A Polysiloxane-Enabled Ternary Eutectic Electrolyte with Fast Ion Transport under Extreme Conditions

Developing lithium–metal batteries under extreme conditions is highly challenging and requires flammable/volatile solvents. In pursuit of safe electrolyte materials, polymers possess slow lithium transport, while eutectic electrolytes (EEs) suffer from interfacial instability, impeding their applications under extreme conditions. Herein, we report that addition of a designed brush-polysiloxane into EE unexpectedly boosted ionic conductivity by nearly 3-fold to 0.59 mS cm–1 at −40 °C compared to that without polymer, fulfilling fast transport kinetics. Spectroscopic characterizations and simulations revealed formation of a ternary EE via intermolecular interactions as well as a stabilized interface, which successfully led to a high capacity of 149 mAh g–1 at −40 °C (85% of room-temperature capacity) and stable fast-charging performance up to 1,000 mA g–1 (6 min recharging) over 100 cycles in Li||LiNi0.6Co0.2Mn0.2O2 cells. The polymer-enhanced electrolyte offers a paradigm shift approach to tune kinetics in high-performance and safe lithium batteries under extreme conditions.