锌电极放电过程及失效机制数值分析

锌-空气电池是一种高能量的电池体系.实验表明, 在大功率工作条件下, 锌电极的材料利用率随电流密度的增加而急剧下降. 为探索其在大功率工作条件下的放电机理, 本文针对这一过程建立了一维数学模型, 通过数值求解模拟多个物理量如离子浓度、传递电流密度、电极孔隙度、固体氧化锌等在电极内部的分布变化情况, 在此基础上分析电极的性能. 数值结果分析表明, 固体氧化锌对电极内质量传输过程的限制是导致电极失效的根本原因. 其析出时间及在电极内部的集中分布位置对电极性能有显著影响; 而仅当其体积分数超过30%-35%的范围后才开始显著限制传质过程. 讨论了电极的优化措施, 模拟表明更高的溶液电导率,更大的电极孔隙度有利于增加大功率工作条件下电极的材料利用率. 但最重要的是保持电极内部氢氧根离子的浓度在一个较高的值,对于封闭式电极可以通过补液实现, 理想情况为设计一个电解液循环式的锌电极.

Numerical Simulation of Discharge Process and Failure Mechanisms of Zinc Electrode

Zinc-air battery is a high-power electrochemical system. Experimental data indicate that material usage decreases significantly with increasing applied current density. A one-dimensional mathematical model was established to simulate the discharge process of a high-power zinc electrode working under high current density conditions. Variable distributions within the electrode such as ionic concentrations, transfer current density, electrode porosity, and volume fraction of solid zinc oxide were predicted based on numerical solutions. The results demonstrate that the limitation of the mass transfer process by precipitation of solid zinc oxide is the main factor causing electrode failure. The precipitation time of solid zinc oxide and its concentrated distribution area have significant impacts on the electrode performance. The limitation of the mass transfer process is greatly aggravated if the volume fraction of zinc oxide exceeds specific values within a small range, approximately 30%-35%. The optimal designs of zinc electrodes were discussed. The numerical results indicate that high-power electrodes with higher ionic conductivities and porosities behave better. However, the most important requirement is to maintain a relatively high concentration of hydroxyl ions. For enclosed electrodes, infusion is an effective method, whereas an ideal design would consist of an open system with a circulating electrolyte, such as fluidized bed electrolyte.