V2O5 nanosheets assembled on 3D carbon fiber felt as a free-standing electrode for flexible asymmetric supercapacitor with remarkable energy density

As an emerging energy storage device, supercapacitor is widely investigated owing to its excellent capability, quick charge-discharge and tremendous cycle life. The operation potential window, energy density and mass loading of supercapacitor must be taken into deep consideration for its practical application. In this work, an outstanding electrode based on CFF@V₂O₅ nanosheets was prepared. Then a free-standing asymmetric supercapacitor with CFF@V₂O₅ composite as positive electrode and CFF@AC as negative electrode was assembled. Owing to the functional groups produced on CFF after the activation, V₂O₅ nanosheets was immobilized. The composite exhibits remarkable specific capabilities of 1465 mF cm^?2 (492 F g^?1). The energy density of the assembled free-standing asymmetric supercapacitor achieves 0.928 mWh cm^?3 when the power density is 17.5 mW cm^?3. After 6000 charging-discharging cycles as under normal, bended and anti-bended conditions for respective 2000 cycles, the device retains 89.7% of the initial capacitance, exhibiting fascinating cycle stabilization. Finally, two devices linked series can lighten a LED of 1.8 V for 2 min after charging for 2.5 min, which is inspiring for the practical application and production of self-supporting asymmetric supercapacitors.     

Morphology‐dependent electrochemical performance of nitrogen‐doped carbon dots@polyaniline hybrids for supercapacitors

In this work, the binary N‐CDs@PANI hybrids were fabricated by introducing zero‐dimensional nitrogen‐doped carbon dots (N‐CDs) into reticulated PANI. Firstly, N‐CDs were prepared by one‐pot microwave method, and then, the N‐CDs were introduced into in situ oxidative polymerization of aniline (ANI) monomer. The N‐CDs with abundant functional groups and high electronic cloud density played a significant role in guiding the polyaniline‐ordered growth into intriguing morphologies. Moreover, morphology‐dependent electrochemical performances of N‐CDs@PANI hybrids were investigated and N‐CDs improve static interaction and enhance the special capacitances in the N‐CDs@PANI hybrids. Especially, the specific capacitance of PC4 hybrid can reach 785 F g^?1, which exceed that of pure PANI (274 F g^?1) at current density of 0.5 A g^?1 according to three‐electrode measurement. And the capacitance retention of the PC4 hybrid still keeps 70% after 2000 cycles of charge and discharge. The N‐CDs@PANI hybrids can have potential applications in electrode materials, supercapacitors, nonlinear optics, and microwave absorption.     

Evaluation of fluctuating voltage topology with fuel cells and supercapacitors for automotive applications

To develop a single‐stage power conversion topology in which energy storage devices can be directly coupled, a fluctuating voltage topology is applied, leading to lower cost and more compactness with the absence of DC/DC converters. This paper investigates such a topology for automotive applications where fuel cells are directly connected to the DC bus of the inverter, resulting in fluctuating voltage across the DC bus. Further, a supercapacitor pack is also introduced to maintain the power capacity and voltage stability. The hybridization principle and practical application of such a topology are then discussed in the time domain and frequency domain. Furthermore, the transient power requirement is decomposed to design the size of fuel cells and supercapacitors. Simulation results from the modeling of the fuel cell‐supercapacitor powertrain demonstrate the feasibility and effectiveness of this topology. The supercapacitors can serve as a low‐pass filter for the fuel cells. In conclusion, the peak power requirement can be successfully achieved because of the lowered system impedance, and the fuel cells only need to supply the average power.     

High-Performance All-Solid-State Supercapacitor Electrode Materials Using Freestanding Electrospun Carbon Nanofiber Mats of Polyacrylonitrile and Novolac Blends

Herein, this paper reports a facile method to prepare electrospun carbon nanofiber mats (ECNFMs) with high specific surface area and interconnected structure using polyacrylonitrile (PAN) as a precursor and novolac resin (NOC) as a polymer sacrificial pore-making agent. Without additional treatment, the prepared ECNFMs have a highly porous structure because NOC decomposes in a wider temperature range than most polymer activators. The NOC content in the PAN nanofibers shows important effects on porosity. The BET specific surface area of ECNFMs reaches a maximum of 1468 m² g⁻¹ when the precursor nanofibers contained 30 wt% NOC (ECNFM-3) after carbonization at 1000 °C. The supercapacitor device from ECNFM-3 electrode and all-solid-state electrolyte shows excellent cycling durability and high specific capacitance: ≈99.72% capacitance retention after 10 000 charge/discharge cycles and ≈320 mF cm⁻² at 0.25 mA cm⁻². Furthermore, it shows a large energy density of ≈11.1 $\mu$Wh cm⁻² under the power density of 500 mW m⁻². Activation of carbon nanofibers simply by the addition of NOC into precursor nanofibers can offer a handy way to prepare ECNFMs for high-performance all-solid-state supercapacitors and other potential applications.     

Fluorine-free binders for Carbon Black based Electrochemical Supercapacitors

Industrially manufactured carbon blacks (CBs) provide highly dispersed carbon materials with a specific surface of up to 1700 m² g^–1. Precompaction at p > 10 MPa in the presence of 3–10 wt% PTFE (provided as a dispersion) is known to lead to stable electrodes for electrochemical supercapacitors. Specific capacitances for single electrodes (C _s,1) were measured by constant current cycling (CCC) at 34 mA cm^–2 to be up to 250 F g^–1. It is shown that substitution of PTFE by fluorine-free binders, such as aqueous dispersions of polystyrene, styrene/butadien-copolymer and ethylene/acrylic acid copolymer is possible. Optimum systems were with 3–10 wt% binders of butadiene/styrene copolymers. They allowed stable results within hundreds of cycles. No shedding of the CB particles was observed, and swelling of the electrode was minimum.     

磁集成Buck变换器在超级电容充电系统中的建模

同步整流Buck变换器广泛应用于低压充电场合,变换器中采用的交错并联磁集成技术能够有效地减小电感电流纹波,增加变换功率,提高变换器的工作可靠性,同时提高系统的动态响应速度。在超级电容充电阶段,采用状态空间平均法,推导了三相交错并联磁集成同步整流Buck变换器在电流连续模式(CCM)下的大信号和小信号模型,得到了系统开环传递函数。利用Matlab仿真软件得到整个系统开环幅频和相频特性曲线,并以此为依据优化设计控制器的补偿网络以提高系统的稳定性和瞬态响应速度,最后通过仿真和实验进行了验证。     

An Interface‐Induced Co‐Assembly Approach Towards Ordered Mesoporous Carbon/Graphene Aerogel for High‐Performance Supercapacitors

Hierarchically porous composites with mesoporous carbon wrapping around the macroporous graphene aerogel can combine the advantages of both components and are expected to show excellent performance in electrochemical energy devices. However, the fabrication of such composites is challenging due to the lack of an effective strategy to control the porosity of the mesostructured carbon layers. Here an interface‐induced co‐assembly approach towards hierarchically mesoporous carbon/graphene aerogel composites, possessing interconnected macroporous graphene networks covered by highly ordered mesoporous carbon with a diameter of ≈9.6 nm, is reported. And the orientation of the mesopores (vertical or horizontal to the surface of the composites) can be tuned by the ratio of the components. As the electrodes in supercapacitors, the resulting composites demonstrate outstanding electrochemical performances. More importantly, the synthesis strategy provides an ideal platform for hierarchically porous graphene composites with potential for energy storage and conversion applications.