Study On Regulating Solid Electrolyte Interface And Performance

Lithium metal is an ideal anode material for lithium batteries with high specific capacity(3860 m Ah g^-1).However,there are many limitations for the commercialization of lithium metal batteries in practical applications,such as the unstable solid electrolyte interface and the safety issues caused by the growth of lithium dendrites.Therefore,designing a stable solid electrolyte interface for lithium metal anode protection through the study of the solvation structure of is a strategy to achieve a stable lithium metal anode at low cost.In this thesis,effect of the solvation structure on the reduction behavior of the electrolyte is investigated by computational electrochemical tools based on density functional theory,and the electrolyte for Li-metal batteries is designed.The practicality of the designed electrolyte is verified through Li‖Li symmetric cells and full cells.The main contents include:（1）DFT calculations and molecular dynamics simulations of common carbonate electrolyte solvents/additives（EC,PC,VC,FEC,VEC）were conducted.Electronic structure indicates that solvated electrolyte species have higher reduction tendency,and species with high reduction tendency are preferentially reduced on the anode surface.PC was used as solvent and FEC and VEC were used as additives,FEC and VEC showed preferential reduction at the anode to construct SEI,and XPS spectra and scanning electron microscopy analysis show that the SEI films of FEC or VEC-added electrolytes had a more homogeneous composition and morphology than the SEI films formed by pure PC electrolyte.The corresponding Li‖Li symmetric cells showed twice the cycle life of the blank PC electrolyte.The Li‖NCM622 full cell containing both FEC and VEC shows better coulomb efficiency and capacity retention.（2）Lithium perfluorobutane sulfonate（Li PFBS）/glycol dimethyl ether（DME）was developed as an electrolyte for lithium metal batteries based on the difference electronic structure of electrolyte components.Quantum chemical calculation results show that both salts and solvents have different electronic structure in different solvation degree.Based on the effect that electronic structure change with solvation structure.The control of the reduction behavior of the electrolyte at the anode was achieved by regulating the solvent/salt ratio.The stability of the ether electrolyte at the interface with the lithium metal was improved,and the corresponding Li‖Li symmetric cell showed a cycling performance of more than 1000 h.The Li‖Li Co O₂full cell showed a starting capacity of 190 m Ah g^-1 and a capacity retention of 55%after 200 cycles.