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A TEM study of morphological and structural degradation phenomena in LiFePO4‐CB cathodes
Authors:Duc‐The Ngo  Roberto Scipioni  Søren Bredmose Simonsen  Peter Stanley Jørgensen  Søren Højgaard Jensen
Affiliation:1. DTU Energy, Department of Energy Conversion and Storage, Technical University of Denmark, Roskilde, Denmark;2. Electron Microscopy Centre, School of Materials, University of Manchester, Manchester, United Kingdom
Abstract:LiFePO4‐based cathodes suffer from various degradation mechanisms, which influences the battery performance. In this paper, morphological and structural degradation phenomena in laboratory cathodes made of LiFePO4 mixed with carbon black (CB) in a 1 mol/L LiPF6 in EC : DMC (1:1 by weight) electrolyte are investigated by transmission electron microscopy at various preparation, assembling, storage, and cycling stages. High‐resolution transmission electron microscopy imaging shows that continuous SEI layers are formed on the LiFePO4 particles and that both storage and cycling affect the formation. Additionally, loss of CB crystallinity, CB aggregation, and agglomeration is observed. Charge–discharge curves and impedance spectra measured during cycling confirm that these degradation mechanisms reduce the cathode conductivity and capacity. Copyright © 2016 John Wiley & Sons, Ltd.
Keywords:lithium ion battery  cathode degradation  nanoparticles  transmission electron microscopy  high‐resolution transmission electron microscopy
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