Supercapacitor Electrodes at Scale via Electrophoretic Deposition: Graphene Composites with Water-in-Salt Electrolytes

Homogeneous electrode structures in supercapacitors often cause uneven utilization of active materials and create overpotential gradients at the cell level, which harm their electrochemical performance during rapid charge and discharge cycles. To overcome these issues, this study successfully fabricates composite electrode structures with engineered gradients in material distribution using electrophoretic deposition (EPD). These composites of activated carbon (AC) and graphene (G) enhance rate capability and cycling stability compared to conventional uniform electrodes made by slurry casting. EPD electrodes exhibit about 20% higher specific capacitance in both organic and water-in-salt electrolytes (WISE). Additionally, A7 pouch cells equipped with composite and spatially graded G electrodes show superior capacitance retention, with 10–20% improvements at 10–30 A g−1 during cycling compared to pure AC electrodes. High-power performance testing at currents up to 40 A g−1 reveals that graded and 50% G composites outperform 25% G and AC electrodes. Moreover, using three-dimensional porous nickel foam current collectors improves performance by 15% over traditional two-dimensional aluminum foil collectors in both coin and pouch cells. These results suggest that composite and graded G-based electrodes are promising for industrial applications requiring thick electrodes and high dynamic charge rates.