A dry electrode film of lithium iron phosphate and its preparation method

Abstract

This invention relates to the field of lithium-ion battery technology, and in particular to a dry-process lithium iron phosphate electrode film and its preparation method. The preparation method includes: S1, premixing lithium iron phosphate with a low-tap-density conductive agent to obtain a uniformly mixed first mixture; S2, adding a binder to the first mixture to obtain a uniformly mixed second mixture; S3, converting the second mixture into electrode clusters, and repeatedly folding and calendering the electrode clusters to obtain a positive electrode film with no abnormal appearance. This invention optimizes the input ratio of lithium iron phosphate, conductive agent and PTFE particles by adding a low-tap-density conductive agent to small-particle-size (D50 < 1 μm) lithium iron phosphate, and uses a dry preparation process to obtain a continuous, self-supporting lithium iron phosphate electrode film with no abnormal appearance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a dry electrode film of lithium iron phosphate and its preparation method. Background Technology

[0002] Currently, the fabrication process for lithium-ion battery electrode films is the traditional wet process. This involves mixing powder materials with solvents to prepare a slurry, followed by coating, drying, and solvent recovery. However, this process suffers from high energy consumption, high cost, environmental pollution, electrode delamination, and limitations on electrode thickness. Therefore, the dry electrode process, which eliminates the need for solvents, offers advantages such as lower production costs, lower energy consumption, and environmental friendliness, making it a superior choice.

[0003] The dry electrode process mainly includes steps such as dry powder mixing, fiberization treatment, and dry film formation. Among them, the dry powder mixing step mainly involves mixing active materials, conductive agents, and binders in dry powder form in proportion. Uniform mixing is achieved through mechanical stirring, high-speed shearing, or airflow dispersion to avoid particle agglomeration and ensure that the conductive agents and binders uniformly coat the active materials.

[0004] Existing dry processes can easily prepare negative electrode films, but there are still significant difficulties in preparing positive electrode films, especially for small-sized (D50 < 1 μm) lithium iron phosphate particles (active materials), making it difficult to form a continuous, self-supporting lithium iron phosphate electrode film with an unblemished appearance. Summary of the Invention

[0005] The purpose of this invention is to provide a lithium iron phosphate dry electrode film and its preparation method to solve the problems mentioned in the background art.

[0006] The technical solution adopted in this invention is:

[0007] A method for preparing a lithium iron phosphate dry electrode film, the method comprising the following steps:

[0008] S1. Premix lithium iron phosphate with a low tap density conductive agent to obtain a uniformly mixed first mixture;

[0009] S2. Add a binder to the first mixture to obtain a uniformly mixed second mixture;

[0010] S3. The second mixture is converted into an electrode cluster, and the electrode cluster is repeatedly folded and rolled to obtain a positive electrode film with no abnormal appearance.

[0011] Optionally, the mass ratio of the lithium iron phosphate, the low tap density conductive agent, and the binder is (88~93):(10~5):2.

[0012] Optionally, the mass ratio of lithium iron phosphate, low tap density conductive agent and binder is preferably 93:5:2.

[0013] Optionally,

[0014] The low tap density conductive agent is one of CNT and conductive carbon black;

[0015] The lithium iron phosphate is composed of small-diameter particles with a D50 of <1 μm.

[0016] Optionally, the lower the tap density of the low-tap-density conductive agent, the less of the low-tap-density conductive agent is required to form a continuous, non-abnormally-appearing self-supporting positive electrode film.

[0017] Optionally, in steps S1 and S2, mixing is carried out using a stirring tank, the temperature of which is controlled between 0 and 15°C.

[0018] Optionally, in step S1, the stirring of the mixing tank includes:

[0019] In the first stirring stage, the stirring time is controlled between 60 and 180 seconds.

[0020] The second stirring stage is controlled between 300 and 900 seconds.

[0021] Optionally, in step S2, the stirring of the mixing tank includes:

[0022] Slow stirring, wherein the slow stirring time is controlled between 60 and 180 seconds;

[0023] Rapid stirring, with the rapid stirring time controlled between 60 and 180 seconds.

[0024] Optionally, in step S2, the adhesive needs to be cooled and sieved before being added to the first mixture.

[0025] Optionally, the lithium iron phosphate dry electrode film is prepared by the same method used for preparing lithium iron phosphate dry electrode films.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] By adding a low-taper-density conductive agent to small-particle-size (D50 < 1 μm) lithium iron phosphate and optimizing the input ratio of lithium iron phosphate, conductive agent and PTFE particles, a continuous self-supporting lithium iron phosphate electrode film with no abnormal appearance can be obtained using a dry preparation process. Detailed Implementation

[0028] Given the current technology, it is difficult to form a continuous, self-supporting lithium iron phosphate electrode film with no abnormal appearance for small-sized (D50 < 1 μm) lithium iron phosphate particles (active materials). Example 1

[0029] This embodiment provides a method for preparing a dry-process lithium iron phosphate electrode film. In this embodiment, the active material is small-particle-size (D50 < 1 μm) lithium iron phosphate, the low-tap-density conductive agent is CNT with a tap density of 0.025 g / cm³, and the binder is PTFE. The preparation method includes the following steps:

[0030] 1. First, add lithium iron phosphate particles and CNTs into a mixing tank, turn on the chilled water, and control the temperature between 0 and 15°C. Reverse the stirring shaft at 150 rpm, while simultaneously rotating the mixing tank forward at 45 rpm. Control the stirring time between 60 and 180 seconds, preferably 120 seconds, to premix the lithium iron phosphate particles and CNTs. At the same time, prevent CNT dust from being emitted. Preventing CNT dust is an existing technology and will not be described in detail here.

[0031] 2. Keep the chilled water on and control the temperature between 0 and 15°C. Reverse the stirring shaft at 2250 rpm, while simultaneously rotating the stirring tank forward at 45 rpm. Control the stirring time between 300 and 900 seconds, preferably 600 seconds, to coat the lithium iron phosphate particles with CNTs and obtain a uniformly mixed first mixture.

[0032] 3. First, refrigerate the PTFE particles in the refrigerator for about 24 hours. Before feeding, sieve them through a 2mm sieve to prevent PTFE particles from clumping. Keep the chilled water on and control the temperature between 0 and 15°C. Add the PTFE particles to the first mixture and stir slowly with the stirring shaft reversed at 150 rpm and the stirring tank rotated forward at 45 rpm. The stirring time should be controlled between 60 and 180 seconds, preferably 120 seconds. Then, stir rapidly with the stirring shaft reversed at 2250 rpm and the stirring tank rotated forward at 45 rpm. The stirring time should be controlled between 60 and 180 seconds, preferably 120 seconds. This will result in a second mixture of lithium iron phosphate particles, CNTs, and PTFE particles that are mixed evenly. This will also reduce the particle size of the PTFE particles from 425-525 μm to about 10 μm without fiberization.

[0033] 4. Turn off the chilled water, reverse the stirring shaft to 4500 rpm, and at the same time, rotate the stirring tank forward to 45 rpm. The temperature rises to between 60 and 90°C. Preferably, the stirring is stopped when the temperature rises to 70°C. The uniformly mixed powder is transformed into electrode clusters by inducing the fibrillation of PTFE particles. The fibrillation of PTFE particles is an existing technology and will not be described in detail here.

[0034] 5. Place the electrode bundle in a 100℃ oven and bake for 2 hours to promote further fibrillation of the PTFE particles; control the ambient humidity to within 10% to prevent the PTFE particles from absorbing water and sticking to the rollers; then place the baked electrode bundle between the two rollers of the open mill at a temperature of 120℃, a gap of 200μm, and a differential speed ratio of 3 to obtain a low-strength film. After folding it in half, place it again between the two rollers of the open mill with the same parameters to obtain a film with improved strength. Repeat this process 2-4 times to obtain a smooth lithium iron phosphate cathode film without wrinkles or cracks. By adjusting the gap, a self-supporting film with a thickness of 100μm can be obtained.

[0035] The mass ratio of lithium iron phosphate, CNT and PTFE is 93:5:2. Example 2

[0036] This embodiment provides a method for preparing a dry-process lithium iron phosphate electrode film. In this embodiment, the active material is small-particle-size (D50 < 1 μm) lithium iron phosphate, the low-tap-density conductive agent is CNT with a tap density of 0.025 g / cm³, and the binder is PTFE. The preparation method includes the following steps:

[0037] 1. First, add lithium iron phosphate particles and CNTs into a mixing tank, turn on the chilled water, and control the temperature between 0 and 15°C. Reverse the stirring shaft at 150 rpm, while simultaneously rotating the mixing tank forward at 45 rpm. Control the stirring time between 60 and 180 seconds, preferably 120 seconds, to premix the lithium iron phosphate particles and CNTs. At the same time, prevent CNT dust from being emitted. Preventing CNT dust is an existing technology and will not be described in detail here.

[0038] 2. Keep the chilled water on and control the temperature between 0 and 15°C. Reverse the stirring shaft at 2250 rpm, while simultaneously rotating the stirring tank forward at 45 rpm. Control the stirring time between 300 and 900 seconds, preferably 600 seconds, to coat the lithium iron phosphate particles with CNTs and obtain a uniformly mixed first mixture.

[0039] 3. First, refrigerate the PTFE particles in the refrigerator for about 24 hours. Before feeding, sieve them through a 2mm sieve to prevent PTFE particles from clumping. Keep the chilled water on and control the temperature between 0 and 15°C. Add the PTFE particles to the first mixture and stir slowly with the stirring shaft reversed at 150 rpm and the stirring tank rotated forward at 45 rpm. The stirring time should be controlled between 60 and 180 seconds, preferably 120 seconds. Then, stir rapidly with the stirring shaft reversed at 2250 rpm and the stirring tank rotated forward at 45 rpm. The stirring time should be controlled between 60 and 180 seconds, preferably 120 seconds. This will result in a second mixture of lithium iron phosphate particles, CNTs, and PTFE particles that are mixed evenly. This will also reduce the particle size of the PTFE particles from 425-525 μm to about 10 μm without fiberization.

[0040] 4. Turn off the chilled water, reverse the stirring shaft to 4500 rpm, and at the same time, rotate the stirring tank forward to 45 rpm. The temperature rises to between 60 and 90°C. Preferably, the stirring is stopped when the temperature rises to 70°C. The uniformly mixed powder is transformed into electrode clusters by inducing the fibrillation of PTFE particles. The fibrillation of PTFE particles is an existing technology and will not be described in detail here.

[0041] 5. Place the electrode bundle in a 100℃ oven and bake for 2 hours to promote further fibrillation of the PTFE particles; control the ambient humidity to within 10% to prevent the PTFE particles from absorbing water and sticking to the rollers; then place the baked electrode bundle between the two rollers of the open mill at a temperature of 120℃, a gap of 200μm, and a differential speed ratio of 3 to obtain a low-strength film. After folding it in half, place it again between the two rollers of the open mill with the same parameters to obtain a film with improved strength. Repeat this process 2-4 times to obtain a smooth lithium iron phosphate cathode film without wrinkles or cracks. By adjusting the gap, a self-supporting film with a thickness of 100μm can be obtained.

[0042] The mass ratio of lithium iron phosphate, CNT and PTFE is 88:10:2.

[0043] The difference between this embodiment and Embodiment 1 is that the mass ratio of lithium iron phosphate, CNT and PTFE in this embodiment is 88:10:2. Example 3

[0044] This embodiment provides a method for preparing a dry-process lithium iron phosphate electrode film. In this embodiment, the active material is small-particle-size (D50 < 1 μm) lithium iron phosphate, the low-tap-density conductive agent is CNT with a tap density of 0.08 g / cm³, and the binder is PTFE. The preparation method includes the following steps:

[0045] 1. First, add lithium iron phosphate particles and CNTs into a mixing tank, turn on the chilled water, and control the temperature between 0 and 15°C. Reverse the stirring shaft at 150 rpm, while simultaneously rotating the mixing tank forward at 45 rpm. Control the stirring time between 60 and 180 seconds, preferably 120 seconds, to premix the lithium iron phosphate particles and CNTs. At the same time, prevent CNT dust from being emitted. Preventing CNT dust is an existing technology and will not be described in detail here.

[0046] 2. Keep the chilled water on and control the temperature between 0 and 15°C. Reverse the stirring shaft at 2250 rpm, while simultaneously rotating the stirring tank forward at 45 rpm. Control the stirring time between 300 and 900 seconds, preferably 600 seconds, to coat the lithium iron phosphate particles with CNTs and obtain a uniformly mixed first mixture.

[0047] 3. First, refrigerate the PTFE particles in the refrigerator for about 24 hours. Before feeding, sieve them through a 2mm sieve to prevent PTFE particles from clumping. Keep the chilled water on and control the temperature between 0 and 15°C. Add the PTFE particles to the first mixture and stir slowly with the stirring shaft reversed at 150 rpm and the stirring tank rotated forward at 45 rpm. The stirring time should be controlled between 60 and 180 seconds, preferably 120 seconds. Then, stir rapidly with the stirring shaft reversed at 2250 rpm and the stirring tank rotated forward at 45 rpm. The stirring time should be controlled between 60 and 180 seconds, preferably 120 seconds. This will result in a second mixture of lithium iron phosphate particles, CNTs, and PTFE particles that are mixed evenly. This will also reduce the particle size of the PTFE particles from 425-525 μm to about 10 μm without fiberization.

[0048] 4. Turn off the chilled water, reverse the stirring shaft to 4500 rpm, and at the same time, rotate the stirring tank forward to 45 rpm. The temperature rises to between 60 and 90°C. Preferably, the stirring is stopped when the temperature rises to 70°C. The uniformly mixed powder is transformed into electrode clusters by inducing the fibrillation of PTFE particles. The fibrillation of PTFE particles is an existing technology and will not be described in detail here.

[0049] 5. Place the electrode bundle in a 100℃ oven and bake for 2 hours to promote further fibrillation of the PTFE particles; control the ambient humidity to within 10% to prevent the PTFE particles from absorbing water and sticking to the rollers; then place the baked electrode bundle between the two rollers of the open mill at a temperature of 120℃, a gap of 200μm, and a differential speed ratio of 3 to obtain a low-strength film. After folding it in half, place it again between the two rollers of the open mill with the same parameters to obtain a film with improved strength. Repeat this process 2-4 times to obtain a smooth lithium iron phosphate cathode film without wrinkles or cracks. By adjusting the gap, a self-supporting film with a thickness of 100μm can be obtained.

[0050] In this embodiment, the mass ratio of lithium iron phosphate, CNT, and PTFE is 88:10:2. The difference between this embodiment and Embodiment 2 is that the tap density of CNT in this embodiment is 0.08 g / cm³. Example 4

[0051] This embodiment provides a method for preparing a dry-process lithium iron phosphate electrode film. In this embodiment, the active material is small-particle-size (D50 < 1 μm) lithium iron phosphate, the low-tap-density conductive agent is conductive carbon black with a tap density of 0.16 g / cm³, and the binder is PTFE. The preparation method includes the following steps:

[0052] 1. First, add lithium iron phosphate particles and conductive carbon black into a mixing tank, turn on the chilled water, control the temperature between 0~15℃, reverse the stirring shaft at 150 rpm, and at the same time, rotate the mixing tank forward at 45 rpm. Control the stirring time between 60~180 seconds, preferably 120 seconds, to premix the lithium iron phosphate particles and conductive carbon black.

[0053] 2. Keep the chilled water on and control the temperature between 0 and 15°C. Reverse the stirring shaft at 2250 rpm, while simultaneously rotating the stirring tank forward at 45 rpm. Control the stirring time between 300 and 900 seconds, preferably 600 seconds, to coat the lithium iron phosphate particles with conductive carbon black and obtain a uniformly mixed first mixture.

[0054] 3. First, refrigerate the PTFE particles in the refrigerator for about 24 hours. Before feeding, sieve them through a 2mm sieve to prevent clumping. Keep the chilled water on and control the temperature between 0 and 15°C. Add the PTFE particles to the first mixture and stir slowly with the stirring shaft reversed at 150 rpm and the stirring tank rotating forward at 45 rpm. The stirring time should be controlled between 60 and 180 seconds, preferably 120 seconds. Then, stir rapidly with the stirring shaft reversed at 2250 rpm and the stirring tank rotating forward at 45 rpm. The stirring time should be controlled between 60 and 180 seconds, preferably 120 seconds. This will result in a second mixture of lithium iron phosphate particles, conductive carbon black, and PTFE particles that are evenly mixed. This will also reduce the particle size of the PTFE particles from 425-525 μm to about 10 μm without fiberization.

[0055] 4. Turn off the chilled water, reverse the stirring shaft to 4500 rpm, and at the same time, rotate the stirring tank forward to 45 rpm. The temperature rises to between 60 and 90°C. Preferably, the stirring is stopped when the temperature rises to 70°C. The uniformly mixed powder is transformed into electrode clusters by inducing the fibrillation of PTFE particles. The fibrillation of PTFE particles is an existing technology and will not be described in detail here.

[0056] 5. Place the electrode bundle in a 100℃ oven and bake for 2 hours to promote further fibrillation of the PTFE particles; control the ambient humidity to within 10% to prevent the PTFE particles from absorbing water and sticking to the rollers; then place the baked electrode bundle between the two rollers of the open mill at a temperature of 120℃, a gap of 200μm, and a differential speed ratio of 3 to obtain a low-strength film. After folding it in half, place it again between the two rollers of the open mill with the same parameters to obtain a film with improved strength. Repeat this process 2-4 times to obtain a smooth lithium iron phosphate cathode film without wrinkles or cracks. By adjusting the gap, a self-supporting film with a thickness of 100μm can be obtained.

[0057] The mass ratio of lithium iron phosphate, conductive carbon black and PTFE is 58:40:2.

[0058] The difference between this embodiment and Embodiment 1 is that the low tap density conductive agent in this embodiment is conductive carbon black with a tap density of 0.16 g / cm3, wherein the mass ratio of lithium iron phosphate, conductive carbon black and PTFE is 58:40:2.

[0059] Furthermore, comparing Examples 1 to 4, it can be seen that, under the premise of ensuring that the positive electrode film with no abnormal appearance is obtained, there is a certain regularity between the tap density of the low tap density conductive agent and the amount of low tap density conductive agent required for film formation.

[0060] As shown in the table below:

[0061]

[0062] As shown in the table above, the lower the tap density of the low-tap-density conductive agent, the less low-tap-density conductive agent is required to form a continuous, non-abnormal self-supporting lithium iron phosphate electrode film.

[0063] As shown in the table above, adding only 5% of CNTs with ultra-low tap density (0.025 g / cm3) can form a continuous, non-abnormal appearance self-supporting lithium iron phosphate electrode film.

[0064] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a dry-process lithium iron phosphate electrode film, characterized in that, The preparation method includes the following steps: S1. Lithium iron phosphate with D50 < 1 μm is premixed with a conductive agent in a stirred tank at a temperature of 0~15℃ to obtain a uniformly mixed first mixture. S2. Add a binder to the first mixture and stir in a mixing tank at a temperature of 0~15°C to obtain a uniformly mixed second mixture; S3. The temperature of the second mixture is raised to 60~90℃, and the second mixture is transformed into electrode clusters by inducing fibrillation of the binder. The electrode clusters are placed in an oven for baking, and the baked electrode clusters are repeatedly folded and calendered to obtain a positive electrode film with no abnormal appearance. in, The conductive agent has a tap density of 0.025 g / cm³. 3 The CNT or tap density is 0.08 g / cm³. 3 The CNT or tap density is 0.16 g / cm³. 3 Conductive carbon black.

2. The preparation method according to claim 1, characterized in that, The mass ratio of lithium iron phosphate, conductive agent and binder is (88~93):(10~5):

2.

3. The preparation method according to claim 2, characterized in that, The mass ratio of lithium iron phosphate, conductive agent, and binder is 93:5:

2.

4. The preparation method according to claim 1, characterized in that, The lower the tap density of the conductive agent, the less conductive agent is required to form a continuous, non-abnormal self-supporting positive electrode film.

5. The preparation method according to claim 1, characterized in that, In step S1, the stirring of the mixing tank includes: In the first stirring stage, the stirring time is controlled between 60 and 180 seconds. The second stirring stage is controlled between 300 and 900 seconds.

6. The preparation method according to claim 1, characterized in that, In step S2, the stirring of the mixing tank includes: Slow stirring, wherein the slow stirring time is controlled between 60 and 180 seconds; Rapid stirring, with the rapid stirring time controlled between 60 and 180 seconds.

7. The preparation method according to claim 1, characterized in that, In step S2, the adhesive needs to be cooled and sieved before being added to the first mixture.

8. A dry-process lithium iron phosphate electrode film, characterized in that, The lithium iron phosphate dry electrode film is prepared by the method described in any one of claims 1-7.

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