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U Tokyo team proposes new high-capacity rechargeable battery system based on oxide-peroxide redox reaction

27 July 2014

Srep05684-f1
(a) Charge and discharge voltage curves in repeated charge/discharge cycles at 45 mA g−1. (b) Charge and discharge voltage curves at various current densities (13.5–1080 mA g−1). Click to enlarge.

Researchers at the University of Tokyo, led by Dr. Noritaka Mizuno (“oxygen rocking”, earlier post), in collaboration with Nippon Shokubai Co., Ltd. are proposing a new sealed rechargeable battery system operating on a redox reaction between an oxide (O2-) and a peroxide (O22-) in the cathode. As described in a paper in the Nature open access journal Scientific Reports, the proposed battery system would have a theoretical specific energy of 2,570 Wh kg-1 (897 mAh g-1, 2.87 V)—about on par with Li-sulfur’s very high theoretical energy density of ~2,600 Wh kg-1 (based on lithium-sulfur redox couple, e.g., earlier post).

The team showed that a cobalt-doped Li2O cathode exhibited a reversible capacity above 190 mAh g-1, a high rate capability, and good cyclability with a superconcentrated lithium bis(fluorosulfonyl)amide electrolyte in acetonitrile. The present specific capacity of the Co-doped Li2O cathode is lower than its theoretical capacity of 556 mAh g−1 (based on the weight of Li2O in the Co-doped Li2O).

Fig1 Eng-thumb-350x201-2496
The new sealed battery system, with a theoretical specific energy of 2570 Wh kg−1, is based on the reaction 2Li + Li2O2 → 2Li2O. The theoretical capacity puts it—conceptually—much above that of current advanced Li-ion approaches, but below the theoretical capacity of Li-air systems. The demonstrated reversible capacity of more than 190 mAh g−1 using a Co-doped Li2O cathode is largely dominated by the reduction of Li2O2 to form Li2O, with some contribution of the redox reaction of Co ions. Click to enlarge.

Another approach [to the development of high energy density post Li-ion batteries] is a development of a lithium-air (Li-O2) battery by use of atmospheric O2 with a theoretical specific energy of 3400 Wh kg−1 even including the weight of oxygen in the discharged product (Li2O2). However, the actual capacity or the energy is dependent on the pore volumes of the cathode matrices where Li2O2 is formed, the pores are clogged with solids, and the discharge is prohibited by the limitation of the oxygen supply. In addition, there are more serious inherent problems of the open device, suffering from the coexisting moisture and CO2, and safety for the application to electronic vehicles. The main discharge product for Li-O2 batteries is Li2O2

The subsequent reduction of Li2O2 has recently been pointed out to take place to form Li2O during the deep discharge … However, there is no report on the repetition of the charge and discharge utilizing the reaction between Li2O (or O2−) and Li2O2 (or O22−). The investigation on LIB cathodes such as LiCoO2 and Li-rich layered oxides shows not only the charge compensation mechanism involving transition metal ions but also some contribution of the reversible redox reaction of oxygen atoms.

Therefore, we have reached an idea that Li2O2 would act as a 3 V-level cathode utilizing the redox couple of oxide (O2−)/peroxide (O22−). In addition, a certain electrode catalyst or mediator would selectively accelerate the thermodynamically more favorable backward reaction.

—Okuoka et al.

The team evaluated a number of different ratios of cobalt to lithium doping, and found that the best charge-discharge performance came with Co-doped Li2O (Co/Li = 0.1). Rhodium and Iridium (Rh2O3 and IrO2 instead of Co3O4 could also be used.)

The researchers built a cell consisting of the Co-doped Li2O cathode, a Li metal anode, and a superconcentrated 4 M LiFSA electrolyte for testing electrochemical performance. The charge voltage gradually increased and reached approximately 3.2 V above 150 mAh g−1. The discharge and charge curves from the first to 15th cycle remained almost unchanged, with the constant coulombic efficiency of around 96% at 45 mA g−1.

First discharge capacity reached 195 mAh g−1 at a low current density of 13.5 mA g−1 and the capacity of 133 mAh g−1 can be discharged even at a very high current density of 1080 mA g−1 at which the capacity of 200 mAh g−1 can be charged in 11 minutes.

The team suggested that investigating the roles of cobalt in the redox reaction between the oxide and peroxide and the state of the O22− species in the Co-doped Li2O would lead to the improvement of the specific capacity.

This research was supported by the Japan Society for the Promotion of Science (JSPS) through its “Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program)”.

Resources

  • Shin-ichi Okuoka, Yoshiyuki Ogasawara, Yosuke Suga, Mitsuhiro Hibino, Tetsuichi Kudo, Hironobu Ono, Koji Yonehara, Yasutaka Sumida, Yuki Yamada, Atsuo Yamada, Masaharu Oshima, Eita Tochigi, Naoya Shibata, Yuichi Ikuhara & Noritaka Mizuno (2014) “A New Sealed Lithium-Peroxide Battery with a Co-Doped Li2O Cathode in a Superconcentrated Lithium Bis(fluorosulfonyl)amide Electrolyte,” Scientific Reports 4, Article number: 5684 doi: 10.1038/srep05684

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