Water‐Soluble Multifunctional Binder with Extraordinary Bonding Strength for High‐Voltage Sodium‐Ion Batteries

Abstract With the ever‐increasing demand for low‐cost energy storage systems, sodium‐ion (Na‐ion) batteries have received great attention. However, the large volume change, sluggish reaction kinetics, and unstable electrode/electrolyte interphase during cycling inevitably deteriorate the performance of Na‐ion batteries. Herein, a high‐voltage water‐soluble multifunctional binder with an extraordinary bonding strength is investigated. Such water‐soluble binder not only exhibits an excellent adhesion strength to maintain the mechanical integrity and enhance the Na‐ion diffusion across the interfac but also constructs a robust protective layer to prevent side reactions and improve the cycle durability at high voltages. As a result, a specific capacity of 91.3 mAh g −1 at 10.0C and high capacity retention of 92.3% for 1000 cycles are achieved. A good cycle stability and rate performance between 2.5 and 4.4 V can be observed after pairing with a high‐voltage electrode, and the practical application of the high‐voltage water‐soluble multifunctional binder is further confirmed by a 0.95 Ah Na‐ion pouch cell.