Modulating solvated structure of Zn2+ and inducing surface crystallography by a simple organic molecule with abundant polar functional groups to synergistically stabilize zinc metal anodes for long-life aqueous zinc-ion batteries.

Aqueous zinc-ion batteries (AZIBs) have attracted significant attention owing to their inherent security, low cost, abundant zinc (Zn) resources and high energy density. Nevertheless, the growth of zinc dendrites and side reactions on the surface of Zn anodes during repeatedly plating/stripping shorten the cycle life of AZIBs. Herein, a simple organic molecule with abundant polar functional groups, 2,2,2-trifluoroether formate (TF), has been proposed as a high-efficient additive in the ZnSO4 electrolyte to suppress the growth of Zn dendrites and side reaction during cycling. It is found that TF molecules can infiltrate the solvated sheath layer of the hydrated Zn2+ to reduce the number of highly chemically active H2O molecules owing to their strong binding energy with Zn2+. Simultaneously, TF molecules can preferentially adsorb onto the Zn surface, guiding the uniform deposition of Zn2+ along the crystalline surface of Zn(002). This dual action significantly inhibits the formation of Zn dendrites and side reactions, thus greatly extending the cycling life of the batteries. Accordingly, the Zn//Cu asymmetric cell with 2 % TF exhibits stable cycling for more than 3,800 cycles, achieving an excellent average Columbic efficiency (CE) of 99.81 % at 2 mA cm-2/1 mAh cm-2. Meanwhile, the Zn||Zn symmetric cell with 2 % TF demonstrates a superlong cycle life exceeding 3,800 h and 2,400 h at 2 mA cm-2/1 mAh cm-2 and 5 mA cm-2/2.5 mAh cm-2, respectively. Simultaneously, the Zn//VO2 full cell with 2 % TF possesses high initial capacity (276.8 mAh/g) and capacity retention (72.5 %) at 5 A/g after 500 cycles. This investigation provides new insights into stabilizing Zn metal anodes for AZIBs through the co-regulation of Zn2+ solvated structure and surface crystallography.

Rod-like Ni-CoS2@NC@C: Structural design, heteroatom doping and carbon confinement engineering to synergistically boost sodium storage performance.

Currently, conversion-type transition metal sulfides have been extensively favored as the anodes for sodium-ion batteries due to their excellent redox reversibility and high theoretical capacity; however, they generally suffer from large volume expansion and structural instability during repeatedly Na+ de/intercalation. Herein, spatially dual-confined Ni-doped CoS2@NC@C microrods (Ni-CoS2@NC@C) are developed via structural design, heteroatom doping and carbon confinement to boost sodium storage performance of the material. The morphology of one-dimensional-structured microrods effectively enlarges the electrode/electrolyte contact area, while the confinement of dual-carbon layers greatly alleviates the volume change-induced stress, pulverization, agglomeration of the material during charging and discharging. Moreover, the introduction of Ni improves the electrical conductivity of the material by modulating the electronic structure and enlarges the interlayer distance to accelerate Na+ diffusion. Accordingly, the as-prepared Ni-CoS2@NC@C exhibits superb electrochemical properties, delivering the satisfactory cycling performance of 526.6 mA h g-1 after 250 cycles at 1 A g-1, excellent rate performance of 410.9 mA h g-1 at 5 A g-1 and superior long cycling life of 502.5 mA h g-1 after 1,500 cycles at 5 A g-1. This study provides an innovative idea to improve sodium storage performance of conversion-type transition metal sulfides through the comprehensive strategy of structural design, heteroatom doping and carbon confinement.

Heterogeneous engineering and carbon confinement strategy to synergistically boost the sodium storage performance of transition metal selenides.

Transition metal selenides (TMSs) stand out as a promising anode material for sodium-ion batteries (SIBs) owing to their natural resources and exceptional sodium storage capacity. Despite these advantages, their practical application faces challenges, such as poor electronic conductivity, sluggish reaction kinetics and severe agglomeration during electrochemical reactions, hindering their effective utilization. Herein, the dual-carbon-confined CoSe2/FeSe2@NC@C nanocubes with heterogeneous structure are synthesized using ZIF-67 as the template by ion exchange, resorcin-formaldehyde (RF) coating, and subsequent in situ carbonization and selenidation. The N-doped porous carbon promotes rapid electrolyte penetration and minimizes the agglomeration of active materials during charging and discharging, while the RF-derived carbon framework reduces the cycling stress and keeps the integrity of the material structure. More importantly, the built-in electric field at the heterogeneous boundary layer drives electron redistribution, optimizing the electronic structure and enhancing the reaction kinetics of the anode material. Based on this, the nanocubes of CoSe2/FeSe2@NC@C exhibits superb sodium storage performance, delivering a high discharge capacity of 512.6 mA h g-1 at 0.5 A g-1 after 150 cycles and giving a discharge capacity of 298.2 mA h g-1 at 10 A g-1 with a CE close to 100.0 % even after 1000 cycles. This study proposes a viable method to synthesize advanced anodes for SIBs by a synergy effect of heterogeneous interfacial engineering and a carbon confinement strategy.

Heterometallic Electrocatalysts Derived from High-Nuclearity Metal Clusters for Efficient Overall Water Splitting.

The development of cost-effective electrocatalysts with an optimal surface affinity for intermediates is essential for sustainable hydrogen fuel production, but this remains insufficient. Here we synthesize Ni2P/MoS2-CoMo2S4@C heterometallic electrocatalysts based on the high-nuclearity cluster {Co24(TC4A)6(MoO4)8Cl6}, in which Ni2P nanoparticles were anchored to the surface of the MoS2-CoMo2S4@C nanosheets via strong interfacial interactions. Theoretical calculations revealed that the introduction of Ni2P phases induces significant disturbances in the surface electronic configuration of Ni2P/MoS2-CoMo2S4@C, resulting in more relaxed d-d orbital electron transfers between the metal atoms. Moreover, continuous electron transport was established by the formation of multiple heterojunction interfaces. The optimized Ni2P/MoS2-CoMo2S4@C electrocatalyst exhibited ultralow overpotentials of 198 and 73 mV for oxygen and hydrogen evolution reactions, respectively, in alkaline media, at 10 mA cm-2. The alkali electrolyzer constructed using Ni2P/MoS2-CoMo2S4@C required a cell voltage of only 1.45 V (10 mA cm-2) to drive overall water splitting with excellent long-term stability.

Optimizing Interplanar Spacing, Oxygen Vacancies and Micromorphology via Lithium-Ion Pre-Insertion into Ammonium Vanadate Nanosheets for Advanced Cathodes in Aqueous Zinc-Ion Batteries.

Ammonium vanadates, featuring an N─H···O hydrogen bond network structure between NH4 + and V─O layers, have become popular cathode materials for aqueous zinc-ion batteries (AZIBs). Their appeal lies in their multi-electron transfer, high specific capacity, and facile synthesis. However, a major drawback arises as Zn2+ ions tend to form bonds with electronegative oxygen atoms between V─O layers during cycling, leading to irreversible structural collapse. Herein, Li+ pre-insertion into the intermediate layer of NH4 V4 O10 is proposed to enhance the electrochemical activity of ammonium vanadate cathodes for AZIBs, which extends the interlayer distance of NH4 V4 O10 to 9.8 Å and offers large interlaminar channels for Zn2+ (de)intercalation. Moreover, Li+ intercalation weakens the crystallinity, transforms the micromorphology from non-nanostructured strips to ultrathin nanosheets, and increases the level of oxygen defects, thus exposing more active sites for ion and electron transport, facilitating electrolyte penetration, and improving electrochemical kinetics of electrode. In addition, the introduction of Li+ significantly reduces the bandgap by 0.18 eV, enhancing electron transfer in redox reactions. Leveraging these unique advantages, the Li+ pre-intercalated NH4 V4 O10 cathode exhibits a high reversible capacity of 486.1 mAh g-1 at 0.5 A g-1 and an impressive capacity retention rate of 72% after 5,000 cycles at 5 A g-1 .

Hollow VO2 microspheres anchored on graphene as advanced cathodes for aqueous zinc-ion batteries.

Vanadium dioxide-based materials have been proved to be promising cathodes for aqueous zinc ion batteries (AZIBs) due to their cost-effectiveness and high theoretical specific capacity; nevertheless, the low electronic conductivity and poor cycle stability restrict their application. Herein, hollow VO2 microspheres anchored on graphene oxide (H-VO2@GO) are synthesized via a facile simple hydrothermal reaction as high-performance cathodes for AZIBs. The hollow micromorphology of the material provides a large specific surface area and effectively alleviates the volume changes during cycling, while the anchoring of VO2 on graphene oxide greatly improves the electronic conductivity and inhibits the agglomeration and pulverization of the material. Resulting from the combination of unique micromorphology and graphene oxide anchoring, the as-prepared H-VO2@GO exhibits the impressive specific capacity of 400.1 mAh/g at 0.5 A/g and excellent cycling performance with 96.1 % of capacity retention after 1500 cycles at 10 A/g. This investigation provides a use reference for designing high-performance cathodes materials for AZIBs by optimizing the microstructure of electrode materials.

High-efficiency activated phosphorus-doped Ni2S3/Co3S4/ZnS nanowire/nanosheet arrays for energy storage of supercapacitors.

Transition metal sulfides (TMS) have been considered as a promising group of electrode materials for supercapacitors as a result of their strong redox activity, but high volumetric strain of the materials during electrochemical reactions causes rapid structural collapse and severe capacity loss. Herein, we have synthesized phosphorus-doped (P-doped) Ni2S3/Co3S4/ZnS battery-type nanowire/nanosheet arrays as an advanced cathode for supercapacitor through a two-step process of hydrothermal and annealing treatments. The material has a one-dimensional nanowire/two-dimensional nanosheet-like coexisting microscopic morphology, which facilitates the exposure of abundant active centers and promotes the transport and migration of ions in the electrolyte, while the doping of P significantly enhances the conductivity of the electrode material. Simultaneously, the element phosphorus with similar atomic radii and electronegativity to sulfur may act as electron donors to regulate the electron distribution, thus providing more effective electrochemically active sites. In gratitude to the synergistic effect of microstructure optimization and electronic structure regulation induced by the doing of P, the P-Ni2S3/Co3S4/ZnS nanoarrays provide a superior capacity of 2716 F g-1 at 1 A/g, while the assembled P-Ni2S3/Co3S4/ZnS//AC asymmetric supercapacitor exhibits a high energy density of 48.2 Wh kg-1 at a power density of 800 W kg-1 with the capacity retention of 89 % after 9000 cycles. This work reveals a possible method for developing high-performance transition metal sulfide-based battery-like electrode materials for supercapacitors through microstructure optimization and electronic structure regulation.

High-Energy-Density Cathode Achieved via the Activation of a Three-Electron Reaction in Sodium Manganese Vanadium Phosphate for Sodium-Ion Batteries.

Sodium superionic conductor (NASICON)-type Na3 V2 (PO4 )3 has attracted considerable interest owing to its stable three-dimensional framework and high operating voltage; however, it suffers from a low-energy density due to the poor intrinsic electronic conductivity and limited redox couples. Herein, the partial substitution of Mn3+ for V3+ in Na3 V2 (PO4 )3 is proposed to activate V4+ /V5+ redox couple for boosting energy density of the cathodes (Na3 V2- x Mnx (PO4 )3 ). With the introduction of Mn3+ into Na3 V2 (PO4 )3 , the band gap is significantly reduced by 1.406 eV and thus the electronic conductivity is greatly enhanced. The successive conversions of four stable oxidation states (V2+ /V3+ , V3+ /V4+ , and V4+ /V5+ ) are also successfully achieved in the voltage window of 1.4-4.0 V, corresponding to three electrons involved in the reversible reaction. Consequently, the cathode with x = 0.5 exhibits a high reversible discharge capacity of 170.9 mAh g-1 at 0.5 C with an ultrahigh energy density of 577 Wh kg-1 . Ex-situ x-ray diffraction (XRD) analysis reveals that the sodium-storage mechanism for Mn-doped Na3 V2 (PO4 )3 consists of single-phase and bi-phase reactions. This work deepens the understanding of the activation of reversible three-electron reaction in NASICON-structured polyanionic phosphates and provides a feasible strategy to develop high-energy-density cathodes for sodium-ion batteries.

Efficient Suppression of Dendrites and Side Reactions by Strong Electrostatic Shielding Effect via the Additive of Rb2 SO4 for Anodes in Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries (AZIBs) have attracted considerable attention due to their low cost and environmental friendliness. However, the rampant dendrite growth and severe side reactions during plating/stripping on the surface of zinc (Zn) anode hinder the practicability of AZIBs. Herein, an effective and non-toxic cationic electrolyte additive of Rb2 SO4 is proposed to address the issues. The large cation of Rb+ is preferentially adsorbed on the surface of Zn metal to induce a strong shielding effect for realizing the lateral deposition of Zn2+ ions along the Zn surface and isolating water from Zn metal to effectively inhibit side reactions. Consequently, the Zn||Zn symmetric cell with the addition of 1.5 mm Rb2 SO4 can cycle more than 6000 h at 0.5 mA cm-2 /0.25 mAh cm-2 , which is 20 times longer than that without Rb2 SO4 . Besides, the Zn||Cu asymmetric cell with Rb2 SO4 achieves a very high average Coulombic efficiency of 99.16% up to 500 cycles. Moreover, the electrolyte with Rb2 SO4 well matches with the VO2 cathode, achieving high initial capacity of 412.7 mAh g-1 at 5 A g-1 and excellent cycling stability with a capacity retention of 71.6% at 5 A g-1 after 500 cycles for the Zn//VO2 full cell.

Molybdenum-optimized electronic structure and micromorphology to boost zinc ions storage properties of vanadium dioxide nanoflowers as an advanced cathode for aqueous zinc-ion batteries.

Recently, vanadium dioxide (VO2) has been recognized as one of the most prospective cathodes for aqueous zinc ion batteries (AZIBs) for its high reversible specific capacity; nevertheless, its Zn2+ diffusion kinetics and cycling stability have not yet met expectations. Herein, Mo ions are introduced into VO2 to optimize the intrinsic electronic structure and micromorphology of VO2, achieving significantly enhanced zinc-ion storage. It is found that the substitution of Mo for V narrows the band gap of VO2 and thus enhances the conductivity of the material, while VO2 nanorods are transformed into VO2 nanoflowers which are self-assembled from ultra-thin nanosheets after the introduction of Mo, exposing much more active sites to enhance the migration kinetics of Zn2+. Consequently, the Mo-substituted VO2 (0.5-Mo-VO2) exhibits excellent electrochemical properties, presenting a high initial capacity of 494.5 mAh/g at 0.5 A/g, excellent rate capability of 336 mA h g-1 at 10 A/g and brilliant cycling stability with the capacity retention of 82% over 2000 cycles at 10 A/g. This work provides significant guidance for the design of advanced cathodes for AZIBs by optimizing the electronic structure and tailoring morphology of V-based materials.

Critical triple roles of sodium iodide in tailoring the solventized structure, anode-electrolyte interface and crystal plane growth to achieve highly reversible zinc anodes for aqueous zinc-ion batteries.

Aqueous rechargeable Zn-ion batteries (ARZIBs) are promising for energy storage. However, the Zn dendrite and corrosive reactions on the surface of Zn anode limit the practical uses of ARZIBs. Herein, we present a valid electrolyte additive of NaI, in which I- can modulate the morphology of Zn crystal growth by adsorbing on specific crystal surfaces (002), and guide Zn deposition by inducing a negative charge on the Zn anode. Simultaneously, it enhances the reduction stability of water molecules by participating in the solvation structure of Zn(H2O)62+ by forming ZnI(H2O)5+. At 10 mA cm-2, the assembled Zn symmetrical batteries can run stably over 1,100 h, and the depth of discharge (DOD) can reach 51.3 %. At 1 A g-1, the VO2||Zn full-cell in 2 M ZnCl2 electrolyte with 0.4 M NaI (2 M ZnCl2-0.4 M NaI) maintains of the capacity retention of 75.7 % over 300 cycles. This work offers an insight into inorganic anions as electrolyte additives for achieving stable zinc anodes of ARZIBs.

Constructing MIL-53(Fe)@ZIF-67(Co) binary metal-organic framework hierarchical heterostructure electrodes for efficient oxygen evolution.

Improving the efficiency of the anodic oxygen evolution reaction (OER) is important to solve the global energy crisis and greenhouse gas emission problems. In this paper, a preparation method for a MIL-53(Fe)@ZIF-67(Co) composite electrode is proposed. The hierarchical structure formed by the combination of MIL-53(Fe) and ZIF-67(Co) provides a rich channel for the transport of electrons and mass in the OER process. XPS analysis and DFT calculations revealed that Fe electrons in MIL-53(Fe) were transferred to Co in ZIF-67(Co) through O, which confirmed the rapid charge transfer effect of this transport channel. The MIL-53(Fe)@ZIF-67(Co) electrode has significant OER performance. When the current density reaches 10 mA cm-2, the overpotential is only 193 mV. This study inaugurates a new way for the rational design of a multiphase interface and the construction of new MOF channel structures.

Homologous Heterostructured NiS/NiS2 @C Hollow Ultrathin Microspheres with Interfacial Electron Redistribution for High-Performance Sodium Storage.

Nickel sulfides with high theoretical capacity are considered as promising anode materials for sodium-ion batteries (SIBs); however, their intrinsic poor electric conductivity, large volume change during charging/discharging, and easy sulfur dissolution result in inferior electrochemical performance for sodium storage. Herein, a hierarchical hollow microsphere is assembled from heterostructured NiS/NiS2 nanoparticles confined by in situ carbon layer (H-NiS/NiS2 @C) via regulating the sulfidation temperature of the precursor Ni-MOFs. The morphology of ultrathin hollow spherical shells and confinement of in situ carbon layer to active materials provide rich channels for ion/electron transfer and alleviate the effects of volume change and agglomeration of the material. Consequently, the as-prepared H-NiS/NiS2 @C exhibit superb electrochemical properties, satisfactory initial specific capacity of 953.0 mA h g-1 at 0.1 A g-1 , excellent rate capability of 509.9 mA h g-1 at 2 A g-1 , and superior longtime cycling life with 433.4 mA h g-1 after 4500 cycles at 10 A g-1 . Density functional theory calculation shows that heterogenous interfaces with electron redistribution lead to charge transfer from NiS to NiS2 , and thus favor interfacial electron transport and reduce ion-diffusion barrier. This work provides an innovative idea for the synthesis of homologous heterostructures for high-efficiency SIB electrode materials.

Multilevel spatial confinement of transition metal selenides porous microcubes for efficient and stable potassium storage.

Recently, potassium-ion batteries (PIBs) have been considered as one of the most promising energy storage systems; however, the slow kinetics and large volume variation induced by the large radius of potassium ions (K+) during chemical reactions lead to inferior structural stability and weak electrochemical activity for most potassium storage anodes. Herein, a multilevel space confinement strategy is proposed for developing zinc-cobalt bimetallic selenide (ZnSe/Co0.85Se@NC@C@rGO) as high-efficient anodes for PIBs by in-situ carbonizing and subsequently selenizing the resorcinol-formaldehyde (RF)-coated zeolitic imidazolate framework-8/zeolitic imidazolate framework-67 (ZIF-8/ZIF-67) encapsulated into 2D graphene. The highly porous carbon microcubes derived from ZIF-8/ZIF-67 and carbon shell arising from RF provide rich channels for ion/electron transfer, present a rigid skeleton to ensure the structural stability, offer space for accommodating the volume change, and minimize the agglomeration of active material during the insertion/extraction of large-radius K+. In addition, the three-dimensional (3D) carbon network composed of graphene and RF-derived carbon-coated microcubes accelerates the electron/ion transfer rate and improves the electrochemical reaction kinetics of the material. As a result, the as-synthesized ZnSe/Co0.85Se@NC@C@rGO as the anode of PIBs possesses the excellent rate capability of 203.9 mA h g-1 at 5 A g-1 and brilliant long-term cycling performance of 234 mA h g-1 after 2,000 cycles at 2 A g-1. Ex-situ X-ray diffraction (Ex-situ XRD) diffraction reveals that the intercalation/de-intercalation of K+ proceeds through the conversion-alloying reaction. The proposed strategy based on the spatial confinement engineering is highly effective to construct high-performance anodes for PIBs.

One-pot synthesis of NiFe nanoarrays under an external magnetic field as an efficient oxygen evolution reaction catalyst.

Designing and developing earth-abundant electrocatalysts for the oxygen evolution reaction (OER) in alkaline media is a critical element in the societal development of sustainable energy. MIL-53(Fe-Ni)/NF-2200Gs was synthesized under an external magnetic field. Such MIL-53(Fe-Ni)/NF-2200Gs show exceptionally high catalytic activity and require an overpotential of only 174 mV to drive a geometrical catalytic current density of 10 mA cm-2 in 1.0 M KOH, superior to RuO2 and most Fe, Ni-based electrocatalysts. Our work emphasizes the optimization of catalytic activity originating from the improvement of the magnetic properties of the catalyst, which enhances the spin polarization and tailors the d-electron structure of cations, leading to outstanding OER activity. This work would open new opportunities to design and develop transition-metal-based nanometer arrays toward efficient and stable water oxidation in alkaline media for applications.

Heteroatom-Modulated Assembly of Hexalanthanoid-Containing Polyoxometalate-Based Coordination Networks.

Two series of lanthanoid (Ln)-containing polyoxometalates (POMs) {[Ln6(ampH)4(H2O)24-n(ampH2)n(PW11O39)2]·21H2O (Ln = Tb, n = 0 (1), Ln = Er, n = 1 (2)) and K2[Ln6(ampH)4(H2O)22(SiW11O39)2]·23H2O (Ln = Tb (3), Er (4)) (ampH2 = (aminomethyl) phosphonic acid)} have been synthesized with tri-lacunary Keggin-type POMs containing different types of heteroatoms. Compounds 1 and 2 display neutral organic-inorganic hybrid POM molecules containing {Ln6(ampH)4} ({Ln6}) cores sandwiched by two {PW11O39} units. By changing the heteroatoms from PV to SiIV, the extended 2D networks of 3 and 4 were successfully isolated where the adjacent {Ln6} clusters were connected by {SiW11O39} moieties. Luminescence performances and magnetic properties of 1-4 have been systematically surveyed. The solid-state fluorescence spectra of 1-4 display characteristic emissions of Ln components resulting from the 4f-4f transitions, and energy transfer from the POM segments to Ln3+ centers in 1 and 3 has been observed based on the lifetime decay behaviors. Furthermore, all compounds can be utilized as electrocatalysts toward reduction of nitrite with high stability.

Polymetallic sulfide nanosheet arrays with composite structure as a highly efficient oxygen evolution electrocatalyst.

Designing an earth-abundant and cost-effective electrocatalyst for oxygen evolution reaction (OER) is the crux to the hydrogen production by water electrolysis on industrial scale. Herein, we developed a trimetallic sulfide hybrid of CoS1.097/Fe1-xS/Ni3S2/NF nanoarrays by the combination of morphology optimization and interface modulation. The unique morphology of ultrathin nanosheets significantly enriches the reaction sites of the catalyst, while the abundant heterogeneous interfaces effectively regulate the local electron structure and thus intrinsically enhances the catalytic activity of the material. As a result, the catalyst delivers the superior OER performance with the ultralow overpotential of 229 mV at the current density of 50 mA cm-2 and Tafel slope of 30.2 mV dec-1. Furthermore, the current density of the material keeps constant for 50 h in 1.0 M KOH. This work proposes a strategy for the synthesis of polymetallic sulfide catalysts with composite structure as an efficient OER catalyst by morphology optimization and interface modulation.

Na superionic conductor-type compounds as protective layers for dendrites-free aqueous Zn-ion batteries.

Aqueous rechargeable Zn-ion batteries (ARZIBs) have attracted much attention owing to their safety, high energy density and environmental friendliness. However, dendrite formation and corrosive reactions on Zn anode surface limit the development of ARZIBs. Here, Ga3+-doped NaV2(PO4)3 with Na superionic conductor (NASICON) structure [NVP-Ga(x), x = 0, 0.25, 0.5, 0.75] have been exploited as the high-efficiency artificial layer to stabilize Zn anode. The optimal NVP-Ga(0.5) layer can homogenize ion flux and promote uniform deposition of zinc, the dendrite growth and the parasitic reactions can be greatly inhibited. The symmetric cell based on this unique protection layer can stably operate over 1,300 h at 0.5 mA cm-2 with 0.5 mAh cm-2. Benefitting from the high-performance Zn metal anode, the full batteries paired with MnO2 cathode deliver a high discharge capacity of 106 mAh/g with the capacity retention rate of 85 % after 8,000 cycles. This work provides an advanced strategy to stabilize Zn anode for the industrialization of ARZIBs in the near future.

Effect of electronic structure modulation and layer spacing change of NiAl layered double hydroxide nanoflowers caused by cobalt doping on supercapacitor performance.

Layered double hydroxides (LDHs) with high theoretical capacity have broad prospectsin energy storage applications. However, their slow charge transfer kinetics and easy agglomerate hinder their applications in high-performance supercapacitors. Herein, Co2+-doped nickel aluminum layered double hydroxides (NiAl-LDH-Co2+-x, x = 0, 0.3, 0.6, 0.9, 1.2, 1.5) have been designed and prepared by a convenient hydrothermal process. The multicomponent layer structure formed by cobalt doping facilitates sufficient penetration of the electrolyte and accelerates the charge transfer kinetics. Furthermore, the more open layer spacing and electronic interactions induced by Co2+ doping are conducive to accelerating ion de-intercalation, thereby further improving the kinetic behavior of charge storage. Benefiting from the unique microstructure and Co2+ doping effect, the prepared NiAl-LDH-Co2+-0.9 provides a superior specific capacity of 985 C g-1 at 1 A g-1. In addition, the assembled hybrid supercapacitor with the NiAl-LDH-Co2+-0.9 as the positive electrode provides a remarkable energy density of 22.51 Wh kg-1 at a power density of 800 W kg-1 and exhibits an excellent cycle life with 80 % capacity retention after 20,000 cycles. This study demonstrates the great potential of efficient microstructure design and doping strategy in enhancing the charge storage of electrode materials.

Copper Hexacyanoferrate Solid-State Electrolyte Protection Layer on Zn Metal Anode for High-Performance Aqueous Zinc-Ion Batteries.

Zinc (Zn) metal possesses broad prospects as an anode for aqueous zinc-ion batteries (AZIBs) due to its considerable theoretical capacity of 820 mAh g-1 . However, the Zn anode suffers from dendrite growth and side reactions during Zn stripping/plating. Herein, a Prussian blue analog of copper hexacyanoferrate (CuHCF) with a 3D open structure and rich polar groups (CN) is coated on Zn foil as a solid-state electrolyte (SSE) protection layer to protect the Zn anode. The CuHCF protection layer possesses low activation energy of 26.49 kJ mol-1 , the high ionic conductivity of 7.6 mS cm-1 , and a large Zn2+ transference number of 0.74. Hence, the Zn@CuHCF||Zn@CuHCF symmetric cell delivers high cycling stability over 1800 h at 5 mA cm-2 , an excellent depth of discharge of 51.3%, and the accumulative discharge capacity over 3000 mAh cm-2 . In addition, the Zn//Ti@CuHCF asymmetric cell achieves the coulombic efficiency (CE) of 99.87% after 2000 cycles. More importantly, the Zn@CuHCF//V2 O5 full cell presents outstanding capacity retention of 87.6% at 10 A g-1 after 3000 cycles. This work develops a type of material to form an artificial protection layer for high-performance AZIBs.