Microstructure evolution of Li uptake/removal in MoO2@C nanoparticles with high lithium storage performance

A facile one pot strategy of a hydrothermal methodology was applied to synthesize the carbon coated MoO2 (MoO2@C) nanostructured particles, which are composed of ultra fine nanoparticles with homogeneous carbon coating about several nanometers. As an electrode in lithium ion batteries, the MoO2@C shows a high specific capacity and reversible capacity (730 mA h g−1 after 60 cycles). Microstructure investigations, by using a high resolution transmission electron microscopy, of the MoO2@C based electrodes employed at various states during the first discharge/charge cycle were conducted to elucidate the lithium ion uptake/removal mechanism and cycling behavior. In the lithium uptake process, the original MoO2 phase transfers into Li0.98MoO2 through an addition type reaction, and then nanosized metallic Mo emerges as a result of a conversion reaction. In turn, Mo could be oxidized to the intermediate Li0.98MoO2 before converting to hyperfine MoO2 phase on upcoming lithium removal process.