Positive electrode active material and preparation method and application thereof

Abstract

The invention relates to the technical field of new energy batteries, in particular to a positive electrode active material and a preparation method and application thereof. The positive electrode active material provided by the invention comprises a high-nickel material, and the high-nickel material contains a tantalum element, a magnesium element and a boron element; the chemical general formula of the high-nickel material is Li < 1 + x > Ni M < 1-a > Nb < O2 >, M is selected from at least one of Co and Mn, and N comprises a tantalum element, a magnesium element and a boron element; 0.90 < = a < = 0.98, 0.02 < = x < = 0.10, and 0.001 < = b < = 0.05. The positive electrode active material provided by the invention has excellent capacity, first effect, rate, cycle performance and thermal safety.

Description

A positive electrode active material, its preparation method and application Technical Field

[0001] This invention relates to the field of new energy battery technology, specifically to a positive electrode active material, its preparation method, and its application. Background Technology

[0002] Currently, increasing the nickel content in high-nickel materials can significantly improve the energy density of lithium-ion batteries. However, when the nickel content in high-nickel materials exceeds 90%, the following problems arise: First, nickel ions tend to occupy lithium vacancies during the release process, causing lithium-nickel mixing, hindering lithium ion diffusion, and catalyzing electrolyte decomposition, thus deteriorating the battery's capacity, initial efficiency, and rate performance. Second, high-nickel materials undergo drastic phase transitions during charge and discharge, generating enormous internal stress, leading to cracks and collapse in the high-nickel materials, thus worsening cycle performance. Third, nickel ions in high-nickel materials are prone to reduction reactions under high charge states, resulting in lattice oxygen loss. The released oxygen reacts violently with the electrolyte, triggering battery thermal runaway. At the same time, oxygen vacancies affect the structural stability of high-nickel materials. Summary of the Invention

[0003] In a first aspect, the present invention provides a positive electrode active material, comprising a high-nickel material, wherein the high-nickel material contains tantalum, magnesium, and boron; the chemical formula of the high-nickel material is Li. 1+x Ni a M 1-a N b O2, wherein M is selected from at least one of Co and Mn, and N includes tantalum, magnesium and boron; 0.90≤a≤0.98, 0.02≤x≤0.10, 0.001≤b≤0.05.

[0004] In one optional embodiment, the concentration of tantalum in the positive electrode active material is 0.015 mol%-1.4 mol, based on the total molar amount of nickel, cobalt and manganese in the positive electrode active material.

[0005] In one optional embodiment, the concentration of magnesium in the positive electrode active material is 0.075 mol%-2.85 mol, based on the total molar amount of nickel, cobalt and manganese in the positive electrode active material.

[0006] In one optional embodiment, the concentration of boron in the positive electrode active material is 0.01 mol%-0.8 mol, based on the total molar amount of nickel, cobalt and manganese in the positive electrode active material.

[0007] In one alternative embodiment, at least a portion of the surface of the high-nickel material is provided with a first coating layer, the first coating layer comprising lithium aluminum oxide or a boron-containing compound.

[0008] Furthermore, in an optional embodiment, when the first coating layer contains lithium aluminum oxide, the thickness of the first coating layer is 2nm-20nm.

[0009] Furthermore, in an optional embodiment, when the first coating layer contains a boron-containing compound, the thickness of the first coating layer is 1 nm-10 nm.

[0010] In one alternative embodiment, at least a portion of the surface of the high-nickel material is provided with a first coating layer, the first coating layer comprising lithium aluminum oxide; at least a portion of the surface of the first coating layer is provided with a second coating layer, the second coating layer comprising a boron-containing compound.

[0011] Furthermore, in an optional embodiment, the thickness of the first coating layer is 2nm-20nm.

[0012] Furthermore, in one optional embodiment, the thickness of the second coating layer is 1nm-10nm.

[0013] Secondly, the present invention also provides a method for preparing a positive electrode active material, comprising the following steps: mixing a high-nickel material precursor, a first lithium source, a tantalum source, a magnesium source and a first boron source, and sintering to obtain a positive electrode active material.

[0014] In one optional embodiment, the ratio of the molar sum of transition metal elements in the high-nickel precursor to the molar amount of lithium in the first lithium source is 1:(1.02-1.10).

[0015] In one optional embodiment, the molar sum of transition metal elements in the high-nickel precursor, the molar ratio of tantalum in the tantalum source, magnesium in the magnesium source, and boron in the boron source is 1:(0.0002-0.018):(0.001-0.035):(0.0002-0.012).

[0016] In one alternative embodiment, the tantalum source includes at least one of tantalum oxide and lithium tantalate.

[0017] In one alternative embodiment, the magnesium source includes at least one of magnesium oxide, magnesium hydroxide, and magnesium carbonate.

[0018] In one alternative embodiment, the first boron source includes at least one of boron oxide, boric acid, and lithium metaborate.

[0019] In one alternative embodiment, the first lithium source is selected from at least one of lithium hydroxide and lithium nitrate.

[0020] In one alternative embodiment, the sintering is performed in an oxygen-containing atmosphere.

[0021] In one alternative embodiment, the sintering heating rate is 1-5°C / min.

[0022] In one alternative embodiment, the sintering time is 5-15 hours.

[0023] In one alternative embodiment, the sintering temperature is 650-800°C.

[0024] In one optional embodiment, the sintering process further includes a step of coating with a first coating layer, selected from one of the following (A)-(B): (A) mixing the sintered product, a second lithium source, and an aluminum source, and heat-treating them to obtain a positive electrode active material; (B) mixing the sintered product with a second boron source and calcining it to obtain a positive electrode active material.

[0025] Further heat treatment and coating of the sintered product with a second lithium source and an aluminum source can improve the structural stability of the positive electrode active material, thereby improving the cycle performance of the battery. This is because the second lithium source has a lower melting point and can form a liquid phase at the heat treatment temperature, which helps the aluminum source to be evenly distributed on the surface of the high-nickel material, thereby improving the coating uniformity of the first coating layer. Moreover, the generated lithium aluminum oxide can form chemical bonds with the high-nickel material, improving the structural stability of the positive electrode active material. Furthermore, there may be a trace amount of lithium loss on the surface of the product obtained after sintering. The lithium element in the second lithium source can also diffuse to the surface of the high-nickel material to replenish the missing lithium ions, thereby reducing the interfacial impedance and improving the first efficiency.

[0026] Meanwhile, the sintered product is further mixed with a second boron source to create a boron-containing compound coating layer on the surface of the positive electrode active material, which can further improve the structural stability of the positive electrode active material and thus improve the cycle performance of the battery.

[0027] Further, in an optional embodiment, the molar ratio of nickel, cobalt and manganese in the sintered product, the molar ratio of lithium in the second lithium source and aluminum in the aluminum source is 1:(0.01-0.05):(0.002-0.01).

[0028] Furthermore, in an alternative embodiment, the heat treatment is performed in an oxygen-containing atmosphere.

[0029] Furthermore, in an optional embodiment, the heating rate of the heat treatment is 1-5°C / min.

[0030] Furthermore, in one optional embodiment, the heat treatment time is 5-15 hours.

[0031] Furthermore, in an optional embodiment, the heat treatment temperature is 700-850°C.

[0032] Furthermore, in an optional embodiment, the aluminum source includes at least one of aluminum oxide, aluminum hydroxide, and aluminum nitrate.

[0033] Furthermore, in an optional embodiment, the second lithium source is selected from at least one of lithium hydroxide and lithium nitrate.

[0034] Further, in an optional embodiment, the molar ratio of nickel, cobalt and manganese in the sintered product to boron in the second boron source is 1:(0.0005-0.002).

[0035] Furthermore, in an optional embodiment, the second boron source includes at least one of boric acid and boron oxide.

[0036] Furthermore, in an optional embodiment, the heating rate of the calcination is 1-5°C / min.

[0037] Furthermore, in one optional embodiment, the calcination time is 3-10 hours.

[0038] Furthermore, in an optional embodiment, the calcination temperature is 250-400°C.

[0039] In an optional embodiment, the sintering process further includes the steps of coating a first coating layer and a second coating layer, including the following steps: (1) mixing the sintered product, a second lithium source, and an aluminum source, and heat-treating them to obtain a high-nickel material coated by the first coating layer; (2) mixing the high-nickel material coated by the first coating layer with a second boron source and calcining it to obtain a positive electrode active material.

[0040] Further, in an optional embodiment, the molar ratio of nickel, cobalt and manganese in the sintered product, the molar ratio of lithium in the second lithium source and aluminum in the aluminum source is 1:(0.01-0.05):(0.002-0.01).

[0041] Furthermore, in an alternative embodiment, the heat treatment is performed in an oxygen-containing atmosphere.

[0042] Furthermore, in an optional embodiment, the heating rate of the heat treatment is 1-5°C / min.

[0043] Furthermore, in one optional embodiment, the heat treatment time is 5-15 hours.

[0044] Furthermore, in an optional embodiment, the heat treatment temperature is 700-850°C.

[0045] Furthermore, in an optional embodiment, the aluminum source includes at least one of aluminum oxide, aluminum hydroxide, and aluminum nitrate.

[0046] Furthermore, in an optional embodiment, the second lithium source is selected from at least one of lithium hydroxide and lithium nitrate.

[0047] Further, in an optional embodiment, the molar ratio of nickel, cobalt and manganese in the high-nickel material coated by the first coating layer to the molar ratio of boron in the second boron source is 1:(0.0005-0.002).

[0048] Furthermore, in an optional embodiment, the second boron source includes at least one of boric acid and boron oxide.

[0049] Furthermore, in an optional embodiment, the heating rate of the calcination is 1-5°C / min.

[0050] Furthermore, in one optional embodiment, the calcination time is 3-10 hours.

[0051] Furthermore, in an optional embodiment, the calcination temperature is 250-400°C.

[0052] Thirdly, the present invention also provides the application of the positive electrode active material prepared by the preparation method of the positive electrode active material described in the first aspect or the positive electrode active material described in the second aspect in lithium-ion batteries.

[0053] The technical solution of this invention has the following advantages: 1. The positive electrode active material provided by this invention includes a high-nickel material, wherein the high-nickel material contains tantalum, magnesium, and boron elements; the chemical formula of the high-nickel material is Li. 1+x Ni a M 1-a N b O2, wherein M is selected from at least one of Co and Mn, and N includes tantalum, magnesium, and boron; 0.90≤a≤0.98, 0.02≤x≤0.10, 0.001≤b≤0.05. The positive electrode active material provided by this invention has excellent capacity, first-time efficiency, rate capability, cycle performance, and thermal safety.

[0054] First, the ionic radius of tantalum is similar to that of nickel ions in high-nickel materials, allowing tantalum to preferentially occupy transition metal sites and form Ta-O with oxygen, stabilizing the oxygen layer framework. This can suppress lattice oxygen loss and lattice distortion during charging and discharging, which is beneficial to the battery's cycle performance and thermal safety. It can also provide a more stable crystal environment for magnesium and boron, preventing structural collapse during cycling, which is beneficial to the battery's cycle performance. Secondly, the ionic radius of magnesium is similar to that of lithium ions, allowing magnesium to preferentially occupy lithium sites. On one hand, magnesium has stronger stability because it does not participate in redox reactions; doping with magnesium can improve the stability of the lithium layer and widen the interlayer spacing, thereby promoting lithium ion diffusion. On the other hand, it can also prevent nickel ions from occupying vacancies in the lithium layer, thus avoiding the undesirable phenomenon of lithium-nickel mixing, thereby improving the battery's capacity, initial efficiency, and rate performance. Finally, boron can strengthen the grain boundaries of high-nickel materials, reduce intergranular cracks, and improve the structural stability of the cathode active material, which is beneficial to the battery's cycle performance. At the same time, boron can also promote the uniform doping of tantalum and magnesium, avoiding local stress concentration caused by uneven doping, thereby improving the battery's structural stability.

[0055] 2. The positive electrode active material provided by the present invention, further coated with a first coating layer containing lithium aluminum oxide or a second coating layer containing boron, can improve the structural stability of the positive electrode active material, thereby improving the cycle performance of the battery.

[0056] 3. The method for preparing the positive electrode active material provided by the present invention is simple and has high production efficiency. Detailed Implementation

[0057] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0058] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0059] Experimental Example 1 This experimental example provides a method for preparing a positive electrode active material, including the following steps: (1) mixing lithium hydroxide (LiOH·H2O) and Ni 0.9 Co 0.06 Mn 0.04The (OH)₂ ternary precursor was thoroughly mixed with additives tantalum oxide (Ta₂O₅), magnesium oxide (MgO), and boron oxide (B₂O₃) in a high-speed mixer at a ratio of 1.04:1 (Li:Ni+Co+Mn molar ratio of 1.04:1). The molar ratio of tantalum, magnesium, and boron to the total molar amounts of nickel, manganese, and cobalt in the ternary precursor was 0.0056:0.0111:0.004:1. The mixture was placed in a muffle furnace and sintered at 700℃ for 6 hours under an oxygen atmosphere at a heating rate of 2℃ / min to obtain a high-nickel material.

[0060] (2) Mix high-nickel material, lithium hydroxide and aluminum oxide (Al2O3) (the molar ratio of Ni, Co and Mn in the high-nickel material to lithium in the lithium hydroxide in step (2) is 1:0.02, and the amount of Al added is 0.5 mol% of the molar ratio of Ni, Co and Mn in the high-nickel material). After mixing, place it in a muffle furnace and heat it to 780℃ at 2℃ / min for 10h in an oxygen atmosphere. After crushing and sieving, the high-nickel material coated with the first coating layer is obtained.

[0061] (3) Take 800g of the high-nickel material coated by the first coating layer, wash it with water at a water-to-material ratio of 1:0.6 (water:material), filter it, dry it and mix it with boric acid (H3BO3, the amount of B element added is 0.1mol% of the molar sum of Ni, Co and Mn in the high-nickel material coated by the first coating layer), and calcine it in air at 280℃ for 6h at a temperature of 2℃ / min to obtain the positive electrode active material.

[0062] The chemical formula of high-nickel materials has been determined to be Li. 1.04 Ni 0.9 Co 0.06 Mn 0.04 N 0.018 Based on the total molar amount of nickel, cobalt and manganese in the high-nickel material, the concentration of tantalum in the high-nickel material is 0.5 mol%, the concentration of magnesium is 1.0 mol%, and the concentration of boron is 0.3 mol%; the thickness of the first coating layer is 8 nm, and the thickness of the second coating layer is 3 nm.

[0063] Experimental Example 2 This experimental example provides a method for preparing a positive electrode active material. Compared with Experimental Example 1, the only difference is that step (3) is not performed.

[0064] Experimental Example 3 This experimental example provides a method for preparing a positive electrode active material. Compared with Experimental Example 1, the only difference is that step (2) is not performed.

[0065] Experimental Example 4 This experimental example provides a method for preparing a positive electrode active material, including the following steps: (1) mixing lithium hydroxide and Ni 0.9 Co 0.06Mn 0.04 The (OH)₂ ternary precursor was thoroughly mixed with additives lithium tantalate, magnesium hydroxide, and lithium metaborate in a high-speed mixer at a ratio (Li:Ni+Co+Mn molar ratio of 1.08:1). The molar ratio of tantalum, magnesium, and boron to the total molar amounts of nickel, manganese, and cobalt in the ternary precursor was 0.0156:0.0311:0.012:1. The mixture was placed in a muffle furnace and sintered at 800℃ for 5 hours under an oxygen atmosphere at a rate of 5℃ / min to obtain a high-nickel material.

[0066] (2) Mix high-nickel material, lithium hydroxide and aluminum hydroxide (the molar ratio of Ni, Co and Mn in the high-nickel material to the molar ratio of lithium in lithium hydroxide in step (2) is 1:0.01, and the amount of Al added is 0.2 mol% of the molar ratio of Ni, Co and Mn in the high-nickel material). After mixing, place it in a muffle furnace and heat it at 850°C for 5 hours under an oxygen atmosphere. After crushing and sieving, the high-nickel material coated with the first coating layer is obtained.

[0067] (3) Take 800g of the high-nickel material coated by the first coating layer, wash it with water at a water-to-material ratio of 1:0.6 (water:material), filter it, dry it and mix it with boron oxide (the amount of B element added is 0.2 mol% of the sum of the moles of Ni, Co and Mn in the high-nickel material coated by the first coating layer), and calcine it in air at 400℃ for 3h at a temperature of 2℃ / min to obtain the positive electrode active material.

[0068] The chemical formula of high-nickel materials has been determined to be Li. 1.08 Ni 0.9 Co 0.06 Mn 0.04 N 0.05 Based on the total molar amount of nickel, cobalt and manganese in the high-nickel material, the concentration of tantalum in the high-nickel material is 1.4 mol%, the concentration of magnesium is 2.8 mol%, and the concentration of boron is 0.8 mol%; the thickness of the first coating layer is 18 nm, and the thickness of the second coating layer is 8 nm.

[0069] Example 5 This example provides a method for preparing a positive electrode active material, including the following steps: (1) mixing lithium nitrate and Ni 0.9 Co 0.06 Mn 0.04The (OH)₂ ternary precursor was thoroughly mixed with additives tantalum oxide (Ta₂O₅), magnesium carbonate, and boron oxide (B₂O₃) in a high-speed mixer at a ratio of 1.02:1 (Li:Ni+Co+Mn molar ratio of 1.02:1). The molar ratio of tantalum, magnesium, and boron to the total molar amounts of nickel, manganese, and cobalt in the ternary precursor was 0.0002:0.001:0.0002:1. The mixture was placed in a muffle furnace and sintered at 650℃ for 15 hours under an oxygen atmosphere at a heating rate of 2℃ / min to obtain a high-nickel material.

[0070] (2) Mix high-nickel material, lithium nitrate and aluminum nitrate (Al2O3) (the molar ratio of Ni, Co and Mn in the high-nickel material to lithium in lithium nitrate in step (2) is 1:0.05, and the amount of Al added is 1 mol% of the molar ratio of Ni, Co and Mn in the high-nickel material). After mixing, place it in a muffle furnace and heat it to 700℃ at 2℃ / min for 15h under an oxygen atmosphere. After crushing and sieving, the high-nickel material coated with the first coating layer is obtained.

[0071] (3) Take 800g of the high-nickel material coated by the first coating layer, wash it with water at a water-to-material ratio of 1:0.6 (water:material), filter it, dry it and mix it with boric acid (H3BO3, the amount of B element added is 0.1mol% of the molar sum of Ni, Co and Mn in the high-nickel material coated by the first coating layer), and calcine it in air at 250℃ for 10h at a temperature of 2℃ / min to obtain the positive electrode active material.

[0072] The chemical formula of high-nickel materials has been determined to be Li. 1.02 Ni 0.9 Co 0.06 Mn 0.04 N 0.001 Based on the total molar amount of nickel, cobalt and manganese in the high-nickel material, the concentration of tantalum in the high-nickel material is 0.015 mol%, the concentration of magnesium is 0.075 mol%, and the concentration of boron is 0.01 mol%; the thickness of the first coating layer is 5 nm, and the thickness of the second coating layer is 3 nm.

[0073] Comparative Example 1 This comparative example provides a method for preparing a positive electrode active material. The only difference from Experimental Example 1 is that tantalum oxide is not added in step (1).

[0074] Comparative Example 2 This comparative example provides a method for preparing a positive electrode active material. The only difference from Experimental Example 1 is that magnesium oxide is not added in step (1).

[0075] Comparative Example 3 This comparative example provides a method for preparing a positive electrode active material. The only difference from Experimental Example 1 is that boron oxide is not added in step (1).

[0076] Comparative Example 4 provides a method for preparing a positive electrode active material. The only difference from Experimental Example 1 is that magnesium oxide, tantalum oxide, and boron oxide are not added in step (1).

[0077] Test Examples: This test example provides performance tests for the positive electrode active materials in various experimental and comparative examples, as follows: Positive electrode active material, carbon black, and PVDF (polyvinylidene fluoride) were weighed and mixed at a mass ratio of 90:5:5. An appropriate amount of N-methylpyrrolidone was added to obtain a positive electrode slurry, which was then uniformly coated onto carbon-coated aluminum foil with a coating density of 12 cm³. 2 / mg, after vacuum drying at 80℃ for 2h in a vacuum oven, sliced ​​to obtain the positive electrode sheet; under an argon atmosphere in a glove box, the negative electrode sheet, electrolyte, separator, electrolyte, and positive electrode sheet are assembled in sequence to form a CR2032 button half-cell; wherein, lithium metal sheet is used as the negative electrode sheet, the separator is a Celgard 2500 separator, the electrolyte is a 1mol / L LiPF6 solution, and the solvent in the electrolyte includes ethylene carbonate: dimethyl carbonate: methyl ethyl carbonate in a volume ratio of 1:1:1.

[0078] Test method: (1) First charge and discharge test: At 25℃, charge at a constant current of 0.1C to 4.25V, switch to constant voltage until the current drops to 0.05C, and then discharge at a constant current of 0.1C to 2.8V. Record the first discharge specific capacity and first effect (first effect = first discharge capacity / first charge capacity).

[0079] (2) Rate performance test: At 25℃, the battery was charged and discharged at different rates (0.2C / 0.5C / 1C / 2C) to obtain the discharge capacity at different rates. The discharge capacity retention rate at each rate was calculated (discharge capacity retention rate = discharge capacity at each rate / 0.2C discharge capacity).

[0080] (3) Cyclic performance test: The battery was subjected to constant current charge and discharge cycles at 25°C with a 1C rate between 2.8V and 4.25V. The capacity retention rate after the 100th cycle was recorded (capacity retention rate = (discharge specific capacity of the 100th cycle / discharge specific capacity of the 3rd cycle) × 100%).

[0081] (4) Thermal safety test (DSC): The positive electrode plate charged to 4.25V is removed from the battery and sealed with the electrolyte in a high-pressure crucible. Its initial heat release temperature is tested by differential scanning calorimetry (DSC). The higher the initial heat release temperature, the better the thermal safety.

[0082] Table 1. Test results for each experimental example and comparative example.

[0083] As shown in Table 1, the battery made from the positive electrode active material provided by the present invention has excellent 0.1C discharge specific capacity, first-time efficiency, rate capability, cycle life, and thermal safety. As can be seen from the comparison between Experimental Example 1 and Comparative Examples 1-4, the present invention simultaneously dopes tantalum, magnesium, and boron elements into the positive electrode active material, which can significantly improve the structural stability of the positive electrode active material and suppress adverse phenomena such as lattice oxygen loss, lattice distortion, and lithium-nickel mixing during the charging and discharging process, thereby improving the 0.1C discharge specific capacity, first-time efficiency, rate capability, cycle life, and thermal safety of the battery.

[0084] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A positive electrode active material, characterized in that, This includes high-nickel materials, which contain tantalum, magnesium, and boron; the general chemical formula of the high-nickel materials is Li. 1+x Ni a M 1-a N b O2, wherein M is selected from at least one of Co and Mn, and N includes tantalum, magnesium and boron; 0.90≤a≤0.98, 0.02≤x≤0.10, 0.001≤b≤0.

05.

2. The positive electrode active material according to claim 1, characterized in that, Based on the total molar amount of nickel, cobalt and manganese in the positive electrode active material, the concentration of tantalum in the positive electrode active material is 0.015 mol%-1.4 mol%; and / or, based on the total molar amount of nickel, cobalt and manganese in the positive electrode active material, the concentration of magnesium in the positive electrode active material is 0.075 mol%-2.85 mol%; and / or, based on the total molar amount of nickel, cobalt and manganese in the positive electrode active material, the concentration of boron in the positive electrode active material is 0.01 mol%-0.8 mol%.

3. The positive electrode active material according to claim 1 or 2, characterized in that, At least a portion of the surface of the high-nickel material is provided with a first coating layer, the first coating layer containing lithium aluminum oxide or a boron-containing compound; preferably, when the first coating layer contains lithium aluminum oxide, the thickness of the first coating layer is 2nm-20nm; preferably, when the first coating layer contains a boron-containing compound, the thickness of the first coating layer is 1nm-10nm.

4. The positive electrode active material according to claim 3, characterized in that, At least a portion of the surface of the high-nickel material is provided with a first coating layer, the first coating layer containing lithium aluminum oxide; at least a portion of the surface of the first coating layer is provided with a second coating layer, the second coating layer containing a boron-containing compound; preferably, the thickness of the first coating layer is 2nm-20nm; preferably, the thickness of the second coating layer is 1nm-10nm.

5. A method for preparing a positive electrode active material, characterized in that, The process includes the following steps: mixing a high-nickel precursor, a first lithium source, a tantalum source, a magnesium source, and a first boron source, and sintering them to obtain a positive electrode active material.

6. The method for preparing the positive electrode active material according to claim 5, characterized in that, The ratio of the molar sum of transition metal elements in the high-nickel precursor to the molar amount of lithium in the first lithium source is 1:(1.02-1.10); and / or, the molar ratio of the molar sum of transition metal elements in the high-nickel precursor, the molar amount of tantalum in the tantalum source, the molar amount of magnesium in the magnesium source, and the molar amount of boron in the boron source is 1:(0.0002-0.018):(0.001-0.035):(0.0002-0.012).

7. The method for preparing the positive electrode active material according to claim 5 or 6, characterized in that, The tantalum source includes at least one of tantalum oxide and lithium tantalate; and / or, the magnesium source includes at least one of magnesium oxide, magnesium hydroxide, and magnesium carbonate; and / or, the first boron source includes at least one of boron oxide, boric acid, and lithium metaborate; and / or, the first lithium source is selected from at least one of lithium hydroxide and lithium nitrate; and / or, the sintering is carried out in an oxygen-containing atmosphere; and / or, the sintering heating rate is 1-5 °C / min; and / or, the sintering time is 5-15 h; and / or, the sintering temperature is 650-800 °C.

8. The method for preparing the positive electrode active material according to any one of claims 5-7, characterized in that, The sintering process further includes a step of coating with a first coating layer, selected from one of the following (A)-(B): (A) mixing the sintered product, a second lithium source, and an aluminum source, and heat-treating to obtain a positive electrode active material; (B) mixing the sintered product with a second boron source and calcining to obtain a positive electrode active material; preferably, the molar ratio of nickel, cobalt, and manganese in the sintered product, the molar ratio of lithium in the second lithium source, and the molar ratio of aluminum in the aluminum source is 1:(0.01-0.05):(0.002-0.01); preferably, the heat treatment is carried out in an oxygen-containing atmosphere; preferably, the heating rate of the heat treatment is 1-5℃ / min; preferably, the heat treatment time is... The heat treatment process is performed for 5-15 hours; preferably, the heat treatment temperature is 700-850°C; preferably, the aluminum source includes at least one of alumina, aluminum hydroxide, and aluminum nitrate; preferably, the second lithium source is selected from at least one of lithium hydroxide and lithium nitrate; preferably, the molar ratio of nickel, cobalt, and manganese in the sintered product to boron in the second boron source is 1:(0.0005-0.002); preferably, the second boron source includes at least one of boric acid and boron oxide; preferably, the calcination heating rate is 1-5°C / min; preferably, the calcination time is 3-10 hours; preferably, the calcination temperature is 250-400°C.

9. The method for preparing the positive electrode active material according to claim 8, characterized in that, The sintering process further includes the steps of coating a first coating layer and a second coating layer, comprising the following steps: (1) mixing the sintered product, a second lithium source, and an aluminum source, and heat-treating to obtain a high-nickel material coated with the first coating layer; (2) mixing the high-nickel material coated with the first coating layer with a second boron source and calcining to obtain a positive electrode active material; preferably, the molar ratio of nickel, cobalt, and manganese in the sintered product, the molar ratio of lithium in the second lithium source, and the molar ratio of aluminum in the aluminum source is 1:(0.01-0.05):(0.002-0.01); preferably, the heat treatment is carried out in an oxygen-containing atmosphere; preferably, the heating rate of the heat treatment is 1-5℃ / min; preferably, the heat treatment time is... The calcination time is 5-15 hours; preferably, the heat treatment temperature is 700-850℃; preferably, the aluminum source includes at least one of alumina, aluminum hydroxide, and aluminum nitrate; preferably, the second lithium source is selected from at least one of lithium hydroxide and lithium nitrate; preferably, the molar ratio of nickel, cobalt, and manganese in the high-nickel material coated by the first coating layer to the molar ratio of boron in the second boron source is 1:(0.0005-0.002); preferably, the second boron source includes at least one of boric acid and boron oxide; preferably, the calcination heating rate is 1-5℃ / min; preferably, the calcination time is 3-10 hours; preferably, the calcination temperature is 250-400℃.

10. The application of a positive electrode active material according to any one of claims 1-4 or a positive electrode active material prepared by any one of claims 5-9 in a lithium-ion battery.

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