V. Focused Fundamental Research - EERE - U.S. Department of ...

ARGONNE2_CDJ403T me Pro ile
V.C.7 Three-Dimensional Anode Architectures and Materials (ANL)
Vaughey – ANL
Because there are no insulating organic binders and
other additives in the electrode, a comparison to a standard
complex electrode architectures, including buried pore
networks and sub-surface interfaces.
electrode was done. Electrochemical studies of these i f
copper-silicon electrodes showed a four-fold enhancement
3
in power capability compared to more standard PVDF-
2.5
based electrodes and a similar volume-expansion
2
dependence on cycle life. Analysis of the MAS-NMR data
also showed under certain annealing conditions the process 1.5
used oxidized the surface of the silicon particles hindering
1
their activity. This coating would probably also hinder
0.5
power capability and its formation process is being
investigated. 0
The electrodes have been evaluated for cycle life as a
function of the capacity. By varying the capacity of the
underlying Si materials, the impact of a variety of
2
electrode volume expansions (LiSi has ~ 120%, based on
crystallographic data) can be evaluated. In Figure V - 97, the
cycling of materials of the electrode composition CuSi 4 is
plotted against various lithium contents. For samples
cycled to the approximate composition “LiSi 2 ”, the
electrode can maintain this capacity for nearly 50 cycles,
for higher volume expansion (Li 3 Si 4 , LiSi) the cycle life is
lower. Figure V - 98 highlights the first 10 cycles for the
CuSi 4 laminate cycled to the composition LiSi 2 .
Capacity (mAh/g)
1200
1000
800
Voltage (V)
Voltage (V)
Voltage Vo lt age ( V (V) )/ Curren t ( mA ) Voltage l
t ( V (V)
)/ Cu rr en t
(mA)
1.75
1.5
1.25
1
0.75
0.5
0.25
ARGONNE2_CDJ403T me Pro ile
0 10 20 30 40 50 60 70 80
Time (hou
ours)
Time (hours)
ARGONNE2_CDJ422Time Profile
0
0 5 10 15 20 25 30 35
Time (hours)
Time (hours)
Figure V - 98: The cycling profile for CuSi4 electrodes cycled to the
composition LiSi2.
600
Copper substrate current collectors were
400
electrodeposited with a wide range of parameters in order
200
to develop two robust, yet distinctly different
0
morphologies (in terms of porosity and tortuosity).
0 20 40 60 80 Applied current, deposition time, additive concentration,
Cycle #
annealing temperature, and annealing time were
systematically altered and the resulting substrates were
Figure V - 97: The cycling capacity of a series of CuSi4 electrodes cycles to analyzed by scanning electron microscopy. It was
LiSi, Li3Si4, and LiSi2. determined that 1 A depositions for 30 seconds with 2
Based on cycling data to date, the more copper in the
sample relative to silicon the better the laminate holds
together and the more controlled the silicon’s volume
expansion the better the cycling. Plots of the cycling
profile over time and an individual profile are shown in
Figure V - 98.
Tomography
Improving the performance and lifetime of volumechanging
anode materials requires a detailed knowledge of
3d structure as a function of synthesis parameters and cell
operating conditions. To that end, high resolution, high
speed synchrotron-based microtomography experiments at
the 2-BM-A beamline at Argonne’s Advanced Photon
Source have been used to ‘look inside’ a cycling electrode.
Microtomography enables non-destructive visualization of
different Cl - concentrations (one 4x the other), and
annealing at 500°C for 48+ hours reproducibly produced
strong substrates with surface features well-suited for
microtomography.
Both electroless and electrodeposition were used to
coat the copper substrates with tin. It was expected that
the electroless bath would be ideal due to its tailored
throwing power (ability to coat subsurface features with
the same ease as high-altitude features), yet the electroless
trials applied very thick tin coating despite short
immersion times. Four electrodeposition procedures (3
galvanic square waves and 1 galvanostatic) were tested, all
designed to deposit the same number of moles of tin onto
the copper surfaces. The galvanic square waves, as
expected, produced the least dendritic tin coatings. The
final deposition procedure was determined to be (-10 mA,
1 s / -1 mA, 5 s) x 240, from a solution of tin sulfate,
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Energy Storage R &D 562 FY 2011 Annual Progress Report