A composite electrolyte based on aluminum oxide filler/polyester polymer via in situ thermal polymerization for long-cycle sodium metal batteries

Abstract

Sodium metal batteries (SMBs) are widely regarded as the most promising candidate for the next generation of electrochemical energy storage devices. However, critical challenges of slow Na⁺ diffusion at room temperature, unstable solid electrolyte interphase (SEI), and uncontrolled growth of sodium dendrites still hinder its practical applications. Herein, an organic–inorganic composite solid electrolyte (CSE), formed through in situ thermal polymerization of trimethylolpropane trimethacrylate (TMPTMA) and hexanediol diacrylate (HDDA) with an aluminum oxide (Al₂O₃) filler, is developed to achieve high-performance SMBs. As demonstrated experimentally, the addition of the Al₂O₃ filler effectively enhances the transport of Na⁺, resulting in a high ionic conductivity of 5.59 × 10⁻³ S cm⁻¹ at 25 °C. Furthermore, the solvation structures of Na⁺ are actively regulated to facilitate fast kinetics and the formation of stable inorganic-rich interface. The Na∥Na symmetrical cell maintains a low polarization voltage even after 1000 h, indicating the successful inhibition of sodium dendrite growth and achievement of uniform Na depositions. Benefiting from the design of the organic–inorganic CSE, the Na∥NVP cell demonstrates a capacity retention of 88% after 2000 cycles at 2 C, indicating superior cycling stability. The cleverly designed strategy creates opportunities to boost the development of CSEs for SMBs.