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The water catalysis at oxygen cathodes of lithium-oxygen cells.

Li F, Wu S, Li D, Zhang T, He P, Yamada A, Zhou H - Nat Commun (2015)

Bottom Line: However, even in the state-of-the-art lithium-oxygen cells the charge potentials are as high as 3.5 V that are higher by 0.70 V than the discharge potentials.This can significantly reduce the charge overpotential to 0.21 V, and results in a small discharge/charge potential gap of 0.32 V and superior cycling stability of 200 cycles.The overall reaction scheme will alleviate side reactions involving carbon and electrolytes, and shed light on the construction of practical, rechargeable lithium-oxygen cells.

View Article: PubMed Central - PubMed

Affiliation: 1] Energy Interface Technology Group, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1, Umezono, Tsukuba 305-8568, Japan [2] Department of Chemical System Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.

ABSTRACT
Lithium-oxygen cells have attracted extensive interests due to their high theoretical energy densities. The main challenges are the low round-trip efficiency and cycling instability over long time. However, even in the state-of-the-art lithium-oxygen cells the charge potentials are as high as 3.5 V that are higher by 0.70 V than the discharge potentials. Here we report a reaction mechanism at an oxygen cathode, ruthenium and manganese dioxide nanoparticles supported on carbon black Super P by applying a trace amount of water in electrolytes to catalyse the cathode reactions of lithium-oxygen cells during discharge and charge. This can significantly reduce the charge overpotential to 0.21 V, and results in a small discharge/charge potential gap of 0.32 V and superior cycling stability of 200 cycles. The overall reaction scheme will alleviate side reactions involving carbon and electrolytes, and shed light on the construction of practical, rechargeable lithium-oxygen cells.

No MeSH data available.


Characterization of the discharged/charged cathodes.(a) Ex situ XRD patterns of the discharged and charged Ru/MnO2/SP cathodes in DMSO-based electrolyte with 120 p.p.m. H2O. (b) IR spectra of the charged and discharge cathodes. (c,d) SEM images of the discharged and charged cathodes, in comparison to the fresh cathode (e).
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f2: Characterization of the discharged/charged cathodes.(a) Ex situ XRD patterns of the discharged and charged Ru/MnO2/SP cathodes in DMSO-based electrolyte with 120 p.p.m. H2O. (b) IR spectra of the charged and discharge cathodes. (c,d) SEM images of the discharged and charged cathodes, in comparison to the fresh cathode (e).

Mentions: The discharged and charged Ru/MnO2/SP cathodes in the DMSO-based electrolyte containing water have been characterized by X-ray diffraction (XRD). As shown in Fig. 2a, the discharge products are identified as a mixture of LiOH and Li2O2, referring to the standard powder diffraction files of 01-085-0777 and 00-009-0355, respectively. The diffraction peaks of LiOH become sharper and stronger at the cathode with a discharge capacity of 4,000 mAh g−1 and addition of more electrolyte (Supplementary Fig. 5), suggesting more LiOH converted from Li2O2. To avoid the effect of MnO2, quantification of LiOH and Li2O2 was conducted on the Ru/SP cathode with the same discharge capacity as in Fig. 1 via iodometric titration. The discharge product Li2O2 reacts with H2O via Li2O2(s)+2H2O(l)→H2O2(l)+2LiOH(aq)3031, where H2O2 further oxidizes iodide to iodine, the titrated target. The LiOH and Li2O2 in the discharged cathode were titrated via two steps (Supplementary Figs 6 and 7; titration processes in Supplementary Methods) and estimated to 16.02 and 1.48 μmol, respectively, which are in agreement with the XRD patterns of the discharged cathode in Fig. 2a. The majority of LiOH formed at a discharged cathode is revealed by the characteristic absorbance peak in the infrared (IR) spectra in Fig. 2b. Based on the electrons passing through the cathode and the oxygen derived from the discharge products of LiOH and Li2O2 by iodometric titration, the discharging process is a 1.97 e−/O2 process, quite close to the theoretical value of 2.00 e−/O2. It is confirmed that in other electrolytes, like DME-, G3- and G4-based electrolytes, the discharging process is also a ∼2.00 e−/O2 process, as listed in Supplementary Table 1. This suggests that LiOH is converted from Li2O2 via a chemical, not an electrochemical, process in the discharging processes.


The water catalysis at oxygen cathodes of lithium-oxygen cells.

Li F, Wu S, Li D, Zhang T, He P, Yamada A, Zhou H - Nat Commun (2015)

Characterization of the discharged/charged cathodes.(a) Ex situ XRD patterns of the discharged and charged Ru/MnO2/SP cathodes in DMSO-based electrolyte with 120 p.p.m. H2O. (b) IR spectra of the charged and discharge cathodes. (c,d) SEM images of the discharged and charged cathodes, in comparison to the fresh cathode (e).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525193&req=5

f2: Characterization of the discharged/charged cathodes.(a) Ex situ XRD patterns of the discharged and charged Ru/MnO2/SP cathodes in DMSO-based electrolyte with 120 p.p.m. H2O. (b) IR spectra of the charged and discharge cathodes. (c,d) SEM images of the discharged and charged cathodes, in comparison to the fresh cathode (e).
Mentions: The discharged and charged Ru/MnO2/SP cathodes in the DMSO-based electrolyte containing water have been characterized by X-ray diffraction (XRD). As shown in Fig. 2a, the discharge products are identified as a mixture of LiOH and Li2O2, referring to the standard powder diffraction files of 01-085-0777 and 00-009-0355, respectively. The diffraction peaks of LiOH become sharper and stronger at the cathode with a discharge capacity of 4,000 mAh g−1 and addition of more electrolyte (Supplementary Fig. 5), suggesting more LiOH converted from Li2O2. To avoid the effect of MnO2, quantification of LiOH and Li2O2 was conducted on the Ru/SP cathode with the same discharge capacity as in Fig. 1 via iodometric titration. The discharge product Li2O2 reacts with H2O via Li2O2(s)+2H2O(l)→H2O2(l)+2LiOH(aq)3031, where H2O2 further oxidizes iodide to iodine, the titrated target. The LiOH and Li2O2 in the discharged cathode were titrated via two steps (Supplementary Figs 6 and 7; titration processes in Supplementary Methods) and estimated to 16.02 and 1.48 μmol, respectively, which are in agreement with the XRD patterns of the discharged cathode in Fig. 2a. The majority of LiOH formed at a discharged cathode is revealed by the characteristic absorbance peak in the infrared (IR) spectra in Fig. 2b. Based on the electrons passing through the cathode and the oxygen derived from the discharge products of LiOH and Li2O2 by iodometric titration, the discharging process is a 1.97 e−/O2 process, quite close to the theoretical value of 2.00 e−/O2. It is confirmed that in other electrolytes, like DME-, G3- and G4-based electrolytes, the discharging process is also a ∼2.00 e−/O2 process, as listed in Supplementary Table 1. This suggests that LiOH is converted from Li2O2 via a chemical, not an electrochemical, process in the discharging processes.

Bottom Line: However, even in the state-of-the-art lithium-oxygen cells the charge potentials are as high as 3.5 V that are higher by 0.70 V than the discharge potentials.This can significantly reduce the charge overpotential to 0.21 V, and results in a small discharge/charge potential gap of 0.32 V and superior cycling stability of 200 cycles.The overall reaction scheme will alleviate side reactions involving carbon and electrolytes, and shed light on the construction of practical, rechargeable lithium-oxygen cells.

View Article: PubMed Central - PubMed

Affiliation: 1] Energy Interface Technology Group, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1, Umezono, Tsukuba 305-8568, Japan [2] Department of Chemical System Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.

ABSTRACT
Lithium-oxygen cells have attracted extensive interests due to their high theoretical energy densities. The main challenges are the low round-trip efficiency and cycling instability over long time. However, even in the state-of-the-art lithium-oxygen cells the charge potentials are as high as 3.5 V that are higher by 0.70 V than the discharge potentials. Here we report a reaction mechanism at an oxygen cathode, ruthenium and manganese dioxide nanoparticles supported on carbon black Super P by applying a trace amount of water in electrolytes to catalyse the cathode reactions of lithium-oxygen cells during discharge and charge. This can significantly reduce the charge overpotential to 0.21 V, and results in a small discharge/charge potential gap of 0.32 V and superior cycling stability of 200 cycles. The overall reaction scheme will alleviate side reactions involving carbon and electrolytes, and shed light on the construction of practical, rechargeable lithium-oxygen cells.

No MeSH data available.