New polymer electrolyte design promises safer, longer-lasting solid-state lithium batteries
A research team affiliated with UNIST has demonstrated a simple yet effective method to extend the lifespan of all-solid-state batteries—by simply stretching film-shaped electrolytes to improve safety and performance.
Led by Professor Seok Ju Kang from the School of Energy and Chemical Engineering at UNIST, in collaboration with Professor Se Hun Joo from Sookmyung Women’s University, the research team have developed a new type of film-forming electrolyte, capable of enabling longer-lasting solid-state batteries.
The study is published in the journal Energy Storage Materials.
How the new electrolyte works
Electrolytes serve as the medium for lithium ions to move between the cathode and anode within a battery. Currently, commercial electric vehicle batteries and large-scale energy storage systems primarily use flammable liquid electrolytes.
While replacing these with solid polymer electrolytes reduces fire and explosion risks, they have historically suffered from lower lithium-ion mobility, resulting in capacity loss over repeated charge and discharge cycles.
The research team developed a fluorinated polymer-based film electrolyte (PVDF-TrFE-CFE) that significantly enhances lithium-ion transport. The key innovation lies in the application of a uniaxial stretching process, which aligns the polymer chains in a single direction.
This physical stretching unfolds the convoluted polymer structure, opening up continuous pathways for lithium-ion movement. Additionally, incorporating ceramic powder (LLZTO) into the polymer matrix enhances mechanical flexibility, flame retardancy, and ion conductivity.
Performance and safety improvements
Experimental results show that the lithium-ion diffusion rate in the stretched polymer electrolyte increased by 4.8 times compared to unstretched samples, with ionic conductivity improving by 72%.
When integrated into lithium-metal batteries with lithium iron phosphate (LFP) cathodes, the stretched electrolyte contributed to a notable increase in battery lifespan. After 200 charge-discharge cycles, these batteries retained approximately 78% of their initial capacity, compared to only 55% in batteries using unstretched electrolyte.
Flame retardancy tests confirmed the safety benefits of the new electrolyte; flames extinguished within just four seconds of ignition.
Implications for battery commercialization
Jonggeon Na from the School of Energy and Chemical Engineering at UNIST, the first author of the study, said:
This research demonstrates that the inherent issues of polymer electrolytes—such as hindered lithium-ion transport—can be effectively addressed through a simple physical process like stretching,
Professor Kang added,
Polymer electrolytes are more flexible and easier to produce at scale compared to inorganic solid electrolytes.
”The method developed in this study can be applied to various types of polymer electrolytes, accelerating the commercialization of safer, longer-lasting all-solid-state batteries.”
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