Cathode active material for high voltage lithium secondary battery and lithium secondary battery including the same

Abstract

Disclosed are a cathode active material for high voltage lithium secondary batteries and a lithium secondary battery including the same and, more particularly, the present invention relates to a cathode active material for lithium secondary batteries that includes a lithium transition metal oxide having a lithium molar fraction of greater than 1, containing a relative excess of nickel, and having a composition represented by Formula 1 below, wherein the lithium transition metal oxide has a Li.sub.2MnO.sub.3-like structure phase:
Li.sub.1+aNi.sub.bCo.sub.cMn.sub.1−(a+b+c+d)M.sub.dO.sub.2-tA.sub.t  (1) wherein 0.05≦a≦0.2, 0.4≦b≦0.7, 0.1≦c≦0.4, 0≦d≦0.1, and 0≦t<0.2; M is at least one divalent or trivalent metal; and A is at least one monovalent or divalent anion.

Claims

1. A cathode active material for a lithium secondary battery, consisting of a lithium transition metal oxide having a lithium molar fraction of greater than 1, and having a composition represented by Formula 1 below,
Li.sub.1+aNi.sub.bCo.sub.cMn.sub.1−(a+b+c+d)M.sub.dO.sub.2−tA.sub.t  (1) wherein 0.05≦a≦0.2, 0.4≦b≦0.7, 0.1≦c≦0.4, 0≦d≦0.1, 0.1≦1−(a+b+c+d)≦0.2, and 0≦t≦0.2; M is at least one divalent or trivalent metal; and A is at least one monovalent or divalent anion.

2. The cathode active material according to claim 1, wherein a molar fraction a of Li of the lithium transition metal oxide satisfies the following condition: 0.05≦a≦0.15.

3. The cathode active material according to claim 1, wherein a molar fraction b of Ni of the lithium transition metal oxide satisfies the following condition: 0.45≦b≦0.6.

4. The cathode active material according to claim 1, wherein a molar fraction c of Co of the lithium transition metal oxide satisfies the following condition: 0.2<c≦0.3.

5. The cathode active material according to claim 1, wherein M is at least one selected from the group consisting of B, Mg, Al, Ca, Sr, Cr, Cu, Fe, Ti, Y, and Zn.

6. The cathode active material according to claim 1, wherein A is at least one selected from the group consisting of F, Cl, Br, and S.

7. The cathode active material according to claim 1, wherein an amount of the lithium transition metal oxide is 50 wt % to 100 wt % based on a total weight of the cathode active material.

8. A cathode comprising the cathode active material according to claim 1.

9. A lithium secondary battery comprising the cathode according to claim 8.

Description

EXAMPLE 1

(1) Li.sub.1.1Ni.sub.0.45Co.sub.0.27Mn.sub.0.18O.sub.2 as a cathode active material, a conductive material, and PVdF as a binder were added in a weight ratio of 92:4:4 (active material:conductive material:binder) to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a cathode mixture slurry. Subsequently, 95 wt % of artificial graphite as an anode active material, 1.5 wt % of Super-P as a conductive material, and 3.5 wt % of PVdF as a binder were added to NMP as a solvent to prepare an anode mixture slurry. The cathode mixture slurry and the anode mixture slurry were respectively coated onto Al foil and Cu foil, dried, and pressed, thereby completing fabrication of a cathode and an anode.

(2) Thereafter, a porous polyethylene separator was interposed between the cathode and the anode and an electrolyte containing 1M LiPF.sub.6 in a mixed carbonate solvent of EC and EMC in a volume ratio of 1:2 was injected thereinto, thereby completing manufacture of a battery.

COMPARATIVE EXAMPLE 1

(3) A battery was manufactured in the same manner as in Example 1, except that LiNi.sub.0.5Co.sub.0.3Mn.sub.0.2O.sub.2 was used alone as a cathode active material.

COMPARATIVE EXAMPLE 2

(4) A battery was manufactured in the same manner as in Example 1, except that LiNi.sub.1/3Mn.sub.1/3Co.sub.1/3O.sub.2 was used alone as a cathode active material.

EXPERIMENTAL EXAMPLE 1

Initial Charge and Discharge Characteristics

(5) Charge and discharge capacities of each of the batteries manufactured according to Example 1 and Comparative Examples 1 and 2 were measured at a current of 0.1 C. and at a voltage of 2.5 V to 4.4 V using an electrochemical analyzer (Toscat 3100U manufactured by Toyo Systems). Results are shown in Table 1 below.

(6) TABLE-US-00001 TABLE 1 Initial charge Initial discharge capacity capacity Sample (mAh/g) (mAh/g) Example 1 201 181 Comparative 202 182 Example 1 Comparative 188 169 Example 2

(7) As shown in Table 1 above, it can be confirmed that the battery of Example 1 has lower initial charge and discharge capacities than those of the battery of Comparative Example 1, while having far higher initial charge and discharge capacities than those of the battery of Comparative Example 2.

EXPERIMENTAL EXAMPLE 2

Lifespan Characteristics

(8) Lifespan characteristics of each of the batteries of Example 1 and Comparative Examples 1 and 2 were evaluated by performing 50 charging and discharging cycles at a current of 1.0 C. and at 45° C. Results are shown in Table 2 below.

(9) TABLE-US-00002 TABLE 2 Lifespan characteristics 50.sup.th/1.sup.st discharge capacity (%) Example 1 90 Comparative 85 Example 1 Comparative 91 Example 2

(10) As shown in Table 2 above, it can be confirmed that the battery of Example 1 exhibits similar lifespan characteristics to those of the battery of Comparative Example 2, while exhibiting superior lifespan characteristics to those of the battery of Comparative Example 1.

(11) 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.