Mesocarbon Microbeads Research Articles

Facile synthesis of α-MnO2 nanowires/spherical activated carbon composite for supercapacitor application in aqueous neutral electrolyte

One-dimensional (1-D) α-MnO2 nanowires/spherical activated carbon composite, namely the α-MnO2 nanowires growth onto the surface of activated mesocarbon microbeads (a-MCMB), has been prepared by using a simple hydrothermal synthesis method. The α-MnO2 nanowires are found to be less than 50 nm in diameter and have a characteristic length up to 2 μm. The novel α-MnO2 nanowires/a-MCMB composite when used for supercapacitor electrode material exhibits a specific capacitance (C s) of 357 F g−1 in 1 M Na2SO4 aqueous neutral solution. The C s based on the α-MnO2 nanowires is estimated to be as high as 890 F g−1. A good cycling stability of this composite material is also demonstrated for supercapacitor application.

A lithium ion battery exploiting a composite Fe2O3 anode and a high voltage Li1.35Ni0.48Fe0.1Mn1.72O4 cathode

In this paper we report a new lithium ion battery (LIB) consisting of a conversion-type, high capacity Fe2O3–Meso Carbon Micro Beads (MCMB) composite anode and a high voltage, Li1.35Ni0.48Fe0.1Mn1.72O4 cathode, prepared by using facile, low cost synthetic pathways. These electrodes have been characterized by a series of techniques including scanning and transmission electron microscopy, X-ray diffraction analysis, potentiodynamic cycling with galvanostatic acceleration (PCGA) and galvanostatic cycling tests in lithium cells at different C-rates. The results show that the Fe2O3–MCMB anode benefits by a composite, sub micrometric morphology and by a stable specific capacity ranging from 800 to 600 mA h g−1, evolving around 0.9 V, while the Li1.35Ni0.48Fe0.1Mn1.72O4 cathode is formed by an agglomeration of micrometric crystals delivering a reversible capacity of about 115 mA h g−1 at a 4.7 V high voltage. The combination of the Fe2O3–MCMB anode with the Li1.35Ni0.48Fe0.1Mn1.72O4 cathode leads to a complete lithium ion battery having an operating voltage of about 3 V, a high coulombic efficiency and a stable capacity of about 100 mA h g−1, which translates into in a theoretical energy density of about 300 Wh kg−1.

Effects of preparation temperature on electrochemical performance of nitrogen-enriched carbons

The activated nitrogen-enriched novel carbons (NENCs) were prepared by direct carbonization using polyaniline coating activated mesocarbon microbead composites as the precursor. Herein the influences of the carbonization temperature on the structure and morphology of the NENCs samples were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N2 adsorption/desorption isotherm at 77 K. The electrochemical properties of the supercapacitors were characterized by cyclic voltammetry, galvanostatic charge/discharge, electrochemical impedance spectroscopy (EIS), cycle life, leakage current and self-discharge measurements in 6 mol/L KOH solution. The results demonstrate that the NENC samples carbonized at 600 °C show the highest specific capacitance of 385 F/g at the current density of 1 A/g and the lowest ESR value (only 0.93 Ω). Furthermore, the capacity retention ratio of the NENCs-600 supercapacitor is 92.8 % over 2500 cycles.

Dimethyl sulfite as an additive for lithium bis(oxalate)borate/γ-Butyrolacton electrolyte to improve the performance of Li-ion battery

Dimethyl sulfite (DMS) is studied as an additive in lithium bis(oxalate)borate (LiBOB)/γ-Butyrolacton(GBL) electrolyte with LiCoO2 cathode and mesocarbon microbeads (MCMB) anode. Electrochemical performances of LiCoO2/DMS-electrolyte/Li and Li/DMS-electrolyte/MCMB half cells are studied by cyclic voltammetry, battery cycler, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Thermal behaviors of electrode–electrolyte coexisting systems are evaluated using a C80 micro-calorimeter. The electrochemical results show that the polarization of LiCoO2 is decreased and the capacity is improved with the addition of proper content of DMS. The XPS and SEM examination show that the presence of DMS decreases the decomposition of BOB anion and modifies the formation of SEI film on the surface of MCMB anode. The C80 micro-calorimeter analysis shows that the electrode materials with a LiBOB/GBL+proper DMS electrolyte begin to release heat at higher temperature and generate less heat than that with a common electrolyte. Therefore, using proper content (such as 20%) of DMS as an additive in LiBOB/GBL electrolyte is beneficial for the performance of Li-ion batteries.

Mapping the Entropic Coefficient of the NMC Pouch Cell at Various Temperatures and State-of-Charge Levels

A unique characteristic of lithium batteries, as compared to other cell chemistries, is the thermal behavior exhibited during cycling. There are several sources of heat within a lithium cell but they ultimately can be categorized as being either irreversible (always exothermic) in nature or as being reversible. The contribution of the entropic (reversible) heat source alternates between endothermic or exothermic in behavior depending on the state-of-charge (SOC). Past researchers have attributed this to a phase change of the active material.1The entropic coefficient itself is not a constant factor and its value varies with different SOC levels. This makes heat generation within a cell a rather complicated study but one that must be taken. The amount of heat generated within a cell affects its temperature and, in turn, affects its performance.The role of the entropic coefficient in calculating the quantity of reversible heat, Qrev, is described as follows: Qrev = Tcell * (dVoc/dT) * I (1)where Tcell is the temperature of the cell, dVoc/dT is the change in the open circuit voltage of the cell that results in a change of cell temperature, and I is the current in amps. dVoc/dT is the entropic coefficient. It is determined by measuring the open circuit voltage (OCV) of the battery at a set SOC value and noting its change as the temperature of the cell varies a given amount in an environmental chamber. The Varying Effects of Entropic Heat The impact of entropic heat on the overall heat generation within a cell runs the gamut from being negligible to significant depending on the chemistry. Kim et al.2 found a strong influence of entropic heating at the 1C-rate for a LiMn2O4 spinel coin cell. In contrast, Lu and Prakash3 found nearly no effect at the same 1C rate for the C/Li half-cell that utilized mesocarbon microbeads (MCMB).In this study, the researchers focused on quantifying the entropic coefficient for the Nickel Manganese Cobalt (NMC) lithium-ion electrochemistry. Leading battery manufacturers are focusing more intently on integrating the NMC cell into powertrain applications. By finding the right combination of these three metals for the cathode, they can offer a good balance between power, safety, and life. As a result, this particular type of cell is commercially available in rather large capacities for both pouch and prismatic formats.The objective of this research will be to fully map the varying entropic coefficient values of the NMC cell. This value will be calculated from data taken at different SOC levels as well as different temperatures. This map will be compared to one compiled for a lithium iron phosphate (LFP) pouch cell done previously by the authors. Experimental Setup The SOC levels range from full charge to full discharge in 5% increments. The temperature levels will vary from 55 0C to -200C in 50C increments. A commercially available 12Ah lithium-ion Kokam pouch cell will be used. Eventually the entropic map will be composed of 315 data points (21 SOC levels and 15 different temperature settings). In order to accelerate the data collection process, three cells will be set at SOC levels that are 5% apart and all will be simultaneously exposed to the full range of temperature changes. Each new temperature setting will dictate that the cells have 8 hours of soak time to stabilize its OCV. The effects of self-discharge on OCV will also be quantified and removed from the measured data. SOC levels and data acquisition is to be performed by a Maccor System Model 4200 10-channel cycler. Entropic Coefficient Map for LFP The data acquired by the authors in previous work has shown entropic behavior not uncovered by previous literature on the subject. Other studies that have used larger SOC and temperature increments found the entropic coefficient to be almost linear and independent of temperature.4 However, a study by the authors on a LFP cell found the entropic coefficient to be influenced by temperature at extreme SOC levels.5 References [1] R. Tamamushi, Electrochemistry, second ed., Maruzen, Tokyo, 2001.[2] J.-S. Kim, J. Prakash, and J.R. Selman, Electrochemical Solid State Letters, 4, A141 (2001)[3] W. Lu and J. Prakash, Journal of the Electrochemical Society, 150, A262 (2003)[4] K. Onda, H. Kameyama, T. Hanamoto, and K. Ito, Journal of the Electrochemical Society, 150 (2003) A285.[5] S. Bazinski and X. Wang, The Influence of Cell Temperature on the Entropic Coefficient of a Lithium Iron Phosphate Pouch Cell across the Full State-of-Charge Spectrum, 221st ECS Meeting, Seattle WA, May 2012.

Effect of temperature on the dissolution of solid electrolyte interface on mesocarbon microbeads electrodes in propylene carbonate-based electrolytes

The effects of temperature on the dissolution of solid electrolyte interface (SEI) films in the propylene carbonate (PC)-based electrolyte are investigated. The SEI films on the mesocarbon microbeads (MCMB) electrode of the Li|1.0M LiPF6-PC/DEC (= 7/3, v/v)|MCMB cell are characterized by cyclic voltammetry, scanning electron microscopy (SEM), AC impedance, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The SEM and electrochemical results show that the MCMB electrode cannot undergo the lithiation and delithiation process at 30°C due to the co-intercalation of PC and the exfoliation of MCMB. By contrast, the Li∥MCMB cell can be successfully discharged and charged at 0°C because a PC-based SEI film forms on MCMB. The energy capacity of the MCMB electrode is 281.3 mAh g−1 at 0.2C. However, the SEI film dissolves in the PC-based electrolyte as the temperature is increased to 30°C. The results of Raman spectroscopy and XPS also confirm that the composition of the PC-based SEI formed at 0°C consists of LiF, LixPFy, LixPOyFz, ROLi, and ROCO2Li.

Lithium compound deposition on mesocarbon microbead anode of lithium ion batteries after long-term cycling.

Lithium compound deposition on mesocarbon microbead (MCMB) anode after long-term cycling was studied in LiCoO2/MCMB battery. Lithium compound deposition did not generate on the activated MCMB anode, but it generated unevenly on the long-term cycled anode. Gray deposition composed of dendrites and particles was formed on the lower surface of the MCMB layer first, then on the upper surface. The deposition and MCMB layer peeled off from the current collector, and a bump was formed in the cycled anode. The exfoliation and thick deposition increased the ohmic resistance, film resistance, and charge transfer resistance of the cell and decreased the capacity significantly. Metallic lithium did not exist in either the upper or the lower deposition layer according to the results of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), the discharge curve, and anode potential. The outer region of both the lower and the upper deposition layers consisted of Li2CO3, LiOH, ROCO2Li, and ROLi. The inner region of the etched lower deposition layer mainly consisted of Li2O, LiF, and Li2CO3, and that of the etched upper deposition layer mainly consisted of Li2CO3, ROCO2Li, ROLi, and LiF. Solid electrolyte interphase (SEI) film hindering the intercalation of lithium ions into carbon layers and LiCoO2 cathode providing lithium source for the deposition were the two reasons leading to the formation of lithium compound deposition during long-term cycles. Because SEI film on the lower surface of MCMB layer was thicker than that on the upper surface, lithium compound deposition generated on the lower surface first.

Low temperature process modified MCMB for lithium ion batteries

The negative electrode of a lithium-ion battery should have the characteristics of large charge capacity, excellent charge and discharge cycle, steady discharge voltage, low irreversible charge capacity, and stable electrolyte. Natural graphite and mesocarbon microbeads (MCMB) are the most common materials used for the negative electrodes of such batteries. This study examines the effect of the use of homemade non-modified MCMB (HMM), modified MCMB (HMMQ), and natural graphite (NG) to produce electrodes on the batteries' high current charge–discharge behavior. In this experiment, the charge–discharge results showed that the voltage plateaus of HMM and HMMQ sloped due to short-range structural order, which enabled the intercalation and deintercalation of lithium ions to occur at different voltages. When HMMQ was charging and discharging high current at a rate of 2C, the battery's charge capacity reached 160mAh·g−1 and the coulometric efficiency exceeded 96%. Following the start of charging and discharging, a stable solid electrolyte interface (SEI) layer formed on HMMQ. The charge capacity of HMMQ was approximately 167mAh·g−1 after 100 charge–discharge cycles at 1C, and the cycles were stable. According to FTIR analysis, the content of the SEI layer produced within HMMQ consisted of Li2CO3 and (CH2OCOLi)2, and was stable, non-soluble, and passive. Negative electrodes made using modified material displayed good stability throughout many cycles when charging and discharging at a high current.

Preparation of binderless nanopore-isotropic graphite for inhibiting the liquid fluoride salt and Xe135 penetration for molten salt nuclear reactor

Mesocarbon microbeads and the isostatic pressing method were used to prepare binderless nanopore-isotropic graphite (NPIG) as a neutron moderator and reflector, to inhibit liquid fluoride salt and Xe135 penetration during use in a molten salt nuclear reactor. The microstructure, thermophysical, and other properties of the NPIG were studied and compared with isostatic graphite (IG-110, TOYO TANSO CO., Ltd., Japan). A high-pressure reactor and a vacuum device were constructed to evaluate the molten salt and Xe135 penetration in the graphite, respectively. The results indicated that NPIG possessed a graphitization degree of 74% and excellent properties such as a high bending strength of 94.1±2.5MPa, a high compressive strength of 230±3MPa, a low porosity of 8.7%, and an average pore diameter of 69nm. The fluoride salt occupation of IG-110 was 13.5wt% under 1.5atm, whereas the salt gain in NPIG remained steady even up to 10atm with an increase of <0.06wt%, demonstrating that the graphite could inhibit the liquid fluoride salt infiltration effectively. The helium diffusion coefficient for NPIG was 8.76×10−5cm2/s, much less than 1.21×10−2cm2/s for IG-110. The NPIG could effectively inhibit liquid fluoride salt and Xe135 penetration.

Synthesis and characterization of anisotropically expanded graphite oxide compounds derived from spherical graphite

Anisotropically expanded graphite oxide (GO) compounds with controlled interlayer distances were synthesized through the intercalation of various quaternary ammonium cations in GO derived from mesocarbon microbeads (MCMB). It was found that the interlayer distance of the as-prepared anisotropically expanded GO varies with the intercalated cations. In tetrabutylammonium (TBA), tetraoctylammonium (TOA) and dioctadecyldimethyl ammonium (DDA) cation intercalated GO compounds (TBA-GO, TOA-GO, TOA-GO) the corresponding interlayer distances were found to be 1.1nm, 1.9nm and 2.9nm, respectively. Moreover, significant morphology changes were observed for TOA-GO and DDA-GO. Our study suggests that it is possible to tailor both the interlayer distance and morphology of GO by choosing proper intercalated cations. It was also found that the expanded GO compounds show lower water content and improved thermal stability than those of pristine GO. The obtained GO compounds were investigated as electrode material for electrochemical capacitors and all of them delivered typical capacitive behavior.

Thermo-Electrochemical Simulation of Li-Ion Cells Under Abuse Condition

Safety of lithium-ion cells is one of the most important aspects of battery research [1]. As a pilot study preliminary to building an early-alert heat management system for lithium-ion cells, we present 1D multi-scale simulation of a single cell with exothermic reactions which induce thermal runaway. The thermo-electrochemical model used in this work includes electrochemical and thermochemical kinetics in range from micro to macro scales [2]. Lithium insertion and extraction in active materials are assumed to follow Butler-Volmer kinetics. The model cell in this study has mesocarbon microbeads (MCMB) in anode and a blended electrode of LiMn2O4 (LMO) and LiNi0.8Co0.15Al0.05O2 (NCA) in cathode. The thermodynamic properties of the pure electrode materials are obtained through published half-cell potentials [3,4,5]. The property of blend material is formulated based on an assumption observed through experiments by Tran et al [6].To simulate runaway events, we take into account thermal degradation mechanisms both at anode and cathode sides at elevated temperature. At the anode, four exothermic reactions are considered; solid electrolyte interface (SEI) decomposition, SEI formation, ethylene oxidation and reaction of lithium with water. Similarly, oxygen release from NCA and oxidation of solvent (ethylene carbonate) are modeled at the cathode. The reactions are assumed to follow Arrhenius behavior and Tafel type expression for non-charge transfer reaction and charge transfer reaction, respectively. The pre-exponential factor and activation energies of the reactions are taken from either literature or fits with published differential scanning calorimetry (DSC) experiments.Thermal simulations are used to predict the onset of runaway events under cycling from room temperature up to 333 K of ambient temperature. The cycles are tested under current rates of 1, 2, 3 and 4C. Figure 1 shows the heat resulting from cycling with 4C leading to a chain of exothermic reactions approximately at 350 K inducing thermal runaway.Furthermore, predictions of temperature and kinetic behavior in case of short circuits are presented (Figure 2). The comparison with experimental measurement is discussed. Acknowledgement Financial support by the Volkswagen foundation is gratefully acknowledged.

Submicron lithium nickel manganese oxide spinel with long cycling stability and high rate performance prepared by a facile route

Lithium nickel manganese oxide (LiNi0.5Mn1.5O4) shows promising applications in next-generation Li-ion batteries due to its high working voltage. In this work, submicron LiNi0.5Mn1.5O4 has been synthesized by a facile solid-phase route and its electrochemical performance has been investigated in both half cells and full cells using mesocarbon microbeads as anodes. In LiNi0.5Mn1.5O4–Li cells, LiNi0.5Mn1.5O4 shows excellent rate performance and high-rate cycling stability. At 20 C, LiNi0.5Mn1.5O4 can yield a discharge capacity of 105.8 mAh g−1. After 1400 cycles at 1 C, a discharge capacity of around 80 mAh g−1 can be still delivered. The LiNi0.5Mn1.5O4-limited full cells exhibit a working voltage of around 4.5 V and a discharge capacity of 90.0 mAh g−1 after 120 cycles at 1 C. The excellent electrochemical performance of LiNi0.5Mn1.5O4 can be attributed to a combination of submicron size, durability of Mn3+ at high rates and small-size induced protective film.

A method to observe the structure of the interface between mesocarbon microbeads and pitch

It is known that mesocarbon microbeads (MCMBs) have ordered structure and grow after absorbing molecules from pitch. However, the structure of pitch used for preparing MCMBs is disordered. Thus question of whether there is a region where the molecules absorbed from pitch change their orientations is a very interesting problem. In this paper, an interface between MCMBs and their pitch matrix has been found and the structure of the interface was observed by scanning electron microcopy. There are some ordered regions in the interface but the number of ordered regions in the interface is much fewer than the number inside the MCMBs. This indicates that the interface between the MCMBs and the pitch is the region where the orientations of the molecules absorbed from pitch change.

Electrochemical Characteristics of Li4Ti5O12 - Coated MCMB as an Anode Material for Hybrid Capacitor

In recent years, the over consumption of fossil fuels leads to critical environmental problems and increasing attentions are being paid on energy security issues. The green energy sources, such as solar and wind, are typically periodic or intermittent and therefore requires an electrical energy storage for utilization purposes. Great research effort has been focused on the energy storage systems of capacitors and batteries. The hybrid capacitor incorporates a faradaic lithium ion battery system in combination with a non faradaic electric double layer capacitor system in a unit cell. This combination called hybrid capacitors can be used to obtain better performance in power/energy demands. In this research, we coated Li4Ti5O12 onto meso - carbon micro beads (MCMB) to form a core - shell structure by a sol–gel process followed by calcinations. This MCMB-Li4Ti5O12 of core-shell structure was prepared to improve low electric conductivity of Li4Ti5O12 and cycling behavior. Prepared MCMB-Li4Ti5O12 composite was analyzed by XRD and SEM. The electrochemical performances of hybrid capacitor were investigated using MCMB-Li4Ti5O12 as the negative electrode and LiMn2O4, Active Carbon Fiber (ACF) as the positive electrode. The anodes were prepared by coating slurries containing the active materials (76wt%), Super P (17wt%), and polytetrafluroethylene (PTFE, 7wt%) on Al foil. The cathodes were made by dispersing 85wt% LiMn2O4, 10wt% Super P and 5wt% PTFE binder. The electrolyte consisted of 1M LiPF6in a mixture of ethylene carbonate(EC) / dimethyl carbonate(DMC) / ethyl-methyl carbonate(EMC) with a volume ratio of 1:1:1. The electrochemical behaviors of hybrid capacitor using organic electrolytes were characterized by charge/discharge, cyclic voltammetry, impedence and cycle tests. The hybrid capacitor using MCMB-Li4Ti5O12/LiMn2O4 electrodes had better capacitance than MCMB hybrid systems and was able to deliver a specific energy as high as 67 Wh/kg at a specific power of 781 W/kg. Also, it was found that MCMB-Li4Ti5O12 composite exhibited very good cycle life performance.

Structural Improvement of Pitch-Derived Mesocarbon Microbeads by Preprocessing Raw Material

Mesocarbon microbeads (MCMBs) were synthesized by pyrolyzing the hexane insoluble (HI) extracted from the coal-tar pitch in the dimethyl silicone dispersant. Structural development of product thus prepared was investigated by X-ray diffractometer, scanning electron microscope and particle size analyzer. Experimental results indicated that the HI-derived MCMBs possessed well-graphitized structure, excellent spherical morphology and even particle size due to preprocessing of the pitch raw material. It was suggested that structural improvement benefited from homogenous nucleation and good fluidity of the mesophase spherules.

Electrochemical investigation of Li-excess layered oxide cathode materials/mesocarbon microbead in 18650 batteries

The electrochemical performance of the 18650 lithium-ion batteries for layered Li-excess oxide Li1.144Ni0.136Co0.136Mn0.544O2(LNCMO) cathode material and mesocarbon microbead (MCMB) anode material is investigated. The battery shows an excellent rate capability with the capacity of 227 mAh g−1 at 8 C-rate (the cut-off voltage is 4.5V). Furthermore, it exhibits excellent cycle performance that the capacity retention over 300 cycles in the voltage ranges of 2.5-4.5V (vs. MCMB) and at 0.2 C-rate is about 85%. Although the medium voltage of the battery greatly reduces during the first 30 cycles, it keeps stable in the following cycles. The mechanisms of the capacity fade and voltage decay are also studied based on energy dispersive spectrometry, X-ray photoelectron spectroscopy, charge-discharge curves, and dQ/dV plots.

Effect of pre-lithiation degrees of mesocarbon microbeads anode on the electrochemical performance of lithium-ion capacitors

Lithium ion capacitors are assembled with pre-lithiated mesocarbon microbeads (LMCMB) anode and activated carbon (AC) cathode. The effect of pre-lithiation degrees on the crystal structure of MCMB electrode and the electrochemical capacitance behavior of LIC are investigated by X-ray diffraction (XRD) and the charge-discharge test of three-electrode cell. The structure of graphite still maintained when the pre-lithiation capacity is less than 200 mAh g−1, phase transition takes place with the increase of pre-lithiation capacity from 250 mAh g−1 to 350 mAh g−1. Pre-lithiation degrees of MCMB anode greatly affect the charge-discharge process and behavior, which impact on the electrochemical performance of LIC. The LIC with pre-lithiation capacity of 300 mAh g−1 has the optimal electrochemical performance. The energy density of LIC300 is up to 92.3 Wh kg−1, the power density as high as 5.5kWkg−1 and the capacity retention is 97.0% after 1000 cycles. The excellent electrochemical performance benefits from the appropriate pre-lithiation capacity of negative electrode. The appropriate pre-lithiation ensures the working voltage of negative electrode in low and relative stable charge-discharge platform corresponding to the mutual phase transition from the second stage graphite intercalation compound (LiC12) to the first stage graphite intercalation compound (LiC6). The stable charge-discharge platform of negative electrode is conductive to the sufficient utilization of AC positive electrode.

Lithium intercalation properties of SnSb/C composite in carbonthermal reduction as the anode material for lithium ion battery

The SnSb/C composite material is prepared by using the carbonthermal reduction to deal with the mixture of SnO2 and SbO3, respectively with different carbon reductant-glucose and mesocarbon microbead (MCMB). The morphologies and electrochemical properties of two kinds of structures of SnSb/C composite are compared. To characterize the phase and morphology of the composite material, X-ray diffraction, Raman spectra and scanning electron microscope are used. The current charge and discharge, cyclic voltammograms and AC impedancetests are also used to test the electrochemical performance of SnSb/C. The experimental results show that a kind of core-shell structure, of which the alloy particle serves as the core and the pyrolytic carbon as the outside shell, is formed when the glucose is used as the reducing agent. The first discharge specific capacity is 793.379 mA·h/g and it is still kept at 449.987 mA·h/g after 50 cycles. However, when the MCMB is used as the reducing agent, there are only a few of alloy particles attaching to the surface of MCMB, and it is not a kind of core-shell structure but a mixture of alloy particles and MCMB spheres. Its initial discharge specific capacity is 1164.938 mA·h/g, and after 50 cycles it is only 290.807 mA·h/g.

非晶質Li&lt;sub&gt;3&lt;/sub&gt;PS&lt;sub&gt;4 &lt;/sub&gt;を固体電解質として用いた電気化学セルにおける炭素系負極材料(MCMB) の電気化学的特性

Electrochemical properties of the mesocarbon microbeads (MCMBs) were investigated as anode active materials for an all-solid-state cell in which amorphous Li3PS4 (a – Li3PS4) was used as solid electrolytes and Li – In alloy was used as a counter electrode. The amount of Li+ ions that were inserted into the MCMBs denoted as x in the notation LixC6 (0 < x < 1). X-ray diffraction measurements suggested that Li+ ions were inserted into the disordered portions of MCMBs at the initial reaction stage with the composition range of 0 < x < 0.13. After the initial reaction stage, Li+ ions were intercalated into the graphite layers of MCMBs in the composition range of 0.13 < x < 0.91. The Li+ ions inserted into the disordered portions of MCMBs could not be extracted in the discharge process and then caused the irreversible capacity of the first charge-discharge cycle. On the other hand, Li+ ions that were intercalated into the graphite layers can be reversibly deintercalated in the composition range of 0.13 < x < 0.91. The charge-discharge capacity of the MCMBs was gradually decreased with an increase in the cycle number. Raman spectroscopy suggested that the capacity fading during the charge-discharge cycles would be caused by the deterioration of the MCMBs’ crystallinity.

The Impact of Vinylene Carbonate, Fluoroethylene Carbonate and Vinyl Ethylene Carbonate Electrolyte Additives on Electrode/Electrolyte Reactivity Studied Using Accelerating Rate Calorimetry

The effects of vinylene carbonate (VC), fluoroethylene carbonate (FEC) and vinyl ethylene carbonate (VEC) electrolyte additives on electrode/electrolyte reactivity at elevated temperatures were investigated using accelerating rate calorimetry (ARC). Li(Ni1/3Mn1/3Co1/3)O2 (NMC) and graphite (mesocarbon microbeads (MCMB)) were utilized as the electrodes and 1.0 M LiPF6 in ethylene carbonate (EC):diethyl carbonate (DEC) (1:2 by volume) was chosen as control electrolyte. Adding 10 wt% VC, FEC or VEC to the electrolyte does not significantly impact the reactivity of delithiated NMC compared to the control electrolyte. However, the three additives affected the reactivity between lithiated graphite and electrolyte at elevated temperatures in different ways. Adding VC (up to 10%) reduces the reactivity between lithiated graphite and electrolyte below about 200°C, adding VEC does not affect the reactivity at all, while adding over 5 wt% FEC causes a small exotherm beginning as low as 50°C. After this small exotherm completes, electrolytes with 10 wt% FEC show more reactivity with lithiated graphite than control electrolyte above 130°C. These results give a head to head comparison of the reactivity of electrolytes containing VC, VEC or FEC with charged electrode materials at elevated temperatures and show that the use of VC and VC at levels of 10 wt% or less should not compromise the safety of Li-ion batteries.