High Airtightness Passivation Layer for High-Temperature All-Solid-State Thin-Film Batteries

All-solid-state thin-film lithium-ion batteries (ASSTFLBs) offer remarkable advantages, including high safety and excellent compatibility with microelectronic devices, which endow them with extensive application prospects in the industrial Internet of Things (IoT), particularly for powering industrial wireless sensor network nodes at high temperature. Nevertheless, the materials composing ASSTFLBs are highly reactive with moisture, oxygen, and carbon dioxide in air, triggering spontaneous chemical reactions that cause material degradation. This phenomenon leads to a rapid decline in battery performance and severely restricts the practical utilization of ASSTFLBs. To address this challenge, we propose a high airtightness Si₃N₄/Al₂O₃/PDMS composite passivation film for ASSTFLB protection at high temperature. A 600-nm Si₃N₄ film is fabricated via magnetron sputtering, while a 30-nm dense Al₂O₃ film is deposited using atomic layer deposition (ALD) to overcome the step coverage limitations of sputtered Si₃N₄. Additionally, a 15-μm PDMS film is spin-coated to enhance the mechanical robustness of the composite structure. The composite passivation film exhibits excellent thermal stability, chemical stability and mechanical robustness, thereby offering enhanced passivation for ASSTFLBs at high temperature. Experimental results indicate that, ASSTFLBs with composite passivation film exhibit remarkable cycling stability in air at room temperature, retaining 80.5% of their initial capacity after 150 cycles, which is significantly superior to that of unpassivated ASSTFLBs, which only maintain 4.7%. More importantly, under an industrial-grade high temperature of 85 °C, ASSTFLBs with composite passivation film show good cycling and thermal stability, retaining 90.2% of their initial capacity after 100 cycles in air, confirming superior thermal and air stability. These findings underscore the strong potential of the proposed passivation strategy for enabling reliable ASSTFLB operation in real-world IoT applications.