Li, Jianwei; (2021) Vanadium oxides and their derivatives as superb cathodes for aqueous zinc ion batteries. Doctoral thesis (Ph.D), UCL (Univerisity College London).

Preview

Text PhD thesis from Jianwei Li .pdf Download (9MB) | Preview

Abstract

Aqueous zinc ion batteries have drawn great attention recently due to remarkable properties compared with conventional batteries systems, which attains benefits from the low-cost and ultra-safe aqueous electrolyte, and the stable metallic zinc anode. However, cathode materials in aqueous zinc ion batteries still require a breakthrough because of relatively slow kinetics and unstable microstructures for Zn2+ intercalation/extraction in aqueous zinc salt electrolyte compared with other metal ions batteries. Therefore, this thesis targets on design and development of vanadium-based cathodes and their derivatives to overcome the issues and bring a deep insight into the energy storage mechanism. Step-by step investigations of novel cathode materials were carried out to evaluate their physiochemical properties, electrochemical performance and microstructures/chemical states evolutions upon charge/discharge process. Moreover, Density functional theory (DFT) and 3D-tomorgraphy simulations were adopted to elucidate specific characteristics of as-prepared cathode materials and their corresponding electrodes. Finally, the as-fabricated zinc ion batteries exhibit competitive performance in terms of high energy/power density and long cycling stability compared with reported researches in this area. The details of the work was summarized into three main aspects shown as follows: (1) Vanadium oxides cathodes are widely utilized as electrode materials in batteries system because of active redox species and various accessible microstructures for ions accommodation. However, conventional vanadium oxides still suffer from poor conductivity, irreversible phase transformation, structure collapse and confined ion migrations channels as cathode in aqueous zinc ion batteries, which results in unfavourable battery performance in previous reported works. Therefore, as vanadium pentoxide analogues, hydrated vanadium bronzes stepped into the spotlight recently because of their special two dimensional microstructures consisting of V2O¬5 matrix, pre-intercalated ions and/or water molecules accommodated within the layer space, which effectively overcome the issues. Here, an investigations of hydrated vanadium bronzes, δ‐Ni0.25V2O5.nH2O / Co0.25V2O5.nH2O , was carried to uncover the reaction mechanism and beneficial effects derived from pre-intercalated species. Moreover, different electrochemical behaviours between nickel vanadium bronze and cobalt vanadium bronze were discussed with a verdict of an importance of choosing competent pre-intercalated species for aqueous zinc ion batteries applications. Rational designed cathode electrode prepared by porous δ‐Ni0.25V2O5.nH2O micro-ribbons delivered a specific capacity of 402 mAh g−1 at current density of 0.2 A g−1 and a capacity retention of 98% over 1200 cycles at 5 A g−1, which achieved the uppermost performance compared with the literature. Meanwhile, a versatile design principle for novel vanadium bronzes was suggested for high performance energy storage materials. (2) Vanadium bronzes cathode materials have exhibited promising capability in aqueous zinc ion batteries. However, researches on improving as-developed vanadium bronzes are rare, which inevitably hinder their practical applications such as grid-scale energy storage system and portable devices. Therefore, higher power/energy density and cycling stability are eagerly needed for such purposes. In this work, a two-pronged approach of oxygen deficiency enriched and water-lubricated ammonium vanadium bronze (NH4V4O10) cathodes for high performance aqueous zinc ion batteries was exploited by tailored synthetic protocol consisting of induced defects and interlayer-spacing engineering. In particular, the conventional phase of NH4V4O10 were demonstrated as an adequate Zn2+ storage/extraction host with active redox sites in “double-layer” motif of VOx polyhedra and the introducing hydrogen-bonded NH4+ as the “pillar”. Oxygen deficiency and lattice water were successfully introduced into NH4V4O10, which demonstrated significantly improved Zn2+ storage properties, such as enhanced specific capacity of 435 mAh g-1 at 0.2 A g-1 and improved stability (negligible capacity decay after 1500 cycles at 10 A g-1). Combined with widely recognized beneficial pre-intercalated species of water and NH4+, the as-developed oxygen deficient NH4V4O10 illustrated a universal strategy for the design of superior vanadium bronze cathodes in aqueous zinc ion batteries and their broader sphere of applications in other types of aqueous metal-ion batteries. (3) Prussian blue analogues have been successfully adopted as cathodes materials for aqueous zinc ion batteries with relatively high discharge plateau, but they are limited by extremely low specific capacity (<70 mAh g-1) and poor cycling stability (self-dissolution in aqueous electrolyte). Moreover, conventional Prussian blue analogues consist of two metal ions coordinated with a cyanide group, which exhibits a rigid cubic crystal structure. The limited tunnel size and artificially introduced defects give rise to unstable electrochemical reactions and slow ion diffusion coefficient upon Zn2+ insertion/extraction. Therefore, a new Prussian blue analogues, vanadyl hexacyanoferrate and its defected analogue were proposed in this work. The resulting superb battery performance caused by an unique crystal structure, in which, the oxycation (vanadyl) occupy the ligand of [Fe(CN)6]4- generating similar cubic crystallography with spontaneously stable vacancy on its facets. Additionally, highly active vanadyl redox reaction between 3+ to 5+ and iron cyanide group contribute to a record-high specific capacity of 226 mAh g-1 at current density of 0.2 A g-1. Meanwhile, a hydrogel shield strategy was carried out to enhance the stability of the materials which exhibit extraordinarily long-cycling capability and optimized kinetics due to stabilization from surface anchoring polymerization, interfacial hydroxylation and accessible ion channels within the hydrogel. Furthermore, the as-obtained vanadyl hexacyanoferrate was assembled into a flexible quasi-solid state device with superior performance and robust durability under multiple mechanical measurements, demonstrating a promising potential for practical applications.

Download activity - last month

Export as CSVXMLJSON

Download activity - last 12 months

Export as XMLCSVJSON

Downloads by country - last 12 months

Export as CSVXMLJSON

Archive Staff Only

View Item