Improving rate capability and cycling stability of P2-type sodium-ion layered cathode by synergistic effect of K/Ti co-doping strategy

As the sodium host, the P2-NaxMnO2 cathode suffers from multiple structural transformations caused by the Jahn-Teller distortion, incurring rapid voltage decay and capacity degradation of the sodium-ion batteries. Herein, K and Ti elements have been co-doped into the P2-NaxMnO2 to adjust the Na+/vacancy ordering and to reduce the Jahn-Teller distortion-caused structural transformations by lowering the Mn3+ concentration. The prepared P2-Na0.66K0.01Mn0.9Ti0.1O2 shows high structural stability and rate performance with capacity retention of 87.4% after 200 cycles at a current density of 200 mA g−1, which is 60% higher than that of Na0.67MnO2. Moreover, the P2-Na0.66K0.01Mn0.9Ti0.1O2 also exhibits a good rate performance of 95.4 mAh g−1 at the same current density (74 mAh g−1 for Na0.67MnO2). The ex-situ XRD analyses demonstrate that the remarkable electrochemical performance of Na0.66K0.01Mn0.9Ti0.1O2 cathode should benefit from the high structural stability during the charge and discharge process and the improved diffusion kinetics.