Thermodynamic Suppression of Deprotonation in Succinonitrile‐Based Electrolyte for Durable Solid‐State Sodium‐Metal Batteries

Abstract

Solid‐state sodium‐metal batteries (SSMBs) offer a low‐cost, safe, and high‐energy‐density energy‐storage technology. While succinonitrile (SN) is widely adopted in solid and gel electrolytes for its high dielectric constant, exceptional oxidative stability, and robust cathode compatibility, its practical application is limited by parasitic reactions with Na metal, including deprotonation and polymerization. Herein, we demonstrated a thermodynamic suppression strategy of deprotonation that substantially inhibits parasitic reactions in SN‐based electrolytes for durable SSMBs. By utilizing an acrylonitrile (AN) based polymer as the host framework, we establish an optimized interaction with free SN that thermodynamically disfavors the parasitic decomposition, effectively stabilizing the α‐hydrogens of the methylene groups against deprotonation. The rationally designed electrolyte exhibits high ionic conductivity of 2.17 mS cm −1 and exceptional compatibility with Na metal, enabling stable cycling of Na | Na symmetric cells for 6200 h. Na | Vanadium phosphate sodium full cells retain 95.6% capacity after 5000 cycles at 1.0 C, 93.4% after 10000 cycles at 2.0 C, and pouch cells with an ultra‐high cathode loading of 20 mg cm −2 demonstrate stable performance. This work establishes thermodynamic suppression of deprotonation as a foundational design principle for high‐energy‐density and long‐lifespan SSMBs.