Controllably Enriched Oxygen Vacancies through Polymer Assistance in Titanium Pyrophosphate as a Super Anode for Na/K-Ion Batteries.

Although sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) are promising prospects for next-generation energy storage devices, their low capacities and inferior kinetics hinder their further application. Among various phosphate-based polyanion materials, titanium pyrophosphate (TiP2O7) possesses outstanding ion transferability and electrochemical stability. However, it has rarely been adopted as an anode for SIBs/PIBs due to its poor electronic conductivity and nonreversible phase transitions. Herein, an ultrastable TiP2O7 with enriched oxygen vacancies is prepared as a SIB/PIB anode through P-containing polymer mediation carbonization, which avoids harsh reduction atmospheres or expensive facilities. The introduction of oxygen vacancies effectively increases the pseudocapacitance and diffusivity coefficient and lowers the Na insertion energy barrier. As a result, the TiP2O7 anode with enriched oxygen vacancies exhibits ultrastable Na/K ion storage and superior rate capability. The synthetic protocol proposed here may offer a simple pathway to explore advanced oxygen vacancy-type anode materials for SIBs/PIBs.