Vacuum evaporation magnesium film and preparation method and application thereof

Abstract

The invention relates to the technical field of magnesium foil materials, in particular to a vacuum evaporation magnesium film and a preparation method and application thereof.The magnesium film comprises a substrate and a thin film layer, and the thin film layer is made of magnesium and covers the surface of the substrate in a vacuum evaporation mode; the preparation method comprises the following steps: taking an aluminum foil, a copper foil, a gold foil, a silver foil, a nickel foil, a molybdenum foil, a titanium foil, a tin foil, a stainless steel foil, a polymer composite metal foil, a metal alloy foil, a carbon-coated metal foil, polyimide and a high polymer material as a substrate, and uniformly depositing a layer of high-purity magnesium film on the surface of the substrate by controlling a vacuum evaporation process; when the magnesium film is applied to the magnesium battery, the substrate provides good conductivity and mechanical support, and the magnesium layer serves as an active substance to directly participate in electrochemical reaction, so that the energy density of the magnesium battery is improved, the cycle life of the magnesium battery is prolonged, the manufacturing process flow is simplified, and the cost is reduced; the magnesium negative electrode prepared by the method has excellent electrochemical performance and stability, and has a good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium foil materials, and particularly relates to a preparation method of a vacuum-evaporated magnesium film and its application in magnesium batteries. Background Art

[0002] With the rapid development of fields such as portable electronic devices, electric vehicles, and energy storage systems, the demand for high-performance secondary batteries is increasing day by day. Although traditional lithium-ion batteries have been widely used, factors such as their safety issues and resource limitations have prompted researchers to seek more ideal alternatives. Magnesium batteries have received extensive attention due to their large theoretical capacity, low cost, and difficulty in forming dendrite structures with high danger.

[0003] In the magnesium battery system, the current collector is one of the key components connecting the external circuit and the internal electrode material. Ideally, it should possess excellent electrical conductivity, sufficient mechanical strength, and good chemical compatibility.

[0004] For magnesium batteries, using magnesium as the negative electrode material is a natural choice. However, due to the characteristics of magnesium itself, there are a series of challenges in preparing very thin magnesium foils. Although traditional rolling techniques can produce magnesium foils with a certain thickness, when it comes to the ultra-thin specifications required for batteries, the cost will increase significantly, and material stress is likely to be generated during the rolling process, affecting the quality, consistency, and uniformity of the final product.

[0005] In addition, the electrodeposition method is also an effective method for preparing magnesium foils. However, it is very easy to introduce impurities during the preparation of magnesium foils by electrodeposition, resulting in low purity; chemical solutions need to be used, which may cause environmental pollution; and there are certain limitations on the shape and type of the substrate material, making it unsuitable for substrates with complex shapes.

[0006] In addition, evaporated aluminum films have been widely used in fields such as packaging, construction, and the electronics industry. However, compared with magnesium, Al has a higher boiling point (2470 °C) and higher latent heat of evaporation (10500 kJ / kg), while magnesium has a lower boiling point (1092 °C) and lower latent heat of evaporation (5200 kJ / kg). At the same time, it has a density smaller than that of aluminum and good electromagnetic shielding ability, which makes magnesium have an important role in lightweight and electromagnetic shielding. Summary of the Invention

[0007] The present invention aims to provide a vacuum-evaporated magnesium film, and apply the vacuum-evaporated magnesium film to multiple fields, especially the magnesium battery field, to improve the uniformity of the magnesium film.

[0008] To achieve the above object, the present invention adopts the following technical solution: A vacuum-evaporated magnesium film, comprising a substrate and a thin film layer. The thin film layer covers the surface of the substrate by means of vacuum evaporation, and the material of the thin film layer is magnesium.

[0009] Preferably, as an improvement, the substrate is one or more of metal materials such as aluminum foil, copper foil, gold foil, silver foil, nickel foil, molybdenum foil, titanium foil, tin foil, stainless steel foil, metal alloy foil, polymer composite metal foil, carbon-coated metal foil, polyimide or polymer materials.

[0010] Preferably, as an improvement, the thickness of the thin film layer is 0.001 μm - 30 μm.

[0011] The present invention also provides a method for preparing a vacuum-evaporated magnesium film, comprising the following steps:

[0012] S1. Substrate pretreatment: ultrasonically cleaning and plasma etching the substrate;

[0013] S2. Establishing a vacuum environment: pumping the vacuum degree of the coating chamber to 9×10 -6 -5×10 -1 Pa, then filling with argon gas, and then pumping the vacuum degree of the coating chamber to 9×10 -6 -5×10 -2 Pa again;

[0014] S3. Substrate loading: fixing the substrate on the substrate plate and placing the magnesium material in the evaporation boat;

[0015] S4. Evaporation process: heating the evaporation boat to 50 - 1800 °C, controlling the substrate temperature to be room temperature - 300 °C, and rotating at a speed of ≤25 revolutions per minute, and maintaining the deposition rate at

[0016] Preferably, as an improvement, the purity of argon gas is ≥99.99%, the distance between the evaporation boat and the substrate is 200 - 600 mm, and the thickness of the prepared magnesium film is 0.001 μm - 30 μm.

[0017] Preferably, as an improvement, after S4, it further includes the step of depositing In, Sn, Bi, Sb, Si, Ge, Ga, Se, Ag, Au, Te elements and their 2 - 11 element alloys, organic / inorganic compounds on the evaporated magnesium film, and the thickness of the composite layer is 0.001 μm - 6 μm.

[0018] Preferably, as an improvement, the magnesium material placed on the evaporation boat is a magnesium rod, magnesium wire or magnesium particles.

[0019] The present invention further provides an application of the vacuum-evaporated magnesium film, applying the aforementioned magnesium film to a magnesium battery.

[0020] Preferably, as an improvement, the thickness of the magnesium film is 9 μm.

[0021] The technical effects of this solution are as follows: The evaporated magnesium film can be applied in multiple fields. In the field of magnesium batteries, compared with the metal-rolled magnesium film, the magnesium film prepared by the vacuum evaporation method in this solution has higher uniformity, and exhibits excellent long-term cycle stability and low overpotential. At the same time, it has the advantages of environmental friendliness, low cost, and simple preparation process, showing good application prospects.

[0022] In addition, although the electrodeposition method can also be used to prepare magnesium films, it is very easy to introduce impurities during the preparation process of the electrodeposition method, resulting in relatively low purity; the electrodeposition method requires the use of chemical solutions, which may cause environmental pollution; and there are certain limitations on the shape and type of substrate materials, making it unsuitable for substrates with complex shapes. In contrast, the vacuum evaporation method for preparing magnesium films on copper foils has higher purity, better uniformity, and stronger bonding strength compared to the electrodeposition method and the rolling method. Since this solution is carried out in a vacuum environment, this method reduces the introduction of impurities and oxides, can precisely control the deposition rate and thickness, is suitable for substrates with complex shapes, and avoids chemical pollution, making it suitable for large-scale industrial production. These advantages make the vacuum evaporation method more competitive in application scenarios that require high purity, high uniformity, and high bonding strength.

[0023] In addition, the research on the application of the vacuum evaporation method in the field of magnesium batteries is relatively scarce, which is due to the challenges brought by the inherent characteristics of magnesium battery technology itself and the specific difficulties faced by the vacuum evaporation method in this field.

[0024] Compared with traditional batteries, magnesium battery technology has many bottlenecks that need to be urgently overcome. First of all, the chemical properties of magnesium ions are relatively active. During the charge and discharge process of the battery, they are prone to side reactions with the electrolyte, etc., generating various complex compounds, which not only reduces the energy conversion efficiency of the battery but also affects the cycle life of the battery. For example, an uneven passivation film will form on the magnesium metal anode in some electrolytes, resulting in an increase in the internal resistance of the battery and a decline in the charge and discharge performance. This unstable chemical reaction characteristic makes it necessary to more carefully consider the process conditions when using the vacuum evaporation method to prepare magnesium battery-related materials to avoid unnecessary reactions between the materials and trace impurities in the environment, which undoubtedly increases the difficulty of process control.

[0025] Secondly, the choice of electrode materials for magnesium batteries is limited and their performance needs to be improved. Currently, common electrode materials often cannot achieve efficient ion insertion and extraction during the interaction with magnesium ions, resulting in low battery capacity. For example, when some transition metal oxides are used as magnesium battery materials, due to the relatively large radius of magnesium ions, the diffusion rate in the crystal lattice is slow, which limits the charge and discharge rate of the battery. The vacuum evaporation method has a unique impact on the atomic structure and surface characteristics of electrode materials.

[0026] From the perspective of the application of the vacuum evaporation method itself in the field of magnesium batteries, there are also specific difficulties. On the one hand, the melting point of magnesium is relatively high, at 650 °C, and the boiling point is 1090 °C. This requires a higher temperature during the vacuum evaporation process to achieve the evaporation of magnesium. The high-temperature environment not only poses extremely high requirements for the evaporation equipment, increasing the equipment cost, but also may lead to a decrease in the stability of the equipment during long-term operation. At the same time, it is difficult to precisely control the evaporation rate of magnesium at high temperatures. Once the evaporation rate is unstable, it will affect the uniformity of magnesium deposition on the substrate, and thus affect the performance of the battery electrode.

[0027] On the other hand, there are challenges in the compatibility of the magnesium thin film prepared by the vacuum evaporation method with other components of the battery. Magnesium batteries usually require the electrode to work in coordination with components such as the electrolyte and the separator. However, the surface characteristics of the magnesium thin film prepared by the vacuum evaporation method may not match those of traditional electrolytes and separators. For example, the microstructure on the film surface may be unfavorable for the infiltration of the electrolyte, resulting in blocked ion transport and affecting the overall performance of the battery.

[0028] This solution creatively proposes to use the vacuum evaporation method to prepare magnesium films. By controlling aspects such as the preparation method and the thickness of the thin film layer, the prepared magnesium film covers the thin film layer on the surface of the substrate. The material of the thin film layer is magnesium, forming a Cu@Mg integrated electrode. Compared with the rolled magnesium film, it exhibits more excellent long-term cycle stability and low overpotential; the material preparation process is simple, the cost is low, and it can be industrially produced on a large scale; the vacuum evaporation method avoids the internal stress of the material caused by mechanical processing, improving the mechanical stability and durability of the finished product; evaporation in a high-vacuum environment can effectively prevent the mixing of oxides and other impurities, ensuring the purity of the magnesium film; the copper foil serves as a current collector to provide a good conduction path, while the magnesium layer directly participates in the electrochemical reaction. This composite structure helps to improve the cycle life of the magnesium battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is the SEM cross-section and planar scan diagram of the 9-μm-thick magnesium foil prepared by the vacuum evaporation method in Example 1 of the present invention;

[0030] Figure 2 It is the comparison chart of the charge-discharge curves of the rolled magnesium foil and the evaporated magnesium foil of the present invention applied to a symmetric battery under a high current density (2 mA / cm 2 -2 mAh / cm 2 ) in Example 2 of the present invention;

[0031] Figure 3 It is the nucleation overpotential curve of the rolled magnesium foil and Cu@Mg under the conditions of 0.2 mA cm -2 , 0.2 mAh cm -2 in Example 3 of the present invention;

[0032] Figure 4 is the nucleation overpotential curve of rolled magnesium foil and Cu@Mg under the conditions of 1 mA cm -2 , 1 mAh cm -2 in Example 4 of the present invention;

[0033] Figure 5 is the charge-discharge curve of the Mg / / Cu and Cu@Mg / / Cu half-cells in the first cycle under the condition of 0.2 mA cm -2 in Example 5 of the present invention;

[0034] Figure 6 is the contact angle of the APC electrolyte on the rolled magnesium foil and Cu@Mg in Example 6 of the present invention;

[0035] Figure 7 is the AFM potential difference diagram of the polished rolled magnesium foil and Cu@Mg in Example 7 of the present invention;

[0036] Figure 8 is the time-voltage curve of rolled magnesium and modified magnesium in 0.01 mAcm -2 0.005 mAhcm -2 in the 0.5 M Mg(TFSI)2 in DME electrolyte in Example 8 of the present invention;

[0037] Figure 9 is the schematic diagram of the vacuum evaporation coating equipment;

[0038] Figure 10 are the effect diagrams before and after evaporating magnesium on the copper substrate. Specific Embodiments

[0039] The following is a further detailed description through specific embodiments:

[0040] This specific embodiment provides a vacuum-evaporated magnesium film, including a substrate and a thin film layer. The thin film layer covers the surface of the substrate by vacuum evaporation, and the effect is as Figure 10 shown. The material of the thin film layer is magnesium. In the text, the thin film layer, magnesium film, and magnesium foil have the same meaning, and the thickness is 0.001 μm - 30 μm.

[0041] The substrate is one or more of metal materials such as aluminum foil, copper foil, gold foil, silver foil, nickel foil, molybdenum foil, titanium foil, tin foil, stainless steel foil, metal alloy foil, polymer composite metal foil, carbon-coated metal foil, polyimide, or polymer materials.

[0042] This specific embodiment also includes a method for preparing a vacuum-evaporated magnesium film, including the following steps:

[0043] S1. Substrate pretreatment: ultrasonically clean and plasma etch the substrate;

[0044] S2. Establishment of vacuum environment: Pump the vacuum degree of the coating chamber of the vacuum evaporation coating equipment to 9×10 -6 -5×10 - 1 Pa, then fill it with argon, the purity of argon ≥ 99.99%, and then pump the vacuum degree of the coating chamber to 9×10 -6 -5×10 -2 Pa;

[0045] S3. Substrate loading: The substrate is pasted on the lower surface of the metal substrate in the vacuum chamber of the vacuum evaporation coating equipment as shown in Figure 9 . The evaporation boat is located below the substrate, and the distance between the evaporation boat and the substrate is 200 - 600 mm. Put magnesium rods / magnesium wires / magnesium particles on the evaporation boat;

[0046] S4. Evaporation coating process: Heat the evaporation boat to 50 - 1800 °C, control the substrate temperature at room temperature - 300 °C, and rotate at a speed of ≤ 25 revolutions per minute. The deposition rate is maintained at

[0047] It also includes the step of depositing In, Sn, Bi, Sb, Si, Ge, Ga, Se, Ag, Au, Te elemental substances and their 2 - 11 - element alloys, organic / inorganic compounds on the magnesium film obtained by evaporation coating in S4. The thickness of the deposited composite layer is 0.001 μm - 6 μm.

[0048] The aforementioned magnesium foil can be applied to magnesium batteries, and the thickness of the magnesium film for magnesium batteries is preferably 9 μm.

[0049] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments:

[0050] Example 1

[0051] This example provides a magnesium foil, which includes a copper foil and a thin film layer. The thin film layer covers the surface of the substrate by means of vacuum evaporation coating, and the material of the thin film layer is magnesium.

[0052] The magnesium foil provided in this example is prepared by the following steps: Fix the copper foil on the metal substrate in the vacuum chamber of the vacuum evaporation coating equipment, place the magnesium rods / magnesium wires / magnesium particles on the evaporation boat; Use a molecular pump and other auxiliary systems to pump the vacuum degree of the coating chamber to ≤ 5×10 - 1 Pa, then fill it with argon, and then pump the vacuum degree of the coating chamber to ≤ 5×10 - 2 Pa; Heat the crucible to 50 - 1800 °C, control the temperature of the substrate at room temperature - 300 °C, and rotate at a speed of 0 - 25 revolutions per minute. The deposition rate is maintained at Figure 1 SEM scanning image of a magnesium film with a thickness of 9 μm prepared by vacuum evaporation method.

[0053] The following examples conduct experiments on the application of magnesium foil in the field of magnesium batteries.

[0054] Example 2

[0055] This example presents a magnesium foil, which includes a copper foil and a thin film layer. The thin film layer is covered on the surface of the substrate by vacuum evaporation, and the material of the thin film layer is magnesium.

[0056] The magnesium foil proposed in this example is prepared by the following steps: Fix the copper foil on the metal substrate in the vacuum chamber of the vacuum evaporation coating equipment, place the magnesium rod / magnesium wire / magnesium particles on the evaporation boat; use a molecular pump and other auxiliary systems to pump the vacuum degree of the coating chamber to ≤5×10- 1 Pa, then fill it with argon, and then pump the vacuum degree of the coating chamber to ≤5×10- 2 Pa again; heat the crucible to 50 - 1800 °C, control the substrate temperature to be room temperature - 300 °C, and rotate at a speed of 0 - 25 revolutions per minute, and maintain the deposition rate at

[0057] In an argon glove box with a water oxygen value less than 1 ppm, use the copper foils covered with magnesium of different thicknesses obtained in this example as the positive and negative electrodes respectively, and the rolled magnesium foil as the positive and negative electrodes. The separator uses a GF / A glass fiber separator, and the electrolyte selects a total of 100 μL of APC electrolyte. Assemble a CR2032 button battery in the order of negative electrode case → negative electrode sheet → separator → electrolyte → positive electrode sheet → gasket → elastic sheet.

[0058] Under the condition of a temperature of 30 °C, use a Neware battery test system to conduct a constant current charge-discharge test on the battery. The test conditions are that the current density is 2 mA / cm 2 , the charge-discharge process is controlled by time, the charge-discharge time is 1 h for both, and there is a 30 s interval between each charge and discharge process, and cycle 9999 times. Obtain the charge-discharge curves of the symmetric batteries of the rolled magnesium foil and the copper foil covered with 9 μm magnesium at a high current density (2 mA / cm 2 -2 mAh / cm 2 ), as shown in Figure 2 shown.

[0059] The symmetric batteries composed of the rolled magnesium foil and the copper foil covered with 9 μm magnesium respectively are subjected to a constant current charge-discharge test at a current density of 2 mA / cm 2 , as shown in Figure 2As shown, it can be clearly observed that during the long-term charge-discharge cycles within 800 h, compared with the rolled magnesium foil, the copper foil covered with magnesium exhibits an obvious reduction in overpotential. The overpotential of the copper foil covered with magnesium is significantly lower than that of the rolled magnesium foil component symmetric cell. Moreover, the symmetric cell assembled with the rolled magnesium foil short-circuited around 630 h, indicating that the copper foil covered with magnesium is beneficial to the uniform deposition of Mg ions and conducive to improving the cycle life of magnesium-ion batteries.

[0060] Example 3

[0061] This example presents a magnesium foil, which includes a copper foil and a thin film layer. The thin film layer is covered on the surface of the substrate by means of vacuum evaporation, and the material of the thin film layer is magnesium.

[0062] The magnesium foil proposed in this example is prepared by the following steps: Fix the copper foil on the metal substrate in the vacuum chamber of the vacuum evaporation coating equipment. Place the magnesium rod / magnesium wire / magnesium particles on the evaporation boat. 1 Pa, then fill it with argon, and then evacuate the coating chamber vacuum to ≤5×10- 2 Pa again; Heat the crucible to 50 - 1800 °C, control the substrate temperature at room temperature - 300 °C, and rotate at a speed of 0 - 25 revolutions per minute, and maintain the deposition rate at

[0063] In an argon glove box with a water-oxygen value less than 1 ppm, use the copper foil covered with magnesium prepared in this example and the rolled magnesium foil obtained in this example as the negative electrode, the copper foil as the positive electrode, the GF / A glass fiber diaphragm as the separator, and select a total of 100 μL of APC electrolyte as the electrolyte. Assemble a CR2032 coin cell in the order of negative electrode shell → negative electrode sheet → separator → electrolyte → positive electrode sheet → gasket → spring piece.

[0064] Under the condition of a temperature of 30 °C, a nucleation overpotential test was carried out on the battery using a Neware battery test system. The test conditions were a current density of 0.2 mA / cm 2 , and the discharge time was 1 h.

[0065] As Figure 3 shown, at a current density and areal capacity of 0.2 mA cm -2 and 0.2 mAh cm -2When the overpotential for nucleation of Cu@Mg is 0.155 V, the overpotential for nucleation of the rolled magnesium foil is as high as 0.949 V. The overpotential for nucleation of Cu@Mg is significantly lower than that of the rolled magnesium foil, indicating that the Cu@Mg negative electrode has a lower nucleation energy barrier and better magnesium affinity. Cu@Mg improves the electrochemical activity of the overall metallic magnesium negative electrode, provides nucleation sites for magnesium deposition, and promotes nucleation and uniform growth.

[0066] Example 4

[0067] This example presents a magnesium foil comprising a copper foil and a thin film layer. The thin film layer is covered on the surface of the substrate by means of vacuum evaporation, and the material of the thin film layer is magnesium.

[0068] The magnesium foil proposed in this example is prepared by the following steps: Fix the copper foil on the metal substrate in the vacuum chamber of a vacuum evaporation coating equipment. Place a magnesium rod / magnesium wire / magnesium particles on the evaporation boat; 1 Pa, then fill with argon, and then evacuate the coating chamber vacuum to ≤5×10- 2 Pa again; Heat the crucible to 50 - 1800 °C, control the substrate temperature to be room temperature - 300 °C, and rotate at a speed of 0 - 25 revolutions per minute, and maintain the deposition rate at

[0069] In an argon glove box with a water oxygen value less than 1 ppm, use the copper foil covered with magnesium prepared in this example and the rolled magnesium foil as the negative electrode respectively, the copper foil as the positive electrode, the GF / A glass fiber diaphragm as the separator, and select 100 μL of APC electrolyte in total. Assemble a CR2032 coin cell in the order of negative electrode case → negative electrode sheet → separator → electrolyte → positive electrode sheet → gasket → shrapnel.

[0070] Under the condition of a temperature of 30 °C, the overpotential for nucleation of the battery was tested using a Neware battery test system. The test conditions were a current density of 1 mA / cm 2 , and the discharge time was 1 h. As Figure 4 shown, when the current density and areal capacity increased to 1 mA cm -2 , 1 mAh cm -2 , the overpotential for nucleation of the rolled magnesium foil (0.860 V) was still higher than that of Cu@Mg (0.561 V). In the two groups of overpotential for nucleation tests, the overpotential for nucleation of Cu@Mg was significantly lower than that of the rolled magnesium foil, indicating that the Cu@Mg negative electrode has a lower nucleation energy barrier and better magnesium affinity. Cu@Mg improves the electrochemical activity of the overall metallic magnesium negative electrode, provides nucleation sites for magnesium deposition, and promotes nucleation and uniform growth.

[0071] Example 5

[0072] This example presents a magnesium foil, which includes a copper foil and a thin film layer. The thin film layer is covered on the surface of the substrate by means of vacuum evaporation, and the material of the thin film layer is magnesium.

[0073] The magnesium foil proposed in this example is prepared by the following steps: Fix the copper foil on the metal substrate in the vacuum chamber of the vacuum evaporation coating equipment, place the magnesium rod / magnesium wire / magnesium particles on the evaporation boat; use a molecular pump and other auxiliary systems to pump the vacuum degree of the coating chamber to ≤5×10- 1 Pa, then fill it with argon, and then pump the vacuum degree of the coating chamber to ≤5×10- 2 Pa again; heat the crucible to 50 - 1800 °C, control the substrate temperature to be room temperature - 300 °C, and rotate at a speed of 0 - 25 revolutions per minute, and maintain the deposition rate at

[0074] Put the copper foil covered with magnesium prepared in this example in an argon glove box with the water oxygen value less than 1 ppm. Respectively use the copper foil covered with magnesium obtained in this example as the positive and negative electrodes, the rolled magnesium foil as the positive and negative electrodes, use a GF / A glass fiber diaphragm as the separator, and select a total of 100 μL of APC electrolyte as the electrolyte. Assemble it into a CR2032 coin cell in the order of negative electrode case → negative electrode sheet → separator → electrolyte → positive electrode sheet → gasket → elastic sheet.

[0075] Under the condition of a temperature of 30 °C, use a Neware battery test system to perform constant current charge and discharge tests on the rolled magnesium foil and the Cu@Mg half-cell under the condition of a current density of 0.2 mA cm -2 The condition is carried out, the charge and discharge time for each time is 1 h, the charging cut-off voltage is 1 V, and a 30 s pause is made between each charge and discharge time.

[0076] The charge and discharge curves of the Mg / / Cu and Cu@Mg / / Cu half-cells in different cycles are as Figure 5 shown. In the APC electrolyte, there is a certain activation process for both the rolled magnesium foil and the evaporated magnesium film negative electrode at the initial stage of cycling. The overpotential of the first cycle of Cu@Mg / / Cu is 238 mV, which is lower than 342 mV of the Mg / / Cu half-cell, indicating that the introduction of the Cu substrate in the evaporated magnesium foil makes the energy barrier for deposition / dissolution of Mg in the initial phase change process lower, resulting in a lower voltage hysteresis in the first cycle. 2+ In the initial phase change process, the energy barrier for deposition / dissolution is lower, resulting in a lower voltage hysteresis in the first cycle.

[0077] Example 6

[0078] This embodiment provides a magnesium foil, which includes a copper foil and a thin film layer. The thin film layer covers the surface of the substrate by means of vacuum evaporation, and the material of the thin film layer is magnesium.

[0079] The magnesium foil proposed in this embodiment is prepared by the following steps: Fix the copper foil on the metal substrate in the vacuum chamber of the vacuum evaporation coating equipment, place the magnesium rod / magnesium wire / magnesium particles on the evaporation boat and on the evaporation boat; use a molecular pump and other auxiliary systems to pump the vacuum degree of the coating chamber to ≤5×10- 1 Pa, then fill it with argon, and then pump the vacuum degree of the coating chamber to ≤5×10- 2 Pa again; heat the crucible to 50-1800 °C, control the substrate temperature to be room temperature - 300 °C, and rotate at a speed of 0-25 revolutions per minute, and maintain the deposition rate at

[0080] As Figure 6 shown by the contact angle test results, the contact angle between the rolled magnesium foil and the APC electrolyte is 45.72°, while the contact angle between the evaporated magnesium foil Cu@Mg and the APC electrolyte is only 22.83°, which is much smaller than the contact angle between the rolled magnesium foil and the APC electrolyte. The smaller contact angle indicates that the surface of the evaporated magnesium foil Cu@Mg is more easily wetted by the electrolyte, which helps to improve the contact efficiency between the electrolyte and the electrode material, thereby improving the ion transport performance and electrochemical reaction kinetics of the battery. In contrast, the larger contact angle of the rolled magnesium foil indicates its poor wettability, which may lead to an increase in interfacial resistance and a decrease in battery performance.

[0081] Example 7

[0082] This embodiment provides a magnesium foil, which includes a copper foil and a thin film layer. The thin film layer covers the surface of the substrate by means of vacuum evaporation, and the material of the thin film layer is magnesium.

[0083] The magnesium foil proposed in this embodiment is prepared by the following steps: Fix the copper foil on the metal substrate in the vacuum chamber of the vacuum evaporation coating equipment, place the magnesium rod / magnesium wire / magnesium particles on the evaporation boat and on the evaporation boat; use a molecular pump and other auxiliary systems to pump the vacuum degree of the coating chamber to ≤5×10- 1 Pa, then fill it with argon, and then pump the vacuum degree of the coating chamber to ≤5×10- 2 Pa again; heat the crucible to 50-1800 °C, control the substrate temperature to be room temperature - 300 °C, and rotate at a speed of 0-25 revolutions per minute, and maintain the deposition rate at From Figure 7As can be seen from the AFM potential difference diagram shown, the average potential difference of the evaporated magnesium film is 24.236 mV, which is lower than that of the rolled magnesium foil at 31.958 mV. The lower potential difference indicates that the evaporated magnesium film is more stable in the electrochemical reaction, can embed and de-embed magnesium ions more efficiently, reduce polarization phenomena and energy loss, thereby improving the charge-discharge efficiency and cycle stability of the battery. At the same time, the low potential difference also means fewer interfacial side reactions, which helps to extend the battery life. In contrast, the higher potential difference of the rolled magnesium foil may lead to greater polarization, energy loss and side reactions, affecting the battery performance and life. Therefore, the evaporated magnesium film has more advantages in electrochemical performance as the negative electrode and is more suitable for high-performance battery applications.

[0084] Example 8

[0085] This example presents a magnesium foil, which includes a copper foil and a thin film layer. The thin film layer is covered on the surface of the substrate by means of vacuum evaporation, and the material of the thin film layer is magnesium.

[0086] The magnesium foil proposed in this example is prepared by the following steps: Fix the copper foil on the metal substrate in the vacuum chamber of the vacuum evaporation coating equipment, place the magnesium rod / magnesium wire / magnesium particles on the evaporation boat; use a molecular pump and other auxiliary systems to pump the vacuum degree of the coating chamber to ≤5×10- 1 Pa, then fill it with argon, and then pump the vacuum degree of the coating chamber to ≤5×10- 2 Pa again; heat the crucible to 50 - 1800 °C, control the substrate temperature to be room temperature - 300 °C, and rotate at a speed of 0 - 25 revolutions per minute, and maintain the deposition rate at Subsequently, deposit a layer of InSnBi alloy on the magnesium film.

[0087] Place the copper foil covered with magnesium prepared in this example in an argon glove box with a water oxygen value less than 1 ppm. Using the modified magnesium obtained in this example as the positive and negative electrodes respectively, the rolled magnesium foil as the positive and negative electrodes, the separator is a GF / A glass fiber separator, and the electrolyte is 100 μL of 0.5 M Mg(TFSI)2 in DME electrolyte. Assemble a CR2032 button cell in the order of negative electrode case → negative electrode sheet → separator → electrolyte → positive electrode sheet → gasket → spring piece.

[0088] Under the condition of a temperature of 30 °C, use a Neware battery test system to conduct a constant current charge-discharge test on the battery. The test conditions are a current density of 0.01 mA / cm 2 , the charge-discharge process is controlled by time, the charge-discharge time is 0.5 h each, and there is a 30 s interval between each charge and discharge process, and it is cycled 9999 times. As Figure 8 shown, obtain at 0.01 mA / cm 2, 0.005 mAh / cm 2 Time-voltage curves of modified magnesium and rolled magnesium under this condition.

[0089] Symmetric cells composed of modified magnesium and rolled magnesium respectively were subjected to constant current charge-discharge tests at a current density of 0.01 mA / cm 2 . It can be clearly observed that the overpotential of modified magnesium is significantly less than that of rolled magnesium, and it also has a longer cycle life. From Figure 8 it can be seen that the overpotential of modified magnesium is about 0.8 V, which is significantly less than 2 V of rolled magnesium foil; in addition, the symmetric cell composed of rolled magnesium short-circuited at 280 h, while modified magnesium short-circuited at about 680 h. The modified magnesium negative electrode exhibits excellent deposition / dissolution cycle stability.

[0090] The above are only the embodiments of the present invention. Specific technical solutions and / or common knowledge such as characteristics well known in the art are not described in detail herein. It should be noted that for those skilled in the art, without departing from the technical solution of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application should be subject to the content of its claims, and the specific implementation manners and the like recorded in the specification can be used to interpret the content of the claims.

Claims

1. A vacuum-evaporated magnesium film, characterized in that: It includes a substrate and a thin film layer. The thin film layer is covered on the surface of the substrate by means of vacuum evaporation, and the material of the thin film layer is magnesium.

2. A vacuum-evaporated magnesium film according to claim 1, wherein: The substrate is one or more of metal materials such as aluminum foil, copper foil, gold foil, silver foil, nickel foil, molybdenum foil, titanium foil, tin foil, stainless steel foil, metal alloy foil, polymer composite metal foil, carbon-coated metal foil, polyimide or polymer materials.

3. A vacuum-evaporated magnesium film according to claim 2, characterized in that: The thickness of the thin film layer is 0.001μm - 30μm.

4. A method for preparing a vacuum-evaporated magnesium film, characterized in that: It includes the following steps: S1. Substrate pretreatment: The substrate is ultrasonically cleaned and plasma etched. S2. Establishment of vacuum environment: Pump the vacuum degree of the coating chamber to 9×10 -6 -5×10 -1 Pa, then fill it with argon gas, and then pump the vacuum degree of the coating chamber to 9×10 -6 -5×10 -2 Pa; S3. Substrate loading: The substrate is fixed on the substrate plate, and the magnesium material is placed in the evaporation boat. S4. Evaporation process: Heat the evaporation boat to 50 - 1800 °C, control the substrate temperature at room temperature - 300 °C, and rotate at a speed of ≤ 25 revolutions per minute, with the deposition rate maintained at 5. The preparation method of a vacuum-evaporated magnesium film according to claim 4, characterized in that: The purity of argon is ≥99.99%, the distance between the evaporation boat and the substrate is 200 - 600mm, and the thickness of the obtained magnesium film is 0.001μm - 30μm.

6. The preparation method of a vacuum-evaporated magnesium film according to claim 5, characterized in that: After S4, it also includes the step of depositing In, Sn, Bi, Sb, Si, Ge, Ga, Se, Ag, Au, Te elements and their 2 - 11 - element alloys, organic / inorganic compounds on the obtained magnesium film by evaporation, and the thickness of the composite layer is 0.001μm - 6μm.

7. A method for preparing a vacuum-evaporated magnesium film according to claim 6, characterized in that: The magnesium material placed on the evaporation boat is a magnesium rod, magnesium wire or magnesium particles.

8. Application of vacuum-evaporated magnesium film, characterized in that: A magnesium film of claims 1 - 3 or a magnesium film prepared by the preparation method of a vacuum - evaporated magnesium film of claims 4 - 7 is applied to a magnesium battery.

9. The application of a vacuum-evaporated magnesium film according to claim 8, characterized in that: The thickness of the magnesium film is 9μm.

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