Alkali metal salts based on novel anions for solid polymer electrolytes

Abstract

The chemistry of the lithium salt employed plays a pivotal role in dictating the physico-chemical and electrochemical performance of any solid polymer electrolytes (SPEs), and thus also influences the performance of solid-state lithium metal batteries (SSLMBs). The lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, first suggested as salt for SPEs in 1986, possesses low lattice energy and the TFSI' anion has a large structural flexibility, both due to the anion¿s highly delocalized negative charge and flexible center [e.g., ¿SO2¿N(¿)¿SO2¿] and has therefore been commonly used for SPE-based SSLMBs. However, low lithium-ion transference number (TLi+) and poor solid electrolyte interphase (SEI) creating properties, resulting in severe cell polarization and simultaneously notorious dendritic growth on the Li° anode. Therefore, in this thesis, several novel lithium salts were designed and synthesized to suppress anionic mobility and enhance TLi+, but without sacrificing significantly the ionic conductivity, and simultaneously with the aim of forming excellent SEI layers on the Li° anode to improve interfacial compatibility and stability towards Li° anode.