Positive electrode slurry and preparation method thereof

Abstract

The invention belongs to the technical field of battery materials, and particularly relates to positive electrode slurry and a preparation method thereof. By accurately introducing the lithium supplementing agent adaptive to the lithium iron phosphate system, permanent lithium source loss caused by SEI film formation in the first cycle of the battery can be supplemented in a targeted manner, the first coulombic efficiency of the battery is improved from the source, and the core defect that lithium consumption is too high in a traditional dry method process is effectively overcome; meanwhile, the preparation process of the positive electrode slurry is innovatively optimized, and a step-by-step composite strategy of firstly preparing a binder colloidal dispersion, then realizing nano-scale deagglomeration dispersion of a conductive agent, and finally adding a positive electrode active material and a lithium supplement agent for interface coating is adopted; the limitation that a traditional dry process depends on mechanical shear force and lacks solvent-assisted infiltration is broken through, the interfacial tension and agglomeration resistance of the powder are greatly reduced, and the industrial pain point that the dispersion time of the traditional process is too long is solved.

Description

Technical Field

[0001] This application belongs to the field of battery cathode material technology, specifically relating to a lithium iron phosphate cathode slurry with added lithium supplementation agent. Background Technology

[0002] Lithium iron phosphate cathode slurry is a core functional material in the manufacture of lithium-ion battery cathodes. It is mainly made by mixing lithium iron phosphate (LFP) cathode active material, conductive agents (such as carbon black, carbon nanotubes, graphene, etc.), binders (such as PVDF) and organic solvents (such as NMP) in a specific ratio. The uniformity of component dispersion and viscosity stability directly determine the conductivity and structural strength of the cathode sheet, which in turn affects the energy density, cycle life and production consistency of the battery.

[0003] Currently, the preparation methods for lithium iron phosphate cathode slurries are mainly divided into two categories: dry and wet processes. The wet process requires all raw materials to be mixed and dispersed in a solvent throughout the entire process, relying on the synergistic effect of solvent wetting and mechanical shearing to achieve dispersion. However, it suffers from problems such as large solvent consumption, high subsequent recycling costs, and long production cycles. The dry process, on the other hand, uses mechanical shearing force as its core, first pre-mixing the solid powder, and then gradually adding solvent for kneading and dispersion. It features lower solvent consumption, easier improvement of solid content, and better environmental friendliness. Because traditional wet processes suffer from high environmental costs and low production efficiency, and because dry processes can reduce binder usage and increase slurry solid content by optimizing the mixing steps, the current mainstream and most common preparation method is dry twin-screw kneading slurry preparation. This method utilizes the strong shearing and conveying action of the screw to efficiently achieve uniform mixing of solid powder and thorough kneading of the subsequent solvent, ensuring stable slurry performance. For example, patent application number 202411972474.2 discloses a method for dry preparation of modified lithium iron phosphate cathode slurry, specifically including: firstly, dry mixing lithium iron phosphate cathode material, binder PVDF and first conductive agent (composed of at least two of carbon black, carbon nanotubes and graphene) to obtain a first premix; adding an organic solvent (preferably NMP) to the first premix and gradually increasing the stirring speed, stirring continuously for at least 55 minutes to obtain a second premix; then adding a second conductive agent (within the same material range as the first conductive agent), binder PVP and an appropriate amount of organic solvent to the second premix, and continuing to gradually increase the stirring speed for at least 90 minutes to obtain lithium iron phosphate cathode slurry. Performance test results show that the solid content of the modified slurry is stable at 55%~65%, and the viscosity is controlled at 4000~9000mPa・s. The positive electrode sheet prepared using this slurry has a resistivity as low as 15~17Ω・cm and a peel strength of 75~85N / m. Compared with products made by traditional processes (resistivity 19~21Ω・cm, peel strength 30~40N / m), the conductivity and structural bonding stability are significantly improved.

[0004] However, both the active material and the conductive agent of lithium iron phosphate are ultrafine powders that are prone to agglomeration. The uniform coating of the binder on the powder surface is achieved solely by mechanical shearing force, which requires overcoming the interfacial tension and agglomeration resistance of the powder, resulting in a significantly longer dispersion and kneading time. Furthermore, due to the bottleneck of uniformity in dry mixing, the binder is prone to local over-coating or missing areas, and the conductive agent is prone to forming isolated conductive regions. This not only leads to an intensified reaction between the surface of the active material and the electrolyte, forming a thicker irreversible SEI film, resulting in a lower initial coulombic efficiency and permanent lithium source loss, but also directly offsets the theoretical performance gain brought by the high solid content, ultimately reducing the overall energy density of the battery. Summary of the Invention

[0005] This application provides a method for preparing a positive electrode slurry that is simple to prepare and has a higher overall energy density in the battery, which is achieved through the following technical solution: A method for preparing a positive electrode slurry includes the following steps: placing a binder in a solvent and dissolving it by stirring to obtain a colloidal dispersion; introducing a conductive agent into the colloidal dispersion and dispersing it by high-speed shearing to form a conductive composite slurry; adding a positive electrode active material and a lithium supplement agent to the conductive composite slurry and achieving interfacial wetting by mechanical stirring to obtain a slurry precursor; and performing vacuum degassing treatment on the slurry precursor to obtain the positive electrode slurry.

[0006] Preferably, the lithium supplement includes at least one of lithium difluorooxalate borate, lithium oxalate, lithium-rich nickel oxide, lithium silicate, lithium squaric acid, and lithium ferrite.

[0007] Preferably, the conductive agent is a composite system of super carbon black and carbon nanotubes, with a mass ratio of (2:1) to (4:1).

[0008] Preferably, the proportions of the positive electrode active material, conductive agent, binder, and lithium supplementer, calculated by mass, are 90.0~96.0 parts, 1.5~3.5 parts, 1.2~2.5 parts, and 1.0~5.0 parts, respectively.

[0009] Preferably, an antifoaming agent is added during the vacuum degassing process, and the antifoaming agent is selected from organosilicon or polyether-modified organosilicon compounds.

[0010] Preferably, the amount of defoamer added is 0.1 to 0.5 parts by weight.

[0011] A positive electrode slurry prepared by any of the above-described preparation methods.

[0012] Preferably, the solid content of the positive electrode slurry is greater than 72%.

[0013] Compared with the prior art, this application has the following beneficial effects: This application precisely introduces a lithium replenishing agent adapted to the lithium iron phosphate system, which can specifically replenish the permanent lithium source loss caused by SEI film formation during the first cycle of the battery, fundamentally improving the battery's first coulombic efficiency and effectively making up for the core shortcoming of excessive lithium consumption in traditional dry processes. At the same time, it innovatively optimizes the cathode slurry preparation process, adopting a step-by-step composite strategy of "first preparing a binder colloidal dispersion, then achieving nanoscale deagglomeration and dispersion of the conductive agent, and finally adding the cathode active material and lithium replenishing agent for interfacial coating". With the synergistic effect of pre-wetting and dispersion of the powder by the colloidal dispersion, it overcomes the limitations of traditional dry processes that rely on mechanical shear force and lack solvent-assisted wetting, and significantly reduces the interfacial tension of the powder. The reduction of agglomeration resistance not only significantly improves the uniformity of slurry dispersion and interfacial compatibility, but also greatly shortens the overall preparation time compared to traditional dry processes, solving the industry pain point of excessively long dispersion time in traditional processes. In addition, the solid content of the slurry prepared in this application can be stably higher than 72%. While maintaining the advantage of high active material ratio in the electrode due to high solid content, the lithium source supplementation of the lithium supplementing agent and the interface optimization of the stepwise dispersion process avoid the problems of uneven conductive network and insufficient interfacial bonding that are prone to occur in traditional high solid content slurries. Ultimately, it achieves simultaneous improvement in battery energy density, cycle stability and production efficiency, perfectly meeting the core requirements of lithium iron phosphate batteries for high comprehensive performance and low-cost mass production. Attached Figure Description

[0014] The attached diagram will be briefly described below: Figure 1 This is the first Coulomb comparison image in the performance test; Figure 2 This is a comparison chart of battery cell cycles during performance testing. Detailed Implementation

[0015] The present application will now be further described by way of specific embodiments. Those skilled in the art will be able to implement the present application based on these descriptions. Furthermore, the embodiments of the present application described below are generally only a part of the embodiments of the present application, and not all of the embodiments. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present application without inventive effort should fall within the scope of protection of the present application. Example 1

[0016] A method for preparing a positive electrode slurry includes the following steps: Ingredient weighing: Weigh each component according to the mass ratio, where the ratio of lithium iron phosphate (LFP), superconducting carbon black (SP), carbon nanotubes (CNT), polyvinylidene fluoride (PVDF), lithium difluorooxalate borate (LiDFOB, lithium supplement), and defoamer is 94:1.8:0.6:2:1.5:0.1. The amount of N-methylpyrrolidone (NMP) used is based on adjusting the slurry solid content to 72%.

[0017] Preparation of PVDF adhesive: Take the NMP solvent in the formula and slowly add the PVDF powder to it. Under constant temperature of 25℃, stir (e.g., stir at low speed for 60-90 minutes) to completely dissolve the PVDF and form a uniform and transparent adhesive (without visible particles, ensuring that the binder is fully swollen and provides a stable carrier for subsequent dispersion).

[0018] Dispersing the conductive agent: First, put SP and CNT dry powder into a premixing device and premix at a low speed (e.g., 500-800 rpm) for 10-15 minutes to initially break up the agglomerates of the two and achieve uniform mixing; then slowly add the premixed conductive agent powder to the prepared PVDF adhesive while stirring (to avoid local agglomeration) to form a conductive agent-binder mixture system.

[0019] High-speed stirring and dispersion: Transfer the above mixture to a planetary mixer and stir at a high speed of 2000 rpm for 40 minutes to thoroughly break up the tangled agglomerates of CNTs (dispersing them into single strands or a small number of bundles) using strong shear force, while allowing SP to be evenly distributed in the adhesive to build a preliminary conductive network.

[0020] Add active material and lithium supplementer: Add LFP powder to the system in 2-3 batches (stir for 10-15 minutes after each addition until there is no obvious clumping), then add lithium supplementer LiDFOB, switch the stirrer speed to 1200 rpm and stir continuously for 90 minutes to ensure that the LFP particles are fully coated by the conductive agent-binder system, ensuring that the active material is in close contact with the conductive network (at the same time, LiDFOB is uniformly dispersed to prepare for the subsequent lithium supplementation reaction).

[0021] Adding defoamer and vacuum defoaming: Add the prescribed amount of defoamer and stir for 5-10 minutes to ensure uniform dispersion; then, under a vacuum of -0.095 MPa, stir at a low speed of 500 rpm for 40 minutes to remove air bubbles introduced by high-speed dispersion in the slurry through a vacuum environment and gentle stirring (to avoid defects such as pinholes and insufficient adhesive during coating). After discharge, test the viscosity of the slurry; if it meets the requirements, it can be used for the coating process of the positive electrode current collector (aluminum foil). Example 2

[0022] A method for preparing a positive electrode slurry includes the following steps: Ingredient weighing: Weigh each component according to the mass ratio, where the ratio of lithium iron phosphate (LFP), superconducting carbon black (SP), carbon nanotubes (CNT), polyvinylidene fluoride (PVDF), lithium oxalate (lithium supplement), and defoamer is 90:1.5:2:1.2:5:0.5. The amount of N-methylpyrrolidone (NMP) used is based on adjusting the slurry solid content to 72%.

[0023] Preparation of PVDF adhesive: Take the NMP solvent in the formula and slowly add the PVDF powder to it. Under constant temperature of 25℃, stir (e.g., stir at low speed for 60-90 minutes) to completely dissolve the PVDF and form a uniform and transparent adhesive (without visible particles, ensuring that the binder is fully swollen and provides a stable carrier for subsequent dispersion).

[0024] Dispersing the conductive agent: First, put SP and CNT dry powder into a premixing device and premix at a low speed (e.g., 500-800 rpm) for 10-15 minutes to initially break up the agglomerates of the two and achieve uniform mixing; then slowly add the premixed conductive agent powder to the prepared PVDF adhesive while stirring (to avoid local agglomeration) to form a conductive agent-binder mixture system.

[0025] High-speed stirring and dispersion: Transfer the above mixture to a planetary mixer and stir at a high speed of 2000 rpm for 40 minutes to thoroughly break up the tangled agglomerates of CNTs (dispersing them into single strands or a small number of bundles) using strong shear force, while allowing SP to be evenly distributed in the adhesive to build a preliminary conductive network.

[0026] Add active material and lithium supplement: Add LFP powder to the system in 2-3 batches (stir for 10-15 minutes after each addition until there is no obvious clumping), then add lithium supplement, switch the mixer speed to 1200 rpm and stir continuously for 90 minutes to ensure that the LFP particles are fully coated by the conductive agent-binder system, ensuring that the active material is in close contact with the conductive network.

[0027] Adding defoamer and vacuum defoaming: Add the prescribed amount of defoamer and stir for 5-10 minutes to ensure uniform dispersion; then, under a vacuum of -0.095 MPa, stir at a low speed of 500 rpm for 40 minutes to remove air bubbles introduced by high-speed dispersion in the slurry through a vacuum environment and gentle stirring (to avoid defects such as pinholes and insufficient adhesive during coating). After discharge, test the viscosity of the slurry; if it meets the requirements, it can be used for the coating process of the positive electrode current collector (aluminum foil). Example 3

[0028] A method for preparing a positive electrode slurry includes the following steps: Ingredient weighing: Weigh each component according to the mass ratio, wherein the ratio of lithium iron phosphate (LFP), superconducting carbon black (SP), carbon nanotubes (CNT), polyvinylidene fluoride (PVDF), lithium-rich nickel oxide (lithium supplement), and defoamer is 94:1:0.5:2.5:1:0.1. The amount of N-methylpyrrolidone (NMP) used is based on adjusting the slurry solid content to 72%.

[0029] Preparation of PVDF adhesive: Take the NMP solvent in the formula and slowly add the PVDF powder to it. Under constant temperature of 25℃, stir (e.g., stir at low speed for 60-90 minutes) to completely dissolve the PVDF and form a uniform and transparent adhesive (without visible particles, ensuring that the binder is fully swollen and provides a stable carrier for subsequent dispersion).

[0030] Dispersing the conductive agent: First, put SP and CNT dry powder into a premixing device and premix at a low speed (e.g., 500-800 rpm) for 10-15 minutes to initially break up the agglomerates of the two and achieve uniform mixing; then slowly add the premixed conductive agent powder to the prepared PVDF adhesive while stirring (to avoid local agglomeration) to form a conductive agent-binder mixture system.

[0031] High-speed stirring and dispersion: Transfer the above mixture to a planetary mixer and stir at a high speed of 2000 rpm for 40 minutes to thoroughly break up the tangled agglomerates of CNTs (dispersing them into single strands or a small number of bundles) using strong shear force, while allowing SP to be evenly distributed in the adhesive to build a preliminary conductive network.

[0032] Add active material and lithium supplement: Add LFP powder to the system in 2-3 batches (stir for 10-15 minutes after each addition until there is no obvious clumping), then add lithium supplement, switch the mixer speed to 1200 rpm and stir continuously for 90 minutes to ensure that the LFP particles are fully coated by the conductive agent-binder system, ensuring that the active material is in close contact with the conductive network.

[0033] Adding defoamer and vacuum defoaming: Add the prescribed amount of defoamer and stir for 5-10 minutes to ensure uniform dispersion; then, under a vacuum of -0.095 MPa, stir at a low speed of 500 rpm for 40 minutes to remove air bubbles introduced by high-speed dispersion in the slurry through a vacuum environment and gentle stirring (to avoid defects such as pinholes and insufficient adhesive during coating). After discharge, test the viscosity of the slurry; if it meets the requirements, it can be used for the coating process of the positive electrode current collector (aluminum foil). Example 4

[0034] A method for preparing a positive electrode slurry includes the following steps: Ingredient weighing: Weigh each component according to the mass ratio, where the ratio of lithium iron phosphate (LFP), superconducting carbon black (SP), carbon nanotubes (CNT), polyvinylidene fluoride (PVDF), lithium silicate (lithium supplement), and defoamer is 96:1.8:0.6:1.2:5:0.1. The amount of N-methylpyrrolidone (NMP) used is based on adjusting the slurry solid content to 72%.

[0035] Preparation of PVDF adhesive: Take the NMP solvent in the formula and slowly add the PVDF powder to it. Under constant temperature of 25℃, stir (e.g., stir at low speed for 60-90 minutes) to completely dissolve the PVDF and form a uniform and transparent adhesive (without visible particles, ensuring that the binder is fully swollen and provides a stable carrier for subsequent dispersion).

[0036] Dispersing the conductive agent: First, put SP and CNT dry powder into a premixing device and premix at a low speed (e.g., 500-800 rpm) for 10-15 minutes to initially break up the agglomerates of the two and achieve uniform mixing; then slowly add the premixed conductive agent powder to the prepared PVDF adhesive while stirring (to avoid local agglomeration) to form a conductive agent-binder mixture system.

[0037] High-speed stirring and dispersion: Transfer the above mixture to a planetary mixer and stir at a high speed of 2000 rpm for 40 minutes to thoroughly break up the tangled agglomerates of CNTs (dispersing them into single strands or a small number of bundles) using strong shear force, while allowing SP to be evenly distributed in the adhesive to build a preliminary conductive network.

[0038] Add active material and lithium supplement: Add LFP powder to the system in 2-3 batches (stir for 10-15 minutes after each addition until there is no obvious clumping), then add lithium supplement, switch the mixer speed to 1200 rpm and stir continuously for 90 minutes to ensure that the LFP particles are fully coated by the conductive agent-binder system, ensuring that the active material is in close contact with the conductive network.

[0039] Adding defoamer and vacuum defoaming: Add the prescribed amount of defoamer and stir for 5-10 minutes to ensure uniform dispersion; then, under a vacuum of -0.095 MPa, stir at a low speed of 500 rpm for 40 minutes to remove air bubbles introduced by high-speed dispersion in the slurry through a vacuum environment and gentle stirring (to avoid defects such as pinholes and insufficient adhesive during coating). After discharge, test the viscosity of the slurry; if it meets the requirements, it can be used for the coating process of the positive electrode current collector (aluminum foil).

[0040] Comparative Example 1 The only difference between this comparative example and Example 1 is that it is prepared using the dry twin-screw kneading pulping process disclosed in the cited patent in the background art (such as the patent with application number 202411972474.2). The types of raw materials, the amount of each component added, and the specifications of the final target product used in both are consistent, so as to highlight the improvement effect of the optimized process of Example 1 on the pulp performance and the overall battery performance through parallel comparison.

[0041] Performance testing This performance test used the cathode slurries prepared in Example 1 and Comparative Example 1 to prepare battery cells, and systematically compared the initial coulombic efficiency and cycle performance of the cells to verify the significant advantages of the optimized process in this application. As shown in the "Initial Coulombic Efficiency Comparison" figure, the initial coulombic efficiency of Example 1 (orange curve) remained stable above 95% from the first week with minimal fluctuations, exhibiting highly consistent and excellent electrochemical reversibility; while Comparative Example 1 (blue curve) hovered in the 88%~92% range for a long time, and showed a significant drop in multiple cycles, indicating poor interface stability, irreversible side reactions or local structural damage, leading to continuous lithium source loss. This result fully demonstrates that the strategy of stepwise construction of the colloidal dispersion-conductive network-active material interface and precise introduction of lithium replenishment agent in this application effectively optimizes the ion / electron transport path inside the electrode, suppresses excessive growth of the SEI film and electrolyte decomposition in the first cycle, thereby significantly reducing irreversible capacity loss and improving lithium utilization. Regarding cycle performance, the "cell cycle" diagram further reveals the long-term impact of process differences: the cell corresponding to Example 1 (orange solid line) exhibits superior capacity retention in the early stages of cycling, with a significantly slower decay rate than Comparative Example 1 (blue solid line). Especially after 1000 cycles, the difference between the two gradually widens, demonstrating stronger structural stability and interface durability. In summary, the process of this application not only achieves a stable improvement in coulombic efficiency for the first time but also fundamentally enhances the cycle stability of the cell, providing reliable technical support for the large-scale application of high-energy-density, long-life lithium-ion batteries.

Claims

1. A method for preparing a positive electrode slurry, characterized in that, Includes the following steps: The binder is placed in a solvent and dissolved by stirring to obtain a colloidal dispersion; A conductive agent is introduced into a colloidal dispersion and dispersed by high-speed shearing to form a conductive composite slurry; The positive electrode active material and lithium supplementing agent are added to the conductive composite slurry, and the interface is wetted by mechanical stirring to obtain the slurry precursor. The slurry precursor was subjected to vacuum degassing to obtain the positive electrode slurry.

2. The method for preparing a positive electrode slurry according to claim 1, characterized in that, The lithium supplement includes at least one of lithium difluorooxalate borate, lithium oxalate, lithium-rich nickel oxide, lithium silicate, lithium squartz oxide, and lithium ferrite.

3. The method for preparing a positive electrode slurry according to claim 1, characterized in that, The conductive agent adopts a composite system of super carbon black and carbon nanotubes, with a mass ratio of (2:1) to (4:1).

4. The method for preparing a positive electrode slurry according to claim 1, characterized in that, Based on mass parts, the addition ratios of the positive electrode active material, conductive agent, binder, and lithium supplement are 90.0~96.0 parts, 1.5~3.5 parts, 1.2~2.5 parts, and 1.0~5.0 parts, respectively.

5. The method for preparing a positive electrode slurry according to claim 4, characterized in that, In the vacuum degassing process, a defoamer also needs to be added. The defoamer is selected from organosilicon compounds or polyether-modified organosilicon compounds.

6. The method for preparing a positive electrode slurry according to claim 5, characterized in that, The amount of defoamer added is 0.1 to 0.5 parts by weight.

7. A positive electrode slurry prepared by the preparation method according to any one of claims 1 to 6.

8. The positive electrode slurry according to claim 7, characterized in that, The solid content of the positive electrode slurry is greater than 72%.

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