Multifunctional binders for sustainable sodium-ion batteries: From interfacial engineering to life-cycle solutions

Sodium-ion batteries (SIBs) offer a low-cost, sustainable alternative to lithium-ion systems for grid-scale energy storage, yet their commercialization is hindered by electrode instability arising from Na+-induced mechanical and interfacial degradation. This review critically examines the transformative role of polymeric binders—evolving from inert additives to multifunctional mediators—in bridging the gap between laboratory innovation and practical SIB deployment. We systematically deconstruct binder functionality mechanisms, from physical/chemical adhesion to their critical influence on solid-electrolyte interphase (SEI) formation. Emerging binder systems are classified and evaluated, including bio-derived aqueous polymers, advanced solvent-based matrices, and functional designs (self-healing, ion-conductive networks). A key focus is electrode-specific tailoring for cathodes (layered oxides, polyanionic compounds, Prussian blue analogs) and anodes (hard carbon, alloying materials) to address distinct failure modes. Crucially, this review extends beyond electrochemical performance to analyze binders' contributions to sustainability: enhancing safety via flame retardancy, improving rate capability through ion-transport pathways, and enabling green manufacturing via water-based processing and biodegradable materials. We critically assess persistent challenges—notably the mechanical strength–ionic conductivity trade-off—and propose a roadmap for rational design of smart, adaptive binders. By integrating polymer chemistry, interfacial engineering, and circular economy principles, this work provides a strategic framework for developing binder systems that stabilize SIBs while advancing their environmental and economic viability for renewable energy integration.