【作者】 陈皓；

【导师】 高超；

【作者基本信息】 浙江大学 ， 高分子化学与物理， 2017， 博士

【摘要】 铝离子电池是一种以金属铝为负极,铝基离子液体为电解质的新型电化学储能器件,具有负极容量高,安全性好及成本低等优点。而目前铝离子电池的发展主要受限于其正极性能,如容量低,循环性差等,这限制了其进一步发展和未来的实际应用。因此寻找合适的铝离子电池正极材料,特别是性能相对突出的石墨烯正极材料,并深入研究反应机理以提高铝离子电池的性能是目前铝离子电池研究方向的重中之重。石墨烯是一种在电学、力学、光学及柔性等方面均展现出了卓越性能的新型二维碳材料。优异的导电率、极高的二维材料宽厚比和表面积使得石墨烯目前已经在能源存储材料领域展现出了非常重要的应用价值。因此,探究石墨烯本身的核心参数与电极反应中的重要因素之间的关系是目前推进石墨烯在能源领域应用的关键。为此本论文瞄准“高质量石墨烯设计”,以铝离子电池中的“短板”正极为切入点,通过针对性的立足于完美石墨烯中关键性的“无缺陷”和“低堆叠”特征与电极性能之间的关系,极大的提高了铝离子电池中石墨烯正极的电化学性能并探究相关机理,并扩展至其他电池电极的设计中。主要内容如下:1.提出针对铝离子电池石墨烯正极的首要“无缺陷原则”:缺陷越少,电化学性能越好。开发一种可大规模制备的无缺陷石墨烯气凝胶正极,其比容量可达100mAhg-1,可在7.2秒内充满电(最高电流密度达100Ag-1),且可在25,000圈循环内保持容量稳定。通过计算知其能量密度可达60 Wh kg-1,功率密度可达30 kW kg-1,均达到甚至超出商业化超级电容器的水平。通过原位实验证明石墨烯中的缺陷的存在导致电化学性能的降低,缺陷的产生导致循环中容量的衰减。同时证明该种铝离子电池的原型具有快充慢放、柔性折叠及耐火安全的优点,在未来可穿戴、高功率密度或需要高安全性的电化学储能领域均可发挥极大作用。2.提出“高质量石墨烯设计”,通过针对性的褶皱引入和高温热还原等关键技术创新,实现了可大量制备的无缺陷、低堆叠、高连续的石墨烯微花粉体材料,并阐明了其中“无缺陷”和“低堆叠”因素对铝离子电池中的石墨烯正极的电化学性能起到的决定性作用。无缺陷石墨烯微花应用于铝离子正极时比容量可达100mAh g-1,在5,000圈循环内保持容量稳定,最快可在18秒内充满电(最高电流密度达20 A g-1),远远超出低质量石墨烯正极的电化学性能。同时作者也将该原则延伸至锂硫电池中的硫正极中。无缺陷石墨烯微花-硫复合物正极的面容量最高可达5.2 mAh cm-2,超出低质量石墨烯材料-硫复合物的电化学性能,证明了该“高质量石墨烯设计”为普适性原则。3.首次证明在以室温离子液体为电解质、铝箔为负极的铝离子电池中枝晶现象的存在。发现了表面天然氧化膜在抑制枝晶生长、维持负极稳定方面的重要作用;阐明了在表面致密氧化膜均匀的保护下,金属铝箔与离子液体电解液反应的机理,有助于推动铝离子电池的进一步深入思考和实用化发展。更多还原

【Abstract】 Aluminium-ion battery is a novel energy storage device using aluminium metal anode and aluminium-based ionic liquid electrolyte.It have unique advantages of high anodic capacity,safety and low-cost.However,the progress of Al-ion battery is now restricted by its cathodic performance such as low capacity and insufficient cycling stability,which impede its further pratical application in the future.Hence finding a matched cathode material(especially well-performed graphene-based cathode material)and study the cathodic reation mechanism to improve its electrochemical performance is of vital importance.Graphene is a novel two dimensional nano-carbon material with excellent mechanical strength and flexibility,outstanding optical property and ultrahigh electronic conductivity.Such excellent electronic conductivity,ultra-large aspect ratio and surface area enables great application potential of graphene in energy storage material field.Exploring the relationship between key indexes of graphene and important factors during electrode reaction is the crux of the promoting graphene’s application in energy storage field.Accordingly,this thesis presented systemic studies on "high-quality graphene design" with the break point of "short lab" graphene cathode of Al-ion battery,studied relation between the fundamental "defect-free","few-stack" characteristic and electrode performance to significantly improve the electrochemical performances of graphene cathode of Al-ion battery and expand the"high-quality graphene design" to other battery systems.The main results are listed as follows.1.Propose the primary "defect-free princi(?)le" for graphene cathode of Al-ion battery:the fewer the defects,the better the performance.We successfully fabricated a large-scale producible defect-free graphene aerogel cathode affording excellent performances:high specific capacity of 100 mAh g-1,fast charge in 7.2 seconds(highest current densities of 100 A g-1),stable cycling performance within 25,000 cycles.Such Al-graphene aerogel battery can deliver moderate energy density of 60 Wh kg-1 and power density of 30 kW kg-1,achieving or surpassing the commercialized supercapacitors.We demonstrated that the defects in graphene leads to the degradation and decay of performance.We also proved the fast charge/slow discharge,flexible and foldable,fire-resistance and safe advantages of Al-graphene battery,exhibiting its great potential as future wearable,high power density and safe energy storage devices.2.Propose the "high-quality graphene design".We achieved a scalable defect-free,few-stack and highly continuous graphene microflower powder material by inducing key technologie such as targeted crumple and high temperature annealing.We also explained the decisive effect of the "defect-free" and"few-stack" characteristic on graphene cathode of Al-ion battery.The defect-free GmF3000 cathode of Al-ion battery can deliever high and stable specific capacity of 100 mAh g-1 withing 5,000 cycles,and can be fast charged in 18 seconds(highest current densities of 20 A g-1),far surpassing those of low-quality graphene cathode.We also expand the "high-quality graphene design" to sulfur cathode of Li-S battery.The defect-free GmF3000-S composite cathode can achieve a high areal capacity of 5.2 mAh cm-2 also surpassing those of low-quality graphene-sulfur control composites,demonstrating the general applicability of"high-quality graphene design".3.Demonstrate the existance of aluminium dendrites in Al-ion battery using room temperature ionic liquid electrolyte and aluminum metal anode.We discover the vital role of native oxide film in preventing dendrite growth and maintaing the intergrity of Al metal anode;explain the reaction mechanism of Al metal with ionic liquid electrolyte under the full-scale surficial protection of native oxide film,which can promote further deep thought and practical development of Al-ion battery.更多还原