ORCID Profile
0000-0002-3980-9478
Current Organisation
Waseda University
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Publisher: The Electrochemical Society
Date: 23-11-2020
DOI: 10.1149/MA2020-024664MTGABS
Abstract: Nonaqueous Li-oxygen batteries have garnered considerable research interest over the past decade due to their extremely high theoretical energy densities. For instance, the theoretical energy density based on the reaction, 2Li + O 2 = Li 2 O 2 , is calculated to be 3154 Whkg -1 by multiplying its specific capacity, 1168 Ahkg -1 , by an assumed voltage of 2.7 V. 1) However, its practical energy density is at most about 500 Whkg -1 with very limited cycle life at present technology level. 2) The major reasons to limit the energy density and cycle life are too much excess electrolyte weight and its consumption by parasitic reactions, respectively. Tetraethylene glycol dimethyl ether (TEGDME) and LiN(CF 3 SO 2 ) 2 (LiTFSI) are the most popular solvent and Li salt, respectively, for Li/O 2 cells due to their relatively high stability. 1,3) Although there are many papers to indicate that TEGDME decomposes during discharge and charge, it is only reported that the formation of Li 2 O 2 on the first discharge (ORR) was accompanied by the formation of Li 2 CO 3 , HCO 2 Li, CH 3 CO 2 Li, polyethers/esters, CO 2 , H 2 O 4) and CH 3 OH, CH 3 OCH 2 CH 2 OH, CH 3 O(CH 2 CH 2 O) 2 CH 3 , 5) and the electrochemical decomposition of Li 2 O 2 to O 2 on recharge (OER) was accompanied by more sever decomposition with the similar by-products 5) (OER/ORR 0.9). We have examined decomposition products in O 2 cathode by using a 2-compartment cell design (Fig. 1), where anode and cathode compartments were separated by a lithium ion solid electrolyte to eliminate possible interference from the reactions at anode. 6) The used carbon electrode was a self-standing sheet consisting of a Ketjenblack (6.5 mgcm -2 -carbon), and the electrolyte (30 μlcm -2 in the cathode) was selected from (a) 1 M LiTFSI in TEGDME and (b) 0.5 M LiTFSI + 0.5 M LiNO 3 + 0.2 M LiBr in TEGDME. The discharge/charge was carried out at 0.4 mAcm -2 (cut-off: 4 mAhcm -2 , 615 mAhg -1 -carbon). We have observed negligible H 2 O formation during discharge under O 2 atmosphere and gradual increase of H 2 O during recharge under He atmosphere detected by on-line mass spectrometry (Fig. 2). This H 2 O behavior during cycling was monitored by on-line gas chromatography (Fig. 3), and it was found that H 2 O is consumed during discharge. Some papers insist that H 2 O can be an advantageous additive to increase discharge capacity and decrease the charge overpotential, 7) however, our observation on the H 2 O consumption might indicate the parasitic reactions with LiO 2 /Li 2 O 2 . H 2 O is reproduced by oxidative decomposition of TEGDME during charge, followed by the oxidation of CH 3 OH/other organic fragments with the accumulation of HCHO/HCOOH, which are eventually converted to CO 2 and H 2 O at the final stage of charge. 1) M. Ue and K. Uosaki, Curr. Opin. Electrochem. , 17 ,106 (2019). 2) M. Ue, K. Sakaushi, and K. Uosaki, Mater. Horiz., DOI: 10.1039/D0MH00067A (2020). 3) L. Carbone, P. T. Moro, M. Gobet, S. Munoz, M. Devany, S. G. Greenbaum, and J. Hassoun, ACS Appl. Mater. Interfaces , 10 , 16367 (2018). 4) S. A. Freunberger, Y. Chen, N. E. Drewett, L. J. Hardwick, F. Barde, and P. G. Bruce, Angew. Chem. Int. Ed. , 50 , 8609 (2011). 5) M. Marinaro, S. Theil, L. Jörissen, and M. Wohlfahrt-Mehrens, Electrochim. Acta , 108 , 795 (2013). 6) S. Meini, S. Solchenbach, M. Piana, and H. A. Gasteiger, J. Electrochem. Soc. , 161 , A1306 (2014). 7) Y. Qiao, S. Wu, J. Yi, Y. Sun, S. Guo, S. Yang, P. He, and H. Zhou, Angew. Chem. Int. Ed. , 56 , 4960 (2017). Figure 1
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0MH00067A
Abstract: The basic knowledge in battery research bridging the gap between academia and industry was reviewed by the authors from both fields.
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0RA07924C
Abstract: The material balance in the O 2 electrode of a Li–O 2 cell with a Ketjenblack-based porous carbon electrode and a tetraethylene glycol dimethyl ether-based electrolyte under more practical conditions of less electrolyte amount and high areal capacity.
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