HIGH-RESOLUTION ACCURATE-MASS SPECTROMETRY continued a 1
the structure of the unknowns (Figure 3). The retention time window in the anion- exchange gradient-elution chromatogram for trivalent species is labeled as such. The peak at 27.73 minutes elutes in the trivalent elution region, and the mass spectral information is shown. The accurate mass of 161.0092 m/z for a possible chemical formula of C5
H5 2 O6 has 3 b 1
a mass accuracy of 0.2 ppm. In general, mass accuracy values less than 2 ppm are considered high-confidence matches. The ion-exchange properties suggest a tricarboxylate structure, so a possible chemical identification is ethane- tricarboxylate. Identification of a compound of interest with four-decimal-point accuracy is extremely important, since, in addition to validating a proposed degradation pathway, it avoids the need for additional resources. The possible chemical identification based on both the behavior by anion exchange and four-decimal-place accuracy of mass-to-charge in the HRAMS is shown in Table 2.
Conclusion 2
Ion chromatography coupled with high- resolution accurate-mass spectrometry helped elucidate the degradation pathways of lithium- ion batteries. Information on the valency of functional groups present in each analyte was instrumental in defining the structural properties of degradation products obtained from surface deposits on lithium-ion battery anodes with varying degrees of capacity loss. Compound classes and specific compounds found in these samples are listed above.
3 Figure 2 – Elution of anions detected by the conductivity detector (a) and the mass spectrometer (b).
using an increasing concentration gradient of hydroxide, the analytes generally elute in this order: monovalent, divalent, trivalent and higher. Thus, retention time relative to known analytes such as monovalent chloride, divalent sulfate and trivalent phosphate provides in- formation on the ionizable functional groups present in the unknowns that elute in those
regions of the chromatogram. This information is especially useful when combined with the accurate-mass data to identify possible chemi- cal composition.
Structural information based on ion-exchange selectivity can be used with that from the HRAMS to give a more complete picture of
AMERICAN LABORATORY 36 MAY 2016
Results from this study suggest that identify- ing key electrolyte degradation products using chemical analysis may complement electrochemical measurements in areas such as charge transfer and failure analysis testing. In addition to determining correlation of a relative change in battery performance with formation of a specific degradation product (or class of products), information on chemical identifi- cation can provide insight into mechanistic pathways. Actions can then be taken to block the formation of a degradation product known to inhibit battery performance and provide improved degradation resistance, leading to longer-lasting lithium-ion batteries.
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