Phosphorus-Containing Electrolytes - Expansion to Include Phosphoranimines for Li-Ion Batteries

The use of organic carbonates as the principle solvent component in electrolytes for Li-ion batteries (LIBs) has been well established. For low to medium voltage applications these compounds are effective, yet for high voltage applications, issues arise. Other problems, associated with the overall safety and stability of carbonate-based electrolytes, have also been observed. Small and highly oxygenated carbonates are both volatile and combustible. This combination is ill-suited for applications where a high level of safety is desired, such as in electric vehicles. To improve battery safety there has been significant interest in phosphorus-containing electrolytes due to their inherent non-flammability. Included in this broad class of electrolyte components are phosphazenes which contain a phosphorus-nitrogen (P=N) bond. Previous work in the energy storage arena has looked at the use of poly-phosphazenes as electrolyte additives, polymeric electrolytes and as electrode components.

            As electrolyte components, poly-phosphazenes, including cyclotriphosphazenes, have been shown effective at mitigating safety issues and in enhancing electrolyte stability.¹ While successful, these compounds possess limitations related to total loading capacity in the electrolyte and also experience decreased performance at intermediate cycling rates. In order to alleviate some of the issues associated with the larger cyclotriphosphazenes, recent research has shifted to the investigation of linear phosphoranimines which contain a single P=N unit. These compounds which have lower molecular weight than other poly-phosphazenes, show promise in negating some of the limitations associated with the larger molecules.  The initial electrochemical, chemical and physical characterization of phosphoranimines will be presented.

 

1. H. W. Rollins, M. K. Harrup, E. J. Dufek, D. K. Jamison, S. V. Sazhin, K. L. Gering, et al., J. Power Sources, 263 (2014) 66-74