Preparation And Lithium Storage Performance Of Freestanding Carbon/Iron-based Alloy Hybrid Nanofiber Membranes As Anodes For Lithium-ion Batteries

With rapid development of flexible and foldable electronic products,people's demand for high-energy flexible lithium-ion batteries is increasing.The key to flexible lithium-ion batteries is to use flexible electrodes with high conductivity to ensure fast charge and discharge,while having high capacity.In this paper,flexible C/FeCo and C/FeNi hybrid nanofiber membranes were fabricated by a facile electrospinning process combined with subsequent heat treatment,it can be directly used as the anodes of lithium ion batteries.The obtained nanofibers were characterized by XRD,SEM,TEM,Raman,XPS and electrochemical tests.The influences of the carbonization temperature and salt content in precursor solution on the structure,composition,morphology and lithium storage performance of the hybrid nanofiber membranes were investigated in detail.Pure carbon nanofibers were prepared using the same condition to compare the effects of iron-based alloy on lithium storage performance.The research results are as follows:With increasing the temperatures of the carbonization,the specific capacity of flexible C/FeCo hybrid nanofiber membranes electrode first increase and then decrease.The specific capacity of C/FeCo hybrid nanofiber membranes electrode first increase and then decrease with the increasing of salt content in precursor solution.The C/FeCo hybrid nanofiber membranes with 8%salt content at 600°C carbonization temperature has a discharge specific capacity of 566.5 mAh g^-1 after 100 cycles of cycling at a current density of 100 mA g^-1,its good lithium storage performance is attributed to the synergistic effecte of electronic conductivity of nanofiber membranes,defect concentration and interface area.With increasing of carbonization temperature,the specific capacity of C/FeNi hybrid nanofiber membranes electrode first increase and then decrease.At the same carbonization temperature,the specific capacity of C/FeNi hybrid nanofiber membranes electrode increase first and then decrease with the increasing of salt content in precursor solution.When the carbonization temperature is 600°C,and the salt content is 10%,the C/FeNi flexible electrode shows better lithium storage performance.The discharge specific capacity of the flexible electrode is still approximately 406.5 mAh g^-1 after 100 cycles of charge and discharge at a current density of 100 mA g^-1.Comparing pure carbon nanofibers and hybrid nanofiber membranes under 600°C carbonization condition,it is found that the presence of iron-based alloy improve greatly the electrochemical performance of lithium-ion batteries,mainly due to synergistic effect between metal alloy and carbon fibers.The three-dimensional structure of carbon fibers provides a good conductive network,which can shorten the transmission distance of lithium ions,buffer volume change caused by lithium repeated intercalation/de-intercalation and maintain the structural stability of the material.The alloy particles improve electrical conductivity of the material,and facilitate a fast electrochemical kinetic process during charge/discharge at high current density.