Electrolyte design for rechargeable magnesium batteries -Methoxyethyl-amine chelants as electrolyte additives
Typ
Examensarbete för masterexamen
Program
Publicerad
2022
Författare
Wilske, Lova
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Rechargeable magnesium batteries (RMBs) have been pointed out as promising
candidates for future electrical energy storage and conversion system due to high
theoretical volumetric energy density, low tendency of Mg metal anode to form
dendrites, and the high abundance of Mg in the Earth’s crust. Today’s RMBs,
however, suffer from low coulombic efficiencies and poor cycle life. Finding suitable
electrolytes is the key to overcome these issues. A recently discovered family of
electrolyte additives, methoxyethyl-amine chelants, has shown to improve battery
performance by providing Mg2+ ion selective first solvation shells. This thesis aims
to further explore the properties of these additives by evaluating their compatibility
and performance with other electrolyte components and electrode materials, study
the imposed morphology of deposits, and conduct EIS analysis to gain insight to
the transport properties.
Galvanostatic cycling experiments show that 2-methoxyethyl-amine (M3) and 1-
methoxy-2-propylamine (M4) increase the coulombic efficiency and lowers overpotential
for 0.5 M Mg(TFSI)2:glyme systems. Mean Coulombic efficiencies up to 97%
for first 100 cycles were recorded for Mg||SS cells. The additive also displays good
performance with the organic cathode material PAQS-CNT. Best performance is
achieved with electrolytes with a 1:6 molar ratio between the Mg2+ ions and the
additive. Surprisingly, these electrolytes separate into two immiscible phases.
Mg metal deposits formed in the presence of the additive are generally larger and
exhibit higher Mg purity as shown by SEM and EDS analysis. This indicates that
the additive suppresses side reactions and imposes good ion transport at the electrode
surface. The very same conclusion was drawn from the EIS analysis, where
the interfacial impedance was found to be remarkably low for electrolytes containing
the additive.