Publication Date

2023

Document Type

Dissertation/Thesis

First Advisor

Cheng, Yingwen

Degree Name

Ph.D. (Doctor of Philosophy)

Legacy Department

Department of Chemistry and Biochemistry

Abstract

Batteries with low-cost, high energy and safe features density are now widely demanded.This dissertation systematically and comprehensively studies the materials and electrochemical interfaces of sodium (Na) metallic anodes and metal-free anodes for high energy density sodium metal batteries (SMB) to meet energy storage demands. This dissertation is divided into two sections, with the first section focusing on the modifications made to pristine metallic sodium anodes using 1.6 at % tin (Sn) to create Na-Sn alloy anodes. The results confirm that the Na-Sn anode features interconnected Na15Sn4 backbones that support sodium structurally, enhance Na+/Na redox kinetics, and facilitate dendrite-free Na plating with more stable solid-electrolyte interfaces (SEI). The composite Na@Na15Sn4 anode enabled very stable cycling of symmetric cells even at 5.0 mA cm−2 and improved the stability of full cells coupled with 3.0 mAh cm−2 Na3V2(PO4)3 cathodes to >90% capacity retention for 300 cycles. The second section (Chapter 3-4) reports the electrochemical interfaces studies of Na reversibility on zinc (Zn), copper (Cu) and aluminum (Al) surfaces. Specifically, Chapter 3 systematically investigates electrochemical interfaces for Na plating and stripping and describes the use of the Zn surface to develop nearly fully reversible Na anodes with 1.0 M NaPF6 in a diglyme-based electrolyte. The high performance includes consistently higher than 99.9% Faradaic efficiencies for a wide range of cycling currents between 0.5 and 10 mA cm−2, much more stable interfacial resistance and nearly no formation of mossy Na after 500 cycles compared with conventional Al and Cu surfaces. This improved reversibility was further confirmed under lean electrolyte conditions with a wide range of electrolyte concentrations and cycling temperatures and can be attributed to the strong interfacial binding and intrinsic sodiophilic properties of the Zn surface with Na. As a result, full cells assembled with Na-free Zn foil and a high capacity Na3V2(PO4)3 cathode delivered ∼90% capacity retention for 100 cycles, higher than the 73% retention of Cu foils and much higher than the 39% retention of Al foils. Chapter 4 focuses on the most practical Al foil current collectors and systematically examines the effect of nano-sized carbon coating on improving Na plating and stripping stability. This study identified that the carbon-Al junction interface generated by carbon coating is crucial in enabling uniform Na depositing with lower overpotentials, delivering higher than 99.8% Faradaic efficiencies for a wide range of cycling currents between 0.5 and 3.0 mA cm-2. The results show that the performance is much better than the 96.4% efficiency observed on uncoated Al foils under the same conditions and was also confirmed under lean electrolyte (5 µL) and freezing electrolyte conditions (-30 °C). This enhanced electrochemical performance can be attributed to the stronger interfacial binding and sodiophilic properties of the carbon-aluminum junction sites. These sites not only ensure uniform Na plating but also eliminate side reactions that would otherwise cause electrolyte depletion. As a result, Na-metal free full cells assembled with high capacity Na3V2(PO4)3 cathode delivered ~93% capacity retention for 100 cycles, higher than the ~ 42% of retention of uncoated Al foil.

Extent

162 pages

Language

eng

Publisher

Northern Illinois University

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In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

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