Ultrafine VN quantum dots modified with a nitrogen-doped reduced graphene oxide anode material for enhanced rate capability and lifespan of lithium-ion batteries

Abstract

Vanadium nitride (VN) has gained significant attention as a potential material for use in lithium-ion batteries (LIBs) due to its excellent electrical conductivity and high theoretical capacity. However, the huge volume changes and sluggish Li⁺ reaction kinetics while using VN materials limit the rate capability and cycling stability of LIBs. In this work, a composite of VN quantum dots (VNQDs) and nitrogen-doped reduced graphene oxide (NrGO) (VNDQs@NrGO) was fabricated using an indirect ammonia thermal reduction method. VNQDs were grown in situ on the surface of the layered reduced graphene oxide. The anchored VNQDs not only prevented the unprompted stacking of the graphene layers, but also enabled the in situ growth of ultrafine VNQDs. This is beneficial for the buffer volume expansion of the VNQDs, thereby improving their structural stability and electrolyte diffusion kinetics. As a result, the VNQDs@NrGO-5 nanocomposite maintained a specific capacity of 323.8 mA h g⁻¹ after completing 10 000 cycles at 2.0 A g⁻¹. Moreover, the assembled full cell with a LiFePO₄ (LFP) cathode achieved an adequate capacity of 53.47 A h g⁻¹ after completing 5000 cycles at 0.5 A g⁻¹. The excellent electrochemical performance of the nanocomposite is attributed to the large capacity of the conductive network and buffer skeleton of the VNQDs and NrGO.