Evaluating the effect of solid electrolyte interphase formers on lithium depth profiles of the solid electrolyte interphase layer and bulk electrode material in LiNi0.4Mn0.4Co0.2O2/graphite pouch cells obtained with lithium nuclear reaction analysis

Abstract Lithium loss resulting from positive electrode deterioration and lithium accumulation within the solid electrolyte interphase (SEI) at the negative electrode leads to charge capacity loss in lithium-ion batteries (LIBs). We present a novel method to quantify origins of capacity loss resulting from positive electrode degradation and lithium immobilization within the SEI by comparative lithium depth profiles using Lithium Nuclear Reaction Analysis (Li-NRA). Li(Ni 0.4 Mn 0.4 Co 0.2 )O 2 /artificial graphite (NMC442/AG) pouch cells were cycled with electrolytes containing 1 M LiPF 6 in either 1:1 ethylene carbonate (EC)/dimethyl carbonate (DMC) or DMC with 3% vinylene carbonate (VC) SEI former. Lithium accumulated rapidly within the SEI in cells containing EC as compared to cells containing VC. Lithium loss from the positive electrode occurred at a linear rate, after formation, which was independent of electrolyte composition tested. The technique and methods provide quantitative insight into the impact of materials on capacity loss.