Microtubular carbon fibers derived from bamboo and wood as sustainable anodes for lithium and sodium ion batteries

Herein, a brief and scalable strategy to convert bamboo and woods into uniform hollow cellulose fibers with micrometer-size through a simple delignification process in nitric acid solutions is presented. Next, these cellulose fibers are further transformed into individual microtubular carbon fibers by a carbonization treatment. The evolved carbon fibers show an amorphous organization, large interlayer distances (0.39–0.40 nm) and narrow pore size distributions (0–10 nm), consequently exhibit superior electrochemical performance (vs. Li/Li⁺) in comparison with practical graphite anode. A high reversible capacity of 435 mA h g⁻¹ at 50 mA g⁻¹, as well as competitive rate capacity (up to 150 mA h g⁻¹ at 2 A g⁻¹) and stability over long-term cycling (76% capacity retention at 500 mA g⁻¹ after 500 cycles) is achieved. Furthermore, a majority of reversible capacity was delivered by these carbon fibers at an obvious low discharging-charging potential plateau (0–0.1 V) as lithium ion battery anodes. When the carbon fibers derived from bamboo and paulownia are tested vs. Na/Na⁺, reversible capacities of 320 and 302 mA h g⁻¹ at 50 mA g⁻¹ are delivered, respectively.