A Zwitterionic Gel Polymer Electrolyte with High Ionic Conductivity and a High Li plus Transference Number for Stable Lithium-Sulfur Batteries

Abstract

Lithium-sulfur (Li-S) batteries are regarded as one of the most promising high-energy-density batteries. However, their practical use is hindered by the polysulfide shuttle effect and the growth of Li dendrites. Herein, it is shown that these challenges can be overcome with a gel polymer electrolyte (GPE) containing zwitterions and poly(ethylene glycol). The zwitterionic GPE endows Li-S batteries with exceptional Li+ transport performance (e.g., a high ionic conductivity of 2.01 mS cm-1 and a high Li+ transference number of 0.72), remarkable flame retardancy, and the capability to function efficiently under low-temperature conditions. The use of the zwitterionic GPE in Li//Cu cells leads to suppressed Li dendrite growth and an enhanced Columbic efficiency (92.17% vs 64.96%), while leading to elongated plating/stripping cycling lifetime with reduced polarization (500 h at 0.05 V vs 140 h at 0.2 V) in Li//Li symmetric cells. When used in Li-S cells, the zwitterionic GPE provides the devices with remarkable electrochemical performance in terms of specific capacity (1272 mA h g-1), cycling stability (0.15% capacity decay per cycle over 400 cycles), and low-temperature performance (e.g., at -20 degrees C). This work provides a new GPE design principle for accessing safe and stable Li-S batteries.