Among the two broad classes of solid electrolytes, inorganic ceramics currently offer the highest room-temperature conductivities (10⁻³–10⁻² S cm⁻¹) but demand high-temperature sintering, are mechanically brittle, and suffer from large interfacial impedance with composite electrode [1].
Solid polymer electrolytes (SPEs), such as polyethylene oxide (PEO)–LiTFSI, polycarbonates, and block-copolymer systems, trade some conductivity (10⁻⁵–10⁻³ S cm⁻¹ at 60–90 °C) for exceptional processability. Moreover, SPEs can be cast as free-standing films, laminated at low pressure to electrodes, and formulated with ceramic fillers or ionic plasticizers to tune modulus and transport [2]. Crucially, SPE layers conform intimately to the nanoscale features of structured cathodes and accommodate volume changes during high-voltage cycling, maintaining robust electrode–electrolyte interfaces in flexible cell formats. These attributes underpin scalable roll-to-roll manufacturing of flexible, high-voltage solid-state batteries in which the SPE simultaneously serves as separator and ion conductor, paving the way for next-generation SSB architectures [3].
Since the main function of any electrolyte is to transport ions, the ionic conductivity is of fundamental importance when benchmarking an SPE material. Moreover, there are a number of properties that a functional SPE material typically should possess for operation in Li batteries of which some are strongly related to the ionic transport properties.
A good SPE must possess these following properties:
- a good dissolution of Li salts
- a high Li transference number (T+)
- a low glass transition temperature (Tg)
- electrochemical stability towards most common electrode materials
- a low degree of crystallinity
- mechanical stability
- low temperature sensitivity
- ability to produce pin-hole-free membranes of sufficiently small thickness [4].
References
- Lv, Q., Jiang, Y., Wang, B., Chen, Y., Jin, F., Wu, B., … & Dou, S. (2022). Suppressing lithium dendrites within inorganic solid-state electrolytes. Cell Reports Physical Science, 3(1).
- Jiang, Y., Yan, X., Ma, Z., Mei, P., Xiao, W., You, Q., & Zhang, Y. (2018). Development of the PEO based solid polymer electrolytes for all-solid state lithium ion batteries. Polymers, 10(11), 1237.
- Zhang, Q., Liu, K., Ding, F., & Liu, X. (2017). Recent advances in solid polymer electrolytes for lithium batteries. Nano Research, 10(12), 4139-4174.
- Kundu, S., & Ein-Eli, Y. (2023). A review on design considerations in polymer and polymer composite solid-state electrolytes for solid Li batteries. Journal of Power Sources, 553, 232267.
- Pourzolfaghar, H., Wang, P. Y., Jiang, X. Y., Kositsarakhom, S., Jirasupcharoen, W., Suwantri, C., … & Li, Y. Y. (2024). Emerging trends and innovations in all-solid-state lithium batteries: A comprehensive review. Chemical Engineering Journal, 500, 157394.
See also: Solid Polymer Electrolyte, Solid State Battery, Ionic Liquid Electrolytes