Rocking‐chair based lithium‐ion batteries (LIBs) have extensively applied to consumer electronics and electric vehicles (EVs) for solving the present worldwide issues of fossil fuel exhaustion and environmental pollution. However, due to the growing unprecedented demand of LIBs for commercialization in EVs and grid‐scale energy storage stations, and a shortage of lithium and cobalt, the increasing cost gives impetus to exploit low‐cost rechargeable battery systems. Dual‐ion batteries (DIBs), in which both cations and anions are involved in the electrochemical redox reaction, are one of the most promising candidates to meet the low‐cost requirements of commercial applications, because of their high working voltage, excellent safety, and environmental friendliness compared to conventional rocking‐chair based LIBs. However, DIB technologies are only at the stage of fundamental research and considerable effort is required to improve the energy density and cycle life further. We review the development history and current situation, and discuss the reaction kinetics involved in DIBs, including various anionic intercalation mechanism of cathodes, and the reactions at the anodes including intercalation and alloying to explore promising strategies towards low‐cost DIBs with high performance.

Potassium‐based energy storage devices (PESDs) are promising candidates for large‐scale energy storage applications owing to potassiums abundant in nature, the low standard redox potential (−2.93 V for K/K+ vs the standard hydrogen electrode) of potassium (K), and high ionic conductivity of K‐ion based electrolytes. However, lack of proper cathode and anode materials hinder practical applications of PESDs. In this work, carbon nanosheets doped with an ultrahigh content of nitrogen (22.7 at%) are successfully synthesized as an anode material for a K‐ion battery, which delivers a high capacity of 410 mAh g−1 at a current density of 500 mA g−1, which is the best result among the carbon based anodes for PESDs. Moreover, the battery exhibits an excellent cycling performance with a capacity retention of 70% after 3000 cycles at a high current density of 5 A g−1. In situ Raman, galvanostatic intermittent titration, and density functional theory calculations reveal that the ultrahigh N‐doped carbon nanosheet (UNCN) simultaneously combines the diffusion and pseudocapacitive mechanisms together, which remarkably improves its electrochemical performances in K‐ion storage. These results demonstrate the good potential of UNCNs as a high‐performance anode for PESDs.

Potassium-ion batteries are a compelling technology for large scale energy storage due to their low-cost and good rate performance. However, the development of potassium-ion batteries remains in its infancy, mainly hindered by the lack of suitable cathode materials. Here we show that a previously known frustrated magnet, KFeC 2 O 4 F, could serve as a stable cathode for potassium ion storage, delivering a discharge capacity of~112 mAh g −1 at 0.2 A g −1 and 94% capacity retention after 2000 cycles. The unprecedented cycling stability is attributed to the rigid framework and the presence of three channels that allow for minimized volume fluctuation when Fe 2+ /Fe 3+ redox reaction occurs. Further, pairing this KFeC 2 O 4 F cathode with a soft carbon anode yields a potassium-ion full cell with an energy density of~235 Wh kg −1 , impressive rate performance and negligible capacity decay within 200 cycles. This work sheds light on the development of low-cost and high-performance K-based energy storage devices.