nitrogen-sulfur dopant, and stirring; (3) adding the mixed solution, stirring, carrying out hydrothermal reaction, cooling, centrifuging, washing and drying; (4) and (4) performing heat treatment in an inert atmosphere to obtain the product. In the composite material, lithium iron phosphate is a pure phase, the particle size of particles is 50-200 nm, and nitrogen and sulfur co-doped graphene is completely coated on the surface of the lithium iron phosphate particles; the assembled lithium ion battery has high specific capacity, high rate capability and good cycling stability; the method has the advantages of simple operation, low cost and strong controllability, and is suitable for industrial production. However, the graphene and lithium iron phosphate of the present invention have poor binding, and the positive electrode material has poor stability at high magnification and after cycling.
In summary, when the lithium nickel phosphate in the prior art is used as a lithium battery cathode material, the lithium nickel phosphate has the defects of poor conductivity and poor rate performance, so that the development of a lithium nickel phosphate cathode material with high conductivity and good rate performance has important significance.
Disclosure of Invention
Therefore, when the lithium nickel phosphate is used as the positive electrode material of the lithium battery, the lithium nickel phosphate has the defects of poor conductivity and rate performance. Aiming at the situation, the invention provides the graphene-loaded nano nickel lithium phosphate lithium battery positive electrode material and the preparation method thereof, and the prepared nickel lithium phosphate material has the advantages that the ionic conductivity and the electronic conductivity are both obviously improved, and the stability and the charge and discharge performance under high multiplying power are improved.
In order to achieve the purpose, the invention relates to the following specific technical scheme:
a preparation method of a graphene-loaded nano nickel lithium phosphate lithium battery positive electrode material comprises the following specific steps:
(1) dispersing graphene oxide nanosheets in deionized water, carrying out ultrasonic treatment for 2-3 h, then adding a nitrogen source and a sulfur source, transferring to a hydrothermal reaction kettle, heating to 200-220 ℃, reacting for 8-10 h, and then filtering, washing and freeze-drying to obtain nitrogen-sulfur doped graphene nanosheets;
(2) adding the nitrogen-sulfur doped graphene nanosheets prepared in the step (1) into a mixed solvent of N, N-dimethylformamide and water, ultrasonically dispersing for 2-3 h, adding a nickel source, stirring for 20-30 min, and then ultrasonically treating for 3-5 h to enable the nickel source to be loaded on the surface and between the graphene nanosheets to form a suspension;
(3) adding a lithium source and a phosphorus source into the suspension prepared in the step (2), stirring for 10-20 min, adding phenanthroline and stirring for 20-30 min, transferring to a hydrothermal reaction kettle, heating to 150-160 ℃, reacting for 5-6 h, controlling crystal growth by the phenanthroline to obtain a nanorod-shaped lithium nickel phosphate precursor, loading the nanorod-shaped lithium nickel phosphate precursor on the surface of the graphene nanosheet and between sheets, heating in a non-sealed environment to enable water to be partially volatilized to form gel, and drying by using an oven to obtain the nitrogen-sulfur doped graphene loaded nanorod-shaped lithium nickel phosphate precursor xerogel;
(4) grinding the precursor xerogel prepared in the step (3) into powder, heating to 300-350 ℃ at a speed of 8-10 ℃/min to pre-burn for 1-2 h in the presence of protective gas, heating to 600-650 ℃ at a speed of 4-6 ℃/min to calcine for 2-4 h, and naturally cooling to room temperature to prepare the nitrogen-sulfur doped graphene loaded nano nickel lithium phosphate cathode material.
By adopting the graphene nanosheets to load the lithium nickel phosphate, the graphene has excellent conductivity, so that the defect of poor conductivity of the lithium nickel phosphate material can be obviously improved. In addition, the graphene nanosheets are used as a framework, and the lithium nickel phosphate is fixed on the surfaces of the nanosheets and among the nanosheets, so that the lithium nickel phosphate can be prevented from falling off due to the immersion of an electrolyte in the charging and discharging process, and the stability and the charging and discharging performance of the lithium nickel phosphate under high multiplying power are improved.
Because the nitrogen atom and the sulfur atom can provide additional electrons and electron carriers, the nitrogen and sulfur co-doping is carried out on the graphene, the conductive capability of the graphene can be further enhanced, and the electronic conductivity of the nickel lithium phosphate material is obviously improved. Meanwhile, nitrogen atoms and sulfur atoms can partially enter the structure of the nickel lithium phosphate to induce the structure to generate defects, so that the activation energy of lithium ion diffusion is reduced, and the ionic conductivity of the nickel lithium phosphate material is improved. As a preferable scheme of the invention, the nitrogen source is one of ammonia water, ethylenediamine and urea, and the sulfur source is one of elemental sulfur, hydrogen sulfide and thiourea.
In order to achieve a good doping modification effect of graphene and not to affect the loading capacity of graphene, the doping amounts of nitrogen and sulfur need to be limited, as a preferred scheme of the invention, the weight of nitrogen contained in the nitrogen source is 4-8% of the weight of graphene oxide, and the weight of sulfur contained in the sulfur source is 3-5% of the weight of graphene oxide.
Preferably, in the mixed solvent of the N, N-dimethylformamide and water, the weight ratio of the N, N-dimethylformamide to the water is 1: 2-2: 1.
According to the invention, a nickel source is loaded on a framework of the nitrogen-sulfur doped graphene nanosheet, and then hydrothermal reaction is carried out on the nickel source, the lithium nickel phosphate generated later is enabled to form firm load and uniform distribution on the graphene nanosheet, and the firm and uniform load of the nickel source on the nanosheet is very important initially. In a preferred embodiment of the present invention, the nickel source is one of nickel hydroxide and nickel oxyhydroxide. Generally, there are many nickel sources available for synthesizing lithium nickel phosphate, such as nickel sulfate, nickel hydroxide, nickel carbonate, nickel oxalate, nickel phosphate, nickel oxyhydroxide, etc., but the molecular structures of nickel hydroxide and nickel oxyhydroxide contain OH-And the nickel source can form O-H … N bond or O-H … S bond with N atoms and S atoms doped in graphene, so that stable load can be formed more favorably, and therefore, the preferred nickel source is nickel hydroxide and nickel oxyhydroxide.
In a preferred embodiment of the present invention, the lithium source is one of lithium carbonate, lithium oxalate and lithium phosphate, and the phosphorus source is one of ammonium phosphate and ammonium dihydrogen phosphate.
In the invention, the molar ratio of nickel, lithium and phosphorus in the nickel source, the lithium source and the phosphorus source is preferably 1: 1.5-2: 1. The excess of lithium is, on the one hand, due to the volatilization of lithium at high temperatures and, on the other hand, we have found that it is easier to obtain lithium nickel phosphate materials of small size when the stoichiometric excess of lithium is not less than 0.5 times. Therefore, the molar excess of lithium is preferably 0.5 to 1 times.
In the process of synthesizing the nickel lithium phosphate by the hydrothermal reaction, the o-phenanthroline is used as a complexing agent, so that the growth of crystals in the reaction process can be controlled, and the crystal size and the crystal form are affected. When the crystal grows by taking the graphene nanosheet framework as a carrier, flaky crystals tend to be formed, the phenanthroline tends to promote the spherical growth of the crystal, and the crystal is converted into thin rod-shaped growth under the combined action of the flaky crystals and the phenanthroline. The phenanthroline also can prevent the fusion between nickel phosphate lithium crystal grains, and finally the nano rod-shaped nickel phosphate lithium material is formed. Preferably, the addition amount of the phenanthroline is 3-5% of the total weight of the suspension.
Preferably, the protective gas is nitrogen or helium.
The invention also provides a graphene-loaded nano nickel lithium phosphate lithium battery anode material prepared by the preparation method, wherein the graphene-loaded nano nickel lithium phosphate is prepared by firstly preparing nitrogen-sulfur-doped graphene nanosheets by a hydrothermal method, then loading a nickel source on the surface and between sheets of the graphene nanosheets, then adding a lithium source and a phosphorus source, carrying out hydrothermal reaction under the control of phenanthroline to generate a graphene-loaded nano rodlike nickel lithium phosphate precursor, then drying to obtain a precursor xerogel, grinding into powder and then sintering, and the prepared anode material has the electron conductivity of 1.8-2.2 × 10-1S/cm, and the ionic conductivity is 1.4-1.8 × 10-1S/cm, the first charge-discharge specific capacity of the assembled button cell is 150-157 mAh/g at 0.1C rate, and the capacity retention rate after 50 weeks of charge-discharge circulation is 95-97%; the 1C multiplying power is 140-150 mAh/g, and the capacity retention rate after 50 weeks of charge-discharge cycle is 92-94%; the 5C multiplying power is 118-125 mAh/g, and the capacity retention rate after 50 weeks of charge-discharge circulation is 85-88%; the 10C multiplying power is 96-100 mAh/g, and the capacity retention rate after 50 weeks of charge-discharge cycle is 78-80%.
The invention provides a graphene-loaded nano nickel phosphate lithium battery positive electrode material and a preparation method thereof, and compared with the prior art, the graphene-loaded nano nickel phosphate lithium battery positive electrode material has the outstanding characteristics and excellent effects that:
1. according to the preparation method, the graphene nanosheets are used for loading the nickel lithium phosphate, so that the electronic conductivity, the stability under high rate and the charge and discharge performance of the nickel lithium phosphate are improved, and further, the graphene is subjected to nitrogen and sulfur co-doping, so that the electronic conductivity and the ionic conductivity are improved.
2. The preparation method of the invention firstly contains OH-The nickel source is stably loaded on the nitrogen-sulfur doped graphene nanosheets, so that firm loading and uniform distribution of the generated lithium nickel phosphate are facilitated, and the stability is improved.
3. According to the preparation method, the phenanthroline is used as a complexing agent, crystal growth is controlled in the hydrothermal reaction process, the prepared nickel lithium phosphate is in a nano rod shape, the lithium ion migration path is shortened, and the ion conductivity can be obviously improved.
Detailed Description
The present invention will be described in further detail with reference to specific embodiments, but it should not be construed that the scope of the present invention is limited to the following examples. Various substitutions and alterations can be made by those skilled in the art and by conventional means without departing from the spirit of the method of the invention described above.
Example 1
(1) Dispersing graphene oxide nanosheets in deionized water, carrying out ultrasonic treatment for 2.5h, then adding a nitrogen source and a sulfur source, transferring to a hydrothermal reaction kettle, heating to 210 ℃, reacting for 8.5h, then filtering, washing, and freeze-drying to obtain nitrogen-sulfur doped graphene nanosheets; the nitrogen source is ammonia water; the weight of nitrogen in the nitrogen source is 7% of that of graphene oxide; the sulfur source is elemental sulfur; the weight of sulfur contained in the sulfur source is 3.5 percent of that of the graphene oxide;
(2) adding the nitrogen-sulfur doped graphene nanosheets prepared in the step (1) into a mixed solvent of N, N-dimethylformamide and water, ultrasonically dispersing for 2.5h, then adding a nickel source, stirring for 24min, and then ultrasonically treating for 3.5h to enable the nickel source to be loaded on the surface and between the graphene nanosheets to form a suspension; the nickel source is nickel hydroxide; in a mixed solvent of N, N-dimethylformamide and water, the weight ratio of the N, N-dimethylformamide to the water is 1: 1;
(3) adding a lithium source and a phosphorus source into the suspension prepared in the step (2), stirring for 16min, adding phenanthroline and stirring for 24min, transferring to a hydrothermal reaction kettle, heating to 156 ℃ for reaction for 5.5h, heating in a non-sealed environment to volatilize part of water to form gel, and drying by using an oven to prepare the nitrogen-sulfur doped graphene-loaded nano rod-shaped nickel lithium phosphate precursor xerogel; the lithium source is lithium carbonate; the phosphorus source is ammonium phosphate; the molar ratio of nickel, lithium and phosphorus in the nickel source, the lithium source and the phosphorus source is 1:1.7: 1; the addition amount of the phenanthroline is 4.5 percent of the total weight of the suspension;
(4) grinding the precursor xerogel prepared in the step (3) into powder, heating to 330 ℃ at a speed of 9 ℃/min for presintering for 1.5h in the presence of protective gas, heating to 630 ℃ at a speed of 5 ℃/min for calcining for 3h, and naturally cooling to room temperature to prepare the nitrogen-sulfur doped graphene loaded nano nickel lithium phosphate cathode material; the protective gas is nitrogen.
Example 2
(1) Dispersing graphene oxide nanosheets in deionized water, carrying out ultrasonic treatment for 2h, adding a nitrogen source and a sulfur source, transferring to a hydrothermal reaction kettle, heating to 205 ℃, reacting for 9.5h, filtering, washing, and freeze-drying to obtain nitrogen-sulfur doped graphene nanosheets; the nitrogen source is ethylenediamine; the weight of nitrogen in the nitrogen source is 5% of that of graphene oxide; the sulfur source is hydrogen sulfide; the weight of sulfur contained in the sulfur source is 3.5 percent of that of the graphene oxide;
(2) adding the nitrogen-sulfur doped graphene nanosheets prepared in the step (1) into a mixed solvent of N, N-dimethylformamide and water, ultrasonically dispersing for 2h, then adding a nickel source, stirring for 22min, and then ultrasonically treating for 4.5h to enable the nickel source to be loaded on the surface and between the graphene nanosheets to form a suspension; the nickel source is hydroxyl nickel oxide; in a mixed solvent of N, N-dimethylformamide and water, the weight ratio of the N, N-dimethylformamide to the water is 1: 2;
(3) adding a lithium source and a phosphorus source into the suspension prepared in the step (2), stirring for 12min, adding phenanthroline and stirring for 23min, transferring to a hydrothermal reaction kettle, heating to 152 ℃, reacting for 6h, heating in a non-sealed environment to volatilize part of water to form gel, and drying by using an oven to prepare the nitrogen-sulfur doped graphene-loaded nano rod-shaped nickel-lithium phosphate precursor xerogel; the lithium source is lithium oxalate; the phosphorus source is ammonium dihydrogen phosphate; the molar ratio of nickel, lithium and phosphorus in the nickel source, the lithium source and the phosphorus source is 1:1.6: 1; the addition amount of the phenanthroline is 3.5 percent of the total weight of the suspension;
(4) grinding the precursor xerogel prepared in the step (3) into powder, heating to 340 ℃ at the rate of 8 ℃/min for presintering for 1h in the presence of protective gas, heating to 610 ℃ at the rate of 4 ℃/min for calcining for 3.5h, and naturally cooling to room temperature to prepare the nitrogen-sulfur doped graphene loaded nano nickel lithium phosphate cathode material; the shielding gas is helium.
Example 3
(1) Dispersing graphene oxide nanosheets in deionized water, carrying out ultrasonic treatment for 3h, adding a nitrogen source and a sulfur source, transferring to a hydrothermal reaction kettle, heating to 215 ℃, reacting for 8.5h, filtering, washing, and freeze-drying to obtain nitrogen-sulfur doped graphene nanosheets; the nitrogen source is urea; the weight of nitrogen in the nitrogen source is 7% of that of graphene oxide; the sulfur source is thiourea; the weight of sulfur contained in the sulfur source is 4.5 percent of that of the graphene oxide;
(2) adding the nitrogen-sulfur doped graphene nanosheets prepared in the step (1) into a mixed solvent of N, N-dimethylformamide and water, ultrasonically dispersing for 3 hours, adding a nickel source, stirring for 28 minutes, and then ultrasonically treating for 4.5 hours to enable the nickel source to be loaded on the surface and interlayer of the nitrogen-sulfur doped graphene nanosheets to form a suspension; the nickel source is nickel hydroxide; in a mixed solvent of N, N-dimethylformamide and water, the weight ratio of the N, N-dimethylformamide to the water is 2: 1;
(3) adding a lithium source and a phosphorus source into the suspension prepared in the step (2), stirring for 18min, adding phenanthroline and stirring for 28min, transferring to a hydrothermal reaction kettle, heating to 158 ℃, reacting for 5h, heating in a non-sealed environment to volatilize part of water to form gel, and drying by using an oven to prepare the nitrogen-sulfur doped graphene-loaded nano rod-shaped nickel-lithium phosphate precursor xerogel; the lithium source is lithium phosphate; the phosphorus source is ammonium phosphate; the molar ratio of nickel, lithium and phosphorus in the nickel source, the lithium source and the phosphorus source is 1:1.9: 1; the addition amount of the phenanthroline is 4.5 percent of the total weight of the suspension;
(4) grinding the precursor xerogel prepared in the step (3) into powder, heating to 340 ℃ at a rate of 9 ℃/min for presintering for 2h in the presence of protective gas, heating to 640 ℃ at a rate of 6 ℃/min for calcining for 2.5h, and naturally cooling to room temperature to prepare the nitrogen-sulfur doped graphene loaded nano nickel lithium phosphate cathode material; the protective gas is nitrogen.
Example 4
(1) Dispersing graphene oxide nanosheets in deionized water, carrying out ultrasonic treatment for 2h, adding a nitrogen source and a sulfur source, transferring to a hydrothermal reaction kettle, heating to 200 ℃, reacting for 10h, filtering, washing, and freeze-drying to obtain nitrogen-sulfur doped graphene nanosheets; the nitrogen source is ammonia water; the weight of nitrogen in the nitrogen source is 4% of that of graphene oxide; the sulfur source is elemental sulfur; the weight of sulfur contained in the sulfur source is 3% of that of the graphene oxide;
(2) adding the nitrogen-sulfur doped graphene nanosheets prepared in the step (1) into a mixed solvent of N, N-dimethylformamide and water, ultrasonically dispersing for 2h, then adding a nickel source, stirring for 20min, and then ultrasonically treating for 3h to enable the nickel source to be loaded on the surface and interlayer of the nitrogen-sulfur doped graphene nanosheets to form a suspension; the nickel source is hydroxyl nickel oxide; in a mixed solvent of N, N-dimethylformamide and water, the weight ratio of the N, N-dimethylformamide to the water is 1: 2;
(3) adding a lithium source and a phosphorus source into the suspension prepared in the step (2), stirring for 10min, adding phenanthroline and stirring for 20min, transferring to a hydrothermal reaction kettle, heating to 150 ℃, reacting for 6h, heating in a non-sealed environment to volatilize part of water to form gel, and drying by using an oven to prepare the nitrogen-sulfur doped graphene-loaded nano rod-shaped nickel-lithium phosphate precursor xerogel; the lithium source is lithium carbonate; the phosphorus source is ammonium dihydrogen phosphate; the molar ratio of nickel, lithium and phosphorus in the nickel source, the lithium source and the phosphorus source is 1:1.5: 1; the addition amount of the phenanthroline is 3 percent of the total weight of the suspension;
(4) grinding the precursor xerogel prepared in the step (3) into powder, heating to 300 ℃ at a speed of 8 ℃/min for presintering for 2h in the presence of protective gas, heating to 600 ℃ at a speed of 4 ℃/min for calcining for 4h, and naturally cooling to room temperature to prepare the nitrogen-sulfur doped graphene loaded nano nickel lithium phosphate cathode material; the shielding gas is helium.
Example 5
(1) Dispersing graphene oxide nanosheets in deionized water, carrying out ultrasonic treatment for 3h, adding a nitrogen source and a sulfur source, transferring to a hydrothermal reaction kettle, heating to 220 ℃, reacting for 8h, filtering, washing, and freeze-drying to obtain nitrogen-sulfur doped graphene nanosheets; the nitrogen source is ethylenediamine; the weight of nitrogen in the nitrogen source is 8% of that of graphene oxide; the sulfur source is hydrogen sulfide; the weight of sulfur contained in the sulfur source is 5% of that of the graphene oxide;
(2) adding the nitrogen-sulfur doped graphene nanosheets prepared in the step (1) into a mixed solvent of N, N-dimethylformamide and water, ultrasonically dispersing for 3 hours, adding a nickel source, stirring for 30min, and ultrasonically treating for 5 hours to enable the nickel source to be loaded on the surface and between the graphene nanosheets to form a suspension; the nickel source is nickel hydroxide; in a mixed solvent of N, N-dimethylformamide and water, the weight ratio of the N, N-dimethylformamide to the water is 2: 1;
(3) adding a lithium source and a phosphorus source into the suspension prepared in the step (2), stirring for 20min, adding phenanthroline and stirring for 30min, transferring to a hydrothermal reaction kettle, heating to 160 ℃, reacting for 5h, heating in a non-sealed environment to volatilize part of water to form gel, and drying by using an oven to prepare the nitrogen-sulfur doped graphene-loaded nano rod-shaped nickel-lithium phosphate precursor xerogel; the lithium source is lithium phosphate; the phosphorus source is ammonium phosphate; the molar ratio of nickel, lithium and phosphorus in the nickel source, the lithium source and the phosphorus source is 1: 2: 1; the addition amount of the phenanthroline is 5 percent of the total weight of the suspension;
(4) grinding the precursor xerogel prepared in the step (3) into powder, heating to 350 ℃ at a speed of 10 ℃/min for presintering for 1h in the presence of protective gas, heating to 650 ℃ at a speed of 6 ℃/min for calcining for 2h, and naturally cooling to room temperature to prepare the nitrogen-sulfur doped graphene loaded nano nickel lithium phosphate cathode material; the protective gas is nitrogen.
Example 6
(1) Dispersing graphene oxide nanosheets in deionized water, carrying out ultrasonic treatment for 2.5h, then adding a nitrogen source and a sulfur source, transferring to a hydrothermal reaction kettle, heating to 210 ℃, reacting for 9h, then filtering, washing, and freeze-drying to obtain nitrogen-sulfur doped graphene nanosheets; the nitrogen source is urea; the weight of nitrogen in the nitrogen source is 6% of that of graphene oxide; the sulfur source is thiourea; the weight of sulfur contained in the sulfur source is 4% of that of the graphene oxide;
(2) adding the nitrogen-sulfur doped graphene nanosheets prepared in the step (1) into a mixed solvent of N, N-dimethylformamide and water, ultrasonically dispersing for 2.5h, then adding a nickel source, stirring for 25min, and then ultrasonically treating for 4h to enable the nickel source to be loaded on the surface and interlayer of the nitrogen-sulfur doped graphene nanosheets to form a suspension; the nickel source is hydroxyl nickel oxide; in a mixed solvent of N, N-dimethylformamide and water, the weight ratio of the N, N-dimethylformamide to the water is 1: 1;
(3) adding a lithium source and a phosphorus source into the suspension prepared in the step (2), stirring for 15min, adding phenanthroline and stirring for 25min, transferring to a hydrothermal reaction kettle, heating to 155 ℃, reacting for 5.5h, heating in a non-sealed environment to volatilize part of water to form gel, and drying by using an oven to prepare the nitrogen-sulfur doped graphene-loaded nano rod-shaped nickel lithium phosphate precursor xerogel; the lithium source is lithium oxalate; the phosphorus source is ammonium dihydrogen phosphate; the molar ratio of nickel, lithium and phosphorus in the nickel source, the lithium source and the phosphorus source is 1:1.8: 1; the addition amount of the phenanthroline is 4 percent of the total weight of the suspension;
(4) grinding the precursor xerogel prepared in the step (3) into powder, heating to 320 ℃ at a speed of 9 ℃/min to presintered for 1.5h in the presence of protective gas, heating to 625 ℃ at a speed of 5 ℃/min to calcine for 3h, and naturally cooling to room temperature to prepare the nitrogen-sulfur doped graphene loaded nano nickel lithium phosphate cathode material; the shielding gas is helium.
Comparative example 1
In the preparation process, nitrogen and sulfur co-doping is not carried out on the graphene, and other preparation conditions are consistent with those of example 6.
Comparative example 2
In the preparation process, no phenanthroline is added, and other preparation conditions are the same as those in example 6.
Comparative example 3
In the preparation process, graphene is not adopted for loading, and other preparation conditions are consistent with those of example 6.
And (3) performance testing:
the anode material prepared by the invention is prepared into an anode plate, Celgard 2400 polypropylene microporous membrane is taken as a diaphragm, and 1mol/L LiPF6The button cell of model CR2025 was assembled in an argon-filled glove box using the mixed organic solvent (EC: DMC =1:1, volume ratio) as the electrolyte and a metal lithium plate as the counter plate, and the following tests were performed:
(1) electron conductivity, ion conductivity: after electrochemical circulation is carried out for 1 week by adopting a Land CT2001A battery test system, the electrochemical impedance of the material is measured by using a Zahner IM6ex type electrochemical workstation, the measurement frequency range is 10 kHz-10 mHz, the perturbation voltage is 5mV, and the electronic conductivity and the ionic conductivity of the anode material are tested and calculated;
(2) and (3) testing specific capacity through charge and discharge circulation: and (3) carrying out charge-discharge cycle test by adopting a battery performance test system, wherein the charge-discharge voltage range is 2-4V, and the charge-discharge specific capacity of the first time and 50-week cycle under the multiplying power of 0.1C, 1C, 5C and 10C is respectively tested.
The data obtained are shown in Table 1.
Table 1:
Claims (9)
1. a preparation method of a graphene-loaded nano lithium nickel phosphate lithium battery cathode material comprises the specific steps of (1) dispersing oxidized graphene nanosheets in deionized water, carrying out ultrasonic treatment for 2-3 hours, adding a nitrogen source and a sulfur source, transferring the mixture into a hydrothermal reaction kettle, heating the hydrothermal reaction kettle to 200-220 ℃, reacting for 8-10 hours, filtering, washing and freeze-drying to obtain nitrogen-sulfur-doped graphene nanosheets, (2) adding the nitrogen-sulfur-doped graphene nanosheets prepared in the step (1) into a mixed solvent of N, N-dimethylformamide and water, carrying out ultrasonic dispersion for 2-3 hours, adding a nickel source, stirring for 20-30 minutes, carrying out ultrasonic treatment for 3-5 hours to enable the nickel source to be loaded on the surface and interlayer of the nitrogen-sulfur-doped graphene nanosheets to form a suspension, and (3) adding a lithium source into the suspension prepared in the step (2), A phosphorus source is stirred for 10-20 min, then phenanthroline is added and stirred for 20-30 min, the mixture is transferred to a hydrothermal reaction kettle and heated to 150-160 ℃ to react for 5-6 h, a nano rod-shaped nickel lithium phosphate precursor is obtained by controlling the crystal growth through phenanthroline and loaded on the surface and between sheets of a graphene nanosheet, then the mixture is heated in a non-sealed environment to enable partial water to volatilize to form gel, then an oven is used for drying, a nitrogen-sulfur doped graphene loaded nano rod-shaped nickel lithium phosphate precursor xerogel is prepared, 4) the precursor xerogel prepared in the step (3) is ground into powder, under the existence of protective gas, the temperature is firstly raised to 300-350 ℃ at 8-10 ℃/min for preburning for 1-2 h, then the temperature is raised to 600-650 ℃ at 4 ℃/min for calcining for 2-4 h, the mixture is naturally cooled to room temperature, and the nitrogen-sulfur doped graphene loaded nano nickel lithium phosphate anode material is prepared, the method is characterized in that:
the nickel source is one of nickel hydroxide and nickel oxyhydroxide.
2. The preparation method of the graphene-supported nano nickel lithium phosphate lithium battery positive electrode material according to claim 1, characterized by comprising the following steps:
the nitrogen source is one of ammonia water, ethylenediamine and urea;
the sulfur source is one of elemental sulfur, hydrogen sulfide and thiourea.
3. The preparation method of the graphene-supported nano nickel lithium phosphate lithium battery positive electrode material according to claim 1, characterized by comprising the following steps:
the weight of nitrogen in the nitrogen source is 4-8% of the weight of graphene oxide;
the weight of sulfur contained in the sulfur source is 3-5% of that of the graphene oxide.
4. The preparation method of the graphene-supported nano nickel lithium phosphate lithium battery positive electrode material according to claim 1, characterized by comprising the following steps: in the mixed solvent of the N, N-dimethylformamide and water, the weight ratio of the N, N-dimethylformamide to the water is 1: 2-2: 1.
5. The preparation method of the graphene-supported nano nickel lithium phosphate lithium battery positive electrode material according to claim 1, characterized by comprising the following steps:
the lithium source is one of lithium carbonate, lithium oxalate and lithium phosphate;
the phosphorus source is one of ammonium phosphate and ammonium dihydrogen phosphate.
6. The preparation method of the graphene-supported nano nickel lithium phosphate lithium battery positive electrode material according to claim 1, characterized by comprising the following steps: the molar ratio of nickel, lithium and phosphorus in the nickel source, the lithium source and the phosphorus source is 1: 1.5-2: 1.
7. The preparation method of the graphene-supported nano nickel lithium phosphate lithium battery positive electrode material according to claim 1, characterized by comprising the following steps: the adding amount of the phenanthroline is 3-5% of the total weight of the suspension.
8. The preparation method of the graphene-supported nano nickel lithium phosphate lithium battery positive electrode material according to claim 1, characterized by comprising the following steps: the protective gas is nitrogen or helium.
9. The graphene-supported nano nickel phosphate lithium battery positive electrode material prepared by the preparation method of any one of claims 1 to 8.
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