Tunable Electrochemical Activity of P2–Na<sub>0.6</sub>Mn<sub>0.7</sub>Ni<sub>0.3</sub>O<sub>2–<i>x</i></sub>F<sub><i>x</i></sub> Microspheres as High-Rate Cathodes for High-Performance Sodium Ion Batteries
Wenpei Kang, Ping Ma, Zhanning Liu, Yuyu Wang, Xiaotong Wang, Huang Chen, Tinglei He, Weicong Luo, Daofeng Sun
Abstract
As an important cathode candidate for the high-performance sodium ion batteries (SIBs), P2-type oxides with layered structures are needed to balance the specific capacities and cycling stability. As a result, a cation and anion codoped strategy has been adopted to tune the electrochemical activity of the redox centers and modulate the structure properties. Herein, a series of P2–Na0.6Mn0.7Ni0.3O2–xFx (x = 0, 0.03, 0.05, and 0.07) cathodes with microsphere structures are synthesized, using a solid-state reaction in the presence of MnO2 microsphere self-templates. Compared with the cation-doped Na0.6Mn0.7Ni0.3O2, additional F-doping can affect the lattice parameters and redox centers of Na0.6Mn0.7Ni0.3O2–xFx. Comprehensively considering the specific capacities, cycling stability, and rate capability, the optimized x value in Na0.6Mn0.7Ni0.3O2–xFx is determined to be 0.05. In the half cells, Na0.6Mn0.7Ni0.3O1.95F0.05 (F-0.05) maintains a capacity of 90.5 mA h g–1 in the first cycle at 1.0 A g–1, giving a capacity retention of 78% within 900 cycles. The superior rate capability of F-0.05 is guaranteed by the larger diffusion coefficient of Na+ (DNa) combined with higher charge transfer speed. In addition, when coupled with MoSe2/PC anodes, the full cells also exhibit impressive electrochemical performance.