In Situ Electrochemical Polymerization to Construct Robust Solid Electrolyte Interphase for Advanced Alloy‐Type Anode Materials in Sodium‐Ion Batteries

Abstract High‐quality solid electrolyte interphases (SEI) are important to advanced sodium‐ion batteries, particularly on anode materials. Their large structure strain/stress usually aggravates the rupture and dissolution of the SEI, then degrades the electrochemical performance. Here, sodium vinylsulfonate (SVS) is reported as a model to achieve the polymer incorporation into the SEI by in situ electrochemical polymerization. The sulfonate group in SVS activates the vinyl group and interacts with the other components, enabling the polymer to be a robust and flexible backbone of the SEI. This enhances the mechanical properties and reduces the SEI dissolution, improving the electrochemical performance of anode materials. Using commercial tin microparticles (µ‐Sn) as an example, they exhibit a capacity of 516.3 mAh g ⁻¹ after 2000 cycles at 4 A g ⁻¹ , a record‐high performance at high rates. This strategy is also successful in the cases of µ‐Bi and µ‐Sb. These results are obtained based on commercial microparticles without carbon coating. So, it is believed that it is a new and simple way to improve the electrochemical performance of Na‐ion batteries.