Interfacial engineering meets process optimization: Highly stable silicon-graphite anodes via pre-calendering polyvinylidene difluoride-MgO coatings

Silicon/graphite (Si/Gr) composites, promising high-capacity anodes for next-generation lithium-ion batteries, suffer from instability due to silicon's large volume expansion and deleterious interfacial degradation. This work introduces a synergistic composite coating of poly(vinylidene fluoride) (PVDF) and magnesium oxide (MgO) nanoparticles, applied via facile immersion to Si/Gr electrodes, to stabilize the electrode structure and the critical electrode-electrolyte interface. Compared to pristine and PVDF-only controls, the PVDF-MgO coating significantly enhanced long-term cycling, achieving over 760 cycles with 77 % capacity retention, high Coulombic efficiencies (>99.9 %), and improved rate capability. Post-mortem analysis confirmed the PVDF-MgO coatings preserved electrode integrity, dramatically suppressing thickness expansion (from ∼137 % for pristine to ∼49 % for optimized PVDF-MgO) after hundreds of cycles. Significantly, the PVDF-MgO coating suppressed lithium dendrite formation under high-rate (5C) and capacity-driven (20 % over-lithiation) conditions, promoting uniform, non-dendritic Li deposition. This suppression is attributed primarily to MgO's beneficial lithiophilicity and Lewis acid-base characteristics guiding Li nucleation and homogenizing ion flux, enabled by the composite structure. Crucially, the processing sequence was found to be paramount; applying the coating before electrode calendering, rather than after, unlocks the material's full potential and yields optimal performance. This discovery of a non-obvious process-structure-property relationship, where process engineering dictates interfacial stability, establishes the synergistic PVDF-MgO composite coating as an effective, scalable strategy for enhancing the durability, efficiency, and safety of high-energy Si/Gr anodes. Sequential optimization of coating composition and processing dramatically enhances the cycling stability and capacity retention of Silicon-Graphite anodes. • Synergistic PVDF-MgO coating stabilizes Si/Gr anodes via interface control. • PVDF-MgO coated Si/Gr anode shows >760 cycles (77 % retention) with >99.9 % CE. • Suppresses hazardous Li dendrites on Si/Gr anodes under high-rate/over-lithiation • Process optimization: pre-calendering PVDF-MgO application unlocks peak performance.