Advancing zinc-ion batteries: holistic solutions for cathode, anode, and electrolyte optimisation

Thesis

Zinc-ion batteries (ZIBs) have emerged as promising energy storage systems owing to compatibility of zinc anodes with aqueous electrolytes. While aqueous electrolytes provide advantages in safety, they also introduce critical challenges at both electrodes. At the zinc anode, parasitic side reactions and dendritic growth compromise reversibility, while Mn-based cathodes suffer from Mn dissolution, limiting cycle life. Together, these interfacial instabilities hinder the practical deployment of ZIBs in large-scale applications.

This thesis develops an understanding of degradation mechanism and proposes strategies to overcome them. Firstly, the zinc anode–electrolyte interface is investigated. While high current densities can promote planar Zn growth, they are incompatible with cathode operation. To resolve this, an approach using uniaxial mechanical pressure is introduced, enabling stable zinc plating/stripping under practical current densities.

Secondly, the focus shifts to the MnO2 cathode–electrolyte interface. Using operando analysis, it is shown that the primary charge storage mechanism proceeds via reversible Mn dissolution and redeposition. Furthermore, the role of Mn2+ additives is found to act as a soluble redox reservoir, supplying additional active material during charging. These findings highlight the strong coupling between battery electrochemical performance and electrolyte composition.

Thirdly, recognising that many challenges are inherent to aqueous environments, zinc-metal-free cell architectures are explored. A new zinc-containing disordered rocksalt (DRX) cathode, ZnMnO2, is developed to pair with a zinc-free current collector. This anode free cell demonstrated promising electrochemical performance, offering advantages such as extended shelf life and higher energy density.

Finally, to further mitigate side reactions, non-aqueous ZIBs are explored. To unlock efficient Zn2+ diffusion in DRX cathodes under non-aqueous conditions, cation vacancies are engineered by delithiating Li-based DRX precursors, leading to improved Zn2+ transport and enhanced battery performance.

These insights provide guiding principles for the rational design of next-generation ZIBs with improved stability and performance.

Authors: Li, Z

• DOI: 10.5287/ora-pryrxqy7y
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: aqueous battery; cathode; Zn ion battery