Nano fabricated silicon nanorod array with titanium nitride coating for on-chip supercapacitors

Atomic Layer Deposition-A Versatile Toolbox for Designing/Engineering Electrodes for Advanced Supercapacitors

Atomic layer deposition (ALD) has become the most widely used thin-film deposition technique in various fields due to its unique advantages, such as self-terminating growth, precise thickness control, and excellent deposition quality. In the energy storage domain, ALD has shown great potential for supercapacitors (SCs) by enabling the construction and surface engineering of novel electrode materials. This review aims to present a comprehensive outlook on the development, achievements, and design of advanced electrodes involving the application of ALD for realizing high-performance SCs to date, as organized in several sections of this paper. Specifically, this review focuses on understanding the influence of ALD parameters on the electrochemical performance and discusses the ALD of nanostructured electrochemically active electrode materials on various templates for SCs. It examines the influence of ALD parameters on electrochemical performance and highlights ALD's role in passivating electrodes and creating 3D nanoarchitectures. The relationship between synthesis procedures and SC properties is analyzed to guide future research in preparing materials for various applications. Finally, it is concluded by suggesting the directions and scope of future research and development to further leverage the unique advantages of ALD for fabricating new materials and harness the unexplored opportunities in the fabrication of advanced-generation SCs.

Planar Microsupercapacitors Based on Oblique Angle Deposited Highly Porous TiN Thin Films

Microsupercapacitors are gaining increasing interest for energy storage in miniaturized electronic devices. However, the production of porous electrode material with standard microfabrication techniques is a big problem. Here, we report on the oblique angle deposition of highly porous and nanostructured columnar titanium nitride (TiN) films on silicon substrate using magnetron sputtering for high-performance microsupercapacitors. The intercolumnar porosity of the sputtered TiN films can be systematically controlled as a function of the oblique angle α achieved by tilting the substrate. The denser morphologies in TiN films deposited at α = 0° lead to moderate capacitive behavior in a 1 M Na₂SO₄ electrolyte solution. Meanwhile, a high areal capacitance of 17.5 mF·cm^-2 is obtained for a 60° oblique angle due to high intercolumnar porosity in films, which increases the specific surface area and facilitates easy electrolyte permeation. The electrodes also retain 88.2% of the initial specific capacitance after 10,000 charging/discharging cycles. A planar interdigitated microsupercapacitor has been subsequently fabricated based on an optimized TiN thin film serving as both an efficient electrode and a current collector. TThe device was electrochemically tested using polyvinyl alcohol (PVA)-Na2SO4 hydrogel electrolyte allowing a voltage window of 1.8 V and showed energy densities of 0.46 μWh·cm^-2 while maintaining a high-power density of 703.12 μWh·cm^-2. This work gives insight into the use of oblique angle deposition for obtaining highly porous films of other electrode materials for microsupercapacitor applications with the advantage of using a simple microfabrication process.

Advances in Si and SiC Materials for High-Performance Supercapacitors toward Integrated Energy Storage Systems

Silicon (Si), as the second most abundant element on Earth, has been a central platform of modern electronics owing to its low mass density and unique semiconductor properties. From an energy perspective, all-in-one integration of power supply systems onto Si-based functional devices is highly desirable, which inspires significant study on Si-based energy storage. Compared to the well-known Si-anode Li-ion batteries, Si-based supercapacitors possess high power density, long life, and simple working mechanisms, which enables their ease of integration onto a wide range of devices and applications. Besides Si, silicon carbide (SiC), as a physicochemically stable wide-bandgap semiconductor, also attracts research attention as an energy storage material in harsh environments. In this review, a detailed overview of latest advances in materials design, synthesis methods, and performances of Si-based and SiC-based supercapacitors will be provided. Some successful integrated devices, future perspectives, and potential research directions are also highlighted and discussed.

Chemically Roughened, Sputtered Au Films with Trace-Loaded Manganese Oxide for both On-Chip and Off-Chip High Frequency Supercapacitors

High frequency supercapacitors (HFSCs) are promising in alternating current line filtering and adaptable storage of high-frequency pulse electrical energy. Herein, we report a facile yet integrated-circuit-compatible fabrication of HFSC electrodes by combining chemical roughening of the sputtered metal (Au) films and in situ trace loading of a pseudocapacitive material (MnO x ). The developed electrode fabrication route is versatile for different substrates, and is described with the application paradigms of both on-chip (with Si/SiO2 substrate) and off-chip (without Si/SiO2 substrate, with Ti substrate as an example in this study) HFSCs. With Au/MnO x films on Si/SiO2 substrates as the working electrodes, the derived on-chip HFSC displayed satisfactory performance in high frequency applications (i.e., an areal capacitance of 131.7 µF cm-2, a phase angle of -78°, and a RC time constant of 0.27 ms, at 120 Hz).

Porous Thin-Wall Hollow Co3O4 Spheres for Supercapacitors with High Rate Capability

In this study, a zeolitic imidazolate framework-67 (ZIF-67) was prepared as a precursor using a facile hydrothermal method. After a calcination reaction in the air, the as-prepared precursor was converted to porous thin-wall hollow Co3O4 with its original frame structure almost preserved. The physical and chemical characterizations of the nanomaterial were analyzed systemically. The electrochemical tests indicate that the obtained Co3O4 possesses large specific capacitances of 988 and 925 F/g at 1 and 20 A/g accompanying an outstanding rate capability (a 93.6% capacitance retention) and retains 96.6% of the specific capacitance, even after 6000 continuous charge/discharge cycles. These excellent properties mark the Co3O4 a promising electrode material for high performance supercapacitors.

High-Performance On-Chip Supercapacitors Based on Mesoporous Silicon Coated with Ultrathin Atomic Layer-Deposited In2O3 Films

On-chip supercapacitors have attracted considerable attention because of their high power density, long cycling life, and compatibility with integrated circuits. One critical drawback that restricts their practical application is the low energy density. In this work, low-resistivity mesoporous silicon with a high aspect ratio is prepared by Pt film-assisted chemical etching and utilized as the scaffold of the supercapacitors. Subsequently, low-resistivity (<0.0015 Ω·cm) and ultrathin In₂O₃ films are coated on the mesoporous silicon scaffold by atomic layer deposition at 200 °C, serving as the active electrode material. The electrochemical measurements reveal that the coating of the In₂O₃ film remarkably improves the performance of the supercapacitors compared with those without the In₂O₃ coating. The supercapacitors with a 4.5 nm In₂O₃ film coating exhibit a capacitance density of 1.36 mF/cm² at a scan rate of 10 mV/s as well as a better stability against the scan rate. In addition, it is found that the pristine mesoporous silicon walls are collapsed after 400 times of sweeping while those with the In₂O₃ film coating are still intact even after 2000 times of sweeping. Meanwhile, a high energy density is also achieved without sacrificing the power performance.