A green route to synthesize low-cost and high-performance hard carbon as promising sodium-ion battery anodes from sorghum stalk waste

Sodium-ion batteries（SIBs） have been considered to be potential candidates for next-generation low-cost energy storage systems due to the low-cost and abundance of Na resources. However, it is a big challenge to find suitable anode materials with low-cost and good performance for the application of SIBs. Hard carbon could be a promising anode material due to high capacity and expectable low-cost if originating from biomass. Herein, we report a hard carbon material derived from abundant and abandoned biomass of sorghum stalk through a simple carbonization method. The effects of carbonization temperature on microstructure and electrochemical performance are investigated. The hard carbon carbonized at 1300 ℃ delivers the best rate capability(172 mAh g;at 200 mA g;) and good cycling performance(245 mAh g;after 50 cycles at 20 mA g;,96% capacity retention). This contribution provides a green route for transforming sorghum stalk waste into "treasure"of promising low-cost anode material for SIBs.