Study On Graphene Conductive Additives To Improve The Performance Of Lithium Iron Phosphate Cathode Material

Lithium-ion batteries（LIBs）are extensively employed as energy storage fields owing to their high energy density,long cycle life,and portability.The performance of lithium-ion batteries depends to a large extent on its cathode material.Li Fe PO₄has become one of the main cathode materials for commercial lithium-ion batteries due to its large theoretical specific capacity,good cycle stability,inexpensiveness and environment friendly.However,due to the low conductivity between the lithium iron phosphate particles,the electrochemical performance is very limited.Adding conductive additives into electrode materials is the most effective strategy to improve electrode conductivity.Among many conductive additives,graphene has attracted extensive attention of researchers due to its good electrical conductivity and unique molecular structure.However,traditional graphene has complicated preparation process,high production cost,and steric hindrance at high current density,which limits its development in the field of lithium-ion batteries.In view of this,in this paper,liquid phase exfoliated graphene（LG）was prepared by optimizing the process,and its effect on the capacity and rate performance of lithium-ion batteries was explored by using graphene composite conductive additives and carbon-coated lithium iron phosphate.The specific research results are as follows:First,graphene was successfully synthesized by the liquid phase exfoliation method,and its plane size was mainly distributed in 200-400 nm,and The number of layers is mainly a few layers.Using graphene alone as a conductive additives for lithium iron phosphate cathode materials,its"point-to-surface"contact with lithium iron phosphate can significantly improve"long-range"conductivity.Compared with commercially conductive carbon black（SP）at low rates,the battery capacity can be improved at a lower content.The specific discharge capacity of 10 wt%LG as a conductive additive was 155.2 m Ah/g after 50 cycles at 0.5 C,and the capacity retention rate was as high as 101.72%.The composite of graphene and carbon black as conductive additives can take into account both"short-range"and"long-range"conductivity to improve low-rate and high-rate performance,and the discharge specific capacity of 3 wt%SP+7 wt%LG is as high as 162.7 m Ah/g at 0.5 C,the cathode can maintain 93.5%reversible capacity after 200 cycles.At the same time,the capacity reaches 98.1 m Ah/g at the high rate of 5 C.Then,in order to further improve the high rate performance of lithium iron phosphate,carbon-coated lithium iron phosphate（C@LFP）with glucose as carbon source was synthesized by hydrothermal method,and 3 wt%SP+7 wt%LG was used as conductive additives to explore different the effect of carbon content on battery performance.the conductivity between lithium iron phosphate particles can be further improved after carbon coating,showing excellent high rate performance.The battery performance is optimal when the carbon content is 7%,and the capacity retention rate is close to 100%after 50 cycles at 0.5 C,while the specific capacity is 113.6 m Ah/g at a high rate of 5 C,and the capacity retention rate is as high as 90.9%after 500 cycles.This material has high specific capacity,stable cycle performance and excellent rate performance,and will provide more contributions to high-power lithium-ion batteries in power vehicles.