Influence of phosphorus activation and carbonization temperature on the electrochemical performance of hard carbon made from olive pomace as an anode for sodium-ion batteries†

Carbon electrode materials derived from biomass have attracted important interest in studying high-performance electrochemical energy storage devices that are environmentally friendly. Therefore, this study focuses on producing hard carbon (HC) from olive pomace. This is evaluated as a negative electrode in a sodium-ion battery (SIB) with a primary purpose of evaluating the effect of carbonization temperature on HC properties. The preparation of HC from olive pomace was carried out using a chemical activation method with phosphoric acid as an activator and then carbonizing at different temperatures. The generated solid carbon was characterized using various analytical methods, including SEM, HR-TEM, Raman spectroscopy, XRD, FTIR, TGA, and BET. The findings demonstrated that the carbonization temperature significantly affected the morphology, structural characteristics, and disorder level of the synthesized carbon materials. The resultant materials exhibit initial discharge/charge specific capacities for sodium-ion batteries of 307/146, 408/193, and 404/272 mA h g⁻¹ for HC-750, HC-1000, and HC-1250 °C electrodes, respectively, giving an initial coulombic efficiency ratio of 47%, 48%, and 67%. The electrochemical evaluations indicated that HC carbonized at elevated temperatures, particularly at 1250 °C, exhibited superior performance characteristics. Following 100 cycles, a capacity of 248 mA h g⁻¹ was achieved, accompanied by an exceptional capacity retention ratio of 99.9% and good rate capabilities. These results illuminate the significance of the chemical activation process (phosphorus doping) and the carbonization temperature in enhancing electrode performance. By employing this methodology, the utilization of olive pomace effectively yields sustainable biomass-derived HCs in the fabrication of cost-efficient negative materials with enhanced performance for sodium-ion batteries.