Effect of pre-treatment conditions on the electrochemical performance of hard carbon derived from bio-waste

Sodium-ion batteries (SIBs) offer several advantages over traditional lithium-ion batteries, including a more uniform sodium distribution, lower-cost materials, and safer transportation options. A promising development in SIBs is the use of hard carbons as anode materials due to their low insertion voltage and larger interlayer spacing, which improve sodium-ion insertion. Traditionally, hard carbons are made from costly carbon sources, but recent advancements have focussed on using abundant bio-waste, like coffee grounds. This approach reduces costs and helps manage global waste. This research investigates the electrochemical performance of bio-waste-derived hard carbons, which is significantly impacted by various pre-treatment methods. Techniques such as BET, XRD, TEM, and XPS are employed to examine the effects of pre-treatment variables, including washing solvents (organic, acidic, or distilled water), pre-oxidation temperatures, and post-heating processes. These factors influence the structural properties and purity of the hard carbon, impacting its effectiveness as an anode material in SIBs. A significant finding is a mesoporous hard carbon produced from coffee grounds that, after washing with distilled water, pre-oxidation at 150 °C, and thermal treatment at 1300 °C in argon, shows a 23% yield, a reversible capacity of 304 mA h g^-1, and Initial coulombic efficiency of 78%. This study underscores the importance of pre-treatments in removing impurities and enhancing the material's sodium storage capabilities.