Electrochemical Lithium Intercalation Properties of ρ-Ti₂O(PO₄)₂·2H₂O

Titanium compounds, especially oxides and oxyanionic salts, have received considerable attention as lithium- or sodium-based battery anode materials that offer faster and safer operations at potentials with enough margin down to those of metal deposition. Among them, titanium phosphates possess a wide variety of framework structures that can host intercalant guest ions. Here, we report electrochemical Li + intercalation properties of a titano phosphate oxide hydrate, ρ-Ti 2 O(PO 4 ) 2 ·2H 2 O, in non-aqueous and hydrate-melt electrolytes. The reactions occur at ca. 2.42 V vs. Li/Li + with a bi-phasic phase evolution up to α ~ 1 in ρ-Li α Ti 2 O(PO 4 ) 2 ·2H 2 O, where lithium ions are in a space forming large tunnels coordinated by phosphates and crystal water. Applying conventional dilute-salt aqueous electrolytes with large water activity led to quick capacity decay due to the electrode instability issues caused by dissolution and hydrogen evolution.