A Zwitterionic Gel Polymer Electrolyte with High Ionic Conductivity and a High Li ⁺ 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 °C). This work provides a new GPE design principle for accessing safe and stable Li–S batteries.