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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.


Rate capability and cycling performance of the Li–O2 cells with Ru/MnO2/SP.(a) Discharge/charge profiles of the tenth run at varied current densities from 250 to 500 and 1,000 mA g−1. (b) Discharge/charge profiles of the selected runs over the 200 cycles at 500 mA g−1. The cell was at rest for 1 min between each run. (c) Plot of discharge/charge capacities and the corresponding coulombic efficiencies against cycle number and error bars (s.e.m.) in the first 100 cycles.
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f4: Rate capability and cycling performance of the Li–O2 cells with Ru/MnO2/SP.(a) Discharge/charge profiles of the tenth run at varied current densities from 250 to 500 and 1,000 mA g−1. (b) Discharge/charge profiles of the selected runs over the 200 cycles at 500 mA g−1. The cell was at rest for 1 min between each run. (c) Plot of discharge/charge capacities and the corresponding coulombic efficiencies against cycle number and error bars (s.e.m.) in the first 100 cycles.

Mentions: The Li–O2 cell with Ru/MnO2/SP and the DMSO-based electrolyte containing p.p.m.-leveled H2O was examined at varied current densities, as shown in Fig. 4a. The polarization is obviously increased with the current density from 250 to 500 and 1,000 mA g−1. The overpotential in the discharging and charging process at 250 mA g−1 is 0.11 V and 0.21 V, respectively, leading to a small discharge/charge potential gap of 0.32 V. The Li–O2 cell was continuously discharged and charged at 500 mA g−1 for 200 cycles and ∼800 h, and the selected runs of discharge and charge are shown in Fig. 4b. The discharge and charge curves during the first 150 cycles are almost overlapped except the first charge. A slight charge potential increase beyond the 150 cycles can also be observed, which could be related to the electrolyte instability during many cycles (Supplementary Fig. 11)3738. This indicates superior cycling stability of the Li–O2 cell, which is in sharp contrast to that without MnO2 in Fig. 3. The discharge and charge capacities in the 200 cycles are almost constant, and the corresponding coulombic efficiency in each run is approaching 98% (Fig. 4c), indicative of good reversibility. This may be partially benefited from the conversion of chemically active Li2O2 to LiOH. The reversible formation and decomposition of LiOH and Li2O2 during the 200 cycles are further confirmed by ex situ XRD patterns in Supplementary Fig. 12 and SEM images in Supplementary Fig. 13 (Supplementary Note 3). The low charge potentials sustained for so many cycles, to the best of our knowledge, have never been achieved before. The small discharge/charge potential gap and good cycling stability of the Li–O2 cell are rewarded by the ‘water catalysis' at the Ru/MnO2/SP cathode.


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)

Rate capability and cycling performance of the Li–O2 cells with Ru/MnO2/SP.(a) Discharge/charge profiles of the tenth run at varied current densities from 250 to 500 and 1,000 mA g−1. (b) Discharge/charge profiles of the selected runs over the 200 cycles at 500 mA g−1. The cell was at rest for 1 min between each run. (c) Plot of discharge/charge capacities and the corresponding coulombic efficiencies against cycle number and error bars (s.e.m.) in the first 100 cycles.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Rate capability and cycling performance of the Li–O2 cells with Ru/MnO2/SP.(a) Discharge/charge profiles of the tenth run at varied current densities from 250 to 500 and 1,000 mA g−1. (b) Discharge/charge profiles of the selected runs over the 200 cycles at 500 mA g−1. The cell was at rest for 1 min between each run. (c) Plot of discharge/charge capacities and the corresponding coulombic efficiencies against cycle number and error bars (s.e.m.) in the first 100 cycles.
Mentions: The Li–O2 cell with Ru/MnO2/SP and the DMSO-based electrolyte containing p.p.m.-leveled H2O was examined at varied current densities, as shown in Fig. 4a. The polarization is obviously increased with the current density from 250 to 500 and 1,000 mA g−1. The overpotential in the discharging and charging process at 250 mA g−1 is 0.11 V and 0.21 V, respectively, leading to a small discharge/charge potential gap of 0.32 V. The Li–O2 cell was continuously discharged and charged at 500 mA g−1 for 200 cycles and ∼800 h, and the selected runs of discharge and charge are shown in Fig. 4b. The discharge and charge curves during the first 150 cycles are almost overlapped except the first charge. A slight charge potential increase beyond the 150 cycles can also be observed, which could be related to the electrolyte instability during many cycles (Supplementary Fig. 11)3738. This indicates superior cycling stability of the Li–O2 cell, which is in sharp contrast to that without MnO2 in Fig. 3. The discharge and charge capacities in the 200 cycles are almost constant, and the corresponding coulombic efficiency in each run is approaching 98% (Fig. 4c), indicative of good reversibility. This may be partially benefited from the conversion of chemically active Li2O2 to LiOH. The reversible formation and decomposition of LiOH and Li2O2 during the 200 cycles are further confirmed by ex situ XRD patterns in Supplementary Fig. 12 and SEM images in Supplementary Fig. 13 (Supplementary Note 3). The low charge potentials sustained for so many cycles, to the best of our knowledge, have never been achieved before. The small discharge/charge potential gap and good cycling stability of the Li–O2 cell are rewarded by the ‘water catalysis' at the Ru/MnO2/SP cathode.

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.