Non-flammable ultralow concentration mixed ether electrolyte for advanced lithium metal batteries

High energy density lithium (Li) metal batteries (LMBs) hold great promise to become next-generation energy storage devices. However, their commercialization process is severely hindered by low Coulombic efficiency (CE) and potential safety hazard caused by non-uniform Li deposition and flammable electrolytes. Herein, a brand-new ultralow concentration (0.3 M) mixed ether electrolyte is proposed to regulate the electrolyte structure, flammability and solid electrolyte interphase (SEI) composition for LMBs. The high proportion of flame retarded inert solvent (94% by volume) remarkably improves the security of LMBs and promotes anions involving in Li+ solvent sheath structures. Therefore, differing from Li+−solvent dominant solvent sheaths in traditional low concentration electrolyte, the abundant Li+−anion aggregate cluster in this ULCE could lead to sufficient decomposition of anion and formation of inorganic-rich SEI. Based on this electrolyte design, the average Li deposition/stripping CE reaches > 99.3% under 2 mA cm−2 and 1 mAh cm−2 among 250 cycles. Moreover, superior electrochemical performance of Li||Li4Ti5O12 and Li||sulfur full cells also confirm the practical application value of this ULCE. This work proposes a fresh strategy to design low concentration electrolytes with unique solvated structures for high energy density metal batteries.