Investigations of an organic coverage to Ni-rich cathode materials: Effects on deteriorated, cathode electrolyte interphase, and chemical crossover

Ni-rich cathodes inherit surface residual lithium compounds (SRLCs) for several reasons, such as cation mixing, oxygen vacancies, and the spontaneous reduction of high-Ni valence ions. Consequently, Ni-rich compounds must be treated before use to maximize their performance. This study describes the development of an organic coverage (OC) that can be directly utilized with a deteriorated Ni-rich cathode. The OC is synthesized from 5,5dimethylbarbituric acid and polyethylene glycol diacrylate to provide two functions for the deteriorated Ni-rich cathode surface: spontaneous ion exchange and the self-electrochemical oxidation of Ni ions. SRLCs, such as Li2CO3 and LiOH, decompose through a transformation reaction from the trioxo to the dioxo form of the OC structure. Then this lithiated OC forms an organic artificial cathode electrolyte interface on the cathode surface, which further reduces the effects of chemical crossover on the anode side. It is also believed that the dioxo form promotes Ni2+ self-oxidation on the surface of Ni-rich cathodes and recovers the original Ni3+ valence state by Li+ re-intercalation. Thus, the capacities of the deteriorated LiNiO2 and LiNi0.8Mn0.1Co0.1O2 recover almost to their original values and retain the same excellent cycle performance as that of the fresh compounds.