Electrochemical Protocols to Assess the Effects of Dissolved Transition Metal in Graphite/LiNiO2 Cells Performance

Abstract

The deployment of energy dense positive electrode materials such as Ni-rich NMC (LiNixMnyCozO2 with 0 < x, y, z < 1 and x + y + z = 1) for Li-ion batteries is plagued by numerous interfacial limitations. Among them, dissolution of transition metals (TMs) was shown to trigger deleterious growth of solid electrolyte interphase (SEI) and/or lithium plating at the anode. Although numerous post-mortem analysis and cycling data showed a causal relationship between TMs deposition and capacity fading, quantifying and discriminating the major source of degradation proves tedious. Herein, using graphite/LiNiO2 chemistry, we quantitatively demonstrate that TMs in solution permeate inside the SEI to be reduced, which precipitates cell aging following a loss of lithium inventory at the anode. This loss induces a change in intercalation staging at the graphite anode, allowing the recovery of LiNiO2 intercalation plateau at high potential, thus leading to a “S”-shape evolution of capacity as function of cycling. Furthermore, aging study in temperature show that TMs do not favor lithium plating but rather destabilize the SEI, especially at high temperature. Beyond the sole understanding of the graphite/LiNiO2 chemistry, this work offers practical routes towards evaluating LIBs degradations using electrochemical diagnosis methods.