Lithophilic three-dimensional porous current collector for lithium batteries, preparation method and application thereof

Abstract

The present invention discloses a lithiumophilic three-dimensional porous current collector for a lithium battery, its preparation method and application. The preparation method includes: cleaning and drying a copper foil, where the copper foil is brass; under light-shielded conditions, immersing the treated copper foil in an AgNO3 solution for reaction, followed by cleaning and drying; placing the treated copper foil into a vacuum tube furnace, introducing an inert gas or a mixed gas of hydrogen and an inert gas, heating at a heating rate of 5 - 30 °C / min to 660 - 900 °C, and holding the temperature; after the reaction is completed, a three-dimensional porous copper foil is obtained, and it is taken out after the temperature in the furnace cools to room temperature; cleaning and drying the three-dimensional porous copper foil, and thus obtaining it. The present invention does not use corrosive reagents, and realizes the synchronous alloying and dealloying of the lithiumophilic material matrix through a green and environmentally friendly dealloying method, achieving a dense combination of silver and the matrix, shortening the preparation process, reducing the preparation cost, and improving the yield rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of anode materials for lithium batteries, and particularly relates to a lithiumophilic three-dimensional porous current collector for lithium batteries, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-ion batteries have high energy density, low self-discharge rate, high voltage and long cycle life, so they are widely used in all walks of life. However, with the rapid development of science and technology, the capacity of lithium-ion batteries has gradually reached the theoretical value. Some researchers have developed many high-capacity materials from the perspective of replacing or improving the anode material to replace the traditional graphite anode with a theoretical capacity of only 372 mAh g -1 Lithium metal has a high theoretical specific capacity of 3860 mAh g -1 and the lowest electrode potential (-3.04V vs. standard hydrogen electrode), so it is considered to be the "holy grail" of the next generation of secondary batteries.

[0003] Lithium metal is highly reactive and will react strongly with the electrolyte to form a solid electrolyte interface film (SEI) on the surface of the metal anode. Due to the large volume change of lithium metal during charge and discharge, the SEI film is easily broken, causing new lithium to be exposed to the electrolyte and generating a new SEI film. The repeated formation of the SEI film results in continuous consumption of the electrolyte and lithium, which will lead to a decrease in the Coulombic efficiency of lithium metal batteries (LMBs) and poor cycle stability. In addition, the uneven deposition and stripping of lithium on the two-dimensional current collector will cause dendrite growth. Especially at high currents, the dendrites may penetrate the separator, resulting in a short circuit between the positive and negative electrodes, causing fire or even explosion.

[0004] By designing a current collector with a high surface area, the local current density on the anode surface can be reduced to inhibit the growth of lithium dendrites. The surface of the current collector is compounded with a lithiumophilic material, which can reduce the energy barrier of lithium nucleation and thus achieve uniform deposition of lithium. Therefore, modifying the current collector plays an important role in improving the performance of lithium batteries. By depositing a lithiumophilic material on the surface of the current collector, lithium can be guided to deposit more uniformly, significantly reducing the growth of lithium dendrites.

[0005] At present, most of the methods for preparing three-dimensional materials focus on chemical dealloying, template method and powder metallurgy method. The chemical dealloying method requires the use of corrosive reagents, and the template method has a low yield and the template is easy to remain. Therefore, both of these two methods are not easy to achieve mass production. The powder metallurgy method is difficult to press ultra-thin materials, so the materials prepared by it are difficult to be applied to lithium batteries. Therefore, it is necessary to prepare three-dimensional structures in a high-yield and environmentally friendly manner and fully modify the current collector by combining with lithiumophilic modification. Summary of the Invention

[0006] To solve the above problems, the present invention provides a method for preparing a lithiumophilic three-dimensional porous current collector for a lithium battery, which does not use corrosive reagents, realizes the simultaneous alloying and dealloying of the lithiumophilic material matrix through a green and environmentally friendly dealloying method, achieves a dense combination of silver and the matrix, shortens the preparation process, reduces the preparation cost, and improves the yield.

[0007] The second object of the present invention is to provide a lithiumophilic three-dimensional porous current collector obtained by the method for preparing a lithiumophilic three-dimensional porous current collector for a lithium battery.

[0008] The third object of the present invention is to provide an application of the method for preparing a lithiumophilic three-dimensional porous current collector for a lithium battery in lithium batteries.

[0009] The technical solution adopted by the present invention is a method for preparing a lithiumophilic three-dimensional porous current collector for a lithium battery, which includes the following steps:

[0010] S1. Clean and dry the copper foil, and the copper foil is brass.

[0011] S2. Under light-shielded conditions, immerse the copper foil treated in S1 into an AgNO3 solution with a concentration of 0.009 - 0.05 mol / L, and react at room temperature (22 - 26°C) for 10 - 60 min, then clean and dry.

[0012] The activities of both zinc and copper in brass are higher than that of silver, so the copper foil can be combined with silver by reacting with the AgNO3 solution. Since the activity of zinc is higher than that of copper, zinc will react with the AgNO3 solution prior to copper, and the uniformity of the zinc distribution will determine the uniformity of silver. And when the content of AgNO3 is too low, the reaction will proceed unevenly, resulting in an uneven distribution of silver elements after the reaction.

[0013] The AgNO3 solution is prone to decomposition when exposed to light, so light needs to be avoided during the reaction. The reaction time should not be too short, as too short a reaction time will result in a low silver content on the copper foil surface, further reducing its lithium affinity for the copper foil. At the same time, the reaction time should not be too long, as too long a reaction time will, on the one hand, lead to the appearance of large-sized silver particles, reducing the uniformity of silver element distribution, and on the other hand, cause excessive consumption of the AgNO3 solution.

[0014] S3. Put the copper foil treated in S2 into a vacuum tube furnace, evacuate the air in the tube, and when the vacuum degree is lower than 1 Pa - 100 Pa, introduce an inert gas or a mixed gas of hydrogen and an inert gas, with a gas flow rate of 150 - 300 ml / min; heat at a heating rate of 5 - 30°C / min to 660 - 900°C, and hold for 10 - 120 min. If the gas flow rate is too low, the evaporated gas is difficult to be exhausted completely, and if it is too high, the cost will increase.

[0015] A three-dimensional structure is formed by utilizing the difference in the saturated vapor pressures of different components of the alloy at high temperatures; at high temperatures and high vacuum degrees, the saturated vapor pressure of zinc is much higher than that of copper. Therefore, dealloying can be carried out by means of vacuum annealing. The removal of zinc will leave vacancies in the original area, and multiple vacancies will be connected to form pores, thereby forming a three-dimensional structure.

[0016] The saturated vapor pressure of the lithium-philic element silver is similar to that of copper. Therefore, it can ensure that the lithium-philic silver element does not lose during the dealloying process. At high temperatures, silver will diffuse into the interior of the alloy to form a copper-silver alloy, and its bonding force is much stronger than the mechanical bonding between silver and the copper foil.

[0017] An air flow is introduced to remove the evaporated gaseous zinc. The speed of the gas flow determines the efficiency of removing gaseous zinc. Therefore, the air flow speed should not be too slow; if the air flow speed is too fast, it will affect the stability of the furnace atmosphere; hydrogen is a reducing gas, which can reduce the oxides in the alloy during annealing and avoid the formation of oxides at high temperatures.

[0018] S4. After the reaction is completed, a three-dimensional porous copper foil is obtained. Close the valve of the vacuum pump, and take it out after the temperature in the furnace cools down to room temperature;

[0019] S5. Clean the three-dimensional porous copper foil and dry it, and it is obtained.

[0020] Furthermore, the S1 includes the following steps:

[0021] S11. Put the copper foil with a thickness of 20 - 40 μm into sulfuric acid with a concentration of 0.1 mol / L - 2.0 mol / L, deionized water, and absolute ethanol in sequence, and ultrasonically clean them for 20 - 60 s respectively; the lower the acid concentration, the slower the surface treatment speed, but too high a concentration will waste sulfuric acid and increase costs. If the ultrasonic time is too short, the cleaning effect cannot be achieved; if the ultrasonic time is too long, the cost will increase.

[0022] S12. Dry the cleaned copper foil in a vacuum drying oven at 60 - 100 °C for 30 - 120 min. After the reaction, a silver-white luster can be observed on the surface of the copper foil.

[0023] Furthermore, the copper foil in the S1 is H62 brass.

[0024] Furthermore, in the S2, after the reaction ends, place the copper foil in absolute ethanol to clean the residual solution on the surface, and after cleaning, vacuum dry it in a vacuum drying oven at 60 - 100 °C for 30 - 120 min.

[0025] Further, in S3, one end of a vacuum tube furnace is connected to a gas cylinder, and the other end is connected to a vacuum pump; the vacuum pump is started to extract the air inside the tube, and the inside of the tube furnace is pumped down to below 1 Pa to 100 Pa, and then the vacuum pump is closed; then an inert gas or a mixed gas of hydrogen and an inert gas is introduced through the gas cylinder, and the inert gas or the mixed gas is closed after the air pressure inside the tube is higher than the standard atmospheric pressure by 100 to 1000 Pa (too high will waste gas and increase costs); the vacuum pump is started again to extract the residual air inside the tube; the operation is continuously repeated to exhaust the air inside the tube. The lower the vacuum degree, the higher the requirements for the equipment. To save costs, it can be controlled within 100 Pa; most existing vacuum pumps can pump down to below 1 Pa.

[0026] Further, in S3, the volume ratio of hydrogen in the mixed gas is 3.5% to 4%; if the volume ratio of hydrogen exceeds 4%, safety accidents such as explosion may be induced, and too little hydrogen is difficult to reduce oxides and it is difficult to ensure that dealloying is carried out in a reducing atmosphere.

[0027] Further, in S5, the steps of cleaning and drying are the same as those in S1.

[0028] A lithiumophilic three-dimensional porous current collector for a lithium battery is prepared by using the above-mentioned preparation method of a lithiumophilic three-dimensional porous current collector for a lithium battery.

[0029] An application of a preparation method of a lithiumophilic three-dimensional porous current collector for a lithium battery in the field of lithium batteries.

[0030] The beneficial effects of the present invention are as follows:

[0031] 1. The present invention performs gas-phase dealloying on brass with a non-dealloying component coating on the surface, utilizes alloy components with a large difference in saturated vapor pressure, and removes the high-saturated vapor pressure components through a vacuum high-temperature environment to realize the dealloying process, so as to prepare a lithiumophilic three-dimensional current collector.

[0032] 2. The present invention synchronizes the brass dealloying process and the lithiumophilic material and matrix alloying process under a single annealing treatment, realizes the dense bonding of silver and the matrix, greatly reduces the complexity of the process, saves time and economic costs, and improves the yield compared with the template method.

[0033] 3. The porous copper foil prepared by the present invention has a strong binding property with the lithiumophilic material on the basis of having a porous structure compared with the copper foil used in commercial lithium batteries, and can regulate the uniform deposition of lithium metal, thereby improving the stability of the lithium metal negative electrode.

[0034] 4. The raw materials used in the present invention can be directly purchased without additional preparation, and the raw material sources are rich; at the same time, by selecting a copper foil with a thickness lower than that of a commercial lithium metal negative electrode as a precursor, the volume energy density can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0036] Figure 1 It is a scanning electron microscope image of H62 commercial brass foil.

[0037] Figure 2 It is a scanning electron microscope image of Example 1, Comparative Example 1 and Comparative Example 2.

[0038] Figure 3 It is a scanning electron microscope image of Examples 2 to 6.

[0039] Figure 4 It is a scanning electron microscope image of Comparative Examples 3 to 13.

[0040] Figure 5 It is a scanning electron microscope image of Example 1 and the distribution maps of copper, zinc and silver elements.

[0041] Figure 6 It is an EDS energy spectrum diagram of the porous copper foils prepared in Example 1 and Comparative Example 2.

[0042] Figure 7 It is the nucleation overpotential diagram of Example 1 and Comparative Example 2.

[0043] Figure 8 It is the long cycle performance diagram of Comparative Example 1 and Comparative Example 2 at a 1C rate.

[0044] Figure 9 It is the long cycle performance diagram of Example 1 at a 1C rate. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0046] Basic concept of the embodiment of the present invention: By utilizing the difference in the saturated vapor pressure of metal components at high temperatures, the components with high saturated vapor pressure are removed. And since the diffusion ability of each component is greatly enhanced at high temperatures, the matrix alloying process formed by the self-diffusion of the lithiophilic element and the matrix alloy is promoted. It should be noted that the dealloying efficiency increases with the increase in temperature, while the porosity does not increase with the increase in temperature. Because the increase in temperature leads to an enhancement in the diffusion ability of each component of the alloy, and the diffusion coefficient of copper changes faster with temperature than that of zinc. At too high temperatures, the effect of pore closure due to copper diffusion will become dominant, resulting in a decrease in porosity. Therefore, the temperature of the dealloying process needs to be strictly controlled. Most of the lithiophilic materials are more reactive than Cu and Zn, such as Mg and Al, so it is difficult to simply obtain them through displacement reactions; Sn has a lower reactivity, but the commercially available reagent is SnCl2 solution, which is easily oxidized by air and difficult to store. Therefore, this reagent is not considered for modification in the embodiment of the present invention; most of the other composite methods require the use of high-end equipment or complex processes, such as laser lithography and ion sputtering, which are costly and have low yields. Or directly add lithiophilic materials during melting. Although this method is relatively simple, it requires the use of expensive precision rollers to achieve, and its cost and process complexity far exceed the method of the embodiment of the present invention.

[0047] Example 1

[0048] A preparation method of a lithiophilic three-dimensional porous current collector for a lithium metal battery, comprising the following steps:

[0049] S1. Clean and dry the copper foil.

[0050] S11. Immerse a copper foil with a thickness of 20 μm in 0.5 mol / L sulfuric acid, deionized water, and absolute ethanol for ultrasonic cleaning for 30 s in sequence to remove surface stains and their oxides. The copper foil is H62 brass foil, see Figure 1 ;

[0051] S12. Place the cleaned copper foil in a vacuum drying oven and dry it at a constant temperature of 100 °C for 1 h.

[0052] S2. Composite the copper foil with the lithiophilic material.

[0053] S21. At room temperature (25 °C), immerse the dried copper foil in 0.01 mol / L AgNO3 solution for reaction for 30 minutes. The reaction container is wrapped with cloth to avoid light shining into the container interior;

[0054] S22. After the reaction ends, place the copper foil in absolute ethanol to wash the residual solution. After gently shaking the absolute ethanol for 20 s, put the copper foil into a vacuum drying oven and keep it at 60 °C for 1 h.

[0055] S3, dealloying and alloying the lithium-philic material with the substrate.

[0056] S31, sandwiching the dried copper foil between two iron nets and placing them in a tubular furnace; first, turning on a vacuum pump to extract the air in the tube, and when the vacuum degree drops below 1.0 Pa, turning off the vacuum pump, and turning on a mixed gas of argon + hydrogen (hydrogen accounts for 4% of the gas volume), so that the pressure of the mixed gas in the tube is 100 Pa higher than the normal atmospheric pressure, turning off the mixed gas, and turning on the vacuum pump again to further extract the residual air in the tube, and repeating the operation for more than two times;

[0057] S32. When the vacuum degree drops to 1.0 Pa, start the mixed gas and control the gas flow rate to 200 mL / min; start the vacuum pump and keep it turned on to maintain a high vacuum environment in the tube;

[0058] S33. Heat the quartz tube to 700°C at a heating rate of 30°C / min and keep it at that temperature for 60 minutes. Since the alloy is in the gas phase when it is released, a condensing device can be added to recover the released components.

[0059] S4. When the tube furnace cools down to room temperature, close the vacuum pump and the mixed gas valve, and take out the copper foil. The surface color of the taken-out copper foil approaches that of pure copper due to the release of zinc element.

[0060] S5. Use 0.5 mol / L sulfuric acid solution, deionized water, and anhydrous ethanol for ultrasonic cleaning in sequence for 20 seconds to remove the residual zinc layer and residual solution on the surface; then use a vacuum drying oven to dry the sample at a temperature of 100°C for 1 hour. After drying, a lithium-philic three-dimensional porous nano-copper current collector can be obtained.

[0061] Example 2

[0062] A method for preparing a lithium-philic three-dimensional porous current collector for a lithium metal battery comprises the following steps:

[0063] S1. Clean and dry the copper foil.

[0064] S11, placing a copper foil with a thickness of 20 μm in 0.1 mol / L sulfuric acid, deionized water, and anhydrous ethanol in turn for ultrasonic cleaning for 60 seconds to remove surface stains and oxides; the copper foil is H62 brass foil;

[0065] S12. Place the cleaned copper foil in a vacuum drying oven and dry it at a constant temperature of 60° C. for 1 h.

[0066] S2. The copper foil is compounded with the lithium-philic material.

[0067] S21. At room temperature (26°C), immerse the dried copper foil in a 0.01 mol / L AgNO3 solution for 40 minutes. Wrap the reaction container with cloth to prevent light from irradiating the inside of the container.

[0068] S22. After the reaction is completed, place the copper foil in anhydrous ethanol to clean the residual solution. After gently shaking the anhydrous ethanol for 20 seconds, place the copper foil in a vacuum drying oven and keep it at 60°C for 1 hour.

[0069] S3, dealloying and alloying the lithium-philic material with the substrate.

[0070] S31, sandwiching the dried copper foil between two iron nets and placing them in a tube furnace, first turning on the vacuum pump to extract the air in the tube, and turning off the vacuum pump when the vacuum degree is as low as 500Pa, and turning on the argon + hydrogen mixed gas (hydrogen accounts for 3.5% of the gas volume), so that the mixed gas pressure in the tube is 1000Pa higher than the normal atmospheric pressure, turning off the mixed gas, and turning on the vacuum pump again to further extract the residual air in the tube;

[0071] S32, when the vacuum degree is as low as 500Pa, start the mixed gas and control the gas flow rate to 300ml / min, while the vacuum pump remains on to maintain a high vacuum environment in the tube;

[0072] S33. Heat the quartz tube to 660°C at a heating rate of 30°C / min and keep it at that temperature for 120 min.

[0073] S4. When the tube furnace cools down to room temperature, close the vacuum pump and the mixed gas valve, and take out the copper foil. The surface color of the taken-out copper foil approaches that of pure copper due to the release of zinc element.

[0074] S5. Use 0.5 mol / L sulfuric acid solution, deionized water, and anhydrous ethanol for ultrasonic cleaning in sequence for 30 seconds to remove the residual zinc layer and residual solution on the surface; then use a vacuum drying oven to dry the sample at a temperature of 60°C for 1 hour. After drying, a lithium-philic three-dimensional porous nano-copper current collector can be obtained.

[0075] Example 3

[0076] A method for preparing a lithium-philic three-dimensional porous current collector for a lithium metal battery comprises the following steps:

[0077] S1. Clean and dry the copper foil.

[0078] S11, placing a copper foil with a thickness of 40 μm in 2 mol / L sulfuric acid, deionized water, and anhydrous ethanol for ultrasonic cleaning for 20 seconds to remove surface stains and oxides; the copper foil is H62 brass foil;

[0079] S12. Place the cleaned copper foil in a vacuum drying oven and dry it at a constant temperature of 60°C for 1 h.

[0080] S2. Composite the copper foil with a lithiumophilic material.

[0081] S21. At room temperature (22°C), immerse the dried copper foil in a 0.01 mol / L AgNO3 solution and react for 60 minutes. Wrap the reaction vessel with cloth to prevent light from shining inside the vessel.

[0082] S22. After the reaction ends, place the copper foil in absolute ethanol to wash the residual solution. Gently shake the absolute ethanol for 20 seconds and then put the copper foil into a vacuum drying oven and keep it at 60°C for 1 h.

[0083] S3. Perform dealloying and alloying of the lithiumophilic material with the matrix.

[0084] S31. Clamp the dried copper foil between two iron meshes and put it into a tube furnace. First, turn on the vacuum pump to extract the air inside the tube. When the vacuum degree is reduced to 100 Pa, turn off the vacuum pump and turn on the argon gas. After the argon gas pressure inside the tube is 500 Pa higher than the normal atmospheric pressure, turn off the argon gas and turn on the vacuum pump again to further extract the residual air inside the tube.

[0085] S32. When the vacuum degree is reduced to 100 Pa, turn on the argon gas and control the gas flow rate to 300 ml / min. At the same time, keep the vacuum pump on to maintain a high-vacuum environment inside the tube.

[0086] S33. Heat the temperature of the quartz tube to 700°C at a heating rate of 5°C / min and keep it for 120 min.

[0087] S4. When the tube furnace cools down to room temperature, turn off the vacuum pump and the mixed gas valve, and take out the copper foil. The color of the taken-out copper foil approaches that of pure copper due to the removal of zinc elements.

[0088] S5. Ultrasonically clean with 0.5 mol / L sulfuric acid solution, deionized water, and absolute ethanol in sequence for about 30 s to remove the residual zinc layer and residual solution on the surface; then use a vacuum drying oven to dry the sample at a drying temperature of 60°C for 1 h. After drying, a lithiumophilic three-dimensional porous nano copper current collector can be obtained.

[0089] Example 4

[0090] A preparation method of a lithiumophilic three-dimensional porous current collector for a lithium metal battery, comprising the following steps:

[0091] S1. Clean and dry the copper foil.

[0092] S11. Place a copper foil with a thickness of 30 μm into 0.5 mol / L sulfuric acid, deionized water, and absolute ethanol successively, and ultrasonically clean it for 30 s to remove surface stains and their oxides. The copper foil is an H62 brass foil.

[0093] S12. Place the cleaned brass foil in a vacuum drying oven and dry it at a constant temperature of 70 °C for 60 min.

[0094] S2. Composite the copper foil with a lithiumophilic material.

[0095] S21. At room temperature (25 °C), immerse the dried copper foil in a 0.01 mol / L AgNO3 solution and react for 20 minutes. Wrap the reaction vessel with cloth to prevent light from shining inside the container.

[0096] S22. After the reaction ends, place the copper foil in absolute ethanol to wash the residual solution. After gently shaking the absolute ethanol for 20 seconds, put the copper foil into a vacuum drying oven and keep it at 70 °C for 60 min.

[0097] S3. Perform dealloying and alloying of the lithiumophilic material with the matrix.

[0098] S31. Clamp the dried copper foil between two pieces of iron mesh and place it in a tube furnace. First, turn on the vacuum pump to extract the air inside the tube. When the vacuum degree is as low as 1.0 Pa, turn off the vacuum pump, and turn on the mixed gas of argon + hydrogen (hydrogen accounts for 4% of the gas volume) to make the pressure of the mixed gas inside the tube slightly higher than the normal atmospheric pressure, then turn off the mixed gas, and turn on the vacuum pump again to further extract the residual air inside the tube. Repeat the operation more than twice.

[0099] S32. When the vacuum degree is as low as 1.0 Pa, turn on the mixed gas and control the gas flow rate at 200 ml / min. At the same time, keep the vacuum pump turned on to maintain a high-vacuum environment inside the tube.

[0100] S33. Heat the temperature of the quartz tube to 800 °C at a heating rate of 10 °C / min and keep it for 30 min.

[0101] S4. When the tube furnace cools to room temperature, turn off the vacuum pump and the mixed gas valve, and take out the copper foil. The color of the taken-out copper foil approaches that of pure copper due to the removal of zinc elements.

[0102] S5. Use 0.5 mol / L sulfuric acid solution, deionized water, and absolute ethanol for ultrasonic cleaning, and the cleaning duration is about 20 s to remove the residual zinc layer and residual solution on the surface. Then use a vacuum drying oven to dry the sample. The drying temperature is 70 °C and the duration is 60 min. After drying, the lithiumophilic three-dimensional porous nano copper current collector can be obtained.

[0103] Example 5

[0104] The differences from Example 4 are as follows:

[0105] In S12, it is dried at a constant temperature of 60 °C for 120 min;

[0106] In S21, the concentration of the AgNO3 solution is 0.009 mol / L; the reaction time is 10 min;

[0107] In S22, it is dried in a vacuum drying oven at 60 °C for 120 min;

[0108] In S32, the gas flow rate is controlled to be 150 ml / min;

[0109] In S33, the temperature is heated to 700 °C at a heating rate of 5 °C / min and kept for 120 min;

[0110] In S5, the drying temperature is 60 °C and the duration is 120 min.

[0111] The remaining steps are the same as those in Example 4.

[0112] Example 6

[0113] The differences from Example 4 are as follows:

[0114] In S12, it is dried at a constant temperature of 100 °C for 30 min;

[0115] In S21, the concentration of the AgNO3 solution is 0.05 mol / L; the reaction time is 60 min;

[0116] In S22, it is dried in a vacuum drying oven at 100 °C for 30 min;

[0117] In S32, the gas flow rate is controlled to be 250 ml / min;

[0118] In S33, the temperature of the quartz tube is heated to 900 °C at a heating rate of 30 °C / min and kept for 10 min;

[0119] In S5, the drying temperature is 100 °C and the duration is 30 min.

[0120] The remaining steps are the same as those in Example 4.

[0121] Comparative Example 1

[0122] S2 treatment is not carried out, and the remaining steps are the same as those in Example 1.

[0123] Comparative Example 2

[0124] S3 and S4 treatments are not carried out, and the remaining steps are the same as those in Example 1.

[0125] Comparative Example 3

[0126] The difference from Example 4 is that in S1, it is dried at a constant temperature of 30°C; the remaining steps are the same as those in Example 4.

[0127] Comparative Example 4

[0128] The difference from Example 4 is that in S12, it is dried at a constant temperature for 140 min; the remaining steps are the same as those in Example 4.

[0129] Comparative Example 5

[0130] The difference from Example 4 is that in S21, the reaction time is 8 min; the remaining steps are the same as those in Example 4.

[0131] Comparative Example 6

[0132] The difference from Example 4 is that in S21, the reaction time is 70 min; the remaining steps are the same as those in Example 4.

[0133] Comparative Example 7

[0134] The difference from Example 4 is that in S32, the gas flow rate is controlled at 100 ml / min; the remaining steps are the same as those in Example 4.

[0135] Comparative Example 8

[0136] The difference from Example 4 is that in S3, the gas flow rate is controlled at 500 ml / min; the remaining steps are the same as those in Example 4.

[0137] Comparative Example 9

[0138] The difference from Example 4 is that in S3, the heating rate is 35°C / min; the remaining steps are the same as those in Example 4.

[0139] Comparative Example 10

[0140] The difference from Example 4 is that in S3, the heating temperature is 650°C; the remaining steps are the same as those in Example 4.

[0141] Comparative Example 11

[0142] The difference from Example 4 is that in S3, the heating temperature is 950°C; the remaining steps are the same as those in Example 4.

[0143] Comparative Example 12

[0144] Except that the copper foil in S1 is H68 brass foil; the remaining steps are the same as those in Example 4.

[0145] Comparative Example 13

[0146] Except that the thickness of the copper foil in S1 is 100 μm; the remaining steps are the same as those in Example 4.

[0147] As Figure 2 shown, the products prepared in Example 1, Comparative Example 1, and Comparative Example 2 were subjected to morphological analysis under a scanning electron microscope. It can be seen that in Comparative Example 1, the reaction with silver nitrate was not carried out, and there were relatively uniformly distributed gully pores on its surface. The width of the gullies was about 1 μm. Its morphology was similar to that of Example 1, but the gully length in Example 1 was shorter, and circular pores about 1 μm in length of dendrites were evenly distributed. This was mainly because the presence of silver would reduce the area of dealloying to a certain extent, so the gully length in Example 1 was smaller. Both Example 1 and Comparative Example 1 had a porous morphology on the surface, indicating that the sample with composite silver would not prevent the appearance of the porous morphology due to the presence of silver particles on the surface. Due to the influence of the increased element diffusion rate brought about by high temperature, the surface silver particles would be more likely to diffuse into the matrix and undergo alloying. Therefore, there were no large amounts of white particles on the surface morphology of Example 1.

[0148] In Comparative Example 2, it can be seen that silver was distributed in a granular form and evenly. The dealloying in Example 1 was carried out on the basis of Comparative Example 2. Therefore, the silver on the porous copper surface prepared in Example 1 based on Comparative Example 2 could also be evenly distributed. The main purpose of setting Comparative Example 2 was to observe the distribution of silver and further illustrate the rationality of the silver nitrate concentration and reaction time in steps S1 - S2.

[0149] From Figure 5 it can be known that the distribution of silver elements on the surface was very uniform under annealing treatment, and due to the diffusion of silver into the alloy interior, so Figure 6 the intensity of the silver phase peak detected by XRD in Example 1 was lower than that in Comparative Example 2.

[0150] Taking Example 1 and Comparative Example 2 as current collectors and lithium sheets as reference electrodes, half-cells were assembled and subjected to repeated lithium deposition and stripping experiments under the conditions of a current density of 1 mA / cm 2 and a specific capacity of 1 mAh / cm 2 ; One side of the prepared three-dimensional current collector was compounded with molten lithium at 300 °C to prepare a composite electrode, and then the composite electrode was assembled with lithium iron phosphate (LFP) into a full cell and subjected to long-term cycling tests at a 1C rate.

[0151] The first-cycle discharge curve and nucleation overpotential of the half-cell were as Figure 7 shown. The nucleation overpotential of Example 1 with the addition of the lithiumophilic element silver was 40.6 mV, much lower than 124.1 mV of Comparative Example 2. A lower nucleation overpotential means that lithium metal is more likely to be uniformly deposited on the surface of the current collector, thus helping to reduce the formation of lithium dendrites.

[0152] The long-term cycling diagram of the full cell was as Figure 8 and Figure 9 shown; Figure 8 and Figure 9Among them, due to the addition of the lithiophilic element silver, both Example 1 and Comparative Example 2 have relatively high cycle capacities. However, in Comparative Example 2, silver is combined with the matrix by physical bonds, and the binding force is weak. Therefore, silver is likely to detach from the matrix during the cycling process, thereby reducing the enhancement of the lithiophilic effect of silver on the matrix. In Example 1, silver is alloyed with the matrix. Therefore, a capacity retention rate of 90% can still be achieved under a long cycle of 400 cycles.

[0153] Figure 3 Samples prepared in Examples 2-6 are shown. The three-dimensional structure construction of copper foil and alloying with lithium can be achieved within a given range, but the surface morphologies under different processes have their own characteristics. The sample in Example 2 is prepared by long-term dealloying at a relatively low temperature. The surface holes are interconnected and mainly in the shape of gullies. This is because the dealloying energy provided by the low temperature is limited, and the number of pore-forming sites is much less than that at high temperature. Therefore, zinc elements will preferentially de-alloy in regions with high defect energy such as grain boundaries and scratches. And due to the formation of a concentration gradient between the grain boundary and the grain interior as the zinc concentration decreases at the grain boundary, since the zinc concentration in the grain interior is higher than that at the grain boundary, the zinc in the grain interior will diffuse towards the low-concentration regions such as the grain boundary. Since the diffusion and removal of zinc continuously occur in regions with high defect energy, the pores will gradually increase. Moreover, the grain boundary scratches and other defects are one or more lines on the surface. Therefore, dealloying occurs along the entire "line" to form gullies.

[0154] In Example 3, the reaction time in Step S2 is longer, and the silver content on the copper foil surface is relatively high. Therefore, there are still some unalloyed silver particles after heat treatment. Therefore, obvious white silver particles can be seen in the SEM image. In order to ensure that there is sufficient silver alloyed with the current collector to improve the lithiophilic performance of the current collector, it is necessary to appropriately extend the reaction time of the copper foil with silver nitrate. At a reaction time of 60 min, the silver particle sizes on the surface of the three-dimensional current collector are similar and evenly distributed. Therefore, it will not affect the performance of the current collector, and there are fewer residual particles on the surface, resulting in less waste of silver. Therefore, 60 min is a relatively reasonable range.

[0155] The morphology of Example 4 is similar to that of Example 5, mainly because the temperature adopted in Example 4 is higher, so the dealloying speed is faster, and the effect of 700℃ insulation for 2h in Example 5 can be achieved in 30min. The temperature adopted in Example 6 is the highest, and the dealloying speed is very fast, so a large number of holes can be generated in 10min, and because the ability of zinc atoms to overcome the constraints of surrounding atoms is enhanced at high temperature, a large area of dealloying can appear on the surface of the sample, resulting in the appearance of holes with a diameter of 100~300nm in Example 6. The number of nanoscale holes is huge and uniformly dense, which can achieve the purpose of increasing the specific surface area of the three-dimensional current collector and meet the requirements of the three-dimensional current collector. It can be found from the morphology of the high-temperature sample that the position of the hole is everywhere. This is mainly because the high temperature can provide a lot of energy, so the zinc release no longer depends on the defect energy, so the holes on the sample surface are also very dense, and because zinc does not need to diffuse to the area with high defect energy to directly dealloy, the holes formed will also be smaller.

[0156] Figure 4 In the comparative example 3, due to the low drying temperature, some liquid left over from washing the sample still remained on the surface of the copper foil during the heat treatment, so the degree of dealloying of the prepared samples was significantly different. The comparative example 4 took a longer drying time, so the surface state of the sample was better and the color was more uniform, but it was meaningless to continue to keep the sample warm for a long time after drying. Considering the economy, it is not recommended to dry for too long.

[0157] In Comparative Example 5, the sample reacts with silver nitrate for a short time, so the silver particles on the surface of the sample are extremely scarce. In Comparative Example 6, on the contrary, the long reaction with silver nitrate causes the silver particles to grow irregularly, and the surface is covered with a large amount of silver that is difficult to alloy. However, too much silver cannot be alloyed with the copper matrix, which will cause a waste of silver nitrate.

[0158] The slower gas flow rate in Comparative Example 7 makes it difficult to remove the evaporated zinc, so the pores of the sample after the heat treatment are very shallow. Although the excessively fast gas flow rate in Comparative Example 8 can achieve the purpose of removing zinc, it will also cause waste of inert gas, so a too fast gas flow rate is not recommended.

[0159] Comparative Example 9 adopts a faster heating rate, which can achieve the purpose of heat treatment, but the requirements for equipment will be higher, which will increase the cost of material preparation. The heat treatment temperature in Comparative Example 10 is relatively low, and a lower heat treatment temperature will lead to a decrease in the dealloying speed, reduce production efficiency, and the holes formed by short-term dealloying at low temperature are very sparse and shallow.

[0160] Comparative Example 11 adopted an excessively high dealloying temperature, which would lead to a very rapid removal of zinc. When the zinc content decreased, the pore formation rate of the copper foil would gradually be lower than the pore closing rate caused by copper diffusion, and the pores began to close. In Comparative Example 12, due to the lower zinc content of the H68 brass foil, the number of pores formed would also be lower; the H65 and H68 brass foils had less Zn content, so fewer pores could be formed. In Comparative Example 13, an overly thick copper foil was used. Although this had no impact on the preparation of three-dimensional porous copper, copper did not provide energy in the battery. Therefore, the overly thick copper current collector would reduce the energy density of the battery, so an overly thick copper foil was not recommended.

[0161] Each embodiment in this specification is described in a related manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and reference can be made to the relevant part of the method embodiment for the relevant content.

[0162] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A preparation method of a lithiumophilic three-dimensional porous current collector for a lithium battery, characterized in that, It includes the following steps: S1. Clean and dry the copper foil, and the copper foil is brass; S2. Under light-shielded conditions, immerse the copper foil treated in S1 into an AgNO3 solution with a concentration of 0.009 - 0.05 mol / L for 10 - 60 min, then clean and dry it; S3. Put the copper foil treated in S2 into a vacuum tube furnace, evacuate the air in the tube. When the vacuum degree is lower than 100 Pa, introduce an inert gas or a mixed gas of hydrogen and an inert gas, and the gas flow rate is 150 - 300 ml / min; heat it at a heating rate of 5 - 30 °C / min to 660 - 900 °C, and keep it warm for 10 - 60 min; S4. After the reaction is completed, obtain a three-dimensional porous copper foil, and take it out after the temperature in the furnace cools down to room temperature; S5. Clean and dry the three-dimensional porous copper foil, and that's it; The S1 includes the following steps: S11. Put the copper foil with a thickness of 20 - 40 μm into sulfuric acid with a concentration of 0.1 mol / L - 2.0 mol / L, deionized water, and absolute ethanol respectively, and ultrasonically clean it for 20 - 60 s; S12. Dry the cleaned copper foil in a vacuum drying oven at 60 - 100 °C for 30 - 120 min.

2. The preparation method of a lithiumophilic three-dimensional porous current collector for a lithium battery according to claim 1, wherein, The copper foil in S1 is H62 brass.

3. The preparation method of a lithiumophilic three-dimensional porous current collector for a lithium battery according to claim 1, characterized in that, In S2, after the reaction ends, place the copper foil in absolute ethanol for cleaning, and after cleaning, vacuum dry it in a vacuum drying oven at 60 - 100 °C for 30 - 120 min.

4. The preparation method of a lithiumophilic three-dimensional porous current collector for a lithium battery according to claim 1, characterized in that, In S3, one end of the vacuum tube furnace is connected to a gas bottle, and the other end is connected to a vacuum pump; start the vacuum pump to extract the air in the tube, pump the inside of the tube furnace to below 100 Pa, and then close the vacuum pump; then introduce an inert gas or a mixed gas of hydrogen and an inert gas through the gas bottle, close it after the pressure of the inert gas or the mixed gas in the tube is higher than the standard atmospheric pressure, and then start the vacuum pump again to extract the residual air in the tube; continuously repeat the operation to evacuate the air in the tube.

5. The preparation method of a lithiumophilic three-dimensional porous current collector for a lithium battery according to claim 1, characterized in that, In S3, the volume ratio of hydrogen in the mixed gas to the overall mixed gas is 3.5% - 4%.

6. The preparation method of a lithiumophilic three-dimensional porous current collector for a lithium battery according to claim 1, characterized in that, In S5, the steps of cleaning and drying are the same as those in S1.

7. A lithiumophilic three-dimensional porous current collector for a lithium battery, characterized in that, It is prepared by using the preparation method of a lithiumophilic three-dimensional porous current collector for a lithium battery described in any one of claims 1 - 6.

8. Application of the preparation method of a lithiumophilic three-dimensional porous current collector for a lithium battery described in claim 1 in lithium batteries.

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