A small amount of copper (II) oxide (CuO) powder is added into a nickel-doped manganese spinel (LiNi0.5Mn1.5O4, LNMO) positive electrode to function as a hydrogen fluoride (HF) scavenger. The direct contact experiment between CuO powder and HF solution shows that CuO reacts with HF and water to form copper (II) fluoride dihydrate (CuF2 center dot 2H(2)O). In the Li/LNMO cell prepared without added CuO, HF is generated as a product of electrolyte decomposition. HF attacks the LNMO electrode to dissolve the metal and/or inorganic film components, and both processes will enlarge the electrode surface area exposed to the electrolyte solution. Consequently, the electrolyte decomposition and concomitant film deposition are continued to cause cell polarization and eventually cell failure. In the cell fabricated with the CuO-added LNMO electrode, the HF concentration in the electrolyte solution is lower due to its scavenging by CuO, thereby protecting the metal from dissolution. As a result, the change in the electrode surface area is less significant, and the electrolyte decomposition and film deposition are mitigated. The low level of film deposition reduces the cell polarization and therefore improves the cell performance. (C) 2017 The Electrochemical Society. All rights reserved.