Customized Electrolyte and Host Structures Enabling High-Energy-Density Anode-Free Potassium–Metal Batteries

Potassium shows great potential to replace lithium in energy storage for its high abundance and comparable energy density. However, issues including an unstable interphase, dendrite growth, and volume change restrict the development of potassium metal batteries, and so far, there is no single cure that works once and for all. Here an anode-free potassium metal battery is demonstrated by introducing a customized electrolyte and host structures that simultaneously promote efficiency, reversibility, and energy density. First, a diluted high-concentration electrolyte with fast kinetics and high stability triggers an inorganic-rich durable interphase. Meanwhile, a carbonaceous host containing narrowly distributed mesopores (MCNF) favors reduced surface area but enough inner space. Together, they achieve a high average Coulombic efficiency (CE) of 99.3% and an initial CE of 95.9% at 3 mA cm–2–3 mA h cm–2. Anode-free MCNF||Prussian blue (PB) potassium cells are delivered with 100 reversible cycles and a high energy density of 362 W h kg–1.