Structure and Electrochemical Properties of Bronze Phase Materials Containing Two Transition Metals

Abstract

Bronze phase transition-metal oxides have recently attracted attention as high-rate lithium-ion battery anode materials. Their crystal structures are distinguished by large tunnels and an open framework, facilitating lithium-ion diffusion and high-rate charge–discharge properties. The presence of two transition metals also offers a route to achieve high energy density from multielectron redox. In this paper, we report the chemistry, structure, and electrochemical properties of two different bronze phase compositions having the same stoichiometry: W3Nb2O14 and Mo3Nb2O14. These materials provide insight into how the transition metals affect the electrochemical behavior and structural stability of bronze phase materials. Mo3Nb2O14 exhibits greater than 1 electron redox per transition metal leading to lithium capacities above 200 mAh g–1 at C/2 but is unable to maintain this high capacity at high rates due to incomplete Mo redox reactions. In contrast, W3Nb2O14 exhibits reversible redox reactions and retains its open structure on cycling. This study highlights the potential of bronze phase materials containing two transition metals to exhibit fast charging properties with a high energy density.