A method for homogenizing a composite cathode slurry

Abstract

This invention provides a homogenization method for a composite cathode slurry, comprising the following steps: mixing a ternary slurry with a lithium manganese iron phosphate slurry to obtain a composite cathode slurry; the preparation method of the ternary slurry comprises the following steps: adding a conductive adhesive to the ternary material and stirring to obtain a ternary slurry, the ternary slurry having a solid content of 76%–80% and a viscosity of 4000–7000 mPa·s; the preparation method of the lithium manganese iron phosphate slurry comprises the following steps: dry mixing lithium manganese iron phosphate with a second conductive agent and stirring to obtain a mixed dry material, then adding a second adhesive to the mixed dry material to obtain a lithium manganese iron phosphate slurry, the lithium manganese iron phosphate slurry having a solid content of 58%–62% and a viscosity of 7000–20000 mPa·s. The homogenization method provided by this invention can achieve sufficient dispersion of ternary materials and lithium manganese iron phosphate with different particle sizes, thereby improving the yield of composite cathode slurry preparation.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically, it relates to a homogenization method for composite cathode slurry. Background Technology

[0002] In recent years, with the widespread application of lithium batteries in power and energy storage batteries, safety issues have become increasingly prominent. Both lithium manganese iron phosphate (LMFP) and lithium iron phosphate (LFP) possess stable olivine structures and good safety. Furthermore, due to the higher operating voltage of manganese, LMFP has a theoretical specific capacity 13% higher than LFP, making it considered the most promising cathode material to replace LFP. However, current LMFP still suffers from low specific capacity and poor electrochemical performance. Ternary materials (NCMs) have a similar voltage range to LMFP, leading researchers to explore the possibility of moderately doping them into LMFP to improve the specific capacity and kinetic performance of the composite cathode material. Moreover, with minimal doping of ternary materials, small LMFP particles can encapsulate larger ternary material particles with lower thermal stability, achieving an increase in battery energy density through material composite methods while ensuring battery safety.

[0003] However, since lithium manganese iron phosphate and ternary materials have different particle sizes, structural characteristics and physical properties, if lithium manganese iron phosphate and ternary materials are directly physically mixed, problems such as uneven particle dispersion and low slurry stability are likely to occur in the subsequent uniform homogenization step, which seriously restricts the yield of battery preparation. Summary of the Invention

[0004] The purpose of this invention is to provide a homogenization method for composite cathode slurry, which solves the problems of uneven physical mixing and dispersion of lithium manganese iron phosphate and ternary materials and poor slurry stability in the homogenization process of composite cathode slurry in the prior art.

[0005] According to another aspect of the present invention, a method for homogenizing a composite cathode slurry is provided, comprising the following operations: mixing a ternary slurry with a lithium manganese iron phosphate slurry to obtain a composite cathode slurry; wherein the preparation method of the ternary slurry comprises the following operations: adding a conductive adhesive to the ternary material and stirring to obtain a ternary slurry, wherein the solid content of the ternary slurry is 76% to 80% and the viscosity is 4000 to 7000 mPa·s; the conductive adhesive comprises a first adhesive and a first conductive agent; wherein the preparation method of the lithium manganese iron phosphate slurry comprises the following operations: dry mixing lithium manganese iron phosphate with a second conductive agent and stirring to obtain a mixed dry material, and then adding a second adhesive to the mixed dry material to obtain a lithium manganese iron phosphate slurry, wherein the solid content of the lithium manganese iron phosphate slurry is 58% to 62% and the viscosity is 7000 to 20000 mPa·s.

[0006] Because lithium manganese iron phosphate (LMFP) has a small particle size, small LMFP particles have a large specific surface area and strong adsorption capacity, and are prone to agglomeration. Therefore, this invention uses a semi-dry slurry process (dry mixing LMFP and the second conductive agent and then adding the second adhesive) to prepare lithium manganese iron phosphate slurry, which is beneficial to promote the uniform dispersion of LMFP particles. Based on this, by further controlling the solid content and viscosity of the lithium manganese iron phosphate slurry, the slurry has a low solid content and a high viscosity, which is beneficial to maintain good bonding strength between LMFP particles while ensuring good dispersion effect, thus improving the stability of the lithium manganese iron phosphate slurry. Because ternary materials have a large particle size, large-particle ternary materials have good processing capabilities and are not prone to agglomeration. Therefore, by using a wet homogenization process (mixing conductive adhesive with ternary materials) to prepare ternary slurry, it is beneficial to maintain good van der Waals forces between the conductive adhesive and the ternary materials. Based on this, by further controlling the solid content and viscosity of the ternary slurry, it is beneficial to make the ternary slurry have both good stability and fluidity. At the same time, it is convenient to uniformly homogenize the ternary slurry with lithium manganese iron phosphate slurry in the subsequent process, so that the resulting composite cathode slurry has the advantages of high stability and uniform dispersion.

[0007] In summary, this invention employs a wet process to prepare ternary slurry and a semi-dry process to prepare lithium manganese iron phosphate slurry, while controlling the solid content and viscosity of the ternary slurry and lithium manganese iron phosphate slurry respectively. This results in a composite cathode slurry with excellent uniformity and stability. Therefore, the homogenization method provided by this invention is applicable to cathode active materials of different particle sizes, achieving sufficient dispersion of ternary materials and lithium manganese iron phosphate of varying particle sizes, effectively preventing particle agglomeration and sedimentation, and improving the yield of composite cathode slurry preparation. Furthermore, this homogenization method is simple to operate, has high production efficiency, and is suitable for industrial production.

[0008] Preferably, the solid content of the ternary slurry is 77.5% to 78.5%, and the viscosity is 5500 mPa·s to 6500 mPa·s.

[0009] Preferably, the solid content of the lithium manganese iron phosphate slurry is 59.5% to 60.5%, and the viscosity is 10000 mPa·s to 14000 mPa·s.

[0010] Preferably, the ternary material includes lithium nickel cobalt manganese oxide (NCM), which includes at least one of NCM333, NCM523, NCM622, and NCM811.

[0011] Preferably, the first adhesive comprises an adhesive and a solvent.

[0012] Preferably, the second adhesive comprises an adhesive and a solvent.

[0013] Preferably, the first conductive agent includes at least one of a first solid conductive agent and a first conductive agent slurry; the specific surface area of ​​the first solid conductive agent is 50 m². 2 / g~200m 2 / g, particle size D50 is 20nm~70nm; the specific surface area of ​​the solid conductive agent in the first conductive agent slurry is 100m². 2 / g~1000m 2 / g, with a particle size D50 of 4nm to 17nm. Conductive agents with smaller specific surface areas and larger particle sizes disperse better and are less prone to agglomeration, while conductive agents with larger specific surface areas and smaller particle sizes disperse poorly, are prone to agglomeration, and easily absorb solvents, which is detrimental to the flowability of the slurry. Therefore, by preparing conductive agents with higher specific surface areas and aspect ratios into conductive agent slurries and then adding them to ternary materials, it is beneficial to promote the dispersion of conductive agents and reduce the risk of poor slurry stability and quality deterioration caused by uneven dispersion of conductive agents.

[0014] Preferably, the first conductive agent comprises a first solid conductive agent, and the mass ratio of the first adhesive to the first solid conductive agent is (45-50):(2-5), wherein the solid content of the first adhesive is 5.5-6.5% and the viscosity is 1000-1800 mPa·s. By controlling the ratio of the first adhesive to the first solid conductive agent in the conductive adhesive, as well as the solid content and viscosity of the first adhesive, it is beneficial to ensure that the first adhesive fully wets and disperses the first solid conductive agent. At the same time, it is beneficial to effectively control the solid content and viscosity of the conductive adhesive, ensuring that the conductive adhesive can fully bond and disperse the subsequently added ternary materials, thereby further optimizing the stability and uniformity of the ternary slurry prepared in this way.

[0015] Preferably, the first conductive agent further includes a first conductive agent slurry, calculated by mass fraction ratio as follows: first adhesive liquid: first solid conductive agent: first conductive agent slurry = (45-50): (2-5): (20-30); wherein the solid content of the first conductive agent slurry is 3-8%.

[0016] Preferably, the mass ratio of the ternary material to the conductive adhesive is 70:(20-30). By controlling the mass ratio of the ternary material to the conductive adhesive, it is beneficial to maintain a strong van der Waals force between the ternary material and the conductive adhesive, and it is also beneficial to control the solid content and viscosity of the resulting ternary slurry, thereby further optimizing the stability and uniformity of the ternary slurry.

[0017] Preferably, the specific operation of adding conductive adhesive to the ternary material is as follows: S1. Add a portion of conductive adhesive to the ternary material and stir; S2. Add a portion of conductive adhesive to the mixture obtained after S1 and stir; S3. Add the remaining conductive adhesive to the mixture obtained after S2 and stir, thereby obtaining a ternary slurry; wherein, the amount of conductive adhesive added is determined according to the mass ratio of conductive adhesive in S1: conductive adhesive in S2: conductive adhesive in S3 = (15~25):(35~45):(35~45). By adding the conductive adhesive to the ternary material step by step and reasonably setting the step-by-step addition amount of conductive adhesive, it is beneficial to ensure that the conductive adhesive fully wets and disperses the ternary material, thereby improving the uniformity and stability of the ternary slurry obtained, and preventing particle agglomeration and sedimentation from adversely affecting the quality of the slurry.

[0018] Preferably, the solid content of the second adhesive is 7%–10%, and the viscosity is 2000–4000 mPa·s. Because lithium manganese iron phosphate (LMFP) has a small particle size and a large specific surface area, adding a second adhesive with a higher viscosity to the small LMFP particles helps ensure effective bonding between the LMFP particles, improves the stability of the resulting LMFP slurry, and prevents problems such as pulverization and sedimentation.

[0019] Preferably, the mass ratio of lithium manganese iron phosphate: second conductive agent: second adhesive is 60:(0.2-0.8):(10-20). Mixing the second adhesive with LMFP particles and the second conductive agent in a suitable proportion facilitates effective control of the solid content and viscosity of the lithium manganese iron phosphate slurry, promotes the full dispersion of solid particles (LMFP particles and the second conductive agent) in the slurry, and further optimizes the dispersibility and uniformity of the lithium manganese iron phosphate slurry.

[0020] Preferably, during the preparation of ternary slurry and / or lithium manganese iron phosphate slurry, the stirring temperature is 30–50°C. These temperature conditions are beneficial for improving the dispersion ability of solid particles in the slurry and optimizing the slurry's uniformity.

[0021] Preferably, the ternary material has a particle size of 5–15 μm, and the lithium manganese iron phosphate has a particle size of 1–3 μm.

[0022] According to another aspect of the present invention, a composite positive electrode slurry is provided, which is prepared by the homogenization method of the above-described composite positive electrode slurry.

[0023] According to another aspect of the present invention, a lithium battery is provided, comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode active coating, the positive electrode active coating comprising the above-described composite positive electrode slurry. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0025] Example 1

[0026] This invention provides a composite positive electrode slurry, the preparation method of which includes the following operations:

[0027] 1. Preparation of ternary slurry

[0028] (1) Preparation of the first adhesive solution

[0029] 117.6 kg of solvent N-methylpyrrolidone (NMP) and 7.5 kg of binder polyvinylidene fluoride (PVDF) were added to a 200 L stirring tank. The stirring speed was 20 rpm, the rotation speed was 1000 rpm, the temperature was 45℃, and the stirring time was 300 minutes to make the vacuum degree of the mixture ≤ -0.085 MPa.

[0030] Then, with a revolution speed of 20 rpm and a rotation speed of 1000 rpm, the mixture is stirred until the temperature drops to 25°C to obtain the first adhesive solution. The first adhesive solution has a solid content of 6.0% and a viscosity of 1400 mPa·s.

[0031] (2) Preparation of conductive adhesive liquid

[0032] Add 47.9 kg of the first adhesive solution and 24 kg of the first conductive agent slurry (CNT conductive agent slurry) into the mixing tank. The revolution speed is 25 rpm, the rotation speed is 2000 rpm, the temperature is 45℃, and the mixing time is 120 minutes to make the vacuum degree of the mixed system ≤ -0.085 MPa.

[0033] Then, 3.2 kg of the first solid conductive agent, conductive carbon black (SP), was added to a mixing tank. The tank was stirred at a revolution speed of 25 rpm, a rotation speed of 2000 rpm, a temperature of 40°C, and a stirring time of 120 minutes to ensure that the vacuum degree of the mixture was ≤-0.085 MPa, thus obtaining a conductive adhesive solution. The specific surface area of ​​the first solid conductive agent was 100 m². 2 / g, with a particle size D50 of 35nm.

[0034] (3) Preparation of ternary slurry

[0035] S1: Add 70kg NCM (NCM particle size is 6μm) and 4.5kg conductive adhesive liquid to the mixing tank, with a revolution speed of 5rpm, a rotation speed of 800rpm, a temperature of 40℃, and a mixing time of 15 minutes.

[0036] S2: Add 9kg of conductive adhesive liquid to the mixing tank, with a revolution speed of 5rpm, a rotation speed of 800rpm, a temperature of 40℃, and a mixing time of 15 minutes;

[0037] S3: Add 9kg of conductive adhesive liquid to the mixing tank, with a revolution speed of 15rpm, a rotation speed of 1500rpm, a temperature of 40℃, and a mixing time of 10 minutes;

[0038] S4: Revolution speed 25 rpm, rotation speed 2000 rpm, temperature 40℃, stirring time 120 minutes, to ensure that the vacuum degree of the mixed system is ≤-0.085Mpa;

[0039] S5: Revolution speed: 15 rpm, rotation speed: 300 rpm, stir until the temperature drops to 25℃, so that the vacuum degree of the mixed system is ≤-0.085Mpa; a ternary slurry is obtained, which has a solid content of 78% and a viscosity of 6000mPa·s.

[0040] 2. Preparation of lithium manganese iron phosphate (LMFP) slurry

[0041] Step 1: Add 0.5 kg of the second conductive agent SP and 60 kg of LMFP (LMFP has a particle size of 2 μm) to a 100 L stirring tank, with a revolution speed of 25 rpm, a temperature of 45 °C, and a stirring time of 15 minutes;

[0042] Step 2: Add 22.3 kg of NMP solvent to the stirring tank, with an orbital speed of 25 rpm, a rotational speed of 500 rpm, a temperature of 45℃, and a stirring time of 15 minutes;

[0043] Step 3: The revolution speed is 25 rpm, the rotation speed is 1500 rpm, the temperature is 45℃, and the stirring time is 120 minutes, so that the vacuum degree of the mixed system is ≤-0.085Mpa;

[0044] Step 4: Add 5 kg of CNT conductive agent slurry to the mixing tank, with a revolution speed of 25 rpm, a rotation speed of 1500 rpm, a temperature of 45℃, and a mixing time of 120 minutes, so that the vacuum degree of the mixed system is ≤-0.085 MPa;

[0045] Step 5: Add 15.5 kg of the second adhesive solution to the mixing tank, with a revolution speed of 25 rpm, a rotation speed of 2000 rpm, a temperature of 45℃, a mixing time of 90 minutes, and a vacuum degree of ≤-0.085 MPa;

[0046] Step 6: With a revolution speed of 15 rpm and a rotation speed of 200 rpm, stir until the temperature drops to 25℃ to obtain lithium manganese iron phosphate slurry. The solid content of the lithium manganese iron phosphate slurry is 60.0% and the viscosity is 12000 mPa·s.

[0047] 3. Preparation of composite cathode slurry

[0048] (1) Add 14.6 kg NMP, 26.4 kg ternary slurry and 80 kg lithium manganese iron phosphate slurry to a 200 L mixing tank, with a revolution speed of 25 rpm, a rotation speed of 2000 rpm, a temperature of 45℃ and a mixing time of 120 minutes, so that the vacuum degree of the mixed system is ≤-0.085 MPa.

[0049] (2) The orbital speed is 20 rpm and the rotational speed is 1000 rpm. Stir until the temperature drops to 25°C to obtain the composite positive electrode slurry of this embodiment.

[0050] Example 2

[0051] This embodiment refers to Example 1 for preparing composite cathode slurry. The differences between this embodiment and Example 1 are: (1) the solid content of the first adhesive used in this embodiment is 5.5%, and the viscosity is 1000 mPa·s; (2) the solid content of the ternary slurry obtained in this embodiment is 77.5%, and the viscosity is 5500 mPa·s. Apart from the above differences, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0052] Example 3

[0053] This embodiment refers to Example 1 for preparing composite cathode slurry. The differences between this embodiment and Example 1 are: (1) the solid content of the first adhesive used in this embodiment is 6.5%, and the viscosity is 1800 mPa·s; (2) the solid content of the ternary slurry obtained in this embodiment is 78.1%, and the viscosity is 6500 mPa·s. Apart from the above differences, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0054] Example 4

[0055] This embodiment refers to Example 1 for preparing the composite cathode slurry. The difference between this embodiment and Example 1 is that in the preparation of the ternary slurry, the amount of NCM added is adjusted to 74.5 kg, so that the solid content of the ternary slurry obtained in this embodiment is 79% and the viscosity is 7000 mPa·s. Apart from the above differences, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0056] Example 5

[0057] This embodiment refers to Example 1 for preparing the composite cathode slurry. The difference between this embodiment and Example 1 is that in the preparation of the ternary slurry, the amount of NCM added is adjusted to 66.5 kg, so that the solid content of the ternary slurry obtained in this embodiment is 77% and the viscosity is 5000 mPa·s. Apart from the above differences, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0058] Example 6

[0059] This embodiment refers to Example 1 for preparing the composite positive electrode slurry. The difference between this embodiment and Example 1 is that in the preparation of the ternary slurry, the mass ratio of the conductive adhesive in S1 to the conductive adhesive in S2 to the conductive adhesive in S3 is 10:45:45. Apart from the above difference, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0060] Example 7

[0061] This embodiment refers to Example 1 for preparing the composite positive electrode slurry. The difference between this embodiment and Example 1 is that in the preparation of the ternary slurry in this embodiment, the mass ratio of the conductive adhesive in S1 to the conductive adhesive in S2 to the conductive adhesive in S3 is 30:35:35. Apart from the above difference, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0062] Example 8

[0063] This embodiment refers to Example 1 for preparing the composite cathode slurry. The difference between this embodiment and Example 1 is that in the preparation of the ternary slurry, carbon nanotubes (CNTs) of the same mass are used instead of conductive carbon black (SP) as the first solid conductive agent. The specific surface area of ​​the carbon nanotubes is 200 m². 2 / g, particle size D50 is 10nm. Apart from the differences mentioned above, the materials and processes used in this embodiment are strictly consistent with those in Example 1.

[0064] Example 9

[0065] This embodiment refers to Example 1 for preparing composite cathode slurry. The differences between this embodiment and Example 1 are: (1) the solid content of the second adhesive used in this embodiment is 7%, and the viscosity is 2000 mPa·s; (2) the solid content of the lithium manganese iron phosphate slurry obtained in this embodiment is 59.85%, and the viscosity is 10000 mPa·s. Apart from the above differences, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0066] Example 10

[0067] This embodiment refers to Example 1 for preparing composite cathode slurry. The differences between this embodiment and Example 1 are: (1) the solid content of the second adhesive used in this embodiment is 10%, and the viscosity is 3000 mPa·s; (2) the solid content of the lithium manganese iron phosphate slurry obtained in this embodiment is 60.2%, and the viscosity is 13000 mPa·s. Apart from the above differences, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0068] Example 11

[0069] This embodiment refers to Example 1 for preparing the composite cathode slurry. The difference between this embodiment and Example 1 is that in the preparation of the lithium manganese iron phosphate slurry, the amount of LMFP is adjusted to 57.6 kg, so that the solid content of the obtained lithium manganese iron phosphate slurry is 59% and the viscosity is 7000 mPa·s. Apart from the above differences, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0070] Example 12

[0071] This embodiment refers to Example 1 for preparing the composite cathode slurry. The difference between this embodiment and Example 1 is that in the preparation of the lithium manganese iron phosphate slurry, the amount of LMFP is adjusted to 62.5 kg, so that the solid content of the obtained lithium manganese iron phosphate slurry is 61% and the viscosity is 17000 mPa·s. Apart from the above differences, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0072] Comparative Example 1

[0073] This comparative example provides a composite cathode slurry, the preparation method of which includes the following steps:

[0074] (1) Add 0.5kg of conductive agent SP, 42kg of LMFP and 18kg of NCM to a 100L mixing tank, with a revolution speed of 25rpm, a temperature of 25℃ and a mixing time of 15 minutes;

[0075] (2) Add 22.3 kg NMP into the mixing tank, with a revolution speed of 25 rpm, a rotation speed of 500 rpm, a temperature of 25℃, and a mixing time of 15 minutes;

[0076] (3) Revolution speed 25 rpm, rotation speed 1500 rpm, temperature 45℃, stirring time 120 minutes, vacuum degree ≤ -0.085Mpa;

[0077] (4) Add 5kg of CNT conductive agent slurry to the mixing tank, with a revolution speed of 25rpm, a rotation speed of 1500rpm, a temperature of 45℃, a mixing time of 120 minutes, and a vacuum degree of ≤-0.085Mpa.

[0078] (5) Add 15.5 kg of the second adhesive solution prepared in Example 1 into a mixing tank. The revolution speed is 25 rpm, the rotation speed is 2000 rpm, the temperature is 45℃, the mixing time is 90 minutes, and the vacuum degree is ≤-0.085Mpa.

[0079] (6) The composite positive electrode slurry of this comparative example was prepared by stirring at a revolution speed of 15 rpm and a rotation speed of 200 rpm until the temperature dropped to 25℃. The solid content of the composite positive electrode slurry was 60.0% and the viscosity was 5000 mPa·s.

[0080] Comparative Example 2

[0081] This comparative example prepares a composite cathode slurry according to Example 1. The difference between this comparative example and Example 1 is that this comparative example prepares a ternary slurry using the same method as the lithium manganese iron phosphate slurry preparation method in Example 1; and prepares a lithium manganese iron phosphate slurry using the same method as the ternary slurry preparation method in Example 1. Apart from the above differences, the materials and process operations used in this comparative example are strictly consistent with those in Example 1.

[0082] The specific method for preparing the composite cathode slurry in this comparative example is as follows:

[0083] 1. Preparation of lithium manganese iron phosphate (LMFP) slurry

[0084] (1) Preparation of the first adhesive solution

[0085] 117.6 kg of solvent N-methylpyrrolidone (NMP) and 7.5 kg of binder polyvinylidene fluoride (PVDF) were added to a 200 L stirring tank. The stirring speed was 20 rpm, the rotation speed was 1000 rpm, the temperature was 45℃, and the stirring time was 300 minutes to make the vacuum degree of the mixture ≤ -0.085 MPa.

[0086] Then, with a revolution speed of 20 rpm and a rotation speed of 1000 rpm, the mixture is stirred until the temperature drops to 25°C to obtain the first adhesive solution. The first adhesive solution has a solid content of 6.0% and a viscosity of 1400 mPa·s.

[0087] (2) Preparation of conductive adhesive liquid

[0088] Add 47.9 kg of the first adhesive solution and 24 kg of the first conductive agent slurry (CNT conductive agent slurry) into the mixing tank. The revolution speed is 25 rpm, the rotation speed is 2000 rpm, the temperature is 45℃, and the mixing time is 120 minutes to make the vacuum degree of the mixed system ≤ -0.085 MPa.

[0089] Then, 3.2 kg of the first solid conductive agent, conductive carbon black (SP), was added to a mixing tank. The tank was stirred at a revolution speed of 25 rpm, a rotation speed of 2000 rpm, a temperature of 40°C, and a stirring time of 120 minutes to ensure that the vacuum degree of the mixture was ≤-0.085 MPa, thus obtaining a conductive adhesive solution. The specific surface area of ​​the first solid conductive agent was 100 m². 2 / g, with a particle size D50 of 35nm.

[0090] (3) Preparation of lithium manganese iron phosphate slurry

[0091] S1: Add 70kg of LMFP (LMFP particle size is 2μm) and 4.5kg of conductive adhesive liquid to the mixing tank, with a revolution speed of 5rpm, a rotation speed of 800rpm, a temperature of 40℃, and a mixing time of 15 minutes.

[0092] S2: Add 9kg of conductive adhesive liquid to the mixing tank, with a revolution speed of 5rpm, a rotation speed of 800rpm, a temperature of 40℃, and a mixing time of 15 minutes;

[0093] S3: Add 9kg of conductive adhesive liquid to the mixing tank, with a revolution speed of 15rpm, a rotation speed of 1500rpm, a temperature of 40℃, and a mixing time of 10 minutes;

[0094] S4: Revolution speed 25 rpm, rotation speed 2000 rpm, temperature 40℃, stirring time 120 minutes, to ensure that the vacuum degree of the mixed system is ≤-0.085Mpa;

[0095] S5: Revolution speed: 15 rpm, rotation speed: 300 rpm, stir until the temperature drops to 25℃, so that the vacuum degree of the mixed system is ≤-0.085Mpa; obtain lithium manganese iron phosphate slurry, the solid content of the lithium manganese iron phosphate slurry is 78%, and the viscosity is 6000mPa·s.

[0096] 2. Preparation of ternary slurry

[0097] Step 1: Add 0.5 kg of the second conductive agent SP and 70 kg of NCM (NCM has a particle size of 6 μm) to a 100 L stirring tank, with a revolution speed of 25 rpm, a temperature of 45 °C, and a stirring time of 15 minutes;

[0098] Step 2: Add 22.3 kg of NMP solvent to the stirring tank, with an orbital speed of 25 rpm, a rotational speed of 500 rpm, a temperature of 45℃, and a stirring time of 15 minutes;

[0099] Step 3: The revolution speed is 25 rpm, the rotation speed is 1500 rpm, the temperature is 45℃, and the stirring time is 120 minutes, so that the vacuum degree of the mixed system is ≤-0.085Mpa;

[0100] Step 4: Add 5 kg of CNT conductive agent slurry to the mixing tank, with a revolution speed of 25 rpm, a rotation speed of 1500 rpm, a temperature of 45℃, and a mixing time of 120 minutes, so that the vacuum degree of the mixed system is ≤-0.085 MPa;

[0101] Step 5: Add 15.5 kg of the second adhesive solution to the mixing tank, with a revolution speed of 25 rpm, a rotation speed of 2000 rpm, a temperature of 45℃, a mixing time of 90 minutes, and a vacuum degree of ≤-0.085 MPa;

[0102] Step 6: With a revolution speed of 15 rpm and a rotation speed of 200 rpm, stir until the temperature drops to 25℃ to obtain a ternary slurry. The solid content of the ternary slurry is 60.0% and the viscosity is 12000 mPa·s.

[0103] 3. Preparation of composite cathode slurry

[0104] (1) Add 14.6 kg NMP, 26.4 kg ternary slurry and 80 kg lithium manganese iron phosphate slurry to a 200 L mixing tank, with a revolution speed of 25 rpm, a rotation speed of 2000 rpm, a temperature of 45℃ and a mixing time of 120 minutes, so that the vacuum degree of the mixed system is ≤-0.085 MPa.

[0105] (2) The orbital speed is 20 rpm and the rotational speed is 1000 rpm. Stir until the temperature drops to 25℃ to obtain the composite positive electrode slurry of this comparative example.

[0106] Comparative Example 3

[0107] This comparative example prepares a composite cathode slurry according to Example 1. The difference between this comparative example and Example 1 is that in the preparation of the ternary slurry, the amount of NCM added is adjusted to 85 kg, so that the solid content of the obtained ternary slurry is 81% and the viscosity is 11000 mPa·s. Apart from the above differences, the materials and process operations used in this comparative example are strictly consistent with those in Example 1.

[0108] Comparative Example 4

[0109] This comparative example prepares a composite cathode slurry according to Example 1. The difference between this comparative example and Example 1 is that in the preparation of the ternary slurry, the amount of NCM added is adjusted to 50.5 kg, so that the solid content of the obtained ternary slurry is 72% and the viscosity is 3000 mPa·s. Apart from the above differences, the materials and process operations used in this comparative example are strictly consistent with those in Example 1.

[0110] Comparative Example 5

[0111] This comparative example prepares a composite cathode slurry according to Example 1. The difference between this comparative example and Example 1 is that in the preparation of the lithium manganese iron phosphate slurry, the amount of LMFP added is adjusted to 70.5 kg, so that the solid content of the obtained lithium manganese iron phosphate slurry is 72% and the viscosity is 23000 mPa·s. Apart from the above differences, the materials and process operations used in this comparative example are strictly consistent with those in Example 1.

[0112] Comparative Example 6

[0113] This comparative example prepares a composite cathode slurry according to Example 1. The difference between this comparative example and Example 1 is that in the preparation of the lithium manganese iron phosphate slurry, the amount of LMFP added is adjusted to 49.3 kg, so that the solid content of the obtained lithium manganese iron phosphate slurry is 55% and the viscosity is 6500 mPa·s. Apart from the above differences, the materials and process operations used in this comparative example are strictly consistent with those in Example 1.

[0114] Test Example 1

[0115] 1. Test subject:

[0116] The composite cathode slurries prepared in Examples 1-12 and Comparative Examples 1-6 were used as the test objects in this test example.

[0117] 2. Test items:

[0118] (1) Solid content of composite cathode slurry: The composite cathode slurry to be tested is placed in a pre-weighed container, and the solvent in the liquid is evaporated or volatilized by heating or vacuum drying, leaving solid matter. Then the mass of the solid matter is weighed and the solid content is calculated.

[0119] (2) Fineness of composite positive electrode slurry: Take a spoonful of composite positive electrode slurry and place it on the scraper fineness gauge. Place the scraper horizontally on the upper end of the scraper fineness gauge so that the scraper is perpendicular to the surface of the scraper fineness gauge. Pull the scraper from the deep part of the groove to the shallow part at an appropriate speed and read the scale value at the point where the particles are uniformly exposed in the groove. The reading value is the fineness of the composite positive electrode slurry.

[0120] (3) Initial viscosity and viscosity after 24 hours of composite cathode slurry: Install the viscometer so that the horizontal bubble on the machine body is placed in the black circle. Immerse the rotor in the composite cathode slurry up to the groove mark on the rotor rod. Click start. After the viscosity reading stabilizes, read the viscosity value of the composite cathode slurry.

[0121] 3. Test Results:

[0122] Table 1. Performance test results of Examples 1-12 and Comparative Examples 1-6

[0123]

[0124]

[0125] The test results are shown in Table 1. Comparing the performance test results of Example 1 and Comparative Example 1, it can be found that the fineness and 24-hour viscosity change of the composite cathode slurry prepared in Comparative Example 1 are significantly higher than those in Example 1. The reason is that, under the same conditions of other materials and operations for preparing the composite cathode slurry, Comparative Example 1 directly mixed NCM and LMFP. Since lithium manganese iron phosphate and ternary materials have different particle sizes, structural characteristics, and physical properties, directly mixing the two main materials leads to problems such as uneven particle dispersion, low slurry stability, and excessively high viscosity in the subsequent uniform homogenization step, thus significantly deteriorating the dispersibility and stability of the composite cathode slurry.

[0126] Comparing the performance test results of Example 1 and Comparative Example 2, it can be found that the fineness and 24-hour viscosity change of the composite cathode slurry prepared in Comparative Example 2 are significantly higher than those in Example 1. This is because, under the same conditions of other materials and operations for preparing the composite cathode slurry, Comparative Example 2 uses a semi-dry process to prepare NCM. Due to the larger size of the NCM particles, the solid content of the ternary slurry prepared by the semi-dry process is relatively low, which is not conducive to maintaining good van der Waals forces between the conductive adhesive and the ternary materials. Conversely, using a wet process to prepare LMFP, due to the smaller size and larger specific surface area of ​​LMFP particles, results in strong adsorption capacity, making slurry homogenization difficult and thus significantly worsening the dispersibility and stability of the composite cathode slurry.

[0127] Comparing the performance test results of Example 1 with those of Comparative Examples 3-6, it can be found that the fineness and 24-hour viscosity change of the composite cathode slurry prepared in Comparative Examples 3-6 are significantly higher than those in Example 1. This is because, under the same conditions of other materials and operations for preparing the composite cathode slurry, the solid content and viscosity of the ternary slurry prepared in Comparative Examples 3 and 4 are too high and too low, respectively, while the solid content and viscosity of the lithium manganese iron phosphate slurry prepared in Comparative Examples 5 and 6 are too high and too low, respectively. This results in poor dispersion of active particles in the slurry, easy agglomeration and sedimentation, thus significantly deteriorating the dispersibility and stability of the composite cathode slurry.

[0128] The performance test results of Examples 1 and 2-5 were compared. Table 1 shows that, under the same conditions of other materials and operations for preparing the composite cathode slurry, the ternary slurry in Example 4 had higher solid content and viscosity, while the ternary slurry in Example 5 had lower solid content and viscosity. Consequently, the fineness and 24-hour viscosity change of the resulting composite cathode slurry were higher than those of Examples 1-3. This indicates that, compared to Examples 4-5, Examples 1-3, by further controlling the solid content and viscosity of the ternary slurry, facilitated the uniform dispersion of different particles, thereby improving the dispersibility and stability of the composite cathode slurry.

[0129] The performance test results of Example 1 were compared with those of Examples 6-7. Table 1 shows that, under the same conditions of other materials and operations in preparing the composite cathode slurry, the initial addition amount of the conductive agent in S1 during the preparation of the ternary slurry in Examples 6 and 7 was lower and higher, respectively. Consequently, the fineness and 24-hour viscosity change of the resulting composite cathode slurry were higher than those in Example 1. This indicates that, compared to Examples 6-7, Example 1, by adding the conductive agent to the ternary material step by step and rationally setting the step-by-step addition amount, facilitates the thorough wetting and dispersion of the ternary material by the conductive agent, thereby improving the uniformity and stability of the resulting ternary slurry and composite cathode slurry, and preventing particle agglomeration and sedimentation from adversely affecting the slurry quality.

[0130] Comparing the performance test results of Examples 1 and 8, it can be found that the fineness and 24-hour viscosity change of the composite cathode slurry prepared in Example 8 are higher than those in Example 1. This is because, under the same conditions of other materials and operations in preparing the composite cathode slurry, the first solid conductive agent used in Example 8 during the preparation of the ternary slurry was carbon nanotubes. Due to the small particle size and large specific surface area of ​​carbon nanotubes, their dispersion effect is poor. Directly introducing them into the slurry in solid form leads to uneven particle dispersion, reduced slurry stability, and increased viscosity, thereby deteriorating the dispersibility and stability of the composite cathode slurry.

[0131] The performance test results of Example 1 were compared with those of Examples 9-12. Table 1 shows that, under the same conditions of other materials and operations for preparing the composite cathode slurry, the lithium manganese iron phosphate slurry prepared in Example 11 had lower solid content and viscosity, while the lithium manganese iron phosphate slurry prepared in Example 12 had higher solid content and viscosity. Therefore, the fineness and 24-hour viscosity change of the resulting composite cathode slurry were higher than those of Example 1. This indicates that, compared to Examples 9-10, Examples 1 and 11-12 further controlled the solid content and viscosity of the lithium manganese iron phosphate slurry, which is beneficial for promoting uniform dispersion among different particles, thereby improving the dispersibility and stability of the composite cathode slurry.

[0132] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A method for homogenizing a composite positive electrode slurry, characterized in that, The process includes the following steps: mixing ternary slurry with lithium manganese iron phosphate slurry to obtain a composite cathode slurry; The preparation method of the ternary slurry includes the following operations: The ternary slurry is prepared by adding a conductive adhesive to a ternary material and stirring it. The solid content of the ternary slurry is 76%~80%, and the viscosity is 4000mPa·s~7000mPa·s. The conductive adhesive includes a first adhesive and a first conductive agent. The preparation method of the lithium manganese iron phosphate slurry includes the following operations: Lithium manganese iron phosphate is dry-mixed with a second conductive agent and stirred to obtain a mixed dry material. Then, a second adhesive is added to the mixed dry material to obtain the lithium manganese iron phosphate slurry. The solid content of the lithium manganese iron phosphate slurry is 58-62%, and the viscosity is 7000-20000 mPa·s. The ternary material includes lithium nickel cobalt manganese oxide; the particle size of the ternary material is 5~15μm, and the particle size of lithium manganese iron phosphate is 1~3μm.

2. The homogenization method for the composite positive electrode slurry as described in claim 1, characterized in that, The first conductive agent includes at least one of a first solid conductive agent and a first conductive agent slurry; The specific surface area of ​​the first solid conductive agent is 50 m². 2 / g~200m 2 / g, with a particle size D50 of 20nm~70nm; The specific surface area of ​​the solid conductive agent in the first conductive agent slurry is 100 m². 2 / g~1000m 2 / g, with a particle size D50 of 4nm~17nm.

3. The homogenization method for the composite positive electrode slurry as described in claim 2, characterized in that, The first conductive agent includes a first solid conductive agent, and the mass ratio of the first adhesive liquid to the first solid conductive agent is (45~50):(2~5), wherein the solid content of the first adhesive liquid is 5.5~6.5% and the viscosity is 1000mPa·s~1800mPa·s.

4. The homogenization method for the composite positive electrode slurry as described in claim 3, characterized in that, The mass ratio of the ternary material to the conductive adhesive is 70:(20~30).

5. The homogenization method for the composite positive electrode slurry as described in claim 4, characterized in that, The specific steps for adding the conductive adhesive to the ternary material are as follows: S1. Add a portion of the conductive adhesive to the ternary material and stir. S2. Add a portion of the conductive adhesive to the mixture obtained after S1 and stir. S3. Add the remaining conductive adhesive to the mixture obtained after S2 and stir to obtain the ternary slurry; The amount of conductive adhesive added is determined according to the following formula: mass of conductive adhesive in S1: mass of conductive adhesive in S2: mass of conductive adhesive in S3 = (15~25): (35~45): (35~45).

6. The homogenization method for the composite positive electrode slurry as described in claim 1, characterized in that, The second adhesive has a solid content of 7% to 10% and a viscosity of 2000 to 4000 mPa·s.

7. The homogenization method for the composite positive electrode slurry as described in claim 6, characterized in that, The mass ratio of lithium manganese iron phosphate to the second conductive agent to the second adhesive is 60: (0.2~0.8): (10~20).

8. The homogenization method for the composite positive electrode slurry according to any one of claims 1 to 7, characterized in that, During the preparation of the ternary slurry and / or the lithium manganese iron phosphate slurry, the stirring temperature is 30~50℃.

9. A composite positive electrode slurry, characterized in that, It is prepared by the homogenization method of the composite positive electrode slurry according to any one of claims 1 to 8.

10. A lithium battery, characterized in that, It includes a positive electrode sheet, the positive electrode sheet including a positive electrode active coating, the positive electrode active coating including the composite positive electrode slurry as described in claim 9.

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