Comprehensive electrolyte extraction and quantitative analysis reveal formation-induced electrolyte reactions in lithium-ion batteries

Abstract

As the global demand for lithium-ion batteries (LIBs) continues to rise, significant research and industrial efforts have been devoted to improving their active components. Recently, electrolytes, serving as essential carriers for lithium ions, have attracted increasing attention, as their total quantity and compositional changes during electrochemical reactions critically determine cell stability and performance. Despite ongoing efforts to develop advanced electrolytes through various organic solvents and functional additives, the ability to qualitatively and quantitatively evaluate electrolytes during cell formation and operation remains limited. Here, we present a systematic strategy to quantify the absolute amounts of electrolyte components in LIBs incorporating graphite// Li(Ni0.6Co0.2Mn0.2)O2 electrodes, revealing previously unrecognized side reactions and electrolyte consumption during the formation process. To achieve this, we developed optimized extraction method with a relative mass deviation of less than 0.153%. Through complementary liquid chromatography and nuclear magnetic resonance analysis, we identified that approximately 21% of the injected electrolyte (ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate) underwent side reactions to form new compounds (dimethyl 2,5-dioxahexanedioate, dimethyl carbonate, and diethyl 2,5-dioxahexanedioate) during formation. These findings provide fundamental insights into electrolyte degradation pathways and byproduct formation, offering valuable design guidelines for developing next-generation electrolytes that enhance the performance and durability of LIBs.