Localized high-concentration carbonate electrolyte creating functional in situ interfaces: Side reaction inhibition for lithium sulfur batteries

Lithium–sulfur batteries have sparked a lot of interests because of their high specific capacity and low cost. However, due to the ‘shuttle effect’, unstable Li metal and side reactions, the performance of LSBs is less than expected. Herein, we design a localized high-concentration electrolyte (LHCE), using carbonate as the base solvent, hexafluoroisopropyl methyl ether (HFME) as the diluent, and vinylene carbonate (VC) as the filmogen to realize a stable solid-solid cyclic process in LSBs. For the cathode side, carbonate solvent molecules with Li+-coordination can reduce the nucleophilic side reactivity with lithium sulfide. The initial surface reaction between VC and lithium sulfide forms an effective cathode electrolyte interface (CEI), which can continuously protect the cathode active substances and realize a stable solid-solid conversion process. For the anode side of lithium metal, in combination with Li+-coordinated TFSI− in LHCE, a stable solid electrolyte interface (SEI) can be formed by VC on Li anode which improves the stability of Li anode. As a result, the cyclic performance of LSBs is significantly improved, demonstrating a high specific capacity and stability. Furthermore, the self-discharge is nearly stopped. This work provides a universal strategy to design new electrolytes to improve Li–S battery performance.