3D Printed Micro-Electrochemical Energy Storage Devices: From Design to Integration

With the continuous development and implementation of the Internet of Things (IoT), the growing demand for portable, flexible, wearable self-powered electronic systems significantly promotes the development of micro-electrochemical energy storage devices (MEESDs), such as micro-batteries (MBs) and micro-supercapacitors (MSCs). By overcoming the limitations of traditional fabrication processes, 3D printing techniques have been attracting much attention in recent years. Theoretically, 3D printing technologies can manufacture any customized arbitrary geometry and structure of electrodes and other components by fast prototyping at a relatively low cost to achieve desirable electrochemical performance and simplified integration. To that end, a comprehensive review of recent progress on the applications of 3D printing in MEESDs is presented herein. Emphasis is given to the generally classified seven types of 3D printing techniques (their working principle, process control, resolution, advantages, and disadvantages), their applications to fabricate electrodes, and other components with different configurations. Finally, the integration of other electronics into MEESDs and a future perspective on the research and development direction in this important field are further discussed.     

Polyaziridine-Encapsulated Phosphorene-Incorporated Flexible 3D Porous Graphene for Multimodal Sensing and Energy Storage Applications

Heteroatom-incorporated graphene represents a prominent family of materials utilized as active electrodes for multimodal sensing and energy storage applications. Herein, a novel polyaziridine-encapsulated phosphorene (PEP)-incorporated flexible 3D porous graphene (3DPG) electrode is developed using facile, cost-effective laser writing, and drop-casting techniques. Owing to the excellent electrochemical characteristics and surface functionality of the highly stable PEP, the fabricated PEP/3DPG is evaluated as a potential electrode for immunosensing, electrocardiogram (ECG) recording, and microsupercapacitors (MSCs). Under optimized conditions, the produced PEP/3DPG-based carcinoembryonic immunosensor exhibits linear ranges of 0.1–700 pg mL⁻¹ and 1–100 ng mL⁻¹ with a detection limit of 0.34 pg mL⁻¹ and high selectivity. The finger touch-based ECG sensor demonstrates a relatively low and stable impedance at the skin-electrode interface; therefore, the signal-to-noise ratio of the ECG signal received from the fabricated sensor (13.5 dB) is comparable to that of conventional Ag/AgCl electrodes (13.9 dB). Besides, the highest areal capacitance of the prepared MSC reached a magnitude of 16.94 mF cm⁻², which is six times higher than that of a non-doped 3DPG-based MSC. These results demonstrate the effectiveness of the described fabrication procedure and the high utilization potential of the encapsulated phosphorene-doped 3D graphene in multimodal applications.     

Inkjet Printed Disposable High-Rate On-Paper Microsupercapacitors

On-paper microsupercapacitors (MSCs) are a key energy storage component for disposable electronics that are anticipated to essentially address the increasing global concern of electronic waste. However, nearly none of the present on-paper MSCs combine eco-friendliness with high electrochemical performance (especially the rate capacity). In this work, highly reliable conductive inks based on the ternary composite of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS), graphene quantum dots and graphene are developed for scalable inkjet printing of compact (footprint area ≈ 20 mm²) disposable MSCs on commercial paper substrates. Without any post treatment, the printed patterns attain a sheet resistance as low as 4 Ω ?^?1. The metal-free all-solid-state MSCs exhibit a maximum areal capacitance > 2 mF cm^?2 at a high scan rate of 1000 mV s^?1, long cycle life (>95% capacitance retention after 10 000 cycles), excellent flexibility, and long service time. Remarkably, the “totally metal-free” MSC arrays are fully inkjet printed on paper substrates and also exhibit high rate performance. The life cycle assessment indicates that these printed devices have much lower eco-toxicity and global warming potential than other on-paper MSCs.     

An outlook on printed microsupercapacitors: Technology status,remaining challenges,and opportunities

The concept of the Internet of Things is dramatically changing the way society interacts with physical spaces and portable technologies. For the last couple of years, intensive research has been devoted on the design of several flexible and even wearable devices, such as displays and health-care sensors. Further developments on these new technologies are heavily conditioned by the lack of compatible energy storage/conversion units. Contrary to lithium-ion batteries, supercapacitors can be easily miniaturized and integrated on flexible/wearable technologies without losing their electrochemical performance. In this review, some of the most recent developments on the design and printing of light, flexible, and thin microsupercapcitors along with promising and further practical applications are presented.     

Direct Graphene‐Carbon Nanotube Composite Ink Writing All‐Solid‐State Flexible Microsupercapacitors with High Areal Energy Density

The advancement of miniaturized electronic devices requires the development of high‐performance microsupercapacitors. The low areal energy density of microsupercapacitors with the interdigitated architecture is the major challenge hindering the application. Here, a simple method for the scalable fabrication of all‐solid‐state, flexible microsupercapacitors is demonstrated by direct graphene‐carbon nanotube composite ink writing technology. The microsupercapacitors demonstrate good electrochemical performance with a high areal energy density of 1.36 µWh cm^–2 and power density of 0.25 mW cm^–2, good cycling stability, and excellent mechanical flexibility. The method developed here sheds light on the simple method of preparing high‐performance, all‐solid‐state, flexible microsupercapacitors in a straightforward and scalable process.     

Intercalation of Metal Ions into Ti3C2Tx MXene Electrodes for High‐Areal‐Capacitance Microsupercapacitors with Neutral Multivalent Electrolytes

Microsupercapacitors (MSCs) with neutral multivalent electrolytes are safer, cheaper, and exhibit higher theoretical energy densities compared with the MSCs with acidic and alkaline electrolytes. Multivalent charge carriers (e.g., Mg²⁺, Zn²⁺) in the MSCs with Ti₃C₂T_x MXene electrodes have not been demonstrated, which could theoretically achieve higher specific capacitances and energy densities. However, because of the larger size of multivalent charge carriers, the MXene electrodes require further modifications to facilitate reversible electrochemical reactions. Herein, through spontaneous intercalation of various metal ions into MXene multilayers, twelve metal ion intercalated MXene electrodes (Mⁿ⁺‐MXene) are fabricated and demonstrate improved electrochemical performance. Different nanopillar effects are observed between divalent Be²⁺ and trivalent Al³⁺ intercalants, which are systematically investigated by electrochemical impedance spectroscopy and molecular dynamics simulation. Among all Mⁿ⁺‐MXene electrodes, the Be²⁺‐MXene electrode largely facilitates the charge‐transfer process with minimal disturbance of electrolyte diffusion rates, showing improved specific capacitances and high rate performance in univalent (Li₂SO₄, Na₂SO₄, K₂SO₄) and multivalent electrolytes (BeSO₄, MgSO₄, ZnSO₄). Finally, flexible Be²⁺‐MXene MSCs with neural ZnSO₄ gel electrolytes are fabricated, demonstrating superior areal capacitances (77.2 mF cm^?2) and high energy density (3.86 μWh cm^?2 at 0.12 mW cm^?2) together with high user safety.     

Electrophoretic Deposition of Binder-Free MOF-Derived Carbon Films for High-Performance Microsupercapacitors

Recently, miniaturized power supplies have become essential components of micro-electromechanical systems (MEMS) and portable microdevices due to their high-power density, moderate specific energy, and superior long-term cyclability. In this study, microsupercapacitors with ZIF-8-derived carbons as active materials were successfully fabricate by electrophoretic deposition method. The carbon materials on microsupercapacitors, which are directly deposited or obtained by pyrolyzing predeposited ZIF-8 particles, play a crucial role in achieving outstanding electrochemical performances. The microsupercapacitor of 16 interdigital finger electrodes, prepared by electrophoretic deposition of ZIF-8 particles and subsequent pyrolysis, shows maximum specific power 687.6 mW cm⁻³, specific energy 2.87 mWh cm⁻³, and 97.8 % capacitance retention rate after 10 000 cycles. The simple and facile process of electrophoretic deposition and subsequent pyrolysis of ZIF-8 particles generates a film of densely populated microporous carbon particles on microsupercapacitor, leading to superior capacitive performances.