Supercapacitors Research Articles

Enhancement in photocatalytic and electrochemical performance of hydrothermally synthesized β-Bi2O3 via Ni incorporation

β-Bi2O3 and Ni-incorporated β-Bi2O3 nanoparticles with different Ni incorporating amounts (0, 2, and 4 at. wt. %) were successfully synthesized through a viable hydrothermal process. As-synthesized nanoparticles were analyzed by complementary analytical tools such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), UV–visible spectroscopy (UV–Vis), and photoluminescence spectroscopy (PL) for structural, microstructural, compositional, and spectral properties. The photocatalytic performance of synthesized nanoparticles was assessed by subjecting them to visible light irradiation and monitoring the decomposition of rhodamine-B dye. The findings demonstrated that the inclusion of Ni(4%) in β-Bi2O3 nanoparticles significantly enhanced its photocatalytic activity compared to pristine β-Bi2O3 which is desirable for environmental remediation. This improvement may be caused by increased generation of electron-hole (e−-h+) pairs, reduced recombination rate of these pairs, enhanced absorption of visible light, and a decreased band gap energy. To evaluate the specific capacitance characteristics of synthesized electrode materials, cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance analyses were conducted. The super capacitance activities of prepared electrode materials were observed in the order of Bi2O3 < Ni(2%)-Bi2O3 < Ni(4%)-Bi2O3. Notably, Ni(4%)-Bi2O3 nanocomposite exhibited higher supercapacitance, which can be attributed to the effective role of appropriate nickel incorporation in Bi2O3. These results suggested that the incorporation of Ni(4%) into β-Bi2O3 to form a nanocomposite showed greater capability as an effective electrode material for advanced energy storage devices, especially supercapacitors.

High Porous Activated Carbon Electrode Derived from Watermelon Peel Biomass Exposed with DC Glow Discharge Plasma Applied for Super Capacitors

The growing demand for sustainable and environmentally-friendly technologies has spurred the exploration of innovative methods for waste management and resource utilization. Among the various bio-wastes generated globally, watermelon peel emerges as a significant contributor. To characterize carbon materials in the presence of functional groups, for morphological analysis, and intensity, we subjected activated fruit peel carbon to X-ray diffraction, Fourier-transform infrared spectroscopy, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, and Raman studies. Furthermore, we examined its electrochemical performance. Another method used to assess wettability is the contact angle. Watermelon-rind-activated carbon was exposed to a DC glow discharge oxygen and air plasma with a 450 V applied potential. The air-treated carbon demonstrated a noteworthy capacitance of 1669 F g−1 at 0.5 mA g−1 in a 2 M KOH electrolyte. Our study found that the properties of the activated carbon were enhanced through cold plasma treatment. This research provides valuable insights into the potential resources of fruit peels and proposes a novel adsorbent with cost-effective advantages in supercapacitors, which could provide effective energy storage for portable gadgets, electric cars, and renewable energy systems, thus presenting a solution for sustainable waste management.

Scalable one-step synthesis of reduced graphene oxide: Towards flexible transparent conductive films and active supercapacitor electrodes

The reduced graphene oxide (rGO) thin films have attracted much attention in flexible electronic devices and supercapacitors (SCs). However, the chemical reduction mechanism of GO needs to be clarified, and the one-step process at low temperatures for preparing high-quality rGO thin films from GO dispersions is still blank in the research field. Here, we propose a one-step operation to spray GO dispersions onto substrate or current collector under a hydroiodic acid (HI) atmosphere while simultaneously achieving the preparation of rGO thin films. This pioneering metal-free, transfer-free, fast, low-temperature, environmentally friendly, and scalable spraying technology enables large-scale production of high-quality rGO. This method realizes the preparation of highly conductive and high transmittance rGO thin films on flexible polyimide and polyethylene terephthalate substrates, as well as the preparation of rGO thin films on current collectors as SCs electrodes. Density functional theory calculations show that oxygen-containing functional groups on the surface of GO exhibit a stronger adsorption energy for HI, and have a low energy barrier during reduction by HI. Ab initio molecular dynamics simulated the possible reduction reaction path between GO and HI at 90 °C, demonstrating that HI molecules can effectively reduce GO. Furthermore, the sheet resistance of the transparent conductive film created using the method developed in this study reaches approximately 1000 Ω/sq (80 % transparency), and the specific capacitance of the SCs electrode film created in this method is 433.2 F/g (5 mV/s, 1 M H2SO4). Our study not only validates the efficacy of the one-step synthesis method for rGO thin films but also provides theoretical insights into the underlying reaction mechanism. This work holds significant promise for advancing applications in various electronics by facilitating large-scale production of high-quality rGO thin films.

Fabrication of CNT-N@Manganese Oxide Hybrid Nanomaterials through a Versatile One-Pot Eco-Friendly Route toward Engineered Textile Supercapacitors.

The expansion of the Internet of Things market and the proliferation of wearable technologies have generated a significant demand for textile-based energy storage systems. This work reports the engineered design of hybrid electrode nanomaterials of N-doped carbon nanotubes (CNT-N) functionalized with two types of manganese oxides (MOs)-birnessite (MnO2) and hausmannite (Mn3O4)-and their application in solid-state textile-based hybrid supercapacitors (SCs). A versatile citric acid-mediated eco-friendly one-pot aqueous precipitation process is proposed for the fabrication of the hybrids. Remarkably, different types of MOs were obtained by simply changing the reaction temperature from room temperature to 100 °C, without any post-thermal treatment. Asymmetric textile SCs were developed using cotton fabrics coated with CNT-N and the hybrids as textile electrodes, and poly(vinyl) alcohol/orthophosphoric acid as the solid-gel electrolyte. The asymmetric devices presented enhanced energy storage performance relative to the symmetric device based on CNT-N and excellent cycling stability (>96%) after 8000 charge/discharge cycles owing to synergistic effects between CNT-N and the MOs, which endowed nonfaradaic and pseudocapacitive features to the SCs. The asymmetric SC based on CNT-N@MnO2 featured 47% higher energy density and comparable power density to the symmetric CNT-N-based device (8.70 W h cm-2 at 309.01 μW cm-2 vs. 5.93 W h cm-2 at 346.58 μW cm-2). The engineered hybrid CNT-N@MO nanomaterials and the eco-friendly citric acid-assisted one-pot precipitation route open promising prospects not only for energy storage, but also for (photo)(electro)catalysis, wastewater treatment, and (bio)sensing.

Roles of Metal Nanoparticles for Supercapacitors: A Review

AbstractRecent research on supercapacitors (SCs) has been attractive due to the potential application in a variety of fields related to energy storage. Electrode materials play a very important role for the performance of SCs and various metal nanoparticles are involved in the SC electrodes. In this paper, the roles of metal nanoparticles for SCs are reviewed and discussed. They can serve as a dopant to modify the surface of electrode materials, or be embedded in a composite to effectively reduce the resistance and lead to an enhanced specific capacitance. Some metal nanoparticles can be also employed as electrode materials directly, but easily being oxidized. Metallic nanoparticles can even act as current collectors, especially for these noble metals with excellent stability and high conductivity. Nanoporous metals prepared by dealloying and electrochemical method can be used as both pseudocapacitive materials and current collector of SCs. Some important experimental data on this issue are summarized. A brief discussion on the future directions, challenges and opportunities in this topic is also provided.

Prelithiation of electrodes in lithium-ion capacitors: A review

Lithium-ion capacitors (LICs) are one of the modern state-of-the-art hybrid capacitors, comprising a high potential window and imparting a higher energy density than supercapacitors (SCs). These LICs encompass elevated power density and a longer life span than lithium-ion batteries (LIBs). Preparation of high-performance electrode materials with electrochemically active microstructure and prelithiation are two efficient approaches to fabricate highly efficient LICs. But it comes across as a real dilemma of low initial Columbic efficiency if only microstructure is considered as an efficient way to enhance the performance. Nevertheless, prelithiation plays a crucial role in the manufacturing of LICs, improving the initial Coulombic efficiency and enlarging the voltage window. This paper reviews the recent lithiation approaches for lithium-ion capacitors by providing their methods and discussing their results concerning their energy and power density.

Enhanced electrochemical energy storage devices utilizing a one-dimensional (1D) α-MnO2 nanocomposite encased in onion-like carbon

AbstractThis work describes the fabrication of a novel one-dimensional (1D) α-MnO2 nanorods encased in onion-like carbon (or) carbon nano-onions (OLC) via microwave irradiation techniques employing electrolytic manganese dioxide (EMD), which is especially beneficial for rapid ion and electron transfer, and great structural stability. The composite of α-MnO2 and OLC demonstrates exceptional performance as an electrode across various electrochemical energy storage systems, including zinc-ion batteries (ZIB), sodium-ion batteries (SIB), and supercapacitors (SC) than the pristine α-MnO2. In SIB systems, the composite exhibits a specific capacity of 266 mAh g−1 at initial cycle with 50% capacity retention over 500 cycles, whereas the pristine electrode delivers only 39% capacity retention. The rapid yet controlled charge transfer kinetics facilitated by OLC addition in the α-MnO2 matrix outperforms as the ZIB cathode with an excellent specific capacity of 476 mAh g−1 with 100% capacity retention, while the pristine sample exhibits 77.5% capacity retention. As a SC electrode, the α-MnO2/OLC composite exhibits better electrochemical properties such as rectangular behavior, increased specific capacitance (792 F g−1), excellent capacity retention at high current densities, and others. The higher surface area that could be offered by the OLC to the α-MnO2 matrix facilitates the improved electrochemistry in the pristine sample and this kind of modification can be a viable solution to overcome the limitations of α-MnO2 for electrochemical energy storage applications. It is important to note that the performance outputs of α-MnO2/OLC composite are far better than the regular carbon (graphite, graphene) in α-MnO2 electrodes. Further, OLC provided with high surface area and ordered morphology can play the role of conductivity booster, structural stabilizer, and electrochemical active material in all the energy storage applications which may give a significant research attention in near future.

Recent Advances in Biomass Waste Derived Carbon Materials for Supercapacitors: A Review

As the core component of supercapacitors (SCs), the electrode material plays a decisive role in performance. Among electrode materials, carbon materials are the most widely used due to high porosity and specific surface area (SSA, 1000–3000 m2 g−1). Biomass carbon stands out in carbon materials because of its wide source, low cost, and less pollution. This work reviews the recent advances on carbon materials derived from biomass waste for SCs and explores the effects of different biomass sources including plant, animal, and aquatic organism waste on the performance of biomass waste‐derived carbon materials (BWDCs). Because of its high conductivity (1.25 × 103 ≈ 3 × 105 S m−1), power density (&gt;10 kW kg−1), and extended cycle life (&gt;10 000 cycles), BWDCs are advancing quickly in energy storage. It also discusses different methods and optimization pathways of BWDCs thoroughly. Finally, the challenges and future prospects for BWDCs are summarized. Overall, this critical will help researchers to gain a better understanding of source selection, structural classification, and research strategies for BWDCs, thereby promoting the application of BWDCs in electrochemistry and resource utilization.

Synthesis and evaluation of mixed 3d transition metal organic frameworks for energy application

Mixed metal-organic frameworks (MOFs) have generated considerable interest in the field of energy storage and conversion, attributed to their synergistic effects and exceptional electro chemical performance. In this work, a series of bimetallic-MOFs were synthesized utilizing same organic component i.e. benzene-1, 4-dicarboxylic acid (BDC) and changing the metal ions viz. Cu/Fe, Cu/Co, Cu/Ni and Cu/Zn, envisaging synergistic catalysing performance by various metal ions. All the synthesized MOFs were characterized, and the parameters were optimized. Under optimal experimental conditions, among the various MOFs examined, Cu/Co-BDC MOF exhibited the highest specific capacitance of 1892 Fg−1 at a scan rate of 1 mVs−1 with the energy density of 95.78 Whkg−1 and power density of 1915 Wkg−1. This material displayed exceptional supercapacitance performance, characterized by a superior capacitive retention of 85.5% even after 5000 cycles. These finding highlight its potential suitability for super capacitor applications.

A review of synthesis strategies for nickel cobaltite-based composites in supercapacitor applications

Supercapacitors (SCs), known for their exceptional power and reasonably high energy densities, long lifespan, and lower production costs, have emerged as an ideal solution to meet the growing demand for various energy storage applications. The characteristics of supercapacitors are greatly influenced utilizing the choice of electrode materials, developing novel electrode materials a focal point for extensive research in the field of high-performance supercapacitors. In recent years, NiCo2O4 has garnered increasing attention as a supercapacitor electrode material owing to its notable edges, including high theoretical capacity, low cost, abundant availability, and ease of synthesizing. However, the performance of NiCo2O4 is hindered by its low electrical conductivity and limited surface area, leading to significant capacity deterioration. Therefore, it is imperative to systematically and comprehensively summarize the advancements in comprehending and adjusting NiCo2O4-based electrodes from multiple perspectives. The present review primarily focuses on the synthetic approaches employed to produce NiCo2O4 nanomaterials with diverse morphologies for their application in supercapacitors. This review article provides a comprehensive overview of the synthesis approaches utilized for developing nickel cobaltite-based composites tailored for supercapacitor applications. Various synthesis methods, including sol-gel, hydrothermal, and co-precipitation techniques, are discussed in detail, emphasizing the importance of optimizing synthesis parameters to enhance the electrochemical performance of the composites. The potential applications of nickel cobaltite-based composites in supercapacitors are explored, highlighting their promising prospects in energy storage technologies. Future research directions in this field are also discussed.

Integrated free-standing WS2 3D-printed carbon supercapacitor with solid state electrolyte

ABSTRACT There is a huge need for energy storage devices due to the depletion of natural gas and the increasing requirement for portable electronic gadgets. Fused deposition modeling (FDM) 3D-printing has drawn tremendous interest for the fabrication of batteries and supercapacitors (SCs) due to its tabletop manufacturing technique, bespoke design, fast prototyping and user-friendly process. However, there are fewer available conductive filaments for FDM printing that are ideal from an energy storage standpoint. 2D transition metal dichalcogenide WS2 has been discovered to be a favourable material for electrochemical energy storage. As a result, in this work, we modified a carbon electrode that was 3D-printed by incorporating WS2 in order to enhance the capacitive performance of the SC electrode. The WS2-coated 3D-printed carbon electrode (WS2/3D-PCE) exhibits 2.8 times higher specific capacitance than the 3D-printed carbon electrode at 50 mV s−1. A solid-state symmetric supercapacitor (SS-SC) was fabricated with WS2/3D-PCE and polyvinyl alcohol (PVA)/Li2SO4 as gel electrolytes. Such modified 3D-PCE opens up the opportunities to design any custom-shaped electrode with tailored properties and pave a route for future research that will lead to more electrochemical devices for portable electronics.

Smart Control Strategy for Adaptive Management of Islanded Hybrid Microgrids

This research paper presents a smart power control approach specifically designed for an independent microgrid. The proposed hybrid system consists of various crucial components, including a PV array, super capacitor, DC bus, battery bank, and AC bus working together to generate and store electricity within the microgrid. To address the challenges arising from random fluctuations in ecological parameters and changes in load demand, a supervisory controller is developed to enhance the standalone hybrid microgrid. This allows for optimized power management within the micro grid. The Liebenberg Marquardt algorithm is used to retrieve the trained ANN machine. The two and three hidden layered ANN machines have 96% accuracy on an average, whereas the single-layer ANN machine have poor predictive ability. The proposed model is implemented and analysed using MATLAB/Simulink. The observed results from the simulation experiments validate the effectiveness of integrating available resources in ensuring the resilience and reliability of microgrids.

Zinc Cobalt Sulfide/Reduced Graphene Oxide Nanocomposite for High‐Performance Asymmetric Supercapacitor: A Microwave‐Assisted Synthesis

In this work, the microwave‐assisted synthesis of ZnxCo1–xS/reduced graphene oxide (rGO) nanocomposite and the evaluation of its electrochemical properties for supercapacitor (SC) application are dealt with. The synergistic effect between ZnxCo1–xS and rGO along with the conducting network provided by rGO facilitates the conducive movement of ions and enhances the electrochemical performance of the nanocomposite. The stoichiometric ratio of Zn:Co:rGO plays a crucial role in the SC behavior of the material. In three electrode systems, a material shows a high specific capacitance of 1094 F g−1 at current density 1 A g−1. The material stores charge both diffusively as well as capacitively. An asymmetric SC with acetylene black as the negative electrode and ZnxCo1–xS/rGO as the positive electrode has a stable potential window 0–1.6 V. For the fabrication of the electrodes, Ni foam is used as the current collector. The energy density and power density of the SC are found to be 32.71 and 431.95 W kg−1, respectively. The Coulombic efficiency of the SC is found to be 107% while its capacitance retention is 86% after 10 000 galvanostatic charge–discharge cycles. The energy and power density of the SC are comparatively higher than many recently reported literature. The material exhibits superior electrochemical stability and reversibility and can be a suitable electrode material for SCs.

Self-charging hybrid energy devices collaborated with enzymatic biofuel cells and supercapacitors

Enzymatic biofuel cells (EBFCs) are promising as a biocompatible power source for implantable and wearable devices, converting chemical energy of body fluids into electricity. However, they have intrinsic limitations, such as low power density and requirement for continuous fuel supply. To overcome the difficulties, hybrid energy devices (HEDs) that are combinative device of supercapacitor (SC) and EBFC are suggested in this study. They consist of anode and cathode including (i) enzymes reacting with respective fuels and (ii) mediators promoting transfer and storage of electrons. As EBFCs, HEDs exhibit exceptional fuel reactivity, achieving 0.91 and 0.51 mA/cm2 in glucose oxidation reaction and oxygen reduction reaction, while they play as SCs with excellent power and specific storage capacitance of 0.93 mW/cm2 and 307 mF/cm2. Moreover, HEDs show self-charging property that is uniquely observed in devices operated by the collaboration of enzyme and mediator. By this benefit, their open circuit voltage is well preserved in absent of fuels, while they can discharge even without supply of fuel. These features are obvious evidence that HEDs can be considered as advanced power sources for implantable and wearable devices.

Nano Metal–Organic Frameworks as Advanced Electrode Materials in Electrochemical Energy Storage

AbstractNano metal–organic frameworks as an attractive new class of porous materials, are synthesized via metal ions and organic ligands. With their desirable properties of abundant pores, high specific surface areas, fully exposed active sites and controllable structures, nano MOFs are acknowledged to be one of the most vital materials in electrochemical energy storages. However, in their practical applications, nano MOFs are still confronted with various difficulties and challenges because of their low conductivity, poor stability, and other disadvantages. The selection and development of MOF composites, MOF–derived materials and modified MOFs might be beneficial to use as better electrode materials to greatly improve the electrochemical properties of energy storage devices. This paper mainly focuses on the recent developments of nano MOFs as prospective materials in electrochemical energy storage applications, including lithium–ion batteries (LIB), lithium–sulfur batteries (LSB), zinc–ion batteries (ZIB), and supercapacitors (SCs). Finally, the challenges faced by these kinds of energy storage devices are proposed, along with the current directions and prospect.

Green one-pot synthesis of spongy hierarchical porous carbon with interconnected channels towards high-performance supercapacitors

Green and convenient construction of three-dimensional (3D) hierarchical porous carbon for supercapacitors (SCs) has drawn widespread attention due to their effective ion adsorption and transport capabilities. In this study, sucrose-derived spongy hierarchical porous carbon materials were successfully prepared using a one-step carbonization process with sodium chloride and sodium bicarbonate acting as collaborative pore-forming agents. The optimal carbon material exhibits a distinct 3D spongy structure with interconnected channels, high specific surface area, and proper pore size distribution. Consequently, it displays a specific capacitance of 263.5 F g−1 at 0.5 A g−1 and could retain 221.9 F g−1 (84.21%) at 20 A g−1. Additionally, the as-fabricated device delivers a supreme energy density of 17.0 Wh kg−1 at 80 W kg−1 and possesses exceptional cycling stability of 94.36% after 20000 cycles. Through the combination of raw material carbonization properties and synergistic pore-making mechanisms, the present work provides an effective and eco-friendly approach for fabricating 3D spongy hierarchical porous carbon materials with interconnected channels for high-performance SCs.

State-of-charge estimation for supercapacitors based on salp swarm algorithm-optimized high and low degree cubature Kalman filters considering temperature uncertainty

The accurate estimation of state-of-charge (SOC) is crucial for the supercapacitor (SC) management system of electric vehicles. In this paper, a salp swarm algorithm (SSA)-optimized high and low degree cubature Kalman filters (CKFs) for SC SOC estimation is proposed. Firstly, the key parameters are identified for the Thevenin model by SSA under SC test data. Secondly, a temperature-varied model with temperature uncertainty is constructed by polynomial fitting. Thirdly, an adaptive rule based on SSA is designed to regulate the noise covariance matrix information in real time. Combining this rule and CKFs, SSA-based generalized high-degree CKF (SSA-GHCKF) and SSA-based low-degree CKF (SSA-CKF) are developed with the minimum prediction error as the objective. Finally, the effectiveness of improved CKFs is evaluated by the urban dynamometer driving schedule in varying temperatures. The simulation results show that the root mean square errors of SOC estimation by CKF, GHCKF, and SSA-CKF are kept within 1.4553 %, 1.2880 % and 1.2152 %, while for SSA-GHCKF, this metric is merely 1.1933 %. The proposed SSA-GHCKF enables superior accuracy and robustness for SOC estimation at extreme temperatures.

One‐Step Preparation Pitch‐Based Porous Carbon via Carbonization and Co‐Activation for High‐Performance Supercapacitors

AbstractHierarchical porous carbon (HPC) materials for supercapacitor (SC) application are synthesized via a one‐step carbonization and activation method, using a novel composite activating agent with synergistic activation effect from mesophase pitch (MP) as precursor. The prepared mesophase pitch‐based porous carbon (MPPC) exhibits an ultra‐high specific surface area (SSA) of 2955.0 m2 g−1, well‐controlled pore size distribution (PSD), and exceptional electrochemical performance. The specific capacitance of MPPC‐4 attains up to 338.1 F g−1 at 1 A g−1 and 250.1 F g−1 at 20 A g−1, demonstrating remarkable rate capability. Furthermore, the assembled symmetric SC achieves a high energy density of 29.83 Wh kg−1 at a power density of 999.93 W kg−1 and still maintains 6.56 Wh kg−1 at a high power density of 19.89 kW kg−1. Furthermore, the SC exhibits advantageous cyclic stability, as evidenced by its remarkable capacitance retention rate of 88.55 % even after 5000 cycles. The utilization of this novel composite activating agent in the synthesis of pitch‐derived porous carbon (PC) electrode materials is an exceptionally effective and inventive process.

Research on Energy Hierarchical Management and Optimal Control of Compound Power Electric Vehicle

In response to the challenges posed by the low energy utilization of single-power pure electric vehicles and the limited lifespan of power batteries, this study focuses on the development of a compound power system. This study constructs a composite power system, analyzes the coupling characteristics of multiple systems, and investigates the energy management and optimal control mechanisms. Firstly, a power transmission scheme is designed for a hybrid electric vehicle. Then, a multi-state model is established to assess the electric vehicle’s performance under complex working conditions and explore how these conditions impact system coupling. Next, load power is redistributed using the Haar wavelet theory. The super capacitor is employed to stabilize chaotic and transient components in the required power, with low-frequency components serving as input variables for the controller. Further, power distribution is determined through the application of fuzzy logic theory. Input parameters include the system’s power requirements, power battery status, and super capacitor state of charge. The result is the output of a composite power supply distribution factor. To fully exploit the composite power supply’s potential and optimize the overall system performance, a global optimization control strategy using the dynamic programming algorithm is explored. The optimization objective is to minimize power loss within the composite power system, and the optimal control is calculated through interpolation using the interp function. Finally, a comparative simulation experiment is conducted under UDDS cycle conditions. The results show that the composite power system improved the battery discharge efficiency and reduced the number of discharge cycles and discharge current of the power battery. Under the cyclic working condition of 1369 s, the state of charge of the power battery in the hybrid power system decreases from 0.9 to 0.69, representing a 12.5% increase compared to the single power system. The peak current of the power battery in the hybrid power system decreases by approximately 20 A compared with that in the single power system. Based on dynamic programming optimization, the state of charge of the power battery decreases from 0.9 to 0.724. Compared with that of the single power system, the power consumption of the proposed system increases by 25%, that of the hybrid power fuzzy control system increases by 14.2%, and that of the vehicle decreases by 14.7% after dynamic programming optimization. The multimode energy shunt relationship is solved through efficient and reasonable energy management and optimization strategies. The performance and advantages of the composite energy storage system are fully utilized. This approach provides a new idea for the energy storage scheme of new energy vehicles.

Designing hollow mesoporous carbon sphere for high-rate supercapacitor in water-in-salt electrolyte

The expansion of the operational voltage in supercapacitors (SCs) through the utilization of water-in-salt electrolytes (WISEs) has garnered considerable attention for achieving elevated energy density. However, the poor rate performance of assembled SCs persists due to the heightened viscosity of WISEs (e.g., 17.0 mol kg−1 NaClO4), so designing the porous structure of electrode materials to improve the rate performance of SC in WISEs has become a research focus. In this study, we present a straightforward approach to fabricate hierarchical porous carbon spheres, designing to expedite ion infilling and transport within WISE-based SCs. The hollow porous carbon is synthesized via one-step pyrolysis process, wherein the decomposition of inner colloid particles yields gases, while the outer resorcinol–formaldehyde resin carbonizes to form a spherical shell. In the WISE of 17.0 mol kg−1 NaClO4, the resulting symmetric SCs exhibit an operational voltage of 2.6 V and significantly improved rate capability with a capacitance retention of 47.7 % at 100 A g−1. Notably, the energy density can reach 31.0 Wh kg−1 at a power density of 2.4 kW kg−1. Even under high power density conditions of 120.0 kW kg−1, the energy density of 14.7 Wh kg−1 can remain. Additionally, the SC device manifests an impressive capacitance retention of 99.1 % after 20,000 cycles, showcasing exceptional cyclic stability. This research introduces a novel synthesis strategy for hierarchical porous carbon materials, enabling the development of high-rate SCs with both elevated energy density and power density.