Preparation And Study Of Lithium Iron Phosphate/Carbon Fiber Composite Cathode Materials

At present,people are increasingly pursuing a comfortable and clean environment.The development of battery technology has become the core of the development of all new-generation clean energy automobile industries.Oil-powered vehicles have been gradually replaced by electric vehicles,plug-in hybrid electric vehicles and other new energy vehicles.In addition,batteries are widely used in various electronic products,so continuous development and optimization of battery technology have become the key to the development of new energy devices^[1].Breakthroughs in battery performance are determined by the degree of development of the components that make up the battery.Lithium-ion batteries using polyanionic lithium iron phosphate?LiFePO₄?as cathode materials have been widely used commercially due to its advantages of low cost,good safety performance,non-toxic and harmless.However,LiFePO₄also has some disadvantages,such as poor electrical conductivity,low lithium ion diffusion coefficient and low tapping density.In this paper,the electrospinning method was focused on the synthesis of?010?preferred LiFePO₄/carbon fibers?LFP/CF?cathode materials with good conductivity and ion diffusion by controlling the preparation conditions.The specific experimental contents are as follows:1.Integrated LFP/CF composites were synthesized using simple and easy-to-operate electrostatic spinning technology.Polyvinylpyrrolidone?PVP?polymer was used as carbon source and polymer.Control of spinning and the sintering temperature,humidity and low spinning liquid precursor of PVP concentration?10 wt.%?,relatively high humidity?30%?,when the sintering temperature of 700?,the synthesis of composite materials?LFP/CF-700-P10-H?in the?010?crystal plane of LiFePO₄ is most advantage to grow,and used as no metal fluid,no binder when the support electrode showed excellent electrochemical performance.After 50 cycles of 0.1 C,the specific capacity was 157 mA h g^-1.After different rates of 0.2C,0.5 C,1 C,2 C and 5 C,the specific capacity was returned to 0.2 C with a retention rate of 99.4%.2.On the basis of the previous experiment,other conditions remain unchanged,only the content of lithium in the spinning precursor solution is changed to regulate the particle size of the calcined product LiFePO₄ and the orientation of?010?crystal surface.The stoichiometric ratios of Li:Fe:P were set as1.02:1:1 and 1.04:1:1,respectively.Electrochemical tests show that LiFePO₄ still has?010?surface preferential growth when lithium content is 2%(sample L_1.02FP/CF-700-P10-H),and LiFePO₄ no longer has?010?surface preferential growth when lithium content is 4%.The sample L_1.02FP/CF-700-P10-H also has good multiplier performance,a 0.5 C long cycle capacity of 500 cycles is 143.9 mA h g^-1,and capacity retention rate of 97.9%.3.To explore the reasons for the optimal growth of LiFePO₄?010?crystal surface in the lithium iron phosphate/carbon fiber?LFP/CF?composites prepared by electrostatic spinning.The effects of PVP,lithium content in spinning precursor and spinning environment humidity were investigated.The results show that the above conditions can affect the selective growth of LiFePO₄?010?crystal surface.