The Influence of Calendering on the Fast Charging Performance and Lithium Plating of Hard Carbon Blend Anodes

Abstract

Lithium-ion batteries ensuring high energy densities are the focus of ongoing research. The main challenge is the fast charging capability, which is restricted by transport limitations of the lithium-ions. For this reason, graphite (Gr) and hard carbon (HC) blend anodes at different calendering degrees and, thus, electrode densities are investigated in terms of their structural features as well as their electrochemical performance. The motivation of blend anodes is the combination of the advantageous properties of these materials. Due to the different microstructures of Gr and HC, major differences in the lithiation process can be found. While the turbostratic structure of HC enables fast charging, its large specific surface area is associated with a low initial Coulombic efficiency and, thus, a loss of capacity. Consequently, the combination with Gr in blends is reasonable. While the lithium-ion diffusion is enhanced using HC, the availability of the interporous structure of HC is highly dependent on the electrode density. In addition to an increase in adhesion strength and reduction in electrical resistance, a reduction in tortuosity and lithium plating can be demonstrated. Furthermore, a higher capacity retention in the charge rate test (up to 3C) at low coating densities was found for the blends.