Grant: Research Tools and Instruments

This proposal is for an advanced ultraviolet-visible (UV-vis) spectrometer for the quantitative analysis of electrolyte degradation species formed in lithium and sodium-ion battery cells during cycling. An advanced UV-vis spectrometer would enable many battery electrolyte degradation experiments that would have high value for the academic community and our industrial partner Tesla. We have an extensive program on extending the lifetime of battery cells to several tens of thousands of cycles (16,000 cycles already demonstrated to date), which would translate to multi-decade lifetimes in stationary battery packs for renewable energy storage or multi-million-kilometer driving ranges in electric vehicles. For the success of this program, we need to understand changes to the electrolyte over prolonged cycling in a quantitative way. We were the first group to show such dramatic color changes of battery electrolyte after high temperature cycling and could correlate them to the in-situ generation of a redox active species that acts as a chromophore in its reduced oxidation state. The ability to detect this and other battery electrolyte decomposition product is extremely important for advanced lithium-ion cells, since they can lead to self-discharge during storage and inefficiency during cycling. UV-vis is ideally suited to detect and quantify small concentrations of such chromophores in battery electrolytes. In order to enable long lifetime batteries based on sustainable and affordable elements we need to eliminate transition metal dissolution from cathode materials like lithium manganese iron phosphate (LMFP) and lithium manganese oxide (LMO). Detection of dissolved transition metal ions in a battery electrolyte via UV-vis spectroscopy can be enabled by chemical probes that will combine with the ion and alter the absorption spectrum. A quantitative correlation between dissolved transition metals and the UV-vis absorption signal can be established, making it a simple and reliable test method. The proposed UV-Vis spectrometer has no moving parts, which ensures permanent optical alignment. It has four individual temperature zones that can be heated with Peltier elements. The heated zones are very important for the analysis of battery degradation products since the chemical decomposition reactions usually follow the Arrhenius law, i.e., they are accelerated at higher temperatures. Our lab recently demonstrated that lithium-ion cells can have long lifetimes even at extreme operating temperatures of 70, 85 and 100°C. The spectrometer provides fast and accurate temperature control from 0 to 110°C, which is perfect for our high temperature battery tests. The equipment proposed in this RTI application can yield fundamental understanding of electrolyte decomposition and transition metal dissolution kinetics. This will ultimately lead to long-lived LMFP and LMO cells with lower cost and higher sustainability.