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 MoO 3 and MoO 2 , respectively), high chemical stability, and low cost. The low electronic conductivity of MoO 3 limits their charge–discharge rate performances and delithiation capability. By controlling the valence state of MoO x with carbon, partial MoO 3 can be reduced to MoO 2 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 MoO 2 /MoO 3 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 MoO 3 /MoO 2 /NCNTs anode delivers an unparalleled high gravimetric capacity of 970 mA h g −1 , over 100-cycle stability and high rate capability.