Impact of Trace Impurities in the Electrolyte on the Electrochemistry of Positive Electrodes for Lithium-Ion Batteries

Abstract The overarching aim of this work was to understand how strategies aligned with the circular economy, particularly recycling and purification methods of battery materials, affect the electrochemical behavior of lithium-ion batteries based on recycled components. We investigated the impact of trace impurities, specifically transition metal ions (Ni²⁺, Mn²⁺, and Co²⁺) with relevant anions, on the electrochemical performance of Ni-rich cathodes for lithium-ion batteries (LIBs), focusing on NMC811 and NCA materials. Electrolytes were deliberately contaminated with salts of these metals, and half-cell configurations were employed to isolate the effects on the positive electrodes. Results indicate that nickel impurities have the most detrimental impact on capacity retention and electrode stability, followed by manganese and cobalt, with specific effects varying by anion type. Electrochemical measurements and X-ray photoelectron spectroscopy analysis confirmed the formation of cathode-electrolyte interphase layers, significantly altering ionic conductivity and surface impedance. The findings emphasize the need for improved recycling and purification methods to mitigate contamination effects, ensuring long-term viability and efficiency of LIBs.