Fabrication of Three Dimensional Hierarchical Carbon Microelectrodes As High-Performance Anode for Lithium-Ion Batteries

Introduction Lithium-Ion batteries (LIB) are one of the potential energy storage devices that are used in a wide range of applications from miniaturized devices to high power-driven electric vehicles[1,2]. In electric vehicle requirements, LIB has to deliver high energy/power density. It is a fact that the electrochemical performance of a LIB is majorly dependent on its active electrode materials. Hence, the design and material aspects of electrodes have become an exciting area for the scientific community to achieve high energy/power densities. In this paper, candle soot (CS) and reduced graphene oxide (rGO) are synthesized using facile flame synthesis and modified hummers method, respectively. Later on, these materials are integrated with three-dimensional (3-D) carbon microelectrode to fabricate hierarchical electrodes via a simple drop-casting method. As prepared electrode samples are characterized physically and structurally using SEM and Raman spectroscopy, respectively. Further, these 3-D hierarchical electrodes are electrochemically characterized using them as an anode in half-cell configuration. Experimental: SU 8 3D micropillars with 50µm height, 25µm diameter, and 35µm spacing are prepared on SS wafer using UV Flood Exposure Lithography Technique. Thus, obtained micropillars are pyrolyzed under the controlled N 2 atmosphere in a tubular furnace at 900ºC to obtain 3D carbon microelectrodes [3]. Later for the preparation of hybrid electrodes, the rGO and CS are drop-casted on the microelectrodes to yield 3-D hierarchical electrodes named GHE and CHE respectively. As fabricated, 3-D hierarchical hybrid electrodes are used as a working electrode, lithium foil as the counter electrode in the coin cell (CR2032) half-cell assembly for electrochemical testing. Results and discussions: Figure 1a shows the SEM image of CHE on the SS substrate. The unique and uniform mushroom topology of the CHE is presented in figure 1a. This is due to the instant vaporization of ethanol solvent during the heat treatment drop-casting technique. Figure 1 shows the interconnected CS nanoparticles present in the spaces and as well as on microelectrodes. Therefore, we could fabricate a multiscale hybrid high surface area electrodes where carbon nanoparticles are deposited on carbon microelectrodes. The electrochemical performance of CHE at different current densities is summarized in figure 1b. The cell exhibits high discharge capacities of 645, 551, 466, 356, and 264 mAhg -1