Practical Aspect of Electrophoretic Deposition to Produce Commercially Viable Activated Carbon Supercapacitor Electrode

Abstract

Recent years are seeing many published evidences in the successful electrophoretic deposition (EPD) of energy storage electrodes (notably electrodes for lithium-ion battery [1], solid-state electrolyte [2] supercapacitor [3] and flow batteries [4,5]), but their advancement for industrialization are still far from actual adoption [6]. An obvious reason is because the deposited thickness of the coating’s layer in these studies are very thin (less than 1 mm), which give the extreme performance values that are attributed to a complete utilization of low-density active materials (< 1 mg cm-2) for fast accessibility of electrons and ions through the thin layer to the current collector surface. While these fundamental studies are useful for identifying the maximum achievable properties, they are absolutely impractical for any commercial applications which demand thick layers (50 to 80 µm) and high-density active materials (5 to 20 mg cm-2) to provide usable capacity at all power extraction capabilities.This is particularly true for a packed supercapacitor device whereby it is essential to account for the entire mass of the system, which include current collectors, separators, electrode films, binder, electrolyte, connectors and packing materials [7]. This applies even if the estimation is based upon industrial-level active material mass loadings of 10 mg cm-2 or beyond. In such circumstances, the active material mass is only about 30% of the total weight of the device [8]. This means that the system performance calculated from the electrode property has to be divided by 3 or 4 [9]. The divisor is raised to 30 if a thinner electrode having a mass loading of 1 mg cm-2 is employed [7]. Thus, sufficient mass loading of an electrode is required to lower overheads from inactive materials, which can ensure a decent electrochemical performance for a supercapacitor.In view of closing the knowledge gap between fundamental studies and commercial applications, this presentation will show the practical aspects of energy storage electrodes produced by EPD (Figure 1). Activated carbon (AC) particles are sourced from a commercial supplier, and used as an exemplary system of supercapacitor investigation. Practical supercapacitor electrodes with industrially relevant parameters are demonstrated, specifically high-density active material and thick coating layers. This presentation will discuss: (a) formulation of colloidal electrolyte containing activated carbon particles, (b) methodologies and processes of electrophoretic deposition, (c) use of 2D foil vs 3D microporous structure as deposition substrate, (d) impact of post-process calendaring on electrode properties, and (e) electrochemical cycling activities in coin cell assembly, in particular cyclic voltammogram, capacitance, current density, electrochemical impedance spectroscopy and cycle number in comparison to the performance of a scaled-up AC electrode in an A7 sized pouch cell. Overall, this presentation will emphasize the practical aspects of EPD for producing high-quality commercially viable supercapacitors.