124
6 Nanomaterials for Batteries
At the same time, LiFePO 4 also has some shortcomings. The electronic conductivity and ionic diffusion rate of materials are low, so the material performance
requires higher particle size, and the density of material is relatively low. To overcome
these shortcomings, the modification of LiFePO 4 materials is mainly focused on three
aspects: improving the electronic conductivity, ion diffusion rate, and compaction
density of materials. The main methods are doping and coating, such as common
doping elements Mg (Wang et al. 2004), Nb, Ti, Co (Wang et al. 2005), Zn (Liu et al.
2006), etc., and common coating C (Cui et al. 2014), TiO 2 (Chang et al. 2008) and
conductive polymerization (PPy, PANI).
Layered LiNiCoMnO 2 Cathode Material
Among the cathode materials, LiMn 1/3 Ni 1/3 Co 1/3 O 2 , which are characterized by
high voltage and high capacity, have become the research focus in recent years.
The obvious synergistic effect has been shown in this kind of positive material after
introducing Ni, Co, and Mn. The introduction of Co can effectively suppress the
cation mixing phenomenon of Li
+ and Ni
2+ , stabilize the structure of materials, and
improve the conductivity of materials. However, too high Co concentration leads to
the reduction of Li capacity. The introduction of Ni as an electronic active material can effectively enhance the electrochemical capacity and the current density of
materials. The introduction of Mn can effectively reduce the cost of the materials
and enhance the safety of the materials. LiNi 1/3 Co 1/3 Mn 1/3 O 2 and LiCoO 2 have
the similar structure of alpha-NaFeO 2 , R-3 m space group, trigonal system, O
2−
accounted for a cubic close-packed structure of the lattice, in position 6C. Li
+ and
transition metal ions occupy octahedral voids of the close-packed structure and are
arranged alternately on the (111) surface of cubic packing structure, which is located
at the position of 3a and 3b, respectively. The chemical bonds formed between transition metal ions and O
2− are stronger and are combined with Li
+ in the way of
electrostatic interaction, so that Li
+ can be reversibly embedded and deactivated,
thus forming a two-dimensional lithium-ion diffusion channel.
There are two models for the spatial structure of the transition metal layer of
the LiNi 1/3 Co 1/3 Mn 1/3 O 2 material. Figure A shows the spatial model based on
Wood’s notation theory. Transition metal Ni, Co, Mn are three elements orderly and
regularly arranged in the transition metal layer plane, forming triangular lattices.
Figure B shows another model, “piled-up model”, in which CoO 2 , NiO 2 , and
MnO 2 have a regular accumulation in the transition metal layer. In the layered
LiNi x Co y Mn 1−x−y O 2 cathode materials, the valence of Co is + 3, which is consistent with the electronic structure of Co in the LiCoO 2 material. However, Ni and
Mn valence, respectively, are + 2, + 4 value, which show that the electronic structures were different from that of LiNiO 2 and LiMnO 2 . Take the LiNi 1/3 Co 1/3 Mn 1/3 O 2
material charge and discharge process as an example, the redox reaction of Ni
2+ /Ni
3+
electron pair is mainly in the range of 0 ≤ x ≤ 1
3; in the range of 1
3 ≤ x ≤ 2
3,
mainly Ni
3+ /Ni
4+ electrons occur Redox reaction; Co
3+ /Co
4+ electron pair in the
range of 2
3 ≤ x ≤ 1 redox reaction. The valence of manganese throughout the
charge/discharge process does not change. It is generally believed that Mn
4+ does
6 Nanomaterials for Batteries
At the same time, LiFePO 4 also has some shortcomings. The electronic conductivity and ionic diffusion rate of materials are low, so the material performance
requires higher particle size, and the density of material is relatively low. To overcome
these shortcomings, the modification of LiFePO 4 materials is mainly focused on three
aspects: improving the electronic conductivity, ion diffusion rate, and compaction
density of materials. The main methods are doping and coating, such as common
doping elements Mg (Wang et al. 2004), Nb, Ti, Co (Wang et al. 2005), Zn (Liu et al.
2006), etc., and common coating C (Cui et al. 2014), TiO 2 (Chang et al. 2008) and
conductive polymerization (PPy, PANI).
Layered LiNiCoMnO 2 Cathode Material
Among the cathode materials, LiMn 1/3 Ni 1/3 Co 1/3 O 2 , which are characterized by
high voltage and high capacity, have become the research focus in recent years.
The obvious synergistic effect has been shown in this kind of positive material after
introducing Ni, Co, and Mn. The introduction of Co can effectively suppress the
cation mixing phenomenon of Li
+ and Ni
2+ , stabilize the structure of materials, and
improve the conductivity of materials. However, too high Co concentration leads to
the reduction of Li capacity. The introduction of Ni as an electronic active material can effectively enhance the electrochemical capacity and the current density of
materials. The introduction of Mn can effectively reduce the cost of the materials
and enhance the safety of the materials. LiNi 1/3 Co 1/3 Mn 1/3 O 2 and LiCoO 2 have
the similar structure of alpha-NaFeO 2 , R-3 m space group, trigonal system, O
2−
accounted for a cubic close-packed structure of the lattice, in position 6C. Li
+ and
transition metal ions occupy octahedral voids of the close-packed structure and are
arranged alternately on the (111) surface of cubic packing structure, which is located
at the position of 3a and 3b, respectively. The chemical bonds formed between transition metal ions and O
2− are stronger and are combined with Li
+ in the way of
electrostatic interaction, so that Li
+ can be reversibly embedded and deactivated,
thus forming a two-dimensional lithium-ion diffusion channel.
There are two models for the spatial structure of the transition metal layer of
the LiNi 1/3 Co 1/3 Mn 1/3 O 2 material. Figure A shows the spatial model based on
Wood’s notation theory. Transition metal Ni, Co, Mn are three elements orderly and
regularly arranged in the transition metal layer plane, forming triangular lattices.
Figure B shows another model, “piled-up model”, in which CoO 2 , NiO 2 , and
MnO 2 have a regular accumulation in the transition metal layer. In the layered
LiNi x Co y Mn 1−x−y O 2 cathode materials, the valence of Co is + 3, which is consistent with the electronic structure of Co in the LiCoO 2 material. However, Ni and
Mn valence, respectively, are + 2, + 4 value, which show that the electronic structures were different from that of LiNiO 2 and LiMnO 2 . Take the LiNi 1/3 Co 1/3 Mn 1/3 O 2
material charge and discharge process as an example, the redox reaction of Ni
2+ /Ni
3+
electron pair is mainly in the range of 0 ≤ x ≤ 1
3; in the range of 1
3 ≤ x ≤ 2
3,
mainly Ni
3+ /Ni
4+ electrons occur Redox reaction; Co
3+ /Co
4+ electron pair in the
range of 2
3 ≤ x ≤ 1 redox reaction. The valence of manganese throughout the
charge/discharge process does not change. It is generally believed that Mn
4+ does