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Westman, K. (2016) Diglyme as an electrolyte solvent for sodium-ion batteries. Göteborg : Chalmers University of Technology
BibTeX
@mastersthesis{
Westman2016,
author={Westman, Kasper},
title={Diglyme as an electrolyte solvent for sodium-ion batteries},
abstract={For storing energy in future sustainable energy systems, sodium-ion batteries (SIB) have
emerged as an alternative to the current state-of-the-art lithium-ion batteries (LIBs), since
SIBs are potentially cheaper. For LIBs and SIBs alike, the development of stable systems
depends on employing stable or metastable electrolytes, forming a SEI. Ether compounds
have earlier been investigated for use in electrolytes, due to a presumed high reductive
stability. In this project diglyme, an ether solvent, mixed with 1 M NaPF6 has been
evaluated for use with Na-metal reference electrodes and a SIB electrode platform comprising
Na3V2(PO4)2F3 (NVPF) and hard carbon (HC), and with a model system using
Na3V2(PO4)3 (NVP) at both electrodes. Furthermore, this electrolyte has been investigated
for electrochemical stability, and for possible degradation mechanisms. Techniques
used are galvanostatic cycling (GCPL), cyclic voltammetry (CV) and electrical impedance
spectroscopy (EIS), coupling these to ab-initio calculations and physico-chemical characterisation
methods. Using these techniques, Na-metal is shown to provide a stable reference
electrode. In spite of the electrochemical stability of 1 M NaPF6 in diglyme appearing
promising when conducting CV, cells of NVPF|HC are shown to exhibit a c of 99.13 %,
a high initial irreversibility (30 %), and an inferior capacity retention, when compared to
equivalent cells using a EC50:DMC50-based electrolyte. NVP|NVP cells, on the other hand,
show outstanding capacity retention and low initial irreversibility. The problems experienced
in NVPF|HC cells are proposed to arise due to a set of different mechanisms: binder
degradation, vanadium dissolution-deposition, and possibly reduction of the electrolyte.
No coherent indications are given for the formation of an SEI. However, reduction schemes
drawn still allow for undetectable reduction products. By independently exploring different
voltage regions of the active materials the oxidative stability of 1 M NaPF6 in diglyme
is put to question despite earlier indications of stability. Future studies should aim to
change the type of binder to avoid losses. NVP should be tested separately with both the
active materials NVPF/HC to determine where most of the loss occurs along with further
investigations to confirm if there is a reduction of the electrolyte at sodiated HC, since
any lack thereof could point towards a future SEI-free system.},
publisher={Institutionen för fysik (Chalmers), Chalmers tekniska högskola},
place={Göteborg},
year={2016},
keywords={Sodium-ion Batteries, Electrolytes, Diglyme, Electrolyte Degradation, Galvanostatic Cycling, Electrochemistry},
note={86},
}
RefWorks
RT Generic
SR Electronic
ID 247414
A1 Westman, Kasper
T1 Diglyme as an electrolyte solvent for sodium-ion batteries
YR 2016
AB For storing energy in future sustainable energy systems, sodium-ion batteries (SIB) have
emerged as an alternative to the current state-of-the-art lithium-ion batteries (LIBs), since
SIBs are potentially cheaper. For LIBs and SIBs alike, the development of stable systems
depends on employing stable or metastable electrolytes, forming a SEI. Ether compounds
have earlier been investigated for use in electrolytes, due to a presumed high reductive
stability. In this project diglyme, an ether solvent, mixed with 1 M NaPF6 has been
evaluated for use with Na-metal reference electrodes and a SIB electrode platform comprising
Na3V2(PO4)2F3 (NVPF) and hard carbon (HC), and with a model system using
Na3V2(PO4)3 (NVP) at both electrodes. Furthermore, this electrolyte has been investigated
for electrochemical stability, and for possible degradation mechanisms. Techniques
used are galvanostatic cycling (GCPL), cyclic voltammetry (CV) and electrical impedance
spectroscopy (EIS), coupling these to ab-initio calculations and physico-chemical characterisation
methods. Using these techniques, Na-metal is shown to provide a stable reference
electrode. In spite of the electrochemical stability of 1 M NaPF6 in diglyme appearing
promising when conducting CV, cells of NVPF|HC are shown to exhibit a c of 99.13 %,
a high initial irreversibility (30 %), and an inferior capacity retention, when compared to
equivalent cells using a EC50:DMC50-based electrolyte. NVP|NVP cells, on the other hand,
show outstanding capacity retention and low initial irreversibility. The problems experienced
in NVPF|HC cells are proposed to arise due to a set of different mechanisms: binder
degradation, vanadium dissolution-deposition, and possibly reduction of the electrolyte.
No coherent indications are given for the formation of an SEI. However, reduction schemes
drawn still allow for undetectable reduction products. By independently exploring different
voltage regions of the active materials the oxidative stability of 1 M NaPF6 in diglyme
is put to question despite earlier indications of stability. Future studies should aim to
change the type of binder to avoid losses. NVP should be tested separately with both the
active materials NVPF/HC to determine where most of the loss occurs along with further
investigations to confirm if there is a reduction of the electrolyte at sodiated HC, since
any lack thereof could point towards a future SEI-free system.
PB Institutionen för fysik (Chalmers), Chalmers tekniska högskola,
LA eng
LK http://publications.lib.chalmers.se/records/fulltext/247414/247414.pdf
OL 30
