Flame retardant vermiculite coated on polypropylene separator for lithium-ion batteries

Abstract

Lithium-ion batteries (LIBs) are being used in a variety of applications due to their desirable energy storage characteristics required for modern electronic devices. However, LIBs are prone to thermal runaway due to the flammable liquid electrolyte, decomposition of solid electrolyte interphase from anode surfaces, and melting of polypropylene (PP) separators. The separator provides a pathway for Li+ transfer and divides electrodes from electrical contact, avoiding a short circuit, a potentially catastrophic event. A separator that can endure higher temperatures may restrict a cell from causing thermal runaway. This paper demonstrates that vermiculite, a mineral stable over 1000 °C, could act as a separator lining in LIBs with a lithium-ion phosphate (LFP) cathode and lithium anode. Though the standard PP separator shrinks or melts above 130 °C, the vermiculite and binder will continue to provide electronic isolation, allowing the battery to delay a thermal runaway scenario. The battery containing the vermiculite modified separator released 1.675 kJ g−1 less exothermic energy during the thermal runaway, as well as demonstrating a 3.38 °C higher separator melting temperature, indicating enhanced safety in examined LIBs.