Philipp Schweigart, Weicheng Hua, Pedro Alonso Sánchez, Camilla Lian, Inger-Emma Nylund, David Wragg, Samson Yuxiu Lai, Federico Cova, Ann Mari Svensson, Maria Valeria Blanco
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引用次数: 0
摘要
在石墨(Gr)阳极中添加硅(Si)是提高锂离子电池能量密度的有效方法,但同时也会因(脱)锂反应导致硅体积变化而引发机械不稳定性。在这项研究中,通过操作同步辐射 X 射线衍射和差分容量图分析,揭示了富硅(30 和 70 wt.% Si)SiGr 阳极在不同充放电 C 速率下的特定成分(脱)锂化动力学,并与纯石墨电极(100Gr)进行了比较。结果显示,无定形硅在≈200 mV 以上优先发生石墨化,而 Gr、无定形硅和晶体硅在≈200 mV 以下发生竞争性石墨化。放电是通过锗和无定形硅化锂的顺序脱锂进行的。与 100Gr 相比,硅改变了石墨插层化合物的相互转换电位,降低了 Gr 的电荷状态。 在 30% 硅电极中,发现晶体硅在电位 <110 mV 时的非晶化在 C 速率高于 C/5 时会受到动力学阻碍,这可能是提高 SiGr 阳极循环稳定性的关键。70% 硅电极在 Gr 中的锂扩散受到限制,硅完全非晶化,并形成 Li15Si4。这些与 SiGr 混合物的电位和电流动态变化有关的发现对于设计稳定的高能量密度 SiGr 阳极至关重要。
Deciphering the Impact of Current, Composition, and Potential on the Lithiation Behavior of Si-Rich Silicon-Graphite Anodes
Adding silicon (Si) to graphite (Gr) anodes is an effective approach for boosting the energy density of lithium-ion batteries, but it also triggers mechanical instability due to Si volume changes upon (de)lithiation reactions. In this work, component-specific (de)lithiation dynamics on Si-rich (30 and 70 wt.% Si) SiGr anodes at various charge/discharge C-rates are unveiled and compared to a graphite-only electrode (100Gr) via operando synchrotron X-ray diffraction coupled with differential capacity plots analysis. Results show preferential lithiation of amorphous Si above ≈200 mV and competing lithiation of Gr, amorphous Si, and crystalline Si below ≈200 mV. Discharge proceeds via sequential delithiation of Gr and amorphous lithium silicide. Si shifts the interconversion potentials of graphite intercalation compounds, lowering the Gr state of charge compared to 100Gr. In the 30% Si electrode, crystalline Si amorphization at potentials <110 mV is found to be kinetically hindered at C-rates higher than C/5, which can be key for enhancing the cycling stability of SiGr anodes. The 70% Si electrode exhibits restricted lithium diffusion in Gr, full Si amorphization, and Li15Si4 formation. These findings related to the potential- and current-dependent dynamic changes on SiGr blends are crucial for designing stable high energy density SiGr anodes.
期刊介绍:
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