Separation and Quantification of Organic Electrolyte Components in Lithium-ion Batteries via a Developed HPLC Method.
A state-of-the-art electrolyte used in commercial lithium ion batteries contain LiPF6 as conducting salt dissolved in a mixture of organic carbonates. Following organic carbonates are established for manufacturing of the electrolytes: ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Vinylene carbonate is a common electrolyte additive which supports the formation of a protective layer on the anode important for long lifetime of the batteries.
Shimadzu´s HPLC systems offer a solution to analyse the electrolytes. As shown in the following publication, the HPLC-UV/Vis is a powerful tool for analysis of organic carbonates as well as different low-concentrated additives and impurities. The method can be used for quality control and for investigation of aging phenomena of batteries since concentration changes of the organic carbonates provide information about the aging state of lithium ion batteries. For flame retardant additives, HPLC is the method of choice compared to GC because of the high boiling point and the bad evaporation behaviour.
Qualitative Investigation of the Decomposition of Organic Solvent Based Lithium Ion Battery Electrolytes with LC-IT-TOF-MS
Structural elucidation of lithium ion battery electrolyte main components and especially their partly still unknown generated aging products may be conducted with HPLC hyphenated to an ion-trap time-of-flight mass spectrometer (IT-TOF-MS). For the analysis, Shimadzu´s LCMS IT-TOF was used. The advantage of the unique LCMS IT-TOF is the combination of IT and TOF technology. This enables MSn analysis with simultaneous high resolution and high mass accuracy of a TOF in each MSn stage.
In this publication, the aging products were generated during electrochemical cycling of batteries at different temperatures and under presence of water. In the aged electrolytes, the structures of a wide range of aging products, including oligocarbonate aging products, organic phosphates as well as organofluorophosphates were clearly elucidated. The investigation is important, as especially organofluorophosphates are known to be toxic. This facilitates the investigation of the occurring aging process in electrolytes during electrochemical cycling and the influence of different temperatures on the electrolyte aging.
Quantitative Investigation of the Decomposition of Organic Lithium Ion Battery Electrolytes with LC-MS/MS
HPLC hyphenated to tandem mass spectrometry (LC-MS/MS) allows the accurate separation and quantification of organic carbonate-based lithium ion battery electrolytes. A method for the quantification of electrolyte solvents and aging products using Shimadzu´s LC-MS TQ (triple quadrupole) is presented in the following publication. For the quantification, a standard for each substance is necessary. A problem in LIB research is, that standards are not commercially available for all aging products. To deal with that problem, a quantitative approach for certain aging products was conducted. The quantification was conducted with thermally aged electrolytes (60 °C and 60 °C with the addition of water) and with electrochemically aged electrolytes (20°C and 60 °C and with higher upper cut-off potentials (4.95 V, 5.20 V and 5.60 V vs. Li/Li+)). Thermal aging with the addition of water led to the formation of higher amounts of oligocarbonates. Electrochemical aging at higher cut-off potentials led to the increased generation of oligocarbonates and triethyl phosphate (TEP).