Slurrying method for long-circulation lithium iron phosphate battery

Abstract

The invention provides a pulping method for a long-circulation lithium iron phosphate battery. According to the preparation method of the acid lithium iron slurry, a high-concentration first glue solution and a low-concentration second glue solution are prepared in advance; adding the first glue solution into a mixture of a first conductive agent and lithium iron phosphate to obtain a second mixture; adding the second conductive agent into the second glue solution step by step to obtain a third mixture; dropwise adding the third mixture into the second mixture, stirring and kneading to obtain a fourth mixture; and stirring and vacuumizing the fourth mixture to obtain the lithium iron phosphate slurry. The temperature of the second mixture is increased by stirring, so that the adsorption of the first conductive agent and the first glue solution by the lithium iron phosphate is facilitated, and the overall dispersity and consistency of the second mixture are improved. Polyvinylidene fluoride has relatively large surface tension, so that the dispersity of the second conductive agent in the second glue solution is improved. The invention also provides application of the lithium iron phosphate slurry prepared by the preparation method in preparation of a lithium ion battery.

Description

Technical Field

[0001] The invention relates to the technical field of lithium batteries, and in particular to a pulping method for long-cycle lithium iron phosphate batteries. Background Art

[0002] With the continuous improvement of social energy-saving awareness and the continuous improvement of lithium-ion battery manufacturing technology, lithium iron phosphate positive electrode materials have been widely used. As a common green energy source, lithium-ion batteries have been widely used in many products closely related to life, such as electric vehicles, mobile phones, computers, etc. Lithium iron phosphate has become one of the most promising positive electrode materials in the industry because of its outstanding advantages such as good safety, low cost, and stable structure. Lithium iron phosphate has the advantages of good safety performance, long cycle life, wide source of raw materials, and no pollution, but it also has the fatal disadvantage of poor conductivity. In order to improve the conductivity of lithium iron phosphate, conductive agents such as graphene and carbon nanotubes with high conductivity are usually added when preparing lithium iron phosphate positive electrode slurry. However, since the conductive agent is easy to agglomerate and difficult to disperse, the dispersion and consistency of lithium iron phosphate positive electrode slurry are poor. The dispersion and consistency of lithium iron phosphate slurry directly affect the quality of slurry coating, and then affect the final electrical performance of the battery. Summary of the invention

[0003] In order to solve the problems and shortcomings in the prior art, the present invention provides a long-cycle lithium iron phosphate battery slurrying method, which improves the slurry preparation process to achieve the effect of improving the slurry dispersion and consistency, and ultimately improves the electrochemical performance of the battery.

[0004] Specifically, the present invention provides a long-cycle lithium iron phosphate battery pulping method, comprising the following steps: S1, stirring and kneading the first conductive agent and lithium iron phosphate for the first time to obtain a first mixture; S2, dripping a pre-made first glue into the first mixture at a uniform speed within a first preset time, and obtaining a second mixture by stirring and kneading for a second time; the first glue is a mixture of polyvinylidene fluoride and N-methylpyrrolidone; S3, adding the second conductive agent to the pre-made second glue solution at least twice, and dispersing by ultrasonication to obtain a third mixture; the first glue solution is a mixture of polyvinylidene fluoride and N-methylpyrrolidone; the content of polyvinylidene fluoride in the second glue solution is lower than the content of polyvinylidene fluoride in the first glue solution; S4, uniformly dropping the third mixture into the second mixture within a second preset time, and stirring and kneading for the third time to obtain a fourth mixture; S5, stirring the fourth mixture for a third preset time according to a preset stirring setting, and evacuating the mixture to obtain lithium iron phosphate slurry.

[0005] Optionally, the first conductive agent is conductive carbon black; The second conductive agent is carbon nanotube.

[0006] Optionally, the mass ratio of polyvinylidene fluoride to N-methylpyrrolidone in the first glue solution is (4-4.5): (5-20); The mass ratio of polyvinylidene fluoride to N-methylpyrrolidone in the second glue solution is (0.5~1): (75~90); the mass ratio of polyvinylidene fluoride in the first glue solution and the second glue solution to N-methylpyrrolidone in the first glue solution and the second glue solution is 5:95.

[0007] Optionally, in step S1, the revolution stirring speed of the first stirring and kneading is 300 to 500 revolutions per minute, and the stirring time of the first stirring and kneading is 8 to 10 minutes.

[0008] Optionally, in step S2, the first preset time length is 15 to 25 minutes; the rotation stirring speed of the second stirring and kneading is 1000 to 1200 rpm; the revolution stirring speed of the second stirring and kneading is 500 to 800 rpm; and the stirring time of the second stirring and kneading is 8 to 10 minutes.

[0009] Optionally, in step S3, the stirring speed of the ultrasonic dispersion is 300-400 rpm, and the stirring time of the ultrasonic dispersion is 25-30 min.

[0010] Optionally, in step S4, the second preset time length is 15 to 25 minutes; The third stirring and kneading has a rotation stirring speed of 1000-1200 rpm, a revolution stirring speed of 500-800 rpm, and a stirring time of 8-10 min.

[0011] Optionally, in step S5, the preset stirring setting includes: the rotation stirring speed of the preset stirring setting is 1500-1800 rpm, the revolution stirring speed of the preset stirring setting is 1200-1500 rpm; and the third preset time length is 2-3 hours.

[0012] Optionally, the first glue solution and the second glue solution are stirred at a constant temperature of 50-60° C. for 0.5-1.5 hours, and then vacuumed and allowed to stand for 1.5-2.5 hours.

[0013] Furthermore, the present invention also provides the use of the long-cycle lithium iron phosphate battery pulping method described in any one of the above items in the preparation of lithium-ion batteries.

[0014] In the long-cycle lithium iron phosphate battery pulping method of the present invention, the mass fraction of polyvinylidene fluoride in the first glue solution is higher than the mass fraction of polyvinylidene fluoride in the first glue solution. The lithium iron phosphate and the first conductive agent are stirred and kneaded to obtain a first mixture, and the first glue solution is uniformly added to the first mixture, and the second mixture is stirred and kneaded to obtain a second mixture. During the stirring and kneading process, the moving particles collide and rub against each other, so that the agglomerated structure is broken; at the same time, the stirring causes the temperature of the second mixture to rise, which is conducive to the adsorption of the first conductive agent and the first glue solution by lithium iron phosphate, and improves the overall dispersibility and consistency of the second mixture. The second conductive agent is added to the prefabricated second glue solution in batches, and the second conductive agent is dispersed in the second glue solution by ultrasonic stirring to obtain a third mixture. During the dispersion process, the polyvinylidene fluoride in the second glue solution has a large surface tension, which reduces the resistance encountered by the second conductive agent during the dispersion process, thereby breaking up the agglomerated structure of the second conductive agent and improving the dispersion performance of the second conductive agent in the second glue solution. The dispersibility and consistency of the third mixture and the second mixture are improved, so that the dispersibility and consistency of the lithium iron phosphate slurry obtained after the third mixture and the second mixture are mixed, stirred and vacuumed are improved.

[0015] Based on the following detailed description of specific embodiments of the present invention in conjunction with the accompanying drawings, those skilled in the art will become more aware of the above and other objects, advantages and features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings: Figure 1 is a flow chart of preparing lithium iron phosphate slurry according to one embodiment of the present invention; Figure 2 is a SEM image of lithium iron phosphate used in the present invention; Figure 3 is a process capability diagram of lithium iron phosphate slurry obtained in a comparative example of the present invention; Figure 4 This is the process capability diagram of the lithium iron phosphate slurry obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0017] Refer to the following Figures 1 to 4To describe a long-cycle lithium iron phosphate battery pulping method of an embodiment of the present invention. In the description of this embodiment, it should be understood that the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features, that is, include one or more of the features. In the description of the present invention, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. When a feature "includes or contains" one or some of the features it covers, unless otherwise specifically described, this indicates that other features are not excluded and may further include other features.

[0018] In the description of the present embodiment, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0019] Figure 1 FIG. 1 is a flow chart of preparing lithium iron phosphate slurry according to an embodiment of the present invention. Figure 1 As shown, combined with Figure 2 and Figure 4 The embodiment of the present invention provides a pulping method for a long-cycle lithium iron phosphate battery, and the pulping method for a long-cycle lithium iron phosphate battery comprises the following steps: S1, stirring and kneading the first conductive agent and lithium iron phosphate for the first time to obtain a first mixture; S2, dripping the pre-made first glue into the first mixture at a uniform speed within a first preset time, and obtaining a second mixture by stirring and kneading for a second time; the first glue is a mixture of polyvinylidene fluoride and N-methylpyrrolidone; S3, adding the second conductive agent to the pre-made second glue solution at least twice, and dispersing by ultrasonication to obtain a third mixture; the second glue solution is a mixture of polyvinylidene fluoride and N-methylpyrrolidone; the content of polyvinylidene fluoride in the second glue solution is lower than the content of polyvinylidene fluoride in the first glue solution; S4, dropping the third mixture into the second mixture at a uniform speed within a second preset time, and stirring and kneading for a third time to obtain a fourth mixture; S5, stirring the fourth mixture for a third preset time according to a preset stirring setting, and evacuating the mixture to obtain lithium iron phosphate slurry.

[0020] The specific implementation process of this embodiment includes: pre-preparing polyvinylidene fluoride and N-methylpyrrolidone to prepare a first glue solution and a second glue solution for standby use. The mass fraction of polyvinylidene fluoride in the first glue solution is higher than the mass fraction of polyvinylidene fluoride in the second glue solution. The first conductive agent and lithium iron phosphate are stirred and kneaded for the first time to obtain a first mixture; the first glue solution is dripped into the first mixture within a first preset time to obtain a second mixture, and the stirring state is maintained during the dripping process. The second conductive agent is added to the second glue solution to obtain a third mixture, and the addition is carried out at least twice, and the second glue solution is ultrasonically stirred during the addition process. The third mixture is dripped into the second mixture within the second preset time, and the fourth mixture is obtained by stirring and kneading for the third time. The fourth mixture is stirred according to the preset conditions, and a lithium iron phosphate slurry is obtained by vacuuming.

[0021] In this embodiment, during the stirring and kneading process, the moving particles collide and rub against each other, so that the agglomerated structure is broken; at the same time, the stirring causes the temperature of the second mixture to rise, which is conducive to the adsorption of lithium iron phosphate on the first conductive agent and the first glue, and improves the overall dispersibility and consistency of the second mixture. During the dispersion process of the second conductive agent and the second glue to prepare the third mixture, the polyvinylidene fluoride in the second glue has a large surface tension, which reduces the resistance encountered during the dispersion of the second conductive agent, thereby breaking up the agglomerated structure of the second conductive agent and improving the dispersion performance of the second conductive agent in the second glue. The dispersibility and consistency of the third mixture and the second mixture are improved, so that the dispersibility and consistency of the lithium iron phosphate slurry obtained after the third mixture and the second mixture are mixed, stirred and vacuumed and defoamed are improved.

[0022] In the long-cycle lithium iron phosphate battery pulping method of the present invention, the first conductive agent is conductive carbon black, and the second conductive agent is carbon nanotubes.

[0023] Conductive agents, as key auxiliary materials for lithium-ion batteries, play an important role in improving the conductivity, capacity, rate performance, and cycle performance of lithium batteries. Existing mainstream conductive agents include conductive carbon black, carbon nanotubes, and graphene. In this embodiment, conductive carbon black and carbon nanotubes are selected as conductive agents. The conductive carbon black forms a point-to-point contact with lithium iron phosphate, and the carbon nanotubes and lithium iron phosphate form a line-contact conductive network, thereby more fully constructing a conductive network with high cost performance.

[0024] In the long-cycle lithium iron phosphate battery pulping method of the present invention, the mass ratio of polyvinylidene fluoride and N-methylpyrrolidone in the first glue solution is (4~4.5): (5~20); the mass ratio of polyvinylidene fluoride and N-methylpyrrolidone in the second glue solution is (0.5~1): (75~90); the mass ratio of polyvinylidene fluoride in the first glue solution and the second glue solution to N-methylpyrrolidone in the first glue solution and the second glue solution is 5:95.

[0025] Specifically, 5 parts of polyvinylidene fluoride and 95 parts of N-methylpyrrolidone were weighed, 4 to 4.5 parts of polyvinylidene fluoride and 5 to 20 parts of N-methylpyrrolidone were used to prepare a first glue solution, and the remaining polyvinylidene fluoride and the remaining N-methylpyrrolidone were used to prepare a second glue solution.

[0026] In this embodiment, the second glue has a lower solid content, which is beneficial to the dispersion of carbon nanotubes.

[0027] In the long-cycle lithium iron phosphate battery pulping method of the present invention, in step S1, the revolution stirring speed of the first stirring and kneading is 300-500 rpm, and the stirring time of the first stirring and kneading is 8-10 minutes.

[0028] In the long-cycle lithium iron phosphate battery pulping method of the present invention, in step S2, the first preset time length is 15 to 25 minutes; the rotation stirring speed of the second stirring and kneading is 1000 to 1200 revolutions per minute, the revolution stirring speed of the second stirring and kneading is 500 to 800 revolutions per minute, and the stirring time of the second stirring and kneading is 8 to 10 minutes.

[0029] In the long-cycle lithium iron phosphate battery pulping method of the present invention, in step S3, the stirring speed of ultrasonic dispersion is 300-400 rpm, and the stirring time of ultrasonic dispersion is 25-30 min.

[0030] In the long-cycle lithium iron phosphate battery pulping method of the present invention, in step S4, the second preset time length is 15 to 25 minutes, the rotation stirring speed of the third stirring and kneading is 1000 to 1200 revolutions per minute, the revolution stirring speed of the third stirring and kneading is 500 to 800 revolutions per minute, and the stirring time of the third stirring and kneading is 8 to 10 minutes.

[0031] In the long-cycle lithium iron phosphate battery pulping method of the present invention, in step S5, the preset stirring setting includes: the preset stirring setting has a rotation stirring speed of 1500 to 1800 rpm, the preset stirring setting has a revolution stirring speed of 1200 to 1500 rpm, and the third preset time length is 2 to 3 hours.

[0032] In this embodiment, the rapidly moving particles collide and rub against each other, further improving the dispersibility of the lithium iron phosphate slurry.

[0033] In the long-cycle lithium iron phosphate battery pulping method of the present invention, the first glue solution and the second glue solution are stirred at a constant temperature of 50-60° C. for 0.5-1.5 hours, and then vacuumed and allowed to stand for 1.5-2.5 hours.

[0034] In this embodiment, the vacuum is drawn and then left to stand, so that the polymer chains in the first glue solution and the second glue solution are fully stretched, which helps to improve the film-forming performance.

[0035] Furthermore, the present invention also provides the use of the long-cycle lithium iron phosphate battery pulping method in any of the above embodiments in the preparation of lithium-ion batteries.

[0036] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below through specific examples. The following examples are specific implementations of the present invention, but the implementations of the present invention are not limited to the following examples. The test methods used in the examples and / or comparative examples are conventional methods unless otherwise specified. The manufacturer of lithium iron phosphate is Gansu Daxiang Energy Technology Co., Ltd., model DXF-04; the manufacturer of conductive carbon black is Swiss Termigo Co., Ltd., model SP-Li; the manufacturer of carbon nanotubes is China Green Energy Power Co., Ltd.; the manufacturer of polyvinylidene fluoride is Solvay, USA, model SOLEF-5130. The materials, reagents, etc. used can be obtained from commercial channels. Example 1

[0037] Step S110, pre-prepare the first glue solution and the second glue solution: weigh 50g of polyvinylidene fluoride and 950g of N-methylpyrrolidone, take 45g of polyvinylidene fluoride and 150g of N-methylpyrrolidone to prepare the first glue solution, take 5g of polyvinylidene fluoride and 800g of N-methylpyrrolidone to prepare the second glue solution, and obtain 195g of the first glue solution and 805g of the second glue solution.

[0038] Step S120, stirring the first glue solution and the second glue solution at a constant temperature of 50°C for 1 hour, and then evacuating the solution and letting it stand for 2 hours.

[0039] Step S130, weigh 2375g of lithium iron phosphate and 50g of conductive carbon black, stir and mix to obtain a first mixture, the revolution stirring speed during stirring and mixing is 300rpm, and the stirring and mixing time is 8min.

[0040] Step S140, according to the adding speed of 7.8g / min, all the first glue solution is delivered to the stirring device where the first mixture is located through the automatic delivery pipe, and stirred to obtain the second mixture; during stirring, the rotation stirring speed is 1000rpm, the revolution stirring speed is 5000rpm, and the stirring time is 8min.

[0041] Step S150, weigh 500g of carbon nanotubes, add the carbon nanotubes to the second glue solution twice to obtain a third mixture, and continue to perform ultrasonic dispersion during the adding process. After all the carbon nanotubes are added, continue stirring at a frequency of 300rpm for 25min.

[0042] Step S160, adding the third mixture to the stirring device where the second mixture is located at an adding speed of 33.2 g / min, and stirring to obtain a fourth mixture; during stirring, the rotation stirring speed is 1000 rpm, the revolution stirring speed is 500 rpm, and the stirring time is 8 minutes.

[0043] Step S170, the fourth mixture is stirred at a stirring speed of 1500 rpm for rotation and 1200 rpm for revolution, and the stirring is continued for 2 hours, and then vacuum is evacuated to obtain lithium iron phosphate slurry. Example 2

[0044] Step S210, pre-prepare the first glue solution and the second glue solution: weigh 50g of polyvinylidene fluoride and 950g of N-methylpyrrolidone, take 42g of polyvinylidene fluoride and 100g of N-methylpyrrolidone to prepare the first glue solution, take 8g of polyvinylidene fluoride and 850g of N-methylpyrrolidone to prepare the second glue solution, and obtain 142g of the first glue solution and 858g of the second glue solution.

[0045] Step S220, stirring the first glue solution and the second glue solution at a constant temperature of 50°C for 1 hour, and then evacuating the solution and letting it stand for 2 hours.

[0046] Step S230, weigh 2375g of lithium iron phosphate and 50g of conductive carbon black, stir and mix to obtain a first mixture, the revolution stirring speed during stirring and mixing is 400rpm, and the stirring and mixing time is 9min.

[0047] Step S240, according to the adding speed of 7.1g / min, all the first glue solution is delivered to the stirring device where the first mixture is located through the automatic delivery pipe, and stirred to obtain the second mixture; during stirring, the rotation stirring speed is 1100rpm, the revolution stirring speed is 700rpm, and the stirring time is 9min.

[0048] Step S250, after step S240, carbon nanotubes are added to the second glue solution twice to obtain a third mixture, and ultrasonic dispersion is continuously performed during the adding process. After all the addition is completed, stirring is continuously performed at a frequency of 350 rpm for 28 minutes.

[0049] Step S260, adding the third mixture to the stirring device where the second mixture is located at an adding speed of 44.2 g / min, and stirring to obtain a fourth mixture; during stirring, the rotation stirring speed is 1100 rpm, the revolution stirring speed is 700 rpm, and the stirring time is 9 minutes.

[0050] In step S270, the fourth mixture is stirred at a stirring speed of 1700 rpm for rotation and 1400 rpm for revolution, and the stirring is continued for 2.5 hours, and then vacuum is evacuated to obtain lithium iron phosphate slurry. Example 3

[0051] Step S310, pre-prepare the first glue solution and the second glue solution: weigh 50g of polyvinylidene fluoride and 950g of N-methylpyrrolidone, take 40g of polyvinylidene fluoride and 50g of N-methylpyrrolidone to prepare the first glue solution, take 10g of polyvinylidene fluoride and 900g of N-methylpyrrolidone to prepare the second glue solution, and obtain 90g of the first glue solution and 910g of the second glue solution.

[0052] Step S320, stirring the first glue solution and the second glue solution at a constant temperature of 50°C for 1 hour, and then evacuating the solution and letting it stand for 2 hours.

[0053] Step S330, weigh 2375g of lithium iron phosphate and 50g of conductive carbon black, stir and mix to obtain a first mixture, the revolution stirring speed during stirring and mixing is 500rpm, and the stirring and mixing time is 10min.

[0054] Step S340, according to the adding speed of 6.0g / min, all the first glue solution is delivered to the stirring device where the first mixture is located through the automatic delivery pipe, and stirred to obtain the second mixture; during stirring, the rotation stirring speed is 1200rpm, the revolution stirring speed is 800rpm, and the stirring time is 10min.

[0055] Step S350, after step S240, adding carbon nanotubes into the second glue solution twice to obtain a third mixture, performing ultrasonic dispersion continuously during the adding process, and stirring continuously at a frequency of 400 rpm for 30 minutes after all the addition is completed.

[0056] Step S360, adding the third mixture to the stirring device where the second mixture is located at an adding speed of 62.3 g / min, and stirring to obtain a fourth mixture; during stirring, the rotation stirring speed is 1200 rpm, the revolution stirring speed is 800 rpm, and the stirring time is 10 minutes.

[0057] Step S370: The fourth mixture is stirred at a stirring speed of 1800 rpm for rotation and 1500 rpm for revolution. The stirring is continued for 3.0 hours and then vacuumized to obtain lithium iron phosphate slurry.

[0058] Comparative Example Step S410, weigh 50g and 950g of N-methylpyrrolidone for later use, and use 50g of polyvinylidene fluoride and 450g of N-methylpyrrolidone to prepare a polyvinylidene fluoride glue solution with a solid content of 10%.

[0059] Step S420, evacuate the prepared polyvinylidene fluoride glue solution and let it stand for 12 hours.

[0060] Step S430, allowing the prepared polyvinylidene fluoride adhesive to stand for 12 hours.

[0061] Step S430, after standing, a certain amount of polyvinylidene fluoride is transported to the slurry preparation mixer through a sealed pipe by a metering pump, and 25g of conductive carbon black is added to the mixer by N-methylpyrrolidone-assisted spraying. At the same time, the mixer is started to rotate and revolve, the revolution stirring speed is 25rpm, the rotation speed is set to 500rpm, and the stirring time is 1.0h.

[0062] Step S440, add 1187.5g of lithium iron phosphate to the above mixer, the revolution stirring speed is 30rpm, the rotation speed is set to 300rpm, after stirring for 5min, add another 1187.5g of lithium iron phosphate, and continue stirring for 1.5h. N-methylpyrrolidone is used to assist spraying during the addition of lithium iron phosphate.

[0063] Step S450, spray all the remaining N-methylpyrrolidone into the mixer, and continue stirring at a rotation speed of 35 r / min and an orbital speed of 800 r / min. After stirring for 30 minutes, adjust the orbital speed to 1300 r / min and continue stirring for 1.5 hours.

[0064] Step S460, transferring the slurry obtained in step S450 into a transfer tank, and performing vacuum defoaming.

[0065] Figure 3 is a process capability diagram of lithium iron phosphate slurry prepared in a comparative example of the present invention; Figure 4 1 is a process capability diagram of the lithium iron phosphate slurry prepared in Example 1 of the present invention. Figure 4 and Figure 3 ,obvious Figure 4 It is shown that the dispersion and consistency of lithium iron phosphate slurry are improved.

[0066] At this point, those skilled in the art should recognize that, although multiple exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived based on the content disclosed in the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and recognized as covering all these other variations or modifications.

Claims

1. The present invention provides a long-cycle lithium iron phosphate battery pulping method, characterized in that: The preparation method comprises the following steps: S1, stirring and kneading the first conductive agent and lithium iron phosphate for the first time to obtain a first mixture; S2, dripping the pre-made first glue into the first mixture at a uniform speed within a first preset time, and obtaining a second mixture through a second stirring and kneading; the first glue is a mixture of polyvinylidene fluoride and N-methylpyrrolidone; S3, adding the second conductive agent to the pre-made second glue at least twice, and obtaining a third mixture through ultrasonic dispersion; the first glue is a mixture of polyvinylidene fluoride and N-methylpyrrolidone; the content of polyvinylidene fluoride in the second glue is lower than the content of polyvinylidene fluoride in the first glue; S4, uniformly dropping the third mixture into the second mixture within a second preset time, and stirring and kneading for the third time to obtain a fourth mixture; S5, stirring the fourth mixture for a third preset time under preset stirring conditions, and evacuating the mixture to obtain lithium iron phosphate slurry.

2. The method for making pulp of long-cycle lithium iron phosphate battery according to claim 1, characterized in that: The first conductive agent is conductive carbon black; The second conductive agent is carbon nanotube.

3. The method for making pulp of a long-cycle lithium iron phosphate battery according to claim 1 or 2, characterized in that: The mass ratio of polyvinylidene fluoride to N-methylpyrrolidone in the first glue solution is (4-4.5): (5-20); The mass ratio of polyvinylidene fluoride to N-methylpyrrolidone in the second glue solution is (0.5~1): (75~90); the mass ratio of polyvinylidene fluoride in the first glue solution and the second glue solution to N-methylpyrrolidone in the first glue solution and the second glue solution is 5:

95.

4. The method for making pulp of a long-cycle lithium iron phosphate battery according to claim 1 or 2, characterized in that: In step S1, the revolution stirring speed of the first stirring and kneading is 300 to 500 revolutions per minute, and the stirring time is 8 to 10 minutes.

5. The method for making pulp of long-cycle lithium iron phosphate battery according to claim 1 or 2, characterized in that: In step S2, the first preset time length is 15 to 25 minutes; the rotation stirring speed of the second stirring and kneading is 1000 to 1200 rpm, the revolution stirring speed is 500 to 800 rpm, and the stirring time is 8 to 10 minutes.

6. The method for making pulp of a long-cycle lithium iron phosphate battery according to claim 1 or 2, characterized in that: In step S3, the stirring speed of the ultrasonic dispersion is 300-400 rpm, and the stirring time is 25-30 min.

7. The method for making pulp of a long-cycle lithium iron phosphate battery according to claim 1 or 2, characterized in that: In step S4, the second preset time length is 15 to 25 minutes; The third stirring and kneading has a rotation stirring speed of 1000-1200 rpm, a revolution stirring speed of 500-800 rpm, and a stirring time of 8-10 min.

8. The method for making pulp of a long-cycle lithium iron phosphate battery according to claim 1 or 2, characterized in that: In step S5, the stirring conditions include: the rotation stirring speed is 1500-1800 rpm, the revolution stirring speed is 1200-1500 rpm; and the third preset time length is 2-3 hours.

9. The method for making pulp of a long-cycle lithium iron phosphate battery according to claim 1 or 2, characterized in that: The first glue solution and the second glue solution are stirred at a constant temperature of 50-60° C. for 0.5-1.5 hours, and then vacuumed and allowed to stand for 1.5-2.5 hours.

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