Organic carbonates currently compromise the bulk solvent components in electrolytes for Li-ion and Na-ion batteries.  With interest in improving the safety and stability of electrolytes under more aggressive use conditions (i.e. higher temperature, higher voltage etc.) there is the need to investigate alternatives for the traditional carbonate mixtures. One key class of electrolyte compounds which has received significant interest is phosphorus-containing electrolytes. As a class of compounds improvements in both electrolyte stability and safety have been observed. Included in the class of phosphorus-containing compounds are phosphazenes. The presentation will describe early work using a sub-class of phosphazenes, phosphoranimines (PAs), as a partial replacement of carbonates in alkali-ion batteries. 

            Early investigations suggest that the PAs may improve both the stability and safety of alkali-ion batteries due to their wide thermal stability and due to the ability to achieve loading levels which surpass those seen for larger phosphazene compounds. As an example, open-cup flashpoint analysis of high PA content electrolytes shows that the flashpoint can be increased by up to 20˚C and at loading levels of 35% by volume the viscosity of the solution is maintained below 8 cP. As a component in an electrolyte system the use of PAs show the ability to retain capacity on par with traditional carbonate blends. The presentation will discuss cycling performance of a host of electrolyte combinations which contain PAs including the interaction seen with additives such as vinylene carbonate and fluoroethylene carbonate. Also included will be a discussion of synthetic preparation and characterization of this sub-class of phosphazenes.