Overcoming Hydrated Zn²⁺ Diffusion Barriers via Molecular Intercalation Activation of Ramie Fiber-Derived Flexible Zinc-Ion Hybrid Capacitors with High Energy Density

Abstract

Biomass-derived self-supporting carbon materials are considered promising cathodes for zinc-ion capacitors owing to their structural tunability and cost-effectiveness. Natural ramie fibers form a 3D interpenetrating network, which provides excellent mechanical support for flexible electrodes. However, conventional high-temperature activation often induces structural collapse. Although surface etching preserves flexible frameworks, it limits pore development, resulting in underutilized surface area and poor pore-carrier compatibility. These limitations create a trade-off between electrochemical performance and structural flexibility. This study presents a top–down intercalation activation strategy for precise pore regulation in natural plant fiber-derived carbon. To completely preserve the flexible fiber skeleton, this approach successfully constructs an interconnected hierarchical channel system, which effectively reduces the ion diffusion barrier. Consequently, the flexible electrode exhibits abundant defect structures and a high specific surface area of 2477 m² g⁻¹, which is 50 times that of directly carbonized ramie fibers. These features significantly increase the number of active sites available for charge storage. The assembled zinc-ion hybrid capacitor exhibits an excellent specific capacity of 212 mAh g⁻¹ at 0.2 A g⁻¹ and an energy density of 168 Wh kg⁻¹, and retains 91% of its capacity after 50,000 cycles. Notably, the assembled flexible device maintains normal operations under multi-angle bending conditions, indicating excellent stability. The proposed strategy provides an innovative approach for the precise regulation of pore size in biomass-derived carbon fibers and enables the efficient preparation of other cellulose-based self-supporting carbon materials.

Graphical Abstract

Keywords

Zinc-ion hybrid capacitors / Cellulose / Intercalation activation / Pore structure regulation / Flexibility

References

[1] Xu J, Zhang J, Pollard TP, Li Q, Tan S, Hou S, Wan H, Chen F, He H, Hu E, Xu K, Yang X-Q, Borodin O, Wang C. Electrolyte design for Li-ion batteries under extreme operating conditions. Nature, 2023, 614: 694

[2] Wang F, Chen L, Wei J, Diao C, Li F, Du C, Bai Z, Zhang Y, Malyi OI, Chen X, Tang Y, Bao X. Pushing slope- to plateau-type behavior in hard carbon for sodium-ion batteries via local structure rearrangement. Energ Environ Sci, 2025, 18: 4312

[3] Shang Z, An X, Nie S, Li N, Cao H, Cheng Z, Liu H, Ni Y, Liu L. Design of B/N co-doped micro/meso porous carbon electrodes from CNF/BNNS/ZIF-8 nanocomposites for advanced supercapacitors. J Bioresour Bioprod, 2023, 8: 292

[4] Jin H, Zhang T, Tian Z, Jiang S. Study on capacitive performance of bamboo-derived thick carbon electrodes using one-step activation method. J For Eng, 2024, 9103

[5] Li L, Nam JS, Kim MS, Wang Y, Jiang S, Hou H, Kim I-D. Sulfur–carbon electrode with PEO-LiFSI-PVDF composite coating for high-rate and long-life lithium–sulfur batteries. Adv Energy Mater, 2023, 13 2302139

[6] Guo M, Lin Z, Du W. Research progress of wood for hydrovoltaic generation. J For Eng, 2024, 9: 1

[7] Zeng S, Duan G, Yu R, Qin Q, He S, Jiang S, Yang H, Han X, Han J, Xia BY. Microstructure and bionic engineering of triphase reaction interface for zinc-air batteries. Prog Mater Sci, 2025, 147 101356

[8] Liu Y, Xiang K, Zhou W, Deng W, Zhu H, Chen H. Investigations on tunnel-structure MnO₂ for utilization as a high-voltage and long-life cathode material in aqueous ammonium-ion and hybrid-ion batteries. Small, 2024, 20: 2308741

[9] Wen XY, Li W, Chen H, Zhou W, Xiang KX. Zn₃V₃O₈ nanorods with outstanding electrochemical kinetics as novel anode for aqueous ammonium-ion batteries. Rare Met, 2025

[10] Guo T, Tang LB, Deng WN, Liu GD, Zhou W, Wan H, Meng LC, Chen H. CuxO as an ultra-stable voltage plateaus and long-life cathode material in aqueous ammonium-ion batteries. Rare Met, 2025, 44: 3881

[11] Jiang S, Fang J, Liu H, Tang X, Zhu H, Zong E, Cai Y, Zhao Z, Guo J, Liu Y. Bioelectricity-driven, sulfurized Fe species anode in situ generate sulfate radicals from sulfates in antibiotic wastewater for enhanced ciprofloxacin hydrochloride removal: performance and mechanism. Chem Eng J, 2024, 502 157745

[12] Wang Z, Zhu M, Pei Z, Xue Q, Li H, Huang Y, Zhi C. Polymers for supercapacitors: boosting the development of the flexible and wearable energy storage. Mat Sci Eng Rep, 2020, 139 100520

[13] Lv X, Liu Y, Yu J, Li Z, Ding B. Smart fibers for self-powered electronic skins. Adv Fiber Mater, 2023, 5: 401

[14] Yan D, Ye J, Zhou Y, Lei X, Deng B, Xu W. Research progress of fabrics with different geometric structures for triboelectric nanogenerators in flexible and wearable electronics. Adv Fiber Mater, 2023, 5: 1852

[15] Wang X, Lu X, Liu B, Chen D, Tong Y, Shen G. Flexible energy-storage devices: design consideration and recent progress. Adv Mater, 2014, 26: 4763

[16] Wang D, Han C, Mo F, Yang Q, Zhao Y, Li Q, Liang G, Dong B, Zhi C. Energy density issues of flexible energy storage devices. Energy Storage Mater, 2020, 28: 264

[17] Kong Y, Li C, Xu Y, An Y, Zhao S, Zhang X, Yi S, Gong Y, Sun X, Wang K, Zhang X, Ma Y. Vacancy chemistry regulated cobalt oxide nanostructures with fast kinetics for high-performance lithium-ion capacitors. Energy Mater Adv, 2025, 6: 0180

[18] Wang H, Zhu C, Chao D, Yan Q, Fan HJ. Nonaqueous hybrid lithium-ion and sodium-ion capacitors. Adv Mater, 2017, 29: 1702093

[19] Wang H, Wang M, Tang Y. A novel zinc-ion hybrid supercapacitor for long-life and low-cost energy storage applications. Energy Storge Mater, 2018, 13: 1

[20] Tong W, Liang X, Zhou X, Huang F, Chen L, Niu M. Comparation of porous bamboo activated carbon using KOH co-thermal activation and hydrothermal activation methods. J For Eng, 2024, 9: 77

[21] Zaini MSM, Arshad M, Syed-Hassan SSA. Adsorption isotherm and kinetic study of methane on palm kernel shell-derived activated carbon. J Bioresour Bioprod, 2023, 866

[22] Javed MS, Najam T, Hussain I, Idrees M, Ahmad A, Imran M, Shah SSA, Luque R, Han W. Fundamentals and scientific challenges in structural design of cathode materials for zinc-ion hybrid supercapacitors. Adv Energy Mater, 2023, 13 2202303

[23] Sun C, Han Z, Wang X, Liu B, Li Q, Li H, Xu J, Cao JM, Wu XL. Advanced carbons nanofibers-based electrodes for flexible energy storage devices. Adv Funct Mater, 2023, 33: 2305606

[24] Ibitoye SE, Mahamood RM, Jen TC, Loha C, Akinlabi ET. An overview of biomass solid fuels: biomass sources, processing methods, and morphological and microstructural properties. J Bioresour Bioprod, 2023, 8: 333

[25] Javed MS, Asim S, Najam T, Khalid M, Hussain I, Ahmad A, Assiri MA, Han W. Recent progress in flexible Zn-ion hybrid supercapacitors: fundamentals, fabrication designs, and applications. Carbon Energy, 2022

[26] Arbaz SJ, Ramulu B, Yu JS. Micro-supercapacitors based on fungi-derived biocarbon microfibers infused with NiMoO nanoparticles for biomedical and E-skin applications. Adv Fiber Mater, 2024, 6: 1008

[27] Xue B, Xu J, Feng Y, Ma M, Xiao R, Wang X. Morphology engineering of biomass-derived porous carbon from 3D to 2D towards boosting capacitive charge storage capability. J Colloid Interface Sci, 2023, 642: 736

[28] Zheng X, Tao Y, Jin L, Zheng Z, Sun J, Sun Y, Du J, Zheng X, Wu S, Pang Y, Shen Z, Du P, Chen H. Flame retardant mechanism-inspired fabrication of all-biomass-derived porous carbons for zinc-ion hybrid supercapacitors. Ind Crops Prod, 2024, 218 119034

[29] Zou Z, Luo X, Wang L, Zhang Y, Xu Z, Jiang C. Highly mesoporous carbons derived from corn silks as high performance electrode materials of supercapacitors and zinc ion capacitors. J Energy Storge, 2021, 44 103385

[30] Wei X, Qiu B, Xu L, Qin Q, Zhang W, Liu Z, Wei F, Lv Y. High performance hierarchical porous carbon derived from waste shrimp shell for supercapacitor electrodes. J Energy Storge, 2023, 62 106900

[31] Zhao H, Liu L, Vellacheri R, Lei Y. Recent advances in designing and fabricating self-supported nanoelectrodes for supercapacitors. Adv Sci, 2017, 4: 1700188

[32] Xu Z, Sun Z, Shan J, Jin S, Cui J, Deng Z, Seo MH, Wang X. O,N-codoped, self-activated, holey carbon sheets for low-cost and high-loading zinc-ion supercapacitors. Adv Funct Mater, 2024, 34 2302818

[33] Long Y, An X, Yang Y, Yang J, Liu L, Tong X, Liu X, Liu H, Ni Y. Gradient porous carbon superstructures for high‐efficiency charge storage kinetics. Adv Funct Mater. 2025;2424551.

[34] Zhang Q, Ma Y, Lu Y, Zhou X, Lin L, Li L, Yan Z, Zhao Q, Zhang K, Chen J. Designing anion-type water-free Zn²⁺ solvation structure for robust Zn metal anode. Angew Chem Int Ed, 2021, 60: 23357

[35] Marcus Y. A simple empirical model describing the thermodynamics of hydration of ions of widely varying charges, sizes, and shapes. Biophys Chem, 1994, 51: 111

[36] Huang H, Tang Q, Lin G, Yu C, Wang H, Li Z. High-efficiency and recyclable ramie cellulose fiber degumming enabled by deep eutectic solvent. Ind Crops Prod, 2021, 171 113879

[37] Manian AP, Cordin M, Pham T. Extraction of cellulose fibers from flax and hemp: a review. Cellulose, 2021, 28: 8275

[38] Jin H, Zha C, Gu L. Direct dissolution of cellulose in NaOH/thiourea/urea aqueous solution. Carbohydr Res, 2007, 342: 851

[39] Xiong B, Zhao P, Hu K, Zhang L, Cheng G. Dissolution of cellulose in aqueous NaOH/urea solution: role of urea. Cellulose, 2014, 21: 1183

[40] Cai J, Zhang L, Liu S, Liu Y, Xu X, Chen X, Chu B, Guo X, Xu J, Cheng H, Han CC, Kuga S. Dynamic self-assembly induced rapid dissolution of cellulose at low temperatures. Macromolecules, 2008, 41: 9345

[41] Hribernik S, Stana Kleinschek K, Rihm R, Ganster J, Fink H-P, Sfiligoj SM. Tuning of cellulose fibres’ structure and surface topography: influence of swelling and various drying procedures. Carbohydr Polym, 2016, 148: 227

[42] Hu X, Wang G, Li J, Huang J, Liu Y, Zhong G, Yuan J, Zhan H, Wen Z. Significant contribution of single atomic Mn implanted in carbon nanosheets to high-performance sodium–ion hybrid capacitors. Energy Environ Sci, 2021, 14: 4564

[43] Zhu H, Hu Y, Men X, Zhang Q, Pang L, Xiao P, Luo H, Zhou W, Li Y. Design of C_f/SiC_f/Si₃N_4f multifiber layered composite with enhanced electromagnetic wave absorption properties. J Am Ceram Soc, 2025, 108 e20301

[44] Jorio A, Souza Filho AG. Raman studies of carbon nanostructures. Annu Rev Mater Res, 2016, 46: 357

[45] Wu Y, Wang B, Li J, Cao D, Xu J, Zeng J, Gao W, Ji X, Chen K. Carbonization of bacterial cellulose with structure retention and nitrogen/sulfur/oxygen doping for application in supercapacitors electrode. Chem Eng J, 2024, 495 153590

[46] Ma H, Chen H, Wu M, Chi F, Liu F, Bai J, Cheng H, Li C, Qu L. Maximization of spatial charge density: an approach to ultrahigh energy density of capacitive charge storage. Angew Chem Int Ed, 2020, 59: 14541

[47] Yang H, Abdurashid A, Jamal R, Abdiryim T, Wang X, Song K, Zhou Y, Liu Y, Fan N. Boron and nitrogen co-doped carbon nano framework composites for high performance energy storage. Carbon, 2025, 235 120028

[48] Long L, Zhang Y, Zhu H, Nie Y, Zhou W, Li Y. In situ growth of the Y₃Si₂C₂ interphase in SiCf-reinforced mullite ceramics for enhanced electromagnetic wave absorption. J Am Ceram Soc, 2025, 108 e20506

[49] Pan Z, Qian Y, Li Y, Xie X, Lin N, Qian Y. Novel bilayer-shelled N,O-doped hollow porous carbon microspheres as high performance anode for potassium-ion hybrid capacitors. Nano-Micro Lett, 2023, 15: 151

[50] Zheng Y, Chen K, Jiang K, Zhang F, Zhu G, Xu H. Progress of synthetic strategies and properties of heteroatoms-doped (N, P, S, O) carbon materials for supercapacitors. J Energy Storge, 2022, 56 105995

[51] Zhou Q, Chen Q, Xu W, Wang F, Du X, Zhou Y, Zhan Y, Jiang M. Nitrogen and sulfur co-doped carbonized lignin nanotubes for supercapacitor applications. Chem Eng J, 2024, 496 154126

[52] Gao Y, Zheng S, Fu H, Ma J, Xu X, Guan L, Wu H, Wu Z-S. Three-dimensional nitrogen doped hierarchically porous carbon aerogels with ultrahigh specific surface area for high-performance supercapacitors and flexible micro-supercapacitors. Carbon, 2020, 168: 701

[53] Tian Z, Yang C, Guo Z, Duan G, Huang Y, Yang H, Han X, Zhang C, He S, Jiang S. Co-crosslinking and anchoring strategy: one-step preparation of N-doped porous carbon for supercapacitors and zinc ion hybrid capacitors. Fuel, 2025, 381 133298

[54] Huang L, Tong D, Chen H, Zhu H, Zhang F, Sheng Y, Hu Z, Qian T, Liu H. Synthesis of ZIF-L-derived hollow carbons for zinc-ion capacitors. ACS Sustain Chem Eng, 2023, 11: 3702

[55] Du J, Han Q, Chen Y, Peng M, Xie L, Chen A. Micro/meso-porous double-shell hollow carbon spheres through spatially confined pyrolysis for supercapacitors and zinc-ion capacitor. Angew Chem Int Ed, 2024, 63 e202411066

[56] Xiao K, Jiang X, Zeng S, Chen J, Hu T, Yuan K, Chen Y. Porous structure-electrochemical performance relationship of carbonaceous electrode-based zinc ion capacitors. Adv Funct Mater, 2024, 34 2405830

[57] Li H, Wu J, Wang L, Liao Q, Niu X, Zhang D, Wang K. A zinc ion hybrid capacitor based on sharpened pencil-like hierarchically porous carbon derived from metal–organic framework. Chem Eng J, 2022, 428 131071

[58] Li J, Zhang J, Yu L, Gao J, He X, Liu H, Guo Y, Zhang G. Dual-doped carbon hollow nanospheres achieve boosted pseudocapacitive energy storage for aqueous zinc ion hybrid capacitors. Energy Storge Mater, 2021, 42: 705

[59] Wang C, Pei Z, Meng Q, Zhang C, Sui X, Yuan Z, Wang S, Chen Y. Toward flexible zinc-ion hybrid capacitors with superhigh energy density and ultralong cycling life: the pivotal role of ZnCl₂ salt-based electrolytes. Angew Chem Int Ed, 2021, 60: 990

[60] Wei F, Wei Y, Wang J, Han M, Lv Y. N, P dual doped foamy-like carbons with abundant defect sites for zinc ion hybrid capacitors. Chem Eng J, 2022, 450 137919

[61] Mao K, Shi J, Zhang Q, Hou Y, Wen L, Liu Z, Long F, Niu K, Liu N, Long F, Gao Y. High-capacitance MXene anode based on Zn-ion pre-intercalation strategy for degradable micro Zn-ion hybrid supercapacitors. Nano Energy, 2022, 103 107791

[62] Liang Q, Wang S, Lu X, Jia X, Yang J, Liang F, Xie Q, Yang C, Qian J, Song H, Chen R. High-entropy MXene as bifunctional mediator toward advanced Li–S full batteries. ACS Nano, 2024, 18: 2395

[63] Yang G, Zhang Q, He C, Gong Z, Liu Z, Song J, Jiang S, Han J, Yang H, Li X, Pei Z, He S. Bionic hollow porous carbon nanofibers for energy-dense and rapid zinc ion storage. Angew Chem Int Ed, 2024, 64 e202421230

[64] Li F, Liu Yl, Wang GG, Zhang SY, Zhao DQ, Fang K, Zhang HY, Yang HY. 3D porous H-Ti₃C₂T_x films as free-standing electrodes for zinc ion hybrid capacitors. Chem Eng J, 2022, 435 135052

[65] Zheng Y, Zhao W, Jia D, Liu Y, Cui L, Wei D, Zheng R, Liu J. Porous carbon prepared via combustion and acid treatment as flexible zinc-ion capacitor electrode material. Chem Eng J, 2020, 387 124161

[66] He H, Lian J, Chen C, Xiong Q, Li CC, Zhang M. Enabling multi-chemisorption sites on carbon nanofibers cathodes by an in-situ exfoliation strategy for high-performance Zn–ion hybrid capacitors. Nano-Micro Lett, 2022, 14: 106

[67] Lin C, Zhang Y, Lieu WY, Xu Y, Li DS, Sliva A, Yang HY. Boosting zinc-ion storage capability in longitudinally aligned MXene arrays with microchannel architecture. Adv Funct Mater, 2025, 35 2413613

[68] Chen J, Chen M, Zhou W, Xu X, Liu B, Zhang W, Wong C. Simplified synthesis of fluoride-free Ti₃C₂T_x via electrochemical etching toward high-performance electrochemical capacitors. ACS Nano, 2022, 16: 2461

[69] Liu Y, Li B, Wang J, Li C, Yang H, Song Y, Zhang S, Deng C. Asymmetric Zn-N₄ atomic sites embedded hollow fibers as stable Zn anode for high-performance Zn-ion hybrid capacitor. J Energy Chem, 2024, 97: 460

Funding

Natural Science Foundation of Jiangsu Province(BK20241898)

RIGHTS & PERMISSIONS

Donghua University, Shanghai, China