Abstract An interlaboratory study was performed to determine the heat capacity of an active material for lithium-ion batteries with layered structure and nominal composition LiNi1/3 · Mn1/3Co1/3O2 (NMC111). The commercial sample, which was characterized using powder X-ray diffraction and inductively coupled plasma–optical emission spectroscopy, is single phase (α-NaFeO2 crystal structure) with a composition of Li1.02Ni0.32Mn0.31Co0.30O2. Heat capacity measurements of the homogeneous sample were performed at five laboratories using different operators, methods, devices, temperature ranges, gas atmospheres and crucible materials. The experimental procedures from each laboratory are presented and the results of the individual laboratories are analyzed. Based on a comprehensive evaluation of the data from each laboratory, the heat capacity of the NMC111 sample from 315 K to 1 020 K is obtained with an expanded reproducibility uncertainty of less than 1.22 %.