Mixed-valence Nickel Hydroxide Morphology And Electrochemical Performance

Ni-MH batteries with high specific power and specific energy density are considered to be one of the most promising choices for electric vehicle and hydride electric vehicle applications. The nickel electrode material has been the key factor to improve the ability of Ni-MH batteries.The new active materials spherical Ni(OH)x for nickel electrodes were synthesized by spherical P-Ni(OH)2 surface modified with chemical oxidized NiOOH nanoparticles. The average nickel oxidation state, microstructure and morphology of the spherical Ni(OH)x are investigated by complexometric titration, XRD, SEM, TEM and SAED. It is demonstrated that the NiOOH with a flaky-like morphology are dispersed randomly on the surface of the spherical P-Ni(OH)2. The average nickel oxidation state of different samples is between 2.03 and 2.10. The existence of chemical oxidized NiOOH nanoparticles in the nickel electrode contributes great effect on the improvement of electrochemical performance. The Ni(OH)x(x=2.05) show considerable electrochemical performance with the discharge capacity of 300 mAh·g-1 at 0.2 C rate and 253 mAh·g-1 at 5 C rate, respectively. A good electrochemical performance is observed at high discharge density with the capacity maintenance above 96% after 200 cycles at 2 C rate. The results of the XRD, TEM and SAED of Ni(OH)x(x=2.05) after charge-discharge show that the structure of the material has been changed in the process of change-discharge cycles with chemical oxidized NiOOH. Therefore, the coated samples show excellent discharge performance at different charge-discharge rates.Micron-size multiphase Ni(OH)2 with nanosheets structure were synthesized by coordination homogeneous precipitation method and the new electrode materials flaky-like Ni(OH)x were prepared by their surface coated with chemical oxidized NiOOH nanoparticles. The average nickel oxidation state of flaky-like Ni(OH)x is between 2.03 and 2.09 investigated by complexometric titration. The samples were characterized by XRD and SEM. Results show that the NiOOH with a flaky-like morphology are dispersed randomly on the surface of the multiphase Ni(OH)2. The existence of chemical oxidized NiOOH nanoparticles in the nickel electrode contributes great effect on the improvement of electrochemical performance. The multiphase Ni(OH)2 as positive active material show the discharge capacity of 306 mAh·g-1 at 0.2 C rate. The discharge capacity of flaky-like Ni(OH)x(x=2.07) sample can reach to 326 mAh·g-1 at 0.2 C, a first discharge capacity of 305 mAh·g-1 at 2 C and 278 mAh·g-1 after 200 cycles.The new nickel electrode materials Al-a-Ni(OH)x were synthesized by a simple route of chemical oxidation on the prepared Al-α-Ni(OH)2. The average nickel oxidation state of the samples is between 2.02 and 2.15. XRD, FT-IR, SEM, TEM and SAED results show that a core/shell structure is formed with the badly crystallineγ-NiOOH coating outside after surface modification. The Ni-MH battery models with the above treated samples as positive materials show considerable electrochemical performance. The Al-α-Ni(OH)x(x=2.07) sample has a discharge capacity of 352 mAh·g-1 at 0.2 C and 310 mAh·g-1 at 5 C. Besides, the capacity retains more than 96% after 200 cycles at 2 C. It illustrates that the existence of chemical oxidized NiOOH in the nickel electrode contributes great effect on the improvement of electrochemical performance.