Preparation,segregation And Conductivity Of Layered Oxide Cathode Materials

Layered transition-metals oxides has shown various merits of thermal stability,life time,and energy density,besides environmental consideration.But also face the challenge of poor cyclability,rate capacity and safety,which is closely relate to surface chemistry and conductivity.Therefore become the forefront issue for advanced lithium-ion batteries.,some of the key questions still remain unclear:is segregation of transition metal elements dependent on the chemical composition of layered transition-metal oxides?What can one expect for the variation of the conductivity of oxide cathodes with Element Segregation?There is two section to answers these questions,as follow:Above all,the role of composition in structure,surface segregation behavior and electronic conductivity were investigated in LiNiaCo1-2xMnxO2(0.1 ? x ? 0.4)serial cathode materials.With the increase of Ni and Mn content,lattice parameter of a and c increases,while c/a ratio shows a decreasing trend.Comparing to average increase rate of 0.13 for ionic radii with Ni/Mn content,slightly large expansion rates of 0.15 for parameters of a and c/3 is close related with an increase of eg electron that enhances the columbic repulsion between transition metal and oxygen ions.XPS depth profiling results show that surface composition is significantly deviated from bulk,in which Ni and Mn atoms tend to enrich in the surface region,while Co species is relatively deficient to show anti-segregation behavior,because of the stability of oxygen octahedra is different Further,with the Ni/Mn content increasing,the stronger bond.Ni2+-Mn4+ increase which contribute to the decrease of relative segregation.Element segregation leads to higher resistance,lower electrical conductivity and larger activation energy of grain boundary.With the Ni/Mn content increasing,the bulk activation energy increase due to the contraction of lithium layer.These results suggest that element segregation and conductivity could be adjusted through changing the composition.Secondly,Li1.2Mn0.56Ni0.16Co0.08O2 was chosen as layered rich-lithium basing on the rule of segregation.Effect of synthesis routes on electrochemical performances were study.The results of electrochemical tests show that sample with co-precipitation route exhibit highest initial discharge capacity and Coulombic efficiency,good rate capability,and excellent cycle stability.The variation of electrochemical performance for four samples may be attributed to different surface chemistry,micro-nano structure and less impedance which cause by the different synthesis routes.