Electrode Materials For Capacitors Research Articles

Machine learning-based prediction of supercapacitor capacitance for MgCo2O4 electrodes.

Electrode materials are essential in the electrochemical process of storing charge in supercapacitors and have a significant impact on the cost and capacitive performance of the final product. Hence, it is imperative to make precise predictions regarding the capacitance of electrode materials in order to further the development of supercapacitors. MgCo2O4, with a theoretical capacitance of up to 3122 F g-1, holds immense research value as an electrode material. The objective of this study is to predict the capacitance of MgCo2O4 with high accuracy. This will be achieved by extracting numerous data from published papers and using some parameters as input features. The Recursive Feature Elimination (RFE) method was employed, using Random Forest (RF), Extreme Gradient Boosting (XGBoost) and Regression Tree (RT) as selectors to identify the optimal feature subset. Then, combining them with these three regression models to construct nine machine learning (ML) models. After performance evaluation and outlier analysis, the XGB-RFE-XGB model achieved R-squared (R²), root mean squared error (RMSE), and mean absolute error (MAE) of 0.95, 111.83 F g-1 and 68.25 F g-1, respectively, demonstrating its stability and reliability. Therefore, the XGB-RFE-XGB model can be used as a reliable predictive tool in subsequent experimental designs.

Unraveling the energy storage mechanism in graphene-based nonaqueous electrochemical capacitors by gap-enhanced Raman spectroscopy

Graphene has been extensively utilized as an electrode material for nonaqueous electrochemical capacitors. However, a comprehensive understanding of the charging mechanism and ion arrangement at the graphene/electrolyte interface remain elusive. Herein, a gap-enhanced Raman spectroscopic strategy is designed to characterize the dynamic interfacial process of graphene with an adjustable number of layers, which is based on synergistic enhancement of localized surface plasmons from shell-isolated nanoparticles and a metal substrate. By employing such a strategy combined with complementary characterization techniques, we study the potential-dependent configuration of adsorbed ions and capacitance curves for graphene based on the number of layers. As the number of layers increases, the properties of graphene transform from a metalloid nature to graphite-like behavior. The charging mechanism shifts from co-ion desorption in single-layer graphene to ion exchange domination in few-layer graphene. The increase in area specific capacitance from 64 to 145 µF cm–2 is attributed to the influence on ion packing, thereby impacting the electrochemical performance. Furthermore, the potential-dependent coordination structure of lithium bis(fluorosulfonyl) imide in tetraglyme ([Li(G4)][FSI]) at graphene/electrolyte interface is revealed. This work adds to the understanding of graphene interfaces with distinct properties, offering insights for optimization of electrochemical capacitors.

Growth of Atomic layer-deposited Monoclinic Molybdenum Dioxide Films Stabilized by Tin Oxide Doping for DRAM Capacitor Electrode Applications.

Dynamic random-access memory (DRAM) capacitor electrodes, exemplified by TiN, face performance limitations owing to their relatively low work functions in addition to the formation of a low-k interfacial layer caused by their insufficient chemical stability. With recent advances in device scaling, these issues have become increasingly problematic, prompting the exploration of alternative electrode materials to replace TiN. Molybdenum dioxide (MoO2) has emerged as a promising candidate for this application, outperforming TiN due to its low resistivity, high work function (>5 eV), and excellent chemical stability. Moreover, monoclinic MoO2 exhibits a distorted rutile structure, enabling the in situ growth of high-k rutile TiO2 on MoO2 at low deposition temperatures. However, MoO2 deposition poses challenges because of its metastable nature compared to the more stable molybdenum oxide (MoOx) phases, such as MoO3 and Mo4O11. In this work, we successfully fabricated Sn-doped MoOx (TMO) films by atomic layer deposition (ALD) at 300 °C. A stabilized monoclinic MoO2 phase was achieved using ALD by incorporating SnOx into MoOx on both SiO2 and TiN substrates. The ALD TMO process comprised MoOx and SnOx subcycles, and the MoOx:SnOx subcycle ratio was varied from 100:1 to 20:1. High growth rates ranging from 0.19 to 0.34 nm/cycle were achieved for ALD TMO with varying the MoOx:SnOx subcycle ratio from 20:1 to 100:0. After post-deposition annealing at 500 °C, polycrystalline TMO films were obtained with smooth surface morphology. ALD TMO exhibited excellent interface quality with ALD TiO2, possessing a negligible low-k interfacial layer. Moreover, a rutile TiO2 film with a high dielectric constant of 136 was successfully grown on a 20% Sn-TMO electrode. Overall, this study provides a strategy to stabilize metastable MoO2 films using ALD, and it demonstrates the superiority of ALD TMO as a promising DRAM capacitor electrode material.

Enhancing the Electrochemical Performances of Disordered Li1.23Ni0.3Nb0.3Fe0.16O0.85F0.15 Cathode Material for Lithium-Ion Batteries by LiNbOx Coating.

For the next generation of lithium-ion batteries (LIBs), it is primary to seek high capacity and long-lifetime electrode materials. Li-excess disordered rock-salt structure (DRS) cathodes have gained much attention due to their high specific capacity. However, Li-excess can lead to a decrease in the structural stability of an electrode material. A new Li-rich DRS oxyfluorides, Li1.23Ni0.3Nb0.3Fe0.16O0.85F0.15 (F0.15) with a series amounts of LiNbOx (LN) coating (0, 5, 10, and 15 wt % denoted as F0.15-LN0, F0.15-LN5, F0.15-LN10, and F0.15-LN15, respectively), are successfully synthesized and evaluated as cathode materials in LIBs. Among them, F0.15-LN10 exhibits the highest initial discharge specific capacity of 296.1 mAh g-1 (at a current density of 20 mA g-1) with the capacity retention rate of 14% higher than that of the uncoated F0.15 after 80 cycles. Even at 300 mA g-1, F0.15-LN10 still delivers the highest discharge specific capacity of 130 mAh g-1. After 20 cycles, the charge-transfer impedance of F0.15-LN10 remained the smallest. The characterizations indicate that LN coating reduces the surface polarization of the cathode materials, slows the interfacial side reactions between the electrolyte and the electrode, and speeds up the Li+ diffusion. These results demonstrate that LN coating is an effective strategy to improve the electrochemical performance.

Effect of Aggregation Structure on Capacitive Energy Storage in Conducting Polymer Films.

Conducting polymers (CPs), a significant class of electrochemical capacitor electrode materials, exhibit exceptional capacitive energy storage performance in aqueous electrolytes. Current research primarily concentrates on enhancing the electrical conductivity and capacitive performance of CPs via molecular design and structural control. However, the absence of a comprehensive understanding of the impact of molecular chain spatial order on ion/electron transport and capacitive performance impedes the development and optimization of advanced electrode materials. Here, a solvent treatment strategy is employed to modulate the molecular chain spatial order of PEDOT : PSS films. The results of electrochemical performance tests and Grazing Incidence Wide Angle X-ray Scattering (GIWAXS) show that Poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonic acid) (PEDOT : PSS) films with both face-on and edge-on orientations exhibit exceptional electronic conductivity and ion diffusion efficiency, with capacitive performance 1.33 times higher than that of PEDOT : PSS films with only edge-on orientation. Consequently, molecular chain orientations conducive to charge transport not only enhance inter-chain coupling, but also effectively reduce ion transport resistance, enabling efficient capacitive energy storage. This research provides novel insights for the design and development of higher performance CPs-based electrode materials.

Facile synthesis of MgO-carbon nanocomposites for advanced capacitive electrode materials

Facile synthesis of MgO-carbon nanocomposites for advanced capacitive electrode materials

Preparation of polyimide-based activated carbon fibers and their application as the electrode materials of electric double-layer capacitors

Preparation of polyimide-based activated carbon fibers and their application as the electrode materials of electric double-layer capacitors

Analysis of CNT and rGO Mediation for an Efficient Super-Capacitive Response in Cr-Doped Co3O4 Based Composites

The synthesis of novel and high capacitance electrode materials has attracted much attention over the last few decades to meet the needs of electrode materials in supercapacitors. Cobalt oxide, one of several vanadium oxides, has recently gained popularity due to its unique layered structure, phase transition, and applications in supercapacitors. Here, we present structural, morphological, and electrochemical analysis of Cr-doped Co3O4 nanostructures and their carbon nanotubes/reduced graphene oxide (CNT/rGO) based composites. Hydrothermal and solvothermal routes are followed to prepare the samples. The active material is developed via a polymer-based binder and is used as the electrode in a three-electrode electrochemical system. X-ray diffraction confirms the spinel-type cubic crystal structure, while the stoichiometric elemental contents are verified via an energy dispersive X-ray spectroscopy. Well-shaped layered growth of the nanocomposites is revealed by field emission scanning electron microscopy. The electrochemical analysis is performed using a 2 M KOH electrolyte solution and a three-electrode electrochemical setup. The pure and Cr-doped nanocomposite samples reveal a pseudo capacitive behavior in all samples. The systematic capacitive and resistive response of the samples has also been presented in this report. The aforementioned attributes make the synthesized specimen a potential candidate for an electrode material.

Hydrogen-Assisted Thermal Treatment of Electrode Materials for Electrochemical Double-Layer Capacitors.

The capacitance of electrode materials used in electrochemical double-layer capacitors (EDLCs) is currently limited by several factors, including inaccessible isolated micropores in high-surface area carbons, the finite density of states resulting in a quantum capacitance in series to Helmholtz double-layer capacitance, and the presence of surface impurities, such as functional groups and adsorbed species. To unlock the full potential of EDLC active materials and corresponding electrodes, several post-production treatments are commonly proposed to improve their capacitance and, thus, the energy density of the corresponding devices. In this work, we report a systematic study of the effect of a prototypical treatment, namely H2-assisted thermal treatment, on the chemical, structural, and thermal properties of activated carbon and corresponding electrodes. By combining multiple characterization techniques, we clarify the actual origins of the improvement of the performance (e.g., > +35% energy density for the investigated power densities in the 0.5-45 kW kg-1 range) of the EDLCs based on treated electrodes compared to the case based on the pristine electrodes. Contrary to previous works supporting a questionable graphitization of the activated carbon at temperatures <1000 °C, we found that a "surface graphitization" of the activated carbon, detected by spectroscopic analysis, is mainly associated with the desorption of surface contaminants. The elimination of surface impurities, including adsorbed species, improves the surface capacitance of the activated carbon (CsurfAC) by +37.1 and +36.3% at specific currents of 1 and 10 A g-1, respectively. Despite the presence of slight densification of the activated carbon upon the thermal treatment, the latter still improves the cell gravimetric capacitance normalized on the mass of the activated carbon only (CgAC), e.g., + 28% at 1 A g-1. Besides, our holistic approach identifies the change in the active material and binder contents as a concomitant cause of the increase of cell gravimetric capacitance (Cg), accounting for the mass of all of the electrode materials measured for treated electrodes compared to pristine ones. Overall, this study provides new insights into the relationship between the modifications of the electrode materials induced by H2-assisted thermal treatments and the performance of the resulting EDLCs.

Nanofeather ruthenium nitride electrodes for electrochemical capacitors.

Fast charging is a critical concern for the next generation of electrochemical energy storage devices, driving extensive research on new electrode materials for electrochemical capacitors and micro-supercapacitors. Here we introduce a significant advance in producing thick ruthenium nitride pseudocapacitive films fabricated using a sputter deposition method. These films deliver over 0.8 F cm-2 (~500 F cm-3) with a time constant below 6 s. By utilizing an original electrochemical oxidation process, the volumetric capacitance doubles (1,200 F cm-3) without sacrificing cycling stability. This enables an extended operating potential window up to 0.85 V versus Hg/HgO, resulting in a boost to 3.2 F cm-2 (3,200 F cm-3). Operando X-ray absorption spectroscopy and transmission electron microscopy analyses reveal novel insights into the electrochemical oxidation process. The charge storage mechanism takes advantage of the high electrical conductivity and the morphology of cubic ruthenium nitride and Ru phases in the feather-like core, leading to high electrical conductivity in combination with high capacity. Accordingly, we have developed an analysis that relates capacity to time constant as a means of identifying materials capable of retaining high capacity at high charge/discharge rates.

Borate-Functionalized Disiloxane as Effective Electrolyte Additive for 4.5 V LiNi0.8Co0.1Mn0.1O2/Graphite Batteries.

Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) is considered the most prominent cathode material to establish a practical high energy density of lithium-ion batteries (LIBs) for future electric vehicles. The energy density of LIBs is greatly determined by the capacity of electrode materials and the operating voltage of the cells. To further improve the cycle lifespan of NCM811 batteries to meet the requirement of driving range for the electric vehicle market, it is vital to design a novel electrolyte additive that can enhance the stability of the cathode/electrolyte interface at a wide range of voltage. Herein, a novel borate functionalized disiloxane compound, 1,1,1,3,3-pentamethyl-3-(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)propyl) disiloxane (PMBPDS), is synthesized as cathode electrolyte interphase (CEI) film-forming additive to improve the cycling performance of NCM811 batteries. Systematic studies reveal that PMBPDS can construct a stable CEI film on the NCM811 surface and efficiently scavenge hydrofluoric acid (HF). The PMBPDS-derived CEI prevents the dissolution of transmission metals in the NCM811 cathode and enhances the capacity retention of NCM811/graphite cells from 68.3 to 70.6% after 200 cycles at 1 C in the voltage window of 3-4.5 V. This work provides more understanding on designing the molecular structure of additive compounds for improving the electrochemical performance of LIBs.

Na2MnSiO4/C as hybrid capacitive deionization electrode material to enhance desalination performance

The utilization of Na2MnSiO4 as a Faraday electrode in hybrid capacitive deionization (HCDI) is investigated to achieve efficient desalination. The Na2MnSiO4/C (NMSO) materials were fabricated via a simple sol–gel method, in which the synthesis process was modulated by adjusting the volume ratio of ethanol to water. When maintaining the volume ratio of water to ethanol at 3:1, the resultant NMSO-3/1 exhibited expected salt adsorption capacity of 31.06 mg g−1 and salt adsorption rate of 20.43 mg g−1 min−1. This distinguished desalination performance was mainly attributed to its inherent multiple redox pairs, as well as the integration of ethanol, which enhanced both specific capacitance and hydrophilicity of the material. This study opens a new perspective for the development of highly efficient materials in HCDI.

Polyaniline packed activated carbon as pseudocapacitive negative electrodes

Hybrid supercapacitors (HSCs) are attracting more attentions due to their potential high power and energy density. To exploring high capacity negative electrode materials, especially the capacitive materials, is more critical for further enhancing the energy density of HSC in comparing with more reported advanced battery-type positive materials. For perfect combination of electrochemical double layer and pseudocapacitive capacitance in negative electrode, the method of evenly filling polyaniline on nanopores of activated carbon is developed herein with keeping large surface area, the suitable ion-diffusion structure of activated carbon and further obtaining rich surface redox-active sites. The polyaniline packed activated carbons exhibit high specific capacitance (437.9 F g−1 at 0.5 A g−1) in negative voltage window (0 to −1.0 V), superior rate performance (378.0 F g−1 at 30 A g−1), and excellent capacitance retention even at a high mass loading and a high current density (326.5 F g−1 at 10 mg cm−2 and 20 A g−1). Additionally, an aqueous HSC based on the polyaniline packed activated carbon negative electrode and Ni-Co-LDH positive electrode presents higher energy density of 44.6 Wh kg−1 at a power density of 377.1 W kg−1. The present study presents novel method and materials for developing high performance capacitive negative electrode materials.

DFT Study of Borophene/Graphene (B/G) Heterostructure Properties as Sodium-Ion Battery Anode

As an alternative to lithium-ion batteries, sodium-ion batteries are gaining more attention as a solution to issues including the high cost and restricted supply of lithium. Nonetheless, issues including low voltage, limited capacity, and low electrode material capacity need to be fixed for sodium-ion battery applications. The proposed borophene/graphene heterostructure anode material for sodium-ion batteries was studied using density functional theory (DFT) to ascertain its properties. The findings demonstrate that there is sufficient interlayer spacing in the borophene/graphene heterostructure to allow for Na-intercalation. The interspace heterostructure has the highest Na adsorption energy of -2.02 eV. As a result, its maximum energy specific capacity is around 969.65 mAh/g. The borophene/graphene heterostructure anode exhibits strong diffusivity of Na ions, as evidenced by the activation energy of Na ion mobility in the heterostructure being less than 0.2 eV.

Hierarchical Electrode Constructed by carbon-coated Metal-Organic Framework Derivatives Supported on two-dimensional Ti3C2 nanosheets for Hybrid Li-ion Capacitors

BackgroudMetal-organic frameworks (MOFs) (e.g., Co-MOF) had been a popular platform for synthesis electrode materials for lithium-ion capacitors (LICs) because of their high theoretical specific capacity and unique structural advantages. Recent researches have focused on the development of MOFs derivative-based composites with high specific surface area, high structural stability, and high electrical conductivity. Methods: Here a distinct Ti3C2/Co3O4@C heterostructure composite was prepared by a straightforward method via hydrogen bonding with carbon-coated Co-MOF derivative anchored on Mxene-Ti3C2 nanosheets. The carbon-coated hollow Co3O4 polyhedra could shorten Li+ diffusion paths, increase the specific surface area and mitigate structural changes during the Li+ storage process. Moreover, Ti3C2 sheets were acted as a conductive network, which could increase the Li+ transport rate and stability of the structure. SignificantServing as anode material, Ti3C2/Co3O4@C electrode showed a specific capacity of 1341 mAh/g at current density of 0.1 A/g, with 93% capacity maintenance at 2 A/g after 1000 cycles in the lithium-ion half cell. Furthermore, Ti3C2/Co3O4@C//AC LIC delivered a high energy of 106 Wh/kg at 7632 W/kg. The distinct heterostructure, straightforward, and excellent performance of the Ti3C2/Co3O4@C composite as anode could provide application prospects in LICs with high energy/power density.

Preparation of Electrodes with β-Nickel Hydroxide/CVD-Graphene/3D-Nickel Foam Composite Structures to Enhance the Capacitance Characteristics of Supercapacitors.

Supercapacitors have the characteristics of high power density, long cycle life, and fast charge and discharge rates, making them promising alternatives to traditional capacitors and batteries. The use of transition-metal compounds as electrode materials for supercapacitors has been a compelling research topic in recent years because their use can effectively enhance the electrical performance of supercapacitors. The current research on capacitor electrode materials can mainly be divided into the following three categories: carbon-based materials, metal oxides, and conductive polymers. Nickel hydroxide (Ni(OH)2) is a potential electrode material for use in supercapacitors. Depending on the preparation conditions, two crystal phases of nickel hydroxide, α and β, can be produced. When compared to α-NiOH, the structure of β-Ni(OH)2 does not experience ion intercalation. As a result, the carrier transmission rate of α-Ni(OH)2 is slower, and its specific capacitance value is smaller. Its carrier transport rate can be improved by adding conductive materials, such as graphene. β-Ni(OH)2 was chosen as an electrode material for a supercapacitor in this study. Homemade low-pressure chemical vapor deposition graphene (LPCVD-Graphene) conductive material was introduced to modify β-Ni(OH)2 in order to increase its carrier transport rate. The LPCVD method was used to grow high-quality graphene films on three-dimensional (3D) nickel foam substrates. Then, a hydrothermal synthesis method was used to grow β-Ni(OH)2 nanostructures on the 3D graphene/nickel foam substrate. In order to improve the electrical properties of the composite structure, a high-quality graphene layer was incorporated between the nickel hydroxide and the 3D nickel foam substrate. The effect of the conductive graphene layer on the growth of β-Ni(OH)2, as well as its electrical properties and electrochemical performance, was studied. When this β-Ni(OH)2/CVD-Graphene/3D-NF (nickel foam) material was used as the working electrodes of the supercapacitor under a current density of 1 A/g and 3 A/g, they exhibited a specific capacitance of 2015 F/g and 1218.9 F/g, respectively. This capacitance value is 2.62 times higher than that of the structure without modification with a graphene layer. The capacitance value remains at 99.2% even after 1000 consecutive charge and discharge cycles at a current density of 20 A/g. This value also improved compared to the structure without graphene layer modification (94.7%).

Construction of ultra-stable and high-performance sodium-ion hybrid capacitors via CoMoO4 nanorods anode

In recent years, researchers show great interest in electrode materials for sodium-ion hybrid capacitors (SIHCs) that combine the advantages of batteries and capacitors. And the high specific capacity transition metal oxides that can be used as anodes for SIHCs attract widespread attention. Herein, one-step facile hydrothermal synthesis of the CoMoO4 nanorods as the transition metal oxides are successfully obtained. Due to the well bear to the volume change, the SIHCs exhibit superior electrochemical performance and stability with CoMoO4 nanorods anode during charge and discharge. At a current density of 0.05 A g−1, with an expanded potential from 0 to 3.0 V, the specific capacitance and the high energy density of CoMoO4//AC are 37.2 F g−1 and 63.3 Wh kg−1, respectively. Meanwhile, the stability of the CoMoO4//AC in the long cycle is as expected. After 6000 cycles, the capacity retention of the CoMoO4//AC SIHC is 90% while the coulombic efficiency is always around 99%.

Effect of Sn addition on the low temperature shrinkage of Ni nanoparticles

In this study, in-situ formation of intermetallic compound (IMC) was proposed to reduce the sintering shrinkage mismatch between Ni electrode and dielectric material for multilayer ceramic capacitors (MLCCs). Tin (Sn) was selected as an alloying element and introduced in the form of SnCl2 into Ni nanopowder. The Sn precursor was decomposed at ∼450 °C and a cubic Ni3Sn intermetallic phase was formed at 500 °C, which was gradually transformed to a hexagonal Ni3Sn phase at 700 °C and thereafter thermally decomposed above 800 °C forming the Ni–Sn solid solution. The Sn addition shifted the shrinkage onset temperature of Ni electrode to a higher temperature by 300–400 °C and effectively retarded the low temperature densification through in-situ formation of Ni3Sn intermetallics by inhibiting the inter-diffusion between Ni nanoparticles. Furthermore, the sintered Sn added Ni (Ni–3Sn) electrode exhibited an electrical conductivity comparable to that of pure Ni electrode, demonstrating its suitability as an alternative electrode for MLCCs.

Facile Preparation of Petroleum Pitch-Based Activated Carbon with Open Macropore Walls for High Energy Density Supercapacitors

Electric double-layer capacitors have attracted considerable attention for energy storage because of their excellent power capability, high stability, and long cycle life. Activated carbon is the most widely employed electrode material for electric double-layer capacitors owing to its high specific surface area, hierarchical porous structure, and high electrical conductivity. However, to increase the energy density of the devices, new synthetic methods for enhancing their specific capacitances are required. We developed a facile preparation method for petroleum pitch-based activated carbon and investigated the optimal conditions to improve its electrochemical performance in terms of rate capability, specific capacitance, and cycle life. The obtained activated carbon exhibited a high specific capacitance (163.67 F/g at 0.1 A/g), which can be attributed to the efficient charge transport due to the micropores developed in the open macroporous walls of the carbon structure and the high electrical conductivity. Our approach provides an efficient strategy for synthesizing activated carbon with excellent properties. The results reveal a correlation between the physicochemical and electrochemical properties of activated carbon.

Self-supported heterojunction nanofibrous membranes for high-performance flexible asymmetric capacitors

Rational design of an electrode material with high flexibility and electrochemical performance is the key to wearable energy storage devices. Herein, a facile and productive needleless electrospinning method was introduced to prepare self-supported and flexible nanofibrous electrode materials for asymmetric capacitor. The MnO2 nanoclusters and ZIF67-derived Co3O4 nano-sheets were sequentially deposited on the surface of N, B-doped carbon nanofibers (hetero-junction MnO2/Co3O4/NB-PCNF). Attributing to the constructed multi-pathway for redox reactions on electrode, the specific capacitance of NB-PCNF and MnO2/Co3O4/NB-PCNF can reach up to 204.2F/g and 141.43F/g at a small current density of 0.1 A/g, respectively. In long-term cycling tests, the electrode materials exhibited excellent cycling stability and good rate capability. The electrodes were assembled with Potassium-ion hydrogel electrolyte to form a flexible asymmetric solid-state supercapacitor (FASS-SC). FASS-SC can reach a voltage window of 1.6 V. It provided 28.2 W h/kg at an energy density of 600 W/kg and a specific capacitance retention of 94.18 % after 10,000 cycles. The FASS-SC offers new research ideas for future flexible devices and wearable technologies.