Thermal transport–driven interfacial reliability and cooperative deformation in Cu/PI/Cu multilayers

Abstract Cu/polymer/Cu multilayers have been proposed as safer current collectors to replace conventional Cu foils; however, mechanical mismatch between metal films and polymer substrates often leads to interfacial degradation under cyclic deformation. In this work, 1 μm-thick Cu films were deposited on both sides of a 50 μm polyimide (PI) substrate via magnetron sputtering, where interfacial integrity was regulated by controlling thermal transport during deposition. Under NTI and TI configurations, different heat dissipation pathways during deposition led to steady-state substrate temperatures of approximately 182 ℃ and 140 ℃, respectively. The results show that elevated temperature under NTI induces strengthening of PI, reducing deformation compatibility and promoting crack formation during bending. In contrast, moderated thermal input under TI maintains a more balanced mechanical response, enabling cooperative deformation between the film and substrate. Consequently, the TI sample preserves structural integrity after 10,000 bending cycles with limited resistivity increase, whereas the NTI sample exhibits severe cracking and degradation. The TI sample also shows more stable electrochemical behavior, maintaining higher coulombic efficiency during cycling compared with the NTI sample. These findings demonstrate that thermal transport during deposition governs the mechanical state of polymer substrates and interfacial reliability, providing a practical strategy for designing durable polymer–metal multilayer systems.