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Researcher Zhang Zhang & Professor Zhou Zhen from Zhengzhou University: Innovative MOF Linker Engineering in PVDF-HFP Gel Electrolyte Boosts Solid-State Lithium-Oxygen Batteries
Lithium-air batteries (LOBs) are considered strong candidates for next-generation energy storage technologies due to their high theoretical energy density. However, the commercialization of solid-state lithium-air batteries (SSLOBs) has been limited by insufficient ionic conductivity and poor cycling stability of electrolytes. To address this, researchers have explored gel polymer electrolytes (GPEs) and electrospinning technology to enhance both the mechanical properties and ionic conductivity of electrolytes. Additionally, the introduction of metal-organic frameworks (MOFs) and redox mediators (RMs) has further optimized ion transport and reaction kinetics. These strategies not only improve the overall performance of electrolytes but also significantly enhance the electrochemical performance of SSLOBs, providing important directions for advancing their technological development and commercial applications.
Recently, Professor Zhou Zhen and Researcher Zhang Zhang from Zhengzhou University published a research article titled "Innovative MOF linker engineering in PVDF-HFP gel electrolyte matrix for solid-state lithium-oxygen batteries" in the internationally renowned journal *Chemical Engineering Journal*. The study successfully fabricated a novel gel-based electrolyte using electrospinning by incorporating zeolitic imidazolate framework (ZIF-8) into a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix. The resulting electrolyte exhibited a high lithium-ion transference number (0.88) and room-temperature ionic conductivity of 9.13 × 10⁻⁴ S/cm.
These enhanced electrochemical properties can be attributed to the incorporation of ZIF-8, which promotes well-defined lithium-ion conduction channels while reducing the energy barrier associated with lithium-ion migration. Furthermore, the strategic integration of Ir(acac)₃ as an RM in SSLOBs enabled operation at a reduced charging potential of 3.7 V while demonstrating sustained electrochemical stability over 145 charge-discharge cycles.A particularly notable feature of this system is the integration of ZIF-8 frameworks into the GPE, where its hierarchical structure serves a dual purpose: it effectively suppresses the shuttling of Ir(acac)₃ through multifaceted molecular interactions while promoting uniform lithium plating kinetics via its ordered microporous structure. These complementary mechanisms significantly mitigate conventional degradation pathways at the lithium anode interface.
Figure 1: Preparation of gel electrolytes.
A high-performance gel polymer electrolyte (GPE) was prepared by uniformly dispersing ZIF-8 nanocrystals in a PVDF-HFP matrix. X-ray diffraction (XRD) confirmed the high crystallinity of ZIF-8, and BET analysis revealed a specific surface area of 1071.3 m²/g with pore sizes primarily in the 1-2 nm range, indicating a predominantly microporous structure. High-resolution scanning electron microscopy (SEM) analysis showed the regular structure of ZIF-8 crystals, with sizes around 500 nm, which facilitates the construction of ultrathin solid-state electrolyte films, optimizing ion conduction channels and accelerating lithium-ion transport kinetics.Comparing PVDF-HFP films prepared by electrospinning and doctor-blade methods revealed that electrospinning reduces residual solvent content and minimizes the adverse effects of DMF on the electrolyte. XRD and Raman spectroscopy further confirmed the structural integrity of ZIF-8 in the composite electrolyte and the amorphous characteristics of PVDF-HFP. The uniform dispersion and structural stability of ZIF-8 enhanced the amorphous properties of the electrolyte, and the 45 μm-thick PZIF-8 electrolyte formed a more compact gel structure conducive to rapid lithium-ion migration.
Figure 2: Electrochemical performance of gel electrolytes.
In solid-state lithium-air batteries, ion transport kinetics is one of the key factors affecting battery performance. By introducing MOF linkers, the researchers significantly improved the lithium-ion transference number and ionic conductivity of the electrolyte. Experimental results showed that the new electrolyte achieved a lithium-ion transference number of 0.88 and a room-temperature ionic conductivity of 9.13 × 10⁻⁴ S cm⁻¹. This optimization not only improved the charge-discharge efficiency of the battery but also reduced energy losses during ion transport, providing strong support for high-performance solid-state lithium-air batteries.
Figure 3: Performance comparison of lithium symmetric batteries.
Figure 4: Performance comparison of lithium-oxygen batteries.
The introduction of redox mediator Ir(acac)₃ into PVDF-HFP and PZIF-8-based gel polymer electrolytes (GPEs) significantly enhanced the performance of SSLOBs. Experiments demonstrated that Ir(acac)₃ in GPEs effectively promotes the decomposition kinetics of Li₂O₂, optimizing the charge-discharge characteristics of the battery. Simultaneously, the incorporation of ZIF-8 further improved the ion transport efficiency and oxygen reduction reaction activity of the electrolyte, enabling the battery to exhibit excellent discharge capacity and rate performance at different current densities. Additionally, the PZIF-8 electrolyte, through its unique three-dimensional porous structure and adsorption mechanism, effectively suppressed the shuttling effect of Ir(acac)₃, significantly improving the cycling stability of the battery, which maintained good performance even after 145 cycles. These results indicate that the synergistic effects of MOF linkers and molecular catalysts can effectively address key challenges in solid-state lithium-air batteries, providing new insights for the design of high-performance SSLOBs.
Paper link: [https://doi.org/10.1016/j.cej.2025.164013](https://doi.org/10.1016/j.cej.2025.164013)
