Enhanced Lithium Storage in Hierarchically Porous Carbon Derived from Waste Tea Leaves

In this study, highly nanoporous carbon (HCl-TW-Car) was successfully synthesized using a facile procedure combining acid treatment with a carbonization process that uses waste tea leaves from spent tea bags as raw materials. The acid treatment not only promotes the efficient removal of unnecessary inorganic impurities but also increases the product porosity to enable synthesis of hierarchically porous carbon materials with various micro-, meso-, and macropores. When used as an anode material for lithium-ion batteries, HCl-TW-Car demonstrated a much higher discharge capacity than is theoretically possible using graphite [479 mAh g−1 after the 200th cycle at a rate of 0.2C (1C = 372 mA g−1)] and exhibited greater rate capabilities compared with those of carbonated products from tea waste without acid treatment. It was shown that the good electrochemical properties of HCl-TW-Car can be ascribed to large Brunauer–Emmett–Teller (BET) surface area, well-formed hierarchical pores, and the prevention of unexpected electrochemical reactions from the reduction of metallic atoms.