A recent article in Nature Communications introduced a bioinspired gel polymer electrolyte (GPE) designed for high-energy-density lithium metal batteries that can operate reliably across a wide temperature range (–30 to 80 °C). The weakly solvated GPE (WSGPE) was synthesized using a branched polymer with side chains double-coupled to asymmetric analogs.
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Background
Commercial lithium-ion batteries typically function within –20 to 60 °C. Beyond this range, especially at elevated temperatures, safety concerns arise due to the use of flammable and low-boiling-point liquid electrolytes. While solid-state lithium batteries offer improved safety, they often perform poorly at subzero temperatures.
GPEs are promising alternatives that combine features of both solid and liquid electrolytes. However, conventional GPEs tend to exhibit high desolvation energy and reduced ion mobility at low temperatures (<25 °C), and are prone to side reactions at elevated temperatures (>80 °C).
To address these issues, this study draws inspiration from the structure of water grass, which uses branched networks to control interactions with water. The researchers applied this concept to design a GPE with regulated polymer-liquid interactions and a brush-like polymer network that increases contact sites, enabling weak solvation behavior.
Methods
The WSGPE was synthesized using a mixture of fluoroethylene carbonate (FEC), trifluoroethyl methacrylate (TFMA) as the monomer, poly(ethylene glycol) diacrylate (PEGDA) as the crosslinker, and 2,2’-azobis(2-methylpropionitrile) as the initiator. These were dissolved in a lithium bis(trifluoromethanesulfonyl)imide-ethyl 3,3,3-trifluoropropanoate (LiTFSI-FEP) precursor.
The electrolytes were characterized using Fourier-transform infrared (FTIR) and Raman spectroscopy, followed by nuclear magnetic resonance (NMR). Flame-retardant properties were evaluated with combustion tests.
Electrochemical measurements were performed in an environmental chamber. Ionic conductivity was assessed using electrochemical impedance spectroscopy (EIS) in Li|SS cells. Linear sweep voltammetry (LSV) measured the electrochemical window at 25 °C.
Li | |LiNi0.8Co0.1Mn0.1O2 (NCM811) and Li | | LiCoO2 (LCO) cells were assembled using a slurry-coating method with the prepared WSGPE. Their rate and cycling performance were evaluated using a battery test system.
Post-cycling analysis of Li foils and NCM811 cathodes was conducted using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and high-resolution transmission electron microscopy (HRTEM). Molecular dynamics simulations were also carried out to determine the working mechanism of the proposed WSGPE.
Results and Discussion
The WSGPE showed strong electrochemical performance, with an electrochemical stability window up to 5.05 V, a lithium-ion transference number of 0.83, and ionic conductivity of 4.40 × 10-4 S/cm at room temperature. These characteristics make WSGPE suitable for use in high-voltage lithium metal batteries.
In Li|WSGPE|NCM811 cells, the electrolyte supported a specific capacity of 154.8 mAh/g, maintaining 92.5 % retention after 300 cycles. In contrast, cells using conventional liquid electrolyte achieved only 85.0 mAh/g and 50.1 % capacity retention. At a current of 376 mA/g, the WSGPE cell still delivered 130.4 mAh/g after 200 cycles with 90.8 % retention.
Li|WSGPE | NCM811 cells showed good rate and cycling performance with a positive electrode mass loading of up to 3 mg/cm2. Notably, the capacity remained stable even when the loading was increased to 7 mg/cm2.
WSGPE also proved compatible with high-voltage LiCoO2 cathodes. Li|WSGPE|LCO cells operated effectively in the 3.0–4.6 V window, delivering discharge capacities of 148.8 mAh/g over 150 cycles at a current density of 220 mA/g.
In symmetric Li|WSGPE|Li cells, the voltage-time curves showed an overpotential of around 200 mV, with no evidence of soft short-circuiting even at 1 mA/cm2. This confirmed the WSGPE’s ability to suppress lithium dendrite formation.
TOF-SIMS analysis confirmed a uniform and LiF-rich solid electrolyte interphase (SEI) across the lithium surface. The high LiF content was distributed at the surface and throughout the SEI. In contrast, the presence of Li2CO3 from solvent decomposition was minimal, indicating a stable interphase and limited side reactions.
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Conclusion
The study demonstrated the successful development of a bioinspired weakly solvated GPE via asymmetric double dipole coupling. The in situ polymerized PTFMA interacted with FEP to form a weak solvation structure that removed solvent molecules from the primary lithium-ion coordination shell.
This weak solvation enabled better interfacial charge transfer at low temperatures and promoted the formation of LiF-rich, wide-temperature-stable interphases. As a result, the WSGPE stabilized both lithium metal and high-voltage cathodes, enabling Li|WSGPE|NCM811 cells to operate from –30 to 80 °C.
This design approach—modulating coordination structure and interfacial chemistry—offers a pathway toward safer, more reliable lithium metal batteries suited for various temperatures.
Journal Reference
Liu, S., et al. (2025). Bioinspired gel polymer electrolyte for wide temperature lithium metal battery. Nature Communications. DOI: 10.1038/s41467-025-57856-w, https://www.nature.com/articles/s41467-025-57856-w
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