Plowing-Extrusion Processes and Performance of Functional Surface Structures of Copper Current Collectors for Lithium-Ion Batteries

Abstract

Most copper current collectors for commercial lithium-ion batteries (LIBs) are smooth copper foils, which cannot form a stable and effective combination with electrode slurry. They are likely to deform or fall off after long-term operation, resulting in a sharp decline in battery performance. What is worse is that this condition inevitably causes internal short circuits and thus brings about security risks. In this study, a process route of fabricating the functional surface structures on the surface of a copper collector for LIBs by twice-crisscross micro-plowing (TCMP) is proposed, which provides a new idea and an efficient method to solve the above problems from the perspective of manufacturing. The finite element simulation of TCMP combined with the cutting force test and morphological characterization is conducted to verify the forming mechanism of the surface structures on a copper sheet and its relationship with the processing parameters. The influence of several key processing parameters on the surface characteristics of the copper sheet is comprehensively explored. A series of functions is tested to obtain the optimal parameters for performance improvement of the current collector. Results show that the structured copper sheet with the cutting distance of 250 μm, cutting depth of 80 μm, and cutting crossing angle of 90° enables the best surface features of the current collector; the contact angle reaches 0°, the slurry retention rate is up to 89.2%, and the friction coefficient reaches 0.074. The battery using the as-prepared structured copper sheet as the current collector produces a specific capacity of 318.6 mAh/g after 50 cycles at a current density of 0.2 C, which is 132.7% higher than the one based on a smooth surface. The capacity reversibility of the sample with the new current collector is much better than that of the traditional samples, yielding a lower impedance.