Siloxane-Based Polymer Gel Electrolytes for Sodium Metal Batteries with Long Lifespan at High Rates and Low Temperatures

To address the scarcity of lithium metal resources and the leakage issues associated with traditional liquid batteries, the development of solid-state sodium metal batteries (SMBs) is necessary. However, the advancement of solid SMBs has been significantly impeded by the low ionic conductivity of solid electrolytes and poor electrode compatibility. To overcome these challenges, this study employs an in-situ polymerization method to synthesize a gel polymer electrolyte, by incorporating 3-(Trimethoxysilyl)propyl methacrylate (TPM) into the polymer network. When 5 % TPM is added, the room-temperature ionic conductivity and sodium-ion transference number of GPE are notably enhanced to 4.54×10⁻² S cm⁻¹ and 0.58, respectively, with an oxidation voltage reaching 4.59 V. Due to the formation of a dense SEI film rich in F and Cl on the surface of sodium metal, the sodium symmetric batteries using GPE-TPM-5 can work stably for more than 3200 h at the current density of 0.1 mA cm⁻². The NVP|GPE-TPM-5|Na batteries exhibit excellent cycle life of over 15000 cycles at a rate of 10 C, with a capacity retention rate of 91 %. It also demonstrates more than 800 cycles with a capacity retention rate of 94 % at −20 °C and 1C. This research provides a new approach for preparing gel polymer electrolytes for SMBs with superior long-term cycling performance at a high rate and a low temperature.