The capacity fading phenomenon of high energy lithium-ion batteries (LIBs) using a silicon monoxide (SiO) anode and a nickel-rich transition metal oxide cathode were investigated during life test. The capacity loss of this electrode couple was found to increase not only with cycles (cycle life), but also with rest time (calendar life). The capacity fading rate for this type of LIB using SiO as the anode was found to be time-dependent, rather than cycle-count-dependent. Further detailed investigation revealed that the capacity loss of this electrode couple during rest was caused by the parasitic reactions on the anode, which consumed the lithium ions and lead to less cyclable lithium in the battery system. (C) The Author(s) 2018. Published by ECS.