Gradient Polarity Solvent Wash for Separation and Analysis of Electrolyte Decomposition Products on Electrode Surfaces

Abstract

The solid electrolyte interphase (SEI) formed during the cycling of lithium-ion batteries (LIBs) by decomposition of electrolyte molecules has key impact on device performance. However, the detailed decomposition process and distribution of products remain a mystery due to the wide variety of electrochemical pathways and the lack of facile analytical methods for chemical characterization of SEIs. In this report, a gradient polarity solvent wash technique involving the use of solvents with gradually increased polarities is employed to sequentially remove different SEI components from electrode surfaces. Fourier transform infrared (FTIR) spectroscopy is utilized to characterize the SEI composition. The impacts of electrolyte additives and discharge rates over SEI formation are illustrated. This study presents a new concept of rationally controlled solvent wash technique for electrode surface analysis that can selectively remove targeted components. The findings in this study provide experimental support for the slow charge formation processes commonly employed for LIBs in industry.

Large Molecule Decomposition Products of Electrolytes and Additives Revealed by On-Electrode Chromatography and MALDI

“…The feasibility of on-electrode chromatography has been demonstrated with both Cu and silicon electrodes in our previous report. 39 In the present study, onelectrode chromatography prior to MALDI measurements has proven critical for effective MALDI analysis MALDI measurement of electrodes could be easily hindered by the complicated chemical environment on the electrode surfaces. Through proper solvent elution (left part of the figure) to fractionate different molecular species on electrode surfaces (such as ethylene carbonate, the green molecules), onelectrode chromatography can realize separation of the organic SEI components.…”

“…In our previous report, 39 we demonstrated that 3:7 ethyl acetate (EA):hexane (Hex) elution (v/v) could reliably remove residual EC electrolyte from the electrode surface, exposing underlying polymeric species. This controlled elution condition was the minimum polarity needed for separating EC, and would not lead to outstanding removal of the high-mass polymeric SEI components.…”

“…Copper (Cu) electrodes 9/16" in diameter were punched from Cu foil. The synthetic poly(TEGMA) reference sample was obtained as previously reported 39.…”

Highly Ordered Carbon Coating Prepared with Polyvinylidene Chloride Precursor for High‐Performance Silicon Anodes in Lithium‐Ion Batteries

“…Significant research efforts have been devoted to development of next‐generation rechargeable batteries to meet the demand of the rapidly growing energy storage market, [3–7] as the graphite anodes in current LIBs have a rather limited theoretical capacity of 372 mAh/g. Silicon materials, with a nearly 10‐fold higher theoretical capacity of 3579 mAh/g, relatively low discharge potential (<0.5 V vs. Li/Li + ), and abundant resource, have been considered as promising anode materials for LIBs [8–10] . However, a major obstacle for silicon anodes is the dramatic volume change of silicon that occurs during lithiation and de‐lithiation, which undermines the electrode's integrity and disrupts the solid electrolyte interface (SEI).…”

“…Silicon materials, with a nearly 10-fold higher theoretical capacity of 3579 mAh/g, relatively low discharge potential (< 0.5 V vs. Li/Li + ), and abundant resource, have been considered as promising anode materials for LIBs. [8][9][10] However, a major obstacle for silicon anodes is the dramatic volume change of silicon that occurs during lithiation and de-lithiation, which undermines the electrode's integrity and disrupts the solid electrolyte interface (SEI). The breakdown of the SEI layers during cycling results in a range of problems, such as low Coulombic efficiency (CE), quick capacity fading and poor cycling stability.…”