An electric double layer regulator empowers robust solid-electrolyte interphase for potassium metal batteries

The electric double layer (EDL) plays a key role in constructing solid electrolyte interphase (SEI) for high-energy metal anodes. Nevertheless, the significance of EDL and its associated influence remain elusive especially in the potassium metal battery realm. Here we propose an EDL regulation strategy via separator modification targeting durable and longevous potassium metal batteries. We employ universal metal hydroxide combined with sulfur-doped graphene layer and show that the H-bond effect exerted by metal hydroxide could overcome the EDL repulsion thus rearrange the anode interface to enrich anion population. In this sense, a robust inorganic-rich SEI is generated, which manages to sustain dynamic evolutions not only in the initial formation stage but also during the cycling stage. Consequently, uniform and stable potassium electroplating is gained even under harsh conditions, enabling high-rate capability at 10 mA cm^–2 and elongated lifespan over 6000 h at 8.0 mA cm^–2/8.0 mAh cm^–2. Our separator modification concept with vast explored design space offers an appealing path for fast-charging and long-lifespan potassium metal batteries.