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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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References
  1. D. Saurel, B. Orayech, B. Xiao, D. Carriazo, X. Li et al., From charge storage mechanism to performance: a roadmap toward high specific energy sodium-ion batteries through carbon anode optimization. Adv. Energy Mater. 8(17), 1703268 (2018). https://doi.org/10.1002/aenm.201703268
  2. X. Chen, C. Liu, Y. Fang, X. Ai, F. Zhong et al., Understanding of the sodium storage mechanism in hard carbon anodes. Carbon Energy 4(6), 1133–1150 (2022). https://doi.org/10.1002/cey2.196
  3. J. Zheng, W. Liu, S. Li, Y. Lai, J. Li et al., Spatial confinement strategy modulated by kinetic diameters of gaseous molecules for sodium storage. Energy Storage Mater. 73, 103835 (2024). https://doi.org/10.1016/j.ensm.2024.103835
  4. J.H. Li, Y.B. Zhang, Y.R. Jia, C.X. Yang, Y. Chu et al., Progress and challenges in the use of carbon anodes for high-energy and fast-charging sodium-ion batteries. New Carbon Mater. 39(5), 729–742 (2024). https://doi.org/10.1016/S1872-5805(24)60870-X
  5. D. Ma, Z. Zhao, Y. Wang, X. Yang, M. Yang et al., Unlocking the design paradigm of in-plane heterojunction with built-in bifunctional anion vacancy for unexpectedly fast sodium storage. Adv. Mater. 36(4), 2310336 (2024). https://doi.org/10.1002/adma.202310336
  6. K.Y. Liang, Y.B. Guan, B. Qiu, L.D. Wang, H.D. Wei et al., Expansion-induced spontaneous polarization facilitates sodium-ion storage in red phosphorus anode. Rare Met. 44(12), 9975–9985 (2025). https://doi.org/10.1007/s12598-025-03588-1
  7. S. Luo, Z. Hou, Z. Qi, Q. Li, Y. Pang et al., Insights into targeted effects of salt and solvent on Na+ storage in hard carbon anodes toward ultra-low temperature sodium batteries. Sci. China Chem. 69(3), 1425–1433 (2026). https://doi.org/10.1007/s11426-025-2947-2
  8. J.-T. Li, N. Sawut, Y.-C. Zhao, P. Liu, Y.-X. Wang et al., Microstructure-mechanism-performance relationships in hard carbon anode materials for sodium-ion batteries. New Carbon Mater. 40(4), 860–868 (2025). https://doi.org/10.1016/S1872-5805(25)61023-7
  9. Z. Chen, J. Shen, W. Deng, Y. Huang, P. Shan et al., Achieving over 200 Wh kg–1 sodium-ion pouch cell by quantitative engineering of hard carbon pores. Natl. Sci. Rev. 13(3), nwaf566 (2026). https://doi.org/10.1093/nsr/nwaf566
  10. W. Deng, Y. Wang, Z. Chen, H. Huang, C. Chen et al., Catalyst-assisted chemical vapor deposition engineering of hard carbon with abundant closed pores for high-performance sodium-ion batteries. Adv. Funct. Mater. 35(41), 2501721 (2025). https://doi.org/10.1002/adfm.202501721
  11. J.M. Stratford, A.K. Kleppe, D.S. Keeble, P.A. Chater, S.S. Meysami et al., Correlating local structure and sodium storage in hard carbon anodes: insights from pair distribution function analysis and solid-state NMR. J. Am. Chem. Soc. 143(35), 14274–14286 (2021). https://doi.org/10.1021/jacs.1c06058
  12. Y. Li, A. Vasileiadis, Q. Zhou, Y. Lu, Q. Meng et al., Origin of fast charging in hard carbon anodes. Nat. Energy 9(2), 134–142 (2024). https://doi.org/10.1038/s41560-023-01414-5
  13. Z. Song, M. Di, X. Zhang, Z. Wang, S. Chen et al., Nanoconfined strategy optimizing hard carbon for robust sodium storage. Adv. Energy Mater. 14(43), 2401763 (2024). https://doi.org/10.1002/aenm.202401763
  14. J. Duan, Z. Xu, M. Li, P. Yang, H. Hu et al., Structure regulation of hard carbon with enriched semi-closed ultramicropores for enhanced rapid sodium storage. Adv. Funct. Mater. 35(46), 2508822 (2025). https://doi.org/10.1002/adfm.202508822
  15. J. Zheng, C. Guan, H. Li, D. Wang, Y. Lai et al., Unveiling the microscopic origin of irreversible capacity loss of hard carbon for sodium-ion batteries. Adv. Energy Mater. 14(15), 2303584 (2024). https://doi.org/10.1002/aenm.202303584
  16. Y. Zhang, S.-W. Zhang, Y. Chu, J. Zhang, H. Xue et al., Redefining closed pores in carbons by solvation structures for enhanced sodium storage. Nat. Commun. 16, 3634 (2025). https://doi.org/10.1038/s41467-025-59022-8
  17. M. Liu, F. Wu, Y. Gong, Y. Li, Y. Li et al., Interfacial-catalysis-enabled layered and inorganic-rich SEI on hard carbon anodes in ester electrolytes for sodium-ion batteries. Adv. Mater. 35(29), 2370207 (2023). https://doi.org/10.1002/adma.202370207
  18. Y. Sun, D. Zuo, C. Xu, B. Peng, J.C. Li et al., A “grafting technique” to tailor the interfacial behavior of hard carbon anodes for stable sodium-ion batteries. Energy Environ. Sci. 18(4), 1911–1919 (2025). https://doi.org/10.1039/D4EE05305B
  19. P. Wang, B. Wang, Y. Li, W. Wang, Y. Sun et al., Selecting the molecular components of a pitch to produce a hard carbon anode with a high sodium storage capacity. New Carbon Mater. 41(1), 142–155 (2026). https://doi.org/10.1016/S1872-5805(25)60971-1
  20. Y. Chai, J. Guo, C. Hong, Z. Yi, W. Li et al., Reducing steric hindrance to enhance the oxidation reactivity of coal precursors for high-performance hard carbons in sodium-ion batteries. Energy Storage Mater. 83, 104678 (2025). https://doi.org/10.1016/j.ensm.2025.104678
  21. Y. Wang, W. Li, C. Huang, Z. Jiang, F. Liu et al., High-crystallinity wrinkled hard carbon via molecular-level anchoring glucose molecules with cooperative-assembly of intermolecular hydrogen bonds for sodium-ion batteries. Adv. Funct. Mater. 35(17), 2570102 (2025). https://doi.org/10.1002/adfm.202570102
  22. M.M. Tang, R. Bacon, Carbonization of cellulose fibers: I. Low temperature pyrolysis. Carbon 2(3), 211–220 (1964). https://doi.org/10.1016/0008-6223(64)90035-1
  23. J. Huang, E. Li, B. Dai, T. Lu, J. Teng et al., Regulating the active hydroxyl group of starch: revealing the evolution of hard carbon structure and sodium storage behavior. Carbon 229, 119527 (2024). https://doi.org/10.1016/j.carbon.2024.119527
  24. Z. Wen, R. Zhao, T. Tian, T. Zhang, X. Wang et al., Molecular stitching in polysaccharide precursor for fabricating hard carbon with ultra-high plateau capacity of sodium storage. Adv. Mater. 37(18), 2420251 (2025). https://doi.org/10.1002/adma.202420251
  25. M.X. Song, L.J. Xie, J.Y. Cheng, Z.L. Yi, G. Song et al., Insights into the thermochemical evolution of maleic anhydride-initiated esterified starch to construct hard carbon microspheres for lithium-ion batteries. J. Energy Chem. 66, 448–458 (2022). https://doi.org/10.1016/j.jechem.2021.08.050
  26. G. Kresse, J. Furthmüller, Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput. Mater. Sci. 6(1), 15–50 (1996). https://doi.org/10.1016/0927-0256(96)00008-0
  27. J.P. Perdew, K. Burke, M. Ernzerhof, Generalized gradient approximation made simple. Phys. Rev. Lett. 77(18), 3865–3868 (1996). https://doi.org/10.1103/physrevlett.77.3865
  28. P. Sun, Z. Qiao, X. Dong, R. Jiang, Z.-T. Hu et al., Designing 3d transition metal cation-doped MRuOx as durable acidic oxygen evolution electrocatalysts for PEM water electrolyzers. J. Am. Chem. Soc. 146(22), 15515–15524 (2024). https://doi.org/10.1021/jacs.4c04096
  29. H.J. Monkhorst, J.D. Pack, Special points for Brillouin-zone integrations. Phys. Rev. B 13(12), 5188–5192 (1976). https://doi.org/10.1103/physrevb.13.5188
  30. Z. Qiao, R. Jiang, H. Xu, D. Cao, X.C. Zeng, A general descriptor for single-atom catalysts with axial ligands. Angew. Chem. Int. Ed. 63(40), e202407812 (2024). https://doi.org/10.1002/anie.202407812
  31. S. Grimme, J. Antony, S. Ehrlich, H. Krieg, A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 132(15), 154104 (2010). https://doi.org/10.1063/1.3382344
  32. Z. Hou, Y. Zhao, Y. Du, F. Wu, W. He et al., Expediting sodium energy of hard carbon by cation/anion co-interfering chemistry. Adv. Funct. Mater. 35(36), 2505468 (2025). https://doi.org/10.1002/adfm.202505468
  33. Y. Shen, Y. Wang, H. Li, Y.S. He, Z.F. Ma et al., Air-stabilization creates non-crosslinked starch ps for high-performance hard carbon anodes. Adv. Funct. Mater. 36(1), e09126 (2026). https://doi.org/10.1002/adfm.202509126
  34. S. Yao, K. Zhang, K. Jiao, W. Hu, Evolution of coal structures: FTIR analyses of experimental simulations and naturally matured coals in the Ordos Basin, China. Energy Explor. Exploit. 29(1), 1–19 (2011). https://doi.org/10.1260/0144-5987.29.1.1
  35. X.K. Shan, S.L. Zhao, Y.Y. Ma, W. Mo, X.Y. Wei, Analysis of pyrolysis performance and molecular structure of five kinds of low-rank coals in Xinjiang based on the TG-DTG method. ACS Omega 7(10), 8547–8557 (2022). https://doi.org/10.1021/acsomega.1c06350
  36. P. Saires, C.A. Barraza, M. Bertero, R. Pujro, M. Falco et al., Characterization of pyrolytic tars derived from different biomasses. Processes 12(4), 817 (2024). https://doi.org/10.3390/pr12040817
  37. L. Zhang, S. Qi, N. Takeda, S. Kudo, J. Hayashi et al., Characteristics of gas evolution profiles during coal pyrolysis and its relation with the variation of functional groups. Int. J. Coal Sci. Technol. 5(4), 452–463 (2018). https://doi.org/10.1007/s40789-017-0175-0
  38. F. Zhao, Z. Yang, L. Zhang, C. Zhang, T. Wang et al., The effect of temperature on pyrolysis products during oil shale thermal decomposition. Sci. Rep. 15, 26135 (2025). https://doi.org/10.1038/s41598-025-11050-6
  39. J. Zheng, Y. Wu, C. Guan, D. Wang, Y. Lai et al., Lignin-derived hard carbon anode with a robust solid electrolyte interphase for boosted sodium storage performance. Carbon Energy 6(9), e538 (2024). https://doi.org/10.1002/cey2.538
  40. J. Huang, S. Liu, E. Li, B. Dai, T. Lu et al., Double functionalization strategy: using acetate metal salt as medium to optimize hard carbon. Carbon 234, 119981 (2025). https://doi.org/10.1016/j.carbon.2024.119981
  41. E.A. Pillar-Little, M.I. Guzman, J.M. Rodriguez, Conversion of iodide to hypoiodous acid and iodine in aqueous microdroplets exposed to ozone. Environ. Sci. Technol. 47(19), 10971–10979 (2013). https://doi.org/10.1021/es401700h
  42. K. Kim, B. Kim, Y.-Y. Ahn, K.D. Tran, H.T.M. Truong et al., Production of molecular iodine via a redox reaction between iodate and organic compounds in ice. J. Phys. Chem. A 127(12), 2830–2838 (2023). https://doi.org/10.1021/acs.jpca.3c00482
  43. J. Chen, X. Chen, B. Xu, L. Chen, C. Wang et al., Atomistic mechanisms of oxygen-containing functional groups in hard carbon precursors for enhanced sodium storage performance. Energy Storage Mater. 85, 104886 (2026). https://doi.org/10.1016/j.ensm.2026.104886
  44. H. Yamamoto, S. Muratsubaki, K. Kubota, M. Fukunishi, H. Watanabe et al., Synthesizing higher-capacity hard-carbons from cellulose for Na- and K-ion batteries. J. Mater. Chem. A 6(35), 16844–16848 (2018). https://doi.org/10.1039/c8ta05203d
  45. Z. Hong, Y. Zhen, Y. Ruan, M. Kang, K. Zhou et al., Rational design and general synthesis of S-doped hard carbon with tunable doping sites toward excellent Na-ion storage performance. Adv. Mater. 30(29), 1802035 (2018). https://doi.org/10.1002/adma.201802035
  46. Y. Youn, B. Gao, A. Kamiyama, K. Kubota, S. Komaba et al., Nanometer-size Na cluster formation in micropore of hard carbon as origin of higher-capacity Na-ion battery. Npj Comput. Mater. 7, 48 (2021). https://doi.org/10.1038/s41524-021-00515-7
  47. H. Zhong, Q. Huang, M. Zou, F. Li, Y. Liu et al., From food to hard carbon: citric acid enhanced biomass-derived anodes for high-performance sodium storage. Chem. Eng. J. 508, 160879 (2025). https://doi.org/10.1016/j.cej.2025.160879
  48. Y. Sun, T. Shen, Z. He, S. Wang, Crosslinking modification of starch improves the structural stability of hard carbon anodes for high-capacity sodium storage. J. Colloid Interface Sci. 678, 1142–1150 (2025). https://doi.org/10.1016/j.jcis.2024.09.191
  49. G. Yang, J. Zhang, Z. Zhang, X. Qin, Q. Teng et al., Surface functionalized porous spherical hard carbon material derived from taro starch for high performance sodium storage. Electrochim. Acta 521, 145935 (2025). https://doi.org/10.1016/j.electacta.2025.145935
  50. S. Xu, W. Liu, S. Mao, Y. Wu, B. Yuan et al., Lotus root starch derived sustainable hard carbon for fast-charging sodium-ion batteries. Chem. Eng. J. 519, 165014 (2025). https://doi.org/10.1016/j.cej.2025.165014
  51. J. Zhao, X. Liu, H. Yuan, S. Feng, K. Xiong et al., Insights into the microstructure evolution of starch-derived hard carbon for sodium-ion battery. J. Power. Sources 647, 237367 (2025). https://doi.org/10.1016/j.jpowsour.2025.237367
  52. J. Xie, H. Ai, K. Du, R. Lv, Regulating ultramicropores and closed-pores in starch-derived hard carbons for efficient sodium ion storage. Carbon 247, 121077 (2026). https://doi.org/10.1016/j.carbon.2025.121077
  53. L. Chen, L. Zhang, Y. Jiang, J. Zhao, F. Xu et al., Regulation of surface oxygen functional groups in starch-derived hard carbon via pre-oxidation: a strategy for enhanced sodium storage performance. Mater. Today Chem. 41, 102314 (2024). https://doi.org/10.1016/j.mtchem.2024.102314
  54. H. Zeng, J. Zhang, J. He, Q. Zeng, N. Li et al., Starch-derived N-doped hard carbons for sodium-ion storage: preparation and enhanced electrochemical performance. J. Power. Sources 654, 237850 (2025). https://doi.org/10.1016/j.jpowsour.2025.237850
  55. W. Chen, M. Wan, Q. Liu, X. Xiong, F. Yu et al., Heteroatom-doped carbon materials: synthesis, mechanism, and application for sodium-ion batteries. Small Meth. 3(4), 1800323 (2019). https://doi.org/10.1002/smtd.201800323
  56. V. Augustyn, P. Simon, B. Dunn, Pseudocapacitive oxide materials for high-rate electrochemical energy storage. Energy Environ. Sci. 7(5), 1597 (2014). https://doi.org/10.1039/c3ee44164d
  57. P. Wang, S. Xu, S. Wang et al., Unlocking interlayer confinement enables all-slope hard carbon with ultrafast and highly reversible sodium storage. ACS Nano 19(44), 38735–38748 (2025). https://doi.org/10.1021/acsnano.5c14641
  58. Y. Zhu, Z. Lao, M. Zhang, T. Hou, X. Xiao et al., A locally solvent-tethered polymer electrolyte for long-life lithium metal batteries. Nat. Commun. 15, 3914 (2024). https://doi.org/10.1038/s41467-024-48078-7
  59. Y. He, F. Yu, K. Liu, L. Bai, Y. Liu et al., Tuning hard carbon pores at the ångstrom scale facilitates sodium-ion pre-desolvation in high-performance sodium-ion batteries. Adv. Energy Mater. 16(5), e04760 (2026). https://doi.org/10.1002/aenm.202504760
  60. X. Feng, F. Wu, Y. Li, Y. Fu, Y. Li et al., Critical role of ultra-microporous tunnel structure within hard carbon in boosting sodium-ion storage. Adv. Mater. 38(1), e01779 (2026). https://doi.org/10.1002/adma.202501779
  61. Q. Li, X. Liu, Y. Tao, J. Huang, J. Zhang et al., Sieving carbons promise practical anodes with extensible low-potential plateaus for sodium batteries. Natl. Sci. Rev. 9(8), 084 (2022). https://doi.org/10.1093/nsr/nwac084
  62. Z. Song, M. Di, S. Chen, Y. Bai, Three-dimensional N/O co-doped hard carbon anode enabled superior stabilities for sodium-ion batteries. Chem. Eng. J. 470, 144237 (2023). https://doi.org/10.1016/j.cej.2023.144237
  63. J. Yan, Y. Zhang, P. Kim, A. Pinczuk, Electric field effect tuning of electron-phonon coupling in graphene. Phys. Rev. Lett. 98(16), 166802 (2007). https://doi.org/10.1103/physrevlett.98.166802
  64. Y. Zeng, J. Yang, H. Yang, Y. Yang, J. Zhao, Bridging microstructure and sodium-ion storage mechanism in hard carbon for sodium ion batteries. ACS Energy Lett. 9(3), 1184–1191 (2024). https://doi.org/10.1021/acsenergylett.3c02751
  65. Z. Wang, X. Feng, Y. Bai, H. Yang, R. Dong et al., Probing the energy storage mechanism of quasi-metallic Na in hard carbon for sodium-ion batteries. Adv. Energy Mater. 11(11), 2003854 (2021). https://doi.org/10.1002/aenm.202003854
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