With the rapid maturation of the state-of-the-art lithium (Li) ion batteries (LIBs), rechargeable Li metal batteries (LMBs) have been regarded as the “holy grail” for the next generation of high-energy storage systems. [1] However, their practical application is hindered by low Coulombic efficiency (CE) and safety concerns due to unstable Li|electrolyte interface and dendrite growth in Li metal anodes (LMAs) during cycling. [2] Some high concentration electrolytes (HCEs) are stable with Li and lead to high CE of Li metal anode (LMA), but their practical applications are still hindered by high cost, high viscosity, and poor wetting capability to cathodes. [3] With addition of selected co-solvents to HCEs, we recently developed some new dilute electrolytes that enable stable cycling of LMAs with CE over 99% and 4-V class cathodes (e.g., NMC). The new dilute electrolytes can thus overcome these drawbacks while maintaining or even enhancing the advantages of HCEs. In addition, these electrolytes are non-flammable. Therefore, they are good candidates to be used for safe and high-energy rechargeable LMBs.

1. J. M. Tarascon and M. Armand, Nature 414, 359–367 (2001).
2. J.-G. Zhang, W. Xu and W. A., Henderson, Lithium Metal Anode and Rechargeable Li Metal Batteries. (Springer International Publishing), 249, (2017).
3. J. Zheng, J. A. Lochala, A. Kwok, Z. D. Deng and J. Xiao, Adv. Sci., 1700032, (2017).