Capacitive energy storage from single pore to porous electrode identified by frequency response analysis

Abstract

Rate capability, peak power, and energy density are of vital importance for the capacitive energy storage (CES) of electrochemical energy devices. The frequency response analysis (FRA) is regarded as an efficient tool in studying the CES. In the present work, a bi-scale impedance transmission line model (TLM) is firstly developed for a single pore to a porous electrode. Not only the TLM of the single pore is re-parameterized but also the particle packing compactness is defined in the bi-scale. Subsequently, the CES properties are identified by FRA, focused on rate capability vs. characteristic frequency, peak power vs. equivalent series resistance, and energy density vs. low frequency limiting capacitance for a single pore to a porous electrode. Based on these relationships, the CES properties are numerically simulated and theoretically predicted for a single pore to a porous electrode in terms of intra-particle pore length, intra-particle pore diameter, inter-particle pore diameter, electrolyte conductivity, interfacial capacitance & exponent factor, electrode thickness, electrode apparent surface area, and particle packing compactness. Finally, the experimental diagnosis of four supercapacitors (SCs) with different electrode thicknesses is conducted for validating the bi-scale TLM and gaining an insight into the CES properties for a porous electrode to a single pore. The calculating results suggest, to some extent, the inter-particle pore plays a more critical role than the intra-particle pore in the CES properties such as the rate capability and the peak power density for a single pore to a porous electrode. Hence, in order to design a better porous electrode, more attention should be given to the inter-particle pore.