Date of Award

Winter 2022

Project Type

Dissertation

Program or Major

Chemical Engineering

Degree Name

Doctor of Philosophy

First Advisor

Xiaowei Teng

Second Advisor

Young Jo Kim

Third Advisor

Nan Yi

Abstract

Electrochemical energy storage is essential to free various electronic devices from electric wiring. Besides the prominent lithium-ion batteries, next-generation batteries using zinc ions as charge carriers in aqueous electrolytes have risen as attractive alternatives due to their superior safety, environmental-friendliness, low cost, and excellent theoretical performance. However, high-performance cathode materials to accommodate the capacity and cyclability of zinc-ion storage have been lacking because of the strong electrostatic interaction between multivalent Zn-ions and host cathode materials. This study suggests a few varieties of vanadium oxide derivatives with large interlayer spaces, excellent structural stability, and finely tuned structural properties. Alkali-intercalated vanadates (MVOs) are synthesized via dissolution-recrystallization processes, and their final structures showed a meaningful relationship with the alkali ions’ hydration properties. The smallest lithium-ion attracts the most water molecules to form the most oversized hydration shell to form LiVO with the most significant structural void spaces (intercalation spacing of 11.3 Å) that offer the best intercalation properties of charge carriers. Consequently, synthesized LiVO provides a higher specific capacity of 308 mAh g-1 at a current density of 0.05 A g-1. Improved redox kinetics has improved the cycling life of 96% capacity retention after 200 cycles at 0.4 A g-1 and 89% for 800 cycles at 1 A g-1. The potentiodynamics of MVOs are further investigated with in situ XRD/PDF analysis and ex situ XAS measurement. Disorder and ample interlayer spacing flexibly host sequential co-intercalation of zinc ions and protons reversibly. Also, the effects of electrolyte composition have been studied, revealing the lubricating effect of pre-intercalated water molecules and additives to reinforce the structural durability of the cathode material. Additional sodium ions played the common-ion effect in Zn/NaVO system to prevent NaVO dissolution and stabilize the cycling performance of Zn/NaVO cells with capacity retention of up to 62% after 300 cycles, significantly higher than the cells only using the original ZnSO4 electrolyte (7.6%). Moreover, vanadyl ions provide an additional conversion mechanism (VO2+ ↔ V2O5) to the existing intercalation mechanism for improved capacity and cyclability while preserving and participating in the pre-existing co-intercalation mechanism of zinc ions and protons. Consequently, the system boasts a remarkable storage capacity of 450 mAh g-1 at a current density of 0.05 A g-1 and excellent capacity retention of 82% after 500 cycles at 0.4 A g-1. Lastly, an interesting system with a manganese oxide cathode (sodium birnessite, Na0.27MnO2) with VOSO4 electrolyte additive is introduced. Initial investigations confirmed an excellent discharge capacity of 250 mAh g-1 at 0.05 A g-1 but with a poor cycling life. However, the in situ XRD suggests a possible breakthrough in cyclability by applying VO2+ to the ZnSO4 electrolyte to prevent phase inactivation processes. This study further highlights the possibility of disordered vanadium oxide species as a host material for more complicated but far more advanced charge storage systems.

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