Structural stability of P2-Na0.67Fe0.5Mn0.5O2 by Mg doping

As a cathode material for sodium-ion batteries (SIBs), P2-Na0.67Fe0.5Mn0.5O2 has the advantages of high capacity and high working voltage. However, the irreversible phase transition of P2-O2 causes the electrochemical performances to rapidly decline with cycling. The phase stability and therefore cycle stability could be effectively improved by cation doping. The precursor Fe0.5Mn0.5CO3 is prepared by coprecipitation method. The initial discharge-specific capacity of P2-Na0.67Fe0.5Mn0.5O2 in the voltage range of 2–4.3 V is 164 mAh·g−1, and its capacity retention rate after 100 cycles is 48.6%. Mg doping can improve the cycling stability and rate capability, while slightly reducing the initial capacity. The capacity retention is improved from 48.6 to 75.3% with Mg doping.