Method of forming a solid state cathode for high energy density secondary batteries
A method for making a solid state cathode comprises the following steps: forming an alkali free first solution comprising at least one transition metal and at least two ligands; spraying this solution onto a substrate that is heated to about 100 to 400° C. to form a first solid film containing the transition metal(s) on the substrate; forming a second solution comprising at least one alkali metal, at least one transition metal, and at least two ligands; spraying the second solution onto the first solid film on the substrate that is heated to about 100 to 400° C. to form a second solid film containing the alkali metal and at least one transition metal; and, heating to about 300 to 1000° C. in a selected atmosphere to react the first and second films to form a homogeneous cathode film. The cathode may be incorporated into a lithium or sodium ion battery.
1. A method of forming a solid state cathode comprising the steps of:
a) forming a generally planar substrate;
b) forming a substantially alkali-free first solution comprising at least one transition metal and at least two ligands;
c) spraying said first solution onto said substrate while maintaining said substrate at a temperature between about 100 and 400° C. to form a first solid film containing said transition metal on said substrate;
d) forming a second solution comprising at least one alkali metal, at least one transition metal, and at least two ligands;
e) spraying said second solution onto said first solid film on said substrate while maintaining said substrate at a temperature between about 100 and 400° C. to form a second solid film containing said alkali metal and at least one transition metal; and,
f) heating to a temperature between about 300 and 1000° C. in a selected atmosphere to react said first and second films to form a homogeneous cathode film.
2. The method of claim 1 wherein said first solution comprises:
at least one transition metal selected from the group consisting of: Mn, Co, Ni, Al, Fe, and Sn; and,
at least two ligands selected from the group consisting of: urea, acetic acid, citric acid, hydrochloric acid, sulfuric acid, nitric acid, lithium citrate, sodium citrate, triethanolamine, ethylenediamine, ammonia, nitrilotriacetic acid, phosphoric acid, and acetonitrile.
3. The method of claim 1 wherein said second solution comprises:
an alkali metal selected from the group consisting of: Li and Na;
at least one transition metal selected from the group consisting of: Mn, Co, Ni, Al, Fe, and Sn; and,
at least two ligands selected from the group consisting of: urea, acetic acid, citric acid, hydrochloric acid, sulfuric acid, nitric acid, lithium citrate, sodium citrate, triethanolamine, ethylenediamine, ammonia, nitrilotriacetic acid, and acetonitrile.
4. The method of claim 1 wherein said substrate is selected from the group consisting of: stainless steel foil, nickel foil, nickel-clad copper foil, and aluminum foil.
5. The method of claim 1 wherein said homogeneous cathode film comprises a compound selected from the group consisting of:
LiMn 2-x M1 x O 4 where M1 is selected from the group consisting of Al, Sn, Zn, and Fe, and 0≦x≦0.05;
LiCo 1-x M2 x O 2 where M2 is selected from the group consisting of Ni and Al, and 0≦x≦0.5;
LiNi 1-x M3 x O 2 where M3 is selected from the group consisting of Co and Al, and 0≦x≦0.5;
LiMn x Ni y Co z Al t O 2 where x+y+z+t=1, and 0≦(x, y, z, and t)≦1;
LiM4PO 4 where M4 is selected from the group consisting of Fe, Co, Ni, and Mn;
NaMn 2-x M5 x O 4 where M5 is selected from the group consisting of Al, Sn, Zn, and Fe, and 0≦x≦0.05;
NaCo 1-x M6 x O 2 where M6 is selected from the group consisting of Ni and Al, and 0≦x≦0.5;
NaNi 1-x M7 x O 2 where M7 is selected from the group consisting of Co and Al, and 0≦x≦0.5;
NaMn x Ni y Co z Al t O 2 where x+y+z+t=1, and 0≦(x, y, z, and t)≦1; and,
NaM8PO 4 where M8 is selected from the group consisting of Fe, Co, Ni, and Mn.
6. The method of claim 1 further comprising the step of calendaring to increase the density of said deposited films prior to heating step (f).
7. The method of claim 6 wherein said calendaring comprises applying a mechanical pressure of at least 2000 psi.