Competition between dual alkali metal ions fuels high-performance sodium-ion batteries

Dual alkali metal ion battery is expected to apply in future high-efficiency energy storage applications as it can skillfully combine the advantages of Li+ and Na+. However, the specific insertion and extraction processes of the two ions are not well explained. Herein, a layered sodium transition metal oxide electrode with ordered mixing of Na/Li ions is prepared by ion exchange method. The ion behavior is explained in terms of activation energy of chemical reaction and Gibbs free energy. Based on thermodynamic analysis and material characterizations, the priorities of Na+ and Li+ deblock reactions are determined. The competition mechanism of alkali metal ions and the double gain effect of Li are revealed by electrochemical experiments. This work is expected to provide a positive impact on the future design of multifunctional cathodes for advanced rechargeable batteries.