Search

With the explosive development of wearable electronics and the Internet of Things (IoT), it is highly desirable to develop miniaturized power sources with high performance, low-cost, environmental friendliness and integratable characteristics. Rechargeable microbatteries (MBs) can be used as the main power sources of future miniaturized wearable electronics, which have drawn broad attention recently. However, ever-reported MBs, such as micro-lithium batteries, have intrinsic safety hazards and environmental threats, and are not fully compatible with the green initiative of the IoT. Here, we report aqueous Zn//MnO2 MBs, with the merits of green, low cost and sustainability. By using a simple and scalable fabrication strategy, Zn//MnO2 MBs constructed with a three-dimensional (3D) MnO2@nickel nanocone array (NCA) cathode, a Zn@NCA anode, and a mild aqueous electrolyte containing ZnSO4 and MnSO4 can be prepared on a large scale. The as-prepared Zn//MnO2 MB reveals a superior capacity of 53.5 μA h cm−2 μm−1 at 1 C rate and a working voltage of 1.4 V. Moreover, it achieves a superior volumetric energy density of 71.3 μW h cm−2 μm−1, together with a peak power density of 1621.4 μW cm−2 μm−1, substantially higher than those of the reported lithium-ion MBs. Such an ultrathin (74 μm in thickness), lightweight (30 mg per unit) and flexible Zn//MnO2 MB component can power three pieces of LEDs. Last but not least, the fabrication strategy of our Zn//MnO2 MBs is fully compatible with flexible electronic fabrication processes. For instance, we have demonstrated that these Zn//MnO2 MBs could share the same fabrication process platform with radio frequency identification (RFID) tags. We envisage that our current technology would accelerate the use of miniaturized power sources for IoT applications, and inspire the development of intelligent manufacturing technology.

Flexible supercapacitors have advanced rapidly in recent years and contributed to the development of wearable electronics. However, the operating temperature of the flexible supercapacitors usually falls within a narrow range, because of the constraints of the electrode materials and the electrolytes. Here, we report a flexible supercapacitor that can operate at extreme temperatures (down to −40 °C and up to 200 °C) with excellent electrochemical property and high durability. This device allows a maximum area specific capacitance of 330 mF/cm2. It has 2 F/cm3 volume specific capacitance and 1.7 mWh/cm3 energy density. The high stability of this supercapacitor enables 90% capacitance retention after 105 cycles. Moreover, deformation at extreme temperature does not reduce its energy storage ability.

Supercapacitors have drawn numerous attentions in recent years since they can deliver relatively high power and energy densities. This article introduces an all-printed paper based surface mountable supercapacitor (SMS), which could withstand the reflow soldering process when integrated into microelectronic systems. The device was fabricated by screen printing and stencil printing processes, contributing to low cost and large-scale fabrication. Furthermore, building electronic devices on ubiquitous paper substrates had advantages of light weight, low cost, and eco-friendliness, etc. Based on activated carbon electrode material and ionic liquid electrolyte, the capacity of the supercapacitor could reach 14 mF at the device volume of 3.2 mm × 2.5 mm × 0.175 mm, besides, the specific volumetric capacity was superior than most of the commercial SMS devices.

Developing supercapacitor electrodes with an ultra-long cycle life and a high specific capacitance is critical to the future energy storage devices. Herein, we report a scalable synthesis technology of mixed-valence manganese oxide nanoparticles anchored to reduced graphene oxide (rGO/MnOx) as the high-performance supercapacitor electrodes. First, 2-dimensional (2D) δ-MnO2 nanosheets are formed on a graphene oxide (GO) template, which is then in situ reduced by hydrazine vapour to mixed-valence manganese oxide nanoparticles evenly distributed on a rGO conductive network. The obtained rGO/MnOx electrode material exhibits a high specific capacitance of 202 F g−1 (mass loading of 2 mg cm−2), a large areal specific capacitance of 2.5 F cm−2 (mass loading of up to 19 mg cm−2), and a super-long-life stability of 106% capacitance retention after 115 000 charge/discharge cycles. By using an ionic liquid electrolyte and an activated carbon anode, asymmetric supercapacitors (AScs) are also constructed and can be packaged into a high performance miniaturized energy storage component in either a tailorable or surface mountable configuration. Our ASc shows superior performance characteristics, with typical figures of merit including maximum energy densities of 47.9 W h kg−1 at 270 W kg−1 and 19.1 W h kg−1 at the maximum power density of 20.8 kW kg−1. The capacitance retention of the ASc is 96% after 80 000 charge/discharge cycles, which is the most excellent stability performance in an ionic liquid electrolyte as compared with the recently reported pseudo-supercapacitors. This technology may find vast applications in future miniaturized portable and wearable electronics.

With the development of wearable/flexible electronics, a formidable challenge is to integrate electronic components which were large in their original size into a flexible, thin, and arbitrary layout. As an indispensible component in electronics, commercial micro-supercapacitors are disadvantageous in their clumsy cuboid geometry and limited capacity, and are not promising for future applications. In comparison, film-like micro-supercapacitors are superior in miniaturized system integration since they can be folded to fit in restricted spaces while maintaining a high level of volumetric energy density. Here, we carried out a benchmark study of a state-of-the-art well-packaged thin film micro-supercapacitor toward commercial micro-supercapacitor and aluminum electrolyte capacitor. The micro-planar supercapacitor not only exhibits 3.75 times of a commercial micro-supercapacitor and 8785 times of an aluminum electrolytic capacitor in volumetric energy density under 1000 mV s −1 scan rate, but can also be tailored into diversified shapes, rolled up, and plugged into tiny interstitial spaces inside a device. Such ultrathin (18 µm) micro-supercapacitor component with high volumetric energy density (0.98 mWh cm −3 in LiCl-PVA gel, 5.7 mWh cm −3 in ionic liquid), can be integrated into an electronic device system and shows a series of superior performance characteristics over current commercial benchmarks, which may find vast applications.

Supercapacitors, which serve as a kind of novel energy storage devices, are proven a promising solution for developing miniaturized, flexible, wearable electronics. Lightweight thin film electrodes that can be implemented is a potential developing orientation. Nevertheless, insufficient device energy density impedes its practical applications. To elevate device energy density, complicated assembly of nanostructured two-dimensional electrodes is a useful technique but results in high cost. Herein, we report a magnetic-assisted technology to fabricate tailorable, tractable, and flexible NiCo oxyfluoride non-woven cloth (NOC) for cathode, which can reveal superior electrochemical performance and excellent mechanical flexibility. A superb high areal capacitance up to 3.07 F cm−2 and no significant capacitance decay after 5000 cycles reveal the great potential in practical applications of the NOC electrodes.

With the rapid development of portable electronics, such as e-paper and other flexible devices, power sources with a high flexibility become an important prerequisite. In this run, supercapacitors with a small form factor are recently emerging as a competitive candidate. Here, we introduce an all-printed paper based supercapacitor (PPS) assembled by screen printing and stencil printing technology, which shows superior electrochemical performance; moreover, it is compatible with mass production processes. The key electrode material, δ-MnO 2 nanosheets, synthesized by one-step synthetic process exhibit a high specific capacitance of 120 F g−1. Using this δ-MnO 2 nanosheets electrode material and aqueous electrolyte, the capacity of the device could reach 4.7 mF g−1 with the volume of 2.0*1.7*0.2mm3. More important, the supercapacitor is lightweight and miniaturized, which can well cater to the development of future wearable electronics.

Supercapacitors with an outstanding electrochemical performance have emerged as a rapidly rising star on the horizon of energy storage devices and consumer electronics applications. With the rapid development of miniaturized and portable electronic technology, flexible ultrathin micro-supercapacitors have become more important than ever. The 2D network structure of graphene oxide (GO) with excellent mechanical and electrochemical performances has been reduced into reduced graphene oxide (rGO) by a pulse laser, which is a competitive candidate for the preparation of micro-planar supercapacitors. Micro-supercapacitors based on laser-reduced graphene with an ultrathin thickness of 20 µm exhibit a very high area capacitance up to 4.8 mF/cm2 at a current density of 0.3 mA/cm2 in LiCl-PVA gel electrolyte. Additionally, the energy storage device can possess a fantastic aesthetic property by virtue of the laser technology, which not only reveals the aesthetic art side of supercapacitors, but also provides a palette for the state-of-the-art micro-supercapacitors.

Over the last decade, significant efforts have been made to develop electrode architectures of the electrochemical energy storage (EES) devices. The involvement of electrostatic field, magnetic field, and electromagnetic field for electrode fabrication plays a vital role to enhance performance of supercapacitors in comparison with conventional roots. Electromagnetic techniques are advantageous over others because of several reasons including material's interactions at molecular level, noncontact energy, and chemical transportations to extract physical phase changings, and large-scale production with a cost-effective way. Recently, these techniques became a powerful tool for constructing hierarchical and well-ordered nanostructured electrodes. Their novel mechanisms and forms show high efficiency with numerous advantages such as green, simple, and mild reaction conditions. Herein, recent progress involving electromagnetic techniques for supercapacitor is reviewed; their potential future applications are also highlighted. The present review aims to serve as a guideline for fabrication techniques of next generation supercapacitor electrodes.