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Abstract: The effects of six types of aprotic organic solvents on the discharge performance and discharge products in Li-O2 batteries are systematically investigated. A large amount of Li2O2 is identified in the air electrodes discharged in glyme-based electrolytes, while only a small amount of Li2O2 is detected in the air electrodes discharged in the electrolytes of nitrile, ionic liquid, phosphate, and sulfoxide. Li2CO3 and LiF are also found as byproducts whose compositions are related to the solvents. Li2CO3 is produced from oxidation and decomposition of the solvent, not from the oxidation of the carbon-based air electrode, as revealed by using a 13C-labeled carbon electrode and the solid-state 13C-magic angle spinning nuclear magnetic resonance technique. LiF in the discharge products can be attributed to the attack of superoxide radical anions to the Teflon binder and/or the F-containing imide salt. The formation of these byproducts will significantly reduce the Coulombic efficiency and cycle life of the Li-air batteries. Among the studied solvents, dibutyl diglyme is the suitable solvent for Li-O2 batteries based on its overall properties. However, better electrolytes that can ensure the formation of Li2O2 but minimize other reaction products need to be further investigated for long cycling rechargeable Li-air batteries. [Copyright &y& Elsevier]

Abstract: To understand the limited cycle life performance and poor energy efficiency associated with rechargeable lithium–oxygen (Li–O2) batteries, the discharge products of primary Li–O2 cells at different depths of discharge (DOD) were systematically analyzed using XRD, FTIR and Ultra-high field MAS NMR. When discharged to 2.0V, the reaction products of Li–O2 cells include a small amount of Li2O2 along with Li2CO3 and RO–(C;OLi in the alkyl carbonate-based electrolyte. However, regardless of the DOD, there is no Li2O detected in the discharge products in the alkyl-carbonate electrolyte. For the first time it was revealed that in an oxygen atmosphere the high surface area carbon significantly reduces the electrochemical operation window of the electrolyte, and leads to plating of insoluble Li salts on the electrode at the end of the charging process. Therefore, the impedance of the Li–O2 cell continues to increase after each discharge and recharge process. After only a few cycles, the carbon air electrode is completely insulated by the accumulated Li salt terminating the cycling. [Copyright &y& Elsevier]