The Application Of Nano-sized SnO₂ In Lithium-ion Batteries

On the base of introduction about the developments of Lithium-ion batteries and materials in detail in the paper, nano-sized SnO2 were observed by means of X-radial Diffraction, Scanning Electron Microscope, Transmission Electron Microscope, BET Ratio Surface, and so on. With some important parameters, such as reversible capacity, cyclic performance, coulombic efficiency, etc. electrochemistry performance of SnO2 and the mechanism were researched.Nano-sized SnO2 synthesized by the sol-gel method had tetragonal structure and was about 30nm on average size. Anodes manufacture and batteries assembly were introduced and some key processes in anodes manufacture were discussed in detail. Ethanol getting rid of air bubbles in the slurries, suitable stirring time uniforming the slurries, certain mass binders strengthening the stickiness, all these approaches were helpful in the improvement of anodes, avoiding pulverization, desquamating or fracturing. The anodes made by the shaving-spreading method were more uniform and the cyclic performance was better. Appropriate drying temperature and time could vaporize the water in the anodes without making anodes fragile. The anodes should not be pressed by a heavy pressure for once but by light pressure for some times.Under the current density of 0.5mA/cm2, the initial reversible capacity of SnO2 bounded by aqueous binder LA133 was 644mAh/g, about twice larger than that by polyvinylidene fluoride (PVDF); the capacity retention ratio of SnO2 by LA133 was 68.3% after 15 cycles, also twice of that by PVDF; and furthermore the irreversible capacity of SnO2 by LA133 during charge process was about 200mAh/g, far smaller than that by PVDF 500mAh/g. The initial reversible capacity of SnO2 was improved a little with the content of LA133 increasing. When the content of LA133 was 10%, the initial reversible capacity of SnO2 was 619mAh/g, and the capacity retention ratio of SnO2 was 67.7% after 15 cycles, which would have some decrease if the content of LA133 was above 10%. The smaller the current density was, the larger the initial reversible capacity was, but the capacity lost faster and the capacity retention ratio was lower. When the upper cutoff voltage was below 0.8V, the aggregation of metal Sn particles was avoided efficiently, which helped greatly to improve the cyclic performance of SnO2, especially when the voltage was 0-0.8V, the initial reversible capacity of SnO2 was 453mAh/g, and the capacity retention ratio was high to 96.4% after 20 cycles. Because the deoxidization peak potentials of SnO2 reacting with lithium were below 0.3V, it was helpful to diminish the lower cutoff voltage in the increase of the reversible capacity of SnO2. The impedances of SnO2 at different charge states were investigated by AC impedance method, and the results showed that there were different electrochemistry reactions according to different depth of discharge (DOD). In the cases of high or low temperatures, the initial reversible capacity of SnO2 was 450mAh/g, the capacity retention ratio after 15 cycles was about 95%, and the batteries kept well in appearance, which showed good performance. Compared with carbon black, the capacity of SnO2 with acetylene black or VGCF as conductivity faded faster.