Wadsley-Roth (W-R) structured oxides featured with wide channels represent one of the most promising material families showing compelling rate performance for lithium ion batteries. But the structural origin for the fast kinetics of W-R structures is not well understood. Herein, we report an in-depth study on the fast and extensive intercalation chemistry of phosphorus stabilized W-R phase PNb9O25 and its application in high energy and fast-charging devices. We explore the intercalation geometry of PNb9O25 and identify two geometrical types of stable insertion sites with the total amount (2.22 per Nb ion) much higher than conventional intercalation-type electrodes. We reveal the ion transportation kinetics that the Li ions initially diffuse along the open type III channels and then penetrate to type-α edge sites with low kinetic barriers. Through in-situ TEM and ex-situ XRD investigations, we confirm that the whole intercalation/deintercalation process proceeds via a solid-solution behavior with continuous lithium (de)occupying/(re)ordering on the identified insertion sites exhibiting nearly “zero-stress” characteristics. Therefore, the oxide framework of PNb9O25 keeps almost intact with all the fast diffusion channels and insertion cavities well-maintained upon cycling, which accomplishes the unconventional electrochemical performance of W-R structured electrodes.