The Solid Electrolyte Interphase Engineering for Enhanced Cycling Stability in Sodium‐Ion Batteries: Strategies, Mechanistic Insights, and Performance Optimization

Sodium‐ion batteries have received considerable interest as a novel material for large‐scale energy storage owing to their plentiful sodium resources and very low cost. Hard carbon (HC), the ideal anode material, presently faces an important drawback of poor cycling stability, mostly due to the instability of the solid‐electrolyte interphases (SEI). This work systematically reviews the recent advancements in SEI modification strategies, emphasizing alterations in the composition, structure, and creation routes of SEI throughout cycling, alongside its correlation with cycling stability. It elucidates the mechanism via which the stability of SEI influences cycle stability. This review provides an in‐depth analysis of the influence of electrode design (pore size regulation, coating alteration, doping modification) and electrolyte system optimization on SEI regulation. Present research has transitioned from “passive modification to mitigate SEI formation” to “active modification to generate high‐quality SEI”. Notwithstanding a large number of research studies, the formation mechanism of SEI remains contentious and needs further elucidation in the future. This document serves as a systematic reference for SEI modification, significantly aiding the development and application of high‐performance sodium‐ion batteries (SIBs).