Preparation method of positive electrode, positive electrode and application

Abstract

The invention discloses a preparation method of a positive electrode, the positive electrode and application. Comprising the following steps: mixing raw materials containing an active material, a conductive agent, a liquid retaining agent and a binder, shearing and stirring, performing, rolling to obtain a positive electrode film, and attaching the positive electrode film to a current collector to obtain the positive electrode.

Description

Technical Field

[0001] The present application relates to a method for preparing a positive electrode, a positive electrode and applications, and belongs to the field of electrochemistry. Background Art

[0002] Although lithium-ion batteries have been extensively and intensively studied, their potential unsafety, scarce lithium resources, and limited energy density have hindered their further development. In recent years, aqueous zinc-ion batteries (ZIBs) have gradually become the focus of research due to their advantages such as low cost, high safety, and good ionic conductivity. The positive electrode materials of ZIBs can be divided into manganese-based, vanadium-based, and Prussian blue, etc. Among them, manganese-based materials are the preferred positive electrode materials, which are not only simple to manufacture and have high voltage, but also environmentally friendly and have diverse structures. However, at present, the traditional wet coating process has reached its limit in improving the volume density of the electrode, and it is urgent to develop a new electrode preparation process. The traditional wet coating process has many disadvantages: (1) Energy waste: The wet coating and subsequent drying process require a total production line energy consumption of 1 million pounds per year; (2) High cost and pollution: The electrode slurry mixing process requires a large amount of NMP, which is costly and toxic. Therefore, a recovery device must be established during the drying process of large-scale production to collect and reprocess the evaporated NMP; (3) Electrode stratification: During the solvent evaporation process, due to capillary action and diffusion, the binder and conductive agent float near the surface and agglomerate, while the active material precipitates, resulting in electrode stratification, destroying the construction of the three-dimensional conductive network in the electrode and reducing the bonding strength between the active material and the integrated circuit; (4) Limited electrode thickness: Wet coating often causes problems such as cracks, delamination and poor flexibility, especially in thick electrodes. Therefore, the wet coating manufacturing process of the electrode greatly limits the thickness of the electrode; (5) Not suitable for sulfide all-solid-state batteries (ASSBs): Solid electrolytes, especially sulfides, are extremely sensitive to water and polar organic solvents. Therefore, only non-polar or weakly polar solvents can be used, which reduces the ionic conductivity of the solid electrolyte and limits the choice of binders. Summary of the invention

[0003] In recent years, in order to overcome the above problems, a dry process has been developed to prepare battery electrodes. Compared with wet coating, the dry process has the following advantages: (1) Reduced cost. Dry film production technology saves the cost of solvents, solvent evaporation, recovery and drying facilities. (2) Suppression of stratification. During the dry mixing process, the different components of the electrode material can be evenly distributed due to the shear and friction of the mixer and particles. Since there is no slurry in the dry mixing process, the film stratification caused by solvent evaporation will no longer exist. (3) Unlimited electrode thickness. Dry film technology can easily control the electrode thickness and uniformity, so it has unique advantages in the preparation of thick electrodes, which can effectively improve the energy density of the battery. (4) Compatible with electrolytes such as sulfides. Dry film preparation technology avoids the use of organic / polar solvents and only requires a very small amount of binder during the film preparation process, which is particularly suitable for the production of sulfide ASSBs. Since sulfide electrolytes react severely with organic solvents, dry film technology helps to protect sulfide electrolytes and maintain high ionic conductivity.

[0004] According to one aspect of the present application, a method for preparing a positive electrode is provided, comprising the following steps:

[0005] The raw materials containing active materials, conductive agents, liquid retaining agents and binders are mixed, sheared and stirred, preformed, and rolled to obtain a positive electrode film, and the positive electrode film is laminated to a current collector to obtain the positive electrode.

[0006] The active material is selected from at least one of MnO2, vanadium pentoxide, and CuFe(CN)6;

[0007] The conductive agent is selected from at least one of acetylene black, conductive carbon black, multi-walled carbon nanotubes, graphene, and high-purity carbon nanofibers;

[0008] The liquid retaining agent is selected from at least one of bentonite, montmorillonite powder, illite powder, kaolin powder and halloysite powder;

[0009] The binder is selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, sodium carboxymethyl cellulose, carboxymethyl cellulose and styrene-butadiene rubber.

[0010] The mass content of each substance in the raw materials is:

[0011] Active substance 80-90wt%;

[0012] Conductive agent 8-13wt%;

[0013] Liquid retaining agent 1-3wt%;

[0014] Binder 1~4wt%.

[0015] The shear stirring time is 10 to 30 minutes;

[0016] The shear stirring temperature is 20 to 80°C;

[0017] The shear stirring speed is 10000-15000 t / min.

[0018] The preforming is a roller pressing pretreatment;

[0019] The pressure of the roller pressing pretreatment is 5 to 40T;

[0020] The temperature of the roller pressing pretreatment is 25-80°C.

[0021] The current collector is selected from at least one of stainless steel foil, titanium foil, stainless steel mesh, and titanium mesh.

[0022] According to another aspect of the present application, a positive electrode is provided, which is prepared by the above-mentioned preparation method.

[0023] According to another aspect of the present application, an aqueous zinc ion battery is provided, comprising the above-mentioned positive electrode.

[0024] Specifically,

[0025] Step 1: pre-mix the active material, conductive agent and liquid retaining agent through a mixing device, with a stirring time of 20min-40min and a stirring speed of 800r / min-1000r / min to obtain a mixed powder A; then add a binder and continue stirring at the original stirring speed for 20min-40min to obtain a mixed powder B.

[0026] Step 2: Shear and stir the powder B evenly mixed in step 1 in a high-speed stirring device to obtain a highly fibrous electrode material. The shear stirring time is 10-30 minutes, the shear stirring temperature is 20°C-80°C, and the shear stirring speed is 10000r / min-15000r / min.

[0027] Step 3: The highly fibrous powder obtained in step 2 is transferred to a three-dimensional roller pressing device for preforming to obtain a self-supporting semi-finished dry electrode membrane.

[0028] Step 4: The semi-finished dry electrode membrane obtained in step 3 is subjected to rolling and pressing treatment to form the semi-finished dry electrode membrane into a finished dry electrode membrane.

[0029] Step 5: Lay the finished dry electrode film obtained in step 4 on the current collector to form a finished dry electrode.

[0030] Step 6: Cut the finished dry electrode obtained in step 5 into round pieces with a diameter of 15 mm to form finished dry electrode pole pieces.

[0031] Step 7: Place the finished dry-process electrode sheets obtained in step 6 in the order of "positive electrode shell-finished dry-process positive electrode sheet-diaphragm-electrolyte-finished dry-process negative electrode sheet-gasket-spring-negative electrode shell", assemble, and obtain a dry-process prepared aqueous zinc ion button battery.

[0032] The negative electrode active material is commercial laboratory-grade zinc foil, with Zn≥99.999% and a thickness of 100 μm.

[0033] The diaphragm is at least one of non-woven fabric, blotting paper, Whatman glass fiber diaphragm, and Celgard hydrophilic composite diaphragm.

[0034] The beneficial effects that can be produced by the present application include: no NMP organic solvent is used in the film-forming process, which is environmentally friendly; the process is simple and the production cost is reduced; and a high-load electrode can be made, thereby improving the energy density of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a cross-sectional SEM image of the manganese dioxide positive electrode film in Example 2, with a scale of 10 μm.

[0036] Figure 2 This is a SEM image of the surface of the manganese dioxide positive electrode film, with a scale of 1μm.

[0037] Figure 3 This is the cycle of the aqueous zinc ion full battery assembled in Example 6 at room temperature 25°C and 0.1C current density. DETAILED DESCRIPTION

[0038] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0039] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0040] Example 1

[0041] Step 1: Mixing. Weigh 90g of manganese dioxide powder, 7g of PTFE powder, and 3g of multi-walled carbon nanotubes in a container and stir them thoroughly in a high-speed mixer. Parameter settings: speed 1000rpm, time 20min.

[0042] Step 2: Ball milling. Take out the mixed materials and put them in the ball milling jar, take 5g of each, add ball milling beads, and the bead-to-material ratio is 10:1. The parameters of the planetary ball mill are set as follows: speed 500rpm, time 4h.

[0043] Step 3: Rolling. The ball-milled material is rolled under a roller mill. First, the material is rolled into a thin sheet under an appropriate roller gap, and then it decreases in sequence from 300μm, 200μm, and 100μm, and finally a manganese dioxide self-supporting pole piece of about 100μm is obtained. Rolling machine parameter settings: temperature 25℃, rolling speed 5m / h.

[0044] Step 4: Compounding the pole piece with titanium foil. Take a titanium foil with a thickness of 0.01 mm, use a 100 μm scraper to apply conductive glue on the titanium foil, and then put it in an oven and bake it at 60°C for 6 hours until the conductive glue is completely compounded with the titanium foil. Compound the rolled manganese dioxide self-supporting pole piece with the titanium foil coated with conductive glue under a rolling mill to obtain a manganese dioxide electrode. The hot rolling temperature is 80°C.

[0045] Step 5: Cut the manganese dioxide electrode sheet into 15mm diameter discs and assemble the battery.

[0046] Example 2

[0047] Step 1: Mixing. Weigh 80g of manganese dioxide powder, 3g of montmorillonite, and 13g of high-purity nanocarbon fiber in a container and stir them thoroughly in a high-speed mixer to obtain material A. Parameter setting: speed 1000rpm, time 20min. Then weigh 4g of PTFE powder into material A and continue stirring at the original speed for 20min to obtain material B.

[0048] Step 2: High-speed stirring. Put the mixed material B in a high-speed mixer and stir it at high speed to make it fiberized. Parameter setting: speed 10000rpm, time 20min.

[0049] The third step: rolling. The material after high-speed stirring is rolled under a roller mill. First, the material is rolled into a thin sheet under an appropriate roller gap, and then it decreases in sequence from 300μm, 200μm, and 100μm, and finally a manganese dioxide self-supporting pole piece of about 100μm is obtained. The roller press parameter settings are: temperature 25℃, rolling speed 5m / min. Figure 1 , Figure 2 This is a SEM image of a dry-process manganese dioxide electrode film. It can be seen that the dry-process electrode is made by fibrous PTFE binder to tightly wrap the active material and the conductive agent together to form a film with a total thickness of about 100 μm, which will provide more active materials for the positive electrode and greatly improve the energy density of the battery.

[0050] Step 4: Compounding of pole piece and titanium foil. Take a titanium foil with a thickness of 0.01 mm, use a 100 μm scraper to apply conductive glue on the titanium foil, and then put it in an oven at 60°C for 6 hours until the conductive glue is completely compounded with the titanium foil. Compound the rolled manganese dioxide self-supporting pole piece and the titanium foil coated with conductive glue under a rolling mill to obtain a manganese dioxide electrode. The hot rolling temperature is 80°C.

[0051] Step 5: Cut the manganese dioxide electrode sheet into 15mm diameter discs and assemble the battery.

[0052] Example 3

[0053] This embodiment provides a method for preparing a dry positive electrode sheet. The difference from Embodiment 2 is that the ratio of active material, binder, conductive agent, and liquid retaining agent is different. In this case, active material: binder: conductive agent: liquid retaining agent = 80:4:11:5.

[0054] Example 4

[0055] This embodiment provides a method for preparing a dry-process positive electrode sheet, which is different from Embodiment 2 in that the liquid retaining agent is different. In this case, the liquid retaining agent is bentonite.

[0056] Example 5

[0057] This embodiment provides a method for preparing a dry-process positive electrode sheet, which is different from Embodiment 2 in that the liquid retaining agent is different. In this case, the liquid retaining agent is illite powder.

[0058] Example 6

[0059] The negative electrode material used is a commercial laboratory-grade zinc plate with Zn ≥ 99.999% and a thickness of 200 μm, which is cut into a 15 mm diameter disc that is symmetrical with the positive electrode. Afterwards, the finished dry-process electrode plates obtained in Example 2 are placed and assembled in the order of “positive electrode shell-finished dry-process positive electrode sheet-diaphragm-electrolyte-zinc sheet-gasket-shrapnel-negative electrode shell” to obtain a dry-process prepared aqueous zinc ion button battery. The diaphragm used is Whatman glass fiber filter GF / D, and the electrolyte used is 2M zinc sulfate + 0.2M manganese sulfate. The battery is then cycled at a current density of 0.1C, as shown in FIG. Figure 3 It can be seen from the figure that at a current density of 0.1C, the battery surface capacity can reach 4mAh / cm2 and the capacity efficiency can reach 98%.

[0060] The above are only several embodiments of the present application and are not intended to limit the present application in any form. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent embodiments and fall within the scope of the technical solution.

Claims

1. A method for preparing a positive electrode, characterized in that: The following steps are involved: The raw materials containing active materials, conductive agents, liquid retaining agents and binders are mixed, sheared and stirred, preformed, and rolled to obtain a positive electrode film, and the positive electrode film is laminated to a current collector to obtain the positive electrode.

2. The preparation method according to claim 1, characterized in that: The active material is selected from at least one of MnO2, vanadium pentoxide, and CuFe(CN)6; The conductive agent is selected from at least one of acetylene black, conductive carbon black, multi-walled carbon nanotubes, graphene, and high-purity carbon nanofibers; The liquid retaining agent is selected from at least one of bentonite, montmorillonite powder, illite powder, kaolin powder and halloysite powder; The binder is selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, sodium carboxymethyl cellulose, carboxymethyl cellulose and styrene-butadiene rubber.

3. The preparation method according to claim 1, characterized in that: The mass content of each substance in the raw materials is: Active substance 80-90wt%; Conductive agent 8-13wt%; Liquid retaining agent 1-3wt%; Binder 1~4wt%.

4. The preparation method according to claim 1, characterized in that: The shear stirring time is 10 to 30 minutes; The shear stirring temperature is 20 to 80°C; The shear stirring speed is 10000-15000 t / min.

5. The preparation method according to claim 1, characterized in that: The preforming is a roller pressing pretreatment; The pressure of the roller pressing pretreatment is 5 to 40T; The temperature of the roller pressing pretreatment is 25-80°C.

6. The preparation method according to claim 1, characterized in that: The current collector is selected from at least one of stainless steel foil, titanium foil, stainless steel mesh, and titanium mesh.

7. A positive electrode, characterized in that It is prepared by the preparation method according to any one of claims 1 to 7.

8. An aqueous zinc ion battery, characterized in that: It includes the aqueous dry-process positive electrode as described in claim 7.

9. An aqueous zinc ion battery, characterized in that: Applied to high energy density zinc-manganese button secondary batteries.

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