Research report: Lithium-salt anion regulation of ion transport and interfacial stability in PVDF-HFP/PAN/LLZTO composite polymer electrolytes

A membrane containing 30 wt% lithium bis(trifluoromethanesulfonyl)imide, known as LiTFSI, reached an ionic conductivity of 6.08 × 10−4 S cm−1, a tensile strength of about 8.5 MPa and a lithium-ion transference number of 0.58. The corresponding membrane containing lithium difluoro(oxalato)borate, or LiODFB, showed lower mechanical strength and poorer lithium-ion transport. The researchers developed the materials as potential solid or quasi-solid alternatives to conventional liquid electrolytes in lithium-ion batteries.

According to the study background, liquid electrolytes can undergo oxidative decomposition during prolonged operation, while parasitic reactions at electrode–electrolyte interfaces can contribute to impedance growth and capacity decay. For the experiment, poly(vinylidene fluoride-co-hexafluoropropylene), abbreviated PVDF-HFP, and polyacrylonitrile, or PAN, formed the polymer host. The researchers added LLZTO, a Ta-substituted form of lithium lanthanum zirconate, as an inorganic ceramic filler.

They then prepared two composite membranes by separately introducing LiTFSI or LiODFB. In both formulations, the salt dosage was fixed at 30 wt% calculated from the combined mass of PVDF-HFP and PAN, allowing the two salt identities to be compared within the same general electrolyte design. The formulation designated PSI 30% contained LiTFSI, while the membrane designated PFB 30% contained LiODFB.

PSI 30% combined an ionic conductivity of 6.08 × 10−4 S cm−1 with a tensile strength of approximately 8.5 MPa and a lithium-ion transference number of 0.58. PFB 30% performed less well on the reported mechanical-strength and lithium-ion transport measures. Electrochemical testing was performed in LiFePO₄/CPE/Li cells, which paired a lithium iron phosphate cathode with the composite polymer electrolyte and a lithium-metal anode.

Cells assembled with PSI 30% delivered discharge capacities of 162.61 mAh g−1 at a 0.1 C rate and 107.14 mAh g−1 at 1 C. The lower capacity at the higher rate shows that the membrane’s strong material-level results did not translate into identical discharge performance across the two tested rates. After 100 cycles, the PSI 30% cells retained a capacity above 159 mAh g−1, corresponding to nearly 98% retention.

This is a cell-level result obtained with lithium iron phosphate electrodes, lithium-metal anodes, the tested composite electrolyte and the study’s specified discharge rates. It provides evidence of stable electrochemical performance over the reported 100-cycle test, while the scope of the result remains tied to that laboratory cell configuration and test period. Under the reported conditions, the LiTFSI-containing composite outperformed the LiODFB-containing composite on the stated mechanics and transport measures, and cells using the former sustained nearly all of their capacity through 100 cycles.

The findings support lithium-salt selection as a potential lever for coordinating material properties and cell behavior in PVDF-HFP/PAN/LLZTO composite electrolytes. For battery researchers, the practical appeal of the work is that it compares two salt choices without changing the broad architecture of the composite.

Subject of Research: Effects of lithium-salt identity on composite polymer electrolyte transport, mechanics and cell performance

Article Title: Lithium-salt anion regulation of ion transport and interfacial stability in PVDF-HFP/PAN/LLZTO composite polymer electrolytes

Article References: Ou, Y., Huang, L., Lan, L., Liang, X., Dong, J., Chen, P., Zhang, L., & Mo, Q. (2026). Lithium-Salt Anion Regulation of Ion Transport and Interfacial Stability in PVDF-HFP/PAN/LLZTO Composite Polymer Electrolytes. Frontiers in Chemistry, 14, 1961300. https://doi.org/10.3389/fchem.2026.1961300

Image Credits: AI Generated

DOI: 10.3389/fchem.2026.1961300

Keywords: LiTFSI, LiODFB, polymer electrolytes, lithium-ion batteries, PVDF-HFP, PAN, LLZTO, ionic conductivity, lithium-ion transference, capacity retention, Lithium-salt, anion