Active-Material-Free Carbon Nanotube Film Anodes Enabled by Alignment-Controlled SEI Stabilization

Abstract

Carbon nanotube films (CNTFs) are investigated as free-standing anodes for lithium-ion batteries, providing a simplified electrode architecture without the need for additional active materials, conductive additives, polymer binders, or metallic current collectors. This binder-free and current-collector-free configuration highlights the intrinsic lithium-storage capability of CNTFs and establishes a distinct strategy for developing lightweight and structurally integrated anodes. In this study, the effect of CNT alignment on interfacial behavior is examined by comparing unidirectional (UD) and bidirectional (BD) CNTF structures. The UD-CNTF exhibits a lower initial defect ratio (I_D/I_G = 0.60) than the BD-CNTF (I_D/I_G = 0.89), which promotes the formation of a more uniform and stable solid electrolyte interphase (SEI). In contrast, the higher defect density of the BD-CNTF intensifies electrolyte decomposition, resulting in an excessively thick and resistive SEI layer. Electrochemical impedance spectroscopy (EIS) further confirms that the BD-CNTF exhibits substantially higher interfacial impedance, indicating less efficient charge-transfer kinetics. Consequently, the UD-CNTF delivers superior capacity retention and cycling stability. These results demonstrate that CNT alignment governs defect-mediated SEI formation and interfacial charge transport, thereby providing a mechanistic basis for optimizing free-standing CNTF anodes that operate without conventional active materials.