Identification of the Primary Correlate of Cyclability in Silicon-based Composite Anodes: SWCNT-induced Structural Stabilization

Abstract

As demand for high-energy-density lithium-ion batteries increases, silicon-based composite anodes with high capacity are emerging as promising candidates for battery systems. However, severe volume changes in silicon induce electrode pulverization, loss of electrical contact, and rapid capacity fading. This work investigates the hierarchical relationship between electrode formulation, electrode properties, and cell-level cyclability in silicon-based composite anodes comprising single-walled carbon nanotube(SWCNT). The formulation composition was designed by varying the amount of SWCNT per active material area, and the electrical and mechanical properties of the electrode were comprehensively evaluated. Previous studies have largely been limited to qualitative demonstrations of CNT structural stability. However, this study goes further by establishing a quantitative relationship between CNT loading and both cohesion and adhesion. Moreover, by hierarchically correlating formulation, electrode, and cell- level performance with explicit quantitative metrics, it is demonstrated that mechanical properties show a stronger correlation with capacity retention than electrical conductivity does. In other words, once a sufficient level of electrical conductivity is secured, improving mechanical and structural stability becomes more critical for cyclability than further enhancing conductivity. In this study, this hierarchical analysis demonstrates that the mechanical stress imposed on CNT is a crucial parameter in electrode formulation. In fact, most previous studies aiming to improve cyclability using CNT have focused primarily on CNT loading itself as the main compositional design parameter. However, this study confirms that the stress imposed on CNT shows a stronger correlation with capacity retention than CNT content. Therefore, future electrode formulation should move beyond CNT-loading–centric design and explicitly adopt CNT stress as a key design parameter. Therefore, this study indicates that electrode design should move beyond conventional CNT- loading–driven approaches and instead adopt mechanics- and microstructure-oriented engineering that minimizes stress on CNT. In addition, the key intrinsic property of CNT responsible for improving cycle life in silicon anodes is confirmed to be their mechanical properties. Because the high cost of CNT limits their industrial adoption, this study proposes a rational design strategy in which CNT loading is reduced to the minimum level required to ensure electrical conductivity, while mechanical properties are enhanced through binder design.