Silicon-Based 3D All-Solid-State Micro-Supercapacitor with Superior Performance

1.8 V all-solid-state flexible asymmetric microsupercapacitors based on direct-writing electrodes

Increasing the energy density of microsupercapacitors is a key challenge in promoting their practical applications. Accordingly, the construction of asymmetric microsupercapacitors (AMSCs) based on pseudocapacitive materials by increasing the capacitance of devices and widening their working voltage is an effective way to address this challenge. In this work, double-electric-layer-structured pseudocapacitive electrodes were designed and prepared for AMSCs via a one-step direct-writing method. Benefiting from the structural advantages and complementary voltage of the electrodes, AMSCs delivered a wide operating voltage window of up to 1.8 V in a polyvinyl alcohol/LiCl gel electrolyte and showed a high areal capacitance of 42 mF cm-2, resulting in an outstanding areal energy density of 18.9 μW h cm-2. This study provides a new approach for developing high-performance microsupercapacitors for portable electronic devices.

In Situ Construction of the Fe-Cu Hydroxide Interlocking Structure with Solution-Derived Cu/Ag Current Collectors for Flexible Symmetric Supercapacitors

The current collector serves as a crucial element in supercapacitors, acting as a medium between the electrode material and the substrate. Due to its excellent conductivity, a metal collector is typically favored. Enhancing the binding strength between the collector and the substrate as well as between the collector and the electrode material has emerged as a critical factor for enhancing the capacitance performance. In this study, a Ag film with a grass root-like structure was initially grown on a PI substrate through the surface modification and ion exchange (SMIE) process. This Ag interlocking structure contributes to strong binding between the PI substrate and Ag without compromising the mechanical properties of the Ag film. To further enhance the electrochemical properties at low scan rates, electroless-plated Cu was subsequently deposited on the Ag film to form the Cu/Ag current collector. Moreover, the Cu within the Cu/Ag current collector served as a precursor for the growth of FeOOH-Cu(OH)2 via a two-step in situ method. The resulting FeOOH-Cu(OH)2/Cu/Ag structure as a whole is binder-free. Supercapacitors employing symmetric FeOOH-Cu(OH)2/Cu/Ag structures were assembled, and their energy storage properties were investigated. The solution-based low-temperature process used in this study offers the potential for cost-effective and large-scale applications.

Laser-induced graphene electrodes scribed onto novel carbon black-doped polyethersulfone membranes for flexible high-performance microsupercapacitors

A facile and expandable methodology was successfully developed to fabricate laser-induced graphene from novel pristine aminated polyethersulfone (amPES) membranes. The as-prepared materials were applied as flexible electrodes for microsupercapacitors. The doping of amPES membranes with various weight percentages of carbon black (CB) microparticles was then performed to improve their energy storage performance. The lasing process allowed the formation of sulfur- and nitrogen-codoped graphene electrodes. The effect of electrolyte on the electrochemical performance of as-prepared electrodes was investigated and the specific capacitance was significantly enhanced in 0.5 M HClO₄. Remarkably, the highest areal capacitance of 47.3 mF·cm^-2 was achieved at a current density of 0.25 mA·cm^-2. This capacitance is approximately 12.3 times higher than the average value for commonly used polyimide membranes. Furthermore, the energy and power densities were as high as 9.46 µWh·cm^-2 and 0.3 mW·cm^-2 at 0.25 mA·cm^-2, respectively. The galvanostatic charge-discharge experiments confirmed the excellent performance and stability of amPES membranes during 5,000 cycles, where more than 100% of capacitance retention was achieved and the coulombic efficiency was improved up to 96.67%. Consequently, the fabricated CB-doped PES membranes offer several advantages including low carbon fingerprint, cost-effectiveness, high electrochemical performance and potential applications in wearable electronic systems.

Advanced Three-Dimensional Microelectrode Architecture Design for High-Performance On-Chip Micro-Supercapacitors

The rapid development of miniaturized electronic devices has greatly stimulated the endless pursuit of high-performance on-chip micro-supercapacitors (MSCs) delivering both high energy and power densities. To this end, an advanced three-dimensional (3D) microelectrode architecture design offers enormous opportunities due to high mass loading of active materials, large specific surface areas, fast ion diffusion kinetics, and short electron transport pathways. In this review, we summarize the recent advances in the rational design of 3D architectured microelectrodes including 3D dense microelectrodes, 3D nanoporous microelectrodes, and 3D macroporous microelectrodes. Furthermore, the emergent microfabrication strategies are discussed in detail in terms of charge storage mechanisms and structure-performance correlation for on-chip MSCs. Finally, we conclude with a perspective on future opportunities and challenges in this thriving field.

On-chip integration of bulk micromachined three-dimensional Si/C/CNT@TiC micro-supercapacitors for alternating current line filtering

Three-dimensional (3D) micro-supercapacitors (MSCs) with superior performances are desirable for miniaturized electronic devices. 3D interdigitated MSCs fabricated by bulk micromachining technologies have been demonstrated for silicon wafers. However, rational design and fabrication technologies of 3D architectures still need to be optimized within a limited footprint area to improve the electrochemical performances of MSCs. Herein, we report a 3D interdigitated MSC based on Si/C/CNT@TiC electrodes with high capacitive properties attributed to the excellent electronic/ionic conductivity of CNT@TiC core–shells with a high aspect ratio morphology. The symmetric MSC presents a maximum specific capacitance of 7.42 mF cm⁻² (3.71 F g⁻¹) at 5 mV s⁻¹, and shows an 8 times areal capacitance increment after material coating at each step, fully exploiting the advantage of 3D interdigits with a high aspect ratio. The all-solid-state MSC delivers a high energy density of 0.45 μW h cm⁻² (0.22 W h kg⁻¹) at a power density of 10.03 μW h cm⁻², and retains ∼98% capacity after 10 000 cycles. The MSC is further integrated on-chip in a low-pass filtering circuit, exhibiting a stable output voltage with a low ripple coefficient of 1.5%. It is believed that this work holds a great promise for metal-carbide-based 3D interdigitated MSCs for energy storage applications.

A novel fabrication strategy for the realization of a bulk micromachined 3D Si/C/CNT@TiC micro-supercapacitor is experimentally demonstrated.

Laser-Induced Interdigital Structured Graphene Electrodes Based Flexible Micro-Supercapacitor for Efficient Peak Energy Storage

The rapidly developing demand for lightweight portable electronics has accelerated advanced research on self-powered microsystems (SPMs) for peak power energy storage (ESs). In recent years, there has been, in this regard, a huge research interest in micro-supercapacitors for microelectronics application over micro-batteries due to their advantages of fast charge–discharge rate, high power density and long cycle-life. In this work, the optimization and fabrication of micro-supercapacitors (MSCs) by means of laser-induced interdigital structured graphene electrodes (LIG) has been reported. The flexible and scalable MSCs are fabricated by CO₂-laser structuring of polyimide-based Kapton ^® HN foils at ambient temperature yielding interdigital LIG-electrodes and using polymer gel electrolyte (PGE) produced by polypropylene carbonate (PPC) embedded ionic liquid of 1-ethyl-3-methyl-imidazolium-trifluoromethansulphonate [EMIM][OTf]. This MSC exhibits a wide stable potential window up to 2.0 V, offering an areal capacitance of 1.75 mF/cm² at a scan rate of 5.0 mV/s resulting in an energy density (E_a) of 0.256 µWh/cm² @ 0.03 mA/cm² and power density (P_a) of 0.11 mW/cm² @0.1 mA/cm². Overall electrochemical performance of this LIG/PGE-MSC is rounded with a good cyclic stability up to 10,000 cycles demonstrating its potential in terms of peak energy storage ability compared to the current thin film micro-supercapacitors.

State-of-the-art anodes of potassium-ion batteries: synthesis, chemistry, and applications

The growing demand for green energy has fueled the exploration of sustainable and eco-friendly energy storage systems. To date, the primary focus has been solely on the enhancement of lithium-ion battery (LIB) technologies. Recently, the increasing demand and uneven distribution of lithium resources have prompted extensive attention toward the development of other advanced battery systems. As a promising alternative to LIBs, potassium-ion batteries (KIBs) have attracted considerable interest over the past years owing to their resource abundance, low cost, and high working voltage. Capitalizing on the significant research and technological advancements of LIBs, KIBs have undergone rapid development, especially the anode component, and diverse synthesis techniques, potassiation chemistry, and energy storage applications have been systematically investigated and proposed. In this review, the necessity of exploring superior anode materials is highlighted, and representative KIB anodes as well as various structural construction approaches are summarized. Furthermore, critical issues, challenges, and perspectives of KIB anodes are meticulously organized and presented. With a strengthened understanding of the associated potassiation chemistry, the composition and microstructural modification of KIB anodes could be significantly improved.

A High Energy Density 2D Microsupercapacitor Based on an Interconnected Network of a Horizontally Aligned Carbon Nanotube Sheet

Highly aligned carbon nanotubes (HACNT sheets) have recently attracted great attention in developing high-performing ultrathin supercapacitors, which take advantage of the long-range alignment to improve electrochemical performance. While there are investigations into sandwich electrode CNT sheet devices, there are no known reports on interdigitated electrode (IDE) HACNT sheet microsupercapacitors (MSCs). This paper reports a facile method for rapidly fabricating high energy density ultrathin HACNT sheet-based MSCs with IDE planar configuration. Increasing the electrode thickness from 32 nm (5 layers) to 300 nm (50 layers) results in an approximately three times factor in performance. The 50 layer devices (MSC-50L) yield a top energy density of 10.52 mWhcm^-3 and power density of 19.33 Wcm^-3, making its performance comparable to those of microbatteries with potential for further improvement. Additionally, incorporation of MnO₂ nanoparticles (NPs) within the MSCs-50L improves specific capacitance (242 Fcm^-3), energy density (33.7 mWhcm^-3), and power density (31 Wcm^-3), outperforming current thin-film MSCs and matching the performance of 3D MSCs. MSCs also demonstrate a long cycle life (7000 charge-discharge cycles) with less than 5% capacitance fade. These findings suggest that HACNT sheets have substantial potential as active electrode materials for ultrathin high energy density microscale power sources.