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

JOURNAL OF POWER SOURCES

卷:307

Article

Scipioni, Roberto¹  Jorgensen, Peter S.¹  Ngo, Duc-The^1,3  Simonsen, Soren B.¹  Liu, Zhao²  Yakal-Kremski, Kyle J.²  Wang, Hongqian²  Hjelm, Johan¹  Norby, Poul¹  Barnett, Scott A.²  Jensen, Soren H.¹ 

[1] Tech Univ Denmark, Dept Energy Convers & Storage, DTU Riso Campus,Frederiksborgvej 399, DK-4000 Roskilde, Denmark

[2] Northwestern Univ, Dept Mat Sci & Engn, 2220 Campus Dr, Evanston, IL 60208 USA

[3] Univ Manchester, Sch Mat, Oxford Rd, Manchester M13 9PL, Lancs, England

关键词: Low accelerating voltage;    Focused ion beam scanning electron microscopy;    Three-dimensional analysis of LiFePO4/Carbon electrode;    Degradation mechanism;    Loss in electron percolation;   

DOI  :  10.1016/j.jpowsour.2015.12.119

来源: Elsevier

【 摘 要 】

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. (C) 2016 The Authors. Published by Elsevier B.V.

【 授权许可】

Free