SK On has successfully co-developed a polymer electrolyte for lithium metal batteries that can operate at room temperature in collaboration with Professor John B. Goodenough’s research team from the University of Texas. This breakthrough is expected to improve solid-state battery performance and accelerate the development of all-solid-state batteries.
SK On developed the new polymer electrolyte known as ‘SIPE’ (single-ion conducting polymer electrolyte) with Professor Hadi Khani, a former student of Professor Goodenough.
Professor Goodenough pioneered the battery field, having doubled the capacity of lithium-ion batteries. In 2019, at 97, he was awarded the Nobel Prize in Chemistry, setting the record for the oldest Nobel Laureate. Since 2020, SK On has been collaborating with him on developing solid electrolytes to realize lithium metal batteries. Professor Khani led the research team after passing in June of last year.
This research was published in the prestigious journal J. Electrochemical Society.
Polymer electrolytes are favored as the next generation of solid battery materials due to their low cost and ease of manufacture. However, their low ionic conductivity compared to oxide or sulfide systems, requiring operation at high temperatures (70-80°C), has been a challenge.
SIPE improves ionic conductivity and lithium ion transport rates, addressing these issues. It has increased the room temperature ionic conductivity of existing polymer electrolytes by approximately ten times (1.1×10-4S/cm), and the lithium-ion transference number has also increased nearly fivefold from 0.2 to 0.92, enabling operation at room temperature. Ionic conductivity measures the tendency of a material to conduct ions, and a higher value indicates easier ion movement within the electrolyte. The transference number represents the proportion of charge carriers that transport electricity, with a higher lithium ion transference number indicating increased movement of lithium cations.
Higher lithium ion conductivity and transference rates enhance the battery’s output and charging performance. In experimental results, SIPE batteries maintained 77% of their discharge capacity during high-speed charging and discharging (2C) compared to low-speed (0.1C). Solid electrolytes typically experience a significant reduction in discharge capacity during fast charging due to their low ionic conductivity, but this issue is minimized with SIPE.
SIPE also enhances the stability of the Solid Electrolyte Interphase, preventing the formation of dendrites. Lithium metal batteries use metallic lithium instead of graphite for the anode, greatly increasing energy density. However, solving the persistent dendrite issue is crucial for commercialization. Dendrites, branch-like crystals that form on the anode surface during charging and discharging, degrade battery life and safety.
Furthermore, SIPE possesses high mechanical durability, enabling mass production, and excellent thermal stability, tolerating temperatures above 250°C. It holds promise for application in next-generation composite solid-state batteries to improve charging speed and low-temperature performance.
Kim Tae-Kyung, Director of SK On’s Next-Generation Battery Center, stated, “This research achievement will accelerate the development of solid-state batteries incorporating polymer electrolytes. SK On will continue to seize growth opportunities in the next-generation battery sector by leveraging our competitive edge in new material technologies.”
SK On is developing two types of all-solid-state batteries: polymer-oxide composites and sulfide systems. It plans to produce pilot products in 2025 and 2026, respectively, and commercialize them by 2028 and 2029. The sulfide-based next-generation battery pilot plant under construction at the Daejeon Battery Research Institute is expected to be completed in the second half of next year.