Copper foils for high-energy-density lithium batteries: Composite vs. ultrathin

The escalating demand for higher energy density in lithium-ion batteries (LIBs) and anode-free lithium metal batteries (AFLMBs) has driven the exploration of lightweight current collectors (CCs). Conventional Cu foils face critical limitations in cost and thickness reduction, necessitating innovative alternatives. Composite Cu foils have emerged as a promising solution, offering ultra-lightweight design, orthogonal conductivity, and intrinsic safety. However, they concurrently face challenges such as interfacial instability, electronic transport inefficiencies, and immature manufacturing scalability. This study systematically compares PET-based composite Cu foils (PETCu) with ultrathin Cu foils in graphite (Gr)-based LIBs and AFLMBs. PET-Cu shows higher tensile strength and buffers Gr volume expansion, enhancing capacity retention to 93.9 % after 290 cycles in LIBs, though its insulating layer increases interfacial resistance. In AFLMBs, PET-Cu enables uniform Li deposition initially but succumbs to rapid capacity decay due to interfacial deterioration. While excelling in energy density, PET-Cu faces trade-offs in conductivity and cyclability. The study highlights the need for interface engineering and scalable manufacturing to optimize composite CC design.