We propose a new sealed battery operating on a redox reaction between an oxide (O2−) and a peroxide (O22−) with its theoretical specific energy of 2570 Wh kg−1 (897 mAh g−1, 2.87 V) and demonstrate that a Co-doped Li2O cathode exhibits a reversible capacity over 190 mAh g−1, a high rate capability, and a good cyclability with a superconcentrated lithium bis(fluorosulfonyl)amide electrolyte in acetonitrile. The reversible capacity is largely dominated by the O2−/O22− redox reaction between oxide and peroxide with some contribution of the Co2+/Co3+ redox reaction.

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A Co-doped Li2O (CDL) was synthesized using a planetary ball mill and examined as a cathode material for lithium-ion batteries. When vinylene carbonate, which is often employed as an additive in an electrolyte, was used not only as an additive in the electrolyte but also as a treatment agent for CDL, the specific capacity of CDL was greatly enhanced and the charge–discharge cycles with specific charging and discharging capacities of 400 mAh/g could be repeated for more than 50 times. Co K-edge XANES spectroscopy and quantitative analysis of peroxide species revealed that the redox reactions of cobalt ions, formation/neutralization of O 2p electron holes, and generation/annihilation of peroxide species occurred during the charge–discharge process.

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