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New Discoveries In Sodium-Ion Storage Mechanisms In Hard Carbons FAST CHARGING IN HARD CARBON ANODES
SEI-INDEPENDENT PRE-DESOLVATION
Li et. al. [1] unveiled a unified storage mechanism for Li and Na in hard carbon anodes, introducing an underpotential deposition (UPD)-like process for Na+ storage in wedge-shaped nanopores.
Lu et. al. [2] redefined the sodium-ion storage mechanism in hard carbons by identifying a novel SEI-independent pre-desolvation process within nanopores, driven by capillary effects and osmotic pressure. Unlike traditional SEI models, this mechanism alters the electrolyte solvation structure, achieving a record-high initial Coulombic efficiency (ICE) of 99.09% after 10 days of aging.
This mechanism facilitates quasi-metallic Na clustering at a slightly higher plateau potential due to interface energy differences between Na and graphene walls. These insights enabled the development of 26700-type cells with 3 Ah capacity, achieving 83% retention after 3,000 cycles at an ultra-fast 6.5C rate with no Na plating. The study also highlighted the optimal pore size (~1 nm) for balancing storage capacity and fast kinetics, providing a fundamental understanding of how nanopore geometry drives performance.
The insights led to the development of a dual-SEI model, distinguishing between a surface SEI (S-SEI) and an internal nanopore SEI (I-SEI). The I-SEI’s thinner, inorganic-rich composition facilitates Na+ transport with reduced resistance, enabling a negative-to-positive (N/P) capacity ratio of 1.02 and energy density of 282 Wh/kg in full cells. These findings challenge prior models by showing that nanopores actively shape Na+ storage behavior.
Source: [1] Li, Y., Vasileiadis, A., Zhou, Q. et al. Origin of fast charging in hard carbon anodes. Nat Energy 9, 134–142 (2024) [2] Lu, Z., Yang, H., Guo, Y. et al. Consummating ion desolvation in hard carbon anodes for reversible sodium storage. Nat Commun 15, 3497 (2024).
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