阅读说明：本技术 一种磷酸铁锂正极的制备方法 (Preparation method of lithium iron phosphate anode ) 是由 朱虎 于 2019-10-17 设计创作，主要内容包括：本发明提供了一种磷酸铁锂正极的制备方法,所述正极的活性物质包括第一活性物质层,第二活性物质层和第三活性物质层,其中每一活性物质层中的磷酸铁锂的平均粒径均不相同；所述方法包括,提供第一平均粒径的磷酸铁锂配成的浆料a,第二平均粒径的磷酸铁锂配成的浆料b,第三平均粒径的磷酸铁锂配成的浆料c,其中浆料a,b,c按照不同的配比混合得到第一浆料,第二浆料和第三浆料。本发明的方法中,浆料a,b,c稳定性高,混料后能够存储较长时间,待涂布电极前,再将其按配比配置浆料,有利于延长生产线,降低成本,并且制备得到的电极性能稳定,倍率性能和循环性能都很优异。(the invention provides a preparation method of a lithium iron phosphate positive electrode, wherein an active material of the positive electrode comprises a first active material layer, a second active material layer and a third active material layer, wherein the average particle sizes of lithium iron phosphate in each active material layer are different; the method comprises the steps of providing a slurry a prepared from lithium iron phosphate with a first average particle size, a slurry b prepared from lithium iron phosphate with a second average particle size, and a slurry c prepared from lithium iron phosphate with a third average particle size, wherein the slurries a, b and c are mixed according to different proportions to obtain a first slurry, a second slurry and a third slurry. In the method, the pastes a, b and c have high stability, can be stored for a long time after being mixed, are prepared into the paste according to the proportion before being coated on the electrode, are beneficial to prolonging the production line and reducing the cost, and the prepared electrode has stable performance and excellent rate performance and cycle performance.)

1. A preparation method of a lithium iron phosphate anode is characterized by comprising the following steps: the preparation method comprises the following steps:

1) providing lithium iron phosphate particles with the average particle size of 50-80nm, sequentially adding a dispersing agent, a binder, conductive carbon black and the lithium iron phosphate particles into an organic solvent, vacuumizing and uniformly stirring to obtain slurry a, wherein the solid content of the slurry a is 52-53%, and the mass ratio of the lithium iron phosphate particles is as follows: conductive carbon black: adhesive: the dispersant is 100:5-7:2.8-3.6: 2.5-3;

2) Providing lithium iron phosphate particles with the average particle size of 120-150nm, sequentially adding a dispersing agent, a binder, conductive carbon black and the lithium iron phosphate particles into an organic solvent, vacuumizing and uniformly stirring to obtain slurry b, wherein the solid content of the slurry b is 55-56%, and the mass ratio of the lithium iron phosphate particles is as follows: conductive carbon black: adhesive: dispersant is 100:5-7:3.5-4.2: 2-2.6;

3) Providing lithium iron phosphate particles with the average particle size of 150-200nm, sequentially adding a dispersing agent, a binder, conductive carbon black and the lithium iron phosphate particles into an organic solvent, vacuumizing and uniformly stirring to obtain slurry c, wherein the solid content of the slurry c is 58-60%, and the mass ratio of the lithium iron phosphate particles is as follows: conductive carbon black: adhesive: dispersant is 100:5-7:4.6-5: 1-1.8;

4) storing the slurry a, b, c for a predetermined time;

5) Mixing the slurry a, the slurry b and the slurry c according to the mass ratio of 100:44-52:5-10, sequentially adding the slurry b and the slurry c into the slurry a under the stirring state, and vacuumizing and stirring to obtain first slurry;

6) Mixing the slurry a, the slurry b and the slurry c according to the mass ratio of 15-30:75-85:100, sequentially adding the slurry a and the slurry b into the slurry c under the stirring state, and vacuumizing and stirring to obtain a second slurry;

7) mixing the slurry a, the slurry b and the slurry c according to the mass ratio of 5-10:100:45-50, sequentially adding the slurry a and the slurry c into the slurry b under the stirring state, vacuumizing and stirring to obtain third slurry;

8) and sequentially coating and drying the first slurry, the second slurry and the third slurry on a current collector to obtain a first active material layer, a second active material layer and a third active material layer, and carrying out hot pressing to obtain the anode.

2. the method of claim 1, wherein the lithium iron phosphate is selected from carbon-coated lithium iron phosphate, metal-doped modified lithium iron phosphate, or carbon-coated metal-doped jointly modified lithium iron phosphate.

3. the method according to claim 1, wherein the thickness ratio of the first active material layer, the second active material layer and the third active material layer is 5-15:30-40: 20-30.

4. The method according to any of the preceding claims 1-2, wherein the time stored in step 4 is between 0 and 72h, preferably between 12 and 72h, further preferably between 24 and 72h, further preferably between 48 and 72 h.

5. The method according to claims 1 to 3, wherein the conductive carbon black has an average particle diameter of 5 to 20 nm.

6. the method of claims 1-4, wherein the dispersing agent is sodium carboxymethyl cellulose.

7. the method of claims 1-5, wherein the vacuum stirring time is 4-8 hours.

8. A lithium iron phosphate positive electrode prepared by the preparation method of any one of claims 1 to 6, wherein the active material of the positive electrode comprises a first active material layer, a second active material layer and a third active material layer, and the average particle diameters of lithium iron phosphate in the active material layers are different.

Technical Field

the invention relates to the technical field of lithium ion battery production, in particular to a preparation method of a lithium iron phosphate anode.

Background

The lithium iron phosphate has the advantages of low price, good safety and the like, and is widely used in the anode material of the lithium ion battery, but the tap density of the lithium iron phosphate is lower, so that the density of a pole piece is improved to become the key for improving the energy density of the lithium ion battery, and the lithium iron phosphate particles with different particle sizes are generally mixed together in the prior art, so that the stacking density of an anode active material layer is improved.

Disclosure of Invention

On the basis, the invention provides a preparation method of a lithium iron phosphate positive electrode, wherein the active material of the positive electrode comprises a first active material layer, a second active material layer and a third active material layer, wherein the average particle size of lithium iron phosphate in each active material layer is different; the method comprises the steps of providing a slurry a prepared from lithium iron phosphate with a first average particle size, a slurry b prepared from lithium iron phosphate with a second average particle size, and a slurry c prepared from lithium iron phosphate with a third average particle size, wherein the slurries a, b and c are mixed according to different proportions to obtain a first slurry, a second slurry and a third slurry, then sequentially coating and drying a current collector to obtain a first active material layer, a second active material layer and a third active material layer, and carrying out hot pressing to obtain the anode. In the method, the pastes a, b and c have high stability, can be stored for a long time after being mixed, are prepared into the paste according to the proportion before being coated on the electrode, are beneficial to prolonging the production line and reducing the cost, and the prepared electrode has stable performance and excellent rate performance and cycle performance.

The specific scheme is as follows:

A preparation method of a lithium iron phosphate anode is characterized by comprising the following steps: the preparation method comprises the following steps:

1) Providing lithium iron phosphate particles with the average particle size of 50-80nm, sequentially adding a dispersing agent, a binder, conductive carbon black and the lithium iron phosphate particles into an organic solvent, vacuumizing and uniformly stirring to obtain slurry a, wherein the solid content of the slurry a is 52-53%, and the mass ratio of the lithium iron phosphate particles is as follows: conductive carbon black: adhesive: the dispersant is 100:5-7:2.8-3.6: 2.5-3;

2) Providing lithium iron phosphate particles with the average particle size of 120-150nm, sequentially adding a dispersing agent, a binder, conductive carbon black and the lithium iron phosphate particles into an organic solvent, vacuumizing and uniformly stirring to obtain slurry b, wherein the solid content of the slurry b is 55-56%, and the mass ratio of the lithium iron phosphate particles is as follows: conductive carbon black: adhesive: dispersant is 100:5-7:3.5-4.2: 2-2.6;

3) Providing lithium iron phosphate particles with the average particle size of 150-200nm, sequentially adding a dispersing agent, a binder, conductive carbon black and the lithium iron phosphate particles into an organic solvent, vacuumizing and uniformly stirring to obtain slurry c, wherein the solid content of the slurry c is 58-60%, and the mass ratio of the lithium iron phosphate particles is as follows: conductive carbon black: adhesive: dispersant is 100:5-7:4.6-5: 1-1.8;

4) Storing the slurry a, b, c for a predetermined time;

5) mixing the slurry a, the slurry b and the slurry c according to the mass ratio of 100:44-52:5-10, sequentially adding the slurry b and the slurry c into the slurry a under the stirring state, and vacuumizing and stirring to obtain first slurry;

6) mixing the slurry a, the slurry b and the slurry c according to the mass ratio of 15-30:75-85:100, sequentially adding the slurry a and the slurry b into the slurry c under the stirring state, and vacuumizing and stirring to obtain a second slurry;

7) mixing the slurry a, the slurry b and the slurry c according to the mass ratio of 5-10:100:45-50, sequentially adding the slurry a and the slurry c into the slurry b under the stirring state, vacuumizing and stirring to obtain third slurry;

8) And sequentially coating and drying the first slurry, the second slurry and the third slurry on a current collector to obtain a first active material layer, a second active material layer and a third active material layer, and carrying out hot pressing to obtain the anode.

further, the lithium iron phosphate is selected from carbon-coated lithium iron phosphate, metal-doped modified lithium iron phosphate, or carbon-coated metal-doped combined modified lithium iron phosphate.

further, the thickness ratio of the first active material layer, the second active material layer and the third active material layer is 5-15:30-40: 20-30.

further, the storage time in the step 4 is 0 to 72 hours, preferably 12 to 72 hours, further preferably 24 to 72 hours, further preferably 48 to 72 hours.

further, the average particle diameter of the conductive carbon black is 5-20 nm.

Further, the dispersing agent is sodium carboxymethyl cellulose.

Further, the vacuum stirring time is 4-8 h.

Further, the lithium iron phosphate anode is prepared by the preparation method, and the active material of the anode comprises a first active material layer, a second active material layer and a third active material layer, wherein the average particle size of lithium iron phosphate in each active material layer is different.

the invention has the following beneficial effects:

1) In the slurries a, b and c, the average particle size of the lithium iron phosphate is stable, the binders and the dispersants with different contents are matched according to the particle size, the obtained slurry is high in stability and can be stored for a long time, and the slurry is prepared according to the proportion before being used, so that the storage time of the slurry is prolonged, the storage and the transportation of the slurry are facilitated, and the production cost is reduced;

2) The lithium iron phosphate with different particle sizes is mixed in the electrode, and particles with small particle sizes can be inserted into gaps of large particles, so that the stacking density of the positive active material layer is improved;

3) The ratio of active materials with different particle sizes is adjusted according to the positions of different active material layers, so that the rate performance of the electrode can be effectively improved;

4) The positive electrode obtained by the preparation method has the advantages that the structure of the active material layer is stable, and the cycle performance is good.

Detailed Description

the present invention will be described in more detail below with reference to specific examples, but the scope of the present invention is not limited to these examples. The lithium iron phosphate particles used in the examples and comparative examples of the present invention were LiFe_0.98Mg_0.02PO₄C (3%), the conductive carbon black is a superconducting carbon black SP having an average particle diameter of 10 nm.