Engineering Amorphous Metal Sulfide And Polymer Solid Electrolyte Towards High-Performance Lithium-ion Batteries

Lithium-ion batteries?LIBs?have significant advantage of high energy/power density,charge-discharge efficiency,long cycle life and no memory effect.They are widely used in small electronic devices such as mobile phones and digital cameras.To meet the energy storage requirements of electric vehicles,smart grid and other industries,potential breakthroughs are needed to further improve the energy density and power performance of LIBs.The development of high-performance conversion-type anodes is an effective way to improve the overall performance of LIBs.Conversion-type transition metal sulfides have great potential application because of their theoretical specific capacities,low cost and wide sources.However,this kind of material has some shortcomings of low intrinsic conductivity,poor cycling performance and volume expansion.Hence,Li anode can effectively improve the output voltage and further affect the energy density because of the lowest redox potential and high theoretical capacity.Nevertheless,the application of Li metal is limited due to the safe problem of lithium dendrite growth in organic liquid electrolyte.The introduction of solid electrolyte can greatly improve the stability and safety for LIBs.In this thesis,based on the design of molecular structure for molybdenum sulfide,the ionic conductivity of the material was improved and the volume effect was alleviated;subsequently,polyethylene oxide?PEO?-based composite polymer electrolyte with inorganic filler was prepared,companying with improved stability and safety.Two anodes provide effective design strategies for improving the energy density of LIBs.The research contents are as following two directions:?1?Amorphous MoS_x@C nanospheres were prepared by solvent-thermal method and characterized;the molecular structure was simulated by density functional theory?DFT?.MoS_x@C could provide more open sites for Li-storage and shorten lithium ion migration path.Hence,isotropy of amorphous MoS_x@C can greatly alleviate the electrode volume expansion.The amorphous MoS_x@C exhibits excellent rate performance and cyclic stability,which is attributed to the contribution of pseudocapacitance and structural stability.Further,the full cell has a discharge capacity of 150.6 mA h g^-1 at 0.1 C,indicating that high energy density is expected to achieved.?2?A method of combining recovery-reuse method with PEO-based electrolyte preparation was proposed to improve stability with Li anode.Recycled product from waste LiMn₂O₄ battery was used as nano-filler in PEO-LiTFSI to form composite solid electrolyte.The electrolyte exhibits high ionic conductivity,Li⁺transference number?0.75?and a wide electrochemical window?5.1 V?.Further,the full cell delivers a specific capacity of 150.2 mA h g^-1 in the first cycle at 0.1 C with a capacity retention of 86.4%after 60 cycles.