Preparation And Electrochemical Properties Of Doped Carbon Fibers For Lithium Metal Batteries

The rapid development of portable electronic products,electric vehicles and so on has promoted the research and development of secondary batteries with high performance.Due to the advantages of high theoretical specific capacity,high energy density and low cost,lithium metal batteries,including lithium sulfur(Li-S)batteries,Li-O₂ batteries and other lithium metal based batteries with high energy density,are recognized as one of the most promising next-generation energy storage systems.However,lithium metal batteries have many problems to be solved in practical applications.Among them,the problem of dendrite lithium during the deposition and stripping process is urgently solved.The protuberance of high voltage electric field attracts more lithium ions to deposit on the protuberance surface of lithium sheet quickly,thus forming dendrite structure.The growth of lithium dendrites is uncontrollable,which will lead to a large number of"dead lithium"and short circuit of batteries.This kind of safety hazard seriously hinders the commercial application of lithium metal batteries.In recent years,interlayers have been an important direction for suppressing lithium dendrites.In this paper,two types of interlayer materials have been successfully prepared using electro-blow spinning and electrospinning technologies.New three-dimensional Ag-doped carbon nanofiber interlayers(Ag-PCNFs coating)and a three-dimensional flexible MnO/N-doped porous carbon nanofiber interlayer(MnO-PCNFs interlayer)are used to guide the uniform deposition of lithium metal.Firstly,three-dimensional porous carbon fibers(Ag-PCNFs)with silver nanoparticles were prepared by electro-blow spinning and in situ growth of silver nanoparticles.The high specific surface area and good conductivity of Ag-PCNFs are beneficial to the electrochemical reaction kinetics,and reduce the local current density of the lithium anode,thereby improving the interface impedance.The multi-channel structure enables Ag-PCNFs to have a higher Li loading capacity due to their rich internal cavities,while the silver particles can make the PCNFs pro-lithium,which designed a lithium-friendly nano-silver anchored on porous carbon nanofiber to guide the deposition of metallic lithium.The electrochemical cycling performance of Li-Li symmetrical batteries shows that Ag-PCNFs coating can inhibit lithium dendrite growth and improve cycle stability.When a full cell is formed with a sulfur electrode,the experimental results prove that the lithium metal electrode with Ag-PCNFs coating can effectively guide the deposition of lithium,thereby improving the electrochemical cycle stability performance.Secendly,a stable interlayer to limit Li for the Li metal anode has been effectively prepared via the electrospinning and in-situ growth of MnO method,the eletrospun flexible MnO nanoparticle/nitrogen(N)-doped(polyimide)PI-based porous carbon nanofiber films(MnO-PCNFs).It is revealed that the attraction of the implanted MnO with Li,the lithiophilic nature of the N dopants and the capillary force of the porous architectures are beneficial to the preeminent Li wettability of the MnO-PCNFs interlayer.Furthermore,the stable and conductive structures of the MnO-PCNFs could be well retained,offering the rapid charge transfer for Li redox reactions,the reduced local current density during cycling process and the homogeneous distribution of deposited Li.Consequently,the anodes with MnO-PCNFs interlayers could successfully relieve the volume change and inhibit the growth of Li dendrites,proving a remarkable lifetime in lithium metal cells at high current.