Preparation method and application of zinc oxide electrode

Abstract

The invention belongs to the technical field of battery materials, and discloses a preparation method and application of a zinc oxide electrode. The preparation method of the zinc oxide electrode comprises the following steps that a metal layer is deposited on the surface of an unmodified zinc oxide electrode, and the thickness of the metal layer is 3-5 nm. By depositing the metal sites on the surface of the ZnO electrode, the conductivity of ZnO is improved, and meanwhile, the uniformity of Zn deposition on the surface of the electrode is improved, so that the growth of Zn dendritic crystals is inhibited, and the cycle performance of the alkaline aqueous nickel-zinc battery is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a preparation method and application of a zinc oxide electrode. Background Art

[0002] Alkaline nickel-zinc secondary batteries have been widely used commercially since the late 19th century. Zinc metal, with its high theoretical capacity, low redox potential (-1.26V vs. standard hydrogen electrode), and good corrosion resistance, is a good anode material. Furthermore, because water is non-flammable, various aqueous batteries utilizing aqueous electrolytes can significantly improve battery safety. This makes zinc-based batteries environmentally friendly, with relatively high energy density and low cost. Alkaline nickel-zinc batteries, in particular, have attracted widespread attention due to their high operating voltage (approximately 1.6V), compared to other alkaline zinc-based batteries, which mostly operate below 1.5V.

[0003] However, the commercialization of secondary zinc-based batteries, especially nickel-zinc batteries with relatively low-cost ZnO materials as the initial active material, still generally has the problem of low cycle performance of the zinc negative electrode. The main reason is that during use, the zinc negative electrode will undergo many problems such as shape change, passivation (such as the formation of "dead zinc"), zinc corrosion, zinc dendrites, etc. The fundamental reason is that the high solubility of zinc oxide in alkaline electrolytes leads to the problem of uneven redistribution of zinc during charging and discharging. In the electrochemical reaction, the zinc oxide negative electrode material will undergo "ZnO-Zn(OH)4 2- -Zn" undergoes a solid-solution-solid phase transition. During this process, zincate ions may deposit on the battery separator or nickel positive electrode, resulting in irreversible loss of zinc. These uneven depositions will form a passivation layer, triggering the growth of zinc dendrites. From a microscopic perspective, the uneven aggregation of zincate ions during ion migration and ion deposition will lead to differences in the ion environment in the local area near the electrode, thereby forming zinc dendrites and a passivation layer. Therefore, optimizing the transition process between the solid phase and the liquid phase and improving the performance of ZnO negative electrode materials are key issues that need to be addressed in current research. Summary of the Invention

[0004] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the primary purpose of the present invention is to provide a method for preparing a zinc oxide electrode.

[0005] Another object of the present invention is to provide a zinc oxide electrode prepared by the above method.

[0006] Another object of the present invention is to provide an application of the zinc oxide electrode in an alkaline nickel-zinc battery.

[0007] The purpose of the present invention is achieved through the following solutions:

[0008] A method for preparing a zinc oxide electrode comprises the following steps: depositing a metal layer on the surface of an unmodified zinc oxide electrode, wherein the thickness of the metal layer is 3-5 nm.

[0009] The unmodified zinc oxide electrode is prepared by coating a mixed powder of ZnO and Zn on a current collector.

[0010] The thickness of the zinc oxide layer in the unmodified zinc oxide electrode is 3-5 μm.

[0011] The metal includes at least one of a transition metal and a rare earth metal.

[0012] The metal includes at least one of Sn, Bi, Ni, Fe, Co, Ti, Cr, Mo, Au, In, W, Ir, Pt, and Ta.

[0013] The deposition method includes one of chemical vapor deposition (CVD) and atomic layer deposition (ALD).

[0014] The chemical vapor deposition is to place the metal element to be deposited into a reaction chamber, heat and activate it to sublime it into a gaseous precursor, and then deposit it until the metal layer reaches the required thickness and then stop heating.

[0015] The chemical vapor deposition specifically includes the following steps: placing an unmodified zinc oxide electrode in a chemical vapor deposition device, adding a metal element, heating and activating it into a metal gaseous precursor, and depositing it until the metal layer reaches a desired thickness.

[0016] The heating voltage is 150-200V; the deposition speed is The deposition time is 25-40s.

[0017] The atomic layer deposition is to blow a gaseous precursor of a single metal element into a reaction chamber to deposit it into a single atomic layer, and repeat the above steps until all the metal elements to be deposited are deposited layer by layer in the form of single atomic layers.

[0018] The zinc oxide electrode prepared by the above method.

[0019] Application of the above zinc oxide electrode in alkaline nickel-zinc batteries.

[0020] The mechanism of the present invention is:

[0021] The present invention uses a ZnO / Zn powder-coated electrode as a substrate and further deposits nanometal particles on the surface of the ZnO electrode to form metal islands. These metal particles do not completely cover the ZnO particle surface, which improves the conductivity of the ZnO electrode. They also serve as nucleation sites, promoting uniform Zn deposition on the electrode surface, inhibiting the growth of Zn dendrites, and improving the cycling performance of alkaline aqueous nickel-zinc batteries.

[0022] In the chemical vapor deposition method of the present invention, an unmodified zinc oxide electrode is placed in the reaction chamber as a substrate. The metal element placed in the reaction chamber is heated and activated to a gaseous precursor, and then chemical adsorption or chemical reaction occurs on the surface of the substrate. This process will generate the metal particles required for deposition, which are attached to the surface of the zinc oxide to form a metal film on the surface, while the excess gaseous precursors and products of the metal elements will be blown away from the chamber by the continuously flowing inert gas flow. After a period of time, the heating can be stopped when the metal film reaches the required thickness, and a zinc oxide electrode with a deposited metal film can be obtained. In the atomic layer deposition method, only a small amount of a single precursor is blown into the reaction chamber each time. After chemical adsorption or chemical reaction occurs on the surface of the substrate, only a single atomic layer is formed on the surface of the substrate, and the above steps are repeated until all the metal elements required to be deposited are deposited layer by layer in the form of a single atomic layer.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] The present invention improves the conductivity of ZnO by depositing metal sites on the surface of the ZnO electrode, while also improving the uniformity of Zn deposition on the electrode surface, thereby inhibiting the growth of Zn dendrites and improving the cycle performance of alkaline aqueous nickel-zinc batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the structure of the zinc oxide electrode obtained in the present invention.

[0026] Figure 2 This is a schematic diagram of the working principle of the zinc oxide electrode obtained in the present invention.

[0027] Figure 3 Surface SEM image of the unmodified ZnO electrode.

[0028] Figure 4 Surface SEM images of the zinc oxide electrodes obtained in Examples 1-2, wherein a is the zinc oxide electrode obtained in Example 1, and b is the zinc oxide electrode obtained in Example 2.

[0029] Figure 5 Graphs showing the battery performance of electrodes before and after the deposition of metal particles, where a represents the unmodified zinc oxide electrode and b represents the zinc oxide electrode obtained in Example 1. DETAILED DESCRIPTION

[0030] The present invention will be described in further detail below with reference to the Examples and accompanying drawings, but the embodiments of the present invention are not limited thereto. Where specific conditions are not specified in the Examples, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used, where the manufacturer is not specified, are commercially available conventional products.

[0031] Unless otherwise specified, all reagents used in the examples can be purchased from the market.

[0032] Example 1

[0033] (1) Preparation of unmodified zinc oxide electrode

[0034] 71% zinc oxide, 19% zinc metal, and 10% binder (polyvinylidene fluoride (PVDF)) were mixed by mass to obtain a zinc oxide slurry; the zinc oxide slurry was coated on the surface of a tin-plated copper foil current collector with a scraper to a thickness of 4 μm, and then placed in a vacuum oven and dried at 60°C for 5 hours to obtain an unmodified zinc oxide electrode.

[0035] (2) Deposition of metal layer

[0036] The unmodified zinc oxide electrode was cut into 12mm diameter original slices using a circular slicer and placed in a chemical vapor deposition device; metal Bi was placed in the deposition device for deposition. The heating voltage during deposition was 170V. The metal was heated and activated and sublimated into gas. The gaseous precursor was adsorbed in the chamber and deposited on the electrode. The deposition rate was controlled to The deposition time was 30 s, and the final deposition thickness was controlled at 3 nm, thereby obtaining a zinc oxide electrode containing a Bi metal layer.

[0037] Example 2

[0038] The difference from Example 1 is that the deposited metal is Ti, and a zinc oxide electrode containing a Ti metal layer is obtained.

[0039] Figure 1 Schematic diagram of the structure of the zinc oxide electrode obtained in the present invention, wherein ① is the deposited metal particles, ② is the zinc oxide layer, and ③ is the electrode current collector.

[0040] Figure 2 Schematic diagram of the working principle of the zinc oxide electrode obtained in the present invention, wherein ① is the zincate ions generated during the battery reaction, and ② is the deposition point of the zincate ions after the migration is suppressed, that is, the metal nucleation site.

[0041] Test Example:

[0042] The material characterization was carried out by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) to test the surface morphology of the unmodified and modified zinc oxide electrodes, respectively. Figure 3 and Figure 4 As shown in Figure 2, the surface of the unmodified zinc oxide electrode is covered with zinc oxide and zinc particles, and there are some uniform flake areas, but there are also some cracks. The surface of the modified zinc oxide electrode is distributed with clusters of small metal particles, such as Figure 4 In a, metal Bi is distributed on the electrode surface, such as Figure 4In b, metal Ti is distributed on the electrode surface, which proves that the metal is successfully deposited on the surface of the ZnO electrode by CVD.

[0043] The zinc oxide electrodes obtained in Example 1 were assembled into button cells. The positive electrode used commercial nickel hydroxide / nickel, and PTFE was used as the binder. A commercial double-layer membrane was used as the separator. A 12M KOH solution was used as the electrolyte. Conventional button cell assembly methods were used to assemble the cells. In addition, batteries of the same specifications without metal deposition modification were prepared for performance testing and comparison.

[0044] Use electrochemical workstation to test battery performance. Performance test is mainly long cycle test, test results are as follows Figure 5 As shown, the test steps are to activate the battery first, and then discharge at a rate of 0.5C until the voltage is less than 1.2V, and then discharge at a rate of 0.3C until the voltage is less than 1.2V. After standing for 10 minutes, charge at a rate of 0.3C until the voltage is greater than 1.9V, followed by constant voltage charging at 1.9V until the current rate is less than 0.1C or this step has been greater than 30 minutes, and then stand for 10 minutes, and discharge at a rate of 0.3C until the voltage is less than 1.2V. After completing the above steps, repeat the cycle of standing, charging at a rate of 0.3C, charging at a constant voltage of 1.9V, standing, and discharging at a rate of 0.3C again, and the cycle ends with 300 turns. Figure 5 The battery capacity changes in the first 30 cycles are given to show its performance. Figure 5 In b, the battery capacity after deposition modification remains stable at around 300mAh after 30 cycles, and the coulombic efficiency remains above 95%. Figure 5 The battery capacity of the unmodified zinc oxide electrode in a showed a significant downward trend in less than 30 cycles, gradually decreasing from about 160mAh to about 20mAh, and the coulombic efficiency was also extremely unstable, decreasing from about 90% to about 50%. That is, the modified zinc oxide electrode battery has more stable cycle stability and capacity retention rate, while the unmodified zinc oxide electrode battery has extremely poor performance, showing low cycle stability and capacity retention rate at a relatively small number of cycles.

[0045] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a zinc oxide electrode, characterized in that: The following steps are involved: A metal layer is deposited on the surface of the unmodified zinc oxide electrode, wherein the thickness of the metal layer is 3-5 nm.

2. The method for preparing the zinc oxide electrode according to claim 1, wherein: The unmodified zinc oxide electrode is prepared by coating a mixed powder of ZnO and Zn on a current collector; the thickness of the zinc oxide layer in the unmodified zinc oxide electrode is 3-5 μm.

3. The method for preparing the zinc oxide electrode according to claim 1, wherein: The metal includes at least one of a transition metal and a rare earth metal.

4. The method for preparing the zinc oxide electrode according to claim 1 or 3, wherein: The metal includes at least one of Sn, Bi, Ni, Fe, Co, Ti, Cr, Mo, Au, In, W, Ir, Pt, and Ta.

5. The method for preparing the zinc oxide electrode according to claim 1, wherein: The deposition method includes one of chemical vapor deposition and atomic layer deposition.

6. The method for preparing the zinc oxide electrode according to claim 5, wherein: The chemical vapor deposition is to place the metal element to be deposited into a reaction chamber, heat and activate it to sublime it into a gaseous precursor, and then deposit it until the metal layer reaches the required thickness and then stop heating.

7. The method for preparing the zinc oxide electrode according to claim 6, wherein: The chemical vapor deposition specifically comprises the following steps: Place the unmodified zinc oxide electrode in a chemical vapor deposition device, add a metal element, heat and activate it into a metal gaseous precursor, and deposit it until the metal layer reaches the desired thickness; The heating voltage is 150-200V; the deposition speed is The deposition time is 25-40s.

8. The method for preparing the zinc oxide electrode according to claim 5, wherein: The atomic layer deposition is to blow a gaseous precursor of a single metal element into a reaction chamber to deposit it into a single atomic layer, and repeat the above steps until all the metal elements to be deposited are deposited layer by layer in the form of single atomic layers.

9. A zinc oxide electrode prepared by the method according to any one of claims 1 to 8.

10. Use of the zinc oxide electrode according to claim 9 in alkaline nickel-zinc batteries.

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