AC impedance electrochemical modeling of lithium-ion positive electrodes.
Under Department of Energy's Advanced Technology Development Program,various analytical diagnostic studies are being carried out to examine the lithium-ion battery technology for hybrid electric vehicle applications, and a series of electrochemical studies are being conducted to examine the performance of these batteries. An electrochemical model was developed to associate changes that were observed in the post-test analytical diagnostic studies with the electrochemical performance loss during testing of lithium ion batteries. While both electrodes in the lithium-ion cell have been studied using a similar electrochemical model, the discussion here is limited to modeling of the positive electrode. The positive electrode under study has a composite structure made of a layered nickel oxide (LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2}) active material, a carbon black and graphite additive for distributing current, and a PVDF binder all on an aluminum current collector. The electrolyte is 1.2M LiPF{sub 6} dissolved in a mixture of EC and EMC and a Celgard micro-porous membrane is used as the separator. Planar test cells (positive/separator/negative) were constructed with a special fixture and two separator membranes that allowed the placement of a micro-reference electrode between the separator membranes [1]. Electrochemical studies including AC impedance spectroscopy were then conducted on the individual electrodes to examine the performance and ageing effects in the cell. The model was developed by following the work of Professor Newman at Berkeley [2]. The solid electrolyte interface (SEI) region, based on post-test analytical results, was assumed to be a film on the oxide and an oxide layer at the surface of the oxide. A double layer capacity was added in parallel with the Butler-Volmer kinetic expression. The pertinent reaction, thermodynamic, and transport equations were linearized for a small sinusoidal perturbation [3]. The resulting system of differential equations was solved numerically using a partial differential equation solver (FlexPDE) over the frequency range of interest. The electrochemical AC impedance model was used as a diagnostic tool to examine ageing effects associated with the positive electrode, and to investigate ways to reduce the impact of these effects on the overall cell performance.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- EE
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 963256
- Report Number(s):
- ANL/CMT/CP-110711; TRN: US0903152
- Resource Relation:
- Conference: 204th Meeting of the Electrochemical Society; Oct. 12, 2003 - Oct. 16, 2003; Orlando, FL
- Country of Publication:
- United States
- Language:
- ENGLISH
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