The kinetics of the dissolution and deposition of aluminum from a first generation ionic liquid consisting of AlCl3/1-ethyl-3-methylimidazolium chloride (molar ratio 2:1) was studied. Electrochemical impedance spectroscopy shows that the double layer capacitance and the charge–transfer resistance depend on the state of the electrode surface. The impedance spectra are strongly influenced by mass transport. The rate–determining step of the aluminum deposition, as determined from the cathodic Tafel slope evaluated from current step experiments, was found to be either a chemical step, releasing the complexing agent chloride, while aluminum is in the divalent oxidation state (AlCl3 − → AlCl2 + Cl−) or an electron transfer from the divalent to the monovalent aluminum occurring twice for the overall reaction to occur once (Al2+ + e− → Al+). The rate–determining step for aluminum dissolution was found to be the transfer of an electron from elemental aluminum to the monovalent oxidation state (Al0 → Al+ + e−). A linear slope in the low cathodic overpotential region of the Tafel plot suggests a change in the cathodic rate–determining step. The Tafel slope indicates a chemical step, releasing the complexing agent chloride, after the last electron transfer (AlCl− → Al0 + Cl−) to be the rate–determining step for overpotentials below 50 mV. Density functional theory calculations support the proposed reduction and oxidation mechanisms.

Understanding the electrochemical and morphological properties of the Li-electrolyte interface plays a central role in the implementation of metallic Li in safe and efficient electrochemical energy storage. The current study explores the influence of soluble polysulfides (PS) and lithium nitrate (LiNO3) on the characteristics of the solid electrolyte interphase (SEI) layer, formed spontaneously on the Li surface, prior to electrochemical cycling. Special attention is paid to the evolution of the electrochemical impedance and nanoscale morphology of the interface, influenced by the contact time and electrolyte composition. The basic tools applied in this investigation are electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM) performed at the nanoscale, and X-ray photoelectron spectroscopy (XPS). The individual addition of polysulfides and LiNO3 increases the interface resistance, while the simultaneous application of these components is beneficial, reducing the SEI resistive behavior. The electrochemical cycling of Li in nonmodified 1,2-dimethoxy ethane (DME) and tetraethylene glycol dimethyl ether (TEGDME) based electrolytes leads to slight morphological changes, compared to the pristine Li pattern. In contrast, we found that in the presence of PS and LiNO3, the interface displays a rough and inhomogeneous morphology.

In the introduction of "Aluminum Deposition and Dissolution in [EMIm]Cl-based Ionic Liquids-Kinetics of Charge-Transfer and the Rate-determining Step" [J. Electrochem. Soc. 167, Vol. 10, 102516 (2020)], paragraph four, we stated, that to our knowledge there are no systematic investigations regarding the rate-determining step of the deposition and dissolution of aluminum from [EMIm] Cl-based ILs. Obviously this statement was not correct.Recently, the work of Wang and Hussey regarding aluminum dissolution in high temperature molten salts 1 and [EMIm]Cl-based room temperature ILs (RTIL) 2 was brought to our attention. The authors investigated the kinetics of the dissolution of aluminum in the respective electrolytes and reported an anodic transfer coefficient α a and an exchange current density j 0 of 0.168 ± 0.006 and 190 mA cm −2 for LiAlBr 4 -NaAlCl 4 -KAlCl 4 (30-50-20 m/o) at 151 °C, 1 respectively and 0.19 ± 0.05 (average) and 0.02 mA cm −2 (average) for [EMIm]Al 2 Cl 7 at 32 °C, 2 respectively.The reported anodic transfer coefficients are close to the one determined in our work (α a = 0.17 ± 0.01). Furthermore, Wang and Hussey stated that this indicates a rate-determining step (RDS) involving neither AlCl 4 − nor Al 2 Cl 7 −

The speciation of Cr, Zn, and Sn in AlCl3/1-ethyl-3-methylimidazolium chloride containing CrCl2, ZnCl2, and SnCl2, respectively, has been studied by cyclic voltammetry (CV), Raman spectroscopy and density functional theory (DFT) calculations. Addition of the respective metal salt causes the current waves in the CV to decrease, indicating a reaction of the metal salts with Al2Cl7 -. Compared to the neat electrolyte, the Raman peaks of Al2Cl7 - decrease while the AlCl4 - peak increases in intensity, broadens and shifts towards lower wavenumbers. Calculated wavenumbers of metal complexes [Me(AlCl4)3]- reflect these observations. DFT calculations of the Gibbs free energies of formation, solvation and reaction support the formation of the proposed complexes. The central ions are coordinated by three bidentate AlCl4 - ligands that are arranged planar–trigonally. Due to the occupied Sn–5s orbital, repulsive forces cause a trigonal–pyramidal geometry in case of the Sn complex. Based on the similarities in the experimental observations and the orbital configuration of Zn2+ compared to Cr2+, the spontaneous formation of the species [Cr(AlCl4)3]- can be assumed.

The growing demand for advanced portable electronics and electric vehicles calls for the development of Li-ion batteries with enhanced performance and safety. Among the major goals still to achieve is the improvement of cycling stability and safety, where electrolyte and electrode interfacial properties play a central role. It is generally known that during the first battery charge, a thin film called solid electrolyte interphase (SEI) is formed on the negative electrode due to the decomposition of the electrolyte components. The chemical nature and the morphology of the SEI are important factors for the battery performance. Ideally, the SEI layer is stable and prevents further electrolyte decomposition by blocking the electron transfer through the interface, while concomitantly preserving Li+transport. The most reliable way to control the SEI formation is via electrolyte additives, which have a positive impact on the interface properties without affecting the main electrolyte functions. There is extensive research available on polymerizable additives, where vinylene carbonate (VC) is most widely researched and commercialized. In the last years, however, battery safety is of increasing concern, still limiting the implementation of Li-ion batteries in some industrial fields. In relation to the safety issues one appropriate solution is the design of electrolytes with low flammability. The application of diphenyloctyl phosphate (DPOF) as an additive with a twofold input, acting as a SEI improving and additionally as flame-retarding component was recently reported [1]. However, the structural aspects of the functional improvement of electrode interfacial properties are not fully understood and require further analysis. The central aim of this paper is to correlate the electrical and structural properties of the SEI layer built on the graphite anode under the influence of DPOF and comparison with its commercial analogue - VC. Galvanostatic cycling, cyclic voltammetry and electrochemical impedance spectroscopy (EIS) of graphite anodes were performed in 1M LiPF6in ethylene carbonate (EC) / dimethyl carbonate (DMC) / diethyl carbonate (DEC) (vol. 1:1:1), containing VC or DPOF as additives. The cells with DPOF additive showed the best performance in terms of capacity and rate capability. EIS analysis was performed in symmetric cell configuration, allowing individual interpretation of the impedance parameters for both electrodes [2,3]. After five initial cycles at C/20 used for the formation of the SEI the cells were stopped at 50% SoC and disassembled. The graphite electrodes were re-assembled in symmetric cells, using the same electrolyte type. The EIS spectra of the graphite symmetric cells consist of at least two overlapping semicircles for higher and a Warburg line at low frequencies. They can be fitted by the equivalent circuit proposed in the literature [3], (Fig.1A). In general, the electrical parameters extracted in the presence of the VC closely resemble these of the control cell (without electrolyte additives). After addition of 2% VC EIS showed a slight decrease of SEI resistance R1 and at the same time a minimal increase of SEI capacitance C1. In contrast, the addition of DPOF to the electrolyte resulted in a substantial decrease in R1 and C1. The structural reason for the lower resistance and capacitance of DPOF formed SEI was analysed by means of X-Ray Photoelectron Spectroscopy (XPS). The analysis showed the presence of typically visible SEI features for all samples (Fig. 1B). C1s peaks at around 285eV and 287eV are attributed to a lithium alkyl carbonates. The O1s peaks at 533eV, 532.5eV and 534eV are assigned to σC-O bond in carbonates (Li2CO3 and non–lithiated alkyl carbonates) and O2C=O groups. Beside the discussed C1s components, a low energy peak (dominant for DPOF and less pronounced for VC and control samples) related to the σC-C bonds from the graphite substrate, suggests a formation of much thinner SEI. The F1s core peaks of all samples consist of two main components at 687.0eV and 685.0eV, related to LiPF6 and LiF, respectively. The P2p spectra are composed of one unresolved doublet (2p3/2 and 2p1/2), common for all three samples and attributed to LiPF6. Additionally, the DPOF samples have a component at 136.8eV, originating from decomposed oxidized phosphorous compounds [1]. The correlation of EIS and XPS analysis indicates that the formation of low-resistive and stable SEI by the assistance of DPOF is related to the growth of much thinner and compact structure, containing oxidized phosphorous compounds. References: [1] I. Park, T. Nam, J. Kim, J. Power Sources, 244 (2013) 122-128. [2] R. Petibon, N. Sinha, J. Burns, C. Aiken, H. Ye, C. VanElzen, G. Jain, S. Trussler, J. Dahn J. Power Sources, 251 (2014) 187-194. [3] C. Chen, J. Liu, K. Amine, J. Power Sources, 96 (2001) 321-328. Figure 1