Vanadium-based and Manganese-based Cathode Material for Rechargeable Aqueous Zinc-ion Batteries

Abstract

Rechargeable batteries offer a feasible solution to storing the intermittent energy supplies associated with renewable energy production. Despite the dominance of lithium-ion batteries (LIBs) in the current battery market, their application is hindered by the scarcity of lithium resources, unaffordable costs, and safety concerns. Consequently, rechargeable aqueous zinc-ion batteries (RAZBs) with mildly acidic electrolytes have garnered attention due to their cost-effectiveness, high safety and environmental friendliness. However, identifying suitable zinc ion intercalation-type cathode materials that meet commercial standards remains a significant challenge, impeding the widespread adoption of RAZBs. Vanadium- and manganese-based compounds, recognized for their unique structures and substantial theoretical capacities, are among the foremost cathode materials for RAZBs. Nonetheless, these materials often suffer from structural degradation during cycling, limited electrical conductivity, and severe side reactions, substantially restricting their practical applications. In this thesis, we introduce strategies to improve the electrochemical performance of vanadium-based and manganese-based cathodes in RAZBs through ionic pre-intercalation techniques and the integration of cathode-electrolyte interface layers, respectively. In particular, the RAZB with an improved vanadium-based cathode maintains 90% capacity after 4000 cycles and achieves a discharge specific capacity of 209 mAh g-1 at 5 C. Furthermore, our in-depth analysis of the reaction mechanisms in vanadium-based cathodes with pre-intercalated ions uncovered a reversible dual-cation (Zn2+ and Na+) intercalation chemistry. This not only stabilizes the vanadium-based material structure, but also facilitates the free access of ions from the electrolyte to the cathode, thus mitigating structural collapse or failure due to ion insertion during cycling. In the study of MnO2 cathodes, we have prioritized the exploration of the intrinsic failure mechanism and disclosed the phenomenon of "ionic crosstalk" between electrodes for the first time. The release of a significant amount of Mn2+ ions from the MnO2 cathode detrimentally impacts the ion concentration on the Zn anode surface, which is detrimental to the uniform deposition of zinc metal and exacerbates the growth of dendrites as well as anode corrosion; simultaneously, the stripping of Zn2+ ions from the zinc anode results in the formation of by-products on the cathode and triggers irreversible phase transitions in the cathode material. These ionic crosstalk effects exacerbate electrode deterioration, culminating in the failure of the Zn-MnO2 battery system. To address this, we apply a hierarchical porous membrane on the MnO2 cathode surface to mitigate ionic crosstalk and promote reversible dissolution/deposition reactions. As a result, the cell demonstrates an exceptional capacity retention of 97% after 1000 cycles at 2 C and an operational lifespan exceeding 500 hours, markedly outperforming previously reported aqueous Zn-MnO2 batteries by over 1.5 times. Furthermore, to explore the commercial potential of MnO2 cathode materials, we combine the liquid-phase in situ encapsulation method with a straightforward heat treatment to cover a Bi2O3 layer on the MnO2 material surface. This approach facilitates a significant increase in the mass loading of the cathode material to 16 mg cm-2. Our findings reveal that these cathodes exhibit exceptional cycling stability and Coulombic efficiency in larger battery configurations, with an exceptional capacity retention of 72.7% over 330 cycles (equivalent to a calendar life of 60 days), showcasing its superior performance and reliability for high-energy-density battery applications. These results not only underscore the significant potential of Bi2O3 coating technology to advance the development of aqueous Zn-MnO2 batteries but also lay a solid foundation for the commercialization of aqueous batteries.