Challenges and Perspectives on Improving Cycle Life of Lithium Metal Batteries

Lithium (Li) metal batteries (LMBs) has been regarded as one of the most promising energy storage systems for the next generation high density energy storage systems.^1,2 In recent years, significant improvement has been made on the cycle life of LMBs. Several new concepts (including high concentration electrolyte, ¹ localized high concentration electrolyte, ² and weakly solvating electrolyte (WSE) ^3,4 beyond conventional electrolyte used in Li ion batteries have been developed to improve the coulombic efficiency (CE) of LMBs. A high coulombic efficiency of ~99.5% in Li||Cu half-cells (so called Li-CE) have been reported by several groups using different design concepts. However, a CE value of ~99.5% seems to be a bottleneck which is difficult to overcome. In addition, the electrolytes with the similar Li-CE can lead to different long-term stability of Li||NMC full-cells even all other conditions (cathode, Li metal anode, cell assembly etc) are the same. This means a good Li-CE is a necessary condition, but not an enough condition determining the long-term cycle life of LMBs. Other parameters, such as ionic conductivity and wettability of electrolytes, stability/solvability of SEI layers etc. may play a comparable or even more important roles on the long-term stability of LMBs once Li-CE exceeding ~99.5%. In this talk, the fundamental mechanism leading to this CE-bottleneck will be analyzed. Potential approaches to further improve CE for both half-cell (Li||Cu) and full cell (Li||NMC811) will be explored.

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