Nano- and micro-sized LiNi0.5Mn1.5O4 particles are prepared via the thermal decomposition of a ternary eutectic Li–Ni–Mn acetate. Lithium acetate, nickel acetate and manganese acetate can form a ternary eutectic Li–Ni–Mn acetate below 80°C. After further calcination, nano-sized LiNi0.5Mn1.5O4 particles can be obtained at an extremely low temperature (500°C). When the sintering temperature goes above 700°C, the particle size increases, and at 900°C micro-sized LiNi0.5Mn1.5O4 particles (with a diameter of about 4μm) are obtained. Electrochemical tests show that the micro-sized LiNi0.5Mn1.5O4 powders (sintered at 900°C) exhibit the best capacity retention at 25°C, and after 100 cycles, 97% of initial discharge capacity can still be reached. Nano-sized LiNi0.5Mn1.5O4 powders (sintered at 700°C) perform the best at low temperatures; when cycled at −10°C and charged and discharged at a rate of 1C, nano-sized LiNi0.5Mn1.5O4 powders can deliver a capacity as high as 110mAhg−1.