Lopez Jeffrey, Pei Allen, Oh Jin Young, Wang Ging-Ji Nathan, Cui Yi, Bao Zhenan
Department of Chemical Engineering , Kyung Hee University , Yongin 17104 , Republic of Korea.
Stanford Institute for Materials and Energy Sciences , SLAC National Accelerator Laboratory , Menlo Park , California 94025 , United States.
J Am Chem Soc. 2018 Sep 19;140(37):11735-11744. doi: 10.1021/jacs.8b06047. Epub 2018 Sep 10.
The electrodeposition of lithium metal is a key process in next-generation, high energy density storage devices. However, the high reactivity of the lithium metal causes short cycling lifetimes and dendrite growth that can pose a serious safety issue. Recently, a number of approaches have been pursued to stabilize the lithium metal-electrolyte interface, including soft polymeric coatings that have shown the ability to enable high-rate and high-capacity lithium metal cycling, but a clear understanding of how to design and modify these coatings has not yet been established. In this work, we studied the effects of several polymers with systematically varied chemical and mechanical properties as coatings on the lithium metal anode. By examining the early stages of lithium metal deposition, we determine that the morphology of the lithium particles is strongly influenced by the chemistry of the polymer coating. We have identified polymer dielectric constant and surface energy as two key descriptors of the lithium deposit size. Low surface energy polymers were found to promote larger deposits with smaller surface areas. This may be explained by a reduced interaction between the coating and the lithium surface and thus an increase in the interfacial energy. On the other hand, high dielectric constant polymers were found to increase the exchange current and gave larger lithium deposits due to the decreased overpotentials at a fixed current density. We also observed that the thickness of the polymer coating should be optimized for each individual polymer. Furthermore, polymer reactivity was found to strongly influence the Coulombic efficiency. Overall, this work offers new fundamental insights into lithium electrodeposition processes and provides direction for the design of new polymer coatings to better stabilize the lithium metal anode.
锂金属的电沉积是下一代高能量密度存储设备中的关键过程。然而，锂金属的高反应活性导致循环寿命短以及枝晶生长，这可能会引发严重的安全问题。最近，人们采取了多种方法来稳定锂金属 - 电解质界面，包括柔软的聚合物涂层，这些涂层已显示出能够实现高倍率和高容量的锂金属循环，但对于如何设计和改性这些涂层尚未有清晰的认识。在这项工作中，我们研究了几种化学和机械性能系统变化的聚合物作为锂金属阳极涂层的效果。通过研究锂金属沉积的早期阶段，我们确定锂颗粒的形态受到聚合物涂层化学性质的强烈影响。我们已确定聚合物介电常数和表面能是锂沉积尺寸的两个关键描述符。发现低表面能聚合物会促进形成表面积较小的较大沉积物。这可能是由于涂层与锂表面之间的相互作用减少，从而界面能增加所致。另一方面，发现高介电常数聚合物会增加交换电流，并由于在固定电流密度下过电位降低而产生更大的锂沉积物。我们还观察到，对于每种聚合物，都应优化聚合物涂层的厚度。此外，发现聚合物反应活性对库仑效率有强烈影响。总体而言，这项工作为锂电沉积过程提供了新的基础见解，并为设计新型聚合物涂层以更好地稳定锂金属阳极提供了方向。
