Composite aqueous binder and application thereof in lithium-rich manganese-based material

Abstract

The invention relates to the technical field of lithium batteries, in particular to a composite aqueous binder and application thereof to a lithium-rich manganese-based material. The preparation method of the composite aqueous binder comprises the following steps: S1-1, mixing and stirring a carboxymethyl chitosan solution and polyvinylidene fluoride to obtain a PC solution; s1-2, humic acid is added into the PC solution, deionized water is added for dilution until the solid content is 4-6 wt%, and the composite water-based binder is obtained. The composite aqueous binder and the lithium-rich manganese-based material are jointly used for preparing the positive electrode slurry. And the preparation of the positive electrode slurry comprises the following steps: S2-1, mixing and stirring the lithium-rich manganese-based material, the conductive agent and the composite aqueous binder, adding N-methyl pyrrolidone, and grinding to obtain the positive electrode slurry.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and specifically to a composite aqueous binder and its application on lithium-rich manganese-based materials. Background Art

[0002] In recent years, the popularization of new energy vehicles and the wide use of various electronic products in people's daily lives have greatly promoted the vigorous development of lithium-ion batteries. Lithium-rich manganese-based cathode materials have become a hot research topic today due to their advantages such as high specific capacity, long lifespan, and low price. However, there are many problems in the practical application of lithium-rich materials, such as severe voltage drop, low first-cycle Coulombic efficiency, and poor rate performance during cycling, which limit their further development and wide application in the field of lithium-ion batteries.

[0003] Among the numerous components of lithium-ion batteries, although the amount of binder used is low, it plays a crucial role in improving battery performance. The binder can not only connect the active material and the conductive agent to the current collector, effectively reducing the internal resistance of the electrode, but also promote the rapid formation of a stable SEI film on the electrode surface, further improving the rate capability and cycling performance of the battery. Polyvinylidene fluoride has the advantages of high purity, small dosage, simple coating operation, and certain adhesiveness. At the same time, it has chemical inertness and electrochemical stability within the operating potential range of the battery, and also has good electrolyte wettability, so it is widely used in the production of lithium-ion batteries.

[0004] However, in practical applications, polyvinylidene fluoride has the following problems: First, polyvinylidene fluoride will react with graphite or lithium metal to form LiF and unsaturated -C=CF- bonds, generating a large amount of Joule heat at high temperatures, resulting in the peeling of electrode materials; Second, since polyvinylidene fluoride is an electronic insulator and an ionic insulator, it will increase the electrode resistance, especially during high-rate cycling, and cannot adapt to the rapid transmission of ions and electrons; Third, in the electrolyte, polyvinylidene fluoride is prone to swelling, resulting in a decrease in binding ability; Fourth, its linear structure and -C-F- functional groups result in weak binding ability, making it difficult to withstand large volume changes of electrode materials during battery charge and discharge.

[0005] In summary, to solve the above problems, a composite aqueous binder and its application on lithium-rich manganese-based materials are of great significance. Summary of the Invention

[0006] The purpose of the present invention is to provide a composite aqueous binder and its application on lithium-rich manganese-based materials to solve the problems raised in the above background art.

[0007] To solve the above technical problems, the present invention provides the following technical solutions:

[0008] Preferably, the preparation of the composite aqueous binder comprises the following steps:

[0009] S1-1: Mix and stir a carboxymethyl chitosan (CCTS) solution and polyvinylidene fluoride (PVDF) to obtain a PC solution;

[0010] S1-2: Add humic acid (HA) to the PC solution, add deionized water for dilution until the solid content is 4-6 wt%, to obtain a composite aqueous binder.

[0011] In a further embodiment, the PC solution is obtained by mixing and stirring a carboxymethyl chitosan (CCTS) solution and polyvinylidene fluoride (PVDF); wherein, P refers to polyvinylidene fluoride, and C refers to carboxymethyl chitosan.

[0012] Preferably, in the raw materials of the composite aqueous binder, the mass ratio of humic acid to the PC solution is (1-2):(1-2).

[0013] Preferably, in the raw materials of the PC solution, the mass ratio of the carboxymethyl chitosan solution to polyvinylidene fluoride is (0.8-1.2):(0.8-1.2); the mass fraction of the carboxymethyl chitosan solution is 4 wt%-6 wt%.

[0014] Preferably, the composite aqueous binder and the lithium-rich manganese-based material are jointly used to prepare a positive electrode slurry.

[0015] Preferably, the preparation of the positive electrode slurry comprises the following steps:

[0016] S2-1: Mix and stir the lithium-rich manganese-based material, the conductive agent, and the composite aqueous binder, add N-methylpyrrolidone, and grind to obtain a positive electrode slurry.

[0017] In a further embodiment, the grinding time is 20-40 min.

[0018] Preferably, the positive electrode slurry comprises a lithium-rich manganese-based material, a conductive agent, and a composite aqueous binder in a mass ratio of 7.5-8.5:0.5-1.5:0.5-1.5.

[0019] In a further embodiment, the lithium-rich manganese-based material is a lithium-rich manganese-based positive electrode material; the conductive agent is acetylene black; the positive electrode slurry is a lithium-rich manganese-based positive electrode slurry.

[0020] Preferably, the preparation of the lithium-rich manganese-based material comprises the following steps:

[0021] S2-1: Add manganese acetate, nickel acetate, and cobalt acetate to deionized water, and stir to obtain solution A; add lithium acetate dihydrate and citric acid monohydrate to deionized water, and stir to obtain solution B;

[0022] S2-2: Add solution A to solution B to obtain solution C;

[0023] S2-3: Add the ammonia water solution to solution C, adjust the pH to 6.9 - 7.1, heat to a viscous state, and dry to obtain the lithium-rich manganese-based material.

[0024] In a further embodiment, the stirring temperature of solution A is 10 - 30 °C.

[0025] In a further embodiment, the lithium-rich manganese-based material is prepared by the sol-gel method.

[0026] In a further embodiment, in S2-2, specifically, a peristaltic pump is used to pump solution A into solution B at a pressure of 0.2 - 0.4 Kpa to obtain solution C.

[0027] In a further embodiment, the heating temperature is 75 - 85 °C; the drying temperature is 75 - 85 °C, and the drying time is 11 - 13 hours.

[0028] Among them, the electrode constructed with CCTs as the binder exhibits high specific capacity and voltage stability, which can be attributed to the following aspects: First, the chemical structure of the CCTs binder contains groups such as hydroxyl (-OH), carboxymethyl (-COOCH3), and amino (-NH2), which are easy to form strong hydrogen bond interactions with the oxygen atoms on the surface of the lithium-rich manganese-based material, strengthening the bonding strength and increasing the bonding sites, thereby generating a large adhesive force between the active material (lithium-rich manganese-based cathode material), the conductive agent (acetylene black), and the current collector (aluminum foil). Second, the double-helical structure of CCTs can produce a strong mechanical interlocking effect with the lithium-rich manganese-based material, forming a strong mechanical force on the surface of the electrode, which has an inhibitory effect on the shedding of material particles during the cycling process. Third, CCTs can form a coating layer on the surface of the material particles, protecting the integrity of the particle surface while also inhibiting the side reactions between the material and the electrolyte. In addition, CCTs can inhibit the corrosion of the aluminum foil in the subsequent preparation of the electrode sheet and strengthen the adhesion between the material and the current collector aluminum foil.

[0029] Preferably, the raw materials of solution C include solution A and solution B with a mass ratio of 0.6 - 0.65:1.

[0030] Preferably, the raw materials of solution A include manganese acetate, nickel acetate, and cobalt acetate with a molar ratio of 4 - 4.5:1:1;

[0031] The raw materials of solution B include lithium acetate dihydrate and citric acid monohydrate with a molar ratio of 1:1.5 - 1.7.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] 1. The composite aqueous binder prepared by modifying PVDF with CCTs having a double - helix structure in the solution can alleviate the attenuation of the electrode voltage and improve the cycling stability.

[0034] 2. In the solution, PVDF is modified by the compound of CCTs and HA, and CCTs and HA play a synergistic role, which can improve the structural stability of the electrode and avoid particle separation. In addition, a conductive network is formed by forming a π - π conjugate system to accelerate electron transfer, enhance the mechanical properties of the electrode sheet, and thus improve the electrochemical performance of the battery. Specific Embodiments

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0036] It should be noted that the following parts are parts by mass, and there are no special restrictions on the purchase manufacturers of all raw materials involved in the present invention. Exemplarily, in the following embodiments, ammonia water is purchased from Shijiazhuang Reagent Factory; manganese acetate is purchased from Sinopharm Chemical Reagent Co., Ltd.; cobalt acetate is purchased from Sinopharm Chemical Reagent Co., Ltd.; lithium acetate dihydrate is purchased from Sinopharm Chemical Reagent Co., Ltd.; citric acid monohydrate is purchased from Sinopharm Chemical Reagent Co., Ltd.; N - methylpyrrolidone is purchased from Sinopharm Chemical Reagent Co., Ltd.; carboxymethyl chitosan is purchased from Aladdin Reagent; humic acid is purchased from Aladdin Reagent; the model of polyvinylidene fluoride is PVDF5130; the metal lithium sheet is battery - grade and is purchased from Kelude; the material of the aluminum foil is acetylene black, battery - grade, and is purchased from Hefei Keping; acetylene black is purchased from Hefei Keping; the separator is battery - grade and is purchased from Celgard Company, USA.

[0037] Example 1: An application of a composite aqueous binder on a lithium - rich manganese - based material, comprising the following steps:

[0038] Step 1: The preparation of the lithium - rich manganese - based cathode material is carried out by a sol - gel method: 0.054 mol of manganese acetate, 0.013 mol of nickel acetate, and 0.013 mol of cobalt acetate are added to 100 mL of deionized water, and stirred at 20 °C until completely dissolved to obtain solution A; 0.126 mol of lithium acetate dihydrate and 0.202 mol of citric acid monohydrate are added to 125 mL of deionized water and stirred until dissolved to obtain solution B; solution A is pumped into solution B with a peristaltic pump at a pressure of 0.3 KPa to obtain solution C; an ammonia water solution is added to solution C, the pH is adjusted to 7.0, and it is placed in an oil bath of a constant - temperature stirrer at 80 °C and heated until it becomes a viscous gel, placed in a porcelain crucible, and transferred to a vacuum drying oven at 80 °C for drying for 12 hours to obtain the lithium - rich manganese - based cathode material;

[0039] Step 2: Preparation of the composite aqueous binder: Mix a 5wt% carboxymethyl chitosan solution and PVDF in a mass ratio of 1:1 and stir for 30 min to obtain a PC solution; add HA to the PC solution in a mass ratio of 1:1, stir well to make it evenly mixed, add deionized water for dilution until the solid content is 5wt% to obtain the composite aqueous binder;

[0040] Step 3: Pour the lithium-rich manganese-based cathode material, conductive agent, and composite aqueous binder into a mortar in a mass ratio of 8:1:1, add N-methylpyrrolidone and grind and mix well for 30 min to obtain the lithium-rich manganese-based cathode slurry.

[0041] Example 2: An application of a composite aqueous binder and its use on a lithium-rich manganese-based material, including the following steps:

[0042] Step 1: Preparation of the lithium-rich manganese-based cathode material is carried out by the sol-gel method: Add 0.054 mol of manganese acetate, 0.013 mol of nickel acetate, and 0.013 mol of cobalt acetate to 100 mL of deionized water, stir at 20 °C until completely dissolved to obtain solution A; add 0.126 mol of lithium acetate dihydrate and 0.202 mol of citric acid monohydrate to 125 mL of deionized water, stir until dissolved to obtain solution B; use a peristaltic pump to pump solution A into solution B at a pressure of 0.3 Kpa to obtain solution C; add an ammonia water solution to solution C, adjust the pH to 7.0, and place it in an oil bath on a constant temperature stirrer at 80 °C and heat until it becomes a viscous gel, place it in a porcelain crucible, transfer it to a vacuum drying oven and dry at 80 °C for 12 hours to obtain the lithium-rich manganese-based cathode material;

[0043] Step 2: Preparation of the composite aqueous binder: Mix a 5wt% carboxymethyl chitosan solution and PVDF in a mass ratio of 1:1 and stir for 30 min to obtain a PC solution; add HA to the PC solution in a mass ratio of 2:1, stir well to make it evenly mixed, add deionized water for dilution until the solid content is 5wt% to obtain the composite aqueous binder;

[0044] Step 3: Pour the lithium-rich manganese-based cathode material, conductive agent, and composite aqueous binder into a mortar in a mass ratio of 8:1:1, add N-methylpyrrolidone and grind and mix well for 30 min to obtain the lithium-rich manganese-based cathode slurry.

[0045] Example 3: An application of a composite aqueous binder and its use on a lithium-rich manganese-based material, including the following steps:

[0046] Step 1: Preparation of the lithium-rich manganese-based cathode material: The sol-gel method is used for preparation. 0.054 mol of manganese acetate, 0.013 mol of nickel acetate, and 0.013 mol of cobalt acetate are added to 100 mL of deionized water, and stirred at 20 °C until completely dissolved to obtain solution A. 0.126 mol of lithium acetate dihydrate and 0.202 mol of citric acid monohydrate are added to 125 mL of deionized water, and stirred until dissolved to obtain solution B. Solution A is pumped into solution B with a peristaltic pump at a pressure of 0.3 KPa to obtain solution C. Ammonia water solution is added to solution C, the pH is adjusted to 7.0, and it is placed in an 80 °C constant temperature stirrer for oil bath heating until it becomes a viscous gel. It is placed in a porcelain crucible and transferred to a vacuum drying oven for drying at 80 °C for 12 hours to obtain the lithium-rich manganese-based cathode material;

[0047] Step 2: Preparation of the composite aqueous binder: A 5 wt% carboxymethyl chitosan solution and PVDF are mixed and stirred at a mass ratio of 1:1 for 30 min to obtain a PC solution. HA is added to the PC solution at a mass ratio of 1:2, stirred well to make it uniformly mixed, and deionized water is added for dilution until the solid content is 5 wt% to obtain the composite aqueous binder;

[0048] Step 3: The lithium-rich manganese-based cathode material, conductive agent, and composite aqueous binder are poured into a mortar at a mass ratio of 8:1:1, and N-methylpyrrolidone is added and ground and mixed well for 30 min to obtain the lithium-rich manganese-based cathode paste.

[0049] Comparative Example 1: Based on Example 1, polyvinylidene fluoride is used as the binder instead of the composite aqueous binder, and the rest of the process remains unchanged. Specifically:

[0050] Step 1: Preparation of the lithium-rich manganese-based cathode material: The sol-gel method is used for preparation. 0.054 mol of manganese acetate, 0.013 mol of nickel acetate, and 0.013 mol of cobalt acetate are added to 100 mL of deionized water, and stirred at 20 °C until completely dissolved to obtain solution A. 0.126 mol of lithium acetate dihydrate and 0.202 mol of citric acid monohydrate are added to 125 mL of deionized water, and stirred until dissolved to obtain solution B. Solution A is pumped into solution B with a peristaltic pump at a pressure of 0.3 KPa to obtain solution C. Ammonia water solution is added to solution C, the pH is adjusted to 7.0, and it is placed in an 80 °C constant temperature stirrer for oil bath heating until it becomes a viscous gel. It is placed in a porcelain crucible and transferred to a vacuum drying oven for drying at 80 °C for 12 hours to obtain the lithium-rich manganese-based cathode material;

[0051] Step 2: The lithium-rich manganese-based cathode material, conductive agent, and binder are poured into a mortar at a mass ratio of 8:1:1. The binder is polyvinylidene fluoride, and N-methylpyrrolidone is added and ground and mixed well for 30 min to obtain the lithium-rich manganese-based cathode paste.

[0052] Comparative Example 2: Based on Example 1, PC solution was used to replace the composite aqueous binder, and the rest of the process remained unchanged. Specifically:

[0053] Step 1: The preparation of the lithium-rich manganese-based cathode material was carried out by the sol-gel method: 0.054 mol of manganese acetate, 0.013 mol of nickel acetate, and 0.013 mol of cobalt acetate were added to 100 mL of deionized water, and stirred at 20 °C until completely dissolved to obtain solution A; 0.126 mol of lithium acetate dihydrate and 0.202 mol of citric acid monohydrate were added to 125 mL of deionized water, and stirred until dissolved to obtain solution B; solution A was pumped into solution B with a peristaltic pump at a pressure of 0.3 Kpa to obtain solution C; ammonia water solution was added to solution C, the pH was adjusted to 7.0, and it was placed in an oil bath on a constant temperature stirrer at 80 °C and heated until it became a viscous gel, placed in a porcelain crucible, and transferred to a vacuum drying oven to be dried at 80 °C for 12 hours to obtain the lithium-rich manganese-based cathode material;

[0054] Step 2: The preparation of the composite aqueous binder: A 5 wt% carboxymethyl chitosan solution and PVDF were mixed and stirred at a mass ratio of 1:1 for 30 min to obtain a PC solution;

[0055] Step 3: The lithium-rich manganese-based cathode material, conductive agent, and PC solution were poured into a mortar according to a mass ratio of 8:1:1, and N-methylpyrrolidone was added and ground and mixed thoroughly for 30 min to obtain the lithium-rich manganese-based cathode paste.

[0056] Detection experiment: The lithium-rich manganese-based cathode pastes prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were respectively made into electrode sheets and button cells, and their performances were detected:

[0057] The preparation process of the electrode sheet was as follows: The lithium-rich manganese-based cathode pastes of Examples 1 to 3 and Comparative Examples 1 to 2 were respectively and evenly coated on aluminum foil with a film applicator, the coating thickness was 200 μm, vacuum dried at 80 °C for 12 hours, and cut and pressed into circular electrode sheets with a diameter of 11 mm with a manual slicing machine, that is, the electrode sheets of Examples 1 to 3 and Comparative Examples 1 to 2 were obtained.

[0058] The preparation process of the button cell was as follows: Assemble a button cell of model CR2025: The electrode sheets obtained in Examples 1 to 3 and Comparative Examples 1 to 2 above were used as the positive electrode sheets; a metal lithium sheet with a diameter of 15.6 mm and a thickness of 0.45 mm was used as the negative electrode sheet; a Celgard 2400 polypropylene film with a diameter of 16 mm was used as the separator; a 5V high-voltage electrolyte LB111 was used as the electrolyte; the specific formula of the electrolyte was: the solute was lithium hexafluorophosphate (LiPF6), the solute accounted for 10 wt% of the total electrolyte, and the solvent was a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) with a volume ratio of 1:1.

[0059] Assemble the negative electrode case, lithium metal sheet, a little electrolyte, separator, electrolyte, positive electrode sheet, gasket, elastic sheet, and positive electrode case in sequence and seal them using a hydraulic press. Then leave them standing for 12 hours to obtain the button batteries of Examples 1 to 3 and Comparative Examples 1 to 2 respectively.

[0060] (1) Peel test: Cut a circular electrode sheet with a diameter of 11 mm into a strip with dimensions of 40×25 mm. Then stick 3M double-sided tape on its back, and stick the other side of the double-sided tape on a prepared glass slide. Then stick 3M double-sided tape with a specification of 9×1 mm on the surface of the positive electrode sheet. After flipping the tape, stick one side of the tape on the upper fixture of a microcomputer-controlled electronic universal testing machine, and stick the other end of the glass slide on the lower fixture of the testing machine. Select the tensile-displacement mode, and then set the stretching speed to 5 mm / min. The test results are shown in Table 1;

[0061] (2) Charge-discharge performance test: Use the CT2001A type blue power battery test system and CT-4008 type Neware battery test system to test the cycle performance and rate performance of the button batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 2 in a constant current charge-discharge mode. With the standard of 1C = 200 mAg -1 current density, calculate the charge-discharge current density at different rates according to the content of the active material on each electrode sheet for cycle and rate performance tests, and calculate the capacity retention rate. The test voltage range is 2 to 4.8 V, and the test ambient temperature is 25°C. The test results are shown in Table 1;

[0062]

[0063] Table 1

[0064] Result analysis: It can be seen from the data analysis in Table 1 that in this solution, HA containing polar functional groups and CCTs are used to modify PVDF to form a composite water-based binder to modify the lithium-rich manganese-based positive electrode. By adjusting the mass ratio of HA and CCTs and observing the test results, the following conclusions are obtained:

[0065] (1) The composite binder added with HA effectively improves the cycle stability and rate performance of the lithium-rich manganese-based positive electrode material. Compared with the modification with single CCTs, the discharge specific capacity and the later cycle stability are increased.

[0066] (2) The peel test results show that the polymer HA in the composite water-based binder can crosslink with CCTs with a double helix structure to form a dense binder network, making the active material, conductive agent, and current collector adhere tightly to each other, improving the viscosity.

[0067] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention.

Claims

1. A composite aqueous binder, characterized in that: The preparation of the composite aqueous binder comprises the following steps: S1-1: Mix and stir a carboxymethyl chitosan solution and polyvinylidene fluoride to obtain a PC solution; S1-2: Add humic acid to the PC solution, add deionized water for dilution until the solid content is 4-6 wt%, to obtain the composite aqueous binder.

2. The composite aqueous binder according to claim 1, wherein: In the raw materials of the composite aqueous binder, the mass ratio of humic acid to the PC solution is (1-2):(1-2).

3. The composite aqueous binder according to claim 2, characterized in that: In the raw materials of the PC solution, the mass ratio of the carboxymethyl chitosan solution to polyvinylidene fluoride is (0.8-1.2):(0.8-1.2); the mass fraction of the carboxymethyl chitosan solution is 4 wt%-6 wt%.

4. Application of a composite aqueous binder to a lithium-rich manganese-based material, characterized in that: The composite aqueous binder as described in claim 1 is jointly used for preparing a positive electrode paste.

5. The application of a composite aqueous binder according to claim 4 to a lithium-rich manganese-based material, characterized in that: The preparation of the positive electrode paste comprises the following steps: S2-1: Mix and stir a lithium-rich manganese-based material, a conductive agent, and the composite aqueous binder, add N-methylpyrrolidone, and grind to obtain the positive electrode paste.

6. The application of a composite aqueous binder according to claim 5 to a lithium-rich manganese-based material, characterized in that: The positive electrode paste contains a lithium-rich manganese-based material, a conductive agent, and the composite aqueous binder in a mass ratio of 7.5-8.5:0.5-1.5:0.5-1.

5.

7. Use of a composite aqueous binder according to claim 6 on a lithium-rich manganese-based material, characterized in that: The preparation of the lithium-rich manganese-based material comprises the following steps: S2-1: Add manganese acetate, nickel acetate, and cobalt acetate to deionized water, and stir to obtain solution A; add lithium acetate dihydrate and citric acid monohydrate to deionized water, and stir to obtain solution B; S2-2: Add solution A to solution B to obtain solution C; S2-3 Add an ammonia water solution to solution C, adjust the pH to 6.9-7.1, heat until viscous, and dry to obtain the lithium-rich manganese-based material.

8. Use of a composite aqueous binder according to claim 7 on a lithium-rich manganese-based material, characterized in that: In the raw materials of solution C, solution A and solution B are included in a mass ratio of 0.6-0.65:

1.

9. Use of a composite aqueous binder according to claim 8 on a lithium-rich manganese-based material, characterized in that: In the raw materials of solution A, manganese acetate, nickel acetate, and cobalt acetate are included in a molar ratio of 4-4.5:1:1; In the raw materials of solution B, lithium acetate dihydrate and citric acid monohydrate are included in a molar ratio of 1:1.5-1.7.

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