Cathode materials based on carbon nanotubes for high-energy-density lithium–sulfur batteries

The rational integration of conductive nanocarbon scaffolds and insulative sulfur is an efficient method to build composite cathodes for high-energy-density lithium–sulfur batteries. The full demonstration of the high-energy-density electrodes is a key issue towards full utilization of sulfur in a lithium–sulfur cell. Herein, carbon nanotubes (CNTs) that possess robust mechanical properties, excellent electrical conductivities, and hierarchical porous structures were employed to fabricate carbon/sulfur composite cathode. A family of electrodes with areal sulfur loading densities ranging from 0.32 to 4.77 mg cm⁻² were fabricated to reveal the relationship between sulfur loading density and their electrochemical behavior. At a low sulfur loading amount of 0.32 mg cm⁻², a high sulfur utilization of 77% can be achieved for the initial discharge capacity of 1288 mAh g_S⁻¹, while the specific capacity based on the whole electrode was quite low as 84 mAh g_{C/S+binder+Al}⁻¹ at 0.2 C. Moderate increase in the areal sulfur loading to 2.02 mg cm⁻² greatly improved the initial discharge capacity based on the whole electrode (280 mAh g_{C/S+binder+Al}⁻¹) without the sacrifice of sulfur utilization. When sulfur loading amount further increased to 3.77 mg cm⁻², a high initial areal discharge capacity of 3.21 mAh cm⁻² (864 mAh g_S⁻¹) was achieved on the composite cathode.     

A high-capacity lithium–air battery with Pd modified carbon nanotube sponge cathode working in regular air

We report a lithium–air battery with a free-standing, highly porous Pd-modified carbon nanotube (Pd–CNT) sponge cathode. The Pd-CNT sponge was synthesized through a chemical vapor deposition growth followed with an electrochemical deposition process. To build a whole lithium–air battery, the air cathode is integrated with a ceramic electrolyte-protected lithium metal anode and non-volatile ionic liquid electrolyte. The lithium anode is stable during the operation and long-time storage and the ionic liquid is chemically inert. By controlling the amount of ionic liquid electrolyte, the sponge is wet but not fulfilled by the electrolyte. Such configuration offers a tricontinuous passage for lithium ions, oxygen and electrons, which is propitious to the discharge reaction. In addition, the existence of Pd nanoparticles improves the catalytic reactivity of the oxygen reduction reaction. The battery is durable to any humidity level and delivers a capacity as high as 9092 mA h g⁻¹.     

Recyclable biobased materials based on Diels–Alder cycloaddition

Poly(ethylene glycol) diglycidyl ether-furfurylamine (PGFA) containing pendant furan was synthesized, and a series of crosslinked materials with thermally reversible capacity were synthesized through a furan/maleimide Diels–Alder (DA) reaction between PGFA and bismaleimide (BMI). The kinetics of the PGFA/BMI DA reaction were studied by Fourier transform infrared spectroscopy (FTIR). The reaction conversion rate, the reaction rate constant, and the energy of the DA reaction at different temperatures were calculated. In addition, the retro Diels–Alder (rDA) reaction was studied via ¹H-NMR, differential scanning calorimetry, and in situ FTIR. The occurrence of the retro DA reaction has been characterized clearly. Finally, the mechanical properties of the materials were obtained by dynamic mechanical and tensile tests. The storage modulus decreased obviously when the temperature reached over 90 °C, which proved that the materials were thermally reversible at high temperature. By changing the proportion of the crosslinking agent BMI, the best-performing materials were obtained, and the properties of the materials were basically unchanged after recycling. Thus we have obtained an excellent reusable material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47352.     

Status and prospects in sulfur–carbon composites as cathode materials for rechargeable lithium–sulfur batteries

Sulfur stands as a very promising cathode candidate for the next-generation rechargeable batteries due to its high energy density, natural abundance, low cost and environmental friendliness. However, the application of lithium–sulfur batteries suffers from low sulfur utilization and poor cycle life of the sulfur cathode. The problems are mainly ascribed to the electrically insulating nature of sulfur and the discharge products, and to the dissolution of the reaction intermediates of polysulfides. Among various approaches, fabricating sulfur–carbon composite cathodes with sulfur embedded within conductive carbon frameworks has been proven promising. Carbon materials, including nanoporous carbon, carbon nanotubes, graphene nanosheets and some other forms, have excellent conductivity, robust chemistry, good mechanical stability, and great abundance. By constraining sulfur within carbon frameworks, the conductivity of the sulfur electrode can be greatly enhanced, and the dissoluble loss of intermediate sulfur species in the liquid electrolyte can also be restrained due to the sorption properties of carbon, leading to a much improved electrochemical performance. This review summarizes the progresses in the sulfur–carbon composite cathodes for lithium–sulfur batteries in recent years, and introduces the roles and the effectiveness of various carbon structures on the electrochemical properties.     

Preparation,structural and thermo-mechanical properties of lithium aluminum silicate glass–ceramics

Lithium aluminum silicate glasses of composition (wt%) 12.6Li₂O–71.7SiO₂–5.1Al₂O₃–4.9K₂O–3.2B₂O₃–2.5P₂O₅ were prepared by the melt quench technique. These glasses were converted to glass–ceramics based on DTA data. X-ray diffraction (XRD) and Fourier transform infra-red spectroscopy (FTIR) were used to discern the phases evolved in the glass–ceramics. Phase morphology was studied using scanning electron microscopy (SEM). Thermal expansion coefficient (TEC) and glass transition temperature (T_g) of all samples were measured using thermo-mechanical analyzer (TMA). It was found that 3 h dwell time at crystallization temperature yielded samples with good crystallinity with a TEC of 9.461 × 10⁻⁶ °C⁻¹. Glass–ceramic-to-metal compressive seal with SS-304 was fabricated using LAS glass–ceramic. The presence of metal housing and compressive stresses at the glass–ceramic-to-metal interface reduced average grain size and changed the overall microstructure.     

The Mechanism of corrosion of MgOCaZrO3–calcium silicate materials by cement clinker

The chemical reactions involved in the corrosion of MgOCaZrO₃–calcium silicate materials by cement clinker were studied using a hot-stage microscope up to 1600 °C. The phases formed at 1500 °C were characterized by RLOM and SEM–EDS of the crystalline phases conducted near the reaction front and on unreacted refractory area.The general corrosion mechanism of attack on MgOCaZrO₃–calcium silicate materials involves a mechanism of matter diffusion of the liquid clinker phase through the grain boundaries and pores into the refractory substrate. The liquid phases in the clinker mainly enriched in calcium, iron and aluminium are rapidly diffused and preferentially react with magnesium spinel, calcium zirconate and magnesia, which are the major constituents in the refractory substrates. The dissolution of the CaZrO₃ refractory phase produces the enrichment with zirconium of the liquid phase increasing its viscosity and hindering the liquid phase diffusion.     

Effect of oxygen and titanium contents on the stability of nanocrystalline Ti–Ru–Fe–O cathode materials for chlorate electrolysis

Electrodes made from nanocrystalline Ti:Ru:Fe (2–y:1+y/2:1+y/2), with y varying from 0 to 1 by step of 0.25, and Ti:Ru:Fe:O (2:1:1:w), with w varying from 0 to 2 by step of 0.5, were prepared and tested as activated cathodes for the hydrogen evolution reaction in typical chlorate electrolysis conditions. These electrodes were subjected to an accelerated aging test, consisting of a succession of cycles of hydrogen discharge (HER) and open-circuit (OCP) conditions. In addition to monitoring the cathodic overpotential value during the aging test, visual inspection and mass loss measurements were performed on the electrodes at the end of the test to assess their stability. In the case of Ti:Ru:Fe (2:1:1), a large increase of the cathodic overpotential value is observed after 20 cycles. Adding O to the formulation causes a remarkable improvement of the long-term stability of the electrodes. As little as [O] = 10 at.% in nanocrystalline Ti:Ru:Fe:O (2:1:1:w) materials is sufficient for the electrode to show absolutely no sign of degradation after 50 cycles of HER/OCP, the longest accelerated test conducted. Adding more O to the formulation of the material does not lead to further stability improvement. A better stability under the conditions of the accelerated aging test can also be observed for nanocrystalline Ti:Ru:Fe (2–y:1+y/2:1+y/2) materials with y > 0. In that case however, the level of improvement is dependent on the value of y. The best results are obtained for y = 0.75. A hypothesis is proposed to explain the improved stability obtained by lowering the Ti content and/or by adding O. The similarity and difference between both ways of improving the stability of the nanocrystalline Ti:Ru:Fe materials are also discussed.     

Particle size control of cathode components for high-performance all-solid-state lithium–sulfur batteries

Understanding the size effect of each component on battery performance is essential for designing high-performance Li₂S/S cathode for all-solid-state Li–S batteries. However, the size effects of different components are always coupled because ball-milling, an indispensable process to synthesize reversible cathode, simultaneously and uncontrollably reduces the particle size of all the components. Here, a liquid-phase method, without ball-milling, is developed to synthesize the Li₂S composite cathode, so that the particle size of the active material Li₂S and the solid electrolyte Li₃PS₄ (LPS) can be independently controlled at nano- or microscale. This helps reveal that compositing Li₂S and the conductive agent at nanoscale is essential for enhancing the reaction kinetics, whereas the nanoscale particle size and homogenous distribution of LPS is important for accommodating the large volume change of the cathode. By reducing the particle size of Li₂S to 9.4 nm and that of LPS to 44 nm, the liquid-phase-synthesized composite cathode exhibits reversible capacity and 100% utilization of Li₂S under 0.1 C rate.     

The effect of SiO_2 particle size on iron based F–T synthesis catalysts

The effect of particle size of silica, as catalyst binder, on the chemical and mechanical properties of iron based FT catalyst was studied in this work. The samples were characterized using XRD, BET, TEM, FT-IR, and H2-TPR, respectively. The attrition resistance and the FT activity were tested. Si-8–Si-15 catalysts prepared with 8–15 nm silica sol show good attrition resistance(attrition loss b 4%), especially Si-13 with an attrition loss of 1.89%. Hematite appeared in XRD patterns when silica sol above 15 nm is used. TEM micrographs show that no obvious Si O_2 particles appear when silica sol particle with size less than 8 nm was used, but Si O_2 particles coated with small ferrihydrite particles appear when silica sol above 8 nm was used. Si–O–Si vibration peak in FT-IR spectra increases with increasing silica sol size. Samples prepared with silica sol show good stability of FT reactions, and the average molecular weight of FT products increases with the increase of Si O_2 particle.     

Synthesis and characterization of hybrid organic–inorganic materials based on sulphonated polyamideimide and silica

The preparation of hybrid organic–inorganic membrane materials based on a sulphonated polyamideimide resin and silica filler has been studied. The method allows the sol–gel process to proceed in the presence of a high molecular weight polyamideimide, resulting in well dispersed silica nanoparticles (<50 nm) within the polymer matrix with chemical bonding between the organic and inorganic phases. Tetraethoxysilane (TEOS) was used as the silica precursor and the organosilicate networks were bonded to the polymer matrix via a coupling agent aminopropyltriethoxysilane (APTrEOS). The structure and properties of these hybrid materials were characterized via a range of techniques including FTIR, TGA, DSC, SEM and contact angle analysis. It was found that the compatibility between organic and inorganic phases has been greatly enhanced by the incorporation of APTrEOS. The thermal stability and hydrophilic properties of hybrid materials have also been significantly improved.     

Microwave dielectric materials based on the MgO–SiO2–TiO2 system

Ceramics in the system MgO–SiO₂–TiO₂ were prepared by standard mixed oxide route. By adding ZnO–B₂O₃ to the starting mixtures, the firing temperature of the ceramics could be reduced to 1160 °C. Small additions of MnCO₃ and CaTiO₃ improve microwave dielectric properties leading to an increase in insulation resistance and a decrease in temperature coefficient of capacitance. By adding Co₂O₃ grain growth can be inhibited and the dielectric Qf value greatly increased. The resultant ceramic material exhibited low dielectric constant and low dielectric loss: relative permittivity (ε_r): 20±2; temperature coefficient of capacitance (τ_c): 0±30 ppm/°C; Qf: 100,000 (at 10 GHz); insulation resistance: 10¹³ Ω cm:     

Fischer–Tropsch principles of co-hydrogenation on iron catalysts

The temporal changes of product composition together with changes of the catalyst in composition and structure have been investigated for Fischer–Tropsch synthesis with an alkalized precipitated iron catalyst at 250°C, 1 MPa, using a special synthesis gas with a molar H₂/CO₂-ratio of three. It was observed that the steady state of synthesis developed in processes of self-organization during several episodes with individual kinetic regimes. Thetrue FT catalyst apparently was constructed at reaction conditions under complete consumption of -iron and formation of iron carbide (Fe₅C₂). The magnetite phase disappeared partially and a new unknown (probably FeO_x) phase was formed. It has been concluded from the data of chain growth and branching probability that during self-organization only the number of sites increased but their nature remained unchanged. Strong spatial constraints appear to apply at the sites. On iron catalysts, the FT sites are very stable, invariant against changes in reaction conditions, in contrast to FT synthesis on cobalt. There the sites show a dynamic behavior.     

Synthesis and electrochemical performance of LiVOPO4–Li3V2(PO4)3 cathode materials for lithium ion batteries

Lithium-ion batteries (LIBs) present the advantages of long cycle life, high voltage, and energy density and are widely made in the field of energy storage. LiVOPO₄ (LVOP), a cathode material used in LIBs, has a high conceptual capacity of 159 mAh g⁻¹ and high operating voltage of 3.9 V. However, its low electrical conductivity and cycle performance limit its commercial applications. According to the X-ray diffraction results, orthogonal crystal LVOP and monoclinic crystal Li₃V₂(PO₄)₃ (LVP) coexisted in the synthesised composite material. The transmission electron microscopy results also indicated that the LVOP and LVP phases coexist, which were coated by carbon layer of about 2.5 nm. The discharge of LVOP–LVP composite material initially was 143.2 mAh g⁻¹, and that after 120 cycles was 132.2 mAh g⁻¹ (at 0.1 C and 3–4.5 V). Thus, the electronic conductivity and first discharge specific capacity of the material enhanced due to the introduction of fast ion conductor LVP into LVOP. Electrochemical performance improved because the introduction of LVP led to an increase in Li⁺ pervasion channels in the original material and the acceleration of the Li⁺ transmission speed.     

Influence of novel shrinkage-reducing polycarboxylate superplasticizer on the nature of calcium–silicate–hydrates

Currently, a novel shrinkage-reducing polycarboxylate superplasticizer (SR-PCA) is used to control cementitious shrinkage. To clarify its mechanism when applied in cementitious materials, the influence of SR-PCA on the composition, morphology, and structure of synthetic calcium–silicate–hydrate (C–S–H), together with the interaction between SR-PCA and C–S–H at the atomic level, is investigated. For comparison, a commercial polycarboxylate superplasticizer (PCA) is also employed. The results show PCA and SR-PCA can adsorb on the C–S–H surface rather than intercalate into the layers. Compared with PCA, SR-PCA has a milder impact on C–S–H crystallinity. SR-PCA refines the pore structure of C–S–H drastically, whereas PCA loosens the structure by increasing the mesopore volume. In addition, the adsorption effect of SR-PCA on the C–S–H surface is less significant than that of PCA. At the atomic level, this less adsorption of SR-PCA is attributed to the lower adhesion energy of the C–S–H/SR-PCA interface due to the weaker Ca–O bond strength.     

Low voltage resistive memory devices based on graphene oxide–iron oxide hybrid

Low cost resistive switching memory devices using graphene oxide–iron oxide (GF) hybrid thin films, sandwiched between platinum (Pt) and indium-tin-oxide (ITO) electrodes, were demonstrated. The fabricated devices with Pt/GF/ITO structure exhibited reliable and reproducible bipolar resistive switching performance, with an ON/OFF current ratio of 5 × 10³, excellent retention time longer than 10⁵ s, SET voltage of 0.9 V, and good endurance properties. In all aspects of the device characteristics, the GF based devices outperformed graphene oxide (GO) based devices. Ohmic conduction was found to be dominant current conduction mechanism in all switching regions except for the high voltage regime where space charge limited conduction and trap charge limited conduction were found to be the main current conduction mechanism. X-ray photoelectron spectroscopy and transmission electron microscopy/selected area diffraction analysis revealed γ-Fe₂O₃ and Fe₃O₄ iron oxide phases coexist in the hybrid films. While the desorption/adsorption of oxygen-related functional groups on the GO sheets is the dominant resistive switching mechanism in Pt/GO/ITO devices, the formation/rupture of multiple highly conducting Fe₃O₄ filaments at the iron oxide/GO interface additionally facilitate the switching in the present Pt/GF/ITO devices. Thereby, excellent electrical switching performance was achieved.     

Corrosion behaviour of carbon materials exposed to molten lithium chloride–potassium chloride salt

The corrosion behaviour of four carbon materials namely low density graphite, high density graphite, glassy carbon and pyrolytic graphite were investigated in molten LiCl–KCl electrolyte medium at 600 °C for 2000 h under high pure argon atmosphere. Structural and microstructural changes in the carbon materials after exposure to molten chloride salt were investigated from the weight change and using scanning electron microscopy, atomic force microscopy, X-ray diffraction and laser Raman spectroscopic techniques. Microstructural analysis of the samples revealed the poor corrosion resistance of high density and low density graphite and severe attack was observed at several places on the surface. On the other hand, glassy carbon and pyrolytic graphite were relatively inert, while pyrolytic graphite showed the best corrosion resistance to molten salt attack. In the order of increasing corrosion resistance to molten salt, the carbon materials were found to follow the sequence: low density graphite < high density graphite < glassy carbon < pyrolytic graphite.     

High-temperature synthesis of composite materials based on (Cr,Mn, V)–Al–C MAX phases

Composite materials based on (Cr, Mn, V)–Al–C MAX phases were obtained by self-propagating high-temperature synthesis (SHS). Regularities of synthesis of composite materials from mixtures containing chromium (III) oxide, manganese (IV) oxide, vanadium (V) oxide, calcium (IV) oxide, aluminum, and carbon powders were studied. The synthesis of 30-g blend was carried out in an SHS reactor with a volume of 3 l under Ar pressure (5 MPa). Variation in the amount of the starting reagents markedly affected the process parameters, phase composition, and microstructure of combustion products. The combustion products were characterized by XRD, SEM, and EDS analysis. For Cr–Al–C system, MAX Cr₂AlC phase in addition to chromium aluminide Cr₅Al₈ and chromium carbides (Cr₇C₃, Cr₃C₂) was detected. SEM studies showed that Cr₂AlC has a laminated structure with layer thickness varying from 3 to 20 nm. XRD pattern of Mn–Cr–Al–C composite material were found to have signals belonging (Cr_xMn_1–x)₂AlC solid solution, Mn₃AlC, and Cr₂Al. It was shown that V–Al–C composite material contains nano-layered MAX V₂AlC phase and particles VC_х, VAl₃.     

Study on compression–expansion behaviour of PBXs substitutive materials

ABSTRACT

In this work, polymer-bonded sugars were used as a substitutive material for polymer-bonded explosives (PBXs). Their production process and damage mechanism under compressive process were analysed. We also investigated the initial Poisson’s ratio of PBXs as well as their mechanical properties under quasi-static compression and variation of Poisson’s ratio during the one-dimensional compressive process. Compressive expansion behaviour due to compressive loading was investigated comprehensively. It was found that due to the damage caused by the loading process, volumetric strain and Poisson’s ratio showed three stages characteristic. Experimental results proved that compression–expansion had occurred during the one-dimensional compressive process. Simulation results verified that PBXs crystal underwent mainly transgranular fracture under quasi-static compression.