全钒液流电池多层膜内Donnan效应与离子输运耦合作用机理及其对电池性能的影响

The large-scale utilization of clean and efficient energy has gradually become a hot spot in the global energy field. Due to the independence of battery capacity with power, long cycle life and high safety, the all-vanadium redox flow battery (VRFB) has become the most promising device for large-scale energy storage. However, the high cost and vanadium crossover of the membrane restricts the commercialization of VRFB seriously. To address it, this project proposes the idea of multilayer membrane optimization to take advantage of each layer for high-performance VRFB. The key problem of basic science is the coupling mechanism of Donnan effect and ion transport in multilayer membrane and its influence on battery performance. Based on the basic theory of multiphysics coupled transport and electrochemical reaction, this project will construct a VRFB model that considers the Donnan effect and ion transport in multilayer membrane, combined with the mechanism experiments for ion selective adsorption and ion transport in the membrane, to study the ion transport process in multilayer membrane and operating performance of VRFB. The Donnan effect in multilayer membrane is revealed, as well as its coupling mechanism with ion transport. The variation of ion transport characteristics in multilayer membrane and its influence on battery performance are obtained. The results will fill the theoretical lack of ion transport mechanism in complex structural membrane, and provide theoretical support and prediction tools to develop new membranes for VRFBs.

清洁高效能源的规模化利用是全球能源领域的关注热点，全钒液流电池（VRFB）因功率和容量相互独立、循环寿命长、安全性高等特点成为最具前景的大型储能装置。然而，膜的高成本、低阻钒性严重制约了VRFB商业化进程。由此，本项目提出多层膜优化以利用各膜层优势来获得高性能VRFB的思想，关键基础科学问题是多层膜内Donnan效应与多离子输运的耦合作用机理及其对电池性能的影响机制。本项目将基于多物理场耦合输运、电化学反应等基础理论，构建考虑多层膜内Donnan效应与离子输运的VRFB模型，结合膜内离子选择吸附和传输机理实验，系统研究多层膜内离子输运过程和VRFB性能，重点揭示多层膜内复杂Donnan效应及其与多离子输运的耦合作用机理，掌握膜内离子传输特性的变化特点及其对电池性能的影响机制。研究成果将填补VRFB复杂结构膜内离子输运机理的理论缺失，为开发新型高性能VRFB膜提供理论支撑和有效预测工具。

清洁高效能源的规模化利用是全球能源领域的关注热点，全钒液流电池（VRFB）因功率和容量相互独立、循环寿命长、安全性高等特点成为最具前景的大型储能装置。关注以隔膜为主的电池关键部件，围绕其内部多离子输运与电化学耦合复杂过程，旨在探索VRFB性能优化的理论支撑与实施策略。本项目以多层结构为特色，分别针对阴离子交换膜、双极膜、多层膜以及推广至多层电极展开系列研究。提出了可描述以上各类型膜内荷质输运过程的VRFB瞬态电化学模型，克服了不同结构下Donnan效应准确预测难题，实现了对各类膜的关键参数如何影响电池性能的捕捉。对于阴离子交换膜，离子选择吸附的模拟结果与实验高度一致，模型准确性高；电池模型可通过调整膜参数实现膜性能的优化预测；发现AEM中电流密度由H+和HSO4−共同承担，H+占比可通过调整膜参数而超过50%。高电流密度下，增加膜孔隙率极大提高了电压效率，同时保持高库仑效率；结合调整固定电荷浓度，进一步获得最佳容量衰减率。对于双极膜，薄阴离子交换层抑制了钒离子对流，从而显著减少了钒离子窜流，减缓了容量衰减并提高了库仑效率。高电流密度下，具有薄阴离子交换层的双极膜显示出比传统离子交换膜更高的能量效率；当阴离子交换层紧邻负极时，容量衰减得到更好的缓解。对于多层膜，离子对流传输机制受小电渗透系数的膜层约束；VRFB性能表现中庸，但其优势为在相对宽泛的运行工况范围内综合性能保持相对偏好。同时，通过组合两个不同孔隙率的碳毡层，制备了具有梯度孔隙率分布的复合电极。小孔隙率层位于膜侧，大孔隙率层位于流场侧。结果表明，电极厚度比为0.9 mm GF/0.6 mm CF、电解液流速为30 mL min-1，在电流密度为200 mA cm-2时达到82.7%的高能量效率，在400 mA cm-2时放电容量为240 mAh，是相同厚度常规石墨毡电极的2.18倍。以上工作为高性能VRFB的膜等关键部件设计提供了思路和理论支撑。