【作者】 周钢；

【导师】 王太宏；

【作者基本信息】 湖南大学 ， 凝聚态物理， 2014， 博士

【摘要】 锂离子电池和超级电容器是储能的两个重要方向,它们的电化学性能和能量密度决定着它们今后的道路。然而,目前的储能电极材料一方面在具有高容量的同时,它的电化学循环和倍率容量性能却很差,需要进行改性处理；另一方面电极材料的电化学性能和储能容量和它的形貌有着密切的关系,实现电极材料的形貌最优化制备对提升电极材料电化学性能和能量密度有着重要意义。1.金属氧化物的理论储锂容量比较高,是石墨的2-3倍,但是它的循环性能却很差,需要进行改性处理。可充电锂离子二次电池的电化学性能主要和脱嵌锂电极中Li的固相扩散动力问题以及材料表面特性相关。我们以油酸为碳源,发明了一种新颖的制备氧化镍／碳复合纳米片的技术,这种以油酸为碳源,氧化镍纳米片为前驱体制备的NiO@C复合材料在50次循环后仍然展现出883mAh g-1的可逆容量,大大改善了NiO在充放电过程中的循环衰减问题和倍率问题,制备了一种高能量密度且循环性能优异的锂电负极材料,并在实验中比较了两种不同碳包覆效果对材料的影响,对碳包覆表面改性处理方式的差异提供了重要依据。2.我们研究了羟磷铁锂结构LiFe(PO4)(OH)xF1-x分层微球的形貌-变量的电化学性能,包括壳结构和中空结构的创建。实验结果表明材料的电化学性能会随着其形貌的改变而明显变化。与其它颗粒相比,由纳米棒和多孔微球组成的羟磷铁锂微球表现出优异的电化学性能,这可以归因于锂离子扩散途径被缩短,材料比表面积增大。据我们所知,这是第一次就形貌对可很好定义结构的羟磷铁锂电极材料的电化学活性的影响进行系统的研究。这种易于实现的合成不同形貌羟磷铁锂材料的方法能为进一步研究羟磷铁锂结构LiFe(PO4)(OH)xF1-x形状-变量材料的电化学性能研究提供一个有趣的平台。3.硅是自然界储锂容量最高的,但同时它的循环性能很差。我们从材料结构设计入手,合成了一种柔性外壳包裹弹性内核的核壳结构的石墨烯包裹单颗粒硅纳米结构。通过对纳米硅进行化学修饰,实现纳米硅与氧化石墨烯的自组装,然后采用环保的维生素C(抗坏血酸)在微波辅助下还原氧化石墨烯,形成石墨烯包裹单颗粒纳米硅复合材料。利用石墨烯的高比表面积、良好导电性和多孔结构来抑制硅在脱嵌锂过程中的体积膨胀,提高其电化学性能。通过对它的电化学性能研究和与纯硅性能的对比验证了石墨烯的包覆能有效改善硅的循环性能和倍率性能,为制备高能量密度硅基材料提供了思路。4.为了进一步验证材料的颗粒大小和形貌对储能材料电化学性能的影响,我们利用简单的静电纺丝后空气退火的方法制备出一维(1D)多孔ZnCo2O4纳米管(PNTs)并首次应用于超级电容器(SCs),并与ZnCo2O4纳米颗粒的超电容性能做了系统的对比研究,实验证明这种一维多孔ZnCo2O4纳米管的比容量、循环性能以及倍率性能等明显优于ZnCo2O4纳米颗粒。我们的一系列实验证明通过改变材料的形貌确实可以实现优化电化学性能的目的。更多还原

【Abstract】 Lithium-ion battery and supercapacitor are two of important energy storage devices. Their electrochemical performance, especially in the energy density, strongly influence the future applications in electric vehicles. However, on one hand present battery electrode materials with higher capacity have poor electrochemical performance in cycling and rate capacity, thus they require further modification. On the other hand, the electrochemical performance and corresponding energy storage are closely related with the morphologies of electrode materials. To find a optimal morphologe of electrode materials is of great significance to enhance the electrochemical performance and energy density.1. Lithium storage capacity of metal oxides is two or three times higher than that of graphite. However, their cycle performance is poor, thus modification is necessary. The performance of rechargeable Li-ion batteries is mainly associated with their kinetic problems linked to the solid-state diffusion of Li in intercalation electrodes and the quality of interfaces, we prepared the NiO@C nanocomposites as excellent anodes by a novel coating technique using oleic acid and NiO nanoplates as carbon resource and precursor, respectively. The as-prepared NiO@C using oleic acid and NiO nanoplates as precursors exhibited a reversible capacity of883mAhg"1over50cycles. This work demonstrates such coating precursor techniques are effective to solve above-mentioned kinetic problems of electrode materials related with cycling and rate capacity. Additionally, this work also studied the difference between two different coating processes, and the effects of corresponding materials on their electrochemical performance.2. We investigate the shape-dependent electrochemical property over tavorite LiFe(PO4)(OH)xF1-x hierarchical microspheres, including architecture of shell structure and creation of interior space. Our experimental results demonstrate that the electrochemical performances vary significantly with particle shape. The tavorite microspheres composed of nanorods and hollow microspheres exhibit superior electrochemical properties, compared to the other particles, which can be attributed to their shorter Li+ion diffusion and higher specific surface area. To the best of our knowledge, this is the first study to systematically investigate the shape effect on electrochemical activity of tavorite electrode materials with well-defined architectures. It is highly expected this facile synthesis of tavorite particles with different morphologies can provide an interesting platform for further fundamental investigation into the shape-dependent electrochemical performance of tavorite LiFe(PO4)(OH)xFi1-x.3. We synthesized a kind of core-shell structure which flexible elastic graphene shell ecapsulate silicon particles kernel. Silicon has the highest theorical capacity among all anode materials, however, it has extremely poor cycling ability as the same as metal oxides. Herein we describe a self-assembled graphene-encapsulated silicon (GE-Si) by coassembly between negatively charged graphene oxide and positively charged oxide nanoparticles. The process is driven by the mutual electrostatic interactions of the two species, and is followed by chemical reduction with combining the green reductive agent of ascorbic acid and microwave technique. This hierarchical structure can accommodate a large volume change of Si nanoparticles during cycling, provide a high electrical conductivity for the whole electrode, and generate many nanospaces in the electrode for lithium ion diffusion. Electrochemical tests demonstrated that Si@rGO nanocomposite had better performance in cycling and rate ability than pure Si nanoparticles. This will provide novel ideas for designing high-energy-density silicon-based nanocomposites.4. In order to further verify the influence of size and shape of materials on their electrochemical performance, we also studied the peseocapacitive characteristics of porous ZnCo2O4nanotubes synthesized via the electrospunning and annealing processes. Electrochemical tests demonstrated that the as-synthesized porous ZnCo2O4nanotubes had better electrochemical performance than ZnCo2O4nanoparticles. In summary, we found that the optimized electrochemical performance could be obtained through adjusting morphology of materials.更多还原