Research And Application Of Carbon-based Micro-supercapacitor By Laser Direct Writing Technology

The popularization and application of miniaturized and intelligent electronic products have stimulated the rapid development of miniature energy storage devices with electrochemical reliability and flexibility.Among them,micro-supercapacitors have attracted the attention of the scientific community due to their ultra-high power density,long cycle life,strong flexibility,high safety,and high efficiency.However,the relatively low energy density of micro-supercapacitors limited their further commercial applications.This work aimed to realize the high energy output of micro-supercapacitors.Two carbon-based micro electrodes with high conductivity and large specific surface area,which were constructed via laser direct writing technology,were studied their application in micro-supercapacitors using ionic liquids with stable performance under high voltage operation as electrolyte.Firstly,improving their energy density of in-plane micro-supercapacitors within a limited storage area was research focus.However,the low ionic contact area of planar electrode materials limits the energy output of micro-supercapacitors.We designed a stable microemulsion system using Tween 20,ionic liquid（TW20-IL）and MXene（Ti₃C₂T_x）.The microemulsion droplets could uniformly adhere to the graphite paper current collector,forming a tightly packed MXene-Tween 20-ionic liquid-graphite paper thin film（MXene-TW20-IL-CP thin film）.During the process of heat treatment,with the disappearance of Tween 20,the ionic liquids as spacers and electrolytes are retained between the layers of the MXene films,which effectively increase the ionic contact area of the MXene-based electrodes.Therefore,the micro-supercapacitors based on the flexible MXene-IL-CP films exhibit high areal capacitance（44.6 m F/cm~2）and high areal energy density（50.7μWh/cm~2）,exceeding most reported MXene-based Micro-supercapacitors.And the micro-supercapacitor units can be arbitrarily integrated according to various energy and voltage requirements.Among them,the integrated array of 30 micro-supercapacitor units in series achieves a high-voltage output of 90 V,which broadens its application range in a new generation of micro-electronic devices.Then,the MXene-reduced graphene oxide（MXene-rGO）electrode with three-dimensional structure was fabricated in an one-step with the waste heat during the laser direct writing.A large number of enthalpy changes generated in the laser reduction process trigger the reduction of the graphene oxide,and a large amount of gas coming from the reduction process lead to the"explosion"of the electrode material sheets,realizing the transformation from two-dimensional structure to three-dimensional structure.Meanwhile,heterogeneous film bonding effect between MXene and graphene sheets overlapped the loose and disordered reducing graphene oxide nanosheets during the reduction process,effectively preventing the damage of a three-dimensional MXene-rGO micro-electrode.In addition,the introduction of MXene with pseudocapacitive properties effectively improves the capacitive performance of the MXene-rGO micro-supercapacitor.The fabricated MXene-rGO thin films provided fast ion transport channels and sufficient active sites,which can enchance the performance of MXene-rGO micro-supercapacitors.Therefore,the MXene-rGO micro-supercapacitor with a three-dimensional structure showed a capacitance value of 60.40 m F/cm~2 and an area energy density of 68.14μWh/cm~2 at a current density of 0.6 m A/cm~2.When the current density increased from 0.6 m A/cm~2 to 1.0 m A/cm~2,the capacitance retention was77.33%.Therefore,the MXene-rGO micro-supercapacitors exhibited good electrochemical performance.