| In this paper, Co-substitutedβ-Ni(OH)2 and Co-Mn substituted multiphase Ni(OH)2 were prepared by chemical co-precipitation. In the process, salt and ammonia-alkali solution dropped into the solution at the same time, with ammonia as the chelating reagent. Single factor experiments were used to study the relation between performance and reaction conditions: such as pH, mol ratio of ammonia and alkali, reaction temperature, aging time and the content of substituted element. Then we found the optimization condition. We analyzed the structure and appearance of the sample synthesized under the optimization condition,and primary analyzed the relation between discharge capability and structure of nickel hydroxide.The Co-substituted nickel hydroxide was studied by XRD,IR and TG-DTA, and the results showed that it was beta crystal. From the SEM, we knew that using ammonia as chelating reagent, better orbicular nickel hydroxide can be prepared under the certain condition. We studied the factors (pH, the concentration of ammonia, reaction temperature and aging time)which could influence the structure and electrochemical capability ofβ-Ni(OH)2. The optimization condition as follows: pH is 11.5, the ratio of ammonia and alkali is 2:1, the temperature is 60℃, and the aging time is 15 hours, the content of Co reached to 2%～3%. The discharge capacity of nickel hydroxide could reach to 230 mAh/g, cycle capability was much better.Though the structure, appearance and heat stability analyzed (such as: XRD, IR, SEM, TG-DTA and so on) of the Co-Mn substituted nickel hydroxide, we could confirm that the Co-Mn-substituted nickel hydroxide which were prepared by co-precipitation method containedα-Ni(OH)2 andβ-Ni(OH)2 at the same time. The manganese hydroxide and cobalt hydroxide were not detected during the XRD and IR, because they had substituted into the crystal. From the IR, we could find that there was water in the Co-Mn substituted sample. It is confirmed that there wereα-Ni(OH)2 in the sample. And according to the SEM, we knew the samples which had multiphase were different fromβ-Ni(OH)2, they looked like flowers.According to the single factor experiment, we could find the optimization condition of tap density as follows: pH is 11.5, temperature is 50℃, the ratio of ammonia and alkali is 0.5:1, the content of Co and Mn both are 3%, the tap density could reach 1.45 g/cm3. The optimization condition of electrochemical capability: pH is 11.7, temperature is 60℃, the ratio of ammonia and alkali is 1:1, the content of Mn is 20%, the discharge could reach 303.76 mAh/g, swelling rate could be the lowest, and reached 1.5%, charge plat voltage could be 1.496 V, discharge plat voltage could be 1.210 V.Co-substituted nickel hydroxide could be propitious to form crystal disorder and improved the electrochemical capability of nickel hydroxide material. At the same time,substituting Co-Mn into the crystal,could be propitious to formα-Ni(OH)2.The preparation of multiphase nickel hydroxide, reducing the cost of nickel electrode and improving the electrochemical capability, may be a promising positive active material for alkaline rechargeable batteries. |
