From waste to resources: transforming olive leaves to hard carbon as sustainable and versatile electrode material for Li/Na-ion batteries and supercapacitors

Over the last few years, biomass-derived hard carbon materials are drawing more and more attention because of their high abundance, cost breakdown, high performance, and fast regeneration. In this context, the synthesis of hard carbon from olive leaves, a widely available by-product of table olive and olive oil industries, is here reported and its performance, as a sustainable electrode material for Li-ion batteries (LIBs), Na-ion batteries (NIBs), and supercapacitors (SCs), are evaluated. According to the in- formation acquired by structural characterization, a disordered structure is confirmed for the synthesized hard carbon. When tested as anode for LIBs and NIBs, electrodes based on Na-CMC green binder show discharge capacities of 331.0 mAh/g and 265.4 mAh/g at 1C (with minor irreversibility), respectively, with promising cycling stability. In SC application, the electrode delivers a high specific capacitance of 169.6 F/ g at 0.5 A/g and remarkable capacity retention of 96.7% after more than 20,000 cycles at 10 A/g. As a result, this work confirms the possibility to use olive leaves-derived hard carbon material for the low- cost, environmental-friendly fabrication of electrodes with high energy and power capabilities.