【作者】 蒋永；

【导师】 焦正；

【作者基本信息】 上海大学 ， 环境工程， 2013， 博士

【摘要】 随着社会经济的发展，人们对于清洁能源以及生态环境越来越关注。超级电容器作为一种新型的储能器件，由于其无污染、高效的优良特性，越来越受到人们的重视。锂离子二次电池具有高能量密度、高输出电位和无污染等优势，在手机、相机、笔记本电脑等小型电器方面获得广泛应用，同时，在新能源存储和电动汽车领域也展示了良好的应用前景。石墨烯自2004年问世以来，已经在诸多领域引起了广泛的关注，各国科学家都在争先恐后的研究石墨烯的各种特殊的性质。石墨烯的理论比表面积高达2630m2/g，而且其导电性非常好，是制造储能器件的理想材料。本论文旨在为满足高性能超级电容器和锂离子电池的需求，基于石墨烯与过渡金属氧化物之间的交互作用原理合成系列具有新型结构的、适于能量存储的石墨烯/金属氧化物纳米材料。探索纳米结构复合材料的形成机理，并研究电极形貌结构等参数对于其电化学性能的影响。论文的主要研究结果如下：（1）通过200⁹00℃不同温度热解氧化石墨，得到不同氧化程度的石墨烯，利用XRD、FTIR、EDS、Raman、BET等测试探讨不同热解温度石墨烯的微观结构，系统研究了层间距、氧含量、比表面积和无序程度对其电容性能的影响。研究发现含氧基团对电容性能起主导作用，200℃热解得到的石墨烯具有最高的比电容，在0.4A/g电流密度下为260.5F/g。（2）运用自组装机制的水热法，合成了多孔氧化铜/石墨烯片-片复合材料。实验过程中，首先通过形貌控制合成氢氧化铜纳米线前驱体，随后沿[010]晶面定向排列形成氧化铜片状结构。电容测试发现，在0.6A/g的电流密度下石墨烯/氧化铜复合材料的电容达到331.9F/g。当电流密度提高到2A/g和8A/g时，容量分别保持在305F/g和221F/g，显示了良好的倍率性能。2A/g的电流密度下经过1000循环后容量依然保持在95.1%，显示其作为超级电容器材料极大的应用前景。（3）采用不同方法，合成了不同结构系列NiO/石墨烯复合材料。a.共沉淀法制备单层石墨烯/NiO纳米复合材料：在这种复合材料中石墨烯作为导电网络，提高了氧化镍的导电性；同时石墨烯的限域作用，可有效防止氧化镍颗粒过度增长（⁵nm），并将不同的氧化镍颗粒隔离开来，防止纳米颗粒团聚，进一步提高复合材料比表面积。b.以十六烷基三甲基溴化铵（CTAB）为表面活性剂，回流法制备花状氧化镍/石墨烯。通过改变回流时间，调节石墨烯上氧化镍的负载量，并提出花状球形结构可能的形成机理。c.以甘油/水为混合溶剂，水热法制备花状多孔氧化镍/石墨烯复合材料。电化学测试表明该材料独特的三维孔状结构保证了电极活性物质与电解液的充分接触，片上的纳米孔道缩短了离子在电极活性物质体相的扩散距离，加之石墨烯良好的导电性有效改善了复合材料的电化学性能。（4）通过在较低温度下的水热法，以醋酸钠小分子为结构导向剂，合成α-FeOOH/GNS复合物前驱体，300℃下退火2小时，得到形貌结构保持的氧化铁纳米棒/石墨烯复合物。通过对不同水热时间产物的透射电镜分析，提出棒状结构氧化铁/石墨烯复合材料的生长机理：在水热过程中，α-FeOOH刚开始时表现出无规则的片状，随着水热时间的延长，片状会发生卷曲，然后断裂成为棒状，呈典型的卷曲-破裂-生长（RGB）生长机制。电化学测试结果表明，复合材料0.1C首次可逆容量达到1063.2mAh/g，并显示出良好的倍率和循环性能。（5）利用石墨烯和柠檬酸共同修饰，通过喷雾干燥方法合成Li₃V₂（PO₄）₃/（G+C）材料，并研究石墨烯、无定形碳对产物形貌结构及电化学性能的影响。三维结构的石墨烯和Li₃V₂（PO₄）₃一次颗粒相互交织缠绕，有利于电子的迁移；同时柠檬酸碳化生成的碳层包覆在Li₃V₂（PO₄）₃表面，减小了颗粒生长并提高其导电性。该材料在0.1C倍率、电压区间为3.0⁴.3V和3.0⁴.8V的放电比容量分别能达到131.4和181.5mAh/g，接近于理论容量，而且在100次循环后只有微弱的容量衰减。更多还原

【Abstract】 With the economic development, the clean energy and ecological environmenthave become increasingly concerned. As a new kind of energy storage device,supercapacitor has been thought as the most important energy storage device becauseof high power density, excellent cycle ability and environment protection.Meanwhile, lithium-ion batteries （LIBs） have been used widely in portable electronicdevices such as cell phones, digital camera and laptop, because of their high energydensity, high voltage and non-pollution. Furthermore, they have a greatapplication-potential in the fields of energy storage for renewable energy sources andelectric vehicles.Graphene, a monolayer of carbon atoms packed into a dense honeycomb crystalstructure, has attracted tremendous attention from both the experimental andtheoretical scientific communities since it was found in2004. Due to the uniquenanostructure and extraordinary properties, graphene based materials have shownpromising applications in electronics and energy storage.In this work， we designed various novel graphene/transition metal oxidecomposites with suitable nanostruetures for supercapacitors and rapidinsertion/desertion of lithium ions by utilizing the confinement effect and interfacialinteraction between metal oxide and graphene sheets （GNS）. Then, the formationmechanisms of these nano-structured composites were studied. And the effects ofmorphologies on the electrochemical performances for these graphene/transitionmetal oxide composites were investigated in detail.1. Graphene oxide is prepared from nature graphite via a way of modifiedHummer’s method, and then reduced by pyrolytic deoxidation method. GNS withdifferent reduction levels have been produced through thermal reduction of grapheneoxide in the temperature range of200–900°C. The effects of interlayer spacing, oxygen content, BET specific surface area and disorder degree on their specificcapacitance are explored systematically. The variation of oxygen-containing groupsis shown to be a main factor influencing the electrochemical double layer capacitorsperformances of the pyrolytic graphene. The highest capacitance of260.5F/g at acharge/discharge current density of0.4F/g is obtained for the sample thermallyreduced at about200°C.2. The layer-by-layer porous CuO/graphene nanocomposites have beensuccessfully synthesized by the oriented attachment mechanism based on a facilehydrothermal method. The as-prepared composite is characterized using XRD,Raman, SEM, TEM and nitrogen adsorption/desorption. The growth mechanism isdiscussed by monitoring the early growth stages. It is shown that the CuOnanoleaves are formed through oriented attachment of tiny Cu（OH）2nanowires.Electrochemical characterization demonstrates that the leaf-like CuO/graphene arecapable of delivering specific capacitance of331.9and305F/g at the current densityof0.6and2A/g, respectively. A capacity retention of95.1%can be maintained after1000continuous charge-discharge cycles, which should be attributed to theimprovement of electrical contact by graphene and mechanical stability bylayer-by-layer structure.3. Series of NiO/graphene composites have been synthesized by many differentmethods.（1） Co-precipitation method was used to synthesize mono-graphene/NiOnanocomposite, in which graphene conduct as conductive matrix and NiO with adiameter of3-5nm were grown on the two sides of graphene. The two-dimensionstructure can prevent the aggregation of nanomaterials, enlarge specific surface areaand improve wetting ability of the composite. The test results reflect that thecomposite with novel structure shows high capacity and excellent cyclic ability, thespecific capacitance is525F/g at current density of200mA/g and the capacityretention is95.4%after1000cycles.（2） The flower-like NiO/graphene compositeswere synthesized by a refluxing method in the presence of graphene, the amount of NiO loaded is adjusted by controlling the refluxing times. The three-dimensionalcomposites possessed improved electrochemical performance and high specificcapacitance. At the electric current density of200mA/g, the discharge specificcapacitance of the obtained composite materials was about687.6F/g. Thiscapacitance is very impressive by comparison with pure NiO, which owns only276.4F/g at the same conditions. The capacity retention of90.8%can be maintainedafter2000continuous charge-discharge cycles, demonstrating its promising potentialto be used for supercapacitors.（3） The hydrothermal method is an important methodfor nanomaterials. The flower-like porous NiO/graphene was synthesized byhydrothermal method with mixed glycerol and DI-water solvents, and characterizedby SEM, TEM, XRD, BET and so on. Then the electrochemical performances of theobtained composite materials were studied by CHI660C. It shows that the dischargespecific capacitance was about413F/g at the current density of200mA/g. Whengalvanostatic charge/discharge at current density of1A/g, the capacity retention is89.8%after2000cycles.4. A nanorod-like Fe2O3/graphene nanocomposite is synthesized by a faciletemplate-free hydrothermal method and a following calcination in the air at300°Cfor2h. The Fe2O3nanorods with diameter of20-30nm and length of150-250nmare homogenous distributed on both sides of graphene. The morphologies ofintermediates at different hydrothermal reaction times are investigated by TEMcharacterization and a possible growth mechanism of this one-dimensional structureis proposed. It is shown that the α-FeOOH rod-like precursors are formed through arolling-broken-growth （RGB） model, which are then transformed into α-Fe2O3nanorods during calcinations, preserving the same rod-like morphology.Electrochemical characterizations demonstrate that the nanorod-like Fe2O3/graphenecomposites exhibit a very large reversible capacity of1063.2mAh/g at currentdensity of100mA/g as well as good cycling performance.5. The Li₃V₂（PO₄）₃material modified by graphene and citric acid shows high specific capacity and excellent cycling stability. The3D network graphene andLi₃V₂（PO₄）₃primary nanoparticles embedded in micro-sized spherical secondaryparticles interlaced with each other. And this special nanostructure facilitatedelectron migration throughout the secondary particles. Meanwhile, the citricacid-derived amorphous carbon species are covered on the surface of Li₃V₂（PO₄）₃,which would diminish particle growth and improve the conductivity. The dischargecapacity of the composite could severally achieve131.4and181.5mAh/g in thevoltage range3.0–4.3V and3.0–4.8V at0.1C discharge rate, both of them showedfaint capacity decay when cycled for100times.更多还原