Preparation method of high-rate pole piece of lithium battery

Abstract

The invention provides a preparation method of a high-rate pole piece of a lithium battery, and relates to the technical field of lithium batteries, mesoporous material powder, conductive agent powder and binder powder are mixed and stirred to obtain a first mixture; s2, adding a solvent into the first mixture in the S1 to wet the first mixture, diluting with the solvent, stirring, dispersing, kneading and scraping to obtain a second mixture; s3, adding active substance powder into the second mixture in the S2 to wet the second mixture, then diluting with a solvent, stirring, dispersing, kneading and scraping, and then carrying out vacuum defoaming to obtain a third mixture; and S4, coating the surfaces of the two sides of a foil with the third mixture obtained in S3, drying, forming a pole piece material layer on the foil, rolling to obtain a pole piece, and adding a mesoporous material with open pore channels and a high liquid absorption value into the pole piece, so that the wettability of the thick coating or the high-compaction-density pole piece and an electrolyte and the rate and cycle performance of the battery can be obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and more specifically, to a method for preparing a high-rate electrode sheet for a lithium battery. Background Art

[0002] With the vigorous promotion of new energy vehicles, the demand for power batteries is increasing. In particular, the demand for high-energy, high-safety, and long-cycle-life lithium-ion power batteries is particularly prominent. High-energy-density lithium-ion power batteries usually have: (1) high active material content per unit mass (volume space), (2) high-gram capacity positive / negative electrode materials, (3) packaging materials with lower mass density, etc. In recent years, many lithium battery manufacturers have increased the space occupancy ratio of active materials by increasing the thickness of the electrode active material coating or the compaction density to achieve the purpose of improving the overall energy density of the battery. However, the thick coating layer of the electrode increases the contact distance between the underlying active material and the electrolyte, prolongs the migration distance of lithium ions, and makes the infiltration and absorption of the electrolyte more difficult, making the battery internal resistance larger, the polarization potential of the battery charging and discharging process higher, the capacity is not normal, the rate performance is poor, the low-temperature lithium precipitation, the cycle capacity decay is fast, and a series of problems. In particular, charging and discharging under high current density and low temperature environment leads to the formation of lithium dendrites, and the lithium dendrites pierce the isolation membrane to cause a short circuit between the positive and negative electrodes, which poses certain safety hazards. In addition, the formation of lithium dendrites increases the side reaction between the electrolyte and metallic lithium, consumes lithium active substances, and reduces the battery recycling rate.

[0003] With respect to the existing thick coating or high compaction density electrode plates, the technicians in this field mainly adopt the following methods to improve the electrolyte infiltration to increase the migration rate of lithium ions, thereby solving the problems of large concentration polarization inside the thick coating electrode plates, poor rate performance, and poor consistency of the plates: (1) preparing an active material slurry containing different pore-forming agent concentrations to coat the current collector to obtain a coated electrode plate with a porosity gradient in the thickness direction, so as to improve the penetration and infiltration of the electrolyte and improve the transmission of lithium ions or electrons in the electrode, such as Chinese invention patent application No. 201110247550X Thick electrode with good electrochemical performance and preparation method thereof, 2 012101919565 A method for preparing a lithium-ion secondary battery electrode; (2) A thick-coated electrode electrode with different porosity gradients is prepared by multiple layered coating, such as Chinese invention patent application No. 2012105412846 A method for preparing a thick electrode with a low solid content slurry for lithium-ion batteries; (3) Use a laser to punch holes in the electrode along the thickness direction to improve the battery's rate performance, such as Chinese invention patent application No. 2023115139340 A negative electrode sheet and its preparation method and application, 2024107624508 Negative electrode sheet and preparation method, lithium-ion battery, and electrical device.

[0004] In the above-mentioned improved method, while improving the problem of electrolyte permeability of thick coated pole pieces, it also brings different negative effects such as uneven local lithium deintercalation of micron-scale pores formed by pore-forming agents, complex multi-layer coating process, and high-temperature damage to materials around the holes caused by laser drilling. Therefore, the existing method for manufacturing thick coated electrode pole pieces of high energy density lithium-ion power batteries needs to be improved. However, as Chinese invention patent application No. 2024115258679, a porous alumina powder, battery separator, battery, and electrical equipment for lithium-ion batteries, discloses a porous alumina coated separator, which can increase the electrolyte wettability of the polymer separator and significantly improve the electrolyte diffusion radius of the separator. The ion diffusion path in lithium batteries is divided into the internal diffusion path of the negative electrode piece, the internal diffusion path of the separator, and the internal diffusion path of the positive electrode piece. However, the inventors found that this method can only improve the diffusion inside the separator, and is powerless for the diffusion inside the positive and negative electrode pieces. In thick electrode or high-pressure electrode systems, the ion conduction restricted area is actually inside the pole piece, not the separator, so the effect of this method is poor.

[0005] To this end, the present application proposes to add mesoporous materials to the pole piece to achieve the purpose of improving the wettability and battery rate of thick coating or high compaction density pole pieces. Summary of the invention

[0006] The technical problem to be solved by the present invention is that the existing thick-coated electrode pole pieces have large internal concentration polarization, poor rate performance, and poor pole piece consistency. In view of the problems existing in the prior art, a method for preparing high-rate pole pieces for lithium batteries is provided.

[0007] The purpose and effect of the present invention are achieved by the following specific technical means: A method for preparing a high-rate electrode for a lithium battery comprises the following steps: S1, mixing and stirring the mesoporous material powder, the conductive agent powder and the binder powder to obtain a first mixture; S2, adding a solvent to the first mixture in S1 to wet the first mixture, and then diluting, stirring, dispersing, kneading and scraping with the solvent to obtain a second mixture; S3, adding active substance powder to the second mixture in S2 to moisten the second mixture, then diluting, stirring, dispersing, kneading and scraping with a solvent, and then performing vacuum degassing to obtain a third mixture; S4, coating the third mixture of S3 on both sides of the foil, and after drying, forming a pole sheet material layer on the foil, and rolling it to obtain a positive pole sheet and a negative pole sheet.

[0008] A further preferred embodiment: the mesoporous material powder in step S1 is a mesoporous metal oxide material or a mesoporous silicon-based material, including one or more combinations of aluminum oxide, titanium oxide, zirconium oxide and silicon oxide.

[0009] A further preferred embodiment: the binder powder in step S1 is one or more combinations of vinylidene fluoride, polyvinylidene fluoride, homopolymer of vinylidene fluoride, polyvinylidene fluoride copolymer, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polyacrylamide, styrene-butadiene rubber and styrene-propylene rubber.

[0010] A further preferred embodiment: the conductive agent powder in step S1 is selected from one or more combinations of conductive carbon black, carbon nanotubes, graphene, and carbon fibers.

[0011] A further preferred embodiment: the solvent in step S2 is selected from one or more combinations of N-methylpyrrolidone, N-dimethylformamide, dimethyl sulfoxide and water.

[0012] A further preferred embodiment: the active material powder described in step S3 is a positive electrode and a negative electrode active material powder, and the positive electrode active material powder includes one or more combinations of lithium cobalt oxide, lithium iron phosphate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadium phosphate, lithium vanadate, lithium manganate, lithium nickel oxide, lithium nickel cobalt manganate, and lithium-rich manganese-based materials; The negative electrode active material powder is one or more combinations of hard carbon, graphite, mesophase carbon microspheres, silicon dioxide, silicon, and lithium titanate.

[0013] A further preferred embodiment: the amount of the mesoporous material powder added in step S1 is 0.1%-5% of the amount of the active substance powder added in step S3.

[0014] A further preferred embodiment: the kneading solid content of the first mixture and the second mixture in steps S1 and S2 is 50%-75%.

[0015] A further preferred solution: in step S4, the single-sided thickness of the positive electrode sheet is ≥80um, the single-sided thickness of the negative electrode sheet is ≥50um, the compaction of the positive electrode sheet is ≥3.5g / cm³, and the compaction of the negative electrode sheet is ≥1.5g / cm³.

[0016] Beneficial effects of the present invention: 1. The present invention adds mesoporous materials with open pores and high liquid absorption values ​​to the electrode, which can significantly improve the wettability of thick coatings or high compaction density electrodes with electrolytes, as well as the rate and cycle performance of the battery. Compared with methods such as pore-forming agents, multi-layer coatings, and laser pore-forming, the "sponge" liquid absorption channel formed by using mesoporous materials has the characteristics of strong liquid absorption capacity, small pores, uniform lithium release and adsorption, simple process, and no damage to the materials around the pores.

[0017] 2. Compared with carbon-based materials, mesoporous metal oxides or silicon-based materials will not undergo electrochemical reactions with the electrolyte due to their non-conductive properties, thus reducing side reactions inside the battery cell and coulombic efficiency losses. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described below in conjunction with the accompanying drawings.

[0019] Figure 1 This is a schematic diagram of the layered structure of the pole piece preparation material of the present invention; Figure 2 Schematic diagram of battery performance test of Examples 1 and 2 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0020] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The following embodiments are only examples of implementing the present invention. It must be pointed out that the disclosed embodiments do not limit the scope of the present invention. On the contrary, changes and modifications made without departing from the scope of the present invention are all within the scope of patent protection of the present invention.

[0021] See also Figure 1-Figure 2 , a method for preparing a high-rate electrode for a lithium battery, comprising the following steps: S1, mixing and stirring the mesoporous material powder, the conductive agent powder and the binder powder to obtain a first mixture; Preferably, the mesoporous material powder is a mesoporous metal oxide material or a mesoporous silicon-based material, including one or more combinations of aluminum oxide, titanium oxide, zirconium oxide, and silicon oxide; Preferably, the binder powder is one or more combinations of vinylidene fluoride, polyvinylidene fluoride, homopolymer of vinylidene fluoride, polyvinylidene fluoride copolymer, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polyacrylamide, styrene-butadiene rubber, and styrene-acrylic rubber; Preferably, the conductive agent powder is selected from one or more combinations of conductive carbon black, carbon nanotubes, graphene, and carbon fibers.

[0022] S2, adding a solvent to the first mixture in S1 to wet the first mixture, and then diluting, stirring, dispersing, kneading and scraping with the solvent to obtain a second mixture; Preferably, the solvent is selected from one or more combinations of N-methylpyrrolidone, N-dimethylformamide, dimethyl sulfoxide and water.

[0023] Furthermore, the kneading solid contents of the first mixture and the second mixture during the stirring stage are both 50%-75%.

[0024] S3, adding active substance powder to the second mixture in S2 to moisten the second mixture, then diluting, stirring, dispersing, kneading and scraping with a solvent, and then performing vacuum degassing to obtain a third mixture; Preferably, the active material powder is a positive electrode and a negative electrode active material powder, and the positive electrode active material powder includes one or more combinations of lithium cobalt oxide, lithium iron phosphate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadium phosphate, lithium vanadate, lithium manganate, lithium nickel oxide, lithium nickel cobalt manganate, and lithium-rich manganese-based materials; The negative electrode active material powder is one or more combinations of hard carbon, graphite, mesophase carbon microspheres, silicon dioxide, silicon, and lithium titanate.

[0025] Furthermore, the amount of mesoporous material powder added is 0.1%-5% of the amount of active substance powder added in S3.

[0026] S4, coating the third mixture of S3 on both sides of the foil, and after drying, forming a pole sheet material layer on the foil, and rolling to obtain a positive pole sheet and a negative pole sheet; Preferably, the thickness of the single side of the positive electrode sheet is ≥80um, the thickness of the single side of the negative electrode sheet is ≥50um, the compaction of the positive electrode sheet is ≥3.5g / cm³, and the compaction of the negative electrode sheet is ≥1.5g / cm³.

[0027] Finally, the electrode sheet, electrolyte and separator are assembled to prepare a lithium-ion battery, wherein the electrode sheet can be a positive electrode sheet obtained by the above preparation method, and a negative electrode sheet without mesoporous material prepared by a conventional method; Or a positive electrode sheet without mesoporous material prepared by conventional methods is matched with a negative electrode sheet prepared by the above preparation method; Or the positive electrode sheet and the negative electrode sheet obtained by the above preparation method are matched together.

[0028] Example 1, preparation of positive electrode sheet: Providing lithium nickel cobalt manganese oxide powder, mesoporous alumina powder, polyvinylidene fluoride powder and conductive carbon black powder in a predetermined ratio, wherein the predetermined ratio is 96.5:1:1.5:1; mixing and stirring the mesoporous alumina powder, polyvinylidene fluoride powder and conductive carbon black powder in a water bath cooled and sealed environment to obtain a first mixture; Adding N-methylpyrrolidone to the first mixture to wet the first mixture, and then diluting, stirring, dispersing, kneading and scraping with a solvent to obtain a second mixture; Adding lithium nickel cobalt manganate powder to the second mixture to wet the second mixture, then diluting, stirring, dispersing, kneading and scraping with N-methylpyrrolidone, and then vacuum degassing to obtain a third mixture; The third mixture is coated on both sides of the aluminum foil respectively. After drying, a positive electrode material layer is formed on the aluminum foil, and then rolled to obtain a positive electrode sheet with a compaction density of 3.65 g / cm³. The prepared positive electrode sheet containing mesoporous material, conventional negative electrode sheet, electrolyte and separator were assembled to prepare a lithium-ion battery to obtain a 3.5Ah soft-pack battery, denoted as C1, and the performance was tested.

[0029] Example 2, preparation of positive electrode sheet: Lithium nickel cobalt manganese oxide powder, mesoporous alumina powder, polyvinylidene fluoride powder and conductive carbon black powder were prepared in a predetermined ratio of 96:1.5:1.5:1, and the rest was the same as in the above-mentioned Example 1. Then, the positive electrode plate, the conventional negative electrode plate, the electrolyte and the separator were assembled to prepare a lithium-ion battery, wherein the negative electrode plate, the electrolyte and the separator were the same as in Example 1, and a 3.5Ah soft-pack battery was obtained, recorded as C2, and the performance was tested.

[0030] Comparative Example 1, preparation of positive electrode sheet: Lithium nickel cobalt manganese oxide powder, polyvinylidene fluoride powder and conductive carbon black powder were prepared in a predetermined ratio of 97.5:1.5:1, and the rest was the same as in Example 1. The positive electrode sheet, the negative electrode sheet, the electrolyte and the separator were assembled to prepare a lithium-ion battery, wherein the negative electrode sheet, the electrolyte and the separator were the same as in Example 1, and a 3.5Ah soft-pack battery was obtained, recorded as C3, and the performance was tested.

[0031] The battery performance test results of Examples 1-2 and Comparative Example 1 are given as follows: (1) Rate performance comparison: At 25°C, 0.33C charge / 0.33C discharge, 1C charge / 1C discharge, 2C charge / 2C discharge, and 3C charge / 3C discharge tests were performed, with a voltage range of 3.0-4.2V, and 0.33C charge / 0.33C discharge capacity was used as the benchmark capacity. (2) Cycle performance comparison: At 25°C, 1C / 1C cycles were performed with a voltage range of 3.0-4.2V, and the capacity retention rate at the 600th cycle was taken.

[0032] like Figure 2 The battery performance test results of Examples 1-2 and Comparative Example 1 are shown in Figure 2 It can be seen from the data that the C1 battery and C2 battery with the addition of mesoporous materials have higher 2C and 3C capacity retention rates than the C1 battery. This is because the mesoporous alumina uniformly dispersed in the electrode can provide cross-network channels for rapid migration of lithium ions after absorbing the electrolyte, thereby reducing the battery concentration polarization and improving the battery's discharge capacity at high rates.

[0033] The 2C and 3C capacity retention rates of the C2 battery are higher than those of the C1 battery. This is because the C2 battery adds more mesoporous alumina, which allows it to have a more developed cross-network channel for lithium ion migration.

[0034] The cycle performance of C1 and C2 batteries is also better than that of C3 batteries. This is because mesoporous alumina with high liquid absorption value and pore volume can form a "sponge"-like liquid absorption channel inside the electrode, which has a higher adsorption capacity for organic solvents in the electrolyte and a short lithium ion diffusion path and a fast diffusion rate, which extend the cycle life of the battery.

Claims

1. A method for preparing a high-rate electrode for a lithium battery, characterized in that: The following steps are involved: S1, mixing and stirring the mesoporous material powder, the conductive agent powder and the binder powder to obtain a first mixture; S2, adding a solvent to the first mixture in S1 to wet the first mixture, and then diluting, stirring, dispersing, kneading and scraping with the solvent to obtain a second mixture; S3, adding active substance powder to the second mixture in S2 to moisten the second mixture, then diluting, stirring, dispersing, kneading and scraping with a solvent, and then performing vacuum degassing to obtain a third mixture; S4, coating the third mixture of S3 on both sides of the foil, and after drying, forming a pole sheet material layer on the foil, and rolling it to obtain a positive pole sheet and a negative pole sheet.

2. The method for preparing a high-rate electrode for a lithium battery according to claim 1, characterized in that: The mesoporous material powder described in step S1 is a mesoporous metal oxide material or a mesoporous silicon-based material, including one or more combinations of aluminum oxide, titanium oxide, zirconium oxide, and silicon oxide.

3. The method for preparing a high-rate electrode sheet for a lithium battery according to claim 1, characterized in that: The binder powder described in step S1 is one or more combinations of vinylidene fluoride, polyvinylidene fluoride, homopolymer of vinylidene fluoride, polyvinylidene fluoride copolymer, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polyacrylamide, styrene-butadiene rubber, and styrene-propylene rubber.

4. The method for preparing a high-rate electrode for a lithium battery according to claim 1, characterized in that: The conductive agent powder described in step S1 is selected from one or more combinations of conductive carbon black, carbon nanotubes, graphene, and carbon fibers.

5. The method for preparing a high-rate electrode for a lithium battery according to claim 1, characterized in that: The solvent described in step S2 is selected from one or more combinations of N-methylpyrrolidone, N-dimethylformamide, dimethyl sulfoxide and water.

6. A method for preparing a high-rate electrode for a lithium battery according to claim 1, characterized in that: The active material powders described in step S3 are positive electrode and negative electrode active material powders, and the positive electrode active material powders include one or more combinations of lithium cobalt oxide, lithium iron phosphate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadium phosphate, lithium vanadate, lithium manganate, lithium nickel oxide, lithium nickel cobalt manganate, and lithium-rich manganese-based materials; The negative electrode active material powder is one or more combinations of hard carbon, graphite, mesophase carbon microspheres, silicon dioxide, silicon, and lithium titanate.

7. The method for preparing a high-rate electrode for a lithium battery according to claim 1, characterized in that: The amount of the mesoporous material powder added in step S1 is 0.1%-5% of the amount of the active substance powder added in step S3.

8. The method for preparing a high-rate electrode for a lithium battery according to claim 1, characterized in that: The kneading solid content of the first mixture and the second mixture in steps S1 and S2 is 50%-75%.

9. The method for preparing a high-rate electrode for a lithium battery according to claim 1, characterized in that: In step S4, the thickness of the single side of the positive electrode sheet is ≥80um, the thickness of the single side of the negative electrode sheet is ≥50um, the compaction of the positive electrode sheet is ≥3.5g / cm³, and the compaction of the negative electrode sheet is ≥1.5g / cm³.

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