Interlayer Engineering of VS2 Nanosheets via In Situ Aniline Intercalative Polymerization toward Long-Cycling Magnesium-Ion Batteries.

Rechargeable magnesium batteries (RMBs) show great potential in large-scale energy storage systems, due to Mg2+ with high polarity leading to strong interactions within the cathode lattice, and the limited discovery of functional cathode materials with rapid kinetics of Mg2+ diffusion and desirable cyclability retards their development. Herein, we innovatively report the confined synthesis of VS2/polyaniline (VS2/PANI) hybrid nanosheets. The VS2/PANI hybrids with expanded interlayer spacing are successfully prepared through the exfoliation of VS2 and in situ polymerization between VS2 nanosheets and aniline. The intercalated PANI increases the interlayer spacing of VS2 from 0.57 to 0.95 nm and improves its electronic conductivity, leading to rapid Mg-ion diffusivity of 10-10-10-12 cm2 s-1. Besides, the PANI sandwiched between layers of VS2 is conducive to maintaining the structural integrity of electrode materials. Benefiting from the above advantages, the VS2/PANI-1 hybrids present remarkable performance for Mg2+ storage, showing high reversible discharge capacity (245 mA h g-1 at 100 mA g-1) and impressive long lifespan (91 mA h g-1 after 2000 cycles at 500 mA g-1). This work provides new perspectives for designing high-performance cathode materials based on layered materials for RMBs.

Controlled Synthesis of Flower-like Hierarchical NiCo-Layered Double Hydroxide Integrated with Metal-Organic Framework-Derived Co@C for Supercapacitors.

Layered double hydroxides (LDHs) have come to the foreground recently, considering their unique layered structure and short ion channels when they act as electrode materials for supercapacitors (SCs). However, due to their poor rate and cycle performance, they are not highly sought after in the market. Therefore, a flower-like hierarchical NiCo-LDH@C nanostructure with flake NiCo-LDH anchored on the carbon skeleton has emerged here, which is constructed by calcination and hydrothermal reaction and applying flake ZIF-67 as a precursor. In this structure, NiCo-LDH grows outward with abundant and homogeneously distributed Co nanoparticles on Co@C as nucleation sites, forming a hierarchical structure that is combined tightly with the carbon skeleton. The flower-like hierarchical nanostructures formed by the composite of metal-organic frameworks (MOFs) and LDHs have successfully enhanced the cycle and rate performance of LDH materials on the strength of strong structural stability, large specific surface area, and unique cooperative effect. The NiCo-LDH@C electrode displays superb electrochemical performance, with a specific capacitance of 2210.6 F g-1 at 1 A g-1 and 88.8% capacitance retention at 10 A g-1. Furthermore, the asymmetric supercapacitor (ASC) constructed with NiCo-LDH@C//RGO reveals a remarkable energy density of 45.02 W h kg-1 with a power density of 799.96 W kg-1. This project aims to propose a novel avenue to exploit NiCo-LDH electrode materials and provide theory and methodological guidance for deriving complex structures from MOF derivatives.

A nickel-based metal-organic framework as a new cathode for chloride ion batteries with superior cycling stability.

Chloride ion batteries (CIBs) have drawn growing attention as attractive candidates for large-scale energy storage technology because of their high theoretical energy densities (2500 W h L-1), dendrite-free characteristics and abundance of chloride-containing materials available worldwide. However, the further development of CIBs is greatly limited by sluggish Cl- diffusion and distinct structural variation of cathode materials, resulting in severe decayed capacity and inferior rate performance. Metal-organic framework (MOF) materials possess regular pores/channels and flexible structural designability to accommodate charge carrier ions, but the application of MOFs in anion-type batteries has not been reported. Here, we demonstrate the first example of Ni(dpip) with two different opening sizes of tubular channels serving as the cathode for high performance CIBs. The Ni-based MOF exhibited a stable reversible capacity of 155 mA h g-1 with an admirable low capacity decay of 0.026% per cycle over 500 cycles and superior kinetics with a 10-10 cm2 s-1 average diffusion coefficient for chloride ions as well. The high performance of the Ni(dpip) cathode results from the synergetic redox couples of Ni metal nodes and N-ligands, the unique double-channel structure for reversible Cl-storage, and the low chloride diffusion energy barrier. This work switches on the new application of MOF-based materials as cathodes for CIBs.

Introducing high-valence molybdenum to stimulate lattice oxygen in a NiCo LDH cathode for chloride ion batteries.

Layered double hydroxides (LDHs) have been intensively investigated as promising cathodes for the new concept chloride ion battery (CIB) with multiple advantages of high theoretical energy density, abundant raw materials and unique dendrite-free characteristics. However, driven by the great compositional diversity, a complete understanding of interactions between metal cations, as well as a synergetic effect between metal cations and lattice oxygen on LDH host layers in terms of the reversible Cl-storage capability, is still a crucial but elusive issue. In this work, we synthesized a series of chloride-inserted trinary Mox-doped NiCo2-Cl LDH (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) with gradient oxygen vacancies as enhanced cathodes toward CIBs. The combination of advanced spectroscopic techniques and theoretical calculations reveals that the Mo dopant facilitates oxygen vacancy formation and varies the valence states of coordinated transition metals, which can not only tune the electronic structure effectively and promote Cl-ion diffusion, but improve the redox activity of LDHs. The optimized Mo0.3NiCo2-Cl LDH delivers a reversible discharge capacity of 159.7 mA h g-1 after 300 cycles at 150 mA g-1, which is almost a triple enhancement compared to that of NiCo2Cl LDH. The superior Cl-storage of trinary Mo0.3NiCo2Cl LDH is attributed to the reversible intercalation/deintercalation of chloride ions in the LDH gallery along with the oxidation state changes in Ni0/Ni2+/Ni3+, Co0/Co2+/Co3+ and Mo4+/Mo6+ couples. This simple vacancy engineering strategy provides critical insights into the significance of the chemical interaction of various components on LDH laminates and aims to effectively design more LDH-based cathodes for CIBs, which can even be extended to other halide-ion batteries like fluoride ion batteries and bromide ion batteries.

A High-Nickel Layered Double Hydroxides Cathode Boosting the Rate Capability for Chloride Ion Batteries with Ultralong Cycling Life.

Chloride-ion batteries (CIBs) have drawn growing attention in large-scale energy storage applications owing to their comprehensive merits of high theoretical energy density, dendrite-free characteristic, and abundance of chloride-containing materials. Nonetheless, cathodes for CIBs are plagued by distinct volume effect and sluggish Cl- diffusion kinetics, leading to inferior rate capability and short cycling life. Herein, an unconventional Ni5 Ti-Cl LDH is reported with a high nickel ratio as a cathode material for CIB. The reversible capacity of Ni5 Ti-Cl LDH retains 127.9 mAh g-1 over 1000 cycles at a large current density of 1000 mA g-1 , which exceeds that of ever reported CIBs, with extraordinary low volume change of 1.006% during a whole charge/discharge process. Such superior Cl-storage performance is attributed to synergetic contributions consisting of high redox activity from Ni2+ /Ni3+ and pinning Ti that restrains local structural distortion of LDH host layers and enhances adsorption intensity of chloride atoms during the reversible Cl- intercalation/de-intercalation in LDH gallery, which are revealed by a comprehensive study including X-ray photoelectron spectroscopy, kinetic investigations, and DFT calculations. This work provides an effective strategy to design low-cost LDHs materials for high-performance CIBs, which are also applicable to other types of halide-ion batteries (e.g., fluoride-ion and bromide-ion batteries).

Electronic structure engineering on NiSe2 micro-octahedra via nitrogen doping enabling long cycle life magnesium ion batteries.

Multivalent ion batteries have attracted great attention because of their abundant reserves, low cost and high safety. Among them, magnesium ion batteries (MIBs) have been regarded as a promising alternative for large-scale energy storage device owing to its high volumetric capacities and unfavorable dendrite formation. However, the strong interaction between Mg2+ and electrolyte as well as cathode material results in very slow insertion and diffusion kinetics. Therefore, it is highly necessary to develop high-performance cathode materials compatible with electrolyte for MIBs. Herein, the electronic structure of NiSe2 micro-octahedra was modulated by nitrogen doping (N-NiSe2) through hydrothermal method followed by a pyrolysis process and this N-NiSe2 micro-octahedra was used as cathode materials for MIBs. It is worth noting that N-NiSe2 micro-octahedra shows more redox active sites and faster Mg2+ diffusion kinetics compared with NiSe2 micro-octahedra without nitrogen doping. Moreover, the density functional theory (DFT) calculations indicated that the doping of nitrogen could improve the conductivity of active materials on the one hand, facilitating Mg2+ ion diffusion kinetics, and on the other hand, nitrogen dopant sites could provide more Mg2+ adsorption sites. As a result, the N-NiSe2 micro-octahedra cathode exhibits a high reversible discharge capacity of 169 mAh g-1 at the current density of 50 mA g-1, and a good cycling stability over 500 cycles with a maintained discharge capacity of 158.5 mAh g-1. This work provides a new idea to improve the electrochemical performance of cathode materials for MIBs by the introduction of heteroatom dopant.

Rationally designed Mn2O3@ZnMn2O4/C core-shell hollow microspheres for aqueous zinc-ion batteries.

Manganese-based oxides are common cathode materials for aqueous zinc ion batteries (AZIBs) because of their great capacity and high working voltage. However, the sharp decline of capacity caused by the dissolution of manganese-based cathode materials and the low-rate performance restrict their development. To address these problems, unique core-shell structured Mn2O3@ZnMn2O4/C hollow microspheres are reported as an ideal cathode material for AZIBs. Benefiting from the hollow structure, the zeolitic imidazolate framework (ZIF)-derived carbon and ZnMn2O4. Its application in AZIBs as the cathode demonstrates its satisfactory rate performance, high cycle stability, and excellent reversibility. Its high reversible capacity is remarkable, which reaches its maximum of 289.9 mA h g-1 at 200 mA g-1 and maintains a capacity of 203.5 mA h g-1 after cycling for 700 times at 1000 mA g-1. These excellent performances indicate that this material is a potential cathode material of AZIBs.

Enhanced Li-Ion Diffusion and Cycling Stability of Ni-Free High-Entropy Spinel Oxide Anodes with High-Concentration Oxygen Vacancies.

High-entropy oxide (HEO) is an emerging type of anode material for lithium-ion batteries with excellent properties, where high-concentration oxygen vacancies can effectively enhance the diffusion coefficient of lithium ions. In this study, Ni-free spinel-type HEOs ((FeCoCrMnZn)3O4 and (FeCoCrMnMg)3O4) were prepared via ball milling, and the effects of zinc and magnesium on the concentration of oxygen vacancy (OV), lithium-ion diffusion coefficient (DLi+), and electrochemical performance of HEOs were investigated. Ab initio calculations show that the addition of zinc narrows down the band gap and thus improves the electrical conductivity. X-ray photoelectron spectroscopy (XPS) results show that (FeCoCrMnZn)3O4 (42.7%) and (FeCoCrMnMg)3O4 (42.5%) have high OV concentration. During charge/discharge, the OV concentration of (FeCoCrMnZn)3O4 is higher than that of (FeCoCrMnMg)3O4. The galvanostatic intermittent titration technique (GITT) results show that the DLi+ value of (FeCoCrMnZn)3O4 is higher than that of (FeCoCrMnMg)3O4 during charge and discharge. All of that can improve its specific discharge capacity and enhance its cycle stability. (FeCoCrMnZn)3O4 achieved a discharge capacity of 828.6 mAh g-1 at 2.0 A g-1 after 2000 cycles. This work provides a deep understanding of the structure and performance of HEO.

Controllable construction of hierarchically porous carbon composite of nanosheet network for advanced dual-carbon potassium-ion capacitors.

Benefitting from the abundance and inexpensive nature of potassium resources, potassium-ion energy storage technology is considered a potential alternative to current lithium-ion systems. Potassium-ion capacitors (PICs) as a burgeoning K-ion electrochemical energy storage device, are capable of delivering high energy at high power without sacrificing lifespan. However, owing to the sluggish kinetics and significant volume change induced by the large K+-diameter, matched electrode materials with good ion accessibility and fast K+ intercalation/deintercalation capability are urgently desired. In this work, pine needles and graphene oxide (GO) are utilized as precursors to fabricate oxygen-doped activated carbon/graphene (OAC/G) porous nanosheet composites. The introduction of GO not only induces the generation of interconnected nanosheet network, but also increases the oxygen-doping content of the composite, thus expanding the graphite interlayer spacing. Experimental analysis combined with first-principle calculations reveal the transport/storage mechanism of K+ in the OAC/G composite anode, demonstrating that the high surface area, sufficient reactive sites, enlarged interlayer distance and open channels in the porous nanosheet network contribute to rapid and effective K+ diffusion and storage. When incorporated with pine needle-activated carbon as cathode, the assembled dual-carbon PICs can function at a high voltage of 5 V, exhibiting a high energy density of 156.7 Wh kg-1 at a power density of 500 W kg-1 along with a satisfied cycle life, which highlights their potential application in economic and advanced PICs.

An improved bioinspired strategy to construct nitrogen and phosphorus dual-doped network porous carbon with boosted kinetics potassium ion capacitors.

Potassium-ion capacitors (PICs) have drawn appreciable attention because PICs can masterly integrate the virtues of the high energy density of battery-type anode and high power density of capacitor-type cathode. However, the sanguine scenario involves the incompatible capacity and sluggish kinetics in the PIC device. Herein, we report the synthesis of nitrogen and phosphorus-doped network porous carbon materials (NPMCs) via a self-sacrifice template strategy, which possesses a desired three-dimensional structure and prosperous electrochemical properties for K+ storage capacity. The obtained hierarchical porous carbon delivers a high reversible capacity of 420 mA h g-1 at 0.05 A g-1 and good cycling performance owing to its high concentration of reversible carbon defects and strong charge transfer kinetics. As expected, an advanced PIC device was assembled with a working voltage as high as 4.5 V, delivering an extraordinary energy density of 81.6 W h kg-1 as well as a splendid long life. Systematic characterization analysis combined with density functional theory calculations indicates that the strategy for preparing PIC devices with outstanding performance in this work can provide new insights for the development of PICs for an extensive range of applications.

Polyvinylpyrrolidone assisted transformation of Cu-MOF into N/P-co-doped Octahedron carbon encapsulated Cu3P nanoparticles as high performance anode for lithium ion batteries.

The large volume expansion and poor electrical conductivity of copper phosphide (Cu3P) during the cycle limit their further application as anode of lithium-ion batteries. Therefore, polyvinylpyrrolidone (PVP) modified Cu3(BTC)2-derived (BTC = 1, 3, 5-Benzentricarboxylic acid) in-situ N/P-co-doped Octahedron carbon encapsulated Cu3P nanoparticles (Cu3P@NPC) are successfully prepared through a two-step process of carbonization and phosphating. The N/P-co-doped Octahedron carbon matrix improves the conductivity of Cu3P and moderates the volume expansion during the lithiation/delithiation process. Meanwhile, the interaction between the Cu3P and the doped carbon matrix is methodically explored by using density functional theory (DFT). Through the analysis of the partial charge density, the density of states and the Bader charge, and the calculation results verify the correctness of the experimental observation results, that is, Cu3P@NPC has good electrochemical performance. The results show that Cu3P@NPC, as the anode of Lithium-ion batteries, has excellent electrochemical performance: it exhibits satisfactory rate performance (251.9 mAh g-1 at 5.0 A g-1) and excellent cycle performance (336.4 mAh g-1 at 1 A g-1 over 1000 cycles). This article provides an effective strategy for the encapsulation of metal phosphide nanoparticles in a doped carbon matrix.

Carbon defects applied to potassium-ion batteries: a density functional theory investigation.

Functionalized carbon nanomaterials are potential candidates for use as anode materials in potassium-ion batteries (PIBs). The inevitable defect sites in the architectures significantly affect the physicochemical properties of the carbon nanomaterials, thus defect engineering has recently become a vital research area for carbon-based electrodes. However, one of the major issues holding back its further development is the lack of a complete understanding of the effects accounting for the potassium (K) storage of different carbon defects, which have remained elusive. Owing to pressing research demands, the construction strategies, adsorption difficulties, and structure-activity relationships of the carbon defect-involved reaction centers for the K adsorption are systematically summarized using first principles calculations. Carbon defects affect the ability to trap K by affecting the geometry, charge distribution, and conductive behavior of the carbon surface. The results show that carbon doping with pyridinic-N, pyrrolic-N, and P defect sites tend to act as trapping K sites because of electron-deficient sites. However, graphite-N and sulfur doping are less capable of trapping K. In addition, it has been proved using calculations that the defects can inhibit the growth of the K dendrite. Finally, using the molten salt method, we prepared the undoped and nitrogen-doped carbon materials for comparison, verifying the results of the calculation.

Design of a Scalable Dendritic Copper@Ni2+, Zn2+ Cation-Substituted Cobalt Carbonate Hydroxide Electrode for Efficient Energy Storage.

Design and fabrication of novel electrode materials with excellent specific capacitance and cycle stability are urgent for advanced energy storage devices, and the combinability of multiple modification methods is still insufficient. Herein, Ni2+, Zn2+ double-cation-substitution Co carbonate hydroxide (NiZnCo-CH) nanosheets arrays were established on 3D copper with controllable morphology (3DCu@NiZnCo-CH). The self-standing scalable dendritic copper offers a large surface area and promotes fast electron transport. The 3DCu@NiZnCo-CH electrode shows a markedly improved electrochemical performance with a high specific capacity of ∼1008 C g-1 at 1 A g-1 (3.2, 2.83, and 1.26 times larger than Co-CH, ZnCo-CH, and NiCo-CH, respectively) and outstanding rate capability (828.8 C g-1 at 20 A g-1) due to its compositional and structural advantages. Density functional theory (DFT) calculation results illustrate that cation doping adjusts the adsorption process and optimizes the charge transfer kinetics. Moreover, an aqueous hybrid supercapacitor based on 3DCu@NiZnCo-CH and rGO demonstrates a high energy density of 42.29 Wh kg-1 at a power density of 376.37 W kg-1, along with superior cycling performance (retained 86.7% of the initial specific capacitance after 10,000 cycles). Impressively, these optimized 3DCu@NiZnCo-CH//rGO devices with ionic liquid can be operated stably in a large potential range of 4 V with greatly enhanced energy density and power capability (110.12 Wh kg-1 at a power density of 71.69 W kg-1). These findings may shed some light on the rational design of transition-metal compounds with tunable architectures by multiple modification methods for efficient energy storage.

CuO@NiCoFe-S core-shell nanorod arrays based on Cu foam for high performance energy storage.

Growing electroactive materials directly on a three-dimensional conductive substrate can effectively reduce the "ineffective area" of the electrode during the electrochemical reaction, increase the utilization rate of the material, and thus increase the energy density of the device. Using the network structure of the three-dimensional conductive substrate to design electrode materials with unique microstructures can also improve the stability of the materials. In this work, we obtained different copper-based materials on the copper foam (CF) by in-situ growth method, and designed an independent three-dimensional layered CuO@NiCoFe-S (CuO@NCFS) core-shell nanostructure composite material. CuO@NCFS exhibits excellent electrochemical performance, reaching a specific capacitance of 4551 mF cm-2 at a current density of 1 mA cm-2 with good cycle stability (94.2% after 5000 cycles). In addition, the asymmetric supercapacitor (ASC) uses CuO@NCFS as the positive electrode and rGO as the negative electrode, which can provide an energy rate density of 4.5 mW cm-2 at a high energy density of 99.9 µWh cm-2. The findings provide some insight into rational design of electrode materials for high performance energy storage.

One-step phosphating synthesis of CoP nanosheet arrays combined with Ni2P as a high-performance electrode for supercapacitors.

A transition metal phosphide is an excellent candidate for supercapacitors due to its superior electrical conductivity and high theoretical capacity. In addition, compared with traditional 3D nano-materials, 2D nanosheets possess a greater specific surface area and shorter electron transport distance. In this study, a reasonable approach is proposed for the synthesis of ZIF-67 nanosheets on nickel foam with subsequent phosphorization by chemical vapor deposition (CVD) to obtain flake-like CoP combined with Ni2P (NCP/NF), in which nickel foam serves as the current collector as well as the resource of Ni to form Ni2P. Benefiting from the nanosheet array of CoP, the NCP/NF can improve the capacity of Ni2P from 0.57 C cm-2 to 1.43 C cm-2 at 1 mA cm-2. Furthermore, the NPC/NF/reduced graphene oxide (RGO) asymmetric supercapacitor (ASC) shows an energy density of 26.9 µW h cm-2 at a power density of 0.896 mW cm-2, and excellent cycling performance with a capacity retention of 93.75% after 5000 cycles at 10 mA cm-2.

Dandelion-like nickel/cobalt metal-organic framework based electrode materials for high performance supercapacitors.

Metal-organic frameworks (MOFs), serving as a promising electrode material in the supercapacitors, have attracted tremendous interests in recent years. Here, through modifying the molar ratio of the Ni2+ and Co2+, we have successfully fabricated Ni-MOF and Ni/Co-MOF by a facile hydrothermal method. The Ni/Co-MOF with a dandelion-like hollow structure shows an excellent specific capacitance of 758 F g-1 at 1 A g-1 in the three-electrode system. Comparing with Ni-MOF, the obtained Ni/Co-MOF has a better rate capacitance (89% retention at 10 A g-1) and cycling life (75% retention after 5000 circulations). Besides, the assembled asymmetric supercapacitor based on Ni/Co-MOF and active carbon exhibits a high specific energy density of 20.9 W h kg-1 at the power density of 800 W kg-1. All these results demonstrate that the mixed-metal strategy is an effective way to optimize the morphology and improve the electrochemical property of the MOFs.

An Asymmetric Supercapacitor Based on Activated Porous Carbon Derived from Walnut Shells and NiCo2O4 Nanoneedle Arrays Electrodes.

A facile method was utilized to convert a common biomass of walnut shells into activated porous carbon by carbonization and activation with nitricacid treatment. The obtained activated carbon (WSs-2) exhibited excellent electrochemical performance with high specific capacitance of 137 F · g-1 at 1 A · g-1 and super cycling performance of 96% capacitance retention at 5 A · g-1 after 5000 cycles. In addition, NiCo2O4 nanoneedle arrays with good electrochemical properties were successfully prepared by a simple hydrothermal method. An aqueous asymmetric supercapacitor (ASC) device based on WSs-2 and NiCo2O4 was assembled, which delivered 21 Wh · kg-1 at a power density of 424.5 W · kg-1, and maintained 19 Wh · kg-1 at power density of 4254 W · kg-1 as well as excellent cycling stability of 99.3% capacitance retention after 5000 cycles at 4 A · g-1. Through this method, low-cost, environmentally friendly and large-scale carbon materials can be fabricated and applied in supercapacitor electrodes.

Multilayer hexagonal silicon forming in slit nanopore.

The solidification of two-dimensional liquid silicon confined to a slit nanopore has been studied using molecular dynamics simulations. The results clearly show that the system undergoes an obvious transition from liquid to multilayer hexagonal film with the decrease of temperature, accompanied by dramatic change in potential energy, atomic volume, coordination number and lateral radial distribution function. During the cooling process, some hexagonal islands randomly appear in the liquid first, then grow up to grain nuclei, and finally connect together to form a complete polycrystalline film. Moreover, it is found that the quenching rate and slit size are of vital importance to the freezing structure of silicon film. The results also indicate that the slit nanopore induces the layering of liquid silicon, which further induces the slit size dependent solidification behavior of silicon film with different electrical properties.