THESIS
2017
xviii, 88 pages : illustrations (some color) ; 30 cm
Abstract
The lithium metal battery is one of the lightest battery systems with an extremely high
theoretical specific capacity (3860 mAh g
-1), a low density (0.59 g cm
-3), and the lowest
negative electrochemical potential (-3.040 V vs. the standard hydrogen electrode).
However, for the past 40 years, lithium metal batteries have been investigated but
remain unsuccessful in commercialization due to the low coulombic efficiency and the
safety concerns accompanied by dendrite growth of lithium metal anode. Addressing
the problems of the lithium metal anode is essential to realize the application of high
energy battery systems including lithium sulfur and lithium air batteries.
To optimize the electrochemical performance of lithium metal anode, two types of
3-dimensional (3D) current collec...[
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The lithium metal battery is one of the lightest battery systems with an extremely high
theoretical specific capacity (3860 mAh g
-1), a low density (0.59 g cm
-3), and the lowest
negative electrochemical potential (-3.040 V vs. the standard hydrogen electrode).
However, for the past 40 years, lithium metal batteries have been investigated but
remain unsuccessful in commercialization due to the low coulombic efficiency and the
safety concerns accompanied by dendrite growth of lithium metal anode. Addressing
the problems of the lithium metal anode is essential to realize the application of high
energy battery systems including lithium sulfur and lithium air batteries.
To optimize the electrochemical performance of lithium metal anode, two types of
3-dimensional (3D) current collector were designed. The first one is copper (Cu) based
3D current collector that was synthesized by first employing the chemical reaction
between copper and ammonium ion, hydroxide ion to produce blanket of copper
hydroxide nanowires on copper foam skeleton, then further dehydration and reduction.
The 3D Cu current collector exhibited a high Coulombic efficiency (CE) above 97%
for lithium stripping and plating after 400 cycles and a much lower dendrite formation.
The improvement may be attributed to the increased surface area and the decreased
areal current density during charge/discharge process suppressing the dendrite growth
rate. The second one is carbon nanofiber (CNF) based current collector with two sides
having different compositions. It was synthesized by electrospinning and magnetron sputtering. The freestanding CNF membrane was first obtained by simple
electrospinning of polyacrylonitrile (PAN) and carbonization at 1000 ˚C. Then its two
sides were sputtered with two components for certain time and depth. The upper side
(facing the separator) was coated with non-conducive zinc oxide (ZnO) which can
effectively prevent the lithium dendrite from further growth and the bottom side with
highly conductive Cu layer, aiming to induce the lithium ion deposition. The CE
performance was much enhanced by using this CNF based current collector and the cell
assembled with lithium titanate (LTO) electrode revealed a reversible capacity of
around 160 mAh g
-1 under 1C current density for 100 cycles. The dendrite forming
phenomenon in the lithium anode surface was also alleviated.
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