Lithium metal negative electrode and preparation method and application thereof

Abstract

The application discloses a lithium metal negative electrode and a preparation method and application thereof, and belongs to the technical field of lithium batteries. The lithium metal negative electrode has a protective coating on the surface, the protective coating slurry is coated on the surface of the lithium metal foil, and the protective coating is formed through drying and crosslinking; the protective coating slurry comprises the following raw materials in percentage by mass: 12-20 parts of furan-based aromatic polyamide, 12-20 parts of furan-based polyester, 1-3 parts of a crosslinking agent, and 80 parts of a solvent; and the crosslinking agent comprises a bismaleimide. The rigid groups and the flexible groups in the furan-based aromatic polyamide and the furan-based polyester are combined to realize the combination of rigidity and flexibility of the coating, to prevent lithium dendrite puncture and to improve brittle fracture. The use of the furan-based aromatic polyamide and the furan-based polyester can reduce the dependence on petroleum resources, the introduced furan ring is a polar group, has high lithium affinity, can adjust the transmission of lithium ions through polar-polar interaction, can improve the non-uniform deposition of lithium, and can inhibit dendrites.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a lithium metal anode, its preparation method, and its application. Background Technology

[0002] The negative electrode material is the carrier of lithium ions and electrons during battery charging, playing a role in energy storage and release. There are many types of negative electrode materials for lithium-ion batteries, mainly divided into carbon materials and non-carbon materials. Carbon materials are primarily graphite or amorphous carbon materials, while non-carbon materials include silicon-based, tin-based, and metallic lithium. Different materials possess different properties, with metallic lithium being theoretically the optimal negative electrode material, exhibiting extremely low density, the lowest electrode potential, and an ultra-high theoretical specific capacity.

[0003] Despite the enormous application potential of lithium metal anodes, several issues prevent their practical application. Firstly, uneven lithium-ion conduction and the tip effect lead to uneven lithium deposition, resulting in lithium dendrite formation on the anode surface. When dendrites grow to a certain extent, they can pierce the separator, causing safety hazards such as short circuits, fires, and even explosions. If the dendrites break off and form "dead lithium," capacity loss occurs. Compared to intercalated electrodes like graphite and silicon, lithium metal is a hostless electrode material, undergoing unlimited volume changes during electroplating / stripping. Lithium dendrites further exacerbate these volume changes, increasing the contact area between the electrode and the electrolyte. This makes the unstable solid-state electrolyte interface (SEI) prone to breakage. The highly reactive lithium metal reacts with the electrolyte, repeatedly forming new SEI films, consuming both electrolyte and lithium metal, ultimately resulting in low coulombic efficiency and increased interfacial impedance. The susceptibility of lithium metal anodes to electrolyte decomposition and dendrite formation reduces cycle life and safety, and the formation of dead lithium also lowers coulombic efficiency. These defects severely hinder the application of lithium metal anodes. Summary of the Invention

[0004] This invention provides a lithium metal anode, its preparation method, and its application, which can solve the problem of lithium dendrite formation in existing lithium metal anodes reducing cycle performance.

[0005] The objective of this invention can be achieved through the following technical solutions: A lithium metal anode, wherein the surface of the lithium metal anode has a protective coating, and the protective coating slurry is coated on the surface of the lithium metal foil and then dried and crosslinked to form the protective coating. The protective coating slurry comprises the following raw materials by mass fraction: 12-20 parts of furanyl aromatic polyamide, 12-20 parts of furanyl polyester, 1-3 parts of crosslinking agent, and 80 parts of solvent; The crosslinking agent includes bismaleimide.

[0006] In the prior art, the polymers used to prepare polymer protective coatings are often polyethylene (PEO), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), and polyvinyl alcohol (PVA). Brittle coatings are prone to breakage due to pressure during cycling, while overly soft coatings are prone to decomposition when encountering protrusions or damage during battery assembly.

[0007] Furan-based aromatic polyamides and furan-based polyesters are high-performance polymers based on bio-based furan rings, which can reduce dependence on petroleum resources. In furan-based aromatic polyamides, the amide bond structure is stable and possesses certain double bond characteristics, making it less prone to rotation in the molecular chain and enhancing molecular rigidity. The ester groups in furan-based polyesters typically exhibit high flexibility, especially in the molecular chain, where the CO bonds of the ester groups are relatively long and easily rotate, thus imparting high flexibility to the molecular chain. Crosslinking of furan-based aromatic polyamides and furan-based polyesters can combine rigid and flexible components, preventing dendrite penetration while adapting to volume changes during cycling and avoiding brittle cracking.

[0008] The furan rings in furan-based aromatic polyamides and furan-based polyesters are polar groups, which can regulate lithium-ion transport through polar-polar interactions, improve uneven lithium deposition, and suppress dendrite formation. Furthermore, under the action of crosslinking agents, furan-based aromatic polyamides and furan-based polyesters form interpenetrating crosslinked networks using furan rings as reaction sites, increasing coating density and enabling complete coverage of the lithium metal electrode. The ester groups in furan-based polyesters ensure electrolyte wettability and reduce interfacial impedance. Although both ester and amide groups are polar groups, ester groups do not possess hydrogen bonding capabilities, while amide groups, containing nitrogen atoms, can form hydrogen bonds, constructing a hydrogen bond network and enhancing the structural stability of the coating.

[0009] Furthermore, the thickness of the protective coating is 10-30 μm.

[0010] Furthermore, the furanyl aromatic polyamide is formed by the condensation polymerization of 2,5-furandicarboxylic acid and an aromatic diamine.

[0011] Furthermore, the furanyl polyester is formed by the condensation of 2,5-furandicarboxylic acid and C2–C6 diol.

[0012] Furthermore, the crosslinking agent also includes a trifunctional aziridine crosslinking agent, the mass of which is 5-10% of bismaleimide. The aziridine groups in the trifunctional aziridine crosslinking agent undergo a ring-opening reaction with the residual carboxyl groups of the furanyl aromatic polyamide and furanyl polyester to form a three-dimensional network structure. The reaction does not require high temperatures, which promotes rapid curing of the coating.

[0013] Furthermore, the mass ratio of furanyl aromatic polyamide to furanyl polyester is (4-6):(4-6).

[0014] Furthermore, the solvent is a mixture of NMP and hexafluoroisopropanol in a volume ratio of (1-2):(1-2).

[0015] The present invention also provides a method for preparing the lithium metal anode as described above, comprising the following steps: Step 1: Dissolve furanyl aromatic polyamide and furanyl polyester in a solvent, and heat and stir to form a homogeneous solution; Step 2: Add a crosslinking agent to the homogeneous solution and stir to obtain a protective coating slurry; Step 3: A protective coating is applied to the surface of the lithium metal foil, and then vacuum dried to crosslink and form a protective coating, thus obtaining the lithium metal anode.

[0016] Furthermore, the heating and stirring temperature is 50-55℃, and the heating and stirring time is 3-5 hours; The vacuum drying crosslinking temperature is 70-90℃, and the vacuum drying crosslinking time is 6-8h.

[0017] The present invention also provides an application of the lithium metal anode as described above, wherein the lithium metal anode is used as an anode in the preparation of a lithium battery.

[0018] The beneficial effects of this invention are: (1) By combining the rigid groups (aromatic rings, amide groups) and flexible groups (ester groups) in furan-based aromatic polyamides and furan-based polyesters, a combination of rigidity and flexibility in the coating is achieved, which prevents lithium dendrite penetration while improving brittle fracture. The use of furan-based aromatic polyamides and furan-based polyesters can not only reduce dependence on petroleum resources, but the introduced furan rings are polar groups with high lithium affinity. They can regulate lithium ion transport through polar-polar interactions, improve uneven lithium deposition, and inhibit dendrite formation.

[0019] (2) Furan-based aromatic polyamides and furan-based polyesters react with bismaleimide upon heating to form a covalent cross-linked network, which improves the density of the coating, achieves complete coverage of the lithium metal electrode, and inhibits the production of lithium dendrites. Due to the reversibility of the reaction, the material can self-repair after being damaged by heating.

[0020] (3) Adding trifunctional aziridine crosslinking agent as a crosslinking agent can utilize the carboxyl groups contained in furanyl aromatic polyamide and furanyl polyester as crosslinking sites to enhance the structural stability of the crosslinking network, improve the mechanical strength of the coating, and inhibit the puncture of lithium dendrites. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1 Preparation of furanyl aromatic polyamides: Under a nitrogen atmosphere, 30 mL of N-methylpyrrolidone was added to a 150 mL three-necked flask. 11 mmol of 2,5-furandicarboxylic acid and 1.5 g of lithium chloride were then added to the flask and stirred until dissolved. 10 mmol of p-phenylenediamine, 7 mL of pyridine, and 6 mL of triphenyl phosphite were then added. The molar ratio of 2,5-furandicarboxylic acid to p-phenylenediamine was 1.1:1. After stirring and mixing thoroughly, the mixture was heated to 110 °C and reacted for 2 h, then heated to 130 °C and reacted for 4 h to obtain a furanyl aromatic polyamide solution. The solution was poured into methanol to precipitate the polyamide, which was then washed five times with hot water and methanol to remove impurities. The polyamide was dried at 80 °C to obtain the furanyl aromatic polyamide.

[0023] Preparation of furan-based polyesters: Under a nitrogen atmosphere, 0.1 mol of 2,5-furandicarboxylic acid, 0.16 mol of ethylene glycol, and 0.0001 mol of stannous oxalate were added to a 150 mL three-necked flask. The mixture was stirred and heated to 210 °C for 5 h, then heated to 240 °C and reacted under a vacuum of 70 Pa for 2 h. The product was dissolved in o-chlorophenol, and then methanol was added to precipitate the product. The product was dried under vacuum at 120 °C for 48 h to obtain furanyl polyester.

[0024] A lithium metal anode has a protective coating on its surface. The protective coating slurry is applied to the surface of a lithium metal foil and then dried and crosslinked to form the protective coating.

[0025] The protective coating slurry comprises the following raw materials by mass fraction: The composition comprises 12 parts furanyl aromatic polyamide, 18 parts furanyl polyester, 1 part bismaleimide, and 80 parts solvent. The mass ratio of furanyl aromatic polyamide to furanyl polyester is 4:6, and the solvent is a mixture of NMP and hexafluoroisopropanol with a volume ratio of 1:2.

[0026] Preparation of lithium metal anode: Step 1: Dissolve furanyl aromatic polyamide and furanyl polyester in a solvent, heat to 50°C and stir for 4 hours to form a homogeneous solution; Step 2: Add bismaleimide to the homogenized solution and stir to obtain a protective coating slurry; Step 3: Apply a protective coating to the surface of the lithium metal foil and vacuum dry and crosslink at 80°C for 6 hours to form a protective coating with a thickness of 15μm.

[0027] Example 2 The only difference from Example 1 is that the mass ratio of furan-based aromatic polyamide to furan-based polyester in the protective coating slurry is adjusted to 5:5, and the volume ratio of NMP and hexafluoroisopropanol in the solvent is adjusted to 1:1 for adaptability adjustment.

[0028] Preparation of furanyl aromatic polyamides: Under a nitrogen atmosphere, 30 mL of N-methylpyrrolidone was added to a 150 mL three-necked flask. 11 mmol of 2,5-furandicarboxylic acid and 1.5 g of lithium chloride were then added to the flask and stirred until dissolved. 10 mmol of p-phenylenediamine, 7 mL of pyridine, and 6 mL of triphenyl phosphite were then added. The molar ratio of 2,5-furandicarboxylic acid to p-phenylenediamine was 1.1:1. After stirring and mixing thoroughly, the mixture was heated to 110 °C and reacted for 2 h, then heated to 130 °C and reacted for 4 h to obtain a furanyl aromatic polyamide solution. The solution was poured into methanol to precipitate the polyamide, which was then washed five times with hot water and methanol to remove impurities. The polyamide was dried at 80 °C to obtain the furanyl aromatic polyamide.

[0029] Preparation of furan-based polyesters: Under a nitrogen atmosphere, 0.1 mol of 2,5-furandicarboxylic acid, 0.16 mol of ethylene glycol, and 0.0001 mol of stannous oxalate were added to a 150 mL three-necked flask. The mixture was stirred and heated to 210 °C for 5 h, then heated to 240 °C and reacted under a vacuum of 70 Pa for 2 h. The product was dissolved in o-chlorophenol, and then methanol was added to precipitate the product. The product was dried under vacuum at 120 °C for 48 h to obtain furanyl polyester.

[0030] A lithium metal anode has a protective coating on its surface. The protective coating slurry is applied to the surface of a lithium metal foil and then dried and crosslinked to form the protective coating.

[0031] The protective coating slurry comprises the following raw materials by mass fraction: The mixture comprises 15 parts furanyl aromatic polyamide, 15 parts furanyl polyester, 1 part bismaleimide, and 80 parts solvent. The mass ratio of furanyl aromatic polyamide to furanyl polyester is 5:5, and the solvent is a mixture of NMP and hexafluoroisopropanol with a volume ratio of 1:1.

[0032] Preparation of lithium metal anode: Step 1: Dissolve furanyl aromatic polyamide and furanyl polyester in a solvent, heat to 50°C and stir for 4 hours to form a homogeneous solution; Step 2: Add bismaleimide to the homogenized solution and stir to obtain a protective coating slurry; Step 3: Apply a protective coating to the surface of the lithium metal foil and vacuum dry and crosslink at 80°C for 6 hours to form a protective coating with a thickness of 15μm.

[0033] Example 3 The only difference from Example 1 is that the mass ratio of furan-based aromatic polyamide to furan-based polyester in the protective coating slurry is adjusted to 6:4, and the volume ratio of NMP and hexafluoroisopropanol in the solvent is adjusted to 2:1 for adaptability.

[0034] Preparation of furanyl aromatic polyamides: Under a nitrogen atmosphere, 30 mL of N-methylpyrrolidone was added to a 150 mL three-necked flask. 11 mmol of 2,5-furandicarboxylic acid and 1.5 g of lithium chloride were then added to the flask and stirred until dissolved. 10 mmol of p-phenylenediamine, 7 mL of pyridine, and 6 mL of triphenyl phosphite were then added. The molar ratio of 2,5-furandicarboxylic acid to p-phenylenediamine was 1.1:1. After stirring and mixing thoroughly, the mixture was heated to 110 °C and reacted for 2 h, then heated to 130 °C and reacted for 4 h to obtain a furanyl aromatic polyamide solution. The solution was poured into methanol to precipitate the polyamide, which was then washed five times with hot water and methanol to remove impurities. The polyamide was dried at 80 °C to obtain the furanyl aromatic polyamide.

[0035] Preparation of furan-based polyesters: Under a nitrogen atmosphere, 0.1 mol of 2,5-furandicarboxylic acid, 0.16 mol of ethylene glycol, and 0.0001 mol of stannous oxalate were added to a 150 mL three-necked flask. The mixture was stirred and heated to 210 °C for 5 h, then heated to 240 °C and reacted under a vacuum of 70 Pa for 2 h. The product was dissolved in o-chlorophenol, and then methanol was added to precipitate the product. The product was dried under vacuum at 120 °C for 48 h to obtain furanyl polyester.

[0036] A lithium metal anode has a protective coating on its surface. The protective coating slurry is applied to the surface of a lithium metal foil and then dried and crosslinked to form the protective coating.

[0037] The protective coating slurry comprises the following raw materials by mass fraction: The composition comprises 18 parts furanyl aromatic polyamide, 12 parts furanyl polyester, 1 part bismaleimide, and 80 parts solvent. The mass ratio of furanyl aromatic polyamide to furanyl polyester is 4:6, and the solvent is a mixture of NMP and hexafluoroisopropanol in a volume ratio of 2:1.

[0038] Preparation of lithium metal anode: Step 1: Dissolve furanyl aromatic polyamide and furanyl polyester in a solvent, heat to 50°C and stir for 4 hours to form a homogeneous solution; Step 2: Add bismaleimide to the homogenized solution and stir to obtain a protective coating slurry; Step 3: Apply a protective coating to the surface of the lithium metal foil and vacuum dry and crosslink at 80°C for 6 hours to form a protective coating with a thickness of 15μm.

[0039] Examples 4-5 The only difference from Example 2 is that the mass percentage of furanyl aromatic polyamide and furanyl polyester in the protective coating slurry is increased. The specific raw material formulation of the protective coating slurry is shown in Table 1: Table 1

[0040] Example 6 The only difference from Example 4 is that the crosslinking agent includes bismaleimide and trifunctional aziridine crosslinking agent, and the protective coating slurry contains 2 parts of bismaleimide and 0.1 parts of trifunctional aziridine crosslinking agent.

[0041] Preparation of furanyl aromatic polyamides: Under a nitrogen atmosphere, 30 mL of N-methylpyrrolidone was added to a 150 mL three-necked flask. 11 mmol of 2,5-furandicarboxylic acid and 1.5 g of lithium chloride were then added to the flask and stirred until dissolved. 10 mmol of p-phenylenediamine, 7 mL of pyridine, and 6 mL of triphenyl phosphite were then added. The molar ratio of 2,5-furandicarboxylic acid to p-phenylenediamine was 1.1:1. After stirring and mixing thoroughly, the mixture was heated to 110 °C and reacted for 2 h, then heated to 130 °C and reacted for 4 h to obtain a furanyl aromatic polyamide solution. The solution was poured into methanol to precipitate the polyamide, which was then washed five times with hot water and methanol to remove impurities. The polyamide was dried at 80 °C to obtain the furanyl aromatic polyamide.

[0042] Preparation of furan-based polyesters: Under a nitrogen atmosphere, 0.1 mol of 2,5-furandicarboxylic acid, 0.16 mol of ethylene glycol, and 0.0001 mol of stannous oxalate were added to a 150 mL three-necked flask. The mixture was stirred and heated to 210 °C for 5 h, then heated to 240 °C and reacted under a vacuum of 70 Pa for 2 h. The product was dissolved in o-chlorophenol, and then methanol was added to precipitate the product. The product was dried under vacuum at 120 °C for 48 h to obtain furanyl polyester.

[0043] A lithium metal anode has a protective coating on its surface. The protective coating slurry is applied to the surface of a lithium metal foil and then dried and crosslinked to form the protective coating.

[0044] The protective coating slurry comprises the following raw materials by mass fraction: The composition comprises 18 parts furanyl aromatic polyamide, 18 parts furanyl polyester, 2 parts bismaleimide, 0.1 parts trifunctional aziridine crosslinking agent, and 80 parts solvent. The mass ratio of furanyl aromatic polyamide to furanyl polyester is 5:5, and the solvent is a mixture of NMP and hexafluoroisopropanol with a volume ratio of 1:1.

[0045] Preparation of lithium metal anode: Step 1: Dissolve furanyl aromatic polyamide and furanyl polyester in a solvent, heat to 50°C and stir for 4 hours to form a homogeneous solution; Step 2: Add bismaleimide and trifunctional aziridine crosslinking agent to the homogeneous solution, and stir to obtain a protective coating slurry; Step 3: Apply a protective coating to the surface of the lithium metal foil and vacuum dry and crosslink at 80°C for 6 hours to form a protective coating with a thickness of 15μm.

[0046] Example 7 The only difference from Example 4 is that the crosslinking agent includes bismaleimide and trifunctional aziridine crosslinking agent, and the protective coating slurry contains 2 parts of bismaleimide and 0.16 parts of trifunctional aziridine crosslinking agent.

[0047] Preparation of furanyl aromatic polyamides: Under a nitrogen atmosphere, 30 mL of N-methylpyrrolidone was added to a 150 mL three-necked flask. 11 mmol of 2,5-furandicarboxylic acid and 1.5 g of lithium chloride were then added to the flask and stirred until dissolved. 10 mmol of p-phenylenediamine, 7 mL of pyridine, and 6 mL of triphenyl phosphite were then added. The molar ratio of 2,5-furandicarboxylic acid to p-phenylenediamine was 1.1:1. After stirring and mixing thoroughly, the mixture was heated to 110 °C and reacted for 2 h, then heated to 130 °C and reacted for 4 h to obtain a furanyl aromatic polyamide solution. The solution was poured into methanol to precipitate the polyamide, which was then washed five times with hot water and methanol to remove impurities. The polyamide was dried at 80 °C to obtain the furanyl aromatic polyamide.

[0048] Preparation of furan-based polyesters: Under a nitrogen atmosphere, 0.1 mol of 2,5-furandicarboxylic acid, 0.16 mol of ethylene glycol, and 0.0001 mol of stannous oxalate were added to a 150 mL three-necked flask. The mixture was stirred and heated to 210 °C for 5 h, then heated to 240 °C and reacted under a vacuum of 70 Pa for 2 h. The product was dissolved in o-chlorophenol, and then methanol was added to precipitate the product. The product was dried under vacuum at 120 °C for 48 h to obtain furanyl polyester.

[0049] A lithium metal anode has a protective coating on its surface. The protective coating slurry is applied to the surface of a lithium metal foil and then dried and crosslinked to form the protective coating.

[0050] The protective coating slurry comprises the following raw materials by mass fraction: The composition comprises 18 parts furanyl aromatic polyamide, 18 parts furanyl polyester, 2 parts bismaleimide, 0.16 parts trifunctional aziridine crosslinking agent, and 80 parts solvent. The mass ratio of furanyl aromatic polyamide to furanyl polyester is 5:5, and the solvent is a mixture of NMP and hexafluoroisopropanol with a volume ratio of 1:1.

[0051] Preparation of lithium metal anode: Step 1: Dissolve furanyl aromatic polyamide and furanyl polyester in a solvent, heat to 50°C and stir for 4 hours to form a homogeneous solution; Step 2: Add bismaleimide and trifunctional aziridine crosslinking agent to the homogeneous solution, and stir to obtain a protective coating slurry; Step 3: Apply a protective coating to the surface of the lithium metal foil and vacuum dry and crosslink at 80°C for 6 hours to form a protective coating with a thickness of 15μm.

[0052] Example 8 The only difference from Example 4 is that the crosslinking agent includes bismaleimide and trifunctional aziridine crosslinking agent, and the protective coating slurry contains 2 parts of bismaleimide and 0.2 parts of trifunctional aziridine crosslinking agent.

[0053] Preparation of furanyl aromatic polyamides: Under a nitrogen atmosphere, 30 mL of N-methylpyrrolidone was added to a 150 mL three-necked flask. 11 mmol of 2,5-furandicarboxylic acid and 1.5 g of lithium chloride were then added to the flask and stirred until dissolved. 10 mmol of p-phenylenediamine, 7 mL of pyridine, and 6 mL of triphenyl phosphite were then added. The molar ratio of 2,5-furandicarboxylic acid to p-phenylenediamine was 1.1:1. After stirring and mixing thoroughly, the mixture was heated to 110 °C and reacted for 2 h, then heated to 130 °C and reacted for 4 h to obtain a furanyl aromatic polyamide solution. The solution was poured into methanol to precipitate the polyamide, which was then washed five times with hot water and methanol to remove impurities. The polyamide was dried at 80 °C to obtain the furanyl aromatic polyamide.

[0054] Preparation of furan-based polyesters: Under a nitrogen atmosphere, 0.1 mol of 2,5-furandicarboxylic acid, 0.16 mol of ethylene glycol, and 0.0001 mol of stannous oxalate were added to a 150 mL three-necked flask. The mixture was stirred and heated to 210 °C for 5 h, then heated to 240 °C and reacted under a vacuum of 70 Pa for 2 h. The product was dissolved in o-chlorophenol, and then methanol was added to precipitate the product. The product was dried under vacuum at 120 °C for 48 h to obtain furanyl polyester.

[0055] A lithium metal anode has a protective coating on its surface. The protective coating slurry is applied to the surface of a lithium metal foil and then dried and crosslinked to form the protective coating.

[0056] The protective coating slurry comprises the following raw materials by mass fraction: The composition comprises 18 parts furanyl aromatic polyamide, 18 parts furanyl polyester, 2 parts bismaleimide, 0.2 parts trifunctional aziridine crosslinking agent, and 80 parts solvent. The mass ratio of furanyl aromatic polyamide to furanyl polyester is 5:5, and the solvent is a mixture of NMP and hexafluoroisopropanol with a volume ratio of 1:1.

[0057] Preparation of lithium metal anode: Step 1: Dissolve furanyl aromatic polyamide and furanyl polyester in a solvent, heat to 50°C and stir for 4 hours to form a homogeneous solution; Step 2: Add bismaleimide and trifunctional aziridine crosslinking agent to the homogeneous solution, and stir to obtain a protective coating slurry; Step 3: Apply a protective coating to the surface of the lithium metal foil and vacuum dry and crosslink at 80°C for 6 hours to form a protective coating with a thickness of 15μm.

[0058] Comparative Example 1 The only difference from Example 1 is that the protective coating slurry in this comparative example is replaced with an equal mass of furan-based aromatic polyamide instead of furan-based polyester, and the solvent is NMP.

[0059] Preparation of furanyl aromatic polyamides: Under a nitrogen atmosphere, 30 mL of N-methylpyrrolidone was added to a 150 mL three-necked flask. 11 mmol of 2,5-furandicarboxylic acid and 1.5 g of lithium chloride were then added to the flask and stirred until dissolved. 10 mmol of p-phenylenediamine, 7 mL of pyridine, and 6 mL of triphenyl phosphite were then added. The molar ratio of 2,5-furandicarboxylic acid to p-phenylenediamine was 1.1:1. After stirring and mixing thoroughly, the mixture was heated to 110 °C and reacted for 2 h, then heated to 130 °C and reacted for 4 h to obtain a furanyl aromatic polyamide solution. The solution was poured into methanol to precipitate the polyamide, which was then washed five times with hot water and methanol to remove impurities. The polyamide was dried at 80 °C to obtain the furanyl aromatic polyamide.

[0060] A lithium metal anode has a protective coating on its surface. The protective coating slurry is applied to the surface of a lithium metal foil and then dried and crosslinked to form the protective coating.

[0061] The protective coating slurry comprises the following raw materials by mass fraction: 30 parts of furanyl aromatic polyamide, 1 part of bismaleimide, and 80 parts of NMP.

[0062] Preparation of lithium metal anode: Step 1: Dissolve furanyl aromatic polyamide in NMP and heat to 50°C while stirring for 4 hours to form a solution; Step 2: Add bismaleimide to the solution and stir to obtain a protective coating slurry; Step 3: Apply a protective coating to the surface of the lithium metal foil and vacuum dry and crosslink at 80°C for 6 hours to form a protective coating with a thickness of 15μm.

[0063] Comparative Example 2 The only difference from Example 1 is that the protective coating slurry in this comparative example is replaced with an equal mass of furan-based polyester instead of furan-based aromatic polyamide, and the solvent is hexafluoroisopropanol.

[0064] Preparation of furan-based polyesters: Under a nitrogen atmosphere, 0.1 mol of 2,5-furandicarboxylic acid, 0.16 mol of ethylene glycol, and 0.0001 mol of stannous oxalate were added to a 150 mL three-necked flask. The mixture was stirred and heated to 210 °C for 5 h, then heated to 240 °C and reacted under a vacuum of 70 Pa for 2 h. The product was dissolved in o-chlorophenol, and then methanol was added to precipitate the product. The product was dried under vacuum at 120 °C for 48 h to obtain furanyl polyester.

[0065] A lithium metal anode has a protective coating on its surface. The protective coating slurry is applied to the surface of a lithium metal foil and then dried and crosslinked to form the protective coating.

[0066] The protective coating slurry comprises the following raw materials by mass fraction: 30 parts furanyl polyester, 1 part bismaleimide, and 80 parts hexafluoroisopropanol.

[0067] Preparation of lithium metal anode: Step 1: Dissolve furanyl polyester in hexafluoroisopropanol solvent, heat to 50°C and stir for 4 hours to form a solution; Step 2: Add bismaleimide to the solution and stir to obtain a protective coating slurry; Step 3: Apply a protective coating to the surface of the lithium metal foil and vacuum dry and crosslink at 80°C for 6 hours to form a protective coating with a thickness of 15μm.

[0068] Comparative Example 3 The only difference from Example 1 is that the protective coating slurry in this comparative example does not contain a crosslinking agent.

[0069] Preparation of furanyl aromatic polyamides: Under a nitrogen atmosphere, 30 mL of N-methylpyrrolidone was added to a 150 mL three-necked flask. 11 mmol of 2,5-furandicarboxylic acid and 1.5 g of lithium chloride were then added to the flask and stirred until dissolved. 10 mmol of p-phenylenediamine, 7 mL of pyridine, and 6 mL of triphenyl phosphite were then added. The molar ratio of 2,5-furandicarboxylic acid to p-phenylenediamine was 1.1:1. After stirring and mixing thoroughly, the mixture was heated to 110 °C and reacted for 2 h, then heated to 130 °C and reacted for 4 h to obtain a furanyl aromatic polyamide solution. The solution was poured into methanol to precipitate the polyamide, which was then washed five times with hot water and methanol to remove impurities. The polyamide was dried at 80 °C to obtain the furanyl aromatic polyamide.

[0070] Preparation of furan-based polyesters: Under a nitrogen atmosphere, 0.1 mol of 2,5-furandicarboxylic acid, 0.16 mol of ethylene glycol, and 0.0001 mol of stannous oxalate were added to a 150 mL three-necked flask. The mixture was stirred and heated to 210 °C for 5 h, then heated to 240 °C and reacted under a vacuum of 70 Pa for 2 h. The product was dissolved in o-chlorophenol, and then methanol was added to precipitate the product. The product was dried under vacuum at 120 °C for 48 h to obtain furanyl polyester.

[0071] A lithium metal anode has a protective coating on its surface. The protective coating slurry is applied to the surface of a lithium metal foil and then dried and crosslinked to form the protective coating.

[0072] The protective coating slurry comprises the following raw materials by mass fraction: The composition comprises 12 parts furanyl aromatic polyamide, 18 parts furanyl polyester, and 80 parts solvent. The mass ratio of furanyl aromatic polyamide to furanyl polyester is 4:6, and the solvent is a mixture of NMP and hexafluoroisopropanol in a volume ratio of 1:2.

[0073] Preparation of lithium metal anode: Step 1: Dissolve furanyl aromatic polyamide and furanyl polyester in a solvent, heat to 50°C and stir for 4 hours to form a homogeneous solution, and obtain a protective coating slurry; Step 2: Apply a protective coating to the surface of the lithium metal foil and vacuum dry at 80°C for 6 hours to form a protective coating with a thickness of 15μm.

[0074] The lithium metal anode used in the examples and comparative examples is used as the anode of the lithium-ion battery. It is combined with a separator, an electrolyte and a cathode to form a battery. The separator is a PP porous membrane, the electrolyte is a lithium hexafluorophosphate solution, the solvent is ethylene carbonate and diethylene carbonate in a molar ratio of 1:1, the solute is lithium hexafluorophosphate with a concentration of 1 mol / L, and the cathode is lithium iron phosphate.

[0075] The obtained battery underwent electrochemical performance testing, including charge-discharge cycle testing at a 2C rate for 500 cycles. The results are shown in Table 1. Table 1

[0076] As shown in Table 1, Example 2, with a mass ratio of furanyl aromatic polyamide to furanyl polyester of 1:1, can construct a dense and balanced cross-linked network structure of rigid and flexible components, which can effectively suppress lithium dendrite growth on the negative electrode during cycling, improve cycling performance, and increase coulombic efficiency. Increasing the polymer content in the slurry can form a denser coating, but excessive amounts result in excessive slurry viscosity, poor leveling, and reduced coating uniformity. Under the conditions of Example 5, its cycling performance is slightly worse than that of Example 4. Examples 6-8 involve adding a trifunctional aziridine cross-linking agent to bismaleimide. The different cross-linking mechanisms combined make the coating denser, and the electrochemical performance is improved compared to Example 4. In Comparative Examples 1 and 2, coatings prepared with a single furanyl polymer cannot achieve the same protective effect on the lithium negative electrode as the combined polymer coating, resulting in poor cycling performance.

[0077] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0078] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A lithium metal anode, characterized in that, The lithium metal anode surface has a protective coating. The protective coating slurry is coated on the surface of the lithium metal foil and then dried and crosslinked to form the protective coating. The protective coating slurry comprises the following raw materials by mass fraction: 12-20 parts of furanyl aromatic polyamide, 12-20 parts of furanyl polyester, 1-3 parts of crosslinking agent, and 80 parts of solvent; The crosslinking agent includes bismaleimide.

2. The lithium metal anode according to claim 1, characterized in that, The thickness of the protective coating is 10-30 μm.

3. A lithium metal anode according to claim 1, characterized in that, The furanyl aromatic polyamide is formed by the condensation polymerization of 2,5-furandicarboxylic acid and aromatic diamine.

4. A lithium metal anode according to claim 1, characterized in that, The furanyl polyester is formed by the condensation of 2,5-furandicarboxylic acid and C2–C6 diol.

5. A lithium metal anode according to claim 1, characterized in that, The crosslinking agent also includes a trifunctional aziridine crosslinking agent, wherein the mass of the trifunctional aziridine crosslinking agent is 5-10% of that of bismaleimide.

6. A lithium metal anode according to claim 1, characterized in that, The mass ratio of furanyl aromatic polyamide to furanyl polyester is (4-6):(4-6).

7. A lithium metal anode according to claim 1, characterized in that, The solvent is a mixture of NMP and hexafluoroisopropanol, with a volume ratio of (1-2):(1-2).

8. A method for preparing a lithium metal anode as described in any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Dissolve furanyl aromatic polyamide and furanyl polyester in a solvent, and heat and stir to form a homogeneous solution; Step 2: Add a crosslinking agent to the homogeneous solution and stir to obtain a protective coating slurry; Step 3: A protective coating is applied to the surface of the lithium metal foil, and then vacuum dried to crosslink and form a protective coating, thus obtaining the lithium metal anode.

9. The method for preparing a lithium metal anode according to claim 8, characterized in that, The heating and stirring temperature is 50-55℃, and the heating and stirring time is 3-5 hours. The vacuum drying crosslinking temperature is 70-90℃, and the vacuum drying crosslinking time is 6-8h.

10. An application of the lithium metal anode as described in any one of claims 1-7, characterized in that, The lithium metal anode is used as the anode in the preparation of lithium batteries.

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