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

Battaglia – LBNL
V.E.1 Electrode Fabrication and Failure Analysis (LBNL)
analysis. Theories of energy or power fade are shared with
Diagnostocs and Modeling teams and follow-on
experiments are designed. Materials with purported
advancements are also examined rigorously and
correlations of physical properties with performance are
sought. Results are shared with the suppliers.
Results
Side reactions of full-cells versus half-cells. During
the first quarter, we investigated the rate of side reactions
in full-cells versus half-cells. Through careful cell design
and analysis of the charge and discharge curves, one can
measure the rate of side reactions occuring in both
electrodes of a cell, although not the rate on lithium. The
process is more expeditious for full cells through the
introduction of a reference electrode, and meaningful if the
introduction does not contribute to cell leakage. Figure V -
180 shows the fraction of integrated current that goes
toward the side reaction for NCM (from ANL) when tested
against Li, for graphite (Conoco Phillips) when tested
against Li, and for graphite when tested against NCM.
Fractional Capacity Shift
18%
16%
14%
12%
10%
NCM(p98)-Li
CPG8(Honghe)-Li
CPG8(p113)-Li-1
CPG8(p113)-Li-2
L3-CPG8-4 (NCM limited)
L3-CPG8-12 (NCM limited)
8%
6%
4%
2%
0%
-2%
0 5
10
15 20 25 30
cycle
Figure V - 180: Fraction of capacity shift per cycle as a result of side reactions.
One sees that the side reaction on graphite when Li is
the counter electrode is about three times less than when
NCM is the counter electrode. We also see that the rate of
the side reaction on NCM is the same whether graphite or
Li is the ecountre electrode. This suggests that the side
reaction is a result of a “natural” shuttle in the cell that is
formed from the products of either the electrolyte
oxidation or reduction. It also suggests that the coulombic
efficiency is not a good indicator of cell life if the side
reactions are mostly benign.
Characterizing LiNi 1/2 Mn 3/2 O 4 . Through ABR
Program resources, a high-voltage spinel material was
identified. From there, we wanted to investigate its
cycleability. Through half cell experiments it was
determined that this material will not cycle well when the
upper cut-off voltage exceeds 4.88 V at C/10. However,
when cycling such a cell with a Li counter electrode,
instabilities appear as reflected in the voltage curve, see
Figure V - 181.
While cycling full cells with a graphite anode, it was
discovered that these voltage instabilities stopped and that
the upper-cutoff voltage is no longer 4.88 V but 5.3 V.
The present inductive reasoning is that the istabilites
found in half cells are a result of oxidation products that
are either gases or form gases upon migration to the
lithium counter electrode. We intend to follow up on this
speculation with some experiments that might capture any
gases that are being formed.
FY 2011 Annual Progress Report 629 Energy Storage R&D