Akihiko Yamaji

Ethylene carbonate-propylene carbonate mixed electrolytes for lithium batteries

Abstract Electrolytic characteristics of propylene carbonate (PC)ue5f8ethylene carbonate (EC) mixed electrolytes were studied, compared with those in PC electrolytes. Conductivity and Li charge—discharge efficiency values increased with EC contents increasing. For example, 1 M LiClO4ue5f8ECue5f8PC (EC mixing molar ratio; [EC]/[PC] = 4) showed the conductivity of 8.5 ohm−1 cm−1, which value was 40% higher than that in PC. Also, 1 M LiClO4ue5f8ECue5f8PC([EC]/[PC] = 5) showed the Li charge—discharge efficiency of 90.5% at 0.5 mA cm−2, 0.6 C cm−2, which value was ca. 25% higher than that in PC. ECue5f8PC mixed electrolytes were considered to be practically available for ambient lithium batteries in regard to the high Li+ ion conductivity and also high Li charge—discharge efficiency.

Cathode Characteristics of Organic Electron Acceptors for Lithium Batteries

Discharge and charge characteristics of cathode-active materials for lithium batteries were studied. Electron acceptors of charge transfer complex with high electron affinity were examined as cathode-active materials because they were expected to have high cell voltage. These electron acceptors are 2,4,7-trinitro-9-fluorenone (TNF), 2,4,5,7-tetranitro-9-fluorenone, 7,7,8,8-tetracyanoquinodimethane, 9, 10-phenanthrenequinone, and 13 other compounds. Among these compounds, TNF showed the highest discharge capacity (1050 A-hr/kg) and the highest energy density (2030 W-hr/kg). Cycle lives of TNF were 400 and 54 times at charge-discharge capacity of 100 of A-hr/kg (1.2 electron transfer per 1 mol TNF) and 200 A-hr/kg (2.4 electron transfer per 1 mol TNF), respectively. The cycle tests indicate reversibility of TNF up to two-electron transfer. 19 references.

Phthalocyanine Cathode Materials for Secondary Lithium Cells

Discharge and charge characteristics of various phthalocyanine cathodes coupled with lithium metal are studied. The best capacity based only on cathode active material weight is 1440 A-hr/kg in the lithium/iron phthalocyanine system, and the cycle life of the lithium/Cu phthalocyanine system is more than 100 times at the discharge depth of 157 A-hr/kg. The cathode reaction mechanism is supposed to be lithium intercalation between phthalocyanine molecules. The results indicate that these phthalocyanines are promising cathode active materials for lithium secondary batteries. 15 refs.

Dialkoxyethane—propylene carbonate mixed electrolytes for lithium secondary batteries

Abstract The electrolytic characteristics of various 1,2-dialkoxyethane (DAE)-propylene carbonate (PC) mixed solvent electrolytes for Li secondary batteries have been examined. DAE[H3C(CH2)nOC2H4O(CH2)nCH3] is a low viscous, non-cyclic, aprotic solvent. As DAEs, dimethoxyethane (DME), diethoxyethane (DEE), and dibutoxyethane (DBE) were used. The conductivities of PC/DME and of PC/DEE showed maximum values around PC/DAE volume ratios of 1/1 and at 1M solute, due mainly to the high dielectric constant of PC and the low viscosity of DAE. The Li+ ion conductivity changed according to the DAE molecular volume. 1M LiAsF6ue5f8PC/DME (1/1) showed an approximately 2.6 times higher conductivity, 13.8 × 10−3 ohm−1 cm−1, than PC alone. Lithium charge—discharge efficiency on the Li substrate increased with decreasing reactivity between Li and DAE, which would be expected from the oxidation potential for DAE. LiClO4ue5f8PC/DME and PC/DEE showed a greater than 90% Li cycling efficiency.

Inhibiting effects of Al corrosion by polymer ammonium chlorides in alkaline electrolyte

Abstract To inhibit Al corrosion in primary cells with Al anodes and alkaline electrolyte, the inhibiting effects of polymers with ammonium cation were studied. Two polymers, polyvinylbenzyltrimethylammonium chloride (PVBA) and polydiallydimethylammonium chloride (PDDA), inhibited Al corrosion effectively. Corrosion current icorr of pure Al was 5.40 mA cm−2 in 1 N KOH with PVBA at 5 × 10−2 M and 4.03 mA cm−2 with PDDA at 3 × 10−1 M. It is noted that they inhibited cathodic predominantly, which was preferable to the Al anode, because Ecorr shifted more negative (−22.00 V vs sce). The cathodic inhibiting effect of polymer cation seems to be due to the thicker double layer of polymer cation which prevents H+ ions from approaching the Al surface. The results to double layer capacitance measurement support this assumption.

The influence of catalyst-supporting methods on electrochemical activity and the resultant stability of air electrodes activated with iron phthalocyanine

To improve the performance of air electrodes, the dependence of iron phthalocyanine (FePc) catalytic effects on preparation methods was examined. The methods used were mixture (Electrode 1), impregnation (Electrode 2) and direct synthesis (Electrode 3). Electrodes 2 and 3 showed higher potentials during cathodic polarization up to 10 mA cm−2 than Electrode 1. The rate of chemical destruction of H2O2 decreased in the order Electrode 3 > Electrode 2 > Electrode 1. Electrode 3 showed the smallest potential drop for a discharge at 10 mA cm−2, 0.09 V after 50 h. However, the potential of Electrode 2 decreased with discharge, becoming 0.09 V lower than that of Electrode 3 after a 50 h discharge at 10mA cm−2. Once the potential drop occurred, the potential was not recovered by resting or by drying the electrode. The potential drop may be caused by deactivation of FePc. One possible reason for such deactivation is the presence of H2SO4, which remained on the electrode after impregnation of the FePc-H2SO4 solution.

Effect of method of preparation of FePc oxygen reduction catalyst on the activity of practical air electrodes

The catalytic effects if iron phthalocyanine (FePc) on two types (A and B) of practical air electrodes were examined, and compared with those of cobalt phthalocyanine (CoPc). For Type A electrodes, polytetrafluoroethylene (PTFE) powder was heat-treated at 400° C. For Type B electrodes, PTFE dispersions were used with treatment at 250° C. Both FePc and CoPc showed high H2O2 decomposition rates, which resulted in low oxygen electrode polarization at high current density. However, the catalytic effects for Type A electrodes were not shown at low current density (< 1 mA cm−2), despite the fact that a 4-electron reduction process took place on FePc at these current densities. For the Type B electrodes, the effect of FePc at low current density became clearer: under these conditions, the electrode with FePc showed a higher potential than that with CoPc and showed a higher open circuit potential (OCV) (0.218V). Type B electrodes showed good performance in the entire current density region compared with Type A electrodes. With FePc catalysts, Type B electrodes showed a larger current region for the 4-electron process (0-0.1 mA cm−2) compared with Type A electrodes (0-0.02 mA cm−2). The improved performance of Type B electrode is considered to be due to the presence of many pores as a result of the PTFE ‘yarn’ connecting carbon substrate particles.

Layered materials for lithium secondary batteries

Abstract Discharge and charge characteristics of SnSe2 and Cu2V2O7 cathode lithium batteries, whose cathodes are expected to be topochemically reacted with Li cation, are studied. Both cathodes show good rechargeability in the range of LixSnSe2 (0 ≦ x ≦ 1) and LixCu2V2O7 (0 ≦ x ≦ 2). After discharging, cathode materials were examined by powder X-ray analysis and the movement of Bragg peaks, which suggest Li cation intercalates to cathode materials, were observed. The capacity of the Li/SnSe2 couple (calculated on the basis of the cathode material only) was 148 mA h/g and the cycle life was 15 times to 0.4 Li equiv. (38 mA h/g). For the Li Cu 2 V2O7 couple, the capacity was 459 mA h/g and the cycle life was 31 times to 1 Li equiv. (78 mA h/g).

Additive effects of Li+ ion solvation compounds on LiClO4-propylene carbonate electrolytic properties

Abstract The additive effects of cation solvation compounds (CSC) on the Li + ionic conductivity and also on the Li charge-discharge characteristics for 1M L The Li charge-discharge efficiency increased by about 15% on addition of TMEDA solution. This is assumed to be due to the protecting effect of TMEDA or

Electrochemical reactivity of aromatic compounds for use in Li cells

The electrochemical reactivity of aromatic compounds coupled with Li in LiClO4-propylene carbonate was studied. Simple aromatic compounds, triphenylmethane compounds and quinone imine dyes were used. Discharge results for aromatic cathode-Li cells indicated that the relation between discharge voltage measured and reduction potential reported was approximately linear, which suggested that the discharge products were ion complexes. Also, the discharge voltage increased with an increase of their electron accepting groups and with a decrease of the electron donating strength of alkyl groups in their amino end groups. Among these compounds, rosaniline derivatives, bromo-substituted phenol red and thiazine dyes showed higher discharge voltages than 2.5 V. Methylene blue (MB) showed the largest energy density of 363 Wh kg−1. Details of MB charge-discharge behavior were examined. The dynamic charge-discharge tests and cyclic voltammetry results suggested that the MB-Li cell could be cycled up to 2e per mol of MB depth. Direct reaction between the Li anode and dissolved MB seemed to be small as indicated by the Li+ ion conductive film formation on the Li anode.