REVIEW ● OPEN ACCESSRead More
Huaizhi Liu, Guanhua Zhang, Xin Zheng, Fengjun Chen, Huigao Duan
The ever-growing demands for micro/nanosystems such as microelectromechanical system (MEMS), micro/nanorobots, intelligent portable/wearable microsystems, and implantable miniaturized medical devices, have pushed forward the development of specific miniaturized energy storage devices (MESDs) and their extreme manufacturing processes, as displayed in figure 1. MESDs are a type of miniaturized power supply with the electrode size in the range of micrometer, which cannot only serve as a compatible energy source for micro/nanosystems but also integrate with micro/nanodevices directly to satisfy the need for integration, intelligence, ultracompactness, and extremely lightweight. Researchers have published various reviews on the material preparation, structure design, electrode fabrication strategy, functionalization, and the future challenges associated with the miniaturized batteries and supercapacitors, while a wide-ranging survey from the early design to latter target-oriented electrode manufacturing and the integrated application of MESDs is still highly desirable.
Dr. Huaizhi Liu, Prof. Guanhua Zhang, Xin Zheng, Prof. Fengjun Chen and Prof. Huigao Duan from Hunan University, China, wrote a review " Emerging Miniaturized Energy Storage Devices for Microsystem Applications: From Design to Integration" on IJEM. In this article, the authors provide a comprehensive summary that includes configuration design, microelectrode manufacturing, and material processing, as well as typical applications of MESDs, shown in figure 2. Moreover, on-chip integrated microsystems consisting of MESDs and a collection of practical microelectronic devices is further discussed. In the end, the authors discuss the future research to better promote the development and practical application of MESDs.
Figure 1. Integration and application of MESDs in various micro/nanosystems. Micro/Nanorobots, MEMS, Implantable Medical Devices, Smart Electronics.
Figure 2. Illustration of the review of MESDs: configuration design, microelectrode manufacturing, typical applications, and on-chip integrated microsystems.
MESDs mainly include classic microbatteries (MBs), microsupercapacitors (MSCs), and newly developed microhybrid metal ion capacitors (MHMICs) based on the different ways of storing energy. Being easy integration with targeted microelectronic devices and achieving specific electrochemical properties makes MESDs the most suitable candidate of energy storage components for miniaturized electronic devices and integrated microsystem applications. Figure 3 shows the sharp growth in the number of publications concerning MESDs (MBs, MSCs, and MHMICs) over the last decade (2010-2019), which is indicative of their ever-increasing importance to miniaturized energy storage systems and the necessity for further in-depth research. Figure 4 shows the general configuration designs and figure 5 demonstrates the advanced manufacturing technologies for the microelectrode of MESDs.
Figure 3. Statistical analysis of the number of research publications related to MESDs over the last decade.
Figure 4. Schematic of the typical types of MESDs.
Figure 5. Advanced manufacturing technologies for the microelectrode of MESDs
3. Recent Advances
Recent advances in miniaturized energy storage devices have been divided into three sections: microbatteries, microsupercapacitors, and microhybrid metal ion capacitors. In each section, the principle, background, classification and recent research is discussed in turn. In particular, the on-chip integrated microsystems consisting of MESDs and other microelectronic devices is discussed.
To meet the urgent need for miniaturized electronic devices, it is highly important to construct high-powered, miniaturized batteries with excellent mechanical stability and satisfactory energy for direct integration with various electronic systems. Figure 6 shows the different applications of lithium ion microbatteries.
Figure 6. Microbatteries-LIMBs. (a) Schematic illustration of flexible LIMB. Reproduced with permission. Copyright 2012, American Chemical Society. (b, c) 3D interdigitated microbattery. Reproduced with permission. Copyright 2013, WILEY. (d, e, f) Fully 3D-printed LIMBs. Reproduced with permission. Copyright 2018, WILEY.
Interest in microsupercapacitors has increased as alternative miniaturized power sources with high power density, outstanding rate performance, high-frequency response, and long cycling capability in recent years. Figure 7 shows the typical pseudocapacitive MSCs and their potential in numerous microsystem applications.
Figure 7. Pseudocapacitive Microsupercapacitors. (a, b, c) Stamping of the MXene inks and GCD profiles. Reproduced with permission. Copyright 2018, WILEY. (d, e, f) SEM image of the NiFe2O4, CV and GCD profiles. Reproduced with permission. Copyright 2016. (g, h) Schematic of (VN)//MnO2 MSCs. Reproduced with permission. Copyright 2018, Elsevier.
Microhybrid Metal Ion Capacitors
A typical hybrid metal ion capacitor consists of one capacitive electrode as a power source and the other battery-type faradaic electrode as an energy source. From the perspective of an energy storage mechanism, the capacitive cathode functions through an ion adsorption/desorption on the surface and the anode works via a cation insertion/extraction process. These two asymmetric charging/discharging processes for electrodes tend to work in different potentials, thereby contributing to an enlarged operating potential window in an effective way and improving the energy density of electronic devices as well. Figure 8 demonstrates two typical applications of microhybrid capacitors, which hold significant promise in the development of miniaturized device applications and highly integrated microsystems.
Figure 8. Microhybrid metal ion capacitors. (a, b, c) Schematic diagram of LTO//AG-MHLICs and electrochemical performance. Reproduced with permission. Copyright 2018, The Royal Society of Chemistry. (d, e, f) Schematic illustration of VS2@EG//AC MHSICs and electrochemical performance. Reproduced with permission. Copyright 2019, WILEY
On-Chip Integrated Microsystems
An ideal on-chip integrated system based on MESDs should not only possess high electrochemical performance with good durability but also be well endowed with the desired properties for specific purposes. In this field, MESDs integrated with harvesters, screen displays, fuel cells, transmitters, and electrochromic and miscellaneous sensors have been extensively studied so far. Figure 9 shows the integration of MESDs with different microelectronics.
Figure 9. On-chip integrated microsystems. (a, b) Flexible all-in-one system composed of photocatalytic fuel cells (PFCs) and asymmetric MSCs. Reproduced with permission. Copyright 2019, American Chemical Society. (c, d) Schematic illustration of the light permeability and hazing effect of the microbattery. Reproduced with permission. Copyright 2018, The Royal Society of Chemistry. (e) A photograph and a schematic of the transmitter. Reproduced with permission. Copyright 2017, Elsevier. (f) Schematic of the tandem MSCs bridging solar cells and a gas sensor to store solar energy and supply energy. Reproduced with permission. Copyright 2017, WILEY.
From the recent advances and achievements of MESDs, it is worth noting that the challenges are not only to enhance the electrochemical property, such as high energy and high power density, in a limited footprint with a durable lifetime but also to integrate with multifunctional properties, matching up with multiple demands of microelectronic devices and microsystems. In order to better promote the development of MESDs, future research on miniaturized energy storage devices should pay more attention to the following aspects. 1) Advanced configuration design and micro/nanostructures design. 2) Practical microelectrode fabrication technologies. 3) High-performance and multifunctional active materials and characterization methods. 4) Appropriate and effective electrolytes. 5) On-chip integrated microsystems with microelectronics.
5. About the Authors
Guanhua Zhang received her PhD degree from Hunan University, P. R. China in 2016. From 2014 to 2016, she joined Arizona State University, as a visiting PhD student. Currently, she is an Associate Professor at the College of Mechanical and Vehicle Engineering, and a member of the State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, P. R. China. Her current research is focused on nanofabrication for energy conversion and storage (including lithium/sodium secondary batteries, supercapacitors, and their miniaturization), and electrocatalysis.