An aqueous capacitor battery hybrid device based on Na-ion insertion-deinsertion in λ-MnO2 positive electrode.

A high-performance capacitor battery AC/ λ -MnO 2 based on Na-ion insertion-deinsertion into λ -MnO 2 in 1 mol dm −3 Na 2 SO 4 solution is successfully demonstrated. A simple acid leaching technique is used to produce λ -MnO 2 by treating LiMn 2 O 4 with H 2 SO 4 . X-ray power diffraction and inductively coupled plasma analysis provide supporting evidences for the extraction of Li + from the LiMn 2 O 4 , and the particle morphology of λ -MnO 2 is studied by scanning and transmission electron microscopy. A high specific capacity of 390.7 mAh g −1 is obtained for the λ -MnO 2 electrode at a current density of 13.6 mA g −1 with a nearly 100% efficiency. The capacitor battery AC/ λ -MnO 2 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. [ABSTRACT FROM AUTHOR]