Graphene Regulated Ceramic Electrolyte for Solid-State Sodium Metal Battery with Superior Electrochemical Stability

Employing solid ceramic electrolyte in sodium (Na) metal batteries enables safe and cost-effective energy storage solution toward the advent of sustainable energy. Nevertheless, the development of solid-state Na batteries is hindered by the large interfacial charge transfer resistance between electrodes and solid electrolyte. Here, a novel and scalable design approach is utilized to significantly reduce the interfacial resistance through the direct growth of graphene-like interlayer on Na⁺ superionic conductor (NASICON) ceramic electrolyte, resulting in a 10-fold decrease of interfacial resistance. Benefiting from the graphene regulated NASICON, extremely stable Na plating/stripping cycling performance using solid electrolyte at a current density up to 1 mA/cm² with a cycling capacity of 1 mAh/cm² for 500 cycles (1000 h) is demonstrated for the first time. The surface of Na electrode after 1000 h of cycling remained smooth because of uniform Na⁺ flux across graphene-coated-NASICON/Na interface enabled by the abundant graphene defects network for efficient Na⁺ transport. Solid-state room temperature battery consists of graphene-regulated NASICON electrolyte, Na₃V₂(PO₄)₃ cathode and Na anode delivered a reversible initial capacity of 108 mAh/g at 1C current density for 300 cycles with 85% capacity retention, far superior than the battery with pristine NASICON. This work can be a valuable contribution toward a safe and stable solid-state Na metal battery system, and provide insights for solid-state lithium metal batteries as well.