Redox activity of an organosulfur compound with multiple thiol groups and its application to a cathode active material of lithium batteries are described. To accelerate a slow redox reaction of organosulfur compounds such as 2,5-dimercapto-1,3,4-thiadiazole (DMcT), conducting polymer polyaniline (PAn) is mixed with organosulfur compounds, yielding a composite material. Within the composite, DMcT and PAn interact at molecular-level and the redox reaction of DMcT is successfully accelerated by PAn. The DMcT /PAn composite shows a promise as a high energy cathode active material with the discharge capacity of 185 Ah/kg-cathode and the average discharge voltage at 3.4 V. Furthermore, using a copper foil as a cathode current collector, battery performances of the composite cathode are significantly improved. The observed improvement is attributed to a formation of a complex between a copper ion and DMcT, which accelerates the redox reaction of DMcT. The discharge capacity of the composite cathode on a copper current collector is 225 Ah/kg-cathode. The discharge capacity is further increased to 500 Ah/kg-cathode by adding elemental sulfur to the composite.
The Kolbe electrolysis of a variety of carboxylates was examined on ordinary (hydrophilic) and PTFE composite-plated (hydrophobic) platinum anodes in aqueous electrolytic solutions. The electrolysis of hydrophobic carboxylates such as long-chain or fluorinated ones was substrate-selectively suppressed on the hydrophobic (PTFE/Pt) anode. The mechanism of the above unique hydrophobic effect was discussed on the basis of preparative electrolysis, voltammetry and hydrophilic/hydrophobic interaction between the anode surface and carboxylate ions.
Copper self-sputtering is investigated to fill deep holes in a Silicon wafer. The dimensions of the holes are 0.6 μm in diameter 1.2 μm in depth. The distance between the substrate and the target is 173 mm, 5.5 times the erosioncenter radius. This distance is chosen to attempt to improve the filling characteristics. The substrate temperature between 300°C and 550°C. The thickness of copper films deposited is in the range of 0.8 μm to 1.5μm. The base pressure of the sputtering process is a extremely high vacuum (XHV, less than 1×10−8 Pa). It is found that two-step self-sputtering of copper is very effective to fill up the contact holes without using a barrier metal However when using barrier metal films of TiN, the reflow processes after the deposition of total films at room temperature obtains good results.
Magnetic fields were applied to the electropolymerization of pyrrole as a novel technique to control the properties of conducting polymers. The p-toluenesulfonate-doped polypyrrole films prepared in the magnetic fields exhibited a more negative cathodic peak in the cyclic voltammograms. This voltammetric change at the reduction process was explained as change from the anion undoping to the cation doping, and such dopingundoping behavior was confirmed by the measurements of electrochemical quartz crystal microbalance.
Extensive researches on LiNiO2 as a new cathode material for lithium ion secondary batteries have been performed. They will be able to achieve both the higher capacity and the lower cost than those of the conventional cathode material, LiCoO2. However, it is well known that LiNiO2 has low stability and its capacity decreases with increasing charge/discharge cycles in spite of the good performance at the first cycle. We tried to observe the cross sections of LiNiO2 particles by using SIM (Scanning Ion Microscopy), and compared the particles between initial and after charge/discharge cycles. Those powders were single crystals prepared by CSD(Citric Spray Drying) process. LiNiO2 particles after 10 cycles were broken into pieces, whose sizes were the range from 0.1 to 0.5 μm. We expect that the destroy of particles was caused by the stress with expansion and contraction of the crystal.