Power Sources For Electronics Research Articles

An all paper based triboelectric nanogenerators with high output performance in extreme environment manufactured by multi-layer papers forming technology

Triboelectric nanogenerators (TENGs) are regarded as a promising technology to drive the development of flexible/wearable electronics and self-powering sensor. Application of cellulose paper as the triboelectric positive materials makes TENGs more environmentally friendly. However, the limited output performance and stability in harsh environments and oxidation and corrosion of the metal electrodes have limited the practical application of cellulose paper based triboelectric nanogenerators (CPTENGs). Here, we have integrated cellulose paper-based triboelectric material and electrode in one sheet by using multi-layer forming technology in paper industry; the upper triboelectric layer shows excellent triboelectric positive performance, hydrophobicity and acid and alkali resistance, while the bottom electrode exhibits promise conductivity. The all CPTENGs can yield a maximum open-circuit voltage (VOC) of 227.1 V, a short-circuit current (ISC) of 6.9 μA. Furthermore, the VOC values of the all CPTENGs increase from 0.02 V to 225.1 V at the load resistance of 100 Ω∼10 GΩ; and a power density of 520 mW·m−2 is also obtained at a load resistance of 30 MΩ. Moreover, the VOC of CPTENGs not only retains up to 78 % of its initial value at a high relative humidity of 90 %, but also almost maintains unchanged in a wide range of the pH environment (pH = 1∼13). More importantly, the CPTENGs can be readily matched with paper-based zinc supercapacitor (P-ZISC) to act as an all paper based self-charging power system (PSCPS). The PSCPS is capable of driving various miniaturized electronics, such as electronic watch, temperature/humidity indicator, demonstrating its potential application in a sustainable power source for portable and green electronics.

Decoding Electrochemical Processes of Lithium‐Ion Batteries by Classical Molecular Dynamics Simulations

AbstractLithium‐ion batteries (LIBs) have played an essential role in the energy storage industry and dominated the power sources for consumer electronics and electric vehicles. Understanding the electrochemistry of LIBs at the molecular scale is significant for improving their performance, stability, lifetime, and safety. Classical molecular dynamics (MD) simulations could directly capture the atomic and molecular motions and thus provide dynamic insights into the electrochemical processes and ion transport in LIBs during charging and discharging that are usually challenging to observe experimentally, which is momentous in developing LIBs with superb performance. This review discusses developments in MD approaches using non‐reactive force fields, reactive force fields, and machine learning potential for modeling chemical reactions and transport of reactants in the electrodes, electrolytes, and electrode‐electrolyte interfaces. It also comprehensively discusses how molecular interactions, structures, transport, and reaction processes affect electrode stability, energy capacity, and interfacial properties. Finally, the remaining challenges and envisioned future routes are commented on for high‐fidelity, effective simulation methods to decode the invisible interactions and chemical reactions in LIBs.

Human Body Electrode Enabled Direct Current Triboelectric Nanogenerator for Self‐Powered Wireless Human Motion and Environment Monitoring

AbstractTriboelectric nanogenerator (TENG) is a promising technology, which can convert biokinetic energy into electricity and be utilized as self‐powered sensors and power sources for wearable electronics. The existing designs of conventional TENGs require complex fabrication processes and device structures, and they need to be attached on human body for wearable application, which is uncomfortable and may lead to malfunction under intense body moment. Here, a direct current TENG is proposed by utilizing natural human body, basketball, shoes, and ground floor. A unidirectional peak voltage and current output up to 700 V and 23 µA can be generated when a player plays a basketball, which can lighten up an array of 240 LEDs, and charge a 100 µF capacitor to 3.2 V in 1 min. The output of TENG is utilized to identify different movements of a basketball player using machine learning algorithm with an accuracy up to 96.7%. Moreover, the human body enabled direct current TENG (HBDC‐TENG) is used as a self‐powered sensor and an energy harvester for a wireless sensing system, which can collect human motion and environmental information, and transmit them wirelessly. The HBDC‐TENG has a great significance for self‐powered wearable electronics, providing a viable solution for human motion status and ambient environment monitoring.

Highly conductive and mechanically robust composite cathodes based on 3D interconnected elastomeric networks for deformable lithium‐ion batteries

AbstractDeformable lithium‐ion batteries (LIBs) can serve as the main power sources for flexible and wearable electronics owing to their high energy capacity, reliability, and durability. The pivotal role of cathodes in LIB performance necessitates the development of mechanically free‐standing and stretchable cathodes. This study demonstrates a promising strategy to generate deformable cathodes with electrical conductivity by forming 3D interconnected elastomeric networks. Beginning with a physically crosslinked polymer network using poly(vinylidene fluoride‐co‐hexafluoropropylene) and 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]), subsequent exchange with a 1 M LiPF6 electrolyte imparts elastic characteristics to the cathodes. The resulting LiFePO4 composite electrodes maintained their resistance under 500 consecutive bending cycles at an extremely small bending radius of 1.8 mm and showed high discharge capacity of 158 mAh g−1 with stable potential plateaus in charging and discharging curves. Moreover, flexible cells utilizing the composite electrodes exhibited superior operational stability under rolling, bending, and folding deformations.image

A Compact Multifunctional Power Electronic Interface for Plug-In Hybrid Electric Vehicles Using IoT

Abstract: The main objective of this endeavor is to construct a hybrid electric vehicle that recharges its battery using a range of electrical energy sources, such as solar, wind, and dynamo power using multifunctional power electronic sources. These are the forms of renewable energy that regenerate more quickly than they exhaust. Voltage sensors are attached to the PIC microcontroller, battery, solar panel, wind turbine, and dynamo in order to measure voltages. This measured voltage will be displayed on an LCD, and embedded C language will be used to upload the values, along with the date and time using ESP8266 WIFI-Module, to the THINGSPEAK cloud. This project's primary goals are to use rechargeable batteries to store source energy from solar, wind and dynamo power in an electric vehicle (EV) while using THINGSPEAK to monitor and record data, and update the LCD display with measured voltages

Using Natural Dye Additives to Enhance the Energy Conversion Performance of a Cellulose Paper-Based Triboelectric Nanogenerator.

Green and sustainable power sources for next-generation electronics are being developed. A cellulose paper-based triboelectric nanogenerator (TENG) was fabricated to harness mechanical energy and convert it into electricity. This work proposes a novel approach to modify cellulose paper with natural dyes, including chlorophyll from spinach, anthocyanin from red cabbage, and curcumin from turmeric, to enhance the power output of a TENG. All the natural dyes are found to effectively improve the energy conversion performance of a cellulose paper-based TENG due to their photogenerated charges. The highest power density of 3.3 W/m2 is achieved from the cellulose paper-based TENG modified with chlorophyll, which is higher than those modified with anthocyanin and curcumin, respectively. The superior performance is attributed not only to the photosensitizer properties but also the molecular structure of the dye that promotes the electron-donating properties of cellulose.

Sequentially Deposited Elastomer‐Based Ternary Active Layer for High‐Performance Stretchable Organic Solar Cells

AbstractStretchable organic solar cells (OSCs) with high power conversion efficiency and good mechanical deformation are promising as power sources for wearable electronics. However, synergistic improvement of both photovoltaic efficiency and mechanical ductility is challenging for state‐of‐the‐art polymer donor: non‐fullerene acceptor (NFA)‐based photovoltaic active layers. Here, a high‐performance stretchable OSC with a power conversion efficiency of 16.54% and a crack‐onset strain of 26.38% by synergetic optimization film microstructure of sequentially deposited ternary active layer consisting of a polymer donor poly[2,6‐(4,8‐bis(5‐(2‐ethylhexyl‐3‐fluoro)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b']dithiophene))‐alt‐5,5'‐(5,8‐bis(4‐(2‐butyloctyl)thiophen‐2‐yl)dithieno[3',2':3,4;2'',3'':5,6]benzo[1,2‐c][1,2,5]thiadiazole)] (D18), an NFA 2,2'‐((2Z,2'Z)‐((12,13‐bis(2‐ethylhexyl)‐3,9‐diundecyl‐12,13‐dihydro‐[1,2,5]thiadiazolo[3,4‐e]thieno[2'',3'':4',5']thieno[2',3':4,5]pyrrolo[3,2‐g]thieno[2',3':4,5]thieno[3,2‐b]indole‐2,10‐diyl)bis(methanylylidene)bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalonitrile) (Y6), and an elastomer polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene (SEBS) is reported. Adding a low‐content solvent additive para‐xylene into main solvent carbon disulfide induces high‐density fibers networks with low crystallinity in bottom D18 layer, and this further suppresses the large phase separation between Y6 and SEBS in top layer. Moreover, incorporating a solid additive 1,3‐dibromo‐5‐chlorobenzene with better compatibility with Y6 can promote Y6 dispersions to form smaller ordered domains in SEBS matrix. Finally, the optimal ternary active layer shows significantly higher efficiency and stretchability, resulting in a large efficiency‐stretchability factor of 4.36%, which is among the best values for stretchable OSCs.

In Situ Polymerization of Hydrogel Electrolyte on Electrodes Enabling the Flexible All-Hydrogel Supercapacitors with Low-Temperature Adaptability.

All-hydrogel supercapacitors are emerging as promising power sources for next-generation wearable electronics due to their intrinsic mechanical flexibility, eco-friendliness, and enhanced safety. However, the insufficient interfacial adhesion between the electrode and electrolyte and the frozen hydrogel matrices at subzero temperatures largely limit the practical applications of all-hydrogel supercapacitors. Here, an all-hydrogel supercapacitor is reported with robust interfacial contact and anti-freezing property, fabricated by in situ polymerizing hydrogel electrolyte onto hydrogel electrodes. The robust interfacial adhesion is developed by the synergistic effect of a tough hydrogel matrix and topological entanglements. Meanwhile, the incorporation of zinc chloride (ZnCl2) in the hydrogel electrolyte prevents the freezing of water solvents and endows the all-hydrogel supercapacitor with mechanical flexibility and fatigue resistance across a wide temperature range of 20°C to -60°C. Such all-hydrogel supercapacitor demonstrates satisfactory low-temperature electrochemical performance, delivering a high energy density of 11mWhcm-2 and excellent cycling stability with a capacitance retention of 90% over 10000 cycles at -40°C. Notably, the fabricated all-hydrogel supercapacitor can endure dynamic deformations and operate well under 2000 tension cycles even at -40°C, without experiencing delamination and electrochemical failure. This work offers a promising strategy for flexible energy storage devices with low-temperature adaptability.

Waterproof and ultraflexible organic photovoltaics with improved interface adhesion

Ultraflexible organic photovoltaics have emerged as a potential power source for wearable electronics owing to their stretchability and lightweight nature. However, waterproofing ultraflexible organic photovoltaics without compromising mechanical flexibility and conformability remains challenging. Here, we demonstrate waterproof and ultraflexible organic photovoltaics through the in-situ growth of a hole-transporting layer to strengthen interface adhesion between the active layer and anode. Specifically, a silver electrode is deposited directly on top of the active layers, followed by thermal annealing treatment. Compared with conventional sequentially-deposited hole-transporting layers, the in-situ grown hole-transporting layer exhibits higher thermodynamic adhesion between the active layers, resulting in better waterproofness. The fabricated 3 μm-thick organic photovoltaics retain 89% and 96% of their pristine performance after immersion in water for 4 h and 300 stretching/releasing cycles at 30% strain under water, respectively. Moreover, the ultraflexible devices withstand a machine-washing test with such a thin encapsulation layer, which has never been reported. Finally, we demonstrate the universality of the strategy for achieving waterproof solar cells.

(Invited) Performance Improvement and Potential Applications of Ultrathin Organic Solar Cells

Flexible and thin photovoltaics can supply a variety of applications such as power sources for wearable electronics and soft robots. We reduce the total thickness of such organic photovoltaics down to several μm, which enables extreme bendability and lightweight properties. The important parameters include high efficiency and stability in ambient air conditions. Here we show our recent progress with ultra-thin organic solar cells and potential applications for wearable electronics and soft robots.The current best power conversion efficiency (PCE) for ultrathin organic solar cells is 15.8% reported by ourselves1). We have solved the specific issues behind the usage of ultrathin substrate films to achieve almost comparable PCE with those using normal flexible organic solar cells. One specific technology is the usage of polymer films having good thermal stability and smooth surface roughness2). Another important technology is the development of stable charge carrier injection layers and interfaces at the active layer. The state-of-the-art active layer materials such as PM6:Y6 is known not to be stable in ambient air and other environmental stresses. We verified the degradation occurred by the diffusion of Zn atoms from the conventional electron-transport layer (ETL) of ZnO obtained from the sol-gel process to the active layer, and solved it by replacing the ETL with more stable organic/inorganic hybrid material1,3). Such improved ETL and interface achieved highly balanced performance and stability, enabling good PCE on ultrathin substrates.We improved both PCE and environmental stabilities simultaneously. The stabilities include mechanical robustness3), water-proof property4), thermal stability2), and storage stability in ambient air5). Material development and process engineering enable such improved stabilities. In addition, such environmental stability can offer another practical usage. Our ultrathin solar cells have excellent thermal stability up to 120 ℃. This is capable of the hot-melt process which is a mature technology for the apparel industry. We can adhere our ultrathin organic solar cells directly onto textiles with such hot-melt films without any degraded performances. Apart from the improvement of the performance of ultrathin organic solar cells, we are focusing on how to implement such flexible devices onto three-dimensional surfaces5).We demonstrated some potential applications using our ultrathin organic solar cells used as a power source for wearable sensor applications7,8). We fabricated ultrathin organic solar cell modules and sensors. The sensor was powered by the solar cells under light illumination and monitored electrocardiogram signals with a high signal-to-noise ratio. In addition to this, we also demonstrated rechargeable cyborg insects9). In this research, we adhered our ultrathin organic solar cells onto a living insect abdomen and demonstrated a recharging wireless locomotion control system.We are focusing on both performance improvements of ultrathin organic solar cells and the integration of these cells to supply power to wearable electronics. By accelerating system-level integration research in the next decade to meet the required specifications of appropriate target applications, ultrathin organic solar cells will solve the problems associated with the supply of power for various electronics and will contribute to the overall development of society.1) S. Xiong et al., Adv. Sci. 2022, 9, 2105288.2) X. Xu et al., Proc. Natl. Acad. Sci. 2018, 115, 4589.3) F. Qin et al., Nat. Commun. 2020, 11, 4508 .4) H. Jinno et al., Nat. Energy 2017, 2, 780.5) Z. Jiang et al., Proc. Natl. Acad. Sci. 2020, 117, 6391.6) S. I. Rich, S. Lee, K. Fukuda, and T. Someya, 2022, 34, 2106683.7) S. Park et al., Nature 2018, 561, 516.8) H. Jinno et al., Nat. Commun. 2021, 12, 2234.9) Y. Kakei et al., npj Flex. Electron. 2022, 6, 78. Figure 1

Noise-less hybrid nanogenerator based on flexible WPU and siloxene composite for self-powered portable and wearable electronics

The rapid growth of portable and wearable electronics demands innovative battery solutions that are both sustainable and eco-friendly. Biomechanical energy-harvesting technology is a promising approach for operating wearable electronic devices without battery dependence. In this study, a novel noise-less hybrid nanogenerator (NLHN) was developed using 3D-printed elastic resin springs and burr-shaped water-based polyurethane (water-based PU: WPU)@Siloxene nanocomposite to effectively harvest low-frequency biomechanical energy from various human movements without generating any physical noise. By rationally integrating electromagnetic generators with triboelectric nanogenerators in a sliding mode and two contact modes, the proposed NLHN exhibited excellent output performance under random low-frequency and wide-range vibrational excitations. The WPU@Siloxene was first introduced as a highly flexible positive triboelectric layer and a noise suppressor during the sliding mode operation, while elastic resin springs significantly improved the energy harvesting performance thereby suppressing the physical noise during contact-separation. The NLHN exhibited an optimal output power of 101 mW at 6 Hz and 1.5 g acceleration. Moreover, the NLHN suppressed operating noise to only 41 dB during operation and maintained a stable output performance after 50,000 cycles. The NLHN was demonstrated to function as a continuous power source for powering portable and wearable electronics, such as smart bracelets and smartphones as well as battery-free wearable ECG monitoring systems. Conclusively, the proposed NLHN has substantial potential for silent biomechanical energy harvesting as a sustainable and eco-friendly power source for portable electronics and wearable healthcare sensing devices.

Challenges and Advances in Rechargeable Batteries for Extreme-Condition Applications.

Rechargeable batteries are widely used as power sources for portable electronics, electric vehicles and smart grids. Their practical performances are, however, largely undermined under extreme conditions, such as in high-altitude drones, ocean exploration and polar expedition. These extreme environmental conditions not only bring new challenges for batteries but also incur unique battery failure mechanisms. To fill in the gap, it is of great importance to understand the battery failure mechanisms under different extreme conditions and figure out the key parameters that limit battery performances. In this review, the authors start by investigating the key challenges from the viewpoints of ionic/charge transfer, material/interface evolution and electrolyte degradation under different extreme conditions. This is followed by different engineering approaches through electrode materials design, electrolyte modification and battery component optimization to enhance practical battery performances. Finally, a short perspective is provided about the future development of rechargeable batteries under extreme conditions.

A stable and efficient quasi-solid-state photo/betavoltaic-powered electrochemical cell based on 3-dimensional CdS/ZnO heterostructure

Electrochemical betavoltaic (EBV) cells are promising power sources for low-power electronics in remote and harsh environments. However, their practical applications are limited by the organic liquid electrolytes with the inferior temperature stability and narrow electrochemical window. In this work, a quasi-solid-state EBV cell was fabricated using a high-conductive gel-based quasi-solid-electrolyte (QSE), a CdS-modificated ZnO nanorod arrays (ZNRAs) structure as the anode material, a radioactive 63Ni sheet as the cathode as well as the irradiation source. Monte Carlo (MC) simulations are utilized to determine the optimized length (2.97 μm) of the ZNRAs filled by electrolyte, Electrochemical photovoltaic (EPV) cells were used to assess and optimize the content of CdS loaded on the ZNRAs. The optimum EBV cell demonstrated an excellent long-term stability and a high energy-conversion efficiency of 10.09 % with a short-circuit current density of 0.755 μA cm−2 and an open-circuit voltage of 0.288 V. The porous CdS@ZNRAs core–shell structure filled by soft ionic liquids (IL)/gel-based QSE enables a large specific area of electrochemical interface network. The synergistic effects of 3-D CdS/ZnO heterostructure with type-II band alignment and IL/gel-based QSE are responsible for the enhanced ECE and improved long-term stability of EBV/EPV cells.

Protection for AC transmission line between DFIG wind farm and MMC station

The characteristics of power electronic controlled sources are reflected at both ends of the AC line applied to the integration of long-distance wind farms into the MMC-HVDC converter station, and the fault characteristics of the system have undergone fundamental changes. For the doubly-fed wind power AC transmission line with a modular multilevel converter, the short-circuit current characteristics provided by the power supply at both ends of the line lead to the inadaptability of longitudinal differential protection. In view of the significant difference in the complexity of the short-circuit current component provided by the doubly-fed wind power and the converter at both ends of the AC transmission line, a line pilot protection idea based on the complexity of the current component is proposed. The complexity of the current component is characterized by singular entropy theory, and then the singular entropy algorithm and its scheme for pilot protection are constructed. A refined electromagnetic transient model of MMC-HVDC for doubly-fed wind farms is built in PSCAD for simulation verification. The simulation results show that the proposed method can quickly and reliably identify various types of internal and external faults, and solve the problem of incorrect action of traditional protection in this scenario. In addition, the scheme is not affected by fault type, location, or transition resistance.

Integratable Paper‐Based Iontronic Power Source for All‐In‐One Disposable Electronics

AbstractWith the emergence of disposable electronics, compatible safe, flexible, and recyclable power sources have become a critical challenge. Here, an ultra‐thin paper‐based iontronic power source is enabled by highly efficient translational Li+ transport within 2D nanofluidic channels of graphene oxide under a salinity gradient and the fine‐tuned interfacial redox reactions. The paper‐based source can generate volumetric power and energy densities of 438.02 mW cm−3 and 30.02 mWh cm−3, respectively. Its areal power density is 1095.05 mW cm−2, surpassing most flexible batteries. It maintains a working state when bent or even cut and can be simply recycled by incineration. By filling 2D nanofluidic inks in different pens, the power source can be drawn on paper when needed, which not only overcomes the inherent defect of self‐discharge for most batteries but also enables writing directly on any insulating substrates. Furthermore, all‐in‐one disposable electronics comprised of an energy management system (paper‐based triboelectric nanogenerator and iontronic power source) and wireless sensing system (temperature sensor with NFC circuits) are integrated onto one piece of paper by duplex printing, demonstrating the huge potential of such integratable iontronic power sources for soft, wireless, and conformable disposable electronics.

Realization of a highly-performing triboelectric nanogenerator utilizing molecular self-assembly

Triboelectric nanogenerator (TENG) is promising as a sustainable power source for energy-autonomous electronics. This work demonstrates for the first time that a highly-performing TENG can be realized by utilizing molecular self-assembly of small molecules. It is found that molecular self-assembly modifies the orbital energy levels of the corresponding tribo-layer that causes reduced energy gap between the tribo-layers for charge transfer. It is also found that an expansion of the electron-rich regions occurs due to molecular self-assembly that in turn increases the probability of the electron cloud/potential well overlap. Both the phenomena result in significantly-enhanced charge transfer between the tribo-positive and tribo-negative layers of a TENG during contact electrification. A low-cost, simple, and straightforward technique that does not require sophisticated equipment is adopted for the molecular self-assembly of a naturally abundant small molecule. Spectroscopic analysis, atomic force microscopy, and electron microscopy reveal that the modified molecules are capable of building high order self-assembled structure. A TENG with a self-assembled layer (SAL-TENG) generated voltage and power density of ∼1340 V and ∼11.75 W m−2, respectively, as compared with, ∼200 V and ∼3.5 W m−2 respectively, for another TENG comprising the same molecules but are not self-assembled (NSA-TENG).

Wire-shaped, all-solid-state, high-performance flexible asymmetric supercapacitors based on (Mn,Fe) oxides/reduced graphene oxide/oxidized carbon nanotube fiber hybrid electrodes

Wire-shaped flexible supercapacitors (FSCs) have attracted tremendous attention due to their tiny volume, lightweight, high flexibility, and wearability. In the present study, we report the MnO2- or Fe2O3-loaded three-dimensional (3D) nanostructure networks of reduced graphene oxide (rGO) composite on oxidized CNT (denoted as the OCNTF/3D-rGO/MnO2 and OCNTF/3D-rGO/Fe2O3) fibers as the cathode and anode, respectively, for the fabrication of a high-performance, wire-shaped, all-solid-state, flexible asymmetric supercapacitor (FASC). To this end, the 3D-rGO/OCNTF hierarchical structure was electrochemically fabricated, followed by further pulse electrodeposition of MnO2 and Fe2O3, respectively, into the 3D porous graphene networks and the insides of the OCNTF. As such, they were restricted to nano-sized particles and linked by the graphene and the OCNTF. The OCNTF/3D-rGO/MnO2 as the cathode was assembled with the OCNTF/3D-rGO/Fe2O3 as the anode with the carboxymethyl cellulose sodium (CMC)-Na2SO4 gel electrolyte, producing a wire-shaped, all-solid-state FASC that achieved a high specific capacitance of 59.2 F·cm−3 (171 mF·cm−2) and an exceptional energy density of 26.7 mWh·cm−3. The FASC device also showed good flexibility and cyclability, promising to advance power sources for wearable electronics.

Stability enhancement of silver nanowire-based flexible transparent electrodes for organic solar cells

Flexible organic solar cells (OSCs) are one of the most promising power sources for wearable electronics. A high-quality transparent electrode is one of the indispensable components for OSCs because it guarantees sufficient light transparency and electrical conductivity. Silver nanowires (AgNWs) are considered to be an ideal candidate over commercial rigid indium tin oxide as flexible transparent electrodes (FTEs) because of their superior optoelectronic properties, excellent mechanical flexibility, solution treatability, and high compatibility with semiconductors. However, the stability of AgNWs-based FTEs (AgNWs-FTEs) hinders their further application. In this perspective, we provide state-of-the-art solution-processed AgNWs with enhanced stability and their applications in flexible OSCs. We start with a systematic analysis of the failure mechanisms and evaluation methods of AgNWs-FTEs. Then the key reinforced materials are summarized. Next, the main stability enhancement strategies are briefly discussed. Applications of AgNWs-FTEs in flexible and stretchable OSCs are further surveyed. Finally, an outlook on the current status, future challenges, and emerging strategies in this field is presented.

Piezoelectric driven self-powered supercapacitor for wearable device applications

The universal energy demand and pollution have prompted research scientists to explore other energy harvesting technologies that can generate energy from the natural resource environment, mainly due to the use of conventional energy sources. Energy harvester can be extracted and to convert into useful electric energy. The piezoelectric energy harvester is an excellent method of extracting mechanical energy due to its high electric and mechanical combination and piezoelectric harvester coefficient to compare electro-static, electro-magnetic, and triboelectric transitions. Therefore, the harvesting of piezoelectric energy is highly appreciated by the scientific community. Energy harvesters can be used to convert electrical energy into strong vibrations, which can be to store and used on a variety of ultra-low power electronic devices. With the advent of a various variety of wearable digital devices and fitness tracking devices, the piezoelectric generator suitable for portable and wearable electronic power source is one of the most interesting.

Minimally invasive power sources for implantable electronics

AbstractAs implantable medical electronics (IMEs) developed for healthcare monitoring and biomedical therapy are extensively explored and deployed clinically, the demand for non‐invasive implantable biomedical electronics is rapidly surging. Current rigid and bulky implantable microelectronic power sources are prone to immune rejection and incision, or cannot provide enough energy for long‐term use, which greatly limits the development of miniaturized implantable medical devices. Herein, a comprehensive review of the historical development of IMEs and the applicable miniaturized power sources along with their advantages and limitations is given. Despite recent advances in microfabrication techniques, biocompatible materials have facilitated the development of IMEs system toward non‐invasive, ultra‐flexible, bioresorbable, wireless and multifunctional, progress in the development of minimally invasive power sources in implantable systems has remained limited. Here three promising minimally invasive power sources summarized, including energy storage devices (biodegradable primary batteries, rechargeable batteries and supercapacitors), human body energy harvesters (nanogenerators and biofuel cells) and wireless power transfer (far‐field radiofrequency radiation, near‐field wireless power transfer, ultrasonic and photovoltaic power transfer). The energy storage and energy harvesting mechanism, configurational design, material selection, output power and in vivo applications are also discussed. It is expected to give a comprehensive understanding of the minimally invasive power sources driven IMEs system for painless health monitoring and biomedical therapy with long‐term stable functions.