In a groundbreaking development poised to revolutionize energy storage technologies, researchers Park, D., Kim, H., and Kim, Y. have unveiled a novel class of flexible lithium supercapacitors featuring water-processable solid-state electrolytes. Published in the upcoming 2026 issue of npj Flexible Electronics, this study introduces an innovative electrolyte system rooted in aromatic acid-doped branched poly(ethylene imine) platforms, promising significant advancements in safety, flexibility, and device performance. This pioneering work addresses longstanding challenges plaguing conventional lithium-ion battery and supercapacitor technologies, particularly in the realm of wearable and flexible electronics.

The surge in demand for flexible energy storage solutions stems from the rapid proliferation of wearable devices, soft robotics, and flexible displays. However, traditional lithium-ion batteries, with their liquid electrolytes, pose severe safety hazards, including leakage and flammability, and suffer from mechanical rigidity, limiting their integration in flexible platforms. Solid-state electrolytes (SSEs) have emerged as a promising alternative due to their inherent safety and stability advantages, but they often encounter issues related to ionic conductivity and processability that impede their commercial adoption.

Against this backdrop, the research team drew inspiration from polymer chemistry and green processing techniques to engineer a new electrolyte matrix capable of marrying mechanical flexibility with outstanding electrochemical performance. Their approach leveraged the unique molecular architecture of branched poly(ethylene imine) (bPEI), a polymer known for its high density of amine groups, and strategically doped it with aromatic acids to enhance ionic transport pathways. This synergy not only optimizes lithium-ion mobility but also facilitates electrolyte fabrication through environmentally friendly water-based processing methods.

The doping of bPEI with aromatic acids imparts several critical functionalities. Aromatic acids bestow rigidity and electronic delocalization within the polymer matrix, which supports the formation of stable ion-conducting networks. This doping fundamentally alters the polymer’s microstructure, tailoring its free volume and facilitating the transport of lithium ions across the electrolyte. The resultant material exhibits a remarkable balance between mechanical robustness—allowing for bending and twisting—and ionic conductivity, which rivals that of traditional liquid electrolytes.

Water processability represents a significant leap forward in sustainable manufacturing of flexible energy devices. Conventional polymer electrolytes often require toxic organic solvents or complicated synthesis protocols, limiting scalability and environmental compatibility. The ability to process the new electrolyte in aqueous media simplifies fabrication, reduces costs, and enhances the potential for large-scale roll-to-roll manufacturing of flexible supercapacitors and batteries. This eco-friendly aspect aligns with global sustainability goals and strengthens the commercial viability of next-generation energy storage systems.

Electrochemical characterization of the newly developed supercapacitors revealed impressive performance metrics. The devices demonstrate high specific capacitance and excellent rate capability, maintaining stable charge-discharge cycles over extended periods. Crucially, the solid-state nature of the electrolyte effectively suppresses dendritic lithium growth, a major challenge that causes short circuits and catastrophic failure in lithium-metal batteries. This safety enhancement is particularly crucial for flexible applications where mechanical deformation could exacerbate dendrite formation.

Moreover, the mechanical testing underscored the electrolyte’s resilience under dynamic deformation. The supercapacitors sustain stable electrochemical performance even after multiple bending tests, mimicking real-world application conditions such as wearable textiles and foldable devices. The polymer matrix’s branched architecture absorbs mechanical stress, preventing microcracks and delamination that typically deteriorate device longevity. This robustness opens pathways to integrate lithium supercapacitors into versatile form factors previously inaccessible to rigid battery chemistries.

The theoretical underpinning for the enhanced ionic conductivity was explored through molecular dynamics simulations and spectroscopic analysis. These studies revealed that the aromatic acid dopants serve as both lithium-ion coordination centers and physical crosslinks within the bPEI network, creating continuous lithium-ion conduction pathways. This contrasts with typical polymer electrolytes where ionic clusters form isolated domains that impede charge transport. The design principle showcased here demonstrates how chemical tailoring at the molecular level can profoundly influence macroscopic device properties.

The researchers also explored the electrolyte’s thermal stability, a critical parameter for real-world deployment. Thermal gravimetric analysis and differential scanning calorimetry confirmed that these materials remain stable across a wide temperature range, preventing degradation under harsh operating conditions. This attribute is essential not only for flexible electronics subjected to varying ambient conditions but also for high-power applications where heat generation can impair battery life or pose safety risks.

Integration of the solid-state electrolyte within flexible device architectures leveraged straightforward fabrication techniques, including solution casting and layer-by-layer assembly. The compatibility with standard lithographic and printing methods underscores its adaptability to diverse manufacturing environments. The seamless assembly of the supercapacitor components ensures uniform electrolyte distribution, intimate electrode-electrolyte contact, and minimal interfacial resistance, which are paramount for optimal device efficiency.

The implications of this research extend beyond flexible energy storage. The design concept of aromatic acid-doped branched polyamines could be expanded to develop other functional polymer systems for energy conversion, including solid polymer electrolytes for fuel cells or electrochromic devices. The water-processable and environmentally benign processing methodology further positions this platform as a versatile candidate for green electronics manufacturing.

Looking forward, the study lays a robust foundation for incorporating additional functional dopants to tailor electrolyte properties for specific applications—such as enhanced ionic selectivity, improved mechanical strength, or self-healing capabilities. Coupling these materials with emerging electrode chemistries, including lithium metal or silicon-based anodes, may unlock unprecedented energy densities for flexible supercapacitors, tackling limitations inherent in current lithium-ion technology.

As wearable and flexible electronics become pervasive, the need for energy storage systems that are not only high-performing but also safe, scalable, and environmentally friendly grows exponentially. The work by Park and colleagues represents a major milestone in achieving this balance, demonstrating an elegant interplay of molecular design, green chemistry, and device engineering. Their innovative solid-state electrolyte platform heralds a new era in flexible lithium supercapacitors that could transform consumer electronics, healthcare devices, and beyond.

The prominence of this new electrolyte system is expected to catalyze further research efforts aimed at bridging the gap between laboratory prototypes and market-ready products. Industry stakeholders are particularly interested in its compatibility with existing manufacturing infrastructure and its potential to circumvent safety concerns associated with liquid electrolytes. This advancement is well aligned with the increasing regulatory emphasis on safe and sustainable battery technologies worldwide.

In conclusion, the introduction of aromatic acid-doped branched poly(ethylene imine) to create water-processable solid-state electrolytes marks a significant step toward flexible, safe, and durable lithium supercapacitors. The exemplary performance, coupled with environmentally conscious processing approaches, positions these materials at the forefront of next-generation energy storage innovation. As the digital age embraces flexibility and mobility, such breakthroughs are indispensable in powering our increasingly connected world.

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Subject of Research: Development of flexible lithium supercapacitors leveraging water-processable solid-state electrolytes based on aromatic acid-doped branched poly(ethylene imine) platforms.

Article Title: Flexible Lithium Supercapacitors with Water-Processable Solid-State Electrolytes Based on Aromatic Acid-Doped Branched-Poly(ethylene imine) Platforms.

Article References:
Park, D., Kim, H. & Kim, Y. Flexible Lithium Supercapacitors with Water-Processable Solid-State Electrolytes Based on Aromatic Acid-Doped Branched-Poly(ethylene imine) Platforms. npj Flex Electron (2026). https://doi.org/10.1038/s41528-026-00600-1

Image Credits: AI Generated

In the relentless quest to revolutionize energy storage technologies, sodium metal batteries (SMBs) have surfaced as a highly promising alternative to conventional lithium-ion systems. Leveraging the abundant availability of sodium and benefiting from a supply chain less susceptible to geopolitical and economic fluctuations, SMBs present a compelling case for large-scale adoption. However, critical challenges have hampered their practical deployment, specifically the demand for ultrafast charging rates coupled with long cycle life and robust safety profiles. Addressing these issues has pushed researchers to innovate beyond the conventional boundaries of electrolyte design, and a groundbreaking approach has now emerged that promises to reshape the fundamental limits of SMB performance.

Conventional quasi-solid-state electrolytes (QSEs), while offering some advantages in terms of safety and mechanical integrity compared to liquid electrolytes, are significantly hindered by two primary bottlenecks. First, the transport of sodium ions (Na⁺) through the bulk electrolyte is inhibited due to the dominant movement of anions, resulting in reduced Na⁺ transference numbers typically ranging between 0.4 to 0.7. This imbalance precipitates concentration polarization, reducing the effective ionic mobility at high current densities and limiting ultrafast charging capabilities. Second, ionic diffusion at the interfaces between electrolyte and electrodes—the bilateral interphases—is often sluggish, fostering dendrite formation on the anode and accelerating electrolyte degradation, thereby compromising both longevity and safety of SMBs.

Shattering these limitations, a research consortium from Southeast University, in partnership with HiNa Battery Technology Co., Ltd. and Yangzhou University, has introduced an innovative dual interlocked mediator electrolyte system. This novel quasi-solid-state electrolyte, designated as Sn-FB QSE, achieves near-unity Na⁺ transference numbers alongside exceptional ionic conductivity without resorting to complex polymer functionalizations typically required in single-ion conducting strategies. The secret lies in the synergistic engineering of two mediators—cationic Sn²⁺ ions and anionic difluoro(oxalato)borate (DFOB⁻)—that simultaneously modulate the bulk electrolyte structure and interfacial chemistry, delivering unprecedented electrochemical performance tailored for ultrafast charging and extended battery life.

The dual interlocked mediator mechanism operates on two intertwined fronts. During the synthesis phase, Sn²⁺ initiates a controlled in situ cationic polymerization of 1,3-dioxolane (PDOL), constructing a uniformly cross-linked amorphous polymer network that imparts mechanical strength while facilitating ion transport. Simultaneously, DFOB⁻ acts as a polymerization retarder, preventing excessive cross-linking and maintaining an optimal network polydispersity index around 1.6—a value significantly lower than single-mediator systems—thus balancing mechanical robustness with ion mobility. This finely tuned polymer matrix strengthens puncture resistance to 8.5 kPa, crucial for preventing dendrite penetration while supporting flexible form factors.

At the molecular level, sophisticated simulations reveal that DFOB⁻ preferentially coordinates with Na⁺ ions, effectively attenuating the strong Na⁺-polymer oxygen interactions that traditionally bind salts tightly within polymer matrices. This chemical modulation reduces the average coordination number from 4.87 to 2.81, liberating a substantial fraction of free Na⁺ ions that are free to migrate swiftly through the electrolyte. The resulting diffusion coefficient, calculated at 16.8 Ų/ns, marks a sixfold enhancement over conventional liquid electrolytes, thereby enabling rapid Na⁺ conduction even under aggressive charging regimes.

Upon cell operation, an elegant interfacial transformation ensues shaped by the distinct frontier orbital energies of the two mediators. Sn²⁺$, possessing a low LUMO energy level of −4.87 eV, is preferentially reduced at the sodium metal anode surface, forming a hybrid solid-electrolyte interphase (SEI) composed of nano-scale NaSn alloys embedded within inorganic-rich matrices. This SEI effectively homogenizes local electric fields, dramatically reducing nucleation overpotentials to approximately 50 mV and creating a mechanically stable protective barrier that mitigates dendrite initiation and growth. Concurrently, the DFOB⁻ anion, with its higher HOMO energy of −8.12 eV, undergoes sacrificial oxidation at the cathode to establish a thin yet resilient cathode–electrolyte interphase (CEI) approximately 14 nm thick. This CEI exhibits an extraordinary Young’s modulus near 8.9 GPa, an order of magnitude greater than single-mediator counterparts, mitigating mechanical degradation during repeated cycling.

Electrochemical testing validates the transformative impact of this dual mediator approach. Symmetric Na|Na cells sustain stable cycling over an unprecedented 6000 hours at 0.1 mA cm⁻² with minimal polarization (~0.1 V) and no dendritic short-circuit events, comparable to nearly continuous operation for over eight months. The critical current density surges to 3.0 mA cm⁻², while the exchange current density rises to 10 μA cm⁻², reflecting enhanced interfacial kinetics. When paired with Na₃V₂(PO₄)₃ (NVP) cathodes, full cells demonstrate retention of 90% capacity after 2000 cycles at a rapid 3C charge-discharge rate, retaining 80.1 mAh g⁻¹ at an extraordinary 15C, and maintaining 53.4 mAh g⁻¹ after 800 cycles even at 5C. The electrochemical stability window is also broadly expanded to 4.7 V vs. Na⁺/Na, paving the way for compatibility with high-voltage cathode materials.

To bridge the gap between laboratory innovation and practical application, the research team scaled their Sn-FB QSE technology into high-mass-loading full cells containing 5 mg cm⁻² NVP cathodes, achieving 75% capacity retention after 500 cycles at 1C. Pouch cells without applied pressure, measuring 4 × 5 cm², demonstrated impressive mechanical resilience by retaining 84% capacity after 19 cycles and powering smartphones continuously even through repeated full folding. Additionally, compatibility with advanced sodium nickel iron manganese oxide (NaNi₁/₃Fe₁/₃Mn₁/₃O₂, NFM) cathodes with high mass loading (17.54 mg cm⁻²) was confirmed, showcasing initial capacities of 129.9 mAh g⁻¹ and stable cycling performance over multiple cycles, indicating versatility across diverse cathode chemistries.

This pioneering dual interlocked mediator electrolyte paradigm overturns the long-standing trade-offs in electrolyte design—simultaneously achieving single-ion conduction, high mechanical strength, and adaptive bilateral interphases, properties traditionally viewed as mutually exclusive. By harnessing the complementary chemical and electronic properties of the Sn²⁺ and DFOB⁻ mediators, the approach delivers holistic control over ion transport and interfacial stability, unlocking performance metrics previously deemed unattainable for quasi-solid-state sodium electrolytes. Moreover, its intrinsic scalability via in situ polymerization and compatibility with existing battery manufacturing infrastructures spotlight this innovation as a viable candidate for commercial deployment.

Looking forward, this versatile mediator strategy harbors significant potential beyond sodium systems. Its principles may be extended to lithium and potassium metal batteries, where similar challenges in ion selectivity and interface stability prevail. Moreover, integrating this dual mediator system into fully solid-state configurations could yield safer, denser energy storage solutions with ultrafast charging capabilities. Concurrently, advancing mechanistic understanding through AI-guided frontier orbital screening may expedite the discovery of new mediator pairs optimized for specific chemistries, ushering an era of rational electrolyte design tailored to next-generation battery demands.

In essence, the dual interlocked mediator engineering approach pioneers a transformative paradigm for battery electrolytes that bridges performance, safety, and manufacturability. By breaking free from the restrictions imposed by traditional electrolyte designs, sodium metal batteries can now realistically aspire to meet the rigorous demands of ultrafast charging, long cycle life, and intrinsic safety at scale. This breakthrough marks a critical milestone propelling sodium batteries from a niche laboratory curiosity to a formidable contender in the mainstream energy storage landscape, drawing us closer to a sustainable energy future predicated on earth-abundant and cost-effective materials.

Subject of Research:
Article Title: Dual Interlocked Mediators Enable Single‑Ion‑Conducting Quasi‑Solid‑State Electrolytes for Ultrafast‑Charging Long‑Life Sodium Metal Batteries
News Publication Date: 21-May-2026
Web References: http://dx.doi.org/10.1007/s40820-026-02236-2
Image Credits: Yuan Zhang, Long Pan, Cheong Wa Leong, Xing-Guo Qi, Xiaozhong Huang, Xinyi Cai, Mufan Cao, Min Gao, Haoyu Zhang, Dawei Sha, Yang Zhou, ZhengMing Sun*

Keywords

Sodium Metal Batteries, Quasi-Solid-State Electrolytes, Single-Ion Conduction, Dual Interlocked Mediators, Sn-FB QSE, Polymer Electrolytes, Solid-Electrolyte Interphase, Cathode-Electrolyte Interphase, Ultrafast Charging, Electrochemical Stability, Ion Transport, Battery Cycle Life

In remote surveillance trailers and mobile surveillance towers, a stable power supply is essential to keeping equipment online.

While we make batteries based on many different chemistries, nothing has approached the massive scale at which we can produce lithium batteries. That scale makes the economics of lithium-ion batteries hard to compete with. Even if we develop a superior battery technology, it's unclear whether we can get manufacturing costs down quickly enough to compete with the efficiency of the lithium supply chain and manufacturing.

The one thing that could change the dynamics is a supply crunch. While lithium is extremely widespread, lithium that can be extracted economically is a different matter. It's cheapest to extract it from brines, and lithium-rich brines are largely limited to South America. We do obtain some lithium from other sources, but it's considerably more expensive.

In today's issue of Science, however, a research team has identified an energy-efficient means of extracting lithium from rocks. The process they've designed uses far less energy than existing ones, regenerates all its starting chemicals, and produces byproducts that could also be sold.

Read full article

Comments

© Cavan Images

While we make batteries based on many different chemistries, nothing has approached the massive scale at which we can produce lithium batteries. That scale makes the economics of lithium-ion batteries hard to compete with. Even if we develop a superior battery technology, it's unclear whether we can get manufacturing costs down quickly enough to compete with the efficiency of the lithium supply chain and manufacturing.

The one thing that could change the dynamics is a supply crunch. While lithium is extremely widespread, lithium that can be extracted economically is a different matter. It's cheapest to extract it from brines, and lithium-rich brines are largely limited to South America. We do obtain some lithium from other sources, but it's considerably more expensive.

In today's issue of Science, however, a research team has identified an energy-efficient means of extracting lithium from rocks. The process they've designed uses far less energy than existing ones, regenerates all its starting chemicals, and produces byproducts that could also be sold.

Read full article

Comments

© Cavan Images

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