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, wherein about 85% (>330 mAh g) 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) in NIBs but is similar to the graphite anode in LIBs. When coupled with air-stable NaCuFeMnO oxide cathode, a high-energy density of ∼240 Wh kg 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.