Oscillatory Current Behavior in Energy Storage Electrode Materials

Abstract

Here we report on unexpected oscillations in current observed during a step potential electrochemical spectroscopy (SPECS) study of manganese dioxide and nickel hydroxide electrodes in an alkaline electrolyte, conditions traditionally considered as a battery system, although more often now associated with electrochemical capacitors. These oscillations in current were observed at short times (<0.5 s) after each potential step in the SPECS experiment and were modelled in a similar fashion to a damped harmonic oscillator. They were associated with capacitive processes in the electrode because of their response time and were interpreted in terms of the competition between the rates of charge transfer and surface charge dissipation from the three-phase boundary between the electroactive material, the conductive additive and the electrolyte in the electrode. The presence of current oscillations in fundamentally insightful but detracts from the overall performance of these electrodes.

Understanding Rapid Intercalation Materials One Parameter at a Time

“…Simplification naturally eliminates completeness where comprehensive models exist with a correspondingly expansive list of fit terms. [ 59,77,153–156 ] As noted above, the parallel model is consistent with two separate sources of current operating in tandem. Here the surface‐limited current source is often interpreted as charge storage within a capacitive near‐surface region whereas the separate diffusion‐limited current source is associated with interior intercalation (Figure 3).…”

“…The parallel model in this context has met with criticism. [ 59,60,63,77 ] Another perspective is that intercalation pseudocapacitance operates by charge storage via normal intercalation with additional rate‐controlling processes such as a surface‐limited faradaic reaction or ohmic drop in the pores. [ 63,78–80 ] As more rapid intercalation processes are discovered it is expected that other processes may increasingly become rate limiting.…”

FIB‐Patterned Nano‐Supercapacitors: Minimized Size with Ultrahigh Performances

“…The volumetric capacitance of NSCs with an interspacing of 100 nm can reach an amazing value of 14 400 F cm −3 , which is even higher than the theoretical maximum pseudocapacitance of 1T'‐MoTe 2 (no more than 8500 F cm −3 , based on calculations21). To assess this atypical phenomenon and investigate the possible charge storage mechanisms of the NSCs, the contributions of faradaic and nonfaradaic processes are analyzed by relating the current ( i ) to sweep rate (ν) in CV experiments, namely where k 1 ν and k 2 ν 1/2 represent the current from adsorption‐controlled EDLC and diffusion‐controlled faradaic processes, respectively 22. As a consequence, making plots of i /ν 1/2 versus ν 1/2 should present an approximate straight line, while k 1 and k 2 are the fitting slope and intercept of the line, respectively.…”

Application of step potential electrochemical spectroscopy in pouch cell prototype capacitors

“…Moreover, it allows separation of charge storage mechanisms, such as electrical double layer and diffusion-limited processes [41,42]. This technique has the potential to characterise the kinetic behaviour of the electrochemical cell over a full range of sweep rates [43] and also to provide additional information about the existence of the residual current such as leakage and self-discharge current, the stability of electrode materials, the ionic mobility of various electrolyte species, the equivalent series resistance of the electrode materials and the effectiveness of the engineering of the device [44][45][46]. The SPECS method has also been used for deconvoluting different charge storage mechanisms such as capacitive and diffusional processes in electrochemical energy storage technologies [43].…”