An ultra-thin composite zinc anode and its preparation method and application

Abstract

The present invention provides an ultra-thin composite zinc anode and its preparation method and application, which relates to the technical field of aqueous zinc-ion batteries; the specific preparation method is as follows: by pyrolyzing polytetrafluoroethylene (PTFE) powder at high temperature, gas-phase deposition occurs during the heat preservation and cooling processes, and a hydrophobic protective layer with a thickness of about 1 μm is introduced onto the rough surface of a 10-μm copper foil. Then, zinc with a capacity of 5 mAh / cm² (theoretically about 8.5 μm) is uniformly electrodeposited between the copper foil substrate and the hydrophobic protective layer to obtain an ultra-thin composite zinc anode with a thickness of about 20 μm. This hydrophobic protective film layer can achieve effective conduction of zinc ions, thereby inducing bottom-up selective deposition of zinc. The composite zinc anode of the present invention can effectively inhibit the growth of zinc dendrites and prevent zinc metal from being corroded by the electrolyte when applied to aqueous zinc-ion batteries, thereby realizing zinc-ion batteries with a long cycle life. At the same time, it improves the utilization rate of zinc metal and reduces the waste of zinc metal materials.

Description

Technical Field

[0001] The present invention relates to the technical field of aqueous zinc-ion batteries, and specifically refers to an ultra-thin composite zinc anode and its preparation method and application. Background Art

[0002] Lithium-ion batteries (LIBs) currently dominate the commercial battery market due to their high energy density and long cycle life, and are widely used in portable electronic devices and electric vehicles. However, the shortage of metallic lithium resources and the safety hazards associated with the use of toxic and flammable organic electrolytes have severely hindered the further application and development of lithium-ion batteries. Among them, rechargeable aqueous zinc-ion batteries (ZIBs) have attracted much attention from researchers because of their simple preparation, low cost, safety, environmental friendliness, relatively high energy and power densities, and fast charge and discharge capabilities, and have become potential alternatives to lithium-ion batteries.

[0003] An aqueous zinc-ion battery uses an aqueous solution containing Zn 2+ as the electrolyte, and realizes the storage and conversion of energy through the shuttle transfer of Zn 2+ between the positive and negative electrodes. Metallic zinc is the metal element with the highest energy that can be stable in an aqueous solution. At the same time, China has rich reserves of zinc metal. The many advantages of zinc, such as non-toxicity and easy treatment, make metallic zinc the main negative electrode material in zinc-ion batteries. However, during the battery cycling process, dendrite growth, slow corrosion, and inevitable hydrogen evolution reaction on the surface of the metallic zinc anode are fundamental problems affecting the safety and stability of zinc-ion batteries, and are obstacles to the commercialization of rechargeable aqueous zinc batteries; at the same time, most of the current zinc anode modification strategies are based on relatively thick zinc metal (usually 100 μm), and the mass of the entire zinc metal anode is more than ten times that actually utilized during cycling. Such a design not only leads to wasted materials due to excessive energy, but also greatly increases the thickness and mass of the negative electrode. Summary of the Invention

[0004] Aiming at the problems of zinc dendrites, corrosion and hydrogen evolution, short cycle life, and waste of zinc metal anode materials in the zinc anode during charge and discharge cycling in the background art, the present invention provides an ultra-thin composite zinc anode and its preparation method and application, aiming to reduce the volume ratio of the negative electrode in the entire battery, reduce the zinc metal anode material, and the phenomenon of excessive energy; at the same time, use a hydrophobic protective layer to inhibit various side reactions of metallic zinc in an aqueous electrolyte; construct an aqueous battery based on the composite zinc anode to achieve high stability of the negative electrode structure and reduce the volume ratio of the negative electrode in the entire battery, and obtain a zinc-ion battery with high energy density, long cycle life, and low cost.

[0005] To achieve the above object, an embodiment of the present invention provides a composite zinc anode, including a copper foil substrate, deposited zinc, and a continuous, dense, ultrathin hydrophobic protective film layer coated on the surface of the copper foil substrate. The ultrathin hydrophobic protective film layer is mainly a carbon layer with uniformly dispersed polytetrafluoroethylene particles, and short chains of polytetrafluoroethylene are uniformly distributed on the carbon layer.

[0006] Further, the average particle size of the polytetrafluoroethylene particles is 100 - 500 nm, the thickness of the carbon layer is 1 μm, and the thickness of the copper foil is 10 μm.

[0007] Further, the contact angle between the ultrathin hydrophobic protective film layer and the electrolyte is 107°.

[0008] Based on the general concept of an invention, the present invention also provides a preparation method of the above composite zinc anode, including the following steps:

[0009] S1. Pyrolyze polytetrafluoroethylene powder at high temperature in a tube furnace, and form an ultrathin hydrophobic protective film layer on the copper foil during the cooling process;

[0010] S2. Clean with an organic solvent and dry to obtain a modified ultrathin current collector;

[0011] S3. Deposit zinc on the modified ultrathin current collector by an electrochemical deposition method to obtain an ultrathin composite zinc anode.

[0012] Preferably, step S1 specifically includes the following steps:

[0013] S1.1. Alternately clean the copper foil with deionized water and absolute ethanol;

[0014] S1.2. Cover the copper foil cleaned in S1.1 on a square crucible, spread polytetrafluoroethylene powder at the bottom of the crucible, and put them into the tube furnace together;

[0015] S1.3. Then raise the temperature to decompose polytetrafluoroethylene, keep the temperature for a certain time, and then cool down with the furnace;

[0016] S1.4. After the tube furnace cools to room temperature, pass argon gas to remove the decomposed tetrafluoroethylene gas, open the tube furnace and take out the copper foil to obtain a current collector with an ultrathin hydrophobic protective film layer.

[0017] Preferably, in S1.2, the dosage of polytetrafluoroethylene powder is 1 - 5 g, and the particle size of the polytetrafluoroethylene powder < 1 μm; more preferably, the dosage of polytetrafluoroethylene powder is 3 g.

[0018] Preferably, in S1.2, the state inside the tube furnace is vacuum or argon gas is passed through, and more preferably, the inside of the tube furnace is in a vacuum state.

[0019] Preferably, the heating rate in S1.3 is 3 - 10 °C / min, more preferably 5 °C / min.

[0020] Preferably, the final temperature of the heating is 500 - 700 °C, more preferably 600 °C.

[0021] Preferably, the heat preservation time is 30 - 90 min, more preferably 60 min.

[0022] Preferably, in S1.4, the time for passing argon after cooling to room temperature is 30 min.

[0023] Preferably, in S2, the organic solvent is at least one of anhydrous ethanol and acetone.

[0024] Preferably, in S2, the drying condition is vacuum, the temperature is 50 - 80 °C, more preferably 60 °C.

[0025] Preferably, in S3, the electrochemical deposition equipment is one of a button cell and an electrolytic cell.

[0026] Preferably, in the electrochemical method, the applied current density is 0.1 - 5 mA / cm -2 , more preferably 0.25 mA / cm -2 , the applied current time is 1 - 50 h, more preferably 20 h.

[0027] The present invention also provides the application of the above composite zinc negative electrode, assembling the above composite zinc negative electrode into a symmetric battery or assembling the above composite zinc negative electrode with a V2O5 positive electrode to obtain an aqueous zinc ion battery.

[0028] The above solution of the present invention has the following beneficial effects:

[0029] (1) The above solution of the present invention uses a commercial copper foil as the substrate, and prepares a uniform and dense hydrophobic protective film on the surface of the copper foil by the method of high-temperature pyrolysis of polymers, and then combines the electrochemical deposition method to obtain an ultra-thin composite zinc negative electrode with an overall thickness of about 20 μm. Under the protection of the film layer, the corrosion of the zinc metal by the zinc sulfate electrolyte is reduced, and the zinc ion conduction ability of the film layer enables the deposited zinc to have a bottom-up selectivity, inhibits the growth of dendrites, and achieves the effect of uniform deposition. At the same time, the volume advantage of the ultra-thin composite zinc negative electrode is exerted, the utilization rate of active zinc is improved, and the waste of metal zinc materials is reduced;

[0030] (2) The present invention is beneficial to reducing the cost of the zinc negative electrode and improving the cycle stability of the zinc negative electrode. By combining the zinc negative electrode structure design and the anti-corrosion strategy, the performance of the aqueous zinc ion battery is effectively improved;

[0031] (3) The hydrophobic protective film layer in the present invention has certain hydrophobic properties while maintaining high ionic conductivity. This hydrophobic property is mainly provided by polytetrafluoroethylene particles uniformly distributed on the carbon layer (as shown in Figure 1 ). During the cycling process, the polytetrafluoroethylene particles can prevent water molecules from approaching the zinc negative electrode side, thereby inhibiting the occurrence of related side reactions (such as hydrogen evolution, etc.);

[0032] (4) The present invention first modifies the copper foil current collector, and then obtains a three-layer composite zinc negative electrode (copper foil substrate - deposited zinc - protective layer) by electrochemical deposition. The hydrophobic protective film layer does not adopt any coating method, but in a tube furnace under vacuum, polytetrafluoroethylene is evaporated and a protective layer is formed on the copper foil. Its method is vapor deposition, that is, a hydrophobic protective carbon layer is deposited on the copper foil surface during the evaporation process, and no chemical reaction occurs with the copper foil;

[0033] (5) In the embodiment of the present invention Figure 7 In the SEM image of the surface deposition morphology of the ultra-thin composite zinc negative electrode after cycling, due to the good conductivity of the copper foil substrate and the high ionic conductivity of the protective film layer, zinc is deposited between the copper foil substrate and the hydrophobic protective film layer. The role of the film layer is to transport ions and inhibit the growth of dendrites;

[0034] (6) The thickness of the carbon layer with uniformly dispersed polytetrafluoroethylene particles introduced in the present invention is only about 1 μm. And the present invention pays more attention to the regulation of the thickness of the entire negative electrode. The overall thickness of the copper foil substrate, deposited zinc, and protective layer will be controlled at about 20 μm (as shown in Figure 4 ), so as to prepare an ultra-thin composite zinc negative electrode. Description of the Drawings

[0035] Figure 1 is the SEM image of the ultra-thin hydrophobic film composed of polytetrafluoroethylene particles and carbon layer deposited on the surface of the copper foil current collector obtained in Example 1 of the present invention;

[0036] Figure 2 is the contact angle test diagram of the modified copper foil current collector and 2M zinc sulfate electrolyte obtained in Example 1 of the present invention;

[0037] Figure 3 is the cycle number - efficiency diagram of the coulombic efficiency test of the half-cell assembled with the ultra-thin hydrophobic film layer modified copper foil current collector and a zinc sheet with a diameter of 16 mm in Example 1 of the present invention. The comparison is with the unmodified commercial copper foil;

[0038] Figure 4 is the cross-sectional SEM image of the ultra-thin composite zinc negative electrode obtained by electro-depositing 5 mAh / cm 2 zinc in Example 1 of the present invention;

[0039] Figure 5It is the time-voltage graph of the cyclic stability test of the symmetric battery assembled with the ultra-thin composite zinc negative electrode obtained in Example 1 of the present invention. For comparison, it is the negative electrode of commercial copper foil deposited with 5 mAh / cm 2 Negative electrode of zinc;

[0040] Figure 6 It is the specific capacity and efficiency graph of the full battery cycle assembled with the ultra-thin composite zinc negative electrode obtained in Example 1 of the present invention and the V2O5 positive electrode. For comparison, it is the negative electrode of commercial copper foil deposited with 5 mAh / cm 2 Negative electrode of zinc;

[0041] Figure 7 It is the SEM graph of the surface deposition morphology after the ultra-thin composite zinc negative electrode obtained in Example 1 of the present invention is cycled 50 times;

[0042] Figure 8 It is the cycle number-efficiency graph of the Coulomb efficiency test of the half-cell assembled with the ultra-thin hydrophobic film layer modified copper foil current collector obtained in Example 2 of the present invention;

[0043] Figure 9 It is the time-voltage graph of the cyclic stability test of the symmetric battery assembled with the ultra-thin composite zinc negative electrode obtained in Example 3 of the present invention;

[0044] Figure 10 It is the SEM graph of the surface of the copper foil current collector obtained in Comparative Example 1 of the present invention;

[0045] Figure 11 It is the SEM graph of the surface of the ultra-thin composite zinc negative electrode obtained in Comparative Example 1 of the present invention after 50 cycles;

[0046] Figure 12 It is the SEM graph of the surface of the copper foil current collector obtained in Comparative Example 2 of the present invention;

[0047] Figure 13 It is the cycle number-efficiency graph of the Coulomb efficiency test of the copper foil current collector obtained in Comparative Example 2 of the present invention. Detailed implementation manners

[0048] To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0049] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0050] Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the present invention can be obtained through the market or can be prepared by existing methods.

[0051] Aqueous zinc ion batteries use an aqueous solution containing Zn 2+ as the electrolyte, and achieve energy storage and conversion through the shuttle transfer of Zn 2+ between the positive and negative electrodes. Metallic zinc is the metal element with the highest energy that can be stable in an aqueous solution. At the same time, China has rich reserves of zinc metal. The many advantages of zinc being non-toxic and easy to process make metallic zinc the main negative electrode material in zinc ion batteries. However, during the battery cycling process, problems such as dendrite growth, slow corrosion, and inevitable hydrogen evolution reaction on the surface of the metallic zinc negative electrode are fundamental issues affecting the safety and stability of zinc ion batteries, and are obstacles to the commercialization of rechargeable aqueous zinc batteries; at the same time, most of the current zinc negative electrode modification strategies are based on relatively thick zinc metal (usually 100 μm), and the mass of the entire zinc metal negative electrode is more than ten times that actually utilized during cycling. That is, there are problems such as zinc dendrites, corrosion and hydrogen evolution, short cycle life, and waste of zinc metal negative electrode materials during the charge and discharge cycling of the zinc negative electrode.

[0052] In order to reduce the volume ratio of the negative electrode in the entire battery, reduce the zinc metal negative electrode material, and the phenomenon of excess energy. At the same time, use a hydrophobic protective film layer to inhibit various side reactions that occur to metallic zinc in an aqueous electrolyte. The present invention provides an ultra-thin composite zinc negative electrode, its preparation method and application, constructs an aqueous battery based on the composite zinc negative electrode, realizes high stability of the negative electrode structure, reduces the volume ratio of the negative electrode in the entire battery, and obtains a zinc ion battery with high energy density, long cycle life, and low cost.

[0053] An embodiment of the present invention provides a composite zinc negative electrode, including a copper foil substrate, deposited zinc, and a continuous and dense ultra-thin hydrophobic protective film layer coated on the surface of the copper foil substrate. The ultra-thin hydrophobic protective film layer is mainly a carbon layer with uniformly dispersed polytetrafluoroethylene particles, and short chains of polytetrafluoroethylene are uniformly distributed on the carbon layer.

[0054] Furthermore, the average particle size of the polytetrafluoroethylene particles is 100 - 500 nm, the thickness of the carbon layer is 1 μm, and the thickness of the copper foil is 10 μm.

[0055] Furthermore, the contact angle between the ultra-thin hydrophobic protective film layer and the electrolyte is 107°.

[0056] The present invention provides a preparation method for the above composite zinc negative electrode, including the following steps:

[0057] S1. Pyrolyze polytetrafluoroethylene powder at high temperature in a tube furnace, and form an ultra-thin hydrophobic protective film layer on the copper foil during the cooling process;

[0058] S2. Use an organic solvent for cleaning and drying to obtain a modified ultra-thin current collector;

[0059] S3. Zinc is electrochemically deposited on the modified ultra-thin current collector to obtain an ultra-thin composite zinc negative electrode.

[0060] Preferably, S1 specifically includes the following steps:

[0061] S1.1. The copper foil is alternately cleaned with deionized water and absolute ethanol.

[0062] S1.2. The copper foil cleaned in S1.1 is covered on a square crucible, and polytetrafluoroethylene powder is spread at the bottom of the crucible, and they are placed in a tube furnace together.

[0063] S1.3. Then the temperature is raised to decompose the polytetrafluoroethylene, and after holding the temperature, it is cooled with the furnace.

[0064] S1.4. After the tube furnace is cooled to room temperature, argon is introduced to remove the decomposed tetrafluoroethylene gas, the tube furnace is opened, and the copper foil is taken out to obtain a current collector with an ultra-thin hydrophobic protective film layer.

[0065] Preferably, in S1.2, the tube furnace used has an outer diameter of 50 mm, an inner diameter of 44 mm, and a length of 600 mm, the square crucible has dimensions of 100*30*20 mm, and the amount of polytetrafluoroethylene powder used is 1 - 5 g. More preferably, the amount of polytetrafluoroethylene powder used is 3 g.

[0066] Preferably, the state inside the tube furnace in S1.2 is vacuum or argon is introduced. More preferably, the state inside the tube furnace is a vacuum state.

[0067] Preferably, in S1.3, the heating rate is 3 - 10 °C / min, more preferably 5 °C / min.

[0068] Preferably, the final temperature of the heating is 500 - 700 °C, more preferably 600 °C.

[0069] Preferably, the holding time is 30 - 90 min, more preferably 60 min.

[0070] Preferably, in S1.4, the time for introducing argon after cooling to room temperature is 30 min.

[0071] Preferably, in S2, the organic solvent is at least one of absolute ethanol and acetone.

[0072] Preferably, in S2, the drying condition is vacuum, and the temperature is 50 - 80 °C, further preferably 60 °C.

[0073] Preferably, in S3, the electrochemical deposition equipment is one of a coin cell and an electrolytic cell.

[0074] Preferably, the applied current density in the electrochemical method is 0.1 - 5 mA / cm² -2, more preferably 0.25 mA / cm² -2 , the current application time is 1 to 50 h, more preferably 20 h.

[0075] The present invention also provides an application of the above composite zinc negative electrode, assembling the above composite zinc negative electrode into a symmetric battery or assembling the above composite zinc negative electrode with a V₂O₅ positive electrode to obtain an aqueous zinc ion battery.

[0076] Example 1

[0077] First, prepare a commercial copper foil to be modified: take a commercial copper foil with a certain size area and a thickness of about 10 μm. One side of the copper foil is rough and the other side is smooth. Then, alternately rinse the surface with deionized water and absolute ethanol, and then place it in an oven at 60 °C for drying for later use.

[0078] Preparation of an ultrathin hydrophobic film layer on the surface of the copper foil: Weigh 3 g of polytetrafluoroethylene powder and spread it flat on the bottom of the crucible. Cover the previously cleaned copper foil on the crucible with the rough side facing up. Place the crucible in a tube furnace, place furnace plugs on both sides, sequentially put an inner flange sleeve and an O-ring on the quartz tube, evenly apply vacuum grease on the O-ring, align the outer flange with the inner flange and press it tightly, and uniformly fix it with hexagon bolts. Close the vacuum valves on both sides of the quartz tube, connect one side to a vacuum pump, after turning on the vacuum pump, slowly open the vacuum valve, pump the pressure inside the quartz tube to less than -0.1 MPa, and wait for 30 min to check the airtightness of the quartz tube. Subsequently, set the tube furnace program, start heating at room temperature for 120 min, the termination temperature is 600 °C, about 5 °C / min, then start insulation, the time is 60 min, the termination temperature is 600 °C, and then end the heating program, and wait for the tube furnace to cool to room temperature. Subsequently, connect the tube furnace to argon to discharge the residual gas inside the tube, and the ventilation time is about 30 min. Then open the vacuum valve, remove the flange, and take out the copper foil. Then punch it into a disc with a diameter of 14 mm with a punching machine. After washing with distilled water, place it in an oven at 60 °C for drying for 60 min, and thus obtain a copper foil current collector covered with an ultrathin hydrophobic film layer.

[0079] Figure 1 is the SEM image of the copper foil current collector covered with the ultrathin hydrophobic film layer obtained in Example 1. It can be seen that the carbon layer on the surface adheres continuously and densely to the rough surface of the copper foil, and the polytetrafluoroethylene particles are evenly dispersed. The hydrophobic property of polytetrafluoroethylene has a contact angle of 107° with 2 M zinc sulfate, as Figure 2 shown, which is beneficial to inhibiting the side reaction between zinc metal and water during the subsequent deposition process.

[0080] Figure 3 shows the Coulomb efficiency test of the copper foil current collector covered with the ultrathin hydrophobic film layer prepared in Example 1, and the unmodified commercial copper foil is used for comparison. The half-cell assembled with the copper foil current collector and a zinc sheet has a current density of 1 mA / cm² -2The test was carried out at a current density of [current density value], and the copper foil current collector covered with the ultrathin hydrophobic film layer could cycle more than 700 times.

[0081] Electrochemical deposition of zinc: The copper foil current collector covered with the obtained ultrathin hydrophobic film layer was used as the positive electrode, and the zinc sheet was used as the negative electrode to assemble a battery. At a current density of 0.25 mA / cm -2 It was discharged for 20 h, and a uniform and dense zinc coating was formed on the surface of the current collector to achieve the composite of the current collector and zinc, and an ultrathin composite zinc negative electrode was obtained.

[0082] Figure 4 Figure [figure number] is the SEM picture of the cross-section of the ultrathin composite zinc negative electrode obtained in Example 1. The dense and uniform deposition makes the negative electrode have no obvious dendrites, and at the same time, the overall thickness of the negative electrode is controlled at about 20 μm.

[0083] Figure 5 This is the test of the symmetric battery assembled with the ultrathin composite zinc negative electrode in Example 1 of the present invention. It can cycle ≥1200 h at a current density of 1 mA / cm -2 , showing stable cycling performance. The ultrathin composite zinc negative electrode and the V2O5 positive electrode sheet were assembled into a full battery, and charge-discharge tests were carried out at a current density of 3 A / g. When cycling 2500 times, the capacity retention rate could be maintained at 84%, as shown in Figure 6 shown.

[0084] Figure 7 Figure [figure number] is the deposition morphology of the ultrathin composite zinc negative electrode in Example 1 after cycling 50 times in a symmetric battery. It can be observed that hexagonal zinc metal flakes are uniformly and densely deposited under the hydrophobic protective film layer.

[0085] Example 2

[0086] A parallel experiment similar to Example 1 was carried out. The preparation method was basically the same as that of Example 1, except that: the heating-up time was 110 min, and the heating was started to 550 °C for heat preservation. The obtained modified copper foil current collector was assembled into a half-cell for cyclic stability-Coulomb efficiency test, as shown in Figure 8 shown. It cycled nearly 400 times under the same test conditions, similar to the results in Example 1.

[0087] Example 3

[0088] A parallel experiment similar to Examples 1 and 2 was carried out. The preparation method was basically the same as that of Example 1, except that: during the electrochemical deposition process, it was discharged at a current density of 1 mA / cm -2 for 5 h to achieve the preparation of the ultrathin composite zinc negative electrode, and then it was continuously charged and discharged for 30 min each at a current density of 1 mA / cm -2 to test the cyclic stability, as shown in Figure 9 shown. The cycling duration was close to 1000 h, similar to the results in Example 1.

[0089] Comparative Example 1

[0090] The preparation method is basically the same as that of Example 1, except that: the heating-up time is 80 min, and the heat preservation starts when the temperature is raised to 400 °C.

[0091] Figure 10 It is the SEM image of the surface of the copper foil current collector obtained in Comparative Example 1. As shown in the figure, no film layer formation was observed on the surface of the current collector prepared under this condition, and only the copper particles on the rough surface of the bare copper foil were observed. This may be due to the fact that the temperature did not reach the pyrolysis temperature of polytetrafluoroethylene.

[0092] Figure 11 It is the SEM image of the surface of the ultra-thin composite zinc negative electrode obtained in Comparative Example 1 after 50 cycles. Due to the lack of a hydrophobic protective film layer, the deposited zinc grows perpendicular to the electrode surface, forming zinc dendrites, which is not conducive to the stable cycling of the zinc negative electrode.

[0093] Comparative Example 2

[0094] The preparation method is basically the same as that of Example 1, except that: the heat preservation starts when the temperature is raised to 800 °C.

[0095] Figure 12 It is the SEM image of the surface of the copper foil current collector obtained in Comparative Example 2. As shown in the figure, the film layer on the surface of the copper foil current collector prepared under this condition has undergone severe carbonization, and the presence of polytetrafluoroethylene particles cannot be observed. Moreover, the prepared film layer is not dense and uniform, showing wrinkles and breakages. This is because the higher heating temperature causes all the polytetrafluoroethylene powder to pyrolyze or carbonize, and the higher the temperature, the more severe the carbonization phenomenon. Due to the lack of the hydrophobic property of polytetrafluoroethylene particles, zinc metal is easily corroded by the electrolyte during charge and discharge, and the electrochemical performance shows an obvious decline.

[0096] Figure 13 It is the Coulomb efficiency test chart of the copper foil current collector obtained in Comparative Example 2. Limited by the breakage of the surface film layer, the cycling stability shows an obvious decline.

[0097] The above-mentioned solution of the present invention has the following beneficial effects:

[0098] (1) The above solution of the present invention uses commercial copper foil as the substrate, and prepares a uniform and dense hydrophobic protective film on the surface of the copper foil by the method of high-temperature pyrolysis of polymers. Then, an ultra-thin composite zinc negative electrode with an overall thickness of about 20 μm is obtained by combining the electrochemical deposition method. Under the protection of the hydrophobic film layer, the corrosion of the zinc metal by the zinc sulfate electrolyte is reduced. The zinc ion conduction ability of the film layer enables the zinc deposition to have a bottom-up selectivity, inhibits the growth of dendrites, and achieves the effect of uniform deposition. At the same time, the volume advantage of the ultra-thin composite zinc negative electrode is exerted, the utilization rate of active zinc is increased, and the waste of metal zinc materials is reduced.

[0099] (2) The present invention is beneficial to reducing the cost of the zinc negative electrode and improving the cycle stability of the zinc negative electrode. By combining the zinc negative electrode structure design and the anti-corrosion strategy, the performance of the aqueous zinc ion battery is effectively improved.

[0100] (3) The hydrophobic protective film layer in the present invention has a certain hydrophobic property while maintaining high ionic conductivity. This hydrophobic property is mainly provided by polytetrafluoroethylene particles uniformly distributed on the carbon layer (as Figure 1 shown). During the cycling process, the polytetrafluoroethylene particles can prevent water molecules from approaching the zinc negative electrode side, thereby inhibiting the occurrence of related side reactions (such as hydrogen evolution, etc.).

[0101] (4) The present invention takes the lead in modifying the copper foil current collector, and then obtains a three-layer structure composite zinc negative electrode (copper foil substrate - deposited zinc - protective layer) by electrochemical deposition. The hydrophobic protective film layer does not adopt any coating method, but in a tube furnace under vacuum, polytetrafluoroethylene is evaporated and a protective layer is formed on the copper foil. Its method is vapor deposition, that is, a hydrophobic protective carbon layer is deposited on the surface of the copper foil during the evaporation process, and no chemical reaction occurs with the copper foil.

[0102] (5) In the SEM image of the surface deposition morphology of the ultra-thin composite zinc negative electrode after cycling in the embodiment of the present invention, due to the good conductivity of the copper foil substrate and the high ionic conductivity of the protective film layer, zinc is deposited between the copper foil substrate and the hydrophobic protective film layer. The role of the film layer is to transport ions and inhibit the growth of dendrites. Figure 7 In the SEM image of the surface deposition morphology of the ultra-thin composite zinc negative electrode after cycling in the embodiment of the present invention, due to the good conductivity of the copper foil substrate and the high ionic conductivity of the protective film layer, zinc is deposited between the copper foil substrate and the hydrophobic protective film layer. The role of the film layer is to transport ions and inhibit the growth of dendrites.

[0103] (6) The thickness of the carbon layer with uniformly dispersed polytetrafluoroethylene particles introduced in the present invention is only about 1 μm. And the present invention pays more attention to the regulation of the thickness of the whole negative electrode. The overall thickness of the copper foil substrate, deposited zinc and protective layer will be controlled at about 20 μm (as Figure 4 shown), so as to prepare an ultra-thin composite zinc negative electrode.

[0104] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the present invention, and any modification or partial replacement without departing from the spirit and scope of the present invention shall be covered by the scope of the claims of the present invention.

Claims

1. An ultra-thin composite zinc negative electrode, characterized in that: It includes a copper foil substrate, deposited zinc, and a continuous and dense ultra-thin hydrophobic protective film layer coated on the surface of the copper foil substrate. The ultra-thin hydrophobic protective film layer is mainly a carbon layer with evenly dispersed polytetrafluoroethylene particles. A preparation method of an ultra-thin composite zinc negative electrode, comprising the following steps: S1. Put the copper foil and polytetrafluoroethylene powder into a tube furnace, pyrolyze the polytetrafluoroethylene powder at high temperature, and form an ultra-thin hydrophobic protective film layer on the surface of the copper foil during the cooling process; S2. Clean and dry the copper foil covered with the ultra-thin hydrophobic protective film layer with an organic solvent to obtain a modified ultra-thin current collector; S3. Galvanize the modified ultra-thin current collector by electro-deposition method to obtain a composite zinc negative electrode.

2. The ultrathin composite zinc anode according to claim 1, characterized in that: The average particle size of the polytetrafluoroethylene particles is 100 - 500 nm, the thickness of the carbon layer is 1 μm, and the thickness of the copper foil is 10 μm.

3. An ultra-thin composite zinc anode according to claim 1 or 2, characterized in that: The contact angle between the ultra-thin hydrophobic protective film layer and the electrolyte is 107 °.

4. An ultra-thin composite zinc negative electrode according to claim 1, characterized in that, The specific steps of S1 are as follows: S1.

1. Alternately clean the copper foil with deionized water and absolute ethanol; S1.

2. Take the polytetrafluoroethylene powder, spread it on the bottom of the crucible, then cover the cleaned copper foil on the crucible, and put them into the tube furnace together; S1.

3. Raise the temperature, decompose the polytetrafluoroethylene, keep the temperature, and cool with the furnace; S1.

4. When the tube furnace cools to room temperature, pass argon gas to remove the decomposed tetrafluoroethylene gas, and then take out the copper foil to obtain the copper foil covered with the ultra-thin hydrophobic protective film layer.

5. The ultra-thin composite zinc negative electrode according to claim 4, characterized in that: In S1.2, the dosage of the polytetrafluoroethylene powder is 1 - 5 g, and the particle size of the polytetrafluoroethylene powder is < 1 μm.

6. The ultrathin composite zinc anode according to claim 4, characterized in that: In S1.3, the heating rate is 3 - 10 °C / min, heat up to 500 - 700 °C, and the heat preservation time is 30 - 90 min. In S1.4, the argon gas passing time is 30 min.

7. An ultra-thin composite zinc negative electrode according to claim 1, characterized in that: In S2, the organic solvent is at least one of absolute ethanol and acetone, and the drying conditions are vacuum and the temperature is 50 - 80 °C.

8. An ultra-thin composite zinc negative electrode according to claim 1, characterized in that: In S3, the electrochemically depositing device is one of a button cell and an electrolytic cell, and the current density applied in the electrochemically depositing method is 0.1~5 mAcm -2 , and the time for applying the current is 1~50 h.

9. An application of an ultra-thin composite zinc negative electrode as described in any one of claims 1 to 8, characterized in that: Assemble the composite zinc negative electrode into a symmetric battery or assemble the composite zinc negative electrode and a V2O5 positive electrode into an aqueous zinc ion full battery.

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