Preparation method and application of a composite coating for protection of negative electrode of aqueous zinc ion battery

Abstract

The application relates to the technical field of aqueous zinc ion batteries, and discloses a preparation method and application of a composite coating for protecting the negative electrode of an aqueous zinc ion battery, which comprises the following steps: step one: adding a Tris-HCl buffer into a dopamine hydrochloride aqueous solution, and obtaining a polydopamine suspension through polymerization; step two: preparing powder-like polydopamine by sequentially treating the polydopamine suspension; step three: mixing and grinding powder-like silicate minerals and the powder-like polydopamine to prepare a composite material; step four: mixing the composite material, a binder and a solvent to prepare a composite slurry; and step five: coating the composite slurry on the surface of a zinc sheet and drying to obtain a composite coating. The polydopamine nanospheres are inlaid around natural silicate minerals, the silicate mineral / polydopamine composite material has high conductivity, and the obtained composite coating has the advantages of high safety, excellent electrochemical performance and mechanical performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aqueous zinc-ion batteries, and more particularly relates to a preparation method and application of a composite coating for anode protection of an aqueous zinc-ion battery. BACKGROUND

[0002] Aqueous zinc-ion batteries have become one of the most promising sustainable energy storage technologies due to their low production cost, high safety, high theoretical specific capacity and energy density (820 mA·g -1 and 5854 mAh·cm -3 ), and low redox potential (compared to the standard hydrogen electrode (SHE) -0.763 V).

[0003] As one of the core components of aqueous zinc-ion batteries, zinc anodes still have many problems during the charging and discharging process of the battery: (1) due to uneven electric field distribution and "tip effect" in the battery, zinc ion deposition is not uniform, and zinc dendrites are easily formed; the detached zinc dendrites will form "dead zinc", thereby losing active electrode material, on the other hand, severe zinc dendrite growth will pierce the separator and cause battery short circuit failure; (2) there is a reduction competition between hydrogen ions and zinc ions in the electrochemical process, and the generated hydrogen gas will cause the battery to bulge and swell, which poses a safety hazard; (3) the high activity of zinc metal causes self-corrosion in the electrolyte, which increases the local hydroxyl ion concentration at the anode interface, and then reacts with zinc ions to generate a difficult-to-dissolve byproduct Zn4(SO4)OH6•nH2O passivation layer on the electrode surface, increasing the polarization and resistance of the electrode and exacerbating the further growth of zinc dendrites. Constructing an artificial protective layer on the surface of the zinc anode to improve the cycle stability and coulombic efficiency of the battery is one of the main means of current aqueous zinc-ion battery anode modification research. SUMMARY

[0004] The main purpose of the present application is to provide a preparation method and application of a composite coating for anode protection of an aqueous zinc-ion battery, which has the advantages of simple process, low cost, high safety, etc., and can prepare a negative electrode protection composite coating with excellent electrochemical performance, excellent mechanical performance and high stability, which is of great significance to promote the commercial application of aqueous zinc-ion batteries. The method mixes and grinds polydopamine and silicate minerals to form inorganic silicate materials inlaid with organic layers, which can improve the mechanical properties and stability of traditional silicate materials.

[0005] In order to achieve the above purpose, the present application is realized by the following technical scheme:

[0006] The present application provides a preparation method of a composite coating for anode protection of an aqueous zinc-ion battery, which comprises the following steps:

[0007] Step one: add Tris-HCl buffer to the aqueous solution of dopamine hydrochloride, adjust the pH value to 10-14, and obtain a polydopamine suspension through polymerization;

[0008] Step two: obtain powder-like polydopamine by sequentially centrifuging, washing, and drying the polydopamine suspension;

[0009] Step three: obtain a silicate mineral / polydopamine composite material by mixing and grinding the powder-like silicate mineral and the powder-like polydopamine;

[0010] Step four: obtain a composite slurry by mixing the silicate mineral / polydopamine composite material, a binder, and a solvent;

[0011] Step five: coat the composite slurry on the surface of a zinc sheet, and obtain a composite coating through drying.

[0012] Preferably, in step one, the concentration of the aqueous solution of dopamine hydrochloride is 0.1-10 g / L; and the amount of the Tris-HCl buffer added is 0.1-10 mL / g.

[0013] Preferably, in step one, the aqueous solution of dopamine hydrochloride is obtained by adding dopamine hydrochloride into deionized water and stirring to fully dissolve the dopamine hydrochloride, with a stirring time of 1-60 min.

[0014] Preferably, in step one, the buffer is one of ammonia, a sodium hydroxide solution, or a Tris-HCl buffer solution.

[0015] Preferably, in step one, the drying temperature is 20-200 ℃, and the drying time is 1-48 h; and the drying method is air drying, sun drying, air drying, oven drying, or vacuum drying.

[0016] Preferably, in step one, the polymerization time is 12-48 h.

[0017] Due to the difference in the buffer, the size of the polydopamine nanospheres formed through polymerization will be different. The buffer controls the pH value of the solution and the reaction time to regulate the self-polymerization degree of the polydopamine nanospheres, and thus affects the size. The more the buffer is added, the smaller the particle size of the dopamine nanospheres will be. Large-size polydopamine nanospheres will lead to insufficient contact of the active substance with the electrolyte. When the environment is aerobic, dopamine will not be completely polymerized in anoxic environment, and the nanosphere morphology will not be formed. The synergistic effect between polydopamine and silicate minerals will also be poor.

[0018] Preferably, in step three, the micro-morphology of the powdered polydopamine is nanospheres, the particle size of the nanospheres is distributed in 50-700 nm, and the average particle size is 100-500 nm; the powder particle size of the powdered silicate mineral is distributed in 500-3000 nm, the micro-morphology of the powdered silicate mineral is lamellar or nanotube, and the tube diameter of the silicate mineral with nanotube micro-morphology is distributed in 100-1000 nm.

[0019] Preferably, in step three, the silicate mineral is one or a combination of kaolin, attapulgite, vermiculite, allophane, zinnwaldite, montmorillonite, halloysite, talc, pyrophyllite, potassium feldspar, sodium feldspar, and white clay.

[0020] Preferably, in step three, the mass ratio of the powdered silicate mineral to the powdered polydopamine is 1:(0.1-10).

[0021] This is because if the amount of dopamine added is too small, it will not play a mechanical stress role; if the amount of dopamine added is too large, it will block the layered structure of the above-mentioned natural silicate mineral, reduce the zinc ion transmission efficiency, and exacerbate the formation of zinc dendrites.

[0022] Preferably, in step three, the mixing and grinding time is 5-30 min.

[0023] The in-situ polymerized dopamine neutralizes the surface / interlayer potential of the silicate mineral, and the in-situ polymerized dopamine binds to the hydroxyl groups on the surface / interlayer of the silicate mineral (or the negative charge caused by defects in the allophane layer) to achieve the in-situ polymerization effect. After in-situ polymerization, the surface functional groups or negative charges are neutralized and will no longer promote the uniform deposition of zinc ions, but will suppress the natural conduction of the silicate mineral to zinc ions, increasing the risk of zinc dendrites piercing the separator, and the battery will be more prone to short circuit. Compared with the traditional in-situ polymerization, the present application combines polyaniline with silicate minerals by grinding, which can effectively promote the hydrogen bond linkage between the silicate mineral and the polydopamine, further improve the mechanical properties of the coating, enhance the reversibility of the coating, and thus prolong the cycle life of the battery.

[0024] In addition, the polydopamine forms a dense (like a shell) organic layer, and if in-situ polymerization (coating layer structure) is formed on the surface of the silicate mineral, it will completely block the layered structure of the silicate mineral, so that the zinc ions are isolated from the active material. Therefore, the polydopamine is combined with the silicate material by grinding, so that the functions of both can be fully played.

[0025] Preferably, in step four, the mass ratio of the silicate mineral / polydopamine composite material to the binder is 1:(0.1-0.5); and the mass ratio of the silicate mineral / polydopamine composite material to the total mass of the solvent and the binder is 1:(2-10).

[0026] Preferably, in step five, the thickness of the composite slurry coated on the surface of the zinc sheet is 1-300 microns.

[0027] Preferably, in step five, the drying temperature is 20-200 degrees Celsius, and the drying time is 1-48 hours; and the drying method is air drying, sun drying, air drying, oven drying or vacuum drying.

[0028] The application also provides a water-based zinc ion battery comprising a negative electrode sheet comprising the composite coating described above.

[0029] Preferably, the composite coating is composed of polydopamine nanospheres and silicate minerals, and the overall structure is a silicate structure inlaid with a polydopamine organic layer.

[0030] Compared with the prior art, the application has the following advantages:

[0031] (1) The application retains the structural characteristics of natural silicate minerals while introducing polydopamine nanospheres with ion confinement effect. Compared with single silicate materials, these polydopamine nanospheres inlaid around the natural silicate minerals can effectively alleviate the mechanical stress caused by volume change during the zinc ion extraction process of the zinc negative electrode, thereby improving the structural stability thereof; and the natural silicate minerals act as a skeleton to provide attachment sites for the polydopamine; on the other hand, the rigid skeleton of the silicate minerals enhances the overall mechanical properties, and plays a structural support role during the extraction of zinc ions.

[0032] (2) When the application is used for an artificial interfacial layer, the introduction of polydopamine nanospheres with good electrical conductivity enhances the overall electrical conductivity of the material, which helps to balance the local electric field on the surface of the zinc negative electrode, thereby inhibiting the formation of zinc dendrites; the amino and hydroxyl groups in the polydopamine molecular chain can not only promote the zinc ion transmission rate, but also form hydrogen bonds with the hydroxyl groups in the silicate minerals, which can greatly improve the toughness of the coating and maintain the integrity of the coating during long-term cycling of the battery.

[0033] (3) When the application is used as a water-based zinc ion battery, the strong attraction of the polydopamine nanospheres to water molecules promotes the full contact of the electrolyte with the zinc negative electrode, while also capturing water molecules in the zinc ion solvent sheath, promoting the desolvation of zinc ions, further enhancing the charge and discharge efficiency of the battery; the silicate mineral as the main active material can adjust the ion flux and deposition behavior of zinc ions through the ion confinement effect, so that the zinc ions are deposited on the dense accumulation surface of the zinc negative electrode, thereby improving the reversibility of Zn 2+ / Zn interconversion, further improving the cycle stability and rate performance of the water-based zinc ion battery, and solving the problem of insufficient zinc ion transmission rate in a single polydopamine coating material, which helps to increase the charge and discharge efficiency of the battery. At the same time, the negative nature of the interlayer of the natural silicate mineral helps to promote the uniform deposition of zinc ions, alleviate the problems of zinc dendrite growth and dead zinc peeling caused by non-uniform deposition of zinc ions, greatly improve the retention rate of coulombic efficiency and prolong the cycle life of the battery.

[0034] (4) The polydopamine / silicate mineral composite coating prepared by the application has the advantages of simple process, low cost, high safety, excellent electrochemical performance and mechanical performance when used as a negative electrode of a water-based zinc ion battery, and has great significance for promoting the commercial application of water-based zinc ion batteries. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 X-ray diffraction pattern of the silicate mineral / polydopamine material prepared in Example 2;

[0036] Figure 2 Scanning electron microscope image of the silicate mineral / polydopamine material prepared in Example 2;

[0037] Figure 3 Scanning electron microscope image of the incompletely polymerized polydopamine / silicate mineral material prepared in Comparative Example 2;

[0038] Figure 4 Scanning electron microscope image of the in-situ polymerized silicate mineral / polydopamine material prepared in Comparative Example 3;

[0039] Figure 5 Scanning electron microscope image of the silicate mineral / polydopamine material with excess polydopamine prepared in Comparative Example 4;

[0040] Figure 6 Optical photograph of the composite coating prepared in Comparative Example 5;

[0041] Figure 7 Scanning electron microscope image of the silicate mineral / polydopamine material with oversized polydopamine prepared in Comparative Example 6;

[0042] Figure 8Symmetric cell assembled with the silicate mineral / polydopamine material modified zinc metal anode prepared in Example 2, after 2000 h of cycling at a current density of 1 mA·cm -2 and a deposition capacity of 1 mA·cm -2 of the negative electrode after 2000 h of cycling at a current density of 1 mA·cm

[0043] Figure 9 Symmetric cell assembled with pure zinc foil in Comparative Example 1, after 200 h of cycling at a current density of 1 mA·cm -2 and a deposition capacity of 1 mAh cm-2of the negative electrode after 200 h of cycling at a current density of 1 mA·cm

[0044] Figure 10 Symmetric cell assembled with the silicate mineral / polydopamine material modified zinc metal anode prepared in situ in Comparative Example 3, after 200 h of cycling at a current density of 1 mA·cm -2 and a deposition capacity of 1 mAh·cm -2 of the negative electrode after 200 h of cycling at a current density of 1 mA·cm

[0045] Figure 11 Voltage-time graph obtained for the symmetric cell assembled with the zinc ion battery anode material in Example 1, at a current density of 1 mA·cm -2 and a deposition capacity of 1 mAh·cm -2 of the negative electrode after 200 h of cycling at a current density of 1 mA·cm

[0046] Figure 12 Voltage-time graph obtained for the symmetric cell assembled with the zinc ion battery anode material in Example 2, at a current density of 1 mA·cm -2 and a deposition capacity of 1 mAh·cm -2 of the negative electrode after 200 h of cycling at a current density of 1 mA·cm

[0047] Figure 13 Time-voltage graph obtained for the symmetric cell assembled with pure zinc foil in Comparative Example 1, at a current density of 1 mA·cm -2 and a deposition capacity of 1 mAh·cm -2 of the negative electrode after 200 h of cycling at a current density of 1 mA·cm DETAILED DESCRIPTION

[0048] The technical content and effects of the present application are further described in detail below in conjunction with the examples, but the present application is not limited thereby.

[0049] Comparative Example 1 (pure zinc sheet electrode)

[0050] (1) A zinc sheet substrate with a thickness of 0.05 mm was polished by sandpaper with a particle size of 1000 mesh, and then immersed in anhydrous ethanol solution for ultrasonic cleaning for 5 min to remove oil and other impurities on the surface;

[0051] (2) The above treated pure zinc sheet electrode material is cut into an electrode round sheet with a diameter of 1.2 cm.

[0052] Comparative Example 2 (incompletely polymerized polydopamine)

[0053] Step one: 0.5 g of dopamine hydrochloride is added to 100 mL of deionized water, and the dopamine hydrochloride is fully dissolved by stirring to obtain a 5 g / L dopamine hydrochloride aqueous solution; a Tris-HCl buffer is added to adjust the pH value of the solution to 8, and the reaction container is sealed at room temperature to create an anoxic environment, and the polymerization reaction is carried out for 48 h to obtain an incompletely polymerized polydopamine suspension;

[0054] Step two: The polydopamine suspension is centrifuged, and then washed with deionized water and anhydrous ethanol three times alternately, and then vacuum dried at 70°C, ground, and then a powder of polydopamine is prepared;

[0055] Step three: 0.1 g of halloysite powder (powder particle size distribution is 500-1000 nm) is mixed and ground with 0.2 g of powder polydopamine (incompletely polymerized, forming irregular block polydopamine, and the particle size of the irregular block polydopamine is greater than 1000 nm) for 10 min to obtain a halloysite / polydopamine composite material;

[0056] Step four: the halloysite / polydopamine composite material is mixed with a 5% mass concentration of polyvinylidene fluoride in N-methyl pyrrolidone solution at a mass ratio of 1:9 using polyvinylidene fluoride as a binder, and a uniformly dispersed composite slurry is obtained after magnetic stirring for 12 h;

[0057] Step five: a zinc sheet with a thickness of 0.05 mm is polished by SiC sandpaper with a particle size of 400 mesh for 30 s, and then placed in anhydrous ethanol and ultrasonically cleaned to remove impurities such as oil stains on the surface of the zinc sheet to obtain a treated zinc sheet; the composite slurry is coated on the surface of the treated zinc sheet with a coating thickness of 100 μm, and then vacuum dried at 70°C to obtain a zinc metal negative electrode material with a halloysite / polydopamine composite coating.

[0058] Step six: the above zinc metal negative electrode material with a halloysite / polydopamine composite coating is cut into an electrode round sheet with a diameter of 1.2 cm.

[0059] Comparative Example 3 (polydopamine / halloysite polymerized in situ)

[0060] Step one: 0.5 g of dopamine hydrochloride and 0.1 g of halloysite powder (powder particle size distribution in 500-1000 nm, nanotube morphology) were added into 100 mL of deionized water, and the two were fully mixed by stirring to obtain a blended suspension of dopamine hydrochloride and halloysite; concentrated ammonia water was added to adjust the pH value of the solution to 12, and in-situ polymerization was carried out at room temperature for 48 h to obtain a suspension containing in-situ polymerized polydopamine / halloysite composite material;

[0061] Step two: the suspension of polydopamine / halloysite composite material was subjected to centrifugal treatment, and then was washed with deionized water and anhydrous ethanol alternately three times, and was vacuum dried at 70°C, ground, and then in-situ polymerized polydopamine / halloysite composite material was prepared;

[0062] Step three: the in-situ polymerized polydopamine / halloysite composite material was mixed with a 5% mass concentration polyvinylidene fluoride N-methyl pyrrolidone solution at a mass ratio of 1:9 using polyvinylidene fluoride as a binder, and a uniformly dispersed composite slurry was obtained after magnetic stirring for 12 h;

[0063] Step four: a zinc sheet with a thickness of 0.05 mm was polished for 30 s by SiC sandpaper with a particle size of 400 mesh, and then was placed in anhydrous ethanol and ultrasonically cleaned to remove oil stains and other impurities on the surface of the zinc sheet to obtain a treated zinc sheet; the above composite slurry was coated on the surface of the treated zinc sheet with a coating thickness of 100 μm, and then was vacuum dried at 70°C to obtain a zinc metal negative electrode material with a polydopamine / halloysite composite coating of in-situ polymerization.

[0064] Step five: the zinc metal negative electrode material with the polydopamine / halloysite composite coating of in-situ polymerization was cut into an electrode round sheet with a diameter of 1.2 cm.

[0065] Comparative Example 4 (excessive addition of polydopamine)

[0066] Step one: 0.5 g of dopamine hydrochloride was added into 100 mL of deionized water, and the dopamine hydrochloride was fully dissolved by stirring to obtain a 5 g / L dopamine hydrochloride aqueous solution; concentrated ammonia water was added to the dopamine hydrochloride aqueous solution to adjust the pH value of the solution to 12, and a polymerization reaction was carried out at room temperature for 48 h to generate a polydopamine suspension;

[0067] Step two: the polydopamine suspension was subjected to centrifugal treatment, and then was washed with deionized water and anhydrous ethanol alternately three times, and was vacuum dried at 70°C, ground, and then a powdered polydopamine was prepared;

[0068] Step three: 0.1 g of bentonite powder (powder particle size distribution in 500-1000 nm) was mixed with 20 g of powdered polydopamine (nanospheres with a particle size distribution of 50-200 nm, and an average particle size of 180 nm) for 10 min to obtain a bentonite / polydopamine composite material;

[0069] Step four: The bentonite / polydopamine composite material was mixed with a 5% mass concentration of polyvinylidene fluoride in N-methyl pyrrolidone solution as a binder at a mass ratio of 1:9, and a uniformly dispersed composite slurry was obtained after magnetic stirring for 12 h;

[0070] Step five: A 0.05 mm thick zinc sheet was polished for 30 s with a SiC sandpaper with a particle size of 400 mesh, then placed in anhydrous ethanol and ultrasonically cleaned to remove oil stains and other impurities on the surface of the zinc sheet, obtaining a treated zinc sheet; the composite slurry was coated on the surface of the treated zinc sheet with a coating thickness of 100 μm, and after vacuum drying at 70 °C, a zinc metal negative electrode material with a bentonite / polydopamine composite coating was obtained.

[0071] Step six: The zinc metal negative electrode material with a bentonite / polydopamine composite coating was cut into an electrode round sheet with a diameter of 1.2 cm.

[0072] Comparative Example 5 (excessive amount of silicate mineral / polydopamine composite material added in the composite slurry)

[0073] Step one: 0.5 g of dopamine hydrochloride was added to 100 mL of deionized water, and the dopamine hydrochloride was fully dissolved by stirring to obtain a 5 g / L dopamine hydrochloride aqueous solution; concentrated ammonia was added to the dopamine hydrochloride aqueous solution to adjust the pH of the solution to 12, and a polymerization reaction was carried out at room temperature for 48 h to generate a polydopamine suspension;

[0074] Step two: The polydopamine suspension was centrifuged, and then washed with deionized water and anhydrous ethanol three times alternately, and then vacuum dried at 70 °C, ground to prepare powdered polydopamine;

[0075] Step three: 0.1 g of bentonite powder (powder particle size distribution in 500-1000 nm) was mixed with 20 g of powdered polydopamine (nanospheres with a particle size distribution of 50-200 nm, and an average particle size of 180 nm) for 10 min to obtain a bentonite / polydopamine composite material;

[0076] Step four: the bentonite / polydopamine composite material was mixed with a N-methyl pyrrolidone solution containing 5% by mass of polyvinylidene fluoride at a mass ratio of 1:20 using polyvinylidene fluoride as a binder, and a uniformly dispersed composite slurry was obtained after magnetic stirring for 12 h;

[0077] Step five: a zinc sheet with a thickness of 0.05 mm was polished for 30 s using a SiC sandpaper with a particle size of 400 mesh, and then was placed in anhydrous ethanol and ultrasonically cleaned to remove oil stains and other impurities on the surface of the zinc sheet, thereby obtaining a treated zinc sheet; the composite slurry was coated on the surface of the treated zinc sheet to a thickness of 100 μm, and the zinc metal negative electrode material with a bentonite / polydopamine composite coating was obtained after vacuum drying at 70 °C.

[0078] Step six: the zinc metal negative electrode material with the bentonite / polydopamine composite coating was cut into an electrode round sheet with a diameter of 1.2 cm.

[0079] Comparative Example 6 (particle size of polydopamine nanospheres is too large)

[0080] Step one: 0.5 g of dopamine hydrochloride was added to 100 mL of deionized water, and the dopamine hydrochloride was fully dissolved by stirring to obtain a 5 g / L aqueous solution of dopamine hydrochloride; concentrated ammonia was added to the aqueous solution of dopamine hydrochloride to adjust the pH of the solution to 8, and a polymerization reaction was carried out at room temperature for 72 h to generate a polydopamine suspension;

[0081] Step two: the polydopamine suspension was subjected to centrifugal treatment, and then was washed with deionized water and anhydrous ethanol alternately three times, and was vacuum dried at 70 °C, ground, and then was prepared into a powder of polydopamine;

[0082] Step three: 0.1 g of bentonite powder (powder particle size distribution: 500-1000 nm) was mixed and ground with 0.5 g of the powder of polydopamine (nanospheres with a particle size distribution of 500-1000 nm and an average particle size of 860 nm) for 10 min to obtain a bentonite / polydopamine composite material;

[0083] Step four: the bentonite / polydopamine composite material was mixed with a N-methyl pyrrolidone solution containing 5% by mass of polyvinylidene fluoride at a mass ratio of 1:9 using polyvinylidene fluoride as a binder, and a uniformly dispersed composite slurry was obtained after magnetic stirring for 12 h;

[0084] Step five: the zinc sheet with a thickness of 0.05 mm was polished by SiC sandpaper with a particle size of 400 mesh for 30 s, then was put into anhydrous ethanol and ultrasonically cleaned to remove the oil stains and other impurities on the surface of the zinc sheet, thereby obtaining a treated zinc sheet; the composite slurry was coated on the surface of the treated zinc sheet with a coating thickness of 100 μm, and after vacuum drying at 70 °C, a zinc metal negative electrode material with a bentonite / polydopamine composite coating was obtained.

[0085] Step six: the zinc metal negative electrode material with a bentonite / polydopamine composite coating was cut into an electrode round sheet with a diameter of 1.2 cm.

[0086] Example 1

[0087] Step one: 0.5 g of dopamine hydrochloride was added to 100 mL of deionized water, and the dopamine hydrochloride was fully dissolved by stirring to obtain a 5 g / L dopamine hydrochloride aqueous solution; concentrated ammonia water was added to the dopamine hydrochloride aqueous solution to adjust the pH value of the solution to 12, and a polymerization reaction was carried out at room temperature for 48 h to generate a polydopamine suspension;

[0088] Step two: the polydopamine suspension was centrifuged, and then was washed with deionized water and anhydrous ethanol alternately three times, and after vacuum drying at 70 °C, grinding, a powder-like polydopamine was prepared;

[0089] Step three: 0.1 g of bentonite powder (powder particle size distribution of 500-1000 nm) was mixed and ground with 0.5 g of powder-like polydopamine (nanospherical particle size distribution of 50-200 nm, average particle size of 180 nm) for 10 min to obtain a bentonite / polydopamine composite material;

[0090] Step four: the bentonite / polydopamine composite material was mixed with a 5% mass concentration of polyvinylidene fluoride in N-methyl pyrrolidone solution at a mass ratio of 1:9, and a uniformly dispersed composite slurry was obtained after magnetic stirring for 12 h;

[0091] Step five: the zinc sheet with a thickness of 0.05 mm was polished by SiC sandpaper with a particle size of 400 mesh for 30 s, then was put into anhydrous ethanol and ultrasonically cleaned to remove the oil stains and other impurities on the surface of the zinc sheet, thereby obtaining a treated zinc sheet; the composite slurry was coated on the surface of the treated zinc sheet with a coating thickness of 100 μm, and after vacuum drying at 70 °C, a zinc metal negative electrode material with a bentonite / polydopamine composite coating was obtained.

[0092] Step six: the zinc metal negative electrode material with a bentonite / polydopamine composite coating was cut into an electrode round sheet with a diameter of 1.2 cm.

[0093] Example 2

[0094] Step one: 0.5 g of dopamine hydrochloride was added to 100 mL of deionized water, and the dopamine hydrochloride was fully dissolved by stirring to obtain a 5 g / L dopamine hydrochloride aqueous solution; concentrated ammonia water was added to the dopamine hydrochloride aqueous solution, and the pH value of the solution was adjusted to 12, and a polymerization reaction was carried out at room temperature for 48 h to generate a polydopamine suspension;

[0095] Step two: the polydopamine suspension was subjected to centrifugal treatment, and then was washed three times alternately with deionized water and anhydrous ethanol, and was subjected to vacuum drying treatment at 70°C, and was ground to prepare a powder-like polydopamine;

[0096] Step three: 0.1 g of halloysite powder (powder particle size distribution of 500-1000 nm, nanotubular morphology) was mixed and ground with 0.2 g of powder-like polydopamine (nanospherical particle size distribution of 50-200 nm, average particle size of 180 nm) for 10 min to obtain a halloysite / polydopamine composite material;

[0097] Step four: the halloysite / polydopamine composite material was mixed with a 5% mass concentration of polyvinylidene fluoride in N-methylpyrrolidone solution at a mass ratio of 1:9 using polyvinylidene fluoride as a binder, and a uniformly dispersed composite slurry was obtained after magnetic stirring for 12 h;

[0098] Step five: a zinc sheet with a thickness of 0.05 mm was polished for 30 s using a SiC sandpaper with a particle size of 400 mesh, and was then placed in anhydrous ethanol and ultrasonically cleaned to remove impurities such as oil stains on the surface of the zinc sheet to obtain a treated zinc sheet; the composite slurry was coated on the surface of the treated zinc sheet to a coating thickness of 200 μm, and the zinc metal negative electrode material with a halloysite / polydopamine composite coating was obtained after vacuum drying at 70°C.

[0099] Step six: the zinc metal negative electrode material with the halloysite / polydopamine composite coating was cut into an electrode round sheet with a diameter of 1.2 cm.

[0100] Example 3

[0101] Step one: 0.5 g of dopamine hydrochloride was added to 100 mL of deionized water, and the dopamine hydrochloride was fully dissolved by stirring to obtain a 5 g / L dopamine hydrochloride aqueous solution; concentrated ammonia water was added to the dopamine hydrochloride aqueous solution, and the pH value of the solution was adjusted to 12, and a polymerization reaction was carried out at room temperature for 48 h to generate a polydopamine suspension;

[0102] Step two: centrifugal treatment was performed on the polydopamine suspension, followed by three times of alternate cleaning with deionized water and anhydrous ethanol, vacuum drying treatment at 70℃, grinding, and then powder polydopamine was prepared;

[0103] Step three: 0.1 g of kaolin powder (powder particle size distribution of 1000-2000 nm) was mixed and ground with 0.1 g of powder polydopamine (nanospheres with particle size distribution of 50-200 nm, and average particle size of 180 nm) for 10 min to obtain a kaolin / polydopamine composite material;

[0104] Step four: the kaolin / polydopamine composite material was mixed with a 5% mass concentration polyvinylidene fluoride N-methyl pyrrolidone solution as a binder at a mass ratio of 1:9, and a uniformly dispersed composite slurry was obtained after magnetic stirring for 12 h;

[0105] Step five: a 0.05 mm thick zinc sheet was polished with a 400 mesh SiC sandpaper for 30 s, then placed in anhydrous ethanol and ultrasonically cleaned to remove oil stains and other impurities on the surface of the zinc sheet to obtain a treated zinc sheet; the composite slurry was coated on the surface of the treated zinc sheet with a coating thickness of 50 μm, and after vacuum drying treatment at 70℃, a zinc metal negative electrode material with a kaolin / polydopamine composite coating was obtained.

[0106] Step six: the zinc metal negative electrode material with a kaolin / polydopamine composite coating was cut into an electrode round sheet with a diameter of 1.2 cm.

[0107] Example 4

[0108] Step one: 0.5 g of dopamine hydrochloride was added to 100 mL of deionized water, and the dopamine hydrochloride was fully dissolved by stirring to obtain a 5 g / L dopamine hydrochloride aqueous solution; sodium hydroxide was added to the dopamine hydrochloride aqueous solution to adjust the pH value of the solution to 14, and a polymerization reaction was carried out at room temperature for 48 h to generate a polydopamine suspension;

[0109] Step two: centrifugal treatment was performed on the polydopamine suspension, followed by three times of alternate cleaning with deionized water and anhydrous ethanol, vacuum drying treatment at 70℃, grinding, and then powder polydopamine was prepared;

[0110] Step three: 0.1 g of kaolin powder (powder particle size distribution of 1000-2000 nm) was mixed and ground with 0.1 g of powder polydopamine (nanospheres with particle size distribution of 50-200 nm, and average particle size of 180 nm) for 10 min to obtain a kaolin / polydopamine composite material;

[0111] Step four: the attapulgite / polydopamine composite material was mixed with N-methyl pyrrolidone solution containing 5% mass concentration of polyvinylidene fluoride at a mass ratio of 1:9, and a uniform dispersed composite slurry was obtained after magnetic stirring for 12 h;

[0112] Step five: a zinc sheet with a thickness of 0.05 mm was polished by SiC sandpaper with a particle size of 400 mesh for 30 s, and then was placed in anhydrous ethanol and ultrasonically cleaned to remove oil stains and other impurities on the surface of the zinc sheet, thereby obtaining a treated zinc sheet; the composite slurry was coated on the surface of the treated zinc sheet with a coating thickness of 200 μm, and after vacuum drying at 70 °C, a zinc metal negative electrode material with an attapulgite / polydopamine composite coating was obtained.

[0113] Step six: the zinc metal negative electrode material with the attapulgite / polydopamine composite coating was cut into an electrode round sheet with a diameter of 1.2 cm.

[0114] Example 5

[0115] Step one: 1.0 g of dopamine hydrochloride was added to 100 mL of deionized water, and the dopamine hydrochloride was fully dissolved by stirring to obtain a 10 g / L dopamine hydrochloride aqueous solution; Tris-HCl was added to the dopamine hydrochloride aqueous solution to adjust the pH value of the solution to 12, and a polymerization reaction was carried out at room temperature for 48 h to generate a polydopamine suspension;

[0116] Step two: the polydopamine suspension was centrifuged, and then was washed with deionized water and anhydrous ethanol alternately for three times, and was vacuum dried at 70 °C, ground, and then a powder-like polydopamine was prepared;

[0117] Step three: 0.1 g of attapulgite powder (powder particle size distribution of 1000-2000 nm) was mixed and ground with 0.2 g of powder-like polydopamine (nanospherical particle size distribution of 50-200 nm, average particle size of 180 nm) for 10 min to obtain an attapulgite / polydopamine composite material;

[0118] Step four: the attapulgite / polydopamine composite material was mixed with N-methyl pyrrolidone solution containing 5% mass concentration of polyvinylidene fluoride at a mass ratio of 1:9, and a uniform dispersed composite slurry was obtained after magnetic stirring for 12 h;

[0119] Step five: a 0.05 mm thick zinc sheet was polished with SiC sandpaper of 400 mesh for 30 s, then placed in anhydrous ethanol and ultrasonically cleaned to remove oil stains and other impurities on the surface of the zinc sheet, obtaining a treated zinc sheet; the composite slurry was coated on the surface of the treated zinc sheet with a coating thickness of 200 μm, and after vacuum drying at 70 °C, a zinc metal negative electrode material with an attapulgite / polydopamine composite coating was obtained.

[0120] Step six: the above zinc metal negative electrode material with an attapulgite / polydopamine composite coating was cut into an electrode round piece with a diameter of 1.2 cm.

[0121] Example 6

[0122] Step one: 1.0 g of dopamine hydrochloride was added to 100 mL of deionized water, and the dopamine hydrochloride was fully dissolved by stirring to obtain a 10 g / L dopamine hydrochloride aqueous solution; Tris-HCl was added to the dopamine hydrochloride aqueous solution to adjust the pH of the solution to 10, and a polymerization reaction was carried out at room temperature for 48 h to obtain a polydopamine suspension;

[0123] Step two: the polydopamine suspension was centrifuged, then washed with deionized water and anhydrous ethanol alternately three times, vacuum dried at 70 °C, ground, and then a powder-like polydopamine was prepared;

[0124] Step three: 0.1 g of vermiculite powder (powder particle size distribution of 800-2000 nm) was mixed and ground with 0.2 g of powder-like polydopamine (nanospherical particle size distribution of 180-600 nm, average particle size of 440 nm) for 10 min to obtain a vermiculite / polydopamine composite material;

[0125] Step four: the vermiculite / polydopamine composite material was mixed with a 5% mass concentration polyvinylidene fluoride N-methyl pyrrolidone solution as a binder at a mass ratio of 1:9, and a uniformly dispersed composite slurry was obtained after magnetic stirring for 12 h;

[0126] Step five: a 0.05 mm thick zinc sheet was polished with SiC sandpaper of 400 mesh for 30 s, then placed in anhydrous ethanol and ultrasonically cleaned to remove oil stains and other impurities on the surface of the zinc sheet, obtaining a treated zinc sheet; the composite slurry was coated on the surface of the treated zinc sheet with a coating thickness of 200 μm, and after vacuum drying at 70 °C, a zinc metal negative electrode material with an attapulgite / polydopamine composite coating was obtained.

[0127] Step six: the above zinc metal negative electrode material with an attapulgite / polydopamine composite coating was cut into an electrode round piece with a diameter of 1.2 cm.

[0128] Example 7

[0129] Step one: 0.5 g of dopamine hydrochloride was added into 100 mL of deionized water, and the dopamine hydrochloride was fully dissolved by stirring to obtain a 5 g / L dopamine hydrochloride aqueous solution; concentrated ammonia water was added into the dopamine hydrochloride aqueous solution to adjust the pH value of the solution to 12, and a polymerization reaction was carried out at room temperature for 48 h to generate a polydopamine suspension;

[0130] Step two: the polydopamine suspension was subjected to centrifugal treatment, and then was washed with deionized water and anhydrous ethanol alternately for three times, and was subjected to vacuum drying treatment at 70 °C, and was ground to prepare a powder-like polydopamine;

[0131] Step three: 0.1 g of bentonite powder (powder particle size distribution: 500-1000 nm) was mixed and ground with 1 g of the powder-like polydopamine (nanospherical particle size distribution: 50-200 nm, average particle size: 180 nm) for 10 min to obtain a bentonite / polydopamine composite material;

[0132] Step four: the bentonite / polydopamine composite material was mixed with a 5% mass concentration polyvinylidene fluoride N-methyl pyrrolidone solution as a binder at a mass ratio of 1:6, and a uniformly dispersed composite slurry was obtained after magnetic stirring for 12 h;

[0133] Step five: a zinc sheet with a thickness of 0.05 mm was polished by a SiC sandpaper with a particle size of 400 mesh for 30 s, and then was placed into anhydrous ethanol and was subjected to ultrasonic cleaning to remove impurities such as oil stains on the surface of the zinc sheet to obtain a treated zinc sheet; the composite slurry was coated on the surface of the treated zinc sheet with a coating thickness of 100 μm, and after vacuum drying treatment at 70 °C, a zinc metal negative electrode material with a bentonite / polydopamine composite coating was obtained.

[0134] Step six: the zinc metal negative electrode material with the bentonite / polydopamine composite coating was cut into an electrode round sheet with a diameter of 1.2 cm.

[0135] The electrode round sheets obtained in Examples 1-7 and Comparative Examples 1-6 were used as positive and negative electrodes, glass fiber was used as a separator, and a 2.0 mol•L -1 -1 zinc sulfate solution was used as an electrolyte to assemble a symmetric battery. After the zinc ion half-battery was placed at 25 °C for 12 h, the cyclic performance test was carried out at a current density of 1 mA / cm 2 , and a deposition capacity of 1 mAh / cm 2 . The polarization voltage and the cycle time of the symmetric battery under the same current density and area capacity are shown in Table 1.

[0136] Table 1

[0137] Polarization voltage (V) Longest cycle time (h) Comparative Example 1 0.4 200 Comparative Example 2 0.3 300 Comparative Example 3 0.3 300 Comparative Example 4 0.3 300 Comparative Example 5 0.4 200 Comparative Example 6 0.3 150 Example 1 0.15 2000 Example 2 0.15 1800 Example 3 0.2 1500 Example 4 0.2 1600 Example 5 0.15 1400 Example 6 0.15 1500 Example 7 0.15 1800

[0138] As can be seen from Table 1, the composite coating in the application can better protect the zinc metal negative electrode, prolong the service life, and the polymerization degree of polydopamine, the combination form of polydopamine and silicate minerals, the particle size and the amount of polydopamine added will all affect the overall performance of the electrode material. Compared with in-situ polymerization, the application has a longer cycle and better overall performance.

[0139] By Figure 1 As can be seen, the X-ray diffraction peaks of the halloysite / polydopamine material prepared in Example 2 all correspond to halloysite nanotubes, indicating that the addition of polydopamine does not affect the structure of the original silicate material.

[0140] By Figure 2 As can be seen, the halloysite / polydopamine material prepared in Example 2 has a clear structure of silicate minerals with dopamine inlay, and dopamine is closely attached to the skeleton of silicate minerals.

[0141] By Figure 3 As can be seen, the silicate mineral / polydopamine material in Comparative Example 2 that is not completely polymerized has agglomeration of polyaniline, and the silicate mineral and polyaniline are separated from each other.

[0142] By Figure 4 As can be seen, the silicate mineral is completely submerged by the polydopamine after in-situ polymerization in Comparative Example 3, at this time, the silicate mineral will not play any role.

[0143] By Figure 5 As can be seen, after too much polydopamine is added in Comparative Example 4, the pores of the silicate mineral are completely blocked, at this time, polydopamine occupies the main part and fixes the silicate mineral, which does not play a role in increasing the mechanical properties of the coating.

[0144] By Figure 6 As can be seen, after the amount of the binder is reduced in Comparative Example 5, the coating surface appears cracking phenomenon, the coating part has weak bonding force with the zinc sheet, and even falls off.

[0145] By Figure 7 As can be seen, after the polydopamine with a particle size of about 780 nm is added in Comparative Example 6, the polydopamine nanospheres are all gathered on the surface of the silicate mineral, which completely isolates the silicate mineral, the steric hindrance effect between them is too large, resulting in poor mechanical properties of the coating.

[0146] By Figure 8 As can be seen, after 2000 h of cycling, the surface of the composite coating in Example 2 still maintains uniformity, without dendrite and byproduct generation.

[0147] By Figure 9 As can be seen, a large amount of dendrites and by-products are generated on the surface of the pure zinc sheet of Comparative Example 1 after 200 h of cycling.

[0148] By Figure 10 As can be seen, a large amount of by-products are generated on the surface of the in-situ polymerized silicate mineral / polydopamine material coating in Comparative Example 3 after 200 h of cycling, accompanied by problems such as peeling of the coating.

[0149] By Figures 11-13 As can be seen, in comparison of Examples 1-2 and Comparative Example 1, the cycle stability of the zinc negative electrode with the composite coating in the present application is significantly improved due to the optimization of zinc ion transmission kinetics, and the aqueous zinc ion battery realizes 2000 h of continuous stable operation. In addition, the overpotential of zinc deposition / peeling is reduced, thereby reducing the electrode polarization phenomenon, further enhancing the performance of the electrode.

[0150] The above examples of the present application are merely examples for illustrating the present application, and are not intended to limit the embodiments of the present application. Based on the above description, other different forms of changes and variations can be made by those of ordinary skill in the art. It is impossible to exhaust all the embodiments here. Any obvious changes or variations derived from the technical solutions of the present application still fall within the protection scope of the present application.

Claims

1. A method for preparing a composite coating for the negative electrode protection of an aqueous zinc-ion battery, characterized in that, Includes the following steps: Step 1: Add the buffer to the dopamine hydrochloride aqueous solution, adjust the pH value to 10-14, and obtain a polydopamine suspension through polymerization reaction; Step 2: The polydopamine suspension is centrifuged, washed, and dried sequentially to obtain powdered polydopamine; Step 3: Mix and grind powdered silicate minerals and powdered polydopamine to obtain a silicate mineral / polydopamine composite material; the powdered polydopamine has a microstructure of nanospheres with a particle size distribution of 50~700 nm and an average particle size of 100~500 nm; the powdered silicate minerals have a particle size distribution of 500~3000 nm; the mass ratio of powdered silicate minerals to powdered polydopamine is 1:(0.1~10); Step 4: Mix the silicate mineral / polydopamine composite material, binder, and solvent to prepare a composite slurry; the mass ratio of the silicate mineral / polydopamine composite material to the binder is 1:(0.1~0.5); the mass ratio of the silicate mineral / polydopamine composite material to the total mass of the solvent and binder is 1:(2~10). Step 5: Apply the composite slurry to the surface of the zinc sheet and dry it to obtain the composite coating.

2. The method for preparing the composite coating for the negative electrode protection of aqueous zinc-ion batteries as described in claim 1, characterized in that, In step one, the concentration of the dopamine hydrochloride aqueous solution is 0.1–10 g / L; the buffer is one of ammonia, sodium hydroxide solution, or Tris-HCl buffer solution.

3. The method for preparing the composite coating for the negative electrode protection of aqueous zinc-ion batteries as described in claim 1, characterized in that, In step one, the polymerization reaction takes 12 to 48 hours.

4. The method for preparing the composite coating for the negative electrode protection of aqueous zinc-ion batteries as described in any one of claims 1-3, characterized in that, In step three, the silicate minerals are one or more combinations of kaolin, attapulgite, vermiculite, diaspore, purple clay, montmorillonite, halloysite, talc, pyrophyllite, potassium feldspar, sodium feldspar, and kaolin.

5. The method for preparing the composite coating for the negative electrode protection of aqueous zinc-ion batteries as described in claim 1, characterized in that, In step three, the mixing and grinding time is 5 to 30 minutes.

6. The method for preparing the composite coating for the negative electrode protection of aqueous zinc-ion batteries as described in claim 1, characterized in that, In step five, the thickness of the composite slurry coating on the zinc sheet surface is 1~300 μm.

7. An aqueous zinc-ion battery, characterized in that, Includes a negative electrode sheet containing the composite coating as described in any one of claims 1-6.

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