A three-layer modified layer and surface-doped positive electrode material and preparation method thereof

Abstract

The present invention relates to a three-layer modified layer and a surface-doped positive electrode material and a preparation method thereof, belonging to the technical field of lithium-ion batteries. The positive electrode material comprises an NCM body material, an inner coating layer, an intermediate coating layer, and an outer coating layer. The body is lithium zirconate uniformly doped with zirconium, the intermediate coating layer is a nano-zirconium oxide coating layer, and the outer coating layer is a lithium aluminum zirconium phosphate fast ion conductor layer. The total mass of the coating layer is 1% to 1.5% of the mass of the NCM body material. The shared Zr element at different interfaces strengthens the crystal structure and improves conductivity.

Description

Technical Field

[0001] The invention relates to a three-layer modified layer and a surface-doped positive electrode material and a preparation method thereof, belonging to the technical field of lithium ion batteries. Background Art

[0002] In recent years, to meet the growing demand for clean and sustainable energy, lithium-ion batteries (LIBs) have been widely used in portable electronics, electric vehicles, aerospace equipment, and other fields due to their high energy density and reusability. Nickel-cobalt-manganese (NCM) cathode materials are considered as a potential cathode material due to their superior specific capacity, low cost, low polarization, and good thermal stability.

[0003] However, to date, NCM cathode materials still have problems such as capacity fading and poor rate performance, especially under high cut-off voltage and high temperature conditions. and Ni 2+ The ionic radius of Ni 2+ Ions easily from Li + The ion occupied 3a position migrates to 3b position. + / Ni 2+ Ionic disorder forms an irreversible phase transition from layered structure to spinel structure or rock salt phase, and this transition becomes more serious with the increase of nickel content. This surface structural transition greatly increases the Li + The kinetic barrier of ion diffusion leads to rapid capacity decay of high nickel cathode.

[0004] In order to solve these problems, it is particularly important to find a means of multiple modification to improve the high-voltage and high-temperature cycle stability of NCM cathode materials and reduce Li + / Ni 2+ However, a single modification method cannot solve the above problems simultaneously. Single coating may lead to uneven coating layer, which may fall off during long cycles. Secondly, single coating cannot achieve the synergistic modification effect of accelerating lithium ion transmission and improving the high-temperature stability of the material. Therefore, the preparation of high-nickel cathode with good high-temperature cycling stability remains a challenge. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a positive electrode material having three modified layers and surface doping thereof and a preparation method thereof.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A three-layer modified layer and a positive electrode material doped with the same on its surface. The positive electrode material comprises an NCM body material, an inner coating layer, an intermediate coating layer, and an outer coating layer. The NCM body material is lithium zirconate and is uniformly doped with zirconium in the bulk phase. The intermediate coating layer is a nano-zirconium oxide coating layer, and the outer coating layer is a lithium aluminum zirconium phosphate fast ion conductor layer. The total mass of the coating layers is 1%-1.5% of the mass of the NCM body material.

[0008] Preferably, the NCM main body material is a single crystal particle of 3-5 microns, and the thicknesses of the inner cladding layer, the middle cladding layer and the outer cladding layer are 1-5 nm, 5-10 nm and 5-10 nm respectively.

[0009] Preferably, the NCM main body material is LiNi x Co y Mn 1-x-y O2, 0.8≤x<1, 0 <y≤0.1,0<(1-x-y)≤0.1。

[0010] A method for preparing the three-layer modified layer and the surface-doped positive electrode material of the present invention comprises the following steps:

[0011] (1) preparing a mixed solution of soluble nickel salt, manganese salt and cobalt salt; adding the mixed solution, a precipitant and a complexing agent to a reactor in parallel to carry out a coprecipitation reaction, controlling the pH in the reactor to be 10.5 to 11.5; after the reaction is completed, adding a zirconium source solution to carry out a precipitation reaction until the particle size D50 value of the reaction slurry reaches the target particle size D50 value of the precursor material, and then stopping the reaction;

[0012] (2) subjecting the solid-liquid mixture obtained in step (1) to solid-liquid separation, collecting the solid, washing it, and drying it to obtain a nickel-cobalt-manganese-zirconium hydroxide precursor;

[0013] (3) dispersing the nickel-cobalt-manganese-zirconium hydroxide precursor obtained in step (2) with a lithium source and an aluminum source in an organic solvent, and then adding a phosphorus source and mixing them uniformly to obtain a mixture; wherein the molar ratio of the nickel-cobalt-manganese-zirconium hydroxide precursor, the lithium source, the aluminum source, and the phosphorus source is 1:1.02-1.08:0.005-0.05:0.015:0.15;

[0014] (4) The mixture obtained in step (3) is vacuum dried and calcined at 300-600° C. for 5-15 h in an oxygen atmosphere, and then calcined at 600-900° C. for 5-30 h. After the calcination, a three-layer modified layer and a surface-doped positive electrode material are obtained.

[0015] Preferably, in step (1), the nickel concentration in the nickel salt solution is 1 to 5 mol / L; the manganese concentration in the manganese salt solution is 2 to 7 mol / L; the cobalt concentration in the cobalt salt solution is 1 to 6 mol / L; the zirconium concentration in the zirconium source solution is 1 to 7 mol / L; and the flow rate of the solutions remains consistent.

[0016] Preferably, in step (1), the nickel salt is one or more of nickel nitrate, nickel carbonate, nickel sulfate and nickel chloride; the manganese salt is one or more of manganese nitrate, manganese carbonate, manganese sulfate and manganese chloride; the cobalt salt is one or more of cobalt nitrate, cobalt carbonate, cobalt sulfate and cobalt chloride; the zirconium source is one or more of zirconium oxide, zirconium nitrate, zirconium sulfate and zirconium chloride; the precipitant is sodium hydroxide solution and / or potassium hydroxide solution; and the complexing agent is aqueous ammonia solution.

[0017] Preferably, in step (1), the target particle size D50 value of the precursor material is 1 to 5 μm.

[0018] Preferably, in step (3), the lithium source is one or more of lithium hydroxide, lithium carbonate and lithium nitrate; the aluminum source is one or more of aluminum oxide, aluminum carbonate and aluminum nitrate; and the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphoric acid.

[0019] Preferably, in step (3), the organic solvent is one or more of methanol, ethanol and propanol.

[0020] A lithium ion battery, wherein the positive electrode material of the battery is the positive electrode material with three modified layers and surface doping as described in the present invention.

[0021] Beneficial effects

[0022] The present invention provides a positive electrode material with three modified layers and surface doping thereof. The three-layer coating has a good synergistic effect. The inner coating layer of lithium zirconate strengthens the connection between the main material and the coating layer, and the locally formed Zr-O bonds strengthen the crystal structure. At the same time, the zirconium ions between the lithium zirconate and the nano zirconium oxide share zirconium electron pairs, so that the coatings of the two are closely connected, and the electron transmission efficiency is enhanced. The outermost layer of lithium zirconium aluminum phosphate further enhances the ion conductivity. Generally speaking, the shared Zr element at different interfaces strengthens the crystal structure and improves the conductivity.

[0023] The present invention provides a method for preparing a three-layer modified layer and a surface-doped positive electrode material. First, nano-zirconium oxide reacts with residual lithium on the surface of the ternary electrode to form lithium zirconate, ensuring that the interior is lithium zirconate. Unreacted zirconium oxide forms a second coating layer on the surface of the finished lithium zirconate. Because the temperature for synthesizing lithium zirconium aluminum phosphate is higher than that for synthesizing zirconium oxide, lithium zirconium aluminum phosphate forms last and constitutes the outermost coating layer. The method is simple, has low production costs, and has minimal environmental pollution, making it suitable for industrial production.

[0024] The present invention provides a lithium ion battery, wherein the positive electrode material adopts the positive electrode material of the present invention comprising a three-layer modified layer and a surface doped positive electrode material, wherein Zr is doped into the TM layer in the crystal structure and forms a Zr-O bond with stronger bond energy by combining with oxygen in the crystal lattice; 4+ Doping into the Li site inhibits Li / Ni mixing and widens the lattice spacing. Simultaneously, the lithium zirconate generated on the surface further consumes residual lithium on the surface, preventing Li / Ni mixing. The nano-zirconia coating, with its unique microstructure, improves the material's thermal insulation while maintaining its high-temperature resistance. Both lithium zirconate and lithium aluminum zirconium phosphate are fast ion conductors, ensuring the material's conductivity after long cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a TEM image of the positive electrode material obtained in Example 1 of the present invention;

[0026] Figure 2 This is a HRTEM image of the positive electrode material obtained in Example 1 of the present invention;

[0027] Figure 3 This is a TEM image of the positive electrode material obtained in Comparative Example 3 of the present invention;

[0028] Figure 4 This is a TEM image of the positive electrode material obtained in Comparative Example 5 of the present invention;

[0029] Figure 5 The cycle performance curves of the batteries obtained in Example 1 and Comparative Examples 1-5 are shown. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that what is described are only some embodiments of the present invention, not all embodiments, and these embodiments should not be used to interpret the limitation of the scope of protection requested by the claims of this application. Based on the embodiments of the present invention, all other changes or modifications obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the claims of this application.

[0031] Example 1

[0032] (1) Mix 0.46 L of 2 mol / L NiSO4·6H2O solution, 0.02 L of 2 mol / L CoSO4·7H2O solution, and 0.02 L of 2 mol / L MnSO4·H2O solution to obtain a mixed solution;

[0033] (2) The mixed solution of step (1), 5 L of 5 mol / L NH3·H2O solution, and 0.35 L of 6 mol / L NaOH solution were added to a reactor in parallel, and the mixture was stirred continuously. The pH value of the reaction system was controlled to be 10.8 and the concentration of aqueous ammonia was controlled to be 2 mol / L. A coprecipitation reaction was performed. After the reaction was completed, 0.015 L of 1 mol / L ZrO2 was added and the mixture was reacted for 35 h to obtain a solid-liquid mixture.

[0034] (3) performing solid-liquid separation on the solid-liquid mixture obtained in step (2), collecting the solid, washing the solid, and drying it to obtain a precursor;

[0035] (4) Dispersing 1 mol of the precursor obtained in step (3) with 0.01 mol of Al(NO3)4 and 1.04 mol of lithium nitrate in anhydrous ethanol, and then adding 0.03 mol of phosphoric acid, mixing well, the solid-liquid ratio is 1 g:5 mL, and a mixture is obtained;

[0036] (5) The mixture obtained in step (4) was continuously stirred, the solvent was evaporated, and the mixture was sintered at 600°C for 10 hours and then sintered at 830°C for 20 hours to obtain a positive electrode material with a three-layer modified layer and a surface doped LiNi 0.92 Co 0.04 Mn 0.04 Zr 0.005 O2@1%[Li2ZrO3-ZrO2-Li2AlZr(PO4)3].

[0037] The TEM of the positive electrode material is as follows Figure 1 As shown, the surface is covered with a uniform coating layer with a thickness of about 5-15nm. Figure 2 The three-layer coating structure can be clearly seen from the HRTEM.

[0038] Example 2

[0039] (1) Mix 0.46 L of 2 mol / L NiSO4·6H2O solution, 0.02 L of 2 mol / L CoSO4·7H2O solution, and 0.02 L of 2 mol / L MnSO4·H2O solution to obtain a mixed solution;

[0040] (2) The mixed solution of step (1), 5 L of 5 mol / L NH3·H2O solution, and 0.35 L of 6 mol / L NaOH solution were added to a reactor in parallel, and the mixture was stirred continuously. The pH value of the reaction system was controlled to be 10.8 and the concentration of aqueous ammonia was controlled to be 3 mol / L. A coprecipitation reaction was performed. After the reaction was completed, 0.02 L of 1 mol / L ZrO2 was added and the mixture was reacted for 35 h to obtain a solid-liquid mixture.

[0041] (3) performing solid-liquid separation on the solid-liquid mixture obtained in step (2), collecting the solid, washing the solid, and drying it to obtain a precursor;

[0042] (4) Dispersing 1 mol of the precursor obtained in step (3) with 0.015 mol of Al(NO3)4 and 1.06 mol of lithium nitrate in anhydrous ethanol, and then adding 0.045 mol of phosphoric acid, mixing well, the solid-liquid ratio is 1 g:5 mL, and a mixture is obtained;

[0043] (5) The mixture obtained in step (4) was continuously stirred, the solvent was evaporated, and the mixture was sintered at 600°C for 10 hours and then sintered at 830°C for 20 hours to obtain a positive electrode material with a three-layer modified layer and a surface doped LiNi 0.92 Co 0.04 Mn 0.04 Zr 0.005 O2@1.5%[Li2ZrO3-ZrO2-Li2AlZr(PO4)3].

[0044] Comparative Example 1

[0045] (1) Mix 0.46 L of 2 mol / L NiSO4·6H2O solution, 0.02 L of 2 mol / L CoSO4·7H2O solution, and 0.02 L of 2 mol / L MnSO4·H2O solution to obtain a mixed solution;

[0046] (2) The mixed solution of step (1), 5 L of 5 mol / L NH3·H2O solution, and 0.35 L of 6 mol / L NaOH solution were added to a reactor in parallel, and the mixture was stirred continuously. The pH value of the reaction system was controlled to be 10.8, and the concentration of aqueous ammonia was controlled to be 2 mol / L. A coprecipitation reaction was performed. After the reaction was completed, 0.015 L of 1 mol / L ZrO2 solution was added and the mixture was reacted for 35 h to obtain a solid-liquid mixture.

[0047] (3) performing solid-liquid separation on the solid-liquid mixture obtained in step (2), collecting the solid, washing the solid, and drying it to obtain a precursor;

[0048] (4) Add lithium nitrate to the precursor obtained in step (3) at a ratio of 1:1.05, sinter at 600°C for 10h, and then sinter at 830°C for 20h to obtain the positive electrode material LiNi0.92 Co 0.04 Mn 0.04 Zr 0.005 O2@1%Li2ZrO3-ZrO2.

[0049] Comparative Example 2

[0050] (1) Mix 0.46 L of 2 mol / L NiSO4·6H2O solution, 0.02 L of 2 mol / L CoSO4·7H2O solution, and 0.02 L of 2 mol / L MnSO4·H2O solution to obtain a mixed solution;

[0051] (2) The mixed solution of step (1), 5 L of 5 mol / L NH3·H2O solution, and 0.35 L of 6 mol / L NaOH solution were added to the reactor in parallel, and the mixture was stirred continuously. The pH value of the reaction system was controlled to be 10.8, the concentration of ammonia water was controlled to be 2 mol / L, and a coprecipitation reaction was carried out for 35 h to obtain a solid-liquid mixture.

[0052] (3) performing solid-liquid separation on the solid-liquid mixture obtained in step (2), collecting the solid, washing the solid, and drying it to obtain a precursor;

[0053] (4) Dispersing 1 mol of the precursor obtained in step (3) with 0.01 mol of Al(NO3)4 and 1.04 mol of lithium nitrate in anhydrous ethanol, then adding 0.03 mol of phosphoric acid and 0.01 mol / L ZrO2 solution and mixing evenly, adjusting the solid-liquid ratio to 1 g:5 mL to obtain a mixture;

[0054] (5) The mixture obtained in step (4) was continuously stirred, the solvent was evaporated, and the mixture was sintered at 600°C for 10 hours and then sintered at 830°C for 20 hours to obtain the positive electrode material LiNi 0.92 Co 0.04 Mn 0.04 O2@1% Li2AlZr(PO4)3.

[0055] Comparative Example 3

[0056] (1) Mix 0.46 L of 2 mol / L NiSO4·6H2O solution, 0.02 L of 2 mol / L CoSO4·7H2O solution, and 0.02 L of 2 mol / L MnSO4·H2O solution to obtain a mixed solution;

[0057] (2) The mixed solution of step (1), 5 L of 5 mol / L NH3·H2O solution, and 0.35 L of 6 mol / L NaOH solution were added to the reactor in parallel, and the mixture was stirred continuously. The pH value of the reaction system was controlled to be 10.8, the concentration of ammonia water was controlled to be 2 mol / L, and a coprecipitation reaction was carried out for 35 h to obtain a solid-liquid mixture.

[0058] (3) performing solid-liquid separation on the solid-liquid mixture obtained in step (2), collecting the solid, washing the solid, and drying it to obtain a precursor;

[0059] (4) Add lithium nitrate to the precursor obtained in step (3) at a ratio of 1:1.05, sinter at 600°C for 10h, and then sinter at 830°C for 20h to obtain the positive electrode material LiNi 0.92 Co 0.04 Mn 0.04 O2.

[0060] The positive electrode material LiNi in this embodiment 0.92 Co 0.04 Mn 0.04 TEM of O2 Figure 3 As shown, there is no coating on the surface.

[0061] Comparative Example 4

[0062] (1) Mix 0.46 L of 2 mol / L NiSO4·6H2O solution, 0.02 L of 2 mol / L CoSO4·7H2O solution, and 0.02 L of 2 mol / L MnSO4·H2O solution to obtain a mixed solution;

[0063] (2) The mixed solution of step (1), 5 L of 5 mol / L NH3·H2O solution, and 0.35 L of 6 mol / L NaOH solution were added to a reactor in parallel, and the mixture was stirred continuously. The pH value of the reaction system was controlled to be 10.8, and the concentration of aqueous ammonia was controlled to be 2 mol / L. A coprecipitation reaction was performed. After the reaction was completed, 0.105 L of 1 mol / L ZrO2 solution was added and the mixture was reacted for 35 h to obtain a solid-liquid mixture.

[0064] (3) performing solid-liquid separation on the solid-liquid mixture obtained in step (2), collecting the solid, washing the solid, and drying it to obtain a precursor;

[0065] (4) Dispersing 1 mol of the precursor obtained in step (3) with 0.1 mol of Al(NO3)4 and 1.22 mol of lithium nitrate in anhydrous ethanol, and then adding 0.3 mol of phosphoric acid, mixing well, the solid-liquid ratio is 1 g:5 mL, and a mixture is obtained;

[0066] (5) The mixture obtained in step (4) was continuously stirred, the solvent was evaporated, and the mixture was sintered at 510°C for 12 hours and then sintered at 800°C for 24 hours to obtain the positive electrode material LiNi 0.92 Co 0.04 Mn 0.04 Zr 0.005 O2@10%Li2ZrO3-ZrO2-Li2AlZr(PO4)3.

[0067] Comparative Example 5

[0068] (1) Mix 0.46 L of 2 mol / L NiSO4·6H2O solution, 0.02 L of 2 mol / L CoSO4·7H2O solution, and 0.02 L of 2 mol / L MnSO4·H2O solution to obtain a mixed solution;

[0069] (2) The mixed solution of step (1), 5 L of 5 mol / L NH3·H2O solution, and 0.35 L of 6 mol / L NaOH solution were added to a reactor in parallel, and the mixture was stirred continuously. The pH value of the reaction system was controlled to be 10.8, and the concentration of aqueous ammonia was controlled to be 2 mol / L. A coprecipitation reaction was performed. After the reaction was completed, 0.015 L of 1 mol / L ZrO2 was added and the mixture was reacted for 35 h to obtain a solid-liquid mixture.

[0070] (3) performing solid-liquid separation on the solid-liquid mixture obtained in step (2), collecting the solid, washing the solid, and drying it to obtain a precursor;

[0071] (4) Dispersing 1 mol of the precursor obtained in step (3), 0.01 mol of Al(NO3)4, and 1.04 mol of lithium nitrate in anhydrous ethanol, and then adding 0.03 mol of phosphoric acid, mixing well, and adjusting the solid-liquid ratio to 1 g:5 mL to obtain a mixture;

[0072] (5) The mixture obtained in step (4) was continuously stirred, the solvent was evaporated, and sintered at 830° C. for 20 h to obtain a positive electrode material.

[0073] The TEM images of the positive electrode materials in this embodiment are shown in FIG. Figure 4 As shown, the coating layer is chaotic and uneven, and cannot form a stable coating.

[0074] The positive electrode materials obtained in Example 1 and Comparative Examples 1-5 were assembled into button batteries: the positive electrode material, acetylene black, and polyvinylidene fluoride (PVDF) were made into a slurry at a mass ratio of 8:1:1 and coated on aluminum foil. The dried aluminum foil loaded with the slurry was cut into small discs with a diameter of about 1 cm using a cutting machine as the positive electrode. A metal lithium sheet was used as the negative electrode, Celgard2500 was used as the diaphragm, and a 1M carbonate solution was used as the electrolyte (wherein the solvent was a mixed solution of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1, and the solute was LiPF6). CR2025 button batteries were assembled in an argon atmosphere glove box. The cycle performance of the button battery was tested, and the results are as follows. Figure 5As shown, at 2.75-4.6 V and 50° C., the 1C first discharge gram capacity of the batteries using the positive electrode materials of Example 1 and Comparative Examples 1-5 are 225.5 mA h / g, 221.4 mA h / g, 220.6 mA h / g, 220.2 mA h / g, 221.6 mA h / g, and 220.3 mA h / g, respectively. After 200 cycles at 1C, the capacities were 180mA h / g, 168.4mA h / g, 164.7mA h / g, 101.4mA h / g, 148.2mA h / g, and 154.7mA h / g, respectively, with capacity retention rates of 79.8%, 76.06%, 74.66%, 46.05%, 66.88%, and 70.22%, respectively. At 2.75-4.6V and 50°C, the battery using the positive electrode material of Example 2 had a 1C first discharge capacity of 221.6mA h / g; after 200 cycles at 1C, the capacity was 174mA h / g, with a capacity retention rate of 778.5%. The results demonstrate that the cycle performance of the battery using the positive electrode material of the present invention is greatly improved.

[0075] In summary, the invention includes but is not limited to the above embodiments. Any equivalent replacement or partial improvement made under the spirit and principle of the present invention shall be deemed to be within the scope of protection of the present invention.

Claims

1. A three-layer modified layer and a surface-doped positive electrode material, characterized in that: The positive electrode material includes a nickel-cobalt-manganese (NCM) main body material, an inner coating layer, an intermediate coating layer, and an outer coating layer, wherein the inner coating layer is lithium zirconate and is uniformly doped with zirconium in the bulk phase, the intermediate coating layer is a nano-zirconium oxide coating layer, and the outer coating layer is a lithium zirconium aluminum phosphate fast ion conductor layer; the total mass of the coating layer is 1%-1.5% of the mass of the NCM main body material.

2. The positive electrode material having three modified layers and surface doping thereof according to claim 1, characterized in that: The NCM main body material is a single crystal particle of 3-5 microns, and the thicknesses of the inner cladding layer, the middle cladding layer and the outer cladding layer are 1-5 nm, 5-10 nm and 5-10 nm respectively.

3. The positive electrode material having three modified layers and surface doping thereof according to claim 1, characterized in that: The NCM main material is LiNi x Co y Mn 1-x-y O2, 0.8≤x< 1, 0 <y≤0.1,0 <(1-x-y)≤0.1。 4. A method for preparing a cathode material having a three-layer modification layer and a surface doped cathode material according to any one of claims 1 to 3, characterized in that: The method steps include: (1) preparing a mixed solution of soluble nickel salt, manganese salt and cobalt salt; adding the mixed solution, precipitant and complexing agent into a reactor in parallel to carry out a coprecipitation reaction, controlling the pH in the reactor to be 10.5-11.5; after the reaction is completed, adding a zirconium source solution to carry out a precipitation reaction until the particle size D50 value of the reaction slurry reaches the target particle size D50 value of the precursor material, and then stopping the reaction; (2) subjecting the solid-liquid mixture obtained in step (1) to solid-liquid separation, collecting the solid, washing it, and drying it to obtain a nickel-cobalt-manganese-zirconium hydroxide precursor; (3) dispersing the nickel-cobalt-manganese-zirconium hydroxide precursor obtained in step (2) with a lithium source and an aluminum source in an organic solvent, and then adding a phosphorus source and mixing them uniformly to obtain a mixture; wherein the molar ratio of the nickel-cobalt-manganese-zirconium hydroxide precursor, the lithium source, the aluminum source, and the phosphorus source is 1:1.02-1.08:0.005-0.05:0.015:0.15; (4) The mixture obtained in step (3) is vacuum dried and calcined at 300-600°C for 5-15 hours and then at 600-900°C for 5-30 hours in an oxygen atmosphere. After calcination, a three-layer modified layer and a surface-doped positive electrode material are obtained.

5. The method for preparing a positive electrode material having a three-layer modified layer and a surface doped positive electrode material as claimed in claim 4, characterized in that: In step (1), the nickel concentration in the nickel salt solution is 1-5 mol / L; the manganese concentration in the manganese salt solution is 2-7 mol / L; the cobalt concentration in the cobalt salt solution is 1-6 mol / L; the zirconium concentration in the zirconium source solution is 1-7 mol / L; and the flow rate of the solution remains consistent.

6. The method for preparing a three-layer modified layer and a surface-doped positive electrode material according to claim 4, characterized in that: In step (1), the nickel salt is one or more of nickel nitrate, nickel carbonate, nickel sulfate and nickel chloride; the manganese salt is one or more of manganese nitrate, manganese carbonate, manganese sulfate and manganese chloride; the cobalt salt is one or more of cobalt nitrate, cobalt carbonate, cobalt sulfate and cobalt chloride; the zirconium source is one or more of zirconium oxide, zirconium nitrate, zirconium sulfate and zirconium chloride; the precipitant is sodium hydroxide solution and / or potassium hydroxide solution; and the complexing agent is aqueous ammonia solution.

7. The method for preparing a positive electrode material having three modified layers and surface doping thereof according to claim 4, characterized in that: In step (1), the target particle size D50 value of the precursor material is 1-5 μm.

8. The method for preparing a three-layer modified layer and a surface-doped positive electrode material according to claim 4, characterized in that: In step (3), the lithium source is one or more of lithium hydroxide, lithium carbonate and lithium nitrate; the aluminum source is one or more of aluminum oxide, aluminum carbonate and aluminum nitrate; and the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphoric acid.

9. The method for preparing a positive electrode material having three modified layers and surface doping thereof according to claim 4, characterized in that: In step (3), the organic solvent is one or more of methanol, ethanol and propanol.

10. A lithium-ion battery, characterized in that: The positive electrode material of the battery is a positive electrode material comprising three modified layers and surface doping thereof as described in any one of claims 1 to 3.

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