Lightweight and binder–free sandwich anode of carbon–coated SiO_x thin films on free–standing carbon nanofibers for enhanced lithium–ion storage

High–capacity silicon oxide (SiO_x)–based anodes show great potential for lithium–ion batteries (LiBs) due to their superior theoretical capacity. However, their practical application is hindered because of their severe volume expansion, poor electrical conductivity, and unstable solid–electrolyte interphase (SEI). Herein, we present a novel flexible anode architecture, where a thin–film amorphous SiO_x layer is uniformly deposited between ultralight, free–standing carbon nanofiber mats and a carbon encapsulation layer, forming a robust C–SiO_x–C sandwich structure. The optimized C–SiO_x–C composite demonstrates exceptional electrochemical performance, including outstanding cycling stability (specific capacity of 1120 mAh g⁻¹, capacity retention of ∼88.8% over 300 cycles at 0.2 A g⁻¹), enhanced rate capability, and markedly reduced SEI resistance compared with uncoated SiO_x–C. Electrochemical impedance spectroscopy and galvanostatic intermittent titration reveal that the carbon coating effectively enhances electronic conductivity, stabilizes the SEI, and promotes lithium–ion diffusion kinetics (9.83 × 10 cm² s⁻¹). Furthermore, full–cell tests of our SiO_x anode paired with a thin–film NCM622 cathode exhibits stable cycling for over 400 cycles, affirming its potential for next–generation, fast–charging, and high–energy–density LiBs systems.