【作者】 杨峰；

【导师】 王太宏；

【作者基本信息】 湖南大学 ， 微电子学与固体电子学， 2008， 硕士

【摘要】 本论文在详细介绍了锂离子电池及相关材料研究进展的基础上,以纳米SnO2为研究对象,运用XRD、SEM、TEM、BET比表面积等现代分析测试技术对合成材料进行了表征,并围绕材料的可逆容量、循环性能和库仑效率等主要性能指标,对SnO2的电化学性能以及相关机理进行了系统研究。由溶胶-凝胶法制备的纳米SnO2,SnO2呈球形颗粒,平均晶粒大小约为30nm。详细介绍了锂离子电池负极片的制作流程和扣式电池的装配工艺,并对极片制作流程中的关键步骤进行了讨论。适量的无水乙醇可以有效地除去浆料中的气泡,合适的搅拌时间可以提高浆料的均匀程度,适量的粘结剂有助于提高极片的质量,避免出现粉化、剥落或龟裂等现象。采用刮涂法制作出的极片更加均匀平整,循环性能也更好。合适的干燥温度和干燥时间可以避免极片太脆,同时最大程度地蒸发极片里的水分。压片时避免使用较大的压力一次性压到位,应该使用较小的压力多压几次。在0.5mA/cm2电流密度下,使用水性粘结剂LA133时,SnO2的首次可逆容量约644mAh/g,约为使用PVDF时3倍,15个循环后的容量保持率达到68.3%,是使用PVDF时的2倍,而且LA133的电池首次充电过程中会产生约200mAh/g的不可逆容量,远小于使用PVDF时的500mAh/g。随着LA133含量的增加,SnO2的平均首次可逆容量略有增加,当LA133的含量为10%时,SnO2的首次可逆容量为619mAh/g,15个循环后,SnO2的平均容量保持率为67.7%,但是当LA133的含量超过10%时,SnO2的容量保持率会有不同程度的下降。电流密度越小,首次可逆容量越高,但容量衰减越快,容量保持率越低。当上限截止电压低于0.8V时,可以有效的避免金属Sn微粒的团聚,极大地提高SnO2的循环性能,当电压范围为0-0.8V时,首次可逆容量为453mAh/g,20个循环后的平均容量保持率高达96.4%;由于SnO2与金属锂反应的可逆还原峰电位低于0.3V,所以适当降低下限截止电压有利于提高SnO2的可逆容量。用交流阻抗法分析了电池在不同荷电状态下的交流阻抗,发现不同的放电深度对应不同的电化学过程。SnO2在高低温条件下,首次可逆容量在450mAh/g,15个循环后的容量保持率为约95%,而且测试后的电池,目测其外观规整,无变形和破裂,显示出较好的高低温性能。与碳黑相比,使用乙炔黑或VGCF做导电剂时,SnO2的容量衰减更快。更多还原

【Abstract】 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.更多还原