Study On Lithium Storage Performance Of Electrospun Flexible Composite Fibers

With the development of flexible and bendable portable electronic devices,there is an increasing demand for flexible energy storage devices having high energy density,long cycle life and low environmental pollution.The ideal flexible electrode should have some key characteristics,including high conductivity,structural stability,and fast ion transport capabilities.However,traditional electrode materials need to be mixed with conductive additives and polymer binders,which reduce the utilization of the electrode materials to some extent.In recent years,electrospinning technology has been proved to be an effective way to prepare fiber membranes with unique three-dimensional network structure and good mechanical strength.In this paper,carbon fiber composite materials were successfully synthesized by electrospinning method,and the fabricated materials have high specific surface area,excellent electrical conductivity and good flexibility.It can be directly used as self-supporting anode of LIBs,and its lithium storage properties have been studied as follows.Two-dimensional boron nitride nanosheets have attracted attention because of their superior chemical stability,high thermal conductivity and excellent mechanical properties.One-dimensional carbon fiber materials possess high conductivity.The flexible carbon fiber/boron nitride?BN/CFs?composite material is obtained by electrospinning and subsequent heat treatment using polyimide?PI?as the precursor,the diameters of fibers are in the range of 100 to 450 nm,and BN nanosheets are uniformly dispersed in the carbon fibers.The composite material was used as binder-free anodes for LIBs,and reversible capacity was 240 m Ah·g^-1 after 500cycles at a current density of 100 m A·g^-1.When the current density increases to 1000m A·g^-1,the specific capacity of the battery can still reach 140 m Ah·g^-1.The excellent electrochemical performance of BN/CFs anodes can be ascribed to the unique structure of carbon fibers and excellent electrical conductivity.Silicon has unprecedented theoretical capacity(4200 m Ah g^-1,which is approximately 10-fold of the current commercial graphite electrode),silicon/carbon fibers hierarchical core-shell electrode?Si@CFs?was prepared by coaxial electrospinning.In addition,the effect of the doping concentration of Si nanoparticles in composite on the cycle performance of the battery was investigated.The CFs derived from PI has good structural stability and can be directly used as flexible electrode material for LIBs.Among them,Si@CFs-15wt%composite electrode exhibits excellent performance at a current density of 100 m A·g^-1.It has an initial reversible capacity of 621 m Ah g^-1 and a high capacity retention rate of 77.8%after 200 cycles.Excellent cycle performance is primarily due to this layered core-shell structure.It not only compensates for the insulation properties of Si,but also has the ability to buffer volume expansion during repeated charge and discharge process.