Benefits of Copper and Magnesium Cosubstitution in Na0.5Mn0.6Ni0.4O2 as a Superior Cathode for Sodium Ion Batteries

Transition metal oxides are considered to be one kind of the most promising cathode materials for sodium ion batteries. Here, P2-type Na0.5Mn0.6Ni0.2Cu0.1Mg0.1O2 cathode material was designed and synthesized by a solgel method for the first time. The cosubstitution of copper and magnesium in Na0.5Mn0.6Ni0.2Cu0.1Mg0.1O2 inhibits the P-2-O-2 phase transition and enhances lattice spacing to reduce the resistance of sodium ion deintercalation and intercalation, which is beneficial to the improvement of electrochemical properties. A Na0.5Mn0.6Ni0.2Cu0.1Mg0.1O2 electrode delivers an initial specific capacity of 126.1 mAh g(-1) with a high average voltage of 3.6 V (24.6 V) and 96.7% capacity retention after 100 cycles at 0.1C. More importantly, the full cells using this cathode material and hard carbon as anode exhibit initial reversible specific capacity of 70.8 mAh g(-1) with energy density of 226.56 Wh kg(-1) and high capacity retention of 90.1% after 200 cycles at 0.5C. Therefore, Na0.5Mn0.6Ni0.2Cu0.1Mg0.1O2 is able to be a cathode material with high operation voltage, good stability, high energy density, and excellent rate performance for sodium ion battery applications.