Page 390 - Handbook of Battery Materials

12.13 Other Spinel Oxides 361

130
Specific capacity (mAh/g) 110 Bare LiMn 1.42 Ni 0.42 Co Ni 0.16 O Co O
120

100
4
90
Al 2 O 3 coated LiMn 1.42 Ni 0.42 Co 0.16 O 4
ZnO coated LiMn
80
0.42
1.42
4
0.16
Bi O coated LiMn
Co
O
Ni
2
1.42
0.42
0.16
3
70
AlPO 4 coated LiMn 1.42 Ni 0.42 Co 0.16 O 4 4
60
0 10 20 30 40 50
Cycle number
Figure 12.16 Cycling performances of pristine unmodified
(‘bare’) LiMn 1.42 Ni 0.42 Co 0.16 O 4 compared with the same ma-
terial coated with 2 wt% Al 2 O 3 , ZnO, Bi 2 O 3 ,and AlPO 4 .
X-ray photoelectron spectroscopic (XPS) analysis has shown that the surface
modification indeed suppresses the formation of thick SEI layers and thereby
improves the rate capability [89].
12.13
Other Spinel Oxides
Both LiTi 2 O 4 and LiV 2 O 4 crystallize in the normal spinel structure (Li) 8a [M 2 ] 16d O 4
(M = Ti and V) and are metallic as a result of the direct M-M interactions
with a partially filled t 2g band. LiTi 2 O 4 caninsertanadditional lithiuminto
the empty 16c octahedral sites to give the lithiated spinel Li 2 Ti 2 O 4 ,which oc-
curs with a flat discharge profile at a much lower voltage of around 1.5 V
[90]. Accordingly, (Li) 8a [Ti 1.67 Li 0.33 ] 16d O 4 or Li 4 Ti 5 O 12 , which is much easier to
4+
synthesize than LiTi 2 O 4 due to the fully oxidized Ti , has become appeal-
ing as an anode. (Li) 8a [Ti 1.67 Li 0.33 ] 16d O 4 and the corresponding lithiated spinel
(Li 2 ) 16c [Ti 1.67 Li 0.33 ] 16d O 4 differ in unit cell volume by only 0.1%, which is attrac-
tive to maintain good electrode integrity and capacity retention, unlike LiMn 2 O 4 .
−1
However, the higher voltage (1.5 V) and lower capacity (175 mAh g )ofLi 2 Ti 5 O 12
make it uncompetitive compared to the currently available carbon anodes (∼0.1 V
−1
and 372 mAh g ). LiV 2 O 4 also inserts an additional lithium into the 16c sites. The
lithium ions could also be extracted from the 8a tetrahedral sites of LiV 2 O 4 [91].
However, LiV 2 O 4 suffers from vanadium-ion migration during these processes,
which leads to poor capacity retention.
Spinels LiCr 2 O 4 and LiFe 2 O 4 are not known and have not been investigated. Al-
though LiCo 2 O 4 cannot be made by conventional high-temperature methods, it can
be synthesized in the spinel structure by chemically extracting 50% of the lithium
with aqueous acid or NO 2 PF 6 in an acetonitrile medium from the low-temperature