Cation Chemistry and Molecular Weight Effects on the Ion Conductivity in PEO-based Electrolytes
Chrysostomos Papamichail, Olympia Techlemtzi, Georgia Nikolakakou, Emmanouil Glynos
Abstract
High Resolution Image Download MS PowerPoint Slide This study investigates the fundamental influence of cation chemistry on the ionic conductivity of PEO-based electrolytes, with implications for advancing polymer electrolyte design. Two PEO systems─high molecular weight ( M w = 100 kg/mol) and low molecular weight ( M w = 0.35 kg/mol)─were blended with LiTFSI and NaTFSI salts to explore ion transport mechanisms. In the high- M w PEO, where ion hopping dominates, smaller Li + ions exhibit higher conductivity (σ LiTFSI > σ NaTFSI ). In contrast, the low- M w PEO, where ion diffusion is the primary mechanism, shows higher conductivity for larger Na + ions (σ NaTFSI > σ LiTFSI ). In the former, rheology measurements indicate that larger Na + cations form more transient EO:Na + contact, hindering cation hopping and reducing conductivity. In the latter, the stronger EO:Li + interactions lead to a larger hydrodynamic radius and slower diffusion. Notably, PEO-0.35K:NaTFSI exhibits a room-temperature conductivity of σ NaTFSI ≈ 4 × 10 –4 S/cm, meeting the requirements for practical applications. These findings highlight the potential of low- M w PEO and Na-based electrolytes for the development of efficient Na-ion batteries.