Ho Rim

Development of AB2-type Zr–Ti–Mn–V–Ni–Fe hydride electrodes for Ni–MH secondary batteries

Abstract A series of multicomponent Zr 0.5 Ti 0.5 Mn 0.4 V 0.6 Ni 1− x Fe x ( x =0.00, 0.15, 0.30, 0.45 and 0.60) alloys are prepared and their crystal structure and P – C – T curves are examined. The electrochemical properties of these alloys such as discharge capacity, cycling performance and rate capability are also investigated. Zr 0.5 Ti 0.5 Mn 0.4 V 0.6 Ni 1− x Fe x alloys ( x =0.00, 0.15, 0.30, 0.45 and 0.60) have the C14 hexagonal Laves phase structure. Their hydrogen storage capacities do not show significant differences. The discharge capacity just after activation decreases with the increase in the amount of the substituted Fe but the cycling performance is improved. The discharge capacity after activation of the alloy with x =0.00 is about 240 mAh/g at the current density 60 mA/g. Zr 0.5 Ti 0.5 Mn 0.4 V 0.6 Ni 0.85 Fe 0.15 is the best composition with a relatively large discharge capacity and a good cycling performance. The increase in the discharge capacity of Zr 0.5 Ti 0.5 Mn 0.4 V 0.6 Ni 0.85 Fe 0.15 with the increase in the current density (from 60 to 125 mA/g) is considered to result from the self-discharge property of the electrode. During activation Ni-rich regions form on the electrode surface, which may act as active sites for the electrochemical reaction. The formation of more minute cracks in the large particles of the alloys with higher Fe content is considered to result from the more severe destruction of the crystal structure due to more dissolution of zirconium and iron into the solution.

Synthesis of Cathode Materials LiNi 1-y Co y O 2 from Various Starting Materials and their Electrochemical Properties

The LiNi 1-y Co y O₂ samples were synthesized at 800℃ and 850℃, by the solid-state reaction method, from the various starting materials LiOH, Li₂CO₃, NiO, NiCO₃, Co₃O₄, CoCO₃, and their electrochemical properties are investigated. The LiNi 1-y Co y O₂ prepared from Li₂CO₃, NiO, and Co₃O₄ exhibited the α-NaFeO₂ structure of the rhombohedral system (space group; R3m). As the Co content increased, the lattice parameters a and c decreased. The reason is that the radius of Co ion is smaller than that of Ni ion. The increase in c/a shows that two-dimensional structure develops better as the Co content increases. The LiNi 0.7 Co 0.3 O₂ [HOO(800,0.3)] synthesized at 800℃ from LiOH, NiO, and Co₃O₄ exhibited the largest first discharge capacity 162 mAh/g. The size of particles increases roughly as the valve of y increases. The samples with the larger particles have the larger first discharge capacities. The cycling performances of the samples with the first discharge capacity larger than 150 mAh/g were investigated. The LiNi 0.9 Co 0.1 O₂[COO(850,0.1)] synthesized at 850℃ from Li₂CO₃, NiO, and Co₃O₄ showed an excellent cycling performance. The sample with the larger first discharge capacity will be under the more severe lattice destruction, due to the expansion and contraction of the lattice during intercalation and deintercalation, than the sample with the smaller first discharge capacity. As the first discharge capacity increases, the capacity fading rate thus increases.