Electrolyte materials and interfacial engineering for high-energy-density aqueous potassium-ion batteries

Aqueous potassium-ion batteries (AKIBs) have emerged as highly attractive candidates for grid-scale energy storage due to their intrinsic safety, low cost, and fast ion transport kinetics. However, their practical deployment is severely impeded by insufficient energy density, typically falling below 80 Wh kg^-1, which is largely attributed to the narrow electrochemical stability window of conventional dilute electrolytes and subsequent electrode degradation. To address this critical bottleneck, this article provides a systematic overview dedicated to boosting the energy density of AKIBs. We comprehensively evaluate recent advances from two key dimensions: phase-transition mitigation and structural hydration engineering through water-in-salt electrolytes and hydrogen-bond regulation. Specifically, the evolution of electrolyte design from super-concentrated formulations to cost-effective fluorine-free alternatives and less salt hybrid concepts are elucidated. Finally, we outline persisting challenges and offer strategic outlooks regarding interfacial chemistry and realistic full-cell metrics to facilitate the practical development and commercialization of high-energy-density AKIBs.