Nobuhiro Furukawa

Manganese oxides for a lithium secondary battery — composite dimensional manganese oxide (CDMO)

Abstract Manganese dioxide was adopted as a positive material for a lithium secondary battery that is both inexpensive and has a high discharge voltage. In this report, the rechargeability of several manganese oxides that contain lithium in their structures was investigated by cycle tests on flat cells and by X-ray diffractometry (XRD). The results were compared with the rechargeability of γ/β-MnO 2 . In a cycle test at a depth of 0.14 e/Mn, spinel LiMn 2 O 4 and CDMO (heat treated LiOH·MnO 2 ) showed much better rechargeability than γ/β-MnO 2 . At a depth of 0.26 e/Mn, the rechargeability of CDMO was better than that of spinel LiMn 2 O 4 . The crystal structure of CDMO consists of Li 2 MnO 3 and γ/β-MnO 2 (composite dimension). We also investigated the optimum lithium molar ratio from which CDMO could be prepared. We consider that the optimum molar ratio of lithium is between 30 and 50 mole percent.

Characteristics of a lithium secondary battery using chemically-synthesized conductive polymers

Several conductive polymers (polyacetylene, polypyrrole, polythiophene, polyiminodibenzyl, polycarbazole, polyfuran, polyphenothiazine) have been synthesized by a chemical polymerization method and examined for their suitability as positive electrode material for lithium secondary batteries. A test cell, using polypyrrole as a positive electrode, showed good charge/discharge characteristics. Oxidizing agents for the synthesis of polypyrrole have been investigated for further improvement, and polypyrrole prepared by a new method of synthesis using a Cu(BF4)2/nitrile system exhibited excellent performance.

Development and commercialization of nickel-metal hydride secondary batteries

Hydrogen-absorbing alloys used for the negative electrode of nickel-metal hydride (Ni-MH) secondary batteries must combine the two roles of a hydrogen storage media and an electrochemical catalyt. Alloys for secondary batteries must also offer endurance during charge/discharge cycles. Hydrogen-absorbing alloys for batteries have been developed from these viewpoints. The hydrogen-absorbing alloys used for Ni-MH can be divided into two main types: the LaNi5-type and the TiNix-type. In the LaNi5-type, we have substituted La for Misch-metal (Mm), which is a mixture or rare earth elements such as La, Ce, Pr and Nd, and we have partially substituted Ni for Co and Al to lengthen the charge/discharge cycle life. To adjust the hydrogen-absorbing equilibrium pressure, we have partially substituted Ni for Mn and Al. Another type of positive electrode, different from that of Ni-Cd secondary batteries, was developed for the use with Ni-MH to study the environment. A Zn-Co additive prevented electrode swelling by suppressing the production of γ-NiOOH at charging. As a result, cadmium-free, low-pollution, nickel electrodes were developed. As for cell construction materials, new separators were also developed that suggest improved cell reliability. Ni-MH can now be practically charged at 1C using the -ΔV charging method, and discharge at 4C. Its 1C charge/discharge cycle life is more than 500 cycles. This enables the commercial application of Ni-MH to a wide variety of cordless equipment.

Lithium batteries with polymer electrodes

Lithium primary batteries are a comparatively new type of primary battery. Since they were first introduced, however, they have found a variety of applications, mainly in consumer uses. Lithium batteries have the lightweight properties of lithium, such as low specific gravity (0.53) and low potential (− 3.0 V vs NHE), and by using a non-aqueous electrolyte solution, they have the following superior characteristics: 1. High voltage (approximately 3 V) 2. High energy density 3. Low self-discharge rate 4. Wide operating temperature range

Lithium-containing manganese dioxide (composite dimensional manganese oxide: CDMO) as positive material for a lithium secondary battery

Abstract Lithium-containing manganese dioxide (CDMO) has been developed as the positive material for lithium secondary batteries. CDMO is prepared from lithium salt and manganese dioxide by heat treatment. It is a composite oxide of γ/β-MnO 2 and Li 2 MnO 3 . The influence on rechargeability of lithium salts, heat-treatment temperature, and manganese dioxide type has been investigated by conducting cycle tests with flat cells. Lithium hydroxide is more reactive with MnO 2 in the production of Li 2 MnO 3 than either Li 2 O or Li 2 CO 3 . The optimum condition for preparing CDMO is to heat treat LiOH and MnO 2 at about 375 °C. CDMO prepared from EMD (electrolytic manganese dioxide) yields a larger and more stable capacity than CDMO prepared from CMD (chemical manganese dioxide). Sodium-free EMD exhibits the largest discharge capacity.

Relation between equilibrium hydrogen pressure and lattice parameters in pseudobinary ZrMn alloy systems

Abstract The influence of transition elements (M ≡ V, Fe, Co, Ni) in ZrMn2 − xMx alloy systems on the equilibrium hydrogen pressure and lattice parameters was studied in order to develop metal hydride materials for use in heat storage and heat transportation systems operating at temperatures between 100 and 250 °C, for which there is great demand in industrial heat processes. The equilibrium characteristics and lattice parameters of as-cast pseudobinary alloys ZrMn2 − xMx (M ≡ V, Fe, Co, Ni; 0 ⩽ x ⩽ 0.6) were evaluated by measuring pressure-composition isotherms at 200 °C and by analysing X-ray diffraction patterns using Rietvelds method. The crystal structures of all the pseudobinary alloys were the C14-type Laves phase. The decrease of the unit cell volume increased the equilibrium hydrogen pressure in the alloys modified by vanadium, iron or cobalt, but the alloys modified by nickel showed an opposite tendency. These results were interpreted in terms of Miedemas rule. Consequently, cobalt and vanadium were found to be the most effective elements for control of the equilibrium hydrogen pressure and therefore for extension of the available temperature range of pseudobinary ZrMn alloy systems of the C14-type Laves phase.

Development of hydrogen-absorbing alloys for nickel-metal hydride secondary batteries

Abstract The effect of the stoichiometry of Mm(Ni 0.64 Co 0.2 Mn 0.12 Al 0.04 ) x alloy on the hydrogen absorption capacity, and the reactivity of two-phase alloys in alkaline solution, were investigated. Furthermore, the electrochemical characteristics of non-stoichiometric hydrogen-absorbing alloys with a second phase were investigated. Nonstoichiometric hydrogen-absorbing alloys ( x =4.5–4.8) with boron added were found to have higher electrochemical capacities and superior electrochemical reactivities than those of stoichiometric alloys without boron added.

Improvement of lithium-containing manganese dioxide (composite dimensional manganese oxide: CDMO) as positive material for lithium secondary batteries

Abstract Lithium-containing manganese dioxide (CDMO) has been developed as the positive material for lithium secondary batteries. CDMO is prepared from lithium salt and manganese dioxide by heat treatment. The material is a composite oxide of γ/β-MnO2 and Li2MnO3. The charge condition has been investigated in order to develop an improved CDMO that will exhibit a higher discharge voltage and a larger capacity. CDMO charged to a high potential (i.e., 3.6 V versus LiAl electrode) displays higher discharge voltage and larger capacity than CDMO subjected to normal charge (i.e., 3.3 V versus LiAl). It is concluded that when CDMO is charged to a high potential, lithium inserted not only by electrochemical reaction but also by heat treatment are removed from the γ/β-MnO2 phase. The optimum conditions for preparing improved CDMO is to heat treat LiOH and electrolytic manganese dioxide (EMD) at a Li/Li+Mn atomic ratio of 0.3 at ∼250 °C. The improved CDMO delivers a discharge capacity of over 200 mA h g−1. Also, excellent rechargeability is experienced, even when CDMO is charged to a high potential.

Characteristics of hydrogen-absorbing Zr-Mn alloys for heat utilization

Abstract The substitution of various metals into ZrMn2 to produce possible materials for heat utilization systems was studied in the temperature range 200–250 °C. As a result, vanadium was found to be the most effective element for decreasing the equilibrium hydrogen pressure of the ZrMn2 alloy, cobalt was found to be an effective element for reducing the plateau slope of the ZrMn2 alloy and the ternary Zr-Mn-V alloy, and vanadium was found to be an effective element for reducing the hysteresis of the ZrMn2 alloy. Results show that quaternary Zr-Mn-Co-V alloy has excellent equilibrium characteristics in the temperature range 200–250 °C for heat utilization systems.

Effect of storage conditions on the performance of phosphoric acid fuel cells

Abstract In this study, start/stop tests have been conducted on small, single cells at various storage temperatures. Cell service-life has been observed, along with changes in the distribution of phosphoric acid in the cell components that accompany fluctuations in the phosphoric acid volume. The results show that, with each repetition of the operation-storage cycle, the volume of phosphoric acid changes (i.e., increases/decreases). This behaviour influences both the cell service-life and the phosphoric acid distribution in the cell components. Therefore, in order attain stable cell performance for a long period, it is necessary to optimize the conditions under which cells are stored.