“Thermodiffusion in Lithium and Sodium Symmetric Electrochemical Cells with Polymer Electrolyte”

Dept: Chemical & Biomedical Engineering

Chair: Daniel Hallinan, Jr., Ph.D.

Abstract

Thermogalvanic cells can convert low-grade waste heat into electrical energy by generating a voltage when a temperature gradient is applied across an electrolyte. This project investigated the thermal voltage response of solid polymer electrolytes based on poly(ethylene oxide)(PEO) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI). Two polymer molecular weights were studied (PEO 8,000 g/mol and PEO 4,000,000 g/mol) at a fixed salt loading of 0.085 mol cation per ethylene oxide unit, over a temperature range of 60–80 °C. Across both molecular weights, the LiTFSI–PEO systems produced slightly higher Seebeck coefficients than the NaTFSI–PEO systems. These results suggest that cation identity and ion–PEO coordination dominate the thermoelectric response in these solid polymer electrolytes, and they can provide initial guidance for selecting polymer–salt combinations for waste-heat recovery using thermogalvanic cells.