Research On The Construction And Application Of NiFe Battery

With the rapid development of society,environmental problems are increasingly serious.Rechargeable secondary cycle batteries play an increasingly important role in solving fossil energy consumption and environmental pollution.NiFe secondary battery have attracted more attentions due to their high theoretical energy density,long cycle life,no secondary pollution to the environment,wide source and low price of electrode materials.However,the lower specific capacity,energy density and coulombic efficiency of commercial NiFe batteries limit their large-scale applications.It is urgent to improve the performance of the positive and negative electrodes,further improving performance of NiFe batteries.In this thesis,the intermediate phase?-?-Ni?OH?₂/carbon nanofiber?CNF?composites were prepared by controlling the doping amount of Co in the Ni?OH?₂ lattice,which has high specific capacity,low internal resistance and long cycle life.We also prepared?-Fe₂O₃@C composites with core-shell sturcture and?-Fe₂O₃/carbon nanotube?CNT?composites by different methods.Its electrochemical properties were measured.The possible formation mechanisms were proposed.A positive electrode prepared from?-?-Ni?OH?₂/CNFs and a negative electrode prepared from?-Fe₂O₃@C or?-Fe₂O₃/CNT composite are assembled into NiFe batteries,which display high energy density,coulomb effeciency and long cycle life.The contents of the study are as follows:Nickel positive electrode:Co-substituted Ni?OH?₂/CNFs composites were prepared by a simple chemical co-precipitation method.The phase and morphology of the samples were characterized by XRD and TEM.The prepared working electrode was tested by CV,EIS and charge-discharge.The XRD pattern evidences that the sample is an?-?intermediate phase structure.There was no peak splitting phenomenon in the CV curve,further confirming that the composite material was an intermediate phase?-?-Ni_1-xCo_x?OH?₂.EIS testing indicates that the internal resistance of the composite is small.The intermediate phase?-?-Ni_1-xCo_x?OH?₂/CNFs composite has high specific capacity,low electrochemical resistance and long cycle stability.NiZn battery assembled by using composites display excellent electrochemical performance.After 1500 cycles,theenergy capacity retained 215.24Wh·kg^-1,98%of the initial value at a charge and discharge current density of 23 mA·cm^-2.The relationship between structure and the electrochemical performance was analyzed and discussed in detail.Iron negative:?1?Using PVP as surfactant and source of carbon,?-Fe₂O₃ or FeO?OH?absorbed by PVP molecules are first synthesized by hydrolysis method under hydrothermal treatment.And then Calcining the above sample at a high temperature,FeO?OH?transformed into?-Fe₂O₃and PVP on the surface of?-Fe₂O₃ carbonize to elemental carbon to form?-Fe₂O₃@C core-shell nano-composite.IR spectrum evicence PVP molecules absorbing on the surface of?-Fe₂O₃ or FeO?OH?.XRD pattern indicates that the phase of product after calcination is?phase.TEM images show that the morphology of?-Fe₂O₃ is nanorod coated with a carbon layer of about 5 nm thick.Some of them have graphitized structure.The formation mechanism is proposed.CV,EIS and charge discharge of single electrode are tested.The results show that the prepared working electrode has a high specific capacity and small internal resistance.Using?-Fe₂O₃@C as the active material of negative electrode,Ni_1-xCo_x?OH?₂/CNFs composite?x=0.01?as the active material of positive electrode,NiFe battery was assembled and its electrochemical performances are tested.The cycle life is more than 400 times.After the 400th cycle,the NiFe battery still maintains 114.81 mAh·g^-1 of the specific capacity and 117.7 Wh·kg^-1 of the energy density,and the more than 90%of coulomb efficiency.?2?The?-Fe₂O₃/CNT composite was synthesized by thermal decomposition.The phase structure and morphology of the product were characterized by XRD and TEM.The results show that Fe₂O₃ is?phase,and the morphology of?-Fe₂O₃ is nanoparticle with a size ranging from a few nanometers to several hundred nanometers.?-Fe₂O₃is tightly anchored on the surface of carbon nanotubes to form?-Fe₂O₃/CNT composite.The optimal synthesis conditions were obtained based on the results of CV testing of the electrode prepared by?-Fe₂O₃/CNT composite.EIS testing indicates the small internal resistance of the composite.Using?-Fe₂O₃/CNT as the active material of negative electrode,Ni_1-xCo_x?OH?₂/CNFs composite?x=0.01?as the active material of positive electrode,NiFe battery was assembled and its electrochemical performances are tested.The cycle life is more than 500 times at the charge-discharge current density 30 mA·cm^-2.After the 500th cycle,the NiFe battery still maintains 120.02 mAh·g^-1 of the specific capacity and 133.38 Wh·kg^-1 of the energy density,and the more than 94%of coulomb efficiency.In addition,the rate performance test results show that it has good rate performance.