A study of lithium ion batteries cycle aging by thermodynamics techniques

Kenza Maher, Rachid Yazami

Research output: Contribution to journalArticle

41 Citations (Scopus)

Abstract

Lithium ion batteries (LiB) are cycled under a galvanostatic regime (∼C/2-rate) between 2.75 V and 4.2 V for up to 1000 cycles. After each completed 100 cycles, the discharge capacity, capacity loss, average discharge potential were determined under the same C/2 rate. Then cells undergo an additional charge and discharge cycle at C/6 rate followed by a thermodynamics measurements test. This enables open-circuit potential (OCP), entropy (ΔS) and enthalpy (ΔH) data to be assessed. It is found that with increasing cycle number, the entropy and enthalpy profiles show more significant changes than those observed in the discharge and the OCP curves especially at particular SOC and OCP values. These differences are attributed to the higher sensitivity of entropy and enthalpy state functions to changes in the crystal structure of the graphite anode and the lithiated cobalt oxide (LCO) induced by cycle aging compared to the free energy ΔG (OCP) alone. The thermodynamics data are supported by post-mortem X-ray diffractometry (XRD) and Raman scattering (RS) analyses on the electrode materials. The results show important LCO crystal structure degradation, whereas, surprisingly, the graphite anode remains almost unaffected by heavy cycling, if not improved.

Original languageEnglish
Pages (from-to)527-533
Number of pages7
JournalJournal of Power Sources
Volume247
DOIs
Publication statusPublished - 1 Jan 2014

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Keywords

  • Cycle aging
  • Enthalpy
  • Entropy
  • Lithium ion batteries
  • Phase transition
  • Thermodynamics

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Energy Engineering and Power Technology
  • Physical and Theoretical Chemistry
  • Electrical and Electronic Engineering

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