Interphase–Microstructure Synergy in Al Foil Anodes Enabled by Ball-Milled Al–CNT Composites

Abstract

To advance binder-free aluminum (Al) foil anodes beyond the conventional trade-off between mechanical integrity and interfacial instability, we couple bulk microstructure programming with interphase engineering in a single, process-realistic architecture. Al–carbon nanotube (CNT) composite foils are fabricated via spark plasma sintering of ball-milled powders followed by rolling, which builds an electronically percolated CNT network and activates the pre-existing and milling-refreshed surface oxide. A modest CNT loading (1 vol%) yields an ultrafine-grained Al matrix (~0.83 μm) with a pronounced hardness increase while preserving a favorable strength–ductility balance. Critically, prelithiation converts the mechano-chemically fragmented Al2O3 into a Li2O-rich inorganic passivation layer that compensates lithium-inventory and provides a mechano-chemically stable interface. With this interphase, CNTs primarily redistribute flux that homogenizes electrochemical activity, suppresses localized reaction hot spots, and guides lithiation into a partitioned phase-transformation pathway. This cooperative mechanism preserves a conductive α-Al filament network within the β-LiAl matrix, sustaining electronic continuity and mitigating strain localization during repeated alloying/dealloying. Consequently, the prelithiated Al-1 vol% CNT foil anode achieves stable full-cell cycling approaching ~630 cycles, while delivering the lowest charge-transfer resistance and improved rate capability among the anodes studied. Therefore, it is established that a general design principle that mechano-chemical oxide activation combined with prelithiation could convert native oxide into a robust inorganic interphase, enabling CNT-reinforced bulk architectures to translate into long-term practical Al foil anodes for next-generation lithium-ion batteries.