Employing high-rate ion-intercalation electrodes represents a feasible way to mitigate the inherent trade-off between energy density and power density for electrochemical energy storage devices, but efficient approaches to boost the charge-storage kinetics of electrodes are still needed. Here, we demonstrate a water-incorporation strategy to expand the interlayer gap of α-MoO₃, in which water molecules take the place of lattice oxygen of α-MoO₃. Accordingly, the modified α-MoO₃ electrode exhibits theoretical-value-close specific capacity (963 C g⁻¹ at 0.1 mV s⁻¹), greatly improved rate capability (from 4.4% to 40.2% at 100 mV s⁻¹) and boosted cycling stability (from 21 to 71% over 600 cycles). A fast-kinetics dual-ion-intercalation energy storage device is further assembled by combining the modified α-MoO₃ anode with an anion-intercalation graphite cathode, operating well over a wide discharge rate range. Our study sheds light on a promising design strategy of layered materials for high-kinetics charge storage.