Prestressed Silicon Thin Films: Linking Stress Regulation to Electrochemical Stability

The mechanical reliability of silicon (Si) anodes is fundamentally limited by lithiation‐induced stress, leading to cracking and rapid degradation. Here, magnetron‐sputtered Si thin films are employed to disentangle stress evolution from electrochemical reaction dynamics. Although lithiation remains the fundamental origin of stress generation, this strategy effectively suppresses electrochemical complexities, thereby enabling a more direct and unambiguous visualization of stress–performance correlations. Designed Li–Si films show a progressive transition from compressive to tensile stress during lithiation, accompanied by surface cracking and dramatic losses in hardness and Young's modulus. By tuning sputtering pressure, the residual stress of pure Si films can be precisely controlled: low pressure generates compressive stress, high‐pressure tensile stress, and graded deposition achieves a near stress‐free state. The Si films with initial compressive stress exhibit enhanced cycling stability, retaining 95.8% of capacity over 11 cycles. This work establishes prestress engineering as a general strategy to mitigate lithiation‐induced damage and design mechanically resilient, high‐capacity Si anodes.