Gradient doping type lithium iron manganese phosphate positive electrode material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a gradient doping type lithium iron manganese phosphate positive electrode material and a preparation method and application thereof. The invention provides a gradient doping type lithium iron manganese phosphate positive electrode material which comprises mixed doping elements, and the mixed doping elements at least comprise four different elements. The gradient-doped lithium manganese iron phosphate positive electrode material is of a core-shell structure, and the mixed doping elements are distributed in a gradient increasing mode along the core-shell structure. The gradient doping type lithium manganese iron phosphate positive electrode material provided by the invention adopts a core-shell structure, and mixed doping elements are distributed in a gradient increasing manner, so that the problem of lattice distortion is effectively relieved through the change of concentration gradient, the structural stability of the material is enhanced, the phase change and volume change in a circulation process are reduced, and a charge transmission path is optimized; asynchronous reaction among particles is reduced, voltage attenuation in the charging and discharging process is effectively inhibited, and the energy density is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a gradient-doped lithium manganese iron phosphate positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] In the lithium ion battery technology system, the lithium iron phosphate (LFP) positive electrode material stands out with high intrinsic safety, excellent cycle stability and environmental friendly characteristics, and becomes the core choice of new energy vehicle power systems and large-scale energy storage power stations. However, due to the upper limit of the theoretical specific capacity, it is difficult to meet the development needs of terminal equipment lightweight and long endurance in high-power application scenarios such as unmanned aerial vehicles and high-end electric tools, and it is urgent to develop a new positive electrode material system with high energy and high safety.

[0003] To break through this technical bottleneck, researchers developed a lithium manganese iron phosphate (LMFP for short) material system through partial Fe-Mn element replacement strategy. Benefiting from the higher redox potential of Mn 2+ / Mn 3+ , the material system realizes significant improvement of energy density. However, with the increase of the doping ratio of manganese element, the material system faces multiple performance challenges: first, the Jahn-Teller effect of Mn 3+ causes serious lattice distortion, leading to frequent phase transition and volume change in the cycle process, and then destroying the material structure stability; second, the difference in inter-particle reaction kinetics is aggravated, causing the tilt of charge-discharge voltage platform, leading to voltage attenuation and energy density loss; third, under the conditions of long cycle and high rate charge-discharge, the capacity attenuation rate of the material is significantly accelerated, and the cycle life is difficult to meet the actual application requirements. Although existing research has tried to suppress the Jahn-Teller effect by uniformly doping Ti, Mg, V and other elements, the inhibition effect has obvious limitations, and the improvement effect on voltage attenuation problem is not as expected, and the microscopic mechanism of voltage attenuation still lacks systematic theoretical explanation.

[0004] It can be seen that the traditional doping strategy cannot effectively improve the cycle stability and voltage attenuation problem of the olivine-type manganese-rich phosphate positive electrode material, and it cannot meet the actual application requirements. SUMMARY

[0005] The purpose of the present application is to provide a gradient-doped lithium manganese iron phosphate positive electrode material and a preparation method and application thereof, aiming at solving the problem that the existing technology cannot effectively improve the cycle stability and voltage attenuation of the olivine-type manganese-rich phosphate positive electrode material.

[0006] To achieve the above application purposes, the technical solutions adopted by the present application are as follows:

[0007] In a first aspect, the application provides a gradient-doped lithium iron manganese phosphate positive electrode material, the gradient-doped lithium iron manganese phosphate positive electrode material comprises mixed doping elements, the mixed doping elements comprise at least four different elements; and the gradient-doped lithium iron manganese phosphate positive electrode material has a core-shell structure, and the mixed doping elements are distributed in a gradient-increasing manner along the core-shell structure.

[0008] In some embodiments, the gradient-increasing distribution is that the concentration of the mixed doping elements gradually increases from the inner core to the outer shell; and the following conditions are met:

[0009] (a) in the inner core interface region: the doping amount is 1% to 5%;

[0010] (b) in the intermediate transition region: the doping amount is 2.5% to 10%;

[0011] (c) in the outer shell interface region: the doping amount is 5% to 15%.

[0012] In some embodiments, the mixed doping elements comprise at least the following four different elements:

[0013] at least one of rare earth elements La and Y;

[0014] at least one of transition metal elements Ti, V, Ni, and Cr;

[0015] at least one of transition metal elements Zn, Zr, and Nb;

[0016] at least one of light metal elements Mg and Al;

[0017] and the atomic percentage of each element is 0.02 to 0.04.

[0018] In some embodiments, the configuration entropy ΔS of the gradient-doped lithium iron manganese phosphate positive electrode material is 1.0R to 1.5R.

[0019] In some embodiments, the particle size distribution of the gradient-doped lithium iron manganese phosphate positive electrode material satisfies: D 10 ≤0.5μm, D 50 ≤1.0μm, D 90 ≤4.0μm.

[0020] In some embodiments, the gradient-doped lithium iron manganese phosphate positive electrode material further comprises a carbon coating layer, wherein the thickness of the carbon coating layer is 4nm to 8nm.

[0021] In some embodiments, the carbon content is 1.2wt% to 1.5wt% based on the total mass of the gradient-doped lithium iron manganese phosphate positive electrode material.

[0022] In some embodiments, the mixed doping elements are selected from a combination of Al, V, Ni, Zn, and Y.

[0023] In a second aspect, the application provides a preparation method of a gradient-doped lithium iron manganese phosphate cathode material, comprising the following steps:

[0024] providing a precursor comprising low concentrations of mixed doping elements;

[0025] sintering the precursor once to obtain a sintered material;

[0026] mixing, granulating, and sintering the composite carbon source, the mixed metal source containing doping elements, and the sintered material to obtain the gradient-doped lithium iron manganese phosphate cathode material.

[0027] In some embodiments, the content of the mixed doping elements in the precursor comprising low concentrations of mixed doping elements is 1.0% to 1.5%.

[0028] In some embodiments, the total mass of the sintered material is 100%, and the carbon content is 0.01wt% to 0.1wt%.

[0029] In some embodiments, the composite carbon source is selected from at least two of glucose, PEG, and oleic acid.

[0030] In some embodiments, the temperature of the first sintering is 500°C to 600°C, the heating rate is 5°C / min to 7°C / min, and the time is 6h to 10h.

[0031] In some embodiments, the temperature of the second sintering is 750°C to 800°C, the heating rate is 5°C / min to 7°C / min, and the time is 10h to 16h.

[0032] In some embodiments, in the step of mixing the composite carbon source, the mixed metal source containing doping elements, and the sintered material, wet ball milling mixing treatment is adopted, wherein the ball-to-material ratio is 3 / 1 to 6 / 1, the ball milling time is 2h to 6h, and the ball milling solvent is pure water or a mixture of water and anhydrous ethanol.

[0033] In some embodiments, in the obtained slurry, the solid content is 40% to 50%, and the particle size D 50 is 0.3μm to 0.6μm.

[0034] In some embodiments, before granulation, the slurries with different particle sizes are mixed in proportion, wherein the slurry with a particle size D 50 of 0.28μm to 0.32μm accounts for 20% to 30%, and the slurry with a particle size D 50 of 0.58μm to 0.62μm accounts for 70% to 80%.

[0035] In a third aspect, the present application discloses a lithium-ion battery positive electrode plate, comprising the above-mentioned gradient-doped lithium manganese iron phosphate positive electrode material, a conductive agent and a binder.

[0036] In a fourth aspect, the present application discloses a lithium-ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode adopts the above-mentioned lithium-ion battery positive electrode sheet.

[0037] The gradient-doped lithium manganese iron phosphate cathode material provided in the first aspect of the present application adopts a core-shell structure and the mixed doping elements are distributed in a gradient-increasing manner, so that a special chemical environment is formed inside the material; on the one hand, through the change of concentration gradient, the lattice distortion problem is effectively alleviated, the structural stability of the material is enhanced, and the phase change and volume change during the cycle are reduced, thereby significantly improving the cycle performance of the material; on the other hand, the gradient distribution of doping elements optimizes the charge transfer path, reduces the asynchronous reaction between particles, effectively suppresses the voltage decay during the charge and discharge process, and improves the energy density; at the same time, the introduction of high entropy can suppress the Mn 3+ The Jahn-Teller distortion caused by the disproportionation reaction improves the structural stability of the material and prevents the aggregation of doping elements during the cycle; on the other hand, the high entropy environment may reduce the activation energy of Li+ migration and enhance the kinetics, which is beneficial to improving the overall performance of the lithium manganese iron phosphate positive electrode material.

[0038] The second aspect of this application provides a method for preparing a gradient-doped lithium iron manganese phosphate cathode material. This method employs a process that first prepares a precursor containing a low concentration of mixed doping elements, followed by two sintering treatments. This allows for precise control of the distribution of the doping elements and the structure of the material. The first sintering treatment initially establishes the material's crystal structure and basic properties. The second sintering treatment, combined with a composite carbon source and a mixed metal source containing the doping elements, further optimizes the material's structure and properties, creating a gradient doping and carbon coating effect, which is conducive to large-scale industrial production.

[0039] The lithium-ion battery positive electrode plate provided in the third aspect of the present application comprises the above-mentioned gradient-doped lithium manganese iron phosphate positive electrode material with excellent performance, combined with a conductive agent and a binder to form a good electrode structure, thereby ensuring the conductivity and stability of the electrode.

[0040] The lithium-ion battery provided in the fourth aspect of the present application, which uses the positive electrode sheet, has a higher energy density, longer cycle life and better rate performance as a whole due to the improvement in the performance of the positive electrode material. It has broader application prospects in new energy vehicles, energy storage systems and other fields, and can meet the market demand for high-performance lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description only constitute some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort.

[0042] Figure 1 is the XRD analysis diagram of the sample provided by the embodiment 1, the embodiment 2 and the comparative example of the present application. DETAILED DESCRIPTION

[0043] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clear, the present application will be further described in detail in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0044] In the present application, the term "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. Wherein A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after it.

[0045] In the present application, "at least one" means one or more, and "multiple" means two or more. "At least one" or similar expressions mean any combination of these items, including any combination of single item or multiple items. For example, "at least one of a, b or c", or "at least one of a, b and c", can mean a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, wherein a, b and c can be single or multiple.

[0046] It should be understood that in various embodiments of the present application, the size of the sequence number of the above processes does not mean the order of execution, and part or all steps can be executed in parallel or in sequence, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0047] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0048] The weight of the related components mentioned in the embodiment specification of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of each component. Therefore, as long as the content of the related components in the embodiment specification of the present application is scaled up or down in proportion, it is within the scope disclosed in the embodiment specification of the present application. Specifically, the mass in the embodiment specification of the present application can be μg, mg, g, kg, etc. mass units commonly known in the chemical industry.

[0049] The terms "first", "second" are only for descriptive purposes and are used to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. For example, without departing from the scope of the present application, the first XX can also be referred to as the second XX, and similarly, the second XX can also be referred to as the first XX. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features.

[0050] The first aspect of the embodiment of the present application provides a gradient-doped lithium manganese iron phosphate positive electrode material. The gradient-doped lithium manganese iron phosphate positive electrode material includes mixed doping elements, which at least include four different elements. The gradient-doped lithium manganese iron phosphate positive electrode material has a core-shell structure, and the mixed doping elements are distributed in a gradient increasing manner along the core-shell structure.

[0051] The gradient-doped lithium manganese iron phosphate positive electrode material provided by the first aspect of the embodiment of the present application adopts a core-shell structure and the mixed doping elements are distributed in a gradient increasing manner, so that a special chemical environment is formed inside the material. On the one hand, by changing the concentration gradient, the lattice distortion problem is effectively alleviated, the structural stability of the material is enhanced, the phase change and volume change in the cycle process are reduced, and the cycle performance of the material is significantly improved. On the other hand, the gradient distribution of the doping elements optimizes the charge transport path, reduces the asynchronous reaction between particles, effectively suppresses the voltage decay during charging and discharging, improves the energy density, and introduces high entropy, which can suppress the Jahn-Teller distortion caused by disproportionation reaction, thereby improving the structural stability of the material and preventing the aggregation of doping elements in the cycle process; on the other hand, the high-entropy environment can reduce the Li+ migration activation energy, improve the kinetics, and help to improve the overall performance of the lithium manganese iron phosphate positive electrode material. 3+

[0052] ​In the manganese iron phosphate positive electrode material, at least four different elements are doped, which can realize electronic structure regulation, interface stability enhancement, and entropy value improvement. Compared with traditional doping strategies, high-entropy doping emphasizes the equal proportion of synergistic regulation rather than flexible concentration adjustment. The effects of high-entropy doping may include (1) cocktail effect - complex synergistic interaction to achieve precise regulation of material performance; (2) local regulation effect - special chemical environment formed by multiple components to optimize charge transport; (3) structural stability - lattice strain reduction and phase transition inhibition through high-entropy configuration formation; (4) high-disorder characteristics - increased disorder degree in the internal environment of the material to improve electrochemical performance; and (5) entropy expansion effect - multiple elements leading to an increase in entropy in a specific region.

[0053] Further, the gradient-doped lithium manganese iron phosphate positive electrode material has a core-shell structure, and the mixed doping elements are distributed in a gradient increasing manner along the core-shell structure.

[0054] In some embodiments, the gradient increasing distribution is that the concentration of the mixed doping elements gradually increases from the inner core to the outer shell; and the following conditions are met:

[0055] (a) In the inner core interface region: the doping amount is 1% to 5%; the inner core doping amount is relatively small, and the stress caused by lattice distortion is small.

[0056] (b) In the intermediate transition region: the doping amount is 2.5% to 10%; avoiding large local stress differences caused by large differences in inner and outer doping amounts, and playing a buffering role.

[0057] (c) In the outer shell interface region: the doping amount is 5% to 15%. The outer shell doping amount is relatively large, and the stress caused by lattice distortion is large, but the stress of the outer shell can be released.

[0058] The concentration of the mixed doping elements gradually increases from the inner core to the outer shell, and each region has a specific doping amount range. This precise concentration gradient setting allows the inner core region to have a lower doping amount, maintaining the basic electrochemical activity of the material; the doping amount in the intermediate transition region and the outer shell region gradually increases, further optimizing the surface properties and ion diffusion performance of the material. For example, the higher doping amount in the outer shell region can form a stable interface layer, enhance the compatibility of the material with the electrolyte, reduce the occurrence of side reactions, and at the same time, accelerate the diffusion speed of lithium ions, improving the performance of the material under high-rate charging and discharging conditions.

[0059] In some embodiments, the doping amount of the mixed doping elements in the core interface region includes, but is not limited to, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.5%, 2.7%, 3.0%, 3.2%, 3.5%, 3.7%, 4.0%, 4.2%, 4.5%, 4.7%, 5.0%, and the like typical but non-limiting values.

[0060] In some embodiments, the doping amount of the mixed doping elements in the intermediate transition region includes, but is not limited to, 2.5%, 2.7%, 3.0%, 3.2%, 3.5%, 3.7%, 4.0%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.7%, 6.0%, 6.2%, 6.5%, 6.7%, 7.0%, 7.2%, 7.5%, 7.7%, 8.0%, 8.2%, 8.5%, 8.7%, 9.0%, 9.2%, 9.5%, 9.7%, 10%, and the like typical but non-limiting values.

[0061] In some embodiments, the doping amount of the mixed doping elements in the shell interface region includes, but is not limited to, 5%, 5.2%, 5.5%, 5.7%, 6.0%, 6.2%, 6.5%, 6.8%, 7.0%, 7.2%, 7.5%, 7.7%, 8%, 8.2%, 8.5%, 8.7%, 9.0%, 9.2%, 9.5%, 9.7%, 10%, 10.2%, 10.5%, 10.7%, 11%, 11.2%, 11.5%, 11.7%, 12%, 12.2%, 12.5%, 12.7%, 13%, 13.2%, 13.5%, 13.7%, 14%, 14.2%, 14.5%, 14.7%, 15%, and the like typical but non-limiting values.

[0062] In some embodiments, the mixed doping elements include at least the following four different elements:

[0063] at least one of rare earth elements La, Y;

[0064] at least one of transition metal elements Ti, V, Ni, Cr;

[0065] at least one of transition metal elements Zn, Zr, Nb;

[0066] at least one of light metal elements Mg, Al.

[0067] The mixed doping elements include a combination of rare earth elements, multiple transition metal elements, and light metal elements, and a synergistic effect is generated between different types of elements. Among them, the rare earth elements La or Y can polarize the effect to reduce the Li+ migration barrier and regulate the oxygen vacancy concentration; the transition metal elements Ti, V, Ni, or Cr can improve the electronic conductivity, inhibit the Jahn-Teller distortion, and widen the lithium layer spacing, which is conducive to adjusting the electronic structure of the material and optimizing the ion diffusion channel; the transition metal elements Zn, Zr, or Nb form a stable oxide framework, which can inhibit the generation of oxygen vacancies and enhance the Li+ diffusion channel; the light metal elements Mg or Al can form a covalent bond with oxygen, enhance the structural rigidity, and inhibit the generation of oxygen vacancies and the expansion of the material during the charge-discharge process. The multiple elements work together to not only effectively inhibit the adverse effects of Mn 3+ , but also comprehensively improve the overall electrochemical performance of the material, such as improving the charge-discharge efficiency, prolonging the cycle life, and improving the energy density. 3+

[0068] Further, an atomic percentage of each element of 0.02-0.04 is beneficial to avoid capacity loss of the positive electrode material caused by excessive doping. In some specific embodiments, the atomic percentage of each element includes but is not limited to typical but non-limiting values such as 0.02, 0.03, 0.04, and the like.

[0069] In some embodiments, the configuration entropy ΔS of the gradient-doped lithium manganese iron phosphate positive electrode material is 1.0R-1.5R. Wherein, R is a gas constant connecting the micro and macro scales, and standardizes the entropy value calculation. R = 8.314 J / mol / K.

[0070] The configuration entropy ΔS of 1.0R-1.5R indicates that the material is in a high-entropy state, and the uniform distribution of elements can reduce the Gibbs free energy, improve the phase stability, and inhibit the phase transition and particle breakage during the cycle process. In some specific embodiments, the entropy value ΔS of the gradient-doped lithium manganese iron phosphate positive electrode material includes but is not limited to typical but non-limiting values such as 1.0R, 1.1R, 1.2R, 1.3R, 1.4R, 1.5R, and the like.

[0071] In some embodiments, the particle size distribution of the gradient-doped lithium manganese iron phosphate positive electrode material satisfies: D 10 ≤0.5 μm, D 50 ≤1.0 μm, and D 90 ≤4.0 μm. According to the distribution of the particle size, it can be seen that the particle size of the provided positive electrode material has a narrow particle size distribution, which can ensure good uniformity of the electrode coating and reduce local stress concentration. A smaller particle size can be beneficial to shorten the lithium ion diffusion path and improve the rate performance.

[0072] ​In some embodiments, the gradient-doped lithium manganese iron phosphate positive electrode material further comprises a carbon coating layer, wherein the thickness of the carbon coating layer is 4 nm to 8 nm. The ultra-thin carbon coating layer is conducive to balancing the conductivity and lithium ion transmission resistance. In some specific embodiments, the thickness of the carbon coating layer includes but is not limited to 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, and the like typical but non-limiting values.

[0073] In some embodiments, the carbon content is 1.2 wt% to 1.5 wt% based on 100% of the total mass of the gradient-doped lithium manganese iron phosphate positive electrode material. Precise control of the carbon content avoids excessive carbon reducing the volumetric energy density while providing a continuous conductive network. In some specific embodiments, the carbon content includes but is not limited to 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, and the like typical but non-limiting values based on 100% of the total mass of the gradient-doped lithium manganese iron phosphate positive electrode material.

[0074] In some embodiments, the mixed doping elements are selected from the combination of Al, V, Ni, Zn, and Y. The specific combination (Al / V / Ni / Zn / Y) provided forms a complementary effect. Al3+-Y 3 +Stabilize the oxygen framework, Ni 2 +-V 3 +Build a double transmission channel, Zn 2+ Break through the ion diffusion bottleneck, and it is possible to achieve a "structure-dynamics-interface" triple breakthrough.

[0075] The second aspect of the embodiments of the present application provides a preparation method of a gradient-doped lithium manganese iron phosphate positive electrode material, comprising the following steps:

[0076] S01. Providing a precursor comprising a low concentration of mixed doping elements;

[0077] S02. Sintering the precursor once to obtain a sintered material;

[0078] S03. Mixing, granulating, and sintering the composite carbon source, the mixed metal source containing doping elements, and the sintered material to obtain the gradient-doped lithium manganese iron phosphate positive electrode material.

[0079] The preparation method of the gradient-doped lithium manganese iron phosphate positive electrode material provided in the second aspect of the embodiments of the present application adopts a preparation process of first preparing a precursor containing a low concentration of mixed doping elements, and then sintering twice, which can accurately control the distribution of doping elements and the structure of the material. The first sintering process can preliminarily form the crystal structure and basic performance of the material, and the second sintering process combines the composite carbon source and the mixed metal source containing doping elements to further optimize the structure and performance of the material, forming the effects of gradient doping and carbon coating, which is conducive to realizing large-scale industrial production.

[0080] In step S01, a precursor including a low concentration of mixed doping elements is provided. The precursor can be prepared by any one of a liquid phase method, a solid phase method, and a precipitation method.

[0081] In some embodiments, the content of the mixed doping elements in the precursor including a low concentration of mixed doping elements is 1.0% to 5.0%. In some specific embodiments, the content of the mixed doping elements in the precursor including a low concentration of mixed doping elements includes but is not limited to 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, and the like typical but non-limiting values.

[0082] In some specific embodiments, the preparation method of the precursor including a low concentration of mixed doping elements includes the following steps: weighing appropriate amounts of lithium source, manganese source, iron source, and phosphorus source according to the stoichiometric ratio, and additionally adding carbon source and a plurality of metal ion dopants to prepare an LMFP low-doping precursor. The preparation of the LFMP low-doping precursor can adopt existing processes such as sol-gel method, self-heating evaporation liquid phase method, and the like.

[0083] In the formula, the stoichiometric ratio of each raw material is Li:(Mn+Fe):P is (1.02-1.06):1:(1.01-1.04). The lithium source includes but is not limited to lithium carbonate or lithium hydroxide, the manganese source includes but is not limited to manganese nitrate or manganese acetate, the iron source includes but is not limited to iron nitrate, and the phosphorus source includes but is not limited to ammonium dihydrogen phosphate or di-ammonium hydrogen phosphate.

[0084] In the formula, the plurality of metal ion dopants are selected from the mixture of the above-mentioned elements. In some specific embodiments, the plurality of metal ion dopants are selected from the doping elements Al, V, Ni, Zn, and Y, each of which uses a corresponding 0.005-0.01 atomic percent of oxide or nitrate as a dopant.

[0085] In some embodiments, the total mass of the calcined material is 100%, and the carbon content is 0.01wt% to 0.1wt%. Controlling the carbon content of the calcined material to be less ensures that a too thick carbon coating layer is not formed, which is conducive to subsequent gradient coating.

[0086] In step S02, the precursor is subjected to a first sintering treatment to obtain a calcined material.

[0087] In some embodiments, the temperature of the first sintering is 500°C to 600°C, the heating rate is 5°C / min to 7°C / min, and the time is 6h to 10h.

[0088] In some embodiments, the temperature of the first sintering includes, but is not limited to, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, and the like typical but non-limiting values.

[0089] In some embodiments, the time of the first sintering includes, but is not limited to, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, and the like typical but non-limiting values.

[0090] In step S03, the composite carbon source, the mixed metal source containing doping elements, and the first sintered material are mixed, granulated, and subjected to secondary sintering treatment to obtain the gradient-doped lithium iron manganese phosphate positive electrode material.

[0091] In some embodiments, the composite carbon source is selected from at least two of glucose, PEG, and oleic acid. In some embodiments, the added amount of the composite carbon source includes, but is not limited to, 1.2wt%-1.5wt%, based on the total weight of the secondary sintered product being 100%.

[0092] In some embodiments, the plurality of metal ion dopants in the mixed metal source containing doping elements are selected from a mixture of the above-mentioned elements. In some embodiments, the plurality of metal ion dopants are selected from the doping elements Al, V, Ni, Zn, and Y, each using a corresponding 0.015-0.03 atomic percent of oxide or nitrate as a dopant.

[0093] In some embodiments, in the step of mixing the composite carbon source, the mixed metal source containing doping elements, and the first sintered material, wet ball milling mixing treatment is used, wherein the ball-to-material ratio is 3 / 1-6 / 1, the ball milling time is 2-6h, and the ball milling solvent is pure water or a mixture of water and anhydrous ethanol. In some specific embodiments, wet ball milling mixing treatment is used, wherein the ball-to-material ratio is 5 / 1, and the ball milling time is 4h.

[0094] In some embodiments, in the obtained slurry, the solid content is 40%-50%, and the particle size D 50 is 0.3-0.6μm.

[0095] In some embodiments, before granulation, the slurry of different particle sizes is mixed in proportion, wherein the slurry with a particle size D 50 of 0.28-0.32μm accounts for 20%-30%, and the slurry with a particle size D 50 of 0.58-0.62μm accounts for 70%-80%.

[0096] Further, after the particle size is qualified, the slurry with a particle size D 50 of 0.28-0.32μm and a particle size D 50The slurry with a particle size of 0.58-0.62 μm is mixed uniformly at a ratio of 20%-30%:70%-80%, and then is converted into a spray drying for granulation.

[0097] In some embodiments, the temperature of the secondary sintering is 750-800℃, the heating rate is 5-7℃ / min, and the time is 10-16h.

[0098] In some specific embodiments, the temperature of the secondary sintering includes but is not limited to 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, etc., typical but limited values; the time includes but is not limited to 10h, 11h, 12h, 13h, 14h, 15h, 16h, etc., typical but non-limiting values.

[0099] The third aspect of the embodiments of the present application discloses a lithium ion battery positive electrode sheet, which comprises the above-mentioned gradient-doped lithium manganese iron phosphate positive electrode material, a conductive agent and a binder.

[0100] The lithium ion battery positive electrode sheet provided in the third aspect of the embodiments of the present application comprises the above-mentioned gradient-doped lithium manganese iron phosphate positive electrode material with excellent performance, and the conductive agent and the binder can form a good electrode structure, ensuring the conductivity and stability of the electrode.

[0101] The fourth aspect of the embodiments of the present application discloses a lithium ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode adopts the above-mentioned lithium ion battery positive electrode sheet.

[0102] The lithium ion battery provided in the fourth aspect of the embodiments of the present application adopts the positive electrode sheet, and due to the improvement of the performance of the positive electrode material, the overall battery has higher energy density, longer cycle life and better rate performance, has a wider application prospect in the fields of new energy vehicles, energy storage systems, etc., and can meet the market demand for high-performance lithium ion batteries.

[0103] The specific embodiments will be described below.

[0104] Embodiment 1

[0105] The present embodiment provides a gradient-doped lithium manganese iron phosphate positive electrode material and a preparation method thereof.

[0106] The gradient-doped lithium manganese iron phosphate positive electrode material is HeGD-LiMn 0.6 Fe 0.3 (Al 0.02 V 0.02 Ni 0.02 Zn 0.02 Y 0.02)PO4; (wherein HeGD represents high-entropy gradient doping); other physical indicators of the sample are shown in Table 1.

[0107] The preparation method comprises the following steps:

[0108] (1) A lithium source lithium acetate, a manganese source manganese acetate, a iron source ferrous oxalate, and a phosphorus source ammonium dihydrogen phosphate are added in a molar ratio of 1.05:0.6:0.3:1.03; citric acid is used as a chelating agent, ascorbic acid is used as a stabilizer, glucose is used as a carbon source and a reducing agent, and water is used as a solvent; (the amount of glucose added is determined according to the condition that the carbon content after the first calcination is not higher than 0.1%, and the doping elements Al, V, Ni, Zn, and Y are respectively doped with corresponding 0.005 atomic percentage of an aluminum source aluminum nitrate, a vanadium source vanadyl acetylacetonate, a nickel source nickel acetate, a zinc source zinc acetate, and a yttrium source yttrium nitrate); according to the following steps: ① A metal cation-citric acid complex solution is prepared, and ammonia water is used to control the pH of the solution to be near 4; ② The lithium source lithium acetate, the phosphorus source ammonium dihydrogen phosphate, and the carbon source glucose are added, and ammonia water is used to control the pH of the solution to be near 5.2; ③ The solvent is evaporated in a water bath, and the solution is gelled; ④ Vacuum drying is performed to obtain a corresponding precursor LMFP low-doping precursor.

[0109] (2) The LMFP low-doping precursor prepared in step (1) is crushed and then calcined at 550°C for 10 hours, with a heating rate controlled at 6°C / min, and the calcined product is crushed.

[0110] (3) The crushed product of step (2) is dispersed in an appropriate amount of water together with a certain amount of a composite carbon source (glucose+PEG, the amount of which is determined according to the condition that the carbon content of the final product after the second calcination reaches 1.4%) and metal ion dopants (the doping elements Al, V, Ni, Zn, and Y are respectively doped with corresponding 0.015 atomic percentage of an aluminum source aluminum nitrate, a vanadium source vanadyl acetylacetonate, a nickel source nickel acetate, a zinc source zinc acetate, and a yttrium source yttrium nitrate), and ball milling is performed. 50 The particle size of the slurry is controlled to be D 50 : 0.28μm~0.32μm and D 50 : 0.58μm~0.62μm), and then the slurry with D

[0111] (4) The material after the spray drying of step (3) is calcined at 780°C for 16 hours, with a heating rate controlled at 6°C / min, and the calcined product is crushed to obtain a gradient-doped lithium manganese iron phosphate positive electrode material HeGD-LiMn 0.6 Fe 0.3 (Al0.02 V 0.02 Ni 0.02 Zn 0.02 Y 0.02 )PO4.

[0112] Example 2

[0113] This embodiment provides a gradient-doped lithium manganese iron phosphate positive electrode material and a preparation method thereof.

[0114] The gradient doped lithium manganese iron phosphate cathode material is HeGD-LiMn 0.6 Fe 0.3 (Al 0.02 V 0.02 Ni 0.02 Zn 0.02 Y 0.02 )PO4; other physical indicators of the samples are shown in Table 1.

[0115] The preparation method comprises the following steps:

[0116] (1) Lithium source lithium acetate, manganese source manganese acetate, iron source ferrous oxalate, phosphorus source ammonium dihydrogen phosphate are mixed in a molar ratio of 1.05:0.6:0.3:1.03; (the amount of glucose added is based on the carbon content after calcination being no higher than 0.1%, and the doping elements Al, V, Ni, Zn, and Y are respectively used as doping agents with a corresponding 0.02 molar atomic percentage of aluminum source aluminum nitrate, vanadium source acetylacetonate vanadium, nickel source nickel acetate, zinc source zinc acetate, and yttrium source yttrium nitrate), and then citric acid is used as a chelating agent, ascorbic acid is used as a stabilizer, glucose is used as a carbon source and reducing agent, and water is used as a solvent; according to the following steps: ① prepare a metal cation-citric acid complex solution, and use ammonia water to adjust the solution pH to about 4; ② add lithium source lithium acetate, phosphorus source ammonium dihydrogen phosphate and carbon source glucose, and use ammonia water to adjust the solution pH to about 5.2; ③ evaporate the solvent in a water bath, and gel the solution; ④ vacuum dry to obtain the corresponding precursor LMFP low-doping precursor.

[0117] (2) The LMFP low-doped precursor prepared in step (1) was crushed and calcined at 550° C. for 10 h with a heating rate of 6° C. / min, and the calcined material was crushed.

[0118] (3) The pulverized material from step (2) was dispersed in an appropriate amount of water together with a certain amount of composite carbon source (glucose + PEG, the amount of which was added was such that the carbon content of the finished product after the second calcination reached 1.4%), and ball milled (the amount of water added was such that the solid content of the slurry reached 40%, and the ball milled slurry particle size D 50 They are controlled at 0.28μm~0.32μm and 0.58μm~0.62μm respectively. After the particle size is qualified, D 50: 0.28 μm ~ 0.32 μm and D 50 : 0.58 μm ~ 0.62 μm slurry is mixed uniformly at a ratio of 20% ~ 30% : 70% ~ 80%, and then converted to spray drying for granulation.

[0119] (4) The spray-dried material of step (3) is subjected to secondary firing at 780°C for 16 h, with a temperature increase rate of 6°C / min, and the secondary firing product is crushed to obtain the gradient-doped lithium manganese iron phosphate positive electrode material HeDG-LiMn 0.6 Fe 0.3 (Al 0.02 V 0.02 Ni 0.02 Zn 0.02 Y 0.02 )PO4.

[0120] Example 3

[0121] The present example provides a gradient-doped lithium manganese iron phosphate positive electrode material and a preparation method thereof.

[0122] The gradient-doped lithium manganese iron phosphate positive electrode material is HeGD-LiMn 0.6 Fe 0.3 (Al 0.02 V 0.02 Ti 0.02 Zr 0.02 La 0.02 )PO4; the conventional physical indicators of the sample are shown in Table 1.

[0123] Compared with Example 1, the preparation method is modified as follows: in steps (1) and (3), the doping elements Al, V, Ni, Zn, and Y are modified to Al, V, Ti, Zr, and La; and the corresponding dopants are modified to aluminum nitrate, vanadium acetylacetonate, titanium dioxide, zirconium acetylacetonate, and lanthanum nitrate as the corresponding raw materials, and the other contents remain unchanged.

[0124] Example 4

[0125] The present example provides a gradient-doped lithium manganese iron phosphate positive electrode material and a preparation method thereof.

[0126] The gradient-doped lithium manganese iron phosphate positive electrode material is HeGD-LiMn 0.6 Fe 0.3 (Mg 0.02 V 0.02 Cr 0.02 Nb 0.02 La 0.02 )PO4; the conventional physical indicators of the sample are shown in Table 1.

[0127] The preparation method is compared with example 1, and the doping elements Al, V, Ni, Zn, Y in steps (1) and (3) are modified to Mg, V, Cr, Nb, La, and the corresponding dopants are modified to magnesium oxide, vanadium acetylacetone, chromium nitrate, niobium pentoxide, and lanthanum nitrate; the other contents are unchanged.

[0128] Example 5

[0129] The embodiment provides a gradient-doped lithium manganese iron phosphate positive electrode material and a preparation method thereof.

[0130] The gradient-doped lithium manganese iron phosphate positive electrode material is HeGD-LiMn 0.55 Fe 0.3 (Al 0.03 V 0.03 Ni 0.03 Zn 0.03 Y 0.03 )PO4; the conventional physical indexes of the sample are shown in Table 1.

[0131] The preparation method is compared with example 1, and the doping elements Al, V, Ni, Zn, Y in steps (1) and (3) are modified to Mg, V, Cr, Nb, La, and the corresponding dopants are modified to magnesium oxide, vanadium acetylacetone, chromium nitrate, niobium pentoxide, and lanthanum nitrate; the other contents are unchanged.

[0132] Example 6

[0133] The embodiment provides a gradient-doped lithium manganese iron phosphate positive electrode material and a preparation method thereof.

[0134] The gradient-doped lithium manganese iron phosphate positive electrode material is HeGD-LiMn 0.5 Fe 0.3 (Al 0.04 V 0.04 Ni 0.04 Zn 0.04 Y 0.04 )PO4; the conventional physical indexes of the sample are shown in Table 1.

[0135] The preparation method is compared with Example 1, and step (1) is modified from "doping elements Al, V, Ni, Zn, Y, respectively, with corresponding 0.005 atomic percent of oxide or nitrate as a dopant" to "doping elements Al, V, Ni, Zn, Y, respectively, with corresponding 0.01 atomic percent of oxide or nitrate as a dopant"; step (3) is modified from "respectively using Al, V, Ni, Zn, Y corresponding 0.015 atomic percent of oxide or nitrate as a dopant" to "respectively using Al, V, Ni, Zn, Y corresponding 0.03 atomic percent of oxide or nitrate as a dopant", and the rest remains unchanged.

[0136] Comparative Example 1

[0137] The present comparative example provides a common doped lithium manganese iron phosphate positive electrode material and a preparation method thereof.

[0138] The common doped lithium manganese iron phosphate positive electrode material is LiMn 0.6 Fe 0.4 PO4. The conventional physical indicators of the sample are shown in Table 1.

[0139] The preparation method comprises the following steps: (1) lithium source lithium acetate, manganese source manganese acetate, iron source ferrous oxalate, and phosphorus source ammonium dihydrogen phosphate in a molar ratio of 1.05:0.6:0.3:1.03; citric acid as a chelating agent, ascorbic acid as a stabilizer, glucose as a carbon source and a reducing agent, and water as a solvent; (the amount of glucose added is not higher than 0.1% after burning, and the following steps are used: ① preparing a metal cation-citric acid complex solution, and adjusting the pH of the solution to about 4 with ammonia water; ② adding lithium source lithium acetate, phosphorus source ammonium dihydrogen phosphate, and carbon source glucose, and adjusting the pH of the solution to about 5.2 with ammonia water; ③ water bath evaporation of the solvent, and gelation of the solution; and ④ vacuum drying to obtain the corresponding precursor LMFP low-doped precursor.

[0140] (2) crushing the LMFP precursor prepared in step (1) and calcining at 550°C for 10h, with a heating rate controlled at 6°C / min, and crushing the calcined product.

[0141] (3) dispersing the crushed product of step (2) in a certain amount of water together with a certain amount of composite carbon source (glucose and PEG, the amount of which is added to ensure that the carbon content of the finished product after the second calcination is 1.4%), and ball-milling the mixture (the amount of water added is to ensure that the solid content of the slurry reaches 40%, and the particle size of the ball-milled slurry is controlled at D 50 0.28μm~0.32μm and 0.58μm~0.62μm, respectively), and after the particle size is qualified, D 50 0.28μm~0.32μm and D 50: 0.58-0.62 μm slurry is mixed uniformly at a ratio of 20-30:70-80, and then is converted into spray drying for granulation.

[0142] (4) The spray-dried material of step (3) is subjected to secondary firing at 780°C for 16 h, with a temperature increase rate of 5-7°C / min, and is crushed to obtain the general doped lithium manganese iron phosphate positive electrode material LiMn 0.6 Fe 0.4 PO4.

[0143] Table 1

[0144]

[0145]

[0146] Performance test

[0147] To verify the progressiveness of the embodiments of the present application, the above embodiments and comparative examples are subjected to the following performance tests:

[0148] (1) The HeGD-LiMn 0.6 Fe 0.3 (Al 0.02 V 0.02 Ni 0.02 Zn 0.02 Y 0.02 )PO4 prepared in Example 1, the HeD-LiMn 0.6 Fe 0.3 (Al 0.02 V 0.02 Ni 0.02 Zn 0.02 Y 0.02 )PO4 prepared in Example 2, and the LiMn 0.6 Fe 0.4 PO4 prepared in Comparative Example 1 are subjected to X-ray diffraction tests.

[0149] (2) The samples prepared in the embodiments and comparative examples are subjected to 45°C high-temperature discharge cycle performance tests.

[0150] Result analysis

[0151] (1) The HeGD-LiMn 0.6 Fe 0.3 (Al 0.02 V 0.02 Ni 0.02 Zn 0.02 Y 0.02 )PO4 prepared in Example 1, the HeD-LiMn 0.6Fe 0.3 (Al 0.02 V 0.02 Ni 0.02 Zn 0.02 Y 0.02 )PO4, LiMn 0.6 Fe 0.4 PO4, respectively, and the XRD patterns thereof are shown in FIG. 1. It can be seen that the prepared samples all have an olivine structure, and the diffraction peak positions of the examples are shifted compared with the comparative examples, indicating that the high-entropy gradient doping changes the microcrystal structure. Figure 1

[0152] (2) The samples prepared in the examples and the comparative example were respectively subjected to a 45°C high-temperature discharge cycle performance test, and the results are shown in Table 2.

[0153] Table 2

[0154]

[0155] According to Table 2, it can be seen from the cycle performance data of Examples 1-6 and Comparative Example 1 that all the examples exhibit significantly better battery performance than the comparative example. In the 1C rate cycle test, the discharge capacity retention rate of the example group generally maintains above 99% after 100 cycles, among which Examples 3, 4 and 5 even show a small capacity increase, showing excellent cycle stability. In contrast, the capacity retention rate of Comparative Example 1 is only 85.8% after the same number of cycles, with a decay of more than 14%, showing a significant performance disadvantage. In terms of voltage stability, the discharge voltage retention rate of the example group is all higher than 99.3% (Example 3 reaches 99.73%), while that of Comparative Example 1 drops to 93.9%, indicating that the example material has better structural stability and smaller polarization phenomenon.

[0156] Further analysis shows that the high performance of the example group mainly reflects in three key dimensions: first, the charge and discharge efficiency is always maintained above 99.4% (up to 99.72%), which is much higher than 98.14% of Comparative Example 1, indicating that the side reaction is effectively inhibited; second, the first circle efficiency of Example 4 is 98.13%, which is the highest among all samples, reflecting its optimized interface characteristics; third, the capacity and voltage retention rate show a high degree of synergy, and the decay amplitude of both is less than 1% in the example group, while Comparative Example 1 shows a synchronous large decrease. This difference may be due to the fact that the example material is a high-entropy gradient-doped lithium manganese iron phosphate positive electrode material.

[0157] ​In summary, the embodiment group, especially embodiment 4, exhibits the "high initial efficiency (>98%) - high efficiency (>99.4%) - high retention rate (>99.7%)" three-in-one characteristics, indicating that the material system has made breakthroughs in crystal structure stability, interface compatibility and kinetic performance. This performance advantage may be due to the gradient doped manganese iron phosphate positive electrode material provided in a core-shell structure and the gradient increasing distribution of mixed doped elements, which forms a special chemical environment inside the material. On the one hand, through the change of the concentration gradient, the lattice distortion problem is effectively alleviated, the structure stability of the material is enhanced, and the phase change and volume change in the cycle process are reduced, thereby significantly improving the cycle performance of the material. On the other hand, the gradient distribution of the doped elements optimizes the charge transport path, reduces the out-of-sync reaction between particles, effectively suppresses the voltage attenuation in the charging and discharging process, and improves the energy density. At the same time, the introduction of high entropy can inhibit the Jahn-Teller distortion caused by the disproportionation reaction of Mn 3+ , thereby improving the structural stability of the material and preventing the aggregation of doped elements during the cycle process. On the other hand, the high-entropy environment may reduce the Li+ migration activation energy and improve the kinetics, which is conducive to improving the overall performance of the manganese iron phosphate positive electrode material.

[0158] The above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A gradient-doped lithium manganese iron phosphate positive electrode material, characterized in that: The gradient-doped lithium manganese iron phosphate positive electrode material includes mixed doping elements, and the mixed doping elements include at least four different elements; and the gradient-doped lithium manganese iron phosphate positive electrode material is a core-shell structure, and the mixed doping elements are distributed in a gradient-increasing manner along the core-shell structure.

2. The gradient-doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The gradient-increasing distribution means that the concentration of the mixed doping element gradually increases from the core to the shell; and the following conditions are met: (a) In the core interface region: doping amount is 1% to 5%; (b) In the intermediate transition region: the doping amount is 2.5% to 10%; (c) In the shell interface area: the doping amount is 5% to 15%.

3. The gradient-doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The mixed doping elements include at least the following four different elements: At least one of the rare earth elements La and Y; At least one of the transition metal elements Ti, V, Ni, and Cr; At least one of the transition metal elements Zn, Zr, and Nb; At least one of the light metal elements Mg and Al; And, the atomic percentage of each element is 0.02-0.

04.

4. The gradient-doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The configuration entropy ΔS of the gradient-doped lithium manganese iron phosphate positive electrode material is 1.0R to 1.5R.

5. The gradient-doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The particle size distribution of the gradient-doped lithium manganese iron phosphate positive electrode material satisfies: 10 ≤0.5μm, D 50 ≤1.0μm, D 90 ≤4.0μm.

6. The gradient-doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The gradient-doped lithium manganese iron phosphate cathode material further includes a carbon coating layer, wherein the thickness of the carbon coating layer is 4 nm to 8 nm; and / or, Based on the total mass of the gradient-doped lithium manganese iron phosphate positive electrode material being 100%, the carbon content is 1.2 wt% to 1.5 wt%.

7. The gradient-doped lithium manganese iron phosphate positive electrode material according to any one of claims 1 to 6, characterized in that: The mixed doping element is selected from a combination of Al, V, Ni, Zn, and Y.

8. A method for preparing a gradient-doped lithium manganese iron phosphate positive electrode material, characterized in that: The steps include: Providing a precursor including a mixed doping element at a low concentration; The precursor is subjected to a sintering process to obtain a sintered material; The composite carbon source, the mixed metal source containing the doping element and the once-fired material are mixed, granulated, and subjected to a secondary sintering treatment to obtain a gradient-doped lithium manganese iron phosphate positive electrode material.

9. The method for preparing a gradient-doped lithium manganese iron phosphate positive electrode material according to claim 8, characterized in that: The precursor comprising a low concentration of mixed doping elements has a content of the mixed doping elements of 1.0% to 5.0%; and / or, Taking the total mass of the burnt material as 100%, the carbon content is 0.01wt% to 0.1wt%; and / or, The composite carbon source is selected from at least two of glucose, PEG and oleic acid.

10. The method for preparing a gradient-doped lithium manganese iron phosphate positive electrode material according to claim 8, characterized in that: The primary sintering temperature is 500° C. to 600° C., the heating rate is 5° C. / min to 7° C. / min, and the time is 6 h to 10 h; and / or, The secondary sintering temperature is 750° C. to 800° C., the heating rate is 5° C. / min to 7° C. / min, and the time is 10 h to 16 h; and / or, In the step of mixing the composite carbon source, the mixed metal source containing the doping element and the calcined material, wet ball milling is used for mixing, wherein the ball-to-material ratio is 3 / 1 to 6 / 1, the ball milling time is 2 to 6 hours, and the ball milling solvent is pure water or a mixture of water and anhydrous ethanol.

11. The method for preparing a gradient-doped lithium manganese iron phosphate positive electrode material according to claim 8, characterized in that: The slurry obtained by mixing has a solid content of 40% to 50%, and a particle size D of the slurry 50 0.3 μm to 0.6 μm; and / or, Before the granulation, slurries of different particle sizes are mixed in proportion, wherein the particle size D 50 The slurry with a particle size of 0.28μm to 0.32μm accounts for 20% to 30%, and the particle size D 50 The slurry with a particle size of 0.58 μm to 0.62 μm accounts for 70% to 80%.

12. A positive electrode plate for a lithium-ion battery, characterized in that: The invention comprises the gradient-doped lithium manganese iron phosphate positive electrode material according to any one of claims 1 to 7, a conductive agent and a binder.

13. A lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode adopts the positive electrode sheet of the lithium-ion battery according to claim 12.

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