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by Rosanne W. Slingsby, Paul J. Voelker, Christopher Pohl, Charanjit Saini, Kate Comstock, John Moote, Michael P. Balogh and Ramona Y. Ying


Ion-Exchange Selectivity and High-Resolution Accurate-Mass Spectrometry Elucidate Lithium-Ion Battery Degradation Pathways

Improved performance and lifetime of lithium- ion batteries is important for automobile manufacturers that produce cars powered electrochemically by lithium-ion battery packs. Electrochemical measurements are commonly used to correlate capacity loss and impedance increase to the formation of degradation products in the solid electrolyte interface (SEI). Chemical analysis can complement elec- trochemical measurements by identifying degradation products.

Ion chromatography (IC) combined with high-resolution accurate-mass spectrometry (HRAMS) effectively characterizes ionized and ionizable components in electrode samples from aged lithium-ion batteries. IC-HRAMS is used to identify probable chemical species in the analytes based on both ion-exchange selectivity behavior and on exact mass to an accuracy of at least four decimal places.

This article focuses on the use of gradient anion-exchange ion chromatography with a conductivity detector coupled with HRAMS with an electrospray interface (ESI) to analyze the degradation products obtained from sur- face deposits on lithium-ion battery anodes, which are cycle- and calendar-aged to varying degrees of capacity loss. Information on the an- ion-exchange elution behavior correlates with chemical-formula information from HRAMS to provide accurate results. Compound classes and specific compounds found in these anode wash samples include solvent-degradation products such as methyl carbonate; anionic contaminants such as chloride and sulfate; elec- trolyte breakdown products such as fluoride,

phosphate and pyrophosphate; organic acids derived from degradation of the anode; as well as ionic materials generated from reactions be- tween various ion classes found in the samples, including sulfate esters, phosphate esters and fluorophosphate esters. Using IC on samples containing complex mixtures of anionic spe- cies can help elucidate chemical structures of unknown components.

HRAMS provides accurate analyte identifica- tion, while IC delivers confirmatory information about ionizable functional groups. Together, these techniques provide insight into the identity of anionic degradation products in lithium-ion batteries.

Experimental Figure 1 is a schematic of the ion chromato-

graph with conductivity detector and HRAMS

(IC-CD-HRAMS) hardware. Thermo Scientific Xcalibur and Thermo Scientific Dionex Chromeleon Chromatography Data System (CDS) software were used for system control and data collection.

Ion chromatography Sample components were separated by

anion-exchange selectivity. Instrumentation was as follows: 1) Thermo Scientific ICS2100 Reagent-Free Ion Chromatograph (Sunnyvale, Calif.)—pump, eluent generator fitted with a KOH EGC cartridge and a conductiv- ity detector; 2) Thermo Scientific Dionex AXP pump—delivered 90/10 v/v acetonitrile/de- ionized water to a mixing tee positioned after the conductivity detector cell and before the electrospray inlet to the mass spectrometer— gradient elution conditions are shown in


AMERICAN LABORATORY 34 MAY 2016 Figure 1 – Ion chromatograph with conductivity detector and HRAMS.

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