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Title: Expanded hydrated vanadate for high-performance aqueous zinc-ion batteries
Hydrated vanadates are promising layered cathodes for aqueous zinc-ion batteries owing to their specific capacity as high as 400 mA h g −1 ; however, the structural instability causes serious cycling degradation through repeated intercalation/deintercalation reactions. This study reveals the chemically inserted Mn( ii ) cations act as structural pillars, expand the interplanar spacing, connect the adjacent layers and partially reduce pentavalent vanadium cations to tetravalent. The expanded interplanar spacing to 12.9 Å reduces electrostatic interactions, and transition metal cations collectively promote and catalyze fast and more zinc ion intercalation at higher discharge current densities with much enhanced reversibility and cycling stability. Manganese expanded hydrated vanadate (MnVO) delivers a specific capacity of 415 mA h g −1 at a current density of 50 mA g −1 and 260 mA h g −1 at 4 A g −1 with a capacity retention of 92% over 2000 cycles. The energy efficiency increases from 41% for hydrated vanadium pentoxide (VOH) to 70% for MnVO at 4 A g −1 and the open circuit voltage remains at 85% of the cutoff voltage in the MnVO battery on the shelf after 50 days. Expanded hydrated vanadate with other transition metal cations for high-performance aqueous zinc-ion more » batteries is also obtained, suggesting it is a general strategy for exploiting high-performance cathodes for multi-valent ion batteries. « less
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Journal Name:
Energy & Environmental Science
Page Range or eLocation-ID:
2273 to 2285
Sponsoring Org:
National Science Foundation
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  1. Hydrated vanadium pentoxide (VOH) can deliver a gravimetric capacity as high as 400 mA h g −1 owing to the variable valence states of the V cation from 5+ to 3+ in an aqueous zinc ion battery. The incorporation of divalent transition metal cations has been demonstrated to overcome the structural instability, sluggish kinetics, fast capacity degradation, and serious polarization. The current study reveals that the catalytic effects of transition metal cations are probably the key to the significantly improved electrochemical properties and battery performance because of the higher covalent character of 55% in the Cu–O bond in comparison with 32% in the Mg–O bond in the respective samples. Cu( ii ) pre-inserted VOH (CuVOH) possesses a significantly enhanced intercalation storage capacity, an increased discharge voltage, great transport properties, and reduced polarization, while both VOH and Mg( ii ) pre-inserted VOH (MgVOH) demonstrate similar electrochemical properties and performances, indicating that the incorporation of Mg cations has little or no impact. For example, CuVOH has a redox voltage gap of 0.02 V, much smaller than 0.25 V for VOH and 0.27 V for MgVOH. CuVOH shows an enhanced exchange current density of 0.23 A g −1 , compared to 0.20 Amore »g −1 for VOH and 0.19 A g −1 for MgVOH. CuVOH delivers a zinc ion storage capacity of 379 mA h g −1 , higher than 349 mA h g −1 for MgVOH and 337 mA h g −1 for VOH at 0.5 A g −1 . CuVOH shows an energy efficiency of 72%, superior to 53% for VOH and 55% for MgVOH. All of the results suggest that pre-inserted Cu( ii ) cations played a critical role in catalyzing the zinc ion intercalation reaction, while the Mg( ii ) cations did not exert a detectable catalytic effect.« less
  2. Abstract

    Currently, there is considerable interest in developing advanced rechargeable batteries that boast efficient distribution of electricity and economic feasibility for use in large-scale energy storage systems. Rechargeable aqueous zinc batteries are promising alternatives to lithium-ion batteries in terms of rate performance, cost, and safety. In this investigation, we employ Cu3(HHTP)2, a two-dimensional (2D) conductive metal-organic framework (MOF) with large one-dimensional channels, as a zinc battery cathode. Owing to its unique structure, hydrated Zn2+ions which are inserted directly into the host structure, Cu3(HHTP)2, allow high diffusion rate and low interfacial resistance which enable the Cu3(HHTP)2cathode to follow the intercalation pseudocapacitance mechanism. Cu3(HHTP)2exhibits a high reversible capacity of 228 mAh g−1at 50 mA g−1. At a high current density of 4000 mA g−1(~18 C), 75.0% of the initial capacity is maintained after 500 cycles. These results provide key insights into high-performance, 2D conductive MOF designs for battery electrodes.

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