KAIST uncovers cause of performance drop in high-nickel batteries for electric vehicles
High-nickel batteries, which are high-energy lithium-ion batteries primarily used in electric vehicles, offer high energy density but suffer from rapid performance degradation. A research team at KAIST has, for the first time worldwide, identified the root cause of this rapid degradation and proposed a new approach to solving the problem.
KAIST announced on December 3rd that a research team led by Professor Nam-Soon Choi from the Department of Chemical and Biomolecular Engineering, in collaboration with a research team led by Professor Dong-Hwa Seo from the Department of Materials Science and Engineering, has found that the electrolyte additive succinonitrile (CN4), used to improve battery stability and lifespan, is the main cause of performance degradation in high-nickel batteries.
In a battery, electricity is generated by lithium ions migrating between the cathode and the anode. The electrolyte contains a small amount of CN4 to facilitate the movement of the lithium. The research team confirmed through computer calculations that CN4, which has two nitrile structures (-CN), binds excessively to the nickel ions on the surface of the high-nickel cathode.
The nitrile structure is a “hook-like” structure in which carbon and nitrogen are linked by a triple bond, allowing it to adhere strongly to metal ions. This strong bond disrupts the protective electrical double layer (EDL) that should form on the cathode surface. During charging and discharging, the cathode structure becomes distorted (Jahn-Teller distortion), and electrons are even drawn from the cathode into the CN4, leading to rapid cathode damage.
Nickel ions released during this process migrate through the electrolyte to the anode surface, where they accumulate. This nickel acts as a “poor catalyst,” accelerating electrolyte decomposition and wasting lithium, which further accelerates battery degradation.
Various analyses confirmed that CN4 transforms the nickel-rich cathode surface into an abnormal nickel-deficient layer, converting the normally stable structure into an abnormal “rock salt structure”.
This proves the dual nature of CN4: While it is useful in LCO (lithium cobalt oxide) batteries, it actually causes structural breakdown in batteries with a high nickel content.
This research is of great importance because it represents a precise analysis that goes beyond simply controlling the charge/discharge conditions and even elucidates the actual electron transfer between metal ions and electrolyte molecules. Based on these results, the research team plans to develop a new electrolyte additive optimized for high-nickel cathodes.
Professor Nam-Soon Choi, explained:
A precise understanding at the molecular level is essential to improving the lifespan and stability of batteries.
”This research will pave the way for the development of new additives that do not excessively bind to nickel, thus making an important contribution to the commercialization of next-generation high-performance batteries.”
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KAIST uncovers cause of performance drop in high-nickel batteries for electric vehicles, source
