Role of impurity copper in Li-ion battery recycling to LiCoO₂ cathode materials

Copper is a dominating impurity in Co-rich Li(Co,Ni,Mn)O₂ battery waste fractions and may exist in similar quantities (e.g. 6 wt%) as Li, Ni and Mn. This paper investigates the behavior of copper from waste batteries up to recycled active materials and the findings highlight that copper contamination is not necessarily detrimental for the active materials in trace amounts, but can rather increase the discharge capacity at high rates. Firstly, industrially crushed battery waste was treated hydrometallurgically to produce Li₂CO₃ and CoSO₄·2H₂O precipitates for re-use, before being calcined to prepare fresh LiCoO₂ materials. Results suggest that during the hydrometallurgical recycling process, Cu is likely to co-extract along the Co; in the current work both high and low Cu-contaminated CoSO₄·2H₂O precipitates were obtained and in the former case, formation of CuO as a secondary phase occurred upon calcination. The presence of Cu contamination induced up to ca. 35 mAh/g decrease in the specific capacity, compared to pure LiCoO₂. However, a low level of Cu inclusion was found to be advantageous at high discharge rates (4.0C and 5.0C) resulting in a doubling of the capacity (110–120 mAh/g) when compared with pure LiCoO₂ (40–60 mAh/g).