Pyrophosphate compound and production process thereof
To provide a positive electrode active material containing a pyrophosphate compound, ensuring that mixing of impurities is easily prevented to facilitate the synthesis and a high capacity battery is obtained, and a lithium ion battery using the positive electrode material. That is, the present invention relates to a pyrophosphate compound represented by the formula: Li 2 M 1-x Fe x P 2 O 7 (wherein M represents one or more elements selected from Mn, Zr, Mg, Co, Ni, V and Cu, and 0.3≦x≦0.9).
1. A pyrophosphate compound represented by the formula:
Li 2 M 1-x Fe x P 2 O 7
(wherein M represents one or more elements selected from Mn, Zr, Mg, Co, Ni, V and Cu, and 0.3≦x≦0.9).
2. The pyrophosphate compound as claimed in claim 1 , wherein x is 0.7≦x≦0.9.
3. The pyrophosphate compound as claimed in claim 1 , wherein M is Mn.
4. The pyrophosphate compound as claimed in claim 1 , having a low-temperature phase crystal structure or a high-temperature phase crystal structure.
5. A production process for a pyrophosphate compound, comprising mixing starting materials of the pyrophosphate compound claimed in claim 1 , and firing the obtained raw material mixture at a temperature of 350 to 900° C.
6. The production process for a pyrophosphate compound as claimed in claim 5 , wherein firing is performed at a temperature of 400 to 700° C.
7. A positive electrode active material containing the pyrophosphate compound claimed in claim 1 .
8. A lithium ion battery using a positive electrode containing the positive electrode active material claimed in claim 7 .