A capillary electrophoresis (CE) method with ultraviolet/visible (UV–Vis) spectroscopy for iron speciation in lithium ion battery (LIB) electrolytes was developed. The complexation of Fe²⁺ with 1,10‐phenantroline (o‐phen) and of Fe³⁺ with ethylenediamine tetraacetic acid (EDTA) revealed effective stabilization of both iron species during sample preparation and CE measurements. For the investigation of small electrolyte volumes from LIB cells, a sample buffer with optimal sample pH was developed to inhibit precipitation of Fe³⁺ during complexation of Fe²⁺ with o‐phen. However, the presence of the conducting salt lithium hexafluorophosphate (LiPF₆) in the electrolyte led to the precipitation of the complex [Fe(o‐phen)₃](PF₆)₂. Addition of acetonitrile (ACN) to the sample successfully re‐dissolved this Fe²⁺‐complex to retain the quantification of both species. Further optimization of the method successfully prevented the oxidation of dissolved Fe²⁺ with ambient oxygen during sample preparation, by previously stabilizing the sample with HCl or by working under counterflow of argon. Following dissolution experiments with the positive electrode material LiFePO₄ (LFP) in LIB electrolytes under dry room conditions at 20°C and 60°C mainly revealed iron dissolution at elevated temperatures due to the formation of acidic electrolyte decomposition products. Despite the primary oxidation state of iron in LFP of +2, both iron species were detected in the electrolytes that derive from oxidation of dissolved Fe²⁺ by remaining molecular oxygen in the sample vials during the dissolution experiments.

中文翻译：

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通过毛细管电泳研究基于LiFePO4的锂离子电池正极中Fe的氧化态。

开发了毛细管电泳（CE）方法和紫外/可见（UV-Vis）光谱技术，用于锂离子电池（LIB）电解质中的铁形态。Fe ²⁺与1,10-菲咯啉（o -phen ）的络合和Fe ³⁺与乙二胺四乙酸（EDTA）的络合揭示了样品制备和CE测量期间两种铁物种的有效稳定。用于从LIB细胞小电解质体积的调查，具有最佳样品的pH值的样品缓冲液中开发的Fe禁止沉淀³⁺铁络合期间²⁺与ø -苯。但是，存在导电盐六氟磷酸锂（LiPF ₆）导致电解质中[Fe（o- phen）₃ ]（PF ₆）₂的沉淀。在样品中添加乙腈（ACN）成功地重新溶解了这种Fe ²⁺复合物，从而保留了两种物质的定量。通过预先用HCl稳定样品或在氩气逆流下进行操作，该方法的进一步优化成功地防止了样品制备过程中溶解的Fe ²⁺被环境氧气氧化。在使用正极材料LiFePO ₄进行溶解实验之后在20°C和60°C的干燥室内条件下，LIB电解质中的LFP（LFP）主要显示出铁的溶解，这归因于酸性电解质分解产物的形成。尽管LFP中铁的主要氧化态为+2，但在电解质中检测到两种铁物种，这是由于在溶解实验过程中样品瓶中残留了分子氧，从而使溶解的Fe ²⁺氧化而产生的。