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 owing to their intrinsic safety, low cost, and fast ion-transport kinetics. However, their practical deployment is severely impeded by insufficient energy density, which typically remains below 80 Wh∙kg⁻¹. This limitation is largely attributed to the narrow electrochemical stability window of conventional dilute electrolytes and the resulting electrode degradation. To address this critical bottleneck, this review provides a systematic overview of strategies for enhancing the energy density of AKIBs. Recent advances are comprehensively evaluated from two key perspectives: phase-transition mitigation and structural hydration engineering through water-in-salt electrolytes and hydrogen-bond regulation. Specifically, the evolution of electrolyte design from superconcentrated formulations to cost-effective fluorine-free alternatives and low-salt hybrid concepts is elucidated. Finally, persistent challenges are outlined, and strategic perspectives on interfacial chemistry and realistic full-cell metrics are provided to facilitate the practical development and commercialization of high-energy-density AKIBs.