In recent years, due to its pliability and lightness, flexible and micro energy storage devices have shown great potential in wearable electronic devices, smart skins, and portable smart phones. Among them, the flexible all-solid supercapacitor has the advantages of simple structure, easy fabrication, high power density, rapid charge and discharge, and long cycle life, and has become a research focus of energy storage devices.
At present, all-solid-state supercapacitors mainly include two structures: a conventional sandwich-structured solid supercapacitor and a planar structure of a micro-supercapacitor. High-performance supercapacitor electrode materials need to have good electrochemical stability, high electrical conductivity, and excellent capacitance performance.
As a novel transition metal carbide (a compound consisting of a transition metal and a Group III or IV (Al, Ge, Si, etc.) and carbon or nitrogen), MXene (such as Ti3C2Tx) is unique The two-dimensional layered structure, high electrical conductivity, and chemical and thermal stability are widely used in lithium ion batteries, supercapacitors, and electrocatalytic reactions. However, studies have found that the size of MXene (≈200 nm) is relatively small, which is not conducive to the construction of high-performance, flexible large-area thin-film all-solid-state supercapacitor electrodes.
Professor Feng Xinliang, Dresden University of Technology, Dr. Zhuang Xiaodong and the Niu Li researcher (co-corresponding author) of the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, took this as the focus and co-developed graphene nanocomposite film electrode based on MXene and electrochemical stripping. And apply it to traditional solid super capacitors and planar micro super capacitors.
The composite film has two advantages: First, the electrochemically exfoliated high-quality graphene layer can serve as a mechanical support for the entire membrane electrode, further enhancing the overall flexibility, stability, and long-range conductivity of the membrane electrode; The MXene nanosheets are interposed between the graphene sheets and can provide a large number of interlayer spacings, which facilitates the rapid insertion and extraction of ions during charge and discharge.
After the assembled membrane electrode is assembled into a traditional symmetrical flexible supercapacitor, the volumetric capacitance is as high as 216 F cm-3 at a current density of 0.1 A cm-3, and the specific capacity can be maintained after 2500 charge and discharge cycles. 85.2%. In addition, the interdigitated micro-supercapacitor fabricated by masking the solution phase of MXene/electrochemically exfoliated graphene ink has an area and volumetric capacitance as high as 3.26 at a cyclic voltammogram scan rate of 5 mV s-1. mF cm-2 and 33 F cm-3, these performance indicators are higher than those reported in most of the current literature.
Subsequently, the micro-supercapacitor was subjected to a cyclic test in a flexible state under bending, and after 2500 cycles of charge and discharge, its capacitance performance could still maintain 82%. It is worth noting that in this work, we used electro-stripping graphene prepared by our own electrochemical stripping device with high yield, high C/O ratio, and high dispersibility.
The work optimizes the electrode structure and uses a simple method to prepare high-performance supercapacitor electrode materials. This opens up a new idea for the preparation of low-cost, high-efficiency flexible energy storage devices.
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