A lithium metal negative electrode, a lithium metal battery and an electric device

Abstract

This application provides a lithium metal anode, a lithium metal battery, and an electrical device. In the lithium metal anode provided in this application, a first modification layer with a highly conductive ion-conducting compound is formed on the surface of the lithium metal substrate, improving ion transport performance. Simultaneously, a second modification layer containing a polymer with dynamic interaction bonds is formed on the surface of the first modification layer, enabling interface self-repair through reversible breakage and recombination of these dynamic interaction bonds via heating or mechanical stress. Furthermore, the functional groups on the surface of the second modification layer balance polarity and hydrophobicity, thereby optimizing lithium-ion transport efficiency, reducing localized lithium-ion deposition overpotential, regulating lithium-ion deposition uniformity, suppressing lithium dendrite formation, and improving interface stability. Therefore, this application improves upon the problem of existing lithium metal anodes having a significant risk of lithium dendrite growth, which easily leads to interface failure and capacity decay.

Description

Technical Field

[0001] This application relates to the field of battery manufacturing technology, and in particular to a lithium metal anode, a lithium metal battery, and an electrical device. Background Technology

[0002] Currently, lithium metal anodes are favored due to their high specific capacity (3861 mAh g). -1 Its low electrochemical potential (-3.041V compared to the standard hydrogen electrode) makes it an ideal choice for next-generation battery anodes.

[0003] However, the uneven thickness of the SEI film on the surface of traditional lithium metal anodes results in high interfacial impedance, posing a significant risk of lithium dendrite growth. Furthermore, their poor mechanical properties and high brittleness make them prone to cracking during lithium ion deposition and stripping, leading to interfacial failure, capacity decay, and ultimately, serious safety risks. Summary of the Invention

[0004] The technical problem to be solved by this application is to provide a lithium metal anode, a lithium metal battery and an electrical device to solve the problem that existing lithium metal anodes have a large risk of lithium dendrite growth, which easily leads to interface failure and capacity decay.

[0005] To solve the above problems, this application provides the following technical solution: This application discloses a lithium metal anode, wherein the lithium metal anode comprises: Lithium metal matrix; The first modification layer is disposed on at least one surface of the sodium metal substrate and contains a highly ionicly conductive compound. The second modification layer is disposed on the surface of the first modification layer away from the lithium metal matrix and contains a polymer with dynamic bonds. The surface of the second modified layer is modified with functional groups, including at least one of -NH2, -SO3H, -CF3, and -C6H5.

[0006] Furthermore, in the lithium metal anode, the dynamic interaction bonds include at least one of disulfide bonds and hydrogen bonds.

[0007] Furthermore, in the lithium metal anode, the polymer with dynamic interaction bonds includes at least one of polyurethane (PU), polysiloxane (PDMS), polyacrylate, polyamide, hydroxyethyl cellulose, polyethylene glycol hydroxyl, poly(ε-caprolactone)-disulfide (PCL-SS), polysiloxane-disulfide (PDMS-SS), polyvinyl alcohol-disulfide (PVA-SS), thiol-disulfide interchangeable polymers, polyurethane-urea disulfide polymer (PU-SS), and hyperbranched polydimethylsiloxane-disulfide (PDMS-SS-HB).

[0008] Furthermore, in the lithium metal anode, the highly conductive ionic compound includes lithium bis(trifluoromethanesulfonylimide) (LiTFSI) and lithium phosphorus sulfide LPS (Li7P3S). 11 At least one of lithium sulfide-phosphorus pentasulfide (Li2S-P2S5).

[0009] Furthermore, in the lithium metal anode, the functional groups include -SO3H and -CF3.

[0010] Furthermore, in the second modification layer, the molar ratio of -SO3H to -CF3 is 1:1 to 1:2.

[0011] Furthermore, in the lithium metal anode, the thickness of the first modification layer is 0.5~2μm; and / or The thickness of the second modification layer is 100~300 nm.

[0012] Furthermore, in the lithium metal anode, the contact angle of the lithium metal anode is 30°~60°.

[0013] This application also proposes a lithium metal battery, wherein the aforementioned lithium metal anode is included.

[0014] This application also proposes an electrical device, which includes the aforementioned lithium metal battery, serving as the power supply for the electrical device.

[0015] Compared with the prior art, the embodiments of this application have the following advantages: In this embodiment, the lithium metal anode includes: a lithium metal substrate; a first modification layer disposed on at least one surface of the lithium metal substrate, comprising a highly conductive ion-exchange compound; and a second modification layer disposed on the surface of the first modification layer facing away from the lithium metal substrate, comprising a polymer with dynamic interaction bonds. The surface of the second modification layer is modified with functional groups, including at least one of -NH2, -SO3H, -CF3, and -C6H5. The first modification layer with a highly conductive ion-exchange compound on the surface of the lithium metal substrate improves ion transport performance. Simultaneously, the second modification layer containing a polymer with dynamic interaction bonds on the surface of the first modification layer enables interface self-repair through reversible breakage and recombination of the dynamic interaction bonds. The functional groups on the surface of the second modification layer balance polarity and hydrophobicity, thereby optimizing lithium-ion transport efficiency, reducing local overpotential of lithium ions, regulating lithium-ion deposition uniformity, suppressing lithium dendrite formation, and improving interface stability. Therefore, this embodiment improves upon the problem of existing lithium metal anodes having a significant risk of lithium dendrite growth, which easily leads to interface failure and capacity decay.

[0016] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the lithium metal anode structure in an embodiment of this application.

[0018] Explanation of reference numerals in the attached figures: 10-Lithium metal anode, 20-Lithium metal substrate, 31-First modification layer, 32-Second modification layer. Detailed Implementation

[0019] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] To address the aforementioned problems, this application provides a lithium metal anode, such as... Figure 1 As shown, the lithium metal anode 10 includes a lithium metal substrate 20, a first modification layer 31, and a second modification layer 32; wherein, the first modification layer 31 is disposed on at least one side surface of the lithium metal substrate 20, and the first modification layer 31 contains a highly conductive ion-conducting compound; the second modification layer 32 is disposed on the side surface of the first modification layer 31 opposite to the lithium metal substrate 20, and the second modification layer 32 contains a polymer with dynamic interaction bonds; the surface of the second modification layer 32 is also modified with functional groups, including at least one of -NH2, -SO3H, -CF3, and -C6H5.

[0021] The first modification layer, which is a highly conductive ion-conducting compound, is applied to the surface of the lithium metal substrate, thereby improving ion transport performance. The second modification layer, which is a polymer containing dynamic interaction bonds, is applied to the surface of the first modification layer, enabling interface self-repair through reversible breakage and recombination of the dynamic interaction bonds. Furthermore, the functional groups on the surface of the second modification layer, including at least one of -NH2, -SO3H, -CF3, and -C6H5, can effectively balance polarity and hydrophobicity, thereby optimizing lithium-ion transport efficiency, reducing local overpotential of lithium ions, regulating the uniformity of lithium-ion deposition, inhibiting the formation of lithium dendrites, and improving interface stability.

[0022] Therefore, the embodiments of this application improve the problem that existing lithium metal anodes have a large risk of lithium dendrite growth, which easily leads to interface failure and capacity decay.

[0023] Optionally, in one embodiment, the aforementioned highly conductive ionic compound includes lithium bis(trifluoromethanesulfonylimide) (LiTFSI) and lithium phosphorus sulfide LPS (Li7P3S). 11 It contains at least one of lithium sulfide and lithium pentasulfide (Li2S-P2S5), which has high ionic conductivity and good mechanical ductility, and can efficiently provide migratable lithium ions, thereby optimizing lithium ion transport efficiency.

[0024] In some embodiments, the qualitative testing methods for the functional groups modified on the surfaces of the first modified layer, the second modified layer, and the second modified layer are as follows: The lithium metal sheet sample (including the self-healing layer) was cut to a size suitable for FTIR testing (e.g., 1 cm²). Nitrogen gas was used to protect the environment from oxidation and direct contact with air was avoided. An ATR (attenuated total internal reflection) attachment was used, ensuring the light path was perpendicular to the surface of the self-healing layer. The scanning range was 400–4000 cm². - ¹, resolution 4 cm - ¹, scanned 32 times. Similarly, FTIR detection revealed the C=O stretching vibration of the ester group of polycaprolactone (approximately 1720 cm⁻¹). - ¹) and the characteristic peaks of disulfide bond SS (approximately 500 cm⁻¹) - ¹) The functional groups modified on the surface of the second modification layer can be obtained by photoelectron spectroscopy (XPS). Analyzing the S 2p spectrum, the S 2p3 / 2 binding energy of the sulfonic acid group (-SO3H) is about 168.0~168.5 eV; analyzing the F 1s spectrum, the F1s binding energy of the -CF3 group is about 688.0~688.5 eV.

[0025] In some embodiments, the method for testing the thickness of functional groups on the surfaces of the first and second modification layers is as follows: The lithium sheet and each modification layer composite sample are cut into cross-sections (using ion beam cutting or focused ion beam (FIB)). The cross-sections are then gold-plated (e.g., sputtered gold film) to reduce charge accumulation. The cross-sectional morphology is observed using TEM (transmission electron microscopy). After characteristic element scanning of the cross-section, the thickness of the first and second modification layers is measured using software (e.g., ImageJ).

[0026] In some embodiments, the highly conductive ionic compound can be determined by XRD, specifically by cutting a modified lithium metal sheet into 1*1cm pieces. 2 The size was determined, the sample was placed in the test card slot and sealed, and then placed in an XRD testing device for testing. The testing range was 5° to 80°, with a step size of 0.02° and a scanning speed of 3° / min. The test results were compared with a standard PDF card to confirm the category of the highly conductive ionic compound.

[0027] In this embodiment, the first modification layer includes not only a highly conductive ion-conducting compound but also a polymer, such as polyethylene oxide (PEO), poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), poly(4-vinylpyridine) (P4VP), and poly(2-acrylamide-2-methylpropanesulfonic acid) (PAMPS). The highly conductive ion-conducting compound is dispersed in the polymer. The polymer not only has good flexibility and good interfacial contact with the electrode, but also its long chain polar groups can coordinate with lithium ions, helping them migrate.

[0028] In one embodiment, the thickness of the first modification layer is 0.5~2μm, which is sufficient to form a continuous ion transport channel, reduce interfacial impedance, balance ion transport efficiency and mechanical strength, reduce interfacial failure during cycling, and ensure mechanical compatibility with the second modification layer to form an interfacial bond, thereby improving the overall stability of the film.

[0029] In some embodiments, the thickness of the first modification layer can be a range of one or any two of 0.5 μm, 0.6 μm, 0.7 μm, 1 μm, 1.1 μm, 1.5 μm, and 2.0 μm.

[0030] In one embodiment, the first modification layer is formed by cross-linking and polymerization of a polymer containing a highly conductive ionic compound on the surface of a lithium metal substrate.

[0031] For example, LiTFSI / PEO solution or Li7P3S is prepared under a nitrogen atmosphere. 11The PEO solution or Li2S-P2S5 / PEO solution is completely dissolved and then an initiator is added. The solution is then coated onto the lithium metal surface using a dip-coating process and dried at 60°C. After being irradiated with ultraviolet light, PEO crosslinking is initiated. In-situ polymerization is then carried out under the action of the initiator to form the first modified layer. The initiator can be a photoinitiator such as Irgacure 2959.

[0032] Optionally, the content of the highly conductive ionic compound in the above polymer monomer solution is 5-15 wt%, and the solvent is anhydrous acetonitrile (ACN) / tetrahydrofuran (THF) (ACN to THF volume ratio 1:1, requiring complete drying). After complete dissolution at room temperature or under heating (e.g., 60-80°C), 0.1-0.5 wt% of Irgacure 2959 photoinitiator is added and stirred evenly. After dip coating (dip coating speed: 1-5 mm / s), dwell time (dwell time: 5-10 seconds), and pull-out (pull-out speed: 1-5 mm / s), it is dried at 60°C. Finally, after irradiation with ultraviolet light for 5-10 minutes to initiate PEO crosslinking, a dense film with a thickness of 0.5-2 μm is formed by in-situ polymerization under the action of the initiator as the above-mentioned first modification layer.

[0033] Optionally, in one embodiment, the dynamic interaction bonds include at least one of disulfide bonds and hydrogen bonds, which can be reconnected after damage to achieve self-repair.

[0034] In some implementations, the aforementioned dynamic interaction bonds can be determined using FTIR.

[0035] The specific method for determining disulfide bonds is as follows: The lithium metal sheet sample (including the self-healing layer) was cut into a size suitable for FTIR testing (e.g., 1 cm). 2 Use nitrogen to protect the environment from oxidation and avoid direct contact with air. Use an ATR (attenuated total internal reflection) accessory to ensure that the light path is perpendicular to the surface of the self-healing layer. Scanning range: 400~4000 cm. -1 4 cm resolution -1 Scan 32 times. Recognizes distances of 500-600 cm. -1 If the characteristic SS peak is present and a thiol group (-SH) is present, further observation is needed at 2500–2600 cm⁻¹. -1 The peaks are visible, but attention should be paid to interference from CF4 groups (CF4 peaks are typically found at 1150–1300 cm⁻¹). -1 (The strong absorption may be unrelated to the SS peak.) Comparing the FTIR spectrum without the self-healing layer, it was confirmed that the SS peak only comes from the self-healing layer.

[0036] The specific method for determining hydrogen bonds is as follows: The lithium metal sheet sample (including the self-healing layer) was cut into a size suitable for FTIR testing (e.g., 1 cm). 2 Use nitrogen to protect the environment from oxidation and avoid direct contact with air. Use an ATR (attenuated total internal reflection) accessory to ensure that the light path is perpendicular to the surface of the self-healing layer. Scanning range: 400~4000 cm. -1 4 cm resolution -1 32 scans were performed. The scan depth was between 3000 and 3600 cm. -1 This corresponds to the OH / NH stretching vibration region; additionally, heating the sample (e.g., to 80°C) allows for observation of the dynamic changes in hydrogen bonds. Without heating, hydrogen bonds result in an OH peak (approximately 3200–3600 cm⁻¹). -1 Broadening and shifting to lower frequencies (e.g., from 3400 cm⁻¹) -1 Move to 3200 cm -1 Upon heating, the hydrogen bonds break, and the peak shifts back to 3400 cm⁻¹. -1 The peaks become sharper when viewed from the left and right sides. Comparing the FTIR spectrum with that without the self-healing layer confirms that the peaks originate solely from the self-healing layer.

[0037] Optionally, in one embodiment, the functional bonds of the self-healing functional layer include at least one of disulfide bonds and hydrogen bonds, which not only achieves reversibility at room temperature or under mild conditions, but can also be directly generated by the oxidation of thiol groups or free radical polymerization, thus endowing the first modified layer with high flexibility and stretchability without complex reaction conditions.

[0038] Optionally, in one embodiment, the polymer with dynamically self-healing dynamic bonds includes at least one of polyurethane (PU), polysiloxane (PDMS), polyacrylate, polyamide, hydroxyethyl cellulose, polyethylene glycol hydroxyl, poly(ε-caprolactone)-disulfide (PCL-SS), polysiloxane-disulfide (PDMS-SS), polyvinyl alcohol-disulfide (PVA-SS), thiol-disulfide interchangeable polymers, polyurethane-urea disulfide polymers (PU-SS), and hyperbranched polydimethylsiloxane-disulfide (PDMS-SS-HB). The thiol-disulfide interchangeable polymer can be a polyethylene glycol (PEG)-based thiol-disulfide interchangeable polymer (PEG-SH).

[0039] Among them, polyurethane (PU), polysiloxane (PDMS), polyacrylate (Polyacrylate), polyamide (Polyamide, PA), polyethylene glycol hydroxyl (PEG-OH), and hydroxyethyl cellulose (HEC) can form hydrogen bond networks through hydroxyl, amide, and carboxylic acid groups, providing dynamic interaction bonds containing hydrogen bonds.

[0040] Among them, poly(ε-caprolactone)-disulfide bonds (PCL-SS), polysiloxane-disulfide bonds (PDMS-SS), disulfide crosslinked polymers (such as PVA-SS), thiol-disulfide bond interchangeable polymers (such as PCL-SH / SS), polyurethane-urea disulfide polymers (PU-SS), and hyperbranched polydimethylsiloxane-disulfide (PDMS-SS-HB) not only contain dynamic interaction bonds of disulfide bonds that can reconnect after damage and achieve self-repair, but also have good flexibility, chain segment mobility and mechanical strength introduced by disulfide bonds, which can improve stability under high temperature and mechanical stress.

[0041] Optionally, in one embodiment, the thickness of the second modification layer is 100~300 nm, which can ensure the density and distribution of dynamic interaction bonds (such as disulfide bonds) to effectively balance crack repair capability, repair efficiency and interface impedance, while effectively absorbing the stress generated by lithium dendrite growth and ensuring the bonding force with the first modification layer formulation, thereby reducing film rupture and improving the overall cycle life of the film.

[0042] Optionally, in some embodiments, the thickness of the second modification layer can be a range of one or any two of 100nm, 120nm, 150nm, 180nm, 200nm, 250nm, and 300nm.

[0043] In one embodiment, the second modification layer is formed by coating the surface of the first modification layer with a compound having the aforementioned dynamic interaction bonds and then heating and recombining it; wherein the compound having the aforementioned dynamic interaction bonds is formed by polymerizing a monomer containing dynamic interaction bonds.

[0044] For example, polycaprolactone (PCL) prepolymer (molecular weight 80,000~100,000 g / mol) is dissolved in CHCl3 to form a solution with a concentration of 5~10 wt%. Dimethyl dithiodipropionate (DMDP) is added as a disulfide bond precursor at a molar ratio of dimethyl dithiodipropionate to PCL of 1:1~1:2. The mixture is heated to 60~80℃ for 2~4 hours under nitrogen protection. The thiol groups (-SH) in DMDP undergo transesterification with the terminal hydroxyl groups of PCL to generate PCL-SS. The resulting solution is then spin-coated or dip-coated onto the surface of a lithium metal substrate with the first modified layer. Heating at 80~100℃ for 1~2 hours promotes the dynamic recombination of disulfide bonds (simulating a self-healing process), thus forming a second modified layer with uniform thickness, moderate thickness, and self-healing properties.

[0045] In this embodiment, polar groups (such as -COOH, -OH, -C=O, -NH2, -SO3H) and hydrophobic groups (such as -CF3, -CF) are introduced by surface modification of the second modification layer.2- (-C6H5) can enhance the affinity between the interface and the electrolyte, promote lithium-ion transport and reduce interfacial impedance by using polar groups, while reducing surface energy, inhibiting electrolyte penetration and reducing interfacial side reactions (such as SEI film instability) by using hydrophobic groups.

[0046] Optionally, in one embodiment, the functional groups modified on the surface of the second modified layer can be formed by plasma treatment of the second modified layer body. Plasma treatment of the second modified layer body not only allows for the modification of the surface with functional groups such as -NH2, -SO3H, -CF3, and -C6H5 to adjust surface chemical properties and balance interfacial polarity and hydrophobicity, but also increases surface roughness and interfacial contact area, enhances surface chemical activity, and promotes subsequent interfacial reactions.

[0047] Optionally, in one embodiment, the functional groups include at least one hydrophilic group and at least one hydrophobic group, which can more effectively balance interfacial polarity and hydrophobicity.

[0048] Optionally, in one embodiment, the functional groups include -SO3H and -CF3, wherein -SO3H, through its strong lithiophilicity, guides the uniform distribution of lithium ions at the interface, optimizing the deposition behavior of lithium; while -CF3, by forming a robust LiF layer, mechanically suppresses dendrites and chemically resists corrosion; the combination of the two can exert a synergistic effect, simultaneously introducing sulfoxy groups and fluorine-containing components at the interface, constructing a composite interface layer with both high ionic conductivity and mechanical strength.

[0049] Optionally, in one embodiment, the molar ratio of -SO3H and -CF3 in the second modified layer is 1:1 to 1:2, for example, it can be one or any two of 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, so that the composite interface layer constructed by the second modified layer has better ionic conductivity and mechanical strength.

[0050] Optionally, in one embodiment, the second modified layer body is subjected to O2 / CF4 plasma treatment, wherein the molar ratio of O2 to CF4 is controlled to be 1:1.5 to 1:2.5, the power is 150 to 250 W, the pressure is 10 to 30 Pa, and the treatment time is 10 to 15 minutes, so that -SO3H and -CF3 can be formed on the surface of the second modified layer, and the molar ratio of -SO3H and -CF3 can be 1:1 to 1:2.

[0051] In this process, O2 is decomposed into highly reactive oxygen atoms and oxygen radicals in high-energy plasma (such as radio frequency or microwave discharge). The highly reactive oxygen atoms can oxidize the surface of the second modified layer and introduce sulfonic acid groups through sulfonation. In addition, the highly reactive oxygen atoms can also attack the carbon chains on the surface of the second modified layer to form -SOH3 groups. CF4 molecules are decomposed into active fluorine species in the plasma, and then react with the carbon chains on the PCL-SS surface to produce -CF3 groups.

[0052] Optionally, in one embodiment, the functional groups include -SO3H and -CF3, which can balance hydrophilicity and hydrophobicity and optimize lithium-ion transport efficiency, thereby reducing local deposition overpotential of lithium ions, promoting uniform lithium deposition, and thus improving interface stability, suppressing non-uniform dendrite growth and extending cycle life.

[0053] Optionally, in one embodiment, the molar ratio of -SO3H to -CF3 in the second modification layer is 1:1 to 1:2, which can effectively balance hydrophilicity and hydrophobicity, as well as reactivity and side reaction inhibition, and promote uniform lithium deposition, thereby effectively suppressing non-uniform dendrite growth and improving interface stability.

[0054] Optionally, in one embodiment, the molar ratio of -SO3H and -CF3 in the second modification layer is one or any two of the following: 1:1, 1:1.1, 1:1.2, 1:1.5, 1:1.8, 1:2.

[0055] Alternatively, in one embodiment, the elemental composition (such as the relative content of -SO3H and -CF3) of the surface of the second modified layer can be analyzed by X-ray photoelectron spectroscopy (XPS), and then the molar ratio of -SO3H and -CF3 can be calculated by integrating the peak area.

[0056] Optionally, in one embodiment, the contact angle of the lithium metal anode is 30°~60°, that is, its hydrophilicity is moderate, taking into account both interfacial wettability and hydrophobicity, which can maintain ion transport efficiency, reduce interfacial impedance, and effectively suppress side reactions, thereby ensuring cycle stability.

[0057] Optionally, in one embodiment, the surface roughness RMS of the lithium metal anode is less than 20 nm through surface modification such as plasma treatment, resulting in excellent interfacial contact area and lithium-ion transport efficiency of the lithium metal anode.

[0058] Alternatively, in another embodiment, the molar ratio of C=O to CF on the surface of the second modified layer is (0.8~1.2):1, which can balance hydrophilicity and hydrophobicity and optimize lithium-ion transport efficiency.

[0059] Optionally, in one embodiment, in the XPS characteristic peaks on the surface of the second modified layer, the intensity of CO accounts for 10-30%, the intensity of C=O accounts for 5-15%, and the intensity of F 1s accounts for 5-20%.

[0060] Optionally, in the embodiments of this application, the Young's modulus of the first and second modification layers on the surface of the lithium metal anode is 3 GPa to 7 GPa, which can dynamically adapt to the volume expansion of lithium metal and block the lateral growth of dendrites.

[0061] Optionally, in the embodiments of this application, the exchange current density of the first and second modification layers on the surface of the lithium metal anode is 0.17~0.3 mA / cm². 2 It can optimize charge transfer efficiency, reduce interface impedance, and improve battery cycle life.

[0062] Optionally, in the embodiments of this application, the activation energies of the first and second modification layers on the lithium metal anode surface are 8 kJ / mol to 10.1 kJ / mol, which balances the reaction activity and the inhibition of side reactions, thereby improving the deposition and stripping performance and interface stability.

[0063] Optionally, in the embodiments of this application, the first modification layer and the second modification layer on the surface of the lithium metal anode are at a current density of 1 mA / cm². 2 The nucleation overpotential is 112~188mV, which can promote uniform lithium deposition and suppress non-uniform dendrite growth, thereby extending cycle life.

[0064] This application also proposes a lithium metal battery, including the aforementioned lithium metal negative electrode.

[0065] The negative electrode sheet of the secondary battery provided in this application uses the above-mentioned lithium metal negative electrode. Because a second modification layer containing a polymer with dynamic interaction bonds is provided on the surface of the first modification layer, the interface can be self-repaired by utilizing the dynamic interaction bonds that can be reversibly broken and recombined. The functional groups modified on the surface of the second modification layer can balance polarity and hydrophobicity, thereby optimizing lithium ion transport efficiency, reducing local deposition overpotential of lithium ions, adjusting the uniformity of lithium ion deposition, suppressing the formation of lithium dendrites, and improving interface stability.

[0066] The battery provided in this application embodiment also includes a positive electrode, a separator, and an electrolyte.

[0067] The aforementioned positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes a positive active material, which includes a lithium-ion transition metal oxide, selectable from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium phosphates with an olivine structure. Optionally, the aforementioned lithium-ion transition metal oxide includes at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, and lithium iron phosphate.

[0068] In some embodiments of this application, the positive electrode sheet further includes a conductive agent, which includes at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, hard carbon, carbon fiber, and carbon microspheres.

[0069] In some embodiments of this application, the positive electrode sheet further includes an adhesive, which includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0070] In some embodiments of this application, the positive electrode sheet is prepared as follows: the components used to prepare the positive electrode sheet, such as the positive electrode active material including the above-mentioned positive electrode active material, binder and conductive agent, are dispersed in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; the positive electrode slurry is coated on a positive electrode current collector such as aluminum foil; after drying, rolling, die cutting and other processes, the positive electrode sheet can be obtained.

[0071] In this embodiment, the electrolyte acts as a conductor of ions between the positive and negative electrodes. The electrolyte can be liquid, gel-like, or entirely solid. In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent, wherein the electrolyte salt is a lithium salt.

[0072] Optionally, the aforementioned lithium metal battery includes any one of liquid lithium-ion battery, quasi-solid-state lithium-ion battery, quasi-solid-state lithium metal battery, all-solid-state lithium-ion battery, and solid-state lithium metal battery.

[0073] In practical applications, lithium metal anode, separator and positive electrode are stacked in sequence to obtain cell assembly, cell assembly is packaged to obtain bare cell, bare cell is baked and then injected with liquid, formed, resealed and sorted to obtain the above-mentioned secondary battery.

[0074] This application also proposes an electrical device, which includes the aforementioned lithium metal battery, and the lithium metal battery serves as the power supply for the aforementioned electrical device.

[0075] The above-described lithium metal battery embodiments and electrical device embodiments include the aforementioned lithium metal anode and achieve the same technical effects. To avoid repetition, they will not be described again here. For relevant details, please refer to the description of the lithium metal anode embodiments.

[0076] To make the inventive objectives, technical solutions, and beneficial effects of this application clearer, the application is further described below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application.

[0077] The present application will be described in detail below through embodiments.

[0078] Test methods Example 1 (1) Preparation of positive electrode sheet By weight, 95 parts of positive electrode active material LiFePO4, 3 parts of conductive agent acetylene black, and 2 parts of binder PVDF are dry-mixed to obtain a dry mixture. Then, solvent NMP is added to the dry mixture, and after grinding evenly, it is coated, vacuum baked, and punched to obtain a positive electrode sheet with a diameter of 12mm.

[0079] (2) Preparation of lithium metal anode a. Add 5 wt% LiTFSI and PEO to anhydrous ACN / THF (1:1 ratio, requires complete drying) solvent, heat to 60℃ until completely dissolved, then add 0.2 wt% Irgacure 2959 photoinitiator and stir until homogeneous. Dip-coat the lithium sheet (dip-coating speed: 3 mm / s), hold (hold time: 8 seconds), pull-out (pulling speed: 2 mm / s), and dry at 60℃. Finally, irradiate with UV light for 8 minutes to initiate PEO crosslinking, and in-situ polymerize a dense film with a thickness of 1 μm as the first modification layer under the action of the initiator.

[0080] b. Polycaprolactone (PCL) prepolymer (molecular weight 80,000~100,000 g / mol) was dissolved in CHCl3 to form a 5wt% solution. Dimethyl dithiodipropionate (DMDP) was added as a dynamic interaction bond precursor at a molar ratio of 1:1 to PCL. The reaction was carried out under nitrogen protection at 60°C for 2 hours. The thiol groups (-SH) in DMDP were used to undergo transesterification with the terminal hydroxyl groups of PCL. The resulting solution was then spin-coated onto the surface of the first modified layer and heated at 100°C for 1 hour to promote the dynamic recombination of the dynamic interaction bonds and form a second modified layer with a thickness of 200 nm. c. The second modified layer body is subjected to O2 / CF4 plasma treatment to introduce functional groups -SO3H and -CF3. The molar ratio of O2 to CF4 is controlled to be 1:1, the power is 160W, the pressure is 20Pa, and the treatment time is 12 minutes. After cutting and punching, a lithium metal anode with a diameter of 12mm is obtained.

[0081] (3) Preparation of electrolyte Ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC): propylene carbonate (PC) were mixed in a volume ratio of 1:2:1:1. The lithium salts were lithium bis(trifluoromethyl)imide (LiTFSI, 5 wt%) and lithium bis(fluoroimide) (LiFSI, 3 wt%). Then, 0.8 wt% ethanol sulfur, 0.3 wt% Al2O3 (particle size 20~30 nm) and 0.3 wt% fluoroethylene carbonate (FEC) were added and mixed evenly to prepare the electrolyte.

[0082] (4) Preparation of lithium metal batteries Commercially available nickel-cobalt-manganese ternary materials (nickel:cobalt:manganese ratio of 8:1:1) were used as the positive electrode material. The positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 7:2:1. After grinding and mixing evenly, an electrode slurry was prepared, coated on aluminum foil, and vacuum dried at 80°C for 24 hours. The slurry was then punched into small circular pieces with a diameter of 12 mm to serve as the positive electrode. A lithium metal negative electrode was then used as the counter electrode to assemble a coin cell.

[0083] Examples 2-3 The only difference from Example 1 is that LiTFSI is adjusted to Li7P3S. 11 Li2S-P2S5.

[0084] Examples 4-5 The only difference from Example 1 is that the polycaprolactone was changed to polysiloxane and polyurethane, respectively.

[0085] Example 6 The difference from Example 1 is that low molecular weight polycaprolactone diol (PCL-OH) (e.g., 10000~30000 g / mol) was dissolved in a mixed solvent (ethanol: acetone = 8:2), and then the PCL-OH solution was spin-coated onto the surface of the first modified layer (PEO / LiTFSI). Then, it was heated at 50°C for 1 hour to promote the dynamic recombination of the hydrogen bond network and obtain a hydrogen bond layer. The temperature was controlled at 25°C during O2 / CF4 plasma treatment.

[0086] Examples 7-8 The only difference from Example 1 is that the gas flow ratios O2:CF4 = 2:1 and O2:CF4 = 1:2 are adjusted respectively, so that the molar ratios of -SO3H and -CF3 are 1:1 and 1:2 respectively.

[0087] Example 9 The only difference from Example 1 is that the processing gases are adjusted to NH3 (ammonia) and C6H6 (benzene), and the gas molar ratio NH3:C6H6 is controlled to be 4:3, so that the introduced polar group is -NH2 and the hydrophobic group is -C6H5.

[0088] Examples 10-11 The only difference from Example 1 is that the thickness of the first modified layer is 0.5 μm and 2 μm respectively, achieved by increasing the lifting speed (5 mm / s) and decreasing the lifting speed (1.5 mm / s); Examples 12-13 The only difference from Example 1 is that the concentration of the PCL solution was reduced (2.5 wt%), the spin coating speed was increased (2000 rpm), and the spin coating time was shortened (30 s) to obtain a second modified layer with a thickness of 100 nm; then, the concentration of the PCL / DMDP solution was increased (7.5 wt%), the spin coating speed was decreased (500 rpm), and the spin coating time was extended (2 min) to obtain a second modified layer with a thickness of 300 nm.

[0089] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that, in the preparation process of the lithium metal anode, the lithium sheet is directly punched into a lithium metal sheet with dendrites of 12 mm as the lithium metal anode.

[0090] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in the preparation process (c) of the lithium metal anode, the lithium metal anode sheet with the second modification layer body formed is directly punched to form a lithium metal sheet with dendrites of 12 mm as the lithium metal anode.

[0091] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that step (b) is omitted, and in the preparation process (c) of the lithium metal anode, the lithium metal anode sheet with the first modification layer formed is directly punched into a lithium metal sheet with dendrites of 12 mm as the lithium metal anode.

[0092] The process parameters for each embodiment and comparative example are shown in Table 1.

[0093] Table 1

[0094] Test example: (1) In a glove box with a water oxygen content of less than 0.1 ppm, the lithium metal anodes prepared in the above embodiments and comparative examples were used as counter electrodes, and coin cells were assembled with glass fiber separators and electrolytes. Surface activation energy, exchange current density, nucleation overpotential, contact angle, and cycle performance were tested. The test data are shown in Table 2. The test methods are as follows: 1.1 Activation Energy Test Method: The assembled symmetrical cell was placed at 25℃, 30℃, 35℃, 40℃, and 45℃ to measure the electrochemical impedance spectroscopy (EIS). The high-frequency impedance (Z) was extracted using EIS to calculate the ionic conductivity σ (σ = A / Zd). A plot of ln(σ) against 1 / T yielded the activation energy (Ea) = -R·slope. Where d is the electrolyte thickness, A is the electrode area, and R is the gas constant 8.314.

[0095] 1.2 Exchange current density test method: Test the Tafel curve of the symmetrical cell at a scan rate of 1 mV / s and a voltage range of -0.2~0.2V to determine the linear part (Tafel region) of the anode and cathode regions. Determine the exchange current density by extrapolation. Extrapolate the Tafel linear part to the overpotential of 0. The current density corresponding to this point is the exchange current density.

[0096] 1.3 Nucleation overpotential test: at 1 mA / cm 2 At a current density, the assembled symmetrical battery is stripped, and the nucleation overpotential is determined by the starting point of the voltage change in the charge-discharge curve (i.e. the critical point at which lithium metal begins to nucleate).

[0097] 1.4 Contact Angle Test: Under a protective atmosphere, the modified lithium metal electrode is placed on the test stage, and the final static contact angle is measured by a contact angle measuring instrument. The liquid used for the contact angle test is pure water.

[0098] (2) Cyclic stability test, the test method is as follows: a. The modified lithium metal electrodes prepared in the examples and comparative examples were assembled into symmetrical batteries and then tested. That is, two identical modified lithium metal electrodes served as the positive and negative electrodes of the battery, with one side having an interface layer close to the separator and the other side having metallic lithium to ensure electron conduction.

[0099] b. Test on a Newway battery tester, with a test current density of 1 mA / cm². 2 The deposition stripping capacity is 1 mAh / cm³. 2 Symmetrical battery cycle tests are performed, and the cycle life of the electrode plates is evaluated by the cycle time. When the cycle voltage deviates significantly from the normal voltage, it is determined to be a cycle failure. (3) Ratio performance test, the test method is as follows: The full cells prepared in each embodiment and comparative example were subjected to rate performance testing on a Xinwei battery tester. The test voltage range was 2.8~4.25V. After the battery was fully charged at 0.5C, the corresponding discharge capacity was obtained by testing at 1C and 6C respectively. Rate performance = 6C discharge capacity / 1C discharge capacity × 100%.

[0100] Table 2

[0101] The experimental results of Examples 1-13 and Comparative Examples 1-3 show that the embodiments of this application ensure high lithium-ion flux performance by setting a first modification layer with a highly conductive ion compound on the surface of the lithium metal substrate. Simultaneously, a second modification layer containing a polymer with dynamic interaction bonds is set on the surface of the first modification layer, enabling interface self-repair through reversible breakage and recombination of the dynamic interaction bonds via heating or mechanical stress. Furthermore, the functional groups on the surface of the second modification layer balance polarity and hydrophobicity, thereby optimizing lithium-ion transport efficiency, reducing local overpotential of lithium-ion deposition, regulating the uniformity of lithium-ion deposition, suppressing the formation of lithium dendrites, and improving interface stability. Therefore, the embodiments of this application improve upon the problem of significant lithium dendrite growth risk in existing lithium metal anodes, which easily leads to interface failure and capacity decay.

[0102] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present application.

[0103] The foregoing has provided a detailed description of a lithium metal anode, a lithium metal battery, and an electrical device provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A lithium metal anode, characterized in that, include: Lithium metal matrix; The first modification layer is disposed on at least one surface of the lithium metal substrate and contains a highly ion-conducting compound. The second modification layer is disposed on the surface of the first modification layer away from the lithium metal matrix and contains a polymer with dynamic bonds. The surface of the second modified layer is modified with functional groups, including at least one of -NH2, -SO3H, -CF3, and -C6H5.

2. The lithium metal anode according to claim 1, characterized in that, The dynamic interaction bond includes at least one of disulfide bond and hydrogen bond.

3. The lithium metal anode according to claim 1, characterized in that, The polymers with dynamic interaction bonds include at least one of polyurethane, polysiloxane, polyacrylate, polyamide, hydroxyethyl cellulose, polyethylene glycol hydroxyl, polycaprolactone diol, poly(ε-caprolactone)-disulfide, polysiloxane-disulfide, polyvinyl alcohol-disulfide, thiol-disulfide interchangeable polymers, polyurethane-urea disulfide polymers, and hyperbranched polydimethylsiloxane-disulfide.

4. The lithium metal anode according to claim 1, characterized in that, The highly conductive ionic compounds include lithium bis(trifluoromethanesulfonylimide) (LiTFSI) and lithium phosphorus sulfide LPS (Li7P3S). 11 At least one of lithium sulfide-phosphorus pentasulfide (Li2S-P2S5).

5. The lithium metal anode according to claim 1, characterized in that, The functional groups include -SO3H and -CF3.

6. The lithium metal anode according to claim 5, characterized in that, In the second modified layer, the molar ratio of -SO3H to -CF3 is 1:1 to 1:

2.

7. The lithium metal anode according to claim 1, characterized in that, The thickness of the first modification layer is 0.5~2μm; and / or The thickness of the second modification layer is 100~300 nm.

8. The lithium metal anode according to claim 1, characterized in that, The contact angle of the lithium metal anode is 30°~60°.

9. A lithium metal battery, characterized in that, Including the lithium metal anode as described in any one of claims 1 to 8.

10. An electrical appliance, characterized in that, The device includes the lithium metal battery of claim 9, wherein the secondary battery serves as the power supply for the electrical equipment.

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