Rational design of cell configurations for high-performance Na-O2 batteries

Xiaoting Lin, The University of Western Ontario

Abstract

Na-O₂ batteries are considered as the promising candidates for electric vehicles due to their ultrahigh theoretical energy densities. However, state-of-the-art Na-O₂ batteries suffer from serious challenges including 1) pore clogging and insufficient O₂ transportation within the air electrode; 2) degradation of air electrode, 3) Na dendrite growth; and 4) Na corrosion induced by O₂/O₂^- crossover. This thesis, therefore, focuses on rational design of cell configurations to address these problems and understanding the insight mechanisms.

3D printing of “O₂ breathable” air electrodes for Na-O₂ batteries were first developed. The unique air electrode structure features non-competitive pathways for O₂, electrons, and Na⁺, leading to high-capacity and long-life Na-O₂ batteries.

Except for air electrode, it is found that the Na anode also plays crucial roles in determining the Na-O₂ cell performance. To prevent the Na dendrite growth and Na degradation induced by O₂/O₂^- crossover, novel Na-O₂ batteries using carbon paper protected Na anode was first designed. Besides, hybrid solid-state Na-O₂ batteries based on solid-state electrolytes and protected Na anodes were successfully developed.

Furthermore, the cycling stability of Na@alucone anode was investigated. It is revealed that the chemical stability of Na protective layer against O₂^- is critical to the cycling stability of Na anode, and a universal approach was proposed to achieve high-performance Na-O₂ batteries.

A flame-resistant, dendrite-free and O₂/O₂^-- impermeable composite electrolyte was fabricated, both safety and electrochemical performance of Na-O₂ batteries can be enhanced significantly.

In summary, the discoveries in this thesis provide important guidance to achieve high-performance Na-O₂ batteries.