KAIST Research Team
Applies Ultra-Thin Copolymer Polymer Protective Film
Domestic researchers have succeeded in extending the lifespan of lithium metal batteries, which are gaining attention as next-generation batteries, by more than six times.
KAIST announced on the 28th that a joint research team led by Professor Il-Doo Kim from the Department of Materials Science and Engineering and Professor Sung-Gap Lim from the Department of Bio and Chemical Engineering successfully applied an ultra-thin copolymer polymer protective film that swells (polymer compounds absorb solvent and increase in volume) in the electrolyte of lithium-ion batteries, dramatically extending the lifespan of lithium metal batteries.
Lithium metal, which is attracting attention as an ideal anode material for lithium secondary batteries, has a capacity ten times higher than the currently commercialized graphite (372mAh/g). However, it has not been commercialized due to a fundamental problem where needle-like deposits called lithium dendrites easily form during charge and discharge cycles.
To prevent low Coulombic efficiency, short battery life, and explosion risks of lithium metal, various studies have been conducted to artificially create a solid-electrolyte interphase (SEI) layer as a protective film to facilitate smooth lithium ion transport and suppress dendrite growth. However, existing artificial SEI layers are thick, causing high internal resistance in the battery. During operation over hundreds of cycles, they detach from the lithium metal, making it difficult to maintain long-term stability of the lithium metal anode. Moreover, the formation process of the SEI layer often causes damage to highly reactive lithium, making it difficult to form the desired SEI layer.
The research team used the 'initiated chemical vapor deposition (iCVD)' method to control the high reactivity of lithium metal and solve the problems of dendrite growth and electrolyte depletion. The process is carried out under mild conditions without using solvents to apply a functional polymer thin film uniformly and thinly as a protective layer on the lithium metal surface without damage.
Using the polymer thin film manufactured by the iCVD process, the research team stabilized the interface of the lithium electrode. The lithium anode coated with the polymer protective film, which swells threefold upon contact with the electrolyte to form a soft SEI structure, exhibited world-class lithium ion transport number (0.95) and ionic conductivity (6.54 mS cm-1). Notably, even at a thin thickness of 100 nm, it effectively suppressed lithium dendrite growth. By manufacturing a battery cell using the PDMS-coated lithium anode and a commercial cathode (LiNi0.6Co0.2Mn0.2O2), they achieved world-class performance with stable operation for over 600 cycles.
Measurement of electrolyte swelling ratio and performance evaluation of Li-NMC full cells. Image source=KAIST.
The research team stated, "We succeeded in developing a lithium metal battery with lifespan characteristics improved by more than six times compared to lithium metal by applying an ultra-thin polymer protective film that swells in the electrolyte using the iCVD process." They added, "This is expected to contribute to accelerating the commercialization of lithium anodes, which are essential not only for high-capacity lithium secondary batteries but also for next-generation secondary batteries such as lithium-sulfur batteries and lithium-air batteries."
The study was published online on the 8th in the international journal Advanced Energy Materials and was selected as a cover paper. (Paper title: Reinforcing native solid-electrolyte interphase layers via electrolyte-swellable soft-scaffold for lithium metal anode).
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