Ethyl Methyl Carbonate Electrolyte Research Articles

Graphitic Co‐Products of Clean Hydrogen Production Enabling High‐Rate‐Performance Dual‐Carbon Batteries

AbstractMethane pyrolysis (CH4 → 2H2 + C) is a promising H2 production process with zero CO2 emissions. Utilizing its solid carbon co‐products can make it economically more competitive. Herein, this work demonstrates that graphitic carbon from methane pyrolysis can work as both cathodes and anodes to enable high‐rate‐performance dual‐carbon batteries (DCBs), outperforming commercial natural and synthetic graphite. The graphite purity can reach 99.32 and 97.59 wt%, respectively, using a standard high‐temperature thermal treatment or a room‐temperature electrochemical method. Compared to graphite, they have smaller crystalline sizes and larger surface areas, enabling faster surface redox reactions and better structural stability upon electrolyte ion intercalation. DCB full cells with LiPF6 ethyl methyl carbonate electrolyte deliver energy storage capacities of 75.1 and 74.7 mAh g−1 at 500 mA g−1 with capacity retentions of 79.2% and 93.4% after the high‐rate charge–discharge over 5000 mA g−1, respectively. They can also be cycled at 500 mA g−1 over 300 cycles without capacity decay, demonstrating excellent cycling stability. They show energy densities of 168.7 and 159.7 Wh kg−1 at power densities of 10.6 and 10.8 kW kg−1, outperforming recently reported DCBs. These findings open a new application of graphite co‐product from the emission‐free H2 production process.

Examining CO2 as an Additive for Solid Electrolyte Interphase Formation on Silicon Anodes

We demonstrate that the addition of CO2 to a standard 1.0 M LiPF6 3:7 wt% ethylene carbonate:ethyl methyl carbonate electrolyte results in the formation of a thinner insoluble solid electrolyte interphase (SEI) that is dominated by the presence of LiF. In contrast, cells without CO2 result in a thicker insoluble SEI layer containing more organic constituents. The CO2 is incorporated in the dimethyl carbonate soluble part of the SEI composed primarily of polymeric poly(ethylene oxide) (PEO) on the surface of a thin inorganic layer. This combination of properties from CO2 addition provides an improved cycling performance through the reduction of irreversible side reactions, leading to higher coulombic efficiency. The results indicate that CO2 incorporates into the SEI and plays a role similar to additives like fluorinated ethylene carbonate and vinylene carbonate with respect to polymeric components.

Tuning the Reactivity of Electrolyte Solvents on Lithium Metal by Vinylene Carbonate

Organic solvents undergo degradation reactions when in contact with lithium metal. These reactions form a layer of decomposition products that partly prevents further electrolyte decomposition—passivation. Still, the chemical processes in this system are complex and have not yet been fully understood though it is of high relevance for lithium metal batteries. Scanning Electrochemical Microscopy (SECM) in feedback mode as well as GC-MS are used for analyzing the interface as well as soluble decomposition products. SECM data show that the native interface thickness on metallic lithium from ethylene carbonate (EC) and ethyl methyl carbonate (EMC) electrolyte solutions is reduced by approx. 98% by adding 5 wt% vinylene carbonate (VC) to the solution. The addition of VC changed significantly the dynamics of the growth of the deposition layer. GC-MS studies of the EC:EMC electrolyte solution proof an ongoing reaction of the metallic lithium with the electrolyte even after several days. In comparison, the addition of VC appears to stabilize the interface and no decomposition products could be identified. It is concluded that the addition of VC to the electrolyte solution from EC:EMC prevents the trans-esterification of EMC by surface passivation and not by scavenging alkoxides as claimed in literature.

Reformulation of Electrolyte for Enhanced Fast-Charge Capability of Li-Ion Battery

Solvent crucially determines ionic conductivity and operating temperature range of liquid electrolytes, which consequently affects the cycling performance of Li-ion batteries. Aimed to enhance fast-charge capability, in this work the effects of 1,2-dimethoxyethane (DME) and ethyl acetate (EA) on the rate capability and cycle life of Li-ion batteries are studied by selecting a graphite-LiNi0.80Co0.15Al0.05O2 chemistry and replacing 10 wt% of ethyl methyl carbonate (EMC) with either DME or EA in a 1.0 m LiPF6 3:7 (wt.) ethylene carbonate (EC)/EMC electrolyte. It is shown that both of DME and EA increase ionic conductivity of the resultant electrolytes whereas their adverse impacts on the electrochemical stability and the formation of solid electrolyte interphase with the graphite anode are negligible. As such, the rate capabilities for both of the discharging and charging processes are enhanced in the order of DME > EA > the baseline electrolyte. Analyses on the Li-ion cell’s impedance reveal that enhancements in the rate capability of Li-ion batteries are attributed to a significantly reduced charge-transfer resistance, or in other words, a significantly increased cell reaction kinetics.

Unlocking the True Capability of Graphite-Based Dual-Ion Batteries with Ethyl Methyl Carbonate Electrolyte

Graphite-based dual-ion batteries (DIBs), which involve the intercalation of anions into the carbon layers, are promising for high-power applications. Many researchers inevitably choose ethyl methy...

Comsol Simulation of Hierarchical Ordered Porous Microstructure Electrode

High specific energy is always desirable in battery systems, especially for electric vehicles. A key towards improving specific energy for a particular combination of anode and cathode active material is to maximize the mass fraction of active material, which means minimizing the fraction of inactive material such as the separator, the binder, electrode additives for improving electronic conductivity, and the current collector. A seemingly simple strategy for maximizing the mass fraction of active materials is to make the electrodes as thick as possible. However, ion transport in thick electrodes can be particularly problematic since salt diffusion into and through the electrode pore space is slow and can easily limit the battery charge / discharge rate. An ideal microstructure is one that allows for direct line of sight or path for the electrode active material access to the electrolyte, for rapid ion-transport throughout the entire electrode thickness. Therefore, a need exists for electrode fabrication methods that create microstructures that maximize electrolyte transport, as is needed to achieve high-rate charging/discharging in electrodes having high mass loading. Optimal microstructures in electrodes help to achieve the ideal balance of active material and electrolyte mass to give high gravimetric and volumetric energy density. As to design a microstructure with the goal of Li ion salt transport facilitation, we synthesized ordered porous microstructure electrodes using combination of freeze cast and tape cast techniques. This method enjoys the combination of conventional tape casting, a main technique in manufacturing Li ion electrodes in industrial scale, and freeze casting. This study simulate two dimensional ordered porous electrode cross-sections and presents the electrochemical performance results of Mo-doped LTO in a electrochemical cell consist of a lithium metal anode, polymer separator, and liquid ethylene carbonate and ethyl methyl carbonate electrolyte. The electrochemical performance of ordered porous microstructure is investigated by varying electronic conductivity, tortuosity, particle size, electrode thickness, and C rate. We show that these engineered porous electrodes considerably reduces the electrolytes mass transport limitation and electrochemical response of electrode is independent of tortuosity, making it possible to synthesize ultra thick electrode for high energy and power density applications. Simulation results show that 10 micron thickness of wall and pore freeze tape cast Mo-doped LTO with electronic conductivity of 1 S/m, tortuosity as high as 10, electrode thickness of 458 micron and mass loading of 30 mg/cm^2 can deliver full capacity even at 2 C-rate.

Some Physical Properties of Ethylene Carbonate-Free Electrolytes

Physical properties of LiPF6 in ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) electrolytes were studied by conductivity measurements, Fourier transform infrared spectroscopy (FT-IR) and differential thermal analysis (DTA). Conductivity measurements show that the addition of additive levels of FEC to EMC electrolyte can dramatically increase the conductivity of EC-free EMC electrolytes at low salt concentrations below 0.4 M. FT-IR results show that the added FEC hinders ion pair formation by competing with EMC to dissociate LiPF6 resulting in increased conductivity in EMC electrolytes. Conductivity measurements show that the conductivity of DMC electrolytes decreases significantly below 0°C due to the high melting point of DMC. Differential thermal analysis was used to determine the LiPF6-DMC phase diagram which then can be used to explain the conductivity results. The results presented here identify avenues by which EC-free electrolytes can be improved for use in practical Li-ion cells.

Lithium rich cathode/graphite anode combination for lithium ion cells with high tolerance to near zero volt storage

Management of reversible lithium is an advantageous approach to design lithium ion cells that are tolerant to near zero volt (NZV) storage under fixed resistive load towards highly controllable, enhanced user-inactive safety. Presently, the first cycle loss from a high energy density Li-rich HE5050 cathode is used to provide excess reversible lithium when paired with an appropriately capacity matched mesocarbon microbead (MCMB) anode. Cells utilizing 1.2 M LiPF6 3:7 v/v ethylene carbonate:ethyl methyl carbonate electrolyte and a lithium reference were used for 3-electrode testing. After conditioning, a fixed resistive load was applied to 3-electrode cells for 72 or 168-h during which the anode potential and electrode asymptotic potential (EAP) remained less than the copper dissolution potential. After multiple storage cycles (room temperature or 40 °C), the NZV coulombic efficiency (cell reversibility) exceeded 97% and the discharge capacity retention was >98%. Conventional 2-electrode HE5050/MCMB pouch cells stored at NZV or open circuit for 3 days had nearly identical rate capability (up to 5C) and discharge performance stability (for 500 cycles under a 30% depth of discharge low-earth-orbit regime). Thus, lithium ion cells with appropriately capacity matched HE5050/MCMB electrodes have excellent tolerance to prolonged NZV storage, which can lead to enhanced user-inactive safety.

Dramatic Effects of Low Salt Concentrations on Li-Ion Cells Containing EC-Free Electrolytes

Different concentrations of LiPF6 (0.3 M–2 M) in ethyl methyl carbonate (EMC) electrolyte and ethylene carbonate (EC)-based electrolyte were studied in LiNi0.4Mn0.4Co0.2O2 (NMC442)/graphite pouch cells. Fresh cells containing 0.3 M LiPF6 in EMC electrolyte showed extremely large charge transfer resistance while those with 0.3 M LiPF6 in EC/EMC electrolyte did not. Impedance spectra taken on symmetric cells and ionic conductivity measurements suggest this difference is due to difficulty in dissociating and desolvating Li+ ions from the EMC-based electrolyte to intercalate into both the electrodes. After elevated temperature storage experiments at 4.5 V, cells with 0.3 M LiPF6 in EC/EMC showed a large increase in positive electrode charge transfer impedance, presumably caused by electrolyte oxidation. With salt concentrations greater than 1 M, charge transfer resistance was much smaller in EMC-based electrolytes and was stable during storage for both electrolyte types. Conductivity and cycle testing measurements suggest that 1.5 M LiPF6 should be used in EC-free EMC-based electrolytes to optimize cell performance.

Variation of Coulombic Efficiency Versus Upper Cutoff Potential of Li-Ion Cells with Different Electrolyte Solvents

Introduction One of the easiest ways to increase the energy density of Li-ion cells is to increase the operating voltage range. However, the instability of state-of-the-art electrolyte towards high voltage is a great challenge [1, 2]. Electrolyte oxidation reactions can cause gas generation and impedance growth, result in swelling, capacity loss and cell failure. Accurate measurements of the coulombic efficiency (CE) of Li-ion cells are valuable to characterize these parasitic reaction rates occurring between the electrodes and the electrolyte. In this presentation, the impact of the various solvent blends on CE, charge endpoint capacity slippage, cell impedance and gas evolution during ultra high precision coulometry (UHPC) cycling tests were measured at 4.2, 4.4 and 4.5 V. Careful analysis of CE was made to determine the effect of different electrolyte solvents separately on the positive electrode and negative electrode as the upper cut-off voltage increases. Symmetric cells were made to distinguish the effect of the electrolyte solvents on the impedance at the positive or negative electrode. Experimental The pouch cells employed in this study were LaPO4-coated Li[Ni0.4Mn0.4Co0.2]O2 (NMC442)/graphite cells with a capacity of 180 mAh balanced for 4.7 V operation. Three electrolyte systems including 2 wt.% PES + 1 wt.% DTD + 1 wt.% TTSPi (PES 211) in 1M LiPF6 ethylene carbonate (EC):ethyl methyl carbonate (EMC) 3:7, 2 wt.% PES in 1M LiPF6 fluoroethylene carbonate (FEC) and bis(2,2,2-trifluoroethyl) carbonate (TFEC) 1:1 and 2 wt.%VC + 2 wt.% TAP in 1M LiPF6 sulfolane (SL):EMC 3:7 were chosen for this study. The cells then underwent a formation protocol during which they were opened and re-vacuum sealed at 3.5 V and 4.5 V to remove any gas generated during the first charge. After formation, cells were moved to Ultra High Precision Charger (UHPC) and cycled 15 times using “barn-charge” protocols [3]. After UHPC cycling, these cells were opened in the glovebox where symmetric cells were made. The detailed procedure for making symmetric cells has been described by Petibon et al.[4]. Some cells were studied using battery isothermal calorimetry as outlined by Downie et al. [5] Results and discussion Figure 1a shows the fractional charge endpoint capacity slippage per hour and the fractional capacity fade per hour plotted versus upper cutoff potential for cells containing EC:EMC, FEC:TFEC as well as SL:EMC electrolytes. Figure 1a allows one to determine which parasitic reactions, electrolyte oxidation at the positive electrode or Li consumption in the SEI at the negative electrode, play the dominant role in reducing the coulombic efficiency (CE) or increasing 1-CE when the upper cutoff potential increases [3]. Figure 1a shows that the fractional slippage per hour (positive electrode) increases dramatically when the upper cut-off potential increases from 4.2 V to 4.5 V, while, by contrast, the fractional fade per cycle (negative electrode) does not change dramatically with potential. Figure 1a shows the FEC:TFEC electrolyte has smaller slippage but higher capacity fade rate compared to SL:EMC or EC:EMC electrolyte at high voltages. This means the FEC:TFEC electrolyte partially fixes the positive side (small fractional slippage per hour) but has problems at the negative electrode side (larger fractional fade per hour). Figures 1b, 1c and 1d show the area-specific Nyquist plots of negative and positive electrode symmetric cells as well as full coin cells constructed from electrodes after UHPC cycling tests. Figures 1b to 1d show that cells containing FEC:TFEC electrolyte have much smaller positive impedance but higher negative electrode impedance, compared to cells containing SL:EMC and EC:EMC electrolytes after UHPC cycling. Figures 1b to 1d further prove that the benefit of using FEC:TFEC electrolyte is mainly on the positive side by hindering the electrolyte oxidation at the positive electrode/electrolyte interface. Microcalorimetry results which support this interpretation will also be shown. References L. Ma, J. Xia and J. R. Dahn, J. Electrochem. Soc., 161, A2250 (2014).K.J. Nelson, J. Xia and J.R. Dahn, J. Electrochem. Soc., 161, A1884 (2014).J. Xia, M. Nie, L. Ma and J. R. Dahn, J. Power Sources, 306, (2016) 233.R. Petibon, C. P. Aiken, N. N. Sinha, J. C. Burns, H. Ye, C. M. VanElzen, G. Jain, S. Trussler, and J. R. Dahn J. Electrochem. Soc., 160, A117 (2013).L.E. Downie and J. R. Dahn, J. Electrochem. Soc. 161, A1782 (2014). Figure captions Figure 1 a) Fractional charge endpoint capacity per hour and fractional fade per hour plotted versus the upper cutoff potential for the NMC442/graphite pouch cells with different electrolytes. The area-specific Nyquist plot of b) negative electrode symmetric cells, c) positive electrode symmetric cells and d) full coin cells made from the NMC442 pouch cells after the UHPC cycling to 4.5 V. Figure 1

Impact of electrolyte solvent and additive choices on high voltage Li-ion pouch cells

The effects that various electrolyte solvents and electrolyte additives had on both LaPO4-coated LiNi0.4Mn0.4Co0.2O2 and uncoated LiNi0.4Mn0.4Co0.2O2/graphite pouch cells were studied using automated storage, electrochemical impedance spectroscopy, gas production and long-term cycling experiments. Storage experiments showed that the voltage drop during storage at 4.3 or 4.4 V for both coated and uncoated cells was very similar for the same electrolyte choice. At 4.5 V or above, the LaPO4-coated cells had a significantly smaller voltage drop than the uncoated cells except when fluorinated electrolytes were used. Automated charge discharge cycling/impedance spectroscopy testing of cells held at 4.5 V for 24 h every cycle showed that all cells containing ethylene carbonate:ethyl methyl carbonate electrolyte or sulfolane:ethyl methyl carbonate electrolyte exhibited severe capacity fade. By contrast, cells containing fluorinated electrolytes had the best capacity retention and smallest impedance growth during these aggressive cycling/hold tests. Long-term cycling experiments to 4.5 V confirmed that cells containing fluorinated electrolyte had the best cycling performance in the uncoated LiNi0.4Mn0.4Co0.2O2/graphite cells while cells containing sulfolane:ethyl methyl carbonate electrolyte had the best cycling performance in coated LiNi0.4Mn0.4Co0.2O2/graphite cells.

Improving sulfolane-based electrolyte for high voltage Li-ion cells with electrolyte additives

An electrolyte mixture containing 1 M LiPF6 in sulfolane:ethylmethyl carbonate 3:7 with vinylene carbonate and other electrolyte additives exhibited promising cycling and storage performance in high voltage Li(Ni0·4Mn0·4Co0.2)O2/graphite pouch type Li-ion cells tested to 4.5 V. Voltage drop during storage, coulombic efficiency, charge endpoint capacity slippage during ultra high precision cycling, charge-transfer resistance after storage or cycling, gas evolution during storage and cycling as well as capacity retention during long-term cycling were examined. The results for cells with sulfolane-based electrolytes were compared with those for cells with ethylene carbonate-based electrolytes containing state-of-the-art electrolyte additives. This survey showed that the combination of vinylene carbonate and triallyl phosphate as electrolyte additives in sulfolane:ethylmethyl carbonate electrolyte yielded cells capable of better performance during tests to 4.5 V than cells with ethylene carbonate-based electrolytes. These results suggest that sulfolane-based electrolytes may be promising for high voltage Li-ion cells.

A Study of Li-Ion Cells Operated to 4.5 V and at 55°C

The long-term cycling behavior of 24 promising electrolyte blends were systematically studied in LaPO4-coated Li(Ni0.4Mn0.4Co0.2)O2/graphite pouch type Li-ion cells tested to 4.5 V at 55°C. Capacity fade during cycling, charge-transfer resistance (Rct) before and after cycling as well as gas evolution during formation and also during cycling were examined and compared head-to-head. Of all the electrolytes tested, triallyl phosphate containing electrolytes including 2% vinylene carbonate + 2% triallyl phosphate in 1 M LiPF6 sulfolane:ethyl methyl carbonate and 2% prop-1-ene sultone + 2% triallyl phosphate in 1M LiPF6 ethylene carbonate:ethyl methyl carbonate electrolytes showed the best capacity retention, the least impedance growth and manageable amounts of gas evolution during long-term cycling. Pyridine boron trifluoride -based additives also showed excellent cycling performance but cells with those additives had higher gas evolution during cycling. Cells containing fluorinated electrolytes had similar cycling performance to cells containing 2% prop-1-ene sultone in ethylene carbonate:ethyl methyl carbonate electrolyte but with much more gas evolution and higher impedance after long-term cycling. The results suggest that electrolytes containing the additives triallyl phosphate or pyridine boron trifluoride may be promising for high voltage Li-ion cells at elevated temperature.

Gas Evolution during Unwanted Lithium Plating in Li-Ion Cells with EC-Based or EC-Free Electrolytes

Lithium plating can be induced in any Li-ion cell that has a graphite negative electrode by increasing the charge rate sufficiently at fixed temperature or by lowering the temperature at a fixed charge rate. Recently, ethylene carbonate (EC)-free electrolytes, such as 1 M LiPF6 in 98% ethyl methyl carbonate (EMC): 2% vinylene carbonate (VC), have been shown to passivate lithiated graphite effectively and allow Li[Ni0.42Mn0.42Co0.16]O2/graphite (NMC442/graphite) Li-ion cells to operate effectively for hundreds of charge discharge cycles. High charge rates and low temperatures were applied to Li[Ni1/3Mn1/3Co1/3]O2/graphite (NMC111/graphite) pouch cells containing EC-free EMC-based electrolytes with additives to study unwanted lithium plating. In such electrolytes, the plated lithium metal is not well passivated and reacts to create gas while in the same cells with 1 M LiPF6 EC:EMC (3:7) electrolyte no gas is observed when Li plating occurs because EC passivates metallic Li well. The volume of the pouch cells with EC-free electrolytes increased sharply when Li plating occurred as measured using in-situ methods. In cells having both EC-based and EC-free electrolytes, lithium plating was the cause of rapid capacity loss at high charge rates at both 10°C and 22°C.

Sulfolane-Based Electrolyte for High Voltage Li(Ni0.4Mn0.4Co0.2)O2 (NMC442)/Graphite Pouch Cells

Introduction The development of high voltage Li-ion batteries is one of the best ways to increase their energy density. However, this simple approach has proven to be difficult since electrolyte solvents and additives are unstable at high potentials and the parasitic degradation of these components results in gas evolution, severe impedance growth, low coulombic efficiency (CE) and poor capacity retention [1-2]. Therefore, the development of high voltage electrolyte systems is one of the major bottlenecks in the path of lithium-ion cells with high energy density. In this presentation, the sulfolane (SL) – ethylmethyl carbonate (EMC) – vinylene carbonate (VC) system is shown to be viable in NMC442/graphite pouch cells that can be cycled at least to 4.5 V for several months. The introduction of electrolyte additives has been shown to improve battery performance indicators such as coulombic efficiency (CE), self discharge, etc. and while maintaining acceptable impedance when cells are cycled to high voltage. Long-term cycling results were also made to compare with 1 M LiPF6EC/EMC (3:7 wt.%) with and without additives. Experimental The pouch cells employed in this study were uncoated Li[Ni0.4 Mn0.4Co0.2]O2 (NMC442)/graphite cells with a capacity of 240 mAh and coated NMC442/graphite cells with a capacity of 180 mAh. The positive electrode material in the coated cells has been coated with 3 wt% of LaPO4 which appears as nanoparticles on the NMC particle surfaces. Both types of cells were balanced for 4.7 V operation. 1 M LiPF6EC/EMC (3:7 wt.% ratio, BASF, 99.99%) was used as the control electrolyte. The NMC442/graphite pouch cells were filled with 0.75 mL of electrolyte (0.90 g for EC:EMC electrolyte and 0.86 g for SL:EMC:2% VC electrolyte). The cells then underwent a formation protocol during which they were opened and re-vacuum sealed at 3.5 V and again at 4.5 V to remove any gas generated during the first charge. After formation, cells were moved to the Ultra High Precision Charger (UHPC). The cycling/storage procedure was as follows: cells were first charged to 4.400 V using currents corresponding to C/10, stored open circuit at 4.4 V for 20.00 h and then discharged to 2.800 V using currents corresponding to C/10. The cycling/storage procedure was designed so that the cells were exposed to higher potentials for significant fractions of their testing time. After these tests, cells were charged or discharged to 3.8 V where impedance spectra were measured. Results and discussion Figures 1 a-d compare the cycling/storage data collected on the UHPC for NMC442/graphite pouch cells containing 2% VC in SL:EMC:VC and “PES-211” in EC:EMC 3:7. Figures 1 a-d show the SL:EMC:VC system has similar delta V, discharge capacity, charge endpoint capacity slippage and CE to “PES-211” in EC:EMC 3:7. Figure 1e shows long-term cycling results for the unclamped NMC442/graphite pouch cells with control, “PES-211” in EC:EMC 3:7 and cells with 2% VC, 2% VC +1% MMDS, 2% VC + 2% PES and 2% VC +2% TAP in SL:EMC electrolyte. We can clearly see that cells containing 2% VC + 2% TAP in SL:EMC electrolyte show better cycling performance than cells with “PES-211” in EC:EMC 3:7. References L. Ma, J. Xia and J. R. Dahn, J. Electrochem. Soc., 161, A2250–A2254 (2014).L. Ma, J. Xia, and J. R. Dahn, Promising sulfur-containing electrolyte additives or ternary Electrolyte additive mixtures for Li-ion cells that promote long lifetime and better safety, 2015, submitted to J. Electrochem. Soc. Figure caption Figure 1. (a-d) The cycling data collected on the UHPC including DV, the charge endpoint capacity, the discharge capacity, and CE for NMC442/graphite pouch cells containing 2% VC in Sulfolane/EMC=3/7 system and PES-211 in EC/EMC=3/7 system. (e) Long-term cycling without clamps between 2.8 and 4.5 V at C/2.5 (100 mA) and 40 ± 0.1ºC with different additive sets in SL:EMC electrolyte. Figure 1

Thermal stability of LiPF 6/EC + DMC + EMC electrolyte for lithium ion batteries

The thermal stability of lithium-ion battery electrolyte could substantially affect the safety of lithiumion battery. In order to disclose the thermal stability of 1.0 mol·L −1 LiPF 6/ethylene carbonate (EC) + dimethyl carbonate (DMC) + ethylmethyl carbonate (EMC) electrolyte, a micro calorimeter C80 micro calorimeter was used in this paper. The electrolyte samples were heated in argon atmosphere, and the heat flow and pressure performances were detected. It is found that LiPF 6 influences the thermal behavior remarkably, with more heat generation and lower onset temperature. LiPF 6/EC shows an exothermic peak at 212 °C with a heat of reaction − 355.4 J·g −1. DMC based LiPF 6 solution shows two endothermic peak temperatures at 68.5 and 187 °C in argon filled vessel at elevated temperature. EMC based LiPF 6 solution shows two endothermic peak temperatures at 191 and 258 °C in argon filled vessel. 1.0 mol·L −1 LiPF 6/EC + DMC + EMC electrolyte shows an endothermic and exothermic process one after the other at elevated temperature. By comparing with the thermal behavior of single solvent based LiPF 6 solution, it can be speculated that LiPF 6 may react with EC, DMC and EMC separately in 1.0 mol·L −1 LiPF 6/EC + DMC + EMC electrolyte, but the exothermic peak is lower than that of 1.0 mol·L −1 LiPF 6/EC solution. Furthermore, The 1.0 mol·L −1 LiPF 6/EC + DMC + EMC electrolyte decomposition reaction order was calculated based on the pressure data, its value is n = 1.83, and the pressure rate constants k p = 6.49 × 10 −2 kPa· −0.83·min −1.

Lithium Ethylene Dicarbonate Identified as the Primary Product of Chemical and Electrochemical Reduction of EC in 1.2 M LiPF6/EC:EMC Electrolyte

Lithium ethylene dicarbonate ((CH2OCO2Li)2) was chemically synthesized and its Fourier transform infrared (FTIR) spectrum was obtained and compared with that of surface films formed on Ni after cyclic voltammetry (CV) in 1.2 M lithium hexafluorophosphate (LiPF6)/ethylene carbonate (EC):ethyl methyl carbonate (EMC) (3:7, w/w) electrolyte and on metallic lithium cleaved in-situ in the same electrolyte. By comparison of IR experimental spectra with that of the synthesized compound, we established that the title compound is the predominant surface species in both instances. Detailed analysis of the IR spectrum utilizing quantum chemical (Hartree-Fock) calculations indicates that intermolecular association through O...Li...O interactions is very important in this compound. It is likely that the title compound in the passivation layer has a highly associated structure, but the exact intermolecular conformation could not be established on the basis of analysis of the IR spectrum.

LiPF 6–EC–EMC electrolyte for Li-ion battery

We studied the effect of salt concentration and solvent ratio on the cycling performance of LiMn 2O 4 cathode and graphite anode in LiPF 6–ethylene carbonate (EC)–ethyl methyl carbonate (EMC) electrolytes. The results show that solvent ratio has negligible impact on the performance of both electrodes but does affect the issues of thermal compatibility and ionic conductivity. Salt concentration affects the performance in two reverse ways: LiMn 2O 4 cathode requires low concentration, while graphite anode requires high concentration. It is observed that, during the first cycle, both electrodes produce irreversible capacity and form a solid electrolyte interface (SEI) film on their surface. From the view point of operation at low temperatures, 1 M LiPF 6 3:7 EC–EMC is recommended for Li-ion cells.

00/02585 A Tabu search algorithm for maintenance scheduling of generating units

Management of reversible lithium is an advantageous approach to design lithium ion cells that are tolerant to near zero volt (NZV) storage under fixed resistive load towards highly controllable, enhanced user-inactive safety. Presently, the first cycle loss from a high energy density Li-rich HE5050 cathode is used to provide excess reversible lithium when paired with an appropriately capacity matched mesocarbon microbead (MCMB) anode. Cells utilizing 1.2 M LiPF6 3:7 v/v ethylene carbonate:ethyl methyl carbonate electrolyte and a lithium reference were used for 3-electrode testing. After conditioning, a fixed resistive load was applied to 3-electrode cells for 72 or 168-h during which the anode potential and electrode asymptotic potential (EAP) remained less than the copper dissolution potential. After multiple storage cycles (room temperature or 40 °C), the NZV coulombic efficiency (cell reversibility) exceeded 97% and the discharge capacity retention was >98%. Conventional 2-electrode HE5050/MCMB pouch cells stored at NZV or open circuit for 3 days had nearly identical rate capability (up to 5C) and discharge performance stability (for 500 cycles under a 30% depth of discharge low-earth-orbit regime). Thus, lithium ion cells with appropriately capacity matched HE5050/MCMB electrodes have excellent tolerance to prolonged NZV storage, which can lead to enhanced user-inactive safety.