Modified positive electrode active material, preparation method thereof and lithium ion battery containing modified positive electrode active material

Abstract

The invention provides a modified positive electrode active material, a preparation method thereof and a lithium ion battery comprising the same. The modified positive electrode active material comprises an inner core and a coating layer coating a local area of the surface of the inner core, the inner core comprises a bulk phase doped region located in the inner core and an interface doped region located on the surface layer of the inner core; the material of the inner core is a positive active material doped with an element M, and the content of the element M in the interface doping region is higher than that of the bulk phase doping region; and the material of the coating layer is an oxide of an element M. The modified positive electrode active material is obtained by performing three-step sintering at different temperatures. The modified positive electrode active material provided by the invention has good dynamic performance and thermodynamic stability, and is beneficial to reducing the internal resistance of the lithium ion battery and improving the cycling stability.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a modified positive electrode active material, a preparation method thereof and a lithium ion battery comprising the same. Background Art

[0002] At present, the electric vehicle industry is developing rapidly, and the demand for power batteries has increased significantly. As one of the four main materials of power batteries, positive electrode materials play a key role in electrical performance. As electric vehicles develop towards long-range and high-safety, the requirements for the energy density, service life, safety and stability of positive electrode materials are also getting higher and higher.

[0003] Hexagonal layered high nickel ternary material LiNi x Co y Mn z O 2 It has received widespread attention due to its high energy density. For fast-charging batteries, it is necessary to balance the kinetic performance and thermodynamic stability of the material. Doping can change the crystal structure of the positive electrode active material and improve the structural stability of the material. Coating can provide a channel for the diffusion of Li ions and at the same time block the active material from the electrolyte, thereby protecting the material body from electrolyte erosion. However, kinetic modification will increase the surface activity of the material and deteriorate the thermodynamic stability of the material. Therefore, how to simultaneously improve the kinetic performance and thermodynamic stability of the positive electrode material is a problem that needs to be solved urgently in this field. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention aims to provide a modified positive electrode active material, a preparation method thereof and a lithium ion battery comprising the same. The modified positive electrode active material has both good kinetic performance and thermodynamic stability, helps to reduce the internal resistance of the lithium ion battery and improve the cycle stability.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a modified positive electrode active material, the modified positive electrode active material comprising a core, and a coating layer coated on a local area of ​​the surface of the core;

[0007] The core includes a bulk doping region located inside the core and an interface doping region located on the surface of the core;

[0008] The material of the core is a positive electrode active material doped with an element M, and the content of the element M in the interface doping region is higher than the content of the element M in the bulk doping region;

[0009] The material of the coating layer is an oxide of element M;

[0010] The element M is selected from one or more of Al, Zr, Y, Sr, W, Ti, Sb, Ce, Mg, Co, Mo and V.

[0011] It should be noted that the element M in the present invention may be the same as certain elements in the positive electrode active material (for example, the positive electrode active material is lithium nickel cobalt manganese oxide, and the element M is Co). In this case, the element M and the element contained in the positive electrode active material should be regarded as different elements and measured separately.

[0012] In the present invention, the coated area on the surface of the core can be isolated from each other (e.g., island-shaped coating) or continuous. The interior of the core where the bulk doping region is located refers to the region in the core surrounded by the interface doping region. Usually, the region in the core other than the interface doping region is the bulk doping region.

[0013] The modified positive electrode active material provided by the present invention uses the same element M to dope and coat the positive electrode active material. The content of the element in the interface doping area is higher than that in the bulk phase doping area, that is, it is distributed in a gradient in the radial direction of the particle. Among them, the element M doped in the bulk phase of the particle can refine the grains and increase the Li + The element M doped in the nanolayer of the particle interface can increase the volume of the interface unit cell, making Li + The electrochemical reaction at the interface (the interface without the coating layer) is smoother, which improves the kinetic performance of the material; the element M in the coating layer can block the positive electrode active material and the electrolyte, play a certain protective role on the positive electrode active material, and improve the thermodynamic stability of the material. By utilizing the mutual cooperation of the above-mentioned gradient doping and coating, the modified positive electrode active material obtained has both good kinetic performance and thermodynamic stability.

[0014] In some embodiments of the present invention, the positive electrode active material is lithium nickel cobalt manganese oxide.

[0015] In some embodiments of the present invention, the molecular formula of the core is Li a Ni b-m Co c Mn d M m O 2 .

[0016] Wherein, 1<a<1.1, for example, it can be 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08 or 1.09, etc.;

[0017] 0.5≤b<0.99, for example, it can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or 0.99, etc.;

[0018] 0<c≤0.2, for example, it can be 0.01, 0.02, 0.03, 0.05, 0.06, 0.08, 0.1, 0.12, 0.13, 0.15, 0.16, 0.18 or 0.2, etc.;

[0019] 0<d≤0.3, for example, it can be 0.01, 0.02, 0.03, 0.05, 0.06, 0.08, 0.1, 0.12, 0.13, 0.15, 0.16, 0.18, 0.2, 0.22, 0.23, 0.25, 0.26, 0.28 or 0.3, etc.;

[0020] b+c+d=1;

[0021] 0.0002≤m≤0.008, for example, it can be 0.0002, 0.0003, 0.0005, 0.0006, 0.0008, 0.001, 0.0015, 0.002, 0.0025, 0.003, 0.0035, 0.004, 0.0045, 0.005, 0.0055, 0.006, 0.0065, 0.007, 0.0075 or 0.008, etc.

[0022] In some embodiments of the present invention, 1.03≤a≤1.05, 0.0015≤m≤0.006.

[0023] In some embodiments of the present invention, the ratio of the total molar amount of Ni, Co, Mn and element M in the core to the molar amount of element M in the coating layer is 1:(0.0001-0.002), for example, it can be 1:0.0001, 1:0.0002, 1:0.0003, 1:0.0005, 1:0.0006, 1:0.0008, 1:0.001, 1:0.0012, 1:0.0013, 1:0.0015, 1:0.0016, 1:0.0018 or 1:0.002, etc.; preferably, it is 1:(0.0005-0.002).

[0024] In some embodiments of the present invention, the thickness of the interface doping region is ≤100 nm, for example, it can be 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, 50 nm, 40 nm, 30 nm, 20 nm, 10 nm or 5 nm.

[0025] In some embodiments of the present invention, the D of the modified positive electrode active material 50 The particle size is 3-18 μm, for example, 3 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm or 18 μm, etc.

[0026] In a second aspect, the present invention provides a method for preparing the modified positive electrode active material as described in the first aspect, the preparation method comprising the following steps:

[0027] (1) mixing a hydroxide precursor of a positive electrode active material, a lithium source and a first M source, and sintering them in an oxygen-containing atmosphere at 730-950° C. (for example, 730° C., 750° C., 760° C., 780° C., 800° C., 820° C., 830° C., 850° C., 860° C., 880° C., 900° C., 920° C., 930° C. or 950° C.) to obtain a first intermediate product;

[0028] (2) mixing the first intermediate product with a second M source, and sintering the mixture in an oxygen-containing atmosphere at 550-700° C. (e.g., 550° C., 560° C., 580° C., 600° C., 620° C., 630° C., 650° C., 660° C., 680° C., or 700° C.) to obtain a second intermediate product;

[0029] (3) mixing the second intermediate product with the third M source, and sintering them in an oxygen-containing atmosphere at 200-400°C (for example, 200°C, 220°C, 230°C, 250°C, 260°C, 280°C, 300°C, 320°C, 330°C, 350°C, 360°C, 380°C or 400°C, etc.) to obtain the modified positive electrode active material.

[0030] In the present invention, the ratio of the elements added in the above preparation method can be determined according to the ratio of the elements in the modified positive electrode active material to be prepared.

[0031] In the present invention, after sintering in step (1), a positive electrode active material uniformly doped with element M is formed; after sintering in step (2), a core of the modified positive electrode active material is formed; after sintering in step (3), an oxide coating layer of element M is formed on a local area of ​​the core surface. By adopting the above three-step sintering method at different temperatures, a modified positive electrode active material having a gradient doping and coating structure in the radial direction is obtained.

[0032] In some embodiments of the present invention, the hydroxide precursor is Ni b Co c Mn d (OH) 2 Among them, b, c, d and the core molecular formula Li a Ni b-m Co c Mn d M m O 2 The same letters have the same meaning.

[0033] In some embodiments of the present invention, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide and lithium nitrate.

[0034] In some embodiments of the present invention, the first M source, the second M source, and the third M source are each independently selected from one or more of the oxides, hydroxides, carbonates, and oxalates of the element M.

[0035] In some embodiments of the present invention, the oxygen-containing atmosphere is an oxygen atmosphere, an air atmosphere, or a mixed atmosphere of air and oxygen.

[0036] In some embodiments of the present invention, the preparation method further comprises: after the sintering in step (1), step (2) and step (3) is completed, crushing the obtained product.

[0037] In some embodiments of the present invention, the preparation method further comprises: before step (3), washing the second intermediate product with water and then drying. The washing is mainly used to wash away the residual alkali on the surface of the second intermediate product to prevent it from deteriorating the performance of the modified positive electrode active material.

[0038] In some embodiments of the present invention, the molar ratio of the hydroxide precursor to the element M in the first M source is 1:(0.0001-0.006), preferably 1:(0.001-0.004). If the amount of element M added in step (1) is too small, its corresponding effect is difficult to play; if the amount added is too large, the battery capacity will be significantly reduced.

[0039] In some embodiments of the present invention, the sintering time in step (1) is 6-12 hours; for example, it can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, etc.

[0040] In some embodiments of the present invention, the molar ratio of the hydroxide precursor to the element M in the second M source is 1:(0.0001-0.002), preferably 1:(0.0005-0.002). If the amount of element M added in step (2) is too small, its corresponding effect is difficult to play; if the amount added is too large, the capacity of the battery will decrease and the internal resistance will increase.

[0041] In some embodiments of the present invention, the sintering time in step (1) is 6-12 hours; for example, it can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, etc.

[0042] In some embodiments of the present invention, the molar ratio of the hydroxide precursor to the element M in the third M source is 1:(0.0001-0.002), preferably 1:(0.0005-0.002). If the amount of element M added in step (3) is too small, its corresponding effect is difficult to play; if the amount added is too large, the coating layer on the surface of the modified positive electrode active material will be too thick, which will reduce the capacity of the battery and increase the impedance.

[0043] In some embodiments of the present invention, the sintering time in step (1) is 4-12 hours; for example, it can be 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, etc.

[0044] In a third aspect, the present invention provides a positive electrode plate, comprising the modified positive electrode active material as described in the first aspect, or the modified positive electrode active material prepared by the preparation method as described in the second aspect.

[0045] In a fourth aspect, the present invention provides a lithium-ion battery, comprising the positive electrode sheet described in the third aspect.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] The modified positive electrode active material provided by the present invention uses the same element to dope and coat the positive electrode active material, and the element is distributed in a gradient in the radial direction of the particle. Among them, the element doped in the particle body can refine the grains and increase the Li + The elements doped in the nanolayer of the particle interface can increase the volume of the interface unit cell, making Li + The electrochemical reaction at the interface (the interface without the coating layer) is smoother, which improves the kinetic performance of the material; the elements coated on the surface of the particles can block the positive electrode active material and the electrolyte, play a certain protective role on the positive electrode active material, and improve the thermodynamic stability of the material. By utilizing the mutual coordination of the above-mentioned gradient doping and coating, the modified positive electrode active material obtained has both good kinetic performance and thermodynamic stability, which helps to reduce the internal resistance of lithium-ion batteries and improve cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A schematic diagram of the structure of a modified positive electrode active material provided in an embodiment of the present invention;

[0049] Figure 2 This is a SEM image of the modified positive electrode active material provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0050] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementations. It should be understood by those skilled in the art that the specific implementations are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0051] Example 1

[0052] This embodiment provides a modified positive electrode active material, and its structural schematic diagram is as follows Figure 1 As shown, it includes a core, and a coating layer coated on a local area of ​​the surface of the core;

[0053] The core includes a bulk doping region located inside the core and an interface doping region located on the surface of the core;

[0054] The molecular formula of the core is Li 1.05 Ni 0.8965 Co 0.05 Mn 0.05 W 0.0035 O 2 , and the content of element W in the interface doping region is higher than that in the bulk doping region;

[0055] The material of the coating layer is WO 3 .

[0056] The preparation method of the modified positive electrode active material described in this embodiment is as follows:

[0057] (1) Polycrystalline hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 Mix with lithium hydroxide and add WO 3 , hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 , Li and W in a molar ratio of 1:1.05:0.002, sintered at 750°C for 8h in a pure oxygen atmosphere, and crushed after cooling to obtain a polycrystalline first intermediate product;

[0058] (2) Releasing the first intermediate product with WO 3 Mixed, hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 The molar ratio of W added in this step is 1:0.0015, sintering at 600°C for 8h in a pure oxygen atmosphere, and crushing after cooling to obtain a polycrystalline second intermediate product;

[0059] (3) mixing the second intermediate product and pure water in a mass ratio of 2:1, stirring at 300 rpm for 3 min, and then filtering with suction, and drying the filter cake in a vacuum oven at 150° C. for 4 h to obtain a washed second intermediate product;

[0060] (4) The second intermediate product after washing in step (3) is mixed with WO 3 Mixed, hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 The molar ratio of W added in this step is 1:0.001, and the product is sintered at 400° C. for 6 h in a pure oxygen atmosphere, and then crushed after cooling to obtain a polycrystalline modified positive electrode active material.

[0061] The surface morphology of the modified positive electrode active material provided in this embodiment was characterized by scanning electron microscopy (SEM). Figure 2 As shown. Figure 2 It can be seen that the surface of the modified positive electrode active material provided in this embodiment has an island-like coating structure, and the D50 particle size of the material particles is 10 μm.

[0062] Example 2

[0063] This embodiment provides a modified positive electrode active material, which is different from the embodiment 1 only in that the WO in step (1), step (2) and step (4) is 3 Replaced with the same molar amount of SrCO 3 .

[0064] Example 3

[0065] This embodiment provides a modified positive electrode active material, which is different from the embodiment 1 only in that the hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 The molar ratio of W to step (1) is 1:0.005.

[0066] Example 4

[0067] This embodiment provides a modified positive electrode active material, which is different from the embodiment 1 only in that the hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 The molar ratio of W to step (2) is 1:0.002.

[0068] Example 5

[0069] This embodiment provides a modified positive electrode active material, which is different from the embodiment 1 only in that the hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 The molar ratio of W in step (4) is 1:0.0015.

[0070] Example 6

[0071] This embodiment provides a modified positive electrode active material, which is different from the embodiment 1 only in that the hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 The molar ratio of W to step (4) is 1:0.003.

[0072] Example 7

[0073] This embodiment provides a modified positive electrode active material, and the preparation method thereof is as follows:

[0074] (1) Polycrystalline hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 Mix with lithium hydroxide and add Al(OH) 3 , hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 The molar ratio of Li and Al is 1:1.05:0.004, sintered at 750°C for 12 hours in a pure oxygen atmosphere, and crushed after cooling to obtain a polycrystalline first intermediate product;

[0075] (2) Releasing the first intermediate product with Al(OH) 3 Mixed, hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 The molar ratio of Al added in this step is 1:0.0005, sintering at 700°C for 6 hours in a pure oxygen atmosphere, and crushing after cooling to obtain a polycrystalline second intermediate product;

[0076] (3) mixing the second intermediate product and pure water in a mass ratio of 2:1, stirring at 300 rpm for 3 min, and then filtering with suction, and drying the filter cake in a vacuum oven at 150° C. for 4 h to obtain a washed second intermediate product;

[0077] (4) The second intermediate product after washing in step (3) is mixed with Al(OH) 3Mixed, hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 The molar ratio of Al added in this step is 1:0.002, and the mixture is sintered at 300° C. for 8 h in a pure oxygen atmosphere, and crushed after cooling to obtain a polycrystalline modified positive electrode active material.

[0078] Example 8

[0079] This embodiment provides a modified positive electrode active material, and the preparation method thereof is as follows:

[0080] (1) Polycrystalline hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 Mix with lithium hydroxide and add ZrO 2 , hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 The molar ratio of Li and Zr is 1:1.05:0.001, sintered at 760°C for 12h in a pure oxygen atmosphere, and crushed after cooling to obtain a polycrystalline first intermediate product;

[0081] (2) The first intermediate product is reacted with ZrO 2 Mixed, hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 The molar ratio of the Zr added in this step is 1:0.001, sintering at 550°C for 6 hours in a pure oxygen atmosphere, and crushing after cooling to obtain a polycrystalline second intermediate product;

[0082] (3) mixing the second intermediate product and pure water in a mass ratio of 2:1, stirring at 300 rpm for 3 min, and then filtering with suction, and drying the filter cake in a vacuum oven at 150° C. for 4 h to obtain a washed second intermediate product;

[0083] (4) The second intermediate product after washing in step (3) is mixed with ZrO 2 Mixed, hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 The molar ratio of Zr added in this step is 1:0.0005, and the product is sintered at 200° C. for 12 h in a pure oxygen atmosphere, and crushed after cooling to obtain a polycrystalline modified positive electrode active material.

[0084] Example 9

[0085] This embodiment provides a modified positive electrode active material, which is different from the embodiment 1 only in that WO 3 Replace with Y 2 O 3 , the molar amount of Y is the same as that of W.

[0086] Example 10

[0087] This embodiment provides a modified positive electrode active material, which is different from the embodiment 1 only in that WO 3 Replace with Sb 2 O 5 , the molar amount of Sb is the same as that of W.

[0088] Embodiment 11

[0089] This embodiment provides a modified positive electrode active material, which is different from the embodiment 1 only in that WO 3 Replaced with the same molar amount of CeO 2 .

[0090] Example 12

[0091] This embodiment provides a modified positive electrode active material, which is different from the embodiment 1 only in that WO 3 Replace with V 2 O 5 , the molar amount of V is the same as that of W.

[0092] Comparative Example 1

[0093] This comparative example provides a modified positive electrode active material, which is different from Example 1 only in that WO is not added in step (1), step (2) and step (4). 3 .

[0094] Comparative Example 2

[0095] This comparative example provides a modified positive electrode active material, which differs from Example 1 only in that WO is not added in step (4). 3 .

[0096] Comparative Example 3

[0097] This comparative example provides a modified positive electrode active material, which is different from Example 1 only in that the polycrystalline hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 and WO in step (1) 3 The molar ratio of WO is 1:0.0035, and WO is not added in step (2). 3 .

[0098] Comparative Example 4

[0099] This comparative example provides a modified positive electrode active material, which differs from Example 1 only in that WO is not added in step (1). 3 , polycrystalline hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH) 2 and WO in step (2) 3 The molar ratio is 1:0.0035.

[0100] Performance Test:

[0101] The modified positive electrode active material, conductive carbon black and PVDF (polyvinylidene fluoride) provided in the above embodiment and comparative example with a mass ratio of 92:5:3 were respectively taken, a certain amount of N-methylpyrrolidone (NMP) was added and mixed evenly, coated on aluminum foil, and dried to form a positive electrode sheet (the thickness of the positive electrode active layer was 100 μm), and then mixed with a separator (24 μm PP separator), an electrolyte (containing 1.1 mol / L LiPF 6 , the solvent consisted of EC, PC and EMC in a volume ratio of 1:2:7), the negative electrode sheet (Li metal) was assembled into a button battery in a glove box, left for 12 hours, and the battery performance was tested.

[0102] First discharge specific capacity: Charge the battery to 4.3V at 0.1C constant current, then charge to 0.05C at constant voltage, and then discharge to 3.0V at 0.1C to test the first discharge specific capacity;

[0103] 50% SOC-DCR (internal resistance at 50% state of charge): Charge the battery at 1C constant current to 4.3V, then charge at constant voltage to 0.05C, discharge at 1C for 30min, let stand for 30min, then discharge at 4C for 10s, and discharge at 1C to 3V.

[0104] DCR = (4C discharge 10s end voltage - static end voltage) / 4C current

[0105] Cycle stability: Cycle for 80 cycles at a temperature of 45°C, a charge and discharge voltage of 3.0-4.3V, and a charge and discharge current of 1C, test the discharge specific capacity, and calculate the capacity retention rate.

[0106] The results of the above tests are shown in Table 1 below:

[0107] Table 1

[0108]

[0109] It can be seen from the test results in Table 1 that, compared with Comparative Example 1 (without doping and coating), the battery using the modified positive electrode active material provided in the embodiment of the present invention has a smaller 50% SOC-DCR and a higher capacity retention rate after 80 cycles at 45°C, indicating that the modified positive electrode active material provided by the present invention has both good kinetic properties and thermodynamic stability.

[0110] Compared with Example 1, in Example 6, due to the excessive amount of W used in step (4), the surface coating of the modified positive electrode active material is excessive and the coating layer is thicker, which reduces the capacity of the battery and increases the DCR.

[0111] Compared with Example 1, Comparative Example 2 does not add WO in step (4). 3 , no coating layer is formed, resulting in decreased kinetic performance and thermodynamic stability of the modified positive electrode active material, increased battery DCR, and decreased cycle performance.

[0112] Compared with Example 1, Comparative Example 3 does not add WO in step (2). 3 The doping elements in the formed core are evenly distributed, resulting in a reduction in the fast ion conductor at the interface of the modified positive electrode active material, Li + The transmission is restricted, so the DCR of the battery increases. At the same time, the interface protection of the modified positive electrode active material is weak, so the cycle attenuation of the battery is aggravated.

[0113] Compared with Example 1, Comparative Example 4 does not add WO in step (1). 3 , resulting in the absence of doped elements in the bulk phase of the modified positive electrode active material, increasing the bulk impedance, and failing to protect the material structure, thus reducing the battery's cycle performance.

[0114] The above description is only a specific embodiment of the present disclosure, so that those skilled in the art can understand or implement the present disclosure. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure will not be limited to the embodiments described herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A modified positive electrode active material, It is characterized in that The modified positive electrode active material comprises a core, and a coating layer coated on a local area of ​​the surface of the core; The core includes a bulk doping region located inside the core and an interface doping region located on the surface of the core; The material of the core is a positive electrode active material doped with an element M, and the content of the element M in the interface doping region is higher than the content of the element M in the bulk doping region; The material of the coating layer is an oxide of element M; The element M is selected from one or more of Al, Zr, Y, Sr, W, Ti, Sb, Ce, Mg, Co, Mo and V.

2. The modified positive electrode active material according to claim 1, It is characterized in that The positive electrode active material is lithium nickel cobalt manganese oxide; Preferably, the molecular formula of the core is Li a Ni b-m Co c Mn d M m O 2 ; Among them, 1<a<1.1, 0.5≤b<0.99, 0<c≤0.2, 0<d≤0.3, b+c+d=1, 0.0002≤m≤0.008; Preferably, 1.03≤a≤1.05, 0.0015≤m≤0.006; Preferably, the ratio of the total molar amount of Ni, Co, Mn and element M in the core to the molar amount of element M in the coating layer is 1:(0.0001-0.002), preferably 1:(0.0005-0.002).

3. The modified positive electrode active material according to claim 1 or 2, It is characterized in that The thickness of the interface doped region is ≤100nm; Preferably, the D of the modified positive electrode active material 50 The particle size is 3-18μm.

4. A method for preparing a modified positive electrode active material according to any one of claims 1 to 3, It is characterized in that The preparation method comprises the following steps: (1) mixing a hydroxide precursor of a positive electrode active material, a lithium source and a first M source, and sintering them in an oxygen-containing atmosphere at 730-950° C. to obtain a first intermediate product; (2) mixing the first intermediate product with a second M source, and sintering the mixture in an oxygen-containing atmosphere at 550-700° C. to obtain a second intermediate product; (3) Mixing the second intermediate product with a third M source, and sintering them in an oxygen-containing atmosphere at 200-400° C. to obtain the modified positive electrode active material.

5. The preparation method according to claim 4, It is characterized in that The hydroxide precursor is Ni b Co c Mn d (OH) 2 ; Preferably, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide and lithium nitrate; Preferably, the first M source, the second M source, and the third M source are each independently selected from one or more of oxides, hydroxides, carbonates, and oxalates of element M; Preferably, the oxygen-containing atmosphere is an oxygen atmosphere, an air atmosphere, or a mixed atmosphere of air and oxygen; Preferably, the preparation method further comprises: after the sintering in step (1), step (2) and step (3) is completed, crushing the obtained product; Preferably, the preparation method further comprises: before step (3), washing the second intermediate product with water and then drying it.

6. The preparation method according to claim 4 or 5, It is characterized in that The molar ratio of the hydroxide precursor to the element M in the first M source is 1:(0.0001-0.006), preferably 1:(0.001-0.004); Preferably, the sintering time in step (1) is 6-12 hours.

7. The preparation method according to any one of claims 4 to 6, It is characterized in that The molar ratio of the hydroxide precursor to the element M in the second M source is 1:(0.0001-0.002), preferably 1:(0.0005-0.002); Preferably, the sintering time in step (1) is 6-12 hours.

8. The preparation method according to any one of claims 4 to 7, It is characterized in that The molar ratio of the hydroxide precursor to the element M in the third M source is 1:(0.0001-0.002), preferably 1:(0.0005-0.002); Preferably, the sintering time in step (1) is 4-12 hours.

9. A positive electrode sheet, It is characterized in that The invention comprises the modified positive electrode active material as claimed in any one of claims 1 to 3, or the modified positive electrode active material prepared by the preparation method as claimed in any one of claims 4 to 8.

10. A lithium ion battery, It is characterized in that Comprising the positive electrode sheet as claimed in claim 9.

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