Experimental Studies of Carbon Electrodes With Various Surface Area for Li–O₂ Batteries

Li−O₂ batteries with carbon electrodes made from three commercial carbons and carbon made from waste tea leaves are investigated in this study. The waste tea leaves are recycled from household tea leaves and activated using KOH. The carbon materials have various specific surface areas, and porous structures are characterized by the N₂ adsorption/desorption. Vulcan XC 72 carbon shows a higher specific surface area (264.1 m²/g) than the acetylene black (76.5 m²/g) and Super P (60.9 m²/g). The activated tea leaves have an extremely high specific surface area of 2868.4 m²/g. First, we find that the commercial carbons achieve similar discharge capacities of ∼2.50 Ah/g at 0.5 mA/cm². The micropores in carbon materials result in a high specific surface area but cannot help to achieve higher discharge capacity because it cannot accommodate the solid discharge product (Li₂O₂). Mixing the acetylene black and the Vulcan XC 72 improves the discharge capacity due to the optimized porous structure. The discharge capacity increases by 42% (from 2.73 ± 0.46 to 3.88 ± 0.22 Ah/g) at 0.5 mA/cm² when the mass fraction of Vulcan XC 72 changes from 0 to 0.3. Second, the electrode made from activated tea leaves is demonstrated for the first time in Li−O₂ batteries. Mixtures of activated tea leaves and acetylene black confirm that mixtures of carbon material with different specific surface areas can increase the discharge capacity. Moreover, carbon made from recycled tea leaves can reduce the cost of the electrode, making electrodes more economically achievable. This study practically enhances the discharge capacity of Li−O₂ batteries using mixed carbons and provides a method for fabricating carbon electrodes with lower cost and better environmental friendliness.