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

• The carbon-coated MoO2 (MoO2@C) ultra fine nanoparticles are synthesized by one-pot hydrothermal method.
• MoO2@C nanoparticles have high specific capacity, excellent cycling performance and rate performance.
• Phase transformations for lithium ion uptake/removal are examined carefully by TEM.
• Phase transformations are highly reversible during the redox process.

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.

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