Method for synthesizing lithium iron phosphate by using anhydrous amorphous iron phosphate

Abstract

The invention belongs to the technical field of preparation of lithium iron phosphate, and particularly relates to a method for synthesizing lithium iron phosphate by using anhydrous amorphous iron phosphate. The preparation method comprises the following steps: mixing anhydrous amorphous iron phosphate, a lithium source, an organic carbon source and liquid alcohol to obtain a mixed wet material; grinding the mixed wet material, and performing spray drying to obtain lithium iron phosphate precursor powder; and calcining the lithium iron phosphate precursor powder in a protective gas atmosphere to obtain the olivine type lithium iron phosphate. According to the invention, anhydrous amorphous iron phosphate is adopted as a raw material and can be easily and fully mixed with a lithium source, an organic carbon source and liquid alcohol, and the lithium iron phosphate positive electrode material in which lithium is fully embedded can be obtained after subsequent roasting, so that the energy density of the positive electrode material is improved; meanwhile, the introduction of magnetic foreign matters is effectively reduced, and the energy consumption in the synthesis process of the lithium iron phosphate positive electrode material is effectively reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium iron phosphate preparation, and specifically relates to a method for synthesizing lithium iron phosphate by using anhydrous amorphous iron phosphate. Background Art

[0002] Lithium iron phosphate has attracted much attention as a new generation of lithium battery positive electrode material. With the development of the lithium battery industry, lithium iron phosphate positive electrode material is considered to be a new generation of lithium-ion positive electrode material due to its advantages such as safety, non-toxicity, environmental friendliness, and high specific capacity.

[0003] At present, the synthesis of lithium iron phosphate is usually to mix olivine iron phosphate with lithium source and carbon source with deionized water, grind and spray dry, and then roast to obtain olivine lithium iron phosphate positive electrode material. The disadvantage of this method is that olivine iron phosphate needs to be roasted in a rotary kiln at 600-700°C for several hours. On the one hand, this method consumes a lot of energy. On the other hand, the friction between the material and the rotary kiln wall will inevitably introduce magnetic impurities into the material. Such magnetic impurities are difficult to remove in subsequent processes, thereby affecting the quality of the lithium iron phosphate positive electrode material. Summary of the invention

[0004] The object of the present invention is to provide a method for synthesizing lithium iron phosphate using anhydrous amorphous iron phosphate. The method provided by the present invention can improve the quality of lithium iron phosphate positive electrode materials, while reducing the energy consumption of the synthesis process, and is suitable for industrial production.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a method for synthesizing lithium iron phosphate using anhydrous amorphous iron phosphate, comprising the following steps:

[0007] Mixing anhydrous amorphous ferric phosphate, a lithium source, an organic carbon source and liquid alcohol to obtain a mixed wet material;

[0008] Grinding the mixed wet material and then spray drying it to obtain lithium iron phosphate precursor powder;

[0009] The lithium iron phosphate precursor powder is calcined in a protective gas atmosphere to obtain olivine-type lithium iron phosphate.

[0010] Preferably, the lithium source includes lithium carbonate and / or lithium hydroxide.

[0011] Preferably, the molar ratio of iron ions in the anhydrous amorphous ferric phosphate to lithium ions in the lithium source is 1:1.

[0012] Preferably, the organic carbon source comprises glucose and / or sucrose.

[0013] Preferably, the mass of the organic carbon source accounts for 10-20% of the total mass of the anhydrous amorphous iron phosphate and the lithium source.

[0014] Preferably, the liquid alcohol includes liquid fatty alcohol and / or liquid aromatic alcohol; the liquid fatty alcohol includes one or more of methanol, ethanol, propanol, ethylene glycol and glycerol; the liquid aromatic alcohol includes benzyl alcohol and / or phenylethyl alcohol.

[0015] Preferably, the mass of the liquid alcohol accounts for 120-150% of the total mass of the anhydrous amorphous ferric phosphate, the lithium source and the organic carbon source.

[0016] Preferably, the grinding time is 3 to 5 hours; after the grinding, a slurry is obtained, and the slurry is spray-dried; the particle size D of the slurry is 50 It is 0.4~0.5μm.

[0017] Preferably, the rotation speed of the spray drying is 10000-15000 rpm; and the particle size of the lithium iron phosphate precursor powder is 35-40 μm.

[0018] Preferably, the calcination temperature is 600-900° C., and the holding time is 8-10 h; the heating rate from room temperature to the calcination temperature is 1-10° C. / min; and the calcination is carried out in a tunnel kiln.

[0019] The present invention provides a method for synthesizing lithium iron phosphate using anhydrous amorphous iron phosphate, comprising the following steps: mixing anhydrous amorphous iron phosphate, a lithium source, an organic carbon source and a liquid alcohol to obtain a mixed wet material; grinding the mixed wet material and spray drying it to obtain a lithium iron phosphate precursor powder; calcining the lithium iron phosphate precursor powder in a protective gas atmosphere to obtain olivine-type lithium iron phosphate. Compared with the prior art, the present invention has at least the following beneficial effects:

[0020] 1. The present invention uses anhydrous amorphous ferric phosphate as a raw material. Since anhydrous amorphous ferric phosphate is an amorphous substance with very small particles, it is easy to be fully mixed with a lithium source, an organic carbon source and a liquid alcohol. After subsequent roasting, a lithium iron phosphate positive electrode material fully embedded with lithium can be obtained, thereby improving the energy density of the positive electrode material;

[0021] 2. The present invention uses anhydrous amorphous iron phosphate as raw material, and no pretreatment step of roasting in a rotary kiln is required, which effectively reduces the introduction of magnetic foreign matter, improves the quality of lithium iron phosphate positive electrode materials and the safety performance of lithium iron phosphate batteries;

[0022] 3. The present invention uses anhydrous amorphous iron phosphate as raw material, the raw material does not contain crystal water, and there is no need to perform a pretreatment step of roasting in a rotary kiln, which can effectively reduce the energy consumption in the synthesis process of lithium iron phosphate positive electrode materials. DETAILED DESCRIPTION

[0023] The present invention provides a method for synthesizing lithium iron phosphate using anhydrous amorphous iron phosphate, comprising the following steps:

[0024] Mixing anhydrous amorphous ferric phosphate, a lithium source, an organic carbon source and liquid alcohol to obtain a mixed wet material;

[0025] Grinding the mixed wet material and then spray drying it to obtain lithium iron phosphate precursor powder;

[0026] The lithium iron phosphate precursor powder is calcined in a protective gas atmosphere to obtain olivine-type lithium iron phosphate.

[0027] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well known to those skilled in the art.

[0028] The present invention mixes anhydrous amorphous iron phosphate, a lithium source, an organic carbon source and a liquid alcohol to obtain a mixed wet material. In the present invention, the anhydrous amorphous iron phosphate refers to FePO4 that does not contain crystal water and has no crystal form (amorphous state). The present invention has no special requirements for the source of the anhydrous amorphous iron phosphate, and the anhydrous amorphous iron phosphate can be a commercially available product. In the present invention, the lithium source preferably includes lithium carbonate and / or lithium hydroxide. The mass ratio of the anhydrous amorphous iron phosphate and the lithium source is preferably based on the molar ratio of the iron ions in the anhydrous amorphous iron phosphate to the lithium ions in the lithium source being 1:1. The organic carbon source preferably includes glucose and / or sucrose. The mass of the organic carbon source accounts for 10 to 20% of the total mass of the anhydrous amorphous iron phosphate and the lithium source, and more preferably 13 to 15%. In the present invention, the liquid alcohol refers to an alcohol organic compound that is in a liquid state at normal temperature and pressure. The liquid alcohol preferably includes liquid fatty alcohol and / or liquid aromatic alcohol. The liquid fatty alcohol preferably includes one or more of methanol, ethanol, propanol, ethylene glycol and glycerol. The liquid aromatic alcohol preferably includes benzyl alcohol and / or phenylethyl alcohol. The liquid alcohol is more preferably methanol or ethanol. The mass of the liquid alcohol accounts for 120-150% of the total mass of the anhydrous amorphous ferric phosphate, the lithium source and the organic carbon source. The mixing preferably includes the following steps: mixing the anhydrous amorphous ferric phosphate and the lithium source, and then adding the organic carbon source and the liquid alcohol in sequence for mixing. The present invention has no special requirements for the specific implementation of the mixing.

[0029] After obtaining the mixed wet material, the present invention grinds the mixed wet material and then spray-dries it to obtain lithium iron phosphate precursor powder. In the present invention, the grinding time is preferably 3 to 5 hours, more preferably 3 to 3.5 hours. After the grinding, a slurry is obtained, and the present invention spray-dries the slurry. The particle size D of the slurry 50 Preferably, the particle size D of the slurry obtained in the embodiment is 0.4 to 0.5 μm. 50 It is 0.43μm or 0.45μm. The rotation speed of the spray drying is preferably 10000-15000rpm, and the rotation speed of the spray drying is the rotation speed of the spray atomizing wheel during spray drying. The particle size of the lithium iron phosphate precursor powder is preferably 35-40μm. The particle size of the lithium iron phosphate precursor powder obtained in the embodiment is 37.1μm or 36.8μm. The present invention preferably removes the liquid alcohol in the slurry by spray drying.

[0030] After obtaining the lithium iron phosphate precursor powder, the present invention calcines the lithium iron phosphate precursor powder in a protective gas atmosphere to obtain olivine-type lithium iron phosphate. In the present invention, the calcination temperature is preferably 600-900°C, and the holding time is preferably 8-10h. In an embodiment of the present invention, the calcination temperature is 750°C, and the holding time is 8.5h or 9h. The heating rate from room temperature to the calcination temperature is preferably 1-10°C / min, more preferably 5-10°C / min. The protective gas for the calcination is preferably nitrogen. The calcination is preferably carried out in a tunnel kiln.

[0031] After the calcination to obtain olivine-type lithium iron phosphate, the present invention preferably crushes and screens the olivine-type lithium iron phosphate in sequence to obtain an olivine-type lithium iron phosphate product. The present invention has no special requirements for the specific implementation process of the crushing and screening.

[0032] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0033] Example 1

[0034] Lithium carbonate and anhydrous amorphous ferric phosphate were mixed in a lithium ion to iron ion molar ratio of 1:1, and sucrose accounting for 13% of the total mass of lithium carbonate and anhydrous amorphous ferric phosphate was added to mix, and then ethanol was added according to 120% of the total mass of the materials (lithium carbonate, anhydrous amorphous ferric phosphate and sucrose) to mix evenly and grind. After grinding for 3 hours, the slurry was taken out and the slurry particle size D was tested. 50=0.46 μm, and the obtained slurry is spray-dried, and the speed of the spray atomizer wheel during spray drying is 14316 rpm, and the particle size of the obtained lithium iron phosphate precursor powder is 37.1 μm; the prepared lithium iron phosphate spray precursor with a large spray particle size is heated at a heating rate of 5°C / min under the protection of a nitrogen atmosphere, and after reaching 750°C, the temperature is kept constant for 8.5 hours to obtain sintered lithium iron phosphate, and the sintered lithium iron phosphate is then crushed and sieved to obtain the final lithium iron phosphate product.

[0035] Example 2

[0036] Lithium hydroxide and anhydrous amorphous ferric phosphate were mixed in a molar ratio of lithium ion to iron ion of 1:1, and glucose accounting for 15% of the total mass of lithium carbonate and anhydrous amorphous ferric phosphate was added to mix, and then methanol accounting for 120% of the total mass of the materials (lithium carbonate, anhydrous amorphous ferric phosphate and sucrose) was added to mix evenly and grinded. After grinding for 3.5 hours, the slurry was taken out and the slurry particle size D was tested. 50 =0.43 μm, and the obtained slurry is spray-dried, and the speed of the spray atomizer wheel during spray drying is 14115 rpm, and the particle size of the obtained lithium iron phosphate precursor powder is 36.8 μm; the prepared lithium iron phosphate spray precursor with a large spray particle size is heated at a heating rate of 10°C / min under the protection of a nitrogen atmosphere, and after reaching 750°C, the temperature is maintained for 9 hours to obtain sintered lithium iron phosphate, and the sintered lithium iron phosphate is crushed and sieved to obtain the final lithium iron phosphate product.

[0037] It can be seen from the above embodiments that the method provided by the present invention is very small because the particles of anhydrous amorphous iron phosphate are very small, and therefore it is easy to be fully mixed with a lithium source (lithium carbonate or lithium hydroxide) and an organic carbon source (glucose or sucrose) and a liquid alcohol (methanol or ethanol). After subsequent roasting, a lithium iron phosphate positive electrode material fully embedded with lithium can be obtained, thereby improving the energy density of the positive electrode material; at the same time, the present invention effectively reduces the introduction of magnetic foreign matter, improves the quality of the lithium iron phosphate positive electrode material and the safety performance of the lithium iron phosphate battery; and can also effectively reduce the energy consumption in the synthesis process of the lithium iron phosphate positive electrode material.

[0038] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for synthesizing lithium iron phosphate using anhydrous amorphous iron phosphate, characterized in that: The following steps are involved: Mixing anhydrous amorphous ferric phosphate, a lithium source, an organic carbon source and liquid alcohol to obtain a mixed wet material; Grinding the mixed wet material and then spray drying it to obtain lithium iron phosphate precursor powder; The lithium iron phosphate precursor powder is calcined in a protective gas atmosphere to obtain olivine-type lithium iron phosphate.

2. The method according to claim 1, characterized in that The lithium source includes lithium carbonate and / or lithium hydroxide.

3. The method according to claim 1 or 2, characterized in that: The molar ratio of the iron ions in the anhydrous amorphous ferric phosphate to the lithium ions in the lithium source is 1:

1.

4. The method according to claim 1, characterized in that: The organic carbon source includes glucose and / or sucrose.

5. The method according to claim 1 or 4, characterized in that: The mass of the organic carbon source accounts for 10-20% of the total mass of the anhydrous amorphous iron phosphate and the lithium source.

6. The method according to claim 1, characterized in that The liquid alcohol includes liquid fatty alcohol and / or liquid aromatic alcohol; the liquid fatty alcohol includes one or more of methanol, ethanol, propanol, ethylene glycol and glycerol; the liquid aromatic alcohol includes benzyl alcohol and / or phenylethyl alcohol.

7. The preparation method according to claim 1 or 6, characterized in that: The mass of the liquid alcohol accounts for 120-150% of the total mass of the anhydrous amorphous ferric phosphate, the lithium source and the organic carbon source.

8. The method according to claim 1, characterized in that The grinding time is 3 to 5 hours; the slurry is obtained after the grinding, and the slurry is spray-dried; the particle size of the slurry is D 50 It is 0.4~0.5μm.

9. The method according to claim 1, characterized in that: The rotation speed of the spray drying is 10000-15000 rpm; the particle size of the lithium iron phosphate precursor powder is 35-40 μm.

10. The preparation method according to claim 1 or 9, characterized in that: The calcination temperature is 600-900° C., and the heat preservation time is 8-10 hours; the heating rate from room temperature to the calcination temperature is 1-10° C. / min; and the calcination is carried out in a tunnel kiln.