Ethyl Methyl Carbonate Research Articles

Determining the Composition of Carbonate Solvent Systems Used in Lithium-Ion Batteries without Salt Removal

In this work, two methods were investigated for determining the composition of carbonate solvent systems used in lithium-ion (Li-ion) battery electrolytes. One method was based on comprehensive two-dimensional gas chromatography with electron ionization time-of-flight mass spectrometry (GC×GC/EI TOF MS), which often enables unknown compound identification by their electron ionization (EI) mass spectra. The other method was based on comprehensive two-dimensional gas chromatography with flame ionization detection (GC×GC/FID). Both methods were used to determine the concentrations of six different commonly used carbonates in Li-ion battery electrolytes (i.e., ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC) in model compound mixtures (MCMs), single-blind samples (SBS), and a commercially obtained electrolyte solution (COES). Both methods were found to be precise (uncertainty < 5%), accurate (error < 5%), and sensitive (limit of detection <0.12 ppm for FID and <2.7 ppm for MS). Furthermore, unlike the previously reported methods, these methods do not require removing lithium hexafluorophosphate salt (LiPF6) from the sample prior to analysis. Removal of the lithium salt was avoided by diluting the electrolyte solutions prior to analysis (1000-fold dilution) and using minimal sample volumes (0.1 µL) for analysis.

Electrolytes Containing Triethyl Phosphate Solubilized Lithium Nitrate for Improved Silicon Anode Performance

An electrolyte consisting of lithium nitrate (LiNO3) and lithium difluoro(oxalato)borate (LiDFOB) in ethylene carbonate (EC), ethylmethyl carbonate (EMC), and triethyl phosphate (TEP) is used to improve the long-term cycling stability of silicon anodes. TEP was selected for its ability to dissolve LiNO3 in carbonates to a concentration of ∼0.2 M. The large amount of LiNO3 combined with the LiDFOB salt leads to a capacity retention of 87.1% after one hundred cycles due to the formation of a relatively stable solid electrolyte interphase (SEI). Ex-situ surface analysis reveals that the SEI consists of oxalates, lithium alkyl carbonates, borates, and nitrate reduction products. By selecting two components which are preferentially reduced (LiNO3 and LiDFOB), the SEI is able to inhibit continuous solvent decomposition and allows for improved electrochemical cycling for pure silicon anodes.

Tuning Fluorination of Linear Carbonate for Lithium-Ion Batteries

Liquid electrolyte engineering plays a critical role in modern lithium-ion batteries. However, the existing electrolytes fall short when used with some trending battery chemistries such as high-voltage and high-energy-density electrodes. Fluorination of electrolyte solvents has been identified as an effective approach for improved cyclability, but few works systematically studied the effects of fluorination extent of carbonate solvents on battery performance. Here we design and synthesize a family of fluorinated ethyl methyl carbonates. Different numbers of F atoms are finely tuned to yield monofluoroethyl methyl carbonate (F1EMC), difluoroethyl methyl carbonate (F2EMC) and trifluoroethyl methyl carbonate (F3EMC). The cycling behavior of several types of lithium-ion pouch cells, including graphite (Gr)/single-crystalline LiNi0.8Mn0.1Co0.1O2 (SC-NMC811), Gr-SiOx/LiNi0.6Mn0.2Co0.2O2 (NMC622), high-voltage Gr/LiNi0.5Mn1.5O4 (LNMO), Gr/layered Li-rich Mn-based oxide (LLMO) and fast-charging Gr/NMC622, were systematically investigated to understand the impact of fluorination degree. Compared to the commercially available F3EMC, we found that the partially-fluorinated F1EMC and F2EMC in some cases showed improved cycling stability, which we attribute to their locally-polar –CH2F and –CHF2 groups and thus fast ion conduction than –CF3. This work suggests that highly or fully fluorinated solvents are not necessarily desirable; instead, fluorination degree needs to be rationally and finely tuned for optimized lithium-ion cell performance.

A zwitterionic salt with one sulfonate and two ether functional groups as an additive for lithium-ion battery electrolyte

An imidazolium-based zwitterionic compound bearing two ether groups at the C-1 and C-2 positions and one sulfonate group at the C-3 position of the imidazolium ring was successfully synthesized. The compound was characterized using nuclear magnetic resonance spectroscopy and elemental analysis. The product (2.5 wt%) was added to a commercial electrolyte for lithium-ion batteries containing 1 M LiPF6 in ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (1:1:1 by volume). The resulting electrolyte had a slightly higher ionic conductivity in the range 10–70 °C than the model electrolyte, implying that the additive had a beneficial impact, possibly due to the C-2 rather than the C-1 ether group. Cyclic voltammetry analysis indicated that the electrochemical stability of the electrolyte did not change. The effect of the electrolyte additive on the cell’s 1C cycling performance was also examined: it was found that a stable discharge capacity was maintained for up to 100 cycles. Fourier transform infrared spectra of complexes formed by the synthesized product and LiPF6 at different ratios showed that the Li+ ions interacted with all the functional groups.

Ethylene Carbonate‐Free Electrolytes for Stable, Safer High‐Nickel Lithium‐Ion Batteries

AbstractEthylene carbonate (EC) is an important component in state‐of‐the‐art electrolytes for lithium‐ion batteries (LIBs). However, EC is highly susceptible to oxidation on the surface of high‐nickel layered oxide cathodes, making it undesirable for next‐generation high‐energy‐density LIBs. In this study, a simple, yet effective, EC‐free electrolyte (20F1.5M‐1TDI) is presented by adding 20 wt% fluoroethylene carbonate (FEC) and 1 wt% lithium 4,5‐dicyano‐2‐(trifluoromethyl)imidazole (LiTDI) into 1.5 m LiPF6 in an ethyl methyl carbonate (EMC) electrolyte. The 20F1.5M‐1TDI electrolyte is found to efficiently passivate the graphite anode and stabilize high‐nickel cathodes by a synergistic decomposition of FEC and LiTDI. The LiNi0.9Mn0.05Al0.05O2 (NMA90)/graphite full cell with the 20F1.5M‐1TDI electrolyte, therefore, exhibits an enhanced cycling stability and a suppressed voltage hysteresis growth compared to that with an EC‐containing baseline electrolyte (1 m LiPF6 in EC:EMC, 3:7 in weight, with 2 wt% vinyl carbonate). Advanced analytical tools, such as time‐of‐flight secondary ion mass spectrometry and X‐ray photoelectron spectroscopy, are employed to understand the underlying working mechanism of the EC‐free electrolyte. The present study clearly showcases the great potential of EC‐free electrolytes as a straightforward, practical approach for LIBs with high‐nickel cathodes.

Optimization of LIB Electrolyte and Exploration of Novel Compounds via the Molecular Dynamics Method

Due to great interest in the development of electric vehicles and other applications, improving the performances of lithium-ion batteries (LIBs) is crucial. Specifically, components of electrolytes for LIBs should be adequately chosen from hundreds of thousands of candidate compounds. In this study, we aimed to evaluate some physical properties expected for combinations of molecules for electrolytes by microscopic simulations. That is, the viscosity, ionic conductivity, degree of dissociation, diffusion coefficient, and conformation of each molecule were analyzed via molecular dynamics (MD) simulations. We aimed to understand how molecular-sized structures and properties collaboratively affect the behavior of electrolytes. The practical models of molecules we used were ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone (GBL), γ-valerolactone (GVL), dimethyl carbonate (DMC), ethyl-methyl carbonate (EMC), diethyl carbonate (DEC), and lithium hexafluorophosphate (LiPF6). Many molecular systems of electrolytes were simulated, in which one molar LiPF6 was mixed into a single or combined solvent. It was found that small solvent molecules diffused with relative ease, and they contributed to the higher ionic conductivity of electrolytes. It was clarified that the diffusion coefficient of lithium (Li) ions is greatly affected by the surrounding solvent molecules. We can conclude that high-permittivity solvents can be selectively coordinated around Li ions, and Li salts are sufficiently dissociated, even when there is only a small content of high-permittivity solvent. Thus, we can confirm solely by MD simulation that one of the better candidates for solvent molecules, formamide (F), will exhibit higher performance than the current solvents.

Electrolyte Reactivity at the Charged Ni-Rich Cathode Interface and Degradation in Li-Ion Batteries.

The chemical and electrochemical reactions at the positive electrode–electrolyte interface in Li-ion batteries are hugely influential on cycle life and safety. Ni-rich layered transition metal oxides exhibit higher interfacial reactivity than their lower Ni-content analogues, reacting via mechanisms that are poorly understood. Here, we study the pivotal role of the electrolyte solvent, specifically cyclic ethylene carbonate (EC) and linear ethyl methyl carbonate (EMC), in determining the interfacial reactivity at charged LiNi0.33Mn0.33Co0.33O2 (NMC111) and LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes by using both single-solvent model electrolytes and the mixed solvents used in commercial cells. While NMC111 exhibits similar parasitic currents with EC-containing and EC-free electrolytes during high voltage holds in NMC/Li4Ti5O12 (LTO) cells, this is not the case for NMC811. Online gas analysis reveals that the solvent-dependent reactivity for Ni-rich cathodes is related to the extent of lattice oxygen release and accompanying electrolyte decomposition, which is higher for EC-containing than EC-free electrolytes. Combined findings from electrochemical impedance spectroscopy (EIS), TEM, solution NMR, ICP, and XPS reveal that the electrolyte solvent has a profound impact on the degradation of the Ni-rich cathode and the electrolyte. Higher lattice oxygen release with EC-containing electrolytes is coupled with higher cathode interfacial impedance, a thicker oxygen-deficient rock-salt surface reconstruction layer, more electrolyte solvent and salt breakdown, and higher amounts of transition metal dissolution. These processes are suppressed in the EC-free electrolyte, highlighting the incompatibility between Ni-rich cathodes and conventional electrolyte solvents. Finally, new mechanistic insights into the chemical oxidation pathways of electrolyte solvents and, critically, the knock-on chemical and electrochemical reactions that further degrade the electrolyte and electrodes curtailing battery lifetime are provided.

Long-Term Stability of Redox Mediators in Carbonate Solvents.

Scanning electrochemical microscopy (SECM) used in the feedback mode is one of the most powerful versatile analytical tools used in the field of battery research. However, the application of SECM in the field of lithium-ion batteries (LIBs) faces challenges associated with the selection of a suitable redox mediator due to its high reactivity at low potentials at lithium metal or lithiated graphite electrodes. In this regard, the electrochemical/chemical stability of 2,5-di-tert-butyl-1,4-dimethoxybenzene (DBDMB) is evaluated and benchmarked with ferrocene. This investigation is systematically carried out in both linear and cyclic carbonates of the electrolyte recipe. Measurements of the bulk current with a microelectrode prove that while DBDMB decomposes in ethyl methyl carbonate (EMC)-containing electrolyte, bulk current remains stable in cyclic carbonates, ethylene carbonate (EC) and propylene carbonate (PC). Ferrocene was studied as an alternative redox mediator, showing superior electrochemical performance in ethyl methyl carbonate-containing electrolytes in terms of degradation. The resulting robustness of ferrocene with SECM is essential for a quantitative analysis of battery materials over extended periods. SECM approach curves depict practical problems when using the decomposing DBDMB for data acquisition and interpretation. This study sheds light towards the use of SECM as a probing tool enabled by redox mediators.

Li-Metal Anode in a Conventional Li-Ion Battery Electrolyte: Solid Electrolyte Interphase Formation using Ab Initio Molecular Dynamics

Ab initio molecular dynamics simulations were performed for Li+ conducting electrolytes based on 1M lithium hexafluorophosphate (Li+ ) in ethylene carbonate (EC)-ethylmethyl carbonate (EMC) (3:7wt) with 5 wt% vinylene carbonate (VC) in contact with Li-metal (electrode), finding a variety of products due to dissociations of all electrolyte components. The formed solid electrolyte interphase from electrolyte degradation arranges in an outer layer composed of denser materials (sitting over the anode surface) such as Li2(CH2O)2 from EC, Li2CO3, Li2C2H2 and Li2CO2 from VC, and Li2C3H5O2 and LiCH3O from EMC dissociations. Then follows an inner layer made of Li-binary compounds, Li3CO, Li2O and Li3C from EC, Li2O, Li2C2 and LiH from VC, and LiF and Li3P from dissociations. We calculated electron affinities of electrolyte molecules during their decomposition using a polarizable continuum model to consider solvent effects molecules degradation. has the highest first and second electron affinities, despite explicit Coulomb repulsion, which eventually dissociates the molecule right after capturing an electron from the metal-anode; therefore, is also the fastest to dissociate. EMC has the lowest first and second electron affinities, thus it is the least prone to accept electrons and the least likely to dissociate at the Li-metal interface.

Impedimetric Chemosensing of Volatile Organic Compounds Released from Li-Ion Batteries.

Detection of toxic and flammable gases and volatile organic compounds (VOCs) released from Li-ion batteries during thermal runaway can generate an early warning. A submicron (∼0.15 μm)-thick poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) sensor film is coated on a platinum electrode through a facile aqueous dispersion. The resulting sensor reliably detected different volatile organic compounds (VOCs) released during the early stages of thermal runaway of lithium-ion batteries (LIBs) even at low concentrations. The single-electrode sensor utilizes impedance spectroscopy to measure ethyl methyl carbonate and methyl formate concentrations at 5, 15, and 30 ppm independently and in various combinations using ethanol as a reference. In contrast to DC resistance measurement, which provides a single parameter, impedance spectroscopy provides a wealth of information, including impedance and phase angle at multiple frequencies as well as fitted charge transfer resistance and constant-phase elements. Different analytes influence the measurement of different parameters to varying degrees, enabling distinction using a single sensing material. The response time for ethyl methyl carbonate was measured to be 6 s. Three principal components (PCs) preserve more than 95% of information and efficiently enable discrimination of different classes of analytes. Application of low-power PEDOT:PSS-based gas sensors will facilitate cost-effective early detection of VOCs and provide early warning to battery management systems (BMS), potentially mitigating catastrophic thermal runaway events.

In-depth investigation of the exothermic reactions between lithiated graphite and electrolyte in lithium-ion battery

Thermal runaway is a critical issue for the large application of lithium-ion batteries. Exothermic reactions between lithiated graphite and electrolyte play a crucial role in the thermal runaway of lithium-ion batteries. However, the role of each component in the electrolyte during the exothermic reactions with lithiated graphite has not been fully understood. In this paper, the exothermic reactions between lithiated graphite and electrolyte of lithium-ion battery are investigated through differential scanning calorimetry (DSC) and evolved gas analysis. The lithiated graphite in the presence of electrolyte exhibit three exothermic peaks during DSC test. The reactions between lithiated graphite and LiPF6 and ethylene carbonate are found to be responsible for the first two exothermic peaks, while the third exothermic peak is attributed to the reaction between lithiated graphite and binder. In contrast, diethylene carbonate and ethyl methyl carbonate contribute little to the total heat generation of graphite-electrolyte reactions. The reaction mechanism between lithiated graphite and electrolyte, including the major reaction equations and gas products, are summarized. Finally, DSC tests on samples with various amounts of electrolyte are performed to clarify the quantitative relationship between lithiated graphite and electrolyte during the exothermic reactions. 2.5 mg of lithiated graphite (Li0.8627C6) can fully react with around 7.2 mg electrolyte, releasing a heat generation of 2491 J g−1. The results presented in this study can provide useful guidance for the safety improvement of lithium-ion batteries.

Evaluating the roles of electrolyte components on the passivation of silicon anodes

A protocol was recently developed to compare calendar life using a constant potential while monitoring the electrical current required to maintain the potential. Here, this calendar life protocol is used with electrolyte formulations containing various mole fractions of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and LiPF6 to elucidate the role each component plays in passivation for high silicon anodes. Together, EC and LiPF6 lead to higher currents, and thus poorer passivation, whereas EMC acts as a spectator. The variation of the components’ mole fraction also changes the solid-electrolyte interphase (SEI) composition, as measured by x-ray photoelectron spectroscopy. Importantly, higher LiPF6 content leads to increased LiF as well as increased current, indicating that higher LiF content does not enhance the passivation of the silicon surface. Finding that EC did not yield a passivating SEI, instead ethylene sulfite, sulfolane, and propylene carbonate (PC) were used in place of EC. Using ethylene sulfite and sulfolane resulted in poorer passivation compared to EC, whereas PC resulted in superior passivation. The superior passivation may be related to more stable lithium-solvent complexes.

High-voltage nickel-rich layered cathodes in lithium metal batteries enabled by a sulfolane / fluorinated ether/ fluoroethylene carbonate-based electrolyte design

Electrolyte system with high electrochemical stability and interfacial compatibility is essential to the high-performance lithium metal battery. Herein, we introduce an electrolyte design of 1 M Lithium bistrifluoromethosulfonimide (LiTFSI) sulfolane/1,1,2,2-Tetrafluoroethyl 2,2,3,3-Tetrafluoropropyl Ether (HFE)/Fluoroethylene carbonate (FEC) to improve the high voltage performance (4.7 V) for LiNi0.8Mn0.1Co0.1O2 based lithium metal batteries. Such a designed electrolyte exhibits a high-voltage limit of 5.1 V，compared to 4.3 V of the carbonated-based electrolyte (1 M Lithium hexafluorophosphate (LiPF6) ethylene carbonate（EC）/dimethyl carbonate (DMC)/ethyl methyl carbonate (EMC) 1:1:1). The cell with the designed electrolyte improves the coulombic efficiency, rate and cycle capability. The cell with the designed electrolyte delivers a reversible capacity of ∼220 mAh g−1 at 0.1C, with a capacity retention of ∼85% after 150 cycles (0.5C charge/discharge, 3.0–4.7 V), while the commercial electrolyte only exerts a capacity retention of 71.60%. X-Ray Powder Diffraction (XRD)，Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) analysis reveal the designed electrolyte effectively improve the structural and interfacial stability on cathode. It also suppresses the lithium-dendrite growth and facilitates the stable lithium-plating/stripping on lithium metal anode. While the carbonate-based electrolyte forms thick and unstable interface on cathode and grows dendrite-liked surface on lithium anode.

Comprehensive characterization of propylene carbonate based liquid electrolyte mixtures for sodium-ion cells

In this study, 1 M sodium perchlorate (NaClO4) containing binary electrolytes based on propylene carbonate and X (X = dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ethylene carbonate, 1,2-butylene carbonate, monoglyme, diglyme, tetraglyme, sulfolane) are studied due to their electrochemical and physicochemical properties as well as compatibility with sodium metal. The reactivity towards sodium is compared between mixtures with and without NaClO4 and degradation products are analyzed by gas chromatography. It is shown that NaClO4 plays a crucial role in electrolyte decomposition and gas formation. It could be shown that mixtures of linear and cyclic carbonates form coupling products during storage with Na metal, namely dialkane propane-1,2-diyl dicarbonates, independently of the presence of sodium perchlorate. Additionally, gas analysis of PC electrolyte over Na shows a pronounced formation of CO and propylene oxide during storage if NaClO4 is present in the sample. Overall, the electrolyte “PC+EC+NaClO4” is identified as most favorable system within the examined series with respect to decomposition characteristics (formation of decomposition products) as well as acceptable physicochemical and electrochemical properties, e.g. plating-stripping behavior, cycle tests, conductivity and solubility. A sustainability screening of the electrolyte formulations reveals a high toxic concern in case of glyme-based mixtures as well as sulfolane. From a life cycle perspective, however, glyme-based mixtures have in overall lower environmental footprints.

Study on oxidation and pyrolysis of carbonate esters using a micro flow reactor with a controlled temperature profile. Part II: Chemical kinetic modeling of ethyl methyl carbonate

Little is known on reactivity of ethyl methyl carbonate (EMC), which is widely used as an electrolyte solvent in lithium-ion batteries (LIB). A better understanding on the reactivity of EMC and its chemical kinetics are required to assess the fire risks of LIB. The reactivity of a stoichiometric EMC/air mixture was investigated with a weak flame in a micro flow reactor with a controlled temperature profile (MFR) at atmospheric pressure and a maximum wall temperature (Tw,max) of 1300 K. To investigate species evolution formed in EMC oxidation (equivalence ratios of 0.5, 1.0 and 1.5) and pyrolysis, species measurements were performed in MFR at atmospheric pressure and Tw,max range of 700–1300 K. These experimental insights were used for modeling and validation of a chemical kinetic mechanism for EMC. The first chemical kinetic mechanism of EMC was developed based on reactions of dimethyl carbonate (DMC) and diethyl carbonate (DEC), and literature data.The present EMC mechanism reproduced measured species profiles well. Both experiments and computations showed two-stage increases in CO2 mole fraction: initial fuel decomposition producing CO2 at Tw,max = 850 K and subsequent CO oxidation to CO2 at Tw,max = 1050 K. In the first CO2 increase region, a series of decomposition reaction of EMC produced CO2, C2H4 and CH3OH via methyl formic acid. The oxidation of CH3OH and C2H4 proceeded in the region corresponding to second CO2 increase. The present EMC mechanism also reproduced experimental weak flame position of EMC well. Computational weak flame structure of EMC indicated a three-stage reaction: EMC decomposition, oxidation of decomposition products to CO and oxidation of CO to CO2. The three-stage reaction initiated by fuel decomposition reaction is distinct from the one initiated by low-temperature oxidation of ordinary hydrocarbons. This novel three-stage reaction was also observed for DEC, which has two ethyl groups.

Lithium and Potassium Cations Affect the Performance of Maleamate-Based Organic Anode Materials for Potassium- and Lithium-Ion Batteries.

In this study we prepared potassium-ion batteries (KIBs) displaying high output voltage and, in turn, a high energy density, as replacements for lithium-ion batteries (LIBs). Organic electrode materials featuring void spaces and flexible structures can facilitate the mobility of K+ to enhance the performance of KIBs. We synthesized potassium maleamate (K-MA) from maleamic acid (MA) and applied as an anode material for KIBs and LIBs, with 1 M potassium bis(fluorosulfonyl)imide (KFSI) and 1 M lithium bis(fluorosulfonyl)imide (LiFSI) in a mixture of ethylene carbonate and ethyl methyl carbonate (1:2, v/v) as respective electrolytes. The K-MA_KFSI anode underwent charging/discharging with carbonyl groups at low voltage, due to the K···O bond interaction weaker than Li···O. The K-MA_KFSI and K-MA_LiFSI anode materials delivered a capacity of 172 and 485 mA h g−1 after 200 cycles at 0.1C rate, respectively. K-MA was capable of accepting one K+ in KIB, whereas it could accept two Li+ in a LIB. The superior recoveries performance of K-MA_LiFSI, K-MA_KFSI, and Super P_KFSI at rate of 0.1C were 320, 201, and 105 mA h g−1, respectively. This implies the larger size of K+ can reversibly cycling at high rate.

Chemical Interplay of Silicon and Graphite in a Composite Electrode in SEI Formation.

We investigated the effect of the Si/graphite weight ratio in half-cells on the solid electrolyte interphase (SEI) layer's chemistry. The nominal concentrations of active materials were (wt % Si/wt % Gr) 15/73, 30/58, 60/28, and 80/0. The electrolyte in the cells consisted of either 1.2 M LiPF6 in ethylene carbonate/ethyl methyl carbonate (3:7 by wt) or 1.2 M LiPF6 in ethylene carbonate:ethyl methyl carbonate (3:7 by wt) + 10 wt % fluoroethylene carbonate. These coin cells were cycled five times at the C/10 rate. As expected, the addition of silicon to the electrode significantly increased the measured capacity. Examination of the aged composite material showed that the electrolyte influenced the concentration of chemical environments on the surface. Depth profiling revealed that these concentrations of surface environments changed with sputtering time. A statistics-of-mixtures model was used to deconvolute how silicon and graphite interacted during the formation of these species and how the interaction changed with depth.

Hybrid poly-ether/carbonate ester electrolyte engineering enables high oxidative stability for quasi-solid-state lithium metal batteries

Building safe and high-energy-density lithium metal batteries (LMBs) is currently being pursued to sustain our modern lifestyles. However, new electrolyte engineering is rigorously required that is capable of simultaneously providing good protection on lithium metal anode and sustaining high oxidative stability at the cathode, besides sufficient bulk conductivity and low interfacial resistance. Here, we report a novel hybrid poly-ether/carbonate ester quasi-solid-state electrolyte with high oxidative stability formed by a simple and efficient in situ polymerization of strategy, in which ring-opening polymerization of ether-based 1,3-dioxolane (DOL) and ester-based ethylene carbonate (EC)-ethylmethyl carbonate (EMC) is initiated by rare-earth triflate catalyst Sc(OTf)3 at room temperature. Such electrolyte engineering not only achieves a sufficiently high ionic conductivity of 5 × 10−4 S cm−1 but enables a high anodic voltage limit of 5 V while maintaining feasible battery manufacture technology. The hybrid poly-DOL/EC/EMC quasi-solid-state electrolyte is capable of producing a stable solid electrolyte interphase (SEI) featuring Li plating/stripping over 500 h at 0.5 mA cm−2 and decreased charge transfer resistance. The derived Li||LiFePO4 quasi-solid-state LMB, benefited from the enhanced oxidative stability of electrolyte, exhibits a notable capacity of 169 mAh g−1 at 1C with no capacity decay after 300 cycles.

Study on oxidation and pyrolysis of carbonate esters using a micro flow reactor with a controlled temperature profile. Part I: Reactivities of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate

Carbonate esters such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are widely used as electrolyte solvents in a lithium-ion battery (LIB) and are considered as one of potential fire causes. This study investigates a difference in gas-phase reactivities of DMC, EMC and DEC. Species measurements for oxidation (equivalence ratio of 1.0) and pyrolysis of DMC and DEC at maximum wall temperatures of Tw,max = 700–1300 K and atmospheric pressure were performed using a gas chromatograph connected to a micro flow reactor with a controlled temperature profile (MFR). Measured mole fractions of C2H4 and CO2 in the DEC case started increasing at a low temperature (Tw,max = 750 K), while those of CH4 and CO2 in the DMC case started increasing at an intermediate temperature (Tw,max = 1050 K). Gas-phase reactivities of the three carbonate esters were found to be DMC < EMC ≈ DEC through observation of their weak flames. Computational species and heat release rate profiles of DEC showed a three-stage reaction: thermal decomposition, oxidation of decomposition products to CO and CO oxidation to CO2. This three-stage reaction of DEC is distinct from the one driven by low-temperature oxidation observed with n-heptane and DME in earlier studies. Rate of production analysis indicated that principal fuel consumption reactions of DMC were H-atom abstraction reactions and that of DEC was a thermal decomposition reaction producing C2H4. Based on reaction path analysis of DEC oxidation, initial-stage reactions produced few active radicals at the low temperature region. The reactivity difference between DMC and DEC is, therefore, mainly driven by the difference in the primary fuel consumption reactions that relies on fuel molecular structure. Considering the existence of ethyl ester group in EMC, a dominant EMC consumption reaction would be similar to DEC.

Exploring the performance of carbonate and ether-based electrolytes for anode-free lithium metal batteries operating under various conditions

An anode-free lithium metal battery (AFLMB) configuration can be used to develop electrolytes for wide-temperature applications. The charge/discharge performance of an electrolyte consisting of lithium hexafluorophosphate (LiPF 6 ) in a mixture of fluoroethylene carbonate (FEC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and ethyl methyl carbonate (EMC) has been is reported as an electrolyte for lithium metal batteries. It has a good passivating capability and wide electrochemical windows relative to the commercial electrolyte. Conversely, its lower ionic conductivity and high viscosity impede practical application. Hence, an electrolyte of 1 M LiPF 6 in EA/FEC/TTE/EMC (2:1:5:2 by vol.) is developed by adding a quaternary solvent of ethyl acetate (EA). The electrolyte exhibits a lower viscosity and higher ionic conductivity than 1 M LiPF 6 in FEC/TTE/EMC (3:5:2 by vol.). At 0 °C, 1 M LiPF 6 in EA/FEC/TTE/EMC (2:1:5:2 by vol.) provides capacity retention of 30 % and the average Coulombic efficiency (av. CE) of 95 % using the Cu||NMC111 after 40 cycles at a current density of 0.2 mA/cm 2 . The synergy of higher ionic conductivity and formation of LiF layer in the developed electrolyte extends the service-temperature range of AFLMB. This study opens an avenue in developing low-temperature electrolytes using an AFLMB. • The cycling performance of an anode-free battery is extended under various conditions. • 1 M LiPF 6 in EA/FEC/TTE/EMC (2:1:5:2 by vol.) electrolyte is developed. • At 0 °C, it provides capacity retention of 30% using Cu.||NMC111 after 40 cycles. • The high solvation power of EA gives lower viscosity and higher ionic conductivity. • The developed electrolyte has stable cycling compared to EC/DEC electrolyte.