Lithium battery positive electrode mixed slurry, preparation method thereof and lithium ion battery

Abstract

The invention discloses a lithium battery positive electrode mixed slurry, a preparation method thereof and a lithium ion battery, and the method comprises the following steps: mixing polyvinylidene fluoride (PVDF) and N-methyl pyrrolidone (NMP) with a preset mass to obtain a material A, adding a conductive agent SP into the material A, and stirring and mixing to obtain a material B; sequentially adding N-methyl pyrrolidone NMP and nickel cobalt lithium manganate with preset mass into the material B, and stirring and mixing to obtain a material C; adding lithium manganate with a preset mass into the material C, and performing vacuum stirring to obtain a material D; adding lithium manganese iron phosphate with a preset mass into the material D, and performing vacuum stirring in batches to obtain a material E; and sieving and demagnetizing the material E to obtain the lithium battery positive electrode mixed slurry. The invention aims to obtain the high-safety lithium battery positive electrode mixed slurry and reduce the production cost of the battery at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a lithium battery cathode blending slurry, a preparation method thereof, and a preparation method of a lithium-ion battery. Background Art

[0002] At present, due to the characteristics of environmental protection, high efficiency, and sustainability, the industrial scale of new energy vehicles has grown rapidly in recent years. New energy vehicles include pure electric vehicles, range-extended electric vehicles, hybrid vehicles, fuel cell electric vehicles, hydrogen engine vehicles, etc. Among them, one of the mainstream batteries used is the ternary lithium battery. The reason is that the lithium battery has advantages such as high energy density, long cycle life, and low self-discharge rate, making it the first choice in the field of new energy vehicles. However, the ternary lithium battery is prone to safety hazards during use, and the cost is relatively high.

[0003] The existing invention patent with the publication number CN112542585 A discloses a process for preparing a cathode lithium iron phosphate slurry. The process includes the following steps: (1) weighing materials; (2) checking the stirring tank; (3) pouring a carbon nanotube CNT solution with a ratio of 4%-6%, a PVDF solution with a ratio of 8%-10%, and an NMP solvent with a ratio of 84-88% into the stirring tank for preliminary dispersion and stirring; (4) evacuating the stirring environment of the stirring tank to -0.08 - 0.09 MPa and performing dispersion and stirring again; (5) adding a cathode lithium iron phosphate material and an SP conductive agent to the mixed solution for preliminary dispersion and stirring; (6) evacuating the stirring environment of the stirring tank to -0.08 - 0.09 MPa and performing dispersion and stirring again; (7) pouring out the slurry after stirring is completed. Although this invention improves the process and changes the traditional three-step stirring to two steps, greatly improving the efficiency of the slurry preparation process and shortening the slurry preparation time, the safety performance of the lithium battery cell manufacturing has not been effectively improved. Summary of the Invention

[0004] The main purpose of the present invention is to provide a lithium battery cathode blending slurry, a preparation method thereof, and a lithium-ion battery, aiming to solve the technical problem that existing lithium-ion batteries have potential safety hazards.

[0005] To achieve the above object, the present invention provides a preparation method of a lithium battery cathode blending slurry. The method includes the following steps:

[0006] Step 1, mixing a preset mass of polyvinylidene fluoride PVDF and N-methylpyrrolidone NMP to obtain Material A, and adding a preset mass of conductive agent SP to Material A, and stirring and mixing to obtain Material B, where the mass ratio of PVDF, NMP, and SP is: (2.0 - 2.3) : (40.0 - 43.0) : (2.3 - 2.5);

[0007] Step 2: Sequentially add a preset mass of N-methylpyrrolidone (NMP) and lithium nickel cobalt manganese oxide to Material B to avoid uneven distribution of the materials after they are added to the slurry, and stir and mix them to obtain Material C;

[0008] Step 3: Add a preset mass of lithium manganese oxide to Material C, and perform vacuum stirring to obtain Material D;

[0009] Step 4: Add a preset mass of lithium iron manganese phosphate to Material D, and perform vacuum stirring in batches to obtain Material E;

[0010] Step 5: Screen and demagnetize Material E to obtain the lithium battery cathode blending slurry.

[0011] Optionally, in Step 1, the viscosity of Material A is 600 - 1200 mPa·s.

[0012] Optionally, in Step 2, the mass ratio of the added N-methylpyrrolidone (NMP) to lithium nickel cobalt manganese oxide is (0.5 - 0.8):(6.1 - 6.9).

[0013] Optionally, in Step 3, the mass ratio of the added lithium manganese oxide to polyvinylidene fluoride (PVDF) in Step 1 is (1.5 - 3.5):(0.20 - 0.23).

[0014] Optionally, in Step 4, the mass ratio of the added lithium iron manganese phosphate to polyvinylidene fluoride (PVDF) in Step 1 is (1.5 - 3.5):(0.20 - 0.23).

[0015] Optionally, in Steps 2 - 4, the mass ratio of the respectively added lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate is (6.1 - 6.9):(1.5 - 3.5):(1.5 - 3.5).

[0016] Optionally, in Step 4, add a preset mass of lithium iron manganese phosphate to Material D, and use a blender to perform vacuum stirring twice to obtain Material E, wherein the fineness of Material E < 30 μm, the solid content is 68 - 72%, and the viscosity is 6000 - 11000 mPa·s.

[0017] Optionally, in Step 5, screen Material E under vacuum conditions using a 150-mesh metal screen, and then use a magnet device to remove the magnetic substances in the slurry to obtain the lithium battery cathode blending slurry, wherein the vacuum degree is -0.01 mPa.

[0018] In addition, to achieve the above object, the present invention also provides a lithium battery cathode blending slurry prepared by the method described in any one of the above.

[0019] In addition, to achieve the above object, the present invention further provides a lithium-ion battery. The lithium-ion battery is prepared by first coating, rolling, and die-cutting the lithium battery cathode blending slurry prepared by the method described in any one of the above, and then laminating and heat-sealing to obtain a semi-finished battery cell. After the semi-finished battery cell is vacuum baked until the moisture is qualified, electrolyte is injected, and then the target lithium-ion battery is produced through formation and grading processes.

[0020] Beneficial effects:

[0021] By adopting the process principle of step-by-step dispersion and gradient compounding, the lithium battery cathode blending slurry of the present invention realizes the compound use of ternary materials, lithium iron manganese phosphate, lithium manganate and other materials, and can give play to the complementary advantages of the three materials of ternary materials, lithium iron manganese phosphate, and lithium manganate. The compounding of the three materials of ternary materials, lithium iron manganese phosphate, and lithium manganate can produce a synergistic effect, and enables the lithium battery cathode blending slurry to achieve a balance between energy density and safety. The principle is that the particles of lithium iron manganese phosphate are small, the particles of lithium manganate are moderate, and the particles of ternary materials are large. Therefore, the small particles of lithium iron manganese phosphate can effectively fill the gaps between ternary and lithium manganate, which helps to increase the tap density of the cathode material, thereby improving the energy density of the battery. Moreover, the thermal stability of lithium iron manganese phosphate is good, and after filling, it helps to improve the thermal stability of the cathode material. Therefore, the composite ternary lithium-ion battery produced by the present invention significantly improves the disadvantage of poor safety of single ternary material batteries. At the same time, due to the low cost of lithium manganate and lithium iron manganese phosphate, the overall cost can be reduced when mixed with ternary materials. Description of the drawings

[0022] Figure 1 It is a schematic flow chart of Embodiment 1 of a method for preparing a lithium battery cathode blending slurry of the present invention.

[0023] The realization, functional characteristics, and advantages of the object of the present invention will be further described with reference to Embodiment 1 and the accompanying drawings. Detailed implementation manners

[0024] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] See Figure 1 , a schematic flow chart of a method for preparing a lithium battery cathode blending slurry provided by the present invention. The method includes the following steps:

[0026] Step 1, since the dissolution rate of polyvinylidene fluoride (PVDF) powder is slow, in order to completely dissolve the PVDF powder, first mix a preset mass of PVDF and N-methylpyrrolidone (NMP) solvent to obtain Material A, and the viscosity of Material A is 600-1200 mPa·s; then continue to add a preset mass of conductive agent SP to Material A. Since PVDF in Material A serves as a dispersion medium, the conductive agent SP is more easily and uniformly dispersed, avoiding the agglomeration of the conductive agent. After stirring and mixing, Material B is obtained, and the mass ratio of PVDF, NMP, and SP is: (2.0-2.3):(40.0-43.0):(2.3-2.5).

[0027] Specifically, stir PVDF and NMP with a stirrer. PVDF, as a binder, needs to be dissolved in the NMP solvent to form a uniform solution. In order to quickly disperse PVDF and ensure uniform mixing of the materials, and to avoid local overheating or dead spots during stirring, the self-rotation speed of the stirrer can be set relatively high and the revolution speed relatively low. Then set the self-rotation speed of the stirrer to 2500-2700 rpm and the revolution speed to 20-35 rpm. In order to balance the dissolution rate of PVDF and the evaporation rate of NMP, the stirring temperature should not be too high or too low. Then set the stirring temperature of the stirrer to 25-45°C. Since the dissolution of PVDF is slow, in order to ensure complete dissolution of PVDF, the stirring duration of the stirrer can be set relatively long. Then set the stirring duration of the stirrer to 3-5 h for sufficient stirring. After stirring and mixing, Material A is obtained, and the viscosity of Material A is controlled to be 600-1200 mPa·s; then add SP to Material A and stir with a stirrer. The self-rotation speed of the stirrer is 2300-2500 rpm, the revolution speed is 20-35 rpm, the stirring temperature is 25-45°C, and the stirring duration is 1-2 h to obtain Material B.

[0028] Step 2, sequentially add a preset mass of NMP and lithium nickel cobalt manganese oxide to Material B and stir and mix to obtain Material C. Among them, the stirring step is carried out with a stirrer. The self-rotation speed of the stirrer is 400-600 rpm, the revolution speed is 20-35 rpm, the stirring temperature is 25-45°C, and the stirring duration is 15-25 min. And the preset mass ratio of the added NMP and lithium nickel cobalt manganese oxide is (0.5-0.8):(6.1-6.9).

[0029] Step 3: Add a preset mass of lithium manganese oxide to Material C, and obtain Material D after vacuum stirring. Specifically, the vacuum stirring step is carried out using a blender. The self-rotation speed of the blender is 280 - 620 rpm, the revolution speed is 14 - 30 rpm, the stirring temperature is 25 - 45°C, the stirring duration is 0.5 - 1 h, and the vacuum degree is greater than -0.080 MPa to obtain Material D. Preferably, the mass ratio of the added lithium manganese oxide to the polyvinylidene fluoride (PVDF) in Step 1 is (3.0 - 3.5):(0.20 - 0.23). The vacuum stirring in this step can reduce bubbles and improve the uniformity of the slurry.

[0030] Step 4: Add a preset mass of lithium iron manganese phosphate to Material D, and obtain Material E after batch vacuum stirring. Specifically, add a preset mass of lithium iron manganese phosphate to Material D, and carry out two vacuum stirrings using a blender to obtain Material E. Preferably, the first vacuum stirring step is carried out using a blender. The self-rotation speed of the blender is 2400 - 2700 rpm, the revolution speed is 14 - 32 rpm, the stirring temperature is 25 - 45°C, the stirring duration is 0.5 - 1 h, and the vacuum degree is greater than -0.080 MPa. The second vacuum stirring step is carried out using a blender. The self-rotation speed of the blender is 1700 - 1900 rpm, the revolution speed is 20 - 35 rpm, the stirring temperature is 25 - 45°C, the stirring duration is 1 - 2 h, and the vacuum degree is greater than -0.080 MPa. Finally, obtain Material E, and the fineness of Material E < 30 μm, the solid content is 68 - 72%, and the viscosity is 6000 - 11000 mPa·s. Preferably, the mass ratio of the added lithium iron manganese phosphate to the polyvinylidene fluoride (PVDF) in Step 1 is (1.5 - 3.5):(0.20 - 0.23). In addition, the sequentially added lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate are in a mass ratio of (6.1 - 6.9):(1.5 - 3.5):(1.5 - 3.5), and the lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate are added in stages to reduce the risk of particle aggregation through gradient mixing. Step 5: Screen and demagnetize Material E to obtain the lithium battery cathode blending slurry.

[0031] Specifically, screen Material E under vacuum conditions using a 150-mesh metal screen, and then use a magnet device to remove magnetic substances in the slurry to obtain the lithium battery cathode blending slurry, where the vacuum degree is -0.01 mPa.

[0032] Furthermore, through the above preparation process, a lithium battery cathode blending slurry of ternary blended lithium manganese oxide and lithium iron manganese phosphate can be obtained, and the addition of lithium manganese oxide and lithium iron manganese phosphate can significantly reduce costs.

[0033] Furthermore, to better illustrate the preparation process of the lithium battery cathode blending slurry in the present invention, the following is described through specific examples.

[0034] Example 1

[0035] Weigh 6.5 kg of lithium nickel cobalt manganese oxide, 3.25 kg of lithium manganate, 3.25 kg of lithium iron manganese phosphate, 0.2438 kg of SP, and 0.2167 kg of PVDF with a solid content of 100%.

[0036] Step 1: Mix PVDF with 4.152 kg of NMP, start the mixer to stir. The rotation speed of the mixer is 2600 rpm, the revolution speed is 30 rpm, the temperature is 25 - 45°C, and the stirring duration is 4 h to obtain Material A; the viscosity is 815 mPa.s, and the glue liquid is visually transparent, clear, and without particles.

[0037] And add SP to Material A, start the mixer to stir. The rotation speed of the mixer is 2400 rpm, the revolution speed of stirring is 30 rpm, the stirring temperature is 25 - 45°C, and the stirring duration is 1.3 h to obtain Material B;

[0038] Step 2: Sequentially add 0.6772 kg of NMP and 6.5 kg of lithium nickel cobalt manganese oxide to Material B. After adding, start the mixer to stir. The rotation speed of stirring is 600 rpm, the revolution speed is 30 rpm, the stirring temperature is 25 - 45°C, and the stirring duration is 25 min to obtain Material C.

[0039] Step 3: After adding lithium manganate to Material C, start the mixer to stir. The rotation speed of the mixer is 330 rpm, the revolution speed is 25 rpm, the stirring duration is 0.5 - 1 h, the stirring temperature is 25 - 45°C, and the vacuum degree is greater than -0.080 MPa to obtain Material D.

[0040] Step 4: Add lithium iron manganese phosphate to Material D, start the mixer to stir, conduct the first stirring. Control the rotation speed of the mixer to be 2560 rpm, the revolution speed to be 22 rpm, the stirring duration to be 0.5 - 1 h, the stirring temperature to be 25 - 45°C, and the vacuum degree to be greater than -0.080 MPa. Then conduct the second stirring. Control the rotation speed of the mixer to be 1800 rpm, the revolution speed of the mixer to be 30 rpm, the stirring duration to be 2 h, the stirring temperature to be 25 - 45°C, and the vacuum degree to be greater than -0.080 MPa to obtain Material E. Among them, the fineness of Material E < 30 μm, the viscosity is 6680 mPa.s, and the solid content is 68%.

[0041] Step 5: Set the vacuum degree to -0.01 mPa and use a 150 - mesh metal screen to screen Material E, and then use a magnet device to remove the magnetic substances in the slurry to obtain the positive electrode slurry of ternary - doped lithium manganate and lithium iron manganese phosphate.

[0042] Example 2

[0043] Compared with Example 1, in Example 2, the mass ratio of lithium nickel cobalt manganese oxide + lithium manganese oxide + lithium iron manganese phosphate (2:1:1) was changed to (3:1:1), and the rest remained unchanged.

[0044] Example 3

[0045] Compared with Example 1, in Example 3, the mass ratio of lithium nickel cobalt manganese oxide + lithium manganese oxide + lithium iron manganese phosphate (2:1:1) was changed to (4:1:1), and the rest remained unchanged.

[0046] Furthermore, the ternary blended lithium manganese oxide and lithium iron manganese phosphate positive electrode slurries prepared in the above examples were subjected to coating, rolling, and die-cutting processes, and then stacked and heat-sealed to form semi-finished battery cells. After vacuum baking the semi-finished battery cells until the moisture was qualified, electrolyte was injected, and then high-safety finished 50Ah lithium-ion batteries were produced through processes such as formation and grading. Finally, the finished 50Ah lithium-ion batteries were subjected to safety tests after being fully charged according to the standard. The various relevant test results are shown in Table 1 below.

[0047] Table 1 - Performance Tests of Lithium Batteries in Examples 1 - 3

[0048]

[0049]

[0050] Comparative Example 1

[0051] Weigh 6.5 kg of lithium nickel cobalt manganese oxide, 3.25 kg of lithium manganese oxide, 3.25 kg of lithium iron manganese phosphate, 0.2438 kg of SP, and 0.2167 kg of PVDF with a solid content of 100%.

[0052] Step 1.1, mix PVDF with 4.152 kg of NMP, start the mixer to stir. The rotation speed of the mixer is 2600 rpm, the revolution speed is 30 rpm, the temperature is 25 - 45°C, and the stirring duration is 4 h to obtain Material A; the viscosity is 838 mPa.s, and the glue liquid is visually transparent, clear, and without particles. Then add SP to Material A, start the mixer to stir. The rotation speed of the mixer is 2400 rpm, the revolution speed of stirring is 30 rpm, the stirring temperature is 25 - 45°C, and the stirring duration is 1.3 h to obtain Material B;

[0053] Step 1.2: First, add 0.6772 kg of NMP to Material B, then simultaneously add lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate into it. Start the blender for stirring, conduct the first stirring, control the rotation speed of the blender's self-rotation at 2560 rpm, the revolution speed at 22 rpm, the stirring duration at 0.5 - 1 h, the stirring temperature at 25 - 45 °C, and the vacuum degree greater than -0.080 MPa. Then conduct the second stirring, control the rotation speed of the blender's self-rotation at 1800 rpm, the revolution speed of the blender at 30 rpm, the stirring duration at 2 h, the stirring temperature at 25 - 45 °C, and the vacuum degree greater than -0.080 MPa to obtain Material E1. Among them, the fineness of Material E1 < 30 μm, the viscosity is 6570 mPa·s, and the solid content is 67%.

[0054] Step 1.3: Set the vacuum degree to -0.01 mPa and use a 150-mesh metal screen to screen Material E1, and then use a magnet device to remove magnetic substances in the slurry to obtain the ternary-doped lithium manganese oxide and lithium iron manganese phosphate cathode slurry 2.

[0055] In Example 1, the main cathode materials lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate are added step by step, while in Comparative Example 1, the main cathode materials lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate are added simultaneously. Compared with Example 1, in Comparative Example 1, the viscosity change of the doped lithium manganese oxide and lithium iron manganese phosphate with ternary material cathode slurry is large and sedimentation occurs. When conducting safety performance test items such as overcharging, over-discharging, external short circuit, pinprick, drop, and extrusion on the battery, phenomena such as smoking, catching fire, and even explosion will occur.

[0056] Comparative Example 2

[0057] Compared with Example 1, for the ternary-doped lithium manganese oxide and lithium iron manganese phosphate cathode slurry 2 prepared in Comparative Example 2, except that the PVDF dosage is halved, other conditions are the same as in Example 1. The viscosity change of the doped lithium manganese oxide and lithium iron manganese phosphate with ternary material cathode slurry 2 is relatively large and sedimentation occurs. When conducting safety performance test items such as overcharging, over-discharging, external short circuit, pinprick, drop, and extrusion on the battery, phenomena such as smoking, catching fire, and even explosion will occur.

[0058] Comparative Example 3

[0059] Weigh 6.5 kg of lithium nickel cobalt manganese oxide, 3.25 kg of lithium manganese oxide, 3.25 kg of lithium iron manganese phosphate, 0.2438 kg of SP, and 0.2167 kg of PVDF with a solid content of 100%.

[0060] Step 3.1: Mix SP and PVDF with 4.152 kg of NMP simultaneously, start the blender for stirring. The self-rotation speed of the blender is 2600 rpm, the revolution speed is 30 rpm, the temperature is 25 - 45°C, and the stirring duration is 4 h to obtain Material B1; the viscosity is 915 mPa.s, and the glue liquid is visually transparent, clear, and without particles.

[0061] Step 3.2: Add 0.6672 kg of NMP and 6.5 kg of lithium nickel cobalt manganese oxide to Material B1 in sequence. After adding, start the blender for stirring. The self-rotation speed of the stirring is 600 rpm, the revolution speed is 30 rpm, the stirring temperature is 25 - 45°C, and the stirring duration is 25 min to obtain Material C1.

[0062] Step 3.3: After adding lithium manganese oxide to Material C1, start the blender for stirring. The self-rotation speed of the blender is 330 rpm, the revolution speed is 25 rpm, the stirring duration is 0.5 - 1 h, the stirring temperature is 25 - 45°C, and the vacuum degree is greater than -0.080 MPa to obtain Material D1.

[0063] Step 3.4: Add lithium iron manganese phosphate to Material D1, start the blender for stirring, and conduct the first stirring. Control the self-rotation speed of the blender to be 2560 rpm, the revolution speed to be 22 rpm, the stirring duration to be 0.5 - 1 h, the stirring temperature to be 25 - 45°C, and the vacuum degree to be greater than -0.080 MPa. Then conduct the second stirring. Control the self-rotation speed of the blender to be 1800 rpm, the revolution speed of the blender to be 30 rpm, the stirring duration to be 2 h, the stirring temperature to be 25 - 45°C, and the vacuum degree to be greater than -0.080 MPa to obtain Material E2. Among them, the fineness of Material E2 < 30 μm, the viscosity is 7895 mPa.s, and the solid content is 68%.

[0064] Step 3.5: Set the vacuum degree to -0.01 mPa and use a 150-mesh metal sieve to screen Material E2, and then use a magnet device to remove the magnetic substances in the slurry to obtain the ternary blended lithium manganese oxide and lithium iron manganese phosphate cathode slurry 3 with high safety for lithium batteries.

[0065] Compared with Example 1, for the ternary blended lithium manganese oxide and lithium iron manganese phosphate cathode slurry 3 prepared in Comparative Example 3, in Example 1, PVDF and SP were added step by step, while in Comparative Example 3, PVDF and SP were added simultaneously. Other conditions are the same as in Example 1. The viscosity of the blended cathode slurry of lithium manganese oxide, lithium iron manganese phosphate, and ternary material prepared has a large change and agglomeration phenomenon occurs. During the safety performance test items such as overcharging, over-discharging, external short circuit, pinprick, drop, and extrusion of the battery, phenomena such as smoking, fire, and even explosion will occur.

[0066] Comparative Example 4

[0067] Weigh 6.5 kg of lithium nickel cobalt manganese oxide, 3.25 kg of lithium manganate, 3.25 kg of lithium iron manganese phosphate, 0.2438 kg of SP, and 0.2167 kg of PVDF with a solid content of 100%.

[0068] Step 4.1: Mix PVDF with 4.152 kg of NMP, start the mixer to stir. The rotation speed of the mixer is 2600 rpm, the revolution speed is 30 rpm, the temperature is 25 - 45 °C, and the stirring duration is 2 h to obtain Material A; the viscosity is 885 mPa.s, and the glue liquid is visually transparent, clear, and without particles.

[0069] And add SP to Material A, start the mixer to stir. The rotation speed of the mixer is 2400 rpm, the revolution speed of stirring is 30 rpm, the stirring temperature is 25 - 45 °C, and the stirring duration is 1.3 h to obtain Material B2;

[0070] Step 4.2: Add 0.6772 kg of NMP and 6.5 kg of lithium nickel cobalt manganese oxide to Material B in sequence, then add Material B again. After adding, start the mixer to stir. The rotation speed of stirring is 600 rpm, the revolution speed is 30 rpm, the stirring temperature is 25 - 45 °C, and the stirring duration is 25 min to obtain Material C2.

[0071] Step 4.3: After adding lithium manganate to Material C2, start the mixer to stir. The rotation speed of the mixer is 330 rpm, the revolution speed is 25 rpm, the stirring duration is 0.5 - 1 h, the stirring temperature is 25 - 45 °C, and the vacuum degree is greater than -0.080 MPa to obtain Material D2.

[0072] Step 4.4: Add lithium iron manganese phosphate to Material D2, start the mixer to stir, and conduct the first stirring. Control the rotation speed of the mixer to be 2560 rpm, the revolution speed to be 22 rpm, the stirring duration to be 0.5 - 1 h, the stirring temperature to be 25 - 45 °C, and the vacuum degree to be greater than -0.080 MPa. Then conduct the second stirring. Control the rotation speed of the mixer to be 1800 rpm, the revolution speed of the mixer to be 30 rpm, the stirring duration to be 2 h, the stirring temperature to be 25 - 45 °C, and the vacuum degree to be greater than -0.080 MPa to obtain Material E3. Among them, the fineness of Material E3 < 30 μm, the viscosity is 6798 mPa.s, and the solid content is 68%.

[0073] Step 4.5: Set the vacuum degree to -0.01 mPa and use a 150 - mesh metal sieve to screen Material E3, and then use a magnet device to remove the magnetic substances in the slurry to obtain the ternary - doped lithium manganate and lithium iron manganese phosphate cathode slurry 4.

[0074] Compared with Example 1, the ternary mixed lithium manganese oxide and lithium iron manganese phosphate positive electrode slurry 4 prepared in Comparative Example 4, when PVDF and NMP are mixed, except that the stirring time is halved, the rest is the same as Example 1. The viscosity of the prepared lithium manganese oxide and lithium iron manganese phosphate mixed positive electrode slurry with ternary materials changes greatly. When the battery is subjected to safety performance tests such as overcharging, over-discharging, external short circuit, puncture, falling, and extrusion, smoke, fire, and even explosion will occur.

[0075] Comparative Example 5

[0076] Weigh 6.5 kg of lithium nickel cobalt manganese oxide, 3.25 kg of lithium manganese oxide, 3.25 kg of lithium iron manganese phosphate, 0.2438 kg of SP, and 0.2167 kg of PVDF with a solid content of 100%.

[0077] Step 5.1, add 4.152 kg NMP to PVDF and mix, start the stirrer for stirring, the stirrer rotation speed is 2600 rpm, the revolution speed is 30 rpm, the temperature is 25-45 ° C, the stirring time is 4 hours, and material A is obtained; the viscosity is 815 mPa.s, and the glue liquid is transparent and clear without particles.

[0078] Add SP to material A, start the mixer, the mixer rotation speed is 2400 rpm, the stirring revolution speed is 30 rpm, the stirring temperature is 25-45°C, the stirring time is 1.3 h, and material B is obtained;

[0079] Step 5.2, add 0.6772 kg NMP and 6.5 kg lithium nickel cobalt manganese oxide to material B in sequence, and start stirring with a stirrer. The stirring speed is 600 rpm, the revolution speed is 30 rpm, the stirring temperature is 25-45 ° C, and the stirring time is 2 h to obtain material C3.

[0080] Step 5.3, after adding lithium manganate to material C3, start stirring with a stirrer, the rotation speed of the stirrer is 330 rpm, the revolution speed is 25 rpm, the stirring time is 0.5 to 1 h, the stirring temperature is 25 to 45 ° C, the vacuum degree is greater than -0.080 MPa, and material D3 is obtained.

[0081] Step 5.4, add lithium iron manganese phosphate to material D3, start the stirrer for stirring, perform the first stirring, control the stirrer rotation speed to 2560rpm, the revolution speed to 22rpm, the stirring time to 0.5-1h, the stirring temperature to 25-45°C, the vacuum degree to be greater than -0.080MPa, and then perform the second stirring, control the stirrer rotation speed to 1800rpm, the stirrer revolution speed to 30rpm, the stirring time to 2h, the stirring temperature to 25-45°C, the vacuum degree to be greater than -0.080MPa, and obtain material E4, wherein the fineness of material E4 is <30μm, the viscosity is 6680mPa.s, and the solid content is 68%.

[0082] Step 5.5, set the vacuum degree to -0.01 mPa and use a 150-mesh metal screen to sieve material E4, and then use a magnet device to remove the magnetic material in the slurry to obtain a ternary mixed lithium manganese oxide and lithium iron manganese phosphate positive electrode slurry 5.

[0083] Compared with Example 1, the ternary mixed lithium manganese oxide and lithium iron manganese phosphate positive electrode slurry 5 prepared in Comparative Example 5 was stirred with a stirrer after adding nickel cobalt lithium manganese oxide, and the stirring time was extended to 2 hours, and the rest was the same as Example 1. The viscosity of the prepared lithium manganese oxide and lithium iron manganese phosphate mixed positive electrode slurry with ternary materials changed greatly and sedimentation occurred. When the battery was subjected to safety performance test items such as overcharging, over-discharging, external short circuit, puncture, falling, and extrusion, smoke, fire, and even explosion occurred.

[0084] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or system. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or system including the element.

[0085] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0086] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a lithium battery positive electrode mixed slurry, characterized in that: The method comprises the following steps: Step 1, mixing a preset mass of polyvinylidene fluoride PVDF and N-methylpyrrolidone NMP to obtain material A, and adding a preset mass of conductive agent SP to material A, stirring and mixing to obtain material B, wherein the mass ratio of PVDF, NMP and SP is: (2.0-2.3): (40.0-43.0): (2.3-2.5); Step 2, adding preset masses of N-methylpyrrolidone NMP and lithium nickel cobalt manganese oxide to material B in sequence to avoid uneven distribution of the materials after being added to the slurry, and stirring and mixing to obtain material C; Step 3, adding a preset mass of lithium manganate to material C, and obtaining material D after vacuum stirring; Step 4, adding a preset mass of lithium iron manganese phosphate to material D, and vacuum stirring in batches to obtain material E; Step 5: Screen and demagnetize material E to obtain a lithium battery positive electrode mixed slurry.

2. The method for preparing a lithium battery positive electrode mixed slurry according to claim 1, characterized in that: In step 1, the viscosity of material A is 600-1200 mPa.s.

3. The method for preparing a lithium battery positive electrode mixed slurry according to claim 1, characterized in that: In step 2, the mass ratio of the added N-methylpyrrolidone NMP to the lithium nickel cobalt manganese oxide is (0.5-0.8):(6.1-6.9).

4. The method for preparing a lithium battery positive electrode mixed slurry according to claim 1, characterized in that: In step 3, the mass ratio of the added lithium manganate to the polyvinylidene fluoride PVDF in step 1 is (1.5-3.5):(0.20-0.23).

5. The method for preparing a lithium battery positive electrode mixed slurry according to claim 1, characterized in that: In step 4, the mass ratio of the added lithium manganese iron phosphate to the polyvinylidene fluoride PVDF in step 1 is (1.5-3.5):(0.20-0.23).

6. The method for preparing a positive electrode mixed slurry for a lithium battery according to claim 1, characterized in that: In step 2-4, the mass ratio of lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate added respectively is (6.1-6.9):(1.5-3.5):(1.5-3.5).

7. The method for preparing a lithium battery positive electrode mixed slurry according to claim 1, characterized in that: In step 4, a preset mass of lithium manganese iron phosphate is added to material D, and vacuum stirring is performed twice using a mixer to obtain material E, wherein the fineness of material E is less than 30 μm, the solid content is 68-72%, and the viscosity is 6000-11000 mPa.s.

8. The method for preparing a positive electrode mixed slurry for a lithium battery according to claim 1, characterized in that: In step 5, material E is sieved using a 150-mesh metal screen under vacuum conditions, and then a magnet device is used to remove magnetic substances in the slurry to obtain a lithium battery positive electrode mixed slurry, wherein the vacuum degree is -0.01 mPa.

9. A lithium battery positive electrode blending slurry prepared by the method according to any one of claims 1 to 8.

10. A lithium ion battery, characterized in that: The lithium-ion battery is prepared by coating, rolling and die-cutting the lithium battery positive electrode mixed slurry prepared by the method described in any one of claims 1 to 8, and then laminating and heat-sealing to obtain a semi-finished battery cell, and then vacuum-baking the semi-finished battery cell until the moisture content is qualified, injecting electrolyte, and then going through formation and capacity separation processes to make the target lithium-ion battery.

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