Synthesis And Electrochemical Li-Absorption/Extraction Properties Of Tin-based Anode Materials

Lithium ion battery is currently one of the best rechargeable batteries and has been extensively applied in various portable electronic equipments.R&D for lithium ion batteries with higher capacity and higher power is undergoing and will help their application in electric vehicles.However,the low capacity and safety of the traditional carbon anode material are becoming the bottleneck to any further improvement of the battery performances.In this thesis,a series of tin-based composites were synthesized through pyrolysisof precursor,which were prepared with liquid precipitation and mechanical milling method,as new anode materials for lithium ion batteries.The prepared samples exhibited large lithium storage capacities and the reversible capacities were about the range from 300 to 800 mAh/g.The influence of reaction conditions on components and construction and particle size was studied.The influence of these properties of the samples on the capacities and cycle-abilities was discussed.A mechanism of Li storage in tin-based composites and characterizations of the electrode reactions were studied.Meanwhile,the structure and morphology of lithium insertion/desertion into/from the electrode as well as the capacity fading were discussed. The approaches for improving the cycle life were researched.SnO₂ short nanorods were synthesized using the tin(â…£)chloride as precursor by the hydrothermal method,which diameters and lengths are up to 20-100nm and 50-400 nm, respectively.Their electrochemical properties were also studied.The results show that voltage windows,current density for charge and discharge,and particle morphology effect on their specific capacities,cyclability and rate capability.The short nano-rod shows the best electrochemical properties:the initial discharge capacity was 1166mAh/g and the reversible capacity was 631mAh/g with a rate of capacity fading of 0.8%after 20 cycles at 0.5C rate in the potential range of 0-1.0V.The mechanism of lithium insertion-desertion was proved by cyclic voltammetry tests and the differential capacity.Nano-SnOy-SiO₂ composites were prepared by a modified hydrothermal method, using SnCl₂ and equal amounts of Si(OMe)₄ as the starting materials and CO(NH₂)₂ as PH regulator.Fine powders of tin oxide as active materials were doped with highly dispersed silicon oxide as inert materials in atomic or nano-meter scale.In the first lithium insertion step,three clear voltage plateaus on 0.4V,0.9V and 0.7V-0.1V were observed,which were consistent with Sn-Li alloying process.A discharge capacity of 1208 mAh·g^-1and a charge capacity of 756 mAh·g^-1were achieved,a coulombic efficiency was more than 90%except for the first cycles(62.6%),and the capacity loss per cycle was about 0.9%after cycling 20 times which suggests that tin oxide-based materials work as high capacity anodes for lithium-ion rechargeable batteries.,Highly dispersed Sn-Zn-O nano-composite oxides were synthesized using nano-SnO₂ and Zinc powders as the starting materials by solid state reaction method at high temperature(600℃or 800℃).The as-prepared powders were characterized by XRD and SEM.The results indicated the sample sintered at 600℃were composed of Sn,SnO,ZnO multiphase,and the sample sintered at 800℃were composed of Sn,SnO,ZnO and Zn₂SnO₄ multiphase.The gravimetric discharge(Li insertion)-charge(Li extraction)properties of the Sn-Zn-O anodes were measured by an electrolyte of 1 M LiPF₆ solution in a 1:1(v:v)mixture of ethylene carbonate(EC)and dimethyl carbonate (DMC).The results showed that the first reversible capacity of sample sintered at 800℃was 772mAh/g,the coulombic efficiency in the first cycle was 60.1%,the reversible capacity maintained 376 mAh/g after 20 cycles.Meanwhile,the sample was sintered at 600℃,the first reversible capacity was 641mAh/g,the coulombic efficiency in the first cycle was 49.4%and the reversible capacity maintained 272 mAh/g after 20 cycles.The electrochemical performance of the Sn-Zn-O composite sintered at 800℃was better than that sintered at 600℃.The preparation and characterization of Sn-Mo composites derived by mechanical milling and coprecipitation process were carried out and comparatively studied.The reversible capacity was more than 390mAh/g and the capacity loss was only 1.1%per cycle after being cycled 20 times for the sample derived by coprecipitation reaction, while that of the sample derived by mechanical milling method was 307mAh/g and 3.9%, respectively.These results show that Sn-Mo comopsites prepared by coprecipitation method possess better electrochemical properties due to their smaller particle size and more uniform distribution of particles sizes.The Sn-Cr composites were prepared by mechanical milling method.The curves of the cyclic voltammetry and the differential capacity of the Sn-Cr electrodes were analysed.The initial discharge capacity of 577mAh/g and a charge capacity of 374mAh/g were achieved and a coulombic efficiency was more than 67%.The mechanism of lithium insertion into Sn-Cr alloy based on their composition and crystal structure was discussed.Furthermore,an ideal microstructural model for alloy anode materials was constructed.