Battery-grade iron phosphate as well as preparation method and application thereof

Abstract

The invention discloses battery-grade iron phosphate as well as a preparation method and application thereof. The battery-grade iron phosphate is of a core-shell structure, D50 is 20-40 [mu] m, the core is 50% of an internal area in the radius direction, the shell is the other external area, the porosity of the core is 1%-10%, the porosity of the shell is 30%-70%, and when the battery-grade iron phosphate is used for preparing a lithium iron phosphate material, natural grading can be achieved without iron phosphate compounding; the prepared lithium iron phosphate material has high compaction density.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, to a battery-grade iron phosphate, its preparation method, and its application. Background Technology

[0002] As a core power source in the new energy field, the performance of the cathode material in lithium-ion batteries directly determines the battery's energy density, cycle life, and safety. Lithium iron phosphate (LFP) has become one of the preferred cathode materials for power batteries and energy storage systems due to its advantages such as high theoretical capacity, excellent thermal stability, and low cost. However, the compaction density of traditional LFP materials is generally low, resulting in limited battery volumetric energy density and making it difficult to meet the needs of high-range electric vehicles and compact energy storage devices. Improving compaction density is highly dependent on the physical properties of the precursor iron phosphate. Patents CN117303340A and CN118561257A achieve high-compact LFP by pre-mixing two types of iron phosphate to form a particle size distribution, while patents CN118515253A and CN118324108A achieve high-compact LFP by directly preparing composite iron phosphate. However, these patents all achieve high-compact LFP through particle size distribution, which has disadvantages such as high energy consumption, complex processes, and poor process compatibility.

[0003] Therefore, developing an iron phosphate precursor that has low energy consumption and simple process in the preparation of high-density lithium iron phosphate is of great significance for optimizing the production cost and automating the production of lithium iron phosphate. Summary of the Invention

[0004] To address the above technical problems, this invention provides a battery-grade lithium iron phosphate that can be sintered at low temperatures under high pressure and a method for its preparation, by controlling the microstructure.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] On one hand, the present invention provides a battery-grade iron phosphate, wherein the battery-grade iron phosphate has a core-shell structure with a D50 of 20-40 μm, wherein the core is the inner region of 50% along the radial direction, and the shell is the remaining outer region. The porosity of the core is 1%-10%, for example 2%, 4%, 6%, 8%, and the porosity of the shell is 30%-70%, for example 35%, 40%, 45%, 50%, 55%, 60%, 65%.

[0007] Preferably, the specific surface area of ​​the battery-grade iron phosphate is 2-8 m². 2 / g, for example, 4m 2 / g、6m 2 / g, iron-to-phosphorus ratio is 0.960-0.975, for example 0.965 or 0.970, tap density is 1.0-1.5 g / cm³3 For example, 1.1 g / cm 3 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 .

[0008] On the other hand, the present invention provides a method for preparing battery-grade iron phosphate, the method comprising the following steps:

[0009] S1. Dissolve iron oxide red in phosphoric acid solution to obtain iron phosphate complex solution;

[0010] S2. Dilute the obtained ferric phosphate complex solution, add pure iron and dissolve it to obtain a mixed solution of ferrous dihydrogen phosphate and ferric phosphate complex.

[0011] S3. Heat the obtained mixed solution, add an oxidant while stirring, and after aging the reaction, obtain a reaction slurry;

[0012] S4. The obtained slurry is filtered, washed, further dried and calcined to obtain anhydrous ferric phosphate.

[0013] In some examples of the present invention, the ratio of iron oxide red to phosphoric acid solution in step S1 is 1:(6-10) in terms of the molar ratio of iron oxide red to phosphoric acid, for example 1:7, 1:8, 1:9.

[0014] Preferably, the mass concentration of the phosphoric acid solution is 30-60%, for example 35%, 40%, 45%, 50%, or 55%.

[0015] In some examples of the present invention, in step S2, phosphorus in the solution is diluted with pure water to 15-25 wt%, for example 18 wt%, 20 wt%, 22 wt%, or 24 wt%, based on the phosphoric acid concentration (total phosphorus converted to phosphoric acid); the pure iron is one or more of iron powder, iron sheet, and iron blocks.

[0016] Preferably, the total iron source added in steps S2 and S1, calculated as pure iron, has a molar ratio of 1:(2-4) with the phosphoric acid added in step S1, for example, 1:2.5, 1:3, or 1:3.5, and the molar amount of iron source added in step S2 does not exceed the molar amount of iron oxide added in step S1.

[0017] In some examples of the present invention, in step S3, the reaction temperature is 60-100°C, the oxidant is one or more of hydrogen peroxide solution, air, oxygen, and ozone; the total amount of oxidant added is 1-10 times the molar amount of pure iron in step S2, and the aging temperature is 0-20°C higher than the reaction temperature.

[0018] In some examples of the present invention, in step S4, the washing is performed with deionized water, the drying temperature is 80-200°C, and the drying time is 2-12 hours. The calcination conditions are: calcination at 500-650°C for 3-6 hours.

[0019] The present invention also provides an application of the battery-grade iron phosphate obtained by the method described above in the preparation of high-density lithium iron phosphate.

[0020] The beneficial effects of this invention are as follows: the preparation method of this invention is simple to operate, the reaction conditions are mild, the process flow is short, and it is suitable for large-scale industrial production; this invention prepares ferric phosphate with a sheet-like, closely packed spherical morphology by utilizing the difference in crystallization kinetics between the oxidation precipitation of ferrous phosphate and the decomposition precipitation of the ferric phosphate complex, through the preparation of a mixed solution of ferrous dihydrogen phosphate and ferric phosphate complex. These spherical spheres exhibit a core-shell structure, with a core porosity of 1%-10% and a shell porosity of 30%-70%, and a tap density of 1.0-1.5 g / cm³. 3 The iron phosphate provided by this invention can achieve natural gradation when preparing high-density lithium iron phosphate, without the need for iron phosphate compounding or lithium iron phosphate double sintering process, thus resulting in lower energy consumption and simpler process in production, which is conducive to optimizing lithium iron phosphate production costs and automated production. Attached Figure Description

[0021] Figure 1 The electron microscope image shows the morphology of the iron phosphate prepared in Example 1.

[0022] Figure 2 This is a cross-sectional morphology diagram of the iron phosphate prepared in Example 1.

[0023] Figure 3 This is a cross-sectional morphology diagram of the iron phosphate prepared for Comparative Example 1.

[0024] Figure 4 This is a cross-sectional morphology diagram of the iron phosphate prepared for Comparative Example 2. Detailed Implementation

[0025] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0026] The “range” disclosed herein takes the form of a lower limit and an upper limit. It can consist of one or more lower limits and one or more upper limits. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges that can be defined in this way are inclusive and composable; that is, any lower limit can be combined with any upper limit to form a range.

[0027] In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0028] In this invention, unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0029] The preferred embodiments of the present invention will be described in detail below with reference to specific examples. However, it should be understood that those skilled in the art can make reasonable changes, improvements and combinations to these embodiments without departing from the scope defined by the claims, thereby obtaining new specific implementation methods. These new specific implementation methods obtained through changes, improvements and combinations are also included within the protection scope of the present invention.

[0030] Example 1

[0031] Ferric phosphate was prepared according to the following method:

[0032] S1. Dissolve 500g of iron oxide red in a 50% phosphoric acid solution to obtain an iron phosphate complex solution. The amount of raw materials used is 1:8 based on the molar ratio of iron oxide red to phosphoric acid.

[0033] S2. Based on the phosphorus concentration in the solution as phosphoric acid, add water to dilute the solution to a concentration of 25 wt%, then add 160 g of reduced iron powder and dissolve it to obtain a mixed solution of ferrous dihydrogen phosphate and ferric phosphate complex.

[0034] S3. Heat the obtained solution to 80°C, add 794.81g of 27.5% hydrogen peroxide solution while stirring, and then heat to 90°C to age to obtain the reaction slurry;

[0035] S4. The obtained slurry was filtered and washed with deionized water, dried at 120°C for 6 hours, and calcined at 600°C for 3 hours to obtain anhydrous ferric phosphate.

[0036] The electron microscopic morphology of the iron phosphate prepared in this embodiment is shown in the following image. Figure 1 As shown, the product exhibits a spherical morphology formed by close-packed sheets. Additionally, the cross-sectional morphology of the iron phosphate prepared in this embodiment is shown in the image below. Figure 2 As shown, image processing software was used to... Figure 2 The process involved processing and calculating the porosity, where the core (50% of the internal region along the radial direction) had a porosity of 3%, and the shell (the remaining region) had a porosity of 41%. The iron phosphate prepared in this example had a D50 of 25 μm and a specific surface area of ​​3.2 m². 2 / g, iron-to-phosphorus ratio is 0.972, tap density is 1.3g / cm³ 3 .

[0037] Example 2

[0038] Ferric phosphate was prepared according to the following method:

[0039] S1. Dissolve 100g of iron oxide red in a 30% phosphoric acid solution to obtain an iron phosphate complex solution. The amount of raw materials used is 1:9 based on the molar ratio of iron oxide red to phosphoric acid.

[0040] S2. Based on the phosphorus concentration in the solution as phosphoric acid, add water to dilute the solution to a concentration of 15 wt%, then add 30 g of reduced iron powder and dissolve it to obtain a mixed solution of ferrous dihydrogen phosphate and ferric phosphate complex.

[0041] S3. Heat the obtained solution to 60°C, add 198.7g of 27.5% hydrogen peroxide solution while stirring, and then heat to 80°C to age and obtain the reaction slurry.

[0042] S4. The obtained slurry was filtered and washed with deionized water, dried at 180°C for 3 hours, and calcined at 500°C for 6 hours to obtain anhydrous ferric phosphate.

[0043] In this embodiment, the iron phosphate core comprises 50% of the internal region along the radial direction, with a porosity of 5%, while the shell constitutes the remaining region, with a porosity of 54%. The iron phosphate prepared in this embodiment has a D50 of 29 μm and a specific surface area of ​​6.5 m². 2 / g, iron-to-phosphorus ratio is 0.967, tap density is 1.2g / cm³ 3 .

[0044] Example 3

[0045] Ferric phosphate was prepared according to the following method:

[0046] S1. Dissolve 500g of iron oxide red in a 60% phosphoric acid solution to obtain an iron phosphate complex solution. The amount of raw materials used is 1:6 based on the molar ratio of iron oxide red to phosphoric acid.

[0047] S2. Based on the phosphorus concentration in the solution as phosphoric acid, dilute the solution to a concentration of 20 wt%, add 100 g of reduced iron powder and dissolve it to obtain a mixed solution of ferrous dihydrogen phosphate and ferric phosphate complex.

[0048] S3. Heat the obtained solution to 100°C, add 397.4g of 27.5% hydrogen peroxide solution while stirring, and continue aging at 100°C to obtain the reaction slurry;

[0049] S4. The obtained slurry was filtered and washed with deionized water, dried at 80°C for 12 hours, and calcined at 550°C for 4 hours to obtain anhydrous ferric phosphate.

[0050] In this embodiment, the iron phosphate core comprises 44% of the internal region along the radial direction, with a porosity of 8%, while the shell constitutes the remaining region, with a porosity of 60%. The iron phosphate prepared in this embodiment has a D50 of 32 μm and a specific surface area of ​​9.5 m². 2 / g, iron-to-phosphorus ratio is 0.961, tap density is 1.0 g / cm³ 3 .

[0051] Example 4

[0052] Ferric phosphate was prepared according to the following method:

[0053] S1. Dissolve 150g of iron oxide red in a 40% phosphoric acid solution to obtain an iron phosphate complex solution. The amount of raw materials used is 1:10 based on the molar ratio of iron oxide red to phosphoric acid.

[0054] S2. Based on the phosphorus concentration in the solution as phosphoric acid, dilute the solution to a concentration of 20 wt%, add 50 g of reduced iron powder and dissolve it to obtain a mixed solution of ferrous dihydrogen phosphate and ferric phosphate complex.

[0055] S3. Heat the obtained solution to 70°C, add 298.05g of 27.5% hydrogen peroxide solution while stirring, and then heat to 80°C to age to obtain the reaction slurry;

[0056] S4. The obtained slurry was filtered and washed with deionized water, dried at 100℃ for 6 hours, and calcined at 650℃ for 5 hours to obtain anhydrous ferric phosphate.

[0057] In this embodiment, the iron phosphate core comprises 50% of the internal region along the radial direction, with a porosity of 6%, while the shell constitutes the remaining region, with a porosity of 43%. The iron phosphate prepared in this embodiment has a D50 of 21 μm and a specific surface area of ​​2.8 m². 2 / g, iron-to-phosphorus ratio is 0.973, tap density is 1.4g / cm³ 3 .

[0058] Comparative Example 1

[0059] Ferric phosphate was prepared using a method essentially the same as that in Example 1, except that reduced iron powder was not added in step S2.

[0060] The cross-sectional morphology of the iron phosphate prepared in this comparative example is shown in the figure below. Figure 3 As shown, the product has very few pores in its internal structure, with no core-shell distinction, and an overall porosity of 1%.

[0061] Comparative Example 2

[0062] Ferric phosphate was prepared using a method essentially the same as in Example 1, except that 200g of reduced iron powder was added in step S2, and 900g of 27.5% hydrogen peroxide solution was added in step S3.

[0063] The microstructure of the iron phosphate prepared in this comparative example is shown in the figure below. Figure 4 As shown, the product has many pores in its internal structure, with no core-shell distinction, and an overall porosity of 48%.

[0064] Comparative Example 3

[0065] Ferric phosphate was prepared using a method essentially the same as in Example 1, except that in step S1, the amount of phosphoric acid added was based on a molar ratio of 1:12 between iron oxide red and phosphoric acid.

[0066] The iron phosphate core prepared in this comparative example is the inner region of 50% along the radial direction with a porosity of 15%, and the shell is the remaining region with a porosity of 80%.

[0067]

Application Example 1

[0068] Using the iron phosphate prepared in Example 1 as raw material, lithium iron phosphate was prepared by sand milling according to the following method:

[0069] 1000g of iron phosphate was mixed with 501.2g of lithium carbonate, 8g of titanium dioxide and 160g of glucose and placed in a sand mill. The speed of the sand mill was adjusted to 2000 rpm. When the solid D50 reached 550nm, it was spray dried and calcined at 780℃ for 10 hours in a nitrogen atmosphere. After cooling to room temperature, it was crushed and passed through a 200-mesh sieve to obtain lithium iron phosphate.

[0070]

Application Example 2

[0071] Lithium iron phosphate was prepared using essentially the same method as in Application Example 1, except that the iron phosphate raw material prepared in Example 1 was replaced with the same mass of iron phosphate raw material prepared in Example 2.

[0072]

Application Example 3

[0073] Lithium iron phosphate was prepared using essentially the same method as in Application Example 1, except that the iron phosphate raw material prepared in Example 1 was replaced with the same mass of iron phosphate raw material prepared in Example 3.

[0074]

Application Example 4

[0075] Lithium iron phosphate was prepared using essentially the same method as in Application Example 1, except that the iron phosphate raw material prepared in Example 1 was replaced with the same mass of iron phosphate raw material prepared in Example 4.

[0076]

Application Example 5

[0077] Lithium iron phosphate was prepared using a method essentially the same as that used in Application Example 1, except that the iron phosphate raw material prepared in Example 1 was replaced with the same mass of iron phosphate raw material prepared in Comparative Example 1.

[0078]

Application Example 6

[0079] Lithium iron phosphate was prepared using a method essentially the same as that used in Application Example 1, except that the iron phosphate raw material prepared in Example 1 was replaced with the same mass of iron phosphate raw material prepared in Comparative Example 2.

[0080]

Application Example 7

[0081] Lithium iron phosphate was prepared using a method essentially the same as that used in Application Example 1, except that the iron phosphate raw material prepared in Example 1 was replaced with the same mass of iron phosphate raw material prepared in Comparative Example 3.

[0082] Lithium iron phosphate battery performance evaluation

[0083] Using the aforementioned lithium iron phosphate as raw material, prepare lithium battery cathode materials according to the following methods:

[0084] The prepared lithium iron phosphate was used as the positive electrode material and mixed with a cyclohexane solution of carbon black and polyvinylidene fluoride (PVDF) at room temperature and pressure to form a slurry (the effective material mass ratio was positive electrode material: carbon black: PVDF = 85:10:5). The slurry was uniformly coated on an aluminum foil substrate to serve as the positive electrode of the simulated battery. The negative electrode of the simulated battery used a lithium sheet, and the electrolyte was 1 mol LiPF6 dissolved in 1 L of a mixed solvent of EC and DMC (volume ratio 1:1). The separator was a composite membrane of polypropylene and polyethylene. The positive electrode, negative electrode, electrolyte, and separator were assembled into a simulated battery in an argon-protected glove box, and the performance of the simulated battery was tested.

[0085] <1C discharge capacity>

[0086] First, charge the battery to 4.2V at 30mA / g, then discharge it to 2.5V at 1C current. The capacity discharged is the 1C discharge capacity.

[0087] <Powder Compaction>

[0088] The compaction density of lithium iron phosphate powder was tested under 30 kN conditions.

[0089] Table 2. Battery performance test results

[0090] 1C discharge capacity / mAh / g <![CDATA[Powder Compaction Density / g / cm 3 > Application Example 1 145 2.55 Application Example 2 144 2.52 Application Example 3 146 2.53 Application Example 4 144 2.53 Application Example 5 131 2.52 Application Example 6 152 2.18 Application Example 7 140 2.49

[0091] As can be seen from the comparison of the above application examples, the lithium iron phosphate prepared by iron phosphate provided in Comparative Example 1 has a low 1C discharge capacity, and the lithium iron phosphate prepared by iron phosphate provided in Comparative Example 2 has a low powder compaction density and no practical value. The iron phosphate provided in Example 1 of the present invention has a significantly improved compaction density or discharge capacity when applied to lithium iron phosphate batteries.

[0092] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A battery-grade iron phosphate, wherein the battery-grade iron phosphate has a core-shell structure with a D50 of 20-40 μm, wherein the core is the internal region of 50% along the radial direction, the shell is the remaining external region, the porosity of the core is 1%-10%, and the porosity of the shell is 30%-70%.

2. The iron phosphate as described in claim 1, characterized in that, The specific surface area of ​​the battery-grade iron phosphate is 2-8 m². 2 / g, iron-to-phosphorus ratio is 0.960-0.975, tap density is 1.0-1.5g / cm³ 3 .

3. The method for preparing ferric phosphate as described in claim 1 or 2, characterized in that, The method includes the following steps: S1. Dissolve iron oxide red in phosphoric acid solution to obtain iron phosphate complex solution; S2. Dilute the obtained ferric phosphate complex solution, add pure iron and dissolve it to obtain a mixed solution of ferrous dihydrogen phosphate and ferric phosphate complex. S3. Heat the obtained mixed solution, add an oxidant while stirring, and after aging the reaction, obtain a reaction slurry; S4. The obtained slurry is filtered, washed, further dried and calcined to obtain anhydrous ferric phosphate.

4. The preparation method according to claim 3, characterized in that, In step S1, the ratio of iron oxide red to phosphoric acid solution is 1:(6-10) in terms of the molar ratio of iron oxide red to phosphoric acid; and / or, the mass concentration of the phosphoric acid solution is 30-60%.

5. The preparation method according to claim 3 or 4, characterized in that, In step S2, the phosphorus in the solution is diluted to 15-25 wt% by adding pure water, based on the phosphoric acid concentration (total phosphorus converted to phosphoric acid); and / or, the pure iron is one or more of iron powder, iron sheet, and iron blocks.

6. The preparation method according to any one of claims 3-5, characterized in that, The total iron source added in steps S2 and S1, calculated as pure iron, has a molar ratio of 1:(2-4) to the phosphoric acid added in step S1, and the molar amount of iron source added in step S2 does not exceed the molar amount of iron oxide added in step S1.

7. The preparation method according to any one of claims 3-6, characterized in that, In step S3, the reaction temperature is 60-100℃, and the oxidant is one or more of hydrogen peroxide solution, air, oxygen, and ozone. The total amount of oxidant added is 1-10 times the molar amount of pure iron in step S2, and the aging temperature is 0-20℃ higher than the reaction temperature.

8. The preparation method according to any one of claims 3-6, characterized in that, In step S4, the washing is done with deionized water, the drying temperature is 80-200℃, and the drying time is 2-12h. The calcination conditions are: calcination at 500-650℃ for 3-6h.

9. The application of iron phosphate as described in claim 1 or 2, or iron phosphate prepared by any one of the preparation methods described in claims 3-8, in high-density lithium iron phosphate.

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