Abstract: In search of room-temperature electrolytes for fluoride-shuttle batteries, fluorohydrogenate ionic liquids (FHILs) have emerged, showing high ionic conductivities and better operational practicality. To enhance the performance of these electrolytes, the charge–discharge behavior of copper metal as positive electrodes in FHILs was investigated in this study. In the [C 2 C 1 im][(FH) 2.3 F] (C 2 C 1 im = 1-ethyl-3-methylimidazolium) FHIL electrolyte, although the 1st discharge capacity of 599 mAh (g-Cu) −1 included the reductive reaction of surface oxide films, the 2nd discharge capacity of 444 mAh (g-Cu) −1 that corresponds to 53% of the theoretical capacity was achieved. However, the capacity declines to 167 mAh (g-Cu) −1 at the 20th cycle, indicating low capacity retention. In contrast, the adoption of [C 2 C 1 pyrr][(FH) 2.3 F] (C 2 C 1 pyrr = N -ethyl- N -methylpyrrolidinium) electrolyte confers improved cycleability across the cycles with a higher discharge capacity of 210 mAh (g-Cu) −1 at the 20th cycle. Scanning electron microscopy and energy-dispersive X-ray spectroscopy performed on the electrode surfaces confirm reduced electrode degradation characterized by suppressed aggregation of copper particles in [C 2 C 1 pyrr][(FH) 2.3 F] due to its low CuF 2 solubility compared with [C 2 C 1 im][(FH) 2.3 F]. Herein, we demonstrate the use of FHILs with low CuF 2 solubilities as a strategy for improving the charge–discharge performance of copper metal positive electrodes in fluoride-shuttle batteries.

Abstract: This study investigated the ionic species and electrochemical reduction of silicate ions at a solid graphite electrode in molten NaCl–CaCl 2 eutectic melts with various concentrations of O 2− ion at 1023 K. Silicate ion species in the melts with various O 2− /SiO 2 ratios ( r O 2 − / SiO 2 ) were determined by Raman spectroscopy. The dominant species was SiO 3 2− for r O 2 − / SiO 2 = 1.0, and SiO 4 4− for r O 2 − / SiO 2 = 1.5 and 2.0. From cyclic voltammetry, XRD, and SEM analyses, electrochemical reduction was indicated for SiO 3 2− and SiO 4 4− at more negative than 1.0 V and 0.80 V vs Na + /Na, respectively. Formation of CaSi 2 was confirmed at 0.50 V in all molten salts with r O 2 − / SiO 2 = 1.0, 1.5, and 2.0. The potential ranges for pure Si deposition are almost the same in molten salts with r O 2 − / SiO 2 = 1.0 and 1.5.

Abstract: Dual-carbon batteries (DCBs), in which both the positive and negative electrodes are composed of carbon-based materials, are promising next-generation batteries owing to their limited usage of scarce metals and high operating voltages. In typical DCBs, metal cations and anions in the electrolytes are consumed simultaneously at the negative and positive electrodes, respectively, which can rapidly deplete the charge carrier ions in the electrolytes. In this study, to solve this challenge, we focused on ionic liquids (ILs) as DCB electrolytes because they are solely composed of ions and are therefore intrinsically highly concentrated electrolytes. Charge–discharge behavior of the graphite positive electrodes was investigated in several IL electrolytes containing alkali metal cations (Li + , Na + , and K + ) and amide anions (FSA − and FTA − ; FSA = bis(fluorosulfonyl)amide, FTA = (fluorosulfonyl)(trifluoromethylsulfonyl)amide). It was found that FTA-based ILs conferred superior cycling stability and higher capacities to graphite electrodes compared to FSA-based ILs, which was explained by the suppression of the corrosion of the aluminum current collector at high voltages. The highest reversible capacity of approximately 100 mAh g −1 was obtained for the K-ion system using FTA-based ILs at 20 mA g −1 , which involved the formation of FTA–graphite intercalation compounds, as confirmed by ex situ X-ray diffraction.

Abstract: 1. Introduction Lithium secondary batteries have been widely used as power sources for small electronic devices. However, there are still many challenges for the widespread use as large storage batteries, such as the volatility and flammability of the organic-solvent-based electrolytes, and the uneven distribution and scarcity of lithium and cobalt resources. Therefore, we have been developing sodium and potassium-ion secondary batteries using FSA-based ionic liquid (IL) electrolytes (FSA = bis(fluorosulfonyl)amide) because the FSA-based ILs have excellent electrochemical stability and ionic conductivities, and sodium and potassium resources are abundant in the Earth’s crust [1,2]. In this study, we focus on FTA-based ILs (FTA = (fluorosulfonyl)(trifluoromethylsulfonyl)amide) as promising electrolytes for alkali metal-ion batteries. The FTA-based ILs have lower melting points and higher thermal stability than the FSA-based ones, which is advantageous for broadening the operating temperature range of batteries [3,4]. The physicochemical properties of M[FTA] –[C 4 C 1 pyrr][FTA] ILs (molar fraction x (M[FTA]) = 0.20; M = Li, Na, K, Rb, Cs; C 4 C 1 pyrr = N -butyl- N -methylpyrrolidinium) were investigated to discuss the effect of alkali metal-ion species. 2. Experimental All reagents were handled under argon atmosphere. The M[FTA]–[C 4 C 1 pyrr][FTA] ( x (M[FTA]) = 0.20; M = Li, Na, K, Rb, Cs) ionic liquids were prepared, and their ionic conductivities, viscosities, densities, and electrochemical windows were measured. The electrochemical windows were determined by cyclic voltammetry (CV) measurements using a three-electrode cell. The components of the three-electrode cell were as follows; a copper disk electrode and a glassy carbon disk electrode were used in the negative and positive potential region as the working electrodes, respectively, a platinum mesh electrode was used as the counter electrode, and an Ag + /Ag electrode was used as the reference electrode. 3. Result and discussion Fig. 1 shows the Arrhenius plots of the ionic conductivities for M[FTA]–[C 4 C 1 pyrr][FTA] ILs. The order of the ionic conductivities (mS cm −1 ) is Na(1.7) 〈 Li(2.0) 〈 K(2.2) 〈 Rb(2.3) 〈 Cs(2.6) at 298 K. In terms of ion size, the smallest Li + is considered to be the most favorable for the ionic conduction. However, its ionic conductivity is lower than those of K + , Rb + , and Cs + -based systems. One possible explanation is that the higher charge densities of Li + and Na + lead to the strong ion interaction with FTA − , resulting in the lower ion mobilities of alkali-metal ion complexes. We also measured their viscosities and densities of the FTA-based ILs at 273–368 K and constructed a Walden plot, which suggested that all the FTA-based ILs do not have a special ion conduction mechanism such as the Grotthuss mechanism. Fig. 2 summarizes the results of the CV measurements for M[FTA]–[C 4 C 1 pyrr][FTA] ILs. The order of their electrochemical windows (V) is Na(5.33) 〈 Li(5.45) 〈 K(5.58) 〈 Rb(5.64) 〈 Cs(5.74) at 298 K. The redox peaks were observed in the negative potential regions for all the electrolytes, which corresponds to the deposition and dissolution of alkali metals. On the other hand, irreversible oxidation currents were observed in the positive potential region for all the electrolytes. Since there was little difference in the anode limits for all the electrolytes, these oxidation currents are considered to be the decomposition of FTA − anions [4]. The trends of the physicochemical properties obtained in this study are very similar to those for FSA-based ionic liquids reported by our group [1] . R eferences [1] T. Yamamoto, K. Matsumoto, R. Hagiwara, T. Nohira, J. Phys. Chem. C , 121 , 18450 (2017). [2] R. Hagiwara, K. Matsumoto, J. Hwang, T. Nohira, Chem. Rec. , 18 , 1 (2018). [3] K. Kubota, T. Nohira, R. Hagiwara, H. Matsumoto, Chem. Lett. , 39 , 1303 (2010). [4] K. Kubota, H. Matsumoto, J. Phys. Chem. C , 117 , 18829 (2013). Figure 1

Abstract: Oxide-based all-solid-state batteries (OX-SSBs) have been expected as next generation rechargeable batteries. Although various kinds of high Li+ conductive solid electrolytes have been prepared such as Li 7 La 3 Zr 2 O 12 (LLZ), NASICON-structured Li 1.3 Al 0.3 Ti 2 (PO 4 ) 3 (LATP), LiTaPO4 etc, there are serious problems to develop low-resistive positive electrode/high Li + conductive solid electrolyte interface. Because these high Li+ conductive solid electrolytes are crystallized at 800-1000 ℃, high temperature sintering is common way to combine them with conventional crystalline insertion electrode materials (LiCoO 2 (LCO), LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM111) etc). However, both electrodes and solid electrolytes are composed of different elements with different concentrations, such high temperature sintering process frequently provide mutual diffusion region around the interface in addition to structural degradation and then seriously impede the interfacial resistance. Thus, one strategy to prevent those side reactions will be to apply low temperature sintering or densification process. We have focused on aerosol deposition, AD, a room temperature ceramic coating process. AD can realize quick speed and wide area ceramic coating and has been estimated as a cost-effective process technology for oxide-based energy conversion devices. AD make it possible to prepare electrode-solid electrolyte composite electrodes at room temperature and LiCoO 2 film electrode on LiPON film. In addition, AD enables us to investigate the effects of annealing temperature on the interfacial resistances and then limiting temperature for sintering. In this presentation, our recent works on Ox-SSBs using the AD will be introduced 1) 4V- and 5V-class bulk-type Ox-SSBs, 2) effects of annealing temperature on interfacial resistivity, an example of LCO-LATP system to determine limiting temperature for sintering.

Abstract: Abstract A high energy-density laminate cell with high safety and durability was realized. The energy-density of over 250 Wh/kg was obtained using high nickel-content cathode material of NCM811. Sufficient robustness against nail penetration test was also obtained in 60 Ah cell adopting a high heat-resistant separator and a heat-suppressing electrolyte (HSE). Moreover, a long durability of over 1000 charge/discharge cycles has been obtained by optimizing the surface conditions of the NCM811-based cathode electrodes with the S-based electrolyte additives. 1. Introduction Recently, the needs of high energy-density LIBs for EV have increased. Ensuring the safety characteristics and long duration are strongly required for high energy-density LIBs. For the next generation of EV, long cruising range is one of the most important elements in the market demand. Other than EV, there is expectation of high energy-density cells for realizing compactness of the battery system.High energy-density LIBs of around 250 Wh/kg have already been developed using cylindrical cells of lower than 5 Ah in cell-capacity in recent years [1]. It is considered that the cylindrical cells are suitable for higher energy-density but difficult to realize larger capacity. And its durability and safety characteristics have not been mentioned in detail. On the other hand, the laminate cells have been considered that they are suitable for larger capacity because of the flexibility of cell-design and its higher heat radiation. However, as the cell-capacity becomes larger, the safety generally becomes more disadvantageous. Furthermore, the thermal instability of higher nickel-content cathode becomes more serious for securing the safety [2] . Therefore, there has been an obstacle to realize the laminate LIBs for large cell-capacity with high energy-density. In this study, the method that can achieve high energy-density and high safety is presented. The characteristics of 60 Ah laminate cells using this method are also shown. 2. Results and Discussion 60 Ah laminate cells with high energy-density of over 250 Wh/kg, keeping high safety, were realized. Such a high energy-density cell was obtained featuring a high nickel-content cathode material based on NCM811. The nail penetration tests under the penetrating-speed of 10 mm/s with the nails of 3 mm in diameter were carried out. The results were no-fire and no-smoke even when the cell-capacity was up to 60 Ah (The photo inset in Fig.1). It was caused by the combination of a high heat-resistant separator and an HSE. It was found that the hard-short area was not increased, because of the small shrinkage of the separator near the penetrated nail. These effects enable us to secure sufficient robustness against the nail penetration test for 60 Ah laminate cells with high energy-density of over 250 Wh/kg. The safety tests except for nail penetration tests were also acceptable for the demand of application.Cycle performances were tested for the obtained cells. The result showed 90% of capacity retention after 1000 cycles at 25 deg. C. (Fig. 1). This result was obtained by optimizing the surface conditions of the cathode electrodes using the S-based electrolyte additives. The cell resistance was not increased after 1000 cycles. By impedance analysis, it was found that the charge-transfer resistances for the cathode electrodes were not increased. This result suggests that the specific S-based electrolyte additives effectively prevent the surface deterioration of NCM811 by forming surface film on cathodes, as well as anodes. 3. Conclusion In conclusion, 60 Ah laminate cells with high energy-density of over 250 Wh/kg were successfully realized, featuring NCM811-based cathode, optimized surface conditions for electrodes, and the combination of the heat-resistant separator and the HSE. The cell-series using such novel materials and process integration technologies can be applicable for wide-range applications, such as large-capacity EV, ESS, and also high-current power-supply devices attached to E-assisted vehicles, UPS, robots, and drones. References [1] V. Muenzel, A. F. Hollenkamp, A. I. Bhatt, J. D. Hoog, M. Brazil, D. A. Thomas, and I. Mareels, J. Electrochem. Soc., 162, A1592-A1600 (2015) [2] G. Kimand and J. R. Dahn, J. Electrochem. Soc., 161, A1394-A1398 (2014) Figure 1

Abstract: Abstract not Available.

Abstract: Abstract not Available.

Abstract: 1. Introduction Fluoride-shuttle batteries (FSBs) are attracting increasing attention because they possess superior energy densities compared to conventional lithium-ion batteries. In the past decade, fluoride-ion conducting solid electrolytes have been widely studied for FSBs [1,2] . However, most of them require operating temperature higher than 373 K. To decrease the operating temperature, ether-based organic solvents and ionic liquids were recently applied to FSBs [3–5]. We have focused on fluorohydrogenate ionic liquids (FHILs) for FSBs because FHILs exhibit ionic conductivities much higher than conventional liquid electrolytes. For example, [C 2 C 1 im][(FH) 2.3 F] (C 2 C 1 im = 1-ethyl-3-methylimidazolium) shows an ionic conductivity as high as 100 mS cm −1 at room temperature (298 K) [6,7]. We have already reported charge–discharge behaviors of CuF 2 electrodes in this IL [8]. In the present study, charge–discharge behaviors of copper-based positive electrodes were further investigated in several FHILs at room temperature. 2. Experimental All experiments were conducted at room temperature (ca. 298 K). Three-electrode cells were used for electrochemical measurements. The working electrode was composed of the active material (CuF 2 or metallic copper), acetylene black as a conductive agent, and polytetrafluoroethylene as a binder. Both the counter and reference electrodes were CuF 2 /Cu electrodes. Two FHILs, [C 2 C 1 im][(FH) 2.3 F] and [C 2 C 1 pyrr][(FH) 2.3 F] (C 2 C 1 pyrr = N -ethyl- N -methylpyrrolidinium), were used as electrolytes. Cyclic voltammetry was performed at 10 mV s −1 before charge–discharge tests. The working electrodes after the tests were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS). Prior to these analyses, the electrolytes were removed by washing with dehydrated ethanol, and the samples were transferred to all the analytical instruments without air exposure. The solubility of CuF 2 was measured by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The solution for the ICP-AES measurement was prepared by immersion and stirring of excess CuF 2 particles in each FHIL for 1 day. 3. Results and Discussion Fig. 1 shows charge–discharge curves of a metallic copper electrode in [C 2 C 1 im][(FH) 2.3 F] electrolyte at a rate of 0.05C (= 42.2 mA (g-Cu) −1 ). The initial charge and discharge capacities are 439 and 599 mAh (g-Cu) −1 , respectively. The results of XRD and XPS analyses suggested the reversible reactions during charge–discharge cycling. Cu + 6[(FH) 2 F] − ⇌ CuF 2 + 4[(FH) 3 F] − + 2e − (1) The discharge capacity larger than the charge capacity in the initial cycle may be attributed to the presence of oxide film on the surface of copper particles. The discharge capacity rapidly decreases after the 2nd cycle, and reaches 167 mAh (g-Cu) −1 at the 20th cycle, which corresponds to the capacity retention ratio of 28%. The SEM observation indicates that this steep decline in reversible capacities is likely ascribed to aggregation of active materials. Concerning [C 2 C 1 pyrr][(FH) 2.3 F] electrolyte, the same charge–discharge test was performed at 0.05C rate. Fig. 2 summarizes the cycling properties of discharge capacities in the two electrolytes. Initial discharge capacity obtained in [C 2 C 1 pyrr][(FH) 2.3 F] is 400 mAh (g-Cu) −1 , which is lower than that in [C 2 C 1 im][(FH) 2.3 F]. However, the discharge capacity is 210 mAh (g-Cu) −1 at the 20th cycle, exhibiting the improved capacity retention of 53%. This improved cycleability is probably originated from the lower solubility of CuF 2 formed in the charging reaction. According to the ICP-AES results, the solubilities of CuF 2 were ca. 100 and 20 ppm for [C 2 C 1 im][(FH) 2.3 F] and [C 2 C 1 pyrr][(FH) 2.3 F], respectively. Due to the higher solubility in [C 2 C 1 im][(FH) 2.3 F], the dissolution and reprecipitation of CuF 2 occur more severely on the surface of the working electrode, leading to more intense aggregation of the active material. The utilization of [C 2 C 1 pyrr][(FH) 2.3 F] mitigates such degradation of the electrode. Acknowledgments This study is based on results obtained from a project, "Research and Development Initiative for Scientific Innovation of New Generation Batteries (RISING2)", JPNP16001, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References [1] A. Reddy et al. , J. Mater. Chem. , 21 (2011) 17059. [2] Gschwind et al. , J. Fluorine Chem. , 182 (2016) 76. [3] Okazaki et al. , ACS Energy Lett. , 2 (2017) 1460. [4] Konishi et al. , J. Electrochem. Soc. , 164 (2017) A3702. [5] K. Davis et al. , Science , 362 (2018) 1144. [6] Hagiwara et al. , J. Fluorine Chem. , 99 (1999) 1. [7] Hagiwara et al. , J. Electrochem. Soc. , 149 (2002) D1. [8] Yamamoto et al. , ACS Appl. Energy Mater. , 2 (2019) 6153. Figure 1

Abstract: A great deal of attention has been paid to all-solid-state-lithium battery, which can theoretically achieve a higher energy density than Li ion batteries. One of the key technologies to achieve a high energy density for all-solid-state-lithium battery is to realize highly reversible Li metal anode free from the short-circuiting of solid-state electrolyte (SE). Many of oxide SEs such as Li 7 La 3 Zr 2 O 12 (LLZ) are mechanically hard materials with shear moduli on the order of 10 2 GPa. So, it had been believed that an oxide SE could act as a separator to prevent Li dendrite growth from the anode side through the SE. However, short-circuiting events have been found to still occur even with the SE. Figure 1 shows voltage transients during Li plating/stripping cycles at various current densities using Li/Ta-doped LLZ (LLZT)/Li symmetric cells 1 . Short-circuiting events occurred in any cells, but it was found that the cycling stability significantly depended on the surface treatment. SiC-polishing removed surface Li 2 CO 3 and LiOH from LLZT samples but simultaneously created thin damage layers on the surface. This damage layer was electrochemically inactive. Hence, LLZT etched in a 1.0 mol dm −3 aqueous solution exihbited the longest cycling stability because damge layers were removed from the surface during the etching. Many researchers have put a lot of effort into controlling the Li plating/stripping processes in solid-state battery, but there is still a lack of fundamental understanding of electrochemical Li deposition and dissolution in solid-state electrolyte systems. I will present the results of our recent studies on Li plating/stripping reactions at “Li-free” interface as well as Li/SE interface 2,3 . Acknowledgement This work was in part supported by JSPS KAKENHI Grant Number JP19H05813 (Grant-in-Aid for Scientific Research on Innovative Areas “Interface IONICS”). References [1] M. Motoyama et al., “The Active Interface of Ta-Doped Li 7 La 3 Zr 2 O 12 for Li Plating/ Stripping Revealed by Acid Aqueous Etching ”, ACS Appl. Energy Mater., 2, 6720 (2019). [2] M. Motoyama et al., “Modeling the Nucleation and Growth of Li at Metal Current Collector/LiPON Interfaces”, J. Electrochem. Soc., 162, A7067 (2015). [3] M. Motoyama et al., “In Situ Scanning Electron Microscope Observations of Li Plating/Stripping Reactions with Pt Current Collectors on LiPON Electrolyte”, J. Electrochem. Soc., 165, A1338 (2018). Fig. 1. (Left) Voltage transients during galvanostatic cycling of Li plating/stripping with various LLZT samples: (top) #3000-polished, (middle) #400-polsihed, (bottom) 5m-HCl-etched. (Right) Optical images of molten Li in contact with LLZT samples prepared by each polishing or etching condition on the left-hand-side figure. Figure 1