CN114275826A - Graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material and preparation method thereof - Google Patents
Graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material, and a preparation method of the positive electrode material comprises two steps; the first step is as follows: dissolving a nickel source, a cobalt source and a manganese source in a solvent to obtain a mixed solution 1, adding a graphene coating agent into the mixed solution 1 to obtain a mixed solution 2, adding urea into the mixed solution 2 to obtain a mixed solution 3, heating the mixed solution 3 to 100 ℃ and 150 ℃, reacting for 10-20h, cooling, centrifugally separating, collecting a precipitate, washing and drying to obtain a nickel cobalt lithium manganate composite graphene precursor; the second step is that: and mixing the nickel cobalt lithium manganate composite graphene precursor with a lithium source, and calcining at high temperature to obtain the graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material. The graphene carbon coating can effectively protect electrode active particles, prevent the surface of a material from being corroded by electrolyte, and improve the cycle performance and stability and safety of the material.
Description
Technical Field
The invention relates to the technical field of lithium batteries, in particular to a graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material and a preparation method thereof.
Background
The lithium ion battery mainly comprises a positive electrode material, a negative electrode material, a diaphragm, electrolyte and the like. Upon charging, Li+The cathode is separated from the anode and is embedded into the anode, and meanwhile, electrons flow to the anode from the cathode through an external circuit; on the contrary, upon discharge, Li+The cathode is embedded into the cathode after being separated from the cathode, and electrons flow from the cathode to the anode through an external circuit; li+The electrolyte is inserted and separated between the positive electrode and the negative electrode to reciprocate, corresponding to the charge and discharge process. The lithium ion battery anode material is an indispensable part of a lithium ion secondary battery, and not only can be used as an electrode material to participate in electrochemical reaction, but also can provide a lithium source for the lithium ion battery to maintain normal operation of the lithium ion battery.
Currently, lithium ion battery positive electrode materials that are commercialized can be roughly classified into the following three types according to their structures: the first type is a lithium metal oxide LiMO having a layered structure2(M ═ Ni, Co, Mn), and lithium cobaltate (LiCO) is a main representative material thereof2) Ternary lithium Nickel Cobalt Manganese (NCM) and ternary lithium Nickel Cobalt Aluminate (NCA); the second type is a material having a spinel structure, and a representative material thereof is spinel-type lithium manganate (LiMn)2O4) (ii) a The third class is materials with polyanionic structures. LiNi1-x-yCoxMnyO2(NCM) is a synergistic effect by Ni-Co-Mn, which absorbs and binds LiNiO2、LiCoO2、LiMnO2The advantages of three positive electrode materials: LiNiO2High specific capacity of, LiCoO2Excellent cycle performance and LiMnO2Good safety and low cost, etc. With conventional single LiMO2Compared with (M ═ Ni, Co and Mn) electrode materials, the layered nickel cobalt lithium manganate ternary positive electrode material has the advantages of large specific discharge capacity, good thermal stability, excellent cycle performance, low cost and the like, and is a material which is very likely to replace LiMO2The electrode material is widely applied to the fields of digital products and new energy automobiles, and is one of the novel lithium ion battery anode materials with the most extensive development prospect at present.
The layered nickel cobalt lithium manganate ternary positive electrode material generally has the following problems, namely Li+And Ni2+The cation mixed discharging effect of (2) can cause the charging and discharging efficiency of the high-nickel ternary material to be low; secondly, the corrosion of active substances and the decomposition of dielectric medium can seriously affect the charge transfer of an electrode/electrolyte interface, thereby affecting the stability of the lithium battery; third, the structure of the material is unstable with the deintercalation of lithium ions during charge and discharge to cause collapse and destruction. The main method for solving the problems is doping modification and surface coating, while the nickel-cobalt-manganese ternary positive electrode material is modified by doping, certain defects exist, firstly, the capacity of the battery is lost due to doping of inactive substance elements, secondly, oxide erosion occurs on the surface of the battery due to contact of active particles and electrolyte in the charging and discharging processes, so that transition metal ions are dissolved, the surface structure is formed to collapse, the cycle performance is poor, and the problem of matching with the electrolyte cannot be fundamentally solved. The protective layer provided by the surface coating isolates active substances in the material from electrolyte, effectively reduces the corrosion of HF to the active substances, effectively relieves the dissolution of metal ions, and slows down the collapse of the electrode material structure in the long-term circulation process.
CN 103887489A discloses a preparation method of a high-specific-capacity graphene-coated nickel cobalt lithium manganate material, the method comprises the steps of adopting a nickel cobalt lithium manganate material and a graphene sheet, dissolving the graphene sheet in a DMF solution at 180 ℃ to prepare a graphene DMF solution with the concentration of 100 plus 1000ppm, dropwise adding the DMF solution into the prepared nickel cobalt lithium manganate material under the stirring condition, and then putting the obtained material into a vacuum drying box for drying at the temperature of 110 plus 140 ℃ to obtain a finished product.
Disclosure of Invention
In view of the above defects in the prior art, the technical problem to be solved by the present invention is to solve the problem that the electrochemical performance of the material is not good due to uneven dispersion of graphene in the graphene carbon-coated nickel cobalt lithium manganate ternary positive electrode material in the prior art.
In order to achieve the purpose, the graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material provided by the invention has the advantages that the conductivity of the prepared positive electrode material is improved by coating a graphene carbon layer on the surface of the nickel cobalt lithium manganate material, so that the rate capability of the prepared battery is improved, the coating layer can effectively protect electrode active particles, the surface of the material is prevented from being corroded by electrolyte, and the cycle performance and stability safety of the material are improved.
In order to achieve the purpose of the invention, the invention adopts the following technical scheme:
the preparation method of the graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material comprises the following steps:
s1, dissolving nickel salt, cobalt salt and manganese salt in a solvent, adding a graphene coating agent and urea, uniformly mixing to obtain a mixed solution, heating the mixed solution to 100 ℃ and 150 ℃, reacting for 10-20h, cooling, centrifugally separating, collecting precipitates, washing and drying to obtain a nickel cobalt lithium manganate composite graphene precursor;
s2, mixing the nickel cobalt lithium manganate composite graphene precursor with lithium salt, and calcining at high temperature to obtain the graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material.
Preferably, the preparation method of the graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material comprises the following steps:
s1, dissolving a nickel source, a cobalt source and a manganese source in a solvent, adding a graphene coating agent and urea, and uniformly mixing to obtain a mixed solution; heating the mixed solution to the temperature of 100-150 ℃, reacting for 10-20h, cooling to the temperature of 30-40 ℃, performing centrifugal separation, collecting precipitates, washing the precipitates for 2-3 times respectively by using water and absolute ethyl alcohol, and then placing the precipitates in a drying box at the temperature of 60-80 ℃ for drying for 20-24h to obtain a nickel cobalt lithium manganate composite graphene precursor;
s2, mixing the nickel cobalt lithium manganate composite graphene precursor with a lithium source, and calcining at the temperature of 400-600 ℃ for 3-5h at the heating rate of 1-5 ℃/min under the argon atmosphere to obtain the graphene carbon surface modified nickel cobalt lithium manganate ternary cathode material.
In the step S1, the nickel source is one or a mixture of two or more of nickel hydroxide, nickel acetate, nickel carbonate, nickel nitrate and nickel oxalate; the cobalt source is one or a mixture of two or more of cobalt hydroxide, cobalt acetate, cobalt carbonate, cobalt nitrate and cobalt oxalate; the manganese source is one or a mixture of two or more of manganese hydroxide, manganese acetate, manganese carbonate, manganese nitrate and manganese oxalate; the mass ratio of the nickel source to the cobalt source to the manganese source is 6-10:1-2: 1-3.
The solvent in the step S1 is one of ethanol water solution and polyethylene glycol; the preferred solvent is polyethylene glycol with molecular weight of 200, and the ratio of the polyethylene glycol to the total amount of the nickel source, the cobalt source and the manganese source is 5-10: 1.
the ratio of the amount of the urea substance to the total amount of the nickel source, the cobalt source and the manganese source in the step S1 is 0.05-0.1: 1.
In the step S1, the graphene coating agent is graphene oxide, and the ratio of the amount of the graphene coating agent to the total amount of the nickel source, the cobalt source and the manganese source is 0.1-0.2: 1.
Preferably, the graphene coating agent is modified graphene oxide, and the preparation method thereof is as follows: placing graphene oxide in an ethanol water solution for ultrasonic dispersion, adding 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide and 1-butyl-3-methylimidazolium dicyanamide, performing ultrasonic treatment to obtain a reaction solution, reacting at 30-40 ℃ for 10-12h, centrifuging, filtering and collecting a precipitate, washing the precipitate with the ethanol water solution, drying, and grinding to obtain the modified graphene oxide.
More preferably, the preparation method of the modified graphene oxide is as follows:
placing graphene oxide in 50-80mL of 90-99 wt% ethanol water solution, performing ultrasonic dispersion to obtain a suspension 2, adding 1-2g of 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide and 1-2g of 1-butyl-3-methylimidazolium dicyanamide into the suspension 2, performing ultrasonic treatment for 20-30min to obtain a reaction solution, heating the reaction solution to 30-40 ℃, reacting for 10-12h, centrifuging, filtering and collecting a precipitate, washing the precipitate for 2-3 times with 200 mL of 70-90 wt% ethanol water solution, placing the washed precipitate in a drying oven at 60-80 ℃ for drying for 20-24h, and grinding to obtain the modified graphene oxide.
At present, common carbon-coated modified nickel cobalt lithium manganate ternary positive electrode materials are obtained by mixing and sintering a carbon source, a positive electrode material and a lithium source, and carbon coating layers prepared by the method cannot be uniformly distributed on the surface of the positive electrode material, so that uniform and compact carbon coating layers cannot be formed, partial surface of the positive electrode material still can be in contact with electrolyte to generate side reaction, and the electrochemical performance of the material is reduced. The inventor inserts 1-ethyl-3-methylimidazole bis (trifluoromethylsulfonyl) imide and 1-butyl-3-methylimidazole dicyanamide into the sandwich structure of graphene oxide through pi-pi action, hydrogen bond action and electrostatic adsorption by modifying the graphene oxide with the 1-ethyl-3-methylimidazole bis (trifluoromethylsulfonyl) imide and the 1-butyl-3-methylimidazole dicyanamide, the distance between the graphene layer and the layer is increased, the agglomeration of the graphene is effectively prevented, the graphene oxide is uniformly dispersed on the electrode material, the graphene carbon layer and the nickel cobalt lithium manganate are tightly combined during high-temperature carbonization to form a uniform and compact graphene carbon coating layer, so that the surface of the positive electrode material is prevented from reacting with an electrolyte in a contact manner, and the electrochemical performance of the material is improved.
In the step S2, the lithium source is one or a mixture of two or more of lithium hydroxide, lithium acetate, lithium carbonate, lithium nitrate and lithium oxalate, and the ratio of the amount of the lithium source to the total amount of the nickel source, the cobalt source and the manganese source is 1.03-1.3: 1.
the average particle size of the graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material is 4.5-5 mu m, and the specific surface area is 1.2-1.5m2/g。
Compared with the prior art, the invention has the beneficial effects that:
1. according to the invention, the graphene carbon layer is coated on the surface of the nickel cobalt lithium manganate electrode by a wet chemical method, instead of coating the nickel cobalt lithium manganate powder, so that a complete graphene carbon coating layer is formed on the surface of the electrode, and the coating layer can not only avoid the contact of a matrix ternary positive electrode material with moisture and carbon dioxide in the air, but also effectively inhibit the corrosion of electrolyte to the positive electrode material and the side reaction of the surface of the electrode, stabilize the surface structure of the electrode and improve the cycle performance of the electrode.
2. The graphene has excellent conductivity, extremely high specific surface area and excellent structural stability, can establish a three-dimensional conductive network and also can serve as a surface coating layer to effectively prevent the reaction of an electrode material and electrolyte, thereby effectively avoiding the corrosion of the electrode material.
3. Graphene is modified to be uniformly dispersed on an electrode, and when the graphene is carbonized at high temperature, a graphene carbon layer can be uniformly and tightly combined with an electrode material to form a compact graphene carbon coating layer, so that the surface of a positive electrode material is prevented from being contacted with electrolyte to react, and the electrochemical performance of the material is improved.
Detailed Description
Part of raw materials used in the invention are as follows:
lithium acetate purchased from Shanghai Europe gold industries Co., Ltd, CAS number 546-89-4, content not less than 99%.
Nickel acetate was purchased from Guangshi electronics, Inc., Shandong, under CAS number 373-02-4, at a content of 99%.
Cobalt acetate, purchased from Shandong standing grain torch electronic technologies, Inc., having a CAS number of 71-48-7, at a content of 99%.
Manganese acetate, available from Shandong standing grain torch electronic technology, Inc., CAS number 19513-05-4, at a content of 99%.
Triethanolamine, available from Yushun-Jia chemical Co., Ltd, Guangzhou, CAS number 102-71-6, density 1.1242g/cm3The content is 99%.
Polyethylene glycol 200, purchased from tengpo chemical ltd, has a flash point of 171 ℃, a boiling point of 250 ℃ and a refractive index of 1.458-1.461.
Graphene oxide purchased from Hangzhou Zhi Ti purification technology Co., Ltd, having an average thickness of 1-3nm, a diameter of 4-7 μm, 2-5 layers, and a specific surface area of 20-50m2The electric conductivity is more than or equal to 1000S/cm.
1-Ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide, available from Wuhan Povlov Biotech Ltd, CAS number 174899-82-2, at 99% level.
1-butyl-3-methylimidazolium dicyanamide, available from Wuhan Kamike technologies, Inc., 99% in content, CAS number 448245-52-1.
Example 1
The preparation method of the graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material comprises the following steps:
s1, weighing nickel acetate, cobalt acetate and manganese acetate according to the mass ratio of Ni to Co to Mn of 7 to 1, and dissolving the nickel acetate, the cobalt acetate and the manganese acetate in polyethylene glycol 200 to obtain a solution 1; adding a graphene coating agent into the solution 1 to obtain a mixed solution 2; adding urea into the mixed solution 2 to obtain a mixed solution 3, heating the mixed solution 3 to 120 ℃, reacting for 20 hours, cooling to 35 ℃, performing centrifugal separation, collecting precipitates, washing the precipitates for 3 times by using water and absolute ethyl alcohol respectively, and then placing the precipitates in a drying oven at 80 ℃ for drying for 24 hours to obtain a nickel cobalt lithium manganate composite graphene precursor; the ratio of the polyethylene glycol 200, the graphene coating agent, the urea to the total substance of the nickel source, the cobalt source and the manganese source is 5: 0.2: 0.1: 1.
s2, mixing the nickel cobalt lithium manganate composite graphene precursor with a lithium source, and calcining at the high temperature of 500 ℃ for 4h at the heating rate of 1 ℃/min in the argon atmosphere to obtain the graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material; the ratio of the amount of the lithium source to the total amount of the nickel source, the cobalt source and the manganese source is 1.1: 1.
the graphene coating agent is graphene oxide.
Example 2
The preparation method of the graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material comprises the following steps:
s1, weighing nickel acetate, cobalt acetate and manganese acetate according to the mass ratio of Ni to Co to Mn of 7 to 1, and dissolving the nickel acetate, the cobalt acetate and the manganese acetate in polyethylene glycol 200 to obtain a solution 1; adding a graphene coating agent into the solution 1 to obtain a mixed solution 2; adding urea into the mixed solution 2 to obtain a mixed solution 3, heating the mixed solution 3 to 120 ℃, reacting for 20 hours, cooling to 35 ℃, performing centrifugal separation, collecting precipitates, washing the precipitates for 3 times by using water and absolute ethyl alcohol respectively, and then placing the precipitates in a drying oven at 80 ℃ for drying for 24 hours to obtain a nickel cobalt lithium manganate composite graphene precursor; the ratio of the polyethylene glycol 200, the graphene coating agent, the urea to the total substance of the nickel source, the cobalt source and the manganese source is 5: 0.2: 0.1: 1.
s2, mixing the nickel cobalt lithium manganate composite graphene precursor with a lithium source, and calcining at the high temperature of 500 ℃ for 4h at the heating rate of 1 ℃/min in the argon atmosphere to obtain the graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material; the ratio of the amount of the lithium source to the total amount of the nickel source, the cobalt source and the manganese source is 1.1: 1.
the graphene coating agent is modified graphene oxide, and the preparation method comprises the following steps: placing graphene oxide in 80mL of 99 wt% ethanol aqueous solution, performing ultrasonic dispersion to obtain a suspension 2, adding 3.2g of 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide into the suspension 2, performing ultrasonic treatment for 20min to obtain a reaction solution, heating the reaction solution to 40 ℃, reacting for 12h, centrifuging, filtering and collecting a precipitate, washing the precipitate with 300mL of 90 wt% ethanol aqueous solution for 3 times, placing the washed precipitate in a drying oven at 80 ℃, drying for 24h, and grinding to obtain the modified graphene oxide.
Example 3
The preparation method of the graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material comprises the following steps:
s1, weighing nickel acetate, cobalt acetate and manganese acetate according to the mass ratio of Ni to Co to Mn of 7 to 1, and dissolving the nickel acetate, the cobalt acetate and the manganese acetate in polyethylene glycol 200 to obtain a solution 1; adding a graphene coating agent into the solution 1 to obtain a mixed solution 2; adding urea into the mixed solution 2 to obtain a mixed solution 3, heating the mixed solution 3 to 120 ℃, reacting for 20 hours, cooling to 35 ℃, performing centrifugal separation, collecting precipitates, washing the precipitates for 3 times by using water and absolute ethyl alcohol respectively, and then placing the precipitates in a drying oven at 80 ℃ for drying for 24 hours to obtain a nickel cobalt lithium manganate composite graphene precursor; the ratio of the polyethylene glycol 200, the graphene coating agent, the urea to the total substance of the nickel source, the cobalt source and the manganese source is 5: 0.2: 0.1: 1.
s2, mixing the nickel cobalt lithium manganate composite graphene precursor with a lithium source, and calcining at the high temperature of 500 ℃ for 4h at the heating rate of 1 ℃/min in the argon atmosphere to obtain the graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material; the ratio of the amount of the lithium source to the total amount of the nickel source, the cobalt source and the manganese source is 1.1: 1.
the graphene coating agent is modified graphene oxide, and the preparation method comprises the following steps: placing graphene oxide in 80mL of 99 wt% ethanol aqueous solution, performing ultrasonic dispersion to obtain a suspension 2, adding 3.2g of 1-butyl-3-methylimidazol dicyanamide into the suspension 2, performing ultrasonic treatment for 20min to obtain a reaction solution, heating the reaction solution to 40 ℃, reacting for 12h, centrifuging, filtering, collecting a precipitate, washing the precipitate with 300mL of 90 wt% ethanol aqueous solution for 3 times, placing the washed precipitate in a drying oven at 80 ℃, drying for 24h, and grinding to obtain the modified graphene oxide.
Example 4
The preparation method of the graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material comprises the following steps:
s1, weighing nickel acetate, cobalt acetate and manganese acetate according to the mass ratio of Ni to Co to Mn of 7 to 1, and dissolving the nickel acetate, the cobalt acetate and the manganese acetate in polyethylene glycol 200 to obtain a solution 1; adding a graphene coating agent into the solution 1 to obtain a mixed solution 2; adding urea into the mixed solution 2 to obtain a mixed solution 3, heating the mixed solution 3 to 120 ℃, reacting for 20 hours, cooling to 35 ℃, performing centrifugal separation, collecting precipitates, washing the precipitates for 3 times by using water and absolute ethyl alcohol respectively, and then placing the precipitates in a drying oven at 80 ℃ for drying for 24 hours to obtain a nickel cobalt lithium manganate composite graphene precursor; the ratio of the polyethylene glycol 200, the graphene coating agent, the urea to the total substance of the nickel source, the cobalt source and the manganese source is 5: 0.2: 0.1: 1.
s2, mixing the nickel cobalt lithium manganate composite graphene precursor with a lithium source, and calcining at the high temperature of 500 ℃ for 4h at the heating rate of 1 ℃/min in the argon atmosphere to obtain the graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material; the ratio of the amount of the lithium source to the total amount of the nickel source, the cobalt source and the manganese source is 1.1: 1.
the graphene coating agent is modified graphene oxide, and the preparation method comprises the following steps: placing graphene oxide in 80mL of 99 wt% ethanol aqueous solution, performing ultrasonic dispersion to obtain a suspension 2, adding 1.8g of 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide and 1.4g of 1-butyl-3-methylimidazolium dicyanamide into the suspension 2, performing ultrasonic treatment for 20min to obtain a reaction solution, heating the reaction solution to 40 ℃, reacting for 12h, centrifuging, filtering and collecting a precipitate, washing the precipitate with 300mL of 90 wt% ethanol aqueous solution for 3 times, placing the washed precipitate in a drying oven at 80 ℃, drying for 24h, and grinding to obtain the modified graphene oxide.
Test example
Assembling the battery: the ternary positive electrode materials prepared in examples 1 to 4 were subjected to battery assembly and testing, and the operation procedure was: weighing a ternary positive electrode material, acetylene black and polyvinylidene fluoride according to a mass ratio of 7:2:1, uniformly mixing, adding N-methyl pyrrolidone, stirring for 4 hours to prepare slurry, uniformly coating the slurry on an aluminum foil, wherein the coating thickness is usually 10 microns, vacuum drying is carried out at 100 ℃ for 12 hours, tabletting to obtain a pole piece with uniform thickness of 12mm, a lithium piece with the diameter of 16mm is used as a negative electrode, and LiPF is selected as a lithium battery electrolyte6(ethylene carbonate: dimethyl carbonate: methyl ethyl carbonate ═ 1:1:1 wt%) mixed solution was used as an electrolyte, and a polypropylene microporous membrane was used as a separator, and the button cell was assembled in a glove box filled with argon gas. And carrying out capacity test (3.0-4.3V, 0.1C/0.1C) and cycle test (3.0-4.3V, 1C/1C) on the assembled button cell.
Electrochemical properties of the assembled cell are shown in table 1:
table 1: electrochemical performance test result table of assembled battery
As can be seen from the data in table 1, the electrochemical performance of the graphene carbon surface-modified nickel cobalt lithium manganate ternary cathode material prepared in example 4 is significantly better than that of the other examples, while example 5 is different from that of the other examples in that graphene oxide modified by 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide and 1-butyl-3-methylimidazolium dicyanamide is added to graphene oxide, possibly because 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide and 1-butyl-3-methylimidazolium dicyanamide are inserted into the interlayer structure of graphene oxide through pi-pi action, hydrogen bonding action and electrostatic adsorption, the graphene layer-to-layer distance is increased, the aggregation of graphene is effectively prevented, and the graphene oxide is uniformly dispersed on the electrode material, the graphene carbon layer and the nickel cobalt lithium manganate are tightly combined during high-temperature carbonization to form a uniform and compact graphene carbon coating layer, so that the surface of the positive electrode material is prevented from reacting with an electrolyte in a contact manner, and the electrochemical performance of the material is improved.
Claims (10)
1. A preparation method of a graphene carbon surface modified nickel cobalt lithium manganate ternary positive electrode material is characterized by comprising the following steps:
s1, dissolving a nickel source, a cobalt source and a manganese source in a solvent, adding a graphene coating agent and urea, uniformly mixing to obtain a mixed solution, heating the mixed solution to 100-150 ℃, reacting for 10-20h, cooling, centrifugally separating, collecting precipitates, washing and drying to obtain a nickel cobalt lithium manganate composite graphene precursor;
s2, mixing the nickel cobalt lithium manganate composite graphene precursor with a lithium source, and calcining at high temperature to obtain the graphene carbon surface modified nickel cobalt lithium manganate ternary cathode material.
2. The method of claim 1, comprising the steps of:
s1 dissolving a nickel source, a cobalt source and a manganese source in a solvent, adding a graphene coating agent and urea, uniformly mixing to obtain a mixed solution, heating the mixed solution to 100 ℃ and 150 ℃, reacting for 10-20h, cooling to 30-40 ℃, performing centrifugal separation, collecting precipitates, washing the precipitates for 2-3 times with water and absolute ethyl alcohol respectively, and drying in a drying box at 60-80 ℃ for 20-24h to obtain a nickel cobalt lithium manganate composite graphene precursor;
s2, mixing the nickel cobalt lithium manganate composite graphene precursor with a lithium source, and calcining at a high temperature of 400-600 ℃ at a heating rate of 1-5 ℃/min in an argon atmosphere to obtain the graphene carbon surface modified nickel cobalt lithium manganate ternary cathode material.
3. The method of claim 1 or 2, wherein: in the step S1, the nickel source is one or a mixture of two or more of nickel hydroxide, nickel acetate, nickel carbonate, nickel nitrate and nickel oxalate.
4. The method of claim 1 or 2, wherein: in the step S1, the cobalt source is one or a mixture of two or more of cobalt hydroxide, cobalt acetate, cobalt carbonate, cobalt nitrate and cobalt oxalate.
5. The method of claim 1 or 2, wherein: in the step S1, the manganese source is one or a mixture of two or more of manganese hydroxide, manganese acetate, manganese carbonate, manganese nitrate and manganese oxalate.
6. The method of claim 1 or 2, wherein: the solvent in the step S1 is one of ethanol aqueous solution and polyethylene glycol.
7. The method of claim 1 or 2, wherein: in the step S2, the graphene coating agent is graphene oxide, and the ratio of the amount of the graphene coating agent to the total amount of the nickel source, the cobalt source and the manganese source is 0.1-0.2: 1.
8. The preparation method according to claim 1 or 2, wherein the graphene coating agent in the step S1 is graphene oxide or modified graphene oxide; the preparation method of the modified graphene oxide comprises the following steps: placing graphene oxide in an ethanol water solution for ultrasonic dispersion, adding 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide and 1-butyl-3-methylimidazolium dicyanamide, performing ultrasonic treatment to obtain a reaction solution, heating the reaction solution to 30-40 ℃, reacting for 10-12h, centrifuging, filtering and collecting a precipitate, washing the precipitate with an ethanol water solution, drying, and grinding to obtain the graphene coating agent.
9. The graphene carbon surface modified lithium nickel cobalt manganese oxide ternary positive electrode material is prepared by the preparation method of any one of claims 1 to 8.
10. The graphene-carbon surface-modified lithium nickel cobalt manganese oxide ternary positive electrode material of claim 9, wherein: the average particle diameter of the anode material is 4.5-5 mu m, and the specific surface area is 1.2-1.5m2/g。
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