An electrochemical pore-forming method and its application in water-based batteries

Abstract

The present invention relates to an electrochemical pore forming method, wherein an alkaline salt that can be electrochemically converted in water is added to the positive electrode plate of a water-based battery based on an aqueous electrolyte, and a large number of pores are electrochemically formed inside the positive electrode plate by utilizing the electrochemical conversion process of the alkaline salt during the battery charging and discharging process, so that the positive electrode plate is transformed into a three-dimensional porous structure. The beneficial effects of the present invention are as follows: the present invention incorporates the alkaline salt into the positive electrode plate by simple physical mixing, and utilizes the electrochemical conversion of the alkaline salt during the charging and discharging process, thereby electrochemically forming a large number of pores inside the positive electrode plate. The method has simple process, low cost, non-toxic and harmless, safe and pollution-free, suitable for large-scale production, and effectively constructs a three-dimensional porous electrode structure, greatly increases the specific surface area of ​​the electrode plate in contact with the electrolyte, and increases the ion migration and diffusion speed, improves the utilization rate of the active material of the electrode plate, improves the battery cycle stability, and improves the battery electrochemical performance.

Description

Technical Field

[0001] The invention belongs to the technical field of secondary water-based batteries, and in particular relates to an electrochemical pore-forming method and an application thereof in water-based batteries. Background Art

[0002] Energy storage battery technology is the foundation of new energy promotion and energy revolution. "High safety, low cost, long life, easy recycling" is the core requirement of energy storage battery technology, and it is also the development direction of energy storage battery technology in the future. The development of electrochemical energy storage technology with high safety, low cost and environmental friendliness is also the key to realizing large-scale energy storage applications in the future.

[0003] Water-based secondary batteries have become a hot spot for the next generation of energy storage due to their safety, environmental protection, and high energy density. However, the current battery energy density is low, it is very easy to decay, and the rate performance is poor. The main reason is that the pH of the solution fluctuates greatly during the charge and discharge process, which easily generates irreversible products. After the thickness of the battery pole is increased, the energy density can be improved, but the pole has poor liquid absorption capacity and is difficult to exchange ions with the electrolyte. Patent CN107331878A uses fatty acid polyoxyethylene esters, fatty alcohol polyoxyethylene ethers and their isomers as basic salts to manufacture porous manganese dioxide positive electrodes, but the heat treatment process will produce toxic and harmful gases such as aldehydes; Patent CN110224112A incorporates organic materials into the pole piece by heating and melting, and increases the pole piece porosity after extraction, but the process is complicated and is not applicable to the pole piece of water-based batteries.

[0004] Therefore, developing a simple and effective pore-making method to increase the porosity of the electrode and enhance battery performance is of great significance to the development of water-based batteries. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems of poor cycle stability and low utilization rate of active materials in water-based secondary batteries, and to provide an electrochemical pore-forming method and its application in water-based batteries.

[0006] This electrochemical pore-forming method involves adding an alkaline salt that can be electrochemically converted in water to the positive electrode of a water-based battery based on an aqueous electrolyte, and utilizing the electrochemical conversion process of the alkaline salt during the battery's charge and discharge process to electrochemically form a large number of pores inside the positive electrode, transforming the positive electrode into a three-dimensional porous structure.

[0007] Preferably, the basic salt includes one or more of basic sulfate, basic carbonate, basic chloride, basic nitrate, basic acetate, basic methane sulfonate and the like.

[0008] Preferably, the basic sulfate includes one or more of basic zinc sulfate, basic copper sulfate, basic magnesium sulfate, basic lead sulfate and the like.

[0009] Preferably, the basic carbonate includes one or more of basic zinc carbonate, basic copper carbonate, basic magnesium carbonate, basic lead carbonate and the like.

[0010] Preferably, the basic chloride salt includes one or more of basic zinc chloride, basic copper chloride, basic magnesium chloride, basic lead chloride and the like.

[0011] Preferably, the basic nitrate is basic copper nitrate or the like.

[0012] Preferably, the basic acetate includes one or more of basic zinc acetate, basic copper acetate, basic magnesium acetate, basic lead acetate, etc.

[0013] Preferably, the mass ratio of the basic salt to the positive electrode active material is (0.01-10):1; the positive electrode active material includes one or more of iron-based compounds, manganese-based compounds, cobalt-based compounds, nickel-based compounds, and lead-based compounds; the negative electrode includes one or more of metals or alloys such as zinc, copper, magnesium, and lead.

[0014] Preferably, the aqueous electrolyte contains one or more acid salts of zinc ions, copper ions, magnesium ions, lead ions, etc. that can undergo electrochemical conversion reactions with basic salts, and the acid radicals in the acid salts include one or more of sulfate, hydrochloride, nitrate, acetate, methanesulfonate, etc.

[0015] The positive electrode sheet made by this electrochemical pore-forming method is used in water-based batteries.

[0016] The beneficial effects of the present invention are as follows: the present invention incorporates basic salts into the positive electrode plate by simple physical mixing, and utilizes the electrochemical conversion of the basic salts during the charge and discharge process to electrochemically form a large number of pores inside the positive electrode plate. The method has simple process, low cost, non-toxicity, safety and pollution-free, is suitable for large-scale production, and effectively constructs a three-dimensional porous electrode structure, which greatly increases the specific surface area of ​​the electrode plate in contact with the electrolyte and improves the ion migration and diffusion rate, thereby improving the utilization rate of the active material in the electrode plate, improving the battery cycle stability, and improving the battery electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a microstructure diagram of the electrode of the comparative example of the present invention.

[0018] Figure 2 It is a cycle performance diagram of a full battery of a comparative example of the present invention (the upper curve in the figure represents the coulombic efficiency, and the lower curve represents the specific capacity).

[0019] Figure 3 This is a diagram of the electrode microstructure of Example 1 of the present invention.

[0020] Figure 4 It is a cycle performance diagram of the full battery of Example 1 of the present invention (the upper curve in the figure represents the coulombic efficiency, and the lower curve represents the specific capacity).

[0021] Figure 5 The graph is a cycle performance graph of the full battery of Examples 2-4 of the present invention (the top curve in the graph represents the coulombic efficiency, and the three curves below represent the specific capacity). DETAILED DESCRIPTION

[0022] The present invention is further described below in conjunction with embodiments. The description of the following embodiments is only used to help understand the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principles of the present invention, several improvements and modifications may be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0023] Comparative Example:

[0024] Manganese dioxide is used to prepare the positive electrode, metal zinc is used as the negative electrode, and zinc sulfate and manganese sulfate aqueous solution are used as the electrolyte. The specific preparation steps are as follows;

[0025] 1. Preparation of zinc electrode: Use zinc foil as the zinc negative electrode.

[0026] 2. Electrolyte preparation: Prepare aqueous solution of dissolved zinc sulfate and manganese sulfate.

[0027] 3. Preparation of manganese dioxide electrode: Weigh 0.7g manganese dioxide, 0.2g acetylene black, and 4g 5% polyvinylidene fluoride N-methylpyrrolidone solution, ball-mill them evenly and apply them on titanium foil. After drying at 50℃, cut them into positive electrode sheets of the required size. The microstructure of the electrode sheet is as follows: Figure 1 As shown, the pole piece is dense and basically free of holes.

[0028] The assembled full battery has an open circuit voltage of 1.4V, a constant current charge and discharge cut-off voltage of 0.8-1.85V, and a current density of 2A. -1 , the battery test results are as follows Figure 2 As shown in the figure, due to the poor porosity of the electrode microstructure and the weak ion exchange capacity with the electrolyte, the battery capacity decays rapidly and the cycle stability is poor. After 100 cycles, the battery capacity is only 50 mAh g -1 about.

[0029] Embodiment 1:

[0030] Manganese dioxide and basic zinc sulfate are used to prepare the positive electrode, metal zinc is used as the negative electrode, and zinc sulfate and manganese sulfate aqueous solution are used as the electrolyte. The specific preparation steps are as follows;

[0031] 1. Preparation of zinc electrode: Use zinc foil as the zinc negative electrode.

[0032] 2. Electrolyte preparation: Prepare aqueous solution of dissolved zinc sulfate and manganese sulfate.

[0033] 3. Preparation of manganese dioxide electrode: Weigh 0.47g manganese dioxide, 0.23g basic zinc sulfate, 0.2g acetylene black, and 4g 5% polyvinylidene fluoride N-methylpyrrolidone solution, ball mill evenly and apply them on titanium foil, dry at 50°C and cut into positive electrode sheets of required size.

[0034] The assembled full battery constant current charge and discharge cut-off voltage is 0.8-1.85V, and the current density is 2Ag -1 The microstructure of the electrode sheet after charge and discharge cycles is as follows: Figure 3 As shown in FIG. 1 , compared with the above comparative example, the electrode in this embodiment has an obvious porous structure. This three-dimensional porous structure is conducive to the ion diffusion and transport process of the electrolyte, and improves the capacity and stability of the battery. Furthermore, the full battery cycle performance is shown in FIG. Figure 4 As shown, the full battery can be stably cycled with a specific capacity of up to 150 mAh g -1 .

[0035] Embodiment 2:

[0036] Manganese dioxide and basic zinc sulfate are used to prepare the positive electrode, metal zinc is used as the negative electrode, and zinc sulfate and manganese sulfate aqueous solution are used as the electrolyte. The specific preparation steps are as follows;

[0037] 1. Preparation of zinc electrode: Use zinc foil as the zinc negative electrode.

[0038] 2. Electrolyte preparation: Prepare an aqueous solution to dissolve zinc sulfate and manganese sulfate.

[0039] 3. Preparation of manganese dioxide electrode: Weigh 0.6g manganese dioxide, 0.1g basic zinc sulfate, 0.2g acetylene black, and 4g 5% polyvinylidene fluoride N-methylpyrrolidone solution, ball mill evenly and apply them on titanium foil, dry at 50°C and cut into positive electrode sheets of required size.

[0040] The assembled full battery constant current charge and discharge cut-off voltage is 0.8-1.85V, and the current density is 2Ag -1 , can be cycled stably, the battery cycle results are as follows Figure 5 As shown, the specific capacity is as high as 185 mAh g -1 .

[0041] Embodiment 3:

[0042] Manganese dioxide and basic zinc chloride are used to prepare the positive electrode, metallic zinc is used as the negative electrode, and zinc sulfate and manganese sulfate aqueous solution are used as the electrolyte. The specific preparation steps are as follows;

[0043] 1. Preparation of zinc electrode: Use zinc foil as the zinc negative electrode.

[0044] 2. Electrolyte preparation: Prepare aqueous solution of dissolved zinc sulfate and manganese sulfate.

[0045] 3. Preparation of manganese dioxide electrode: Weigh 0.6g manganese dioxide, 0.1g basic zinc chloride, 0.2g acetylene black, and 4g 5% polyvinylidene fluoride N-methylpyrrolidone solution, ball mill them evenly and apply them on titanium foil. After drying at 50°C, cut them into positive electrode sheets of the required size.

[0046] The assembled full battery has a constant current charge and discharge cut-off voltage of 0.8-1.85V and a current density of 2Ag -1 , can be cycled stably, the battery cycle results are as follows Figure 5 As shown, the specific capacity is as high as 135 mAh g -1 .

[0047] Embodiment 4:

[0048] Manganese dioxide and basic magnesium sulfate are used to prepare the positive electrode, metal zinc is used as the negative electrode, and zinc sulfate and manganese sulfate aqueous solution are used as the electrolyte. The specific preparation steps are as follows;

[0049] 1. Preparation of zinc electrode: Use zinc foil as the zinc negative electrode.

[0050] 2. Electrolyte preparation: Prepare aqueous solution of dissolved zinc sulfate and manganese sulfate.

[0051] 3. Preparation of manganese dioxide electrode: Weigh 0.6g manganese dioxide, 0.1g basic magnesium sulfate, 0.2g acetylene black, and 4g 5% polyvinylidene fluoride N-methylpyrrolidone solution, ball mill them evenly and apply them on titanium foil. After drying at 50°C, cut them into positive electrode sheets of the required size.

[0052] The assembled full battery has a constant current charge and discharge cut-off voltage of 0.8-1.85V and a current density of 2Ag -1 , can be cycled stably, the battery cycle results are as follows Figure 5 As shown, the specific capacity is as high as 155 mAh g -1 .

Claims

1. An electrochemical pore forming method, characterized in that: A basic salt that can be electrochemically converted in water is added to the positive electrode plate of a water-based battery based on an aqueous electrolyte, and the electrochemical conversion process of the basic salt during the battery charging and discharging process is used to electrochemically form holes inside the positive electrode plate to transform the positive electrode plate into a three-dimensional porous structure; the mass ratio of the basic salt to the active material of the positive electrode plate is (0.01-10):1; the active material of the positive electrode plate includes one or more of iron-based compounds, manganese-based compounds, cobalt-based compounds, nickel-based compounds or lead-based compounds; the negative electrode includes one or more of zinc, copper, magnesium or lead; the basic salt includes one or more of basic sulfate, basic carbonate, basic chloride, basic nitrate, basic acetate or basic methane sulfonate.

2. The electrochemical pore forming method according to claim 1, characterized in that: The basic sulfate includes one or more of basic zinc sulfate, basic copper sulfate, basic magnesium sulfate or basic lead sulfate.

3. The electrochemical pore forming method according to claim 1, characterized in that: The basic carbonate includes one or more of basic zinc carbonate, basic copper carbonate, basic magnesium carbonate or basic lead carbonate.

4. The electrochemical pore forming method according to claim 1, characterized in that: The basic chloride salt includes one or more of basic zinc chloride, basic copper chloride, basic magnesium chloride or basic lead chloride.

5. The electrochemical pore forming method according to claim 1, characterized in that: The basic nitrate is basic copper nitrate.

6. The electrochemical pore forming method according to claim 1, characterized in that: The basic acetate includes one or more of basic zinc acetate, basic copper acetate, basic magnesium acetate or basic lead acetate.

7. The electrochemical pore forming method according to claim 1, characterized in that: The aqueous electrolyte contains one or more acid salts of zinc ions, copper ions, magnesium ions, and lead ions that can undergo electrochemical conversion reactions with basic salts, and the acid radicals in the acid salts include one or more of sulfate, hydrochloride, nitrate, acetate, or methanesulfonate.

8. Use of a positive electrode sheet made by the electrochemical pore-forming method as claimed in claim 1 in a water-based battery.

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