Hard Carbon Anodes in Sodium-Ion Battery Technologies

Hard carbon materials have emerged as the leading anode choice for sodium-ion batteries owing to their low cost, structural tunability and ability to accommodate the larger sodium ion. Unlike graphite in lithium-ion systems, hard carbons feature a disordered arrangement of graphene fragments, a broad distribution of micropores and closed pore domains that collectively underpin high reversible capacity at low voltages. Storage mechanisms involve sodium adsorption at edge defects, intercalation between curved carbon layers and eventual pore filling that gives rise to a characteristic low-voltage plateau. Synthetic routes span direct pyrolysis of biomass precursors, hydrothermal pre-treatment and heteroatom doping, each tailored to control pore architecture, defect concentration and surface chemistry. Advances in operando spectroscopy and scattering techniques have refined our mechanistic understanding, while interfacial engineering of the solid electrolyte interphase has unlocked improved rate capability and cycle life. These developments underpin the global drive to deploy sodium-ion technology for grid-scale storage and cost-sensitive applications where resource abundance and sustainability are paramount.

Research from Nature Portfolio

Recent work employing waste wood-derived precursors has elucidated the formation of closed pore structures that are central to the low-voltage plateau capacity of hard carbon anodes. High-crystallinity cellulose pathways decompose into long-range carbon layers acting as the walls of closed pores, while amorphous components hinder over-graphitisation and promote crispation of these layers. Optimised materials achieve reversible capacities in excess of 430 mAh g⁻¹ at moderate currents, with plateau contributions approaching 300 mAh g⁻¹, and retain over 85 per cent capacity after hundreds of cycles. This study provides a clear mechanistic link between precursor microstructure, closed pore formation and enhanced sodium storage performance, enabling rational design of next-generation anodes.

Hard Carbon Anodes in Sodium-Ion Battery Technologies publication trend

The graph below shows the total number of articles in hard carbon anodes in sodium-ion battery technologies across all publications each year (not limited to Nature Index journals).

Technical terms

Hard carbon: A non-graphitised, disordered carbon material characterised by curved graphene fragments, defects and a network of micro- and closed pores.

Solid electrolyte interphase (SEI): A passivation layer formed on the anode surface during initial cycling that influences ion transport, stability and cycle life.

Low-voltage plateau: The region in the discharge profile, typically below 0.1 V vs Na⁺/Na, where sodium storage is dominated by pore filling and cluster formation.

Defect sites: Imperfections such as edges, vacancies or heteroatom substitutions in the carbon lattice that act as high-energy binding locations for sodium ions.

Sodium clustering: The aggregation of sodium atoms into quasi-metallic clusters within sufficiently large pores, contributing to the low-voltage capacity.

References

1. Regulating solid electrolyte interphase film on fluorine‐doped hard carbon anode for sodium‐ion battery. Carbon Energy (2024).
2. A revised mechanistic model for sodium insertion in hard carbons. Energy & Environmental Science (2020).
3. Revealing the closed pore formation of waste wood-derived hard carbon for advanced sodium-ion battery. Nature Communications (2023).
4. Sieving carbons promise practical anodes with extensible low-potential plateaus for sodium batteries. National Science Review (2022).