Safe, Low‐Cost, Fast‐Kinetics and Low‐Strain Inorganic‐Open‐Framework Anode for Potassium‐Ion Batteries

A key challenge for potassium‐ion batteries is to explore low‐cost electrode materials that allow fast and reversible insertion of large‐ionic‐size K + . Here, we report an inorganic‐open‐framework anode (KTiOPO 4 ), which achieves a reversible capacity of up to 102 mAh g −1 (307 mAh cm −3 ), flat voltage plateaus at a safe average potential of 0.82 V (vs. K/K + ), a long lifespan of over 200 cycles, and K + ‐transport kinetics ≈10 times faster than those of Na‐superionic conductors. Combined experimental analysis and first‐principles calculations reveal a charge storage mechanism involving biphasic and solid solution reactions and a cell volume change (9.5 %) even smaller than that for Li + ‐insertion into graphite (≈10 %). KTiOPO 4 exhibits quasi‐3D lattice expansion on K + intercalation, enabling the disintegration of small lattice strain and thus high structural stability. The inorganic open‐frameworks may open a new avenue for exploring low‐cost, stable and fast‐kinetic battery chemistry.