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Title: Capacity Fade and Its Mitigation in Li-Ion Cells with Silicon-Graphite Electrodes

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 LiPF 6-based electrolytes. The presence of SiO xF y 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 LiPF 6 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 andmore » degrade the Si surface.« less
Authors:
ORCiD logo [1] ; ORCiD logo [1] ;  [1] ;  [2] ; ORCiD logo [1]
  1. Argonne National Lab. (ANL), Argonne, IL (United States). Chemical Sciences and Engineering Div.
  2. Argonne National Lab. (ANL), Argonne, IL (United States). Chemical Sciences and Engineering Div.; KTH Royal Institute of Technology, Stockholm (Sweden)
Publication Date:
Grant/Contract Number:
AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 121; Journal Issue: 38; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (EE-3V)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 25 ENERGY STORAGE; NMR; XPS; electrochemistry; hydrolysis; lithium ion battery; polymer binder; silicon electrode
OSTI Identifier:
1405319