Synthesis And Lithium Storage Properties Research Of Iron-based Fluoride-carbon Composites Cathode

Metal fluoride has the advantages of large theoretical discharge capacity,environmental friendliness and low cost,and is expected to replace the traditional cathode materials to achieve the lithium ion batteries with high energy density.However,the low intrinsic conductivity,large volume expansion and serious electrochemical interface side reaction of metal fluoride hinder its commercialization process,which is the bottleneck problem to be solved urgently.Construction of metal fluoride-carbon composites have been proved to be an effective means to alleviate the bottleneck problem of metal fluoride.This paper,based on carbon materials building,puts forward three kinds of metal fluoride-carbon composite materials with special structure.The effect of different structures on the electrochemical performance for metal fluoride was systematically studied.Besides,the possible side reactions between active materials and electrolyte during the cycling were analyzed deeply.This work provides more references for the construction of metal fluoride-carbon composites.The main research contents of this paper are as follows:（1）A simple and scalable flexible carbon-coated FeF₂nano-particle composite was proposed,and the effect of the coating on the electrochemical performance of FeF₂cathode was systematically studied from the aspects of the macroscopic electrode,microstructure,and lithium ion migration kinetics.Through the effective coating method,the problems of low conductivity,large volume expansion and bad interface side reaction are successfully relieved,and the FeF₂cathodes achieved the100 cycles at 40C,and can still charge and discharge steadily at 80C.（2）A current collection modification strategy for metal fluoride cathode was proposed,the FeF₂electrodes with high mechanical/chemical stability was successfully prepared by a simple and scalable preparation method.The FeF₂cathodes realized 4500 cycles at 1C and still had a capacity release of 300 mAh·g^-1.At the same time,the advantage of thick electrode was utilized to realize the FeF₂cathodes with ultra-high mass loading(20 mg·cm^-2)and ultra-high areal capacity(6mAh·cm^-2,100 cycles).In addition,the stability of the cathode-electrolyte interface（CEI）and the contact compactness between the active materials and the current collector were systematically studied by means of advanced electron microscopy.A direction for the development of the metal fluoride cathodes are established in this work.（3）Self-supporting-double-carbon-FeF₃electrode were prepared,and the effects of different annealing temperatures on electrode structure and electrochemical properties were systematically analyzed.By temperature control,the capacity loss caused by electric contact failure of FeF₃cathode in the cycling process was successfully mitigated.An outstanding performance of 2000 cycles at 560 mA·g^-1is achieved,which provides a new reference for the structural design of FeF₃cathode.