TY - JOUR
T1 - Electron microscopy investigations of changes in morphology and conductivity of LiFePO4/C electrodes
AU - Scipioni, Roberto
AU - Jørgensen, Peter S.
AU - Ngo, Duc-The
AU - Simonsen, Søren Bredmose
AU - Liu, Zhao
AU - Yakal-Kremski, Kyle J.
AU - Wang, Hongqian
AU - Hjelm, Johan
AU - Norby, Poul
AU - Barnett, Scott A.
AU - Jensen, Søren Højgaard
PY - 2016
Y1 - 2016
N2 - 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.
AB - 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.
KW - Degradation mechanism
KW - Focused ion beam scanning electron microscopy
KW - Loss in electron percolation
KW - Low accelerating voltage
KW - Three-dimensional analysis of LiFePO4/Carbon electrode
U2 - 10.1016/j.jpowsour.2015.12.119
DO - 10.1016/j.jpowsour.2015.12.119
M3 - Journal article
SN - 0378-7753
VL - 307
SP - 259
EP - 269
JO - Journal of Power Sources
JF - Journal of Power Sources
ER -