Energy Storage and Distributed Resources Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
Department of Mechanical Engineering, University of California, Berkeley, California 94720, United States.
ACS Appl Mater Interfaces. 2023 Feb 8;15(5):6755-6767. doi: 10.1021/acsami.2c19484. Epub 2023 Jan 25.
Si anodes for Li-ion batteries are notorious for their large volume expansion during lithiation and the corresponding detrimental effects on cycle life. However, calendar life is the primary roadblock for widespread adoption. During calendar life aging, the main origin of impedance increase and capacity fade is attributed to the instability of the solid electrolyte interphase (SEI). In this work, we use ex situ nano-Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy to characterize the structure and composition of the SEI layer on amorphous Si thin films after an accelerated calendar aging protocol. The characterization of the SEI on non-washed and washed electrodes shows that brief washing in dimethyl carbonate results in large changes to the film chemistry and topography. Detailed examination of the non-washed electrodes during the first lithiation and after an accelerated calendar aging protocol reveals that PF and its decomposition products tend to accumulate in the SEI due to the preferential transport of PF ions through polyethylene oxide-like species in the organic part of the SEI layer. This work demonstrates the importance of evaluating the SEI layer in its intrinsic, undisturbed form and new strategies to improve the passivation of the SEI layer are proposed.
对于锂离子电池来说，硅阳极在嵌锂过程中会发生严重的体积膨胀，这对其循环寿命有不利影响，这是出了名的。然而，日历寿命是广泛采用的主要障碍。在日历寿命老化期间，阻抗增加和容量衰减的主要原因是固体电解质界面（SEI）的不稳定性。在这项工作中，我们使用非原位纳米傅里叶变换红外光谱和 X 射线光电子能谱来表征非晶态硅薄膜在加速日历老化协议后的 SEI 层的结构和组成。对未经清洗和清洗电极的 SEI 的表征表明，在碳酸二甲酯中短暂清洗会导致薄膜化学性质和形貌发生很大变化。在第一次嵌锂和加速日历老化协议后对未经清洗的电极进行详细检查表明，由于 PF 离子通过 SEI 层有机部分中的聚氧化乙烯样物质优先传输，PF 和其分解产物倾向于在 SEI 中积累。这项工作证明了在其固有、未受干扰的形式下评估 SEI 层的重要性，并提出了改善 SEI 层钝化的新策略。
