Sustainable Free-Standing Electrode from Biomass Waste for Sodium-Ion Batteries

Battery sustainability is often neglected in favor of higher performance and economic efficiency in battery technology. The standard electrode containing the use of binder and toxic solvent has a detrimental impact on the environment. For the first time, a sustainable and free-standing carbonized silk battery anode is prepared from woven silk biomass waste. The unique mechanical structural properties and surface functionality make this material not only avoid the use of binder and organic solvent, but with the possibility of achieving high energy density batteries. An outstanding initial Coulombic efficiency of 75.6 % and a remarkable capacity retention of 100 % after 100 cycles are achieved for the electrode carbonized at 1300 °C (CS_1300 °C) when using a non-volatile and non-flammable superconcentrated ionic liquid electrolyte. A uniformly NaF-distributed solid electrolyte interphase (SEI) layer is produced on the CS_1300 °C surface to facilitate Na⁺ transfer kinetics, and high capacity utilization. Surface functional groups are elucidated by X-ray photoelectron spectroscopy (XPS), while density functional theory calculations reveal that these groups accelerate fast Na⁺ ion adsorption on the surface, but hinder Na⁺ intercalation kinetics due to the strong binding energy from the sodiophilic sites. This scalable and cost-efficient strategy opens up a new avenue for mass-production of battery anode materials, and proposes an argument for the role of surface functional groups in SEI formation and electrochemical performance.