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The upcoming ubiquitous electronics era, which will find widespread popularity of flexible/wearable electronics, self-powered devices, and the Internet of Things (IoT), stimulates us to develop a new concept of advanced power sources beyond currently available battery technologies. Among several approaches to reach this goal, printed power sources with various form factors and flexibility have recently garnered considerable attention as a promising system. The form factor-free, printed power sources, driven by their design diversity, shape/performance compatibility with electronics, and scalable/low-cost processability, enable monolithic/seamless integration with complex/unconventional-shaped electronic devices, in comparison to conventional rigid/bulky counterparts. Here, we review the current status and challenges of the form factor-free, printed power sources, with a focus on their materials development. Various printing techniques and their process parameters exploited for the printed power sources are briefly described. Subsequently, ink materials and chemistry of major cell components are discussed. Based on the understanding of the printing techniques and materials, applications of the printed power sources are overviewed to highlight their exceptional shape aesthetics and electrochemical characteristics in the integrated electronics. Finally, we propose development directions and outlook of the form factor-free, printed power sources as a device-customized energy storage system, along with prospects of their future applications.

Summary The forthcoming smart and ubiquitous electronics era presents significant interest in wireless interconnectivity and shape aesthetics. To fulfill this demand, a new class of advanced power sources with various form factors that are different from existing commercial ones is needed. Printed power sources have recently garnered substantial attention because of their design diversity, shape and performance compatibility with electronics, and scalable and low-cost processability. They are fabricated directly on complex-structured objects via application-customized printing techniques, enabling monolithic integration and electrochemical coupling with target devices. In this Perspective, we describe the current status and challenges of printed power sources, focusing on their role as built-in power sources. Various printing techniques and ink materials and chemistry of electrodes and electrolytes are discussed as key enabling factors. Noteworthy progress in printed built-in power sources is reviewed to highlight their design diversity and electrochemical superiority. Finally, development direction and outlook of printed built-in power sources are discussed in conjunction with their application fields.

With the ever-growing interests in ubiquitous smart electronics and the Internet of Things, the demand for high-energy-density power sources with aesthetic versatility has increased tremendously. High-energy-density Li-metal batteries have attracted considerable attention for fulfilling the high-energy-density requirement of smart electronics. To obtain form factor-free Li-metal batteries with both design diversity and electrochemical reliability, printed solid-state electrolytes are required as a key component because of their viability for the printing/solidification-based fabrication process and electrode-customized chemical/physical properties. This review present an overview of printed solid-state electrolytes for form factor-free Li-metal batteries with a focus on the materials chemistry and fabrication requirements. In addition, their structural/physical/electrochemical properties were discussed in terms of compatibility with Li-metal batteries.

With the advent of the ubiquitous electronics era, high-performance power sources with aesthetic diversity are indispensably needed as a key-enabling technology. Printed batteries have recently emerged as a crispy energy storage system to address this issue. Printed batteries are fabricated through simple, low-cost, and scalable printing processes. Their salient features include various form factors, shape conformability, and monolithic integration with devices of interest. Research directions on printed batteries are currently focused on (i) the design of battery shapes and configurations, (ii) synthesis of battery component inks with tunable rheological properties and electrochemical performances, and (iii) adoption of suitable printing techniques. We describe the current status and challenges of printed batteries, with a particular focus on the form factors, battery component inks, printing techniques, cell performances, and integration with other systems. The development directions and outlook of prin...

Solid-state microsupercapacitors with ultrahigh areal-number-density are integrated on a chip via high-fidelity printing., Microsupercapacitors (MSCs) have garnered considerable attention as a promising power source for microelectronics and miniaturized portable/wearable devices. However, their practical application has been hindered by the manufacturing complexity and dimensional limits. Here, we develop a new class of ultrahigh areal number density solid-state MSCs (UHD SS–MSCs) on a chip via electrohydrodynamic (EHD) jet printing. This is, to the best of our knowledge, the first study to exploit EHD jet printing in the MSCs. The activated carbon-based electrode inks are EHD jet-printed, creating interdigitated electrodes with fine feature sizes. Subsequently, a drying-free, ultraviolet-cured solid-state gel electrolyte is introduced to ensure electrochemical isolation between the SS–MSCs, enabling dense SS–MSC integration with on-demand (in-series/in-parallel) cell connection on a chip. The resulting on-chip UHD SS–MSCs exhibit exceptional areal number density [36 unit cells integrated on a chip (area = 8.0 mm × 8.2 mm), 54.9 cells cm−2] and areal operating voltage (65.9 V cm−2).

Wirelessly rechargeable solid-state supercapacitors are studied for soft, smart contact lenses with continuous operations., Recent advances in smart contact lenses are essential to the realization of medical applications and vision imaging for augmented reality through wireless communication systems. However, previous research on smart contact lenses has been driven by a wired system or wireless power transfer with temporal and spatial restrictions, which can limit their continuous use and require energy storage devices. Also, the rigidity, heat, and large sizes of conventional batteries are not suitable for the soft, smart contact lens. Here, we describe a human pilot trial of a soft, smart contact lens with a wirelessly rechargeable, solid-state supercapacitor for continuous operation. After printing the supercapacitor, all device components (antenna, rectifier, and light-emitting diode) are fully integrated with stretchable structures for this soft lens without obstructing vision. The good reliability against thermal and electromagnetic radiations and the results of the in vivo tests provide the substantial promise of future smart contact lenses.

Recent advances in smart contact lenses are essential to the realization of medical applications and vision imaging for augmented reality through wireless communication systems. However, previous research on smart contact lens has been driven by external electrical wired systems or wireless power transfer with temporal and spatial restrictions, which can limit their continuous use. Therefore, an essential prerequisite for electronic smart contact lenses is their monolithic integration with energy storage devices. However, conventional rigid, large sized, and fixed-shaped energy storage devices are not suitable for the soft, smart contact lens. Here, we demonstrate a new class of wirelessly-rechargeable solid-state supercapacitors directly printed on smart contact lenses. Supercapacitors are known to exhibit long cycle lives and high-power density, which are suitable for consistent fast wireless charging and discharging for operating the electronic devices in the smart contact lens. The arc-shaped form factor and limited area of the printed supercapacitor require a high-precision microscale direct ink writing (DIW) process and tailored component inks. The printed solid-state supercapacitor integrated smart contact lens show great potential as an effective/scalable platform for wearable electronics with continuous operation.

The ongoing surge in demand for flexible/wearable electronics, self-powered systems, soft robotics, and Internet of Things (IoT) has inspired the relentless pursuit of form factor-free, high-performance power sources that can be monolithically and seamlessly integrated with various electronics. To reach this challenging goal, a new class of advanced power sources with various form factors that are different from existing commercial ones are needed. From the viewpoint of power source design and architecture, traditional cell materials and fabrication have resulted in power sources that feature a lack of variety in form factors and flexibility. In specific, most of the current power sources are manufactured by winding or stacking of slurry-casted electrode sheets and separator membranes, followed by the injection of liquid electrolytes inside a fixed form of canisters or pouch packaging substances; these methods impose stringent restrictions on the unitization of power sources with electronic devices. Printed power sources have recently garnered considerable attention as a fresh and game-changing approach due to their design diversity, shape/performance compatibility with electronic devices, and scalable/low-cost processability. Printed power sources based on high-fidelity printing techniques and rationally designed material chemistry are fabricated directly on complex-shaped objects, thereby enabling monolithic integration and electrochemical coupling with target devices that lie far beyond those achievable with conventional power source technologies. Here, this talk introduces form factor-free, printed built-in power sources, with particular attention to their dimensional conformability and performance compatibility with newly emerging complex-structured electronic devices. A key-enabling technology for the printed power sources is the design of battery inks (specifically, electrode and electrolyte inks), with a focus on their rheology and electrochemistry. Our research interests are directed to discussing effects of the battery inks on printing processability, microstructure (focusing on bicontinuous ion/electron transport channels) and electrochemical performance of the resultant printed power sources. We envision that the printed power sources open a new avenue towards form factor-free/monolithic integrated power sources with object-tailored design versatility and dimensional conformability. References [1] Kwon-Hyoung Lee, David B. Ahn, Jung-Hui Kim, Ju-Won Lee, Sang-Young Lee*, Matter , 2020, 345. [2] Kwon-Hyoung Lee, Seong-Sun Lee, David B. Ahn, Jaehyun Lee, Doyouong Byun, Sang-Young Lee*, Sci. Adv. , 2020, eaaz1692. [3] Jihun Park, David B. Ahn, Joohee Kim, Eunkyung Cha, Byeong-Soo Bae, Sang-Young Lee*, Jang-Ung Park*, Sci. Adv. , 2019, eaay0764. [4] Keun-Ho Choi, David B. Ahn and Sang-Young Lee*, ACS Energy Lett. 2018, 3, 220. [5] Keun-Ho Choi, JongTae Yoo, Chang Kee Lee and Sang-Young Lee*, Energy & Environ. Sci. 2016, 9, 2812. Figure 1