Multifunctional polyzwitterion ionic liquid based solid-state electrolytes for enhancing the low-temperature performance of lithium-metal batteries

The extensive development of solid-state batteries (SSB) is still hindered by their insufficient charge transfer kinetics and severe interfacial problems at low temperatures. In this paper, a polyzwitterion ionic liquid based solid-state electrolyte (SSE) containing fluoroalkyl side chains is developed. The Lewis acid segment in the polymer backbone enhances the dissociation of lithium salts and modulates the Li+ transport. The experimental results showed that the −SO3- groups at the end of the zwitterions constructed a fast ion transport pathway, and the fluoroalkyl side chain can weaken the affinity between Li+ and the coupling site. In addition, the electrostatic shielding effect of zwitterions at the interface mitigated the tip effect, and the fluorinated alkyl side chains participated in the SEI film formation. As a result, the ionic conductivity of the designed electrolyte is as high as 1.39 × 10-4 S cm−1 at −30 °C, and the polarization rate of Li||Li symmetric battery at −10 °C is about 80 mV after 4000 h. The assembled Li||LiFePO4 pouch full cell delivers impressive performance in the wide temperature range from –23 to 99 °C. The proposed strategy has considerable potential for SSB application at low temperatures.