LITHIUM ION BATTERY AND POSITIVE ELECTRODE MATERIAL THEREOF

Abstract

The present invention provides a lithium ion battery and positive electrode material thereof. The positive electrode material includes a high nickel material having a chemical formula of LiNi.sub.xM.sub.1-xO.sub.2 and a coating layer, wherein 0.5X<1, M is selected from at least one of Co, Mn, Al, Mg, Ti and Zr, a specific surface area of the positive electrode material is 0.2 to 0.6 m.sup.2/g, and a residual lithium content on a surface of the positive electrode material is 200 to 1000 ppm. Compared with the prior art, the positive electrode material for lithium ion battery of the present invention is prepared by solid phase reaction, which not only can significantly reduce the residual lithium content on the surface of the positive electrode material, but also can avoid increase of the specific surface area of the positive electrode material for lithium ion battery.

Claims

1. A positive electrode material for lithium ion battery comprising a high nickel material having a chemical formula of LiNi.sub.xM.sub.1-xO.sub.2 and a coating layer, wherein 0.5x<1, M is selected from at least one of Co, Mn, Al, Mg, Ti and Zr, a specific surface area of the positive electrode material is 0.2 to 0.6 m.sup.2/g, and a residual lithium content on a surface of the positive electrode material is 200 to 1000 ppm.

2. The positive electrode material of claim 1, wherein the specific surface area of the positive electrode material is 0.3 to 0.5 m.sup.2/g.

3. The positive electrode material of claim 1, wherein the coating layer comprising at least one of lithium phosphate, lithium sulfate, lithium nitrate and lithium fluoride.

4. A method for preparing the positive electrode material of claim 1, comprising the steps of: (1) converting residual lithium on a surface of a high nickel material into stable lithium salts via solid phase reaction and obtaining an intermediate product; and (2) sintering the intermediate product obtained in step (1) and obtaining the positive electrode material for lithium ion battery.

5. The method of claim 4, wherein in step (1), the solid phase reaction comprises the step of mixing the high nickel material with at least one of phosphates, sulfates, nitrates and fluorides and reacting.

6. The method of claim 5, wherein an add amount of at least one of phosphates, sulfates, nitrates and fluorides is calculated based on the residual lithium content on the surface of the high nickel material.

7. The method of claim 6, wherein the residual lithium content on the surface of the high nickel material is calculated via chemical titration method.

8. The method of claim 4, wherein in step (2), a temperature for sintering the intermediate product is 400 to 800 C., a time for sintering the intermediate product is 3 to 12 h, and a heating rate for sintering the intermediate product is 1 to 5 C./min.

9. The method of claim 8, wherein the temperature for sintering the intermediate product is 500 to 600 C., the time for sintering the intermediate product is 6 to 8 h, and the heating rate for sintering the intermediate product is 2 to 3 C./min.

10. A lithium ion battery, comprising a positive electrode, a negative electrode, a separator between the positive electrode and negative electrode, and electrolyte, wherein the positive electrode comprises the positive electrode material for lithium ion battery of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Other advantages and novel features will be drawn from the following detailed description of preferred embodiments with the attached drawings, in which:

[0028] FIG. 1 depicts an SEM image (30000) of a positive electrode material for lithium ion battery according to Comparative Example 1;

[0029] FIG. 2 depicts an SEM image (30000) of a positive electrode material for lithium ion battery according to Example 1 of the present invention;

[0030] FIG. 3 depicts an SEM image (30000) of a positive electrode material for lithium ion battery according to Comparative Example 4;

[0031] FIG. 4 depicts an energy dispersive X-ray spectrum of phosphorus element distribution on a surface of the positive electrode material for lithium ion battery according to Example 1 of the present invention;

[0032] FIG. 5 depicts a comparison chart of cycle stability curves of positive electrode materials for lithium ion battery of Examples 8 to 9 of the present invention and Comparative Examples 7 to 8; and

[0033] FIG. 6 depicts a comparison chart of gas production performance during storage of positive electrode materials for lithium ion battery of Examples 8 to 9 of the present invention and Comparative Examples 7 to 8.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0034] Example embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.

EXAMPLE 1

[0035] The high nickel material of Example 1 has a chemical formula of LiNi.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2. The method for preparing the positive electrode material for lithium ion battery of Example 1 includes the steps of:

[0036] determining the residual lithium (LiOH, Li.sub.2CO.sub.3) content on the surface of the high nickel material by chemical titration method, and calculating the theoretical amount of NH.sub.4H.sub.2PO.sub.4 required for complete precipitation of lithium residues;

[0037] fully mixing the high nickel material with NH.sub.4H.sub.2PO.sub.4 and obtaining an intermediate product, wherein a molar ratio of NH.sub.4H.sub.2PO.sub.4 added to the residual lithium (Li.sup.+) content on the surface of the high nickel material is 1: 3; and

[0038] sintering the intermediate product at 500 C. for 6 h at a heating rate of 2 C./min, and obtaining the positive electrode material for lithium ion battery having a coating layer of lithium phosphate. The SEM image of the positive electrode material for lithium ion battery of Example 1 is shown in FIG. 2, and the EDS diagram of phosphorus element distribution on the surface is shown in FIG. 4.

EXAMPLE 2

[0039] The high nickel material of Example 2 has a chemical formula of LiNi.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2. The method for preparing the positive electrode material for lithium ion battery of Example 2 differs from Example 1 in that, in Example 2, the heating rate is 5 C./min and the intermediate product is sintered at 600 C. for 4 h. The positive electrode material for lithium ion battery obtained has a coating layer of lithium phosphate.

EXAMPLE 3

[0040] The high nickel material of Example 3 has a chemical formula of LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2. The method for preparing the positive electrode material for lithium ion battery of Example 3 differs from Example 1 in that, in Example 3, the heating rate is 5 C./min and the intermediate product is sintered at 700 C. for 4 h. The positive electrode material for lithium ion battery obtained has a coating layer of lithium phosphate.

EXAMPLE 4

[0041] The high nickel material of Example 4 has a chemical formula of LiNi.sub.0.5Co.sub.0.5O.sub.2. The method for preparing the positive electrode material for lithium ion battery of Example 4 differs from Example 1 in that, in Example 4, the heating rate is 2 C./min and the intermediate product is sintered at 800 C. for 3 h. The positive electrode material for lithium ion battery obtained has a coating layer of lithium phosphate.

EXAMPLE 5

[0042] The high nickel material of Example 5 has a chemical formula of LiNi.sub.0.6Co.sub.0.2Mn.sub.0.15Ti.sub.0.05O.sub.2. The method for preparing the positive electrode material for lithium ion battery of Example 5 includes the steps of:

[0043] determining the residual lithium (LiOH, Li.sub.2CO.sub.3) content on the surface of the high nickel material by chemical titration method, and calculating the theoretical amount of (NH.sub.4).sub.2SO.sub.4 required for complete precipitation of lithium residues; fully mixing the high nickel material with (NH.sub.4).sub.2SO.sub.4 and obtaining an intermediate product, wherein a molar ratio of (NH.sub.4).sub.2SO.sub.4 added to the residual lithium (Li.sup.+) content on the surface is 1: 2; and

[0044] sintering the intermediate product at 500 C. for 6 h at a heating rate of 2 C./min and obtaining the positive electrode material for lithium ion battery having a coating layer of lithium sulfate.

EXAMPLE 6

[0045] The high nickel material of Example 6 has a chemical formula of LiNi.sub.0.6Co.sub.0.2Mn.sub.0.15Zr.sub.0.05O.sub.2. The method for preparing the positive electrode material for lithium ion battery of Example 6 includes the steps of:

[0046] determining the residual lithium (LiOH, Li.sub.2CO.sub.3) content on the surface of the high nickel material by chemical titration method, and calculating the theoretical amount of NH.sub.4NO.sub.3 required for complete precipitation of lithium residues;

[0047] fully mixing the high nickel material with NH.sub.4NO.sub.3 and obtaining an intermediate product, wherein a molar ratio of NH.sub.4NO.sub.3 added to the residual lithium (Li.sup.+) content on the surface is 1:1; and

[0048] sintering the intermediate product at 500 C. for 6 h at a heating rate of 2 C./min and obtaining a positive electrode material for lithium ion battery having a coating layer of lithium nitrate.

EXAMPLE 7

[0049] The high nickel material of Example 7 has a chemical formula of LiNi.sub.0.5Co.sub.0.25Mn.sub.0.25O.sub.2. The method for preparing the positive electrode material for lithium ion battery of Example 7 includes the steps of:

[0050] determining the residual lithium (LiOH, Li.sub.2CO.sub.3) content on the surface of the high nickel material by chemical titration method, and calculating the theoretical amount of NH.sub.4F and NH.sub.4NO.sub.3 required for complete precipitation of lithium residues;

[0051] fully mixing the high nickel material with NH.sub.4F and NH.sub.4NO.sub.3 and obtaining an intermediate product, wherein a molar ratio of NH.sub.4F and NH.sub.4NO.sub.3 added to the residual lithium (Li.sup.+) content on the surface is 1:1; and

[0052] sintering the intermediate product at 400 C. for 8 h at a heating rate of 2 C./min and obtaining the positive electrode material for lithium ion battery having a coating layer including lithium fluoride and lithium nitrate.

EXAMPLE 8

[0053] The positive electrode material for lithium ion battery of Example 1, the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) are added into N-methylpyrrolidone solvent system at a weight ratio of 94:3:3 to obtain a mixture, the mixture is fully stirred to obtain a slurry, the slurry is coated on an aluminum foil, dried and cold pressed to obtain a positive electrode.

[0054] The active materials artificial graphite and hard carbon, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR) and the thickening agent carbon methyl cellulose sodium (CMC) are added into deionized water solvent system at a weight ratio of 90:5:2:2:1 to obtain a mixture, the mixture is fully stirred to obtain a slurry, and the slurry is coated on a copper foil, dried and cold pressed to obtain a negative electrode.

[0055] PE porous polymer film is used as the separator.

[0056] The positive electrode, the separator and the negative electrode are stacked in order with the separator set between the positive electrode and the negative electrode to obtain an electrode group. The electrode group is wound to obtain a bare cell. The bare cell is placed in a package. The electrolyte is injected into the package. A lithium ion battery is finally obtained after encapsulating the battery package.

EXAMPLE 9

[0057] Example 9 differs from Example 8 in that, in Example 9, the positive electrode material is the positive electrode material for lithium ion battery obtained in Example 2.

COMPARATIVE EXAMPLE 1

[0058] The positive electrode material of Comparative Example 1 is an untreated positive electrode material having a chemical formula of LiNi.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2, and the SEM image of Comparative Example 1 is shown in FIG. 1.

COMPARATIVE EXAMPLE 2

[0059] The positive electrode material of Comparative Example 2 is an untreated positive electrode material having a chemical formula of LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2.

COMPARATIVE EXAMPLE 3

[0060] The positive electrode material of Comparative Example 3 is an untreated positive electrode material having a chemical formula of LiNi.sub.0.5Co.sub.0.5O.sub.2.

COMPARATIVE EXAMPLE 4

[0061] Comparison Experiment of Removing Residual Lithium from High Nickel Material by Liquid Phase Method

[0062] The high nickel material has a structural formula of LiNi.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2. The residual lithium (LiOH, Li.sub.2CO.sub.3) content on the surface of the high nickel material is determined by chemical titration method. The theoretical amount of phosphate ion required for complete precipitation of lithium residues is calculated. The calculated value is converted to the dosage of NH.sub.4H.sub.2PO.sub.4. Corresponding NH.sub.4H.sub.2PO.sub.4 is dispersed in water to obtain a NH.sub.4H.sub.2PO.sub.4 solution.

[0063] The high nickel material is soaked in NH.sub.4H.sub.2PO.sub.4 solution and stirred for 3 hours to disperse evenly to obtain an intermediate product. The intermediate product is then dried.

[0064] The obtained dried intermediate product is sintered at 500 C. in an air atmosphere for 6 h at a heating rate of 3 C./min to obtain a high nickel material with the residual lithium removed by liquid phase method, the SEM image of which is shown in FIG. 3.

COMPARATIVE EXAMPLE 5

[0065] Comparison Experiment of Removing Residual Lithium from the High Nickel Material by Liquid Phase Method

[0066] The high nickel material has a structural formula of LiNi.sub.0.5Co.sub.0.5O.sub.2. The residual lithium (LiOH, Li.sub.2CO.sub.3) content on the surface of the high nickel material is determined by chemical titration method. The theoretical amount of phosphate ion required for complete precipitation of lithium residues is calculated. The calculated value is converted to the dosage of NH.sub.4H.sub.2PO.sub.4. Corresponding NH.sub.4H.sub.2PO.sub.4 is dispersed in ethanol to obtain a NH.sub.4H.sub.2PO.sub.4 solution.

[0067] The high nickel material is soaked in NH.sub.4H.sub.2PO.sub.4 solution and stirred for 3 hours to disperse evenly to obtain an intermediate product. The intermediate product is then dried.

[0068] The obtained dried intermediate product is sintered at 500 C. in an air atmosphere for 6 h at a heating rate of 3 C./min to obtain a high nickel material with the residual lithium removed by liquid phase method.

COMPARATIVE EXAMPLE 6

[0069] Comparison Experiment of Removing Residual Lithium from High Nickel Material by Liquid Phase Method

[0070] The high nickel material has a structural formula of LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2. The residual lithium (LiOH, Li.sub.2CO.sub.3) content on the surface of the high nickel material is determined by chemical titration method. The theoretical amount of phosphate ion required for complete precipitation of lithium residues is calculated. The calculated value is converted to the dosage of NH.sub.4H.sub.2PO.sub.4. Corresponding NH.sub.4H.sub.2PO.sub.4 is dispersed in water to obtain a NH.sub.4H.sub.2PO.sub.4 solution.

[0071] The high nickel material is soaked in NH.sub.4H.sub.2PO.sub.4 solution and stirred for 3 hours to disperse evenly to obtain an intermediate product. The intermediate product is then dried.

[0072] The obtained dried intermediate product is sintered at 500 C. in an air atmosphere for 6 h at a heating rate of 3 C./min to obtain a high nickel material with the residual lithium removed by liquid phase method.

COMPARATIVE EXAMPLE 7

[0073] The high nickel material of Comparative Example 1, the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) are added into N-methylpyrrolidone solvent system at a weight ratio of 94:3:3 to obtain a mixture, the mixture is fully stirred to obtain a slurry, and the slurry is coated on an aluminum foil, dried and cold pressed to obtain a positive electrode.

[0074] The active materials artificial graphite and hard carbon, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR) and the thickening agent carbon methyl cellulose sodium (CMC) are added in to deionized water solvent system at a weight ratio of 90:5:2:2:1 to obtain a mixture, the mixture is fully stirred to obtain a slurry, the slurry is coated on a copper foil, dried and cold pressed to obtain a negative electrode.

[0075] PE porous polymer film is used as a separator.

[0076] The positive electrode, the separator and the negative electrode are stacked in order with the separator set between the positive electrode and the negative electrode to obtain an electrode group. The electrode group is wound to obtain a bare cell. The bare cell is placed in a package. The electrolyte is injected into the package. A lithium ion battery is finally obtained after encapsulating the battery package.

COMPARATIVE EXAMPLE 8

[0077] Comparative Example 8 differs from Comparative Example 7 only in that the high nickel material of Comparative Example 1 is the high nickel material obtained in Comparative Example 4 via removing the residual lithium by liquid phase method.

COMPARATIVE EXAMPLE 9

[0078] Comparative Example 9 differs from Comparative Example 7 only in that the high nickel material of Comparative Example 9 is the high nickel material obtained in Comparative Example 5 via removing the residual lithium by liquid phase method.

Comparative Experiment 1

Comparison of Residual Lithium (Li.SUP.+.) Content and Specific Surface Area (BET)

[0079] The positive electrode materials for lithium ion battery prepared in Examples 1 to 7 and Comparative Examples 1 to 6 are subjected to comparative experiment of residual lithium (Li.sup.+) content and specific surface area (BET) under same condition.

[0080] Method of comparative experiment of residual lithium (Li.sup.+) content uses acid-base titration method, in which hydrochloric acid standard solution is used to titrate lithium carbonate and lithium hydroxide in the high-nickel material, pH electrode is used as the indicator electrode, the end point is determined by a sudden change of the potential change, and the residual lithium content on the surface of the positive electrode material is calculated. The experimental results are shown in Table 1.

TABLE-US-00001 TABLE 1 Residual lithium content and specific surface area of the high nickel material of Examples 1 to 7 and Comparative Examples 1 to 6 Items Unit E 1 E 2 E 3 E 4 E 5 E 6 E 7 CE 1 CE 2 CE 3 CE 4 CE 5 CE 6 Li.sup.+ ppm 720 750 857 360 734 746 350 1362 1532 735 754 372 865 BET m.sup.2/g 0.28 0.30 0.37 0.35 0.36 0.35 0.32 0.27 0.35 0.32 0.58 0.71 0.72
Example 1 is simplified as E 1, Comparative Example 1 is simplified as CE 1, and so on.

[0081] It can be seen from Table 1, compared with the original high nickel material in Comparative Examples 1 to 3, the residual lithium content on the surface of the positive electrode material prepared by the method of the present invention is reduced remarkably, which indicates that the residual lithium on the surface of the positive electrode material is converted into other lithium salts effectively. According to FIG. 4, the residual lithium (Li.sub.2CO.sub.3 and LiOH) is converted to Li.sub.3PO.sub.4. In addition, compared with the original high nickel material in Comparative Examples 1 to 3, the BET of the positive electrode material prepared by the method of the present invention does not increase significantly, while the BET of the material prepared by the liquid phase method is doubled.

Comparative Experiment 2

Comparison of Cycle Stability

[0082] The positive electrode materials for lithium-ion battery prepared in Examples 8 to 9 and Comparative Examples 7 to 8 are subjected to the experiment of cycle stability under same condition.

[0083] In the experiment, the battery is charged to 4.2V at 1 C (C for the battery capacity) constant current and is discharged at 1 C constant current at 25 C.

[0084] The experimental results are shown in FIG. 5. It can be seen that, the cycle stability of the battery having the positive electrode material prepared by the method of the present invention is improved remarkably, which indicates that the coating layer on the surface of the positive electrode material for lithium ion battery can improve the cycle stability effectively. At the same time, via comparison of the data of Examples 8 to 9 and Comparative Examples 7 to 8, it can be found that the battery having the positive electrode material with the residual lithium removed by liquid phase method has poor cycle stability. Also referring to the specific surface area data in Table 1, it is shown that the contact area between the material modified by liquid phase method and the electrolyte is larger, the side reaction is more and the cycle stability is worse.

Comparative Experiment 3

[0085] Comparison of Gas Production Performance during Storage

[0086] The positive electrode materials for lithium-ion battery prepared in Examples 8 to 9 and Comparative Examples 7 to 8 are subjected to the comparative experiment of gas production performance during storage under same condition.

[0087] The experimental method includes the steps of: fully charging the batteries, placing the batteries in an incubator at 60 C., and testing the volume of each battery every 15 days.

[0088] The experimental results are shown in FIG. 6. It can be seen from FIG. 6 that gas generated during storage of the battery having the positive electrode material prepared by the method of the present invention is less. The liquid-phase method can hardly reduce the gas generated during storage, mainly due to the damage to the surface of the material due to liquid phase treatment, exposure of more active sites, larger specific surface area of the material, which results in more side effects under high temperature conditions. Thus, the amount of gas produced of the Comparative Example is relatively larger relative to the method of the present invention.

[0089] Compared with the prior art, the lithium ion battery and the positive electrode material thereof according to the present invention have the following advantages:

[0090] 1) The positive electrode material for lithium ion battery of the present invention is a high nickel material having low residual lithium content on a surface thereof and desirable cycle performance. There is no significant increase in specific surface area.

[0091] 2) The method for preparing the positive electrode material for lithium ion battery of the present invention includes the step of removing the residual lithium on the surface of the high nickel material via solid phase reaction method, which can avoid increase of the specific surface area of the material due to the liquid phase reaction.

[0092] 3) The lithium ion battery of the present invention adopts the high nickel material having low residual lithium content on the surface thereof and a small specific surface area as the positive electrode material. The lithium ion battery has a slower capacity fading rate during the cycle process.

[0093] Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although the foregoing descriptions describe example embodiments, it should be appreciated that alternative embodiments without departing from the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.