High heat-tolerance and safety of lithium metal batteries using a high-concentration phase-change electrolyte

Although lithium metal batteries using localized high concentration electrolytes (LHCEs) exhibit promising life, their safety and survivability in hot summers are of great concern due to highly flammable and volatile solvents and diluents comprising LHCEs. In this work we present a nonflammable high-concentration phase-change electrolyte (HPCE) by addition of sulfolane (SF) and demonstrate it in single-layer Cu/NMC811 anode-free batteries (AFBs). The high dielectric constant of SF raises the LiFSI concentration of HPCE, enabling the AFB cells to possess stable solid electrolyte interphase (SEI) and operate at 60 °C with exceptional cycling stability of 76 cycles at 80 % capacity retention. In addition, the solidified HPCE at room temperature due to the high melting point of SF allows the AFB cells to rest under open circuit with low degradation and high safety. Moreover, the high boiling point and high autoignition temperature of SF as well as the low amount of volatile components in the HPCE thermodynamically suppress the potency of electrolyte combustion; consequently in the single-layer internal short circuit test, the HPCE-cell needs much higher shorting current (104.3 A) (i.e. heating power) than the LHCE-cell (80.1 A) to trigger a battery fire.