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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.


Discharge/charge profiles of the fifth cycles of the Li–O2 cell at 250 mA g−1.(a) Discharge capacity is limited for 250 and 500 mAh g−1. (b) Discharge capacity is limited for 1,000 and 2,000 mAh g−1. The cathode is Ru/MnO2/SP and the DMSO-based electrolyte containing 120 p.p.m. of H2O is applied.
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f7: Discharge/charge profiles of the fifth cycles of the Li–O2 cell at 250 mA g−1.(a) Discharge capacity is limited for 250 and 500 mAh g−1. (b) Discharge capacity is limited for 1,000 and 2,000 mAh g−1. The cathode is Ru/MnO2/SP and the DMSO-based electrolyte containing 120 p.p.m. of H2O is applied.

Mentions: In addition, by controlling the discharge depth of the Li–O2 cells, the discharge product can be ranged from LiOH only to a majority of Li2O2 plus LiOH with the same amount of electrolytes used in cells. The cathode with a relatively small discharge capacity of 250 mAh g−1 was covered with LiOH, on which no Li2O2 was detected by iodometric titration. It is in the shape of thin disks as shown in Supplementary Fig. 14 (refs 25, 33). In the following charging process, the potentials are increased to ∼3.65 V and similar to that with 281 p.p.m. of H2O in electrolytes in Fig. 6. The low charge potentials at ∼3.20 V can be observed again when the discharge capacity is increased to 500, 1,000 and 2,000 mAh g−1, as shown in Fig. 7. At large discharge capacities, the H2O molecules in the electrolyte can be consumed by Li2O2, producing surface-clean LiOH/Li2O2 in the cathode. This suggests that the relative amounts of H2O, LiOH and Li2O2 coexisting at a cathode side affect the charging overpotentials. The detailed formation/decomposition mechanism of LiOH and Li2O2 in the presence of water in electrolytes and the dependence of their decomposition potentials on their morphologies deserve further investigation.


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)

Discharge/charge profiles of the fifth cycles of the Li–O2 cell at 250 mA g−1.(a) Discharge capacity is limited for 250 and 500 mAh g−1. (b) Discharge capacity is limited for 1,000 and 2,000 mAh g−1. The cathode is Ru/MnO2/SP and the DMSO-based electrolyte containing 120 p.p.m. of H2O is applied.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f7: Discharge/charge profiles of the fifth cycles of the Li–O2 cell at 250 mA g−1.(a) Discharge capacity is limited for 250 and 500 mAh g−1. (b) Discharge capacity is limited for 1,000 and 2,000 mAh g−1. The cathode is Ru/MnO2/SP and the DMSO-based electrolyte containing 120 p.p.m. of H2O is applied.
Mentions: In addition, by controlling the discharge depth of the Li–O2 cells, the discharge product can be ranged from LiOH only to a majority of Li2O2 plus LiOH with the same amount of electrolytes used in cells. The cathode with a relatively small discharge capacity of 250 mAh g−1 was covered with LiOH, on which no Li2O2 was detected by iodometric titration. It is in the shape of thin disks as shown in Supplementary Fig. 14 (refs 25, 33). In the following charging process, the potentials are increased to ∼3.65 V and similar to that with 281 p.p.m. of H2O in electrolytes in Fig. 6. The low charge potentials at ∼3.20 V can be observed again when the discharge capacity is increased to 500, 1,000 and 2,000 mAh g−1, as shown in Fig. 7. At large discharge capacities, the H2O molecules in the electrolyte can be consumed by Li2O2, producing surface-clean LiOH/Li2O2 in the cathode. This suggests that the relative amounts of H2O, LiOH and Li2O2 coexisting at a cathode side affect the charging overpotentials. The detailed formation/decomposition mechanism of LiOH and Li2O2 in the presence of water in electrolytes and the dependence of their decomposition potentials on their morphologies deserve further investigation.

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.