재활용 방법에 따른 하이니켈 NCM 양극 활물질의 전기화학 성능 비교

Dependence of Electrochemical Performance of Ni-Rich NCM Cathode Materials on Recycling Methods

In this study, electrochemical analysis of the hydrometallurgy-recycled and direct-reused Li[Ni0.90Co0.05Mn0.05]O2, Li[Ni0.86Co0.08Mn0.06]O2 cathode materials were conducted to investigate performance difference depending on recycling methods. Electrochemical analysis showed direct-reused cathode have lower capacity and cycle retention than hydrometallurgy-recycled cathode. From the differential capacity profile (dQ dV-1), it was found that the direct-reused cathode was more vulnerable to structural changes due to phase transition than the hydrometallurgy-recycled cathode. Microcracking resulting from phase transition expedited electrolyte permeation and accelerated surface degradation of cathode materials. As a result of electrochemical impedance spectroscopy (EIS), the direct-reused cathode has higher charge transfer resistance (Rct) than the hydrometallurgy-recycled cathode, which means the more surface degradation occurred in the direct-reused cathode. These results indicate that direct reused cathode material without any other process such as hydrometallurgy recycling, can lead to significant capacity fading, and in particular, solution to surface degradation are required.