Method for making a composite electrode material
View Patent ↗A composite material includes a first phase which comprises Li x M y (PO 4 ) z wherein M is at least one metal, y and z are independently 0, and x is less than or equal to 1. The material includes a second phase which has an electronic and/or lithium ion conductivity greater than that of the first phase. The material is prepared by heating a starting mixture which includes lithium, iron, a phosphate ion, and a catalyst in a reducing atmosphere. Also disclosed are electrodes which incorporate the material and batteries which utilize those electrodes as cathodes.
1. A method for synthesizing a composite material, said method comprising the steps of:
providing a starting mixture which includes lithium, at least one metal M, a phosphate ion, and a catalyst comprising vanadium, which promotes the formation of a phase which enhances electron and/or lithium ion transport;
heating said mixture in a reducing environment so as to produce a composite material which includes a first phase which comprises Li x M y (PO 4 ) z wherein M is said at least one metal, y and z are independently greater than 0, and x is less than or equal to 1; and a second phase which has an electronic and/or lithium ion transport greater than that of the first phase.
2. The method of claim 1 , wherein x is greater than 0.
3. The method of claim 1 , wherein said catalyst promotes the reduction of the phosphate ion.
4. The method of claim 1 , wherein said second phase includes M and phosphorus.
5. The method of claim 4 , wherein said second phase further includes oxygen, and the atomic ratio of oxygen to phosphorus is less than 4:1.
6. The method of claim 1 , wherein said at least one metal M includes iron.
7. The method of claim 6 , wherein said second phase comprises a member selected from the group consisting of: Fe 2 P 2 O 7 ; FeP; Fe 2 P; Fe 3 P and combinations thereof.
8. The method of claim 1 , wherein said first phase comprises 80-95 mole percent of said composite material and said second phase comprises 5-20 mole percent of said composite material.
9. The method of claim 1 , wherein said vanadium is introduced in the starting mixture in the form of V 2 O 5 .
10. The method of claim 1 , wherein said catalyst promotes the reduction of a carbon-containing species, so as to generate free carbon.
11. The method of claim 10 , wherein said carbon is at least partially sp 2 bonded, and the ratio of sp 2 to sp 3 bonded carbon generated in the presence of said catalyst is greater than it would be in the absence of said catalyst.
12. The method of claim 1 , wherein said reducing environment comprises a gaseous environment which includes one or more of hydrogen, carbon monoxide and ammonia.
13. The method of claim 6 , wherein the iron in said starting mixture is in the form of an Fe +3 ion.
14. The method of claim 1 , including the further step of grinding said mixture prior to heating said mixture in the reducing environment.
15. The method of claim 14 , wherein the step of grinding said mixture comprises grinding said mixture in a ball mill.
16. The method of claim 1 , wherein the step of heating said mixture comprises heating said mixture to a temperature in the range of 300-600° C.
17. The method of claim 1 , wherein the catalyst is a nucleating agent which promotes the growth of the second phase.
18. The method of claim 1 , wherein said starting mixture includes a source of carbon.
19. The method of claim 18 , wherein said source of carbon is an organic compound.