Coupling of Defective VSe_2-x with Graphene via V─C Bonds for High-Rate and Long-Life Sodium-Ion Storage

Covalent bonding has been extensively applied in the synthesis of advanced energy storage materials due to its strong interfacial interactions, significantly enhancing mechanical stability. However, the inherent electron localization characteristic of pure covalent bonds substantially restricts electronic mobility and conductivity at heterogeneous interfaces. Introducing partial metallic character into covalent interactions to form mixed covalent-metallic bonds presents a promising approach to enhance electron transport across such interfaces. In this work, vanadium-carbon (V─C) bonds are established at the interface between selenium-deficient VSe_2-x and graphene via selenium vacancy engineering through in situ growth and subsequent annealing treatment. Selenium vacancies modulate the local charge distribution, enhance metallicity and facilitate electron redistribution, which consequently strengthens the interfacial coupling at the VSe_2-x-graphene interface. Benefiting from these synergistic interactions, resulting coupled VSe_2-x-graphene (co-VSe_2-x-G) anode exhibits exceptional performance in sodium ion battery, achieving over 6000 cycles at 20.0 A g^-1 and 327.6 mAh g^-1 at 75.0 A g^-1. The assembled full cell also maintains high cycling stability beyond 1100 cycles at 3.0 A g^-1. This study offers a novel strategy for improving electronic conductivity at heterogeneous interfaces.