Topic Name: Electrolytes Made of Rigid Polymers Show Promise in Lithium Batteries

Category: Electric Vehicle

Research persons: Northwestern University

Location: Chicago, United States

Details

Goal: Synthesize and test a new class of rigid polymer electrolytes for rechargeable lithium batteries Lithium-based batteries offer great potential for commercially practical, full-range electric and hybrid electric vehicles because of their promising electrochemical characteristics. Continuing research is aimed at optimizing energy storage, rechargability, battery weight, and other characteristics while reducing costs. Such batteries essentially consist of two electrodes separated by an electrolytic material. Much research today involves finding an electrolyte that has high conductivity for lithium ions and good mechanical properties, while reacting chemically with lithium as little as possible Scope of Work Previously, researchers at Northwestern University developed a rigid polymer system, poly(1,3-dioxolan-2-one-4,5-diyl oxalate) (PVICOX), that displayed favorable conductivity and mechanical properties. However, when a polymer electrolyte containing PVICOX was incorporated into lithium cells, the energy capacities of the cells were found to be low because a highly resistive layer formed between the lithium anode and the electrolyte as a result of chemical reactions. Impedance of Lilthium/Polysulfone Electrolyte SystemThe impedance of an early lithium/polysulfone electrolyte system. Since then, the researchers have synthesized rigid polymers containing sulfone groups, as it was expected that polymers containing sulfur-oxygen bonds should provide rapid ion transport and have very good stability in the presence of lithium. Several polysulfones have been synthesized, and electrochemical cells containing electrolytes based on them were fabricated and tested. Results and Future Plans The polysulfone-containing polymer electrolytes were found to be more stable toward lithium metal than PVICOX, since after 64 h of operation, test-cell resistance only tripled (see figure), in contrast to PVICOX, whose use led to increases in resistance of two orders of magnitude in only a few hours. A capacity of up to 100 mAh per gram of active cathode material was achieved at current density of 15 µA/cm2. However, the capacity dropped significantly with an increase in current density to 40 µA/cm2, due to high cell resistance. The researchers are now synthesizing more promising sulfone-containing polymers. They are exploring different synthetic routes for these polymer, with emphasis on high yield, and anticipate that when doped with salt, they will display higher ionic conductivities than previous polymers. They also expect higher stability for these polymers toward lithium. Research Partner Northwestern University