Multi-ion strategies towards emerging rechargeable batteries with high performance

The development of lithium-ion batteries (LIBs) is hindered by the limited lithium resources and their uneven geographical distribution. Novel rechargeable batteries based on abundant elements (e.g., Na+, K+, Mg2+, Ca+, Zn2+, Al3+) show great promising alternatives to LIBs. However, several challenges still remain for these emerging batteries, such as sluggish kinetics, poor reversibility, lack of suitable electrode materials, etc., induced by large radius and/or high charge density of primary ions. Among various strategies to address these challenges, multi-ion strategies show great feasibility to enhance the electrochemical performance of these emerging rechargeable battery systems. These multi-ion strategies involve electrochemistry of multiple ions in different electrode materials and electrolytes, and are devoted to combining individual merits of multiple ions as primary ions in rechargeable batteries. So far, several multi-ion strategies have been proposed, including dual-ion, triple-ion, and quadruple-ion strategies. It is demonstrated that such strategies, not only are beneficial to enhance diffusion kinetics and cycling reversibility, and/or to increase working voltage, but also provide more options of electrode materials for these emerging rechargeable batteries. In this review, we outline the challenges involved in these emerging rechargeable batteries. The fundamental configurations and corresponding reaction mechanisms of multi-ion strategies are tangibly discussed. Then, special focuses are on the applications of multi-ion strategies in merging rechargeable batteries, in which we elaborate and discuss in detail the enhanced effect of multi-ion strategies on electrochemical performance. Finally, the state-of-the-art challenges and the future directions of multi-ion strategies are highlighted and discussed.