| With the continuous application of lithium-ion batteries in life?electric vehicles,portable electronic devices?,many problems such as lack of resources for cathode materials,high costs and low specific capacity have been exposed.In recent years,iron fluoride cathode materials have attracted interest because of their high output voltage,abundant raw material reserves,and high theoretical capacity(712 mAhg-1).Despite its high voltage platform and specific capacity,its strong ionicity and low electronic conductivity limit its use as a cathode material.In order to make full use of the advantages of metal fluoride materials,some methods,such as adjusting the grain size and internal structure,optimizing grain morphology,and combining with good conductivity carbon materials and other technical means,were used to improve the conductivity of metal fluoride and shorten the transport path of lithium ions,thereby achieving stable cycling performance and high capacity.In this paper,the synthesis and modification of the above problems were studied.The effect of reaction time on FeF3·3H2O/CNT and the composite material of FeF3containing trace water grown in situ on carbon nanotubes and graphene were studied by simple coprecipitation method.At the same time,a variety of characterization methods were used to explore its physical and chemical properties and electrochemical properties.The content was summarized as follows:?1?The effects of different reaction times on the structure and properties of the synthesized FeF3·3H2O/CNT composites using the co-precipitation method were explored.XRD confirmed that the prepared sample was FeF3·3H2O/CNT composite material.SEM results showed that CNT and FeF3·3H2O particles were intertwined,and the particles were tightly bound.The good conductivity of carbon nanotubes improved the electrical conductivity of the composite and was conducive to electron conduction.The first cycle discharge capacities of FeF3·3H2O/CNT with reaction time of 1,2,and3 hours were 230.2 mAh g-1,247.7 mAh g-1,and 201.4 mAh g-1,respectively.After 60cycles of circulation,the remaining capacities of the three samples were 88.3 mAh g-1,95.2 mAh g-1,and 83 mAh g-1,respectively.The sample reacted for 2h showed the best reversible capacity and the best capacity retention rate.It was confirmed that when the reaction time was 2h,the prepared FeF3·3H2O/CNT material had the best electrochemical performance.?2?The prepared FeF3·3H2O/CNT was dehydrated by heat treatment to obtain FeF3·0.33H2O/CNT and FeF3/CNT composite materials.XRD test showed that the two samples were FeF3·0.33H2O/CNT and FeF3/CNT composite materials.A small amount of crystal water in the FeF3·0.33H2O material helped to stabilize the structure and ease the volume expansion during the conversion reaction.The first cycle discharge capacities of FeF3·0.33H2O/CNT and FeF3/CNT samples were 333.9 mAh g-1 and 264.5mAh g-1,respectively.After 50 cycles of circulation,the remaining capacities of the two samples were 147.3 mAh g-1 and 106.7 mAh g-1,respectively.The capacity of the FeF3·0.33H2O/CNT electrode had been higher than that of the FeF3/CNT electrode,showing good cycle performance.?3?FeF3·3H2O/rGO composite material was synthesized by co-precipitation method,which was heat-treated and dehydrated to obtain FeF3·0.33H2O/rGO and FeF3/rGO composite material.FTIR results indicated that there was a C-F bond between the prepared FeF3·0.33H2O and rGO,which improved its stability.FeF3·0.33H2O particles growed on graphene.Graphene provided a conductive network for FeF3·0.33H2O particles,which facilitated the insertion and extraction of lithium ions and improved their conductivity and stability.The current densities of FeF3·3H2O/rGO,FeF3·0.33H2O/rGO and FeF3/rGO composites at 20 mA g-1,the remaining capacities after 50 cycles were 105.3 mAh g-1,139.5 mAh g-1 and 104.2mAh g-1,respectively.The FeF3·0.33H2O/rGO material exhibited the most cycle stability,and exhibited excellent variable rate performance under variable rate charge and discharge. |
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