Yan Ruiting, Ghilane Jalal, Phuah Kia Chai, Pham Truong Thuan Nguyen, Adams Stefan, Randriamahazaka Hyacinthe, Wang Qing
Department of Materials Science and Engineering, Faculty of Engineering, National University of Singapore , Singapore 117576.
Université Paris Diderot, Sorbonne Paris Cité, ITODYS , UMR 7086 CNRS, SIELE group, 15 rue Jean Antoine de Baïf, 75013 Paris, France.
J Phys Chem Lett. 2018 Feb 1;9(3):491-496. doi: 10.1021/acs.jpclett.7b03136. Epub 2018 Jan 16.
The redox targeting reaction of Li-storage materials with redox mediators is the key process in redox flow lithium batteries, a promising technology for next-generation large-scale energy storage. The kinetics of the Li-coupled heterogeneous charge transfer between the energy storage material and redox mediator dictates the performance of the device, while as a new type of charge transfer process it has been rarely studied. Here, scanning electrochemical microscopy (SECM) was employed for the first time to determine the interfacial charge transfer kinetics of LiFePO/FePO upon delithiation and lithiation by a pair of redox shuttle molecules FcBr and Fc. The effective rate constant k was determined to be around 3.70-6.57 × 10 cm/s for the two-way pseudo-first-order reactions, which feature a linear dependence on the composition of LiFePO, validating the kinetic process of interfacial charge transfer rather than bulk solid diffusion. In addition, in conjunction with chronoamperometry measurement, the SECM study disproves the conventional "shrinking-core" model for the delithiation of LiFePO and presents an intriguing way of probing the phase boundary propagations induced by interfacial redox reactions. This study demonstrates a reliable method for the kinetics of redox targeting reactions, and the results provide useful guidance for the optimization of redox targeting systems for large-scale energy storage.
锂存储材料与氧化还原介质之间的氧化还原靶向反应是氧化还原液流锂电池中的关键过程，氧化还原液流锂电池是一种很有前景的下一代大规模储能技术。储能材料与氧化还原介质之间锂耦合异质电荷转移的动力学决定了该装置的性能，而作为一种新型的电荷转移过程，其研究很少。在此，首次采用扫描电化学显微镜（SECM），通过一对氧化还原穿梭分子FcBr和Fc来测定LiFePO/FePO在脱锂和锂化过程中的界面电荷转移动力学。对于双向准一级反应，有效速率常数k被确定为约3.70 - 6.57×10 cm/s，其对LiFePO的组成呈线性依赖关系，验证了界面电荷转移而非体相固体扩散的动力学过程。此外，结合计时电流法测量，SECM研究反驳了LiFePO脱锂的传统“缩核”模型，并提出了一种探测界面氧化还原反应引起的相界传播的有趣方法。该研究展示了一种用于氧化还原靶向反应动力学的可靠方法，研究结果为大规模储能氧化还原靶向系统的优化提供了有用的指导。
