A novel capillary electrophoresis (CE) method with ultraviolet–visible spectroscopy (UV–Vis) detection for the investigation of dissolved Cu⁺ and Cu²⁺ in lithium ion battery (LIB) electrolytes was developed. This method is of relevance, as the current collector at the anode of LIBs may dissolve under certain operation conditions. In order to preserve the actual oxidation states of dissolved copper in the electrolytes and to prevent any precipitation during sample preparation and CE measurements, neocuproine (NC) and ethylenediamine tetraacetic (EDTA) were effectively applied as complexing agents for both ionic copper species. However, precipitation and loss of the Cu⁺‐NC‐complex for quantification occurred in presence of the commonly applied conducting salt lithium hexafluorophosphate (LiPF₆). Therefore, acetonitrile (ACN) was added to the sample in order to suppress this precipitation. Dissolution experiments with copper‐based negative electrode current collectors in a LIB electrolyte were conducted at 60°C under non‐oxidizing atmosphere. First findings regarding the copper species via CE revealed dissolved Cu⁺ and mainly Cu²⁺. However, primarily Cu⁺ dissolved from the passivating oxide layer (Cu₂O and CuO) of the current collector due to the formation of acidic electrolyte decomposition products. Due to the instability of Cu⁺ in the electrolyte a further disproportionation reaction to Cu⁰ and Cu²⁺ occurred. The results show the high potential of this CE method for prospective investigations regarding the current collector stability in new battery electrode formulations and correlations of dissolution events with dissolution mechanisms and battery cell operation conditions.

中文翻译：

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了解锂离子电池中溶解的负极集流体的铜氧化态。

开发了一种新型的毛细管电泳（CE）方法和紫外可见光谱（UV-Vis）检测技术，用于研究锂离子电池（LIB）电解质中溶解的Cu ⁺和Cu ²⁺。此方法具有相关性，因为在某些操作条件下，LIB阳极处的集电器可能会溶解。为了保持电解质中溶解的铜的实际氧化态并防止样品制备和CE测量过程中出现任何沉淀，新铜氨碱（NC）和乙二胺四乙酸（EDTA）被有效地用作两种离子铜物质的络合剂。但是，Cu ^+的沉淀和损失用于定量的NC络合物是在常用的导电盐六氟磷酸锂（LiPF ₆）的存在下发生的。因此，将乙腈（ACN）添加到样品中以抑制这种沉淀。在60°C的非氧化气氛下，使用LIB电解液中的铜基负极集电器进行溶解实验。通过CE有关铜种类的最初发现表明溶解了Cu ⁺，主要是Cu ²⁺。然而，由于形成酸性电解质分解产物，因此主要从集流体的钝化氧化物层（Cu ₂ O和CuO）溶解了Cu ⁺。由于Cu ⁺的不稳定性在电解液中，进一步发生歧化反应，生成Cu ⁰和Cu ²⁺。结果表明，该CE方法具有潜力，可用于有关新型电池电极配方中集电器的稳定性以及溶解事件与溶解机理和电池工作条件之间的相关性的前瞻性研究。