Cathode active material for lithium battery and method of manufacturing the same

Abstract

A cathode active material for a lithium secondary battery is provided which comprises a first region and a second region. The first region is represented by Chemical Formula1 wherein M1, M2 and M3 are constant: Li.sub.a1M1.sub.x1M2.sub.y1M3.sub.z1O.sub.2+. The second region is formed around the first regions and is represented by Chemical Formula 2 Li.sub.a2M1.sub.x2M2.sub.y2M3.sub.z2M4.sub.wO.sub.2+. The concentrations of M1, M2 and M3 are changed from Chemical Formula 1. In both Chemical Formula 1 and 2, M1, M2 and M3 is selected from a group including Ni, Co, Mn and combinations thereof, M4 is selected from a group including Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B and combinations thereof, 0<a11.1, 0<a21.1, 0x11, 0x21, 0y11, 0y21, 0z11, 0z21, 0<w0.1, 0.00.02, 0<x1+y1+z11, 0<x2+y2+z21.

Claims

1. A cathode active material for a lithium secondary battery, the cathode active material comprising: a first region represented by following Chemical Formula 1, wherein concentrations of M1, M2 and M3 are constant, and wherein the first region is a core with radius R1; and a second region formed around the first region, wherein a thickness of the second region is D2, and wherein concentrations of M1, M2, M3 and M4 are changed from the composition shown in the Chemical Formula 1 into the following composition shown in Chemical Formula 2, thereby the second region shows the composition of the Chemical Formula 2 at the outer shell,
Li.sub.a1M1.sub.x1M2.sub.y1M3.sub.z1O.sub.2+[Chemical Formula 1]
Li.sub.a2M1.sub.x2M2.sub.y2M3.sub.z2M4.sub.wO.sub.2+[Chemical Formula 2] (wherein in Chemical Formula 1 and Chemical Formula 2, each of M1, M2 and M3 is selected from the group consisting of Ni, Co, Mn and combinations thereof, M4 is Al, 0<a11.1, 0<a21.1, 0x11, 0x21, 0y11, 0y21, 0z11, 0z21, 0.003w0.0075, 0.00.02, 0<x1+y1+z11, and 0<x2+y2+z21).

2. The cathode active material of claim 1, wherein M4 shows concentration gradient in at least a portion of a particle.

3. The cathode active material of claim 1, wherein M4 shows concentration gradient from a portion of the second region to the outer shell of the second region.

4. The cathode active material of claim 3, wherein the concentration of M4 increases as going to the outer shell of the second region from a portion of the second region.

5. The cathode active material of claim 1, wherein x1c2, y1y2 and z1z2.

6. The cathode active material of claim 1, wherein the concentration gradients of M1, M2 and M3 are constant in the second region.

7. The cathode active material of claim 1, wherein the second region comprises a region M1-1 and a region M1-2 of which concentration gradients of M1 are different from each other.

8. The cathode active material of claim 1, wherein the second region comprises a region M2-1 and a region M2-2 of which concentration gradients of M2 are different from each other.

9. The cathode active material of claim 1, wherein the second region comprises a region M3-1 and a region M3-2 of which concentration gradients of M3 are different from each other.

10. The cathode active material of claim 1, wherein at least one of M1, M2, and M3 has constant concentration gradient at an entire region which has concentration gradient of M4.

11. A cathode active material for a lithium secondary battery, wherein average composition of total particles are represented by following Chemical Formula 4,
Li.sub.aM1.sub.xM2.sub.yM3.sub.zM4.sub.wO.sub.2+,[Chemical Formula 4] wherein each of M1, M2 and M3 is selected from the group consisting of Ni, Co, Mn and combinations thereof, wherein M4 is Al, and wherein at least one of M1, M2 and M3 has concentration gradient in at least a portion of the particle, and wherein 0x1, 0y1, 0z1, 0.003w0.0075 and 0.00.02.

12. The cathode active material of claim 11, wherein at least one of M1, M2 and M3 shows concentration gradient in the whole particle.

13. The cathode active material of claim 11, wherein one of M1, M2 and M3 shows constant concentration in the whole particle.

14. The cathode active material of claim 11, wherein M4 shows concentration gradient in at least a portion of the particle.

15. The cathode active material of claim 11, wherein concentration of M4 decreases as going to the center of the particle from the surface of the particle.

16. The cathode active material of claim 11, wherein at least one of M1, M2 and M3 has constant concentration gradient at an entire region which has concentration gradient of M4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The inventive concept will become more apparent in view of the attached drawings and accompanying detailed descriptions.

(2) FIGS. 1 and 2 show the concentration ratio of metal ions in cross-section of active material which were manufactured by embodiments of the inventive concept (FIG. 1) and a comparative concept (FIG. 2).

(3) FIGS. 3 through 6 show results of measuring characteristics for batteries which include active material manufactured by embodiments of the inventive concept;

(4) FIGS. 7 and 8 show results of measuring the element ratio in active material by EPMA as moving from the center to the surface; and

(5) FIGS. 9 and 10 show results of measuring characteristics for batteries which include active material manufactured by embodiments of the inventive concept.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the inventive concept are shown. It should be noted, however, that the inventive concept is not limited to the following embodiments, and may be implemented in various forms.

Example Embodiment 1

(7) In order to make an active material coated by aluminum, in which nickel concentration is continuously decreasing as going to the surface from the center, and cobalt and manganese concentration is increasing as going to the surface from the center, first of all, 2.4M first metal salt solution in which nickel sulfate: cobalt sulfate:manganese sulfate are mixed at the molar ratio of 78:0:22 and a second metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate are mixed at the molar ratio of 54:19:27 were prepared. Distilled water 4 liters was poured into a coprecipitation reactor (capacity 4 L, rotation motor power 80 W) and nitrogen gas was supplied into the reactor at the rate of 0.5 liter/min to remove dissolved oxygen followed by stirring at 1000 rpm while keeping the reactor temperature at 50 C.

(8) The first metal salt solution was continuously put into the reactor at the rate of 0.3 liter/hour, and 3.6 M ammonia solution was continuously put into the reactor at the rate of 0.03 liter/hour. Further, for adjusting pH, 4.8 M sodium hydroxide (NaOH) solution was supplied thereto to keep pH at 11. Impeller speed of the reactor was controlled to 1000 rpm such that coprecipitation reaction was performed until the diameter of getting sediment is 1 m. Average retention time of the solution in the reactor became about 2 hours by controlling flow rate. After reaching the reaction at normal status, normal status duration was given to reactant such that coprecipitation composite with higher density was manufactured.

(9) The first metal salt solution and the second metal salt solution were poured into the reactor with changing mixture ratio at the rate of 0.3 liter/hour, and 3.6 M ammonia solution was put into at the rate of 0.03 liter/hour, 4.8 M NaOH solution was put was supplied for adjusting pH to keep pH at 11. Impeller speed of the reactor was controlled to 1000 rpm, thereby coprecipitation reaction was performed.

(10) The composite was filtered and washed followed by drying in 110 C. hot air dryer for 15 hours, thereby an active material precursor was manufactured.

(11) Aluminum solution Al(OH).sub.3 as M4 was mixed to the manufactured active material precursor followed by heat treatment, thereby a precursor doped with aluminum of 1% concentration was manufactured.

(12) LiNO.sub.3 solution as lithium salt was mixed, heated at the rate of 2 C./min and kept at 280 C. for 10 hours for conducting pre-calcination. Then, the result material was calcined at 750 C. for 15 hours to obtain final active material particle. The diameter of the final active material particle was 12 m.

Comparative Embodiment 1

(13) Particles of a comparison embodiment 1 were manufactured by the example embodiment 1 except for without mixing the aluminum solution.

Example Embodiment 2

(14) For manufacturing particles showing two concentration gradient slopes of metal concentration, first of all, 2.4M metal solution as a first metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 98:0:2, a metal solution as a second metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 91:3:6, and a metal solution as a third metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 63:6:31 were prepared.

(15) The first metal salt solution and the second metal salt solution were poured into the reactor at the rate of 0.3 liter/hour by changing mixture ratio thereof, and the second metal salt solution and the third metal salt solution were introduced into the reactor by changing mixture ratio thereof for conducting coprecipitation reaction, thereby manufacturing precursor particles with two concentration gradient slopes of metal.

(16) Aluminum solution as M4 were mixed into the active material precursor followed by thermal treatment, thereby a precursor doped with 0.5% aluminum were manufactured.

Example Embodiment 3

(17) For manufacturing particles having a concentration gradient portion around a constant concentration core portion, 2.4M metal solution as a first metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 95:1:4 and metal solution as a second metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 55:15:30 were prepared.

(18) The first metal salt solution were supplied in a predetermined time to manufacture a core portion with constant concentration of metal, and the first metal salt solution and the second metal salt solution were introduced into the reactor by changing the mixture ratio thereof for conducting coprecipitation reaction, thereby particles including the concentration gradient portion around the core portion with constant concentration of metal were manufactured.

(19) Aluminum solution as M4 were mixed with the result active material precursor followed by thermal treatment, thereby a precursor doped with 0.3% aluminum were manufactured.

Example Embodiment 4

(20) For manufacturing particles showing two concentration gradient slopes of metal concentration, first of all, 2.4M metal solution as a first metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 98:0:2, a metal solution as a second metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 95:2:3, and a metal solution as a third metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 70:5:25 were prepared.

(21) The first metal salt solution and the second metal salt solution were poured into the reactor at the rate of 0.3 liter/hour by changing mixture ratio thereof, and the second metal salt solution and the third metal salt solution were introduced into the reactor by changing mixture ratio thereof for conducting coprecipitation reaction, thereby manufacturing precursor particles with two concentration gradient slopes of metal.

(22) Aluminum solution were mixed into the active material precursor followed by thermal treatment, thereby a precursor doped with 0.75% aluminum were manufactured.

Comparison Embodiment 2

(23) Particles of a comparison embodiment 2 were manufactured by the example embodiment 4 except for without mixing the aluminum solution.

Test Embodiment 1: Confirmation of Concentration Gradient Structure in the Precursor Particle

(24) For confirming each concentration gradient structures of metal as going to the surface from the center of the precursor particles which were manufactured in the example embodiment 1, atomic ratio of each precursor particle manufactured in the example embodiment 1 and the comparative embodiment 1 was measured as moving to the surface from the center using EPMA (Electron Probe Micro Analyzer). The result of the measurement is shown in FIGS. 1 and 2.

(25) As shown in FIGS. 1 and 2, the precursor manufactured in the example embodiment 1 shows concentration gradient of Al.

Manufacturing Batteries

(26) Batteries were manufactured by using the active material which was manufactured in the example embodiments 1 through 4, and the comparative embodiments 1 and 2.

Measuring Battery Characteristics

(27) Battery characteristics measured from each battery which includes active material manufactured in the example embodiments 1 through 4 and the comparative embodiments 1 and 2 are shown in following table 1.

(28) TABLE-US-00001 TABLE 1 Life Time Property (%) Capacity (mAh/g) 2.7-4.3, 0.5 C, DSC ( C.) 2.7-4.3 V, 0.1 C 100 cycle 4.3 V cut off Example 187.2 97.6 288.1 Embodiment 1 Example 219.9 96.8 272.3 Embodiment 2 Example 213.4 97.1 278.7 Embodiment 3 Example 223.7 95.8 260.3 Embodiment 4 Comparative 189.3 96.0 280.3 Embodiment 1 Comparative 225.6 93.8 250.8 Embodiment 2

(29) The result of measuring the life time property for the battery which includes active material particles manufactured in the example embodiment 1 and the comparative embodiment 1 are shown in FIG. 3. In FIG. 3, if different metal according to the present embodiment shows concentration gradient, the example embodiment with doping is the same as the comparative embodiment in the initial capacity, however, are higher than the comparative embodiment 1 in the capacity after 150 cycles, thereby it is confirmed that the life time was improved.

(30) Charge/discharge characteristic, life time property and DSC characteristic were measured from the battery which includes active material particles manufactured in the example embodiment 4 and the comparative embodiment 2. The result was shown in FIGS. 5 through 6. In FIGS. 5 and 6, if different metal according to the present embodiment shows concentration gradient, the example embodiment with doping is the same as the comparative embodiment in the initial capacity but has improved life time property, and has considerably improved thermal stability in FIG. 6.

Example Embodiment 5

(31) For manufacturing particles showing two concentration gradient slopes of metal concentration, first of all, 2.4M metal solution as a first metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 98:0:2, a metal solution as a second metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 92:3:5, and a metal solution as a third metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 67:8:25 were prepared.

(32) The first metal salt solution and the second metal salt solution were poured into the reactor at the rate of 0.3 liter/hour by changing mixture ratio thereof, and the second metal salt solution and the third metal salt solution were introduced into the reactor by changing mixture ratio thereof for conducting coprecipitation reaction, thereby manufacturing precursor particles with two concentration gradient slopes of metal.

(33) Titanium solution were mixed into the active material precursor followed by thermal treatment, thereby a precursor doped with 0.75% titanium were manufactured.

Example Embodiment 6

(34) For manufacturing particles having a concentration gradient in entire portion as going to the surface from the center, 2.4M metal solution as a first metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 90:0:10 and metal solution as a second metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 54:15:31 were prepared.

(35) The first metal salt solution were supplied in a predetermined time to manufacture a core portion with constant concentration of metal, and the first metal salt solution and the second metal salt solution were introduced into the reactor by changing the mixture ratio thereof for conducting coprecipitation reaction, thereby particles with the concentration gradient of metal in the entire portion as going to the surface from the center were manufactured.

(36) Titanium solution as M4 were mixed with the result active material precursor followed by thermal treatment, thereby a precursor doped with 0.3% titanium were manufactured.

Example Embodiment 7

(37) For manufacturing particles showing two concentration gradient slopes of metal concentration, first of all, 2.4M metal solution as a first metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 98:0:2, a metal solution as a second metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 90:3:7, and a metal solution as a third metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 70:5:25 were prepared.

(38) The first metal salt solution and the second metal salt solution were poured into the reactor at the rate of 0.3 liter/hour by changing mixture ratio thereof, and the second metal salt solution and the third metal salt solution were introduced into the reactor by changing mixture ratio thereof for conducting coprecipitation reaction, thereby manufacturing precursor particles with two concentration gradient slopes of metal.

(39) Titanium solution were mixed into the active material precursor followed by thermal treatment, thereby a precursor doped with 1.0% titanium were manufactured.

Example Embodiment 8

(40) For manufacturing particles having a core portion with constant concentration and a shell portion with concentration gradient around the core portion, 2.4M metal solution as a first metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 98:0:2 and metal solution as a second metal salt solution in which nickel sulfate:cobalt sulfate:manganese sulfate were mixed at the molar ratio of 90:3:7 were prepared.

(41) The first metal salt solution were supplied in a predetermined time to manufacture a core portion with constant concentration of metal, and the first metal salt solution and the second metal salt solution were introduced into the reactor by changing the mixture ratio thereof for conducting coprecipitation reaction, thereby particles including the shell portion with concentration gradient of metal around the core portion.

(42) Titanium solution as M4 were mixed with the result active material precursor followed by thermal treatment, thereby a precursor doped with 0.25% titanium were manufactured.

Comparative Embodiment

(43) Particles of comparative embodiments 3 and 4 were manufactured by the example embodiments 5 and 6 except for without mixing the titanium solution.

Test Embodiment: Confirmation of Concentration Gradient Structure in the Active Material Particle

(44) For confirming each concentration gradient structure of metal as going to the surface from the center of the precursor particles which were manufactured in the example embodiment 5 and the comparative embodiment 3, atomic ratio of each precursor particle manufactured in the example embodiment 1 and the comparative embodiment 1 was measured as moving to the surface from the center using EPMA (Electron Probe Micro Analyzer). The result of the measurement was shown in FIGS. 7 and 8.

(45) As shown in FIGS. 7 and 8, the precursors manufactured in the example embodiment 5 and the comparative embodiment 3 show concentration gradients of Ni, Co and Mn from the center to the surface of the particle, and it is confirmed that the doped Ti in the embodiment 5 also shows concentration gradient.

Measuring Battery Characteristics

(46) Battery characteristics measured from each battery which includes active material manufactured in the example embodiments 5 through 9 and the comparative embodiments 3 and 4 are shown in following table 2.

(47) TABLE-US-00002 TABLE 2 Life Time Property (%) Capacity (mAh/g) 2.7-4.3, 0.5 C, DSC ( C.) 2.7-4.3 V, 0.1 C 100 cycle 4.3 V cut off Example 222.8 95.2 261.7 Embodiment 5 Example 193.1 96.3 290.0 Embodiment 6 Example 220.6 95.4 267.3 Embodiment 7 Example 225.8 94.1 251.1 Embodiment 8 Comparative 225.1 92.1 250.8 Embodiment 2 Comparative 194.3 95.5 282.1 Embodiment 3

(48) The result of measuring the life time property for the battery which includes active material particles manufactured in the example embodiment 5 and the comparative embodiment 3 are shown in FIG. 9. As shown in FIG. 9, a particle with concentration gradient of different metal manufactured by the present embodiment is the same as the comparative embodiment in the initial capacity, however, is higher than the comparative embodiment 1 in the capacity after 60 cycles, thereby it is confirmed that the life time was improved.

(49) As shown in FIG. 10, it is confirmed that a particle with concentration gradient of different metal manufactured by the present embodiment is more improved than the comparative embodiment in thermal stability.

(50) According to embodiments of the inventive concept, the cathode active material for lithium battery may show concentration gradient of different metal which is coated or coating as well as concentration gradient of Ni, Mn and Co such that the cathode active material is more structurally stable. Therefore deterioration can be restrained during high temperature preservation and heat stability is superior during charging.

(51) The cathode active material for lithium battery according to present embodiments is more stable in structural because different metal as well as Ni, Mn and Co shows concentration gradients, thereby deterioration can be restrained during high temperature preservation and heat stability is superior during charging.