Na superionic conductor-structured phosphates have attracted wide interest due to their high working voltage and fast Na+ migration facilitated by the robust 3D open framework. However, they usually suffer from low-rate capability and inferior cycling stability due to the low intrinsic electronic conductivity and limited activated Na+ ions. Herein, a doping protocol with Na+ in the V3+ site is developed to activate extra electrochemical Na+ ions and expand the migration path of Na+, leading to the improvement of the electronic conductivity and diffusion kinetics. It is also disclosed that the generated stronger Na-O bonds with high ionicity significantly conduce to the enhanced structural stability in the Na+-substituted Na3.05V1.975Na0.025(PO4)3/C cathode. The obtained composite can deliver an excellent rate capacity of 83.8 mA h g-1 at 20 C and a moderate cycling persistence of 91.3% over 1500 cycles at 10 C with great fast-charging properties. The reversible structure evolution is confirmed by the ex situ XRD, XPS, and ICP characterization. This work sheds light on awakening electroactive Na+ ions and designing phosphates with superior electrochemical stability for practical Na-ion batteries.
Keywords: NASICON cathode; Na-activation engineering; Na-ion batteries; Na3V2(PO4)3; fast-charging performance; structural regulation.