Mesocarbon Microbeads Electrode Research Articles

Utilization of surface-induced capacitive behavior: A promising strategy to improve low temperature performance of Li-ion batteries

Graphite anode suffers from tremendous electrochemical performance fading at low temperature. To investigate the reason of this fading at low temperature from Li+ storage mechanism perspective, three different carbon structures with various amounts of defect and interlayer spacing are employed in this work, including natural graphite, hard carbon (HC) and mesocarbon microbead (MCMB). The galvanostatic charge/discharge (GCD) tests indicate that amorphous HC electrode shows higher lithiation capacity than graphite and MCMB electrode at −20 °C. Cyclic voltammetry tests reveal that higher lithiation capacity of HC electrode mainly stems from the surface-induced capacitive storage mechanism. This work confirms that the utilization of surface-induced capacitive storage mechanism could be considered as a promising strategy to improve the low temperature electrochemical performance.

A process for developing spherical graphite from coal tar as high performing carbon anode for Li-ion batteries

A new cost-effective method is developed to synthesize crystalline spherical graphite known as mesocarbon microbeads (MCMB) by the heat treatment of coal tar without the need of catalysts or additives and tested for its performance as anode material in Lithium-ion batteries (LIB). Two types of MCMB samples with varying morphological properties were prepared by the heat treatment of coal tar. The resulting MCMB samples were graphitized at 2350οC and were tested for their electrochemical performance as an anode for LIBs. Both MCMB electrodes show high specific capacity and good cycling stability for over 60 cycles and high-rate capability. The porous nature of MCMB with spherical morphology provides large surface area and electrolyte percolation while the high conductivity originating from highly graphitized structure could facilitate good electron transport throughout the MCMB surface. Therefore, MCMB synthesized by this additive free synthesis approach can be used for the cost-effective development of high-performing MCMB based electrode for LIBs.

Enabling Longer-Lasting Rechargeable Batteries Via Synchronizing Lithium and Lithium-Ion Batteries

Synchronized lithium metal and lithium-ion battery (SLLIB) exhibits high energy storage device and longer-lasting rechargeable batteries through reservoir-replenishment and reservoir-boost processes. In SLLIB, lithium-electrode acts as a reservoir and booster-electrode to mitigate the formation cycle capacity loss in LiFePO4 cathode vs. mesocarbon microbeads (MCMB) anode. The recovered specific charge-discharge capacities of 146/ 144 mAh g–1 at 0.2 C was achieved for SLLIB, as compared to half-cell capacities 142/ 143 mAh g–1 at 0.2 C. The irreversible capacity compensation from the reservoir, offered to a renewed flat-voltage profile at 3.3/ 3.2 V and renewed electrode characteristics of 144 mAh g–1 for LiFePO4 and 390 mAh g–1 for MCMB. The energy reduced cell (due to formation cycles) was replenished/ boosted to increased energy density of 455 Wh kg–1 with retained flat-voltage profile through Li+ ion replenishment from the lithium-electrode to MCMB anode. Further, reservoir-reserved mode yielded the charge-discharge capacities of 126/ 124 mAh g– 1 at 0.2 C for lithium battery associated with the Li+ ion transport from reservoir-electrode to LiFePO4 cathode, confirmed by Li+ ion diffusion path through MCMB electrode. Eventually, the reservoir-replenishment, reservoir-boost and reservoir-reserved mode cycling processes of synchronized lithium and lithium-ion battery pointed out towards longer-lasting rechargeable batteries for advanced storage applications. Figure 1

Understanding composition and morphology of solid-electrolyte interphase in mesocarbon microbeads electrodes with nano-conducting additives

Solid-electrolyte interface (SEI) between the active material and the electrolyte is critically important to the electrochemical performance of a lithium-ion battery. In this work, a depth profile measurement of the SEI layer after prolonged electrochemical cycling is reported in order to quantify the influence of conducting additives in the development of this layer in mesocarbon microbeads (MCMB) electrodes. It is shown that the SEI in the electrodes having multiwalled carbon nanotubes (CNT) as conductive additive is primarily a multi-layered structure consisting of an outer organic layer near the electrolyte/SEI interface and an inner inorganic layer near the SEI/electrode interface. The chemical analysis of such electrodes exhibits that the inorganic layer is made up of compounds such as Li2O, LiF and Li2CO3, while the outer layer consists mainly of organic carbonates, oligomers, traces of randomly distributed LixPOyFz and undissociated LiPF6. The chemical analysis of electrodes with carbon black (CB) as conducting additive reveals a similar composition of the outer layer, whereas the inner layer shows a relatively uniform molar amount of organic and inorganic carbonates and species like LixPOyFz and LixPOy, resulting in a porous SEI layer which as confirmed in AFM and SEM characterizations. On the other hand, the electrodes containing hybrid (CB-CNT) conducting additives show a relatively higher oligomer content than the electrodes with CNT only. The SEI formed on electrodes with CB-CNT as additives is shown to offer increased flexibility to accommodate partial strain generated due to volume change with narrow cracks exhibited in the SEM micrographs. Further, the variation in surface features and roughness augment the XPS findings.

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.

A collaborative diagnosis on mesocarbon microbeads electrodes in dual-carbon cells with non-metal electrolytes

Dual-carbon cells are a promising candidate for new energy storage devices. Recently, a 4V asymmetric capacitor based on non-metal electrolytes has been proposed. Two kinds of mesocarbon microbeads（MCMB）samples with different treatments (potassium hydroxide activated MCMB and graphitized MCMB, labeled as AMCMB and GMCMB, respectively) have served as electrode materials in this study. The charge storage behaviors of MCMB electrodes are studied by in situ X-ray diffraction (XRD), in situ dilatometry and conventional electrochemical measurements. (−)AMCMB/GMCMB(+) is synergistically diagnosed as a superior electrode collocation from the viewpoint of structural changes, which consists of adequate activation (7.65% irrecoverable expansion) for AMCMB and suitable stretch (13.67% recoverable expansion) for GMCMB. The intercalation-induced activation of AMCMB is indiscernible in XRD patterns but becomes conspicuous as dilatometric responses. A quantitative correlation between the two in situ measurements is established in the research of GMCMB electrodes. Expansions in the two dimensions are closely related to the type and size of intercalated ions, the shrinkage behavior of electrodes is especially synchronous in the discharging process. These findings guide the design of advanced cells and emphasize the necessity combining in situ characterizations.

Engineering novel synthetic strategy to develop mesocarbon microbeads for multi-functional applications

To assess the challenge of affordable technology, present synthetic strategies can be extended to new low-cost synthesis and processing methods that have potential to tailor the properties of the materials. Here we report, a novel method for the synthesis of mesocarbon microbeads (MCMB) through a pre-processing involved pyrolysis technique. The resulting MCMB is compressed into a product and effects of heat treatment temperature on different properties of MCMB is studied. The use of MCMB for the electromagnetic interference (EMI) shielding is new and hence, the effect of heat treatment temperature on EMI shielding effectiveness is studied in X-band. It is observed that EMI shielding effectiveness increases to −39.6 dB on increasing the heat treatment temperature. The high conductivity of MCMB plate heat treated upto 2500 °C contributes to highly conducting networks. Additionally, to investigate the electrochemical performance of MCMB as an anode material for lithium ion batteries, 2500 °C heat treated MCMB powder is used to fabricate the electrode. The MCMB electrode exhibits high discharge capacity of 345 mAh g−1 with a stable capacity for over 50 cycles and good rate capability. Thus, MCMB synthesized by this novel approach can be used for the development of high performance anode materials for Li-ion batteries.

A New CuO-Fe2 O3 -Mesocarbon Microbeads Conversion Anode in a High-Performance Lithium-Ion Battery with a Li1.35 Ni0.48 Fe0.1 Mn1.72 O4 Spinel Cathode.

A ternary CuO-Fe2 O3 -mesocarbon microbeads (MCMB) conversion anode was characterized and combined with a high-voltage Li1.35 Ni0.48 Fe0.1 Mn1.72 O4 spinel cathode in a lithium-ion battery of relevant performance in terms of cycling stability and rate capability. The CuO-Fe2 O3 -MCMB composite was prepared by using high-energy milling, a low-cost pathway that leads to a crystalline structure and homogeneous submicrometrical morphology as revealed by XRD and electron microscopy. The anode reversibly exchanges lithium ions through the conversion reactions of CuO and Fe2 O3 and by insertion into the MCMB carbon. Electrochemical tests, including impedance spectroscopy, revealed a conductive electrode/electrolyte interface that enabled the anode to achieve a reversible capacity value higher than 500 mAh g-1 when cycled at a current of 120 mA g-1 . The remarkable stability of the CuO-Fe2 O3 -MCMB electrode and the suitable characteristics in terms of delivered capacity and voltage-profile retention allowed its use in an efficient full lithium-ion cell with a high-voltage Li1.35 Ni0.48 Fe0.1 Mn1.72 O4 cathode. The cell had a working voltage of 3.6 V and delivered a capacity of 110 mAh gcathode-1 with a Coulombic efficiency above 99 % after 100 cycles at 148 mA gcathode-1 . This relevant performances, rarely achieved by lithium-ion systems that use the conversion reaction, are the result of an excellent cell balance in terms of negative-to-positive ratio, favored by the anode composition and electrochemical features.

Experimental assessment and model development of cycling behavior in Li-ion coin cells

The electrochemical performance of mesocarbon microbeads (MCMB)-lithium manganese oxide (LMO) spinel cells is examined by cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy. The loss in capacity in full-cells is attributed to occurrence of parasitic reactions at the two electrodes. The contribution of each electrode in full-cell degradation is ascertained through testing of MCMB and LMO half-cells, with the former exhibiting a faster rate of degradation as compared to the latter. Lithium diffusion coefficient of MCMB and LMO electrodes are determined using the galvanostatic intermittent titration technique at various stages of cycling. The experimentally measured parameters are used to simulate the electrochemical behavior of MCMB and LMO half-cells. The computed capacity and cell potential variation show good agreement with experimentally obtained data for half-cells at 1C and 2C currents. The MCMB half-cell simulations reveal that loss in discharge capacity occurs due to thickening of SEI film, increase in gas formation and loss in cyclable lithium. Simulations of LMO half-cells show that capacity loss with cycling is a result of reduction in active material, increase in surface resistance with inactive material deposition and loss in cyclable lithium.

Numerical Investigation of Capacity Fade in Mcmb Electrodes

Mesocarbon microbead (MCMB), artificial and natural graphite has been used as a commercial anode material due to its low redox potential (Li/Li+), good ionic/electronic conductivity and high structural stability during the process Li intercalation/deintercalation1. However, solid electrolyte interface (SEI) film formation due to solvent reduction at negative electrode is a major factor which is responsible for the capacity degradation in these anodes. Investigations of capacity degradation due to film formation have been carried out by various research groups by conducting experiments and simulations of MCMB/LiMn2O4 full cells2-4. In these systems, capacity loss is a concurrent effect of SEI formation with gas evolution at anode and manganese dissolution at cathode5. Hence, the contribution to capacity loss at each electrode could not be ascertained through the analysis of full cells. To fill this gap and investigate the capacity loss due to solvent reduction at anode, MCMB half cells have been studied thorough experimental measurements and numerical simulations. For this purpose, various electrochemical techniques such as galvanostatic intermittent titration (GITT), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), galvanostatic charge and discharge have been applied on MCMB half cells. For conducting the numerical study, certain parameters of ideal cell and SEI growth model have been measured and the rest calibrated with experimental findings. Using this calibrated model, numerical simulations have been carried out to quantitatively analyze the effect of SEI film and generated gas on the cycling performance of MCMB electrode with respect to cycle number. Figure 1 (a) shows the experimentally obtained capacity from cycling of MCMB coin cell at 1C rate for first 100 cycles. The first cycle discharge capacity of the cell was 1.58 mAh, which decreases gradually as cycle number increases due to associated side reactions such as electrolyte reduction to form solid precipitates and its deposition over the active particle of the MCMB electrode. The capacity obtained after 100 cycles was 0.99 mAh which is 62.65% of 1st cycle capacity. Figure 1 (b) shows the cell potential vs. charging and discharging capacity for 1st and 100th cycle which also indicates capacity loss of 37.34% at the end of 100thcycle. The results obtained from this study will assist in quantification of the individual mechanisms of gas evolution and SEI formation on the capacity loss of cells with MCMB as the negative electrode. References S. Hossain, Y.-K. Kim, Y. Saleh, and R. Loutfy, J. Power Sources, 114, 264 (2003).M. Doyle, and J. Newman, A. S. Gozdz, C. N. Schmutz and J. M. Tarascon, J. Electrochem. Soc. , 143, 1890 (1996).M. Rashid and A. Gupta, “Mathematical model for combined effect of SEI formation and gas evolution in li-ion batteries”, ECS Electrochem. Lett., 3, A95 (2014).M. Rashid, A. Gupta, “Effect of relaxation periods over cycling performance of a li-ion battery”, J. Electrochem. Soc., 162, A3145 (2015).P. Arora, R. E. White, S. Carolina and M. Doyle, J. Electrochem. Soc., 145, 3647 (1998). Figure 1

High‐Capacity NiO–(Mesocarbon Microbeads) Conversion Anode for Lithium‐Ion Battery

AbstractA conversion‐type, NiO–MCMB (mesocarbon microbeads) composite anode prepared by high‐energy ball milling is here characterized and tested in lithium half and full cells. An optimized and submicrometric morphology allows the NiO–MCMB electrode to achieve high cell performance and excellent rate capability, that is, delivering specific capacities of 515 and 450 mAh g−1 when cycled at current densities as high as 545 and 1090 mA g−1, respectively. The NiO–MCMB composite anode is studied in a full lithium‐ion battery using a high‐voltage LiNi0.5Mn1.5O4 electrode that is considered a suitable cathode in combination with conversion‐type electrodes. The battery delivers a specific capacity of 90 mAh g−1 with high coulombic efficiency and an average working voltage of 4.1 V. The electrochemical results suggest the viability of the alternative cell configuration here adopted for the development of low‐cost, high‐energy‐density lithium‐ion batteries.

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.

Electrolytic deposition of Sn-coated mesocarbon microbeads as anode material for lithium ion battery

Deposited of crystalline tin (Sn) coatings on mesocarbon microbead (MCMB) powder as anodes of lithium ion (Li-ion) battery was conducted in the SnSO4 solution by a cathodic electrochemical synthesis. The Sn-coated MCMB specimens were characterized by X-ray diffraction, scanning electron microscopy, and charge/discharge tests. The synthesis condition of Sn-coated MCMB was optimized by considering the agglomeration, size, and adhesion of the samples to the current collectors in the battery. The Sn-coated MCMB electrodes exhibit increased reversible capacity without sacrificing its cycling behavior, compared with bare MCMB electrodes. It is concluded that electrolysis-deposited Sn-coated MCMB electrodes may emerge as a practical and promising anode material for secondary Li-ion batteries.

Changing of SEI Film and Electrochemical Properties about MCMB Electrodes during Long-Term Charge/Discharge Cycles

The reasons for the capacity loss of mesocarbon microbead (MCMB) in lithium ion cells during long-term charge-discharge cycles were evaluated in this paper. The MCMB electrodes were charged and discharged for 2000, 2500 and 3000 cycles after activation. Solid electrolyte interphase (SEI) film was deposited on the surface of MCMB particles after activation. The contents of O and F in SEI film tended to increase continuously. Li2O was generated firstly, then LiF was produced later and the content of LiF increased with the cycles proceeding. During the cycles, the voltage differences between charge and discharge platforms increased gradually and the specific capacity decreased. The cell resistances increased continuously and the peak currents of intercalation/de-intercalation reactions in cyclic voltammetry curves were reduced. The decline of electrochemical properties was related to both the growth of SEI films and the consumption of electrolyte salt LiPF6.

Effect of Sodium Chloride as Electrolyte Additive on the Performance of Mesocarbon Microbeads Electrode

Effect of Sodium Chloride as Electrolyte Additive on the Performance of Mesocarbon Microbeads Electrode

Core‐Shelled MCMB‐Li4Ti5O12 Anode Material for Lithium‐ion Batteries

AbstractIn this study, we have synthesized and characterized Li4Ti5O12 (LTO)‐coated meso‐carbon micro beads (MCMB) as an anode material for Li‐batteries. The surface of MCMB powders was uniformly coated by the LTO nanoparticles to form a core‐shell structure via a sol‐gel process, followed by calcination. The average size of MCMB core was 15 μm while the thickness of LTO shell was 80 to 120 nm. We found that LTO‐coated MCMB had better rate‐capability and cycle life, compared with the pristine MCMB. Electrochemical impedance spectroscopy (EIS) results showed that after 40 cycles, the cell resistance of the LTO‐coated MCMB electrode increased slightly, while that of the pristine MCMB electrode increased significantly. The enhanced performance of the LTO‐coated MCMB electrode is attributed to the LTO coating, which suppresses the increase in the charge‐transfer resistance during prolonged cycle.

Fluoroethylene Carbonate as an Electrolyte Additive for Improving the Performance of Mesocarbon Microbead Electrode

Fluoroethylene carbonate (FEC) was used as a kind of film-forming electrolyte additive for lithium-ion battery. The cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) were used to study the influence of FEC additive on the electrochemical properties of mesocarbon microbead (MCMB)/Li cell. The results show that a thin, low-resistive and uniform SEI film was formed on the surface of MCMB electrode, which cause the excellent cyclability of the electrode.

Effects of fluoroethylene carbonate on low temperature performance of mesocarbon microbeads anode

Effects of fluoroethylene carbonate (FEC) on low temperature performance of mesocarbon microbeads (MCMB) anode are investigated in 1molL−1 LiPF6–ethylene carbonate (EC)/propylene carbonate (PC)/ethyl methyl carbonate (EMC) (1:3:8vol.%). The addition of FEC is found to improve deintercalation capacity, rate performance and cycling performance at low temperature to some extent. The surface morphology and chemical composition of the solid electrolyte interphase (SEI) formed on the surface of the MCMB electrode are studied through scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. The results show that a stabler and more conductive SEI film is formed by introducing the FEC to the electrolyte. Combined with the electrochemical impedance spectrum (EIS) analysis, the presence of FEC is found to decrease the LiF content in SEI layer, which enhances the ion conductivity of SEI film and accelerates the migration of lithium ion through SEI film.

Li4Ti5O12-coated graphite as an anode material for lithium-ion batteries

In this study, we have synthesized and characterized Li4Ti5O12 (LTO)-coated meso-carbon micro beads (MCMB) as an anode material for Li-batteries. The surface of MCMB powders was uniformly coated by the LTO nanoparticles to form a core–shell structure via a sol–gel process, followed by calcination. The average size of MCMB core was 20μm while the thickness of LTO shell was 80–120nm. We found that LTO-coated MCMB has better rate-capability and cycle life, compared with the pristine MCMB. Electrochemical impedance spectroscopy (EIS) results showed that after 40 cycles, the cell resistance of the LTO-coated MCMB electrode increased slightly, while that of the pristine MCMB electrode increased significantly. The enhanced performance of the LTO-coated MCMB electrode is attributed to the LTO coating, which suppresses the increase in the charge-transfer resistance during prolonged cycle.

Fluoroethylene Carbonate as an Electrolyte Additive for Improving the Performance of Mesocarbon Microbead Electrode

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