Stress-Engineered SS/LiCoO₂ Thin-Film Electrodes With Enhanced Structural Integrity and Electrochemical Performance

The delamination of LiCoO₂ (LCO) films on stainless steel (SS) substrates has remained a critical bottleneck for advancing all-solid-state thin-film lithium batteries (TFLBs). Here, we introduce a stress-engineering approach that fundamentally resolves this challenge through simultaneous monitoring, regulation, and utilization of film stress. In situ stress measurements revealed a universal transition of LCO films from tensile to compressive states during growth, with residual compressive stress in amorphous films originating from an "atomic pinning" mechanism. Among deposition parameters, working pressure was identified as the dominant factor for stress tuning, enabling precise control of stress evolution. Complementarily, substrate pre-annealing at 800°C in Ar released residual stresses and stabilized the SS surface, while moderate post-annealing of LCO films at 550°C preserved both mechanical integrity and electrochemical performance. This dual strategy effectively suppressed crack formation and delamination, yielding robust SS/LCO thin-film electrodes. By scaling this process to square-meter-scale SS/LCO/LiPON multilayers, all-solid-state TFLB cells were successfully fabricated, delivering an initial areal capacity of 38.4 µAh/(cm²·µm) and retaining 97.1% capacity after 1000 cycles. This work not only elucidates the intrinsic stress evolution and its atomic origins in LCO thin films but also pioneers a scalable route toward mechanically resilient, high-performance TFLBs.