A lithium ion battery positive electrode slurry, a preparation method thereof, and a lithium ion battery positive electrode sheet and a preparation method thereof

Abstract

The application provides a lithium ion battery positive electrode slurry and a preparation method thereof and a lithium ion battery positive electrode sheet and a preparation method thereof, and relates to the technical field of battery materials.The lithium ion battery positive electrode active material, conductive carbon black, a first dispersant and a first solvent are mixed to perform first dispersion treatment; the obtained first dispersion system is mixed with a binder to perform second dispersion treatment; the obtained second dispersion system is mixed with carbon nanotube conductive slurry to perform third dispersion treatment; the obtained third dispersion system is mixed with a third solvent to perform fourth dispersion treatment, so that the lithium ion battery positive electrode slurry is obtained.The scientific quantification of the dispersant and the feeding sequence control of "first main material pre-adsorption occupation, then carbon nanotube conductive slurry" can fundamentally avoid the competitive adsorption of the active material and the carbon nanotube on the dispersant, effectively inhibit the agglomeration of the carbon nanotube in the slurry, improve the storage stability and processing consistency of the slurry, and finally improve the electrochemical performance consistency of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a lithium-ion battery positive electrode slurry and its preparation method, and a lithium-ion battery positive electrode sheet and its preparation method. Background Technology

[0002] In lithium-ion battery cathode slurry systems, carbon nanotubes (CNTs) are typically introduced as conductive components to improve electrode conductivity.

[0003] In existing technologies, CNTs are often dispersed in a solvent using polymer dispersants to obtain a suspension, which is then mixed with active materials (such as LFP and NCM), binders (such as PVDF), and solvents (such as NMP) to prepare the cathode slurry. However, CNTs have a high specific surface area, and due to van der Waals forces, if CNTs lose the steric hindrance and static resistance of the dispersant, they are prone to aggregation. In particular, the active material and CNTs compete for the adsorption of dispersant molecules. Since the active material usually has a larger amount added, a larger total surface area, and a stronger adsorption tendency, it will continuously compete for the adsorption of dispersant molecules from the system. Even if a pre-dispersed CNT suspension is used, after mixing, the dispersant molecules already adsorbed on its surface may be reduced due to the presence of the active material, causing CNTs to be re-exposed and aggregate. This process is called harmful interfacial adsorption reconstruction. If the CNT dispersant is not stable during the cathode slurry preparation process, the CNTs are prone to forming conductive aggregates, making them difficult to redisperse uniformly. This can lead to issues such as excessively low or high levels of conductive agent in certain areas, unstable viscosity, and poor batch-to-batch consistency, hindering large-scale continuous coating production. The slurry's inhomogeneity directly results in poor uniformity of the prepared electrode coating, leading to an incomplete and unevenly distributed conductive network within the electrode. This, in turn, causes uneven internal resistance distribution, inconsistent capacity and rate performance, and rapid cycle life degradation, reducing the overall reliability and lifespan of the battery pack and making it difficult to meet the stringent consistency requirements of high-end applications. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a lithium-ion battery cathode slurry and its preparation method, as well as a lithium-ion battery cathode sheet and its preparation method. The preparation method provided by this invention can effectively suppress the agglomeration of carbon nanotubes in the cathode slurry, and the resulting lithium-ion battery cathode slurry has high stability and high consistency, meeting the application requirements of high-performance batteries.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a lithium-ion battery cathode slurry, comprising the following steps: A lithium-ion battery positive electrode active material, conductive carbon black, a first dispersant, and a first solvent are mixed and subjected to a first dispersion treatment to obtain a first dispersion system; the first dispersant is added at 0.8 to 1.6 times the saturated adsorption capacity of the lithium-ion battery positive electrode active material. The first dispersion system is mixed with the binder and subjected to a second dispersion treatment to obtain a second dispersion system; The second dispersion system is mixed with the carbon nanotube conductive slurry and then subjected to a third dispersion treatment to obtain a third dispersion system; the carbon nanotube conductive slurry is a dispersion composed of carbon nanotubes, a second dispersant, and a second solvent. The third dispersion system is mixed with the third solvent and subjected to a fourth dispersion treatment to obtain the lithium-ion battery cathode slurry.

[0006] Preferably, the first dispersant and the second dispersant independently comprise one or more of ionic dispersants, nonionic dispersants, and cellulose derivatives, wherein the ionic dispersant comprises sodium dodecylbenzenesulfonate and / or sodium dodecyl sulfonate, and the nonionic dispersant comprises one or more of polyvinylpyrrolidone, polyvinyl alcohol, and polyphosphate dispersants.

[0007] Preferably, the method for determining the saturated adsorption amount includes the following steps: The first dispersant and the first solvent were mixed to prepare a series of first dispersant solutions of different concentrations; The positive electrode active material of the lithium-ion battery is mixed with the first dispersant solution of the series concentrations and shaken until adsorption equilibrium is reached; the mixtures obtained at adsorption equilibrium are centrifuged and the concentration of the residual first dispersant in the corresponding supernatant is measured. The concentration of the residual first dispersant in the supernatant is the equilibrium concentration of the first dispersant. The adsorption amount of the lithium-ion battery positive electrode active material on the dispersant is calculated based on the initial concentration and corresponding equilibrium concentration of the first dispersant solution of each series concentration; an adsorption isotherm is plotted with the equilibrium concentration as the abscissa and the adsorption amount as the ordinate, and the saturated adsorption amount is obtained by data fitting.

[0008] Preferably, the concentration range of the first dispersant solution of the series concentrations is 0~50 mg / g, and is not 0; the mass ratio of the lithium-ion battery positive electrode active material to the first dispersant solution of the series concentrations is 1:(10~200).

[0009] Preferably, the temperature of the oscillation treatment is 25±2℃, and the oscillation frequency is 50~500rpm.

[0010] Preferably, the mass ratio of the carbon nanotubes to the second dispersant is (0.2~10):1; the D90 particle size of the carbon nanotubes in the carbon nanotube conductive slurry is ≤2μm.

[0011] Preferably, based on the total mass of the lithium-ion battery positive electrode active material, binder, carbon nanotubes and conductive carbon black in the lithium-ion battery positive electrode slurry, the mass percentages of the lithium-ion battery positive electrode active material, binder, carbon nanotubes and conductive carbon black are 96.5~98.0%, 1.0~2.0%, 0.2~0.8% and 0.5~1.5%, respectively.

[0012] This invention provides a lithium-ion battery cathode slurry prepared by the preparation method described above.

[0013] The present invention provides a positive electrode sheet for a lithium-ion battery, comprising a current collector and a positive electrode material composited on the surface of the current collector, wherein the positive electrode material is formed from the lithium-ion battery positive electrode slurry described in the above technical solution.

[0014] This invention provides a method for preparing the positive electrode sheet of a lithium-ion battery as described above, comprising the following steps: The lithium-ion battery positive electrode slurry is coated onto the surface of the current collector, and then dried and compacted in sequence to obtain the lithium-ion battery positive electrode sheet.

[0015] This invention provides a method for preparing a positive electrode slurry for lithium-ion batteries. By scientifically quantifying the dispersant and controlling the order of addition—"pre-adsorption and site occupancy of the main material (i.e., the positive electrode active material) followed by the addition of carbon nanotube conductive slurry"—this invention solves the problem of carbon nanotube (CNT) agglomeration in the positive electrode slurry. Specifically, the method is as follows: Step 1: Pre-meet the adsorption requirements of the main material. The saturated adsorption capacity of the dispersant on the positive electrode active material is precisely determined experimentally. Based on this quantitative data, the active material is mixed with a sufficient amount of dispersant in the initial stage to ensure that its surface adsorption points are completely saturated, forming a stable pre-adsorption site-occupying state of the dispersant. Step 2: Creating a stable dispersion environment for CNTs. The pre-dispersed main material that has achieved pre-adsorption is mixed with the independently prepared CNT conductive paste with excellent dispersion. At this point, there is no longer any driving force for the main material surface to compete for the adsorption of the dispersant, and the dispersant in the CNT conductive paste can stably maintain the dispersion state of CNTs, thereby completely avoiding secondary agglomeration after mixing.

[0016] This invention fundamentally avoids the harmful competitive adsorption of dispersants between the positive electrode active material and carbon nanotubes. This method effectively inhibits the aggregation of carbon nanotubes in the positive electrode slurry, improves the storage stability and processing consistency of the positive electrode slurry, thereby achieving uniform dispersion of carbon nanotubes in the electrode, constructing a stable and complete conductive network, and ultimately improving the electrochemical performance consistency of lithium-ion batteries.

[0017] The present invention provides a lithium-ion battery cathode slurry prepared by the preparation method described above. The lithium-ion battery cathode slurry provided by the present invention has high stability and high consistency, excellent storage stability and rheological properties, and is suitable for large-scale continuous production of electrode sheets, ensuring the uniformity of electrode coating.

[0018] This invention provides a positive electrode sheet for lithium-ion batteries, which can be used to assemble lithium-ion batteries with excellent performance and high consistency, thereby improving the battery's capacity, rate performance, cycle life, and batch consistency, and meeting the application requirements of high-performance batteries. Attached Figure Description

[0019] Figure 1 The adsorption isotherm and its Langmuir model fitting curve are from Example 1; Figure 2 This is a microscopic morphology diagram of the electrode sheet in Example 1; Figure 3 The image shows the microstructure of the electrode in Comparative Example 1. Figure 4 The image shows the microstructure of the electrode in Comparative Example 4. Figure 5 This is a microscopic morphology diagram of the electrode in Comparative Example 5. Detailed Implementation

[0020] This invention provides a method for preparing a lithium-ion battery cathode slurry, comprising the following steps: A lithium-ion battery positive electrode active material, conductive carbon black, a first dispersant, and a first solvent are mixed and subjected to a first dispersion treatment to obtain a first dispersion system; the first dispersant is added at 0.8 to 1.6 times the saturated adsorption capacity of the lithium-ion battery positive electrode active material. The first dispersion system is mixed with the binder and subjected to a second dispersion treatment to obtain a second dispersion system; The second dispersion system is mixed with the carbon nanotube conductive slurry and then subjected to a third dispersion treatment to obtain a third dispersion system; the carbon nanotube conductive slurry is a dispersion composed of carbon nanotubes, a second dispersant, and a second solvent. The third dispersion system is mixed with the third solvent and subjected to a fourth dispersion treatment to obtain the lithium-ion battery cathode slurry.

[0021] Unless otherwise specified, all raw materials involved in this invention are commercially available products well known in the art.

[0022] The present invention mixes lithium-ion battery positive electrode active material, conductive carbon black, a first dispersant and a first solvent, and performs a first dispersion treatment to obtain a first dispersion system.

[0023] This invention does not impose any special requirements on the positive electrode active material (also referred to as the main material) of the lithium-ion battery. Commonly used active materials for lithium-ion batteries can be used, such as lithium iron phosphate (LFP), lithium cobalt oxide (LCO), lithium manganese iron phosphate, lithium manganese oxide, and NCM materials with different nickel-cobalt-manganese ratios. This invention does not impose any special requirements on the conductive carbon black; conductive carbon black well-known to those skilled in the art, such as SP, can be used. This invention does not impose any special requirements on the first solvent; commonly used solvents for lithium-ion battery positive electrode slurries can be used, such as N-methylpyrrolidone (NMP) or deionized water. In this invention, the first dispersant preferably includes one or more of ionic dispersants, non-ionic dispersants, and cellulose derivatives. The ionic dispersant preferably includes sodium dodecylbenzenesulfonate and / or sodium dodecyl sulfonate. The non-ionic dispersant preferably includes one or more of polyvinylpyrrolidone (PVP, such as K30), polyvinyl alcohol, and polyphosphate dispersants. The cellulose derivative can be sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose.

[0024] In this invention, the first dispersant is defined according to the saturation adsorption capacity (Q) of the lithium-ion battery positive electrode active material on the dispersant. max 0.8 to 1.6 times (i.e., 0.8Q) max ~1.6Q max Preferably 1.0Q max ~1.4Q max It can be 1.0Q max 1.1Q max 1.2Q max 1.3Q max 1.4Q max Add the adsorption. In this invention, the method for determining the saturated adsorption amount preferably includes the following steps: The first dispersant and the first solvent were mixed to prepare a series of first dispersant solutions of different concentrations; The positive electrode active material of the lithium-ion battery is mixed with the first dispersant solution of the series concentrations and shaken until adsorption equilibrium is reached; the mixtures obtained at adsorption equilibrium are centrifuged and the concentration of the residual first dispersant in the corresponding supernatant is measured. The concentration of the residual first dispersant in the supernatant is the equilibrium concentration of the first dispersant. The adsorption amount of the lithium-ion battery positive electrode active material on the dispersant is calculated based on the initial concentration and corresponding equilibrium concentration of the first dispersant solution of each series concentration; an adsorption isotherm is plotted with the equilibrium concentration as the abscissa and the adsorption amount as the ordinate, and the saturated adsorption amount is obtained by data fitting.

[0025] In this invention, the concentration range of the first dispersant solution of the series of concentrations is preferably 0~50 mg / g (and not 0), specifically determined according to the adsorption properties of the active material and the dispersant. The number of the first dispersant solutions of the series of concentrations is preferably greater than 6, more preferably greater than 8. In the embodiments of this invention, lithium iron phosphate was used as the active material and polyvinylpyrrolidone was used as the dispersant, and first dispersant solutions with concentrations of 0.02, 0.05, 0.10, 0.20, 0.50, 1.00, 2.00, 3.00, 5.00, and 10.00 mg / g were prepared respectively.

[0026] In this invention, the preferred mass ratio of the lithium-ion battery positive electrode active material to a series of concentrations of the first dispersant solution is 1:(10~200); the lithium-ion battery positive electrode active material is preferably dried before use, preferably under vacuum, and the preferred temperature for vacuum drying is 120°C. Preferably, the lithium-ion battery positive electrode active material is placed in a series of centrifuge tubes, and a series of concentrations of the first dispersant solution are added to each, ensuring a homogeneous solid-liquid system. In this invention, the preferred temperature for the oscillation treatment is 25±2°C, more preferably 25±1°C (25±0.5°C in this embodiment), and the preferred oscillation frequency is 50~500 rpm, more preferably 100~300 rpm, and can be 200 rpm. Preferably, the centrifuge tubes are sealed before oscillation treatment; the oscillation treatment can be mechanical oscillation, vortex oscillation, ultrasonic-assisted oscillation, or a combination thereof. In this embodiment, a constant-temperature oscillator is used for mechanical oscillation to ensure uniform system temperature and eliminate the influence of temperature on adsorption equilibrium. In this invention, the centrifugation separation is preferably ultracentrifugation separation, and the centrifugation conditions are preferably: relative centrifugal force > 40000×g (can be > 80000×g), centrifugation duration > 60 min (can be ≥ 120 min). After centrifugation, the supernatant is collected and filtered to determine the concentration of the residual first dispersant in the supernatant; the filtration is preferably performed through a 0.22 μm polytetrafluoroethylene needle filter. In this invention, the method for determining the concentration of the residual first dispersant in the supernatant (i.e., the equilibrium concentration of the first dispersant) is adjusted according to the solvent type and dispersant type, and techniques such as UV-VIS-NIR, TOC (total organic carbon), and gel permeation chromatography can be used. This invention does not have special requirements for the specific operation and test conditions for testing the concentration of the residual first dispersant in the supernatant using UV-VIS-NIR, TOC, or gel permeation chromatography techniques; operation and test conditions familiar to those skilled in the art can be used.

[0027] In this invention, the calculation of the adsorption amount of the lithium-ion battery positive electrode active material on the first dispersant based on the initial concentration and corresponding equilibrium concentration of the first dispersant solution of each series of concentrations is specifically calculated according to formula (1): Formula (1), Where Q is the adsorption amount of the first dispersant by a unit mass of lithium-ion battery positive electrode active material (mg / g), C0 is the initial concentration of the first dispersant solution in each series of concentrations (mg / g), and C e For equilibrium concentration (mg / g), m1 is the mass (g) of the first dispersant solution, and m2 is the mass (g) of the positive electrode active material of the lithium-ion battery.

[0028] In this invention, the data fitting is performed using a suitable adsorption isotherm model (confirmed by goodness of fit, etc.), such as the Langmuir model or the Freundlich model (to meet the goodness of fit R). 2 The saturated adsorption amount is determined by using >0.90 as the standard.

[0029] In existing slurry mixing processes, the amount of dispersant added is mostly determined based on a broad range of experience or repeated trial and error, lacking precise guidance on the interaction between specific active materials and dispersants. Insufficient addition leads to poor dispersion, while excessive addition may cause abnormal slurry viscosity, deterioration of electrode electrochemical stability, and increased costs. This invention uses the determination of the saturated adsorption capacity of the dispersant on the positive electrode active material as the core basis for quantitative addition, replacing experience-based trial and error, achieving precise control and optimization of the process, and reducing the amount of dispersant used.

[0030] In this invention, the first dispersion treatment can employ a dual planetary mixer or a twin-screw mixer. In this embodiment, the first dispersion treatment specifically employs a dual planetary mixer. Under vacuum conditions, the mixture is first stirred at a low speed (5 / 10 rpm) for 5 minutes to wet the material, and then switched to a high speed (30 / 60 rpm) for 120 minutes to disperse. After the first dispersion treatment, the surface of the positive electrode active material reaches adsorption saturation, forming a stable pre-adsorbed dispersant structure. In this invention, the first dispersion system is also referred to as the main material pre-dispersion.

[0031] After obtaining the first dispersion system, the present invention mixes the first dispersion system with a binder and performs a second dispersion treatment to obtain the second dispersion system.

[0032] This invention does not have special requirements for the binder; commonly used binders for lithium-ion batteries, such as PVDF, can be used. In this embodiment, the PVDF is added in the form of a PVDF solution with a mass fraction of 6%. Preferably, the binder is added to the first dispersion system. In this invention, the second dispersion treatment can employ a dual planetary mixer or a twin-screw mixer. In this embodiment, the second dispersion treatment specifically employs a dual planetary mixer, stirred at a medium speed (10 / 30 rpm) under vacuum conditions for 60 minutes.

[0033] After obtaining the second dispersion system, the present invention mixes the second dispersion system with carbon nanotube conductive slurry and performs a third dispersion treatment to obtain the third dispersion system.

[0034] In this invention, the carbon nanotube conductive paste is a dispersion composed of carbon nanotubes, a second dispersant, and a second solvent. Specifically, the carbon nanotube conductive paste is obtained by mixing and dispersing carbon nanotubes, a second dispersant, and a second solvent. Preferably, the specific surface area of ​​the carbon nanotubes is 200-1000 m². 2 / g, which can be 300~600m 2 / g; the second dispersant preferably includes one or more of ionic dispersants, nonionic dispersants, and cellulose derivatives. The ionic dispersant preferably includes sodium dodecylbenzenesulfonate and / or sodium dodecyl sulfonate. The nonionic dispersant preferably includes one or more of polyvinylpyrrolidone (PVP, such as K30), polyvinyl alcohol, and polyphosphate dispersants. The cellulose derivative can be sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose. The second dispersant can be the same as or different from the first dispersant. In this invention, the mass ratio of the carbon nanotubes to the second dispersant is preferably (0.2~10):1, and can be (2~5):1, specifically determined according to the specific surface area of ​​the carbon nanotubes and the type of dispersant. This invention does not have special requirements for the second solvent; solvents commonly used in lithium-ion battery cathode slurries, such as NMP, can be used. In this invention, the D90 particle size of the carbon nanotubes in the carbon nanotube conductive slurry is preferably ≤2μm (can be <1μm); the dispersion can be carried out using high-energy dispersion equipment such as sand mill, homogenizer, emulsifier, etc., to meet the above-mentioned D90 particle size requirement; in the embodiment of the invention, the dispersion is specifically carried out using a sand mill, with zirconia beads as the grinding medium.

[0035] Preferably, carbon nanotube conductive slurry is added to the second dispersion system in this invention. In this invention, the third dispersion treatment can be performed using a dual planetary mixer or a twin-screw mixer. In this embodiment, the third dispersion treatment specifically uses a dual planetary mixer, and is performed under vacuum conditions at a medium speed (revolution / revolution: 10 / 30 rpm) for 60 minutes.

[0036] After obtaining the third dispersion system, the present invention mixes the third dispersion system with the third solvent and performs a fourth dispersion treatment to obtain the lithium-ion battery positive electrode slurry.

[0037] This invention does not have special requirements for the third solvent; any solvent commonly used in lithium-ion battery cathode slurry, such as NMP, can be used. In this invention, the fourth dispersion treatment can employ a dual planetary mixer or a twin-screw mixer. In this embodiment, the fourth dispersion treatment specifically employs a dual planetary mixer, where the mixture is stirred at low speed (5 / 10 rpm) for 30 minutes under vacuum conditions to perform final viscosity adjustment and degassing.

[0038] In this invention, based on the total mass of the lithium-ion battery positive electrode active material, binder, carbon nanotubes and conductive carbon black in the lithium-ion battery positive electrode slurry, the mass percentages of the lithium-ion battery positive electrode active material, binder, carbon nanotubes and conductive carbon black are preferably 96.5~98.0% (can be 97.3%), 1.0~2.0% (can be 1.8%), 0.2~0.8% (can be 0.3%) and 0.5~1.5% (can be 0.6%), respectively.

[0039] In this invention, the solid content of the lithium-ion battery positive electrode slurry is preferably 40-80 wt%, specifically determined according to the type of positive electrode active material. For example, when the positive electrode active material is lithium iron phosphate (LFP), the solid content of the lithium-ion battery positive electrode slurry can be 40-70 wt%; when the positive electrode active material is lithium cobalt oxide (LCO) or NCM material, the solid content of the lithium-ion battery positive electrode slurry can be 50-80 wt%. In this invention, the mass of the first solvent is preferably 20-60% of the total solvent mass in the positive electrode slurry; the mass percentage of the second solvent in the carbon nanotube conductive slurry is preferably 90-99%; and the mass of the third solvent is preferably 5-20% of the total solvent mass in the positive electrode slurry.

[0040] Conventional slurry mixing methods struggle to effectively suppress the aggregation of carbon nanotubes. Furthermore, regardless of whether a single-stage mixing or pre-dispersed carbon nanotube slurry is used, the active material competes with the dispersant molecules when the positive electrode active material and carbon nanotubes coexist. This weakens or destroys the original dispersant coating on the carbon nanotube surface, leading to secondary aggregation of the carbon nanotubes in the final slurry, rendering the pre-existing dispersion efforts futile. Due to these dispersion and adsorption issues, the resulting slurry is prone to sedimentation and exhibits significant viscosity variations over time. This not only increases the difficulty of the coating process but also causes fluctuations in electrode coating quality between different batches and even within the same batch, impacting the efficiency and product yield of large-scale production. This invention experimentally determines the saturated adsorption capacity of the dispersant on the positive electrode active material, and uses this as the core basis for quantitative addition, replacing trial and error based on experience, and achieving precise control and optimization of the process. By adding materials in the order of "pre-adsorption and site occupancy of the main material first, followed by addition of carbon nanotube conductive slurry", harmful competitive adsorption between the active material and carbon nanotubes is fundamentally avoided, ensuring that the dispersion stability of carbon nanotubes is maintained after final slurry mixing, thereby obtaining a positive electrode slurry with high stability and high consistency.

[0041] This invention provides a lithium-ion battery cathode slurry prepared by the preparation method described above.

[0042] The lithium-ion battery cathode slurry provided by this invention can effectively suppress carbon nanotube aggregation, has excellent storage stability and rheological properties, is suitable for large-scale continuous production of electrodes, and ensures the uniformity of electrode coating.

[0043] The present invention provides a positive electrode sheet for a lithium-ion battery, comprising a current collector and a positive electrode material composited on the surface of the current collector, wherein the positive electrode material is formed from the lithium-ion battery positive electrode slurry described in the above technical solution.

[0044] The present invention does not have any special requirements for the current collector; commonly used current collectors for lithium-ion batteries, such as aluminum foil, can be used.

[0045] The lithium-ion battery positive electrode sheet provided by this invention has low resistance. With the lithium-ion battery positive electrode sheet provided by this invention, high-performance and highly consistent lithium-ion batteries can be assembled, reducing the internal resistance of the battery, improving the battery's capacity, rate performance, cycle life and batch consistency, and meeting the application requirements of high-performance batteries.

[0046] This invention provides a method for preparing the positive electrode sheet of a lithium-ion battery as described above, comprising the following steps: The lithium-ion battery positive electrode slurry is coated onto the surface of the current collector, and then dried and compacted in sequence to obtain the lithium-ion battery positive electrode sheet.

[0047] This invention does not have specific requirements for the coating method; any coating method well-known to those skilled in the art can be used to ensure uniform coating of the slurry. The preferred coating thickness is 200 μm. In this invention, the drying is preferably staged drying; specifically, after preliminary drying in a 110°C convection oven, it is transferred to a 120°C vacuum oven for thorough drying. In this invention, a roller press (such as a double roller press) can be used to compact the dried electrode sheet to a predetermined compaction density (which can be 2.40 ± 0.05 g / cm³). 3 After compaction, the electrode sheet can be cut to the required specifications.

[0048] This invention also provides a lithium-ion battery using the positive electrode sheet described in the above technical solution. This invention does not impose special requirements on other electrode materials and electrolytes of the lithium-ion battery; appropriate electrode materials and electrolytes well-known to those skilled in the art can be used. In the embodiments of this invention, the positive electrode sheet of the lithium-ion battery is used as the working electrode, a lithium metal sheet as the counter electrode and reference electrode, a polyolefin microporous membrane as the separator, and a carbonate electrolyte containing lithium salt (such as LiPF6) is injected. The cells are then assembled into CR2032 type coin cell half-cells under a dry atmosphere. For full-cell testing, graphite negative electrodes need to be prepared in pairs and assembled into pouch cells or cylindrical cells according to standard processes.

[0049] To further illustrate the present invention, the following detailed description, in conjunction with examples, of the lithium-ion battery positive electrode slurry and its preparation method and the lithium-ion battery positive electrode sheet and its preparation method provided by the present invention, shall not be construed as limiting the scope of protection of the present invention.

[0050] Example 1: Preparation of LFP system cathode slurry, electrode sheet and battery 1. Precise determination of the saturated adsorption capacity of the dispersant To obtain a scientific benchmark for dispersant dosage, the concentration of polyvinylpyrrolidone (PVP, K30) in lithium iron phosphate (LFP, D50 = 1.2 μm, specific surface area ~12 m²) was first determined. 2 The saturated adsorption capacity on (g). The specific steps are as follows: PVP was dissolved in N-methylpyrrolidone (NMP) to prepare solutions with concentration gradients of 0.02, 0.05, 0.10, 0.20, 0.50, 1.00, 2.00, 3.00, 5.00, and 10.00 (mg / g). 1.0000 g (±0.0010 g) of LFP sample, vacuum-dried at 120 °C, was accurately weighed and placed in a series of 200 mL NMP-resistant centrifuge tubes. 100.00 g of the above solution was added to each tube to ensure homogeneity of the solid-liquid system. The centrifuge tubes were sealed and placed in a constant-temperature shaker at 25.0±0.5 °C, continuously shaken at 200 rpm for 24 h to ensure adsorption equilibrium was reached.

[0051] After equilibration, the centrifuge tubes were placed in an ultracentrifuge and centrifuged at a relative centrifugal force of 100,000 × g for 120 min to achieve complete sedimentation of the solid phase. The supernatant from the middle of the centrifuge tube was carefully aspirated using a micropipette, avoiding disturbance of the bottom precipitate, and filtered through a 0.22 μm polytetrafluoroethylene (PTFE) syringe filter to obtain a clear test solution. The filter was rinsed with NMP before use. The concentration of free PVP in the clear test solution was determined using gel permeation chromatography-differential refractive index (DRCI). The mobile phase was N-methylpyrrolidone containing lithium bromide, the column was an organic phase size exclusion column compatible with N-methylpyrrolidone, and the detector was a DCI detector.

[0052] A standard solution of PVP of the same brand as the dispersant in the test system was prepared, and the peak area of ​​the PVP polymer was measured under the same chromatographic conditions to establish a standard curve between PVP concentration and peak area. The clarified test solution was injected and analyzed under the same chromatographic conditions. The polymer peak corresponding to PVP in the sample was integrated, and the equilibrium concentration Ce(C) of free PVP in the supernatant after adsorption equilibrium was calculated according to the calibration relationship. e (Unit: mg / g), calculate the adsorption capacity Q (mg / g) per unit mass of LFP according to formula (1): (1); In formula (1), C0 is the initial concentration (mg / g), m1 is the solution mass (100.00g), and m2 is the LFP mass (1.0000g).

[0053] Then, at equilibrium concentration C e Adsorption isotherms were plotted with K as the x-axis and the adsorption amount Q as the y-axis. The Langmuir adsorption model (formula (2), where K is the adsorption equilibrium constant) was used to fit the data, and the goodness of fit R0 was determined. 2 >0.95. Figure 1 The adsorption isotherm and its Langmuir model fitting curve are shown in Table 1. The saturated adsorption capacity Q is obtained. max ≈1.59mg / g.

[0054] (2).

[0055] Table 1. Fitting results of the Langmuir model

[0056] 2. Based on Q max Preparation of positive electrode slurry The core of this invention lies in Q max The total amount of dispersant to be added is determined, and a specific feeding sequence is adopted. The specific steps in this embodiment are as follows: (1) Formulation design: The fixed mass ratio of the main solid materials (excluding dispersant) is determined to be LFP:PVDF (binder):CNT (carbon nanotubes):SP (conductive carbon black) = 97.3:1.8:0.3:0.6. The amount of LFP is set at 973.0g. Based on this ratio, the amounts of other components are calculated as follows: PVDF dosage = 973.0g × (1.8 / 97.3) = 18.00g CNT dosage = 973.0g × (0.3 / 97.3) = 3.00g SP dosage = 973.0g × (0.6 / 97.3) = 6.00g Total mass of solids (excluding dispersant) = 973.0 + 18.00 + 3.00 + 6.00 = 1000.00 g.

[0057] Dispersant quantification: based on the aforementioned measured Q max Based on (1.59 mg / g) and a multiplier of 1.3, the amount of external dispersant PVP is calculated to be ~2.07 g. This portion of PVP will be added entirely during the pre-dispersion stage of the main material.

[0058] (2) Slurry preparation process: (2.1) Pre-adsorption dispersion of main materials: 973.0g LFP, 6.00g SP, and all 2.07g PVP, along with the first portion of NMP (420g), were added to a dual planetary mixer. Under a vacuum of <-0.095MPa, the mixture was first stirred at a low speed (5 / 10 rpm) for 5 minutes to wet the materials, and then the speed was switched to high speed (30 / 60 rpm) for 120 minutes to disperse the materials. The core purpose of this step is to saturate the LFP surface with adsorption and form a stable pre-adsorption structure of the dispersant.

[0059] (2.2) Independent preparation of CNT conductive paste: In another container, 20.00g of CNT (385m) conductive paste was prepared separately. 2 The mixture of 10.0g PVP (an additional dispersant separate from the above 2.07g, specifically for CNT dispersion) and 970g NMP was used as the grinding medium in a sand mill at a linear velocity of 13m / s for 2 hours until the particle size distribution D90 was measured to be <1.0μm.

[0060] (2.3) Sequential mixing: Add the pre-dissolved PVDF solution (6%, 18.00g PVDF dissolved in NMP) to the pre-dispersed main material obtained in step (2.1). In the same stirring equipment, vacuum stir at medium speed (10 / 30 rpm) for 60 min. Then, add 150g of CNT conductive paste prepared in step (2.2) (CNT content is 3.00g), and continue stirring under the same conditions for 60 min to ensure uniform mixing.

[0061] (2.4) Viscosity Adjustment and Degassing: Add the remaining NMP (150g) to make up the total solvent. Finally, stir for 30 min at low speed (5 / 10 rpm) and under vacuum to perform final viscosity adjustment and degassing, obtaining a uniform, stable, and suitable flowable final cathode slurry. The viscosity was measured to be 4500±500 mPa·s using a rotational viscometer at 25℃ and 20 rpm.

[0062] (3) Preparation of electrode sheets and batteries and system testing The above slurry was uniformly coated onto a 12μm thick aluminum foil current collector to a set wet film thickness of 200μm. After preliminary drying in a 110℃ convection oven, it was transferred to a 120℃ vacuum oven for thorough drying for 6 hours. The electrode sheet was then compacted to 2.40±0.05g / cm² using a roller mill at room temperature. 3 The compaction density was determined. The electrode resistance was measured using a two-probe resistance meter, repeated nine times at different locations. The average value and standard deviation were calculated to evaluate the electrode conductivity uniformity. The electrodes were then cut into 14mm diameter discs.

[0063] In a glove box, using the aforementioned electrode as the positive electrode and a lithium metal sheet as the negative electrode, a suitable amount of 1.0M LiPF6 in EC / DMC / EMC (volume ratio 1:1:1) electrolyte was added to assemble a CR2032 coin cell. After standing for 12 hours, tests were conducted at a constant temperature of 25℃. First, activation was performed by charge-discharge at a rate of 0.1C (1C=170mA / g), followed by rate performance tests (charge-discharge at 0.2C, 0.5C, 1C, and 2C rates, respectively). The electrochemical impedance spectroscopy of the battery was measured using an electrochemical workstation in the frequency range of 1MHz to 0.01Hz and an amplitude of 5mV. The charge transfer resistance (Rct) value was obtained by equivalent circuit fitting.

[0064] Comparative Example 1 Comparative Example 1 used the same main solid materials as Example 1 (LFP 973.0g, PVDF 18.00g, CNT 3.00g, SP 6.00g) and a total added PVP amount of 2.07g. The key difference in its preparation process compared to Example 1 lies in the order of material addition: First, CNT conductive paste was prepared independently using the same method as in Example 1. Then, in a mixer, all PVP (2.07g), CNT conductive paste, PVDF solution (6wt%, obtained by dissolving 18.00g of PVDF in NMP), and most of the NMP solvent (420g) were mixed at once. Finally, the dry powder mixture of LFP and SP was added to the above liquid and dispersed at a high speed with a total duration and intensity comparable to Example 1; the remaining NMP (150g) was added to replenish the total solvent, and the final viscosity adjustment and degassing were performed using the same procedures as in Example 1.

[0065] Comparative Example 2 Comparative Example 2 used the exact same main solid materials and total added PVP (2.07g) as Example 1. The difference was that all the dispersant was integrated into the CNT slurry preparation stage: that is, all 2.07g of PVP was used to prepare the CNT slurry (in the CNT slurry preparation process, in addition to the PVP originally used for CNT dispersion, extra PVP was added, with an additional PVP:CNT ratio of 2.07:3.00), and no dispersant was added during the pre-dispersion stage of the main materials (LFP and SP). The subsequent slurry mixing steps were the same as in Comparative Example 1, that is, this CNT slurry was mixed with PVDF solution, solvent, and LFP+SP dry powder. This scheme aimed to test the effect of "concentrating all dispersant resources on CNT dispersion".

[0066] Comparative Example 3 Comparative Example 3 used the exact same main solid material and feeding sequence as Example 1. The difference was that the total amount of externally added PVP was significantly reduced to 0.5Q. maxThe calculated addition amount is: 973.0g × 1.59mg / g × 0.5 ≈ 769mg, or 0.773g. This comparative example is used to verify the effect on the system when the amount of dispersant added is below the scientifically recommended range based on the saturated adsorption capacity.

[0067] Comparative Example 4 Comparative Example 4 used the exact same main solid materials and total added PVP (0.773g) as Comparative Example 3. The difference was that the dispersant addition order was the same as Comparative Example 1: that is, PVP, LFP, SP, CNT conductive paste, PVDF solution and all NMP were mixed evenly in a similar manner to Comparative Example 1, except that the amount of PVP added was changed from 2.07g to 0.773g.

[0068] Comparative Example 5 Comparative Example 5 used the exact same main solid material as Example 1. The difference was that the total amount of added PVP was increased to 2.5Q. max Furthermore, the feeding sequence followed the non-preferred sequence of Comparative Example 1. The PVP addition amount was: 973.0g × 1.59mg / g × 2.5 ≈ 3867mg, or 3.867g. This comparative example was used to investigate whether the effect of the present invention could be achieved simply by adding an excessive amount of dispersant under a non-preferred process.

[0069] All comparative examples, except for Comparative Example 2, maintained strict consistency with Example 1 in CNT slurry preparation, electrode fabrication process parameters, battery assembly specifications, and testing conditions to ensure data comparability. Test results are shown in Table 2.

[0070] Table 2 Summary of test results for both examples and comparative examples

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium-ion battery positive electrode slurry, characterized in that, Includes the following steps: A lithium-ion battery positive electrode active material, conductive carbon black, a first dispersant, and a first solvent are mixed and subjected to a first dispersion treatment to obtain a first dispersion system; the first dispersant is added at 0.8 to 1.6 times the saturated adsorption capacity of the lithium-ion battery positive electrode active material. The first dispersion system is mixed with the binder and subjected to a second dispersion treatment to obtain a second dispersion system; The second dispersion system is mixed with the carbon nanotube conductive slurry and then subjected to a third dispersion treatment to obtain a third dispersion system; the carbon nanotube conductive slurry is a dispersion composed of carbon nanotubes, a second dispersant, and a second solvent. The third dispersion system is mixed with the third solvent and subjected to a fourth dispersion treatment to obtain the lithium-ion battery cathode slurry.

2. The preparation method according to claim 1, characterized in that, The first and second dispersants independently include one or more of ionic dispersants, nonionic dispersants, and cellulose derivatives, wherein the ionic dispersants include sodium dodecylbenzenesulfonate and / or sodium dodecyl sulfonate, and the nonionic dispersants include one or more of polyvinylpyrrolidone, polyvinyl alcohol, and polyphosphate dispersants.

3. The preparation method according to claim 1, characterized in that, The method for determining the saturated adsorption amount includes the following steps: The first dispersant and the first solvent were mixed to prepare a series of first dispersant solutions of different concentrations; The positive electrode active material of the lithium-ion battery is mixed with the first dispersant solution of the series concentrations and shaken until adsorption equilibrium is reached; the mixtures obtained at adsorption equilibrium are centrifuged and the concentration of the residual first dispersant in the corresponding supernatant is measured. The concentration of the residual first dispersant in the supernatant is the equilibrium concentration of the first dispersant. The adsorption amount of the lithium-ion battery positive electrode active material on the dispersant is calculated based on the initial concentration and corresponding equilibrium concentration of the first dispersant solution of each series concentration; an adsorption isotherm is plotted with the equilibrium concentration as the abscissa and the adsorption amount as the ordinate, and the saturated adsorption amount is obtained by data fitting.

4. The preparation method according to claim 3, characterized in that, The concentration range of the first dispersant solution of the series concentrations is 0~50mg / g, and is not 0; the mass ratio of the lithium-ion battery positive electrode active material to the first dispersant solution of the series concentrations is 1:(10~200).

5. The preparation method according to claim 3, characterized in that, The oscillation treatment temperature is 25±2℃, and the oscillation frequency is 50~500rpm.

6. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of the carbon nanotubes to the second dispersant is (0.2~10):1; the D90 particle size of the carbon nanotubes in the carbon nanotube conductive slurry is ≤2μm.

7. The preparation method according to claim 1, characterized in that, Based on the total mass of the lithium-ion battery positive electrode active material, binder, carbon nanotubes and conductive carbon black in the lithium-ion battery positive electrode slurry, the mass percentages of the lithium-ion battery positive electrode active material, binder, carbon nanotubes and conductive carbon black are 96.5~98.0%, 1.0~2.0%, 0.2~0.8% and 0.5~1.5%, respectively.

8. The lithium-ion battery cathode slurry prepared by the preparation method according to any one of claims 1 to 7.

9. A positive electrode sheet for a lithium-ion battery, characterized in that, It includes a current collector and a positive electrode material composited on the surface of the current collector, the positive electrode material being formed from the lithium-ion battery positive electrode slurry of claim 8.

10. The method for preparing the positive electrode sheet of a lithium-ion battery according to claim 9, characterized in that, Includes the following steps: The lithium-ion battery positive electrode slurry is coated onto the surface of the current collector, and then dried and compacted in sequence to obtain the lithium-ion battery positive electrode sheet.

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