Anodic Stripping Voltammetry Detection of Bismuth in Highly Alkaline Electrolyte for Battery Separator Testing

Anodic stripping voltammetry (ASV) is a sensitive and versatile technique used for measuring metal ion concentrations in neutral or acidic aqueous solutions. However, expanding the technique to alkaline electrolyte is of interest for alkaline battery research. In these batteries, the high solubility of active materials such as Zn, Mn, Cu, and Bi can lead to shorting from dendrites, active material loss, and buildup of inactive phases by unwanted chemical reactions. For instance, Bi/Cu-stabilized 2e^- MnO₂ cathodes suffer from Bi and Cu diffusion away from the cathode and the formation of irreversible ZnMn₂O₄ when [Zn(OH)₄]^2- migrates from the Zn anode to the cathode. To mitigate these issues, an ion-selective separator – limiting metal ion diffusion but allowing hydroxide diffusion – must be developed but testing these separators can take days or weeks using inductively coupled plasma mass spectrometry (ICP-MS) or complexometric titrations, which also require large dilutions. We have developed an ASV methodology which can be used to measure Bi concentrations in highly alkaline 8.5 M KOH electrolyte with experiment times on the order of minutes or hours with no dilutions required; building on our previous work measuring zincate [Zn(OH)₄]^2- and cuprate [Cu(OH)₄^2-] [1, 2]. The method relies on the complexation of Bi³⁺ with hydroxide ions in alkaline solution to form complexes such as bismuthate, [Bi(OH)₄]^-.We also demonstrate that a Pb deposition mediator improves the linearity of calibration curves and enables a limit of detection of 8.5 ppb. The developed assay is used to measure the diffusion coefficient of [Bi(OH)₄]^- across commercial battery separators. The ASV methodology described here represents a quick and easy way to evaluate alkaline battery separators for ion crossover compared to ICP-MS and titrations.

Sandia National Laboratories is a multi-program laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525. Dr. Imre Gyuk, Director of Energy Storage Research, Office of Electricity is thanked for his financial support. The views expressed herein do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

[1] J. Duay, T. N. Lambert, and R. Aidun. Electroanalysis, 29 (10), pp. 2261-2267, 2017/10/01 2017.

[2] J. Duay, J. E. Ortiz-Santiago, and T. N. Lambert. Electroanalysis, 29 (12), 2685-2688, 2017.