Lithium-ion battery reactions at elevated temperatures.
Date
2001
Authors
MacNeil, Dean Delehanty.
Journal Title
Journal ISSN
Volume Title
Publisher
Dalhousie University
Abstract
Description
In this thesis, the behaviour of charged lithium-ion battery electrodes upon exposure to elevated temperatures has been examined using a combination of Accelerating Rate Calorimetry (ARC) and Differential Scanning Calorimetry (DSC). The bulk of this thesis is concerned with developing a reaction mechanism for the cathode, LiCoO2. The charged electrode (Li0.5CoO2) releases oxygen and forms LiCoO2 and Co3O4 when temperature is raised. In the presence of an organic solvent, the electrode gets further reduced to CoO and the solvent combusts. When the temperature is increased even further in the presence of excess solvent full reduction to cobalt metal occurs. In electrolyte solutions of LiPF6, the HF produced as a side reaction, promotes the polymerization of the solvent at elevated temperatures. The product of polymerization deposits on the surface of the electrode particles and slows the release of oxygen from the structure; thus a more thermally stable electrode is obtained.
The reaction of Li0.5CoO2 at elevated temperatures in various solutions was found to follow Avrami-Erofeev reaction kinetics for the decomposition of solids. The reaction kinetics were then used, in combination with kinetics derived in the literature for the anode, to develop a full thermal model for the exposure of lithium-ion batteries to elevated temperatures. This model can be used to predict the outcome of various thermal events for any cell geometry.
At the anode, ARC studies were used to show that the reaction processes for six different carbon materials were similar. However, the rates of these reactions were strongly dependent on the surface area of the graphitized samples.
In addition to LiCoO2, other possible cathode materials for lithium-ion cells were studied and their thermal reactivity was compared. The results of this thesis are of importance to commercial electrode developers trying to safely increase the size of their electrodes for applications such as electric vehicles.
Thesis (Ph.D.)--Dalhousie University (Canada), 2001.
The reaction of Li0.5CoO2 at elevated temperatures in various solutions was found to follow Avrami-Erofeev reaction kinetics for the decomposition of solids. The reaction kinetics were then used, in combination with kinetics derived in the literature for the anode, to develop a full thermal model for the exposure of lithium-ion batteries to elevated temperatures. This model can be used to predict the outcome of various thermal events for any cell geometry.
At the anode, ARC studies were used to show that the reaction processes for six different carbon materials were similar. However, the rates of these reactions were strongly dependent on the surface area of the graphitized samples.
In addition to LiCoO2, other possible cathode materials for lithium-ion cells were studied and their thermal reactivity was compared. The results of this thesis are of importance to commercial electrode developers trying to safely increase the size of their electrodes for applications such as electric vehicles.
Thesis (Ph.D.)--Dalhousie University (Canada), 2001.
Keywords
Chemistry, Physical., Engineering, Chemical.