A simple reduction process to synthesize MoO₂/C composites with cage-like structure for high-performance lithium-ion batteries

Large-scale MoO₂/carbon composites with a cage-like nanostructure have been synthesized by a simple hydrothermal reduction process. During the hydrothermal process, ammonium molybdate tetrahydrate ((NH ₄)₆Mo₇O₂₄·4H₂O) was employed as starting material and ascorbic acid as a structure directing agent, reductive agent and carbon source. MoO₂/C nanospheres with diameters of about 15-25 nm were interconnected to form a cage-like architecture. Time-dependent experiments illustrated that the cage-like structure was transformed from tightly packed MoO₂ nanoparticles. Furthermore, with a water-soluble binder (sodium alginate), the cage-like MoO₂/C composites exhibited a high discharge capacity and significantly improved cycling performance compared to previously reported MoO₂-based anode materials. The electrodes with the MoO₂/C composites can deliver a capacity of 692.5 mA h g^-1 after 80 charge-discharge cycles at a current density of 200 mA g^-1. After C-rate measurement, the battery still can maintain excellent cycling stability (about 550 mA h g^-1 reversible capacity retained even after 475 cycles). The excellent electrochemical performance can be ascribed to the cage-like structure, which integrates three advantages: porous structure, interconnected MoO₂/C framework and small nano-crystals.