Lithium-Sulfur (Li-S) Batteries are among the most promising energy storage technologies for the fifth generation of batteries, often referred to as post-Li-ion. With a theoretical energy density five times higher than that of conventional Li-ion batteries and an abundant availability of sulfur, the Li-S system offers a unique potential to meet the growing demand for sustainable energy storage. However, current technology is limited by major challenges related to the dissolution of polysulfides in the electrolyte, leading to active sulfur loss, poor cycle life, and insufficient electrochemical performance. These limitations currently hinder the market deployment of this technology.
This thesis aims to explore an alternative approach based on an all-solid electrochemical sulfur conversion mechanism. To achieve this, a next-generation organic solid electrolyte developed in the laboratory will be implemented. This electrolyte features a unique lithium-ion conduction mechanism within a crystalline lattice, preventing polysulfide solubilization. The main objectives are:
1. To understand and control the ionic conduction mechanisms in these electrolytes.
2. To integrate this solid electrolyte into an innovative Li-S system.
3. To optimize the cathode structure for the solid-state mechanism and evaluate the electrochemical performance on a representative prototype scale.
The PhD candidate will use a wide range of characterization and analysis techniques to carry out this project:
• Formulation and characterization of the organic solid electrolyte: Techniques such as FT-IR and NMR to analyze chemical structures and identify the properties of synthesized materials (DSC, TGA, XRD, etc.).
• Electrochemical characterization: Analyses using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and symmetric cell cycling tests to study ionic conduction properties and electrolyte stability.
• Formulation and performance study of the cathode: Formulation of carbon/sulfur composites and sulfur cathodes integrating the solid electrolyte; galvanostatic cycling tests and advanced interface analyses to understand and optimize solid-state sulfur conversion.
The research will progress in three main phases:
1. Development and characterization of the solid electrolyte: Material development, analysis of conduction mechanisms, and optimization of ionic and mechanical properties.
2. Design and optimization of the cathode structure: Improving electrolyte/cathode interfaces for solid-state sulfur conversion.
3. Electrochemical performance evaluation: Experimental validation of prototypes through in-depth tests, including cyclability and power performance.