Intermolecular Cross-Linking Reinforces Polymer Binders for Durable Alloy-Type Anode Materials of Sodium-Ion Batteries

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 from ≈26 cycles of PAA to ≈2000 cycles of PAA-GLY. Meanwhile, the initial Coulombic efficiency is promoted to 90.3%, allowing the fabrication step of electrode presodiation for full cells to be eliminated. Thus, the full cells run 300 cycles at 2 A g−1. In addition, the binder allows the thick electrode to exhibit an areal capacity of 6.8 mAh cm−2. This binder is also applied for µ-Bi and µ-Sb. The simple operation, remarkable improvement, and wide applications indicate the promising prospects of this strategy for advanced electrodes in sodium ion batteries.