Impacts of Dissolved Ni²⁺ on the Solid Electrolyte Interphase on a Graphite Anode

Transition metal (e.g. Ni) ions dissolved from layered-structured Ni-rich cathodes can migrate to the anode side and accelerate the failure of lithium-ion batteries. The investigations of the impact and distribution of Ni species on the solid electrolyte interphase (SEI) on the anode are crucial to understand the failure mechanism. Herein, we used time-of-flight secondary ion mass spectroscopy (TOF-SIMS) coupled with multivariate curve resolution (MCR) analysis to intuitively characterize the distribution of Ni species in the SEI. We find that the SEI on the graphite electrode using an EC-based electrolyte exhibits a multi-stratum structure. During accelerated aging of the LiNi_0.88 Co_0.08 Mn_0.04 O₂ /graphite full cell, the dissolution of Ni aggravates significantly upon cycling. A strong correlation between the dissolved-Ni and organic species in the SEI on graphite is illustrated. The ion-exchange reaction between Ni²⁺ and Li⁺ ions in the SEI is demonstrated to be the main reason for the increase of SEI resistivity.