CNF-Supported Si Freestanding Anode with a Conformal Granular Si/SiO_x Interphase for High-Rate, Long-Life Li-Ion Batteries

Abstract

Freestanding electrodes promise higher energy densities and high-rate capabilities by eliminating inactive mass, but they require an interphase that preserves porosity and percolating electronic pathways during cycling. This paper reports a carbon nanofiber (CNF)-supported Si freestanding anode formed by programming the surface chemistry of electrospun polyacrylonitrile (PAN) to guide SiCl₄ interfacial hydrolysis–condensation, followed by stabilization/carbonization. KOH pretreatment and annealing generate oxygen- and nitrogen-containing groups that nucleate a uniform Si–O precursor; subsequent carbonization anchors a Si-containing oxide-rich interphase (hereinafter denoted as Si/SiO_x, 40–50 nm shell) to the CNF core via Si–O–C bonds. Microscopic and spectroscopic analyses confirmed a conformal carbon-core/Si–SiO_x shell without over-coating or aggregation, maintaining junctions and fiber spacing. The freestanding electrodes delivered 727 and 288 mAh g⁻¹ at 0.1 and 10 A g⁻¹, respectively, retaining 85.9% capacity at 0.2 A g⁻¹ and 79.8% at 1 A g⁻¹, and reduced charge-transfer resistance (approximately 130 → 44 Ω) while increasing pseudocapacitive contribution and Li⁺ diffusivity relative to control electrodes. In LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622)//CNF-supported Si full cells, the full cell delivered 176.5 mAh g⁻¹ and retained 91.6% capacity after 300 cycles (approximately 0.028% capacity fade per cycle), demonstrating high-rate cyclability. To the best of our knowledge, this is the first CNF-supported Si freestanding anode that forms a conformal Si/SiO_x interphase via PAN surface-functionalization-enabled SiCl₄ interfacial hydrolysis–condensation and stabilization/carbonization. The oxide-rich interphase, tethered to the CNF framework, preserves porosity and junctions, buffers Si volume change, stabilizes the solid electrolyte interphase (SEI), and sustains fast ionic/electronic transport, thereby enabling high-rate long-life Li-ion battery operation.

Graphical Abstract

Keywords

Freestanding silicon anode / Carbon nanofiber support / Conformal granular Si/SiO_x interphase / Surface functionalization / Lithium-ion batteries

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Funding

Ministry of Science, ICT and Future Planning(2020R1A6A1A03038540)

Ministry of Education(2022R1A6C101A774)

RIGHTS & PERMISSIONS

Donghua University, Shanghai, China