Modified lithium iron phosphate positive electrode slurry and preparation method thereof

Abstract

The invention provides modified lithium iron phosphate positive electrode slurry and a preparation method thereof.The preparation method comprises the steps that a lithium iron phosphate positive electrode material, a binder PVDF and a first conductive agent are subjected to dry mixing, and a first premix is obtained; adding an organic solvent into the first premix, and stirring for the first time to obtain a second premix; and adding a second conductive agent, an adhesive PVP and an organic solvent into the second premix, and carrying out second stirring to obtain the modified lithium iron phosphate positive electrode slurry. In the preparation process of the modified lithium iron phosphate positive electrode slurry, the binder PVP is added, the binder PVP not only can enable the active substance and the electrode current collector to be bonded together, but also after the binder PVP is added, the viscosity change of the slurry within the preset time is small, and the viscosity stability of the modified lithium iron phosphate positive electrode slurry is further improved. In addition, in the preparation process of the modified lithium iron phosphate positive electrode slurry, the preparation steps are simplified, the production time is shortened, and the production efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion batteries, and in particular to a modified lithium iron phosphate positive electrode slurry and a preparation method thereof. Background Art

[0002] With the rapid development of new energy technologies, lithium-ion batteries have been widely used in many fields. As an important cathode material for lithium-ion batteries, lithium iron phosphate has the advantages of good thermal stability and long cycle life. The traditional preparation process of modified lithium iron phosphate cathode slurry has problems such as low production efficiency and poor slurry viscosity stability, which makes it difficult to meet market demand.

[0003] There are technical problems in the preparation process of modified lithium iron phosphate positive electrode slurry, such as low production efficiency and poor slurry viscosity stability, and no effective solution has been proposed so far. Summary of the invention

[0004] The main purpose of the present invention is to provide a modified lithium iron phosphate positive electrode slurry and a preparation method thereof, so as to solve the technical problems of low production efficiency and poor slurry viscosity stability in the preparation process of modified lithium iron phosphate positive electrode slurry in the prior art.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a method for preparing a modified lithium iron phosphate positive electrode slurry is provided, comprising: dry mixing a lithium iron phosphate positive electrode material, a binder PVDF and a first conductive agent to obtain a first premix; adding an organic solvent to the first premix and performing a first stirring to obtain a second premix; adding a second conductive agent, a binder PVP and an organic solvent to the second premix and performing a second stirring to obtain a modified lithium iron phosphate positive electrode slurry.

[0006] Furthermore, in the step of dry-mixing the lithium iron phosphate positive electrode material, the binder PVDF and the first conductive agent to obtain the first premix, the ratio of the lithium iron phosphate positive electrode material, the first conductive agent, the binder PVDF, the second conductive agent and the adhesive PVP is (95-98) in parts by mass: (0.5-1): (1.5-2.5): (0.01-0.1): (0.05-0.5).

[0007] Furthermore, the preparation method further comprises: adding an organic solvent again to the modified lithium iron phosphate positive electrode slurry to adjust the viscosity and solid content of the lithium iron phosphate positive electrode slurry.

[0008] Further, the first conductive agent is composed of at least two of carbon black, carbon nanotubes and graphene, and / or the second conductive agent is composed of at least two of carbon black, carbon nanotubes and graphene.

[0009] Furthermore, the lithium iron phosphate positive electrode material, the binder PVDF and the first conductive agent are dry-mixed to obtain a first premix, including: placing the lithium iron phosphate positive electrode material, the binder PVDF and the first conductive agent into a high-speed mixer and mixing them at a first preset speed for at least 25 minutes.

[0010] Furthermore, adding an organic solvent to the first premix and mixing to obtain a second premix includes: adding the organic solvent to the first premix, gradually increasing the stirring speed, and continuing stirring for at least 55 minutes.

[0011] Further, a second conductive agent, a binder PVP and an organic solvent are added to the second premix and mixed to obtain a lithium iron phosphate positive electrode slurry, including: adding a second conductive agent, a binder PVP and an organic solvent to the second premix, gradually increasing the stirring speed, and continuing mixing for at least 90 minutes.

[0012] According to another aspect of the present invention, a modified lithium iron phosphate positive electrode slurry is provided. The modified lithium iron phosphate positive electrode slurry is prepared by the above-mentioned preparation method.

[0013] Furthermore, the solid content of the modified lithium iron phosphate positive electrode slurry is 55% to 65%.

[0014] Furthermore, the viscosity of the modified lithium iron phosphate positive electrode slurry is 4000-9000 mPa.s.

[0015] By applying the technical solution of the present invention, the viscosity stability of the modified lithium iron phosphate positive electrode slurry affects the performance and manufacturing process of the battery: unstable viscosity may lead to poor fluidity of the slurry during the coating process, affecting the uniformity of the coating, thereby affecting the consistency and performance of the battery; and, unstable viscosity may cause the slurry to form an uneven pore structure during the drying and curing process, affecting the charge and discharge performance and cycle life of the battery; and, unstable viscosity may cause the coating machine to need to adjust parameters frequently, increasing downtime and maintenance costs during the production process. In order to improve the viscosity stability of the modified lithium iron phosphate positive electrode slurry, in the preparation process of the modified lithium iron phosphate positive electrode slurry, a binder PVP is added. The binder PVP can not only bond the active material to the electrode current collector, but also after adding the binder PVP, the viscosity of the slurry changes less within a preset time, thereby improving the viscosity stability of the modified lithium iron phosphate positive electrode slurry. In addition, in the preparation process of the modified lithium iron phosphate positive electrode slurry, some raw materials are first dry mixed, and then an organic solvent is added for one stirring, and before the second stirring, a variety of raw materials are added, which simplifies the preparation steps, shortens the production time, and thus improves production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0017] Figure 1 A schematic flow chart of a method for preparing a modified lithium iron phosphate positive electrode slurry in the present invention is shown;

[0018] Figure 2 A curve diagram showing the change of slurry viscosity and solid content of the modified lithium iron phosphate positive electrode slurry in Example 1 is shown;

[0019] Figure 3 A curve diagram showing the change of slurry viscosity and solid content of the modified lithium iron phosphate positive electrode slurry in Example 2 is shown;

[0020] Figure 4 A comparison diagram of the resistivity of the positive electrode sheets in Example 1 and Example 2 is shown;

[0021] Figure 5 A comparison chart of the peel strength of the positive electrode sheets in Example 1 and Example 2 is shown. DETAILED DESCRIPTION

[0022] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0023] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0024] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein, for example. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0025] Now, exemplary embodiments according to the present application will be described in more detail with reference to the accompanying drawings. However, these exemplary embodiments may be implemented in a variety of different forms and should not be construed as being limited to the embodiments described herein. It should be understood that these embodiments are provided to make the disclosure of the present application thorough and complete, and to fully convey the concepts of these exemplary embodiments to those of ordinary skill in the art. In the accompanying drawings, for the sake of clarity, the thickness of the layers and regions may be enlarged, and the same reference numerals are used to represent the same devices, and thus their descriptions will be omitted.

[0026] As analyzed in the background technology, the prior art preparation process of modified lithium iron phosphate positive electrode slurry has the technical problems of low production efficiency and poor slurry viscosity stability. In order to solve the above technical problems, the present invention provides a modified lithium iron phosphate positive electrode slurry and a preparation method thereof.

[0027] In a typical embodiment of the present application, a method for preparing a modified lithium iron phosphate positive electrode slurry is provided, such as Figure 1 As shown, the specific steps include:

[0028] Step S1: dry-mixing a lithium iron phosphate positive electrode material, a binder PVDF and a first conductive agent to obtain a first premix.

[0029] Step S2: adding an organic solvent to the first premix and performing a first stirring to obtain a second premix.

[0030] Step S3: adding the second conductive agent, the binder PVP and the organic solvent to the second premix and stirring for the second time to obtain a modified lithium iron phosphate positive electrode slurry.

[0031] The viscosity stability of the modified lithium iron phosphate positive electrode slurry affects the performance and manufacturing process of the battery: unstable viscosity may lead to poor slurry fluidity during the coating process, affecting the uniformity of the coating, thereby affecting the consistency and performance of the battery; and, unstable viscosity may cause the slurry to form an uneven pore structure during the drying and curing process, affecting the charge and discharge performance and cycle life of the battery; and, unstable viscosity may cause the coating machine to need to adjust parameters frequently, increasing downtime and maintenance costs during the production process. In order to improve the viscosity stability of the modified lithium iron phosphate positive electrode slurry, the binder PVP is added during the preparation of the modified lithium iron phosphate positive electrode slurry. The binder PVP can not only bond the active material to the electrode current collector, but also after adding the binder PVP, the viscosity of the slurry changes less within the preset time, thereby improving the viscosity stability of the modified lithium iron phosphate positive electrode slurry. In addition, during the preparation of the modified lithium iron phosphate positive electrode slurry, some of the raw materials are first dry mixed, and then an organic solvent is added for one stirring, and before the second stirring, a variety of raw materials are added, which simplifies the preparation steps, shortens the production time, and thus improves production efficiency.

[0032] Preferably, the organic solvent involved in the embodiments of the present application is NMP (N-methylpyrrolidone), which has excellent solubility and chemical stability.

[0033] In one embodiment of the present application, the method for preparing the modified lithium iron phosphate positive electrode slurry further includes the following steps:

[0034] Step S4: adding an organic solvent to the modified lithium iron phosphate positive electrode slurry again to adjust the viscosity and solid content of the lithium iron phosphate positive electrode slurry.

[0035] It should be noted that after step S3 is completed, the slurry viscosity and slurry solid content of the prepared modified lithium iron phosphate positive electrode slurry are measured. If the slurry viscosity and / or slurry solid content are not within the preset range, it is necessary to add organic solvent to the modified lithium iron phosphate positive electrode slurry again, stir quickly, and then measure the slurry viscosity and slurry solid content again until the slurry viscosity and slurry solid content reach the preset range.

[0036] In one embodiment of the present application, in step S1, the lithium iron phosphate positive electrode material, the binder PVDF and the first conductive agent are dry-mixed to obtain a first premix, and the ratio of the lithium iron phosphate positive electrode material, the first conductive agent, the binder PVDF, the second conductive agent and the adhesive PVP, in parts by mass, is (95-98): (0.5-1): (1.5-2.5): (0.01-0.1): (0.05-0.5).

[0037] Preferably, the first conductive agent consists of at least two of carbon black, carbon nanotubes and graphene, and / or the second conductive agent consists of at least two of carbon black, carbon nanotubes and graphene.

[0038] Further, in step S1, the lithium iron phosphate positive electrode material, the binder PVDF and the first conductive agent are dry-mixed to obtain a first premix, including: placing the lithium iron phosphate positive electrode material, the binder PVDF and the first conductive agent into a high-speed mixer and mixing them at a first preset speed for at least 25 minutes.

[0039] Further, in step S2, an organic solvent is added to the first premix for mixing to obtain a second premix, comprising: adding the organic solvent to the first premix, gradually increasing the stirring speed, and continuing stirring for at least 55 minutes.

[0040] After adding the organic solvent to the first premix, the stirring speed is continuously increased as the first premix continues to dissolve until a homogeneous slurry is formed. During the stirring process, the temperature should be controlled to avoid adverse effects of too high or too low temperature on the slurry performance.

[0041] Further, in step S3, a second conductive agent, a binder PVP and an organic solvent are added to the second premix and mixed to obtain a lithium iron phosphate positive electrode slurry, including: adding a second conductive agent, a binder PVP and an organic solvent to the second premix, gradually increasing the stirring speed, and continuing mixing for at least 90 minutes.

[0042] After adding the second conductive agent, the binder PVP and the organic solvent to the second premix, the stirring speed is continuously increased as the second conductive agent and the binder PVP are continuously dissolved until a homogeneous slurry is formed. During the stirring process, the temperature should be controlled to avoid adverse effects of too high or too low temperature on the slurry performance.

[0043] In a typical embodiment of the present application, a modified lithium iron phosphate positive electrode slurry is provided, and the modified lithium iron phosphate positive electrode slurry is prepared by the above-mentioned preparation method.

[0044] The viscosity stability of the modified lithium iron phosphate positive electrode slurry affects the performance and manufacturing process of the battery: unstable viscosity may lead to poor slurry fluidity during the coating process, affecting the uniformity of the coating, thereby affecting the consistency and performance of the battery; and, unstable viscosity may cause the slurry to form an uneven pore structure during the drying and curing process, affecting the charge and discharge performance and cycle life of the battery; and, unstable viscosity may cause the coating machine to need to adjust parameters frequently, increasing downtime and maintenance costs during the production process. In order to improve the viscosity stability of the modified lithium iron phosphate positive electrode slurry, the binder PVP is added during the preparation of the modified lithium iron phosphate positive electrode slurry. The binder PVP can not only bond the active material to the electrode current collector, but also after adding the binder PVP, the viscosity of the slurry changes less within the preset time, thereby improving the viscosity stability of the modified lithium iron phosphate positive electrode slurry. In addition, during the preparation of the modified lithium iron phosphate positive electrode slurry, some of the raw materials are first dry mixed, and then an organic solvent is added for one stirring, and before the second stirring, a variety of raw materials are added, which simplifies the preparation steps, shortens the production time, and thus improves production efficiency.

[0045] Preferably, the solid content of the modified lithium iron phosphate positive electrode slurry is 55% to 65%.

[0046] Preferably, the viscosity of the modified lithium iron phosphate positive electrode slurry is 4000-9000 mPa.s.

[0047] Preferably, the viscosity change rate of the lithium iron phosphate positive electrode slurry after standing for 48 hours is 40% to 45%.

[0048] The beneficial effects of the present application will be described below in conjunction with specific embodiments and comparative examples.

[0049] Example 1

[0050] Preparation of modified lithium iron phosphate positive electrode slurry in this application:

[0051] 1. Selection of raw materials: In parts by weight, the ratio of lithium iron phosphate positive electrode material, first conductive agent, binder PVDF, second conductive agent and binder PVP is (95-98): (0.5-1): (1.5-2.5): (0.01-0.1): (0.05-0.5). For example, 97 parts by weight of lithium iron phosphate positive electrode material, 0.8 parts by weight of first conductive agent, 2 parts by weight of binder PVDF, 0.05 parts by weight of second conductive agent, and 0.15 parts by weight of binder PVP are weighed.

[0052] 2. Preparation of modified lithium iron phosphate positive electrode slurry: The above-mentioned lithium iron phosphate positive electrode material, the first conductive agent, the binder PVDF, the second conductive agent and the binder PVP are prepared into modified lithium iron phosphate positive electrode slurry according to the following steps.

[0053] Step 1: Put the lithium iron phosphate positive electrode material, the binder PVDF and the first conductive agent into a high-speed mixer, and mix them at an appropriate speed for 25 minutes to obtain a first premix.

[0054] Step 2: After adding the organic solvent to the first premix, stir for the first time, gradually increase the stirring speed, and continue stirring for 55 minutes to obtain the second premix. During the stirring process, pay attention to controlling the temperature to avoid excessively high or low temperature that may adversely affect the slurry properties.

[0055] Step 3: Add the second conductive agent, the binder PVP and the organic solvent to the second premix and stir for the second time, gradually increase the stirring speed, and continue stirring for 90 minutes to obtain a modified lithium iron phosphate positive electrode slurry. During the stirring process, pay attention to controlling the temperature to avoid adverse effects of too high or too low temperature on the slurry performance.

[0056] Step 4: After the second stirring is completed, the viscosity and solid content of the modified lithium iron phosphate positive electrode slurry are tested. If the viscosity of the modified lithium iron phosphate positive electrode slurry is not in the range of 4000-9000mPa.s, and / or the solid content of the modified lithium iron phosphate positive electrode slurry is not in the range of 55%-65%, it is necessary to add organic volume again, stir quickly, and test the viscosity and solid content again until the preparation requirements are met.

[0057] like Figure 2 As shown, after the modified lithium iron phosphate positive electrode slurry prepared in Example 1 was allowed to stand for 48 hours, the solid content of the slurry was always maintained at about 60%, and the slurry viscosity changed from 5000mpa.s to 7100mpa.s, that is, the viscosity change rate of the lithium iron phosphate positive electrode slurry after standing for 48 hours was 40% to 45%, and the solid content remained almost unchanged.

[0058] like Figure 4 As shown, under laboratory conditions, a plurality of positive electrode sheets were prepared using the modified lithium iron phosphate positive electrode slurry in Example 1, and the resistivity of each positive electrode sheet was measured respectively, wherein the resistivity of each positive electrode sheet ranged from 15 to 17 Ω.cm.

[0059] like Figure 5 As shown, under laboratory conditions, a plurality of positive electrode sheets were prepared using the modified lithium iron phosphate positive electrode slurry in this embodiment, and the peel strength of each positive electrode sheet was measured respectively, wherein the peel strength of each positive electrode sheet ranged from 75 to 85 N / m.

[0060] Example 2

[0061] Preparation of modified lithium iron phosphate positive electrode slurry in the prior art:

[0062] 1. Selection of raw materials: In parts by weight, the ratio of lithium iron phosphate positive electrode material, conductive agent and binder PVDF is (95-98): (0.51-1.1): (1.55-3). For example, 97 parts by weight of lithium iron phosphate positive electrode material, 1 part by weight of conductive agent, and 2 parts by weight of binder PVDF are weighed.

[0063] 2. Preparation of modified lithium iron phosphate positive electrode slurry: The above-mentioned lithium iron phosphate positive electrode material, conductive agent, and binder PVDF are prepared into modified lithium iron phosphate positive electrode slurry according to the following steps.

[0064] Step 1: Add an organic solvent to the binder PVDF to fully dissolve it to obtain a first solvent.

[0065] Step 2: Add a conductive agent to the first solvent for dispersion to obtain a second solvent.

[0066] Step 3: Add lithium iron phosphate positive electrode material to the second solvent and stir for the first time to obtain a first slurry.

[0067] Step 4: adding an organic solvent to the first slurry and performing a second stirring to obtain a modified lithium iron phosphate positive electrode slurry.

[0068] like Figure 3 As shown, after the modified lithium iron phosphate positive electrode slurry prepared in Example 2 was allowed to stand for 48 hours, the solid content of the slurry was always maintained at about 60%, and the slurry viscosity changed from 7000 mPa.s to 50000 mPa.s, that is, the viscosity of the lithium iron phosphate positive electrode slurry increased by 6 to 8 times after standing for 48 hours, and the solid content remained almost unchanged.

[0069] like Figure 4 As shown, under laboratory conditions, a plurality of positive electrode sheets were prepared using the modified lithium iron phosphate positive electrode slurry in Example 2, and the resistivity of each positive electrode sheet was measured respectively, wherein the resistivity of each positive electrode sheet ranged from 19 to 21 Ω.cm.

[0070] like Figure 5 As shown, under laboratory conditions, a plurality of positive electrode sheets were prepared using the modified lithium iron phosphate positive electrode slurry in Example 2, and the peel strength of each positive electrode sheet was measured respectively, wherein the peel strength of each positive electrode sheet ranged from 30 to 40 N / m.

[0071] Comparing the above-mentioned Example 1 and Example 2, the modified lithium iron phosphate positive electrode slurry prepared by the preparation method of the present invention has a stronger slurry viscosity stability than the preparation method in the prior art, and the positive electrode sheet prepared thereby has a lower resistivity and a higher peel strength.

[0072] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0073] The viscosity stability of the modified lithium iron phosphate positive electrode slurry affects the performance and manufacturing process of the battery: unstable viscosity may lead to poor slurry fluidity during the coating process, affecting the uniformity of the coating, thereby affecting the consistency and performance of the battery; and, unstable viscosity may cause the slurry to form an uneven pore structure during the drying and curing process, affecting the charge and discharge performance and cycle life of the battery; and, unstable viscosity may cause the coating machine to need to adjust parameters frequently, increasing downtime and maintenance costs during the production process. In order to improve the viscosity stability of the modified lithium iron phosphate positive electrode slurry, the binder PVP is added during the preparation of the modified lithium iron phosphate positive electrode slurry. The binder PVP can not only bond the active material to the electrode current collector, but also after adding the binder PVP, the viscosity of the slurry changes less within the preset time, thereby improving the viscosity stability of the modified lithium iron phosphate positive electrode slurry. In addition, during the preparation of the modified lithium iron phosphate positive electrode slurry, some of the raw materials are first dry mixed, and then an organic solvent is added for one stirring, and before the second stirring, a variety of raw materials are added, which simplifies the preparation steps, shortens the production time, and thus improves production efficiency.

[0074] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0075] In addition to the above, it should be noted that "one embodiment", "another embodiment", "embodiment", etc. mentioned in this specification refer to the specific features, structures or characteristics described in conjunction with the embodiment included in at least one embodiment generally described in this application. The same expression appearing in multiple places in the specification does not necessarily refer to the same embodiment. Further, when describing a specific feature, structure or characteristic in conjunction with any embodiment, it is claimed that the realization of such feature, structure or characteristic in conjunction with other embodiments also falls within the scope of the present invention.

[0076] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a modified lithium iron phosphate positive electrode slurry, characterized in that: include: Dry-mixing a lithium iron phosphate positive electrode material, a binder PVDF and a first conductive agent to obtain a first premix; adding an organic solvent to the first premix and performing a first stirring to obtain a second premix; The second conductive agent, the binder PVP and the organic solvent are added to the second premix and stirred for the second time to obtain a modified lithium iron phosphate positive electrode slurry.

2. The preparation method according to claim 1, characterized in that: In the step of dry-mixing the lithium iron phosphate positive electrode material, the binder PVDF and the first conductive agent to obtain the first premix, the ratio of the lithium iron phosphate positive electrode material, the first conductive agent, the binder PVDF, the second conductive agent and the binder PVP is (95-98) by mass: (0.5-1): (1.5-2.5): (0.01-0.1): (0.05-0.5).

3. The preparation method according to claim 1, characterized in that: The preparation method further comprises: An organic solvent is added again to the modified lithium iron phosphate positive electrode slurry to adjust the viscosity and solid content of the lithium iron phosphate positive electrode slurry.

4. The preparation method according to any one of claims 1 to 3, characterized in that The first conductive agent consists of at least two of carbon black, carbon nanotubes and graphene, and / or the second conductive agent consists of at least two of carbon black, carbon nanotubes and graphene.

5. The preparation method according to any one of claims 1 to 3, characterized in that: The lithium iron phosphate positive electrode material, the binder PVDF and the first conductive agent are dry-mixed to obtain a first premix, comprising: The lithium iron phosphate positive electrode material, the binder PVDF and the first conductive agent are placed in a high-speed mixer and mixed at a first preset speed for at least 25 minutes.

6. The preparation method according to claim 1, characterized in that: Adding an organic solvent to the first premix and mixing them to obtain a second premix, comprising: The organic solvent is added to the first premix, the stirring speed is gradually increased, and the stirring is continued for at least 55 minutes.

7. The preparation method according to claim 1, characterized in that: Adding the second conductive agent, the binder PVP and an organic solvent to the second premix and mixing them to obtain a lithium iron phosphate positive electrode slurry, comprising: The second conductive agent, the binder PVP and the organic solvent are added to the second premix, the stirring speed is gradually increased, and the mixing is continued for at least 90 minutes.

8. A modified lithium iron phosphate positive electrode slurry, characterized in that: The modified lithium iron phosphate positive electrode slurry is prepared by the preparation method described in any one of claims 1 to 7.

9. The modified lithium iron phosphate positive electrode slurry according to claim 8, characterized in that: The solid content of the modified lithium iron phosphate positive electrode slurry is 55% to 65%.

10. The modified lithium iron phosphate positive electrode slurry according to claim 8, characterized in that: The viscosity of the modified lithium iron phosphate positive electrode slurry is 4000-9000 mPa.s.

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