Newly Developed Monolithically Integrated Micro-Supercapacitors (MIMSCs) to Power Electronics

(a) Schematic of the fabrication of M-MIMSCs. (b) Flexibility of M-MIMSCs on a flexible polyethylene terephthalate substrate. (c) Cycling stability for 4000 cycles tested at 2.7 μA of 60 cells connected in series under output voltage of 162 V in PVDF-HFP-EMIMBF4 gel electrolyte. Photo credit: Dr. Sen Wang and Dr. Linmei Li. Credit: Science China Press

In order to achieve the full potential of the Internet of Things (IoT), the development of compact and high-performance micro-supercapacitors (MSCs) with a high cell number density is essential for powering miniaturized electronics. However, the production of scalable MIMSCs still poses several challenges, such as the precise deposition of electrolytes on densely-packed micro-supercapacitors while ensuring electrochemical isolation, sacrificing electrochemical performance during complex microfabrication procedures, and achieving performance uniformity among numerous individual cells.

Combining Multi-Step Lithographic Patterning, Spray Printing of MXene Microelectrodes, and 3D Printing of Gel Electrolyte

To address these challenges, a team of researchers led by Professor Zhong-Shuai Wu has developed an innovative and high-throughput strategy for the mass production of MIMSCs with superior cell number density and high systemic performance. The team's strategy involves combining multi-step lithographic patterning, spray printing of MXene microelectrodes, and 3D printing of gel electrolyte.

High-Resolution Micropatterning Techniques and Unique MXene Nanosheets

The team leveraged high-resolution micropatterning techniques for microelectrode deposition and 3D printing for precise electrolyte deposition, achieving the monolithic integration of electrochemically isolated micro-supercapacitors in close proximity. With the high-resolution of lithographic patterning and unique MXene nanosheets, super-dense microelectrode-arrays were fabricated, with each individual MXene-based MSC exhibiting an extremely small footprint of 1.8 mm2, high areal capacitance of 4.1 mF cm-2, high volumetric capacitance of 457 F cm-3, and stable performance at an ultrahigh scan rate up to 500 V s-1.

Simple, Reliable, and Large Throughput Strategy

The team also developed a simple, reliable, and large throughput strategy for the electrochemical isolation of individual units. They designed a gel electrolyte ink compatible with a novel 3D printing technique, enabling adjacent microcells to be electrochemically isolated at a close proximity of just 600 μm and providing outstanding performance uniformity.

Superior Areal Number Density and Areal Output Voltage

The researchers were able to obtain MIMSCs with a superior areal number density of 28 cells cm-2 (400 cells on 3.5×4.1 cm2), a record areal output voltage of 75.6 V cm-2, and an acceptable systemic volumetric energy density of 9.8 mWh cm-3, far exceeding those of previously reported integrated MSCs.

Excellent Performance Consistency on a Larger Scale

Due to the reliability and uniformity of each step in the microfabrication processes, including lithography, spray printing, lift-off, and 3D printing, the resulting MSCs showed excellent performance consistency on a larger scale. The MIMSCs demonstrated good capacitance retention of 92% after 4000 cycles at an extremely high output voltage of 162 V.

A Technological Platform for Monolithic Micropower Sources

According to Professor Wu, this innovative microfabrication strategy marks a great advance as a new technological platform for monolithic micropower sources and will aid applications where compact integration and high systemic performance are demanded from energy storage units. The paper detailing the team's findings is published in the journal National Science Review.