Galvanostatic Charge-discharge Curves Research Articles

Synthesis and characterization of C@CdS core-shell structures for high-performance capacitors

The present study investigates the synthesis and characterization of carbon@cadium sulphide (C@CdS) core-shell nanostructures for their potential application in electrochemical double-layer (ECDL) capacitors. Two distinct synthesis methods, hydrothermal route and co-precipitation method, were employed to fabricate C@CdS materials, each resulting in unique morphology and growth mechanisms. Detailed microstructural analyses, including high-resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD), revealed nanosheets in co-precipitated sample (CCSP) and core-shell structures in hydrothermally synthesized sample (CCSA). Optical investigations using UV-Vis spectroscopy provided insights into the absorbance properties of the synthesized materials. Electrical characterization, including frequency response testing and impedance analysis, demonstrated distinct capacitive behaviours for CCSP and CCSA, highlighting their potential for use in energy storage applications. Electrical characterization, including frequency response testing, impedance analysis, and galvanostatic charge-discharge (GCD) curve analysis, demonstrated distinct capacitive behaviours for CCSP and CCSA, highlighting their potential for use in energy storage applications. The integration of optical, structural, and electrical analyses provides a comprehensive understanding of the synthesized C@CdS core-shell nanostructures, offering insights into their potential application for ECDL capacitor technology and other emerging energy storage applications. Further optimization of synthesis parameters and exploration of scalable production methods are suggested for future research endeavors.

Zn2+ doped Ni3(NO3)2(OH)4 nanoflower spheres for electrochemical applications

In this present work, Ni3(NO3)2(OH)4 doped with Zn2+ ions are prepared by a solvothermal method using Ni(NO3)2·6H2O, Zn(NO3)2·6H2O, C16H33(CH3)3NBr (CTAB) and C2H5OH as raw materials. Characterization methods such as X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) are used to analyze the materials. Cyclic voltammetry (CV) and galvanostatic charge–discharge curves (GCD) are employed to compare the electrochemical performance of materials with different doping amounts. The electrochemical test results show that doping with Zn2+ significantly enhances the poor electrical conductivity of Ni3(NO3)2(OH)4. Electrochemical tests reveal that the doping amount of 0.4 mmol has the best electrochemical performance with a mass-specific capacitance of 1832 F·g−1 at a current density of 1 A·g−1 in the three-electrode system which is much higher than that of undoping sample (771 F·g−1). Additionally, the assembled NiZn-0.4//AC asymmetric supercapacitor device (ASC) has an energy density of 61.9 Wh·kg−1 at a power density of 747.8 W·kg−1. The Coulombic efficiency retention of the ASC device remains at 98 % after 2000 galvanostatic charge–discharge circles, and the specific capacitance retention is 91 % of the initial value. The doping of Zn2+ provides a valuable approach for enhancing the conductivity and specific capacitance of nickel-based supercapacitor electrode materials.

Cobalt sulfide flower-like derived from metal organic frameworks on nickel foam as an electrode for fabrication of asymmetric supercapacitors

Metal–organic frameworks, as a kind of advanced nanoporous materials with metal centers and organic linkers, have been applied as promising electrode materials in energy storage devices. In this study, we are successfully prepared cobalt sulfide nanosheets (CoS) derived from the metal–organic framework on nickel foam (NF). The prepared electrodes are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, Brunauer–Emmett–Teller and Barrett-Joyner-Halenda and electrochemical methods like voltammetry, galvanostatic charge–discharge curve and electrochemical impedance spectroscopy. The CoS/NF electrode demonstrates a high specific capacity of 377.5 mA h g−1 (1359 C g−1) at the current density of 2 A g−1, considerable rate performance and excellent durability (89.4% after 4000 cycles). A hybrid supercapacitor is assembled using CoS/NF as the positive electrode and activated carbon as the negative electrode, it shows a high energy density of 57.4 W h kg−1 at a power density of 405.2 W kg−1. The electrochemical results suggest that the CoS nanosheet arrays would possess excellent potential for applications in energy storage devices.

A novel approach for facile synthesis of cost-optimal catalyst for high-performance lithium-air battery

We have developed a novel and efficient cathode for advanced lithium-air batteries by employing a new approach and facile strategy. In this method, we prepared core-shell structured ZIF-8@ZIF-67 crystals with epitaxial growth using a hydrothermal technique. By subjecting these crystals to carbonization at a temperature 200 °C higher than the degradation initiation temperature (i.e. 600 °C according to thermogravimetric results), we successfully obtained functionalized nanoporous hybrid carbon materials. These hybrid carbon materials consist of hierarchical nitrogen-doped carbon @ cobalt anchored/nitrogen doped carbon (NC@CNC), where the nitrogen-doped carbon (NC) serves as the core and the cobalt anchored/nitrogen doped carbon (CNC) forms the shell. It is worth noting that electrochemical characterization data strongly support the superior performance of this nanoporous hybrid carbon material. It combines the advantageous properties of individual mesopores of nitrogen-doped carbon and the catalytic activity of cobalt‑nitrogen doped carbon. In particular, the cathode material, i.e. NC@CNC, exhibits a remarkable specific capacitance of 10,000 mAh·g−1, as calculated from the galvanostatic charge-discharge curves obtained at a current density of 50 mA·g−1. This impressive performance highlights the potential of our developed material in enhancing the efficiency and overall performance of lithium-air batteries.

Rare Earth metal oxide nanoparticle-infused polymer nanocomposites for enhanced supercapacitor electrodes

The contemporary energy shortage has spurred scientists to explore other options. In this regard, there's significant interest in utilizing electrochemical energy sources for converting and storing energy. Here, a fresh endeavor involves utilizing a set of semiconducting rare earth Gd2O3/conducting polymers (CP) (CP= polypyrrole, polyindole) for energy storage purposes. The synthesis method involves the straightforward oxidative polymerization of either indole or pyrrole to produce Gd2O3/PIn or Gd2O3/PPy, respectively. The integrity of the garnets synthesized was verified through XRD, Raman, XPS, FESEM, and TEM analysis, ensuring their phase purity and morphology. The scanning electron microscopy (SEM) analysis reveals the particle morphology, with sizes ranging from 100 to 800 nanometers. FTIR and Raman spectroscopy further validate the integration of Gd2O3 into the conducting polymer matrix. XRD shows broad peaks for amorphous structures in Gd2O3/PPy and Gd2O3/PIn nanocomposites. To evaluate its performance in supercapacitors, cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and impedance spectroscopy (EIS) were employed using a three-electrode configuration. The rectangular CV curves indicate the pseudo-capacitance mechanism of the Gd2O3/CP nanocomposite-coated carbon fiber electrode in an H2SO4 electrolyte. Specific capacitance (SC) values for Gd2O3/PPy and Gd2O3/PIn binary nanocomposite electrodes are determined as 341.61 F/g and 305.56 F/g, respectively, from GCD curves. In hybrid energy systems, especially electric automobiles, the Gd2O3/PPy and Gd2O3/PIn nanocomposite-coated carbon fiber electrode has a potential of up to 1.8 V and short charging and discharging durations, implying fast-charging and extended lifespan. The easy oxidative polymerization process utilized to produce gadolinium oxide/conducting polymer nanocomposites for supercapacitors is the main breakthrough of this research.

Capacitive tendency concept alongside supervised machine-learning toward classifying electrochemical behavior of battery and pseudocapacitor materials

In recent decades, more than 100,000 scientific articles have been devoted to the development of electrode materials for supercapacitors and batteries. However, there is still intense debate surrounding the criteria for determining the electrochemical behavior involved in Faradaic reactions, as the issue is often complicated by the electrochemical signals produced by various electrode materials and their different physicochemical properties. The difficulty lies in the inability to determine which electrode type (battery vs. pseudocapacitor) these materials belong to via simple binary classification. To overcome this difficulty, we apply supervised machine learning for image classification to electrochemical shape analysis (over 5500 Cyclic Voltammetry curves and 2900 Galvanostatic Charge-Discharge curves), with the predicted confidence percentage reflecting the shape trend of the curve and thus defined as a manufacturer. It’s called “capacitive tendency”. This predictor not only transcends the limitations of human-based classification but also provides statistical trends regarding electrochemical behavior. Of note, and of particular importance to the electrochemical energy storage community, which publishes over a hundred articles per week, we have created an online tool to easily categorize their data.

Biomass-derived N, P-codoped templated biocarbon@2D-MoS2/polypyrrole based hybrids for U(VI) electrosorption

In this study, hierarchical mesoporous and N/P-codoped templated biocarbon was prepared from Bambusa vulgaris culms through pyrolysis under reducing conditions. The biocarbon was functionalized with 2D-MoS2 nanosheets via hydrothermal reaction and later different mol fractions of polypyrrole (PPy) were electrodeposited to boost the electrode conductivity. The resultant BBC/PPy composites were characterized comprehensively using XRD, FTIR, SEM-EDX and BET. BBC/PPy-3 deposited with PPy-3 (using 0.3 M pyrrole) exhibited superior electro-sorption performance due its enhanced specific resistance, Csp (140.4 F/g) and high specific surface area, Asp (128.77 m2/g). The heteroatoms doping into biocarbon brought the essential chelating capability and hydrophilicity. BBC/PPy-3 showed remarkable sorption capacity of 402.5 mg/g at optimized value of pH (4.5–5.0). The electrochemical impedance spectroscopic (EIS) data revealed that BBC/PPy-3 presented relatively small charge transfer resistance Rct (1.78 Ω cm2), minute electrolytic resistance, Rs (0.97 Ω cm2) and large double layer constant phase element, qdl (0.0357 S sn/ cm2). The galvanostatic charge discharge (GCD) curves showed all composites as stable supercapacitors. BBC/PPy composites proved themselves as competitive and selective materials for the economic removal of U(VI) from effluents containing low concentration of U(VI).

Modified 3D Graphene for Sensing and Electrochemical Capacitor Applications.

Less defective, nitrogen-doped 3-dimensional graphene (N3DG) and defect-rich, nitrogen-doped 3-dimensional graphene (N3DG-D) were made by the thermal CVD (Chemical Vapor Deposition) process via varying the carbon precursors and synthesis temperature. These modified 3D graphene materials were compared with pristine 3-dimensional graphene (P3DG), which has fewer defects and no nitrogen in its structure. The different types of graphene obtained were characterized for morphological, structural, and compositional assessment through Scanning Electron Microscopy (SEM), Raman Spectroscopy, and X-ray Photoelectron Spectroscopy (XPS) techniques. Electrodes were fabricated, and electrochemical characterizations were conducted to evaluate the suitability of the three types of graphene for heavy metal sensing (lead) and Electric Double-Layer Capacitor (EDLC) applications. Initially, the various electrodes were treated with a mixture of 2.5 mM Ruhex (Ru (NH3)6Cl3 and 25 mM KCl to confirm that all the electrodes underwent a reversible and diffusion-controlled electrochemical process. Defect-rich graphene (N3DG-D) revealed the highest current density, followed by pristine (P3DG) and less-defect graphene (N3DG). Further, the three types of graphene were subjected to a sensing test by square wave anodic stripping voltammetry (SWASV) for lead detection. The obtained preliminary results showed that the N3DG material provided a great lead-sensing capability, detecting as little as 1 µM of lead in a water solution. The suitability of the electrodes to be employed in an Electric Double-Layer Capacitor (EDLC) was also comparatively assessed. Electrochemical characterization using 1 M sodium sulfate electrolyte was conducted through cyclic voltammetry and galvanostatic charge-discharge studies. The voltammogram and the galvanostatic charge-discharge (GCD) curves of the three types of graphene confirmed their suitability to be used as EDLC. The N3DG electrode proved superior with a gravimetric capacitance of 6.1 mF/g, followed by P3DG and N3DG, exhibiting 1.74 mF/g and 0.32 mF/g, respectively, at a current density of 2 A/g.

Supercapacitor electrode based on graphene covalently functionalized with cross-linking inorganic-organic molecule

This work presents the fabrication of a supercapacitor electrode based on covalently cross‐linked graphene structure. It introduces a simple method to fabricate modified graphene oxides with an inorganic and organic cross-linked agent. The supercapacitive performance of this cross-linked graphene oxide structure (C-GO) is approved by conventional electrochemical procedures, such as cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy. The calculated specific capacitance amounts of 231 F/g and 240 F/g was achieved via CV and GCD curves at ѵ= 10 mVs−1 and I = 0.8 A g−1, respectively. This C-GO based-supercapacitor indicates a 9 % reduction in specific capacitance value after measurement of 3000 continuous cycles in the CV.

Elucidating the Lithium-Ion Storage Mechanism in Insertion-Available Hard Carbon with Abundant Closed Porosity: Toward a Practical Material for Batteries

Traditionally, standard lithium-ion batteries (LIBs) are composed of a positive electrode made of metal oxides and a negative electrode made of highly crystallized graphite materials. Graphite materials, with a theoretical capacity of 372 mAh g-1, are chosen as the negative electrode because lithium-ion storage in graphite materials involves lithium-ion intercalation/de-intercalation between graphitic interlayers, a characteristic of faradaic reactions. During galvanostatic charge/discharge (GCD), long plateau regions at low voltages (e.g., 0-0.1 V (vs. Li+/Li)) resulting from multi-staged ion intercalation/de-intercalation are achieved. The low voltage of this intercalation/de-intercalation reaction contributes to enhancing the nominal voltage of LIBs, leading to a higher energy density of the battery.On the other hand, sodium-ion batteries (SIBs) have been extensively researched over the past 10 years as alternative to LIBs to compensate for the gradual scarcity of lithium metal resources. Hard carbon (HC) materials, also known as amorphous non-graphitizable carbons, were introduced to be the negative electrode material for SIBs, since most HCs exhibit very similar electrochemical responses in sodium-ion storage as lithium-ion storage in graphite materials.However, when examining the application of HC materials in lithium-ion storage, it becomes apparent that the development has been significantly limited over the past 20 years. Recent research primarily focuses on biomass-derived HCs and heteroatom-doping on these carbons. This type of HC is abundant in heteroatoms (e.g., N, P, and S) inherited from the intrinsic properties of biomass precursors. While high capacities and excellent rate capabilities are claimed for these biomass-derived HCs, the electrochemical responses of lithium-ion storage in these HCs often exhibit capacitive reactions with a completely sloping region on their GCD curves. Consequently, the miscalculation of capacities can be induced by assessing reversible capacities beyond excessively high voltages (> 1.5 V), even reaching 3 V. The appropriate working voltage window for HCs should be lower than 1.5 V to match with the positive electrodes. Thus, if reevaluating these HCs in a normal voltage window, the obtained reversible capacities are relatively small, due to the deficiency of faradaic reactions signified by the plateau region at low voltages on GCD curves. Additionally, very low initial coulombic efficiencies are often obtained for these highly defected and heteroatom-doped HCs, attributed to the vigorous consumption of electrolyte during the SEI layer formation on their defective sites. As a result, in this work, we introduce a straightforward method to fabricate hard carbon microbeads with tunable microporous structures by carbonizing cross-linked phenolic-formaldehyde (PF) resin spheres, produced through microwave-assisted suspension polymerization. The ultimate goal is to transform HC into a practical battery material for the negative electrode in LIBs, which must possess several abilities similar to graphite (i.e., reversible faradaic reactions with an obvious plateau region at low voltages on GCD curves, low surface area to suppress SEI formation, and good cycling stability). Additionally, the lithium-ion storage mechanism in HCs with varying open/closed porosity is carefully elucidated. By probing the porosity of HC with multiple gas (N2, O2, and CO2) adsorptions, a solid correlation between porous properties and electrochemical responses has been successfully established. As displayed in Figure 1, the results indicate that carbon porosity can change with carbonization temperature. With increasing temperatures, open pores are initially transformed into closed pores, and ultimately, non-porous properties are detected. The electrochemical behaviors in these HCs with distinct porosity differ significantly as demonstrated by GCD curves in Figure 2.It has been found that ultra-micro closed pores (<0.7 nm) are capable of providing confined spaces for lithium ions to be inserted/extracted, characterized as faradaic reactions. Therefore, a plateau region at low voltages can be acquired, leading to additional reversible capacities. Unlike some reported methods, such as holding at a constant voltage, charging/discharging at a very small current density, or overcharging to negative voltage regions, these faradaic reactions are easily unlocked at a current density of 50 mA g-1 in a safe voltage window of 0-0.12 V. As a result, the optimized HC delivers a total reversible capacity of 550 mAh g-1 at 50 mA g-1 in the voltage range of 0-1.5 V. The excellent rate capability and cycling stability of optimized HC are also confirmed. Furthermore, by the post-treatment with hydrogen-assisted reduction, the performance is further enhanced, achieving a reversible capacity of 574 mAh g-1 and an initial coulombic efficiency of 75%. These breakthrough outcomes provide valuable insights for the rational design of hard carbon materials. The optimized hard carbon could be a promising candidate for replacing traditional graphite materials in next-generation LIBs. Figure 1

Evaluation of Supercapacitive Properties of a PPY/PANI Bilayer Electrodeposited onto Carbon-Graphite Electrodes Obtained from Spent Batteries

Recently, many efforts have been made to reuse spent batteries in response to the growing demand for sustainable materials production. In parallel, supercapacitors have attracted significant attention for their use in addressing some of the limitations of conventional capacitors and batteries. In this context, this paper describes the preparation, characterization, and supercapacitive performance evaluation of carbon-graphite (CG) electrodes obtained from spent zinc–carbon batteries and modified with polypyrrole (PPY) and polyaniline (PANI). The parameters of PPY and PANI electropolymerization were optimized. CG/PPY, CG/PANI, and CG/PPY/PANI electrodes were obtained to compare their electrochemical responses. Cyclic voltammetry (CV), galvanostatic charge–discharge curves (GCDC), and electrochemical impedance spectroscopy (EIS) were used to evaluate the pseudocapacitive properties of the CG/PPY/PANI-modified electrode. The CG/PPY/PANI electrode showed a specific capacitance of 3416 mF cm−2 in a current density of 2 mA cm−2 and a retention capacity of 76% after 850 GCDC cycles. Thus, CG/PPY/PANI electrodes are shown to be good candidates for use in the development of energy storage devices. In addition, reused CG electrodes from spent batteries have other advantages like low cost, facile construction, and environmental friendliness.

Waste-Wood-Isolated Cellulose-Based Activated Carbon Paper Electrodes with Graphene Nanoplatelets for Flexible Supercapacitors

Waste wood, which has a large amount of cellulose fibers, should be transformed into useful materials for addressing environmental and resource problems. Thus, this study analyzed the application of waste wood as supercapacitor electrode material. First, cellulose fibers were extracted from waste wood and mixed with different contents of graphene nanoplatelets (GnPs) in water. Using a facile filtration method, cellulose papers with GnPs were prepared and converted into carbon papers through carbonization and then to porous activated carbon papers containing GnPs (ACP−GnP) through chemical activation processes. For the morphology of ACP−GnP, activated carbon fibers with abundant pores were formed. The increase in the amount of GnPs attached to the fiber surfaces decreased the number of pores. The Brunauer–Emmett–Teller surface areas and specific capacitance of the ACP−GnP electrodes decreased with an increase in the GnP content. However, the galvanostatic charge–discharge curves of ACPs with higher GnP contents gradually changed into triangular and linear shapes, which are associated with the capacitive performance. For example, ACP with 15 wt% GnP had a low mass transfer resistance and high charge delivery of ions, resulting in the specific capacitance value of 267 Fg−1 owing to micropore and mesopore formation during the activation of carbon paper.

Dual-functional electrochromic supercapacitors with electrospun TiO2 ion storage layer

We have developed dual-functional electrochromic supercapacitors (ECSs) incorporating electrospun TiO2 nanofibers as an ion storage layer (ISL). The prepared ISL-ECSs exhibit excellent integrated electrochromic performances at low driving voltages due to high visible transparency and energy storage capabilities. This study describes direct electrospinning TiO2 on an FTO electrode and fabricating asymmetric electrochromic devices with viologen-based ion gel compositions. The electrospinning technique proved suitable for producing oxide nanostructures that facilitate efficient ion transport. The surface morphology of the fabricated nanoweb was analyzed using SEM and AFM images. The electrochromic performances were evaluated through cyclic voltammetry and spectroelectrochemical measurements, and charge storage properties were examined by galvanostatic charge–discharge curves. The optimized dual-functional devices demonstrated a large transmittance contrast of up to 87 %, high coloration efficiency of 175.7 cm2/C, areal capacitance of 20.53 mF/cm2, and good charging-discharging cyclic stability. Furthermore, the practical feasibility of the ISL-ECSs was demonstrated by evaluating their ability to serve as a power source for illuminating an LED lamp. The findings suggest the potential application of ISL-ECSs for dual-functional smart windows, in which the color intensity visualizes the real-time energy storage status.

Facile synthesis of SnO2/graphene and Bi–SnO2/graphene-based nanocomposites as electrode materials for energy storage devices

Graphene-based nanocomposites are widely investigated as cathode materials for energy storage device. Herein, tin oxide-modified graphene (SnO2/G) and bismuth-doped SnO2/G (Bi–SnO2/G) nanocomposites with nanorod-like morphology were synthesized by the combination of electrochemical and wet chemical methods. The as-prepared nanocomposites were characterized using Raman spectroscopy, X-ray diffraction, fourier-Transform spectroscopy, and scanning electronic microscopy. Further, electrochemical impedance spectroscopy (EIS), galvanostatic charge-discharge (GCD) curves, and cyclic voltammetry (CV) were utilized to assess the ultra-capacitor properties of SnO2/G and Bi–SnO2/G nanocomposites.The electrochemical performance of SnO2/G and Bi–SnO2/G nanocomposites demonstrated exceptional specific capacitance of 487 F/g and 174 F/g, respectively, at 5 mV/s compared to as-prepared pristine graphene (108 F/g) and SnO2 nanoparticles (117 F/g). While, the GCD study confirmed the cyclic stability of these electrodes. Overall, the SnO2/G and Bi–SnO2/G nanocomposites have shown good electrochemical properties in all assays.

Rice husk-derived sodium hydroxide activated hierarchical porous biochar as an efficient electrode material for supercapacitors

In this study, one-step pyrolysis technique and NaOH chemical activation method were used to synthesize hierarchical porous biochar from rice husk. The existence of carbonaceous structure in biochar samples was confirmed by X-ray diffraction, field-emission scanning electron microscopy, elemental mapping, Raman spectroscopy, Brunauer-Emmett-Teller surface area, and X-ray photoelectron spectroscopy analysis. Activation of NaOH in rice husk biochar (ARB) sample suggested seven-fold enhancement of BET specific surface area (307.42 m2 g−1) as compared to rice husk biochar (RB). The NaOH activation also provides the enhancement of specific capacitance in RB. The boosting of supercapacitors (SCs) performance of ARB was proved by a larger loop in cyclic voltammetry and triangular shape along with a longer discharge time in galvanostatic charge-discharge curves as compared to RB. The electrode revealed excellent cyclic stability up to 4000 cycles with 94% retention. Furthermore, electrochemical impedance spectroscopy and galvanostatic charge-discharge curves showed evidence of electrode stability. The mechanisms related NaOH activation and enhancement of supercapacitor performance were well explained. These results suggest that NaOH treated RB could be promising low-cost electrode material for SCs application.

Spherical LiMn0.7Fe0.3PO4/C Cathode Materials for Lithium-Ion Batteries

Lithium manganese iron phosphates (LiMnxFe1-xPO4) [1] are attractive as next-generation cathode materials for lithium-ion batteries because they are safer than conventional lithium transition metal oxides (e.g. LiCoO2) [2] and are Co- and Ni-free. However, due to their low electronic conductivity [3], they can deliver much lower electrochemical properties than theoretically expected one. Therefore, many researchers have focused on chemical composition, reducing primary particle size, and carbon coating. On the other hand, granulation of LiMnxFe1-xPO4 primary nanoparticles is effective in improving poor handling of LiMnxFe1-xPO4 primary nanoparticles during cathode slurry preparation. However, electrochemical properties of granulated LiMnxFe1-xPO4 have not been well studied in previous reports. In this study, the electrochemical properties of the spherical LiMn0.7Fe0.3PO4/C composed of primary nanoparticles are reported. Spherical LiMn0.7Fe0.3PO4/C was synthesized by hydrothermal method followed by granulation and carbon coating. The synthesized spherical LiMn0.7Fe0.3PO4/C was characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM). Electrochemical properties of spherical LiMn0.7Fe0.3PO4/C were examined using CR2032 coin-type cells. Fig. 1 (a) shows the SEM images of spherical LiMn0.7Fe0.3PO4/C. As shown in Fig. 1 (a), spherical particle 10 μm in diameter composed of homogeneously sized primary nanoparticles were observed. Fig. 1 (b) shows the galvanostatic charge-discharge curves for spherical LiMn0.7Fe0.3PO4/C at discharge current rates of 0.2, 1, 5, and 10 C in a voltage range of 1.5–4.5 V at 30 °C. Spherical LiMn0.7Fe0.3PO4/C delivered a 0.2 C discharge capacity of 153 mAh g−1. At the 10C rate, spherical LiMn0.7Fe0.3PO4/C also delivered a high discharge capacity of 137 mAh g−1, which was 89 % of the 0.2C discharge capacity. Detailed data of our study including blended cathode of LiNiaMnbCocO2 and spherical LiMn0.7Fe0.3PO4/C will be presented in the meeting.

Unveiling the potential of P3 phase in enhancing the electrochemical performance of a layered oxide cathode

Controlling the phase structure of layered oxide cathodes is considered an effective strategy to realize high-performance Na-ion batteries. Herein, we unveil the synthesis and electrochemical behavior of a hitherto unreported monophasic P3 structure in Na0.75Mn0.75Ni0.25O2 (NNM) calcined at 750 °C. The conversion of P3 to a P2-type single phase (at 850 °C) upon increasing the calcination temperature, with P2/P3 biphasic structures at intermediate temperatures, was confirmed by the Rietveld refinement of the x-ray diffraction (XRD) data. The monophasic P3 cathode showed a specific capacity of 190 mAh/g at 0.1 C and retained 90% of its initial capacity after 200 cycles at 1 C in the 1.5–4.2 V range. The galvanostatic charge-discharge (GCD) curves also showed a decrease in specific capacity with an increase in the P2 phase. The P3-dominant biphasic cathodes displayed superior rate performance, exhibiting capacities up to 97 mAh/g at 6 C, attributed to their smaller particle size and optimal P2/P3 phase fraction. Operando Synchrotron XRD data confirmed the suppression of P3→O′3 + O3 transformation in the biphasic cathode that was present in the monophasic P3 structure during charge-discharge cycling. The superior electrochemical performance and excellent structural stability of biphasic cathodes make them ideal for stationary and mobile storage applications.

Synergistic Effect of Nickel and Cobalt in Nanowire Array for High Energy Storage with Rapid Charge Transfer in Asymmetric Supercapacitor

AbstractWe introduce a unique asymmetric supercapacitor design that combines a vertically aligned Ni−Co alloy‐type nanowire (NiCoNW) array electrode with a graphene flakes (GFs) electrode. The sandwiching of these two electrodes enables the device to operate at a high working potential window of 2.0 V. The improved response of the device is attributed to the asymmetric design and a high charge transfer in the NiCoNWs compared with pure metals. The optimized presence of Co in the alloy increases the rate of hydroxide formation in an alkaline solution during the gas evolution reaction. The use of GFs to modify the graphite electrode (GFs@Graphite) provided a more stable response at high current densities. We obtain extremely stable cyclic voltammetry (CV) plots even at very high scan rates (500 V/s) and galvanostatic charge–discharge curves with longer charge–discharge times. The highest capacitance achieved for the assembled device (Asy‐NiCoNWs/GFs@Graphite) is 339 F/cm3 (volumetric) at a current density of 5.0 A/cm3. In addition, a remarkable cycling retention of ∼100 % is observed after 10000 continuous potential cycles.

Quasi 2D Ruddlesden–Popper perovskite thin film electrode for supercapacitor application: Role of diffusion and capacitive process in charge storage mechanism

Hybrid halide perovskites are the most widely explored materials in the photovoltaic field. Recently they have been investigated for energy storage applications owing to their unique conductivity. Most reports on supercapacitor applications of halide perovskites are based on Methyl ammonium lead iodide (MAPbI3) and Methyl ammonium lead bromide (MAPbBr3) compounds. These halides are prone to degradation owing to external environmental parameters. Hence, one must look for other stable alternative halides. In this scenario, materials that can yield significant results with better stability are Quasi 2D perovskites, which combine the properties of both 3D and 2D perovskites. We successfully synthesized and characterized 4-Fluorobenzylammine hydroiodide spacer cation-based quasi 2D perovskite in this study. A detailed study was carried out on the effect of the precursor concentration and annealing temperature on the morphology and vertical growth of quasi-2D perovskite. An in-depth analysis of these perovskites' graded, phase-segregated growth was performed. Furthermore, we prepared a composite electrode from a mixture of quasi-2D perovskite with acetylene carbon black to obtain better performance. Our results show a maximum specific capacitance of 8.67 F g−1 from Cyclic Voltammetry curves. Further from the Galvanostatic Charge Discharge (GCD) curves, we obtained a capacitance of 3.39 F g−1. It is the highest value obtained for perovskite thin-film based supercapacitor electrode. The material displayed a low charge transfer resistance indicating a better conducting property, and displayed energy and power density of 170 mWh kg−1 and 109 W kg−1, respectively. Further, the contribution of capacitance and diffusion limited process in the charge storage mechanism of these electrodes were quantified. The electrodes could retain 91% capacitance after working for 1000 cycles, emerging as potential energy storage material for the future.

The features of the solvothermal synthesis of SnSe nanosheets and nanoflowers for supercapacitor applications

In this article, orthorhombic SnSe nanoparticles (NPs) are prepared through hydrothermal method by using Olyelamine and Ethylene glycol solvent named as AN-(OA) and AN-(EG). The SEM and TEM images of the AN-(OA) and AN-(EG) NPs show sheet and flower-like shapes, respectively. The cyclic voltammograms (CV) and Galvanostatic charge/discharge (GCD) studies of AN-(OA) and AN-(EG) electrodes are investigated in 0.5 M of KOH electrolyte. The specific capacitance values calculated through CV curves are 443, 240, 172, 138, 118, 130 and 50 (F/g) of AN-(EG) electrode and 224, 116, 80, 62, 52, 31 and 20 (F/g) of AN-(OA) electrode at the scan rate of 10, 20, 30, 40, 50, 60 and 70 (mV/s), respectively. Further, the specific capacitance values calculated through GCD curves are 83, 66, 58 and 55 (F/g) of AN-(EG) electrode and 52, 33, 29 and 27 (F/g) of AN-(OA) electrode at the current density of 1, 2, 3 and 5 (A/g), respectively. The morphology plays a critical role in capacitive performance of NPs.