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

Nanda – ORNL
V.B.13 Studies on the Local SOC and Underlying Structures in Lithium Battery Electrodes (ORNL)
mentioned above. Figure V - 72a shows the improvement in
the cycle life performance between the two. As shown in
Figure V - 72b the rate performance improved a factor of two
due to an overall increase of the electronic conductivity of
the matrix due to addition of highly conducting CNF.
Notably, after the 5C rate discharge going back to the C/5
rate; we continue to see good capacity retention for the
CNF electrode whereas the standard composition showed
decay with cycling. This shows that CNF additives serves
as an electronic wiring around the Li-rich MNC particles
improving the electronic conduction pathways to improve
both rate performance and capacity retention.
obtained as a result of activation of Li 2 MnO 3 ( > 4.5 V) is
illustrated by the large peak. This feature understandably
disappears after the first cycle charging cycle, after the
formation of MnO 2 . The inset figure shows the CV cycles
at a lower scan rate (25 mV S -1 ) showing explicit
contribution of Mn, Ni and Co to the overall capacity. We
have also undertaken surface studies using X-ray
photoelectron spectroscopy and Micro-Raman to identify
various surface decomposition products during the high
voltage cycling (results not shown here).
(a)
(b)
Figure V - 72: (a) Cycle life comparison between standard binder carbon
black composition and with CNF addition and (b) the corresponding rate
performance comparison.
Cyclic Voltammetry and Surface Studies. One of
the key aspects here is to understand the origin of the first
cycle irreversible capacity loss of the Li rich composition
Li 1.2 Ni 0.175 Co 0.1 Mn 0.525 O 2 and to identify the
electrochemical redox processes during the high voltage
cycling. To this effect, we carried out detailed cyclic
voltammetry (CV) studies at various scan rates. . Figure V - 73
shows the first cycle anodic and cathodic peaks
corresponding to Mn, Ni and Co red-ox transitions (shown
as red dashed line). The second through fifth CV curves
are shown as solid lines. The first cycle excess capacity
Figure V - 73: CV studies on Li1.2Ni0.175Co0.1Mn0.525O2 . first cycle anodic
and cathodic peaks shown as red dashed line, the second through fifth CV
curves are shown as solid lines.
Conclusions and Future Directions
We are undertaking detailed high resolution electronmicroscopy
at various SOCs of the Li-rich MNC
composition to correlate the structural changes as the
voltage profile changes from a layered-layered phase to a
mixed layered-spinel type structure (low voltage).
Experiments are also in progress to coat the Li-rich MNC
with a nanometer thick solid electrolyte, LIPON, to reduce
or minimize the side reaction at the surface due to high
voltage cycling. We notice a dramatic enhancement of the
electrchemcial performance. Full cell studies using Li-rich
and carbon as positive and negative electrode material are
in progress.
FY 2011 Publications/Presentations
Journal Publications
1. J. Nanda, J. T. Remillard, A. O’Neill, D. Bernardi,
Tina Ro, Ken Nietering, Ted J. Miller, “Observation
of Local State of Charge Distributions in Lithium-ion
Battery Electrodes”, Adv. Funct. Mater. 2011, 21,
3282–32900.
FY 2011 Annual Progress Report 531 Energy Storage R&D