Performance of Na0.44Mn1-xMxO2 (M = Ni, Mg; 0 ≤ x ≤ 0.44) as a cathode for rechargeable sodium ion batteries

The influence of partial substitution of manganese by nickel or magnesium in Na(0.44)MnO(2)on cathode performance in sodium ion batteries has been investigated. Partial substitution changes the structure of parent Na0.44MnO2 from tunnel into layered P2-type, or a mixture of P2- and P3-type materials. Substitution smoothes the charge/discharge curves and may significantly improve capacity, albeit with a lower capacity retention relative to pristine Na0.44MnO2. In particular, high discharge capacities are found in the voltage range 2.0-4.2 V at 0.1 C rate for Na0.44Mn0.89Ni0.11O2 (193 mAh g(-1)) and Na0.44Mn0.89Mg0.11O2 (188 mAh g(-1)), with a capacity retention of 74% and 81%, respectively, after 70 cycles.