Specific Capacity Research Articles

Facile synthesis and first principles calculations of Li-MoS2/rGO nanocomposite for high-performance supercapacitor applications

Two-dimensional (2D) nanostructured materials such as graphene oxide nanosheets and molybdenum disulfide (MoS2) are potential candidates for electrochemical energy storage applications. The layered structure of MoS2 makes it a promising active electrode material for supercapacitors. Lithium (Li) interacted with MoS2/reduced graphene oxide (Li-MoS2/rGO) nanocomposite has been synthesized in two steps using a sonochemical dispersion method, and a one-pot hydrothermal method resulting in few-layered MoS2/rGO nanosheets of 2D heterointerfaces. The Li-MoS2/rGO nanocomposite exhibits a high specific capacitance of 173.3 F g−1 at a current density of 1 A g−1. Furthermore, an asymmetric supercapacitor device fabricated with Li-MoS2/rGO achieves a good energy density of 10.6 Wh kg−1 at a power density of 686.3 W kg−1 and outstanding cycling stability with 81.2 % capacity retention over 10,000 cycles. The dispersion of 2D-MoS2 in water is due to the strong electrostatic interface. The structural and electronic properties are theoretically calculated for pristine and Li-interacted MoS2/rGO heterostructure using density functional theory. A comparison of the density of states plots of the two heterostructures and the difference charge density plot of Li-MoS2/rGO heterostructure clearly brings out the importance of the presence of Li. A value of 64 μF cm−2 for the quantum capacitance for pristine MoS2/graphene heterostructure increases to a value 99 μF cm−2 corroborating the experimental observations and we assign this change to the transfer of charge from the Li atom to the outer S atoms in the MoS2/graphene heterostructure. This comprehensive approach, combining experimental synthesis with computational modelling, significantly advances the development and optimization of high-performance supercapacitor materials in the energy storage field. The Li-MoS2/rGO nanocomposite has excellent electrochemical specific capacitance and long-term cyclic stability and has been effectively used for supercapacitor applications with high electrochemical performance.

Soft-templating of biomass derivatives into edge-N doped 3D-interconnected hierarchical porous carbon for multi-scenario supercapacitive energy storage

Rational design of the pore structure for carbon materials is of great significance for solving the low specific capacitance and poor rate capability of supercapacitors. A novel soft-templating strategy is proposed by using biomass-derived sodium lignosulphonate as a carbon precursor and sublimable hexamethylenetetramine as a soft template. The hexamethylenetetramine nanoparticles are formed in the confined spaces of the precursor, and then these templates sublime to leave mesopores after the lignosulfonate transformed from linear structure to bulk structure by thermostabilization treatment. A high nitrogen content of 40 wt% in hexamethylenetetramine is also beneficial for the subsequent in-situ N-doping. The as-obtained nitrogen-doped hierarchical porous carbon microspheres possess a high specific surface area of 1416 m2 g−1 with an N-doping content of 4.32 % (86.26 % edge-N). In a two-electrode system, the soft-templating carbon exhibits a decent specific capacitance of 234 F g−1 at 0.1 A g−1, an excellent rate capability of 62.4 % at 50 A g−1, and a high energy density of 8.1 Wh kg−1 at 15.0 kW kg−1 in 6 M KOH aqueous electrolyte. Moreover, advanced additive manufacturing technology of direct ink writing was applied to construct a quasi-solid-state in-plane interdigital microsupercapacitor by using the soft-templating carbon, and it presents a superior areal/volumetric capacitance, rate performance, mechanical stability, and flexibility with PVA/H2SO4 gel electrolyte. This work broadens the pore structure engineering methodology by novel soft-templating biocarbon for multi-functional and multi-scenario energy storage systems.

High-performance α-Fe2O3 nano cubes as anode for supercapacitors

Abundant availability, high theoretical specific capacitance and low cost of transition metal oxides such as iron oxides, make them attractive as electrode materials for energy storage. In order to achieve improved performance, high conductivity, shorter ion-diffusion path, and faster ion accessibility, rational design of morphology of electrode material is highly desirable. We have successfully synthesized mesoporous α-Fe2O3 nanocubes to achieve high specific capacitance and better retention. The as-prepared and annealed α-Fe2O3 nanocubes show high reversible redox activity along with good thermodynamic stability. These nanostructure give rise to high specific capacitance and ~90 % of the capacitance can be retained even after 1000 redox cycles, suggesting good cyclic stability. The electrochemical performance of mesoporous α-Fe2O3 nanocubes is attributed to the morphological features, which results in efficient K+ ion transport into the pores. A two electrode α-Fe2O3//NiO device is fabricated, which shows excellent power and energy density of ∼627 W/kg and ∼23.32 Wh/kg, respectively. Our work demonstrates that 3D nanoporous α-Fe2O3 electrodes forms promising material system as anode for improved charge storage performance.

In-situ growth of FeCo layered double hydroxide nanorods on MXene for high-performance supercapacitor electrodes

In the pursuit of clean energy solutions, supercapacitors have gained attention due to their exceptional energy storage capabilities. Layered double hydroxide (LDH), a notable material in this field, faces some challenges such as slow charge transfer speed and volumetric expansion. To tackle these issues, a novel FeCo-LDH/MXene composite was synthesized through in-situ hydrothermal growth of FeCo layered double hydroxide (FeCo-LDH) nanorods on MXene using ionic self-assembly, forming a three-dimensional (3D) composite with enhanced rate capability and cycling stability due to the synergetic coupling of MXene and LDH. The FeCo-LDH/MXene electrode significantly improves surface capacitance control performance and exhibits exceptional electrochemical performance, achieving a specific capacitance of 2058.2 F g−1 at 1 A g−1 and maintaining 1732.7 F g−1 at 10 A g−1, with 82.4 % capacity retention. Furthermore, the assembled supercapacitor delivers an energy density of 48.8 Wh kg−1 at 750 W kg−1 and 25.7 Wh kg−1 at 15000 W kg−1, demonstrating excellent rate performance, as well as 80.3 % capacitance after 5000 cycles at 2 A g−1, highlighting its durability. This advancement not only overcomes the specific capacitance challenge of MXene electrodes but also enhances the conductivity and cyclic stability of LDH, making FeCo-LDH/MXene a promising candidate for future high-performance energy storage applications.

Composition-optimized NiGa-LDH on MOF-derived and cobalt-nanoparticles-embedded carbon flakes for enhanced potassium-ion storage

Layered double hydroxides (LDHs), renowned for their distinct nanostructures, efficient ion channels, and high specific capacitance, are promising electrode materials for supercapacitors (SCs). However, commercial applications remain limited due to constraints in the rate capabilities and cycling. The synergistic effects of the composites can be leveraged by pairing LDHs with carbon materials to enhance the conductivity for better SC characteristics. Herein, flaky Zeolitic Imidazolate Framework(ZIF)-67 is deposited on carbon cloth and calcined to produce the MOF-derived composite of carbon nanosheet-embedded nano-cobalt particles (CPEC) on the surface of the carbon cloth. Afterward, NiGa-LDH with a controllable Ni to Ga ratio is synthesized on the CPEC to form a flower-like hierarchical nanostructure NiGa-LDH/CPEC@CC. Co nanoparticles act as nucleation sites for cohesive formation within the carbon cloth framework. Ni2Ga1-LDH/CPEC@CC has the best properties, such as a specific capacitance of 729.6F g−1 at 1 mA cm−2 and 97.3 % capacitance retention at 2 mA cm−2. The asymmetric supercapacitor (ASC) consisting of Ni2Ga1-LDH/CPEC@CC//AC has an excellent energy density of 83.96 Wh kg−1 with a power density of 80 W kg−1. Density-functional theory (DFT) calculations of Ni2Ga1-LDH/CPEC@CC affirm a potassium ion adsorption energy of −2.127 eV and density of state (DOS) near the Fermi level. The study imparts theoretical and technical knowledge about the design of complex nanostructures from MOF precursors.

Molten Salt Assisted Assembly (MASA) of novel mesoporous Ni0.5Mn0.5Co2O4 for high-performance asymmetric supercapacitors

Mesoporous transition metal oxides (TMO) are immensely investigated as electrode materials in supercapacitors. The molten salt assisted self-assembly (MASA) process enables a facile route for the synthesis of the mesoporous TMO. In this study, mesoporous nickel manganese cobaltite (Ni0.5Mn0.5Co2O4) is synthesized for the first time using a MASA process and is evaluated as a novel electrode-active material for asymmetric supercapacitors. The objective of this work is to quantitatively measure the performance improvement in the Ni0.5Mn0.5Co2O4 electrode based on its composition and reveal the improvement mechanism through electrochemical methods. The electrochemical performance of the NiCo2O4 and MnCo2O4 prepared by MASA is also investigated, in order to understand the synergistic effect of Ni and Mn elements in the same cobaltite structure. In line with the data obtained from half cells, a full asymmetric cell is prepared by assembling the appropriate amount of Ni0.5Mn0.5Co2O4 and activated carbon through the charge balance theory. The test results show that the specific capacitance (Cs) values are 2.62F/cm2 (92.1F/g) for mesoporous NiCo2O4, 0.26F/cm2 (9.8F/g) for mesoporous MnCo2O4, and 9.53F/cm2 (338.5F/g) for mesoporous Ni0.5Mn0.5Co2O4 under the test conditions of 5 mA/cm2. The asymmetric supercapacitor assembled with Ni0.5Mn0.5Co2O4 and activated carbon demonstrates a superior energy density of 79.52 Wh.kg−1 at 1 mA/cm2. The findings of the study highlight the importance of substituting the electrode with Ni0.5Mn0.5Co2O4 to enhance the Cs by achieving proper surface properties and electrochemical activity.

Enhanced cyclability of O3-NaNi0.33Fe0.31Mn0.36O2 by Mg and Cu synergistic doping with strengthened Mn[sbnd]O bonds

Among some practical O3-type layered oxide cathodes, NaNi1/3Fe1/3Mn1/3O2 (NFM) features a high specific capacity and moderate cyclability. However, sluggish Na+ transfer kinetics, low structural stability, and rapid capacity loss during long-term cycling, are still posing a challenge to commercial applications of this material. In this work, we propose a Mg and Cu co-doped O3-type NaMg0.02Cu0.02Ni0.33Fe0.27Mn0.36O2 (MC-NFM) with a stable structure and good cycling stability. It was found that the MnO bonds in MC-NFM are obviously reinforced by synergistic doping with small amounts of Mg and Cu, leading to enhanced structural robustness, decreased Na+ migration barrier, and delayed O3-P3 phase transition. As a result, longer cycle life and enhanced rate performance are achieved. MC-NFM can yield a specific capacity of 142.1 mAh g−1 at 0.1C and 116.0 mAh g−1 at 5C, and maintain 83.6 % of its initial capacity after 400 cycles at 1C. This work provides a promising design of O3-type cathode for sodium-ion batteries.

Changing Horses in Midstream: Modern Pentathlon After the 2024 Olympic Games.

The decision of the Union Internationale de Pentathlon Moderne to replace horse riding with Obstacle after the 2024 Olympic Games challenges training, testing, and recovery management in Modern Pentathlon. This commentary discusses physiological, technical, and tactical effects of rule changes in the 5 disciplines with a specific focus on the new discipline Obstacle. Modern Pentathlon requires athletes to develop specific endurance capacities relying on both the aerobic and anaerobic systems while simultaneously increasing lower- and upper-body strength capabilities. In addition, movements must be repeatedly executed in an explosive and precise manner. Running and swimming must be fast but economical. Swapping from horse riding to Obstacle will prioritize the explosive strength of the upper extremities and core while keeping high levels of endurance and precision in swimming, fencing, and shooting. Moreover, condensing the Modern Pentathlon competition to a 90-minute television-friendly format enables more competitions in the future. Athletes and coaches will thus also need to develop and maintain effective individual peri-exercise routines (before, during, and after the competition) to successfully meet the resulting tactical and physical challenges of the new format. This commentary aims to stimulate the discussion on the effect of the Union Internationale de Pentathlon Moderne's decisions to replace riding with the new Obstacle discipline and implement a more television-friendly format with a focus on physiological, technical, and tactical aspects.

Polymerization of redox-active alizarin in biomass porous carbon with enhanced cycling stability for supercapacitor

Redox-active organic molecules have optimistic application prospects in energy storage due to their high theoretical capacitance, designable electrochemical activity and environmental friendliness. However, low conductivity and solubility in electrolyte severely hinder their redox activity. Here, alizarin molecules containing carbonyl and phenolic hydroxyl are encapsulated in biomass-derived porous carbon, and stable alizarin polymers are further grown on porous carbon substrate by electrochemical polymerization. Porous carbon as conductive network can improve electron transport properties, and provide suitable accommodation environment for confinement and polymerization of alizarin. The electrochemical polymerization strategy on carbon substrate allows alizarin to be connected by rigid C-O-C bond, which inhibits the dissolution of organic monomers while maintaining redox activity. The optimized polyalizarin/porous carbon composite (PAZ/PC-0.5) exhibits superior charge storage performance, with a specific capacitance of 355.8 F g−1 at 1 A g−1 and 220.8 F g−1 at high current density of 30 A g−1. Moreover, PAZ/PC electrode has more durable long-term charge-discharge stability (capacitance retention is 98 % after 10,000 charge and discharge cycles). The assembled symmetrical supercapacitor exhibits excellent energy-power characteristics (21.4 Wh kg−1 at 700 W kg−1) and durable cycle stability. This work sheds light on the design of stable organic electrode towards high-performance supercapacitor.

Preparation of microalgae-based carbon materials with Ni(OH)2 doping and their electrochemical performance

Supercapacitors are a new type of energy storage devices with many advantages. In this study a novel composite material named NiC were synthesized to improved their electrochemical performance in supercapacitors. It was composite of Ni(OH)2 and microalgae-based N-doped activated carbon materials. Activated carbon material prepared from defatted microalgae was excellent electrode material because of their nitrogen-rich characterization and porous structure. The Ni(OH)2 as a metallic material could provide considerable pseudo-capacitance for capacitors. In this study, Ni(OH)2 was successfully doped into carbon materials using a hydrothermal method at a temperature of 150 °C for 4 h. The flower-like structure of metallic materials was observed in SEM images and two forms of elemental Ni ions (Ni3+ and Ni2+) were detected in XPS. The porosity of the composite materials NiC was retained to some extent (specific surface area of 502 m2/g for sample NiC10). Moreover, the specific capacitance value of composite material NiC20 was increased by 190 % compared to its parent carbon material, indicating that the capacitive performance of the composite materials was significantly improved. The capacitance retention of NiC20//NiC20 in a two-electrode system was up to 75.29 % over 5000 cycles. This research will provide necessary information for high-performance electrochemical materials based on microalgae-based carbon materials.

Recycling of activated carbons from spent supercapacitors to refabricate improved supercapacitors

The growing market of commercial electric double-layer capacitors (EDLCs) will lead to a vast accumulation of waste as they arrive out of operation. Recycling the spent electrode activated carbon is a closed-loop solution to provide environmental and economic advantages for EDLC use. However, effectively regenerated methods of high-purity activated carbons are still lacked despite their considerable expense. Herein, a simple steam physical activation method is developed to regenerate high-class activated carbons from spent EDLCs. The process is first demonstrated that can effectively eliminate few electrolytes and complex organics as well as regenerate electrode carbon materials. The activation-recycled carbon materials preserve the physicochemical properties of fresh activated carbons and enhance their mesopore ratios, which contributes to improved EDLC performance, obviously surpassing recycled carbon materials by calcination method, including superior specific capacitance of 103.3 F g−1 at 0.5 A g−1, rate performance and cycling stability, equal to fresh activated carbons. Moreover, the assembled activation-recycled carbon material EDLC delivers low self-discharge rate (89 % of initial voltage after 72 h), wide temperature range (−40 to 85 °C), excellent cycling stability (92.2 % capacitance retention after 10,000 cycles) even at elevated voltages (3.0 V) and temperature (65 °C) test. The present work provides an effective and economic method of recycling high-grade activated carbons for sustainable EDLCs.

Critical role of submicropores in lignin-based carbon for enhanced supercapacitive performance in aqueous electrolyte

Lignin-based microporous carbon is prepared by KOH activation method. Nitrogen sorption analysis shows that the specific surface area is 1473 m2 g−1 and the micropore size is mainly distributed at 0.65 nm, leading to a capacitance value of 252 F g−1 in H2SO4 electrolyte. To tune the microstructure for better electrochemical performance, cobalt acetate is introduced in the mixture of lignin/KOH. The catalysis of cobalt acetate reduces the heteroatom content of the final porous carbon, resulting in an increased graphitization degree. Moreover, the microporous structure is also tuned by generating more submicropores with pore size of 0.65–0.85 nm. Even though the specific surface area is only 1543 m2 g−1, the submicropore surface area is increased to 1097 from 662 m2 g−1. With the increased graphitization degree and submicropore content, the prepared porous carbon can accommodate more electrolyte ions, contributing to a specific capacitance of 332 F g−1 in H2SO4 electrolyte. This capacitance value is increased by 31.7 % compared with previous carbon without adding cobalt acetate. The assembled supercapacitor cell can deliver a high energy density of 13.4 Wh kg−1. Our findings provide a guide on the microstructure modulation of porous carbon to match aqueous electrolytes with different ionic size.

Recycling the Spent Lithium-ion Battery into Nanocubes Cobalt Oxide Supercapacitor Electrode

Background:: Cobalt oxide nanocubes have garnered significant attention as potential supercapacitor electrodes due to their unique structural and electrochemical properties. The spent lithium-ion batteries (LiBs) are considered as zero-cost source for cobalt oxide production. Objective:: The aim of this work is to recover cobalt oxide from spent LiBs and study its electrochemical performance as a supercapacitor electrode material. Method:: This study uses an electrodeposition method to obtain cobalt oxide honeycomb-like anodes coated on Ni foam substrates from spent Li-ion batteries for supercapacitors applications. The effect of annealing temperature on the cobalt oxide anode has been carefully investigated; 450 ºC annealing temperature results in nanocubes on the surface of the cobalt oxide electrode. X-ray diffraction confirmed the formation of the Co3O4-NiO electrode. Results:: The Co3O4-NiO nanocubes electrode has shown a high specific capacitance of 1400 F g-1 at 1 A g-1 and high capacitance retention of ~96 % after 2250 cycles at a constant current density of 10 A g-1 compared to 900 F g-1 at 1 A g-1 as for prepared Co3O4 honeycomb. Conclusion:: This strategy proves that the paramount importance of Co3O4-NiO nanocubes, meticulously synthesized at elevated temperatures, as a supremely effective active material upon deposition onto transition metal foam current collectors, establishing their indispensability for supercapacitor applications.

Cellulose-based water-in-salt ZnBr2 hydrogels with multiple functions for energy storage devices

A new simple preparation method for water-in-salt-type cellulose hydrogels filled with ZnBr2 is reported. The ZnBr2 hydrogel electrolyte can be applied to zinc-ion hybrid supercapacitors and Zn-Br interfacial batteries. The water-in-salt ZnBr2 hydrogel serves as a stable electrolyte for good electrochemical performance in zinc-ion hybrid supercapacitors without redox reactions and can participate in the charging/discharging process of the Zn‒Br interfacial battery through the redox reaction of halogen anions. The assembled zinc-ion hybrid supercapacitor exhibits a specific capacitance of 241.8 F g-1 at 0.5 A g-1. Furthermore, after a 10000-cycle-long charging/discharging test at 5 A g-1, the coulombic efficiency is found at nearly 100%. The interfacial battery reaches the highest energy efficiency of 66% at a current density of 3 mA cm-2 at 0–1.8 V and displays a good cycle life with an 88% average coulombic efficiency at 3 mA cm-2. This work expands the application of hydrogels and provides new possibilities for optimizing the high performance of electrolytes.

An insight into synergistic effect of polyaniline and noble metal (Ag) on vanadium pentoxide nanorods for enhanced energe storage performance

The widespread applications of vanadium pentoxide (V2O5) are limited because of its low electrical conductivity and restricted ion diffusion coefficient. To address these constraints, the present study includes a straightforward and effective approach for fabricating polyaniline based silver-decorated vanadium pentoxide (Ag-V2O5/PANi) as an electrode material. The structural and morphological investigation of prepared electrode materials were made by X-ray diffraction analysis and scanning electron microscopy respectively. In comparison to pure Ag-V2O5, the Ag-V2O5/PANi composite demonstrated enhanced performance in various aspects. Specifically, the Ag-V2O5/PANi showed a higher specific capacitance (628 Fg−1) when subjected to a current density (1 Ag−1) in KOH electrolyte. Additionally, it has an energy density of 153 Whkg−1. Furthermore, the Ag-V2O5/PANi composite exhibited superior stability even after undergoing 3000 charge to discharge cycles. Exceptional capabilities shown can be ascribed to synergistic interaction between PANi and Ag-V2O5. The remarkable outcomes obtained from these electrode materials have the potential to foster novel prospects in high-energy-density storage systems.

Activated biomass-derived 3-dimensional porous graphene-like carbon for high-performance energy storage electrode materials

This article reports studies on the fabrication of active material for supercapacitor electrodes, from 3D porous graphene-like carbon (GLC), synthesized by carbonization from coffee waste (CW) and tea waste (TW) at 550 °C, followed by thermochemical activation in KOH at 850 °C in a quartz tubular furnace. The microstructure of coffee and tea waste shows the form of micro- and mesopores during carbonization and further chemical activation forms hierarchically highly porous 3D graphene-like carbon. GLC-CW exhibited a higher specific surface area (SSA) of 3486 m2/g according to the Brunauer-Emmett-Teller (BET) method, compared to GLC-TW, which had an SSA of 2407 m2/g. These results highlight the effectiveness of graphene-like carbon derived from coffee and tea waste, demonstrating its potential as a promising material for high-capacity supercapacitors. The electrochemical characteristics of the assembled supercapacitors using GLC-CW and GLC-TW revealed significantly higher specific capacitance values of 214 F/g and 182 F/g respectively, along with cycling stability of 98 % and 95 % during 5000 cycles of charge and discharge at 2 A/g current density. This approach can produce high-performance electrode materials for supercapacitors at a reasonable cost and with easy scalability.

External ligand-free nickel-catalyzed synthesis of polypyrazines towards stable, high-capacity and low-potential sodium ion storage

Sodium ion batteries (SIBs) have been regarded as a promising alternative to lithium-ion battery owing to low cost and good sustainability, but its competitiveness in energy storage is still limited largely by the development of suitable electrode materials. Traditional inorganic anode materials for SIBs face the problems of sluggish electrochemical kinetics and large volume strain due to the insertion/extraction of large size Na+. By comparison, organic anodes have the advantages of abundance resources, renewability, and designability, but suffer from the lack of stable electrode materials with both high specific capacity and low redox potential. Here, a class of pyrazine rings-rich organic polymers (polypyrazines) were designed and synthesized through external ligand-free nickel-catalyzed carbon–carbon coupling reactions. Among them, poly(2,6-pyrazine) shows the lowest synthetic cost, the highest porosity and the best conductivity. Consequently, as the anode of SIBs, poly(2,6-pyrazine) delivers a low redox potential (about 1 V, vs Na+/Na), high-specific-capacity (617.2 mA h/g at 0.1 A/g), excellent rate-capability (300 mA h/g at 10 A/g) and long-term cycling stability (81 % after 1000 cycles at 1.0 A/g). The low preparation cost and outstanding electrochemical performance of poly(2,6-pyrazine) make it a promising anode candidate for further boosting the energy density of SIBs.

Microcrystalline-Fe2P4O12 as eco-friendly and efficient anode for high-performance dual-ion battery

Dual-ion batteries (DIBs) have garnered significant interest because of their cost-effectiveness and high level of safety. However, the anode typically utilized tends to show low cyclic stability in complete batteries when the only sources of lithium are primarily consumed in the electrolyte following the development of a solid electrolyte interphase (SEI) during the initial electrochemical process. Here, a simple approach is used to produce microcrystalline carbon-coated Fe2P4O12 at a mild temperature. This material has the ability to store lithium ions, resulting in a specific capacity of 215 mAh/g at a potential range of 1 to 2.5 V vs Li+/Li0. Furthermore, it demonstrates a remarkable coulombic efficiency of 99 % in the initial cycles, even in the absence of a solid electrolyte interphase (SEI) formation. On the other hand, the issue of the high voltage plateau of the graphite cathode is addressed by selecting a total of 4.2 V as the optimal voltage range in DIBs. Simultaneously, the composite Fe2P4O12 also demonstrates exceptional ion diffusion kinetics and reduced interfacial impedance due to its microcrystalline structure. The utilization of the proposed Fe2P4O12 anode addresses a crucial deficiency in the complete range of deep in-situ bioremediation techniques, hence expediting the industrialization process.

Edge‑nitrogen/sulfur co-doping boost high potassium ion storage of carbon nanosheet anode materials

Potassium-ion batteries (PIBs) have garnered considerable attention as a potential alternative to lithium-ion batteries. However, the larger radius of K+ poses challenges, including slow kinetic processes and significant volume changes, which adversely affect the rate performance and cycling stability of electrode materials. Herein, N, S co-doped carbon nanosheets (xNS-HC) are synthesized as anode materials of PIBs by carbonization of citric acid and CH₄N₂S precursors in LiCl/KCl molten salts. Of these, 5NS-HC possesses a high N content of 20.19 at.% with 90.90 % of edge N-species and a S content of 2.53 at.%. The 5NS-HC material exhibits a high specific K+ storage capacity of 368.2 mAh g−1 at 0.1 A g−1, superior rate capability (106.1 mAh g−1 at 10 A g−1), and long-term cycling stability (205.8 mAh g−1 after 2800 cycles at 1 A g−1). In-depth analysis via in-situ XPS and DFT calculations reveals that the active sites doped with edge-N/S exhibit a profound affinity towards K+, thus contributing to the outstanding electrochemical K+ storage performance observed in 5NS-HC. The full cell of K0.4Mn0.9Li0.1O2·0.33H2O||5NS-HC exhibits a high specific capacity of 141.2 mAh g−1, supporting a high energy density of 147.1 Wh kg−1. These compelling results illustrate that edge-N/S co-doping can significantly enhance the K+ storage of carbon anode materials.

Solid-state preparation of in-situ grown graphene-embedded bi-metallic NiMnS hybrids for high-performance asymmetric supercapacitor

Endowed with intrinsic redox-rich features and superior electronic conductivities, mixed-metallic sulphides offer high prospects in electrochemical charge storage, especially in supercapacitors. Hence, their rational design and scalable preparation are of great scientific significance. Herein, we report the in-situ growth of nanostructured hybrids of NiMnS directly embedded into graphene sheets by a straightforward, scalable solid-state synthesis method. In this environment-friendly approach, the metal precursors, elemental sulphur, and graphene oxide (GO) are homogeneously mixed under ball-milling, followed by controlled thermal treatment. Incited from their unique synergistic contribution, the resulting NiMnS/G hybrids exhibit impressive electrochemical performance as a battery-type electrode in an aqueous electrolyte. The NiMnS/G hybrid electrode displayed a high specific capacity of 871.7C g−1 at 2 A g−1 with superior rate capability. Moreover, the asymmetric supercapacitor (ASC) device assembled based on the surface-enhanced NiMnS/G nanohybrid as the positive electrode and activated carbon (AC) as the negative electrode achieves an intriguing performance, delivering a maximum energy density of 53.4 Wh kg−1 at a power density of 500 W kg−1. The ASCs were successfully cycled over 10,000 cycles with 87 % capacitance retention and around 99 % Coulombic efficiency. This simple yet scalable strategy holds high promise and may pave the way for preparing other multimetallic sulphide-based hybrid electrode materials for electrochemical energy storage applications.