Energy Density Of Supercapacitors Research Articles

Flower‐like NiCo/rGO effective nanocomposite electrode for high‐performance supercapacitors

Novel electrode materials with unique architectures are always favored to improve the capacity and energy density of supercapacitors. Herein, we have designed a composition of transition metal and reduced graphene oxide (rGO) as advanced electrode for enhanced‐performance supercapacitors. Particularly, a facial one‐pot hydrothermal approach was applied for in‐situ growth of NiCo/rGO composite. It displayed the best electrochemical performance attributing to the three‐dimensional flower‐like architecture in combination with conductive rGO. Among all the electrodes, NiCo/rGO exhibited impressive areal capacitance of 2565 mF/cm2 at a current density of 1 mA/cm2, and a high energy density of μWh/cm2 at a power density of 200 μW/cm2. The electrochemical impedance spectroscopy confirms feasible charge transfer kinetics at the interface with small internal resistance and rapid diffusion, resulting an improved electrochemical performance.

(Nanocarbons Division Poster Award, 1st Place) Nd2O3 Templated Carbon Nanostructures for Energy Storage

Increased energy consumption has triggered the development of various energy storage devices. Supercapacitors have gained attention as energy storage devices due to their high-power density and long cycle life. The energy density of supercapacitor can be increased by combining electric double layer capacitance (EDLC) and pseudocapacitance (PC). A hybrid material based on rare-earth metal oxide templated carbon will be presented that combines both EDLC and PC within the same material. Specifically, neodymium hydroxide (Nd(OH)3) reacted with acetylene and steam to form carbon coated Nd2O3. Both Nd(OH)3 nanorods and nanospheres were used to prepared templated carbon followed by partial or complete washing of metal oxide. The resulting carbon exhibit the surface area of 1245 m2/g. Asymmetric coin cell was constructed with capacitance of 180.5 F/g and energy density of 76.8 Wh/kg This work paves the door to develop novel hybrid supercapacitors.

Core-shell structured MgCo2O4@Ni(OH)2 nanorods as electrode materials for high-performance asymmetric supercapacitors

In the field of energy storage, supercapacitors have received extensive attention in recent years. However, achieving the expected electrochemical performance and energy density of supercapacitors is still a huge challenge. The design and synthesis of binder-free composite electrode with core–shell structure is an effective strategy to improve the electrochemical performance of supercapacitors. In this paper, a heterogeneous core–shell structured and binder-free electrode material MgCo2O4@Ni(OH)2 (MCO@NH) grown on nickel foam (NF) is prepared by a simple hydrothermal and oil bath method. The unique core–shell structure makes the MCO@NH have a large specific surface area, which provides abundant active sites for ion transport and storage, thereby improving the electrochemical performance. The MCO@NH/NF nanocomposite demonstrates a high specific capacitance (Cs) of 1583 F g−1 at 1 A/g. A solid-state asymmetric supercapacitor (ASC) assembled with MCO@NH/NF and active carbon (AC) exhibits excellent energy density (45 Wh kg−1 at 457.5 W kg−1) and outstanding capacitance (89.51 %) and coulombic efficiency (97.8 %) after 12,000 cycles, evidencing its good operation stability and potential practical applications. Therefore, the prepared core–shell MCO@NH/NF electrode can be a promising candidate for energy storage devices.

Free-standing snowflake-like Mn-doped ZnO@CoCo2O4 nanofilm boosting cycle stability and energy density of supercapacitor

CoCo2O4 is considered as one of the most promising electrode materials owing to its inherently electrochemical performance and low cost. Nevertheless, the further practical application of CoCo2O4 as high-performance electrode material is hindered by its weak cycle stability. Herein, a free-standing snowflake-like Mn-doped ZnO@CoCo2O4 (MZCC) nanofilm is synthesized via hydrothermal method. The unique snowflake structure of this nanofilm composite exhibits obviously large specific surface area, thus promoting the redox reaction of the electrode material. The specific capacitance of the MZCC attains 1245F g−1 at 0.5 A/g. Furthermore, the assembled supercapacitor device with the MZCC and active carbon shows an energy density of 25.7 Wh kg−1 at a power density of 400 W kg−1. The device also demonstrated intriguingly outstanding cyclic stability, maintaining its original specific capacitance of 80.1 % after 3000 cycles at 2 A/g. This study delivers an effective method to construct high-performance free-standing metal oxide nanofilm electrodes for advanced supercapacitors.

Boosting the Electrical Transfer by Molybdenum Doping for Robust and Flexible NiSe-Based Supercapacitor.

NiSe is a promising electrode material for enhancing the energy density of supercapacitors, but it faces challenges such as sensitivity to electrolyte anions, limited specific capacity, and unstable cycling. This study employs a strategy of metal atom doping to address these issues. Through a hydrothermal reaction, Mo-doped NiSe demonstrates significant improvement in electrochemical performance, exhibiting high capacity (799.90Cg-1), splendid rate performance, and excellent cyclic stability (90% capacity retention). The introduction of Mo induces charge redistribution in NiSe, leading to a reduction in the band gap. Theoretical calculation reveals that Mo doping can effectively enhance the electrical conductivity and the adsorption energy of NiSe. A flexible printed hybrid Mo-doped NiSe-based supercapacitor is fabricated, demonstrating superior electrochemical performance (367.04mFcm-2) and the ability to power timers, LEDs, and toy fans. This research not only deepens the understanding of the electrochemical properties of metal-doped NiSe but also highlights its application potential in high-performance supercapacitors.

Can Aqueous Na2SO4-Based Neutral Electrolyte Increase Energy Density of Monolithic Wood Biochar Electrode Supercapacitor?

The performance of supercapacitors is significantly influenced by both the nature and the concentration of the electrolyte employed. This study investigates the impact of a neutral electrolyte on the electrochemical properties of the maple-derived monolithic wood biochar (MWB)–sodium sulfate (Na2SO4) supercapacitor. The goal is to determine if a neutral electrolyte, in this case Na2SO4, can increase the supercapacitor energy density compared to a previous study employing a KOH electrolyte. Starting from examining the ion sizes and conductivities of salt species in KOH and Na2SO4 electrolytes, the difference in voltage window, measured specific capacitance, and resistance are discussed. By switching the electrolyte from 4 M KOH to 0.5/1 M Na2SO4, the voltage stability window was extended from 0.8 V to 1.4 V. For 1 M Na2SO4, the supercapacitor attains a specific capacitance of 46 F/g at 5 mA/g, accompanied by an energy density of 12.5 Wh/kg and a maximum power density of 300 W/kg. The MWB electrode, derived from naturally abundant wood, when combined with the non-toxic Na2SO4 electrolyte, offers an environmentally friendly and cost-effective energy storage solution. With a prolonged lifetime and minimal maintenance requirements, MWB-Na2SO4 supercapacitors emerge as a promising choice for diverse applications.

A high potential (2.5 V) carbon fiber paper-based asymmetric supercapacitor with oxygen vacancies and hierarchical porous hollow structure

The inherent limited energy density in supercapacitors constitutes a substantial impediment to their widespread adoption and large-scale production. In this study, we have devised a novel cathodic electrode denoted as OV-TiO2-X@HPHCFP, featured with rich oxygen vacancies and its hierarchical porous hollow structure. The OV-TiO2-X@HPHCFP cathode manifests an impressive areal capacitance of 1608.2 mF cm−2 at the current density of 2 mA cm−2, coupled with a remarkable capacitance retention of 97.7 % after 10,000 charge–discharge cycles. Theoretical calculations corroborate that the presence of oxygen vacancies enhances the conductivity of the electrode, facilitating expedited charge transfer kinetics. Furthermore, the electrode integrated into a double electrolyte flexible supercapacitor configuration, denoted as OV-TiO2-X@HPHCFP//PVA-Na2SO4/PVA-LiCl//OV-MoO3-Y@CFP, operated at an effective potential of 2.5 V, can yield an energy density of 1.96 × 10−1 mWh cm−2 at a power density of 1.25 mW cm−2. This investigation thereby delineates a promising strategy for the development of supercapacitors that can attain elevated operational potentials with concomitant enhancements in energy density.

A High Voltage Symmetric Supercapacitor Comprising Concentrated NaCl: PVA Electrolyte and Partially Reduced Graphene Oxide Electrodes

AbstractStrategies to improve energy density in supercapacitors are mainly based on utilizing electrodes providing larger effective surfaces and electrolytes allowing op eration in wider voltage windows. Here, a water‐based, binder‐free, environmentally friendly, high voltage, and quasi‐solid‐state symmetric supercapacitor is presented comprising partially reduced graphene oxide active electrodes and concentrated NaCl: polyvinyl alcohol gel electrolyte. It is shown that the ionic diffusion through the electrode‐electrolyte interface is augmented by the partial reduction of the graphene oxide electrodes up to an optimum level. The safe operation voltage window is 4 V; the high field endurance is attributed to the ion‐saturated hydrogel electrolyte used. At a scan rate of 25 mV/s, the provided capacitance and stored energy are 0.1 F.cm−2 and 5.6 e−5 W.h.cm−2, respectively. The optimized device retains ~90 % of its initial capacitance after 1000 charge‐discharge cycles; no meaningful sign of degradation is detected afterwards up to the 2000 cycles examined. These results place further emphasis on the potentials of the gel polymer electrolytes in the fabrication of environmentally friendly supercapacitors. Our findings are anticipated to accelerate improvements in the properties of the graphene‐based electrodes, particularly in conjunction with the proposed electrolyte.

The effect of thermoelectric augmentation dramatically increased the specific capacity for electrochemical energy storage

Conventional methods to enhance the performance of electrode materials include morphological modification and defect engineering, but the limited number of active sites for the electrode remains a huge obstacle to achieving high-performance supercapacitors. In this work, we proposed a strategy to improve the electrode performance under the condition of limited active sites through the thermoelectric effect, and designed thermoelectric electrodes of the p-type Fe0.3Co0.7Sb3 cathode and the n-type Cu0.3Ag1.7Se anode for supercapacitors, respectively. In particular, the charge carriers generated by the thermoelectric effect accelerate the electrochemical reaction process at the interface between the thermoelectric electrode and the electrolyte under the temperature difference (ΔT) condition, thus increasing the specific capacity of the electrode. The p-Type Fe0.3Co0.7Sb3 cathode and the n-Type Cu0.3Ag1.7Se anode exhibit a 150% and 208% increase in the specific capacity, respectively. Furthermore, electrodes with different conduction types and various thermoelectric properties, such as n/p-type bismuth telluride and n/p-type half-Heusler thermoelectric materials are also studied, confirming the universality of the above phenomenon in thermoelectric electrodes. This work provides a universal route for the thermoelectric effect to promote the energy density of supercapacitors used in high temperature difference environments.

Hierarchical heterostructures of MXene and mesoporous hollow carbon sphere for improved ion accessibility and rate performance

The development of electrode materials with a hierarchically porous structure and good electrical connection is key to improving the charging-discharging rate and energy density of supercapacitors. However, the restacking issue of two-dimensional nanomaterials, such as MXene, seriously hinders the diffusion of electrolyte ions. Different from the extensively used sacrificing template method, a hierarchical heterostructure of electrically conducting mesoporous hollow carbon spheres (MHCS) and MXene composite electrode is designed and achieved through simple vacuum filtration without further template removing procedures. This direct preparation strategy not only effectively improves the specific surface area of the electrode but also enhances the abundant surface pores and good conductivity of MHCS, improving the penetration of the electrolyte solution and shortening the ion transport path, leading to a pronounced improvement in specific capacitance and rate performance of the electrodes. Additionally, the influence of sheath thickness of MHCSs on ion transfer rate is deeply discussed. The introduction of carbon nanotubes (CNTs) further improves conductivity and stability while maintaining good flexibility. Consequently, the MXene/MHCS/CNT film delivers a high specific capacitance (395F g−1 at 2 mV s−1), outstanding rate performance (70.9 % at 1000 mV s−1), and excellent cycling stability (98.3 % capacity retention after 10,000 cycles). Furthermore, the assembled symmetric supercapacitor provides a maximum energy density of 14.48 Wh kg−1. This work provides a quick and effective approach for constructing high performance 3D MXene architectures for fast ion transfer electrodes.

Design and Fabrication of Island‐Like CoNi2S4@NiCo‐LDH/Biomass Carbon Heterostructure as Advanced Electrodes for High‐Performance Hybrid Supercapacitors

AbstractThe utilization of heterostructured electrodes offers an effective approach to boost the energy density of supercapacitors without sacrificing their power density. However, the adoption of such materials is frequently impeded by sluggish reaction kinetics. Herein, an island‐like CoNi2S4@NiCo‐layered double hydroxide/biomass carbon (CoNi2S4@NiCo‐LDH/BC) heterostructure is synthesized by embedding CoNi2S4 in the interlayer of NiCo‐LDH nanosheets on BC through a partial in situ sulfidation process. Theoretical and experimental analyses indicate that this unique structural configuration lowers transport barriers and enhances ion adsorption capacity, leading to a significant improvement in ion/electron reaction kinetics. In addition, the embedded structural design effectively alleviates the significant volume expansion during charge–discharge process, while the robust BC framework prevents electrode degradation, thereby enhancing stability. These advantages enable the developed electrode material to achieve a high specific capacity (1655.75 C g−1 at 1 A g−1) and an extended cycle life (86.82% capacity retention after 10 000 cycles). Significantly, the assembled hybrid supercapacitor CoNi2S4@NiCo‐LDH/BC// activated carbon demonstrates a remarkable energy density of 95.57 Wh kg−1 at 866.61 W kg−1 and exceptional cycling stability, maintaining 95.16% capacity after 10 000 cycles. This research offers an effective strategy to promote ion/charge transfer and adsorption capacity of heterostructure and provides a new approach to the development of advanced supercapacitor electrodes.

Significantly improved electrical conductivity and cycling stability of manganese dioxide by poly (3,4-ethylene-dioxythiophene) coating

Abstract Manganese dioxide (MnO2) is widely acknowledged as a prospective pseudocapacitive material aimed at alleviating the issue of low energy density in supercapacitors. Nevertheless, hampered by its intrinsic low conductivity and poor structural stability, MnO2-based energy storage materials often exhibit lower practical capacity in practical applications. During this investigation, the synthesis of MnO2@PEDOT (poly(3,4-ethylenedioxythiophene)) composite materials involved an in-situ oxidative polymerization approach, whereby PEDOT nanowires were integrated onto the MnO2 nanoparticle surface. Notably, the internal configuration of the MnO2@PEDOT composite material demonstrated a high surface area morphology, while the externally entwined PEDOT nanowire layer further expanded the material’s specific surface area. As a result, the MnO2@PEDOT composite material demonstrated a specific capacitance reaching 214 F g-1, a 91% improvement compared to unmodified MnO2. Furthermore, the winding of PEDOT nanowires effectively suppressed the structural disintegration of MnO2. The MnO2@PEDOT composite material exhibited a remarkable improvement in cycling stability, maintaining 81% of its initial capacity after 5000 cycles. The electron-rich PEDOT not only improved the conductivity of the inner MnO2 through electron migration but also prevented MnO2 structural degradation by tightly enveloping it. The outcomes of our study propose a method for constructing MnO2 featuring a structurally stable configuration and a prolonged cycling lifespan, offering valuable insights for designing electrode materials with high cycling stability in supercapacitors.

The Mass-Balancing between Positive and Negative Electrodes for Optimizing Energy Density of Supercapacitors.

Supercapacitors (SCs) are some of the most promising energy storage devices, but their low energy density is one main weakness. Over the decades, superior electrode materials and suitable electrolytes have been widely developed to enhance the energy storage ability of SCs. Particularly, constructing asymmetric supercapacitors (ASCs) can extend their electrochemical stable voltage windows (ESVWs) and thus achieve high energy density. However, only full utilization of the electrochemical stable potential windows (ESPWs) of both positive and negative electrodes can endow the ASC devices with a maximum ESVW by using a suitable mass-ratio between two electrodes (the mass-balancing). Nevertheless, insufficient attention is directed to mass-balancing, and even numerous misunderstandings and misuses have appeared. Therefore, in this Perspective, we focus on the mass-balancing: summarize theoretic basis of the mass-balancing, derive relevant relation equations, analyze and discuss the change trends of the specific capacitance and energy density of ASCs with mass-ratios, and finally recommend some guidelines for the normative implementation of the mass-balancing. Especially, the issues related to pseudocapacitive materials, hybrid devices, and different open circuit potentials (OCPs) of the positive and negative electrodes in the mass-balancing are included and emphasized. These analyses and guidelines can be conducive to understanding and performing mass-balancing for developing high-performance SCs.

Enhancing power and energy densities of supercapacitors with slit porous carbon electrodes by playing with pore width and ion shapes

The energy and power performances of double-layer supercapacitors can be affected by pore size, the nature of the electrolyte, and electrode–electrolyte interaction. We performed molecular dynamics simulations of mixtures of ionic liquids confined into slit-shaped carbon electrodes with pores of 0.75 and 1.5nm under applied voltage to investigate the interplay of pore size, and ion shape to the performance of supercapacitor. Inside the pores of 1.5nm the ions are organized into two layers, and a single layer inside the pore of 0.75nm. The tetramethylammonium cations ([TMA]+) is steric hindered to fill the pores of 0.75nm that can be only filled by 1-ethyl-3-methyl-imidazolium cations ([EMIM]+) and bis(trifluoromethanesulfonyl)imide anions ([NTf2]−). The increase of [TMA][NTf2] in the mixtures results in small pores with a decreased density of ions or empty at the non-charged state of the electrode. Upon the application of voltage, these empty or partially filled pores have only the adsorption of counter ions, which are responsible for the best performance of mixtures with mole fraction of [TMA]+ equals to 0.25 and 0.75.

Enhancing Energy Storage Capacity of 3D Carbon Electrodes Using Soft Landing of Molecular Redox Mediators.

The incorporation of redox-active species into the electric double layer is a powerful strategy for enhancing the energy density of supercapacitors. Polyoxometalates (POM) are a class of stable, redox-active species with multielectron activity, which is often used to tailor the properties of electrochemical interfaces. Traditional synthetic methods often result in interfaces containing a mixture of POM anions, unreactive counter ions, and neutral species. This leads to degradation in electrochemical performance due to aggregation and increased interfacial resistance. Another significant challenge is achieving the uniform and stable anchoring of POM anions on substrates to ensure the long-term stability of the electrochemical interface. These challenges are addressed by developing a mass spectrometry-based subambient deposition strategy for the selective deposition of POM anions onto engineered 3D porous carbon electrodes. Furthermore, positively charged functional groups are introducedon the electrode surface for efficient trapping of POM anions. This approach enables the deposition of purified POM anions uniformly through the pores of the 3D porous carbon electrode, resulting in unprecedented increase in the energy storage capacity of the electrodes. The study highlights the critical role of well-defined electrochemical interfaces in energy storage applications and offers a powerful method to achieve this through selective ion deposition.

Armoring hydrophilic wood-structured ultrathick electrode with bimetallic nitride enables high energy-density supercapacitor

Thick electrodes can reduce the ratio of inactive constituents in a holistic energy storage system while improving energy and power densities. Unfortunately, traditional slurry-casting electrodes induce high-tortuous ionic diffusion routes that directly depress the capacitance with a thickening design. To overcome this, a novel 3D low-tortuosity, self-supporting, wood-structured ultrathick electrode (NiMoN@WC, a thickness of ∼1400 μm) with hierarchical porosity and artificial array-distributed small holes was constructed via anchoring bimetallic nitrides into the monolithic wood carbons. Accompanying the embedded NiMoN nanoclusters with well-designed geometric and electronic structure, the vertically low-tortuous channels, enlarged specific surface area and pore volume, superhydrophilic interface, and excellent charge conductivities, a superior capacitance of NiMoN@WC thick electrodes (∼5350 mF cm−2 and 184.5 F g−1) is achieved without the structural deformation. In especial, monolithic wood carbons with gradient porous network not only function as the high-flux matrices to ameliorate the NiMoN loading via cell wall engineering but also allow fully-exposed electroactive substance and efficient current collection, thereby deliver an acceptable rate capability over 75% retention even at a high sweep rate of 20 mA cm−2. Additionally, an asymmetric NiMoN@WC//WC supercapacitor with an available working voltage of 1.0–1.8 V is assembled to demonstrate a maximum energy density of ∼2.04 mWh cm−2 (17.4 Wh kg−1) at a power density of 1620 mW cm−2, along with a decent long-term lifespan over 10,000 charging-discharging cycles. As a guideline, the rational design of wood ultrathick electrode with nanostructured transition metal nitrides sketch a promising blueprint for alleviating global energy scarcity while expanding carbon-neutral technologies.

Synthesis, Fabrication, and Performance Evaluation of Nickel-Cobalt Sulfide Nanostructures for Enhancing Energy Density of Supercapacitors in Energy Storage Applications

Synthesis, Fabrication, and Performance Evaluation of Nickel-Cobalt Sulfide Nanostructures for Enhancing Energy Density of Supercapacitors in Energy Storage Applications

Facile Solid-State Chemical Synthesis of CoMoO4 Nanorods for High-Performance Supercapacitors.

The development of electrode materials with excellent performance serves as the key for researchers to enhance the energy density of supercapacitors. Cobalt molybdate (CoMoO4) nanomaterials have been regarded as one of the most prospective electrode materials for supercapacitors due to their high theoretical capacitance and excellent electrical conductivity. In this paper, three kinds of CoMoO4 nanorods were prepared directly via simple and environmentally friendly solid-phase chemical reactions with solid inorganic salts as raw materials. According to X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) test results, different reagents had certain effects on the size and morphology of CoMoO4, and these affected its electrochemical performance. In particular, the samples prepared with Co(NO3)2·6H2O as raw material took on a more uniform micromorphology, with a better crystallinity. Simultaneously, electrochemical test results showed that the samples synthesized with Co(NO3)2·6H2O presented relatively good electrical conductivity and a large specific capacitance (177 F g-1). This may be due to the nitrates reacting more slowly during the reaction and the crystals having difficulty aggregating during growth. Therefore, the structure of the prepared CoMoO4 nanomaterial was more uniform, and it was resistant to collapse during the charging and discharging process; thus, the capacitor presents the best performance.

Development of Supercapacitors with 3D Porous Structures

AbstractThe pursuit of supercapacitors with simultaneous high power and energy densities has led to extensive research and successful outcomes through the integration of three‐dimensional (3D) electrodes, encompassing both 3D active materials and 3D porous current collectors. This mini review provides a summary of recent developments in supercapacitors featuring 3D structures. The incorporation of both 3D active materials and 3D current collectors proves effective in enhancing the mass loading of active materials without compromising their specific capacitance. The presence of pores in 3D porous current collectors contributes to additional double‐layer capacitance by offering a large surface area. Moreover, 3D porous transition metal current collectors can provide both double‐layer and faradic capacitances through the in‐situ surface oxidation mechanism. Beyond materials and geometries, this review also discusses synthesis strategies for electrodes, offering insights into the process‐structure‐property relationship crucial for supercapacitors. By combining 3D active materials with 3D current collectors, the energy density of supercapacitors could be substantially improved.

Construction of MOFs derived porous carbon based core–shell hetero-structure electrode for superior asymmetric supercapacitor

The design of electrode materials with high performance is very important to improve the energy density of supercapacitors (SCs). The combination of electrical double layer capacitor and pseudo-capacitive materials can significantly improve the electrochemical performance of material, but reasonable structural design can inhibit the slow Faraday dynamic mismatch caused by different storage mechanisms. In this study, NiCoB nanosheets were grown on the surface of cobalt metal-organic frameworks (Co-MOF) derived porous carbon (Co-C) by chemical precipitation method to form a core–shell hetero-structure Co-C@NiCoB electrode. The Co-C@NiCoB electrode has the specific capacitance of 2990 F g−1 at 1 A g−1, which is significantly higher than that of Co-C (416 F g−1) and NiCoB (1052 F g−1). In order to further increase the energy density of the device, the carbon nano-sheets with cactus shape as cathode were obtained by calcination of Co-MOF (CNS). The asymmetric SCs with CNS as cathode and Co-C@NiCoB as anode have a high energy density of 66.03 Wh kg−1 at the power density of 763.35 W kg−1 and exceptional cycling life with capacitance retention of 92.1 % over 10,000 cycles.