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

V.C.14 Hard Carbon Materials for High-Capacity Li-ion Battery Anodes (ORNL)
Dai – ORNL
the carbons after surface coating is improved, especially
under high rate conditions (Figure V - 131B).
for electric vehicle applications where high power and
high energy is needed.
4.0
3.5
3.0
(A)
2.5
-1 E / V
)
Capacity (mAh g
2.0
1.5
1.0
0.5
C550; CE = 0.574
C550-PALi; CE = 0.597
C550-PSSALi-MALi; CE = 0.604
0.0
0 200 400 600 800 1000 1200 1400 1600 180
Capacity / mAh g -1
1800
1600
C550 (B)
1400
C550-PALi
C/20
C550-PSSA-co-MALi
1200
1000
C/10
800
C/20
600
C/5
C/2
400
C
200
0
0 5 10 15 20 25 30 35 40 45 50
Cycle number
Figure V - 131: (A) First cycle of MC550 with 10wt% surface coating of
single ion conductors under the rate of C/20 (B) Cycle performance of
MC550 with 10wt% surface coating of single ion conductors under different
rate conditions.
While we were trying different techniquse to improve
the performance of our mesoporus carbon as a potential
anode for electric vehicle applications, we were asked to
focus on evaluating commercial carbons. We
systematically investigated the performance of commercial
carbons from Pred Materials and MTI Corporation versus
our mesoporous carbon under the same rate conditions. As
seen in Figure V - 132, all the commercial carbons have poor
rate capability compared to the mesoporus carbon under
the same rate conditions. For example, at low 1C rate the
capacities of natural graphite, Potato Graphite, Mesophase
Graphite and MesoCarbon MicroBeads (MCMB) are all
lower than 250 mAh g -1 while that of mesoporous carbon
delivers a capacity that is more than 400 mAh g -1 , which is
higher than the theoretical capacity of graphite (372
mAh g -1 ). With increasing cycling rate, the difference
between our mesoporous carbon and the commercial
carbons becomes bigger. At 10C rate, the capacities of
commercial carbons drop to nearly zero while that of
mesoporous carbon remains around 100mAh g -1 .
The above comparisons show that the mesoporous
carbon is superior to those commercial carbons under high
rate conditions, which is an important factor to consider
Figure V - 132: Comparison of the rate capability of different commercial
carbons with the house synthesized mesoporous carbon. Natural graphite,
potaot graphite and mesophase graphite all come from Pred. Materials.
MCMB (MesoCarbon MicroBeads) comes from MTI Corporation.
Conclusions and Future Directions
Mesoporous carbon has clear advantages over
commercial carbons in terms of capacity and rate
capability. However, the cycling stability and the initial
coulombic efficiency clearly need to be improved. Coating
the carbon surface with single ion conductor can prevent
the initial contact of the electrolytes with electrodes,
however, the electrolyte can swell the surface coating and
eventually contact the electrode and decompose, which
results in capacity loss with cycling. Inelastic coatings
such as crosslinked materials or inorganic lithium
compounds could eliminate the swelling effect and thus
improve the initial coulombic efficiency and cycling
stability.
FY 2011 Publications/Presentations
1. 2011 DOE Annual Peer Review Meeting Presentation.
2. B. K. Guo, X. Q. Wang, M. F Chi, S. M. Mahurin, X.
G. Sun, S. Dai, “One-step Synthesis of Mesoporous
Carbon for Lithium-ion Batteries with High Capacity
and Rate Capability”, abstract #1399, the 220th
Electrochemical Society Meeting, Boston, Oct. 9-14,
2011.
3. B. K. Guo, X. Q. Wang, M. F Chi, S. M. Mahurin, X.
G. Sun, S. Dai, Soft-Templated Mesoporous Carbon-
Carbon Nanotube Composites for High Performance
Lithium-ion Batteries, Advanced Materials, 2011,
23, 4661.
References
1. Dai et al., U.S. Patent 7,449,165
2. Dai et al., Angew. Chem. Inter. Ed. 2008, 47, 3696.
Energy Storage R &D 592 FY 2011 Annual Progress Report