Cathode active material, method of preparing the same, and cathode and secondary battery including the same

1 . A cathode active material comprising a compound represented by Formula 1 and having an olivine structure:

Li 1−α CO 1−x−y In x M y PO 4   Formula 1

wherein in Formula 1, 0≤α<1, 0.01≤x≤0.05, and 0.01≤y≤0.07, and

M in Formula 1 is a divalent element, a trivalent element other than In, a tetravalent element, a pentavalent element, or a combination thereof, wherein M in Formula 1 is Nb, Ni, Ti, or Mo, wherein a ratio of x to y in Formula 1 is about 1:1 to about 1:7.

2 . The cathode active material of claim 1 , wherein α in Formula 1 satisfies the condition of 0<α<1.

3 . The cathode active material of claim 1 , wherein α in Formula 1 is about 0.01 to about 0.3.

4 . The cathode active material of claim 1 , wherein the compound represented by Formula 1 comprises a compound represented by Formulae 2 to 54:

Li 1−α Co 1−x−y In x Nb y PO 4   Formula 2

wherein, in Formula 2, 0≤α<1, 0.01≤x≤0.05, and 0.01≤y≤0.071,

Li 1−α Co 1−x−y In x Ti y PO 4   Formula 3

wherein, in Formula 3, 0≤α<1, 0.01≤x≤0.15, and 0.01≤y≤0.07,

Li 1−α Co 1−x−y In x Mo y PO 4   Formula 4

wherein, in Formula 4, 0≤α<1, 0.01≤x≤0.05, and 0.01≤y≤0.07,

Li 1−α Co 1−x−y In x Ni y PO 4   Formula 5

wherein, in Formula 5, 0≤α<1, 0.01≤x≤0.05, and 0.01≤y≤0.07 or a combination thereof.

5 . The cathode active material of claim 4 , wherein a ratio of x to y in Formulae 2 to 5 is about 1:1 to about 1:7.

6 . The cathode active material of claim 1 , wherein the cathode active material is

Li 1−α Co 0.9 In 0.05 Nb 0.05 PO 4 , Li 1−α Co 0.94 In 0.01 Ti 0.05 PO 4 , Li 1−α Co 0.9 In 0.05 Ni 0.05 PO 4 , Li 1−α Co 0.98 In 0.01 Mo 0.01 PO 4 , Li 1−α Co 0.96 In 0.01 Mo 0.03 PO 4 , Li 1−α Co 0.96 In 0.01 Ti 0.03 PO 4 , Li 1−α Co 0.92 In 0.01 Ti 0.07 PO 4 , Li 1−α Co 0.92 In 0.01 Nb 0.07 PO 4 , Li 1−α Co 0.94 In 0.01 Nb 0.05 PO 4 , Li 1−α Co 0.9 In 0.05 Ti 0.05 PO 4 , Li 1−α Co 0.94 In 0.01 Ni 0.05 PO 4 , Li 1−α Co 0.94 In 0.01 Mo 0.05 PO 4 , or a combination thereof, wherein 0≤α<1.

7 . The cathode active material of claim 1 , wherein the cathode active material is

Li 0.8 Co 0.9 In 0.05 Nb 0.05 PO 4 , Li 0.82 Co 0.9 In 0.06 Nb 0.04 PO 4 , Li 0.89 Co 0.94 In 0.01 Ti 0.05 PO 4 , Li 0.9 Co 0.94 In 0.02 Ti 0.04 PO 4 , Li 0.95 Co 0.9 In 0.05 Ni 0.05 PO 4 , Li 0.94 Co 0.9 In 0.06 Ni 0.04 PO 4 , Li 0.97 Co 0.98 In 0.01 Mo 0.01 PO 4 , Li 0.95 Co 0.97 In 0.01 Mo 0.02 PO 4 , Li 0.93 Co 0.96 In 0.01 Mo 0.03 PO 4 , Li 0.92 Co 0.95 In 0.02 Mo 0.03 PO 4 , Li 0.97 Co 0.9 In 0.01 Ti 0.01 PO 4 , Li 0.95 Co 0.97 In 0.01 Ti 0.02 PO 4 , Li 0.93 Co 0.96 In 0.01 Ti 0.03 PO 4 , Li 0.92 Co 0.95 In 0.02 Ti 0.03 PO 4 , Li 0.78 Co 0.92 In 0.01 Nb 0.07 PO 4 , Li 0.8 Co 0.92 In 0.02 Nb 0.06 PO 4 , Li 0.84 Co 0.94 In 0.01 Nb 0.05 PO 4 , Li 0.6 Co 0.94 In 0.02 Nb 0.04 PO 4 , Li 0.85 Co 0.9 In 0.05 Ti 0.05 PO 4 , Li 0.86 Co 0.9 In 0.06 Ti 0.04 PO 4 , Li 0.99 Co 0.94 In 0.01 Ni 0.05 PO 4 , Li 0.98 Co 0.94 In 0.02 Ni 0.04 PO 4 , Li 0.89 Co 0.94 In 0.01 Mo 0.05 PO 4 , Li 0.9 Co 0.94 In 0.02 Mo 0.04 PO 4 , Li 0.85 Co 0.92 In 0.01 Ti 0.07 PO 4 , or a combination thereof.

8 . The cathode active material of claim 1 , wherein the cathode active material has a crystal structure belonging to an orthorhombic crystal system, and the crystal structure of the cathode active material belongs to a Pnma space group.

9 . The cathode active material of claim 1 , wherein an average discharge voltage of the cathode active material is about 4.4 Volts or greater, and a specific capacity of the cathode active material at 25° C. is about 130 milliampere-hours per gram or greater.

10 . A secondary battery comprising:

the cathode comprising the cathode active material of claim 1 ;

an anode; and

an electrolyte between the cathode and the anode.

11 . The secondary battery of claim 10 , wherein the secondary battery is a lithium secondary battery or an all-solid-state battery.

12 . The secondary battery of claim 11 ,

wherein the all-solid-state battery is a multi-layer-ceramic battery or a film battery,

and the multi-layer ceramic battery comprises a stack structure comprising a plurality of unit cells, each unit cell comprising:

the cathode wherein the cathode comprises a cathode active material layer comprising the cathode active material,

the electrolyte wherein the electrolyte is a solid electrolyte

wherein the solid electrolyte is between the cathode and the anode, and

the anode wherein the anode comprises an anode active material layer,

optionally wherein the cathode active material layer and an anode active material layer of an adjacent unit cell face each other.

13 . The secondary battery of claim 12 , wherein the secondary battery comprises:

the cathode comprising the cathode active material layer, a cathode current collector,

wherein the anode active material layer comprises a first anode active material layer, a second anode active material layer, or a combination thereof, and an anode current collector, and

the solid electrolyte is between the cathode and the anode,

wherein the cathode active material layer is between the cathode current collector and a first surface of the solid electrolyte, and

wherein the first anode active material layer, the second anode active material layer, or a combination thereof, is between the anode current collector and a second surface of the solid electrolyte.

14 . The secondary battery of claim 13 , wherein the secondary battery further comprises a film between the anode current collector and the first anode active material layer, or between the anode current collector and the second anode active material layer, wherein the film comprises a metal that forms an alloy with lithium, an alloy of the metal, or a combination thereof.

15 . A method of preparing a cathode active material, the method comprising: mixing an indium precursor, a metal precursor, a lithium precursor, a cobalt precursor, and a phosphorus precursor to prepare a precursor mixture; and

heat-treating the precursor mixture to prepare the cathode active material of claim 1 , wherein

a metal of the metal precursor is the divalent element, the trivalent element other than In, the tetravalent element, the pentavalent element, or a combination thereof.

16 . The method of claim 15 , wherein the heat-treating comprises heat-treating at about 600° C. to about 900° C. in an oxidizing atmosphere or an inert atmosphere.

17 . A cathode active material comprising a compound represented by Formula 1 and having an olivine structure:

Li 1−α CO 1−x−y In x M y PO 4   Formula 1

wherein in Formula 1, 0≤α<1, 0.01≤x≤0.05, and 0.01≤y≤0.07, and

M in Formula 1 is a divalent element, a trivalent element other than In, a tetravalent element, a pentavalent element, or a combination thereof,

wherein M in Formula 1 comprises Mo.