Superior and safer lithium sulfur batteries realized by robust polysulfides-retarding dam with high flame retardance

The unparalleled energy density has granted lithium-sulfur batteries(LSBs)with attractive usages.Unfortunately,LSBs still face some unsurpassed challenges in industrialization,with polysulfides shuttling,dendrite growth and thermal hazard as the major problems triggering the cycling instability and low safety.With the merit of convenience,the method of designing functional separator has been adapted.Concretely,the carbon aerogel confined with CoS_(2)(CoS_(2)-NCA)is constructed and coated on Celgard separator surface,acquiring CoS_(2)-NCA modified separator(CoS_(2)-NCA@C),which holds the promoted electrolyte affinity and flame retardance.As revealed,CoS_(2)-NCA@C cell gives a high discharge capacity 1536.9 mAh/g at 1st cycle,much higher than that of Celgard cell(987.1 mAh/g).Moreover,the thermal runaway triggering time is dramatically prolonged by 777.4 min,corroborating the promoted thermal safety of cell.Noticeably,the higher coulombic efficiency stability and lower overpotential jointly confirm the efficacy of CoS_(2)-NCA@C in suppressing the lithium dendrite growth.Overall,this work can provide useful inspirations for designing functional separator,coping with the vexing issues of LSBs.

Ten-Minute Synthesis of a New Redox-Active Aqueous Binder for Flame-Retardant Li-S Batteries

As a critical role in battery systems,polymer binders have been shown to efficiently suppress the lithium polysulfide shuttling and accommodate volume changes in recent years.However,preparation processes and safety,as the key criterions for Li-S batteries'practical applications,still attract less attention.Herein,an aqueous multifunction binder(named PEI-TIC)is prepared via an easy and fast epoxy-amine ring-opening reaction(10 min),which can not only give the sulfur cathode a stable mechanical property,a strong chemical adsorption and catalytic conversion ability,but also a fire safety improvement.The Li-S batteries based on the PEI-TIC binder display a high discharge capacity(1297.8 mAh g^(-1)),superior rate performance(823.0 mAh g^(-1)at 2 C),and an ultralow capacity decay rate of 0.035%over more than 800 cycles.Even under 7.1 mg cm^(-2)S-loaded,the PEI-TIC electrode can also achieve a high areal capacity of 7.2 mA h g^(-1)and excellent cycling stability,confirming its application potential.Moreover,it is also noted that TG-FTIR test is performed for the first time to explore the flame-retardant mechanism of polymer binders.This work provides an economically and environmentally friendly binder for the practical application and inspires the exploration of the flame-retardant mechanism of all electrode components.

Biobased Furfurylated Poplar Wood for Flame-Retardant Modification with Boric Acid and Ammonium Dihydrogen Phosphate

Furfurylated wood exhibits excellent dimensional stability and corrosion resistance,making it a promising material for constructing buildings,but it is highly flammable.Herein,flame-retardant furfurylated poplar wood was produced via a two-step process utilizing boric acid(BA)and ammonium dihydrogen phosphate(ADP)as flame-retardant components,and biomass-derived furfuryl alcohol(FA)as a modifier.The acidity of BA and ADP allowed them to catalyze the polymerization of FA,which formed a cross-linked network that immobilized BA and ADP inside the wood.The addition of BA/ADP substantially delayed the time to ignition from 10 to 385 s and reduced the total heat release and total smoke release by 58.75%and 77.31%,respectively.Analysis of the pyrolysis process showed that the decomposition products of BA and ADP protected the underlying furfurylated wood and diluted combustible gases.This method significantly improved the fire retardancy and smokeless properties of furfurylated wood,providing promising prospects for its application as an engineering material.

Sulfolane‑Based Flame‑Retardant Electrolyte for High‑Voltage Sodium‑Ion Batteries

Sodium-ion batteries hold great promise as next-generation energy storage systems.However,the high instability of the electrode/electrolyte interphase during cycling has seriously hindered the development of SIBs.In particular,an unstable cathode–electrolyte interphase(CEI)leads to successive electrolyte side reactions,transition metal leaching and rapid capacity decay,which tends to be exacerbated under high-voltage conditions.Therefore,constructing dense and stable CEIs are crucial for high-performance SIBs.This work reports localized high-concentration electrolyte by incorporating a highly oxidation-resistant sulfolane solvent with non-solvent diluent 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether,which exhibited excellent oxidative stability and was able to form thin,dense and homogeneous CEI.The excellent CEI enabled the O3-type layered oxide cathode NaNi_(1/3)Mn_(1/3)Fe_(1/3)O_(2)(NaNMF)to achieve stable cycling,with a capacity retention of 79.48%after 300 cycles at 1 C and 81.15%after 400 cycles at 2 C with a high charging voltage of 4.2 V.In addition,its nonflammable nature enhances the safety of SIBs.This work provides a viable pathway for the application of sulfolane-based electrolytes on SIBs and the design of next-generation high-voltage electrolytes.

Coordination bond cleavage of metal–organic frameworks and application to flame-retardant polymeric materials

The physicochemical properties of metal–organic frameworks(MOFs)are closely dependent on the topology,pore characteristics,and chemical composition,which can be tuned through targeted design.Relative to direct synthesis,the post-synthesis methods of MOFs,including ion exchange,ligand replacement as well as destruction,provide a significant increase in their application range and potential.A method based on the coordination bond cleavage of MOFs has been proved to be very effective in modulating the structure and was evaluated for its application in the flame retardant field.Herein,the construction of peculiar MOF structures is categorized based on flame-retardant features through the cleavage of coordination bonds at the molecular level,and the corresponding MOFs exhibit superior flame-retardant and smoke-suppressing properties.Different approaches are highlighted to achieve coordination bond breaking to modulate MOFs properties,involving chemical composition,topology,and pore structure.This review systematically summarizes and generalizes the direct construction of highefficiency MOF-based flame retardants based on the structure–activity relationship and their further functionalization through coordination bond cleavage,as well as the associated challenges and prospects.It is also hoped that this work will quickly guide researchers through the field and inspire their next studies.

Study on the Flame-retardant Properties of High Flame-retardant Acrylic Fiber Knitted Fabrics

This paper involved five kinds of weft-knitted fabrics made from high flame-retardant acrylic/cotton(0/100,30/70,50/50,70/30,100/0).The article adopted the vertical burning method,limiting oxygen index method and Cone Calorimeter test method for testing fabric flame retardant property.By comparison with these five fabrics,the effects on the properties of high flame-retardant acrylic fiber knitted fabrics due to the content of high flame-retardant acrylic fiber were analyzed.

Flame-retardant Mechanism of Magnesium Oxychloride in Epoxy Resin

Flame-retardant mechanism of magnesium oxychloride （M OC） in EP was in-vestigated by limiting oxygen index （LOI）, XRD, SEM, TG-DTG and DSC. The results show that MOC performed well as an inorganic flame-retardant in EP. When the content of MOC is 50%, the LOI of EP reaches 29.6% and mass of residual char reaches 9.6%. The flame retarde mechanism of MOC is due to the synergies of diluting, cooling, catalyzing char forming and obstructing effects.

STUDIES ON FLAME-RETARDANT PC/ABS MULTIPLE-ELEMENT ALLOY

The preparation technology of flame-retardant PC/ABS alloys was studied in this paper. Using a high-efficiency flame retardant system and by means of multiple-ingredient compatibilizing, PC/ABS alloys with excellent impact strength and flame retardant property were prepared. The experimental results showed that by using PS-g-MAH and SMA as synergistic compatibilizers, the notched Izod impact strength and flammability of PC/ABS alloy obtained in the present work can be up to 175 J/m and UL-94 VO, respectively.

Intumescent Flame-retardant Modification of Polypropylene/Carbon Fiber Composites

To improve the flame resistance of polypropylene(PP)/carbon fiber(CF)composite materials,triazine char-forming agent(TCA)was compounded with ammonium polyphosphate(APP)or modified APP(CS-APP)in a 2:1 ratio to prepare intumescent flame retardant(IFR)and the modified intumescent flame retardant(CS-IFR)in this paper.Flame retardancy and thermal degradation behaviors of the composites modified by IFR and CS-IFR were characterized by Fourier Transform Infrared(FTIR),contact angle measurement,oxygen index(OI),vertical burning tests(UL-94),thermogravimetric analyer(TGA),and thermogravimetric analyzer coupled with Fourier transform infrared(TG-FTIR).It was found that 25.0 phr of IFR and 24.0 phr of CS-IFR could improve the LOI value of PP/CF composites to 28.3%and 28.9%,respectively.At the same time,a UL-94 V-0 rating was achieved.The experimental results show that the IFR and CS-IFR prepared could effectively improve the flame retardancy and thermostability of PP/CF composites,and they would greatly expand the application range of PP/CF composite materials.

Flame-retardant concentrated electrolyte enabling a Li F-rich solid electrolyte interface to improve cycle performance of wide-temperature lithium–sulfur batteries

Lithium–sulfur batteries have been regarded as the most promising high-energy electrochemical energy storage device owing to the high energy density, low cost and environmental friendliness. However, traditional lithium–sulfur batteries using ether-based electrolytes often suffer from severe safety risks(i.e. combustion). Herein, we demonstrated a novel kind of flame-retardant concentrated electrolyte(6.5 M lithium bis(trifluoromethylsulphonyl)imide/fluoroethylene carbonate) for highly-safe and widetemperature lithium–sulfur batteries. It was found that such concentrated electrolyte showed superior flame retardancy, high lithium-ion transference number(0.69) and steady lithium plating/stripping behavior(2.5 m Ah cm^(-2) over 3000 h). Moreover, lithium–sulfur batteries using this flame-retardant concentrated electrolyte delivered outstanding cycle performance in a wide range of temperatures(-10 °C, 25 °C and 90 °C). This superior battery performance is mainly attributed to the LiF-rich solid electrolyte interphase formed on lithium metal anode, which can effectively suppress the continuous growth of lithium dendrites. Above-mentioned fascinating characteristics would endow this flame-retardant concentrated electrolyte a very promising candidate for highly-safe and wide-temperature lithium–sulfur batteries.

Thermal Runaway of Lithium-Ion Batteries Employing Flame-Retardant Fluorinated Electrolytes

Fluorinated electrolytes possess good antioxidant capacity that provides high compatibility to high-voltage cathode and flame retardance;thus,they are considered as a promising solution for advanced lithium-ion batteries carrying both high-energy density and high safety.Moreover,the fluorinated electrolytes are widely used to form stable electrolyte interphase,due to their chemical reactivity with lithiated graphite or lithium.However,the influence of this reactivity on the thermal safety of batteries is seldom discussed.Herein,we demonstrate that the flame-retardant fluorinated electrolytes help to reduce the flammability,while the lithium-ion batteries with flame-retardant fluorinated electrolytes still undergo thermal runaway and disclose their different thermal runaway pathway from that of battery with conventional electrolyte.The reduction in fluorinated components(e.g.,LiPF 6 and fluoroethylene carbonate(FEC))by fully lithiated graphite accounts for a significant heat release during battery thermal runaway.The 13%of total heat is sufficient to trigger the chain reactions during battery thermal runaway.This study deepens the understanding of the thermal runaway mechanism of lithium-ion batteries employing flame-retardant fluorinated electrolytes,providing guidance on the concept of electrolyte design for safer lithium-ion batteries.

Borate-Modified,Flame-Retardant Paper Packaging Materials for Archive Conservation

Paper packaging materials like cardboards are widely used to protect archives which are a major kind of cultural relics.Unfortunately,paper is a combustible material,and thus exploring environment-friendly flame retardant for paper-based archive packaging material plays an important role.Herein,boric acid,borax and disodium octaborate are used to modify the craft paper-based packaging materials for archive conservation to improve fire safety.The modified craft paper exhibits much higher flame retardancy than the pristine one dose based on vertical burning tests,without much influence on mechanical properties such as tensile strength and elongation at break.Thermogravimetric analysis(TGA),scanning electron microscope(SEM),and X-ray photoelectron spectroscopy(XPS)reveal that porous glass structure is formed during the combustion,because thermal decomposition of boric acid,borax and disodium octaborate will produce porous glassy matter as B_(2)O_(3).The porous glass covers the paper surface as an insulating layer which retards the further pyrolysis and combustion,resulting in a denser carbon layer.Our study provides a robust way to reduce the fire hazard of the archive packaging material by applying environment-friendly boron-based fire retardants.

Flame-retarding battery cathode materials based on reversible multi-electron redox chemistry of phenothiazine-based polymer

Polymeric organic battery materials are promising alternatives to the transition-metal-based ones owing to their enriched chemistries. However, the flammability of organic compounds brings in serious concern on battery safety. In addition to use flame-retarding electrolyte/electrolyte additives or battery separators,flame retardancy can readily be achieved through the integration of flame-retarding unit into the polymer backbone, imparting the flame retardancy permanently. The as-designed polymer based on phenothiazine shows significantly shortened self-extinguished time without deteriorating its intrinsic thermodynamic and electrochemical properties. Moreover, two electron per phenothiazine molecule is realized for the first time in a highly reversible manner with discharge voltages of 3.52 V and 4.16 V versus Li+/Li and an average capacity of ca. 120 mAh g-1 at a current rate of 2 C. The origin of the reversibility is investigated through density functional theory(DFT) calculations. These findings address the importance of molecular design for safer and more stable organic materials for batteries.

Characterizations of Phosphorus-containing Flame-retardant Poly(Ethylene Terephthalate) Copolyester

Copolyesters of phosphorus - containing flame - retardant poly(Ethylene Terephthalate) (PET) have been prepared and characterized with the objection of producing an effective, environmentally friendly, nonfugitive alternatives to halogen flame retardant system for practical application. With means of NMR, DSC, DTA/TGA, SEM and LOI, structure, thermal property and flam-mability are investigated which reveal that the flame -retardant PET when copolymerized with 2 - carboxyethyl (phenylphosphinic) acid (CEPP) confers excellent fire retardancy with LOI 】 28, broader thermal degradation temperature and increased char formation.

Synthesis, Characterization and Flame-retardant Properties of Epoxy Resins and AACHH Composites

Flame retardant epoxy resins were prepared by a simple mixed method using ammonium aluminum carbonate hydroxy hydrate （AACHH） as a halogen-free flame retardant. The prepared samples were characterized by X-ray diffraction, thermogravimetric and differential scanning calorimetry, scanning electron microscope and limiting oxygen index（LOI） experiments. Effects of AACHH content on LOI of epoxy resins/AACHH composite and flame retardant mechanism were investigated and discussed. Results show that AACHH exhibites excellent flame-retardant properties in epoxy resin（EP）. When the content of AACHH was 47.4%, the LOI of EP reached 32.2%. Moreover, the initial and terminal decomposition temperature of EP increased by 48 ℃ and 40 ℃, respectively. The flame retarded mechanism of AACHH is due to the synergic flame retardant effects of diluting, cooling, decomposition resisting and obstructing.

PRELIMINARY STUDIES ON STRUCTURES AND PROPERTIES OF WATER-RETENTIVE, FLAME-RETARDANT ACRYLIC FIBERS

The blend fibers of acrylonitrile-vinylidene chloride-sodium methallysulfonate copolymer(AN-VDC-SMAS) and cellulose acetate (CA) with various blend ratios were investigated bymeans of SEM, DDV, WAXD, etc. The results show that AN-VDC-SMAS and CA areincompatibale; the numerous microvoids in the blend fiber resulted from the phase seperationcan remarkably improve the water absorbability and the dyeing behavior but hardly influencethe mechanical properties. On the other hand, the crystal structure of the continuous phaseAN-VDC-SMAS is not influnced by the dispersed phase CA.

Porous Flame-retarded Asphalt Pavement for Highway Tunnel

A new way to improve the tunnel fire protection by using flame-retarded porous asphalt pavement containing ATH powders was introduced. Based on the miniature burning test designed and conducted, the burning time and temperature of porous asphalt （PA） and flame-retarded porous asphalt （FRPA） were studied comparing with cement concrete pavement, dense-graded lIMA and SMA. Results of burning test and pavement performance test indicate that FRPA is appropriate and suitable as the pavement material of highway tunnel.

Pyrolysis Mechanism of a Cyclotriphosphazene-Based Flame-Retardant Epoxy Resin by ReaxFF Molecular Dynamics

Cyclotriphosphazene derivatives can effectively improve the flame retardancy and fire safety of epoxy resins(EPs)via their influence on the pyrolysis process.In this work,the effects of hexa(5-methyl-2-pyridinoxyl)cyclotriphosphazene(HMPOP)incorporation on the initial pyrolysis of an EP at 500–3500 K were studied using the ReaxFF method.The pyrolysis fragments,initial reaction pathways,and main products were identified for the EP and EP/HMPOP composites.The activation energies were derived by fitting the weight percentage curves for solid species during the pyrolysis reactions and the obtained values were in good agreement with experimental data.The initial EP pyrolysis reactions included four major decomposition modes,which primarily involved the cleavage of C–O and C–N bonds.The main pyrolysis products were H_(2)O,CO,C_(2)H_(4),and CH_(2)O.HMPOP bonded with the oxygen-containing fragments to form larger molecular fragments and reduced the amounts of C_(0)–C_(4) products,especially that of the harmful gas CH_(2)O.Thus,HMPOP promoted the formation of carbon clusters and reduced the generation of combustible gases,ultimately decreasing the capacity for fire propagation.

Deflagration characteristics of freely propagating flames in magnesium hydride dust clouds

The flame propagation processes of MgH_(2)dust clouds with four different particle sizes were recorded by a high-speed camera.The dynamic flame temperature distributions of MgH_(2)dust clouds were reconstructed by the two-color pyrometer technique,and the chemical composition of solid combustion residues were analyzed.The experimental results showed that the average flame propagation velocities of 23μm,40μm,60μm and 103μm MgH_(2)dust clouds in the stable propagation stage were 3.7 m/s,2.8 m/s,2.1 m/s and 0.9 m/s,respectively.The dust clouds with smaller particle sizes had faster flame propagation velocity and stronger oscillation intensity,and their flame temperature distributions were more even and the temperature gradients were smaller.The flame structures of MgH_(2)dust clouds were significantly affected by the particle sinking velocity,and the combustion processes were accompanied by micro-explosion of particles.The falling velocities of 23μm and 40μm MgH_(2)particles were 2.24 cm/s and 6.71 cm/s,respectively.While the falling velocities of 60μm and 103μm MgH_(2)particles were as high as 15.07 cm/s and 44.42 cm/s,respectively,leading to a more rapid downward development and irregular shape of the flame.Furthermore,the dehydrogenation reaction had a significant effect on the combustion performance of MgH_(2)dust.The combustion of H_(2)enhanced the ignition and combustion characteristics of MgH_(2)dust,resulting in a much higher explosion power than the pure Mg dust.The micro-structure characteristics and combustion residues composition analysis of MgH_(2)dust indicated that the combustion control mechanism of MgH_(2)dust flame was mainly the heterogeneous reaction,which was affected by the dehydrogenation reaction.