A lithium-rich manganese-based positive thick electrode, a preparation method and applications thereof

Abstract

The application belongs to the technical field of lithium ion battery materials, and relates to a preparation method of a lithium-rich manganese-based positive thick electrode and application thereof. In the method, a binder sodium carboxymethyl cellulose and an additive ethylene carbonate are dissolved in a mixed solvent of deionized water and N-methyl pyrrolidone, a double conductive agent is added and then dispersed, two kinds of lithium-rich manganese-based positive electrode materials with different particle sizes are compounded, and a pore-forming agent is introduced to obtain a mixed slurry. The slurry is coated on a current collector, and finally, the thick electrode is prepared through segmented drying and rolling. The application utilizes particle size grading to improve the compaction density, cooperates with a pore-forming process to construct an ion transmission channel, and cooperates with a segmented drying process to eliminate internal stress of the thick electrode. The prepared thick electrode has significantly improved peeling strength, excellent specific capacity and cycle stability under 1C high rate, and solves the problems of easy cracking and poor kinetic performance of the thick electrode. The application is suitable for the field of high-energy-density lithium ion batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a lithium-rich manganese-based thick cathode electrode, its preparation method, and its application. Background Technology

[0002] With the rapid development of electric vehicles (EVs), portable electronic devices, and large-scale energy storage systems globally, the market demand for lithium-ion battery energy density is becoming increasingly urgent. Currently, the theoretical specific capacity of commercially available cathode materials such as lithium iron phosphate (LiFePO4) and ternary materials (NCM / NCA) is approaching its limit. Against this backdrop, lithium-rich manganese-based cathode materials (xLi2MnO3˙(1-x)LiMO2) are widely recognized as a core competitive material for developing next-generation high-energy-density batteries due to their high specific capacity (over 250 mAh / g), low cost, and good thermal safety. Besides improvements to the material itself, increasing the areal loading of the electrode (i.e., fabricating thick electrodes) is another effective way to improve the energy density of battery systems. By increasing the thickness of the active material, the mass and volume ratio of inactive materials such as current collectors and separators in the battery can be significantly reduced. However, in the actual industrialization process, lithium-rich manganese-based thick electrodes face a series of challenging technical bottlenecks: First, ion transport kinetics limitations: as the electrode thickness increases, the diffusion path of lithium ions inside the electrode becomes significantly longer. Traditional single-type particle size distributions often lead to uneven pore structures and excessive tortuosity within the electrode, limiting the electrolyte wetting rate and rapid ion migration, resulting in poor rate performance of thick electrodes. Second, mechanical failure and uneven stress distribution: During the drying process after coating, uneven solvent migration in thick electrodes easily leads to surface skinning and internal stress concentration, causing cracks in the electrode and even detachment from the aluminum foil current collector. Furthermore, the large volume change of lithium-rich manganese-based materials during cycling makes thick electrodes more prone to accumulating mechanical stress, causing rapid capacity decay. Third, difficulties in constructing the conductive network: Ensuring electrons can penetrate the entire thickness direction (from the current collector to the electrode surface) under high loads is a significant challenge. Single conductive agents cannot simultaneously meet the requirements of point-to-point and long-range conductivity, and the contact resistance between active material particles inside thick electrodes accumulates with increasing thickness. Fourth, processing challenges: Traditional aqueous slurries suffer from poor dispersion stability and difficulty in balancing solid content with flowability when used for thick coatings. If the drying rate and pore formation cannot be effectively controlled, the resulting electrode often has a high compaction density but extremely low electrochemical activity.

[0003] Among the existing thick electrode pore-forming technologies, Chinese patent document with publication number "CN117317133A" proposes "A method for preparing a thick electrode with a three-dimensional pore structure." However, this method has the following problems: 1. The preparation process conditions are extremely harsh, requiring the electrode to be frozen in an extremely low temperature environment such as -85°C, and relying on vacuum drying for up to 24 hours to sublimate and remove ice crystals to form pores. This results in huge energy consumption, high equipment requirements, and high production costs, making it difficult to meet the needs of large-scale industrial production; 2. Under conventional drying conditions, the solvent migration inside the traditional thick electrode is uneven, and stress concentration during drying can easily lead to cracking of the electrode or peeling off from the current collector; 3. Due to the increased thickness, electrolyte wetting is difficult, resulting in increased battery polarization and a significant decrease in rate performance. Summary of the Invention

[0004] The purpose of this invention is to provide a lithium-rich manganese-based thick cathode electrode, its preparation method, and its applications, aiming to solve the bottleneck problems in existing thick electrodes, such as high areal capacity but poor rate performance, easy cracking during drying, and difficulty in electrolyte wetting. Through the synergistic effect of multi-level particle size compounding technology and programmed pore-forming process, a highly efficient ion transport network is constructed while maintaining high compaction density.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a lithium-rich manganese-based thick cathode electrode, comprising the following steps: Step 1: Add the binder sodium carboxymethyl cellulose and the additive ethylene carbonate to a mixed solvent and mix thoroughly to obtain a mixed solution. The mixed solvent is prepared by mixing deionized water and N-methylpyrrolidone. Step 2: Add the conductive agent to the mixed solution and mix thoroughly to obtain the mixture; Step 3: Mix the two lithium-rich manganese-based cathode materials with the mixture at different particle sizes. Step 4: Add pore-forming agent and mix to obtain a mixed slurry; Step 5: Coat the mixed slurry onto the current collector and prepare a thick electrode by segmented drying.

[0006] Furthermore, the mass ratios of the above-mentioned lithium-rich manganese-based cathode material, conductive agent, and binder are 90%~95%, 2%~3%, and 2%~5%, respectively; the additive accounts for 2~5% of the total mass of the active component, conductive agent, and binder; and the pore-forming agent accounts for 3~6% of the total mass of the active component, conductive agent, and binder.

[0007] Furthermore, in step three above, the particle sizes of the two lithium-rich manganese-based cathode materials are 200~300nm and 3~5μm, respectively, and the mass ratio of the two cathode materials is 3-4:6-7.

[0008] Furthermore, in step one above, the mass ratio of deionized water to N-methylpyrrolidone is 10:1.

[0009] Furthermore, in step two above, the conductive agent is a mixture of conductive carbon black and multi-walled carbon nanotubes, with a mass ratio of conductive carbon black to multi-walled carbon nanotubes of 1:1.

[0010] Furthermore, in step four above, the pore-forming agent is at least one of isopropanol or isobutanol, and the solid content of the mixed slurry is controlled at 40-50%.

[0011] Furthermore, in step five above, the thickness of the scraper coated on the current collector is 300~500μm.

[0012] Furthermore, in step five above, the segmented drying step includes: (1) drying the coated thick electrode sheet in air at 60°C for 4 hours; (2) then drying it in air at 100°C for 6-8 hours; (3) finally drying it in a vacuum at 120°C for 12-16 hours.

[0013] Furthermore, the thick electrode prepared by the above method.

[0014] Furthermore, the above-mentioned lithium-rich manganese-based thick electrodes are used in lithium-ion batteries.

[0015] Compared with the prior art, the present invention has the following significant advantages: 1. This invention possesses extremely high areal capacity and loading capacity: By introducing a rigid-flexible polymer network of sodium carboxymethyl cellulose and ethylene carbonate into an aqueous slurry, combined with a self-supporting skeleton constructed by the close packing of nano- and micro-sized particles, the thickness of the scraper can be controlled between 300 and 500 μm, and the single-sided loading capacity is between 18 and 25 mg / cm². 2 This significantly reduced the proportion of inactive substances.

[0016] 2. This invention possesses excellent kinetic characteristics: This invention uses alcohols as pore-forming agents. The interconnected pores created by this pore-forming agent through its unique volatilization mechanism, combined with the high specific surface area provided by nanoparticles, solve the "concentration polarization" problem of thick electrodes during high-current charge and discharge. The low-boiling-point alcohols selected in this invention not only perform conventional pore-forming functions, but more importantly, they can co-construct a ternary liquid-phase system with a "low-medium-high" boiling point gradient, together with the main solvent water and the co-solvent NMP. During the drying process, the selected pore-forming agent preferentially volatilizes from the inside out before the main solvent water, leaving interconnected microchannels in the dense structure encapsulated by the active material and binder. This design effectively reduces the tortuosity of ion transport in thick electrodes, allowing the electrolyte to quickly penetrate to the deep current collector side.

[0017] 3. This invention ensures the rheological stability of the slurry under high load by finely adjusting the component ratio. Specifically, this invention uses a blend of 200-300 nm nano-sized particles and 3-5 μm micro-sized particles. The small particles fill the tetrahedral or octahedral voids formed by the large particles, significantly improving the theoretical packing density of the electrode, thereby increasing the volumetric energy density without sacrificing porosity.

[0018] 4. Strong Mechanical Stability: This invention uses sodium carboxymethyl cellulose (CMC) and ethylene carbonate (EC) to construct a rigid-flexible polymer plasticizing mechanism at the microscopic level, combining CMC and EC. While CMC provides strong basic adhesion, it is prone to brittle cracking of the electrode after drying due to the rigidity of its macromolecular chains. The highly polar EC molecules can intercalate between cellulose polymer chains, breaking inherent hydrogen bonds and physical cross-linking, acting as a molecular-level "plasticizer" and significantly increasing the free volume of the polymer chains. The introduction of this flexible additive effectively releases the capillary shrinkage stress of the thick electrode during water evaporation, improving the flexibility of the dried electrode and effectively inhibiting material loss and crack growth during rolling and cycling. Simultaneously, water as the main solvent ensures the complete dissolution of CMC, while the addition of a small amount of NMP regulates the surface tension of the slurry, preventing "porosity" caused by uneven surface tension during thick coating and improving the dispersion uniformity of the conductive tube in the aqueous system. This invention incorporates ethylene carbonate (EC) as a flexible additive to enhance the flexibility of the dried electrode sheet. Combined with a segmented drying process, it effectively suppresses material loss and crack growth in thick electrode sheets during rolling and cycling.

[0019] 5. This invention designs a three-stage heat treatment path, which effectively solves the problem of high shrinkage stress during the drying of thick electrodes: First, constant temperature and humidity initial drying (60℃) is used to slowly remove low-boiling-point pore-forming agents and some moisture to prevent the surface from forming a blocking layer too quickly; then, the temperature is increased to enhance drying (100℃) to quickly remove most of the solvent, at which point the electrode skeleton is basically shaped; finally, high temperature vacuum deep drying (120℃) thoroughly removes residual polar molecules and bound water deep in the micropores, eliminates residual stress, and ensures electrochemical cycle stability. Attached Figure Description

[0020] Figure 1 Digital photographs of Comparative Example 1, Example 1, Example 2, Example 3, and Example 4; Figure 2 Scanning electron microscope (SEM) images of Comparative Example 1, Example 1, Example 2, Example 3, and Example 4; Figure 3 Selected area SEM image and elemental energy spectrum surface scan of Example 1; Figure 4This is a comparison chart of the peel strength of Comparative Example 1 and Example 1; Figure 5 Cyclic voltammetry curves for Comparative Example 1, Example 1, Example 2, Example 3, and Example 4; Figure 6 The first charge-discharge curves at 0.1C and the first charge-discharge curves at 1C are shown for Comparative Example 1, Example 1, Example 2, Example 3, and Example 4. Figure 7 The cyclic curves of Comparative Example 1, Example 1, Example 2, Example 3, and Example 4 at 1C are shown. Detailed Implementation

[0021] The preparation method of the present invention will be further illustrated below with reference to specific embodiments and accompanying drawings. Those skilled in the art should understand that the embodiments are merely illustrative of the invention and should not be construed as limiting the invention.

[0022] The technical solution provided by this invention involves fully dissolving sodium carboxymethyl cellulose binder and ethylene carbonate additive in a mixed solvent, then adding a conductive agent and fully dispersing it. Subsequently, two lithium-rich manganese-based cathode materials with different particle sizes are uniformly mixed with the mixture. Finally, a pore-forming agent is added and mixed to obtain a mixed slurry. The mixed slurry is coated onto a current collector, and after segmented drying and rolling, a thick electrode is obtained. The raw material components of the thick electrode, by weight percentage, are: 90%–95% electrode active component, 2%–3% conductive agent, and 2%–4% binder; the additive accounts for 2–5% of the total mass of the active component, conductive agent, and binder; and the pore-forming agent accounts for 3–6% of the total mass of the active component, conductive agent, and binder. The solid content of the mixed slurry is controlled at 40–50%. The mixed solvent is deionized water and N-methylpyrrolidone, with a mass ratio of 10:1. The conductive agent is a mixture of conductive carbon black and multi-walled carbon nanotubes, with a mass ratio of 1:1. The two lithium-rich manganese-based cathode materials have particle sizes of 200~500nm and 3~5μm, respectively, and the mass ratio of the two cathode materials is 3-4:6-7. The pore-forming agent is at least one of isopropanol or isobutanol. The characteristic is that the thickness of the scraper coated on the current collector is 300~500μm. The segmented drying steps include: (1) drying the coated thick electrode sheet in air at 60°C for 4h; (2) subsequently drying it in air at 100°C for 6~8h; (3) finally drying it in vacuum at 120°C for 12~16h.

[0023] Comparative Example 1: A method for preparing a lithium-rich manganese-based thick cathode electrode, comprising the following steps: Step 1: Add the binder sodium carboxymethyl cellulose and the additive ethylene carbonate to a mixed solvent and mix thoroughly to obtain a mixed solution. The mixed solvent is deionized water and N-methylpyrrolidone, and the mass ratio of the two solvents is 10:1.

[0024] Step 2: Add conductive carbon black to the mixed solution and mix thoroughly to obtain a mixture; Step 3: A slurry is prepared by uniformly mixing lithium-rich manganese-based cathode material with a particle size of 5 μm with the mixture. The slurry comprises 93% electrode active component, 2% conductive agent, and 5% binder, with additives accounting for 2% of the total mass of the active component, conductive agent, and binder. The solid content is controlled at 40%. The slurry is then coated onto a current collector with a coating thickness of 400 μm using a scraper. Subsequently, it is dried in air at 100°C for 6 hours and in vacuum at 120°C for 12 hours to obtain a dried electrode sheet. Finally, it is rolled to obtain the final thick electrode.

[0025] Example 1: This invention provides a method for preparing a lithium-rich manganese-based thick cathode electrode, comprising the following steps: Step 1: Add the binder sodium carboxymethyl cellulose and the additive ethylene carbonate to a mixed solvent and mix thoroughly to obtain a mixed solution. The mixed solvent is prepared from deionized water and N-methylpyrrolidone in a mass ratio of 10:1.

[0026] Step 2: The conductive agent added to the mixed solution is thoroughly mixed and dispersed to obtain a mixture. The conductive agent is conductive carbon black and multi-walled carbon nanotubes in a mass ratio of 1:1.

[0027] Step 3: Mix two lithium-rich manganese-based cathode materials with particle sizes of 300 nm and 5 μm respectively with the mixture at a mass ratio of 4:6.

[0028] Step 4: Add isopropanol, a pore-forming agent, to obtain a mixed slurry with a solid content controlled at 40%.

[0029] Step 5: Coat the mixed slurry onto the current collector, with a coating thickness of 400 μm. The coated thick electrode sheet is then subjected to segmented drying: first, drying in air at 60°C for 4 hours; then drying in air at 100°C for 6 hours; finally, drying in a vacuum at 120°C for 12 hours to obtain the electrode sheet. Finally, it is rolled to obtain the final thick electrode.

[0030] In the above steps, the lithium-rich manganese-based cathode material accounts for 93%, the conductive agent accounts for 2%, and the binder accounts for 5%; the additive accounts for 2% of the total mass of the active component, conductive agent, and binder, and the pore-forming agent accounts for 5% of the total mass of the active component, conductive agent, and binder. Example 2: The present invention provides a method for preparing a lithium-rich manganese-based thick cathode electrode. The difference from Example 1 is that in step three, two lithium-rich manganese-based cathode materials with particle sizes of 300 nm and 5 μm are uniformly mixed with the mixture at a mass ratio of 3:7.

[0031] Example 3: The present invention provides a method for preparing a lithium-rich manganese-based thick cathode electrode and its application, comprising the following steps: The difference from Example 1 is that the solid content is controlled at 45%, and the thickness of the scraper coated on the current collector is 300 μm.

[0032] The thick electrodes from Comparative Example 1 and Examples 1-3 were cut and used as positive electrodes, with the loading maintained at 20 mg / cm³. 2 The positive and negative lithium electrodes were assembled into lithium-ion coin cells, and the electrochemical performance of the prepared positive electrode material was investigated by setting different test parameters.

[0033] like Figure 1 As shown in the digital photographs, slight cracking appeared on the surface of Comparative Example 1 in the coated thick electrode, while the electrodes of Examples 1, 2, and 3 all maintained structural integrity. Combined with... Figure 2 Further observation using scanning electron microscopy (SEM) images revealed obvious microcracks on the surface of the thick electrode in Comparative Example 1, while the thick electrode sheets of Examples 1-3 prepared using the process of this invention had dense surfaces without cracks.

[0034] like Figure 3 As shown, the elemental energy dispersive spectroscopy (EDS) results of the thick electrode in Example 1 indicate that the Mn and Ni elements in the cathode material and the C elements in the conductive agent are uniformly distributed on the electrode surface.

[0035] pass Figure 4 As can be seen from the peel strength comparison chart, the peel strength of the modified Example 1 reaches 20.1 N / m, which is about 17 times that of Comparative Example 1 (1.2 N / m). This indicates that the method of the present invention significantly enhances the adhesion between the active material and the current collector.

[0036] from Figure 5 The cyclic voltammetry curves show that all electrode materials in Comparative Example 1 and Examples 1-3 exhibit clear and reversible redox peaks of transition metals and oxygen, proving that the electrochemical reaction activity inside the thick electrode is normal.

[0037] In the first charge-discharge test at a rate of 0.1C (1C=200mA / g) (see...) Figure 6 Compared to the initial discharge specific capacity of Comparative Example 1 (272 mAh / g), the specific capacities of Examples 1-3 were all significantly improved. Specifically, the initial discharge specific capacity of Example 1 reached 305 mAh / g, an increase of approximately 33 mAh / g compared to Comparative Example 1. At a high rate of 1C, the discharge specific capacity of Comparative Example 1 was only 102 mAh / g, while the specific capacity of Example 1 remained at 226 mAh / g. Figure 7The 1C cycling curves show that after 50 cycles, the capacity retention of Comparative Example 1 is only 53.2%, while the cycling performance of Examples 1-3 is significantly improved, with capacity retention rates of 85.74%, 86.95%, and 73.02%, respectively. In summary, within a room temperature (29°C) and voltage range of 2.0-4.8V, the examples modified using the method of this invention significantly improve the initial discharge specific capacity of the lithium-rich manganese-based cathode material and exhibit superior cycling stability.

[0038] Of the above embodiments, Embodiment 1 is the best embodiment.

[0039] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for preparing a lithium-rich manganese-based thick cathode electrode, characterized in that: Includes the following steps: Step 1: Add the binder sodium carboxymethyl cellulose and the additive ethylene carbonate to a mixed solvent and mix thoroughly to obtain a mixed solution. The mixed solvent is prepared by mixing deionized water and N-methylpyrrolidone. Step 2: Add the conductive agent to the mixed solution and mix thoroughly to obtain the mixture; Step 3: Mix the two lithium-rich manganese-based cathode materials with the mixture at different particle sizes. Step 4: Add pore-forming agent and mix to obtain a mixed slurry; Step 5: Coat the mixed slurry onto the current collector and prepare a thick electrode by segmented drying.

2. The method for preparing a lithium-rich manganese-based thick cathode electrode according to claim 1, characterized in that: The mass ratios of the lithium-rich manganese-based cathode material, conductive agent, and binder are 90%–95%, 2%–3%, and 2%–5%, respectively. The additives comprise 2-5% of the total mass of the active ingredients, conductive agents, and binders. The pore-forming agent accounts for 3-6% of the total mass of the active component, conductive agent, and binder.

3. The preparation method according to claim 1, characterized in that: In step three, the particle sizes of the two lithium-rich manganese-based cathode materials are 200~300nm and 3~5μm, respectively, and the mass ratio of the two cathode materials is 3-4:6-7.

4. The method for preparing a lithium-rich manganese-based thick cathode electrode according to claim 1, characterized in that: In step one, the mass ratio of deionized water to N-methylpyrrolidone is 10:

1.

5. The method for preparing a lithium-rich manganese-based thick cathode electrode according to claim 1, characterized in that: In step two, the conductive agent is a mixture of conductive carbon black and multi-walled carbon nanotubes, with a mass ratio of 1:

1.

6. The method for preparing a lithium-rich manganese-based thick cathode electrode according to claim 1, characterized in that: In step four, the pore-forming agent is at least one of isopropanol or isobutanol, and the solid content of the mixed slurry is controlled at 40-50%.

7. The method for preparing a lithium-rich manganese-based thick cathode electrode according to claim 1, characterized in that: In step five, the thickness of the scraper coated on the current collector is 300~500μm.

8. The method for preparing a lithium-rich manganese-based thick cathode electrode according to claim 1, characterized in that: In step five, the segmented drying steps include: (1) drying the coated thick electrode sheet in air at 60°C for 4 hours; (2) drying it in air at 100°C for 6-8 hours; and (3) finally drying it in a vacuum at 120°C for 12-16 hours.

9. A thick electrode prepared by the preparation method according to any one of claims 1 to 7.

10. The application of the lithium-rich manganese-based thick electrode according to claim 1 in lithium-ion batteries.

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