Impacts of environmental relative humidity (RH) on lithium nickel-cobalt-aluminum oxide (LiNi0.8Co0.15Al0.05O2) based cell performance is investigated. LiNi0.8Co0.15Al0.05O2 (NCA) cathode electrodes are prepared in different environmental relative humidity (RH), 20% RH, 40% RH and 60% RH, respectively. Significant impact of the environmental RH on the cell discharge and coulombic efficiency is observed, specifically, 179.1, 175, and 159.5 mAh/g with the relative humidity, 20% RH, 40% RH and 60% RH, respectively; and corresponding first Coulombic efficiency is 84.9%, 82.2%, and 80.1%. However, the cycling stability of LiNi0.8Co0.15Al0.05O2 cathode is similar regardless of the environmental RH content. To understand the root cause for the disparity on initial discharge capacity and first Coulombic efficiency, local surface morphology/chemistry of the NCA cathode prepared at different environmental RH has been characterized via multiple advanced techniques, including: SEM, XRD, and XPS. Severe electrolyte decomposition and microstructure changes are seen in the cathode prepared at high moisture content after the first cycle. The severe electrolyte decomposition on the cathode surface and structural degradation of the cathode particles is attributed to the high humidity content. This is believed to be the source of the poor electrochemical performance of NCA cathode. Therefore, environmentally RH control is a critical factor to yield superior electrochemical performance for NCA during electrode processing. (C) 2018 Elsevier B.V. All rights reserved.