A co-doped lithium iron phosphate material, a preparation method and application thereof

Abstract

The application provides a co-doped lithium iron phosphate material and a preparation method and application thereof. The co-doped lithium iron phosphate material comprises iron site doping elements and lithium site doping elements. The content of the iron site doping elements in the co-doped lithium iron phosphate material is I F , the content of the lithium site doping elements in the co-doped lithium iron phosphate material is I L , I F and I L satisfy the following relationship: I = 4 x (I F 2 / I L ) / 9(I F +I L ), wherein 0 < I ≤ 1. The co-doped lithium iron phosphate material is co-doped at the lithium site and the iron site, and the relationship between the doping contents is reasonably controlled, so that the ion diffusion rate and the conductivity of the material are improved, and meanwhile, the capacity of the lithium iron phosphate material is normally exerted, and the cycle service life is not affected.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a co-doped lithium iron phosphate material, its preparation method and application. Background Technology

[0002] Olivine-type LiFePO4 cathode materials have attracted widespread attention and application due to their advantages such as high specific energy, high operating voltage, stable cycle performance, no memory effect, and no environmental pollution. However, LiFePO4 has low electronic conductivity (<10). - 9 S·cm -1 ) and low ion diffusion coefficient (10 -16 ~10 -14 cm 2 ·S -1 This has hindered its widespread application. Since the development of LiFePO4... 4 Incorporating a small amount of metal ions into the structure enhances the LiFePO4 structure. 4 With conductivity starting at around 8 orders of magnitude, existing technologies have focused on doping modifications to improve or enhance the electrochemical performance of this material.

[0003] Doping modification of LiFePO4 refers to the chemical process of introducing elements into the structure of LiFePO4 to replace one or more elements, thereby improving the electrochemical performance of LiFePO4. For example, CN 116053467A discloses a doped lithium iron phosphate material and its preparation method, as well as a lithium-ion battery. The doped lithium iron phosphate material includes a doped lithium iron phosphate core and a carbon coating layer covering the surface of the doped lithium iron phosphate core. The doped lithium iron phosphate core is a B and M co-doped lithium iron phosphate, where M represents a doping metal element selected from at least one of Ti, Nb, and Al, and B represents boron. By co-doping B with other elements (at least one of Ti, Nb, and Al) into lithium iron phosphate, the rate performance of the carbon-coated lithium iron phosphate material is improved, solving the problem of low electronic and ionic conductivity of lithium iron phosphate. However, in existing technologies, after modifying lithium iron phosphate with dopants, the capacity of the lithium iron phosphate material often fails to be fully utilized, and the cycle life is affected.

[0004] Based on the above research, there is a need to provide a co-doped lithium iron phosphate material that can improve the ion diffusion rate and conductivity of the material, while ensuring the normal performance of the lithium iron phosphate material's capacity and not affecting its cycle life. Summary of the Invention

[0005] The purpose of this invention is to provide a co-doped lithium iron phosphate material, its preparation method, and its application. The co-doped lithium iron phosphate material improves the ion diffusion rate and conductivity of the material by co-doping lithium sites and iron sites, and by reasonably controlling the relationship between the doping amounts, while ensuring that the capacity of the lithium iron phosphate material is fully utilized and its cycle life is not affected.

[0006] To achieve this objective, the present invention employs the following technical solution:

[0007] In a first aspect, the present invention provides a co-doped lithium iron phosphate material, the co-doped lithium iron phosphate material comprising an iron-site doping element and a lithium-site doping element, wherein the content of the iron-site doping element in the co-doped lithium iron phosphate material is I. F The content of lithium doping elements in co-doped lithium iron phosphate materials is I. L I F and I L The following relationship must be satisfied:

[0008] I = 4 × (I F 2 / I L ) / 9(I F +I L ), where 0 < I ≤ 1.

[0009] This invention utilizes iron site element doping amount I F and the amount of lithium doping element I L The relationship between the two is defined by a specific formula, which allows the resulting lithium iron phosphate material to possess both high ion diffusion rate and conductivity, while maintaining normal capacity and unaffected cycle performance. This is because the iron-doped elements weaken the Li-O bond interaction, increasing lithium-ion mobility and diffusion coefficient. Furthermore, the incorporation of iron-doped elements facilitates smaller particles and a larger specific surface area, thus gradually enhancing capacity resistance to degradation. Simultaneously, the lithium-doped elements replace lithium-ion sites to form a solid solution. Under the premise of solid solution formation, doping reduces the cell volume and results in smaller Li-ion density. + The insertion and desorption impedance exhibits low polarization and strong conductivity, which can improve the cycling stability of the material and avoid the problems that cause the cycle retention rate of lithium iron phosphate materials to decrease due to unreasonable iron doping amount, and unreasonable lithium doping amount will affect the capacity performance.

[0010] The value 0 < I ≤ 1 can be, for example, 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, with 0.5 ≤ I ≤ 1 being the preferred value.

[0011] Preferably, 4000ppm≤I F ≤6000ppm, for example, it can be 4000ppm, 4500ppm, 5000ppm, 5500ppm or 6000ppm, but is not limited to the listed values. Other unlisted values ​​within the range also apply.

[0012] When the doping amount of the iron site doping element described in this invention is too high, it will lead to a decrease in the cycle retention rate of lithium iron phosphate material; when the doping amount is too low, the doping effect cannot be exerted.

[0013] Preferably, 2000ppm≤I L ≤4000ppm, for example, it can be 2000ppm, 2500ppm, 3000ppm, 3500ppm or 4000ppm, but is not limited to the listed values. Other unlisted values ​​within the range also apply.

[0014] The I described in this invention F and I L The mass of co-doped lithium iron phosphate material is used as the benchmark.

[0015] When the doping amount of the lithium-doped element described in this invention is too high, it will lead to a reduction in lithium ions and affect the capacity performance; when the doping amount is too low, it will not be able to play an effective role.

[0016] Preferably, the iron-doped element includes Sn and / or Ti, with Sn being the most preferred.

[0017] The preferred iron-doping element in this invention is Sn. Since Sn occupies the iron sites, it weakens the interaction of Li-O bonds, thereby increasing the mobility and diffusion coefficient of lithium ions. At the same time, the incorporation of Sn is beneficial to obtaining smaller particles and a larger specific surface area, thus gradually revealing the capacity resistance to decay.

[0018] Preferably, the lithium-site doping element includes elements with an ionic radius smaller than that of Li. + The preferred metallic element is Mg.

[0019] This invention uses elements with a smaller radius than the lithium ion as lithium-site doping elements, such as Mg. 2+ (0.072nm) than Li + (0.076nm) and Fe 2+ The ionic radii (0.078 nm) are all small, causing Mg to... 2+ It preferentially replaces lithium ion sites with similar radii to form a solid solution.

[0020] The lithium doping element in this invention is preferably Mg. Since Mg preferentially replaces lithium ions with similar radii, under the premise of forming a solid solution, the cell volume is reduced, the lithium ion insertion and desorption resistance is reduced, and it exhibits smaller polarization and stronger conductivity, thereby improving the cycle stability of the material.

[0021] In a second aspect, the present invention provides a method for preparing co-doped lithium iron phosphate material as described in the first aspect, the method comprising the following steps:

[0022] The co-doped lithium iron phosphate material is obtained by mixing and calcining lithium source, iron source, phosphorus source and doping element source;

[0023] The doping element sources include iron-site doping element sources and lithium-site doping element sources.

[0024] The co-doped lithium iron phosphate material of the present invention can be obtained simply by mixing and calcining the lithium source, iron source, phosphorus source and dopant element source. The preparation process is simple, short, and easy to synthesize, without involving complex preparation processes.

[0025] Preferably, the mixing process includes first mixing a lithium source, an iron source, a phosphorus source, and a lithium site doping element source, then drying and pulverizing the mixture, and then mixing the pulverized material with the iron site doping element source.

[0026] In the doping process of this invention, lithium-site doping elements are doped first, followed by drying and pulverization, and then iron-site doping elements are doped. Compared with the method of simultaneous co-doping, this can promote the doping of elements at different sites. Since magnesium compounds have large particles, they need to be ground into fine particles by sand milling, so that they can be mixed with the material more evenly. Sn compounds are nanomaterials with relatively small particles. That is, the particle size of the iron-site doping element source is smaller than that of the lithium-site doping element source. During wet sand milling, they are prone to agglomeration, resulting in uneven doping. However, the material can be evenly mixed by ultracentrifugal dry mixing.

[0027] Preferably, the amount of lithium source and iron source added satisfies the molar ratio of Li to Fe as (0.99-1.01):1, for example, it can be 0.99:1, 1:1 or 1.01:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the amount of iron source and phosphorus source added satisfies the molar ratio of Fe to P as (0.999-1.001):1, for example, it can be 0.999:1, 1.000:1 or 1.001:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the lithium source, iron source, phosphorus source and lithium dopant element source are mixed by wet grinding.

[0030] Preferably, a carbon source is also added when the lithium source, iron source, phosphorus source and lithium-doped element source are mixed.

[0031] Preferably, the carbon source includes carbon nanotubes.

[0032] Preferably, the drying method includes spray drying.

[0033] Preferably, the spray drying pressure is 0.2-0.3 MPa, for example, 0.2 MPa, 0.25 MPa or 0.3 MPa, and the temperature is 150-250℃, for example, 150℃, 200℃ or 250℃, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the pulverization method includes air jet milling.

[0035] Preferably, the method of mixing the pulverized material with the iron site doping element source includes centrifugal mixing.

[0036] Preferably, the centrifugal mixing speed is 9000-11000 rpm / min, for example, it can be 9000 rpm / min, 10000 rpm / min or 11000 rpm / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the calcination temperature is 650-750℃, for example, 650℃, 700℃ or 750℃, and the time is 6-8h, for example, 6h, 7h or 8h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the heating rate of the calcination is 1-3℃ / min, for example, it can be 1℃ / min, 2℃ / min or 3℃ / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the calcination is carried out in nitrogen and / or an inert gas.

[0040] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0041] (1) The lithium source, iron source, phosphorus source, carbon source and lithium site doping element source are wet-milled, then spray-dried at a temperature of 150-250℃ and a pressure of 0.2-0.3MPa, and then pulverized by air jet milling to obtain pulverized material. The pulverized material is centrifuged and mixed with the iron site doping element source at a speed of 9000-11000rpm / min to obtain a mixture.

[0042] The amount of lithium source and iron source added satisfies the molar ratio of Li to Fe as (0.99-1.01):1, and the amount of iron source and phosphorus source added satisfies the molar ratio of Fe to P as (0.999-1.001):1.

[0043] (2) The mixture described in step (1) is calcined in nitrogen and / or inert gas at a temperature of 650-750°C for 6-8 hours at a heating rate of 1-3°C / min to obtain the co-doped lithium iron phosphate material.

[0044] Thirdly, the present invention provides a lithium-ion battery comprising the co-doped lithium iron phosphate material as described in the first aspect.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] This invention improves the ion diffusion rate and conductivity of the material by controlling the relationship between the doping amounts of the doping element and the iron-site doping element, while ensuring that the capacity of the lithium iron phosphate material is maintained and its cycle life is unaffected. The iron-site doping element weakens the Li-O bond interaction, increases the mobility and diffusion coefficient of lithium ions, resulting in smaller particles and a larger specific surface area, thus gradually revealing the capacity resistance to degradation. The lithium-site doping element can replace lithium ion sites to form a solid solution, reducing the size of the unit cell and the Li-site doping coefficient. + Impedance during insertion and extraction improves the cyclic stability of the material. Attached Figure Description

[0047] Figure 1 This is a charge-discharge curve of the battery prepared by the co-doped lithium iron phosphate material described in Example 1 of the present invention. Detailed Implementation

[0048] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0049] Example 1

[0050] This embodiment provides a co-doped lithium iron phosphate material, wherein the content of the iron-site doping element in the co-doped lithium iron phosphate material is I.F The content of lithium doping elements in co-doped lithium iron phosphate materials is I. L I F and I L The following relationship must be satisfied: I = 4 × (I F 2 / I L ) / 9(I F +I L ), where, I=1, I F =6000ppm, I L =2000ppm;

[0051] The iron-doping element is Sn, and the lithium-doping element is Mg;

[0052] The preparation method of the co-doped lithium iron phosphate material includes the following steps:

[0053] (1) Lithium hydroxide, iron phosphate, carbon nanotubes and magnesium oxide are wet-milled, wherein carbon nanotubes, magnesium oxide and iron phosphate are added in a mass ratio of 5%:0.2%:1, and then spray-dried at a temperature of 200°C and a pressure of 0.4MPa, and then pulverized by air jet milling to obtain pulverized material. The pulverized material is mixed with an iron site doping element source by ultra-high speed centrifugation at a speed of 10000rpm / min to obtain a mixture, wherein tin oxide is added in a mass ratio of 0.6%:1 to iron phosphate.

[0054] The amount of lithium hydroxide and iron phosphate added satisfies that the molar ratio of Li to Fe is 1:1, and the molar ratio of Fe to P is 1:1.

[0055] (2) The mixture described in step (1) is calcined in nitrogen at a temperature of 700°C for 7 hours at a heating rate of 2°C / min to obtain the co-doped lithium iron phosphate material.

[0056] The charge-discharge curves of the batteries prepared from the co-doped lithium iron phosphate material are shown in the figure below. Figure 1 As shown.

[0057] Example 2

[0058] This embodiment provides a co-doped lithium iron phosphate material, wherein the content of the iron-site doping element in the co-doped lithium iron phosphate material is I. F The content of lithium doping elements in co-doped lithium iron phosphate materials is I. L I F and I L The following relationship must be satisfied: I = 4 × (I F 2 / I L ) / 9(IF +I L ), where, I=1, I F =6000ppm, I L =2000ppm;

[0059] The iron-doping element is Sn, and the lithium-doping element is Mg;

[0060] The preparation method of the co-doped lithium iron phosphate material includes the following steps:

[0061] (1) Lithium hydroxide, iron phosphate, carbon nanotubes and magnesium oxide are wet-milled, wherein the carbon nanotubes are added to magnesium oxide and iron phosphate at a mass ratio of 5%:0.2%:1, and then spray-dried at a temperature of 150°C and a pressure of 0.2MPa, and then pulverized by air jet milling to obtain pulverized material. The pulverized material is mixed with an iron site doping element source by ultra-high speed centrifugation at a speed of 11000rpm / min to obtain a mixture, wherein tin oxide is added at a mass ratio of 0.6%:1 to iron phosphate.

[0062] The amount of lithium hydroxide and iron phosphate added satisfies the requirement that the molar ratio of Li to Fe is 1.01:1, and the molar ratio of Fe to P is 0.999:1.

[0063] (2) The mixture described in step (1) is calcined in nitrogen at a temperature of 750°C for 6 hours at a heating rate of 1°C / min to obtain the co-doped lithium iron phosphate material.

[0064] Example 3

[0065] This embodiment provides a co-doped lithium iron phosphate material, wherein the content of the iron-site doping element in the co-doped lithium iron phosphate material is I. F The content of lithium doping elements in co-doped lithium iron phosphate materials is I. L I F and I L The following relationship must be satisfied: I = 4 × (I F 2 / I L ) / 9(I F +I L ), where, I=1, I F =6000ppm, I L =2000ppm;

[0066] The iron-doping element is Sn, and the lithium-doping element is Mg;

[0067] The preparation method of the co-doped lithium iron phosphate material includes the following steps:

[0068] (1) Lithium hydroxide, iron phosphate, carbon nanotubes and magnesium oxide are wet-milled, wherein the carbon nanotubes are added to magnesium oxide and iron phosphate at a mass ratio of 5%:0.2%:1, and then spray-dried at a temperature of 250°C and a pressure of 0.3MPa, and then pulverized by air jet milling to obtain pulverized material. The pulverized material is mixed with an iron site doping element source by ultra-high speed centrifugation at a speed of 9000rpm / min to obtain a mixture, wherein tin oxide is added at a mass ratio of 0.6%:1 to iron phosphate.

[0069] The amount of lithium hydroxide and iron phosphate added satisfies that the molar ratio of Li to Fe is 1:1, and the molar ratio of Fe to P is 1:1.

[0070] (2) The mixture described in step (1) is calcined in nitrogen at a temperature of 650°C for 8 hours at a heating rate of 3°C / min to obtain the co-doped lithium iron phosphate material.

[0071] Example 4

[0072] This embodiment provides a co-doped lithium iron phosphate material, wherein the co-doped lithium iron phosphate material has I = 0.5, I F =4000ppm, I L Except for 2268.75 ppm, everything else is the same as in Example 1.

[0073] Example 5

[0074] This embodiment provides a co-doped lithium iron phosphate material, wherein the co-doped lithium iron phosphate material has I = 0.2, I F =4000ppm, I L Except for 4289.32 ppm, everything else is the same as in Example 1.

[0075] Example 6

[0076] This embodiment provides a co-doped lithium iron phosphate material, wherein the co-doped lithium iron phosphate material, except for I... F =5000ppm, I L Except for 1666.67 ppm, everything else is the same as in Example 1.

[0077] Example 7

[0078] This embodiment provides a co-doped lithium iron phosphate material, wherein the co-doped lithium iron phosphate material, except for I... F =3750ppm, I L Except for 5000ppm, everything else is the same as in Example 1.

[0079] Example 8

[0080] This embodiment provides a co-doped lithium iron phosphate material, wherein the co-doped lithium iron phosphate material, except for I... F =3000ppm, I L Except for 1000ppm, everything else is the same as in Example 1.

[0081] Example 9

[0082] This embodiment provides a co-doped lithium iron phosphate material, wherein the co-doped lithium iron phosphate material, except for I... F =7000ppm, I L Except for 2333.33 ppm, everything else is the same as in Example 1.

[0083] Example 10

[0084] This embodiment provides a co-doped lithium iron phosphate material. Except for the fact that tin oxide and magnesium oxide are added together in step (1) of the preparation method to change the obtained co-doped lithium iron phosphate material, the rest is the same as in Example 1.

[0085] Example 11

[0086] This embodiment provides a co-doped lithium iron phosphate material. Except for the fact that the order of adding tin oxide and magnesium oxide in step (1) is interchanged in the preparation method, so that the co-doped lithium iron phosphate material is changed accordingly, the rest is the same as in Example 1.

[0087] Example 12

[0088] This embodiment provides a co-doped lithium iron phosphate material, which is the same as that in Embodiment 1 except that the iron site doping element is Ti.

[0089] Example 13

[0090] This embodiment provides a co-doped lithium iron phosphate material, which is the same as that in Embodiment 1 except that the lithium site doping element is Al.

[0091] Comparative Example 1

[0092] This comparative example provides a lithium iron phosphate material, which is the same as that in Example 1 except that it does not include lithium site doping elements and iron site doping elements.

[0093] The preparation method of the lithium iron phosphate material is the same as that in Example 1, except that magnesium oxide and tin oxide are not added.

[0094] Comparative Example 2

[0095] This comparative example provides a co-doped lithium iron phosphate material, wherein, except for I = 1.2, I... F =6000ppm, I L Except for 1725.81 ppm, all other values ​​are the same as in Example 1.

[0096] The lithium iron phosphate material, carbon black conductive agent, PVDF binder, and NMP described in the above embodiments and comparative examples were mixed uniformly in a mass ratio of 95:2.5:2.5:5 to prepare a battery positive electrode slurry. This slurry was coated onto a 30 μm thick aluminum foil, vacuum dried, and rolled to form a positive electrode sheet. Then, using a lithium metal sheet as the negative electrode and a 1.15 M LiPF6 EC:DMC (1:1 vol%) electrolyte, coin cells were assembled. Electrochemical performance was tested at 25°C using a Blue Battery testing system, with a test voltage range of 2.0V-3.75V. The obtained capacity and 50-week capacity retention are shown in Table 1.

[0097] Table 1

[0098]

[0099]

[0100] From Table 1, we can see that:

[0101] This invention achieves its goal by increasing the content of doping elements by I F and I L Satisfying specific relationships ensures the full utilization of the capacity and cycle performance of lithium iron phosphate materials, while simultaneously improving the lithium-ion transport rate. As shown in Example 1 and Comparative Examples 1-2, without doping elements or when the relationship between doping element content is not within the range defined in this application, the battery performance is lower than that of Example 1. As shown in Example 1 and Examples 4-5, the I value of this invention is in the range of 0 to 1 (excluding 0). With the increase of the I value, the capacity and cycle performance of the material are significantly improved, and I is preferably in the range of 0.5-1. As shown in Example 1 and Examples 6-9, this invention, while ensuring the magnitude of the I value, also... F and I L The value of the dopant is within a reasonable range, which can further improve the overall performance of the material. As can be seen from Examples 1 and 10-11, the feeding sequence of the dopant source of the present invention can further promote the role of the dopant. As can be seen from Examples 1 and 12-13, the iron site dopant of the present invention is preferably Sn, and the lithium site dopant is preferably Mg. Specific dopant elements can further improve the overall performance of the material.

[0102] In summary, this invention provides a co-doped lithium iron phosphate material, its preparation method, and its application. By co-doping lithium iron phosphate materials with lithium and iron sites and by rationally controlling the relationship between the doping amounts, the ion diffusion rate and conductivity of the material are improved, while ensuring that the capacity of the lithium iron phosphate material is fully utilized and its cycle life is not affected.

[0103] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A co-doped lithium iron phosphate material, characterized in that, The co-doped lithium iron phosphate material includes an iron-site doping element and a lithium-site doping element, wherein the content of the iron-site doping element in the co-doped lithium iron phosphate material is I. F The content of lithium doping elements in co-doped lithium iron phosphate materials is I. L I F and I L The following relationship must be satisfied: I = 4×(I F 2 / I L ) / 9(I F +I L ), where 0.5 ≤ I ≤ 1; 4000ppm≤I F ≤6000ppm; 2000ppm≤I L ≤4000ppm; The iron-doping element is Sn; The lithium-doping element is Mg.

2. A method for preparing the co-doped lithium iron phosphate material as described in claim 1, characterized in that, The preparation method includes the following steps: The co-doped lithium iron phosphate material is obtained by mixing and calcining lithium source, iron source, phosphorus source and doping element source; The doping element source includes an iron site doping element source and a lithium site doping element source; The mixing process involves first mixing a lithium source, an iron source, a phosphorus source, and a lithium site doping element source, then drying and pulverizing the mixture, and finally mixing the pulverized material with the iron site doping element source.

3. The preparation method according to claim 2, characterized in that, The amount of lithium source and iron source added satisfies the molar ratio of Li to Fe as (0.99-1.01):

1.

4. The preparation method according to claim 2, characterized in that, The amount of iron source and phosphorus source added satisfies the molar ratio of Fe to P as (0.999-1.001):

1.

5. The preparation method according to claim 2, characterized in that, The method for mixing the lithium source, iron source, phosphorus source and lithium doping element source includes wet grinding.

6. The preparation method according to claim 5, characterized in that, A carbon source was also added when the lithium source, iron source, phosphorus source and lithium doping element source were mixed.

7. The preparation method according to claim 6, characterized in that, The carbon source includes carbon nanotubes.

8. The preparation method according to claim 2, characterized in that, The drying method includes spray drying.

9. The preparation method according to claim 8, characterized in that, The spray drying pressure is 0.2-0.3 MPa, and the temperature is 150-250℃.

10. The preparation method according to claim 2, characterized in that, The pulverization method includes air jet milling.

11. The preparation method according to claim 2, characterized in that, The method of mixing the pulverized material with the iron site doping element source includes centrifugal mixing.

12. The preparation method according to claim 11, characterized in that, The centrifugal mixing speed is 9000-11000 rpm / min.

13. The preparation method according to claim 2, characterized in that, The calcination temperature is 650-750℃, and the time is 6-8 hours.

14. The preparation method according to claim 13, characterized in that, The heating rate for calcination is 1-3℃ / min.

15. The preparation method according to claim 13, characterized in that, The calcination is carried out in nitrogen and / or an inert gas.

16. The preparation method according to any one of claims 3-15, characterized in that, The preparation method includes the following steps: (1) The lithium source, iron source, phosphorus source, carbon source and lithium site doping element source are wet-milled, then spray-dried at a temperature of 150-250℃ and a pressure of 0.2-0.3MPa, and then pulverized by air jet milling to obtain pulverized material. The pulverized material is centrifuged and mixed with the iron site doping element source at a speed of 9000-11000rpm / min to obtain a mixture. The amount of lithium source and iron source added satisfies the molar ratio of Li to Fe as (0.99-1.01):1, and the amount of iron source and phosphorus source added satisfies the molar ratio of Fe to P as (0.999-1.001):

1. (2) The mixture described in step (1) is calcined in nitrogen and / or inert gas at a temperature of 650-750°C for 6-8 hours at a heating rate of 1-3°C / min to obtain the co-doped lithium iron phosphate material.

17. A lithium-ion battery, characterized in that, The lithium-ion battery includes the co-doped lithium iron phosphate material as described in claim 1.

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