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钴基高循环性能锂空气电池正极材料的研究
商超群
Thesis Advisor崔光磊
2015-05
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline化学工程
Keyword钴基催化剂 锂空气电池 电化学性能 Li202结构 Lio2
Abstract高性能动力电池是发展新能源汽车的重要技术支撑,锂空气电池具有高理论能量密度,未来有望用作电动汽车动力电池。针对目前锂空气电池存在充放电能量转化效率低、深度放电循环寿命短等核心问题,本论文从开发有机体系锂空气电池关键正极材料的角度开展研究。钴基催化剂在锂空气电池中表现出良好的活性,通过制备几种钴基催化剂,探究了钴基锂空气电池正极催化剂的作用机制,主要取得了以下研究成果: (1)ZnCo2O4球具有微孔介孔复合结构,微孔结构能够提供更多的氧还原的活性位点,介孔结构有助于提供更多的氧气还原反应的三相界面,提供了锂离子和氧气传输通道,保证了放电产物的存储空间。ZnCo2O4介孔球用作锂空气电池正极催化剂,具有比Super P电极低200 mV的充电电压,能够相对减少副反应的发生,表现出较好的循环稳定性。截止比容量到1000 mAh g-1电池循环可以达到140次并且充电极化没有明显变化。实验表明ZnCo2O4介孔球具有一定的催化氧析出的能力,是一种有潜力的锂空气电池正极材料。 (2)Fe3O4@CoO介孔球壳层花状CoO作为电催化剂,具有很多介孔的存在,有助于提供更多利于氧气还原和析出的活性位点,同时提供了稳定的三相界面,增加了放电产物的存储空间。Fe3O4@CoO介孔球作为锂空气电池正极催化剂,表现出高放电起始电位,低充电起始电位和充电过电势,首次库伦效率92.7%。Fe3O4的优良导电性保证在充放电过程中快速的电子转移。截止比容量进行循环测试,50次循环后,放电平台稳定,其电压衰减仅0.04 V。结果表明Fe3O4@CoO能够明显降低过电势,在锂空气电池中有重要的应用前景。 (3)Co3O4介孔球通过进一步氨气处理得到CoO介孔球,将CoO介孔球作为正极催化剂组装锂空气电池进行测试发现,能够有效降低充电电压至3.75 V,库伦效率高达99.8%;通过截止比容量至1000 mAh g-1进行循环测试,300次循环后放电终止电压约2.5 V,同时充电终止电压约4.0 V,证明了其高循环稳定性。分别将Co3O4介孔球与CoO介孔球作为催化剂组装锂空气电池进行深度充放电测试,30次循环后,CoO的表现出的稳定性明显优于Co3O4。考虑到相同的制备过程,二者主要区别在于晶体结构的不同。结合密度泛函理论,分别对Co3O4和CoO的不同晶面与放电产物中间体(LiO2)形成的稳定的吸附结构进行模拟计算发现,CoO的每个晶面与LiO2的吸附结构都比Co3O4的吸附结构稳定。实验结果证明在充电过程中,CoO更容易与LiO2形成稳定的吸附结构,从而有效减少了LiO2与碳材料的接触,避免了副反应的发生,表现出高循环稳定性。 (4)可溶性催化剂CoPP的存在,得到的放电产物是一维状Li2O2,能够有效降低充电电压,减小充放电之间的极化,提高库伦效率。通过电池“重组”测试,CoPP在充电过程中不能促进红细胞状Li2O2的分解,而一维状的Li2O2在充电过程中不需要CoPP依旧表现出低充电电压和高库伦效率。CoPP主要在放电过程中影响O2-向Li2O2的转变,使之形成具有一维结构的Li2O2,同时结合ABF-STEM分析对其进行理论模拟。实验证明CoPP促进生成具有有序缺陷结构的Li2O2,造成未成对自旋进而改变表面电子结构,提高了Li2O2表面电子和离子的传输。
Other AbstractIt is required to develop high specific energy density battery systems for the development of electrical vehicles. The Li-O2 battery is a potential candidate to meet this demand owing to its high theoretical energy density. In this study, the cathode materials are designed based on the concept of fabricating the catalyst for oxygen reactions, aiming at improving the energy conversion efficiency and cycle stability of Li-O2 battery. Cobalt-based materials have been shown to have excellent catalytic activities. Various nanostructured Co-based catalysts are employed as cathode in Li-O2 batteries. The main contents are listed as follows: (1) ZnCo2O4 mesoporous spheres possess obvious mesoporous structures, where micropores provide more active sites for oxygen reduction reaction (ORR) and mesopores supply ORR three-phase interface, fast Li+ and O2 transport, as well as discharge product storage space. ZnCo2O4 as the cathode in Li-O2 batteries lower the charge overpotential of 200 mV, which would alleviate the side reactions and exhibit stable cycling performance. The ZnCo2O4-based battery cycled 140 times with fixed specific capacity of 1000 mAh g-1, and the charge overpotential was stable. ZnCo2O4 mesoporous spheres lowered the charge overpotential because of its activity of oxygen evolution reaction (OER). The poor electronic conductivity of ZnCo2O4 increased discharge overpotential slightly. (2) Core-shell Fe3O4@CoO mesoporous spheres possess mesopores in the CoO shell, which provide active sites for oxygen reduction reaction (ORR) and stable ORR three-phase interface, and discharge product storage space. Fe3O4@CoO as the cathode in Li-O2 batteries has higher starting discharge voltage, lower starting charge voltage with a relatively lower charge overpotential. And the initial coulombic efficiency is 92.7%. The high electronic conductivity of Fe3O4 ensures fast electron transport during discharge and charge. The Fe3O4@CoO-based battery cycled 50 times with fixed specific capacity of 1000 mAh g-1, and the discharge voltage was stable with reduction of only 0.04 V. (3) CoO mesoporous spheres were prepared by the calcinations of Co3O4 mesoporous spheres under NH3 atmosphere. CoO as the cathode in Li-O2 batteries displayed lower charge voltage of 3.75 V, higher coulombic efficiency of 99.8%. After 300 cycles with fixed capacity of 1000 mAh g-1, the terminal discharge and charge voltage of CoO-based battery are about 2.5 V and 4.0 V. Co3O4 mesoporous spheres were also investigated as the cathode under deep discharge/charge, CoO cathode exhibited superior cycle performance than that of Co3O4. This improved cycle performance can be ascribed to a more favorable adsorption configuration of LiO2 on CoO surface, which is demonstrated through DFT calculation. The favorable adsorption of LiO2 plays an important role in the enhanced cycle performance, which alleviated the contact of LiO2 to carbon materials and further alleviated the side reactions during charge process. This compatible interface design may provide an effective approach in protecting carbon-based cathodes in metal-oxygen batteries. (4) The discharge product with soluble catalyst CoPP in the electrolyte is one dimensional (1D) Li2O2. CoPP would lower the charge voltage, enhance the coulombic efficiency. By “rebuilt” tests, CoPP did not promote the decomposition of toroid Li2O2 during charge. 1D Li2O2 exhibited low charge overpotential and high coulombic efficiency without CoPP. The possible mechanism is that CoPP influenced the second reduction step from superoxide to peroxide and obtained 1D Li2O2 with ordered defects. Combined with ABF-STEM analysis and simulation, the ordered defects may result in unpaired spin and thus change the surface electronic properties. The surface spin can facilitate the electron and ion transport of Li2O2, which is the key to the electrochemically reversible formation and decomposition.
Department仿生能源与储能系统团队
Date Available2016-06-30
Subtype博士 ; 学位论文
Language中文
Document Type学位论文
Identifierhttp://ir.qibebt.ac.cn/handle/337004/8078
Collection仿生与固态能源系统研究组
Affiliation中国科学院青岛生物能源与过程研究所
Recommended Citation
GB/T 7714
商超群. 钴基高循环性能锂空气电池正极材料的研究[D]. 北京. 中国科学院大学,2015.
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