The Construction Of Mesophase Nickel Hydroxide And Its Application In Nickel-zinc Batteries

The problems of resources and environment increase the demand for saving of energy and clean energy.It is urgent to develop new chemical power or improve the performance of the‘old'chemical power to help solve the problem of environmental pollution.As a kind of green chemical power,nickel zinc battery attracts more attentions due to high-performance,eco-friendly,safe and low-cost features.The development of its electrode materials has become a research focus.In this thesis,the intermediate phase?-?-Ni_1-xMn_x?OH?₂ was synthesized by doping Mn in Ni?OH?₂ lattices.The effect of Mn amounts on the structure and properties of?-?-Ni_1-xMn_x?OH?₂ was studied.On this basis,?-?-Ni_1-xMn_x?OH?₂ grown on the surface of carbon nanotubes?CNT?to prepare?-?-Ni_1-xMn_x?OH?₂/CNT composite.The NiZn battery assembled by using?-?-Ni_1-x Mn_x?OH?₂ or?-?-Ni_1-xMn_x?OH?₂/CNT composite as the cathode material showed high energy density,Coulomb effeciency and long cycle life.The specific research contents are as follows:?1?The intermediate phase?-?-Ni_1-x Mn_x?OH?₂ was prepared by chemical co-precipitation method.Transmission electron microscope?TEM?images and Energy dispersive spectroscopy?EDS?mapping evidenced that Mn was successfully doped into the lattice of Ni?OH?₂.The phase and structure of the samples were characterized by X-ray diffractometer?XRD?and Fourier transform infrared spectrum?FTIR?.The influence of Mn doping amount on the structure of the samples was carefully investigated.The results showed that the samples were intermediate phase?-?-Ni_1-x Mn_x?OH?₂ when the Mn doping amount was less than 20%.The relationships between the structures and electrochemical properties were investigated.The specific capacitance of the intermediate phase?-?-Ni_1-xMn_x?OH?₂ was higher than that of?-Ni?OH?₂ under the same test conditions.Cyclic voltammetry?CV?test results demonstrated that the optimal doping amount of Mn was 3%.The specific capacitance of?-?-Ni_1-x Mn_x?OH?₂?x=0.03?was 286.23 mAh·g^-1 under the scan rate of 1 mV·s^-1.The NiZn battery assembled by using?-?-Ni_1-x Mn_x?OH?₂ as the cathode material still retained the energy density of 201.03Wh·kg^-1 and Coulomb efficiency of above 97%under the charge and discharge current density of 25 mA·cm^-2 after 1200 cycles.?2?To better display the electrochemical performance of intermediate phase?-?-Ni_1-xMn_x?OH?₂,?-?-Ni_1-x Mn_x?OH?₂/CNT composite were prepared by?-?-Ni_1-xMn_x?OH?₂ directly grown on the surface of CNTs in two-step method.TEM images evidenced that the composites were successfully prepared.XRD pattern demonstrated that the phase of Ni_1-x Mn_x?OH?₂ in the composites was still?-?phase.CV test results showed that the specific capacitance of?-?-Ni_1-xMn_x?OH?₂/CNT?x=0.03?composite was 321.77 mAh·g^-1 under the scan rate of 2 m V·s^-1 and higher than that of the material without CNTs and exceeds the theoretical value of?-Ni?OH?₂.Using?-?-Ni_1-xMn_x?OH?₂/CNT?x=0.03?composite as the positive electrode,Zn foil as the negative electrode,charge and discharge cycles of the assembled NiZn pouch cell reached to1400,and the energy density and Coulomb efficiency were more than 201.88 Wh·kg^-1 and 96%.?3?Simulating commercial nickel zinc batteries,NiZn pouch cell was constructed by?-?-Ni_1-x Mn_x?OH?₂/CNT?x=0.03?composite positive electrode and basic zinc carbonate negative electrode and its electrochemical performances were studied.The energy density reduced by 8%from 156.32 to 144.03 mAh·g^-1 when the current density increased from 10 to 50 mA·cm^-2,showing a good rate performance.When the cycle numbers were more than 1400 times at the charge-discharge current density 20 mA·cm^-2,the NiZn battery still maintained 150 Wh·kg^-1 of the energy density,which was 97%of the original energy density,and the Coulomb efficiency was more than 96%.