High-compaction lithium iron phosphate material, preparation method thereof and lithium ion battery

Abstract

The invention provides a high-compaction lithium iron phosphate material, a preparation method thereof and a lithium ion battery. The preparation method comprises the following steps: mixing a ferrous source and a water solvent, and grinding to obtain first slurry; adding a lithium source, a carbon source and the titanium hydrolysis precursor into the first slurry, and blending to obtain second slurry; mixing a carbonate aqueous solution with the second slurry, and carrying out precipitation reaction to obtain third slurry; and calcining the third slurry to obtain the high-compaction lithium iron phosphate material. By adopting the water solvent, the safety risk is reduced, the particle size of the ferrous source is controlled, and a foundation is laid for subsequent product morphology control; the stability of the product structure is improved by introducing the titanium hydrolysis precursor; the carbonate aqueous solution is introduced to uniformly precipitate lithium in the lithium source on the surface of the ferrous source, so that the structural stability of the material can be improved, the interface bonding capacity between the ferrous source and other materials or phases which may be in contact with the ferrous source can be improved, more transmission channels and paths are provided for electrons, and the energy barrier of lithium ion diffusion is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly relates to a high tap density lithium iron phosphate material, a preparation method thereof, and a lithium ion battery. Background Art

[0002] In the current industry, in the process of preparing lithium iron phosphate by the oxalic acid method (oxalic acid + lithium dihydrogen phosphate + carbon source), methanol is required as a solvent. This is because methanol is an organic solvent with strong solubility. It can dissolve raw materials such as oxalic acid and lithium dihydrogen phosphate, and methanol has a low boiling point and is easy to remove, and has good chemical stability. However, for lithium dihydrogen phosphate, it is more soluble in water and only slightly soluble in methanol solvent. Moreover, methanol has a low flash point and is flammable, which will affect the stability of the reaction system. It also has strong toxicity, volatility, and diffusibility, and has relatively large potential safety hazards.

[0003] The lithium iron phosphate prepared by the ferrous oxalate method has obvious advantages in tap density compared with the conventional iron phosphate method, and the high tap density lithium iron phosphate has a broad market prospect. However, there are many deficiencies in the process of preparing lithium iron phosphate by the ferrous oxalate method in the prior art, including: the morphology of the ferrous oxalate raw material is difficult to control, resulting in poor processing performance of the finished lithium iron phosphate; there are safety risks; the crystal size of the prepared product is large, the particle size is not easy to control, the distribution is uneven, and the morphology is irregular, which will cause large fluctuations in the quality of lithium iron phosphate; the mixing uniformity of the raw materials is difficult to control; generally, secondary calcination is required, the synthesis time is long, and the production cycle is long.

[0004] Therefore, there is an urgent need to provide a preparation method for high tap density lithium iron phosphate materials, which can not only accurately control the morphology of raw materials and products, improve the quality of high tap density lithium iron phosphate, but also has a short cycle and high safety, which is the key research direction at present. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a high tap density lithium iron phosphate material, a preparation method thereof, and a lithium ion battery. The present invention uses an aqueous solvent, which not only reduces the safety risk, but also accurately controls the particle size of the ferrous source through grinding, laying a foundation for the subsequent control of the product morphology; secondly, a titanium hydrolysis precursor is introduced, which can be hydrolyzed into nano-sized titanium dioxide with good dispersibility, which is beneficial to improving the structural stability of the product and the rapid transmission of electrons and ions; finally, an aqueous carbonate solution is introduced to participate in the precipitation reaction, so that lithium in the lithium source precipitates uniformly on the surface of the ferrous source, which can further improve the structural stability of the material. At the same time, the uniformly precipitated lithium can act as a "bridge" to improve the interfacial bonding ability between the ferrous source and other materials or phases that may come into contact. In addition, the uniform lithium precipitation can provide more transmission channels and paths for electrons, reducing the energy barrier for lithium ion diffusion.

[0006] To achieve the object of the present invention, the following technical solutions are adopted in the present invention:

[0007] In a first aspect, the present invention provides a method for preparing a high tap density lithium iron phosphate material, and the preparation method includes the following steps:

[0008] Mix a ferrous source and an aqueous solvent, and grind to obtain a first slurry.

[0009] Add a lithium source, a carbon source and a titanium hydrolysis precursor to the first slurry, and blend to obtain a second slurry.

[0010] Mix an aqueous carbonate solution and the second slurry, and carry out a precipitation reaction to obtain a third slurry.

[0011] Calcine the third slurry to obtain the high tap density lithium iron phosphate material.

[0012] The present invention uses an aqueous solvent, which not only reduces the safety risk, but also precisely controls the particle size of the ferrous source through grinding, laying a foundation for the control of the subsequent product morphology; secondly, introducing a titanium hydrolysis precursor can hydrolyze into nanoscale titanium dioxide with good dispersibility, which is beneficial to improving the structural stability of the product and the rapid transmission of electrons and ions; finally, introducing an aqueous carbonate solution to participate in the precipitation reaction enables the lithium in the lithium source to precipitate uniformly on the surface of the ferrous source, which can further improve the structural stability of the material. At the same time, the uniformly precipitated lithium can act as a "bridge" to improve the interfacial bonding ability between the ferrous source and other materials or phases that may come into contact. In addition, the uniform lithium precipitation can provide more transmission channels and paths for electrons and reduce the energy barrier for lithium ion diffusion.

[0013] Preferably, the ferrous source includes any one or a combination of at least two of ferrous oxalate, ferrous sulfate, ferrous chloride, ferrous oxide or ferrous hydroxide, and preferably ferrous oxalate.

[0014] In the present invention, ferrous oxalate is used as one of the raw materials to prepare a high tap density lithium iron phosphate material. In the prior art, organic solvents such as methanol are commonly used, which have risks such as flammability and explosiveness and pose great potential hazards. Therefore, the present invention uses an aqueous solvent to pre-grind ferrous oxalate, which not only has a low process safety risk, but also makes the ground ferrous oxalate mix more uniformly with the subsequent raw materials, which is more conducive to the high tap density performance of the lithium iron phosphate material.

[0015] Preferably, the aqueous solvent includes pure water and / or deionized water.

[0016] Preferably, the grinding method includes sand grinding.

[0017] In the present invention, the ferrous source dissolved in an aqueous solvent is treated by sand milling, which can not only reduce the particle size, but also make the particle size distribution of the ferrous source more uniform, facilitating the uniform mixing and reaction of each raw material in subsequent reactions and laying a foundation for the high tap density lithium iron phosphate material.

[0018] Preferably, during the sand milling process, the temperature is 40 - 60 °C, such as 40 °C, 50 °C or 60 °C, etc.

[0019] In the present invention, controlling the sand milling temperature within an appropriate range can keep the ferrous source in a stable crystal structure during the sand milling process, avoiding affecting the crystal growth and structural integrity of lithium iron phosphate in subsequent steps and ensuring that the final product has good electrochemical performance; at the same time, the appropriate temperature helps to make the sand milling process more uniform, improve the particle size uniformity, and thus enhance the consistency and stability of the lithium iron phosphate material.

[0020] Preferably, the rotation speed of the sand milling is 600 - 1000 rpm, such as 600 rpm, 700 rpm, 800 rpm, 900 rpm or 1000 rpm, etc.

[0021] In the present invention, an appropriate sand milling rotation speed can fully mill the ferrous source particles, making the particle size distribution of the ferrous source more uniform, facilitating the uniform mixing and reaction of each raw material in subsequent reactions and laying a foundation for the high tap density lithium iron phosphate material.

[0022] Preferably, in the first slurry, the particle size D50 of the ferrous source is 2 - 5 μm, such as 2 μm, 3 μm, 4 μm or 5 μm, etc.

[0023] In the present invention, the ferrous source with a particle size D50 of 2 - 5 μm has a relatively large specific surface area, a larger contact area with other preparation raw materials, more sufficient reaction, shorter reaction time, improving production efficiency; secondly, this particle size distribution is beneficial to improving the tap density of lithium iron phosphate and endowing it with better electrochemical performance.

[0024] Preferably, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium oxalate, lithium acetate, lithium dihydrogen phosphate or lithium nitrate.

[0025] Preferably, the carbon source includes any one or a combination of at least two of glucose, sucrose, starch, citric acid, carbon nanotubes, stearic acid or polyethylene glycol.

[0026] Preferably, in the second slurry, the carbon element content is 1.2 - 2.5 wt%, for example, it can be 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt% or 2.5 wt%, etc., and the titanium element content is 0.15 - 0.35 wt%, for example, it can be 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt% or 0.35 wt%, etc.

[0027] Preferably, in the second slurry, the molar ratio of lithium element to iron element is (1 - 1.1):1, for example, it can be 1:1, 1.02:1, 1.04:1, 1.06:1, 1.08:1 or 1.1:1, etc.

[0028] Preferably, the titanium hydrolysis precursor includes any one or a combination of at least two of titanium oxychloride, titanium tetrachloride, tetrabutyl titanate or titanium oxysulfate.

[0029] Exemplarily, TiOCl2 + 2OH - = TiO2·H2O↓ + 2Cl - .

[0030] Preferably, stirring is accompanied during the blending process.

[0031] Preferably, the blending temperature is 90 - 120 °C, for example, it can be 90 °C, 95 °C, 100 °C, 105 °C, 110 °C, 115 °C or 120 °C, etc.

[0032] In the present invention, if the blending temperature is too low, the hydrolysis reaction is difficult to occur.

[0033] Preferably, the solid content of the second slurry is 30 - 50 wt%, for example, it can be 30 wt%, 35 wt%, 40 wt%, 45 wt% or 50 wt%, etc.

[0034] Preferably, the aqueous carbonate solution includes any one or a combination of at least two of ammonium bicarbonate aqueous solution, ammonium carbonate aqueous solution, sodium carbonate aqueous solution or potassium carbonate aqueous solution.

[0035] Preferably, when the aqueous carbonate solution is mixed with the second slurry, the following condition is satisfied: the molar ratio of lithium ions to carbonate ions is (1.9 - 2.1):1, for example, it can be 1.9:1, 1.95:1, 2:1, 2.05:1 or 2.1:1, etc.

[0036] In the present invention, an appropriate molar ratio is conducive to the full reaction of carbonate ions in the aqueous carbonate solution with lithium ions.

[0037] Preferably, the method of mixing the aqueous carbonate solution and the second slurry is as follows: the aqueous carbonate solution is added to the second slurry at a flow rate of 20 - 100 mL / min for mixing. For example, it can be 20 mL / min, 40 mL / min, 60 mL / min, 80 mL / min, or 100 mL / min, etc.

[0038] In the present invention, an appropriate flow rate helps to uniformly mix the components of the reaction system, so that the reaction system can better reach kinetic equilibrium, enabling the reaction to proceed along the expected path and rate, which is conducive to controlling the process of the precipitation reaction and improving production efficiency.

[0039] Preferably, during the mixing of the aqueous carbonate solution and the second slurry, a pH regulator is further added to adjust the pH of the mixed slurry to 5 - 7. For example, it can be 5, 5.5, 6, 6.5, or 7, etc.

[0040] In the present invention, adjusting the pH to 5 - 7 can make the reaction system in a specific acid - base environment, promoting the reaction to proceed in the direction of generating the target precipitate. For example, the following reaction occurs:

[0041] 2LiH2PO4+CO3 2- =Li2CO3↓+2H2PO4 - .

[0042] It should be noted that the present invention does not limit the type of the pH regulator. Exemplarily, for example, it can be ammonia water, etc.

[0043] Preferably, the temperature of the precipitation reaction is 60 - 85 °C. For example, it can be 60 °C, 70 °C, 80 °C, or 85 °C, etc.

[0044] In the present invention, an appropriate temperature helps to promote the full progress of the precipitation reaction, and can balance the nucleation rate and growth rate, which is beneficial to forming precipitates with uniform particle size and regular morphology. This is crucial for improving the tap density and electrochemical performance of lithium iron phosphate.

[0045] Preferably, the time of the precipitation reaction is 0.5 - 3 h. For example, it can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, or 3 h, etc.

[0046] Preferably, before the first calcination, the third slurry is first subjected to a drying treatment.

[0047] Preferably, the drying treatment method includes spray drying.

[0048] Preferably, the temperature of the drying treatment is 200 - 280 °C, for example, it can be 200 °C, 210 °C, 220 °C, 230 °C, 240 °C, 250 °C, 260 °C, 270 °C or 280 °C, etc.

[0049] Preferably, the calcination is a single calcination.

[0050] The present invention adopts the technical means of single calcination. Compared with double calcination, the process flow is simplified, the operation complexity is reduced, and it is beneficial to the uniform growth of lithium iron phosphate particles, making the particle size distribution of the product more uniform. The lithium iron phosphate particles with uniform particle size can be better stacked during the electrode preparation process, improving the compaction density of the electrode, thereby enhancing the electrochemical performance of the battery.

[0051] Preferably, the single calcination includes two-stage calcination, and the two-stage calcination includes the first-stage calcination and the second-stage calcination.

[0052] Preferably, the temperature of the first-stage calcination is lower than that of the second-stage calcination.

[0053] In the present invention, the first-stage calcination is carried out at a lower temperature, which can cause a preliminary chemical reaction of the material and lay a foundation for the subsequent second-stage calcination.

[0054] Preferably, the single calcination is carried out in an inert atmosphere. Exemplarily, for example, it can be nitrogen or argon, etc.

[0055] Preferably, the preparation method includes the following steps:

[0056] (1) Add the ferrous source to the aqueous solvent and carry out sand grinding at 40 - 60 °C to obtain the first slurry; wherein, in the first slurry, the particle size D50 of the ferrous source is 2 - 5 μm.

[0057] (2) Add the lithium source, carbon source and titanium oxychloride to the first slurry and stir and blend at 90 - 120 °C to obtain the second slurry with a solid content of 30 - 50 wt%; wherein, in the second slurry, the carbon element content is 1.2 - 2.5 wt%, the titanium element content is 0.15 - 0.35 wt%, and the molar ratio of lithium element to iron element is (1 - 1.1):1.

[0058] (3) At 30 - 50 °C (for example, it can be 30 °C, 40 °C or 50 °C, etc.), dissolve the carbonate in the aqueous solvent to obtain an aqueous carbonate solution.

[0059] Add the aqueous carbonate solution to the second slurry and mix, then add a pH regulator to adjust the pH of the mixed slurry to 5 - 7. Subsequently, carry out a precipitation reaction at 60 - 85 °C for 0.5 - 3 h to obtain a third slurry; wherein, in the mixed slurry, the molar ratio of lithium ions to carbonate ions is (1.9 - 2.1):1.

[0060] (4) Dry the third slurry at 200 - 280 °C to obtain a dried material; wherein, the drying method includes spray drying.

[0061] (5) Under the condition of an inert atmosphere, perform a first calcination on the dried material. First, carry out the first - stage calcination at 300 - 550 °C (such as 300 °C, 350 °C, 400 °C, 450 °C, 500 °C or 550 °C, etc.) for 3 - 6 h (such as 3 h, 4 h, 5 h or 6 h, etc.), and then carry out the second - stage calcination at 730 - 790 °C (such as 730 °C, 740 °C, 750 °C, 760 °C, 770 °C, 780 °C or 790 °C, etc.) for 5 - 10 h (such as 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, etc.) to obtain a calcined product.

[0062] (6) Carry out air - flow pulverization treatment on the calcined product to disperse and obtain a powdery high - tap - density lithium iron phosphate material.

[0063] In a second aspect, the present invention provides a high - tap - density lithium iron phosphate material, which is prepared by using the preparation method as described in the first aspect; the tap density of the high - tap - density lithium iron phosphate material is greater than 2.65 g / cm 3 , for example, it can be 2.7 g / cm 3 , 2.75 g / cm 3 , 2.8 g / cm 3 , 2.85 g / cm 3 or 2.9 g / cm 3 etc.

[0064] In a third aspect, the present invention provides a lithium - ion battery, and the positive electrode of the lithium - ion battery includes the high - tap - density lithium iron phosphate material as described in the second aspect.

[0065] The numerical ranges described in the present invention not only include the above - listed point values, but also include any point values between the above - mentioned numerical ranges that are not listed. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the ranges.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] (1) The present invention uses an aqueous solvent, which not only reduces the safety risk, but also precisely controls the particle size of the ferrous source through grinding, laying a foundation for the subsequent control of the product morphology. Secondly, introducing a titanium hydrolysis precursor can hydrolyze into nanoscale titanium dioxide with good dispersibility, which is beneficial to improving the structural stability of the product and the rapid transmission of electrons and ions. Finally, introducing an aqueous carbonate solution to participate in the precipitation reaction enables the lithium in the lithium source to precipitate uniformly on the surface of the ferrous source, which can further improve the structural stability of the material. At the same time, the uniformly precipitated lithium can act as a "bridge" to improve the interfacial bonding ability between the ferrous source and other materials or phases that may come into contact. In addition, the uniform lithium precipitation can provide more transmission channels and paths for electrons and reduce the energy barrier for lithium ion diffusion.

[0068] (2) Based on the preparation method provided by the present invention, not only can a high tap density lithium iron phosphate material with a tap density of more than 2.75 g / cm 3 be obtained, but also the electrochemical performance of the high tap density lithium iron phosphate material can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 is a schematic process flow diagram provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0070] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0071] Example 1

[0072] This example provides a preparation method for a high tap density lithium iron phosphate material, and its schematic process flow diagram is as Figure 1 shown. The preparation method includes the following steps:

[0073] (1) Add ferrous oxalate to pure water and perform sand grinding at 50 °C with a sand grinding speed of 800 rpm to obtain a first slurry. Among them, in the first slurry, the particle size D50 of ferrous oxalate is 3 μm.

[0074] (2) Add lithium dihydrogen phosphate, glucose, and titanium oxychloride to the first slurry and stir and blend at 100 °C to obtain a second slurry with a solid content of 40 wt%. Among them, in the second slurry, the carbon element content is 2 wt%, the titanium element content is 0.2 wt%, and the molar ratio of lithium element to iron element is 1.1:1.

[0075] (3) Dissolve ammonium bicarbonate in pure water at 40 °C to obtain an ammonium bicarbonate aqueous solution.

[0076] The ammonium bicarbonate aqueous solution is added to the second slurry at a flow rate of 60 mL / min for mixing, and ammonia water is added to adjust the pH of the mixed slurry to 6. Subsequently, a precipitation reaction is carried out at 70 °C for 2 h to obtain a third slurry; wherein, in the mixed slurry, the molar ratio of lithium ions to carbonate ions is 2:1.

[0077] (4) At 240 °C, the third slurry is dried by spray drying to obtain a dried material.

[0078] (5) Under the condition of a nitrogen atmosphere, the dried material is calcined once. First, a first-stage calcination is carried out at 400 °C for 5 h, and then a second-stage calcination is carried out at 760 °C for 7 h to obtain a calcined product.

[0079] (6) The calcined product is subjected to air-flow pulverization treatment to disperse and obtain a powdery high-compact lithium iron phosphate material.

[0080] Example 2

[0081] This example provides a method for preparing a high-compact lithium iron phosphate material, and the preparation method includes the following steps:

[0082] (1) Ferrous oxalate is added to pure water and milled at 40 °C, and the rotation speed of the milling is 1000 rpm to obtain a first slurry; wherein, in the first slurry, the particle size D50 of ferrous oxalate is 2 μm.

[0083] (2) Lithium dihydrogen phosphate, glucose, and titanium oxychloride are added to the first slurry and stirred and blended at 90 °C to obtain a second slurry with a solid content of 30 wt%; wherein, in the second slurry, the carbon element content is 1.2 wt%, the titanium element content is 0.15 wt%, and the molar ratio of lithium element to iron element is 1:1.

[0084] (3) At 30 °C, ammonium carbonate is dissolved in pure water to obtain an ammonium carbonate aqueous solution.

[0085] The ammonium carbonate aqueous solution is added to the second slurry at a flow rate of 20 mL / min for mixing, and ammonia water is added to adjust the pH of the mixed slurry to 5. Subsequently, a precipitation reaction is carried out at 60 °C for 3 h to obtain a third slurry; wherein, in the mixed slurry, the molar ratio of lithium ions to carbonate ions is 1.9:1.

[0086] (4) At 240 °C, the third slurry is dried by spray drying to obtain a dried material.

[0087] (5) Under the condition of a nitrogen atmosphere, the dried material is calcined once. First, the first-stage calcination is carried out at 300 °C for 6 h, and then the second-stage calcination is carried out at 730 °C for 10 h to obtain a calcined product.

[0088] (6) The calcined product is subjected to air-flow pulverization treatment to disperse and obtain a powdery high-compact lithium iron phosphate material.

[0089] Example 3

[0090] This example provides a preparation method of a high-compact lithium iron phosphate material. The preparation method includes the following steps:

[0091] (1) Ferrous oxalate is added to deionized water and milled at 60 °C with a milling speed of 600 rpm to obtain a first slurry. Among them, in the first slurry, the particle size D50 of ferrous oxalate is 5 μm.

[0092] (2) Lithium dihydrogen phosphate, glucose and titanium oxychloride are added to the first slurry and stirred and blended at 120 °C to obtain a second slurry with a solid content of 50 wt%. Among them, in the second slurry, the carbon element content is 2.5 wt%, the titanium element content is 0.35 wt%, and the molar ratio of lithium element to iron element is 1.1:1.

[0093] (3) At 50 °C, sodium carbonate is dissolved in deionized water to obtain an aqueous sodium carbonate solution.

[0094] The aqueous sodium carbonate solution is added to the second slurry at a flow rate of 100 mL / min for mixing, and ammonia water is added to adjust the pH of the mixed slurry to 5. Subsequently, a precipitation reaction is carried out at 85 °C for 1 h to obtain a third slurry. Among them, in the mixed slurry, the molar ratio of lithium ions to carbonate ions is 2.1:1.

[0095] (4) At 280 °C, the third slurry is dried by spray drying to obtain a dried material.

[0096] (5) Under the condition of a nitrogen atmosphere, the dried material is calcined once. First, the first-stage calcination is carried out at 550 °C for 3 h, and then the second-stage calcination is carried out at 790 °C for 5 h to obtain a calcined product.

[0097] (6) The calcined product is subjected to air-flow pulverization treatment to disperse and obtain a powdery high-compact lithium iron phosphate material.

[0098] Example 4

[0099] The difference between this example and Example 1 is that the milling in step (1) is replaced by ball milling.

[0100] The remaining preparation methods and parameters are the same as those in Example 1.

[0101] Example 5

[0102] The difference between this example and Example 1 is that the rotation speed of the sanding in step (1) is 500 rpm.

[0103] The remaining preparation methods and parameters are the same as those in Example 1.

[0104] Example 6

[0105] The difference between this example and Example 1 is that the rotation speed of the sanding in step (1) is 1200 rpm.

[0106] The remaining preparation methods and parameters are the same as those in Example 1.

[0107] Example 7

[0108] The difference between this example and Example 1 is that in the first slurry in step (1), the particle size D50 of ferrous oxalate is 1 μm.

[0109] The remaining preparation methods and parameters are the same as those in Example 1.

[0110] Example 8

[0111] The difference between this example and Example 1 is that in the first slurry in step (1), the particle size D50 of ferrous oxalate is 8 μm.

[0112] The remaining preparation methods and parameters are the same as those in Example 1.

[0113] Example 9

[0114] The difference between this example and Example 1 is that the temperature of the blending in step (2) is 80 °C.

[0115] The remaining preparation methods and parameters are the same as those in Example 1.

[0116] Example 10

[0117] The difference between this example and Example 1 is that in the mixed slurry in step (3), the molar ratio of lithium ions to carbonate ions is 1.5:1.

[0118] The remaining preparation methods and parameters are the same as those in Example 1.

[0119] Example 11

[0120] The difference between this example and Example 1 is that in the mixed slurry in step (3), the molar ratio of lithium ions to carbonate ions is 2.3:1.

[0121] The remaining preparation methods and parameters are the same as those in Example 1.

[0122] Example 12

[0123] The difference between this example and Example 1 is that the aqueous ammonium bicarbonate solution in step (3) is directly added to the second slurry instead of in the form of a flow rate.

[0124] The remaining preparation methods and parameters are the same as those in Example 1.

[0125] Example 13

[0126] The difference between this example and Example 1 is that ammonia water is not added as a pH regulator in step (3).

[0127] The remaining preparation methods and parameters are the same as those in Example 1.

[0128] Example 14

[0129] The difference between this example and Example 1 is that the temperature of the precipitation reaction in step (3) is 50 °C.

[0130] The remaining preparation methods and parameters are the same as those in Example 1.

[0131] Example 15

[0132] The difference between this example and Example 1 is that the temperature of the precipitation reaction in step (3) is 100 °C.

[0133] The remaining preparation methods and parameters are the same as those in Example 1.

[0134] Comparative Example 1

[0135] The difference between this comparative example and Example 1 is that the sanding process in step (1) is not carried out.

[0136] The remaining preparation methods and parameters are the same as those in Example 1.

[0137] Comparative Example 2

[0138] The difference between this comparative example and Example 1 is that pure water is replaced by methanol in step (1).

[0139] The remaining preparation methods and parameters are the same as those in Example 1.

[0140] Comparative Example 3

[0141] The difference between this comparative example and Example 1 is that titanium oxychloride is replaced by titanium dioxide in step (2).

[0142] The remaining preparation methods and parameters are the same as those in Example 1.

[0143] Comparative Example 4

[0144] The difference between this comparative example and Example 1 is that in step (3), aqueous ammonium bicarbonate solution is not added to the second slurry.

[0145] The remaining preparation methods and parameters are the same as those in Example 1.

[0146] Comparative Example 5

[0147] The difference between this comparative example and Example 1 is that steps (2) and (3) are combined, that is, lithium dihydrogen phosphate, glucose and titanium oxychloride are simultaneously added to the first slurry together with the aqueous ammonium bicarbonate solution to obtain the second slurry, and then the pH is adjusted for precipitation reaction.

[0148] The remaining preparation methods and parameters are the same as those in Example 1.

[0149] Performance Test

[0150] I. The tap density of the high tap density lithium iron phosphate materials provided in the above examples and comparative examples was tested. The test method was as follows: Weigh 1 g of the sample and the pressure was 20 MP.

[0151] II. Using the high tap density lithium iron phosphate materials provided in the above examples and comparative examples as the positive electrode active materials, conductive carbon black and polyvinylidene fluoride were used as the conductive agent and binder respectively, and wet pulping and coating were carried out. The coating amount was 10.9 mg / cm 2 , using a lithium sheet as the counter electrode and a Ceglard membrane as the separator, assembled into a 2032 button electrode, and the first discharge capacity at 1C was detected.

[0152] The above results are shown in Table 1.

[0153] Table 1

[0154]

[0155]

[0156] Analysis:

[0157] As can be seen from Table 1, based on the preparation method provided by the present invention, not only can a lithium iron phosphate material with a high tap density be obtained, but also the first discharge specific capacity of the lithium iron phosphate material can be improved.

[0158] As can be seen from Example 1 and Example 4, if the sand grinding described in step (1) is replaced by ball milling, the ball milling may take a longer time to achieve the desired grinding effect, the cost increases, and it is difficult to accurately control the particle size of the material, affecting the tap density of the lithium iron phosphate material.

[0159] As can be seen from Example 1 and Examples 5-6, if the rotation speed of the sanding in step (1) is too low, the grinding efficiency is low and the dispersibility is poor, resulting in a decrease in the tap density of the lithium iron phosphate material and a deterioration of the electrochemical performance; if the rotation speed of the sanding in step (1) is too high, the energy consumption increases, and the material may be overly dispersed, affecting the tap density and electrochemical performance of the subsequent lithium iron phosphate material.

[0160] As can be seen from Example 1 and Examples 7-8, if the particle size D50 of ferrous oxalate in the first slurry in step (1) is too small, the specific surface area increases significantly, which may lead to an uncontrollably fast subsequent reaction and affect the electrochemical performance of the lithium iron phosphate material. At the same time, the small-particle-size ferrous oxalate is prone to agglomeration, which in turn affects the tap density of the lithium iron phosphate material; if the particle size D50 of ferrous oxalate in the first slurry in step (1) is too large, the particle size distribution of the generated lithium iron phosphate particles will be uneven, which will lead to a decrease in the tap density of the lithium iron phosphate material and also cause incomplete reaction in the preparation process, affecting the charge-discharge performance of the lithium iron phosphate material.

[0161] As can be seen from Example 1 and Example 9, if the temperature of the blending in step (2) is too low, it is difficult to achieve uniform mixing, affecting the uniformity of the subsequent reaction and the consistency of the product, resulting in poor performance of the lithium iron phosphate material.

[0162] As can be seen from Example 1 and Examples 10-11, if the molar ratio of lithium ions to carbonate ions in the mixed slurry in step (3) is too small, at this time ammonium bicarbonate is in excess, and the unreacted ammonium bicarbonate will decompose during the product spraying or sintering stage, forming a porous structure, which is not conducive to the improvement of the tap density; if the molar ratio of lithium ions to carbonate ions in the mixed slurry in step (3) is too large, it will lead to insufficient conversion of lithium dihydrogen phosphate in the solution to nanoscale lithium carbonate, the viscosity of the system is too high, the dispersion of each component is difficult, and the particle size of the product after spray drying is too large. Finally, the product particles after sintering are all relatively large, and in addition, it is easy to cause equipment blockage.

[0163] As can be seen from Example 1 and Example 12, if the aqueous ammonium bicarbonate solution in step (3) is directly added to the second slurry instead of in the form of a flow rate, the mixing effect is poor, it is difficult to mix evenly, and local agglomeration is likely to occur, resulting in out-of-control subsequent reactions and affecting the performance of the lithium iron phosphate material.

[0164] As can be seen from Example 1 and Example 13, if ammonia water is not added as a pH regulator in step (3), the subsequent precipitation reaction is incomplete and the reaction proceeds slowly, ultimately leading to a decline in material performance.

[0165] As can be seen from Example 1 and Examples 14-15, if the temperature of the precipitation reaction in step (3) is too low, the solubility of lithium carbonate increases, the viscosity of the system is too high, it is difficult to disperse each component, and the particle size of the product after spray drying is too large. Finally, the particles of the product after sintering are all large. In addition, it is easy to cause equipment blockage; if the temperature of the precipitation reaction in step (3) is too high, a large amount of ammonium bicarbonate decomposes, that is, NH4HCO3→NH3↑+H2O+CO2↑, resulting in the loss of carbonate ions, which is not conducive to the uniform precipitation of lithium carbonate on the surface of ferrous oxalate, and is not conducive to the compaction of the product and the improvement of electrical properties.

[0166] As can be seen from Example 1 and Comparative Example 1, if the sanding process in step (1) is not carried out, it will lead to uneven particle size distribution of the final lithium iron phosphate particles, a decrease in the tap density of the lithium iron phosphate material, and incomplete reaction in the preparation process, affecting the charge and discharge performance of the lithium iron phosphate material.

[0167] As can be seen from Example 1 and Comparative Example 2, if pure water in step (1) is replaced with methanol, although it has little impact on the tap density and charge and discharge performance of the lithium iron phosphate material, it greatly increases the risk of explosion and fire, and the safety factor drops suddenly.

[0168] As can be seen from Example 1 and Comparative Example 3, if titanium oxychloride in step (2) is replaced with titanium dioxide, the dispersibility is poor, affecting the tap density and charge and discharge performance of the lithium iron phosphate material.

[0169] As can be seen from Example 1 and Comparative Example 4, if no ammonium bicarbonate aqueous solution is added to the second slurry in step (3), it is difficult to achieve uniform precipitation of lithium in the lithium source on the surface of the ferrous source, the structural stability of the material becomes poor, and the tap density and charge and discharge performance of the lithium iron phosphate material become poor.

[0170] As can be seen from Example 1 and Comparative Example 5, if the lithium source, carbon source, titanium hydrolysis precursor and carbonate aqueous solution are added to the first slurry together, part of the carbonate aqueous solution may react with the titanium hydrolysis precursor, consuming part of the carbonate aqueous solution and the titanium hydrolysis precursor, so that sufficient reaction products cannot be obtained, resulting in a decline in material performance.

[0171] It should be noted that the present invention uses the above examples to illustrate the process method of the present invention, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a high-density lithium iron phosphate material, characterized in that: The preparation method comprises the following steps: Mixing a ferrous source and a water solvent, and grinding the mixture to obtain a first slurry; Adding a lithium source, a carbon source and a titanium hydrolysis precursor into the first slurry and blending them to obtain a second slurry; Mixing the carbonate aqueous solution and the second slurry to perform a precipitation reaction to obtain a third slurry; The third slurry is calcined to obtain the high-density lithium iron phosphate material.

2. The method for preparing high-density lithium iron phosphate material according to claim 1, characterized in that: The ferrous source includes any one of ferrous oxalate, ferrous sulfate, ferrous chloride, ferrous oxide or ferrous hydroxide, or a combination of at least two thereof; Preferably, the aqueous solvent includes pure water and / or deionized water.

3. The method for preparing the high-density lithium iron phosphate material according to claim 1 or 2, characterized in that: The grinding method includes sand grinding; Preferably, the sand mill has a rotation speed of 600-1000 rpm; Preferably, in the first slurry, the particle size D50 of the ferrous source is 2-5 μm.

4. The method for preparing the high-density lithium iron phosphate material according to any one of claims 1 to 3, characterized in that: The lithium source includes any one of lithium carbonate, lithium oxalate, lithium acetate, lithium dihydrogen phosphate or lithium nitrate, or a combination of at least two thereof; Preferably, the carbon source includes any one of glucose, sucrose, starch, citric acid, carbon nanotubes, stearic acid or polyethylene glycol, or a combination of at least two thereof; Preferably, in the second slurry, the content of carbon element is 1.2-2.5wt%, and the content of titanium element is 0.15-0.35wt%; Preferably, in the second slurry, the molar ratio of lithium element to iron element is (1-1.1):1; Preferably, the titanium hydrolysis precursor includes any one of titanium dichloride, titanium tetrachloride, tetrabutyl titanate or titanium oxysulfate, or a combination of at least two thereof.

5. The method for preparing the high-density lithium iron phosphate material according to any one of claims 1 to 4, characterized in that: The blending process is accompanied by stirring; Preferably, the blending temperature is 90-120°C; Preferably, the solid content of the second slurry is 30-50 wt %.

6. The method for preparing the high-density lithium iron phosphate material according to any one of claims 1 to 5, characterized in that: The carbonate aqueous solution includes any one of an aqueous solution of ammonium bicarbonate, an aqueous solution of ammonium carbonate, an aqueous solution of sodium carbonate or an aqueous solution of potassium carbonate, or a combination of at least two thereof; Preferably, the carbonate aqueous solution and the second slurry are mixed to meet the following conditions: the molar ratio of lithium ions to carbonate ions is (1.9-2.1):1; Preferably, the carbonate aqueous solution and the second slurry are mixed in the following manner: the carbonate aqueous solution is added to the second slurry at a flow rate of 20-100 mL / min; Preferably, during the mixing process of the carbonate aqueous solution and the second slurry, a pH regulator is also added to adjust the pH of the mixed slurry to 5-7.

7. The method for preparing the high-density lithium iron phosphate material according to any one of claims 1 to 6, characterized in that: The temperature of the precipitation reaction is 60-85°C; Preferably, the precipitation reaction time is 0.5-3h; Preferably, the calcination is a single calcination; Preferably, the primary calcination includes two-stage calcination, and the two-stage calcination includes a first-stage calcination and a second-stage calcination; Preferably, the temperature of the first stage calcination is lower than the temperature of the second stage calcination.

8. The method for preparing the high-density lithium iron phosphate material according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: (1) adding a ferrous iron source to an aqueous solvent and performing sand milling at 40-60° C. to obtain a first slurry; wherein the particle size D50 of the ferrous iron source in the first slurry is 2-5 μm; (2) adding a lithium source, a carbon source and titanium dichloride to the first slurry, stirring and blending at 90-120° C. to obtain a second slurry with a solid content of 30-50 wt %; wherein the second slurry has a carbon content of 1.2-2.5 wt %, a titanium content of 0.15-0.35 wt %, and a molar ratio of lithium to iron of (1-1.1):1; (3) dissolving carbonate in a water solvent at 30-50° C. to obtain a carbonate aqueous solution; The carbonate aqueous solution is added to the second slurry and mixed, and a pH adjuster is added to adjust the pH of the mixed slurry to 5-7, and then a precipitation reaction is carried out at 60-85° C. for 0.5-3 hours to obtain a third slurry; wherein the molar ratio of lithium ions to carbonate ions in the mixed slurry is (1.9-2.1):1; (4) drying the third slurry at 200-280° C. to obtain a dried material; wherein the drying method includes spray drying; (5) calcining the dried material once under an inert atmosphere, first calcining at 300-550° C. for 3-6 h, and then calcining at 730-790° C. for 5-10 h, to obtain a calcined product; (6) The calcined product is subjected to air flow pulverization treatment to disperse and obtain a powdery high-density lithium iron phosphate material.

9. A high-density lithium iron phosphate material, characterized in that: The high-density lithium iron phosphate material is prepared by the preparation method according to any one of claims 1 to 8; The compaction density of the high-compacted lithium iron phosphate material is greater than 2.65 g / cm 3 .

10. A lithium ion battery, characterized in that: The positive electrode of the lithium-ion battery comprises the high-density lithium iron phosphate material as claimed in claim 9.

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