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A monoclinic polymorph of sodium birnessite for ultrafast and ultrastable sodium ion storage.

ABSTRACT: Sodium transition metal oxides with layered structures are attractive cathode materials for sodium-ion batteries due to their large theoretical specific capacities. However, these layered oxides suffer from poor cyclability and low rate performance because of structural instability and sluggish electrode kinetics. In the present work, we show the sodiation reaction of Mn₃O₄ to yield crystal water free NaMnO_2-y-?(OH)_2y, a monoclinic polymorph of sodium birnessite bearing Na/Mn(OH)₈ hexahedra and Na/MnO₆ octahedra. With the new polymorph, NaMnO_2-y-?(OH)_2y exhibits an enlarged interlayer distance of about 7?Å, which is in favor of fast sodium ion migration and good structural stability. In combination of the favorable nanosheet morphology, NaMn_2-y-?(OH)_2y cathode delivers large specific capacity up to 211.9?mAh?g^-1, excellent cycle performance (94.6% capacity retention after 1000 cycles), and outstanding rate capability (156.0?mAh?g^-1 at 50?C). This study demonstrates an effective approach in tailoring the structural and electrochemical properties of birnessite towards superior cathode performance in sodium-ion batteries.

SUBMITTER: Xia H

PROVIDER: S-EPMC6269426 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature

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A monoclinic polymorph of sodium birnessite for ultrafast and ultrastable sodium ion storage.

Xia Hui H Zhu Xiaohui X Liu Jizi J Liu Qi Q Lan Si S Zhang Qinghua Q Liu Xinyu X Seo Joon Kyo JK Chen Tingting T Gu Lin L Meng Ying Shirley YS

Nature communications 20181130 1

Sodium transition metal oxides with layered structures are attractive cathode materials for sodium-ion batteries due to their large theoretical specific capacities. However, these layered oxides suffer from poor cyclability and low rate performance because of structural instability and sluggish electrode kinetics. In the present work, we show the sodiation reaction of Mn3O4 to yield crystal water free NaMnO2-y-δ(OH)2y, a monoclinic polymorph of sodium ...[more]

PMID: 30504861

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Project description:HighlightsUnique "Janus" interfacial assemble strategy of 2D MXene nanosheets was proposed firstly. Ternary heterostructure consisting of high capacity transitional metal chalcogenide, high conductive 2D MXene and N rich fungal carbonaceous matrix was achieved for larger radius Na/K ions storages. The highly accessible surfaces and interfaces of the strongly coupled 2D based ternary heterostructures provide superb surficial pseudocapacitive storages for both Na and K ions with low energy barriers was verified. Combining with the advantages of two-dimensional (2D) nanomaterials, MXenes have shown great potential in next generation rechargeable batteries. Similar with other 2D materials, MXenes generally suffer severe self-agglomeration, low capacity, and unsatisfied durability, particularly for larger sodium/potassium ions, compromising their practical values. In this work, a novel ternary heterostructure self-assembled from transition metal selenides (MSe, M = Cu, Ni, and Co), MXene nanosheets and N-rich carbonaceous nanoribbons (CNRibs) with ultrafast ion transport properties is designed for sluggish sodium-ion (SIB) and potassium-ion (PIB) batteries. Benefiting from the diverse chemical characteristics, the positively charged MSe anchored onto the electronegative hydroxy (-OH) functionalized MXene surfaces through electrostatic adsorption, while the fungal-derived CNRibs bonded with the other side of MXene through amino bridging and hydrogen bonds. This unique MXene-based heterostructure prevents the restacking of 2D materials, increases the intrinsic conductivity, and most importantly, provides ultrafast interfacial ion transport pathways and extra surficial and interfacial storage sites, and thus, boosts the high-rate storage performances in SIB and PIB applications. Both the quantitatively kinetic analysis and the density functional theory (DFT) calculations revealed that the interfacial ion transport is several orders higher than that of the pristine MXenes, which delivered much enhanced Na+ (536.3 mAh g-1@ 0.1 A g-1) and K+ (305.6 mAh g-1@ 1.0 A g-1 ) storage capabilities and excellent long-term cycling stability. Therefore, this work provides new insights into 2D materials engineering and low-cost, but kinetically sluggish post-Li batteries.

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A monoclinic polymorph of sodium birnessite for ultrafast and ultrastable sodium ion storage.

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A monoclinic polymorph of sodium birnessite for ultrafast and ultrastable sodium ion storage.

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