Designing an elastomeric binder for large-volume-change electrodes for lithium-ion batteries.
Date
2004
Authors
Chen, Zonghai.
Journal Title
Journal ISSN
Volume Title
Publisher
Dalhousie University
Abstract
Description
It is of commercial importance to develop high capacity negative and positive electrode materials for lithium-ion batteries to meet the energy requirements of portable electronic devices. Excellent capacity retention has been achieved for thin sputtered films of amorphous Si, Ge and Si-Sn alloys even when cycled to 2000 mAh/g and above, which suggests that amorphous alloys are capable of extended cycling. However, PVDF-based composite electrodes incorporating a-Si0.64Sn0.36/Ag powder (10 wt% silver coating) (∼10mum) still suffer from severe capacity fading because of the huge volumetric changes of a-Si0.64Sn0.36/Ag during charge/discharge cycling. It is the objective of this thesis to understand the problem scientifically and to propose practical solutions to solve this problem.
Mechanical studies of binders for lithium battery electrodes have never been reported in the literature. The mechanical properties of commonly used binders, such as poly(vinylidene fluoride) (PVDF), haven't been challenged because commercially used active materials, such as LiCoO2 and graphite, have small volumetric changes (<10%) during charge/discharge cycling. However, the recently proposed metallic alloys have huge volumetric changes (up to 250%) during cycling. In this case, the mechanical properties of the binder become critical.
A tether model is proposed to qualitatively understand the capacity fading of high-volume-change electrodes, and to predict the properties of a good binder system. A crosslinking/coupling route was used to modify the binder system according to the requirements of the tether model. A poly(vinylidene fluoride-tetrafluoroethylenepropylene)-based elastomeric binder system was designed to successfully improve the capacity retention of a-Si0.64 Sn0.36/Ag composite electrodes.
In this thesis, it has also proven nontrivial to maximize the capacity retention of large-volume-change electrodes even when a fixed elastomeric binder system was used. The parameters that affect the capacity retention of large-volume-change electrodes at least include the mass loading of the active material, the lower cutoff voltage, the compression pressure on the electrodes, and the salt in the electrolyte.
Thesis (Ph.D.)--Dalhousie University (Canada), 2004.
Mechanical studies of binders for lithium battery electrodes have never been reported in the literature. The mechanical properties of commonly used binders, such as poly(vinylidene fluoride) (PVDF), haven't been challenged because commercially used active materials, such as LiCoO2 and graphite, have small volumetric changes (<10%) during charge/discharge cycling. However, the recently proposed metallic alloys have huge volumetric changes (up to 250%) during cycling. In this case, the mechanical properties of the binder become critical.
A tether model is proposed to qualitatively understand the capacity fading of high-volume-change electrodes, and to predict the properties of a good binder system. A crosslinking/coupling route was used to modify the binder system according to the requirements of the tether model. A poly(vinylidene fluoride-tetrafluoroethylenepropylene)-based elastomeric binder system was designed to successfully improve the capacity retention of a-Si0.64 Sn0.36/Ag composite electrodes.
In this thesis, it has also proven nontrivial to maximize the capacity retention of large-volume-change electrodes even when a fixed elastomeric binder system was used. The parameters that affect the capacity retention of large-volume-change electrodes at least include the mass loading of the active material, the lower cutoff voltage, the compression pressure on the electrodes, and the salt in the electrolyte.
Thesis (Ph.D.)--Dalhousie University (Canada), 2004.
Keywords
Chemistry, Physical., Energy.