锂离子电池Cu纳米线阵列复合电极的制备及性能研究

【作者】 韩冰；

【导师】 周荣； 张世超；

【作者基本信息】 昆明理工大学 ， 材料学， 2015， 硕士

【摘要】 锂离子电池因其有能量密度高、使用寿命长和对环境无污染的优点,被广泛的应用在动力电动汽车、电动车和电力储能等方面。然而,由于目前被商业化应用的石墨电极已经达到了其理论容量的极限372mAh g-1,已经不能满足逐渐增长的能源需求。因此人们在寻找一种新的电极材料代替石墨。而过渡金属氧化物和锡基材料是比价常见的。如今具有高理论容量的负极材料,受到了人们的广泛关注。其中Fe3O4、Sn-Sb合金,SnCo合金是研究得比较多的活性物质体系,它们都具有容量高的特点。但是Fe304和锡基材料的一个最大的问题就是充放电过程中体积变化太大,最终导致电极材料的粉碎,影响电化学性能。而纳米材料和三维(3D)电极结构,给这个问题带来了解决的方法。并且,随着便携式储能设备的增多以及便携式电子设备向小型化的不断发展,推动了锂离子电池向微型电池方向发展的趋势,从而三维微型电池开始受到广泛关注。为此,本文设计了三维的、高长径比的纳米线阵列电极材料,缓解锂离子在充放电过程中产生的体积膨胀,从而提高电池的循环性能和变电流密度下的电化学性能,并有希望应用到锂离子微型电池上。本文通过模板法制备出高长径比的Cu纳米线集流体。探索脉冲时间、电流等因素对制备的影响。然后使用恒压电沉积法在三维纳米线集流体上沉积Fe3O4,使用恒电流法沉积Sn-Sb和Sn-Sb-C0,用来探索制备过程中电沉积时间、沉积电流、热处理等因素对电极材料制备的影响,确定了Fe3O4体系中最佳制备参数为水溶液体系中,U=7V, T=1.5h. Sn-Sb 和 Sn-Sb-Co最佳制备参数为T=10min,沉积电流密度为10mA cm-2,热处理的条件下制备的三维复合电极材料三维形貌最佳。通过与平面电极的对比,对三个体系的电化学性能进行研究,发现三维Cu@Fe3O4纳米线阵列电极材料的首次放电容量、循环稳定性和变电流密度下的放电容量等性能都比平面电极材料优异。但是从整体上看,这种材料并没有达到理想的高放电容量的效果。因此通过改变活性物质体系,进行进一步实验,来探索三维Cu@SnSb纳米线阵列电极材料的电化学特性,经过测试,其首次放电容量为1800μAh cm-2,但是在经过80圈的循环稳定测试后,Cu@SnSb材料的电容量程下降趋势,并且对其循环后的电极材料进行表征发现,经过充放电反应,三维纳米线阵列结构存在一定程度的破坏。为此在此体系的基础上,引入Co元素。通过电化学性能表征发现,经过热处理的三维Cu@SnSbCo纳米线阵列电极材料表现出比Cu@Fe3O4、Cu@SnSb更优异的电化学性能,首次放电容量达到1019μAh cm-2,首次不可逆反应后电容量达到800μAh cm-2,经过80次循环后,电容量几乎没有进一步衰减。循环后极片材料微观形貌表征发现,三维结构维持良好。更多还原

【Abstract】 Currently, lithium-ion batteries (LIBs) have been applied in various fields, such as hybrid electric vehicles (HEVs), electric vehicles (EVs) and stationary energy storage due to their advantages of high energy density, long lifespan and environmental friendly effect. However, the current commercial graphite anode which has the limited theoretical capacity of 372mAh g-1 could hardly meet the increasing requirements of energy. Therefore, it is significant to find better alternative anode materials. Transition metal oxide and tin-based material are common anode materials which have high theoretical capacities. Fe3O4, Sn-Sb alloy and Sn-Co alloy have been studied frequently. They all have high theoretical capacities But the big problem with Fe3O4 and tin-based materials is large volume variation during the charge and discharge process, and eventually it would lead to the aggregation of nanoparticles and the disintegration of the electrode, and then influence the electrochemical properties. However, nanometer materials and three-dimensional (3D) structured electrode, bring the solution to the problem. And, with the increasing requirements for portable energy storage and the miniaturization of portable, electronic devices have led to the rapid development of electrochemical power sources that meet the size and energy needs. Three-dimensional microbattery (3D-MB) architecture has been proposed. For this, this paper designed one kind of 3D and high-aspect-ratio nanowires array electrode materials which can accommodate the volume expansion. Thus, it also can improve the cycle performance and rate performance of the battery. It also has the opportunities to be used in the microbattery.This paper synthesized 3D nanowires array electrodes through template-assisted method. We investigated the pulse time, current and other factors which affected the synthesis of the electrode. Then the active materials of Fe3O4, SnSb and SnSbCo were deposited onto the Cu nanowires array through electrodeposition. In order to determine the best parameters eventually, we explored the deposition time, current and the heat treatment which affected the synthesis of the hybrid electrode. Comparing with planar electrodes, we characterized the electrochemical properties of their counterpart 3D electrodes. It is found that 3D Cu@Fe3O4 nanowires array electrode performs better than the planar one on the first discharge capacity, cycle stability and rate performance. But overall, the material did not achieve the ideal result of high discharge capacity. Therefore, we changed the active material system and explored the electrochemical properties of 3D Cu@SnSb nanowires array electrode. We found that, the first discharge capacity was 1800 uAh cm-2, nearly 800μAh cm-2 higher than that of the Cu@Fe3O4 electrode. But after 80 cycles, the capacity of Cu@SnSb electrode declined. We characterized the electrode materials after cycling, and found that the structure of the 3D electrode had been damaged more or less after the charge/discharge reactions. Therefore, we added Co elements into the SnSb. Through the electrochemical measurements, we found the 3D Cu@SnSbCo electrodes performed better than Cu@Fe3O4, and Cu@SnSb electrodes after heat treatment.3D Cu@SnSbCo electrodes have the high first discharge capacity of 1019μAh cm-2, after the irreversible reaction, the capacity declined to 800μAh cm-2. And after 80 cycles, there were almost no further decline. We characterized the morphology of the after-cycling electrode and found that the 3D structure maintained good.更多还原