A high-performance capacitor battery AC/lambda-MnO2 based on Na-ion insertion-deinsertion into lambda-MnO2 in 1 mol dm-3 Na2SO4 solution is successfully demonstrated. A simple acid leaching technique is used to produce lambda-MnO2 by treating LiMn2O4 with H2SO4. X-ray power diffraction and inductively coupled plasma analysis provide supporting evidences for the extraction of Li+ from the LiMn2O4, and the particle morphology of lambda-MnO2 is studied by scanning and transmission electron microscopy. A high specific capacity of 390.7 mAh g(-1) is obtained for the lambda-MnO2 electrode at a current density of 13.6 mAg(-1) with a nearly 100% efficiency. The capacitor battery AC/lambda-MnO2 can operate at a cell voltage as high as 2.2 V, and it exhibits a specific energy of 19.7 Wh Kg(-1) at a high power density of 3500 W Kg(-1) and a high energy density of 71.7 Wh Kg(-1) at a low power density of 403 W Kg(-1). It has potentials to be used as an energy storage device for the integration of solar and wind power into the electrical power grid. (C) 2014 Elsevier Ltd. All rights reserved.