Chemical vapor deposition of Li-ion conductive covalent organic framework coatings on solid-state electrolytes

초록

Solid-state lithium batteries offer enhanced energy density, safety, and thermal stability over conventional liquid electrolyte systems, positioning them as a promising energy solution for next-generation electronics and electric vehicles. However, the interfacial instability—particularly in systems employing sodium superionic conductor (NASICON)-type electrolytes—remains a critical challenge. Here, we report a rapid, solvent-free chemical vapor deposition strategy based on gas–solid interfacial polymerization to directly grow an ultrathin β-ketoenamine covalent organic framework (COF) film on lithium aluminum germanium phosphate (LAGP) pellets. The resulting COF coating, 82–175 nm thick, functions as a protection layer that suppresses Ge⁴⁺ reduction while offering abundant pore channels for Li⁺ transport. Molecular dynamics simulations reveal a Li⁺ diffusion coefficient of 7.3 × 10⁻¹² m² s⁻¹ within the COF layer. The COF-LAGP electrolyte was employed in symmetric cells, showcasing exceptional cycling stability that is 2.5 times longer than uncoated LAGP—and in solid-state full cells, retaining 90.8% of its initial 170 mAh g⁻¹ capacity after 455 cycles. Mechanistic investigations revealed that the COF layer not only suppresses Ge⁴⁺ reduction at the Li|electrolyte interface but also promotes the formation of a smooth, defect-free surface and a stable solid electrolyte interphase. These findings highlight gas–solid interfacial polymerization as a scalable strategy for engineering robust solid electrolyte interfaces, advancing the development of next-generation solid-state batteries.

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