有机共熔电解液实现高能量密度有机液流电池的普适性策略

非水有机液流电池的工作电压能够克服水分解电压的限制，但其能量密度一直受到活性分子溶解度的限制。一般来讲，有机活性分子的溶解性与分子的分子间作用力和溶剂极性有关。分子间作用力弱的有机分子通常在多种溶剂中均具有高溶解度，但电解液加入支持电解质或者分子被还原或氧化后的有机分子的溶解度明显下降。普遍采用的提高溶解度的方法有：有机合成修饰改性、形成共熔电解液/或浆料体系、氧化还原靶向反应策略等。共熔电解液通过利用组分间的分子间相互作用力能够非常简便的实现高浓度电解液。目前对该体系的研究比较分散，亟需从分子结构角度深入研究共熔电解液的形成机理，为今后发掘更多合适共熔电解液体系提供理论支撑。

近日，美国得克萨斯州大学奥斯汀分校的余桂华教授团队和苏州大学赵宇教授合作，通过考察一系列有机分子与碱金属TFSI、FSI盐之间的相互作用发现，含有羰基、硝酰自由基和甲氧基团的有机分子更容易有机共熔电解液。其中电化学惰性的甲氧基团与金属盐的相互作用力受到活性分子氧化还原反应得失电子的影响较小，不论在氧化态还是还原态下有机分子均可能形成共熔电解液。基于此机理合成的甲氧基取代的二茂铁衍生物也证实了这一观点，而且与锂组装的复合电池的能量密度达到188 Wh L^-1。该研究成果以“General Design Methodology for Organic Eutectic Electrolytes toward High-Energy-Density Redox Flow Batteries”为题发表在国际顶级期刊Advanced Materials上。

图1 a) BQ与LiTFSI摩尔比1:1时形成的有机共熔电解液。（b-d）BQ-LiTFSI有机共熔电解液理论计算及分子间的相互作用。（e）LiTFSI, NaTFSI, KTFSI与TEMPO在摩尔比1:5, 1:2, 1:5时形成的Li-TEMPO, Na-TEMPO, 和K-TEMPO 有机共熔电解液。（f-g）Li-TEMPO 有机共熔体的分子间作用力分布。（h）LiTFSI与MeOTEMPO摩尔比1:1形成的有机共熔电解液。（i-j）Li-MeOTEMPO有机共熔体的分子间作用力分布。

图2 (a) 合成Fc-1和Fc-2二茂铁衍生物与LiTFSI和NaTFSI形成共熔电解液及分子间相互作用。

图3 (a-b) 2 M Fc-1的锂基复合电池的充放电循环性能及曲线. (c) EC-LiTFSI-Fc-1 有机共熔电解液. (d) EC-LiTFSI-Fc-1 有机共熔电解液的分子间相互作用。(e) 不同浓度下共熔电解液的锂基复合电池的充放电能量密度. (f) 完全充电后EC-LiTFSI-Fc-1有机共熔电解液。

Changkun Zhang, Hui Chen, Yumin Qian, Gaole Dai, Yu Zhao, Guihua Yu. General Design Methodology for Organic Eutectic Electrolytes toward High-Energy-Density Redox Flow Batteries. Adv. Mater., 2021, DOI:10.1002/adma.202008560

余桂华教授领导的团队专注于新型液流电池的研究和设计，综合了化学科学，材料科学和能源科学的跨学科研究，包括通过有机合成对活性物质的物理/化学特性进行优化，利用共熔材料的特性实现高浓度的电解液，同时结合分子水平的电化学反应机理和反应动力学研究，借助理论的计算分析，发展了一系列新型有机液流电池、仿生液流电池。在液流电池领域的更多重大开创性工作和综述文章可见：

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