Microstructure Optimization of Na₃SbS₄/Na₃Zr₂Si₂PO₁₂ Composite Solid Electrolytes for Improving Cycling Stability in...

Sulfide-based solid electrolytes have attracted significant attention for all-solid-state batteries due to their high ionic conductivity. However, their practical application is limited by interfacial instability at the sodium metal anode, leading to side reactions that form Na₂S and Na₃Sb, and by structural defects such as voids and cracks that create electronic leakage pathways. To address these issues, a composite electrolyte was developed by incorporating Na₃Zr₂Si₂PO₁₂ (NZSP), a stable NASICON-type oxide, into Na₃SbS₄ (NSS). The optimized 90-10 wt.% NSS-NZSP composite improves microstructural integrity by filling voids and mitigating crack formation, enabling efficient Na⁺ transport. As a result, the ionic conductivity increases from 3.7 × 10^-4 to 3.97 × 10^-4 S cm^-1, while the activation energy decreases from 0.25 to 0.22 eV. A half-cell configuration (Na_2/3Fe_1/2Mn_1/2O₂|90-10 wt.% electrolyte|Na) demonstrates stable cycling over 100 cycles at 0.05 A g^-1, delivering a discharge capacity of 118.9 mAh g^-1 at room temperature.