Composition of novel positive electrode functional layer precursor and preparation method thereof

Abstract

The invention discloses a composition of a novel positive electrode functional layer precursor, and in the processing process, the composition can present a dough-like state at a proper temperature, and is soft, plastic, elastic and easy to process; in the processing process, a small amount of solvent is used, high-speed stirring equipment does not need to be used for long-time dispersion, better uniformity can be achieved in pole piece processing, and the lithium ion battery positive pole piece with low energy consumption, low pollution, high consistency and high safety is obtained, so that the stability, reliability and safety of the lithium ion battery are improved.

Description

Technical Field

[0001] This invention relates to a novel positive electrode functional layer composition precursor for lithium-ion batteries, lithium-ion battery electrodes, and lithium-ion batteries, belonging to the field of lithium-ion battery technology. Background Technology

[0002] Lithium-ion batteries are among the most commonly used batteries in the field of mobile power supplies due to their high energy density, small volumetric density, long cycle life, and low environmental impact. This has led to their widespread and in-depth application in electric vehicles, commercial drones, aerospace, information and communication, and a variety of portable electronic devices.

[0003] The positive electrode of a lithium-ion battery consists of a positive electrode functional layer precursor, a binder, a conductive agent, and a current collector. Current technology for preparing the positive electrode functional layer precursor involves dispersing the binder, positive electrode material, and conductive agent in a solvent at specific ratios and solid content using high-speed stirring equipment for an extended period. This process suffers from drawbacks such as high solvent consumption, high energy consumption, and significant environmental pollution. Furthermore, the prolonged mechanical stirring and dispersion increases the risk of metal ion introduction. In addition, the positive electrode functional layer precursor prepared using traditional methods is in slurry form, which is then coated onto the current collector using a roller coating process. This slurry is a non-Newtonian fluid, and its viscosity varies with shear force, leading to viscosity rebound and significant fluctuations in the surface density of the electrode coating, resulting in poor electrode uniformity.

[0004] The uniformity of the positive electrode has a significant impact on the performance of lithium-ion batteries. First, poor electrode uniformity leads to variations in parameters such as the content of active material and conductivity across different regions of the electrode. This can result in localized overcharging or over-discharging during charging and discharging, causing premature damage to certain areas of the electrode and affecting overall battery performance. Second, uniform electrodes help maintain stable internal resistance, while non-uniform electrodes can cause fluctuations in internal resistance, affecting battery stability and reliability. Third, poor electrode uniformity can also lead to localized temperature differences within the battery, causing internal thermal runaway, which in turn can lead to performance degradation or even safety incidents. Therefore, the uniformity of the positive electrode is a critical factor in the design and manufacturing of lithium-ion batteries, decisively influencing battery performance and safety. Summary of the Invention

[0005] The problems this invention aims to solve are: first, the existing process suffers from high solvent consumption, high energy consumption, and significant environmental pollution; second, it addresses the defect that the cathode functional layer precursor, being a slurry, experiences large fluctuations in the surface density of the coated electrode due to varying shear forces, thus affecting electrode uniformity. Therefore, there is an urgent need to develop a cathode functional layer precursor that uses less solvent, has high coating efficiency, and exhibits good electrode uniformity, in order to reduce energy consumption, decrease pollution, and improve battery stability, reliability, and safety.

[0006] The objective of this invention is to provide a novel composition for a positive electrode functional layer precursor. During processing, this composition, at a suitable temperature, exhibits a dough-like state—soft, malleable, and elastic—making it easy to process and improving the uniformity of electrode areal density. The processing uses very little solvent, eliminating the need for prolonged dispersion using high-speed stirring equipment, thus avoiding the increased risk of metal ion introduction associated with prolonged mechanical stirring. Furthermore, it achieves better uniformity during electrode processing, resulting in low-energy-consumption, low-pollution, highly consistent, and highly safe lithium-ion battery positive electrode sheets, thereby improving the stability, reliability, and safety of lithium-ion batteries.

[0007] Solution to the problem: Through extensive experiments, tests, and comparisons, the inventors discovered that by selecting appropriate solvents and solvent ratios during the processing of the positive electrode functional layer precursor, a "dough-like" composition can be obtained. When processing the positive electrode sheet, compared to the slurry state of the traditional positive electrode functional layer precursor, viscosity rebound will not occur due to inconsistent shear forces. This can effectively reduce the amount of solvent used and greatly improve the uniformity and stability of the electrode sheet.

[0008] The objective of this invention is achieved through the following technical solution: a novel positive electrode functional layer precursor composition, comprising 1 part powder material and 0.1-0.6 parts solvent; wherein the powder material comprises 90-99 parts positive electrode active material, 0.2-5 parts conductive agent, and 0.8-5 parts binder, wherein the solvent is selected from one or more combinations of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. When the solvent is selected from ethylene carbonate, propylene carbonate, and fluoroethylene carbonate, 0.1-0.6 parts of solvent can ensure uniform and stable distribution of the powder material, allowing the positive electrode functional layer precursor composition to have a dough-like state, and the powder material can be uniformly and stably distributed. Furthermore, the selected solvent will not negatively impact the existing material system of lithium-ion batteries. This dough-like positive electrode functional layer precursor composition, compared to traditional slurry-like precursors, does not exhibit shear thickening or shear thinning during electrode processing, thus effectively avoiding viscosity rebound, significantly reducing solvent consumption, and greatly improving the uniformity and stability of the electrode.

[0009] In this invention, the composition of the novel positive electrode functional layer precursor contains a positive electrode active material selected from one or more combinations of lithium iron phosphate, lithium cobalt oxide, ternary lithium, lithium manganese oxide, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0010] In this invention, the binder of the novel positive electrode functional layer precursor composition is polyvinylidene fluoride.

[0011] In this invention, the conductive agent in the composition of the novel positive electrode functional layer precursor is selected from one or more combinations of carbon nanotubes, conductive carbon, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, carbon black, carbon black, graphite, carbon fiber, carbon nanofibers, Ketjen black, and acetylene black.

[0012] In this invention, the solvent for the novel positive electrode functional layer precursor composition is selected from either ethylene carbonate or fluoroethylene carbonate. After extensive experimentation, the inventors discovered that these two solvents have low melting points and can more easily form a dough-like state at room temperature, which facilitates better and more uniform dispersion of the novel positive electrode functional layer precursor composition and results in better processing performance during electrode fabrication.

[0013] In this invention, the composition of the novel positive electrode functional layer precursor is prepared by a method comprising the following steps: S1, add 90-99 parts of positive electrode active material, 0.2-5 parts of conductive agent, and 0.8-5 parts of binder powder to a mixer, control the temperature at 0-60℃, and mix for 0.8-2 hours to obtain mixture 1; S2, transfer mixture 1 to an internal mixer, add solvent with a mass fraction of 10%-60% of the total mass of the three powders as a basis, control the temperature at 30-100℃, and mix for 1-3 hours to form a rubbery fluid. Discharge the mixture to obtain mixture 2. S3, after cooling mixture 2, extrude and granulate it.

[0014] In this invention, the mixing machine is rotated at a speed of 5-80 r / min during the preparation of the novel positive electrode functional layer precursor composition.

[0015] The positive electrode functional layer described in this invention comprises a composition containing any of the above-mentioned novel positive electrode functional layer precursors. The positive electrode functional layer refers to a coating applied to the positive electrode current collector after the positive electrode sheet has been processed.

[0016] The positive electrode sheet for lithium-ion secondary batteries described in this invention includes a positive current collector and the positive electrode functional layer as described above.

[0017] The lithium-ion secondary battery described in this invention has the above-mentioned positive electrode sheet for lithium-ion secondary batteries.

[0018] The beneficial effects of this invention are as follows: Compositions of novel positive electrode functional layer precursors using appropriate solvents and solvent ratios can make them resemble "dough" during electrode processing, which can significantly reduce solvent consumption, energy consumption, and pollution.

[0019] The composition of the novel positive electrode functional layer precursor does not require long-term, continuous dispersion using high-speed stirring equipment, thus avoiding the risk of metal ion introduction caused by prolonged mechanical stirring and dispersion.

[0020] The novel positive electrode functional layer precursor composition avoids the use of slurry roller coating process during electrode processing, and does not cause viscosity rebound due to changes in shear force, effectively reducing the density fluctuation of the coating surface, thereby significantly improving the uniformity and stability of the battery electrode. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below through specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] In the examples and comparative examples, the methods for preparing the composition of the novel positive electrode functional layer precursor, determining the metal ion content, measuring the electrode surface density fluctuation, and testing the cycle performance of the secondary battery are as follows: Preparation of novel positive electrode functional layer precursor compositions Add the positive electrode active material, conductive agent, and binder powders to a mixer, control the temperature at 0-60℃, set the mixer speed at 5-80 r / min, and mix for 0.5-2 hours to obtain mixture 1. Transfer mixture 1 to an internal mixer, add solvent at 10%-60% of the total mass of the three powders, control the temperature at 30-100℃, and mix for 1-3 hours to form a rubbery fluid. Discharge to obtain mixture 2. After cooling mixture 2, control the temperature at 60-120℃ and extrude and granulate.

[0023] [Measurement of Electrode Surface Density Fluctuation] Test method: Weighing method Sampling object: continuously coated electrode sheet.

[0024] Test method: At 25℃ + / -2℃ and humidity <30%, use a 50mm diameter circular sampler to take three samples sequentially at a distance of 5cm from the edge along the width of the electrode sheet. Take three samples at each 10-meter interval, for a total of three locations, with three samples at each location. Weigh each sheet, calculate the areal density, and compare the areal density consistency.

[0025] Excellent: Areal density uniformity ≥99% Good: Areal density consistency 99%-98.6% General: Areal density uniformity 98.6%-98.2% Poor: Areal density uniformity <98.2% [Electrode Resistance Test] Electrode resistivity was measured using a film resistivity meter. Cut the prepared electrode into 60mm*80mm test pieces, measure the thickness of the electrode with a micrometer, and then test it with a film resistance meter. The test head diameter is 10mm, the test pressure is 7MPa, the electrode thickness is input, and the resistivity is measured at 5 points: the four corners and the center of the test piece. The resistivity result is taken as the average value.

[0026] Excellent: Resistivity < 0.3 Ω*cm Good: Resistivity is 0.3-0.5 Ω*cm Generally, the resistivity is 0.5-0.7 Ω*cm. Difference: Resistivity > 0.8 Ω*cm Secondary battery cycle performance Ten lithium-ion secondary batteries were fabricated and charged to 4.2V and discharged to 3V using a constant current method at 0.2C at 25℃, constituting one cycle. 200 cycles were performed. The ratio of the capacitance after 200 cycles to the average capacitance at the end of 5 cycles was calculated. The discharge capacity retention rate = (average capacitance at the end of 200 cycles / average capacitance at the end of 5 cycles) * 100.

[0027] Excellent: Discharge capacity retention > 80% Good: Discharge capacity retention rate is 70-80%. Generally, the discharge capacity retention rate is 60-70%. Poor: Discharge capacity retention < 60% Specific Implementation Example 1

[0028] Add 97 parts of positive electrode active material, 1.5 parts of conductive agent, and 1.5 parts of binder powder to an AKS10 mixer, control the temperature at 20℃, set the speed at 30 r / min, and mix for 1.8 hours to obtain mixture 1. Transfer mixture 1 to a Sentech S20L internal mixer, add 30% by mass of ethylene carbonate based on the sum of the three powder masses, control the temperature at 55℃, and internally mix for 2 hours to form a rubbery fluid. Discharge to obtain mixture 2. After cooling mixture 2, put it into a BP-8177-B extruder granulator, control the temperature at 75℃, and extrude and granulate. Example 2

[0029] Add 90 parts of positive electrode active material, 5 parts of conductive agent, and 5 parts of binder powder to an AKS10 mixer, control the temperature at 10℃, set the speed at 10r / min, and mix for 2 hours to obtain mixture 1. Transfer mixture 1 to a Sentech S20L internal mixer, add 15% by mass of propylene carbonate based on the sum of the three powder masses, control the temperature at 35℃, and mix for 2.8 hours to form a rubbery fluid. Discharge to obtain mixture 2. After cooling mixture 2, put it into a BP-8177-B extruder granulator, control the temperature at 65℃, and extrude and granulate. Example 3

[0030] Add 99 parts of positive electrode active material, 0.2 parts of conductive agent, and 0.8 parts of binder powder to an AKS10 mixer, control the temperature at 55℃, set the speed at 70 r / min, and mix for 0.8 hours to obtain mixture 1. Transfer mixture 1 to a Sentech S20L internal mixer, add propylene carbonate at 55% of the total mass of the three powders, control the temperature at 95℃, and mix for 1.2 hours to form a rubbery fluid. Discharge to obtain mixture 2. After cooling mixture 2, put it into a BP-8177-B extruder granulator, control the temperature at 115℃, and extrude and granulate. Example 4

[0031] Add 97.5 parts of positive electrode active material, 1 part of conductive agent, and 1.5 parts of binder powder to an AKS10 mixer, control the temperature at 30℃, set the speed at 35 r / min, and mix for 2 hours to obtain mixture 1. Transfer mixture 1 to a Sentech S20L internal mixer, add 25% by mass of ethylene carbonate based on the sum of the three powder masses, control the temperature at 85℃, and mix for 1.5 hours to form a rubbery fluid. Discharge to obtain mixture 2. After cooling mixture 2, put it into a BP-8177-B extruder granulator, control the temperature at 80℃, and extrude and granulate. Example 5

[0032] Add 96.5 parts of positive electrode active material, 2.5 parts of conductive agent, and 1 part of binder powder to an AKS10 mixer, control the temperature at 30℃, set the speed at 45 r / min, and mix for 1.5 hours to obtain mixture 1. Transfer mixture 1 to a Sentech S20L internal mixer, add 35% by mass of fluoroethylene carbonate based on the sum of the three powder masses, control the temperature at 50℃, and mix for 2.5 hours to form a rubbery fluid. Discharge to obtain mixture 2. After cooling mixture 2, put it into a BP-8177-B extruder granulator, control the temperature at 85℃, and extrude and granulate. Example 6

[0033] Add 97 parts of positive electrode active material, 1.8 parts of conductive agent, and 1.2 parts of binder powder to an AKS10 mixer, control the temperature at 45℃, set the speed at 60 r / min, and mix for 1 hour to obtain mixture 1. Transfer mixture 1 to a Sentech S20L internal mixer, add 40% by mass of propylene carbonate based on the sum of the three powder masses, control the temperature at 75℃, and mix for 1.5 hours to form a rubbery fluid. Discharge to obtain mixture 2. After cooling mixture 2, put it into a BP-8177-B extruder granulator, control the temperature at 95℃, and extrude and granulate. Example 7

[0034] Add 96 parts of positive electrode active material, 2.2 parts of conductive agent, and 1.8 parts of binder powder to an AKS10 mixer, control the temperature at 15℃, set the speed at 8r / min, and mix for 2 hours to obtain mixture 1. Transfer mixture 1 to a Sentech S20L internal mixer, add 15% by mass of ethylene carbonate based on the sum of the three powder masses, control the temperature at 35℃, and mix for 3 hours to form a rubbery fluid. Discharge to obtain mixture 2. After cooling mixture 2, put it into a BP-8177-B extruder granulator, control the temperature at 65℃, and extrude and granulate. Example 8

[0035] Add 98 parts of positive electrode active material, 0.3 parts of conductive agent, and 1.7 parts of binder powder to an AKS10 mixer, control the temperature at 55℃, set the speed at 75 r / min, and mix for 1 hour to obtain mixture 1. Transfer mixture 1 to a Sentech S20L internal mixer, add 60% by mass of fluoroethylene carbonate based on the sum of the three powder masses, control the temperature at 98℃, and mix for 1.2 hours to form a rubbery fluid. Discharge to obtain mixture 2. After cooling mixture 2, put it into a BP-8177-B extruder granulator, control the temperature at 118℃, and extrude and granulate. Example 9

[0036] Add 98.5 parts of positive electrode active material, 0.7 parts of conductive agent, and 0.8 parts of binder powder to an AKS10 mixer, control the temperature at 35℃, set the speed at 50 r / min, and mix for 1.1 hours to obtain mixture 1. Transfer mixture 1 to a Sentech S20L internal mixer, add 50% by mass of ethylene carbonate based on the sum of the three powder masses, control the temperature at 65℃, and mix for 1.9 hours to form a rubbery fluid. Discharge to obtain mixture 2. After cooling mixture 2, put it into a BP-8177-B extruder granulator, control the temperature at 88℃, and extrude and granulate.

[0037] Comparative Example 1 97 parts of positive electrode active material, 1.5 parts of conductive agent, and 1.5 parts of binder powder were added to an AKS10 mixer. The temperature was controlled at 20℃ and the rotation speed was set at 30 r / min. The mixture was mixed for 1.8 hours to obtain mixture 1. Mixture 1 was then transferred to a Sentech S20L internal mixer. Based on the sum of the masses of the three powders, 30% by mass of N-methylpyrrolidone was added. The temperature was controlled at 55℃ and the mixture was internally mixed for 2.2 hours to form a rubbery fluid. The mixture was then discharged to obtain mixture 2. After cooling, mixture 2 was fed into a BP-8177-B extruder and granulated at 75℃.

[0038] Comparative Example 2 96 parts of positive electrode active material, 2.2 parts of conductive agent, and 1.8 parts of binder powder were added to an AKS10 mixer. The temperature was controlled at 15℃ and the speed was set at 8r / min. The mixture was mixed for 2 hours to obtain mixture 1. Mixture 1 was transferred to a Sentech S20L internal mixer. Based on the sum of the masses of the three powders, 70% by mass of ethylene carbonate was added. The temperature was controlled at 35℃ and the mixture was internally mixed for 3 hours to form a rubbery fluid. The mixture was then discharged to obtain mixture 2. After cooling, mixture 2 was placed into a BP-8177-B extruder granulator. The temperature was controlled at 65℃, but extrusion granulation was not possible.

[0039] Comparative Example 3 97 parts of positive electrode active material, 1.8 parts of conductive agent, and 1.2 parts of binder powder were added to an AKS10 mixer. The temperature was controlled at 45℃ and the rotation speed was set at 60 r / min. The mixture was mixed for 1 hour to obtain mixture 1. Mixture 1 was then transferred to a Sentech S20L internal mixer. Based on the sum of the masses of the three powders, 9% by mass of propylene carbonate was added. The temperature was controlled at 75℃ and the mixture was internally mixed for 1.5 hours. However, a rubbery fluid could not be formed, and mixture 2 could not be successfully discharged. Extrusion granulation could not be completed.

[0040] Table 1 Test Results

[0041] Analysis of experimental results: As demonstrated by Comparative Example 1 and Examples 1-9, using N-methylpyrrolidone as a solvent results in significant fluctuations in electrode areal density, high electrode resistance, and poor cycle performance of the secondary battery. When the solvent is selected from one or more combinations of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate, it can exhibit a dough-like state at suitable temperatures, becoming soft, malleable, and elastic, making it easy to process and effectively reducing the fluctuations in electrode areal density.

[0042] As can be seen from Comparative Example 2 and Examples 1-9, when the amount of solvent is greater than 0.6 parts, the resulting rubbery fluid cannot form a dough-like state due to the excessive solvent content, and therefore cannot be extruded and granulated.

[0043] As can be seen from Comparative Example 3 and Examples 1-9, when the amount of solvent is less than 0.09 parts, the solvent content is too low to form a rubbery fluid, so the mixture 2 cannot be successfully discharged and extrusion granulation cannot be completed.

[0044] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A composition of a novel positive electrode functional layer precursor, characterized by, The powder material is composed of 90-99 parts of positive electrode active material, 0.2-5 parts of conductive agent, and 0.8-5 parts of binder. The powder material is composed of 90-99 parts of positive electrode active material, 0.2-5 parts of conductive agent, and 0.8-5 parts of binder. The solvent is selected from a combination of one or more of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate.

2. The composition of the novel positive electrode functional layer precursor according to claim 1, wherein, The positive electrode active material is selected from a combination of one or more of lithium iron phosphate, lithium cobaltate, ternary lithium, lithium manganate, lithium iron manganese phosphate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminum.

3. The composition of the novel positive electrode functional layer precursor according to claim 1, wherein, The binder is polyvinylidene fluoride.

4. The composition of the novel positive electrode functional layer precursor according to claim 1, wherein, The conductive agent is selected from a combination of one or more of carbon nanotubes, conductive carbon, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, carbon black, carbon black, graphite, carbon fibers, carbon nanofibers, Ketjen black, and acetylene black.

5. The composition of the novel positive electrode functional layer precursor according to claim 1, wherein, The solvent is selected from any one of ethylene carbonate and propylene carbonate.

6. The composition of the novel positive electrode functional layer precursor according to any one of claims 1 to 5, characterized by, The method comprises the following steps: S1. Add 90-99 parts of positive electrode active material, 0.2-5 parts of conductive agent, and 0.8-5 parts of binder to a mixer, control the temperature at 0-60℃, and mix for 0.8-2 hours to obtain a mixture 1. S2. Transfer the mixture 1 to an internal mixer, add 10%-60% of the total mass of the three powders as a solvent, control the temperature at 30-100℃, and internally mix for 1-3 hours to form a rubber state fluid, discharge, and obtain a mixture 2. S3. After cooling the mixture 2, extrude and granulate.

7. The composition of the novel positive electrode functional layer precursor according to claim 6, wherein The mixer speed is 5-80 r / min.

8. A positive electrode functional layer characterized by comprising: A composition comprising the novel positive electrode functional layer precursor of any one of claims 1-5.

9. A positive electrode sheet for a lithium-ion secondary battery, characterized by: A positive electrode comprising the positive electrode functional layer of claim 8.

10. A lithium ion secondary battery having the positive electrode sheet for lithium ion secondary batteries of claim 9.

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