CAS OpenIR
石墨烯基过渡金属氧化物的可控合成及其在锂离子电池中的应用
陈家元
Thesis Advisor陈运法
2018-06
Degree Grantor中国科学院大学
Degree Name博士
Degree Discipline材料学
Keyword锂离子电池,负极材料,电化学性能,石墨烯,过渡金属氧化物
Abstract

随着电动汽车市场的快速发展,开发高比能、高倍率和长使用寿命的新一代动力锂离子电池成为行业研究的热点。传统石墨负极材料因理论比容量较低(372 mAh g?1)而能量密度提升空间受限。相比之下,过渡金属氧化物(TMOs)具有更高的理论比容量(~1000 mAh g?1),且其具有环境友好、成本较低等优势。本论文从TMOs纳米结构设计、构建石墨烯基复合材料体系和引入多级孔结构的角度出发,提升电极材料的导电性、结构稳定性和锂离子传输效率,从而显著提高其可逆比容量、倍率性能和循环寿命等电化学性能。此外,高质量石墨烯的大规模制备工艺是限制其作为锂电负极材料的主要瓶颈。本文以非氧化插层工艺开展高质量石墨烯的宏量制备探索。主要研究内容和结果如下:(1)以氧化石墨烯、金属盐前驱体和氨水为原料采用水热方法一步合成TMOs纳米颗粒/氮掺杂石墨烯(NG)复合材料。纳米化的TMOs提供了丰富的嵌脱锂活性位点,石墨烯的锚定作用缓解了循环过程中纳米颗粒的体积变化。而且,氮掺杂处理有效克服了还原氧化石墨烯导电性恢复不足的问题。电极材料封装于CR2025型纽扣半电池中经历150圈连续循环后,Mn3O4/NG和Fe2O3/NG分别保持高达1208.4和650 mAh g?1的可逆比容量。且在5.0 C的高电流密度下,Mn3O4/NG和Fe2O3/NG可以保持284和313 mAh g?1的比容量。EIS测试结果也表明复合材料中氮掺杂石墨烯作为高导电基底可以显著增强电子及离子传导。(2)通过金属-氨配合物化学反应机理设计合成了一系列空心TMOs(Co3O4、NiO、CuO-Cu2O和ZnO)/氮掺杂石墨烯复合材料。TMOs空心球均匀锚定在氮掺杂石墨烯基底上,并且其壳层具有微小纳米晶组成的多级多孔结构。氮掺杂石墨烯完整的导电网络及TMOs独特的空心多孔结构能够有效缩短电子及离子的传输路径,从而大大增强其倍率性能。所得复合材料中N/C原子比介于9.1–17.3 at.%之间,高于文献报道中4–8.3 at.%的氮掺杂水平。选取H-Co3O4/NG和H-NiO/NG复合材料进行储锂性能研究。两者在经历200圈连续循环后分别保持825和1046 mAh g-1的可逆比容量。且在5.0 C时,H-Co3O4/NG和H-NiO/NG复合材料仍具有446和422 mAh g-1的可逆比容量,显示出优异的高倍率性能。(3)利用水热-热处理两步法,通过调控设计合成了NiO纳米晶化学键合在三维石墨烯骨架(3D-GF)表面的新颖纳米结构。其中,3D-GF相互连接的网络结构既防止了电极反应过程中石墨烯的再堆叠,又能提供电解液及离子传输的多级孔结构。超细的NiO纳米晶键合在石墨烯骨架表面进一步增多了电极反应的活性位点,并且键合作用的存在防止了纳米晶的脱落和团聚。这些优异的结构特性使得复合电极材料比容量和循环寿命的显著增加成为了可能。在0.2 C的电流密度下,经历250圈的长周期循环后,NiO/3D-GF复合电极材料仍保持1104 mAh g?1的可逆比容量,明显优于对应的空白对比样及文献报道中的NiO基负极材料。(4)针对目前石墨烯负极应用及其规模化制备存在的问题,开展高质量石墨烯宏量制备工艺探索。传统还原氧化石墨烯制备工艺流程复杂、环境污染严重,且所得石墨烯导电性较差。当用作锂电负极材料时,其在低电压下的充放电曲线缺乏明显平台特征,限制其能量密度的提升。本部分采用新颖的非氧化丁胺插层工艺,探索机械液相剪切剥离方法宏量制备高浓度、高质量石墨烯乳液。当用作锂电负极材料时,200 mA g-1电流密度下循环100圈及500 mA g-1高电流密度下循环300圈后,其可逆比容量分别保持高达499 mAh g?1和384 mAh g?1。当以PVP为表面活性剂,水系中重复上述剪切剥离过程时,仍可制得高质量石墨烯。以冻干所得PVP-G为原料,通过水热方法及后续热处理过程可以制得MoS2/G复合负极材料,进一步拓展高质量石墨烯的应用。;With the booming of electric vehicle market, it is urgent to develop a new generation of traction lithium-ion batteries (LIBs) with high specific capacity, outstanding rate capability and long service life. Due to the low theoretical capacity (372 mAh g?1), traditional graphite anode material has limited space for energy density improvement. In contrast, transition metal oxides (TMOs) have high theoretical capacity (~1000 mAh g?1), environmental friendliness, and relatively low cost. In this paper, we focus on the nanostructured design of TMOs, construction of graphene-based composite system and introduction of hierarchical porous structure to improve the conductivity, structural stability and Li+ diffusion efficiency of the electrode material. Meanwhile, these strategies are very effective to promote the specific capacity, rate capability and cycle life of the electrode materials. In addition, the large-scale production of high-quality graphene is a major bottleneck limiting its use as anode material. The non-oxidation intercalation technology is used to develop scale-production of high-quality graphene. The main research contents and results of this thesis are as follows:(1) TMOs nanoparticles/N-doped graphene (NG) hybrids were synthesized by hydrothermal method using graphene oxide, metal salt precursor and ammonia as raw materials. The nanosized TMOs provide abundant active sites for insertion/desertion of Li+. The flexible graphene substrates effectively mitigate the volume change of nanoparticles during cycling. Nitrogen doping treatment further improves the conductivity of reduced graphene oxides. When packaged in CR2025 button half cell and experienced 150 cycles, the Mn3O4/NG and Fe2O3/NG reached high reversible specific capacities of 1208.4 and 650 mAh g?1. Even at high current density of 5.0 C, the specific capacities of Mn3O4/NG and Fe2O3/NG hybrids still maintained at 284 and 313 mAh g?1. The EIS results indicated that N-doped graphene in hybrids provided a highly conductive matrix for the fast transfer of Li+ and electron.(2) On the basis of metal-amine complex chemistry, a series of hollow TMOs (Co3O4, NiO, CuO-Cu2O and ZnO)/NG were synthesized. The TMOs hollow spheres are uniformly anchored on N-doped graphene surface, and the shell layer had a hierarchical porous structure consisting of tiny nanocrystals. The integrated conductive network of NG and the unique hollow porous structure of TMOs can effectively shorten the transport path of electrons and ions, thereby greatly enhancing their rate performance. The hybrids had a higher N/C atomic ratio between 9.1–17.3 at.% than that (4–8.3 at.%) reported in the literatures. When used as anode materials for LIBs, the H-Co3O4/NG and H-NiO/NG hybrids exhibited high reversible specific capacities of 825 and 1046 mAh g-1 after 200 successive cycles at the current density of 0.1 C and excellent rate capacities of 446 and 422 mAh g-1 at 5.0 C.(3) The novel NiO nanocrystals bonded on 3D graphene framework were synthesized by two-step strategy involving hydrothermal treatment followed by thermal annealing. The 3D-GF interconnected network not only prevented the re-stacking of graphene, but also provided hierarchical porous structure for electrolyte and Li+ transport. The ultrafine NiO nanocrystals further increase the active sites for electrode reaction, and the presence of bonding effect prevented the shedding and agglomeration of the NiO. The as-prepared NiO/3D-GF electrode exhibits ultra-high reversible capacity, superior rate capability and excellent capacity retention. After 250 successive cycles at 0.2 C, the NiO/3D-GF electrode maintained a reversible capacity of 1104 mAh g?1, which was far better than those of the bare counterparts and other NiO-based anode materials reported in the previous literatures.(4) To meet the application requirements, the large-scale production of high-quality graphene was explored. The traditional preparation process of reduced graphene oxide was complicated as well as environmentally harmful, and the resulting graphene has poor electrical conductivity. When used as anode material, the charge-discharge curve showed no voltage platform, limiting its increase in energy density. When used as anode material, the reversible capacity remained as high as 499 mAh g?1 under the current density of 200 mA g-1 after 100 cycles. The reversible capacity maintained at 384 mAh g?1 after continuous 300 cycles under high current density of 500 mA g-1. When used PVP as surfactant, high-quality graphene could still be produced by repeating the shear stripping process in water system. Using PVP-G as raw material, the MoS2/G hybrids could be prepared, which further expand the application of high-quality graphene anode. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/26946
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
陈家元. 石墨烯基过渡金属氧化物的可控合成及其在锂离子电池中的应用[D]. 中国科学院大学,2018.
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