Green components for high-power energy storage devices

In response to the need for sustainable energy storage solutions aligned with the European Green Deal, this thesis explores the development of next-generation supercapacitors using scalable and eco-friendly methods. The research integrates waste-derived activated carbon, water-processable binders, and sustainable electrolytes to create an environmentally responsible supercapacitor production process. Chapter 1 introduces the global energy landscape, emphasizing the role of supercapacitors in reducing fossil fuel dependence. The study is structured into three key areas. Chapter 2 focuses on the valorization of biodigester waste into high-performance activated carbon, achieving a surface area of 1867 m²/g and capacitance of 200 F/g in aqueous KOH. Prototypes demonstrated double the capacitance of commercial devices, validating industrial scalability. Chapter 3 investigates biodegradable binders and water-soluble separators as sustainable alternatives to conventional toxic materials. Pullulan-glycerol binders supported large-scale electrode production, achieving a high active material content and competitive performance with green electrolytes like γ-valerolactone and propylene carbonate. Pouch cells assembled with these materials exhibited an energy density of 17 Wh/kg and a power density of 7 kW/kg, with low degradation over cycling. Chapter 4 introduces alternative electrolytes, including water-in-salt electrolytes (WiSE) and deep eutectic solvents (DES), to enhance the electrochemical stability window and increase cell voltage. Symmetric EDLCs with WiSE using potassium acetate achieved superior stability (1.7 V vs. 1.2 V) and capacitance retention over 6000 cycles. Additionally, a patent-pending hybrid redox capacitor using DES-based electrolytes with redox-active species reached an energy density of 108 Wh/kg and a specific power of 30 kW/kg. This research demonstrates the feasibility of sustainable supercapacitors by integrating waste-derived materials, biodegradable binders, and novel electrolytes. The findings contribute to advancing green energy storage technologies, supporting renewable energy systems and electric mobility, while addressing industrial scalability and market applicability.