Preparation of High-Performance Internal Tandem Electric Double-Layer Capacitors (IT-EDLCs) from Melt-Spun Lignin Fibers

<p>Activated carbon fibers (ACFs) with large surface area were easily prepared from melt-spun fibers of polyethylene glycol lignin (PEGL). To fabricate electric double-layer capacitors (EDLCs) with a wide potential window and a high energy density in an EDLC package, electrodes (mainly composed of ACFs) were internally laminated and connected in series, in parallel, or in a series/parallel combination. Such resultant EDLCs are termed internal tandem (IT) EDLCs. As expected, the potential window was expanded by the series connection, and the capacitance was increased by the parallel connection. As a result, the energy density in the parallel-connected EDLC was remarkably increased by 66% (16.6 Wh kg<sup>−1</sup>) compared with that of a single-cell EDLC. The EDLC with the combination connection showed both advantages. Thus, based on the package weight, the electrochemical performance of the EDLCs was remarkably improved by the IT-type lamination of electrodes.</p>