A composite lithium metal negative electrode and its preparation method and application

Abstract

The present invention provides a composite lithium metal anode, a preparation method, and an application thereof. The preparation method comprises the following steps: 1) coating a fluorine-containing solution on the surface of a lithium metal sheet to obtain a lithium metal sheet having a liquid film formed on the surface; and 2) placing the lithium metal sheet having the liquid film formed on the surface in a dielectric barrier discharge (DBD) device to perform an in-situ synthesis reaction to obtain the composite lithium metal anode. The present invention places the lithium metal sheet coated with the fluorine-containing solution in the DBD device, locally creates a plasma state of the substance, and bombards the surface of the lithium metal sheet with high-energy ions, effectively etching the lithium layer on the surface of the lithium metal sheet, thereby forming a porous three-dimensional lithium fluoride structure in situ. This provides a path and space for the migration of lithium ions and the lateral growth of lithium dendrites, while suppressing the longitudinal growth of dendrites and the occurrence of side reactions, shortening the reaction time, and achieving precise control of the material morphology, thereby facilitating the long-cycle charge and discharge of the lithium metal anode.

Description

Technical Field

[0001] The present invention belongs to the field of lithium batteries, and in particular relates to a composite lithium metal negative electrode and a preparation method and application thereof. Background Art

[0002] With the development of electric technology, more and more industrial products are becoming electrified. Batteries play a crucial role in electrified products and often determine the user experience of these products. As people continue to explore and experiment with electrode materials with higher specific capacity and energy, and as they gradually understand and study the charging and discharging principles of chemical batteries, lithium-ion secondary batteries have been a key research focus.

[0003] Lithium metal is one of the electrode materials with the highest known specific energy per mass. Research on lithium metal as anode materials in batteries has long garnered widespread attention. Comparing the specific energy of different batteries, lithium metal secondary batteries have a clear advantage in specific energy. Consequently, since 1962, research has begun on new high-energy batteries that directly use lithium metal as the anode material. However, lithium metal electrodes are prone to forming lithium dendrites during the charge and discharge process. These dendrites easily detach from the plates, breaking electrical contact with the plates and becoming inaccessible to charge and discharge reactions, resulting in reduced battery capacity. If lithium dendrites grow, they can pierce the separator and extend to the positive electrode, causing an internal short circuit, fire, or explosion. This problem has plagued researchers, and progress has been limited.

[0004] By the 1990s, with the successful commercialization of lithium-ion batteries, researchers focused their attention on lithium-ion and polymer lithium-ion batteries, while research on metal lithium secondary batteries languished. However, with technological advancements, there was an urgent need for high-energy-density batteries to meet the trend toward miniaturization and ultra-thinness in various electrical appliances. This exposed the inherent weakness of lithium-ion batteries—low specific energy. Since graphite has a theoretical capacity of only 372 mAh / g and suffers from significant irreversible capacity loss during the first charge-discharge cycle, it is not an ideal anode material for high-energy-density batteries. Research on other intercalation-type anode materials, such as amorphous carbon, tin oxides, or silicides, has made limited progress. Metal lithium, with a theoretical specific capacity of 386 mAh / g, still has a capacity of 960 mAh / g even at a utilization rate of only 25%. Furthermore, the lithium electrode's high exchange current density and low polarization make it an ideal electrode material. Consequently, many research institutions and well-known battery companies, both domestically and internationally, have revived research on metal lithium secondary batteries. At the same time, with the continuous improvement of the performance of solid electrolytes (including colloidal electrolytes), the practical application of lithium metal batteries has become possible again, and related research has continued to increase.

[0005] In the past few decades, there have been many attempts to inhibit the growth of dendrites in lithium metal anodes, such as constructing a SEI film on the surface of lithium metal anodes, using solid electrolytes to physically inhibit dendrites, or adding specific electrolyte additives. For example, CN114552017A discloses a method for stabilizing lithium metal anodes with electrolyte additives. This electrolyte additive is tetrabutylammonium fluoride, with a molecular formula of C 16 H 36 FN; the electrolyte is an ether or carbonate electrolyte for lithium metal secondary batteries; the lithium metal secondary battery described is a secondary battery using lithium metal and other lithium-containing materials, such as lithium-carbon composites, lithium-silicon composites, or lithium alloy compounds such as lithium-zinc alloys, lithium-tin alloys, and lithium-indium alloys, as the negative electrode. However, these methods often fail to achieve good full battery cycle performance and are too expensive to use in industrial production. Lithium fluoride is an excellent lithium ion transport material with a high lithium ion transport rate, which can be used to suppress dendrites on the surface of lithium metal negative electrodes. Lithium fluoride also has excellent insulating properties for electrons, and coating the electrode surface with it can significantly reduce the occurrence of common battery side reactions at the electrode interface. However, the lithium fluoride film easily breaks down during battery charging and discharging, losing its original function. Constructing a three-dimensional lithium fluoride structure on the lithium metal negative electrode can maintain its dendrite and side reaction suppression effects during battery cycling. However, the three-dimensional structure is difficult to quickly obtain through conventional reaction methods and is also difficult to control. Existing technologies include chemical reaction method, microwave synthesis method, hydrothermal method, etc. Their common disadvantages are slow chemical reaction kinetics and difficulty in accurately controlling the morphology of the material; in addition, the hydrothermal method has the disadvantages of large randomness in material synthesis and difficulty in repeatability; the chemical reaction method has the disadvantage of difficulty in maintaining the material morphology; other material synthesis and modification methods such as chemical vapor deposition have high process difficulty and low yield, which is not conducive to large-scale production and cost control of materials.

[0006] Therefore, how to effectively construct the three-dimensional structure of lithium fluoride so that it can not only inhibit dendrite growth and side reactions, but also improve the chemical reaction kinetics and achieve precise control of the material morphology is a technical problem that needs to be solved urgently. Summary of the Invention

[0007] In response to the shortcomings of the prior art, the present invention aims to provide a composite lithium metal anode, its preparation method, and application. The present invention places a lithium metal sheet coated with a fluorine-containing solution in a dielectric barrier discharge (DBD) device. By locally creating a plasma state of the material, the surface of the lithium metal sheet is bombarded with high-energy ions, effectively etching the lithium layer on the surface of the lithium metal sheet, thereby forming a porous three-dimensional lithium fluoride structure in situ. This provides a path and space for the migration of lithium ions and the lateral growth of lithium dendrites, while suppressing the longitudinal growth of dendrites on the surface of the lithium metal sheet and the occurrence of side reactions, shortening the reaction time and achieving precise control of the material morphology, which helps the lithium metal anode achieve long-cycle charge and discharge.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing a composite lithium metal negative electrode, the preparation method comprising the following steps:

[0010] (1) coating a fluorine-containing solution on the surface of a lithium metal sheet to obtain a lithium metal sheet with a liquid film formed on the surface;

[0011] (2) placing the lithium metal sheet with the liquid film formed on the surface in a dielectric barrier discharge (DBD) device to perform an in-situ synthesis reaction to obtain the composite lithium metal negative electrode.

[0012] The present invention places a lithium metal sheet coated with a fluorine-containing solution in a dielectric barrier discharge (DBD) device, locally creates a plasma state of a substance, and then uses high-energy ion states to bombard the surface of the lithium metal sheet, effectively etching the lithium layer on the surface of the lithium metal sheet, thereby forming a porous lithium fluoride three-dimensional structure in situ. This provides a path and space for the migration of lithium ions and the lateral growth of lithium dendrites, while inhibiting the longitudinal growth of dendrites on the surface of the lithium metal sheet and the occurrence of side reactions. It can also react across the reaction energy barrier on the material surface, shortening the reaction time, achieving precise control of the material morphology, and helping the lithium metal negative electrode to achieve long-cycle charge and discharge.

[0013] It should be noted that dielectric barrier discharge (DBD) generally utilizes gases such as Ar to be converted into a plasma state under a high-pressure environment, thereby bombarding the groups of compounds on the surface of the dielectric into free radicals and activating the reaction, thereby reducing the reaction energy barrier and improving the reaction kinetics.

[0014] Preferably, the solute in the fluorine-containing solution in step (1) includes ammonium bifluoride.

[0015] In the preparation method provided by the present invention, ammonium bifluoride is excited into various free radicals (including -NH, -F, -NH2, and -H, etc.) in a plasma state in the local electric field within the DBD device. This excitation reduces the energy barrier required for the reaction (NH4HF+Li→LiF+NH3+H2), thereby greatly increasing the reaction rate and shortening the reaction time.

[0016] Preferably, in the fluorine-containing solution of step (1), the volume ratio of the solvent to the solute is 10:(1-5), for example, it can be 10:1, 10:2, 10:3, 10:4 or 10:5.

[0017] Preferably, the fluorine-containing solution in step (1) is dispersed and dehydrated before being applied to the surface of the lithium metal sheet. The purpose of dehydration is to reduce the water content of the solution. The present invention does not limit the dehydrating agent used, and for example, it can be a dehydrating molecular sieve.

[0018] The present invention does not limit the dispersion method, and for example, ultrasonic dispersion may be used.

[0019] Preferably, the dispersion time is 15-30 min, for example, 15 min, 17 min, 19 min, 20 min, 22 min, 24 min, 26 min, 28 min or 30 min.

[0020] Preferably, the coating method in step (1) includes spin coating and / or drop coating.

[0021] In the present invention, the spin coating method is used to keep the liquid level at the same height on the surface of the lithium sheet, which is conducive to forming a uniform surface lithium fluoride layer, thereby reducing concentration polarization during lithium deposition and facilitating the inhibition of the longitudinal growth of dendrites.

[0022] Preferably, in the spin coating method, the spin coating rate is 600-1100 rpm, for example, it can be 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm or 1100 rpm.

[0023] Preferably, the coating time in step (1) is 0.5-5 min, for example, it can be 0.5 min, 1 min, 1.5 min, 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min, or 5 min, etc., preferably 1-3 min.

[0024] Preferably, the power of the DBD device can be adjusted in the range of 40-60 W, for example, 40 W, 42 W, 44 W, 46 W, 48 W, 50 W, 52 W, 54 W, 56 W, 58 W or 60 W.

[0025] In the present invention, by adjusting the power of the DBD device, reaction conditions can be directly controlled, thereby achieving varying degrees of surface modification. If the DBD device power is too low, the voltage between the upper and lower plates will be too low at a fixed frequency setting, preventing plasma from forming to modify the surface. If the DBD device power is too high, the voltage between the upper and lower plates will be too high at a fixed frequency setting, causing plasma to break down the surface, destroying the surface morphology and preventing the formation of a dense pore structure.

[0026] Preferably, in the DBD device, the operating voltage is 15-40V, for example, 15V, 20V, 25V, 30V, 35V or 40V.

[0027] Preferably, the frequency of the DBD device is adjusted so that the current of the DBD device is stabilized in the range of 2-3A, for example, 2A, 2.1A, 2.2A, 2.3A, 2.4A, 2.5A, 2.6A, 2.7A, 2.8A, 2.9A or 3A.

[0028] In the present invention, by adjusting the frequency of the DBD device, the discharge current can be varied, thereby adjusting the reaction penetration depth and reaction rate. If the DBD current is too low, the modification reaction will be incomplete, the surface area of ​​the formed LiF will be too low, and the inhibition effect on lithium dendrites will be reduced. If the DBD current is too high, the surface temperature will continue to rise, and some ammonium bifluoride will be directly decomposed into hydrogen fluoride and ammonium fluoride, preventing it from participating in the reaction.

[0029] Preferably, the time of the in situ synthesis reaction in step (2) is 10-30 min, for example, it can be 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, 22 min, 24 min, 26 min, 28 min or 30 min.

[0030] In the present invention, if the in-situ synthesis reaction time is too short, some ammonium bifluoride will remain on the surface and not participate in the reaction; if the in-situ synthesis reaction time is too long, the plasma Ar gas will gradually destroy the dense pore structure on the surface.

[0031] Preferably, the gas in the DBD device in step (2) includes an inert gas, and the inert gas includes Ar gas.

[0032] Preferably, the gas in the DBD device further includes hydrogen fluoride gas.

[0033] Preferably, the volume ratio of the inert gas to the hydrogen fluoride gas is (80-99):(1-20), wherein the selection range of the inert gas "80-99" can be, for example, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98 or 99, and the selection range of the hydrogen fluoride gas "1-20" can be, for example, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19 or 20, etc.

[0034] In the present invention, if the volume ratio of the inert gas to the hydrogen fluoride gas is too small, that is, the content of the hydrogen fluoride gas is too high, the LiF surface layer will be too thick, which is not conducive to the migration of lithium ions on the lithium metal surface.

[0035] As a preferred technical solution, the preparation method comprises the following steps:

[0036] (1) dispersing and removing water from the fluorine-containing solution, and then spin-coating the fluorine-containing solution on the surface of the lithium metal sheet at a rate of 600-1100 rpm for 0.5-5 minutes to obtain a lithium metal sheet with a liquid film formed on the surface;

[0037] The volume ratio of the solvent to the solute in the fluorine-containing solution is 10:(1-5).

[0038] (2) placing the lithium metal sheet with the liquid film formed on the surface in a DBD device, introducing an inert gas, adjusting the power and frequency of the DBD device, and performing an in-situ synthesis reaction for 10-30 minutes to obtain a lithium metal negative electrode containing a lithium fluoride surface modification layer;

[0039] The volume ratio of the inert gas to the hydrogen fluoride gas is (80-99):(1-20), the power adjustment range of the DBD device is 40-60W, the operating voltage is 15-40V, and the current of the DBD device is stable within the range of 2-3A.

[0040] In a second aspect, the present invention provides a composite lithium metal negative electrode prepared by the preparation method described in the first aspect, wherein the composite lithium metal negative electrode comprises a lithium metal sheet and a lithium fluoride modification layer located on the surface of the lithium metal sheet, wherein the lithium fluoride modification layer is a porous three-dimensional structure.

[0041] The lithium fluoride modified layer prepared by the present invention has a flat, porous three-dimensional structure, which is beneficial to inhibiting the longitudinal growth of dendrites on the surface of the lithium metal negative electrode.

[0042] Preferably, the thickness of the lithium fluoride modification layer is 10-60 nm, for example, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm or 60 nm.

[0043] In a third aspect, the present invention provides an application of the composite lithium metal negative electrode as described in the second aspect, wherein the composite lithium metal negative electrode is applied in the field of lithium batteries.

[0044] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] (1) The present invention places a lithium metal sheet coated with a fluorine-containing solution in a dielectric barrier discharge (DBD) device, locally creates a plasma state of a substance, and then uses a high-energy ion state to bombard the surface of the lithium metal sheet, effectively etching the lithium layer on the surface of the lithium metal sheet, thereby forming a porous lithium fluoride three-dimensional structure in situ. This provides a path and space for the migration of lithium ions and the lateral growth of lithium dendrites, while inhibiting the longitudinal growth of dendrites on the surface of the lithium metal sheet and the occurrence of side reactions, shortening the time required for the reaction and achieving precise control of the material morphology.

[0047] (2) The in-situ generated three-dimensional lithium fluoride structure provided by the present invention has better contact with the lithium metal negative electrode, can effectively reduce the contact resistance, and is not prone to falling off and failure.

[0048] (3) The composite lithium metal negative electrode prepared by the preparation method provided by the present invention has a longer normal charge and discharge time in the constant current charge and discharge cycle test, and its cycle time is increased by more than 50%.

[0049] (4) The preparation method provided by the present invention has low process cost and good development prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 Schematic diagram of the DBD device used in preparing the composite lithium metal negative electrode in Example 1 of the present invention. DETAILED DESCRIPTION

[0051] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0052] Example 1

[0053] This embodiment provides a method for preparing a composite lithium metal negative electrode, the preparation method comprising the following steps:

[0054] (1) Dimethyl sulfoxide and ammonium bifluoride were prepared into 10 mL of ammonium bifluoride solution at a volume ratio of 10:1 and ultrasonically dispersed for 15 min. Then, 2 g of dehydrating molecular sieves were added to remove water.

[0055] (2) placing a lithium metal sheet on a spin coater in a glove box, and dripping 0.1 mL of ammonium bifluoride solution onto the surface of the lithium metal sheet at a rate of 1100 rpm for 1 min to obtain a lithium metal sheet with a liquid film formed on the surface;

[0056] (3) placing the lithium metal sheet with the liquid film formed on the surface in a DBD device, opening the gas path in the DBD device, passing Ar gas for 5 minutes to clean the pipeline, then keeping the Ar gas flowing, adjusting the power of the DBD device to 40W, the operating voltage to 15V, adjusting the frequency of the DBD device to stabilize the current at 2.7A, and performing an in-situ synthesis reaction for 10 minutes. After the reaction is completed, the DBD device is closed to obtain a lithium metal negative electrode containing a lithium fluoride surface modification layer, i.e., a composite lithium metal negative electrode;

[0057] Wherein, the thickness of the lithium fluoride surface modification layer is 15 nm.

[0058] Figure 1 This is a schematic diagram of the DBD device used to prepare the composite lithium metal negative electrode in this example. As can be seen from the figure, the device consists of two upper and lower plates, a reaction chamber, and inlet and outlet gas pipes. When started, voltage is applied to both sides of the plates. The device is equipped with a controller to regulate and display the internal current size and circuit frequency of the device after startup.

[0059] Example 2

[0060] This embodiment provides a method for preparing a composite lithium metal negative electrode, the preparation method comprising the following steps:

[0061] (1) Dimethyl sulfoxide and ammonium bifluoride were prepared into 10 mL of ammonium bifluoride solution at a volume ratio of 10:3 and ultrasonically dispersed for 15 min. Then, 2 g of dehydrating molecular sieves were added to remove water.

[0062] (2) placing a lithium metal sheet on a spin coater in a glove box, and dripping 0.1 mL of ammonium bifluoride solution onto the surface of the lithium metal sheet at a rate of 900 rpm for 2 minutes to obtain a lithium metal sheet with a liquid film formed on the surface;

[0063] (3) placing the lithium metal sheet with the liquid film formed on the surface in a DBD device, opening the gas path in the DBD device, passing Ar gas for 5 minutes to clean the pipeline, then keeping the Ar gas flowing, adjusting the power of the DBD device to 50W, the operating voltage to 30V, adjusting the frequency of the DBD device to stabilize the current at 1.7A, and performing an in-situ synthesis reaction for 20 minutes. After the reaction is completed, the DBD device is closed to obtain a lithium metal negative electrode containing a lithium fluoride surface modification layer, i.e., a composite lithium metal negative electrode;

[0064] Wherein, the thickness of the lithium fluoride surface modification layer is 35 nm.

[0065] Example 3

[0066] This embodiment provides a method for preparing a composite lithium metal negative electrode, the preparation method comprising the following steps:

[0067] (1) Dimethyl sulfoxide and ammonium bifluoride were prepared into 10 mL of ammonium bifluoride solution in a volume ratio of 2:1 and ultrasonically dispersed for 30 min. Then, 2 g of dehydrating molecular sieves were added to remove water.

[0068] (2) placing a lithium metal sheet on a spin coater in a glove box, and dripping 0.1 mL of ammonium bifluoride solution onto the surface of the lithium metal sheet at a rate of 600 rpm for 5 minutes to obtain a lithium metal sheet with a liquid film formed on the surface;

[0069] (3) placing the lithium metal sheet with the liquid film formed on the surface in a DBD device, opening the gas path in the DBD device, passing Ar gas for 5 minutes to clean the pipeline, then keeping the Ar gas flowing, adjusting the power of the DBD device to 60W, the operating voltage to 40V, adjusting the frequency of the DBD device to stabilize the current at 1.5A, and performing an in-situ synthesis reaction for 30 minutes. After the reaction is completed, the DBD device is closed to obtain a lithium metal negative electrode containing a lithium fluoride surface modification layer, i.e., a composite lithium metal negative electrode;

[0070] Wherein, the thickness of the lithium fluoride surface modification layer is 55 nm.

[0071] Example 4

[0072] This embodiment provides a method for preparing a composite lithium metal negative electrode, the preparation method comprising the following steps:

[0073] (1) Dimethyl sulfoxide and ammonium bifluoride were prepared into 10 mL of ammonium bifluoride solution at a volume ratio of 10:1 and ultrasonically dispersed for 15 min. Then, 2 g of dehydrating molecular sieves were added to remove water.

[0074] (2) placing a lithium metal sheet on a spin coater in a glove box, and dripping 0.1 mL of ammonium bifluoride solution onto the surface of the lithium metal sheet at a rate of 1100 rpm for 1 min to obtain a lithium metal sheet with a liquid film formed on the surface;

[0075] (3) placing the lithium metal sheet with the liquid film formed on the surface in a DBD device, opening the gas path in the DBD device, passing Ar gas for 5 minutes to clean the pipeline, and then passing a mixture of Ar gas and hydrogen fluoride gas with a volume ratio of 95:5, adjusting the power of the DBD device to 60W, the operating voltage to 24V, adjusting the frequency of the DBD device to stabilize the current at 2.5A, and performing an in-situ synthesis reaction for 30 minutes. After the reaction is completed, the DBD device is closed to obtain a lithium metal negative electrode containing a lithium fluoride surface modification layer, i.e., a composite lithium metal negative electrode;

[0076] Wherein, the thickness of the lithium fluoride surface modification layer is 25 nm.

[0077] Example 5

[0078] The difference between this embodiment and embodiment 4 is that the volume ratio of Ar gas to hydrogen fluoride gas in step (3) is 80:20.

[0079] The rest of the preparation methods and parameters remained the same as in Example 1.

[0080] Example 6

[0081] The difference between this embodiment and embodiment 4 is that the volume ratio of Ar gas to hydrogen fluoride gas in step (3) is 99:1.

[0082] The rest of the preparation methods and parameters remained the same as in Example 1.

[0083] Example 7

[0084] The difference between this embodiment and embodiment 1 is that the power of the DBD device in step (3) is 20W.

[0085] The rest of the preparation methods and parameters remained the same as in Example 1.

[0086] Example 8

[0087] The difference between this embodiment and embodiment 1 is that the power of the DBD device in step (3) is 80W.

[0088] The rest of the preparation methods and parameters remained the same as in Example 1.

[0089] Example 9

[0090] The difference between this embodiment and embodiment 1 is that the current of the DBD device in step (3) is 0.5A.

[0091] The rest of the preparation methods and parameters remained the same as in Example 1.

[0092] Example 10

[0093] The difference between this embodiment and embodiment 1 is that the current of the DBD device in step (3) is 4A.

[0094] The rest of the preparation methods and parameters remained the same as in Example 1.

[0095] Example 11

[0096] The difference between this embodiment and embodiment 1 is that the time of the in situ synthesis reaction in step (3) is 2 minutes.

[0097] The rest of the preparation methods and parameters remained the same as in Example 1.

[0098] Example 12

[0099] The difference between this embodiment and embodiment 1 is that the time of the in-situ synthesis reaction in step (3) is 50 minutes.

[0100] The rest of the preparation methods and parameters remained the same as in Example 1.

[0101] Example 13

[0102] The difference between this embodiment and embodiment 4 is that the volume ratio of Ar gas to hydrogen fluoride gas in step (3) is 70:30.

[0103] The rest of the preparation methods and parameters remained the same as in Example 1.

[0104] Comparative Example 1

[0105] This comparative example provides a method for preparing a composite lithium metal negative electrode, the preparation method comprising the following steps:

[0106] The lithium metal sheet was immersed in 10 mL of ammonium bifluoride solution prepared by dimethyl sulfoxide and ammonium bifluoride in a volume ratio of 10:1. After standing and reacting for 12 hours, the lithium sheet was taken out and the excess liquid on the surface was washed with DMF. Then, it was vacuum dried at 50°C for 2 hours to obtain a lithium metal negative electrode sheet with a lithium fluoride surface modification layer.

[0107] Comparative Example 2

[0108] The difference between this comparative example and Example 1 is that the ammonium bifluoride in step (1) is replaced by ammonium bichloride.

[0109] The rest of the preparation methods and parameters remained the same as in Example 1.

[0110] Performance Testing

[0111] The composite lithium metal sheets (2 sheets) prepared in Examples 1-13 and Comparative Examples 1-2 were assembled with a separator to obtain a lithium symmetrical battery. The button-type symmetrical battery was subjected to a constant current charge and discharge cycle test until the voltage range at a fixed capacity in the cycle exceeded more than 1 / 3 of the previous cycle. Lithium dendrite growth was considered to have occurred on the surface of the lithium sheet. The cycle was terminated and the time was recorded.

[0112] Test conditions: constant current charge and discharge current 3mA, constant current time 1h.

[0113] The test results are shown in Table 1.

[0114] Table 1

[0115]

[0116] analyze:

[0117] As can be seen from the above table, the composite lithium metal negative electrode prepared by the preparation method provided in this application has a longer normal charge and discharge time in the constant current charge and discharge cycle test, and its cycle time is increased by more than 50%.

[0118] From the comparison of the data results of Examples 1-3 and Examples 4-6, it can be seen that adding hydrogen fluoride gas to the introduced gas can further increase the surface area of ​​the generated LiF layer, thereby providing a shorter migration path for lithium ions.

[0119] From the comparison of the data results of Example 1 and Examples 7-8, it can be seen that if the power of the DBD device is too low, the energy of the plasma state Ar will be too low, which will result in the inability to effectively break the molecular bonds of ammonium bifluoride, resulting in too little surface LiF generated; if the power of the DBD device is too high, then under a fixed frequency setting, the voltage between the upper and lower plates will be too large, the plasma will break down the surface, causing damage to the surface morphology, and it will be impossible to form a dense pore structure.

[0120] From the comparison of the data results of Example 1 and Examples 9-10, it can be seen that if the current of the DBD device is too low, the modification reaction will be insufficient, the surface area of ​​LiF formed will be too low, and the inhibition effect on lithium dendrites will be reduced; if the current of the DBD device is too high, the surface temperature will rise too quickly during the modification, thereby causing a portion of the ammonium bifluoride to decompose and be unable to participate in the reaction normally.

[0121] From the comparison of the data results of Example 1 and Examples 11-12, it can be seen that if the in situ synthesis reaction time is too short, the surface modification reaction will be insufficient, thereby reducing the inhibitory effect on lithium dendrites; if the in situ synthesis reaction time is too long, the skeleton layer structure of the surface LiF layer will be destroyed, thereby reducing the unit surface area of ​​LiF and reducing the inhibitory effect on lithium dendrites.

[0122] From the comparison of the data results of Example 4 and Example 13, it can be seen that if the volume ratio of Ar gas to hydrogen fluoride gas is too small, the content of plasma Ar will be reduced, thereby reducing the efficiency of plasma Ar collision on surface modification, and at the same time, the LiF surface layer will be too thick, which is not conducive to the migration of lithium ions on the lithium metal surface.

[0123] From the comparison of the data results of Example 1 and Comparative Example 1, it can be seen that the conventional chemical immersion method may result in incomplete reaction, less LiF formed on the surface and a low unit surface area of ​​LiF, resulting in poor inhibition effect on lithium dendrites.

[0124] From the comparison of the data results of Example 1 and Comparative Example 2, it can be seen that if ammonium bifluoride is replaced by ammonium bichloride, the surface modification layer obtained is lithium chloride, which will relatively reduce the migration speed of lithium ions in the surface layer, resulting in a decrease in the inhibitory effect on lithium dendrites.

[0125] The applicant states that while the above-described embodiments illustrate the process of the present invention, the present invention is not limited to the above-described process steps, nor does it imply that the present invention must rely on the above-described process steps for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent substitutions for the raw materials used, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a composite lithium metal negative electrode, characterized in that: The preparation method comprises the following steps: (1) coating the surface of a lithium metal sheet with a fluorine-containing solution to obtain a lithium metal sheet having a liquid film formed on the surface; The solute in the fluorine-containing solution in step (1) includes ammonium bifluoride; The coating method in step (1) is spin coating; (2) placing the lithium metal sheet with the liquid film formed on the surface in a dielectric barrier discharge (DBD) device to perform an in-situ synthesis reaction, thereby in-situ forming a porous lithium fluoride three-dimensional structure to obtain the composite lithium metal negative electrode; The power of the DBD device is adjusted in the range of 40-60W; the frequency of the DBD device is adjusted so that the current of the DBD device is stabilized in the range of 2-3A; and the time of the in-situ synthesis reaction in step (2) is 10-30min.

2. The preparation method according to claim 1, characterized in that In the fluorine-containing solution of step (1), the volume ratio of the solvent to the solute is 10:(1-5).

3. The preparation method according to claim 1, characterized in that In step (1), the fluorine-containing solution is dispersed and dehydrated before being coated on the surface of the lithium metal sheet.

4. The preparation method according to claim 1, characterized in that In the spin coating method, the spin coating speed is 600-1100 rpm.

5. The preparation method according to claim 1, characterized in that The coating time in step (1) is 0.5-5 minutes.

6. The preparation method according to claim 5, characterized in that The coating time in step (1) is 1-3 minutes.

7. The preparation method according to claim 1, characterized in that In the DBD device, the operating voltage is 15-40V.

8. The preparation method according to claim 1, characterized in that The gas in the DBD device in step (2) includes an inert gas, and the inert gas includes Ar gas.

9. The preparation method according to claim 8, characterized in that The gas in the DBD device further includes hydrogen fluoride gas.

10. The preparation method according to claim 9, characterized in that The volume ratio of the inert gas to the hydrogen fluoride gas is (80-99):(1-20).

11. The preparation method according to claim 1, characterized in that The preparation method comprises the following steps: (1) Dispersing and removing water from the fluorine-containing solution, and then spin-coating the fluorine-containing solution on the surface of the lithium metal sheet at a rate of 600-1100 rpm for 0.5-5 minutes to obtain a lithium metal sheet with a liquid film formed on the surface; The volume ratio of the solvent to the solute in the fluorine-containing solution is 10:(1-5). (2) placing the lithium metal sheet with the liquid film formed on the surface in a DBD device, introducing inert gas and hydrogen fluoride gas, adjusting the power and frequency of the DBD device, and performing an in-situ synthesis reaction for 10-30 minutes to obtain a lithium metal negative electrode containing a lithium fluoride surface modification layer; The volume ratio of the inert gas to the hydrogen fluoride gas is (80-99):(1-20), the power adjustment range of the DBD device is 40-60W, the operating voltage is 15-40V, and the current of the DBD device is stable within the range of 2-3A.

12. A composite lithium metal negative electrode prepared by the preparation method according to any one of claims 1 to 11, characterized in that: The composite lithium metal negative electrode includes a lithium metal sheet and a lithium fluoride modification layer located on the surface of the lithium metal sheet, and the lithium fluoride modification layer is a porous three-dimensional structure.

13. The composite lithium metal negative electrode according to claim 12, characterized in that The thickness of the lithium fluoride modification layer is 10-60 nm.

14. Use of the composite lithium metal negative electrode according to claim 12 or 13, characterized in that: The composite lithium metal negative electrode is used in the field of lithium batteries.

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