Composite lithium metal negative electrode as well as preparation method and application thereof

Abstract

The invention provides a composite lithium metal negative electrode and a preparation method and application thereof, and belongs to the field of batteries. The composite lithium metal negative electrode comprises a lithium metal layer; the protective layer is arranged on the surface of one side of the lithium metal layer, the protective layer comprises a polyvinyl alcohol nanofiber layer and a lithium nitride interface layer, and the lithium nitride interface layer is located between the polyvinyl alcohol nanofiber layer and the lithium metal layer. A large number of polar groups are arranged on the polyvinyl alcohol nanofiber layer, and the polar groups can be in direct contact reaction with lithium ions to form C-O-Li bonds. On one hand, a C-O-Li bond can uniformly disperse the ion flux on the surface of the electrode, the migration efficiency of lithium ions is improved, meanwhile, uniform deposition of metal lithium is promoted, volume expansion is slowed down, and dynamic protection of the metal lithium is achieved; and on the other hand, the formed C-O-Li can provide active sites for nitriding treatment, and a homogeneous lithium nitride interface layer is constructed in situ below the C-O-Li, so that the cycle performance of the battery is remarkably improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a composite lithium metal anode, its preparation method, and its application. Background Technology

[0002] The widespread use of electric vehicles, portable and wearable devices has driven a continuous increase in demand for high-energy-density batteries. Lithium metal anodes, with their high specific capacity of 3860 mAh / g and the lowest reduction potential (relative to the standard hydrogen electrode of -3.04V), are an important system for the development of high-energy-density battery technology.

[0003] However, the application of lithium metal batteries is hindered by inherent challenges such as uneven lithium deposition, uncontrolled dendrite formation, and side reactions between lithium and the electrolyte. For decades, researchers have been working to address these issues using various methods, including constructing structured anodes with three-dimensional current collectors and inducing uniform lithium-ion deposition with functionalized interface layers. However, these measures all have their limitations. For example, three-dimensional metal current collectors are too heavy, affecting the battery's specific energy; three-dimensional carbon-based current collectors have poor mechanical properties; and the introduction of additional interface layers increases electrode interface impedance, limiting the battery's rate performance. Furthermore, once damaged or covered by inactive components during cycling, the interface function fails due to its inability to self-repair. Therefore, there is an urgent need to develop an interface structure that combines fast ion conduction, structural stability, and self-healing capabilities to achieve long-term cycling stability of lithium metal anodes. Summary of the Invention

[0004] This application provides a composite lithium metal anode, its preparation method, and its application to solve the following technical problem: how to achieve long-term cycle stability of lithium metal anodes.

[0005] In a first aspect, this application provides a composite lithium metal anode, the composite lithium metal anode comprising: Lithium metal layer; and A protective layer is disposed on one side of the lithium metal layer. The protective layer includes a polyvinyl alcohol nanofiber layer and a lithium nitride interface layer, wherein the lithium nitride interface layer is located between the polyvinyl alcohol nanofiber layer and the lithium metal layer.

[0006] Optionally, the thickness of the lithium metal layer is 50 μm to 100 μm.

[0007] Optionally, the thickness of the protective layer is 5μm to 10μm.

[0008] Secondly, this application provides a method for preparing the composite lithium metal anode according to any embodiment of the first aspect, the method comprising: The lithium metal layer is bonded to the polyvinyl alcohol nanofiber layer to obtain the laminated product; The laminated material is pressed to obtain a shaped product; In an inert gas atmosphere, the molded article is heated with a nitrogen source to nitrid the molded article, thereby obtaining the composite lithium metal anode.

[0009] Optionally, the method for preparing the polyvinyl alcohol nanofiber layer includes: Polyvinyl alcohol is mixed with an organic solvent to obtain a spinning solution; The spinning solution was electrospun to obtain a polyvinyl alcohol nanofiber layer.

[0010] Optionally, the mass concentration of polyvinyl alcohol in the spinning solution is 8% to 15%; and / or, The mixing temperature is 25℃~60℃, and the mixing time is 4h~12h.

[0011] Optionally, the electrospinning includes the following parameters: voltage of 10KV to 30kV, distance between the receiving tube and the needle of 10cm to 30cm, inner diameter of the needle of 0.2mm to 1mm, flow rate of the spinning solution of 0.01mL / min to 0.2mL / min, and rotation speed of the receiving tube of 300rpm to 1000rpm.

[0012] Optionally, the nitriding treatment includes the following parameters: heating rate of 0.5℃ / min to 3℃ / min, heating temperature of 180℃ to 250℃, and holding time of 3h to 10h; and / or, The nitrogen source includes at least one of the following: urea and melamine.

[0013] Optionally, the number of compressions is 3 to 5, the pressure of each compression is 0.5 MPa to 3 MPa, and the time of each compression is 2 min to 10 min.

[0014] Thirdly, this application provides a battery comprising a composite lithium metal anode as described in any embodiment of the first aspect.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a composite lithium metal anode, comprising: a lithium metal layer; and a protective layer disposed on one side of the lithium metal layer. The protective layer comprises: a polyvinyl alcohol nanofiber layer and a lithium nitride interface layer, wherein the lithium nitride interface layer is located between the polyvinyl alcohol nanofiber layer and the lithium metal layer. Firstly, the polyvinyl alcohol nanofiber layer has a large number of highly polar and active polar groups (hydroxyl groups). These polar groups can coordinate with lithium ions, directly reacting to form CO-Li bonds. On one hand, the CO-Li bonds can uniformly disperse the ion flux on the electrode surface, improving the migration efficiency of lithium ions, while simultaneously promoting uniform lithium metal deposition and mitigating volume expansion, thus achieving dynamic protection of the lithium metal. On the other hand, the formed CO-Li can provide active sites for nitriding treatment, allowing a homogeneous lithium nitride interface layer to be constructed in situ beneath it. Secondly, the lithium nitride interface layer is located between the polyvinyl alcohol nanofiber layer and the lithium metal layer. Because the lithium nitride surface layer has excellent lithium affinity and high ionic conductivity, the lithium nitride interface layer will provide uniform and abundant ion transport channels for the electrode-electrolyte interface, significantly improve the interfacial reaction kinetics of the battery, effectively suppress dendrite growth, and thus significantly improve the cycle performance of the battery. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of a composite lithium metal anode provided in an embodiment of this application; Figure 2 A schematic flowchart illustrating a method for preparing a composite lithium metal anode provided in this application embodiment; Figure 3 The cycle performance diagram of the composite lithium metal anode provided in Example 2 of this application and the symmetrical battery of Comparative Example 1 is shown. Figure label: 1-Lithium metal layer, 2-Protective layer, 21-Lithium nitride interface layer, 22-Polyvinyl alcohol nanofiber layer. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0021] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple. "Parts representation" such as parts by weight or parts by mass indicates the proportional relationship between components. In the proportional relationships discussed in this article, parameters that need to be described by proportion should be understood as the first term of the proportion in the order of description, while the proportion figure should be understood as the second term. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substances A, B, and C should correspond one-to-one with the proportion figure in the proportion in the order of description, i.e., the mass of substance A : the mass of substance B : the mass of substance C = 1:2:3.

[0022] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0023] Figure 1 This is a schematic diagram of a composite lithium metal anode provided in an embodiment of this application.

[0024] like Figure 1 As shown, this application provides a composite lithium metal anode, the composite lithium metal anode comprising: Lithium metal layer 1; and A protective layer 2 is disposed on one side of the lithium metal layer 1. The protective layer 2 includes a polyvinyl alcohol nanofiber layer 22 and a lithium nitride interface layer 21. The lithium nitride interface layer 21 is located between the polyvinyl alcohol nanofiber layer 22 and the lithium metal layer 1.

[0025] The composite lithium metal anode mainly consists of two parts: a lithium metal layer 1, which serves as the main body of the anode and is responsible for storing and releasing lithium ions; and a protective layer 2, located on one side of the lithium metal layer 1, designed to provide protection and improve electrochemical performance.

[0026] The protective layer 2 consists of two layers, from the outside to the inside: a polyvinyl alcohol nanofiber layer 22 and a lithium nitride interface layer 21.

[0027] The polyvinyl alcohol nanofiber layer 22 has a large number of highly polar and active polar groups (hydroxyl groups). These polar groups can coordinate with lithium ions and directly react to form CO-Li bonds. On the one hand, CO-Li bonds can uniformly disperse the ion flux on the electrode surface, improve the migration efficiency of lithium ions, promote uniform deposition of lithium metal and slow down volume expansion, thus achieving dynamic protection of lithium metal. On the other hand, the formed CO-Li can provide active sites for nitriding treatment, and a homogeneous lithium nitride interface layer 21 can be constructed in situ below it.

[0028] The lithium nitride interface layer 21 is located between the polyvinyl alcohol nanofiber layer 22 and the lithium metal layer 1. Due to the excellent lithium affinity and high ionic conductivity of the lithium nitride surface layer, the lithium nitride interface layer 21 will provide a uniform and abundant ion transport channel for the electrode-electrolyte interface, significantly improve the interfacial reaction kinetics of the battery, effectively suppress dendrite growth, and thus significantly improve the cycle performance of the battery.

[0029] Thus, protective layer 2 achieves dynamic protection of lithium metal through the CO-Li bonds formed between the polyvinyl alcohol nanofiber layer 22 and lithium ions, and the high ionic conductivity of the lithium nitride interface layer 21. During cycling, even if the alloy interface is damaged, the polymer fiber layer can promptly supply functional ions for in-situ repair. Simultaneously, protective layer 2 normalizes the lithium ion flux, mitigating the volume expansion of lithium metal during charging and discharging. Furthermore, the abundant polar hydroxyl groups on the polyvinyl alcohol of protective layer 2 interact with Li... + The coordination between them constructed a continuous Li + High-speed transmission channel improves Li + The migration efficiency of Li. The presence of nitrogen in protective layer 2 can significantly improve the migration efficiency of Li. + Intrinsic ion diffusion kinetics of polyvinyl alcohol nanofiber membranes.

[0030] In summary, the composite lithium metal anode forms a protective layer 2 with regenerative function by nitriding a polymer fiber layer (especially the polyvinyl alcohol nanofiber layer 22) with a lithium layer. This protective layer 2 not only enables uniform lithium deposition and inhibits dendrite growth, but also supplies functional ions in a timely manner during cycling to repair damaged areas in situ, thereby achieving long-term "dynamic protection" of the lithium metal anode and significantly improving the electrochemical performance and cycle performance of the battery.

[0031] In some embodiments, the thickness of the lithium metal layer 1 is 50 μm to 100 μm.

[0032] Limiting the thickness of the lithium metal layer 1 to 50 μm to 100 μm provides sufficient lithium content, ensuring a high energy density for the battery. This is crucial for applications requiring long battery life and high performance. Simultaneously, an appropriate thickness of the lithium metal layer 1 helps reduce volume changes during charge-discharge cycles, thereby improving battery cycle stability and lifespan. Furthermore, the lithium metal layer 1 allows for better control of lithium ion release and absorption, reducing the risk of short circuits caused by lithium dendrite growth, thus improving battery safety. It is also easier to handle and process, contributing to reduced production costs and increased production efficiency. For example, the thickness of the lithium metal layer 1 can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, etc.

[0033] In some embodiments, the thickness of the protective layer 2 is 5 μm to 10 μm.

[0034] The protective layer 2 has a thickness of 5μm to 10μm. This protective layer 2 effectively isolates the lithium metal layer 1 from direct contact with the electrolyte, reducing side reactions and protecting the lithium metal layer 1 from corrosion and damage. Simultaneously, the appropriate thickness of the protective layer 2 ensures smooth lithium ion transport at the electrode-electrolyte interface, improving the battery's ion conduction efficiency. Furthermore, it provides sufficient mechanical strength to resist the internal pressure generated during charging and discharging, preventing damage to the battery structure. For example, the thickness of the protective layer 2 is 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc.

[0035] Figure 2 This is a schematic flowchart illustrating a method for preparing a composite lithium metal anode, as provided in an embodiment of this application.

[0036] like Figure 2 As shown, based on a general inventive concept, this application provides a method for preparing the composite lithium metal anode described in any of the above embodiments, the method comprising: S1. The lithium metal layer 1 and the polyvinyl alcohol nanofiber layer 22 are bonded together to obtain the bonded product. In some implementations... In some embodiments, the method for preparing the polyvinyl alcohol nanofiber layer 22 includes: Polyvinyl alcohol is mixed with an organic solvent to obtain a spinning solution; The spinning solution was electrospun to obtain a polyvinyl alcohol nanofiber layer 22.

[0037] It should be noted that electrospinning is a spinning technology developed based on the principle of high-speed jetting of conductive fluid under a high-voltage electrostatic field. During electrospinning, the polymer solution or melt forms a Taylor cone under the influence of a strong electric field. When the electric field strength exceeds a certain critical value, the surface tension of the solution or melt is overcome, forming charged jets. These jets are stretched and refined at high speed under the influence of the electric field force, and dry during the jetting process, ultimately falling onto a receiving device to form fibers.

[0038] In some embodiments, the mass concentration of polyvinyl alcohol in the spinning solution is 8% to 15%; and / or, The mixing temperature is 25℃~60℃, and the mixing time is 4h~12h.

[0039] Limiting the polyvinyl alcohol (PVA) concentration to 8%–15% ensures a suitable viscosity in the spinning solution—neither too viscous to cause spinning difficulties nor too thin to result in insufficient fiber strength. Simultaneously, it allows the spinning solution to form stable, continuous fiber bundles during electrospinning, improving spinning efficiency and fiber quality. Furthermore, the moderate interactions between PVA molecular chains contribute to the formation of nanofibers with excellent mechanical properties and chemical stability. For example, the PVA concentration can be 8%, 9%, 10%, 11%, 13%, 14%, 15%, etc.

[0040] Limiting the mixing temperature to 25℃–60℃ and the mixing time to 4h–12h helps polyvinyl alcohol (PVA) dissolve uniformly in the organic solvent, reducing energy consumption and time during the dissolution process. Simultaneously, it ensures that the PVA molecular chains fully expand and dissolve in the solvent, forming a homogeneous spinning solution. Sufficient dissolution and a homogeneous spinning solution contribute to the formation of nanofibers with uniform diameter and dense structure, improving the strength and toughness of the fibers. For example, the mixing temperature can be 25℃, 35℃, 45℃, 55℃, 60℃, etc., and the mixing time can be 4h, 6h, 8h, 10h, 12h, etc.

[0041] In some embodiments, the electrospinning includes the following parameters: voltage of 10kV to 30kV, distance between the receiving tube and the needle of 10cm to 30cm, inner diameter of the needle of 0.2mm to 1mm, flow rate of spinning solution of 0.01mL / min to 0.2mL / min, and rotation speed of the receiving tube of 300rpm to 1000rpm.

[0042] The voltage is limited to 10kV to 30kV. This voltage generates a sufficient electric field to form a stable Taylor cone in the spinning solution at the needle tip, allowing for the smooth stretching of nanofibers. However, if the voltage exceeds 30kV, the electric field strength becomes too high, causing electrical breakdown and affecting the stability of the spinning process and the fiber quality.

[0043] Limiting the distance between the receiving tube and the needle to 10cm–30cm allows the fiber sufficient flight time in the electric field to fully stretch and solidify, forming nanofibers with uniform diameter and dense structure. Conversely, a distance shorter than 10cm may cause the fiber to fall onto the receiving tube before complete solidification, resulting in fiber adhesion or accumulation; a distance longer than 30cm may increase the fiber's exposure time in the air, making it more susceptible to contamination and interference.

[0044] By limiting the inner diameter of the needle to 0.2 mm to 1 mm, nanofibers with uniform diameter and meeting the requirements can be prepared. Appropriate spinning solution flow rate ensures the stability and continuity of the spinning process, preventing fiber breakage or accumulation. Simultaneously, a stable spinning solution flow rate helps form nanofibers with uniform diameter and dense structure, improving fiber strength and toughness.

[0045] Limiting the receiving cylinder rotation speed to 300 rpm to 1000 rpm ensures uniform fiber distribution on the cylinder, preventing fiber accumulation or adhesion. Simultaneously, it increases the collecting area and efficiency of the receiving cylinder, thereby accelerating the fabrication speed of the nanofiber layer.

[0046] For example, the voltage can be 10 kV, 15 kV, 20 kV, 30 kV, etc., the distance between the receiving tube and the needle can be 10 cm, 15 cm, 20 cm, 25 cm, 28 cm, 30 cm, etc., and the inner diameter of the needle can be 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.8 mm, 1 mm, etc. The flow rate of the spinning solution can be 0.01 mL / min, 0.02 mL / min, 0.03 mL / min, 0.04 mL / min, 0.05 mL / min, 0.08 mL / min, 0.1 mL / min, 0.12 mL / min, 0.15 mL / min, 0.2 mL / min, etc. The rotation speed of the receiving tube can be 300 rpm, 500 rpm, 800 rpm, 1000 rpm, etc.

[0047] S2. Press the laminated product to obtain a shaped product; Pressing the bonded products together is primarily to increase their density and mechanical strength, while also helping to reduce the possibility of cracks or delamination during subsequent nitriding processes.

[0048] In some embodiments, the number of compressions is 3 to 5, the pressure of each compression is 0.5 MPa to 3 MPa, and the duration of each compression is 2 min to 10 min.

[0049] By pressing 3 to 5 times, the internal density of the laminate can be gradually increased, making the bond between each layer of material stronger. This helps to improve the overall mechanical strength of the molded product, enabling it to withstand greater external forces and pressures during use. A single pressing pressure between 0.5 MPa and 3 MPa ensures a tight bond between materials while preventing deformation or damage, helping to form a stable bonding interface and improving the overall performance of the molded product. A single pressing time between 2 and 10 minutes ensures sufficient time for the materials to fully bond and cure, helping to eliminate voids and defects within the laminate and improving overall density and mechanical strength. For example, the number of pressings can be 3, 4, or 5; the single pressing pressure can be 0.5 MPa, 0.8 MPa, 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, or 3 MPa; and the single pressing time can be 2 minutes, 3 minutes, 4 minutes, 5 minutes, 7 minutes, 9 minutes, or 10 minutes.

[0050] S3. In an inert gas atmosphere, the molded article is heated with a nitrogen source to nitrid the molded article to obtain the composite lithium metal anode.

[0051] In some embodiments, the nitriding treatment includes the following parameters: heating rate of 0.5℃ / min to 3℃ / min, heating temperature of 180℃ to 250℃, and holding time of 3h to 10h; and / or, The nitrogen source includes at least one of the following: urea and melamine.

[0052] It should be noted that urea is a commonly used nitrogen source, with advantages such as low price and easy availability. During nitriding, urea decomposes to produce gases such as ammonia and carbon dioxide. Ammonia can combine with active sites in the molded product to form a nitrided layer. Melamine is also an effective nitrogen source, possessing high thermal and chemical stability. During nitriding, melamine decomposes to produce active species such as nitrogen and carbon atoms. These species can combine with metallic lithium and other components in the molded product to form a nitrided layer.

[0053] Limiting the heating rate to 0.5℃ / min to 3℃ / min helps ensure uniform heating of the molded product during the heating process, avoiding thermal stress concentration and cracking caused by excessive temperature gradients. Simultaneously, a slower heating rate allows the nitrogen source to more fully combine with the active sites on the surface of the molded product, improving the nitriding effect. Limiting the heating temperature to 180℃ to 250℃ ensures the structural stability of the polyvinyl alcohol nanofiber layer 22 and other components in the molded product, while allowing the nitrogen source to undergo an effective nitriding reaction. Higher temperatures help accelerate the nitriding reaction rate, but excessively high temperatures may cause some components in the molded product to decompose or deteriorate. Limiting the holding time to 3h to 10h ensures the nitriding reaction proceeds fully, resulting in a more uniform distribution of nitrogen in the molded product. Simultaneously, the holding time also helps eliminate internal stress and defects generated during nitriding, improving the overall performance of the molded product. For example, the heating rate of the nitriding treatment can be 0.5℃ / min, 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, etc., the heating temperature can be 180℃, 200℃, 210℃, 220℃, 240℃, 250℃, etc., and the holding time can be 3h, 5h, 7h, 9h, 10h, etc.

[0054] The method for preparing composite lithium metal anodes provided in this application, through the coordination of various steps, can prepare composite anodes with excellent mechanical and electrochemical properties, which is beneficial to improving the overall performance of batteries.

[0055] The product prepared by the method of preparing the composite lithium metal anode is the aforementioned composite lithium metal anode. The chemical composition and microstructure of the composite lithium metal anode prepared by the method can be referred to the above embodiments. Since the method of preparing the composite lithium metal anode adopts some or all of the technical solutions of the composite lithium metal anode embodiments, it has at least all the beneficial effects brought about by the technical solutions of the composite lithium metal anode embodiments, which will not be elaborated here.

[0056] Based on a general inventive concept, this application provides a battery comprising a composite lithium metal anode as described in any of the embodiments above.

[0057] This application embodiment combines a nitrided polymer fiber layer with a lithium layer to obtain a composite negative electrode with a regenerative protective layer. This composite negative electrode can induce uniform lithium deposition, inhibit dendrite growth, and simultaneously supply functional ions for in-situ repair, thereby achieving long-term "dynamic protection" of the lithium metal negative electrode and improving the electrochemical performance of the battery.

[0058] The composite lithium metal anode and its preparation method provided in this application have the following significant advantages: (1) Excellent electrochemical performance: Through the CO-Li bond formed between the polyvinyl alcohol nanofiber layer and lithium ions, and the high ionic conductivity of the lithium nitride interface layer, dynamic protection of lithium metal is achieved, which significantly improves the migration efficiency of lithium ions and the interfacial reaction kinetics of the battery. At the same time, the lithium nitride interface layer provides a uniform and abundant ion transport channel for the electrode-electrolyte interface, effectively suppressing dendrite growth, thereby significantly improving the cycle performance of the battery.

[0059] (2) Long-term dynamic protection: The polyvinyl alcohol nanofiber layer in the protective layer has a regenerative function, which can supply functional ions in a timely manner during the cycle to repair the damaged area in situ, thus extending the service life of the lithium metal anode. At the same time, the tight bond between the lithium metal layer and the protective layer reduces the volume expansion during the charge and discharge process, further improving the cycle stability and safety of the battery.

[0060] (3) Controllable lithium metal layer thickness: The lithium metal layer thickness is limited to between 50 μm and 100 μm, providing sufficient lithium content to ensure the high energy density of the battery. An appropriate lithium metal layer thickness helps to reduce volume changes during charge and discharge cycles, improving the cycle stability and lifespan of the battery.

[0061] (4) Efficient and stable preparation of protective layer: The polyvinyl alcohol nanofiber layer is prepared by electrospinning technology, which has controllable fiber diameter and uniform fiber distribution, improving the mechanical strength and chemical stability of the protective layer. At the same time, the pressing step increases the internal density and mechanical strength of the laminate, reducing the possibility of cracks or delamination during the subsequent nitriding process.

[0062] (5) Flexible nitriding parameters: The flexible selection of nitriding parameters (heating rate, heating temperature, and holding time) ensures the full progress of the nitriding reaction and the uniform distribution of nitrogen. At the same time, the selection of nitrogen sources such as urea and melamine provides a low-cost and readily available nitriding pathway.

[0063] (6) Broad application prospects: This composite lithium metal anode and its preparation method are suitable for various applications requiring long driving range and high performance, such as electric vehicles and energy storage systems. At the same time, by optimizing the preparation parameters and process conditions, the electrochemical performance and cycle performance of the battery can be further improved to meet the needs of different fields.

[0064] In summary, the composite lithium metal anode prepared by this method and its preparation method show significant advantages in terms of electrochemical performance, long-term stability, control of lithium metal layer thickness, efficiency of protective layer preparation, flexibility of nitriding treatment, and application prospects.

[0065] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0066] Example 1 This embodiment provides a composite lithium metal anode, and the preparation method of the composite lithium metal anode may include the following steps: Step 1, with N, N Dimethylformamide (DMF) was used as a solvent. Polyvinyl alcohol (PVA) was added to DMF and mixed with magnetic stirring to form a uniform spinning solution. The mass concentration of polyvinyl alcohol in the spinning solution was 8%, the mixing temperature was 25°C, and the mixing time was 12 hours. Step 2: Electrospin the spinning solution and dry it to obtain a polyvinyl alcohol nanofiber membrane. The electrospinning parameters include: voltage of 10kV, distance between the receiving tube and the needle of 10cm, needle inner diameter of 0.2mm, flow rate of spinning solution of 0.01 mL / min, rotation speed of the receiving tube of 300rpm; and drying temperature of 50℃.

[0067] Step 3: Lay the polyvinyl alcohol nanofiber film onto the lithium foil and press it to obtain the shaped product; the pressing is performed 3 times; the pressure of each pressing is 3 MPa and the pressing time is 10 min. Step 4: Place the molded product and urea in a tube furnace; introduce argon gas into the tube furnace; heat the tube furnace to the nitriding temperature to nitrid the molded product, obtaining a composite lithium metal anode. The nitriding treatment includes the following parameters: heating rate of 0.5℃ / min, heating temperature of 180℃, and holding time of 10h. The thickness of the lithium metal layer of the composite lithium metal anode is 50μm, and the thickness of the protective layer (the sum of the thicknesses of the polyvinyl alcohol nanofiber layer and the lithium nitride interface layer) is 5μm.

[0068] Example 2 This embodiment provides a composite lithium metal anode, and the preparation method of the composite lithium metal anode may include the following steps: Step 1, with N, N Dimethylformamide (DMF) was used as a solvent. Polyvinyl alcohol (PVA) was added to DMF and mixed by magnetic stirring to form a homogeneous spinning solution. The mass concentration of polyvinyl alcohol in the spinning solution was 11%, the mixing temperature was 40°C, and the mixing time was 6 h. Step 2: Electrospin the spinning solution and dry it to obtain a polyvinyl alcohol nanofiber membrane. The electrospinning parameters include: voltage of 20 kV, distance between the receiving tube and the needle of 20 cm, needle inner diameter of 0.6 mm, spinning solution flow rate of 0.1 mL / min, receiving tube rotation speed of 600 rpm; and drying temperature of 60 ℃.

[0069] Step 3: Lay the polyvinyl alcohol nanofiber film onto the lithium foil and press it to obtain the shaped product; the pressing is performed 4 times; the pressure of each pressing is 1.5 MPa and the pressing time is 5 min. Step 4: Place the molded product and urea in a tube furnace; introduce argon gas into the tube furnace; heat the tube furnace to the nitriding temperature to nitrid the molded product, obtaining a composite lithium metal anode. The nitriding treatment includes the following parameters: heating rate of 1.5℃ / min, heating temperature of 200℃, and holding time of 6h. The thickness of the lithium metal layer of the composite lithium metal anode is 70μm, and the thickness of the protective layer (the sum of the thicknesses of the polyvinyl alcohol nanofiber layer and the lithium nitride interface layer) is 8μm.

[0070] Example 3 This embodiment provides a composite lithium metal anode, and the preparation method of the composite lithium metal anode may include the following steps: Step 1, with N, N Dimethylformamide (DMF) was used as a solvent. Polyvinyl alcohol (PVA) was added to DMF and mixed with magnetic stirring to form a homogeneous spinning solution. The mass concentration of polyvinyl alcohol in the spinning solution was 15%, the mixing temperature was 60°C, and the mixing time was 4 hours. Step 2: Electrospin the spinning solution and dry it to obtain a polyvinyl alcohol nanofiber membrane. The electrospinning parameters include: voltage of 30 kV, distance between the receiving tube and the needle of 30 cm, needle inner diameter of 1 mm, spinning solution flow rate of 0.2 mL / min, receiving tube rotation speed of 1000 rpm, and drying temperature of 70 ℃.

[0071] Step 3: Lay the polyvinyl alcohol nanofiber film onto the lithium foil and press it to obtain the shaped product; the pressing is performed 5 times; the pressure of each pressing is 3 MPa and the pressing time is 2 minutes. Step 4: Place the molded product and urea in a tube furnace; introduce argon gas into the tube furnace; heat the tube furnace to the nitriding temperature to nitrid the molded product, obtaining a composite lithium metal anode. The nitriding treatment includes the following parameters: heating rate of 3℃ / min, heating temperature of 250℃, and holding time of 3h. The thickness of the lithium metal layer of the composite lithium metal anode is 100 μm, and the thickness of the protective layer (the sum of the thicknesses of the polyvinyl alcohol nanofiber layer and the lithium nitride interface layer) is 10 μm.

[0072] Comparative Example 1 Comparative Example 1: The lithium metal anode is an aluminum foil with a thickness of 70 μm.

[0073] The composite lithium metal anodes of Examples 1-3 and the pure lithium metal of Comparative Example 1 were assembled into coin cells in an argon-filled glove box for performance testing. The results of the cycling test are shown in Table 1. The deposition / stripping cycling test had a current density of 1.44 mA / cm². 2 The cycle capacity is 1.44 mAh / cm³. 2 The test results are as follows: Figure 3 As shown.

[0074] Table 1. Cycle performance of composite lithium metal anodes in Examples 1-3 and pure lithium metal in Comparative Example 1

[0075] In Table 1, the composite lithium metal anodes of Examples 1-3 have an overpotential of ≤25mV after 20 h of cycling and an overpotential of ≤30mV after 40 h of cycling, which is much lower than the overpotential of the pure lithium metal in the comparative example.

[0076] Figure 3 The image shows the cycle performance of the composite lithium metal anode provided in Example 2 of this application and the symmetrical battery of Comparative Example 1.

[0077] Depend on Figure 3 As can be seen, compared with Comparative Example 1, the composite lithium metal anode containing lithium nitride polymer fiber membrane in Example 2 maintains very low voltage polarization and remains stable for 40 hours.

[0078] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: In this embodiment, by combining the nitrided polymer fiber layer with the lithium layer, a composite negative electrode with a regenerative protective layer is obtained. This allows for the timely supply of functional ions to repair the lithium metal negative electrode in situ while inducing uniform lithium deposition and inhibiting dendrite growth, thus achieving long-term "dynamic protection" of the lithium metal negative electrode and improving the electrochemical performance of the battery.

[0079] In the embodiments of this application, by coordinating the various steps, a composite negative electrode with excellent mechanical and electrochemical properties can be prepared, which is beneficial to improving the overall performance of the battery.

[0080] In the embodiments of this application, the superior effects of the protective layer include: (1) the protective layer normalizes the lithium-ion flux and slows down volume expansion; (2) the abundant polar hydroxyl groups on polyvinyl alcohol can react with Li + Coordination occurs between them, constructing continuous Li + Fast transmission channel, improve Li + (3) The presence of nitrogen in nitrided polymer fibers can significantly improve the migration efficiency of Li. + Intrinsic ion diffusion kinetics of polyvinyl alcohol nanofiber membranes.

[0081] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A composite lithium metal anode, the composite lithium metal anode comprising: Lithium metal layer; as well as A protective layer is disposed on one side of the lithium metal layer. The protective layer includes a polyvinyl alcohol nanofiber layer and a lithium nitride interface layer, wherein the lithium nitride interface layer is located between the polyvinyl alcohol nanofiber layer and the lithium metal layer.

2. The composite lithium metal anode according to claim 1, characterized in that, The thickness of the lithium metal layer is 50 μm to 100 μm.

3. The composite lithium metal anode according to claim 1, characterized in that, The thickness of the protective layer is 5μm to 10μm.

4. A method for preparing a composite lithium metal anode according to any one of claims 1 to 3, the method comprising: The lithium metal layer is bonded to the polyvinyl alcohol nanofiber layer to obtain the laminated product; The laminated material is pressed to obtain a shaped product; In an inert gas atmosphere, the molded article is heated with a nitrogen source to nitrid the molded article, thereby obtaining the composite lithium metal anode.

5. The method according to claim 4, characterized in that, The method for preparing the polyvinyl alcohol nanofiber layer includes: Polyvinyl alcohol is mixed with an organic solvent to obtain a spinning solution; The spinning solution was electrospun to obtain a polyvinyl alcohol nanofiber layer.

6. The method according to claim 5, characterized in that, The polyvinyl alcohol concentration in the spinning solution is 8%–15%; and / or, The mixing temperature is 25℃~60℃, and the mixing time is 4h~12h.

7. The method according to claim 5, characterized in that, The electrospinning process includes the following parameters: voltage of 10KV to 30kV, distance between the receiving tube and the needle of 10cm to 30cm, needle inner diameter of 0.2mm to 1mm, flow rate of spinning solution of 0.01mL / min to 0.2mL / min, and rotation speed of the receiving tube of 300rpm to 1000rpm.

8. The method according to claim 4, characterized in that, The nitriding treatment includes the following parameters: heating rate of 0.5℃ / min to 3℃ / min, heating temperature of 180℃ to 250℃, and holding time of 3h to 10h; and / or, The nitrogen source includes at least one of the following: urea and melamine.

9. The method according to claim 4, characterized in that, The compression is performed 3 to 5 times, the pressure of each compression is 0.5 MPa to 3 MPa, and the compression time is 2 to 10 minutes.

10. A battery comprising a composite lithium metal anode as described in any one of claims 1 to 3.

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