Operando visualisation of kinetically-induced lithium heterogeneities in single-particle layered Ni-rich cathodes

Chao Xu; Alice J. Merryweather; Shrinidhi S. Pandurangi; Zhengyan Lun; David S. Hall; Vikram S. Deshpande; Norman A. Fleck; Christoph Schnedermann; Akshay Rao; Clare P. Grey

doi:10.26434/chemrxiv-2022-qb80n-v2

Materials Chemistry

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Operando visualisation of kinetically-induced lithium heterogeneities in single-particle layered Ni-rich cathodes

Working Paper

Chao Xu Yusuf Hamied Department of Chemistry, University of Cambridge & Cavendish Laboratory, University of Cambridge & The Faraday Institution & ShanghaiTech University ,
Alice J. Merryweather Yusuf Hamied Department of Chemistry, University of Cambridge & Cavendish Laboratory, University of Cambridge & The Faraday Institution ,
Shrinidhi S. Pandurangi Department of Engineering, University of Cambridge & The Faraday Institution ,
Zhengyan Lun The Faraday Institution & Yusuf Hamied Department of Chemistry, University of Cambridge & Cavendish Laboratory, University of Cambridge ,
David S. Hall The Faraday Institution & Yusuf Hamied Department of Chemistry, University of Cambridge ,
Vikram S. Deshpande The Faraday Institution & Department of Engineering, University of Cambridge ,
Norman A. Fleck The Faraday Institution & Department of Engineering, University of Cambridge ,
Christoph Schnedermann The Faraday Institution & Cavendish Laboratory, University of Cambridge ,
Akshay Rao The Faraday Institution & Cavendish Laboratory, University of Cambridge ,
Clare P. Grey Yusuf Hamied Department of Chemistry, University of Cambridge & The Faraday Institution

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Abstract

Understanding how lithium-ion dynamics affect the (de)lithiation mechanisms of state-of-the-art nickel-rich layered oxide cathodes is crucial to improving electrochemical performance. Here, we directly observe two distinct kinetically-induced lithium heterogeneities within single-crystal LiNixMnyCo(1-x-y)O2 (NMC) particles using recently developed operando optical microscopy, challenging the notion that uniform (de)lithiation occurs within individual particles. Upon delithiation, a rapid increase in lithium diffusivity at the beginning of charge results in particles with lithium-poor peripheries and lithium-rich cores. The slow ion diffusion at near-full lithiation states – and slow charge transfer kinetics – also leads to heterogeneity at the end of discharge, with a lithium-rich surface preventing complete lithiation. Finite-element modelling confirms that concentration-dependent diffusivity is necessary to reproduce these phenomena. Our results show that diffusion limitations cause first-cycle capacity losses in Ni-rich cathodes.