A New Concept of Flexible Electrodes for Lithium/Sulfur Batteries

Abstract

According to the progress of electronics industry, electronic devices have been diversified to various forms such as roll-up displays, smart cards, and wearable devices. Flexible electronic devices are demanding has various properties such as lightweight, ultrathin, and flexibility. Therefore, batteries as their power sources are required to have same properties. In addition, high energy density and operational safety are needed. Until now commercial lithium-ion batteries (LIBs) are the only viable candidates for flexible devices. Recently, the flexible lithium/sulfur (Li/S) battery has been proposed with a high theoretical energy density of 2600 Wh kg-1. As most active materials considered in these studies are rigid and brittle, flexible cathodes were achieved by the physical combination of rigid active materials with flexible current collectors such as carbon-based materials or polymers. This integrated design has two inevitable disadvantages; (1) during deformation the active material can detach from the current collector; (2) the capacity per electrode is reduced by the presence of electrochemically inactive materials such as current collector, binder and conducting agents. Therefore, there is a strong need for a new approach to the flexible cathode which consists of only active material without a separate current collector. Sulfurized polyacrylonitrile (SPAN) composite could be a good candidate due to its good electric conductivity, high sulfur utilization, and stable cycle life. In addition, it can be fabricated as either particle or nanofiber. However, the SPAN electrodes reported so far were prepared by mixing SPAN, conductive agent, and binder which were pasted on metallic current collector. In carbon nanotube paper and graphene paper, it is well-known that the strain during deformation decreases with the diameter of the fiber. Therefore, in this work, the SPAN nanofiber web cathode which does not include conductive agent, binder, as well as current collector was fabricated from PAN nanofiber web and sulfur by heat treatment process. Also, pre-lithiated carbon felt was used as anode in order to make all flexible full cell and investigated its electrochemical properties.