Composite positive electrode material precursor, preparation method therefor, and use thereof

Abstract

A composite positive electrode material precursor, a preparation method therefor, and the use thereof. The composite positive electrode material precursor comprises an N element-doped ferric phosphate core and an M element-doped ferric phosphate coating layer which coats the surface of the ferric phosphate core, the N element including at least one of Mn, Ni, Co, Cr, V, Mg, Sr, Nb, La, Nd, Ce and Y, and the M element including at least one of Al, Ti and Zr. The doping elements N and M are respectively introduced into the core and the coating layer of the positive electrode material precursor, so that the crystal structure of ferric phosphate can be regulated, thereby improving the conductivity and the ion diffusion rate thereof. Secondly, the doping elements N and M form a synergistic effect in the composite positive electrode material precursor, which optimizes the crystal nucleus structure, enhances the stability of the coating layer, regulates the electron structure and the like, thus comprehensively improving the structural stability, the cycle life, the ion transmission rate and electrochemical properties of positive electrode materials.

Description

A composite positive electrode material precursor and its preparation method and application Technical Field

[0001] The present disclosure belongs to the technical field of battery materials, and particularly relates to a composite positive electrode material precursor and a preparation method and application thereof. Background Art

[0002] Iron phosphate is an important cathode material precursor widely used in lithium-ion batteries and other energy storage devices. However, lithium iron phosphate (LiFePO4) materials synthesized from traditional iron phosphate precursors have limitations in compaction, cycling performance, and electrochemical properties. Due to inherent material limitations, LiFePO4 materials suffer from poor conductivity, slow lithium ion diffusion, and low specific capacity. These issues are currently being addressed through structural optimization, doping, and surface coating of LiFePO4 materials.

[0003] In order to improve the uniformity and controllability of doping and coating in lithium iron phosphate and improve the electrochemical performance and stability of lithium iron phosphate, it is necessary to develop a preparation method of iron phosphate, a precursor of the positive electrode material, to improve the performance and stability of the lithium iron phosphate material.

[0004] Summary of the Invention

[0005] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0006] In response to the shortcomings of the prior art, the present disclosure aims to provide a composite cathode material precursor, its preparation method, and application. By introducing doping elements N and M into the core and coating of the cathode material precursor, respectively, the present disclosure can adjust the crystal structure of iron phosphate and improve its conductivity and ion diffusion rate. Secondly, the doping elements N and M form a synergistic effect in the composite cathode material precursor, which comprehensively improves the structural stability, cycle life, ion transport rate, and electrochemical performance of the cathode material by optimizing the crystal core structure, enhancing the stability of the coating layer, and regulating the electronic structure. This design concept provides a potential innovative approach for the development of materials in new lithium-ion batteries and other electrochemical devices.

[0007] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0008] In a first aspect, the present disclosure provides a composite cathode material precursor, comprising an N-doped iron phosphate core and an M-doped iron phosphate coating layer coated on the surface of the iron phosphate core;

[0009] The N element includes at least one of Mn, Ni, Co, Cr, V, Mg, Sr, Nb, La, Nd, Ce and Y, and the M element includes at least one of Al, Ti and Zr.

[0010] The present disclosure introduces doping elements N and M into the core and coating layer of the cathode material precursor, respectively, to adjust the crystal structure of iron phosphate and improve its conductivity and ion diffusion rate. Secondly, the doping elements N and M form a synergistic effect in the composite cathode material precursor, and by optimizing the crystal core structure, enhancing the stability of the coating layer, and regulating the electronic structure, the structural stability, cycle life, ion transport rate and electrochemical performance of the cathode material are comprehensively improved. This design concept provides a potential innovative approach for the development of materials in new lithium-ion batteries and other electrochemical devices.

[0011] In the present disclosure, the doping element M introduced into the coating layer can change the electron cloud density and crystallization state of the coating layer to a certain extent, thereby affecting the surface reactivity and stability of the iron phosphate, and supporting and stabilizing the interlayer structure of the iron phosphate; the doping element N introduced into the core provides additional charge compensation, changes the conductivity and ion diffusion properties of the crystal core, helps to improve the conductivity and ion transfer rate of the material, and can appropriately increase the specific capacity of the material. It can be seen that different ions play different functions in different positions of the material. The core doping element provides additional charge compensation, which increases the specific capacity of the material, and the coating doping element plays a role in stabilizing the main body.

[0012] In the present disclosure, different doping elements in the core and the coating layer will lead to the formation of an interface between the core and the coating layer, and the interfacial interaction of different elements can optimize the energy band structure of the interface. Through a reasonable doping combination, the energy band bending and electronic state density at the interface can be adjusted, thereby improving the carrier transfer efficiency on the interface, promoting electron transfer, and improving the conductive properties of the material. In addition, this interfacial interaction can increase the electron transfer rate between the electrode and the electrolyte, enhance the electrochemical activity of the electrode, and also enhance the bonding strength and stability of the interface. During the electrochemical cycle, the electrode material will undergo volume expansion and contraction, which will cause stress and shear force to be generated between the core and the coating layer. Therefore, by enhancing the interface strength and stability, the peeling and damage of the interface can be effectively prevented, and the cycle life of the material can be improved.

[0013] In the present disclosure, different doping elements in the core and coating layer will cause changes in the concentration of carriers such as free electrons and holes. By regulating the concentration of carriers, the conductivity and electron mobility of the material can be changed. In addition, element doping can change the band gap width, energy level barrier and Fermi level position of the material, making it easier for valence band electrons to jump to the conduction band. The effective regulation of the Fermi level of the core and shell materials can promote the transfer of charge and improve the conductivity between the interfaces. The different doping elements in the core and coating layer work together to improve the overall performance of the entire material.

[0014] In particular, the doping elements Al, Ti, and Zr in the coating layer offer the following advantages: ① They can enhance the thermal stability of the structure and extend the service life of the material; ② The doping ions replace some of the iron ions, increasing vacancies and defects in the crystal structure, thereby increasing the mobility of lithium ions within the crystal; ③ They can improve the electronic and ionic conductivity of the material, thereby enhancing the charge and discharge rate and performance of the battery. Titanium doping can affect the growth rate and size of the crystals, forming smaller crystal particles, which helps improve the battery's compaction performance and capacity retention. The doping elements Mn, Ni, Co, Cr, V, Mg, Sr, Nb, La, Nd, Ce, and Y in the core have the following advantages: they can enhance the lithium ion diffusion rate and electron mobility, improving the material's rate performance and capacity. However, since these ions are prone to dissolution to a certain extent, exacerbating side reactions with the electrolyte, to suppress the occurrence of dissolution, the construction of a core-shell structure can achieve interfacial interaction between the inner and outer doped ions. The outer doping can inhibit the stability of the core doping element and reduce dissolution.

[0015] In the present disclosure, there are many combinations of N elements and M elements, including Mn+Ti, Mn+Al, Mn+Zr, Co+Al, Co+Zr, V+Al, V+Zr and other different combinations. In the Mn+Ti combination, the doping of the Mn element improves the ionic conductivity and the embedding / de-embedding ability, and improves the capacity of the material. At the same time, the Mn doping introduces additional electronic energy levels in the core. The additional electronic states increase the electronic state density, resulting in more electrons being able to jump from the valence band to the conduction band, thereby improving the conductivity of the material; the Ti element stabilizes the crystal structure and inhibits side reactions. The doping of the Ti element controls the crystal growth size while increasing the compaction performance of the material. At the same time, the Ti element can also introduce additional electronic energy levels. Therefore, the inner and outer layers will form a superimposed electronic state density at the interface, increasing the possibility of band offset at the interface, affecting the transportability and conductivity of the electrons.

[0016] As an optional technical solution of the present disclosure, the thickness of the iron phosphate coating layer is 0.1-4 μm, for example, it can be 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc.

[0017] In the present disclosure, if the thickness of the iron phosphate coating layer is too small, the surface of the inner core layer cannot be evenly coated, the coating is incomplete, and the performance cannot be maximized; if the thickness of the iron phosphate coating layer is too large, the lithium ion insertion and extraction performance will be reduced, the material activity will be hindered, the inner layer structure performance cannot be expressed, and the electrochemical performance will be reduced.

[0018] In one embodiment, the particle size D50 of the composite cathode material precursor is 1-10 μm, for example, 1 μm, 3 μm, 5 μm, 7 μm or 9 μm.

[0019] As an optional technical solution of the present disclosure, the chemical formula of the iron phosphate core is Fe y N 1-y PO4, the chemical formula of the iron phosphate coating is Fe x M 1-x PO4, 0.9≤x<1, 0.9≤y<1.

[0020] In the present disclosure, 0.9≤x<1, for example, it can be 0.9, 0.92, 0.94, 0.96 or 0.98, and 0.9≤y<1, for example, it can be 0.9, 0.92, 0.94, 0.96 or 0.98, etc.

[0021] In the present disclosure, if the doping amount of N element is too large, it will easily cause crystal structure distortion, and more N element will be dissolved in the synthetic lithium iron phosphate during the discharge process, affecting the electrical conductivity and ion diffusion coefficient of the material, thereby affecting the rate performance; if the doping amount of M element is too large, it will inhibit the growth of small particles, resulting in reduced compaction performance. At the same time, the M atoms hinder the diffusion channel of ions, resulting in a decrease in the capacity of lithium iron phosphate.

[0022] In one embodiment, 0.95≤x<1, 0.95≤y<1.

[0023] In the present disclosure, within the range of 0.95≤x<1, 0.95≤y<1, the electrical conductivity and lithium ion diffusion performance can be improved from within the material, the structural stability can be enhanced, the element dissolution can be reduced, and the electrochemical performance of the material can be improved.

[0024] In one embodiment, the doping molar ratio of the N element and the M element is (0.25-1): (1-0.25), wherein the selection range of the N element "0.25-1" can be, for example, 0.25, 0.5 or 0.75, and the selection range of the M element "1-0.25" can be, for example, 1, 0.75 or 0.25, etc.

[0025] In the present disclosure, if the doping molar ratio of the N element and the M element is too large, it is easy to cause the doping element to dissolve, block the diffusion channel of lithium ions, and affect the electrochemical performance of the positive electrode material; if the doping molar ratio of the N element and the M element is too small, it cannot play the role of doping, the carrier concentration between the valence band and the conduction band is reduced, the conductivity is deteriorated, and the electrochemical performance is reduced.

[0026] In a second aspect, the present disclosure provides a method for preparing the composite cathode material precursor as described in the first aspect, the preparation method comprising the following steps:

[0027] (1) mixing a first iron source, a N-containing dopant, and a first solvent to obtain a molten metal A, and mixing a second iron source, a phosphorus source, an oxidant, a M-containing dopant, and a second solvent to obtain a molten metal B;

[0028] (2) adjusting the pH of the metal liquid A and performing heat treatment to obtain a solid C, and then mixing the solid C with an activator and activating it to obtain a slurry;

[0029] (3) The slurry and the metal liquid B are mixed and heat treated to obtain the composite positive electrode material precursor.

[0030] The preparation method provided by the present disclosure can synthesize a doped@coated precursor. The doping element M introduced into the coating layer supports and stabilizes the interlayer structure of the iron phosphate; the doping element N introduced into the core provides additional charge compensation, changes the conductivity and ion diffusion properties of the crystal core, helps to improve the conductivity and ion transfer rate of the material, and can appropriately increase the specific capacity of the material.

[0031] As an optional technical solution of the present disclosure, the N-containing dopant in step (1) includes at least one compound containing Mn, Ni, Co, Cr, V, Mg, Sr, Nb, La, Nd, Ce and Y elements, for example, it can be manganese sulfate, nickel sulfate, cobalt acetate, magnesium sulfate, cobalt acetate tetrahydrate, lanthanum nitrate or cerium carbonate.

[0032] It should be noted that the N-containing dopant needs to be soluble in the acid solution.

[0033] In one embodiment, the M-containing dopant in step (1) includes at least one compound containing Al, Ti and Zr elements, such as titanium trichloride, aluminum trichloride hexahydrate, aluminum nitrate, aluminum sulfate or zirconium carbonate.

[0034] It should be noted that the M-containing dopant must be soluble in the acid solution.

[0035] In one embodiment, in step (1), the first iron source and the second iron source independently comprise a divalent iron source or a trivalent iron source.

[0036] It should be noted that if the first iron source and the second iron source are only divalent iron sources, an oxidant needs to be added for oxidation to convert them into trivalent iron sources.

[0037] In one embodiment, the ferrous iron source includes ferrous sulfate, and the ferric iron source includes at least one of ferric sulfate, ferric chloride, ferric oxalate, and ferric nitrate.

[0038] In one embodiment, the phosphorus source in step (1) includes at least one of phosphoric acid, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, sodium phosphate, sodium dihydrogen phosphate, sodium monohydrogen phosphate and potassium phosphate.

[0039] It should be noted that if the phosphorus source is ammonium dihydrogen phosphate or ammonium monohydrogen phosphate, the phosphorus source can not only provide phosphorus element, but also play a role in regulating pH.

[0040] In one embodiment, the oxidant in step (1) comprises hydrogen peroxide and / or sodium peroxide.

[0041] In one embodiment, in step (1), the first solvent and the second solvent are both water.

[0042] In one embodiment, the method for adjusting the pH of the molten metal A in step (2) comprises the following steps:

[0043] The pH adjuster is added dropwise to the metal liquid A under stirring.

[0044] In the present disclosure, the pH of the metal liquid A is adjusted to the precipitation pH of iron phosphate.

[0045] In one embodiment, the pH adjuster includes a phosphorus-containing compound, and the phosphorus-containing compound includes at least one of phosphoric acid, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, sodium phosphate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, and potassium phosphate.

[0046] It should be noted that if the phosphorus-containing compound is ammonium dihydrogen phosphate or ammonium monohydrogen phosphate, the phosphorus source can not only provide phosphorus element, but also play a role equivalent to that of alkali solution.

[0047] In one embodiment, the pH adjuster further includes an alkali solution, and the alkali solution includes at least one of ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, NaOH, ammonia water and urea.

[0048] In the present disclosure, the alkali solution can regulate the pH of the reaction solution and control the synthesis of the iron phosphate precipitate.

[0049] In one embodiment, the pH adjuster further comprises an oxidizing agent, and the oxidizing agent comprises hydrogen peroxide and / or sodium peroxide.

[0050] In the present disclosure, the purpose of adding the oxidant is to oxidize the ferrous iron in the reaction solution into ferric iron. Ferrous iron cannot form a precipitate with phosphoric acid, so the ferrous iron needs to be oxidized.

[0051] In one embodiment, the dropping rate is (0.05-0.25)×V1g / min, where V1 is the volume of the molten metal A, for example, it can be 0.05V1g / min, 0.1V1g / min, 0.15V1g / min, 0.2V1g / min or 0.25V1g / min.

[0052] In the present disclosure, the dripping rate is (0.05-0.25)×V1 g / min, which helps to control the precipitation rate of the molten metal and regulate the particle size and morphology of the product.

[0053] In one embodiment, after adjusting the pH of the metal liquid A in step (2), the pH value of the metal liquid A is 1.6-2.1, for example, it can be 1.6, 1.7, 1.8, 1.9, 2 or 2.1.

[0054] In the present disclosure, if the pH value of the metal liquid A is too low, the precipitation pH of iron phosphate cannot be reached, and the metal liquid A will not produce precipitation; if the pH value of the metal liquid A is too high, it is easy to reach the precipitation pH of iron hydroxide, resulting in iron hydroxide precipitation, affecting the uniformity and consistency of the product.

[0055] In one embodiment, the temperature of the heat treatment in step (2) is 60-100°C, for example, 60°C, 70°C, 80°C, 90°C or 100°C, and the time is 0.5-5h, for example, 0.5h, 1.5h, 2.5h, 3.5h or 4.5h.

[0056] In the present disclosure, if the heat treatment temperature is too low, it is easy to cause incomplete crystallization of ferric phosphate and poor subsequent activation effect; if the heat treatment temperature is too high, it is easier to complete the crystallization and the subsequent activation effect is better, without obvious adverse effects, but energy consumption increases, which is not conducive to cost reduction and efficiency improvement. At the same time, the material may be too loose, which may easily clog the filter cloth during filtration and affect production continuity.

[0057] As an optional technical solution of the present disclosure, the activator in step (2) is an acid-alcohol mixed solution.

[0058] The present invention uses an acid-alcohol mixed solution as an activator, which can dissolve small particles on the surface of the seed crystal and form a porous structure, thereby improving the hydrophilicity, dispersibility and crystal growth rate of iron phosphate. This porous structure can adjust the structure and morphology of the product, increase its surface area, and facilitate the interaction between the electrode material and the electrolyte, thereby optimizing its electrochemical properties and application performance.

[0059] In one embodiment, the acid in the acid-alcohol mixed solution comprises at least one of sulfuric acid, phosphoric acid and nitric acid.

[0060] In the present disclosure, the acid in the acid-alcohol mixed solution can dissolve small particles on the surface of the seed crystal, forming a porous structure and adjusting the product structure and morphology.

[0061] In one embodiment, the molar concentration of the acid in the acid-alcohol mixed solution is 0.1-0.4 mol / L, for example, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L or 0.4 mol / L.

[0062] In the present disclosure, the molar concentration of the acid is 0.1-0.4 mol / L, which can achieve excellent activation effect. If it is too high, over-activation will occur, and too many small particles will be dissolved; if it is too low, incomplete activation will result, and the activation requirements cannot be met.

[0063] In one embodiment, in the acid-alcohol mixed solution, the alcohol comprises at least one of methanol, ethanol, ethylene glycol, propylene glycol and glycerol.

[0064] In the present disclosure, the alcohol in the acid-alcohol mixed solution can improve the surface properties of the seed crystals, increase the hydrophilicity and dispersibility of the seed crystals, promote the seed crystal induction effect, and increase the growth rate of the crystals and product quality.

[0065] In one embodiment, the molar ratio of acid to alcohol in the acid-alcohol mixed solution is 1:(0.5-3), for example, it can be 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5 or 1:3.

[0066] In the present disclosure, if the molar ratio of the acid to the alcohol is too small, it is easy to cause particle agglomeration and poor dispersibility; if the molar ratio of the acid to the alcohol is too large, it is easy to cause poor activation effect.

[0067] In one embodiment, the activation method in step (2) includes mechanical activation or immersion activation.

[0068] In one embodiment, the activation temperature in step (2) is 40-70°C, such as 40°C, 50°C, 60°C or 70°C, and the activation time is 0.5-2h, such as 0.5h, 1h, 1.5h or 2h.

[0069] In the present disclosure, selecting appropriate activation temperature and activation time helps to accelerate the reaction rate and increase the interaction between the seed crystals and the acidic solution, thereby optimizing the activation effect.

[0070] As an optional technical solution of the present disclosure, the amount of slurry added in step (3) = ((0.10-1.00) × Fe mass concentration of molten metal B × V2) / solid content of slurry, wherein V2 is the volume of molten metal B, for example, it can be 0.1 × Fe mass concentration of molten metal B × V2) / solid content of slurry, 0.3 × Fe mass concentration of molten metal B × V2) / solid content of slurry, 0.5 × Fe mass concentration of molten metal B × V2) / solid content of slurry, 0.7 × Fe mass concentration of molten metal B × V2) / solid content of slurry or 0.9 × Fe mass concentration of molten metal B × V2) / solid content of slurry, etc.

[0071] In the present disclosure, the amount of slurry added satisfies the above relationship, which can effectively control the thickness of the core-shell layer and the particle size of the product.

[0072] In one embodiment, the temperature of the heat treatment in step (3) is 80-95°C, for example, 80°C, 85°C, 90°C or 95°C, and the time is 3-5h, for example, 3h, 3.5h, 4h, 4.5h or 5h.

[0073] In the present disclosure, selecting an appropriate heat treatment temperature and time is beneficial to improving the degree of crystallization of ferric phosphate while increasing the specific surface area of ​​the product without causing excessive energy waste.

[0074] It should be noted that the heat treatment process is the aging process.

[0075] In one embodiment, after the heat treatment in step (3) is completed, solid-liquid separation, washing, drying and dehydration steps are further performed.

[0076] As an optional technical solution of the present disclosure, the preparation method includes the following steps:

[0077] (I) mixing a first iron source, a N-containing dopant, and a first solvent to obtain a metal liquid A, mixing a second iron source, a phosphorus source, an oxidant, an M-containing dopant, and a second solvent to obtain a metal liquid B, and mixing an alkaline solution, a phosphorus-containing compound, and an oxidant to obtain a pH adjuster;

[0078] (II) Using liquid metal A as the base liquid, a pH adjuster is added dropwise to liquid metal A under stirring to adjust its pH value to 1.6-2.1, then the temperature is raised to 60-100° C. and aged for 0.5-5.0 h, and solid C is obtained after filtration;

[0079] The dropping rate is (0.05-0.25)×V1g / min, where V1 is the volume of the metal liquid A;

[0080] (III) mixing and grinding the solid C and the acid-alcohol mixed solution, and activating the mixture at 40-70° C. for 0.5-2 h to obtain a slurry;

[0081] Wherein, the acid molar concentration of the acid-alcohol mixed solution is 0.1-0.4 mol / L, and the molar ratio of acid to alcohol is 1:(0.5-3);

[0082] (IV) mixing the slurry and the metal liquid B, and heat treating them at 80-95° C. for 3-5 hours. After the heat treatment, solid-liquid separation is performed to obtain a filter cake, and the filter cake is washed, dried, and dehydrated to obtain the composite positive electrode material precursor;

[0083] The amount of slurry added = ((0.10-1.00)×Fe mass concentration of molten metal B×V2) / solid content of slurry, where V2 is the volume of molten metal B.

[0084] In a third aspect, the present disclosure provides a lithium iron phosphate positive electrode material, which is prepared from the composite positive electrode material precursor described in the first aspect.

[0085] The lithium iron phosphate cathode material prepared based on the composite cathode material precursor provided by the present disclosure has excellent electrochemical performance and stability.

[0086] In a fourth aspect, the present disclosure provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery comprises a lithium iron phosphate positive electrode material prepared from the composite positive electrode material precursor as described in the third aspect.

[0087] The numerical range described in the present disclosure includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present disclosure no longer exhaustively lists the specific point values ​​included in the range.

[0088] Compared with the prior art, the present disclosure has the following beneficial effects:

[0089] The present disclosure introduces doping elements N and M into the core and coating layer of the cathode material precursor, respectively, to adjust the crystal structure of iron phosphate and improve its conductivity and ion diffusion rate. Secondly, the doping elements N and M form a synergistic effect in the composite cathode material precursor, and by optimizing the crystal core structure, enhancing the stability of the coating layer, and regulating the electronic structure, the structural stability, cycle life, ion transport rate and electrochemical performance of the cathode material are comprehensively improved. This design concept provides a potential innovative approach for the development of materials in new lithium-ion batteries and other electrochemical devices.

[0090] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0091] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0092] FIG1 is a SEM image of the iron phosphate core in the composite cathode material precursor prepared in Example 1 of the present disclosure.

[0093] FIG2 is a SEM image of the iron phosphate coating layer in the composite cathode material precursor prepared in Example 1 of the present disclosure.

[0094] FIG3 is a SEM image of the iron phosphate core in the composite cathode material precursor prepared in Example 3 of the present disclosure.

[0095] FIG4 is a SEM image of the iron phosphate coating layer in the composite cathode material precursor prepared in Example 3 of the present disclosure. DETAILED DESCRIPTION

[0096] The technical solution of the present disclosure is further described below through specific implementation methods. It should be understood by those skilled in the art that the embodiments are only used to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

[0097] Example 1

[0098] This embodiment provides a composite cathode material precursor, comprising an N-doped iron phosphate core and an M-doped iron phosphate coating layer coated on the surface of the iron phosphate core; the N element is Mn, and the M element is Ti;

[0099] The thickness of the iron phosphate coating layer is 1.5 μm, and the particle size D50 of the composite positive electrode material precursor is 5 μm;

[0100] The general chemical formula of the iron phosphate core is Fe 0.998 Mn 0.002 PO4, the chemical formula of the iron phosphate coating is Fe 0.998 Ti 0.002 The doping molar ratio of PO4, N element and M element is 1:1.

[0101] This embodiment also provides a method for preparing the composite positive electrode material precursor, the preparation method comprising the following steps:

[0102] (1) 1112 g of a first iron source and 8 g of a Mn-containing dopant were dissolved in 4 L of a first solvent to obtain a metal liquid A (wherein Fe = 55.64 g / L and Mn = 0.30 g / L). 1588 g of a second iron source, 660 g of a phosphorus source, 460 g of an oxidant, and 31.3 g of a Ti-containing dopant were dissolved in 8 L of a second solvent to obtain a metal liquid B (wherein the concentrations of Fe, P, and Ti were 39.95 g / L, 21.53 g / L, and 0.11 g / L, respectively). 414 g of an alkali solution, 70 g of a phosphorus-containing compound, and 310 g of an oxidant were mixed in 4 L of pure water and filtered to obtain a pH regulator (wherein the concentration of P was 26.65 g / L).

[0103] The first iron source is ferrous sulfate heptahydrate, the Mn-containing dopant is manganese sulfate, the first solvent is pure water, the second iron source is ferrous sulfate heptahydrate, the phosphorus source is phosphoric acid, the Ti-containing dopant is titanium trichloride, the second solvent is pure water, the alkali solution is ammonium dihydrogen phosphate, the phosphorus-containing compound is phosphoric acid, and the oxidant in the metal liquid B and the oxidant in the pH adjuster are both hydrogen peroxide;

[0104] (2) Using liquid metal A with a volume of V1 as the base liquid, a pH regulator was added dropwise to the liquid metal A under stirring to adjust its pH value to 1.8, and then the temperature was raised to 90°C and aged for 3 hours. After filtration, solid C was obtained with a water content of about 38%;

[0105] The dropping rate is 0.15×V1g / min, V1 is the volume of the metal liquid A, 4L;

[0106] (3) 40 g of 98% concentrated sulfuric acid and 58 g of 95% ethanol were added to 1.9 L of pure water to prepare an activator (containing 0.2 mol / L sulfuric acid and 0.6 mol / L ethanol). 1000 g of the solid C was added to 1.5 L of the activator and mixed and ground until the D50 was 1 μm. The mixture was then activated at 50° C. for 1 h to obtain a slurry.

[0107] Wherein, the molar ratio of acid to alcohol is 1:3;

[0108] (4) adding 1 kg of the slurry into 8 L of liquid metal B and heat treating at 95° C. for 2 h. After the heat treatment, solid-liquid separation is performed to obtain a filter cake. The filter cake is washed, dried, and dehydrated to obtain the composite positive electrode material precursor;

[0109] The amount of slurry added is calculated as follows: (0.2 × Fe mass concentration of molten metal B × V2) / solid content of slurry, where V2 is the volume of molten metal B (8 L), the Fe mass concentration of molten metal B is 39.95 g / L, and the solid content of the slurry is 40%.

[0110] Figures 1 and 2 respectively show the SEM images of the iron phosphate core and the iron phosphate coating layer in the composite positive electrode material precursor prepared in this embodiment. It can be seen from Figure 1 that the core iron phosphate is a flaky structure with a diameter of 1 μm. Figure 2 shows that the diameter of the iron phosphate particles induced by the core is 4 μm, and the thickness of the coating layer is 1.5 μm.

[0111] Example 2

[0112] This embodiment provides a composite cathode material precursor, comprising an N-doped iron phosphate core and an M-doped iron phosphate coating layer coated on the surface of the iron phosphate core; the N element is Mn, and the M element is Al;

[0113] The thickness of the iron phosphate coating layer is 1 μm, and the particle size D50 of the composite positive electrode material precursor is 3 μm;

[0114] The general chemical formula of the iron phosphate core is Fe 0.998 Mn 0.002 PO4, the chemical formula of the iron phosphate coating is Fe 0.998 Al 0.002 The doping molar ratio of PO4, N element and M element is 1:1.

[0115] This embodiment also provides a method for preparing the composite positive electrode material precursor, the preparation method comprising the following steps:

[0116] (1) 1112 g of a first iron source and 8 g of a Mn-containing dopant were dissolved in 4 L of a first solvent to obtain a metal liquid A (wherein Fe = 56.55 g / L and Mn = 0.31 g / L). 1588 g of a second iron source, 660 g of a phosphorus source, 460 g of an oxidant, and 31.3 g of an Al-containing dopant were dissolved in 8 L of a second solvent to obtain a metal liquid B (wherein the concentrations of Fe, P, and Ti were 40.55 g / L, 21.74 g / L, and 0.212 g / L, respectively). 414 g of an alkali solution, 70 g of a phosphorus-containing compound, and 310 g of an oxidant were mixed in 4 L of pure water and filtered to obtain a pH regulator (wherein the concentration of P was 26.81 g / L).

[0117] The first iron source is ferrous sulfate heptahydrate, the Mn-containing dopant is manganese sulfate, the first solvent is pure water, the second iron source is ferrous sulfate heptahydrate, the phosphorus source is phosphoric acid, the Al-containing dopant is aluminum chloride hexahydrate, the second solvent is pure water, the alkali solution is ammonium dihydrogen phosphate, the phosphorus-containing compound is phosphoric acid, and the oxidant in the metal liquid B and the oxidant in the pH adjuster are both hydrogen peroxide;

[0118] (2) Using liquid metal A with a volume of V1 as the base liquid, a pH regulator was added dropwise to the liquid metal A under stirring to adjust its pH value to 1.6, and then the temperature was raised to 90°C and aged for 4 hours. After filtration, solid C was obtained with a water content of about 38%;

[0119] The dropping rate is 0.05×V1g / min, V1 is the volume of the metal liquid A, 4L;

[0120] (3) 30 g of 98% concentrated sulfuric acid and 43 g of 95% ethanol were added to 1.9 L of pure water to prepare an activator (containing 0.15 mol / L sulfuric acid and 0.45 mol / L ethanol). 1000 g of the solid C was added to 1.5 L of the activator and mixed and ground until the D50 was 1 μm. The mixture was then activated at 40° C. for 1 h to obtain a slurry.

[0121] Wherein, the molar ratio of acid to alcohol is 1:3;

[0122] (4) adding 0.5 kg of the slurry into 8 L of liquid metal B and heat treating at 95° C. for 2 h. After the heat treatment, solid-liquid separation is performed to obtain a filter cake. The filter cake is washed, dried, and dehydrated to obtain the composite positive electrode material precursor;

[0123] The amount of slurry added is calculated as follows: (0.4 × Fe mass concentration of molten metal B × V2) / solid content of slurry, where V2 is the volume of molten metal B (8 L), the Fe mass concentration of molten metal B is 39.95 g / L, and the solid content of the slurry is 40%.

[0124] Example 3

[0125] This embodiment provides a composite cathode material precursor, comprising an N-doped iron phosphate core and an M-doped iron phosphate coating layer coated on the surface of the iron phosphate core; the N element is Mg, and the M element is Al;

[0126] The thickness of the iron phosphate coating layer is 1 μm, and the particle size D50 of the composite positive electrode material precursor is 3 μm;

[0127] The general chemical formula of the iron phosphate core is Fe 0.9985 Mg 0.0015 PO4, the chemical formula of the iron phosphate coating is Fe 0.9975 Al 0.0025 The doping molar ratio of PO4, N element and M element is 1:1.

[0128] This embodiment also provides a method for preparing the composite positive electrode material precursor, the preparation method comprising the following steps:

[0129] (1) 1200 g of a first iron source and 7 g of a Mg-containing dopant were dissolved in 4 L of a first solvent, and the mixture was filtered to obtain a metal liquid A (wherein Fe = 59.19 g / L and Mn = 0.24 g / L). 1588 g of a second iron source, 660 g of a phosphorus source, 460 g of an oxidant, and 20 g of an Al-containing dopant were dissolved in 8 L of a second solvent to obtain a metal liquid B (wherein the concentrations of Fe, P, and Ti were 39.99 g / L, 21.84 g / L, and 0.266 g / L, respectively). 850 g of an alkali solution, 500 g of a phosphorus-containing compound, and 350 g of an oxidant were mixed in 4 L of pure water, and the mixture was filtered to obtain a pH regulator (wherein the concentration of P was 32.60 g / L).

[0130] The first iron source is ferrous sulfate heptahydrate, the Mg-containing dopant is magnesium sulfate monohydrate, the first solvent is pure water, the second iron source is ferrous sulfate heptahydrate, the phosphorus source is phosphoric acid, the Al-containing dopant is aluminum chloride hexahydrate, the second solvent is pure water, the alkali solution is sodium hydroxide, the phosphorus-containing compound is phosphoric acid, and the oxidant in the metal liquid B and the oxidant in the pH adjuster are both hydrogen peroxide;

[0131] (2) Using liquid metal A with a volume of V1 as the base liquid, a pH regulator was added dropwise to the liquid metal A under stirring to adjust its pH value to 2.1, and then the temperature was raised to 90°C and aged for 4 hours. After filtration, solid C was obtained with a water content of about 38%;

[0132] The drop rate is 0.25×V1g / min, V1 is the volume of the metal liquid A, 4L;

[0133] (3) 30 g of 98% concentrated sulfuric acid and 43 g of 95% ethanol were added to 1.9 L of pure water to prepare an activator (containing 0.15 mol / L sulfuric acid and 0.45 mol / L ethanol). 1000 g of the solid C was added to 1.5 L of the activator and mixed and ground until the D50 was 1 μm. The mixture was then activated at 70° C. for 1 h to obtain a slurry.

[0134] Wherein, the molar ratio of acid to alcohol is 1:3;

[0135] (4) adding 0.5 kg of the slurry into 8 L of liquid metal B and heat treating at 95° C. for 2 h. After the heat treatment, solid-liquid separation is performed to obtain a filter cake. The filter cake is washed, dried, and dehydrated to obtain the composite positive electrode material precursor;

[0136] The amount of slurry added is calculated as follows: (0.2 × Fe mass concentration of molten metal × V2) / solid content of slurry, where V2 is the volume of molten metal B (8 L), the Fe mass concentration of molten metal B is 39.99 g / L, and the solid content of the slurry is 40%.

[0137] Figures 3 and 4 respectively show SEM images of the iron phosphate core and the iron phosphate coating layer in the composite positive electrode material precursor prepared in this embodiment. It can be seen from Figure 1 that the diameter of the core layer is 0.5-1um, and from Figure 2 that the diameter of the shell layer is about 3-4μm, and the thickness of the coating layer is about 1.5-2μm.

[0138] Example 4

[0139] The difference between this embodiment and embodiment 1 is that the thickness of the iron phosphate coating layer is 0.05 μm by adjusting the amount of the added metal liquid B.

[0140] The rest of the preparation methods and parameters remained the same as in Example 1.

[0141] Example 5

[0142] The difference between this embodiment and embodiment 1 is that the thickness of the iron phosphate coating layer is 6 μm by adjusting the amount of the added metal liquid B.

[0143] The rest of the preparation methods and parameters remained the same as in Example 1.

[0144] Example 6

[0145] The difference between this embodiment and embodiment 1 is that the amount of the Mn dopant added is adjusted so that the chemical formula of the iron phosphate core is Fe 0.8 Mn 0.2 PO4.

[0146] The rest of the preparation methods and parameters remained the same as in Example 1.

[0147] Example 7

[0148] The difference between this embodiment and embodiment 1 is that the amount of the Ti-containing dopant is adjusted so that the chemical formula of the iron phosphate coating layer is Fe 0.8 Ti 0.2 PO4.

[0149] The rest of the preparation methods and parameters remained the same as in Example 1.

[0150] Example 8

[0151] The difference between this embodiment and embodiment 1 is that the doping molar ratio of N element to M element in the composite positive electrode material precursor is 0.1:1 by adjusting the added amount of Mn-containing dopant and the added amount of Ti-containing dopant.

[0152] The rest of the preparation methods and parameters remained the same as in Example 1.

[0153] Example 9

[0154] The difference between this embodiment and embodiment 1 is that the amount of the added Mn-containing dopant and the amount of the added Ti-containing dopant are adjusted so that the doping molar ratio of the N element and the M element in the composite positive electrode material precursor is 1:0.1.

[0155] The rest of the preparation methods and parameters remained the same as in Example 1.

[0156] Example 10

[0157] The difference between this embodiment and embodiment 1 is that no pH adjuster is added in step (2), that is, no pH adjuster is prepared in step (1).

[0158] The rest of the preparation methods and parameters remained the same as in Example 1.

[0159] Example 11

[0160] The difference between this embodiment and embodiment 1 is that no activator is added in step (3).

[0161] The rest of the preparation methods and parameters remained the same as in Example 1.

[0162] Example 12

[0163] The difference between this embodiment and embodiment 1 is that the activator in step (3) contains only concentrated sulfuric acid, that is, 58 g of ethanol is replaced by 58 g of concentrated sulfuric acid.

[0164] The rest of the preparation methods and parameters remained the same as in Example 1.

[0165] Example 13

[0166] The difference between this embodiment and embodiment 1 is that the activator in step (3) contains only ethanol, that is, 40 g of concentrated sulfuric acid is replaced by 40 g of ethanol.

[0167] The rest of the preparation methods and parameters remained the same as in Example 1.

[0168] Comparative Example 1

[0169] The difference between this comparative example and Example 1 is that the chemical formula of the iron phosphate core is Fe 0.998 Ti 0.002 PO4, the chemical formula of the iron phosphate coating is Fe 0.998 Mn 0.002 PO4, that is, exchanging the Mn-containing dopant in the metal liquid A with the Ti-containing dopant in the metal liquid B, the specific steps include:

[0170] 1112 g of the first iron source and 21.4 g of the Ti-containing dopant were dissolved in 4 L of the first solvent to obtain liquid metal A (wherein Fe = 56.01 g / L, Ti = 0.30 g / L), and 1588 g of the second iron source, 660 g of the phosphorus source, 460 g of the oxidant, and 10 g of the Mn-containing dopant were dissolved in 8 L of the second solvent to obtain liquid metal B (wherein the concentrations of Fe, P, and Ti were 40.61 g / L, 21.78 g / L, and 0.11 g / L, respectively).

[0171] The rest of the preparation methods and parameters remained the same as in Example 1.

[0172] Comparative Example 2

[0173] The difference between this comparative example and Example 1 is that the chemical formula of the iron phosphate core and the chemical formula of the iron phosphate coating are both Fe 0.998 Ti 0.002 PO4, that is, 8 g of Mn-containing dopant is replaced by 24.1 g of titanium trichloride.

[0174] The rest of the preparation methods and parameters remained the same as in Example 1.

[0175] Comparative Example 3

[0176] The difference between this comparative example and Example 1 is that the chemical formula of the iron phosphate core and the chemical formula of the iron phosphate coating are both Fe 0.998 Mn 0.002 PO4, i.e., 31.3 g of Ti-containing dopant was replaced with 10 g of manganese sulfate.

[0177] The rest of the preparation methods and parameters remained the same as in Example 1.

[0178] Comparative Example 4

[0179] The difference between this comparative example and Example 1 is that the chemical formula of the iron phosphate core is FePO4, that is, the core is not doped, and no Mn-containing dopant is added in step (1).

[0180] The rest of the preparation methods and parameters remained the same as in Example 1.

[0181] Comparative Example 5

[0182] The difference between this comparative example and Example 1 is that the chemical formula of the iron phosphate coating layer is FePO4, that is, the coating layer is not doped, and no Ti-containing dopant is added in step (1).

[0183] The rest of the preparation methods and parameters remained the same as in Example 1.

[0184] Performance Testing

[0185] 1. The physical and chemical indicators of the composite cathode material precursors prepared in the above examples and comparative examples were tested. The specific element data were obtained by ICP-AES testing. The test results are shown in Table 1.

[0186] Table 1

[0187] analyze:

[0188] As can be seen from Table 1, the (Fe+M+N) / P ratio of the iron phosphate products prepared in Examples 1-3 meets the designed ratio (Fe / P=0.97-0.98), and the BET of the iron phosphate synthesized in Examples 1-3 is higher than that in Comparative Examples 1-3, which is beneficial to improving the activity of synthesized lithium iron phosphate and improving the compaction performance of the product.

[0189] Using the composite cathode material precursors prepared in the above examples and comparative examples as raw materials, lithium iron phosphate cathode materials were synthesized. A commercially available lithium iron phosphate cathode material was used as a control. Lithium-ion batteries were then fabricated and subjected to electrochemical performance testing: 1) Initial discharge specific capacity and initial efficiency were tested at room temperature (25°C), a charge-discharge voltage of 2.0-3.65V, and an initial charge-discharge rate of 0.1C; 2) 200-cycle cycling performance and powder compaction performance were tested at room temperature (25°C), a charge-discharge voltage of 2.0-3.65V, and a charge-discharge rate of 1C. The test results are shown in Table 2.

[0190] Table 2

[0191] analyze:

[0192] As can be seen from Table 2, by doping N element and M element into the iron phosphate core and coating layer respectively, it is possible to construct doped@coated iron phosphate, improve the powder characteristics, and increase the compaction density and discharge specific capacity of the synthesized lithium iron phosphate.

[0193] From the comparison of the data results of Example 1 and Examples 4-5, it can be seen that if the thickness of the iron phosphate coating layer is too small, the coating uniformity will deteriorate, the doping elements will be easily dissolved, and the synthesis of lithium iron phosphate will easily lead to poor cycle life and rate performance; if the thickness of the iron phosphate coating layer is too large, the synthesis of lithium iron phosphate will easily lead to blockage of lithium ion diffusion channels, and small particles will not be able to grow, thereby reducing the compaction performance.

[0194] From the comparison of the data results of Example 1 and Examples 6-7, it can be seen that if the doping amount of the Mn element in the iron phosphate core or the doping amount of the Ti element in the iron phosphate coating is too large, it is easy to block the lithium ion diffusion channel after the synthesis of lithium iron phosphate and inhibit the growth of small particles, thereby leading to compaction and reduced capacity.

[0195] From the comparison of the data results of Example 1 and Examples 8-9, it can be seen that if the doping molar ratio of the N element and the M element is too small, the inner layer doping elements are too much, which can easily lead to more Mn dissolution, inhibiting the growth of the particles, resulting in low capacity and compaction; if the doping molar ratio of the N element and the M element is too large, the outer layer doping elements are likely to block the lithium ion diffusion channel, resulting in a low capacity of the synthesized lithium iron phosphate.

[0196] From the comparison of the data results of Example 1 and Example 10, it can be seen that if the pH regulator is not added, no precipitation can be obtained, resulting in the inability to synthesize the composite positive electrode material precursor.

[0197] From the comparison of the data results of Example 1 and Example 11, it can be seen that if no activator is added, the slurry activity is poor, the iron phosphate particles synthesized by induction are larger, and although the obtained product has a higher compaction, the capacity is relatively low.

[0198] From the comparison of the data results of Example 1 and Examples 12-13, it can be seen that if the activator contains only concentrated sulfuric acid or ethanol, the BET value of the synthesized iron phosphate is likely to be too small and the activity is insufficient, thereby resulting in compaction or low capacity after the synthesis of lithium iron phosphate.

[0199] From the comparison of the data results of Example 1 and Comparative Example 1, it can be seen that if the doping positions of the N element and the M element are exchanged, the M element is likely to be dissolved, resulting in slightly poor discharge and compaction performance of the positive electrode material.

[0200] From the comparison of the data results of Example 1 and Comparative Example 2, it can be seen that if both the core and the shell are doped with Ti element, the carrier concentration between the interfaces is reduced after the synthesis of lithium iron phosphate, resulting in a slightly lower capacity despite the higher compaction performance.

[0201] From the comparison of the data results of Example 1 and Comparative Example 3, it can be seen that if both the core and the shell are doped with Mn element, although the discharge specific capacity of the material can be improved, the dissolution of Mn element may occur during the synthesis process, resulting in the compaction performance being lower than that of Example 1.

[0202] From the comparison of the data results of Example 1 and Comparative Examples 4-5, it can be seen that if the iron phosphate core is not doped, the capacity of the synthesized lithium iron phosphate is slightly lower; if the iron phosphate coating is not doped, the capacity of the synthesized lithium iron phosphate is slightly lower and the compaction performance is lower.

Claims

1. A composite cathode material precursor, comprising an N-doped iron phosphate core and an M-doped iron phosphate coating layer coated on the surface of the iron phosphate core; The N element includes at least one of Mn, Ni, Co, Cr, V, Mg, Sr, Nb, La, Nd, Ce and Y, and the M element includes at least one of Al, Ti and Zr.

2. The composite cathode material precursor according to claim 1, wherein: The thickness of the iron phosphate coating layer is 0.1-4 μm.

3. The composite cathode material precursor according to claim 1 or 2, wherein: The particle size D50 of the composite positive electrode material precursor is 1-10 μm.

4. The composite cathode material precursor according to any one of claims 1 to 3, wherein: The general chemical formula of the iron phosphate core is Fe y N 1-y PO4, the chemical formula of the iron phosphate coating is Fe x M 1-x PO4, 0.9≤x<1, 0.9≤y<1.

5. The composite cathode material precursor according to claim 4, wherein: 0.95≤x<1, 0.95≤y<1.

6. The composite cathode material precursor according to any one of claims 1 to 5, wherein: The doping molar ratio of the N element to the M element is (0.25-1):(1-0.25).

7. A method for preparing a composite positive electrode material precursor according to any one of claims 1 to 6, comprising the following steps: (1) mixing a first iron source, an N-containing dopant and a first solvent to obtain a molten metal A, and mixing a second iron source, a phosphorus source, an oxidant, an M-containing dopant and a second solvent to obtain a molten metal B; (2) adjusting the pH of the molten metal A and performing heat treatment to obtain a solid C, and then mixing the solid C with an activator and activating it to obtain a slurry; (3) The slurry and the metal liquid B are mixed and heat treated to obtain the composite positive electrode material precursor.

8. The preparation method according to claim 7, wherein: The method for adjusting the pH of the metal liquid A in step (2) comprises the following steps: The pH adjuster is added dropwise to the metal liquid A under stirring.

9. The preparation method according to claim 8, wherein: The pH adjuster includes a phosphorus-containing compound, and the phosphorus-containing compound includes at least one of phosphoric acid, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, sodium phosphate, sodium dihydrogen phosphate, sodium monohydrogen phosphate and potassium phosphate.

10. The preparation method according to claim 8 or 9, wherein: The pH adjuster further includes an alkali solution, and the alkali solution includes at least one of diammonium phosphate, monoammonium hydrogen phosphate, NaOH, ammonia water and urea.

11. The preparation method according to any one of claims 8 to 10, wherein: The pH adjuster further includes an oxidant, and the oxidant includes hydrogen peroxide and / or sodium peroxide.

12. The preparation method according to any one of claims 8 to 11, wherein: The dropping rate is (0.05-0.25)×V1g / min, wherein V1 is the volume of the metal liquid A.

13. The preparation method according to any one of claims 7 to 12, wherein: After adjusting the pH of the metal liquid A in step (2), the pH value of the metal liquid A is 1.6-2.

1.

14. The preparation method according to any one of claims 7 to 13, wherein: The heat treatment temperature in step (2) is 60-100° C. and the time is 0.5-5 h.

15. The preparation method according to any one of claims 7 to 14, wherein: The activator in step (2) is an acid-alcohol mixed solution; Optionally, in the acid-alcohol mixed solution, the acid comprises at least one of sulfuric acid, phosphoric acid and nitric acid; Optionally, in the acid-alcohol mixed solution, the molar concentration of the acid is 0.1-0.4 mol / L; Optionally, in the acid-alcohol mixed solution, the alcohol includes at least one of methanol, ethanol, ethylene glycol, propylene glycol and glycerol; Optionally, in the acid-alcohol mixed solution, the molar ratio of acid to alcohol is 1:(0.5-3); Optionally, the activation temperature in step (2) is 40-70°C and the activation time is 0.5-2h.

16. The preparation method according to any one of claims 7 to 15, wherein: The amount of the slurry added in step (3) = ((0.10-1.00) × Fe mass concentration of molten metal B × V2) / solid content of slurry, wherein V2 is the volume of molten metal B; Optionally, the heat treatment temperature in step (3) is 80-95° C. and the time is 3-5 h; Optionally, after the heat treatment in step (3) is completed, solid-liquid separation, washing, drying and dehydration steps are also performed.

17. The preparation method according to any one of claims 7 to 16, wherein: The preparation method comprises the following steps: (I) mixing a first iron source, a N-containing dopant and a first solvent to obtain a metal liquid A, mixing a second iron source, a phosphorus source, an oxidant, an M-containing dopant and a second solvent to obtain a metal liquid B, and mixing an alkali solution, a phosphorus-containing compound and an oxidant to obtain a pH adjuster; (II) With liquid metal A as the base liquid, a pH adjuster is added dropwise to liquid metal A under stirring to adjust its pH value to 1.6-2.1, and then the temperature is raised to 60-100° C. for aging for 0.5-5 h, and solid C is obtained after filtration; The dropping rate is (0.05-0.25)×V1g / min, where V1 is the volume of the metal liquid A; (III) mixing and grinding the solid C and the acid-alcohol mixed solution, and activating the mixture at 40-70° C. for 0.5-2 h to obtain a slurry; Wherein, the acid molar concentration of the acid-alcohol mixed solution is 0.1-0.4 mol / L, and the molar ratio of the acid to the alcohol is 1:(0.5-3); (IV) mixing the slurry and the metal liquid B, and subjecting the mixture to a heat treatment at 80-95° C. for 3-5 hours. After the heat treatment, solid-liquid separation is performed to obtain a filter cake. The filter cake is washed, dried and dehydrated to obtain the composite positive electrode material precursor. The amount of slurry added = ((0.10-1.00) × Fe mass concentration of liquid metal B × V2) / solid content of slurry V2 is the volume of molten metal B.

18. A lithium iron phosphate positive electrode material prepared from the composite positive electrode material precursor according to any one of claims 1 to 6.

19. A lithium ion battery comprising the lithium iron phosphate positive electrode material according to claim 18.

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