Molecular Characterization of Electrolytes and Electrodes in Lithium Ion Batteries

The performances of lithium-ion batteries (LIBs) are closely related to the control of the electrolyte composition and solid-electrolytes interface (SEI) stability [1-2]. To decrease the capacity fading electrolyte formulation has been continuously optimized over years and much attention has been paid to identifying the SEI composition. However, deciphering the molecular diversity of both liquid electrolytes and solid interphase remains extremely challenging because few analytical techniques show the appropriate sensitivity and spatial resolution without modifying their composition. Here, Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) was used for the first time to characterize at the molecular level both parts of LIBs. The liquid electrolytes were characterized using atmospheric pressure chemical ionization to cover a broad polarity range. Surprisingly, obtained mass spectra revealed hundreds of signals even if the initial electrolytes cocktail was prepared using 10 species. Using mass defect molecular maps, it was possible to delimit regions of interest for each component and easily perform reverse engineering. Two anodes coming from LIBs with different performances were analyzed using laser desorption ionization operated in imaging mode. After the subtraction of species coming from the carbon reference electrode, the unique contribution of each distinct SEI was observed and known reaction products of electrolytes were researched and identified.