Na 3 LaP 2 O 8 -enabled microstructural engineering for enhanced mechanical robustness and ionic transport behavior in NaSICON solid electrolytes

NaSICON-type Na1+xZr2SixP3−xO12 (0 ≤ x ≤ 3, NZSP) were synthesized via a solution-assisted solid-state reaction method, and the effect of Na3LaP2O8 (NLP) addition on their microstructure, mechanical properties, and electrical performance was systematically investigated. NLP incorporation refined the grain structure, yielding a more uniform grain size distribution, reduced porosity, and suppressed microcrack formation, which collectively enhanced densification and mechanical performance. The optimized composition (2.5 mol% NLP) exhibited substantial increases in elastic modulus, hardness and fracture toughness compared to original NZSP. However, excessive NLP addition hindered ionic transport due to the insulating nature of NLP, revealing a trade-off between mechanical robustness and ionic conductivity. This work establishes a quantitative correlation between the mechanical and electrical properties of NLP-modified NZSP and provides a design strategy for mechanically reinforced, high-performance solid-electrolytes for all-solid-state sodium batteries.