Life of superoxide in aprotic Li–O2 battery electrolytes: simulated solvent and counter-ion effects. Issue 15 (7th March 2016)

• Record Type: Journal Article
• Authors: Scheers, J.; Lidberg, D.; Sodeyama, K.; Futera, Z.; Tateyama, Y.
• Is Part Of: Physical chemistry chemical physics. Volume 18:Issue 15(2016)
• Page Start: 9961
• Page End: 9968
• Publication Date: 2016-03-07
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c5cp08056h
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Combining DFT-MD and DFT simulations we probe the bond length and the electronic properties of O2 * − in three aprotic solvents – in the presence of Li + or TBA + . Abstract : Li–air batteries ideally make use of oxygen from the atmosphere and metallic lithium to reversibly drive the reaction 2Li + O2 ↔ Li2 O2 . Conceptually, energy throughput is high and material use is efficient, but practically many material challenges still remain. It is of particular interest to control the electrolyte environment of superoxide (O2 * − ) to promote or hinder specific reaction mechanisms. By combining density functional theory based molecular dynamics (DFT-MD) and DFT simulations we probe the bond length and the electronic properties of O2 * − in three aprotic solvents – in the presence of Li + or the much larger cation alternative tetrabutylammonium (TBA + ). Contact ion pairs, LiO2 *, are favoured over solvent-separated ion pairs in all solvents, but particularly in low permittivity dimethoxyethane (DME), which makes O2 * − more prone to further reduction. The Li + –O2 * − interactions are dampened in dimethyl sulfoxide (DMSO), in relation to those in DME and propylene carbonate (PC), which is reflected by smaller changes in the electronic properties of O2 * − in DMSO. The additive TBA + offers an alternative, more weakly interacting partner to O2 * −, which makes it easier to remove the unpaired electron and oxidation more feasible. In DMSO, TBA + has close to no effect on O2 * −, which behaves as if no cation is present. This is contrasted by a much stronger influence of TBA + on O2 * − in DME – comparable to that of Li + in DMSO. An important future goal is to compare and rank the effects of different additives beyond TBA + . Here, the results of DFT calculations for small-sized cluster models are in qualitative agreement with those of the DFT-MD simulations, which suggests the cluster approach to be a cost-effective alternative to the DFT-MD simulations for a more extensive comparison of additive effects in future studies.