Quantitative Electrochemical Analysis Method for Cu Impurities in Nickel-Cobalt-Manganese Cathode Materials.

Lithium-ion batteries are among the most important energy-storage devices. In this regard, nickel-cobalt-manganese (NCM) cathodes are widely used because of their high energy density and stability. Cu on NCM can enhance the overall performance by aiding lithium-ion transport through cation mixing; however, it leads to issues, such as internal short circuits. The precipitation pH of Cu is high, making its chemical separation from the NCM challenging. Given the impacts and the challenge of separation, an accurate quantification of the residual Cu content in the NCM cathode is essential. Inductively coupled plasma methods struggle with the accurate quantification of trace impurities in NCM owing to the high contents of material elements, leading to instrument malfunction and time-consuming labor. In this study, the introduction of electrochemical methods significantly weakened the matrix effect and facilitated the pretreatment of the solution. In particular, a thin-film electrode (TFE) made of Rh allowed quantification of the Cu present in commercial NCM powder. Cyclic voltammetry and an electrochemical quartz crystal microbalance were used to confirm the formation of two types of underpotential deposition (UPD) Cu on the Rh TFE. Square-wave voltammetry was used to analyze the kinetic differences in Cu