兰州大学机构库 >物理科学与技术学院
Alternative TitleManganese Compounds Composited with Graphene for Electrochemical Energy Storage
Thesis Advisor贺徳衍
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Keyword锂离子电池 氧化锰 硫化锰 还原氧化石墨烯 结构稳定性

大部分金属氧化物/硫化物都是重要的半导体材料,其禁带宽度较大,电子迁移率较低,电学、热学、磁学性质相对特殊,因此,在多个领域获得了广泛应用。许多金属氧化物/硫化物均可与锂离子发生转换反应,具有优异的储锂能力,它们的理论比容量是石墨的2-3倍,且储量丰富,制备简单,成本低廉,成为下一代高容量锂离子电池负极的候选材料。但是,由于在锂化/去锂化过程中,金属氧化物/硫化物体积变化较大,易导致失活,使得电池容量迅速衰减。本论文以锰化合物为研究对象,为改善它们作为锂离子电池负极材料的电化学性能,我们分别设计并制备了氧化锰(MnO)、硫化锰(MnS)与还原氧化石墨烯(rGO)的纳米复合材料,并较为系统地研究了它们的电化学特性。纳米复合结构不仅减小了锂离子在活性材料中的迁移距离、抑制了活性材料的团聚、缓和了活性材料体积变化所造成的应力,而且还提升了电极的导电性、保证了电极结构的完整性、使电极的循环稳定性得到了有效改善。主要研究内容和结果如下:纳米枝晶状碳包覆MnO与rGO复合材料(C-MnO/rGO)的制备及其锂离子电池负极特性。采用简单的真空抽滤法并结合热处理工艺在泡沫镍上制备了组分不同的C-MnO/rGO纳米复合材料,并直接作为锂离子电池的负极。实验表明,组分优化的C-MnO/rGO复合材料(前驱物质量比MnO2:GO=3:1)电极具有优异的倍率特性和循环性能:在经过电流密度从100 mA g-1阶梯增加到5000 mA g-1的倍率测试后,当电流密度切回到100 mA g-1时,可逆容量达到了1357.8 mAh g-1;在1000 mA g-1的电流密度下循环250次后,依旧维持了577.8 mAh g-1的可逆容量。实验观察到,在充放电循环过程中,C-MnO纳米枝晶粉碎为尺寸更小的纳米颗粒依然镶嵌在rGO中,小的纳米颗粒为电化学反应提供了更多的活性位点,更有利于电化学活性的增强。蜂窝状α-MnS纳米晶体/N、S共掺杂rGO(NSG)复合材料(α-MnS/NSG)的制备及其锂离子电池负极特性。采用简单的一锅煮水热法并结合热处理工艺制备了蜂窝状α-MnS/NSG复合材料,并研究了它们的锂离子电池负极特性。实验结果表明,α-MnS/NSG具有优异的电化学特性:在100 mA g-1的电流密度下循环100次,放电容量保持在763.5 mAh g-1;当电流密度增大到1000 mA g-1时,循环2000次后电池保持有576.7 mAh g-1的可逆容量,每次循环的容量损失平均仅为0.019%;在非对称的充放电电流密度下,电极依然具有突出的循环特性。随着循环的进行,α-MnS纳米晶碎裂成超细的α-MnS晶粒依然锚定在石墨烯上,不仅赋予了电极良好的电接触,也提供了更多的活性位点,进一步提高了电极的电化学性能。

Other Abstract

Most of metal oxides/sulfides are important semiconductor materials. Generally, they have relatively wide energy gap and low electronic conductivity. They have been widely applied in many fields due to their special thermal, electrical and magnetic properties. Many metal oxides/sulfides can reversibly storage lithium ion and act as anode materials of lithium ion batteries (LIBs), and their theoretical capacity of metal oxides/sulfides is 2~3 times higher than traditional graphite anode. Moreover, they are abundant, cheap and facile preparation, have become the potential candidate of anode materials for the new generation LIBs. However, the huge volume changes in lithiation and delithiation process lead the loss of active materials, which induce the capacity fade of lithium ion battery.

This thesis mainly focuses on manganese compounds. In order to improve their electrochemical performance when acted as anode materials of lithium ion batteries, we prepared MnO/rGO and MnS/rGO nano-composites and systematically studied their electrochemical performance. Nano-composites not only shorten Li+ transport distance in active materials, suppress the active materials agglomeration, alleviate the stress derived from huge volume changes of active materials, and also improve the electrode electrical conductivity, and maintain the electrode integrity, ultimately, improve the electrode cycle stability.The main research contents and conclusions are as follows:Fabrication of the composites of carbon-wrapped MnO nanodendrites and rGO (C-MnO/rGO) and used as an anode for LIBs.Different mass ratios of C-MnO/rGO composites were prepared on nickel foam by a facile vacuum filtration and a subsequent thermal treatment. As a binder-free anode of lithium ion battery, components optimized C-MnO/rGO composites (quality ratio of precursors for MnO2 and GO is 3:1) have excellent rate capability, which show discharge capacities of 930.3, 799.3, 646.9, 513.0, 360.3, and138.9 mAh g-1 at current densities of 100, 200, 500, 1000, 2000, and 5000 mA g-1, respectively, and finally recovers to 1357.8 mAh g-1 when the current density goes back to 100 mA g-1. It still maintains reversible capacity of 577.8 mAh g-1 at 1000 mA g-1 after 250 cycles. In addition, The MnO nanodendrites become much smaller nanoparticles embeded in graphene sheets after several lithiation/delithiation cycles, which is beneficial to further increasing specific capacity and life span of the electrode.Preparation of the composits of nanoscale α-MnS particles/nitrogen and sulfur co-doped rGO (NSG) (α-MnS/NSG) for long-life lithium-ion batteries.The honeycomb α-MnS/NSG composites were prepared by one pot hydrothermal synthesis and a heat treatment process. α-MnS/NSG anodes show excellent cyclability, which keep a high capacity of 763.5mAh g-1 at a current density of 100 mA g-1 after 100 cycles and a reversible capacity of 576.7 mAh g-1 at 1000 mA g-1 after 2000 cycles. More interestingly, the α-MnS/NSG electrodes also display superior cyclability (450 cycles) at an asymmetrical charge/discharge current density. Furthermore, nanoscale α-MnS become ultrafine MnS particles embeded in NSG framework during the charge/discharge process, which not only endow the good electronic contact, but also provide more active sites reaction, and further enhance electrochemical performance.

Document Type学位论文
Recommended Citation
GB/T 7714
刘博丽. 锰化合物与石墨烯的复合及其储锂性能研究[D]. 兰州. 兰州大学,2017.
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