Vanadate glasses have long attracted attention for energy applications because vanadium is a transition metal that readily adopts multiple oxidation states, chiefly V⁴⁺ and V⁵⁺. This flexibility allows electronic charge carriers—electrons or small polarons—to hop between vanadium sites through the disordered amorphous network, giving the glasses a form of electronic conduction that coexists with the ionic conduction supplied by mobile lithium ions. The result is a mixed ionic-electronic conductor, a class of material that is particularly valuable in electrodes, where both electrons and ions must move efficiently. The starting composition in the new study, 60V₂O₅–20BaO–20Li₂O, was designed in earlier work by the same group, and the team progressively replaced barium oxide and lithium oxide with their fluoride counterparts, barium fluoride and lithium fluoride, ending at 60V₂O₅–20BaF₂–20LiF. Crucially, the vanadium pentoxide content was held constant at 60 mole percent throughout, so any change in properties could be attributed cleanly to the fluorine substitution rather than to shifts in the electroactive component.

The thermal behavior of the glasses told one part of the story. As fluorine content increased, the glass transition temperature rose monotonically, indicating that fluorine was tightening the structural network rather than loosening it. This is somewhat counterintuitive, since fluorine is often introduced into oxide glasses to break bridging bonds and reduce network connectivity; in many fluorophosphate and fluorosilicate systems it acts as a network modifier, lowering working temperatures and softening the glass. Here, however, the steadily increasing transition temperature suggests that fluorine in the vanadate matrix occupies sites that strengthen the overall framework, perhaps by forming strong V–F bonds or by altering the coordination environment of vanadium in ways that stiffen the network against thermal agitation. For device engineers, a higher glass transition temperature is welcome news, since it signals better thermal stability for materials that may need to operate warm.

The electrical conductivity, by contrast, refused to follow a simple trend. Rather than rising or falling smoothly with fluorine content, the conductivity varied non-monotonically, a hallmark of competing transport mechanisms whose relative strengths shift as the structure evolves. The team observed an intriguing phenomenon in the temperature-dependent conductivity plots: at lower temperatures, the oxyfluoride glasses displayed double plateaus in conductivity—two distinct regions where the conductivity changes character—which then merged into single plateaus at temperatures above roughly 190 degrees Celsius. This two-plateau behavior implies that two different conduction or relaxation processes dominate in different temperature windows, plausibly reflecting the interplay between ionic hopping of Li⁺ ions and electronic polaronic hopping between V⁴⁺ and V⁵⁺ sites. To analyze the data quantitatively, the researchers fitted both the single- and double-plateau regions using Jonscher’s power law, the standard empirical description of the universal dielectric response in disordered solids, in which the frequency-dependent conductivity follows a power-law exponent that encodes the nature of the charge carrier interactions with the lattice.

Understanding exactly what fluorine was doing to the glass structure required an arsenal of spectroscopic probes. Fourier-transform infrared spectroscopy revealed that the distorted VO₆ octahedra characteristic of vanadate glasses are actually present in the network as VO₄ tetrahedra and VO₅ square pyramids—shorter, tighter coordination units that form the backbone of the amorphous structure. Raman spectroscopy then provided a window into how these units reorganize as fluorine is introduced, tracking changes in vanadium–oxygen bond lengths and bond orders across the series. Electron paramagnetic resonance spectroscopy complemented the Raman data by sensing the unpaired electrons on V⁴⁺ ions, allowing the team to follow the changing concentrations of V⁴⁺ and V⁵⁺ in the matrix. The two techniques told a mutually consistent story, with the structural features inferred from Raman spectra independently confirmed by the EPR analysis. Together they showed that fluorine substitution does not merely dilute the oxide network—it actively perturbs the vanadium valence balance, which in turn modulates the polaronic electronic conductivity riding on top of the lithium ionic conductivity.

The electrical characterization went beyond simple conductivity measurements. The team employed impedance spectroscopy analyzed through Cole-Cole plots, the classical complex-plane representation that separates bulk, grain-boundary, and electrode contributions to the measured impedance, and they applied the electric modulus formalism, which suppresses electrode polarization effects and isolates the bulk relaxation dynamics of the mobile ions. These approaches allowed a detailed interpretation of the relaxation mechanism—how charge carriers in the glass respond to alternating electric fields across a range of frequencies and temperatures, and how the characteristic relaxation times shift with composition. Such analyses are essential for distinguishing genuine bulk transport from interfacial artifacts, and they lent confidence to the composition-property trends extracted from the study.

The electrochemical tests were where the practical payoff became apparent. Using cyclic voltammetry, the researchers probed the reversibility of the redox processes at the glass electrodes and evaluated their suitability for charge storage. Galvanostatic charge-discharge measurements then provided direct determinations of specific capacitance at controlled current densities, the key metric for supercapacitor performance. The fully fluorinated VBOLF glass emerged as the standout: it combined the best electrical conductivity of the series with the highest specific capacitance, 242.7 F/g at 0.1 A/g, and it maintained good stability over repeated charge-discharge cycling. The synergy makes physical sense—a more conductive glass delivers electrons and ions to the electrochemical interface more efficiently, while the fluorine-modified vanadium environment appears to support favorable redox activity and structural resilience during cycling.

The findings arrive amid a broader resurgence of interest in vanadium-based amorphous and glassy materials for energy storage. Vanadate-borate glasses have been proposed as high-capacity cathodes for rechargeable lithium-ion batteries, and glass-ceramic-like vanadate cathodes have demonstrated high-rate performance, exploiting the multi-electron redox chemistry of vanadium. Fluoride-containing electrode materials, meanwhile, are prized for their high working voltages and the improved cycling stability that fluorine can impart to disordered rock-salt oxyfluoride cathodes. The Bangalore study ties these threads together at the level of fundamental glass science, providing a coherent mechanistic picture of why fluorine helps: it tunes the balance between the two dominant charge carriers, stiffens the network thermally, and reorganizes the vanadium coordination units in ways that benefit both conduction and capacitive storage.

What makes the work particularly valuable methodologically is the disciplined one-variable-at-a-time design combined with cross-validating spectroscopy. Because the vanadium oxide content was fixed, and barium and lithium components were converted one-for-one from oxides to fluorides, the study isolates the role of the anion sublattice with unusual clarity. The agreement between Raman-derived structural models and EPR-derived valence data gives the conclusions a robustness that single-technique studies often lack. And the observation of double conductivity plateaus—with their eventual merger above 190 degrees Celsius—offers a rich phenomenological fingerprint that future theoretical models of mixed conduction in oxyfluoride glasses will need to reproduce.

For now, the message is straightforward: fluorine substitution is not merely a compositional tweak but a genuine steering mechanism for the functional properties of vanadate glasses. By dialing in the right amount of fluorine, materials scientists can tilt a glass toward higher ionic mobility, stronger electronic conduction, or superior electrochemical storage—and the fully fluorinated composition examined here suggests that, for supercapacitor applications at least, the dial has room yet to turn. As demand grows for cheap, stable, and easily processed electrode materials, amorphous oxyfluoride conductors like VBOLF may find themselves moving from the impedance spectrometer to the prototype cell.

The collaboration unites Prof. Toshinori Okura and Santosh Miryala from Kogakuin University with Prof. Kaushal Kumar from IIT (ISM) Dhanbad. Together, the teams will investigate Narpsio-V glass-ceramics, a promising class of materials commonly described as sodium-ion superionic conductors.

Narpsio-V systems are attracting intense interest because they combine high ionic conductivity with strong chemical stability—two properties that are essential for practical solid electrolytes. Their glass-ceramic architecture also offers the opportunity to tune phase formation and transport pathways during processing.

A central theme of the research is to deepen understanding of structural and microstructural evolution as materials transition from glassy precursors to functional crystalline phases embedded within an amorphous matrix. This evolution is expected to directly influence sodium-ion mobility and long-term performance under operating conditions.

The joint work will integrate experimental investigations across multiple length scales, from compositional and phase analysis to microstructural characterization that probes grain-scale features relevant to ion transport. By correlating these observations with electrochemical behavior, the researchers aim to establish clear structure–property relationships.

Within energy storage and conversion, sodium-ion superionic conductors are key candidates for solid-state sodium-ion batteries and related electrochemical devices. These technologies can benefit from replacing flammable liquid electrolytes with robust solid alternatives, improving safety and enabling new design constraints.

The partners also plan to explore strategies to optimize performance by refining synthesis and processing conditions. Such approaches may help control ionic transport pathways, mitigate degradation mechanisms, and enhance conductivity while maintaining chemical reliability.

“Narpsio glass-ceramic materials offer tremendous potential for next-generation energy storage because of their exceptional sodium-ion conductivity and versatility. Through this collaboration, we aim to deepen our understanding of these materials and accelerate the development of advanced solid electrolytes,” said Prof. Toshinori Okura.

“This academic collaboration represents more than a joint research project as it reflects the growing scientific partnership between Japan and India,” Santosh Miryala added. Prof. Kaushal Kumar emphasized that leveraging complementary expertise will create a strong platform for long-term cooperation and innovation in advanced glass materials.

Subject of Research: Next-generation multifunctional glass-ceramic materials; sodium-ion superionic conductors (Narpsio-V) for energy storage and conversion.
Article Title: Kogakuin University–IIT (ISM) Dhanbad Collaboration Advances Narpsio-V Glass-Ceramic Solid Electrolytes
News Publication Date:
Web References:
References:
Image Credits: Kogakuin University

Keywords

Sodium-ion batteries; solid electrolytes; glass-ceramics; superionic conductors; ionic conductivity; phase evolution; microstructural characterization; energy materials.

A groundbreaking study recently published in Nature Nanotechnology by a collaborative team spearheaded by Prof. CHENG Huiming and PENG Jing at the Shenzhen Institute of Advanced Technology, alongside Prof. HU Renzong from South China University of Technology, proposes an ingenious solution to this challenge. The researchers engineered a novel composite solid electrolyte that remarkably decouples ionic conduction pathways from mechanical flexibility. This innovation results in a material that boasts superionic conduction rivaling liquid electrolytes and simultaneously retains the mechanical adaptability necessary for intimate electrode contact and volume change accommodation.

At the heart of this new electrolyte design lies a sophisticated composite architecture characterized by alternating layers of perpendicularly aligned LixMyPS3 (where M denotes Cd or Mn) nanosheets interleaved with layers of polyethylene oxide (PEO). This layered configuration crafts continuous and highly efficient conduits for lithium-ion movement through the battery, while the PEO layers impart a flexibility that preserves the structural integrity and intimate contact with the electrodes throughout charge-discharge cycles. The strategic alignment of nanosheets ensures that ion diffusion pathways are uninterrupted and highly directional, a key factor enabling ultra-high ionic mobility.

Performance evaluations of the PA-LiCdPS/PEO composite electrolyte illustrated its ionic conductivity reaching 10.2 mS cm^-1 at ambient conditions (25 °C), an unprecedented achievement that places it among the best solid electrolytes and on par with many conventional liquid electrolytes. Notably, this superionic conductivity is attained without sacrificing mechanical compliance, a balance rarely struck in prior electrolyte formulations. Furthermore, to demonstrate the versatility and reproducibility of the structural design, a variant of the electrolyte incorporating manganese—PA-LiMnPS/PEO—exhibited robust ionic conduction at 6.1 mS cm^-1 under identical conditions. This suggests a flexible platform for tailoring electrolyte properties by varying the transition metal component.

Leveraging these composite electrolytes, the team fabricated all-solid-state lithium metal batteries capable of high-performance operation with minimal external pressure. Traditional sulfide-based solid electrolytes often require substantial stack pressure—sometimes exceeding hundreds of MPa—to maintain battery integrity and interfacial contact. By contrast, the flexible layered electrolyte system accommodated electrode expansion and contraction during cycling inherently, eliminating the need for substantial external compression. For instance, Li||LiNi0.8Co0.1Mn0.1O2 coin cells assembled with PA-LiCdPS/PEO retained an impressive 92% of their initial capacity after 600 cycles at a moderate current density of 0.2 mA cm^-2 under stack pressures below 0.5 MPa.

Even more compelling is the demonstration of practical scalability and operational stability in pouch cell configurations. The pressure-less Li||LiFePO4 battery cells, utilizing the same electrolyte architecture, affirmed the feasibility of this electrolyte concept for real-world battery designs where applying large mechanical clamping forces is impractical or undesirable. This breakthrough reduces both complexity and manufacturing costs by obviating the need for heavy fixtures and stringent pressure management systems commonly used in solid-state battery assembly.

Besides mechanical and electrochemical advantages, the PA-LiMPS/PEO composite electrolytes exhibited exceptional chemical stability in ambient conditions, a notorious challenge for sulfide-based electrolytes typically prone to rapid degradation. Over seven days of exposure to humid air, these composite samples maintained their high ionic conductivity with negligible hydrogen sulfide (H2S) release, a toxic and corrosive byproduct often associated with sulfide decomposition. This atmospheric resilience not only simplifies handling and processing but also enhances the safety profiles of batteries assembled with these electrolytes.

The foundational principle of this research lies in the biomimetic design strategy: decoupling ion conduction and mechanical function into dedicated structural components. By mimicking natural systems where pathways and mechanical frameworks serve distinct but complementary roles, the researchers surmounted what was once thought an immutable trade-off. The continuous ion transport routes along the perpendicularly oriented nanosheets ensure uninterrupted lithium ion flow, while the flexible polymeric layers absorb mechanical stress. This synergy creates a solid-state electrolyte that is both mechanically adaptive and electrochemically superior.

Such a design paradigm is poised to accelerate the commercialization of all-solid-state lithium batteries, facilitating safer, more reliable, and higher energy density power sources for electric vehicles, portable electronics, and grid storage. Moreover, by enabling battery operation without external pressure applications, these electrolytes break new ground in simplifying battery cell designs—a critical enabler for mass production and integration into diverse form factors where space and weight constraints are paramount.

This research exemplifies a significant leap forward in electrolyte science, providing a replicable blueprint for engineering composite materials that meet stringent, multi-faceted performance criteria. The intrinsic flexibility paired with exceptional ionic conduction addresses critical bottlenecks, signaling a promising horizon for the realization of robust, long-lasting all-solid-state battery technologies. Future work will likely explore the tunability of the layered structures, scaling up fabrication techniques, and integrating these electrolytes within full battery systems for industrial evaluation.

In summary, the innovative approach to designing composite solid electrolytes reported in this study not only resolves a long-standing conflict in materials science but also ushers in new avenues for creating flexible, high-performance batteries that marry safety with energy density. The perpendicularly aligned nanosheet/polymer layered structure emerges as a compelling platform for next-generation energy storage devices, setting the stage for transformative advances in sustainable energy technology.

Subject of Research: Development of composite solid electrolytes for all-solid-state lithium batteries that decouple ionic conduction and mechanical flexibility.

Article Title: Decoupling Ion Conduction from Mechanical Flexibility in Composite Solid Electrolytes for All-Solid-State Lithium Batteries.

News Publication Date: Not specified.

Web References:

• Nature Nanotechnology article
• DOI: 10.1038/s41565-025-02106-9

References: Not specified beyond the article itself.

Image Credits: Not provided.

Keywords

Solid electrolytes, composite electrolytes, superionic conductivity, all-solid-state batteries, lithium-ion conduction, mechanical flexibility, perpendicularly aligned nanosheets, polyethylene oxide, LiNi0.8Co0.1Mn0.1O2, LiFePO4, sulfide electrolytes, air stability, battery cycle life, battery safety.