Rechargeable Li-CO₂ batteries are intriguing because of their combination of carbon capture and energy technology. However, the discharge product—Li₂CO₃ is difficult to decompose upon recharge. As the team laid out in their earlier paper on graphene:

Rechargeable Li–O₂ batteries have been attracting much attention owing to their high specific energy density, which is comparable to that of gasoline. However, the development of batteries that operate in air still represents a great challenge owing to the influence of moisture and CO₂ on their performance. Recently, Zhou and Zhang developed Li–air batteries that operate in ambient air, and they found that reversible reactions related to Li₂CO₃, which is the product of Li₂O₂ with CO₂ in air, occurred. Although CO₂ contamination was found to increase the discharge capacity of the cell, the presence of CO₂ during discharge dramatically influenced the electrochemical process.

This phenomenon was also reported by Takechi et al. [earlier post]; when batteries were operated with a mixture of O₂ and CO₂, the capacity could reach three times that of the batteries operated with pure O₂. Reversible Li–CO₂/O₂ (1:1, v/v) batteries were also investigated with different dielectric electrolytes, and it was found that dimethyl sulfoxide (DMSO) might be the optimal electrolyte for the reversible formation and decomposition of Li₂CO₃. However, in the above cases, CO₂ was not involved in the electrochemical reactions that proceed with electron transfer.

Recently, it was reported that a true Li–CO₂ battery (without O₂) could be cycled and exhibited a moderate discharge capacity The theoretical voltage of approximately 2.8 V can be determined according to the following equation: 4Li+CO₂→2Li₂CO₃+ C. Li–CO₂ batteries were also developed by Archer et al. [Xu et al. 2013], but their primary Li–CO₂ batteries only showed good discharge capacities at high temperatures.

—Zhang Zhang et al. (2015)

To create the cathodes for the latest study, the team mixed a slurry containing 90 wt. % CNTs and 10 wt.% PVDF spread it on carbon paper. Electrochemical performance was evaluated in Swagelok-type cells. The cells were assembled in a glove box filled with high-purity argon (O₂ and H2O < 1 ppm). The cells consisted of lithium metal anodes, ploytetrafluoroethylene (PTFE) separators, and CNT cathodes. The electrolyte composed of 1 mol L^-1 LiTFSI dissolved in TEGDEM.

Resources

• Xin Zhang, Qiang Zhang, Zhang Zhang, Yanan Chen, Zhaojun Xie, Jinping Wei and Zhen Zhou (2015) “Rechargeable Li-CO₂ batteries with carbon nanotubes as air cathodes” Chem. Commun. doi: 10.1039/C5CC05767A

• Zhang, Z., Zhang, Q., Chen, Y., Bao, J., Zhou, X., Xie, Z., Wei, J. and Zhou, Z. (2015), The First Introduction of Graphene to Rechargeable Li–CO₂ Batteries. Angew. Chem. Int. Ed., 54: 6550–6553. doi: 10.1002/anie.201501214

• Yali Liu, Rui Wang, Yingchun Lyu, Hong Li and Liquan Chen (2014) “Rechargeable Li/CO₂–O₂ (2:1) battery and Li/CO₂ battery” Energy Environ. Sci. 7, 677-681 doi: 10.1039/C3EE43318H

• Shaomao Xu, Shyamal K. Dasa and Lynden A. Archer (2013) “The Li–CO₂ battery: a novel method for CO₂ capture and utilization” RSC Adv. 3, 6656-6660 doi: 10.1039/C3RA40394G