New Method Maps NCM Cathode Degradation in 3D, Paving Way for Better Batteries
Researchers have made significant strides in understanding the degradation processes of lithium nickel manganese cobalt oxide (NCM) cathodes, crucial components in rechargeable batteries. A team led by Jian Yang, Anil K. Nanda, and Bernd Rellinghaus has developed a novel method to map atomic structure, chemical composition, and electronic states in 3D, providing fresh insights into the complex mechanisms at play.
The team's study, published on arXiv, demonstrates that NCM111 cathodes undergo structural phase transitions, shifting from layered to spinel-like and eventually to a rock-salt structure. Atomic-resolution measurements confirmed these changes, which are driven by a complex interplay of bulk and surface degradation mechanisms. Key factors influencing the functional stability and long-term performance of NCM cathodes are the three-dimensional valence state distribution and chemical inhomogeneity.
Investigating the evolution of NCM111 cathodes through multiple electrochemical cycles, scientists observed capacity loss after each cycle. They tracked this evolution through 50, 100, and 200 cycles, revealing that cathode failure is driven by ion movement and material dissolution, leading to nanoscale inhomogeneity and valence gradients. Interestingly, while chemical composition evolved uniformly, valence state changes were strongly surface-localized and depth-dependent.
The new multi-modal correlative microscopy approach allows for a comprehensive understanding of degradation pathways in lithium-rich layered oxide cathode materials. By revealing oxygen vacancy formation and manganese dissolution as key degradation pathways, this research paves the way for improved battery design and longevity. Further studies using this technique could lead to enhanced performance and safety in rechargeable batteries.
