Sodium-ion batteries show promising potential for large-scale energy storage. However, the large size and heavy mass of Na+ always results in huge volume change and inferior electrochemical stability, especially in alloy-type anode materials. Here, molecular engineering of the polymer binders, i.e., cross-linking of poly(acrylic acid) with glycerin (PAA-GLY), reinforces the mechanical properties, eliminates the active protons of PAA, and benefits electrolyte diffusion, thereby remarkably improving electrochemical performance. Using µ-Sn as an example, the cycle life at 2 A g−1 is extended f...