Mesocarbon Microbeads Research Articles

Rapid synthesis and enhanced microwave absorption of carbon-supported high-entropy metal oxide

Complex preparation process and long annealing time of high-entropy metal oxide (HEO) limit its extensive application as microwave absorber at civil and military fields. Herein, a rapid synthesis method of mesocarbon microbeads (MCMB)-loaded spinel structure (FeCoCrNiMnCu)O is studied via plasma flow. In the presence of extreme plasma heating rate, a nanoscale high-entropy phase can be formed while modifying the surface activity of carbon. Simultaneously, due to the short synthesis time, gaseous conversion of carbon under high temperature aerobic conditions is avoided. By appending of carbon, the dual-media absorber exhibits better absorption performance with a maximum peak (-44.7 dB), which achieves over 90 % absorption in 11.2–15.5 GHz with a thickness of only 1.9 mm. Interestingly, the real and imaginary parts of complex permittivity increase remarkably. The former change is attributed to the expansion of heterogeneous hole carrier region and the latter dues to the interfacial polarization of the strongly coupled interface. The increase of dielectric loss and conductance loss leads to great improvement of microwave absorption. Our study injects new vitality into the preparation of HEO for advanced applications and the as-prepared HEOM is promised to be high-efficient microwave absorber based on robust stability and excellent absorbing performance.

Quantifying the Temperature Dependence of the Multi-Species, Multi-Reaction Model: Part II. Estimation of Entropy Coefficient for Meso-Carbon Micro-Bead Graphite

In Part 1 of this paper, the temperature impact on the Multi-Species, Multi Reaction (MSMR) model was studied. This was accomplished by acquiring data from slow rate lithiation and delithiation of a meso-carbon micro-bead (MCMB) graphite. Through this analysis, the temperature impact on the total fraction of available host sites in a particular MSMR gallery (Xj), the impact on the reference potential ( Ujo ), and the impact on the parameter detailing the deviation from Nernstian behavior (ω j) was determined. Here, the intercalation material is discussed, compared to traditional methods of acquiring the entropy coefficient, and comparison is made to previous mathematical estimates. Some of the challenges in using temperature dependent constant rate charge and discharge data as compared to the potentiodynamic entropy coefficient calculation method are also discussed, and a recommendation for future applications is proposed.

Quantifying the Temperature Dependence of the Multi-Species, Multi-Reaction Model. Part 1: Parameterization for a Meso-Carbon Micro-Bead Graphite

In this work, the temperature impact on the Multi-Species, Multi-Reaction (MSMR) model is studied. This is accomplished by acquiring data from slow rate lithiation and delithiation of a meso-carbon micro-bead (MCMB) graphite. The MSMR model is used to simulate linear-sweep voltammetry data of a porous electrode composed of graphite, and because the electrode is close to a state of dynamic equilibrium, the peaks in the differential voltage spectroscopy plot can be analyzed. Through this analysis, the temperature impact on the total fraction of available host sites in a particular MSMR gallery (Xj), the impact on the reference potential (U°j), and the impact on the parameter detailing the deviation from Nernstian behavior (ω j) can be found. This is the first time the temperature dependence of the MSMR parameters have been experimentally analyzed. In Part 2, the impact of the temperature dependence of the MSMR parameters on the entropy coefficient of an intercalation material will be studied.

Biomimetic structure-driven high strength and toughness in continuous SiC skeleton-reinforced graphite composites

Graphite-matrix structural composites with excellent mechanical properties and long-term reliability are ungently required in aerospace and nuclear industries. However, the enhancement of graphite-matrix composites by mainstream surface coating techniques or second-phase particle reinforcement is rather limited. Inspired by the structural-functional feature of plant cells, silicon carbide (SiC, cytoderm) coated mesocarbon microbeads (MCMB, cytoplasm) powders were prepared by combustion synthesis (CS), which were then densified via spark plasma sintering (SPS) to obtain the biomimetic cellular-structured SiC-reinforced MCMB (M@SiC) composites. The in-situ formed SiC ‘cytoderm’ ensures good interfacial bonding and contributed to the densification of the composites. Additionally, the continuous SiC skeleton and cellular-structured configuration improved the mechanical properties of M@SiC composites. Owing to the complex crack deflection, branching and bridging effects at the MCMB/SiC interfaces and graphite nanoflakes inside MCMB, the biomimetic M@SiC composite with SiC content of 47 vol% exhibited strengthening and toughening, with flexural strength and fracture toughness of 245 MPa and 3.82 MPa m1/2, respectively. The developed biomimetic graphite-matrix composites with excellent mechanical properties are expected to be applied in reusable spacecrafts and high-temperature gas-cooled reactors.

Preparation of graphite/silicon carbide based on SLS/LSI and study of properties

In this paper, graphite/silicon carbide composites with an integrated structure–function were prepared by selective laser sintering (SLS) and liquid silicon infiltration (LSI). The study investigated the influence of different factors on the microstructure, mechanical properties, and thermal conductivity of graphite/silicon carbide composites. The results demonstrated that the open porosity of the precast body gradually decreased with an increase in the content of mesocarbon microbeads (MCMB), while the carbon content gradually increased. The density, mechanical strength, and thermal conductivity (TC) of the composites initially increased, followed by a subsequent decrease. In the absence of MCMB, micropores and a significant amount of free silicon were observed within the composite after LSI, leading to reduced density and mechanical properties. Conversely, the inclusion of 20 wt% MCMB led to the elimination of micropores and free silicon within the composite, resulting in the highest density and TC values of 2.52 g/cm3 and 73.22 W/m·K, respectively. The measured TC values were consistent with those calculated by the Effective Medium Theory Model (EMT). At a 40 wt% addition, micropores and free silicon reappeared within the composites, leading to a decrease in density and properties. Furthermore, the calculated values of the five thermal conductivity models were found to be higher than the measured values. This paper presents a further improvement in the process of preparing graphite-ceramic composites with a complex structure, achieved by controlling the amount of MCMB added. This contributes to the subsequent research.

Understanding and Strategies for High Energy Density Lithium‐Ion/Lithium Metal Hybrid Batteries

AbstractA pressing need for high‐capacity anode materials beyond graphite is evident, aiming to enhance the energy density of Li‐ion batteries (LIBs). A Li‐ion/Li metal hybrid anode holds remarkable potential for high energy density through additional Li plating, while benefiting from graphite's stable intercalation chemistry. However, limited comprehension of the hybrid anode has led to improper utilization of both chemistries, causing their degradation. Herein, this study reports an effective hybrid anode design considering material properties, the ratio of intercalation‐to‐plating capacity, and Li‐ion transport phenomena on the surface. Mesocarbon microbeads (MCMB) possesses desirable properties for additional Li plating based on its spherical shape, lithiophilic functional group, and sufficient interparticle space, alongside stable intercalation‐based storage capability. Balancing the ratio of intercalation‐to‐plating capacity is also crucial, as excessive Li plating occurs on the top surface of the anode, eventually deactivating the intercalation chemistry by obstructing upper pores. To address this issue, electrospun polyvinylidene fluoride (PVDF) is introduced to prevent Li metal accumulation on the upper surface, leveraging its non‐conductive, polar nature, and high dielectric constant. By implementing these strategies, a LiNi0.8Co0.15Al0.05O2 (NCA)‐paired pouch cell delivers an outstanding energy density of 1101.0 Wh L−1, highlighting its potential as an advanced post‐LIBs with practical feasibility.

The Potential Regulation of Working Anode for Long-Term Zero-Volt Storage at 37°C in Li-Ion Batteries.

The advanced lithium-ion batteries that can tolerate zero-volt storage (ZVS) are in high demand for implantable medical devices and spacecraft. However, ZVS can raise the anode potential, leading to Cu current collector dissolution and solid-electrolyte interphase (SEI) degradation, especially at 37°C. In this contribution, by quantitatively regulating the dosage of Li6CoO4 cathode additives, controllable potential of the working anode under abusive-discharge conditions is demonstrated. The addition of Li6CoO4 keeps zero-crossing potential (ZCP) and the potential of ZVS below 2.0 V (vs Li/Li+) for LiCoO2|mesocarbon microbead cells at 37°C. The capacity retention ratio (CRR) increases from 69.1% and 35.9% to 98.6% and 90.8% after 10 and 20 days of ZVS, respectively. The Cu dissolution and SEI degradation are effectively suppressed, while the over-lithiated cathode exhibits high reversible capacity after ZVS. The limiting conditions of long-term ZVS are further explored and a corresponding guide map is designed. When quantitatively regulating ZCP and the potential in ZVS, Cu dissolution, SEI degradation, and irreversible conversion of the cathode constitute the limiting conditions. This contribution designs the most reasonable potential range for ZVS protection at 37°C, and realizes the best CRR record through precise potential regulation for the first time.

Study on the characterization and thermal conversion behavior of sequential extraction products from medium temperature coal pitch

To achieve the high value-added clean utilization of medium temperature coal pitch (MTP), five fractions were separated from MTP by the sequential extraction method using n-heptane, n-butanol, toluene, tetrahydrofuran and quinoline as solvents. Briefly, the extracts were analysed using proximate analysis, elemental analysis, fourier infrared spectrum (FTIR), ultraviolet visible spectrum (UV–vis), fluorescence spectrum, and thermogravimetric analysis (TGA) to investigate their structural parameters, aromatic condensation degree and pyrolysis properties. Meanwhile, Raman spectrum, X-ray diffraction (XRD), and polarizing microscope were used to quantitatively analyze the microstructures of thermal conversion products of the extracts. This allowed for investigation of the thermal conversion mechanism and determination of the thermal conversion behavior. In fact, the chain index (CH3/CH2), aromatic index (Iar), aromatic condensation degree and thermal stability of the extracts increase gradually with deeper extraction. Extracts with high aromatic condensation degree are more favorable for the formation of mesocarbon microbeads (MCMBs). However, overly aromatic condensation degree will lead to excessive coalescence of MCMBs. The ideal carbon microcrystalline content increases with higher temperatures during the thermal conversion of the same fraction. But the change of amorphous carbon content has no obvious regularity. The results of this work will provide theoretical and experimental support for the selection of precursors for carbon/graphite materials.

Surface decoration of mesocarbon microbeads with multifunctional TiNbO4−x@C coating layer as high rate and stable anode of Li-ion batteries

Surface decoration of mesocarbon microbeads with multifunctional TiNbO4−x@C coating layer as high rate and stable anode of Li-ion batteries

Synthesis of mesocarbon microbeads from high‐temperature coal tar pitch: Effects of quinoline insoluble

AbstractMesocarbon microbeads (MCMBs) were a kind of functional artificial carbon materials, which was widely used in varied areas with its excellent properties. MCMB was generally produced by thermal‐polymerization of high‐temperature coal tar pitch under oxygen‐free atmosphere. Generally, the content of primary quinoline insoluble (PQI) play a key role on the quality of the derived MCMB. In order to confirm the relationship between the content of PQI and the properties of MCMB, 15 kinds of high‐temperature coal tar pitch with varied content of PQI were used as the raw materials to produce MCMB. The particle size distribution, optical micro‐structure, surface morphology, and carbon micro‐crystalline of calcinated MCMB were determined in this work. The results shown that the content of PQI from 7% to 13% was a suitable content to generate high quality MCMB. What is more, the derived MCMB has a high yield of 33.09% with good sphericity, the uniformity index of particle size was 1.02, and the graphite carbon content of calcinated MCMB (calcinated temperature of 1100°C) was 79.92%. Thus, the high‐temperature coal tar pitch with the PQI content of 7%–13% was the preferably raw materials to produce high‐quality MCMB by thermal‐polymerization method.

Purification of Quinoline Insolubles in Heavy Coal Tar and Preparation of Meso-Carbon Microbeads by Catalytic Polycondensation.

The quinoline-insoluble (QI) matter in coal tar and coal tar pitch is an important factor affecting the properties of subsequent carbon materials. In this paper, catalytic polycondensation was used to remove QI from heavy coal tar, and meso-carbon microbeads could be formed during the purification process. The results showed that AlCl3 had superior catalytic performance to CuCl2, and the content of QI and heavy components, including pitch, in the coal tar was lower after AlCl3 catalytic polycondensation. Under the condition of catalytic polycondensation (AlCl3 0.9 g, temperature 200 °C, and time 9 h), AlCl3 could reduce the QI content in heavy coal tar. The formed small particles could be filtered and removed, and good carbon materials could be obtained under the condition of catalytic polycondensation (AlCl3 0.9 g, temperature 260 °C, and time 3 h).

Interlayer Confined Water Enabled Pseudocapacitive Sodium-Ion Storage in Nonaqueous Electrolyte.

Electrochemical capacitors have faced the limitations of low energy density for decades, owing to the low capacity of electric double-layer capacitance (EDLC)-type positive electrodes. In this work, we reveal the functions of interlayer confined water in iron vanadate (FeV3O8.7·nH2O) for sodium-ion storage in nonaqueous electrolyte. Using an electrochemical quartz crystal microbalance, in situ Raman, and ex situ X-ray diffraction and X-ray photoelectron spectroscopy, we demonstrate that both nonfaradaic (surficial EDLC) and faradaic (pseudocapacitance-dominated Na+ intercalation) processes are involved in the charge storages. The interlayer confined water is able to accelerate the fast Na+ intercalations and is highly stable (without the removal of water or co-intercalation of [Na-diglyme]+) in the nonaqueous environment. Furthermore, coupling the pseudocapacitive FeV3O8.7·nH2O with EDLC-type activated carbon (FeVO-AC) as the positive electrode brings comprehensive enhancements, displaying the enlarged compaction density of ∼2 times, specific capacity of ∼1.5 times, and volumetric capacity of ∼3 times compared to the AC electrode. Furthermore, the as-assembled hybrid sodium-ion capacitor, consisting of an FeVO-AC positive electrode and a mesocarbon microbeads negative electrode, shows a high energy density of 108 Wh kg-1 at 108 W kg-1 and 15.3 Wh kg-1 at 8.3 kW kg-1. Our results offer an emerging route for improving both specific and volumetric energy densities of electrochemical capacitors.

Identification and classification of disordered carbon materials in a composite matrix through machine learning approach integrated with Raman mapping

Identification and classification of different types of highly disordered carbon materials present in a polymer matrix with similar Raman spectra have been carried out using a machine learning approach. Convolutional neural network (CNN) has been used for the classification of disordered carbon materials such as graphene oxide (GO), functionalized carbon nanotube (f-CNT), carbon fiber (Cf), carbon black (CB), pyrolytic carbon (PyC), coke, and mesocarbon microbeads (MCMB). The hyperparameters of the machine learning model have been optimized by the Bayesian optimization algorithm. CNN gave an accuracy of 91.9 %, F1 score of 92 %, precision of 92.1 %, recall of 92 % and area-under-curve (AUC) of 0.99. Gradient-weighted Class Activation Mapping (Grad-CAM) has been utilized for getting the explainability in the classification process of the CNN model. The CNN along with Raman area scanning could successfully map different disordered carbon materials in the polymer matrix composite.

Functionalized graphene assisted the formation of mesocarbon microbeads with ultra-large size and loose microcrystalline structure from petroleum pitch for sodium-ion batteries anode

It is a significant way to improve the sodium storage performance of mesocarbon microbeads (MCMBs) by adjusting the size and microcrystalline structure of it. A petroleum-based MCMBs with an ultra-large size and loose microcrystalline structure was synthesized by introducing functionalized graphene (FNG). The results indicate that the FNG can hinder the ordered stacking of planar aromatic macromolecules, prevent the coalescence and prolong the growth time of mesophase spheres. Mesophase spheres are easier to grow to an ultra-large size with looser microcrystalline structure. The MCMBs with a size of 250 µm and a larger microcrystalline spacing can be achieved by adding 1.0 wt% FNG during the polycondensation process. Such MCMBs deliver a competitive specific capacity of 123.4 mAh g−1 at a current density of 1.0 A g−1 with a high initial coulombic efficiency of 81.79% and an excellent stability of cycle performance when applied as anode of SIBs. This work provides a valuable and efficient method to enhance the SIB performance by designing the size and microcrystalline structure of MCMBs.

Research on selective laser sintering process of ternary composite materials (PP/MCMB/CNT)

The composite material composed of polypropylene and conductive filler has good corrosion resistance, light weight and good conductivity, and is one of the preferred materials for fuel cell bipolar plates. The formation of ternary composite materials composed of polypropylene, mesocarbon microbeads and carbon nanotubes is realized by selective laser sintering. The influences of laser power, scanning speed, scanning spacing and defocus amount on forming quality are studied. The formability of mixed powders with different composition proportions as well as the conductivity, bending strength and hydrophobicity of the formed samples are investigated. The results show that when the input energy density is insufficient, it is easy to form defects such as spheroidized particles and worm-like structures. The parameters with good forming quality are in the following range: defocus amount is + 3 mm; line energy density is 2.94–3.85 J/mm2; peak power density is 1.13 × 104-1.48 × 104 W/mm2 and scanning spacing is 0.1–0.14 mm. The conductive filler in composite material is beneficial to improving the conductivity, but it will reduce the formability of the mixed powders and reduce the bending strength and hydrophobicity of the sample. The effect of mesocarbon microbeads on improving conductivity or on reducing hydrophobicity is smaller than that of carbon nanotubes.

Amidation structure design of carbon materials enables high energy and power density symmetric Sodium-ion battery

Structure design of carbon materials, like the heteroatom doping, is one of the effective strategies to develop high-performance anode of sodium-ion battery (SIB). However, challenges remain in sodium ion storage capacity, rate capability and cycle life. Here, an amidation structure design strategy is rationally proposed, and the regulated electrode exhibits not only remarkable electrochemical performance, but also great potential in scale commercial production. Mesocarbon microbead (MCMB), a graphitic spherical particle with excellent physiochemical properties but low-cost production process, is applied to the amidation process, achieving enlarged interlayer distances up to ∼ 0.42 nm and rich –CONH2 active sites. The amidated MCMB (MCMBO-NH2) anode displays a high specific capacity of 220 mAh/g, with a retention rate of about 83.6 % after 500 cycles. The MCMBO-NH2 cathode remains stable at the specific capacity of 141 mAh/g after 250 cycles. The symmetric sodium-ion full cell then demonstrates a high energy density of 145 Wh/kg at a large power density of 12,500 W/kg, and an excellent capacity retention rate of 96.1% after 500 cycles, which is superior to the previous work of the symmetric SIBs. The amidation design of carbon materials comes with outstanding battery performance and cost-effective production process, offering a significant commercial value for the industrialization of SIBs.

Prussian blue microcubes-derived FeF3 cathodes for high-energy and ultra-stable lithium and lithium-ion batteries

Iron trifluoride (FeF3) is highlighted as a competitive cathode for next-generation lithium and lithium-ion batteries with higher energy densities and lower cost. However, the FeF3 cathode is typically hindered by rapid capacity fade for their poor electronic/ionic conductivity and unstable electrode/electrolyte interphase. Herein, a microcubic FeF3@C composite, where the nanosized FeF3 particles (<40 nm) are encapsulated by graphitized carbon and linked through surrounding amorphous carbon matrix, is firstly synthesized through the Prussian blue microcubes. When using as the cathode of coin-type lithium batteries, it can achieve stable and ultralong lifespan (over 1000 cycles) at FeF3 mass loading of ∼2 mg cm−2, ascribing to the compact and thick wrapping of carbon shell and stable cathode solid electrolyte interphase (CEI) during cycling. Besides, the FeF3–Li pouch cell, FeF3 full batteries with pre-lithiated Li4Ti5O12 (PLLTO) and pre-lithiated mesocarbon microbeads (PLMCMB) anodes are successfully constructed. To interpret the capacity rising of as-prepared FeF3 cathodes within initial cycles, the detailed electrochemical behaviors and electrode kinetics are investigated. The results show that the decay of the high-potential decomposition process cannot catch up with the activation of the low-potential conversion reaction The repeated electrochemical activation within initial cycles causes multiple interface and increased Li+ diffusion coefficient (resulted from the amorphization of FeF3 particle), which induce the capacity rising.

Molten salt synthesis and antioxidation property of SiC‐coated mesocarbon microbeads

AbstractMesocarbon microbead (MCMB) is a prospective candidate as the raw material for nuclear graphite. However, the poor resistance to high‐temperature oxidation limits its application. Herein, a dense SiC coating was prepared by molten salt synthesis on the surface of MCMB to improve its antioxidation performance. The effect of molten salt synthesis reaction time on the phase composition, microstructure, and antioxidation performance of the SiC‐coated MCMB particles was investigated. A theoretical model was established to explain the SiC coating growth rule well, in conformity with the carbon vacancy diffusion mechanism in SiC coating. The SiC coating synthesized for 7 h with the thickness of .385 µm remarkably promoted the high‐temperature antioxidation property of MCMB. The kinetics analysis indicated that the SiC coating obstructed the oxygen diffusion effectively during the oxidation process. The as‐fabricated SiC‐coated MCMBs with good oxidation resistance show great promise for application in nuclear industry and other antioxidative fields.

KOH-treated mesocarbon microbeads used as high-rate anode materials for potassium-ion batteries

KOH-treated mesocarbon microbeads used as high-rate anode materials for potassium-ion batteries

Crude Mesocarbon Microbeads as an Economical and Efficient Electrode Material for Safe Symmetrical-Carbon Cells

Crude Mesocarbon Microbeads as an Economical and Efficient Electrode Material for Safe Symmetrical-Carbon Cells