The story of phosphate esters in batteries has long been a tale of ironic failure. Molecules such as trimethyl phosphate (TMP) and triethyl phosphate (TEP) burn with remarkable reluctance, a property that made them obvious candidates for safer electrolytes in lithium-ion systems. Yet in molecular orbital terms, their lowest unoccupied molecular orbital, or LUMO, sits at an energy level that makes them easy to reduce. At the low potentials demanded by graphite and lithium-metal anodes, phosphate solvents decompose relentlessly, failing to form the dense, protective solid electrolyte interphase (SEI) that conventional carbonates achieve at ordinary salt concentrations. Their highest occupied molecular orbital, meanwhile, is too high in energy, limiting oxidation resistance to roughly 4.2 to 4.5 volts against lithium and causing them to degrade at high-voltage cathodes. Even used as additives at about one percent, they failed to make lithium batteries fully non-flammable while still degrading performance.

Sodium changes the thermodynamic picture in a way that inverts these liabilities. Sodium’s redox potential of −2.71 volts, compared with −3.04 volts for lithium, sits closer to the reduction threshold of phosphate esters, so the molecules are far less prone to reductive decomposition against a sodium metal anode. The larger ionic radius of sodium ions also alters interfacial chemistry, promoting faster ion transport at the electrode surface and helping to build a compact, inorganic-rich SEI in which phosphate compounds participate more actively. Meanwhile, the moderate oxidation potential of phosphate solvents aligns comfortably with the cathode windows of sodium cells, which typically do not exceed 4.0 volts against sodium. The result is a solvent whose weaknesses in lithium chemistry become strengths in sodium chemistry, allowing stable interfaces to form without the extreme salt concentrations of 5 molar and above that lithium systems required.

The review breaks down the three workhorse solvents of the field in detail. TMP offers a dielectric constant near 21, facilitating sodium salt dissociation, with low viscosity of roughly 1.8 millipascal-seconds at 25 degrees Celsius and a freezing point of −46 degrees Celsius that suits cold-climate operation. TEP trades some dielectric strength for superior thermal stability, boiling at 219.3 degrees Celsius and remaining liquid to −56.5 degrees Celsius. Tris(2,2,2-trifluoroethyl) phosphate, or TFEP, adds fluorination to the mix, raising thermal stability with a flash point above 150 degrees Celsius and promoting the formation of protective sodium fluoride-rich interfaces. According to the review’s analysis, dielectric constant and viscosity govern not merely how fast ions travel through the bulk electrolyte but also how the solvation shell is constructed, which in turn determines whether solvent molecules or salt anions decompose first at the electrode surface.

The flame-retardant mechanism itself operates on two fronts. When phosphate esters are heated during combustion, they release phosphorus-containing radicals such as PO· and HPO2·, which quench the high-energy H· and OH· radicals that sustain gas-phase flame chains through reactions like PO· + H· → HPO and PO· + OH· → HPO2·. Simultaneously, in the condensed phase, phosphates promote a cross-linked carbon char layer that acts as a physical barrier to flammable volatile release. TFEP compounds this defense by releasing fluorine radicals that further enhance gas-phase quenching. This dual mechanism, the authors note, is what distinguishes phosphates from simple additives and underpins their role as primary solvents rather than supplements.

Turning theory into working cells has required a toolbox of interfacial engineering strategies. The pioneering formulation of Yuliang Cao’s team, 0.8 molar NaPF6 in TMP with 10 volume percent fluoroethylene carbonate (FEC), delivered ionic conductivity of 5.41 millisiemens per centimeter across a 0 to 4.5 volt window, allowing an antimony anode to retain 94 percent capacity over 80 cycles. Subsequent refinements tuned salt-to-solvent molar ratios to improve hard carbon compatibility, achieving 84 percent capacity retention after 1,500 cycles with coulombic efficiency above 99.8 percent. Additives such as vinylene carbonate (VC), which stabilizes the cathode interface, and sodium bis(oxalato)borate (NaBOB) salts, which enable fluorine-free, low-cost formulations, extended cycling further. In one system, a hard carbon cathode against Prussian white retained 73.7 percent capacity after 1,000 cycles at a demanding 10C rate.

For sodium-metal batteries, where dendrites and interfacial instability loom largest, the field has converged on locally high-concentration electrolytes (LHCEs). By diluting concentrated salt solutions with fluorinated ethers such as bis(2,2,2-trifluoroethyl) ether (TTE), researchers steer sodium ions into anion-rich solvation shells that decompose into protective inorganic layers rather than dissolving solvent. A dual-salt system of 0.8 molar NaPF6 plus 0.1 molar NaDFOB in TMP/TTE produced a phosphorus- and boron-rich gradient cathode interphase that preserved 85.2 percent capacity after 800 cycles at 4.2 volts. Other groups pushed oxidation resistance to 4.7 volts, with cells surviving over 1,000 cycles, while a ‘salt-as-diluent’ strategy using sodium nitrate delivered 5.99 millisiemens per centimeter conductivity and 80 percent retention after 500 cycles at a fraction of typical cost.

TEP-based systems have followed a parallel trajectory with distinctive advantages at elevated temperatures. A 1 molar NaPF6 electrolyte in TEP/FEC with the scavenger additive TMSPi enabled a sodium half-cell to retain 84 percent capacity after 1,000 cycles at 60 degrees Celsius and 86 percent after 100 cycles at 70 degrees Celsius, marking the first demonstration of a sodium-ion full cell cycling stably beyond 100 cycles at that temperature. Systematic salt screening by Van Ekeren and colleagues identified NaFSI as the optimal pairing with TEP, yielding 6.5 millisiemens per centimeter conductivity and 88 percent retention in 1 ampere-hour pouch cells. Perhaps most strikingly, a formulation balancing solvent dielectric constant and binding energy produced a 6.61 ampere-hour pouch cell with an energy density of 152.3 watt-hours per kilogram that showed no smoke or expansion during nail penetration testing, the brutal industry benchmark for thermal abuse.

Gel polymer architectures push the safety envelope further still. Encapsulating TEP within crosslinked polymer networks produced electrolytes with transference numbers as high as 0.61, enabling sodium symmetric cells to run for over 1,000 hours dendrite-free and full cells to retain 87.8 percent capacity across 1,000 cycles at 2C. In-situ gelated formulations built around TFEP and phosphorus-containing monomers achieved capacity decay of only 0.0035 percent per cycle over 1,000 cycles in 2.4 ampere-hour pouch cells, with oxidation windows approaching 5.0 volts. Beyond liquid and gel systems, mixed-solvent formulations blending phosphates with glyme ethers and alkyl-chain-extended derivatives such as tris(2-ethylhexyl) phosphate (TOP) are broadening the design space, with TOP-based electrolytes sustaining 95.7 percent capacity retention over 1,800 cycles at room temperature.

The review’s authors are candid about the remaining obstacles. Anion-rich solvation structures, so often celebrated as a design goal, do not guarantee stable interfaces if the decomposition products dissolve or if reaction kinetics are too sluggish to passivate the electrode before further solvent degradation. Most phosphorus-based flame retardants still compromise oxidative stability to some degree, and the complex influence of phosphates on sodium ion desolvation and interfacial transport remains incompletely understood. On the industrial side, advanced phosphate formulations can cost an order of magnitude more than carbonate systems once expensive NaFSI salts and fluorinated diluents are counted, a decisive factor for grid storage economics. The authors propose machine-learning-guided molecular discovery, operando atomic-scale interfacial diagnostics, realistic large-format cell validation across −40 to 60 degrees Celsius, and greener synthesis routes as the pillars of future progress. If those threads converge, the fireproof chemistry that lithium batteries could not tame may prove to be exactly what sodium batteries needed all along.

Subject of Research: Phosphate ester based nonaqueous electrolytes for safe, high-performance sodium batteries

Article Title: Phosphate ester based nonaqueous electrolytes for sodium batteries

Article References: Xu, X., Hao, Y., Cao, S., Liu, T., Zhang, J., & Zhang, D. (2026). Phosphate ester based nonaqueous electrolytes for sodium batteries. Discover Electrochemistry, 3(1), Article 80. https://doi.org/10.1007/s44373-026-00167-6

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00167-6

Keywords: sodium-ion batteries, sodium-metal batteries, phosphate ester electrolytes, flame-retardant electrolytes, solid electrolyte interphase, trimethyl phosphate, triethyl phosphate, TFEP, locally high-concentration electrolytes, gel polymer electrolytes, battery safety, grid energy storage

The novel composite gel polymer electrolytes synthesized in this study combine the biocompatibility of CMC with the electrifying efficiency of CNTs. CMC serves not only as a stabilizing matrix but also contributes to the overall ionic conductivity by providing a conducive medium for ion transport. The researchers meticulously measured various structural and electrochemical properties, advancing our understanding of how each component interacts at a molecular level. The optimal combination of CMC and NH4I with CNTs leads to enhancements that are crucial for applications where efficiency and safety are paramount.

In terms of electrochemical performance, the researchers conducted extensive testing to ascertain the ionic conductivity rates and electrochemical stability of the synthesized nanocomposite gel electrolyte. They reported significant improvements in ionic conductivity compared to conventional polymer electrolytes. These advancements could pave the way for more efficient and safer batteries, supercapacitors, and other energy storage devices that rely on liquid or gel electrolytes, addressing long-standing challenges such as leakage and instability in traditional systems.

The incorporation of carbon nanotubes allowed for a marked increase in electrical conductivity, which is an essential characteristic of any effective electrolyte. The unique one-dimensional structure of CNTs not only facilitates ion transport but also fortifies the mechanical integrity of the composite, offering a dual benefit. Such durability is crucial, especially in applications associated with physical stress and thermal fluctuations. This material could effectively withstand pressure and thermal changes inherent to operational conditions found in biocompatible electrochemical devices, making it a frontrunner in the field.

Moreover, the compatibility of CNT-doped CMC-based electrolytes with biocompatible applications positions this new technology as a leading candidate for medical devices. As healthcare technology advances, materials that can safely interact with biological systems while facilitating efficient energy storage are growing in demand. The research details how these advanced materials can be instrumental in developing implantable medical devices that require both energy and biocompatibility, such as biosensors and drug delivery systems that operate seamlessly within the human body.

The researchers also focused on the feasibility of scaling up the production of these nanocomposite gel electrolytes, which has traditionally been a barrier to commercialization. Through their innovative approaches, they have presented methods that could ease the manufacturing processes. The aim is to produce these materials at significant volumes and reduced costs while maintaining the superior qualities that they exhibited in laboratory settings. This is an essential step toward bringing these advanced materials closer to market readiness.

In terms of structural characterization, various techniques were employed to analyze the arrangement and interactions of the polymer chains within the ionic matrix. Techniques such as scanning electron microscopy (SEM) and X-ray diffraction (XRD) offered insights into the nano-scale features that contribute to the enhanced performance observed. The researchers meticulously analyzed how the incorporation of CNTs disrupted or modified the crystalline structures and amorphous regions of the polymer, providing a deeper understanding of the underpinnings of ionic mobility.

The researchers also presented findings on the thermal stability of the new materials, elucidating how the interaction of CMC with NH4I and CNTs affects the thermal properties of the gel. Elevated thermal stability is particularly crucial when considering the applications of these gel electrolytes in environments where high temperatures may be encountered. Understanding the thermal behavior of these materials is vital for ensuring long-term stability and performance in actual applications.

In conclusion, the advances presented in this study highlight the transformative potential of nanocomposite materials combining CMC, ammonium iodide, and carbon nanotubes. The comprehensive examination of their structural, electrochemical, and electrical properties portrays a promising future for biocompatible electrochemical devices. As the demand for innovative energy solutions continues to grow, such materials may well represent the nexus of performance, safety, and biocompatibility, addressing contemporary challenges in energy storage systems.

The research encapsulates a significant advancement in the realm of polymer electrolytes. By elucidating the mechanisms that underpin the enhanced properties of CNT-doped CMC-based nanocomposite gel polymer electrolytes, Singh and colleagues set the stage for future exploration and application. The potential for using these materials in cutting-edge biocompatible devices could lead to significant breakthroughs, transforming how we think about energy storage and its integration into health applications.

Researchers in the field are excited about the implications of this work, as it opens up new avenues for innovation in energy storage technologies. As we transition towards more sustainable and effective systems, leveraging advanced materials like those studied will be crucial to achieving the necessary improvements in performance and safety. The work by Singh et al. serves as a clarion call to the scientific community to explore these materials further and capitalize on their unique properties for the betterment of technology and society at large.

In light of these findings, future research will undoubtedly expand upon the properties of these materials, as well as investigate the scaling up of production processes necessary for widespread application. With continued collaboration and exploration, the vision of integrating efficient energy solutions into a variety of devices, including those used in healthcare, is becoming an increasingly tangible reality.

Subject of Research: Nanocomposite gel polymer electrolytes

Article Title: Structural, electrochemical and electrical studies of CNT doped [CMC: NH₄I] based plasticized nanocomposite gel polymer electrolytes for biocompatible electrochemical devices.

Article References:

Singh, S., Singh, C.P., Shukla, P.K. et al. Structural, electrochemical and electrical studies of CNT doped [CMC: NH₄I] based plasticized nanocomposite gel polymer electrolytes for biocompatible electrochemical devices.
Ionics (2026). https://doi.org/10.1007/s11581-026-06973-7

Image Credits: AI Generated

DOI: 30 January 2026

Keywords: Nanocomposite, gel polymer electrolytes, carbon nanotubes, biocompatibility, electrochemical devices

Addressing this age-old challenge, a team of engineers and materials scientists at South China University of Technology (SCUT) have pioneered a cutting-edge manufacturing technique by integrating digital light processing (DLP) 3D printing with gel-polymer electrolyte (GPE) design. DLP is a state-of-the-art additive manufacturing process wherein ultraviolet light selectively cures polymer resins layer by layer, enabling intricate three-dimensional architectures with micron-scale precision. This breakthrough allows for unprecedented control over electrolyte microstructures, directly tuning the mechanical stresses at the zinc anode interface.

Their findings, recently published in the International Journal of Extreme Manufacturing, showcase how manipulating the polymerization degree, pore size distribution, and layer thickness via DLP empowers researchers to program interfacial stress fields within these quasi-solid-state electrolytes. By modulating these parameters with micron accuracy, the researchers demonstrated remarkable suppression of uneven zinc deposition, fostering stable, dendrite-free cycling even under harsh temperature fluctuations from −10 °C to 60 °C.

Mechanical stresses within batteries, traditionally regarded as undesirable byproducts of electrochemical reactions, have long posed significant challenges in battery design. Conventional gel electrolytes with irregular, stochastic pore structures yield unpredictable stress distributions, accelerating interface deformation and failure. However, SCUT investigators flipped this paradigm on its head by embracing stress as an engineerable material attribute rather than a liability. Through DLP-facilitated control over electrolyte microarchitecture, they effectively designed stress to be uniform and balanced, optimizing ionic pathways while preserving intimate contact between the zinc anode and the GPE.

The SCUT team employed multiphase-field simulations combined with both in situ and ex situ characterization techniques to elucidate zinc-ion transport and deposition dynamics within their designer electrolytes. They observed that even minute variations in electrolyte thickness or porosity introduced localized stress imbalances, triggering non-uniform zinc plating and subsequent dendrite nucleation. By leveraging the exquisite precision of DLP printing, these microstructural features were finely tuned, ensuring homogeneous zinc ion flux and uniform deposition layers that sustain long-term battery integrity.

Performance metrics of the batteries crafted using this method are nothing short of impressive. Symmetrical zinc cells cycled stably for over 2,000 hours without significant degradation, while full cells retained over 91% of their initial capacity after 8,000 charge-discharge cycles. Such longevity under wide-ranging thermal conditions signifies a major leap toward practical zinc-ion battery deployment in real-world applications where reliability and safety are paramount.

Beyond their immediate achievements, SCUT’s work heralds a transformative approach to electrochemical device engineering. The ability to digitally manufacture electrolytes with tailored stress landscapes paves the way for next-generation energy storage technologies, including flexible batteries and fuel cells, which demand mechanical robustness alongside electrochemical performance. This capability also opens new avenues for adaptive design, where evolving software algorithms could optimize electrolyte architectures in silico before physical fabrication.

Looking forward, the SCUT group intends to push the boundaries further by exploring multilayered and more complex 3D electrolyte constructs. Coupling advanced design algorithms with adaptive photopolymerization strategies may unlock even greater control over mechanical and ionic properties at critical electrochemical interfaces. Such innovations hold promise for batteries that are not only safer and longer-lasting but also highly predictable in performance, transforming the paradigm of electrochemical energy storage into a realm where mechanical stress is no longer a threat but a deliberately engineered asset.

Professor Wei Yuan, the study’s lead author, encapsulates the significance: “This marks a fundamental shift in how we perceive and manage mechanical stress in battery systems. By treating stress as a designable feature instead of an uncontrollable weakness, we unlock pathways to safer, more durable batteries engineered at the microscopic level.” With this pioneering integration of digital light 3D printing and polymer chemistry, the dream of robust, ultralong-life zinc batteries is closer to reality than ever before.

As global demand surges for greener and more resilient energy storage, innovations like these underscore the pivotal role of interdisciplinary research at the intersection of materials science, manufacturing, and electrochemistry. The SCUT team’s advances envisage a future where additive manufacturing transforms battery interfaces into meticulously engineered systems, fostering sustainable technologies that meet the rigorous demands of modern energy infrastructures.

Subject of Research: Zinc-ion battery anode-electrolyte interface stabilization via digitally manufactured gel polymer electrolytes

Article Title: Precise regulation of zinc-anode interface stresses by digital-light-processed gel polymer electrolytes for ultralong-life zinc batteries

News Publication Date: 29-Sep-2025

Web References:

• International Journal of Extreme Manufacturing Journal
• Article DOI

Image Credits: By Yangfan Zhou, Wei Yuan, Xuyang Wu, Qing Liu, Xiaoqing Zhang, Tengjia Gao, Pei Wang, Chun Li, Guanhua Zhang, Yubin Zeng and Yong Tang.

Keywords: Batteries, Energy storage, Zinc, Gel polymer electrolytes, Digital light processing, 3D printing, Additive manufacturing, Anodes, Electrodes, Mechanical stress, Ionic conductivity, Materials engineering