Electrode active material, lithium secondary battery containing the electrode active material, and method of preparing the electrode active material
An electrode active material includes: a core active material having a layered structure and capable of reversibly incorporating and deincorporating lithium; a dopant including boron and a first metal element, wherein the dopant is in the core active material; and a nanostructure disposed on a surface of the core active material and including a metal borate compound including a second metal element, wherein the second metal element is the same as the first metal element.
1. An electrode active material comprising:
a core active material having a layered structure and capable of reversibly incorporating and deincorporating lithium;
a dopant comprising boron and a first metal element in the core active material, wherein the boron and the first metal element are paired together in the layered structure of the core active material; and
a coating having a nanostructure disposed on a surface of the core active material and comprising a metal borate compound comprising a second metal element,
wherein the second metal element is the same as the first metal element,
wherein the metal borate compound is represented by Formula 1,
M x B y O z Formula 1
wherein, in Formula 1,
M is aluminum, zirconium, calcium, barium, bismuth, tin, zinc, silicon, strontium, titanium, vanadium, chromium, iron, copper, niobium, molybdenum, ruthenium, palladium, silver, cadmium, tantalum, tungsten, iridium, platinum, gold, or a combination thereof, and
x, y, and z satisfy 1≤x<30, 1≤y<10, and 1<z<40, and
wherein the core active material is a compound represented by Formula 3,
LiNi x M 1 1-x O 2-e M′ e Formula 3
wherein, in Formula 3,
M 1 is a Group 4 to a Group 14 element, or a combination thereof,
M′ is an anion element comprising F, S, Cl, Br, or a combination thereof, and
x and e satisfy 0.7≤x<1 and 0≤e<1.
2. The electrode active material of claim 1 , wherein the first metal element is configured to contract or expand the layered structure of the core active material, and comprises aluminum, zirconium, calcium, barium, bismuth, tin, zinc, silicon, strontium, titanium, vanadium, chromium, iron, copper, niobium, molybdenum, ruthenium, palladium, silver, cadmium, tantalum, tungsten, iridium, platinum, gold, or a combination thereof.
3. The electrode active material of claim 2 , wherein the dopant further comprises lithium.
4. The electrode active material of claim 1 , wherein the boron and the first metal element are configured to contract or expand the layered structure of the core active material.
5. The electrode active material of claim 1 , wherein a total amount of boron and the first metal element in the dopant, and boron and the second metal element contained in the metal borate compound is in a range of about 0.3 mole percent to about 10 mole percent based on 1 mole of the core active material.
6. The electrode active material of claim 5 , wherein the total amount of the first metal element and the second metal element is about 0.25 mole percent or greater based on 1 mole of the core active material.
7. The electrode active material of claim 1 , wherein a molar ratio of the total amount of the first metal element and the second metal element to the total amount of boron in the dopant and boron contained in the metal borate compound is in a range of about 1:10 to about 30:1.
8. The electrode active material of claim 1 , wherein an aspect ratio of the nanostructure is in a range of about 1 to about 200.
9. The electrode active material of claim 1 , wherein the nanostructure comprises a nanowire, a nanorod, a nanoplate, a nanobelt, a nanoribbon, or a combination thereof.
10. The electrode active material of claim 1 , wherein the metal borate compound is an aluminum borate compound, a zirconium borate compound, a Li-containing aluminum borate compound, a Li-containing zirconium borate compound, or a combination thereof.
11. The electrode active material of claim 10 , wherein the aluminum borate compound comprises AlBO 3 , Al 4 B 2 O 9 , Al 5 BO 9 , Al 18 B 4 O 33 , or a combination thereof.
12. The electrode active material of claim 10 , wherein the zirconium borate compound comprises ZrBO 3 , ZrB 2 O 5 , LiZrB 3 O 7 , Li 2 ZrB 4 O 9 , or a combination thereof.
13. The electrode active material of claim 10 , wherein the dopant comprises AlB, Al 4 B 2 , Al 5 B, Al 18 B 4 , ZrB, ZrB 2 , ZrB 3 , ZrB 4 , or a combination thereof.
14. The electrode active material of claim 1 , wherein an interlayer distance of the layered structure of the core active material with the dopant is increased as compared to an interlayer distance of the layered structure of the core active material without the dopant.
15. The electrode active material of claim 1 , wherein the residual lithium is in an amount in a range of about 100 parts per million to about 20,000 parts per million.
16. The electrode active material of claim 1 , wherein the core active material is a secondary particle comprising agglomerated primary particles, and the coating having a nanostructure comprising the metal borate is disposed on a surface of the primary particle, a grain boundary between the primary particles, a surface of the secondary particle, or a combination thereof.
17. A lithium secondary battery comprising:
a positive electrode, and
a negative electrode,
wherein at least one of the positive electrode or the negative electrode comprises the electrode active material of claim 1 .
18. A method of preparing the electrode active material of claim 1 , the method comprising:
dry-mixing a precursor material for the core active material of Formula 3, a first metal element precursor, and a borate precursor to prepare a mixture; and
heat-treating the mixture to prepare the electrode active material, wherein the electrode active material comprises
the core active material having a layered structure and capable of reversibly incorporating and deincorporating lithium,
the dopant comprising boron and the first metal element in the core active material, wherein the boron and the first metal element are paired together in the layered structure of the core active material, and
the coating having a nanostructure disposed on a surface of the core active material and comprising a metal borate compound comprising a second metal element,
wherein the second metal element is the same as the first metal element,
wherein the metal borate compound is represented by Formula 1,
M x B y O z Formula 1
wherein, in Formula 1,
M is aluminum, zirconium, calcium, barium, bismuth, tin, zinc, silicon, strontium, titanium, vanadium, chromium, iron, copper, niobium, molybdenum, ruthenium, palladium, silver, cadmium, tantalum, tungsten, iridium, platinum, gold, or a combination thereof, and
x, y, and z satisfy 1≤x<30, 1≤y<10, and 1<z<40, and
wherein the core active material is a compound represented by Formula 3,
LiNi x M 1 1-x O 2-e M′ e Formula 3
wherein, in Formula 3,
M 1 is a Group 4 to a Group 14 element, or a combination thereof,
M′ is an anion element comprising F, S, Cl, Br, or a combination thereof, and
x and e satisfy 0.7≤x<1 and 0≤e<1.
19. The method of claim 18 , wherein the precursor material for the core active material is in the form of a hydrate.
20. The method of claim 18 , wherein the metal element precursor comprises an aluminum precursor, a zirconium precursor, an aluminum hydrate precursor, a zirconium hydrate precursor, or a combination thereof.
21. The method of claim 20 , wherein the aluminum precursor comprises Al(NO 3 ) 3 , Al 2 O 3 , AlPO 4 , Al(OH) 3 , Al(ClO 4 ) 3 , AlK(SO 4 ) 2 , Al 2 (SO 4 ) 3 , Al 2 S 3 , AlF 3 , or a combination thereof;
the zirconium precursor comprises of Zr(NO 3 ) 4 , ZrO 2 , Zr(HPO 4 ) 2 , Zr(OH) 4 , Zr(ClO 4 ) 4 , Zr(SO 4 ) 2 , (CH 3 CO 2 ) x Zr(OH) y , wherein x+y=4, ZrCl 4 , ZrF 4 , or a combination thereof; and
the borate precursor comprises H 2 BH 3 , LiBH 4 , NaBO 4 , KBH 4 , Mg(BH 4 ) 2 , Ca(BH 4 ) 2 , Sr(BH 4 ) 2 , NH 3 BH 3 , Al(BH 4 ) 3 , or a combination thereof.
22. The method of claim 18 , wherein an amount of the metal element precursor and the borate precursor are selected such that a molar ratio of the metal element in the metal element precursor to boron is in a range of about 1:10 to about 30:1.
23. The method of claim 18 , wherein the heat-treating of the mixture is performed in air or in an oxygen atmosphere at a temperature of about 600° C. to about 1,000° C.
24. The method of claim 18 , further comprising washing the electrode active material after the heat-treating.
25. The method of claim 24 , wherein an amount of residual lithium in the electrode active material before the washing is in a range of about 1,000 parts per million to about 20,000 parts per million, and an amount of residual lithium in the electrode active material after the washing is in a range of about 100 parts per million to about 5,000 parts per million.