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 (KTiOPO₄ ), 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 %). KTiOPO₄ 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.