Preparation And Electrochemical Performance Of Modified Porous Carbon Nanofibers For Lithium-based Batteries

Since the first commercialization of Li-ion batteries（LIBs）,LIBs have been played an essential role in providing power to diverse cordless electric devices.The enormous interest on high-tech electrical vehicles and electronics have constantly stimulated to improve the energy density of LIB.As the battery technology regarding manufacturing process and material science has grown into maturity,the energy density has been marvelously increased.However,the conventional LIB system,which is comprised of lithium transition-metal oxide and a carbonaceous material as cathode and anode respectively,is now facing the theoretical limit of the energy density.However,while improving the theoretical specific capacity of the energy storage system,many disadvantages of the high-capacity electrode materials,such as the volume change of the lithium ion battery anode and the“shuttle effect”of the lithium-sulfur battery during the cycle life,are becoming prominent gradually.Ultimately,these emerged shortcomings impede the commercialization of Li metal battery over the past decades.We prepared PVA/PTFE nanofibers by solution blowing electrospinning and pre-oxidation techniques.Using pre-oxidized PVA/PTFE nanofibers as a porous matrix precursor,cob-like ZnS nanoparticles anchored on PCNFs were rationally designed and prepared by subsequent solvothermal reaction and carbonization.The obtained zinc sulfide nanoparticles modified porous carbon nanofiber composites（ZnS/PCNFs）as anode materials for lithium ion batteries which displays good electrochemical performance.The high reversible capacity of 718 m Ah g^-1 after 150 cycles at 0.2 A g^-1demonstrates excellent cycle stability.The discharge capacity of 438 m Ah g^-1 at 2 A g^-1 reflects excellent rate performance.All the results demonstrated the feasibility of PCNFs as conductive matrix to optimize active ZnS and the promising potential for ZnS/PCNFs composite as anode material for high-performance LIBs.We constructed a multifunctional interlayer between cathode and separator consisting N-doped honeycomb-like porous carbon nanofibers（PCNFs）film modified prepared MgAl layered double hydroxides（LDHs）through electrospinning blow,high temperature carbonization and in situ growth.In the prepared interlayer,the hierarchically porous PCNFs can suppress the“shuttle effect”of the dissolved intermediate lithium polysulfide（Li PS）in the electrolyte through the physical confinement of the porous structure and the chemical adsorption of doping N.Furthermore,the excellent conduction of the interlayer including PCNFs is acted as second current collector,and the structure of hierarchical pores is beneficial to adapt the volume change during the process of charge-discharge.More importantly,the obtained MgAl LDHs with layered structure and polar character in and on the surface of the PCNF can strongly form chemical interaction with Li PS.Meanwhile,a cooperative interface through forming active catalytic sites to effectively encapsulate the Li PS and facilitate the reaction kinetics during the redox process.Based on the above advantages of the interlayer,the cathodic interlayers including LDH@PCNFs were used in for Li-S batteries and the inspiring electrochemical performances can be achieved.As a result,the as-prepared Li-S cell obtained a high initial discharge capacity of 1452 m Ah g^-1 at 0.2 C,superior rate capability up to 2 C rate with a capacity of 952m Ah g^-1,and excellent long-term cycling stability by retaining a discharge capacity of700 m Ah g^-1 after 500 cycles at 1 C.This work provides a cost-efficient and effective method to significantly improve the overall performances of Li-S battery with porous-carbon-based cathodic interlayers.