Phosphorus-carbon negative electrode aqueous slurry and preparation method thereof

Abstract

The invention discloses phosphorus-carbon negative electrode aqueous slurry and a preparation method thereof, and belongs to the technical field of lithium battery materials. The preparation method comprises the following steps: mixing a phosphorus-carbon material with a conductive agent to obtain a precursor; adding alkaline lithium salt into the precursor, and reacting to obtain a mixture A; adding an acid-resistant polyacrylic acid binder into the mixture A, and uniformly stirring to obtain a mixture B; adding a cellulose thickener into the mixture B, and uniformly stirring to obtain a mixture C; and adding a rubber binder into the mixture C to obtain the phosphorus-carbon negative electrode aqueous slurry. Through a specific process sequence of firstly adding the conductive agent and stirring and then adding the alkaline lithium salt, a lithium phosphate fast ion conductor is generated on the surface of the phosphorus-carbon material in situ, the pH value of the slurry is adjusted, and the stability of the slurry, the processing performance of a pole piece and the electrochemical performance of the battery are remarkably improved in combination with the use of the acid-resistant PAA binder.

Description

Technical Field

[0001] This invention relates to the field of lithium battery materials technology, specifically to a phosphorus-carbon anode aqueous slurry and its preparation method. Background Technology

[0002] Lithium-ion batteries, as high-energy-density energy storage devices, are widely used in portable electronic devices, electric vehicles, and large-scale energy storage. Improving their energy density and rate performance remains a research hotspot. Phosphorus-based anode materials, due to their advantages such as high theoretical specific capacity and moderate lithium intercalation potential, are considered one of the important directions for overcoming the performance bottlenecks of existing graphite anodes. However, elemental phosphorus is easily oxidized in air and forms an acidic environment during aqueous homogenization, leading to the deactivation of conventional binders and subsequently causing problems such as electrode cracking and active material detachment, severely restricting the industrial application of phosphorus-carbon anode materials.

[0003] To address these issues, researchers have attempted to isolate phosphorus-carbon materials from air oxidation by surface coating, such as depositing red phosphorus onto a porous carbon support and coating it with a fast ion conductor layer. However, due to the low melting point and sublimation temperature of red phosphorus, traditional high-temperature coating processes struggle to achieve uniform and dense coatings, leaving exposed areas on the surface of the phosphorus-carbon material. During aqueous homogenization, the localized acidic environment causes binder failure, leading to defects such as powdering and cracking on the electrode sheets. Therefore, how to maintain the high capacity advantage of phosphorus-carbon materials while solving their stability issues in aqueous homogenization processes has become a critical technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0004] In view of this, the present invention provides a phosphorus-carbon anode aqueous slurry and its preparation method. By first adding a conductive agent and stirring, and then adding an alkaline lithium salt, a fast lithium phosphate conductor is generated in situ on the surface of the phosphorus-carbon material and the pH value of the slurry is adjusted. Combined with the use of an acid-resistant PAA (polyacrylic acid) binder, the stability of the slurry, the electrode processing performance and the electrochemical performance of the battery are significantly improved.

[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 method for preparing a phosphorus-carbon anode aqueous slurry, comprising the following steps: S1. Mix the phosphorus-carbon material with a conductive agent to obtain the precursor; S2. Add alkaline lithium salt to the precursor, and after reaction, obtain mixture A; S3. Add an acid-resistant polyacrylic acid binder to the mixture A and mix well to obtain mixture B; S4. Add a cellulose-based thickener to mixture B and mix well to obtain mixture C; S5. Add a rubber-based binder to the mixture C to obtain the phosphorus-carbon anode aqueous slurry.

[0006] A further embodiment: the conductive agent is at least one of carbon nanotubes, Ketjen black, acetylene black, conductive carbon black, and graphene.

[0007] A further option is that the alkaline lithium salt is at least one of lithium hydroxide and lithium carbonate.

[0008] A further option: the acid-resistant polyacrylic adhesive is polyacrylic acid or its acid-resistant salt derivative.

[0009] A further option: In step S2, the reaction temperature is 20-30℃ and the time is 40-60 min.

[0010] A further embodiment: the amount of alkaline lithium salt added is 0.1-0.3% of the mass of the phosphorus-carbon material; The cellulose-based thickener is sodium carboxymethyl cellulose, and the amount added is 0.06-2.2% of the mass of the phosphorus-carbon material. The rubber-based adhesive is styrene-butadiene latex, with a solid content of 35-45%, preferably 40%, and its addition amount is 1.62-1.66% of the mass of the phosphorus-carbon material; The amount of the conductive agent added is 4.15-4.35% of the mass of the phosphorus-carbon material.

[0011] A further solution: The pH value of the phosphorus-carbon anode aqueous slurry is 4-8.5. At a pH of 4-8.5, the phosphorus-carbon anode aqueous slurry is significantly better than the acidic environment of conventional slurries with a pH of 2-3, effectively avoiding binder deactivation and electrode foil detachment problems caused by excessively low pH.

[0012] A further option is to use a phosphorus-carbon anode aqueous slurry with a solid content of 34%-55%.

[0013] A further embodiment: a phosphorus-carbon anode aqueous slurry, characterized in that it is prepared by the above-described preparation method.

[0014] Secondly, the present invention discloses a phosphorus-carbon negative electrode sheet, comprising a current collector and a coating disposed on the current collector, wherein the coating is formed by coating and drying the aforementioned phosphorus-carbon negative electrode aqueous slurry.

[0015] Thirdly, the present invention discloses a lithium-ion battery, including the aforementioned phosphorus-carbon negative electrode sheet.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention forms a stable slurry system by thoroughly mixing phosphorus-carbon materials with aqueous carbon nanotubes and adding them to alkaline lithium salts. This effectively avoids the problem of elemental phosphorus being easily oxidized in air, significantly increases the pH value of the slurry, and solves the problems of binder deactivation, electrode cracking, and powdering caused by low slurry pH in traditional methods.

[0017] This invention employs a preparation method that involves first adding a conductive agent (such as carbon nanotubes) and stirring, followed by the addition of an alkaline lithium salt. This method achieves two key improvements: firstly, it allows for the in-situ growth of fast-ion conductors of lithium phosphate on the surface of the phosphorus-carbon material, bonding them to the carbon nanotubes and enhancing the material's fast-charging performance; secondly, it adjusts the pH of the slurry and adds acid-resistant PAA for homogenization, significantly improving the slurry's fluidity and stability, enhancing the controllability of the coating process, and resolving the foil detachment problem caused by binder deactivation in traditional methods. This effectively overcomes the performance limitations of traditional graphite anode materials due to their low theoretical capacity and small lithium-ion diffusion coefficient. The preparation method of this invention is simple, with easily controllable parameters, good repeatability, and is suitable for large-scale production, meeting the stringent requirements of high-performance lithium-ion batteries for anode materials.

[0018] First, after the phosphorus-carbon material and carbon nanotubes are fully mixed, alkaline lithium hydroxide is added. On the one hand, a fast-ion conductor layer of lithium phosphate is generated in situ on the surface of the phosphorus-carbon material, and the carbon nanotubes are anchored to the surface of the material, thus constructing an efficient electron and ion transport network and significantly improving the fast-charging performance of the material. On the other hand, the addition of alkaline substances effectively adjusts the pH value of the slurry, creating a suitable environment for the stable existence of the subsequent binder.

[0019] Secondly, this invention employs a composite binder system composed of acid-resistant PAA, CMC, and SBR, combined with a sequential feeding process, ensuring that each binder functions under optimal pH conditions. This fundamentally solves the industry problem of binder deactivation, electrode cracking, and foil detachment caused by acidic environments in traditional aqueous slurries of phosphorus-carbon materials. The prepared slurry exhibits excellent fluidity and stability, significantly improving the controllability of the coating process.

[0020] Finally, the phosphorus-carbon anode material prepared by the method of this invention exhibits excellent electrochemical performance, effectively overcoming the performance limitations of traditional graphite anode materials such as low theoretical capacity and small lithium-ion diffusion coefficient, and providing a feasible phosphorus-carbon anode solution for high-performance lithium-ion batteries. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the preparation of the phosphorus-carbon material negative electrode sheet according to the present invention; Figure 2 This is an electron microscope image of the phosphorus-carbon material negative electrode sheet prepared in Example 1 of the present invention; Figure 3The first charge-discharge curve of the phosphorus-carbon anode material prepared in Example 1 of this invention; Figure 4 This is a comparison chart of the cycle performance of the phosphorus-carbon anode materials prepared in Example 1 and Comparative Example 1 of the present invention; Figure 5 This is a comparison chart of the rate performance of the phosphorus-carbon anode materials prepared in Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0022] 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 more thorough and complete understanding of the disclosure of the present invention.

[0023] 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.

[0024] 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.

[0025] Example 1 This embodiment provides a phosphorus-carbon anode aqueous slurry, electrode sheet, its preparation method, and a lithium-ion battery. The specific steps are as follows: S1. Weigh 2000g of phosphorus-carbon material, 85g of conductive carbon black (SP), and 543g of aqueous carbon nanotubes in sequence, place them in a stirring device, set the revolution speed to 20 rpm and the rotation speed to 200 rpm, and stir at 23℃ for 20 min to obtain the phosphorus-carbon slurry precursor.

[0026] S2. Add 4g of lithium hydroxide powder to the above phosphorus-carbon slurry precursor, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 50 min to obtain mixed slurry A.

[0027] S3. Add 544g of acid-resistant PAA (Indira, LA136Y) to mixed slurry A, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 20 min; then add 361g of deionized water, and vacuum stir for 70 min under the conditions of revolution speed to 20 rpm, rotation speed to 2500 rpm, temperature to 23℃ and pressure to -100 kPa to obtain mixed slurry B.

[0028] S4. Add 24g of sodium carboxymethyl cellulose (92.5% solid content) to the mixed slurry B, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 20 min; then add 1547g of deionized water, and vacuum stir for 70 min at a revolution speed of 20 rpm, a rotation speed of 2500 rpm, a temperature of 23℃ and a pressure of -100 kPa to obtain mixed slurry C.

[0029] S5. Add 82g of styrene-butadiene latex (solid content 40%) to the mixed slurry C, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 20 min to obtain a phosphorus-carbon anode aqueous slurry with a solid content of 42% and a pH value of 6.3.

[0030] S6. The above slurry is coated onto carbon-coated copper foil with a coating thickness of 60 μm. After drying under vacuum at 80°C, it is rolled to obtain a phosphorus-carbon negative electrode sheet.

[0031] Example 2 This embodiment provides a phosphorus-carbon anode aqueous slurry, electrode sheet, its preparation method, and a lithium-ion battery. The specific steps are as follows: S1. Weigh 2000g of phosphorus-carbon material, 87g of conductive carbon black (SP), and 556g of aqueous carbon nanotubes in sequence, place them in a stirring device, set the revolution speed to 30 rpm and the rotation speed to 300 rpm, and stir at 23℃ for 30 min to obtain the phosphorus-carbon slurry precursor.

[0032] S2. Add 6g of lithium hydroxide powder to the above phosphorus-carbon slurry precursor, set the revolution speed to 30 rpm and the rotation speed to 700 rpm, and stir at 23℃ for 60 min to obtain mixed slurry A.

[0033] S3. Add 926g of acid-resistant PAA (Indira, LA136Y) to mixed slurry A, set the revolution speed to 30 rpm and the rotation speed to 700 rpm, and stir at 23℃ for 50 min; then add 261g of deionized water, and vacuum stir for 90 min at a revolution speed of 30 rpm, a rotation speed of 3000 rpm, a temperature of 23℃ and a pressure of -100 kPa to obtain mixed slurry B.

[0034] S4. Add 48g of sodium carboxymethyl cellulose (92.5% solid content) to the mixed slurry B, set the revolution speed to 30 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 20 min; then add 2650g of deionized water, and vacuum stir for 90 min at a revolution speed of 30 rpm, a rotation speed of 3000 rpm, a temperature of 23℃ and a pressure of -100 kPa to obtain mixed slurry C.

[0035] S5. Add 83g of styrene-butadiene latex (solid content 40%) to the mixed slurry C, set the revolution speed to 30 rpm and the rotation speed to 700 rpm, and stir at 23℃ for 20 min to obtain a phosphorus-carbon anode aqueous slurry with a solid content of 34% and a pH value of 8.3.

[0036] S6. The above slurry is coated onto carbon-coated copper foil with a coating thickness of 80 μm. After drying under vacuum at 80°C, it is rolled to obtain a phosphorus-carbon negative electrode sheet.

[0037] Example 3 This embodiment provides a phosphorus-carbon anode aqueous slurry, electrode sheet, its preparation method, and a lithium-ion battery. The specific steps are as follows: S1. Weigh 2000g of phosphorus-carbon material, 83g of conductive carbon black (SP), and 538g of aqueous carbon nanotubes in sequence, place them in a stirring device, set the revolution speed to 10 rpm and the rotation speed to 250 rpm, and stir at 23℃ for 20 min to obtain the phosphorus-carbon slurry precursor.

[0038] S2. Add 2g of lithium hydroxide powder to the above phosphorus-carbon slurry precursor, set the revolution speed to 10 rpm and the rotation speed to 500 rpm, and stir at 23℃ for 40 min to obtain mixed slurry A.

[0039] S3. Add 358g of acid-resistant PAA (Indira, LA136Y) to mixed slurry A, set the revolution speed to 10 rpm and the rotation speed to 500 rpm, and stir at 23℃ for 40 min; then add 569g of deionized water, and vacuum stir for 60 min at a revolution speed of 10 rpm, a rotation speed of 2000 rpm, a temperature of 23℃ and a pressure of -100 kPa to obtain mixed slurry B.

[0040] S4. Add 12g of sodium carboxymethyl cellulose (92.5% solid content) to the mixed slurry B, set the revolution speed to 10 rpm and the rotation speed to 500 rpm, and stir at 23℃ for 20 min; then add 294g of deionized water, and vacuum stir for 60 min at a revolution speed of 10 rpm, a rotation speed of 2000 rpm, a temperature of 23℃ and a pressure of -100 kPa to obtain mixed slurry C.

[0041] S5. Add 81g of styrene-butadiene latex (solid content 40%) to the mixed slurry C, set the revolution speed to 10 rpm and the rotation speed to 500 rpm, and stir at 23℃ for 25 min to obtain a phosphorus-carbon anode aqueous slurry with a solid content of 55% and a pH value of 4.1.

[0042] S6. The above slurry is coated onto carbon-coated copper foil with a coating thickness of 50 μm. After drying under vacuum at 80°C, it is rolled to obtain a phosphorus-carbon negative electrode sheet.

[0043] Comparative Example 1 This comparative example provides a phosphorus-carbon anode aqueous slurry, electrode sheet, and its preparation method. The specific steps are as follows: S1. Weigh 2000g of phosphorus-carbon material, 85g of conductive carbon black (SP), and 543g of aqueous carbon nanotubes in sequence, place them in a stirring device, set the revolution speed to 20 rpm and the rotation speed to 200 rpm, and stir at 23℃ for 20 min to obtain the phosphorus-carbon slurry precursor.

[0044] S2. Add 544g of acid-resistant PAA (Indira, LA136Y) directly to the above phosphorus-carbon slurry precursor, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 20 min; then add 361g of deionized water, and vacuum stir for 70 min under the conditions of revolution speed to 20 rpm, rotation speed to 2500 rpm, temperature to 23℃ and pressure to -100 kPa to obtain mixed slurry B.

[0045] S3. Add 24g of sodium carboxymethyl cellulose (92.5% solid content) to the mixed slurry B, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 20 min; then add 1547g of deionized water, and vacuum stir for 70 min at a revolution speed of 20 rpm, a rotation speed of 2500 rpm, a temperature of 23℃ and a pressure of -100 kPa to obtain mixed slurry C.

[0046] S4. Add 82g of styrene-butadiene latex (solid content 40%) to the mixed slurry C, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 20 min to obtain a phosphorus-carbon anode aqueous slurry with a solid content of 42%. The pH of the slurry was measured to be 2.3.

[0047] S5. The above slurry is coated onto carbon-coated copper foil with a coating thickness of 60 μm. After drying under vacuum at 80 °C, it is rolled to obtain a phosphorus-carbon negative electrode sheet.

[0048] Comparative Example 2 This comparative example provides a phosphorus-carbon anode aqueous slurry, electrode sheet, its preparation method, and a lithium-ion battery. The specific steps are as follows: S1. Weigh 2000g of phosphorus-carbon material, 85g of conductive carbon black (SP), and 543g of aqueous carbon nanotubes in sequence, place them in a stirring device, set the revolution speed to 20 rpm and the rotation speed to 200 rpm, and stir at 23℃ for 20 min to obtain the phosphorus-carbon slurry precursor.

[0049] S2. Add 4g of lithium hydroxide powder to the above phosphorus-carbon slurry precursor, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 50 min to obtain mixed slurry A.

[0050] S3. Add 544g of non-acid-resistant conventional PAA (Indira, LA136D) to mixed slurry A, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 20 min; then add 361g of deionized water, and vacuum stir for 70 min at a revolution speed of 20 rpm, a rotation speed of 2500 rpm, a temperature of 23℃, and a pressure of -100 kPa to obtain mixed slurry B.

[0051] S4. Add 24g of sodium carboxymethyl cellulose (92.5% solid content) to the mixed slurry B, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 20 min; then add 1547g of deionized water, and vacuum stir for 70 min at a revolution speed of 20 rpm, a rotation speed of 2500 rpm, a temperature of 23℃ and a pressure of -100 kPa to obtain mixed slurry C.

[0052] S5. Add 82g of styrene-butadiene latex (solid content 40%) to the mixed slurry C, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 20 min to obtain a phosphorus-carbon anode aqueous slurry with a solid content of 42% and a pH value of 5.9.

[0053] S6. The above slurry is coated onto carbon-coated copper foil with a coating thickness of 60 μm. After drying under vacuum at 80°C, it is rolled to obtain a phosphorus-carbon negative electrode sheet.

[0054] Comparative Example 3 This comparative example provides a phosphorus-carbon anode aqueous slurry, electrode sheet, its preparation method, and a lithium-ion battery. The difference from Example 1 is that carbon nanotubes and lithium hydroxide are added simultaneously in stage S1. The specific steps are as follows: S1. Weigh 2000g of phosphorus-carbon material, 85g of conductive carbon black (SP), 543g of aqueous carbon nanotubes, and 4g of lithium hydroxide powder in sequence, place them in a stirring device, set the revolution speed to 20 rpm and the rotation speed to 200 rpm, and stir at 23℃ for 20 min to obtain the phosphorus-carbon slurry precursor.

[0055] S2. Add 544g of acid-resistant PAA (Indira, LA136Y) to the above phosphorus-carbon slurry precursor, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 20 min; then add 361g of deionized water, and vacuum stir for 70 min under the conditions of revolution speed to 20 rpm, rotation speed to 2500 rpm, temperature to 23℃ and pressure to -100 kPa to obtain mixed slurry B.

[0056] S3. Add 24g of sodium carboxymethyl cellulose (92.5% solid content) to the mixed slurry B, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 20 min; then add 1547g of deionized water, and vacuum stir for 70 min at a revolution speed of 20 rpm, a rotation speed of 2500 rpm, a temperature of 23℃ and a pressure of -100 kPa to obtain mixed slurry C.

[0057] S4. Add 82g of styrene-butadiene latex (solid content 40%) to the mixed slurry C, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 20 min to obtain a phosphorus-carbon anode aqueous slurry with a solid content of 42% and a pH value of 6.2.

[0058] S5. The above slurry is coated onto carbon-coated copper foil with a coating thickness of 60 μm. After drying under vacuum at 80 °C, it is rolled to obtain a phosphorus-carbon negative electrode sheet.

[0059] Comparative Example 4 This embodiment provides a phosphorus-carbon anode aqueous slurry, electrode sheet, its preparation method, and a lithium-ion battery. The specific steps are as follows: S1. Weigh 2000g of phosphorus-carbon material, 85g of conductive carbon black (SP), and 543g of aqueous carbon nanotubes in sequence, place them in a stirring device, set the revolution speed to 20 rpm and the rotation speed to 200 rpm, and stir at 23℃ for 20 min to obtain the phosphorus-carbon slurry precursor.

[0060] S2. Add 4g of sodium hydroxide powder to the above phosphorus-carbon slurry precursor, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 50 min to obtain mixed slurry A.

[0061] S3. Add 544g of acid-resistant PAA (Indira, LA136Y) to mixed slurry A, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 20 min; then add 361g of deionized water, and vacuum stir for 70 min under the conditions of revolution speed to 20 rpm, rotation speed to 2500 rpm, temperature to 23℃ and pressure to -100 kPa to obtain mixed slurry B.

[0062] S4. Add 24g of sodium carboxymethyl cellulose (92.5% solid content) to the mixed slurry B, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 20 min; then add 1547g of deionized water, and vacuum stir for 70 min at a revolution speed of 20 rpm, a rotation speed of 2500 rpm, a temperature of 23℃ and a pressure of -100 kPa to obtain mixed slurry C.

[0063] S5. Add 82g of styrene-butadiene latex (solid content 40%) to the mixed slurry C, set the revolution speed to 20 rpm and the rotation speed to 600 rpm, and stir at 23℃ for 20 min to obtain a phosphorus-carbon anode aqueous slurry with a solid content of 42% and a pH value of 6.2.

[0064] S6. The above slurry is coated onto carbon-coated copper foil with a coating thickness of 60 μm. After drying under vacuum at 80°C, it is rolled to obtain a phosphorus-carbon negative electrode sheet.

[0065] Test case 1) Battery assembly The phosphorus-carbon negative electrode sheets obtained in Examples 1-3 and Comparative Examples 1-4 were respectively prepared into pouch cells: Positive electrode: High-nickel ternary material (LiNi) 0.8 Co 0.1 Mn 0.1 O2 is used as the positive electrode active material. It is mixed with conductive agent and binder in a conventional ratio and then coated on aluminum foil. After drying and rolling, the positive electrode sheet is obtained.

[0066] Negative electrode: Phosphorus-carbon negative electrode sheet prepared using the above-described embodiments or comparative examples.

[0067] Diaphragm: A polypropylene (PP) microporous diaphragm is used.

[0068] Electrolyte: LiPF6 is used as the lithium salt with a concentration of 1 mol / L. The solvent is a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1.

[0069] Assembly conditions: In a dry room with a dew point temperature ≤ -35℃, the positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, and then packaged, injected with liquid, formed, and aged to produce a soft-pack battery cell.

[0070] 2) Test items and conditions All electrochemical performance tests were conducted at a constant temperature of 25℃±2℃. The voltage range for charge-discharge tests was set to 2.0 V to 3.8 V. For rate performance testing, constant current charge-discharge cycles were performed at current densities of 0.33C, 0.5C, 1C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, and 0.33C, with 3 cycles at each rate. The discharge specific capacity at each rate was recorded, and the capacity retention rate was calculated based on the 0.33C discharge specific capacity. For cycle performance testing, constant current charge-discharge cycles were performed at a 1C current density, with the charge-discharge voltage range also from 2.0 V to 3.8 V. The discharge specific capacity was recorded after 500 cycles, and the capacity retention rate was calculated.

[0071] The electrode expansion rate test was conducted under full battery charge conditions. After charging the battery to 3.8 V at a constant current of 1 C, the battery was disassembled in a drying room, and the negative electrode was removed. It was rinsed three times with anhydrous dimethyl carbonate (DMC) to remove electrolyte residue. After air drying at room temperature for 30 min, the electrode thickness was measured using a micrometer with an accuracy of 0.001 mm at at least five measurement points, and the average value was taken. Using the electrode thickness before cycling as the initial thickness, the electrode expansion rate was calculated using the following formula: Electrode expansion rate (%) = (Electrode thickness after full charge - Initial electrode thickness) / Initial electrode thickness × 100%.

[0072] During the characterization using scanning electron microscopy, the phosphorus-carbon negative electrode sheet prepared in Example 1 was dried under vacuum conditions, and the surface morphology and material distribution of the electrode sheet were observed using a scanning electron microscope. The accelerating voltage was set to 5 kV, and the magnification was 5000 times.

[0073] The test results are shown in Table 1 below.

[0074] Table 1

[0075] According to Table 1, Figure 4 , Figure 5 The results show that: Compared with Comparative Example 1: When 0.2%, 0.3%, and 0.1% lithium hydroxide were added to Examples 1, 2, and 3, respectively, the specific capacity increased from 1.93 Ah to 2.07 Ah, 1.98 Ah, and 2.01 Ah, and the initial coulombic efficiency increased from 76.32% to 85.32%, 80.21%, and 81.23%. This indicates that the addition of lithium hydroxide during the slurry mixing process forms lithium phosphate during the aqueous slurry mixing process, and a small portion of carbon nanotubes are embedded in the phosphorus-carbon surface. This reduces the loss of the SEI film formed during the lithium insertion / extraction process of nano-red phosphorus and improves the conductivity of the electrode, resulting in improved specific capacity, initial coulombic efficiency, and cycle performance. Furthermore, lithium phosphate is a fast ion conductor, which improves the rate performance of Example 1. Compared with Example 1, Example 2, by increasing the proportion of binder and the amount of lithium hydroxide added, resulted in a decrease in specific capacity and initial coulombic efficiency, while the electrode expansion rate did not change significantly. Example 2 reduced the proportion of active material in the slurry mixing process and increased the proportion of binder, making the electrode more brittle and causing the binder to block the micropores inside the electrode, slowing down the penetration of electrolyte and prolonging the ion transport channel. The addition of more lithium hydroxide led to greater deactivation of nano-sized red phosphorus, which increased the overpotential of the electrode during lithium insertion / extraction, resulting in increased polarization, thereby reducing specific capacity and initial coulombic efficiency. Compared with Example 1, Example 3 reduced the proportion of binder and the amount of lithium hydroxide, resulting in a decrease in specific capacity and initial coulombic efficiency, and an increase in electrode expansion rate. The reduced proportion of binder weakened the adhesion of the electrode, which amplified the destructive effect of volume expansion during the lithium insertion / extraction process of red phosphorus, leading to sedimentation and agglomeration of phosphorus-carbon materials, thus reducing specific capacity and initial coulombic efficiency and increasing electrode expansion rate.

[0076] Compared to Example 1, Comparative Example 1 did not add lithium hydroxide during the slurry mixing process, resulting in a lower pH of the slurry. This caused the sodium carboxymethyl cellulose and styrene-butadiene latex binder to become deactivated during the lithium insertion / extraction process of nano-red phosphorus. The electrode was only bonded by acid-resistant PAA, resulting in a brittle electrode with insufficient adhesion. This led to the phenomenon of active material falling off the current collector and amplified the destructive effect of volume expansion, resulting in a decrease in specific capacity and initial coulombic efficiency, and an increase in electrode expansion rate.

[0077] Compared to Example 1, Comparative Example 2 did not use acid-resistant PAA. Since the phosphorus carbon surface is oxidized and then reacts with lithium hydroxide to form lithium phosphate, the reaction and oxidation continue during the slurry mixing process. This results in oxidized phosphorus carbon on the surface of the binder and phosphorus carbon material. In aqueous conditions, phosphoric acid will be generated. As a result, some binder will be deactivated due to the strong acidity, leading to the phenomenon of active material falling off the current collector, which reduces the specific capacity and initial coulombic efficiency and increases the electrode expansion rate.

[0078] Compared with Example 1, in Comparative Example 3, carbon nanotubes and lithium hydroxide were added together in the first step of slurry mixing. This resulted in the phosphorus-carbon main material not being fully mixed with the carbon nanotubes. Furthermore, due to the large specific surface area of ​​the carbon nanotubes, the phosphorus-carbon and lithium hydroxide formed agglomerates. Subsequently, the oxides on the surface of the phosphorus-carbon could not fully contact the lithium hydroxide, resulting in the inability to uniformly generate lithium phosphate on the surface of the phosphorus-carbon and the inability of the carbon nanotubes to embed into the surface of the phosphorus-carbon. This led to a decrease in specific capacity and initial coulombic efficiency, and an increase in electrode expansion rate.

[0079] Compared to Example 1, Comparative Example 4 replaced lithium hydroxide with sodium hydroxide. Since sodium hydroxide was added to the lithium-ion battery system, sodium phosphate was formed during the aqueous slurry process. Sodium phosphate is not a fast ion conductor of lithium batteries and it depletes the active material. However, the pH value of the slurry system was adjusted to prevent the electrode from being powdered due to the acidity of the active material. Therefore, the specific capacity and initial coulombic efficiency decreased and the electrode expansion rate increased. However, compared with Comparative Example 1, the capacity and electrode expansion rate decreased and the initial coulombic efficiency increased.

[0080] 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.

[0081] 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 method for preparing a phosphorus-carbon anode aqueous slurry, characterized in that, Includes the following steps: S1. Mix the phosphorus-carbon material with a conductive agent to obtain the precursor; S2. Add alkaline lithium salt to the precursor, and after reaction, obtain mixture A; S3. Add an acid-resistant polyacrylic acid binder to the mixture A and mix well to obtain mixture B; S4. Add a cellulose-based thickener to mixture B and mix well to obtain mixture C; S5. Add a rubber-based binder to the mixture C to obtain the phosphorus-carbon anode aqueous slurry.

2. The preparation method according to claim 1, characterized in that, The conductive agent is at least one of carbon nanotubes, Ketjen black, acetylene black, conductive carbon black, and graphene.

3. The preparation method according to claim 1, characterized in that, The alkaline lithium salt is at least one of lithium hydroxide and lithium carbonate.

4. The preparation method according to claim 1, characterized in that, The acid-resistant polyacrylic adhesive is polyacrylic acid or its acid-resistant salt derivative.

5. The preparation method according to claim 1, characterized in that, In step S2, the reaction temperature is 20-30℃ and the time is 40-60 min.

6. The preparation method according to claim 1, characterized in that, The amount of alkaline lithium salt added is 0.1-0.3% of the mass of the phosphorus-carbon material; The cellulose-based thickener is sodium carboxymethyl cellulose, and the amount added is 0.6-2.4% of the mass of the phosphorus-carbon material. The rubber-based adhesive is styrene-butadiene latex, with a solid content of 35-45%, and its addition amount is 1.62-1.66% of the mass of the phosphorus-carbon material; The amount of the conductive agent added is 4.15-4.35% of the mass of the phosphorus-carbon material.

7. The preparation method according to claim 1, characterized in that, The pH of the phosphorus-carbon anode aqueous slurry is 4-8.

5.

8. The preparation method according to claim 1, characterized in that, The solid content of the phosphorus-carbon anode aqueous slurry is 34%-55%.

9. A phosphorus-carbon anode aqueous slurry, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. A phosphorus-carbon negative electrode sheet, characterized in that, It includes a current collector and a coating disposed on the current collector, the coating being formed by coating and drying the phosphorus-carbon anode aqueous slurry of claim 9.

11. A lithium-ion battery, characterized in that, Includes the phosphorus-carbon negative electrode sheet as described in claim 10.

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