Simulations and Interpretation of Three-Electrode Cyclic Voltammograms of Pseudocapacitive Electrodes

Abstract

This study aims to provide physical interpretation of cyclic voltammograms obtained from pseudocapacitive electrodes using three-electrode systems. It presents numerical simulations based on a recent continuum model able to reproduce experimental CV curves obtained with different Nb 2 O 5-based electrodes and LiClO 4 in propylene carbonate as electrolyte. First, the respective contributions of faradaic and electric double layer charge storage mechanisms were clearly identified along with the associated faradaic and capacitive regimes. This was further illustrated by comparing CV curves for pseudocapacitive (Nb 2 O 5) and EDLC (carbon) electrodes. Transition from the faradaic to the capacitive regime was caused by Li + starvation at the electrode/electrolyte interface and the formation of ClO − 4 electric double layer. Moreover, the effects of electrode crystallinity on CV curves were reproduced and interpreted in terms of enhanced transport properties for lithium intercalation and electrode electrical conductivity. Finally, the electrode thickness featured an optimum corresponding to a compromise between accommodating large amounts of intercalated lithium and minimizing the potential drop across the electrode to drive faradaic reactions. 2 Nomenclature a Effective ion diameter (nm) b b-value, power constant in j t = a v b c Ion concentration (mol/L) c max Maximum ion concentration, c max = 1/N A a 3 (mol/L) C s,int Integral areal capacitance (F/m 2) c 1,P,0 Initial concentration of intercalated Li in the pseudocapacitive electrode (mol/L) c 1,P,max Maximum concentration of intercalated Li, c 1,C,max = m ρ/M (mol/L)

Electrochemical Characterization of Na-Ion Charge-Storage Properties for Nanostructured NaTi2(PO4)3as a Function of Crystalline Order

“…49 Greater capacitive contribution outside the potential regions of the redox peaks also suggests a higher capacitive contribution arising from the electric double layer, which was also observed by experimental and numerical predictions of pseudocapacitive T-Nb 2 O 5 . 51 The aforementioned analysis underscores the key finding that amorphous NTP is able to store charge under a surface-limited regime whereas nanocrystalline NTP is limited by semi-infinite diffusion. In addition, in order to enhance charge-storage kinetics, it is crucial to incorporate a conductive carbon network (rGO) to improve through-conductivity of the bulk electrode film.…”

Multidimensional Cyclic Voltammetry Simulations of Pseudocapacitive Electrodes with a Conducting Nanorod Scaffold

“…Figures 9a and 9b also show C T,g and C T,B ET as functions of L r for a planar electrode with the same electrolyte and electrode properties for scan rate v = 1 V/s. 55 The predicted values of the total gravimetric capacitance C T,g ranged between 20 F/g and 200 F/g. These values were comparable with capacitances measured for electrodes with similar morphologies and ranging between 60 F/g and 800 F/g.…”

“…Note that for given electrode and electrolyte dimensions, the total capacitance C T,g or C T,B ET for planar pseudocapacitive electrodes increased with increasing electrical conductivity σ P and ion diffusion coefficient D 1, p in the electrode. 55 Moreover, during charging, transport properties D 1, p decreased 98 and σ P increased [99][100][101] due to the presence of Li + intercalated in the metal oxide structure. The dependence of D 1, p and σ P on the local intercalated Li + concentration does not seem to be available in the literature and accounting for these processes falls outside the scope of the present simulations.…”

“…53 Moreover, experimental characterization of pseudocapacitive electrodes typically uses a three-electrode configuration with the pseudocapacitive electrode of interest serving as the working electrode along with a counter electrode and a reference electrode. 7,[9][10][11]15,19,20,22,23,[26][27][28]30,31,33,36,[59][60][61] Girard et al 55 simulated three-electrode experiments for planar pseudocapacitive electrodes supported by a planar current collector. Such one-dimensional simulations qualitatively reproduced experimental measurements and provided qualitative physical interpretation of experimentally measured cyclic voltammograms for dense and porous Nb 2 O 5 electrodes in LiClO 4 /PC electrolyte.…”

“…39,[45][46][47][48][49][50][51][52][53][54][55] They investigated the effect of electrode composition, 45,49 solid-state ion diffusion in the electrode, 46 and moving reaction fronts. 50 These models assumed constant double layer capacitance throughout the charging/discharging cycle period and uniform ion concentrations throughout the electrolyte.…”