Lithium metal negative electrode containing artificial SEI (solid electrolyte interface) film as well as preparation method and application of lithium metal negative electrode

Abstract

The invention discloses a lithium metal negative electrode containing an artificial SEI (solid electrolyte interface) film as well as a preparation method and application of the lithium metal negative electrode. The lithium metal negative electrode comprises a copper foil, a lithium metal layer on the surface of the copper foil, a Cu-Li2S interface layer on the surface of the lithium metal layer and a sulfur-containing polymer coating on the surface of the Cu-Li2S interface layer, and the artificial SEI film consists of the Cu-Li2S interface layer and the sulfur-containing polymer coating. The preparation method comprises the following steps: preparing the sulfur-containing polymer coating on the surface of the copper foil, enabling elemental sulfur at the interface contact position of the copper foil and the sulfur-containing polymer coating to react with copper through temperature and time driving to form the Cu2S interface layer, and performing replacement reaction on the Cu2S interface layer and part of lithium metal in the lithium deposition process to form the Cu-Li2S interface layer. And the lithium metal negative electrode jointly modified by the sulfur-containing polymer coating and the Cu-Li2S interface layer is formed. The artificial SEI film on the surface of the lithium metal negative electrode has flexibility of a sulfur-containing polymer coating and rigidity of a Cu-Li2S interface layer, SEI film breakage, lithium dendrite puncture and pulverization in the cycle process of the lithium metal negative electrode are effectively avoided, and the long cycle life can be achieved.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium metal batteries, and specifically discloses a lithium metal anode containing an artificial SEI film, its preparation method and application. Background Technology

[0002] Lithium metal batteries, due to the high specific capacity and low potential of lithium metal anodes, have become the most promising rechargeable battery technology. However, lithium metal anodes possess extremely high electrochemical activity. Once in contact with the electrolyte, lithium metal reacts with lithium salts, solvents, and additives in the electrolyte, forming an unstable SEI film. This leads to problems such as low coulombic efficiency and short cycle life commonly found in current lithium metal anodes. To address these issues, researchers have proposed modifying the surface of lithium metal with an artificial SEI film to avoid lithium dendrite growth and the resulting low coulombic efficiency and short cycle life. Inorganic artificial SEI films have been widely studied and reported due to their outstanding advantages of high lithium-ion conductivity and high mechanical strength. Lithium metal anodes modified with inorganic artificial SEI films show significantly suppressed dendrite growth and improved cycle stability. Invention patent CN116344749A describes a method of forming a lithium nitride artificial SEI film on the surface of lithium metal using nitrogen-containing plasma discharge. Similarly, invention patent CN 111029589A prepared Li2S by using sulfur powder or transition metal sulfides as the loading material and through processes such as atomic layer deposition, vapor deposition and electrochemical reduction. n (n=1 or n=2) Artificial SEI film. To further improve the cycle life of lithium metal anodes, invention patent CN 118156421B constructed a lithium sulfide / lithium oxide interpenetrating bilayer inorganic artificial SEI film to overcome the shortcomings of single-layer inorganic artificial SEI films, achieving a superlinear synergistic effect of 1+1>2. However, inorganic artificial SEI films lack sufficient toughness, leading to the rupture of the surface SEI film during long-term deep charge-discharge cycles due to repeated volume expansion and contraction of the lithium metal anode, subsequently inducing dendrite growth. In response, invention patent CN 116779858A proposed using organic polymers and inorganic metal nitrates as precursors, utilizing the spontaneous reaction between metal nitrates and organic polymers and lithium metal to generate a multifunctional artificial SEI film including lithiophilic metal particles, inorganic lithium oxynitride, and flexible organic polymers, significantly improving the cycle performance of lithium metal anodes. However, lithium-loving metal particles readily undergo alloying reactions with lithium metal, causing significant volume effects and deteriorating the interfacial compatibility between the artificial SEI film and the lithium metal anode. Therefore, there is an urgent need to develop efficient, stable, and flexible artificial SEI films to improve the cycle life of lithium metal anodes and facilitate their industrial application. Summary of the Invention

[0003] To address the common problems of lithium metal anodes, this invention aims to provide a lithium metal anode comprising an artificial SEI film, its preparation method, and its applications. The artificial SEI film on the surface of the lithium metal anode in this invention combines the flexibility of a sulfur-containing polymer coating with the rigidity of a Cu-Li2S interface layer, effectively preventing SEI film rupture, lithium dendrite penetration, and pulverization during lithium metal anode cycling, thus achieving a long cycle life.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] A lithium metal anode comprising an artificial SEI film includes a copper foil, a lithium metal layer on the surface of the copper foil, a Cu-Li2S interface layer on the surface of the lithium metal layer, and a sulfur-containing polymer coating on the surface of the Cu-Li2S interface layer. The artificial SEI film is composed of a sulfur-containing polymer coating that has not reacted with copper and a Cu-Li2S interface layer obtained after a two-step reaction with copper and lithium.

[0006] Furthermore, the sulfur-containing polymer coating is obtained by coating a slurry prepared from a mixture of elemental sulfur and an adhesive. The thickness of the sulfur-containing polymer coating is 5-20 μm. If the thickness of the sulfur-containing polymer coating is too thin, this artificial SEI film lacks sufficient strength to suppress the volume effect and lithium dendrite problem during repeated deep charge-discharge processes. If the sulfur-containing polymer coating is too thick, ion transport becomes more difficult, which can easily lead to increased battery polarization, capacity decay, and reduced cycle life.

[0007] Furthermore, the particle size of the elemental sulfur is 10-500 nm, preferably 50-200 nm. If the elemental sulfur particle size is too small, it is prone to agglomeration during the preparation of the sulfur-polyvinylidene fluoride slurry, resulting in uneven sulfur distribution in the coating and directly affecting the formation of the subsequent Cu2S interface layer and Cu-Li2S interface layer, thus leading to poor performance. If the elemental sulfur particle size is too large, the reaction kinetics between S and Cu during the drying process are too slow, making it impossible to form a sufficient Cu2S interface layer, ultimately affecting the formation of the Cu-Li2S interface layer.

[0008] Furthermore, the adhesive is any one or a mixture of polyvinylidene fluoride, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene copolymer, acrylonitrile, polytetrafluoroethylene, polymethyl methacrylate, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, calcium carboxymethyl cellulose, and polyacrylic acid.

[0009] The present invention also provides a method for preparing the lithium metal anode containing the artificial SEI film, comprising the following steps:

[0010] (1) Elemental sulfur and adhesive are uniformly dispersed in N-methylpyrrolidone or deionized water to form a slurry, which is then coated on the surface of copper foil. The copper foil electrode with sulfur-containing polymer coating / Cu2S interface layer is dried by adjusting the oven temperature and time. The oven temperature is 60~120 ℃ and the time is 4~12 h.

[0011] (2) Using the copper foil electrode modified with sulfur-containing polymer coating / Cu2S interface layer obtained in step (1) as the working electrode and lithium sheet as the counter electrode, lithium metal is loaded onto the copper foil surface by electrodeposition in an organic lithium salt electrolyte, so that the lithium metal reacts with the Cu2S interface layer on the copper foil electrode to form a Cu-Li2S interface layer, and finally a lithium metal anode modified with sulfur-containing polymer coating / Cu-Li2S interface layer is formed, that is, a lithium metal anode containing an artificial SEI film is obtained, wherein the current density of electrodeposition is 1 mA / cm 2 The areal capacity of electrodeposition is 3 mAh / cm². 2 .

[0012] Furthermore, in step (1), the mass ratio of elemental sulfur to adhesive is (40~80):(60~20). If the elemental sulfur content is too low, a sufficient Cu2S interface layer cannot be formed during the coating drying process, thus affecting the formation of the Cu-Li2S interface layer. Once the Cu-Li2S interface layer content is too low, the final artificial SEI film lacks sufficient rigidity and cannot suppress the growth of lithium dendrites for a long time, easily leading to performance deterioration. If the elemental sulfur content is too high, the adhesive content will be insufficient, preventing the coating from forming a good bond with the copper foil substrate, ultimately affecting the quality of the coating and causing performance deterioration.

[0013] Furthermore, in step (1), the oven temperature is controlled at 60~120 ℃, and the drying time is 4~12 h. If the drying temperature is too low, the driving force for the reaction between elemental sulfur in the coating and copper foil is insufficient, and a sufficient Cu2S interface layer cannot be formed, which in turn leads to the inability to form a sufficient Cu-Li2S interface layer, ultimately resulting in insufficient rigidity of the artificial SEI film on the surface of the lithium metal anode. If the drying temperature is too high, copper oxide will form on the surface of the copper foil, and elemental sulfur will also volatilize, resulting in uneven formation of the Cu2S interface layer, ultimately leading to the instability of the Cu-Li2S interface layer and affecting battery performance. If the drying time is too short, the driving force for the reaction between elemental sulfur in the coating and copper foil is insufficient, and a sufficient Cu2S interface layer cannot be formed, which in turn leads to the inability to form a sufficient Cu-Li2S interface layer, ultimately resulting in insufficient rigidity of the artificial SEI film on the surface of the lithium metal anode. If the drying time is too long, the formation of copper oxide on the surface of the copper foil will affect the uneven formation of the Cu2S interface layer, ultimately leading to the instability of the Cu-Li2S interface layer. In addition, excessively long drying time for the coating can cause cracking, leading to unstable lithium-ion transport and severely degrading battery performance.

[0014] Furthermore, the current density for electrodeposition in step (2) is 0.5~2 mA / cm². 2 The areal capacity of electrodeposition is 2~5 mAh / cm². 2 If the current density is too low, the lithium metal deposits will be too large, resulting in a loose lithium metal layer and a loose Cu-Li2S interface layer on the lithium metal surface. This will prevent the lithium metal anode from achieving stable charge-discharge cycles over a long period. If the current density is too high, the lithium ions in the electrolyte will be consumed too quickly, easily causing concentration polarization, which in turn will lead to uneven lithium deposition. If the areal capacity is too low, although a relatively stable sulfide-carboxymethyl cellulose lithium coating and Cu-Li2S interface layer can be formed on the lithium metal surface, once the lithium metal is lost during cycling, it cannot be replenished, leading to a significant reduction in the cycle life of the lithium metal anode. If the areal capacity is too high, the lithium metal anode modified with the sulfide-carboxymethyl cellulose lithium coating and Cu-Li2S interface layer cannot withstand such a high areal capacity, and lithium dendrite growth is highly likely to occur.

[0015] Furthermore, the electrolyte in step (2) is composed of lithium salt and organic solvent, wherein the lithium salt is any one or a mixture of multiple of LiFSI, LiTFSI, LiNFBS, and LiDFOB, and the solvent is a mixture of DME and TTE, with an electrolyte concentration of 0.5~4 M. If the electrolyte concentration is too low, concentration polarization is easily generated during the deposition of lithium metal, resulting in uneven lithium metal deposition, which in turn leads to the reaction of lithium metal with Cu2S to form an uneven Cu-Li2S interface layer, ultimately deteriorating the cycle performance of the lithium metal anode. If the electrolyte concentration is too high, the viscosity of the electrolyte will increase significantly, making it more difficult for lithium ions to migrate to the copper foil surface, resulting in uneven lithium metal deposition.

[0016] This invention also provides the application of the lithium metal anode containing an artificial SEI film in lithium metal batteries, wherein the lithium metal anode containing an artificial SEI film is combined with LiNi x Co y Mn z O2 cathode (where x+y+z=1), LiNi 0.8 Co 0.15 Al 0.05 A lithium metal battery is composed of an O2 cathode, a LiMn2O4 cathode, a LiFePO4 cathode, a LiCoO2 cathode, a S cathode, and an O2 cathode.

[0017] The lithium metal anode containing an artificial SEI film of the present invention has the following advantages: (1) The artificial SEI film is composed of a sulfur-containing polymer coating with good flexibility and a Cu-Li2S interface layer with high mechanical strength, which can ensure that the lithium metal anode maintains high structural stability during deep charge and discharge, and avoid dendrite growth problems caused by the cracking of the surface SEI film. (2) The artificial SEI film formed by chemical reaction has good bonding force with lithium metal, avoiding separation of the artificial SEI film from the lithium metal layer during cycling, which would cause increased polarization and reduced lifetime. The specific formation process is as follows: First, the elemental sulfur in the sulfur-containing polymer coating reacts with the copper foil at the interface to form a Cu2S interface layer (2Cu + S = Cu2S). Then, during the lithium deposition process, Cu2S reacts with the lithium metal to form a Cu-Li2S interface layer (Cu2S + 2Li = 2Cu + Li2S). (3) Moreover, this lithium metal anode containing an artificial SEI film possesses the characteristics of gradient ion conduction and reverse gradient electron conduction. The ion conduction capability gradually decreases from the sulfur-containing polymer coating to the Cu-Li2S interface layer and then to the lithium metal layer, while the electron conduction capability gradually decreases from the lithium metal layer to the Cu-Li2S interface layer and then to the sulfur-containing polymer coating. This facilitates the rapid transport of lithium ions in the electrolyte to electrons on the copper foil surface. In addition, this lithium metal anode preparation method is simple, safe, and easy to scale up and apply. Thanks to the above advantages, the lithium metal anode containing an artificial SEI film prepared by this invention exhibits a long cycle life and is expected to promote the commercial application of lithium metal batteries.

[0018] Instruction manual illustrations

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of a lithium metal anode containing an artificial SEI film in Example 1, where 1 is a copper foil; 2 is a lithium metal layer; 3 is a Cu-Li2S interface layer; and 4 is a sulfur-containing polymer coating. Detailed Implementation

[0021] The following is a detailed description of the preferred embodiments of the present invention, which does not constitute any limitation on the present invention. That is, the present invention is not limited to the above embodiments, and common variations or alternative compounds in this technical field are all included within the scope defined by the claims of this application.

[0022] Example 1

[0023] The method for preparing the lithium metal anode including the artificial SEI film in this embodiment is as follows:

[0024] (1) 60 nm elemental sulfur and polyvinylidene fluoride (PVDF) were uniformly dispersed in N-methylpyrrolidone at a mass ratio of 50:50 to form a sulfur-PVDF slurry. The slurry was then coated onto the surface of a commercial copper foil and dried in an oven at 80 °C for 6 h to form a coating with a thickness of 12 μm. During the drying process, the elemental sulfur in the sulfur-PVDF slurry that was in direct contact with the copper foil reacted to form a Cu2S interface layer, thus obtaining a copper foil electrode modified with a sulfur-PVDF coating and a Cu2S interface layer.

[0025] (2) A copper foil electrode modified with a sulfur-polyvinylidene fluoride coating and a Cu2S interface layer was used as the working electrode, a lithium metal sheet was used as the counter electrode, and a 2 M LiFSI / DME-TTE organic lithium salt solution was used as the electrolyte. The electrolyte was prepared at 1 mA / cm². 2 Current density and 3mAh / cm 2 Lithium deposition is performed at a specific area capacity. During lithium deposition, the Cu2S interface layer reacts with the lithium metal to form a Cu-Li2S interface layer, resulting in a lithium metal anode modified with a sulfur-polyvinylidene fluoride coating and a Cu-Li2S interface layer, which in turn yields a lithium metal anode containing an artificial SEI film. Figure 1 ).

[0026] A lithium metal anode including an artificial SEI film was coupled with a 3 mAh / cm² electrolyte. 2 A battery composed of a LiFePO4 cathode (with a mass ratio of LiFePO4, conductive carbon black, and polyvinylidene fluoride of 96:2:2) was cycled at 1C rate, and the corresponding test results are shown in Table 1. Thanks to the combination of rigidity and flexibility of the artificial SEI film and its good adhesion to lithium metal, high anode structural stability can be maintained during deep charge and discharge processes, avoiding dendrite growth problems caused by the rupture of the surface SEI film. Therefore, the LiFePO4 battery exhibits excellent initial coulombic efficiency (97.1%) and discharge specific capacity (163.8 mAh / g), and can achieve stable cycling for up to 721 cycles.

[0027] Comparative Example 1

[0028] Commercial copper foil was used as the working electrode, lithium metal sheet as the counter electrode, and 2 M LiFSI / DME-TTE organic lithium salt solution as the electrolyte, at 1 mA / cm². 2 Current density and 3 mAh / cm 2Lithium deposition was performed at the areal capacity level to obtain a lithium metal / copper foil anode. The lithium metal / copper foil anode was then used in conjunction with the LiFePO4 cathode from Example 1 to form a battery, which was cycled at 1C rate. The corresponding test results are shown in Table 1. Because the lithium metal / copper foil anode lacks a stable artificial SEI film for protection, it is highly susceptible to side reactions with the electrolyte, leading to rapid loss of active lithium. Furthermore, lithium dendrite growth is prone to occur during cycling, resulting in significantly lower initial efficiency (96.4%), discharge specific capacity (159.5 mAh / g), and cycle life (119 cycles) compared to the lithium metal anode with an artificial SEI film.

[0029] Comparative Example 2

[0030] Polyvinylidene fluoride (PVDF) was uniformly dispersed in N-methylpyrrolidone (NMP) to form a PVDF slurry. This slurry was then coated onto a commercial copper foil surface and dried in an oven at 80 °C for 6 h, resulting in a 12 μm thick coating, thus obtaining the PVDF-coated copper foil electrode. This electrode was then used as the working electrode, with a lithium metal sheet as the counter electrode and a 2 M LiFSI / DME-TTE organic lithium salt solution as the electrolyte, at a speed of 1 mA / cm². 2 Current density and 3 mAh / cm 2 Lithium deposition was performed at the areal capacity level to obtain a lithium metal anode modified with a polyvinylidene fluoride (PVDF) coating. Finally, the PVDF-coated lithium metal anode and the LiFePO4 cathode from Example 1 were used to form a battery, which was cycled at 1C rate. The corresponding test results are shown in Table 1. The PVDF coating on the lithium metal anode can alleviate the interfacial side reactions between the electrolyte and the lithium metal anode to a certain extent. Therefore, this anode exhibits a higher initial coulombic efficiency (96.7%), discharge specific capacity (160.7 mAh / g), and cycle life (159 cycles) than the lithium metal / copper foil anode. However, the PVDF coating, as an organic artificial interface layer, lacks sufficient strength to suppress lithium dendrite growth, and therefore its performance is far inferior to that of the lithium metal anode containing a rigid-flexible artificial SEI film.

[0031] Comparative Example 3

[0032] 60 nm Cu₂S particles and polyvinylidene fluoride (PVDF) were uniformly dispersed in N-methylpyrrolidone (NMP) at a mass ratio of 50:50 to form a Cu₂S-PVDF slurry. This slurry was then coated onto a commercial copper foil surface and dried in an oven at 80 °C for 6 h, resulting in a 12 μm thick coating, thus obtaining a Cu₂S-PVDF coated copper foil electrode. This electrode was then used as the working electrode, with a lithium metal sheet as the counter electrode and a 2 M LiFSI / DME-TTE organic lithium salt solution as the electrolyte, at a speed of 1 mA / cm². 2 Current density and 3 mAh / cm 2Lithium deposition was performed at the areal capacity level to obtain a lithium metal anode modified with a Cu2S-polyvinylidene fluoride coating. Finally, the lithium metal anode modified with the Cu2S-polyvinylidene fluoride coating and the LiFePO4 cathode from Example 1 were used to form a battery, which was cycled at 1C. The corresponding test results are shown in Table 1. The Cu2S-polyvinylidene fluoride coating possesses a certain degree of rigidity and flexibility, which can alleviate the volume effect of the lithium metal anode during deep charge and discharge processes. Therefore, the LiFePO4 battery exhibits a high initial coulombic efficiency (96.9%) and discharge specific capacity (161.4 mAh / g), and can cycle stably for 274 cycles. However, this SEI film is not formed through a chemical reaction, and therefore lacks good adhesion. Furthermore, this SEI film does not possess the characteristics of gradient ion and anti-gradient electron transport, resulting in a cycle life of less than 38% of that in Example 1.

[0033] Table 1 Cyclic performance of Example 1 and Comparative Examples 1-3

[0034]

[0035] Example 2

[0036] Elemental sulfur and polyvinylidene fluoride (PVDF) with particle sizes of 3, 10, 50, 100, 200, 500, and 1000 nm were uniformly dispersed in N-methylpyrrolidone at a mass ratio of 50:50 to form a sulfur-PVDF slurry. The slurry was then coated onto a commercial copper foil surface and dried in an oven at 100 °C for 6 h, resulting in a 10 μm thick sulfur-PVDF coating and a Cu₂S interface layer modified copper foil electrode. This electrode was then used as the working electrode, with a lithium metal sheet as the counter electrode and a 2 M LiFSI / DME-TTE organic lithium salt solution as the electrolyte, at a speed of 1 mA / cm². 2 Current density and 3 mAh / cm 2 Lithium deposition was performed at a specific isometric capacity to obtain a lithium metal anode with a sulfur-polyvinylidene fluoride coating and a Cu-Li2S interface layer modification. Finally, this lithium metal anode was coupled with a 3 mAh / cm² electrode. 2 LiNi 0.6 Co 0.2 Mn 0.2 O2 cathode (where LiNi) 0.6 Co 0.2 Mn 0.2 A battery composed of O2, conductive carbon black and polyvinylidene fluoride in a mass ratio of 96:2:2 was cycled at 1C rate. The corresponding test results are shown in Table 2.

[0037] Table 2 Cycle performance of lithium metal anodes prepared from elemental sulfur of different particle sizes

[0038]

[0039] The lithium metal anode prepared using elemental sulfur within a preferred particle size range (50-200 nm) exhibits the best performance. If the elemental sulfur particle size is too small, it is prone to agglomeration during the preparation of the sulfur-polyvinylidene fluoride slurry, resulting in uneven sulfur distribution in the coating. This directly affects the formation of the subsequent Cu2S and Cu-Li2S interface layers, thus leading to poor performance. If the elemental sulfur particle size is too large, the reaction kinetics between S and Cu during the drying process are too slow, failing to form a sufficient Cu2S interface layer, ultimately affecting the formation of the Cu-Li2S interface layer.

[0040] Example 3

[0041] 100 nm of elemental sulfur, polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF) were uniformly dispersed in N-methylpyrrolidone (NMP) at a mass ratio of 50:25:25 to form a sulfur-PTFE / PVDF slurry. This slurry was then coated onto a commercial copper foil surface and dried in an oven at 100 °C for 6 h. After drying, copper foil electrodes with sulfur-PTFE / PVDF coatings and Cu₂S interface layers of thicknesses of 2, 5, 10, 20, and 30 μm were formed. These electrodes were then used as the working electrode, with a lithium metal sheet as the counter electrode and a 2 M LiFSI / DME-TTE organic lithium salt solution as the electrolyte, at a speed of 1 mA / cm². 2 Current density and 3 mAh / cm 2 Lithium deposition was performed at a specific isometric capacity to obtain a lithium metal anode modified with a sulfur-PTFE / PTFE coating and a Cu-Li2S interface layer. Finally, this lithium metal anode was coupled with the LiNi electrode from Example 2. 0.6 Co 0.2 Mn 0.2 The O2 cathode battery was cycle-tested at a 1C rate, and the corresponding test results are shown in Table 3.

[0042] Table 3 Cycle performance of lithium metal anodes prepared with different sulfur-containing polymer coating thicknesses

[0043]

[0044] The lithium metal anode prepared using an optimal sulfur-containing polymer coating thickness (5-20 μm) exhibits the best performance. If the sulfur-containing polymer coating is too thin, this artificial SEI film lacks sufficient strength to suppress volume effects and lithium dendrite formation during repeated deep charge-discharge cycles. If the sulfur-containing polymer coating is too thick, ion transport becomes more difficult, easily leading to increased battery polarization, capacity decay, and reduced cycle life.

[0045] Example 4

[0046] 80 nm elemental sulfur and lithium carboxymethyl cellulose were uniformly dispersed in deionized water at mass ratios of 20:80, 40:60, 60:40, 80:20, and 90:10 to form a sulfur-carboxymethyl cellulose lithium slurry. This slurry was then coated onto a commercial copper foil surface and dried in an oven at 100 °C for 9 h, resulting in a 15 μm thick sulfur-carboxymethyl cellulose lithium coating and a Cu₂S interface layer modified copper foil electrode. This electrode was then used as the working electrode, with a lithium metal sheet as the counter electrode and a 2 M LiFSI / DME-TTE organic lithium salt solution as the electrolyte, at a speed of 1 mA / cm². 2 Current density and 3 mAh / cm 2 Lithium deposition was performed at a specific isometric capacity to obtain a lithium metal anode with a sulfur-carboxymethyl cellulose lithium coating and a Cu-Li2S interface layer modification. Finally, this lithium metal anode was coupled with a 3 mAh / cm² electrode. 2 LiNi 0.8 Co 0.1 Mn 0.1 O2 cathode (where LiNi) 0.8 Co 0.1 Mn 0.1 A battery composed of O2, conductive carbon black and polyvinylidene fluoride in a mass ratio of 96:2:2 was cycle-tested at 1C rate. The corresponding test results are shown in Table 4.

[0047] Table 4 Cycle performance of lithium metal anodes prepared with different mass ratios of elemental sulfur and carboxymethyl cellulose lithium

[0048]

[0049] The optimal mass ratio of elemental sulfur to carboxymethyl cellulose adhesive is (40~80):(60~20). Within this range, the lithium metal anode exhibits the best performance. If the elemental sulfur content is too low, a sufficient Cu2S interface layer cannot be formed during coating drying, thus affecting the formation of the Cu-Li2S interface layer. If the Cu-Li2S interface layer content is too low, the final artificial SEI film lacks sufficient rigidity and cannot suppress lithium dendrite growth for an extended period, easily leading to performance degradation. If the elemental sulfur content is too high, the adhesive content will be insufficient, preventing the coating from forming a good bond with the copper foil substrate, ultimately affecting the coating quality and causing performance degradation.

[0050] Example 5

[0051] The slurry prepared from 80 nm elemental sulfur and lithium carboxymethyl cellulose in a 60:40 mass ratio in Example 4 was coated onto the surface of a commercial copper foil. It was then dried at 40, 60, 90, 120, and 180 °C for 5 h each, forming a 15 μm thick sulfur-carboxymethyl cellulose lithium coating and a Cu2S interface layer modified copper foil electrode. This electrode was then used as the working electrode, with a lithium metal sheet as the counter electrode and a 2 M LiFSI / DME-TTE organic lithium salt solution as the electrolyte, at a speed of 1 mA / cm². 2 Current density and 3 mAh / cm 2 Lithium deposition was performed at a specific area capacity to obtain a lithium metal anode with a sulfur-carboxymethyl cellulose lithium coating and a Cu-Li2S interface layer modification. Finally, this lithium metal anode was coupled with the LiNi electrode from Example 4. 0.8 Co 0.1 Mn 0.1 The O2 cathode battery was cycle-tested at a 1C rate, and the corresponding test results are shown in Table 5.

[0052] Table 5 Cycle performance of lithium metal anodes prepared at different drying temperatures

[0053]

[0054] The optimal performance of the lithium metal anode is obtained within the preferred drying temperature range (60~120 °C). If the drying temperature is too low, the driving force for the reaction between elemental sulfur in the coating and the copper foil is insufficient, failing to form a sufficient Cu2S interface layer. Consequently, a sufficient Cu-Li2S interface layer cannot be formed, ultimately resulting in insufficient rigidity of the artificial SEI film on the surface of the lithium metal anode. Conversely, if the drying temperature is too high, copper oxide will form on the copper foil surface, and elemental sulfur will volatilize, leading to uneven formation of the Cu2S interface layer. Ultimately, this results in the unstable formation of the Cu-Li2S interface layer, affecting battery performance.

[0055] Example 6

[0056] The slurry prepared from 80 nm elemental sulfur and lithium carboxymethyl cellulose in a 60:40 mass ratio in Example 4 was coated onto the surface of a commercial copper foil. After drying at 90 °C for 2, 4, 8, 12, and 20 h, respectively, a copper foil electrode with a sulfur-carboxymethyl cellulose lithium coating and a Cu2S interface layer modification was formed with a thickness of 15 μm. This electrode was then used as the working electrode, with a lithium metal sheet as the counter electrode, and a 2 M LiFSI / DME-TTE organic lithium salt solution as the electrolyte, at a speed of 1 mA / cm². 2 Current density and 3 mAh / cm 2 Lithium deposition was performed at a specific area capacity to obtain a lithium metal anode with a sulfur-carboxymethyl cellulose lithium coating and a Cu-Li2S interface layer modification. Finally, this lithium metal anode was compared with the LiNi alloy from Example 4.0.8 Co 0.1 Mn 0.1 The O2 cathode battery was cycle-tested at a 1C rate, and the corresponding test results are shown in Table 6.

[0057] Table 6 Cycle performance of lithium metal anodes prepared at different times

[0058]

[0059] The optimal performance of the lithium metal anode is obtained within the preferred drying time range (4–12 h). If the drying time is too short, the driving force for the reaction between elemental sulfur in the coating and the copper foil is insufficient, preventing the formation of a sufficient Cu2S interface layer. Consequently, a sufficient Cu-Li2S interface layer cannot be formed, ultimately resulting in insufficient rigidity of the artificial SEI film on the surface of the lithium metal anode. Conversely, if the drying time is too long, the formation of copper oxide on the copper foil surface will affect the uneven formation of the Cu2S interface layer, ultimately leading to the unstable formation of the Cu-Li2S interface layer. Furthermore, excessively long coating drying time can cause cracking, resulting in unstable lithium-ion transport and severely degrading battery performance.

[0060] Example 7

[0061] The copper foil electrode modified with a sulfur-carboxymethyl cellulose lithium coating and a Cu2S interface layer obtained by drying for 8 h in Example 6 was used as the working electrode, with a lithium metal sheet as the counter electrode, and organic lithium salt solutions of different concentrations of LiTFSI / DME-TTE as the electrolyte, at a speed of 1.5 mA / cm². 2 Current density and 4 mAh / cm 2 Lithium deposition was performed at a specific area capacity to obtain a lithium metal anode with a sulfur-carboxymethyl cellulose lithium coating and a Cu-Li2S interface layer modification. Finally, this lithium metal anode was compared with the LiNi alloy from Example 4. 0.8 Co 0.1 Mn 0.1 The O2 cathode battery was cycle-tested at 1C rate, and the corresponding test results are shown in Table 7.

[0062] Table 7 Cycle performance of lithium metal anodes prepared in electrolytes of different concentrations

[0063]

[0064] The optimal performance of the lithium metal anode is obtained within the preferred electrolyte concentration range (0.5~4 M). If the electrolyte concentration is too low, concentration polarization easily occurs during lithium metal deposition, leading to uneven lithium metal deposition. This, in turn, causes lithium metal to react with Cu₂S to form an uneven Cu-Li₂S interface layer, ultimately deteriorating the cycle performance of the lithium metal anode. If the electrolyte concentration is too high, the viscosity of the electrolyte will increase significantly, making it more difficult for lithium ions to migrate to the copper foil surface, resulting in uneven lithium metal deposition. This, in turn, forms an uneven Cu-Li₂S interface layer, further deteriorating the cycle performance of the lithium metal anode.

[0065] Example 8

[0066] The copper foil electrode modified with a sulfur-carboxymethyl cellulose lithium coating and a Cu2S interface layer, obtained by drying for 8 h in Example 6, was used as the working electrode. A lithium metal sheet was used as the counter electrode, and a 0.5 M LiTFSI + 0.5 M LiFSI / DME-TTE organic lithium salt solution was used as the electrolyte. Lithium deposition was performed at different current densities and areal capacities to obtain a lithium metal anode modified with a sulfur-carboxymethyl cellulose lithium coating and a Cu-Li2S interface layer. Finally, this lithium metal anode was compared with the LiNi electrode from Example 4. 0.8 Co 0.1 Mn 0.1 The O2 cathode battery was cycle-tested at 1C rate, and the corresponding test results are shown in Table 8.

[0067] Table 8 Cycle performance of lithium metal anodes prepared under different current densities and areal capacities

[0068]

[0069] Within the preferred current density range (0.5~2 mA / cm²) 2 ) and area capacity range (2~5 mAh / cm²) 2Within a certain range, the lithium metal anode exhibits the best performance. If the current density is too low, the lithium metal deposits will be large, resulting in a loose lithium metal layer and an unstable Cu-Li2S interface layer on the lithium metal surface. This prevents the lithium metal anode from achieving stable charge-discharge cycles over a long period. If the current density is too high, lithium ions in the electrolyte will be consumed too quickly, easily causing concentration polarization, which in turn leads to uneven lithium deposition. Therefore, the reaction between lithium metal and Cu2S will form an uneven Cu-Li2S interface layer, ultimately deteriorating the cycle performance of the lithium metal anode. Similarly, if the areal capacity is too low, although a relatively stable sulfide-carboxymethyl cellulose lithium coating and Cu-Li2S interface layer can be formed on the lithium metal surface, once lithium metal is lost during cycling, it cannot be replenished, leading to a significant reduction in the cycle life of the lithium metal anode. Conversely, if the areal capacity is too high, the lithium metal anode modified with the sulfide-carboxymethyl cellulose lithium coating and Cu-Li2S interface layer cannot withstand such a high areal capacity, easily causing lithium dendrite growth. In other words, when reacting with LiNi... 0.8 Co 0.1 Mn 0.1 Before the O2 positive electrode is formed into a battery, lithium dendrites already exist on the surface of the negative electrode, resulting in extremely poor electrochemical performance of this lithium metal negative electrode.

[0070] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A lithium metal anode comprising an artificial SEI film, characterized in that: The lithium metal anode containing the artificial SEI film comprises a copper foil, a lithium metal layer on the surface of the copper foil, a Cu-Li2S interface layer on the surface of the lithium metal layer, and a sulfur-containing polymer coating on the surface of the Cu-Li2S interface layer, wherein the artificial SEI film is composed of the Cu-Li2S interface layer and the sulfur-containing polymer coating.

2. The lithium metal anode comprising an artificial SEI film according to claim 1, characterized in that: The sulfur-containing polymer coating is obtained by coating a slurry prepared by mixing elemental sulfur and an adhesive. The thickness of the sulfur-containing polymer coating is 5~20 μm, and the mass ratio of elemental sulfur to adhesive is (40~80):(60~20).

3. The lithium metal anode comprising an artificial SEI film according to claim 2, characterized in that: The particle size of the elemental sulfur is 10~500 nm.

4. The lithium metal anode comprising an artificial SEI film according to claim 2, characterized in that: The adhesive is any one or a mixture of polyvinylidene fluoride, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene copolymer, acrylonitrile, polytetrafluoroethylene, polymethyl methacrylate, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, calcium carboxymethyl cellulose, and polyacrylic acid.

5. The method for preparing a lithium metal anode comprising an artificial SEI film according to any one of claims 1 to 4, characterized in that... Includes the following steps: (1) Elemental sulfur and adhesive are uniformly dispersed in N-methylpyrrolidone or deionized water to form a slurry, which is then coated on the surface of copper foil. The oven temperature and time are then controlled to dry the copper foil electrode to form a sulfur-containing polymer coating / Cu2S interface layer modified copper foil electrode. (2) The copper foil electrode modified with sulfur-containing polymer coating / Cu2S interface layer obtained in step (1) is used as the working electrode, and the lithium sheet is used as the counter electrode. In the organic lithium salt electrolyte, lithium metal is loaded onto the surface of the copper foil by electrodeposition to obtain a lithium metal layer. At the same time, some lithium metal reacts with the Cu2S interface layer on the copper foil electrode to form a Cu-Li2S interface layer, and finally a lithium metal anode modified with sulfur-containing polymer coating / Cu-Li2S interface layer is formed, that is, a lithium metal anode containing an artificial SEI film is obtained.

6. The method for preparing a lithium metal anode comprising an artificial SEI film according to claim 5, characterized in that: In step (1), the particle size of elemental sulfur is 10~500 nm, the mass ratio of elemental sulfur to adhesive is (40~80):(60~20), and the thickness of sulfur-containing polymer coating is 5~20 μm.

7. The method for preparing a lithium metal anode comprising an artificial SEI film according to claim 5, characterized in that: In step (1), the oven temperature is adjusted to 60~120 ℃ and the time is 4~12 h.

8. The method for preparing a lithium metal anode comprising an artificial SEI film according to claim 5, characterized in that: The current density for electrodeposition in step (2) is 0.5~2 mA / cm². 2 The areal capacity of electrodeposition is 2~5 mAh / cm². 2 .

9. The method for preparing a lithium metal anode comprising an artificial SEI film according to claim 5, characterized in that: The organic lithium salt electrolyte in step (2) is composed of lithium salt and organic solvent, wherein the lithium salt is any one or a mixture of multiple of LiFSI, LiTFSI, LiNFBS, and LiDFOB, and the organic solvent is a mixture of DME and TTE, and the electrolyte concentration is 0.5~4M.

10. The application of a lithium metal anode comprising an artificial SEI film as described in any one of claims 1 to 4 in a lithium metal battery, characterized in that: A lithium metal anode containing an artificial SEI film, combined with LiNi x Co y Mn z O2 positive electrode, where x+y+z=1, LiNi 0.8 Co 0.15 Al 0.05 A lithium metal battery can be composed of an O2 cathode, a LiMn2O4 cathode, a LiFePO4 cathode, a LiCoO2 cathode, an S cathode, or an O2 cathode.

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