Post‐Annealing Induced Interdiffusion Layer Enhancing the Stability and Electrochemical Properties of LiCoO ₂ Thin Film Battery

Recently, thin film batteries without binder are an important power supplier for many low‐power microelectronic devices due to their compact size, flexibility for integration. The significance of the post‐annealing process in enhancing the stability of the electrodes in a “thin film battery” is investigated. The LiCoO ₂ (LCO) film annealed at 600 °C for 4 h exhibited the higher first cycle charge (discharge) capacity of 102.5 mAhg ⁻¹ (80 mAhg ⁻¹ ), initial coulombic efficiency of 78.04%, as well as capacity retention of 59.37% at 0.2 C over 100 cycles as compared to the as‐deposited LCO films. The enhanced battery performances are attributed to the enhanced physical and chemical stability of the annealed film to endure the structural and composition evolutions. Specifically, an interfacial layer of Li–Co–Al–O compound formed upon annealing, verified by elemental analysis along with transmission electron microscopy, resulting from the interdiffusion of Co and Al. The Li–Co–Al–O compound demonstrates higher chemical bonding capability, leading to higher stability performance and longer battery lifetime, even unfavorable for electronic conduction. Apparently, this work inspires the next‐generation high‐power battery systems to reflect the trade‐off study of electrochemical performance and stability of batteries.