Atomic Layer Deposited Silicon Anode with Nanoporous Fluorinated Surface Modulation Enabling Invertible Electrochemical Lithium Storage

Silicon anodes lose energy density during cycling due to baneful volume expansions and unfavorable interfacial rearrangements. In this work, silicon active materials are synthesized upon carbon black (CB@Si) using alternating pulses of SiCl4 and Si₂H₆ by H/Cl exchange mechanism via atomic layer deposition. The loading and thickness of the deposited silicon material can be precisely tuned by changing the deposition cycle. 13.6 nm is demonstrated as the optimal thickness of the silicon layer based on the trade-off between capacity and stability. Next, a nanoporous fluorinated lithicone (LiFHQ) is controllably deposited onto CB@Si by molecular layer deposition. The pores in LiFHQ act as a buffer layer to relieve the silicon bulk from severe deformation by squeezing or ripping of pores, while the rich F groups in LiFHQ helps to construct a robust LiF-rich natural solid electrolyte interphase (nSEI)/LiFHQ hybrid skin. Molecular dynamics (MD) calculations verify that these pores allow a faster Li⁺ permeation kinetics compared to a dense AlFHQ layer. The anode exhibits an impressive capacity retention of 70.2% at 2 A g⁻¹ after 1000 cycles. This work demonstrates the advantages of atomic/molecular layer deposition strategies to synthesize the bulk and surface configurations of silicon anodes with high energy densities.