Tailoring the electrochemical properties of catholytes for solid-state sodium batteries
type: CreativeWork
description: Sodium-based all-solid-state batteries (ASSBs) represent a promising alternative to lithium-based systems due to their inherent safety and the abundance and low cost of sodium resources. However, their large-scale adoption is hindered by limited solid electrolyte ionic conductivity, poor interfacial compatibility with layered-oxide cathodes, and reduced cathode-level energy density resulting from inactive components within the composite electrodes. This dissertation investigates the electrochemical properties of solid electrolytes functioning as catholytes in ASSBs and establishes fundamental design principles for achieving high ionic conductivity, interfacial stability, and cathode-level energy density. The first part of this work focuses on polycarbonate-based solid polymer electrolytes incorporating sodium bis(fluorosulfonyl)imide (NaFSI) salts. These studies clarify the role of polymer–salt coordination in governing ionic transport and interfacial stability. Optimized formulations exhibit improved sodium-ion conductivity and cycling stability with layered-oxide cathodes and Na–Sn alloy anodes, supported by analysis of gas evolution and interfacial degradation pathways through online electrochemical mass spectrometry and post-mortem microscopy. The second part explores low-cost aluminum halide-based catholytes with tunable structural and electrochemical characteristics. Mechanochemical synthesis of NaAlCl₄ and its oxygen- and fluorine-modified derivatives reveals the critical influence of anion substitution and surface phase formation on sodium-ion transport and electrochemical performance. Oxygen incorporation produces composite electrolytes with conductivities exceeding 0.1 mS cm⁻¹ ; fluorination yields AlF₃–NaAlCl₄ mixtures with improved ionic conductivity, but no change in oxidative stability, so artificial cathode coatings are found to be necessary for high-voltage cycling stability. These findings are further explored by elucidating the chemical decompositi…
abstract: Sodium-based all-solid-state batteries (ASSBs) represent a promising alternative to lithium-based systems due to their inherent safety and the abundance and low cost of sodium resources. However, their large-scale adoption is hindered by limited solid electrolyte ionic conductivity, poor interfacial compatibility with layered-oxide cathodes, and reduced cathode-level energy density resulting from inactive components within the composite electrodes. This dissertation investigates the electrochemical properties of solid electrolytes functioning as catholytes in ASSBs and establishes fundamental design principles for achieving high ionic conductivity, interfacial stability, and cathode-level energy density. The first part of this work focuses on polycarbonate-based solid polymer electrolytes incorporating sodium bis(fluorosulfonyl)imide (NaFSI) salts. These studies clarify the role of polymer–salt coordination in governing ionic transport and interfacial stability. Optimized formulations exhibit improved sodium-ion conductivity and cycling stability with layered-oxide cathodes and Na–Sn alloy anodes, supported by analysis of gas evolution and interfacial degradation pathways through online electrochemical mass spectrometry and post-mortem microscopy. The second part explores low-cost aluminum halide-based catholytes with tunable structural and electrochemical characteristics. Mechanochemical synthesis of NaAlCl₄ and its oxygen- and fluorine-modified derivatives reveals the critical influence of anion substitution and surface phase formation on sodium-ion transport and electrochemical performance. Oxygen incorporation produces composite electrolytes with conductivities exceeding 0.1 mS cm⁻¹ ; fluorination yields AlF₃–NaAlCl₄ mixtures with improved ionic conductivity, but no change in oxidative stability, so artificial cathode coatings are found to be necessary for high-voltage cycling stability. These findings are further explored by elucidating the chemical decompositi…
author: Ruoff, Erick
language: English
keywords: Solid state batteries, Sodium batteries
date published: 2025-12
date modified: 2026-07-24T05:01:10Z
provider: University of Texas
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: The University of Texas at Austin

PropertyValue
property ID: Handle
value: https://hdl.handle.net/2152/135906

PropertyValue
property ID: DOI
value: 10.26153/tsw/63219