Controllable Preparation And Their Eletrochemical Properties Of CoSnO₃ Anode And Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ Cathode

In recent years,it has been found that tin based metal oxide anodes and lithium rich cathodes have higher theoretical capacity than the current graphite anode and lithium cobalt oxide cathode,and have great potential for application in lithium ion batteries.But the main problems for tin based metal oxide anodes are the large volume change of active particles during cycling and their intrinsic poor electronic conductivity,which would in turn cause the cracking of active materials and slow electrochemical reaction kinetics,resulting in limited cycling and rate performances.While the lithium rich cathodes have some problems,such as large irreversible capacity during first cycle,poor cycling and rate performance.These problems seriously impede the commercial application of the tin based metal oxide anodes and the lithium rich cathodes.Constructing tin based metal oxide anode materials with hollow nanostructures can not only ease the volume expansion of active materials,but also shorten the migration distance of lithium ions,finally improving the cycling and rate performance of electrode materials.Graphene shows excellent electrical conductivity and flexibility.The combination of tin based metal oxide anode materials with graphene can enhance the overall conductivity and limit the volume change of the electrode materials to some extent.The structure changes of the lithium rich cathodes by coating a spinel structured layer can be effectively inhibited during recycling process.The spinel structured layer can not only improve the migration coefficient of lithium ions,but also prevent the active material from corroding by electrolyte so as to enhance the cycling and rate performance,and reduce the initial irreversible capacity.The main contents and conclusions of this thesis are as follows:(1)A simple co-precipitation method combined with subsequent heating treatment in argon atmosphere has been used to prepare graphene coated amorphous cobalt stannate(H-CoSnO3@RGO)hollow nanocubes,single cobalt stannate solid(S-CoSnO3)and hollow(H-CoSnO3)nanocubes.And the morphology,microstructures and lithium storage properties of the obtained three samples were tested and compared.The synergistic effect between different metal oxide components,the special hollow structure and the modification of graphene endow H-CoSnO3@RGO anode with high reversible capacity,excellent cycling and rate performances.The specific capacities of 1919 mA h g-1 can be maintained after 500 cycles at a current density of 500 mA g-1 and of 528 mA h-1 can still be harvested even at the current density as high as 5000 mA g-1.(2)Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode materials have been prepared by firstly fabricating the corresponding precursor using a co-precipitation method and then mixing with lithium salt at high temperature.The structure,morphology and electrochemical properties of the samples annealed at different temperature(750 ?,800?,850 ?,900 ?)were investigated systematically.The sample collected at 850? showed the best electrochemical performance.In order to further enhance the lithium storage properties,the samples collected at 850 ? were coated with dopamine,and then carbonized to form spinel structured modified layer on the surface of cathodic materials.The prepared Li[Li0.2Mn0.54Ni0.13Co0.13]O2@SPINEL cathode material delivered a reversible capacity of 258 mA h g-1 after 50 cycles at a current density of 0.2 C,an initial Coulombic efficiency of 82.3%,and a specific capacity of 175 mA h g-1 even at a large current density of 5.0 C,showing excellent cycling and rate performances.