Rah Kyunil, Choi Byunghee, Kim Changoh
Institute of Battery R&D, LG Energy Solution, 188 Moonji-ro Yuseong-gu, Daejeon 34122, South Korea.
Langmuir. 2024 Apr 9;40(14):7550-7559. doi: 10.1021/acs.langmuir.4c00113. Epub 2024 Mar 28.
Upon forming, the intensity or thickness of the solid electrolyte interphase (SEI) in a Li-ion battery (LIB) evolves to various states depending on the cell materials and operation conditions. Despite a crucial role in comprehending the behaviors of an LIB, its quantitative measure is far from satisfactory mainly because of the undue complexity of the concentration profiles of the comprising chemical species. Here, we calculate the depth profiles of atomic mole fractions of C and F and their ratio as = C/F of graphite anodes for LIBs in comparison to an X-ray photoelectron spectroscopy (XPS) experiment. To this end, we take a differential equation approach to d/d*, where * is the reduced XPS etching time for depth. As a result, the respective analytical expression derived for C, F, and () is verified to accurately account for the experiment. Moreover, we show that () in the state can be practically expressed in , where γ is a constant for a given anode. Based on this, we suggest ξ = (α + β - β)/α as a measure of the SEI thickness evolution from the to state in terms of the cycle number. As an intriguing finding, the SEI thickness evolves up to about 3 times that of its initial state, beyond which it does not appear to grow any more.
在锂离子电池（LIB）中，固体电解质界面（SEI）形成后，其强度或厚度会根据电池材料和运行条件演变为各种状态。尽管SEI在理解LIB的行为方面起着关键作用，但其定量测量却远不能令人满意，主要是因为构成化学物质的浓度分布过于复杂。在这里，我们计算了LIB石墨阳极中C和F的原子摩尔分数深度分布及其C/F比，并与X射线光电子能谱（XPS）实验进行了比较。为此，我们采用微分方程方法处理d/d*，其中是深度的XPS蚀刻时间。结果表明，为C、F和（）推导的各自解析表达式能够准确地解释实验结果。此外，我们表明，在该状态下的（*）实际上可以用表示，其中γ是给定阳极的常数。基于此，我们建议用ξ = (α + β - β)/α作为从该状态到该状态的SEI厚度随循环次数演变的度量。一个有趣的发现是，SEI厚度增长到初始状态的约3倍，超过这个值后似乎不再增长。
