In Situ Synthesis of MoC_1–x Nanodot@Carbon Hybrids for Capacitive Lithium-Ion Storage

In this study, in situ synthesis of carbon-coated MoC_1–x nanodots anchored on nitrogen-doped carbon (MoC_1–x@C) for lithium storage is reported. The obtained MoC_1–x@C hybrids exhibit intriguing structural characteristics including ultrafine particle size (ca. 1.2 nm) of MoC_1–x nanodots, porous structure of nitrogen-doped carbon matrix, and good robustness. When evaluated as anodes for lithium-ion batteries, the optimized MoC_1–x@C sample demonstrates a superior specific capacity (1099.2 mA h g^–1 at 0.1 A g^–1) and good rate capability (369.1 mA h g^–1 at 5 A g^–1). The MoC_1–x@C anode also presents remarkable cycling stability with a much higher specific capacity (657.9 mA h g^–1) than that of commercial bulk MoC (91.4 mA h g^–1) after 500 cycles at 1 A g^–1. Kinetics analysis of the anodes reveals the charge storage mechanism, which demonstrates the existence of capacitive redox reactions occurring at the shallow surface of the MoC_1–x nanodots and closely relating to the particle size. The outstanding electrochemical performance results from the synergistic effect of the elastic carbonaceous encapsulation to accommodate the huge volume expansion and the ultrafine MoC_1–x nanodots to provide more reactive sites for capacitive lithium storage.