Very High Surface Capacity Observed Using Si Negative Electrodes Embedded in Copper Foam as 3D Current Collectors

摘要

Cu foam is evaluated as a replacement for metal foil current collectors to create 3D composite electrodes with the objective to produce Si-based anodes with high loadings. The electrodes are prepared by casting the slurry into the porosity of the foam. With such a design, the loading and the surface capacity can reach values as high as 10 mg cm−2 and 10 mAh cm−2. Compared to the common 2D design, the 3D copper framework shows a great advantage in the cycle life (more than 400 cycles at a Si loading of 10 mg cm−2 with commercial micrometric particles) and power performance. The thinness of the composite coating on the foam walls favors a better preservation of the electronic wiring upon cycling and fast lithium ion diffusion. A higher coulombic efficiency in half cells with lithium metal as the counter electrode is achieved by using carbon nanofibers (CNF) rather than carbon black (CB). The possibility to reach, in practice, higher surface capacity could allow a significant increase in both the volumetric and gravimetric energy densities by 23% and 19%, respectively, for the Cu foam-silicon//LiFePO4 stack compared to the graphite/LiFePO4 stack of traditional design.