Ultralong Cycling Stability Research Articles

A Stress Self-Adaptive Structure to Suppress the Chemo-mechanical Degradation for High Rate and Ultralong Cycle Life Sodium Ion Batteries.

Transition-metal phosphides (TMPs) as typical conversion-type anode materials demonstrate extraordinary theoretical charge storage capacity for sodium ion batteries, but the unavoidable volume expansion and irreversible capacity loss upon cycling represent their long-standing limitations. Herein we report a stress self-adaptive structure with ultrafine FeP nanodots embedded in dense carbon microplates skeleton (FeP@CMS) via the spatial confinement of carbon quantum dots (CQDs). Such an architecture delivers a record high specific capacity (778 mAh g-1 at 0.05 A g-1) and ultra-long cycle stability (87.6% capacity retention after 10,000 cycles at 20 A g-1), which outperforms the state-of-the-art literature. We decode the fundamental reasons for this unprecedented performance, that such an architecture allows the spontaneous stress transfer from FeP nanodots to the surrounding carbon matrix, thus overcomes the intrinsic chemo-mechanical degradation of metal phosphides.

Covalent sulfur/CoS2-decorated honeycomb-like carbon hierarchies for high-performance sodium storage with ultra-long high-rate cycling stability

Transition metal sulfides (TMSs) with high theoretical sodium storage capacity have been regarded as one of the most competitive and promising anode materials for sodium-ion batteries. Nevertheless, great challenges still exist for TMS to achieve long-cycle life owing to the poor conductivity and volume expansion during the sodiation/desodiation process. The conventionally used pure carbon coating method can effectively solve the above problems. However, the low sodium ion storage capability of carbon will decrease the capacity of the anode. Thus the functionalization of well-designed carbon nanostructures with exotic elements (e.g., sulfur) or high-specific-capacity materials has been regarded as an efficient route to enhance sodium storage performance. Herein, we developed a facile strategy to incorporate covalent sulfur and CoS2 nanoparticles into honeycomb-like carbon matrices (denoted as S/CoS2@C), where sulfur is vaporized under vacuum and reacted with the Co-decorated carbon hierarchies, leading to the formation of CoS2 nanoparticles as well as the covalent C–Sx–C bonds. Consequently, the as-prepared S/CoS2@C composite demonstrates excellent sodium storage performance, with high initial coulomb efficiency (ICE) of 83 % and capacity retention of 95 % (478.5 mAh g−1) after 700 cycles at 0.2 A g−1, and an outstanding high-rate long-term cycling stability with a high reversible capacity of 396.1 mAh g−1 after 5000 cycles at 2 A g−1 (an average decay rate of only 0.0014 %). Furthermore, electrochemical analyses reveal that both covalent sulfur and CoS2 contribute to the sodium storage capacity via a predominantly surface-induced capacitive process, and the well-designed S/CoS2@C composite with encapsulation of covalent sulfur and CoS2 into the highly interconnected porous carbon matrices efficiently buffer the volume changes and well maintain the electrode integrity/conductivity upon sodiation/desodiation cycling.

Nitrogen-doped carbon/V2O3 nanorod composites as cathode material for high-performance aqueous Zn-ion battery

At present, the main challenge facing the aqueous zinc ion batteries (ZIBs) system is to find a kind of cathode material with high stability and large capacity. In this study, the precursor of metal-organic framework (MOF) was synthesized by hydrothermal method. Then, the carbon composite vanadyl oxide (N/C@V2O3) was synthesized by vacuum heat treatment and used as cathode material for ZIBs. The electrode material underwent an in situ phase change process during the first charge, where the corundum structure of N/C@V2O3 was oxidized and transformed into layered basic zinc vanadate (N/C@Zn2(OH)3(VO3)). The layered structure helps to achieve fast and stable storage and transport of zinc ions. Resulting in stable electrochemical performance, high specific capacity up to 285 mAh g−1 (1 A g−1), and ultra-long cycle stability (capacity retention of 98% at 10 A g−1 after 4500 cycles). In situ phase transition takes place inside the battery, which is a simple method to improve the theoretical capacity limit of materials, and has positive significance for realizing large magnification and long cycle ZIBs cathode materials.

Liquid Template Assisted Activation for "Egg Puff"-Like Hard Carbon toward High Sodium Storage Performance.

The slow solid diffusion dynamics of sodium ions and the side-reaction of sodium metal plating at low potential in the hard carbon anode of sodium ion batteries (SIBs) pose significant challenges to the safety manipulation of high-rate batteries. Herein, a simple yet powerful fabricating method is reported on for "egg puff"-like hard carbon with few N doping using rosin as a precursor via liquid salt template-assisted and potassium hydroxide dual activation. The as-synthesized hard carbon delivers promising electrochemical properties in the ether-based electrolyte especially at high rates, based on the absorption mechanism of fast charge transfer. The optimized hard carbon exhibits a high specific capacity of 367mAhg-1 at 0.05Ag-1 and 92.9% initial coulombic efficiency (ICE), 183mAhg-1 at 10Ag-1 , and ultra-long cycle stability of reversible discharge capacity of 151mAhg-1 after 12,000 cycles at 5Ag-1 with the average coulombic efficiency of ≈99% and the decay of 0.0026% per cycle. These studies will undoubtedly provide an effective and practical strategy for advanced hard carbon anode of SIBs based on adsorption mechanism.

Highly redox-active oligomers between graphene sheets as ultrahigh capacitance/rate and stable electrodes for supercapacitors

Organic electrodes have emerged as promising candidates for supercapacitors due to their sustainability, structural diversity, and high electrochemical activity. However, the intrinsic poor electronic conductivity and solubility in electrolytes impede their further applications. Herein, we propose a facile strategy for the synthesis of pyrogallic (PG) oligomer confined in-between graphene layers (FRGO) as high-performance electrodes for supercapacitors. The PG oligomer exhibits both physiochemical properties of small molecules and organic polymers, such as fast reaction kinetics and structural stability in aqueous electrolyte. Conjugated sp2 carbon plane with abundant electroactive groups (-OH and -C=O) possess high electrochemical activity and construct fast electron transfer tunnels crossing the longitudinal graphene layers. Accordingly, FRGO delivers an excellent rate performance (835 F g−1 at 0.5 A g−1, 233 F g−1 at 200 A g−1) and ultra-long cycle stability. The symmetric supercapacitor exhibits an ultra-high energy density of 82.4 Wh kg−1 at 300 kW kg−1, dramatic power density of 90 kW kg−1 at 4 Wh kg−1, and remarkable stability of 90% retention after 20000 cycles. This work may open a new window for the rational design of organic oligomers in energy storage and conversion fields.

Spinel-structured MnV2O4 @nitrogen-doped carbon microspheres for sodium ion batteries with ultra-long cycle stability

Vanadium oxide is provided with abundant redox centers for high theoretical capacity as anode of sodium-ion batteries (SIBs), but still has poor inherent conductivity and volume expansion leading to fast capacity decay during cycling. In the study, the manganese vanadate microspheres enclosed in nitrogen-doped carbon layers (MnV2O4 @NC) are availably constructed via reflux vanadization of Mn glycerol precursor and in situ thermal decomposition. The MnV2O4 @NC microspheres shows excellent the long-cycle stability as anode materials for SIBs, remaining the specific capacity of 205 mAh g−1 at current of 1000 mA g−1 after nearly 4000 cycles. Due to the increased valence range of bimetallic oxides and three-dimensional channels of spinel structure, the cubic MnV2O4 encapsulated by carbon shell can effectively enhance charge transfer, optimize electronic structure, stabilize crystal structure, and improve cycle stability. These results disclose the prospects of vanadate-based spinel material in high performance SIBs.

High performance hybrid supercapacitor based on hierarchical MOF derived CoFe2O4 and NiMn2O4 composite for efficient energy storage

We have synthesized the hierarchical FeCo-MIL-88 (FC-MOF) derived CoFe2O4 and NiMn2O4 (CFO@NMO) composite using a hydrothermal route. The combination and formation process were presented. The prepared composite of CFO@NMO is studied using XRD, XPS, FESEM with EDS, HRTEM, and nitrogen adsorption and desorption isotherm. The formation of composite with CoFe2O4 (CFO) and NiMn2O4 (NMO) may effectively boost the conductivity thereby enhance the performance of electrochemical activity. Benefitting from the formation of composite, the hybrid CFO@NMO electrode achieved a high specific capacity (i.e., 353.6 mAh/g), 86.1 % retention in capacity after 5000 galvanostatic charging and discharging (GCD) cycles. To utilize the advantages of ultra-long cycling stability and high specific capacity, the aqueous electrolyte-based hybrid supercapacitor (HSC) device with AC//NF as a negative electrode and CFO@NMO//NF as a positive electrode was fabricated. The assembled HSC device provided a specific capacitance 312.8 F/g, 88.4 % retention in capacitance after 10,000 GCD cycles along with high energy density (90.3 Wh/kg) and power density (12.9 kW/kg). An easy and cost-effective preparation of CFO@NMO composite with outstanding supercapacitor performance demonstrates an excessive potential for utilization in the near future.

Molten salt synthesis of high quality 2D δ‑MnO2 nanosheets for advanced aqueous Zn/MnO2 batteries

Rechargeable zinc-ion batteries (ZIBs) have garnered the attention of numerous researchers due to their environmentally friendly features, high safety, and abundance of raw materials. In this study, we present a zinc-manganese oxide (defined as Zn/NaMnO) battery system that employs the layered monocrystalline hexagonal phase, δ-MnO2, as the cathode, synthesized via the molten salt-assisted method. Our findings demonstrate that the ultra-thin δ-phase monocrystalline structure augments the active sites of electrochemical reaction, enhances surface interface interactions, and facilitates H+ diffusion kinetics, thus promoting high-rate performance. The Zn/NaMnO battery exhibits impressive capacity (335 mA h g−1 at 0.5 C) and ultra-long cycling stability at high current density (4000 stable cycles at 20 C with 90 % capacity retention). This work provides a novel methodology for the development of rechargeable ZIBs systems with excellent performance and mass production potential.

Preparation of Ni–Zn dual-doped polyhedral LiMn2O4 for endurable cycling lithium ion batteries at high rate

Jahn-Teller distortion and manganese dissolution are always the dominant problem of attenuating long cyclic performance and rate capacity of spinel LiMn2O4 cathode materials. Herein, a Ni–Zn dual-doping strategy is proposed to synthesize various LiNi0.05ZnxMn1.95-xO4 (x = 0–0.05) materials via a solid phase combustion method. All the as-prepared Ni–Zn co-doping materials have a good spinel structure with Fd3m space group and present unique polyhedron morphology with exposed (111) facets, which is conductive to relieving the manganese dissolution and Jahn-Teller effect. Moreover, the Ni–Zn co-doping gives rise to the extended Li–O bond and increased cell volume, hence boosting the favorable intercalation and deintercalation kinetics of Li+ ions. Consequently, the optimized LiNi0·05Zn0·02Mn1·93O4 cathode exhibits good electrochemical performance with the initial discharge capacity of 127.30 mAh g−1 and capacity retention of 70% after 1000 cycles at 1 C. At 5 C, an ultra-long cycle stability with a capacity retention of 61% is obtained up to 1800 cycles. Even at the high current rates of 10 C and 20 C, the relatively high first discharge capacities of 106.50 mAh g−1 and 99.40 mAh g−1 are also delivered, respectively. The Ni–Zn co-doping polyhedral LiMn2O4 will provide a solution for developing high-performance cathode materials in lithium ion battery.

Ultra-long cycle life flexible quasi-solid-state alkaline zinc batteries enabled by PEDOT:PSS encapsulated Ni3S2 nanorods

Alkaline nickel-zinc (Ni-Zn) batteries are considered as one of the most promising rechargeable battery systems. However, the poor cycling stability of the Ni cathode limit their service life. Herein, a conductive polymer (PEDOT:PSS) encapsulated Ni3S2 hollow nanorod structure via facile immersion is proposed. PEDOT:PSS coating layer can not only provide adhesion for Ni3S2 nanorods to prevent Ni3S2 from falling off the substrate during cycling, but also facilitate electron transfer via the complete conductive pathway. The hollow nanorods structure of Ni3S2 is beneficial to mitigate the volume change and accelerate the rapid transport of ions. Besides, a gel electrolyte with double network porous structure in our battery system is well designed. The ionic association of sodium alginate on Zn2+ can effectively reduce the activity of bound water molecules in the solvation sheath of Zn2+, inhibit the side reaction and dendrite generation through the ion-confinement effect, to achieve uniform deposition of zinc ions. As a consequence, the as-designed quasi-solid-state flexible Ni-Zn battery demonstrates a high specific capacity of 1.06 mAh cm−2 (276.04 mAh g−1) at 8 mA cm−2 and an ultra-long cycle stability over 10,000 cycles with a capacity retention of 88.96% at 30 mA cm−2.

Multiscale Structural Engineering of Sulfur/Carbon Cathodes Enables High Performance All-Solid-State LiS Batteries.

Constructing all-solid-state lithium-sulfur batteries (ASSLSBs) cathodes with efficient charge transport and mechanical flexibility is challenging but critical for the practical applications of ASSLSBs. Herein, a multiscale structural engineering of sulfur/carbon composites is reported, where ultrasmall sulfur nanocrystals are homogeneously anchored on the two sides of graphene layers with strong SC bonds (denoted as S@EG) in chunky expanded graphite particles via vapor deposition method. After mixing with Li9.54 Si1.74 P1.44 S11.7 Cl0.3 (LSPSCL) solid electrolytes (SEs), the fabricated S@EG-LSPSCL cathode with interconnected "Bacon and cheese sandwich" feature can simultaneously enhance electrochemical reactivity, charge transport, and chemomechanical stability due to the synergistic atomic, nanoscopic and microscopic structural engineering. The assembled InLi/LSPSCL/S@EG-LSPSCL ASSLSBs demonstrate ultralong cycling stability over 2400 cycles with 100% capacity retention at 1 C, and a record-high areal capacity of 14.0mAhcm-2 at a record-breaking sulfur loading of 8.9mgcm-2 at room temperature as well as high capacities with capacity retentions of ≈100% after 600 cycles at 0 and 60°C. Multiscale structural engineered sulfur/carbon cathode has great potential to enable high-performance ASSLSBs for energy storage applications.

CuFeSe2/Cu2Se@C heterostructures as high-rate ultra-stable anodes for sodium ion half/full batteries

Transition metal selenides can be potentially implemented as a new generation of sodium storage anode owing to their abundance and high theoretical specific capacity. However, their practical applications are limited by large volume changes and slow kinetics. Therefore, the construction of transition metal selenide heterojunctions with long cycle stability and high capacity as anodes in sodium ion batteries remains challenging. In this study, carbon coated CuFeSe2/Cu2Se heterojunctions (CFS/CS@C) were successfully prepared via a simple aging and annealing strategy. The abundant heterojunction interfaces and carbon layers accelerated charge transfer, promoted the reaction kinetics, enhanced the electrical conductivity, and extended the cycle life. Consequently, the target material yielded ultra-long cycle stability (301.2 mAh/g at 10.0 A/g after 3000 cycles) and excellent rate performance (330.96 mAh/g at 20 A/g). The directly constructed full cell also exhibited remarkable cycling stability (138.6 mAh/g after 200 cycles at 0.5 A/g). Accordingly, this work demonstrated the construction of transition metal selenide composites as high-performance electrochemical energy storage electrodes.

Phosphate-based gel polymer electrolyte enabling remarkably long cycling stable sodium storage in a wide-operating-temperature

Gel polymer electrolytes are regarded as one of the efficient strategies to substitute traditional liquid electrolytes for achieving safer high energy density sodium ion batteries. However, operating under wide temperature range especially at low temperature under zero is still a great challenge for most gel polymer electrolytes and becomes a hindrance to sodium ion batteries further development. Herein, a multifunctional phosphate gel copolymer electrolyte with larger crosslinking degree and encapsulation over a broader operation temperature range (−20 to 70 °C) is designed and synthesized via in situ free radical copolymerization. This gel polymer electrolyte displays a wide electrochemical stability window up to 5.1 V (vs. Na+/Na) and high ionic conductivity even at low temperature of − 20 °C (>1.0 × 10−3 S cm−1). Moreover, its outstanding interfacial stability is confirmed via alternating-current impedance and Na plating/stripping experiments. The morphology and X-ray photoelectron spectroscopy data of separators after long cycling suggest the gel electrolyte has ability to inhibit the decomposition of liquid electrolyte and suppress the growth of sodium dendrite, hence enhance the cycling stability of battery efficiently at wide temperature range. As a result, the assembled gel Na||Na3V2(PO4)3 battery delivers outstanding ultralong cycling stability with superior discharge capacity retention over wide temperature range, including at room temperature (0.002% capacity decay per cycle for 3000 cycles), 60 °C (0.005% fade per cycle for 1500 cycles) and −10 °C (0.002% fade per cycle for 1200 cycles).

Conjugated microporous polyimide cathodes for sodium/lithium-ion batteries with ultra-long cycling performance

Conjugated microporous polyimides (CMPs) have been emerging as the promising electrode materials for sodium-ion batteries (SIBs) and lithium-ion batteries (LIBs) owing to their low cost, tunable structures, environmental benefit, and high porosity. However, the low intrinsic conductivity, poor structural stability and sluggish diffusion kinetics have hindered their further applications. Herein, a novel conjugated microporous polyimide trapped by multi-walled carbon nanotubes (TAPBA-NTCDA@MWCNTs) as cathodes for SIBs/LIBs have been prepared by in situ polycondensation. The addition of MWCNTs profits greatly in conductivity and structural stability of electrode materials. Consequently, when explored as cathode materials for SIBs, TAPBA-NTCDA@MWCNTs exhibits the good reversible specific capacity, predominant rate capability and ultra-long cycling stability. Moreover, the reaction mechanism and outstanding reversibility are investigated by the detailed ex-situ XPS/FT-IR/SEM analysis. Finally, the cathode also delivers an excellent lithium storage performance. In view of the outstanding cycle stability and such simple synthetic route, this work perhaps provides an effective strategy to fabricate high-performance conjugated microporous polyimide-based cathodes for energy storage and conversion devices.

Solvent-mediated oxidative polymerization to atomically dispersed iron sites for oxygen reduction

Fe single-atom catalysts open up broad prospects for oxygen reduction reaction (ORR), but the chemical state evolution of Fe species before forming isolated sites is rarely understood. Herein, mechanistic investigation on the formation of isolated Fe sites is presented through solvent-mediated oxidative pyrrole polymerization strategy. The slow reaction kinetics of oxidative Fe3+ ions with the predesigned methanol solvent molecules can endow highly dispersed Fe sites in polypyrrole and thus Fe single-atom catalysts after pyrolysis. The Fe single-atom catalyst (Fe-SA/PNC) performs superior ORR activity with a half-wave potential of 0.90 V versus RHE and 12.8 times higher turnover frequency than that of commercial Pt/C. When assembled into Zn-air batteries, the Fe-SA/PNC cathode delivers a 1.68 V open circuit potential and ultra-long cycling stability over 9000 cycles, superior to the most reported catalysts so far. Experimental and theoretical results reveal that the rich adjacent non-coordinated graphitic nitrogen atoms can enhance electronic conductivity and promote O2 adsorption and OH- desorption, thus enabling high oxygen reduction and battery performances.

Realizing high-efficient oxygen reduction reaction in alkaline seawater by tailoring defect-rich hierarchical heterogeneous assemblies

The development of efficient and stable oxygen reduction reaction (ORR) electrocatalysts in seawater electrolyte is the key to realizing marine resource utilization and expanding metal-air battery applications. Herein, defect-rich Fe-doped Co nanoparticles encapsulated by N-doped hierarchical carbon (D-FeCo@NHC) are rationally designed and synthesized. It is worth mentioning that the Fe doping helps to promote the generation of metal defect and adjust the electronic structure of D-FeCo@NHC. Density functional theory (DFT) demonstrate that the metal defect and carbon defect jointly optimize the d-band center of D-FeCo@NHC. As a result, in alkaline seawater electrolyte, D-FeCo@NHC display a half-wave potential of 0.874 V, and the assembled liquid Zn-air battery exhibit a high peak power density (173 mW cm−2) and ultra-long cycling stability (over 800 h). This work highlights the defect engineering in the construction of seawater-based oxygen reduction electrocatalysts, which provide a significant and promising approach for seawater-based metal-air cathode materials.

Sulfur-grafted hard carbon with expanded interlayer spacing and increased defects for high stability potassium-ion batteries

Carbon materials have been proven to be an effective anode for potassium-ion batteries (PIBs) due to their high safety, low cost, and environmental benignity. However, the repeated insertion/extraction of K-ions with a larger size into/from electrode at low voltage region will inevitably cause obvious volume expansion, easily resulting in poor cycle stability. Hence, we synthesize S-doped hard carbon material (NSHCM2) using biomass as carbon and thiourea as S sources. Various characterizations demonstrate that the introduced S-heteroatom not only expands the distance between carbon layers, but also creates more defects. The former ensures the free intercalation/deintercalation of K-ions without structure deformation, while the latter can provide numerous active sites to adsorb K-ions, all these together contribute to structure stability and reversible capacity. As a result, the optimized NSHCM2 electrode delivers a high capacity of 294 mAh g−1 at 200 mA g−1 and an ultra-long cycling stability by achieving 220 mAh g−1 at 2000 mA g−1 over 5000 cycles. This simple and high effective synthesis route makes durable and fast potassium storage possible.

Ultralong-Cycling and Free-Standing Carboxylated Graphene/PEDOT:PSS Films as Electrode for Flexible Supercapacitors

The rapid development of current wearable electronics motivates the promotion of energy storage devices. Supercapacitor with flexible, lightweight, highly efficient, and long cycling life is one of the potential and glittering candidates. Here, the composite film of carboxylated graphene (CG) and commercially available poly (3, 4-ethylene dioxythiophene): poly (styrene sulfonate) (PEDOT:PSS) are prepared as electrodes for flexible electrochemical capacitors by ultrasonication and vacuum filtration. The CG/PEDOT:PSS films were roundly characterized by SEM, XPS, FTIR, XRD and Raman spectrometer. The as-prepared free-standing films exhibited high specific capacitance (192.7 F g-1 at 0.5 A g-1), excellent rate capability (up to 80.4% from 0.5 to 20 A g-1), and good electrochemical stability (95.5% of specific capacitance retention after 50000 cycles). Surprisingly, the post treated free-standing films by Dimethyl Formamide (DMF) shows better capacitive properties than those of the pristine electrode, such as higher specific capacitance (204.3 F g-1 at 0.5 A g-1), and ultralong-cycling stability (104.6% retention at a high current density of 20 A g-1 after 50000 cycles). It is expected that the free-standing CG/PEDOT:PSS films can be used as flexible electrodes for various wearable energy storage devices.

Electrostatic Interaction‐directed Construction of Hierarchical Nanostructured Carbon Composite with Dual Electrical Conductive Networks for Zinc‐ion Hybrid Capacitors with Ultrastability

Metal–organic framework (MOF)‐derived carbon composites have been considered as the promising materials for energy storage. However, the construction of MOF‐based composites with highly controllable mode via the liquid–liquid synthesis method has a great challenge because of the simultaneous heterogeneous nucleation on substrates and the self‐nucleation of individual MOF nanocrystals in the liquid phase. Herein, we report a bidirectional electrostatic generated self‐assembly strategy to achieve the precisely controlled coatings of single‐layer nanoscale MOFs on a range of substrates, including carbon nanotubes (CNTs), graphene oxide (GO), MXene, layered double hydroxides (LDHs), MOFs, and SiO2. The obtained MOF‐based nanostructured carbon composite exhibits the hierarchical porosity (Vmeso/Vmicro: 2.4), ultrahigh N content of 12.4 at.% and “dual electrical conductive networks.” The assembled aqueous zinc‐ion hybrid capacitor (ZIC) with the prepared nanocarbon composite as a cathode shows a high specific capacitance of 236 F g−1 at 0.5 A g−1, great rate performance of 98 F g−1 at 100 A g−1, and especially, an ultralong cycling stability up to 230 000 cycles with the capacitance retention of 90.1%. This work develops a repeatable and general method for the controlled construction of MOF coatings on various functional substrates and further fabricates carbon composites for ZICs with ultrastability.

A highly-stable bifunctional NiCo2S4 nanoarray@carbon paper electrode for aqueous polysulfide/iodide redox flow battery

Aqueous polysulfide/iodide redox flow battery (SIFB) has the advantages of the high solubility of active materials, flexible designability, and low cost, which shows great potential in the field of grid-scale energy storage. However, the poor electrochemical activity of polysulfide limits the energy density and power density of the battery, which hinders its further commercial application. Herein, self-supported NiCo2S4 nanoneedle arrays are successfully synthesized on carbon paper (CP) through a two-step hydrothermal method. The as-prepared materials not only possess unique adsorption and electrocatalytic properties for polysulfide, but also promote the electrocatalytic process of iodide, which realizes bifunctional catalysis. The polysulfide/iodide redox flow battery with NiCo2S4@CP electrode can achieve a peak power density of 82.4 mW cm−2 at 160 mA cm−2 which is much higher than that with the pure CP electrode (∼12 mW cm−2). It can operate stably for more than 3400 h at a current density of 10 mA cm−2 with a capacity fade decay rate of 0.218% per day, exhibiting ultra-long cycle stability.