Mesocarbon Microbeads Research Articles

Strongly Coupled Pyridine-V2 O5 ·nH2 O Nanowires with Intercalation Pseudocapacitance and Stabilized Layer for High Energy Sodium Ion Capacitors.

Developing pseudocapacitive cathodes for sodium ion capacitors (SICs) is very significant for enhancing energy density of SICs. Vanadium oxides cathodes with pseudocapacitive behavior are able to offer high capacity. However, the capacity fading caused by the irreversible collapse of layer structure remains a major issue. Herein, based on the Acid-Base Proton theory, a strongly coupled layered pyridine-V2 O5 ·nH2 O nanowires cathode is reported for highly efficient sodium ion storage. By density functional theory calculations, in situ X-ray diffraction, and ex situ Fourier-transform infrared spectroscopy, a strong interaction between protonated pyridine and VO group is confirmed and stable during cycling. The pyridine-V2 O5 ·nH2 O nanowires deliver long-term cyclability (over 3000 cycles), large pseudocapacitive behavior (78% capacitive contribution at 1 mV s-1 ) and outstanding rate capability. The assembled pyridine-V2 O5 ·nH2 O//graphitic mesocarbon microbead SIC delivers high energy density of ≈96 Wh kg-1 (at 59 W kg-1 ) and power density of 14 kW kg-1 (at 37.5 Wh kg-1 ). The present work highlights the strategy of realizing strong interaction in the interlayer of V2 O5 ·nH2 O to enhance the electrochemical performance of vanadium oxides cathodes. The strategy could be extended for improving the electrochemical performance of other layered materials.

Bimetallic NiCo2S4 Nanoneedles Anchored on Mesocarbon Microbeads as Advanced Electrodes for Asymmetric Supercapacitors

HighlightsA facile method was used to anchor pseudocapacitive bimetallic NiCo2S4 (NCS) nanoneedles on mesocarbon microbeads (MCMBs), forming a novel urchin-like structure.The NCS@MCMB electrode and an assembled asymmetric supercapacitor displayed good electrochemical performance.

Effects of Charge Cutoff Potential on an Electrolyte Additive for LiNi0.6Co0.2Mn0.2O2–Mesocarbon Microbead Full Cells

Tris(trimethylsilyl)phosphite (TMSPi) has been reported to be an excellent electrolyte additive. However, scarce reports exist on the effect of the charge cutoff potential on the cyclic stability using high‐performance LiNi0.6Co0.2Mn0.2O2 (NCM622)–mesocarbon microbead (MCMB) full cells. Herein, a high‐loading and repeatable NCM622–MCMB coin‐type full cell is successfully prepared, and the role of TMSPi on such a full cell at charge cutoff potentials of 4.25 and 4.45 V is studied. Theoretical calculations and detailed analyses reveal that it is oxidized in the first charging process due to its unsaturated P—O bonds, thus forming a stable P—O—F‐rich cathode electrolyte interphase and preventing severe decomposition of the electrolyte over NCM622 during long‐term cycling. In addition, the P—O and Si—O bonds of TMSPi both display HF‐scavenging ability. Moreover, TMSPi may react directly with the LiPF6‐based electrolyte to form some intermediate products that can be reduced on the MCMB electrode, thereby modifying the solid electrolyte interphase and improving the stability of MCMB during lithium intercalation.

Fabrication and Investigation of MCMB–LiNi0.5Mn1.5O4Pouch Cells for High Energy Density Lithium-Ion Batteries: Indigenous Efforts and Challenges for Realization

In the present work, we have fabricated indigenous 300 mAh lithium-ion rechargeable pouch cells using laboratory made LiMn1.5Ni0.5O4 cathode and commercial meso carbon micro-beads anode. Required mass balancing was performed to yield pouch cell of 300 mAh capacity at C/4 rate. When charged and discharged at C/4 and C/3 rates the fabricated pouch cells retained ~ 79% of their capacities after 50 cycles. Post-mortem analysis of the cycled pouch cell indicated the dissolution of Mn and Ni from cathode and deposition of the same at anode and separator. The observed bulging of the cycled pouch cell could be due to evolution of gases through chemical decomposition of conventional organic electrolyte. Though active material dissolution and gas evolution might reduce deliverable capacity and operating voltage of the fabricated pouch cells, yet the reported electrochemical characteristics were far superior to many of the existing literature reports.

An In Situ Interface Reinforcement Strategy Achieving Long Cycle Performance of Dual‐Ion Batteries

AbstractDual‐ion batteries (DIBs) with high operation voltage offer promising candidates for low‐cost clean energy chemistries. However, there still exist tough issues, including structural collapse of the graphite cathode due to solvent co‐intercalation and electrolyte decomposition on the electrode/electrolyte interface, which results in unsatisfactory cyclability and fast battery failure. Herein, Li4Ti5O12 (LTO) modified mesocarbon microbeads (MCMBs) are proposed as a cathode material. The LTO layer functions as a skeleton and offers electrocatalytic active sites for in situ generation of a favorable and compatible cathode electrolyte interface (CEI) layer. The synergetic LTO‐CEI network can change the thermodynamic behavior of the PF6− intercalation process and maintain the structural integrity of the graphite cathode, as a “Great Wall” to protect the cathode from structural collapse and electrolyte decomposition. Such LTO‐CEI reinforced cathode exhibits a prolonged cyclability with 85.1% capacity retention after 2000 cycles even at cut‐off potential of 5.4 V versus Li+/Li. Moreover, the LTO‐modified MCMB (+)//prelithiated MCMB (−) full cell exhibits a high energy density of ≈200 Wh kg−1, remarkably enhanced cyclability with 93.5% capacity retention after 1000 cycles. Undoubtedly, this work offers in‐depth insight into interface chemistry, which can arouse new originality to boost the development of DIBs.

Triglyme-based electrolyte for sodium-ion and sodium-sulfur batteries

Herein, we investigate a lowly flammable electrolyte formed by dissolving sodium trifluoromethanesulfonate (NaCF3SO3) salt in triethylene glycol dimethyl ether (TREGDME) solvent as suitable medium for application in Na-ion and Na/S cells. The study, performed by using various electrochemical techniques, including impedance spectroscopy, voltammetry, and galvanostatic cycling, indicates for the solution high ionic conductivity and sodium transference number (t+), suitable stability window, very low electrode/electrolyte interphase resistance and sodium stripping/deposition overvoltage. Direct exposition to flame reveals the remarkable safety of the solution due to missing fire evolution under the adopted experimental setup. The solution is further investigated in sodium cells using various electrodes, i.e., mesocarbon microbeads (MCMBs), tin-carbon (Sn–C), and sulfur-multiwalled carbon nanotubes (S-MWCNTs). The results show suitable cycling performances, with stable reversible capacity ranging from 90 mAh g−1 for MCMB to 130 mAh g−1 for Sn–C, and to 250 mAh g−1 for S-MWCNTs, thus suggesting the electrolyte as promising candidate for application in sustainable sodium-ion and sodium-sulfur batteries.

Functional additives assisted ester-carbonate electrolyte enables wide temperature operation of a high-voltage (5 V-Class) Li-ion battery

Nowadays, wide temperature range and high-energy Li-ion batteries are increasingly required. However, it is difficult to get a compromise between subzero temperature performance and high temperature performance. Herein, methyl acetate co-solvent with a freezing point of −98.1 °C (50% by volume) is blended with carbonates to obtain a high-conductivity LiPF6-based electrolyte, which contains tris(trimethylsilyl) phosphite and 1,3-propanediolcyclic sulfate binary functional additives to significantly enhance cycling performance of a challenging high-voltage (5 V-class) battery system using a LiNi0.5Mn1.5O4 cathode and a graphitic mesocarbon microbead anode, unprecedentedly ranging from −60 °C to 50 °C. High reactivity between methyl acetate co-solvent and graphitic mesocarbon microbead anode is innovatively proposed to be associated with graphitic mesocarbon microbead anode catalytic formation of methoxy free radical. More importantly, high reactivity between methyl acetate co-solvent and graphitic mesocarbon microbead anode can be greatly suppressed by species derived from functional additives. This paper highlights the crucial rule of both high Li+ conductivity and favorable graphite anode interface layer for achieving high performance wide temperature range Li-ion batteries.

Bimetallic Pd96Fe4 nanodendrites embedded in graphitic carbon nanosheets as highly efficient anode electrocatalysts.

A facile route to anchor a nanoalloy catalyst on graphitic carbon nanosheets (GCNs) has been developed for preparing high-performance electrode materials for application in direct alcohol fuel cells (DAFCs). Uniformly dispersed bimetallic Pd–Fe nanoparticles (NPs) with tunable composition have been immobilized on GCNs derived from mesocarbon microbeads (MCMBs) by a one-pot radiolytic reduction method. The Pd–Fe/GCN hybrid shows promising electrocatalytic activity for the methanol, ethanol, ethylene glycol, tri-ethylene glycol and glycerol oxidation reactions in alkaline medium. The as-prepared flower-shape Pd96Fe4/GCN nanohybrids have high mass activity for the ethanol oxidation reaction (EOR), which is ∼36 times (11 A per mg Pd) higher than that of their monometallic counterparts. Moreover, the onset oxidation potential for the EOR on the Pd96Fe4/GCN nanohybrids negatively shifts ca. 780 mV compared to that on commercial Pd/C electrocatalysts, suggesting fast kinetics and superior electrocatalytic activity. Additionally, chronoamperometry measurements display good long-term cycling stability of the Pd96Fe4/GCN nanohybrids for the EOR and also demonstrate only ∼7% loss in forward current density after 1000 cycles. The superior catalytic activity and stability may have originated from the modified electronic structure of the Pd–Fe nanoalloys and excellent physicochemical properties of the graphitic nanosheets. The present synthetic route using GCNs as the supporting material will contribute to further design of multimetallic nanoarchitectures with controlled composition and desired functions for fuel cell applications.

LiFePO4-Coated LiNi0.5Co0.2Mn0.3O2 Cathode Materials with Improved High Voltage Electrochemical Performance and Enhanced Safety for Lithium Ion Pouch Cells

The applicable nickel-rich cathode materials (LiNi0.5Co0.2Mn0.3O2, NCM) under high cutoff voltage for high energy density lithium ion batteries shows a broad prospect, but creates enormous challenges for safety. In this work, the LiFePO4-coated LiNi0.5Co0.2Mn0.3O2 (NCM-LFP) composites were prepared on a large scale by the high-speed dispersion and mechanical fusion method, attempting to improve the electrochemical performance and safety of pouch full cells worked under a high cutoff voltage of 4.5 V. Performances have been greatly enhanced, especially for the heat generation during the charge process: the temperature rise of a 5Ah NCM-LFP/MCMB (mesocarbon microbeads) pouch cell was 18.7°C, much lower than that of a NCM/MCMB pouch cell (42.7°C). Also, no thermal runaway was observed of NCM-LFP/MCMB pouch cells at 100% state of charge (SOC) during the extrusion and metallic nail penetration tests. The results of ex-situ impedance measurement, high magnification transmission electron microscope (HR-TEM) and in-situ X-Ray Diffraction (XRD) during heating revealed that the enhanced high voltage safety was contributed to the suppressed structure evolution from layer to spinel to rock salt, as a result of a dense and uniform LFP protective layer on NCM.

SEI Grown on MCMB-Electrode with Fluoroethylene Carbonate and Vinylene Carbonate Additives as Probed by In Situ DRIFTS

The formation of solid electrolyte interphase (SEI) on electrodes of Lithium ion batteries (LiBs) is known to influence the electrochemical performance of LiBs. In this work, the effect of fluoroethylene carbonate (FEC) and vinylene carbonate (VC) on the SEI formation on mesocarbon microbeads (MCMB) anode is examined by in situ DRIFTS (diffuse reflectance infrared Fourier-transformed spectroscopy). Formation of SEI species on MCMB starts in the first lithiation cycle with an onset potential corresponding to the electrochemical reduction potential of the additive. However, both VC and FEC result in continuous SEI formation in subsequent cycles with no onset potential. Similar SEI species are found in the first lithiation cycle and in the subsequent cycles. This suggests the presence of an electrochemical initiation of SEI species formation with a subsequent propagation, similar with what we found previously over Si-based anode. [Y. B. Yohannes, S. D. Lin and N.-L. Wu, J. Electrochem. Soc., 164, A3641 (2017)] The contribution of the observed SEI species for the improved electrochemical impedances through cycling and its implications are discussed.

Communication—Introduction of Polyurethane-Polyacrylic Acid as a Binder for Electrochemical Activation of Expanded Mesocarbon Microbeads in Organic Supercapacitors

The electrochemical activation is a common technique enhancing the capacitive performances of carbons in high-voltage supercapacitors while volume expansion during the activation process often makes the active materials detachment, dropping the capacitance. In this work, the KOH-neutralized polyurethane-crosslinked-polyacrylic acid (PUPAH10-xKx) polymers are proposed to replace the polyvinylidene fluoride (PVDF) as a binder for expanded mesocarbon microbead (EMCMB) electrodes to buffer the volume expansion. The effects of binder rheology, morphology and neutralization degree on the capacitive performance of EMCMB are investigated. Introducing PUPAH6K4 with moderate viscoelasticity to EMCMB forms an expansion-buffering electrode and promotes the electrochemical activation process.

Electrochemical performance of graphene-coated activated mesocarbon microbeads as a supercapacitor electrode.

Hybrid activated carbon/graphene materials are prospective candidates for use as high performance supercapacitor electrode materials, since they have the superior characteristics of high surface area, abundant micro/mesoporous structure due to the presence of activated carbon and good electrical conductivity as a result of the presence of graphene. In this work, the electrochemical performance of facile and low-cost graphene-coated activated mesocarbon microbeads (g-AM) is carefully studied. The results show that g-AM can only be formed at a very high temperature over a long activation time, resulting in the formation of a large pore size and low specific surface area, further resulting in poor electrochemical performance (110 F g−1 at 0.1 A g−1 in 6 M KOH solution). Ball milling for a short time is an effective way to improve the electrochemical performance (191 F g−1 at 0.1 A g−1 in 6 M KOH solution). Moreover, due to the strong resistance to aggregation and good electrical conductivity of graphene flowers, the g-AM had nearly 100% rate capability when increasing the current density from 5 to 50 A g−1. The as-assembled two-electrode symmetric supercapacitor exhibits a high energy and power density (5.28 W h kg−1 at 10 000 W kg−1) in organic LiPF6 electrolyte, due to its better electrical conductivity. It is expected that this type of hybrid structure holds great potential for scalable industrial manufacture as supercapacitor electrodes.

A systematic study of kinetics in mesocarbon microbeads anodes in presence of nano-conductive additives

Nano-conductive additives in composite electrodes play a significant role in influencing the electrochemical performance of the carbon anode in Li-ion batteries. These additives with a high electronic conductivity lead to the formation of a uniform solid-electrolyte interfacial layer, improved cycle life, and rate capability. In this work, the parameters that lead to such a performance improvement, namely the kinetic and transport properties, are carefully studied with carbon black (CB), carbon nanotubes (CNT) and a mixture of the two as conductive additives in mesocarbon microbeads (MCMB) anode. Experimental measurements indicate that the electrochemical reaction rate is controlled by interfacial kinetics up to moderately high C-rate (<6C). Though nano-additives do not affect the solid phase diffusivity, the diffusion of Li-ion is considerably influenced by stages and their coexistence that is revealed through X-ray diffraction of cells at different depths of discharge. Using electrochemical impedance spectroscopy of half-cells cycled at different temperatures, the activation energy for charge transfer reaction and activation energy for SEI layer diffusion are estimated. The results exhibit an improvement in electron transfer and an ionically conducting SEI layer with the use of a mixture of CB and CNT as conductive additives. It is expected that the estimated kinetic and transport parameters and their temperature dependence for the additives under consideration will be of tremendous utility in the thermal, electrochemical, or aging modeling of batteries employing MCMB as anode material.

Mesocarbon Microbead Production from Fluid Catalytic Cracking Slurry Oil: Improving Performance through Supercritical Fluid Extraction

The utilization of fluid catalytic cracking (FCC) slurry oil is a wide concern in modern refineries because of its poor processability. The present study used FCC slurry oil (SLO) as feedstock to produce mesocarbon microbeads (MCMBs) according to its rich aromatic content. A supercritical fluid extraction technique was adopted to remove the undesirable components and thus improve the mesophase development performance. Three different alkanes were used as the supercritical fluids, and the chemical composition of the derived fractions (SFEO) was analyzed. Four stages of mesophase development were observed in the carbonization process. The results showed that heavier feedstock reacted faster and reached the coalescence stage earlier, forming a bulk mesophase. MCMBs with a smooth surface and good morphology were prepared from iso-butane-derived SFEO at a reaction time of 3 h. The quality of the bulk mesophase produced from SFEOs was significantly improved in comparison to DQ SLO.

The understanding of solid electrolyte interface (SEI) formation and mechanism as the effect of flouro‐o‐phenylenedimaleimaide (F‐MI) additive on lithium‐ion battery

Solid electrolyte interface (SEI) is a critical factor that influences battery performance. SEI layer is formed by the decomposition of organic and inorganic compounds after the first cycle. This study investigates SEI formation as a product of electrolyte decomposition by the presence of flouro‐o‐phenylenedimaleimaide (F‐MI) additive. The presence of fluorine on the maleimide‐based additive can increase storage capacity and reversible discharge capacity due to high electronegativity and high electron‐withdrawing group. The electrolyte containing 0.1 wt% of F‐MI‐based additive can trigger the formation of SEI, which could suppress the decomposition of remaining electrolyte. The reduction potential was 2.35 to 2.21 V vs Li/Li+ as examined by cyclic voltammetry (CV). The mesocarbon microbeads (MCMB) cell with F‐MI additive showed the lowest SEI resistance (Rsei) at 5898 Ω as evaluated by the electrochemical impedance spectroscopy (EIS). The morphology and element analysis on the negative electrode after the first charge‐discharge cycle were examined by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X‐ray photoelectron spectroscopy (XPS). XPS result showed that MCMB cell with F‐MI additive provides a higher intensity of organic compounds (RCH2OCO2Li) and thinner SEI than MCMB cell without an additive that provides a higher intensity of inorganic compound (Li2CO3 and Li2O), which leads to the performance decay. It is concluded that attaching the fluorine functional group on the maleimide‐based additive forms the ideal SEI formation for lithium‐ion battery.

Three-dimensional porous composite framework assembled with CuO microspheres as anode current collector for lithium-ion batteries

The surface structure and material composition of current collectors have significant effects on the electrochemical performances of lithium-ion batteries (LIBs). In this work, a three-dimensional (3D) porous composite framework is applied as the anode current collector in LIBs. This unique 3D skeleton is composed of conductive carbon fiber/Cu core/shell fibrous structure. With an oxidation treatment upon the copper shell, the porous framework is assembled with CuO microspheres. Using mesocarbon microbead (MCMB) graphite powders as the active material, the cell with this 3D porous composite current collector shows an improved reversible discharge-charge capacity of 415 mAh g–1 at a current rate of 0.1 C after 50 cycles, which is much higher than that of the cell with a flat Cu foil ( 127 mAh g–1 ). It is demonstrated that this unique fibrous network of the 3D current collector coupled with the morphological effects of the CuO microspheres greatly improve the cell performance in terms of electrical conductivity, reversible capacity and cycling stability.

Nitrogen-doped amorphous carbon coated mesocarbon microbeads as excellent high rate Li storage anode materials

A composite anode material consisting of a stable inner core of mesocarbon microbeads and a porous nitrogen-doped amorphous carbon shell active for lithium storage is prepared. The thin birnessite MnO2 nanosheets hydrothermally deposited on mesocarbon microbeads are in situ replaced by polypyrrole, which is then transformed to nitrogen-doped amorphous carbon layer by calcination in nitrogen atmosphere. The surface modified mesocarbon microbeads exhibit average discharge capacities of 444 and 103 mA h g−1 at the current densities of 0.1 and 3 A g−1, respectively, obvious higher than the corresponding values of the bare sample, 371 and 60 mA h g−1. Moreover, the composite anode maintains a discharge capacity of 306 mA h g−1 after 500 cycles at 1 A g−1, suggesting an excellent cycle stability. It is believed that the nitrogen-doped amorphous carbon layer has provided additional lithium storage capacity and stabilized the structure integrity of mesocarbon microbeads. This work demonstrates that the capacity and rate performance of commercial graphitic carbons can be much improved by simply introducing a nitrogen-doped carbon coating layer active for Li storage, making them attractive for high power Li-ion batteries.

Enhancement of mesocarbon microbead (MCMB) preparation through supercritical fluid extraction and fractionation

Mesocarbon microbeads (MCMBs) are a valuable carbon material, and the production of this material highly depends on the reaction conditions and feedstock properties. In the present study, supercritical fluid extraction fractionation (SFEF) technology was used to separate coal tar pitch (CTP) into a series of fractions to enhance MCMB preparation. After SFEF separation, most of the toluene-insoluble (TI) components were concentrated into the unextracted residue. First, optimal carbonization conditions were obtained for CTP through systematic experimental evaluations. Then, the SFEF fractions were heat-treated under the optimal conditions to produce MCMBs, and the relationship between chemical composition and product quality was revealed. Compared with CTP products, MCMBs produced from extracted SFEF fractions showed better morphology, and only a bulk mesophase with poor texture was generated from the unextractable residue. Moreover, the TI fraction had a significant negative impact on MCMB production in carbonaceous mesophase development. The results indicate that supercritical fluid extraction can be used to improve the quality of produced MCMBs by removing undesirable components.

Lithium difluoro(oxalate)borate improving the zero-volt storage performance of lithium-ion batteries by offering anode SEI film tolerance to high potentials

Keeping lithium-ion batteries (LIBs) in a state of zero charge is an effective way to prevent the risks of thermal runaway during their storage and transportation. It is of importance to achieve excellent zero-volt storage performance, meaning that the performance of LIBs changes little after long-term storage at zero volt. This paper proposes a reliable approach to improve the zero-volt storage performance, that is, the combination of electrochemical pre-lithiation to lower the zero-volt crossing potential (ZCP) and the use of appropriate electrolyte additives to enhance the stability of solid electrolyte interface (SEI) film on anodes to tolerate high potentials for a long time. We use an electrolyte additive, lithium difluoro(oxalate)borate (LiDFOB), as an SEI-film stabilizer. By comparing the chemical composition of SEI film on mesocarbon microbeads (MCMB) anode prior and subsequent to holding at 3.3 V for 10 days, we clarify how LiDFOB offers the SEI film tolerance to high potentials. The validity of the approach is confirmed by a LiCoO2 full cell using an MCMB anode pre-lithiated in the electrolyte containing 2 wt% LiDFOB. This full cell shows a recovery ratio of capacity as high as 93.3% after 7-week zero-volt storage.

The ultrasound thermal cracking for the tar-sand bitumen

The influence of ultrasonic irradiation on the tar-sand bitumen in the process of thermal cracking with an inert atmosphere was investigated thoroughly. The product distribution and coke characteristic produced by the conventional thermal cracking (CTC) and ultrasound thermal cracking (UTC) were invested at the following condition: ultrasound frequency 20 kHz, ultrasonic power 2000 W, reaction time 2 h, reaction temperature from 400 to 440 °C. The result of the liquid products distribution indicated that UTC can significantly increase gasoline yield and diesel yield, and dramatically reduce VGO (Vacuum Gas Oil) yield and residuum (greater than 500 °C) yield. The analysis of gas products showed that there were no significant differences for the gas distribution between the two reactions (methods), indicating that reaction of UTC still conformed to a radical chain mechanism, but the ratio of olefin/paraffin was greatly reduced in the process of UTC, which was attributed to the hydrogen transfer reaction promoted by ultrasound. The result of the analysis by SEM, FT-IR, Raman, XRD and Zeta potential demonstrated that there was a significant difference for the morphology of cokes produced by the two methods. Mesocarbon microbeads (MCMB) was discovered in the process of UTC, which should be due to that the polymerization of the free macro-radicals produced from PAHs (Polycyclic Aromatic Hydrocarbons) promoted by ultrasonic cavitation. In addition, it can be inferred that the viscosity of the second liquid phase was reduced by ultrasonic mechanical function through the breakage of the stack of asphaltene molecules cross-linked by van der Waals force. According to the mesophase theory, the ultrasound irradiation promoted the formation of the second liquid phase, extended its existence time and reduced its viscosity, resulting in the formation of MCMB controlled by the surface tension during the process of UTC.