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 LiFePO₄/FePO₄ upon delithiation and lithiation by a pair of redox shuttle molecules FcBr₂⁺ and Fc. The effective rate constant k_eff was determined to be around 3.70–6.57 × 10^–3 cm/s for the two-way pseudo-first-order reactions, which feature a linear dependence on the composition of LiFePO₄, 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 LiFePO₄ 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.

中文翻译：

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扫描电化学显微镜测定电池材料中Li ⁺偶联的氧化还原靶向反应动力学

Li ⁺储存材料与氧化还原介体的氧化还原靶向反应是氧化还原液流锂电池的关键工艺，这是下一代大规模储能的有希望的技术。储能材料和氧化还原介体之间Li ⁺耦合的异质电荷转移的动力学决定了器件的性能，而作为新型电荷转移过程的研究很少。在这里，第一次使用扫描电化学显微镜（SECM）来确定LiFePO ₄ / FePO ₄的界面电荷转移动力学，该过程是通过一对氧化还原穿梭分子FcBr ₂ ⁺和Fc进行脱锂和锂化时的。有效率常数对于双向伪一级反应，k _eff被确定为大约3.70–6.57×10 ^–3 cm / s，其特征在于对LiFePO ₄的成分具有线性依赖性，从而验证了界面电荷转移的动力学过程。比散装固体扩散。此外，结合计时电流法测量，SECM研究还证明了LiFePO ₄脱磁的传统“收缩核”模型并提出了一种探索界面氧化还原反应引起的相界传播的有趣方法。这项研究证明了一种可靠的氧化还原靶向反应动力学方法，并且该结果为优化用于大规模能量存储的氧化还原靶向系统提供了有用的指导。