126
6 Nanomaterials for Batteries
the graph, we can see that the potential between 3.0 and 4.8 V, vanadium lithium
phosphate has four charging platforms, and the plateau potential is 3.6, 3.7, 4.1, and
4.6 V, respectively. The corresponding phase transition reactions are Li 3 V 2 (PO 4 ) 3 →
Li 2.5 V 2 (PO 4 ) 3 → Li 2 V 2 (PO 4 ) 3 → LiV 2 (PO 4 ) 3 → V 2 (PO 4 ) 3 .
Among them, the first lithium ion removal is divided into two steps, corresponding
to the 3.6 and 3.7 V potential platforms. When three lithium ions are removed from
the lithium phosphate, the volume of the lithium phosphate is reduced by ~7.8%
and V 2 (PO 4 ) 3 is generated. In V 2 (PO 4 ) 3 , V (1) and V (2) have the same bond
energy, bond distance and oxidation state (+4.5) resulting in the lithium ion disorderly
embedded V 2 (PO 4 ) 3 during the discharge process, which leads to a similar solid
dissolve discharge effect, making the discharge curve appear S type. When two
lithium ions are embedded, i.e., Li 2 V 2 (PO 4 ) 3 is generated, the ordered state of lithium
vanadium phosphate is restored, and the discharge behavior changes to a phase
change transition corresponding to the discharge platform of 3.6 V and 3.7 V in the
discharge curve. Specific chemical reaction is as follows:
Charging process: Li 3 V 2 (PO 4 ) 3 − 0.5Li
+
− 0.5e
−
→ Li 2.5 V 2 (PO 4 ) 3 (3.6 V)
Li 2.5 V 2 (PO 4 ) 3 − 0.5Li
+
− 0.5e
−
→ Li 2 V 2 (PO 4 ) 3 (3.7 V)
Li 2 V 2 (PO 4 ) 3 − Li
+
− e
−
→ LiV 2 (PO 4 ) 3 (4.1 V)
LiV 2 (PO 4 ) 3 − Li
+
− e
−
→ V 2 (PO 4 ) 3 (4.6 V)
Discharge process: V 2 (PO 4 ) 3 + 2Li
+
+ 2e
−
→ Li 2 V 2 (PO 4 ) 3 (3.9 − 4.5 V )
Li 2 V 2 (PO 4 ) 3 + 0.5Li
+
+ 0.5e
−
→ Li 2.5 V 2 (PO 4 ) 3 (3.7 V)
Li 2.5 V 2 (PO 4 ) 3 + 0.5Li
+
+ 0.5e
−
→ Li 3 V 2 (PO 4 ) 3 (3.6 V)
When the charge–discharge potential range is in the range of 3.0–4.3 V (Zhai et al.
2010), no solid solution phenomenon occurs in the lithium vanadium phosphate, and
the charge–discharge curve shows three pairs of charge–discharge platforms at 3.6,
3.7 and 4.1 V. The corresponding charge and discharge reactions are
Charging process: Li 3 V 2 (PO 4 ) 3 − 0.5Li
+
− 0.5e
−
→ Li 2.5 V 2 (PO 4 ) 3 (3.6 V)
Li 2.5 V 2 (PO 4 ) 3 − 0.5Li
+
− 0.5e
−
→ Li 2 V 2 (PO 4 ) 3 (3.7 V)
Li 2 V 2 (PO 4 ) 3 − Li
+
− e
−
→ LiV 2 (PO 4 ) 3 (4.1 V)
Discharge process : LiV 2 (PO 4 ) 3 + Li
+
+ e
−
→ Li 2 V 2 (PO 4 ) 3 (4.1 V)
Li 2 V 2 (PO 4 ) 3 + 0.5Li
+
+ 0.5e
−
→ Li 2.5 V 2 (PO 4 ) 3 (3.7 V)
Li 2.5 V 2 (PO 4 ) 3 + 0.5Li
+
+ 0.5e
−
→ Li 3 V 2 (PO 4 ) 3 (3.6 V)
Although lithium vanadium phosphate in the range of 3.0–4.3 V only reversibly
deintercalates two ions, it has no V 2 (PO 4 ) 3 phase formation with poor kinetic
properties, so its cycle stability and electrochemical performance are good.
6 Nanomaterials for Batteries
the graph, we can see that the potential between 3.0 and 4.8 V, vanadium lithium
phosphate has four charging platforms, and the plateau potential is 3.6, 3.7, 4.1, and
4.6 V, respectively. The corresponding phase transition reactions are Li 3 V 2 (PO 4 ) 3 →
Li 2.5 V 2 (PO 4 ) 3 → Li 2 V 2 (PO 4 ) 3 → LiV 2 (PO 4 ) 3 → V 2 (PO 4 ) 3 .
Among them, the first lithium ion removal is divided into two steps, corresponding
to the 3.6 and 3.7 V potential platforms. When three lithium ions are removed from
the lithium phosphate, the volume of the lithium phosphate is reduced by ~7.8%
and V 2 (PO 4 ) 3 is generated. In V 2 (PO 4 ) 3 , V (1) and V (2) have the same bond
energy, bond distance and oxidation state (+4.5) resulting in the lithium ion disorderly
embedded V 2 (PO 4 ) 3 during the discharge process, which leads to a similar solid
dissolve discharge effect, making the discharge curve appear S type. When two
lithium ions are embedded, i.e., Li 2 V 2 (PO 4 ) 3 is generated, the ordered state of lithium
vanadium phosphate is restored, and the discharge behavior changes to a phase
change transition corresponding to the discharge platform of 3.6 V and 3.7 V in the
discharge curve. Specific chemical reaction is as follows:
Charging process: Li 3 V 2 (PO 4 ) 3 − 0.5Li
+
− 0.5e
−
→ Li 2.5 V 2 (PO 4 ) 3 (3.6 V)
Li 2.5 V 2 (PO 4 ) 3 − 0.5Li
+
− 0.5e
−
→ Li 2 V 2 (PO 4 ) 3 (3.7 V)
Li 2 V 2 (PO 4 ) 3 − Li
+
− e
−
→ LiV 2 (PO 4 ) 3 (4.1 V)
LiV 2 (PO 4 ) 3 − Li
+
− e
−
→ V 2 (PO 4 ) 3 (4.6 V)
Discharge process: V 2 (PO 4 ) 3 + 2Li
+
+ 2e
−
→ Li 2 V 2 (PO 4 ) 3 (3.9 − 4.5 V )
Li 2 V 2 (PO 4 ) 3 + 0.5Li
+
+ 0.5e
−
→ Li 2.5 V 2 (PO 4 ) 3 (3.7 V)
Li 2.5 V 2 (PO 4 ) 3 + 0.5Li
+
+ 0.5e
−
→ Li 3 V 2 (PO 4 ) 3 (3.6 V)
When the charge–discharge potential range is in the range of 3.0–4.3 V (Zhai et al.
2010), no solid solution phenomenon occurs in the lithium vanadium phosphate, and
the charge–discharge curve shows three pairs of charge–discharge platforms at 3.6,
3.7 and 4.1 V. The corresponding charge and discharge reactions are
Charging process: Li 3 V 2 (PO 4 ) 3 − 0.5Li
+
− 0.5e
−
→ Li 2.5 V 2 (PO 4 ) 3 (3.6 V)
Li 2.5 V 2 (PO 4 ) 3 − 0.5Li
+
− 0.5e
−
→ Li 2 V 2 (PO 4 ) 3 (3.7 V)
Li 2 V 2 (PO 4 ) 3 − Li
+
− e
−
→ LiV 2 (PO 4 ) 3 (4.1 V)
Discharge process : LiV 2 (PO 4 ) 3 + Li
+
+ e
−
→ Li 2 V 2 (PO 4 ) 3 (4.1 V)
Li 2 V 2 (PO 4 ) 3 + 0.5Li
+
+ 0.5e
−
→ Li 2.5 V 2 (PO 4 ) 3 (3.7 V)
Li 2.5 V 2 (PO 4 ) 3 + 0.5Li
+
+ 0.5e
−
→ Li 3 V 2 (PO 4 ) 3 (3.6 V)
Although lithium vanadium phosphate in the range of 3.0–4.3 V only reversibly
deintercalates two ions, it has no V 2 (PO 4 ) 3 phase formation with poor kinetic
properties, so its cycle stability and electrochemical performance are good.