Plasma magnetron sputtered LaF₃@Si on vertical carbon nanotube arrays: A freestanding anode design addressing volume expansion and SEI instability

Herein, a flexible, free-standing composite anode (LaF₃@Si@VACNT/CC) is fabricated through the in-situ growth of vertically aligned carbon nanotubes (VACNTs) on carbon-cloth (CC), followed by deposition of amorphous Si and a thin LaF₃ layer via radio-frequency plasma-magnetron-sputtering. The robust VACNT framework establishes a three-dimensional conductive network that effectively accommodates Si volume changes during cycling while ensuring continuous electron and ion transport. Concurrently, the LaF₃ coating reacts in-situ with lithium ions during initial cycles to form a LiF-rich solid-electrolyte-interphase (SEI) and La-based species, resulting in a dense, stable, and highly conductive artificial-interfacial-layer. Benefiting from synergistic structural-confinement and interfacial-engineering, the LaF₃@Si@VACNT/CC anode delivers a reversible capacity of 1629.6 mAh g⁻¹ at 0.2 A g⁻¹, maintains 594 mAh g⁻¹ after 220 cycles at 1 A g⁻¹, and retains 287.3 mAh g⁻¹ at 5 A g⁻¹ with 79.3% retention after 700 cycles. The full cell paired with LiFePO₄ exhibits an initial discharge capacity of 153.6 mAh g⁻¹ at 1C and 86.1% retention after 200 cycles. This study demonstrates an effective strategy to mitigate the intrinsic limitations of Si anodes via the synergy of a VACNT skeleton and an LaF₃-assisted artificial SEI, providing new insights for the development of high-performance flexible lithium-ion batteries.