Revealing the degradation behaviors and mechanisms of NCM cathode in scrapped lithium-ion batteries

Existing research has predominantly studied the typical degradation mechanisms of cathodes under accelerated aging conditions in laboratory settings. However, the degradation mechanisms of cathodes from scrapped lithium-ion batteries (LIBs) require more attention due to significant differences in working conditions between actual and laboratory levels. In this work, we systematically investigated the deterioration behaviors and degradation mechanisms of scrapped LiNi0.5Co0.2Mn0.3O2 (SNCM) from commercial LIBs, comparing it with pristine LiNi0.5Co0.2Mn0.3O2 through characterizations and electrochemical tests. Results indicated that SNCM particles were severely disintegrated into scattered primary particles due to altered lattice parameters, which is one of the main reasons for degradation. Furthermore, the surface layer of SNCM experienced significant phase transformations with varying proportions of transition metals in different valence states, while bulk structure of SNCM remained unchanged. Lithium loss, a small amount of transition metals, and thereby a high degree of cation mixing in SNCM are the other degradation factors. It was found that SNCM demonstrated poor electrochemical performance with only 111.8 m Ah g−1 of initial discharge capacity and 50.9% capacity retention after 100 cycles at 0.5C. This work pertinently focused on the degradation mechanisms of SNCM, offering perspectives for improving battery lifespan and regenerating SNCM through appropriate measures. [Display omitted] •The degradation mechanisms of NCM from scrapped lithium ion batteries were revealed.•The apparent collapsed particles of NCM are one of the main reasons for degradation.•The severe phase transformation occurs on the surface layer of scrapped NCM.•Disadjust proportion of Ni, Co, and Mn in valences accounts for surface passivation.