Significance of NMC Particle Morphology – Polycrystalline or Single-Crystal?
Authors: Firlej Natalia , Grygiel Michał , Winkowska-Struzik Magdalena , Struzik Michal , Buchberger Dominika , Czerwiński Andrzej 
Published: December 2024

The electrochemical and structural properties of Li[NixMnyCoz]O2 depend significantly on its composition and structure. As each cation plays a distinct role in materials characteristics, finding the balance in NMC composition is challenging [1]. Currently most promising improvement is increasing nickel content, as it enhances specific discharge capacity but raises safety concerns over cycling [2]. Developing an ideal cathode material requires precise control over microstructure and physicochemical properties [3]. Regardless NMC composition, we observe a large decrease in capacity during cycling, as a result of degradation mechanisms such as cracking of the polycrystalline cathode particles, phase transitions, unwanted side reactions and electrolyte decomposition [4]. One of the current developments is the creation of materials differing in secondary structure, such as single-crystal. This type of morphology provides faster ion diffusion, limits surface reactivity, and eliminates particle cracking due to the absence of grain boundaries, which results in greater energy density and increased durability [5].

The research focuses on comparison of structural and electrochemical properties of morphologically diverse NMC materials developed using the standard annealing method retaining the secondary grain structure and a novel single-crystal technique. This significant change in the approach to NMC materials manufacturing aims to enhance energy density and cycling stability of lithium-ion batteries, which can result in longer battery lifespan. Materials were prepared by coprecipitation method of the complex metal hydroxide precursor NixMnyCoz(OH)2 in Couette-Taylor flow reactor, to maximally control the synthesis process, and subsequently annealed in different processes to obtain the lithiated powders of various structures. This careful precursor synthesis strategy and afterwards calcination of the final product enables to control the particle morphology, which has a significant impact on lithium cations migration capability, and performance characteristics of the assembled Li-ion cells. Understanding the influence of grain and particle characteristics on overall material properties is essential as small particle sizes and high surface areas result in enhancing discharge capacities, whereas monocrystallites should reduce the unwanted grain boundaries cracking. To investigate the material characteristics and thoroughly analyze the differences within materials we used various methods. Scanning electron microscopy was employed to examine the morphologies of the prepared powders, both prior to and following the calcination step. Moreover, X-ray powder diffraction was used to investigate the crystal structure of the prepared materials, providing insight into the phases present and their crystallographic parameters. In order to determine key battery cycling parameter, chronopotentiometry tests were conducted. We correlated the electrochemical properties with structural and morphological characteristics of materials obtained. This investigation will provide insight into future opportunities for material enhancement.

A comprehensive and detailed presentation of the research findings will be given at the conference.

This work was funded by the National Science Center in Poland through the Sonata 17 programme (No. UMO-2021/43/D/ST5/03094).

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