【作者】 王红；

【导师】 马紫峰；

【作者基本信息】 上海交通大学 ， 应用化学， 2014， 博士

【摘要】 可充锂空气电池具有能量密度高（达5200Wh kg-1，氧计算在内），绿色环保等优点，是目前备受关注的电化学能量存储体系。自K. M.Abraham构造出首个可充锂空气电池以来，世界各国科学家已经对其展开大量的基础研究工作。虽然已经取得一些初步研究成果，但是对于可充锂空气电池研究仍然处于初级阶段，在实用化之前，两个关键性问题需要解决：1）在缺乏高效氧还原（ORR）和析氧（OER）双效催化剂时，放电产物（过氧化锂或氧化锂）将会逐渐沉积于空气电极空隙并堵塞电极，从而使得氧气不能顺利进入反应界面，导致电池放电停止；2）碳酸酯及醚类电解液应用在锂空气电池中不稳定，在活性氧作用下非常容易分解，从而使得电池性能劣化。本论文针对氧还原/析氧双效催化剂和电解质体系存在的问题进行应用基础研究。主要研究内容如下：一、使用小分子含氮配体邻菲啰啉螯合过渡金属钴得到钴配合物，将钴配合物负载于BP2000碳载体上，通过热处理制得Co-N/C双效催化剂，探索了热处理温度对Co-N/C催化剂性能的影响。结果表明，800℃热处理的催化剂表现出最优的电化学性能，旋转圆盘测试证实，在有机电解液中为两电子转移机理，氧还原产物为过氧化锂。Co-N/C催化剂在锂空气电池中首圈放电比容量为3221mAh g-（1按空气电极中碳或催化剂质量计算锂空气电池比容量），催化性能与大环化合物钴卟啉（Co-P/C）催化剂相近。二、基于所制备的Co-N/C双效催化剂，制作锂空气电池空气电极进行电解质研究。制备了PVDF-HFP聚合物电解质，研究了纳米SiO2作为添加剂对聚合物电解质电化学性能的影响。结果表明所制备的聚合物电解质表面致密、没有缺陷孔。纳米SiO2的添加降低了聚合物电解质结晶度，提高了聚合物电解质离子电导率（添加量为3%时离子电导率为1.3×10-5S cm-1，锂离子迁移数为0.36），使用该聚合物电解质制作的锂空气电池在电流密度为0.2mA cm-1时，展现了3163mAh g-1放电比容量。三、为进一步提高PVDF-HFP聚合物电解质离子电导率，使用离子液体PP13TFSI替代纳米SiO2对电解质进行改性后，电解质离子电导率提高明显（4.9×10-5S cm-1），使用该聚合物电解质制作的锂空气电池充电极化减小0.2V（充电电压为3.6V），电池的倍率性能得到提高：在电流密度为1mAcm-1时，展现了1246mAh g-1放电比容量。四、针对电解液电化学稳定性差的现象，研究了甲基磷酸二甲酯（DMMP）为有机溶剂的电解液电化学性能。1.0M LiTFSI-DMMP电解液具有较高室温离子电导率（5.1×10-3S cm-1）和较宽电化学窗（5.5Vvs. Li/Li+）。循环伏安测试表明该电解液具有良好溶氧能力和氧气扩散系数，氧还原为多步骤过程，电解液还原起始电位为~2.5VLi/Li+，还原产物的氧化峰电流出现在~3.2VLi/Li+，低于碳酸酯电解液（~3.28VLi/Li+）和四乙二醇二甲醚电解液（~3.56VLi/Li+）。重复扫描50个周期后的循环伏安曲线发现，LiTFSI-DMMP电解液峰电流轻微衰减，表明氧还原产物在玻碳电极表面没有明显积累。五、基于全氟磺酸膜制备了LiTFSI-DMMP/PFSA-Li聚合物电解质。电化学测试表明该电解质具有宽的电化学窗口（5.0V vs. Li/Li+），室温离子电导率高于PVDF-HFP聚合物电解质一个数量级（1.4×10-4Scm-1），锂离子迁移数有所提高（0.48）。使用该聚合物电解质制作锂空气电池，展现出非常高的充放电比容量以及倍率性能，在电流密度为1mA cm-1时，放电比容量2471mAh g-1。限定时间（两小时）三十个充放电周期效率为98%。X射线光电子能谱表明放电产物为锂氧化物，核磁结构分析证实该电解质在锂空气电池循环过程中结构稳定、没有分解。更多还原

【Abstract】 Recently, lithium-air batteries have attracted great interest due to theirhuge theoretical specific energy of5200Wh kg-1including O2. The firstlithium-air battery with a structure of Li|organic electrolyte|air was reportedby Abraham and Jiang, and further developed by many scientists over theworld. However, the investigation and development on lithium-air batteriesis still in its initial stage. Much fundamental research is required before itcan be considered further for technological applications: first, if there is notan effective bifunctional electrocatalyst (oxygen reduction reaction (ORR)and oxygen evolution reaction (OER)), discharge products (Li2O and Li2O2)will precipitate in the pores of the carbon based cathodes, which blocksfurther intake of oxygen and thus abruptly ends cell life. On the other hand,organic carbonates are not suitable as electrolytes for Li/O2batteries. In thisdissertation, high performance non-noble metal catalysts and compositepolymer electrolytes were developed. Electrochemical properties of theprepared materials were studied. The major research contents are presentedas follows: 1. Phenanthroline (phen) was used as a ligand to prepare Co(phen)2complexes, which were coated on BP2000and then heat-treated to obtaincarbon-supported Co-N catalysts (Co-N/C). The influence of heat treatingtemperature on the structure and catalytic performance of the Co-N/Ccatalysts were investigated. The results indicated that the Co-N/C catalystprepared at800℃showed the best performance. Charge/discharge tests ofthe lithium-oxygen cells using the prepared Co-N/C catalyst showeddischarge capacities of3221mAh g-1(The specific capacities werereferenced with respect to the total mass of carbon and cobalt catalyst in thecathode). The catalytic activity of Co-N/C is similar to other non-noblecatalysts, such as Co-P/C electrocatalyst.2. We synthesized a PVDF-HFP composite polymer electrolyte. Theinfluence of silica on the structure and electrochemical performance of thepolymer electrolyte were investigated. The results revealed that polymerelectrolyte membranes showed smooth morphology properties. Theaddition of3%silica in the polymer electrolyte displayed the highest ionicconductivity (1.3×10-5S cm-1). Li ion transference number is as high as0.36. The lithium-oxygen cells using this polymer electrolyte showed thefirst discharge capacity of about3163mAh g-1, at0.2mA cm-1currentdensity.3. Due to low conductivity of PVDF-HFP polymer electrolyte, Ionicliquids PP13TFSI was used to improve the performance of polymer electrolyte. The electrolyte with ionic liquid showed a better ionicconductivity (4.9×10-5S cm-1), and had a smaller polarization on charge(3.6V) and discharge (2.75V). The cycling performance of the lithium-airbattery was also improved.4. Because of poor stability of carbonate based organic solvents inlithium air batteries, we explored dimethyl methyl phosphonate (DMMP)as an organic solvent of electrolyte. The results showed that1.0MLiTFSI-DMMP electrolyte presented high ion conductivity (5.1×10-3Scm-1) and wide electrochemical window (5.5V vs. Li/Li+) at roomtemperature. CV measurements indicate that oxygen reduction inDMMP-based electrolyte is a multistep process. The onset of the oxygenreduction reaction on GC electrode occurred at the potential~2.5VLi/Li+forLiTFSI-DMMP electrolyte and oxidation current peak appeared at~3.2VLi/Li+, lower than the carbonate electrolyte (~3.28VLi/Li+) and TEGDMEbased electrolyte (~3.56VLi/Li+). The CV curves show good reproducibilitywith cycle number increase, only slightly decrease of the peak area isobserved after50cycles, which indicates less accumulation of insolubleORR products on the electrode surface.5. Based on perfluorinated sulfonic, we designed and synthesized anew composite polymer electrolyte LiTFSI-DMMP/PFSA-Li.Electrochemical tests show that the ionic conductivity of the compositeelectrolyte was1.4×10-4S cm-1. The Li ion transference number of the electrolyte membrane is as high as0.48. The lithium-oxygen cells using theLiTFSI-DMMP/PFSA-Li electrolyte showed high rate discharge capacitieswith the first discharge capacity of2471mAh g-1, at1mA cm-1. Noobvious evidence of electrolyte decomposition was observed from theresults of1H,13C and31P NMR experiments.更多还原