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

Abstract

In this study we scrutinize the causes for capacity fade in lithium-ion cells containing silicongraphite (Si-Gr) blends in the negative electrode and examine approaches for minimizing this fade. The causal mechanisms are inferred from data obtained by electrochemistry, microscopy, spectroscopy and thermogravimetry techniques. The presence of SiOxFy signals in the Si-Gr electrode, LixPOyFz compounds in the electrolyte, and SiO2 species on the NCM523 positive electrode, highlight the crucial role of hydrolytically generated HF, which accelerates the degradation of Si particles. The hydrolysis could result from residual moisture in the current electrode fabrication process, which uses aqueous binders. Water can also be released when silanol groups on the Si nanoparticles react with HF to form Si-F compounds. We note that the primary cause of capacity fade in the full cells is the loss of solid electrolyte interphase (SEI) integrity resulting from volume changes in Si particles during electrochemical cycling. Adding fluoroethylene carbonate (FEC) to the conventional electrolyte slows capacity fade through the formation of a cross linked polymer with elastomeric properties. Further gains in cell longevity are possible by excluding water during electrode fabrication, using hydrolytically stable lithium salts, and adopting electrolyte systems that provide more elasticity to the SEI layers.

Authors:
ORCiD logo [1]; ORCiD logo [1];  [1];  [1]; ORCiD logo [1]
  1. Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
Publication Date:
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)
OSTI Identifier:
1429859
DOE Contract Number:
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry. C; Journal Volume: 121; Journal Issue: 38
Country of Publication:
United States
Language:
English
Subject:
LiPF6 hydrolysis; TGA; XPS; fluoroethylene carbonate; fluorophosphates; polyacrylate binders

Citation Formats

Bareño, Javier, Shkrob, Ilya A., Gilbert, James A., Klett, Matilda, and Abraham, Daniel P. Capacity Fade and Its Mitigation in Li-Ion Cells with Silicon-Graphite Electrodes. United States: N. p., 2017. Web. doi:10.1021/acs.jpcc.7b06118.
Bareño, Javier, Shkrob, Ilya A., Gilbert, James A., Klett, Matilda, & Abraham, Daniel P. Capacity Fade and Its Mitigation in Li-Ion Cells with Silicon-Graphite Electrodes. United States. doi:10.1021/acs.jpcc.7b06118.
Bareño, Javier, Shkrob, Ilya A., Gilbert, James A., Klett, Matilda, and Abraham, Daniel P. Fri . "Capacity Fade and Its Mitigation in Li-Ion Cells with Silicon-Graphite Electrodes". United States. doi:10.1021/acs.jpcc.7b06118.
@article{osti_1429859,
title = {Capacity Fade and Its Mitigation in Li-Ion Cells with Silicon-Graphite Electrodes},
author = {Bareño, Javier and Shkrob, Ilya A. and Gilbert, James A. and Klett, Matilda and Abraham, Daniel P.},
abstractNote = {In this study we scrutinize the causes for capacity fade in lithium-ion cells containing silicongraphite (Si-Gr) blends in the negative electrode and examine approaches for minimizing this fade. The causal mechanisms are inferred from data obtained by electrochemistry, microscopy, spectroscopy and thermogravimetry techniques. The presence of SiOxFy signals in the Si-Gr electrode, LixPOyFz compounds in the electrolyte, and SiO2 species on the NCM523 positive electrode, highlight the crucial role of hydrolytically generated HF, which accelerates the degradation of Si particles. The hydrolysis could result from residual moisture in the current electrode fabrication process, which uses aqueous binders. Water can also be released when silanol groups on the Si nanoparticles react with HF to form Si-F compounds. We note that the primary cause of capacity fade in the full cells is the loss of solid electrolyte interphase (SEI) integrity resulting from volume changes in Si particles during electrochemical cycling. Adding fluoroethylene carbonate (FEC) to the conventional electrolyte slows capacity fade through the formation of a cross linked polymer with elastomeric properties. Further gains in cell longevity are possible by excluding water during electrode fabrication, using hydrolytically stable lithium salts, and adopting electrolyte systems that provide more elasticity to the SEI layers.},
doi = {10.1021/acs.jpcc.7b06118},
journal = {Journal of Physical Chemistry. C},
number = 38,
volume = 121,
place = {United States},
year = {Fri Sep 15 00:00:00 EDT 2017},
month = {Fri Sep 15 00:00:00 EDT 2017}
}