A Synergistic Na‐Mn‐O Composite Cathodes for High‐Capacity Na‐Ion Storage

Searching for new‐type cathodes to enhance the capacity of Na‐ion batteries is one of the hot spots in energy storage systems. Many sodium insertion transition metal oxides, i.e., Na‐Mn‐O compounds, are intensively studied owing to their high voltage, abundant resources, and low toxicity. However, its relatively low capacity greatly limits its application. Here, a new synergistic composite, 0.44Na4Mn2O5•0.56Na0.7MnO2, is developed by a feasible method of organic‐acid‐assisted drying and heat treatment. This synergistic composite cathode delivers a reversible sodium storage capacity as high as 278.0 mAh g−1 and stable framework structure due to the synergistic effect. It is achieved by the synergistic effect of high capacity Na4Mn2O5 with multiple Na+ ions insert/extract sites and stable Na0.7MnO2 with layered structure. Even when tested at a high mass loading of 7.42 mg cm−2, this composite cathode demonstrates stable cycling over 400 cycles for sodium storage. Moreover, when coupled with hard carbon anode, Na‐ion full battery delivers excellent charge/discharge performance with capacity retention of 84.0%, showing great application potential in the large‐scale energy storage field. Synergistic composite structured xNa4Mn2O5•(1−x)Na0.7MnO2 is synthesized for the first time. The synergistic composite cathode delivers high reversible sodium storage capacity and stable framework structure due to the synergistic effect. The new synergistic composite structured 0.44Na4Mn2O5•0.56Na0.7MnO2 is a promising cathode material for high‐energy density Na‐ion batteries.