In Situ Growth of Mo2C Crystals Stimulating Sodium-Ion Storage Properties of MoO2 Particles on N-Doped Carbon Nanobundles

Sodium-ion batteries (SIBs) are considered as the candidate for the upcoming large-scale energy storage systems. However, transition-metal oxides still have the problem of insufficient utilization of active sites, mainly signified by the low practical capacity in long cycles. Here, the composite (MoO2@Mo2C/C) of Mo2C crystals in situ grown in N-doped carbon nanobundles (N-CNBs) with MoO2 particles on their surface is designed by self-polymerization and two-step calcination. Through a series of characterizations and tests, it is found that the N-CNBs endow the composite with improved conductivity and reinforced structural stability and effectively alleviates the volume expansion and structural collapse of MoO2 particles. The high integration of Mo2C crystals with MoO2 particles/N-CNBs (Mo2C/C) further enhances the charge-transfer ability and structural stability for the composite. Importantly, the storage sites of MoO2 particles and Mo2C crystals are gradually activated during sodium-ion storage, significantly improving the effective capacity in the long cycles. After 8000 cycles at 5.0 A g-1, the reversible capacity of MoO2@Mo2C/C as a SIB anode gradually increases from 126.2 to 419.1 mAh g-1, with a capacity retention of up to 332.4%. This study fully demonstrates the potential advantages of metal carbides in energy storage and can provide a good reference for the development of metal ion batteries.