Preparation And Electrochemical Properties Of Sn-based Anode Materials For Lithium-ion Batteries

As a new anode material for lithium ion battery, Tin-based material has attracted much attention. Compared to graphite, which is used mainly in present commercialized production of Li-ion batteries, tin-based material exhibited higher theoretical capacity. But, its poor cyclability restricted it application for commercial anode material of lithium ion battery. In order to improve the performance of Sn-based active materials, the nanosized SnO₂ particles,sandwich structural Cu/Sn/Ni and Cu/Ni/Sn eledtrodes, and three-dimensional reticular Sn-Ni alloy electrode were prepared by sol-gel and electrodepositon. The phase structure and surface morphology of the said materials were determined by XRD,TEM and SEM. The electrochemical performance of the electrodes was measured by constant current charge-discharge test.(1) SnO₂ nanoparticles with four different sizes of 5, 10.8, 24.2, and 39.1 nm were synthesized using infrared irradiation and thermal treatment. X-ray diffraction (XRD) results indicated that the particles had tetragonal rutile structure (cassiterite SnO₂). TEM and FT-IR spectra revealed that at 673K, the disperse SnO₂ nanospheres began to aggregate to form bigger size clusters; the oblate spheroids must appear. Electrochemical tests showed that particle size had a significant influence on the lithium ion insertion/desertion properties, and the 10.8 nm-sized SnO₂ nanoparticles electrodes had a superior capacity and cycling stability as compared to the 5, 24.2, and 39.1 nm-sized ones.(2) The nano-structural SnO₂/carbon nanotubes composites were prepared in a solution of SnCl₂ ,ethylene glycol (EG),purified MWCNTs and sodium dodecyl sulfate (SDS) at 160℃. The phase structure and surface morphology of the composites were measured by XRD,HRTEM and SEM. The results indicate that there are high dispersions and high loadings of SnO₂ nanoparticles on MWCNTs. Electrochemical lithium storage performance was studied preliminarily on the obtained samples. MWCNTs modified with SnO₂ nanoparicles were shown to have a higher electrochemical reversible capacity than that of MWCNTs during the charge and discharge process. MWCNTs can accommodate the larger structure strain of the active materials produced during Li-ion insertion and extraction, which may improve the cycle performance of the electrode.(3) The sandwich structural Cu/Sn/Ni and Cu/Ni/Sn deposits, which contained one layers Sn deposits and one-layer Ni deposits, were prepared by electroplating on Cu foil. The results of XRD indicated that after annealing Cu₆Sn₅ and Ni₃Sn₄ were formed on copper current collector with the diffusion between plating material and copper substrate. Charge-discharge test revealed that heat-treatment of the electrodes could improve the cycle performance of electrode. SEM observations showed that sandwich structure of electrode coated with 0.5μm nickel could restrain the volume expansion of active materials.(4) The planar and three-dimensional reticular Sn-Ni alloy deposits were prepared by electrodepositing on Cu foil and foamed Cu, respectively. The X-ray diffraction patterns of the thermally treated Sn-Ni alloy deposit showed that the Sn-Ni alloy had a Ni3Sn4 phase. The surface of planar electrode became rough after annealing, but the surface of three-dimensional reticular electrode didn't change. Charge-discharge test indicated heat-treatment of the electrodes could improve the cycle performance of electrode, and the cycle performance of three-dimensional reticular Sn-Ni alloy was better than that of the planar electrode. SEM result of the Sn-Ni alloy electrode showed that the three-dimensioned reticular structure in Sn-Ni alloy electrode could relax the volume expansion during cycling; three-dimensional reticular structure of Sn-Ni alloy electrodes was also beneficial to diffusion of lithium ion into/out of porous materials.