A lithium iron phosphate slurry production method and a production system device thereof

Abstract

The application provides a lithium iron phosphate slurry production method and a production system device thereof. The lithium iron phosphate slurry production method comprises the following steps: firstly, putting lithium iron phosphate and a conductive agent into a mixing device to mix and obtain mixed powder in a continuous mixing process; secondly, mixing a binder, an additive and a solvent in advance to obtain a glue solution; thirdly, putting the glue solution into the mixing device to continue mixing with the mixed powder and obtain kneaded slurry; and finally, putting the glue solution and the solvent into the mixing device to continue mixing with the kneaded slurry and obtain dispersed slurry. The lithium iron phosphate slurry production method and the production system device thereof can efficiently and continuously produce lithium iron phosphate slurry with high consistency, good stability, low gel aggregation and low manufacturing cost.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery production technology, and particularly relates to a method for producing lithium iron phosphate slurry and its production system. Background Technology

[0002] As the application scope and depth of lithium batteries continue to expand, the requirements for their performance are also increasing. In particular, due to the "weakest link" effect, customers have higher demands for the uniformity and consistency of mass-produced lithium batteries, especially in battery packs. Simultaneously, the lithium battery application market has an urgent need to reduce costs. Therefore, how to increase production capacity and reduce costs while improving the uniformity and consistency of lithium batteries has become a pressing challenge in the field of lithium battery production technology.

[0003] A relatively mature method for producing lithium-ion battery slurry involves using a vacuum planetary mixer. Raw materials for the positive and negative electrode formulations are added to the mixer in a specific order, undergoing mixing, dispersion, and vacuum processes to produce the final slurry. However, because vacuum planetary mixers produce slurries in batches on a tank-by-tank basis, the consistency between slurries from different tanks is poor. Furthermore, given the limited capacity, vacuum planetary mixers require a large footprint and consume a lot of energy, resulting in high manufacturing costs. Currently, the application of continuous production systems for lithium-ion battery slurries offers a solution to the problem of poor slurry consistency.

[0004] CN106362640A discloses a cylindrical lithium battery batching system, including a main material batching system, an admixture batching system, a material guiding and homogenizing system, a slurry batching system, a discharge system, and a control cabinet. This batching system can meet the continuous production needs of lithium battery production lines, but the mixing of powder and liquid materials is not uniform enough, and they are prone to clumping.

[0005] CN107008202A discloses an online lithium battery batching system, which includes a twin-screw mixer continuous powder feeding subsystem and a liquid tank. The twin-screw mixer includes a barrel and a screw disposed within the barrel. The screw includes a powder feeding section, a powder premixing section, a liquid feeding section, a mixing section, a dispersion and homogenization section, a defoaming section, and a discharge section arranged sequentially along the material conveying direction. The discharge port of the continuous powder feeding subsystem is connected to the inlet of the powder feeding section, and the discharge port of the liquid tank is connected to the inlet of the liquid feeding section. This online lithium battery batching system can eliminate the batch batching and mixing method of traditional processes, but the produced slurry is prone to gelation and agglomeration, making it difficult to accurately control the coating quality of the electrode sheets during the coating process.

[0006] CN208049858U discloses a battery slurry production system, including a premixing tank, a solvent tank, a screw continuous kneader, and a mixing tank. The output ends of the premixing tank and the solvent tank are respectively connected to the screw continuous kneader via pipelines, and the output end of the screw continuous kneader is connected to the mixing tank via a pipeline. Although this battery slurry production system can continuously and uniformly produce a consistent slurry, it cannot solve the problems of insufficient dissolution of the positive electrode binder and difficulty in fully dispersing the agglomeration of small particles such as lithium iron phosphate and SP. Consequently, the produced lithium battery positive electrode slurry exhibits poor viscosity stability and sedimentation properties.

[0007] Therefore, how to efficiently and continuously produce lithium iron phosphate slurry with high consistency, good stability, low agglomeration and low manufacturing cost has become an urgent problem to be solved in the field of lithium battery production technology. Summary of the Invention

[0008] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a method and system for producing lithium iron phosphate slurry, which can efficiently and continuously produce lithium iron phosphate slurry with high consistency, good stability, low gelation and agglomeration and low manufacturing cost.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for producing lithium iron phosphate slurry, the method comprising:

[0011] In the continuous mixing process, lithium iron phosphate and conductive agent are first added to the mixing device to obtain mixed powder; binder, additive and solvent are premixed to obtain adhesive; then adhesive is added to the mixing device and mixed with mixed powder to obtain kneaded slurry; finally adhesive and solvent are added to the mixing device and mixed with kneaded slurry to obtain dispersion slurry.

[0012] This invention first mixes lithium iron phosphate and a conductive agent to ensure uniform dispersion of the conductive agent within the lithium iron phosphate, thus avoiding the problem of conductive agent agglomeration in the lithium iron phosphate slurry. Simultaneously, a binder and additives are premixed in a solvent to obtain a colloid, achieving the goal of fully dissolving the binder in the solvent. Furthermore, the additives ensure uniform dispersion of the active material, resulting in good uniformity of the lithium iron phosphate slurry and reducing its tendency to gel and agglomerate.

[0013] This invention involves adding the adhesive in two steps, which effectively avoids swelling of the slurry and improves its stability. Simultaneously, the first addition of the adhesive wets the powder, forming a binder that partially coats the powder particles, preventing the agglomeration of lithium iron phosphate or conductive agents. The simultaneous addition of the solvent and adhesive to the kneaded slurry ensures that the consistency, stability, and settling properties of the lithium iron phosphate slurry are maintained, which is beneficial for subsequent coating operations.

[0014] As a preferred technical solution of the present invention, the lithium iron phosphate slurry production method further includes: grinding and degassing the dispersion slurry sequentially to obtain the lithium iron phosphate slurry.

[0015] This invention grinds highly dispersed slurries to further disperse undispersed agglomerates, followed by further defoaming and degassing to obtain lithium iron phosphate slurries with high consistency, good stability, and resistance to gelation and agglomeration.

[0016] As a preferred embodiment of the present invention, the mixing device is a screw continuous homogenizer.

[0017] Preferably, the rotational speed of the screw continuous kneader is 500 to 3000 r / min, for example, it can be 500 r / min, 1000 r / min, 1500 r / min, 1800 r / min, 2000 r / min, 2200 r / min, 2500 r / min, 2800 r / min or 3000 r / min, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0018] Preferably, the mass ratio of lithium iron phosphate to conductive agent is (94-96.5):(0.3-1.0), for example, it can be 94:0.3, 94:1.0, 94:0.6, 95:0.3, 95:0.6, 95:1.0, 96.5:0.3, 96.5:0.6 or 96.5:1.0, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Preferably, the conductive agent includes any one or a combination of at least two of conductive carbon black, vapor-grown carbon fibers, carbon nanotubes, conductive graphite, or graphene.

[0020] As a preferred technical solution of the present invention, the mass ratio of the adhesive to the additive is (4 to 40):1, for example, it can be 4:1, 8:1, 12:01, 16:01, 20:01, 24:1, 28:1, 32:1, 36:1 or 40:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] This invention specifies a mass ratio of binder to additives of (4-40):1. When the amount of binder remains constant, excessive additives will affect the performance of the battery cell and reduce energy density. This is because additives are organic and cannot volatilize, remaining in the battery cell. Excessive additives will reduce the electronic and ionic conductivity between active materials and increase the weight of the battery cell. When the amount of additives is too small, it cannot promote the dispersion of raw materials and improve the uniformity and stability of the slurry. This is because too little additive cannot effectively reduce the surface energy of particles, thus failing to promote particle dispersion and failing to play its main role in maintaining the stability of the slurry.

[0022] Preferably, the adhesive comprises polyvinylidene fluoride.

[0023] Preferably, the additive includes polyvinylpyrrolidone.

[0024] Preferably, the solvent comprises N-methylpyrrolidone.

[0025] Preferably, the solid content of the adhesive is 4 to 10 wt%, for example, it can be 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt%, or 10 wt%, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0026] Preferably, the mass ratio of the adhesive liquid to the mixed powder is (10-50):(94.3-97.5), for example, it can be 10:94.3, 18:95, 26:95.5, 34:96, 35:96.5, 45:97 or 50:97.5, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] This invention specifies that the mass ratio of adhesive liquid to mixed powder is (10-50):(94.3-97.5). When the amount of mixed powder is constant, if the amount of adhesive liquid is too high, the kneading effect will be poor. This is because the kneading solids content is too low, resulting in insufficient shear force between particles during the kneading process, which is not conducive to breaking up agglomerates. If the amount of adhesive liquid is too low, the kneading effect will also be poor. This is because the kneading solids content is too high, which cannot effectively wet the slurry particles, and the shear force between particles during the kneading process is insufficient, which is not conducive to breaking up agglomerates.

[0028] As a preferred embodiment of the present invention, the mass ratio of the solvent, adhesive, and kneading slurry is (7-37):(6-10):(104.3-147.5), for example, it can be 7:6:104.3, 16:7:110.5, 20:8:120.5, 25:9:130.5, or 37:10:147.5, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] This invention specifies the mass ratio of solvent, adhesive, and kneading slurry as (7-37):(6-10):(104.3-147.5). When the amounts of solvent and kneading slurry remain constant, excessive amounts of adhesive will affect the electrical performance of the battery cell and reduce the coating properties of the slurry. This is because the adhesive is mainly composed of organic and non-volatile binders and additives. Excessive adhesive will reduce the electronic and ionic conductivity between active materials and increase the weight of the battery cell. Insufficient amounts of adhesive will lead to electrode demolding and powder shedding during the manufacturing process and poor battery cell cycle performance. This is because the adhesive mainly serves to bond particles and the coating to the current collector. Insufficient adhesive will result in insufficient electrode adhesion.

[0030] Preferably, the grinding process is carried out in a sand milling device; the rotational speed of the sand milling device is 8 to 18 m / min, for example, it can be 8 m / min, 9 m / min, 10 m / min, 11 m / min, 12 m / min, 13 m / min, 14 m / min, 15 m / min, 16 m / min, 17 m / min or 18 m / min; the filling rate of the sand beads in the sand milling device is 70% to 90%, for example, it can be 70%, 73%, 75%, 78%, 80%, 83%, 85%, 88% or 90%, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0031] As a preferred embodiment of the present invention, the method for producing lithium iron phosphate slurry includes the following steps:

[0032] (1) Lithium iron phosphate and conductive agent are added into a screw continuous homogenizer at a mass ratio of (94~96.5):(0.3~1.0) and mixed at a speed of 500~3000r / min to obtain a mixed powder;

[0033] (2) The binder and additives are added to the solvent at a mass ratio of (4-40):1 to prepare a glue solution with a solid content of 4%-10wt%; then the glue solution is fed into a screw continuous homogenizer, the mass ratio of glue solution to mixed powder is (10-50):(94.3-97.5), and the glue solution and mixed powder are mixed at a speed of 500-3000r / min to obtain a kneaded slurry;

[0034] (3) The solvent and adhesive are put into the screw continuous homogenizer. The mass ratio of solvent, adhesive and kneaded slurry is (7~37):(6~10):(104.3~147.5). The solvent, adhesive and kneaded slurry are mixed at a speed of 500~3000r / min to obtain a dispersed slurry.

[0035] (4) The dispersion slurry obtained in step (3) is fed into a sand milling device. The filling rate of the sand milling device is 70-90%. The dispersion slurry is ground and dispersed at a linear velocity of 8-18 m / min. After degassing, the lithium iron phosphate slurry is obtained.

[0036] In a second aspect, the present invention provides a lithium iron phosphate slurry production system apparatus, which is used to perform the lithium iron phosphate slurry production method described in the first aspect.

[0037] The lithium iron phosphate slurry production system includes a mixing device, a powder feeding unit, a glue-making unit, and a liquid feeding device. Along the material flow direction, the powder feeding unit, the glue-making unit, and the liquid feeding device are respectively connected to the mixing device.

[0038] As a preferred embodiment of the present invention, the mixing device includes a housing, and at least one screw is disposed inside the housing.

[0039] Preferably, at least two screws are provided inside the housing, the screws are arranged in parallel inside the housing, and the threads of the screws are interlocked.

[0040] Preferably, the interior of the shell is divided into a powder mixing zone, a kneading zone, a dispersion and viscosity adjustment zone, and a defoaming and venting zone along the material flow direction.

[0041] Preferably, the housing containing the powder mixing zone has a powder feeding port, and the powder feeding port is externally connected to the powder feeding unit.

[0042] Preferably, the housing containing the kneading zone has an adhesive inlet, which is externally connected to the adhesive preparation unit.

[0043] Preferably, the housing containing the dispersion and viscosity adjustment zone has a liquid feeding port, and the liquid feeding port is connected to a liquid feeding device.

[0044] Preferably, the housing containing the defoaming and venting zone has an vent hole.

[0045] As a preferred embodiment of the present invention, the powder feeding unit includes at least one lithium iron phosphate storage tank and at least one conductive agent storage tank.

[0046] Preferably, the glue-making unit includes a raw material supply device, a glue-making device, a glue storage device, and a glue liquid feeding device connected in sequence along the material flow direction.

[0047] Preferably, the raw material supply device includes at least one binder storage tank and at least one additive storage tank.

[0048] As a preferred embodiment of the present invention, the outlet of the mixing device is further connected to a sand mill and a degassing machine in sequence.

[0049] The system refers to an equipment system, device system, or production device.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] (1) In this invention, the binder and additives are added to the solvent for premixing to obtain the adhesive solution, which avoids the problem that the binder cannot be fully dissolved in the solvent due to continuous kneading and short mixing time. In addition, the additives make the active material dispersed evenly, thus the lithium iron phosphate slurry has good uniformity and is not easy to gel and agglomerate.

[0052] (2) The present invention adds the adhesive in two steps, which can effectively avoid the swelling of the slurry and improve the stability of the slurry. At the same time, it can prevent the agglomeration of lithium iron phosphate and conductive agent while ensuring the viscosity of the slurry, improve the consistency, stability and sedimentation of lithium iron phosphate slurry, and benefit subsequent coating operations.

[0053] (3) The present invention uses a sand mill and a degassing machine to grind, disperse and degas the slurry to obtain a lithium iron phosphate slurry that is not prone to gelation and agglomeration, has high stability and low manufacturing cost. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of a lithium iron phosphate slurry production system provided in a specific embodiment of the present invention.

[0055] Among them, 1-mixing device; 2-powder feeding port; 3-lithium iron phosphate storage tank; 4-conductive agent storage tank; 5-binder storage tank; 6-additive storage tank; 7-adhesive making device; 8-adhesive storage device; 9-adhesive liquid feeding port; 10-solvent storage tank; 11-liquid feeding port; 12-venting port; 13-sand mill; 14-defoaming machine. Detailed Implementation

[0056] It should be understood that in the description of this invention, the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0057] It should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0058] Those skilled in the art should understand that the present invention necessarily includes the necessary pipelines, conventional valves and general pump equipment for achieving complete process, but the above content is not the main inventive point of the present invention. Those skilled in the art can add layouts based on process flow and equipment structure selection, and the present invention does not make any special requirements or specific limitations in this regard.

[0059] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0060] In one specific embodiment, the present invention provides a lithium iron phosphate slurry production system apparatus, such as... Figure 1 As shown, the lithium iron phosphate slurry production system includes a mixing device 1, a powder feeding unit, a glue-making unit, and a liquid feeding device. Along the material flow direction, the powder feeding unit, the glue-making unit, and the liquid feeding device are respectively connected to the mixing device 1.

[0061] The mixing device 1 includes a housing, within which at least one screw is disposed; further, at least two screws are disposed within the housing, the screws being arranged parallel to each other inside the housing, and the threads of the screws interlocking with each other. The interior of the housing is divided along the material flow direction into a powder mixing zone, a kneading zone, a dispersion and viscosity adjustment zone, and a defoaming and venting zone; the housing containing the powder mixing zone has a powder feeding port 2, which is externally connected to the powder feeding unit; the housing containing the kneading zone has a glue feeding port 9, which is externally connected to the glue-making unit; the housing containing the dispersion and viscosity adjustment zone has a liquid feeding port 11, which is externally connected to a liquid feeding device; and the housing containing the defoaming and venting zone has a vent hole 12.

[0062] Furthermore, the powder feeding unit includes at least one lithium iron phosphate storage tank 3 and at least one conductive agent storage tank 4; the adhesive preparation unit includes a raw material supply device, an adhesive preparation device 7, an adhesive storage device 8, and an adhesive liquid feeding device connected sequentially along the material flow direction; the raw material supply device includes at least one binder storage tank 5 and at least one additive storage tank 6.

[0063] Furthermore, the outlet of the mixing device 1 is also connected in sequence to a sand mill 13 and a degassing machine 14.

[0064] Example 1

[0065] This embodiment provides a method for producing lithium iron phosphate slurry, which specifically includes the following steps:

[0066] (1) Lithium iron phosphate and conductive agent were added into a screw continuous homogenizer at a mass ratio of 95:0.6 and mixed at a speed of 1500 r / min to obtain a mixed powder.

[0067] (2) PVDF and PVP were added to NMP at a mass ratio of 22:1 to prepare a slurry with a solid content of 7%; then the slurry was fed into a screw continuous homogenizer with a mass ratio of 28:95.6 between the slurry and the mixed powder. The slurry and the mixed powder were mixed at a speed of 1500 r / min to obtain a kneaded slurry.

[0068] (3) NMP and adhesive solution are put into a screw continuous homogenizer. The mass ratio of NMP, adhesive solution and kneaded slurry is 20:8:123.6. NMP, adhesive solution and kneaded slurry are mixed at a speed of 1500 r / min to obtain a dispersed slurry.

[0069] (4) The dispersion slurry obtained in step (3) is fed into a sand milling device. The filling rate of the sand milling device is 80%. The dispersion slurry is ground and dispersed at a linear velocity of 13 m / min. After degassing, the lithium iron phosphate slurry is obtained.

[0070] Example 2

[0071] This embodiment provides a method for producing lithium iron phosphate slurry, which specifically includes the following steps:

[0072] (1) Lithium iron phosphate and conductive agent were added into a screw continuous homogenizer at a mass ratio of 94:0.3 and mixed at a speed of 500 r / min to obtain a mixed powder.

[0073] (2) PVDF and PVP were added to NMP at a mass ratio of 40:1 to prepare a slurry with a solid content of 4%; then the slurry was fed into a screw continuous homogenizer with a mass ratio of 10:94.3 between the slurry and the mixed powder. The slurry and the mixed powder were mixed at a speed of 500 r / min to obtain a kneaded slurry.

[0074] (3) NMP and adhesive solution are put into a screw continuous homogenizer. The mass ratio of NMP, adhesive solution and kneaded slurry is 37:6:104.3. NMP, adhesive solution and kneaded slurry are mixed at a speed of 500 r / min to obtain a dispersed slurry.

[0075] (4) The dispersion slurry obtained in step (3) is fed into a sand milling device. The filling rate of the sand milling beads in the sand milling device is 70%. The dispersion slurry is ground and dispersed at a linear velocity of 8 m / min. After degassing, lithium iron phosphate slurry is obtained.

[0076] Example 3

[0077] This embodiment provides a method for producing lithium iron phosphate slurry, which specifically includes the following steps:

[0078] (1) Lithium iron phosphate and conductive agent were added into a screw continuous homogenizer at a mass ratio of 96.5:1.0 and mixed at a speed of 3000 r / min to obtain a mixed powder.

[0079] (2) PVDF and PVP were added to NMP at a mass ratio of 4:1 to prepare a slurry with a solid content of 10%; then the slurry was fed into a screw continuous homogenizer with a mass ratio of 50:97.5 between the slurry and the mixed powder. The slurry and the mixed powder were mixed at a speed of 3000 r / min to obtain a kneaded slurry.

[0080] (3) NMP and adhesive solution are put into a screw continuous homogenizer. The mass ratio of NMP, adhesive solution and kneaded slurry is 7:10:147.5. NMP, adhesive solution and kneaded slurry are mixed at a speed of 3000 r / min to obtain a dispersed slurry.

[0081] (4) The dispersion slurry obtained in step (3) is fed into a sand milling device. The filling rate of the sand milling beads in the sand milling device is 90%. The dispersion slurry is ground and dispersed at a linear velocity of 18 m / min. After degassing, lithium iron phosphate slurry is obtained.

[0082] Example 4

[0083] This embodiment provides a method for producing lithium iron phosphate slurry. The difference from Embodiment 1 is that in step (2), PVDF and PVP are added to NMP at a mass ratio of 3:1 to premix and prepare a slurry with a solid content of 7%; in step (3), the mass ratio of NMP, slurry, and kneaded slurry is 16:8:123.6. The remaining process parameters and operating steps are the same as in Embodiment 1.

[0084] Example 5

[0085] This embodiment provides a method for producing lithium iron phosphate slurry. The difference from Embodiment 1 is that in step (2), PVDF and PVP are added to NMP at a mass ratio of 22:0.5 to premix and prepare a slurry with a solid content of 7%; in step (3), the mass ratio of NMP, slurry, and kneaded slurry is 29:8:123.6. The remaining process parameters and operating steps are the same as in Embodiment 1.

[0086] Example 6

[0087] This embodiment provides a method for producing lithium iron phosphate slurry. The difference from Embodiment 1 is that in step (2), the mass ratio of the adhesive solution and the mixed powder is 50:95.6; and in step (3), the mass ratio of NMP, adhesive solution, and kneaded slurry is 22:8:123.6. The remaining process parameters and operating steps are the same as in Embodiment 1.

[0088] Example 7

[0089] This embodiment provides a method for producing lithium iron phosphate slurry. The difference from Embodiment 1 is that in step (2), the mass ratio of the adhesive solution and the mixed powder is 10:95.6; and in step (3), the mass ratio of NMP, adhesive solution, and kneaded slurry is 24:8:123.6. The remaining process parameters and operating steps are the same as in Embodiment 1.

[0090] Example 8

[0091] This embodiment provides a method for producing lithium iron phosphate slurry. The difference from Embodiment 1 is that in step (3), the mass ratio of NMP, adhesive, and kneaded slurry is 20:12:123.6. The remaining process parameters and operating steps are the same as in Embodiment 1.

[0092] Example 9

[0093] This embodiment provides a method for producing lithium iron phosphate slurry. The difference from Embodiment 1 is that in step (3), the mass ratio of NMP, adhesive, and kneaded slurry is 25:4:123.6. The remaining process parameters and operating steps are the same as in Embodiment 1.

[0094] Comparative Example 1

[0095] This comparative example provides a method for producing lithium iron phosphate slurry. The difference from Example 1 is that no additives are added in step (2), and only PVDF is added to NMP for pre-mixing to prepare a slurry with a solid content of 7%; in step (3), the mass ratio of NMP, slurry, and kneaded slurry is 35:8:123.6. The remaining process parameters and operating steps are the same as in Example 1.

[0096] Comparative Example 2

[0097] This comparative example provides a method for producing lithium iron phosphate slurry. The difference from Example 1 is that the step of adding the adhesive solution in two separate steps is omitted; instead, the adhesive solution is directly added to the screw continuous homogenizer in step (2) in one step. In step (2), the mass ratio of the adhesive solution to the mixed powder is 36:95.6, and the adhesive solution and mixed powder are mixed at a speed of 1500 r / min to obtain a kneaded slurry. In step (3), the mass ratio of NMP, adhesive solution, and kneaded slurry is 20:0:123.6. The remaining process parameters and operating steps are the same as in Example 1.

[0098] The performance parameters of the lithium iron phosphate slurries prepared in Examples 1-9 and Comparative Examples 1-2 are shown in Table 1.

[0099] Table 1

[0100]

[0101]

[0102] As can be seen from the data in Table 1:

[0103] (1) The viscosity change rate of the slurry in Examples 1-3 was low after 24 hours of storage, indicating that the slurry prepared by the lithium iron phosphate slurry production method and production system provided by the present invention has good storage stability.

[0104] (2) The viscosity change rate of the slurries in Examples 4 and 5 after 24 hours of storage both reached over 20%, which was much higher than that in Example 1. This is because the amount of additive added in Example 4 was too high, and the amount of additive added in Example 5 was too low. Since the additive is an organic substance and cannot volatilize, it remains in the battery cell. Too much additive will reduce the electronic and ionic conductivity between active materials and increase the weight of the battery cell; when the amount of additive is too low, it cannot effectively reduce the surface energy of the particles, thus failing to promote the dispersion of raw materials and improve the uniformity and stability of the slurry.

[0105] (3) The slurry solid content of Examples 6 and 7 was higher or lower than that of Example 1, and the slurry viscosity was higher or lower than that of Example 1, respectively. Furthermore, the viscosity change rate of the slurries of Examples 6 and 7 after 24 hours of storage was also higher than that of Example 1, which is because the amount of adhesive added in the first step of Example 6 was too high, and the amount of adhesive added in the first step of Example 7 was too low. When the amount of mixed powder is constant, if the amount of adhesive added is too high, the kneading effect will be poor. This is because if the kneading solid content is too low, the shear force between particles during the kneading process will be insufficient, which will not be conducive to breaking up the agglomerates. If the amount of adhesive added is too low, the kneading effect will also be poor. This is because if the kneading solid content is too high, the slurry particles cannot be effectively wetted, and the shear force between particles during the kneading process will be insufficient, which will not be conducive to breaking up the agglomerates.

[0106] (4) The viscosity change rate of the slurries in Examples 8 and 9 after 24 hours of storage also exceeded 15%, which was higher than that in Example 1. This is because the amount of adhesive added in the last step of Example 8 was too high, and the amount of adhesive added in the last step of Example 9 was too low. When the amount of solvent and kneading slurry is constant, if the amount of adhesive added is too high, it will affect the performance of the battery cell and reduce the coating properties of the slurry. This is because the adhesive is mainly composed of organic and non-volatile binders and additives. Too much adhesive will reduce the electronic and ionic conductivity between active materials and increase the weight of the battery cell. If the amount of adhesive added is too low, it will lead to the electrode sheet demolding and powder shedding during the manufacturing process and poor battery cell cycle performance. This is because the adhesive mainly plays the role of bonding between particles and between the coating and the current collector. If the amount of adhesive is too low, the bonding force of the electrode sheet will be insufficient.

[0107] (5) The solid content of the slurry in Comparative Example 1 was much lower than that in Example 1, and the viscosity of the slurry decreased significantly after 24 hours of storage, indicating that the slurry had slight sedimentation. This was because the additive was omitted in Comparative Example 1. The viscosity change rate of the slurry in Comparative Example 2 reached 15% after 24 hours of storage, indicating that the slurry tended to deteriorate after 24 hours of storage. This was because Comparative Example 2 omitted the two-step addition of the adhesive solution and directly added the adhesive solution to the screw continuous homogenizer in step (2). The data from Comparative Examples 1 and 2 show that the addition of additives and the step-by-step addition of adhesive solution play an important role in improving the consistency and stability of lithium iron phosphate slurry and avoiding gel aggregation.

[0108] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for producing a lithium iron phosphate slurry, characterized by, The method for producing lithium iron phosphate slurry includes: In the continuous mixing process, lithium iron phosphate and conductive agent are first added to the mixing device to obtain mixed powder; binder, additive and solvent are premixed to obtain adhesive; then adhesive is added to the mixing device and mixed with mixed powder to obtain kneaded slurry; finally adhesive and solvent are added to the mixing device and mixed with kneaded slurry to obtain dispersion slurry. The lithium iron phosphate slurry was obtained by grinding and degassing the dispersion slurry in sequence. The mass ratio of the adhesive solution to the mixed powder is (10~50):(94.3~97.5); The mass ratio of the solvent, adhesive, and kneading slurry is (7~37):(6~10):(104.3~147.5).

2. The lithium iron phosphate slurry production method according to claim 1, characterized by, The mixing device is a screw continuous homogenizer.

3. The lithium iron phosphate slurry production method according to claim 2, characterized by, The rotational speed of the screw continuous homogenizer is 500~3000 r / min.

4. The lithium iron phosphate slurry production method according to claim 1, characterized by, The mass ratio of lithium iron phosphate to conductive agent is (94~96.5):(0.3~1.0).

5. The method of claim 1, wherein the lithium iron phosphate slurry is produced by the steps of: The conductive agent includes any one or a combination of at least two of conductive carbon black, vapor-grown carbon fibers, carbon nanotubes, conductive graphite, or graphene. ​ 6. The lithium iron phosphate slurry production method according to claim 1, wherein The mass ratio of the binder to the additive is (4~40):

1.

7. The method of claim 1, wherein the lithium iron phosphate slurry is produced by the steps of: The adhesive includes polyvinylidene fluoride. ​ 8. The method of claim 1, wherein the lithium iron phosphate slurry is produced by the steps of: The additives include polyvinylpyrrolidone. ​ 9. The method of claim 1, wherein the lithium iron phosphate slurry is produced by the steps of: The solvent includes N-methylpyrrolidone. ​ 10. The method of claim 1, wherein the lithium iron phosphate slurry is produced by the steps of: The solid content of the adhesive solution is 4~10wt%. ​ 11. The method of claim 1, wherein the lithium iron phosphate slurry is produced by the steps of: The grinding process is carried out in a sand mill. ​ 12. The method of claim 11, wherein the lithium iron phosphate slurry is produced by the steps of: The rotational linear speed of the grinding device is 8~18m / min. ​ 13. The method of claim 12, wherein the lithium iron phosphate slurry is produced by the steps of: The filling rate of the grinding beads in the grinding device is 70%~90%. ​ 14. The method of claim 1, wherein the lithium iron phosphate slurry is produced by the steps of: The method for producing lithium iron phosphate slurry includes the following steps: ​ (1) Lithium iron phosphate and conductive agent are added into a screw continuous homogenizer at a mass ratio of (94~96.5):(0.3~1.0) and mixed at a speed of 500~3000 r / min to obtain a mixed powder; (2) The binder and additives are added to the solvent at a mass ratio of (4~40):1 to prepare a glue solution with a solid content of 4%~10wt%; then the glue solution is fed into a screw continuous homogenizer, the mass ratio of glue solution to mixed powder is (10~50):(94.3~97.5), and the glue solution and mixed powder are mixed at a speed of 500~3000r / min to obtain kneaded slurry; (3) The solvent and adhesive are put into the screw continuous homogenizer. The mass ratio of solvent, adhesive and kneaded slurry is (7~37):(6~10):(104.3~147.5). The solvent, adhesive and kneaded slurry are mixed at a speed of 500~3000 r / min to obtain a dispersed slurry. (4) The dispersion slurry obtained in step (3) is fed into a sand milling device. The filling rate of the sand milling beads in the sand milling device is 70-90%. The dispersion slurry is ground and dispersed at a linear velocity of 8-18 m / min. After degassing, the lithium iron phosphate slurry is obtained.

15. The method of claim 1, wherein the lithium iron phosphate slurry is produced by the steps of: The lithium iron phosphate slurry production method is completed by a lithium iron phosphate slurry production system device; ​ The lithium iron phosphate slurry production system includes a mixing device, a powder feeding unit, a glue-making unit, and a liquid feeding device. Along the material flow direction, the powder feeding unit, the glue-making unit, and the liquid feeding device are respectively connected to the mixing device.

16. The method of claim 15, wherein the lithium iron phosphate slurry is produced by the steps of: The mixing device includes a housing, and at least one screw is disposed inside the housing. ​ 17. The method of claim 16, wherein the lithium iron phosphate slurry is produced by the steps of: The housing contains at least two screws arranged in parallel within the housing, with their threads interlocking. ​ 18. The method of claim 16, wherein the lithium iron phosphate slurry is produced by the steps of: The interior of the shell is divided into a powder mixing zone, a kneading zone, a dispersion and viscosity adjustment zone, and a defoaming and venting zone along the material flow direction. ​ 19. The method of claim 18, wherein the lithium iron phosphate slurry is produced by a process comprising: The housing containing the powder mixing zone has a powder feeding port, which is connected to the powder feeding unit. ​ 20. The method of claim 18, wherein the lithium iron phosphate slurry is produced by a process comprising: The housing containing the kneading zone has an adhesive inlet, which is connected to the adhesive preparation unit. ​ 21. The method of claim 18, wherein the lithium iron phosphate slurry is produced by a process comprising: The housing containing the dispersion and viscosity adjustment zone has a liquid feeding port, and the liquid feeding port is connected to a liquid feeding device. ​ 22. The method of claim 18, wherein the lithium iron phosphate slurry is produced by a process comprising: The shell containing the defoaming and venting zone has an vent hole. ​ 23. The method of claim 15, wherein the lithium iron phosphate slurry is produced by a process comprising: The powder feeding unit includes at least one lithium iron phosphate storage tank and at least one conductive agent storage tank. ​ 24. The method of claim 15, wherein the lithium iron phosphate slurry is produced by a process comprising: The glue-making unit includes a raw material supply device, a glue-making device, a glue storage device, and a glue liquid feeding device connected sequentially along the material flow direction. ​ 25. The method for producing lithium iron phosphate slurry according to claim 24, characterized in that, The raw material supply device includes at least one binder storage tank and at least one additive storage tank.

26. The method of claim 15, wherein the lithium iron phosphate slurry is produced by a process comprising: The outlet of the mixing device is also connected in sequence to a sand mill and a degassing machine. ​

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