Single lithium–ion transport and electrochemical stability triggered by organoborate zwitterions for self-assembled PAS–co–2PEG solid electrolytes for lithium–sulfur battery

Abstract

Super ion-conductive solid polymeric electrolytes (SPEs) with high lithium (Li)–ion selectivity are applied to develop high efficiency, safe, and long-life lithium–sulfur batteries (LSB). Herein, a high-performance SPE is prepared by employing organoborate zwitterions (ZBo) into the flexible self-assembled poly(arylene ether sulfone) electrolytes grafted with dual poly(ethylene glycol) segments (PAS–co–2PEG) in the presence of ionic liquid. The large dipole moment of steric bulky ZBo present in lithium–ion conductive PEG domains phase separated from mechanically reinforced PAS matrix results in the promotion of Li-salt and borate anion/ Li-cation dissociation to facilitate the Li–ion migrations. The versatile functional groups in ZBo, such as ethyl carbonate (−EC), nitrile (−CN), and PEG with high dielectric constant aids Li-hopping without ionic aggregations. Attributed to these unique features, the as-developed SPEs show not only high thermal and mechanical stability above 250 °C and 1 MPa tensile strength, but also large electrochemical stability window of 5.3 V and high ionic conductivity of 1.05 mS cm−1 along with Li-ion transfer number of ∼0.5. The corresponding S/SPE/Li cells show 99.2 % of capacity retention after 200 cycles at 0.2C rate, demonstrating the promise of the advanced development of all-solid-state LSBs.