Hydrogen Bonding-Assisted Synthesis of Silica/Oxidized Mesocarbon Microbeads Encapsulated in Amorphous Carbon as Stable Anode for Optimized/Enhanced Lithium Storage

The practical application of silica-based composites as an alternative to commercial graphite anode materials is hampered by their large volumetric expansion,poor conductivity,and low Coulombic efficiency.In this work,a novel silica/oxidized mesocarbon microbead/amorphous carbon(SiO2/O’MCMB/C)hierarchical structure in which SiO2 is sandwiched between spherical graphite and amorphous carbon shell was succes sfully fabricated through hydrogen bonding-assisted self-assembly and post-carbon coating method.The obtained three-layer hierarchical structure effectively accommodates the volumetric expansion of SiO2 and significantly enhances the electronic conductivity of composite materials.Moreover,the outer layer of amorphous carbon effectively increases the diffusion rate of lithium ions and promotes the formation of stable SEI film.As a result,the SiO2/O’MCMB/C composite exhibits superior electrochemical performance with a reversible capacity of 459.5 mA h/g in the first cycle,and the corresponding Coulombic efficiency is 62.8%.After 300 cycles,the capacity climbs to around 600 mA h/g.This synthetic route provides an efficient method for preparing SiO2 supported on graphite with excellent electrochemical performance,which is likely to promote its commercial applications.

Structural Characteristics of Mesophase Spheres Prepared from Coal Tar Pitch Modified by Phenolic Resin

Mesocarbon microbeads （MCMB） were prepared from coal tar pitch modified by phenolic resin and from the same pitch modified by phenolic resin and hexamethylenetetramine at 440℃ for lh. By investigating the morphology of mesophase spheres and the structure of the MCMB carbonized at 1000℃ for lh using scanning electron microscope （SEM） and XRD, it was found that phenolic resin accelerated the formation and coalescence of mesophase spheres. Some of the obtained MCMB were hi- or tri-spheres with the distorted microtextural carbon layers. Hexamethylenetetramine in the pitch modified by phenolic resin accelerated the condensation of phenolic resin and consequently expedited the combination of mesophase spheres, which was proved by the formation of some tetra-spheres. Owing to the cross-linkage of the additives, MCMB with complex structure were obtained.

Expanded mesocarbon microbead cathode for sodium-based dual-ion battery with superior specific capacity and long-term cycling stability

Dual-ion batteries(DIBs)have attracted tremendous attention owing to their high operating voltage and are considered promising candidates for low-cost clean energy storage devices.However,the decomposition of electrolytes and collapse of the cathode structure may lead to low Coulombic efficiency(CE)and low cycling stability of DIBs.Wide-layered electrode materials can accommodate the intercalation/deintercalation of large anions,which is believed to overcome these issues.Herein,expanded mesocarbon microbeads(200HRO-MCMB)possessing an enlarged interlayer spacing(0.405 nm)were prepared via modified Hummers and subcritical hydrothermal reduction methods.After the indispensable electrochemical activation,200HRO-MCMB(hydrothermal reduction at 200℃)exhibited a high specific capacity(120 mAh·g^(-1)at50 mA·g^(-1))when used as a cathode for a sodium-based DIB,and the CE significantly improved within the 2.0-4.5 V voltage range.Additionally,the cycling stability exceeded over 600 cycles.Remarkably,this cathode possessed enlarged interlayers that decreased the barrier of PF6^(-)transport,and the battery storage mechanism corresponded to a transitioning state between double-layer capacitance and Faradaic intercalation.Undoubtedly,this work will expand the scope of the practical application of low-cost sodium-based DIBs.

Comparative Study on Super Fine Mesophase Powder and MCMB Used to Manufacture High-Density Isotropic Carbon Bulks

Mesocarbon microbeads （MCMB） and super fine mesophase powder （SFMP） were prepared firstly from a coal tar pitch and then hot-condensed into high-density isotropic carbon （HDIC） bulks under 160 MPa and finally sintered at 1 000 ℃. By analyzing the thermogravimetric behavior of the MCMB and SFMP powders, their volume shrinkage and weight loss during sintering and the bulk density and flexural strengths of their sintered bulks, it was found that the smaller sizes and the richer β-resin contents of SFMP ha）re facilitated formation of sintered bulks with more compact isotropic structure and higher flexural strengths than MCMB. Because of the filling and bonding effects of SFMP on MCMB bulks, addition of SFMP, albeit a little, can greatly increase the flexural strengths of sintered bulks of MCMB. However, adding MCMB, even a slight amount, into SFMP can severely impair the flexural strength of sintered bulks. This might be attributed to both the crack initiation along the boundaries between MCMB and SFMP and the formation of layered texture of MCMB sphere.

A high-capacity graphene/mesocarbon microbead composite anode for lithium-ion batteries

The graphene/mesocarbon microbead(MCMB)composite is assessed as an anode material with a high capacity for lithium-ion batteries.The composite electrode exhibits improved cycling stability and rate capability,delivering a high initial charge/discharge capacity of 421.4 mA·h/g/494.8 mA·h/g as well as an excellent capacity retention over 500 cycles at a current density of 40 mA/g.At a higher current density of 800 mA/g,the electrode still retains 35%of its initial capacity which exceeds the capacity retention of pure graphene or MCMB reference electrodes.Cyclic voltammetry and electrochemical impedance spectroscopy reveal that the composite electrode favors electrochemical kinetics as compared with graphene and MCMB separately.Superior electrochemical properties suggest a strong synergetic effect between highly conductive graphene and MCMB.

Mesoporous carbon material as cathode for high performance lithium-ion capacitor

Mesoporous carbon（MC） material with high specific surface area（1432 m^2/g）, large pore volume（2.894 cm^3/g） and appropriate mesopore structure（about 6.5 nm） has been prepared. We use the magnesium citrate as the precursor of the carbon material and the nano-sized magnesium oxide（MgO）particles as template provided by magnesium citrate. The structure characterization and the electrochemical performance of MC are investigated. Compared with commercial activated carbon（AC） cathode, the utilization of MC cathode can obviously improve the energy density of LIC device. When the MC cathode is coupled with pre-lithiated hard carbon（HC） anode, the LIC device shows the optimal electrochemical performance, high energy density up to 95.4 Wh/kg and power density as high as 7.4 kW/kg（based on active material mass of two electrodes）, excellent capacity retention of 97.3% after 2000 cycles. The present work indicates the combination of MC electrode with HC electrodes as promising candidates for the realization of LIC with high energy density, high power density and long cycle life.