Approximately four billion discarded tires end up in landfills each year due to inadequate recycling, contributing to severe environmental concerns. Transforming waste tires into carbon powder for alkali-ion battery anodes presents a promising recycling solution, yet heavy metals and unwanted elements hinder electrochemical performance. Conventional purification methods rely on harsh chemicals like concentrated sulfuric acid and hydrofluoric acid, which pose environmental and scalability issues.
This study proposes a green alternative using hydrothermal treatment to leach impurities while preserving the carbon precursor’s structural integrity. Through multiple-phase analyses, we demonstrate the effects of hydrothermal oxidation, which facilitates the removal of inorganic contaminants and enhances electrochemical performance. Characterization techniques reveal that the hydrothermal process induces rubber degradation through hydroxyl radical-assisted oxidation, forming water-soluble compounds that favor impurity leaching. Complete removal of Ca, Al, Co, Ti, Cu, P, Cl, and K occurs at any temperature, while Si, Fe, Zn, and S leaching increases at lower temperatures.
Post-treatment characterization shows a transition to an sp² carbon structure, with Raman spectroscopy confirming increased basal plane formation. The electrochemical performance of the derived hard carbon is validated for Li, Na, and K-ion batteries, exhibiting long-term cycling stability over 200 cycles. The absence of an electrochemical plateau at 0–0.05V confirms the lack of porosity, while charge-discharge analysis correlates structural features with performance.
The proposed hydrothermal process successfully purifies and activates waste tire-derived carbon, offering a sustainable and cost-effective alternative to conventional pyrolysis. By combining leaching and carbon structure enhancement, this approach treats tire waste and produces high-performance anode materials suitable for alkali-ion batteries.