Impact of functional groups on lithium salt dispersion and mobility in polymer electrolytes

Solid Polymer electrolytes are versatile, highly processible and electrochemically compatible with solid electrode materials. The versatility of these materials is a result of the existence of many possible conductive polymer‐salt, polymer‐polymer and salt‐salt combinations. Despite the wide array of available lithium salts, most polymer electrolyte materials are made using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) due to its long history of achieving relatively high ionic conductivities in polymer electrolyte systems with the most famous being poly(ethylene oxide) (PEO). It is however possible that better ionic conductivities can be achieved with different salts and/or in polymer matrices containing different functional groups. This is because ionic conductivity in polymer electrolytes is partially based on the ability of the polymer matrix to dissolve and bond to the salt. These interactions impact local‐scale ion mobility which can be measured via NMR spectroscopy using pulsed field gradient experiments. In this work, polymer electrolytes are prepared using PEO, hydrogenated nitrile butadiene rubber and poly(propylene) carbonate. Ion mobility, lithium conductivity and salt‐polymer interactions are investigated to compare interactions between LiTFSI and lithium cyano(trifluorosulfonyl)imide in polymers with common salt‐dissociating functional groups such as ethyl, nitrile and carbonate to determine the impact of these interactions on ionic conductivity.