Ethylene Carbonate-dimethyl Carbonate Research Articles

Bismuth-titanium-silicon-based ternary oxide system: A comprehensive analysis and electrochemical utility

A novel TiO2-SiO2/Bi2O3 oxide material (TSB) was prepared for a first time via the sol-gel method. The synthesis was performed using titanium(IV) isopropoxide, tetraethoxysilane and bismuth nitrate pentahydrate as oxide precursors, ammonia as hydrolysis promoter and propan-2-ol as solvent. The properties of the synthesized material were comprehensively analyzed, including dispersion characteristics, morphology, crystalline structure, chemical composition and porous structure parameters. Additionally, to confirm the chemical structure and the presence of characteristic surface groups, Fourier transform infrared spectroscopy was applied. The electrochemical properties of a TiO2-SiO2/Bi2O3 anode, operating in 1M LiPF6 in EC/DMC (ethylene carbonate/dimethyl carbonate), were studied. The key point of the investigation was to demonstrate a potential application of TSB material in a Li-ion cell. Electrodes were analyzed with the use of cyclic voltammetry (CV), galvanostatic charging/discharging tests, and scanning electron microscopical (SEM) evaluations were performed. SEM images of both electrodes after charging/discharging processes showed that they to be covered with a film (electrochemical SEI formation). The reversible capacity of the TiO2-SiO2/Bi2O3 anode after 20 cycles at a low current rate was close to the theoretical value of 250 mAh g−1. However, at increasing current rates it decreased to ca. 200 mAh g−1. The reversibility of the process was close to 95%. Moreover after 100 cycle at 50 mA g−1 the value was 198 mAh g−1.

Graphene scrolls coated Sb2S3 nanowires as anodes for sodium and lithium ion batteries

One-dimensional stibnite (Sb2S3) nanowires templated graphene scrolls (SbGSs) synthesized through two-step wet chemical processes have been applied as anode materials for lithium-ion and sodium-ion batteries (LIB, NIB), where they delivered high reversible capacity of 690 mAh g−1 and 680 mAh g−1 at a current density of 50 mA g−1 without any capacity fading after 50 cycles both in LIB and NIB. Increased current density up to 2000 mA g−1, discharge capacity of 457.6 mAh g−1 in LIB and 444.8 mAh g−1 in NIB can be obtained, indicating that NIB performance is rival to LIB. Further study on optimizing electrolyte manifested that 1 M NaClO4 in ethylene carbonate/dimethyl carbonate (EC/DMC) promoted the electrochemical performance of NIB.

Effect of sodium salts on the cycling performance of tin anode in sodium ion batteries

To determine the effect of electrolyte salts on the cycling properties of tin anodes in sodium ion batteries, sodium/tin cells were prepared using eight electrolytes containing NaCF3SO3, NaBF4, NaClO4, and NaPF6 in ethylene carbonate-dimethyl carbonate (EC-DMC) and EC-DMC/fluoroethylene carbonate (FEC) solvents. The first charge capacity and cycling properties strongly depended on the electrolyte salts. Additionally, an appropriately chosen electrolyte salt in combination with the FEC additive improved the cycling properties of the tin electrode. The tin electrode in the presence of the FEC-containing NaPF6-based electrolyte exhibited the best cycling properties. The first charge capacity and charge capacity after the 45th cycle were 220 and 189 mAh g−1 electrode, respectively at a current density of 84.7 mA g−1 electrode. The rate performance is also studied using the optimized electrolyte which reveals the ability of the electrode to perform in high current application. At a high current density of 4235 mA g−1 electrode, the capacity delivered is 24 mAh g−1 electrode. At a current rate of 1694 mA g−1 electrode, at the end of 1400th cycle, capacity is about 45 mAh g−1 electrode. The results of the study clearly indicate that the electrolyte salts critically affect the electrochemical performance of the tin anode in sodium ion batteries.

Gel Polymer Electrolyte Based on Poly(vinylidene fluoride)/Thermoplastic Polyurethane/Polyacrylonitrile by the Electrospinning Technique

Poly(vinylidene fluoride) (PVdF), thermoplastic polyurethane (TPU), and polyacrylonitrile (PAN) are blended in different ratios by the electrospinning technique. The corresponding composite gel polymer electrolytes (GPEs) are obtained after activating the electrospun membranes in 1.0 mol dm–3 LiPF6 in ethylene carbonate/dimethyl carbonate (EC/DMC). Their morphology and performance are systematically investigated by scanning electron microscopy (SEM), thermal analysis (TGA), charge–discharge tests, and so on. The gel polymer electrolyte (GPE) based on PVdF/TPU/PAN (2/2/1, wt %) exhibits a high ionic conductivity of 6.91 × 10–3 S cm–1, and its electrochemical stability window reaches up to 5.7 V. Furthermore, the Li/GPE/LiFePO4 cell shows a first discharge capacity of 167.52 mAh g–1 at 0.1 C rate at 25 °C. The film also exhibits a high tensile strength (10.3 ± 0.2 MPa) and elongation (102.5 ± 0.2%). It is observed that the PVdF/TPU/PAN (2/2/1, wt %) based GPE is perfectly suitable for high-performance lithi...

A New Thermally Stable and Conducting Electrolyte Based on Litdi As Lithium Salt for Li-Ion Batteries

Most of the LiBs used in electrical devices currently available contain lithium hexafluorophosphate (LiPF6) dissolved in a mixture of alkylcarbonates as the electrolyte. The main reasons for this [1] are the high conductivity of LiPF6 solutions, the formation of a protective SEI layer on graphite and its ability to passivate aluminum, a low-cost metal which can be used as a current collector. Other advantageous properties, which should also be observed by all LiB electrolytes, include low viscosity and a large life-span without safety risks, especially when damaged. However, the thermodynamic instability and moisture sensitivity of LiPF6 induce high risks of releasing HF and/or PF5 via its thermal decomposition or hydrolysis in the presence of traces of water. These drawbacks have been highly criticized justifying the importance in finding a replacement. Owing to (i) its high thermal stability, (ii) low sensitivity to the presence of water and (iii) its electrochemical stability [2], the lithium 4,5-dicyano-2-trifluoromethyl-imidazole (LiTDI) is seen as a promising substitute for LiPF6in LiBs. In a previous study [3] the poor dissociation of ion pairs (IP) of LiTDI in electrolyte solutions was discussed and the IP dissociation coefficient was found to be around 30 % in an ethylene carbonate/dimethyl carbonate (EC/DMC) mixture. The power capability of LiTDI in EC/DMC with an added 2% FEC in half-cells, using either a NMC or a graphite electrode, and in full NMC/graphite systems was investigated and compared to that of LiPF6 in the same solvent mixture. It was noticed that both lithium salts performed equally within graphite half-cells but not in the NMC half-cells where a greater capacity loss was observed in the case of the LiTDI based electrolyte when increasing the NMC lithiation speed. The reason was attributed to the lower IP dissociation of LiTDI; LiPF6 being 85% dissociated in EC/DMC. Taking into account this observation a new solvent mixtures is proposed. We present here the results obtained using this new solvent mixture allowing a better dissociation of LiTDI (37 %), a higher conductivity (8.5 mS.cm-1 instead of 6.1 mS.cm-1in EC/DMC at 25°C) and a lower viscosity (2.4 mPa.s instead of 2.8 mPa.s in EC/DMC at 25°C). In addition a better power capability is achieved at higher current rates. 1. Eshetu, G.G., et al., LiFSI vs. LiPF6 electrolytes in contact with lithiated graphite: Comparing thermal stabilities and identification of specific SEI-reinforcing additives. Electrochimica Acta, 2013. 102(0): p. 133-141. 2. Niedzicki, L., et al., New covalent salts of the 4V class for Li batteries. Journal of Power Sources, 2011. 196(20): p. 8696-8700. 3. Berhaut, C.L., et al., LiTDI as electrolyte salt for Li-ion batteries: transport properties in EC/DMC. Electrochimica Acta, 2015. 180: p. 778-787.

Hard carbon derived from cellulose as anode for sodium ion batteries: Dependence of electrochemical properties on structure

Cellulose, the most abundant organic polymer on Earth, is a sustainable source of carbon to use as a negative electrode for sodium ion batteries. Here, hard carbons (HC) prepared by cellulose pyrolysis were investigated with varying pyrolysis temperature from 700°C to 1600°C. Characterisation methods such as Small Angle X-ray Scattering (SAXS) measurements and N2 adsorption were performed to analyse porosity differences between the samples. The graphene sheet arrangements were observed by transmission electron microscopy (TEM): an ordering of the graphene sheets is observed at temperatures above 1150°C and small crystalline domains appear over 1400°C. As the graphene sheets start to align, the BET surface area decreases and the micropore size increases. To correlate hard carbon structures and electrochemical performances, different tests in Na//HC cells with 1M NaPF6 ethylene carbonate/dimethyl carbonate (EC/DMC) were performed. Samples pyrolysed from 1300°C to 1600°C showed a 300mAh/g reversible capacity at C/10 rate (where C=372mA/g) with an excellent stability in cycling and a very good initial Coulombic efficiency of up to 84%. Furthermore, hard carbons showed an excellent rate capability where sodium extraction rate varies from C/10 to 5C. At 5C more than 80% of reversible capacity remains stable for hard carbons synthesized from 1000°C to 1600°C.

Electrochemical properties of large-sized pouch-type lithium ion batteries with bio-inspired organic cathode materials

To investigate the feasibility of scaling up bio-inspired organic materials as cathode materials in lithium ion batteries, large-sized pouch cells are successfully prepared via tape casting using lumichrome with an alloxazine structure and aqueous styrene butadiene rubber-carboxymethyl cellulose (SBR-CMC) binders. A battery module with a two-in-series, six-in-parallel (2S6P) configuration is also successfully fabricated and is able to power blue LEDs (850 mW). Lumichrome shows no structural changes during the fabrication processes used to produce the positive electrode. The large-sized pouch cells show two sets of cathodic and anodic peaks with average potentials of 2.58 V and 2.26 V vs. Li/Li+, respectively. The initial discharge capacities are 142 mAh g−1 and 148 mAh g−1 for ethylene carbonate-dimethyl carbonate (EC-DMC) and tetraethylene glycol dimethyl ether (TEGDME) electrolytes, respectively, similar to that of a coin cell (149 mAh g−1). The EC-DMC-injected pouch cells exhibit higher rate performance and cyclability than the TEGDME-injected ones. The TEGDME electrolyte is not suitable for lithium metal anodes because of electrolyte decomposition and subsequent cell swelling.

Dual-Carbon Battery Using High Concentration LiPF6 in Dimethyl Carbonate (DMC) Electrolyte

The effects of LiPF6 concentration in ethylene carbonate (EC)–dimethyl carbonate (DMC) on PF6− intercalation into graphitic carbon were studied for a high-energy-density dual-carbon battery. The capacity as well as potential for PF6− intercalation decreased with increasing LiPF6 concentration when EC–DMC was used as an electrolyte. Low-viscosity carbonate was found to be suitable as a high-concentration LiPF6 electrolyte, and DMC is thus a promising electrolyte for high-concentration LiPF6. The PF6− intercalation capacity as well as the intercalation potential in 3.7 M LiPF6/DMC (100 mAh g−1) were almost the same as those in 1 M LiPF6/EC–DMC (89 mAh g−1). Considering the anode capacity, 3.1 M LiPF6 is suitable for the full cell. Using 3.1 M LiPF6 in DMC, the energy density of the dual-carbon battery could be significantly increased.

Role of Mixed Solvation and Ion Pairing in the Solution Structure of Lithium Ion Battery Electrolytes

The solution structures of organic carbonate solvents (ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC)) as electrolyte solutions of LiPF6 were investigated with FTIR and NMR spectroscopy and DFT computational methods. Both coordinated and uncoordinated solvents are observed by IR spectroscopy, allowing the determination of solvent coordination numbers, which a range from 2 to 5. The predominant species in solution changes as a function of LiPF6 concentration. At low salt concentrations (<1.2 M), the predominant species is a solvent-separated ion pair, whereas at high salt concentrations (>2.0 M) the predominant species in solution is the contact ion pair. In mixed solvent systems (PC–DMC, PC–DEC, EC–DMC, or EC–DEC), the mixed solvated cations are observed in the presence of high concentrations of uncoordinated cyclic carbonate despite the much larger dielectric constant of the cyclic carbonates than dielectric constant of linear carbonate.

The effect of LiBF4 concentration on the discharge and stability of LiMn2O4 half cell Li ion batteries

Electrolytes were prepared with different LiBF4 salt concentrations in the ratio of 2:1 (w/w) Ethylene Carbonate (EC): Dimethyl Carbonate (DMC) solvents. Different LiBF4 concentrations were used in the electrolytes to assemble half-cells containing metallic Li anode and nanostructured LiMn2O4 cathode material. To investigate the effect of LiBF4 salt concentration on the electrochemical performance of nanostructured LiMn2O4 cathode material, electrochemical tests were performed at room temperature. For LiBF4–EC–DMC based electrolytes, the optimum LiBF4 salt concentration was found and results showed that higher salt concentration provides higher electrochemical capacity for the bare nanostructured LiMn2O4 cathode materials but did not result in preventing capacity fade due to electrode degradation.

Effect of the nature of a ligand on electrochemical characteristic of tin films in cycling in lithium-ion batteries

Potentiodynamic and galvanostatic cycling in 1 M ethylene carbonate-dimethyl carbonate solution of LiClO4 were used to study electrolytic tin films deposited from complex (tartrate, citrate, and citrate-trilonate) electrolytes. It was shown that the nature of a ligand strongly affects the electrochemical characteristics, specific capacity of tin films, and efficiency of their cycling in lithium power sources. The most stable charge-discharge characteristics are inherent in tin films deposited from the citrate electrolyte.

A single-ion gel polymer electrolyte based on polymeric lithium tartaric acid borate and its superior battery performance

A single-ion gel polymer electrolyte of PLTB@PVDF-HFP (polymeric lithium tartaric acid borate@poly(vinylidene fluoride-co-hexafluoropropene)) was prepared and its ionic conductivity was optimized via solvent composition tailoring. It was manifested that the ethylene carbonate/dimethyl carbonate (EC/DMC) swollen PLTB@PVDF-HFP exhibited a superior lithium ionic conductivity at room temperature to that of the traditional liquid electrolyte system (1 M LiPF6/EC/DMC). The Li4Ti6O12/LiFePO4 cells using the EC/DMC swollen PLTB@PVDF-HFP as polymer electrolyte showed stable charge/discharge voltage profiles with small voltage hysteresis, preferable rate capability and excellent cycle performance at room temperature. These superior performances of EC/DMC swollen PLTB@PVDF-HFP could endow this class of gel polymer electrolyte a very promising alternative to state of the art liquid electrolyte system. (C) 2013 Elsevier B.V. All rights reserved.

Identifying lithium–air battery discharge products through 6Li solid-state MAS and 1H–13C solution NMR spectroscopy

Discharged lithium–O2 battery cathodes are investigated with different catalysts present including Pd, α-MnO2 and CuO, and containing two different electrolyte solvents, 1:1 ethylene carbonate/dimethyl carbonate (EC/DMC) and tetraethylene glycol dimethyl ether (TEGDME). Solid-state 6Li magic angle spinning (MAS) NMR spectroscopy has been used identify lithium products that are formed in the cathodes and differences between products formed with the different catalysts and solvents. There are significant differences in the products formed in Li–O2 cathodes with the two different solvents, EC/DMC and TEGDME. Due to the small chemical shift range of lithium it is difficult to determine exact speciation from 6Li MAS NMR data alone. Fitting of the 6Li NMR peaks with tested Li-oxide powder standards indicates that Li–O2 cathodes discharged in EC/DMC produce primarily Li2CO3 as a lithium product and those discharged in TEGDME produce mainly Li2O2. Solution 2D correlation 1H–13C NMR spectroscopy techniques allow for determination of side-products produced in Li–O2 cathodes.

Suppressed lithium dendrite growth in lithium batteries using ionic liquid electrolytes: Investigation by electrochemical impedance spectroscopy, scanning electron microscopy, and in situ7Li nuclear magnetic resonance spectroscopy

In this work, the formation of lithium dendrites in lithium/Li4Ti5O12 battery cells is studied using different experimental techniques. Electrochemical impedance spectroscopy is presented as a tool to investigate non-invasively the dendritic growth on a lithium metal surface in lithium/Li4Ti5O12 cells during numerous discharging/charging cycles. Scanning electron microscopy is used for visual inspection of the dendrite formation. In situ7Li nuclear magnetic resonance spectroscopy is sensitive to quantitative changes at the lithium metal surface. Application to symmetrical lithium/lithium battery cells allows for a careful comparison of the investigated electrolytes. All these experimental methods provide consistent results. It is demonstrated that the growth of lithium dendrites is significantly correlated to the electrolyte employed. All electrolytes based on the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethane-sulfonyl)azanide (EMIM-TFSA) show reduced dendrite growth in comparison to the standard electrolyte for Li-ion batteries, lithium hexafluorophosphate (LiPF6) in ethylene carbonate/dimethyl carbonate (EC/DMC). LiPF6 in EMIM-TFSA and LiPF6 in EMIM-TFSA/propylene carbonate suppress lithium dendrites most efficiently.

High-performing Sn–Co nanowire electrodes as anodes for lithium-ion batteries

The preparation of Sn2Co3 nanowire arrays (NWs) electrogrown inside the channels of polycarbonate membranes and their characterization as anodes for Li-ion batteries both in half-cell vs. Li and in battery configuration are reported. The Sn2Co3 NW electrodes tested by deep galvanostatic charge/discharge cycles in ethylene carbonate-dimethylcarbonate (1:1) – LiPF6 1 M displayed 80% capacity retention after 200 cycles at C/2 and 30 °C, and a high charge and discharge rate capability at C-rate from C/3 (0.33 A/g) to 10C (10 A/g) at 30° and 10 °C. Electrodes with the highest alloy loading delivered up to 0.6 mAh cm−2 at C/2.The performance of these electrodes in battery configuration with LiFePO4 as cathode is also reported, as well as the effect of the vinylene carbonate additive on the charge/discharge coulombic efficiency of the Sn2Co3 NWs.

In Situ Observation of Solid Electrolyte Interphase Formation in Ordered Mesoporous Hard Carbon by Small-Angle Neutron Scattering

The aim of this work was to better understand the electrochemical processes occurring during the cycling of a lithium half-cell based on ordered mesoporous hard carbon with time-resolved in situ small-angle neutron scattering (SANS). Utilizing electrolytes containing mixtures of deuterated (2H) and nondeuterated (1H) carbonates, we have addressed the challenging task of monitoring the formation and evolution of the solid–electrolyte interphase (SEI) layer. An evolution occurs in the SEI layer during discharge from a composition dominated by a higher scattering length density (SLD) lithium salt to a lower SLD lithium salt for the ethylene carbonate/dimethyl carbonate (EC/DMC) mixture employed. By comparing half-cells containing different solvent deuteration levels, we show that it is possible to observe both SEI formation and lithium intercalation occurring concurrently at the low voltage region in which lithium intercalates into the hard carbon. These results demonstrate that SANS can be employed to bette...

Preparation and application of TEMPO-based di-radical organic electrode with ionic liquid-based polymer electrolyte

In this study we report the synthesis and use of new organic materials, TEMPO di-radical [1,3-bis(4-(2,2,6,6,-tetramethyl-1-oxyl-4-piperidoxyl)butyl) imidazolium trifluorosulfonate]. Two cells were prepared with Li metal anode and the TEMPO di-radical based cathode with a microporous polymer electrolyte [1-butyl-3-methyl imidazolium bis(trifluoromethane sulfonyl) imide (BMImTFSI) in 0.5 M LiTFSI, and in 1 M LiPF6 in ethylene carbonate/dimethyl carbonate (EC/DMC)] hosted in electrospun poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP) membrane. The nature of the solvent was not found to affect the basic redox reaction behavior of TEMPO. The anodic and cathodic peaks were obtained at almost the same position and with some difference in the separation of peaks. The presence of BMImTFSI significantly affects the electrochemical performance of the battery as the cell having this RTIL exhibited far better electrochemical performance with 100% utilization of the active material and reasonably good cycling performance up to 200 cycles. We believe that this composite cell will contribute to organic green rechargeable batteries, although the cell is not fully organic composite.

Layered δ-MnO 2 as positive electrode for lithium intercalation

Layer structured δ-MnO 2 was synthesized by a microwave-assisted hydrothermal method. The morphology of the product consists of flower-like spheres that range from about 200 nm to 3 μm in diameter and are composed of sheets about 5–10 nm in thickness. When tested in the voltage range of 2 to 4.5 V vs. Li +/Li in coin cells, the separator is blocked, handicapping Li + conductivity and leading to cell failure. When tested in the voltage range of 2 to 4 V in ethylene carbonate/dimethyl carbonate (EC/DMC), the δ-MnO 2 delivers an initial reversible capacity of 143.7 mAh g −1 and can maintain 120 mAh g −1 at the 60th cycle. The δ-MnO 2 electrode shows good cycling stability at different current densities and delivers a discharge capacity of about 90 mAh g −1 at 1 C, indicating that it is a promising cathode material for lithium ion batteries.

SnCo nanowire array as negative electrode for lithium-ion batteries

Amorphous SnCo alloy nanowires (NWs) grown inside the channels of polycarbonate membranes by potentiostatic codeposition of the two metals (SnCo- PM) were tested vs. Li by repeated galvanostatic cycles in ethylene carbonate-dimethylcarbonate – LiPF 6 for use as negative electrode in lithium ion batteries. These SnCo electrodes delivered an almost constant capacity value, near to the theoretical for an atomic ratio Li/Sn of 4.4 over more than 35 lithiation–delithiation cycles at 1 C. SEM images of fresh and cycled electrodes showed that nanowires remain partially intact after repeated lithiation–delithiation cycles; indeed, several wires expanded and became porous. Results of amorphous SnCo nanowires grown inside anodic alumina membranes (SnCo- AM) are also reported. The comparison of the two types of NW electrodes demonstrates that the morphology of the SnCo- PM is more suitable than that of the SnCo- AM for electrode stability over cycling. Optimization of NW technology should thus be a promising route to enhancing the mechanical strength and durability of tin-based electrodes.

On the Electrochemical Behavior of Aluminum Electrodes in Nonaqueous Electrolyte Solutions of Lithium Salts

We studied the electrochemical behavior of aluminum electrodes in solutions comprising ethylene carbonate (EC)–dimethyl carbonate (DMC) and lithium salts: lithium hexafluorophospate , lithium perchlorate , or lithium bis(oxalato)borate (LiBOB). Under anodic polarization within the potential range of 3.00–4.00 V in these solutions, aluminum electrodes demonstrate a stable behavior due to their passivation by surface films. Aluminum electrodes passivate in EC–DMC/ and EC–DMC/LiBOB solutions both at 30 and , whereas these electrodes remain active and corrode in EC–DMC/ solutions. LiBOB may decompose at anodic potentials, thus forming passive films comprising and metal-oxalate species on the aluminum electrodes polarized to 4.50–5.30 V. , LiF and , and LiCl species were also detected on the electrodes anodically polarized in LiBOB-, -, and -containing solutions, respectively. At some conditions, current oscillations can be developed on aluminum electrodes upon their polarization at constant potentials. These oscillations may relate to the successive formation and dissolution of the passivating surface films formed on electrodes. The development of species due to the polarization of aluminum electrodes in EC–DMC/ solutions was confirmed by solution NMR studies.