Gamma titanium phosphate as an electrode material for Li-ion and Na-ion storage: performance and mechanism

Gamma titanium phosphate (G-TiP) possesses a lamellar framework with larger interlayer spacing than alpha-type TiP, in which the protons within the P-OH groups can be exchanged by alien ions. Herein, the electrochemical performance of the bulk G-TiP in both lithium and sodium storage has been systematically investigated. The results reveal that the layered G-TiP can store both Li+ and Na+ ions via a local ion exchange process and redox reaction in a wide voltage range. Despite the large radius of Na+, G-TiP exhibits a higher structural tolerance upon (de)sodiation and better capacity retention when cycled at low voltage. For a Na-ion cell, the G-TiP electrode delivers a specific capacity of 161.3 mA h g(-1) within 0.1-2.8 V, showing an obvious plateau in the range of 1.6-2.2 V with a solid solution reaction. For a Li-ion cell, a reversible capacity of 109 mA h g(-1) is attained within 0.8-2.8 V, and a voltage plateau occurs at 2.2-2.6 V.