Pioneering energy storage using facing-target sputtered Al₂O₃ protection layer on Ni-rich NCM622 cathode for high-efficiency all-solid-state thin-film batteries

Thin-film batteries provide compact and efficient energy storage, but their performance is limited by interfacial instability and low energy density. To overcome these challenges, we employ Ni-rich NCM622 thin-film cathodes and introduce a facing-target sputtered (FTS) Al₂O₃ protective layer. FTS enables precise, damage-free deposition, significantly improving the cathode-electrolyte interface by minimizing plasma-induced defects. Annealing at 500 °C optimizes crystallinity while reducing surface cracking. The FTS-Al₂O₃ coating enhances electrochemical stability, achieving 91 % cyclability retention over 400 cycles in a liquid electrolyte. A full cell with a thin-film NCM622 cathode with FTS-Al₂O₃ protection and a carbon anode delivers 325.3 mAh cm⁻³, maintaining 77.8 % of its capacity after 100 cycles. Furthermore, an all-solid-state thin-film battery with LiPON and lithium film anode achieves an energy density of 50.98 mWh cm⁻³. These findings underscore the critical role of FTS-deposited Al₂O₃ in stabilizing interfaces and advancing all-solid-state thin-film batteries for miniaturized applications.