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

V.B.13 Studies on the Local SOC and Underlying Structures in Lithium Battery Electrodes (ORNL)
Nanda – ORNL
350
Capacity (mAhg -1 )
300
250
200
150
100
50
C/10 4.9V
Charge
Discharge
Figure V - 68: Raman maps showing local SOC varition across NCA
electrodes cycled at 4.1 V under constant current condition at 3C with 1 hour
PS. SOC plots show the local inhomogeneity across the electrode surface
and could vary under electrochemical conditions.
Using a similar approach, we also undertook Raman
mapping of high voltage Li-rich MNC composite cathodes
under both cycled as well as pristine electrode conditions.
Figure V - 69 shows the micro-Raman mapping/imaging of
the pristine Li 1.2 Ni 0.175 Co 0.1 Mn 0.525 O 2 electrode showing
the carbon and active material region at a micrometer
resolution. We are currently comparing the SOC Raman
maps with cycled Li-rich MNC electrodes.
0
0 20 40 60 80 100 120 140 160 180 200
Cycle number
Figure V - 70: Capacity as a function of Cycle number for pristine
Li1.2Ni0.175Co0.1Mn0.525O2 with 1.5 wt% CNF
Figure V - 71 includes the first charging profile showing
the high voltage plateaus at 4.5 V responsible for the
higher capacity. The discharge profiles are shown at the
end of 1, 5, 50 and 200 cycles. With successive cycling the
discharge profile shifts to lower voltage indicating loss of
energy, although the total capacity remains the same. This
is an important technical barrier that needs to addressed or
understood before moving forward for using this material
for EV application. Literature results on similar
compositions point to complex structural transitions during
higher voltage charge-discharge as a possible loss of the
voltage profile.
5.0
Figure V - 69: Micro-Raman mapping of the pristine
Li1.2Ni0.175Co0.1Mn0.525O2 electrode
Electrochemical benchmarking of Toda’s high
voltage Li-rich MNC composition. We have investigated
the high voltage cycling performance of the excess Li
MNC composition. Figure V - 70 and Figure V - 71 show the
capacity versus the cycle number and the discharge voltage
profiles at successive cycles. The typical compositions of
these electrodes were 85 % active material, 6 % carbon
black, 1.5 % carbon nanofibers (CNF) and 7.5% PVDF.
They were cycled up to 4.9V using standard 1.2M LiPF 6 /
EC-DMC (1:2 w/w). The bare Li 1.2 Ni 0.175 Co 0.1 Mn 0.525 O 2
composition showed a gradual capacity loss when cycled
over 200 cycles (about 3.5 %) at 4.9 V. The CNF was
used to improve the rate performance. (see next section).
Voltage (V) vs. Li/Li +
4.5
4.0
3.5
3.0
2.5
1
5 1
5
50
50
100
100
200 200
0 50 100 150 200 250 300
Capacity (mAhg -1 )
Figure V - 71: Voltage profile at 1 st , 5 th , 50 th , 100 th and 200 th cycles.
Rate Performance. In order to address the issue of
rate performance, we have for the first time reported an
increase of about a factor of two rate capability of the
excess Lithia composition by addition of a nominal
amount of highly graphitic carbon nanofiber, CNF (1.5
wt%). In Figure V - 72 we show the comparison of the
capacity and rate performance up to 100 cycles between
the CNF electrode and the standard electrode composition
Energy Storage R &D 530 FY 2011 Annual Progress Report