Considering Failure Analysis Testing of Lithium-Ion Batteries

[paul-voelker]

I recently read a fascinating article by Britta Vortmann, et. al, titled, Rapid Characterization of Lithium Ion Battery Electrolytes and Thermal Aging Products by Low-Tempera..., (link to article abstract) that aimed to understand fundamental processes and degradation mechanisms in Li-ion batteries and led to identifying a host of organic and inorganic phosphate decomposition products and pathways. The approach served as a springboard to pursue our own similar investigation.

Our studies were presented in a recent, data-rich webinar, titled, Analysis of Phosphate and Manganese Degradation Products in Cycle and Calendar Aged Lithium Ion Batt..., (link webinar) where you can hear experts discuss the identification of key electrolyte degradation products in failure analysis testing of lithium ion battery electrolyte degradation products by chemical analysis. In addition, the experts demonstrate how ion chromatography with suppressed conductivity detection (IC-CD), ion chromatography coupled with high resolution accurate mass spectrometry (IC-HRAM MS/MS) as well as direct-infusion HRAM MS/MS complement each other in providing an additional level of confidence in component identification that may not be possible using only a single technique. Identifying breakdown products by these techniques provides insight into elucidating a mechanistic pathway, providing the potential to block a pathway of interest and prevent the formation of select downstream breakdown products leading to improved degradation resistance and safer, longer lasting Li-ion batteries.

Ion chromatography provides the means to analyze a range of compound classes under anionic or cationic conditions. Mass spectrometry is widely used to screen targeted known and unknown compounds based on proposed chemical formulas. To identify non-targeted and unknown compounds requires higher-resolution mass spectrometers that provide a higher level of confidence in compound identification from a list of possible candidates. IC-HRAM MS/MS provides the means to correlate elution behavior to chemical formulas, and provide structural results with four (and in some cases five) decimal point accuracy.

Presented are results of the analysis of water soluble electrolyte degradation products formed on the anode surface of cycle and calendar aged Li-ion batteries. Compound classes and specific components that were found in these anode wash samples include solvent degradation products such as methyl carbonate, ubiquitous anionic contaminants such as chloride and sulfate, electrolyte breakdown products such as fluoride, phosphate and pyrophosphate, organic acids derived from degradation of the anode as well as ionic materials derived from reactions between various ion classes found in the samples such as: sulfate esters, phosphate esters, and fluorophosphate esters.

A common source of battery failure includes dissolution of a manganese-based cathode and deposition of electrolyte and manganese containing degradation products on the anode surface. Results from the analysis of the aqueous anode extract by IC-HRAM MS/MS proposed a product with a chemical formula containing manganese, a chemical structure including permanganate, and a retention time consistent with the proposed Mn containing degradation product by IC-CD. The proposed product was also supported with a m/z ratio to two decimal-point accuracy. However, when the m/z was measured to four decimal-point accuracy, IC-HRAM MS/MS disproved the proposed product. The results show that four decimal-point accuracy disputed the proposed product and prevented additional investigations that could have led in a potentially expensive and erroneous direction.

Identification of electrolyte degradation products deposited on the anode surface of an aged Li-ion battery was done using one of our integrated ion chromatography systems (Thermo Scientific Dionex ICS-2000 Integrated IC System) coupled to one of our mass spectrometers (Thermo Scientific Q Exactive Orbitrap MS system) in negative ion mode.

[caption id="attachment_12975" align="aligncenter" width="960"] Figure 1[/caption]

Figure 1 shows results from the measurement of two Li-ion battery degradation products by HRAM MS/MS. Note that while the proposed compounds have different spectra they share the same chemical formula. Measurement to four decimal-point accuracy distinguishes the two species and provides a high level of confidence to propose two different structures, shown in the upper panels. Results by MS/MS provide an additional of confidence in compound identification by analyzing the unique fragmentation signature of the two degradations products, shown in the lower panels.

Identifying key electrolyte degradation products by chemical analysis can provide an understanding of the degradation process and open up avenues of investigation that can lead to safer, longer lasting Li-ion batteries. Chemical analysis may also complement electrochemical measurements by providing a more complete solution to areas of interest such as charge transfer.

 

Do you have questions that were not answered by the webinar? If so, do enter them in the Comments box and I would be pleased to answer them. I look forward to hearing from you.