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, 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 for the all-solid-state battery 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, and the buffer layer includes a metal oxide represented by Formula 2, Li a Ni 1-b M b O 2 Formula 1 Li x A y-1 E y2 O z . Formula 2
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, and
the buffer layer includes a metal oxide represented by Formula 2-2,
Li a Ni 1-b M b O 2 Formula 1
in Formula 1,
M is cobalt (Co), manganese (Mn), aluminum (Al), or a combination thereof, and
a and b satisfy the following relations: 0.95≤a≤1.10, 0<b<0.5, and
Li x A1 y1 Zn y2 O z Formula 2-2
in Formula 2-2,
A1 is Ti, Zr, or a combination thereof, and
x, y1, y2, and z satisfy the following relations: 1≤x≤3, 1≤y1≤4, 1≤y2≤4, and 0<z≤8.
2 . The composite cathode active material as claimed in claim 1 , wherein A1 in Formulae 2-2 is Ti.
3 . The composite cathode active material as claimed in claim 1 , wherein the metal oxide represented by Formula 2-2 includes Li 2 Ti 3 ZnO 8 , Li 2 Zr 3 ZnO 8 , or a combination thereof.
4 . 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 metal oxide represented by Formula 2-2 has a cubic crystal structure or an orthorhombic crystal structure.
5 . The composite cathode active material as claimed in claim 1 , wherein the metal oxide represented by Formula 2-2 is included in the composite cathode active material in an amount of about 0.01 mol % to about 5 mol % based on 100 mol % of the composite cathode active material.
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 0.1 mol % to about 5 mol %,
Mg in an amount of about 0.01 mol % to about 5 mol %, and
Zn in an amount of about 0.1 mol % to about 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 a compound 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 1-1, 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<0.05.
8 . A cathode layer for an all-solid-state battery, comprising the composite cathode active material as claimed in claim 1 .
9 . An all-solid-state battery, comprising:
a cathode layer;
an anode layer; and
a solid electrolyte layer therebetween,
wherein the cathode layer includes the composite cathode active material as claimed in claim 1 .
10 . The all-solid-state battery as claimed in claim 9 , wherein:
the anode layer includes an anode current collector and a first anode active material layer,
the all-solid-state battery further includes a second anode active material layer 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.
11 . The all-solid-state battery as claimed in claim 9 , 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.
12 . The all-solid-state battery as claimed in claim 9 , wherein:
the solid electrolyte layer includes a sulfide solid electrolyte, and
the sulfide solid electrolyte includes 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 —Z m S n , 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 MO 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, or Li 7-x PS 6-x I x , in which 0≤x≤2.
13 . The all-solid-state battery as claimed in claim 9 , wherein:
the solid electrolyte layer includes a sulfide solid electrolyte, and
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 . A method of preparing the composite cathode active material as claimed in claim 1 , the method comprising:
mixing a nickel lithium transition metal oxide represented by Formula 1 and a precursor of a metal oxide represented by Formula 2-2 to obtain a composite cathode active material composition; and
performing a reaction on the composite positive electrode active material composition, and drying and heat-treating the reaction product to a prepare the composite cathode active material,
Li a Ni 1-b M b O 2 Formula 1
wherein, in Formula 1,
M is cobalt (Co), manganese (Mn), aluminum (Al), or a combination thereof, and
a and b satisfy the following relations: 0.95≤a≤1.10, 0<b<0.5, and
Li x A1 y1 Zn y2 O z Formula 2-2
wherein, in Formula 2-2,
A1 is Ti, Zr, or a combination thereof, and
x, y1, y2, and z satisfy the following relations: 1≤x≤3, 1≤y1≤4, 1≤y2≤4, and 0<z≤8.
15 . The method as claimed in claim 14 , wherein the heat treatment is performed at a temperature in a range of about 300° C. to about 700° C. under an oxidizing atmosphere.