Direct Regeneration of Sodium-Rich Phosphate Cathode for Sustainable Sodium Ion Batteries

Upcycling degraded cathode is a sustainable way to deal with spent cathode materials. Herein, we found the sodium-rich crystal framework upon the vanadium phosphate cathode intrinsically endows itself with the capability of being thermally healed and in-situ regenerated. It is revealed that thermal modulation enables the de/intercalation activity of excess sodium ions inside the sodium-rich phosphate to realize interior sodium supply, thereby inducing the spent cathode to retrieve lost capacity. In particular, the redistribution of intercalation ions among different sodium crystallographic sites variates the local electronic environment around the transition metal, promoting the spent cathode to recover from a degraded energy state to the initial energy state. Based on this regeneration mechanism, though having experienced 6000 charge–discharge cycles, the regenerated cathode material restores ∼93.9% of its initial capacity, with a sufficient energy density of 440 Wh kg^–1. This work will provide insights into the direct regeneration of the degraded phosphate cathode for sustainable sodium ion batteries.