The Origin of Gaseous Decomposition Products Formed During SEI Formation Analyzed by Isotope Labeling in Lithium‐Ion Battery Electrolytes

Abstract

Interphase formation during the first charge and discharge cycle(s) of a battery cell is among the least understood processes in lithium-ion batteries (LIBs). The formation of interphases is a result of electrolyte decomposition and accompanied by gassing. The direct analysis of these interphases is challenging and indirect methods are required to obtain information about this process. For example, indirect, ex situ analyses of gaseous decomposition products can help to draw conclusions about occurring reactions in the cell. In this work, the origin of several permanent gases and hydrocarbons (CO, CH 4 , C 2 H 4 and C 2 H 6 ) emerging during the formation of LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) j j graphite pouch type LIBs equipped with a gas sampling port was investigated. Isotope labeled electrolytes ( 13 C 3 -EC, D 4 -EC) were used to assign formation gas products to the individual constituents of the electrolyte mixture. The effect of common linear carbonates in combination with ethylene carbonate (EC) as well as the effect of vinylene carbonate (VC) as film forming additive was investigated. The obtained mass spectra from gas chromatography mass spectrometry (GC-MS) and the mass shift caused by the labeled electrolyte components, enabled an assignment of individual electrolyte components to the resulting gas products. The aim of this work is to gain more information about interphase reactions and thus to improve understanding of the mechanisms behind formation.

The significance of mitigating crosstalk in lithium-ion batteries: a review

“…Winter and coworkers determined the source of gaseous compounds developed during formation via isotopic labeling analysis. 112,113 It turned out that the source of the C atoms in C 2 H 4 formed in the carbonate electrolyte was entirely EC, while a small fraction of the H atoms in C 2 H 4 might come from other solvents. Sun et al visualized gas generation and channel formation inside a Si anode by means of an X-ray imaging method.…”

“…Isotopic labeling offers the possibility of clarifying the crosstalk pathway and allows potential precursors to be traced. 112,113 Synchrotron X-ray imaging, 114 operando optical microscopy, 155 ex situ and operando scanning electron microscopy (SEM) or transmission electron microscopy (TEM)), and cryo-electron microscopy 156,157 show promise for the direct observation of crosstalk species (gas bubbles). The evolution of the electrode crystal structure during crosstalk can be accurately detected with in situ X-ray diffraction (XRD) or neutron diffraction techniques.…”

Radiolysis of Electrolytes in Batteries: A Quick and Efficient Screening Process for the Selection of Electrolyte‐Additive Formulations

“…[47,48] It should be noted that the origin of C 2 H 4 , CO, CH 4, and C 2 H 6 produced during SEI formation is analyzed in details by isotope labeling in reference. [49] Table S2, Supporting Information, also shows that the nature of the additive has an impact on the formation of oxygenated molecules such as ethers, carboxylic acids, and esters. This suggests that the nature of the additive has an impact on reaction channels.…”

Uracil-based additives for enabling robust interphases of high-voltage Li-ion batteries at elevated temperature by substituent effects

“…S11, ESI †) were detected in every pouch cell, including ethylene (C 2 H 4 ), ethane (C 2 H 6 ), carbonic oxide (CO), carbon dioxide (CO 2 ), hydrogen (H 2 ), and so on, which was consistent with the results in the literature. 45 In Fig. 7a, the relative content of C 2 H 4 is higher than other gases for all the cells regardless of the presence of additives, and which is commonly assigned to the reductive product of EC on graphite.…”