Lithium iron phosphate material, preparation method therefor and use thereof

Abstract

The present application discloses a lithium iron phosphate material, a preparation method therefor and a use thereof. The preparation method comprises: mixing a first carbon source, a second carbon source, a lithium source, iron phosphate, and doping agents, and sintering the mixture to obtain the lithium iron phosphate material, wherein the molar ratio of lithium in the lithium source to the iron phosphate is A, the mass ratio of the first carbon source to the iron phosphate is B, the mass ratio of the second carbon source to the iron phosphate is C, the molar ratio of iron to phosphorus in the iron phosphate is D, the doping amount of a first doping agent is E1, the doping amount of a second doping agent is E2, and the doping amount of a third doping agent is E3; E1, E2, and E3 satisfy that J=6×E1 / (5×E2+5×E3); and A, B, C, D, and J satisfy that 0.040≤A2×D2×(B+C)×J≤0.058. According to the preparation method of the present application, a lithium iron phosphate material having excellent performance is obtained by controlling a plurality of factors to satisfy specific relational expressions and exerting a synergistic effect of the factors.

Description

A lithium iron phosphate material and its preparation method and application

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 25, 2023, with application number 202311795813.X. The entire contents of this application are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the technical field of battery materials and relates to a lithium iron phosphate material and a preparation method and application thereof. Background Art

[0003] Lithium iron phosphate has the advantages of long life, good safety, fast charging, low cost, high temperature resistance, large capacity and environmental protection, and is widely used in energy storage batteries. However, its low electronic conductivity (10 -9 S / cm) and ionic conductivity (10 -13 -10 -16 S / cm) results in a low discharge specific capacity. To solve this problem, existing technologies use modification methods such as carbon coating, nano-sizing and doping to improve the discharge specific capacity and cycle performance of lithium iron phosphate materials.

[0004] Among them, carbon coating can improve the conductivity of lithium iron phosphate, thereby improving the discharge specific capacity of lithium iron phosphate. For example, CN117088348A discloses a method for carbon-coated modified lithium iron phosphate positive electrode, wherein iron salt, lithium salt and reducing agent are subjected to liquid-phase lithiation to obtain a precursor mixture A; the precursor mixture A is placed in argon or nitrogen and sintered at high temperature to obtain LiFePO4 positive electrode material; the carbon source is dispersed in an ethanol-water mixed solution and ultrasonically dispersed to obtain a carbon source suspension, the LiFePO4 positive electrode material is added to the carbon source suspension and ultrasonically dispersed to obtain a suspension, and the suspension is dried to obtain a precursor; after grinding the precursor, it is placed in an argon or nitrogen atmosphere and sintered at high temperature to obtain a carbon-coated modified lithium iron phosphate active component; using aluminum foil as a substrate, the carbon-coated modified lithium iron phosphate active component is coated on the substrate to obtain a carbon-coated modified lithium iron phosphate positive electrode.

[0005] In addition, nano-sizing is also a very effective method. By preparing nano-LFP particles, the distance of ion diffusion can be effectively shortened, thereby achieving the purpose of improving the LFP discharge specific capacity. For example, CN116014138A discloses a nano-lithium iron phosphate and its preparation method and application. First, ammonium dihydrogen phosphate, ferrous sulfate, and aniline are used to prepare polyaniline-modified iron phosphate. Then, the modified iron phosphate is used as a precursor and polyvinyl pyrrolidone, lithium carbonate, and a reducing agent are used to prepare polyvinyl pyrrolidone-coated nano-lithium iron phosphate. Finally, tannic acid is used to coat the polyvinyl pyrrolidone-coated nano-lithium iron phosphate again to obtain a new type of nano-lithium iron phosphate composite material. However, nano-sizing the lithium iron phosphate will reduce the cycle performance of the positive electrode material.

[0006] Therefore, the existing technology reduces the particle size of lithium iron phosphate by crushing lithium iron phosphate particles into nanometer scale, controlling the lithium ratio, carbon coating amount, etc., but does not explore the relationship between the above factors affecting the electrochemical properties of lithium iron phosphate, and the influence of each factor on the performance is not clear.

[0007] Based on the above research, it is necessary to provide a method for preparing a lithium iron phosphate material, which can obtain a lithium iron phosphate material with excellent comprehensive performance by regulating various influencing factors so as to achieve synergistic effects between the influencing factors.

[0008] Summary of the Invention

[0009] 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.

[0010] The present application provides a lithium iron phosphate material, a preparation method and an application thereof. The preparation method controls the molar ratio of the lithium source and the iron phosphate, the mass ratio of the carbon source and the iron phosphate, the actual molar ratio of Fe and P in the iron phosphate, and the doping amount of the doping element, so that multiple factors satisfy a specific relationship, exert a synergistic effect between the factors, and obtain a lithium iron phosphate material with excellent electrochemical properties.

[0011] In a first aspect, the present application provides a method for preparing a lithium iron phosphate material, the preparation method comprising the following steps:

[0012] Mixing and sintering a first carbon source, a second carbon source, a lithium source, an iron phosphate precursor, and a dopant to obtain the lithium iron phosphate material, wherein the dopant includes a first dopant, a second dopant, and a third dopant;

[0013] The molar ratio of lithium ions in the lithium source to the iron phosphate precursor is A, the mass ratio of the first carbon source to the iron phosphate precursor is B, the mass ratio of the second carbon source to the iron phosphate precursor is C, the molar ratio of iron to phosphorus in the iron phosphate precursor is D, the doping amount of the first dopant is E1, the doping amount of the second dopant is E2, and the doping amount of the third dopant is E3;

[0014] The E1, E2 and E3 satisfy: J = 6×E1 / (5×E2+5×E3);

[0015] The A, B, C, D and J satisfy the following relationship: L = A 2 ×D 2 ×(B+C)×J, and 0.040≤L≤0.058.

[0016] The present application guides the development of lithium iron phosphate materials by controlling the various factors of the performance of lithium iron phosphate materials to satisfy specific relationships, thereby improving the electrical properties of the material by regulating the relationship between the various factors and combining the synergistic effect of metal element doping (doping can enhance the structural stability of the material, improve the electrical conductivity of the material, and high-valence metal doping can inhibit particle growth), so that the lithium iron phosphate material obtained in the present application has excellent electrochemical properties.

[0017] The 0.040≤L≤0.058 may be, for example, 0.040, 0.042, 0.044, 0.046, 0.048, 0.050, 0.050, 0.054, 0.056 or 0.058, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] Preferably, A is 1.002-1.008, for example, 1.003, 1.005, 1.007 or 1.008, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] When A, B, C, D and J described in the present application satisfy a specific relationship, the molar ratio A of lithium ions in the lithium source to the iron phosphate precursor is within a specific range, which can further improve the battery performance; specifically, an increase in the Li / FePO4 molar ratio is beneficial to the refinement of crystal particles, but an excessive lithium ratio A will increase the possibility of the formation of non-conductive impurity lithium phosphide, thereby reducing the conductivity of the material and significantly reducing the discharge specific capacity. In addition, when the lithium ratio is too large, the grains are refined, which also leads to a larger specific surface area of ​​the battery positive electrode material, and the probability of reaction with the electrolyte during the charge and discharge cycle increases, affecting the battery. Chemical properties; while the lithium ratio A decreases, the grain size of the lithium iron phosphate material increases. During the charge and discharge cycle of the material, the lithium ion migration path becomes longer, which is not conducive to the deintercalation of lithium ions between the positive and negative electrodes, thereby reducing the discharge specific capacity; and when the lithium ratio is too low, it leads to insufficient lithium, the crystallinity of the lithium iron phosphate material is poor, and the electrical properties of the material are also poor. Therefore, when the lithium ratio A is appropriate, a lithium iron phosphate material with uniform particle size distribution is obtained, the lithium is completely delithiated during the charging process, and the lithium ion migration distance during the discharge process is roughly the same, which can effectively avoid the occurrence of over-discharge, making the positive electrode material structure more stable and the cycle life longer.

[0020] Preferably, B is 0.05-0.07, for example, 0.05, 0.055, 0.06, 0.065 or 0.07, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] Preferably, C is 0.06-0.07, for example, 0.06, 0.065 or 0.07, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] The size of B and C in this application determines the amount of carbon source added. Due to the addition of the carbon source, a carbon coating layer will be formed on the surface of the lithium iron phosphate material. The carbon layer can enhance the conductivity of the material, but an excessively thick carbon layer makes the positive electrode material not densely stacked, which is not conducive to the rapid migration of lithium ions during charging and discharging, thereby reducing the electrochemical performance of the positive electrode material; and a carbon layer that is too thin cannot achieve the effect of improving the conductivity of the material.

[0023] Preferably, D is 0.975-0.985, for example, 0.978, 0.980, 0.983 or 0.985, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] When the molar ratio D of iron to phosphorus in the iron phosphate precursor described in the present application increases, the crystal particles will be refined, and the specific surface area of ​​the material will be increased. The probability of the positive electrode material reacting with the electrolyte during the charge and discharge cycle will increase, affecting the electrochemical performance; and if the Fe / P molar ratio D is too small, the crystal particles will be larger, and the lithium ion migration path will become longer during the charge and discharge cycle of the positive electrode material, which is not conducive to the lithium ion deintercalation between the positive and negative electrodes, thereby reducing the discharge specific capacity. Therefore, when the Fe / P molar ratio is appropriate, a positive electrode material with a uniform particle size distribution is obtained, the lithium is completely de-lithiated during the charging process, and the lithium ion migration distance during the discharge process is roughly the same, which can effectively avoid the occurrence of over-discharge, make the positive electrode material structure more stable, and have a longer cycle life.

[0025] Preferably, J is 0.330-0.550, for example, 0.350, 0.400, 0.450, 0.500 or 0.550, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] Preferably, the E1 is 450-500 ppm, for example, 460 ppm, 480 ppm or 500 ppm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0027] Preferably, the E2 is 700-900 ppm, for example, 750 ppm, 800 ppm, 850 ppm or 900 ppm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] Preferably, the E3 is 500-700 ppm, for example, 550 ppm, 600 ppm, 650 ppm or 700 ppm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] In this application, E1, E2 and E3 refer to the doping amounts of the doping elements respectively.

[0030] Preferably, the first dopant comprises Mo 6+ The second dopant comprises a compound containing V 5+ The third dopant comprises a compound containing Nb 5+ of compounds.

[0031] The present application adopts high-valent elements for doping, which can not only improve the structural stability and electrical conductivity of the material, but also the high-valent metal doping can inhibit the growth of particles.

[0032] Preferably, the first carbon source comprises polyethylene glycol.

[0033] Preferably, the second carbon source comprises glucose.

[0034] Preferably, the lithium source comprises lithium carbonate.

[0035] Preferably, a solvent is added during the mixing.

[0036] Preferably, the solvent is water.

[0037] Preferably, the solid content of the mixed slurry obtained by mixing is 35-45wt%, for example, it can be 38wt%, 40wt% or 45wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] Preferably, the mixing method includes sanding.

[0039] Preferably, the number of sanding turns is 12-17 turns, for example, 13 turns, 15 turns or 17 turns, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] Preferably, after the mixing and before the sintering, solid-liquid separation and drying are performed.

[0041] Preferably, the solid-liquid separation method includes filter press.

[0042] Preferably, the pressure of the filter press is 0.4-0.6 MPa, for example, 0.4 MPa, 0.5 MPa or 0.6 MPa, the time is 8-12 min, for example, 9 min, 10 min or 12 min, and the gas used includes nitrogen and / or inert gas.

[0043] Preferably, the drying temperature is 150-180°C, for example, 160°C, 170°C or 180°C, the drying time is 5-6h, for example, 5.3h, 5.7h or 6h, and the rotation speed is 6-8rpm, for example, 6rpm, 7rpm or 8rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] Preferably, the sintering temperature is 780-800°C, for example, 780°C, 790°C or 800°C, and the sintering time is 10-12h, for example, 10h, 11h or 12h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] Preferably, the sintering atmosphere includes nitrogen (nitrogen purity ≥ 99.999%) and / or inert gas.

[0046] As a preferred technical solution of the preparation method described in this application, the preparation method comprises the following steps:

[0047] The first carbon source, the second carbon source, the lithium source, the iron phosphate precursor, the dopant and the solvent are sand-milled, and then pressure-filtered at a pressure of 0.4-0.6 MPa for 8-12 minutes under nitrogen and / or inert gas, and then dried at a temperature of 150-180° C. and a rotation speed of 6-8 rpm for 5-6 hours, and finally sintered at a temperature of 780-800° C. for 10-12 hours under nitrogen and / or inert gas to obtain the lithium iron phosphate material, wherein the dopant includes a first dopant, a second dopant and a third dopant;

[0048] The molar ratio of lithium ions in the lithium source to the iron phosphate precursor is A, the mass ratio of the first carbon source to the iron phosphate precursor is B, the mass ratio of the second carbon source to the iron phosphate precursor is C, the molar ratio of iron to phosphorus in the iron phosphate precursor is D, the doping amount of the first dopant is E1, the doping amount of the second dopant is E2, and the doping amount of the third dopant is E3;

[0049] The E1, E2 and E3 satisfy: J = 6×E1 / (5×E2+5×E3), wherein E1 is 450-500 ppm, E2 is 700-900 ppm, and E3 is 500-700 ppm;

[0050] The A, B, C, D and J satisfy the following relationship: L = A 2 ×D 2 ×(B+C)×J, where L is 0.040-0.058, A is 1.002-1.008, B is 0.05-0.07, C is 0.06-0.07, D is 0.975-0.985, and J is 0.330-0.550.

[0051] In a second aspect, the present application provides a lithium iron phosphate material, which is prepared using the preparation method described in the first aspect.

[0052] In a third aspect, the present application provides a lithium-ion battery, wherein the lithium-ion battery comprises the lithium iron phosphate material as described in the second aspect.

[0053] Compared with the related art, this application has the following beneficial effects:

[0054] The present application controls the molar ratio A of lithium ions to the iron phosphate precursor in the lithium source, the mass ratio B of the first carbon source to the iron phosphate precursor, the mass ratio C of the second carbon source to the iron phosphate precursor, the molar ratio D of the iron element to the phosphorus element in the iron phosphate precursor, and J to satisfy a specific relationship, thereby guiding the development of lithium iron phosphate materials, coordinating various factors affecting the performance of lithium iron phosphate materials, improving material performance, and obtaining lithium iron phosphate materials with excellent electrochemical properties.

[0055] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] FIG1 is a SEM image of the lithium iron phosphate material obtained in Example 1 of the present application;

[0057] FIG2 is a SEM image of the lithium iron phosphate material obtained in Example 8 of the present application;

[0058] FIG3 is a SEM image of the lithium iron phosphate material obtained in Example 9 of the present application. DETAILED DESCRIPTION

[0059] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0060] Example 1

[0061] This embodiment provides a method for preparing a lithium iron phosphate material, the preparation method comprising the following steps:

[0062] (1) adding materials to a sand mill with rotating blades, adding deionized water so that the solid content is 40 wt%, and then adding polyethylene glycol, glucose, lithium carbonate, iron phosphate, molybdenum trioxide, vanadium pentoxide, and niobium pentoxide into the sand mill;

[0063] The molar ratio of lithium ions to iron phosphate in lithium carbonate is 1.005, the mass ratio B of polyethylene glycol to iron phosphate is 0.060, the mass ratio C of glucose to iron phosphate is 0.06, the actual molar ratio D of iron to phosphorus in the iron phosphate is 0.975, the doping amount E1 of molybdenum trioxide is 500 ppm, the doping amount E2 of vanadium pentoxide is 800 ppm, and the doping amount E3 of niobium pentoxide is 600 ppm, and J=6×E1 / (5×E2+5×E3)=0.429;

[0064] A, B, C, D and J satisfy: L = A 2 ×D 2 ×(B+C)×J, L is 0.049;

[0065] (2) Start sand grinding, set the number of sand grinding circles to 15 circles (between 475 and 525 nm), the sand grinding machine speed is 1000 rpm, and the sand grinding time per circle is adjusted to 8 min. After sand grinding for 15 circles, take a sample and measure the particle size using a laser particle size analyzer. The particle size is 515 nm, and the particle size is within the range;

[0066] (3) using a two-in-one filter press device for solid-liquid separation, with a filter press pressure of 0.4 MPa, a filter press time of 10 min, and nitrogen as the filter press gas, and then placing the solid in a double-cone dryer at 150° C. for vacuum drying for 5 h at a dryer speed of 8 rpm; and

[0067] (4) The material from the third step was placed in a graphite crucible and sintered in a box-type atmosphere furnace at 780°C under nitrogen (nitrogen purity ≥ 99.999%) protection, with a heating rate of 1.5°C / min and a heat preservation time of 12 h. The material was then ground at a grinding pressure of 0.4 MPa, fed at 7 Hz, and graded at 140 Hz to obtain the lithium iron phosphate material.

[0068] The SEM image of the lithium iron phosphate material obtained in this example is shown in FIG1 .

[0069] Example 2

[0070] This embodiment provides a method for preparing a lithium iron phosphate material, the preparation method comprising the following steps:

[0071] (1) adding materials to a sand mill with rotating blades, adding deionized water so that the solid content is 35 wt%, and then adding polyethylene glycol, glucose, lithium carbonate, iron phosphate, molybdenum trioxide, vanadium pentoxide, and niobium pentoxide into the sand mill;

[0072] The molar ratio of lithium ions to iron phosphate in lithium carbonate is 1.005, the mass ratio B of polyethylene glycol to iron phosphate is 0.060, the mass ratio C of glucose to iron phosphate is 0.06, the actual molar ratio D of iron to phosphorus in the iron phosphate is 0.985, the doping amount E1 of molybdenum trioxide is 500 ppm, the doping amount E2 of vanadium pentoxide is 800 ppm, and the doping amount E3 of niobium pentoxide is 600 ppm, and J=6×E1 / (5×E2+5×E3)=0.429;

[0073] A, B, C, D and J satisfy: L = A 2 ×D 2 ×(B+C)×J, L is 0.050;

[0074] (2) Start sand grinding, set the number of sand grinding circles to 12 circles (between 475 and 525 nm), the sand grinding machine speed to 1000 rpm, and the sand grinding time per circle to 8 min. After sand grinding for 15 circles, take a sample and measure the particle size using a laser particle size analyzer. The particle size is 515 nm, and the particle size is within the range;

[0075] (3) using a two-in-one filter press device for solid-liquid separation, with a filter press pressure of 0.6 MPa, a filter press time of 8 minutes, and nitrogen as the filter press gas, and then placing the solid in a double-cone dryer at 180°C for vacuum drying for 5 hours at a dryer speed of 6 rpm; and

[0076] (4) The material from the third step was placed in a graphite crucible and sintered in a box-type atmosphere furnace at 800°C under nitrogen (nitrogen purity ≥ 99.999%) protection, with a heating rate of 1.5°C / min and a heat preservation time of 10 h. The material was then ground at a grinding pressure of 0.4 MPa, fed at 7 Hz, and graded at 140 Hz to obtain the lithium iron phosphate material.

[0077] The difference between Examples 3-17 and Comparative Examples 1-2 and Example 1 is that the values ​​of A, B, C, D, J, E1, E2, E3 and L are different, and the rest are the same as Example 1, see Table 1 for details, among which the SEM image of the lithium iron phosphate material obtained in Example 8 is shown in Figure 2, and the SEM image of the lithium iron phosphate material obtained in Example 9 is shown in Figure 3.

[0078] Preparation of button batteries: The lithium iron phosphate material, carbon black, and polyvinylidene fluoride (PVDF) glue (PVDF solid content of 6.25%) prepared in the above Examples 1-17 and Comparative Examples 1-2 were respectively mixed with N-methylpyrrolidone (NMP) in a mass ratio of 90:4:4:2 to obtain a slurry; the slurry was coated on an aluminum foil with a thickness of 20 μm, and the positive electrode sheet was made after vacuum drying and roller pressing. The metal lithium sheet was used as the negative electrode, the electrolyte ratio was 1.15 M LiPF6 / EC:DMC (volume ratio 1:1 vol%), and the button batteries were assembled.

[0079] Battery charging test: The test was conducted at 25°C using the Blue Power Battery Test System with a test voltage range of 2-3.75V. The test was conducted at 0.1C initial charge and discharge capacity, as well as 50 cycles of 0.1C charge and 1C discharge. The test results are shown in Table 2.

[0080] Table 1

[0081] Table 2

[0082] From the above table we can see that:

[0083] (1) From Examples 1-7, it can be seen that when L=A 2 ×D 2×(B+C)×J value satisfies: 0.040≤L≤0.058, and 1.002≤A≤1.008, 0.05≤B≤0.07, 0.06≤C≤0.07, 0.975≤D≤0.985, 0.330≤J≤0.550, the discharge specific capacity and cycle performance of the obtained positive electrode material are both good. The reason is that the positive electrode grain size synthesized within the above protection range is appropriate and uniform (as shown in Figure 1), the lithium is completely delithiation during the charging process, and the lithium ion migration distance during the discharge process is roughly the same, which can effectively avoid the occurrence of overdischarge, making the positive electrode material structure more stable and the cycle life longer; It can be seen from Example 1 and Examples 8-17 that although 0.040≤L≤0.058, when the values ​​of A, B, C or D are not within the preferred range of this application, the electrochemical performance of the obtained lithium iron phosphate material decreases.

[0084] (2) It can be seen from Example 1, Examples 8 and 10 that the value of A is too small, resulting in larger grains of the lithium iron phosphate material. During the charge and discharge cycle of the lithium iron phosphate material, the lithium ion migration path is long, which is not conducive to the deintercalation of lithium ions between the positive and negative electrodes, thereby reducing the discharge specific capacity. In addition, the lithium ratio is too low, resulting in insufficient lithium and poor crystallinity of the positive electrode material, further reducing the electrical properties of the material; It can be seen from Example 1, Examples 9 and 11 that an excessively large value of A leads to crystal refinement, a larger specific surface area of ​​the lithium iron phosphate material, an increased probability of reaction with the electrolyte during the charge and discharge cycle, affecting the electrochemical performance, and an excessive lithium ratio may result in the formation of non-conductive impurity lithium phosphide, reducing the conductivity of the material and significantly reducing the discharge specific capacity.

[0085] (3) It can be seen from Example 1 and Examples 12-15 that when the mass ratio B of PEG and FePO4 and the mass ratio C of glucose and FePO4 are too high, a too thick carbon layer is formed on the surface of the lithium iron phosphate material, making the positive electrode material not densely packed, which is not conducive to the rapid migration of lithium ions during the charge and discharge process and reduces the electrochemical performance of the positive electrode material; when the mass ratio B of PEG and FePO4 and the mass ratio C of glucose / FePO4 are too low, the carbon layer is too thin and the effect of improving the conductivity of the material cannot be achieved; It can be seen from Examples 1 and Examples 16-17 that the molar ratio of Fe to P is too low. If D is too large, the crystal particles will be refined, the specific surface area of ​​the material will be increased, and the probability of the positive electrode material reacting with the electrolyte during the charge and discharge cycle will increase, affecting the electrochemical performance. If the Fe to P molar ratio D is too small, the crystal particles will be larger. During the charge and discharge cycle of the positive electrode material, the lithium ion migration path will be long, which is not conducive to the lithium ion deintercalation between the positive and negative electrodes, thereby reducing the discharge specific capacity. It can be seen from Example 1 and Comparative Examples 1-2 that when L is not within the range of 0.04-0.058, the obtained material performance cannot exert the synergistic effect between the factors, resulting in a significant decrease in the obtained material performance.

[0086] In summary, the present application provides a lithium iron phosphate material, a preparation method and an application thereof. The preparation method controls the molar ratio of the lithium source and iron phosphate, the mass ratio of the carbon source and iron phosphate, the actual molar ratio of Fe and P in the iron phosphate, and the doping amount of the doping element, so that multiple factors satisfy a specific relationship, exert the synergistic effect between the factors, and obtain a lithium iron phosphate material with excellent electrochemical properties.

[0087] The above description is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Those skilled in the art should understand that any changes or replacements that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application fall within the protection scope and disclosure scope of the present application.

Claims

1. A preparation method of lithium iron phosphate material, which comprises the following steps: Mix a first carbon source, a second carbon source, a lithium source, an iron phosphate precursor, and a dopant, and sinter them to obtain the lithium iron phosphate material, wherein, The dopant includes a first dopant, a second dopant and a third dopant; The molar ratio of lithium ions in the lithium source to the iron phosphate precursor is A, the mass ratio of the first carbon source to the iron phosphate precursor is B, the mass ratio of the second carbon source to the iron phosphate precursor is C, the molar ratio of iron element to phosphorus element in the iron phosphate precursor is D, the doping amount of the first dopant is E1, the doping amount of the second dopant is E2, and the doping amount of the third dopant is E3; E1, E2 and E3 satisfy: J = 6×E1 / (5×E2 + 5×E3); A, B, C, D, and J satisfy the following relational expression: L = A 2 × D 2 × (B + C) × J, 0.040 ≤ L ≤ 0.058 2. The preparation method according to claim 1, wherein A is 1.002 - 1.008; Preferably, B is 0.05 - 0.07; Preferably, C is 0.06 - 0.07; Preferably, D is 0.975 - 0.985; Preferably, J is 0.330 - 0.

550.

3. The preparation method according to claim 1 or 2, wherein E1 is 450 - 500 ppm; Preferably, E2 is 700 - 900 ppm; Preferably, E3 is 500 - 700 ppm.

4. The preparation method according to any one of claims 1 to 3, wherein, The first dopant includes a compound containing Mo 6+ ; the second dopant includes a compound containing V 5+ ; and the third dopant includes a compound containing Nb 5+ . Preferably, the first carbon source includes polyethylene glycol; Preferably, the second carbon source includes glucose.

5. The preparation method according to any one of claims 1-4, wherein, A solvent is also added during the mixing; Preferably, the solid content of the mixed slurry obtained by mixing is 35 - 45 wt%; Preferably, the mixing method includes sand grinding; Preferably, the number of sand grinding circles is 12 - 17 circles.

6. The preparation method according to any one of claims 1-5, wherein, After mixing and before sintering, solid-liquid separation and drying are also carried out; Preferably, the solid-liquid separation method includes pressure filtration; Preferably, the pressure of the pressure filtration is 0.4 - 0.6 MPa, the time is 8 - 12 min, and the gases used include nitrogen and / or inert gas; Preferably, the drying temperature is 150 - 180 °C, the time is 5 - 6 h, and the rotation speed is 6 - 8 rpm.

7. The preparation method according to any one of claims 1-6, wherein, The sintering temperature is 780 - 800 °C, and the time is 10 - 12 h; Preferably, the atmosphere used for sintering includes nitrogen and / or inert gas.

8. The preparation method according to any one of claims 1-7, wherein, The preparation method includes the following steps: Sand grind the first carbon source, the second carbon source, the lithium source, the iron phosphate precursor, the dopant and the solvent, then under nitrogen and / or inert gas, carry out pressure filtration at a pressure of 0.4 - 0.6 MPa for 8 - 12 min, then dry at a temperature of 150 - 180 °C and a rotation speed of 6 - 8 rpm for 5 - 6 h, and finally sinter at a temperature of 780 - 800 °C for 10 - 12 h under nitrogen and / or inert gas to obtain the lithium iron phosphate material, wherein the dopant includes a first dopant, a second dopant and a third dopant; The molar ratio of lithium ions in the lithium source to the iron phosphate precursor is A, the mass ratio of the first carbon source to the iron phosphate precursor is B, the mass ratio of the second carbon source to the iron phosphate precursor is C, the molar ratio of iron element to phosphorus element in the iron phosphate precursor is D, the doping amount of the first dopant is E1, the doping amount of the second dopant is E2, and the doping amount of the third dopant is E3; The E1, E2, and E3 satisfy: J = 6×E1 / (5×E2 + 5×E3), where E1 is 450 - 500 ppm, E2 is 700 - 900 ppm, and E3 is 500 - 700 ppm; A, B, C, D, and J satisfy the following relationship: L = A 2 × D 2 × (B + C) × J, where L is 0.040 - 0.058, A is 1.002 - 1.008, B is 0.05 - 0.07, C is 0.06 - 0.07, D is 0.975 - 0.985, and J is 0.330 - 0.

550.

9. A lithium iron phosphate material prepared by the preparation method according to any one of claims 1 - 8.

10. A lithium ion battery comprising the lithium iron phosphate material according to claim 9.

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