A P2-type Na0.44Mn0.6Ni0.3Cu0.1O2 cathode material with high energy density for sodium-ion batteries

Abstract

The lack of high-performance cathode materials is a great challenge for the development of large-scale energy storage sodium ion batteries. Here, a new resource-rich P2-type Na_0.44Mn_0.6Ni_0.4−xCu_xO₂ (0 ≤ x ≤ 0.3) sodium-ion battery (NIBs) cathode material was designed and synthesized by a sol–gel method. Na ions occupy the Na_f sites and the Na_e sites in a proportion of 1 : 1, which maintains the high symmetry and stability of the P2-type structure. The charging/discharging tests show that Na_0.44Mn_0.6Ni_0.3Cu_0.1O₂ has a high initial capacity of 149 mA h g⁻¹ and 80% capacity retention after 50 cycles at 0.1C, showing a high energy density of 469 W h kg⁻¹. The addition of inactive copper enhances the lattice spacing, obviously reducing the irreversible reaction resistance (R_f) during the intercalation and deintercalation of Na⁺, thereby reducing the internal resistance of the battery and improving the cycle performance. In order to maintain the P2-type structure, the voltage is controlled at 1.5–4.0 V during charging and discharging, which inhibits the phase transition of P2-O2, leading to the improvement of cycling performance. Therefore, the Cu-substituted Na_0.44Mn_0.6Ni_0.3Cu_0.1O₂ possibly serves as a promising high capacity, high energy density and stable cathode for sodium ion battery applications.