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Anionic redox reaction in layered NaCr_2/3Ti_1/3S₂ through electron holes formation and dimerization of S-S.

ABSTRACT: The use of anion redox reactions is gaining interest for increasing rechargeable capacities in alkaline ion batteries. Although anion redox coupling of S^2- and (S₂)^2- through dimerization of S-S in sulfides have been studied and reported, an anion redox process through electron hole formation has not been investigated to the best of our knowledge. Here, we report an O3-NaCr_2/3Ti_1/3S₂ cathode that delivers a high reversible capacity of ~186 mAh g^-1 (0.95 Na) based on the cation and anion redox process. Various charge compensation mechanisms of the sulfur anionic redox process in layered NaCr_2/3Ti_1/3S₂, which occur through the formation of disulfide-like species, the precipitation of elemental sulfur, S-S dimerization, and especially through the formation of electron holes, are investigated. Direct structural evidence for formation of electron holes and (S₂)^n- species with shortened S-S distances is obtained. These results provide valuable information for the development of materials based on the anionic redox reaction.

SUBMITTER: Wang T

PROVIDER: S-EPMC6773774 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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Anionic redox reaction in layered NaCr2/3Ti1/3S2 through electron holes formation and dimerization of S-S.

Wang Tian T Ren Guo-Xi GX Shadike Zulipiya Z Yue Ji-Li JL Cao Ming-Hui MH Zhang Jie-Nan JN Chen Ming-Wei MW Yang Xiao-Qing XQ Bak Seong-Min SM Northrup Paul P Liu Pan P Liu Xiao-Song XS Fu Zheng-Wen ZW

Nature communications 20191001 1

The use of anion redox reactions is gaining interest for increasing rechargeable capacities in alkaline ion batteries. Although anion redox coupling of S2- and (S2)2- through dimerization of S-S in sulfides have been studied and reported, an anion redox process through electron hole formation has not been investigated to the best of our knowledge. Here, we report an O3-NaCr2/3Ti1/3S2 cathode that delivers a high reversible capacit ...[more]

PMID: 31575867

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Project description:Anionic redox reactions attributed to oxygen have attracted much attention as a new approach to overcoming the energy-density limits of cathode materials. Several oxides have been suggested as new cathode materials with high capacities based on anionic (oxygen) redox reactions. Although most still have a large portion of their capacity based on the cationic redox reaction, lithia-based cathodes present high capacities that are purely dependent upon oxygen redox. Contrary to Li-air batteries, other systems using pure oxygen redox reactions, lithia-based cathodes charge and discharge without a phase transition between gas and condensed forms. This leads to a more stable cyclic performance and lower overpotential compared with those of Li-air systems. However, to activate nanolithia and stabilize reaction products such as Li2O2 during cycling, lithia-based cathodes demand efficient catalysts (dopants). In this study, Ir based materials (Ir and Li2IrO3) were introduced as catalysts (dopants) for nanolithia composites. Oxide types (Li2IrO3) were used as source materials of catalyst because ductile metal (Ir) can hardly be pulverized during the milling process. Two types of Li2IrO3 were prepared and used for catalyst-sources. They were named '1-step Li2IrO3' and '2-step Li2IrO3', respectively, since they were prepared by '1-step' or '2-step' heat treatment. The nanocomposites prepared using lithia & 2-step Li2IrO3 presented a higher capacity, more stable cyclic performance, and lower overpotential than those of the nanocomposites prepared using lithia & 1-step Li2IrO3. The voltage profiles of the nanocomposites prepared using lithia & 2-step Li2IrO3 were stable up to a limited capacity of 600 mAh·g-1, and the capacity was maintained during 100 cycles. XPS analysis confirmed that the capacity of our lithia-based compounds is attributable to the oxygen redox reaction, whereas the cationic redox related to the Ir barely contributes to their discharge capacity.

Dataset Information

Anionic redox reaction in layered NaCr_2/3Ti_1/3S₂ through electron holes formation and dimerization of S-S.

Publications

Anionic redox reaction in layered NaCr<sub>2/3</sub>Ti<sub>1/3</sub>S<sub>2</sub> through electron holes formation and dimerization of S-S.

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