Electron microscopy investigations of changes in morphology and conductivity of LiFePO4/C electrodes

Publication: Research - peer-reviewJournal article – Annual report year: 2016

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In this work we study the structural degradation of a laboratory Li-ion battery LiFePO4/Carbon Black (LFP/CB) cathode by various electron microscopy techniques including low kV Focused Ion Beam (FIB)/Scanning Electron Microscopy (SEM) 3D tomography. Several changes are observed in FIB/SEM images of fresh and degraded cathodes, including cracks in the LFP particles, secondary disconnected particles, and agglomeration of CB. Low voltage (1 kV) SEM images show that the CB agglomerates have a different brightness than the fresh CB, due to charging effects. This suggests that the electronic conductivity of the CB agglomerates is low compared to that of the fresh CB particles. HRTEM analysis shows that fresh CB particles are quasi crystalline, whereas the LFP/CB interface in the degraded electrode shows amorphous carbon surrounding the LFP particles. The presence of the amorphous carbon is known to impede the electronic conductivity and thereby decreasing percolation in the cathode and reducing the electrode capacity.
Original languageEnglish
JournalJournal of Power Sources
Volume307
Pages (from-to)259-269
Number of pages11
ISSN0378-7753
DOIs
StatePublished - 2016
CitationsWeb of Science® Times Cited: 7

    Keywords

  • Degradation mechanism, Focused ion beam scanning electron microscopy, Loss in electron percolation, Low accelerating voltage, Three-dimensional analysis of LiFePO4/Carbon electrode
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