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Abstract To elucidate the gas generation mechanism due to electrolyte decomposition in commercial lithium-ion cells after long cycling, we developed a device which can accurately determine the volume of generated gas in the cell. Experiments on LixC6/Li1−xCoO2 cells using electrolytes such as 1 M LiPF6 in propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are presented and discussed. In the nominal voltage range (4.2–2.5 V), compositional change due mainly to ester exchange reaction occurs, and gaseous products in the cell are little. Generated gas volume and compositional change in the electrolyte are detected largely in overcharged cells, and we discussed that gas generation due to electrolyte decomposition involves different decomposition reactions in overcharged and overdischarged cells.

Abstract Structural changes and their relationship with thermal stability of charged Li 0.33 Ni 1/3 Co 1/3 Mn 1/3 O 2 cathode samples have been studied using time-resolved X-ray diffraction (TR-XRD) in a wide temperature from 25 to 600 °C with and without the presence of electrolyte in comparison with Li 0.27 Ni 0.8 Co 0.15 Al 0.05 O 2 cathodes. Unique phase transition behavior during heating is found for the Li 0.33 Ni 1/3 Co 1/3 Mn 1/3 O 2 cathode samples: when no electrolyte is present, the initial layered structure changes first to a LiM 2 O 4 -type spinel, and then to a M 3 O 4 -type spinel and remains in this structure up to 600 °C. For the Li 0.33 Ni 1/3 Co 1/3 Mn 1/3 O 2 cathode sample with electrolyte, additional phase transition from the M 3 O 4 -type spinel to the MO-type rock salt phase takes place from about 400 to 441 °C together with the formation of metallic phase at about 460 °C. The major difference between this type of phase transitions and that for Li 0.27 Ni 0.8 Co 0.15 Al 0.05 O 2 in the presence of electrolyte is the delayed phase transition from the spinel-type to the rock salt-type phase by stretching the temperature range of spinel phases from about 20 to 140 °C. This unique behavior is considered as the key factor of the better thermal stability of the Li 1−x Ni 1/3 Co 1/3 Mn 1/3 O 2 cathode materials.

Abstract The physical properties of organic electrolyte used in manganese dioxide-lithium cells play a major role in determining various cell characteristics. The influence on various cell characteristics of electrolytes has been investigated with flat cells. LiCF 3 SO 3 is the suitable solute in terms of low-temperature, storage and overdischarge characteristics. Mixture of ethylene carbonate (EC), 1,2-butylene carbonate (BC) and 1,2-dimethoxyethane (DME) is the suitable solvent in terms of high-rate discharge and storage characteristics.

Abstract Precycling of lithium (Li) metal on a nickel substrate at low temperatures (0 and −20°C) in propylene carbonate (PC) mixed with dimethyl carbonate (DMC) and Li hexafluorophosphate (LiPF 6 ) (LiPF 6 -PC/DMC) was found to enhance Li cycleability in the subsequent cycles at a room temperature (25°C). In contrast when the precycling at the low temperatures was performed in PC mixed with 2-methyltetrahydrofuran (2MeTHF) and LiPF 6 (LiPF 6 -PC/2MeTHF), no improvement in the Li cycling efficiency was observed in the subsequent cycles at 25°C. These results suggest that the low-temperature precycling effect on the Li cycleability depends on a co-solvent used in the PC-based electrolytes. Ac impedance analysis revealed that the precycling in the low-temperature LiPF 6 -PC/DMC electrolyte provided a compact Li interface with a low resistance. In marked constant to this, a Li anode interface formed by the precycling in the LiPF 6 -PC/2MeTHF system was irregular and resistive to Li-ion diffusion. The origins of the low-temperature precycling effect dependent on the co-solvents were discussed.

Abstract The thermal stability of mixed-solvent electrolytes used in lithium cells was investigated by differential scanning calorimetry (DSC) through the use of airtight containers. The electrolytes used were propylene carbonate (PC) and ethylene carbonate (EC)+PC, in which was dissolved 1 M LiPF 6 , 1 M LiBF 4 , 1 M LiClO 4 , 1 M LiSO 3 CF 3 , 1 M LiN(SO 2 CF 3 ) 2 , or 1.23 M LiN(SO 2 CF 3 )(SO 2 C 4 F 9 ). The influence of lithium metal or the Li 0.5 CoO 2 addition on the thermal behavior of these electrolytes was also investigated. The peak temperature of PC-based electrolytes increased following the order of LiPF 6 4 4 2 CF 3 ) 2 3 CF 3 2 CF 3 )(SO 2 C 4 F 9 ). The order of peak temperature of EC–PC-based electrolytes shows a similar tendency to that of EC–PC-based electrolytes, with the exception of the LiN(SO 2 CF 3 ) 2 electrolyte. The EC–PC-based electrolytes with Li metal show a more stable profile compared with the DSC curves of the PC-based electrolytes with the Li metal. The solid electrolyte interphase (SEI) covers the surface of the Li metal and prevents further reduction of the electrolytes. EC may form a better SEI compared with PC. The PC-based electrolytes of LiSO 3 CF 3 , LiN(SO 2 CF 3 ) 2 and LiN(SO 2 CF 3 )(SO 2 C 4 F 9 ) with the coexistence of Li 0.49 CoO 2 show a broad peak at around 200 °C, which may be caused by the reaction of the Li 0.49 CoO 2 surface and electrolytes. The PC-based electrolytes of LiPF 6 , LiClO 4 and LiBF 4 with Li 0.49 CoO 2 show exothermic peaks at higher temperatures than 230 °C. The peak temperatures of the EC–PC-based electrolytes with the coexistence of Li 0.49 CoO 2 are nearly the same temperature as the EC–PC-based electrolytes.

Used dry battery recycling in Japan began under the bilateral proposition issued by the Ministry of Health and Welfare. Although there is no problem even if used dry batteries are treated after being mixed with general house hold garbage, the Government takes care of establishing a system to transport and treat them. The project which was organized by the Ministry in 1986 seems to function fairly well for the time being, in spite of the criticism by the press at that time that the Ministry act was rather opportunistic. This paper outlines the brief history and the present status of the used dry battery collecting and treating system in Japan.

Abstract Direct ethanol fuel cells (DEFCs) with a PtRu anode and a Pt cathode were prepared using an anion exchange membrane (AEM) as an electrolyte instead of a cation exchange membrane (CEM), as in conventional polymer electrolyte fuel cells. The maximum power density of DEFCs significantly increased from 6 mW cm−2 to 58 mW cm−2 at room temperature and atmospheric pressure when the electrolyte membrane was changed from CEM to AEM. The anode and cathode polarization curves showed a decrease in the anode potential and an increase in the cathode potential for AEM-type DEFCs compared to CEM-type. This suggests that AEM-type DEFCs have superior catalytic activity toward both ethanol oxidation and oxygen reduction in alkaline medium than in acidic medium. The product species from the exhausted liquid from DEFCs operated at a constant current density were identified by enzymatic analysis. The main product was confirmed to be acetic acid in AEM-type, while both acetaldehyde and acetic acid were detected in 1:1 ratio in CEM-type. The anodic reaction of AEM-type DEFCs can be estimated to be the oxidation of ethanol to acetic acid via a four-electron process under these experimental conditions.

Abstract In this study, the lattice Boltzmann method (LBM) is used to investigate liquid water transport in the microporous layer (MPL) and gas diffusion layer (GDL) of polymer electrolyte membrane fuel cells (PEMFCs). Two-phase LB simulations are performed with modeled porous geometries that imitate multi-layer porous transport layers (PTLs) consisting of an MPL and a GDL. The simulation conditions are closely matched to the actual liquid water transport conditions in the PEMFCs. The results indicate that invasion-percolation processes due to strong capillary effects govern liquid water transport in PEMFCs. In addition, LB simulations are conducted by varying the intrusion thickness of the MPL and the surface wettability of the PTL. The results clearly show that the liquid water content can be reduced in the PTL by employing a thicker MPL and/or more hydrophobic surfaces. The steady-state water distribution is observed to occur more rapidly as the MPL becomes thicker or as the solid surfaces become more hydrophobic. Furthermore, several dynamic liquid water transport behaviors are identified from the results and explained in detail.

Abstract The development of high-performance polymer electrolyte membrane fuel cells that operate at elevated temperatures is urgently required to overcome the technical problems associated with operation at low temperatures. Here, we report an effective way to enhance electrode performance via simple Pt pulse electrodeposition at room temperature. This electrodeposition process enables both the formation of additional Pt electrocatalysts with extremely low loading (i.e., ~0.05 mg cm−2 for 100 pulse cycles) as a function of pulse number and control of the wetting properties of commercial Pt-based electrodes. Following optimization of the electrode conditions and configurations, the controlled hydrophilicity of the anode enhances the phosphoric acid distribution and the formation of a triple phase boundary in the catalyst layer, resulting in lowered ohmic and charge transfer resistances, respectively. The mass activities of the membrane electrode assembly with the anode modified by Pt pulse electrodeposition is 437.2 mW mgPt−1 (H2/O2), which is approximately 1.36 times higher than that of the pristine membrane electrode assembly. The controlled hydrophilicity allows moderate improvement of the performance, even without additional Pt. The results presented herein demonstrate the importance of surface property control for electrode preparation to achieve enhanced performance of high-performance polymer electrolyte membrane fuel cells.