Enhanced Performance of an Electric Double Layer Microsupercapacitor Based on Novel Carbon-Encapsulated Cu Nanowire Network Structure As the Electrode

A self-sacrificing template strategy: In-situ construction of bimetallic MOF-derived self-supported CuCoSe nanosheet arrays for high-performance supercapacitors

Transition metal selenides (TMSs) are viewed as a prospective high-capacity electrode material for asymmetric supercapacitors (ASCs). However, the inability to expose sufficient active sites due to the limitation of the area involved in the electrochemical reaction severely limits their inherent supercapacitive properties. Herein, a self-sacrificing template strategy is developed to prepare self-supported CuCoSe (CuCoSe@rGO-NF) nanosheet arrays by in situ construction of copper-cobalt bimetallic organic framework (CuCo-MOF) on rGO-modified nickel foam (rGO-NF) and rational design of Se2- exchange process. Nanosheet arrays with high specific surface area are considered to be ideal platforms for accelerating electrolyte penetration and exposing rich electrochemical active sites. As a result, the CuCoSe@rGO-NF electrode delivers a high specific capacitance of 1521.6 F/g at 1 A/g, good rate performance and an excellent capacitance retention of 99.5% after 6000 cycles. The assembled ASC device has a high energy density of 19.8 Wh kg-1 at 750 W kg-1 and an ideal capacitance retention of 86.2% after 6000 cycles. This proposed strategy offers a viable strategy for designing and constructing electrode materials with superior energy storage performance.

Flexible Supercapacitors Based on Stretchable Conducting Polymer Electrodes

Supercapacitors are widely used in various fields due to their high power density, fast charging and discharging speeds, and long service life. However, with the increasing demand for flexible electronics, integrated supercapacitors in devices are also facing more challenges, such as extensibility, bending stability, and operability. Despite many reports on stretchable supercapacitors, challenges still exist in their preparation process, which involves multiple steps. Therefore, we prepared stretchable conducting polymer electrodes by depositing thiophene and 3-methylthiophene on patterned 304 stainless steel (SS 304) through electropolymerization. The cycling stability of the prepared stretchable electrodes could be further improved by protecting them with poly(vinyl alcohol)/sulfuric acid (PVA/H₂SO₄) gel electrolyte. Specifically, the mechanical stability of the polythiophene (PTh) electrode was improved by 2.5%, and the stability of the poly(3-methylthiophene (P3MeT) electrode was improved by 7.0%. As a result, the assembled flexible supercapacitors maintained 93% of their stability even after 10,000 cycles of strain at 100%, which indicates potential applications in flexible electronics.

Large-Pore Ordered Mesoporous Turbostratic Carbon Films Prepared Using Rapid Thermal Annealing for High-Performance Micro-pseudocapacitors

Carbonization by rapid thermal annealing (RTA) of precursor films structured by a brush block copolymer-mediated self-assembly enabled the preparation of large-pore (40 nm) ordered mesoporous carbon (MPC)-based micro-supercapacitors within minutes. The large pore size of the fabricated films facilitates both rapid electrolyte diffusion for carbon-based electric double-layer capacitors and conformal deposition of V₂O₅ without pore blockage for pseudocapacitors. The pores were templated using bottlebrush block copolymers (BBCPs) via cooperative assembly of phenol-formaldehyde resin to produce microphase-segregated carbon precursor films on a variety of substrates. Ultrafast RTA processing (∼50 °C/s) at elevated temperatures (up to 1000 °C) then generated stable, conductive, turbostratic MPC films, resolving a significant bottleneck in rapid fabrication. MPC prepared on stainless steel at 900 °C demonstrated exceptionally high areal and volumetric capacitances of 6.3 mF/cm² and 126 F/cm³ (at 0.8 mA/cm² using 6 M KOH as the electrolyte), respectively, and 91% capacitance retention after 10,000 galvanostatic charge/discharge cycles. Post-RTA conformal V₂O₅ deposition yielded pseudocapacitors with 10-fold increase in energy density (20 μW h cm^-2 μm^-1) without adversely affecting the high power density (450 μW cm^-2 μm^-1). The use of RTA coupled with BBCP templating opens avenues for scalable, rapid fabrication of high-performance carbon-based micro-pseudocapacitors.

Regulating Na deposition by constructing a Au sodiophilic interphase on CNT modified carbon cloth for flexible sodium metal anode

Na metal anode has attracted increasing attentions as the anode of sodium ion batteries (SIBs) due to its high theoretical capacity, low redox potential and high abundance. However, the formation of uncontrollable Na dendrite during repeated plating/stripping cycles hinders its further development and application. Herein, a sodiophilic Na metal anode host is developed by sputtering gold nanoparticles (Au NPs) into interconnected carbon nanotube modified carbon cloth (CNT/CC) to form a Au-CNT/CC architecture. Sodiophilic Au NPs effectively guide the Na metal uniform deposition and three-dimensional (3D) microporous structure offers a large surface area for nucleation and reducing the current densities. The regulated uniform Na metal deposition mechanism is investigated by the in-situ optical microscopy and simulation analysis. As a result, Au-CNT/CC electrode exhibits a low nucleation overpotential (2.2 mV) and stable cycle performance for 1600 h at 1 mA cm^-2 with 2 mAh cm^-2. Moreover, it even exhibits a long cycle stability for more than 800 h at 5 mA cm^-2 with 2 mAh cm^-2. To explore its application, a full cell coupled with a sodium vanadium phosphate coated with carbon layer (NVP@C) cathode is assembled and delivers an average discharge capacity of 80.6 mAh g^-1 and coulombic efficiency of 99.6% for 400 cycles at 100 mAh g^-1. Furthermore, a flexible pouch cell with Na@Au-CNT/CC as the anode is fabricated and demonstrated good flexibility and future application of wearable electronics.

High Mass Loading Asymmetric Micro-supercapacitors with Ultrahigh Areal Energy and Power Density

High mass loading asymmetric micro-supercapacitors (MSCs) are key components for the development of high-performance energy and power supply systems. Here, a concept for achieving high mass loading electrodes is presented and applied to high mass loading micro-supercapacitors with ultrahigh areal energy and power density. The positive electrode is made from porous carbon with birnessite coverage and multiwalled carbon nanotubes (CNTs) as conducting additives (PIC-CNTs-MnO₂). The negative electrode is prepared from hierarchically porous active carbon mixed with CNTs (PICK-CNTs). Both positive and negative electrode materials are tailored to ensure a high content of macro- and mesopores. MSCs with an optimized mass loading of 13.9 mg·cm^-2 (maximum: 23.6 mg·cm^-2) provide an ultrahigh areal capacitance of 1.13 F·cm^-2 (volumetric capacitance: 22.6 F·cm^-3), an outstanding energy of 627.8 μWh·cm^-2, and a maximum power density of 64 mW·cm^-2. About 85% of the initial capacitance remained after 5000 cycles. Moreover, shunt and tandem device testing confirmed a high uniformity of these MSCs, meeting the requirements of adjustable output currents and voltages in microchips.

Progress and Perspectives in Designing Flexible Microsupercapacitors

Miniaturized flexible microsupercapacitors (MSCs) that can be integrated into self-powered sensing systems, detecting networks, and implantable devices have shown great potential to perfect the stand-alone functional units owing to the robust security, continuously improved energy density, inherence high power density, and long service life. This review summarizes the recent progress made in the development of flexible MSCs and their application in integrated wearable electronics. To meet requirements for the scalable fabrication, minimization design, and easy integration of the flexible MSC, the typical assembled technologies consist of ink printing, photolithography, screen printing, laser etching, etc., are provided. Then the guidelines regarding the electrochemical performance improvement of the flexible MSC by materials design, devices construction, and electrolyte optimization are considered. The integrated prototypes of flexible MSC-powered systems, such as self-driven photodetection systems, wearable sweat monitoring units are also discussed. Finally, the future challenges and perspectives of flexible MSC are envisioned.

Nitrogen and boron doped carbon layer coated multiwall carbon nanotubes as high performance anode materials for lithium ion batteries

Lithium ion batteries (LIBs) are at present widely used as energy storage and conversion device in our daily life. However, due to the limited power density, the application of LIBs is still restricted in some areas such as commercial vehicles or heavy-duty trucks. An effective strategy to solve this problem is to increase energy density through the development of battery materials. At the same time, a stable long cycling battery is a great demand of environmental protection and industry. Herein we present our new materials, nitrogen and boron doped carbon layer coated multiwall carbon nanotubes (NBC@MWCNTs), which can be used as anodes for LIBs. The electrochemical results demonstrate that the designed NBC@MWCNTs electrode possesses high stable capacity over an ultra-long cycling lifespan (5000 cycles) and superior rate capability even at very high current density (67.5 A g⁻¹). Such impressive lithium storage properties could be ascribed to the synergistic coupling effect of the distinctive structural features, the reduced diffusion length of lithium ions, more active sites generated by doped atoms for lithium storage, as well as the enhancement of the electrode structural integrity. Taken together, these results indicate that the N, B-doped carbon@MWCNTs materials may have great potential for applications in next-generation high performance rechargeable batteries.

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.

Novel electrode geometry for high performance CF/Fe2O3 based planar solid state micro-electrochemical capacitors

A novel geometry of sharp-edged electrodes for planar micro-electrochemical capacitors is utilized for an enhanced performance compared to the conventionally used interdigitated electrodes. The sharp-edged electrode geometry achieves a 68% enhancement in the electric field at the sharp-edge of the electrodes as compared to interdigitated electrodes. Moreover, carbon foam with high specific surface area loaded with iron oxide nanoparticles allows a large mass loading for the pseudocapacitance in addition to electric double layer capacitance (EDLC). Thus, an enhancement of 235% was obtained in both the areal specific capacitance and energy density when the performance was compared with the interdigitated electrode based supercapacitors. Moreover, an excellent cycling stability (∼99.5%) over 10 000 charge-discharge cycles was also achieved. The high-performance architecture of sharp-edged electrodes paves a way for smart electrochemical capacitors using an efficient planar structure in combination with high-loading materials for large pseudocapacitance as well as EDLC.