【作者】 张静；

【导师】 李合琴；

【作者基本信息】 合肥工业大学 ， 材料物理与化学， 2019， 博士

【摘要】 电子通讯设备和电动交通工具等行业的飞速发展需要高比能、高安全性、成本低廉、环境友好并经久耐用的新型电池。商业化的锂离子电池受正极材料比容量及安全性等因素的限制,难以进一步提高续航能力。锂硫二次电池凭借高达1675mAh/g的理论比容量,以及来源丰富、经济环保等优点,成为新能源领域的研究热点。但是该体系存在导电性差、活性物质利用率低、穿梭效应等缺点,阻碍了其商业化进程。本实验从正极材料成分、“三明治”结构、隔膜等方面对锂硫电池进行改性和机理研究。论文的主要创新之处在于:研究了硬模板法制备介孔碳（MC）时模板剂量对介孔碳及锂硫电池性能的影响;借助TiO₂纳米管（Tnt）和纳米TiO₂颗粒（NT）对正极和隔膜进行改性,提高了循环性能和库伦效率;用物理气相沉积法在正极和碳膜上沉积了金属Al和Ti,改善了正极导电性,制备了“三明治”结构的新型Li-S电池。为提高活性物质利用率,本实验以聚乙烯醇为前驱体碳源,采用硬模板法制备了分层结构的介孔碳,制得三种硫/介孔碳复合正极材料。研究了纳米CaCO₃模板剂与聚乙烯醇的最佳质量比例、介孔碳的造孔机制与Li-S电池性能之间的关系。结果表明,CaCO₃:PVA=1:1.5制备的介孔碳MC2,比表面积为850m²/g,孔容0.57 cm³/g,以之为导电载体的S/MC2正极材料电池在0.5C和1C循环倍率下,首次放电比容量分别为1384mAh/g和1258mAh/g,100次循环后分别保有882mAh/g和861mAh/g的可逆比容量,具有良好的容量保持率和循环可逆性。用阳极氧化法制备了TiO₂纳米管,与纳米TiO₂颗粒混合后,对硫/活性炭（S/AC）正极材料进行改性,制备了S/AC/-NT/Tnt正极材料;并用NT/Tnt对传统Celgard2400隔膜（Cel）进行涂覆修饰,制备了改性隔膜Cel-NT/Tnt。S/AC/-NT/Tnt正极材料组装的Li-S电池,0.5C时的初始比容量为1153mAh/g,100周期后保持在846mAh/g;隔膜涂覆NT/Tnt改性后的电池S/AC/（Cel-NT/Tnt）在0.5C和1C时分别获得了1215mAh/g和1035mAh/g的初始放电比容量,100次循环之后的放电比容量分别为899mAh/g和873mAh/g,200次循环之后的库伦效率仍保持在98%以上。用物理气相沉积法,对传统锂硫电池正极等关键材料进行镀膜包覆,提高电导率,实现了循环性能的提高。首先以活性炭作为导电基体制备了硫/活性炭正极复合材料,再用射频磁控溅射技术,将Al和Ti金属分别沉积在硫/活性炭表面,提高硫的导电性,同时Al和Ti的部分颗粒嵌入活性炭材料表面的孔隙,抑制了多硫离子的穿梭效应,改善了电池的循环稳定性和工作寿命。在硫/活性炭正极材料上溅射镀Al后,电化学性能明显提高,在0.5C倍率下,第1次和第100次放电比容量分别为1257mAh/g和977mAh/g,库仑效率始终保持在97%以上。制备了正极-导电碳膜-隔膜的“三明治”结构新型电池材料。用射频磁控溅射法将Al和Ti分别沉积在滤纸表面,通过高温碳化制备出附着Al和Ti金属的复合导电碳膜,置于S/AC正极材料和隔膜之间,得到了S/AC-导电碳膜-隔膜的“三明治”结构新型锂硫电池。Al和Ti薄膜具有优良的电导率和延展性,改善了碳膜夹层的导电性和柔韧性,能缓冲正极材料的体积溶胀。镀Al碳膜夹层结构的电池在0.5C和1C时分别获得了1394mAh/g和1273mAh/g的初始放电比容量,在100次循环后仍有889 mAh/g和924mAh/g的可逆比容量,200次循环之后的库伦效率仍高于98%,穿梭效应得到有效控制,活性物质利用率明显提高。实验表明磁控溅射技术用于锂硫电池材料改性,能够有效提高电池性能。更多还原

【Abstract】 The rapid development of electronic communication equipment and electric vehicles requires new batteries with high specific energy,high safety,low cost,environmental friendliness and durability.It is difficult for commercial lithium-ion battery to further improve its endurance ascribing to the specific capacity of cathode materials and safety.Lithium-sulfur secondary batteries have become a research hotspot in the field of new energy owing to the high theoretical specific capacity of1675mAh/g,abundant sources,low cost and environmental friendliness.However,there are disadvantages of the system,including poor conductivity,low utilization of active materials,shuttle effect and so on,which hinder its commercialization.In order to solve the problems,the modification of lithium-sulfur batteries was studied in this thesis from the aspects of cathode materials,separator and“sandwich”electrode,and the mechanism of high performance was analyzed.The main innovations are as follows:mesoporous carbon is prepared by hard-template method;the influences of template dosage on the properties of mesoporous carbon and Li-S batteries are studied;the cathode and seperator are modified by TiO₂ nanotubes and nano TiO₂ particles to improve cycle performance and Coulomb efficiency;Al and Ti particles are deposited on the cathode and carbon film by physical vapor deposition,which improves the conductivity of the cathode and new Li-S batteries with sandwich structure are developed.In order to enhance the utilization of active materials,three kinds of mesoporous carbon were prepared by hard-template method with polyvinyl alcohol as precursor carbon source and nano-CaCO₃ as the template to synthesis S/MC cathode materials.The influences of the ratios of nano-CaCO₃ template on the pore-forming mechanism of mesoporous carbon and the electrochemical performance of Li-S battery were investigated.The results show that the mesoporous carbon MC2,prepared with the mass ratio of CaCO₃:PVA=1:1.5,has the specific surface area of850m²/g and pore volume of 0.57cm³/g.The Li-S battery S/MC2 deliverd an initial discharge specific capacities of 1384mAh/g and 1258mAh/g at 0.5C and 1C rates respectively.After 100 cycles,the reversible specific capacities of 882mAh/g and861mAh/g were maintained severally,showing high capacity retention and cyclic reversibility.The modified lithium-sulfur batteries S/AC/-NT/Tnt and S/AC/（Cel-NT/Tnt）were prepared with the mixture of nano-TiO₂ and TiO₂ nanotubes,prepared by anodic oxidation,as the additive for cathode materials and the coating for Celgard 2400separator.The initial discharge specific capacities of S/AC/（Cel-NT/Tnt）at 0.5C and1C were 1215mAh/g and 1035mAh/g,respectively,and the capacity of 899mAh/g and 873mAh/g were obtained after 100 cycles.Furthermore,the Coulomb efficiency remained above 98%after 200 cycles,representing good persistence and cycle stability.Physical vapor deposition was employed to modify the cathode material and carbon interlayer in order to enhance the electrochemical performance of Li-S batteries.Cathode material S/AC was synthesized with commercial activated carbon as the conductive matrix.Al and Ti were deposited on the surface of S/AC electrode by radio frequency magnetron sputtering to improve the conductivity.Besides,Al and Ti particles were embedded into the carbon pores on the surface of the electrode,which restrained the shuttle effect to some extent and improved the cycle stability of the batteries.The cathode coated with Al delivered an initial discharge specific capacity of 1257mAh/g and 977mAh/g at the 100th cycle at 0.5C rate,with the coulomb efficiency greater than 97%.The "sandwich" batteries were assembled with the cathode,conductive carbon film and the separator.Al and Ti were deposited on the filter paper surface by radio frequency magnetron sputtering,and the composite carbon films were prepared by high-temperature carbonization of the coated filter paper and emloyed as conductive interlayer between the cathode and separator.Al and Ti have excellent electrical conductivity and ductility,which enables good conductivity and flexibility of carbon film and helps to increase the kinetic reaction rate as well as buffer the volume swell of cathode.The initial discharge specific capacities of 1394mAh/g and1273mAh/g were obtained at 0.5C and 1C respectively for the battery containing a Al-coated carbon interlayer.The capacity of 889 mAh/g and 924mAh/g were achieved after 100 cycles,respectively.The coulomb efficiency after 200 cycles was still higher than 98%,meaning that the shuttle effect was alleviated efficiently and the utilization sulfur has been increased.Magnetron sputtering has been proved to be an effective method to promote the electrochemical property of Li-S batteries.更多还原