Electrochemical intercalation of lithium in the titanium hydrogeno phosphate Ti(HPO4)2·H2O

The electrochemical reactivity of the layered titanium hydrogeno phosphate Ti(HPO4)2·H2O versus lithium has been studied. Lithium intercalation occurs at ~2.5 V with low polarization, leading to a new lithiated Ti(III) phase, LiTi(HPO4)2·H2O. Ti(HPO4)2·H2O exhibits a reversible capacity of 80 mAh g−1 in the voltage window 1.8–3.5 V at C/10 rate. The stable reversible capacity reveals that the presence of H2O lattice is not affecting the electrochemical reaction. The reversibility of the reaction is demonstrated by extracting lithium from LiTi(HPO4)2·H2O and the host structure is intact. The electrochemical behaviour of dehydrated phases Ti(HPO4)2 and TiP2O7 has also been investigated.