Toward Multifunctional Binders for Sodium-Ion Batteries: Molecular Design Strategies and Material-Specific Requirements.

Although binders constitute a minor mass fraction of electrode, they are indispensable for maintaining the mechanical integrity and electrochemical functionality of sodium-ion batteries (SIBs). Conventional binders are increasingly inadequate for high-capacity electrode materials, which typically suffer from severe volume fluctuations, unstable interfaces, and sluggish reaction kinetics. This review systematically elucidates the crucial relationship between the intrinsic properties of various electrode materials and the required functionalities of advanced binders. First, we delineate the primary failure mechanisms of different cathode and anode materials, translating these fundamental challenges into specific, material-tailored design criteria for polymeric binders. Subsequently, we present a comprehensive overview of state-of-the-art molecular design strategies for multifunctional binders. These approaches are categorized into four key domains: (1) enhancing mechanical robustness through superior adhesion and volume-change accommodation; (2) boosting electronic and ionic conductivity via precise polymer engineering; (3) stabilizing the solid-electrolyte interphase (SEI) and cathode-electrolyte interphase (CEI) utilizing targeted binder chemistries; and (4) ensuring electrode homogeneity by optimizing binder dispersion and interfacial affinity. Finally, we summarize current progress and provide a forward-looking perspective on the rational design of next-generation binders, paving the way for high-performance and durable SIBs suitable for large-scale energy storage applications.