Synergistic design of 3D Na3.2Zr1.9Ca0.1Si2PO12-based composite solid electrolyte via in-situ polymerization for solid-state sodium batteries

The growing demand for sustainable and high-performance energy storage solutions has driven significant advancements in sodium-ion batteries (SIBs) as a cost-effective and eco-friendly alternative to lithium-ion batteries (LIBs). This study introduces a composite solid electrolyte (CSE) designed for solid-state sodium batteries (SSSBs), leveraging a 3D NASICON framework to address challenges associated with ionic conductivity, mechanical stability, and interfacial resistance. The CSE was synthesized through in-situ polymerization of butyl acrylate (BA) within a porous Na_3.2Zr_1.9Ca_0.1Si₂PO₁₂ (NZCSP) framework fabricated via a tape casting method. The resulting structure achieved an ionic conductivity of 7.1 × 10⁻⁴ S cm⁻¹ at 30 °C, electrochemical stability up to 4.88 V versus Na/Na⁺, and a sodium-ion transference number (t_Na⁺) of 0.62. Na|CSE|Na symmetric cells exhibit remarkable sodium stripping/plating stability with minimal overpotential over 1000 h. Na|3D-NZCSP-CSE| Na₃Mg_0.5V_1.95(PO₄)₃@C (NVMP@C) cells exhibited excellent performance, retaining 95 % of their initial capacity after 500 cycles at 1.0C and maintaining a specific discharge capacity of 94.4 mAh g⁻¹. These findings demonstrate the potential of 3D framework-based CSEs to advance the practical application of SSSBs, offering a pathway to safer, more efficient, and cost-effective energy storage technologies.