Doping with W6+ ions enhances the performance of TiNb2O7 as an anode material for lithium-ion batteries

Abstract

Monoclinic TiNb2O7 (TNO) has recently been reported as a promising anode candidate for next-generation high-energy–density lithium-ion batteries (LIBs). Unfortunately, poor electronic and ionic conductivities have limited its practical application. In this study, we prepared selectively W6+-doped TNO to overcome these drawbacks. We demonstrate herein the effect of site-selective substitution on the electrochemical performance of TNO after selectively doping its Ti4+ and Nb5+ sites with W6+ ions. The W6+ ions were incorporated into the TNO lattice without dramatically altering the lattice parameters. The ionic substitution of both Ti4+ and Nb5+ ions with W6+ ions in TNO improved the electronic conductivity because of partial reduction of the Ti4+ and Nb5+ ions as a result of charge compensation. Compared with the Nb-substituted TNO (i.e., the TNO derivative in which some of the Nb5+ ions had been replaced by W6+ ions), the Ti-substituted TNO displayed superior transfer properties, presumably because of its lower effective mass. As a result, the Ti-substituted TNO had the highest energy storage performance with its reversible capacity reaching 156.2 mA h/g, even at a rate of 20 C. After 500 repetitive cycles at 6 C, 85.5% of the capacity was retained without significant capacity fading.