Identifying lithium–air battery discharge products through 6Li solid-state MAS and 1H–13C solution NMR spectroscopy

Abstract

Discharged lithium–O2 battery cathodes are investigated with different catalysts present including Pd, α-MnO2 and CuO, and containing two different electrolyte solvents, 1:1 ethylene carbonate/dimethyl carbonate (EC/DMC) and tetraethylene glycol dimethyl ether (TEGDME). Solid-state 6Li magic angle spinning (MAS) NMR spectroscopy has been used identify lithium products that are formed in the cathodes and differences between products formed with the different catalysts and solvents. There are significant differences in the products formed in Li–O2 cathodes with the two different solvents, EC/DMC and TEGDME. Due to the small chemical shift range of lithium it is difficult to determine exact speciation from 6Li MAS NMR data alone. Fitting of the 6Li NMR peaks with tested Li-oxide powder standards indicates that Li–O2 cathodes discharged in EC/DMC produce primarily Li2CO3 as a lithium product and those discharged in TEGDME produce mainly Li2O2. Solution 2D correlation 1H–13C NMR spectroscopy techniques allow for determination of side-products produced in Li–O2 cathodes.