Methylation Design on Weakly Solvating Ethers for Wide-Temperature Li–SPAN Battery

Sulfurized polyacrylonitrile (SPAN) recently emerges as a prospective cathode for lithium–sulfur (Li–S) batteries owing to its high S utilization, remarkable cycling stability, and liberty from shuttle effect. Despite weakly solvating ether electrolytes exhibiting simultaneously compatibility for SPAN cathode and lithium (Li) anode, they universally suffer from low ionic conductivity and narrow liquid-phase temperature range. However, conventional ether-based electrolytes with excellent ionic conductivity cannot realize reversible solid–solid conversion of SPAN cathode due to Li polysulfide intermediates (LiPSs) dissolving and shuttling. Here, a series of weakly solvating ethers are evaluated by selectively methylating dimethoxymethane (DMM) to fine-tune their solvation capability and liquid-phase temperature range. Enlightened from weakly solvating ether electrolytes, the contact ion pair (CIP)-dominated electrolyte is designed for satisfactory ionic conductivity of electrolyte and reversible solid–solid conversion of SPAN cathode over wide temperature range. The reinforcement mechanisms of the CIP-dominated electrolyte for the Li anode and SPAN cathode are comprehensively elucidated through experimental characterizations and molecular dynamics simulations. Based on the optimized electrolyte, Li||SPAN full cells can steadily operate over wide temperature range from −20 to 60 °C. Furthermore, the 120 mAh Li||SPAN pouch cell can exhibit 85.5% capacity retention after 45 cycles at 0.2 C.