Study On The Microstructure Tailoring And Electrochemical Performance Of Nickel-based Hydroxides

Nickel-based oxide and hydroxide are an important category of electrode materials for application in supercapacitors. Recent research indicates that the electrochemical performance of nickel-based materials depends on their size, morphology and structure. Therefore, controlling on these parameters is the main method for the synthesis of high electrochemical performance electrochemical materials. In this thesis, various nickel-based hydroxides with high electrochemical performance were prepared by hydrothermal method, which includes hierarchically structured nanofelt-like ?-NiOOH nanofibers, surface-tailored ?-Ni?OH?₂ nanosheets, cobalt substituted ?-Ni?OH?₂ nanofibers-composed hierarchical nanostructure and nanofibers-composed dandelion-like CoNiAl triple hydroxide.?1? Preparation of hierarchically structured nanofelt-like ?-NiOOH and investigation on its electrochemical performance: hierarchically structured nanofelt-like ?-NiOOH was prepared at 120 oC by hydrothermal method. This nanostructure guarantees the full contact of material with electrolyte and the intimate connection between material and current collector. Thus, the material has excellent electrical performance: its specific capacitance amounts to 2585 F g^-1 at scan rate of 5 mV s^-1 and remains 1240 F g^-1 at high current density of 30 A g^-1. The unique nanostructure can withstand the strain/stress generated during electrochemical redox reactions, thus greatly promoteing the cycle stability of material. After 4000 charge-discharge cycles, the material still remains 86% of initial capacitance.?2? Preparation of surface-tailored ?-Ni?OH?₂ nanosheets and investigation on their electrochemical performance: ?-Ni?OH?₂ nanosheets were prepared in the presence of glycerol by hydrothermal method. The characterization results indicated that under the mediation of glycerol, the as-prepared ?-Ni?OH?₂ nanosheets presented rougher surface as compared with the sample prepared without using glycerol, which results in the surface area increase of nanosheets from 13.09 m² g^-1 to 22.65 m² g^-1, leading to the improvement of electrochemical performance. The material with 5% glycerol volume fraction presents the maximum specific capacitance of 2100 F g^-1 at current density of 1.3 A g^-1 and its specific capacitance remains 1281 F g^-1 at high current density of 26.3 A g^-1.?3? Preparation of hierarchically structured Co²⁺ doped ?-Ni?OH?₂ and investigation on its electrochemical performance: Hierarchically structured Co²⁺ doped ?-Ni?OH?₂ was grown on the surface of conductive nickel foam. The hierarchical nanostructure and optimized molar ratio of Co and Ni guarantees the high electrochemical performance of obtained samples. The sample doped with 11.1% Co²⁺ presented the maximum specific capacitance of 2687 F g^-1 at current density of 1.1 A g^-1 and its specific capacitance was remained 1335 F g^-1 at high current density of 35.3 A g^-1.?4? Preparation of nanofibers-composed dandelion-like CoNiAl triple hydroxide and investigation on its electrochemical performance: The nanofibers-composed dandelion-like CoNiAl triple hydroxide was grown on the surface of conductive nickel foam. Through optimizing the molar ratio of Co, Ni and Al, the as-prepared material presents high electrochemical performance and excellent charge-discharge cycle stability. The sample prepared with mole ratio of Ni/Co/Al=2:8:1 presented the highest specific capacitance of 2791 F g^-1 at scan rate of 5 mV s^-1. Meanwhile, the sample remained 85% of initial capacitance after 2000 charge-discharge cycles.