Advanced ultraviolet-visible spectrometer for the quantitative analysis of electrolyte degradation species formed in battery cells

本课题旨在建立一种先进的紫外-可见光谱仪，用于定量分析锂离子电池和钠离子电池在循环过程中形成的电解质降解物质。先进的UV-vis光谱仪将实现许多电池电解质降解实验，这对学术界和我们的工业合作伙伴特斯拉具有很高的价值。我们有一个广泛的计划，将电池的寿命延长到数万次循环（迄今为止已经展示了16,000次循环），这将转化为可再生能源存储的固定电池组的数十年寿命或电动汽车的数百万公里行驶里程。为了这个项目的成功，我们需要定量地了解电解液在长时间循环过程中的变化。我们是第一个发现电池电解质在高温循环后发生如此剧烈的颜色变化的研究小组，并将其与原位生成的氧化还原活性物质相关联，该活性物质在其还原氧化状态下充当发色团。对于先进的锂离子电池来说，检测这种和其他电池电解质分解产物的能力非常重要，因为它们会在储存过程中导致自放电，在循环过程中导致效率低下。UV-vis非常适合于检测和量化电池电解质中这种发色团的小浓度。为了实现基于可持续和负担得起的元素的长寿命电池，我们需要消除正极材料中过渡金属的溶解，如磷酸锰铁锂（LMFP）和锰氧化锂（LMO）。通过紫外可见光谱，可以通过化学探针与离子结合并改变吸收光谱来检测电池电解质中溶解的过渡金属离子。可以建立溶解过渡金属与紫外-可见吸收信号之间的定量相关性，使其成为一种简单可靠的测试方法。所提出的UV-Vis光谱仪没有移动部件，这确保了永久的光学对准。它有四个单独的温度区域，可以用珀尔帖元素加热。加热区对于电池降解产物的分析非常重要，因为化学分解反应通常遵循阿伦尼乌斯定律，即在较高温度下加速。我们的实验室最近证明，即使在70°C、85°C和100°C的极端工作温度下，锂离子电池也能有很长的使用寿命。该光谱仪提供从0到110°C的快速准确的温度控制，非常适合我们的高温电池测试。在这个RTI应用中提出的设备可以对电解质分解和过渡金属溶解动力学产生基本的理解。这将最终导致低成本、高可持续性的长寿命LMFP和LMO电池。

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.