LiNi0.5Mn1.5O4 is the most promising 5 V cathode material for Li-ion batteries because of its high voltage and good cycling behavior. We introduced LiNi0.5Mn1.5O4 as a positive electrode for a hybrid electrochemical supercapacitor with an active carbon negative electrode in 1.0 M LiPF6 ethylene carbonate/dimethyl carbonate (1: 2 in volume) solution. It has a sloping voltage profile from 2.8 to 1.5 V, delivers a capacity of 55 Wh/kg based on the total active materials, and shows a good cycling profile with capacity retention of 80 % over 1000 cycles. (c) 2005 The Electrochemical Society. All rights reserved.