Impact of selected supramolecular additives on the initial electrochemical lithium intercalation into graphite in propylene carbonate

Impact of silicon tripodand-type electrolyte additives and graphite pre-treatment agents on the electrochemical intercalation of lithium cations into graphite was investigated. Addition of Si-tripodand-type silanes to propylene carbonate-based electrolytes was found to suppress detrimental solvent co-intercalation and graphite exfoliation. Similar effects were observed for graphite pre-treated with the reported silane agents. It was observed that the presented supramolecular additives allow for the formation of effective passive layers on graphite during first charging, and thus can be considered as novel low-cost film-forming components for rechargeable lithium batteries.      

Electrochemical reduction of some graphite fluorides in propylene carbonate

The reduction of graphite fluorides has been carried out in propylene carbonate by the carbon paste electrode technique. Our results confirm the insertion mechanism of Li⁺ ions during the reduction of CF_x in lithium batteries. The shift of the reduction peak towards more negative potentials when LiClO₄ is replaced by nBu₄NClO₄ as the supporting electrolyte is attributed to the difficulty of the bulky cation to intercalate in the host structure. In this paper, the electrochemical behaviour of several CF_x samples is compared, in relation to their crystallinity and composition.     

Synthesis of few-layer N-doped graphene from expandable graphite with melamine and its application in supercapacitors

In this paper,we introduced a novel method to prepare the few-layer nitrogen-doped graphene(FNG)from expandable graphite with melamine.The super-capacitive properties of FNG were thoroughly characterized by a three-electrode system,and the results showed the FNG electrode achieved a specific capacitance as high as 83.8 mF/cm2 together with excellent cycling stability.This method could be a novel approach to combine the pseudo-capacitors and electric double layer capacitors.     

Acetone as oxidative decomposition product in propylene carbonate containing battery electrolyte

In situ differential electrochemical mass spectrometry (DEMS) and in situ subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) were used to study the oxidative decomposition products of a propylene carbonate (PC) containing battery electrolyte at metal oxide electrodes. Hydrogen, carbon dioxide, ethane, ethene, propane and propene are typically evolved during electrolyte decomposition in lithium-ion batteries. In our SNIFTIRS and DEMS experiments, additional signals were detected which could not be attributed to these known products. Detailed analysis of these signals indicated the possible evolution of acetone as PC is oxidatively decomposed on the electrode surface.     

Catalytic, asymmetric cyanohydrin synthesis in propylene carbonate

Propylene carbonate can be used as a green solvent for asymmetric cyanohydrin synthesis catalyzed by VO(salen)NCS. A range of 10 aromatic and aliphatic aldehydes gave high enantioselectivities (up to 93%) and conversions (up to 100%) in reactions carried out at or near room temperature with reaction times of 24 h or less.     

聚碳酸丙烯酯中碳酸丙烯酯含量的测定

建立了气相色谱分析聚碳酸丙烯酯中碳酸丙烯酯含量的方法,该方法操作简单,准确度高,可满足工业检测需求.     

Flame synthesis of few-layered graphene/graphite films

We report a fast (in 10-40 s) flame synthesis of high quality few-layered graphene/graphite films, offering the advantages of simplicity, high efficiency, energy saving, low cost and the ability to extend to continuous and mass production of graphene.     

Intercalation of few-layer graphite flakes with FeCl3: Raman determination of Fermi level, layer by layer decoupling, and stability

We use anhydrous ferric chloride (FeCl(3)) to intercalate graphite flakes consisting of 2-4 graphene layers and to dope graphene monolayers. The intercalant, staging, stability, and doping of the resulting intercalation compounds (ICs) are characterized by Raman scattering. The G peak of heavily doped monolayer graphene upshifts to ～1627 cm(-1). The 2-4 layer ICs have similar upshifts, and a Lorentzian line shape for the 2D band, indicating that each layer behaves as a decoupled heavily doped monolayer. By performing Raman measurements at different excitation energies, we show that, for a given doping level, the 2D peak can be suppressed by Pauli blocking for laser energy below the doping level. Thus, multiwavelength Raman spectroscopy allows a direct measurement of the Fermi level, complementary to that derived by performing measurements at fixed excitation energy significantly higher than the doping level. This allows us to estimate a Fermi level shift of up to ～0.9 eV. These ICs are thus ideal test-beds for the physical and chemical properties of heavily doped graphenes.     

Simulation and synthesis of graphene oxide from expanded graphite

Russian Journal of General Chemistry - Expanded graphite oxide and multilayered graphene oxide have been synthesized. The processes of thermal expansion of intercalated graphite and oxidation of...     

High yield synthesis of biodegradable poly(propylene carbonate) from carbon dioxide and propylene oxide

A novel SalenCo^III (2,4‐dinitrophenoxy) (Salen = N,N'‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediamino) and 1,10‐phenanthroline monohydrate catalyst system was designed and employed for the copolymerization of CO₂ and propylene oxide (PO). The perfectly alternating copolymerization of CO₂ and PO proceeds effectively under middle temperature and pressure to yield poly(propylene carbonate) with a high yield and a high number average molecular weight of polymer. The structure of polymer was characterized by the IR and NMR measurements. The perfectly alternating copolymer was confirmed. The MALDI‐TOF spectrum insinuates that the copolymerization of CO₂ and PO was initiated by H₂O. Copyright © 2016 John Wiley & Sons, Ltd.     

A simple method of electrochemical lithium intercalation within graphite from a propylene carbonate-based solution

Electrochemical lithium intercalation within graphite from 1 mol dm^− 3 solution of LiClO₄ in propylene carbonate (PC) was investigated at 25 and − 15 °C. Lithium ions were intercalated into and de-intercalated from graphite reversibly at − 15 °C despite the use of pure PC as the solvent. However, ceaseless solvent decomposition and intense exfoliation of graphene layers occurred at 25 °C. The results of the Raman spectroscopic analysis indicated that the interaction between PC molecules and lithium ions became weaker at − 15 °C by chemical exchange effects, which suggested that the thermodynamic stability of the solvated lithium ions was an important factor that determined the formation of a solid electrolyte interface (SEI) in PC-based solutions. Charge–discharge analysis revealed that the nature of the SEI formed at − 15 °C in 1 mol dm^− 3 of LiClO₄ in PC was significantly different from that formed at 25 °C in 1 mol dm^− 3 of LiClO₄ in PC containing vinylene carbonate, 3.27 mol kg^− 1 of LiClO₄ in PC, and 1 mol dm^− 3 of LiClO₄ in ethylene carbonate.     

Improved performances of lithium carbonate coated graphite in the piperidinium-based hybrid electrolyte for lithium-ion battery

The lithium carbonate (Li₂CO₃)-coated carbon microbead composites (LCO/CMB-T) with the coating amount of 1.07, 2.88, and 7.39% are prepared by the impregnation process (IP). Three LCO/CMB-T samples are first used in the piperidinium-based hybrid electrolyte. It is found that the long charge–discharge cycles did not result in the decomposition or exfoliation of Li₂CO₃ coating. They can effectively prevent graphite electrode from exfoliation and suppress the graphite/electrolyte interfacial reaction. In three tested samples (IP-1.07%, IP-2.88% and IP-7.39% for short), the IP-2.88% sample showed the best cell performances and the highest capacity retention (82.9%) after 50 cycles. This work gives a new design method for the application of graphite materials in the ionic liquid-based electrolyte.     

Anodic behavior of stainless steels in electrochemical synthesis of graphite bisulfate

Anodic-corrosion behavior of a number of chromium-nickel steels in a 80% H₂SO₄ solution was studied in order to replace platinum with less expensive electrodes in electrochemical synthesis of graphite bisulfite and corrosion parameters were determined.     

Enhanced electrochemical performance of LiFePO4 cathode with the addition of fluoroethylene carbonate in electrolyte

The effect of the fluoroethylene carbonate (FEC) addition in electrolyte on LiFePO₄ cathode performance was investigated in low-temperature electrolyte LiPF₆/EC/PC/EMC (0.14/0.18/0.68). Cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge tests were conducted in this work. In the presence of FEC, the polarization of LiFePO₄ electrode decreased both at room and low temperatures. Meanwhile, the exchange current density increased. The rate capability of LiFePO₄ electrode was greatly enhanced as well. The morphology of the solid electrolyte interphase (SEI) on LiFePO₄ surface was modified with the addition of FEC as confirmed by scanning electron microscopy measurement. A compact film with small impedance was formed on LiFePO₄ surface compared to the case of FEC-free. The compositions of the film were analyzed by X-ray photoelectron spectroscopic measurement. The contents of Li _x PO _y F _z , LiF, and the carbonate species generated from solvents decomposition were reduced. The modified SEI promoted the migration of lithium ion through the electrode/electrolyte interphase and enhanced the electrochemical performance of the cathode.     

Controlled synthesis of ZnS quantum dots and ZnS quantum flakes with graphene as a template

Novel ZnS quantum dots (QDs) and ZnS quantum flakes (QFs) were successfully prepared with graphene nanosheets (GNs) as a special template, and two unique heterostructures of ZnS/GNs were also obtained. Due to the structure-directing template effect of GNs, the as-synthesized ZnS with different morphologies, dots or flakes, were uniformly distributed on the surface of GNs by controlling nucleation and growth. The two different heterostructures of ZnS/GNs exhibited obvious photovoltaic response, and ZnS/GN QFs-on-sheet heterostructures show higher photovoltage than that of ZnS/GN QDs-on-sheet.     

Effect of cathodic electrolyte on the performance of electrochemical hydride generation from graphite cathode

The classic silver diethyldithiocarbamate (SDDC) spectrophotometric procedure for arsenic determination has been used for investigation of the effect of cathodic electrolyte on the performance of electrochemical hydride generation (HG) from graphite cathode. The results of this study show that the presence of a soft metal ion such as Cd(II), Sn(II) and/or Zn(II) in the acidic cathodic electrolyte can increase effectively the efficiency of electrochemical hydride generation and decrease the effect of interferences. The possible mechanisms of these effects have been discussed in detail. The parameters related to the electrochemical hydride generation were investigated. Also the characteristic data of the electrochemical hydride generation and common hydride generation by NaBH₄ were compared. Under optimised conditions, the system is selective to As(III) and total inorganic analyses can be performed after a pre-reduction stage prior to electrochemical hydride generation. This will allow the differential determination of inorganic arsenic species. The method is appropriate to the determination of 4-40 μg of each arsenic species.     

Straightforward synthesis of conductive graphene/polymer nanocomposites from graphite oxide

The reduction of graphite oxide (GO) in the presence of reactive poly(methyl methacrylate) (PMMA), under mild biphasic conditions, directly affords graphene grafted with PMMA. The resulting nanocomposite shows excellent electrical conductivities resulting from the optimal dispersion and exfoliation of graphene in the polymer matrix.     

Effects of dopant anions and N-substituents on the electrochemical behavior of polypyrrole films in propylene carbonate solution

The electrochemical properties of poly(N-ethylpyrrole) (PEPy) and poly(N-methylpyrrole) (PMPy) films in propylene carbonate (PC) solution, where ion transport is anion-specific, has been investigated using the cyclic electrochemical quartz crystal microbalance (EQCM) technique and electrochemical impedance techniques. The type of dopant anion (PF₆⁻ vs. ClO₄⁻) used for the film preparation and the N-substituents (ethyl vs. methyl) have profound effects on the solvent transport behavior, charge capacity, and ionic resistance of the films.