A negative electrode slurry mixing method

Abstract

This invention relates to a negative electrode slurry preparation method, comprising the following steps: adding powder material to the feed inlet of a twin-screw extruder for dry mixing; conveying the dry-mixed powder material to the twin-screw extruder for pre-kneading; adding deionized water for wetting and controlling the flow rate of deionized water to first increase and then decrease to form wetted powder; adding deionized water for kneading and controlling the flow rate of deionized water to first increase and then decrease to form kneaded powder; adding SBR and deionized water to obtain a semi-finished slurry from the discharge outlet of the twin-screw extruder; passing the semi-finished slurry into a homogenizer for dispersion; and pumping the slurry dispersed in the homogenizer into a dispersion kettle for dispersion and degassing to obtain a negative electrode slurry. This invention targets large-particle-size graphite by gradually increasing the solid content of the side feed by stepwise adjustment of the deionized water flow rate, enhancing the grinding effect, optimizing the slurry particle size, fineness, sedimentation properties, and improving coating stability and electrode peel strength.

Description

Technical Field

[0001] This invention relates to the field of lithium battery manufacturing technology, and in particular to a method for negative electrode slurry preparation. Background Technology

[0002] In the lithium-ion battery manufacturing process, the dispersion and uniformity of the particulate active materials in the positive and negative electrode slurries directly affect the movement of lithium ions between the two electrodes. Therefore, the mixing and dispersion of the slurries for each electrode material is crucial in lithium-ion battery production. The quality of the slurry dispersion directly affects the quality of subsequent lithium-ion battery production and the performance of the product. Therefore, during the electrode preparation process, it is essential to control the mixing and dispersion quality of the lithium-ion battery slurry to improve its uniformity and dispersion stability.

[0003] Currently, lithium-ion battery manufacturers mainly use the continuous pulping method using twin-screw extruders. Continuous pulping using twin-screw extruders divides the traditional batch pulping into several small portions, continuously disperses them, and then combines them into a whole batch. This method is significantly superior to the traditional process in terms of pulping efficiency and pulping uniformity.

[0004] Currently, deionized water is added to the negative electrode slurry at each inlet of the twin-screw extruder, using a fixed flow rate setting. This process produces slurries with good consistency, stable viscosity and solid content, and good production continuity. However, with a fixed flow rate setting, when the graphite feed particle size is large, the main screw's starting current increases significantly when the side feed setting is increased to a certain value, causing screw jamming and preventing production from starting, potentially damaging the equipment. Furthermore, the prepared slurry has a high fineness and rapid settling, easily leading to frequent scraping during subsequent coating, increased feeding pressure, poor coating stability, and abnormal electrode peeling tests after coating. These issues urgently require improvement. Summary of the Invention

[0005] Based on this, and addressing the technical problems of the current negative electrode slurry mixing process, where deionized water is fed to the side and the main screw is fed with a fixed flow rate setting, and when the particle size of the graphite material is too large, the prepared slurry has a large fineness and settles quickly, which easily leads to frequent scraping during subsequent coating, increased feeding pressure, poor coating stability, and abnormal electrode peeling test after coating, this invention provides a negative electrode slurry mixing method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention first provides a method for negative electrode slurry mixing, which includes the following steps:

[0008] S1. Add the powder material to the feed port of the twin-screw extruder for dry mixing, and then convey the dry-mixed powder material into the twin-screw extruder for pre-kneading;

[0009] S2. Add deionized water to wet the powder and control the flow gradient of the deionized water to reduce it, thus forming wetted powder;

[0010] S3. Add deionized water and knead, controlling the flow rate of deionized water to first increase and then decrease, to form kneaded powder;

[0011] S4. Add SBR and deionized water to obtain a semi-finished slurry from the discharge port of the twin-screw extruder;

[0012] S5. The semi-finished slurry is fed into a homogenizer for dispersion;

[0013] S6. The slurry dispersed by the homogenizer is fed into the dispersion vessel for further dispersion and degassing to obtain the negative electrode slurry.

[0014] As a further improvement to the above-mentioned solution of the present invention, in step S2, the flow rate of the deionized water is controlled to increase from the initial flow rate to the second gradient flow rate and then decrease to the third gradient flow rate. The initial flow rate is 270-282 kg / h, the second gradient flow rate is 304-346 kg / h, and the third gradient flow rate is 222-255 kg / h.

[0015] As a further improvement to the above-mentioned solution of the present invention, in step S3, the flow rate of the deionized water is controlled to increase from the initial flow rate to the second gradient flow rate and then decrease to the third gradient flow rate. The initial flow rate is 195-246 kg / h, the second gradient flow rate is 201-252 kg / h, and the third gradient flow rate is 180-196 kg / h.

[0016] As a further improvement to the above-mentioned solution of the present invention, in step S4, the side feed port is located in the eighth section of the twin-screw extruder, the solid content of the semi-finished slurry is 52%-56%, the viscosity is 2000-5000 mPa·s, and the fineness is less than 35 μm.

[0017] As a further improvement to the above-mentioned solution of the present invention, in step S1, the powder material includes graphite, conductive agent and binder.

[0018] As a further improvement to the above-mentioned scheme of the present invention, the graphite has a particle size D90 of 28-30 μm and a Dmax of 54-60 μm.

[0019] As a further improvement to the above-mentioned solution of the present invention, in step S1, the flow rate of the graphite is 675±3.375 kg / h, the flow rate of the conductive agent is 3.5±0.017 kg / h, and the flow rate of the binder is 8.4±0.042 kg / h.

[0020] As a further improvement to the above-mentioned solution of the present invention, in step S4, the flow rate of the SBR is 26.3±0.132kg / h.

[0021] As a further improvement to the above-mentioned solution of the present invention, the rotation speed of the twin-screw extruder is 600±10 rpm; the rotation speed of the homogenizer is 4500±50 rpm; the revolution speed of the dispersion vessel is 25±2 rpm, the rotation speed is 1200±20 rpm, the vacuum degree is ≤-0.090 MPa, and the dispersion time is 2-3h.

[0022] As a further improvement to the above-mentioned solution of the present invention, in steps S1-S5, the temperature of the slurry is controlled at 20-50℃.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This invention targets large-particle-size graphite by gradually increasing the solid content of the side feed through stepwise adjustment of the deionized water flow rate, thereby enhancing the grinding effect, optimizing the particle size, fineness, and sedimentation properties of the slurry, improving coating stability and electrode peel strength, and further enhancing the equipment's capacity to produce high-quality slurry with small fineness, small particle size, and low sedimentation without changing the original structure and rated power of the slurry mixing machine. Detailed Implementation

[0025] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0027] Example 1

[0028] This embodiment provides a negative electrode slurry mixing method, including the following steps:

[0029] S1. Graphite, conductive agent SP, and binder CMC are added to the feed inlet of a twin-screw extruder for dry mixing. The flow rate of graphite is 675 kg / h, the flow rate of conductive agent is 3.5 kg / h, and the flow rate of binder is 8.4 kg / h. The dry-mixed powder is then conveyed into the twin-screw extruder for pre-kneading and dispersion. The twin-screw extruder operates at 6000 rpm, and the slurry temperature is controlled at 40℃.

[0030] S2. Deionized water is added through the inlet of the second section of the twin-screw extruder to wet the powder and form wetted powder. The initial flow rate of deionized water is controlled at 282 kg / h, the second gradient flow rate at 346 kg / h, the third gradient flow rate at 255 kg / h, and the interval between two adjacent gradients is 3 min.

[0031] S3. Add deionized water from the inlet of the seventh section of the twin-screw extruder to knead and disperse the mixture, forming kneaded powder. Control the initial flow rate of the deionized water to be 195 kg / h, the second gradient flow rate to be 221 kg / h, the third gradient flow rate to be 180 kg / h, and the interval between two adjacent gradients to be 3 min.

[0032] S4. Add SBR and deionized water into the eighth section of the twin-screw extruder, controlling the SBR flow rate to 26.3 kg / h and the deionized water flow rate to 84 kg / h. Discharge the material from the twin-screw extruder outlet to obtain a semi-finished slurry. The semi-finished slurry has a solid content of 58%, a viscosity of 3241 mPa·s, and a fineness of 25 μm.

[0033] S5. The semi-finished slurry is fed into a homogenizer with a rotation speed of 4500 rpm for dispersion, wherein the slurry temperature is controlled at 40℃.

[0034] S6. The slurry dispersed by the homogenizer is fed into the dispersion vessel for dispersion and degassing. The dispersion vessel has an orbital speed of 25 rpm, a rotational speed of 1200 rpm, a vacuum degree of ≤-0.090 MPa, a dispersion time of 3 h, and a slurry temperature controlled at 40℃.

[0035] Example 2

[0036] This embodiment provides a negative electrode slurry mixing method, including the following steps:

[0037] S1. Graphite, conductive agent SP, and binder CMC are added to the feed inlet of a twin-screw extruder for dry mixing. The flow rate of graphite is 675 kg / h, the flow rate of conductive agent is 3.5 kg / h, and the flow rate of binder is 8.4 kg / h. The dry-mixed powder is then conveyed into the twin-screw extruder for pre-kneading and dispersion. The twin-screw extruder operates at 6000 rpm, and the slurry temperature is controlled at 40℃.

[0038] S2. Deionized water is added through the inlet of the second section of the twin-screw extruder to wet the powder and form wetted powder. The initial flow rate of deionized water is controlled at 270 kg / h, the second gradient flow rate at 320 kg / h, the third gradient flow rate at 252 kg / h, and the interval between two adjacent gradients is 3 min.

[0039] S3. Add deionized water from the inlet of the seventh section of the twin-screw extruder to knead and disperse the mixture, forming kneaded powder. Control the initial flow rate of the deionized water to be 246 kg / h, the second gradient flow rate to be 201 kg / h, the third gradient flow rate to be 190 kg / h, and the interval between two adjacent gradients to be 3 min.

[0040] S4. Add SBR and deionized water into the eighth section of the twin-screw extruder, controlling the SBR flow rate at 26.3 kg / h and the deionized water flow rate at 84 kg / h. Discharge the material from the twin-screw extruder outlet to obtain a semi-finished slurry. The semi-finished slurry has a solid content of 58%, a viscosity of 2980 mPa·s, and a fineness of 20 μm.

[0041] S5. The semi-finished slurry is fed into a homogenizer with a rotation speed of 4500 rpm for dispersion, wherein the slurry temperature is controlled at 40℃.

[0042] S6. The slurry dispersed by the homogenizer is fed into the dispersion vessel for dispersion and degassing. The dispersion vessel has an orbital speed of 25 rpm, a rotational speed of 1200 rpm, a vacuum degree of ≤-0.090 MPa, a dispersion time of 3 h, and a slurry temperature controlled at 40℃.

[0043] Example 3

[0044] This embodiment provides a negative electrode slurry mixing method, including the following steps:

[0045] S1. Graphite, conductive agent SP, and binder CMC are added to the feed inlet of a twin-screw extruder for dry mixing. The flow rate of graphite is 675 kg / h, the flow rate of conductive agent is 3.5 kg / h, and the flow rate of binder is 8.4 kg / h. The dry-mixed powder is then conveyed into the twin-screw extruder for pre-kneading and dispersion. The twin-screw extruder operates at 6000 rpm, and the slurry temperature is controlled at 40℃.

[0046] S2. Deionized water is added through the inlet of the second section of the twin-screw extruder to wet the powder and form wetted powder. The initial flow rate of deionized water is controlled at 276 kg / h, the second gradient flow rate at 304 kg / h, the third gradient flow rate at 222 kg / h, and the interval between two adjacent gradients is 3 min.

[0047] S3. Add deionized water from the inlet of the seventh section of the twin-screw extruder to knead and disperse the mixture, forming kneaded powder. Control the initial flow rate of the deionized water to be 230 kg / h, the second gradient flow rate to be 252 kg / h, the third gradient flow rate to be 196 kg / h, and the interval between two adjacent gradients to be 3 min.

[0048] S4. Add SBR and deionized water into the eighth section of the twin-screw extruder, controlling the SBR flow rate to 26.3 kg / h and the deionized water flow rate to 84 kg / h. Discharge the material from the twin-screw extruder outlet to obtain a semi-finished slurry. The semi-finished slurry has a solid content of 58%, a viscosity of 3012 mPa·s, and a fineness of 22 μm.

[0049] S5. The semi-finished slurry is fed into a homogenizer with a rotation speed of 4500 rpm for dispersion, wherein the slurry temperature is controlled at 40℃.

[0050] S6. The slurry dispersed by the homogenizer is fed into the dispersion vessel for dispersion and degassing. The dispersion vessel has an orbital speed of 25 rpm, a rotational speed of 1200 rpm, a vacuum degree of ≤-0.090 MPa, a dispersion time of 3 h, and a slurry temperature controlled at 40℃.

[0051] Comparative Example 1

[0052] This comparative example provides a negative electrode slurry mixing method, including the following steps:

[0053] S1. Graphite, conductive agent SP, and binder CMC are added to the feed inlet of a twin-screw extruder for dry mixing. The flow rate of graphite is 652 kg / h, the flow rate of conductive agent is 3.38 kg / h, and the flow rate of binder is 8.1 kg / h. The dry-mixed powder is then conveyed into the twin-screw extruder for pre-kneading and dispersion. The twin-screw extruder operates at 6000 rpm, and the slurry temperature is controlled at 40℃.

[0054] S2. Deionized water is added through the inlet of the second section of the twin-screw extruder to wet the powder and form wetted powder. The flow rate of deionized water is controlled at 342 g / h.

[0055] S3. Add deionized water from the inlet of the seventh section of the twin-screw extruder to knead and disperse the mixture, forming kneaded powder. Control the flow rate of the deionized water to 175 g / h.

[0056] S4. Add SBR and deionized water into the eighth section of the twin-screw extruder, controlling the SBR flow rate to 25.3 kg / h and the deionized water flow rate to 84 kg / h. Discharge the material from the twin-screw extruder outlet to obtain a semi-finished slurry. The semi-finished slurry has a solid content of 56%, a viscosity of 3400 mPa·s, and a fineness of 36 μm.

[0057] S5. The semi-finished slurry is fed into a homogenizer with a rotation speed of 4500 rpm for dispersion, wherein the slurry temperature is controlled at 40℃.

[0058] S6. The slurry dispersed by the homogenizer is fed into the dispersion vessel for dispersion and degassing. The dispersion vessel has an orbital speed of 25 rpm, a rotational speed of 1200 rpm, a vacuum degree of ≤-0.090 MPa, a dispersion time of 3 h, and a slurry temperature controlled at 40℃.

[0059] Comparative Example 2

[0060] This comparative example provides a negative electrode slurry mixing method, including the following steps:

[0061] S1. Graphite, conductive agent SP, and binder CMC are added to the feed inlet of a twin-screw extruder for dry mixing. The flow rate of graphite is 652 kg / h, the flow rate of conductive agent is 3.38 kg / h, and the flow rate of binder is 8.1 kg / h. The dry-mixed powder is then conveyed into the twin-screw extruder for pre-kneading and dispersion. The twin-screw extruder operates at 6000 rpm, and the slurry temperature is controlled at 40℃.

[0062] S2. Add deionized water from the inlet of the second section of the twin-screw extruder to wet the powder and control the flow rate of deionized water to 327 kg / h.

[0063] S3. Add deionized water from the inlet of the seventh section of the twin-screw extruder to knead and disperse the mixture, forming kneaded powder. Control the flow rate of the deionized water to 191 kg / h.

[0064] S4. Add SBR and deionized water into the eighth section of the twin-screw extruder, controlling the SBR flow rate at 25.3 kg / h and the deionized water flow rate at 84 kg / h. Discharge the material from the twin-screw extruder outlet to obtain a semi-finished slurry. The semi-finished slurry has a solid content of 56%, a viscosity of 3568 mPa·s, and a fineness of 32 μm.

[0065] S5. The semi-finished slurry is fed into a homogenizer with a rotation speed of 4500 rpm for dispersion, wherein the slurry temperature is controlled at 40℃.

[0066] S6. The slurry dispersed by the homogenizer is fed into the dispersion vessel for dispersion and degassing. The dispersion vessel has an orbital speed of 25 rpm, a rotational speed of 1200 rpm, a vacuum degree of ≤-0.090 MPa, a dispersion time of 3 h, and a slurry temperature controlled at 40℃.

[0067] Comparative Example 3

[0068] This comparative example provides a negative electrode slurry mixing method, including the following steps:

[0069] S1. Graphite, conductive agent SP, and binder CMC are added to the feed inlet of a twin-screw extruder for dry mixing. The flow rate of graphite is 652 kg / h, the flow rate of conductive agent is 3.38 kg / h, and the flow rate of binder is 8.1 kg / h. The dry-mixed powder is then conveyed into the twin-screw extruder for pre-kneading and dispersion. The twin-screw extruder operates at 6000 rpm, and the slurry temperature is controlled at 40℃.

[0070] S2. Add deionized water from the inlet of the second section of the twin-screw extruder to wet the powder and control the flow rate of deionized water to 312 kg / h.

[0071] S3. Add deionized water from the inlet of the seventh section of the twin-screw extruder to knead and disperse the mixture, forming kneaded powder. Control the flow rate of the deionized water to 206 kg / h.

[0072] S4. Add SBR and deionized water into the eighth section of the twin-screw extruder, controlling the SBR flow rate at 25.3 kg / h and the deionized water flow rate at 84 kg / h. Discharge the material from the twin-screw extruder outlet to obtain a semi-finished slurry. The semi-finished slurry has a solid content of 56%, a viscosity of 4200 mPa·s, and a fineness of 31 μm.

[0073] S5. The semi-finished slurry is fed into a homogenizer with a rotation speed of 4500 rpm for dispersion, wherein the slurry temperature is controlled at 40℃.

[0074] S6. The slurry dispersed by the homogenizer is fed into the dispersion vessel for dispersion and degassing. The dispersion vessel has an orbital speed of 25 rpm, a rotational speed of 1200 rpm, a vacuum degree of ≤-0.090 MPa, a dispersion time of 3 h, and a slurry temperature controlled at 40℃.

[0075] Test case

[0076] The negative electrode slurries prepared in Examples 1-3 and Comparative Examples 1-3 were coated on copper foil to prepare negative electrode sheets; the positive electrode was lithium iron phosphate, and the ratio (by weight) of the positive electrode slurry was LFP:SP:GOs (solid content):PVDF = 96.8:0.7:0.5:2.0. The slurry was mixed and coated on aluminum foil; LiPF6 electrolyte (main components: EC, PC, EMC, DMC, LiPF6, LiPSI, VC, MMDS, FB) was used as the electrolyte, and PP+coated separator was used as the separator. The batteries were assembled and their performance was tested. The battery capacity test method was as follows: the batteries were transferred to the capacity testing area by the elevator and conveyor line. The capacity testing cabinet was equipped with a stacker machine that automatically put the trays carrying the batteries into the cabinet. The capacity testing temperature was (24±3)℃. Capacity testing was carried out according to the production line capacity testing process. Each batch consisted of 10,000 batteries, and the standard deviation of the battery capacity for each batch was calculated. The results of negative electrode slurry coating and battery consistency test are shown in Table 1.

[0077] Table 1

[0078]

[0079] As can be seen from the results in Table 1, after increasing the solid content according to the gradient, the viscosity of the slurry output decreased, the solid content increased, and the fineness decreased. During the material feeding process of the coating trolley, the pressure of the feeding pump decreased from the original 240-280 kPa to 230-240 kPa, and the fineness of the slurry decreased from the original 30-36 micrometers to 20-25 micrometers. The coating effect decreased from the original scraping frequency (5-6 times / batch) to the current (0-1 times / batch). At the same time, the capacity consistency of the cells also improved, and the capacity standard deviation decreased from the original 0.90 Ah to 0.48 Ah. The negative electrode slurry mixing method of this invention improves the utilization rate of the cells.

[0080] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0081] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for negative electrode slurry mixing, characterized in that, It includes the following steps: S1. Add the powder material to the feed port of the twin-screw extruder for dry mixing, and then convey the dry-mixed powder material into the twin-screw extruder for pre-kneading; S2. Add deionized water to wet the powder and control the flow rate of the deionized water to increase from the initial flow rate to the second gradient flow rate and then decrease to the third gradient flow rate. The initial flow rate is 270-282 kg / h, the second gradient flow rate is 304-346 kg / h, and the third gradient flow rate is 222-255 kg / h, to form wetted powder. S3. Add deionized water to knead and control the flow rate of the deionized water to increase from the initial flow rate to the second gradient flow rate, and then decrease to the third gradient flow rate. The initial flow rate is 195-246 kg / h, the second gradient flow rate is 201-252 kg / h, and the third gradient flow rate is 180-196 kg / h, to form kneaded powder. S4. Add SBR and deionized water to obtain a semi-finished slurry from the discharge port of a twin-screw extruder; the solid content of the semi-finished slurry is 52%-56%, the viscosity is 2000-5000 mPa·s, and the fineness is less than 35 μm; S5. The semi-finished slurry is fed into a homogenizer for dispersion; S6. The slurry dispersed by the homogenizer is fed into the dispersion vessel for further dispersion and degassing to obtain the negative electrode slurry.

2. The negative electrode slurry mixing method according to claim 1, characterized in that, In step S1, the powder material includes graphite, conductive agent and binder.

3. The negative electrode slurry mixing method according to claim 2, characterized in that, The graphite has a particle size D90 of 28-30 μm and a Dmax of 54-60 μm.

4. The negative electrode slurry mixing method according to claim 2, characterized in that, In step S1, the flow rate of the graphite is 675±3.375 kg / h, the flow rate of the conductive agent is 3.5±0.017 kg / h, and the flow rate of the binder is 8.4±0.042 kg / h.

5. The negative electrode slurry mixing method according to claim 1, characterized in that, In step S4, the flow rate of the SBR is 26.3 ± 0.132 kg / h.

6. The negative electrode slurry mixing method according to claim 1, characterized in that, The twin-screw extruder has a rotational speed of 600±10 rpm; the homogenizer has a rotational speed of 4500±50 rpm; the dispersion vessel has a revolution speed of 25±2 rpm, a rotational speed of 1200±20 rpm, a vacuum degree of ≤-0.090 MPa, and a dispersion time of 2-3 hours.

7. The negative electrode slurry mixing method according to claim 1, characterized in that, In steps S1-S5, the temperature of the slurry is controlled between 20-50℃.

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