Hybrid supercapacitors using metal-organic framework derived nickel-sulfur compounds.

HYPOTHESIS: Metal-organic frameworks (MOFs) are highly suitable precursors for supercapacitor electrode materials owing to their high porosity and stable backbone structures that offer several advantages for redox reactions and rapid ion transport. EXPERIMENTS: In this study, a carbon-coated Ni9S8 composite (Ni9S8@C-5) was prepared via sulfuration at 500 ℃ using a spherical Ni-MOF as the sacrificial template. FINDING: The stable carbon skeleton derived from Ni-MOF and positive structure-activity relationship due to the multinuclear Ni9S8 components resulted in a specific capacity of 278.06 mAh·g-1 at 1 A·g-1. Additionally, the hybrid supercapacitor (HSC) constructed using Ni9S8@C-5 as the positive electrode and the laboratory-prepared coal pitch-based activated carbon (CTP-AC) as the negative electrode achieved an energy density of 69.32 Wh·kg-1 at a power density of 800.06 W·kg-1, and capacity retention of 83.06 % after 5000 cycles of charging and discharging at 5 A·g-1. The Ni-MOF sacrificial template method proposed in this study effectively addresses the challenges associated with structural collapse and agglomeration of Ni9S8 during electrochemical reactions, thus improving its electrochemical performance. Hence, a simple preparation method is demonstrated, with broad application prospects in supercapacitor electrodes.

The ordered lattice host framework induced guest Li+ disordering in high performance cobalt-free Ni-rich cathode materials.

Recently, due to high price, resource shortage and unstable supply of cobalt, the development of low-cost cobalt-free Ni-rich cathodes has attracted extensive attention with the ever-increasing lithium-ion batteries (LIBs) industry. Selecting cost-effective elements to replace cobalt in Ni-rich cathodes is urgent. However, the principle of structural design of Ni-rich cathode remains unclear, hampering the selection of alternative elements. Herein, the cobalt-free cathodes of LiNi0.95Mg0.05O2 (NiMg) and LiNi0.95Mn0.05O2 (NiMn) are designed as alternatives to LiNi0.96Co0.04O2 (NiCo). NiMg has comparable cycle stability with NiCo, while NiMn has inferior cycle performance. Reverse Monte Carlo modelling was used to generate structural model and uncover local structure by fitting pair distribution function. It reveals Mn causes more severe Jahn-Teller distortions and disordered lattice host framework (Ni0.95M0.05O2, M = Co/Mn/Mg) than Co and Mg due to the strong size effect and coulomb interactions of Mn in Ni0.95Mn0.05O2 layer. The outstanding cycle stability of NiMg and NiCo originates from the ordered lattice host frameworks, which relieve stress and inhibit particle breakage during cycle. Meanwhile, the ordered lattice host framework induced guest Li+ disordering reduces Li+ diffusion energy barrier, improving the rate capability. This study provides a new perspective for the structural design of cobalt-free Ni-rich cathodes.

A Novel Method of Improving the Mechanical Properties of Propellant Using Energetic Thermoplastic Elastomers with Bonding Groups.

The relatively poor mechanical properties of extruded modified double base (EMDB) propellants limit their range of applications. To overcome these drawbacks, a novel method was proposed to introduce glycidyl azide polymer-based energetic thermoplastic elastomers (GAP-ETPE) with bonding groups into the propellant adhesive. The influence of the molecular structure of three kinds of elastomers on the mechanical properties of the resultant propellant was analyzed. It was found that the mechanical properties of the propellant with 3% CBA-ETPE (a type of GAP-ETPE that features chain extensions using N-(2-Cyanoethyl) diethanolamine and 1,4-butanediol) were improved at both 50 °C and -40 °C compared to a control propellant without GAP-ETPE. The elongation and impact strength of the propellant at -40 °C were 7.49% and 6.58 MPa, respectively, while the impact strength and maximum tensile strength of the propellant at 50 °C reached 21.1 MPa and 1.19 MPa, respectively. In addition, all three types of GAP-ETPE improved the safety of EMDB propellants. The friction sensitivity of the propellant with 3% CBA-ETPE was found to be 0%, and its characteristic drop height H50 was found to be 39.0 cm; 126% higher than the traditional EMDB propellant. These results provide guidance for studies aiming to optimize the performance of EMDB propellants.

Preparation and Properties of a Novel High-Toughness Solid Propellant Adhesive System Based on Glycidyl Azide Polymer-Energetic Thermoplastic Elastomer/Nitrocellulose/Butyl Nitrate Ethyl Nitramine.

Glycidyl azide polymer (GAP)-energetic thermoplastic elastomer (GAP-ETPE) propellants have high development prospects as green solid propellants, but the preparation of GAP-ETPEs with excellent performance is still a challenge. Improving the performance of the adhesive system in a propellant by introducing a plasticizer is an effective approach to increasing the energy and toughness of the propellant. Herein, a novel high-strength solid propellant adhesive system was proposed with GAP-ETPEs as the adhesive skeleton, butyl nitrate ethyl nitramine (Bu-NENA) as the energetic plasticizer, and nitrocellulose (NC) as the reinforcing agent. The effects of the structural factors on its properties were studied. The results showed that the binder system would give the propellant better mechanical and safety properties. The results can provide a reference for the structure design, forming process, and parameter selection of high-performance GAP-based green solid propellants.

Conductive MOF on ZIF-Derived Carbon Fibers as Superior Anode in Sodium-Ion Battery.

Superior specific capacity, high-rate capability, and long-term cycling stability are essential to anode materials in sodium-ion batteries, and conductive metal-organic frameworks (cMOF) with good electronic and ionic conductivity may satisfy these requirements. Herein, conductive neodymium cMOF (Nd-cMOF) produced in situ on the zeolitic imidazolate framework (ZIF)-derived carbon fiber (ZIF-CFs) platform is used to synthesize the Nd-cMOF/ZIF-CFs hierarchical structure. Four types of ZIFs with different pore diameters are prepared by electrospinning. In this novel structure, ZIF-CFs provide the electroconductivity, flexible porous structure, and mechanical stability, while Nd-cMOF provides the interfacial kinetic activity, electroconductivity, ample space, and volume buffer, consequently giving rise to robust structural integrity and excellent conductivity. The sodium-ion battery composed of the Nd-cMOF/ZIF-10-CFs anode has outstanding stability and electrochemical properties, such as a specific capacity of 480.5 mAh g-1 at 0.05 A g-1 as well as capacity retention of 84% after 500 cycles.

Preparation and Properties of Hydrophobic Polyurethane Based on Silane Modification.

Waterborne coatings have obtained more and more attention from researchers with increasing concerns in environmental protection, and have the advantages of being green, environmentally friendly and safe. However, the introduction of hydrophilic groups leads to lower hydrophobicity and it is difficult to meet the requirements of complex application environments. Herein, we proposed an optimization approach of waterborne polyurethane (WPU) with vinyl tris(ß-methoxyethoxy) silane (A172), and it was found that the surface roughness, mechanical properties, thermal stability and water resistance of WPU will be increased to a certain extent with the addition of A172. Moreover, the hydrophobicity of the coating film is best when the silicon content is 10% of the acrylic monomer mass and the water contact angle reaches 100°, which could exceed two-thirds of the research results in the last decade. Therefore, our study can provide some theoretical basis for the research of hydrophobic polyurethane coatings.

Interface Engineering via Regulating Electrolyte for High-Voltage Layered Oxide Cathodes-Based Li-Ion Batteries.

Li-rich and Ni-rich layered oxides as next-generation high-energy cathodes for lithium-ion batteries (LIBs) possess the catalytic surface, which leads to intensive interfacial reactions, transition metal ion dissolution, gas generation, and ultimately hinders their applications at 4.7 V. Here, robust inorganic/organic/inorganic-rich architecture cathode-electrolyte interphase (CEI) and inorganic/organic-rich architecture anode-electrolyte interphase (AEI) with F-, B-, and P-rich inorganic components through modulating the frontier molecular orbital energy levels of lithium salts are constructed. A ternary fluorinated lithium salts electrolyte (TLE) is formulated by mixing 0.5 m lithium difluoro(oxalato)borate, 0.2 m lithium difluorophosphate with 0.3 m lithium hexafluorophosphate. The obtained robust interphase effectively suppresses the adverse electrolyte oxidation and transition metal dissolution, significantly reduces the chemical attacks to AEI. Li-rich Li1.2 Mn0.58 Ni0.08 Co0.14 O2 and Ni-rich LiNi0.8 Co0.1 Mn0.1 O2 in TLE exhibit high-capacity retention of 83.3% after 200 cycles and 83.3% after 1000 cycles under 4.7 V, respectively. Moreover, TLE also shows excellent performances at 45 °C, demonstrating this inorganic rich interface successfully inhibits the more aggressive interface chemistry at high voltage and high temperature. This work suggests that the composition and structure of the electrode interface can be regulated by modulating the frontier molecular orbital energy levels of electrolyte components, so as to ensure the required performance of LIBs.

Ultrahigh Nitrogen Content Carbon Nanosheets for High Stable Sodium Metal Anodes.

Sodium metal, with a high theoretical specific capacity of 1165 mAh g-1 , is the ultimate anode for sodium batteries, yet how to deal with the inhomogeneous and dendritic sodium deposition and the infinite relative dimension change of sodium metal anodes during sodium depositing/stripping is still challenging. Here, a facile fabricated sodiuphilic 2D N-doped carbon nanosheets (N-CSs) are proposed as sodium host material for sodium metal batteries (SMBs) to prevent dendrite formation and eliminate volume change during cycling. Revealing from combined in situ characterization analyses and theoretical simulations, the high nitrogen content and porous nanoscale interlayer gaps of the 2D N-CSs can not only concede dendrite-free sodium stripping/depositing but also accommodate the infinite relative dimension change. Furthermore, N-CSs can be easily process into N-CSs/Cu electrode via traditional commercial battery electrode coating equipment that pave the way for large-scale industrial applications. On account of the abundant nucleation sites and sufficient deposition space, N-CSs/Cu electrodes demonstrate a superior cycle stability of more than 1500 h at a current density of 2 mA cm-2 with a high coulomb efficiency of more than 99.9% and ultralow nucleation overpotential, which enable reversible and dendrites-free SMBs and shed light on further development of SMBs with even higher performance.

Influence of Solid Filler on the Rheological Properties of Propellants Based on Energetic Thermoplastic Elastomer.

Glycidyl azide polymer-energetic thermoplastic elastomer propellant (GAP-ETPE) has high development prospects as a green solid propellant, although the preparation of GAP-ETPE with excellent performance is still a challenge. Focusing on the demand of high-strength solid propellants for free-loading rocket motors, a GAP-ETPE model propellant with excellent overall performance was prepared in this work, and the influence of adhesive structure characteristics on its fluidity was studied. Furthermore, the influence of filler on the rheological properties of the model propellant was investigated by introducing hexogen (RDX) and Al, and a corresponding two-phase model was established. The results may provide a reference for the structural design, molding process, and parameter selection of high-performance GAP-based green solid propellants.

Tailoring electrolyte enables high-voltage Ni-rich NCM cathode against aggressive cathode chemistries for Li-ion batteries.

The LiNi0.8Co0.1Mn0.1O2 (Ni-rich NCM) cathode materials suffer from electrochemical performance degradation upon cycling due to detrimental cathode interface reactions and irreversible surface phase transition when operating at a high voltage (≥4.5 V). Herein, a traditional carbonate electrolyte with lithium difluoro(oxalato)borate (LiDFOB) and tris(trimethylsilyl)phosphate (TMSP) as dual additives that can preferentially oxidize and decompose to form a stable F, B and Si-rich cathode-electrolyte interphase (CEI) that effectively inhibits continual electrolyte decomposition, transition metal dissolves, surface phase transition and gas generation. In addition, TMSP also removes trace H2O/HF in the electrolyte to increase the electrolyte stability. Owing to the synergistic effect of LiDFOB and TMSP, the Li/LiNi0.8Co0.1Mn0.1O2 half cells exhibit the capacity retention 76.3% after 500 cycles at a super high voltage of 4.7 V, the graphite/LiNi0.8Co0.1Mn0.1O2 full cells exhibit high capacity retention of 82.8% after 500 cycles at 4.5 V, and Li/LiNi0.8Co0.1Mn0.1O2 pouch cells exhibit high capacity retention 94% after 200 cycles at 4.5 V. This work is expected to provide an effective electrolyte optimizing strategy compatible with high energy density lithium-ion battery manufacturing systems.

Research on Mechanical Properties and Sensitivity of a Novel Modified Double-Base Rocket Propellant Plasticized by Bu-NENA.

The research and development of rocket propellants with a high solid content and superior mechanical and security performance is urgently needed. In this paper, a novel extruded modified double-base (EMDB) rocket propellant plasticized by N-butyl-N-nitratoethyl nitramine (Bu-NENA) was prepared to overcome this challenge. The results indicated that Bu-NENA decreased the mechanical sensitivity successfully, contributing to the mechanical properties against traditional nitroglycerin (NG) based EMDB propellants, while hexogen (RDX), which is beneficial to propellant energy, was not conducive to the elongation and sensitivity of the propellants. By contrast with the blank group (NG-based EMDB propellant, R0), the elongation of the optimized propellant at -40 °C was promoted by 100% from 3.54% to 7.09%. Moreover, the ß-transition temperature decreased from -33.8 °C to -38.1 °C due to superior plasticization by Bu-NENA, which represents a better toughness. The friction sensitivity dropped by 100% from 46% to 0%. Simultaneously, the height for 50% probability of explosion (H50) increased by 87.2% from 17.2 cm to 32.2 cm. The results of this research could be used to predict a potential prospect in tactical weapons.

Preparation and Properties of Double-Crosslinked Hydroxyapatite Composite Hydrogels.

Natural polymer hydrogels have good mechanical properties and biocompatibility. This study designed hydroxyapatite-enhanced photo-oxidized double-crosslinked hydrogels. Hyaluronic acid (HA) and gelatin (Gel) were modified with methacrylate anhydride. The catechin group was further introduced into the HA chain inspired by the adhesion chemistry of marine mussels. Hence, the double-crosslinked hydrogel (HG) was formed by the photo-crosslinking of double bonds and the oxidative-crosslinking of catechins. Moreover, hydroxyapatite was introduced into HG to form hydroxyapatite-enhanced hydrogels (HGH). The results indicate that, with an increase in crosslinking network density, the stiffness of hydrogels became higher; these hydrogels have more of a compact pore structure, their anti-degradation property is improved, and swelling property is reduced. The introduction of hydroxyapatite greatly improved the mechanical properties of hydrogels, but there is no change in the stability and crosslinking network structure of hydrogels. These inorganic phase-enhanced hydrogels were expected to be applied to tissue engineering scaffolds.

Modulation of Redox Chemistry of Na2Mn3O7 by Selective Boron Doping Prompted by Na Vacancies.

The small energy density and chemomechanical degradation of layered manganese oxide limit practical application to sodium-ion batteries (SIBs). Typically, Na2Mn3O7 shows a low redox plateau at 2.1 V versus Na/Na+, and the oxygen redox reaction at a high voltage causes structural collapse. Herein, a Na vacancy-induced boron doping strategy is demonstrated to improve the properties. Boron is incorporated into selective sites in the lattice in the center of the MnO6 octahedral ring at the O-layer. Bonding of boron in the TM layer enhances the electrochemical activity of low-valence Mn, giving rise to two reversible redox peaks at 2.45 and 2.55 V to enhance the average redox voltage. At the same time, the O 2p chemical state becomes weaker around the Fermi level, thus suppressing oxygen overoxidation for the high charge state and strengthening the layered structure during the redox reactions. The reduced Mn-O covalency and small diffusion barrier energy stemming from bonding of boron in the oxygen layer produce excellent rate characteristics. Modulation of the Mn 3d and O 2p orbital in Na2Mn3O7 by Na vacancies leads to selective doping of boron at different sites, and our results reveal that it is an important strategy for studying transition-metal-oxide-layered electrode materials.

Local Structures of Soft Carbon and Electrochemical Performance of Potassium-Ion Batteries.

Due to climate variation and global warming, utilization of renewable energy becomes increasingly imperative. Rechargeable potassium-ion batteries (PIBs) have lately attracted much attention due to their earth-abundance and cost-effectiveness. Because soft carbon materials are cheap, abundant, and safe, extensive feasible research studies have indicated that they could become promising anode materials for PIBs. In spite of gaining achievements, fundamental questions regarding effects of the basic structure unit inside soft carbon on potassium storage potential have not been sufficiently addressed yet. Here, a series of soft carbon pyrolyzed from 900 to 2900 °C were systematically and quantitatively characterized by combining Raman spectroscopy, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, X-ray pair distribution function analysis, and advanced evaluation of wide-angle X-ray scattering data. All these characterizations reveal structural details of soft carbon with increasing pyrolysis temperature. Our results show that the potassium storage behavior, especially the potential plateau is closely correlated to non-uniformity in interlayer distance and defect concentration in soft carbon, which is further confirmed by reverse Monte Carlo (RMC) modeling and density functional theory calculation. On the basis of these results, optimizing strategies are discussed to design an advanced soft carbon anode. This work provides significant insights into the structure engineering of soft carbon for high-performance rechargeable PIBs.

Realization of a High-Voltage and High-Rate Nickel-Rich NCM Cathode Material for LIBs by Co and Ti Dual Modification.

Nickel-rich Li(NixCoyMn1-x-yO2) (x ≥ 0.6) is considered to be a predominant cathode for next-generation lithium-ion batteries (LIBs) due to its towering specific energy density. Unfortunately, serious structural degradation causes rapid capacity degradation with the increase in nickel content. Herein, a Co and Ti co-modified LiNi0.8Co0.1Mn0.1O2 (NCM-811) cathode ameliorates the reversible capacity together with the rate capability by obviously alleviating the lattice structure degradation and microscopic intergranular cracks. Further studies show that the titanium doping effectively reduces the cation mixing and also stabilizes the crystal structure, while the spinel phase formed at the surface by a cobalt oxide coating is much stable than the layered phase at high voltage, which can alleviate the generation of micro-cracks. After 0.5% Co oxide coating and 1% Ti doping (T1Co0.5-NCM), a superior rate capability (121.75 mA h g-1 at 20 C between 2.7 and 4.5 V) and predominant capacity retention (74.2%) are observed compared with the pristine NCM-811 (59.5%) after 400 cycles between 2.7 and 4.7 V. This work supplies an eminent design of high-voltage and high-rate layered cathode materials and has a huge application prospect in the next generation of high-energy LIBs.

Boosting Li/Na storage performance of graphite by defect engineering.

Regulating material properties by accurately designing its structure has always been a research hotspot. In this study, by a simple and eco-friendly mechanical ball milling, we could successfully engineer the defect degree of the graphite. Moreover, according to the accurate deconstruction of the structure by atomic pair distribution function analysis (PDF) and X-ray absorption near-edge structure analysis (XANES), those structural defects of the ball-milled graphite (BMG) mainly exist as carbon atom vacancies within the graphene structure, which are beneficial to enhance the lithium and sodium storage performance of BMG. Therefore, BMG-30 h exhibits superior lithium and sodium storage performance.

Hard carbon spheres prepared by a modified Stöber method as anode material for high-performance potassium-ion batteries.

The Stöber method is a highly efficient synthesis strategy for homogeneous monodisperse polymer colloidal spheres and carbon spheres. This work delivers an extended Stöber method and investigates the synthesis process. By calcining the precursor under appropriate conditions, solid secondary particles of amorphous carbon (SSAC) and hollow secondary particles of graphitized carbon (HSGC) can be directly synthesized. The two materials have a nano-primary particle structure and a closely-packed sub-micron secondary particle structure, which can be used in energy storage. We find that SSAC and HSGC have high potassium-ion storage capacity with reversible capacities of 274 mA h g-1 and 283 mA h g-1 at 20 mA g-1 respectively. Significantly, SSAC has better rate performance with a specific capacity of 107 mA h g-1 at 1 A g-1.

First identification of a Brucella abortus biovar 4 strain from yak in Tibet, China.

Brucellosis is one of the major zoonotic diseases in the world. In China, understanding on its causative agent Brucella is still limited. Recently, we isolated a Brucella strain XZ19-1 from yak in Lhasa, Tibet. Phenotypical characterization proved that it belongs to B. abortus biovar 4, a biotype that has never been reported in China. MLVA-16 genotyping revealed a novel profile (4-5-3-12-2-2-3-3-8-32-8-5-4-3-3-3) in this strain, while MLST sequence typing demonstrated that it belongs to ST 71. Furthermore, the whole genome of XZ19-1 strain was sequenced. Subsequent phylogenetic analysis demonstrated that XZ19-1was genetically more closely related to B. abortus strains originated from European countries rather than to those collected from China previously. Isolation and identification of XZ19-1 strain may thus indicate a unique Brucella lineage existing in Qing-Tibet plateau. These findings will help to improve the diagnosis and epidemiological studies of brucellosis in animals and human in this part of China.

Fabrication of Polytetrafluoroethylene Coated Micron Aluminium with Enhanced Oxidation.

Aluminium (Al) powders of micron size are widely applied to energetic materials as a high energy fuel. However, its energy conversion efficiency is generally low due to low oxidation activity. In this paper, a polytetrafluoroethylene (PTFE) coating layer with both protection and activation action was successfully introduced onto the surface of Al via adsorption and following heat treatment. The preparation conditions were optimized and the thermal activity of this core-shell composite material was studied. The potential enhancement mechanism for Al oxidation was proposed. The results showed that PTFE powders deformed into membrane on the surface of Al after the sintering process. This polymer shell could act as an effective passivation layer protecting internal Al from oxidation during aging. The reduction in metallic Al of Al/PTFE was decreased by 84.7%, more than that in original spherical Al when the aging time is 60 days. Moreover, PTFE could react with Al resulting in a thin AlF3 layer, which could promote the destruction of Al2O3 shell. Thus, PTFE could enhance oxidation activity of micro-Al. The conversion of Al was increased by a factor of 1.8 when heated to 1100 °C. Improved aging-resistant performance and promoted oxidation activity of Al could potentially broaden its application in the field of energetic materials.

In†Situ Self-Assembly of Core-Shell Multimetal Prussian Blue Analogues for High-Performance Sodium-Ion Batteries.

Metal-organic frameworks (MOFs), such as Prussian blue and its analogues (PB and PBAs) with open frameworks have attracted tremendous attentions as cathode materials for sodium-ion batteries, owing to their simple method of synthesis and high theoretical specific capacity. In this study, core-shell-structured PBAs are prepared by an in situ self-assembly method. Owing to the advantages of both constituents, the as-prepared core-shell PBAs show excellent rate and cycling electrochemical properties through a dual-level-controlled charge-discharge depth mechanism. It delivers a specific capacity of 104.3 mAh g-1 at 0.1 C, as well as a remarkably enhanced cycle performance, giving 88.3 % of its initial capacity over 1000 cycles at 300 mA g-1 . In particular, the coating strategy described herein could be extended to other MOF materials, leading to wider application in energy storage.