Non-uniform aging of cycled commercial LiFePO4//graphite cylindrical cells revealed by post-mortem analysis
Journal article, 2014

Aging of power-optimized commercial 2.3 Ah cylindrical LiFePO4//graphite cells to be used in hybrid electric vehicle is investigated and compared for three different aging procedures; (i) using a simulated hybrid electric vehicle cycle within a narrow SOC-range, (ii) using a constant-current cycle over a 100% SOC-range, and (iii) stored during three years at 22 degrees C. Postmortem analysis of the cells is performed after full-cell electrochemical characterization and discharge. EIS and capacity measurements are made on different parts of the disassembled cells. Material characterization includes SEM, EDX, HAXPES/XPS and XRD. The most remarkable result is that both cycled cells displayed highly uneven aging primarily of the graphite electrodes, showing large differences between the central parts of the jellyroll compared to the outer parts. The aging variations are identified as differences in capacity and impedance of the graphite electrode, associated with different SEI characteristics. Loss of cyclable lithium is mirrored by a varying degree of lithiation in the positive electrode and electrode slippage. The spatial variation in negative electrode degradation and utilization observed is most likely connected to gradients in temperature and pressure, that can give rise to current density and potential distributions within the jellyroll during cycling. (C) 2014 Elsevier B.V. All rights reserved.

ELECTRODES

MECHANISMS

LiFePO4/graphite cells

GRAPHITE/LIFEPO4

RAY PHOTOELECTRON-SPECTROSCOPY

PERFORMANCE

Electrode utilization

HIGH-POWER

Hybrid electric vehicle

DEGRADATION

Synchrotron material characterization

Battery aging

TEMPERATURE

LITHIUM-ION BATTERIES

CELLS

CALENDAR

Author

M. Klett

Royal Institute of Technology (KTH)

R. Eriksson

Uppsala University

Jens Groot

Chalmers, Energy and Environment, Electric Power Engineering

P. Svens

Scania

Royal Institute of Technology (KTH)

K. C. Hogstrom

Uppsala University

R. W. Lindstrom

Royal Institute of Technology (KTH)

H. Berg

AB Libergreen

T. Gustafson

Uppsala University

Göran Lindbergh

Royal Institute of Technology (KTH)

K. Edstrom

Uppsala University

Journal of Power Sources

0378-7753 (ISSN)

Vol. 257 126-137

Subject Categories

Inorganic Chemistry

Energy Systems

DOI

10.1016/j.jpowsour.2014.01.105

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