Sodium-ion batteries (SIBs) are promising candidates for large-scale storage systems due to abundant Na resources, low costs, and a similar cell configuration to lithium-ion batteries (LIBs). However, due to the distinct physico-chemical properties of Li$^+$ and Na$^+$ cations, directly transferring concepts and established knowledge from LIBs to SIBs is unfeasible. Therefore, a new out-of-the-box perspective is required in the design of electrode materials, electrolytes, interphases, and other components to account for the unique characteristics of SIBs. This review clarifies the fundamental divergences between Li and Na from the viewpoint of their cation chemistry, including differences in atomic and ionic radii, electronegativity, polarizability and charge density. Based on the differences in cation chemistry, this review elaborates on their impacts on electrolyte bulk and interfacial properties, the design and selection of electrode materials, electrolytes, and the formation of interphases/interfaces. It highlights that the design of SIB components must be considered as independent systems with their own governing principles and design rules, rather than as direct derivatives of Li. This work offers critical insights for optimizing SIBs performance and advancing non-lithium mono-/multivalent cation batteries.