锂空气电池用碳酸锂分解液相催化剂设计、制备与性能研究

Lithium-air battery is the developing orientation of energy storage technology due to its highest theoretical energy density. To enhance the physical contact between catalyst and solid-state discharge products, the utilization of solution-phase catalysts has become a popular trend in the research of secondary Li-air battery. Some soluble redox mediators have been found effective for the catalysis of Li2O2 and/or LiOH decomposition, whereas there is still a lack of solution-phase catalysts for Li2CO3 decompositon, which has the highest decomposition potential among usual discharge products. In preliminary works, the applicant has discovered that a planar binuclear cobalt phthalocyanine is capable of significantly reducing the overpotential of Li2CO3 decomposition. Based on these initial results, the applicant proposes to investigate other metallocyclic molecules to design and prepare new solution-phase catalysts for Li2CO3 decomposition. Firstly, it is proposed to simulate the catalytic behavior of mono-/bi-nuclear cobalt phthalocyanines through theoretical calculations, to build models of catalytic decomposition of Li2CO3, and then to predict the catalytic capability of other metallocyclic molecules. Secondly, it is proposed to design and prepare bi-/poly-nuclear metallophthalocyanines, metalloporphyrins and metallobipyridines according to the calculation results and feedback, to investigate the rules of influences of ligands, bridging groups, metallic ions and substituent groups on the redox potential, activation energy, and other factors, with the emphasis on the bridging group’s coupling effect on the electron transfer of metallic ions and macrocycles. Lastly, it is proposed to test the obtained optimal catalyst in full Li-air cells. Through this project, we expect to promote the development of secondary Li-air batteries.

锂空气电池是理论能量密度最高的储能体系，是其发展的方向。为改善催化剂与固相放电产物接触，液相催化剂成为二次锂空气电池的研究热点。一些可溶性氧化还原介体能够有效催化过氧化锂和氢氧化锂分解，但针对分解电位最高的碳酸锂，对应液相催化剂仍十分匮乏。在前期工作中，申请人率先发现一种双核酞菁钴能够有效降低碳酸锂分解过电位。在此基础上，本项目拟以金属有机大环分子为研究对象，设计、制备新型碳酸锂分解液相催化剂。首先，借助理论计算模拟单/双核酞菁钴催化行为，建立碳酸锂催化分解模型，预测新型金属有机分子的催化能力；其次，结合计算结果和反馈，设计、制备双核/多核金属酞菁、金属卟啉和金属联吡啶等金属有机分子，研究配体、桥联基团、金属离子和取代基对催化剂电位、反应活化能等的影响规律，重点研究桥联基团对金属离子和大环电子传递的耦合作用；最后，将获得的最优催化剂在全电池中进行评测，推进二次锂空气电池技术的发展。

锂-空气电池是理论能量密度最高的储能电池，是其发展的方向。为改善催化剂与固相放电产物接触，液相催化剂成为二次锂-空气电池的研究热点。一些可溶性氧化还原介体（RM）能够有效催化过氧化锂和氢氧化锂分解，但针对分解电位最高的碳酸锂，对应液相催化剂仍十分匮乏。本项目研究了双核酞菁钴（bi-CoPc），单核酞菁钴（mono-CoPc），LiBr和2,2,6,6-四甲基哌啶1-氧基自由基（TEMPO）等RM对碳酸锂氧化分解的催化性能，发现其化学催化氧化分解需要在2电子氧化还原介体（RM）的作用下才可进行，表明其分解过程存在2电子基元反应。而低的RM第二电对电位有利于缓解电解液等电池组分在充电过程中的氧化分解，并提高锂-空气电池循环性能。具有较低第二电对电位的bi-CoPc表现出优异的碳酸锂分解催化性能，同时可分解其他各种固相放电产物，是一种“万能”型液相催化剂。之后，本项目又研究了具有较低第二电对电位的卟啉钴类化合物对碳酸锂的分解性能，发现5,10,15,20-四苯基-21H,23H-卟吩钴(II)（CoTPP）、[5,10,15,20-四(4-甲氧苯基)卟啉]合钴(II) （CoTMPP）、2,3,7,8,12,13,17,18-八乙基-21H,23H-卟吩钴(II) （CoOEP）中，具有较强吸附能力的CoTMPP表现出较好的碳酸锂分解性能。本项目对碳酸锂分解液相催化剂的研究为国际上首次报道，具有强的原始创新性，对于提高金属-空气电池能量效率和循环寿命具有重要意义，此外也可启发其他需要电化学分解碳酸盐的研究课题。