Two-Dimensional Cr-Doped MoO2.5(OH)0.5 Nanosheets: A Promising Anode Material for Lithium-Ion Batteries.

α-MoO3 has gained growing attention as an anode material of lithium-ion batteries (LIBs) because it has a high theoretical specific capacity of 1111 mA h g-1 and unique layer structure. However, the electrochemical reactions of MoO3 exhibit sluggish kinetics and structural instability caused by pulverization during charge and discharge. Herein, we report new two-dimensional Cr-doped MoO2.5(OH)0.5 (doped MoO2.5(OH)0.5) ultrathin nanosheets prepared by a facile hydrothermal process. The formation of the ultrathin nanosheets was clarified by a "doping-adsorption" model. Compared with doped MoO3, doped MoO2.5(OH)0.5 has larger expanded spacing of the {0 l0} crystal planes for fast Li+ storage. The electrodes after cycling were investigated by ex situ transmission electron microscopy in combination with X-ray photoelectron spectroscopy analysis to reveal the reversible conversion reaction mechanism of doped MoO2.5(OH)0.5 nanosheets. Interestingly, for doped MoO2.5(OH)0.5 nanosheet electrodes, it was found that the as-formed intermediate Li xMoO3 nanodots were well-dispersed in the mesoporous amorphous matrix and had an expanded (040) crystal plane after 10 cycles. These unique structural features increased the effective surface of intermediate products Li xMoO3 to react with Li+ and shortened the diffusion length and thus promoted the electrochemical reactions of doped MoO2.5(OH)0.5. Additionally, the presence of Cr also played a critical role in the reversible decomposition of Li2O and enhanced specific capacity. When employed as an anode in LIBs, doped MoO2.5(OH)0.5 nanosheets show superior reversible capacity (294 mA h g-1 at 10 A g-1 after 2000 cycles). Moreover, the reversible capacity after electrochemical activation is quite stable throughout the cycling, thereby presenting a potential candidate anode material for LIBs.