Professor Yuan Zhihao, Professor Zhang Chenguang, EnSM: Intelligent current collector enables supercapacitors to achieve high energy density and electrochromic contrast at the same time and its application for intelligent wearable power supply [Article Information] Intelligent cu

Professor Yuan Zhihao and Professor Zhang Chenguang, EnSM: Intelligent current collector enables supercapacitor to achieve high energy density and high electrochromic contrast and its application for intelligent wearable power supply

[Article information]

[Article information]

Intelligent current collector enables supercapacitor to achieve high energy density and high electrochromic contrast and its application for intelligent wearable power supply

First author: Jiao Xin

Corresponding author: Yuan Zhihao*, Zhang Chenguang*

Unit: Tianjin University of Science and Technology

[Research background]

electrochromic supercapacitor can feedback the internal energy state in real time through reversible appearance colors. It is regarded as an emerging intelligent power supply device and has huge application potential in future intelligent wearable electronic devices. However, existing electrochromic supercapacitors face great challenges in achieving both high electrochromic performance and high energy density energy storage performance. Traditional electrochromic supercapacitors need to achieve full transparency of electrodes, which greatly limits the load amount and type selection range of active materials; although increasing the surface load amount of active materials is the most direct way to increase the energy density of the equipment, it is undesirable for electrochromic supercapacitors, because the increase in material thickness will cause the supercapacitor to lose the transmittance light modulation ability and thus lose the electrochromic function.

Researchers have made many efforts in building new nanostructured electrodes, developing new electrochromic materials, using electrolyte additives, and optimizing the dynamics and equipment structure of electrochemical , but they have not effectively solved the common problems in the field of low energy density of electrochromic supercapacitors. At present, there is a gap of about 1 to 2 orders of magnitude between electrochromic supercapacitors in terms of energy density and conventional energy storage supercapacitors. How to effectively improve the energy density of electrochromic supercapacitors while ensuring good electrochromic performance is an important goal.

​In addition, due to the requirements of existing transmissive electrochromic supercapacitors for background light, they are susceptible to the intensity of wearable background light when used as wearable power supplies, and the recognition of electrochromic is reduced, which further limits the wearable application of electrochromic supercapacitors. Therefore, the development of a new structural design scheme and corresponding high-performance materials and components of electrochromic supercapacitors are of great significance to solve the above problems and promote the practical application of electrochromic supercapacitors.

[Article Introduction]

Recently, Professor Yuan Zhihao from the School of Materials Science and Engineering, Tianjin University of Technology, and Professor Zhang Chenguang's team published the title "Smart Current Collector for High-Energy-Density and High-Contrast Electronic Supercapacitors toward Intelligent and Wearable Power Application” research article.

​This work has developed an intelligent current collector film material with electrochromic function. This intelligent current collector allows the electrochromic supercapacitor to significantly increase the load of energy storage materials while maintaining the energy visualization function and achieve a high area ratio of capacitors and energy density, making up for the gap in energy storage performance between traditional electrochromic supercapacitors and energy storage supercapacitors. Moreover, thanks to the reflective electrochromic behavior of the intelligent current collector, the color contrast of the device is enhanced, the recognition of energy state is improved, and the impact of the light intensity of the wearable back bottom on the device's energy recognition is avoided, showing unique application advantages in wearable intelligent power supply.

Figure 1. Design and working principle diagram of traditional transmission electrochromic supercapacitor and electrochromic supercapacitor built on intelligent current collector.

[Big points of this article]

Key points 1: Design principle of intelligent current collector

Traditional transmissive electrochromic supercapacitors require a fully transparent design of all components for modulation of transmitted light, which not only limits the use of high-performance non-transparent materials, but also limits the load capacity of energy storage active materials. In contrast, the intelligent current collector composed of a transparent substrate, PPy layer and porous Ag bottom layer realizes electrochromicity by modulating reflected light, solving the limitations of the material types and optical properties of the above-mentioned equipment, broadening the material selection range, and allowing a large load of non-transparent high-performance supercapacitor energy storage electrode materials to achieve a significant improvement in energy storage performance.

​Based on structural similarity, the use of intelligent current collectors is expected to enable general non-transparent energy storage supercapacitors to achieve electrochromic capabilities. Among them, the transparent substrate in the intelligent current collector plays a mechanical support role, and its mechanical properties can be rigid or flexible; the PPy layer can achieve reversible color transformation through the redox reaction ; the porous Ag layer plays a conductive role on the one hand, allowing electrons in the electrochromic process and electrochemical energy storage process to be quickly transmitted, and on the other hand, it plays an optical reflection role, making the intelligent current collector show a reflective electrochromic behavior. Due to the porosity of the Ag film, ions can penetrate the Ag film smoothly and quickly and act on the PPy layer, achieving efficient and rapid electrochromic discoloration.

Keypoint 2: Preparation strategies and structural characteristics of intelligent current collectors

Preparation of intelligent current collectors With the help of a liquid phase interface polymerization method developed by Professor Zhang Chenguang's team in the early stage, it can realize the in-situ polymerization preparation of PPy semi-transparent films on various transparent substrate surfaces. This method has the characteristics of low cost, simple and large-area preparation. Then, by the shielding effect during the thermal evaporation process, a high-quality porous Ag film can be formed on the PPy surface with a certain roughness at the microscopic level. A large number of pinhole defects formed during coating can serve as channels for PPy to ionic interaction with the outer layer. It is also proved that the porous Ag film forms a tight interface combination with the PPy layer, promoting interfacial electron transfer and mechanical stability. The appearance color brightness of the intelligent current collector can be well controlled by controlling the thickness of the porous Ag film and PPy film. It also proves that it has excellent conductivity and electrochemical stability, meeting the basic use needs of current collectors of electrochemical equipment.

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Key points three: Electrochromic performance of intelligent current collector

Through research, the team found that the intelligent current collector film has strong electrochromic visual contrast, and then proved that the overall electrochromicity of the film is highly uniform and color consistency. In addition, this paper also used CIE Lab color coordinates to quantify the color of intelligent current collectors and studied its color contrast. It was found that it had a color contrast of up to 51.6 under standard light source testing conditions. The in-situ electrochemical-spectroscopy test revealed the electrochromic mechanism of intelligent current collectors, achieving a high electrochromic efficiency of 111.7 cm2 C-1 and an ultra-short color conversion time of 0.56/0.52 s. The electrochromic performance of intelligent current collectors has high cyclic stability through long cycle testing. In addition, the article also explains why intelligent current collectors have the above excellent electrochromic ability by studying electrochemical kinetic characterization.

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Key points 4: Electrochromic supercapacitors built on intelligent current collectors and their applications in flexible wearable power supplies

Verify the feasibility of intelligent current collectors in electrochromic supercapacitors through actual load energy storage materials, and can be compatible with various electrode materials. Through experimental methods of charging and discharging testing and in-situ optical performance monitoring, the electrochromic supercapacitor not only has ultra-high energy storage capacity, but also can achieve electrochromic transformation with high color contrast characteristics. The intelligent current collector can load up to 4.4 mg cm-2 energy storage electrode materials and can maintain good electrochromic capabilities.In terms of area ratio capacitance, electrochromic supercapacitors based on the load amount of different energy storage materials can reach 101.1~324.4 mF cm-2. In terms of area energy density, it is significantly better than the electrochromic supercapacitors reported in the past, reaching 44.2~122.6 μWh cm-2, which is 1~2 orders of magnitude greater than the electrochromic supercapacitors reported in the past, making up for the huge energy storage performance gap between electrochromic supercapacitors and traditional energy storage supercapacitors, and showing good practical application potential.

​Intelligent current collector strategy can also realize the manufacturing of flexible electrochromic supercapacitors, which can avoid the impact of the low light intensity of the wearable background on electrochromic performance, exhibit a color contrast of up to 65.6 and has good mechanical stability in energy storage. In addition, the authors used flexible electrochromic supercapacitors to be integrated with pulse sensors and solar cell integrated fabric surfaces to become self-powered intelligent wearable systems, which actually verified that flexible electrochromic supercapacitors can support wearable electronic devices to work normally, demonstrating the unique application advantages of wearable smart power supplies that are not affected by the light intensity of wearable back bottom. In addition, the energy state inside the supercapacitor can be known by observing the appearance and color of the power supply equipment, which is expected to realize intelligent energy management of high-performance supercapacitors.

[Article link]

Smart Current Collector for High-Energy-Density and High-Contrast Electronic Supercapacitors towards Intelligent and Wearable Power Application”

https://www.sciencedirect.com/science/article/pii/S2405829722005736

[ Introduction to the corresponding author ]

Zhang Chenguang , male, doctoral, professor, 2003-2007 at Department of Materials, Fuzhou University The School of Science and Engineering received a bachelor's degree in . From 2007 to 2013, he received a master's degree and a doctorate degree from the School of Materials Science and Engineering of Tianjin University. During this period, he conducted study abroad at the Smalley Nanotechnology Center of Rice University in the United States. Later, he worked in postdoctoral research at the School of Materials Science and Engineering of Nanyang Technological University in Singapore. He joined the School of Materials Science and Engineering of Tianjin University of Technology in 2016 and was selected as the Tianjin Overseas High-level Talent Program. He has long been engaged in the research on carbon nanomaterial preparation and flexible energy storage electronic device .

​ as communication/first author on Adv. Energy Mater., ACS Nano, Energy Storage Mater., Carbon, ACS Appl. Mater. Interfaces, Nano Research and other published several research papers in internationally renowned journals, serving as Frontiers in Chemistry journal review editor. He has won the Tianjin Outstanding Doctoral Dissertation Award, the Chinese Instrument and Meter Society Youth Science and Technology Talent Award, and the Tianjin Outstanding Master's Dissertation Instructor, etc.

Yuan Zhihao , male, doctoral, professor, senior engineer, doctoral supervisor. Dean of the "Green Nanotechnology Research Institute" of Tianjin University of Science and Technology, Director of the Key Laboratory of "Optoelectronic Display Materials and Devices" in Tianjin. Tianjin The city’s special professor and the first-level talent of Tianjin’s “131 Innovation Talent Training Project” enjoys special allowance . It is mainly engaged in research on green energy nanomaterials and technology, and has achieved many significant innovations and high application value in the design, preparation and application development of high-performance energy storage devices.

​ undertakes more than 20 projects including the National Natural Science Foundation of China and key projects, the National “973” project, and the Ministry of Science and Technology’s major transformative technology special projects; it has been in Adv Mater, Angew Chem Int Ed, Adv Funct Mater, Adv Energy Mater, Energy Storage Materials, J Mater Chem A, Nano Research, Science China Materials and other journals (including 6 highly cited papers in ESI and 4 journal cover papers); 21 invention patents were authorized, and 5 patent technology achievements were transferred. Related industrialization achievements won the gold medal of the "National First Postdoctoral Innovation and Entrepreneurship Competition Finals" and the National Innovation and Entrepreneurship Outstanding Postdoctoral Postdoctoral, and were also reported by Tianjin TV and Southern Daily and other media.