Robust Pseudocapacitive Sodium Cation Intercalation Induced by Cobalt Vacancies at Atomically Thin Co_1-x Se₂...

Electronic structure engineering on electrode materials could bring in a new mechanism to achieve high energy and high power densities in sodium ion batteries. Herein, we design and create Co vacancies at the interface of atomically thin CoSe₂ /graphene heterostructure and obtain Co_1-x Se₂ /graphene heterostructure electrode materials that facilitate significant Na⁺ intercalation pseudocapacitance. Density functional theory (DFT) calculation suggests that the Na⁺ adsorption energy is dramatically increased, and the Na⁺ diffusion barrier is remarkably reduced due to the introduction of Co vacancy. The optimized electrode delivers a superior capacity of 673.6 mAh g^-1 at 0.1 C, excellent rate capability of 576.5 mAh g^-1 at 2.0 C and ultra-long life up to 2000 cycles. Kinetics analysis indicates that the enhanced Na⁺ storage is mainly attributed to the intercalation pseudocapacitance induced by Co vacancies. This work suggests that the creation of cation vacancy could bestow heterostructured electrode materials with pseudocapacitive Na⁺ intercalation for high-capacity and high-rate energy storage.