全钒液流电池离子跨膜传输模拟研究

The Modeling Study of Ion Crossover in All-Vanadium Redox Flow Batteries

摘要: 本研究针对全钒氧化还原液流电池(VRFB)中钒离子的跨膜传输过程建立了二维瞬态数值模型，通过耦合Donnan界面效应分析了多物理场作用下离子的传输规律。验证结果显示，模型预测的开路电压和充放电曲线与实验数据误差小于3%。研究表明，Nafion膜界面处的H⁺浓度因膜内存在固定阴离子而显著升高，电势分布呈现Donnan突变特性。钒离子通量受电流方向与荷电状态(SOC)协同控制，高SOC时V²⁺与VO₂⁺扩散通量增强，低SOC时V³⁺与VO₂⁺受电场主导。充放电循环中钒离子净迁移呈现从负极向正极传输趋势，导致正极侧钒总浓度增加(40次循环后增加12.5%)，造成正负极钒离子浓度失衡，成为容量衰减主因。该模型揭示了膜内多离子传输竞争机制，为优化膜材料设计与运行策略提供理论依据。

Abstract: This study establishes a two-dimensional transient numerical model to investigate the transmembrane transport process of vanadium ions in vanadium redox flow batteries (VRFBs). By coupling the Donnan interfacial effect, the ion transport mechanisms under multi-physical fields are analyzed. Validation results demonstrate that the model-predicted open-circuit voltage and charge-discharge curves exhibit less than 3% error compared to experimental data. The study reveals that the H⁺ concentration at the Nafion membrane interface significantly increases due to the presence of fixed anions within the membrane, and the potential distribution exhibits Donnan discontinuity characteristics. The vanadium ion flux is jointly controlled by the current direction and the state of charge (SOC). At high SOC, the diffusion fluxes of V²⁺ and VO₂⁺ are enhanced, while at low SOC, V³⁺ and VO₂⁺ are predominantly influenced by the electric field. During charge-discharge cycles, the net migration of vanadium ions shows a trend of transport from the negative to the positive electrode, leading to an increase in the total vanadium concentration at the positive side (12.5% increase after 40 cycles). This results in an imbalance of vanadium ion concentrations between the electrodes, which is identified as the primary cause of capacity decay. The model elucidates the competitive mechanisms of multi-ion transport within the membrane, providing a theoretical foundation for optimizing membrane material design and operational strategies.