Metal Oxides with Distinctive Valence States in an Electron-Rich Matrix Enable Stable High-Capacity Anodes for Li Ion Batteries

Metal oxides are arguably a promising solution to next-generation high-energy-density anode materials. In particular, molybdenum oxides own high theoretical specific capacity (1117 and 838 mA h g⁻¹ for MoO₃ and MoO₂, respectively), high chemical stability, and low cost. The low electronic conductivity of MoO₃ limits their charge–discharge rate performances and delithiation capability. By controlling the valence state of MoO_x with carbon, partial MoO₃ can be reduced to MoO₂ with low electrical resistance and high-rate capacity. Nonetheless, both molybdenum oxides undergo large-volume expansion/shrinkage and even pulverization in the lithiation/delithiation process. Herein, through a facile pyrolysis method a MoO_x/N-doped carbon nanotube (NCNT) anode with controllable valence states of Mo is designed. The high conductivity and flexibility of the NCNT matrix form a stable MoO₂/MoO₃ anode with finely matched lattices and coordinated 3d electrons. Owing to molecularly close contact between electron-rich CNTs and MoO_x, MoO_x/NCNTs own a high conductivity of 0.36 S cm⁻¹, and mitigate the volume expansion in charges and discharges. The MoO₃/MoO₂/NCNTs anode delivers an unparalleled high gravimetric capacity of 970 mA h g⁻¹, over 100-cycle stability and high rate capability.