Tetsuyuki Murata

Impurities in LiFePO4 and Their Influence on Material Characteristics

Li 3 PO 4 impurity was found in hydrothermally grown LiFePO 4 samples made with excess Li. The impurity dissociates in water, leading to an apparent alkaline nature of the LiFePO 4 sample. The impurity can be removed by washing the sample in a neutral buffer solution, after which an increase in specific capacity of the LiFePO 4 sample was observed. Li 3 PO 4 , as an inactive component within the active material, reduces the energy density of LiFePO 4 . Additional experiments were performed to study the reactivity of LiFePO 4 in different environments. It is found that LiFePO 4 decomposes in a strong alkaline solution and the decomposition can be slowed down by carbon coating the material. After prolonged storage in water, the specific capacity of carbon-coated LiFePO 4 is reduced and Fe dissolution is observed. Material degradation is thought to be due to interactions among LiFePO 4 , impurities, and water.

The surface structure and the electrochemical properties of hydrogen-absorbing alloys treated with an HCl aqueous solution

The surface structure and the electrochemical properties of hydrogen-absorbing alloys treated with an HCl aqueous solution were investigated. This process was observed to form a porous layer rich in nickel on the alloy surface because HCl partially dissolved some of the other elements from the alloy. Therefore, the discharge capacity increased by increasing the reaction surface area. However, the overvoltage of an excessively treated alloy increased along with the depth of discharge as the surface layer of the alloy oxidized and thickened. The effects of treatment on alloys were found to be determined by the hydrogen ion amounts in the acid solution per unit mass of the alloy, regardless of the concentration and volume of the solution. The optimal hydrogen ion amount for a treatment solution was found to be 0.1 mol/kg.

The effect of particle size on the electrochemical properties of hydrogen absorbing alloy electrodes

Abstract The investigation of the effect of the particle size of hydrogen-absorbing-alloys on the electrochemical properties of electrodes revealed that the electrochemical reactivity of small-particle electrodes containing conductive powder was excellent, but that the discharge capacity of the alloy electrodes composed of small particles containing no conductive powder was small. A possible reason for this reduced capacity is the existence of particles that cannot be discharged due to weak contact between the particles as the volume of the alloy changed. Thus, batteries made from electrodes composed of particles larger than 25 μm were found to have superior charge–discharge cycle characteristics.