Flexible Electrodes for Aqueous Hybrid Supercapacitors: Recent Advances and Future Prospects

Abstract

Flexible energy storage systems are promising and efficient technologies for realizing large-scale application of portable, bendable, and wearable electronic devices. Among these systems, aqueous hybrid supercapacitors (AHSs) fabricated using redox-active materials with a positive voltage window in aqueous electrolytes and capacitive carbon materials have attracted enormous attention due to their advantages, including a wide operating voltage, a high energy density, a high power density, a long cycling lifespan, and low cost. Thus far, considerable efforts have been made to develop flexible AHSs constructed from various free-standing and flexible electrodes. However, optimizing the configurations of flexible electrodes and the interfacial interaction between flexible substrates and electroactive materials to fully develop the performance through their synergistic effects remains a major challenge. Herein, we have reviewed and summarized recent advances in flexible electrode materials with a variety of configurations based on porous metal supports, carbon substrates, including carbon nanotube networks, graphene and wearable carbon (carbon fibers, carbon cloth, carbon fabric, etc.), and other flexible materials for high-performance AHSs. These flexible electrodes show unique configurations and optimized interfacial structures, resulting in excellent electrochemical performance and superior mechanical stability in AHSs under various harsh conditions, and have great potential for practical applications. Furthermore, the future directions and perspectives for constructing flexible electrodes with novel configurations and AHSs are outlined and discussed, including (1) fabrication of compressible, ultralight, or transparent flexible electrodes for special needs; (2) tailoring and tuning of interfacial properties with robust adhesion between electroactive materials and flexible substrates; (3) development of advanced in situ characterization techniques to uncover the structure evolution rules of flexible electrodes under the operation conditions; (4) matching and optimization of flexible positive and negative electrode materials to assemble advanced AHS devices; (5) design of multifunctional flexible electrodes and AHSs by integrating other specific functions, etc. This timely review is believed to provide deep insights into the intensive research on flexible aqueous energy storage devices.

Graphical Abstract

The recent advances in flexible electrodes with a variety of configurations based on porous metal supports, carbon substrates, and other flexible materials for advanced aqueous hybrid supercapacitors (AHSs) are summarized. The future prospects and directions for constructing flexible electrodes and AHSs are further outlined.

Keywords

Flexible substrates / Electrode configurations / Aqueous hybrid supercapacitors / Energy storage systems

References

[1] Armaroli N, Balzani V. Towards an electricity-powered world. Energy Environ. Sci., 2011, 4: 3193-3222

[2] Lewis NS. Research opportunities to advance solar energy utilization. Science, 2016, 351: eaad1920

[3] Olah GA. Towards oil independence through renewable methanol chemistry. Angew. Chem. Int. Ed., 2013, 52: 104-107

[4] Jean J, Brown PR, Jaffe RL, et al.. Pathways for solar photovoltaics. Energy Environ. Sci., 2015, 8: 1200-1219

[5] Goeppert A, Czaun M, Surya Prakash GK, et al.. Air as the renewable carbon source of the future: an overview of CO₂ capture from the atmosphere. Energy Environ. Sci., 2012, 5: 7833

[6] Kittner N, Lill F, Kammen DM. Energy storage deployment and innovation for the clean energy transition. Nat. Energy, 2017, 2: 17125

[7] Robu V, Flynn D. Outsmart supply dips in renewable energy. Nature, 2017, 544: 161

[8] Polman A, Atwater HA. Photonic design principles for ultrahigh-efficiency photovoltaics. Nat. Mater., 2012, 11: 174-177

[9] Muhich CL, Evanko BW, Weston KC, et al.. Efficient generation of H₂ by splitting water with an isothermal redox cycle. Science, 2013, 341: 540-542

[10] Miller JR, Simon P. Electrochemical capacitors for energy management. Science, 2008, 321: 651-652

[11] Sun YM, Liu N, Cui Y. Promises and challenges of nanomaterials for lithium-based rechargeable batteries. Nat. Energy, 2016, 1: 16071

[12] Ding J, Hu WB, Paek E, et al.. Review of hybrid ion capacitors: From aqueous to lithium to sodium. Chem. Rev., 2018, 118: 6457-6498

[13] Griffith KJ, Wiaderek KM, Cibin G, et al.. Niobium tungsten oxides for high-rate lithium-ion energy storage. Nature, 2018, 559: 556-563

[14] Huskinson B, Marshak MP, Suh C, et al.. A metal-free organic–inorganic aqueous flow battery. Nature, 2014, 505: 195-198

[15] Li NW, Yin YX, Xin S, et al.. Methods for the stabilization of nanostructured electrode materials for advanced rechargeable batteries. Small Methods, 2017, 1: 1700094

[16] Zhao SY, Fang RP, Sun ZH, et al.. A 3D multifunctional architecture for lithium–sulfur batteries with high areal capacity. Small Methods, 2018, 2: 1800067

[17] Li H, Liu FH, Fan BY, et al.. Nanostructured ferroelectric-polymer composites for capacitive energy storage. Small Methods, 2018, 2: 1700399

[18] Sun HT, Dunn BS, Huang Y, et al.. Three-dimensional holey-graphene/niobia composite architectures for ultrahigh-rate energy storage. Meet. Abstr., 2017

[19] Wang FX, Wu XW, Yuan XH, et al.. Latest advances in supercapacitors: From new electrode materials to novel device designs. Chem. Soc. Rev., 2017, 46: 6816-6854

[20] Wang YG, Song YF, Xia YY. Electrochemical capacitors: Mechanism, materials, systems, characterization and applications. Chem. Soc. Rev., 2016, 45: 5925-5950

[21] Xia Y, Mathis TS, Zhao MQ, et al.. Thickness-independent capacitance of vertically aligned liquid-crystalline MXenes. Nature, 2018, 557: 409-412

[22] Choudhary N, Li C, Moore J, et al.. Asymmetric supercapacitor electrodes and devices. Adv. Mater., 2017, 29: 1605336

[23] Huang YL, Zeng YX, Yu MH, et al.. Recent smart methods for achieving high-energy asymmetric supercapacitors. Small Methods, 2018, 2: 1700230

[24] Wen SY, Liu Y, Zhu FF, et al.. Hierarchical MoS₂ nanowires/NiCo₂O₄ nanosheets supported on Ni foam for high-performance asymmetric supercapacitors. Appl. Surf. Sci., 2018, 428: 616-622

[25] Zuo WH, Li RZ, Zhou C, et al.. Battery-supercapacitor hybrid devices: Recent progress and future prospects. Adv. Sci., 2017, 4(71600539

[26] Guan BY, Yu L, Wang X, et al.. Formation of onion-like NiCo₂S₄ particles via sequential ion-exchange for hybrid supercapacitors. Adv. Mater., 2017, 29: 1605051

[27] Zhao Y, Hu LF, Zhao SY, et al.. Preparation of MnCo₂O₄@Ni(OH)₂ core-shell flowers for asymmetric supercapacitor materials with ultrahigh specific capacitance. Adv. Funct. Mater., 2016, 26: 4085-4093

[28] Gu CJ, Liu ZH, Gao X, et al.. Polymerization increasing the capacitive charge storage for better rate performance: a case study of electrodes in aqueous sodium-ion capacitors. Battery Energy, 2022, 1 220031

[29] Boota M, Gogotsi Y. MXene—Conducting polymer asymmetric pseudocapacitors. Adv. Energy Mater., 2019, 9: 1802917

[30] Augustyn V, Simon P, Dunn B. Pseudocapacitive oxide materials for high-rate electrochemical energy storage. Energy Environ. Sci., 2014, 7: 1597-1614

[31] Sun JF, Wu C, Sun XF, et al.. Recent progresses in high-energy-density all pseudocapacitive-electrode-materials-based asymmetric supercapacitors. J. Mater. Chem. A, 2017, 5: 9443-9464

[32] Zhu SJ, Li L, Liu JB, et al.. Structural directed growth of ultrathin parallel birnessite on β-MnO₂ for high-performance asymmetric supercapacitors. ACS Nano, 2018, 12: 1033-1042

[33] Kim HS, Cook JB, Lin H, et al.. Oxygen vacancies enhance pseudocapacitive charge storage properties of MoO_3–X. Nat. Mater., 2017, 16: 454-460

[34] Yang J, Yu C, Fan XM, et al.. Electroactive edge site-enriched nickel–cobalt sulfide into graphene frameworks for high-performance asymmetric supercapacitors. Energy Environ. Sci., 2016, 9: 1299-1307

[35] Yilmaz G, Yam KM, Zhang C, et al.. In situ transformation of MOFs into layered double hydroxide embedded metal sulfides for improved electrocatalytic and supercapacitive performance. Adv. Mater., 2017, 29: 1606814

[36] Yu XY, Yu L, Shen LF, et al.. General formation of MS (M = Ni, Cu, Mn) box-in-box hollow structures with enhanced pseudocapacitive properties. Adv. Funct. Mater., 2014, 24: 7440-7446

[37] Lyu LL, Kim CW, Seong KD, et al.. Defect engineering induced heterostructure of Zn-birnessite@spinel ZnMn₂O₄ nanocrystal for flexible asymmetric supercapacitor. Chem. Eng. J., 2022, 430 133115

[38] Mohammadi Zardkhoshoui A, Ameri B, Saeed Hosseiny Davarani S. α-MnS@Co₃S₄ hollow nanospheres assembled from nanosheets for hybrid supercapacitors. Chem. Eng. J., 2021, 422 129953

[39] Zardkhoshoui AM, Davarani SSH. Construction of complex copper-cobalt selenide hollow structures as an attractive battery-type electrode material for hybrid supercapacitors. Chem. Eng. J., 2020, 402 126241

[40] Mohammadi Zardkhoshoui A, Ameri B, Hosseiny Davarani SS. A high-energy-density supercapacitor with multi-shelled nickel-manganese selenide hollow spheres as cathode and double-shell nickel-iron selenide hollow spheres as anode electrodes. Nanoscale, 2021, 13: 2931-2945

[41] Lu QJ, Zhou T, Zi BY, et al.. Dual supports by cation vacancies and surface optimization for CoNiSe₂-based hybrid supercapacitors with high energy density. ACS Energy Lett., 2023, 8: 3420-3429

[42] Li B, Gu P, Feng YC, et al.. Ultrathin nickel–cobalt phosphate 2D nanosheets for electrochemical energy storage under aqueous/solid-state electrolyte. Adv. Funct. Mater., 2017, 27: 1605784

[43] Zhai T, Wan LM, Sun S, et al.. Phosphate ion functionalized Co₃O₄ ultrathin nanosheets with greatly improved surface reactivity for high performance pseudocapacitors. Adv. Mater., 2017, 29: 1604167

[44] Liang HF, Alshareef HN. A plasma-assisted route to the rapid preparation of transition-metal phosphides for energy conversion and storage. Small Methods, 2017, 1: 1700111

[45] Liang HF, Xia C, Jiang Q, et al.. Low temperature synthesis of ternary metal phosphides using plasma for asymmetric supercapacitors. Nano Energy, 2017, 35: 331-340

[46] Li X, Wu HJ, Elshahawy AM, et al.. Cactus-like NiCoP/NiCo-OH 3D architecture with tunable composition for high-performance electrochemical capacitors. Adv. Funct. Mater., 2018, 28: 1800036

[47] Wu ZY, Jiang L, Tian WC, et al.. Novel sub-5 nm layered niobium phosphate nanosheets for high-voltage, cation-intercalation typed electrochemical energy storage in wearable pseudocapacitors. Adv. Energy Mater., 2019, 9: 1900111

[48] Song Y, Deng P, Qin ZM, et al.. A polyanionic molybdenophosphate anode for a 2.7 V aqueous pseudocapacitor. Nano Energy, 2019, 65: 104010

[49] Liu JQ, Zheng MB, Shi XQ, et al.. Amorphous FeOOH quantum dots assembled mesoporous film anchored on graphene nanosheets with superior electrochemical performance for supercapacitors. Adv. Funct. Mater., 2016, 26: 919-930

[50] Zhao BT, Zhang L, Zhang QB, et al.. Rational design of nickel hydroxide-based nanocrystals on graphene for ultrafast energy storage. Adv. Energy Mater., 2018, 8: 1702247

[51] Gao S, Sun YF, Lei FC, et al.. Ultrahigh energy density realized by a single-layer β-co(OH)₂ all-solid-state asymmetric supercapacitor. Angew. Chem. Int. Ed., 2014, 53: 12789-12793

[52] Yang J, Yu C, Fan XM, et al.. Facile fabrication of MWCNT-doped NiCoAl-layered double hydroxide nanosheets with enhanced electrochemical performances. J. Mater. Chem. A, 2013, 1: 1963-1968

[53] Yang J, Yu C, Hu C, et al.. Surface-confined fabrication of ultrathin nickel cobalt-layered double hydroxide nanosheets for high-performance supercapacitors. Adv. Funct. Mater., 2018, 28: 1803272

[54] Eftekhari A, Mohamedi M. Tailoring pseudocapacitive materials from a mechanistic perspective. Mater. Today Energy, 2017, 6: 211-229

[55] Xie YY, Yu C, Ni L, et al.. Carbon-hybridized hydroxides for energy conversion and storage: Interface chemistry and manufacturing. Adv. Mater., 2023, 35: 2209652

[56] Dong LB, Xu CJ, Li Y, et al.. Breathable and wearable energy storage based on highly flexible paper electrodes. Adv. Mater., 2016, 28: 9313-9319

[57] Dubal DP, Chodankar NR, Kim DH, et al.. Towards flexible solid-state supercapacitors for smart and wearable electronics. Chem. Soc. Rev., 2018, 47: 2065-2129

[58] Kim BC, Hong JY, Wallace GG, et al.. Recent progress in flexible electrochemical capacitors: Electrode materials, device configuration, and functions. Adv. Energy Mater., 2015, 5: 1500959

[59] Liu W, Song MS, Kong B, et al.. Flexible and stretchable energy storage: Recent advances and future perspectives. Adv. Mater., 2017, 29: 1603436

[60] Shao YL, El-Kady MF, Wang LJ, et al.. Graphene-based materials for flexible supercapacitors. Chem. Soc. Rev., 2015, 44: 3639-3665

[61] Yang PH, Mai WJ. Flexible solid-state electrochemical supercapacitors. Nano Energy, 2014, 8: 274-290

[62] Zhao ZY, Xia KQ, Hou Y, et al.. Designing flexible, smart and self-sustainable supercapacitors for portable/wearable electronics: From conductive polymers. Chem. Soc. Rev., 2021, 50: 12702-12743

[63] Yan J, Liu T, Liu XD, et al.. Metal-organic framework-based materials for flexible supercapacitor application. Coord. Chem. Rev., 2022, 452 214300

[64] Gao HC, Xiao F, Ching CB, et al.. Flexible all-solid-state asymmetric supercapacitors based on free-standing carbon nanotube/graphene and Mn₃O₄ nanoparticle/graphene paper electrodes. ACS Appl. Mater. Interfaces, 2012, 4: 7020-7026

[65] Zhang QC, Wang XN, Pan ZH, et al.. Wrapping aligned carbon nanotube composite sheets around vanadium nitride nanowire arrays for asymmetric coaxial fiber-shaped supercapacitors with ultrahigh energy density. Nano Lett., 2017, 17: 2719-2726

[66] Yu XZ, Lu BG, Xu Z. Super long-life supercapacitors based on the construction of nanohoneycomb-like strongly coupled CoMoO₄–3D graphene hybrid electrodes. Adv. Mater., 2014, 26: 1044-1051

[67] Liao QY, Li N, Jin SX, et al.. All-solid-state symmetric supercapacitor based on Co₃O₄ nanoparticles on vertically aligned graphene. ACS Nano, 2015, 9: 5310-5317

[68] Zhang YZ, Wang Y, Cheng T, et al.. Flexible supercapacitors based on paper substrates: A new paradigm for low-cost energy storage. Chem. Soc. Rev., 2015, 44: 5181-5199

[69] Ambade RB, Lee H, Lee KH, et al.. Ultrafast flashlight sintered mesoporous NiO nanosheets for stable asymmetric supercapacitors. Chem. Eng. J., 2022, 436 135041

[70] Wang JY, Dou W, Zhang XT, et al.. Embedded Ag quantum dots into interconnected Co₃O₄ nanosheets grown on 3D graphene networks for high stable and flexible supercapacitors. Electrochim. Acta, 2017, 224: 260-268

[71] Wang LB, Yang HL, Liu XX, et al.. Constructing hierarchical tectorum-like α-Fe₂O₃/PPy nanoarrays on carbon cloth for solid-state asymmetric supercapacitors. Angew. Chem. Int. Ed., 2017, 56: 1105-1110

[72] Xu L, Shi RY, Li HF, et al.. Pseudocapacitive anthraquinone modified with reduced graphene oxide for flexible symmetric all-solid-state supercapacitors. Carbon, 2018, 127: 459-468

[73] Liu WH, Wang ZQ, Su YL, et al.. Molecularly stacking manganese dioxide/titanium carbide sheets to produce highly flexible and conductive film electrodes with improved pseudocapacitive performances. Adv. Energy Mater., 2017, 7: 1602834

[74] Pan ZH, Liu MN, Yang J, et al.. High electroactive material loading on a carbon Nanotube@3D graphene aerogel for high-performance flexible all-solid-state asymmetric supercapacitors. Adv. Funct. Mater., 2017, 27: 1701122

[75] Van Lam D, Shim HC, Kim JH, et al.. Carbon textile decorated with pseudocapacitive VC/V_xO_y for high-performance flexible supercapacitors. Small, 2017, 13: 1702702

[76] Cao LJ, Tang G, Mei J, et al.. Construct hierarchical electrode with Ni_xCo_3-xS₄ nanosheet coated on NiCo₂O₄ nanowire arrays grown on carbon fiber paper for high-performance asymmetric supercapacitors. J. Power Sources, 2017, 359: 262-269

[77] Foo CY, Sumboja A, Tan DJH, et al.. Flexible and highly scalable V₂O₅-rGO electrodes in an organic electrolyte for supercapacitor devices. Adv. Energy Mater., 2014, 4: 1400236

[78] Liao LP, Jiang DG, Zheng K, et al.. Industry-scale and environmentally stable Ti₃C₂T_x MXene based film for flexible energy storage devices. Adv. Funct. Mater., 2021, 31: 2103960

[79] Kumar Das A, Ramulu B, Girija Shankar E, et al.. Binder-free CuS@PEDOT and Co–V–Se electrodes for flexible quasi-solid-state asymmetric supercapacitor. Chem. Eng. J., 2022, 429 132486

[80] Peng HJ, Huang JQ, Zhang Q. A review of flexible lithium–sulfur and analogous alkali metal–chalcogen rechargeable batteries. Chem. Soc. Rev., 2017, 46: 5237-5288

[81] Chen H, Hu LF, Yan Y, et al.. One-step fabrication of ultrathin porous nickel hydroxide-manganese dioxide hybrid nanosheets for supercapacitor electrodes with excellent capacitive performance. Adv. Energy Mater., 2013, 3: 1636-1646

[82] Nagaraju G, Sekhar SC, Yu JS. Utilizing waste cable wires for high-performance fiber-based hybrid supercapacitors: An effective approach to electronic-waste management. Adv. Energy Mater., 2018, 8: 1702201

[83] Wang N, Sun BL, Zhao P, et al.. Electrodeposition preparation of NiCo₂O₄ mesoporous film on ultrafine nickel wire for flexible asymmetric supercapacitors. Chem. Eng. J., 2018, 345: 31-38

[84] Wang QF, Ma Y, Wu YL, et al.. Flexible asymmetric threadlike supercapacitors based on NiCo2Se4 nanosheet and NiCo₂O₄/polypyrrole electrodes. Chemsuschem, 2017, 10: 1427-1435

[85] Xu SS, Su C, Wang T, et al.. One-step electrodeposition of nickel cobalt sulfide nanosheets on Ni nanowire film for hybrid supercapacitor. Electrochim. Acta, 2018, 259: 617-625

[86] Ke X, Zhang ZX, Cheng YF, et al.. Ni(OH)₂ nanoflakes supported on 3D hierarchically nanoporous gold/Ni foam as superior electrodes for supercapacitors. Sci. China Mater., 2018, 61: 353-362

[87] Hao ZB, He XC, Li HD, et al.. Vertically aligned and ordered arrays of 2D MCo₂S₄@Metal with ultrafast ion/electron transport for thickness-independent pseudocapacitive energy storage. ACS Nano, 2020, 14: 12719-12731

[88] Huang M, Zhang YX, Li F, et al.. Facile synthesis of hierarchical Co₃O₄@MnO₂ core–shell arrays on Ni foam for asymmetric supercapacitors. J. Power Sources, 2014, 252: 98-106

[89] Wang QF, Wang XF, Xu J, et al.. Flexible coaxial-type fiber supercapacitor based on NiCo₂O₄ nanosheets electrodes. Nano Energy, 2014, 8: 44-51

[90] Peng SJ, Li LL, Wu HB, et al.. Controlled growth of NiMoO₄ nanosheet and nanorod arrays on various conductive substrates as advanced electrodes for asymmetric supercapacitors. Adv. Energy Mater., 2015, 5: 1401172

[91] Xu JS, Sun YD, Lu MJ, et al.. Fabrication of hierarchical MnMoO₄·H₂O@MnO₂ core-shell nanosheet arrays on nickel foam as an advanced electrode for asymmetric supercapacitors. Chem. Eng. J., 2018, 334: 1466-1476

[92] Guo W, Yu C, Li SF, et al.. High-stacking-density, superior-roughness LDH bridged with vertically aligned graphene for high-performance asymmetric supercapacitors. Small, 2017, 13: 1701288

[93] Chen HC, Jiang JJ, Zhang L, et al.. In situ growth of NiCo₂S₄ nanotube arrays on Ni foam for supercapacitors: Maximizing utilization efficiency at high mass loading to achieve ultrahigh areal pseudocapacitance. J. Power Sources, 2014, 254: 249-257

[94] Hu W, Chen RQ, Xie W, et al.. CoNi₂S₄ nanosheet arrays supported on nickel foams with ultrahigh capacitance for aqueous asymmetric supercapacitor applications. ACS Appl. Mater. Interfaces, 2014, 6: 19318-19326

[95] Kong W, Lu CC, Zhang W, et al.. Homogeneous core–shell NiCo₂S₄ nanostructures supported on nickel foam for supercapacitors. J. Mater. Chem. A, 2015, 3: 12452-12460

[96] Yan ML, Yao YD, Wen JQ, et al.. Construction of a hierarchical NiCo₂S₄@PPy core–shell heterostructure nanotube array on Ni foam for a high-performance asymmetric supercapacitor. ACS Appl. Mater. Interfaces, 2016, 8: 24525-24535

[97] Zhou C, Zhang YW, Li YY, et al.. Construction of high-capacitance 3D CoO@Polypyrrole nanowire array electrode for aqueous asymmetric supercapacitor. Nano Lett., 2013, 13: 2078-2085

[98] He WD, Wang CG, Li HQ, et al.. Ultrathin and porous Ni3S2/CoNi2S4 3D-network structure for superhigh energy density asymmetric supercapacitors. Adv. Energy Mater., 2017, 7: 1700983

[99] Martínez-Periñán E, Down MP, Gibaja C, et al.. Antimonene: A novel 2D nanomaterial for supercapacitor applications. Adv. Energy Mater., 2018, 8: 1702606

[100] Yu JL, Zhou J, Yao PP, et al.. Antimonene engineered highly deformable freestanding electrode with extraordinarily improved energy storage performance. Adv. Energy Mater., 2019, 9: 1902462

[101] Bizuneh GG, Adam AMM, Ma JM. Progress on carbon for electrochemical capacitors. Battery Energy, 2023, 2: 20220021

[102] Chen PC, Shen GZ, Shi Y, et al.. Preparation and characterization of flexible asymmetric supercapacitors based on transition-metal-oxide nanowire/single-walled carbon nanotube hybrid thin-film electrodes. ACS Nano, 2010, 4: 4403-4411

[103] Chen HY, Zeng S, Chen MH, et al.. Oxygen evolution assisted fabrication of highly loaded carbon nanotube/MnO₂ hybrid films for high-performance flexible pseudosupercapacitors. Small, 2016, 12: 2035-2045

[104] Yu JL, Lu WB, Smith JP, et al.. A high performance stretchable asymmetric fiber-shaped supercapacitor with a core-sheath helical structure. Adv. Energy Mater., 2017, 7: 1600976

[105] Lee TH, Pham DT, Sahoo R, et al.. High energy density and enhanced stability of asymmetric supercapacitors with mesoporous MnO₂@CNT and nanodot MoO₃@CNT free-standing films. Energy Storage Mater., 2018, 12: 223-231

[106] Peng HN, Qian GJ, Li N, et al.. Flexible asymmetric supercapacitors with ultrahigh energy density through synergistic design of electrodes. Adv. Sci., 2018, 5: 1800784

[107] Pan ZH, Yang CH, Li Y, et al.. Rational design of A-CNTs/K_xMnO₂ and Ti₃C₂T_x/MoO₃ free-standing hybrid films for flexible asymmetric supercapacitor. Chem. Eng. J., 2022, 428 131138

[108] Wu P, Cheng S, Yao MH, et al.. A low-cost, self-standing NiCo₂O₄@CNT/CNT multilayer electrode for flexible asymmetric solid-state supercapacitors. Adv. Funct. Mater., 2017, 27: 1702160

[109] Xiao X, Peng X, Jin HY, et al.. Freestanding mesoporous VN/CNT hybrid electrodes for flexible all-solid-state supercapacitors. Adv. Mater., 2013, 25: 5091-5097

[110] Chen Z, Augustyn V, Jia XL, et al.. High-performance sodium-ion pseudocapacitors based on hierarchically porous nanowire composites. ACS Nano, 2012, 6: 4319-4327

[111] Wu JB, Gao X, Yu HM, et al.. A scalable free-standing V2O5/CNT film electrode for supercapacitors with a wide operation voltage (1.6 V) in an aqueous electrolyte. Adv. Funct. Mater., 2016, 26: 6114-6120

[112] Chen Z, Augustyn V, Wen J, et al.. High-performance supercapacitors based on intertwined CNT/V₂O₅ nanowire nanocomposites. Adv. Mater., 2011, 23: 791-795

[113] Guo K, Li YJ, Li C, et al.. Compact self-standing layered film assembled by V₂O₅·nH₂O/CNTs 2D/1D composites for high volumetric capacitance flexible supercapacitors. Sci. China Mater., 2019, 62: 936-946

[114] Zhang QC, Xu WW, Sun J, et al.. Constructing ultrahigh-capacity zinc–nickel–cobalt Oxide@Ni(OH)₂ core–shell nanowire arrays for high-performance coaxial fiber-shaped asymmetric supercapacitors. Nano Lett., 2017, 17: 7552-7560

[115] Zhao JW, Chen JL, Xu SM, et al.. Hierarchical NiMn layered double hydroxide/carbon nanotubes architecture with superb energy density for flexible supercapacitors. Adv. Funct. Mater., 2014, 24: 2938-2946

[116] Wang CL, Qu HL, Peng T, et al.. Large scale α-Co(OH)₂ needle arrays grown on carbon nanotube foams as free standing electrodes for supercapacitors. Electrochim. Acta, 2016, 191: 133-141

[117] Peng TQ, Wang HW, Yi H, et al.. Co(OH)₂ nanosheets coupled with CNT arrays grown on Ni mesh for high-rate asymmetric supercapacitors with excellent capacitive behavior. Electrochim. Acta, 2015, 176: 77-85

[118] Li M, Ma KY, Cheng JP, et al.. Nickel–cobalt hydroxide nanoflakes conformal coating on carbon nanotubes as a supercapacitive material with high-rate capability. J. Power Sources, 2015, 286: 438-444

[119] Zhang QC, Sun J, Pan ZH, et al.. Stretchable fiber-shaped asymmetric supercapacitors with ultrahigh energy density. Nano Energy, 2017, 39: 219-228

[120] Pan ZH, Zhong J, Zhang QC, et al.. Ultrafast all-solid-state coaxial asymmetric fiber supercapacitors with a high volumetric energy density. Adv. Energy Mater., 2018, 8: 1702946

[121] Zhou Y, Wang XX, Acauan L, et al.. Ultrahigh-areal-capacitance flexible supercapacitor electrodes enabled by conformal P3MT on horizontally aligned carbon-nanotube arrays. Adv. Mater., 2019, 31: 1901916

[122] Sumboja A, Foo CY, Wang X, et al.. Large areal mass, flexible and free-standing reduced graphene oxide/manganese dioxide paper for asymmetric supercapacitor device. Adv. Mater., 2013, 25: 2809-2815

[123] Sun GZ, Zhang X, Lin RZ, et al.. Hybrid fibers made of molybdenum disulfide, reduced graphene oxide, and multi-walled carbon nanotubes for solid-state, flexible, asymmetric supercapacitors. Angew. Chem. Int. Ed., 2015, 54: 4651-4656

[124] Patil SJ, Kim JH, Lee DW. Graphene-nanosheet wrapped cobalt sulphide as a binder free hybrid electrode for asymmetric solid-state supercapacitor. J. Power Sources, 2017, 342: 652-665

[125] Zhang C, Huang Y, Tang SL, et al.. High-energy all-solid-state symmetric supercapacitor based on Ni₃S₂ mesoporous nanosheet-decorated three-dimensional reduced graphene oxide. ACS Energy Lett., 2017, 2: 759-768

[126] Ji JY, Zhang LL, Ji HX, et al.. Nanoporous Ni(OH)₂ thin film on 3D ultrathin-graphite foam for asymmetric supercapacitor. ACS Nano, 2013, 7: 6237-6243

[127] Xiong GP, He PG, Wang DN, et al.. Hierarchical Ni–co hydroxide petals on mechanically robust graphene petal foam for high-energy asymmetric supercapacitors. Adv. Funct. Mater., 2016, 26: 5460-5470

[128] Zhang ZY, Xiao F, Qian LH, et al.. Facile synthesis of 3D MnO₂–graphene and carbon nanotube–graphene composite networks for high-performance, flexible, all-solid-state asymmetric supercapacitors. Adv. Energy Mater., 2014, 4: 1400064

[129] Sun GZ, Liu JQ, Zhang X, et al.. Fabrication of ultralong hybrid microfibers from nanosheets of reduced graphene oxide and transition-metal dichalcogenides and their application as supercapacitors. Angew. Chem., 2014, 126: 12784-12788

[130] Wang RH, Xu CH, Lee JM. High performance asymmetric supercapacitors: New NiOOH nanosheet/graphene hydrogels and pure graphene hydrogels. Nano Energy, 2016, 19: 210-221

[131] Ma WJ, Chen SH, Yang SY, et al.. Hierarchical MnO₂ nanowire/graphene hybrid fibers with excellent electrochemical performance for flexible solid-state supercapacitors. J. Power Sources, 2016, 306: 481-488

[132] Tang JY, Yuan P, Cai CL, et al.. Combining nature-inspired, graphene-wrapped flexible electrodes with nanocomposite polymer electrolyte for asymmetric capacitive energy storage. Adv. Energy Mater., 2016, 6: 1600813

[133] Gao Z, Yang WL, Wang J, et al.. Flexible all-solid-state hierarchical NiCo₂O₄/porous graphene paper asymmetric supercapacitors with an exceptional combination of electrochemical properties. Nano Energy, 2015, 13: 306-317

[134] Xiong DB, Li XF, Bai ZM, et al.. Rational design of hybrid Co₃O₄/graphene films: Free-standing flexible electrodes for high performance supercapacitors. Electrochim. Acta, 2018, 259: 338-347

[135] Ghosh D, Lim J, Narayan R, et al.. High energy density all solid state asymmetric pseudocapacitors based on free standing reduced graphene oxide-Co₃O₄ composite aerogel electrodes. ACS Appl. Mater. Interfaces, 2016, 8: 22253-22260

[136] Chen ZY, Yang YR, Ma ZH, et al.. All-solid-state asymmetric supercapacitors with metal selenides electrodes and ionic conductive composites electrolytes. Adv. Funct. Mater., 2019, 29: 1904182

[137] Ma WJ, Chen SH, Yang SY, et al.. Flexible all-solid-state asymmetric supercapacitor based on transition metal oxide nanorods/reduced graphene oxide hybrid fibers with high energy density. Carbon, 2017, 113: 151-158

[138] Yu DS, Goh K, Zhang Q, et al.. Controlled functionalization of carbonaceous fibers for asymmetric solid-state micro-supercapacitors with high volumetric energy density. Adv. Mater., 2014, 26: 6790-6797

[139] Yang J, Yu C, Fan XM, et al.. Ultrafast self-assembly of graphene oxide-induced monolithic NiCo–carbonate hydroxide nanowire architectures with a superior volumetric capacitance for supercapacitors. Adv. Funct. Mater., 2015, 25: 2109-2116

[140] Wang XY, Wan F, Zhang LL, et al.. Large-area reduced graphene oxide composite films for flexible asymmetric sandwich and microsized supercapacitors. Adv. Funct. Mater., 2018, 28: 1707247

[141] Xiong DB, Li XF, Bai ZM, et al.. Vertically aligned Co9S8 nanotube arrays onto graphene papers as high-performance flexible electrodes for supercapacitors. Chem. Eur. J., 2018, 24: 2339-2343

[142] Qin KQ, Liu EZ, Li JJ, et al.. Free-standing 3D nanoporous duct-like and hierarchical nanoporous graphene films for micron-level flexible solid-state asymmetric supercapacitors. Adv. Energy Mater., 2016, 6: 1600755

[143] Zhang CY, Cai XY, Qian Y, et al.. Electrochemically synthesis of nickel cobalt sulfide for high-performance flexible asymmetric supercapacitors. Adv. Sci., 2018, 5: 1700375

[144] Liu JL, Zhang LL, Wu HB, et al.. High-performance flexible asymmetric supercapacitors based on a new graphene foam/carbon nanotube hybrid film. Energy Environ. Sci., 2014, 7: 3709-3719

[145] Xiao X, Ding TP, Yuan LY, et al.. WO_3−x/MoO_3−x core/shell nanowires on carbon fabric as an anode for all-solid-state asymmetric supercapacitors. Adv. Energy Mater., 2012, 2: 1328-1332

[146] Shen LF, Che Q, Li HS, et al.. Mesoporous NiCo₂O₄ nanowire arrays grown on carbon textiles as binder-free flexible electrodes for energy storage. Adv. Funct. Mater., 2014, 24: 2630-2637

[147] Jabeen N, Hussain A, Xia QY, et al.. High-performance 2.6 V aqueous asymmetric supercapacitors based on in situ formed Na_0.5MnO₂ nanosheet assembled nanowall arrays. Adv. Mater., 2017, 29: 1700804

[148] Yang PH, Ding Y, Lin ZY, et al.. Low-cost high-performance solid-state asymmetric supercapacitors based on MnO₂ nanowires and Fe₂O₃ nanotubes. Nano Lett., 2014, 14: 731-736

[149] Wang YM, Wang X, Li XF, et al.. A high-performance, tailorable, wearable, and foldable solid-state supercapacitor enabled by arranging pseudocapacitive groups and MXene flakes on textile electrode surface. Adv. Funct. Mater., 2021, 31: 2008185

[150] Xu J, Wang QF, Wang XW, et al.. Flexible asymmetric supercapacitors based upon Co₉S₈ nanorod// Co₃O₄@RuO₂ nanosheet arrays on carbon cloth. ACS Nano, 2013, 7: 5453-5462

[151] Zhou X, Chen Q, Wang AQ, et al.. Bamboo-like composites of V₂O₅/polyindole and activated carbon cloth as electrodes for all-solid-state flexible asymmetric supercapacitors. ACS Appl. Mater. Interfaces, 2016, 8: 3776-3783

[152] Lu XH, Yu MH, Wang GM, et al.. H-TiO₂@MnO₂// H-TiO₂@C core–shell nanowires for high performance and flexible asymmetric supercapacitors. Adv. Mater., 2013, 25: 267-272

[153] Li KZ, Zhao BC, Zhang H, et al.. 3D porous honeycomb-like CoN-Ni3N/N-C nanosheets integrated electrode for high-energy-density flexible supercapacitor. Adv. Funct. Mater., 2021, 31: 2103073

[154] Li H, Lin S, Li H, et al.. Magneto-electrodeposition of 3D cross-linked NiCo-LDH for flexible high-performance supercapacitors. Small Methods, 2022, 6: 2101320

[155] Gao LB, Surjadi JU, Cao K, et al.. Flexible fiber-shaped supercapacitor based on nickel–cobalt double hydroxide and pen ink electrodes on metallized carbon fiber. ACS Appl. Mater. Interfaces, 2017, 9: 5409-5418

[156] Ke QQ, Guan C, Zhang X, et al.. Surface-charge-mediated formation of H-TiO₂@Ni(OH)₂ heterostructures for high-performance supercapacitors. Adv. Mater., 2017, 29: 1604164

[157] Noh J, Yoon CM, Kim YK, et al.. High performance asymmetric supercapacitor twisted from carbon fiber/MnO₂ and carbon fiber/MoO₃. Carbon, 2017, 116: 470-478

[158] Li LL, Peng SJ, Wu HB, et al.. A flexible quasi-solid-state asymmetric electrochemical capacitor based on hierarchical porous V₂O₅ nanosheets on carbon nanofibers. Adv. Energy Mater., 2015, 5: 1500753

[159] Yang Y, Wang H, Hao R, et al.. Transition-metal-free biomolecule-based flexible asymmetric supercapacitors. Small, 2016, 12: 4683-4689

[160] Liu SD, Kang L, Hu JS, et al.. Realizing superior redox kinetics of hollow bimetallic sulfide nanoarchitectures by defect-induced manipulation toward flexible solid-state supercapacitors. Small, 2022, 18: 2104507

[161] Liu Y, Fu NQ, Zhang GG, et al.. Design of hierarchical NiCo@NiCo layered double hydroxide core–shell structured nanotube array for high-performance flexible all-solid-state battery-type supercapacitors. Adv. Funct. Mater., 2017, 27: 1605307

[162] Liu SD, Kang L, Hu JS, et al.. Unlocking the potential of oxygen-deficient copper-doped Co₃O₄ nanocrystals confined in carbon as an advanced electrode for flexible solid-state supercapacitors. ACS Energy Lett., 2021, 6: 3011-3019

[163] Li SF, Yu C, Yang J, et al.. A superhydrophilic “nanoglue” for stabilizing metal hydroxides onto carbon materials for high-energy and ultralong-life asymmetric supercapacitors. Energy Environ. Sci., 2017, 10: 1958-1965

[164] Yu N, Yin H, Zhang W, et al.. High-performance fiber-shaped all-solid-state asymmetric supercapacitors based on ultrathin MnO₂ nanosheet/carbon fiber cathodes for wearable electronics. Adv. Energy Mater., 2016, 6: 1501458

[165] Li HB, Yu MH, Wang FX, et al.. Amorphous nickel hydroxide nanospheres with ultrahigh capacitance and energy density as electrochemical pseudocapacitor materials. Nat. Commun., 2013, 4: 1894

[166] Liu N, Su YL, Wang ZQ, et al.. Electrostatic-interaction-assisted construction of 3D networks of manganese dioxide nanosheets for flexible high-performance solid-state asymmetric supercapacitors. ACS Nano, 2017, 11: 7879-7888

[167] Shen LF, Wang J, Xu GY, et al.. NiCo₂S₄ nanosheets grown on nitrogen-doped carbon foams as an advanced electrode for supercapacitors. Adv. Energy Mater., 2015, 5: 1400977

[168] Yang J, Yu C, Fan XM, et al.. 3D architecture materials made of NiCoAl-LDH nanoplates coupled with NiCo-carbonate hydroxide nanowires grown on flexible graphite paper for asymmetric supercapacitors. Adv. Energy Mater., 2014, 4: 1400761

[169] Liao YZ, Wang HG, Zhu MF, et al.. Efficient supercapacitor energy storage using conjugated microporous polymer networks synthesized from buchwald–hartwig coupling. Adv. Mater., 2018, 30: 1705710

[170] Feng JX, Ye SH, Wang AL, et al.. Flexible cellulose paper-based asymmetrical thin film supercapacitors with high-performance for electrochemical energy storage. Adv. Funct. Mater., 2014, 24: 7093-7101

[171] Zhang LC, Zhu PL, Zhou FR, et al.. Flexible asymmetrical solid-state supercapacitors based on laboratory filter paper. ACS Nano, 2016, 10: 1273-1282

[172] Kurra N, Wang RQ, Alshareef HN. All conducting polymer electrodes for asymmetric solid-state supercapacitors. J. Mater. Chem. A, 2015, 3: 7368-7374

[173] Moon IK, Yoon S, Oh J. 3D highly conductive silver Nanowire@PEDOT: PSS composite sponges for flexible conductors and their all-solid-state supercapacitor applications. Adv. Mater. Interfaces, 2017, 4: 1700860

[174] Liu T, Yan RY, Huang HJ, et al.. A micromolding method for transparent and flexible thin-film supercapacitors and hybrid supercapacitors. Adv. Funct. Mater., 2020, 30: 2004410

[175] Zhu J, Tang SC, Wu J, et al.. Wearable high-performance supercapacitors based on silver-sputtered textiles with FeCo2S4–NiCo2S4 composite nanotube-built multitripod architectures as advanced flexible electrodes. Adv. Energy Mater., 2017, 7: 1601234

[176] Guo YT, Li WS, Yu HT, et al.. Flexible asymmetric supercapacitors via spray coating of a new electrochromic donor–acceptor polymer. Adv. Energy Mater., 2017, 7: 1601623

[177] Vaghasiya JV, Mayorga-Martinez CC, Vyskočil J, et al.. Integrated biomonitoring sensing with wearable asymmetric supercapacitors based on Ti3C2 MXene and 1T-phase WS₂ nanosheets. Adv. Funct. Mater., 2020, 30: 2003673

[178] Niu ZQ, Zhou WY, Chen XD, et al.. Highly compressible and all-solid-state supercapacitors based on nanostructured composite sponge. Adv. Mater., 2015, 27: 6002-6008

[179] Lv ZS, Luo YF, Tang YX, et al.. Editable supercapacitors with customizable stretchability based on mechanically strengthened ultralong MnO₂ nanowire composite. Adv. Mater., 2018, 30: 1704531

[180] Li WW, Gao FX, Wang XQ, et al.. Strong and robust polyaniline-based supramolecular hydrogels for flexible supercapacitors. Angew. Chem. Int. Ed., 2016, 55: 9196-9201

[181] Yang W, Zhang CX, Jiang B, et al.. Electrochemical activation induced phase and structure reconstruction to reveal cobalt sulfide intrinsic energy storage capacity. Chem. Eng. J., 2022, 434 134473

[182] Wang M, Yang J, Liu SY, et al.. Dual hybrid effect endowing nickel–cobalt sulfides with enhanced cycling stability for asymmetrical supercapacitors. ACS Appl. Energy Mater., 2020, 3: 6977-6984

[183] Jiang Q, Kurra N, Alhabeb M, et al.. All pseudocapacitive MXene-RuO₂ asymmetric supercapacitors. Adv. Energy Mater., 2018, 8: 1703043

[184] Qu GM, Wang ZH, Zhang XX, et al.. Designing flexible asymmetric supercapacitor with high energy density by electrode engineering and charge matching mechanism. Chem. Eng. J., 2022, 429 132406

[185] Zhang HX, Du MY, Xing XX, et al.. An azo-based electrode for all-around high-performance flexible supercapacitors. Small Sci., 2023, 3: 2200101

[186] Paul N, Suresh L, Seo J, et al.. Electrohydrodynamically printed solid-state Photo-electro protein micro-capacitors. Energy Storage Mater., 2023, 61 102839

[187] Aivali S, Beaumont C, Leclerc M. Conducting polymers: Towards printable transparent electrodes. Prog. Polym. Sci., 2024, 148 101766

[188] Park Y, Cho K, Kim S. Vertical all-in-one energy systems constructed with thermoelectric generators and microsupercapacitors. J. Power Sources, 2021, 510 230402

[189] Luo SH, Lian EK, He JL, et al.. Flexible transparent electrodes formed from template-patterned thin-film silver. Adv. Mater., 2023, 36 2300058

[190] Bai YH, Li WZ, Tie Y, et al.. A stretchable polymer conductor through the mutual plasticization effect. Adv. Mater., 2023, 35: 2303245

[191] Sui CX, Pu JK, Chen TH, et al.. Dynamic electrochromism for all-season radiative thermoregulation. Nat. Sustain., 2023, 6: 428-437

[192] Guo W, Dun CC, Marcus MA, et al.. The emerging layered hydroxide plates with record thickness for enhanced high-mass-loading energy storage. Adv. Mater., 2023, 35: 2211603

[193] Zhu YL, Li W, Zhang L, et al.. Electrode/electrolyte interphases in high-temperature batteries: A review. Energy Environ. Sci., 2023, 16: 2825-2855

Funding

National Natural Science Foundation of China(22278328)

RIGHTS & PERMISSIONS

Shanghai University and Periodicals Agency of Shanghai University