钴基氧化物纳米结构的构建及其电化学性能的研究

发布时间：2018-02-09 04:28

本文关键词： Co_3O_4 Co_3S_4 热处理异质结构纳米阵列锂离子电池性能　出处：《青岛大学》2017年硕士论文　论文类型：学位论文

【摘要】：过渡金属氧化物因具有较高的储锂容量等优点而成为非常有潜力的锂离子电池负极材料。其中,钴基氧化物由于其高比容量和多价态等优势引起了人们的广泛关注。但是,钴基氧化物存在电导率低、循环稳定性差等缺陷,因此,其尚不能应用于市场化的锂离子电池中。因钴基氧化物的纳米结构对其电化学性能产生很大的影响,故本论文旨在通过调控其微纳结构来提高其储锂性能。首先,本文利用简单的水热法,采用硝酸钴、氟化氨和尿素作为原料,制备出粉红色的前驱体粉末,并通过在不同温度下热处理前躯体,制备出具有规则排列的Co_3O_4一维纳米结构,同时研究了不同煅烧温度对材料颗粒大小、结晶性的影响。通过XRD、SEM、Ramam等手段表征分析了其物相和纳米结构,最后利用LAND电化学测试仪和电化学工作站测试了其电化学性能。通过测试,我们发现当热处理温度为450 o C时,长为60-100 nm,宽为30-40 nm的Co_3O_4纳米柱有较好的结晶性,以及低的电荷转移电阻,可以允许锂离子更容易的进行转移和脱嵌,并且还拥有较好的电化学循环性能,当循环到30圈之后,其比容量仍然能维持在805.8 m Ah g-1。其次,为了避免添加粘接剂和导电剂,将上述的Co_3O_4直接生长于泡沫镍上,成功地制备出Co_3O_4@Ni纳米阵列。该阵列与基底材料之间存在紧密的电化学接触,可直接用作锂离子电池负极。由于泡沫镍具有三维多孔结构,Co_3O_4@Ni纳由于其拥有很小的电荷转移电阻,使得其比容量相对于粉末电极来说有了巨大的提高,其首次比容量高达2012 m Ah g-1。但是,当循环次数达到40圈时,蒲公英状的Co_3O_4@Ni纳米阵列的比容量可以维持到818 m Ah g-1,而片状的Co_3O_4@Ni纳米阵列只能维持到577 m Ah g-1。最后,为了改善上述试验中循环性差的问题,我们对Co_3O_4@Ni进行表面处理。对此我们选择的复合材料为Co_3S_4。我们对Co_3O_4@Ni纳米阵列进行硫化,得到了异质结构的Co_3S_4@Co_3O_4@Ni。在此之前,异质结构的Co_3S_4@Co_3O_4@Ni作为锂离子电池负极材料还没有被报道过。研究发现,该纳米结构能较好的保持前驱体的阵列结构。储锂性能结果表明,该异质结构具有较高的比容量和循环稳定性,其性能更胜于单相Co_3O_4@Ni纳米阵列。Co_3S_4@Co_3O_4纳米阵列的首次放电比容量为1903.1 m Ah g-1,首次充电比容量仍高达1565 m Ah g-1,首次库伦效率为82.25%。
[Abstract]:Transition metal oxides have become potential anode materials for lithium ion batteries due to their high lithium storage capacity, among which cobalt-based oxides have attracted wide attention due to their high specific capacity and multivalent state. Cobalt-based oxides have some defects such as low conductivity and poor cycling stability, so they can not be used in market-oriented lithium-ion batteries, because the nano-structure of cobalt-based oxides has a great influence on their electrochemical performance. Therefore, the aim of this thesis is to improve the lithium-storage performance by regulating its micro-nano structure. Firstly, a pink precursor powder is prepared by using simple hydrothermal method and using cobalt nitrate, ammonia fluoride and urea as raw materials. The one-dimensional Co_3O_4 nanostructures with regular arrangement were prepared by heat treatment at different temperatures, and the effects of different calcination temperatures on the particle size were studied. The effect of crystallization. The phase and nanostructure were characterized and analyzed by means of XRDX SEMN Ramam. Finally, the electrochemical properties were tested by LAND electrochemical tester and electrochemical workstation. It was found that when the heat treatment temperature was 450oC, The Co_3O_4 nanorods, which are 60-100 nm long and 30-40 nm wide, have good crystallinity and low charge transfer resistance, which allow lithium ions to transfer and deintercalate more easily, and also have better electrochemical cycling performance after 30 cycles. The specific capacity can still be maintained at 805.8 mAh g-1.Secondly, in order to avoid adding adhesive and conductive agent, the Co_3O_4 was grown directly on nickel foam. Co_3O_4@Ni nanoarrays have been successfully fabricated. There is close electrochemical contact between the array and the substrate, which can be directly used as negative electrode for lithium-ion batteries. Compared with the powder electrode, the specific capacity was greatly improved, and the first specific capacity was as high as 2012 mAh g-1.However, when the cycle times reached 40 cycles, The specific capacity of dandelion like Co_3O_4@Ni nanoarrays can be maintained up to 818 mAh g-1, while the flake Co_3O_4@Ni nanoarrays can only maintain up to 577mAh g-1.Finally, in order to improve the problem of poor circulability in the above experiments, the specific capacity of dandelion like Co_3O_4@Ni nanoarrays can be maintained up to 818 mAh g-1. We do surface treatment on Co_3O_4@Ni. For this, the composite we choose is Cos _ 3S _ 4. We vulcanized the Co_3O_4@Ni nanoarrays and got the heterostructure Co3S _ 4R _ Co _ 3O _ 4R _ (Nii). Heterostructure Co_3S_4@Co_3O_4@Ni has not been reported as a cathode material for lithium-ion batteries. It has been found that the nanostructure can keep the array structure of the precursor well. The heterostructure has high specific capacity and cyclic stability, and its performance is better than that of single-phase Co_3O_4@Ni nanoarrays. Co3S4Co3O4 nanoarrays have a first discharge specific capacity of 1903.1 mAh g-1, initial charging capacity of 1565 mAh g-1 and first Coulomb efficiency of 82.25.
【学位授予单位】：青岛大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ138.12;TM912

【参考文献】