Na<sup>+</sup>-Activation Engineering in the Na<sub>3</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> Cathode with Boosting Kinetics for Fast-Charging Na-Ion Batteries
Xing Shen, Yuefeng Su, Ni Yang, Xiaoping Jiang, Xingxing Liu, Junlin Mo, Yan Ran, Feng Wu
Abstract
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.