We report on electrochemical properties of NiO-blended spinel Li1.1Mn1.9O4 at elevated temperature (60°C). Thus, we employed two kinds of NiO powders, those are, larger particle size (>10μm) and submicron-sized NiO powders obtained by a ball-milling. These NiO powders were blended to the spinel Li1.1Mn1.9O4 as an additive for fabrication of cathode. The resulting discharge capacity for the larger NiO particle-blended Li1.1Mn1.9O4 had similar electrochemical properties to the bare Li1.1Mn1.9O4. On the other hand, submicron-sized NiO-blended Li1.1Mn1.9O4 brought about slightly increased capacity and excellent capacity retention, maintaining its initial capacity of 99.2% at 25°C and 94% at 60°C when Li metal was employed as the anode. In Li-ion cell using graphite as the anode, the capacity retention was of about 80% during cycling at 60°C, whereas C/Li1.1Mn1.9O4 cell retained around 68% of its initial capacity. Such improved properties would be ascribed to the HF scavenging into the electrolyte by presence of the submicron-sized NiO particles in Li1.1Mn1.9O4 cathode.