Cations and anions regulation through zwitterionic gel electrolytes for stable lithium metal anodes

Abstract

Lithium metal has been regarded as an ideal anode for next-generation energy storage systems with an ultrahigh theoretical capacity and the lowest redox potential. However, the uncontrolled lithium dendrite growth in liquid electrolytes has severely hindered both the performance and safety of lithium metal batteries (LMBs). Here we demonstrate a facile and efficient strategy to stabilize lithium plating/stripping by introducing zwitterionic gel electrolytes (ZGE). Zwitterionic polymers contain both cationic and anionic functional groups along the chains, which can absorb anions and Li+ in the ZGE and serve as their reservoirs, respectively. As a result, the zwitterionic polymers restrain the motion of anions to prevent space charge formation caused by local anion depletion, and meanwhile promote the dissociation of lithium salts and regulate Li+ distribution in the vicinity of anode. The synergistic effect of regulating both Li+ and anions can significantly increase the Li+ transference number from 0.25 to 0.63 and help suppressing lithium dendrite growth. The Li|Li symmetric cells using ZGE are more stable than those in liquid electrolyte with lower overpotential. Improved LiFePO4|Li full cell performance with ZGE is also demonstrated. The ZGE is believed to useful for other metal anodes.