Hard carbon is the most commercially viable anode for sodium-ion batteries, with low operating potential, high reversible capacity, abundant raw materials and low manufacturing cost. However, its intrinsic structural disorder, characterized by randomly stacked turbostratic graphene layers, nanopores and amorphous regions, has sparked long-standing debates on fundamental sodium storage mechanisms, significantly impeding rational electrode design and industrial translation. This review overviews sodium storage processes in hard carbon, analyzes synergistic contributions of intercalation, pore filling and surface adsorption, and establishes microstructural-electrochemical performance correlations. It focuses on four mainstream modification strategies: Precursor engineering, pore structure regulation, heteroatom doping and interface engineering, elucidating their enhancement mechanisms and discussing inherent limitations and trade-offs. Finally, it outlines key challenges and future directions, providing critical theoretical and technical guidance for next-generation hard carbon anodes and practical sodium-ion battery deployment.

Lithium-oxygen (Li-O₂) battery is notable for the high theoretical energy density, and its widespread adoption has the potential to fundamentally transform the energy consumption landscape. However, the development of Li-O₂ batteries has been hindered by issues such as slow reaction kinetics, high overpotential, and unstable cycle life. Rational design of cathode materials has emerged as an effective strategy for addressing these challenges. Biomass, a renewable resource, holds significant importance in the fabrication of derived carbon cathode with exceptional performance; this efficacy is largely due to its intrinsic pore structure and the presence of heteroatoms, representing a significant advancement in the field. This review outlines optimization strategies for biomass-derived carbon cathode based on the reaction mechanism of Li-O₂ batteries. It introduces cross-scale characterization methods to analyze the properties of the carbon materials and explores the theoretical underpinnings of functional atom doping as a means to enhance electrochemical performance. Recent advancements in utilizing biomass-derived carbon as a porous cathode for Li-O₂ batteries are assessed, highlighting the relationship between microstructural development and performance variations. Furthermore, a succinct overview of the challenges faced by biomass-derived carbon-based Li-O₂ batteries is provided, along with proposed perspectives on the direction of development. This work seeks to improve the stability and catalytic efficiency of biomass-derived carbon cathode, ultimately aiming to facilitate the broader commercial application of Li-O₂ battery technology.