Stable Operation of Lithium Metal Batteries by the Formation of Transient High Concentration Electrolyte Layer during Fast Discharge
Authors: Zheng Jianming , Yan Pengfei , Mei Donghai , Engelhard Mark H , Cartmell Samuel , Polzin Bryant J. , Wang Chongmin , Zhang Ji-Guang , Xu Wu 
Published: February 2020

Lithium (Li) metal anode has an ultrahigh theoretical capacity of 3860 mAh/g and the lowest electrochemical potential at -3.040 V vs. standard hydrogen electrode, which makes the rechargeable Li metal batteries as the “holy grail” of energy storage systems.1 However, the development and application of rechargeable Li metal batteries has been hindered in the past decades mainly due to two major problems¾the Li dendrite growth on Li anode during repeated charge/discharge processes and the low Coulombic efficiency. Although several approaches have been reported to suppress Li dendrite growth on Li metal, including forming Li alloys, adding electrolyte additives, using blocking electrolyte membranes, and to improve Coulombic efficiency, the enhancement on Li protection so far is not satisfactory.
Recently, highly concentrated ether-based electrolyte has been reported to be more compatible with Li metal anode because high concentration of Li+ ions in these electrolytes facilities the fast Li deposition/stripping even at high current density conditions.2,3 However, ether-based electrolytes may not be suitable for use at charge cutoff voltage higher than ~4.0 V due to their poor stability against oxidation. In this work, we report for the first time the significantly improved performances of Li metal batteries using a LiNi1/3Mn1/3Co1/3O2 (NMC) cathode and a conventional carbonate solvent-based electrolyte by an appropriate cycling protocol to generate a transient, highly concentrated Li+ ion solution layer in the vicinity of Li metal surface. The highly concentrated electrolyte formed in the vicinity of Li anode surface facilitates the formation of an SEI layer with considerably enhanced stability. It is demonstrated that a high capacity retention >80% after 500 cycles can be achieved for the moderately high areal-capacity Li metal batteries at an optimized charging/discharging process. Based on the results of morphology observation and the composition characterization of the cycled Li metal anodes, a more profound understanding of the underlying mechanism behind the improved performances has been obtained. The fundamental findings of this work provide new insights for the further development of high energy density and long cycle life Li metal batteries. Details of the investigations will be reported and discussed in the presentation.

Acknowledgements

This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies, the Advanced Battery Materials Research Programs of the U.S. Department of Energy (DOE). The microscopy and spectroscopy measurements were performed at the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.

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