Lithium metal negative electrode, battery and preparation method

Abstract

The invention provides a lithium metal negative electrode, a battery and a preparation method. Specifically, the lithium metal negative electrode comprises a lithium metal sheet and a first coating located on the surface of the lithium metal sheet; wherein the first coating layer is prepared from MXene modified by polyethylene glycol and-SH. MXene in the first coating has lithium affinity, a conductive network can be formed on the outer side of the lithium metal sheet, and the compatibility of the first coating and the sulfide solid electrolyte can be improved due to the existence of polyethylene glycol and-SH modification, so that the lithium metal sheet can be prevented from being in direct contact with the sulfide solid electrolyte through the first coating; ion conduction is ensured, electron permeation is inhibited, and self-discharge is reduced; in addition, polyethylene glycol enables the first coating to have certain mechanical flexibility, so that the first coating can adapt to volume change in the lithium deposition / stripping process, dendrite growth is inhibited, the cycle life of the battery is prolonged, and the safety of the battery is improved.

Description

Lithium metal anode, battery and preparation method Technical Field

[0001] This disclosure relates to the field of battery technology, and in particular to a lithium metal anode, a battery, and a method for preparing it. Background Technology

[0002] All-solid-state lithium batteries (ASSLBs) use solid electrolytes instead of liquid electrolytes, offering advantages such as high safety and high energy density. Among these, sulfide solid electrolytes (e.g., Li6PS5Cl) are particularly advantageous due to their high ionic conductivity (10⁻⁶ Ω·cm). -3 ~10 -2 With its low interfacial impedance (S / cm) and high interfacial resistance, lithium metal anodes hold significant promise for applications in high-performance ASSLBs. However, when lithium metal anodes come into direct contact with sulfide electrolytes, byproducts (such as Li2S and Li3P) can be generated based on chemical / electrochemical reactions. This can cause a rapid increase in interfacial impedance, which can easily lead to battery short circuits and other safety accidents during subsequent cycles. At the same time, uneven lithium deposition can easily induce dendrites, causing short circuits and failures. Summary of the Invention

[0003] In view of this, the purpose of this disclosure is to provide a lithium metal anode, a battery, and a method for its preparation.

[0004] For the purposes described above, the first aspect of this disclosure provides a lithium metal anode, comprising a lithium metal sheet and a first coating on the surface of the lithium metal sheet; wherein the first coating comprises MXene modified with polyethylene glycol and -SH.

[0005] In some embodiments, a second coating is further included; the second coating is located between the lithium metal sheet and the first coating; the second coating includes MXene modified with polyethylene glycol.

[0006] In some embodiments, the thickness of the first coating is 0.5 μm to 3 μm; and / or the thickness of the second coating is 1 μm to 6 μm.

[0007] In some embodiments, the thickness ratio of the first coating to the second coating is 3:2 to 1:6; alternatively, the thickness ratio of the first coating to the second coating is 1:1.9 to 1:2.1.

[0008] In some embodiments, the mass percentage of MXene is 8% to 10% based on the total mass of the first coating.

[0009] In some embodiments, the mass percentage of MXene is 40% to 60% based on the total mass of the second coating.

[0010] In some embodiments, the mass percentage of MXene in the second coating is greater than the mass percentage of MXene in the first coating.

[0011] Based on the same inventive concept, the second aspect of this disclosure also provides a method for preparing any of the aforementioned lithium metal anodes, the method comprising: amylating MXene with a silane coupling agent to obtain amino-modified MXene; surface-modifying the amino-modified MXene with methoxy polyethylene glycol and 3-mercaptopropionic anhydride to obtain polyethylene glycol and -SH-modified MXene; and applying the polyethylene glycol and -SH-modified MXene to the surface of the lithium metal sheet to obtain the first coating.

[0012] In some embodiments, the silane coupling agent comprises at least one of (3-aminopropyl)triethoxysilane, (3-aminopropyl)trimethoxysilane, (3-mercaptopropyl)trimethoxysilane, (3-mercaptopropyl)triethoxysilane, (3-glycidyl)propyltriethoxysilane, (3-glycidyl)propyltrimethoxysilane, dimethyldiethoxysilane, hexadecyltrimethoxysilane, trifluoropropyltrimethoxysilane, and tridecafluorooctyltrimethoxysilane.

[0013] Based on the same inventive concept, a third aspect of this disclosure also provides a battery, including a positive electrode, a sulfide solid electrolyte, and a lithium metal negative electrode as described in any of the preceding claims.

[0014] As can be seen from the above, this disclosure provides a lithium metal anode, a battery, and a preparation method. The lithium metal anode includes a lithium metal sheet and a first coating on the surface of the lithium metal sheet. The first coating includes MXene modified with polyethylene glycol and -SH. Here, the MXene in the first coating is lithiophilic and can form a conductive network on the outside of the lithium metal sheet. The presence of polyethylene glycol and -SH modification improves the compatibility between the first coating and the sulfide solid electrolyte, preventing direct contact between the lithium metal sheet and the sulfide solid electrolyte. Furthermore, while ensuring ion conduction, it suppresses electron permeation, reducing self-discharge. In addition, polyethylene glycol gives the first coating a certain degree of mechanical flexibility, allowing it to adapt to volume changes during lithium deposition / stripping, suppressing dendrite growth, and improving battery cycle life and safety. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments.

[0016] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this disclosure should have the ordinary meaning as understood by one of ordinary skill in the art to which this disclosure pertains.

[0017] In this disclosure, the term "range" is used to define a range in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~130 and 70~120 are listed for a specific parameter, it is expected that ranges of 60~120 and 70~130 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this disclosure, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0018] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0019] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions.

[0020] Unless otherwise specified, the terms "comprising" and "including" as used in this disclosure can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0021] Unless otherwise specified, the term "or" is inclusive in this disclosure. For example, the phrase "A or B" means "A, B, or both A and B".

[0022] The term "critical current density" (CCD) is a core indicator for evaluating the interfacial stability and dendrite penetration resistance of solid electrolytes. It represents the maximum current density that an electrolyte can withstand without causing a short circuit in the battery.

[0023] Among related technologies, solutions for improving sulfide solid electrolytes include carbon material coatings and oxide barrier layers. While these solutions can improve interface stability to some extent, they suffer from problems such as electron leakage (self-discharge), poor mechanical matching, and complex processes. MXene materials, with their high conductivity, lithiophilicity, and tunable surface chemistry, are considered potential materials for improving the performance of lithium metal anodes. However, MXene's high electronic conductivity leads to battery self-discharge, and the interfacial compatibility between MXene and sulfide electrolytes needs improvement.

[0024] In view of this, the present disclosure provides a lithium metal anode, a battery, and a preparation method thereof. The lithium metal anode includes a lithium metal sheet and a first coating on the surface of the lithium metal sheet. The first coating includes MXene modified with polyethylene glycol and -SH. Here, the MXene in the first coating is lithiophilic and can form a conductive network on the outside of the lithium metal sheet. The presence of polyethylene glycol and -SH modification improves the compatibility between the first coating and the sulfide solid electrolyte, preventing direct contact between the lithium metal sheet and the sulfide solid electrolyte. Furthermore, while ensuring ion conduction, it suppresses electron permeation, reducing self-discharge. In addition, polyethylene glycol gives the first coating a certain degree of mechanical flexibility, allowing it to adapt to volume changes during lithium deposition / stripping, suppressing dendrite growth, and improving battery cycle life and safety.

[0025] To make the technical solutions of this disclosure clearer and easier to understand, the lithium metal anode, battery and preparation method provided in this disclosure will be described in detail below with reference to specific embodiments.

[0026] Lithium metal anode In a first aspect, embodiments of this disclosure provide a lithium metal anode. Here, the lithium metal anode includes a lithium metal sheet and a first coating on the surface of the lithium metal sheet; wherein the first coating includes MXene modified with polyethylene glycol and -SH.

[0027] It should be noted that MXene is a novel two-dimensional material composed of metal carbides or nitrides. As a transition metal carbide or nitride with a two-dimensional structure, MXene's layered structure and abundant surface functional groups endow it with excellent electrical and mechanical properties. Generally, MXene materials can be represented by the chemical formula M... n+1 X n T m The notation indicates that "M" represents a metallic element, primarily transition metals (such as chromium, molybdenum, manganese, iron, cobalt, copper, aluminum, silver, nickel, palladium, platinum, ruthenium, etc.); the value of n is generally 1~3; "X" represents carbon and nitrogen; "T" represents... m"" represents functional groups on the surface of the material, such as hydroxyl (-OH), -O, halogen groups (-F, -Cl), etc.

[0028] The MXene material is prepared using a method well known to those skilled in the art, obtained by acid etching and washing of MAX phase powder material. The MXene material obtained by acid washing exhibits an overall negative charge due to the presence of negative ion groups on its end face. The MAX phase material includes at least one of Ti3AlC2, Ti2AlC, Ti3AlCN, V2AlC, Nb2AlC, Nb4AlC3, and TiNbAlC.

[0029] The MXene in the first coating is lithium-loving and can form a conductive network on the outside of the lithium metal sheet. The presence of polyethylene glycol and -SH modification can improve the compatibility between the first coating and the sulfide solid electrolyte, so that the first coating can avoid direct contact between the lithium metal sheet and the sulfide solid electrolyte, and suppress electron penetration while ensuring ion conduction and reducing self-discharge. In addition, polyethylene glycol gives the first coating a certain degree of mechanical flexibility, which can adapt to the volume changes during lithium deposition / stripping, suppress dendrite growth, and improve battery cycle life and safety.

[0030] In some embodiments, a second coating is further included; the second coating is located between the lithium metal sheet and the first coating; the second coating comprises polyethylene glycol-modified MXene. Here, the second coating and the first coating work together to form a gradient coating on the surface of the lithium metal sheet, which helps to improve the stability of the lithium-sulfur interface.

[0031] In some embodiments, the mass percentage of MXene in the second coating is greater than the mass percentage of MXene in the first coating.

[0032] For example, MXene comprises 45% by mass in the second coating and 9% by mass in the first coating. For example, MXene comprises 52% by mass in the second coating and 8.5% by mass in the first coating.

[0033] In this scheme, the second coating has a larger percentage of MXene, which can provide high conductivity and uniform electron flux density to guide uniform lithium nucleation; the first coating has a smaller percentage of MXene, which is beneficial for -SH modification and chemical bonding with sulfide solid electrolyte, improving interfacial compatibility with sulfide solid electrolyte, while also achieving the effect of inhibiting electron permeation and reducing self-discharge.

[0034] In some embodiments, the mass percentage of MXene is 8% to 10% based on the total mass of the first coating, for example, 8%, 8.5%, 9%, 10%, etc.

[0035] In some embodiments, the mass percentage of MXene is 40% to 60% based on the total mass of the second coating, for example, 40%, 45%, 50%, 55%, 60%, etc.

[0036] It should be noted that the types of MXene in the first coating and the second coating can be the same or different. For example, the MXene in the first coating may be Ti3C2T. m The MXene in the second coating is also Ti3C2T. m For example, the MXene in the first coating is Ti3C2T. m The MXene in the second coating is also Ti3C2T. m and Nb2CT m This disclosure is not limited in this respect. In some embodiments, the thickness of the first coating is 0.5 μm to 3 μm, such as 0.5 μm, 0.7 μm, 1 μm, 1.5 μm, 2 μm, 2.7 μm, 3 μm, etc. The thickness of the first coating of 0.5 μm to 3 μm can better balance the ability to suppress electron penetration, ion conduction and dendrite suppression.

[0037] In some embodiments, the thickness of the second coating is 1 μm to 6 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, etc. A thickness of 1 μm to 6 μm for the second coating can balance and mitigate dendrite formation and the increase in interfacial impedance.

[0038] For example, the thickness of the first coating is 1 μm and the thickness of the second coating is 2 μm.

[0039] In some embodiments, the thickness ratio of the first coating to the second coating is 3:2 to 1:6, such as 3:2, 1:1, 1:2, 1:3, 1:6, etc. Optionally, the thickness ratio of the first coating to the second coating is 1:1.9 to 1:2.1, such as 1:2.

[0040] By limiting the thickness ratio of the first coating and the second coating, interference between them can be reduced, ensuring that the first coating functions to increase compatibility with sulfide solid electrolytes, suppress electron permeation, and reduce self-discharge, while the second coating functions to improve compatibility with lithium metal sheets and ensure ion conduction.

[0041] In some embodiments, the number-average molecular weight (Mn) of polyethylene glycol can be 1000~4000 (Da), such as 1000, 1500, 2000, 4000, etc. Such a molecular weight helps polyethylene glycol provide suitable mechanical flexibility in coatings.

[0042] Preparation method Secondly, embodiments of this disclosure also provide a method for preparing the lithium metal anode described in any of the foregoing claims. Specifically, the preparation method includes: firstly, modifying MXene with a silane coupling agent by amylation to obtain amino-modified MXene (MXene-Si-NH2); in some embodiments, the silane coupling agent may be amino-functionalized, mercapto-functionalized, epoxy-functionalized, alkyl-functionalized, or fluoroalkyl-functionalized, and this disclosure does not limit this type.

[0043] For example, the amino functional type may include at least one of (3-aminopropyl)triethoxysilane (CH3CH2O)3Si(CH2)3NH2 (APTES / APTMS) and (3-aminopropyl)trimethoxysilane (CH3O)3Si(CH2)3NH2.

[0044] For example, the thiol functional type may include at least one of (3-mercaptopropyl)trimethoxysilane(CH3O)3Si(CH2)3SH and (3-mercaptopropyl)triethoxysilane(CH3CH2O)3Si(CH2)3SH.

[0045] For example, the epoxy functional type may include at least one of (3-glycidyl)propyltriethoxysilane (CH3CH2O)3Si(CH2)3OCH2CH(O)CH2 and (3-glycidyl)propyltrimethoxysilane (CH3O)3Si(CH2)3OCH2CH(O)CH2.

[0046] For example, the alkyl type may include dimethyldiethoxysilane (CH3)2Si(OCH2CH3)2, hexadecyltrimethoxysilane C 16 H 33 At least one of Si(OCH3)3.

[0047] For example, fluoroalkyl types may include trifluoropropyltrimethoxysilane (CF3CH2CH2)Si(OCH3)3 and tridecafluorooctyltrimethoxysilane C8F 13 At least one of CH2CH2Si(OCH3)3.

[0048] With Ti3C2T m As an example of MXene, the method for synthesizing amino-modified MXene (MXene-Si-NH2) is illustrated: Ti3C2T mThe powder (1 g) was dispersed in anhydrous toluene, and then (3-aminopropyl)triethoxysilane (APTMS(CH3CH2O)3Si(CH2)3NH2, 5 mL) was added. The mixture was stirred at 60 °C for 12 h to hydrolyze APTES and react on the surface of MXene to generate MXene-Si-NH2. The powder was collected by centrifugation (8000 rpm, 10 min), washed three times with ethanol, and dried under vacuum to obtain MXene–NH2 powder (approximately 1.0 g).

[0049] Next, the amino-modified MXene was surface-modified using methoxy polyethylene glycol (mPEG-COOH) and 3-mercaptopropionic anhydride to obtain MXene modified with polyethylene glycol and -SH.

[0050] For example, 0.050 g of MXene-NH2 was dispersed in 30 mL of anhydrous 1,3-dioxolane (DOL) / ethylene glycol dimethyl ether (DME), and sonicated for 20 min. Then, 0.5 g of methoxy polyethylene glycol acid mPEG-COOH (Mn=2000), 0.15 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC), and 0.06 g of N-hydroxysuccinimide (NHS) were added, and the reaction was continued at room temperature for 24 h. Then, 0.15 mL of 3-mercaptopropionic anhydride was added, and the reaction was continued with stirring for 12 h to introduce -SH groups and form a functionalized complex (MXene-mPEG-SH). Here, the mass percentage of MXene was 9.09%.

[0051] Finally, MXene modified with polyethylene glycol and -SH is applied to the surface of the lithium metal sheet to obtain the first coating. Exemplarily, the functionalized composite is dispersed in DOL / DME (1 wt% solids), sonicated for 20 min, sprayed onto the lithium metal sheet to a thickness of approximately 0.5 μm to 3 μm, and vacuum dried at 50°C for 2 h.

[0052] In some embodiments, before forming the first coating, the process may further include: surface modification of the amino-modified MXene using methoxy polyethylene glycol (mPEG-COOH) to obtain polyethylene glycol-modified MXene.

[0053] For example, 0.50 g of MXene-NH2 was dispersed in 30 mL of anhydrous DOL / DME and sonicated for 20 min. Then, 0.5 g of methoxy polyethylene glycol mPEG-COOH (Mn=2000), 0.15 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and 0.06 g of N-hydroxysuccinimide (NHS) were added, and the reaction was continued at room temperature for 24 h to generate MXene-mPEG; the MXene content was 50%.

[0054] The second coating is obtained by applying polyethylene glycol-modified MXene to the surface of the lithium metal sheet.

[0055] For example, MXene-mPEG powder was dispersed in DOL / DME (3% solid content), sonicated for 20 min, coated onto the lithium metal surface with a thickness of about 1 μm - 6 μm, and vacuum dried at 50 °C for 2 h.

[0056] Those skilled in the art will understand that when a second coating is first formed on the surface of a lithium metal sheet, the first coating can be formed on top of the second coating.

[0057] Battery A third aspect of this disclosure provides a battery including the lithium metal anode provided above. Here, the battery can be a primary battery or a secondary battery; this disclosure does not limit its use.

[0058] In some embodiments, the battery includes a positive electrode, a negative electrode, and a sulfide solid electrolyte located between the positive and negative electrodes. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The sulfide solid electrolyte acts as a conductor of ions between the positive and negative electrodes.

[0059] Optionally, the negative electrode can be the lithium metal negative electrode provided in the first aspect above.

[0060] Positive electrode sheet The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0061] For example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0062] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (e.g., polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0063] In some embodiments, the positive electrode active material is selected from one or more of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium manganese oxide (LMO), lithium nickel manganese oxide (LNMO), lithium nickel cobalt manganese oxide (NCM), or lithium nickel cobalt aluminum oxide (NCA).

[0064] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0065] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent includes one or a combination of two or more selected from carbon black, acetylene black, graphene, carbon nanotubes, carbon nanofibers, etc., in any proportion.

[0066] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive electrode active material, conductive agent, and binder, in a solvent (e.g., N-methylpyrrolidone) at a mass ratio of 95:2:3 to form a positive electrode slurry; coating the positive electrode slurry onto the surface of the positive electrode current collector, and then performing processes such as drying and cold pressing to obtain the positive electrode sheet. The proportions between the components in the above-mentioned positive electrode slurry are merely examples, and this disclosure does not limit them.

[0067] sulfide solid electrolyte The sulfide solid electrolyte can be selected from any type of sulfide solid electrolyte. The embodiments and comparative examples in this disclosure use Li6PS5Cl as an example, but are not limited thereto.

[0068] Negative electrode sheet The negative electrode can be the lithium metal negative electrode provided in the first aspect mentioned above.

[0069] ExampleThe following describes embodiments of this disclosure. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0070] The lithium metal anode provided in this disclosure can be verified using mold batteries or pouch batteries. Example 1 uses NCM811 as the positive electrode, Li6PS5Cl as the electrolyte, and lithium metal anode to fabricate a full cell.

[0071] The preparation of lithium metal anodes includes: First, Ti3C2T m The powder (1 g) was dispersed in anhydrous toluene, and then (3-aminopropyl)triethoxysilane (APTMS (CH3CH2O)3Si(CH2)3NH2, 5 mL) was added. The mixture was stirred at 60 °C for 12 h to hydrolyze APTES and react on the surface of MXene to generate MXene-Si-NH2. The powder was collected by centrifugation (8000 rpm, 10 min), washed three times with ethanol, and dried under vacuum to obtain MXene–NH2 powder (approximately 1.0 g).

[0072] Next, 0.050 g of MXene-NH2 was dispersed in 30 mL of anhydrous 1,3-dioxolane (DOL) / ethylene glycol dimethyl ether (DME), and sonicated for 20 min. Then, 0.5 g of methoxy polyethylene glycol acid mPEG-COOH (Mn=2000), 0.15 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC), and 0.06 g of N-hydroxysuccinimide (NHS) were added, and the reaction was continued at room temperature for 24 h. Then, 0.15 mL of 3-mercaptopropionic anhydride was added, and the reaction was continued with stirring for 12 h to introduce -SH groups and form a functionalized complex (MXene-mPEG-SH). Here, the mass percentage of MXene was 9.09%.

[0073] Then, MXene-NH2 0.50 g was dispersed in 30 mL of anhydrous DOL / DME and sonicated for 20 min. Methoxy polyethylene glycol acid mPEG-COOH (Mn=2000, 0.5 g), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC, 0.15 g) and N-hydroxysuccinimide (NHS, 0.06 g) were added, and the reaction was continued at room temperature for 24 h to generate MXene-mPEG; here, the mass percentage of Mxene was 50%.

[0074] Next, MXene-mPEG powder was dispersed in DOL / DME (3% solid content), sonicated for 20 min, and then coated onto the lithium metal surface with a thickness of about 2 μm. It was then vacuum dried at 50 °C for 2 h to form the second coating.

[0075] Finally, the functionalized compound was dispersed in DOL / DME (1 wt% solid content), sonicated for 20 min, sprayed onto the second coating to a thickness of about 1 μm, and vacuum dried at 50°C for 2 h, corresponding to the first coating.

[0076] The preparation methods for other embodiments and comparative examples are the same as those for Example 1, except as specified in Table 1.

[0077] In addition, the positive electrode is replaced with a coated lithium metal sheet to assemble a lithium-lithium symmetric battery.

[0078] Test methods The lithium-lithium symmetric batteries and full cells prepared in the above embodiments and comparative examples all use the mold battery as the test standard, and can be tested by the following method: (1) CCD measurement of lithium-lithium symmetric batteries: Apply 0.1 mA / cm to the symmetric battery prepared above at 25°C. 2 Lithium deposition and stripping tests were performed at a current density of 0.1 mA / cm² for 1 hour, followed by subsequent current density measurements. 2 The increase gradually increased, and the test was stopped when a short circuit occurred in the symmetrical battery. The current density at this time was recorded. The charge-discharge time for each cycle was 1 hour.

[0079] (2) Full battery 1C discharge capacity At 25°C, charge the battery with a 1C current to the upper limit voltage (e.g., 4.2V), then charge it at a constant voltage, let it stand for 5-10 minutes, and then discharge it with a 1C current at a constant current to the lower limit voltage (e.g., 2.5V). Record the capacity released during this stage, which is the 1C discharge capacity.

[0080] 1C cycle number At 25°C, charge and discharge cycles were performed at a low rate of 0.1C / 0.1C for 2 weeks, with a test voltage range of 2.5 to 4.2V. Subsequently, charge and discharge cycles were performed at a rate of 1C. The test was stopped when the discharge capacity reached 80% of the discharge capacity of the first cycle at the 1C rate (80% State of Health, 80% SOH), and the number of cycles was recorded.

[0081] Table 1. Lithium metal anode parameters and battery performance test results for different groups of examples and comparative examples.

[0082] As can be seen from Comparative Example 1 and Examples 1 to 14, compared with lithium metal without coating, the coated lithium metal electrode provided by the embodiments of this disclosure can significantly improve the critical current density of symmetrical batteries and greatly increase the number of cycles while maintaining or increasing the discharge capacity of the full battery. It is evident that the coated lithium metal electrode provided by the embodiments of this disclosure is beneficial to improving the cycle performance and safety performance of the battery.

[0083] As can be seen from Examples 1-4, 8, and 9, increasing the thickness of the second coating while keeping the thickness of the first coating constant helps to improve the critical current density of the symmetrical battery, as well as the discharge capacity and cycle number of the full battery. This is likely because increasing the thickness of the second coating increases conductivity and enhances dendrite suppression. When the thickness of the second coating continues to increase beyond 2 μm, the critical current density, discharge capacity, and cycle number of the symmetrical battery all show a decreasing trend. This may be because as the thickness continues to increase, the interfacial impedance increases, and the ion diffusion rate decreases. Optionally, when the thickness of the second coating is 1 μm to 6 μm, the overall performance of the battery is better.

[0084] As can be seen from Examples 1, 5-7, 10, and 11, increasing the thickness of the first coating while keeping the thickness of the second coating constant helps to improve the critical current density of the symmetrical battery, as well as the discharge capacity and cycle number of the full battery. This may be because increasing the thickness of the first coating enhances the suppression of dendrites. When the thickness of the first coating continues to increase from 1 μm, the critical current density, discharge capacity, and cycle number of the symmetrical battery all show a decreasing trend. This may be because as the thickness continues to increase, the interfacial impedance increases, and the ion diffusion rate decreases. Optionally, when the thickness of the first coating is 0.5 μm to 3 μm, the overall performance of the battery is better.

[0085] As can be seen from Examples 1 and 13-14, increasing the Mxene content to 50% in the first coating and to 9.09% in the second coating helps to improve the critical current density of the symmetrical battery, as well as the discharge capacity and cycle number of the full battery. This is likely because the increase in Mxene improves ion transport efficiency. Further increasing the Mxene content in both the first and second coatings results in a decrease in the battery's critical current density, discharge capacity, and cycle number. Optionally, based on the total mass of the first coating, the mass percentage of Mxene is 8%~10%; based on the total mass of the second coating, the mass percentage of Mxene is 40%~60%. Within this range, the battery's overall performance is relatively good.

[0086] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this disclosure (including the claims) is limited to these examples; within the framework of this disclosure, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this disclosure as described above, which are not provided in detail for the sake of brevity.

[0087] This disclosure is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A lithium metal anode, characterized in that, It includes a lithium metal sheet and a first coating on the surface of the lithium metal sheet; wherein the first coating includes MXene modified with polyethylene glycol and -SH.

2. The lithium metal anode according to claim 1, characterized in that, It also includes a second coating; the second coating is located between the lithium metal sheet and the first coating; the second coating includes MXene modified with polyethylene glycol.

3. The lithium metal anode according to claim 1 or 2, characterized in that, The thickness of the first coating is 0.5 μm to 3 μm; and / or the thickness of the second coating is 1 μm to 6 μm.

4. The lithium metal anode according to claim 2, characterized in that, The thickness ratio of the first coating to the second coating is 3:2 to 1:6; optionally, the thickness ratio of the first coating to the second coating is 1:1.9 to 1:2.

1.

5. The lithium metal anode according to claim 1, characterized in that, Based on the total mass of the first coating, the mass percentage of MXene is 8% to 10%.

6. The lithium metal anode according to claim 2, characterized in that, Based on the total mass of the second coating, the mass percentage of MXene is 40% to 60%.

7. The lithium metal anode according to claim 2, characterized in that, The mass percentage of MXene in the second coating is greater than the mass percentage of MXene in the first coating.

8. The method for preparing a lithium metal anode according to any one of claims 1 to 7, characterized in that, The preparation method includes: amylating MXene with a silane coupling agent to obtain amino-modified MXene; surface-modifying the amino-modified MXene with methoxy polyethylene glycol and 3-mercaptopropionic anhydride to obtain polyethylene glycol and -SH-modified MXene; and applying the polyethylene glycol and -SH-modified MXene to the surface of the lithium metal sheet to obtain the first coating.

9. The preparation method according to claim 8, characterized in that, The silane coupling agent includes at least one of (3-aminopropyl)triethoxysilane, (3-aminopropyl)trimethoxysilane, (3-mercaptopropyl)trimethoxysilane, (3-mercaptopropyl)triethoxysilane, (3-glycidyl)propyltriethoxysilane, (3-glycidyl)propyltrimethoxysilane, dimethyldiethoxysilane, hexadecyltrimethoxysilane, trifluoropropyltrimethoxysilane, and tridecafluorooctyltrimethoxysilane.

10. A battery, characterized in that, It includes a positive electrode, a sulfide solid electrolyte, and a lithium metal negative electrode as described in any one of claims 1 to 7.

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