Yali Liu, Hao Zheng, Dongdong Xiao, Yingchun Lyu, Jiayue Peng, Rui Wang, Yongsheng Hu, Lin Gu, Hong Li*, Liquan Chen Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, P.R. ChinaE-mail: hli@iphy.ac.cn

Rechargeable nonaqueous lithium air battery has attracted wide attention due to its very high theoretical energy density. It is still very challenge for operating the batteries in air, partially due to influences of moisture and carbon dioxide. It has been demonstrated that there would be Li2CO3 in the discharge products when the reactive gas contains CO2. It has been thought that Li2CO3 is very difficult to be decomposed during charging.

Therefore, most reported lithium air batteries are investigated under high pure oxygen with CO2 less than 5 ppm. In 2011, Takechi et al reported a Li/CO2:O2 (from 0 to 100% volume CO2) battery, which didn’t show a reversible charge capacity with a cut-off voltage of 4.5 V even in the first cycle. McCloskey et al reported a Li/O2 battery with CO2 as a contamination gas (10% volume).

The battery employed LiTFSI-DME as electrolyte and a sloped charging voltage profile up to 4.8 V was reported in the first cycle. A reversible Li/CO2:O2 (1:1, volume ratio) battery with DME based and DMSO based electrolyte was reported by Kang et al recently. They pointed that Li2CO3 was the main discharge product in this battery and can form reversibly.

We have also reported that Li2CO3 can be decomposed after mixing with NiO as catalyst. Accordingly, there is no doubt that formed Li2CO3 can be decomposed under suitable conditions. Therefore, it is plausible that a rechargeable Li/CO2 battery could be also developed. According to thermodynamic calculation, the specific energy density of Li/CO2 batteries is almost three fourths of Li/O2 battery. It also can be calculated that the theoretical voltage is about 2.8 V based on the equation: 4Li + 3CO2 → 2Li2CO3 + C. The Li/CO2 battery could be attractive especially when CO2 is enriched in atmosphere.

Previously, Archer et al reported a primary Li/CO2 battery which cannot be recharged and only discharge in the high temperature. In this report, we will show that a Li/CO2:O2 (2:1, volume ratio) battery and a Li/CO2 battery can operate reversibly at room temperature when lithium triflate (LiCF3SO3)-TEGDME is used as the electrolyte, various carbon as air electrodes. The polarization of the reactions, products formed under different conditions with different volume ratio of O2: CO2, and the relationship between the electrochemical performances and the structure, morphology and the composition of the products are analyzed based on electrochemical measurements combining with in situ and ex situ STEM, SEM, AFM, FTIR, Raman, XRD, SIMS techniques and DFT calculations.

Hong Li

Institute of Physics, CAS

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