Study On Nickel-based Electrode Materials For Alkaline Batteries, Lithium Ion Batteries And Fuel Cells

Alkaline Zn-MnO₂ primary batteries and nickel-based rechargeable batteries are widely applied in portable electronics, which have high ratio of performance and cost. A new type of high powder primary battery with sphericalβ-NiOOH positive electrode material has been developed in Japan recent years. However, the storage stability ofβ-NiOOH is very poor in electrolyte. The synthetic method and performance improvement of NiOOH are keys for the production of this new type of battery. MH-Ni rechargeable battery has better safe performance compared to other high energy batteries, which is more suitably used in electric vehicle. However, the common sphericalβ-Ni(OH)₂ can not well meet the demand in electric vehicle battery such as high temperature and current charge and discharge, etc.Lithium ion rechargeable battery has the best comprehensive performance and most fast development among the large scale commercial batteries. But the commonly used LCoO₂ positive electrode material in the battery is high cost and harmful to the environment. The low cost and high performance positive electrode material substituting for LCoO₂ is very important and urgent for the extend application of lithium ion rechargeable battery. The LiNiO₂ serial positive electrode materials have advantages such as high specific capacity, specific power and moderate cost, etc. However, the disadvantages of LiNiO₂ such as hard preparation, fast capacity decay, bad storage stability, etc have hampered its practical application.The specific energy of low temperature fuel cells is higher than that of common batteries such as lithium ion and MH-Ni rechargeable batteries. The research of fuel cells is the most active among all electrochemical power sources at present. Pt has the highest electrocatalytic activity than other elements in the fuel cell oxidation and oxygen reduction reactions. But the catalytic activity of pure Pt is not satisfied for the application of direct methanol fuel cells, etc. Furthermore, the cost of Pt is very high, which seriously hinders the commercial use of low temperature fuel cells.This thesis is in order to solve the above problems and the results are following: 1. NiOOH and Ni(OH)₂ as positive electrode materials for alkaline batteriesThe NiOOH products were prepared by chemical oxidation of sphericalβ-Ni(OH)₂ with K₂S₂O8 in KOH solution and the effects of preparation conditions were investigated. The NiOOH with low nickel oxidation state was obtained only in low concentration of KOH solution (1-3M). The NiOOH with high nickel oxidation state was got in high concentration KOH solution (6-9M). The nickel oxidation state of products increased with the ratio of K₂S₂O8 andβ-Ni(OH)₂ increased or the KOH solution increased from 3M to 6M. The NiOOH with nickel oxidation state from ₂.95 (pureβ-NiOOH phase) to 3.55 (pureγ-NiOOH phase) can be obtained by controlled the synthetic conditions. As the nickel oxidation state of NiOOH increased, theγ-NiOOH phase content increased, tap density decreased, spherical particles broke more seriously, specific surface increased, K content increased, Ni content decreased, specific discharge capacity decreased, storage stability in KOH electrolyte increased and the thermal behavior was more similar to pureγ-NiOOH. The NiOOH with nickel oxidation state of 3.04 was suitable as positive electrode material for alkaline Zn-NiOOH primary battery for comprehensive concern.The spherical Al substitutedγ-NiOOH was synthesized by oxidation of spherical Al substitutedα-Ni(OH)₂ with K₂S₂O₈ in 6M KOH solution. The samples were characterized by XRD, SEM, FTIR, TGA-DTG, TPD-MS and HT-XRD. The results indicated that the interlayer distance and the intercalated species decreased while the tap density increased when the Al substitutedα-Ni(OH)₂ was oxidized to Al substitutedγ-NiOOH. And the Al substitutedγ-NiOOH has similar thermal behavior to Al substitutedα-Ni(OH)₂ but the thermal stability of Al substitutedγ-NiOOH was inferior to that of Al substitutedα-Ni(OH)₂. The spherical Al substitutedγ-NiOOH has higher specific discharge capacity of 353mAhg-1 and better storage stability in KOH electrolyte than sphericalβ-NiOOH. Both of spherical Al substitutedγ-NiOOH andβ-NiOOH have good charge-discharge cycleability. The spherical Al substitutedγ-NiOOH has higher tap density (1.53gcm-3) than un-sphericalγ-NiOOH (1.01 gcm-3) but it is lower compared to sphericalβ-NiOOH (2.45 gcm-3).β-Co(OH)₂ coated sphericalβ-Ni(OH)₂ was prepared by the precipitation of β-Co(OH)₂ on the surface of sphericalβ-Ni(OH)₂ particles. Theβ-CoOOH coated sphericalβ-NiOOH was obtained by adding K₂S₂O8 following the product ofβ-Co(OH)₂ coated sphericalβ-Ni(OH)₂. Cyclic voltammetry measurement demonstrated that the coated sphericalβ-Ni(OH)₂ andβ-NiOOH.have better electrochemical performance in charge-discharge and cyclability than uncoated ones, respectively. The sphericalβ-NiOOH also has better storage stability in alkaline electrolyte than uncoated one. The MH-Ni rechargeable battery withβ-Co(OH)₂ coated sphericalβ-Ni(OH)₂ as electrode material has better specific charge-discharge performance, higher active material utilization, charge efficiency at elevate temperature and cycleability than the MH-Ni rechargeable battery with uncoated sphericalβ-Ni(OH)₂ as positive electrode material. The Zn-NiOOH battery withβ-CoOOH coated sphericalβ-NiOOH as positive electrode material can be used not only conveniently as primary battery but also repeatedly as rechargeable battery. The 1000 mA discharge time of Zn-NiOOH battery to 1.1 V is 56 min, which is more than five times and about 0.3 V higher of discharge voltage than conventional alkaline Zn-MnO₂ primary battery. The alkaline Zn-NiOOH/MnO₂ primary battery then has both lower cost compared to Zn-NiOOH battery and higher power compared to alkaline Zn-MnO₂ battery.₂. LiNiO₂@LiCoO₂ as positive electrode material for lithium ion battery The spherical LiNiO₂-LiCoO₂ composite positive electrode material was prepared by sintering sphericalβ-NiOOH@CoOOH with LiOH in air atmosphere. The product with bad stoichiometry and low crystallinity was obtained at too low temperature or short time. The reaction temperature was too high or the reaction time was too long, resulting in production without core-shell structure with bad stoichiometry and high crystallinity. The LiNiO₂@LiCoO₂ with the highest XRD peak intensity ratio of 003 and 004 of 1.79 and the best stoichiometry was obtained from sphericalβ-NiOOH@CoOOH at 600oC and ₂4 h, which also has the best layered structure than ones from sphericalβ-NiOOH orβ-Ni(OH)₂. The first discharge capacity of this LiNiO₂@LiCoO₂ with core-shell structure is 181.41mAhg-1. The LiNiO₂@LiCoO₂ also has better cycleability and storage stability than LiNiO₂. The synthesis of LiNiO₂@LiCoO₂ from sphericalβ-NiOOH@CoOOH can be carried out in air amphorae and at low temperature, which is very facile in large scale produce.3. Ni@Pt core-shell nanoparticle as electrocatalyst for low temperature fuel cells The Ni@Pt nanoparticles with Ni core and Pt shell as electrocatalysts were prepared by successive reduction of nickel and Pt ions with hydrazine in glycol solution. The mean particle size of core-shell nanoparticles increased with the ratio of Pt and Ni increased. The interface of Ni core and Pt shell might be NiPt alloy and the shell was main Pt. The Ni@Pt core-shell nanoparticles have higher catalytic efficiency of methanol oxidation and CO tolerance than pure Pt, especially the NiPt01 sample (01 donate the molar ratio of Pt and Ni is 1:10). The NiPt01 also had good stability in acid electrolyte because the Ni core was coated by Pt. The Ni@Pt core-shell nanoparticles also had better electrochemical oxygen reduction catalytic efficiency than pure Pt by rotating disc electrode tests. The noble metal of Pt was most efficiently dispersed on the un-noble metal of Ni core surface, and the nickel underlay the Pt had co-catalytic effect. Therefore the catalytic efficiency of Ni@Pt core-shell nanoparticles was very high and the noble metal of Pt was most utilized, the cost of fuel cells could be decreased.