WO2021223635A1 - Lithium cobaltate positive electrode material, preparation method therefor and use thereof - Google Patents

Abstract

The present invention relates to the technical field of positive electrode materials of lithium ion batteries, and in particular, to a lithium cobaltate positive electrode material, a preparation method therefor and use thereof. The lithium cobaltate positive electrode material comprises a substrate and a coating layer coated on the outer surface of the substrate. The substrate is a lithium cobaltate substrate doped with a metal element. The composition of the coating layer is represented by a general formula of LiAlO₂/LiF. The lithium cobaltate positive electrode material provided by the present invention has excellent structural stability and electrochemical performance, and in particular, has a high gram specific capacity and good cycle performance under a high voltage, thereby prolonging the actual service life of the lithium cobaltate positive electrode material under high voltage.

Description

Lithium cobalt oxide cathode material and preparation method and application thereof

Cross-references to related applications

This application claims the rights and interests of the Chinese patent application 202010390412.6 filed on May 8, 2020, the content of which is incorporated herein by reference.

Technical field

The invention relates to the technical field of lithium ion battery cathode materials, in particular to a lithium cobalt oxide cathode material and a preparation method and application thereof.

Background technique

The "light and thin" development of smart mobile terminal products has put forward higher requirements for the specific energy of lithium-ion batteries, and lithium cobalt oxide relies on its higher discharge voltage platform and higher volume under high voltage (4.5V). Energy density has become one of the most ideal cathode materials for small high-energy-specific batteries.

In the prior art, the theoretical capacity of the lithium cobalt oxide cathode material is 274mAh/g. The charge cut-off voltage of the material is continuously increased to release more lithium to release higher gram-specific energy. The conventional 4.2V lithium cobalt oxide has a capacity of about 140mAh/g, 4.35V lithium cobalt oxide capacity is about 164mAh/g, 4.4V lithium cobalt oxide capacity is about 173mAh/g. However, more lithium ions are released from the crystal lattice, which will cause structural instability, irreversible phase transition, and collapse of internal structure; the degree of delithiation on the surface of the material is higher, and the structural phase change extends from the surface of the particle to the inside of the particle; Co, whose surface is in a high valence state, has strong oxidizing properties and is easy to catalyze the electrolyte and cause side reactions with it. These factors will cause the cycle life to decay faster and affect the practical application life of high-voltage lithium cobalt oxide.

In order to solve the practical use of lithium cobalt oxide materials under high pressure, there is an urgent need to provide a new lithium cobalt oxide cathode material.

Summary of the invention

The purpose of the present invention is to improve the structural instability and fast cycle life decay of lithium cobalt oxide cathode material in a high delithiation state, and to provide a lithium cobalt oxide cathode material and a preparation method and application thereof. The lithium cobalt oxide cathode material Has excellent structural stability and cycle performance.

In order to achieve the above objective, the first aspect of the present invention provides a lithium cobalt oxide cathode material. The cathode material includes a substrate and a coating layer covering the outer surface of the substrate. The substrate is lithium cobalt oxide doped with metal elements. Matrix; wherein the composition of the coating layer is represented by the general formula LiAlO ₂ /LiF.

Preferably, the chemical formula of the lithium cobalt oxide matrix is Li _x Co _y Al _z M _a O ₂ , wherein 0.95<x<1.05, 0.94<y<0.985, 0.01<z<0.04, 0.005<a<0.02, y +z+a=1, M is a metal element and M is not Al.

Preferably, based on the total weight of the lithium cobalt oxide cathode material, the content of the coating layer is 0.1-1% by weight, more preferably 0.3-0.7% by weight.

The second aspect of the present invention provides a method for preparing a lithium cobalt oxide cathode material, the method comprising:

(1) The cobalt source, the lithium source, and the metal compound are sequentially mixed and sintered to obtain a metal element-doped lithium cobalt oxide matrix;

(2) _{Perform a second mixing of Li 2} CO ₃ and AlF ₃ to obtain a coating agent mixture;

(3) Perform the third mixing and the second sintering of the lithium cobalt oxide matrix and the coating agent mixture in sequence to obtain a lithium cobalt oxide cathode material with a coating layer;

Wherein, the cobalt source is selected from Al-doped cobalt tetroxide.

Preferably, the first sintering includes one-stage calcination and two-stage calcination, wherein the conditions of the one-stage calcination include: a temperature of 700-900°C, preferably 750-850°C, and a time of 2-10 hours, preferably 3-6 hours; The conditions of the two-stage calcination include: the temperature is 1000-1200°C, preferably 1000-1100°C, and the time is 2-20h, preferably 5-12h.

The third aspect of the present invention provides a lithium cobalt oxide cathode material prepared by the above method.

The fourth aspect of the present invention provides an application of the above-mentioned lithium cobalt oxide cathode material in a lithium ion battery.

Compared with the prior art, the present invention has the following advantages:

(1) The present invention obtains a multi-phase coated modified positive electrode material by doping the matrix of the lithium cobalt oxide positive electrode material with metal elements, and carrying out the _{composite coating of LiAlO 2 and LiF on the outer surface;}

(2) The lithium cobalt oxide cathode material provided by the present invention has excellent structural stability and electrochemical performance, especially has a higher gram specific capacity and good cycle performance under high voltage, and prolongs the lithium cobalt oxide cathode material in high temperature. The actual service life under voltage;

(3) The preparation method provided by the present invention has simple process flow, easy control of reaction conditions, and is suitable for industrial production.

Description of the drawings

FIG. 1 is a TEM image of lithium cobalt oxide cathode material S1 prepared in Example 1;

Figure 2 is the XRD pattern of the blank test 1-2 in Example 1.

Detailed ways

The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the end values of each range, between the end values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges. These values The scope should be considered as specifically disclosed herein.

The first aspect of the present invention provides a lithium cobalt oxide cathode material. The cathode material includes a substrate and a coating layer covering the outer surface of the substrate. The substrate is a lithium cobalt oxide substrate doped with metal elements; The composition of the coating layer is represented by the general formula LiAlO ₂ /LiF.

In the present invention, under no special circumstances, the metal element-doped lithium cobalt oxide matrix means that the lithium cobalt oxide matrix is doped with other metal elements. The invention uses doped metal elements to modify the matrix of the lithium cobalt oxide cathode material, and aims to suppress the change of the lattice constant a/c during the delithiation process and improve the structural stability of the lithium cobalt oxide in the high delithiation state.

According to the present invention, preferably, the chemical formula of the lithium cobalt oxide matrix is Li _x Co _y Al _z M _a O ₂ , wherein 0.95<x<1.05, 0.94<y<0.985, 0.01<z<0.04, 0.005<a <0.02, y+z+a=1, M is a metal element and M is not Al; further preferably, the metal element is selected from Mg, Ni, Sr, La, Mn, Ti, Zr, W, Nb and Mo At least one of them.

Preferably, based on the total weight of the lithium cobalt oxide cathode material, the content of the coating layer is 0.1-1% by weight, more preferably 0.3-0.7% by weight.

In the present invention, the coating layer comprising the two compounds, and LiF LiAlO _2, and LiAlO ₂ molar ratio of LiF to 1:2.98-3.01, preferably 1:3. The lithium cobalt oxide cathode material provided by the present invention has a specific coating layer. The inventors of the present invention have realized in research that LiAlO ₂ can be used as a lithium ion conductor, providing good chemical stability, can increase the transmission rate of lithium ions through the particle surface, improve the rate characteristics, and effectively isolate the corrosion of the particle surface by the electrolyte; LiF can provide good electrochemical and chemical stability, can effectively protect the surface of particles and withstand high voltage. The inventor of the present invention adopts a LiAlO ₂ /LiF composite coating layer to provide the positive electrode material in a specific composite ratio to have excellent structural stability and electrochemical performance, and the actual service life under high voltage is prolonged.

The second aspect of the present invention provides a method for preparing a lithium cobalt oxide cathode material, the method comprising:

(1) The cobalt source, the lithium source, and the metal compound are sequentially mixed and sintered to obtain a metal element-doped lithium cobalt oxide matrix;

(2) _{Perform a second mixing of Li 2} CO ₃ and AlF ₃ to obtain a coating agent mixture;

(3) Perform the third mixing and the second sintering of the lithium cobalt oxide matrix and the coating agent mixture in sequence to obtain a lithium cobalt oxide cathode material with a coating layer;

Wherein, the cobalt source is selected from Al-doped cobalt tetroxide.

In the present invention, the content of Al doping in the cobalt source is not particularly limited, as long as it satisfies the chemical formula of the lithium cobalt oxide matrix.

In the present invention, under no special circumstances, the lithium source refers to a compound containing elemental lithium. Preferably, the lithium source is a lithium-containing compound, and is more preferably selected from lithium nitrate, lithium hydroxide, lithium carbonate and At least one of lithium oxide is more preferably lithium carbonate, but the present invention is not limited to this.

According to the present invention, preferably, the metal compound is a compound containing at least one element selected from Mg, Ni, Sr, La, Mn, Ti, Zr, W, Nb, and Mo. More preferably, the metal compound At least one selected from Mg ₂ CO ₃ , TiO ₂ , ZrO ₂ , Mn ₂ O ₃ , La ₂ O ₃ , NiO, SrCO ₃ , Nb ₂ O ₅ and WO ₂ , but the present invention is not limited thereto.

In the present invention, the method of the first mixing is not particularly limited, as long as the Al-doped cobalt source, lithium source, and metal compound are uniformly mixed. In the embodiment of the present invention, the first mixing is performed in a mixer, but the present invention is not limited to this.

According to the present invention, preferably, the molar ratio of the cobalt source as cobalt ion to the lithium source as lithium ion is 1:1-1.1, more preferably 1:1.01-1.07.

In the present invention, the first sintering conditions are not particularly limited, as long as the mixture of the cobalt source doped with Al, the lithium source and the metal compound obtains a lithium cobalt oxide matrix uniformly doped with metal elements. Preferably, the first sintering includes one-stage calcination and two-stage calcination, wherein the conditions of the one-stage calcination include: a temperature of 700-900°C, preferably 750-850°C, and a time of 2-10 hours, preferably 3-6 hours; The conditions of the two-stage calcination include: the temperature is 1000-1200°C, preferably 1000-1100°C, and the time is 2-20h, preferably 5-12h.

According to a preferred embodiment of the present invention, the method further includes: crushing and sieving the first sintered product to obtain a metal element-doped lithium cobalt oxide matrix.

According to the present invention, preferably, the _{molar ratio of Li 2} CO ₃ and AlF ₃ is 2:0.985-1, preferably 2:1, that is, the ratio of Li ₂ CO ₃ and AlF ₃ in the coating agent mixture The amount of the substance at least satisfies the molar ratio in the _{chemical formula 2Li 2} CO ₃ +AlF ₃ = _{LiAlO 2} +3LiF+CO _2.

Preferably, the mass ratio of the lithium cobaltate matrix and the coating agent mixture is 1:0.0016-0.0161, preferably 1:0.0048-0.0113. Using the preferred mass ratio is beneficial to balance the gram specific capacity and cycle performance of the final product.

In the present invention, the second mixing method is not particularly limited, as long as Li ₂ CO ₃ and AlF ₃ are uniformly mixed at a certain molar ratio. Preferably, the second mixing is performed in a mixer , But the present invention is not limited to this.

In the present invention, the third mixing method is not particularly limited, as long as the lithium cobaltate matrix A and the coating agent mixture are uniformly mixed. Preferably, the third mixing is performed in a mixer, but the present invention is not limited to this.

In the present invention, the second sintering conditions are not particularly limited, as long as the lithium cobalt oxide matrix and the coating agent mixture are formed into a lithium cobalt oxide cathode material with a coating layer, namely: Li ₂ CO _{3 The LiAlO 2} /LiF product obtained by the second sintering with AlF ₃ is uniformly coated on the outer surface of the lithium cobalt oxide cathode material. Preferably, the second sintering conditions include: a temperature of 700-950°C, preferably 750-900°C, and a time of 2-15 hours, preferably 5-10 hours. The use of the preferred second sintering conditions is more conducive to the full reaction of the coating agent and the formation of a tightly-coated composite coating layer on the surface of the substrate.

According to a preferred embodiment of the present invention, the method further includes: crushing and sieving the second sintered product to obtain a lithium cobalt oxide cathode material with a coating layer.

In the present invention, the lithium cobalt oxide substrate and the coating layer refer to the above-mentioned definitions, and will not be repeated here.

The third aspect of the present invention provides a lithium cobalt oxide cathode material prepared by the above method.

The method provided by the invention modifies the lithium cobalt oxide cathode material to obtain the lithium cobalt oxide anode material with stable structural performance and electrochemical performance.

The fourth aspect of the present invention provides an application of the above-mentioned lithium cobalt oxide cathode material in a lithium ion battery.

The lithium cobalt oxide cathode material provided by the present invention has excellent electrochemical performance, especially under high voltage, the lithium cobalt oxide cathode material has a higher gram specific capacity and good cycle performance, and prolongs the use of the lithium cobalt oxide cathode material life.

Hereinafter, the present invention will be described in detail through examples.

The parameters of the lithium cobalt oxide cathode materials prepared in Examples 1-12 and Comparative Examples 1-4 are listed in Table 1. Among them, all the raw materials in the Examples and Comparative Examples participate in the reaction, that is, the cobalt source and lithium in step (1) The molar ratio of the source and the metal compound is equivalent to the molar ratio of each ion in the lithium cobaltate matrix.

Example 1

(1) Perform the first mixing and first sintering of Al-doped Co ₃ O ₄ , Li ₂ CO ₃ , MgO and La ₂ O ₃ , where the conditions of the first sintering include: first heating up to 800 ℃ and sintering for 5 hours, Continue to heat up to 1040°C for sintering for 8 hours, crush and siev the first sintered product to obtain a metal element-doped lithium cobalt oxide matrix;

(2) _{Perform a second mixing of Li 2} CO ₃ and AlF _{3 at} a molar ratio of 2:1 to obtain a coating agent mixture;

(3) Perform the third mixing and second sintering of the lithium cobaltate matrix and the coating agent mixture at a mass ratio of 1:0.0081, wherein the second sintering conditions include: heating up to 800°C and sintering for 8 hours to obtain Coated lithium cobalt oxide cathode material S1.

The TEM image of the lithium cobalt oxide cathode material S1 is shown in FIG. 1, and it can be seen from FIG. 1 that the lithium cobalt oxide cathode material S1 has a composite coating layer structure.

Blank test 1

AlF _{3 was} directly placed in a kiln and heated to 800°C for 8 hours, and the sintered material was crushed and sieved to obtain sample-1. The XRD pattern of sample-1 is shown in Figure 2.

Blank test 2

After mixing Li ₂ CO ₃ and AlF ₃ at a molar ratio of 2:1, they are placed in a kiln for sintering at 800°C for 8 hours. The sintered material is crushed and sieved to obtain sample-2. The XRD pattern of sample-2 is as shown in 2. Show.

It can be seen from FIG. 2 that _{the coating agent mixture in which Li 2} CO ₃ and AlF ₃ are uniformly mixed, is mixed with the lithium cobalt oxide matrix and sintered, and a LiAlO ₂ /LiF coating layer is formed on the surface of the lithium cobalt oxide matrix.

Example 2

According to the method of Example 1, the difference is that the mass ratio of the lithium cobaltate matrix and the coating agent mixture is replaced with 1:0.0016 to obtain a lithium cobaltate cathode material S2 with a coating layer.

Example 3

According to the method of Example 1, the difference is that the mass ratio of the lithium cobaltate matrix and the coating agent mixture is replaced with 1:0.0048 to obtain a lithium cobaltate cathode material S3 with a coating layer.

Example 4

According to the method of Example 1, the difference is that the mass ratio of the lithium cobaltate matrix and the coating agent mixture is replaced with 1:0.0113 to obtain a lithium cobaltate cathode material S4 with a coating layer.

Example 5

According to the method of Example 1, the difference is that the mass ratio of the lithium cobaltate matrix and the coating agent mixture is replaced with 1:0.0161 to obtain the lithium cobaltate cathode material S5 with a coating layer.

Example 6

(1) Perform the first mixing and first sintering of Al-doped Co ₃ O ₄ , Li ₂ CO ₃ , MgO and La ₂ O ₃ , where the conditions of the first sintering include: first heating up to 850°C and sintering for 3 hours, Continue to heat up to 1035°C for sintering for 10 hours, and crush and siev the first sintered product to obtain a metal element-doped lithium cobalt oxide matrix;

(2) _{Perform a second mixing of Li 2} CO ₃ and AlF _{3 at} a molar ratio of 2:1 to obtain a coating agent mixture;

(3) Perform the third mixing and second sintering of the lithium cobalt oxide matrix and the coating agent mixture at a mass ratio of 1:0.0081, wherein the second sintering conditions include: heating up to 750°C and sintering for 10 hours to obtain Coated lithium cobalt oxide cathode material S6.

Example 7

(1) Perform the first mixing and first sintering of Al-doped Co ₃ O ₄ , Li ₂ CO ₃ , MgO and La ₂ O ₃ , where the conditions of the first sintering include: first heating up to 850°C and sintering for 3 hours, Continue to heat up to 1045°C and sinter for 6 hours, crush and siev the first sintered product to obtain a metal element-doped lithium cobalt oxide matrix;

(2) _{Perform a second mixing of Li 2} CO ₃ and AlF _{3 at} a molar ratio of 2:1 to obtain a coating agent mixture;

(3) Perform the third mixing and second sintering of the lithium cobalt oxide matrix and the coating agent mixture at a mass ratio of 1:0.0081, wherein the second sintering conditions include: heating up to 850°C and sintering for 5 hours to obtain Coated lithium cobalt oxide cathode material S7.

Example 8

(1) Perform the first mixing and first sintering of Al-doped Co ₃ O ₄ , Li ₂ CO ₃ , NiO and Mn ₂ O ₃ , where the conditions for the first sintering include: first heating up to 750°C and sintering for 5 hours, Continue to heat up to 1030°C and sinter for 12 hours, and crush and siev the first sintered product to obtain a metal element-doped lithium cobalt oxide matrix;

(2) _{Perform a second mixing of Li 2} CO ₃ and AlF _{3 at} a molar ratio of 2:1 to obtain a coating agent mixture;

(3) Perform the third mixing and second sintering of the lithium cobaltate matrix and the coating agent mixture at a mass ratio of 1:0.0081, wherein the second sintering conditions include: heating up to 800°C and sintering for 8 hours to obtain Coated lithium cobalt oxide cathode material S8.

Example 9

(1) Perform the first mixing and first sintering of Al-doped Co ₃ O ₄ , Li ₂ CO ₃ , MgO and ZrO ₂ , where the conditions of the first sintering include: first heating up to 800 ℃ and sintering for 5 hours, and then continue heating up Sintering at 1040°C for 8 hours, crushing and sieving the first sintered product to obtain a metal element-doped lithium cobalt oxide matrix;

(2) _{Perform a second mixing of Li 2} CO ₃ and AlF _{3 at} a molar ratio of 2:1 to obtain a coating agent mixture;

(3) Perform the third mixing and second sintering of the lithium cobaltate matrix and the coating agent mixture at a mass ratio of 1:0.0081, wherein the second sintering conditions include: heating up to 800°C and sintering for 8 hours to obtain Coated lithium cobalt oxide cathode material S9.

Example 10

(1) Perform the first mixing and first sintering of Al-doped Co ₃ O ₄ , Li ₂ CO ₃ , TiO ₂ , WO ₃ and MoO ₃ , where the conditions of the first sintering include: first heating up to 750°C for sintering 5h, continue to heat up to 1030°C and sinter for 12h, crush and siev the first sintered product to obtain a metal element-doped lithium cobalt oxide matrix;

(2) _{Perform a second mixing of Li 2} CO ₃ and AlF _{3 at} a molar ratio of 2:1 to obtain a coating agent mixture;

(3) Perform the third mixing and second sintering of the lithium cobaltate matrix and the coating agent mixture at a mass ratio of 1:0.0081, wherein the second sintering conditions include: heating up to 850°C and sintering for 8 hours to obtain Coated lithium cobalt oxide cathode material S10.

Example 11

(1) Perform the first mixing and first sintering of Al-doped Co ₃ O ₄ , Li ₂ CO ₃ , TiO ₂ , Sr ₂ O ₃ and Nb ₂ O ₅ , wherein the first sintering conditions include: first heating up Sintering at 800°C for 5 hours, continuing to heat up to 1045°C for sintering for 6 hours, crushing and sieving the first sintered product to obtain a metal element-doped lithium cobalt oxide matrix;

(2) _{Perform a second mixing of Li 2} CO ₃ and AlF _{3 at} a molar ratio of 2:1 to obtain a coating agent mixture;

(3) Perform the third mixing and second sintering of the lithium cobalt oxide matrix and the coating agent mixture at a mass ratio of 1:0.0081, wherein the second sintering conditions include: heating up to 800°C and sintering for 8 hours to obtain Coated lithium cobalt oxide cathode material S11.

Example 12

According to the method of Example 1, the difference is that the first sintering conditions include: first heating up to 800° C. and sintering for 5 hours, then continuing to increase the temperature to 1040° C. and sintering for 15 hours to obtain lithium cobalt oxide cathode material S12.

Comparative example 1

According to the method of Example 1, the difference is that the lithium cobalt oxide matrix is not doped with metal elements, namely: (1) Co ₃ O ₄ and Li ₂ CO ₃ are first mixed and first sintered to obtain a lithium cobalt oxide matrix , And perform steps (2) and (3) to obtain lithium cobalt oxide cathode material D1.

Comparative example 2

According to the method of Example 1, the difference is that steps (2) and (3) are not included, that is, the metal element-doped lithium cobalt oxide matrix obtained in step (1) is used as the lithium cobalt oxide cathode material D2.

Comparative example 3

According to the method of Example 1, the difference is that the coating agent mixture is replaced with LiAlO ₂ to obtain lithium cobalt oxide cathode material D3.

Comparative example 4

According to the method of Example 1, the difference is that the coating agent mixture is replaced with LiF to obtain lithium cobalt oxide cathode material D4.

Table 1

Note: *Lithium Cobalt Oxide Cathode Material

**The mass ratio of lithium cobalt oxide substrate and coating layer

***LiAlO ₂ to LiF molar ratio

According to the data in Table 1, the method provided by the present invention can be used to prepare a lithium cobalt oxide cathode material with a coating layer, wherein the chemical formula of the coating layer is LiAlO ₂ /LiF.

Test case

The lithium cobalt oxide cathode materials (S1-S12 and D1-D4) prepared in Examples 1-12 and Comparative Examples 1-4 were subjected to electrochemical performance tests.

(1) Prepare button batteries according to the following steps:

Mix 9.2g of lithium cobalt oxide cathode material, 0.4g of acetylene black and 0.4g of polyvinylidene fluoride (PVDF), coat it on aluminum foil and dry it, press and shape it with a pressure of 100MPa to obtain a diameter of 12mm. A positive pole piece with a thickness of 120 μm, and then the positive pole piece is placed in a vacuum oven and dried at 120° C. for 12 hours.

The negative electrode uses a Li metal sheet with a diameter of 17mm and a thickness of 1mm; the separator uses a polyethylene porous membrane with a thickness of 25μm; the electrolyte uses ethylene carbonate (EC) and diethyl carbonate _{with 1mol/L LiPF 6 as the electrolyte.} DEC) the same amount of mixed liquid.

The positive pole piece, the diaphragm, the negative pole piece and the electrolyte are assembled into a 2025 button cell in an Ar gas glove box with a water content and an oxygen content of less than 5 ppm.

(2) 0.1C discharge specific capacity, rate performance, 1C-50th-cycle performance

0.1C discharge specific capacity:

Place the fabricated button battery for 24 hours. After the open-circuit voltage is stable, charge it to a cut-off voltage of 4.5V with a current density of 20mA/g to the positive electrode, charge it at a constant voltage of 4.5V for 30 minutes, and then discharge it to cut-off at the same current density. The voltage was 3.0V, and the specific discharge capacity was tested at 0.1C. The results are shown in Table 2.

Rate performance (2C/0.1C) test:

When the 0.1C discharge specific capacity test is over, charge the positive electrode with a current density of 100mA/g to a cut-off voltage of 4.3V, charge at a constant voltage of 4.3V for 30 minutes, and then discharge with a current density of 400mA/g to a cut-off voltage of 3.0 V, this result is the 2C discharge specific capacity, so 2C/0.1C=2C discharge specific capacity/0.1C discharge specific capacity, the results are shown in Table 2.

Cycle performance test:

The button cell is activated by constant current and constant voltage charging and discharging cycles in the range of 3.0V to 4.6V. The charging and discharging system is as follows: after 2 weeks of charging and discharging at 0.1C, charge to 4.3V at a constant current and constant voltage at a rate of 0.1C, and the cut-off current of constant voltage charging is 0.01C. This battery is regarded as an activated battery.

Using an activated battery, with a current density of 1C in the voltage range of 3.0-4.6V, and a temperature of 25°C, the cycle retention rate of the material was investigated for 50 cycles. The cycle retention rate = (50th discharge specific capacity / 1st discharge Specific capacity)×100%, the results are shown in Table 2.

Table 2

To	0.1C discharge capacity	First-time efficiency	2C magnification	Circulation retention rate,%
Example 1	184.3	93.8	167.5	87.0
Example 2	183.8	93.0	165.4	80.2
Example 3	184.1	93.3	166.6	84.8
Example 4	183.9	93.7	167.1	87.8

Example 5	183.3	93.0	165.6	88.1
Example 6	189.8	95.3	173.6	85.6
Example 7	175.6	90.1	156.1	91.1
Example 8	184.5	93.9	168.1	86.8
Example 9	183.8	93.8	167.0	87.3
Example 10	184.0	93.9	167.3	87.6
Example 11	184.4	93.9	168.3	86.6
Example 12	183.7	93.8	162.1	86.3
Comparative example 1	194.5	97.2	179.2	41.6
Comparative example 2	183.7	92.6	164.1	72.3
Comparative example 3	183.4	93.9	167.0	83.5
Comparative example 4	182.9	92.3	163.2	84.2

By comparing the data in Table 2, it can be seen that the lithium cobalt oxide cathode provided by the present invention has excellent electrochemical performance, especially under high pressure conditions, the lithium cobalt oxide cathode material has good cycle performance, thereby prolonging the actual application life.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be regarded as the disclosed content of the present invention. All belong to the protection scope of the present invention.

Claims (10)

1. A lithium cobalt oxide cathode material, which comprises a substrate and a coating layer covering the outer surface of the substrate, the substrate being a metal element doped lithium cobalt oxide substrate; wherein the composition of the coating layer The general formula is LiAlO ₂ /LiF.
2. The cathode material according to claim 1, wherein the chemical formula of the lithium cobalt oxide matrix is Li _x Co _y Al _z M _a O ₂ , wherein 0.95<x<1.05, 0.94<y<0.985, 0.01<z< 0.04, 0.005<a<0.02, y+z+a=1, M is a metal element and M is not Al;

   Preferably, the metal element is selected from at least one of Mg, Ni, Sr, La, Mn, Ti, Zr, W, Nb and Mo.
3. The cathode material according to claim 1 or 2, wherein, based on the total weight of the lithium cobalt oxide cathode material, the content of the coating layer is 0.1-1% by weight, preferably 0.3-0.7% by weight;

   Preferably, the molar ratio of LiAlO ₂ and LiF in the coating layer is 1:2.98-3.01.
4. A preparation method of lithium cobalt oxide cathode material, the method comprising:

   (1) The cobalt source, the lithium source, and the metal compound are sequentially mixed and sintered to obtain a metal element-doped lithium cobalt oxide matrix;

   (2) _{Perform a second mixing of Li 2} CO ₃ and AlF ₃ to obtain a coating agent mixture;

   (3) Perform the third mixing and the second sintering of the lithium cobalt oxide matrix and the coating agent mixture in sequence to obtain a lithium cobalt oxide cathode material with a coating layer;

   Wherein, the cobalt source is selected from Al-doped cobalt tetroxide.
5. The method according to claim 4, wherein the metal compound is a compound containing at least one element selected from the group consisting of Mg, Ni, Sr, La, Mn, Ti, Zr, W, Nb, and Mo;

   Preferably, the lithium source is selected from at least one of lithium nitrate, lithium hydroxide, lithium carbonate and lithium oxide, and is preferably lithium carbonate.
6. The method according to claim 4 or 5, wherein the molar ratio of the cobalt source as cobalt ion to the lithium source as lithium ion is 1:1-1.1, preferably 1:1.01-1.07;

   Preferably, the first sintering includes one-stage calcination and two-stage calcination, wherein the conditions of the one-stage calcination include: a temperature of 700-900°C, preferably 750-850°C, and a time of 2-10 hours, preferably 3-6 hours; The conditions of the two-stage calcination include: the temperature is 1000-1200°C, preferably 1000-1100°C, and the time is 2-20h, preferably 5-12h.
7. The method according to claim 4, wherein the molar ratio of _{Li 2} CO ₃ and AlF _{3 is 2:0.985-1;}

   Preferably, the mass ratio of the lithium cobaltate matrix and the coating agent mixture is 1:0.0016-0.0161, preferably 1:0.0048-0.0113;

   Preferably, the second sintering conditions include: a temperature of 700-950°C, preferably 750-900°C, and a time of 2-15 hours, preferably 5-10 hours.
8. The method according to any one of claims 4-7, wherein the chemical formula of the lithium cobalt oxide matrix is Li _x Co _y Al _z M _a O ₂ , wherein 0.95<x<1.05, 0.94<y<0.985 , 0.01<z<0.04, 0.005<a<0.02, y+z+a=1, M is a metal element and M is not Al;

   Preferably, the metal element is selected from at least one of Mg, Ni, Sr, La, Mn, Ti, Zr, W, Nb and Mo;

   Preferably, the composition of the coating layer is represented by the general formula LiAlO ₂ /LiF;

   Preferably, the molar ratio of LiAlO _{2 to} LiF in the coating layer is 1:2.98-3.01;

   Preferably, based on the total weight of the lithium cobalt oxide cathode material, the content of the coating layer is 0.1-1% by weight, more preferably 0.3-0.7% by weight.
9. A lithium cobalt oxide cathode material prepared by the method of any one of claims 4-8.
10. Application of the lithium cobalt oxide cathode material according to any one of claims 1 to 3 and 9 in a lithium ion battery.

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