From atomic modification to structure engineering: layered NiCo-MnO₂ with ultrafast kinetics and optimized stress distribution for aqueous zinc ion storage

The electrochemical performance of manganese dioxide in aqueous zinc-ion batteries (ZIBs) is still impeded by its inferior conductivity and sluggish chemical kinetics. This paper combines atomic modification and structure engineering strategies for fabricating nickel and cobalt-modified δ-MnO₂ (NCMO) as the cathode material for ZIBs. The ordered nanostructure endows NCMO with uniform and lower stress distributions at various current densities, as evidenced via finite-element simulations. The experimental results further demonstrate the success of the strategy. NCMO exhibits enhanced energy storage capacity and ultrafast ion diffusion kinetics. Moreover, the energy storage mechanism of NCMO is investigated to elucidate the reversible insertion/extraction of H⁺ and Zn²⁺ in δ-MnO₂ during charge/discharge processes. Density-functional theory (DFT) calculations further prove that the atomic modification effect of transition metal ions will reduce the adsorption energy and diffusion barrier of zinc ions, improve the electrical conductivity, and optimize the charge density distributions. The assembled flexible quasi-solid-state NCMO//Zn batteries exhibit stable mechanical flexibility and outstanding electrochemical performance under different bending conditions. Overall, this study suggests a new direction for the rational design of high-performance cathode materials for ZIBs, which can allow for the application of ZIBs in flexible wearable devices.