Atomically thin Co₃O₄ nanosheet-coated stainless steel mesh with enhanced capacitive Na⁺ storage for high-performance sodium-ion batteries

Capacitive storage (e.g., double layer capacitance and pseudocapacitance) with Na+ stored mainly at the surface or interface of the active materials rather than inserted into the bulk crystal is an effective approach to achieve high rate capability and long cycle life in sodium-ion batteries (SIBs). Herein, atomically thin Co3O4 nanosheets are successfully synthesized and grown directly on the stainless steel mesh as an anode material for SIBs. This anode delivers a high average capacity of 509.2 mAh g−1 for the initial 20 cycles (excluding the first cycle) at 50 mA g−1, presents excellent rate capability with an average capacity of 427.0 mAh g−1 at 500 mA g−1, and exhibits high cycling stability, which significantly outperforms the electrode prepared from conventional Co3O4 nanostructures, the electrode prepared by conventional casting method, and previously reported Co3O4 electrodes. The superior electrochemical performance is mainly attributable to the atomic thickness of the Co3O4 nanosheets and the direct growth method in electrode processing, which lead to remarkably enhanced surface redox pseudocapacitance and interfacial double layer capacitance. This Na+ capacitive storage mechanism provides a promising strategy for the development of electrode materials with high energy and power densities and ultralong cycle life for SIBs.