Synthesis And Characterization Of Novel Lithium-rich Manganese-based Solid Solution Cathode Materials For Lithium-ion Battery

Lithium-ion battery with a good performance, is currently one of the bestenergy storage methods, and has a wide range of applications, from electroniccomponents to ships, automobile and other traffic areas. The development inautomotive applications of lithium-ion battery is currently one of the most primarydirections. This application requires the lithium-ion battery has a higher energydensity, good cycle stability and rate property, also has a lower cost, safety, andenvironment-friendly features. But current lithium-ion battery cathode materials arehard to meet these requirements. Recently, the layered lithium-richmanganese-based solid solution cathode materials for xLi2MnO3(1-x)LiMO2received extensive attention because of its high energy density and cycleperformance. With a further research, the materials with a ‘layered-layered’structure or ‘layered-spinel’ structure have been developed. Recently, The conceptof embedding a spinel component in high capacity, compositexLi2MnO3(1-x)LiMO2‘layered-layered’ structures to obtain a material with‘layered-layered-spinel’ structure has been exploited. This cathode materials’specific capacity and cycle performance can be further improved.In this thesis, the effect of synthesis method and embedding a spinel componenton the electrochemical properties of materials based on lithium-richmanganese-based solid solution cathode materials had been researched.In the synthesis method, the two-step temperature co-precipitation methodbased on traditional co-precipitation method has been used for the first time toprepare layered-layered structure solid solution cathode material0.5Li2MnO30.5LiMn1/3Ni1/3Co1/3O2. Physical and electrochemical performance testresults showed that the materials synthesized by two-step temperatureco-precipitation method have a layered structure and spherical surface topography.When the initial synthesis temperature is lower, the material can deliver a dischargecapacity of280mA h/g at first cycle under a current density of0.1C (1C=mA h/g),and a discharge capacity of208.7mA h/g at first cycle under a current density of0.5C, and after50cycles, the discharge capacity remained at170mA h/g or more.In order to further improve the materials’ performance,‘layered-layered-spinel’structure lithium-rich manganese based solid solution cathode materialsδ[0.5Li2MnO30.5LiMn1/3Ni1/3Co1/3O2](1-δ)Li0.5Mn4/6Ni1/6Co1/6O2(also can bewritten as LixMn4/6Ni1/6Co1/6Oy) have been synthesized using two-step temperatureco-precipitation method, by lowering the lithium content of a parent‘layered-layered’0.5Li2MnO30.5LiMn1/3Ni1/3Co1/3O2material while maintaining a Mn:Ni:Co ratio of4:1:1. Physical and electrochemical performance test resultsshowed that two-temperature co-precipitation method can prepare cathode materialsLixMn4/6Ni1/6Co1/6Oysuccessfully. The materials Li1.4Mn4/6Ni1/6Co1/6O2.45synthesizedat T1=50℃have a layered structure and spherical surface topography. It can delivera discharge capacity of259.2mA h/g at first cycle under a current density of0.1C,and a discharge capacity of160.6mA h/g at first cycle under a current density of0.5C, and after50cycles, the discharge capacity remained at141.9mA h/g. But ithas a poor rate capability performance. And the materials Li1.3Mn4/6Ni1/6Co1/6O2.4synthesized at T1=60℃also have a layered structure and spherical surfacetopography. It can deliver a discharge capacity of305.3mA h/g at first cycle undera current density of0.1C, the charge-discharge cycling efficiency is74.1%, and adischarge capacity of209.4mA h/g at first cycle under a current density of0.5C,and after50cycles, the discharge capacity remained at168.8mA h/g. But it has apoor rate capacity performance. Further rate performance test showed that thematerial circulate under high rate, still has a good columbic efficiency.