Micro-supercapacitors (MSCs) with a high energy density and a nearly indefinite lifespan can be incorporated into electrical components as power sources. However, the inferior capacitance per unit volume and lower power density of ordinary double-layer carbon supercapacitors significantly restrict their practical uses.
Study: Scalable fabrication of MXene-based flexible micro-supercapacitor with outstanding volumetric capacitance. Image Credit: Hatcha/Shutterstock.com
A pre-proof paper from the Chemical Engineering Journal sets out to address this issue using a straightforward and dependable method for the scalable and environmentally sound production of on-chip and flexible micro-supercapacitors with potential applications in stretchable, versatile, and miniaturized optoelectronics.
Flexible Micro-supercapacitors: Overview and Significance
With the fast growth of 5G and 6G telecommunications and the Internet of Things (IoT), the need for mobile and small devices, such as electromechanical circuits, microsensors, and microrobots, has expanded significantly.
Therefore, there is a demand for highly efficient nanometer-scale electrochemical energy storing systems that can be paired with such electronics to make gadgets independent and self-powered.
Flexible micro-supercapacitors (MSCs) have recently attracted great interest owing to their prospective use as primary power supplies for nanoscale electronics. Flexible micro-supercapacitors provide several benefits, including low maintenance, a long lifespan, rapid charging and discharging cycles, and a high energy density.
Conventional micro batteries have a shorter lifespan (between 500 and 10,000 cycles) and a reduced power density. Also, their volumetric effectiveness features diminish significantly as their size decreases. Therefore, flexible micro-supercapacitors are an intriguing alternative to traditional micro-batteries in the realm of electrolytic energy storage.
MXenes as Building Blocks for Flexible Micro-Supercapacitors
Two-dimensional (2D) materials, such as MXenes, are particularly promising for fabricating flexible micro-supercapacitors. Due to their layered structure, high electrical conductance, high effective surface area, and high wettability, MXenes have been widely researched for a vast array of applications in a variety of industries.
Their high electrical conductance can increase the dissolution rate of electrolyte ions by accelerating the absorption and dissociation of charges. In addition, the high electrolytic interaction of MXenes is advantageous for the rapid and reversible electrochemical reactions in electrocatalytic storage devices.
Therefore, utilizing MXene as the working electrode solution for flexible micro-supercapacitors has substantial advantages over other 2D materials.
Challenges Associated with Scalable Manufacturing of MSCs
Interdigitated MXene electrodes for flexible micro-supercapacitors have been produced on various substrates using a variety of efficient techniques. To increase the electrolytic effectiveness of the devices, techniques like filtration-masking, spraying-masking, and laser scribing have been established in previous studies.
However, these processes are time-consuming and non-scalable, restricting their potential utility in producing flexible micro-supercapacitors based on MXenes.
Recently, scalable technologies, like inkjet mapping, spray dipping, and screen printing, have evolved for depositing the required pattern of electrode compounds onto the surface of flexible micro-supercapacitors. However, due to the rheological qualities of printing substances, conducting additives must be applied to preserve the printed structure.
In addition, the low capacitance and poor energy density resulting from the enormous footprint of the working electrode present a significant obstacle to the broad implementation of these technologies.
Highlights of the Current Study
In this paper, the researchers offer a simple and scalable production method for creating flexible micro-supercapacitors using a microfabrication technique based on photolithography and solvent treatment.
Initially, the micro-supercapacitors were moved from a rigid surface to a flexible polyimide (PI) substrate using the "selective etching approach." Then, 3D nanoporous linked MXenes were produced by creating nanopores on MXene films in a 900°C reduction environment.
Strong van der Waals interactions between neighboring nanosheets in 2D materials, such as MXenes, result in self-restacking. Severe self-restacking reduces the availability of electrolyte ions and has a negative impact on the fundamental electrochemical qualities, such as cyclic stability.
Therefore, the researchers employed carbon nanotubes (CNTs) as 1D spacers to hybridize with MXenes to reduce self-restacking and increase the electrochemical performance of flexible micro-supercapacitors.
Important Findings of the Research
The researchers discovered that the nanopores in MXene films, which are coupled to nanoparticles between MXene layers, improve the transport of ions in the 3D interlinked electrodes considerably. Flexible micro-supercapacitors based on MXenes demonstrated a high initial capacitance, excellent rate-capability retention, and an extremely high-power density.
Scalable production of flexible micro-supercapacitors was demonstrated in a large-scale area comprising 107 chips in an 8-inch wafer. These results indicate that the MXene-based flexible micro-supercapacitors created in this study are promising energy storage materials for applications in next-generation miniaturized microelectronics.
Kim, E. et al. (2022). Scalable fabrication of MXene-based flexible micro-supercapacitor with outstanding volumetric capacitance. Chemical Engineering Journal. Available at: https://doi.org/10.1016/j.cej.2022.138456