Zwitterionic liquid-based gel electrolyte for high performance lithium metal battery at low temperatures

Gel electrolyte (GE) gains intensive attentions for lithium metal battery, especially those targeting to use at low temperatures. The liquid medium, as the core component, of most gel electrolytes (GEs) is organic liquid or ionic liquid, always suffering from serious safety issue and low transference number (t+). The low t + aggravates concentration polarization and thus leads to the increase of overpotential and undesirable side reactions. Herein, zwitterionic liquid (ZIL) with high stability and safety is prepared by mixing zwitterion (ZI) and lithium salt. The ZIL is then encapsulated into a SiO2 matrix to fabricate novel gel electrolyte (SiGE-ZIL). The low freezing point and strong mobility of ZIL confer SiGE-ZIL a high conductivity of 3.36 × 10−4 S cm−1 at −40 °C. Importantly, the large dipole moment of ZI effectively accelerates the dissociation of lithium salt, permitting a high t+ of 0.553 at −40 °C, which is 2.3 times of that of the analogous ionic liquid. The assembled LiFePO4/Li battery exhibits an excellent cycling stability with a capacity of 91.6 mAh g−1 at 600th cycle at 0.5C and 0 °C. Especially at −20 °C, the capacity can reach 67.1 mAh g−1 at 600th cycle under 0.5C, surpassing most of GE-based batteries.