Abstract
The integration of mechanically resilient conducting polymers into zinc- and alkali-ion hybrid capacitors has attracted attention for sustainable, flexible, high-performance, energy storage systems. By exhibiting mixed ionic–electronic conductivity, controllable ion-polymer interactions, electric double-layer, pseudocapacitive, and battery-type behavior, conducting polymers can perform multifunctional roles in both cathodes and anodes, and are capable of supporting all three charge storage mechanisms. As cathodes, conducting polymers provide redox activity and enable versatile integration with carbon or metal oxide hybrids, enhancing both capacity and rate performance. As anodes, conducting polymers serve as ion-selective, conformal coatings that mitigate dendritic growth, buffer structural stress, and stabilize solid–electrolyte interphases. Recent developments in three-dimensional nanostructuring, ion-selective frameworks, and elastomeric composites for wearable applications, along with AI-guided materials discovery and sustainable materials integration, have established conducting polymers as indispensable building blocks for safe, sustainable, and high-performance hybrid capacitors for powering the next generation of electronics and energy storage systems.
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Introduction
Conventional supercapacitors offer excellent power performance, but are limited in terms of energy density. Conversely, batteries excel in energy storage but often suffer from slow charge–discharge rates and limited cycle life. To address these trade-offs, hybrid capacitors (HCs) have emerged as a promising class of energy storage devices that are capable of synergistically combining the advantages of both battery and supercapacitor systems. The HCs are typically constructed in an asymmetric configuration, wherein the anode behaves as a battery-type electrode that supports faradaic redox reactions such as metal plating/stripping (e.g., Zn²⁺ ⇌ Zn⁰), while the cathode functions as a capacitive or pseudocapacitive electrode that can store charge via ion adsorption or surface redox reactions. This structural and functional asymmetry allows the HC to operate via a dual charge storage mechanism, including high-capacity faradaic storage at the anode and fast, reversible non-faradaic or pseudocapacitive storage at the cathode. The integration of these two fundamentally distinct mechanisms enables the HC to achieve both high energy and high power capabilities within a single device architecture.
Among the various HC chemistries, systems based on zinc (Zn²⁺) ions or alkali metal ions such as sodium (Na⁺) or potassium (K⁺) have received increasing attention due to their inherent beneficial characteristics. In particular, Zn is attractive due to its abundance, low cost, and environmental benignity, along with its ability to undergo two-electron redox reactions, thereby offering a high theoretical capacity. Additionally, Zn-based devices can operate in aqueous electrolytes, thereby enhancing their safety and affordability compared to organic lithium-based systems. Similarly, due to their earth-abundance and electrochemical activity, Na⁺ and K⁺ ions present promising alternatives to lithium in hybrid configurations, particularly for large-scale and cost-sensitive applications such as grid storage.
Despite their advantages, Zn and alkali metal-ion HCs continue to face several critical challenges. In Zn-based systems, dendritic growth during plating and stripping, side reactions with aqueous electrolytes, and surface passivation lead to poor reversibility and limited cycling stability. In Na⁺ and K⁺ systems, the larger ionic radii result in sluggish ion kinetics and structural degradation during repeated insertion and extraction, often causing severe volume fluctuations and reduced durability. Addressing these issues requires the development of advanced materials and engineered interfaces that facilitate ion transport, accommodate mechanical strain, and provide enhanced electrochemical stability. In this respect, conducting polymers (CPs) such as polyaniline and polypyrrole have demonstrated significant potential, which makes them promising candidate components for next-generation HC design.
The CPs are a class of organic materials characterized by conjugated π-electron backbones that exhibit intrinsic electrical conductivity upon appropriate chemical or electrochemical doping1. Their unique combination of mixed ionic and electronic conductivity, redox activity, and structural flexibility makes them highly attractive for emerging electrochemical energy storage systems2,3. Representative CPs such as polyaniline (PANI), polypyrrole (PPy), polythiophene, and derivatives such as poly(3,4-ethylenedioxythiophene) (PEDOT) (Fig. 1a) offer distinct advantages in terms of electrical/electrochemical performance, environmental stability, and processability. Several intrinsic properties support the integration of CPs into HC architectures. Firstly, CPs conduct both electrons (via π-conjugated backbones) and ions (via doped/redox sites) (Fig. 1b and c), thereby minimizing interfacial resistance and facilitating rapid charge/discharge kinetics1,4. Secondly, pseudocapacitive behavior (i.e., charge storage via fast, reversible surface or near-surface redox reactions) enhances the energy density while preserving a high power capability (Fig. 1d)5. Thirdly, the mechanical compliance and processability of CPs enable the formation of flexible films or coatings that conform to complex electrode geometries, which makes them suitable for use in flexible and miniaturized devices. Although their solution processability can be limited depending on the polymer structure or doping conditions, alternative deposition methods such as vapor-phase or electrochemical polymerization offer practical fabrication routes6,7. Finally, their chemically tunable structures allow precise control over their redox potential, conductivity, interfacial interactions, and morphology. Moreover, the CPs can serve multiple roles in HC systems (Fig. 1e and f). For instance, as active materials in pseudocapacitive cathodes, they complement metal oxide or carbon-based electrodes to achieve a synergistic energy-storage performance (Fig. 1e). Alternatively, when applied as thin interfacial coatings on Zn or alkali metal anodes, CP layers can suppress dendrite nucleation, buffer volumetric changes during cycling, and promote homogeneous ion flux, thereby enhancing both cycle life and safety (Fig. 1f). These diverse functionalities underscore the strategic importance of CPs in advancing the performance and durability of next-generation HCs.
a The chemical structures of representative CPs, which contain π-conjugated alternating single and double bonds along the polymer backbone. b A typical example of the conduction mechanism arising from inherent conjugation and doping, as illustrated by the electronic band and chemical structures of polythiophene under (i) p-type doping and (ii) n-type doping. Notably, the doping concept for CPs differs from that used in semiconductor physics, as CP conductivity arises from redox reactions along the polymeric backbone (reproduced with permission1 under a CC-BY license, copyright 2019, MDPI). In the CPs, doping generates positive or negative charge-carriers (often referred to as polarons or bipolarons), which are delocalized along the polymer chains, thereby facilitating electronic conductivity. The charges introduced into the polymer backbone by these redox reactions are balanced by the dopant counterions, which are supplied by an oxidizing or reducing agent. c A schematic diagram showing two ion transport mechanisms in CPs, including liquid-like ion transport (lower left), which involves the motion of polymer segments and depends on the segmental relaxation rate, and solid-like ion transport (lower right), which relies on ions jumping over energy barriers in the polymer matrix and occurs within a timescale in which polymer movements are effectively frozen (reproduced with permission4, copyright 2020, ACS). d A schematic diagram of the electrochemical processes for CP electrodes in contact with an electrolyte, along with the corresponding cyclic voltammograms, illustrating (i) capacitive, (ii) faradaic, and (iii) volumetric doping processes (reproduced with permission5 under a CCA 3.0 Unported license, copyright 2019, Wiley). Notably, the faradaic and volumetric doping processes rely on the ionic conductivity of the CP. A radar plot e comparing the key properties of major electrode materials in HCs and a schematic diagram f showing the potential functions of CPs in addressing the cycle life and safety issues of HCs.
Hence, the present review is aimed at providing an in-depth analysis of the roles of CPs in zinc and alkali metal ion-based HCs from a materials perspective, with a particular emphasis on their contributions to the design and performance of both cathode and anode materials. While CPs have long been recognized for their pseudocapacitive behavior and multifunctionality in various electrochemical devices, a unified perspective that connects their influence across all key HC components within Zn and alkali metal ion systems has not yet been fully articulated in the literature.
Fundamental design of HCs
The design and operation of HCs are fundamentally governed by the interplay between the following three distinct energy storage mechanisms: (i) electric double-layer capacitance (EDLC), (ii) pseudocapacitance, and (iii) battery-type faradaic processes (Fig. 2a)8. The HCs are strategically engineered to overcome the inherent trade-offs between key performance parameters such as energy density, power density, and cycling stability, which limit the majority of single-mechanism energy storage devices (Fig. 2b). Furthermore, beyond the underlying energy-storage mechanisms, HCs can also be classified according to the type of electrolyte system employed, namely aqueous or non-aqueous. Aqueous electrolytes, despite their intrinsically narrow voltage window, are often preferred for their non-toxic nature and superior safety. This limitation can be partially mitigated by strategies such as the use of water-in-salt electrolytes, which extend the accessible potential range. In contrast, non-aqueous systems employing organic solvents or ionic liquids offer a much wider electrochemical stability window, thereby enabling higher operating voltages. These two electrolyte classes inherently involve trade-offs between safety and voltage range, which has motivated ongoing efforts to develop hybrid systems, for example, aqueous electrolytes incorporating organic co-solvents, that aim to balance these competing attributes9. In an HC, the cathode and anode typically exhibit asymmetric electrochemical behavior. One electrode—often the battery-type side—undergoes bulk redox or intercalation reactions, while the other stores charge via surface-confined pseudocapacitive redox reactions or ion adsorption at the electrolyte–electrode interface. By pairing electrodes with different redox potentials, the overall operating voltage (ΔV) of the device can be extended to encompass the redox potential range of the faradaic electrode, thereby improving the achievable energy density (Fig. 2c)10. This functional asymmetry enables efficient charge storage across a broader voltage range and facilitates faster charge-transfer kinetics compared to conventional battery systems, while also offering a higher energy density than that of the typical symmetric supercapacitor. Within this electrochemical landscape, CPs are uniquely positioned due to their above-mentioned beneficial properties. Moreover, CPs can be integrated into various HC components, including cathodes and anodes, and are capable of operating across all three primary charge storage mechanisms depending on their redox state, molecular structure, and surrounding environment. Thus, CPs can act as EDLC materials via ion adsorption on doped surfaces, pseudocapacitors via fast surface or near-surface redox reactions, or even battery-type electrodes via ion intercalation or deep redox transformations. Hence, an understanding of these fundamental storage mechanisms and how the CPs combine each of them is essential for rational device engineering. Therefore, the remainder of Section “Fundamental design of HCs” presents detailed discussions on electrode asymmetry, charge storage dynamics, and materials selection in order to clarify the underlying principles that enable the fabrication of high-performance Zn- and alkali metal ion-based HCs. This discussion provides the necessary electrochemical and architectural groundwork for evaluating the component-specific roles of CPs in Sections “Conducting polymers as cathode materials” and “Conducting polymers as anode modifiers or hosts”.
a A schematic diagram showing the electrochemical processes occurring in (i) electric double-layer capacitive (EDLC), (ii) pseudocapacitive, and (iii) battery-type electrodes, along with their characteristic charge–discharge profiles (reproduced with permission8, Copyright 2019, Wiley). b A radar plot comparing the major electrode performance characteristics according to each charge storage mechanism. c The electrochemical characteristics of a typical full-cell HC configuration, in which (i) the device voltage window (ΔV) extends to the redox potential of the battery-type electrode, thereby enhancing the overall energy storage capability, while (ii) the cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) profiles deviate from ideal capacitive behavior due to the coexistence of faradaic and non-faradaic processes, and (iii) the integration of high-capacity electrodes and a wide voltage window improves the energy density and offers faster charge-discharge characteristics than those of conventional batteries (reproduced with permission10, Copyright 2019, Wiley). d A summary and comparison of the material requirements for the cathode and anode in Zn and alkali metal ion HCs, highlighting the complementary roles and tailored strategies needed for each electrode in order to optimize the performance based on the distinct ion behavior. For the cathode, a high surface area, robust electrical and ionic conductivity, chemical/electrochemical stability, and tailored affinity for target ions are essential, and are often achieved or enhanced by CPs. For the anode, the requirements include stable Zn plating/stripping or Na⁺/K⁺ insertion/deinsertion, the suppression of dendrite growth and side reactions, and structural accommodation of volume changes, with CP coatings or matrices providing interface control and cycling stability.
Device architecture: asymmetric vs. symmetric capacitors
The electrochemical performance of an electrochemical capacitor is intimately linked to the device architecture, which governs the mechanisms of charge storage and transfer. Broadly, electrochemical capacitors are categorized into symmetric and asymmetric (or hybrid) configurations, each of which is defined by the nature of the materials used and the underlying storage mechanisms. As mentioned above, an asymmetric architecture is particularly favorable in zinc and alkali metal ion systems. For example, zinc metal anodes provide high theoretical capacity and stable redox potential, while CP-based cathodes offer fast redox activity and mechanical flexibility. Likewise, sodium and potassium ion capacitors benefit from the combination of insertion-type anodes with pseudocapacitive CP cathodes in order to balance the effects of ionic size and kinetic limitations. These ion-specific electrochemical characteristics are inherently mismatched, which makes asymmetric pairing not only logical but necessary for achieving an optimal performance. Ultimately, the asymmetric design philosophy is central to the functionality of the HC by enabling synergistic charge storage, facilitating electrode specialization, and providing a versatile platform for the incorporation of multifunctional materials such as CPs. This architectural foundation sets the stage for a detailed exploration of the storage mechanisms in the section “Zinc and alkali metal ion systems: key electrochemical profiles”.
Zinc and alkali metal ion systems: key electrochemical profiles
Zinc (Zn²⁺), sodium (Na⁺), and potassium (K⁺) ions represent promising charge carriers for aqueous electrolyte systems and HCs, each offering distinct electrochemical characteristics that influence device design, performance, and material compatibility. An understanding of the redox behavior, hydrodynamic properties, and ion transport characteristics is essential for optimizing the electrode–electrolyte interactions in hybrid energy storage systems. Specifically, Zn²⁺ ions undergo a two-electron redox reaction (Zn ↔ Zn²⁺ + 2e⁻) that confers a high theoretical capacity of 820 mAh g−1, which is comparable to that of many lithium-based systems. The compatibility of Zn with aqueous electrolytes also makes it attractive for low-cost and inherently safe energy storage. However, its practical implementation faces significant challenges due to dendrite formation during plating/stripping, hydrogen evolution reactions (HER) in aqueous media, and poor reversibility due to passivation and side reactions. These issues limit the cycle life and efficiency of Zn-based devices, particularly under high-rate or deep cycling conditions. Conversely, Na⁺ and K⁺ ions undergo monovalent redox reactions (Na ↔ Na⁺ + e⁻; K ↔ K⁺ + e⁻) and have larger ionic radii than Zn²⁺ or Li⁺, thus leading to slow bulk diffusion kinetics that often necessitate the use of surface-confined or open-structured electrode materials in order to facilitate ion transport. Nevertheless, both Na⁺ and K⁺ offer distinct advantages. Specifically, Na⁺ is a promising candidate for cost-effective, large-scale storage applications such as stationary grid systems due to its abundance and wide distribution. Meanwhile, K⁺ exhibits a higher ionic conductivity in aqueous and gel electrolytes due to its lower solvation energy and greater mobility; however, its relatively large size requires engineered host structures with expanded lattice frameworks or interlayer spacing to prevent structural degradation during cycling. Moreover, due to their differences in charge, size, and hydration behavior, the three metal cations each interact differently with redox-active CPs. Due to their strongly bound hydration shells, the divalent Zn²⁺ ions encounter substantial desolvation energy barriers at the interface with CPs, which can impede interfacial charge transfer and slow the redox kinetics. By contrast, the less strongly hydrated monovalent Na⁺ and K⁺ ions face fewer interfacial barriers during intercalation and deintercalation, thereby enabling faster and more reversible redox processes. Importantly, by introducing appropriate dopants and tailoring the molecular structure, the ion–CP interactions can be modulated to enhance the kinetic reversibility and overall electrochemical performance. These distinct ion-specific interactions highlight the need for customized material strategies in order to optimize the redox activity and ionic transport properties depending on the targeted ion.
Criteria for ideal electrode materials
The performance, stability, and scalability of the HCs are critically dependent on the electrochemical and mechanical properties of their constituent materials. For Zn and alkali metal ion HCs, all device components, and especially the cathode and anode, must meet specific performance criteria to ensure reliable operation under practical conditions. When used either as standalone components or in hybrid architectures, CPs offer a tunable platform for meeting these demands (Fig. 2d). For the cathode, which often includes a CP or CP-based hybrid, several attributes are essential. For instance, a high electrical conductivity (σ > 10−2 S/cm) is required in order to ensure rapid electron transport across the electrode, while an inherently porous microstructure will facilitate effective ion diffusion and electrochemical activity. In addition, the material must exhibit a stable redox window within the operational voltage range of the electrolyte in order to avoid side reactions or degradation. Furthermore, mechanical and structural integrity during repetitive cycling is critical, especially when undergoing the volumetric expansion and contraction associated with redox processes. Meanwhile, the anode of a Zn-based system must support uniform Zn²⁺ plating and stripping while suppressing dendrite formation, which is a major cause of short circuits and capacity degradation. Ideal anode materials or coatings should effectively suppress dendritic growth, maintain interfacial compatibility with the electrolyte, and accommodate mechanical strain without compromising conductivity. The incorporation of a CP as a surface coating or interfacial layer can help to regulate ion flux, buffer volume changes, and stabilize the electrode–electrolyte interface. Overall, the ideal material system for Zn and alkali metal ion HCs must provide a balance between electronic and ionic transport, structural robustness, and interfacial stability. Due to their unique multifunctionality, the CPs present an integrated materials platform that is capable of satisfying many of these stringent requirements across multiple device components.
Conducting polymers as cathode materials
The aforementioned beneficial properties of CPs make them highly suitable cathode materials for Zn and alkali metal ion HCs, often outperforming traditional carbon or oxide materials via molecular and morphological control within hybrid architectures. However, ensuring long-term electrochemical and structural stability remains a critical challenge that requires advanced polymer engineering11,12.
The pseudocapacitive behavior of CPs
The CPs exhibit intrinsic pseudocapacitive behavior arising from their ability to undergo fast and reversible redox reactions, typically via a doping/dedoping mechanism. In this process, the CP transitions between reduced and oxidized states via the insertion or removal of a counterion (A⁻) from the electrolyte in order to maintain charge neutrality:
This charge storage mechanism features surface- or near-surface confinement, which allows for rapid electron and ion transport, thereby supporting high-rate performance. In contrast to battery-type materials, which rely on slow solid-state diffusion, the CPs offer superior kinetics and higher power capability, while also contributing significantly to high-energy density via their faradaic activity. Several key advantages distinguish the CPs as pseudocapacitive cathode materials. Firstly, their redox transitions proceed more rapidly than typical intercalation reactions, thereby enabling fast charge/discharge responses. Secondly, due to their multi-electron redox capabilities, the CPs exhibit higher specific capacitance values than those of purely capacitive materials such as activated carbon. For instance, PANI can achieve a theoretical capacitance of up to 750 F g−1 due to its ability to access multiple oxidation states13,14,15,16,17,18, while PPy is valued for its cycling stability and ease of polymerization, and PEDOT offers exceptional conductivity, processability, and compatibility with flexible substrates19,20,21,22,23,24,25,26. These properties make the CPs ideal for integration into HC systems, particularly as cathodes, where fast redox activity and high electronic conductivity are essential for balancing the energy and power performance.
Hybrid cathodes: CPs combined with carbon or metal oxides
To overcome the intrinsic limitations of individual materials, particularly in terms of conductivity, structural stability, and energy density, recent efforts have focused on developing hybrid cathodes that integrate CPs with carbon-based materials or transition metal oxides. These hybrid designs leverage the complementary properties of each component to achieve synergistic enhancements in electrochemical performance. In CP/carbon hybrids (Fig. 3), materials such as carbon nanotubes (CNTs), reduced graphene oxide (rGO), or activated carbon serve as highly conductive and mechanically robust frameworks27,28,29,30,31,32,33. These carbon-based components improve the electron transport and reinforce the mechanical integrity of the electrode, as well as providing a large surface area for CP deposition and electrochemical activity. For example, PANI/rGO hybrids with the incorporation of catechol have demonstrated specific capacitance values of >1900 F g−1, along with around 90% retention during 5000 charge/recharge cycles, which is attributed to the uniform dispersion of PANI on the conductive carbon scaffold34. Meanwhile, in CP/metal oxide hybrids (Fig. 4), the CP acts not only as a redox-active material but also as a conductive matrix that addresses the poor intrinsic conductivity of many transition metal oxides35,36,37,38,39,40,41. Commonly used oxides such as manganese dioxide (MnO2) and vanadium pentoxide (V2O5) contribute high theoretical capacitance via their multiple valence states. When combined with CPs such as PEDOT, the resulting hybrids benefit from synergistic pseudocapacitive behavior, improved electrical conductivity, and better structural flexibility. For instance, PPy/ZnxMnO2 hybrid cathodes in aqueous Zn-based HCs have achieved energy densities of >20 Wh kg−1, which far surpass those of conventional symmetric supercapacitors42.
a A schematic diagram showing a typical PANI/rGO hybrid fabrication process (reproduced with permission27, Copyright 2021, ACS). b A high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image and corresponding C and N energy-dispersive X-ray spectroscopy (EDS) mappings of activated carbon-packed PANI (reproduced with permission28, Copyright 2024, Elsevier). The cyclic voltammetry (CV) curves c at a rate of 30 mV s−1 and the galvanostatic charge/discharge (GCD) curves d at a current density of 0.5 A g−1 for various rGO/PANI/iron oxide films, showing their oxidation/reduction potentials and a maximum specific capacitance of 281.1 F g−1, respectively27. e The cycling stability of a PANI@CNT/partially rGO fiber-based solid-state cell during 20,000 cycles at 1 A cm−3, showing over 95% retention (reproduced with permission29, Copyright 2023, Elsevier). f The comparative Ragone plots of various PANI/nanocarbon hybrids27,28,30,31,32. g Operando Raman spectra of the electrolyte with respect to sulfur-enriched imine bonds iminated PANI@rGO-CNTs cathode during the first cycle at 0.5 C, demonstrating the reversible kinetics of the S6–2 species in the electrolyte (reproduced with permission33 under a CC-BY-NC license, Copyright 2023, Wiley). A flexible PANI-based Zn energy storage device, along with h the corresponding GCD curves at various current densities and i the self-discharge behavior, demonstrating a voltage retention of 83% after a 24-h hold period (inset: a schematic of the flexible system) (reproduced with permission32, Copyright 2022, Elsevier).
a A schematic diagram showing a representative fabrication process of a V2O5/PEDOT hybrid, where polymerization and metal oxide nanoparticle formation occur in one step. A TEM image (b) and corresponding EDS mappings (V, O, C, and S) of the V2O5/PEDOT hybrid and c the Raman spectra of the V2O5 and PEDOT starting materials and that of the corresponding hybrid (reproduced with permission35, Copyright 2023, Elsevier). The CV curves d at a scan rate of 20 mV s−1 and the GCD curves e at current densities of 2–6 mA cm−2 for an SiNW/PEDOT@Pt/MnOx hybrid (reproduced with permission36, Copyright 2020, Wiley). f The capacitance retention of a PEDOT NW@MnO2@PEDOT NWHS hybrid after 10,000 cycles at 0.8 mA cm−2 in the voltage window of 0.0−0.8 V, showing 91.2% retention (reproduced with permission37, Copyright 2023, ACS). g The comparative Ragone plots of various PEDOT and metal oxide hybrids38,39,40,41. Photographic images h of a flexible PEDOT NW@MnO2@PEDOT NWHS hybrid in the pristine, folded, and twisted states and i the stable electrochemical properties of the all-solid-state electrode after 500 bending cycles, demonstrating its potential for application in flexible devices37.
In all of these hybrids, the CPs perform additional functions as binders and structural matrices, thereby replacing or reducing the need for non-conductive polymer binders such as poly(vinylidene fluoride)2. This multifunctional role provides enhanced electronic and ionic contact within the electrode, mitigates particle agglomeration, and helps to maintain structural cohesion during repetitive cycling. As such, hybrid architectures that integrate CPs with high surface-area carbon-based materials or high-capacity oxides offer a highly effective strategy for optimizing the energy–power–stability balance in HC cathodes.
Comparison with carbonaceous and transition metal cathodes
As discussed above, the properties of the CP-based cathodes occupy a unique position between those of carbon-based materials and transition metal oxides, thereby providing the opportunity to achieve a balanced combination of electrochemical and mechanical performance in cathode design (Table 1)27,28,30,36,43,44,45,46,47,48. Consequently, a comparative evaluation of these three categories (carbon-based materials, metal oxides, and CPs) reveals distinct trade-offs in terms of energy density, conductivity, structural adaptability, and overall device performance. Thus, carbon-based materials such as activated carbon, rGO, and CNTs, are widely employed as electrode materials in supercapacitors due to their high surface area, excellent electrical conductivity, and exceptional rate performance. However, their charge storage relies exclusively on EDLC formation, which is limited by surface-accessible adsorption and results in a relatively low energy density compared to faradaic systems32,49. Meanwhile, transition metal oxides, including materials such as MnO2, V2O5, and RuO2, provide high specific capacitance and battery-like energy density due to their rich redox chemistry, but suffer from poor intrinsic conductivity and often undergo significant volume changes during cycling, thus leading to performance degradation and mechanical instability in long-term operation. By contrast, CPs offer a pseudocapacitive mechanism that combines fast redox activity with good conductivity and mechanical flexibility. While their energy density may not reach that of the highest-capacity oxides, CPs provide higher energy output than carbon materials, along with fast charge/discharge capability, flexibility, and the potential for solution-based fabrication. However, even though their resilience is superior to that of other rigid or brittle electrode materials, the cycling stability of CPs is often constrained by swelling, chain scission, or degradation of the polymer backbone during prolonged redox cycling.
Limitations: structural degradation, cycling instability
The main limiting factors in the practical application of CPs include structural/mechanical integrity, electrochemical stability, and electrolyte compatibility (Fig. 5a)50,51,52. For instance, a primary concern is the repetitive swelling and shrinkage that occur during redox cycling. During doping and dedoping, the insertion and removal of counterions induce volumetric fluctuations within the polymer matrix. These fluctuations disrupt the polymer chain conformation, thereby generating mechanical stress, microstructural fractures, and ultimately a loss of electrical connectivity. With prolonged cycling, such changes progressively degrade the electrode structure, leading to capacity fading and diminished cyclability. In addition, electrochemical fatigue is a key degradation mechanism, particularly under aqueous or mildly oxidative conditions. During repeated oxidation, the polymer backbone is susceptible to overoxidation or hydrolytic cleavage, thereby resulting in irreversible structural damage. These processes diminish the redox reversibility of the material and progressively impair its pseudocapacitive behavior. For example, PANI and PPy are known to experience a decline in conductivity and capacitance after prolonged cycling due to degradation of their conjugated structures. Specifically, during repeated charge/discharge cycles, the composition of the CP changes. The conjugated structure transforms into hydroxyl- or amino-terminated oligomer forms. Concurrently, morphological changes occur, leading to a reduction in electrical conductivity and a decline in long-term cycle stability53,54,55.
a A schematic diagram showing the CP degradation processes that occur under various conditions during the functioning of electrochemical cells. Thus, CP degradation is primarily driven by volume change, solvent/pH conditions, and repeated exposure to oxidative atmospheres. b Schematic diagrams and images illustrating some advanced engineering examples in which the various limitations of CPs are overcome, including (i) the use of a PANI hydrogel as a supercapacitor electrode material, which exhibits morphological stability due to intermolecular interactions (reproduced with permission56, Copyright 2016, ACS), (ii) the use of a 3D hierarchical Ti3C2Tx@PANI-rGO hydrogel as an anode material with increased surface area and higher electrical conductivity due to the intercalation of PANI (reproduced with permission57, Copyright 2015, ACS), and (iii) the use of a zwitterionic (L-carnitine) coating as a stabilizer in Zn-ion battery electrodes (reproduced with permission58, Copyright 2024, Taylor & Francis). The incorporation of this additive promotes electrochemical activity by mitigating dendrite growth at the electrode surface.
Electrolyte compatibility further complicates the reliable use of CPs. Many CPs exhibit pH-sensitive doping behavior, and their redox potentials can shift depending on the solvent environment. Variations in ion–polymer interactions under different electrolyte conditions can alter the charge transport pathways and accelerate degradation, especially in harsh media. In some cases, the CPs may be unstable in high-voltage or strongly alkaline electrolytes, thereby limiting their applicability across wider electrochemical windows. These environmental sensitivities also make it challenging to pair CPs with non-aqueous or hybrid electrolytes without compromising the performance or stability.
Collectively, these limitations underscore the need for advanced polymer engineering, including crosslinking, hybrid formation, and molecular-level modifications, in order to enhance the structural durability, chemical robustness, and electrolyte compatibility of the CPs. Addressing these challenges is essential to fully realize the potential of CPs in high-performance, long-lifetime HC systems.
Strategies for improvement
Various material design strategies have been developed in order to harness the potential of CPs in HC systems by addressing the limitations relating to structural degradation, cycling stability, and interfacial inefficiency. These strategies operate across multiple scales, from molecular engineering to device-level interfacial design, and are aimed at enhancing the durability, electronic conductivity, and mechanical robustness of the CP-based electrodes (Fig. 5b)56,57,58.
At its core, the energy-storage mechanism of CPs relies on a reversible doping/dedoping process, which gives rise to pseudocapacitance. During charging, CPs undergo reversible oxidation (p-doping) or reduction (n-doping), accompanied by the rapid intercalation or deintercalation of counterions from the electrolyte to maintain charge neutrality. This fast faradaic process enables CPs to achieve significantly higher specific capacitance than EDLC materials. However, the associated volumetric changes during ion migration induce severe mechanical strain and eventual material degradation, thereby limiting cycling stability, particularly in bulk structures. Consequently, subsequent material design strategies primarily focus on optimizing this redox activity by stabilizing the structure against volume variation, accelerating ion transport, and improving the electronic conductivity of the polymer backbone to achieve high specific capacity with long-term durability.
At the molecular level, copolymerization offers a powerful approach for optimizing the trade-offs between key properties such as electrical conductivity, mechanical flexibility, and redox potential. Via the selection of appropriate monomer combinations, the CPs can be tailored for specific electrochemical environments or electrode architectures. In addition, functionalization with ionic groups such as sulfonate, carboxyl, or zwitterionic moieties can significantly enhance ion transport, electrolyte compatibility, and redox stability, particularly in aqueous or gel-based systems. Indeed, the incorporation of sulfonate groups into CP copolymers offers distinct advantages, most notably by enabling self-doping and enhancing specific capacitance. Nevertheless, challenges remain regarding stability: their performance is often compromised when in contact with high-potential cathodes (above 4 V). Although improvements in long-term cycling stability have been reported, these systems are still not sufficiently robust, underscoring the need for further optimization through strategies such as zwitterion induction, electrolyte modification, and related approaches59,60,61.
Nanostructuring is another widely adopted strategy for improving the electrochemical performance of the CPs. By engineering nanotubes, nanowires, or hierarchically porous structures, the effective surface area can be increased while simultaneously shortening the ion diffusion pathways. These architectures facilitate rapid charge storage and extraction, thereby resulting in improved rate capability and more stable cycling behavior. Moreover, hierarchical nanostructures offer additional mechanical resilience by distributing any stress across multiple length scales62,63,64,65,66.
Meanwhile, crosslinking represents an effective method for enhancing the structural stability of CP networks under electrochemical cycling. Covalent crosslinks or hydrogen-bonded networks help to preserve the integrity of the polymer against volumetric expansion and mechanical fatigue. Systems such as PEDOT:PSS, which combine a CP backbone with a flexible polyelectrolyte counterion, exemplify how hybrid design can yield both mechanical robustness and strong substrate adhesion, which are essential for flexible and wearable applications67,68,69.
Finally, interfacial engineering is crucial for optimizing charge transfer between CPs and other electrode or electrolyte components. The use of graded interfaces, e.g., gradual transitions between CPs and carbon or metal oxide phases, can mitigate interfacial resistance and improve electronic percolation. Additionally, zwitterionic surface coatings have demonstrated improved electrolyte compatibility, selective ion transport, and suppression of undesirable side reactions, especially in systems involving multivalent ions (e.g., Zn²⁺)70,71.
Collectively, these strategies provide a comprehensive toolkit for overcoming the intrinsic limitations of CPs and for unlocking their multifunctional potential in high-performance, long-life HCs.
Conducting polymers as anode modifiers or hosts
The CPs play a pivotal role in enhancing the anode performance in Zn and alkali metal ion HCs by combining mechanical flexibility, intrinsic electrochemical activity, and interfacial engineering capabilities that are not typically found in traditional materials. Via strategies such as surface coating, hybrid integration, and functional solid–electrolyte interphase (SEI)-mimicking layers, CPs can be used to improve the anode stability and charge-transfer efficiency, thereby enabling safer and longer-lasting hybrid energy storage systems72.
Challenges of Zn and alkali metal anodes: dendrite formation and irregular deposition
Despite their high theoretical capacities and favorable redox properties, the practical deployment of Zn²⁺, Na⁺, and K⁺ anodes is significantly hindered by a range of interfacial and morphological challenges that compromise the safety, efficiency, and long-term cycling stability of the device (Fig. 6a)73,74,75. In the case of zinc anodes, the plating and stripping of Zn²⁺ during charge and discharge cycles is often highly non-uniform, thus resulting in the growth of dendritic structures. These metallic protrusions can eventually pierce the separator, thereby leading to internal short circuits, which are a major concern for the reliability and safety of the device. Additionally, the reaction of Zn with aqueous electrolytes promotes the formation of surface passivation layers, such as Zn(OH)2 or layered double hydroxides. These by-products hinder ion transport at the electrode–electrolyte interface, reduce the reversibility of Zn redox processes, and contribute to low coulombic efficiency over extended cycling. In the case of Na⁺ and K⁺, these challenges are further complicated by their larger ionic radii, which lead to less uniform intercalation and, hence, a more inhomogeneous ion deposition. This, in turn, creates regions of localized stress and structural defects in the host material. Repeated cycling induces substantial volume expansion and contraction, which results in electrode cracking, pulverization, and eventual loss of electrical contact. These mechanical failures not only degrade the capacity but also create fresh reactive surfaces, thereby exacerbating side reactions. Moreover, another key concern in both Zn and alkali metal systems is the instability of the SEI, which is often chemically and mechanically fragile in aqueous electrolyte systems, thereby promoting continuous parasitic reactions, gas evolution, and progressive loss of coulombic efficiency. Such instability is particularly pronounced at high current densities or during prolonged cycling.
a Schematic diagrams showing the typical problems that occur in anodes, including: (i) surface passivation, i.e., the formation of inactive metal due to side reactions, which significantly hinders charge transfer and reduces cycling stability (reproduced with permission73, Copyright 2021, RSC), (ii) microcrack-induced pulverization of the anode material, which leads to the formation of electrically isolated (“dead”) regions (reproduced with permission74 under a CC-BY license, Copyright 2024, AAAS), and (iii) progressive degradation of the SEI layer under repeated cycles, which promotes the formation of dead anode material and dendrite growth (reproduced with permission75, Copyright 2022, Wiley). b Examples of approaches for overcoming various limitations via interfacial engineering strategies, including: (i) protective coating of the anode material with a CP, e.g., a PPy coating on SiO, to provide enhanced electrical conductivity and a high lithium-ion transfer rate (reproduced with permission76, Copyright 2024, Elsevier), (ii) the introduction of an artificial SEI layer into an Si-based anode to provide high conductivity and mechanical stability(reproduced with permission77, Copyright 2022, Wiley), and (iii) the use of a porous 3D host structure (e.g. N-doped carbon) with high surface area as a scaffold for deposition of the anode material, thereby inhibiting dendrite formation, which would otherwise harm the electrochemical performance (reproduced with permission78, Copyright 2022, Wiley).
Addressing these issues requires the development of advanced interfacial engineering strategies, such as the introduction of protective coatings, artificial SEI layers, and three-dimensional (3D) host structures (Fig. 6b)76,77,78. The CPs have strong potential to regulate ion flux, suppress dendritic growth, and enhance SEI stability, thereby providing a multifunctional platform for improving the reliability and performance of metal anodes in HC systems.
Stabilization of metal (Zn, Na, and K) anodes via CP coatings
One promising approach to mitigating the interfacial and morphological instabilities of metal-based anodes in HCs is the use of CP coatings. As evidenced by their well-established anticorrosive properties, CPs such as PANI and PEDOT form flexible, conformal, and ion-permeable surface layers that deliver multiple functional benefits at the metal–electrolyte interface79. As surface regulators, CPs can modulate the Zn²⁺ flux during plating and stripping, thereby guiding uniform deposition and suppressing dendritic growth. Their mixed ionic and electronic conductivity facilitates charge transfer while preserving electrochemical continuity, even under dynamic interfacial changes. Due to their conformability, CP coatings maintain intimate contact with the metal surface despite repeated volume fluctuations. By distributing the local electric field, they create a homogeneous nucleation landscape, reduce the nucleation overpotential, and promote smoother, reversible metal deposition. The CP layer also serves as a protective barrier, limiting parasitic reactions such as hydrogen evolution and hydroxide formation in aqueous or mildly acidic electrolytes. Additionally, they improve the mechanical robustness and adhesion at the anode–electrolyte interface, thereby enhancing the cycling stability and resistance of the electrode to cracking or delamination (Fig. 7a–c)80.
a A schematic illustration of the effect of a PPy coating on a Zn anode, where the 3D CP structure inhibits dendrite formation and facilitates Zn²⁺ ion transport (reproduced with permission80, Copyright 2022, Elsevier). b Typical voltage profiles of symmetric cells without (red) and with (blue) a CP coating, showing a concave profile and irreversible changes in the absence of the CP coating. c A comparison between the commonly acknowledged representative properties for bare metal and CP-coated metal anodes. Optical microscope images d of bare Zn (top row) and PEDOT-coated Zn (bottom row) anodes operated at 5 mA cm−2 for 45 min, showing dendrite formation on the bare Zn surface, along with e the nucleation overpotentials of bare Zn and PEDOT-coated Zn electrodes at 1 mA cm−2, showing a reduced overpotential in the presence of the CP coating, and f the coulombic efficiencies of Zn||Cu and Zn||Cu–PEDOT cells at a current density of 1 mA cm−2 and an areal discharge capacity of 0.5 mA h cm−2, where the Zn||Cu cell fails after only 140 cycles (reproduced with permission81, Copyright 2024, ACS). Ragone plots of bare Zn and PPy-coated Zn anodes in g AC||Zn and AC||PPy–Zn and h δ-MnO2||Zn and δ-MnO2||PPy–Zn cells, showing higher energy and power densities for the PPy-coated Zn anodes (reproduced with permission82, Copyright 2020, Elsevier). The constant-current cycling performances i of Zn||Zn cells containing bare Zn, PANI-coated Zn, and sponge-PANI-coated Zn electrodes at 0.5 mA cm−2, and the coulombic efficiencies j of asymmetric Zn||Sponge-PANI@Cu and Zn||Cu cells at 1 mA cm−2 with a capacity of 1 mA h cm−2, where the sponge-PANI-coated electrode exhibits a superior performance. In each case, the bare metal anodes exhibit significantly shorter lifetimes than the CP-coated metal anodes (reproduced with permission83, Copyright 2024, Elsevier).
All of these advantages have been demonstrated in experimental studies. For example, PEDOT-coated Zn anodes have shown significantly improved reversibility and coulombic efficiency in mildly acidic Zn-based electrolytes (Fig. 7d–f). The PEDOT layer not only stabilizes the Zn plating/stripping behavior but also extends the cycle life by mitigating interfacial degradation81.
Altogether, CP coatings represent a multifunctional interfacial engineering approach that addresses the core issues of dendrite growth, surface passivation, and SEI instability, thereby positioning them as a key tool for stabilizing Zn, Na, and K metal anodes in next-generation hybrid energy storage systems (Fig. 7g–j)82,83.
Hybrid anodes: CPs combined with tin, antimony, or hard carbon
In addition to surface coatings, CPs have shown considerable promise as structural components within hybrid anodes, particularly for HCs based on Na⁺ or K⁺ ions. The inherent mechanical flexibility, redox activity, and electronic conductivity of the CPs enable them to serve as buffers, matrices, or conductive frameworks that support the operation of active materials that have high capacity but are structurally unstable. The rationale for CP integration is particularly strong in systems that involve alloying-type anodes such as tin (Sn) and antimony (Sb) or insertion-type anodes (e.g., hard carbon). For instance, in Na-ion systems, Sn and Sb offer high theoretical capacities via alloying reactions, but suffer from dramatic volume expansion (up to ~400%), thus leading to rapid mechanical failure84,85. Similarly, hard carbon is commonly used for Na⁺ or K⁺ intercalation, but often experiences particle cracking and electrical isolation due to structural fatigue over long cycling periods86. By embedding these active materials within a CP matrix, the electrode can better accommodate mechanical stress while simultaneously maintaining electronic percolation and interfacial stability (Fig. 8a). Notably, the CPs play multiple roles in these architectures. Their mechanical elasticity allows them to absorb expansion and contraction during charge–discharge cycles, thereby preventing the pulverization of active particles. Their electronic conductivity ensures stable current collection, even when the active material undergoes phase changes or partial detachment. Furthermore, the CPs promote rapid ion and electron transport by providing continuous pathways across the electrode bulk and surface.
a A schematic diagram of a hybrid anode consisting of a CP matrix with alloying- or insertion-type particles, highlighting its functional advantages. A schematic diagram b showing the fabrication of an SnO2 quantum dots@PPy anode, along with c the CV curves obtained during the initial four cycles in the voltage window of 0.1−3.0 V at a scan rate of 0.1 mV s−1, and d the cycling performance of a half-cell at 0.15 A g−1 (reproduced with permission87, Copyright 2024, ACS). e and f Cross-sectional SEM images of electrodes based on hollow multishelled structures (HoMSs), including e SnO2@PPy and f SnO2, at various stages of lithiation/delithiation, where the superior structural stability of the coated sample is revealed by a thickness change of only 14.5% compared to 42.4% for the bare SnO2 HoMSs after 100 cycles (reproduced with permission88, Copyright 2022, Elsevier). The cycling performance (g) and long-term performance h of a PPy@SnS2@N-doped 3D porous graphene (N3DG) hybrid in a Li-ion half-cell, where the SnS2 provides structural integrity by buffering against volume changes during cycling (reproduced with permission89, Copyright 2021, ACS). TEM images of i hollow mesoporous carbon spheres (HMCS) and j PANI-coated HMCS (HMCS@PANI), along with k the corresponding first-cycle charge–discharge curves and l the rate performance characteristics. Here, the PANI-coated anode exhibits a higher initial coulombic efficiency (ICE) and greater specific capacity at all current densities (reproduced with permission90, Copyright 2024, Elsevier).
Representative examples from recent studies underscore the efficacy of this design approach. For instance, PPy–Sn hybrid anodes anchored on carbon nanofibers have demonstrated enhanced capacity retention and stable cycling at high current densities due to the uniform dispersion of Sn nanoparticles within a flexible CP matrix (Fig. 8b–h)87,88,89. Likewise, PANI/hard carbon hybrids have been successfully applied in potassium battery-type systems, where they provide both high energy output and suitable mechanical resilience for wearable applications (Fig. 8i–l)90. These hybrid anode configurations reflect the growing recognition of CPs as both active materials and functional frameworks that can stabilize high-capacity anodes in challenging electrochemical environments.
Advantages over bare metal and inert matrix hosts
The integration of CPs into anode architectures offers notable advantages over both bare metal electrodes and those supported by inert structural matrices such as carbon fibers or metal foams. While each of these systems presents certain strengths, CP-based hybrids provide a uniquely balanced combination of mechanical flexibility, electrochemical functionality, and interfacial stability that addresses the key limitations of traditional designs (Fig. 9a). Anodes based on bare metals such as pure Zn, Na, or K suffer from uncontrolled plating/stripping processes that lead to rapid dendrite formation, low coulombic efficiency, and significant safety risks due to internal short circuits. Although bare metals can deliver high theoretical capacities, their cycling life is typically limited, and their interfacial stability is poor in most aqueous and hybrid electrolytes. Meanwhile, inert carbon-based matrices such as CNT networks, graphene foams, or porous carbon fibers offer improved mechanical integrity and serve as frameworks for supporting active materials. However, because these hosts are typically electrochemically inactive, they contribute little to the total capacity. Their ion transport is passive, and they do not participate in redox reactions or dynamically stabilize the interfacial chemistry. By contrast, CP-functionalized anodes incorporate multiple advantages, including dendrite suppression, facilitated ion transport, volume buffering, and additional redox activity, thereby providing a comprehensive solution beyond conventional metal or inert matrix hosts. These enhancements underscore the role of CPs as both passive binders or scaffolds and multifunctional design elements that actively improve the cycle life, rate performance, and operational safety in metal-based HC anodes91,92.
a A comparison of the key properties of bare metal, inert carbon matrix, and CP-based hybrid anodes. b Schematic diagrams showing various engineering strategies for high-efficiency anode design, including (i) ion-selective CP networks via functionalization, (ii) redox-active CP-SEI layer introduction, (iii) fabrication of nanoporous 3D CP scaffolds, and (iv) tuning of the mechanical properties for flexible electrodes.
Engineering solutions
The persistent challenges associated with metal-based anodes—ranging from dendrite formation to interfacial instability—have prompted the development of advanced CP-based engineering strategies. These approaches aim to harness the inherent electrochemical and mechanical versatility of CPs while introducing architectural and functional innovations that are tailored for high-efficiency hybrid energy storage systems (Fig. 9b). For instance, one promising direction involves the creation of ion-selective porous CP networks in which polymers are functionalized with anionic or zwitterionic side chains that can preferentially interact with Zn²⁺, Na⁺, or K⁺ ions (Fig. 9b(i)). Such functional groups guide directional ion transport, thereby reducing random nucleation and facilitating anisotropic metal plating. This level of ion specificity plays a critical role in minimizing dendritic growth and promoting uniform interfacial reactions60,93,94.
Another approach leverages CPs as redox-active analogs to traditional SEIs (Fig. 9b(ii)). Unlike conventional SEIs, which are often electrically insulating and prone to breakdown, CP-based interphases can serve as reversible, electronically conductive barriers. These self-limiting CP layers regulate electron and ion flow, suppress parasitic reactions, and maintain interfacial stability during cycling—effectively mimicking SEI behavior while contributing additional pseudocapacitance95,96.
The anode performance can be further enhanced by the incorporation of a 3D CP scaffold (Fig. 9b(iii)). Nanoporous CP frameworks provide a large electroactive surface area, enhanced electrolyte accessibility, and multi-directional ion diffusion channels. These porous architectures facilitate homogeneous Zn²⁺ or Na⁺ flux and improve electrode–electrolyte interactions, thereby enabling stable, high-rate operation even under mechanically dynamic conditions97,98,99. Meanwhile, in the context of flexible and wearable energy systems, the mechanical tuning of CPs is an essential aspect (Fig. 9b(iv)). Elastomeric CP hybrids and copolymer blends have been engineered to provide stretchability and bendability without sacrificing conductivity or redox responsiveness. These mechanically compliant materials enable the fabrication of deformable anode architectures that can withstand bending, compression, or torsion, which makes them ideal for next-generation wearable HCs100,101.
Together, these engineering strategies demonstrate the vast potential of CPs not only as active materials, but also as intelligent structural and interfacial elements that adapt to the demanding mechanical and electrochemical conditions of modern energy storage devices.
Outlook
CPs have emerged as a uniquely adaptable class of materials in the field of HCs, where they offer a combination of electrochemical activity, mechanical flexibility, and interfacial tunability. They can be systematically integrated into cathodes and anodes to address persistent challenges in terms of energy density, rate capability, and cycling stability, and may also contribute to the electrolyte phase, for example, as ion-conductive pathways or self-healing gel matrices. Such multifunctional roles position the CPs as not merely supporting materials but core components that are capable of redefining the performance boundaries and design paradigms of the HCs.
The continued evolution of CPs for next-generation HC systems hinges on strategic innovation at the molecular, computational, and systems-integration levels. As conventional electrode materials approach their performance limits, the CPs must advance towards precise molecular design, accelerated discovery, and synergistic device architectures. At the molecular level, the development of novel CP monomers with tailored redox windows, efficient ionic pathways, and chemical robustness under harsh electrochemical conditions will be essential. The incorporation of intrinsic functionalities such as ion selectivity, structural adaptability, and environmental resilience will allow the CPs to perform reliably across diverse electrolytes and voltage ranges.
At the same time, CP development will be accelerated by data-driven discovery. Artificial intelligence (AI) and machine learning (ML), coupled with high-throughput electrochemical screening and predictive modeling, can rapidly identify optimal polymer backbones, dopants, and hybrid morphologies while elucidating structure–function relationships102,103. Specifically, supervised learning models such as Random Forest, XGBoost, Support Vector Machine (SVM), and Artificial Neural Network (ANN) can be employed to predict key properties of CPs, such as electrical conductivity and specific capacitance. While relatively simple models like Random Forest and XGBoost perform well with limited datasets, ANNs are advantageous for handling large and complex data. For the optimal design of novel polymers, the Bayesian Optimization (BO) framework is particularly effective. By leveraging Gaussian Processes (GPs) with acquisition functions, incorporating uncertainty quantification through Bayesian Neural Networks, and adopting multi-objective strategies such as q-Expected Hypervolume Improvement (q-EHVI), design efficiency can be maximized. Collectively, these ML techniques enable a closed-loop design strategy that integrates prediction (ANN) and optimization (BO), thereby advancing the performance of CP-based electrodes in terms of both power and energy density. Beyond traditional polymer chemistry, interdisciplinary integration will unlock new hybrid materials by combining CPs with biopolymers, metal–organic frameworks (MOFs), nanocellulose, or 2D materials such as MXene and graphene91,92,93,94. Such architectures can unify mechanical robustness, ionic conductivity, and electrochemical activity. Among these materials, MXene and MOF have attracted particular attention for high-capacitance applications. MXene combines metallic conductivity with pseudocapacitive ion intercalation within its two-dimensional layers, although restacking can reduce the accessible surface area, which can be mitigated through CP intercalation. In contrast, MOF offers ultra-high porosity and abundant active sites but suffers from low electrical conductivity and poor structural stability. Integrating CP with either material effectively enhances conductivity and mechanical integrity, thereby unlocking their potential as high-performance hybrid electrodes104,105,106. Progress in this direction will rely on synergies among polymer physics, electrochemistry, and nanotechnology in order to bridge the gap between laboratory prototypes and scalable real-world devices.
In view of these prospects, the CPs are well-positioned to play a central role in sustainable, customizable, and smart hybrid energy storage platforms. Their combination of molecular tunability, multifunctionality, and adaptability offers a transformative pathway toward future energy technologies, ranging from wearable electronics to grid-scale systems. Nevertheless, CP-based architectures have long faced challenges related to production cost, processability, and yield. Despite extensive research efforts, these limitations remain major bottlenecks, constraining the large-scale implementation of CP-based systems. However, with the growing demand for miniaturized and wearable devices, the intrinsic value and utilization of CPs, particularly in high-power energy storage, are expected to increase substantially. This expanding market demand is likely to drive higher production volumes and promote economies of scale. As optimal large-scale manufacturing processes are established and production costs decrease, these challenges are anticipated to be progressively alleviated. We remain confident that CPs are well-positioned to bridge the gap between high-performance laboratory demonstrations and commercially viable energy storage technologies.
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Acknowledgements
This research was supported by Basic Science Program (RS-2023-00245105) through the National Research Foundation of Korea (NRF) funded by the Ministry of Education.
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Kim, S., Yoon, H. The strategic role of conducting polymers in zinc- and alkali-ion hybrid capacitors. Commun Mater 6, 278 (2025). https://doi.org/10.1038/s43246-025-01008-6
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DOI: https://doi.org/10.1038/s43246-025-01008-6
