Preparation method of a multi-doped fluorophosphate positive electrode material

Abstract

The application discloses a preparation method of a multi-element doped fluorophosphate positive electrode material, and belongs to the technical field of electrode materials. The preparation method comprises the following steps: S1, mixing ammonium hydrogen phosphate, a mixture of vanadium pentoxide and ammonium metavanadate, graphene and glucose, and performing water sand grinding to obtain a slurry; S2, performing spray drying on the slurry, high-temperature sintering, airflow crushing, and obtaining crushed materials; S3, mixing the crushed materials, lithium fluoride, trimanganese tetroxide, lithium carbonate, nanometer carbon tubes and non-oxidized di-niobium, adding water sand grinding, and performing spray drying to obtain dry powder; and S4, high-speed mixing the dry powder with nanometer aluminum oxide, high-temperature sintering, and crushing to obtain the multi-element doped fluorophosphate positive electrode material. The multi-element doped fluorophosphate positive electrode material has the characteristics of excellent electric conductivity, good processing performance, high point, high energy density, excellent cycle and rate performance. The preparation process is simple, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of electrode material synthesis technology, and in particular to a method for preparing a multi-component doped fluorophosphate cathode material. Background Technology

[0002] With the increasing scarcity of fossil fuel resources and the growing environmental problems they cause, the development and utilization of renewable energy has become an inevitable choice for humankind. However, the random and intermittent nature of renewable energy necessitates its use in energy storage devices (such as batteries) before it can be connected to the power grid. Since its invention in 1990, lithium-ion batteries have been widely used not only in portable electronic products but also in electric vehicles and power storage systems, where their application is receiving increasing attention. Cathode materials are a crucial component of lithium-ion batteries, significantly impacting battery performance and cost. Therefore, it is essential to significantly improve the conductivity, processing performance, and energy density of cathode materials while ensuring their lifespan, cost, and safety.

[0003] Currently, lithium iron phosphate is the main cathode material for commercially available lithium-ion batteries. However, lithium iron phosphate has problems such as low ion conductivity and electronic conductivity, and insufficient specific energy, which have become key factors restricting the large-scale application of lithium iron phosphate batteries.

[0004] In recent years, lithium manganese phosphate (LiMnPO4) with olivine structure has been widely studied as a cathode material for lithium batteries due to its advantages such as high discharge voltage and high power density. However, LiMnPO4 has low conductivity and manganese is easily decomposed in the electrolyte. It needs to be improved, including: (1) reducing the particle size of the material, such as synthesizing nanoscale materials; (2) modifying the material, such as doping with other metal elements or powders with good conductivity, or carbon coating the material.

[0005] Studies have shown that fluorine doping is an effective improvement method. For example, Chinese patent CN104934600A discloses a multi-component composite phosphate nanoparticle cathode material and its preparation method. The structural formula of this multi-component composite phosphate nanoparticle cathode material is: Li 1.01 Mn x Fe 0.98-x Co 0.01 Ni 0.01 PO4F 0.01 / C, where 0≤x≤0.98. By adding fluorinating agents in two different reaction stages, the fluorination efficiency was improved, and the cycle performance of the material was enhanced. However, the above-mentioned multi-component composite phosphate nano cathode material suffers from defects such as poor structural conductivity, poor processing performance, low potential, and low energy density. Summary of the Invention

[0006] To address the technical problems existing in the prior art, this invention proposes a method for preparing multi-component doped fluorophosphate cathode materials. The multi-component doped fluorophosphate cathode materials obtained by this method exhibit excellent structural conductivity, good processability, high potential, high energy density, and excellent cycle performance.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a method for preparing a multi-element doped fluorophosphate cathode material, comprising the following steps:

[0009] S1. Mix ammonium hydrogen phosphate, vanadium pentoxide and ammonium metavanadate, graphene and glucose, then add deionized water and mill in a horizontal sand mill for 3-6 hours to obtain a slurry;

[0010] S2. The slurry obtained in step S1 is spray-dried using an air spray dryer. Then, the dried particles are heated to 720-780°C under nitrogen atmosphere protection and sintered at a constant temperature for 6-9 hours. After that, the sintered product is air-jet pulverized to obtain pulverized material.

[0011] S3. Mix the pulverized material obtained in step S2, lithium fluoride, manganese tetroxide, lithium carbonate, carbon nanotubes and niobium oxide-free powder evenly, add deionized water, and mill for 3-6 hours to obtain a mixture. Then spray dry the mixture to obtain dry powder.

[0012] S4. The dry powder obtained in step S3 is mixed with nano-alumina in a high-speed mixer to obtain a powder coated with nano-alumina. Then, the powder coated with nano-alumina is heated to 700-800℃ under an inert atmosphere and sintered at a constant temperature for 5-8 hours. After that, the sintered product is air-jet pulverized, sieved, and subjected to electromagnetic iron removal to obtain a multi-element doped fluorophosphate cathode material.

[0013] Preferably, in step S1, the mass ratio of the mixture of ammonium hydrogen phosphate, vanadium pentoxide and ammonium metavanadate, graphene and glucose is 196-203:150:5-7:13-16.

[0014] Preferably, in step S1, the solid content of the slurry is 30-50%, and the particle size of the slurry is 100-150 nm.

[0015] Preferably, in step S2, the particle size of the dried particles is 6–9 μm.

[0016] Preferably, in step S2, the particle size of the pulverized material is 10–12 μm.

[0017] Preferably, in steps S2 and S4, the heating rate is 3 to 12 °C / min.

[0018] Preferably, in step S3, the mass ratio of the pulverized material, lithium fluoride, manganese tetroxide, lithium carbonate, carbon nanotubes, and niobium oxide-free material is 260:40-50:2.5-3.5:1.3418:23-25.5:0.98-1.20, and the solid content of the mixture is 30-50%.

[0019] Preferably, in step S4, the mass ratio of the dry powder to nano-alumina is 200:0.5, and the conditions for high-speed mixing are: the circumferential speed of the stirring paddle is 0.3 to 1.8 m / s, and the rotation speed of the reamer is 5 to 40 m / s.

[0020] Another objective of this invention is to provide a multi-component doped fluorophosphate cathode material obtained by the above preparation method.

[0021] Preferably, the multi-element doped fluorophosphate cathode material is a granular powder with a particle size of 10–14 μm.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) In the preparation method of the multi-element doped fluorophosphate cathode material of the present invention, a two-step method is adopted, namely wet mixing and granulation, and the particle size of the slurry after sand milling and the pulverized material after air jet milling are controlled within a specific range during the preparation process (the particle size of the slurry is 100-150 nm, and the particle size of the pulverized material is 10-12 μm). This not only ensures good ion conductivity, but also takes into account good processing performance. At the same time, the primary particle size of 100 nm to 150 nm and a reasonable secondary particle size distribution during sand milling improve the compaction density of the product, thereby improving the energy density of the obtained cathode material. In addition, the introduction of vanadium in the raw materials increases the potential of the obtained cathode material, with a lithium potential of 4.2V.

[0024] (2) In the preparation method of the multi-doped fluorophosphate cathode material of the present invention, carbon nanotubes and graphene are used for three-dimensional coating to form a two-dimensional and three-dimensional conductive layer on the particle surface, which gives it good conductivity. A nano-alumina layer is then wrapped on the conductive layer. The double coating is similar to an egg structure, with the core being lithium vanadium fluorophosphate material, the surface being wrapped with a thin film of carbon nanotubes and graphene composite layer, and the outermost eggshell being an alumina coating layer, which protects the particles from the erosion of the electrolyte, thereby greatly improving the cycle and rate performance. The capacity retention rate is 87% after 3000 cycles at 1C, and the capacity at 10C discharge is 92% of the capacity at 1C discharge.

[0025] (3) The preparation method of the present invention is simple and suitable for large-scale industrial production. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0027] Example 1

[0028] S1. Weigh 198.6363g of ammonium hydrogen phosphate, 150g of vanadium pentoxide and ammonium metavanadate mixture and mix them. Then add 5.5441g of graphene and 13.1699g of glucose and continue mixing. After mixing thoroughly, add deionized water according to the solid content of the obtained slurry of 40%. Sand mill in a horizontal sand mill for 3 hours to obtain a slurry with a particle size of 100-150nm.

[0029] S2. The obtained slurry is spray-dried using an airflow spray dryer to obtain dried particles with a particle size of 6-9 μm. Then, the dried particles are heated to 750℃ at a rate of 8℃ / min under nitrogen atmosphere protection, sintered at a constant temperature for 8h, and then pulverized by airflow to obtain pulverized material with a particle size of 10-12 μm.

[0030] S3. Weigh 260g of the obtained pulverized material, 46.89g of lithium fluoride, 2.78g of manganese tetroxide, 1.3418g of lithium carbonate, 24.88g of carbon nanotubes and 1.05g of niobium oxide-free powder, mix them thoroughly, add deionized water, and grind them for 3 hours to obtain a mixed slurry with a solid content of 40%. Then spray dry to obtain dry powder.

[0031] S4. Mix 200g of the obtained dry powder with 0.5g of nano-alumina in a high-speed mixer to coat the surface of the dry powder with nano-alumina. Then, heat the powder coated with nano-alumina to 720℃ in a nitrogen atmosphere furnace at a rate of 8℃ / min and sinter at a constant temperature for 6 hours. After sintering, use airflow to pulverize the sintered product and sieve the pulverized product to remove iron by electromagnetic means to obtain the final product, namely, a multi-element doped fluorophosphate cathode material with a particle size of 10-14μm.

[0032] Example 2

[0033] S1. Weigh 196.544g of ammonium hydrogen phosphate, 150g of vanadium pentoxide and ammonium metavanadate mixture, mix thoroughly and evenly, then add 6.2864g of graphene and 13.1699g of glucose and continue mixing. After mixing thoroughly and evenly, add deionized water according to the solid content of the obtained slurry of 40%, and sand mill in a horizontal sand mill for 4 hours to obtain a slurry with a particle size of 100-150nm.

[0034] S2. The obtained slurry is spray-dried using an airflow spray dryer to obtain dried particles with a particle size of 6-9 μm. Then, the dried particles are heated to 780°C at a rate of 8°C / min under nitrogen atmosphere protection and sintered at 780°C for 6 hours. The particles are then pulverized by airflow to obtain pulverized material with a particle size of 10-12 μm.

[0035] S3. Weigh 260g of the obtained pulverized material, 40.1926g of lithium fluoride, 3.31g of manganese tetroxide, 1.3418g of lithium carbonate, 23.17g of carbon nanotubes and 0.9815g of niobium oxide-free powder, mix them thoroughly, add deionized water, and then sand mill for 5 hours to obtain a mixed slurry with a solid content of 40%. Then spray dry to obtain dry powder.

[0036] S4. Mix 200g of the obtained dry powder with 0.5g of nano-alumina in a high-speed mixer to coat the surface of the dry powder with nano-alumina. Then, heat the powder coated with nano-alumina to 740℃ in a nitrogen atmosphere furnace at a rate of 3℃ / min and sinter at a constant temperature for 5h. After sintering, use airflow to pulverize the sintered product and sieve the pulverized product to remove iron by electromagnetic means to obtain the final product, namely, a multi-element doped fluorophosphate cathode material with a particle size of 10-14μm.

[0037] Example 3

[0038] S1. Weigh 202.34g of ammonium hydrogen phosphate, 150g of vanadium pentoxide and ammonium metavanadate mixture and mix them. Then add 5.731g of graphene and 15.247g of glucose and mix thoroughly. Add deionized water according to the solid content of the obtained slurry of 40%. Sand mill in a horizontal sand mill for 6 hours to obtain a slurry with a particle size of 100-150nm.

[0039] S2. The obtained slurry is spray-dried using an airflow spray dryer to obtain dried particles with a particle size of 6-9μm. Then, the dried particles are heated to 750℃ at a rate of 3℃ / min under nitrogen atmosphere protection, sintered at a constant temperature for 6h, and then pulverized by airflow to obtain pulverized material with a particle size of 10-12μm.

[0040] S3. Weigh 260g of the obtained pulverized material, 49.35g of lithium fluoride, 3.15g of manganese tetroxide, 1.3418g of lithium carbonate, 25.21g of carbon nanotubes and 1.175g of niobium oxide-free powder, mix them thoroughly, add deionized water, and then sand mill for 5 hours to obtain a mixed slurry with a solid content of 40%. Then spray dry to obtain dry powder.

[0041] S4. Mix 200g of the obtained dry powder with 0.5g of nano-alumina in a high-speed mixer to coat the surface of the dry powder with nano-alumina. Then, heat the powder coated with nano-alumina to 700℃ in a nitrogen atmosphere furnace at a rate of 8℃ / min and sinter at a constant temperature for 8h. After sintering, use airflow to pulverize the sintered product and sieve the pulverized product to remove iron by electromagnetic means to obtain the final product, namely, a multi-element doped fluorophosphate cathode material with a particle size of 10-14μm.

[0042] Example 4

[0043] S1. Weigh 198.6363g of ammonium hydrogen phosphate, 150g of vanadium pentoxide and ammonium metavanadate mixture and mix them. Then add 5.5441g of graphene and 13.1699g of glucose and continue mixing. After mixing thoroughly, add deionized water according to the solid content of the obtained slurry of 40%. Sand mill in a horizontal sand mill for 4 hours to obtain a slurry with a particle size of 100-150nm.

[0044] S2. The obtained slurry is spray-dried using an airflow spray dryer to obtain dried particles with a particle size of 6-9 μm. Then, the dried particles are heated to 720℃ at a rate of 12℃ / min under nitrogen atmosphere protection, sintered at a constant temperature for 9 hours, and then pulverized by airflow to obtain pulverized material with a particle size of 10-12 μm.

[0045] S3. Weigh 260g of the obtained pulverized material, 46.89g of lithium fluoride, 2.78g of manganese tetroxide, 1.3418g of lithium carbonate, 24.88g of carbon nanotubes and 1.05g of niobium oxide-free powder, mix them thoroughly, add deionized water, and grind them for 6 hours to obtain a mixed slurry with a solid content of 40%. Then spray dry to obtain dry powder.

[0046] S4. Mix 200g of the obtained dry powder with 0.5g of nano-alumina in a high-speed mixer to coat the surface of the dry powder with nano-alumina. Then, heat the powder coated with nano-alumina to 800℃ in a nitrogen atmosphere furnace at a rate of 12℃ / min and sinter at a constant temperature for 5h. After sintering, use airflow to pulverize the sintered product and sieve the pulverized product to remove iron by electromagnetic means to obtain the final product, namely, a multi-element doped fluorophosphate cathode material with a particle size of 10-14μm.

[0047] Comparative Example 1

[0048] The results are basically the same as in Example 1, except that carbon nanotubes are not added in step S3 in this Comparative Example 1, while the rest is the same as in Example 1, to obtain a multi-element doped fluorophosphate cathode material.

[0049] Comparative Example 2

[0050] The results are basically the same as in Example 1, except that step S4 is omitted in Comparative Example 2, and the rest is the same as in Example 1, to obtain a multi-element doped fluorophosphate cathode material.

[0051] Performance testing:

[0052] The multi-component doped fluorophosphate cathode materials prepared in Examples 1 and 1-2 were dissolved in 1-methyl-2-pyrrolidone at a mass ratio of 8:1:1 (total mass 0.5 g) with acetylene black and PVDF. After uniform mixing, the mixture was coated onto aluminum foil in a slurry state and vacuum dried to form cathode sheets. The dried electrode sheets were sliced ​​and accurately weighed to serve as the cathodes of the batteries. Simultaneously, using lithium sheets as counter electrodes, microporous polyethylene as separators, and 1.0 mol / L LiPF6+DMC as electrolyte, button cells were assembled using a tablet press in an argon-filled glove box and aged for 8 hours.

[0053] The battery was subjected to constant current charge-discharge cycle testing within a voltage range of 2.7V to 4.8V. The test temperature was 25℃±2℃. The charge-discharge performance, high-rate charge-discharge performance, and low-temperature performance of the assembled lithium-ion battery were measured at charge-discharge rates from 1C (132mA·g⁻¹) to 10C (1320mA·g⁻¹).

[0054] The test results showed that the charge cutoff voltage of the multi-component doped fluorophosphate cathode material prepared in Example 1 was 4.8V, the operating voltage plateau was 4.0V, the specific capacity (graphite electrode) was 142mAh / g (coin charge 0.5C, 2.7-4.8V), and the compaction density was 2.5g / cm³. 3 The capacity retention rate after 3000 cycles at 1C is 87%. After continuous 5C discharge, the 10C discharge capacity is 92% of the 1C discharge capacity. The 1C discharge capacity at -20℃ is 97% of the room temperature capacity, and the 1C discharge capacity at -40℃ is 89% of the room temperature capacity.

[0055] The cathode material prepared in Comparative Example 1 has a 10C discharge capacity of 81% of its 1C discharge capacity and a 1C discharge capacity of 85% at -20℃ compared to that at room temperature; the cathode material prepared in Comparative Example 2 has a 1C cycle capacity retention rate of 80% after 2000 cycles.

[0056] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a multi-component doped fluorophosphate cathode material, characterized in that, Includes the following steps: S1. Mix ammonium hydrogen phosphate, vanadium pentoxide and ammonium metavanadate, graphene and glucose, then add deionized water and mill in a horizontal sand mill for 3-6 hours to obtain a slurry; S2. The slurry obtained in step S1 is spray-dried using an air spray dryer. Then, the dried particles are heated to 720~780℃ under nitrogen atmosphere protection and sintered at a constant temperature for 6~9 hours. After that, the sintered product is air-jet pulverized to obtain pulverized material. S3. Mix the pulverized material obtained in step S2, lithium fluoride, manganese tetroxide, lithium carbonate, carbon nanotubes and niobium pentoxide evenly, then add deionized water, and mill for 3-6 hours to obtain a mixture. Then spray dry the mixture to obtain dry powder. S4. The dry powder obtained in step S3 is mixed with nano-alumina in a high-speed mixer to obtain a powder coated with nano-alumina. Then, the obtained powder coated with nano-alumina is heated to 700~800℃ under an inert atmosphere and sintered at a constant temperature for 5~8h. After that, the sintered product is air-jet pulverized, sieved, and electromagnetically removed to obtain a multi-element doped fluorophosphate cathode material. The multi-doped fluorophosphate cathode material is a granular powder with a particle size of 10~14μm.

2. The method for preparing the multi-component doped fluorophosphate cathode material according to claim 1, characterized in that, In step S1, the mass ratio of the mixture of ammonium hydrogen phosphate, vanadium pentoxide and ammonium metavanadate, graphene and glucose is 196~203:150:5~7:13~16.

3. The method for preparing the multi-component doped fluorophosphate cathode material according to claim 1, characterized in that, In step S1, the solid content of the slurry is 30-50%, and the particle size of the slurry is 100-150 nm.

4. The method for preparing the multi-component doped fluorophosphate cathode material according to claim 1, characterized in that, In step S2, the particle size of the dried particles is 6~9μm.

5. The method for preparing the multi-component doped fluorophosphate cathode material according to claim 1, characterized in that, In step S2, the particle size of the pulverized material is 10~12μm.

6. The method for preparing the multi-component doped fluorophosphate cathode material according to claim 1, characterized in that, In steps S2 and S4, the heating rate is 3~12℃ / min.

7. The method for preparing the multi-component doped fluorophosphate cathode material according to claim 1, characterized in that, In step S3, the mass ratio of the pulverized material, lithium fluoride, manganese tetroxide, lithium carbonate, carbon nanotubes and niobium oxide-free material is 260:40~50:2.5~3.5:1.3418:23~25.5:0.98~1.20, and the solid content of the mixture is 30~50%.

8. The method for preparing the multi-component doped fluorophosphate cathode material according to claim 1, characterized in that, In step S4, the mass ratio of the dry powder to nano alumina is 200:0.5, and the conditions for high-speed mixing are: the circumferential speed of the stirring paddle is 0.3 to 1.8 m / s, and the rotation speed of the reamer is 5 to 40 m / s.