Alkali metals (lithium, sodium, etc.) have been extensively investigated throughout the past several decades as potential anode materials for batteries. Their high theoretical capacities, low redox potentials, and low densities have garnered much attention and effort to yield highly efficient and capable anodes. These metals, through past efforts, have been shown to be highly reactive and unstable, forming layers of “dead” material, thick passivation layers, and producing dendritic structures. Within the past few years, the use of carbon host, support, materials have been employed to control the undesirable growths and reactions, and improve the efficiency and stability of the alkali metal anodes. While past results have shown to improve anode stability and performance, there have not been many studies to understand the fundamental interactions between the alkali metal and the host material. Utilizing a carbon fiber host material, we have observed disparities in the cycle life and performance between lithium and sodium metal. We employ characterization, electrochemical, and computational analysis to determine the differences of the host-metal interactions of lithium and sodium metal. Our results highlight the inherent properties and surface functionalization of the carbon host material that contribute to enhanced stability and performance of the composite anodes.