Showing papers by "Colin A. Vincent published in 1999"

Correlating Capacity Loss of Stoichiometric and Nonstoichiometric Lithium Manganese Oxide Spinel Electrodes with Their Structural Integrity

Abstract: It is known that stoichiometric spinel, , when used as a lithium‐ion battery cathode, exhibits significant capacity fade on cycling at room temperature, whereas by making the spinel slightly nonstoichiometric the capacity retention on cycling is improved to a great extent. To help understand this difference in performance, X‐ray diffraction (XRD) was used to investigate the spinel structure during lithium extraction and reinsertion. The stoichiometric spinel shows degradation during the first lithium extraction which becomes more severe at high rates. The XRD pattern measured at the end of 50 cycles showed significant loss of structural integrity, with several prominent peaks that were not present prior to cycling. In contrast, the nonstoichiometric spinel showed no evidence of degradation up to at least 300 cycles, even at high rates. It is suggested that in the case of stoichiometric spinel, , which forms upon extraction of lithium, accumulates during cycling and, because it becomes disconnected from the active electrode, capacity fade is significant. © 1999 The Electrochemical Society. All rights reserved.

Capacity Loss of Lithium Manganese Oxide Spinel in LiPF6 / Ethylene Carbonate‐Dimethyl Carbonate Electrolytes

Abstract: The stability of lithium manganese oxide spinel in LiPF{sub 6}/EC:DMC (ethylene carbonate-dimethyl carbonate) based electrolytes has been investigated at different states of charge and at temperatures between 21 and 55 C. Reversible capacity loss due to reinsertion of lithium takes place at all states of charge and temperature. This reaction can proceed to the extent of inserting more than one Li per Mn{sub 2}O{sub 4} at 55 C resulting in the formation of tetragonal Li{sub 1+x}Mn{sub 2}O{sub 4}. The second process, irreversible capacity loss due to dissolution of the cathode, makes little contribution to capacity loss in highly charged electrodes, but has an effect comparable to reinsertion in discharged electrodes.