Porous glass-ceramics cation exchangers: Cation exchange properties of porous glass-ceramics with skeleton of fast Li ion-conducting LiTi₂(PO₄)₃ crystal

Lithium titanium orthophosphate LiTi₂(PO₄)₃ (LTP) has attracted attention as a chemically stable fast Li⁺-conductor in ambient atmosphere. It was reported in our previous paper⁷ that monolithic microporous glass-ceramics with a skeleton of this crystal were successfully prepared from glasses in the pseudobinary system of LTP and Ca₃(PO₄)₂. Here we report that these porous glass-ceramics (mean pore diameter: ∼40 nm; total specific surface area: ∼30 m²; porosity: ∼45 vol.%) show excellent cation exchange properties. Approximately 50% of Li⁺ ions in the materials are exchanged with monovalent ions with ionic radii smaller than 130 ppm in 1 h at room temperature. In particular, Li⁺ ions are selectively exchanged with Ag⁺ ions even in the presence of Na⁺ ions. The exchange rate in the porous glass-ceramics is larger by two orders of magnitude than that of sintered LTP. The ratio of these exchange rates is close to that of the total surface areas, indicating that most of the pores in porous LTP glass-ceramics are available for ion exchange reactions. These are the first porous glass-ceramics having excellent cation exchange properties.