Operando X-ray nano-imaging of novel cathode materials for Li-ion batteries

In the search for sustainable energy solutions, the development of advanced materials for energy storage has established itself as a pillar of scientific innovation. Among the cathode materials for Li-ion batteries, lithium-manganese-nickel oxide (LMNO) crystals have received special attention due to their exceptional electrochemical properties, making them promising for high-performance batteries. An in-depth understanding of their structural and morphological characteristics is therefore essential.
The principles of ion disintercalation in battery cathode materials remain poorly understood, in particular, how crystallographic defects (dislocations, grain boundaries, etc.) affect the microscopic characteristics of lithium disintercalation and degradation mechanisms. The analysis of these fundamental properties is crucial.
In recent years, X-ray imaging techniques have emerged as a powerful tool for non-destructive, high-resolution imaging of materials, offering immense potential to advance the understanding of battery materials. This thesis aims to push the limits of the X-ray nano-diffraction (SXDM) technique available at the European synchrotron (ESRF-EBS) for the characterization of LMNO crystals.
The SXDM technique uses a focused X-ray beam at the nanoscale (less than 100 nm). The resulting maps are extremely sensitive to local deformations and disorientations of the network. The combination of this innovative technique with more conventional methods such as micro-focused beam powder diffraction (PXRD) and electron microscopy provides a holistic understanding of the complex crystallography of LMNO. This work focuses on the determination of the complex internal structure, defects, phase transformations and degradation mechanisms within LMNO crystals.
The SXDM operando measurements made it possible to visualize persistent deformation gradients within the single crystals, suggesting that the shape and size of the solid solution domains are guided by lattice defects, guiding the entire delition process. The morphology, deformations and disorientations of the measured crystallographic planes reveal that the phase transitions (Ni2+/3+) and (Ni3+/4+) take place according to different mechanisms, either a "phase field" mechanism with a more localized disintercalation, or a homogeneous "core-shell" transition. This offers a solution to reduce structural degradation in active materials for greater durability.
We also observe plastic deformation occurring in some particles during the phase transition, involving the division of the crystal into three domains inclined relative to each other. Structural distortion is required to accommodate two phases with different lattice parameters in a single crystal. This effect is only partially reversible, resulting in a permanent structural change in the network after the transgression.In the case of the Scandinavian Empire, the
The study of aged particles confirms that persistent defects in the initial particle population guide the long-term structural evolution of the material. The observed dynamic reorientation of the network leads to a continuous development of low-angle grain boundaries over consecutive cycles. In addition, the disorientations are very heterogeneous on the population of particles measured, and only certain particles seem to be affected. The deterioration of the crystals is manifested by a variation in the local orientation of the lattice, probably related to the loss of Mn atoms. This causes a change in the phase transformation mechanisms by delaying or preventing the reaction.

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