Failure Investigation of LiFePO4 Cells in Over-Discharge Conditions

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

49 Scopus Citations
View graph of relations

Author(s)

  • Hao He
  • Yadong Liu
  • Zhefei Li
  • Fan Xu
  • Clif Dun
  • Mei-Xian Wang
  • Jian Xie

Detail(s)

Original languageEnglish
Pages (from-to)A793-A804
Journal / PublicationJournal of the Electrochemical Society
Volume160
Issue number6
Publication statusPublished - 13 Mar 2013
Externally publishedYes

Abstract

The failure mechanism of LiFePO4 cells in over-discharge conditions has been systematically studied using commercial A123 18650 cells at a 1.0 C rate and different conditions - from 5% to 20% over-discharge (DOD = 105% to 120%). SEM/EDAX, high-energy synchrotron XRD (HESXRD), and cyclic voltammetry (CV) were used to characterize the morphology, structure, and electrode potentials of cell components both in situ and ex situ. The failure behaviors of A123 18650 cells experiencing different degrees of over-discharge were found to be similar, and the 20% over-discharge process was analyzed as the representative example. The Cu electrochemical potentials in the 1.2 M LiPF6 EC/EMC electrolyte were measured during the charge/over-discharge process using CV, proving that Cu oxidation and reduction in the cell during the charge/over-discharge cycle were theoretically possible to proceed. A possible failure mechanism is proposed: during the over-discharging process, Cu foil oxidized first to Cu+, then to Cu2+ cations; next, these Cu+ and Cu2+ cations diffused to the cathode side from the anode side; and finally, these Cu2+ cations reduced to Cu + cations, and then reduced further, back to metallic Cu. During charge/over-discharge cycling, Cu dendrites continued growing from the cathode side, penetrating through the separator and forming a copper bridge between the anode and cathode. The copper bridge caused micro-shorting and eventually led to the failure of the cell. During the charge/over-discharge cycles, the continued cell temperature increase at the end of over-discharge is evidence of the micro-shorting. © 2013 The Electrochemical Society.

Citation Format(s)

Failure Investigation of LiFePO4 Cells in Over-Discharge Conditions. / He, Hao; Liu, Yadong; Liu, Qi; Li, Zhefei; Xu, Fan; Dun, Clif; Ren, Yang; Wang, Mei-Xian; Xie, Jian.

In: Journal of the Electrochemical Society, Vol. 160, No. 6, 13.03.2013, p. A793-A804.

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review