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Thesis Format

Integrated Article

Degree

Master of Science

Program

Chemistry

Supervisor

Song, Yang

Abstract

Polysulfide materials have drawn extensive attention for next-generation battery development since the current lithium-ion battery has almost reached its limit regarding energy density and safety issues. Many phosphorus and sodium sulfide materials have been used in different battery types, such as solid-state and sodium-sulfur batteries. However, there are still issues that prevent these techniques from applications. In recent years, there has been increasing attention on investigations of the structural and phase transformations of electrode and electrolyte materials under high pressure. Many studies have shown that external pressure can affect structural properties and influence electrical properties. In this study, three battery-related materials, P4S3, P4S10, and Na2S4, were investigated under high-pressure conditions for the first time using in-situ vibrational spectroscopy. Structural reversibility and phase transition upon compression were studied for all three materials. In terms of P4S3, two phase transitions were identified, one at about 3 GPa and 7 GPa. The amorphous state was at 13 GPa. For P2S5, two phase transitions were observed upon compression at 3 GPa and 7.5 GPa. When the pressure reached above 12 GPa, the material became amorphous. For Na2S4, three phase transitions occurred upon compression at about 1, 6 and 11 GPa. The material would reach the amorphous state at 16 GPa. Overall, our high-pressure studies of these three materials could further understand how these materials react to external compression and could promote the improvement of their performance as battery materials or the development of new battery materials.

Summary for Lay Audience

In recent years, Lithium-ion battery (LIB) as a mature battery technique has been almost reached its limitation due to the increasing demand for batteries with better performance. Several battery techniques have been considered to be the next-generation batteries, such as all-solid-state batteries and sodium-sulfur batteries. Many sulfur-containing materials have been proposed for these battery techniques. In Particular, Polysulfide played an important role in determining battery performance. Therefore, understanding the structures and enabling the structural modifications of these polysulfides are of great importance in improving the battery performance. Moreover, many studies have shown that external pressure can affect structural properties and influence the electrical properties of a material.

In this study, three battery-related polysulfide materials P4S3, P4S10, and Na2S4, were investigated under high-pressure conditions for the first time using in-situ vibrational spectroscopy (Raman and IR). This information allows the precise determination of structural stability and reversibility of these materials. In addition, the pressure-induced modification was also observed for the first time. This new structural information provides a further understanding of how these materials react to external compression and could promote the improvement of their performance as battery materials or the development of new battery materials.

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