【作者】 杨斌；

【导师】 杨占红；

【作者基本信息】 中南大学 ， 应用化学， 2014， 博士

【摘要】 摘要：锌镍电池是一种高能量密度的碱性蓄电池,其电池性能远远高于镉镍和镍氢电池,加上这种电池原材料丰富,电解液和活性物质无毒,电池体系绿色无污染,越来越受到各国研究机构的重视。然而镍锌二次电池中常规负极材料的放电产物易溶于碱性电解液,从而会导致电池循环寿命降低oZnAl-LDH材料由于其新颖的二维纳米结构,在碱性电解液中具有很好的稳定性和电化学活性等优点,被认为最有潜力成为下一代锌镍电池的新型负极材料。然而,单相的ZnAl-LDH材料本身的导电性较差限制了其电化学性能的进一步提升。因此,将ZnAl-LDH材料与导电性较好的碳、金属等复合,通过发挥两种材料各自的优势,改善复合材料的导电性和机械强度,从而极大地提高复合材料的电化学性能。本文围绕新型ZnAl-LDH纳米复合材料的制备和相关电化学性能展开研究,主要内容如下：(1)通过离心分离的方法将ZnAl-LDH固体沉淀和盐溶液分离,再重新分散在超纯水中,使ZnAl-LDH在超纯水环境中水热生长结晶,水热反应24小时后得到了晶形规则、大小均一的二维纳米片材料。相比于常规的水热法和共沉淀法,本方法合成的水滑石结构更加规则,分布更加均匀,没有出现团聚现象,ZnAl-LDH样品呈规则的六边形晶体结构,质量和纯度较高,非常适合应用到锌镍电池负极材料中。(2)利用正负电荷之间的静电力作用,将表面修饰后的碳纳米管和ZnAl-LDH两种纳米材料结合在一起,生成三维ZnAl-LDH/CNTs复合物。对复合物的结构进行表征后发现,CNTs均匀分布在ZnAl-LDH纳米片表面,形成一种导电网状结构。将其作为负极活性物质应用到锌镍电池中,通过恒流充放电曲线研究、CV曲线测试、电池循环性能实验,证明电池的循环稳定性、充放电性能以及电极的放电比容量均有显著提升。(3)运用银镜反应技术,在ZnAl-LDH纳米片表面进行纳米银修饰,首次制备出银包覆ZnAl-LDH纳米片材料。通过电池的恒流充放电实验,发现这种银包覆ZnAl-LDH纳米片材料具有更高的放电容量、更为优异的充放电性能和循环稳定性。进一步采用交流阻抗技术对其进行研究,发现这种银包覆ZnAl-LDH纳米片的电荷转移电阻相比于没有包覆之前有明显的下降,证明了银包覆技术可以显著改善电极的导电性,降低电极的电荷转移电阻,使活性物质的电化学性能显著提升。(4)合成不同银含量的Ag/ZnAl-LDH复合物,研究复合物中银的含量对其电化学性能的影响。通过各种结构表征手段,证明了导电相银包覆在ZnAl-LDH纳米片表面,不同银含量的复合物样品中银包覆层的分布和存在状态不同,当银的含量达到7.49wt.%(AL15)时,形成一层均匀的银包覆层。综合考虑电池的循环稳定性和放电容量,AL15样品的性能最佳,在循环300次以后,AL15的放电容量没有出现明显衰减,在整个300次充放电循环中放电容量始终稳定在-400mAh g-。(5)采用溶液直接还原法,在不用任何还原剂的情况下,将硝酸银溶液中的银离子直接还原成纳米银颗粒,沉积在ZnAl-LDH纳米片表面。电化学性能测试表明Ag-LDH复合物样品相比于纯的ZnAl-LDH,其电化学性能得到了显著改善。电化学交流阻抗谱分析结果表明,Ag-LDH复合物的电荷转移电阻明显降低。这证明了高导电的纳米银颗粒沉积在ZnAl-LDH纳米片表面,可以通过降低电荷转移电阻的方式,提高电极材料的电荷传输速率和电子导电性,改善电极材料的电化学性能。(6)采用自组装的方法将GO和ZnAl-LDH组装在一起,然后通过水热还原法,将GO还原成石墨烯,得到graphene/ZnAl-LDH复合物。对graphene/ZnAl-LDH复合物样品的结构进行表征,证明了超薄的石墨烯将ZnAl-LDH纳米片包裹在中心,形成新颖的胶囊状结构。由于外层的graphene具有非常好的电子传导特性,可以大大加快电子在活性物质之间以及活性物质与集流体之间的传导过程。由于胶囊状graphene/ZnAl-LDH复合物具有以上优点,在电池的循环性能和放电容量方面均有大幅提升。在1C条件下电池恒流充放电循环1000次以后,电池容量仅衰减3%,稳定在～405mAh g-1,这种优异的循环特性,非常适合作为锌镍电池负极活性材料。更多还原

【Abstract】 Abstract:The nickel-zinc rechargeable battery is an attractive power source for various electric appliances and large-scale energy storage systems due to its high specific energy, excellent specific power and high open-circuit voltage. Its battery performance is much than Ni-Cd and Ni-MH battery. However, the most critical problems of Ni-Zn rechargeable batteries are shape change and dendrite formation on the negative side resulting in poor cycling effciency, which limit their widespread commercialization. As is well known, the novel2D architecture of ZnAl-LDH can offer it to the replacement of conventional ZnO anode material in Ni-Zn secondary batteries. However, the practical implementation of ZnAl-LDH as an anode material for Ni-Zn batteries is hampered dramatically by its low intrinsic electrical conductivity. To alleviate this problem and further enhance the electrochemical performance of the ZnAl-LDH, one effective strategy is to design specific nanocomposites (carbon or metal), which could obviously increase the electrical conductivity of the ZnAl-LDH. The main points in this research can be summarized as following:(1) We adopt a new rapid method for the preparation of ZnAl-LDH nanoparticles. In our method, the ZnAl-LDH seeds separated from the mother liquor are re-dispersed in the deionized water and subsequently the ZnAl-LDH nanoparticles are developed at the crystal growth stage under hydrothermal conditions for24h. In contrast to the conventional co-precipitation method and conventional hydrothermal method, this simple process allows us to fabricate ZnAl-LDH nanosheets of high quality and purity. The ZnAl-LDH nanosheets prepared by our method represent a high crystallinity and a hexagonal plate-like structure. These features afford the ZnAl-LDH nanosheets much suitable for anode material in Ni-Zn battery application. (2) Nanostructured ZnAl-LDH/CNTs composite is successfully synthesized by a simple precipitation technique through the electrostatic interaction between positively charged layer of LDH and negatively charged functional groups on modified CNTs. The ZnAl-LDH/CNT composite with unique3D nanostructure is a novel nanomaterial which combines2D LDH nanosheet and ID carbon nanotubes together. The as-prepared LDH/CNT composite samples are used as anode materials for Ni-Zn battery, whose charge-discharge properties, electrochemical impedance spectroscopy and cycle performances are examined in detail. The results show that the improvement in the electrochemical properties is obtained.(3) Ag-coated ZnAl-LDH nanosheets are successfully prepared by a facile silver mirror reaction. The as-prepared Ag-coated ZnAl-LDH demonstrates high discharge capacity, good charge-discharge performance and excellent cycle stability. The EIS indicates that the Ag coating can remarkably decrease the charge-transfer resistance and improve the activity of anode material. This superior electrochemical performance is attributed to the anchored Ag coating which increases the electronic conductivity of anode.(4) The Ag/ZnAl-LDH composites with different Ag contents are fabricated. We investigate the effect of silver additive on the electrochemical performance of ZnAl-LDH. Structure and morphology analysis show that silver additive is dispersed on the surface of ZnAl-LDH nanosheets and the silver phases of composite samples with different Ag contents are not the same. When the silver content reaches to7.49wt.%(AL15), the uniform silver layer is formed. Electrochemical performances were evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge tests. The AL15composite electrode has the highest reversible capacity (-406mAh g-1) than the others and the best cycling stability.(5) Surface decoration of ZnAl-LDH nanosheets with Ag nanoparticles is performed by a novel wet chemical method and no reducing agent is used. The electrochemical performance of the as-prepared Ag-LDH composites is significantly enhanced compared with the pure LDH nanosheets. The EIS measurement shows that the silver nanoparticles decrease the charge transfer resistance of Ag-LDH anodes by high conductive of Ag nanoparticles. Such intriguing electrochemical behavior is attributed to the conductive two-dimensional nanostructure with synergistic effects between a large specific surface area of LDH nanosheets and high conductivity of Ag nanoparticles.(6) GO/ZnAl-LDH composite is fabricated via the electrostatic interaction between positively ZnAl-LDH nanosheets and negatively charged graphene oxide. After hydrothermal reduction, the graphene/ZnAl-LDH composite is obtained. Such excellent electrochemical behavior is attributed to the synergistic effects between ZnAl-LDH nanosheets and high conductive graphene layers on the surface of LDH. The graphene/ZnAl-LDH shows outstanding cyclability, it is only decreased by～3%of the initial capacity at1C-rate even after1000charge-discharge cycles. Based on these observations, these newly designed3D graphene/ZnAl-LDH capsule may offer a promising anode active material for Ni-Zn secondary battery applications.更多还原