Doping Modification And Electrochemical Performance Research Of Sulfide Solid State Electrolyte(Li₇P₃S₁₁)

With the development of science and technology,lithium-ion batteries(LIBs)have been universally applied in energy storage equipment.However,frequent occurrence of safety accidents in recent years arouses people’s attention.The main reason is that the conventional LIBs are confronted with series of safety issues owing to the flammable and leakage nature of organic liquid electrolytes(OLEs).Adopting solid state electrolytes(SSEs)rather than OLEs,is considered as one of the effective ways to fundamentally settle the problems mentioned above benefiting from the intrinsic nonflammable features of SSEs.SSEs consist of organic polymer solid state electrolytes and inorganic solid state electrolytes(including oxide solid electrolytes,sulfide solid state electrolytes and halide solid state electrolytes),among which sulfide solid electrolyte becomes one of the strong candidates due to its high ionic conductivity,wide electrochemical window and good mechanical properties.Nowadays,Li7P3S11 and Li10GeP2S12(LGPS)have been widely studied but due to the high cost of Ge,Li7P3S11 has become attractive.However,the as-prepared Li7P3S11 still has some problems such as low ionic conductivity,poor stability against lithium metal anode and sensibility to humid air.This paper focuses on the abovementioned key issues and studies the influence of doping on their electrochemical performance.The main research contents are specifically as follows:(1)Two methods of solvent-assisted ball milling and high-energy ball milling were used to prepare high-performance sulfide solid electrolyte Li7P3S11.The ionic conductivity prepared by solvent-assisted ball milling and high-energy ball milling is 2.7×10-4 S cm-1 and 1.0×1-3 S cm-1,respectively.Different preparation methods have their own advantages and disadvantages.(2)A new type of Li7P3S11-based solid state electrolyte enabled by alio valent substitution of SnO2 was prepared by solvent-assisted ball milling method based on the hard-softs-acids-bases(HSAB)theory.Through characterization of the structure and morphology,the successful doping of SnO2 was proved,and after optimizing the doping parameters,the ionic conductivity of the prepared electrolyte was 5.3×10-4 S cm-1,which was about twice that of the original electrolyte.At the same time,compared with undoped Li7P3S11,Li7Sn0.1P2.8S10.5O0.2 has better cycling stability against lithium metal anode and improved stability to humid air,and the assembled all-solid-state Li-S battery has higher specific capacity and cycle stability.(3)High-energy ball milling was used to prepare In-doped sulfide solid state electrolytes Li7P3-xS11-xInx.The successful doping of elements was confirmed by XRD,Raman and TEM.Through parameter optimization,the ionic conductivity of the prepared Li7P2.9S10.9In0.1 is as high as 4.1×10-3 S cm-1,which is 4 times as that of Li7P3S11 prepared by the same method,and the critical current density is increased from 0.20 mA cm-2 to 0.45 mA cm-2,which implies that it greatly suppresses lithium dendrites.The assembled LiCoO2/Li7P2.9S10.9In0.1/Li all-solid-state battery has a higher specific capacity and capacity retention rate.