From Black Liquor to Green Energy Resource: Positive Electrode Materials for Li-O2 Battery with High Capacity and Long Cycle Life.

Black liquor caused a tremendous degree of pollution and waste. Exploring utilization of lignin, which is the major component of black liquor, has become a key factor in order to deal with the problem. In this study, lignin derived from black liquor was used as raw materials to prepare carbon materials through different activation methods including KOH, H3PO4 and steam activation. The structure and property of obtained samples was characterized as well as electrochemical performance when applied on lithium-oxygen battery. Results of N2 adsorption/desorption showed all obtained samples possessed high surface area of over 1000 m2/g. XRD, Raman, XPS also indicated obtained samples possessed a large amount of defect area and functional groups. Electrochemical measurements illustrated that all obtained samples exhibited a high discharge capacity over 2.8 mAh/cm2 at 0.02 mA/cm2 while LKAC exhibited highest discharge capacity of 7.2 mAh/cm2. Cycling tests of all obtained samples indicated a long cycle life of at least over 300 cycles. LSAC kept 100% retention rate of capacity and stable terminal voltage even after 800th cycle, and its cycling performance were investigated further by XRD and EIS. This study demonstrated excellent performance for lignin-based carbon materials, and provided alternative materials for positive electrode of lithium-oxygen battery.