Preparation Of Magnesium-based Nanofibers And Their Application In Lithium Batterie

New energy systems have put forward higher requirements for lithium batteries.However liquid batteries are limited by the defects of flammability and leakage of organic electrolyte.While all-solid-state batteries exhibit great potential value for application due to their high energy density and good safety.However,at present,there still exist some problems in composite electrolytes,such as low ionic conductivity,poor compatibility with electrode materials and narrow electrochemical window.In this paper,MgO,Mg F₂ and Li-doped MgO nanofibers were prepared and added into polyethylene oxide（PEO）/bis（trifluoromethane）sulfonilimide（Li TFSI）based electrolyte as fillers for all-solid-state lithium battery.By this strategy,the continuous conductive paths are constructed by combining the high aspect ratio and elemental properties of nanofibers,as well as similar chemical properties of Mg and Li,which all endow the composite electrolyte with high ionic conductivity,excellent electrochemical stability and inhibit the growth of lithium dendrites.（1）MgO and MgF₂ nanofibers（MO NFs and MF NFs）with excellent morphology were prepared by electro-blow spinning,high temperature calcination and carbonization.And they are composited with PEO to prepare all-solid-state electrolyte as fillers.The effects of morphology,doping ratio and composition of filler on electrochemical performance were explored.The ionic conductivity of the electrolytes containing MgO and Mg F₂ nanofibers reach 1.19×10^-4 and 1.39×10^-4 S cm^-1 at 30℃,respectively.They are conducive to decrease the crystallinity of electrolyte and generate Lewis acid interactions at the composite interface,which can effectively promote the dissociation of lithium salt.Mg F₂ can reduce nucleation overpotential of lithium and induce controllable Li⁺deposition.The lower electronic conductivity weakens the nucleation and growth of lithium dendrites.These advantages give the battery a high initial specific capacity of 140.6 m Ah g^-1 and long life of 500 cycles with a decay rate of 0.055%per cycle at 50℃and 0.5 C.（2）Li doped MgO fiber（LMO）was prepared by electro-blow spinning and calcination.The effects of different Li doping amount on the morphology of inorganic fiber,surface oxygen vacancy,physical and chemical properties of electrolyte and electrochemical properties of lithium-ion battery were discussed.It not only utilizes fiber fillers with high length-to-diameter ratio to construct continuous conductive paths in polymer-based electrolytes,but also introduces lithium doping which can generate positively charged oxygen vacancies on the filler surface,which strongly interact with anions as Lewis acid sites and accelerate the release of lithium ions.The ionic conductivity of the electrolyte containing with 20%Li doped MgO fiber is 1.48×10^-4S cm^-1.And the assembled lithium-ion battery exhibits a high initial specific capacity of 147.5 m Ah g^-1 and low decay rate of 0.037%after 600 cycles at 50℃and 0.5 C.In conclusion,Mg-based fiber filler endows composite electrolytes with excellent electrochemical performance through interface optimization and element characteristics,which provides theoretical basis and experimental support for the application and development of composite electrolytes and all-solid lithium batteries.