Life of superoxide in aprotic Li-O-2 battery electrolytes: simulated solvent and counter-ion effects
Artikel i vetenskaplig tidskrift, 2016

Li-air batteries ideally make use of oxygen from the atmosphere and metallic lithium to reversibly drive the reaction 2Li + O-2 <-> Li2O2. 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 (O-2(star-)) 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 O-2(star-) in three aprotic solvents -in the presence of Li+ or the much larger cation alternative tetrabutylammonium (TBA(+)). Contact ion pairs, LiO2 star, are favoured over solvent-separated ion pairs in all solvents, but particularly in low permittivity dimethoxyethane (DME), which makes O-2(star-) more prone to further reduction. The Li+-O-2(star-) 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 O-2(star-) in DMSO. The additive TBA+ offers an alternative, more weakly interacting partner to O-2(star-), which makes it easier to remove the unpaired electron and oxidation more feasible. In DMSO, TBA(+) has close to no effect on O-2(star-), which behaves as if no cation is present. This is contrasted by a much stronger influence of TBA(+) on O-2(star-) 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.

dimethyl-sulfoxide

molecular-dynamics

air batteries

stability

carbonate

acetonitrile

reduction

space gaussian pseudopotentials

anion

instability

Författare

Johan Scheers

Chalmers, Fysik, Kondenserade materiens fysik

David Lidberg

Chalmers, Fysik, Kondenserade materiens fysik

K. Sodeyama

Kyoto University

Japan Science and Technology Agency

National Institute for Materials Science

Z. Futera

National Institute for Materials Science

Y. Tateyama

Kyoto University

National Institute for Materials Science

Japan Science and Technology Agency

Physical Chemistry Chemical Physics

1463-9076 (ISSN) 1463-9084 (eISSN)

Vol. 18 15 9961-9968

Ämneskategorier

Atom- och molekylfysik och optik

DOI

10.1039/c5cp08056h