Recent advances in rocking chair batteries and beyond

Rocking chair batteries (RCBs) are prominent energy storage systems for applications of electric vehicles and electronic devices due to their potentially high energy densities and long cycle life. In RCBs, the charge carriers shuttle back and forth between the positive and negative electrodes during operation without causing a significant change in the electrolyte composition, namely the rocking mechanism. Over the past few years, researchers have reported a variety of promising RCBs based on metal-ion (e.g. Li⁺, Na⁺, K⁺, Mg²⁺, Zn²⁺, Ca²⁺, and Al³⁺) and nonmetal-ion (e.g. NH₄⁺, Cl⁻ and H⁺) charge carriers. Moreover, the electrode material is gradually beyond the intercalated mechanism. In this review, the critical works of different RCB systems in the recent five years are discussed to provide a full picture of the cutting-edge research frontiers. Then the emphasis is given to their challenges and prospects. Together, this review could provide scientific insights for the development of unique, safe, low-cost, and high-performance RCBs.