Graphene-Lii Composite Cathodes for Lithium-Iodine Batteries

Abstract

Development of high energy and power density secondary batteries is of great fundamental and applied interest. Systems which provide high power, without a significant reduction in energy are important for next-generation hybrid and all-electric vehicles. Li-iodine cells have been considered promising because of fast electrochemical conversion of the iodine/triiodide redox pair. To date, there only a few reports on rechargeable Li-iodine cells, in-part because of the drawbacks of iodine. Iodine is highly soluble in aprotic electrolytes, leading to self-discharge due to shuttling. Li-iodine cells use Li metal as an anode, however, Li metal can form dendrites which lead to shorting during cycling. Iodine is volatile even at room temperature, leading to cell fabrication challenges. Finally, iodine based electrodes suffer from low electrical conductivity. Here, we present the fabrication of a reduced graphene oxide (rGO)/LiI composite cathode with a gravimetric energy density of around 270 mAh/g which addresses some of these problems and demonstrate its operation in a full cell. LiI was uniformly coated on rGO by a solution-based method directly forming a free standing electrode. The use of LiI enables use of lithium-free anodes such as graphite, silicon, and tin. Its high melting (469 °C) and boiling points (1171 °C) provide the better thermostability compared to iodine and enables the use of various high temperature synthesis methods. The rGO facilitates rapid electron transfer and suppresses the dissolution of active materials species during cycling. We observe stable cycling performance of rGO/LiI electrodes at both low and high current densities. Promisingly, the rGO/LiI electrodes show good rate performance and a small hysteresis at high c-rates.