The cyclic instability of Si-based anodes can be effectively alleviated by adding carbon nanotube (CNT) networks. However, the ion diffusion and electrochemical performance vary significantly depending on the type of CNTs added, particularly single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs), and the intrinsic mechanism remains unknown. Herein, we revealed that the large volume expansion of Si-based anodes leads to the acupuncture effect of short CNTs, with the compressive stress on the CNTs and the Li-ion (Li⁺) diffusion energy barriers in the solid electrolyte interphase (SEI) exhibiting a linear correlation. Both the SEI and carbon-coating are penetrated by short, thick CNTs with gigapascal (GPa)-scale compressive stress, thereby accelerating electrolyte decomposition and leading to a LiF-rich SEI and an increased Li⁺ diffusion barrier. In contrast, long, slender CNTs exhibit limited compressive stress, thus minimizing the acupuncture effect, and the formed SEI possesses a low energy barrier for smooth Li⁺ diffusion. Thus, long, slender CNTs are ideal for Si-based anodes. This work reveals the structure–property relationships among compressive stress, SEI components and Li⁺ diffusion energy barriers, providing a novel perspective on the development of high-performance electrodes.

中文翻译：

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硅基阳极体积膨胀引起碳纳米管的针刺效应

通过添加碳纳米管（CNT）网络可以有效缓解硅基负极的循环不稳定性。然而，离子扩散和电化学性能根据所添加的碳纳米管的类型而显着变化，特别是单壁碳纳米管（SWCNT）和多壁碳纳米管（MWCNT），并且其内在机制仍然未知。在此，我们揭示了硅基负极的大体积膨胀导致短碳纳米管的针刺效应，碳纳米管上的压应力和固体电解质界面（SEI）中的锂离子（Li ⁺）扩散能垒表现出线性相关性。 SEI 和碳涂层都被具有千兆帕 (GPa) 级压应力的短而厚的 CNT 穿透，从而加速电解质分解并导致富含 LiF 的 SEI 和增加的 Li ⁺扩散势垒。相比之下，细长的碳纳米管表现出有限的压应力，从而最大限度地减少针刺效应，并且形成的SEI具有低能垒，有利于Li ^{+ 的}顺利扩散。因此，细长的碳纳米管非常适合硅基阳极。这项工作揭示了压应力、SEI组分和Li ⁺扩散能垒之间的结构-性能关系，为高性能电极的开发提供了新的视角。