Title

A New Aspect of the Li Diffusion Enhancement Mechanism of Ultrathin Coating Layer on Electrode Materials

Abstract

Atomic layer deposition (ALD) coating on active material particles has been widely considered as an effective and efficient strategy to improve the capacity and cycle life of lithium-ion batteries. One of the key roles of the ALD coating layer is to facilitate the Li ion transfer in electrode particles. Several recent studies demonstrated that an ALD coating layer could significantly improve the effective diffusion coefficients in cathode particles. As such, this enhanced transport property is generally believed to be a result of the higher conductivity of the coating layer itself when compared to that of active materials. However, since the fraction of ALD coating layer is very small, it is questionable that the ultrathin coating layer could lead to such a significant improvement of the diffusivity for the whole particle. Thus, we proposed a new hypothesis about the role of ALD coating layer on Li ion transportation. Due to the agglomeration of particles in an electrode, the surfaces of the particles are partially blocked, and, correspondingly, Li ion intercalation is not uniform over the whole surface. Herein, we propose that the ALD coating could provide a quick path to distribute Li ions over the whole particle surface and allow Li ions to spread uniformly and effectively, leading to improved effective diffusivity of the particles and their utilization. In this work, this hypothesis was validated by simulation and experimental study. It was proved that the particle with an optimal ALD coating thickness has the most uniform Li ion distribution, leading to an optimal discharge capacity. Along with the validation of the hypothesis, a parametric study was conducted by consideration of the flux area, particle size, and current density, which revealed the fundamental role of coating layer on charge transfer, Li ion diffusion, and corresponding battery performance.

Department(s)

Mechanical and Aerospace Engineering

Keywords and Phrases

ALD coating; coating thickness; Li ion diffusion; particle agglomeration; single particle model

International Standard Serial Number (ISSN)

1944-8244; 1944-8252

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2019 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Sep 2019

PubMed ID

31535839

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