The glass phase in the grain boundary of Na3Zr2Si2PO12, created by gallium modulation

Na3Zr2Si2PO12 has been proven to be a promising electrolyte for solid-state sodium batteries. However, its poor conductivity prevents application, caused by the large ionic resistance created by the grain boundary. Herein, we propose an additional glass phase (Na–Ga–Si–P–O phase) to connect the grain boundary via Ga ion introduction, resulting in enhanced sodium-ion conduction and electrochemical performance. The optimized Na3Zr2Si2PO12-0.15Ga electrolyte exhibits Na+ conductivity of 1.65 mS cm−1 at room temperature and a low activation energy of 0.16 eV, with 20% newly formed glass phase enclosing the grain boundary. Temperature-dependent NMR line shapes and spin-lattice relaxation were used to estimate the Na self-diffusion and Na ion hopping. The dense glass-ceramic electrolyte design strategy and the structure–dynamics–property correlation from NMR, can be extended to the optimization of other materials.