Carbon engineering for sodium batteries: multi-role architectures bridging material design and hybrid system...

Sodium (Na) batteries are emerging as sustainable energy storage solutions, but their performance is hindered by intrinsic challenges such as sluggish ion kinetics, dendrite formation, and interfacial incompatibility. Carbon-based materials, with their highly tunable physicochemical properties, offer versatile functionalities to address these limitations across various Na battery systems. In this review, we first explore the multi-role engineering of carbon materials in four Na battery types. Then, the correlation of carbon's structural and chemical properties (including lattice spacing, defect density, graphitic order, and pore hierarchy) with electrochemical performance was established in a functionality-performance matrix to guide material selection for specific battery designs. Building on these insights, we propose a hybrid Na battery paradigm that leverages carbon's dual capabilities: intercalation-driven Na⁺ storage for energy-oriented applications and defect-guided Na deposition for power-oriented needs. This system integrates three adaptive operation modes: standard, boost, and survival, enabling scenario-specific optimization for applications ranging from consumer electronics to grid storage and extreme environments. Finally, we identify critical challenges in carbon engineering, such as dynamic interface evolution during mode-switching and potential-driven phase transitions in hybrid systems. By bridging multi-scale carbon design with hybrid battery electrochemistry, this review provides a roadmap for developing Na batteries with broad application compatibility by carbon engineering, addressing both fundamental and technological challenges in sustainable energy storage.