CATHODE COMPOSITE MATERIAL FOR LITHIUM-ION BATTERY (LIB), AND PREPARATION METHOD THEREOF

Abstract

The present disclosure discloses a cathode composite material for a lithium-ion battery (LIB), and a preparation method thereof. The cathode composite material for an LIB is composed of a lithium-containing matrix and a three-layer coating layer coated on a surface of the matrix, where the three-layer coating layer includes a lithium-deficient matrix material layer, a lithium-deficient lithium cobalt phosphate (LCP) layer, and a cobalt phosphate layer in sequence from inside to outside. The cathode composite material of the present disclosure can reduce the oxidation of a highly-delithiated cathode material to an electrolyte under high voltage, and has a high energy density.

Claims

1. A cathode composite material for a lithium-ion battery (LIB), comprising a lithium-containing matrix and a three-layer coating layer coated on a surface of the matrix, wherein the three-layer coating layer comprises an inner lithium-deficient matrix material layer, an intermediate lithium-deficient lithium cobalt phosphate (LCP) layer, and an outer cobalt phosphate layer.

2. The cathode composite material of claim 1, wherein the lithium-containing matrix is a layered lithium composite oxide, with a chemical formula of Li.sub.aCo.sub.1-b M.sub.bO.sub.2, wherein M is one or more selected from the group consisting of Mg, Al, M, Zr, and W, 0.95≤a≤1.1, and 0.0≤b≤0.01.

3. The cathode composite material of claim 1, wherein the lithium-deficient matrix material layer has a chemical formula of Li.sub.cCo.sub.1-bM.sub.bO.sub.2, wherein M is one or more selected from the group consisting of Mg, Al, M, Zr, and W, 0.0<c<1.0, a<c, and 0.0≤b≤0.01.

4. The cathode composite material of claim 1, wherein the lithium-deficient LCP layer has a chemical formula of Li.sub.dCoPO.sub.4, wherein 0.0<d<1.0.

5. The cathode composite material of claim 1, wherein the cobalt phosphate layer has a chemical formula of Co.sub.m(PO.sub.4).sub.n, wherein m/n=1.3 to 1.7.

6. The cathode composite material of claim 1, wherein the lithium-deficient LCP layer has a thickness of no more than 10 nm, and the cobalt phosphate layer has a thickness of no more than 10 nm.

7. The cathode composite material of claim 1, wherein the D50 particle size is from 6 μm to 23 μm.

8. A preparation method of the cathode composite material of claim 1, comprising the following steps: (1) mixing a cathode material precursor and a lithium source, and subjecting a resulting mixture to a heat treatment for 6 h to 20 h to obtain the lithium-containing matrix; and (2) mixing cobalt phosphate and the lithium-containing matrix, and subjecting a resulting mixture to a heat treatment for 3 h to 9 h to obtain the cathode composite material, wherein a mass ratio of the cobalt phosphate to the cathode material matrix is (0.005:1) to (0.5:1).

9. The preparation method of claim 8, wherein in step (2), when the mass ratio of the cobalt phosphate to the cathode material matrix is (0.005:1) to (0.02:1), the heat treatment is conducted at 400° C. to 600° C. for 3 h to 6 h.

10. The preparation method of claim 8, wherein in step (2), when the mass ratio of the cobalt phosphate to the cathode material matrix is (0.02:1) to (0.04:1), the heat treatment is conducted at 600° C. to 800° C. for 5 h to 9 h.

11. The preparation method of claim 8, wherein in step (2), when the mass ratio of the cobalt phosphate to the cathode material matrix is (0.04:1) to (0.05:1), the heat treatment is conducted at 800° C. to 900° C. for 7 h to 9 h.

12. The preparation method of claim 8, wherein the cobalt phosphate has a particle size of 5 nm to 200 nm.

13. The preparation method of claim 8, wherein the lithium-containing matrix is a layered lithium composite oxide, with a chemical formula of Li.sub.aCo.sub.1-bM.sub.bO.sub.2, wherein M is one or more selected from the group consisting of Mg, Al, Ti, Zr, and W, 0.95≤a≤1.1, and 0.0≤b≤0.01.

14. The preparation method of claim 8, wherein the lithium-deficient matrix material layer has a chemical formula of Li.sub.cCo.sub.1-bM.sub.bO.sub.2, wherein M is one or more selected from the group consisting of Mg, Al, Ti, Zr, and W, 0.0<c<1.0, a<c, and 0.0≤b≤0.01.

15. The preparation method of claim 8, wherein the lithium-deficient LCP layer has a chemical formula of Li.sub.dCoPO.sub.4, wherein 0.0<d<1.0.

16. The preparation method of claim 8, wherein the cobalt phosphate layer has a chemical formula of Co.sub.m(PO.sub.4).sub.n, wherein m/n=1.3 to 1.7.

17. The preparation method of claim 8, wherein the lithium-deficient LCP layer has a thickness of no more than 10 nm, and the cobalt phosphate layer has a thickness of no more than 10 nm.

18. The preparation method of claim 8, wherein the D50 particle size is from 6 μm to 23 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To describe the technical solutions in examples of the present disclosure or in the prior art more clearly, the accompanying drawings required for describing the examples or the prior art will be briefly described below. Apparently, the accompanying drawings in the following description show some examples of the present disclosure, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts.

[0028] FIG. 1 is a transmission electron microscopy (TEM) image of nano-cobalt phosphate;

[0029] FIG. 2 is a TEM image of a mixture of nano-cobalt phosphate and a matrix;

[0030] FIG. 3 is a TEM image of a mixture of nano-cobalt phosphate and a matrix after a heat treatment;

[0031] FIG. 4 shows X-ray diffractometry (XRD) patterns before and after the heat treatment of nano-cobalt phosphate;

[0032] FIG. 5 is a TEM image of a cross section of a cathode composite material;

[0033] FIG. 6a is an X-ray photoelectron spectroscopy (XPS) spectrum of Li and FIG. 6b is an XPS test spectrum of P;

[0034] FIG. 7 is a schematic diagram illustrating situations of a mixture of cobalt phosphate and a cathode material before and after a heat treatment:

[0035] FIG. 8 is a charge-discharge curve diagram of the cathode composite material of Example 1;

[0036] FIG. 9 shows the cycling performance of the cathode materials of Example 5 and Comparative Example 1:

[0037] FIG. 10 shows average discharge voltages of the cathode composite material of Example 2 after different cycles; and

[0038] FIG. 11 shows an electron microscopy image of the cathode composite material of Example 5 and an electron microscopy image of the cathode composite material prepared by the conventional method in Comparative Example 2.

DETAILED DESCRIPTION

[0039] In order to facilitate the understanding of the present disclosure, the present disclosure is described in detail below in conjunction with the accompanying drawings of the specification and the preferred examples, but the protection scope of the present disclosure is not limited to the following specific examples.

[0040] Unless otherwise defined, all technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are merely for the purpose of describing specific examples, and are not intended to limit the protection scope of the present disclosure.

[0041] Unless otherwise specified, various raw materials, reagents, instruments, equipment, and the like used in the present disclosure can be purchased from the market or can be prepared by existing methods.

EXAMPLE 1

[0042] A cathode composite material for an LIB is provided, which has a D50 particle size of 10 μm to 11 μm and is composed of a layered lithium composite oxide matrix with a chemical formula of Li.sub.1.01Co.sub.0.995Al.sub.0.003Mg.sub.0.002O.sub.2 and a three-layer coating layer on a surface of the matrix. The three-layer coating layer is composed of a lithium-deficient matrix material layer, a lithium-deficient LCP layer, and a cobalt phosphate layer with a chemical formula of Co.sub.3(PO.sub.4).sub.2. The cobalt phosphate layer has a thickness of 3 nm to 5 nm, and the lithium-deficient LCP layer has a thickness of 4 nm to 9 nm.

[0043] A preparation method of the cathode composite material is provided, including the following steps:

[0044] (1) cobalt oxide, lithium carbonate, aluminum oxide, and magnesium oxide were thoroughly mixed, subjected to a high-temperature heat treatment at 950° C. for 10 h, and crushed to obtain an LCO matrix with D50 of 10 μm, which had a chemical formula of Li.sub.1.01Co.sub.0.995Al.sub.0.003Mg.sub.0.002O.sub.2; and

[0045] (2) 1 Kg of the LCO matrix prepared in step (1) and 10 g of nano-cobalt phosphate Co.sub.3(PO.sub.4).sub.2.8H.sub.2O were thoroughly mixed through ball-milling, and then subjected to a heat treatment at 550° C. for 4 h to obtain the cathode composite material. The cathode composite material is numbered as LCO-A1, and the untreated LCO matrix is numbered as LCO-A0 (that is, the matrix material prepared in step (1)).

[0046] The morphology of the added nano-cobalt phosphate is shown in FIG. 1, and it can be clearly seen that particles of cobalt phosphate are nano-agglomerated. The morphology of the mixture of the nano-cobalt phosphate and the LCO matrix (before the heat treatment) is shown in the FIG. 2, and it can be clearly seen that the nano-cobalt phosphate is relatively uniformly adsorbed to a surface of the matrix, showing very uniform distribution.

[0047] The morphology of the mixture of the nano-cobalt phosphate and the LCO matrix after the heat treatment is shown in FIG. 3, and it can be seen that the surface of the matrix is uniformly coated, the formed cathode composite material has a smooth surface, and the coating layer is uniform.

[0048] An XRD pattern of the nano-cobalt phosphate after the heat treatment is shown in FIG. 4, and it can be seen that the structure of the nano-cobalt phosphate does not change greatly after the heat treatment.

[0049] Across-sectional TEM image of the cathode composite material formed after the mixture of the nano-cobalt phosphate and the LCO matrix is subjected to the heat treatment is shown in FIG. 5, and it can be clearly seen that there are obvious three layer structures with different lattice fringes at different distances from the material surface.

[0050] In order to indirectly determine element distributions at different distances from the surface, the cathode composite material prepared in this example was subjected to an acid attack treatment, and XPS was used to test element contents at different depths. Specific steps: a dilute hydrochloric acid solution with a concentration of 0.1 mol/L was prepared; 10 g of LCO-A1 was immersed in the solution for 1 min, washed with deionized water, and then dried in an oven at 80° C., and a resulting product was numbered as LCO-A2; and 10 g of LCO-AI was immersed in the solution for 3 min, washed with deionized water, and then dried in an oven at 80° C., and a resulting product was numbered as LCO-A3. The LCO-A1, LCO-A2, and LCO-A3 each were subjected to an XPS test. Test results are shown in FIG. 6. It can be seen from FIG. 6a that the Li content gradually increases from outside to inside, and it can be seen from FIG. 6b that the phosphorus content gradually decreases from outside to inside, which corresponds to the three-layer coating layer structure model and TEM test results of the cathode composite material. A schematic diagram illustrating situations of the mixture of the cobalt phosphate and the cathode material before and after the heat treatment is shown in FIG. 7.

[0051] The LCO-A0 and LCO-A1 were subjected to a charge-discharge test. Charge-discharge curves are shown in FIG. 8, and it can be seen from the figure that the electrochemical polarization degree of the coated cathode composite material is significantly reduced during the charge-discharge process.

EXAMPLE 2

[0052] A cathode composite material for an LIB is provided, which has a D50 particle size of 19 μm to 20 μm and is composed of a layered lithium composite oxide matrix with a chemical formula of Li.sub.1.01Co.sub.0.996Al.sub.0.002Ti.sub.0.001Mn.sub.0.001O.sub.2 and a three-layer coating layer on a surface of the matrix. The three-layer coating layer is composed of a lithium-deficient matrix material layer, a lithium-deficient LCP layer, and a cobalt phosphate layer with a chemical formula of Co.sub.3.5(PO.sub.4).sub.2. The cobalt phosphate layer has a thickness of 3 nm to 5 nm, and the lithium-deficient LCP layer has a thickness of 3 nm to 6 nm.

[0053] A preparation method of the cathode composite material is provided, including the following steps:

[0054] (1) cobalt oxide, lithium carbonate, aluminum oxide, titanium oxide, and manganese oxide were thoroughly mixed, subjected to a high-temperature heat treatment at 1,000° C. for 10 h, and crushed to obtain an LCO matrix with D50 of 19 μm, which had a chemical formula of Li.sub.1.01Co.sub.0.996Al.sub.0.002Ti.sub.0.001Mn.sub.0.001O.sub.2; and

[0055] (2) 1 Kg of the LCO matrix prepared in the above step and 30 g of nano-cobalt phosphate Co.sub.3.5(PO.sub.4).sub.2.8H.sub.2O were thoroughly mixed through ball-milling, and then subjected to a heat treatment at 600° C. for 5 h to obtain the cathode composite material. The cathode composite material is numbered as LCO-C1, and the untreated LCO matrix is numbered as LCO-C0 (that is, the matrix material prepared in step (1)).

[0056] The LCO-C0 and LCO-C1 were subjected to a continuous discharge test, and average discharge voltages after different cycles were recorded. Results are shown in FIG. 10, and it can be seen from the figure that the average discharge voltage of the cathode composite material in this example after multiple cycles is significantly higher than that of the uncoated cathode material, which proves that the cycling stability of the cathode composite material of this example is better than that of the uncoated cathode material.

EXAMPLE 3

[0057] A cathode composite material for an LIB is provided, which has a D50 particle size of 21 μm to 22 μm and is composed of a layered lithium composite oxide matrix with a chemical formula of Li.sub.1.015Co.sub.0.995Ti.sub.0.001Ca.sub.0.002Mn.sub.0.002O.sub.2 and a three-layer coating layer on a surface of the matrix. The three-layer coating layer is composed of a lithium-deficient matrix material layer, a lithium-deficient LCP layer, and a cobalt phosphate layer with a chemical formula of Co.sub.2.8(PO.sub.4).sub.2. The cobalt phosphate layer has a thickness of 4 nm to 6 nm, and the lithium-deficient LCP layer has a thickness of 6 nm to 10 nm.

[0058] A preparation method of the cathode composite material is provided, including the following steps:

[0059] (1) cobalt oxide, lithium carbonate, calcium oxide, titanium oxide, and manganese oxide were thoroughly mixed, subjected to a high-temperature heat treatment at 1.100° C. for 12 h, and crushed to obtain an LCO matrix with D50 of 21 μm, which had a chemical formula of Li.sub.1.015Co.sub.0.995Ti.sub.0.001Ca.sub.0.002Mn.sub.0.002O.sub.2; and

[0060] (2) 1 Kg of the LCO matrix prepared in the above step and 50 g of nano-cobalt phosphate Co.sub.2.8(PO.sub.4)2.8H.sub.2O were thoroughly mixed through ball-milling, and then subjected to a heat treatment at 850° C. for 8 h to obtain the cathode composite material. The cathode composite material is numbered as LCO-D1, and the untreated LCO matrix is numbered as LCO-D0 (that is, the matrix material prepared in step (1)).

[0061] Square aluminum-shell batteries fabricated by LCO-D0 and LCO-D1 were tested for high-temperature storage performance. Results are shown in Table 1, and it can be seen from the test results that a thickness increase of a battery fabricated by the cathode composite material with the three-layer coating layer structure in this example under high temperature is significantly lower than that of a battery fabricated by the uncoated cathode material under the same conditions, indicating that the cathode composite material of this example has better high-temperature stability.

TABLE-US-00001 TABLE 1 High-temperature storage performance of square aluminum-shell batteries LCO-D0 LCO-D1 Battery thickness increase after 6 h at 85° C. (%) 17.7 9.8 Battery thickness increase after 7 d at 60° C. (%) 45.2 26

EXAMPLE 4

[0062] A cathode composite material for an LIB is provided, which has a D50 particle size of 20 μm to 21 μm and is composed of a layered lithium composite oxide matrix with a chemical formula of Li.sub.1.01Co.sub.0.996Al.sub.0.002Ti.sub.0.002O.sub.2 and a three-layer coating layer on a surface of the matrix. The three-layer coating layer is composed of a lithium-deficient matrix material layer, a lithium-deficient LCP layer, and a cobalt phosphate layer with a chemical formula of Co.sub.3(PO.sub.4).sub.2. The cobalt phosphate layer has a thickness of 5 nm to 9 nm, and the lithium-deficient LCP layer has a thickness of 6 nm to 10 nm.

[0063] A preparation method of the cathode composite material is provided, including the following steps:

[0064] (1) cobalt oxide, lithium carbonate, aluminum oxide, and titanium oxide were thoroughly mixed, subjected to a heat treatment at 1,000° C. for 12 h, and crushed to obtain an LCO matrix with D50 of 20 μm, which had a chemical formula of Li.sub.1.01Co.sub.0.996Al.sub.0.002Ti.sub.0.002O.sub.2; and

[0065] (2) 1 Kg of the LCO matrix prepared in the above step and 20 g of nano-cobalt phosphate Co.sub.3(PO.sub.4).sub.2.8H.sub.2O were thoroughly mixed through ball-milling, and then subjected to a heat treatment at 500° C. for 6 h to obtain the cathode composite material. The cathode composite material is numbered as LCO-B1, and the untreated LCO matrix is numbered as LCO-B0 (that is, the matrix material prepared in step (1)).

EXAMPLE 5

[0066] A cathode composite material for an LIB is provided, which has a D50 particle size of 20 μm to 21 μm and is composed of a layered lithium composite ox ide matrix with a chemical formula of Li.sub.1.005Co.sub.0.995Al.sub.0.003Mg.sub.0.001Ti.sub.0.002O.sub.2 and a three-layer coating layer on a surface of the matrix. The three-layer coating layer is composed of a lithium-deficient matrix material layer, a lithium-deficient LCP layer, and a cobalt phosphate layer with a chemical formula of Co.sub.3(PO.sub.4).sub.2. The cobalt phosphate layer has a thickness of 2 nm to 6 nm, and the lithium-deficient LCP layer has a thickness of 5 nm to 9 nm.

[0067] A preparation method of the cathode composite material is provided, including the following steps:

[0068] (1) cobalt oxide, lithium carbonate, aluminum oxide, and magnesium oxide were thoroughly mixed, subjected to a heat treatment at 1,010° C. for 12 h, and crushed to obtain an LCO matrix with D50 of 20 μm, which had a chemical formula of Li.sub.1.005Co.sub.0.995Al.sub.0.003Mg.sub.0.001Ti.sub.0.002O.sub.2; and

[0069] (2) 1 Kg of the LCO matrix prepared in the above step and 11 g of nano-cobalt phosphate Co.sub.3(PO.sub.4).sub.2.8M.sub.2O were thoroughly mixed through ball-milling, and then subjected to a heat treatment at 500° C. for 5 h to obtain the cathode composite material. The cathode composite material is numbered as LCO-F1.

COMPARATIVE EXAMPLE 1

[0070] A preparation method of a cathode composite material includes the following steps:

[0071] (1) cobalt oxide, lithium carbonate, aluminum oxide, and titanium oxide were thoroughly mixed, subjected to a heat treatment at 1,000° C. for 12 h, and crushed to obtain an LCO matrix with D50 of 20 μm, which had a chemical formula of Li.sub.1.01Co.sub.0.996Al.sub.0.002Ti.sub.0.002O.sub.2; and

[0072] (2) 1 Kg of the LCO matrix prepared in the above step and 20 g of purchased cobalt phosphate (microscale) Co.sub.3(PO.sub.4)2.8H.sub.2O were thoroughly mixed through ball-milling, and then subjected to a heat treatment at 500° C. for 6 h to obtain the cathode composite material, numbered as LCO-B2.

[0073] The initial discharge capacity and cycling performance were tested for LCO-B0, LCO-B1, and LCO-B2. Results are shown in Table 2 and FIG. 9, and it can be seen from Table 2 and FIG. 9 that the cathode composite material prepared by coating the cathode material with the purchased micro-cobalt phosphate has a large capacity loss when used for the first time, and shows cycling stability that is improved to some extent compared with that of the uncoated cathode material; and in contrast, the cathode composite material prepared by coating the cathode material with nano-cobalt phosphate (namely, the cathode composite material of Example 4) has no capacity loss when used for the first time under the same conditions, and shows cycling performance that is improved significantly.

TABLE-US-00002 TABLE 2 Test results of the initial discharge capacity LCO-B0 LCO-B1 LCO-B2 Initial capacity (mAhg.sup.−1) 211.2 211.0 209.9

COMPARATIVE EXAMPLE 2

[0074] A preparation method of the cathode composite material is provided, including the following steps:

[0075] (1) 11.9 g of cobalt chloride hexahydrate was dissolved in 1 L of deionized water to obtain a solution A, 5.2 g of sodium dihydrogen phosphate dihydrate was dissolved in 1 L of deionized water to obtain a solution B, and the solution A and the solution B were mixed; a final pH of a mixed solution was controlled to 7, 1 Kg of an LCO matrix was added, and a resulting mixture was thoroughly stirred; and the LCO matrix was dried at 80° C. to obtain cobalt phosphate-coated LCO. An amount of phosphate coated by the wet method is the same as that in Example 5; and

[0076] (2) the coated LCO was subjected to a heat treatment at 500° C. for 5 h to obtain a product, numbered as LCO-F2.

[0077] The morphologies of LCO-F1 and LCO-F2 are shown in FIG. 11, and it can be seen from FIG. 11 that, in the cathode composite material of Example 5, phosphate is uniformly distributed and coated on the surface of the cathode material, but in the composite prepared by the conventional method, phosphate is mostly attached to the surface of the cathode material in an agglomerated state (the structure circled in FIG. 11 indicates the agglomerated cobalt phosphate).