Hideo Yasuda

Low-temperature synthesis of lithium nickelate positive active material from nickel hydroxide for lithium cells

Abstract A novel method of synthesizing lithium nickelate has been proposed by chemical oxidation of nickel hydroxide in a aqueous LiOH solution at lower temperature than 100°C. In this new process “direct-oxidation method”, the oxidation of Ni(OH) 2 and a subsequent ion-exchange reaction successively took place in the same medium. The conversion yield of the ion-exchange process has not been complete and the product has seemed to remain some amount of proton in its structure. In order to increase the reaction rate and its conversion ratio, it was preferable that the reaction was allowed to proceed at higher temperature range 80–100°C, however, electrochemical activity of the product was drastically deteriorated with a lapse of reaction time at those temperature. Co doping in Ni(OH) 2 was found to be effective in depression of the capacity decrease in the long-time reaction. In addition, the product prepared by the direct-oxidation method has a possibility of a further high-capacity active material based on two-electron redox reaction in the range from Ni 2+ to Ni 4+ . It has exhibited larger discharge capacity than 310 mA h g −1 with a smooth potential change between two plateaux corresponding to Ni 2+ /Ni 3+ and Ni 3+ /Ni 4+ redox couples. Its cycle performance has also been superior to that of LiNiO 2 prepared by the other synthetic methods.

Low-crystalline β-FeOOH and vanadium ferrite for positive active materials of lithium secondary cells

Abstract Low-crystalline β-FeOOH and vanadium ferrite were prepared by a simple hydrolysis method. XRD measurement revealed that the former material had a framework of β-FeOOH with somewhat amorphous structure, and that the latter one gave a crystalline structure analogous to that of the hydrated iron orthovanadate. From the electrochemical measurements, it was found that the low-crystalline β-FeOOH positive electrode showed a discharge capacity of 230xa0mAh/g in the potential range of 4.3xa0V and 1.6xa0V versus Li/Li + , and better cycle performance than the high-crystalline one. The vanadium ferrite positive electrode also showed a high discharge capacity over 300xa0mAh/g and superior cycle performance.