122
6 Nanomaterials for Batteries
The common synthetic methods of LiNiO 2 are solid phase method and liquid
phase method (Song and Lee 2002). The solid phase method usually combines
lithium compounds (such as LiOH, LiNO 3 ) with nickel compounds (such as Ni(OH) 2 ,
Ni(NO 3 ) 2 ) and then roasted at high temperature in oxidizing atmosphere, then cooled
and ground to obtain layered LiNiO 2 . Because nickel is difficult to oxidize to + 3
values, it must be carried out at higher temperature. However, too high temperature
is easy to generate lithium deficient LiNiO 2 , so it is difficult to batch produce ideal
LiNiO 2 layered structure. Usually, in the process of synthesis, we should reduce
the synthetic temperature as far as possible and use oxygen atmosphere or lithium
excess to stabilize Ni
3+ , reduce lithium volatilization and inhibit lithium deficiency.
Besides, the electrochemical properties of LiNiO 2 can be enhanced by doping other
elements such as Mg (Muto et al. 2012), Al (Chen et al. 2004), Co (Cai et al. 2001),
Ti and so on.
Spinel Structure (LiMn 2 O 4 ) Cathode Material
LiMn 2 O 4 material was first reported by Thackeray research group (Thackeray et al.
1983). The price of manganese is cheaper than cobalt and nickel, and manganese
has the advantages of innocuity, less pollution, and easy recycling. Therefore, the
LiMn 2 O 4 cathode material of the spinel structure has aroused wide attention and
research. The LiMn 2 O 4 positive material has a tetragonal symmetry Fd-3 m structure.
In one cell, there are 8 lithium atoms, 16 manganese atoms, and 32 oxygen atoms, of
which Mn
3+ and Mn
4+ account for half each. The lithium ion is in the 8A position of
the tetrahedron, and the manganese ion is in the 16d position of the eight-surface body,
and the oxygen ion is in the 32e position of the eight-surface body. The tetrahedral
8a, 48F and eight-hedral 16d coplane form a three-dimensional ion channel for
interworking, which is convenient for lithium ion to release and embed (Jow 2002)
freely in the channel. In addition, there is enough Mn
3+ spinel LiMn 2 O 4 cathode
material space structure, even in the delithiated state, and still can maintain the
stability of the cubic close-packed oxygen distribution, to ensure the smooth slippage
and embedded Li
+ , so the materials have high capacity and voltage platform. The
theoretical specific capacity of LiMn 2 O 4 is 148 mAh g
−1 , In the meantime, the actual
specific capacity can reach 120 mAh g
−1 .
LiMn 2 O 4 is usually prepared by a high temperature solid state reaction technique. Calcination lithium hydroxide and manganese oxide mixture can obtain spinel
LiMn 2 O 4 under 700 °C. However, the synthetic method has some shortcomings, such
as heterogeneous phase, large synthetic particle, wide range of particle size distribution, and long calcination time. The biggest drawback of spinel LiMn 2 O 4 is the
capacity attenuation, especially the high temperature capacity decay. The reason is
derived from the change of spinel structure, the main reason can be summarized as
follows.
1. manganese will dissolve in the electrolyte at high temperature
2. the Jahn–Teller effect and the formation of the passivation layer
3. high oxidation of manganese
4. the electrolyte is decomposed at high potential, destroying the spinel structure.
6 Nanomaterials for Batteries
The common synthetic methods of LiNiO 2 are solid phase method and liquid
phase method (Song and Lee 2002). The solid phase method usually combines
lithium compounds (such as LiOH, LiNO 3 ) with nickel compounds (such as Ni(OH) 2 ,
Ni(NO 3 ) 2 ) and then roasted at high temperature in oxidizing atmosphere, then cooled
and ground to obtain layered LiNiO 2 . Because nickel is difficult to oxidize to + 3
values, it must be carried out at higher temperature. However, too high temperature
is easy to generate lithium deficient LiNiO 2 , so it is difficult to batch produce ideal
LiNiO 2 layered structure. Usually, in the process of synthesis, we should reduce
the synthetic temperature as far as possible and use oxygen atmosphere or lithium
excess to stabilize Ni
3+ , reduce lithium volatilization and inhibit lithium deficiency.
Besides, the electrochemical properties of LiNiO 2 can be enhanced by doping other
elements such as Mg (Muto et al. 2012), Al (Chen et al. 2004), Co (Cai et al. 2001),
Ti and so on.
Spinel Structure (LiMn 2 O 4 ) Cathode Material
LiMn 2 O 4 material was first reported by Thackeray research group (Thackeray et al.
1983). The price of manganese is cheaper than cobalt and nickel, and manganese
has the advantages of innocuity, less pollution, and easy recycling. Therefore, the
LiMn 2 O 4 cathode material of the spinel structure has aroused wide attention and
research. The LiMn 2 O 4 positive material has a tetragonal symmetry Fd-3 m structure.
In one cell, there are 8 lithium atoms, 16 manganese atoms, and 32 oxygen atoms, of
which Mn
3+ and Mn
4+ account for half each. The lithium ion is in the 8A position of
the tetrahedron, and the manganese ion is in the 16d position of the eight-surface body,
and the oxygen ion is in the 32e position of the eight-surface body. The tetrahedral
8a, 48F and eight-hedral 16d coplane form a three-dimensional ion channel for
interworking, which is convenient for lithium ion to release and embed (Jow 2002)
freely in the channel. In addition, there is enough Mn
3+ spinel LiMn 2 O 4 cathode
material space structure, even in the delithiated state, and still can maintain the
stability of the cubic close-packed oxygen distribution, to ensure the smooth slippage
and embedded Li
+ , so the materials have high capacity and voltage platform. The
theoretical specific capacity of LiMn 2 O 4 is 148 mAh g
−1 , In the meantime, the actual
specific capacity can reach 120 mAh g
−1 .
LiMn 2 O 4 is usually prepared by a high temperature solid state reaction technique. Calcination lithium hydroxide and manganese oxide mixture can obtain spinel
LiMn 2 O 4 under 700 °C. However, the synthetic method has some shortcomings, such
as heterogeneous phase, large synthetic particle, wide range of particle size distribution, and long calcination time. The biggest drawback of spinel LiMn 2 O 4 is the
capacity attenuation, especially the high temperature capacity decay. The reason is
derived from the change of spinel structure, the main reason can be summarized as
follows.
1. manganese will dissolve in the electrolyte at high temperature
2. the Jahn–Teller effect and the formation of the passivation layer
3. high oxidation of manganese
4. the electrolyte is decomposed at high potential, destroying the spinel structure.