曽根 理嗣

The authors regret that there was an error in the following section heading, of the above-mentioned article. The error and the collection have been mentioned below: In 2.3. Catalysis, the flow rate of H2 gas “40 L/min” needs to be changed to “40 mL/min”. The authors would like to apologise for any inconvenience caused.

Abstract: This study investigated immobilization (without binders and high-temperature heating) of highly active CO2 methanation catalyst particles, prepared by the polygonal barrel-sputtering method, onto porous Al2O3 plates. The catalyst particles were fixed uniformly and firmly on the plates and retained their high CO2 methanation performance. Graphic Abstract: [Figure not available: see fulltext.]

Water electrolysis cell in which the product gases was separated from liquid water on the surface of the electrode was developed. In order to realize the separation between gas and water, interdigitated diffusion layer (GDL) was designed, and the surface of the GDL was covered by catalyst to form electrode. When the pressurized water was supplied, the water directly made a contact to the proton conductive membrane. Due to the hydrophobic surface condition of the GDLs, gas/water separation along the surface of the electrode was completed. (C) The Author(s) 2020. Published by ECSJ.

Diluted CO2 feeding was recently reported to efficiently generate CH4 at the theoretical Pt electrode potential, however, the reaction was easily deactivated. To solve this problem, we investigated the reaction/deactivation mechanism to produce CH4 from CO2 electroreduction. Using a polymer electrolyte single cell containing a Pt/C catalyst, CO2 was reduced to CH4 without overpotential by simply controlling the CO2 feed concentration. The CH4 synthesis proceeded if the Pt-CO/Pt-H ratio formed on the Pt-catalyst surface was 1 : 11 or higher. The deactivation of the CH4 generating reaction also depends on the Pt-CO/Pt-H ratio (the ratio does not satisfy 1 : 11 or higher). The optimum Pt-CO/Pt-H ratio to produce CH4 was 1 : 18. Furthermore, we achieved 86% recovery of CH4 activity by sweeping the deactivated Pt surface on the cathode up to 0.3 V where the CO2/Pt-CO redox reaction occurred simultaneously. As a result, an efficient less energy-intensive reactivation reaction that we defined as a poisoning-elimination method was established. Overall, this work demonstrated that the application of a polymer electrolyte cell together with a low concentration of CO2 is effective to minimize Pt-electrocatalyst deactivation.

This study investigated the effects of sputtering conditions on the activities of high-performance CO2 methanation catalysts prepared by a co-sputtering technique, employing a polygonal barrel apparatus. Average size of smaller Ru nanoparticles generated by co-sputtering Ru with TiO2 or ZrO2 varied with changes in the area ratio of the sputtering targets. The reaction temperature was decreased with decreases in the Ru particle size, and the most effective target area ratio was Ru:ZrO2 = 1:0.5 when co-sputtering Ru and ZrO2. For this optimized catalyst, increasing the sputtering time did not affect the Ru particle size but improved the catalytic activity. Small Ru particles were maintained even at a reaction temperature of 360 degrees C, indicating that undesirable decreases in catalytic activity due to particle growth can be suppressed using this co-sputtering technique. These highly active co-sputtered catalysts would have applications in systems intended for the reduction of CO2 emissions.

This study elucidates the factors reducing the CO2 methanation reaction temperature of TiO2-supported Ru catalysts prepared via the polygonal barrel-sputtering method (Ru/TiO2(BS)) to investigate the structure-sensitivity mechanism. The smaller nanoparticles deposited in Ru/TiO2(BS) (<4 nm) were amorphous RuO2 because of air exposure after the preparation, and their surfaces were changed to island-shaped structures consisting of amorphous RuO2 and amorphous Ru metal by H-2 exposure. In this case, dissociative hydrogen was also adsorbed in abundance on the amorphous Ru metals. Such hydrogen atoms were not observed in conventional Ru/TiO2 catalysts. Under the supplied CO2 + H-2 at a stoichiometric ratio of 1:4, these hydrogen atoms not only contributed to the generation of a unique CO intermediate (Ru-CO-Ru-H) from room temperature, but also reduced this CO adsorbate to methane even in low-temperature ranges (<= 120 degrees C). These reaction steps were completely different from the reported mechanisms. Accordingly, the formation of amorphous Ru metals and the adsorption of hydrogen atoms on them are essential for reducing the CO2 methanation temperature. These are key factors of structure-sensitivity, which would also be useful for improving activities of various catalysts.

The satellite REIMEI was launched in August 2005, this is one of the first satellites to use Li-ion batteries. REIMEI is a small scientific satellite designed for carrying out aurora observations using three different cameras. The main scientific mission of the satellite ended in 2013. More than 14 years have passed, and the batteries have experienced over 78,100 charge/discharge cycles. REIMEI remains in operation with a new mission dedicated to analyzing its Li-ion battery. In this work, we present a durability analysis for the REIMEI battery based on telemetry data. (C) The Author(s) 2020. Published by ECSJ.

Commercially available 18650 Li-ion cells were exposed to charge-discharge cycling at 0 degrees C using two different charging protocols: constant current-constant voltage (CC-CV) and constant current (CC). The effect of the charge process protocol on the Li-ion cell performance is shown and analyzed. After exposing the cells to low temperature charging, a high voltage plateau appeared at the beginning of the discharge. This high voltage plateau is related to the occurrence of lithium plating during the charging process. Interestingly, the intensity of the observed high voltage plateau decreased with cycling. In addition, the Li-ion cells that were charged using a CC protocol exhibited a larger capacity fade in comparison to those that were charged using a CC-CV protocol. Furthermore, electrochemical impedance spectroscopy (EIS) measurements were carried out during cycling. It was shown that the internal impedance of the cells increased with charge-discharge cycling, indicating the formation of an interphase layer during low temperature cycling. (C) The Author(s) 2020. Published by ECSJ.

Commercially available 18650 LiFePO4-Graphite Li-ion cells were exposed to charge-discharge cycling at 0 degrees C following two different charge methods: constant current-constant voltage (CC-CV) and constant current (CC), and two different discharge rates: 1 C and 0.2 C. The effect of the charge method and discharge rate on the cell performance was analyzed. The cell exposed to CC charge and 1 C discharge-rate showed a high voltage plateau at the beginning of the discharge voltage, while a high voltage plateau was not observed in the discharge profiles of the cells exposed to a discharge rate of 0.2 C. (C) The Author(s) 2020. Published by ECSJ.

In order to elucidate the impact of calendar degradation on charge-discharge cycling under low temperature, we evaluated and compared the performance of fresh and calendar degraded LiFePO4-Graphite Li-ion cells during cycling at -5 degrees C. After exposing fresh and calendar degraded cells to low temperature cycling, the fresh cell exhibited a relatively good performance, while in the case of the calendar degraded cell a poor performance was observed. In addition to this, a high voltage plateau, which usually appears at the beginning of the discharge profiles as a consequence of the occurrence of lithium plating, was not observed in the discharge profiles of the fresh cell. However, in the case of the calendar degraded cell a high voltage plateau appeared at the beginning of the discharge profiles, indicating that lithium plating is more likely to occur in degraded Li-ion cells exposed to low temperature charging. Our investigation results show that calendar degradation can compromise the safety and performance of Li-ion cells during low temperature cycling. (c) 2019 The Electrochemical Society.

In this work, we introduce a water electrolysis and CO2 hydrogenation tandem system which focuses on methane generation. The concept consists of a water electrolyzer thermally coupled to a CO2 hydrogenation reactor, where the power required to generate hydrogen comes from renewable energy. A thermodynamic analysis of the tandem system was carried out. Our analysis exposes that it is possible to increase the exergy efficiency of the water electrolyzer and CO2 hydrogenation system by thermal coupling, where the thermal energy required to split water into H-2 and O-2 during the electrolysis process is compensated by the heat generated during the CO2 hydrogenation reaction. Here, the conditions at which high exergy efficiency can be achieved were identified.

It is important for large-scale lithium-ion secondary cells to function in a safe and stable manner. Little information is available on the parameters determining the transitions between non-heating, self-heating, and thermal runaway processes of degraded lithium-ion secondary cells. Thermal characterization of the degraded cells is important to identify the impact of degradation on the safety limits of these cells. Accelerating rate calorimeter (ARC), operated in a heat-wait-search mode, is capable of characterizing the thermal behavior of lithium-ion cells. Here, the self-heating and relative heat generation rates of storage-degraded lithium-ion cells during thermal runaway are investigated. Twenty-five 18650-type LiCoO2-based secondary cells are degraded during storage at 80 degrees C with various states of charge (SOCs), then the thermal behavior of the cells was analyzed by carrying out ARC measurements. The correlations between the onset temperature of thermal runaway, self-heating rate, and heating rate of each cell are investigated. It was found that the self-heating rate correlates linearly with the onset temperature of thermal runaway, while the relative heat generation rate correlates with it exponentially. The cells charged to 100% SOC presented the lowest onset temperatures of thermal runaway.

Lithium-ion batteries are the technology of choice for a broad range of applications due to their performance and long-term stability. The performance and durability of lithiumion batteries is impacted by various degradation mechanisms. These include the growth of the solid-electrolyte interphase (SEI) and the deposition of metallic lithium on the surface of the negative electrode, referred to as lithium plating. For both processes we develop physically based models.In this contribution we develop a model to describe the performance and lifetime of the batteries of in-orbit satellite REIMEI developed by the Japan Aerospace Exploration Agency. We extend an existing model for SEI growth and incorporate it into a model for fresh cells. Then we simulate the degradation of batteries under cycling in 1D and 3D. To validate the model, we use experimental and in-flight data of the batteries. We show inhomogeneities in the SEI thickness after cycling.

The effect of cycling degradation on the kinetic characteristics of graphitized carbon electroactive material is investigated using laminated Li-ion cells incorporating a reference electrode. By carrying out electrochemical impedance spectroscopy (EIS) measurements at different state of charges and temperatures and obtaining dQ/dE vs. E curves, the pre-exponential factor and activation energy of Li-ion insertion/deinsertion reactions are analyzed as a function of anode potential. The kinetic behavior of charge transfer, Li-ion conduction and Li-ion solvation/desolvation reactions for Li-ion cells without degradation and after cycling degradation are investigated. Structural changes in the crystal structure of graphitized carbon originated from cycling degradation affect the charge transfer reactions, while irregular growing of the SEI affected the Li-ion conduction and Li-ion solvation/desolvation processes.

A water-absorbing porous electrolyte electrolysis cell is presented consisting of a hydrophobic gas diffusion layer (GDL), a controlled-hydrophobicity electrocatalyst layer, and a hydrophilic porous electrolyte layer. The specific character of this cell is that high-pressure water is injected directly into the porous electrolyte layer and is resisted by the electrocatalyst layer and GDL, which have strong water support force. In this study, the preparation method of the electrocatalyst layer and the porous inorganic electrolyte layer, and the evaluation of water electrolysis using the prepared layers were investigated. The optimized conditions and preparation methods of each layer of the MEA (i.e. the GDL, electrocatalyst layer, electrolyte layer) were determined. The assembly method and conditions of these three layers were also determined for fabricating MEAs for water electrolysis. The evaluation of water electrolysis tests using this MEA showed that the hydrogen evolution rate obeyed Faraday's Law in the low current density region (<10 mA cm(-2)). (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

CO2 methanation catalysts were prepared by co-sputtering with Ru and metal oxides such as TiO2 and ZrO2 using the polygonal barrel-sputtering method. The co-sputtering technique not only resulted in the decrease in the reaction temperature but also maintained the deposition of smaller Ru particles during the reaction at higher temperature.[GRAPHICS].

Copyright © 2018 by the International Astronautical Federation (IAF). All rights reserved. Lithium-ion batteries are the technology of choice for a broad range of applications due to their performance and long-term stability. The performance and durability of lithium-ion batteries is heavily impacted by various degradation mechanisms. These include the growth of the solid-electrolyte interphase (SEI) and the deposition of metallic lithium on the surface of the negative electrode, also referred to as lithium plating. By comparing electrochemical simulations with experimental measurements, we now perform state-estimation of lithium-ion batteries in order to improve the characterization and management of the battery, e.g., for the battery of the REIMEI satellite. Our goal is to understand the degradation processes and to observe and detect them while the battery is in operation. As a result, this will improve safety and prolong battery life by reducing capacity fade.

The Japan Aerospace Exploration Agency is now developing life support systems for closed environments in space. The reduction reaction of carbon dioxide is an important technique for the sustainable manned operation in space. Recently, Umeda et al. [J. Appl. Phys. 114, 174908 (2013)] from the Nagaoka University of Technology reported that the reduction reaction of carbon dioxide (CO2) proceeded using a fuel cell under the existence of CO2 and H-2 by supplying those gases to the cathode and the anode, respectively. We observed stable reaction when Pt/Ru-C was used as a catalyst for the cathode and Pt-C for the anode. Different organic materials were obtained depending on the alternated potential and temperature. Furthermore, a fuel cell stack with 8 cells connected in series was tested to demonstrate the stable energy generation by feeding CO2 to the cathode and H-2 to the anode. Published by AIP Publishing.

The characteristics of a water-absorbing porous electrolyte electrolysis cell, in which pressurized water is injected directly into the electrolyte layer, are investigated. High water support force is required for the gas diffusion layer (GDL) in this novel cell design, and therefore here we report a new type of hydrophobic GDL comprising an acetylene black (AB) and poly(tetrafluoroethylene) (PTFE) composite film. The method of preparation of the AB/PTFE slurry, film formation methods, and the AB/PTFE weight ratio were investigated and optimized. The ball-milling and transfer method were suitable for preparing uniform AB/PTFE slurry and successfully covering AB/PTFE film without any cracks on micro-porous layer coated carbon paper, respectively. An investigation about different PTFE weight ratios against AB from 0.1 to 6 showed a serious trade-off character between electrical resistance R, gas permeability V', and water support force P-lim. The 1/2.5 of AB/PTFE weight ratio was most optimal, which showed to have most equivalent R (2.5 Omega cm(-2)), V'(136 mL atm(-1) cm(-2) min-1), and Plim (0.25 MPa). We also confirmed that fabricated GDL with optimal condition was worked as the blocking layer against water injected through electrolyte layer and pressurized by nitrogen gas, and as gas-permeation layer for generated hydrogen gas in water electrolysis test. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Copyright © 2018 by the International Astronautical Federation (IAF). All rights reserved. The satellite 'REIMEI' was launched in August 2005; this satellite is one of the first spacecraft to use Li-ion batteries. The orbit of the satellite is a low earth orbit, over 65000 charge/discharge cycles have been reached and REIMEI is still operating. We are trying to estimate the remaining useful capacity and state of health for the REIMEI Li-ion batteries. However, the estimation of remaining useful life for Li-ion cells is not trivial, since their degradation is caused by many physical and chemical processes which get accelerated depending on the working environment and operating conditions. The satellite uses 2 batteries, each battery consists of 7 cells. The cells use LiMn2O4 and graphite as the positive and negative electro-active materials, respectively. The rated capacity of each cell is 3 Ah. In this work we analyse the performance of the REIMEI batteries based on telemetry data.

© 2018 by the International Astronautical Federation. All rights reserved. The Japan Aerospace Exploration Agency (JAXA) is now studying devices for the life support system in the closed environment in space. The reduction reaction of carbon dioxide, which is known as the 'Sabatier reaction' plays an important role in the current life support systems onboard the International Space Station (ISS). This work focuses on the development a novel CO2 hydrogenation reactor thermally coupled with a water electrolyzer. The system enables the reduction reaction of CO2 using exotherm from the Sabatier reaction to enhance the efficiency of water electrolysis to generate oxygen.

A TiO2-supported Ru–Ni alloy (Ru–Ni/TiO2) catalyst (atomic ratio of Ru:Ni = 50:50) for the CO2 methanation reaction was prepared by the polygonal barrel-sputtering method. Sputtering was performed with an area ratio of the Ru and Ni targets of 1:1, Ar gas pressure of 0.8 Pa, and AC power of the radiofrequency power supply of 100 W without heating. As a result, the Ru–Ni alloy nanoparticles were highly dispersed on the TiO2 particles used as the support. The particle sizes were distributed between 1 and 5 nm (average size: 2.5 nm), which is similar to the size distribution of a Ru/TiO2 sample prepared by the same method in our previous study. However, the CO2 methanation performance of Ru–Ni/TiO2 is not as high as that of the above-mentioned Ru/TiO2 sample. This might be because of the lower catalytic activity of Ni than Ru.

The satellite borne batteries should be composed by safe materials if we don't want to have a risk of explosion caused by batteries. Therefore, we focused on two safe batteries. One is a lithium-ion battery with an ionic liquid electrolyte, and the other is a LiFePO4/C type lithium-ion battery. To check whether the batteries are suit for space applications or not, we demonstrate the ionic liquid type batteries and LiFePO4/C type battery in orbit by mounting on "Hodoyoshi-3" microsatellite, and test LiFePO4/C type cell on the ground at various conditions for a better understanding.On the ground tests, AC impedance and capacity of the cells were initially measured, and charge/discharge cycling was constantly repeated at 10, 23 and 45 degrees C. The cells were discharged by constant current (CC) protocol to DOD 50% with 1.0 C for 30 minutes. They were then charged by a constant-current/constant voltage (CC-CV) protocol to 3.6 V for 65 minutes with 0.5 C. For capacity check, the cells were charged at 1.0 C in CC-CV mode until their charge current becomes 60 mA, and discharged at 1.0 C in CC mode to 2.0 V at 23 degrees C. The AC impedance was measured by applying 100 mA of AC oscillation over the frequency range from 0.01 Hz to 10 kHz at SOC 50%.As a result, the decrease in the impedance for the charge transfer through the cycles was observed at each test condition. Furthermore, especially in over recommended charge condition at 10 degrees C, cells that were charged and discharged at 1.1 A/1.1 A were led to internal short circuit. The results suggested that the negative electrode performed as a "lithium-ion excess" by cycles. We define "lithium-ion excess" that lithium-ion happens to stay inside the negative electrode without desorption after cells discharge.

The lithium-ion secondary batteries have been widely used for the space programs, today. Among them, REIMEI was one of the first satellites using lithium-ion secondary battery. In 2005, the satellite was launched, and injected into the low earth polar orbit. Eleven years has passed since the launch and over 60,000 cycles of charge and discharge was experienced in space.The lithium-ion secondary cell of the REIMEI battery was designed using spinel manganese oxide type material for the positive electrode, and the graphitized type carbon for the negative electrode. The cell case was made of aluminium laminated film and the structure was reinforced by the epoxy resin and aluminium housing. After the operation of eleven years, the cells still maintain the appropriate uniform balance and operative. In order to identify the internal condition of the battery/cell, we calculated the ac impedance by the pulse duration to the on-board battery.

Understanding the behavior of Li-ion cells during thermal runaway is critical to evaluate the safety of these energy storage devices under outstanding conditions. Li-ion cells possess a high energy density and are used to store and supply energy to many aerospace applications. Incidents related to the overheating or thermal runaway of these cells can cause catastrophic damages that could end up costly space missions; therefore, thermal studies of Li-ion cells are very important for ensuring safety and reliability of space missions. This work evaluates the thermal behavior of Li-ion cells before and after storage degradation at high temperature using accelerating rate calorimeter (ARC) equipment to analyze the thermal behavior of Li-ion cells under adiabatic conditions. Onset temperature points of self-heating and thermal runaway reactions are obtained. The onset points are used to identify non-self-heating, self-heating and thermal runaway regions as a function of state of charge. The results obtained can be useful to develop accurate thermo-electrochemical models of Li-ion cells.

Lithium-ion secondary cells are widely used for the space applications, today. Among these applications, REIMEI, which was launched in 2005, was one of the first satellites using lithium-ion battery. The off-the-shelf type cells designed using spinel manganese oxide for the positive and the graphitized carbon for the negative electrode were used. The cell case was made of aluminum laminated film and the structure was reinforced by the aluminum case filled with epoxy resin. Today, ten years has passed, and the battery experienced 55,000 cycles for charge and discharge. The current distribution between two batteries almost coincided together even after the long term operation, which revealed the stable performance of the lithium-ion secondary cells under the microgravity in space. (C) The Electrochemical Society of Japan, All rights reserved.

Copyright © 2016 by the International Astronautical Federation (IAF). All rights reserved. Energy storage devices are very important for space missions, Li-ion cells are used to supply energy to spacecrafts or satellites during the eclipse/night time. These cells possess a high energy density but can cause catastrophic incidents that could end up costly space missions, those incidents are manly related to the overheating or thermal runaway of Li-ion cells, leading to possible fire and explosion as observed by incidents in the electronics and aerospace industries. The thermal analysis of Li-ion secondary cells is very important for ensuring safety and reliability of space missions. The thermal behavior of a Li-ion cell is dominated by the exothermic reactions between its electrolyte and electroactive materials. Thermal runaway occurs when the exothermic reactions go out of control, thus the self-heating rate of the cell increases to the point that it begins to generate more heat than what can be dissipated. Understanding the behavior of Li-ion cells during thermal runaway is critical to evaluate the safety of these energy storage devices under outstanding conditions. In this work we analyze the thermal runaway behavior of 18650 Li-ion cells before and after storage and cycling degradation at high temperatures. The thermal behavior of the cells is analyzed using accelerating rate calorimetry. Non-self-heating, self-heating and thermal runaway regions of the cells as a function of state of charge and temperature are identified and compared among the cells. Li-ion cells were tested inside an accelerating rate calorimeter (ARC) 2000™ to record their thermal behavior under adiabatic conditions. Onset temperatures of self-heating and thermal runaway reactions are identified, and by using these onset points thermal mapping plots are made. We are able to identify non-self-heating, self-heating and thermal runaway regions of degraded and non-degraded Li-ion cells as a function of state of charge. The results shows that degraded Li-ion cells tend to be thermally unstable at low state of charges.

Copyright © 2016 by the International Astronautical Federation (IAF). All rights reserved. The Japan Aerospace Exploration Agency (JAXA) is now developing life support systems for closed environments in space, and the reduction reaction of carbon dioxide is an important technology for the sustainable manned operations in space. Recently, Umeda et al., from Nagaoka University of Technology (NUT) reported that the reduction reaction of carbon dioxide (CO2) proceeded by using a fuel cell and supplying CO2 and H2 to the cathode and anode, respectively. This electrochemical reduction of CO2 generates electricity and produces different organic materials depending on the alternated potential and operation temperature. The continuous operation of the CO2-H2 fuel cell has been proved by carrying out experimental tests. An eight-cells-stack system was prepared, and the continuous generation of electricity was demonstrated for five hours showing a stable potential operability. Water, methane, methanol, ethanol, acetic acid and formic acid have been detected as by-products of the electrochemical reduction of CO2, the generation of these by-products has a dependency on the operational potential and temperature of the fuel cell. The atmosphere of Mars has a high concentration of CO2, and hydrogen and oxygen can be generated using water electrolyzers, the hydrogen can be used as a fuel to reduce the CO2 generated form human activity or taken from the atmosphere of Mars. The management of the resources for the life support is very important for manned missions in space. The by-products from the electrochemical reduction of CO2 could be used as raw materials to produce consumption articles. Further improvements are necessary to increase the electricity generation and to control the selectivity of the by-products, however, the use of CO2-H2 fuel cells seems to be a promising alternative to support human exploration of Mars.

A prototype lithium-ion battery with a bis(fluorosulfonyl)imide (FSI)-based ionic liquid electrolyte was developed. The prototype was mounted on a demonstration module of the "Hodoyoshi-3" microsatellite, which was successfully launched on June 20, 2014. Qualification tests for space application, including radiation tolerance and vacuum tests, revealed negligible degradation of the ionic liquid-based lithium-ion battery (IL-LIB) cell. According to the flight data, the IL-LIB cell can exist stably in an ultra-high vacuum environment despite its thin and flexible pouch casing without any rigid anti-vacuum reinforcements. Furthermore, the power unit showed the same charge-discharge performance as that predicted by the charge-discharge behavior of an identical cell on the ground, suggesting that the IL-LIB cell maintains performance in high vacuum a microgravity environment. These results prove that LIB cells with FSI-based ionic liquids can be used as a power source for space applications. (C) The Electrochemical Society of Japan, All rights reserved.

Kinetic characteristics of LiCoO2 cathode materials are studied using a Li-ion secondary cell incorporating a reference electrode. By carrying out electrochemical impedance spectroscopy (EIS) measurements at different state of charges (SOCs) and temperatures and obtaining dQ/dE vs. E curves, the activation energy, pre-exponential factor, and reaction rate constant of Li-ion insertion/deinsertion reactions are analyzed as a function of cathode potential. The kinetic behavior of Li-ion conduction, Li-ion solvation/desolvation, and charge transfer reactions of LiCoO2 and its dependency on the structural changes of LiCoO2 are studied. The charge transfer, Li-ion conduction, and Li-ion solvation/desolvation reactions exhibited a dependency on the structural changes of the cathode material.

Li-ion insertion/deinsertion reactions of the anode of a Li-ion secondary cell incorporating a reference electrode were analyzed by electrochemical impedance spectroscopy (EIS) at different temperatures and state of charges (SOCs). The cell uses graphitized carbon as anode electroactive material. Impedance spectra fittings were carried out using an equivalent circuit, so that the reaction kinetics could be evaluated accurately. The dependencies of the Li-ion conduction (R-s|1), Li-ion solvation/desolvation (R-s|2) and charge transfer (R-ct) reactions on the SOC and anode potential were evaluated. The results were compared with a dQ/dE vs. E curve of graphite to analyze how the structural changes of graphite affect the Li-ion insertion process. The charge transfer process was found to be dependent on the SOC and anode potential. On the other hand, Li-ion conduction and Li-ion solvation/desolvation processes did not depend on the SOC and anode potential. (C) 2014 Elsevier Ltd. All rights reserved.

The lithium-ion secondary cells/batteries are commonly used for the spacecraft, today. 'REIMEI' satellite is also an example using lithium-ion secondary battery. It used 3 Ah-class off-the-shelf lithium-ion secondary cells, which used the spinel LiMnO4 for the positive and graphite for the negative electrode. Seven cells were connected in series, and two series strings were connected in parallel. The satellite was launched in August, 2005, and injected into the low earth polar orbit. Initially, the battery performance was simulated based on the dependency of the cell performance on temperature. Considering the impedance and discharge performance depending on temperature, the end-of-discharge-voltage during the operation had been precisely controlled. Seven years operation of the lithium-ion secondary battery under the micro-gravity conditions have been demonstrated through the REIMEI operation in space.

An investigation of the thermal deterioration characteristics of a lithium-ion secondary cell is inevitable for its utilization in electric vehicles. An accelerating rate calorimeter study revealed that a thermal runaway of the cell occurs >130&deg;C. We considered that the analysis of the thermal behavior under high-temperature conditions as well as the thermal runaway is indispensable from the viewpoint of safety, but an analysis of the deterioration behavior in the non-heating domain is essential from the viewpoint of the battery&rsquo;s lifetime. In this study, in order to analyze in detail the deterioration of the non-heating region, thermal-deterioration characteristics of the lithium-ion secondary cell stored at 70 &ndash; 100&deg;C were investigated by varying the state of charge (SOC). To evaluate the thermal-deterioration characteristics, we estimated the activation energy from the discharge capacities before and after a heat hazard. On the other hand, impedance spectroscopy measurements of lithium-ion secondary cells at elevated temperature were carried out to determine the activation energy of charge/discharge, which is determined from the electrochemical parameters by using an equivalent circuit. Based on this analysis, the activation energy of the deterioration is known to be about two-times greater in magnitude than the activation energy of the charge/discharge. The charge/discharge and deterioration reactions are independent of each other; however, a comparison of these activation energies is an important element in order to understand the thermal deterioration of lithium-ion secondary cells that takes place in the non-heating region.