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

Chen – LBNL
V.B.11 Crystal Studies on High-energy Density Cathodes (LBNL)
crystals were prepared by the molten salt method, with the
ratio between the Mn and Ni precursors carefully
controlled to achieve the targeted stoichiometry. The
crystals adapted the same octahedron shape and had a
similar size of 2 m. XRD patterns and lattice dimensions
are compared in Figure V - 62a. The ionic radii of octahedralcoordinated
Ni 2+ , Mn 3+ and Mn 4+ are 0.83, 0.785 and 0.67,
respectively. Decreasing Ni 2+ content increases
Mn 3+ /Mn 4+ ratio and therefore leads to a slight expansion
in the cubic lattice, as shown in Figure V - 62b.
Figure V - 63a compares the FTIR spectra of the crystal
samples. Bands at 620 and 560 cm -1 are attributed to Mn-
O vibrations while the band at 590 to that of Ni-O. The
replacement of Ni 2+ by the smaller-sized Mn 3+ leads to
stronger Ni-O bonds and therefore a blue shift of the 590
peak at lower Ni content. The peak ratio of 590/620
increased nearly linearly with Ni content (Figure V - 63b),
suggesting that it may be used as a measure for the Mn 3+
content within this range. Peaks at 430, 560 and 650 are
clearly present when Ni content is above 0.40,
characteristic of an ordered crystal structure. Significant
changes occurred on the spectrum when x decreased to
0.35, suggesting loss of the ordering in samples.
dQ/dV
dQ/dV
dQ/dV
1000
750
500
250
0
-250
-500
-750
a
4.64V
4.78V
4.70V
-1000
3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0
Voltage (V)
1500
1000
500
0
b
4.74V
4.795V
-500
-1000
1 st cycle 4.69V
2 nd cycle
4.73V
-1500
3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0
Voltage (V)
5000
4000
3000
c
4.745V
2000
4.72V
1000
0
-1000
-2000 1 st cycle 4.685V
4.71V
2 nd cycle
-3000
-4000
3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0
Voltage (V)
Voltage (V) Voltag ltage (V) Voltage (V)
5.2
4.8
4.4
4.0
3.6
3.2 0.8C
C/22
2.8
1.3C
C/2 C/5 C/11
0 20 40 60 80 100 120 140 160
Capacity (mAh/g)
5.2
4.8
4.4
4.0
3.6
3.2
C/22
1.3C
0.8C
C/2
C/5
C/11
2.8
0 20 40 60 80 100 120 140 160
Specific capacity (mAh/g)
5.2
4.8
4.4
4.0
3.6
C/22
3.2
1.3C
C/11
0.8C
2.8
0 20 40 60 80 100 120 140 160
Specific capacity (mAh/g)
Figure V - 61: Rate capability comparison of LiNi0.5Mn1.5O4 crystals. Results obtained from half-cell testing with Li foil as counter and reference electrodes, and
1M LiPF6 in 1:1 ethylene carbonate: diethylene carbonate as electrolyte.
FY 2011 Annual Progress Report 521 Energy Storage R&D