Lithium-rich lithium-iron-phosphate lithium supplement material, preparation method and application thereof

Abstract

The application relates to the technical field of lithium ion battery lithium supplement, in particular to a lithium-rich lithium iron phosphate lithium supplement material and a preparation method and application thereof. The preparation method of the lithium-rich lithium iron phosphate lithium supplement material comprises the following steps: mixing a lithium source and an iron source to prepare a Li5FeO4 precursor; the Li5FeO4 precursor is heated to a first temperature at a first rate under an air atmosphere, and is kept for a first time to prepare phase-pure Li5FeO4 powder; the first rate is 4 DEG C / min-6 DEG C / min, the first temperature is 600 DEG C-800 DEG C, and the first time is 20 h-30 h; the phase-pure Li5FeO4 powder is ball milled under a protective gas atmosphere, and the ball milling conditions comprise that the ball-to-material ratio is (5-20):1, and the ball milling time is 3 h-7 h. The preparation method can make the particle size distribution of the lithium iron phosphate lithium supplement material uniform and good in stability, thereby improving the lithium supplement effect of the lithium ion battery.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery lithium replenishment technology, and in particular to lithium-rich lithium iron phosphate lithium replenishment materials, their preparation methods and applications. Background Technology

[0002] During the first charge and discharge cycle of a lithium-ion battery, a solid electrolyte interphase (SEI) film forms on the surface of the negative electrode, leading to the irreversible consumption of some active lithium ions and reducing the battery's initial coulombic efficiency and energy density. Pre-lithiation technology is an effective means to solve this problem. Among them, lithium iron ferrite (Li5FeO4, or LFO) has become a promising positive electrode lithium replenisher due to its advantages such as extremely high lithium replenishment capacity, good compatibility with positive electrode materials, and low cost.

[0003] The particle size and distribution of lithium iron ferrite (LFP) are crucial to its lithium replenishment performance. Excessive particle size results in a small contact area between the material and the electrolyte, a long lithium-ion transport path, and low lithium replenishment efficiency. Conversely, excessively small particle size leads to material agglomeration, decreased processing performance, and an increased probability of side reactions. Traditional improvements to LFP preparation methods have primarily focused on surface modification or increasing phase purity, with limited research on particle size control and product stability. Currently, the problem of unstable lithium replenishment performance due to uncontrollable particle size remains unresolved. Summary of the Invention

[0004] To address the aforementioned problems, one or more embodiments of this application provide lithium-rich lithium iron ferrite supplementary materials, their preparation methods, and applications. This preparation method enables the lithium iron ferrite supplementary material to have a uniform particle size distribution and good stability, thereby improving the lithium supplementation effect of lithium-ion batteries.

[0005] The preparation method of lithium-rich lithium iron phosphate supplementary lithium material according to one or more embodiments of this application includes the following steps:

[0006] A Li5FeO4 precursor was prepared by mixing a lithium source and an iron source.

[0007] The Li5FeO4 precursor is heated to a first temperature at a first rate in an air atmosphere and held at that temperature for a first time to obtain Li5FeO4 powder; the first rate is 4℃ / min-6℃ / min, the first temperature is 600℃-800℃, and the first time is 20h-30h.

[0008] The Li5FeO4 powder was ball-milled under a protective gas atmosphere. The ball-milling conditions included a mass ratio of grinding balls to Li5FeO4 powder of (5-20):1 and a ball-milling time of 3-7 hours.

[0009] In some embodiments, the molar ratio of lithium in the lithium source to iron in the iron source is (5-5.2):1.

[0010] In some embodiments, the step of mixing the lithium source and the iron source includes:

[0011] The lithium source and the iron source are stirred in a dry air environment with a dew point ≤ -30℃.

[0012] In some embodiments, the stirring conditions include: a stirring speed of 200 rpm to 400 rpm and a stirring time of 20 min to 40 min.

[0013] In some embodiments, the step of ball milling the Li5FeO4 powder under a protective gas atmosphere includes:

[0014] The Li5FeO4 powder is placed in a ball mill jar with a sealing component, and the air inside the ball mill jar is replaced with the protective gas;

[0015] After the replacement is completed, the ball mill jar is sealed by the sealing component, and then ball milling is performed.

[0016] In some embodiments, the number of replacements is 1-5, and the duration of each replacement is 5-10 minutes; and / or,

[0017] After the air inside the ball mill jar is replaced with the protective gas, the argon purity inside the ball mill jar is ≥99.99%, and the dew point is ≤-40℃.

[0018] In some embodiments, the ball milling conditions further include: using zirconia balls as the ball milling medium and the ball milling speed is 400 rpm to 500 rpm;

[0019] Optionally, the diameter of the zirconia spheres is 4mm-6mm.

[0020] One or more embodiments of this application also provide lithium-rich lithium iron ferrite supplementary materials, which are prepared by the preparation method of lithium-rich lithium iron ferrite supplementary materials described above.

[0021] In some embodiments, the D50 particle size of the lithium iron phosphate supplemental material is 12 μm-30 μm; and / or,

[0022] The difference between the D90 and D10 particle sizes of the lithium iron ferrite supplementary material is ≤20μm.

[0023] One or more embodiments of this application also provide the application of the lithium-rich lithium iron ferrite supplement material described above as a positive electrode lithium supplement agent in lithium-ion batteries.

[0024] The preparation method of this application involves rapidly heating the Li5FeO4 precursor to 600℃-800℃ in air at a relatively fast rate of 4℃ / min-6℃ / min and holding it at that temperature for 20h-30h. This method quickly overcomes the low-temperature impurity phase formation zone, promoting the simultaneous and uniform nucleation of a large number of crystal nuclei in the high-temperature zone. This results in Li5FeO4 powder with high phase purity, moderate crystallinity, and uniform grain size. This not only provides a structurally stable precursor containing a small number of lattice defects for subsequent ball milling but also avoids the appearance of coarse grains or secondary impurities. Based on this, the obtained Li5FeO4... The powder is ball-milled under a protective gas atmosphere, with a ball-to-powder ratio of 5-20:1 and a milling time of 3-7 hours. This process uniformly breaks down micron-sized particles to a suitable size without introducing a large amount of amorphous phase or mechanically induced impurities due to over-milling. Simultaneously, dislocations, grain boundaries, and surface amorphous thin layers generated during ball milling preferentially germinate at lattice defects left from the sintering stage, forming a continuous lithium-ion rapid diffusion network from the bulk phase to the surface. The protective atmosphere prevents the fresh surface generated during ball milling from re-adsorbing CO2 or H2O, thus preserving the highly active surface obtained in the previous sintering step. Through precise process control in each step, a highly active lithium replenishment material is provided, enabling the battery to simultaneously achieve high lithium ion extraction capacity and rapid release during the first charge, with minimal side reactions, significantly improving the lithium replenishment effect.

[0025] The preparation method of this application is simple, and the resulting lithium ferrite supplementation material has a uniform particle size distribution, good stability, and good lithium supplementation effect. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a comparison graph showing the particle size distribution curves of lithium-rich lithium iron phosphate supplementary materials in the embodiments and comparative examples of this application. Detailed Implementation

[0028] The present application is further described below with reference to embodiments and examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Furthermore, it should be understood that after reading the teachings of this application, those skilled in the art can make various alterations or modifications to this application, and these equivalent forms also fall within the protection scope of the appended claims.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0030] The term "and / or" as used herein includes any one of two or more related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations encompass any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected using at least two conjunctions selected from "and / or," it should be understood that, in this application, the technical solution undoubtedly includes solutions connected using "logical AND," and also undoubtedly includes solutions connected using "logical OR." For example, "A and / or B" includes three parallel solutions: A, B, and A+B. For example, the technical solution of "A, AND / OR, B, AND / OR, C, AND / OR, D" includes any one of A, B, C, and D (that is, a technical solution that is connected by "logical OR"), as well as any and all combinations of A, B, C, and D, that is, combinations of any two or three of A, B, C, and D, and also combinations of all four of A, B, C, and D (that is, a technical solution that is connected by "logical AND").

[0031] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0032] In this application, numerical intervals (i.e., numerical ranges) are involved. Unless otherwise specified, optional numerical distributions within the aforementioned numerical intervals are considered continuous and include the two endpoints (i.e., the minimum and maximum values) of the numerical range, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval points to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints. Furthermore, when multiple ranges are provided to describe features or characteristics, these ranges may be merged. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0033] In this application, weight can be a well-known unit of mass in the field of lithium batteries, such as μg, mg, g, or kg.

[0034] The preparation method of lithium-rich lithium iron phosphate supplementary lithium material according to one or more embodiments of this application includes the following steps:

[0035] A Li5FeO4 precursor was prepared by mixing a lithium source and an iron source.

[0036] The Li5FeO4 precursor was heated to a first temperature at a first rate in air atmosphere and held at that temperature for a first time to obtain Li5FeO4 powder; the first rate was 4℃ / min-6℃ / min, the first temperature was 600℃-800℃, and the first time was 20h-30h.

[0037] Li5FeO4 powder was ball-milled under a protective gas atmosphere. The ball-milling conditions included a ball-to-powder ratio of (5-20):1 and a ball-milling time of 3-7 hours.

[0038] In some embodiments, the first rate is 4°C / min to 6°C / min, for example, it can be 4°C / min, 5°C / min, 6°C / min, etc.

[0039] In some embodiments, the first temperature is 600℃-800℃, for example, it can be 600℃, 700℃, 800℃, etc.

[0040] In some embodiments, the first time is 20h-30h, for example, it can be 20h, 25h, 30h, etc.

[0041] In this embodiment, by rapidly heating the Li5FeO4 precursor to 600℃-800℃ in air at a rate of 4℃ / min-6℃ / min and holding it at that temperature for 20h-30h, the low-temperature impurity phase formation zone can be quickly bypassed, promoting the simultaneous and uniform nucleation of a large number of crystal nuclei in the high-temperature zone. This results in Li5FeO4 powder with high phase purity, moderate crystallinity, and uniform grain size (e.g., 15μm). This not only provides a structurally stable precursor containing a small number of lattice defects for subsequent ball milling but also avoids the appearance of coarse grains or secondary impurities. Based on this, the obtained Li5FeO4 powder... Ball milling is performed under a protective gas atmosphere, with a ball-to-material ratio controlled at 5-20:1 and a milling time of 3-7 hours. This process uniformly breaks micron-sized particles to a suitable size (e.g., 15 μm) without introducing a large amount of amorphous phase or mechanically induced impurities due to excessive milling. Simultaneously, dislocations, grain boundaries, and surface amorphous thin layers generated during milling preferentially germinate at lattice defects left from the sintering stage, forming a continuous lithium-ion rapid diffusion network from the bulk phase to the surface. The protective atmosphere prevents the fresh surface generated during milling from re-adsorbing CO2 or H2O, thus preserving the highly active surface obtained in the previous sintering step. Through precise process control in each step, a highly active lithium replenishment material is provided, enabling the battery to simultaneously achieve high lithium ion extraction capacity and rapid release during the first charge, with minimal side reactions, significantly improving the lithium replenishment effect.

[0042] In some embodiments, the molar ratio of lithium in the lithium source to iron in the iron source is (5-5.2):1.

[0043] In this embodiment, by controlling the molar ratio within a suitable range, it is possible to compensate for the loss of lithium volatilization during the high-temperature sintering process and suppress the formation of lithium-poor impurity phases (such as LiFeO2 and LiFe5O8) while ensuring that the iron source is completely converted into Li5FeO4.

[0044] In some embodiments, the step of mixing the lithium source and the iron source includes:

[0045] The lithium source and iron source were stirred in a dry air environment with a dew point ≤ -30℃.

[0046] In this embodiment, by stirring the lithium source and the iron source in a suitable dry air environment, it is possible to effectively prevent the lithium source (such as LiOH, Li2CO3, etc.) from absorbing moisture from the air and deliquescing or clumping during the stirring process. At the same time, it inhibits the reaction of the lithium source with CO2 to form a surface carbonate passivation layer, ensuring a uniform dispersion state and high reactivity of the lithium source and the iron source.

[0047] In some embodiments, the stirring conditions include: a stirring speed of 200 rpm to 400 rpm and a stirring time of 20 min to 40 min.

[0048] In some embodiments, the stirring speed is 200 rpm to 400 rpm, for example, 200 rpm, 300 rpm, 400 rpm, etc.

[0049] In some embodiments, the stirring time is 20 min to 40 min, for example 20 min, 30 min, 40 min, etc.

[0050] In this embodiment, by controlling the stirring speed and time within a suitable range, it is possible to achieve uniform mixing of lithium source and iron source while avoiding the introduction of excessive mechanical energy, thereby avoiding excessive powder refinement and electrostatic agglomeration caused by stirring.

[0051] In some embodiments, the step of ball milling Li5FeO4 powder under a protective gas atmosphere includes:

[0052] Li5FeO4 powder was placed in a ball mill jar with a sealed component, and the air inside the ball mill jar was replaced with a protective gas;

[0053] After the replacement is completed, the ball mill jar is sealed with a sealing component before ball milling is performed.

[0054] In this embodiment, the replacement and sealing operations can effectively remove residual oxygen, moisture and carbon dioxide from the ball mill jar, and prevent the fresh Li5FeO4 surface generated by mechanical collision during the ball milling process from reacting with air components.

[0055] In some embodiments, the number of replacements is 1-5 times (e.g., 1, 2, 3, 4 or 5 times), and the duration of each replacement is 5-10 minutes (e.g., 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, etc.).

[0056] In some embodiments, after replacing the air in the ball mill jar with a protective gas, the argon purity in the ball mill jar is ≥99.99% and the dew point is ≤-40℃.

[0057] In some embodiments, the ball milling conditions further include: using zirconia balls as the milling medium, and milling at a rotation speed of 400 rpm to 500 rpm, for example, 400 rpm, 450 rpm, 500 rpm, etc.

[0058] In some embodiments, the diameter of the zirconia spheres is 4mm-6mm, for example 4mm, 5mm, 6mm, etc.

[0059] One or more embodiments of this application also provide lithium-rich lithium iron ferrite supplementary materials, which are prepared by the preparation method of lithium-rich lithium iron ferrite supplementary materials described above.

[0060] In some embodiments, the D50 particle size of the lithium iron phosphate supplement material is 12μm-30μm, for example 12μm, 15μm, 18μm, 20μm, 22μm, 25μm, 28μm, 30μm, etc.

[0061] In some embodiments, the difference between the D90 and D10 particle sizes of the lithium iron phosphate supplementary material is ≤20μm, for example, it can be 6μm-20μm, such as 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, etc.

[0062] One or more embodiments of this application also provide the application of the lithium-rich lithium iron ferrite supplement material described above as a positive electrode lithium supplement agent in lithium-ion batteries.

[0063] The lithium-rich lithium iron ferrite supplementary material prepared by the method of this application has a uniform particle size distribution and good lithium supplementation effect.

[0064] The following are some specific examples.

[0065] For experimental parameters not specified in the following specific embodiments, please refer to the guidelines provided in this application, or consult experimental manuals or other known experimental methods in the field, or refer to the manufacturer's recommended experimental conditions. Raw materials and reagents not mentioned can be obtained commercially, or can be prepared by those skilled in the art using known methods.

[0066] Example of raw material usage calculation:

[0067] In the chemical formula of lithium iron ferrite (Li5FeO4), the theoretical molar ratio of Li to Fe is 5:1. Using a molar ratio of Li:Fe = 5.1:1, and taking the preparation of 100g of phase-pure Li5FeO4 as an example, the raw material consumption is calculated as follows:

[0068] (1) Calculate the theoretical amount of Fe2O3:

[0069] The molar mass of Li5FeO4 is 197.75 g / mol. The amount of substance of 100 g of Li5FeO4 is approximately 0.506 mol (100 g ÷ 197.75 g / mol). 1 mol of Li5FeO4 contains 1 mol of Fe, so the required amount of Fe is 0.506 mol. The molar mass of Fe2O3 is 159.69 g / mol. 1 mol of Fe2O3 contains 2 mol of Fe, so the required amount of Fe2O3 is approximately 0.506 mol ÷ 2 ≈ 0.253 mol. The mass of Fe2O3 is approximately 0.253 mol × 159.69 g / mol ≈ 40.4 g (purity 99.5%, actual feed amount is approximately 40.4 g ÷ 99.5% ≈ 40.6 g).

[0070] 2. Calculate the theoretical amount of Li₂O:

[0071] The required amount of Li is 0.506mol × 5.1 ≈ 2.581mol; the molar mass of Li₂O is 29.88g / mol, and 1mol of Li₂O contains 2mol of Li, so the required amount of Li₂O is 2.581mol ÷ 2 ≈ 1.291mol; the mass of Li₂O is 1.291mol × 29.88g / mol ≈ 38.6g (purity 99.9%, actual amount fed is 38.6g ÷ 99.9% ≈ 38.6g).

[0072] Example 1

[0073] This embodiment provides a specific example of the preparation method of the lithium-rich lithium iron phosphate supplementary material of this application:

[0074] (1) Weigh 40.6g of Fe2O3 (purity 99.5%) and 38.6g of Li2O (purity 99.9%), and put them into a double planetary mixer with a molar ratio of Li:Fe = 5.1:1. The stirring paddle is of the paddle type. Mix at a speed of 300rpm for 30min. Dry air (dew point ≤ -30℃) is introduced during the mixing process to obtain Li5FeO4 precursor.

[0075] (2) The Li5FeO4 precursor was placed in a tube furnace and heated to 700°C at a rate of 5°C / min in an air atmosphere. The temperature was held for 24 hours and then naturally cooled to room temperature to obtain phase-pure Li5FeO4.

[0076] (3) Place 50g of phase-pure Li5FeO4 into a stainless steel ball mill jar with a polytetrafluoroethylene sealing gasket, and add 500g of zirconia balls (5mm in diameter) to make the ball-to-material ratio 10:1. Purge the stainless steel ball mill jar with argon gas three times to replace the air inside, each replacement lasting 5 minutes, ensuring the argon purity is ≥99.99% and the dew point is ≤-40℃. After replacement, seal the jar with stainless steel clips. Set the ball mill speed to 450rpm and mill for 5 hours to obtain lithium-rich lithium iron ferrite supplementary material.

[0077] Example 2

[0078] This embodiment provides a specific example of the preparation method of the lithium-rich lithium iron phosphate supplementary material of this application. It adopts the same preparation steps as in Example 1, except that the ball milling time in step (3) is 3h, and the other operations and preparation parameters remain unchanged.

[0079] Example 3

[0080] This embodiment provides a specific example of the preparation method of the lithium-rich lithium iron phosphate supplementary material of this application. It adopts the same preparation steps as in Example 1, except that the ball milling time in step (3) is 7h, and the other operations and preparation parameters remain unchanged.

[0081] Example 4

[0082] This embodiment provides a specific example of the preparation method of the lithium-rich lithium iron phosphate supplementary material of this application. It adopts the same preparation steps as in Example 1, except that 250g of zirconium oxide balls are added in step (3) to make the ball-to-material ratio 5:1. The remaining operations and preparation parameters remain unchanged.

[0083] Example 5

[0084] This embodiment provides a specific example of the preparation method of the lithium-rich lithium iron phosphate supplementary material of this application. It adopts the same preparation steps as in Example 1, except that 1000g of zirconium oxide balls are added in step (3) to make the ball-to-material ratio 20:1. The remaining operations and preparation parameters remain unchanged.

[0085] Example 6

[0086] This embodiment provides a specific example of the preparation method of the lithium-rich lithium iron phosphate supplementary material of this application. It adopts the same preparation steps as in Example 1, except that in step (2), the temperature is increased to 700°C at a rate of 4°C / min, while the other operations and preparation parameters remain unchanged.

[0087] Example 7

[0088] This embodiment provides a specific example of the preparation method of the lithium-rich lithium iron phosphate supplementary material of this application. It adopts the same preparation steps as in Example 1, except that in step (2), the temperature is increased to 700°C at a rate of 6°C / min, while the other operations and preparation parameters remain unchanged.

[0089] Example 8

[0090] This embodiment provides a specific example of the preparation method of the lithium-rich lithium iron phosphate supplementary material of this application. It adopts the same preparation steps as in Example 1, except that in step (2), the temperature is increased to 600°C at a rate of 5°C / min and kept at that temperature for 24 hours. The other operations and preparation parameters remain unchanged.

[0091] Example 9

[0092] This embodiment provides a specific example of the preparation method of the lithium-rich lithium iron phosphate supplementary material of this application. It adopts the same preparation steps as in Example 1, except that in step (2), the temperature is increased to 800°C at a rate of 5°C / min and kept at that temperature for 24 hours. The other operations and preparation parameters remain unchanged.

[0093] Example 10

[0094] This embodiment provides a specific example of the preparation method of the lithium-rich lithium iron phosphate supplementary material of this application. It adopts the same preparation steps as in Example 1, except that in step (2), the temperature is increased to 700°C at a rate of 5°C / min and kept at that temperature for 20h. The other operations and preparation parameters remain unchanged.

[0095] Example 11

[0096] This embodiment provides a specific example of the preparation method of the lithium-rich lithium iron phosphate supplementary material of this application. It adopts the same preparation steps as in Example 1, except that in step (2), the temperature is increased to 700°C at a rate of 5°C / min and kept at that temperature for 30h. The other operations and preparation parameters remain unchanged.

[0097] Comparative Example 1

[0098] This comparative example provides an example of another method for preparing lithium-rich lithium iron phosphate supplementary materials, which adopts the same preparation steps as in Example 1, except that the ball milling operation in step (3) is omitted, that is, the phase-pure Li5FeO4 powder obtained in step (2) is directly used as the final product, and the remaining operations and preparation parameters remain unchanged.

[0099] Comparative Example 2

[0100] This comparative example provides an example of another method for preparing lithium-rich lithium iron phosphate supplemental materials, which adopts the same preparation steps as in Example 1, except that the ball milling time in step (3) is 10h (exceeding the 3-7h range specified in this application), and the other operations and preparation parameters remain unchanged.

[0101] Comparative Example 3

[0102] This comparative example provides an example of another method for preparing lithium-rich lithium iron phosphate supplementary materials, which adopts essentially the same preparation steps as in Example 1, except that the ball-to-material ratio in step (3) is 30:1 (exceeding the 5-20:1 range specified in this application), while the other operations and preparation parameters remain unchanged.

[0103] Comparative Example 4

[0104] This comparative example provides an example of another method for preparing lithium-rich lithium iron phosphate supplemental materials, which adopts essentially the same preparation steps as in Example 1, except that in step (2), the temperature is increased to 700°C at a rate of 1°C / min (lower than the 4-6°C / min range specified in this application), while the other operations and preparation parameters remain unchanged.

[0105] Comparative Example 5

[0106] This comparative example provides an example of another method for preparing lithium-rich lithium iron phosphate supplemental materials, which adopts essentially the same preparation steps as in Example 1, except that in step (2), the temperature is increased to 700°C at a rate of 10°C / min (higher than the range of 4-6°C / min specified in this application), while the other operations and preparation parameters remain unchanged.

[0107] Comparative Example 6

[0108] This comparative example provides an example of another method for preparing lithium-rich lithium iron phosphate supplementary materials, which adopts the same preparation steps as in Example 1, except that in step (2), the temperature is increased to 500°C at a rate of 5°C / min (lower than the 600-800°C range specified in this application), and held at that temperature for 24 hours, while the other operations and preparation parameters remain unchanged.

[0109] Comparative Example 7

[0110] This comparative example provides an example of another method for preparing lithium-rich lithium iron phosphate supplementary materials, which adopts the same preparation steps as in Example 1, except that in step (2), the temperature is increased to 900°C at a rate of 5°C / min (higher than the 600-800°C range specified in this application), and held at that temperature for 24 hours, while the other operations and preparation parameters remain unchanged.

[0111] Comparative Example 8

[0112] This comparative example provides an example of another method for preparing lithium-rich lithium iron phosphate supplementary materials, which adopts the same preparation steps as in Example 1, except that in step (2), the temperature is increased to 700°C at a rate of 5°C / min and held for 10h (lower than the 20-30h range specified in this application), while the other operations and preparation parameters remain unchanged.

[0113] Comparative Example 9

[0114] This comparative example provides an example of another method for preparing lithium iron ferrite supplemental materials, which adopts the same preparation steps as in Example 1, except that in step (3), a protective gas is not introduced into the ball mill jar (i.e., the ball milling is carried out in an air atmosphere), and the other operations and preparation parameters remain unchanged.

[0115] Performance testing:

[0116] 1. Laser particle size analyzer detection

[0117] The particle size distribution of the samples was tested using a laser particle size analyzer to obtain the D10, D50, and D90 particle size parameters. Before testing, the prepared lithium-rich lithium iron ferrite supplementary material was added to a dispersion medium and ultrasonically dispersed to ensure uniform dispersion before detection. During the test, the particle size distribution curve of the samples was recorded, and the particle size distribution span from D90 to D10 was calculated to characterize the concentration of the sample particle size distribution.

[0118] Table 1. Particle size distribution of the examples and comparative examples

[0119]

[0120] According to Table 1, the D50 particle size of the lithium iron phosphate supplementary material in this application embodiment is between 11 μm and 35 μm, with a particle size distribution span between 6 μm and 20 μm. The peak shape is symmetrical and uniformly dispersed, indicating good particle size control. Compared to Example 1 (D50 = 15 μm, span 8 μm, symmetrical peak distribution with concentrated peaks, uniform particle dispersion without agglomeration), Comparative Example 1 omitted the ball milling step, resulting in an increase in D50 particle size to 42 μm, a particle size span of 22 μm, a significant rightward shift and widening of the peak shape, obvious agglomeration, coarse particles, and significant agglomeration. In Comparative Example 2, the ball milling time was increased to 10 h, resulting in a decrease in D50 to 9 μm, an increase in span to 12 μm, a leftward shift of the main peak, and the appearance of fine particle agglomeration. In Comparative Example 3, the ball-to-material ratio was increased to 30:1, resulting in a decrease in D50 to 8 μm, a span of 14 μm, a leftward shift of the main peak, and a dispersed distribution, with secondary agglomeration of fine particles. Comparative Example 4: When the heating rate was reduced to 1℃ / min, D50 = 17μm, span 12μm, peak shape slightly shifted to the right and wider, dispersibility was average; Comparative Example 5: When the heating rate was increased to 10℃ / min, D50 = 16μm, span 13μm, peak shape slightly shifted to the right and local agglomeration occurred; Comparative Example 6: When the sintering temperature was reduced to 500℃, D50 = 10μm, span 16μm, peak shape shifted to the left and wider, fine particles adhered. In Comparative Example 7, the sintering temperature was increased to 900℃, resulting in a D50 of 28μm and a span of 18μm. The peak shape was significantly shifted to the right and became wider, indicating severe sintering and agglomeration. In Comparative Example 8, the holding time was reduced to 10h, resulting in a D50 of 16μm and a span of 12μm. The peak shape was slightly shifted to the right and became wider, indicating moderate dispersibility. In Comparative Example 9, the ball milling atmosphere was changed to air, resulting in a D50 of 20μm and a span of 16μm. The peak shape was shifted to the right and became wider, indicating surface reaction, adhesion, and agglomeration of particles.

[0121] Figure 1 The graph shows a comparison of the particle size distribution curves of the lithium iron phosphate supplementary materials in Examples 1-5. The horizontal axis represents the particle size (μm), and the vertical axis represents the particle volume fraction (%). The distribution curve of Example 1 shows a symmetrical single-peak distribution with the peak concentrated around 15μm, indicating that the particle size distribution is uniform. The peak values ​​of the curves of Examples 2 and 4 are biased to the right, indicating that the proportion of large-diameter particles is relatively increased. The peak values ​​of the curves of Examples 3 and 5 are biased to the left, but the peak intensity is low.

[0122] 2. Battery performance

[0123] The lithium-rich lithium iron ferrite supplementary material prepared using the examples or comparative examples was subjected to half-cell performance testing. The lithium-rich lithium iron ferrite supplementary material, conductive agent, and binder were mixed at a mass ratio of 8:1:1, wherein the conductive agent was acetylene black (Super P), the binder was polyvinylidene fluoride (PVDF), and an appropriate amount of N-methylpyrrolidone (NMP) was added to prepare a slurry. The slurry was then uniformly coated onto the surface of an aluminum foil current collector. The coated electrode was dried, rolled, and punched to obtain the positive electrode.

[0124] Using the aforementioned positive electrode as the working electrode, a lithium metal sheet as the counter electrode, a polyolefin membrane as the separator, and a 1 mol / L LiPF6 EC / DEC / EMC mixed solution as the electrolyte, wherein the volume ratio of EC, DEC, and EMC is 1:1:1, a CR2032 type coin cell was assembled in an inert atmosphere glove box. After assembly, a constant current charge-discharge test was performed after standing. The test voltage range was 2.0V-4.3V, and the test rate was 0.1C, where 1C is calculated as 700 mAh / g. The active lithium release capacity and lithium replenishment performance of the lithium-rich lithium iron phosphate supplementation material were evaluated by the specific capacity of the first charge.

[0125] To evaluate the application effect of the lithium-rich lithium iron phosphate supplementary material of this application as a cathode lithium supplement agent in lithium-ion batteries, the lithium-rich lithium iron phosphate supplementary material was added to a lithium iron phosphate cathode for full-cell testing. Specifically, the amount of the lithium-rich lithium iron phosphate supplementary material added was 3 wt% based on the total mass of the lithium iron phosphate cathode active material.

[0126] In the positive electrode slurry, lithium iron phosphate, lithium iron phosphate supplementary material, conductive agent and binder are mixed in a mass ratio of 91:3:3:3. The conductive agent is SuperP and the binder is polyvinylidene fluoride (PVDF). An appropriate amount of NMP is added to make a slurry, which is then coated on the surface of an aluminum foil current collector. After drying, rolling and punching, a lithium iron phosphate positive electrode sheet is obtained.

[0127] The negative electrode is a graphite negative electrode sheet. In the graphite negative electrode slurry, graphite active material, conductive agent, and binder are formulated according to the commonly used ratios in commercial lithium-ion batteries. Preferably, the mass ratio of graphite, conductive agent, and binder is 95:1.5:3.5, wherein the conductive agent is conductive carbon black, and the binder is a styrene-butadiene rubber / sodium carboxymethyl cellulose (SBR / CMC) system. The resulting slurry is coated onto the surface of a copper foil current collector, and after drying, rolling, and punching, a graphite negative electrode sheet is obtained.

[0128] A lithium-ion full battery was assembled using the lithium iron phosphate positive electrode and graphite negative electrode, with a polyolefin separator and a 1 mol / L LiPF6 EC / DEC / EMC mixed solution as the electrolyte. After assembly, the battery underwent settling and formation processes, followed by charge-discharge testing. Preferably, the test voltage range was 2.5V-4.2V. The lithium-rich lithium iron phosphate supplementation material was evaluated for its lithium-ion battery supplementation effect by comparing the initial charge-discharge capacity, initial coulombic efficiency, and cycle performance of the full battery.

[0129] Table 2 Performance Test Results

[0130]

[0131] According to Table 2, the lithium replenishment material in this embodiment has an initial charge specific capacity of 621.7 mAh / g-700.9 mAh / g, an ICE of 98.5%-99.7% for the full battery after adding 3%, an initial discharge specific capacity of 141.2-147.0 mAh / g, and a retention rate of 85.1%-91.2% after 500 cycles, demonstrating good lithium replenishment performance. Compared to Example 1 (initial charge specific capacity 700.9 mAh / g), the lithium replenishment effect is significantly better. The ball milling step in Comparative Example 1 was omitted, resulting in a decrease in the initial charge specific capacity to 581.6 mAh / g. Comparative Examples 2 and 3 changed the ball milling conditions, increasing the milling time to 10 h and the ball-to-material ratio to 30:1, respectively, leading to a decrease in the initial charge specific capacity and retention rate. Comparative Examples 4 and 5 changed the heating rate, adjusting it to 1℃ / min and 10℃ / min, respectively. In Comparative Example 4, changing the heating rate to 1℃ / min resulted in a decrease in the initial charge specific capacity to 639.4 mAh / g, ICE to 98.8%, and air retention rate to 90.8%. In Comparative Example 5, changing the heating rate to 10℃ / min resulted in a decrease in the initial charge specific capacity to 631.2 mAh / g, ICE to 98.6%, and air retention rate to 2.0%. The sintering temperature of Comparative Example 6 was changed to 500℃, resulting in a decrease in the first charge specific capacity to 512.8 mAh / g, ICE to 97.5%, cycle retention rate to 79.8%, and air retention rate to 78.5%. The sintering temperature of Comparative Example 7 was changed to 900℃, resulting in a decrease in the first charge specific capacity to 558.4 mAh / g, ICE to 97.9%, cycle retention rate to 81.2%, and air retention rate to 81.7%. The holding time of Comparative Example 8 was changed to 10h, resulting in a decrease in the first charge specific capacity to 618.6 mAh / g, ICE to 98.4%, and air retention rate to 88.2%. The ball milling atmosphere of Comparative Example 9 was changed to air (without protective gas), resulting in a first charge specific capacity of only 13.4 mAh / g, an air retention rate of only 1.9%, ICE to 97.2%, and cycle retention rate to 80.5%.

[0132] The technical features of the above-described embodiments and examples can be combined in any suitable manner. For the sake of brevity, not all possible combinations of the technical features in the above-described embodiments and examples are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0133] The embodiments described above merely illustrate several implementation methods of this application and should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Furthermore, it should be understood that after reading the above teachings, those skilled in the art can make various alterations or modifications to this application, and the equivalent forms obtained also fall within the protection scope of this application. It should also be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the protection scope of the appended claims. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing lithium-rich lithium iron phosphate supplementary materials, characterized in that, Includes the following steps: A Li5FeO4 precursor was prepared by mixing a lithium source and an iron source. The Li5FeO4 precursor is heated to a first temperature at a first rate in an air atmosphere and held at that temperature for a first time to obtain Li5FeO4 powder; the first rate is 4℃ / min-6℃ / min, the first temperature is 600℃-800℃, and the first time is 20h-30h. The Li5FeO4 powder was ball-milled under a protective gas atmosphere. The ball-milling conditions included a mass ratio of grinding balls to Li5FeO4 powder of (5-20):1 and a ball-milling time of 3-7 hours.

2. The method for preparing lithium-rich lithium iron phosphate supplementary lithium material according to claim 1, characterized in that, The molar ratio of lithium in the lithium source to iron in the iron source is (5-5.2):

1.

3. The preparation method of the lithium-rich lithium iron phosphate supplementary material according to claim 1, characterized in that, The steps of mixing the lithium source and the iron source include: The lithium source and the iron source are stirred in a dry air environment with a dew point ≤ -30℃.

4. The preparation method of the lithium-rich lithium iron phosphate supplementary material according to claim 3, characterized in that, The stirring conditions include: a stirring speed of 200 rpm to 400 rpm and a stirring time of 20 min to 40 min.

5. The method for preparing lithium-rich lithium iron phosphate supplementary lithium material according to claim 1, characterized in that, The step of ball milling the Li5FeO4 powder under a protective gas atmosphere includes: The Li5FeO4 powder is placed in a ball mill jar with a sealing component, and the air inside the ball mill jar is replaced with the protective gas; After the replacement is completed, the ball mill jar is sealed by the sealing component, and then ball milling is performed.

6. The method for preparing lithium-rich lithium iron phosphate supplementary lithium material according to claim 5, characterized in that, The number of replacements is 1-5, and the duration of each replacement is 5-10 minutes; and / or, After the air inside the ball mill jar is replaced with the protective gas, the concentration of the protective gas inside the ball mill jar is ≥99.99%, and the dew point is ≤-40℃.

7. The method for preparing lithium-rich lithium iron phosphate supplementary lithium material according to any one of claims 1-6, characterized in that, The conditions for ball milling also include: using zirconia balls as the milling medium and milling speed of 400 rpm-500 rpm; Optionally, the diameter of the zirconia spheres is 4mm-6mm.

8. A lithium-rich lithium iron phosphate supplementary material, characterized in that, The lithium-rich lithium ferrite supplementary material is prepared by the method described in any one of claims 1-7.

9. The lithium-rich lithium iron phosphate supplementary material according to claim 8, characterized in that, The D50 particle size of the lithium iron ferrite supplemental material is 12μm-30μm; and / or, The difference between the D90 and D10 particle sizes of the lithium iron ferrite supplementary material is ≤20μm.

10. The application of the lithium-rich lithium iron phosphate supplementary material as a positive electrode lithium supplementary agent in lithium-ion batteries according to claim 8 or 9.

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