Fast Redox Kinetics Research Articles

A phenazine-based conjugated microporous polymer as a high performing cathode for aluminium-organic batteries.

One of the possible solutions to circumvent the sluggish kinetics, low capacity, and poor integrity of inorganic cathodes commonly used in rechargeable aluminium batteries (RABs) is the use of redox-active polymers as cathodes. They are not only sustainable materials characterised by their structure tunability, but also exhibit a unique ion coordination redox mechanism that makes them versatile ion hosts suitable for voluminous aluminium cation complexes, as demonstrated by the poly(quinoyl) family. Recently, phenazine-based compounds have been found to have high capacity, reversibility and fast redox kinetics in aqueous electrolytes because of the presence of a CN double bond. Here, we present one of the first examples of a phenazine-based hybrid microporous polymer, referred to as IEP-27-SR, utilized as an organic cathode in an aluminium battery with an AlCl3/EMIMCl ionic liquid electrolyte. The preliminary redox and charge storage mechanism of IEP-27-SR was confirmed by ex situ ATR-IR and EDS analyses. The introduction of phenazine active units in a robust microporous framework resulted in a remarkable rate capability (specific capacity of 116 mA h g-1 at 0.5C with 77% capacity retention at 10C) and notable cycling stability, maintaining 75% of its initial capacity after 3440 charge-discharge cycles at 1C (127 days of continuous cycling). This superior performance compared to reported Al//n-type organic cathode RABs is attributed to the stable 3D porous microstructure and the presence of micro/mesoporosity in IEP-27-SR, which facilitates electrolyte permeability and improves kinetics.

A homogeneous plating/stripping mode with fine grains for highly reversible Zn anodes

Different from mode I with large nuclei and fast redox kinetics, mode II featured by the reduced nuclei and moderate redox kinetics is conducive to refine the grains and achieve homogeneous Zn plating/stripping toward highly reversible Zn anodes.

An energy-efficient tellurium electrode enabled by a Cs2TeI6 perovskite structure for durable aqueous Zn–Te batteries

CsI in 2 M ZnSO4 aqueous electrolyte facilitates the formation of Cs2TeI6 perovskite phase for Te electrode, effectively suppressing Te4+ hydrolysis and sustaining fast redox kinetics in multi-electron transfer Zn–Te aqueous batteries.

Electrochemical measurement of ruthenium oxide quantum dots synthesized at room temperature

Electrochemical energy storage has evolved into one of the most significant areas of current research to meet the escalating energy demands of contemporary society. Apart from the depletion of conventional sources of energy, the emission of hazardous chemicals is dangerous to the environment and human health as well. Among various electrochemical energy storage systems, the supercapacitor is emerging rapidly because of its elevated lifetime, flexibility, and light weight in various industrial areas. Ruthenium oxide (RuO2) is one of the most promising nanomaterials, with several applications in catalysts, sensors, microelectronics and other fields. Among numerous applications, ruthenium oxide is considered a promising candidate for electrode material for supercapacitors owing to its fast redox kinetics, low resistivity and high thermal and mechanical stabilities. Nowadays, researchers are increasingly turning to the biosynthesis of nanoparticles in order to establish clean, economical, and efficient synthesis techniques. In the present report, we have mycologically synthesised RuO2 quantum dots (RuO2 QDs), and different characterization techniques have been employed for the conformational nature of the quantum dots. Further, electrochemical studies have investigated the electrochemical potential of the mycologically synthesised RuO2 QDs utilising cyclic voltammetric measurements. The specific capacitance of RuO2 QDs coated on carbon cloth electrodes was 230 Fg−1 at a scan rate of 5.0 Ag−1 and the capacitance retention was found to be 95.8 % at the end of the 1000th charge-discharge cycle. The working electrodes derived from RuO2 QDs has rendered corrosion resistance in H2SO4 up to 0.16 M. A working model is also put to the test to find out the feasibility of QDs in practical application.

Cobalt-Nickel Layered Double Hydroxides on Electrospun MXene for Superior Asymmetric Supercapacitor Electrodes.

Flexible electrodes for energy storage and conversion require a micro-nanomorphology and stable structure. Herein, MXene fibers (MX-CNF) are fabricated by electrospinning, and Co-MOF nanoarrays are prepared on the fibers to form Co-MOF@MX-CNF. Hydrolysis and etching of Co-MOF@MX-CNF in the Ni2+ solution produce cobalt-nickel layered double hydroxide (CoNi-LDH). The CoNi-LDH nanoarrays on the MX-CNF substrate have a large specific surface area and abundant electrochemical active sites, thus ensuring effective exposure of the CoNi-LDH active materials to the electrolyte and efficient pseudocapacitive energy storage and fast reversible redox kinetics for enhanced charging-discharging characteristics. The CoNi-LDH@MX-CNF electrode exhibits a discharge capacity of 996 F g-1 at a current density of 1 A g-1 as well as 78.62% capacitance retention after 3,000 cycles at 10 A g-1. The asymmetric supercapacitor (ASC) comprising the CoNi-LDH@MX-CNF positive electrode and negative activated carbon electrode shows an energy density of 48.4 Wh kg-1 at a power density of 499 W kg-1 and a capacity retention of 78.9% after 3,000 cycles at a current density of 10 A g-1. Density-functional theory calculations reveal the charge density difference and partial density of states of CoNi-LDH@MX-CNF confirming the large potential of the CoNi-LDH@MX-CNF electrode in energy storage applications.

Architectural engineering of vertically expanded graphene-CoMn2O4 compounds based interdigital electrode for in-plane micro-supercapacitor

Structurally engineered carbon allotropes and their composites are widely applicable in various electronic/electrochemical devices including energy storage. Herein, we develop an efficient method to fabricate graphene/ceramic hybrid nanostructure based in-plane micro-supercapacitors (MSCs). Via CO2-laser irradiation method, MSCs patterns consisting of CoMn2O4 nanoparticles incorporated in vertically structured laser-induced graphene (CMOLIG) were formed on a freestanding graphene oxide film. The process is extremely convenient, since the laser irradiated CMOLIG patterns serve as the in-plane MSCs electrode, while the untreated graphene oxide acts as the substrate. MSCs with enhanced performance can be fabricated with the CMOLIG hybrid electrode patterns that are made of CoMn2O4 nanoparticles with pseudocapacitive properties anchored on vertically structured high-quality graphene film with excellent electrical property and high surface area. Notably, the CMOLIG electrode patterns exhibit enhanced specific capacitance with fast redox kinetics. Using the technique, customized in-plane MSCs arrays are also fabricated, which demonstrated controllable output voltage and capacitance depending on the array configuration to suit the requirements of various wearable microelectronics.

Nanoarchitectonics of MXene Derived TiO2 /Graphene with Vertical Alignment for Achieving the Enhanced Supercapacitor Performance.

Structural engineering and hybridization of heterogeneous 2D materials can be effective for advanced supercapacitor. Furthermore, architectural design of electrodes particularly with vertical construction of structurally anisotropic graphene nanosheets, can significantly enhance the electrochemical performance. Herein, MXene-derived TiO2 nanocomposites hybridized with vertical graphene is synthesized via CO2 laser irradiation on MXene/graphene oxide nanocomposite film. Instantaneous photon energy by laser irradiation enables the formation of vertical graphene structures on nanocomposite films, presenting the controlled anisotropy in free-standing film. This vertical structure enables improved supercapacitor performance by forming an open structure, increasing the electrolyte-electrode interface, and creating efficient electron transport path. In addition, the effective oxidation of MXene nanosheets by instantaneous photon energy leads to the formation of rutile TiO2 . TiO2 nanoparticles directly generated on graphene enables the effective current path, which compensates for the low conductivity of TiO2 and enables the functioning of an effective supercapacitor by utilizing its pseudocapacitive properties. The resulting film exhibits excellent specific areal capacitance of 662.9 mF cm-2 at a current density of 5mA cm-2 . The film also shows superb cyclic stability during 40000 repeating cycles, maintaining high capacitance. Also, the pseudocapacitive redox reaction kinetics is evaluated, showing fast redox kinetics with potential for high-performance supercapacitor applications.

Fast Ionic Conducting Hydroxyapatite Solid Electrolyte Interphase Enables Ultra-Stable Zinc Metal Anodes.

Zn metal has been extensively utilized as an anode in aqueous zinc-ion batteries attributed to its affordable cost and superior theoretical capacity. Nevertheless, the presence of dendrites and undesirable side reactions poses challenges to its widespread commercialization. To address these issues, herein, a surface coating composed of hydroxyapatite (HAP) was developed on the Zn anode to create an artificial solid electrolyte interphase. After the application of a hydroxyapatite layer, dendrites and corrosion of the Zn anode are sufficiently inhibited. Furthermore, the hydroxyapatite interphase with a low ionic diffusion barrier enables fast anodic redox kinetics. Consequently, the Zn@HAP symmetric cell possesses a durable lifespan over 2000 h at 1 mA cm-2, while maintaining minimal polarization. Moreover, the practical feasibilities of the Zn@HAP anode are also manifested in full batteries combined with MnO2 cathodes, exhibiting exceptional cycling performance up to 500 cycles at 1 A g-1 and excellent rate capability with a retention of 109 mAh g-1 at 5 A g-1.

Investigation on high performance and stabilized surface of AlF3-coated V2O5 micro-flower for zinc energy storage

Vanadium oxide (V2O5) cathode material, possessing abundant reserves and high theoretical capacity, has been extensively researched in aqueous zinc ion batteries (ZIBs). However, its electrochemical performance is significantly hindered by insufficient electronic conductivity, vanadium dissolution into electrolyte, and slow diffusion kinetics. In this study, the V2O5 micro-flower was first synthesized by a solvothermal method, and then modified by coating with AlF3 passivation layer, forming AlF3@V2O5 hybrid material. Impressively, AlF3@V2O5 exhibits excellent electrochemical and kinetic properties due to the special structure of V2O5 and the interfacial protection of AlF3. An exceptional rate property (325 mAh g−1 at 0.1 A g−1, 188 mAh g−1 at 15 A g−1) as well as extraordinary cycling stability with 89.3% capacity retention after 6000 cycles at 10 A g−1 can be attained with 2 wt% AlF3 addition (that is AF-2@V2O5). The computation based on density functional theory (DFT) suggests that AlF3 coating can reduce the interlayer electrostatic interaction and adsorption energy barrier between the intercalated Zn2+ and V2O5 host, thereby enabling fast redox kinetics. This study showcases the efficacy of interfacial modification of passivated coatings and presents an influential approach for material design in ZIBs.

Accordion-like polyoxometalate hybrid architectures for capacity-dense and flexible Zn-Ion battery cathodes

Polyoxometalates (POMs) have received significant attention as functional materials owing to their tunable structures and sizes, versatile electronic properties, and multiple electrochemical redox behaviours. However, the hierarchical architecture of POMs and their unique Zn storage mechanism have yet to be explored for Zn-ion battery (ZIB) applications. Herein, we demonstrate an accordion-like hierarchical architecture of POM-based hybrids (L-rGO/PPy@POM) via a redox-relay Heck reaction, where multi-layered reduced graphene oxide (rGO)/polypyrrole (PPy) hybrid nanosheets are assembled with ultrafine POM nanoparticles through specific interaction. As confirmed through in situ and ex situ spectroscopic methods, the Mo=O bond is more implicated in Zn2+ insertion than the two Mo–O single bonds and two edge-sharing and corner-sharing Mo–Mo bonds. Owing to a fast and facile redox kinetics, the ZIB cells with l-rGO/PPy@POM delivered high specific capacity of 269.3 mAh g−1 at 100 mA g−1, high-rate capacity of 68.0 mAh g−1 at 10,000 mA g−1, and 80.4% of capacity retention over 22,000 cycles in water-in-bisalt electrolytes. Furthermore, flexible quasi-solid-state ZIB full cells with l-rGO/PPy@POM cathode achieved the maximum volumetric energy and power densities of 51.1 mWh cmcell−3 and 1159.9 mW cmcell−3, demonstrating long-term cyclic stability and functional operation of various electronic devices.

Accelerating Sulfur Redox Chemistry by Atomically Dispersed Zn-N4 Sites Coupled with Pyridine-N Defects on Porous Carbon Sheets.

Single-atom catalysts (SACs) with specific N-coordinated configurations immobilized on the carbon substrates have recently been verified to effectively alleviate the shuttle effect of lithium polysulfides (LiPSs) in lithium-sulfur (Li─S) batteries. Herein, a versatile molten salt (KCl/ZnCl2 )-mediated pyrolysis strategy is demonstrated to fabricate Zn SACs composed of well-defined Zn-N4 sites embedded into porous carbon sheets with rich pyridine-N defects (Zn─N/CS). The electrochemical kinetic analysis and theoretical calculations reveal the critical roles of Zn-N4 active sites and surrounding pyridine-N defects in enhancing adsorption toward LiPS intermediates and catalyzing their liquid-solid conversion. It is confirmed by reducing the overpotential of the rate-determining step of Li2 S2 to Li2 S and the energy barrier for Li2 S decomposition, thus the Zn─N/CS guarantees fast redox kinetics between LiPSs and Li2 S products. As a proof of concept demonstration, the assembled Li─S batteries with the Zn─N/CS-based sulfur cathode deliver a high specific capacity of 1132mAhg-1 at 0.1C and remarkable capacity retention of 72.2% over 800cycles at 2C. Furthermore, a considerable areal capacity of 6.14mAhcm-2 at 0.2C can still be released with a high sulfur loading of 7.0mgcm-2 , highlighting the practical applications of the as-obtained Zn─N/CS cathode in Li─S batteries.

Tuning electron delocalization of hydrogen-bonded organic framework cathode for high-performance zinc-organic batteries

Stable cathodes with multiple redox-active centres affording a high energy density, fast redox kinetics and a long life are continuous pursuits for aqueous zinc-organic batteries. Here, we achieve a high-performance zinc-organic battery by tuning the electron delocalization within a designed fully conjugated two-dimensional hydrogen-bonded organic framework as a cathode material. Notably, the intermolecular hydrogen bonds endow this framework with a transverse two-dimensional extended stacking network and structural stability, whereas the multiple C = O and C = N electroactive centres cooperatively trigger multielectron redox chemistry with super delocalization, thereby sharply boosting the redox potential, intrinsic electronic conductivity and redox kinetics. Further mechanistic investigations reveal that the fully conjugated molecular configuration enables reversible Zn2+/H+ synergistic storage accompanied by 10-electron transfer. Benefitting from the above synergistic effects, the elaborately tailored organic cathode delivers a reversible capacity of 498.6 mAh g−1 at 0.2 A g−1, good cyclability and a high energy density (355 Wh kg−1).

A High-Power-Density Low-Temperature Heteropoly Acid Aqueous Redox Flow Battery

Aqueous redox flow batteries (ARFBs) are promising technology for safe and long-duration energy storage owing to their flexible architecture decoupling power and energy, which is the key to achieving massive utilization of intermittent renewable energies (solar and wind power)1. However, the high-power density at low temperatures is prohibited by the weak stability, sluggish kinetics, and limited solubility of active materials. These challenges not only preclude the commercialization of ARFBs in the high-power density market (e.g., electric automobile) but also make the renewable electric grid vulnerable to severe weather fluctuations.In this study, we describe a polyoxometalate-based active material with exceptionally fast redox kinetics and high electron solubility at low temperatures2. We optimize the charging process to achieve high electrochemical performance and will discuss factors that would influence solubility. We evaluate the kinetics of the polyoxometalate-based materials by rotating ring-disk electrodes measurement (RRDE) and adjust the electrolyte composition to increase the energy density and electrochemical stability of polyoxometalate-based electrolytes. We will discuss the full polyoxometalate-based ARFBs’ electrochemical performance, the influence of the supporting, and the possible degradation mechanism of the full cell (e.g., side reaction (hydrogen evolution, decomposition of the active materials) and crossover). Acknowledgment: The work is supported by a grant from the Research Grant Council (RGC) of the Hong Kong Special Administrative Region, China (project no. CUHK 14308622). Reference: (1) Yao, Y.; Lei, J.; Shi, Y.; Ai, F.; Lu, Y.-C. Assessment methods and performance metrics for redox flow batteries. Nature Energy 2021, 6 (6), 582.(2) Ai, F.; Wang, Z.; Lai, N.-C.; Zou, Q.; Liang, Z.; Lu, Y.-C. Heteropoly acid negolytes for high-power-density aqueous redox flow batteries at low temperatures. Nature Energy 2022, 7 (5), 417.

Fabrication of NiCo2O4@polyaniline heterostructure as positive electrode for asymmetrical supercapacitor

AbstractNiCo2O4, as a low‐cost and high‐performance binary transition metal oxide material, has been widely used in the fabrication of supercapacitor electrodes. However, the low energy density of binary metal oxides limits their large‐scale practical applications in supercapacitors, so it is highly desirable to design the structure of the NiCo2O4‐based supercapacitor. Therefore, in this paper, NiCo2O4 is compounded with polyaniline (PANI) to improve its electrochemical performance by exploiting the synergistic effect. The NiCo2O4@PANI composite electrode exhibits a specific capacitance of 561.2 F/g at 10 mV/s. In this study, asymmetric supercapacitors are assembled with NiCo2O4@PANI as the positive electrode and MXene as the negative electrode. The NiCo2O4@PANI‐CC//MXene‐CC supercapacitor has a specific capacitance of 31.95 F/g at a scan rate of 10 mV/s and a good cycle retention capacity of 86.2% after 3000 cycles. The excellent electrochemical performances are attributed to the dynamic equilibrium and fast redox kinetics of the two electrodes.

Redox-active anthraquinone-based π-conjugated polymer anode for high-capacity aqueous organic hybrid flow battery

Organic molecules/polymers are currently investigated as redox species for aqueous low-cost hybrid flow batteries. In this work, a redox-active anthraquinone-based conjugated polymer synthesized via a facile electrochemical polymerization approach is reported, which can be employed as a high-capacity anode material for aqueous hybrid flow batteries. The redox-active anthraquinone polymer displays a two-electron-transfer redox reaction at −0.616 V (versus the standard hydrogen electrode, SHE) with fast redox kinetics in aqueous alkaline electrolytes (pH = 12). Paired with a potassium ferrocyanide catholyte, the aqueous hybrid flow battery employed this redox-active anthraquinone polymer as the anode material in aqueous supporting electrolyte of pH = 12 exhibits an open circuit voltage of about 1.09 V, high specific capacity (103.6 mA h g−1 at 2 A g−1) and large mass power density (9.41 W g−1 at 100 % SOC), along with excellent capacity retention (99.948 % per cycle) and energy efficiency (74.1 %) after 100 cycles.

Field-assisted conductive substrate sparks the redox kinetics of Co9S8 in Li- and Na-ion batteries

As a promising candidate electrode material in both Li- and Na-ion batteries (L/SIBs), the application of Co9S8 is being hindered by its unsatisfactory electrochemical performance caused by the sluggish ion diffusion kinetics and drastic volume expansion. Herein, a hybrid material composed of Co9S8−x, N-doped carbon foam that seeded with Co nanoparticles (Co9S8−x@Co-NC) is constructed. Particularly, theoretical and experimental results imply that a built-in electric field at the interface of Co and NC is observed due to the variation of Fermi levels, forming rich Mott-Schottky-like heterointerfaces, which can significantly enhance the charge transfer capability between the active materials of Co9S8 and conductive NC skeleton. Moreover, the sulfur defects in Co9S8−x can not only effectively lower the energy barrier of the ion diffusion and charge transfer processes, but also endow the target sample with more storage/adsorption/active sites for Li+/Na+ ions, thus improving the rate performance of the Co9S8−x@Co-NC composite. As a result, the Co9S8−x@Co-NC exhibits fast surface-controlled redox kinetics and robust cycling stability. For instance, the Co9S8−x@Co-NC displays impressive Li-storage properties in both half and full cells with a high reversible capacity of 1007.4 mA h g−1 at 0.1 A g−1 after 100 cycles and superior rate capability up to 5 A g−1. Moreover, based on these comprehensive merits, the Co9S8−x@Co-NC composite shows decent electrochemical performance (472.2 and 311.1 mA h g−1 at 0.1 and 10 A g−1, respectively) as an anode for SIBs. This work presents an effective strategy for the construction of Mott-Schottky-like heterointerfaces in Co9S8 based materials and provides specific inspiration for future works designing high-performance electrodes via interfacial engineering.

Calamitic Blatter Radicals for Large‐Area Solution‐Coated Resistive Memories

AbstractRadical molecules exhibit fast redox kinetics, are widely explored for data processing and energy storage. However, the insulating aliphatic matrix isolates the radical units, thus resulting in a weak charge transporting ability. Herein, calamitic Blatter radicals (CBR) with highly conductive [1]benzothieno[3,2‐b]benzothiophene (BTBT) as the conjugated backbone are designed and synthesized. It is found that bistable redox character associated with large conjugated backbone allows these Blatter radical derivatives to be switched with ON/OFF ratio reaching 106 and retention time exceeding 104 s in solution processed devices. In addition, these radicals are unveiled to perform tunable, multi‐mode field‐responsive resistance behaviors, including write‐once‐read‐many (WORM), FLASH, and dynamic random access memory (DRAM), by molecular engineering strategy. This finding provides fundamental understanding for charge transferring dynamics and redox‐switching mechanism of radical molecules with respect to electronic applications.

Flexible All-in-one Quasi-Solid-State Batteries Enabled by Low-water-content Hydrogel Films.

The high conductivities and good mechanical properties of hydrogel electrolyte films are critical for energy storage devices with high flexibility, fast redox kinetics, and long life. Herein, a low water content (6.63wt%) hydrogel film is prepared, and a favorable environment is created, with an electrochemical stability window of 2.26V and a high ionic conductivity of 2.6mScm-1 . The hydrogel film exhibits good folding ability, low in-plane swelling, and anti-freezing abilities. These properties are benefitted by immobilizing free water molecules on the abundant oxygenic groups of polymer fibers in the hydrogel film, offering a unique 3D channel to allow Li+ to quickly transport along the polymer network. Therefore, the hydrogel film-based all-in-one flexible cell exhibits stable cycling performance with a retention of 81.8% of the initial capacity after 500 cycles at room temperature and 66.2% of capacity retention at -30°C. Furthermore, the full cell with high cathode loading (≈21mgcm-2 ) exhibits a high areal capacity of 2.5mAhcm-2 (≈119mAhg-1 ). The overall merits of flexible all-in-one quasi-solid-state batteries demonstrate high potential to be used for power wearable electronics.

Theoretical Insights into Single-Atom Catalysts Supported on N-Doped Defective Graphene for Fast Reaction Redox Kinetics in Lithium-Sulfur Batteries.

Single-atom catalysts are proven to be an effective strategy for suppressing shuttle effect at the source by accelerating the redox kinetics of intermediate polysulfides in lithium-sulfur (Li-S) batteries. However, only a few 3d transition metal single-atom catalysts (Ti, Fe, Co, Ni) are currently applied for sulfur reduction/oxidation reactions (SRR/SOR), which remains challenging for screening new efficient catalysts and understanding the relationship between structure-activity of catalysts. Herein, N-doped defective graphene (NG) supported 3d, 4d, and 5d transition metals are used as single-atom catalyst models to explore electrocatalytic SRR/SOR in Li-S batteries by using density functional theory calculations. The results show that M1 /NG (M1 = Ru, Rh, Ir, Os) exhibits lower free energy change of rate-determining step and Li2 S decomposition energy barrier, which significantly enhance the SRR and SOR activity compared to other single-atom catalysts. Furthermore, the study accurately predicts the by machine learning based on various descriptors and reveals the origin of the catalyst activity by analyzing the importance of the descriptors. This work provides great significance for understanding the relationships between the structure-activity of catalysts, and manifests that the employed machine learning approach is instructive for theoretical studies of single-atom catalytic reactions.

Construction of oxygen vacancies and heterostructure in VO2-x/NC with enhanced reversible capacity, accelerated redox kinetics, and stable cycling life for sodium ion storage

Developing anode materials with high reversible capacity, fast redox kinetics, and stable cycling life for Na+ storage remains a great challenge. Herein, the VO2 nanobelts with oxygen vacancies supported on nitrogen-doped carbon nanosheets (VO2-x/NC) were developed. Benefitting from the enhanced electrical conductivity, the accelerated kinetics, the increased active sites as well as the constructed 2D heterostructure, the VO2-x/NC delivered extraordinary Na+ storage performance in half/full battery. Theoretical calculations (DFT) demonstrated that oxygen vacancies could regulate the adsorption ability for Na+, enhance electronic conductivity, as well as achieve rapid and reversible Na+ adsorption/desorption. The VO2-x/NC exhibited high Na+ storage capacity of 270 mAh g−1 at 0.2 A g−1, and impressive cyclic stability with 258 mAh g−1 after 1800 cycles at 10 A g−1. The assembled sodium-ion hybrid capacitors (SIHCs) could achieve maximum energy density/power output of 122 Wh kg−1/9985 W kg−1, ultralong cycling life with 88.4% capacity retention after 25,000 cycles at 2 A g−1, and practical applications (55 LEDs could be actuated for 10 min), promising to be utilized in a practicable Na+ storage.