Two-Dimensional Cr-Doped MoO_2.5(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 MoO_2.5(OH)_0.5 (doped MoO_2.5(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 MoO_2.5(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 MoO_2.5(OH)_0.5 nanosheets. Interestingly, for doped MoO_2.5(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 MoO_2.5(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 MoO_2.5(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.