Flame-retardant ammonium polyphosphate/MXene decorated carbon foam materials as polysulfide traps for fire-safe and stable lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries are one of the most promising modern-day energy supply systems because of their high theoretical energy density and low cost.However,the development of high-energy density Li-S batteries with high loading of flammable sulfur faces the challenges of electrochemical performance degradation owing to the shuttle effect and safety issues related to fire or explosion accidents.In this work,we report a three-dimensional(3D)conductive nitrogen-doped carbon foam supported electrostatic self-assembled MXene-ammonium polyphosphate(NCF-MXene-APP)layer as a heat-resistant,thermally-insulated,flame-retardant,and freestanding host for Li-S batteries with a facile and costeffective synthesis method.Consequently,through the use of NCF-MXene-APP hosts that strongly anchor polysulfides,the Li-S batteries demonstrate outstanding electrochemical properties,including a high initial discharge capacity of 1191.6 mA h g^(-1),excellent rate capacity of 755.0 mA h g^(-1)at 1 C,and long-term cycling stability with an extremely low-capacity decay rate of 0.12%per cycle at 2 C.More importantly,these batteries can continue to operate reliably under high temperature or flame attack conditions.Thus,this study provides valuable insights into the design of safe high-performance Li-S batteries.

Solid-liquid phase equilibrium for the system ammonium polyphosphate-urea ammonium nitrate-potassium chloride-water at 273.2 K

Based on the dynamic method,a quaternary system of ammonium polyphosphate (APP)-urea ammonium nitrate (UAN,CO(NH_(2))_(2)-NH_(4)NO_(3))-potassium chloride (KCl)-H_(2)O and its subsystems (APP-[CO(NH_(2))_(2)-NH_(4)NO_(3)]-H_(2)O,KCl-[CO(NH_(2))_(2)-NH_(4)NO_(3)]-H_(2)O and APP-KCl-H_(2)O) were systematically investigated at the temperature of 273.2 K.Each ternary phase diagram contains one invariant point and three crystallization regions.The crystallization regions are:(1)(NH_(4))_(3)HP_(2)O_(7),(NH_(4))_(4)P_(2)O_(7)and ((NH_(4))_(3)HP_(2)O_(7)+(NH_(4))_(4)P_(2)O_(7)) for APP-[CO(NH_(2))_(2)-NH_(4)NO_(3)]-H_(2)O diagram;(2) KCl,KNO_(3)and(KCl+KNO_(3)) for KCl-[CO(NH_(2))_(2)-NH_(4)NO_(3)]-H_(2)O diagram and (3)(NH_(4))_(3)HP_(2)O_(7),KCl and((NH_(4))_(3)HP_(2)O_(7)+KCl) for APP-KCl-H_(2)O diagram.The quaternary phase diagram of APP-[CO(NH_(2))_(2)-NH_(4)NO_(3)]-KCl-H_(2)O has no quaternary invariant point but includes four solid phase crystallization regions,i.e.,(NH_(4))_(3)HP_(2)O_(7),(NH_(4))_(4)P_(2)O_(7),KNO_(3)and KCl,in which the KNO_(3)region occupies the largest area.The maximum total nutrient content (N+P_(2)O_(5)+K_(2)O) existing as ionic forms in the APP-[CO(NH_(2))_(2)-NH_(4)NO_(3)]-H_(2)O,KCl-[CO(NH_(2))_(2)-NH_(4)NO_(3)]-H_(2)O,APP-KCl-H_(2)O and quaternary systems is 44.70%,32.86%,45.56%and 46.23%(mass),respectively,indicating that the maximum nutrient content can be reached using raw materials of the corresponding systems to prepare liquid fertilizer.In the quaternary system,the content of NH_(4)~+-N ascends with the increase of the total nutrient content,while the contents of NO_(3)^(-)-N and CO(NH_(2))_(2)-N increase with elevated total N.This work can help optimize the operating parameters for the production,storage and transportation of liquid fertilizers.

Study of Crystal Defects and Spectroscopy Characteristics of Ammonium Polyphosphate

Two kinds of commercial ammonium polyphosphate （APP） and three kinds of APP which were prepared in the laboratory were studied by X-ray diffraction （XRD）, Fourier transforms infrared spectroscopy （FTIR）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. In identification of the form Ⅱ crystal APP by XRD and FTIR, some discrepancies were discussed. It is pointed out that the absorbance of the FTIR spectra at 682 cm^-1 can exist not only in the form Ⅰ APP, but also in the form Ⅱ APP with the crystal lattice defects. The SEM images indicate that the form Ⅱ APP is of multilayer crystal structure. XRD and TEM can reveal the crystal lattice defects.

Synergistic Flame Retardant Effect of Ammonium Polyphosphate and Aluminum Hydroxide on Polyurethane

The flame-retardant properties of polyurethane(PU)containing ammonium polyphosphate(APP)and aluminum hydroxide(ATH)were investigated.Moreover,the flame retardant performance was investigated through thermogravimetric analysis,limiting oxygen index(LOI),vertical combustion(UL 94),and cone calorimeter.When 15 wt%APP and 5 wt%ATH were added together,the PU/15%APP/5%ATH sample shows better thermal stability and flame-retardant properties.When 15 wt%APP and 5 wt%ATH were added together,the LOI value of the PU/15%APP/5%ATH sample was 30.5%,and UL 94 V-0 rating was attained.Compared with PU,the peak heat release rate(PHRR),total heat release(THR),and average effective heat combustion(av-EHC)of the PU/15%APP/5%ATH sample decreased by 43.1%,21.0%,and 29.4%,respectively.In addition,the flame-retardant mechanism was investigated through cone calorimeter.The APP/ATH addition simultaneously exerted condensed phase and gas phase flame retardant effects.APP and ATH have synergistic flame retardant properties.

Infl uencing Mechanism and Interaction of Muscovite on Thermal Decomposition of Ammonium Polyphosphate

The interaction mechanism and phase evolution of ammonium polyphosphate（APP）mixed with muscovite（APP/muscovite）were studied by TG,XRD and SEM,respectively,during heating.When the temperature is not higher than 300 ℃,muscovite has no effect on the thermaldecomposition of APP,and the initialdecomposition temperature of APP/muscovite at 283 ℃ is basically the same as the APP at 295 ℃,and the main thermaldecomposition products are polyphosphoric acid and NH_4H_2PO_4 at 300 ℃.The polyphosphoric acid,the decomposition products of APP,can enable K and Siout of muscovite and interact with muscovite chemically to generate Al_2O_3·2SiO_2,α-SiO_2 and phosphates（AlPO_4 and K_5P_3O_（10））compounds during 400 ℃-800 ℃,which own obvious adhesive phenomenon and porous structure with the apparent porosity of 58.4%.Further reactions between phosphates other than reactions among Al_2O_3·2SiO_2 and α-SiO_2 can generate KAlP_2O_7 at 1 000 ℃ and the density of residualproduct is improved by low melting point phosphate filling pore to form relatively dense structure and decrease the apparent porosity to 44.4%.The flame resistant and self-supported ceramic materials are expected to enhance the fire-retarding synergistic effect between APP and muscovite.

Effect of surface modification of ammonium polyphosphate-diatomite composite filler on the flame retardancy and smoke suppression of cellulose paper

Ammonium polyphosphate-diatomite composite filler(APP-diatomite composite filler)was modified with silane coupling agent KH550 to improve the flame retardancy of filled paper.Cone calorimeter was used to analyze the heat and smoke releasing rates,as well as smoke toxicity of the filled paper.The distribution of the composite filler particles in paper and the morphology of the charred residues after combustion were investigated by scanning electron microscope(SEM),and the chemical structure of the charred residues was studied with fourier transform infrared spectroscopy(FTIR).Results show that the peak heat releasing rate(PHRR),total heat release(THR)and peak mass loss rate(PMLR)of the filled paper with the modified APP-diatomite decreased markedly,compared with those for the control paper,while the charred residue after combustion increased.In addition,the filled paper had an increased peak rate of smoke release(RSR)and increased total smoke release(TSR)and peak CO production rates,but a decreased peak CO_(2) production rate.It was also found that part of the carbon element in the charred residue of the paper loaded with the modified APP-diatomite was in the forms of C=C=C,C≡C and C≡N,and the charred residue had a relatively more intact structure without apparent fiber breakage and longitudinal cracks.

The development road of ammonium phosphate fertilizer in China

Ammonium phosphate fertilizer is the compounds containing nitrogen and phosphorus that are usually produced through the neutralization reaction of phosphoric acid and ammonia.At present,there are a variety of products,such as slurry monoammonium phosphate(MAP),diammonium phosphate(DAP),industrial grade MAP,water soluble MAP,water soluble ammonium polyphosphate(APP)and so on.After more than 60 years of development,China’s ammonium phosphate fertilizer industry has experienced the road of from scratch and from weak to strong.The successful development of the slurry MAP technology ended the history that the high concentration phosphate fertilizer cannot be produced by using the medium and low grade phosphate ore.The continuous,stable and large-scale production of DAP plant provides sufficient guarantee for DAP products in China.The development of new ammonium phosphate fertilizer products,such as industrial grade MAP,water soluble MAP,water soluble APP,provides technical support for the transformation and upgrading of phosphorus chemical enterprises.In this paper,the production methods,the development history and the latest research progress of ammonium phosphate fertilizers were reviewed.

A novel high-efficient P/N/Si-containing APP-based flame retardant with a silane coupling agent in its molecular structure for epoxy resin

A flame retardant containing multiple antiflaming elements usually exhibits high-efficient flame retardancy. Here, a novel P/N/Si-containing ammonium polyphosphate derivative(APTES-APP) is synthesized from ammonium polyphosphate(APP) and silane coupling agent(3-aminopropyl)triethoxysilane(APTES)via cation exchange, which is quite different in the chemical structure from APTES-modified APP for retaining silicon hydroxyls. APTES-APP is highly efficient for the epoxy resin. 8%(mass) APTES-APP imparts excellent flame retardancy to the epoxy resin, with a V-0 rating at the UL-94 test(1.6 mm)and an LOI value of 26%(vol). The peak heat release rate and total smoke production of the flameretardant epoxy resin are decreased by 68.1% and 31.3%, respectively. The synergy of P/N/Si contributes to the well-expanded char residue with a strong and dense surface layer, which is a very good barrier against heat and mass transfer. Besides, there is no significant deterioration in the mechanical properties of flame-retardant epoxy resin thanks to silicon hydroxyls forming hydrogen bonds with epoxy molecules. Meanwhile, other molecules can be grafted onto APTES-APP via these silicon hydroxyls, if needed.Briefly, this work has developed a new strategy for amino silane as flame retardants. In conjunction with a low-cost and simple preparation method, APTES-APP has a promising prospect in the high-performance flame-retardant epoxy.

Preparation and Properties of Bio-Based Flame Retardant Polyvinyl Alcohol

Polyvinyl alcohol (PVA) has been widely used in the fields of medical, food and packaging due to its excellentbiocompatibility, good fiber-forming and film-forming properties. However, the high flammability of PVA hasgreatly limited its wider applications. The flame-retardant PVA was prepared by melt blending of a bio-basedflame retardant (prepared from lignin, phosphoric acid and carbamide) with thermoplastic PVA (TPVA). Thechemical structure, morphology, thermal properties, mechanical properties, fire property and fluidity of thisflame retardant PVA were investigated by Fourier transform infrared spectrometer(FTIR), field emission scanning electron microscope(SEM), thermogravimetric analyzer(TGA), impact tester, universal testing machine,horizontal-vertical burning tester, limiting oxygen indexer(LOI) and melt flow rate meter(MFR). The resultsshowed that the prepared flame retardant had good compatibility with the PVA substrate;The impact strength,melt flow rate, fire property and char residue of this PVA material increased with the content of bio-based flameretardant. When the content of flame retardant was of 20%, the five indices including impact strength, meltflow rate, UL-94 level, LOI and char residual were 11.3 KJ/m^(2), 21.2 g/10 min, V-0 UL-94 level, 33.1%, and19.2%, respectively. This research can promote the high-value utilization of lignin and the application ofPVA in the fields of fire protection.

Preparation and Properties of Bio-Based Flame Retardant L-APP/Poly(L-lactic acid)Composites

Poly(L-lactic acid)(PLLA)is a thermoplastic material with complete degradability,high biocompatibility and excellent mechanical properties.It can replace petroleum-based polymers are currently being used in the fields of packaging,agriculture,textiles,medical and so on.However,PLLA’s extremely flammability greatly limits its wider application.An bio-based flame retardant L-APP/PLLA composites was prepared by melt blending of the L-APP and PLLA.The morphology,impact properties,thermal properties and flame retardant properties of composites were investigated by field emission scanning electron microscope(SEM),impact tester,differential scanning calorimeter(DSC),thermogravimetric analyzer(TGA),limiting oxygen indexer(LOI)and horizontalvertical burning tester.The results showed that the degree of crystallization(X_(c))and LOI of L-APP/PLLA composites increased as increasing of L-APP content.What’s more,the impact strength first increased and then decreased,the glass transition temperature(T_(g))and melting temperature(T_(m))do not changed significantly.The impact strength of composites was 9.1 kJ/m^(2) at a 5 wt%loading for L-APP,which was the highest level.When the content of L-APP was 20%,the LOI was 30.8%,the Xc was 42.3%and the UL-94 level was V-0.This research can promote the value-added utilization of lignin and the application of PLLA in the fields of flame retardant materials.

Simultaneous Improvement in the Flame Retardancy and Water Resistance of PP/APP through Coating UV-curable Pentaerythritol Triacrylate onto APP

To improve the flame-retardant efficiency and water resistance of ammonium polyphosphate（APP）, the UV-curable pentaerythritol triacrylate（PETA） was used to microencapsulate APP via the UV curing polymerization method. The prepared PETA-microencapsulated APP（PETA-APP） was characterized by Fourier transform infrared spectroscopy（FTIR）, scanning electron microscopy（SEM）, and thermogravimetric（TG） analysis. PETA-APP was used as intumescent flame retardant（IFR） alone to flame retard polypropylene（PP）. The water resistance of PP/PETA-APP composites was investigated, and the effect of PETA on the combustion behaviors of PP/APP composites was studied through limiting oxygen index（LOI）, vertical burning test（UL-94） and cone calorimeter（CC） test, respectively. With 40 wt% of PETA-APP, the PP/PETA-APP system could achieve a LOI value of 30.0% and UL-94 V-0 rating after treatment in hot water for 168 h, while the LOI value of the system containing 40 wt% uncoated APP was only 19.2%, and it failed to pass the UL-94 rating. CC test results showed that the heat release rate（HRR）, mass loss rate（MLR） and smoke production rate（SPR） of PP/PETAAPP system decreased significantly compared with PP/APP system, especially the peak of HRR was decreased by 51.4%. The mechanism for the improvement of flame reatardancy for PP/PETA-APP composites was discussed based on FTIR and X-ray photoelectron spectroscopy（XPS） tests. All these results illustrated that simultaneous improvement of flame retardancy and water resistance for PP/APP was achieved through coating UV-curable PETA onto APP.

Experimental design and theoretical evaluation of nitrogen and phosphorus dual-doped hierarchical porous carbon for high-performance sodium-ion storage

Starch has a wide range of sources and can be used as a high-quality precursor for sodium-ion battery anode materials.However,the carbonization yield and specific capacity of carbon materials obtained by directly pyrolyzing starch are low.Herein,starch is used as the carbon source,and ammonium polyphosphate(APP)is used as the cross-linking agent and dopant to prepare a nitrogen and phosphorus co-doped porous carbon(NPPC).As the anode for sodium-ion batteries,NPPC-2 exhibits a high reversible capacity of 385.8 mAhg^(-1)at 50 mAg^(-1).Even after 1000 cycles at a large current density of 5 Ag^(-1),the reversible capacity can still be maintained at 126.9 mAhg^(-1).Based on detailed data and first-principles calculations,the excellent performance of NPPC is due to the effective doping of nitrogen and phosphorus elements,which distorts the graphite sheet,introduces defects,and increases the graphite layer spacing,thereby enhancing the adsorption capacity of the carbon material for sodium ions,reducing the diffusion barrier of sodium ions.This work provides a new idea for heteroatom doping and carbon material modification.