Study On Surface-modified Lithium Metal Anodes And Their Performance

Electric vehicles and portable electronic equipment urgently require advanced rechargeable batteries with high energy density and long lifespan to replace the conventional lithium-ion batteries?LIBs?.Among the possible alternatives,lithium?Li?metal anodes are strongly regarded as the most promising candidates for the next-generation of high-energy density energy storage devices,because Li metal has a high theoretical specific capacity(3862 mAh g^-1),low density(0.53 g cm^-3)and the lowest reduction potential?-3.04 V vs.standard hydrogen electrode?.There are several formidable challenges before the applications of high energy density LMBs.One is the formation of Li dendrites due to the heterogeneous deposition of Li on the surface of Li metal.The growth of Li dendrites would puncture the separator,resulting in short circuits in the battery,while longer Li dendrites would be broken and form“dead Li”during cycling,reducing the active material.The reaction products between Li and electrolyte will constitute a solid electrolyte interphase?SEI?on Li metal anodes.During the cycle,SEI film continuously fractures and regenerates due to the continuous growth of Li dendrites,which will consume the electrolyte and reduce the battery life.Therefore,the formation of Li dendrites and the uneven deposition of Li are the primary problems that need to be solved.This paper mainly solves the above problems from three aspects:?1?We proposed a chemical surface treatment method to polish the surface of Li foil.By dipping lithium metal into a solution of Br₂/CCl₄,the chemical reactions occurred between Li metal and Br₂ effectively removed the pristine film and etch the protrusions on the surface.The treated Li foil significantly inhibited the growth of lithium dendrites and formed a new uniform SEI film.In addition,the treated Li foil exhibited uniform plating/stripping behavior of lithium ions under the flat surface.Uniform deposition of Li ions in the initial plating/stripping stage leaded to uniformly plating/stripping in the subsequent cycle.?2?Ester electrolyte FEC,which can effectively form fluorinated SEI,and Ether electrolyte DME and DOL were mixed as a co-solvent,and LiBr was used as an additive to form a Double halogen electrolyte.However,it was surprisingly found in the research that the Double halogen electrolyte not only formed a good SEI film,but also significantly increased the Li F content in the SEI,and effectively reduced the loose lithium deposition on the lithium metal surface.A uniform lithium deposition layer is formed that is densely arranged by smooth bulk lithium.The Double halogen electrolyte also can improve the cycle life of Li|LTO cells,the coulomb efficiency of Li|Cu cells,and the stability of Li|Li symmetrical cells.?3?An in-situ Li₃PO₄?Lithium Phosphate?/PVA?Polyvinyl alcohol?solid polymer electrolyte protective layer is produced by in situ reaction of P₂O₅?Phosphorus pentoxide?and PVA with Li metal.Lithium phosphate in the protective layer provides channels for lithium ions transport,while PVA ensures the protective layer better adapting to volume changes and binding lithium phosphate particles.The Li₃PO₄?Lithium Phosphate?/PVA?Polyvinyl alcohol?hybrid promotes the formation of a stable and flexible protective layer that enables Li deposition uniformly and suppresses the growth of Li dendrites.Additionally,the in-situ production method gained a perfect interface between protective layer and Lithium metal anode,which effectively isolated the liquid electrolyte and prevented side reactions.With the PP-Li anode,the stability of symmetrical batteries is significantly improved,especially,the battery life under high current densities increased to 800 h.The anode showed a good performance at high rates when it was applied to Li|LTO cells.