Co-solvent strategy for rechargeable post-lithium metal batteries

The potential increase in cost of lithium-ion batteries owing to the limited supply of lithium has prompted investigations into alternative and complementary rechargeable batteries that use post-lithium charge carriers with higher elemental abundance. However, achieving highly reversible post-lithium metal anodes with sufficient kinetics remains challenging. The addition of co-solvents to conventional electrolytes is emerging as an important strategy to resolve these issues. In this Perspective, we discuss the progress of the co-solvent strategy for sodium, potassium, magnesium, calcium, zinc and aluminium post-lithium metal batteries. The coordination ability of co-solvents with post-lithium charge carriers is presented as a useful guide for selecting co-solvents for the respective battery electrolytes, owing to its correlation with several influential factors that affect the electrochemical performance of the metal anodes, such as solvation structure, de-solvation process and solid electrolyte interphase formation. Additionally, a discussion is provided on the importance of unravelling the effects beyond the solvation sheath of cationic charge carriers and for the development of sustainable electrolytes.