Low Graphitization Degree Research Articles

Effect of ozone and oxygen dilution on soot formation in coflow ethylene/oxygen/ozone laminar partially premixed flames

Ozone is a prospective additive for enhancing and controlling combustion, due to its extremely oxidizing property. Ozone can enhance laminar burning velocity, broaden the flammability limit and improve flame stability, but the effect of ozone on soot formation in the combustion process of hydrocarbon fuels is not yet clear. Therefore, the soot from ethylene/oxygen/ozone laminar partially premixed flames was investigated. Besides, the response law of soot formation to different dilution gas ratios, and the effect of ozone participation in the reaction was also investigated. This work found that the addition of ozone significantly shortened the flame height by 4 mm in the cases of 10% dilution ratio. The particle size of soot was larger at low and medium flame heights due to ozone involved in combustion. The main reason was that ozone promotes soot growth. At medium and high flame heights, the larger the percentage of dilution gas, the lower graphitization degree of the soot. The addition of oxygen and ozone both made the ID/IG value increase, which indicated the graphitization degree decreased. The soot from high height of the flame with 10% dilution ratio and the addition of ozone had the largest ID/IG value of 0.970, which indicated a very low degree of graphitization. The signal intensity of the oxygen-containing functional groups on the surface of soot at the high flame height was enhanced with the addition of oxygen and ozone to the reaction.

Investigating the Effects of the Physicochemical Properties of Cellulose-Derived Biocarbon on Direct Carbon Solid Oxide Fuel Cell Performance.

This paper presents a study of the characteristic effects of the physicochemical properties of microcrystalline cellulose and a series of biocarbon samples produced from this raw material through thermal conversion at temperatures ranging from 200 °C to 850 °C. Structural studies revealed that the biocarbon samples produced from cellulose had a relatively low degree of graphitization of the carbon and an isometric shape of the carbon particles. Based on thermal investigations using the differential thermal analysis/differential scanning calorimeter method, obtaining fully formed biocarbon samples from cellulose feedstock was possible at about 400 °C. The highest direct carbon solid oxide fuel cell (DC-SOFC) performance was found for biochar samples obtained via thermal treatment at 400-600 °C. The pyrolytic gases from cellulose decomposition had a considerable impact on the achieved current density and power density of the DC-SOFCs supplied by pure cellulose samples or biochars derived from cellulose feedstock at a lower temperature range of 200-400 °C. For the DC-SOFCs supplied by biochars synthesised at higher temperatures of 600-850 °C, the "shuttle delivery mechanism" had a substantial effect. The impact of the carbon oxide concentration in the anode or carbon bed was important for the performance of the DC-SOFCs. Carbon oxide oxidised at the anode to form carbon dioxide, which interacted with the carbon bed to form more carbon oxide. The application of biochar obtained from cellulose alone without an additional catalyst led to moderate electrochemical power output from the DC-SOFCs. The results show that catalysts for the reverse Boudouard reactions occurring in a biocarbon bed are critical to ensuring high performance and stable operation under electrical load, which is crucial for DC-SOFC development.

Significant Improvement in Thermoelectric Properties of Carbon-Reinforced Cementitious Composites Achieved by Regulating the Graphitization Degree of Expanded Graphite.

Building structures are exposed to direct sunlight for a long time, accumulating a large amount of low-grade thermal energy, which aggravates environmental pollution and energy consumption. Thermoelectric cement-based composites can realize the interconversion of thermal and electrical energy, showing great potential benefits in large-scale heat collection and energy conversion. Although a lot of exploration and research has been carried out on the thermoelectric properties of cement-based composites reinforced with carbon materials, the contribution of the characteristics of carbon materials, such as the graphitization degree, to the thermoelectric properties of cement-based composites is still unclear. In this article, the graphitization degree of expanded graphite (EG) was modulated by etching EG with an acid solution. The low graphitization degree improves the effective mass of carriers and aggravates the electron and phonon scattering at the interface of EG/cement-based composites. Low thermal conductivity was obtained while increasing the Seebeck coefficient of EG/cement-based composites. The power factor (17.1 μW m-1 K-2) and thermoelectric figure of merit (2.95 × 10-3) of the sample are increased by 18.6 times and 44.2 times, respectively, achieving the highest thermoelectric performance in cement-based composites reinforced with carbon materials. This study provides a direction for improving the thermoelectric properties of cement-based composites by structural regulation of carbon materials.

Fabrication of matrix graphite with a high degree of graphitization for spherical fuel elements by using natural microcrystalline graphite fillers

Matrix graphite is used as a structural material, thermal conductor, moderator, and secondary fission product barrier for fuel elements in high-temperature gas-cooled reactors (HTRs). Due to its high graphitization degree and compressibility, natural flake graphite (NFG) is used as the main filler in traditional A3-3 matrix graphite, whereas artificial graphite (AG), with a lower graphitization degree than NFG, serves as an additive for toughness and gas permeability. Matrix graphite could be improved in terms of thermal conductivity, oxidation resistance, and irradiation performance by increasing the degree of graphitization. However, reports on the development of new matrix graphite formulations are scarce. In this study, MG-20 matrix graphite was prepared by mixing 60 wt% NFG, 20 wt% natural microcrystalline graphite (MG), and 20 wt% phenolic resin. Due to the high graphitization degree (higher than AG) and low coefficient of thermal expansion (CTE) of MG, MG-20 exhibited higher thermal conductivity (∼6%) and lower CTE (∼2.4%) than A3-3. Thus, MG-20 with higher graphitization degree and better thermal properties than A3-3 could improve the performance of HTR fuel elements in the future.

Effects of polyoxymethylene dimethyl ethers (PODEn) on soot characteristics in isooctane inverse diffusion flames

Polyoxymethylene dimethyl ethers (PODEn, n = 1–3) such as dimethoxymethane (DMM) and PODE3 are considered highly promising alternative fuels due to their lack of C–C bonds and significant oxygen contents. Particularly, PODE3-blends with diesel have been proven to substantially reduce soot emissions and fuel consumption rates under optimized engine conditions, although the impact on soot nanostructure properties remains unclear. This study explored the effects of DMM and PODE3 on soot characteristics in isooctane (i-octane) inverse diffusion flames, focusing on soot morphology, soot nanostructure, soot nanocrystallite, and soot spectral features. To compare soot particles behavior, DMM and PODE3 blended as the isooctane substitute (by 20% and 40% volumetric fractions) were examined with various diagnostic techniques, including high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS).The results showed that DMM and PODE3 contributed to a reduction in sooting tendency from i-octane flames, whereas the average soot mass decreased significantly as the PODE3 ratio increased, consistent with a higher oxygen concentration. Therefore, 20% PODE3/i-octane exhibited growing disorganized arrangements of soot particles with shorter fringes, smaller crystallite sizes, and a relatively lower degree of graphitization than 20% and 40% DMM additions. However, XPS analysis indicated that soot produced from PODE3/i-octane mixtures had less oxygen atoms because PODE3 has multiple –CH2O- chain groups that can convert oxygen into carbon monoxide with little soot production. Moreover, HRTEM, XRD, and Raman spectra analyses of 40% PODE3-doped flames confirmed an exceptional correlation with turbostratic soot structure, as manifested by the shortest fringe length, longest fringe tortuosity, more amorphous soot with the smallest crystallite dimensions, and least degree of graphitization.

Comparative study on induction brazing of diamond with rare earth Nd-doped crystalline and amorphous Ni-based filler alloy

This essay aims to comparatively study the microscopic morphology and grinding properties of brazed diamonds with amorphous and crystalline filler alloy in the case of rare-earth Nd-doped modified Ni-based filler alloy. The results show that at the same content of Nd, Cr7C3 is mainly generated at the brazing interface of crystalline samples. In contrast, Cr27C6 is mainly generated at the brazing interface of amorphous samples. Amorphous solder material achieves a robust chemical metallurgical union, producing a dense and homogeneous carbide layer. The bonding strength between amorphous solder material and diamond is further enhanced. The addition of rare earth element Nd contributes greatly to the forming ability of amorphous filler alloy. Nd atoms in the amorphous solder material readily bond with Ni atoms, reducing the chemical corrosion of Ni atoms on diamonds and resulting in a lower degree of graphitization. When the amount of Nd added is 1.0 wt%, the morphology of amorphous filler alloy brazing diamond is more complete than the effect of the crystalline state, the degree of thermal damage is lower, and the surface of amorphous filler alloy brazing is smoother. Frictional wear experiments show that the amorphous filler alloy holds diamond better than the crystalline filler alloy, and the diamond specimens prepared with the amorphous filler alloy demonstrate a significantly superior grinding performance in comparison to the diamond specimens prepared with the crystalline filler alloy.

Effect of soluble organic matter on the physicochemical properties of black carbon in marine diesel engines

In the present study, the effects of soluble organic matter (SOF) on the physicochemical properties were revealed to enrich the black carbon (BC) reprocessing strategy for marine engines. The SOF content, oxidation reactivity, graphitization degree, primary particle diameter (Dp) and nanostructure were analyzed by thermogravimetric analysis (TGA), Raman spectrometer and high-resolution transmission electron microscopy (HRTEM). The results showed that the particles with higher SOF content had larger Dp values, lower graphitization degree and higher oxidation reactivity. Based on SOF would adsorb on the BC surface and increase the adhesion between the particles in the cylinder, a quantitative correlation between SOF content and the physicochemical properties of BC was derived. Meanwhile, the SOF inside the particles formed a porous structure, which improved the oxidation reactivity. In summary, the results of this study are important for a deeper understanding of the nature of marine engine particles and the reduction of nanoparticulate emissions.

Low temperature multi-catalytic growth and growth mechanism of carbon nanotubes on carbon fiber surfaces

In order to reduce the etching effect of the catalysts to carbon fibers caused by high temperature during the chemical vapor deposition (CVD) process, four multi-element catalysts, Fe–Co, Fe–Ni, Co–Ni and Fe–Co–Ni, were used to realize the low temperature growth of carbon nanotubes (CNTs) on carbon fibers at 350 °C–400 °C. The results show that the growth state of CNTs has a great relationship with the type of catalysts. The catalytic efficiency of Fe–Co catalysts is low, but the graphitization degree of CNTs is relatively high. The Fe–Co–Ni catalysts has high catalytic efficiency but low graphitization degree of CNTs. The tensile strength of carbon fiber/CNTs reinforcements prepared by Fe–Ni catalysts at 400 °C is the highest, reaching 3.99 GPa, which is 11.14% higher than that of desized fiber. The melt drop phenomenon of the catalysts was found by TEM, indicating the formation of the liquid phase catalysts during the growth of CNTs. This phenomenon can change the diffusion mode of carbon atoms in the catalyst and significantly reduce the growth activation energy of CNTs, so that CNTs can grow at lower temperatures. Based on the detailed analysis of the CVD process, a low temperature growth model of CNTs on carbon fibers was proposed.

Enhanced ablation resistance of carbon/phenolic composites based on mesophase pitch reinforced particles

AbstractPhenolic resin (PR)‐based composites are the main materials used in thermal protection system (TPS) at present. However, the low graphitization degree of the char layer formed by PR easily leads to cracks and other defects. In this study, carbon/phenolic composites were modified by mesophase pitch (MP) to improve the structural strength, fracture toughness and crack propagation resistance. The ablation rate was significantly decreased after MP modification compared with the blank sample. With the increase of MP, the size of cracks and char blocks on the ablation center of the composites were reduced, and the surface was flat and dense. The Interlaminar shear strength (ILSS) of carbonized composites (5 wt% MP) were 9.79 MPa, and the flexural strength was 121.5 MPa, which improved 62.9% and 40.8% relative to the pure sample. The flexural strength of 5 wt% MP‐reinforced carbon/phenolic composites reached 525.6 MPa, which was 26.9% higher than that of pure carbon/phenolic composites, mainly due to the particle reinforcement effect of MP distributed between carbon fibers. The above results show that the carbon/phenolic composites modified by MP has great application prospects in the field of aircraft thermal protection.

Coal/NH3 interactions during co-pyrolysis and their effects on the char reactivity for NO-reduction: A ReaxFF MD study

In this work, the interactions between NH3 and coal during co-pyrolysis and their influences on char structure and char reactivity for NO reduction are investigated using reactive molecular dynamic (ReaxFF MD) simulations, revealing that coal promotes the thermal decomposition of NH3 because it provides H radicals to attack the N-H bonds in NH3. The primary pyrolysis reactions (thermal breaking of weak covalent bonds) of coal are inhibited by NH3·NH3 also influences the secondary reactions in coal pyrolysis through two aspects: (1) promotes tar cracking to generate gas, and (2) inhibits the polymerization of tar to form char. Compared with coal pyrolysis, the H/C ratio of char and number of O and N atoms in char decrease more slowly during coal/NH3 co-pyrolysis. However, NH3 has little influence on the release of H2S. The effect of NH3 on the physicochemical properties of the char is then analyzed. The oxygen atoms are present mainly as hydroxyl, ether, and carbonyl forms, and the nitrogen atoms are present mainly as cyanide and amino forms in both coal pyrolysis char and coal/NH3 co-pyrolysis char. The coal/NH3 co-pyrolysis char has lower helium density, lower graphitization degree, and larger pores compared with coal pyrolysis char. Finally, the reactivity of coal pyrolysis char and coal/NH3 co-pyrolysis char for NO reduction are examined. The coal/NH3 co-pyrolysis char is more conducive to NO chemisorption and N2 generation. Using a first-order kinetics model, the activation energy of NO reduction reactions on coal pyrolysis char and coal/NH3 co-pyrolysis char are determined as 180 and 123 kJ/mol, respectively.

Architecting FeNx on High Graphitization Carbon for High-Performance Oxygen Reduction by Regulating d-Band Center.

Fe single atoms and N co-doped carbon nanomaterials (Fe-N-C) are the most promising oxygen reduction reaction (ORR) catalysts to replace platinum group metals. However, high-activity Fe single-atom catalysts suffer from poor stability owing to the low graphitization degree. Here, an effective phase-transition strategy is reported to enhance the stability of Fe-N-C catalysts by inducing increased degree of graphitization and incorporation of Fe nanoparticles encapsulated by graphitic carbon layer without sacrificing activity. Remarkably, the resulted Fe@Fe-N-C catalysts achieved excellent ORR activity (E1/2 = 0.829V) and stability (19mV loss after 30K cycles) in acid media. Density functional theory (DFT) calculations agree with experimental phenomena that additional Fe nanoparticles not only favor to the activation of O2 by tailoring d-band center position but also inhibit the demetallization of Fe active center from FeN4 sites. This work provides a new insight into the rational design of highly efficient and durable Fe-N-C catalysts for ORR.

The critical condition and kinetics of interaction between residual char and slag in the coal slagging gasifier

Due to low gasification reactivity of carbon feedstock and improper discharge operation, residual char is often found in bath of moving bed slagging gasifier, which affects the carbon conversion and slag discharge significantly. Moreover, the critical condition of interaction between char and slag determines whether char can be wrapped and consumed by slag in bath, while kinetics of interaction affects consumption rate of residual char wrapped by slag. In this work, the critical condition and kinetics of interaction between residual char and slag were investigated in terms of wetting behavior and carbothermal reaction. Results show that the increase of temperature not only lowers the contact angle between the slag and char, but also be beneficial to carbothermal reaction, thus, high temperature can improve wetting behavior at the slag/char interface. According to different factors that affect wettability during heating, the curve of contact angle between char and ash can be divided into three stages. Besides, it was found that the coal char with low graphitization degree is easy to be wrapped by ash with high SiO2/Al2O3 ratio, and quantitative relation between wrapped temperature and property of slag and char was established to predict critical condition of interaction. In addition, a limit of carbothermal reaction in thermodynamics was observed, and non-isothermal kinetic equations of carbothermal reaction were established, which can provide guidance for slag discharge operation of moving-bed slagging gasifier.

Preparation and Electrochemical Performance of Bio-Oil-Derived Hydrochar as a Supercapacitor Electrode Material.

The rapid consumption of fossil energy and the urgent demand for sustainable development have significantly promoted worldwide efforts to explore new technology for energy conversion and storage. Carbon-based supercapacitors have received increasing attention. The use of biomass and waste as a carbon precursor is environmentally friendly and economical. In this study, hydrothermal pretreatment was used to synthetize coke from bio-oil, which can create a honeycomb-like structure that is advantageous for electrolyte transport. Furthermore, hydrothermal pretreatment, which is low in temperature, can create a low graphitization degree which can make heteroatom introduction and activation easier. Then, urea and KOH were used for doping and activation, which can improve conductivity and capacitance. Compared with no heteroatom and activation hydrothermal char (HC) (58.3 F/g at 1 A/g), the prepared carbon material nitrogen doping activated hydrothermal carbon (NAHC1) had a good electrochemical performance of 225.4 F/g at 1 A/g. The specific capacitance of the prepared NAHC1 was improved by 3.8 times compared with that of HC.

Effect of Graphitization Degree of Mesocarbon Microbeads (MCMBs) on the Microstructure and Properties of MCMB-SiC Composites.

Mesocarbon microbead-silicon carbide (MCMB-SiC) composites were prepared by hot-press sintering (2100 °C/40 MPa/1 h) with two different graphitized MCMBs as the second phase, which exhibited good self-lubricating properties. The effects of the graphitization degree of the MCMBs on the microstructure and properties of the composites were investigated contrastively. The results showed that the composites that added raw MCMBs with a low degree of graphitization had excellent self-sintering properties, higher densities, and better mechanical properties; by comparison, the composites that added mature MCMBs with a high degree of graphitization, which has regular and orderly lamellar structures, not only had good mechanical properties but also exhibited a lower and more stable dry friction coefficient (0.35), despite the higher wear rate (2.66 × 10-6 mm3·N-1·m-1). Large amounts of mature MCMBs were peeled off during the friction process to form a uniform and flat graphite lubricating film, which was the main reason for reducing the dry friction coefficient of the self-lubricating composites and making the friction coefficient more stable.

Micro-nano morphology parameters and mechanical properties of soot particles sampled from high pressure jet flames of diesel from direct coal liquefaction

Diesel from direct coal liquefaction (DDCL) is a new type of engine alternative energy. In this study, a premixed constant volume combustion chamber system with soot particle sampling devices were built. High resolution transmission electron microscope (HR-TEM) and atomic force microscopy were applicated to characterize the micro-nano morphology parameters and mechanical properties of soot particles sampled from high pressure jet flames of DDCL. There were two in-house automatic processing codes were developed to process the HR-TEM images and extract the micro-nano morphology parameters of the soot particles. This study has systematically studied the effect of injection pressures on the micro-nano morphology parameters and mechanical properties of soot particles. The test results illustrated that there was a correlation between the micro-nano morphology parameters and mechanical properties of soot particles. Under the same combustion conditions, DDCL soot particles demonstrated smaller size, compacted structure, lower graphitization degree and weaker antioxidant capacity than that of diesel soot particles. The average adhesive force and energy dissipation of diesel soot particles were much higher, which indicated the diesel soot particles have stronger agglomeration performance. The average elastic modulus of DDCL soot particles was smaller than that of diesel, which caused the weaker ability to resist deformation for DDCL soot particles.

Experimental study on the key factors affecting the gasification performance between different biomass: Compare citrus peel with pine sawdust

This work aims to reveal the advantages of citrus peel gasification and investigate the key factors affecting gasification performance. The gasification performance of citrus peel and pine sawdust are compared in a fixed bed reactor, and the reactivity and properties of biochar were investigated. The results showed that the H2 yield and carbon conversion efficiency of citrus peel gasification were 34.35 mol/kgbiomass and 66.30%, respectively, which were higher than those of pine sawdust. Due to the high reactivity of citrus peel char, it only takes 100 min for the citrus peel to complete the gasification reaction, which is significantly faster than pine sawdust. Although the specific surface area of citrus peel char is lower than that of pine sawdust char, both the low degree of graphitization and the high catalytic index (2426.96) are favorable for the conversion of char, which ultimately lead to the high reactivity of citrus peel char.

Investigation and Design of Soybean-Derived Carbon Anode Materials for Potassium-Ion Battery Applications

Lithium-ion battery (LIBs) system is one the most widely used energy storage systems in today’s renewable energy field. However, with the dramatically increased demand over the past decades and limited core material storage, concerns arise regarding its sustainability and large-scale applications. While trying to make more efficient LIBs, the studies of alternative battery systems also appear to be more and more critical. Among many newly studied battery systems, Potassium-ion batteries (PIBs) have caught our attention. With the advantage of high abundance of Potassium (K) and low redox potential of K/K+ (2.93 V vs. standard hydrogen electrode), it appears to be a perfect candidate for substituting many of the current LIBs applications. However, the absence of a suitable carbon anode has hindered the development of PIBs. Herein, we used low-cost and abundant soybean as base material and developed a high-performance hard carbon anode for PIBs. Hard carbon, produced with 500 degrees process, exhibited the highest discharge capacity of 225 mA h g-1, long lifetime of 900 cycles, and good rate capability. Benefited from low activation temperature, the soybean-derived carbon has a medium surface area, large interplanar spacing graphene layers and low degree of graphitization, which are favored by the adsorption-dominated K-ion storage mechanism. To further improve the anode efficiency, a thin layer of Al2O3 coating (~ 2 nm) was applied on the hard carbon by Atomic Layer Deposition (ALD) to function as artificial solid electrolyte interphase and increased the Coulombic efficiency from 99.0% to 99.6%. After investigating the relationship among electrochemical performance, material interface, structural design, and mechanism of potassium-ion storage, we provided new insights for the design and synthesis of carbonaceous materials with improved storage capacity and efficiency for future developments of PIBs.

Waste cooking oil biodiesel and petroleum diesel soot from diesel bus: A comparison of morphology, nanostructure, functional group composition and oxidation reactivity

Biodiesel is one of carbon neutral fuels for diesel engine and waste cooking oil (WCO) would be the most viable source for biodiesel production in China. This paper studied the micromorphology, nanostructure, surface functional group composition, and oxidation activity characteristics of particles emitted from a China V bus fueled by pure WCO biodiesel and petroleum diesel, respectively. Compared with petroleum diesel, the results showed that particle mass (PM) and particle number (PN) of WCO biodiesel decreased by 38.66% and 38.12%, respectively, while the proportion of nucleation mode particles increased by about 10%. The soot particles of WCO biodiesel have higher disordered nanostructure, smaller primary particle size and fringe length, larger fringe separation distance and tortuosity, and lower graphitization degree than those of petroleum diesel. Moreover, the oxygen-containing surface functional groups content and carbon atom hybrid ratio of soot particles of WCO biodiesel were higher than those of petroleum diesel under the same oxidation temperature. And then the activation energy of soot particles from WCO biodiesel which contained more lattice defect structures was 38.43 kJ/mol, 37.8% lower than petroleum diesel, which is easier to be oxidized.

Hydrogen-rich gas production by catalytic steam gasification of rice husk using CeO2-modified Ni-CaO sorption bifunctional catalysts

Hydrogen-rich gas production from rice husk via steam gasification and catalytic reforming using CeO2-modified Ni-CaO sorption bifunctional catalysts synthesized by sol–gel method in a two-stage system was investigated. The results show that the Ce0.7Ni1Ca5 catalyst achieves maximum H2 concentration (85.81(±0.39) vol.%) and H2 yield (35.82(±0.28) mmol g-1biomass) under a condition of 500 °C, S/C (steam/carbon in biomass) molar ratio of 5, catalyst/biomass mass ratio of 2.5, producing the lowest content of CO2 (3.62(±0.16) vol.%), CO (4.27(±0.11) vol.%), CH4 (4.49(±0.18) vol.%), and C2-C3 (1.81(±0.09) vol.%), correspondingly. Ce0.7Ni1Ca5 also exhibits excellent cyclic stability in H2 production, CO2 sorption, and inhibition of carbon deposition. The H2 concentration and H2 yield remain above 81.88 vol% and 32.11 mmol g-1biomass, respectively, and CO2 emission keeps below 4.85 vol% during 10 cyclic tests. The carbon deposition of Ce0.7Ni1Ca5 is only about 30% of that of Ni1Ca5 after 10 cycles and hardly increased after 5 cycles. It is found that well-dispersed CeO2 can effectively prevent the sintering of NiO and delay agglomeration of CaO species, stabilizing CaO carbonation and CO2 sorption, and the strong Ni-O-Ce interaction induces the creation of oxygen vacancies that facilitate the fracture of O–H bonds of water for the formation of H2. Furthermore, the high oxygen transport capacity of CeO2 not only forms abundant mesopores structure to promote WGS and SMR reactions for enhancing H2 production, but also contributes to reforming the carbon deposited on the catalyst surface by lowering the oxidation temperature of amorphous carbon containing low-molecular aromatic or aliphatic compounds with lower degree of graphitization.

Two C-S bonds derived from carbons with different IG/ID values promote high sulfur loads and stable capacity storage

Carbon materials are always used as sulfur carriers in lithium-sulfur batteries. However, storage mechanism of carbon materials with different graphitization degree is different. Carbons with lower graphitization degree (IG/ID value) usually possess many defects and poor electrical conductivities. Carbon materials with high graphitization degree always possess less contact sites. Both two carbon materials are conducive to achieve sulfur loads. However, sulfur-loading capacities of two materials are different. In this paper, two carbon materials with different graphitization degrees are combined to form composite carbon materials. Studies show that composite carbon electrodes with suitable IG/ID values possess good sulfur-loading capacities (80%) because of high conductivity and defect contents. Two kinds of C-S bonds are produced after loading sulfur and both of them are conducive to stable production of polysulfides. One C-S bond is conducive to diffusion of lithium ions on electrode surface and the other C-S bond is conducive to rapid conversion of polysulfides. Under the performance of two C-S bonds, high capacity storage and good cycling stability can be achieved by electrodes under high sulfur-loading conditions.