A gradient distribution composite material, a preparation method thereof and application thereof

Abstract

The application provides a gradient distribution composite material as shown in the formula LiMn x Fe 1‑x PO4C y The carbon layer is coated on the surface of LiMn x Fe 1‑x PO4; and along the direction from the center to the outer surface of the composite material, the content of Mn elements in the LiMn x Fe 1‑x PO4 presents a decreasing trend, the content of Fe elements presents an increasing trend, and the content of C elements in the carbon layer presents a decreasing trend. The application also provides a preparation method and application of the gradient distribution composite material. The gradient distribution composite material provided by the application realizes the stability of the material due to the gradient change of Mn elements, Fe elements and C elements, and has high rate performance as a positive electrode material of a lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a gradient distribution composite material, a preparation method thereof and application thereof. BACKGROUND

[0002] With the rapid development of new energy industry at home and abroad, lithium battery cathode materials represented by lithium iron phosphate (LFP) have become the most critical raw materials for electric vehicles and energy storage business. As a high-voltage upgraded version of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP) has attracted widespread attention due to its high energy density, high stability and low cost. However, it also has typical shortcomings of polyanion materials, such as low electronic conductivity and low ionic conductivity. In addition, the introduction of Mn element also brings the problems of high-temperature dissolution of trivalent Mn ion and gas production. In order to solve the above problems, people usually adopt similar methods to lithium iron phosphate, such as carbon coating, doping and nanocrystallization. These methods are still effective for LMFP, but because the electronic conductivity and ionic conductivity of LMFP are more than two orders of magnitude lower than those of LFP, the effect of traditional methods is not ideal. Therefore, it is difficult to modify LMFP, the cost is high, the output-input ratio is low, and new methods are urgently needed to modify LMFP.

[0003] The currently used LMFP material has a very small particle size, generally about 200 nm or even less than 100 nm. In order to improve the electrical conductivity, conductive carbon is mixed therein, and the content is more than 2wt%. Therefore, the specific surface area is large, generally more than 18m 2 / g. Such material has poor processability, high viscosity and low solid content during preparation of slurry, and it is difficult to coat and bake. In addition, because Mn ions will dissolve in electrolyte at high temperature, general dry or wet carbon coating will always have pores or uneven coating places, and it is difficult to completely avoid LMFP from being exposed (as shown in Figure 1 ). Although deposition type coating can achieve uniform coating effect, the types of materials that can be selected are limited, and the cost is high. Therefore, it is difficult to mass-produce.

[0004] Therefore, the effect of traditional nanocrystallization and carbon coating modification of LMFP is not obvious, and many side effects are caused. SUMMARY

[0005] The technical problem solved by the present application is to provide a gradient distribution composite material. The composite material provided by the present application has good material stability and good rate performance as a cathode material of lithium ion battery.

[0006] The present application also provides a gradient distribution composite material as shown in formula (I),

[0007] LiMn x Fe 1-x PO4C y (I);

[0008] wherein, 0 < x ≤ 1, 0.1 < y < 0.2;

[0009] In the composite material, the carbon layer is coated on the surface of LiMn x Fe 1-x PO4.

[0010] And along the direction from the center to the outer surface of the composite material, the content of Mn element in the LiMn x Fe 1-x PO4decreases in a decreasing trend, the content of Fe element increases in a decreasing trend, and the content of C element in the carbon layer decreases in a decreasing trend.

[0011] Preferably, the content of Mn element decreases at a rate v1, 0.01 mol% / nm < v1 < 0.10 mol% / nm; the content of Fe element increases at a rate v2, 0.01 mol% / nm < v2 < 0.10 mol% / nm; and the content of C element decreases at a rate v3, 0.01 mol% / nm < v3 < 0.10 mol% / nm.

[0012] Preferably, the content of Mn element decreases at a rate v1, 0.01 mol% / nm < v1 < 0.03 mol% / nm; the content of Fe element increases at a rate v2, 0.01 mol% / nm < v2 < 0.03 mol% / nm; and the content of C element decreases at a rate v3, 0.01 mol% / nm < v3 < 0.03 mol% / nm.

[0013] Preferably, the D50 of the composite material is 1.1 μm ~ 1.5 μm, and the D10 is 0.3 ~ 0.8 μm.

[0014] Preferably, the specific surface area of the composite material is 10 ~ 15 m 2 / g, and the powder resistivity of the composite material is 0 ~ 100 Ω·cm.

[0015] The application also provides a preparation method of the gradient distribution composite material, comprising the following steps:

[0016] A) mixing a lithium source, a manganese source, an iron source, a phosphorus source, a reducing agent and a solvent to obtain a mixed solution A;

[0017] Heating and performing combustion reaction on the mixed solution A, and crushing the obtained combustion reaction product to obtain a first precursor;

[0018] mixing the first precursor, the carbon source and the initiator to obtain a mixed solution B;

[0019] B) mixing a lithium source, an iron source, a phosphorus source, a carbon source and a solvent, then dissociating and homogenizing to obtain a slurry C;

[0020] C) adding the slurry C into the mixed solution B to react to obtain a slurry D, and drying the slurry D to obtain a composite precursor;

[0021] D) sintering the composite precursor to obtain a composite material;

[0022] The content of iron ions in the mixed solution B is lower than that in the slurry C;

[0023] The concentration of the carbon source in the mixed solution B is higher than that in the slurry C.

[0024] Preferably, in step A), the lithium source is selected from one or both of lithium carbonate and lithium hydroxide, the manganese source is selected from one or both of manganese nitrate and manganese carbonate, the iron source is selected from one or both of iron nitrate and ferrous nitrate, the phosphorus source is selected from one or more of phosphoric acid, metaphosphoric acid, pyrophosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphorus oxide, the carbon source is selected from one or more of oxirane, ethylene glycol, acrylate, dopamine and aniline, the reducing agent is selected from one or more of urea, citric acid and glucose, the initiator is selected from one or more of ammonium persulfate, azobisisobutyronitrile, cumene hydroperoxide and dibenzoyl peroxide, and the solvent is selected from one or more of water, tetrahydrofuran, acetone, ethanol, methanol, benzene, toluene and xylene; in step B), the lithium source is selected from one or both of lithium carbonate and lithium hydroxide, the iron source is selected from one or more of iron phosphate, ferrous oxalate, ferrous acetate, diiron trioxide and iron oxyhydroxide, the phosphorus source is selected from one or more of phosphoric acid, metaphosphoric acid, pyrophosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphorus oxide, the carbon source is selected from one or more of oxirane, ethylene glycol, acrylate, dopamine and aniline, and the solvent is selected from one or more of water, tetrahydrofuran, acetone, ethanol, methanol, benzene, toluene and xylene.

[0025] Preferably, the rate of adding the slurry C into the mixed solution B is 0.02-0.5 mol / min; the solid content of the slurry C is 10-60 wt%, and the average particle size is 5-200 nm; the drying temperature is 100-500℃, and the time is 2-6 h; the sintering temperature is 500-1000℃, and the time is 5-15 h.

[0026] The application also provides a lithium ion battery, comprising a positive electrode and a negative electrode, wherein the material of the positive electrode is the composite material or the composite material prepared by the preparation method.

[0027] The application also provides an electric device comprising the lithium ion battery as described above.

[0028] The application provides a gradient composite material, wherein the content of Mn gradually decreases from the center to the surface of the particle, the center is LiMnPO4, and gradually changes to LiMn x Fe 1-x PO4(0<x<1) transition LiFePO4, the gradient design of the content of Mn element, the outer layer is mainly LFP, the reaction kinetics is good, the outer layer can be ensured to react first, and the stability of LFP is high, the solubility of electrolyte is low, and the stability of the outer layer structure can be maintained; the inner layer is mainly LMFP, the energy of LMFP is relatively high, but the reaction kinetics is poor, and the reaction starts in the later stage of the charging curve; from the center to the surface of the material, the content of C is also high to low; the LFP in the outer layer has relatively high conductivity, and the mixed content of C is relatively low, while the LMFP in the inner layer has low conductivity, and the mixed content of C is relatively high, and the combination of the high and low collocations can ensure the uniform distribution of the electronic conductivity in the whole material, thereby improving the rate performance of the material.

[0029] On the outer surface of the composite material, part of the carbon is also coated, which is used for establishing the conductive network between the particles; the double-gradient composite material is a single crystal or a single crystal-like particle, and the integrity of the olivine structure in the single particle can be maintained. With the particle center as the origin, the elements in the double-gradient material show a linear change process, the content of Mn and C gradually decreases from the center, and the content of Fe gradually increases from the center, and the gradient change can also ensure that the stress in the material is consistent, and the material will not be cracked due to the difference in thermal expansion. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a structural schematic diagram of LMFP in the prior art of the application;

[0031] Figure 2 It is a structural schematic diagram of the composite material of the application;

[0032] Figure 3 It is a radial distribution curve of the mass content of Mn element, Fe element and C element in the composite material of the application;

[0033] Figure 4 It is a physicochemical parameter diagram of the composite material of the application;

[0034] Figure 5 It is a capacity retention rate column chart of the composite material of the application;

[0035] Figure 6 Resistance column chart of the composite material of the present application;

[0036] Figure 7 Gram capacity column chart of the composite material of the present application. DETAILED DESCRIPTION

[0037] For a further understanding of the present application, preferred embodiments thereof will be described in detail in connection with the following examples, although it is to be understood that various other specific embodiments and modifications can be made thereto without departing from the scope of the present application.

[0038] In view of the technical problem that the modified lithium iron manganese phosphate composite material in the prior art does not have obvious effect, the present application provides a double-gradient composite lithium iron manganese phosphate material and a preparation method thereof, which realizes carbon coating and also has double gradients of Mn elements, Fe elements and C elements, so that the lithium iron manganese phosphate is applied to a positive electrode material and has good rate performance and material stability. Specifically, the present application discloses a gradient distribution composite material as shown in formula (I),

[0039] LiMn x Fe 1-x PO4C y (I);

[0040] wherein 0

[0041] In the composite material, the carbon layer is coated on the surface of LiMn x Fe 1-x PO4.

[0042] And along the direction from the center to the outer surface of the composite material, the content of Mn elements in LiMn x Fe 1-x PO4 shows a decreasing trend, the content of Fe elements shows an increasing trend, and the content of C elements in the carbon layer shows a decreasing trend.

[0043] In the composite material provided by the present application, due to the gradient change of Mn elements and Fe elements, the center is LiMnPO4, which gradually transitions to LiMn x Fe 1-x PO4 (0 Figure 2

[0044] ​Specifically, in the gradient distribution composite material provided by the application, the content of the Mn element decreases at a rate v1, 0.01 mol% / nm < v1 < 0.10 mol% / nm; the content of the Fe element increases at a rate v2, 0.01 mol% / nm < v2 < 0.10 mol% / nm; and the content of the C element decreases at a rate v3, 0.01 mol% / nm < v3 < 0.10 mol% / nm; more specifically, the content of the Mn element decreases at a rate v1, 0.01 mol% / nm < v1 < 0.037 mol% / nm; the content of the Fe element increases at a rate v2, 0.01 mol% / nm < v2 < 0.052 mol% / nm; and the content of the C element decreases at a rate v3, 0.01 mol% / nm < v3 < 0.015 mol% / nm.

[0045] Further, in the double-gradient composite material provided by the application, the particle size is also relatively large, D50 is 1.1 μm ~ 1.5 μm, D10 is 0.3 ~ 0.8 μm, which can reach the level of general high-compacted LFP, and the specific surface area is 10 ~ 15 m 2 / g, so as to ensure good processing performance of the material; and the powder resistivity of the composite material is 0 ~ 100 Ω·cm, so as to ensure good electrical performance of the material.

[0046] The application further provides a preparation method of the gradient distribution composite material, comprising the following steps:

[0047] A) mixing a lithium source, a manganese source, an iron source, a phosphorus source, a reducing agent and a solvent to obtain a mixed solution A;

[0048] heating and performing a combustion reaction on the mixed solution A, and crushing the obtained combustion reaction product to obtain a first precursor;

[0049] mixing the first precursor, a carbon source and an initiator to obtain a mixed solution B;

[0050] B) mixing a lithium source, an iron source, a phosphorus source, a carbon source and a solvent, and then performing dissociation and homogenization to obtain a slurry C;

[0051] C) adding the slurry C into the mixed solution B to obtain a slurry D by reaction, and drying the slurry D to obtain a composite material precursor;

[0052] D) sintering the composite material precursor to obtain a composite material;

[0053] The content of iron ions in the mixed solution B is lower than the content of iron ions in the slurry C;

[0054] The concentration of the carbon source in the mixed solution B is higher than the concentration of the carbon source in the slurry C.

[0055] In the above preparation process, the gradient change of C element is specifically formed as follows: the mixed solution B (high concentration solution) of high concentration polymer monomer contains a polymerization initiator, which can cause the polymer monomer to polymerize and be wrapped on the surface of the first precursor material, wherein the initiator is in excess; the slurry C (low concentration solution) of low concentration polymer monomer does not contain a polymerization initiator, and when it is injected into the high concentration solution at a certain rate, the concentration of the polymer monomer presents a gradient decrease; and the precursor material is also injected into the high concentration solution, and at the same time of injection, the excess initiator initiates the polymerization reaction of the polymer monomer and coats the injected precursor material; due to the gradient change of the polymer concentration in the process, the coating thickness presents a gradient change; in the mixed slurry D, the precursor with different coating thicknesses is uniformly dispersed, and the polymers with different thicknesses form surface coating layers with different carbon contents in the sintering process, thereby forming a carbon gradient change.

[0056] The gradient change of Mn and Fe elements is specifically formed as follows: the first precursor contains a Mn compound, so the Mn content is relatively high; the slurry C does not contain a Mn compound, so the Mn content is relatively low; on the contrary, the Fe content in the first precursor is relatively low, while the Fe content in the slurry C is relatively high; on the basis of the above, when the slurry C is added into the mixed solution B at a certain rate, the slurry C is dispersed and coated on the surface of the first precursor; the Mn content in the composite precursor particle is relatively high in the center, while the Fe content is relatively high on the surface; in the process of heat treatment, Mn and Fe undergo thermal diffusion, Mn element diffuses from the center to the surface, while Fe element diffuses from the surface to the center, and with the increase of the diffusion distance, the content of element diffusion gradually decreases, so Mn and Fe elements present a gradient change.

[0057] In step A), the lithium source is selected from one or both of lithium carbonate and lithium hydroxide, the manganese source is selected from one or both of manganese nitrate and manganese carbonate, the iron source is selected from one or both of iron nitrate and ferrous nitrate, the phosphorus source is selected from one or more of phosphoric acid, metaphosphoric acid, pyrophosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphorus oxide, the carbon source is selected from one or more of oxirane, ethylene glycol, acrylate, dopamine and aniline, the reducing agent is selected from one or more of urea, citric acid and glucose, the initiator is selected from one or more of ammonium persulfate, azobisisobutyronitrile, cumene hydroperoxide and dibenzoyl peroxide, and the solvent is selected from one or more of water, tetrahydrofuran, acetone, ethanol, methanol, benzene, toluene and xylene;

[0058] In step B), the lithium source is selected from one or both of lithium carbonate and lithium hydroxide, the iron source is selected from one or more of iron phosphate, ferrous oxalate, iron acetate, diiron trioxide and iron oxyhydroxide, the phosphorus source is selected from one or more of phosphoric acid, metaphosphoric acid, pyrophosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphorus oxide, the carbon source is selected from one or more of oxirane, ethylene glycol, acrylate, dopamine and aniline, and the solvent is selected from one or more of water, tetrahydrofuran, acetone, ethanol, methanol, benzene, toluene and xylene.

[0059] The solid content of the slurry C is 10-60 wt%, and the average particle size is 5-200 nm. Specifically, the solid content of the slurry C is 20-40 wt%, and the average particle size is 20-150 nm. The injection rate of the slurry C into the mixed solution B is 0.02-0.5 mol / min. Specifically, the injection rate of the slurry C into the mixed solution B is 0.05-0.3 mol / min. During the injection of the slurry C into the mixed solution B, the faster the injection rate, the faster the polymer monomer concentration decreases, and the faster the thickness of the coating layer decreases, thereby achieving the control of the gradient change rate of the C content.

[0060] During the preparation, the sintering temperature is 500-1000°C, and the sintering time is 5-15 h. Specifically, the sintering temperature is 600-900°C, and the sintering time is 8-12 h. The sintering temperature and time can control the diffusion rate and diffusion time of the Mn element and the Fe element, so as to achieve the gradient change of the Mn element and the Fe element content.

[0061] The application also provides a lithium ion battery, which comprises a positive electrode and a negative electrode, and the material of the positive electrode is the composite material described in the above scheme.

[0062] The application also provides an electric device, which comprises the lithium ion battery described in the above scheme.

[0063] In order to further understand the application, the gradient distribution composite material, the preparation method thereof and the application thereof provided by the application are described in detail below in combination with examples, and the protection scope of the application is not limited by the following examples.

[0064] Example 1

[0065] Step 1: Lithium nitrate, iron nitrate, manganese carbonate, phosphoric acid and glucose were mixed in pure water in a molar ratio of Li:Fe:Mn:P:C = 1:0.3:0.7:1:0.6 to prepare a 10 mol / L suspension; the above mixed solution was heated to 500°C to cause self-propagating combustion reaction, and the product was broken by air flow, and a lithium manganese iron phosphate precursor I with an average particle size D50 less than 1 μm was obtained after 2 h; 2-

[0066] Step 2: Lithium carbonate, iron phosphate and dopamine were mixed in pure water in a molar ratio of Li:Fe:dopamine = 1:1:0.05, and were dissociated and homogenized to obtain a low-concentration slurry C, the solid content of the slurry C being 40%; the slurry C was added to the mixed solution B at a rate of 0.1 L / min to initiate polymerization of dopamine by ammonium persulfate in the mixed solution B and coat the lithium iron phosphate precursor, and due to the change in dopamine concentration, the thickness of dopamine coated on the surface of the precursor changes, and a slurry D coated with different contents of dopamine is obtained; the slurry D is dried in an oven at 100 degrees to obtain a composite positive electrode material precursor II with a lithium manganese iron phosphate precursor in the center, a lithium iron phosphate precursor on the outer layer, and a polydopamine coating thickness decreasing from the center to the outer layer.

[0067] Step 3: The precursor II obtained in step 2 was sintered at 600°C for 10 h in high-purity argon, and the double-gradient composite positive electrode material A was obtained after crushing.

[0068] The radial distribution ratio of Mn element, Fe element and C element of the double-gradient composite positive electrode material A was detected, and the results are shown in Figure 3 As can be seen from the table, the content of Mn element and C element gradually decreases from the center to the outer side, and the content of Fe element gradually increases from the center to the outer side. Figure 3 Further, five positions were selected from the center to the surface of the composite positive electrode material A by cross-section SEM, and the element content was analyzed by scanning EDS, and the results are shown in Table 1.

[0069] Table 1: Molar ratio content data of Mn element, Fe element and C element from the center to the surface

[0070]

[0071] Figure 4 The particle size and specific surface area data graph of the double-gradient composite material A prepared in this embodiment is shown in Figure 4 ​It is known that the particle size of the dual-gradient composite material A in this application is large, with a specific surface area of ​​10 m². 2 / g.

[0072] Figures 5-7 This is a bar graph showing the electrochemical performance of the dual-gradient composite material A prepared in this embodiment. Figure 5 It can be seen that the capacity retention of the dual-gradient composite material prepared in this embodiment after 1000 cycles is higher than that of a typical LMFP. Figure 6 It can be seen that, compared with a typical LMFP, the dual-gradient composite material prepared in this embodiment has a lower resistance at 50% SOC-DCR. Figure 7 It can be seen that, compared with a general LMFP, the dual-gradient composite material prepared in this embodiment has a higher gram discharge capacity at a 1C rate.

[0073] The LMFP shown in the above figure is specifically the Tianjin Scoland LMFP64 product.

[0074] Example 2

[0075] Steps 1 and 2 are the same as in Example 1.

[0076] Step 3: In high-purity argon gas, the precursor II obtained in step 2 is sintered at 600℃ for 12 hours, and then crushed to obtain the dual-gradient composite cathode material B.

[0077] Example 3

[0078] Steps 1 and 2 are the same as in Example 1.

[0079] Step 3: In high-purity argon gas, the precursor II obtained in step 2 is sintered at 600℃ for 8 hours, and then crushed to obtain the dual-gradient composite cathode material C.

[0080] Example 4

[0081] Slurry C was added to mixed solution B at a rate of 0.05 mol / min to reduce the gradient change rate of the dopamine coating layer. Other steps were the same as in Example 1 to obtain the dual-gradient composite cathode material D.

[0082] Example 5

[0083] Slurry C was added to mixed solution B at a rate of 0.2 mol / min to increase the gradient change rate of the dopamine coating layer. Other steps were the same as in Example 1 to obtain the dual-gradient composite cathode material E.

[0084] Example 6

[0085] Step 1: Lithium carbonate, ferric nitrate, manganese nitrate, ammonium dihydrogen phosphate, and citric acid were mixed in pure water at a molar ratio of Li:Fe:Mn:P:C = 1:0.3:0.7:1:0.6 to prepare a 10 mol / L suspension. The mixture was heated to 500°C to induce a self-propagating combustion reaction. The product was then crushed using an airflow to obtain lithium manganese iron phosphate precursor I with an average particle size D50 of less than 1 μm. Precursor I, acrylate monomer, and azobisisobutyronitrile (AlBN) were mixed in pure water at a molar ratio of Li:acrylate monomer:AlBN = 1:0.3:0.1 to obtain a 1 mol / L high-concentration mixed solution B.

[0086] Step 2: Lithium hydroxide, iron acetate, phosphoric acid, and acrylate monomers are mixed in pure water at a molar ratio of Li:Fe:P:acrylate monomers = 1:1:1:0.05, and then dissociated and homogenized to obtain a low-concentration slurry C with a solid content of 40%. Slurry C is added to mixed solution B at a rate of 0.05 mol / min, causing the azobisisobutyronitrile in mixed solution B to initiate the polymerization of acrylate monomers and coat them onto the lithium iron phosphate precursor, resulting in slurry D. Slurry D is dried in an oven at 100 degrees Celsius to obtain a composite cathode material precursor II with a lithium manganese iron phosphate precursor at the center, an outer layer of lithium iron phosphate precursor, and a polyacrylate coating thickness that decreases from the center to the outer layer.

[0087] Step 3 is the same as in Example 1, to obtain the dual-gradient composite cathode material F.

[0088] Example 7

[0089] The polymer monomer in Example 6 was replaced with aniline, and the same steps were performed as in Example 6 to obtain the dual-gradient composite cathode material G.

[0090] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0091] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A composite material with a gradient distribution as shown in formula (I), LiMn x Feb 1-x PO4C y (I); in, 0 < x ≤ 1, 0.1 < y < 0.2; In the composite material, a carbon layer is coated with LiMn. x Fe 1-x PO4 surface; And along the direction from the center to the outer surface of the composite material, the LiMn x Fe 1-x The content of Mn in PO4 shows a decreasing trend, while the content of Fe shows an increasing trend. In the direction from the center to the outer surface of the composite material, the content of C element shows a decreasing trend.

2. The composite material according to claim 1, characterized in that, The content of the Mn element decreases at a rate of v1, 0.01 mol% / nm < v1 < 0.10 mol% / nm; the content of the Fe element increases at a rate of v2, 0.01 mol% / nm < v2 < 0.10 mol% / nm; the content of the C element decreases at a rate of v3, 0.01 mol% / nm < v3 < 0.10 mol% / nm.

3. The composite material according to claim 1, characterized in that, The content of the Mn element decreases at a rate of v1, 0.01 mol% / nm < v1 < 0.03 mol% / nm; the content of the Fe element increases at a rate of v2, 0.01 mol% / nm < v2 < 0.03 mol% / nm; the content of the C element decreases at a rate of v3, 0.01 mol% / nm < v3 < 0.03 mol% / nm.

4. The composite material according to claim 1, characterized in that, The D50 of the composite material is 1.1 μm to 1.5 μm, and D10 is 0.3 to 0.8 μm.

5. The composite material according to claim 1, characterized in that, The specific surface area of ​​the composite material is 10~15m². 2 / g, the powder resistivity of the composite material is 0~100Ω·cm.

6. A method for preparing the composite material with a gradient distribution according to claim 1, comprising the following steps: A) Mix a lithium source, a manganese source, an iron source, a phosphorus source, a reducing agent and a solvent to obtain a mixed solution A; Heat the mixed solution A and carry out a combustion reaction, and crush the obtained combustion reaction product to obtain a first precursor; Mix the first precursor, a carbon source and an initiator to obtain a mixed solution B; B) Mix a lithium source, an iron source, a phosphorus source, a carbon source and a solvent, and then carry out dissociation and homogenization to obtain a slurry C; C) Add the slurry C to the mixed solution B, react to obtain a slurry D, and dry the slurry D to obtain a composite material precursor; D) Sinter the composite material precursor to obtain a composite material; The content of iron ions in the mixed solution B is lower than the content of iron ions in the slurry C; The concentration of the carbon source in the mixed solution B is higher than the concentration of the carbon source in the slurry C.

7. The preparation method according to claim 6, characterized in that, In step A), the lithium source is selected from one or two of lithium carbonate and lithium hydroxide; the manganese source is selected from one or two of manganese nitrate and manganese carbonate; the iron source is selected from one or two of ferric nitrate and ferrous nitrate; the phosphorus source is selected from one or more of phosphoric acid, metaphosphoric acid, pyrophosphoric acid, ammonium dihydrogen phosphate, diamine hydrogen phosphate, and phosphorus oxides; the carbon source is selected from one or more of ethylene oxide, ethylene glycol, acrylate, dopamine, and aniline; the reducing agent is selected from one or more of urea, citric acid, and glucose; and the initiator is selected from one or more of ammonium persulfate, azobisisobutyronitrile, cumene hydroperoxide, and benzoyl peroxide. The solvent is selected from one or more of water, tetrahydrofuran, acetone, ethanol, methanol, benzene, toluene, and xylene; in step B), the lithium source is selected from one or two of lithium carbonate and lithium hydroxide, the iron source is selected from one or more of ferric phosphate, ferrous oxalate, ferrous acetate, ferric oxide, and ferric hydroxide, the phosphorus source is selected from one or more of phosphoric acid, metaphosphoric acid, pyrophosphate, ammonium dihydrogen phosphate, diamine hydrogen phosphate, and phosphorus oxide, the carbon source is selected from one or more of ethylene oxide, ethylene glycol, acrylate, dopamine, and aniline, and the solvent is selected from one or more of water, tetrahydrofuran, acetone, ethanol, methanol, benzene, toluene, and xylene.

8. The preparation method according to claim 6, characterized in that, The rate at which slurry C is added to the mixed solution B is 0.02~0.5 mol / min; the solid content of slurry C is 10~60 wt%, and the average particle size is 5~200 nm; the drying temperature is 100~500℃, and the time is 2~6 h; the sintering temperature is 500~1000℃, and the time is 5~15 h.

9. A lithium-ion battery, comprising a positive electrode and a negative electrode, characterized in that, The positive electrode material is the composite material according to any one of claims 1 to 5 or the composite material prepared by the preparation method according to any one of claims 6 to 8.

10. An electrical device comprising the lithium-ion battery as claimed in claim 9.

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