Study On The Preparation And Electrochemical Properties Of A New Electrode Material Spherical ?-Ni?OH?₂

Ni?OH?₂ is a widely used cathode material for secondary batteries such as nickel-hydrogen,nickel-cadmium,and nickel-zinc batteries.Now commercial Ni?OH?₂ is the?type,of which the performance has been extremely developed after decades of research and practical application,closing to its theoretical specific capacity.However,with the development of electric and hybrid vehicles,the performance of the existing?-Ni?OH?2 cannot satisfy the increasing demand for batteries,which is urgently needed to be taken place of by a new positive electrode material with a higher capacity.Therefore,?-Ni?OH?₂ has caught the attention of researchers.Compared to the?-Ni?OH?₂,?-Ni?OH?₂has the following advantages as a cathode material for hydrogen nickel batteries:The?-Ni?OH?₂ would not cause significant expansion of the electrode during the charge and discharge because its crystal density is close to that of the?-NiOOH,benefiting to prolong the cycle life of the battery.The theoretical specific capacity of?-Ni?OH?2 is 482 m Ah/g,higher than that of the?-Ni?OH?₂,which is 289 mAh/g.The discharge platform of?-Ni?OH?₂ is high and its discharge curve is flat.The reversibility and high-current charge and discharge performance of the?-Ni?OH?2 are good.The content of Ni in?-Ni?OH?2 is20%?30%?mass fraction?lower than that in?-Ni?OH?₂,which can effectively reduce the cost of the raw materials.Therefore,the development of?-Ni?OH?2 has great value and commercial prospect,which need to be further studied.In this study,hydrothermal synthesis method was used to synthesize spherical?-Ni?OH?2,during which nickel nitrate and urea were adopted as the raw materials,and the polyethylene glycol?PEG?was used as the active agent.The obtained material is analyzed by multiple tests to manifest its structure and morphology,which showed that the synthesized sample was?-Ni?OH?₂ with a good spherical morphology.The electrochemical performance tests showed that the discharge capacity of the obtained?-Ni?OH?2 was 330 m Ah/g at 0.2C,which was 50 mAh/g higher than that of the commercialized?-Ni?OH?2.Besides,it greatly saved synthetic raw materials and reduced the cost of commercial production to synthesize same quality due to the decreased content of Ni element,?10%in this experiment.On the basis of the above research,in order to improve the stability of the synthesized sample and further improve the electrochemical performance of the?-Ni?OH?₂,trivalent or divalent metal cations?Co,Al,Zn,etc.?were introduced to dope into the?-Ni?OH?₂ lattice using the same synthesis method.It was found that the introduction of these metal cations increased the crystallinity of the?-Ni?OH?₂,making its phase structure more stable in the alkaline,and making it difficult to transform into?-Ni?OH?₂ during long electrochemical cycle.Moreover,the discharge capacity and rate performance were further improved,where the capacity reached to 410mAh/g,which was much higher than the current commercial?-Ni?OH?₂ and closer to the theoretical capacity for the sample doped with 5%Co and 1%Zn.Besides,the?-Ni?OH?₂were easily activated and showed good cycling stability,exhibiting huge commercial application potential.