Li Morphology Evolution during Initial Cycling in a Gel Composite Electrolyte

Tsai, Wan-Yu

Li metal anodes are the potential solution for high-energy batteries. One of the challenges of applying such a high-energy anode is Li dendrite growth, which results in short-circuit and thermal runaway. Current battery research focuses on developing solid electrolytes to serve as a physical barrier to prevent dendrite growth. However, the Li morphology change during plating and stripping, and the mechanisms of how Li dendrite grows and propagates into a complex composite solid electrolyte are poorly understood. Understanding and controlling Li morphology evolution, dendrite formation, and growth during cycling are crucial to developing dendrite suppression strategies for solid electrolytes and enabling high-energy lithium metal batteries.

In this work, Li morphology evolution during initial cycling in a crosslinked PEO-based gel composite electrolyte full cell with NMC 811 cathode is monitored via post-mortem SEM. The results show that severe surface pitting occurs as early as the second stripping cycle. Pit formation and continuous dissolution is the main cause of Li surface roughening and dendrite growth mechanism in the model gel composite electrolyte. Comparing Li dendrite growth mechanisms in liquid, polymer, and solid electrolytes, the observed dendrite growth mechanism resembles that of the liquid electrolyte the most. This study suggests that strategies to improve the electrochemical reversibility of electrodeposited Li reported in liquid electrolytes to control Li morphology and prevent dendrite growth may be transferrable in a gel electrolyte.

This work is sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC for the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. Part of the measurements was performed at the Center for Nanophase Materials Sciences (CNMS), which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences.