Elsevier

Energy Storage Materials

Volume 34, January 2021, Pages 203-210
Energy Storage Materials

Stable aqueous Zn−Ag and Zn−polyoxometalate hybrid battery driven by successive Ag+ cation and polyoxoanion redox reactions

https://doi.org/10.1016/j.ensm.2020.09.011Get rights and content

Highlights

  • An aqueous hybrid battery combining electrochemical features of Zn−Ag battery and Zn−POM battery is firstly proposed.

  • Amorphous POM-based electrode is proposed for the first time in energy storage materials.

  • The severe Ag+ migration and the dissolution of polyoxovanadate clusters in aqueous electrolyte are effectively inhibited.

  • This work provides a promising strategy to design insoluble POMs applied to aqueous batteries.

Abstract

Hybrid batteries with multiple electrochemical reactions that integrate respective advantages and remedy intricate shortages of disparate batteries are both fundamentally interesting and practically attractive. Here, an aqueous hybrid battery combining electrochemical features of Zn−Ag battery and Zn−POM battery is for the first time proposed, which is actuated by successive Ag+ cation and polyoxoanion redox reactions in an insoluble polyoxometalate (POM)-based cathode. The unique POM-based composite material constructed from loose stacking high-nuclearity polyoxovanadate clusters and crystalline Ag nanoparticles not only provides plentiful Zn2+ storage sites but also presents fast ion / electron diffusion kinetics. Meanwhile, both the severe migration of Ag+ ions and the dissolution of POM clusters in aqueous electrolyte are effectively inhibited. The as-fabricated hybrid battery with POM-based cathode exhibits a reversible capacity of 200 mAh g–1 at 10 A g–1 with outstanding capacity retention (97.4% over 7000 cycles) and superior rate capability. Moreover, the stable hybrid energy storage mechanism is revealed in detail. The work presents a promising strategy for the application of POM-based electrode in aqueous batteries and provides heuristic thinking for further developing novel energy storage systems.

Graphical abstract

An aqueous hybrid battery integrating electrochemical features of Zn−Ag battery and Zn−polyoxometalate battery is firstly proposed, in which the severe Ag+ migration and the dissolution of POM clusters are synergisticlly inhibited.

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Introduction

Designing and developing advanced batteries with long cycle life, high energy and power densities, safety reliability and affordable cost has been a focus of global concern to meet people's energy needs in electronics, electric vehicles and smart grids [1,2]. Besides widespread commercially applied lithium ion batteries, very promising aqueous Zn-based batteries (e.g. Zn−ion battery (ZIB), Zn−Ag battery (ZAB), Zn−Ni battery and Zn−air battery) have aroused increasing attention due to their inherent merits of cost-effectivity, nonflammability and environmental benignity [3], [4], [5], [6], [7]. As one of the most mature Zn-based batteries with high operating voltage (>1 V), theoretical energy density (600 Wh kg–1) and power density (2500 W kg–1), ZABs equipped with Ag or silver oxide-based cathodes have already been studied [3,4]. However, the migration of silver ions can lead to metal Ag dendrite growth inside the separator and counter electrode poisoning, resulting in poor cycle performance, which is the main obstacle for enhancing the long-life cycle in rechargeable ZABs [3,8,9]. In recent years, some tentative attempts have been made to alleviate the Ag+ migration by optimizing electrolytes and separators to restrain the dissolution and diffusion of Ag+ ions, nevertheless, the relevant progress is underdeveloped [9,10]. As a result, persistently seeking and finding simple and effective strategies to realize a stable ZAB system with the long-life cycle is still a severe challenge.

Very recently, aqueous ZIBs are emerging as the most compelling candidates on account of high capacity and mild electrochemical reaction environments with neutral (or slightly acidic) electrolytes [11], [12], [13], [14], [15]. Various crystalline Zn2+ host materials such as MnO2 [16,17], V2O5 [18], [19], [20], KCuFe(CN)6 [21], etc. have been developed [12,[22], [23], [24]]. It has proved that crystalline materials with large particle sizes restrict ion diffusion due to the close stacking lattices generating narrow Zn2+ migration channels [25,26]. In contrast, amorphous metal oxides have displayed prominent advantages in energy storage areas because their loose structures equipped with ample active sites, free volume and ion channels for charge storage and diffusion [26], [27], [28]. Thus, some investigations on amorphous Zn2+ host materials such as VN0.9O15 [25], MnO2 [28], V2O5 [29] and FeVO4 [30] have been conducted, which demonstrate apparent performance improvement. The further development of novel amorphous host materials is an attractive and challenging topic. To our knowledge, there is no report on amorphous POMs that have been applied to aqueous ZIBs so far although some crystalline POMs with flexible molecular / electronic structures and unique multi-electron redox behaviors have revealed great potential in various batteries [31], [32], [33], [34]. Besides, the dissolution of POM species in aqueous electrolyte leads to severe capacity fading and hinder their direct applications in aqueous batteries [35]. Therefore, designing and manufacturing amorphous POM-based materials with poor solubility would provide a new opportunity for exploiting high-performance Zn2+ host materials and expanding the application domains of POMs.

In order to tackle the existing problems in both ZABs and POM-based ZIBs, preparing amorphous POM-based Zn2+ storage host with good Ag+ and POM confinement effect is necessary and innovative. Herein, a water-soluble high-nuclearity mixed-valence POM K10[VIV16VV18O82]•20H2O (KV34) that has demonstrated reversible multi-electron redox activity and fast Zn2+ diffusion kinetics [35], was utilized to prepare amorphous Agx[V34O82] (0 < x ≤ 10) (AgV34) precipitates. Due to the strong electrostatic interaction between Ag+ cations and polyoxoanions, there is no enough time to orderly arrange clusters in the precipitation process, and then amorphous AgV34 precipitates would be produced. Meanwhile, the mixed-valence [VIV16VV18O82]10– can efficiently reduce excess Ag+ to Ag nanoparticles, forming an electron conductive Ag and Ag-POM composite material. During the precipitation process, the reduction reaction of Ag+ occurs, which avails to further enhance the electron conductivity of the POM-based cathode. Using Ag@AgV34 as the cathode coupling with a metal Zn anode in 2.5 M Zn(CF3SO3) aqueous electrolyte, an entirely new-type Zn-based hybrid battery that integrates the Zn−POM system with chemical valence changes of V34 clusters and the Zn−Ag system bearing the redox reaction of the Ag0/Ag+ pair has been developed (Fig. 1a), which is completely different from other reported Zn-based hybrid batteries [1,3,[36], [37], [38], [39], [40], [41], [42], [43], [44]]. Owing to the positive synergistic effect between Zn−Ag and Zn−POM systems, the hybrid battery manifests enhanced reversible capacity with admirable capacity retention, superior rate performance and long-term cycling stability.

Section snippets

Results and discussion

Crystalline KV34 precursor with ellipsoid-shaped [VIV16VV18O82]10– anion with sizes of 1.27 × 1.58 nm2 (Fig. 1b) was synthesized according to the reported method and shows good solubility in aqueous solution (see details in the Supplementary Material) [35,45]. The reaction of KV34 with AgNO3 led to the formation of the insoluble Ag@AgV34 composite through strong electrostatic interaction between Ag+ ions and V34 anions and their high redox activity (Fig. S1). Electrospray ionization mass

Conclusion and outlook

We discovered the first aqueous hybrid battery with an amorphous POM-based composite cathode that integrates electrochemical features of Zn−Ag battery and Zn−POM battery through successive Ag+ cationic and polyoxoanionic redox reactions. It should be noted that crystalline Ag nanoparticles and loose packing POM clusters in the matrix engineer unobstructed ion / electron diffusion kinetics. Furthermore, strong electrostatic interactions between Ag+ cations and polyoxoanions efficiently restrain

CRediT authorship contribution statement

Kai Yang: Conceptualization, Data curation, Formal analysis, Writing - original draft, Writing - review & editing. Yuxuan Ying: Data curation, Investigation. Lulu Cui: Data curation, Investigation. Jianchao Sun: Conceptualization, Methodology. Hao Luo: Conceptualization, Methodology. Yuanyuan Hu: Conceptualization, Formal analysis, Funding acquisition, Writing - original draft, Writing - review & editing. Junwei Zhao: Conceptualization, Project administration, Resources, Supervision,

Declaration of Competing Interest

The authors declare no competing interests.

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (21871077, 21671054, 21771052, 21902044), the Program for Innovation Teams in Science and Technology in Universities of Henan Province (20IRTSTHN004), China Postdoctoral Science Foundation (2019M652517), the Major Project of Science and Technology, Education Department of Henan Province (202102310224), the Program of First-Class Discipline Cultivation Project of Henan University (2019YLZDYJ02, CJ1205A0240019

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