High-temperature treatment induced carbon anode with ultrahigh Na storage capacity at low-voltage plateau

Sodium-ion batteries (NIBs) show great prospect on the energy storage applications benefiting from their low cost and the abundant Na resources despite the expected lower energy density compared with lithium-ion batteries (LIBs). To further enhance the competitive advantage, especially in energy density, developing the high-capacity carbon anode materials can be one of the effective approaches to realize this goal. Herein, we report a novel carbon anode made from charcoal with a high capacity of ∼400 mAh g^-1, wherein about 85% (>330 mAh g^-1) of its total capacity is derived from the long plateau region below ∼0.1 V, which differs from those of typical hard carbon materials (∼300 mAh g^-1) in NIBs but is similar to the graphite anode in LIBs. When coupled with air-stable Na_0.9Cu_0.22Fe_0.30Mn_0.48O₂ oxide cathode, a high-energy density of ∼240 Wh kg^-1 is achieved with good rate capability and cycling stability. The discovery of this promising carbon anode is expected to further improve the energy density of NIBs towards large-scale electrical energy storage.