基于锂-空气电池的新型Mn-MOFs/碳复合空气电极的制备及性能研究

Lithium-air battery with non-aqueous electrolyte, as a secondary battery, is one of the most promising technologies among various electrochemical energy storage systems because of its extremely high specific capacity and specific energy. Recently, it is reported that α-MnO2 and Mn2O3, as catalyst component in the air electrode of the Lithium-air battery, exhibit excellent catalytic performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively. However, at present the particles of these manganese oxide are big resulting in a decrease in their specific surface areas when they are supported directly on the porous carbon, which leading to the limited round trip efficiency and cycling performance for lithium-air battery with non-aqueous electrolyte. Metal-Organic Frameworks (MOFs) materials have exhibited the attractive prospects in the catalysis because of their diverse structures, tunable cavity, high specific surface area and porosity. In this study, MOFs with suitable porous structure are synthesized firstly, then the active component, α-MnO2 and Mn2O3 are assembled into the porous of MOFs, thus the air electrode catalysts with excellent catalytic performance for ORR and OER are obtained, respectively. Finally, novel Mn-MOFs/carbon composite air electrodes with high round trip efficiency and cycling performance are prepared by supporting these catalysts on porous carbon. The relationship between the structures and charge/discharge performance of this novel composite air electrode is studied through modern analysis method, and the charge/discharge mechanism of the composite air electrode is also clarified, which provides a scientific basic for the research and development of Lithium-air battery with non-aqueous electrolyte.

非水系锂-空气电池具有很高的比容量和比能量，是应用前景极好的二次电池。最近研究表明，该类电池的空气电极中，α-MnO2和Mn2O3分别是氧气还原和氧气析出性能极优异的催化活性组分。目前将这些锰氧化物催化活性组分负载到多孔碳上制备空气电极时，锰氧化物颗粒比较大，活性比表面积也较小，这大大限制了锂-空气电池的充放电循环效率和循环性能。金属有机骨架（MOFs）材料具有纳米级规整孔道结构、超大比表面积和高的孔隙率。本项目的研究思路是先合成出合适孔道的MOFs材料，然后将α-MnO2、Mn2O3等催化活性组分组装在MOFs的孔中，制备出具有优异氧气还原和氧气析出性能的空气电极催化剂，最后将催化剂涂覆在多孔碳上，制备出新型高充放电循环效率和循环性能的Mn-MOFs/碳复合空气电极。采用现代分析测试手段研究催化剂结构和充放电性能的关系，深入研究复合电极的充放电机理，为开发非水系锂-空气电池提供科学基础。

随着化石能源地不断消耗，环境破坏和能源短缺的问题日益突出。寻求与开发可持续的清洁能源成为当今社会的重要责任。而高效、环保的能源存储与转化技术又是大规模利用清洁能源的重要保障。相比较锂离子电池、铅酸电池等已经规模化应用的能源存储与转化技术，锂-空气电池具有极高的能量密度、零排放、质轻等优点。这引发了近年来对锂-空气电池研究的热潮。但是，目前的研究表明锂-空气电池作为二次电池应用的最大瓶颈在于缺乏高效双功能催化剂。高效双功能催化剂能极大地促进缓慢的放电反应（氧气还原反应，ORR）和缓慢的充电反应（氧气析出反应，OER），从而提高锂-空气电池的充放电循环性能。因而，本项目研究的核心内容在于设计制备高效双功能催化剂，并将其与碳材料复合制备成高性能空气电极应用于锂-空气电池。同时，本项目还深入研究了双功能催化剂的催化机理；建立了催化剂与催化性能的构-效关系；探索了基于双功能催化剂的复合空气电极的充放电机理。. 本项目成功设计制备了基于金属有机骨架材料(MOFs)的高效ORR/OER双功能催化剂包括alfa-MnO2/MIL-101(Cr)、epsilon-MnO2/MOF(Fe)、MOF(Fe)、MOF(Fe/Co)、Co(II, III)/MIL-101(Cr)、ZIF-67/柚子皮衍生的氮掺杂碳以及由MOF(Fe/Co)和碳纳米管混合物衍生的FeCo合金/氮掺杂碳/碳纳米管。此外，本项目还陆续开发了NiMnO3/NiMn2O4复合氧化物、氮掺杂石墨烯(N-rGO)、Co3O4-MnCo2O4/N-rGO以及Ti-Co-Phen/C等高效ORR/OER双功能催化剂。在此基础上，将双功能催化剂(比如FeCo合金/氮掺杂碳/碳纳米管)制备成高性能空气电极应用于锂-空气电池。测试表明，单电池容量可以达到5000 mAh/g以上；并且经过200个充放电循环后其充放电效率依旧维持在65 %以上。本项目还开发了大容量锂-空气电池工程样机。初步性能测试表明，该工程样机总容量高达11000 mAh/g以上；可以实现高效充放电150次，循环效率高达70 %以上。. 本项目的研究为锂-空气电池提供了高效双功能催化剂材料和高性能空气电极，推动了锂-空气电池的商业化进程，实现了能源的清洁高效利用。这对于新能源、新材料产业的创新发展以及相关产业结构的升级都具有重要意义。