Lithium cobalt metal oxide powder, method for making the same, and method for determining content of cobalt (II,III) oxide

Abstract

A lithium cobalt metal oxide powder is disclosed in the present disclosure. The lithium cobalt metal oxide powder has a coating structure. The lithium cobalt metal oxide powder includes a lithium cobalt metal oxide matrix. The lithium cobalt metal oxide powder further includes a Co.sub.3O.sub.4 coating layer. A general formula of the lithium cobalt metal oxide powder is Li.sub.aCo.sub.1-x-yM.sub.xN.sub.yO.sub.2.Math.rCo.sub.3O.sub.4, wherein 0.002<r≤0.05, 1≤a≤1.1, 0<x≤0.02, 0≤y≤0.005, and a<1+3r; M is a doping element; and N is a coating element. A method for making the lithium cobalt metal oxide powder as described above and a method for determining a content of Co.sub.3O.sub.4 therein are further provided. The material made in the present disclosure has an excellent electrochemical performance.

Claims

1. A lithium cobalt metal oxide powder having a coating structure, wherein the lithium cobalt metal oxide powder comprises a lithium cobalt metal oxide matrix and a Co.sub.3O.sub.4 coating layer, a general formula of the lithium cobalt metal oxide powder is Li.sub.aCo.sub.1-x-yM.sub.xN.sub.yO.sub.2.Math.rCo.sub.3O.sub.4, wherein 0.002<r≤0.05, 1≤a≤1.1, 0<x≤0.02, 0≤y≤0.005, and a<1+3r, M is a doping element, and N is a coating element.

2. The lithium cobalt metal oxide powder of claim 1, wherein a molar ratio θ.sub.1 of Li to Co+M+N satisfies: 0.92≤θ.sub.1<1.

3. The lithium cobalt metal oxide powder of claim 1 wherein Co.sub.3O.sub.4 is presented both in an interior and on an outer surface of the lithium cobalt metal oxide matrix, and a mass ratio of the Co.sub.3O.sub.4 in the interior of the lithium cobalt metal oxide matrix to the Co.sub.3O.sub.4 on the outer surface of the lithium cobalt metal oxide matrix is smaller than 1.

4. The lithium cobalt metal oxide powder of claim 1 wherein M is selected from the group consisting of Mg, Ca, Cu, Al, B, Ti, Y, Zr, any combination thereof; and N is selected from the group consisting of Na, K, Mg, Ca, Cu, Al, B, Ti, Y, Zr, Ni, Mn, and any combination thereof.

5. The lithium cobalt metal oxide powder of claim 4, wherein M is selected from the group consisting of Mg, Al, and any combination thereof and N is selected from the group consisting of of Mg, Ti, and any combination thereof.

6. The lithium cobalt metal oxide powder of claim 1 wherein the Co.sub.3O.sub.4 is in a form of spinel phase Co.sub.3O.sub.4, and an amount of residual Li on the outer surface of the lithium cobalt metal oxide matrix is smaller than or equal to 0.05%.

7. A method for making the lithium cobalt metal oxide powder of claim 1, comprising steps of: (1) mixing uniformly and then sintering a Li-containing precursor, a first Co-containing precursor, and a M-containing precursor to obtain a lithium-rich matrix; and (2) if the lithium cobalt metal oxide powder comprises the coating element N, mixing uniformly and then sintering the lithium-rich matrix obtained from the step (1), a second Co-containing precursor, and a N-containing precursor to obtain the lithium cobalt metal oxide powder; if the lithium cobalt metal oxide powder comprises no coating element N, mixing uniformly and then sintering the lithium-rich matrix obtained from the step (1) and a second Co-containing precursor to obtain the lithium cobalt metal oxide powder.

8. The method of claim 7, wherein in the step (2), the second Co-containing precursor is selected from the group consisting of Co(OH).sub.2, CoCO.sub.3, Co.sub.3O.sub.4, and any combination thereof.

9. The method of claim 7, wherein, in the step (1), a sintering temperature is 900° C. to 1100° C., a sintering time is 8 h to 12 h, and the sintering is performed in an air atmosphere; in the step (2), a sintering temperature is 600° C. to 1000° C., a sintering time is 6 h to 12 h, and the sintering is performed in an air atmosphere.

10. A method for determining a content of Co.sub.3O.sub.4 in the lithium cobalt metal oxide powder of claim 1, comprising steps of: (1) adding a soaking agent and a metal ion salt solution to the lithium cobalt metal oxide powder, stirring and dissolving fully to obtain a first solution; (2) filtering the first solution obtained from the step (1) by a filter membrane, and washing a residue on the filter membrane after the filtration is finished; (3) adding the filter membrane along with the residue of the step (2) into a strong acid solution, peeling off the residue totally from the filter membrane into the strong acid solution, thereby obtaining a second solution containing the residue and the strong acid solution; (4) adding a strong acid solution again into the second solution obtained from the step (3) to obtain a mixed solution, heating, evaporating, and drying the mixed solution; (5) cooling and then diluting to a final volume, thereby obtaining a solution to be measured; (6) measuring a content of Co in the solution obtained from the step (5) and then calculating a corresponding content of Co.sub.3O.sub.4 to obtain the content of the Co.sub.3O.sub.4 in the sample.

11. The method of claim 10, wherein the step (4) is repeated at least once before proceeding the step (5).

12. The method of claim 10, wherein the soaking agent is selected from the group consisting of HCl, H.sub.2SO.sub.4, H.sub.3PO.sub.4, and any combination thereof, and at least selected from the group consisting of H.sub.2SO.sub.4, H.sub.3PO.sub.4, and any combination thereof.

13. The method of claim 10, wherein the metal ion salt solution is selected from the group consisting of NiSO.sub.4, NiCl.sub.2, MnSO.sub.4, MnCl.sub.2, FeSO.sub.4, FeCl.sub.2, Cu.sub.2SO.sub.4, CuCl.sub.2, CrSO.sub.4, and CrCl.sub.2, and any combination thereof.

14. The method of claim 10, wherein the strong acid is selected from the group consisting of nitric acid, hydrochloric acid, aqua regia, and any combination thereof, and mass concentrations of the nitric acid, the hydrochloric acid, and the aqua regia are 30% to 70%.

15. The method of claim 10, wherein a stirring time is 0.5 h to 2 h.

16. The method of claim 15, wherein the stirring time is 0.8 h to 1.4 h.

17. The lithium cobalt metal oxide powder of claim 1, wherein 0<y≤0.005.

18. The lithium cobalt metal oxide powder of claim 1, wherein the lithium cobalt metal oxide powder further comprising a hexagonal phase lithium cobalt metal oxide on the outer surface of the lithium cobalt metal oxide matrix.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The drawings to be used in the description of the embodiments or the prior art are described briefly as follows, to more clearly describe the technical solutions according to the embodiments of the present disclosure or according to the prior art. It is apparent that the drawings in the following description are only some embodiments of the present disclosure. Other drawings may be obtained by one of ordinary skill in the art according to these drawings without any creative work.

(2) FIG. 1 shows cycle performance curves of button cell tests of samples made in Examples 1 to 3.

(3) FIG. 2 is a XRD spectrum of the sample made in the Example 1.

(4) FIG. 3 shows cycle performance curves of button cell tests of samples made in Examples 4 to 7.

(5) FIG. 4 is a XRD spectrum of the sample made in the Example 5.

DETAILED DESCRIPTION

(6) For a clear understanding of the present disclosure, the present disclosure will now be described more comprehensively and in detail with reference to the accompanying drawings and preferred embodiments. However, the scope of the present disclosure is not limited to the following specific embodiments.

(7) Unless otherwise defined, all terms used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terms used herein are merely for illustrating the specific embodiments, and are not intended to limit the scope of the present disclosure.

(8) Unless otherwise specified, various raw materials, agents, instruments, equipment and the like used in the present disclosure can all be commercially available or can be obtained by means of existing methods.

Example 1

(9) The method for making the lithium cobalt metal oxide powder includes the steps as follows:

(10) (1) The raw materials are weighed in accordance with a formula Li.sub.1.06Co.sub.0.99Mg.sub.0.01O.sub.2, mixed uniformly, then placed into an elevator furnace which is accessible to air, and then sintered. The Li-containing precursor is lithium carbonate. The Co-containing precursor is Co.sub.3O.sub.4 having a D50 of 15 μm. The Mg-containing precursor is an oxide corresponding thereto. The sintering temperature is 1030° C. The sintering time is 10 h. The whole sintering is in the air atmosphere. The sintered lithium cobalt oxide is sieved, pulverized, and so on. A lithium cobalt oxide LCO-A is obtained.

(11) (2) LCO-A is mixed with different amounts of Co(OH).sub.2 uniformly in accordance with a formula LiCo.sub.0.99Mg.sub.0.01O.sub.2.Math.rCo.sub.3O.sub.4. Then the mixture is placed into the elevator furnace which is accessible to air, and then sintered to obtain the lithium cobalt metal oxide powder. Wherein, the sintering temperature is 900° C. The sintering time is 10 h. The Co(OH).sub.2 has a D50 of 0.8 μm.

(12) A method for determining the content of Co.sub.3O.sub.4 in the above-described lithium cobalt metal oxide powder is further provided in this example, including the steps of:

(13) (1) adding NiSO.sub.4 and H.sub.2SO.sub.4 solutions into the lithium cobalt metal oxide powder, and magnetically stirring and dissolving for 1.5 h, thereby obtaining a first solution;

(14) (2) filtering the first solution obtained from the step (1) by suction filtration, and maintaining the filtration membrane at the filtration state after the filtration is finished while washing the residue on the filtration membrane with pure water;

(15) (3) adding the filtration membrane along with the residue of the step (2) into a nitric acid solution with a mass concentration of 30%, peeling off the residue from the filtration membrane by a ultrasonic treatment, then removing the filtration membrane by tweezers, and washing the trace residue attached on the filtration membrane into the nitric acid solution by using the deionized water, thereby obtaining a second solution containing the residue and the nitric acid;

(16) (4) adding a nitric acid solution again into the second solution obtained from the step (3) to obtain a mixed solution, and heating to have the solution evaporated and dried;

(17) (5) cooling, repeating the step (4) once again, cooling once again, and then diluting to a final volume, thereby obtaining a solution to be measured;

(18) (6) measuring the content of Co in the solution obtained from the step (5) (a measuring method can be selected from the atomic absorption spectrometry and other frequently-used methods), and then calculating the content of Co.sub.3O.sub.4 to obtain the content of Co.sub.3O.sub.4 in LiCo.sub.0.99Mg.sub.0.01O.sub.2.Math.rCo.sub.3O.sub.4.

(19) In this example, the calculated content of Co.sub.3O.sub.4 is 1088 ppm, and the calculated r=0.0005. That is, the chemical formula is LiCo.sub.0.99Mg.sub.0.01O.sub.2.Math.0.0005Co.sub.3O.sub.4. A sample of the lithium cobalt metal oxide powder in this example is labeled as LCO-A1.

Example 2

(20) The only difference between the making method in the example 2 and that in the example 1 is in the amount of Co(OH).sub.2 added in the step (2) during the making. The method for determining the content of Co.sub.3O.sub.4 in this example is the same as that in the example 1.

(21) In this example, the calculated content of Co.sub.3O.sub.4 is 5626 ppm, and the calculated r=0.0055. That is, the chemical formula is LiCo.sub.0.99Mg.sub.0.01O.sub.2.Math.0.0055Co.sub.3O.sub.4. A sample of the lithium cobalt metal oxide powder in this example is labeled as LCO-A2.

Example 3

(22) The only difference between the making method in the example 3 and that in the example 1 is in the amount of Co(OH).sub.2 added in the step (2) during the making. The method for determining the content of Co.sub.3O.sub.4 in this example is the same as that in the example 1.

(23) In this example, the calculated content of Co.sub.3O.sub.4 is 10102 ppm, and the calculated r=0.004. That is, the chemical formula is LiCo.sub.0.99Mg.sub.0.01O.sub.2.Math.0.004Co.sub.3O.sub.4. A sample of the lithium cobalt metal oxide powder in this example is labeled as LCO-A3.

(24) The samples obtained in the examples 1-3 are subjected to a button cell capacity test. As shown in Table 1, when charging and discharging at a rate of 0.1 C in a voltage range of 3.0 V to 4.5V, there is only a slight difference between the capacities of the LCO-A1 and the LCO-A2, while the capacity of the LCO-A3 is decreased for 2 mAh/g as compared to that of the LCO-A1. Taking the content value of Co.sub.3O.sub.4 into account, the residual Co.sub.3O.sub.4 in the LCO-A3 is 10102 ppm and has no electrochemical activity in the charge and discharge processes, thus the capacity is decreased. As shown in FIG. 1, when charging and discharging at a rate of 1 C, a capacity retention during cycling is gradually increased with the increase of the content of the residual Co.sub.3O.sub.4. The reason is that at a relatively high cut-off voltage, the Co.sub.3O.sub.4 having no activity on the surface prevents the side reaction between Co.sup.4+ and the electrolyte solution, thereby increasing the cycle performance of the material. FIG. 2 is a XRD spectrum of the sample LCO-A1 obtained from the example 1, from which it can be seen that the crystal obtained from the example 1 is pure layered lithium cobalt oxide, suggesting that the excess Li in the firstly sintered matrix is absorbed by the excess Co added in the second sintering, thereby producing LiCoO.sub.2. On one hand, the specific discharge capacity of the material can be increased under a not relatively high content of residual Co.sub.3O.sub.4. On the other hand, absorbing the excess Li in the matrix by using Co is favorable to reduce the inflation at high temperature and improve the safety performance and the high temperature performance of the material.

(25) TABLE-US-00001 TABLE 1 Charge and discharge specific capacities and efficiencies of the samples made in the examples 1-3 3.0-4.5 V, 25° C. LCO-A1 LCO-A2 LCO-A3 Charge mAhg.sup.−1 202.0 201.2 199.1 Discharge mAhg.sup.−1 195.3 195.1 193.3 Efficiency % 96.7 97.0 97.1

Example 4

(26) The method for making the lithium cobalt metal oxide powder includes the steps as follows

(27) (1) The raw materials are weighed in accordance with a formula of Li.sub.1.04Co.sub.0.98Al.sub.0.02O.sub.2, mixed uniformly, then placed into an elevator furnace which is accessible to air, and then sintered. The Li-containing precursor is lithium carbonate. The Co-containing precursor is Co.sub.3O.sub.4 having a D50 of 15 μm. The Al-containing precursor is Al.sub.2O.sub.3. The sintering temperature is 1050° C. The sintering time is 10 h. The whole sintering is in the air atmosphere. The sintered lithium cobalt oxide is processed by sieved, pulverized, and so on to obtain a lithium cobalt oxide LCO-B.

(28) (2) LCO-B is mixed with different amounts of Co.sub.3O.sub.4 in accordance with a formula of LiCo.sub.0.98-xAl.sub.0.02Mg.sub.xO.sub.2.Math.rCo.sub.3O.sub.4. MgO having a molar ratio of 0.5% is added to the mixture. The mixture is mixed uniformly, then placed into the elevator furnace which is accessible to air, and then sintered to obtain the lithium cobalt metal oxide powder. The sintering temperature is 900° C. The sintering time is 10 h. The Co.sub.3O.sub.4 includes secondary particles with a D50 of 3 μm. Primary particles have a D50 smaller than 1 μm.

(29) A method for determining the content of Co.sub.3O.sub.4 in the above-described lithium cobalt metal oxide powder is further provided in this example, including the steps of:

(30) (1) adding MnSO.sub.4, H.sub.3PO.sub.4 and HCl solutions into the lithium cobalt metal oxide powder, and magnetically stirring and dissolving for 1.0 h, thereby obtaining a first solution;

(31) (2) filtering the first solution obtained from the step (1) by suction filtration, and maintaining the filtration membrane at the filtration state after the filtration is finished while washing the residue on the filtration membrane with pure water;

(32) (3) adding the filtration membrane along with the residue of the step (2) into a nitric acid solution with a mass concentration of 70%, peeling off the residue from the filtration membrane by a ultrasonic treatment, then removing the filtration membrane by tweezers, washing the trace residue attached on the filtration membrane into the nitric acid solution by using the deionized water, thereby obtaining a second solution containing the residue and the nitric acid;

(33) (4) adding a nitric acid solution again into the second solution obtained from the step (3) to obtain a mixed solution, and heating to have the solution evaporated and dried;

(34) (5) cooling, then repeating the step (4) once again, cooling once again, and then diluting to a final volume, thereby obtaining a solution to be measured;

(35) (6) measuring the content of Co in the solution obtained from the step (5) (a measuring method can be selected from the atomic absorption spectrometry and other frequently-used methods), and then calculating the content of Co.sub.3O.sub.4 to obtain the content of Co.sub.3O.sub.4 in the lithium cobalt metal oxide powder.

(36) In this example, the calculated content of Co.sub.3O.sub.4 is 10105 ppm, and the calculated r=0.005. That is, the chemical formula is LiCo.sub.0.975Al.sub.0.02Mg.sub.0.005O.sub.2.Math.0.005Co.sub.3O.sub.4. A sample of the lithium cobalt metal oxide powder in this example is labeled as LCO-B1.

Example 5

(37) The only difference between the making method in the example 5 and that in the example 4 is in the amount of Co.sub.3O.sub.4 added in the step (2) during the making. The method for determining the content of Co.sub.3O.sub.4 in this example is the same as that in the example 4.

(38) In this example, the calculated content of Co.sub.3O.sub.4 is 21000 ppm, and the calculated r=0.0105. That is, the chemical formula is LiCo.sub.0.975Al.sub.0.02Mg.sub.0.005O.sub.2.Math.0.0105Co.sub.3O.sub.4. A sample of the lithium cobalt metal oxide powder in this example is labeled as LCO-B2.

Example 6

(39) The difference between the making method in the example 6 and that in the example 4 is that, in this example, during the making, the amount of Co.sub.3O.sub.4 added in the step (2) is varied, and TiO.sub.2 with a mol ratio of 0.5%, instead of MgO, is added in the step (2).

(40) A method for determining the content of Co.sub.3O.sub.4 in the lithium cobalt metal oxide powder is further provided in this example, including the steps of:

(41) (1) adding FeSO.sub.4, H.sub.2SO.sub.4 and H.sub.3PO.sub.4 solutions into the lithium cobalt metal oxide powder, and magnetically stirring and dissolving for 0.8 h, thereby obtaining a first solution;

(42) (2) filtering the first solution obtained from the step (1) by suction filtration, and maintaining the filtration membrane at the filtration state after the filtration is finished while washing the residue on the filtration membrane with pure water;

(43) (3) adding the filtration membrane along with the residue of the step (2) into an aqua regia solution, peeling off the residue from the filtration membrane by a ultrasonic treatment, then removing the filtration membrane by tweezers, washing the trace residue attached on the filtration membrane into the aqua regia solution, thereby obtaining a second solution containing the residue and the aqua regia;

(44) (4) adding a aqua regia solution again into the second solution obtained from the step (3) to obtain a mixed solution, and heating to have the solution evaporated and dried;

(45) (5) cooling, then repeating the step (4) once again, cooling once again, and then diluting to a final volume, thereby obtaining a solution to be measured;

(46) (6) measuring the content of Co in the solution obtained from the step (5) (a measuring method can be selected from the atomic absorption spectrometry and other frequently-used methods), and then calculating the content of Co.sub.3O.sub.4 to obtain the content of Co.sub.3O.sub.4 in the lithium cobalt metal oxide powder.

(47) In this example, the calculated content of Co.sub.3O.sub.4 is 19917 ppm, and the calculated r=0.01. That is, the chemical formula is LiCo.sub.0.975Al.sub.0.02Ti.sub.0.005O.sub.2.Math.0.01Co.sub.3O.sub.4. A sample of the lithium cobalt metal oxide powder in this example is labeled as LCO-B3.

Example 7

(48) The difference between the making method in the example 7 and that in the example 4 is that, in this example, during the making, the amount of Co.sub.3O.sub.4 added in the step (2) is varied, and TiO.sub.2 with a mol ratio of 0.5% is further added in the step (2).

(49) A method for determining the content of Co.sub.3O.sub.4 in the lithium cobalt metal oxide powder is further provided in this example, including the steps of:

(50) (1) adding CrCl.sub.2 and CuCl.sub.2 solutions, HCl and H.sub.2SO.sub.4 into the lithium cobalt metal oxide powder, and magnetically stirring and dissolving for 1.2 h, thereby obtaining a first solution;

(51) (2) filtering the first solution obtained from the step (1) by suction filtration, and maintaining the filtration membrane at the filtration state after the filtration is finished while washing the residue on the filtration membrane with pure water;

(52) (3) adding the filtration membrane along with the residue of the step (2) into a nitric acid solution with a mass concentration of 50%, peeling off the residue from the filtration membrane by a ultrasonic treatment, then removing the filtration membrane by tweezers, washing the trace residue attached on the filtration membrane into the aqua regia solution, thereby obtaining a second solution containing the residue and the aqua regia;

(53) (4) adding a nitric acid solution again into the second solution obtained from the step (3) to obtain a mixed solution, and heating to have the solution evaporated and dried;

(54) (5) cooling, then repeating the step (4) once again, cooling once again, and then diluting to a final volume, thereby obtaining a solution to be measured;

(55) (6) measuring the content of Co in the solution obtained from the step (5) (a measuring method can be selected from the atomic absorption spectrometry and other frequently-used methods), and then calculating the content of Co.sub.3O.sub.4 to obtain the content of Co.sub.3O.sub.4 in the lithium cobalt metal oxide powder.

(56) In this example, the calculated content of Co.sub.3O.sub.4 is 20130 ppm, and the calculated r=0.01. That is, the chemical formula is LiCo.sub.0.97Al.sub.0.02Mg.sub.0.005Ti.sub.0.005O.sub.2.Math.0.01Co.sub.3O.sub.4. A sample of the lithium cobalt metal oxide powder in this example is labeled as LCO-B4.

(57) The samples obtained in the examples 4-7 are subjected to a button cell capacity test. As shown in FIG. 3, it can be known by analyzing the LCO-B1 and the LCO-B2 that within a voltage range of 3.0 V to 4.6 V, at charge and discharge rates of 0.5 C, the capacity retention during the cycling is gradually increased with the increase of the content of residual Co.sub.3O.sub.4. It can be known by analyzing the LCO-B2, the LCO-B3, and the LCO-B4 that the Mg and Ni composite coating can provide the most prominent improvements on the cycle performance. FIG. 4 is the XRD spectrum of the sample obtained in the Example 5, from which it can be seen that a sharp diffraction peak corresponding to the spinel phase Co.sub.3O.sub.4 begin to occur with the increase of the content of residual Co, suggesting that the residual Co is presented in the form of the spinel phase Co.sub.3O.sub.4.