Capacity Fade and Its Mitigation in Li-Ion Cells with Silicon-Graphite Electrodes
Journal Article
·
· Journal of Physical Chemistry. C
- Argonne National Lab. (ANL), Argonne, IL (United States). Chemical Sciences and Engineering Div.
- Argonne National Lab. (ANL), Argonne, IL (United States). Chemical Sciences and Engineering Div.; KTH Royal Institute of Technology, Stockholm (Sweden)
Silicon-graphite (Si-Gr) electrodes typically contain lithiated carboxylates as polymer binders that are introduced through aqueous processing. Li-ion cells with such electrodes show significantly faster capacity fade than cells with graphite (Gr) electrodes. Here we examine the causes for capacity loss in Si-Gr cells containing LiPF6-based electrolytes. The presence of SiOxFy in the Si-Gr electrode, fluorophosphate species in the electrolyte, and silica on the positive electrode indicates the crucial role of the hydrolytic cycle. In particular, HF acid that is generated through LiPF6 hydrolysis corrodes Si particles. As it reacts, the released water re-enters the cycle. We trace the moisture initiating this detrimental cycle to the hydration water in the lithiated binders that cannot be fully removed by thermal treatment. The rate of HF corrosion can be reduced through the use of electrolyte additives. For the fluoroethylene carbonate (FEC) additive, the improved performance arises from changes to the solid electrolyte interphase (SEI) that serves as a barrier against HF attack. Here, we propose that the greater extent of polymer cross-linking, that gives FEC-derived SEI elastomer properties, slows down HF percolation through this SEI membrane and inhibits the formation of deep cracks through which HF can access and degrade the Si surface.
- Research Organization:
- Argonne National Laboratory (ANL)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (EE-3V)
- Grant/Contract Number:
- AC02-06CH11357
- OSTI ID:
- 1405319
- Alternate ID(s):
- OSTI ID: 1429859
- Journal Information:
- Journal of Physical Chemistry. C, Journal Name: Journal of Physical Chemistry. C Journal Issue: 38 Vol. 121; ISSN 1932-7447
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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