Composite cathode active material for all-solid-state battery, preparation method thereof, cathode layer for all-solid-state battery, and all-solid-state battery including the cathode layer
A composite cathode active material for an all-solid-state battery including a sulfide solid electrolyte, a preparation method thereof, a cathode layer for an all-solid-state battery, and an all-solid-state battery including the cathode layer, the composite cathode active material including a secondary particle including a plurality of primary particles; and a buffer layer on a surface of the secondary particle, wherein the secondary particle includes a nickel lithium transition metal oxide represented by Formula 1 (Li a Ni 1-b M b O 2 ), the buffer layer includes a first buffer layer adjacent to a surface of the secondary particle and including an oxide represented by Formula 2 (Li x A y O z ); and a second buffer layer including an oxide represented by Formula 3 (Li x E y O z ).
1 . A composite cathode active material for an all-solid-state battery that includes a sulfide solid electrolyte, the composite cathode active material comprising:
a secondary particle including a plurality of primary particles; and
a buffer layer on a surface of the secondary particle,
wherein:
the secondary particle includes a nickel lithium transition metal oxide represented by Formula 1,
the buffer layer includes:
a first buffer layer adjacent to a surface of the secondary particle and including an oxide represented by Formula 2-1; and
a second buffer layer including an oxide represented by Formula 3,
an amount of the oxide represented by Formula 2-1 is in a range of about 0.01 mol % to about 0.5 mol %,
an amount of the oxide represented by Formula 3 is in a range of about 0.01 mol % to about 0.5 mol %, and
a total amount of the oxide represented by Formula 2-1 and the oxide represented by Formula 3 is in a range of about 0.2 mol % to about 0.5 mol %, all mol % being based on 100 mol % of the composite cathode active material,
Li a Ni 1-b M b O 2 Formula 1
in Formula 1,
a and b satisfy the following relations: 0.95≤a≤1.10, 0<b<0.5, and
M is cobalt (Co), manganese (Mn), aluminum (Al), or a combination thereof,
Li x Ti y O z Formula 2-1
in Formula 2-1,
x, y, and z satisfy the following relations: 0≤x≤3, 0<y≤2, 0<z≤4, and
Li x E y O z Formula 3
in Formula 3,
x, y, and z satisfy the following relations: 0≤x≤3, 0<y≤2, 0<z≤4, and
E is Si, Zr, Nb, B, La, Mo, P, Mg, Al, Zn, or a combination thereof.
2 . The composite cathode active material as claimed in claim 1 , wherein:
the oxide represented by Formula 3 is represented by Formula 3-1:
Li x Zr y O z Formula 3-1
in Formula 3-1, x, y, and z satisfy the following relations: 0≤x≤3, 0<y≤2, and 0<z≤4.
3 . The composite cathode active material as claimed in claim 1 , wherein the oxide represented by Formula 2-1 is Li 2 TiO 3 , or a combination thereof.
4 . The composite cathode active material as claimed in claim 1 , wherein the oxide represented by Formula 3 is Li 2 ZrO 3 , ZrO 2 , La 2 O 3 , Nb 2 O 3 , B 2 O 3 , SiO 2 , MgO, Al 2 O 3 , ZnO, Li 3 PO 4 , or a combination thereof.
5 . The composite cathode active material as claimed in claim 1 , wherein:
the nickel lithium transition metal oxide represented by Formula 1 has a layered crystal structure, and
the oxide represented by Formula 2-1 and the oxide represented by Formula 3 each independently have a triclinic crystal structure or a monoclinic crystal structure.
6 . The composite cathode active material as claimed in claim 1 , wherein, according to inductively coupled plasma (ICP) analysis for the composite cathode active material, the composite cathode active material includes:
Ti in an amount of about 0.01 mol % to about 0.5 mol %, and
Zr in an amount of about 0.01 mol % to about 0.5 mol %, all mol % being based on 100 mol % of the composite cathode active material.
7 . The composite cathode active material as claimed in claim 1 , wherein:
the nickel lithium transition metal represented by Formula 1 is represented by Formula 1-1, a compound represented by Formula 1-2, or a combination thereof:
Li a Ni 1-b1-b2 Co b1 Mn b2 O 2 Formula 1-1
in Formula 1-1, a, b1, and b2 satisfy the following relations: 0.95≤a≤1.10, 0<b1+b2<0.5, 0<b1<0.2, and 0<b2<0.2, and
Li a Ni 1-b1-b2 Co b1 Al b2 O 2 Formula 1-2
in Formula 1-2, a, b1, and b2 satisfy the following relations: 0.95≤a≤1.10, 0<b1+b2<0.5, 0<b1<0.2, and 0<b2<0.05.
8 . The composite cathode active material as claimed in claim 1 , wherein:
a total thickness of the buffer layer is in a range of about 5 nm to about 50 nm,
a thickness of the first buffer layer is in a range of about 1 nm to about 20 nm,
a thickness of the second buffer layer is in a range of about 1 nm to about 20 nm, and
a thickness ratio of the first buffer layer to the second buffer layer is in a range of about 0.1 to about 10.
9 . The composite cathode active material as claimed in claim 1 , wherein the first buffer layer and the second buffer layer are conformal coating layers.
10 . A cathode layer for an all-solid-state battery, the cathode layer comprising the composite cathode active material as claimed in claim 1 .
11 . An all-solid-state battery, comprising:
a cathode layer;
an anode layer; and
a sulfide solid electrolyte layer therebetween,
wherein the cathode layer includes the composite cathode active material as claimed in claim 1 .
12 . The all-solid-state battery as claimed in claim 11 , wherein the sulfide solid electrolyte is Li 2 S—P 2 S 5 , Li 2 S—P 2 S 5 —LiX, in which X is a halogen element, Li 2 S—P 2 S 5 —Li 2 O, Li 2 S—P 2 S 5 —Li 2 O—LiI, Li 2 S—SiS 2 , Li 2 S—SiS 2 —LiI, Li 2 S—SiS 2 —LiBr, Li 2 S—SiS 2 —LiCl, Li 2 S—SiS 2 —B 2 S 3 —LiI, Li 2 S—SiS 2 —P 2 S 5 —LiI, Li 2 S—B 2 S 3 , Li 2 S—P 2 S 5 -ZmSn, in which m and n are positive numbers, and Z is germanium (Ge), Zn, or gallium (Ga), Li 2 S—GeS 2 , Li 2 S—SiS 2 —Li 3 PO 4 , Li 2 S—SiS 2 -Li p M O q , in which p and q are positive numbers, and M is P, Si, Ge, B, Al, Ga, or indium (In), Li 7-x PS 6-x Cl x , in which 0≤x≤2, Li 7-x PS 6-x Br x , in which 0≤x≤2, and Li 7-x PS 6-x I x , in which 0≤x≤2.
13 . The all-solid-state battery as claimed in claim 11 , wherein the sulfide solid electrolyte is an argyrodite-type solid electrolyte including Li 6 PS 5 Cl, Li 6 PS 5 Br, or Li 6 PS 5 I.
14 . The all-solid-state battery as claimed in claim 11 , wherein:
the anode layer includes an anode current collector and a first anode active material layer,
a second anode active material layer is on the first anode active material layer, between the anode current collector and the first anode active material layer, or a combination thereof, and
the second anode active material layer includes lithium or a lithium alloy.
15 . The all-solid-state battery as claimed in claim 11 , wherein:
the anode layer includes an anode current collector and a first anode active material layer, and
the all-solid-state battery further includes a carbon layer between the first anode active material layer and the solid electrolyte layer.
16 . A method of preparing a composite cathode active material for an all-solid-state battery as claimed in claim 1 , the method comprising:
mixing a nickel lithium transition metal oxide represented by Formula 1, a precursor of an oxide represented by Formula 2-1, a lithium precursor, an organic solvent, and water to obtain a first mixture;
adding, to the first mixture, a precursor of an oxide represented by Formula 3 and an organic solvent to obtain a second mixture and perform a reaction thereon; and
drying and heat-treating the reaction product to obtain the composite cathode active material:
Li a Ni 1-b M b O 2 Formula 1
wherein, in Formula 1,
a and b satisfy the following relations: 0.95≤a≤1.10, 0<b<0.5, and
M is cobalt (Co), manganese (Mn), aluminum (Al), or a combination thereof,
Li x Ti y O z Formula 2-1
wherein, in Formula 2-1,
x, y, and z satisfy the following relations: 0≤x≤3, 0<y≤2, 0<z≤4, and
Li x E y O z Formula 3
wherein, in Formula 3,
x, y, and z satisfy the following relations: 0≤x≤3, 0<y≤2, 0<z≤4, and
E is Si, Zr, Nb, B, La, Mo, P, or a combination thereof.
17 . The method as claimed in claim 16 , wherein the heat-treating is performed at a temperature in a range of about 250° C. to about 500° C.
18 . The method as claimed in claim 16 , wherein the heat-treating is performed for about 1 hour to about 20 hours under an oxidizing atmosphere.