CN116666638B - Water system zinc ion secondary battery - Google Patents

Abstract

The invention provides an artificial solid/liquid interface protective layer, which is a thin film formed on a metal surface by different molecules through intermolecular interactions through layer-by-layer self-assembly technology. The invention proposes to utilize the interaction between polyelectrolytes to alternately adsorb on the metal surface to form a multi-layer self-assembled protective film, and to apply the oppositely charged natural organic polyelectrolytes chitosan and sodium alginate to the surface of the zinc electrode one by one through electrostatic adsorption. Layer adsorption self-assembles into an artificial solid/liquid interface protective layer for stabilizing zinc anodes. Both polyelectrolytes contain abundant hydroxyl functional groups, which can change the solvation structure of zinc ions, reduce the content of active water molecules, reduce water decomposition reactions, and broaden the stability window of the electrolyte; at the same time, the gel-like film has excellent mechanical strength and can uniformly The electric field strength on the surface adapts to the volume changes caused by zinc deposition and peeling, extending battery life.

Description

A kind of aqueous zinc ion secondary battery

Technical field

The invention belongs to the technical field of aqueous zinc ion secondary batteries, and specifically relates to an artificial solid/liquid interface protective layer based on layer-by-layer self-assembly technology, a metal electrode, a battery and its preparation method and use.

Background technique

Due to the increasing demand for energy in modern society, problems such as shortage of metallic lithium resources, high cost, and high toxicity have seriously hindered the further application of lithium batteries. In search of alternatives, researchers discovered the abundant polyvalent metal zinc (Zn). Because metallic zinc has high conductivity, low redox potential (-0.762VvsSHE), high theoretical specific capacity (820mAh/g, 5851mAh/cm ³ ), low ionic radius (0.075nm), low cost and abundant supply, it Can be used as anode material. The aqueous zinc-ion battery that emerged has attracted great attention due to its simple manufacturing technology, high energy density, and good safety. It is expected to replace lithium batteries as large-scale energy storage devices.

However, the current metallic zinc anode of aqueous zinc-ion batteries faces severe challenges of dendrites and water decomposition. The direct contact between the zinc anode and the water electrolyte leads to uncontrollable side reactions, such as hydrogen evolution reaction and zinc corrosion, which continuously consumes metallic zinc and damages the electrolyte. causing the battery to swell and collapse. In addition, the uneven electric field distribution near the electrolyte/electrode interface leads to severe dendrite growth, seriously threatening the cycle life of the battery.

To overcome these technical problems, a large amount of research has been devoted to exploring zinc host structure, electrolyte modification, and electrode/electrolyte interface engineering. Electrodes with highly conductive three-dimensional structural materials such as copper foam exhibit lower nucleation overpotential and smaller zinc core size to reduce dendrite growth. However, an increase in the number of contact points will intensify hydrogen evolution reactions and corrosion reactions. Another study found that a certain amount of additives such as thiourea, ether and organic matter with polar groups such as carbonyl or amino groups can promote the uniform deposition of zinc. However, unstable electrolytes often limit the widespread use of these materials. Although high-concentration electrolyte can uniformly distribute zinc ions in the deposition, its practical application is limited by high cost. Building a dense protective layer on the surface of the zinc anode can improve the unstable electrolyte/anode interface on the surface of the electrode material and solve major side reactions. CaCO ₃ , TiO ₂ , ZrO ₂ , ZnS, ZIF-8 and MCM41, etc. have been discovered and can be used to form a dense protective layer on the surface of the metal anode to inhibit dendrite growth. However, these delicate coatings are easily damaged by volume changes associated with zinc deposition. Polymer materials such as polyamide coatings can also be used as protective coatings on zinc anodes to improve interfacial properties, but preparing a stable polymer layer in aqueous electrolytes can be a challenge.

The biggest challenge facing aqueous zinc-ion batteries in their application is the side reactions that are difficult to eradicate, of which hydrogen evolution reaction and dendrite growth are the primary solutions. The electrochemical stability window of water is fixed at 1.23V under objective theory. The too narrow stability window prevents batteries with aqueous electrolytes from obtaining greater electromotive force. As the potential changes, water molecules decompose and react to generate hydrogen, causing the battery to expand and collapse. At the same time, the local pH increases, causing the irreversible growth of by-products. The ravines and pits on the surface of the zinc foil that are invisible to the naked eye are amplified during battery cycles. The uneven electrode surface leads to uneven electric field distribution between the anode and cathode, which in turn leads to uneven zinc ions under the action of the "tip effect" Deposition produces dendrites.

The information disclosed in this Background section is merely intended to enhance an understanding of the general background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art that is already known to a person of ordinary skill in the art.

Contents of the invention

In order to solve the above technical bottleneck, the present invention proposes a method of constructing an artificial multi-layer protective film on the electrode surface using interlayer self-assembly technology, reshaping the metal zinc surface electrode/electrolyte interface and optimizing the cycle performance of aqueous zinc-ion batteries.

The driving force for the formation of layer-by-layer self-assembled films is mainly the electrostatic force of polyelectrolyte molecules or charged substances on the solid/liquid interface, and short-range secondary forces (such as hydrophilicity/hydrophobicity, charge transfer, and π-π overlap). , hydrogen bonding, van der Waals forces) also play an important role in the formation of stable layer-by-layer self-assembled films. Self-assembled multilayer films formed by electrostatic force have many advantages, mainly including: (1) There are countless naturally occurring or synthetic polyelectrolytes that can be selected; (2) Self-assembled films generally have good mechanical/ Chemical stability; (3) The structure of the self-assembled film is easy to control through the assembly method and process; (4) By selecting and modifying the assembled polyelectrolyte molecules, polymer self-assembled films with different functions can be obtained. In the present invention, polyelectrolytes, charged polymers, dendrimers, small organic molecules, nanoparticles and biological macromolecules with sulfonic acid groups, carboxyl groups, phosphate groups and hydroxyl groups, such as polypyrrole, polythiophene, polyaniline, DNA, etc. All can form multi-layer self-assembled films through electrostatic adsorption, and the thickness of the film can be precisely controlled at the nanoscale single layer.

In order to achieve the above object, the present invention provides an artificial solid/liquid interface protective layer, which is a thin film formed on a metal surface by different molecules through intermolecular interaction through layer-by-layer self-assembly technology; wherein, The different molecules self-assemble into a single-layer film or a multi-layer film, the thickness of the single-layer film is 30nm~40nm, and the thickness of the multi-layer film is 200nm~400nm; wherein, the driving force of the single-layer film or multi-layer film is Electrostatic force and short-range secondary force, the different molecules include one or more of functional agglomerated electrolytes with opposite charges or different polarities, dendrimers, small organic molecules, nanoparticles, and biological macromolecules.

In one or more specific embodiments, the thickness of the above-mentioned single-layer film is 35nm-38nm, and the thickness of the multi-layer film is 280nm-305nm.

In one or more specific embodiments, the above-mentioned electrostatic forces and short-range secondary forces are hydrophilic/hydrophobic, charge transfer, π-π overlap, hydrogen bonding or van der Waals forces.

In one or more specific embodiments, water, inorganic solvents or organic solvents are selected as the dispersing agent for the above different molecules; preferably, the above dispersing agent is water.

In one or more specific embodiments, the concentration of the above-mentioned molecules in the dispersant is 2-10g/L; preferably, the concentration of the above-mentioned molecules in the dispersant is 2.5-7g/L; most preferably, the concentration of the above-mentioned molecules in the dispersant is 2.5-7g/L. The concentration in the dispersant is 2.5~3.5g/L.

In one or more specific embodiments, the above-mentioned polyelectrolyte is polyamide, polyaniline, polypyrrole, polyvinylpyridine, polyacrylamide, polyvinyl alcohol, polylactic acid, glucose, polyglutamic acid, chitosan, Any one or more of sodium alginate; preferably, the above-mentioned polyelectrolyte is any one or more of chitosan, sodium alginate, polyvinylpyridine, polyacrylamide, polyvinyl alcohol, polylactic acid, glucose, or Various; most preferably, the above-mentioned polyelectrolytes are chitosan and sodium alginate.

In one or more specific embodiments, the above-mentioned dendrimers are any one or more of polyether dendrimers, polyester dendrimers, and amphiphilic dendrimers.

In one or more specific embodiments, the above-mentioned organic small molecule is any one or more of sulfur-based compounds, pyridine, furan, biquaternary ammonium salt, phthalocyanine, and porphyrin.

In one or more specific embodiments, the above-mentioned nanoparticles are any one or more of metal nanoparticles, metal oxide nanoparticles, inorganic nanoparticles, and non-spherical nanoparticles.

In one or more specific embodiments, the above-mentioned biological macromolecule is any one or more of enzymes, proteins, DNA, and bacteria.

In one or more specific embodiments, the above-mentioned artificial solid/liquid interface protective layer is constructed from chitosan and sodium alginate on the surface of the metal electrode based on layer-by-layer self-assembly technology.

Based on the inherent technical problems of aqueous zinc-ion batteries, the present invention selects two natural organic degradable polymers, sodium alginate (SA for short) and chitosan (CS for short), and uses layer-by-layer self-assembly technology to obtain flexible The soft polymer film can effectively separate the metal electrode from the aqueous electrolyte, weakening the decomposition of water molecules; and through screening, the two polymer structures contain rich polar functional groups-hydroxyl groups, which can absorb zinc ions when they pass through the film. The hydrogen bonding effect is used to peel off the water molecules in the zinc ion solvation layer, reducing the water molecules reaching the surface of the zinc electrode and thereby fundamentally weakening the hydrogen evolution reaction; and the two polymers of chitosan and sodium alginate selected in the present invention The film formed by self-assembly is flexible and soft like a gel, which can reconstruct the surface of the zinc anode to make the electrode surface smoother. When the battery is working, the electric field intensity can be uniformed to uniformly deposit zinc ions, and it can adapt to the volume caused by the deposition/stripping of zinc. Variety. In addition, both chitosan and sodium alginate are natural degradable polymers, and enzymatic degradation experiments have confirmed that the self-assembled films formed can be degraded and are non-toxic and harmless.

The present invention also provides a metal electrode, including: a metal electrode sheet and the above-mentioned artificial solid/liquid interface protective layer; wherein the above-mentioned artificial solid/liquid interface protective layer is formed by different molecules on the surface of the metal electrode sheet through intermolecular interactions. film.

In one or more specific embodiments, the metal electrode sheet is selected from any one of zinc electrodes, aluminum electrodes, copper electrodes, zinc alloy electrodes, aluminum alloy electrodes, and copper alloy electrodes; preferably, the metal electrode sheet is Zinc electrode or copper electrode; most preferably, the above-mentioned metal electrode sheet is a zinc electrode.

In one or more specific embodiments, the metal electrode is a zinc foil or copper foil modified with a layer-by-layer self-assembled artificial solid/liquid interface protective layer.

In order to solve the above technical problems, the present invention also provides a method for preparing a metal electrode. The above preparation method includes: forming an artificial layer on the surface of the metal electrode through one or more of the spin coating method, the dropping method, the smearing method, and the soaking adsorption method. Solid/liquid interface protective layer.

When the above preparation method is a spin coating method, the preparation method of the above metal electrode includes the following steps:

(1) Cut the metal electrode piece, soak it in deionized water and ethanol for ultrasonic cleaning, and then vacuum dry it for later use;

(2) Configure the above molecules into a solution of 2 to 10 g/L;

(3) The solution obtained in the adsorption step (2) is spin-coated layer by layer on the metal electrode sheet; the spin-coated metal electrode sheet is vacuum-dried and cut into metal electrodes of different sizes and shapes for later use.

When the above molecules are chitosan and sodium alginate, the above metal electrode sheets are zinc foil and copper foil, and the above chitosan and sodium alginate are adsorbed on the zinc foil and copper foil through spin coating, the above preparation method includes the following steps:

(1) Cut out the zinc foil and copper foil; use sandpaper to remove the oxides on the surface of the zinc foil, then soak it in deionized water and ethanol for ultrasonic cleaning, then vacuum dry it for later use, and soak the copper foil in deionized water and ethanol for ultrasonic cleaning. Vacuum drying for later use;

(2) Prepare 2 to 10g/L chitosan solution and sodium alginate solution; preferably, when dissolving chitosan, glacial acetic acid needs to be added dropwise until the chitosan is completely dissolved, and when dissolving sodium alginate, appropriate heating is required until the chitosan is completely dissolved. all dissolved;

(3) Use a glue leveling machine to spin-coat the surface of zinc foil and copper foil layer by layer to adsorb sodium alginate and chitosan. The spin-coated zinc foil and copper foil are vacuum-dried and cut into electrode sheets of different sizes and shapes for use; , when using a glue leveling machine for spin coating and adsorption, set the low speed to 500 to 1000 rpm and spin coating for 20 to 50 seconds, and the high speed to 1200 to 2000 rpm and spin coating to 7 to 15 seconds; preferably, use a glue leveling machine When using the machine for spin coating and adsorption, set the low speed to 700 rpm and spin coating for 30 seconds, and the high speed to 1500 rpm and spin coating for 10 seconds.

The present invention also provides the use of the above-mentioned artificial solid/liquid interface protective layer for metal electrode protection. The artificial solid/liquid interface protective layer is constructed on the surface of the metal electrode to improve the stability of the metal electrode.

In order to solve the above technical problems, the present invention also provides a secondary metal ion battery, including the above metal electrode or the metal electrode made by the above preparation method.

In one or more specific embodiments, the above-mentioned secondary metal ion battery is a zinc-zinc symmetric button battery assembled with the above-mentioned zinc foil as positive and negative electrode sheets, or a zinc-copper button battery assembled with the above-mentioned copper foil as a positive electrode sheet.

In one or more specific embodiments, an artificial solid/liquid interface protective layer is constructed on the surface of a metal electrode based on layer-by-layer self-assembly technology to improve the stability of the metal anode. Use electrostatic adsorption to select a positively charged chitosan solution and a negatively charged sodium alginate solution, and use simple spin coating to alternately adsorb on the zinc foil surface multiple times to obtain a layer-by-layer self-assembled film; zinc foil substrate Sufficient polishing and cleaning are required before coating the self-assembled film; the concentrations of sodium alginate and chitosan solutions used are both 3g/L.

In one or more specific embodiments, the preparation method of the above-mentioned metal electrode is as follows:

(1) Cut a zinc foil of appropriate size (5×5cm in this plan), polish it with sandpaper to remove surface oxides, and then ultrasonically clean the zinc foil in deionized water and ethanol for 2 minutes, vacuum dry for 30 minutes and set aside; Copper foil only needs to be ultrasonically cleaned before use;

(2) Prepare 3g/L chitosan aqueous solution and 3g/L sodium alginate aqueous solution;

(3) Use a glue leveling machine, adjust the low speed to 700 rpm for 30 seconds, and the high speed to 1500 rpm for 10 seconds. Alternately spin-coat the chitosan solution and seaweed on the cleaned zinc foil and copper foil surfaces. sodium acid solution to obtain self-assembled films with different numbers of layers; the zinc foil modified with the obtained self-assembled film was vacuum dried at 50°C for later use.

In one or more specific embodiments, in step (2), when configuring the chitosan solution and the sodium alginate solution above, when dissolving the chitosan, an appropriate amount of glacial acetic acid needs to be added dropwise until the chitosan is completely dissolved; Sodium alginate needs to be heated appropriately until it is completely dissolved.

In one or more specific embodiments, a copper foil modified with a self-assembled film is used as the positive electrode and a zinc foil is used as the negative electrode to assemble a button battery for electrochemical testing and cycle testing, and a zinc foil is used to assemble a symmetrical button battery for long-term testing. Loop test. The button battery assembled above has four parts, namely the positive electrode sheet, the negative electrode sheet, the battery separator, and the electrolyte. The composition sequence of the button battery is: positive electrode shell-positive electrode sheet (symmetrical battery is zinc foil, zinc-copper battery is copper foil)-glass fiber separator-appropriate electrolyte (this invention is 160 microliters of 2M zinc sulfate solution)-negative electrode sheet ( Zinc foil) - gasket - shrapnel - negative electrode case.

The present invention has the following technical effects:

The layer-by-layer self-assembled film of the present invention can reshape the electrode/electrolyte interface, protect the metal electrode from damage during battery cycling, and enhance zinc ion transfer/deposition kinetics, battery electrode reaction reversibility, and battery cycle life; the invention is a metal The protection of electrodes provides a cheap, simple and green strategy, which is expected to promote the large-scale application of aqueous metal-ion batteries, especially aqueous zinc-ion batteries.

Description of the drawings

Figure 1 is a schematic diagram of layer-by-layer self-assembly to form a film; Figure 1a is a schematic diagram of layer-by-layer self-assembly of oppositely charged polymers chitosan and sodium alginate to form a protective layer; Figure 1b is a schematic diagram of untreated zinc anode during battery cycle Schematic diagram of side reactions; Figure 1c is a schematic diagram of the self-assembled protective layer formed layer by layer by chitosan and sodium alginate on the surface of the zinc anode;

Figure 2 shows the Zeta potential of 3g/L chitosan solution and sodium alginate solution;

Figure 3 shows the linear sweep voltammetry test of different zinc anodes in aqueous electrolyte; Figure 3a shows the hydrogen evolution potential; Figure 3b shows the oxygen evolution potential;

Figure 4 shows the potentiodynamic scanning test of zinc anode modified with/without layer-by-layer self-assembled film in aqueous electrolyte;

Figure 5 shows the potentiostatic plan test of zinc anode modified with/without layer-by-layer self-assembled film in aqueous electrolyte;

Figure 6 shows the long cycle test of a zinc-zinc symmetrical battery assembled with zinc electrodes modified with/without layer-by-layer self-assembled films as positive and negative electrodes respectively, in which the current density is 1mA/cm ² and the capacity is 1mAh/cm ² ;

Figure 7 shows the long cycle test of a zinc-zinc symmetrical battery assembled with zinc electrodes modified with self-assembled films of different thicknesses as the positive and negative electrodes. The current density is 1mA/cm ² and the capacity is 1mAh/cm ² ;

Figure 8 shows the test of a zinc-copper half-cell assembled with a zinc electrode modified with self-assembled films of different thicknesses as the negative electrode and a copper electrode modified with self-assembled films of different thicknesses as the positive electrode; Figure 8a shows a long cycle test, in which the current density is 1mA/cm ² , the capacity is 1mAh/cm ² ; Figure 8b is the charge and discharge curve of the zinc-copper battery modified with layer-by-layer self-assembled films; Figure 8c is the charge and discharge curve of the bare zinc-copper battery;

Figure 9 is a scanning electron microscope image of a zinc anode before and after cycling; Figure 9a is a newly prepared layer-by-layer self-assembled protective film zinc anode; Figure 9b is a cross-sectional view of a newly prepared layer-by-layer assembled protective film zinc anode; Figure 9c is a bare zinc electrode Scanning electron microscopy results after cycling; Figure 9d is the scanning electron microscopy image of the layer-by-layer self-assembled protective film zinc anode after cycling; among them, the current density in Figure 9c and Figure 9d is 1mA/cm ² , the capacity is 1mAh/cm ² , and the cycle is 500 hours ;

Figure 10 shows the ion migration number of symmetric batteries assembled with zinc electrodes modified with self-assembled films of different thicknesses;

Figure 11 shows the reaction activation energy of symmetrical cells assembled with zinc electrodes modified with self-assembled films of different thicknesses.

Detailed ways

Specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

Unless expressly stated otherwise, throughout the specification and claims, the term "comprises" or its variations such as "comprises" or "comprising" will be understood to include the stated elements or components, and to Other elements or other components are not excluded.

Example 1

Preparation of chitosan solution and sodium alginate solution: Prepare 3g/L chitosan aqueous solution and sodium alginate aqueous solution under normal temperature and pressure; weigh 0.6g sodium alginate and chitosan respectively and dissolve them in 200mL deionized water; When chitosan is dissolved, glacial acetic acid needs to be added drop by drop until the chitosan is completely dissolved; when sodium alginate is dissolved, it needs to be heated appropriately and stirred until it is completely dissolved and dropped to room temperature.

Figure 2 shows the Zeta potential of 3g/L chitosan solution and sodium alginate solution measured using a particle size analyzer, which theoretically proves that chitosan and sodium alginate polyelectrolytes with opposite charges can self-assemble through electrostatic interaction. into a multi-layer film.

Example 2

The preparation of layer-by-layer self-assembled protective layer zinc electrodes and copper electrodes is prepared according to the following steps:

Preparation of spin coating solution: Under normal temperature and pressure, prepare 3g/L chitosan aqueous solution and sodium alginate aqueous solution; weigh 0.6g sodium alginate and chitosan respectively and dissolve them in 200mL deionized water; chitosan needs to be dissolved Add glacial acetic acid drop by drop until chitosan is completely dissolved; when sodium alginate is dissolved, it is necessary to heat appropriately and stir until all is dissolved and brought to room temperature;

Zinc electrode and copper electrode preparation: Cut zinc foil and copper foil of appropriate size (5×5cm in this plan), polish the surface of the zinc foil with sandpaper to remove surface oxides, and then place the zinc foil in deionized water and ethanol. Ultrasonically clean for 2 minutes, vacuum dry for 30 minutes and then set aside; before use, the copper foil only needs to be ultrasonically cleaned and vacuum dried for 30 minutes before use;

Spin coating: Use a glue leveling machine, adjust the low speed to 700 rpm for 30 seconds, and the high speed to 1500 rpm for 10 seconds; alternately spin-coat the chitosan solution and seaweed on the cleaned zinc foil and copper foil surfaces. sodium acid solution to obtain self-assembled films with different layers. Among them, one layer of self-assembled film is spin-coated once with chitosan solution and once with sodium alginate solution, recorded as: (chitosan/sodium alginate) ₁ , this The plan selected 2, 4, and 6 layers of self-assembled films for comparative experiments. The experiment showed that the 4-layer self-assembled film was the optimal thickness, recorded as: (chitosan/sodium alginate) ₄ ; after vacuum drying for 30 minutes, the zinc foil and Cut the copper foil into circular electrode sheets with a radius of 6 mm for later use;

Battery assembly: Use bare copper foil and (chitosan/sodium alginate) ₄ -copper foil as the positive electrode, and use bare zinc foil and (chitosan/sodium alginate) ₄ -zinc foil as the negative electrode to assemble a zinc-copper half For the battery, perform a linear sweep voltammetry test and apply different voltages to test to obtain the corresponding potential when water on the electrode surface decomposes to generate hydrogen and oxygen, which are the hydrogen evolution potential and oxygen evolution potential.

Figure 3 shows the linear sweep voltammetry test results. Due to the existence of layer-by-layer assembled protective films that separate the electrode from the electrolyte, fewer water molecules reach the electrode surface, making the aqueous electrolyte more stable and making hydrogen and oxygen evolution more difficult.

Example 3

Zinc electrode preparation: Cut a zinc foil of appropriate size (5×5cm in this plan), polish the surface of the zinc foil with sandpaper to remove surface oxides, and then ultrasonically clean the zinc foil in deionized water and ethanol for 2 minutes, and vacuum Dry for 30 minutes and set aside;

Spin coating: Use a glue leveling machine, adjust the low speed to 800 rpm for 25 seconds, and the high speed to 1300 rpm for 15 seconds. Alternately spin-coat chitosan and sodium alginate solutions on the cleaned zinc foil surface to obtain a 4-layer self-assembled thin film zinc electrode, (chitosan/sodium alginate) ₄ -zinc foil; cut it after vacuum drying for 30 minutes Make 1*2cm electrode pieces for later use;

Battery assembly: A three-electrode system is used. Zinc foil modified with/without self-assembly film is used as the working electrode, platinum sheet electrode is used as the counter electrode, silver/silver chloride electrode is used as the reference electrode, and 2mol/L zinc sulfate solution is used as the electrolyte for operation. potential scan.

The test result Tafel curve is shown in Figure 4. Compared with the bare zinc electrode, the corrosion potential of the (chitosan/sodium alginate) ₄ -zinc electrode becomes more positive and the corrosion current density becomes smaller, proving that the zinc anode is more stable under the protection of the multi-layer self-assembled film. , the corrosion rate is smaller.

Example 4

Zinc electrode preparation: Cut a zinc foil of appropriate size (5×5cm in this plan), polish the surface of the zinc foil with sandpaper to remove surface oxides, and then ultrasonically clean the zinc foil in deionized water and ethanol for 2 minutes, and vacuum Set aside after drying for 30 minutes;

Spin coating: Use a glue leveling machine, adjust the low speed to 600 rpm for 40 seconds, and the high speed to 1800 rpm for 7 seconds; alternately spin-coat the chitosan solution and sodium alginate solution on the cleaned zinc foil surface. , to obtain 4-layer self-assembled thin film zinc electrode and copper electrode, (chitosan/sodium alginate) ₄ -zinc foil. After vacuum drying for 30 minutes, cut it into circular electrode sheets with a radius of 6 mm for later use;

Battery assembly: Zinc foil modified with/without self-assembly film is used as the positive and negative electrodes to assemble a button battery and conduct a potentiostatic polarization test.

Figure 5 shows that as the polarization time increases, the polarization current density of the bare zinc battery continues to increase, indicating that dendrites continue to grow on the surface of the zinc electrode; (chitosan/sodium alginate) ₄ - Polarization current of zinc battery The density stabilized and stopped changing after 200 s, indicating that zinc ions were uniformly reduced and deposited without obvious dendrite growth.

Example 5

Zinc electrode preparation: Cut a zinc foil of appropriate size (5×5cm in this plan), polish the surface of the zinc foil with sandpaper to remove surface oxides, and then ultrasonically clean the zinc foil in deionized water and ethanol for 2 minutes, and vacuum Set aside after drying for 30 minutes;

Spin coating: Use a glue leveling machine, adjust the low speed to 1000 rpm for 15 seconds, and the high speed to 1800 rpm for 7 seconds; alternately spin-coat the chitosan solution and sodium alginate solution on the cleaned zinc foil surface. , obtain a 4-layer self-assembled thin film zinc electrode, (chitosan/sodium alginate) ₄ - After vacuum drying the zinc foil for 30 minutes, cut it into a circular electrode sheet with a radius of 6mm for later use;

Battery assembly: Use bare zinc foil and (chitosan/sodium alginate) ₄ -zinc foil as the positive and negative electrodes of the battery to assemble a zinc-zinc symmetrical battery, and conduct long-term charge and discharge tests, in which the current density is 1mA/cm ² , the capacity is 1mAh/cm ² .

Figure 6 shows the long-term cycle test results of charge and discharge of zinc-zinc symmetrical batteries. The bare zinc electrode symmetrical battery collapsed due to short circuit due to side reactions such as dendrites after 400 hours of cycling. Under the protection of layers of self-assembled films, the zinc-zinc symmetrical battery can cycle for more than 5,000 hours, confirming the excellent protective effect of the self-assembled film of sodium alginate and chitosan on the zinc electrode.

Example 6

Zinc electrode preparation: Cut a zinc foil of appropriate size (5×5cm in this plan), polish the surface of the zinc foil with sandpaper to remove surface oxides, and then ultrasonically clean the zinc foil in deionized water and ethanol for 2 minutes, and vacuum Set aside after drying for 30 minutes;

Spin coating: Use a glue leveling machine, adjust the low speed to 600 rpm for 35 seconds, and the high speed to 1400 rpm for 13 seconds; alternately spin-coat the chitosan solution and sodium alginate solution on the cleaned zinc foil surface. , obtain 2, 4, and 6 layers of self-assembled thin film zinc electrodes, (chitosan/sodium alginate) _{2, 4, 6} -zinc foil, vacuum dry for 30 minutes, and then cut it into circular electrode sheets with a radius of 6 mm for later use. ;

Battery assembly: Use (chitosan/sodium alginate) _2,4,6 -zinc foil as the positive and negative electrodes of the battery to assemble a zinc-zinc symmetrical battery, and conduct long-term charge and discharge tests, in which the current density is 1mA/cm ² , the capacity is 1mAh/cm ² .

Figure 7 shows the long-term cycle test results of charge and discharge of zinc-zinc symmetrical batteries. (Chitosan/Sodium Alginate) ₂ - Symmetrical battery can cycle for more than 1200 hours, (Chitosan/Sodium Alginate) ₆ - Symmetrical battery can cycle for more than 2000 hours, (Chitosan/Sodium Alginate) ₄ - Symmetrical The battery can be cycled for more than 5,000 hours, confirming that the self-assembled film of chitosan/sodium alginate has excellent protective effects on zinc electrodes and improves battery performance. Among them, the 4-layer self-assembled film has the best effect.

Example 7

Preparation of zinc electrodes and copper electrodes: Preparation of zinc electrodes and copper electrodes: Cut zinc foil and copper foil of appropriate size (5×5cm in this plan), polish the surface of the zinc foil with sandpaper to remove surface oxides, and then place the zinc foil Ultrasonically clean in deionized water and ethanol for 2 minutes, vacuum dry for 30 minutes and set aside. The copper foil only needs to be ultrasonically cleaned and vacuum dried for 30 minutes before use;

Spin coating: Use a glue leveling machine, adjust the low speed to 700 rpm for 30 seconds, and the high speed to 1500 rpm for 10 seconds; alternately spin-coat the chitosan solution and seaweed on the cleaned zinc foil and copper foil surfaces. sodium acid solution to obtain a 2, 4, 6-layer self-assembled thin film zinc electrode, (chitosan/sodium alginate) _{2, 4, 6} - zinc foil and copper foil, vacuum dry for 30 minutes and then cut into a radius of 6mm The round electrode pads are spare;

Battery assembly: bare copper foil and (chitosan/sodium alginate _{) 2,4,6} copper foil were used as the positive electrode of the battery, respectively, bare zinc foil and (chitosan/sodium alginate) _{2,4, 6} - Zinc foil is used as the negative electrode of the battery, assembled into a zinc-copper half-battery, and subjected to long-term charge and discharge tests, in which the current density is 1mA/cm ² and the capacity is 1mAh/cm ² .

Figure 8a shows the long cycle test results of zinc-copper half-cell. The zinc-copper half-battery without self-assembled film in the control group failed after cycling for 300 hours. The (chitosan/sodium alginate) ₂ -zinc-copper half-battery and (chitosan/sodium alginate) ₆ -zinc-copper half-battery failed after cycling. After 700 hours, the Coulomb efficiency fluctuated significantly and the battery cycle was unstable. In comparison, the (chitosan/sodium alginate) ₄ -zinc-copper half-cell can cycle stably for more than 2300 hours, and the Coulombic efficiency is stable above 99.6%, indicating that the battery cycle is stable and the electrode reaction is highly reversible. Layer-by-layer self-assembled films can improve battery side reactions and enhance battery cycle performance.

The charge-discharge curves of the zinc-copper battery can be seen in Figure 8b and Figure 8c, in which the nucleation overpotential and polarization potential of the (chitosan/sodium alginate) ₄ -zinc-copper half-cell are lower than those of the bare zinc-copper half-cell, It is proved that the nucleation energy of zinc ions is lower, the nucleation is easier, and the deposition is more uniform.

Example 8

Zinc electrode preparation: Cut a zinc foil of appropriate size (5×5cm in this plan), polish the surface of the zinc foil with sandpaper to remove surface oxides, and then ultrasonically clean the zinc foil in deionized water and ethanol for 2 minutes, and vacuum Set aside after drying for 30 minutes;

Spin coating: Use a glue leveling machine, adjust the low speed to 700 rpm for 30 seconds, and the high speed to 1500 rpm for 10 seconds; alternately spin-coat the chitosan solution and sodium alginate solution on the cleaned zinc foil surface. , obtaining a 4-layer self-assembled thin film zinc electrode, (chitosan/sodium alginate) ₄ -zinc foil;

Battery assembly: Use bare zinc foil and (chitosan/sodium alginate) ₄ -zinc foil as the positive and negative electrodes of the battery to assemble a zinc-zinc symmetrical battery, and conduct long-term charge and discharge tests, in which the current density is 1mA/cm ² , capacity is 1mAh/cm ² ;

Preparation of samples for scanning electron microscopy testing: The newly prepared layer-by-layer self-assembled protective layer (chitosan/sodium alginate) ₄ -zinc electrode was quenched with liquid nitrogen to obtain a cross-sectional scanning electron microscopy test sample. Bare zinc foil and (chitosan/sodium alginate) ₄ -zinc foil were used as the positive and negative electrodes of the battery to assemble a zinc-zinc symmetrical battery. After cycling for 100 hours, the zinc anode was cleaned and vacuum dried to obtain a scanning electron microscope test sample.

Figure 9 shows the scanning electron microscope test results. In Figure 9a, it is observed that the newly prepared layer-by-layer self-assembled film is uniform and transparent. Figure 9b is a cross-sectional electron microscope test picture. It can be observed that the layer-by-layer self-assembled film is evenly attached to the surface of the zinc electrode and can fill up the fine ravines on the surface of the zinc foil. , the thickness is about 300nm. After 100 hours of cycling, there are a large number of sharp and massive dendrites on the surface of the bare zinc anode. As the cycle time increases, the dendrites will gradually become larger and eventually penetrate the separator and destroy the battery. Figure 9d can prove that the (chitosan/sodium alginate) ₄ film can effectively protect the zinc anode, uniform electric field, so that zinc ions are evenly distributed and reduced, and no large diameters are found, proving its effect on improving battery performance. obvious.

Example 9

Zinc electrode preparation: Cut a zinc foil of appropriate size (5×5cm in this invention), polish the surface of the zinc foil with sandpaper to remove surface oxides, and then place the zinc foil in deionized water and ethanol for ultrasonic cleaning for 2 minutes, and vacuum Set aside after drying for 30 minutes.

Spin coating: Use a glue leveling machine, adjust the low speed to 700 rpm for 30 seconds, and the high speed to 1500 rpm for 10 seconds; alternately spin-coat the chitosan solution and sodium alginate solution on the cleaned zinc foil surface. , obtain a 2, 4, 6-layer self-assembled thin film zinc electrode, (chitosan/sodium alginate) _{2, 4, 6} -zinc foil, vacuum dry it for 30 minutes and then cut it into a circular electrode sheet with a radius of 6 mm for later use. ;

Battery assembly: Use bare zinc foil and (chitosan/sodium alginate) _2,4,6 -zinc foil as the positive and negative electrodes of the battery to assemble a zinc-zinc symmetrical battery; conduct a chronocurrent test on the symmetrical battery, and combine the before and after tests The impedance value is calculated according to the published ion migration number of different batteries.

Figure 10 shows that the measured ion migration numbers of zinc electrodes modified with self-assembled films of different layers are all higher than those of bare zinc electrodes (0.3223), among which the (chitosan/sodium alginate) ₄ -zinc electrode has the largest ion migration number (0.7572 ), proving that zinc ion transport kinetics is the fastest and is conducive to uniform deposition of zinc ions.

Example 10

Zinc electrode preparation: Cut a zinc foil of appropriate size (5×5cm in this plan), polish the surface of the zinc foil with sandpaper to remove surface oxides, and then ultrasonically clean the zinc foil in deionized water and ethanol for 2 minutes, and vacuum Set aside after drying for 30 minutes;

Spin coating: Use a glue leveling machine, adjust the low speed to 700 rpm for 30 seconds, and the high speed to 1500 rpm for 10 seconds; alternately spin-coat the chitosan solution and sodium alginate solution on the cleaned zinc foil surface. , obtain 2, 4, and 6 layers of self-assembled thin film zinc electrodes, (chitosan/sodium alginate) _{2, 4, 6} -zinc foil, vacuum dry for 30 minutes, and cut it into circular electrode sheets with a radius of 6 mm for later use. ;

Battery assembly: Use bare zinc foil and (chitosan/sodium alginate) _2,4,6 -zinc foil as the positive and negative electrodes of the battery to assemble a zinc-zinc symmetrical battery.

The reaction activation energies of batteries modified with self-assembled films of different thicknesses are calculated from the impedance values of the batteries at different temperatures and are shown in Figure 11. Among them, the measured reaction activation energies of zinc electrodes modified with self-assembled films of different layers are higher than those of bare zinc batteries (69.62kJ/mol), among which (chitosan/sodium alginate) ₄ -zinc electrode has the largest ion migration number ( 40.76kJ/mol), which proves that the electrode reaction requires less energy, which is conducive to the reduction and uniform deposition of zinc ions.

Table 1 Electrochemical and battery performance test result data of the layer-by-layer self-assembled protective layers of Examples 2, 3, 5, 6, 7, 9, and 10

Table 1 summarizes the electrochemical and battery performance test results of Examples 2, 3, 5, 6, 7, 9, and 10 involving the layer-by-layer self-assembled protective layer. It can be proved that the self-assembled protective layer of the present invention can effectively stabilize the metal. Zinc anode slows down the anode corrosion rate and induces zinc ions to be evenly distributed and deposited, reducing dendrite growth. The transmission kinetics of zinc ions is enhanced and the activation energy of the electrode reaction is reduced, allowing zinc ions to be transported to the electrode surface faster and deposited more easily.

Figure 1 is a schematic diagram of the formation of layer-by-layer self-assembled films. Among them, Figure 1a is a schematic diagram of the layer-by-layer self-assembly of chitosan and sodium alginate on the zinc surface to form a protective film. The structure of chitosan is rich in hydroxyl and amino groups, which can be firmly adsorbed on the surface of zinc foil to form a positively charged film. Then negatively charged sodium alginate is spin-coated on the surface. Sodium alginate is rich in carboxyl groups and can be used at the same time. The amino groups in chitosan are combined and assembled into a film through electrostatic adsorption; then the alternating adsorption of chitosan/sodium alginate is repeated, and finally a layer-by-layer self-assembled film (chitosan/sodium alginate) ₄ film is formed.

Figure 1b is a schematic diagram of the protective function of ₄ pairs of zinc electrodes using layer-by-layer self-assembled films (chitosan/sodium alginate). Both chitosan and sodium alginate are rich in polar functional groups - hydroxyl groups. When hydrated zinc ions pass through the self-assembled film under the action of an electric field, the hydroxyl groups peel off the water molecules in the solvation structure of the zinc ions through hydrogen bonding, reducing the content of water molecules around the zinc ions, thus reducing the occurrence of hydrogen evolution reactions. The change in the volumetric structure of zinc ions reduces the desolvation energy of zinc ions, making it easier to reduce and deposit uniformly.

Figure 1c is a schematic diagram of side reactions occurring in battery cycle tests on bare zinc electrodes without any treatment. Due to the decomposition of water molecules, hydrogen will be generated on the surface of the zinc electrode, causing the battery to swell and collapse. At the same time, the hydrogen evolution reaction will increase the local pH value and generate insoluble by-products, which will gradually lead to zinc passivation and deactivation; in addition, uneven electric field distribution will cause zinc The deposited layer is uneven and eventually forms sharp dendrites.

The above embodiments are only for illustrating the technical concepts and characteristics of the present invention. Their purpose is to enable those familiar with this technology to understand the content of the present invention and implement it. They are not intended to limit the scope of protection of the present invention. Substantial equivalent changes or modifications shall be included in the protection scope of the present invention.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and illustration. These descriptions are not intended to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and its practical application, thereby enabling others skilled in the art to make and utilize various exemplary embodiments of the invention and various different applications. Choice and change. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims (5)

1. An aqueous zinc ion secondary battery, characterized in that the aqueous zinc ion secondary battery includes a metal electrode; the metal electrode includes: a metal electrode sheet and an artificial solid/liquid interface protective layer; the artificial solid/liquid interface The liquid interface protective layer is a thin film constructed of chitosan and sodium alginate on the surface of the metal electrode sheet based on layer-by-layer self-assembly technology; the chitosan and sodium alginate have opposite charges, and the chitosan and sodium alginate have opposite charges. Sodium alginate self-assembles into a multi-layer film, the thickness of the multi-layer film is 300nm; the driving force of the multi-layer film is electrostatic force and short-range secondary force, and the metal electrode sheet is a zinc electrode; the The short-range secondary force is hydrogen bonding; The preparation method of the metal electrode includes the following steps: (1) Cut the zinc foil; use sandpaper to remove the oxides on the surface of the zinc foil, then soak it in deionized water and ethanol for ultrasonic cleaning, then vacuum dry it for later use; (2) Prepare 3g/L chitosan solution and sodium alginate solution; (3) Use a glue leveler to alternately spin-coat and adsorb the sodium alginate solution and chitosan solution on the surface of the zinc foil. After the spin-coating, the zinc foil is vacuum-dried and cut into electrode sheets of different sizes and shapes for later use, to obtain a 4-layer self-assembled film. , the 4-layer self-assembled film is a film obtained by spin coating 4 times of sodium alginate solution and 4 times of chitosan solution; wherein, when using a glue leveling machine for spin coating adsorption, set a low speed of 500-1000 rpm , spin coating for 20-50 seconds, high speed 1200-2000 rpm, spin coating for 7-15 seconds. 2. The aqueous zinc ion secondary battery according to claim 1, characterized in that an inorganic solvent or an organic solvent is selected as the dispersant of the chitosan and sodium alginate. 3. The aqueous zinc ion secondary battery according to claim 2, wherein the inorganic solvent is water. 4. The aqueous zinc ion secondary battery according to claim 1, characterized in that, in step (2), when dissolving chitosan, it is necessary to add glacial acetic acid dropwise until the chitosan is completely dissolved, and when dissolving sodium alginate, it is necessary to Heat appropriately until all is dissolved. 5. The aqueous zinc ion secondary battery according to claim 1, characterized in that, in step (3), when using a glue leveling machine for spin coating and adsorption, set a low speed of 700 rpm, spin coating for 30 seconds, and high speed. The rotation speed is 1500 rpm and spin coating is performed for 10 seconds.