▎ 摘　　要

NOVELTY - Graphene coated lithium-manganese-iron-phosphate cathode material has formula LiFexMn1-xPO4/graphene, where x lies between 0.2 and 0.8. Graphene coated lithium-manganese-iron-phosphate cathode material is prepared by dissolving manganese and phosphate sources in deionized water. Oxidizing agent is added in the manganese source solution. The ratio of n(Mn):n(P) is 1:1. The amount of manganese and phosphorus source solution are mixed uniformly to obtain mixed solution. The dispersion liquid is added to the manganese and phosphorus source mixed solution. USE - Graphene coated lithium-manganese-iron-phosphate cathode material. ADVANTAGE - The graphene coated lithium-manganese-iron-phosphate cathode material has high voltage, high capacity, high circulation stability and excellent electrochemical performance. DETAILED DESCRIPTION - Graphene coated lithium-manganese-iron-phosphate cathode material has formula LiFexMn1-xPO4/graphene, where x lies between 0.2 and 0.8. Graphene coated lithium-manganese-iron-phosphate cathode material is prepared by dissolving manganese and phosphate sources in deionized water. Oxidizing agent is added in the manganese source solution. The ratio of n(Mn):n(P) is 1:1. The amount of manganese and phosphorus source solution are mixed uniformly to obtain mixed solution. The dispersion liquid is added to the manganese and phosphorus source mixed solution. The solution is stirred in a water bath to obtain a precipitate. The precipitate is filtered through suction, washed and dried to obtain manganese phosphate hydrate nano powder. The bath temperature is 30-60 degrees C and stirring time is 1-4 hours. The iron source and the phosphorus source are dissolved in distilled water. The ferrous iron source and oxidizing agent are added in the solution in element ratio of n(Fe):n(P)=1:1. The iron source and phosphorus source solution are added to the solution and solution is stirred. The phosphorus source solution is gradually dropped in iron to obtain iron source and phosphorus source in mixed solution. The dispersion liquid is added to iron and phosphorus source mixed solution. The solution is stirred in a water bath to obtain a precipitate. The precipitate is filtered through suction, washed and dried to obtain iron orthophosphate hydrate nano powder. The bath temperature is 30-60 degrees C and stirring time is 1-4 hours. Lithium metal is dissolved in non aqueous solvent to obtain 15 mole per liter of lithium solution, which is sealed and kept aside. The graphite is added to dispersed solvent to obtain 0.01-0.05 gram per milliliter suspension. The ultrasonic treatment is carried out at a frequency of 30-60 kilohertz for 0.2-4 hours to obtain graphene oxide dispersion. The two nano-powders are placed in ball mill jar in molar ratio of n(Fe):n(Mn)=0.25:4.0. The dispersion medium is added to the powder, uniformly mixed in ball mill for 2-6 hours and dried at 110-130 degrees C for 4-8 hours to obtain a mixed powder. Graphene oxide dispersion is added to mixed powder. The ultrasonic treatment is carried out for 3-6 hours at a frequency of 30-60 kilohertz to obtain a mixed system. The graphene dispersion liquid mass in graphene oxide is 0.1(x+78)-0.3(x+78) times the total molar weight of mixture powder. Lithium solution is slowly added dropwise to mixed system and the solution is stirred uniformly until the reaction is complete. A lithium complexing agent is added to the solution and stirring is continued for 0.5-2 hours. The solution is filtered and washed to obtain a precursor. The precursor is dried in vacuum at 60-90 degrees C for 10-24 hours and then uniformly milled into powder. The powder is loaded into the alumina boat, after sintering in an inert atmosphere in the furnace. The powder is cooled to room temperature to obtain graphene coated lithium-manganese-iron-phosphate cathode material. The sintering temperature is 600-800 degrees C and sintering time is 4-10 hours. The manganese source is manganese acetate, manganese oxalate, manganese formate, manganese sulfate, manganese nitrate, manganese chloride or soluble manganese compounds. The phosphorus source is phosphoric acid, ammonium phosphate, diamonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, potassium phosphate , potassium dihydrogen phosphate, dipotassium hydrogen phosphate, sodium phosphate, sodium dihydrogen phosphate and disodium hydrogen phosphate or soluble phosphorus-containing compound. The iron source is ferric chloride, ferric sulfate, ferric nitrate, ferrous chloride, ferrous sulfate, ferrous nitrate, ferrous oxalate, ferrous acetate, ferrous bromide, ferrous sulfide and other soluble iron compounds. The oxidant is hydrogen peroxide, sodium peroxide, nitric acid, concentrated sulfuric acid, hypochlorous acid and sodium hypochlorite. The dispersion liquid is ethanol, acetone, ethylene glycol, bis(2-ethylhexyl) phosphate, sodium lauryl sulfate, 4-methyl-2-pentanol, cellulose derivatives, polyacrylamide, gul glue and polyethylene glycol esters of fatty acids. The lithium metal is lithium metal powder, lithium metal sheet, block shaped lithium and lithium silk. The non-aqueous solvent is liquid ammonia, ethylene glycol, dimethyl ether, tetrahydrofuran, diethyl ether or dimethyl acetamide. The dispersing solvent is dimethyl ether, diethyl ether or acetone. The dispersion medium is ethanol, ethylene glycol or acetone. The complexing agent is propylene oxide, acetonitrile, dimethylsulfoxide. The inert atmosphere is of helium, argon or nitrogen.