CN115799514A - A kind of single crystal cobalt-free cathode material, preparation method and lithium ion battery - Google Patents

Abstract

The invention discloses a single crystal cobalt-free positive electrode material, a preparation method and a lithium ion battery; wherein, a single crystal cobalt-free positive electrode material includes an inner core and a bromide coating layer coated on the surface of the inner core. With bromide doping, the mass proportion of bromide in the single crystal cobalt-free cathode material is 1-10%; the invention solves the problem of poor performance of the existing single crystal cobalt-free cathode material, and obtains cycle stability and Single crystal cobalt-free cathode material with better rate performance.

Description

A kind of single crystal cobalt-free cathode material, preparation method and lithium ion battery

technical field

The invention relates to the field of lithium ion batteries, in particular to a single crystal cobalt-free positive electrode material, a preparation method and a lithium ion battery.

Background technique

Ternary cathode materials have attracted more and more researchers' attention due to their high energy density. Compared with traditional polycrystalline ternary cathode materials, single crystal ternary cathode materials have attracted extensive attention in the field of lithium-ion batteries due to their higher mechanical strength, energy density, and better cycle performance. However, the currently commonly used single crystal ternary cathode materials all contain cobalt, which increases their cost and pollution, and restricts their development to a certain extent. As a new type of cathode material, single crystal cobalt-free cathode material not only has the advantages of single crystallization, but also reduces cost and pollution. However, the synthesis of single-crystal cobalt-free cathode materials, especially nickel-rich materials, is not simple. The current conventional method is to prepare a single crystal cobalt-free positive electrode material by a high-temperature synthesis method, such as a spinel-type single crystal cobalt-free high-voltage lithium nickel manganese oxide positive electrode material disclosed in Chinese patent CN113178566A, its preparation method and lithium ion battery . However, the increase of sintering temperature will lead to cation mixing and irregular particle shape and size, resulting in significantly poor performance indicators such as cycle performance and rate performance of the material.

Flux growth method, as a new type of synthesis method for single crystal cathode materials, is routinely used in cobalt-containing single crystal ternary cathode materials, and often only has the single effect of reducing the sintering temperature during the preparation process, and In order to avoid the incorporation of impurity elements and ensure the performance of ternary cathode materials, it is usually necessary to remove them in subsequent steps by washing with water, resulting in a complicated preparation process and poor performance of the prepared single crystal cobalt-free cathode materials.

Contents of the invention

Therefore, the purpose of the present invention is to solve the problem of poor performance of existing single crystal cobalt-free cathode materials, and provide a single crystal cobalt-free cathode material, a preparation method and a lithium ion battery with better cycle stability and rate performance.

A single crystal cobalt-free positive electrode material, comprising an inner core and a bromide cladding layer coated on the surface of the inner core, the inner core is a bromide-doped single crystal cobalt-free positive electrode material, bromine in the single crystal cobalt-free positive electrode material The mass proportion of the compound is 1-10%.

The D50 of the single crystal cobalt-free positive electrode material is 1-4 μm, and the thickness of the bromide coating layer is ≤100 nm. Preferably, the D50 of the single crystal cobalt-free positive electrode material is 3-4 μm, and the thickness of the bromide coating layer is ≤20 nm.

The ionic conductivity of the single crystal cobalt-free positive electrode material is 10 ^-8 ~ 10 ^-3 S/cm, the electronic conductivity is 10 ^-6 ~ 10 ^{- 2} S/cm, and the ion diffusion coefficient is 10 ^-13 ~ 10 ^-6 cm ² /s; preferably, the ionic conductivity of the single crystal cobalt-free positive electrode material is 10 ^-4 to 10 ^-3 S/cm, the electronic conductivity is 10 ^-4 to 10 ^-3 S/cm, and the ion diffusion coefficient is 10 ^-10 ～10 ^-9 cm ² /s;

And/or, the intensity ratio of the 003 X-ray diffraction peak to the 104 X-ray diffraction peak of the single crystal cobalt-free positive electrode material is ≥1.5, and the half-maximum width of the 003 X-ray diffraction peak is 0.4°～1.0°; preferably, the single crystal cobalt-free The intensity ratio of the 003 X-ray diffraction peak to the 104 X-ray diffraction peak of the cobalt cathode material is ≥1.6, and the half-maximum width of the 003 X-ray diffraction peak is 0.4°-0.7°;

And/or, the specific surface area of the single-crystal cobalt-free cathode material is 0.01-2m ² /g, and the pH value is ≤11.5; preferably, the specific surface area of the single-crystal cobalt-free cathode material is 0.08-0.1m ² /g;

And/or, the single crystal cobalt-free positive electrode material is LiNi _x M _1-x O ₂ , 0.6≤x≤0.95; M is one of Mn or Al.

A method for preparing a single crystal cobalt-free positive electrode material, comprising:

Mixing a Ni-M-based precursor with a lithium source to obtain a mixed powder a, where M is at least one of Mn or Al;

mixing the mixed powder a with the bromide to obtain the mixed powder b; the mass proportion of the bromide in the mixed powder b is 1-10%;

Raise the mixed powder b to 450-500°C at a rate of 2-10°C/min and keep it warm for 2-3 hours under an oxygen atmosphere; then raise the rate of temperature at 1-3°C/min to 800-900°C and keep it warm 10 to 16 hours, after cooling, the single crystal cobalt-free cathode material is obtained.

The Ni-M-based precursor is Ni _x M _1-x (OH) ₂ , M is one of Mn or Al, where 0.6≤x≤0.95.

The molar ratio of the Ni-M-based precursor to the lithium source is 1:1.06˜1.15.

The lithium source is one of lithium hydroxide, lithium carbonate, lithium nitrate and lithium oxalate, preferably lithium carbonate.

The bromide is at least one of potassium bromide, sodium bromide, magnesium bromide and lithium bromide.

In the preparation process of the mixed powder b, the step of mixing a halide flux in the mixed powder a is also included; the halide flux is potassium fluoride, sodium fluoride, magnesium fluoride, lithium fluoride, chloride At least one of potassium, sodium chloride, magnesium chloride, and lithium chloride; the mass proportion of the halide flux in the mixed powder b is 1-5%.

A lithium ion battery, comprising the above-mentioned single crystal cobalt-free positive electrode material, or a single crystal cobalt-free positive electrode material prepared by the above-mentioned single crystal cobalt-free positive electrode material preparation method.

The technical solution of the present invention has the following advantages:

1. A single crystal cobalt-free cathode material of the present invention, comprising an inner core and a bromide cladding layer coated on the surface of the inner core, the inner core is a bromide-doped single crystal cobalt-free positive electrode material, and the single crystal no cobalt The mass proportion of bromide in the cobalt positive electrode material is 1-10%; the anions and cations in the bromide of the present invention can be doped into the interior of the matrix, and the Br ^- doping in the bromide resists the erosion of hydrogen fluoride from the electrolyte And stronger Br- and metal bonds, therefore, improve the integrity of the interface between the positive electrode and the electrolyte; in addition, the cation doping in the bromide can also occupy the Li site and expand the interlayer distance, thereby improving the diffusion of Li+ rate, further improving the rate performance of single crystal cobalt-free cathode materials. At the same time, the surface of the inner core is also covered with a halide coating layer, which can effectively prevent the direct contact between the material and the electrolyte, and improve the structural stability of the material;

Therefore, compared with conventional single crystal cobalt-free cathode materials, the single crystal cobalt-free cathode material prepared by the present invention has significantly improved cycle stability and rate performance.

2. The preparation method of a single crystal cobalt-free positive electrode material provided by the present invention only needs to use bromide as a flux, add it to the mixed powder a obtained by mixing the Ni-M-based precursor and the lithium source, and perform one sintering, and sintering Finally, it is not necessary to wash with water. In the preparation process, the flux is not only used as a flux to reduce the preparation temperature of the single crystal cobalt-free positive electrode material, but also in the process of preparing the single crystal cobalt-free positive electrode material. The anions and cations in the bromide It can also be doped into the interior of the matrix to prepare a single crystal cobalt-free cathode material with bromide-doped single crystal cobalt-free cathode material as the core and bromide coated on the core surface;

Therefore, in the preparation process of the present invention, the bromide is not only used as a flux to promote the growth of cobalt-free single crystal positive electrode particles and reduce the calcination temperature. On the other hand, anion and cation co-doping can also be realized in situ. While enhancing the resistance to hydrogen fluoride erosion in the electrolyte, it also expands the layer spacing to increase the diffusion rate of lithium ions, and improves the rate performance of single crystal cobalt-free cathode materials. In addition, the coating layer can reduce the surface residue of excess lithium salt and prevent the direct contact between the electrolyte and the material, thereby reducing unnecessary side reactions, preventing the growth of the CEI film and improving the structure of the single-crystal cobalt-free cathode material stability.

Description of drawings

In order to more clearly illustrate the specific implementation of the present invention or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings that need to be used in the specific implementation or description of the prior art. Obviously, the accompanying drawings in the following description The drawings show some implementations of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative work.

The SEM figure of single crystal cobalt-free cathode material in Fig. 1 embodiment 1;

The TEM figure of single crystal cobalt-free cathode material in Fig. 2 embodiment 1;

The XPS figure of Br 3d collected after etching to 0, 60 and 120nm of Fig. 3 embodiment 1;

Fig. 4 is the comparison diagram of cycle performance of the single crystal cobalt-free cathode material prepared by embodiment 1 and comparative example 1;

FIG. 5 is a comparison chart of the rate performance of the single crystal cobalt-free cathode materials prepared in Example 1 and Comparative Example 1. FIG.

Detailed ways

The following examples are provided in order to further understand the present invention better, are not limited to the best implementation mode, and do not limit the content and protection scope of the present invention, anyone under the inspiration of the present invention or use the present invention Any product identical or similar to the present invention obtained by combining features of other prior art falls within the protection scope of the present invention.

If no specific experimental steps or conditions are indicated in the examples, it can be carried out according to the operation or conditions of the conventional experimental steps described in the literature in this field.

Example 1

A method for preparing a single crystal cobalt-free cathode material, the specific process of which is as follows:

(1) Grinding Ni _0.8 Mn _0.2 (OH) ₂ and lithium carbonate according to a molar ratio of 1:1.08 to obtain mixed powder a;

(2) The mixed powder a is completely mixed with magnesium bromide (MgBr ₂ ) and ground evenly, the resulting powder is marked as mixed powder b, and the mass ratio of the flux in the mixed powder b is controlled at 4%;

(3) Then, the mixed powder b was raised to 500°C at a heating rate of 5°C/min and kept for 3 hours under an oxygen atmosphere, then raised to 850°C at a heating rate of 2°C/min and held at a temperature of 14 hours, and then cooled to obtain powder particles;

(4) crushing the powder particles and then sieving to obtain a single crystal cobalt-free cathode material LiNi _0.8 Mn _0.2 O ₂ .

The single crystal cobalt-free positive electrode material LiNi _0.8 Mn _0.2 O ₂ prepared in this example was used for SEM and TEM detection, and the obtained positive electrode material was etched to obtain the Br 3d after etching to 0, 60 and 120 nm respectively. The XPS diagram is shown in Figure 1-3. It can be seen from the SEM scanning electron microscope results in Fig. 1 that the obtained product is a single crystal particle, the surface is smooth and free of impurities, and the particle size is 2 μm-4 μm. From the TEM results in Figure 2, it can be found that the particle surface is coated with a layer of halide. From the XPS results in Figure 3, it can be found that Br ions doped into the interior of the particles.

Example 2

A method for preparing a single crystal cobalt-free cathode material, the specific process of which is as follows:

(1) Grinding Ni _0.8 Mn _0.2 (OH) ₂ and lithium carbonate according to a molar ratio of 1:1.08 to obtain mixed powder a;

(2) The mixed powder a is completely mixed with potassium bromide (KBr) and ground evenly, the resulting powder is marked as mixed powder b, and the mass ratio of the flux in the mixed powder b is controlled at 4%;

(3) Then, the mixed powder b was raised to 500°C at a heating rate of 5°C/min and kept for 3 hours under an oxygen atmosphere, then raised to 850°C at a heating rate of 2°C/min and held at a temperature of 14 hours, and then cooled to obtain powder particles;

(4) crushing the powder particles and then sieving to obtain a single crystal cobalt-free cathode material LiNi _0.8 Mn _0.2 O ₂ .

Example 3

A method for preparing a single crystal cobalt-free cathode material, the specific process of which is as follows:

(1) Grinding Ni _0.8 Mn _0.2 (OH) ₂ and lithium carbonate according to a molar ratio of 1:1.08 to obtain mixed powder a;

(2) The mixed powder a is completely mixed with sodium bromide (NaBr) and ground evenly, the resulting powder is marked as mixed powder b, and the mass ratio of the flux in the mixed powder b is controlled at 4%;

(3) Then, the mixed powder b was raised to 500°C at a heating rate of 5°C/min and kept for 3 hours under an oxygen atmosphere, then raised to 850°C at a heating rate of 2°C/min and held at a temperature of 14 hours, and then cooled to obtain powder particles;

(4) crushing the powder particles and then sieving to obtain a single crystal cobalt-free cathode material LiNi _0.8 Mn _0.2 O ₂ .

Example 4

A method for preparing a single crystal cobalt-free cathode material, the specific process of which is as follows:

(1) Grinding Ni _0.8 Mn _0.2 (OH) ₂ and lithium carbonate according to a molar ratio of 1:1.08 to obtain mixed powder a;

(2) The mixed powder a is completely mixed with lithium bromide (LiBr) and ground evenly, the obtained powder is marked as mixed powder b, and the mass ratio of the flux in the mixed powder b is controlled at 4%;

(3) Then, the mixed powder b was raised to 500°C at a heating rate of 5°C/min and kept for 3 hours under an oxygen atmosphere, then raised to 850°C at a heating rate of 2°C/min and held at a temperature of 14 hours, and then cooled to obtain powder particles;

(4) crushing the powder particles and then sieving to obtain a single crystal cobalt-free cathode material LiNi _0.8 Mn _0.2 O ₂ .

Example 5

A method for preparing a single crystal cobalt-free cathode material, the specific process of which is as follows:

(1) Grinding Ni _0.6 Mn _0.4 (OH) ₂ and lithium nitrate according to a molar ratio of 1:1.13 to obtain mixed powder a;

(2) The mixed powder a is completely mixed with magnesium bromide (MgBr ₂ ) and ground evenly, the obtained powder is marked as mixed powder b, and the mass ratio of the flux in the mixed powder b is controlled at 1%;

(3) Then, the mixed powder b was raised to 450°C at a heating rate of 2°C/min and kept for 2 hours under an oxygen atmosphere, then raised to 900°C at a heating rate of 3°C/min and held at a temperature of 10 hours, and then cooled to obtain powder particles;

(4) The powder particles are crushed and sieved to obtain a single crystal cobalt-free cathode material LiNi _0.6 Mn _0.4 O ₂ .

Example 6

A method for preparing a single crystal cobalt-free cathode material, the specific process of which is as follows:

(1) Grinding Ni _0.9 Mn _0.1 (OH) ₂ and lithium hydroxide according to a molar ratio of 1:1.10 to obtain mixed powder a;

(2) The mixed powder a is completely mixed with magnesium bromide (MgBr ₂ ) and ground evenly, the obtained powder is marked as mixed powder b, and the mass ratio of the flux in the mixed powder b is controlled at 10%;

(3) Then, the mixed powder b was raised to 500°C at a heating rate of 10°C/min and kept for 2.5 hours under an oxygen atmosphere, then raised to 800°C at a heating rate of 1°C/min and kept at a temperature of 16 hours, and then cooled Obtain powder particles;

(4) The powder particles are crushed and sieved to obtain a single crystal cobalt-free cathode material LiNi _0.9 Mn _0.1 O ₂ .

Example 7

A method for preparing a single crystal cobalt-free cathode material, the specific process of which is as follows:

(1) Grinding Ni _0.95 Mn _0.05 (OH) ₂ and lithium carbonate according to a molar ratio of 1:1.10 to obtain mixed powder a;

(2) The mixed powder a is completely mixed with magnesium bromide (MgBr ₂ ) and ground evenly, the obtained powder is marked as mixed powder b, and the mass ratio of the flux in the mixed powder b is controlled at 8%;

(3) Then, the mixed powder b was raised to 500°C at a heating rate of 8°C/min and kept for 2.5 hours under an oxygen atmosphere, then raised to 880°C at a heating rate of 2°C/min and held at a temperature of 16 hours, and then cooled Obtain powder particles;

(4) The powder particles are crushed and sieved to obtain a single crystal cobalt-free cathode material LiNi _0.95 Mn _0.05 O ₂ .

Example 8

A method for preparing a single crystal cobalt-free cathode material, the specific process of which is as follows:

(1) Grinding Ni _0.8 Al _0.2 (OH) ₂ and lithium carbonate according to a molar ratio of 1:1.10 to obtain mixed powder a;

(2) The mixed powder a is completely mixed with magnesium bromide (MgBr ₂ ) and ground uniformly, the obtained powder is marked as mixed powder b, and the mass ratio of the flux in the mixed powder b is controlled at 5%;

(3) Then, the mixed powder b was raised to 500°C at a heating rate of 5°C/min and kept for 2.5 hours under an oxygen atmosphere, then raised to 840°C at a heating rate of 2°C/min and kept at a temperature of 12 hours, and then cooled Obtain powder particles;

(4) The powder particles are crushed and sieved to obtain a single crystal cobalt-free cathode material LiNi _0.8 Al _0.2 O ₂ .

Example 9

A method for preparing a single crystal cobalt-free cathode material, the specific process of which is as follows:

(1) Grinding Ni _0.8 Mn _0.2 (OH) ₂ and lithium carbonate according to a molar ratio of 1:1.08 to obtain mixed powder a;

(2) Mixed powder a, magnesium bromide (MgBr ₂ ), and halide flux sodium chloride (NaCl) are completely mixed and ground evenly, and the resulting powder is marked as mixed powder b. The mass of magnesium bromide in mixed powder b is The ratio is controlled at 4%, and the mass ratio of sodium chloride in the mixed powder b is controlled at 4%;

(3) Then, the mixed powder b was raised to 500°C at a heating rate of 5°C/min and kept for 3 hours under an oxygen atmosphere, then raised to 850°C at a heating rate of 2°C/min and held at a temperature of 14 hours, and then cooled to obtain powder particles;

(4) crushing the powder particles and then sieving to obtain a single crystal cobalt-free cathode material LiNi _0.8 Mn _0.2 O ₂ .

Comparative example 1

A method for preparing a single crystal cobalt-free cathode material, the specific process of which is as follows:

(1) Grinding Ni _0.8 Mn _0.2 (OH) ₂ and lithium carbonate according to a molar ratio of 1:1.08 to obtain mixed powder a;

(2) The mixed powder a is completely mixed with NaCl and ground evenly, the obtained powder is marked as mixed powder b, and the mass ratio of the flux in the mixed powder c is controlled at 4%;

(3) Then, the mixed powder b was raised to 500°C at a heating rate of 5°C/min and kept for 3 hours under an oxygen atmosphere, then raised to 850°C at a heating rate of 2°C/min and held at a temperature of 14 hours, and then cooled to obtain powder particles;

(4) crushing the powder particles and then sieving to obtain a single crystal cobalt-free cathode material LiNi _0.8 Mn _0.2 O ₂ .

Comparative example 2

A method for preparing a single crystal cobalt-free cathode material, the specific process of which is as follows:

(1) Grinding Ni _0.8 Mn _0.2 (OH) ₂ and lithium carbonate according to a molar ratio of 1:1.08 to obtain mixed powder a;

(2) The mixed powder a is raised to 500°C at a heating rate of 5°C/min and kept for 3 hours under an oxygen atmosphere, then raised to 850°C at a heating rate of 2°C/min and held at a temperature of 14 hours, and then cooled to obtain a powder particles;

(3) The powder particles are crushed and sieved to obtain a single crystal cobalt-free cathode material LiNi _0.8 Mn _0.2 O ₂ .

Test example 1

Using the positive electrode material prepared in the examples and comparative examples, its D50, the thickness of the cladding layer, the ion conductivity, the electron conductivity, the ion diffusion coefficient, the intensity ratio of the 003 X-ray diffraction peak to the 104 X-ray diffraction peak, the 003 X-ray diffraction peak The half-height width and specific surface area of the peaks were detected. Among them, D50 is detected by grid sieving method, and the thickness of coating layer is detected by projection electron microscope. The ion conductivity, electronic conductivity and ion diffusion coefficient are all detected by Chenhua electrochemical workstation. The 003 X-ray diffraction peak and the 104 X-ray diffraction peak The intensity ratio of the peaks and the half-peak width of the 003 X-ray diffraction peak were detected by XRD, and the specific surface area was detected by GB/T19587-2004 "Determination of specific surface area of solid substances by gas adsorption BET method". The test results of the above items are shown in Table 1 and Table 2 below.

Table 1

Table 2

Customer case number P20221956

It can be known from the above Tables 1 and 2 that the single crystal cobalt-free cathode material prepared by the present invention has both an inner core and a bromide cladding layer, and the inner core is also doped with bromide. Moreover, bromide doping can effectively improve the ionic conductivity, electronic conductivity and ion diffusion coefficient.

Test example 2

Apply the cathode materials prepared in Examples and Comparative Examples to batteries. The battery assembly process is as follows: first weigh 0.2g of cathode materials, 0.025g of PVDF and 0.025g of graphite, and combine the three according to the mass ratio of 8:1: 1 Put it in a mortar and grind it uniformly for 40 minutes, then add 0.8ml of N-methyl-2-pyrrolidone (NMP) and continue to stir for 10 minutes, so that there is no particle inside the slurry, and then evenly coat it with a spatula Put it on the aluminum foil, then put it into a blast drying oven and dry it at 100°C for 30 minutes. After taking it out, use a cutting machine to cut it into a circular pole piece and an aluminum piece with a diameter of 12mm, and put the two together in a vacuum After drying at 60°C for 12 hours in a drying oven, take it out, weigh it with an electronic balance, and finally assemble the positive pole piece, lithium piece, shrapnel, gasket, positive pole case, negative pole case, diaphragm, and electrolyte in a glove box to become CR2025 type of coin half cell.

The cycle performance and rate performance of the batteries corresponding to the positive electrode materials of different examples and comparative examples were tested, wherein the test results of Example 1 and Comparative Example 1 are shown in FIG. 4 and FIG. 5 . At the same time, obtain the batteries corresponding to each embodiment and comparative example in the voltage range of 2.8-4.3V, customer case number P20221956

The capacity retention rate after 200 cycles at 1C (1C=200mA·g ^-1 ) rate, and the discharge capacity data of each example and comparative example at 5C, the results are shown in Table 3 below.

table 3

According to the above detection results, it can be seen that the single crystal cobalt-free positive electrode material prepared by the present invention has a bromide-doped inner core and a bromide coating layer on the inner core surface, which is compared with a single crystal cobalt-free positive electrode material without bromide doping and coating. As far as the positive electrode material is concerned, both the recapacity retention rate and the discharge capacity are significantly improved, which effectively improves the cycle stability and rate performance of the single crystal cobalt-free positive electrode material.

Apparently, the above-mentioned embodiments are only examples for clear description, rather than limiting the implementation. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. And the obvious changes or changes derived therefrom are still within the scope of protection of the present invention.

Claims (10)

1. A single crystal cobalt-free positive electrode material, characterized in that it comprises an inner core and a bromide cladding layer coated on the inner core surface, bromide doping is provided in the inner core, bromine in the single crystal cobalt-free positive electrode material The mass proportion of the compound is 1-10%. 2 . The single crystal cobalt-free cathode material according to claim 1 , wherein the D50 of the single crystal cobalt-free cathode material is 1-4 μm, and the thickness of the bromide coating layer is ≤100 nm. 3. A single crystal cobalt-free cathode material according to claim 1 or 2, characterized in that the ionic conductivity of the single crystal cobalt-free cathode material is 10 ^-8 ~ 10 ^-3 S/cm, and the electronic conductivity The rate is 10 ^-6 ～10 ^-2 S/cm, and the ion diffusion coefficient is 10 ^-13 ～10 ^-6 cm ² /s; And/or, the intensity ratio of the 003 X-ray diffraction peak to the 104 X-ray diffraction peak of the single crystal cobalt-free positive electrode material is ≥1.5, and the half-maximum width of the 003 X-ray diffraction peak is 0.4°-1.0°; And/or, the specific surface area of the single crystal cobalt-free cathode material is 0.01-2m ² /g, and the pH value is ≤11.5; And/or, the single crystal cobalt-free positive electrode material is LiNi _x M _1-x O ₂ , 0.6≤x≤0.95; M is one of Mn or Al; And/or, the bromide is at least one of potassium bromide, sodium bromide, magnesium bromide and lithium bromide. 4. A method for preparing a single crystal cobalt-free positive electrode material, characterized in that it comprises: Mixing a Ni-M-based precursor with a lithium source to obtain a mixed powder a, where M is at least one of Mn or Al; mixing the mixed powder a with the bromide to obtain the mixed powder b; the mass proportion of the bromide in the mixed powder b is 1-10%; Raise the mixed powder b to 450-500°C at a rate of 2-10°C/min and keep it warm for 2-3 hours under an oxygen atmosphere; then raise the rate of temperature at 1-3°C/min to 800-900°C and keep it warm 10 to 16 hours, after cooling, the single crystal cobalt-free cathode material is obtained. 5. The preparation method according to claim 4, wherein the Ni-M-based precursor is Ni _x M _1-x (OH) ₂ , M is one of Mn or Al, where 0.6≤x ≤0.95. 6. The preparation method according to claim 4 or 5, characterized in that the molar ratio of the Ni-M-based precursor to the lithium source is 1:1.06-1.15. 7. The preparation method according to any one of claims 4-6, wherein the lithium source is one of lithium hydroxide, lithium carbonate, lithium nitrate and lithium oxalate, preferably lithium carbonate. 8. The preparation method according to any one of claims 4-7, wherein the bromide is at least one of potassium bromide, sodium bromide, magnesium bromide and lithium bromide. 9. The preparation method according to any one of claims 4-8, characterized in that, in the preparation process of the mixed powder b, the step of mixing a halide flux in the mixed powder a is also included; The flux is at least one of potassium fluoride, sodium fluoride, magnesium fluoride, lithium fluoride, potassium chloride, sodium chloride, magnesium chloride, lithium chloride; the halide flux in the mixed powder b The mass proportion is 1-5%. 10. A lithium ion battery, characterized in that it comprises a single crystal cobalt-free positive electrode material according to any one of claims 1-3, or comprises a single crystal according to any one of claims 4-9 A single crystal cobalt-free positive electrode material prepared by the method for preparing the cobalt-free positive electrode material.

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