Safer lithium-ion batteries realized by electrolyte with thermoresponsive poly(vinylidene fluoride-co-trifluoroethylene)

Abstract

The increasingly widespread use of electric vehicles has necessitated the development of high-energy batteries capable of operating under harsh conditions, e.g., at elevated temperatures and high charge/discharge rates. Hence, considerable attention has been focused on enhancing the safety of lithium-ion batteries (LIBs). Herein, a thermoresponsive polymer, poly(vinylidene fluoride-co-trifluoroethylene) with 75 mol% vinylidene fluoride and 25 mol% trifluoroethylene (TrFE-25), is employed as an electrolyte additive to enhance the thermal stability of LIBs (LiCoO2/graphite full cells). Under thermal-abuse conditions, i.e., above a certain threshold temperature, the TrFE-25-containing electrolyte turns into a gel, thereby abruptly increasing of the electrolyte viscosity and interfacial resistance. The gel layers block ion transport, suppress exothermic reactions between the electrodes and electrolyte, and hinder separator shrinkage via adhesive bonding to the anode and cathode, thus preventing internal short-circuiting and enhancing battery safety. According to the results of cycling tests, the addition of TrFE-25 to the baseline electrolyte has no negative effects under normal conditions. Therefore, the proposed methodology holds promise for improving the safety of LIBs, particularly those with flammable carbonate-based electrolytes, and paves the way for the widespread use of these batteries in electric vehicles.