Kogakuin University investigates P2O5 based Na⁺ superionic conductive glass-ceramics for all-solid-state batteries

Researchers at Kogakuin University have discovered that adding phosphorus (P₂O₅) to sodium-yttrium-silicate glasses significantly enhances their performance as solid electrolytes for next-generation sodium-ion batteries. This improvement arises from the formation of the high-performance Na₅YSi₄O₁₂ crystal phase, which promotes high ionic conductivity and stability, making sodium-based batteries a safer and promising alternative to lithium-ion technologies. However, the effects of phosphorus on the glass structure and its location after crystallization had not been fully understood.

In fact, sodium-ion batteries are attracting worldwide attention as a sustainable option for next-generation energy storage, thanks to desirable properties such as low cost and the natural abundance of sodium compared with lithium. In this study, researchers at Kogakuin University prepared two yttrium-based silicate glass systems—with and without phosphorus—and performed advanced characterization using state-of-the-art techniques, including X-ray and neutron diffraction, electron microscopy, and solid-state NMR spectroscopy, to investigate how P₂O₅ addition affects the structure of glasses and glass-ceramics after crystallization.

The study revealed that adding phosphorus (P₂O₅) led to a slight polymerization of the three-dimensional network formed by SiO₄ and PO₄ tetrahedra in Na₄Y_0.6P_0.2Si_2.8O₉ glass, without changing its ionic conductivity. In the corresponding glass-ceramic, P was found to be almost entirely incorporated into the Si sites of the Na₅YSi₄O₁₂ crystal, rather than remaining in the residual glass. Substituting Si with P, which is more electronegative, can influence the ionic conductivity of the glass-ceramics.

In essence, this approach offers promising insights into high-performance sodium-ion solid electrolytes, which are crucial for a sustainable future in energy storage applications. The use of non-flammable inorganic electrolytes enhances safety and enables faster charging, making these materials especially attractive for next-generation batteries.

The findings were made available in the journal of Ceramics International on December 4^th, 2025.