Lithium-cobalt based complex oxide having superior lifespan characteristics and cathode active material for secondary batteries including the same

Abstract

Disclosed is a lithium-cobalt based complex oxide represented by Formula 1 below including lithium, cobalt and manganese wherein the lithium-cobalt based complex oxide maintains a crystal structure of a single O3 phase at a state of charge (SOC) of 50% or more based on a theoretical amount:
Li.sub.xCo.sub.1-y-zMn.sub.yA.sub.zO.sub.2(1) wherein 0.95x1.15, 0<y0.3 and 0z0.2; and A is at least one element selected the group consisting of Al, Mg, Ti, Zr, Sr, W, Nb, Mo, Ga, and Ni, wherein the at least one element of A is Mg.

Claims

1. A lithium-cobalt based complex oxide represented by Formula 1 below comprising lithium, cobalt and manganese, wherein the lithium-cobalt based complex oxide maintains a crystal structure of a single O3 phase at a state of charge (SOC) of 50% or more based on theoretical capacity:
Li.sub.xCo.sub.1-y-zMn.sub.yA.sub.zO.sub.2(1) wherein 0.95x1.15, 0<y0.3 and 0<z0.2; and A is at least one element selected the group consisting of Al, Mg, Ti, Zr, Sr, W, Nb, Mo, Ga, and Ni, wherein the at least one element of A contains Mg, wherein the lithium-cobalt based complex oxide maintains the crystal structure of the single O3 phase under operating voltage of 4.35 V or more.

2. The lithium-cobalt based complex oxide according to claim 1, wherein the lithium-cobalt based complex oxide maintains the crystal structure of the single O3 phase when delithiation progresses in 50% or more of the lithium-cobalt based complex oxide.

3. The lithium-cobalt based complex oxide according to claim 1, wherein the lithium-cobalt based complex oxide maintains the crystal structure of the single O3 phase under operating voltage of 4.35 V or more to 4.5 V or less.

4. The lithium-cobalt based complex oxide according to claim 1, wherein y is 0.0001y0.2.

5. The lithium-cobalt based complex oxide according to claim 1, wherein A is Mg.

6. The lithium-cobalt based complex oxide according to claim 1, wherein an average particle size of the lithium-cobalt based complex oxide is 0.5 micrometers to 30 micrometers.

7. A cathode active material comprising the lithium-cobalt based complex oxide according to claim 1.

8. A cathode mixture for secondary batteries comprising the cathode active material according to claim 7.

9. A cathode for secondary batteries comprising the cathode mixture for secondary batteries according to claim 8 coated on a collector.

10. A lithium secondary battery comprising the cathode for secondary batteries according to claim 9.

11. A battery module comprising the lithium secondary battery according to claim 10 as a unit battery.

12. A device comprising the lithium secondary battery according to claim 10.

13. A device comprising the battery module according to claim 11.

14. The device according to claim 12, wherein the device is a mobile phone, a tablet PC, a laptop computer, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for storing power.

15. The device according to claim 13, wherein the device is a mobile phone, a tablet PC, a laptop computer, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for storing power.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graph comparing capacity retention ratios at 25 C. according to Experimental Example 2 of the present invention;

(2) FIG. 2 is a graph comparing capacity retention ratios at 45 C. according to Experimental Example 2 of the present invention;

(3) FIG. 3 is a graph illustrating lifespan characteristics of Example 1, per cycle, at 25 C. according to Experimental Example 2 of the present invention;

(4) FIG. 4 is a graph illustrating lifespan characteristics of Example 2, per cycle, at 25 C. according to Experimental Example 2 of the present invention;

(5) FIG. 5 is a graph illustrating lifespan characteristics of Example 3, per cycle, at 25 C. according to Experimental Example 2 of the present invention;

(6) FIG. 6 is a graph illustrating lifespan characteristics of Comparative Example 1, per cycle, at 25 C. according to Experimental Example 2 of the present invention;

(7) FIG. 7 is a graph illustrating lifespan characteristics of Example 1, per cycle, at 45 C. according to Experimental Example 2 of the present invention;

(8) FIG. 8 is a graph illustrating lifespan characteristics of Example 2, per cycle, at 45 C. according to Experimental Example 2 of the present invention;

(9) FIG. 9 is a graph illustrating lifespan characteristics of Example 3, per cycle, at 45 C. according to Experimental Example 2 of the present invention;

(10) FIG. 10 is a graph illustrating lifespan characteristics of Comparative Example 1, per cycle, at 25 C. according to Experimental Example 2 of the present invention;

(11) FIG. 11 is a graph comparing rate characteristics according to Experimental Example 2 of the present invention; and

(12) FIG. 12 is a graph comparing capacity retention ratios at 45 C. according to Experimental Example 3.

BEST MODE

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

Example 1

(14) A Co source, Mn source and Li source were sufficiently mixed using a dry method to obtain a mixture including Li:Co:Mn:O in a molar ratio of 1.03:0.9982:0.0018:2. The mixture was plasticized at 9001200 C. for 5 to 20 hours. The obtained product was ground and classified. As a result, a lithium-cobalt based complex oxide represented by Li.sub.1.03Co.sub.0.9989Mn.sub.0.0011O.sub.2 was obtained.

Example 2

(15) A Co source, Mn source and Li source were sufficiently mixed using a dry method to obtain a mixture including Li:Co:Mn:O in a molar ratio of 1.03:0.9969:0.0031:2. The mixture was plasticized at 9001200 C. for 5 to 20 hours. The obtained product was ground and classified. As a result, a lithium-cobalt based complex oxide represented by Li.sub.1.03Co.sub.0.9982Mn.sub.0.0018O.sub.2 was obtained.

Example 3

(16) A Co source, Mn source and Li source were sufficiently mixed using a dry method to obtain a mixture including Li:Co:Mn:O in a molar ratio of 1.03:0.9957:0.0043:2. The mixture was plasticized at 9001200 C. for 5 to 20 hours. The obtained product was ground and classified. As a result, a lithium-cobalt based complex oxide represented by Li.sub.1.03Co.sub.0.9975Mn.sub.0.0025O.sub.2 was obtained.

Example 4

(17) A Co source, Mn source and Li source were sufficiently mixed using a dry method to obtain a mixture including Li:Co:Mn:O in a molar ratio of 1.03:0.9933:0.0067:2. The mixture was plasticized at 9001200 C. for 5 to 20 hours. The obtained product was ground and classified. As a result, a lithium-cobalt based complex oxide represented by Li.sub.1.03Co.sub.0.9960Mn.sub.0.0040O.sub.2 was obtained.

Example 5

(18) A Co source, Mn source and Li source were sufficiently mixed using a dry method to obtain a mixture including Li:Co:Mn:O in a molar ratio of 1.03:0.9519:0.0481:2. The mixture was plasticized at 9001200 C. for 5 to 20 hours. The obtained product was ground and classified. As a result, a lithium-cobalt based complex oxide represented by Li.sub.1.03Co.sub.0.9550Mn.sub.0.0450O.sub.2 was obtained.

Example 6

(19) A Co source, Mn source, Mg source and Li source were sufficiently mixed using a dry method to obtain a mixture including Li:Co:Mn:Mg:O in a molar ratio of 1.03:0.9988:0.0011:0.0001:2. The mixture was plasticized at 9001200 C. for 5 to 20 hours. The obtained product was ground and classified. As a result, a lithium-cobalt based complex oxide represented by Li.sub.1.03Co.sub.0.9988Mn.sub.0.0011Mg.sub.0.0001O.sub.2 was obtained.

Example 7

(20) A Co source, Mn source, Mg source and Li source were sufficiently mixed using a dry method to obtain a mixture including Li:Co:Mn:Mg:O in a molar ratio of 1.03:0.9986:0.0011:0.0003:2. The mixture was plasticized at 9001200 C. for 5 to 20 hours. The obtained product was ground and classified. As a result, a lithium-cobalt based complex oxide represented by Li.sub.1.03Co.sub.0.9986Mn.sub.0.0011Mg.sub.0.0003O.sub.2 was obtained.

Comparative Example 1

(21) A Co source and Li source were sufficiently mixed using a dry method to obtain a mixture including Li:Co:O in a molar ratio of 1.03:1:2. The mixture was plasticized at 9001200 C. for 5 to 20 hours. The obtained product was ground and classified. As a result, a lithium-cobalt based complex oxide represented by Li.sub.1.03CoO.sub.2 was obtained.

Experimental Example 1

(22) Lithium-cobalt based complex oxide samples manufactured according to Examples 1 and 4, and Comparative Example 1 were prepared. An X-ray diffraction (XRD) pattern of each sample was collected using a Siemens D500 diffractometer equipped with copper target X-ray tube and diffracted beam monochromator. Since the samples are thick and wide, the samples were manufactured in a flat and rectangular powder-bed shape such that volume irradiated by X-ray beam is constant. Using GSAS of a Rietveld refinement program disclosed in [A. C. Larson and R. B. Von Dreele, General Structure Analysis System (GSAS), Los Alamos National Laboratory Report LAUR 86-748 (2000)], a lattice constant of a unit cell was calculated. Results are summarized in Table 1 below.

(23) Here, crystal structures of unit cells manufactured according to Example 1 and Comparative Example 1 were measured in a full voltage range. The lithium-cobalt based complex oxide sample manufactured according to Example 4 maintained a crystal structure of a single O3 phase in voltage of 4.4 V or more. A crystal structure was not measured below the voltage range.

(24) TABLE-US-00001 TABLE 1 Voltage (V) Cell parameter 4.3 4.35 4.4 4.45 4.5 Comparative a 2.809 2.809 2.812 2.810 2.811 2.812 2.810 2.812 Example 1 c 14.45 14.44 14.40 14.43 14.39 14.40 14.36 14.34 Example 1 a 2.809 2.810 2.810 2.810 2.811 c 14.44 14.43 14.42 14.41 14.40 Example 4 a 2.810 2.811 2.812 c 14.42 14.42 14.40

(25) Referring to Table 1, the lithium-cobalt based oxides manufactured according to Examples 1 and 4 maintained crystal structures of single O3 phases under full charging voltage not exceeding 4.50 V. On the other hand, the lithium-cobalt based complex oxide manufactured according to Comparative Example 1 showed another phase, in addition to an O3 phase, over 4.35 V, resulting in two phases. Subsequently, at 4.50 V, all O3 phases transitioned to the another phase, resulting in formation of one phase.

Experimental Example 2

(26) Using each of the lithium-cobalt based complex oxides manufactured according to Example 1 to 3 and Comparative Example 1, the lithium-cobalt based complex oxide:a conductive material (Denka black):a binder (PVdF) in a weight ratio of 95:2.5:2.5 were added to NMP and then mixed to manufacture a cathode mixture. The cathode mixture was coated to a thickness of 200 m on an aluminum foil and then pressed and dried. As a result, a cathode was manufactured.

(27) To manufacture a lithium secondary battery, Li metal was used as an anode and a carbonate based electrolyte, namely, 1 mol LiPF.sub.6 dissolved in a mixture of ethyl carbonate (EC) and ethyl methyl carbonate (EMC) mixed in a ratio of 1:1 was used as an electrolyte.

(28) Measurement of Initial Charge and Discharge Capacities, and Efficiencies

(29) When the manufactured lithium secondary batteries were charged and discharged at 0.1 C in a voltage range of 3.0 V to 4.4 V, initial capacities and efficiencies were measured. Results are summarized in Table 2 below.

(30) Measurement of Lifespan Characteristics

(31) After charging and discharging the manufactured lithium secondary batteries once at 0.1 C in chambers of 25 C. and in a voltage range of 3.0 V to 4.4 V, lifespan characteristics were measured fifty times while charging at 0.5 C and discharging at 1 C. After charging and discharging once at 0.1 C in a 45 C. chamber and in a voltage range of 3.0 V to 4.5 V, lifespan characteristics were measured fifty times while charging at 0.5 C and discharging at 1 C. Results are summarized in Table 2 below and illustrated in FIGS. 1 to 10.

(32) Measurement of Rate Characteristics

(33) Rate characteristics of the manufactured lithium secondary batteries were tested in a voltage range of 3.0 V to 4.4 V and capacity at each C-rate with respect to capacities at 0.1 C was calculated. Results are summarized in Table 2 below and illustrated in FIG. 11.

(34) TABLE-US-00002 TABLE 2 Lifespan characteristics Initial capacity and efficiency Rate (%, at 50 cycles) Charge Discharge Efficiency characteristics 3.0~4.4 V 3.0~4.5 V (mAh/g) (mAh/g) (%) 1.0 C 2.0 C (25 C.) (45 C.) Example 1 180.5 177.4 98.2 98.0 95.9 97.4 94.4 Example 2 180.3 177.1 98.3 98.4 96.8 98.2 97.1 Example 3 179.6 176 98.0 99.2 98.2 98.3 97.2 Comparative 180.9 176.8 97.8 93.9 88.8 89.4 67.9 Example 1

(35) Referring to Table 2 and FIGS. 1 to 10, initial capacities and efficiencies of lithium secondary batteries using the lithium-cobalt based complex oxides manufactured according to Examples 1 to 3 were slightly higher but were not greatly different, when compared to those of a lithium secondary battery using the lithium-cobalt based complex oxide manufactured according to Comparative Example 1. However, rate characteristics and lifespan characteristics of the lithium secondary batteries using the lithium-cobalt based complex oxides manufactured according to Examples 1 to 3 were superior, when compared to those of a lithium secondary battery using the lithium-cobalt based complex oxide manufactured according to Comparative Example 1. In particular, rate characteristics at a high rate and lifespan characteristics at high temperature were vastly superior.

(36) As described in Experimental Example 1, the lithium-cobalt based complex oxide manufactured according to Example 1 maintained the crystal structure of the single O3 phase even under high voltage. On the other hand, the O3 phase of the lithium-cobalt based complex oxide manufactured according to Comparative Example 1 is partially or entirely changed into the P3 phase and thereby charge and discharge are not maintained and irreversible capacity increases.

(37) For reference, in FIGS. 1 and 2, graphs of Example 2 overlap with graphs of Example 3 and thereby the graphs are not easily distinguished.

Experimental Example 3

(38) Using each of the lithium-cobalt based complex oxides manufactured according to Examples 1, 6 and 7, the lithium-cobalt based complex oxide:a conductive material (Denka black):a binder (PVdF) in a weight ratio of 95:2.5:2.5 were added to NMP and then mixed to manufacture a cathode mixture. The cathode mixture was coated to a thickness of 200 m on an aluminum foil and then pressed and dried. As a result, a cathode was manufactured.

(39) To manufacture a lithium secondary battery, Li metal was used as an anode and a carbonate based electrolyte, namely, 1 mol LiPF.sub.6 dissolved in a mixture of ethyl carbonate (EC) and ethyl methyl carbonate (EMC) mixed in a ratio of 1:1 was used as an electrolyte.

(40) After charging and discharging the manufactured lithium secondary batteries once at 0.1 C in a 45 C. chamber and in a voltage range of 3.0 V to 4.5 V, lifespan characteristics were measured fifty times while charging at 0.5 C and discharging at 1 C. Results are illustrated in FIG. 12.

(41) Referring to FIG. 12, the lithium-cobalt based complex oxides, which are doped with Mg, manufactured according to Examples 6 and 7 showed excellent lifespan characteristics, when compared with the lithium-cobalt based complex oxide manufactured according to Example 1.

(42) 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

(43) As described above, a lithium-cobalt based complex oxide according to the present invention maintains a crystal structure of a single O3 phase at a state of charge (SOC) of 50% or more, namely, under high voltage and thereby collapse of a structure of the lithium-cobalt based complex oxide is prevented, and, accordingly, rate characteristics and lifespan characteristics are improved.