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6 Nanomaterials for Batteries
The alloying mechanism of TCO is like the mechanism of tin oxide alloy. It is
also the mechanism of the two-step reaction. First, TOC and Li react to form Li 2 O,
other oxides and tin, then tin react with Li to form lithium tin alloy. Taking Sn 2 BPO 6
as an example, its mechanism can be expressed as:
4Li + Sn 2 BO 6 → 2Li 2 O + 2Sn + 1
2B 2 O 3 + 1
2P 2 O 5
8.8Li + 2Li 2 O + 2Sn + 1
2B 2 O 3 + 1
2P 2 O 5 2Li 4.4 Sn + 2Li 2 O
+ 1
2B 2 O 3 + 1
2P 2 O 5
The amorphous structure of tin-based composite oxides has little change in volume
before and after charging and discharging. The structure is stable, and it is not easy to
be destroyed. So, the cycle performance of tin-based composite oxides is relatively
good. Moreover, compared with the oxide of crystalline Sn, the structure of the tinbased compound oxide is beneficial to insertion and removal of lithium, and the
increase of the diffusion coefficient of lithium.
Silicon-Based Materials
Silicon (Si)-based materials have been widely studied as the anode materials for
Li-ion batteries (LIB) due to its excellent discharge/charge capacities. However, the
anode materials have a large volume change in the cycle process, causing pulverization of Si, loss of the electric contact, as well as plenty of side reactions. These
disadvantages cause the poor long cycling life and slow the extensive commercial
applications of Si for LIBs. The lithiation/delithiation reaction and interphase reaction mechanism are gradually studied. First, Si maintains a discharge/charge capacity
of about 4200 mAh g
−1 during full lithiation progress. Second, Si anode material
has a considerably low discharge voltage (about 0.4 V vs. Li
+ /Li), which causes the
formation of a high working potential and the current density in the LIBs. Third,
there are some advantages of Si, such as abundant Si element, low cost, good environmentally friendly, excellent chemical stability. Therefore, Si can be considered
as a promising candidate material.
A battery of Si–Li phases consist in the courses of thermal alloying of Si and
Li such as LiSi material, Li 12 Si 7 material, Li 13 Si 4 material, and Li 22 Si 5 material.
For the crystalline phase, it has more stable dynamics than the amorphous phase
owes to the poor formation energy. However, the crystalline phase is not necessarily
beneficial during the lithiation of Si progress. Liu et al. reported an atomic model
of the crystalline Si lithiation. The result vividly confirmed the peeling process of
Li-ions on Si (111) atomic plane. The formation of Li x Si can be investigated by
the in situ transmission electron microscopy (TEM), the Si nanowires (SiNWs) (the
diameter of 130 nm), and the growth direction of (111) plane is used in lithiation
process. The amorphous Li x Si shells are first developed during lithiation progress.
The gradual migration of amorphous and crystalline interface is exhibited in Fig. 6.3.
Meanwhile, the thickness of amorphous and crystalline interface has only ≈1 nm.
6 Nanomaterials for Batteries
The alloying mechanism of TCO is like the mechanism of tin oxide alloy. It is
also the mechanism of the two-step reaction. First, TOC and Li react to form Li 2 O,
other oxides and tin, then tin react with Li to form lithium tin alloy. Taking Sn 2 BPO 6
as an example, its mechanism can be expressed as:
4Li + Sn 2 BO 6 → 2Li 2 O + 2Sn + 1
2B 2 O 3 + 1
2P 2 O 5
8.8Li + 2Li 2 O + 2Sn + 1
2B 2 O 3 + 1
2P 2 O 5 2Li 4.4 Sn + 2Li 2 O
+ 1
2B 2 O 3 + 1
2P 2 O 5
The amorphous structure of tin-based composite oxides has little change in volume
before and after charging and discharging. The structure is stable, and it is not easy to
be destroyed. So, the cycle performance of tin-based composite oxides is relatively
good. Moreover, compared with the oxide of crystalline Sn, the structure of the tinbased compound oxide is beneficial to insertion and removal of lithium, and the
increase of the diffusion coefficient of lithium.
Silicon-Based Materials
Silicon (Si)-based materials have been widely studied as the anode materials for
Li-ion batteries (LIB) due to its excellent discharge/charge capacities. However, the
anode materials have a large volume change in the cycle process, causing pulverization of Si, loss of the electric contact, as well as plenty of side reactions. These
disadvantages cause the poor long cycling life and slow the extensive commercial
applications of Si for LIBs. The lithiation/delithiation reaction and interphase reaction mechanism are gradually studied. First, Si maintains a discharge/charge capacity
of about 4200 mAh g
−1 during full lithiation progress. Second, Si anode material
has a considerably low discharge voltage (about 0.4 V vs. Li
+ /Li), which causes the
formation of a high working potential and the current density in the LIBs. Third,
there are some advantages of Si, such as abundant Si element, low cost, good environmentally friendly, excellent chemical stability. Therefore, Si can be considered
as a promising candidate material.
A battery of Si–Li phases consist in the courses of thermal alloying of Si and
Li such as LiSi material, Li 12 Si 7 material, Li 13 Si 4 material, and Li 22 Si 5 material.
For the crystalline phase, it has more stable dynamics than the amorphous phase
owes to the poor formation energy. However, the crystalline phase is not necessarily
beneficial during the lithiation of Si progress. Liu et al. reported an atomic model
of the crystalline Si lithiation. The result vividly confirmed the peeling process of
Li-ions on Si (111) atomic plane. The formation of Li x Si can be investigated by
the in situ transmission electron microscopy (TEM), the Si nanowires (SiNWs) (the
diameter of 130 nm), and the growth direction of (111) plane is used in lithiation
process. The amorphous Li x Si shells are first developed during lithiation progress.
The gradual migration of amorphous and crystalline interface is exhibited in Fig. 6.3.
Meanwhile, the thickness of amorphous and crystalline interface has only ≈1 nm.