A modified lithium iron phosphate positive electrode material prepared based on a dry process

Abstract

The application discloses a modified lithium iron phosphate positive electrode material prepared based on a dry process, and the preparation comprises the following steps: firstly, dispersing agent is mixed with iron phosphate powder to obtain a mixture, so that the dispersing agent is uniformly coated on the surface of the iron phosphate particles, and the dispersing agent comprises a main dispersing agent and fumed silica; secondly, a lithium source and a carbon source are added into the mixture, and a phosphorus source and / or an iron source is supplemented, and sand grinding is carried out until a target particle size is reached, so as to obtain sand grinding material; finally, the sand grinding material is kept at 350 DEG C-550 DEG C for 1-6 hours in an inert atmosphere, and then kept at a sintering temperature of 600-800 DEG C for 6-24 hours, and after cooling, the lithium iron phosphate is prepared. The modified lithium iron phosphate positive electrode material is based on the dry process, and through the introduction of the silicon source, the overcharge performance of the prepared lithium iron phosphate positive electrode material can be effectively improved, the generation of a side reaction is effectively avoided, the stability of the prepared lithium iron phosphate is improved, and the occurrence of a fire phenomenon caused by long overcharge time is avoided.

Description

Technical Field

[0001] This invention belongs to the field of lithium iron phosphate cathode material preparation technology, and particularly relates to a modified lithium iron phosphate cathode material prepared based on a dry process. Background Technology

[0002] Lithium iron phosphate (LiFePO4) has been widely used in power batteries, energy storage batteries, and other fields due to its advantages such as high safety, long cycle life, and low cost. Currently, the main preparation processes are divided into the iron phosphate method, the iron oxide red method, the ferrous oxalate method, and the liquid phase method. Most of these methods involve liquid-phase mixing systems, i.e., wet processes. These processes suffer from complexity, high wastewater discharge, and high drying costs. Under the current market conditions, further reducing production costs is a pressing issue for the lithium iron phosphate industry.

[0003] Furthermore, as lithium iron phosphate is widely used in the field of energy storage batteries, overcharging is inevitable during its use. This can lead to fires caused by overcharging of the lithium iron phosphate cathode material, thus placing higher demands on the structural stability and safety performance of lithium iron phosphate materials.

[0004] Based on this, we now study a modified lithium iron phosphate cathode material. This cathode material is based on a dry process to reduce costs, improves the stability of the prepared lithium iron phosphate material, effectively avoids the generation of side reactions, and improves overcharge performance. Summary of the Invention

[0005] Purpose of the invention: This invention provides a modified lithium iron phosphate cathode material prepared by a dry process. This modified lithium iron phosphate cathode material can effectively avoid the generation of side reactions, improve stability, and prevent fire caused by overcharging.

[0006] Technical solution: This invention relates to a modified lithium iron phosphate cathode material prepared by a dry process, which is obtained through the following steps:

[0007] (1) The dispersant is mixed with the iron phosphate powder so that the dispersant is uniformly coated on the surface of the iron phosphate particles; the dispersant includes a main dispersant and fumed silica;

[0008] (2) Add lithium source and carbon source to the mixture in step (1), and supplement with phosphorus source and / or iron source, mix and grind to reach the target particle size, and obtain the ground material;

[0009] (3) The sand-milled material is kept at 350℃-550℃ for 1-6 hours in an inert atmosphere, and then kept at 600-800℃ for 6-24 hours in a sintering temperature. After cooling, the modified lithium iron phosphate cathode material is obtained.

[0010] Furthermore, in step (1) of the preparation of the modified lithium iron phosphate cathode material, the amount of fumed silica added is 0.5-5% of the mass of iron phosphate.

[0011] Furthermore, in step (1) of the preparation of the modified lithium iron phosphate cathode material, the main dispersant is selected from polyvinylpyrrolidone, poly(p-hydroxybenzoic acid), graphite or magnesium silanol sulfate, and its addition amount is 0.5-5% of the mass of iron phosphate.

[0012] Furthermore, in step (2) of preparing the modified lithium iron phosphate cathode material, a dopant is added to the mixture. The dopant is one or more compounds containing niobium, zirconium, titanium, aluminum, magnesium, zinc, tin, vanadium, manganese, or cobalt. Preferably, the amount of dopant added is 0.01-2% of the theoretical mass of lithium iron phosphate.

[0013] Furthermore, in step (2) of the preparation of the modified lithium iron phosphate cathode material, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, or lithium dihydrogen phosphate; the iron source is selected from one or more of ferrous oxalate, iron oxide, iron tetroxide, or iron phosphate; and the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, or iron phosphate.

[0014] Furthermore, in step (2) of the preparation of the modified lithium iron phosphate cathode material, the carbon source is selected from one or more of glucose, sucrose, citric acid, polyethylene glycol, polyvinylpyrrolidone, polyacrylate, graphene or conductive carbon black, and its addition amount is 5-15% of the theoretical mass of lithium iron phosphate.

[0015] Furthermore, the molar ratio of Li to P in this modified lithium iron phosphate cathode material is (1.00-1.05):1, and the molar ratio of Fe to P is (0.95-0.99):1.

[0016] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are that, on the one hand, the modified lithium iron phosphate cathode material is prepared by a dry process, which effectively reduces costs and can be adapted to large-scale industrial applications; on the other hand, based on the dry process, the modified lithium iron phosphate cathode material, by adding fumed silica, can effectively improve the overcharge performance of the prepared lithium iron phosphate cathode material, effectively avoid the generation of side reactions, improve the stability of the prepared lithium iron phosphate, and avoid the occurrence of fire caused by long overcharge time. Attached Figure Description

[0017] Figure 1 The above figures show the overcharge test curves of the modified lithium iron phosphate cathode materials prepared in Examples 1, 2, 1, and 2 of this invention. Detailed Implementation

[0018] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0019] It should be noted that the dopant added to the modified lithium iron phosphate cathode material of the present invention can be one or more compounds containing niobium, zirconium, titanium, aluminum, magnesium, zinc, tin, vanadium, manganese, cobalt, and iron. In the following examples and comparative examples, titanium doping is used as an example, and the dopant used is titanium dioxide. The main dispersant used in the following examples and comparative examples is polyvinylpyrrolidone.

[0020] Example 1

[0021] This Example 1 describes a modified lithium iron phosphate cathode material prepared using a dry process, specifically including the following steps:

[0022] (1) Weigh 5 kg of ferric phosphate powder, and weigh 0.5% of fumed silica powder and 2.5% of polyvinylpyrrolidone as the main dispersant, respectively; add the dispersant to the ferric phosphate powder and mix for 10 min in a high-speed mixer with a rotation speed of 500 rap / min.

[0023] (2) Add 1246.25g of lithium carbonate, 7.6g of glucose, 1.8g of polyethylene glycol, 26.4g of titanium dioxide and 28.3g of ferrous oxalate in sequence and mix for 10 minutes to obtain a mixture.

[0024] (3) Add the mixture into a dry sand mill, control the sand milling particle size D50 between 0.6-0.8μm to obtain the sand milled material, and pass the sand milled material through a 120-mesh vibrating screen to obtain the material to be sintered;

[0025] (4) Place the material to be sintered in a box furnace, purge with nitrogen for 30 min, and calcine according to the following procedure: heat up to 350℃ at 3℃ / min and hold for 3 h; heat up to 800℃ at 2℃ / min, purge with nitrogen (flow rate 2.0 L / min), hold for 8 h, and obtain the sintered material after cooling;

[0026] (5) The sintered material is subjected to air jet milling treatment, and the particle size D50 is controlled to be 1.1-1.6μm to obtain lithium iron phosphate product.

[0027] Comparative Example 1

[0028] This comparative example uses a modified lithium iron phosphate cathode material prepared by a dry process. The basic steps are the same as in Example 1, except that conductive carbon black is used instead of fumed silica. Specifically, the steps include:

[0029] (1) Premixing: Weigh 5 kg of iron phosphate powder, and weigh 0.5% of conductive carbon black powder and 2.5% of polyvinylpyrrolidone as the main dispersant. Add the dispersant to the iron phosphate powder and mix for 10 min in a high-speed mixer with a rotation speed of 500 rap / min.

[0030] (2) 1246.25g of lithium carbonate, 7.6g of glucose, 1.8g of PEG-4K, 26.4g of titanium dioxide and 28.3g of ferrous oxalate were added in sequence and mixed for 10 min to obtain a mixture.

[0031] (3) Add the mixture into a dry sand mill, control the sand milling particle size D50 between 0.6-0.8um to obtain the sand milled material, and pass the sand milled material through a 120-mesh vibrating screen to obtain the material to be sintered;

[0032] (4) Place the material to be sintered in a box furnace, purge with nitrogen for 30 min, and calcine according to the following procedure: heat up to 350℃ at 3℃ / min and hold for 3 h; heat up to 800℃ at 2℃ / min, purge with nitrogen (flow rate 2.0 L / min), hold for 8 h, and obtain the sintered material after cooling;

[0033] (5) The sintered material is subjected to air jet milling treatment, and the particle size D50 is controlled to be 1.1-1.6μm to obtain lithium iron phosphate product.

[0034] Example 2

[0035] This Example 2 describes a modified lithium iron phosphate cathode material prepared using a dry process, which is obtained through the following steps:

[0036] (1) Weigh 5 kg of ferric phosphate powder, and weigh 2% of fumed silica powder and 2.5% of polyvinylpyrrolidone by mass of ferric phosphate to form a dispersant; add the dispersant to the ferric phosphate powder and mix for 10 min in a high-speed mixer with a speed of 500 rap / min.

[0037] (2) 1246.25g of lithium carbonate, 7.6g of glucose, 1.8g of PEG-4K, 26.4g of titanium dioxide and 28.3g of ferrous oxalate were added in sequence and mixed for 10 min to obtain a mixture.

[0038] (3) Add the mixture into a dry sand mill, control the sand milling particle size D50 between 0.6-0.8um to obtain the sand milled material, and pass the sand milled material through a 120-mesh vibrating screen to obtain the material to be sintered;

[0039] (4) Place the material to be sintered in a box furnace, purge with nitrogen for 30 min, and calcine according to the following procedure: heat up to 350℃ at 3℃ / min and hold for 3 h; heat up to 800℃ at 2℃ / min, purge with nitrogen (flow rate 2.0 L / min), hold for 8 h, and obtain the sintered material after cooling;

[0040] (5) The sintered material is subjected to air jet milling treatment, and the particle size D50 is controlled to be 1.1-1.6um to obtain lithium iron phosphate product.

[0041] Comparative Example 2

[0042] Comparative Example 2 presents a modified lithium iron phosphate cathode material prepared using a dry process. The basic steps are the same as in Example 2, except that conductive carbon black is used instead of fumed silica. Specifically, the steps include:

[0043] (1) Weigh 5 kg of iron phosphate powder, and weigh 2% of conductive carbon black and 2.5% of polyvinylpyrrolidone by the mass of iron phosphate to form a dispersant; add the dispersant to the iron phosphate powder and mix for 10 min in a high-speed mixer with a speed of 500 rap / min.

[0044] (2) 1246.25g of lithium carbonate, 7.6g of glucose, 1.8g of PEG-4K, 26.4g of titanium dioxide and 28.3g of ferrous oxalate were added in sequence and mixed for 10 min to obtain a mixture.

[0045] (3) Add the mixture into a dry sand mill, control the sand milling particle size D50 between 0.6-0.8um to obtain the sand milled material, and pass the sand milled material through a 120-mesh vibrating screen to obtain the material to be sintered;

[0046] (4) Place the material to be sintered in a box furnace, purge with nitrogen for 30 min, and calcine according to the following procedure: heat up to 350℃ at 3℃ / min and hold for 3 h; heat up to 800℃ at 2℃ / min, purge with nitrogen (flow rate 2.0 L / min), hold for 8 h, and obtain the sintered material after cooling;

[0047] (5) The sintered material is subjected to air jet milling treatment, and the particle size D50 is controlled to be 1.1-1.6um to obtain lithium iron phosphate product.

[0048] Performance testing

[0049] The lithium iron phosphate prepared above was subjected to performance testing, and the results are shown in Table 1 below. The overcharge test curve is shown in the figure below. Figure 1 As shown.

[0050] Table 1 Performance test data of the examples and comparative examples

[0051]

[0052] Combining Example 1 and Example 2 in Table 1, and Figure 1 As can be seen, this invention, based on the dry preparation of lithium iron phosphate cathode materials, uses a main dispersant and fumed silica as the dispersant. First, the fumed silica and iron phosphate are thoroughly mixed and dispersed. Then, they are mixed with carbon source, lithium source, phosphorus source, and other materials, ball-milled, and sintered. The resulting lithium iron phosphate cathode material effectively shortens the time to reach the cutoff voltage to only about 5 minutes. The shorter the time, the more effectively the side reactions are avoided during overcharging, thus obtaining a stable lithium iron phosphate cathode material. Furthermore, combined with Comparative Examples 1 and 2, it can be seen that only by using fumed silica can the aforementioned technical effects be achieved.

[0053] It should be noted that the preparation process and parameters of this invention can achieve the technical effects claimed above, and therefore, no further testing and verification are required. Furthermore, in Examples 1 and 2 of this invention, the added iron source, phosphoric acid, and lithium source achieve a Li:P molar ratio of (1.00-1.05):1 and an Fe:P molar ratio of (0.95-0.99):1 in the prepared lithium iron phosphate cathode material. This calculation method is well-known to those skilled in the art and will not be described in detail here. Similarly, the amount of carbon source (glucose and PEG-4K) added also falls within the range of 5-15% of the theoretical mass of lithium iron phosphate. The amount of titanium dioxide dopant added falls within the range of 0.01-2% of the theoretical mass of lithium iron phosphate.

Claims

1. A modified lithium iron phosphate cathode material prepared by a dry process, characterized in that, It is prepared by the following steps: (1) The dispersant is mixed with the iron phosphate powder so that the dispersant is uniformly coated on the surface of the iron phosphate particles; the dispersant includes a main dispersant and fumed silica; (2) Add lithium source and carbon source to the mixture in step (1), and supplement with phosphorus source and / or iron source, mix and grind to reach the target particle size, and obtain the ground material; (3) The sand-milled material is kept at 350℃-550℃ for 1-6 hours in an inert atmosphere, and then kept at 600-800℃ for 6-24 hours in a sintering temperature. After cooling, the modified lithium iron phosphate cathode material is obtained.

2. The modified lithium iron phosphate cathode material prepared by dry process according to claim 1, characterized in that, In step (1), the amount of fumed silica added is 0.5-5% of the mass of iron phosphate.

3. The modified lithium iron phosphate cathode material prepared by dry process according to claim 1, characterized in that, In step (1), the main dispersant is selected from polyvinylpyrrolidone, poly(p-hydroxybenzoic acid), graphite or magnesium silanol sulfate, and its addition amount is 0.5-5% of the mass of iron phosphate.

4. The modified lithium iron phosphate cathode material prepared by dry process according to claim 1, characterized in that, In step (2), a dopant is added to the mixture, which is one or more compounds containing niobium, zirconium, titanium, aluminum, magnesium, zinc, tin, vanadium, manganese or cobalt.

5. The modified lithium iron phosphate cathode material prepared by dry process according to claim 4, characterized in that, The amount of dopant added is 0.01-2% of the theoretical mass of lithium iron phosphate.

6. The modified lithium iron phosphate cathode material prepared by dry process according to claim 1, characterized in that, In step (2), the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, or lithium dihydrogen phosphate; the iron source is selected from one or more of ferrous oxalate, iron oxide, iron tetroxide, or iron phosphate; and the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, or iron phosphate.

7. The modified lithium iron phosphate cathode material prepared by dry process according to claim 1, characterized in that, In step (2), the carbon source is selected from one or more of glucose, sucrose, citric acid, polyethylene glycol, polyvinylpyrrolidone, polyacrylate, graphene or conductive carbon black, and its addition amount is 5-15% of the theoretical mass of lithium iron phosphate.

8. The modified lithium iron phosphate cathode material prepared by dry process according to claim 1, characterized in that, The molar ratio of Li to P in the lithium iron phosphate cathode material is (1.00-1.05):1, and the molar ratio of Fe to P is (0.95-0.99):1.

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