Influence of Particle Size and Morphology on Electrochemical Properties of Glass Particle-Based Separators for Lithium-Ion Batteries
Authors: Rank Philipp , Spreng Sarah , Müllner Sebastian , Roth Christina , Gerdes Thorsten 
Published: February 2024

Lithium-ion batteries (LIBs) are one of the most important and common energy storage technologies for mobile devices as well as electric vehicles due to their high specific energy density [1]. However, there are still safety concerns in case of overcharge or mechanical damage. The separator as the passive safety-relevant component is placed between the two electrodes to prevent internal short-circuits. Nevertheless, accidental or inhomogeneous deposition of metallic lithium (Li plating) can lead to dendrite growth, which is one of the most common failure mechanisms. If only one dendrite penetrates the separator and forms a conductive path between the two electrodes, a short circuit in the battery leads to its failure [2].

Despite the inherent rigidity of glass materials, previous studies demonstrated the successful application of glass-based separators in LIBs [3, 4]. To meet the requirements of modern battery production, a colloidal water-based system of glass particles and binder is used to manufacture flexible separators. Compared to state-of-the-art polymer-based separators, those flexible glass particle-based separators are superior in many of the required properties such as higher temperature resistance and dimensional stability up to 600 °C [3].

However, the size and morphology of the utilized particles have a significant impact on the manufacturing process, e.g. affect slurry processability and separator formation, and consequently on the electrochemical performance. The effects of these parameters have already been studied for spherical or arbitrarily-shaped particles [5, 6].

In the present work, platelet-shaped particles are utilized to manufacture glass-based separators. To further improve the operational safety of lithium-ion batteries, the benefit of platelet-shaped particles is compared to the use of arbitrarily-shaped particles. The use of these so-called glass flakes serves the purpose of forming an effective barrier against growing lithium dendrites by establishing a self-stabilizing structure. This barrier prevents or at least effectively delays penetration of the separator.

For platelet-shaped particles, thickness and edge length of a particle differ significantly. Particles with a too high aspect ratio (edge length to thickness) block the Li+ diffusion pathway, affecting performance and stability of the final cell. Preliminary tests have shown that increasing the thickness of the glass flakes leads to a slight improvement of ionic conductivity, while increasing the edge length results in a strong reduction of ionic conductivity. However, separators containing particles with higher aspect ratio are expected to show increased piercing resistance. Thus, a trade-off between processability, electrochemical performance and safety barrier function against Li-dendrite growth and penetration is evaluated to understand the influence of particle morphology on the properties of separators using these particles.

The microstructure of separators containing the different particle morphologies is examined using scanning electron microscopy (SEM) and correlated with the results of further characterization methods such as electrochemical impedance spectroscopy (EIS) and galvanostatic cycling.

References

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[3] Schadeck, U., et al.: Flexible, Heat-Resistant, and Flame-Retardant Glass Fiber Nonwoven/Glass Platelet Composite Separator for Lithium-Ion Batteries; Energies 11 (2018) 4; 999–1013

[4] Schadeck, U., et al.: Porous and non-porous micrometer-sized glass platelets as separators for lithium-ion batteries; Journal of Membrane Science 550 (2018); 518–525

[5] Takemura, D., et al.: A powder particle size effect on ceramic powder based separator for lithium rechargeable battery; Journal of Power Sources 146 (2005); 779–783

[6] Kanhere, N., et al.: Electrode-coated alumina separators for lithium-ion batteries - effect of particle size and distribution of alumina powders; Powder Technology 353 (2019); 230–237