Synthesis And Electrochemical Properties Of Novel Two-Dimensional Cr-Doped MoO_2.5?OH?_0.5 Nanosheets

In the past decades,energy and environmental problems have attracted wide attention.In order to meet the great demand of social and economic development for energy,it is imperative to seek and develop new energy.Although solar energy and wind energy and other new energy sources are clean and free-pollution,they are not widely used because they are limited by many conditions at present.As an energy storage system,lithium-ion batteries has many advantages over other energy storage systems.Transition metal oxides plays an important role in energy storage and conversion.At present,as a commercial anode material for lithium ion batteries,graphite has a low theoretical capacity of only 372mAh g^-1,which limits its practical application.Although the theoretical capacity of anode materials such as silicon-based materials is relatively high,but there will be a huge volume change?400%?during the charging and discharging process,and the electrode system is extremely unstable,which limits its practical application to a large extent.?-MoO₃ has gained growing attention as anode material of lithium-ion batteries?LIBs?because of its high theoretical capacity(1111 mAh 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.In this paper,a novel two-dimensional?2D?Cr-doped MoO_2.5?OH?_0.5 ultrathin nanosheet was synthesized by simple hydrothermal reaction.A“doping-adsorption”model was proposed to elucidate the formation of the ultrathin nanosheets.Compared with doped MoO₃,doped MoO_2.5?OH?_0.5 has larger expanded spacing of the{0l0}crystal planes for fast Li⁺storage.The electrodes after cycling were investigated by ex situ TEM in combination with XPS 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_xMoO₃nanodots 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 path,and thus promoted the electrochemical reactions of doped MoO_2.5?OH?_0.5.Additionally,the presence of Cr also played a key role in the reversible decomposition of Li₂O and enhanced specific capacity.When employed as an anode in LIBs,doped MoO_2.5?OH?_0.5.5 nanosheets delivered a superior reversible capacity of 294 mAh 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 promising anode material for LIBs.