Insights into the Dual-Electrode Characteristics of Layered Na_0.5Ni_0.25Mn_0.75O₂ Materials for Sodium-Ion Batteries

Sodium-ion batteries are now close to replacing lithium-ion batteries because they provide superior alternative energy storage solutions that are in great demand, particularly for large-scale applications. To that end, the present study is focused on the properties of a new type of dual-electrode material, Na 0.5 Ni 0.25 Mn 0.75 O 2, synthesized using a mixed hydroxy-carbonate route. Cyclic voltammetry confirms that redox couples, at high and low voltage ranges, are facilitated by the unique features and properties of this dual-electrode, through sodium ion deintercalation/intercalation into the layered Na 0.5 Ni 0.25 Mn 0.75 O 2 material. This material provides superior performance for Na-ion batteries, as evidenced by the fabricated sodium cell that yielded initial charge–discharge capacities of 125/218 mAh g –1 in the voltage range of 1.5–4.4 V at 0.5 C . At a low voltage range (1.5–2.6 V), the anode cell delivered discharge–charge capacities of 100/99 mAh g –1 with 99% capacity retention, which corresponds to highly reversible redox reaction of the Mn 4+/3+ reduction and the Mn 3+/4+ oxidation observed at 1.85 and 2.06 V, respectively. The symmetric Na-ion cell, fabricated using Na 0.5 Ni 0.25 Mn 0.75 O 2, yielded initial charge–discharge capacities of 196/187 μAh at 107 μA. These results encourage the further development of new types of futuristic sodium-ion-battery-based energy storage systems.