Structure–Performance Interplay and Mechanical Degradation Modes in Lithium Cobalt Oxide Cathodes: Implications for Flexible Lithium-Ion Battery Design

Lithium cobalt oxide (LCO) remains the industry-standard cathode for lithium-ion batteries in consumer electronics, but its mechanical reliability under repeated deformation—a critical requirement for flexible and wearable devices—has not been systematically investigated. Here, as-manufactured LCO electrodes are subjected to repeated bending (up to 3000 cycles) at diameters of 100, 50, and 25 mm, followed by post-bending electrochemical, microstructure, and electrical characterization. Bending-induced degradation mechanisms are found to be strongly impacted by the LCO particle size. Coarse-particle electrodes undergo pronounced particle detachment and interfacial failure, medium-particle electrodes exhibit mixed damage modes, and fine-particle electrodes primarily exhibit delamination but retain strong composite cohesion, displaying the highest mechanical durability and electrochemical stability. Even after 3000 bending cycles at a 50 mm diameter, Fine-LCO electrodes retain 88.6% of their initial capacity (123 mAh g−1) at a 2 C rate, whereas other electrodes exhibit capacity losses of up to 97%. Electrode and interface resistances increase with bending severity, but these changes do not fully explain performance loss, underscoring the importance of complementary characterization techniques for elucidating failure mechanisms. These findings identify particle size control as a practical strategy for improving conventional LCO electrodes for flexible battery applications.