Time Evolution of the Impedance Response of a Passive Film: A Simple Application to the Li / SOCl2 system

Abstract

In the 1970s and the beginning of the 1980s the passive film formed on lithium in SOCl 2 -based solutions was a subject of numerous investigations, primarily because it was regarded as a cause of the so-called voltage-delay phenomenon, which, at that time, was a major drawback of the Li/SOCl 2 batteries. To many researchers, however, the system remained interesting even after the voltage-delay problem had been solved (by different electrolyte additives and/or modifications). The persisting interest in this particular lithium system can be explained by several facts: (i) in this system the lithium passive film has a simple composition (basically LiCl), (ii) the electrochemical properties (e.g., the impedance response) of this film have been considered simple to model, (iii) the film electrochemical properties show big and hence easy-to-measure variation with storage time, and (iv) during investigation of the "voltage-delay phenomenon," a huge amount of data using many different techniques were gathered, many of which have remained unexplained or even in direct contradiction. The present paper is an attempt to clarify several of these inconsistencies, particularly those concerning the impedance spectroscopy and related measurements of the passive film.The techniques used to study the spontaneous nucleation and growth of the passive film under consideration have been the potential sweep and step (or pulse) experiments, 1-5 impedance spectroscopy measurements, 6-11 microcalorimetry, 9,12 scanning electron microscopy (SEM), 7,10,13-15 measurements of weight gain of a Li electrode during storage in the electrolyte, 16 and the isotope method. 8 With regard to the kinetics of the initial coverage of the lithium surface with a passive film, most authors have given qualitative estimations such as, "Immediately 4,8,17 after its contact with the electrolyte, the Li surface is covered with a thin passivating film." A more quantitative result was obtained by Hedges et al. 2 who, in microelectrode studies of the Li/Li ϩ couple, found that "a period on open circuit of 100 s is long enough for the formation of a film of thickness sufficient to inhibit corrosion..." (In that experiment 1.7 M solution of LiAlCl 4 in SOCl 2 was used.) Even more specific results were obtained by Moshtev et al., 3 who found it possible to determine the moment when the lithium surface was 100% covered with a thin protective film using the galvanostatic pulse technique. Although not explicitly given in Ref. 3, one may recalculate from Fig. 2 and 3 of that paper that the coverage was completed about 30-40 min after lithium had been exposed to the electrolyte. At that moment the calculated average film thickness was 3.2 nm. Moshtev et al. 3 also reported that after the Li surface had been covered, the dense primary film grew thicker with storage time to reach a thickness of about 10-30 nm within a period of 6 h. Similar results were obtained by Holleck and Brady, 4 who reported that the primary film reached a thickness of 30 nm within 1-20 h after the ex...

Nonaqueous Liquid Electrolytes for Lithium-Based Rechargeable Batteries

“…It is generally accepted that the semicircle at medium frequency corresponds to the ionic migration process in the SEI and the one at lower frequency to the charge-transfer process on lithium, whereas the intercept at the high frequency end with the real axis represents bulk electrolyte resistance. Examination of the interfacial resistance in various electrolyte solutions reveals that the SEI on lithium grows with time of exposure to electrolytes, and the chemical nature of both solvent and salt anion seems to relate closely to the semicircle for the interfacial film. ,− For example, the resistance of the SEI that formed in the LiPF 6 -based electrolyte is smaller than the one formed in the LiClO 4 -based electrolyte, and the presence of EC also renders a more conductive SEI on lithium. ,− An empirical rule (with frequent exceptions though) might be stated here concerning the resistance of the SEI: an electrolyte with higher bulk ion conductivity usually results in an SEI of lower impedance, either on a lithium or carbonaceous electrode, as will be discuss in later sections.

10 Impedance complex plane (Nyquist plots) of lithium electrode in (A) 1.0 M LiPF 6 /EC/PC and (B) 1.0 M LiClO 4 /EC/PC at initial time (0.0 h) and after 24 h. Re and Im stand for the real and imaginary parts of the impedance measured, respectively.

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Solid Electrolyte Interphase Growth on Mg Metal Anode: Case Study of Glyme‐Based Electrolytes

“…The values of L SEI calculated from Equation (3) are, on the other hand, unrealistically small, as previously observed for Li metal electrodes. [ 23 ] To circumvent this problem, Aurbach and others suggested additional assumption that the SEI consists of several mechanically coherent layers on top of each other. [ 11b,24 ] This has however not been experimentally proven.…”

“…[ 25 ] It is rather probable that the observed semicircle corresponds to a composite material, which cannot be approximated by a parallel‐plate capacitor and contains the additional response of concentration polarization or desolvation (4× higher in Mg electrolytes compared with Li(Na) counterparts). [ 23,26a,b,c,27 ] The values of these contributions are hard to estimate as values of Mg transference numbers or desolvation resistances are not readily available from the literature. Indeed, if this semicircle is considered to be solely due to diffusion in the liquid part of the SEI encapsulated in the porous solid, then Ldiff appears to be only one order of magnitude lower than electrolyte thickness.…”

Synthesis of Si-Sb-ZnO Composites as High-Performance Anodes for Lithium-ion Batteries

“…All the plots were composed of semicircles with a large radius of curvature and sloping lines. The semicircle in the high-frequency intercept represents the contact resistance without lithium insertion, charge transfer, and lithium-ion diffusion at the open voltage [26, 27]. The inset of Fig.…”