KAIST researchers have revealed the underlying cause of rapid battery degradation in high-nickel lithium-ion batteries, widely used in electric vehicles.
These batteries are valued for their high energy density but have long struggled with degradation. For the first time, the team has pinpointed the role of succinonitrile (CN4), an electrolyte additive previously introduced to improve stability and lifespan.
The study, led by Professor Nam-Soon Choi of Chemical and Biomolecular Engineering and Professor Dong-Hwa Seo of Materials Science and Engineering, found that CN4 bonds excessively with nickel ions on the cathode surface. This strong attachment disrupts the protective electrical double layer, distorts the cathode structure during cycling, and even extracts electrons, accelerating damage. Nickel ions released in the process migrate to the anode, where they act as a ‘bad catalyst’, hastening electrolyte breakdown and lithium loss.
Analyses confirmed CN4 transforms the cathode into an abnormal nickel-deficient layer, shifting it into a rock-salt structure. While CN4 has proven useful in lithium cobalt oxide systems, its dual nature means it destabilises high-nickel cathodes, leading to battery degradation.
“A precise, molecular-level understanding is essential to enhance battery lifespan and stability,” said Professor Nam-Soon Choi. “This research will pave the way for the development of new additives that do not excessively bond with nickel, significantly contributing to the commercialisation of next-generation high-capacity batteries.”
The findings, published in ACS Energy Letters and supported by Samsung SDI, mark a significant step towards optimised electrolyte additives tailored for high-nickel cathodes.
Image: Schematic diagram of the ligand coordination between CN₄ molecules and Ni³⁺ on the high-nickel cathode surface and the cathode structural degradation process.
