Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Mechanical and Materials Engineering

Supervisor

Zhao, Yang

Abstract

High theoretical capacity, low electrochemical potential, and abundant resources of metallic Na make it an appropriate candidate as the anode material in Na metal batteries (NMBs) and show its potential to complement Li-ion batteries. However, like its Li counterpart, the Na metal anode suffers from uneven plating/stripping behavior leading to dendrite growth, “dead Na” formation and even cell interior short-circuit. Another issue is the low Coulombic efficiency (CE) which results from the formation of unstable solid electrolyte interphase (SEIs) and continuous consumption of the electrolyte. This thesis mainly proposes an effective strategy to overcome the above shortcomings through the improvement of the Na electrode/electrolyte interface stability. Two types of hybrid artificial organic/inorganic SEI layers were developed on the surface of the Na metal anode using advanced atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques. The hybrid SEI can efficiently restrain the growth of Na dendrite and greatly improves the cycling stability performance. This thesis opens a new window to design the nanostructure interfaces for Na metal anodes for the next-generation NMBs.

Summary for Lay Audience

Motivated by the rapidly increasing demand for energy storage systems, lithium-based batteries have gained significant popularity. These types of batteries have been significantly developed in recent years; however, they have some drawbacks such as limited availability and rising costs of lithium resources. To address these limitations, sodium (Na)-based batteries attract huge attention as an alternative and complementarity because of the more abundant and cost-effective Na resources compared to lithium counterparts. Among different types of anode materials, sodium metal anodes have received much attention because they offer high theoretical capacity and low electrode potential. However, Na metal anodes face challenges, including dendrite growth, undesired side reactions, unstable solid electrolyte interphase (SEI), and volume fluctuation. To overcome the above-mentioned issues, researchers have proposed various strategies. One promising approach is interface engineering, which involves creating a stable and uniform solid electrolyte interface (SEI) layer on the surface of the Na metal anode. In this regard, this research work intends to improve the stability and overall performance of Na metal anode through the fabrication of hybrid organic and inorganic coating layers and comprehensive optimization of their structural designs and thicknesses. In addition, a detailed surface analysis of the original electrode and the cycled electrode was carried out to understand the evolution of the SEI formation and investigate the interface properties of the metallic Na electrode and liquid electrolyte. The first section of the thesis contains a design of hybrid multi-layers including metal oxide (Al2O3) and alucone polymer films for the Na metal anodes to achieve stable cycling performance. In the second section, the dual protective layers, inorganic Al2O3 and organic alucone, have been introduced as an effective way to stabilize the electrode-electrolyte interface. Overall, the fundamental understanding of the working mechanism of the SEI layer is critical to the design of hybrid organic and inorganic coating layers and provides valuable insights into improving the performance and durability of Na batteries, bringing us closer to achieving better energy storage systems for various applications.

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