Phosphate-based lithium ion cathode material and preparation method thereof

Abstract

The application provides a phosphate-based lithium ion positive electrode material and a preparation method thereof, and the preparation method comprises the following steps: (1) mixing raw materials of the phosphate-based lithium ion positive electrode material and a first carbon source to obtain a mixture, wherein the first carbon source accounts for 20-35% of the mass of the phosphate-based lithium ion positive electrode material; (2) obtaining a first calcined sample by calcining the mixture, wherein the final temperature of the first calcined sample is 700-800 DEG C, and the holding time of the final temperature is 0-1 h; (3) crushing and sieving the first calcined sample, mixing the first calcined sample with a second carbon source, and then performing second calcination to obtain the phosphate-based lithium ion positive electrode material. The crystallinity of the phosphate-based lithium ion positive electrode material can be improved by the above method, and the first charge capacity can be improved by reducing the crystalline defects.

Description

Technical Field

[0001] This invention relates to the field of cathode material technology, and in particular to a phosphate-based lithium-ion cathode material and its preparation method. Background Technology

[0002] High-rate LiMn x Fe 1-x PO4 cathode material requires Li + It can migrate rapidly, especially at high rates, the lithium-ion diffusion coefficient is much greater than that of other high-density, energy storage cathode materials, and its particles are usually small.

[0003] Small-particle crystalline materials have more defects in their crystal structure. When testing the electrical performance of coin cells, they often exhibit low initial charge capacity and high discharge capacity, while the second charge and discharge capacity remain high. This is because the first charge contains Li... + If the lithium migrates to the defect site but cannot continue migrating to the negative electrode, the lithium in the negative electrode will replenish the positive electrode during the discharge process, allowing the capacity to reach a higher value in the second charge cycle. For a full battery, the electrical performance will directly decrease, resulting in capacity loss.

[0004] To address this issue, an excess of lithium can be added to prepare the cathode material. During multiple charge-discharge cycles, the excess lithium on the particle surface diffuses into the crystal lattice, serving as a lithium replenishment mechanism. However, the excess lithium on the particle surface has adverse effects on the material's slurry processing performance and high-temperature storage.

[0005] Therefore, new technologies are needed to solve the problem of high-rate LiMn x Fe 1-x The problem of low initial charge capacity of PO4 cathode material. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention provides a phosphate-based lithium-ion cathode material and its preparation method. The method improves the crystallinity of small-particle rate-type cathode material by mixing with high carbon source and short-time high-temperature calcination, thereby reducing defects and solving the problem of low initial charge capacity of cathode material. The process is simple and can be industrially applied.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a phosphate-based lithium-ion cathode material, the method comprising:

[0009] (1) The raw materials of the phosphate-based lithium-ion cathode material and the first carbon source are mixed to obtain a mixture, wherein the first carbon source accounts for 20-35% of the mass of the phosphate-based lithium-ion cathode material;

[0010] (2) The mixture is calcined for the first time to obtain a calcined sample, wherein the final temperature of the first calcined sample is 700-800℃ and the final temperature is maintained for 0-1h.

[0011] (3) The first calcined sample is crushed and sieved, and then mixed with the second carbon source and calcined a second time to obtain the phosphate-based lithium-ion cathode material.

[0012] The method for improving the initial charge capacity of phosphate-based lithium-ion cathode materials provided by this invention involves incorporating 20-35% of a first carbon source during the precursor preparation stage. This provides sufficient carbon to compensate for carbon loss during the high-temperature first calcination process and allows for a thicker carbon source coating on the surface of the active components of the cathode material, preventing agglomeration and thus better ensuring the performance of the phosphate-based lithium-ion cathode material. Furthermore, this invention controls the first calcination temperature at 700-800°C, which improves the crystallinity of the phosphate-based lithium-ion cathode material at high temperatures, ultimately increasing the initial charge capacity.

[0013] Furthermore, if the carbon layer on the surface of the sample obtained by adding a large amount of carbon source is too thick, the carbon layer will fall off in large quantities after air jet milling, resulting in uneven coating or exposure. By adding a second carbon source in step (3), the present invention can uniformly coat the carbon layer on the surface of the particles and further improve the crystallization degree of the crystal.

[0014] The first carbon source comprises 20-35% of the mass of the phosphate-based lithium-ion cathode material, for example, 20%, 21%, 22%, 23%, 25%, 28%, 30%, 32%, or 35%. If the carbon content in the calcined sample is too low, impurity phases will form; if the carbon content is too high, the carbon coating will be too thick, requiring more energy to obtain crystals with the same crystallinity, leading to a decrease in crystallinity. Therefore, controlling the amount of the first carbon source within the above-mentioned range results in a product of better quality.

[0015] The final product of this invention is a phosphate-based lithium-ion cathode material. The finished product quality of the phosphate-based lithium-ion cathode material can be calculated simply by calculating the amount of Li, P, Mn, or Fe in the added raw materials.

[0016] It is worth noting that this invention is particularly aimed at high-rate LiMn x Fe 1-x PO4 cathode material has a small particle size, which leads to a low initial charge capacity. This invention addresses this by incorporating a large amount of carbon source and increasing the first calcination temperature to a specific temperature for short-term high-temperature calcination, thereby ensuring both high rate capability and initial charge capacity.

[0017] Preferably, the first calcination in step (2) includes a heating stage and a constant temperature stage.

[0018] Preferably, the heating rate during the heating stage of the first calcination is 3 to 5 °C / min, for example, it can be 3 °C / min, 3.3 °C / min, 3.5 °C / min, 3.7 °C / min, 3.9 °C / min, 4.2 °C / min, 4.4 °C / min, 4.6 °C / min, 4.8 °C / min or 5 °C / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Preferably, the final temperature of the heating stage in the first calcination is 700-800℃, for example, it can be 700℃, 706℃, 712℃, 717℃, 723℃, 728℃, 734℃, 739℃, 745℃ or 800℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, the duration of the isothermal phase in the first calcination is 0–1 hour, for example, it can be 0 hours, 0.2 hours, 0.3 hours, 0.4 hours, 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, or 1 hour, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. At 800°C, the isothermal phase can be 0 hours.

[0021] The present invention preferably sets the final temperature and the isothermal time of the first calcination within the above-mentioned range. High-crystallinity phosphate-based lithium-ion cathode material is obtained by high-temperature calcination, and short-time calcination can improve the crystallinity of the crystal while avoiding excessive crystal growth.

[0022] Preferably, the particle size of the calcined sample is 65-75 nm, for example, it can be 65 nm, 66 nm, 67 nm, 68 nm, 69 nm, 70 nm, 71 nm, 72 nm or 75 nm, etc.

[0023] Preferably, the pulverization in step (3) includes an air jet mill.

[0024] The present invention preferably uses an air jet mill, and the temperature of the air jet mill is selected to be around 90-110°C, which can achieve better pulverization effect and is more conducive to controlling particle size. Compared with dry ball milling, it can avoid the situation of the particle size increasing as it is ground. Compared with wet ball milling, it can avoid the subsequent drying step, consume less energy, and is easier to operate.

[0025] Preferably, the number of air jet milling cycles includes 2 to 4 times, for example, 2, 3 or 4 times.

[0026] Preferably, the mesh size of the sieve is 500 to 1000 mesh, for example, it can be 500 mesh, 550 mesh, 610 mesh, 660 mesh, 720 mesh, 770 mesh, 830 mesh, 880 mesh, 940 mesh or 1000 mesh, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] Preferably, the second calcination in step (3) includes a heating stage and a constant temperature stage.

[0028] Preferably, the heating rate during the heating stage in the second calcination is 3 to 5 °C / min, for example, it can be 3 °C / min, 3.3 °C / min, 3.5 °C / min, 3.7 °C / min, 3.9 °C / min, 4.2 °C / min, 4.4 °C / min, 4.6 °C / min, 4.8 °C / min or 5 °C / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, the final temperature of the heating stage in the second calcination is 300-600℃, for example, it can be 300℃, 330℃, 360℃, 400℃, 430℃, 460℃, 500℃, 530℃, 560℃ or 600℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] Preferably, the time for the isothermal stage in the second calcination is 4 to 8 hours, for example, it can be 4 hours, 4.5 hours, 4.9 hours, 5.4 hours, 5.8 hours, 6.3 hours, 6.7 hours, 7.2 hours, 7.6 hours or 8 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] Preferably, in step (3), the second carbon source accounts for 2 to 5% of the mass of the phosphate-based lithium-ion cathode material, for example, it can be 2%, 2.4%, 2.7%, 3%, 3.4%, 3.7%, 4%, 4.4%, 4.7% or 5%, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] The quality of the phosphate-based lithium-ion cathode material mentioned above refers to the quality of the final product. The quality of the final product can be calculated based on the quality of the mixture in the early stages.

[0033] Preferably, the atmospheres for the first and second calcinations each independently include a nitrogen atmosphere and / or an argon atmosphere, etc.

[0034] Preferably, the raw materials for the phosphate-based lithium-ion cathode material in step (1) include a lithium source, an iron source, and a phosphorus source. Optionally, the raw materials for the phosphate-based lithium-ion cathode material also include a manganese source.

[0035] Preferably, the lithium source includes any one or a combination of at least two of Li2CO3, LiH2PO4, LiOH·H2O, CH3COOLi, or LiNO3, wherein typical but non-limiting combinations are the combination of Li2CO3 and LiH2PO4, the combination of LiOH·H2O and LiH2PO4, the combination of Li2CO3 and LiOH·H2O, the combination of Li2CO3 and CH3COOLi, and the combination of LiNO3 and CH3COOLi.

[0036] Preferably, the iron source includes any one or a combination of at least two of Fe(NO3)3, Fe2O3, or FeSO4·7H2O, wherein typical but non-limiting combinations are the combination of Fe(NO3)3 and Fe2O3, the combination of FeSO4·7H2O and Fe2O3, and the combination of Fe(NO3)3 and FeSO4·7H2O.

[0037] Preferably, the phosphorus source includes any one or a combination of at least two of (NH4)3PO4, NH4H2PO4, LiH2PO4 or H3PO4, wherein typical but non-limiting combinations are the combination of (NH4)3PO4 and NH4H2PO4, the combination of LiH2PO4 and NH4H2PO4, and the combination of (NH4)3PO4 and H3PO4.

[0038] Preferably, the specific process of step (1) is as follows: the raw material, solvent, and first carbon source of the phosphate-based lithium-ion cathode material are mixed and dried to obtain a mixture. Preferably, the solvent includes water. Preferably, the drying temperature in step (1) is 150-300℃, for example, it can be 150℃, 167℃, 184℃, 200℃, 217℃, 234℃, 250℃, 267℃, 284℃, or 300℃, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0039] The present invention preferably uses a drying temperature within the above range to remove solvents and volatile components at the same time.

[0040] Preferably, the first carbon source and the second carbon source each independently comprise any one or at least two combinations of glucose, sucrose, PVDF, carbon black, PEG, paraffin, graphite, or graphene, wherein typical but non-limiting combinations are combinations of glucose and sucrose, combinations of PVDF and sucrose, combinations of glucose and PVDF, combinations of carbon black and sucrose, and combinations of PEG and graphene.

[0041] The present invention does not impose any special restrictions on the drying process described above. Any device and method known to those skilled in the art for drying can be used. Adjustments can also be made according to the actual process. For example, it can be air drying, vacuum drying, oven drying, or freeze drying, or a combination of different methods.

[0042] As a preferred embodiment of the present invention, the method for preparing the phosphate-based lithium-ion cathode material according to the first aspect of the present invention includes:

[0043] (1) The raw materials, solvent and first carbon source of the phosphate-based lithium-ion cathode material are mixed, wherein the first carbon source accounts for 20-35% of the mass of the phosphate-based lithium-ion cathode material, and dried at 150-300°C to obtain a mixture;

[0044] (2) The mixture is heated to 700-800℃ at a rate of 3-5℃ / min and then calcined for the first time, and kept at a constant temperature for 0-1h to obtain a first-calcined sample;

[0045] (3) The first calcination sample is pulverized by air jet milling 2 to 4 times and sieved through 500 to 1000 mesh, and then mixed with the second carbon source and heated to 300 to 600℃ at 3 to 5℃ / min for 4 to 8 hours for a second calcination. The second carbon source accounts for 2 to 5% of the mass of the phosphate-based lithium-ion cathode material, and the phosphate-based lithium-ion cathode material is obtained.

[0046] Secondly, the present invention provides a phosphate-based lithium-ion cathode material, wherein the phosphate-based lithium-ion cathode material is prepared by the preparation method of the phosphate-based lithium-ion cathode material described in the first aspect.

[0047] The phosphate-based lithium-ion cathode material of the second aspect of the present invention is prepared by using the method of the first aspect to improve the first charge capacity of the phosphate-based lithium-ion cathode material, which can obtain a phosphate-based lithium-ion cathode material product with high crystallinity, small crystal defects and small grain size, thereby significantly improving the first charge capacity of the small particle rate-type phosphate-based lithium-ion cathode material.

[0048] Preferably, the phosphate-based lithium-ion cathode material includes LiMn. x Fe 1-x PO4 active components and encapsulated in LiMn x Fe 1-x The carbon film other than the PO4 active component, where 0≤x≤1, can be, for example, 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0049] Preferably, in the phosphate-based lithium-ion cathode material, LiMn x Fe1-x The crystallinity of the PO4 active component is 95-98%, for example, it can be 95%, 95.8%, 96%, 97% or 98%, etc.

[0050] In this invention, crystallinity is crucial for the initial charge capacity. Low crystallinity indicates larger crystal defects, leading to lower Li... + The crystals migrate to the defect site but do not have enough time to continue migrating to the negative electrode, affecting the initial charge capacity. However, when it is possible to produce small-particle rate-capacity phosphate-based lithium-ion cathode materials, crystal defects are difficult to avoid. This invention significantly improves the crystallinity of the crystals by increasing the carbon content and preferably controlling the temperature of the first calcination and using short-time calcination, thereby improving the initial charge capacity.

[0051] Compared with the prior art, the present invention has at least the following beneficial effects:

[0052] (1) The method for improving the first charge capacity of phosphate-based lithium-ion cathode materials provided by the present invention is to mix the precursor with a high carbon source and to preferably control the temperature and time of the first calcination, while controlling the particle size of the first calcination sample, thereby obtaining a cathode material with better rate performance and higher first charge capacity.

[0053] (2) The phosphate-based lithium-ion cathode material provided by the present invention has high rate performance and high initial charge capacity. Attached Figure Description

[0054] Figure 1 Here is an SEM image of a sample from Example 1;

[0055] Figure 2 The LiMn prepared in Example 1 and Comparative Example 5 0.02 Fe 0.98 XRD pattern of the active component of PO4;

[0056] Figure 3 LiMn was prepared in Example 1 0.02 Fe 0.98 Rate performance characterization diagram of PO4 battery. Detailed Implementation

[0057] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0058] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0059] It should be understood that in the description of this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0060] Example 1

[0061] This embodiment provides a method for preparing a phosphate-based lithium-ion cathode material, the method comprising:

[0062] (1) Mix 1.20kgLiNO3, 4.12kgFe(NO3)3, 2.00kgNH4H2PO4, 0.062kgMn(NO3)2, 0.55kgsucrose and 5.91kg water evenly, and spray dry at 180℃ to obtain the dried sample, i.e., the mixture;

[0063] (2) The mixture was heated to 720°C at 4°C / min in a tube furnace under nitrogen atmosphere and calcined for the first time, and kept at the temperature for 1 hour to obtain a calcined sample.

[0064] (3) The first calcined sample was pulverized by air jet milling three times and sieved through 800 mesh. After being mixed with 54.67g of added sucrose, it was calcined again in a tube furnace under nitrogen atmosphere at a temperature of 4℃ / min to 500℃ and held at that temperature for 4h. After pulverization, phosphate-based lithium-ion cathode material was obtained.

[0065] Example 2

[0066] This embodiment provides a method for preparing a phosphate-based lithium-ion cathode material, the method comprising:

[0067] (1) 0.52 kg LiH2PO4, 0.32 kg CH3COOLi, 0.29 kg H3PO4, 1.69 kg Fe(NO3)3, 0.40 kg Mn3(PO4)2·3H2O, 0.32 kg graphene and 6.3 kg water were mixed evenly and spray-dried at 150 °C to obtain the dried sample, i.e., the mixture;

[0068] (2) The mixture was heated to 800°C at 3°C / min in a tube furnace under a nitrogen atmosphere and kept at the temperature for 0h to obtain a calcined sample.

[0069] (3) The first calcination sample was pulverized by air jet milling four times and sieved through 1000 mesh. After being mixed with 54.67g of glucose, it was calcined again in a tube furnace under nitrogen atmosphere at a temperature of 3℃ / min to 600℃ and held at that temperature for 8h. After pulverization, phosphate-based lithium-ion cathode material was obtained.

[0070] Example 3

[0071] This embodiment provides a method for preparing a phosphate-based lithium-ion cathode material, the method comprising:

[0072] (1) 0.42 kg LiOH·H2O, 1.49 kg (NH4)3PO4, 0.76 kg Fe2O3, 0.075 kg MnSO4, 0.55 kg PVDF and 5.1 kg water were mixed evenly and spray-dried at 300℃ to obtain the dried sample, i.e., the mixture;

[0073] (2) The dried sample under nitrogen atmosphere was heated to 700℃ in a tube furnace at 5℃ / min and calcined for the first time, and kept at the temperature for 0.1h to obtain a first-calcined sample;

[0074] (3) The first calcination sample was pulverized twice by air jet milling and sieved through 500 mesh. After being mixed with 68.5g of paraffin wax, it was calcined again in a tube furnace under nitrogen atmosphere at a temperature of 5℃ / min to 300℃ and held at that temperature for 6h. After pulverization, phosphate-based lithium-ion cathode material was obtained.

[0075] Comparative Example 1

[0076] This comparative example provides a method for preparing a phosphate-based lithium-ion cathode material. The preparation method is the same as in Example 1, except that 0.54 kg of sucrose is replaced with 0.11 kg of sucrose.

[0077] Comparative Example 2

[0078] This comparative example provides a method for preparing a phosphate-based lithium-ion cathode material. The preparation method is the same as in Example 1, except that 0.54 kg of sucrose is replaced with 1.37 kg of sucrose.

[0079] Comparative Example 3

[0080] This comparative example provides a method for preparing a phosphate-based lithium-ion cathode material. Except for step (2) where the temperature is raised to 500°C and calcined for the first time, the preparation method is the same as in Example 1.

[0081] Comparative Example 4

[0082] This comparative example provides a method for preparing a phosphate-based lithium-ion cathode material. Except for step (2) where the temperature is raised to 900°C and calcined for the first time, the preparation method is the same as in Example 1.

[0083] Comparative Example 5

[0084] This comparative example provides a method for preparing a phosphate-based lithium-ion cathode material. The preparation method is the existing conventional method for preparing phosphate-based lithium-ion cathode materials. Specifically, except that 0.54 kg of sucrose in step (1) is replaced with 0.27 kg of sucrose; in step (2), the temperature is raised to 400°C for the first calcination and held at that temperature for 3 hours; and in step (3), 82.26 g of sucrose is added and the temperature is raised from room temperature to 500°C at a rate of 4°C / min and held at that temperature for 6 hours, the rest is the same as in Example 1.

[0085] Comparative Example 6

[0086] This comparative example provides a method for preparing a phosphate-based lithium-ion cathode material. Except for the isothermal 6h step (2), the preparation method is the same as that in Example 1.

[0087] Carbon content is tested using a high-frequency infrared carbon-sulfur analyzer; average particle size of primary particles in a single-burn sample: the average value is obtained by statistically analyzing the diameter of no less than 600 particles in the SEM characterization image; relative crystallinity: the ratio of the sum of the intensities of 5 strong characteristic peaks in the XRD spectrum of the sample to the sum of the characteristic peak intensities of a given standard sample.

[0088] The SEM image of the calcined sample in Example 1 is shown below. Figure 1 As shown, from Figure 1 It can be seen that the particle size distribution is uniform and the particle size is small; the XRD patterns of the active components of the phosphate-based lithium-ion cathode materials in Example 1 and Comparative Example 5 are shown below. Figure 2 As shown, from Figure 2 It can be seen that the characteristic peak intensity of Comparative Example 5 is lower than that of Example 1, and the relative crystallinity of Comparative Example 5 is less than that of Example 1. The crystallinity data are shown in Table 1.

[0089] 800g of the positive electrode active component from the above examples and comparative examples, 100g of conductive agent acetylene black, and 100g of binder polyvinylidene fluoride (PVDF) were added to 800g of N-methylpyrrolidone solvent (NMP solvent) and stirred in a vacuum mixer for 2 hours to obtain a positive electrode slurry. The slurry was uniformly coated onto aluminum foil and then dried in a vacuum drying oven at 120°C for 12 hours. After rolling, it was punched into round sheets with a diameter of 14mm as positive electrode sheets. The positive electrode sheet, negative electrode sheet (lithium metal sheet with a diameter of 14.5mm), separator (Celgard 2400 microporous polypropylene membrane), and electrolyte (1mol / L LiPF6 / EC+DMC (volume ratio 1:1)) were assembled into a CR2025 type coin cell lithium-ion battery in a glove box filled with an inert atmosphere.

[0090] Rate performance testing: The prepared test batteries were subjected to charge-discharge tests using a lithium-ion battery charge-discharge testing system at 25±0.5℃. The charge-discharge conditions were: charging termination voltage 3.75V; discharging termination voltage 2.00V; charge-discharge current density: 0.1C, 1C or charge-discharge current density: 1C, 2C, 3C, 5C, 10C. The rate discharge specific capacity-voltage diagram for Example 1 is shown below. Figure 2 As shown, the 10C discharge capacity is 136.10 mAh / g.

[0091] The test results for Examples 1-3 and Comparative Examples 1-6 are shown in Table 1.

[0092] Table 1

[0093]

[0094]

[0095] In Table 1, "-" indicates that there is no relevant data because there are many impurities.

[0096] As can be seen from Table 1, comparing Example 1 and Comparative Examples 1 and 2, the amount of the first carbon source added in Example 1 was 0.55 kg, which was too high and too low compared to the amounts added in Comparative Examples 1 and 2, respectively. This shows that the relative crystallinity of the phosphate-based lithium-ion cathode material obtained in Example 1 was as high as 95.8%, while in Comparative Example 1, due to the low amount of the first carbon source, it could not provide a sufficient reducing atmosphere or reducing substance, resulting in a large number of impurities in the finished product. In Comparative Example 2, due to the high amount of the first carbon source, the relative crystallinity of the phosphate-based lithium-ion cathode material decreased, and the initial charging capacity of the lithium-ion battery decreased. Comparing Example 1 and Comparative Examples 3-4, it can be seen that the final calcination temperature in Example 1 was 720°C, compared to the final calcination temperatures of 500°C and 900°C in Comparative Examples 3-4, respectively. The average particle size of the primary particles in Example 1 was 70 nm, resulting in a high initial charge capacity. In Comparative Example 3, due to the low calcination temperature, the crystallinity of the phosphate-based lithium-ion cathode material was low, leading to a significant decrease in the initial charge capacity. In Comparative Example 4, the excessively high first calcination temperature significantly increased the average particle size. This excessively high temperature caused severe lattice shrinkage, hindering lithium-ion diffusion and reducing electrical performance, resulting in a more significant decrease in the charge capacity of the lithium-ion battery. Comparative Example 6 had an excessively long calcination time, resulting in excessively large primary particles in the primary sample. Even after subsequent air jet milling, these particles could not be pulverized to a smaller size, thus failing to achieve the desired effect of the present invention.

[0097] In summary, by comparing Example 1 and Comparative Example 5, it can be seen that the present invention significantly improves the relative crystallinity of the phosphate-based lithium-ion cathode material and increases the initial charge capacity of the final lithium-ion battery by increasing the carbon content added in the first calcination and increasing the temperature of the first calcination.

[0098] 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 method for producing a phosphate-based lithium-ion positive electrode material, characterized by, The preparation method comprises: (1) mixing raw materials of the phosphate-based lithium ion positive electrode material and a first carbon source to obtain a mixture, the first carbon source accounting for 20-35% of the mass of the phosphate-based lithium ion positive electrode material; (2) obtaining a first calcination sample by first calcining the mixture, the first calcination having a final temperature of 706-800 ℃ and a holding time of 0-0.9 h at the final temperature; (3) crushing and sieving the first calcination sample, mixing the crushed and sieved sample with a second carbon source, and then second calcining to obtain the phosphate-based lithium ion positive electrode material.

2. The production method according to claim 1, characterized by, The first calcination in step (2) comprises a temperature rising stage and a constant temperature stage.

3. The production method according to claim 2, characterized by, The temperature rising rate of the temperature rising stage in the first calcination is 3-5 ℃ / min.

4. The production method according to claim 1, characterized by, The particle size of the first calcination sample is 65-75 nm.

5. The method of claim 1, wherein, The crushing in step (3) comprises air jet milling.

6. The production method according to claim 5, wherein The air jet milling is performed for 2-4 times.

7. The preparation method according to claim 1, characterized in that, The mesh number of the sieving is 500-1000.

8. The method of claim 1, wherein, The second carbon source in step (3) accounts for 2-5% of the mass of the phosphate-based lithium ion positive electrode material.

9. The method of claim 1, wherein, The first carbon source and the second carbon source each independently comprise any one or a combination of at least two of glucose, sucrose, PVDF, carbon black, PEG, paraffin, graphite and graphene.

10. The method of claim 1, wherein, The second calcination in step (3) comprises a temperature rising stage and a constant temperature stage.

11. The method of claim 10, wherein, The temperature rising rate of the temperature rising stage in the second calcination is 3-5 ℃ / min.

12. The method of claim 10, wherein, The final temperature of the temperature rising stage in the second calcination is 300-600 ℃.

13. The preparation method according to claim 10, characterized in that, The time of the constant temperature stage in the second calcination is 4-8 h.

14. The method of claim 1, wherein, The raw materials of the phosphate-based lithium ion positive electrode material in step (1) comprise a lithium source, an iron source and a phosphorus source.

15. The method of claim 14, wherein, The raw materials of the phosphate-based lithium ion positive electrode material further comprise a manganese source.

16. The method of claim 1, wherein, The specific process of step (1) is: mixing the raw materials of the phosphate-based lithium ion positive electrode material, a solvent and the first carbon source, and then drying to obtain the mixture.

17. A phosphate-based lithium-ion cathode material, characterized by, The phosphate-based lithium ion positive electrode material is prepared by the preparation method of the phosphate-based lithium ion positive electrode material according to any one of claims 1-16.

18. The phosphate-based lithium-ion cathode material of claim 17, wherein, The phosphate-based lithium ion cathode material includes LiMn x Fe 1-x PO4active component and a carbon film wrapped outside the LiMn x Fe 1-x PO4active component, wherein 0≤x≤1.

19. The phosphate-based lithium-ion cathode material of claim 18, wherein, The phosphate-based lithium ion positive electrode material has LiMn x Fe 1-x The crystal crystallinity of the PO4 active component is 95-98%.

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