Investigation of the rechargeability of Li–O2 batteries in non-aqueous electrolyte

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 2.0 V, the reaction products of Li–O2 cells include a small amount of Li2O2 along with Li2CO3 and RO–(CO)–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.

► The discharge products at different depth of discharge (DOD) have been investigated by XRD, FTIR and NMR to identify the primary discharge products in the alkyl-carbonate based electrolyte.
► The formation mechanism of the dominant Li2CO3 and LiRCO3 instead of Li2O2 was discussed. It was the intermediate discharge product that reacted with the electrolyte and produced carbonates.
► It was also revealed that the high surface area carbon is not preferred for a rechargeable Li–O2 battery and the limited cycle life of Li–O2 cells are explained in detail in this paper.