A positive electrode active material, a method for manufacturing the same, a positive electrode sheet, and a battery

Abstract

This invention provides a positive electrode active material and its preparation method, a positive electrode sheet, and a battery. The positive electrode active material includes a core material and a shell material disposed on at least a portion of the surface of the core material. The shell material includes lithium aluminum titanium phosphate, and the core material includes M-doped lithium nickel manganese oxide active material, wherein M includes titanium, phosphorus, and yttrium. The positive electrode active material of this invention, based on a dual strategy of titanium, phosphorus, and yttrium co-doping and lithium aluminum titanium phosphate coating, solves the problems of poor structural stability and severe interfacial side reactions of lithium nickel manganese oxide at high temperatures, while also effectively ensuring its normal specific capacity.

Description

Technical Field

[0001] This invention relates to the field of battery materials, and more particularly to a positive electrode active material and its preparation method, a positive electrode sheet, and a battery. Background Technology

[0002] Lithium nickel manganese oxide (LiNi) 0.5 Mn 1.5 O4 (LNMO) has emerged as a potential candidate material to replace traditional ternary materials (such as NCM) and lithium iron phosphate (LFP) due to its high operating voltage (approximately 4.6V), theoretical specific capacity (approximately 146 mAh / g), and thermodynamic stability of its spinel structure. Its high voltage characteristics can significantly improve the energy density of battery systems, while its low cost and structural stability help reduce battery manufacturing costs and improve safety. However, LNMO still faces the problem of insufficient material stability in practical applications, which limits its large-scale commercial application. Summary of the Invention

[0003] To address the above problems, this invention provides a positive electrode active material based on a dual strategy of titanium, phosphorus, and yttrium co-doping and lithium titanium aluminum phosphate (LATP) coating, which solves the problems of poor structural stability and severe interfacial side reactions of lithium nickel manganese oxide (LNMO).

[0004] The present invention also provides a method for preparing the above-mentioned positive electrode active material, which can prepare the above-mentioned positive electrode active material and has a simple process.

[0005] The present invention also provides a positive electrode sheet, which, since it includes the above-mentioned positive electrode active material, helps to improve the cycle stability of the battery.

[0006] The present invention also provides a battery that, because it includes the above-mentioned positive electrode, has excellent cycle stability.

[0007] In a first aspect, the present invention provides a positive electrode active material, comprising: a core material and a shell material disposed on at least a portion of the surface of the core material, wherein the shell material comprises lithium aluminum titanium phosphate, and the core material comprises M-doped lithium nickel manganese oxide active material, wherein M comprises titanium, phosphorus and yttrium.

[0008] As described above, in the positive electrode active material, the manganese content in the lithium nickel manganese oxide active material decreases from the core material to the shell material.

[0009] In the positive electrode active material described above, the mass percentage of phosphorus is 0.01%-2% based on the total mass of the positive electrode active material;

[0010] And / or, based on the total mass of the positive electrode active material, the mass percentage of titanium is 0.01%-2%;

[0011] And / or, based on the total mass of the positive electrode active material, the mass percentage of yttrium is 0.01%-2%;

[0012] And / or, the mass ratio of the core material to the shell material is 400-500:5-10.

[0013] The positive electrode active material described above has a particle size of 5μm-10μm;

[0014] And / or, the specific surface area of ​​the positive electrode active material is 0.4 m². 2 / g-0.5m 2 / g.

[0015] In a second aspect, the present invention provides a method for preparing a positive electrode active material as described in the first aspect, comprising the following steps:

[0016] A mixture of nickel manganese hydroxide, lithium salt, titanium source, phosphorus source and yttrium source is heated to 800-950°C at a heating rate of 3-5°C / min for the first time, held at that temperature for the first time, and then held at that temperature for the second time after the temperature drops to 550-650°C to obtain the nuclear material.

[0017] The core material and shell material are mixed, and the temperature is increased from room temperature to 600-700℃ for the second time at a heating rate of 3-6℃ / min, followed by a third holding period to obtain the positive electrode active material.

[0018] In the preparation method described above, the first heat preservation time is 8-12 hours; and / or, the second heat preservation time is 5-8 hours; and / or, the third heat preservation time is 8-14 hours.

[0019] In the preparation method described above, the first heating, the first holding, the second heating, and the second holding all include the step of introducing a protective gas to bring the gas pressure to 0.2-0.8 Pa.

[0020] And / or, the second heating and the third heat preservation both include the step of: introducing protective gas to bring the gas pressure to 0.5-1.0 Pa.

[0021] The preparation method described above further includes sieving before the core material and shell material are mixed, wherein the mesh size of the sieve is not less than 200 mesh;

[0022] And / or, after the third heat preservation, it also includes crushing, demagnetizing and sieving, wherein the mesh size of the sieve is not less than 300 mesh.

[0023] Thirdly, the present invention provides a positive electrode sheet, comprising the positive electrode active material described in the first aspect or the positive electrode active material prepared by the preparation method described in the second aspect.

[0024] Fourthly, the present invention provides a battery comprising the positive electrode active material described in the first aspect, the positive electrode active material prepared by the preparation method described in the second aspect, or the positive electrode sheet described in the third aspect.

[0025] The positive electrode active material provided by this invention is based on a dual strategy of titanium, phosphorus, and yttrium co-doping and lithium aluminum titanium phosphate (LATP) coating, which solves the problems of poor structural stability and severe interfacial side reactions of lithium nickel manganese oxide (LNMO), while also effectively ensuring the specific capacity of the positive electrode active material. Attached Figure Description

[0026] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0027] Figure 1 The XRD pattern of the positive electrode active material prepared in Example 1 of this invention;

[0028] Figure 2 The image shows a SEM image of the positive electrode active material prepared in Example 6 of this invention.

[0029] Figure 3 SEM image of the positive electrode active material prepared in Example 2 of this invention;

[0030] Figure 4 SEM image of the positive electrode active material prepared in Example 7 of this invention;

[0031] Figure 5 This is Example 2 of the present invention, showing the cycle capacity retention curves obtained from testing batteries assembled with the positive electrode active materials of Comparative Examples 1-3;

[0032] Figure 6 The graphs show the specific capacity performance of batteries assembled with the positive electrode active materials of Comparative Examples 1-3 of this invention. Detailed Implementation

[0033] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," and "right" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation or be constructed and operated in a specific orientation. Therefore, the terms describing positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0035] In this invention, the terms "first," "second," etc., are mainly used to distinguish different devices, elements, or components (the specific types and structures may be the same or different), and are not used to indicate or imply the relative importance and quantity of the indicated devices, elements, or components.

[0036] In existing technologies, modifications to LNMO include doping: introducing metallic elements (such as Mg, Al, Ti, etc.) or non-metallic elements (such as P, B, etc.) into the LNMO lattice to stabilize its structure and suppress transition metal dissolution. However, existing doping methods are insufficient to adequately suppress Mn. 3+ Dissolution and lattice oxygen migration. Coating the surface of LNMO with an inert material (such as Al2O3, Li2ZrO3, LiAlO2, etc.) forms a physical barrier to isolate the electrolyte from direct contact with the cathode material. However, the existing coating materials (such as Al2O3) are not chemically inert enough to effectively block the corrosion of HF.

[0037] It is evident that existing methods cannot effectively address the stability issue of LNMO materials, especially at high temperatures where the stability of LNMO materials deteriorates significantly. The inventors discovered through research that introducing multiple specific doping elements and simultaneously coating with specific materials can synergistically optimize the material structure and interface stability, particularly significantly improving its high-temperature resistance. Therefore, this invention provides the following technical solution:

[0038] In a first aspect, the present invention provides a positive electrode active material, comprising: a core material and a shell material disposed on at least a portion of the surface of the core material, the shell material comprising lithium aluminum titanium phosphate, and the core material comprising M-doped lithium nickel manganese oxide active material, wherein M comprises titanium, phosphorus and yttrium.

[0039] The positive electrode active material provided by this invention is based on titanium, phosphorus, yttrium co-doping and lithium titanium aluminum phosphate (Li). 1.3 Al 0.3 Ti 1.7The dual strategy of coating (PO4)3 with LATP solves the problems of poor structural stability and severe interfacial side reactions of lithium nickel manganese oxide (LNMO) at high temperatures (greater than or equal to 40℃), while ensuring its specific capacity. Specifically, titanium (Ti) stabilizes the lattice oxygen framework, phosphorus (P) optimizes lattice order, and yttrium (Y) promotes the formation of the interfacial SEI film; the three synergistic effects inhibit Mn. 3+ It dissolves and reduces oxygen vacancy migration, and improves the electrochemical performance of materials. In addition, LATP coating can block the corrosion of cathode materials by electrolyte decomposition products (such as HF), while maintaining the rapid transport of lithium ions, thus achieving a balance between interfacial stability and ionic conductivity.

[0040] In one specific embodiment, the manganese content in lithium nickel manganese oxide active materials decreases from the core material to the shell material.

[0041] In the above-described embodiment, from the core material to the shell material, the manganese content is high inside the core material, which utilizes the structural stability of high manganese to serve as a solid foundation for the entire material particle, ensuring the long life and high safety of the positive electrode active material; the manganese content is low outside the core material, which is the main area for electrochemical reactions, further preventing the dissolution of manganese.

[0042] In one specific embodiment, the mass percentage of phosphorus is 0.01%-2% based on the total mass of the positive electrode active material.

[0043] The introduction of phosphorus in the above proportion can further optimize the lattice order of the positive electrode active material, reduce structural defects, and enhance the thermal stability of the material.

[0044] For example, based on the total mass of the positive electrode active material, the mass percentage of phosphorus is any value or a range of any two of the following: 0.01%, 0.02%, 0.05%, 0.07%, 0.1%, 0.12%, 0.15%, 0.17%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.9%, 1.0%, 1.5%, 2.0%.

[0045] In one specific embodiment, the mass percentage of titanium is 0.01%-2% based on the total mass of the positive electrode active material.

[0046] Among them, the above proportion of titanium can enable more Ti 4 ⁺ Replacement for Mn 4+ Entering the crystal lattice can further stabilize the oxygen framework of the positive electrode active material and suppress Mn. 3+ disproportionation reaction (Mn) 3+ →Mn 4+ +Mn 2+ ), reduce dissolution.

[0047] For example, based on the total mass of the positive electrode active material, the mass percentage of titanium is any value or a range of any two of the following: 0.01%, 0.02%, 0.05%, 0.07%, 0.1%, 0.12%, 0.15%, 0.17%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.9%, 1.0%, 1.5%, 2.0%.

[0048] In one specific embodiment, the mass percentage of yttrium is 0.01%-2% based on the total mass of the positive electrode active material.

[0049] Among them, the above proportions of yttrium can enable more Y 3+ Surface enrichment promotes SEI film formation and reduces the interfacial impedance of the positive electrode active material.

[0050] For example, based on the total mass of the positive electrode active material, the mass percentage of yttrium is any value or a range of any two of the following: 0.01%, 0.02%, 0.05%, 0.07%, 0.1%, 0.12%, 0.15%, 0.17%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.9%, 1.0%, 1.5%, 2.0%.

[0051] In the positive electrode active material, the mass proportions of phosphorus, titanium, and yttrium can all be determined by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0052] Because LATP has high ionic conductivity (>10). -3 The core material (S / cm) and chemical inertness can prevent HF corrosion while allowing rapid lithium-ion migration. By adjusting the mass ratio of lithium aluminum titanium phosphate, the balance between conductivity and stability of the positive electrode active material can be further achieved. Therefore, in one specific embodiment, the mass ratio of the core material to the shell material is 400-500:5-10.

[0053] For example, the mass ratio of core material to shell material is any one of the following, or a range of any two ratios: 400:5, 400:6, 400:7, 400:8, 400:9, 400:10, 420:5, 420:6, 420:7, 420:8, 420:9, 420:10, 450:5, 450:6, 450:7, 450:8, 450:9, 450:10, 480:5, 480:6, 480:7, 480:8, 480:9, 480:10, 500:5, 500:6, 500:7, 500:8, 500:9, 500:10, etc.

[0054] In one specific embodiment, the particle size of the positive electrode active material is 5μm-10μm. The relatively uniform particle size of the positive electrode active material in this embodiment facilitates stable Li ion transport and better utilizes the battery's cycle performance. Exemplarily, the particle size of the positive electrode active material is any value or a combination of any two of the following: 5μm, 6μm, 7μm, 8μm, 9μm, and 10μm.

[0055] In one specific embodiment, the specific surface area of ​​the positive electrode active material is 0.4 m². 2 / g-0.5m 2 / g.

[0056] Among these, the positive electrode active materials with the above-mentioned specific surface area have a smaller contact area with the electrolyte, resulting in fewer side reactions and more stable battery cycling. For example, the specific surface area of ​​the positive electrode active material is 0.4 m². 2 / g, 0.42 m 2 / g, 0.44 m 2 / g, 0.45 m 2 / g, 0.47 m 2 / g, 0.49 m 2 / g, 0.5 m 2 Any value in / g, or a range consisting of any two of them.

[0057] In a second aspect, the present invention provides a method for preparing a positive electrode active material as described in the first aspect, comprising the following steps:

[0058] A mixture of nickel manganese hydroxide, lithium salt, titanium source, phosphorus source and yttrium source is heated to 800-950℃ for the first time at a heating rate of 3-5℃ / min, held for the first time, and then held for the second time at 550-650℃ to obtain nuclear material.

[0059] The core material and shell material are mixed, and the temperature is increased from room temperature to 600-700℃ for the second time at a heating rate of 3-6℃ / min, followed by a third holding period to obtain the positive electrode active material.

[0060] The above preparation method, through precise control of the first heat treatment (800-950℃) and the third heat treatment (600-700℃), combined with an annealing process (second heat treatment at 550-650℃), achieves a uniform distribution of dopant element M and a dense LATP coating layer, which helps to further improve the crystallinity and cycle stability of the cathode active material. Specifically, the temperature of the first heat treatment optimizes the uniformity of lattice doping, and the annealing process further releases residual stress, improving the crystallinity of the cathode active material (specifically reflected in enhanced XRD peak intensity). Furthermore, the temperature of the third heat treatment controls the crystallinity of the coating layer, ensuring the bonding strength between LATP and the core material.

[0061] In one specific embodiment, the first heat preservation time is 8-12 hours; and / or, the second heat preservation time is 5-8 hours; and / or, the third heat preservation time is 8-14 hours.

[0062] The first / second heat treatment time can further regulate the uniform distribution of dopant element M and make the manganese content in lithium nickel manganese oxide active materials decrease from the core material to the shell material; the third heat treatment time can make the LATP coating layer thickness moderate, which can maintain interface stability without significantly hindering lithium ion transport and improve high-temperature cycling performance.

[0063] For example, the first heat preservation time is any value or a range of any two of 8h, 9h, 10h, 11h, 12h, etc.; the second heat preservation time is any value or a range of any two of 5h, 6h, 7h, 8h, etc.; and the third heat preservation time is any value or a range of any two of 8h, 9h, 10h, 11h, 12h, 13h, 14h, etc.

[0064] For example, the temperature of the first heat preservation is any value or a range of any two of 800℃, 820℃, 850℃, 880℃, 900℃, 920℃, 950℃, etc. The temperature of the second heat preservation is any value or a range of any two of 600℃, 620℃, 650℃, 680℃, 700℃, etc.

[0065] In one specific embodiment, the first heating, the first holding, the second heating, and the second holding all include the step of introducing protective gas to bring the gas pressure to 0.2-0.8 Pa.

[0066] The protective gas can be nitrogen, oxygen, or a mixture of both. The reaction pressure can be controlled by the protective gas, which can further optimize the surface morphology of the material (SEM shows more uniform particles) and improve its lithium-ion transport efficiency.

[0067] In one specific embodiment, both the second heating and the third heat preservation include the step of introducing protective gas to bring the gas pressure to 0.5-1.0 Pa.

[0068] The protective gas can be nitrogen, oxygen, or a mixture of both. The reaction pressure can be controlled by the protective gas, which can further optimize the thickness of the LATP coating layer, ensure lithium-ion transport efficiency, and take into account the high-temperature stability of the material.

[0069] In one specific embodiment, before mixing the core material and the shell material, the mixture is further subjected to sieving, wherein the mesh size of the sieve is not less than 200 mesh. This sieving process ensures a more uniform reaction between the core material and the shell material, guaranteeing the uniformity of the LATP coating layer.

[0070] In one specific embodiment, after the third heat preservation, the process further includes crushing, demagnetizing, and sieving, wherein the mesh size of the sieve is not less than 300 mesh. This sieving process can control the particle size of the positive electrode active material.

[0071] Thirdly, the present invention provides a positive electrode sheet, comprising the positive electrode active material of the first aspect or the positive electrode active material prepared by the preparation method of the second aspect.

[0072] The above positive electrode can be a wet electrode or a dry electrode, and the present invention does not make any particular limitation on this.

[0073] In some embodiments, the preparation of the positive electrode includes the following process:

[0074] 1. Mix the conductive agent, positive electrode active material, electrolyte and binder evenly by wet or dry method.

[0075] 2. Coat the uniformly mixed slurry onto the current collector and dry it to obtain the positive electrode sheet.

[0076] 3. Densify the positive electrode sheet.

[0077] For example, the binder may be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, sodium polyacrylate, etc.; the conductive agent may be selected from at least one of carbon nanotubes, carbon nanofibers, VGCF, conductive carbon black, Ketjen black, graphene, graphyne, etc.; the material of the positive electrode current collector may be selected from any one or more of copper foil, titanium foil, tin foil, chromium foil, and composite foils of the above metals.

[0078] Fourthly, the present invention provides a battery comprising a positive electrode active material according to the first aspect, a positive electrode active material prepared by the preparation method of the second aspect, or a positive electrode sheet according to the third aspect.

[0079] In some embodiments, the battery further includes a negative electrode sheet, which includes a current collector and a negative electrode material layer located on at least one surface of the current collector. The negative electrode material layer includes a negative electrode active material, a conductive agent, a binder, and a dispersant. The negative electrode active material may be selected from one or more of graphite, hard carbon, soft carbon, silicon-based negative electrode, titanium-based material, nitride, tin compound, and lithium metal. The conductive agent may be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, and graphene. The binder may be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate. The dispersant may be selected from at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, and sodium dodecyl sulfate. The negative electrode current collector may be a conventional negative electrode current collector in the art, such as copper foil.

[0080] In some embodiments, the battery is a lithium-ion battery, and its preparation steps include the following steps:

[0081] 1. The positive electrode, negative electrode, and separator are arranged in an orderly manner to obtain the electrode core.

[0082] 2. Core casing.

[0083] 3. Isostatic pressing treatment of the casing and pole core.

[0084] 4. Cell formation.

[0085] To further understand the present invention, the technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0086] Unless otherwise specified, all reagents involved in the embodiments of this invention are commercially available products and can be purchased through commercial channels.

[0087] Example 1

[0088] The preparation method of the positive electrode active material in this example includes the following steps:

[0089] 1) First, weigh 400g of nickel manganese hydroxide and put it into a mixing tank, then add 80g of lithium carbonate, 1g of titanium dioxide, 8g of lithium phosphate, and 1g of yttrium oxide. Then, use a high-speed mixer to mix at high speed (100 rpm for 10 min).

[0090] 2) For the high-temperature mixed system, the temperature is first increased from room temperature to 900℃ at a rate of 3℃ / min, and held at this temperature for 8 hours. After the first holding, the temperature is lowered to 600℃ and held at this temperature for 6 hours. After the second holding, the temperature is allowed to drop naturally to room temperature. This process must be carried out under nitrogen atmosphere, with the gas pressure maintained between 0.2-0.3 Pa throughout, to obtain the nuclear material.

[0091] 3) The core material undergoes rigorous sieving (using a sieve of 200 mesh or higher) and then is coated and mixed. First, 400g of core material is added, followed by 5g of LATP. The mixture is then mixed at high speed in a high-speed mixer at 500-1500 rpm for 10 minutes. Subsequently, the temperature is increased from room temperature to 650℃ at a rate of 3℃ / min, and then held at that temperature for 8 hours. This process must be carried out under nitrogen atmosphere, with the pressure maintained between 0.5-0.6 Pa throughout. The resulting solid product must undergo rigorous sieving (using a sieve of 300 mesh or higher), airflow pulverization, and demagnetization processes to finally obtain the modified positive electrode active material, which includes the core material and a shell material disposed on at least part of the surface of the core material. The shell material includes lithium aluminum titanium phosphate, and the core material includes M-doped lithium nickel manganese oxide active material, where M includes titanium, phosphorus, and yttrium.

[0092] The products obtained in steps 2) and 3) were characterized by XRD to verify the material type, crystallinity, and purity. The scanning range was 10-90℃, and the scanning speed was 3-5℃ / min. The results showed that the XRD patterns of the products obtained in steps 2) and 3) were compared with the standard XRD card of lithium nickel manganese oxide. The main diffraction peaks of both products appeared at 18.8°, 36.3°, 58.1°, 43.9°, 48.3°, 58.7°, 64.6°, and 67.7°, corresponding to the (111), (311), (222), (400), (331), (511), (440), and (531) crystal planes, respectively. By comparing these peak positions, it can be seen that the crystal structure of both products is spinel type, and the crystallinity of the material is better after the third heat treatment. Figure 1 This is the XRD pattern of the positive electrode active material obtained in step 3).

[0093] Example 2

[0094] The preparation method of the positive electrode active material in this example includes the following steps:

[0095] 1) First, weigh 400g of nickel manganese hydroxide and put it into a mixing tank, then add 80g of lithium carbonate, 1g of titanium dioxide, 8g of lithium phosphate, and 1g of yttrium oxide. Then, use a high-speed mixer to mix at high speed (100 rpm for 10 min).

[0096] 2) For the high-temperature mixed system, the temperature is first increased from room temperature to 900℃ (T2) at a rate of 3℃ / min, and held at this temperature for 10 hours. After the first holding, the temperature is lowered to room temperature and held at 600℃ for 6 hours. After the second holding, the temperature is allowed to drop naturally to room temperature. This process must be carried out under nitrogen atmosphere, with the gas pressure maintained between 0.4-0.5 Pa throughout, to obtain the nuclear material.

[0097] 3) The core material undergoes rigorous sieving (using a sieve of 200 mesh or finer), followed by coating and mixing. First, 400g of the core material is added, then 5g of LATP is added. The mixture is then high-speed mixed in a high-speed mixer at 500-1500 rpm for 10 minutes. The temperature is then increased from room temperature to 650℃ at a rate of 3℃ / min, followed by a third holding period of 10 hours. This process must be carried out under nitrogen atmosphere, with the pressure maintained between 0.6-0.8 Pa throughout. The resulting solid product undergoes rigorous sieving (using a sieve of 300 mesh or finer), airflow pulverization, and demagnetization to finally obtain the modified positive electrode active material.

[0098] Example 3

[0099] The preparation method of the positive electrode active material in this example includes the following steps:

[0100] 1) First, weigh 520g of nickel manganese hydroxide and put it into a mixing tank, then add 104g of lithium carbonate, 1.3g of titanium dioxide, 10.4g of lithium phosphate, and 1.3g of yttrium oxide. Then, use a high-speed mixer to mix at high speed (100 rpm for 10 min).

[0101] 2) For the high-temperature mixed system, the temperature is first increased from room temperature to 900℃ at a rate of 3℃ / min, and held at this temperature for 8 hours. After the first holding, the temperature is lowered to room temperature and held at this temperature for another 8 hours. After the second holding, the temperature is allowed to drop naturally to room temperature. This process must be carried out under nitrogen atmosphere, with the gas pressure maintained between 0.7 and 0.8 Pa throughout, to obtain the nuclear material.

[0102] 3) The core material undergoes rigorous sieving (using a sieve of 200 mesh or finer), followed by coating and mixing. First, 500g of the core material is added, then 10g of LATP is added. The mixture is then high-speed mixed in a high-speed mixer at 500-1500 rpm for 10 minutes. The temperature is then increased from room temperature to 650℃ at a rate of 3℃ / min, followed by a third holding period of 10 hours. This process must be carried out under nitrogen atmosphere, with the pressure maintained between 0.8-1.0 Pa throughout. The resulting solid product undergoes rigorous sieving (using a sieve of 300 mesh or finer), airflow pulverization, and demagnetization to finally obtain the modified positive electrode active material.

[0103] Example 4

[0104] The only difference from Example 2 is that: in step 1), 500g of nickel manganese hydroxide is weighed and placed in a mixing tank, then 120g of lithium carbonate, 1g of titanium dioxide, 8g of lithium phosphate, and 1g of yttrium oxide are added, and then a high-speed mixer is used for high-speed mixing (100 rpm for 10 min); and in step 3), the core material is subjected to strict sieving treatment (a sieve of 200 mesh or higher), and then coated and mixed. First, 450g of core material is added, followed by 7g of LATP, and the rest is the same as in Example 2.

[0105] Example 5

[0106] The only difference from Example 2 is that: in step 1), 400g of nickel manganese hydroxide is weighed and placed in a mixing tank, then 80g of lithium carbonate, 1.5g of titanium dioxide, 10g of lithium phosphate, and 1.5g of yttrium oxide are added. Then, a high-speed mixer is used for high-speed mixing (100 rpm for 10 min).

[0107] Example 6

[0108] The only difference from Example 2 is that the first heat preservation temperature in step 2) is 960°C (T1).

[0109] Example 7

[0110] The only difference from Example 2 is that the first heat preservation temperature in step 2) is 975℃ (T3).

[0111] Comparative Example 1

[0112] The only difference from Example 2 is that yttrium oxide is not added. The resulting positive electrode active material includes a core material and a shell material disposed on at least part of the surface of the core material. The shell material includes lithium aluminum titanium phosphate, and the core material is lithium nickel manganese oxide active material without yttrium doping.

[0113] Comparative Example 2

[0114] The only difference from Example 2 is that step 3 is omitted, and the resulting positive electrode active material is M-doped lithium nickel manganese oxide active material, wherein M includes titanium, phosphorus and yttrium, and does not contain a shell material.

[0115] Comparative Example 3

[0116] The only difference from Example 2 is that yttrium oxide is not added and step 3 is not performed. The resulting positive electrode active material package is a lithium nickel manganese oxide active material without M doping and without shell material.

[0117] Test case

[0118] 1) Scanning electron microscopy (SEM) analysis was performed on lithium nickel manganese oxide after the first heat treatment at different temperatures in Examples 2, 6-7. The results are shown in [link to SEM]. Figure 2 , Figure 3 and Figure 4 By comparing and analyzing the electron micrographs at different temperatures, it can be seen that the lithium nickel manganese oxide particles obtained at the first holding temperature in Example 2 are more uniform in size, with a particle size of about 7 μm, which is more in line with the experimental design and facilitates Li ion transport. At the same time, the particles at this temperature are also more uniform in the first holding temperature, which makes better use of the cycling performance.

[0119] 2) Specific surface area test: The specific surface area of ​​the positive electrode active materials of the examples and comparative examples was tested using a BET specific surface area analyzer. Each test was performed three times, and the average value was calculated. The results are shown in Table 1. Table 1 shows that the specific surface area of ​​the positive electrode active material obtained at the first heat treatment temperature in Example 2 was 0.417 m². 2 The smaller the surface area, the smaller the contact area with the electrolyte, resulting in fewer side reactions and a more stable cycling process.

[0120] Table 1:

[0121]

[0122] 3) Quantitative capacity and cycle stability testing:

[0123] First, a coin cell is prepared using the positive electrode active materials from the above embodiments and comparative examples, including the following steps: Positive electrode active material, conductive agent (Super P), single-walled carbon nanotubes (CNTs), and binder (polyvinylidene fluoride PVDF) are added to N-methylpyrrolidone (NMP) in a mass ratio of 95.5:1.5:0.5:2.5. The mixture is then homogenized using a degassing machine. The homogenized slurry is then coated onto aluminum foil (single-sided density 65 mg / cm³). 2 After drying, heat baking, rolling, and cutting, a positive electrode sheet is obtained. The single-sided coated positive electrode sheet obtained above is stamped into an electrode sheet with a diameter of 12mm. CR2430 coin cells are assembled in an argon glove box. The counter electrode is a 12cm diameter lithium metal sheet. The electrolyte used for the coin cell test is A77 high-voltage electrolyte produced by Shenzhen Xinzhoubang Technology Co., Ltd. The nominal capacity of the coin cell is 147mAh / g. The charging test is a constant current + constant voltage charging test method, charging at 0.33C to 4.95V, which means charging at a constant current rate of 0.33C to 4.95V, and then charging at a constant voltage rate to a current density of 0.05C. The discharging test is a constant current discharging test method, for example, discharging at 0.33C to 3.5V, which means discharging at a rate of 0.33C to 3.5V. The first charge and discharge cycle is counted as one cycle.

[0124] Specific capacity (0.33C discharge capacity): Electrochemical window 3.0~4.95V. The capacity testing procedure is to perform formation of the assembled coin cell by charging and discharging it at 0.1C for two cycles, followed by charging and discharging it at 0.33C for one cycle. The resulting 0.33C discharge specific capacity is the 0.33C discharge capacity. Figure 6 This is a specific capacity performance curve obtained from testing batteries assembled with positive electrode active materials in proportions 1-3.

[0125] High-temperature cycling: Electrochemical window 3.4~4.85V, 50 cycles at 1C charge / discharge at 45℃. The ratio of the discharge capacity after 50 cycles to the discharge capacity after the first cycle is the cycle retention rate of the material; where, Figure 5 This is Example 2, a cycle capacity retention curve obtained from testing batteries assembled with the positive electrode active materials of Comparative Examples 1-3.

[0126] The test results are summarized in Table 2.

[0127] Table 2:

[0128]

[0129] As shown in Table 2, compared with Comparative Examples 1-3, the batteries assembled with the positive electrode active materials in Examples 1-7 have a higher capacity retention rate after 50 cycles, and can also achieve good performance in terms of specific capacity.

[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode active material, characterized in that, include: The core material and the shell material disposed on at least a portion of the surface of the core material, the shell material comprising lithium aluminum titanium phosphate, and the core material comprising M-doped lithium nickel manganese oxide active material, wherein M comprises titanium, phosphorus and yttrium.

2. The positive electrode active material according to claim 1, characterized in that, The manganese content in the lithium nickel manganese oxide active material decreases from the core material to the shell material.

3. The positive electrode active material according to claim 1 or 2, characterized in that, Based on the total mass of the positive electrode active material, the mass percentage of phosphorus is 0.01%-2%; And / or, based on the total mass of the positive electrode active material, the mass percentage of titanium is 0.01%-2%; And / or, based on the total mass of the positive electrode active material, the mass percentage of yttrium is 0.01%-2%; And / or, the mass ratio of the core material to the shell material is 400-500:5-10.

4. The positive electrode active material according to any one of claims 1-3, characterized in that, The particle size of the positive electrode active material is 5μm-10μm; And / or, the specific surface area of ​​the positive electrode active material is 0.4 m². 2 / g-0.5m 2 / g.

5. A method for preparing a positive electrode active material as described in any one of claims 1-4, characterized in that, Includes the following steps: A mixture of nickel manganese hydroxide, lithium salt, titanium source, phosphorus source and yttrium source is heated to 800-950°C for the first time at a heating rate of 3-8°C / min, held for the first time, and then cooled to 550-650°C for the second time to obtain the nuclear material. The core material and shell material are mixed, and the temperature is increased from room temperature to 600-700℃ for the second time at a heating rate of 3-6℃ / min, followed by a third holding period to obtain the positive electrode active material.

6. The preparation method according to claim 5, characterized in that, The first heat preservation time is 8-12 hours; and / or, the second heat preservation time is 5-8 hours; and / or, the third heat preservation time is 8-14 hours.

7. The preparation method according to claim 5, characterized in that, The first heating, the first heat preservation, and the second heat preservation all include the step of introducing protective gas to bring the gas pressure to 0.2-0.8 Pa; And / or, the second heating and the third heat preservation both include the step of: introducing protective gas to bring the gas pressure to 0.5-1.0 Pa.

8. The preparation method according to claim 5, characterized in that, Before the core material is mixed with the shell material, it is further sieved, wherein the mesh size of the sieve is not less than 200 mesh; And / or, after the third heat preservation, it also includes crushing, demagnetizing and sieving, wherein the mesh size of the sieve is not less than 300 mesh.

9. A positive electrode plate, characterized in that, The positive electrode active material includes the positive electrode active material according to any one of claims 1-4 or the positive electrode active material prepared by the preparation method according to any one of claims 5-8.

10. A battery, characterized in that, It includes the positive electrode active material according to any one of claims 1-4, the positive electrode active material prepared by any one of claims 5-8, or the positive electrode sheet according to claim 9.

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