Zerovalent Copper Intercalated Birnessite as a Cathode for Lithium Ion Batteries: Extending Cycle Life

Birnessite type layered manganese dioxides (delta-MnO2) have attracted considerable attention in recent years as 2D intercalation cathodes for rechargeable Li+, Na+, and Mg2+ batteries due to fast ion diffusion through their negatively charged delta-MnO2 sheets separated by interlayer cations and a stable Mn3+/4+ redox couple. Here we report the preparation and electrochemistry of zero and divalent copper co-intercalated birnessite type manganese dioxide ((Cu0.03Cu0.212+Na0.12MnO2)-Cu-0 center dot 0.9H(2)O). The copper intercalated birnessite materials were fully characterized utilizing powder X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy (ICP-OES), transmission electron microscopy (TEM). The mixed valent nature of intercalated Cu-0 and Cu2+ was confirmed by X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS). Electrochemical evaluation results show that zero valent copper intercalated birnessite exhibits higher discharge capability, improved cyclability, and lower impedance compared to the Cu2+ only intercalated (Cu0.26MnO2 center dot 1.0H(2)O) and Cu free Na birnessite (Na0.40MnO2 center dot 1.0H(2)O) materials. Remarkably, zero valent copper birnessite shows almost no fade after 10 cycles at 0.1 mV/s. Electrochemical impedance spectroscopy results suggest that charge transfer resistivity of Cu-0 modified samples was much lower than that of Cu2+ and Cu free birnessite, indicating that the presence of a small amount of Cu-0 improves the conductivity of birnessite and results in better electrochemical cyclability, rate capability, and lower impedance. (C) 2017 The Electrochemical Society. All rights reserved.