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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.


Initial three cycles of discharge and charge.(a) Discharge/charge profiles of the Li–O2 cells with a configuration of (Ru/MnO2/SP)/electrolyte/LiFePO4. The electrolyte is 0.5 M LiClO4 in DMSO with 120 p.p.m. H2O. (b,c) The corresponding dQ/dV curves and the contact angle of the electrolyte on the cathode. The discharge and charge cutoffs are 1,000 mAh g−1 (5,099 μC cm−2 based on the BET surface area of Ru/MnO2/SP) and 4.0 V, respectively. The potentials against Li+/Li are converted from LiFePO4. Rate: 500 mA g−1—based on the total weight of Ru, MnO2 and SP, corresponding to 0.71 μA cm−2; loading: ∼0.5 mg cm−2.
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f1: Initial three cycles of discharge and charge.(a) Discharge/charge profiles of the Li–O2 cells with a configuration of (Ru/MnO2/SP)/electrolyte/LiFePO4. The electrolyte is 0.5 M LiClO4 in DMSO with 120 p.p.m. H2O. (b,c) The corresponding dQ/dV curves and the contact angle of the electrolyte on the cathode. The discharge and charge cutoffs are 1,000 mAh g−1 (5,099 μC cm−2 based on the BET surface area of Ru/MnO2/SP) and 4.0 V, respectively. The potentials against Li+/Li are converted from LiFePO4. Rate: 500 mA g−1—based on the total weight of Ru, MnO2 and SP, corresponding to 0.71 μA cm−2; loading: ∼0.5 mg cm−2.

Mentions: The carbon paper has been demonstrated to have negligible contribution to cell performance (Supplementary Fig. 1; Supplementary Note 1). The Li–O2 cell with Ru/MnO2/SP as cathode and the DMSO-based electrolyte containing p.p.m.-leveled H2O is discharged and charged at 500 mA g−1 (corresponding to 0.71 μA cm−2 based on the Brunauer-Emmett-Teller, (BET) surface area of Ru/MnO2/SP) as shown in Fig. 1a. A charge potential plateau as low as ∼3.20 V, corresponding to an overpotential of ∼0.24 V, can be clearly observed. Its corresponding dQ/dV curve in Fig. 1b shows sharp oxygen reduction reaction and oxygen evolution reaction peaks in the discharging and charging process, respectively, which are consistent with the flat discharge and charge plateaus. In addition, a small plateau at ∼3.60 V is also obtained in the charge profile in Fig. 1a. It could be resulted from the affinity of DMSO with the Ru/MnO2/SP cathode that has a large contact angle of 62°, compared with the discharge and charge profiles of the Li–O2 cell with a dimethoxyethane-(DME-)-based electrolyte and the good wettability of DME on the cathode in Supplementary Fig. 2. This may enable the oxygen evolved in a charging process to accumulate in the voids between the residual discharge product and the cathode, as schematically described in Supplementary Fig. 3 and Supplementary Note 2. It would induce slow diffusion of electrolytes into the voids for the decomposition of the remaining discharge products and result in the relatively large overpotential at ∼3.60 V, which is not observed in the affinitive DME-based electrolyte (Supplementary Fig. 2). Similar observations are also obtained in the other kinds of electrolytes, such as triglyme (G3)- and tetraglyme (G4)-based electrolytes (Supplementary Fig. 4). The trace amount of H2O in electrolytes is demonstrated to play a crucial role on reducing charge overpotentials of Li–O2 cells in all the widely used electrolytes, which was empirically considered as a negative factor in a Li-ion cell29.


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)

Initial three cycles of discharge and charge.(a) Discharge/charge profiles of the Li–O2 cells with a configuration of (Ru/MnO2/SP)/electrolyte/LiFePO4. The electrolyte is 0.5 M LiClO4 in DMSO with 120 p.p.m. H2O. (b,c) The corresponding dQ/dV curves and the contact angle of the electrolyte on the cathode. The discharge and charge cutoffs are 1,000 mAh g−1 (5,099 μC cm−2 based on the BET surface area of Ru/MnO2/SP) and 4.0 V, respectively. The potentials against Li+/Li are converted from LiFePO4. Rate: 500 mA g−1—based on the total weight of Ru, MnO2 and SP, corresponding to 0.71 μA cm−2; loading: ∼0.5 mg cm−2.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Initial three cycles of discharge and charge.(a) Discharge/charge profiles of the Li–O2 cells with a configuration of (Ru/MnO2/SP)/electrolyte/LiFePO4. The electrolyte is 0.5 M LiClO4 in DMSO with 120 p.p.m. H2O. (b,c) The corresponding dQ/dV curves and the contact angle of the electrolyte on the cathode. The discharge and charge cutoffs are 1,000 mAh g−1 (5,099 μC cm−2 based on the BET surface area of Ru/MnO2/SP) and 4.0 V, respectively. The potentials against Li+/Li are converted from LiFePO4. Rate: 500 mA g−1—based on the total weight of Ru, MnO2 and SP, corresponding to 0.71 μA cm−2; loading: ∼0.5 mg cm−2.
Mentions: The carbon paper has been demonstrated to have negligible contribution to cell performance (Supplementary Fig. 1; Supplementary Note 1). The Li–O2 cell with Ru/MnO2/SP as cathode and the DMSO-based electrolyte containing p.p.m.-leveled H2O is discharged and charged at 500 mA g−1 (corresponding to 0.71 μA cm−2 based on the Brunauer-Emmett-Teller, (BET) surface area of Ru/MnO2/SP) as shown in Fig. 1a. A charge potential plateau as low as ∼3.20 V, corresponding to an overpotential of ∼0.24 V, can be clearly observed. Its corresponding dQ/dV curve in Fig. 1b shows sharp oxygen reduction reaction and oxygen evolution reaction peaks in the discharging and charging process, respectively, which are consistent with the flat discharge and charge plateaus. In addition, a small plateau at ∼3.60 V is also obtained in the charge profile in Fig. 1a. It could be resulted from the affinity of DMSO with the Ru/MnO2/SP cathode that has a large contact angle of 62°, compared with the discharge and charge profiles of the Li–O2 cell with a dimethoxyethane-(DME-)-based electrolyte and the good wettability of DME on the cathode in Supplementary Fig. 2. This may enable the oxygen evolved in a charging process to accumulate in the voids between the residual discharge product and the cathode, as schematically described in Supplementary Fig. 3 and Supplementary Note 2. It would induce slow diffusion of electrolytes into the voids for the decomposition of the remaining discharge products and result in the relatively large overpotential at ∼3.60 V, which is not observed in the affinitive DME-based electrolyte (Supplementary Fig. 2). Similar observations are also obtained in the other kinds of electrolytes, such as triglyme (G3)- and tetraglyme (G4)-based electrolytes (Supplementary Fig. 4). The trace amount of H2O in electrolytes is demonstrated to play a crucial role on reducing charge overpotentials of Li–O2 cells in all the widely used electrolytes, which was empirically considered as a negative factor in a Li-ion cell29.

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.