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

摘要

Cobalt is usually co-precipitated with nickel to improve the nickel hydroxide electrode capacity. Herein, we present the acquirement of #beta#-type mixed Ni/Co phases by three different synthetic routes. The first method consists of the electrochemical removal of Li from LiNi_(1-x)Co_xO_2 compounds to form Ni_(1-x)-Co_xO_2 compounds that are then reduced in a KOH-hydrogen peroxide medium to produce Ni_(1-x)Co_x(OH)_2. The second method deals with the aging of #alpha#-type mixed Ni/Co hydroxides in 8M KOH solution at 60 deg C. Finally, the third method consists of the direct precipitation of Ni and Co sulfates using the right sequence and amount of NH_4OH and NaOH bases. A constant capacity was found, independently of the amount of Co, for samples prepared 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 material morphology and surface area arguments. Moreover, we show that cobalt addition in the nickel network enhances the stability of the #beta#(III) phase.