Scalability of Electrode Supercapacitor Technologies

Supercapacitors, also known as electrochemical capacitors, have gained significant attention due to their high power density, rapid charge-discharge cycles, and long cycle life. However, while their features are well-established in small-scale devices and laboratory settings, transitioning to large-scale production poses significant challenges. This thesis focuses on the scalability aspects of supercapacitor electrode technology through a roll-to-roll (R2R) process, in which water-based slurry are used as the main vehicle for coating. In first analysis the rheology of the slurries was under investigation, in order to extrapolate information about how the slurry behaves when it's disrupted. Properties such as viscosity, viscoelasticity and time response to a shear stress are useful parameters that define the quality of the coating in a R2R process. The goal was to reproduce an ink slurry, considered as a reference for the R2R coating, with different material and improve its recipe so that it'll be repeatable. As a factor for improving the electrode's performance, the calendering step has been taken into consideration. The purpose of calendering is to enhance, by heat compression, the adhesion between electrode surface and current collector and reduce the porosity of the substrate, mainly for refine the electrode's structure and decrease internal parasitic resistance. The study was made to define the effectiveness of this step in terms of actual improvements and time required to perform it. The electrodes taken into account for the scaling process are different in terms of physics working principle: Electrical Double Layer Capacitor (EDLC) and Pseudo-capacitor (PS). Activated carbon was used as EDLC active material, in particular the coconut-shell derived YP series, provided by the manufacture Kuraray Coal, as it can provide high surface area per active material. Transition metal-oxide MnO2 was the choice for the pseduo-capacitive one, whose synthesis was performed in laboratory by mixing MnSO4 H2O and KMnO4 in water solution. First, the manufacture and characterization of electrodes was made in a laboratory environment, for extrapolate reference parameters like specific capacitance and bias window potential, and in order to compare them with the actual State of the Art. With the prospect of higher-performance and lower cost devices, with a environment friendly outlook on the use of materials, the K-ion device idea was selected for this thesis. The choice of KPF6 as the electrolyte salt was made for its properties and availability. Symmetric and asymmetric configurations, with the same electrode or different one, were also tested in order to define which is the best in terms of performance, first in small devices and then in bigger one where the electrodes manufacture were made with a R2R machine. As a future perspective in the field of supercapacitor, it was investigated the concept of hybrid configuration, in which a EDLC/PS electrode was combined with a battery-like one; in this case, carbon-black C65 was considered as active material.