电池多孔电极中反应不均匀性的热力学根源及其缓解
Thermodynamic Origin of Reaction Non-Uniformity in Battery Porous Electrodes and its Mitigation
摘要：
多孔电极内的非均匀反应电流分布的发展是电池充电/放电期间普遍存在的现象，并且经常控制电池单元的倍率性能。多孔电极中的反应不均匀性通常归因于电解质和/或固体电极相内的传质的动力学限制。然而，在这项工作中，我们发现，它也受到电极材料的固有热力学行为的强烈影响，特别是平衡电位对荷电状态的依赖性：当平衡电位曲线的斜率减小时，电极反应变得越来越不均匀。我们采用数值模拟和等效电路模型来阐明这种相关性，并表明反应的不均匀性和由此产生的放电容量的程度可以预测的无量纲反应均匀数。对于电极材料，具有平衡电位不敏感的充电状态，并表现出显着的反应不均匀性，我们展示了几种方法来空间上的多孔电极内的反应电流，包括匹配的电子和离子电阻，引入梯度电子电导率和减少表面反应动力学。
英文摘要：
The development of non-uniform reaction current distribution within porous electrodes is a ubiquitous phenomenon during battery charging / discharging and frequently controls the rate performance of battery cells. Reaction inhomogeneity in porous electrodes is usually attributed to the kinetic limitation of mass transport within the electrolyte and/or solid electrode phase. In this work, however, we reveal that it is also strongly influenced by the intrinsic thermodynamic behavior of electrode materials, specifically the dependence of the equilibrium potential on the state of charge: electrode reaction becomes increasingly non-uniform when the slope of the equilibrium potential curve is reduced. We employ numerical simulation and equivalent circuit model to elucidate such a correlation and show that the degree of reaction inhomogeneity and the resultant discharge capacity can be predicted by a dimensionless reaction uniformity number. For electrode materials that have equilibrium potentials insensitive to the state of charge and exhibit significant reaction non-uniformity, we demonstrate several approaches to spatially homogenizing the reaction current inside porous electrodes, including matching the electronic and ionic resistances, introducing graded electronic conductivity and reducing the surface reaction kinetics.
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