Liquid non-aqueous electrolytes for high-voltage and high-safety lithium-ion cells: A review

High-voltage high-safety electrolytes have been proven to be an efficient approach to improve the electrochemical and safety performance of lithium-ion cells under high voltages; therefore, a comprehensive review concerning the research status of liquid non-aqueous high-voltage high-safety electrolytes is presented in this work. Considering the constituents of liquid non-aqueous electrolytes for lithium-ion cells, this review is compromised of three parts. Firstly, typical salts for lithium-ion cells are introduced. The combination among multiple salts, that could overcome each other's defects has been verified to enable high-voltage and high-safety cells. Secondly, representative high-voltage high-safety solvents including high-concentration electrolytes (localized high-concentration electrolytes), fluorinated solvents, ether solvents, nitrile solvents, sulfone solvents, ionic liquids are discussed respectively. Modifying the structure of traditional solvents and mixing several promising solvents to build new electrolyte systems are revealed to effectively improve the characteristics of cells at high voltage. Finally, this review demonstrates the additives for high-voltage high-safety cells, exampled by fluorinated ones, vulcanization ones, nitrile ones, phosphate ester-based ones, and boron-based ones. Although the content of additives within the electrolyte is minor, the existence of an efficient additive could efficaciously inhibit the decomposition of solvents at high voltage and generate robust protective electrode/electrolyte interface layers, consequently enhancing the high-voltage performance of cells.