Huang William, Boyle David T, Li Yuzhang, Li Yanbin, Pei Allen, Chen Hao, Cui Yi
Stanford Institute for Materials and Energy Sciences , SLAC National Accelerator Laboratory , 2575 Sand Hill Road , Menlo Park , California 94025 , United States.
ACS Nano. 2019 Jan 22;13(1):737-744. doi: 10.1021/acsnano.8b08012. Epub 2018 Dec 31.
Battery performance is critically dependent on the nanostructure and electrochemical properties of the solid-electrolyte interphase (SEI)-a passivation film that exists on most lithium-battery anodes. However, knowledge of how the SEI nanostructure forms and its impact on ionic transport remains limited due to its sensitivity to transmission electron microscopy and difficulty in accurately probing the SEI impedance. Here, we track the voltage-dependent, stepwise evolution of the nanostructure and impedance of the SEI on CuO nanowires using cryogenic-electron microscopy (cryo-EM) and electrochemical impedance spectroscopy (EIS). In carbonate electrolyte, the SEI forms at 1.0 V vs Li/Li as a 3 nm thick amorphous SEI and grows to 4 nm at 0.5 V; as the potential approaches 0.0 V vs Li/Li, the SEI on the CuO nanowires forms an 8 nm thick inverted multilayered nanostructure in ethylene carbonate/diethyl carbonate (EC/DEC) electrolyte with 10 vol % fluoroethylene carbonate (FEC) and a mosaic nanostructure in EC/DEC electrolyte. Upon Li deposition, the total SEI thickness grows to 16 nm, and significant growth of the inner amorphous layer takes place in the inverted multilayered nanostructure, indicating that electrolyte permeates the SEI. Using a refined EIS methodology, we isolate the SEI impedance on Cu and find that the SEI nanostructure directly correlates to macroscopic Li-ion transport through the SEI. The inverted layered nanostructure decreases the interfacial impedance upon formation, whereas the mosaic nanostructure continually increases the interfacial impedance during growth. These structural and electrochemical findings illustrate a more complete portrait of SEI formation and guide further improvements in engineered SEI.
电池性能严重依赖于固体电解质界面（SEI）的纳米结构和电化学性质，SEI是一种存在于大多数锂电池负极上的钝化膜。然而，由于SEI对透射电子显微镜敏感且难以准确探测其阻抗，关于SEI纳米结构如何形成及其对离子传输的影响的认识仍然有限。在此，我们使用低温电子显微镜（cryo-EM）和电化学阻抗谱（EIS）追踪了CuO纳米线上SEI的纳米结构和阻抗随电压的逐步演变。在碳酸盐电解质中，SEI在相对于Li/Li为1.0 V时形成3 nm厚的非晶态SEI，并在0.5 V时生长到4 nm；当电位接近相对于Li/Li为0.0 V时，CuO纳米线上的SEI在含有10体积%氟代碳酸乙烯酯（FEC）的碳酸乙烯酯/碳酸二乙酯（EC/DEC）电解质中形成8 nm厚的倒置多层纳米结构，在EC/DEC电解质中形成镶嵌纳米结构。在锂沉积时，SEI的总厚度增长到16 nm，并且在倒置多层纳米结构中内部非晶层有显著生长，这表明电解质渗透到SEI中。使用改进的EIS方法，我们分离出了Cu上的SEI阻抗，并发现SEI纳米结构与通过SEI的宏观锂离子传输直接相关。倒置分层纳米结构在形成时降低了界面阻抗，而镶嵌纳米结构在生长过程中持续增加界面阻抗。这些结构和电化学研究结果描绘了SEI形成的更完整图景，并为工程化SEI的进一步改进提供了指导。
