Propylene Carbonate Electrolyte Solution Research Articles

Electrochromic Behavior of Vanadium Pentoxide Thin Films Prepared by a Sol–Gel Spin Coating Process

Herein, the synthesis of vanadium oxide thin films with high electrochromic coloration efficiency through a simple sol–gel spin coating technique is reported. The structural studies confirm the formation of V2O3V2O5 mixed phase at 250 °C and the pure β‐V2O5 phase at 350 and 450 °C. The decrease in optical bandgap, refractive index, and extinction coefficient improves the transmission ability of the films at higher temperatures. The photoluminescence emission peak observed at 553 nm is due to the recombination of electron–hole pair intrinsic transition from the lowest split‐off V 3d band to the O 2p valence band. The tuning of surface morphology from rod to platelet structure may be due to the higher annealing temperature which assists the disorder movement of the particles. The observed V 2p core levels confirm the existence of V5+ oxidation state with the splitting of 7.2 eV. The electrochromic behavior of vanadium oxide film is detected in 0.5 m LiClO4 in propylene carbonate electrolyte solution. The results show that the film annealed at 450 °C exhibits high coloration efficiency of 110.98 cm2 C−1, good reversibility of 99%, and faster switching speed for bleaching (2.1 s) and coloration (2.4 s) processes.

3D supramolecular chiral crystal structures of radical anion salts of (−)-NDI-Δ and possible magnetic phase diagrams

Supramolecular chiral crystals of radical anion salts of a triangular chiral electron acceptor, (−)-naphthalene diimide (NDI)-Δ, were electrochemically grown in propylene carbonate electrolyte solutions in the presence of cyclic multidentate ligands.

Imaging Cycle-Induced Damage of MnO2 Microparticles

MnO2 has been proposed as an electrode material in electrochemical energy storage devices. However, poor cycle life, especially in aqueous electrolytes, remains a detriment to commercialization. Prior studies have suggested a number of explanations for this capacity loss; however, experiments aimed at elucidating the details of the degradation process (es) are sparse. We describe here a microtube-membrane construct that allows for electrodeposition of monodisperse MnO2 microparticles distributed across the membrane surface, and for subsequent electrochemical cycling of these MnO2 particles. This allowed for a detailed analysis of the effect of cycling on the MnO2, by simply imaging the membrane surface before and after cycling. When an aqueous electrolyte was used, gross changes in particle shape, size and morphology were observed over the course of 500 cycles. Partial dissolution occurred as well. No such changes were observed when the MnO2 particles were cycled (up to 500 times) in a propylene carbonate electrolyte solution.

Highly Durable Ester-Based Electrolyte Solutions for Higher-Voltage Lithium-Ion Batteries

The practical specific capacity of conventional positive electrodes, such as LiCoO2, remained less than the half of graphite negative-electrodes. Hence, increasing the specific capacity of positive-electrodes effectively improves the energy density of lithium-ion batteries (LIBs). A layer-structured LiNi0.5Co0.2Mn0.3O2 positive-electrode can deliver a high discharge capacity of ca. 200 mAh g-1 by charging to around 4.6 V. However, the severe decomposition of conventional electrolyte solutions is a problem at such a high potential. The stability of electrolyte solutions against oxidation can be improved by increasing the concentration, and there are three major problems to be solved toward the practical use; 1) high costs due to an extensive use of lithium salts, 2) high viscosities which make it virtually impossible to inject the electrolyte solutions into cylindrical and laminated cells in the production processes of practical LIBs, and 3) low rate capabilities due to the low ionic conductivity of highly viscous electrolyte solutions. These problems can be settled by diluting the highly concentrated electrolyte solution with an appropriate diluent. We previously reported that propylene carbonate (PC)- and γ-butyrolactone-based concentrated electrolyte solutions showed high stability against oxidation at LiNi0.5Co0.2Mn0.3O2 and 5-V class LiNi0.5Mn1.5O4 [1-3]; irreversible capacities due to the oxidative decomposition of electrolyte solution decreased with increasing the electrolyte concentration, while the discharge capacities increased. In particular, in the nearly saturated 7.25 mol kg-1 LiBF4 /PC electrolyte solution, LiNi0.5Co0.2Mn0.3O2 retained a high discharge capacity of ca. 186 mAh g-1 even after 50 charge/discharge cycles at a C/10 rate. The polarization on charge/discharge reactions remained small even at the very high concentration [2]. Considering the wide operating temperature range of LIBs, the electrolyte solution needs to be stable even at elevated temperatures. 7.25 mol kg-1 LiBF4 /PC allowed charge/discharge cycles of LiNi0.5Mn1.5O4 between 3.5 and 5.0 V at an elevated temperature of 50 °C, whereas not in the nearly saturated 4.27 mol kg-1 LiPF6 /PC [4]. In electrolyte solutions of moderate concentrations, the dissolution of active materials become more of a problem at elevated temperatures. The highly concentrated LiBF4/PC suppressed the dissolution of manganese ions from a LiNi0.5Mn1.5O4 electrode more effectively than LiPF6 /PC [4]. Highly concentrated LiBF4 /PC can be diluted with a diluent to reduce the high viscosity and concentration. Fluorinated solvents have relatively low donor number and high stability against oxidation because they have electron-withdrawing fluorine atoms, and are suitable as diluents for concentrated LiBF4 /PC systems. We explored various kinds of fluoroalkyl ethers [5,6] and esters as a diluent, of these, bis(2,2,2-trifluoroethyl) carbonate (TFEC) has a relatively low HOMO energy, and could hardly dissolve LiBF4. Unfortunately, however, the miscibility between TFEC and concentrated LiBF4 /PC was not high, and hence tris(2,2,2-trifluoroethyl) phosphate (TFEP) was introduced as a co-solvent of PC to prepare 2.03 mol kg-1 LiBF4 /PC + TFEP (1:2 by volume, PC/Li+ molar ratio = 1.35). This concentrated electrolyte solution was diluted with 50 vol.% TFEC to obtain 1.00 mol kg-1 LiBF4 /PC+TFEP+TFEC (1:2:3 by volume, PC/Li + molar ratio = 1.35). The initial discharge capacity reached 192 mhA g- 1 and 98.0% of it was retained even at the 50th cycle (Fig.1) [7]. Thus, the degradation of a LiNi0.5Co0.2Mn0.3O2 electrode was extremely suppressed even though the upper cut-off voltage was as high as 4.6 V. The initial Coulombic efficiency (84.2%) was low, while the average Coulombic efficiency from the 2nd (97.6%) to 50th cycle (99.1%) was high at 98.7%. Thus, the present electrolyte solution has a low viscosity (ca. 7 mPa s), moderate lithium salt concentration, and high stability against oxidation, and is therefore suitable for higher-voltage operating of LIBs. This research has been supported by “Advanced Research Program for Energy and Environmental Technologies” from NEDO, Japan. Reference [1] T. Doi et al., Electrochim. Acta, 209 (2016) 219-224. [2] T. Doi et al., J. Electrochem. Soc., 163 (2016) A2211-A2215. [3] T. Doi et al., ChemElectroChem, 4 (2017) 2398-2403. [4] T. Doi et al., ChemistrySelect, 2 (2017) 8824-8827. [5] T. Doi et al., J. Electrochem. Soc., 164 (2017) A6412-A6416. [6] T. Doi et al., Sustain. Energy Fuels, 2 (2018) 1197–1205. [7] T. Doi et al., Curr. Opin. Electrochem., 9 (2018) 49-55. Figure 1

Electrochemical behavior of multifunctional graphene–polyimide nanocomposite film in two different electrolyte solutions

ABSTRACTThe effect of solvent on specific capacitance, bulk resistance, and charge/discharge capacity of graphene/polyimide composite films is studied by electrochemical methods. Composite films are synthesized by in situ condensation polymerization of poly (amic acid) in the presence of 50 wt % partly exfoliated graphene sheets followed by thermal curing at 250°C. Raman spectrum of the exfoliated graphene sheets show an increase in the ratio of ID to IG peak intensities from 0.167 to 0.222, suggesting increased defects in graphene basal planes. Electrochemical measurements carried out by using 0.4M potassium hexafluorophosphate (KPF6) dissolved in propylene carbonate and N‐methylpyrrolidone at 25°C show that the composite system exhibits both pseudocapacitance and supercapacitance behaviors, with an average capacitance of 40 and 36.5 F g−1, respectively. Bulk resistance of the composite obtained by using KPF6–propylene carbonate electrolyte solution is 300% lower than that obtained in KPF6–N‐methylpyrrolidone solution, with a fairly stable specific capacity of 85 μAhr g−1, with 80% retention observed after 30 charge–discharge cycles. Fourier transform infrared spectroscopy measurements show shifts in the cyclic imide carbonyl peak from 1778 to 1774 cm−1, which suggests that some form of interaction exists between the graphene and polyimide. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42673.

Design of Electrochemcial Interface Between Cathode/Solid Electrolyte By Using Liquid Type Li+ Conducting Materials

Lithium ion secondary batteries have been used widely as power sources of various electric devices, and recently used for larger applications such as electric vehicles. According to this movement, the safety of battery becomes more important. However, it is difficult to realize high safety in current batteries using liquid electrolytes containing flammable organic solvents. Thus, all-solid-state batteries using ceramics electrolytes have been focused in recent years. We have studied about the all-solid-state batteries using Li7La3Zr2O12 (LLZ), which has Li+ conductivity higher than 10-4 S cm-1 at room temperature and chemical stability against lithium metal. Thus, LLZ is a promising solid electrolyte to realize the all-solid-state batteries with high safety and energy density. However, new insights and technologies are needed to form an electrochemical electrolyte/electrode interface in all-solid-state batteries since solid electrolytes have no fluidity. In this study, formation of an appropriate electrochemical interface for all-solid-state batteries is investigated by applying various Li+ conducting materials to the composite cathode formed on a LLZ pellet. LLZ powder was synthesized by solid state reaction and pelletized. LiFePO4 was used as cathode and its slurry containing acetylene black and polyvinilidene difluoride in a weight ratio of 80: 10: 10 in N-methylpyrrolidone was coated on LLZ pellet. After vacuum drying at 85 oC, a small amount of electrolyte materials was impregnated in to the cathode. Then, lithium-metal was attached onto the back side of LLZ pellet as anode. As the electrolyte materials, 1 mol dm-3 LiPF6 in propylene carbonate and lithium bisfluorosulfonylimide-tetraglyme complex (LiFSI-G4) were used. Fig. 1 shows a cross-sectional SEM image of the LLZ pellet with LiFePO4 composite cathode. The composite cathode with a thickness of about 10 μm was well attached onto the LLZ pellet. Fig. 2 shows the cyclic voltammogram of the cell without liquid electrolyte impregnation to the cathode. A couple of oxidation and reduction peaks corresponding to the charge and discharge of LiFePO4 were observed with a relatively high symmetry, centered at around 3.5 V, which agrees with the operating potential of LiFePO4. However, those peak currents were as low as 1 μA, suggesting that only a small amount of LiFePO4 near the LLZ/cathode interface worked. Fig. 3 shows cyclic voltammograms of the cells with LiFePO4 composite cathodes impregnated with (a) 1 mol dm-3 LiPF6 in propylene carbonate and (b) LiFSI-G4. In the case of 1 mol dm-3 LiPF6 in propylene carbonate, the oxidation and reduction peaks corresponding to the charge and discharge of LiFePO4 were observed, and those currents were increased compared with the cell without the electrolyte impregnation (Fig. 2). This improvement can be understood by the formation of Li+ conducting pathways between LiFePO4 in the cathode and LLZ pellet. Similarly, the currents were increased by applying LiFSI-G4. However, the charge and discharge peaks became broader and shifted to positive and negative, respectively. This difference may be due to the lower ionic conductivity and higher viscosity of LiFSI-G4 than those of propylene carbonate electrolyte solution. Further optimization on LLZ/LiFePO4 cathode interface is now underway and the details will be discussed in the meeting. Figure 1

Electrochemical Na Insertion and Solid Electrolyte Interphase for Hard‐Carbon Electrodes and Application to Na‐Ion Batteries

AbstractRecently, lithium‐ion batteries have been attracting more interest for use in automotive applications. Lithium resources are confirmed to be unevenly distributed in South America, and the cost of the lithium raw materials has roughly doubled from the first practical application in 1991 to the present and is increasing due to global demand for lithium‐ion accumulators. Since the electrochemical equivalent and standard potential of sodium are the most advantageous after lithium, sodium based energy storage is of great interest to realize lithium‐free high energy and high voltage batteries. However, to the best of our knowledge, there have been no successful reports on electrochemical sodium insertion materials for battery applications; the major challenge is the negative electrode and its passivation. In this study, we achieve high capacity and excellent reversibility sodium‐insertion performance of hard‐carbon and layered NaNi0.5Mn0.5O2 electrodes in propylene carbonate electrolyte solutions. The structural change and passivation for hard‐carbon are investigated to study the reversible sodium insertion. The 3‐volt secondary Na‐ion battery possessing environmental and cost friendliness, Na+‐shuttlecock hard‐carbon/NaNi0.5Mn0.5O2 cell, demonstrates steady cycling performance as next generation secondary batteries and an alternative to Li‐ion batteries.

Li dendrite growth and Li+ ionic mass transfer phenomenon

Li metal dendrite growth in LiPF6–propylene carbonate (PC) electrolyte was observed in situ by a laser scanning confocal microscope (LSCM) with a metallographic microscope. The development of the electrodeposited Li dendrite length was analyzed, and compared with dendrites grown in LiClO4–PC electrolyte solution. Different anions make different Solid Electrolyte Interphase (SEI) layers on the electrodeposited Li metal. This difference is one factor which causes the morphological variation and the different dendrite growth behavior of Li metal in these electrolytes. The relationship between the Li dendrite growth and Li+ ionic mass transfer rate associated with the electrodeposition of Li metal is examined, and dendrite initiation and growth rate are discussed. The authors find that ionic mass transfer plays an important role in dendrite growth behavior.

In Situ Observation of Dendrite Growth of Electrodeposited Li Metal

The dendrite growth behavior of Li metal galvanostatically electrodeposited on Ni substrate in a –propylene carbonate electrolyte solution was in situ observed by a laser scanning confocal microscope with a metallographic microscope. A Li dendrite precursor is stochastically evolved on Ni substrate probably through a solid electrolyte interphase layer produced by the surface chemical reaction between a reduced Li metal and an organic electrolyte. The measured length of randomly growing Li dendrite arms was statistically analyzed. The initiation period of the dendrite precursor becomes shorter with increasing current density and decreasing concentration. Once it has been initiated, the ionic mass transfer rate starts to govern the growth process of the dendrite arm length, exceeding over the surface chemistry controlling step. The dendrite arm length averaged over the substrate surface grows linearly proportional to the square root of time. The lower the concentration of , the steeper the inclination of the line at , whereas the concentration dependence of inclination is not evident at .

Mass tranfer of ions and solvent at redox processes in poly-3,4-ethylenedioxythiophene films

The work presents the data on mass transfer at the interface of the poly-3,4-ethylenedioxythiophene film with different propylene carbonate electrolyte solutions (TBAPF6, LiClO4, NaClO4, TBAClO4, TBABF4) obtained using the quartz microgravimetry method in combination with cyclic voltammetry. It is shown that two parts of different nature can be observed in the region of electric activity of poly-3,4-ethylenedioxythiophene films on Δm, ΔQ curves. They evidence the change in mass transfer conditions at achieving different film oxidation degrees.

ZnO thin films electrodeposited in propylene carbonate under a magnetic field

Electrochemical processing of ZnO films on fluorine-doped indium tin oxide (FTO/ITO) substrate was investigated in organic propylene carbonate electrolyte solutions containing Zn(NO3)2·6H2O. Much finer and more uniform morphologies of the ZnO films were obtained in comparison with those in aqueous electrolyte solutions. The effects of superimposing a magnetic field to the ZnO films were further examined. Superimposing a magnetic field considerably influenced the transient current density in the initial stage, especially in the mass transfer controlled region at −1.5 V vs Zn wire reference electrode. It also introduced substantially no drastic influence on the microstructure in spite of the appearance of considerably significant morphological variations.

Electrochemical Characteristics of Nanoporous Carbide-Derived Carbon Materials in Various Nonaqueous Electrolyte Solutions

Electrochemical characteristics for the carbide-derived nanoporous carbon (prepared from TiC, , , , and ) in 1 M various tetraalkyl ammonium tetrafluoroborate in acetonitrile, γ-butyrolactone, and propylene carbonate electrolyte solutions has been studied using cyclic voltammetry and electrochemical impedance spectroscopy. The specific surface area, pore size distribution, nanopore volume, and other characteristics, dependent on the precursor carbide used (nanopores are pores in the range of 2 nm and below, i.e., micropores according to IUPAC classification), have been obtained using the gas adsorption measurements at temperature of liquid nitrogen. The region of ideal polarizability, values of series, parallel capacitances and resistances, and other characteristics dependent on the precursor carbide used for carbon synthesis have been established. The dependence of nanoporous material characteristics on the gas-phase properties has been established and discussed.

Ionic mass transfer during electrochemical dissolution of Li metal in PC electrolyte solution

A Li metal anode was electrochemically dissolved in propylene carbonate (PC) containing 0.5 M lithium perchlorate (LiClO 4) and the development of the Li + concentration profile measured in situ by holographic interferometry. As the electrochemical cell configurations both a horizontal anode-over-cathode configuration, with the anode facing upward, and a vertical configuration of the parallel planar electrodes were employed. At low current densities (<2 mA cm −2) no shifting of the interference fringes was observed in either configuration during the initial stage of current passage. Such an incubation period has been observed also during cathodic Li electrodeposition from PC solutions, but in anodic Li dissolution the amount of electricity consumed during the incubation period was found to be appreciably less than in electrodeposition. This incubation phenomenon in electrochemical dissolution may be related to the existence of a solid–electrolyte interface layer on the Li metal surface in PC. The Li + ion mass transfer rate measured after the incubation period agreed with that expected assuming one-dimensional diffusion in stagnant LiClO 4 solution, away from the upward facing horizontal anode. In the case of a vertical plane anode, natural convection of the electrolytic solution was induced by the accumulation of LiClO 4 at the anode. The mass transfer rate of Li + ion measured after incubation was in reasonable agreement with natural convection boundary layer theory.

Long-range transport in an assembly of ZnO quantum dots: the effects of quantum confinement, Coulomb repulsion and structural disorder.

We have studied the storage and long-range transport of electrons in a porous assembly of weakly coupled ZnO quantum dots permeated with an aqueous and a propylene carbonate electrolyte solution. The number of electrons per ZnO quantum dot is controlled by the electrochemical potential of the assembly; the charge of the electrons is compensated by ions present in the pores. We show with optical and electrical measurements that the injected electrons occupy the S, P, and D type conduction electron levels of the quantum dots; electron storage in surface states is not important. With this method of three-dimensional charge compensation, up to ten electrons per quantum-dot can be stored if the assembly is permeated with an aqueous electrolyte. The screening of the electron charge is less effective in the case of an assembly permeated with a propylene carbonate electrolyte solution. Long-range electron transport is studied with a transistor set-up. In the case of ZnO assemblies permeated with an aqueous electrolyte, two quantum regimes are observed corresponding to multiple tunnelling between the S orbitals (at a low occupation) and P orbitals (at a higher occupation). In a ZnO quantum-dot assembly permeated with a propylene carbonate electrolyte solution, there is a strong overlap between these two regimes.

Electrochemical Impedance Spectroscopy at Alkanethiol-Coated Gold in Propylene Carbonate

Electrochemical impedance spectroscopy was successfully employed to investigate ionic permeability into self-assembled monolayers (SAMs) deposited on a Au(111) single crystal in propylene carbonate electrolyte solutions. The ionic permeability strongly depends on the applied dc potential, implying the existence of different potential dependent phases in monolayers exposed to propylene carbonate solutions. Increasing the temperature changes the ionic permeability of the SAM irreversibly. This is suggested to be due to changes in film structure due to Ostwald ripening. An appropriate equivalent circuit for characterization of the ionic conductivity of these self-assembled monolayers was developed.

Hydrothermal synthesis of hexagonal tungsten trioxide from Li 2WO 4 solution and electrochemical lithium intercalation into the oxide

Tungsten trioxides with an open structure were synthesized by a hydrothermal reaction at 120–180°C from an aqueous Li 2WO 4 solution at pH values from 0.5 to 2.0. The products contained some water molecules and lithium ions, e.g. as x(Li 2O)·WO 3· y(H 2O) ( x=0.05–0.11, y=0.6–0.8), and they formed at pH 0.5–1.0 and 1.5–2.0 with hexagonal and orthorhombic cells, respectively. The x value increased with increasing pH of the Li 2WO 4 solution and synthesis temperature. Electrochemical lithium intercalation into the tungsten trioxides was investigated in a LiClO 4–propylene carbonate electrolyte solution. The x(Li 2O)·WO 3· y(H 2O) electrode underwent lithium intercalation up to Li/W=∼1 on discharge until 1.5 V vs. Li/Li +.

Manipulation of electroactive polymer film viscoelasticity: the roles of applied potential and frequency

We describe quartz crystal impedance measurements on thin films of poly(3-hexylthiophene) (PHT) electrochemically maintained at different potentials and exposed to propylene carbonate electrolyte solutions. Film shear modulus values, obtained at fixed potentials corresponding to a range of film oxidation states (“doping levels'), show a marked variation of storage and loss moduli ( G′ and G″, respectively). The p-doped film is substantially softer than the undoped film, and G′ and G″ can show maxima at partial p-doping. Even in nominally “equilibrium' experiments (at fixed potential) there is dramatic hysteresis in shear modulus values determined during stepwise doping and undoping. This general pattern of behaviour is observed at a range of frequencies, corresponding to the fundamental frequency (10 MHz) and higher harmonics (30 MHz to 110 MHz). There are substantial increases in shear modulus with increasing frequency for all doping levels, and the loss tangent ( G″/ G′) is frequency dependent. A Voigt model is qualitatively incompatible with these observations, and a Maxwell model can qualitatively explain some features; more sophisticated models are required to provide quantitative explanations. We discuss these observations in terms of potential-driven film ion and solvent population changes. The data are consistent with non-equilibrium film solvent populations for intermediate doping levels, even though the equilibrium ion populations (charge states) may be established. Together, selection of operating frequency, applied potential and time scale offer the prospect of manipulating film viscoelastic parameters in a controllable manner over several orders of magnitude, from “rubbery' to near “glassy' behaviour.

Fabrication and Characterization of a Hydroquinone-Functionalized Polypyrrole Thin-Film pH Sensor

The physical and chemical properties of polypyrrole (PPy) derivatized at the 3-position with dimethoxybenzyl and dihydroxybenzyl functionalities via a novel high-yield pathway were evaluated for pH response. The monomers were electrochemically polymerized with perchlorate dopant in a propylene carbonate electrolyte solution. The potentiometric characteristics of the resulting films show a sub-Nernstian response of 46.0 mV pH-1 (25 °C); a detection limit of 1 × 10-10 mol dm-1; potential drift of ±1.9 mV and a low hysteresis with Δslope = ±1.9 mV pH-1. X-ray photoelectron spectroscopy (XPS) shows a reduction in the carbon 1s and chlorine 2p photoelectron peaks widths for functionalized PPy in comparison with the PPy indicating presence of β-carbon substituents. Time-of-flight secondary positive ion mass spectra showed peaks at m/z values of 107 and 109, indicating the presence of hydroquinone species at the outermost film surface of the functionalized PPy. The structure of the functionalized monomers was co...

Microwave photoelectrochemical studies of silicon interfaces covered with platinum dots

n-Type Si electrodes either dotted with Pt particles (5–10 nm) or uncoated, in contact with a propylene carbonate electrolyte solution containing the redox couple ferrocene/ferrocenium, have been investigated with time-resolved microwave conductivity (TRMC) and with potential-dependent stationary-microwave reflection measurements. The impact of the penetration depth of the exciting light on the photoinduced microwave reflection and photocurrent signals for the plain Si/electrolyte interface was examined. In addition the effect of changing the concentration of the redox couple in both systems was compared with the impact of Pt-particle treatment on the Si surface. Two electrochemical waves were observed during the oxidation of ferrocene, the second coinciding with an electrochemically induced decrease of surface recombination at the Si/electrolyte interface. This generates a tail-back in the flow of charge carriers and an increased concentration of minority carriers, visible in the microwave reflection signal. In the presence of Pt dots the increase of the first photocurrent wave is negatively shifted (increased open circuit voltage), whereas the tail-back is positively displaced by 100–200 mV. Simultaneously, a decreased surface recombination is indicated by a larger amplitude of the microwave signal. This results in an increased photocurrent density, provided that transport through the electrolyte is not rate limiting. The main effect of Pt treatment is the improved passivation of the semiconductor electrolyte interface under maintenance of an efficient collection of photogenerated charge carriers via the Pt particles.

In Situ Observation and Evaluation of Electrodeposited Lithium by Means of Optical Microscopy with Alternating Current Impedance Spectroscopy

Electrodeposited lithium was evaluated by ac impedance measurement and optical microscopy in two solutions containing; a propylene carbonate (PC) solution and a blended solution consisting of PC and 1,2‐dimethoxyethane (DME) . The ac impedance data were analyzed in the higher frequency region, where the charge‐transfer resistance of can be evaluated. The value of was always larger in the PC electrolyte solution than in the PC‐DME(1:1) electrolyte solution, and depended on the lithium deposition charge. Microscopic observation indicated that lithium deposited more uniformly in PC‐DME (1:1) than in PC solution. The results of morphological evaluation of the electrodeposited lithium using optical microscopy corresponded to the variations in the value of obtained from ac impedance measurements, showing that the behaviour of accurately represented the morphological state. The cycleability of the lithium anode was investigated by charge‐discharge testing. The cycle efficiency was worse in PC than in PC‐DME (1:1) solution; this seems to be related to the morphological properties of the lithium deposits.