Research On Interfacial Modification Of Nitrogen-doped Carbon Fiber And Its Application In Lithium Metal Anode

The development of high-energy-density and reliable energy storage systems（ESSs）is significant to address the challenges of global energy and environment crises.The capacity of graphite is limited(372 mAh g^-1),and the lithium（Li）-ion batteries based on graphite anode are not able to meet the requirements of high energy storage system.Among the existing candidates,Li metal battery is identified as the ideal ESS in terms of the ultrahigh theoretical specific capacity(3860 mAh g^-1)and lowest potential（-3.040 V vs.standard hydrogen electrode）.However,the growth of Li dendrites,uncontrolled volumetric expansion and unstable interface of electrode/electrolyte are the main obstacles to apply Li metal anodes for practical batteries.A three-dimensional host with high stretchability and high electronic conductivity is promising for stable Li metal anodes.Three-dimensional carbon host with the large specific surface area and good structural stress can effectively decrease local current density,regulate the distribution of electric field and buffer volumetric expansion during cycling.However,limited by the nucleation barriers stemming from the inferior adsorption ability of Li⁺ions,carbonaceous host is usually lithophobic,resulting in high nucleation overpotential and limited cycle life.In this thesis,functional lithiophilic nanoparticles embedded in three-dimensional carbon nanofibers were prepared by electrospinning technology to promote the dissociation of Li salt and induce the uniform Li deposition.The specific research contents were listed as follows:（1）Fe₂O₃nanoparticles were coated with a layer of ZrO₂through the hydrolysis of zirconium n-propoxide.Three-dimensional carbon host（Fe₃C@ZrO₂@CNF）embedded with Fe₃C@ZrO₂yolk-shell nanoparticles was prepared by mixing Fe₂O₃@ZrO₂core-shell nanoparticles with polyacrylonitrile spinning solution through electrospinning and carbonization.The Fe₃C yolk demonstrated the strong affinity to the Li⁺ions,delivering an ultralow nucleation barrier for Li metal and inducing uniform Li deposition on its surface.Meanwhile,the external ZrO₂shell presented a strong interaction with the Li salt,promoting the dissociation of Li salt and transportation of Li⁺ions.The full cells assembled by the Li-Fe₃C@ZrO₂@CNF anode and commercial LiFePO₄（LFP）cathode demonstrated a capacity retention of93.3%after 1500 cycles at a discharged/charged current density of 5 C(1C=169 mA g^-1).（2）SiO₂nanoparticles were coated with a layer of ZrO₂through the hydrolysis of zirconium n-propoxide.Three-dimensional carbon host（SiO₂@ZrO₂@CNF）embedded with SiO₂@ZrO₂nanoparticles were prepared by mixing SiO₂@ZrO₂nanoparticles with polyacrylonitrile spinning solution through electrospinning and carbonization.And the nanofiber film with a single-holed structure（SH ZrO₂@CNF）was obtained by hydrothermal reaction of sodium hydroxide solution at high temperature.The full cells assembled by the Li-SH ZrO₂@CNF anode and LFP cathode demonstrated a capacity retention of 95.8%after 1500cycles at a discharged/charged current density of 5 C.