A method for preparing low-cost and high-capacity spherical lithium iron phosphate

Abstract

The present invention provides a low-cost and high-capacity preparation method of spherical lithium iron phosphate, which relates to the technical field of lithium battery materials. The method comprises the following steps: step 1: uniformly mixing a lithium source, an iron source, a phosphorus source, an optional metal dopant and a carbon source with deionized water, and then grinding the mixed slurry; step 2: spray-granulating the ground slurry using a magnetic suspension atomizing spray dryer to obtain a granular material, and then pre-calcining the granular material to obtain a spherical lithium iron phosphate precursor; step 3: dry-mixing the spherical lithium iron phosphate precursor with a carbon source to obtain a sintered precursor; and step 4: sintering the sintered precursor obtained in step 3 at a high temperature under the protection of an inert atmosphere to obtain a spherical lithium iron phosphate product. The method solves the problems that mainstream lithium iron phosphate materials have poor conductivity and cycle performance, and the two-fluid and four-fluid spray equipment used are expensive, which directly leads to increased production costs.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery materials, and in particular to a method for preparing low-cost and high-capacity spherical lithium iron phosphate. Background Art

[0002] Lithium iron phosphate is a battery material with an olivine structure. It has a stable and reliable structure, small deformation during the cycle, and a long life. It has gradually become the first choice for energy storage power stations and new energy electric vehicles as an alternative energy source.

[0003] Currently, the mainstream positive electrode material in the battery industry is lithium iron phosphate, and the preparation method is mostly: wet ultrafine grinding-spray drying-sintering-crushing process. The particle size of the lithium iron phosphate material produced is 0.5μm-3μm. It has high capacity, but the carbon coating effect is poor, and the conductivity and cycle performance are poor. The two-fluid and four-fluid spray equipment used is expensive, which directly leads to increased production costs. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that the traditional carbon coating effect of lithium iron phosphate is poor, and the conductivity and cycle performance are poor. In view of the problems existing in the existing technology, a low-cost and high-capacity preparation method of spherical lithium iron phosphate is provided.

[0005] To solve the problems of the prior art, the present invention discloses a method for preparing spherical lithium iron phosphate with low cost and high capacity, comprising the following steps:

[0006] Step 1: uniformly mixing a lithium source, an iron source, a phosphorus source, an optional metal dopant and a carbon source with deionized water, and then grinding the resulting slurry;

[0007] Step 2: The ground slurry is spray-granulated using a magnetic suspension atomization spray dryer to obtain a granular material, and then the granular material is pre-calcined under an inert atmosphere to obtain a spherical lithium iron phosphate precursor;

[0008] Step 3: dry-mixing the spherical lithium iron phosphate precursor with a carbon source to obtain a sintered precursor;

[0009] Step 4: Sintering the sintered precursor in step 3 at a high temperature under the protection of an inert atmosphere to obtain a spherical lithium iron phosphate material.

[0010] Furthermore, the lithium source in step 1 is any one of lithium hydroxide monohydrate and lithium carbonate, or a combination thereof;

[0011] Preferably, the iron source is any one of iron oxide red and iron phosphate, or a combination thereof;

[0012] Preferably, the phosphorus source is any one of phosphoric acid or ammonium dihydrogen phosphate or a combination thereof;

[0013] Preferably, the optional metal dopant is any one of Ti, V, and Nb compounds or a combination thereof;

[0014] Preferably, the carbon source is any one or more combinations of sucrose, glucose, polyethylene glycol, starch, citric acid, and asphalt;

[0015] Preferably, the molar ratio of the lithium source, iron source, phosphorus source and optional metal dopant is (1.0-1.1): (0.95-1.0): 1: (0-0.01), wherein M is an optional metal dopant.

[0016] Furthermore, in step 1, the carbon source accounts for 0.5%-10% of the total weight of the lithium source, the iron source, the phosphorus source, and the optional metal dopant.

[0017] Furthermore, the particle size of the slurry after grinding in step 1 is 0.1 μm-0.8 μm.

[0018] Furthermore, the linear speed of the magnetic suspension atomization spray dryer in step 2 is 200m / s-600m / s;

[0019] Preferably, in the method of the present invention, step 2 uses a magnetic levitation atomizing spray dryer for spray granulation. The linear speed of the magnetic levitation atomizing spray dryer can reach up to 600 m / s, which is much greater than the current mechanical atomizer and electric atomizer, and is close to supersonic operation. The particle size after granulation using the magnetic levitation atomizing spray dryer is D50 = 5 μm to 10 μm. There is no need to add an airflow crushing process subsequently, which simplifies and shortens the process flow and reduces the investment in airflow crushing equipment. The magnetic levitation atomizing spray dryer saves about 10%-20% energy compared to a conventional centrifugal spray dryer, reduces energy consumption and preparation costs, and improves production efficiency.

[0020] Furthermore, the pre-firing temperature in step 2 is 400°C-700°C, and the pre-firing time is 2h-4h;

[0021] Preferably, the particle size of the spherical lithium iron phosphate precursor is 5 μm to 10 μm.

[0022] Furthermore, the equipment used for dry mixing of the carbon source in step 3 is any one of a V-type high-efficiency mixer, a single-cone vacuum mixing dryer, and a VC mixer;

[0023] Preferably, the dry mixing time is 0.5h-4h.

[0024] Furthermore, the sintering temperature in step 4 is 700° C.-800° C., and the sintering time is 6 h-12 h.

[0025] Preferably, in the method of the present invention, a carbon source is added during the grinding process in step one, the pre-calcination in step two performs the first carbon coating and the first sintering, and in step three, the carbon source is dry mixed and prepared for the second time and sintered. By adopting a two-step carbon coating and a two-step sintering process, the carbon coating effect and gram capacity of the product are significantly improved.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The lithium iron phosphate material has a high tap density, which can effectively increase the compaction density of the lithium battery pole piece. The increased compaction density can improve the overall energy density of the battery, reflecting the effect of high capacity. However, as shown in the comparative test data, the capacity utilization value of batteries made with conventional lithium iron phosphate materials is relatively low, resulting in low product utilization value. The spherical lithium iron phosphate material of the present invention can significantly improve battery performance.

[0028] This lithium iron phosphate material is beneficial to improving the solid content of the slurry and the compaction density of the electrode. It adopts a two-step carbon coating method and does not require air flow crushing, which avoids a certain degree of peeling damage to the carbon coating of the lithium iron phosphate material caused by air flow crushing. The product has a good carbon coating effect and significantly reduces the internal resistance, which is beneficial to improving the gram capacity and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a SEM image of the low-cost, high-capacity spherical lithium iron phosphate material of the present invention;

[0030] Figure 2 This is an SEM image of existing conventional lithium iron phosphate material. DETAILED DESCRIPTION

[0031] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, Figure 1-Figure 2 It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0032] A method for preparing spherical lithium iron phosphate with low cost and high capacity comprises the following steps:

[0033] Step 1: uniformly mixing a lithium source, an iron source, a phosphorus source, an optional metal dopant and a carbon source with deionized water, and then grinding the resulting slurry;

[0034] Furthermore, the lithium source is any one of lithium hydroxide monohydrate and lithium carbonate, or a combination thereof;

[0035] The iron source is any one of iron red and iron phosphate or a combination thereof;

[0036] The phosphorus source is any one of phosphoric acid or ammonium dihydrogen phosphate or a combination of the two;

[0037] The optional metal dopant is any one of Ti, V, and Nb compounds or a combination thereof;

[0038] The carbon source is any one or more combinations of sucrose, glucose, polyethylene glycol, starch, citric acid, and asphalt;

[0039] The molar ratio of Li:Fe:P:M of the lithium source, iron source, phosphorus source and optional metal dopant is (1.0-1.1):(0.95-1.0):1:(0-0.01), wherein M is an optional metal dopant, and the optional metal dopant is preferably any one of titanium dioxide, vanadium pentoxide, and niobium pentoxide, or a combination thereof;

[0040] In the configuration ratio, the percentage of the carbon source to the total weight of the lithium source, the iron source, the phosphorus source, and the optional metal dopant is 0.5%-10%;

[0041] The lithium source, iron source, phosphorus source, optional metal dopant, carbon source and deionized water can be initially stirred and mixed at a low speed in a ball mill, and then sand-milled using a sand mill to obtain a slurry with a particle size of 0.1 μm-0.8 μm.

[0042] Step 2: using a magnetic suspension atomization spray dryer to spray granulate the ground slurry to obtain a granular material, and then pre-calcining the granular material to obtain a spherical lithium iron phosphate precursor with a particle size of 5 μm to 10 μm;

[0043] The linear speed of the magnetic suspension atomization spray dryer is 200m / s-600m / s;

[0044] The granular material is pre-fired under an inert atmosphere such as nitrogen or argon at a temperature of 400°C to 700°C for 2 hours to 4 hours to obtain a spherical lithium iron phosphate precursor with a particle size of 5 μm to 10 μm.

[0045] A magnetic levitation atomizing spray dryer is used for spray granulation, and the inlet temperature of the magnetic levitation atomizing spray dryer is 220°C and the outlet temperature is 95°C. The linear speed of the magnetic levitation atomizing spray dryer can reach up to 600m / s, which is much higher than the linear speed of 200m / s-300m / s of traditional mechanical atomizers and electric atomizers. The linear speed of the magnetic levitation atomizing spray dryer is close to supersonic operation. The particle size D50 of the spherical lithium iron phosphate precursor granulated by the magnetic levitation atomizing spray dryer is 5μm-10μm, which is smaller than the conventional spherical lithium iron phosphate precursor produced by conventional mechanical atomizers and electric atomizers with a particle size D50 of 12μm-40μm.

[0046] A magnetic levitation atomizing spray dryer is used for spray granulation, and the particle size D50 of the spherical lithium iron phosphate material is 5μm-10μm. There is no need to add a subsequent air flow crushing process, which can effectively avoid the peeling damage to the carbon coating of the material caused by air flow crushing, and can simplify the process flow, reduce the investment in air flow crushing equipment, and reduce costs. In addition, the magnetic levitation atomizing spray dryer is more energy-efficient than a conventional centrifugal spray dryer, and can especially solve the problem of high costs of two-fluid spray and four-fluid spray equipment, effectively reduce energy consumption and preparation costs, improve production efficiency, and realize low-cost production of spherical lithium iron phosphate.

[0047] Step 3: dry-mixing the spherical lithium iron phosphate precursor with a carbon source to obtain a sintered precursor;

[0048] The equipment used for the dry mixing of the carbon source is any one of a V-type high-efficiency mixer, a single-cone vacuum mixing dryer, and a VC mixer;

[0049] The dry mixing time is 0.5h-4h;

[0050] During the grinding process of the above step 1, any one or more combinations of sucrose, glucose, polyethylene glycol, starch, citric acid, and asphalt are added as a carbon source, and a lithium source, an iron source, a phosphorus source, and optional metal dopants are uniformly mixed with deionized water, while the pre-calcination process in step 2 performs the first carbon coating and the first sintering;

[0051] Step 4: sintering the sintered precursor in step 3 at a high temperature under an inert atmosphere to obtain a spherical lithium iron phosphate product;

[0052] The sintering temperature is 700-800°C, and the sintering time is 6-12 hours;

[0053] In step three and step four, the carbon source dry mixing preparation process will mix the carbon source twice and sinter, realizing a two-step carbon coating and two-step sintering process, thereby improving the carbon coating effect of the material, reducing the internal resistance, and significantly improving the gram capacity, and finally obtaining a low-cost, high-capacity spherical lithium iron phosphate product.

[0054] Preparation of low-cost, high-capacity spherical lithium iron phosphate (iron phosphate process), Example 1:

[0055] 1200L of deionized water was added to the ball mill for low-speed stirring, and then 480kg of ferric phosphate, 120kg of lithium carbonate, 0.9kg of titanium dioxide, 48kg of anhydrous glucose and 6kg of polyethylene glycol were added respectively, and the mixture was ball-milled at high speed for 2h. The slurry (referring to the slurry obtained by ball milling in the above steps) was then put into a sand mill for sand milling for 2h. The slurry particle size D50 was 0.45μm. Then, a magnetic suspension atomization spray dryer was used for spray granulation, and the inlet temperature of the magnetic suspension atomization spray dryer was 220℃ and the outlet temperature was 95℃. ℃, spray granulation to obtain granular material, the granular material is put into a graphite sagger, and pre-sintered at a temperature of 500℃ for 2h in a kiln protected by an inert atmosphere to obtain a spherical lithium iron phosphate precursor with a particle size D50 of 5μm to 10μm, and then the obtained spherical lithium iron phosphate precursor is placed in a V-type high-efficiency mixer or a single-cone vacuum mixing dryer or a VC mixer, and 12Kg of anhydrous glucose is added, and it is dry-mixed by the mixer for 2h, and finally sintered at a temperature of 750℃ for 10h under the protection of an inert atmosphere to obtain a spherical lithium iron phosphate material.

[0056] Preparation of low-cost and high-capacity spherical lithium iron phosphate (iron red process), Example 2:

[0057] 1200L of deionized water was added to the ball mill for low-speed stirring, and then 220kg of iron oxide red, 330kg of phosphoric acid, 120kg of lithium hydroxide, 0.8kg of titanium dioxide, 42.5kg of anhydrous glucose and 5.3kg of polyethylene glycol were added respectively, and the mixture was ball-milled at high speed for 2h. The slurry (referring to the slurry obtained by ball milling in the above steps) was then put into a sand mill and sand-milled for 2h. The slurry particle size D50 was 0.45μm. Then, a magnetic suspension atomizing spray dryer was used for spray granulation, and the inlet temperature of the magnetic suspension atomizing spray dryer was 220℃ and the outlet temperature was 100℃. The spherical lithium iron phosphate precursor is prepared by spray granulation at a temperature of 95°C and granular material is obtained after spray granulation. The granular material is put into a graphite sagger and pre-sintered at a temperature of 500°C for 2 hours in a kiln protected by an inert atmosphere to obtain a spherical lithium iron phosphate precursor with a particle size D50 of 5μm to 10μm. The obtained spherical lithium iron phosphate precursor is then placed in a V-type high-efficiency mixer or a single-cone vacuum mixing dryer or a VC mixer, and 10.5Kg of anhydrous glucose is added. The precursor is dry-mixed by the mixer for 2 hours, and finally sintered at a temperature of 750°C for 10 hours under the protection of an inert atmosphere to obtain a spherical lithium iron phosphate material.

[0058] Preparation of low-cost, high-capacity spherical lithium iron phosphate (material mixing process), Example 3:

[0059] 1200L of deionized water was added to the ball mill and stirred at a low speed. Then, 179kg of iron oxide red, 89kg of iron phosphate, 265kg of phosphoric acid, 123kg of lithium hydroxide, 0.81kg of titanium dioxide, 42.5kg of anhydrous glucose and 5.3kg of polyethylene glycol were added respectively and ball milled at high speed for 2h. The slurry (referring to the slurry obtained by ball milling in the above steps) was then put into a sand mill and sand milled for 2h. The slurry particle size D50 was 0.45μm. Then, a magnetic suspension atomization spray dryer was used for spray granulation, and the inlet temperature of the magnetic suspension atomization spray dryer was 220℃. The outlet temperature is 95°C, and granular material is obtained after spray granulation. The granular material is loaded into a graphite sagger and pre-sintered at a temperature of 500°C for 2 hours in a kiln protected by an inert atmosphere to obtain a spherical lithium iron phosphate precursor with a particle size D50 of 5μm to 10μm. The obtained spherical lithium iron phosphate precursor is then placed in a V-type high-efficiency mixer or a single-cone vacuum mixing dryer or a VC mixer, and 10.5Kg of anhydrous glucose is added. It is dry-mixed by the mixer for 2 hours, and finally sintered at a temperature of 750°C for 10 hours under the protection of an inert atmosphere to obtain a spherical lithium iron phosphate material.

[0060] Preparation of conventional spherical lithium iron phosphate (conventional iron phosphate process), comparative example 1:

[0061] 1200L of deionized water was added to the ball mill and stirred at low speed. Then, 480kg of iron phosphate, 120kg of lithium carbonate, 0.9kg of titanium dioxide, and 60kg of anhydrous glucose were added respectively and ball-milled at high speed for 2h. The slurry (referring to the slurry obtained by ball milling in the above step) was put into a sand mill and sand-milled for 2h. The slurry particle size D50 was 0.45μm. Then, a centrifugal spray dryer was used for spray granulation to obtain a spray-dried lithium iron phosphate precursor with a particle size D50 of 18μm. The precursor was loaded into a graphite sagger and sintered at a temperature of 750°C for 10h under inert atmosphere to obtain a lithium iron phosphate sintered body. The lithium iron phosphate sintered body was subjected to airflow crushing and classification, wherein the graded material particle size D50 was 0.98μm, and a lithium iron phosphate material was obtained.

[0062] Preparation of conventional spherical lithium iron phosphate (iron red conventional process), comparative example 2:

[0063] 1200L of deionized water was added to the ball mill for low-speed stirring, followed by high-speed ball milling for 2h with 220kg of iron oxide red, 330kg of phosphoric acid, 120kg of lithium hydroxide, 0.8kg of titanium dioxide, and 53kg of anhydrous glucose. The slurry (referring to the slurry obtained by ball milling in the above step) was then put into a sand mill and sand milled for 2h. The slurry particle size D50 was 0.45μm. A centrifugal spray dryer was then used for spray granulation to obtain a spray-dried lithium iron phosphate precursor with a particle size D50 of 18μm. The precursor was loaded into a graphite sagger and sintered at a temperature of 750°C for 10h under inert atmosphere to obtain a lithium iron phosphate sintered body. The lithium iron phosphate sintered body was subjected to airflow crushing and classification, wherein the graded material particle size D50 was 1.8μm, and a lithium iron phosphate material was obtained.

[0064] Test steps:

[0065] The physical and chemical properties of the lithium iron phosphate materials prepared in Examples 1-3 and Comparative Examples 1-2 were tested. The test results are shown in Table 1 below:

[0066]

[0067] The lithium iron phosphate materials prepared in Examples 1-3 and Comparative Examples 1-2 were made into button-type half-cells for testing. The test results are shown in Table 2 below:

[0068] sample 0.1C discharge capacity (mAh / g) First effect% Example 1 161.9 98.6 Example 2 160.8 98.0 Example 3 159.6 97.2 Comparative Example 1 157.5 97.9 Comparative Example 2 150.0 96.5

[0069] As can be seen from Tables 1 and 2, the particle size, tap density, and electrochemical performance of the spherical lithium iron phosphate materials prepared in Examples 1-3 of the present invention are all superior to those in Comparative Examples 1-2. A high tap density can effectively increase the compaction density of lithium battery pole pieces, and this increased compaction density can improve the overall energy density of the battery, demonstrating a high-capacity effect. However, as shown in the comparative example test data, batteries made using conventional lithium iron phosphate materials have relatively low capacity utilization value, resulting in low product utilization value. The spherical lithium iron phosphate materials of the present invention can significantly improve battery performance.

[0070] The lithium iron phosphate materials prepared in Examples 1-3 and Comparative Examples 1-2 were made into 4560130-2.5Ah small soft pack batteries according to the following method:

[0071] The lithium iron phosphate prepared by the present invention is used as the positive electrode material of the lithium ion battery, and acetylene black is used as the conductive agent. After the positive electrode material: conductive agent: PVDF=96:2:2 are mixed to prepare slurry, the slurry is evenly coated on a plain aluminum foil to prepare a positive electrode sheet; graphite is used as the negative electrode material, SP is used as the conductive agent, sodium carboxymethyl cellulose (CMC) is used as the thickener, and LA133 is used as the binder. After the slurry is prepared by mixing the negative electrode material: SP: CMC: LA133=95:1.5:0.4:3.1 with deionized water to prepare slurry, the slurry is evenly coated on a copper foil to prepare a negative electrode sheet; PP16 separator, EC:EMC:DEC=1:1:1+1Mol / LLiPF6 are used as the electrolyte, and a 4560130-2.5Ah small soft-pack single battery is assembled.

[0072] The lithium ion batteries prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to relevant processing and electrical performance tests, and the test data are shown in Table 3 below.

[0073] sample Slurry solid content% Pole compaction (g / cm3) AC internal resistance mΩ Room temperature 0.5℃ gram capacity mAh / g Capacity retention rate at room temperature 1C / 1C500 weeks% Example 1 64% 2.35 6.08 145 97.0% Example 2 63% 2.35 7.43 144 96.9% Example 3 61% 2.30 8.12 143 96.5% Comparative Example 1 60% 2.30 19.63 142 94.0% Comparative Example 2 58% 2.20 23.54 135 92.8%

[0074] It can be seen from Table 3 that the spherical lithium iron phosphate materials prepared in Examples 1-3 of the present invention have a high tap density, which is beneficial to improving the solid content of the slurry and the compaction density of the electrode. The two-step carbon coating method is adopted and no air flow crushing is required, which avoids a certain degree of peeling damage to the carbon coating of the lithium iron phosphate material caused by air flow crushing. The product has a good carbon coating effect and significantly reduces the internal resistance, which is beneficial to improving the gram capacity and cycle performance.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing spherical lithium iron phosphate with low cost and high capacity, characterized in that: The following steps are involved: Step 1: uniformly mixing the lithium source, iron source, phosphorus source, metal dopant and carbon source with deionized water, and then grinding the mixed slurry; Step 2: The ground slurry is spray granulated using a magnetic levitation atomizing spray dryer, the linear speed of the magnetic levitation atomizing spray dryer is 200m / s-600m / s, to obtain a granular material, and then the granular material is pre-calcined to obtain a spherical lithium iron phosphate precursor, the pre-calcination temperature is 400°C-700°C, the pre-calcination time is 2h-4h, and the particle size of the spherical lithium iron phosphate precursor is 5μm-10μm; Step 3: dry-mixing the spherical lithium iron phosphate precursor with a carbon source, wherein the carbon source is anhydrous glucose, to obtain a sintered precursor. The equipment used for the dry-mixing of the carbon source is any one of a V-type high-efficiency mixer, a single-cone vacuum mixing dryer, and a VC mixer. The dry-mixing time is 0.5h-4h. Step 4: Sintering the sintered precursor in step 3 at high temperature under the protection of an inert atmosphere to obtain a spherical lithium iron phosphate product.

2. The preparation method according to claim 1, wherein: The lithium source in step 1 is any one of lithium hydroxide monohydrate and lithium carbonate or a combination thereof; The iron source is any one of iron red and iron phosphate or a combination thereof; The phosphorus source is any one of phosphoric acid or ammonium dihydrogen phosphate or a combination of the two; The metal dopant is any one of Ti, V, and Nb compounds or a combination of the two; The carbon source is any one or more combinations of sucrose, glucose, polyethylene glycol, starch, citric acid, and asphalt; The molar ratio of Li:Fe:P:M of the lithium source, iron source, phosphorus source and optional metal dopant is (1.0-1.1):(0.95-1.0):1:(0-0.01), wherein M is an optional metal dopant.

3. The preparation method according to claim 2, wherein: The percentage of the carbon source in step 1 to the total weight of the lithium source, iron source, phosphorus source and metal dopant is 0.5%-10%.

4. The preparation method according to claim 1, wherein: The particle size of the slurry after grinding in step 1 is 0.1 μm-0.8 μm.

5. The preparation method according to claim 1, wherein: The sintering temperature in step 4 is 700° C.-800° C., and the sintering time is 6 h-12 h.

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