Mechanism elaboration on the thermal decomposition of ether electrolyte in sodium-ion battery

The thermodynamic parameters and thermal decomposition characteristics of the ether electrolyte are important to the performance and safety of sodium-ion batteries. This study offered an underlying understanding in detecting, quantifying and revealing the thermal decomposition mechanism of DEGDME ether electrolyte, especially under the effects of transition metal chalcogenides (TMCs) anode CoS2/C. Firstly, a customized high-pressure reactor was used to address the influences of sodium salt on the exothermic temperature and pressure changes during the thermal decomposition of the ether electrolytes. Secondly, the thermodynamic characteristics of the ether electrolyte under the effects of anode were quantitatively analyzed based on the Arrhenius law. Thirdly, the step-by-step reaction mechanism for the thermal decomposition of the ether electrolyte was explored by an in-situ synchrotron radiation vacuum extreme ultraviolet photoionization mass spectrometry technology, supplemented by DFT simulation calculation. Several interesting phenomena and original mechanisms were discovered, showing that the TMCs anode CoS2/C could reduce the decomposition activation energy of the DEGDME (i.e., the maximum decrease is 10.2 kJ mol−1) and catalytically accelerate the thermal decomposition reaction (i.e., the heating rate was increased by 29.8 times). At the same time, a small amount of O2 produced when the temperature reached 242.5°C, rising the risk of the sodium-ion battery. The research outcomes of this study can provide a guidance to the safety evaluation and optimization of the electrolytes in commercial sodium-ion batteries.