The Preparation Of Mn-and Fe-Based Electrode Materials And Their Electrochemical Properties

Energy is not only an initial power for pushing the economy forward,but also the bottle–neck of the economic advances.Along with the rapid development of the economy,supercapacitor and lithium ion battery,as renewable energy storage devices,have attracted dramatic attentions in recent years.Therefore,the research about the electrode mateials and the development of low cost electrode have become the the core of our research about energy storage devices and have drawn intensive attentions of scientific researchers.This thesis focuses on the research about the supercapacitor performance of Mn-based pseudocapacitance materials and LiFePO₄ cathode materials.We used XRD,SEM,TEM,SAED,FTIR,Nitrogen adsorption/desorption measurements,CV,as well as charge-discharge test method to study the synthesis method,preparation technology,structure characterization,growth mechanism,and electrochemical performance of the electrode mateials.Its specific research content is as follows:1.A facile,one step route was successfully developed to synthesize?-MnOOH nanotubes through a rational layer-structure-to-nanotubes strategy.?-MnOOH nanotubes exhibit good supercapacitor performance;About 97%of initial specific capacitance is maintained after500 cycles at the scan rate of 20 mV s^-1.?-MnOOH nanotubes exhibit features of good electrochemical performance,low cost and facile synthesis route,making them promising supercapactior electrode materials.2.In this thesis,two types of Mn₃O₄ hexagonal plate-shape micro/nano hierarchical architectures were successfully prepared based on a self-assembly approach via a hydrothermal synthesis route at low temperature,which is sparse in literature.These two types of Mn₃O₄ hexagonal plate-shape micro/nano hierarchical architectures were constructed from different building block nanostructures.The formation mechanisms were discussed,and the electrochemical performances were investigated.Electrochemical studies show that these two types of Mn₃O₄ hierarchical architectures exhibit good specific capacitance and electrochemical stability,making them promising electrode materials in electrochemical capacitors.This facile chemical reaction route may provide us a novel strategy to facilitate future design of other metal oxide micro/nano hierarchical materials.3.Three wet chemistry methods for the synthesis of LiFePO₄/C composite materials including intermediate route,hydrothermal route and precipitation route have been investigated.The intermediate route has been determined to own the highest feasibility after comprehensive analysis.Effects of the annealing atmosphere for the synthesis of FePO₄intermediate as well as the ratio of Li to Fe over electrochemical performance of LiFePO₄/C have been studied.Effects of element-type carbon sources,compound-type carbon sources,carbon content and carbonization condition on the rate-discharge and cyclic performances of intermediate route LiFePO4/C have been investigated in details.The general properties of glucose and graphite nanopowder are better than other tested carbon sources.4.Effects of three mixing processes including water-free grinding,general incipient wetness and competitive incipient wetness on the properties of intermediate route LiFePO4/C have been studied systematically which is sparse in literature.Both mixing processes and lithium sources are capable of causing significant differences on the crystallinity,the quality of carbon coating,or even the formation of impurity phases of LiFePO₄/C composites and thus may affect their electrochemical performances.The sample made by the lithium source of lithium hydroxide as well as the mixing process of water-free grinding exhibits the best electrochemical performances.Liquid alkalis?e.g.,dissolved LiOH in water?and competitive cations may cause negative effects on the preparation of LiFePO₄/C.