Electrochemical Deposition and Dissolution Processes of Lithium Compound on Gold from Propylene Carbonate

Abstract

The cathodic electrolysis of propylene carbonate containing lithium perchlorate was studied by means of an in-situ quartz crystal microbalance technique. A lithium compound was deposited at about +1.5 V vs. Li/Li+ and dissolved at about +4.0 V vs. Li/Li+. In constant potential electrolysis at +0.9 V vs. Li/Li+, the deposition process was divided into two stages. In the first stage, in which lithium carbonate was most probably deposited, an electrode reaction of ferrocene which was added to the solution was gradually retarded. In the second stage, in which some chemical reaction proceeded dominantly, the electrode reaction of ferrocene was almost completely blocked. A cathodic charge of +3.0 mC cm−2 was necessary for almost complete blocking.

Surface Film Formation and Lithium Underpotential Deposition on Au(111) Surfaces in Propylene Carbonate

“…The formation of the surface film on a noble metal electrode at potentials more negative than 1.5 V has been confirmed in several reports by using Fourier transform infrared ͑FTIR͒, X-ray photoelectron spectroscopy ͑XPS͒, electrochemical quartz crystal microbalance ͑EQCM͒, and surface-enhanced Raman scattering ͑SERS͒. 15,[21][22][23][24][25][26] The dominant compositions of the surface film were considered as ROCO 2 Li and/or Li 2 CO 3 , which were produced as a result of the one-or two-electron reduction of the solvent. 17,18 Actually, the cathodic charge between 2.0 and 1.0 V in the first scan of CV ͑Fig.…”

“…3aЈ͒. The EQCM measurement showed that the surface film formed on a gold electrode in PC solution containing LiClO 4 or LiAsF 6 at potentials more negative than 1.5 V did not dissolve even when the potential became as positive as 3.0 V. [23][24][25] The gold surface shown in Fig. 3a captured at 2.5 V is expected to be still covered with the surface film.…”

“…Actually, the surface film formation was reported to take place in this potential region during the several initial scans. [23][24][25] Thus, the worm-eaten holes observed in Fig. 3a are concluded to be the holes in the surface film, not in the gold.…”

Analyses of passivation films on lithium and lithium alloys by electrochemical quartz crystal microbalance

“…Comparing the two electrolyte solutions, the frequency changes in the PC-based electrolyte were more than those in the EC-based electrolyte indicating that the amount of passivation films in the PC-based electrolyte was greater than that in the EC-based electrolyte. It was supposed that the resistance in the PC-based electrolyte would also be greater than that in the EC-based electrolyte because the passivation films formed on deposited Li would act as the resistances for Li deposition and dissolution, as many researchers have already reported [13][14][15]. Fig.…”

“…From these results, the passivation film formations of the Pt substrate were supposed to be suppressed compared with the Ti substrate because of electrochemically alloying Li with Pt, preventing side reactions between deposited Li and electrolytes. Also, the change in the surface roughness of the EQCM substrate during chemical reactions is known to affect the resonance frequencies [3,13]. Kanamura et al [3] reported that the Li surface roughness always increased during Li deposition on the Ni substrate of EQCM, which does not alloy with Li, and it was suppressed when a small amount of HF was added to the electrolyte solution to form desirable solid-electrolyte interphase (SEI) on deposited Li.…”