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

Wang, Hickner – PSU
V.C.11 Polymer-Coated Layered SiOx-Graphene Nanocomposite Anodes (PSU)
Synthesis and Evaluation of Polymer Binders. To
evaluate the electrochemical performance of as-prepared
polymer binders, commercial silicon nanoparticles were
mixed with Super-P carbon and the as-prepared polymer
binder in a weight ratio of 7:2:1. The cells were cycled at a
current density of 200 mA g -1 in a voltage range from 0.01
to 1.5 V. The performance of several PEO and trimethoxy
silane-based polymer binders is shown in Table V - 1. The
first cycle efficiencies and cycle life of the silane-PEO and
sulfonate PEO binders is not reasonable compared to the
CMC-SBR baseline. The poor performance is probably
due to high swelling in the EC/DMC battery electrolyte.
Thus, our work on new synthesis of block copolymer Si
nanoparticle binders is ongoing with stiffer, less swellable
blocks to maintain the structural integrity of the binder.
Table V - 1: Charge-Discharge Performance for 1st and 10th cycle for
Silane-PEO (Si PEO) and sulfonate-PEO (S PEO) copolymer binders.
nanoparticles with addition of dispersed functional
graphene sheets, or one-step magnesiothermic reduction of
SiO 2 -graphene nanocomposites. The electrochemical
performance of Si-graphene nanocomposites has been
evaluated in coin-type cells. Results demonstrate that the
as-prepared Si-graphene composites exhibit specific
capacity in excess of ~1,000 mAh/g (gram of composite)
with excellent stability and rate capability at a rate of 2000
mA/g, and exhibit less than 20% first cycle irreversible
loss as well as 90% coulombic efficiency cycle to cycle
thereafter. With regard to novel polymer binders, we have
successfully developed a class of polymer binders for Si
anode. Initial tests have demonstrated that the Radel and
sulfonated Radel (S-Radel) binders show comparable
electrochemical performance to CMC/SBR, indicating that
Radel-based binders are suitable for Si anode.
Binder
1st
Discharge
1st
Charge
Effici
ency
10th
Disharge
10th
Charge
Effici
ency
Si-r-EO
50:50
S-r-EO
50:50
2388 1110 0.465 12.8 8.2 0.641
2557 1486 0.577 25.7 15.5 0.603
1182 553 0.468 27.8 17 0.612
1592 670 0.421 26.1 12.9 0.494
S-r-EO
50:50
PVDF
CMC/
SBR
1250 405 0.324 11.2 5.4 0.482
1166 423 0.363 10.3 3.7 0.359
2697 1470 0.545 17.7 10.7 0.605
2001 1052 0.526 23.2 13.4 0.578
2693 2247 0.834 1060 963 0.908
1921 1675 0.872 1075 993 0.924
In addition, the electrochemical performance of
mechanically robust binders composed of RADEL ®
poly(sulfone) variants have also been tested. Figure V -
116 shows their 1 st and 10 th cycle performance compared
to conventional PVDF and CMC/SBR binders. The Radel
and sulfonated Radel (S-Radel) materials show
comparable performance to CMC/SBR. Longer-term
cycling and optimization of these electrodes is underway.
Interestingly, these Radel binders do not contain
carboxylate groups found on CMC. We are currently
testing their swelling properties in EC/DMC and
evaluating new Radel structures for high performance
binders.
Figure V - 116: Comparison of PVDF and CMC/SBR binders with Radel and
S-Radel.
During the remainder of the project period, future
work will focus on: 1) optimizing the composition of Sigraphene
to balance the high capacity and cyclability; 2)
optimizing the size and morphology of Si and graphene in
the Si-graphene composite to increase the utilization rate
of Si; 3) optimizing the composition and structure of asprepared
polymer binders for Si anodes; and 4) exploring
the application of the optimized polymer binders in the
anode system to further improve the cycling capability of
Si-graphene nanocomposites.
FY 2011 Publications/Presentations
1. Contributed to Prashant Kumta “ Novel Lithium Ion
Anode Structures Overview of New DOE BATT
Anode Projects” 2011 DOE Annual Peer Review
Meeting presentation.
Conclusions and Future Directions
Si-graphene nanocomposites have been prepared
through one-step solvothermal synthesis of Si
FY 2011 Annual Progress Report 579 Energy Storage R&D