Deciphering Interfacial Reactions via Optical Sensing to Tune the Interphase Chemistry for Optimized Na-Ion Electrolyte Formulation

Abstract

Interphases, solid-electrolyte interphase (SEI), and cathode-electrolyte interphase (CEI) are the key influencers in determining battery life and performance. Especially, for technologies such as sodium-ion batteries that are in the development stage, it is crucial to tune the interphase chemistry without which it suffers at present from poor performance metrics for reaching real-life applications. In this study, optical sensors are utilized as a tool to follow operando, the thermal events of interfacial reactions, and establish the role of different electrolyte additives during the SEI/CEI formation. Using the acquired knowledge from sensing, together with complementary studies in Na-ion full-cells, a new electrolyte formulation is proposed that shows stable cycling performance at 0–55 °C with very low self-discharge and improves safety due to mitigated gassing during cycling. Finally, the studies are nurtured by transferring the know-how to prototype cylindrical 18 650 cells. It is hoped that such findings will accelerate the practical development of Na-ion batteries.