Thermal Stability of Polyethylene Oxide Electrolytes in Lithium Nickel Manganese Cobalt Oxide Based Composite Cathodes

Abstract

Thermal runaways induced by parasitic reactions are one of the greatest intrinsic risks for lithium-ion batteries. Therefore, the thermal stability of the electrolyte in contact with electrode materials is of utmost importance for safe battery usage. While solid state electrolytes are said to be safer than liquid ones, appropriate data about their thermal stability is nearly completely missing in literature. To fill this gap, thermogravimetric analysis and differential scanning calorimetry coupled with mass spectrometry was used to analyze the thermal decomposition of composite cathodes in an argon atmosphere. The samples consisted of different polymer electrolytes mixed with lithium nickel manganese cobalt oxide (NMC622). The results show that all examined solid electrolytes are stable up to 300 °C. Above this temperature, decomposition progress depends on the lithium salt. The cathode active material also reacts with the polymer electrolytes at high temperatures. Due to this, the energy output during decomposition increases with regard to the polymer fraction. Such knowledge is fundamental for the practical use of solid polymer electrolytes.