A positive electrode material and its preparation method and application

Abstract

The present invention belongs to the field of battery materials and relates to a positive electrode material, preparation method, and application. The method utilizes laser irradiation on a high-nickel positive electrode material to generate an in-situ, integrated shell on the outer surface of the material, resulting in a core-shell structured positive electrode material. This method overcomes the existing problems of poor thermal stability and high surface residual alkali levels associated with foreign coating materials. The resulting positive electrode material exhibits excellent rate performance, cycle performance, and high capacity for use in lithium-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the field of power source material preparation, and relates to a high-nickel positive electrode material and a preparation method thereof, as well as application in lithium-ion batteries. Background Art

[0002] High-nickel cathode materials for lithium-ion batteries hold great promise in the new energy vehicle market due to their high capacity, low pollution, and high power. However, these materials have high levels of residual alkali on their surface, making them susceptible to moisture absorption and decomposition. This creates stringent environmental requirements for their use, often requiring surface coating to remove the residual alkali. However, high-nickel materials have poor thermal stability, making secondary heat processing difficult, and coating is often performed at the precursor stage.

[0003] CN108878818A discloses a core-shell structure ternary positive electrode material and its preparation method. The material is a nickel-cobalt-manganese hydroxide precursor core material obtained by a coprecipitation method, and a low-nickel-content nickel-cobalt-manganese carbonate mixed solution is further coprecipitated to obtain a shell material, and a core-shell structure ternary positive electrode material is obtained after aging. CN108172799A discloses a core-shell structure lithium-ion battery ternary positive electrode material and its preparation method. The material is a nickel-cobalt-manganese hydroxide precursor obtained by co-precipitating a mixed solution of nickel salt, cobalt salt, manganese salt, and aluminum salt with ammonia water and sodium hydroxide, and then carbon dioxide gas is introduced to form a layer of aluminum hydroxide coating on the surface of the nickel-cobalt-manganese precursor. After filtering, washing, and drying, a lithium source is added for heat treatment to obtain a nickel-cobalt-manganese material with aluminum oxide coated on the surface. In the above method, since the alkaline raw materials used in the precursor sintering process inevitably diffuse to the outer layer, the surface residual alkali content is still relatively high.

[0004] CN108598400A discloses a three-layer core-shell structured positive electrode material, preparation method, and lithium-ion battery. This material is obtained by coating an aluminum oxide layer and a fast ion conductor layer coating the aluminum oxide layer onto a core ternary positive electrode material using a sol-gel method, followed by a solvent thermal reaction at 150-180°C for 5-20 hours. CN112002904A discloses an electrode material with a surface structured with conductive functional zones. Different functional zones are arranged at different locations on the surface of the electrode substrate material, similar to welding points, with each zone performing the functions of ion conduction and electron conduction, respectively. Localized functional modification at different locations on the electrode material surface solves the problem of mutual shielding between electrons and ions during conduction caused by multi-layer full coating or mixed full coating in traditional technologies. The resulting nodes serve as drainage points, not only more effectively improving electrochemical performance but also significantly reducing the mass proportion of the coating in the overall structure and reducing the amount of inactive material used. While this method can achieve good results, it has relatively stringent process requirements, a long preparation time, and multiple steps. For example, the above-mentioned functional area coating requires that there are two or more electronic conductive areas and ion conductive areas on the surface, and the electronic conductive areas and ion conductive areas cannot overlap in space. This places extremely high demands on the process and also has extremely high requirements on the source of the coating, that is, different materials are selected for different electronic conductive functional areas or different ion conductive functional areas. Summary of the Invention

[0005] The inventors have found through research that when using the coating method to solve the problems of thermal stability and high surface residual alkali content of high nickel positive electrode materials, the coating material usually needs to be added additionally. This not only requires the use of complex ingredients and tedious preparation steps, but also in the preparation and sintering process, due to the influence of different densities, uneven material distribution and different thermal expansion degrees, different materials will inevitably have poor compatibility problems, which often leads to complete or partial core-shell separation. There is a vacuum space between the core and the shell, or the core and the shell are only connected by the van der Waals force between molecules. The migration of electrons and ions requires a jump to the vacuum. The migration process consumes a lot of energy and produces a large phase separation resistance. The phase separation effect is as follows. Figure 1 (a) The inventors discovered through further research that the high-nickel ternary cathode material matrix is ​​a poor conductor of heat. When exposed to laser radiation for a short period of time, the heat only decomposes the surface area, forming a protective layer. Preferably, rapid cooling prevents heat from conducting into the interior, thereby preventing it from affecting overall performance. This led to the completion of the present invention, which overcomes many of the problems associated with foreign coating materials in the prior art.

[0006] The present invention provides a positive electrode material, a preparation method thereof, and its application in lithium-ion batteries. This positive electrode material overcomes the high phase separation resistance problem caused by foreign coating materials in the prior art, as well as the thermal stability and high surface residual alkali content problems of high-nickel positive electrode materials.

[0007] In the first aspect of the present invention, a cathode material is provided. The cathode material consists of an in-situ integrated outer shell and inner core, where the chemical composition of the inner core is expressed as Li a Ni x Co y M z O 2-q , and the chemical composition of the outer shell is expressed as Li a-δ Ni x Co y M z O 2-t , M is selected from at least one metal among Fe, Cr, Cu, Ti, Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, Mn, and Al. Among them, 0.9 ≤ a ≤ 1.2, 0.3 ≤ x ≤ 1, 0 < y ≤ 0.5, 0 < z ≤ 0.3, 0.01 ≤ δ ≤ 0.2, and the values of q and t satisfy the electroneutrality rule.

[0008] In the above technical solution, the particle size of the cathode material is 30 nm - 50 μm. [[ID=2�]]

[0009] In the above technical solution, the thickness of the outer shell is 5 - 100 nm, accounting for more than 0.01% of the particle size of the cathode material.

[0010] In the above technical solution, M is selected from at least one metal among Fe, Cr, Cu, Ti, Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, Mn, and Al. Preferably, M is selected from at least one metal among manganese and aluminum.

[0011] In the above technical solution, the cathode material is obtained by laser irradiation of the inner core material to form an in-situ integrated outer shell on the outer surface layer of the inner core material.

[0012] In the above technical solution, the cathode material consists of an in-situ integrated outer shell and inner core, that is, the outer shell is formed by the transformation of the outer layer of the original inner core and is distributed on the outer layer of the inner core in a continuous and gapless state. The force between the outer shell and the inner core is a chemical bond, with strong binding force and no phase separation.

[0013] In the second aspect of the present invention, a preparation method of a cathode material is provided, including: the step of laser irradiation of the inner core material; where the chemical composition of the inner core material is expressed as Li a Ni x Co y M z O 2-q , M is selected from at least one metal among Fe, Cr, Cu, Ti, Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, Mn, and Al. Among them, 0.9 ≤ a ≤ 1.2, 0.3 ≤ x ≤ 1, 0 < y ≤ 0.5, 0 < z ≤ 0.3, and the value of q satisfies the electroneutrality rule.

[0014] In the above technical solution, the conditions of the laser irradiation are as follows: the power is 100 - 10,000 W, the pulse frequency is 0.1 - 150 Hz, the pulse width is 0.3 - 200 ms, the focal length of the focusing lens is 10 - 5,000 mm, and the irradiated spot area is 0.01 - 500 cm 2 , the single irradiation time is 0.01 - 30 s, and the number of irradiation times is 2 - 10 times.

[0015] In the above technical solution, preferably, the conditions of the laser irradiation are as follows: the power is 350 - 550 W, the pulse frequency is 45 - 60 Hz, the pulse width is 0.3 - 0.7 ms, the focal length of the focusing lens is 100 - 200 mm, and the irradiated spot area is 0.01 - 50 cm 2 , the irradiation time is 0.01 - 10 s, and the number of irradiation times is 2 - 10 times.

[0016] In the above technical solution, the positive electrode material is such that the outer layer of the core material forms an in-situ integrated shell after laser irradiation.

[0017] In the above technical solution, for the shell of the positive electrode material, its chemical composition is expressed as Li a-δ Ni x Co y M z O 2-t , M is selected from at least one metal of Fe, Cr, Cu, Ti, Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, Mn, and Al, where 0.3 ≤ x ≤ 1, 0 < y ≤ 0.5, 0 < z ≤ 0.3, 0.01 ≤ δ ≤ 0.2, and the value of t satisfies the electroneutrality rule.

[0018] In the above technical solution, the thickness of the shell is 5 - 100 nm, which is more than 0.01% of the particle size of the positive electrode material.

[0019] In the above technical solution, the particle size of the positive electrode material is 30 nm - 50 μm.

[0020] In the above technical solution, in the positive electrode material, M is selected from at least one metal of Fe, Cr, Cu, Ti, Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, Mn, and Al, preferably, M is selected from at least one of manganese and aluminum.

[0021] In the above technical solution, the material after laser irradiation is preferably rapidly cooled to obtain the positive electrode material. The rapid cooling method includes air cooling, water cooling, or solvent cooling, with the solvent preferably being at least one of ethanol, acetone, and ether. The temperature of the cooling medium can be -20°C to 50°C, and the cooling time is less than 8 hours, preferably 0.01 to 8 hours. In the present invention, the rapid cooling method is used to ensure that the heat from the irradiation only forms a shell on the surface layer, while the core material is unaffected.

[0022] The third aspect of the present invention provides the use of the above-mentioned positive electrode material in a lithium-ion battery.

[0023] In the above technical solution, the application, specifically, includes mixing, coating, and slicing the above-mentioned positive electrode material with a conductive agent and a binder for use as a battery positive electrode. The conductive agent and binder can be various conductive agents and binders conventionally used in the art. For example, the conductive agent can be selected from at least one of acetylene black, Ketjen black, graphite, carbon tubes, and graphene. The binder can be selected from at least one of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and sodium carboxymethyl cellulose (CMC). The amount of the conductive agent and binder can also be the amount conventionally used in the art. For example, based on the total amount of the positive electrode, the mass content of the positive electrode material can be 50%-98%, the mass content of the conductive agent can be 1%-25%, and the mass content of the binder can be 1%-25%.

[0024] In the above technical solution, the structure of the lithium battery is a conventional structure in the field. For example, the lithium-ion battery includes a positive electrode, a negative electrode, a separator and an electrolyte. The present invention has no particular restrictions on the negative electrode, the separator and the electrolyte, and those skilled in the art can select them according to actual needs. For example, in one embodiment of the present invention, metallic lithium is used for the negative electrode, the separator is a US Celllgard 2400 polypropylene separator, a 1 mol / L LiPF6 solution is used for the electrolyte, and the solvent is a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1.

[0025] The method of preparing a lithium battery using a positive electrode material precursor or a positive electrode material is well known in the art and will not be described here.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. After extensive research, the inventors discovered that the original core material matrix is ​​a poor conductor of heat. After a short period of laser irradiation, the heat only decomposes the surface area, and the resulting lithium oxide volatilizes at high temperatures, forming a lithium-deficient composite shell. Rapid cooling is preferably used to prevent heat from conducting into the interior, thereby reducing the impact on the overall performance of the positive electrode material. The method of the present invention is simple to operate, requires mild conditions, and is low-cost. It effectively solves the problems of structural damage to the substrate itself caused by the secondary high-temperature shell coating and the easy formation of phase separation between the core and shell.

[0028] 2. The outer shell and inner core of the cathode material of the present invention are in situ integrated. The interaction between the outer shell and the inner core is a chemical bond, resulting in a strong binding force. Phase separation does not occur during use, thereby facilitating the migration of ions and electrons, reducing internal resistance, and increasing capacity. In addition, the amount of residual alkali on the surface of the cathode material can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of phase separation of cathode materials prepared by conventional coating method (a) and schematic diagram of in-situ coating of cathode materials of the present invention (b);

[0030] Figure 2 This is a SEM image of the ternary cathode material 811 used in Example 1 of the present invention;

[0031] Figure 3 This is an EDS element distribution diagram of a selected area on the surface of the positive electrode material obtained in Example 1 of the present invention;

[0032] Figure 4 This is an element mapping diagram of the ternary cathode material 811 used in Example 1 of the present invention before in-situ coating;

[0033] Figure 5 This is the element mapping diagram of the ternary cathode material 811 after in-situ coating used in Example 1 of the present invention;

[0034] Figure 6 TEM image of the ternary cathode material 811 used in Example 1 of the present invention before in-situ coating;

[0035] Figure 7 This is a TEM image of the ternary cathode material 811 used in Example 1 of the present invention after in-situ coating;

[0036] Figure 8 The AC impedance spectra of the ternary cathode material 811 used in Example 1 of the present invention before and after in-situ coating;

[0037] Figure 9 This is a comparison chart of the charge and discharge curves of the ternary positive electrode material 811 used in Example 1 of the present invention before and after in-situ coating. DETAILED DESCRIPTION

[0038] The technical solutions of the present invention are further described in detail below with reference to the embodiments, but the protection scope of the present invention is not limited to the following embodiments.

[0039] In the present invention, the scanning electron microscope (SEM) images were obtained using a scanning electron microscope of the ZEISS Merlin model manufactured by the German ZEISS company.

[0040] In the present invention, the metal component content is obtained using an X-ray energy dispersive spectrometer (EDS) scanner from Oxford Instruments in the UK. Specifically, the present invention uses an X-ray energy dispersive spectrometer (EDS) scanner to measure the metal components in individual positive electrode material precursor particles. The EDS energy dispersive spectrometer scans the composition of the metals Ni, Co, and M in 400 particles, and calculates the relative standard deviations of the Ni, Co, and M contents in the 400 particles, respectively, as RSD(Ni), RSD(Co), and RSD(M).

[0041] In the present invention, the method for determining the median particle size of the cathode material precursor is a dynamic light scattering technique, which is obtained by a Mastersizer 3000 laser particle size analyzer produced by Malvern Panalytical Company, UK.

[0042] In the present invention, the scanning instrument used for the TEM image is a SUPRA-55 field emission scanning electron microscope produced by the German Zeiss Company.

[0043] In the Examples and Comparative Examples of the present invention, the battery model is a 2032 button cell. The electrochemical performance of the lithium battery can be tested using conventional methods in the art, for example, on a Newway BTS4000 system. The electrochemical performance testing conditions include a temperature of 25°C and a voltage range of 3-4.3V.

[0044] Example 1

[0045] This embodiment uses lithium-ion battery high nickel ternary positive electrode material 811 (LiNi 0.8 Co 0.1 Mn 0.1 O2) as raw material. Figure 2 From the SEM image, it can be seen that the particle size of the material particles is 30nm-50μm.

[0046] Take 1g of high-nickel ternary positive electrode material 811 sample, use a laser with a power of 450W, the focal length of the focusing mirror is 150mm, the spot diameter is adjusted to 0.5cm, the pulse frequency is 10Hz, the pulse width is 0.5ms, the single irradiation is 0.1s, and the irradiation is repeated 3 times after grinding. After each irradiation, it is immediately put into 50ml of room temperature alcohol to cool for 0.01h and dried to obtain an in-situ coated high-nickel ternary positive electrode material.

[0047] The surface selected area EDS element distribution of high nickel ternary cathode material 811 (upper curve) and in-situ coated high nickel ternary cathode material (lower curve) is shown in Figure 3 .Depend on Figure 3 It can be seen that the surface elements of the in-situ coated high nickel ternary cathode material are mainly composed of O, Mn, Co and Ni, and the core material is composed of Li 1.0 Ni 0.8 Co 0.1 Mn 0.1 O 2.0 , the surface material composition after in-situ coating is Li 0.7 Ni 0.8 Co 0.1 Mn 0.1 O 1.9 .

[0048] The element mapping diagrams of the ternary positive electrode material 811 and the in-situ coated high nickel ternary positive electrode material used in Example 1 of the present invention are shown in FIG. Figure 4 and Figure 5 .

[0049] The TEM image of the ternary cathode material 811 used in Example 1 of the present invention is shown in FIG. Figure 6 The TEM image of the in-situ coated high nickel ternary cathode material obtained in Example 1 of the present invention is shown in FIG. Figure 7 .Depend on Figure 7 A clear coating layer can be seen, with a thickness of about 5-60 nm.

[0050] The AC impedance spectra of the ternary positive electrode material 811 (blank sample) and the in-situ coated high nickel ternary positive electrode material (modified sample) used in Example 1 of the present invention are shown in FIG. Figure 8 .Depend on Figure 8 It can be seen that after in-situ coating, the internal resistance is reduced from the initial 178 ohms to 125 ohms, and the internal resistance is significantly reduced.

[0051] The charge and discharge curves of the ternary positive electrode material 811 (blank sample) and the obtained in-situ coated high nickel ternary positive electrode material (in-situ coated sample) used in Example 1 of the present invention are shown in FIG. Figure 9 At a rate of 0.1C and a voltage range of 3-4.3V, the discharge capacity of the in-situ coated material was 202mAh·g -1 Under the same conditions, the capacity of the untreated blank sample is 187 mAh g -1 , indicating that the reversible capacity increases after in situ coating.

[0052] Example 2

[0053] This embodiment uses a lithium-ion battery high nickel ternary positive electrode material NCA (LiNi 0.8 Co0.15 Al 0.05 O2) as raw material.

[0054] Take 1g of NCA material, use a laser with a power of 450W, the focal length of the focusing mirror is 150mm, the spot diameter is adjusted to 1cm, the pulse frequency is 20Hz, the pulse width is 0.5ms, and the irradiation is 0.5 seconds. After grinding, repeat the irradiation 5 times. After each irradiation, immediately put it into 50ml of room temperature deionized water to cool for 8h and dry it to obtain an in-situ coated NCA high-nickel ternary positive electrode material.

[0055] The core composition of the obtained material is LiNi 0.8 Co 0.15 Al 0.05 O2, the outer shell is composed of Li 0.8 Ni 0.8 Co 0.15 Al 0.05 O 1.9 The shell thickness is 10-65nm.

[0056] The performance test of the cathode material obtained in this example was carried out according to the method of Example 1. At a rate of 0.1C and a voltage range of 3-4.3V, the initial discharge capacity was 206 mAh·g -1 The capacity retention rate of the obtained sample at 1C is 85% of the 0.1C capacity, indicating good rate performance.

[0057] Example 3

[0058] This embodiment uses lithium-ion battery ternary positive electrode material 622 (LiNi 0.6 Co 0.2 Mn 0.2 O2) as raw material.

[0059] Take 1g of 622 sample, adjust the laser power to 450W, the focal length of the focusing mirror to 150mm, the spot diameter to 1cm, the pulse frequency to 40Hz, the pulse width to 0.5ms, irradiate for 30s, and perform grinding-irradiation operations for a total of 10 times. Each time, quickly cool with 50ml of deionized water for 1h to obtain the in-situ coated 622 ternary positive electrode material.

[0060] The core composition of the obtained material is LiNi 0.6 Co 0.2 Mn 0.2 O2, the outer shell is composed of Li 0.8 Ni 0.6 Co 0.2 Mn 0.2 O 1.9 , the shell thickness is 5-50nm.

[0061] The obtained material was prepared into a 1 cm 2 The internal resistance of the blank substrate material is 121Ω, while the internal resistance of the material obtained in the present invention is 53Ω, indicating that the conductive performance of the material prepared in this embodiment is enhanced.

[0062] Example 4

[0063] This embodiment uses lithium-ion battery lithium nickel mixed arrangement ternary material (Li 0.98 Ni 0.02 )·(Li 0.05 Ni 0.75 Co 0.1 Mn 0.1 )O2 as raw material.

[0064] Take 1g of mixed material (Li 0.98 Ni 0.02 )·(Li 0.05 Ni 0.75 Co 0.1 Mn 0.1 )O2, use a laser with a power of 450W, the focal length of the focusing mirror is 150mm, the spot diameter is adjusted to 1cm, the pulse frequency is 50Hz, the pulse width is 0.5ms, irradiate for 1s in an air atmosphere, re-grind and irradiate 8 times, and after each laser irradiation, quickly put it into 50ml of deionized water to cool for 0.5h to obtain the laser irradiated in-situ coated mixed positive electrode material.

[0065] The core composition of the obtained material is (Li 0.98 Ni 0.02 )·(Li 0.05 Ni 0.75 Co 0.1 Mn 0.1 )O2, the outer shell is composed of (Li 0.8 Ni 0.02 )·(Li 0.05 Ni 0.75 Co 0.1 Mn 0.1 )O 1.9 , the shell thickness is 5-50nm.

[0066] The performance test of the cathode material obtained in this example was carried out according to the method of Example 1. At a charge and discharge rate of 0.1C and a voltage range of 3-4.3V, the initial discharge capacity was 196mAh·g -1 , 1C discharge capacity reaches 163mAh·g -1 After 50 cycles, the discharge capacity is 155 mAh g -1 , indicating good rate performance and stable cycle performance.

[0067] Example 5

[0068] This embodiment uses lithium-ion battery lithium-rich manganese-based ternary positive electrode material 0.25Li2MnO3·0.75LiNi 0.8 Co 0.1 Mn 0.1 O2 is the raw material.

[0069] Take 1g of lithium-rich manganese-based material 0.25Li2MnO3·0.75LiNi 0.8 Co 0.1 Mn 0.1 O2, using a laser with a power of 450W, the focal length of the focusing mirror is 150mm, the spot diameter is adjusted to 1.5cm, the pulse frequency is 50Hz, the pulse width is 0.5ms, and it is irradiated for 5s in an air atmosphere. It is then re-ground and irradiated three times. After each laser irradiation, it is quickly immersed in 50ml of deionized water and cooled for 0.5h to obtain an in-situ coated lithium-rich manganese-based material.

[0070] The core composition of the obtained material is 0.25Li2MnO3·0.75LiNi 0.8 Co 0.1 Mn 0.1 O2, shell composition is 0.25Li 1.8 MnO 2.9 0.75LiNi 0.75 Co 0.1 Mn 0.1 O 1.875 , the shell thickness is 5-55nm.

[0071] The obtained material was prepared into a 1 cm 2 The internal resistance of the untreated blank substrate material is 150Ω, while the internal resistance of the material obtained in the present invention is 48Ω, which shows that the conductive performance of the material prepared in this embodiment is enhanced.

[0072] Comparative Example 1

[0073] Select lithium-ion battery high nickel ternary material 811 (LiNi 0.8 Co 0.1 Mn 0.1 O2) for in-situ coating.

[0074] Take 1g of high-nickel ternary material 811 sample, use a laser with a power of 450W, the focal length of the focusing mirror is 150mm, the spot diameter is adjusted to 0.5cm, the pulse frequency is 10Hz, the pulse width is 0.5ms, the single irradiation time is 50s, and after grinding, repeat the irradiation 3 times. After each irradiation, immediately put it into 50ml of room temperature alcohol to cool for 0.01h and dry it to obtain an in-situ coated high-nickel ternary positive electrode material.

[0075] The discharge capacity was 125 mAh g at a rate of 0.1 C and a voltage range of 3-4.3 V. -1 , the internal resistance is 230 ohms.

[0076] The above describes in detail the specific embodiments of the present invention, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as the contents disclosed by the present invention and fall within the scope of protection of the present invention.

Claims

1. A positive electrode material, the positive electrode material is composed of an in-situ integrated shell and core, the shell is formed by transforming the outer layer of the original core and is distributed on the outer layer of the core in a continuous and gapless state, wherein the chemical composition of the core is expressed as Li a Ni x Co y M z O 2-q , the shell chemical composition is expressed as Li a-δ Ni x Co y M z O 2-t , M is selected from at least one metal of Mn and Al, wherein, 0.9 ≤ a ≤ 1.2, 0.3 ≤ x ≤ 1, 0 < y ≤ 0.5, 0 < z ≤ 0.3, 0.01 ≤ δ ≤ 0.2, and the values of q and t satisfy the electroneutrality rule; the positive electrode material is obtained by laser irradiation of the core material to form an in-situ integrated outer shell on the outer surface layer of the core material.

2. The positive electrode material according to claim 1, characterized in that The particle size of the positive electrode material is 30 nm - 50 μm.

3. The positive electrode material according to claim 1 or 2, characterized in that The thickness of the outer shell is 5 - 100 nm, accounting for more than 0.01% of the particle size of the positive electrode material.

4. A method for preparing a positive electrode material, comprising: The step of laser irradiation of the core material; The material after laser irradiation is rapidly cooled to obtain the positive electrode material described above; where the chemical composition of the core material is expressed as Li a Ni x Co y M z O 2-q , M is selected from at least one metal of Mn and Al, where 0.9 ≤ a ≤ 1.2, 0.3 ≤ x ≤ 1, 0 < y ≤ 0.5, 0 < z ≤ 0.3, and the value of q satisfies the electroneutrality rule; The laser irradiation conditions are as follows: power of 100-10000W, pulse frequency of 0.1-150Hz, pulse width of 0.3-200ms, focal length of focusing mirror of 10-5000mm, irradiation spot area of ​​0.01-500cm 2 The single irradiation time is 0.01-30s, and the number of irradiations is 2-10 times.

5. The preparation method according to claim 4, characterized in that: The laser irradiation conditions are as follows: power 350-550W, pulse frequency 45-60Hz, pulse width 0.3-0.7ms, focal length of focusing mirror 100-200mm, irradiation spot area 0.01-50cm 2 The irradiation time is 0.01-10s, and the irradiation times are 2-10 times.

6. The preparation method according to claim 4, characterized in that: The core material is irradiated by laser to form an in-situ integral outer shell on the outer surface layer of the core material, and the chemical composition of the outer shell is expressed as Li a-δ Ni x Co y M z O 2-t , M is selected from at least one metal of Mn and Al, wherein, 0.3 ≤ x ≤ 1, 0 < y ≤ 0.5, 0 < z ≤ 0.3, 0.01 ≤ δ ≤ 0.2, and the value of t satisfies the electroneutrality rule.

7. Application of the positive electrode material according to any one of claims 1 - 3 or the positive electrode material prepared by the preparation method according to any one of claims 4 - 6 in a lithium-ion battery.

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