Enhancing the Dendritic Tolerance of NASICON-Based Electrolytes by Grain Boundary Engineering

A grain boundary modification strategy relying on the liquid-sintering method is proposed for using NASICON-type ceramics Na_1+xZr₂Si_<i>x</i>P_3-xO₁₂ as solid-state electrolytes (SSEs) for all-solid-state batteries (ASSBs). It is found that with the addition of Na₃AlF₆, the grain boundaries of Na_3.3Mg_0.15Zr_1.85Si₂PO₁₂ ceramics (MNZSP) are filled with the amorphous and nanocrystalline phase reducing the electronic conductivity and improving the mechanical strength of the electrolyte. This effectively inhibits dendrite initiation and blocks sodium dendrite penetration. Besides, the grain boundary phase with high ionic conductivity is conducive to provide a continuous Na⁺ transport path through the whole electrolyte. Thus, the symmetric cells represent a high critical current density (CCD) of 2.1 mA cm^-2 and demonstrate extended cycling stability over 1200 h at 0.3 mA cm^-2. The high-load-capacity (99.1 mAh g^-1) full-cells based on MNZSP demonstrate remarkable cycling stability for 200 cycles at 0.5 C. This grain boundary modification approach presents a promising pathway for developing practical high-performance SSEs.