Design strategy can mitigate internal cracks in next-generation cathode materials

A research team, led by Professor Hyeon Jeong Lee from the Department of Materials Science and Engineering at UNIST, has identified the root causes of internal cracking in single-crystal lithium nickel manganese oxide (LNMO) cathodes—key materials for high-performance batteries—and proposed an innovative material design strategy to address this challenge.

The study was conducted in collaboration with Dr. Gwanchen Lee at the University of Glasgow, United Kingdom, and Professor Jihoon Lee’s team at Kyungpook National University. The paper is published in the journal Angewandte Chemie International Edition.

Lithium nickel manganese oxide is gaining attention as a high-capacity, cost-effective cathode material owing to its high operating voltage of 4.7V and the absence of expensive cobalt in its chemical composition. When manufactured in single-crystal form, these cathodes can enable batteries that offer higher energy density and longer lifespan.

Unlike conventional polycrystalline cathodes, single-crystal cathodes are composed of a single, continuous crystal without grain boundaries, reducing inter-particle cracking and mitigating undesirable chemical reactions with electrolytes. However, during high-rate charging and discharging, internal cracks can still develop within the crystal structure, compromising performance and longevity.

The research team found that this issue stems from non-uniform lithium-ion diffusion within the crystal, leading to localized stress concentrations. When the internal stress exceeds the crystal’s yield strength, cracks are initiated—an effect exacerbated at higher charge/discharge rates.

To overcome this, the scientists introduced magnesium into the crystal lattice. Acting as a structural pillar, magnesium inhibits the contraction of ion diffusion pathways and enhances lithium-ion mobility, effectively alleviating internal stresses. Experimental results confirmed that magnesium-doped single-crystal cathodes demonstrate remarkable stability under rapid cycling conditions, with significantly reduced crack formation.

Furthermore, utilizing continuum modeling, the team quantified the relationship between lithium-ion diffusion rates, volume changes, and the onset of mechanical failure. This analysis enabled the formulation of design principles for creating mechanically robust single-crystal cathodes capable of operating reliably at targeted current densities.

Professor Lee stated, “This study provides a clear understanding of the mechanical degradation mechanisms in single-crystal cathodes. By integrating experimental and computational approaches, we have established an effective design strategy to enhance their structural integrity, which is crucial for the commercialization of next-generation high-performance batteries.”

The research was led by Hyunsol Shin from the Department of Materials Science and Engineering at UNIST, the first author of the study.