Electrochemical performance comparison between beta-type mixed nickel cobalt hydroxides prepared by various synthesis routes

Cobalt is usually co-precipitated with nickel to improve the nickel hydroxi de electrode capacity. Herein, we present the acquirement of beta -type mix ed Ni/Co phases by three different synthetic routes. The first method consi sts of the electrochemical removal of Li from LiNi1-xCoxO2 compounds to for m Ni1-xCoxO2 compounds that are then reduced in a KOH-hydrogen peroxide med ium to produce Ni1-xCox(OH)(2). The second method deals with the aging of a lpha -type mixed Ni/Co hydroxides in 8M KOH solution at 60 degreesC. Finall y, the third method consists of the direct precipitation of Ni and Co sulfa tes using the right sequence and amount of NH4OH and NaOH bases. A constant capacity was found, independently of the amount of Co, for samples prepare d from a lithiated precursor, in total contrast with samples prepared from the aging and precipitation processes that show a maximum capacity near x = 0.1. We explain such a different electrochemical behavior, based on materi al morphology and surface area arguments. Moreover, we show that cobalt add ition in the nickel network enhances the stability of the beta (III) phase. (C) 2001 Editions scientifiques et medicales Elsevier SAS. All rights rese rved.