Development of Li Metal Batteries with Improved Safety

Development of Li metal batteries (LMBs) has attracted worldwide attention in recent years due to their much higher theoretical energy densities than those of conventional Li ion batteries. LMBs with high energy density and long cycle life have been demonstrated by several institutions and companies recently.1,2 LMBs may be safe in their early stage of cycling due to the small geometric surface area of Li metal anode. However, after long term cycling, mossy/dendritic/“dead Li” will form eventually. They will not only lead to the increase of cell thickness, but also lead to powdered Li which pose a safety concern when exposed to air in the extreme case of mechanical damage, especially for their large scale applications.3 Thus, a paradigm change in the electrolyte design is required to minimize the formation of “dead Li” and improve the thermal stability of the batteries. In this work, several approaches have been used to improve the thermal stability of LMBs. (1) Use of electrolyte with high coulombic efficiency to minimize the formation of “dead Li” or mossy Li; (2) use of non-flammable solvent in electrolyte; (3) use of solvent with high boiling point and high flash point. (4) use of electrolyte enabling formation of large size of Li deposition with minimal surface area. This will enable the formation of a lithiophobic SEI layer which can accommodate stress/strain during large volume changes. (5) Screening additives to improve Li CE and safety. The electrolytes with improved safety/stability at extreme conditions will also be reported in this work. 1 Niu, C. et al. Balancing interfacial reactions to achieve long cycle life in high-energy lithium metal batteries. Nature Energy, (2021). 2 Hu, Q. Li-metal batteries, https://s29.q4cdn.com/695431818/files/doc_presentation/2022/03/March-2022-Investor-Presentation.pdf (2022). 3 Louli, A. J. et al. Diagnosing and correcting anode-free cell failure via electrolyte and morphological analysis. Nature Energy 5, 693-702, (2020).