Synthesis of MoO2/Mo2C/RGO composite in supercritical fluid and its enhanced cycling stability in Li-ion batteries

Herein, we present a new strategy for inhibiting the volume expansion of MoO2 during lithiation and delithiation by preparing MoO2/Mo2C core-shell particles deposited on reduced graphene oxide (RGO). The MoO2/Mo2C/RGO composite was synthesized by first preparing the MoO2/RGO composite in supercritical methanol (scMeOH) followed by carbothermal hydrogen reduction. Carbon migration from RGO and organic moieties attached to the surface of MoO2 particles synthesized in scMeOH produced a Mo2C film during carbothermal reduction. When tested as an anode in lithium ion batteries, the MoO2/Mo2C/RGO composite exhibited an increased initial coulombic efficiency (77%), long-term cyclability (500 mAh g(-1) at 50 mA g(-1) after 150 cycles), and high-rate performance (200 mAh g-1 at 1 A g-1) compared with those of the MoO2/RGO composite (53%; 280 mAh g(-1) at 50 mA g(-1) after 150 cycles; 120 mAh g(-1) at 1 A g(-1)). Electrochemical impedance spectra showed that the MoO2/Mo2C/RGO composite exhibited reduced solid electrolyte interphase (SEI) resistance and facilitated Li ion transport into the electrode. The presence of Mo2C with low electrochemical activity, but high electronic conductivity, could decrease SEI formation and suppress volume expansion, which prolonged the cycling life.