In situ diagnostics for ultra-long-cycling organic redox flow batteries

与其他大规模储能方法相比，有机氧化还原液流电池（ORFB）已成为将可再生能源可靠且具有成本效益地整合到电网中的有前途的技术类别。ORFB通过将溶液相氧化还原活性物质从外部储罐泵入电化学电池中进行操作，能够使用廉价，安全和地球丰富的材料独立缩放能量和功率密度。至于长放电持续时间，ORFB平准化成本主要取决于电解质寿命，开发能够在分子损失的特定机制方面合理化全电池容量衰减的新技术或定制技术至关重要。这对于表现出小于0.1% /天的容量衰减速率的长循环电池尤其如此，对于长循环电池，基于常规恒电流循环的方法已被证明是不可靠的。最近，开发了两种原位NMR方法，能够实时评估电解质分解机制和电池自放电。在这里，我们建议使用这样的方法，沿着与各种电化学技术，deconvolute同时贡献的容量衰减所产生的活性物种交叉和电解质分解。使用基于紫精的活性物质的多样化合成库，我们将根据Midi项目期间获得的初步结果开发，我们将研究循环过程中发生的化学稳定性，溶解度和跨膜通量的变化。此外，通过低聚氧化还原活性物质，还可以研究涉及影响电化学动力学的侧基间电子转移的复杂过程。我们最终希望将这些趋势与氧化还原活性分子和膜材料的结构特征联系起来，以设计新的超长循环ORFB系统。

Compared with other methods of large-scale energy storage, organic redox flow batteries (ORFBs) have emerged as a promising technology class for reliable and cost-effective integration of renewables into the electricity grid. Operated by pumping solution-phase redox active species from external storage tanks into electrochemical cells, ORFBs enable independent scaling of energy and power densities using materials that are cheap, safe and earth-abundant. As for long discharge durations, ORFB levelized costs depend critically on electrolyte lifetime, the development of new or tailored techniques capable of rationalising full cell capacity-fade in terms of specific mechanisms of molecular loss is critical. This is especially true for long-cycling cells exhibiting capacity fade rates of less than 0.1% / day, for which methods based on conventional galvanostatic cycling have proven to be unreliable. Recently, two in situ NMR methods were developed that enabled real-time evaluation of electrolyte decomposition mechanisms and battery self-discharge. Here, we propose to use such methods, along with a variety of electrochemical techniques, to deconvolute simultaneous contributions to capacity-fade arising from active species crossover and electrolyte decomposition. Using a diverse synthetic library of viologen-based active species, which we will develop based on preliminary results obtained during the Midi project, we will investigate changes in chemical stability, solubility and trans-membrane flux that take place during cycling. Additionally, by oligomerising redox active species, complex processes involving inter-pendant electron transfers that influence electrochemical kinetics can also be studied. We ultimately hope to tie these trends to structural features of both the redox active molecules and membrane materials to enable design of new, ultra-long cycling ORFB systems.