Lithium battery negative electrode slurry and preparation method thereof

Abstract

This invention discloses a lithium-ion battery negative electrode slurry and its preparation method. The dry matter of the slurry is composed of the following components by mass percentage: 0.5%–2% conductive agent, 1.7%–2.2% binder, 0.5%–2% thickener, with the balance being negative electrode active material. The conductive agent is conductive carbon black, the thickener is sodium carboxymethyl cellulose, and the binder is a mixture of polyacrylic acid binder and styrene-butadiene rubber binder. The lithium-ion battery negative electrode slurry provided by this invention employs a polyacrylic acid and styrene-butadiene rubber composite binder system, which leverages the high bonding strength and low impedance advantages of PAA while imparting good flexibility to the electrode sheet through SBR, significantly reducing the brittleness and material shedding risk of the electrode sheet. Simultaneously, the slurry does not exhibit a blue discoloration phenomenon, demonstrates excellent stability, and the coated negative electrode sheet has high peel strength and low electrode resistance, effectively suppressing electrode sheet expansion and roller sticking problems, thereby improving the rate performance, low-temperature discharge performance, and cycle life of the lithium-ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a lithium battery negative electrode slurry and its preparation method. Background Technology

[0002] Lithium-ion batteries, with their advantages of high operating voltage, long cycle life, and high energy density, have become the most widely used energy storage devices. As a key component of lithium batteries, the dispersion uniformity, stability, and bonding performance of the negative electrode slurry directly affect the battery's cycle life, rate performance, and safety. Currently, commonly used binder systems in negative electrode slurries include polyacrylic acid (PAA) and styrene-butadiene rubber (SBR). PAA provides high bonding strength and low impedance, while SBR imparts good flexibility to the electrode. However, achieving the synergistic effect of the two binders while avoiding problems such as "blueing" and viscosity runaway in the slurry remains a pressing technical challenge to be solved in this field.

[0003] In existing technologies, to address the issues of uneven dispersion and blue bleed in negative electrode slurries, some solutions employ a single water-based polyacrylate binder to replace the traditional SBR system and optimize the feeding sequence, achieving certain results. For example, Chinese patent CN116093267A discloses a method for preparing a negative electrode slurry, which achieves the effects of preventing blue bleed and improving electrode adhesion by adding a polyacrylate binder at the end. However, this solution completely abandons the flexible SBR binder, leading to increased electrode brittleness and a tendency for material to fall off, affecting the battery's cycle and storage performance. Furthermore, adding the binder in the final step of this solution can easily cause a sharp increase in slurry viscosity in the later stages, affecting not only coating uniformity but also increasing equipment load and production costs. Summary of the Invention

[0004] In view of this, the present invention provides a lithium battery negative electrode slurry and its preparation method. By using a PAA and SBR composite binder and combining it with a specific step-by-step feeding process, the technical problems of high electrode brittleness, material shedding, and excessive viscosity increase are effectively solved while ensuring that the slurry does not float blue and has good stability. This significantly improves the process adaptability of the slurry and the overall performance of the battery.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention discloses a lithium battery negative electrode slurry, the dry matter of which is composed of the following components in mass percentage: Conductive agent 0.5%–2%, Adhesive content: 1.7%–2.2%; Thickener 0.5%–2%; Remaining amount of negative electrode active material; The conductive agent is conductive carbon black, the thickener is sodium carboxymethyl cellulose, and the binder is a mixture of polyacrylic acid binder and styrene-butadiene rubber binder.

[0006] As a further aspect of the present invention: the polyacrylic adhesive is at least one of polyacrylic acid, a derivative of polyacrylic acid, or a copolymer of polyacrylic acid.

[0007] As a further aspect of the present invention: the mass percentage of the polyacrylic acid binder in the negative electrode slurry is 0.7% to 1.7%, and the mass percentage of the styrene-butadiene rubber binder in the negative electrode slurry is 0.6% to 1.3%.

[0008] Secondly, this invention discloses a method for preparing the lithium battery negative electrode slurry as described above, comprising the following steps: S1: Add the thickener to the water and mix well to obtain mixture P1; S2: Add a polyacrylic acid binder to the mixture P1 and mix evenly to obtain mixture P2; S3: Mix the negative electrode active material and the conductive agent evenly to obtain mixture P3; S4: Add the mixture P2 to the mixture P3, knead and disperse to obtain mixture P4; S5: Add a styrene-butadiene rubber binder to the mixture P4 and mix evenly to obtain a lithium battery negative electrode slurry.

[0009] By first pre-dispersing the thickener and PAA-based binder in water to form a glue solution, then dry-mixing the active material and conductive agent, and subsequently adding them step by step to the glue solution for kneading, and finally adding the SBR-based binder, this specific sequence effectively avoids the problems of molecular chain entanglement and a sharp increase in viscosity caused by the simultaneous addition of PAA and SBR.

[0010] As a further aspect of the present invention: in step S1, the stirring speed is 1200–1800 rpm, the stirring time is 0.5–5 h, and the solid content of the mixture P1 is 1%–5%; and / or, In step S2, the stirring speed is 500–1200 rpm, the stirring time is 20–120 min, and the solid content of the mixture P2 is 1%–4%; and / or, In step S3, the stirring speed is 200-500 rpm and the stirring time is 10-60 min.

[0011] Step S1 involves high-speed stirring at 1200-1800 rpm to fully dissolve the CMC and form a homogeneous adhesive solution; Step S2 involves medium-speed dispersion at 500-1200 rpm to avoid high-speed shearing damaging the PAA molecular chain activity; Step S3 involves low-speed dry mixing at 200-500 rpm to ensure the conductive agent adheres uniformly to the surface of the active material. This combination of parameters controls the solid content of the adhesive solution at 1%-5%, providing a suitable initial viscosity window for subsequent stepwise kneading. The fineness of the samples in Examples 1-3 is all controlled within 30 μm, demonstrating the good dispersion effect.

[0012] As a further aspect of the present invention: step S4 specifically involves adding the mixture P2 to the mixture P3 in at least two separate additions; wherein, After adding a portion of the mixture P2 for the first time, stir and knead at a speed of 200–500 rpm for 0.5–3 hours, at which point the solid content will be 60%–80%. After adding the remaining mixture P2 for the second time, stir at 1200-2000 rpm for 0.5-3 hours, add deionized water to adjust the solid content to 40%-60%, and adjust the viscosity to 3000-7000 CP.

[0013] The mixed adhesive solution is added in at least two stages. After the first addition, the mixture is kneaded at low speed for 0.5-3 hours at a high solids content (60%-80%) to ensure that PAA preferentially and fully coats the surface of the active material, enhancing bonding efficiency. After the second addition of the remaining adhesive solution, the mixture is diluted at high speed to a solids content of 40%-60%, achieving overall homogenization of the slurry. This stepwise adhesive addition process significantly inhibits excessive entanglement of PAA molecular chains, avoids false thickening of the slurry, and significantly improves the stability of the slurry.

[0014] By adding PAA adhesive to the negative electrode active material in at least two stages, PAA is preferentially distributed on the surface of graphite and other negative electrode active material particles before the addition of SBR. The PAA has a weight-average molecular weight greater than 1,000,000 Da and an adhesive viscosity not less than 10,000 CP. The carboxyl groups in its molecular chain can interact with polar sites, defect sites, and oxygen-containing functional groups on the surface of the active material particles, thereby improving the wetting state and dispersion stability of the active material particles and forming a stabilizing adsorption layer on the particle surface. The pre-adsorption and staged addition of PAA improves the continuous phase viscoelasticity, interparticle dispersion stability, and the uniformity of SBR latex particle distribution in the slurry system, thereby reducing the tendency of SBR latex particles to accumulate on the slurry surface and suppressing the blueing phenomenon in the slurry.

[0015] As a further aspect of the present invention: the mass of the first added mixture P2 accounts for 60% to 90% of the total mass of the mixture P2. This ratio window is a key parameter after optimization: if it is less than 60%, the initial kneading solid content is insufficient and the PAA does not adequately coat the active material; if it is more than 90%, the amount of glue added in the second time is too small and cannot be effectively diluted and dispersed.

[0016] As a further aspect of the present invention: in step S5, the stirring speed is 15-25 rpm for revolution and 500-1500 rpm for rotation, and the stirring time is 10-60 minutes; after adding the styrene-butadiene rubber binder, water is added to adjust the viscosity to 2000-6000 CP. These gentle stirring conditions prevent the SBR latex particles from breaking down, maintain the integrity of their flexible segments, thereby giving the electrode good flexibility and ensuring the consistency and uniformity of the coating surface density.

[0017] As a further aspect of the present invention: after step S5, a vacuum degassing step is included: the vacuum degree is -80±5kPa, the revolution speed is 15±1rpm, and the processing time is 1~3h. This step effectively removes micro-bubbles inside the slurry, avoids defects such as pinholes and bubbles in the electrode sheet after coating, and improves the smoothness of the coating surface.

[0018] Thirdly, the present invention discloses a negative electrode sheet, comprising a metal foil and a lithium battery negative electrode slurry coated on the surface of the metal foil; the lithium battery negative electrode slurry adopts the above-mentioned lithium battery negative electrode slurry. The lithium battery negative electrode slurry is coated on both sides of a metal foil; the areal density of the negative electrode sheet is 100–260 g / m³. 2 By employing the aforementioned negative electrode slurry of the present invention, the negative electrode sheet achieves an areal density of 100–260 g / m². 2 It maintains good processing and electrochemical performance over a wide range. Specifically, due to the synergistic effect of PAA and SBR composite binder in the slurry and the optimization of slurry stability in the preparation process, the negative electrode sheet has a smooth surface without cracks or material loss after coating and drying, and the compaction density after rolling can reach 1.6 g / cm³. 3 Examples 1-3 were performed at an areal density of 200 g / m³. 2 The negative electrode sheets prepared under these conditions all exhibited good flexibility (only 3 folds of material loss) and bonding strength. In addition, thanks to the low impedance characteristics provided by PAA in the slurry and the flexibility imparted by SBR, the negative electrode sheet can effectively suppress the electrode sheet expansion problem during charging and discharging, and reduce the sticking phenomenon of rollers during coating, thereby improving the rate performance, low temperature discharge performance and cycle life of lithium batteries.

[0019] Compared with the prior art, the beneficial effects of the present invention are: The lithium battery negative electrode slurry provided by this invention adopts a composite binder system of polyacrylic acid and styrene-butadiene rubber (PAA). This system leverages the high bonding strength and low impedance of PAA while using SBR to impart good flexibility to the electrode sheet, significantly reducing the brittleness and risk of material shedding. Simultaneously, the slurry does not exhibit a blue discoloration phenomenon, demonstrates excellent stability, and the coated negative electrode sheet possesses high peel strength and low electrode resistance. This effectively suppresses electrode expansion and roller sticking issues, thereby improving the rate performance, low-temperature discharge performance, and cycle life of the lithium battery.

[0020] The negative electrode slurry preparation method provided by this invention achieves precise control of slurry viscosity by pre-compacting PAA and CMC into a binder solution and employing a specific process flow of dry mixing—stepwise kneading—post-addition of SBR. This effectively avoids the problem of a sharp increase in viscosity caused by the post-addition of binder in traditional processes. This process significantly reduces the viscosity change value of the slurry within 24 hours after preparation, greatly improves viscosity stability, not only improves coating uniformity and consistency, but also reduces damage to equipment, and has good process adaptability and scalability for mass production. Attached Figure Description

[0021] Figure 1 This is a schematic flowchart of the method for preparing the negative electrode slurry in this invention; Figure 2 The viscosity variation curves of the negative electrode slurry in the embodiments and comparative examples of the present invention are shown.

[0022] Figure 3 This is a photograph of the negative electrode slurry of Example 1 of the present invention, showing no blue floating phenomenon on the surface. Detailed Implementation

[0023] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0025] In addition, unless otherwise specified, the preparation processes in the following embodiments are all conventional methods in the prior art, and therefore will not be described in detail; unless otherwise specified, the parts in the following embodiments refer to parts by weight.

[0026] Example 1 (1) Add 0.8 parts of sodium carboxymethyl cellulose thickener and deionized water to a double planetary stirrer, set the revolution speed to 25 rpm and the rotation speed to 1600 rpm, and stir at high speed for 3 hours; at this time the solid content is 1.5±0.5%; (2) Continue to add deionized water and 1 part of PAA adhesive. Set the stirring speed to 25 rpm and the rotation speed to 1200 rpm. Stir for 60 min. The adhesive is dispersed and the solid content is 1.5 ± 0.5%. Take out the adhesive for later use. (3) Add 96 parts of graphite material and 1 part of carbon black conductive agent to a double planetary stirrer, set the revolution speed to 15 rpm and the rotation speed to 600 rpm, and the stirring time to 30 min; (4) Add 80wt% of the mixed adhesive solution from step (2), continue stirring, set the stirring speed to 15rpm and the rotation speed to 600rpm, and perform vacuum kneading for 60min. At this time, the solid content is 70±5%. (5) Add the remaining 20wt% mixed adhesive solution and deionized water, set the stirrer's revolution speed to 25 rpm and rotation speed to 1600 rpm, and stir for 1.5 h. At this time, the solid content is 54±5%. (6) Continue to add deionized water to adjust the viscosity to 3500-4500CP. After the viscosity reaches the standard, add 1.2 parts of SBR binder, set the revolution speed to 15rpm and the rotation speed to 600rpm, stir for 30min, transfer to the transfer tank, and vacuum (-80±5kpa, 15±1rpm, 2h) to obtain the target negative electrode slurry.

[0027] (7) The negative electrode slurry is coated on a coating machine onto the negative electrode current collector. After drying, the surface density is 200 g / m³. 2 A negative electrode sheet with a surface density of (electrode surface density = weight of a negative electrode sheet per unit surface area - weight of foil per unit area).

[0028] Example 2 (1) Add 0.5 parts of sodium carboxymethyl cellulose thickener and deionized water to a double planetary stirrer, set the revolution speed to 25 rpm and the rotation speed to 1600 rpm and stir rapidly for 3 hours; at this time the solid content is 1.5±0.5%; (2) Continue to add deionized water and 0.7 parts of PAA adhesive, set the revolution speed to 25 rpm and the rotation speed to 1200 rpm, stir quickly for 60 min, the adhesive is dispersed, at this time the solid content is 1.5±0.5%, take out the adhesive for later use; (3) Add 97 parts of graphite material and 0.5 parts of carbon black conductive agent to a double planetary stirrer, set the revolution speed to 15 rpm and the rotation speed to 600 rpm, and stir rapidly for 20 min; (4) Add 70wt% of the mixed adhesive solution from step (2), continue stirring, set the stirring speed to 15rpm and the rotation speed to 600rpm, and perform vacuum kneading for 60min. At this time, the solid content is 70±5%. (5) Add the remaining mixture from step (2) and deionized water, set the revolution speed to 25 rpm and the rotation speed to 1600 rpm, and stir rapidly for 1.5 h. At this time, the solid content is 54 ± 5%. (6) Add deionized water to adjust the viscosity to 3500-4500CP. After the viscosity reaches the standard, add 1.3 parts of styrene-butadiene rubber binder, set the revolution speed to 15 rpm and the rotation speed to 600 rpm, stir for 30 min, transfer to the transfer tank, and vacuum (-80±5 kPa, 15±1 rpm, 2 h) to obtain the target negative electrode slurry. (7) The negative electrode slurry is coated on a coating machine onto the negative electrode current collector. After drying, the surface density is 200 g / m³. 2 The negative electrode.

[0029] Example 3 (1) Add 2 parts of CMC thickener and deionized water to a double planetary stirrer, set the stirrer's revolution speed to 25 rpm and its rotation speed to 1600 rpm, and stir for 2 hours; at this time, the solid content is 1.5 ± 0.5%; (2) Continue to add deionized water and 1.1 parts of PAA adhesive, set the stirring speed to 25 rpm and the rotation speed to 1200 rpm, stir for 30 minutes, the adhesive is dispersed, and the solid content is 1.5±0.5%. Take out the adhesive for later use. (3) Add 94.3 parts of graphite material and 2 parts of carbon black conductive agent to a double planetary stirrer, set the revolution speed to 15 rpm and the rotation speed to 600 rpm, and stir for 40 min; (4) Add 60wt% of the mixed adhesive solution from step (2), set the revolution speed to 15rpm and the rotation speed to 600rpm, and perform vacuum kneading for 60min. At this time, the solid content is 70±5%. (5) Add the remaining mixture from step (2) and deionized water, and stir rapidly for 1.5 h at a revolution speed of 25 rpm and a rotation speed of 1600 rpm. At this time, the solid content is 54 ± 5%. (6) Add deionized water to adjust the viscosity to 3500-4500CP. After the viscosity reaches the standard, add 0.6 parts of SBR binder, set the revolution speed to 15 rpm and the rotation speed to 600 rpm, stir for 30 min, transfer to the transfer tank, and vacuum (-80±5 kPa, 15±1 rpm, 2 h) to obtain the target negative electrode slurry. (7) The negative electrode slurry is coated on a coating machine onto the negative electrode current collector. After drying, the surface density is 200 g / m³. 2 The negative electrode.

[0030] Comparative Example 1 (1) Add 0.8 parts of sodium carboxymethyl cellulose thickener and deionized water to a double planetary stirrer, set the revolution speed to 25 rpm and the rotation speed to 1600 rpm, and stir at high speed for 3 hours; at this time the solid content is 1.5±0.5%; (2) Continue to add deionized water and 1 part of PAA adhesive. Set the stirring speed to 25 rpm and the rotation speed to 1200 rpm. Stir for 60 min. The adhesive is dispersed and the solid content is 1.5 ± 0.5%. Take out the adhesive for later use. (3) Add 96 parts of graphite material and 1 part of carbon black conductive agent to a double planetary stirrer, set the revolution speed to 15 rpm and the rotation speed to 600 rpm, and the stirring time to 30 min; (4) Add 80wt% of the mixed adhesive solution from step (2), continue stirring, set the stirring speed to 15rpm and the rotation speed to 600rpm, and perform vacuum kneading for 60min. At this time, the solid content is 70±5%. (5) Add the remaining 20wt% mixed adhesive solution, the remaining 1.2 parts of PAA and deionized water, set the stirrer's revolution speed to 25 rpm and rotation speed to 1600 rpm, and stir for 1.5 h. At this time, the solid content is 54±5%. (6) Continue to add deionized water to adjust the viscosity to 3500-4500CP. After the viscosity reaches the standard, set the revolution speed to 15rpm and the rotation speed to 600rpm. After stirring for 30min, transfer to the transfer tank and vacuum (-80±5kpa, 15±1rpm, 2h) to obtain the negative electrode slurry.

[0031] (7) The negative electrode slurry is coated on a coating machine onto the negative electrode current collector. After drying, the surface density is 200 g / m³. 2 The negative electrode.

[0032] Comparative Example 2 Compared to Example 1, the single variable is: the addition of all the mixed adhesive prepared in step (2); (1) Add 0.8 parts of sodium carboxymethyl cellulose thickener and deionized water to a double planetary stirrer, set the revolution speed to 25 rpm and the rotation speed to 1600 rpm, and stir at high speed for 3 hours; at this time the solid content is 1.5±5%; (2) Continue to add deionized water and 1 part of PAA adhesive. Set the stirring speed to 25 rpm and the rotation speed to 1200 rpm. Stir for 60 min. The adhesive is dispersed and the solid content is 1.5 ± 0.5%. Take out the adhesive for later use. (3) Add 96 parts of graphite material and 1 part of carbon black conductive agent to a double planetary stirrer, set the revolution speed to 15 rpm and the rotation speed to 600 rpm, and the stirring time to 30 min; (4) Add the mixed adhesive solution from step (2), continue stirring, set the stirring speed to 15 rpm and the rotation speed to 600 rpm, and perform vacuum kneading for 60 minutes. At this time, the solid content is 60±5%. Set the stirring speed to 25 rpm and the rotation speed to 1600 rpm, and continue stirring for 1.5 hours. Add deionized water during stirring. At this time, the solid content is 54±5%. (5) Add deionized water to adjust the viscosity to 3500-4500 CP. After the viscosity reaches the standard, add 1.2 parts of SBR binder, set the revolution speed to 15 rpm and the rotation speed to 600 rpm, stir for 30 min, transfer to the transfer tank, and vacuum (-80±5 kPa, 15±1 rpm, 2 h) to obtain the negative electrode slurry.

[0033] (6) The negative electrode slurry is coated on a coating machine onto the negative electrode current collector. After drying, the surface density is 200 g / m³. 2 The negative electrode.

[0034] Comparative Example 3 (1) Add 0.8 parts of sodium carboxymethyl cellulose thickener and deionized water to a double planetary mixer, set the revolution speed to 25 rpm and the rotation speed to 1600 rpm, and stir at high speed for 3 hours. Remove and set aside. At this time, the solid content is 1.5 ± 0.5%. (2) Add 96 parts of graphite material and 1 part of carbon black conductive agent to a double planetary stirrer, set the revolution speed to 15 rpm and the rotation speed to 600 rpm, and the stirring time to 30 min; (3) Add 80wt% of the adhesive solution from step (1), set the revolution speed to 15rpm and the rotation speed to 600rpm, and perform vacuum kneading for 60min. At this time, the solid content is 70±5%. (4) Add the remaining mixed adhesive solution and deionized water, set the revolution speed to 25 rpm and the rotation speed to 1600 rpm, and stir for 1.5 h. At this time, the solid content is 65±5%. (5) Continue to add deionized water and 1 part PAA binder, set the revolution speed to 25 rpm and the rotation speed to 1600 rpm, stir for 1.5 h, at which point the solid content is 54±5%; (6) Add deionized water to adjust the viscosity to 3500-4500CP. After the viscosity reaches the standard, add 1.2 parts of SBR binder, set the revolution speed to 15 rpm and the rotation speed to 600 rpm, stir for 30 min, transfer to the transfer tank, and vacuum (-80±5 kPa, 15±1 rpm, 2 h) to obtain the target negative electrode slurry.

[0035] (7) The negative electrode slurry is coated on a coating machine onto the negative electrode current collector. After drying, the surface density is 200 g / m³. 2 The negative electrode.

[0036] Comparative Example 4 (1) Add 0.8 parts of sodium carboxymethyl cellulose thickener and deionized water to a double planetary stirrer, set the revolution speed to 25 rpm and the rotation speed to 1600 rpm, and stir at high speed for 3 hours; at this time the solid content is 1.5±0.5%; (2) Continue to add deionized water and 1.6 parts of PAA adhesive, set the stirring speed to 25 rpm and the rotation speed to 1200 rpm, and the stirring time to 60 min. The adhesive is dispersed and the solid content is 1.5 ± 0.5%. Take out the adhesive for later use. (3) Add 96 parts of graphite material and 1 part of carbon black conductive agent to a double planetary stirrer, set the revolution speed to 15 rpm and the rotation speed to 600 rpm, and the stirring time to 30 min; (4) Add 80wt% of the mixed adhesive solution from step (2), continue stirring, set the stirring speed to 15rpm and the rotation speed to 600rpm, and perform vacuum kneading for 60min. At this time, the solid content is 70±5%. (5) Add the remaining 20wt% mixed adhesive solution and deionized water, set the stirrer's revolution speed to 25 rpm and rotation speed to 1600 rpm, and stir for 1.5 h. At this time, the solid content is 54±5%. (6) Continue to add deionized water to adjust the viscosity to 3500-4500CP. After the viscosity reaches the standard, add 0.6 parts of SBR binder, set the revolution speed to 15rpm and the rotation speed to 600rpm, stir for 30min, transfer to the transfer tank, and vacuum (-80±5kpa, 15±1rpm, 2h) to obtain the target negative electrode slurry.

[0037] (7) The negative electrode slurry is coated on a coating machine onto the negative electrode current collector. After drying, the surface density is 200 g / m³. 2 The negative electrode.

[0038] The negative electrode sheets obtained in the above embodiments and comparative examples were rolled to achieve a compaction density of 1.6 g / cm³. 3The rolling parameters (pressure 20T, speed 20m / min) were the same. The physical properties of the slurry and corresponding electrode obtained by the test are detailed in Table 1 below.

[0039] Table 1. Comparison of the stability of negative electrode slurries obtained from different embodiments and comparative examples.

[0040] The specific testing method is as follows: Viscosity was tested using a rotational viscometer. Before testing, the negative electrode slurry sample was placed in a constant temperature (25℃±0.5℃) water bath and allowed to stand for 30 minutes. A No. 4 rotor (3.2mm diameter, 115mm length) was selected, and the rotation speed was set to 60 rpm. The rotor was slowly immersed in the slurry to the specified graduation mark. After the viscometer display reading stabilized (fluctuation not exceeding ±1% within 30 seconds), the viscosity value displayed at this point was recorded, in units of CP. Each sample was tested in parallel three times, and the arithmetic mean was taken as the final discharge viscosity and the viscosity after 24 hours.

[0041] Solid content was tested using a halogen moisture analyzer. First, the instrument was preheated to a stable state, with the heating temperature set to 150℃. Approximately 2.0–3.0 g of the negative electrode slurry sample was weighed onto a sample pan using a precision balance (accuracy 0.1 mg), and the initial mass m1 was recorded. The sample pan was placed in the analyzer and continuously heated and dried at 150℃ until the sample mass no longer changed significantly (usually constant weight, i.e., the difference between two consecutive weighings is less than 0.5 mg). The final residual solid mass m2 was recorded. The solid content was calculated using the following formula: Fineness testing was performed using a scraper fineness meter. A scraper fineness meter with a range of 0–50 μm was selected. Before use, the scraper and scraper blade were wiped clean and dried with anhydrous ethanol. A suitable amount of negative electrode slurry sample was taken with a dropper and placed at the deepest end of the groove (the maximum scale value) of the scraper fineness meter, ensuring the sample was free of air bubbles. Holding the scraper blade with both hands, perpendicular to the scraper surface and parallel to the width direction of the scraper, the slurry was scraped down from the deepest end of the groove to the zero scale at a uniform and steady speed (approximately 50–80 mm / s). Observe the position where particles are uniformly exposed in the groove under light with an incident angle of 20–30 degrees for 5–10 seconds above the scraper fineness meter. Record the first continuous scale value where particles are clearly exposed in the groove; this scale value is the fineness value of the slurry, in micrometers (μm). Each sample was tested three times, and the maximum value was taken as the final result.

[0042] Material shedding and folding test: The prepared negative electrode sheet is placed in a flatbed hot press and hot-pressed once at a temperature of 85℃, a pressure of 5 tons, and a time of 90 seconds. After hot pressing, the core is carefully removed and allowed to cool naturally to room temperature. Then, the core is completely disassembled and the negative electrode sheet is removed. Under sufficient light, the radius (R-angle) of the negative electrode sheet (i.e., the bending area of ​​the electrode sheet) is observed using a magnifying glass. The total number of continuous folds or sections (in units of folds or sections) with coating peeling, powdering, or cracking in the R-angle area of ​​the negative electrode is recorded. This value is the material shedding and folding count. At least 3 parallel cores are tested for each formulation of negative electrode slurry, and the arithmetic mean is taken as the final test result.

[0043] Data Analysis: Compared with Example 1, Comparative Example 1 uses (PAA+CMC) instead of the (PAA+CMC+SBR) system. The slurry viscosity stability is poor, and there is no blue floating phenomenon. Due to the lack of flexible SBR, the brittleness of the electrode sheet is greatly increased, the coated electrode sheet cracks severely, and the material loss during the inner folding of the core increases from 3 folds in Example 1 to 10 folds, resulting in severe deterioration of mechanical properties.

[0044] Compared with Example 1, Comparative Example 2 changed the variable from stepwise adhesive application to one-time adhesive application. The viscosity and solid content of the slurry were different from those in Example 1. The slurry showed slight sedimentation after 24 hours, with no blue floating phenomenon. The edge surface of the coated electrode cracked. The material loss from the inner fold of the core increased from 3 folds in Example 1 to 9 folds. Due to the adhesive dispersion problem, the peel strength of the dry electrode after rolling decreased from 8 N / m to 2 N / m (peel strength was tested according to GB / T 2792-2014).

[0045] Compared with Example 1, the variable in Comparative Example 3 was the location of PAA addition. The viscosity of the slurry increased significantly, mainly due to the entanglement of PAA molecular chains. There was no sedimentation or blue floating phenomenon in the slurry after 24 hours. Vertical lines appeared on the coated surface, the surface density fluctuated more, and the material loss during the inner fold of the core increased from 3 folds in Example 1 to 4 folds.

[0046] Compared with Example 1, Comparative Example 3 differed in the ratio of PAA to SBR, with the binder dosage remaining constant. As the amount of PAA increased, the viscosity increased, there was no blue floating phenomenon, the coating surface had slight vertical lines, and the material loss during the inner fold of the core increased from 3 folds in Example 1 to 6 folds.

[0047] The results showed that by adjusting the proportion of binder in the negative electrode slurry system, the slurry of Example 1 had the best stability under the same conditions.

[0048] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0049] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.

Claims

1. A lithium battery negative electrode slurry, characterized in that, Its dry matter consists of the following components in mass percentage: Conductive agent 0.5%–2%; Adhesive content: 1.7%–2.2%; Thickener 0.5%–2%; Remaining amount of negative electrode active material; The conductive agent is conductive carbon black, the thickener is sodium carboxymethyl cellulose, and the binder is a mixture of polyacrylic acid binder and styrene-butadiene rubber binder.

2. The lithium battery negative electrode slurry according to claim 1, characterized in that, The polyacrylic adhesive is at least one of polyacrylic acid, polyacrylic acid derivatives, and copolymers of polyacrylic acid.

3. The lithium battery negative electrode slurry according to claim 1, characterized in that, The polyacrylic acid binder accounts for 0.7% to 1.7% of the mass of the negative electrode slurry, and the styrene-butadiene rubber binder accounts for 0.6% to 1.3% of the mass of the negative electrode slurry.

4. A method for preparing a lithium battery negative electrode slurry as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1: Add the thickener to the water and mix well to obtain mixture P1; S2: Add a polyacrylic acid binder to the mixture P1 and mix evenly to obtain mixture P2; S3: Mix the negative electrode active material and the conductive agent evenly to obtain mixture P3; S4: Add the mixture P2 to the mixture P3, knead and disperse to obtain mixture P4; S5: Add a styrene-butadiene rubber binder to the mixture P4 and mix evenly to obtain a lithium battery negative electrode slurry.

5. The preparation method according to claim 4, characterized in that, In step S1, the stirring speed is 1200–1800 rpm, the stirring time is 0.5–5 h, and the solid content of the mixture P1 is 1%–5%; and / or, In step S2, the stirring speed is 500–1200 rpm, the stirring time is 20–120 min, and the solid content of the mixture P2 is 1%–4%; and / or, In step S3, the stirring speed is 200-500 rpm and the stirring time is 10-60 min.

6. The preparation method according to claim 4, characterized in that, Step S4 specifically involves adding the mixture P2 to the mixture P3 in at least two separate additions; wherein, After adding a portion of the mixture P2 for the first time, stir and knead at a speed of 200–500 rpm for 0.5–3 hours, at which point the solid content will be 60%–80%. After adding the remaining mixture P2 for the second time, stir at 1200-2000 rpm for 0.5-3 hours, add deionized water to adjust the solid content to 40%-60%, and adjust the viscosity to 3000-7000 CP.

7. The preparation method according to claim 6, characterized in that, The mass of the mixture P2 added initially accounts for 60% to 90% of the total mass of the mixture P2.

8. The preparation method according to claim 6, characterized in that, In step S5, the stirring speed is 15-25 rpm for revolution and 500-1500 rpm for rotation, and the stirring time is 10-60 min; after adding styrene-butadiene rubber binder, water is added to adjust the viscosity to 2000-6000 CP.

9. The preparation method according to claim 6, characterized in that, After step S5, a vacuum degassing step is also included: the vacuum degree is -80±5kPa, the revolution speed is 15±1rpm, and the processing time is 1 to 3 hours.

10. A negative electrode sheet, characterized in that, The invention includes a metal foil and a lithium battery negative electrode slurry coated on the surface of the metal foil; the lithium battery negative electrode slurry is the lithium battery negative electrode slurry according to any one of claims 1 to 3; The lithium battery negative electrode slurry is coated on both sides of a metal foil; the areal density of the negative electrode sheet is 100–260 g / m³. 2 .

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