Department of Chemistry, Stony Brook University , Stony Brook, New York 11794-3400, United States.
Department of Chemistry, New York University , 100 Washington Square East, New York, New York 10003, United States.
J Am Chem Soc. 2015 Dec 9;137(48):15209-16. doi: 10.1021/jacs.5b09385. Epub 2015 Nov 25.
Lithium dendrite growth in lithium ion and lithium rechargeable batteries is associated with severe safety concerns. To overcome these problems, a fundamental understanding of the growth mechanism of dendrites under working conditions is needed. In this work, in situ (7)Li magnetic resonance (MRI) is performed on both the electrolyte and lithium metal electrodes in symmetric lithium cells, allowing the behavior of the electrolyte concentration gradient to be studied and correlated with the type and rate of microstructure growth on the Li metal electrode. For this purpose, chemical shift (CS) imaging of the metal electrodes is a particularly sensitive diagnostic method, enabling a clear distinction to be made between different types of microstructural growth occurring at the electrode surface and the eventual dendrite growth between the electrodes. The CS imaging shows that mossy types of microstructure grow close to the surface of the anode from the beginning of charge in every cell studied, while dendritic growth is triggered much later. Simple metrics have been developed to interpret the MRI data sets and to compare results from a series of cells charged at different current densities. The results show that at high charge rates, there is a strong correlation between the onset time of dendrite growth and the local depletion of the electrolyte at the surface of the electrode observed both experimentally and predicted theoretical (via the Sand's time model). A separate mechanism of dendrite growth is observed at low currents, which is not governed by salt depletion in the bulk liquid electrolyte. The MRI approach presented here allows the rate and nature of a process that occurs in the solid electrode to be correlated with the concentrations of components in the electrolyte.
锂离子电池和锂可再充电电池中的锂枝晶生长与严重的安全问题有关。为了解决这些问题，需要对工作条件下枝晶生长的机制有一个基本的了解。在这项工作中，在对称的锂电池中对电解质和锂金属电极进行原位（7）Li 磁共振（MRI），允许研究电解质浓度梯度的行为，并将其与锂金属电极上的微观结构生长的类型和速率相关联。为此，金属电极的化学位移（CS）成像（CS imaging）是一种特别敏感的诊断方法，能够清楚地区分在电极表面发生的不同类型的微观结构生长和最终在电极之间的枝晶生长。CS 成像表明，在每个研究的电池中，从充电开始时，苔藓状的微观结构就开始从阳极表面附近生长，而枝晶生长则发生得晚得多。已经开发了简单的指标来解释 MRI 数据集，并比较在不同电流密度下充电的一系列电池的结果。结果表明，在高充电速率下，枝晶生长的起始时间与电极表面电解质的局部耗尽之间存在很强的相关性，这在实验和通过桑德斯时间模型预测的理论上都得到了观察。在低电流下观察到枝晶生长的另一种机制，它不受体相电解质中盐的耗尽的控制。这里提出的 MRI 方法允许将发生在固体电极中的过程的速率和性质与电解质中各组分的浓度相关联。
