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Vol. 19 (2027)

Ultramicropore-Confined Solvation and Interphase Regulation Unlock High-Performance Hard Carbon Anodes for Sodium-Ion Batteries

https://doi.org/10.1007/s40820-026-02300-x
Shunyuan Tan
National Energy Metal Resources and New Materials Key Laboratory, School of Metallurgy and Environment, Central South University, Changsha 410083, People’s Republic of China
Zhiyuan Cheng
National Energy Metal Resources and New Materials Key Laboratory, School of Metallurgy and Environment, Central South University, Changsha 410083, People’s Republic of China
Jiahao Xing
National Energy Metal Resources and New Materials Key Laboratory, School of Metallurgy and Environment, Central South University, Changsha 410083, People’s Republic of China
Jingkai Gao
National Energy Metal Resources and New Materials Key Laboratory, School of Metallurgy and Environment, Central South University, Changsha 410083, People’s Republic of China
Zimo Huang
National Energy Metal Resources and New Materials Key Laboratory, School of Metallurgy and Environment, Central South University, Changsha 410083, People’s Republic of China
Hongshuai Hou
College of Chemistry and Chemical Engineering, National Energy Metal Resources and New Materials Key Laboratory, State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, People’s Republic of China
Zhongliang Tian
National Energy Metal Resources and New Materials Key Laboratory, School of Metallurgy and Environment, Central South University, Changsha 410083, People’s Republic of China
Yanqing Lai
National Energy Metal Resources and New Materials Key Laboratory, School of Metallurgy and Environment, Central South University, Changsha 410083, People’s Republic of China
Jie Li
National Energy Metal Resources and New Materials Key Laboratory, School of Metallurgy and Environment, Central South University, Changsha 410083, People’s Republic of China
Simin Li
National Energy Metal Resources and New Materials Key Laboratory, School of Metallurgy and Environment, Central South University, Changsha 410083, People’s Republic of China
Xiaobo Ji
College of Chemistry and Chemical Engineering, National Energy Metal Resources and New Materials Key Laboratory, State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, People’s Republic of China

Corresponding Author: Xiaobo Ji

xji@csu.edu.cn

Nano-Micro Letters, Vol. 19 (2027), Article Number: 5

Abstract

Hard carbon (HC) anodes are promising for sodium-ion batteries, yet achieving high initial Coulombic efficiency (ICE), large plateau contribution, and fast charge-transfer kinetics remains challenging due to insufficient control of micro–nanostructure and interphase chemistry. Here, we present a precursor-level molecular engineering strategy that simultaneously regulates sodium desolvation and interphase chemistry in HC. An iodine-mediated oxidative cross-linking process converts starch into spherical HC with uniformly distributed ultramicropores and carbonyl-rich surfaces. These nanoconfined pores are proposed to act as molecular sieves, preferentially excluding bulky solvent molecules while allowing PF6−-coordinated Na+ access, thereby favoring anion-enriched electrolyte structures under confinement. Surface carbonyls exhibit strong PF6− affinity, which may promote fluorine-rich inorganic interphases on pore surfaces. The synergistic effects of anion-selective adsorption and confined desolvation are suggested to favor thin and robust NaF-rich interphases at external surfaces and within nanoconfined pore regions, contributing to reversible interfacial reactions and rapid Na+ storage kinetics. Consequently, the HC delivers an ICE of 88.4%, a reversible capacity of 352.9 mAh g−1 at 0.1C, excellent rate capability (288.9 mAh g−1 at 5C), and 95.6% capacity retention over 200 cycles. This work offers a molecular-level design paradigm integrating efficiency, capacity, and kinetics in HC anodes.


Highlights:
1 An iodine-mediated oxidative cross-linking strategy enables the synthesis of spherical hard carbon with uniformly distributed ultramicropores (< 0.9 nm) and carbonyl-rich surfaces from starch precursors.
2 Ultramicropore-confined solvation favors anion-enriched electrolyte structures, while carbonyl groups promote NaF-rich inorganic interphases, enabling synergistic interfacial regulation.
3 The optimized hard carbon delivers high initial Coulombic efficiency (88.4%), large plateau contribution (64.1%), excellent rate capability (288.9 mAh g−1 at 5C), and stable cycling (95.6% retention after 200 cycles).

Keywords

Sodium-ion batteries Hard carbon Ultramicropores Nanoconfined desolvation NaF-rich interphases
Tan, Shunyuan, Zhiyuan Cheng, Jiahao Xing, Jingkai Gao, Zimo Huang, Hongshuai Hou, Zhongliang Tian, Yanqing Lai, Jie Li, Simin Li, and Xiaobo Ji. 2026. “Ultramicropore-Confined Solvation and Interphase Regulation Unlock High-Performance Hard Carbon Anodes for Sodium-Ion Batteries”. Nano-Micro Letters 19 (July):5. https://doi.org/10.1007/s40820-026-02300-x.
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