Potassium-ion batteries(KIBs)are a promising alternative to Lithium-based energy storage systems owning to the low cost and rich abundance of potassium resources,but are facing challenges in designing low-cost hosts that can reversibly accommodate large-size K+with fast diffusion kinetics.Herein,we report a novel 3D inorganic open framework of Ca2Nb2O7(CNO)as an anode for KIBs.The open framework structure affords interstitial vacancies available for storing K+and allows a facile diffusion of K+,thus resulting in excellent structural stability and fast reaction kinetics.The CNO electrode delivers a reversible specific capacity of 65.3 and 52.2 mAh/g at 5 and 10 mA/g,respectively.Moreover,CNO exhibits excellent long-term cyclability with 92.53％capacity retention over 700 cycles at 10 mA/g.This will trigger more investigations into open-framework-based materials for stable and fast KIBs.