Cathode active material and lithium secondary battery comprising the same

Abstract

Disclosed is a cathode active material for secondary batteries comprising at least one compound selected from the following formula 1:
(1−s−t)[Li(Li.sub.aMn.sub.(1−a−x−y)Ni.sub.xCo.sub.y)O.sub.2]*s[Li.sub.2CO.sub.3]*t[LiOH]  (1)
wherein 0<a<0.2, 0<x<0.9, 0<y<0.5, a+x+y<1, 0<s<0.03, and 0<t<0.03; and a, x and y represent a molar ratio, and a and t represent a weight ratio. The cathode active material has long lifespan at room temperature and high temperatures and provides superior stability, although charge and discharge are repeated at a high current.

Claims

1. A cathode active material for secondary batteries consisting of: a compound of formula (1):
(1−s−t)[Li(Li.sub.a(Mn(.sub.1−x−y)Ni.sub.xCo.sub.y).sub.1−a)O.sub.2]*s[Li.sub.2CO.sub.3]*t[LiOH]  (1)  wherein 0<a<0.2, 0<x<0.9, 0<y<0.5, a+x+y<1, 0.0010≦s<0.0022, 0.0012≦t<0.0026; 0.0022≦s+t<0.0048 and a, x and y represent a molar ratio, and s and t represent a weight ratio.

2. The cathode active material according to claim 1, wherein a satisfies the condition of 0.01<a≦0.19.

3. The cathode active material according to claim 1, wherein x is not lower than 0.02 and is lower than 0.8.

4. The cathode active material according to claim 1, wherein y is higher than 0 and is not higher than 0.3.

5. A cathode mix for second batteries comprising the cathode active material according to claim 1.

6. A cathode for lithium secondary batteries in which the cathode mix according to claim 5 is applied to a current collector.

7. A lithium secondary battery comprising the cathode according to claim 6.

8. A middle- or large-sized battery pack comprising the secondary battery according to claim 7 as a unit battery.

9. An electric vehicle, a hybrid electric vehicle or a plug-in hybrid electric vehicle comprising the middle- or large-sized battery pack of claim 8.

Description

BEST MODE

(1) Now, the present invention will be described in more detail with reference to the following examples. These examples are provided only to illustrate the present invention and should not be construed as limiting the scope and spirit of the present invention.

EXAMPLE 1

(2) Ni.sub.0.53Mn.sub.0.27CO.sub.0.2(OH.sub.0.53).sub.2 was synthesized as a transition metal precursor by co-precipitation in accordance with a method disclosed in Korean Patent Laid-open No. 2009-0105868, and then mixed with Li.sub.2CO.sub.3, and the resulting mixture was baked in a furnace at 940° C. and then cooled by incorporating air at 500 L/min, to synthesize 0.9978Li(Li.sub.0.02(Ni.sub.0.53Mn.sub.0.27Co.sub.0.20).sub.0.98)O.sub.2*0.0012LiOH*0.0010Li.sub.2CO.sub.3 as an active material.

(3) The amounts of LiOH and LiCO.sub.3 of the prepared active material were determined by adding 10 g of the prepared active material to 200 mL of water and measuring the amount of base used for titration with 0.1N HCl.

COMPARATIVE EXAMPLE 1

(4) 0.9971Li(Li.sub.0.02(Ni.sub.0.53Mn.sub.0.27Co.sub.0.20).sub.0.98)O.sub.2*0.0029Li.sub.2CO.sub.3 was prepared as an active material in the same manner as in Example 1 except that a transition metal precursor in which a molar ratio of Ni, Mn, and Co (Ni:Mn:Co) is 53:27:20 was prepared by a general co-precipitation method known in the art and the amount of carbonate was maximized by incorporating CO.sub.2 as an cooling atmosphere at 100 L/min for one hour when passed at 150° C. in a shaking oven.

EXAMPLE 2

(5) 0.9972Li(Li.sub.0.02(Ni.sub.0.53Mn.sub.0.27Co.sub.0.20).sub.0.98)O.sub.2*0.0018LiOH*0.0010Li.sub.2CO.sub.3 was prepared as an active material in the same manner as in Example 1 except that the amount of OH was increased by cooling while passing an air at 300 L/min.

EXAMPLE 3

(6) 0.9972Li(Li.sub.0.02(Ni.sub.0.53Mn.sub.0.27Co.sub.0.20).sub.0.98)O.sub.2*0.0008LiOH*0.0020Li.sub.2CO.sub.3 was prepared as an active material in the same manner as in Example 1 except that CO.sub.2 was incorporated as an cooling atmosphere at 100 L/min for 15 minutes when passed at 150° C. in a shaking oven.

COMPARATIVE EXAMPLE 2

(7) Li(Li.sub.0.02(Ni.sub.0.53Mn.sub.0.27Co.sub.0.20).sub.0.98)O.sub.2 was prepared in the same manner as in Example 1 except that the active material was washed with distilled water to remove a base of the active material prepared in Example 1 and dried at 130° C. in an oven for 24 hours.

EXAMPLE 4

(8) Ni.sub.0.78Mn.sub.0.12Co.sub.0.10(OH.sub.0.53).sub.2 was synthesized as a transition metal precursor by co-precipitation in accordance with a method disclosed in Korean Patent Laid-open No. 2009-0105868, and then mixed with Li.sub.2CO.sub.3, and the resulting mixture was baked in a furnace at 890° C. and then cooled by passing oxygen (O.sub.2) at 200 L/min, to synthesize 0.9952Li(Li.sub.0.02(Ni.sub.0.78Mn.sub.0.12Co.sub.0.10).sub.0.98)O.sub.2*0.0026LiOH*0.0022Li.sub.2CO.sub.3 as an active material.

(9) The amounts of LiOH and LiCO.sub.3 of the prepared material were determined by adding 10 g of the prepared active material to 200 mL of water and measuring the amount of base through titration with 0.1N HCl.

COMPARATIVE EXAMPLE 3

(10) 0.9948Li(Li.sub.0.02(Ni.sub.0.78Mn.sub.0.12Co.sub.0.10).sub.0.98)O.sub.2*0.0052Li.sub.2CO.sub.3 was prepared as an active material in the same manner as in Example 4 except that a transition metal precursor in which a molar ratio of Ni, Mn, and Co (Ni:Mn:Co) is 78:12:10 was prepared by a general co-precipitation method in the art and the amount of carbonate was maximized by incorporating CO.sub.2 as an cooling atmosphere at 100 L/min for one hour when passed at 150° C. in a shaking oven.

COMPARATIVE EXAMPLE 4

(11) Li(Li.sub.0.02(Ni.sub.0.78Mn.sub.0.12Co.sub.0.10).sub.0.98)O.sub.2 was prepared as an active material by treating the active material prepared in Example 4 in the same manner as in Comparative Example 2.

EXAMPLE 5

(12) Ni.sub.0.5Mn.sub.0.4Co.sub.0.1(OH.sub.0.53).sub.2 was synthesized as a transition metal precursor by co-precipitation in accordance with a method disclosed in Korean Patent Laid-open No. 2009-0105868, and then mixed with Li.sub.2CO.sub.3, and the resulting mixture was baked in a furnace at 950° C. and then cooled by passing an air at 500 L/min, to synthesize 0.9967Li(Li.sub.0.1(Ni.sub.0.5Mn.sub.0.4CO.sub.0.1).sub.0.9)O.sub.2*0.0021LiOH*0.0012Li.sub.2CO.sub.3 as an active material.

(13) The amounts of LiOH and LiCO.sub.3 of the prepared material were determined by adding 10 g of the prepared active material to 200 mL of water and measuring the amount of base through titration with 0.1N HCl.

COMPARATIVE EXAMPLE 5

(14) 0.9966Li(Li.sub.0.1(Ni.sub.0.5Mn.sub.0.4Co.sub.0.1))O.sub.2*0.0034Li.sub.2CO.sub.3 was prepared as an active material in the same manner as in Example 4 except that a transition metal precursor in which a molar ratio of Ni, Mn, and Co (Ni:Mn:Co) is 5:4:1 was prepared by a general co-precipitation method in the art and the amount of carbonate was maximized by incorporating CO.sub.2 as an cooling atmosphere at 100 L/min for one hour when passed at 150° C. in a shaking oven.

COMPARATIVE EXAMPLE 6

(15) Li(Li.sub.0.1(Ni.sub.0.5Mn.sub.0.4CO.sub.0.1))O.sub.2 was prepared as an active material by treating the active material prepared in Example 5 in the same manner as in Comparative Example 2.

TEST EXAMPLE 1

(16) A slurry was prepared using each of the active materials synthesized in Examples 1 to 5 and Comparative Examples 1 to 6 such that an active material:conductive material:binder was 95:2.5:2.5 and then coated on an Al foil. The electrode obtained was pressed such that a pore ratio was 23% and punched in the form of a circle to fabricate a coin-type battery. At this time, a Li metal was used as an anode and a solution of 1M LiPF.sub.6 in a carbonate mixed solvent (EC:DMC:DEC=1:2:1, volume ratio) was used as an electrolyte.

(17) The batteries thus fabricated were tested under conditions described in the following Table 1.

(18) TABLE-US-00001 TABLE 1 Electrochemical test results 1.sup.st Rate Cycle Discharge cycle capability capability 30.sup.th capacity efficiency 2.0 C. .Math. 0.1 C. cycle/1.sup.st cycle (mAh/g) (%) (%) (%) Ex. 1 163 88 85 95 Comp. Ex. 1 158 85 78 89 Ex. 2 164 89 86 94 Ex. 3 161 87 84 92 Comp. Ex. 2 165 89 85 82 Ex. 4 195 89 84 92 Comp. Ex. 3 189 86 79 87 Comp. Ex. 4 196 90 85 80 Ex. 5 159 91 87 97 Comp. Ex. 5 149 87 78 89 Comp. Ex. 6 160 91 86 85

(19) As can be seen from Table 1 above, LiOH and Li.sub.2CO.sub.3 play a considerably important in the active materials. As can be seen from Comparative Examples 2, 4 and 6, when LiOH and Li.sub.2CO.sub.3 are not present in the active materials, rate characteristics and cycle characteristics are rapidly reduced. This difference in characteristics is 10 to 15-times higher than the difference shown above, when the active materials are used 300 or 500 cycles, as actual battery cycles, and in particular, the difference may further increase when applied to batteries for electric vehicles. In addition, as can be seen from the results of Comparative Examples 2, 4 and 6, performance is deteriorated although Li.sub.2CO.sub.3 is present alone.

(20) Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

INDUSTRIAL APPLICABILITY

(21) As apparent from the afore-going, the cathode active material comprising lithium nickel-manganese-cobalt composite oxide according to the present invention can secure stability and improve lifespan properties under the conditions of high current charge within a short time and high temperature.