Lithium-philic three-dimensional porous current collector for lithium battery as well as preparation method and application of lithium-philic three-dimensional porous current collector

Abstract

The invention discloses a lithium-loving three-dimensional porous current collector for a lithium battery and a preparation method and application of the lithium-loving three-dimensional porous current collector, and the preparation method comprises the following steps: cleaning and drying a copper foil which is brass; under a dark condition, immersing the treated copper foil into an AgNO3 solution for reaction, cleaning and drying; putting the treated copper foil into a vacuum tube furnace, introducing inert gas or mixed gas of hydrogen and inert gas, heating to 660-900 DEG C at the heating rate of 5-30 DEG C / min, and preserving heat; after the reaction is completed, obtaining a three-dimensional porous copper foil, and taking out the three-dimensional porous copper foil after the temperature in the furnace is cooled to room temperature; and cleaning the three-dimensional porous copper foil and drying to obtain the three-dimensional porous copper According to the method, corrosive reagents are not used, synchronous alloying and dealloying of the lithium-loving material matrix are achieved in a green and environment-friendly dealloying mode, dense combination of silver and the matrix is achieved, the preparation process is shortened, the preparation cost is reduced, and the yield is increased.

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 The lithium metal has a high theoretical specific capacity of 3860 mAh g -1 and the lowest electrode potential (-3.04 V vs. standard hydrogen electrode), so it is considered the "Holy Grail" of the next-generation secondary batteries.

[0003] Lithium metal has high reactivity 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, making the new lithium exposed to the electrolyte and generating a new SEI film. The repeated formation of the SEI film leads to continuous consumption of the electrolyte and lithium, which will result in a decrease in the Coulombic efficiency and poor cycle stability of lithium metal batteries (LMBs). In addition, the uneven deposition and stripping of lithium on the two-dimensional current collector will lead to dendrite growth. Especially at high currents, the dendrites may penetrate the separator, causing a short circuit between the positive and negative electrodes, leading to 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 to reduce the energy barrier of lithium nucleation, thereby realizing 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] Currently, most methods for preparing three-dimensional materials focus on chemical dealloying, template methods, and powder metallurgy methods. 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, so these two methods are not easy to realize 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 a three-dimensional structure in a way with high yield and environmental friendliness 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 preparation method for a lithiumophilic three-dimensional porous current collector for lithium batteries, 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 preparation method for a lithiumophilic three-dimensional porous current collector for lithium batteries.

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

[0009] The technical solution adopted by the present invention is a preparation method for a lithiumophilic three-dimensional porous current collector for lithium batteries, which 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 a AgNO 3 solution with a concentration of 0.009~0.05mol / L, react at room temperature (22-26°C) for 10~60min, and then clean and dry; 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 AgNO 3 solution. Since the activity of zinc is higher than that of copper, zinc will react with the AgNO 3 solution prior to copper. The uniformity of zinc distribution will determine the uniformity of silver, and when the content of AgNO 3 is too low, the reaction will proceed unevenly, resulting in uneven distribution of silver elements after the reaction.

[0010] The AgNO 3 solution is prone to decomposition when exposed to light, so light needs to be avoided during the reaction. The reaction duration should not be too short, as too short a reaction duration will result in a low silver content on the surface of the copper foil, further reducing its lithiumophilicity to the copper foil; at the same time, the reaction duration should not be too long, as too long a reaction duration 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, will cause excessive consumption of the AgNO 3 solution.

[0011] S3. Place 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 1Pa~100Pa, introduce an inert gas or a mixed gas of hydrogen and an inert gas, with a gas flow rate of 150~300ml / min; heat at a heating rate of 5~30°C / min to 660~900°C, and keep warm for 10~120min; 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.

[0012] A three-dimensional structure is formed by utilizing the differences 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. When zinc is removed, vacancies will be left in the original area, and multiple vacancies are connected to form pores, thereby forming a three-dimensional structure.

[0013] 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 flow away 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 copper foil.

[0014] An air flow is introduced to remove the evaporated gaseous zinc. The flow rate of the gas determines the efficiency of removing gaseous zinc. Therefore, the air flow rate should not be too slow; if the air flow rate 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.

[0015] S4. After the reaction is completed, a three-dimensional porous copper foil is obtained. Close the vacuum pump valve, and take it out after the temperature in the furnace has cooled to room temperature. S5. Clean the three-dimensional porous copper foil and dry it, and it is obtained.

[0016] Furthermore, 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; 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.

[0017] 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.

[0018] Furthermore, the copper foil in the S1 is H62 brass.

[0019] 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.

[0020] Further, in S3, one end of the 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, then the vacuum pump is closed; then an inert gas or a mixed gas of hydrogen and 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.

[0021] 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.

[0022] Further, in S5, the steps of cleaning and drying are the same as those in S1.

[0023] 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.

[0024] Application of a preparation method of a lithiumophilic three-dimensional porous current collector for a lithium battery in lithium batteries.

[0025] The beneficial effects of the present invention are as follows: 1. The present invention performs gas-phase dealloying on brass with a non-dealloying component coating on the surface, and utilizes alloy components with a large difference in saturated vapor pressure. The component with a high saturated vapor pressure is removed through a vacuum high-temperature environment to realize the dealloying process, so as to prepare a lithiumophilic three-dimensional current collector.

[0026] 2. The present invention synchronizes the brass dealloying process and the process of alloying the lithiumophilic material with the matrix alloy during a single annealing treatment, realizes the dense combination 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.

[0027] 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.

[0028] 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 the precursor, the volume energy density can be improved. Description of the Drawings

[0029] 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 accompanying drawings required in the description of the embodiments or the prior art. Obviously, the accompanying 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 accompanying drawings can be obtained based on these drawings.

[0030] Figure 1 It is a scanning electron microscope image of H62 commercial brass foil.

[0031] Figure 2 It is a scanning electron microscope image of Example 1, Comparative Example 1 and Comparative Example 2.

[0032] Figure 3 It is a scanning electron microscope image of Examples 2 to 6.

[0033] Figure 4 It is a scanning electron microscope image of Comparative Examples 3 to 13.

[0034] Figure 5 It is a scanning electron microscope image of Example 1 and the distribution maps of copper, zinc and silver elements.

[0035] Figure 6 It is an EDS energy spectrum diagram of the porous copper foils prepared in Example 1 and Comparative Example 2.

[0036] Figure 7 It is the nucleation overpotential diagram of Example 1 and Comparative Example 2.

[0037] Figure 8 It is the long cycle performance diagram of Comparative Example 1 and Comparative Example 2 at a 1C rate.

[0038] Figure 9 It is the long cycle performance diagram of Example 1 at a 1C rate. Specific Embodiments

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying 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.

[0040] Basic concept of the embodiment of the present invention: Utilize the difference in the saturated vapor pressure of metal components at high temperatures to remove components with high saturated vapor pressure. And since the diffusion ability of each component is greatly enhanced at high temperatures, it promotes the matrix alloying process formed by the self-diffusion of the lithiumophilic element and the matrix alloy. 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 the enhancement of the diffusion ability of each component of the alloy, and the diffusion coefficient of copper element changes faster with temperature than that of zinc element. At too high temperatures, the effect of pore closure caused by copper diffusion will be dominant, resulting in a decrease in porosity. Therefore, the temperature of the dealloying process needs to be strictly controlled. Most of the lithiumophilic materials are more active than Cu and Zn, such as Mg, Al, so it is difficult to simply obtain them through substitution reactions; Sn has a lower activity, but the commercially available reagent is SnCl 2 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, with high costs and low yields. Or directly add lithiumophilic materials during melting. Although this method is relatively simple, it requires a high-price precision roller machine to achieve, and its cost and process complexity far exceed the method of the embodiment of the present invention.

[0041] Example 1 A preparation method of a lithiumophilic three-dimensional porous current collector for lithium metal batteries, comprising the following steps: S1. Clean and dry the copper foil.

[0042] 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 ; S12. Place the cleaned copper foil in a vacuum drying oven and dry it at a constant temperature of 100 °C for 1 h.

[0043] S2. Composite the copper foil with the lithiumophilic material.

[0044] S21. At room temperature (25 °C), immerse the dried copper foil in 0.01 mol / L AgNO 3 solution for reaction for 30 minutes. The reaction vessel is wrapped with cloth to avoid light irradiation into the interior of the vessel; 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.

[0045] S3. Perform dealloying and alloying of the lithiumophilic material and the matrix.

[0046] 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; 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; 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.

[0047] S4. When the tube furnace is cooled to room temperature, the vacuum pump and the mixed gas valve are closed, and the copper foil is taken out. The surface color of the taken out copper foil is close to pure copper due to the release of zinc element.

[0048] 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.

[0049] Example 2 A method for preparing a lithium-philic three-dimensional porous current collector for a lithium metal battery comprises the following steps: S1. Clean and dry the copper foil.

[0050] 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; S12. Place the cleaned copper foil in a vacuum drying oven and dry at a constant temperature of 60° C. for 1 h.

[0051] S2. The copper foil is compounded with the lithium-philic material.

[0052] S21. At room temperature (26°C), immerse the dried copper foil in 0.01 mol / L AgNO 3 The solution was reacted for 40 min, and the reaction container was wrapped with cloth to prevent light from irradiating the inside of the container; 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.

[0053] S3, dealloying and alloying the lithium-philic material with the substrate.

[0054] 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; 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; 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.

[0055] S4. When the tube furnace is cooled to room temperature, the vacuum pump and the mixed gas valve are closed, and the copper foil is taken out. The surface color of the taken out copper foil is close to pure copper due to the release of zinc element.

[0056] 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.

[0057] Example 3 A method for preparing a lithium-philic three-dimensional porous current collector for a lithium metal battery comprises the following steps: S1. Clean and dry the copper foil.

[0058] 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; S12. Place the cleaned copper foil in a vacuum drying oven and dry at a constant temperature of 60° C. for 1 h.

[0059] S2. The copper foil is compounded with the lithium-philic material.

[0060] S21. At room temperature (22°C), immerse the dried copper foil in 0.01 mol / L AgNO 3 The reaction was allowed to proceed in the solution for 60 min, and the reaction vessel was wrapped with cloth to prevent light from irradiating the interior of the vessel; 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.

[0061] S3, dealloying and alloying the lithium-philic material with the substrate.

[0062] S31, sandwiching the dried copper foil between two iron nets and placing them in a tube furnace, first turning on a vacuum pump to extract the air in the tube, and turning on the argon gas when the vacuum degree is as low as 100Pa, turning off the vacuum pump, and turning on the argon gas to make the argon gas pressure in the tube higher than the normal atmospheric pressure by 500Pa, turning off the argon gas, and turning on the vacuum pump again to further extract the residual air in the tube; S32, when the vacuum degree is as low as 100Pa, turn on the argon gas and control the gas flow rate to 300ml / min, while keeping the vacuum pump turned on to maintain a high vacuum environment in the tube; S33. Heat the quartz tube to 700°C at a heating rate of 5°C / min and keep it at that temperature for 120 min.

[0063] S4. When the tube furnace is cooled to room temperature, the vacuum pump and the mixed gas valve are closed, and the copper foil is taken out. The surface color of the taken out copper foil is close to pure copper due to the release of zinc element.

[0064] S5. Use 0.5 mol / L sulfuric acid solution, deionized water, and anhydrous ethanol for ultrasonic cleaning in sequence for about 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.

[0065] Example 4 A method for preparing a lithium-philic three-dimensional porous current collector for a lithium metal battery comprises the following steps: S1. Clean and dry the copper foil.

[0066] S11, placing a copper foil with a thickness of 30 μm in 0.5 mol / L sulfuric acid, deionized water, and anhydrous ethanol in turn for ultrasonic cleaning for 30 seconds to remove surface stains and oxides; the copper foil is H62 brass foil; S12. Place the cleaned brass foil in a vacuum drying oven and dry at a constant temperature of 70° C. for 60 min.

[0067] S2. The copper foil is compounded with the lithium-philic material.

[0068] S21. At room temperature (25°C), immerse the dried copper foil in 0.01 mol / L AgNO 3 The solution was reacted for 20 min, and the reaction container was wrapped with cloth to prevent light from irradiating the inside of the container; S22. After the reaction is completed, the copper foil is placed in anhydrous ethanol to clean the residual solution. After gently shaking the anhydrous ethanol for 20 seconds, the copper foil is placed in a vacuum drying oven and kept at 70° C. for 60 minutes.

[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 when the vacuum degree is as low as 1.0 Pa, turning off the vacuum pump, and turning on the argon + hydrogen mixed gas (hydrogen accounts for 4% of the gas volume), turning off the mixed gas after the pressure of the mixed gas in the tube is slightly higher than the normal atmospheric pressure, 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; S32, when the vacuum degree is as low as 1.0Pa, start the mixed gas and control the gas flow rate to 200ml / min, while keeping the vacuum pump turned on to maintain a high vacuum environment in the tube; S33. Heat the quartz tube to 800°C at a heating rate of 10°C / min and keep it at that temperature for 30 minutes.

[0071] S4. When the tube furnace is cooled to room temperature, the vacuum pump and the mixed gas valve are closed, and the copper foil is taken out. The surface color of the taken out copper foil is close to pure copper due to the release of zinc element.

[0072] S5. Use 0.5 mol / L sulfuric acid solution, deionized water, and anhydrous ethanol for ultrasonic cleaning for about 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 70°C for 60 minutes. After drying, a lithium-philic three-dimensional porous nano-copper current collector can be obtained.

[0073] Example 5 The difference from Example 4 is: In S12, the mixture was dried at 60°C for 120 min; In S21, AgNO 3 The solution concentration is 0.009 mol / L; the reaction time is 10 min; In S22, the mixture was dried in a vacuum oven at 60°C for 120 min; In S32, the gas flow rate is controlled to be 150 ml / min; In S33, the temperature is heated to 700°C at a heating rate of 5°C / min and kept at that temperature for 120 min; In S5, the drying temperature is 60°C and the drying time is 120 min.

[0074] The remaining steps are the same as those in Example 4.

[0075] Example 6 The difference from Example 4 is as follows: In S12, it is dried at a constant temperature of 100 °C for 30 min; In S21, the concentration of the AgNO 3 solution is 0.05 mol / L; the reaction time is 60 min; In S22, it is dried in a vacuum drying oven at 100 °C for 30 min; In S32, the gas flow rate is controlled at 250 ml / min; In S33, the temperature of the quartz tube is heated to 900 °C at a heating rate of 30 °C / min and held for 10 min; In S5, the drying temperature is 100 °C and the duration is 30 min.

[0076] The remaining steps are the same as those in Example 4.

[0077] Comparative Example 1 S2 treatment is not carried out, and the remaining steps are the same as those in Example 1.

[0078] Comparative Example 2 S3 and S4 treatments are not carried out, and the remaining steps are the same as those in Example 1.

[0079] Comparative Example 3 The difference from Example 4 is: in S1, it is dried at a constant temperature of 30 °C; the remaining steps are the same as those in Example 4.

[0080] Comparative Example 4 The difference from Example 4 is: in S12, it is dried at a constant temperature for 140 min; the remaining steps are the same as those in Example 4.

[0081] Comparative Example 5 The difference from Example 4 is: in S21, the reaction time is 8 min; the remaining steps are the same as those in Example 4.

[0082] Comparative Example 6 The difference from Example 4 is: in S21, the reaction time is 70 min; the remaining steps are the same as those in Example 4.

[0083] Comparative Example 7 The difference from Example 4 is: in S32, the gas flow rate is controlled at 100 ml / min; the remaining steps are the same as those in Example 4.

[0084] Comparative Example 8 The difference from Example 4 is: in S3, the gas flow rate is controlled at 500 ml / min; the remaining steps are the same as those in Example 4.

[0085] Comparative Example 9 The difference from Example 4 is that in S3, the heating rate is 35 °C / min; the remaining steps are the same as in Example 4.

[0086] Comparative Example 10 The difference from Example 4 is that in S3, the heating temperature is 650 °C; the remaining steps are the same as in Example 4.

[0087] Comparative Example 11 The difference from Example 4 is that in S3, the heating temperature is 950 °C; the remaining steps are the same as in Example 4.

[0088] Comparative Example 12 Except that in S1, the copper foil is H68 brass foil; the remaining steps are the same as in Example 4.

[0089] Comparative Example 13 Except that in S1, the thickness of the copper foil is 100 μm; the remaining steps are the same as in Example 4.

[0090] 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 evenly 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 length of the gullies in Example 1 was shorter, and circular holes about 1 μm in diameter 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 length of the gullies 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 alloy, so there were no large amounts of white particles on the surface morphology of Example 1.

[0091] 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.

[0092] From Figure 5 it can be seen 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.

[0093] Using Example 1 and Comparative Example 2 as current collectors and lithium foils 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 rate of 1C.

[0094] The first-cycle discharge curve and nucleation overpotential of the half-cell are as Figure 7 shown. The nucleation overpotential of Example 1 with the addition of the lithiophilic element silver was 40.6 mV, much lower than 124.1 mV of Comparative Example 2. The lower nucleation overpotential means that lithium metal is more likely to deposit uniformly on the surface of the current collector, thus helping to reduce the formation of lithium dendrites.

[0095] The long-term cycling graph of the full cell is as Figure 8 , Figure 9 shown; Figure 8 , Figure 9 In Figure 8 and Figure 9 , due to the addition of the lithiophilic element silver, both Example 1 and Comparative Example 2 had higher cycling capacities. However, since silver in Comparative Example 2 was bonded to the matrix by physical bonds with a relatively weak binding force, silver was likely to detach from the matrix during cycling, thus reducing the enhancement of the lithiophilic effect of silver on the matrix. In Example 1, silver was alloyed with the matrix, so a capacity retention rate of 90% could still be achieved after 400 cycles of long-term cycling.

[0096] Figure 3 Samples prepared in Examples 2-6 are shown, and the three-dimensional structure of the copper foil and the purpose of alloying with lithium can be achieved within a given range, but the surface morphologies under different processes have their own characteristics. Example 2 is a sample prepared by long-term dealloying at a relatively low temperature. The surface holes are interconnected and mainly in a gully shape. This is because the dealloying energy given by the temperature is limited at low temperatures, and the number of pore-forming sites is much less than that at high temperatures. 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, zinc in the grain interior will diffuse towards low-concentration regions such as the grain boundary. Since zinc diffusion and zinc removal continuously occur in regions with high defect energy, the pores will gradually increase. Moreover, defects such as grain boundary scratches are one or more lines on the surface, so dealloying occurs along the entire "line" to form gullies.

[0097] In Example 3, the reaction time of the sample in Step S2 was longer, and the silver content on the surface of the copper foil was higher. Therefore, there were still some unalloyed silver particles after heat treatment, so obvious white silver particles could be seen in the SEM images. In order to ensure that there is enough silver to alloy with the current collector to improve the lithium-philic 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 were similar and evenly distributed. Therefore, it would not affect the performance of the current collector, and there were fewer residual particles on the surface, resulting in less waste of silver. Therefore, 60 min was a relatively reasonable range.

[0098] Example 4 and Example 5 had similar morphologies, mainly because the temperature adopted in Example 4 was higher, so the dealloying rate was faster, and the effect of holding at 700 °C for 2 h in Example 5 could be achieved in 30 min. In Example 6, the adopted temperature was the highest, and the dealloying rate was very fast. Therefore, a large number of pores could be generated in 10 min. And because the ability of zinc atoms to overcome the binding of surrounding atoms was enhanced at high temperatures, large-area dealloying could occur on the surface of the sample, resulting in the appearance of pores with diameters of 100 - 300 nm in Example 6. The number of nanoscale pores was extremely large and evenly dense, which could 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 could be found from the morphologies of the high-temperature samples that the pores were everywhere. This was mainly because high temperatures could provide a large amount of energy. Therefore, the removal of zinc no longer depended on the defect energy, so the pores on the surface of the sample were also very dense. And because zinc could directly dealloy without diffusing towards the region with high defect energy, the formed pores would be smaller.

[0099] Figure 4 In Comparative Example 3, due to the low drying temperature, some liquid remaining from washing the sample still remained on the surface of the copper foil during heat treatment. Therefore, there were obvious differences in the degree of dealloying on the surface of the prepared sample. In Comparative Example 4, a longer drying time was adopted, so the surface state of the sample was better and the color was more uniform. However, the operation of keeping the sample at a constant temperature for a long time after drying was meaningless. Considering economy, a too long drying time was not recommended.

[0100] In Comparative Example 5, the reaction time of the sample with silver nitrate was short, so the silver particles on the surface of the sample were extremely rare. In contrast, in Comparative Example 6, reacting with silver nitrate for a long time caused the irregular growth of silver particles, and a large amount of silver that was difficult to alloy covered the surface. And too much silver could not alloy with the copper matrix, which would cause waste of silver nitrate.

[0101] In Comparative Example 7, the slow gas flow rate made the evaporated zinc not removed well. Therefore, the pores of the sample were very shallow after heat treatment. In Comparative Example 8, although too fast a gas flow rate could achieve the purpose of removing zinc, it would also cause waste of inert gas. Therefore, too fast a gas flow rate was not recommended.

[0102] Comparative example 9 adopted a relatively fast heating rate, which could achieve the purpose of heat treatment, but had higher requirements for equipment and would increase the cost of material preparation. In comparative example 10, the heat treatment temperature was relatively low. The lower heat treatment temperature would lead to a decrease in the dealloying rate, reduce production efficiency, and the pores formed by short-time dealloying at low temperature were very rare and shallow.

[0103] 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 Zn content of brass foils H65 and H68 was less, so the number of pores that could be formed was also less. In comparative example 13, a too thick copper foil was used. Although this had no effect on the preparation of three-dimensional porous copper, copper did not provide energy in the battery. Therefore, an overly thick copper current collector would reduce the energy density of the battery, so a too thick copper foil was not recommended.

[0104] 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, and the differences between each embodiment and other embodiments are emphasized. In particular, for system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and reference can be made to the relevant parts of the method embodiments for the related content.

[0105] 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 method for preparing a lithium-philic three-dimensional porous current collector for a lithium battery, characterized in that: The following steps are involved: S1. Cleaning and drying copper foil, wherein the copper foil is brass; S2. Immerse the copper foil treated in S1 in a 0.009-0.05 mol / L AgNO3 solution under light-proof conditions for 10-60 min, then wash and dry. S3. Put the copper foil treated with S2 into a vacuum tube furnace, exhaust the air in the tube, and when the vacuum degree is lower than 1Pa~100Pa, introduce inert gas or a mixture of hydrogen and inert gas at a gas flow rate of 150~300ml / min; heat to 660~900℃ at a heating rate of 5~30℃ / min, and keep warm for 10~120min; S4, after the reaction is completed, a three-dimensional porous copper foil is obtained, and the foil is taken out after the temperature in the furnace cools down to room temperature; S5. Clean the three-dimensional porous copper foil and dry it.

2. The method for preparing a lithium-philic three-dimensional porous current collector for a lithium battery according to claim 1, characterized in that: The S1 comprises the following steps: S11, placing a copper foil with a thickness of 20-40 μm in 0.1 mol / L-2.0 mol / L sulfuric acid, deionized water and anhydrous ethanol in turn for ultrasonic cleaning for 20-60 seconds; S12, drying the cleaned copper foil in a vacuum drying oven at 60-100°C for 30-120 minutes.

3. The method for preparing a lithium-philic three-dimensional porous current collector for a lithium battery according to claim 1, characterized in that: The copper foil in S1 is H62 brass.

4. The method for preparing a lithium-philic three-dimensional porous current collector for a lithium battery according to claim 1, characterized in that: In S2, after the reaction is completed, the copper foil is placed in anhydrous ethanol for cleaning, and after cleaning, it is vacuum dried in a vacuum drying oven at 60-100° C. for 30-120 min.

5. The method for preparing a lithium-philic 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; the vacuum pump is started to extract the air in the tube, and the tube furnace is evacuated to below 1Pa~100Pa, and the vacuum pump is turned off; then an inert gas or a mixed gas of hydrogen and inert gas is introduced through the gas bottle, and the inert gas or the mixed gas is turned off after the air pressure in the tube is higher than the standard atmospheric pressure, and the vacuum pump is turned on again to extract the residual air in the tube; the operation is repeated continuously to exhaust the air in the tube.

6. The method for preparing a lithium-philic 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 is 3.5% to 4%.

7. The method for preparing a lithium-philic 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.

8. A lithium-philic three-dimensional porous current collector for a lithium battery, characterized in that: The method for preparing a lithium-philic three-dimensional porous current collector for a lithium battery is used to prepare the lithium-philic three-dimensional porous current collector.

9. Application of the method for preparing a lithium-philic three-dimensional porous current collector for lithium batteries as claimed in claim 1 in lithium batteries.

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