Synergistic Morphological and Defect Optimization in Graphene-based Electrodes with Applications in Microsupercapacitors


Student thesis: Doctoral Thesis

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Awarding Institution
Award date28 Apr 2022


Micro-supercapacitors (MSC) have attracted researchers' widespread attention as emerging energy storage devices. In contrast to traditional supercapacitors (SC) with a sandwich structure, MSC usually uses an interdigitated pattern as its conductive and active path. This design not only dramatically reduces the size of the device but also exhibits excellent charge transfer characteristics due to the minimization of its internal resistance. In addition, MSC also has the advantages of long life, high power density, and easy integration into other microelectronic devices. However, MSC still has many challenges that prevent their practical applications. For example, the manufacturing technology is costly and complicated, device function is limited, energy density is insufficient, and the reliability and stability are poor. This thesis presents a series of works aimed at addressing the above problems.

In Chapter 2, we present a lasing-centric method for defect control and morphological enhancement in laser-induced graphene (LIG) electrodes through unique dual laser pyrolysis. This method encompasses dual lasing pyrolysis, one for the synthesis of defocused LIG, and another for the decoration of Ru nanoparticles to enhance electrochemical performance. Fundamentally, the investigation simultaneously optimizes for defocused lasing distance and lasing speed, which has not been previously reported to the best of our knowledge. The defocused LIG electrode exhibits a remarkably improved electrochemical capacitance of over 25 times (114 mF cm-2) compared to one based on focused laser-induced graphene (FLIG). As a device demonstration, a flexible and self-healable MSC has been fabricated based on DFLIG/Ru-PEDOT/Au electrodes, exhibiting a high areal specific capacitance (25.7 mF cm-2), excellent electrochemical stability (91% retention of specific capacitance after 8000 cycles), and good self-healing performance (85.6% retention of specific capacitance after two cut-heal cycles). This work presents a strategy for the highly controllable and scalable realization of electrodes in micro-energy storage devices by enhancing material properties via dual defocused laser pyrolysis.

In Chapter 3, we present a 3D porous poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/graphene composite sponge (PGCS) fabricated via a facile self-assembly process for highly stretchable, high areal capacitance MSCs. The proposed self-assembly process enables the following simultaneously in one step: (1) separation of PSS and PEDOT from PEDOT:PSS, (2) reduction of graphene oxide (GO) into reduced graphene oxide (rGO), and (3) integration of PEDOT and rGO into a hybrid 3D composite. By tuning the mass ratio of PEDOT:PSS and GO, PGCSs with different porosity, mechanical properties, conductivity, and capacitance can be obtained. With the incorporation of PEDOT into rGO, the PCGS exhibits enhanced electrochemical performance and better mechanical flexibility. The fabricated stretchable MSC exhibits a high areal specific capacitance (19.3 mF cm-2 at a scan rate of 20 mV s-1), good electrochemical stability (88.6% retention of specific capacitance after 5000 cycles), and a remarkable stretchability (87.1% retention of specific capacitance after 50% stretching). This facile approach provides a general strategy for synergistic self-assembly of composite sponges and the design of stretchable 3D MSCs, suitable for energy storage devices with high stretchability and high energy density.

Chapter 4 further summarizes the proposed work and gives a perspective on possible future directions of investigation. This thesis's results and discussions provide essential insights into the rational design for high-performance and functional MSCs.