Researchers at Nankai University in China report their latest advance in developing a rechargeable Li-CO2 battery with the use of carbon nanotubes (CNTs) with high electrical conductivity and porous three-dimensional networks as air cathodes for the rechargeable metal-CO2 batteries. A paper on the work is published in the RSC journal Chemical Communications. (Zhang Zhang et al. 2015).
The team had earlier reported on the introduction of graphene as a cathode material which significantly improved the performance of Li–CO2 batteries, which displayed a superior discharge capacity and enhanced cycle stability. (Xin Zhang et al. 2015) The use of CNTs in the latest study, while extending cycle stability, reduced capacity.
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.
|Summary of electrochemical performance of Li-CO2 batteries with different cathodes at room temperature. X. Zhang et al.|
|Super P||~0 mAh g-1||/|
|High surface area carbon||~750 mAh g-1||/|
|Ketjen Black (Liu et al. 2014)||1032 mAh g-1||7 cycles at 30 mA g-1|
|Graphene (Z. Zhang et al. 2015)||14772 mAh g-1||20 cycles at 50 mA g-1|
|Carbon nanotubes (X. Zhang et al. 2015)||8379 mAh g-1||29 cycles at 50 mA g-1|
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