Coating, zinc negative electrode with coating and preparation method and application of zinc negative electrode

Abstract

The invention discloses a coating, a zinc negative electrode with the coating and a preparation method and application of the zinc negative electrode. The coating is a Nafion film containing inorganic substance quantum dots; wherein the mass fraction of the inorganic quantum dots is greater than 50%. And the thickness of the coating is 1-80 microns. The coating has both physical isolation of an organic layer and high electrochemical activity of the organic layer, dendritic crystals and side reactions are reduced, and the cycle performance of the zinc ion battery is greatly improved. The advantages of an organic layer and an inorganic layer are integrated. The Nafion films consist of hydrophilic and hydrophobic regions and have proved to play a positive role in galvanization / dezincification as well as dendrites. The quantum dot has a large specific surface area, a semiconductor structure, small-size quantum constraint and an edge effect, and is stable and easy to form a composite material, dope and functionalize. The quantum dot modified electrode has better electrochemical activity and conductivity and an increased electron transmission path.

Description

Technical Field

[0001] The present application relates to a coating, a zinc negative electrode with a coating, and a preparation method and application thereof, and belongs to the field of electrochemical materials. Background Art

[0002] As a new generation of rechargeable batteries developed in the post-lithium ion era, aqueous rechargeable zinc ion batteries show good application prospects in the field of large-scale energy storage. Zinc has a high theoretical capacity (820mAh g -1 ), low electrochemical potential (relative to standard hydrogen electrode: 0.762V), operability in aqueous electrolytes, high reserves and environmental friendliness. These advantages have driven the vigorous development of rechargeable zinc-ion batteries in recent years. However, improving the reversibility of the zinc anode is crucial to the pursuit of high cycle stability of rechargeable zinc-ion batteries. Zinc dendrite formation and side reactions lead to low battery coulombic efficiency, capacity decay and internal short circuit. Currently, zinc metal anodes have been intensively studied, and many studies have reported strategies to inhibit dendrites and side reactions.

[0003] Currently reported protection strategies, including inorganic coatings or organic coatings, have certain limitations in improving the performance and life of Zn anodes. Inorganic coatings are brittle and easily break or detach from the Zn metal anode after long-term cycling or rapid galvanizing / stripping. Organic protective layers are flexible, have low ionic conductivity and are easily affected by thickness. Hydrophobic polymer layers lead to Zn 2+ The nucleation potential increases and restricts the 2D diffusion of zinc, and overly hydrophilic polymers are easily dissolved in aqueous electrolytes, resulting in the loss of protective effect. Summary of the invention

[0004] Organic-inorganic hybrid coatings are an effective way to solve the above problems. The coatings have the advantages of both organic and inorganic layers. Nafion membranes are composed of hydrophilic and hydrophobic regions and have been shown to play an active role in zinc plating / stripping and dendrites. Quantum dots have large specific surface area, semiconductor structure, small size quantum confinement and edge effect, are stable and easy to form composite materials, doping and functionalization. Electrodes modified with quantum dots have better electrochemical activity, conductivity and increased electron transport paths.

[0005] According to one aspect of the present application, a coating is provided, wherein the coating is a Nafion membrane containing inorganic quantum dots;

[0006] The mass fraction of the inorganic quantum dots is 50-80%;

[0007] The coating has a thickness of 1 to 80 μm.

[0008] The inorganic quantum dots are selected from at least one of graphene quantum dots, MXene quantum dots, silicene quantum dots, phosphorene quantum dots, transition metal oxide quantum dots, and transition metal halide quantum dots.

[0009] Optionally, MXene quantum dots and graphene quantum dots are used. Graphene is a honeycomb two-dimensional material that is one carbon atom thick. Graphene quantum dots are composed of one or several layers of graphene. The zero-band electronic structure (low electrical conductivity) of graphene seriously hinders its optoelectronic and electronic applications, but when it is converted into quantum dots, it has excellent edge effects and quantum confinement, and can be well used as electrode materials.

[0010] According to another aspect of the present application, a zinc negative electrode is provided, the surface of which has the above-mentioned coating.

[0011] According to another aspect of the present application, a method for preparing the above-mentioned zinc negative electrode is provided, comprising the following steps:

[0012] The zinc negative electrode is placed in a mold, and an N,N-dimethylformamide solution containing Nafion and an N,N-dimethylformamide solution containing inorganic quantum dots are mixed and poured into the mold, heated, and the solvent is evaporated to obtain the zinc negative electrode.

[0013] In the N,N-dimethylformamide solution containing Nafion, the mass content of Nafion is 5 to 20 wt%;

[0014] In the N,N-dimethylformamide solution containing inorganic quantum dots, the mass content of the inorganic quantum dots is 5-20 wt %.

[0015] The mass ratio of Nafion in the N,N-dimethylformamide solution containing Nafion to the mass ratio of inorganic quantum dots in the N,N-dimethylformamide solution containing inorganic quantum dots is 1:1-9.

[0016] The heating temperature is 40-60°C;

[0017] The heating time is 8 to 12 hours.

[0018] Specifically,

[0019] (1) Clean the zinc foil with acetone and ethanol and fix it on a mold with a groove;

[0020] The zinc foil has a thickness of 10 μm to 1000 μm and a size of 9×9 cm.

[0021] (2) Prepare a DMF solution of Nafion at a certain concentration and stir for 2 h;

[0022] The Nafion is obtained by drying a 5% DuPont membrane solution;

[0023] (3) Prepare a DMF dispersion of quantum dots with a certain concentration and perform ultrasonic dispersion for 2 h;

[0024] (4) After the two solutions were mixed, they were stirred for 4 h, ultrasonicated for 4 h, and then poured onto the surface of the zinc foil in the mold. The mold was placed in an oven and allowed to stand at 40 °C for 12 h to slowly evaporate the solvent.

[0025] When the mixed solution is left standing, the quantum dots will form a concentration gradient from bottom to top due to gravity, realizing graded regulation of zinc ion transport and achieving dendrite-free uniform deposition.

[0026] According to another aspect of the present application, an aqueous zinc ion battery is provided, comprising the above-mentioned zinc negative electrode.

[0027] The advantages of this application are:

[0028] In view of the shortcomings of the existing negative electrode protection methods, the solution of the present invention is to provide a method for preparing a zinc negative electrode organic-inorganic hybrid coating. The method combines Nafion with quantum dots to form an organic-inorganic hybrid coating on the surface of the zinc negative electrode. The coating has both the physical isolation of the organic layer and the high electrochemical activity of the organic layer, which reduces dendrites and side reactions and greatly improves the cycle performance of zinc ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a SEM photograph of Example 1 of the present invention, with a scale of 2 μm.

[0030] Figure 2 This is a SEM photograph of Example 2 of the present invention, with a scale of 2 μm.

[0031] Figure 3 The zinc negative electrode symmetric battery prepared in Example 2 of the present invention has a current density of 0.5 mA cm -2 The current density of 1 mAh cm -2 Cycling performance at surface capacity.

[0032] Figure 4 The zinc negative electrode symmetric battery prepared in Example 1 of the present invention has a conductivity of 0.5 mA cm -2 The current density of 1 mAh cm -2 Cycling performance at surface capacity. DETAILED DESCRIPTION

[0033] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0034] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0035] Comparative Example 1

[0036] A 100 μm zinc foil was cleaned alternately with acetone and ethanol and then dried without any other treatment and set aside.

[0037] Example 1

[0038] (1) A 100 μm zinc foil was cleaned with acetone and ethanol and then fixed on a mold with a groove;

[0039] (2) Mix 0.4 g Nafion and 8 mL DMF and stir for 2 h;

[0040] (3) 0.4 g of graphene quantum dots were added to 8 mL of DMF solution and ultrasonically dispersed for 2 h;

[0041] (4) The two solutions were mixed and stirred for 4 h, then ultrasonicated for 4 h, and then poured onto the surface of the zinc foil in the mold, placed in an oven, and allowed to stand at 40 °C for 12 h to slowly evaporate the solvent.

[0042] Figure 1 This is a SEM photo of Example 1 of the present invention, with a scale of 2 μm. It can be seen from the figure that the surface is flat and smooth.

[0043] Example 2

[0044] (1) A 100 μm zinc foil was cleaned with acetone and ethanol and then fixed on a mold with a groove;

[0045] (2) Mix 0.4 g Nafion and 8 mL DMF and stir for 2 h;

[0046] (3) 0.8 g of graphene quantum dots were added to 8 mL of DMF solution and ultrasonically dispersed for 2 h;

[0047] (4) The two solutions were mixed and stirred for 4 h, then ultrasonicated for 4 h, and then poured onto the surface of the zinc foil in the mold, placed in an oven, and allowed to stand at 40 °C for 12 h to slowly evaporate the solvent.

[0048] Figure 2 This is a SEM photo of Example 2 of the present invention, with a scale of 2 μm. It can be seen from the figure that as the concentration of quantum dots increases, agglomeration occurs, resulting in a relatively rough film surface.

[0049] Example 3

[0050] Depositing pure graphene quantum dots onto zinc negative surfaces:

[0051] (1) A 100 μm zinc foil was cleaned with acetone and ethanol and then fixed on a mold with a groove;

[0052] (2) Mix 0.2 g Nafion and 8 mL DMF and stir for 2 h;

[0053] (3) Add 1 g of graphene quantum dots to 8 mL of DMF solution and disperse them by ultrasonication for 2 h;

[0054] (4) The graphene quantum dot solution was poured onto the zinc foil surface in the mold, placed in an oven, and allowed to stand at 40°C to slowly evaporate the solvent for 12 h.

[0055] Example 4

[0056] (1) A 100 μm zinc foil was cleaned with acetone and ethanol and then fixed on a mold with a groove;

[0057] (2) Mix 0.6 g Nafion and 8 mL DMF and stir for 2 h;

[0058] (3) Add 0.6 g of MXene quantum dots into DMF solution and disperse them by ultrasonic for 2 h;

[0059] (4) The two solutions were mixed and stirred for 4 h, then ultrasonicated for 4 h, and then poured onto the surface of the zinc foil in the mold, placed in an oven, and allowed to stand at 40 °C for 12 h to slowly evaporate the solvent.

[0060] Example 5

[0061] (1) A 100 μm zinc foil was cleaned with acetone and ethanol and then fixed on a mold with a groove;

[0062] (2) Mix 0.2 g Nafion and 8 mL DMF and stir for 2 h;

[0063] (3) Add 0.2 g of black phosphorus quantum dots into DMF solution and disperse them ultrasonically for 2 h;

[0064] (4) The two solutions were mixed and stirred for 4 h, then ultrasonicated for 4 h, and then poured onto the surface of the zinc foil in the mold, placed in an oven, and allowed to stand at 40 °C for 12 h to slowly evaporate the solvent.

[0065] Example 6

[0066] (1) The zinc negative electrodes prepared in Examples 1 to 5 and Comparative Example 1 were cut into pole pieces with a diameter of 15 mm and assembled into symmetrical batteries, wherein the positive and negative electrodes were prepared according to the present invention, the separator was glass fiber, and the electrolyte was 2M ZnSO4.

[0067] (2) Symmetrical battery performance test: The assembled symmetrical battery was tested on the Blue Electric test system, with the current set to 0.883 mA and the charge and discharge time for each cycle set to 1 h, i.e., at 0.5 mA cm -2 The current density of 1 mAh cm -2Constant current charge and discharge test was carried out at the surface capacity.

[0068] Figure 3 The zinc negative electrode symmetric battery prepared in Example 2 of the present invention has a current density of 0.5 mA cm -2 The current density of 1 mAh cm -2 Cycling performance at surface capacity.

[0069] Figure 4 The zinc negative electrode symmetric battery prepared in Example 1 of the present invention has a conductivity of 0.5 mA cm -2 The current density of 1 mAh cm -2 Cycling performance at surface capacity.

[0070] As can be seen from the figure, the cycle life of zinc negative electrode modified by Nafion and quantum dots reached more than 1000 hours, and even close to 2000 hours.

[0071] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. 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 implementation cases and fall within the scope of the technical solution.

Claims

1. A coating, characterized in that: The coating is a Nafion membrane containing inorganic quantum dots; The mass fraction of the inorganic quantum dots is 50-80%; The coating has a thickness of 1 to 80 μm.

2. The coating according to claim 1, characterized in that The inorganic quantum dots are selected from at least one of graphene quantum dots, MXene quantum dots, silicene quantum dots, phosphorene quantum dots, transition metal oxide quantum dots, and transition metal halide quantum dots.

3. A zinc negative electrode, characterized in that The surface of the zinc negative electrode has a coating as described in any one of claims 1 or 2.

4. A method for preparing a zinc negative electrode according to claim 3, characterized in that: The following steps are involved: The zinc negative electrode is placed in a mold, and an N,N-dimethylformamide solution containing Nafion and an N,N-dimethylformamide solution containing inorganic quantum dots are mixed and poured into the mold, heated, and the solvent is evaporated to obtain the zinc negative electrode.

5. The preparation method according to claim 4, characterized in that: In the N,N-dimethylformamide solution containing Nafion, the mass content of Nafion is 5 to 20 wt%; In the N,N-dimethylformamide solution containing inorganic quantum dots, the mass content of the inorganic quantum dots is 5-20 wt %.

6. The preparation method according to claim 4, characterized in that: The mass ratio of Nafion in the N,N-dimethylformamide solution containing Nafion to the mass ratio of inorganic quantum dots in the N,N-dimethylformamide solution containing inorganic quantum dots is 1:1-9.

7. The preparation method according to claim 4, characterized in that: The heating temperature is 40-60°C; The heating time is 8 to 12 hours.

8. An aqueous zinc ion battery, characterized in that: Comprising the zinc negative electrode as described in claim 3.

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