Electrochemical Surface Plasmon Resonance Spectroscopy for Investigation of the Initial Process of Lithium Metal Deposition.

The initial process of Li-metal electrodeposition on the negative electrode surface determines the charging performance of Li-metal secondary batteries. However, minute depositions or the early processes of nucleation and growth of Li metal are generally difficult to detect under operando conditions. In this study, we propose an optical diagnostic approach to address these challenges. Surface plasmon resonance (SPR) spectroscopy coupled with electrochemical operation is a promising technique that enables the ultrasensitive detection of the initial stage of Li-metal electrodeposition. The SPR is excited in a thin copper film deposited on a glass substrate, which also serves as a current collector enabling electrochemical Li-metal deposition. For a propylene carbonate (PC)-based Li-ion battery electrolyte, under both cyclic voltammetry and constant-current operation, Li-metal deposition is readily detected by changes in the SPR absorption dip in the reflectance spectrum. Electrochemical SPR is highly sensitive to metal deposition, with a demonstrated capability of detecting an average thickness of approximately 0.1 nm, corresponding to a few atomic layers of Li. To identify the growth mechanism, the SPR reflectance spectra of various possible Li-metal deposition processes were simulated. Comparison of the simulated spectra with the experimental data found good agreement with the well-known nucleation and growth model for Li-metal deposition from PC-based electrolytes. The demonstrated operando electrochemical SPR measurement should be a valuable tool for basic research on the initial Li-metal deposition process.

Anthraquinone-Based Oligomer as a Long Cycle-Life Organic Electrode Material for Use in Rechargeable Batteries.

An anthraquinone (AQ)-based dimer and trimer linked by a triple bond (-C≡C-) were newly synthesized as active materials for the positive electrode of rechargeable lithium batteries. These synthesized oligomers exhibited an initial discharge capacity of about 200 mAh g-1 with an average voltage of 2.2-2.3 V versus Li(C.E.) . These capacity values are similar to that of the AQ-monomer, reflecting the two-electron transfer redox per AQ unit. Regarding their cycling stability, the capacity of the monomer electrode quickly decreased; however, the electrodes of the prepared oligomers showed an improved cycling performance. In particular, the discharge capacities of the trimer remained almost constant for 100 cycles. A theoretical calculation revealed that the intermolecular binding energy can be increased to the level of a weak covalent bonding by oligomerization, which would be beneficial to suppress the dissolution of the organic active materials into the electrolyte solutions. These results show that the cycle-life of organic active materials can be extended without lowering the discharge capacity by the oligomerization of the redox active molecule unit.

Real-Time Observation of Li Deposition on a Li Electrode with Operand Atomic Force Microscopy and Surface Mechanical Imaging.

Nanoscale investigations of Li deposition on the surface of a Li electrode are crucial to understand the initial mechanism of dendrite growth in rechargeable Li-metal batteries during charging. Here, we studied the initial Li deposition and related protrusion growth processes at the surface of the Li electrode with atomic force microscopy (AFM) in a galvanostatic experiment under operand condition. A flat Li-metal surface prepared by precision cutting a Li-metal wire in electrolyte solution (100 mM LiPF6 in propylene carbonate) was observed with peak-force-tapping mode AFM under an inert atmosphere. During the electrochemical deposition process of Li, protrusions were observed to grow selectively. An adhesion image acquired with mechanical mapping showed a specifically small contrast on the surface of growing protrusions, suggesting that the heterogeneous condition of the surface of the Li electrode affects the growth of Li dendrites. We propose that a modification of the battery cell design resulting in a uniform solid-liquid interface can contribute to the homogeneous deposition of Li at the Li electrode during charging. Further, the mechanical mapping of Li surfaces with operand AFM has proven to play a significant role in the understanding of basic mechanisms of the behavior of the Li electrode.

A Monte-Carlo simulation of ionic conductivity and viscosity of highly concentrated electrolytes based on a pseudo-lattice model.

Simulating three transport phenomena-ionic conductivity, viscosity, and self-diffusion coefficient-in a common Monte-Carlo framework, we discuss their relationship to the intermolecular interactions of electrolyte solutions at high concentrations (C/mol l-1 ∼ 1). The simulation is predicated on a pseudolattice model of the solution. The ions and solvents (collectively termed "molecules") are considered dimensionless points occupying the lattice sites. The molecular transport is realized by a repetition of swapping two adjacent molecules by the stochastic Gibbs sampling process based on simple intermolecular interactions. The framework has been validated by the fact that the simulated ionic conductivity and dynamic viscosity of 1:1- and 2:1-salts qualitatively well represent the experimental data. The magnitude of the Coulombic interaction itself is not reflected in the ionic conductivity, but the extent to which the Coulombic interaction is shielded by the dielectric constant has a significant influence. On the other hand, the dielectric constant barely influences the viscosity, while the magnitude of the Coulombic interaction is directly reflected in the viscosity.

Elucidating the Reductive Decomposition Mechanism in Sulfide Solid Electrolyte Li4SnS4.

The sulfide solid electrolyte Li4SnS4 has garnered considerable interest due to its exceptional moisture durability, which is attributed to its stable hydrated state. However, a major limitation of certain sulfide solid electrolytes, including Li4SnS4, is their low reduction durability, which limits their application in the negative electrodes of all-solid-state batteries and impedes qualitative material development assessments. In this study, we introduced a quantitative and straightforward method for evaluating the reductive decomposition of Li4SnS4 to better understand its degradation mechanism. The configuration of the electrochemical evaluation cell was modified from SUS|Li4SnS4|Li to SUS|Li4SnS4|Li3PS4|Li, allowing for stabilization of the reference potential of the counter electrode. The reductive decomposition potential of Li4SnS4 was quantitatively assessed by using cyclic voltammetry in a two-layer electrochemical evaluation cell. We observed a minor irreversible reduction current below +1.2 V and a pronounced decomposition peak at +1.0 V. Notably, reductive decomposition continued below 0 V, which is typically the onset point for Li electrodeposition. Postreduction, the solid electrolyte was comprehensively analyzed through optical microscopy, X-ray diffraction, and X-ray absorption spectroscopy. These analyzes revealed the following: (i) The SnS44- unit in Li4SnS4 initially decomposes into Li2S and ß-Sn with the dissociation of the Sn-S bond; (ii) the resulting ß-Sn forms LixSn alloys such as Li0.4Sn; and (iii) the ongoing reductive decomposition reaction is facilitated by the electronic conductivity of these LixSn alloys. These findings offer crucial methodological and mechanistic insights into the development of higher-performance solid electrolyte materials.

Recycling Compatible Organic Electrode Materials Containing Amide Bonds for Use in Rechargeable Batteries.

Organic rechargeable batteries that do not use any scarce heavy metals are candidates for the next generation of rechargeable batteries; although, it is not easy to realize both high capacity and long cycle life. Organic compounds linked by amide bonds are expected to have superior recycling properties after battery degradation, since they will become a single monomer upon hydrolysis. In this study, anthraquinone was chosen as a model redox active unit, and dimeric and trimeric compounds were synthesized, their cycle performances as electrode materials for use in rechargeable batteries were compared, and a trend in which oligomerization improves cycle properties was confirmed. Furthermore, quantum chemistry calculations suggest that oligomerization decreases solubility, which would support a longer life for oligomerized compounds. This methodology will lead to the development of organic rechargeable batteries with further environmental benefits.

Optical Study of the Surface Film Formed during Li-Metal Deposition and Dissolution Investigated by Surface Plasmon Resonance Spectroscopy.

The features of the electrode surface film during Li-metal deposition and dissolution cycles are essential for understanding the mechanism of the negative electrode reaction in Li-metal battery cells. The physical and chemical property changes of the interface during the initial stages of the reaction should be investigated under operando conditions. In this study, we focused on the changes in the optical properties of the electrode surface film of the negative electrode of a Li-metal battery. Cu-based electrochemical surface plasmon resonance spectroscopy (EC-SPR) was applied because of its high sensitivity to optical phenomena on the electrode surface and its stability against Li-metal deposition. The feature of SPR reflectance dip depends on the optical properties of the electrode surface; namely, the wavelength and depth of the reflectance dip directly connected the refractive index and extinction coefficient (color of electrode surface film), which was confirmed by reflectance simulation. In the operando EC-SPR experiment, various changes in optical properties were clearly observed during the cycles. In particular, the change in the extinction coefficient was more remarkable at the second process than the first process of Li-metal deposition. By electrochemical quartz-crystal microbalance (EQCM) measurements, surface film formation was confirmed during the first Li-metal deposition process. The remarkable change in the extinction coefficient is based on the color change of the surface film, which is caused by the chemical condition change during Li-metal deposition cycles.

Study of the solid electrolyte interphase of Li-O2 battery electrolyte by analytical transmission electron microscopy.

Investigation of solid electrolyte interphases (SEIs) on negative electrode surfaces is essential to improve the stable charge-discharge performance of rechargeable lithium-air batteries (Li-O2 batteries). In this study, a direct investigation of SEI films is conducted using analytical transmission electron microscopy (TEM). A thin Cu specimen is prefabricated for TEM observation and is utilised as a model substrate for SEI formation. The electrochemical cell constructed using dissolved oxygen in the electrolyte exhibits a greater electrochemical overpotential during the Li-metal deposition process than that constructed with a pristine electrolyte. This suggests that different electrochemical passivation features occur in each different electrochemical cell. TEM observation confirms that the surface film formed by O2 dissolute electrolyte is a polycrystalline Li2O film with a thickness of ~5 nm, whereas the film formed by the pristine electrolyte is organic-based, amorphous-like and 20-50 nm thick. The dissolved oxygen molecules are more easily reduced than the components of the electrolyte, leading to the formation of Li2O as a stable passivation SEI film, which is expected to exhibit good charge-discharge features during the operation of the Li-O2 battery.

Viologen Derivatives Extended with Aromatic Rings Acting as Negative Electrode Materials for Use in Rechargeable Molecular Ion Batteries.

Many types of batteries have been proposed as next-generation energy-storage systems. One candidate is a rocking-chair-type "molecular ion battery" in which a molecular ion, instead of Li+ , works as a charge carrier. Previously, we reported a viologen-type derivative as a negative electrode material that releases and receives PF6 - anions during the charge-discharge process; however, its redox potential was not satisfactorily low. Further, the two potential plateaus of this material (difference=0.5 V) should be reduced. In this study, PF6 - salts of viologen (bipyridinium) derivatives extended by aromatic rings were synthesized to obtain a negative electrode material with a lower redox potential and small potential change during the charge and discharge processes. Some of the synthesized viologen derivatives were fluorescent even in solid-state electrodes. In the half-cell configuration, the prepared negative electrode materials showed average voltages of approximately 2 V (vs. Li+ /Li), which is lower than that of conventional viologen derivatives.

Improvement of the Battery Performance of Indigo, an Organic Electrode Material, Using PEDOT/PSS with d-Sorbitol.

Rare-metal-free and high-performance secondary batteries are necessary for improving the efficiency of renewable energy systems. Organic compounds are attractive candidates for the active material of such batteries. Many studies have reported organic active materials that show high energy density per active material weight. However, organic active materials, most of which exhibit low conductivity and low specific density, typically require a large amount of a conductive additive (>50 wt %) to obtain a high utilization rate. Therefore, organic active materials rarely display high energy density per electrode weight. High energy densities per electrode weight can be obtained using high weight fractions of active materials and low weight fractions of conductive additives. Herein, we report that a low-conductivity organic active material, indigo, showed improved net discharge capacity density when even a small amount of a conductive polymer composite, poly(3,4-ethylenedioxythiophene)/polystyrene sulfonic acid (PEDOT/PSS) with d-sorbitol, was used as both a binder and conductive additive. The cycle life was also improved by coating one side of the separator with the composite, which probably hindered the dissolution of the active material. A discharge capacity of 96% of the theoretical capacity of indigo and an improved cycle life were achieved with an electrode containing 80 wt % indigo and with a PEDOT/PSS-coated separator. The optimal fraction of the conductive binder was examined, and the mechanism of conductivity enhancement was discussed. The present scheme allows us to replace the dispersion solvent of the slurry, N-methylpyrrolidone, with water, which can reduce the environmental load during battery manufacturing processes.

Analytical Measurements to Elucidate Structural Behavior of 2,5-Dimethoxy-1,4-benzoquinone During Charge and Discharge.

Organic compounds as electrode materials can contribute to sustainability because they are nontoxic and environmentally abundant. The working mechanism during charge-discharge for reported organic compounds as electrode materials is yet to be completely understood. In this study, the structural behavior of 2,5-dimethoxy-1,4-benzoquinone (DMBQ) during charge-discharge is investigated by using NMR spectroscopy, energy-dispersive X-ray spectroscopy, magnetic measurements, operando Raman spectroscopy, and operando X-ray diffraction. For both lithium and sodium systems, DMBQ works as a cathode accompanied with the insertion and deinsertion of Li and Na ions during charge-discharge processes. The DMBQ sample is found to be in two-phase coexistence state at the higher voltage plateau, and the radical monoanion and dianion phases have no long-distance ordering. These structures reversibly change into the original neutral phase with long-distance ordering. These techniques can show the charge-discharge mechanism and the factors that determine the deterioration of organic batteries, thus guiding the design of future high-performance organic batteries.

Molecular ion battery: a rechargeable system without using any elemental ions as a charge carrier.

Is it possible to exceed the lithium redox potential in electrochemical systems? It seems impossible to exceed the lithium potential because the redox potential of the elemental lithium is the lowest among all the elements, which contributes to the high voltage characteristics of the widely used lithium ion battery. However, it should be possible when we use a molecule-based ion which is not reduced even at the lithium potential in principle. Here we propose a new model system using a molecular electrolyte salt with polymer-based active materials in order to verify whether a molecular ion species serves as a charge carrier. Although the potential of the negative-electrode is not yet lower than that of lithium at present, this study reveals that a molecular ion can work as a charge carrier in a battery and the system is certainly a molecular ion-based "rocking chair" type battery.

Formation of uniform ferrocenyl-terminated monolayer covalently bonded to Si using reaction of hydrogen-terminated Si(111) surface with vinylferrocene/n-decane solution by visible-light excitation.

Electrochemically active self-assembled monolayers (SAM) have been successfully fabricated with atomic-scale uniformity on a silicon (Si)(111) surface by immobilizing vinylferrocene (VFC) molecules through Si-C covalent bonds. The reaction of VFC with the hydrogen-terminated Si (H-Si)(111) surface was photochemically promoted by irradiation of visible light on a H-Si(111) substrate immersed in n-decane solution of VFC. We found that aggregation and polymerization of VFC was avoided when n-decane was used as a solvent. Voltammetric quantification revealed that the surface density of ferrocenyl groups was 1.4×10(-10) mol cm(-2), i.e., 11% in substitution rate of Si-H bond. VFC-SAMs were then formed by the optimized preparation method on n-type and p-type Si wafers. VFC-SAM on n-type Si showed positive photo-responsivity, while VFC-SAM on p-type Si showed negative photo-responsivity.

Application of a microfluidic sperm sorter to the in-vitro fertilization of porcine oocytes reduced the incidence of polyspermic penetration.

The objective of this study was to use a microfluidic sperm sorter (MFSS), designed to isolate motile human spermatozoa with laminar flows (no centrifugation), for porcine IVF. Boar spermatozoa were diluted at 1 x 10(8) cells/mL with a diluent containing 20% seminal fluid and flowed with modified TCM-199 (mM199, with 5 mM caffeine) to introduce motile sperm into the exit chamber for IVF. In Experiment 1, after flowing for 5 min, sperm concentration varied significantly among specific sites within the MFSS collecting chamber (range, 0.8 +/- 0.5 x 10(4) to 575.0 +/- 56.3 x 10(4) cells/mL; mean +/- SEM). In Experiment 2, when porcine IVM oocytes were placed at three locations in the MFSS exit chamber (where only motile spermatozoa accumulated) and subsequently cultured in caffeine-free mM199 for 8 h, sperm penetration rate was not significantly different among places (86.1 +/- 10.5 to 100%), but the monospermic penetration rate was lower (P < 0.05) in oocytes 3.5 mm from the exit position (12.5 +/- 4.8%) than those at 7.5 mm (53.1 +/- 6.0%) or further (41.9 +/- 2.8%) from the exit. In Experiment 3, the normal fertilization index (ratio of monospermic oocytes to number of oocytes examined) 8 h after insemination was higher (P < 0.05) in the MFSS-IVF system (0.375 +/- 0.040) than both standard IVF and transient IVF (0.222 +/- 0.028 and 0.189 +/- 0.027, respectively, with co-culture for 8 h and for 5 min). Developmental competence of fertilized oocytes (blastocyst formation) was higher (P < 0.05) in the MFSS-IVF system (40.9 +/- 2.3%) than in either standard or transient IVF (22.6 +/- 1.4 and 33.7 +/- 3.5%). In conclusion, brief co-culture of porcine oocytes with spermatozoa gradually accumulated in the MFSS chamber improved the efficiency of producing monospermic fertilized embryos and blastocysts. Furthermore, efficiencies were significantly affected by oocyte location within the chamber.

Alkyl and alkoxyl monolayers directly attached to silicon: chemical durability in aqueous solutions.

For practical application of self-assembled monolayers (SAMs), knowledge of their chemical durability in acidic or basic solutions is important. In the present work, a series of SAMs directly immobilized on a silicon (111) surface through Si-C or Si-O-C covalent bonds without a native oxide layer were prepared by thermally activated chemical reactions of a hydrogen-terminated Si(111) substrate with linear molecules, i.e., 1-hexadecene, 1-hexadecanol, 1-dodecanol, and n-dodecanal, to investigate the durability of the SAMs to HF and Na2CO3 solutions. While grazing incidence X-ray reflectivity measurements showed that all the as-prepared SAMs had almost the same film density and molecular coverage, keeping the original step and terrace structure of Si(111) as is observed by atomic force microscopy, they gave different degradation behaviors, i.e., pitting and concomitant surface roughening in both solutions. 1-hexadecene SAM was stable against immersion in both solutions, while the other SAMs were damaged within 60 min, most likely due to the difference in chemical bonding modes at the SAM/Si interface, i.e., Si-C and Si-O-C.

Regulation of pattern dimension as a function of vacuum pressure: alkyl monolayer lithography.

Photopatterning of a hexadecyl (HD) monolayer has been demonstrated using vacuum ultraviolet (VUV; lambda = 172 nm) light under controlled vacuum pressure with the objective of minimizing the pattern dimension. X-ray photoelectron spectroscopy (XPS) and lateral force microscopy (LFM) studies reveal that photodegradation of the HD monolayer not only is limited to the regions exposed to VUV but also spreads under the masked regions. The strong oxidants generated by VUV irradiation to atmospheric oxygen and water vapor diffuse toward the masked regions through the nanoscopic channels and photodissociate the monolayer under the masked area, near the photomask apertures, resulting in broadening of the photopattern. Such broadening decreases with decreased vacuum pressure inside the VUV chamber, associated with a decrease of oxidant concentration and reduction of their diffusion. Gold nanoparticles (AuNPs) were immobilized on the VUV patterned features to probe the dimension of the chemically active pattern. Field emission electron microscopy reveals the construction of 565 nm wide pattern features at a vacuum pressure of 10 Pa. This pattern widens to 1,030 nm at 10 (4) Pa using the same size apertures (500 nm) as printed on the photomask. This study provides insight for fabricating submicron patterns with high reproducibility and its exploitation for different applications, which includes the patterning of nanoparticles, biopolymers, and other nano-objects at submicron dimensions.

Artificial insemination with canine spermatozoa frozen in a skim milk/glucose-based extender.

Due to the recent outbreak of avian influenza, transportation of frozen canine semen with egg yolk has been sharply restricted. Thus, there is urgent need to develop a novel egg yolk-free extender for freezing canine spermatozoa. In the present study, the effect of using skim milk/glucose (SG)-based extender without egg yolk on the motility and fertilizing capacity of canine spermatozoa frozen-thawed in the presence of glycerol was examined. There was a tendency for the proportion of motile spermatozoa exposed to SG-based extender for 3 h to be higher than that exposed for 1 h, but the difference was not significant. The motility and other viability parameters of canine spermatozoa after thawing were similar to those obtained with an egg yolk-based extender. When spermatozoa frozen with SG-based extender containing glycerol after 3 h exposure were transcervically inseminated into 2 recipient bitches, a total of 6 pups were obtained. These results suggest that a simple extender composed of skim milk, glucose and glycerol is useful for cryopreservation of canine spermatozoa, which may contribute to improved exchange of genetic material and efficient production of companion and working dogs, such as guide dogs for the blind.

Thermal immobilization of ferrocene derivatives on (111) surface of n-type silicon: parallel between vinylferrocene and ferrocenecarboxaldehyde.

Monolayers attached to a Si(111) surface through Si-C-C or Si-O-C covalent bonds were prepared by the thermally activated reaction (150 degrees C) of vinylferrocene (VFC) or ferrocenecarboxaldehyde (FCA) molecules with hydrogen-terminated Si(111) substrate in order to compare their reactivities. The resulting monolayers gave a couple of redox waves on voltammograms due to ferrocenyl moieties tethered at the surface. The voltammetric quantification revealed that the growth of electrochemically active layers was terminated within 5 h and the final surface coverages of the active ferrocenyl moieties were 58% and 16% for VFC- and FCA-based monolayers, respectively, indicating that the aldehyde molecule is less reactive. X-ray photoelectron spectroscopy and ellipsometry, however, gave an indication that the growth of the VFC layer did not self-terminate and proceeded beyond a monolayer, while this overgrown part of the layer was not electrochemically active.