Control of Growth Front Evolution by Bi Additives during ZnAu Electrodeposition

The performance of many electrochemical energy storage systems can be compromised by the formation of metal dendrites during charging. Additives in the electrolyte represent a useful strategy to mitigate dendrite formation, but understanding the mechanisms involved requires knowledge of the nanoscale effects of additives during electrochemical deposition. Here we quantify the effects of an inorganic additive on the morphology of an evolving electrochemical growth front, using liquid cell electron microscopy to provide the necessary spatial and temporal resolution. We examine deposition of ZnAu on Au in the presence of Bi additive, and show that low concentrations of Bi delay but do not prevent the formation of growth front instabilities. We describe a model in which Bi segregates at the growth front and promotes the surface diffusion and relaxation of Zn, allowing better coverage of the initial Au electrode surface. A more precise knowledge of the mechanism of inorganic additive effects may help in designing electrolyte chemistry for battery and other applications where morphology control is essential.诸多电化学储能体系在充电过程中，金属枝晶的生成会对其性能造成损害。电解液添加剂是缓解枝晶生成的有效策略，但阐明其背后的作用机制，需要掌握添加剂在电化学沉积过程中的纳米尺度效应。本研究借助可提供高时空分辨率的液相池电子显微镜（liquid cell electron microscopy），定量分析了无机添加剂对电化学生长前沿形貌演化的影响。我们以铋（Bi）添加剂存在下金（Au）基底上的锌金（ZnAu）沉积体系为研究对象，发现低浓度铋可延缓但无法完全抑制生长前沿不稳定性的形成。我们构建了如下模型：铋在生长前沿发生偏析，可促进锌的表面扩散与弛豫，从而实现对初始金电极表面的更均匀覆盖。对无机添加剂作用机制的更精准认知，可为电池及其他需严格调控形貌的应用场景的电解液化学体系设计提供助力。