A smart membrane with negative thermo-responsiveness in battery electrolyte solution

The challenge of thermal runaway in lithium-ion batteries necessitates innovative solutions to enhance their safety. In this work, a negatively thermo-responsive membrane is proposed with grafting poly (N-isopropylacrylamide) onto polydopamine-modified polypropylene (PP) membrane via the Michael addition reaction. The implementation of such smart membrane is achieved based on the upper critical solution temperature (UCST) of the PNIPAM in the electrolyte solution containing 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), ethylene carbonate/diethyl carbonate (EC/DEC), and lithium tetrafluoroborate (LiBF4). The conformational transition of the PNIPAM in the electrolyte solution is intricately influenced by the competing salting-out effect of [EMIM][BF4] and salting-in effect of LiBF4. By maintaining a constant 1.0 M LiBF4 concentration in the electrolyte solution, the UCST of the PNIPAM that is precisely adjusted according to the 45.5 wt%-50 wt% of [EMIM][BF4] in the mixed EC/DEC solution provides the gating temperature. When below the gating temperature, the PNIPAM gating polymer grafted on the PP membrane remains in a shrinkable state to let the electrolyte ions shuttle feely between the electrodes. Conversely, in the event of overheating stemming from inadvertent Li-ion battery mismanagement, the PNIPAM gating polymer becomes extensible above the gating temperatures, resulting in the closure of the separator membrane. This mechanism effectively arrests the mobility of electrolyte ions, thereby contributing to the enhanced safety and security of lithium-ion batteries. The finding in this work offers valuable insights into the design and development of smart battery membranes with enhanced safety features to advance the progress of lithium-ion battery technology.