Abstract
While Li−carbon monofluoride (CFx) is the current energy leader among primary batteries, the technology is maturing, motivating further fundamental study of Li battery chemistry based on C−F redox. This study examines the possibility to conduct multi-electron carbon reduction using a candidate class of liquid CFx analogues, perfluoroalkyl iodides (CnF2n+1I, with F/C ratios of x > 2), in supporting electrolyte as catholytes for Li cells. The large, polarizable iodine supports electrochemical reduction with concerted F− ligand expulsion, forming lithium fluoride (LiF) as the main solid discharge product. Under initial conditions (1 M reactant and 0.3 mA cm−2 in dimethylsulfoxide), only limited defluorination (1.5 e−/molecule) is accessed. Governing factors for C−F bond redox are further investigated, including reactant concentration, discharge rate, temperature, and solvent properties (e.g. catholyte viscosity). A maximum of 8 e−/C6F13I, or 8/13 available F, is accessible in the voltage range 2.8−1.9 V vs Li/Li+ with low reactant concentrations (0.1 M) and rates (20 μA cm−2). The data indicate that multiple handles exist to tailor extended C−F bond activation in these reactants. However, premature reaction termination caused by deactivation of intermediates, which is particularly exacerbated at higher concentrations and/or rates, is likely to be a persistent challenge for practical applications.
Funder
Lincoln Laboratory, Massachusetts Institute of Technology
Publisher
The Electrochemical Society
Subject
Materials Chemistry,Electrochemistry,Surfaces, Coatings and Films,Condensed Matter Physics,Renewable Energy, Sustainability and the Environment,Electronic, Optical and Magnetic Materials
Cited by
2 articles.
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