Study On The Technology And Material Properties Of LiFePO₄/C Composite Powder Prepared By Mechanochemical Method

LiFePO₄ is one of the most promising cathode materials for lithium-ion batteries.At present,the main method of industrial preparation of lithium iron phosphate is the high temperature solid phase method,which has the disadvantages of high reaction temperature,long preparation cycle,high cost,and large particle size and uneven morphology of the prepared powder materials.In this paper,lithium iron phosphate cathode material with excellent electrical properties was obtained by optimizing the mixing and sintering process of lithium iron phosphate powder by means of mechanochemical method and horizontal high-energy ball mill.Graphene was used to modify lithium iron phosphate material around the two inherent shortcomings of poor electron and ionic conductivity.The main research contents and results are as follows:(1)Process optimization of LiFePO₄/C composite powder mixing.The effects of ball milling parameters on the properties of LiFePO₄/C composites were studied by high-energy ball milling method.It was found that,compared with the high temperature solid phase method,the mixing process was optimized,and the mixing time was reduced from 6-8h to 1h,which was greatly shortened.At 0.2C,the first discharge capacity of LiFePO₄/C powder is increased by 19.7%compared with that of unmilled LiFePO₄/C powder.After 300 cycles with 1C ratio,the capacity retention rate is as high as 93.9%,and the cycling stability of LiFePO₄/C powder is improved by 43.1%compared with that of non-ball milling under the same conditions.(2)Sintering process optimization of LiFePO₄/C composite powder.The effects of sintering process parameters on the properties of LiFePO₄/C composites were studied by carbothermal reduction method.It was found that the sintering process was optimized and the sintering temperature was reduced from 800?to 625?compared with the high temperature solid phase method.When the sintering temperature is 625?and the sintering time is 3h,the samples prepared have the best crystallinity and the most uniform dispersion.The charge-discharge capacities at 0.2C are 169.9m Ah/g and165.2m Ah/g,respectively,and the coulomb efficiency reaches 97.2%for the first time.The multiplier performance is the best.After 300 cycles at 1C rate,the capacity was still154.7m Ah/g,and the capacity retention rate was as high as 96.8%.There was basically no attenuation.(3)Graphene to optimize the performance of LiFePO₄/C material.The effect of the amount of graphite on the properties of LiFePO₄/C composites was studied.The study shows that when the amount of graphene is 4%,the composite of graphene and LiFePO₄/C is good and the dispersion is uniform.At 0.2C,the first charge and discharge efficiency reaches 98.1%.After 300 cycles at 5C,there was still 132.1m Ah/g capacity,with a capacity retention rate of 98.4%,and after 300 cycles at 10C,there was still98.1m Ah/g capacity,with a capacity retention rate of 97.3%.Compared with LiFePO₄/C material,the addition of graphene reduces the charge-discharge reaction polarization at low magnification,and the capacity increases by 27.2% at high magnification 5C.