Lithium iron phosphate powder and preparation method thereof
The preparation of lithium iron phosphate powder with three peak particle size distribution through composite precursors solves the problem of low compaction density of lithium iron phosphate, and achieves the effect of high compaction density and high capacity. At the same time, the production process is simplified and energy consumption and cost are reduced.
Patent Information
- Application Number
- CN202510561673.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-30
- Publication Date
- 2025-07-04
AI Technical Summary
In the prior art, the compaction density of lithium iron phosphate is low, resulting in limited increase in battery volume energy density, and the multi-batch sanding and multiple sintering processes are complex and costly.
The composite precursors include amorphous iron phosphate, iron phosphate dihydrate and iron phosphate. Through a single sanding and sintering, lithium iron phosphate powder with a three-peak distribution of particle size is prepared to form a large particle framework and a tightly packed structure between small and medium particles.
The compaction density and discharge specific capacity of lithium iron phosphate powder are improved, the production process is simplified, and energy consumption and cost are reduced.
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of cathode materials, and more particularly, to lithium iron phosphate powder and a preparation method thereof. Background Art
[0002] Lithium iron phosphate (LiFePO, LFP) has become the mainstream cathode material for power batteries due to its high safety, long cycle life, and low cost. However, its relatively low tap density (usually 2.3 - 2.5 g / cc) limits the further improvement of the volumetric energy density of the battery. In the prior art, the core strategies for increasing the tap density include: ① Particle size grading technology: achieving close packing by mixing particles of different sizes, but different-sized precursors need to be separately sanded, with many sanding batches, and multiple batches of slurries are combined later, resulting in a complex process and high costs; ② Optimization of the sintering mechanism: optimizing the material tap density through a two-step sintering process. The main defects of the prior art are that multiple batches of sanding or multiple sinterings lead to increased energy consumption.
[0003] In view of this, in order to simplify the production process, the present invention is specifically proposed. Summary of the Invention
[0004] The purpose of the present invention is to provide lithium iron phosphate powder and a preparation method thereof, which can improve the tap density while simplifying the process and reducing the number of sanding and sintering times.
[0005] The present invention is implemented as follows:
[0006] In a first aspect, the present invention provides a lithium iron phosphate powder, in which the particle size distribution curve of the lithium iron phosphate powder has a first particle size peak, a second particle size peak, and a third particle size peak.
[0007] The peak particle size range of the first particle size peak is 0.05 - 1.00 μm, the peak particle size range of the second particle size peak is 1.00 - 5.00 μm, and the peak particle size range of the third particle size peak is 8.00 - 18.00 μm.
[0008] In the lithium iron phosphate powder, the mass fraction of particles with a particle size of 0.05 - 1.00 μm is 25% - 40%, the mass fraction of particles with a particle size of 1.00 - 5.00 μm is 35% - 55%, and the mass fraction of particles with a particle size of 8.00 - 18.00 μm is 5% - 30%.
[0009] In an alternative embodiment, the Dv50 of the lithium iron phosphate powder is 0.79 μm - 1.4 μm;
[0010] and / or, the tap density of the lithium iron phosphate powder is 2.55 g / cc - 2.65 g / cc;
[0011] And / or, the discharge specific capacity of the lithium iron phosphate powder is 155 mAh / g - 161 mAh / g.
[0012] In a second aspect, the present invention provides a method for preparing lithium iron phosphate powder, comprising:
[0013] Performing sand milling on a mixture comprising a composite precursor, a lithium source, and a carbon source to obtain a mixed slurry, wherein the composite precursor comprises amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate;
[0014] Performing granulation and sintering on the mixed slurry in sequence to obtain the lithium iron phosphate powder.
[0015] In an optional embodiment, the mass ratio of amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate in the composite precursor is (1.5 - 3.5):(0.5 - 2):1.
[0016] In an optional embodiment, titanium is doped in the amorphous iron phosphate;
[0017] And / or, titanium is doped in the iron phosphate dihydrate;
[0018] And / or, titanium is doped in the anhydrous iron phosphate.
[0019] In an optional embodiment, the content of titanium element in the amorphous iron phosphate is 4000 ppm - 10000 ppm;
[0020] And / or, the content of titanium element in the iron phosphate dihydrate is 3000 ppm - 8000 ppm;
[0021] And / or, the content of titanium element in the anhydrous iron phosphate is 1500 ppm - 4500 ppm.
[0022] In an optional embodiment, the method for preparing the composite precursor comprises: wet mixing or dry mixing amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate in proportion;
[0023] And / or, the amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate are all synthesized by a liquid phase method.
[0024] In an optional embodiment, the D50 of the mixed slurry is 0.3 μm - 1.2 μm, and there are three peaks in the particle size distribution curve of the mixed slurry.
[0025] In an optional embodiment, the solid content in the mixed slurry is 35% - 45%;
[0026] And / or, the granulation method is spray granulation.
[0027] In an alternative embodiment, the sintering temperature is 700°C - 850°C, the sintering time is 10h - 20h, and the sintering atmosphere is an inert atmosphere.
[0028] The present invention has the following beneficial effects:
[0029] The lithium iron phosphate powder in this application satisfies a three-peak particle size distribution. When the lithium iron phosphate powder satisfies the three-peak particle size distribution conditions in this application, the lithium iron phosphate powder exhibits a structure of large particle skeletons and close packing of small and medium particles, which is beneficial to improving the tap density and thus beneficial to improving the volumetric specific capacity. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.
[0031] Figure 1 Particle size distribution curve of the lithium iron phosphate cathode powder prepared in Example 1;
[0032] Figure 2 SEM image of the lithium iron phosphate cathode powder prepared in Example 1;
[0033] Figure 3 Particle size distribution curve of the lithium iron phosphate cathode powder prepared in Example 2;
[0034] Figure 4 Particle size distribution curve of the lithium iron phosphate cathode powder prepared in Comparative Example 5;
[0035] Figure 5 Particle size distribution curve of the lithium iron phosphate cathode powder prepared in Comparative Example 7. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchases.
[0037] The embodiments of the present invention provide a lithium iron phosphate powder. There are a first particle size peak, a second particle size peak, and a third particle size peak in the particle size distribution curve of the lithium iron phosphate powder.
[0038] The peak-to-peak particle size range of the first particle size peak is 0.05 - 1.00 μm, the peak-to-peak particle size range of the second particle size peak is 1.00 - 5.00 μm, and the peak-to-peak particle size range of the third particle size peak is 8.00 - 18.00 μm;
[0039] In the lithium iron phosphate powder, the mass fraction of particles with a particle size of 0.05 - 1.00 μm is 25% - 40%, the mass fraction of particles with a particle size of 1.00 - 5.00 μm is 35% - 55%, and the mass fraction of particles with a particle size of 8.00 - 18.00 μm is 5% - 30%.
[0040] The lithium iron phosphate powder in this application satisfies a three-peak particle size distribution. When the lithium iron phosphate powder satisfies the above three-peak particle size distribution conditions, the SEM morphology of the lithium iron phosphate powder presents a structure of large particle skeletons and closely packed small and medium particles, which is beneficial to improving the tap density and further beneficial to improving the volumetric specific capacity.
[0041] In an alternative embodiment, the Dv50 of the lithium iron phosphate powder is 0.79 μm - 1.4 μm, for example, it can be 0.79 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm;
[0042] And / or, the tap density of the lithium iron phosphate powder is 2.55 g / cc - 2.65 g / cc, for example, it can be 2.55 g / cc, 2.57 g / cc, 2.59 g / cc, 2.61 g / cc, 2.63 g / cc, 2.65 g / cc;
[0043] And / or, the discharge specific capacity of the lithium iron phosphate powder is 155 mAh / g - 161 mAh / g, for example, it can be 155 mAh / g, 157 mAh / g, 159 mAh / g, 161 mAh / g.
[0044] The embodiment of the present invention also provides a preparation method of lithium iron phosphate powder, including:
[0045] Performing sand milling on a mixture including a composite precursor, a lithium source, and a carbon source to obtain a mixed slurry, where the composite precursor includes amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate;
[0046] Performing granulation and sintering on the mixed slurry in sequence to obtain the lithium iron phosphate powder.
[0047] In this application, the precursor raw material used for preparing lithium phosphate powder is a composite precursor, which includes amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate. Specifically: amorphous iron phosphate has an amorphous structure, high reaction activity, and is easily ground and broken into small particles (particle size < 0.3 μm), which can fill the gaps between large particles and is beneficial to improving the packing density; iron phosphate dihydrate (FePO₄·2H₂O) can form medium particles (particle size 0.5 - 2 μm) after grinding; anhydrous iron phosphate (FePO₄) has a high crystallinity, can retain larger particles (particle size 1 - 5 μm) after grinding, and has a higher strength after sintering, which can be used as a skeleton to support the compaction structure.
[0048] In the method of this application, the mechanical strengths of the three forms of iron phosphate in the raw materials are different (amorphous < dihydrate < anhydrous). When grinding, soft particles are preferentially broken, and a three-peak distribution is achieved through single grinding, avoiding the need for multi-batch grinding and mixing of slurries with different particle sizes in the traditional grading process; a mixed slurry with a three-peak distribution can be obtained, which is beneficial to the SEM morphology of the lithium iron phosphate cathode powder presenting a structure of large particle skeletons and closely packed medium and small particles, and further beneficial to improving the compaction density and further beneficial to improving the volume specific capacity.
[0049] In an alternative embodiment, the mass ratio of amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate in the composite precursor is (1.5 - 3.5):(0.5 - 2):1, for example, it can be 1.5:2:1, 2:1.5:1, 3:1:1, 3.5:0.5:1, etc.
[0050] The ratio of amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate in the composite precursor affects the particle size distribution of the prepared lithium iron phosphate powder, and further affects the compaction density of the lithium iron phosphate powder. In this application, amorphous iron phosphate provides nano-scale particles to fill the voids, iron phosphate dihydrate forms medium particles, and anhydrous iron phosphate serves as a skeleton support. The three work together to achieve "the densest packing". Under the same other conditions, if the proportion of amorphous iron phosphate is too high, the compaction density of the prepared lithium iron phosphate powder will be low; if the proportion of anhydrous iron phosphate is too high, the capacity will be low; if only anhydrous iron phosphate is used, although the specific capacity can be increased to a certain extent, the compaction density will be low. Therefore, reasonably selecting the proportion of amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate in the composite precursor is beneficial to taking into account the high compaction density and high capacity of lithium iron phosphate.
[0051] In an alternative embodiment, titanium is doped in the amorphous iron phosphate;
[0052] and / or, titanium is doped in the iron phosphate dihydrate;
[0053] and / or, titanium is doped in the anhydrous iron phosphate.
[0054] In titanium-doped iron phosphate, Ti can partially replace Fe to form LiFe 1-x Ti x PO4 solid solution, which is beneficial to improving electrical conductivity and structural stability; at the same time, Ti doping can refine LiFePO grains, avoid excessive grain growth during the sintering process, and is conducive to maintaining the multi-level grading structure.
[0055] In an alternative embodiment, the content of titanium element in the amorphous iron phosphate is 4000 ppm - 10000 ppm, for example, it can be 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm, 10000 ppm;
[0056] And / or, the content of titanium element in the iron phosphate dihydrate is 3000 ppm - 8000 ppm, for example, it can be 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm;
[0057] And / or, the content of titanium element in the anhydrous iron phosphate is 1500 ppm - 4500 ppm, for example, it can be 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm.
[0058] By using a composite precursor composed of Ti-doped amorphous iron phosphate, Ti-doped iron phosphate dihydrate, and Ti-doped anhydrous iron phosphate, it is possible to obtain lithium iron phosphate powder that meets the above requirements for the three-peak particle size distribution under the conditions of no secondary sintering and multi-batch sanding, which is beneficial to achieving both high compaction and high capacity performance. Specifically, since amorphous iron phosphate mainly forms small particles, in order to inhibit the excessive growth of lithium iron phosphate formed by amorphous iron phosphate during the sintering process, the doping amount of Ti in amorphous iron phosphate is relatively large; conversely, anhydrous iron phosphate mainly forms a large particle skeleton, and too high a doping amount of Ti will overly inhibit the growth of lithium iron phosphate formed by anhydrous iron phosphate during the sintering process to form large particles, so the doping amount of Ti is relatively low; similarly, in order to control the particle size of lithium iron phosphate formed by iron phosphate dihydrate, the doping amount of Ti therein may be appropriate.
[0059] In an alternative embodiment, the preparation method of the composite precursor includes: dry-mixing or wet-mixing amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate in proportion; that is, amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate can be mixed under dry conditions, or a solvent can be added to the mixture of amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate for mixing to obtain the composite precursor.
[0060] In an alternative embodiment, the amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate are all synthesized by a liquid-phase method. Specifically, they can be prepared by processes such as the ammonium method or the sodium method.
[0061] In an alternative embodiment, the D50 of the mixed slurry is 0.3 μm - 1.2 μm. For example, it can be 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, and the particle size distribution curve of the mixed slurry contains three peaks.
[0062] In an alternative embodiment, the solid content in the mixed slurry is 35% - 45%. For example, it can be 35%, 37%, 39%, 41%, 43%, 45%; the mixed slurry includes a composite precursor, a lithium source, a carbon source, and water.
[0063] And / or, the granulation method is spray granulation.
[0064] In an alternative embodiment, the sintering temperature is 700°C - 850°C. For example, it can be 700°C, 730°C, 760°C, 790°C, 820°C, 850°C, the sintering time is 10 h - 20 h. For example, it can be 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, and the sintering atmosphere is an inert atmosphere.
[0065] The features and properties of the present invention will be further described in detail below in conjunction with examples.
[0066] Example 1:
[0067] This example provides a method for preparing lithium iron phosphate powder, including the following specific steps:
[0068] (1) Uniformly mix 37.5 kg of amorphous iron phosphate (Ti content 8133 ppm), 22.5 kg of iron phosphate dihydrate (Ti content 5514 ppm), 12 kg of anhydrous iron phosphate (Ti content 2741 ppm), 14.85 kg of lithium carbonate, 3.11 kg of glucose, 4.52 kg of polyethylene glycol 1500, and 140 kg of pure water for 1.5 h, and then grind it to Dv50: 0.45 μm to obtain a mixed slurry with a particle size distribution curve containing three peaks. The solid content in the mixed slurry is 40%;
[0069] (2) After spray granulating the mixed slurry, calcine it at 750°C for 15 h in a nitrogen atmosphere, and then pulverize and screen it to obtain lithium iron phosphate cathode powder with a tap density of 2.62 g / cm 3 The particle size distribution curve is as shown in Figure 1 shown, and the morphology is as shown in Figure 2 the SEM image.
[0070] From Figure 1 it can be seen that the particle size distribution curve of the synthesized lithium iron phosphate shows a three-peak distribution, forming an effect of particle size grading. From Figure 2 it can be seen that the lithium iron phosphate powder is spherical particles, with both large and small particles. The small particles are filled in the gaps between the large particles to form a close-packed structure.
[0071] Example 2:
[0072] This example provides a preparation method of lithium iron phosphate powder, including the following specific steps:
[0073] (1) Uniformly mix 45 kg of amorphous iron phosphate (Ti content 8133 ppm), 15 kg of iron phosphate dihydrate (Ti content 5514 ppm), 12 kg of anhydrous iron phosphate (Ti content 2741 ppm), 14.85 kg of lithium carbonate, 3.11 kg of glucose, 4.52 kg of polyethylene glycol 1500 and 140 kg of pure water for 1.5 h, and grind to Dv50: 0.43 μm to obtain a mixed slurry with three peaks in the particle size distribution curve. The solid content in the mixed slurry is 40%.
[0074] (2) Spray granulate the mixed slurry and then calcine it at 750 °C for 15 h in a nitrogen atmosphere. After pulverizing and sieving, a lithium iron phosphate cathode powder with a tap density of 2.57 g / cm 3 is obtained.
[0075] From Figure 3 it can be seen that the particle size distribution curve of the synthesized lithium iron phosphate also shows a three-peak distribution, forming an effect of particle size grading.
[0076] Example 3:
[0077] This example provides a preparation method of lithium iron phosphate powder, including the following specific steps:
[0078] (1) Uniformly mix 30 kg of amorphous iron phosphate (Ti content 8133 ppm), 22.5 kg of iron phosphate dihydrate (Ti content 5514 ppm), 18 kg of anhydrous iron phosphate (Ti content 2741 ppm), 14.85 kg of lithium carbonate, 3.11 kg of glucose, 4.52 kg of polyethylene glycol 1500 and 140 kg of pure water for 1.5 h, and grind to Dv50: 0.43 μm to obtain a mixed slurry with three peaks in the particle size distribution curve. The solid content in the mixed slurry is 40%.
[0079] (2) Spray granulate the mixed slurry and then calcine it at 780 °C for 20 h in a nitrogen atmosphere. After pulverizing and sieving, a lithium iron phosphate cathode powder with a tap density of 2.64 g / cm 3 is obtained.
[0080] Example 4
[0081] This embodiment provides a method for preparing lithium iron phosphate powder, which includes the following steps:
[0082] (1) Uniformly mix 37.5 kg of amorphous iron phosphate (Ti content 8133 ppm), 15 kg of iron phosphate dihydrate (Ti content 5514 ppm), 18 kg of anhydrous iron phosphate (Ti content 2741 ppm), 15.01 kg of lithium carbonate, 3.41 kg of glucose, 3.99 kg of polyethylene glycol 1500, and 140 kg of pure water for 1.5 h, and then grind it to Dv50: 0.38 μm to obtain a mixed slurry with three peaks in the particle size distribution curve. The solid content in the mixed slurry is 40%.
[0083] (2) Spray granulate the mixed slurry and then calcine it in a nitrogen atmosphere at 810 °C for 18 h. After crushing and screening, a lithium iron phosphate cathode powder with a tap density of 2.60 g / cm 3 is obtained.
[0084] Comparative Example 1
[0085] This comparative example provides a method for preparing lithium iron phosphate. The difference from Example 1 is that in the composite precursor in step (1), both iron phosphate dihydrate and anhydrous iron phosphate are replaced with amorphous iron phosphate (Ti content 8133 ppm), so that the mass ratio of iron element to lithium element in the mixed slurry remains unchanged.
[0086] Comparative Example 2
[0087] This comparative example provides a method for preparing lithium iron phosphate. The difference in the preparation method from Example 1 is that in the composite precursor in step (1), both amorphous iron phosphate and anhydrous iron phosphate are replaced with iron phosphate dihydrate (Ti content 5514 ppm), so that the mass ratio of iron element to lithium element in the mixed slurry remains unchanged.
[0088] Comparative Example 3
[0089] This comparative example provides a method for preparing lithium iron phosphate. The difference in the preparation method from Example 1 is that in the composite precursor in step (1), both amorphous iron phosphate and iron phosphate dihydrate are replaced with anhydrous iron phosphate (Ti content 2741 ppm), so that the mass ratio of iron element to lithium element in the mixed slurry remains unchanged.
[0090] Comparative Example 4
[0091] This comparative example provides a method for preparing lithium iron phosphate. The difference in the preparation method from Example 1 is that in the composite precursor in step (1), amorphous iron phosphate, anhydrous iron phosphate, and iron phosphate dihydrate are all replaced with anhydrous iron phosphate (Ti content 0 ppm), so that the mass ratio of iron element to lithium element in the mixed slurry remains unchanged.
[0092] Comparative Example 5
[0093] This comparative example provides a method for preparing lithium iron phosphate. The difference between the preparation method and that of Example 1 is that: in the composite precursor in step (1), Ti is not doped in amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate, and the mass ratio of iron element to lithium element in the mixed slurry remains unchanged.
[0094] The particle size distribution curve of the lithium iron phosphate prepared in this comparative example is as Figure 4 shown. It can be seen from Figure 4 that the particle size distribution curve of lithium iron phosphate fails to show an obvious three-peak distribution, and the three distribution peaks partially overlap. The overall particle size is relatively large, mainly because Ti is not doped, which fails to inhibit particle growth, and the particle size distribution does not reach the ideal effect.
[0095] Comparative Example 6
[0096] This comparative example provides a method for preparing lithium iron phosphate. The difference between the preparation method and that of Comparative Example 1 is that: the mass ratio of iron element to lithium element in the mixed slurry in step (1) remains unchanged, and the mass ratio of amorphous iron phosphate (Ti content 8133 ppm), iron phosphate dihydrate (Ti content 5514 ppm), and anhydrous iron phosphate (Ti content 2741 ppm) is 60.0:7.5:6.0.
[0097] Comparative Example 7
[0098] This comparative example provides a method for preparing lithium iron phosphate. The difference between the preparation method and that of Example 1 is that: the mass ratio of iron element to lithium element in the mixed slurry in step (1) remains unchanged, and the mass ratio of amorphous iron phosphate (Ti content 8133 ppm), iron phosphate dihydrate (Ti content 5514 ppm), and anhydrous iron phosphate (Ti content 2741 ppm) is 46.9:28.1:0. The particle size distribution curve of the lithium iron phosphate prepared in this comparative example is as Figure 5 shown.
[0099] Comparative Example 8
[0100] This comparative example provides a method for preparing lithium iron phosphate. The difference between the preparation method and that of Example 1 is that: the mass ratio of iron element to lithium element in the mixed slurry in step (1) remains unchanged, and the mass ratio of amorphous iron phosphate (Ti content 8133 ppm), iron phosphate dihydrate (Ti content 5514 ppm), and anhydrous iron phosphate (Ti content 2741 ppm) is 53.6:0:17.2.
[0101] Comparative Example 9
[0102] This comparative example provides a method for preparing lithium iron phosphate. The difference between the preparation method and that of Example 1 is that: in the mixed slurry of step (1), the mass ratio of iron element to lithium element remains unchanged, and the mass ratio of amorphous iron phosphate (Ti content 8133 ppm), iron phosphate dihydrate (Ti content 5514 ppm), and anhydrous iron phosphate (Ti content 2741 ppm) is 0:45.0:24.0.
[0103] Comparative Example 10
[0104] This comparative example provides a method for preparing lithium iron phosphate. The difference between the preparation method and that of Example 1 is that: in the mixed slurry of step (1), the mass ratio of iron element to lithium element remains unchanged, and the mass ratio of amorphous iron phosphate (Ti content 2741 ppm), iron phosphate dihydrate (Ti content 2741 ppm), and anhydrous iron phosphate (Ti content 2741 ppm) is 37.5:22.5:12.0.
[0105] Comparative Example 11
[0106] This comparative example provides a method for preparing lithium iron phosphate. The difference between the preparation method and that of Example 1 is that: in the mixed slurry of step (1), the mass ratio of iron element to lithium element remains unchanged, and the mass ratio of amorphous iron phosphate (Ti content 5514 ppm), iron phosphate dihydrate (Ti content 5514 ppm), and anhydrous iron phosphate (Ti content 5514 ppm) is 37.5:22.5:12.0.
[0107] Comparative Example 12
[0108] This comparative example provides a method for preparing lithium iron phosphate. The difference between the preparation method and that of Example 1 is that: in the mixed slurry of step (1), the mass ratio of iron element to lithium element remains unchanged, and the mass ratio of amorphous iron phosphate (Ti content 8133 ppm), iron phosphate dihydrate (Ti content 8133 ppm), and anhydrous iron phosphate (Ti content 8133 ppm) is 37.5:22.5:12.0.
[0109] The lithium iron phosphate cathode materials prepared in each example and comparative example were made into electrode sheets and assembled into batteries, and the electrochemical performance of the batteries was tested. Specifically:
[0110] The production of electrode sheets and the assembly of batteries include:
[0111] The lithium iron phosphate material is mixed evenly with conductive carbon black, polyvinylidene fluoride, and N-methylpyrrolidone by a high-speed mixer. The mass ratio of the lithium iron phosphate material, conductive carbon black, and polyvinylidene fluoride is 92:4:4. Then, an automatic coater is used to coat, roll, form, and assemble on the aluminum foil to obtain the positive electrode sheet. Using graphite as the negative electrode, the positive electrode case, negative electrode case, positive electrode sheet, negative electrode sheet, separator, and electrolyte are assembled into a button battery according to requirements, and corresponding charge and discharge tests are carried out at room temperature. The test voltage range is 2.0 - 3.75V.
[0112] The performance tests include:
[0113] At room temperature of 25°C, the initial discharge specific capacity and initial charge-discharge efficiency are tested at a charge-discharge voltage of 2.0 - 3.75V and an initial charge-discharge rate of 0.1C.
[0114] At room temperature of 25°C, the discharge specific capacity is tested at a charge-discharge voltage of 2.0 - 3.75V and a charge-discharge rate of 1C.
[0115] The test results are shown in Table 1.
[0116] Table 1
[0117]
[0118]
[0119] As can be seen from Table 1, the comprehensive compaction and capacity performance of the lithium iron phosphate products prepared in the examples are significantly better than those in the comparative examples, especially in Examples 1 and 4. In Comparative Examples 1, 2, and 3, single iron phosphate was used as the precursor, resulting in a relatively low compaction performance. Moreover, due to the different activities of the three iron phosphates, the performance of the synthesized materials varied greatly. In Comparative Example 4, anhydrous iron phosphate was used as the iron source, and due to the absence of Ti doping, both the compaction performance and the capacity were low. In Comparative Example 5, since none of the three precursors were doped with Ti, the amorphous iron phosphate and dihydrate iron phosphate particles grew abnormally. Although the compaction was relatively high, the charge-discharge performance deteriorated. In Comparative Example 6, due to the relatively high proportion of amorphous iron phosphate and many small particles, the grading effect was not obvious, resulting in the filling density of large and small particles unable to meet the requirements of high-compaction iron phosphate, so the compaction performance was lower than that of the examples. In Comparative Example 7, since anhydrous iron phosphate was not used and there were many small particles, the compaction density of the synthesized product was low and the capacity was high. In Comparative Examples 8 and 9, anhydrous iron phosphate was used as one of the iron sources, with a certain grading effect, and the compaction was significantly improved compared to Comparative Example 7. In Comparative Example 10, due to the too low Ti doping amount, the abnormal growth of small particles was not inhibited. Although the compaction was slightly higher, the capacity was low. In Comparative Example 11, since the Ti doping amount was not adjusted adaptively according to the change of the iron source, the grading of particles of various sizes was unreasonable, resulting in too low compaction density. In Comparative Example 12, due to the too high anhydrous Ti doping amount, the inhibitory effect on the growth of small particles was obvious, the compaction was low, and the capacity was high. The results of the electrical properties of the lithium iron phosphate cathode material prepared by the present invention show that through the combination of iron phosphates with different activities, the grading control of particles of different particle sizes can be achieved by single-batch material sanding, thereby improving the compaction and capacity performance of the lithium iron phosphate material.
[0120] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.
Claims
1. A lithium iron phosphate powder, characterized in that, In the particle size distribution curve of the lithium iron phosphate powder, there are a first particle size peak, a second particle size peak, and a third particle size peak. The peak particle size range of the first particle size peak is 0.05 - 1.00 μm, the peak particle size range of the second particle size peak is 1.00 - 5.00 μm, and the peak particle size range of the third particle size peak is 8.00 - 18.00 μm. In the lithium iron phosphate powder, the mass fraction of particles with a particle size of 0.05 - 1.00 μm is 25% - 40%, the mass fraction of particles with a particle size of 1.00 - 5.00 μm is 35% - 55%, and the mass fraction of particles with a particle size of 8.00 - 18.00 μm is 5% - 30%.
2. The lithium iron phosphate powder according to claim 1, wherein The Dv50 of the lithium iron phosphate powder is 0.79 μm - 1.4 μm. And / or, the tap density of the lithium iron phosphate powder is 2.55 g / cc - 2.65 g / cc. And / or, the discharge specific capacity of the lithium iron phosphate powder is 155 mAh / g - 161 mAh / g.
3. A method for preparing lithium iron phosphate powder, characterized in that, It includes: Grinding a mixture including a composite precursor, a lithium source, and a carbon source to obtain a mixed slurry, where the composite precursor includes amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate. Performing granulation and sintering on the mixed slurry in sequence to obtain the lithium iron phosphate powder.
4. The preparation method of the lithium iron phosphate powder according to claim 3, characterized in that, The mass ratio of amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate in the composite precursor is (1.5 - 3.5):(0.5 - 2):
1.
5. The preparation method of the lithium iron phosphate powder according to claim 3, wherein, Titanium is doped in the amorphous iron phosphate. And / or, titanium is doped in the iron phosphate dihydrate. And / or, titanium is doped in the anhydrous iron phosphate.
6. The preparation method of the lithium iron phosphate powder according to claim 5, characterized in that, The content of titanium element in the amorphous iron phosphate is 4000 ppm - 10000 ppm. And / or, the content of titanium element in the iron phosphate dihydrate is 3000 ppm - 8000 ppm. And / or, the content of titanium element in the anhydrous iron phosphate is 1500 ppm - 4500 ppm.
7. The preparation method of the lithium iron phosphate powder according to claim 3, wherein, The preparation method of the composite precursor includes: wet - mixing or dry - mixing amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate in proportion. And / or, amorphous iron phosphate, iron phosphate dihydrate, and anhydrous iron phosphate are all synthesized by a liquid - phase method.
8. The method for preparing lithium iron phosphate powder according to claim 3, characterized in that, The D50 of the mixed slurry is 0.3 μm - 1.2 μm, and there are three peaks in the particle size distribution curve of the mixed slurry.
9. The preparation method of the lithium iron phosphate powder according to claim 3, characterized in that, The solid content in the mixed slurry is 35% - 45%. And / or, the granulation method is spray granulation.
10. The preparation method of the lithium iron phosphate powder according to claim 3, characterized in that, The sintering temperature is 700 °C - 850 °C, the sintering time is 10 h - 20 h, and the sintering atmosphere is an inert atmosphere.