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In liquid electrolytes used for a battery, various metal complexes are formed as a result of ion-solvent and ion-ion interactions, which strongly influence the properties of the electrolyte and thus the performance of the battery. Therefore, the structural characterization of such complexes is of great importance. In this study, the anomalous X-ray scattering (AXS) technique was applied to the potassium hydroxide solution including ∼0.3 mol % zinc, which is widely used in various batteries such as the alkaline battery. In spite of the small amount of the metallic ions, we have successfully extracted a local structure around zinc after careful data analysis. The obtained pair distribution function exhibited not only the short-range correlation corresponding to the Zn-O bond within the zincate anion but also a medium-range correlation above 3.5 Å. The present study demonstrates the capability of the AXS technique to detect local structures around dilute metallic ions in liquid electrolytes, which will largely extend the applicable range of this technique, especially to the field related to batteries.

Enhancing zinc electrode rechargeability is a key for realizing zinc air batteries as promising next generation batteries. Addition of hydrophilic organic materials in alkaline electrolytes has been shown to be effective in durability improvement, however, the oxidation of the organic materials at the positive electrode of batteries should be overcome. Here a solution for this issue is proposed by using organic materials with large molecular weight and keeping them away from the positive electrode by setting a membrane between negative and positive electrodes. It is shown through permeability, solubility, and zinc-nickel cell tests that a selected organic material is impermeable to a OH− permeable membrane, highly soluble in the alkaline electrolyte, and has a positive effect on zinc electrode durability without interfering the positive electrode reaction, which can greatly contribute to the establishment of long-life zinc air batteries.

We report the solid-state reaction of MoO2 nanosheets, obtained from the soft-chemical delamination of Na0.9Mo2O4, into metallic Mo2C single layers that constitute a new family of versatile carbide nanosheets. This so-called pseudotopotactic reaction, i.e., conversion from nanosheet to nanosheet, is aided by the use of cationic polymers as binders for the film growth based on electrostatic self-assembly. Compared to Mo2C in the bulk form, 2D anisotropic Mo2C sheets having a larger surface-area-to-volume ratio are of significant use in potential electrochemical applications, and it is also worth noting that the thickness of Mo2C sheets can be controlled in the nanometer range by altering the stacking number of the precursor nanosheets.

The effects of surfactants as organic additives to electrolyte solutions on potential oscillation behavior and Zn electrodeposition were observed. Applying a constant current density (−20 mA cm−2), we induced the potential oscillation of electrochemical Zn deposition in aqueous solutions of KOH, ZnO, and surfactants. Potential oscillation behavior for Zn electrodeposition was strongly affected by the presence of surfactants. While an anionic surfactant (sodium dodecyl sulfate) slightly increased the period of potential oscillation, even small amounts of nonionic (Triton X-100) and cationic surfactants [cetyltrimethylammonium bromide(CTAB)] greatly increased the period of potential oscillation. The presence of CTAB in an electrolyte produced small spherical Zn deposits, which clearly implies that CTAB plays a role in suppressing dendrite formation during Zn deposition.

Zinc, the most historical material for battery application, is one of the candidates for the high capacity electrodes of the next-generation secondary batteries, and has been applied in Zn/Air, Zn/NiOOH. These zinc-based batteries commonly employ aqueous alkaline electrolytes that have some advantages such as high ionic conductivity for high rate capability and non-flammability for high safety, which are particularly attractive for the mobile and EV applications. However, their insufficient cycle life due to the deterioration modes such as zinc dendrite formation, densification and shape change, has limited the widespread use of the zinc-based secondary batteries. In particular, the shape change is known to be a serious problem, in which the active material is gradually lost at the edge and agglomerates in the center of the electrode in the course of cycling, resulting in the capacity fade. For suppressing this undesirable redistribution of the zinc electrode, it is essential to clarify the growth mechanism of the shape change phenomenon. So far the growth mechanism has been studied and analyzed, especially in the view point of the reaction (current) distribution, by various methods such as direct visual observation, tracing radioisotope, monitoring current distribution with the use of divided electrode, and calculating mathematical model. As the shape change proceeds dynamically with charging-discharging cycles causing electrode composition changes, the detailed observation of the composition change of zinc species during the cycling offer fruitful information on the reaction distribution to understand the growth mechanism of the shape change precisely and key to improve it. In this study, we evaluate the distribution of zinc species in Zn/NiOOH cells to elucidate the way the shape change occurs in the course of cell cycling. References: [1] A. Nakata , H. Arai , H. Murayama , K. Fukuda , T. Yamane , T. Hirai , Y. Uchimoto , J. i. Yamaki , and Z. Ogumi,APL Materials 6, 047703 (2018); https://doi.org/10.1063/1.5011272.

Zinc-based secondary batteries are promising power sources with high energy density but their deterioration modes such as dendritic growth and shape changes need to be solved. These drastic morphology changes of the zinc electrode come from the nature of the discharged product that is easily dissolved in the alkaline electrolyte as zincate species. In this study, we attempt to preserve the zinc electrode morphology by employing the zinc oxidation-reduction processes in the vicinity of electrode, which is attained by controlling the electrolyte solvent property with mixing an organic solvent propylene carbonate (PC). The results show that the use of PC-water mixed solvent is effective in restricting the zincates dissolution into the electrolyte and preserving the zinc electrode morphology with no dendrite formation through 500 oxidation-reduction cycles is demonstrated in the electrolyte with high PC concentrations.

Zinc is a promising negative electrode material for aqueous battery systems whereas it shows insufficient rechargeability for use in secondary batteries. It has been reported that leaf-like dendrite deposits are often the origin of cell-failure, however, their nature and behavior on discharge (oxidation) - charge (reduction) cycling have been only poorly understood. Here we investigate the transformation of the leaf-like zinc dendrites using ex-situ scanning electron microscopy, X-ray computational tomography and in-situ X-ray diffraction. It is shown that the leaf-like zinc dendrites obtained under diffusion-limited conditions are nearly completely dissolved at a low oxidation current density of 1 mA cm−2 and cause re-evolution of the zinc dendrites. Oxidation at a high current density of 10 mA cm−2 leads to the formation of leaf-like zinc oxide residual products that result in particulate zinc deposits in the following reduction process, enabling good rechargeability. The reaction behavior of this oxide residue is detailed and discussed for the development of long-life zinc electrodes.

For the use of the zinc anode in secondary batteries, it is necessary to solve the “shape change” deterioration issue in that zinc species agglomerate in the center of the electrode to fade the available capacity. The local chemical compositions of the zinc electrodes during “shape change” were precisely analyzed using the synchrotron X-ray diffraction mapping analysis of practical zinc-nickel cells in a non-destructive manner. The in situ Zn/ZnO mapping shows that metallic Zn deposition chiefly occurs in the periphery of ZnO while ZnO are left in the center of electrode like a hill on charging. On discharging, the ZnO hill grows to the perpendicular direction on the electrode while metallic zinc is oxidized and dissolved. These findings allow us to propose a mechanism for the shape change; thus dissolved zincate species are decomposed on the ZnO hill during discharging to be accumulated in the center of the electrode. It is suggested that suppressing zincate dissolution and non-uniform zinc deposition slow the growth rate of the ZnO hill to enhance the cyclability of zinc-based secondary batteries.

The liquid phase deposition (LPD) of metal oxide thin films at the liquid−liquid interface was investigated. Just after the start of the LPD reaction, depositions were observed continually at the liquid−liquid interface. The deposition grew two-dimensionally into a self-standing film with thickness of 1 μm and domain size of up to ca. 1 mm without any solid substrates. The self-standing film was formed with asymmetrical morphology, which consisted of flat surface on the side of the liquid−liquid interface and relatively rough surface on the side of the bulk solution. The structure was characterized by Raman spectroscopy, confirming that metastable ammonium titanium oxide fluoride (NH4TiOF3) was first deposited at the liquid−liquid interface, on which anatase-type titanium oxide (TiO2) was deposited second to forming the asymmetrical bilayer structure. It was suggested that the metal fluoride complex of the precursor was concentrated in the vicinity of the liquid−liquid interface compared with the solid−li...

In this study, we successfully synthesized monodispersed metal oxide nanoparticles of high-temperature phases such as monoclinic VO 2 , orthorhombic Ta 2 O 5 under an ambient condition without any post-annealing process, applying the liquid phase deposition (LPD) method in the confined system of reverse micelle (RM). It was suggested that the obtained nanoparticles were highly crystallized due to the depression of surface disorder, indicated by Raman spectrum of rutile type SnO 2 nanoparticles. This procedure represents a simple route for the production of highly crystallized nanoparticles with potentially interesting applications.

To develop a preparation method for size-controlled nanoparticles, we applied a liquid-phase infiltration (LPI) method to the reverse micelle (RM) reaction. The average sizes of the nanoparticles were 4.6 and 2.0 nm for TiO 2 and FeO, respectively. The size distribution was narrow, and particle crystallization was promoted by the nanoscale reaction field. We have also fabricated the TiO 2 /Au films with a highly ordered periodic structure by the LPI method using colloidal crystals as a template. The LPI process is conducive to the preparation of advanced nanoceramics with highly ordered structures.

Summary Cycle performance of the zinc oxide electrode improves by mixing the organic solvent in the electrolyte. However, the organic solvent is concerned to be decomposed at the positive electrode. In order to solve the problem, the zinc oxide negative and the positive electrodes are separated by a membrane, and the organic solvent is added only in the negative electrode side. As a result, the organic solvent decomposition at the positive electrode is avoided and thus the cell shows good cycle performance. 1. Introduction Zinc is widely used as a negative electrode material for primary batteries with its strong reducing power and a high capacity. However, its use as a rechargeable electrode has been limited due to insufficient cycle life. We have shown that water-organic co-solvent electrolytes are effective for restricting the dissolution of the zinc species and thus improving the cycle performance [1]. On the other hand, organic solvents are generally vulnerable to oxidation and hence such water-organic co-solvent electrolytes can be incompatible with positive electrodes such as Ni(OH)2and air electrodes. This study describes a cell setup that is effective for both zinc electrode rechargeability and positive electrode compatibility. Here a membrane that suppresses the transfer of the organic molecules was employed in the cell to show the Ni(OH)2electrode compatibility. 2. Experimental Zinc composite electrodes consisted of ZnO, PbO, carbon and a binder, pasted on a copper current collector. The potential of the zinc negative electrode was measured versus an Hg/HgO reference electrode. The positive electrode was a sintered nickel (Ni(OH)2) electrode. The electrolyte consisted of a 4 M KOH aqueous solution. In the negative electrode side, organic molecules such as alcohol were added to the KOH solution. A hydrophilic membrane was used as a separator to suppress the transfer of the organics to the positive electrode. 3. Results and Discussion The membrane was permeable to small organics (MW A large organic was selected and their effect on the cycle performance was examined. As shown in Fig. 1(a), the use of the organic is effective for improving the cycle life of the zinc electrode. The sintered nickel positive electrode was degraded when tested without a membrane, indicating the reactivity of the organic at the positive electrode. In contrast, when a proper membrane was used as the separator, the nickel electrode functioned without any problem, showing that the organic transfer through the membrane can be disregarded. Small organics were detrimental to the nickel electrode even if a membrane was set between the positive and negative electrodes. The porous structure of the zinc electrode was observed by SEM analysis. Figure 1(b) shows that there are many pores in the composite electrode prior to the cycling test. After 40 charge-discharge cycles, the porous structure were maintained when the organic was used whereas the pores were mostly clogged without using the organic, as shown in Figs. 1 (b) and (c). These results show that the densification [2], which is a typical deterioration mode of the zinc electrode, was suppressed and there were on-site zinc dissolution and deposition with the addition of the organic. It is deduced that the water activity in the electrolyte was reduced in the presence of the organic species and thus the zincate dissolution was suppressed. The shape change behavior [2], another typical deterioration mode of the zinc electrode, was observed by synchrotron X-ray diffraction mapping. The measurement using the zinc-nickel cells demonstrates the effect of the organic also on the shape change behavior. 4. Acknowledgment This work was supported by RISING project of NEDO. 5. References [1] A. Nakata, H. Arai, T. Yamane, T. Hirai and Z. Ogumi, J. Electrochem. Soc., 163, A50-A56 (2016). [2] F.R. McLarnon and E.J. Cairns, J. Electrochem. Soc., 138, 645-664 (1991). Figure 1

Zinc electrodes are of great interest as a candidate for metal negative electrode that has high theoretical energy density, low cost and high safety owing to the use of aqueous electrolytes. However, rechargeable zinc electrodes still suffer from poor cycle life due to dendrite growth and shape change. These degradation phenomena of the zinc electrode are known to be promoted by the high solubility of the zinc species in the electrolyte. In an strong alkaline electrolyte usually employed in aqueous alkaline batteries, a discharge reaction of zinc takes place to produce Zn(OH)4 2-. Such soluble discharge products of zinc can migrate through the electrolyte, resulting in a redistribution of zinc. Therefore, inhibiting the migration of the discharge products of zinc are thought to be effective in minimizing dendrite growth and shape change. In this study, based on the concept of inhibition of the migration of the zinc discharge products into electrolyte, we report the synthesis, characterization and charge-discharge characteristics of porous-TiO2-coated Zn. We have newly synthesized zinc particles uniformly coated with porous TiO2 layers (porous-TiO2-coated Zn), as follows. Fine zinc powder (ca. 0.1-0.6 μm in diameter) was dispersed in the solution of titanium tetrabutoxide diluted with 1-butanol. While stirring and heating this solution, aqueous ammonia was added to form TiO2-precursor nanoparticles by the hydrolysis of titanium tetrabutoxide. Subsequently, in order to attach TiO2-precursor nanoparticles to the surface of zinc particles, urea as a linker molecule was added into this solution. After stirring and heating this solution, the samples obtained by filtration and washing with distilled water were dried and calcined in air. Core particles and uniform coating layers with the thickness of approximately 40 nm were observed in TEM images of the cross-section of the porous-TiO2-coated Zn particles. From a result of EDX analysis, it can be concluded that the coating layers mainly consist of titanium and oxygen. To further elucidate the characteristics of TiO2 coating layers, the pore-size distributions of uncoated-Zn and porous-TiO2-coated Zn were evaluated from nitrogen desorption isotherm. The porous-TiO2-coated Zn contains mainly pores with diameters smaller than 10 nm, in contrast to the uncoated-Zn which has no nano-sized pores. The peak pore diameter of porous-TiO2-coated Zn was 3.5 nm. This indicates that the porous-TiO2-coated Zn is composed of dense zinc particles and nanoporous TiO2coating layers. Comparison of the cycle life between uncoated-Zn and porous-TiO2-coated Zn was carried out. The zinc electrode was assembled in pouch cells with a large and a small sintered Ni(OH)2/NiOOH electrodes, which were respectively used as the counter and reference electrodes. 4 M KOH aqueous solution saturated with dissolved ZnO was used as electrolyte. Test cells were subjected to charge-discharge cycling test at 298 K. During the charge-discharge cycling test, the test cells were charged at 0.5 C rate for 1.5 h (615 mAh/g-Zn, zinc utilization of 75 %) and discharged at 0.5 C rate either for 1.5 h or until the zinc electrode potential reached at the cut-off potential of -0.9 V vs. Hg/HgO. From the charge-discharge cycling tests, reproducible results were obtained that the average values of the cycle life for 3 test cells employed each uncoated-Zn and porous-TiO2-coated Zn were 20 cycles and 117 cycles, respectively. It was found that the negative electrode using the porous-TiO2-coated Zn as an active material has achieved more than 5 times longer cycle life than that using uncoated-Zn in spite of a small TiO2 content. We propose the mechanism of improving the cycle life by using porous-TiO2-coated Zn that porous TiO2 coating layers act as a protection layer for the zinc oxides films formed through the discharge reactions and the pores of the TiO2 layers (< 10 nm) are sufficiently small to keep the zinc oxides. It should be noted that the effect of the TiO2 coating on the cycle performance cannot directly be attributed to the physical inhibition of the Zn(OH)4 2- migration because the average pore size of 3.5 nm is too large to block the migration of Zn(OH)4 2-. Acknowledgement This work was supported by the Research and Development Initiative for Scientific Innovation of New Generation Batteries (RISING) project from NEDO in Japan.

Introduction Zinc-based secondary batteries are promising power sources as inexpensive and high energy density systems, however, they have not fully been established due to the insufficient lifetime of the zinc electrode, mainly caused by the dendrite growth and shape change [1]. To elucidate how the deterioration proceeds, many trials have been made. We have employed operando X-ray diffraction (XRD) [2] and X-ray fluorescence (XRF) imaging [3] to find that the zinc species formed during discharging is dissolved in the electrolyte at least for several minutes before it is precipitated as ZnO even if the electrolyte is preliminarily saturated with ZnO, implying supersaturation of the zinc species. Such dissolved zinc species can induce undesirable morphology change during cycling to cause deterioration. To suppress the dissolution of the zinc species, we have proposed water activity control by using hydrophilic organic compounds dissolved in the alkaline electrolyte [4]. Namely, the formation of the soluble zincate anions Zn(OH)4 2- formed by the electrochemical reaction (1) can be suppressed by moving the equilibrium in the chemical reaction (2) to the right hand side if the water activity is decreased. It has been shown that the addition of the organic compounds decrease the vapor pressure (water activity) and ZnO solubility, leading to long lifetime of the zinc electrode without dendrite growth. Zn + 4OH- = Zn(OH)4 2- + 2e- (1) Zn(OH)4 2- = ZnO + H2O + 2OH- (2) In this study we examine in situ X-ray diffraction (XRD) mapping to show how the addition of the organic compound affects the shape change behavior of the zinc electrode. Experimental Porous ZnO composite electrodes were formed on the copper current collectors and were sandwiched by two NiOOH counter electrodes, inserted with non-woven separators in the experimental cells. They were cycled with 50% utilization in aqueous KOH solutions saturated with ZnO. Organic compounds were occasionally added to the electrolyte. Attention was paid to undesirable oxidation of the organic compound at the counter electrode not to occur. The ZnO and metallic zinc distribution in the zinc electrode of a rectangle shape was evaluated in a non-destructive manner by XRD mapping with ca. 900 pixels per electrode in a transmission mode at synchrotron beamline BL28XU, SPring-8 (Hyogo, Japan). Such non-destructive analysis can prevent undesirable composition changes (metallic zinc oxidation) that can occur when the electrode is exposed to air. Results and Discussion The addition of the organic compound in the alkaline electrolyte was proved by enhance cycle performance. The porosity of the ZnO composite electrode was maintained when the organic compound was added, suggesting that ZnO oxidation and reduction take place without morphology changes. The formation of metallic zinc and ZnO on reduction and oxidation of the zinc electrode, respectively, was monitored by the XRD mapping. On reduction, it was found that metallic zinc was preferentially formed at the periphery of the rectangle. This is probably because of good supply of ions and electrons there. On the other hand, ZnO growth was observed mainly in the center of the electrode, typical of shape change. If metallic zinc formed at the periphery of the electrode is oxidized on the spot, such shape change is unlikely to occur. This implies that zinc transportation through the electrolyte results in the shape change. The shape change can lead to the formation of inactive ZnO in the center of the electrode with insufficient electrical contact with the current collector and finally to the capacity loss. The shape change was suppressed with the addition of the organic compound in the electrolyte; more uniform formation of metallic zinc and ZnO was observed. It is thus expected that the organic compound reducing the water activity contributes to suppression of the zinc dissolution and fixation of the zinc species at the electrode for better rechargeability. Acknowledgment This work was supported by RISING of NEDO. Reference [1] F.R. McLarnon and E.J. Cairns, J. Electrochem. Soc., 138, 645-664 (1991). [2] A. Nakata et al., Electrochim. Acta, 166, 82-87 (2015). [3] A. Nakata et al., Electrochemistry, 83, 849-851 (2015). [4] A. Nakata et al., J. Electrochem. Soc., 163, A50-A56 (2016).

1. Introduction Zinc air batteries are safe and inexpensive aqueous systems with a high theoretical energy density of 1350 Wh/kg (based on zinc mass). The primary zinc air cells have been long used as power sources for hearing aid. Attemps have been made for more than 40 years to use them as electrically rechargeable (secondary) systems, however, the insufficient lifetime of both zinc and air electrodes are still unsolved issues. Recent progress on the air electrode shows promise for better rechargeability. This study focuses on the improvement of the zinc electrode cyclability to show the possibility of “beyond lithium ion batteries”. 2. Results and Discussion Morphology changes such as dendrite formation and shape changes have been indicated as the primary origin of zinc electrode deterioration [1]. Here we apply synchrotron-beam assisted analytical methods, which are currently used for lithium ion systems, to the zinc electrode system to clarify the underlying mechanism. Operando X-ray diffraction [2] and operando X-ray fluorescence imaging [3] suggests that the soluble zincate is the origin of the morphology changes. Namely, zincate anions Zn(OH)4 2-formed by the electrochemical reaction (1) diffuse away from the electrode during discharging before they are decomposed by the following chemical reaction (2) to form the final product zinc oxide ZnO. Zn + 4OH- = Zn(OH)4 2-+ 2e- (1) Zn(OH)4 2- = ZnO + H2O+ 2OH- (2) To restrict the zinc solubility by moving the equilibrium of reaction (2) to the right hand side, H2O activity control was applied by adding organic solvents in alkaline electrolytes [4]. The effect of propylene glycol (PG) was intensively examined as follows. Figures 1(a) and 1(b) show that the addition of PG effectively limits the thermodynamic solubility of ZnO and also kinetically assists the decomposition of supersaturated zinc species in the alkaline solution. The zinc electrode with PG mixed solvents exhibited long cycle life as shown in Fig. 1(c) at a high zinc utilization rate of 75%, revealing the possibility of attaining both long cycle life and high energy density. The vulnerability of PG to oxidation at the air electrode can be evaded by using organic solvents with higher molecular weights. In addition, surface coating of the zinc particles are also effective in enhancing the rechargeability, owing to the zinc oxidation/reduction processes inside the shell of the coat. Acknowledgment This work was supported by the Research and Development Initiative for Scientific Innovation of New Generation Batteries (RISING) project of NEDO (Japan). References [1] F.R. McLarnon and E.J. Cairns, J. Electrochem. Soc., 138, 645 (1991). [2] A. Nakata, H. Murayama, K. Fukuda, T. Yamane, H. Arai, T. Hirai, Y. Uchimoto, J. Yamaki and Z. Ogumi, Electrochim. Acta, 166, 82 (2015). [3] A. Nakata, K. Fukuda, H. Murayama, H. Tanida, T. Yamane, H. Arai, Y. Uchimoto, K. Sakurai and Z. Ogumi, Electrochemistry, 83, 849 (2015). [4] A. Nakata, H. Arai, T. Yamane, T. Hirai and Z. Ogumi, J. Electrochem. Soc., 163, A50 (2016). [5] A. Nakata, T. Kakeya, M. Ono, H. Arai and Z. Ogumi, The 228th Electrochemical Society Meeting, Abstract No. 208 (2015). [6] T. Kakeya, A. Nakata, H. Arai and Z. Ogumi, 56thBattery Symposium in Japan, 1G16 (2015). [7] M. Ono, A. Nakata, H. Arai and Z. Ogumi, 56th Battery Symposium in Japan, 1G17 (2015). Figure 1

The continuous development of silicon devices has been supported by fundamental understanding of the two interfaces that predict the device properties: high-dielectric oxide (high-k)/SiO2 and SiO2/Si. In the absence of metal electrode fabrication, it is challenging to use spectroscopic approaches to deduce the electric dipoles in these interfaces for the prediction of electrical characteristics such as the leakage current and threshold voltage. Here, we propose a method to analyze the permanent dipole at the high-k/SiO2 interface by surface-charge-switched electron spectroscopy (SuCSES). An electron flood gun was used to switch the electrical polarity at the insulating surface to extract the interface-dipole contribution from the macroscopic dielectric polarization in the high-k/SiO2/Si stack structure. TaO3− nanosheet (TaNS) crystallites, which are a family of high-k tantalate materials deposited on the SiO2/Si substrates, were annealed to prepare a nanoscale model interface. The properties of this inter...

Introduction Zinc is an ideal negative electrode material for batteries with aqueous electrolytes, owing to its high reducing power of -1.26 V vs. SHE and high specific capacity of 820 mAh g-1. However, zinc-based secondary batteries have not been established yet due to the insufficient rechargeability, as various deterioration modes of zinc anodes such as dendrite short-circuit, densification and shape changes lead to their limited cycle life and prevent the practical use as secondary batteries. The origin of these deterioration modes are highly soluble nature of the discharge products (eq.1) tetrahydroxozincate anions (Zn(OH)4 2-) in the alkaline electrolyte whose solubility is ca. 1 mol dm-3 (M) in 8 M potassium hydroxide (KOH) aqueous solution for instance, that are not stored in the vicinity of the electrode. The Zn(OH)4 2-is finally decomposed and forms zinc oxide (ZnO) precipitation according to the subsequent chemical reaction (eq.2). Zn + 4OH- = Zn(OH)4 2- + 2e- (1) Zn(OH)4 2- = ZnO + 2OH- + H2O (2) In this paper, we focus on the water activity in equation 2 to reduce the zincate solubility. The reduction of water activity is expected to promote ZnO formation in the vicinity of electrode surface just after the zinc oxidation in equation 1 because equation 2 proceeds in the right side to lead to the soluble Zn(OH)4 2-decomposition and ZnO precipitation. It is shown that the use of alkaline electrolyte containing organic solvents improves the cycle life at high zinc utilization rates. The effect of organic solvents on the zincate solubility including zincate supersaturation is examined and discussed. Experimental We prepared 4 M KOH alkaline electrolytes containing organic solvent by dissolving anhydrous alcohol such as propylene glycol (PG) and 8 M KOH aqueous solution. The alkaline electrolytes with PG-water mixed solvent was saturated with zincate species by mixing ZnO powder and removing residual solid by centrifugation. We demonstrated charge-discharge tests with a three-electrode configuration. A working electrode (W.E.) was made of either planar zinc electrode deposited on copper plate or a porous ZnO electrode formed on the copper current collector. The W.E. electrode was sandwiched by two porous ZnO electrodes as counter electrodes inserted with non-woven separators. W.E. potential was monitored using a Hg/HgO reference electrode. The zinc cell was cycled with various utilization rate up to 75 % at various charge-discharge C-rate. Results and Discussion Figure 1 show the correlation between water pressure and zinc solubility in 4M KOH alkaline electrolyte containing the PG solvent. As shown in Fig.1 (a), the water pressure decrease with PG concentration monotonously, indicating the PG-water mixed solvent effectively suppress the water activity. Zincate solubility also decrease along with the suppression of the water activity. In addition to the thermostatic solubility of the zincate, the thermodynamic zincate supersaturation is also reduced to result in rapid precipitation of ZnO by using the PG-water mixed solvent (when compared with 4 M KOH). Using the alkaline electrolytes with PG-water mixed solvent, we evaluate charge-discharge cycle tests of zinc electrode. Figure 2 shows the cycle performance of zinc electrode with and without PG in 4 M KOH alkaline electrolyte at 75 % utilization of the theoretical capacity. In 4 M KOH without PG, the specific discharge capacity starts to decrease around 100th cycle and achieve 1/3 of the initial capacity at 200thcycle. On the other hand, with PG, the capacity keeps 75% utilization rate even after 900 cycles. After the cycle test, without PG, zinc was lost from the current collector, which was dissolved in alkaline electrolyte as supersaturated zincate species. On the contrary, with PG, zinc was left relatively uniform on copper substrate, owing to the suppression of zincate species dissolution in the PG-water mixed solvent. Other features such as suppression of dendrite formation and densification will be presented at the meeting. Acknowledgment This work was supported by RISING of NEDO. Figure 1

Introduction Zinc is an ideal negative electrode material for batteries with its high specific capacity and high reducing power. However, zinc-based secondary batteries have not been established yet due to the insufficient rechargeability caused by deterioration modes such as dendrite growth and shape changes [1]. Many trials have been made to elucidate how the deterioration proceeds, but they are mostly employed ex situ. Application of in situbattery analytical methods should provide fruitful information on the rechargeability of the zinc electrode system. In this study we examine X-ray diffraction (XRD) mapping to visualize the shape changes and projection-type X-ray fluorescence (XRF) imaging [2] to capture the zinc distribution near the electrode during cycling, and elucidate how the dissolution of the zinc species affects the rechargeability of the zinc electrode. Experimental The shape change phenomena were examined using porous ZnO electrodes formed on the copper current collectors. The ZnO electrode was sandwiched by two NiOOH counter electrodes, inserted with non-woven separators, and was cycled with 50% utilization in aqueous KOH solutions saturated with ZnO. The ZnO and Zn distribution was evaluated in a non-destructive manner by XRD mapping with ca. 900 pixels per electrode in a transmission mode at synchrotron beamline BL28XU, SPring-8 (Hyogo, Japan). The distribution of zinc species near the electrode was evaluated by projection-type XRF imaging in reflection geometry as follows. Zinc was deposited on a copper plate as a working electrode (WE) in ZnO containing 4 M KOH using zinc plate as a counter electrode (CE) and then was oxidized. The images were recorded every 5 s at 9.8 keV near the Zn-K absorption edge using a two-dimensional detector at BL28XU, SPring-8. Results and Discussion The Zn and ZnO formation on reduction and oxidation of the zinc electrode was monitored by XRD mapping. In the course of cycling the ZnO intensity started to decrease at the edge of the electrode. Figure 1(a) depicts the ZnO mapping after the 100threduction cycle in 8 M KOH (ZnO satd.), showing ZnO aggregated in the center of the electrode. This shape change correlated with the loss of the zincate species at the edge and the accumulation in the center leads to the formation of inactive ZnO due to the loss of electrical contact with the current collector and finally to the capacity loss. In contrast, in a less zinc soluble electrolyte of 4 M KOH (ZnO satd.), the shape change was limited as shown in Fig. 1(b), leading to longer cycle life. This implies the importance of fixation of zinc species at the electrode for better rechargeability. The projection-type XRF imaging near the WE clarifies many pillar-like deposits, namely dendrite, formed on the copper substrate (invisible) together with hydrogen bubbles on zinc reduction as shown in Fig. 1(c). A concentrated zincate zone containing such bubbles is seen on oxidation (Fig. 1(d)), indicating the formation of soluble zincate species even in 4 M KOH with ZnO saturation. The zinc rechargeability should also be affected by zinc supersaturation in the alkaline electrolyte and hence the observation of the zinc species in supersaturated solutions by XAFS and NMR would provide useful information. Acknowledgment This work was supported by RISING of NEDO. Reference [1] X.G. Zhang, in Encyclopedia of Electrochemical Power Source, Vol. 5, pp. 454 (2009). [2] A. Nakata et al., Electrochemistry, submitted. Figure 1

Introduction Zinc metal is an ideal electrode material for a battery using aqueous electrolyte, owing to its high capacity of 820 mAh g-1 and high reducing power. However, zinc-based secondary batteries have not been established yet, because several deterioration modes appear during discharge-charge cycle, such as dendrite short-circuit, densification and shape changes. They are the main obstacles to prolong cycle life of zinc-based secondary batteries. Especially, the shape change is a specific phenomenon in that the active material is accumulated in the center of the current collector. This behavior can cause decrease in the discharge capacity, so we should suppress this phenomenon. For this purpose, the mechanism and the structure of the shape change should be studied in detail. In this study, non-destructive synchrotron XRD analysis with precise local resolution was carried out for observing practical zinc composite electrode. Experimental We prepared a porous ZnO electrode (ca. 100 mAh), which consisted of ZnO and some additives, put on the Cu current collector. The electrode size were 18 mm width × 20 mm length. The ZnO electrode was sandwiched by two NiOOH positive electrodes, inserted with non-woven separators. The working electrode potential was monitored using the Hg/HgO reference electrode. The alkaline electrolyte used was a KOH aqueous solution saturated with ZnO. Charge-discharge tests were employed under the following condition; 0.5C-rate at CC-CV charge and CC-discharge with 50% utilization. The cut-off potential was set at -1.5 V and -1.1 V against Hg/HgO potential for charging and discharging, respectively. The electrode structure was evaluated in a non-destructive manner at synchrotron beamline BL28XU, SPring-8 (Hyogo, Japan) in a transmission mode. The X-ray energy and the beam size were 30 keV (λ=0.4133 Å) and 1mm width ×0.4 mm length. Results and Discussion The XRD pattern of the initial electrode (before charging) consisted of peaks that were assigned to ZnO, Cu current collector, and the Ni(OH)2 positive electrode. After 1st charging, metallic zinc appeared uniformly. However, the ZnO intensity at the edge of the electrode was reduced after 5th charging, which supports the dissolving rate is high on the periphery of the electrode. Fig. 1 shows the results after 100 charge-discharge cycles in the charged state. Fig. 1a indicates ZnO was aggregated in the center of the electrode. This was much pronounced when compared with after 5 cycle charging. During the charging-discharging cycles, ZnO on the periphery of electrode gradually dissolved and after 100 charge-discharge cycles ZnO was left only in the center of electrode, which looks like a zinc oxide island. In addition, ZnO islands were surrounded by zinc metal deposits as shown in Fig.1b. The distribution of zinc oxide and zinc metal depended on the alkaline concentration. In the concentrated alkaline electrolyte 8M KOH, ZnO islands grew in the out-of-plane direction of electrode. On the contrary, ZnO grew in the in-plane direction in the dilute alkaline electrolyte of 4M KOH. It is thus suggested that the shape change is originated from the zinc dissolution and deposition mechanism, and driven by the high solubility of zinc species in the alkaline aqueous electrolyte. Acknowledgment This work was funded by NEDO and RISING project.

We have successfully tailored a soft solution process for the synthesis of monodispersed SnO2 nanoparticles, applying a liquid phase deposition technique from an aqueous reaction mixture without an...

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We have studied a novel technique for the direct synthesis of two-dimensional metal oxide films with highly ordered periodic structure. TiO2 films with highly nano-ordered architectures were directly deposited on substrates at room temperature by the liquid phase infiltration (LPI) method. 2D arrays of several kinds of metal oxide rods with diameters ranging from ca. 100 to 1000 nm are fabricated by filling the holes in a Si wafer. We summarized the various kinds of ordered structured metal oxide thin film with this method and the other techniques which have been reported that a novel soft solution process for the direct synthesis of large-area well-crystallized oxides with 1D-3D ordered periodic structure has been developed based on the LPI method. Metal oxide thin films were deposited directly into the nano-space, and thus the nano-space was completely infiltrated with metal oxide. The LPI process provides a direct fabrication route for metal oxide films with highly ordered structures, enabling nanoscale modification of optical properties of photonic crystals.

Nanoscale materials are of great interest scientifically and technologically because of their potential to exhibit interesting properties which cannot be achieved in bulk materials. In particular, nanoparticles have attracted much interest owing to the quantum size effect which causes the peculiar optical and magnetic characters. Especially, nanocrystalline metal oxides have potential or demonstrated application in many technologies, including solar energy conversion, batteries, catalysis and ductile ceramics. It is well-known that the optical, electronic, and chemical properties of the quantum dots are dominated by physical size and the chemistry of their surface and crystal structure. For such materials, various fabrication methods were employed using various chemical and physical techniques. It is especially demanding to make crystalline metal oxide nanopaticles at ambient conditions, as the usual fabrication process performed in water-rich solvent mixtures results in a poor crystallinity which does not possess the desired electronic and relies on a high temperature recrystallization. We have developed and proposed the liquid phase deposition (LPD) method as a novel aqueous solution-based process to prepare various metal oxide thin films and/or nanostructures using ligand-exchange hydrolysis of metal-fluoro complexes and the F consumption reaction with boric acid, aluminum metal and so on[1-3]. The LPD process relies on the chemical equilibrium between the metalfluoro complex and metal oxide by the minute energy difference in the aqueous solution at ambient temperature, which is a typical soft solution process in the homogeneously mixed system. In this study, we investigated the LPD reaction with hydrophilic polymer of polyethyleneglycol known as green materials applied for electrolyte, in order to fabricate monodispersed metal oxide nanoparticles fabricated at ambient condition. For the preparation of nanosized particles of titanium oxide, the guest molecule of PEG were solvated into the metal-fluoro complex aqueous solution of (NH4)2TiF6. After mixing two components, H3BO3 aqueous solution was added into the treatment solution with rapid stirring. The mixed solution was kept in the 303K bath for 20 hours. After the LPD reaction, the solution was centrifuged, and the obtained precipitate was washed in the distilled water by ultrasonic apparatus three times to be separated from the residual PEG and byproducts. It was observed that the transmittance of transparent solution was quickly reduced by dropping boric acid solution into treatment solution and whitened within 10 minutes, although fluoride complex have been stable with only PEG molecules. It was maybe proceeding in boric acid reacted metalfluoro complex under LPD reaction mechanism. The typical TEM images of oxide nanoparticles obtained by the LPD process are shown in Fig.1. The TEM image show so many nanoparticels uniformly distributed without aggregation, whose particle diameter is the average of 3.8nm and standard deviation is 0.4 nm around 10%. The obtained powder was characterized by X-ray diffraction measurement and Raman spectroscopy. It is shown that fluoride complex degraded and generated anatase type of titanium oxide with small size crystallite. In detail investigation with high-resolution TEM, it is shown that the titanium oxide have highly crystallization, reacted under ambient condition as shown in Fig. 2. The particle size distribution was controllable in the degree of from 2-10 nm with PEG concentration. Moreover, the reactivity of metal-fluoride complex was also enlarged with PEG concentration, up to 70% of reactivity. These results may suggest that PEG interact with metal-fluoro complex, which is supported by XPS analysis and Raman spectroscopy study revealing PEG existence on the surface of nanoparticles. Consequently, monodispersed TiO2 nanoparticle was synthesized by the LPD process controlling the size and reactivity of metal-fluoro complex, using polyethyleneglycol. The present method represents a simple route for the production of crystalline metal oxide nanopartciles with potentially interesting applications at ambient condition.