Non-uniform aging of cycled commercial LiFePO4//graphite cylindrical cells revealed by post-mortem analysis
Artikel i vetenskaplig tidskrift, 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.

TEMPERATURE

Synchrotron material characterization

Battery aging

ELECTRODES

LITHIUM-ION BATTERIES

LiFePO4/graphite cells

MECHANISMS

Electrode utilization

DEGRADATION

Hybrid electric vehicle

PERFORMANCE

RAY PHOTOELECTRON-SPECTROSCOPY

GRAPHITE/LIFEPO4

CELLS

HIGH-POWER

CALENDAR

Författare

M. Klett

Kungliga Tekniska Högskolan (KTH)

R. Eriksson

Uppsala universitet

Jens Groot

Chalmers, Energi och miljö, Elkraftteknik

P. Svens

Scania AB

Kungliga Tekniska Högskolan (KTH)

K. C. Hogstrom

Uppsala universitet

R. W. Lindstrom

Kungliga Tekniska Högskolan (KTH)

H. Berg

AB Libergreen

T. Gustafson

Uppsala universitet

Göran Lindbergh

Kungliga Tekniska Högskolan (KTH)

K. Edstrom

Uppsala universitet

Journal of Power Sources

0378-7753 (ISSN)

Vol. 257 126-137

Ämneskategorier

Oorganisk kemi

Energisystem

DOI

10.1016/j.jpowsour.2014.01.105