A self-healing interface film for negative electrodes, its preparation method and application

Abstract

This invention relates to the field of lithium-ion battery anode material technology, specifically to a self-healing interface film for anodes, its preparation method, and its application. The self-healing interface film comprises a cross-linked polymer containing dynamic disulfide bonds and a fluorosulfonyl imide salt ionic liquid dispersed within the cross-linked polymer. This invention provides the framework structure through the cross-linked polymer containing dynamic disulfide bonds, while simultaneously dispersing the fluorosulfonyl imide salt ionic liquid therein. When the SEI film is damaged, the anions in the fluorosulfonyl imide salt ionic liquid can be released and react to generate inorganic components for chemical repair. When this self-healing interface film is applied to the anode of a lithium-ion battery, it can effectively improve the self-healing capability and interface stability of the SEI film during cycling.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a self-healing interface film for anodes, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, with their high energy density and long cycle life, have been widely used in power batteries, energy storage devices, and other fields. However, the stability of the SEI film (solid electrolyte interphase) at the negative electrode interface remains a core bottleneck restricting battery life. During charge-discharge cycles, the negative electrode undergoes volume expansion and contraction, leading to repeated rupture and disordered regeneration of the SEI film. This process continuously consumes electrolyte and active lithium, and induces lithium dendrite growth, resulting in a surge in interfacial impedance and a decrease in coulombic efficiency.

[0003] To address the aforementioned issues, existing technologies primarily focus on enhancing the mechanical strength of the SEI film or optimizing its composition. For example, this involves adding electrolyte additives such as FEC (fluoroethylene carbonate) and VC (ethylene carbonate) to generate a LiF-rich SEI film, or artificially constructing a ceramic / polymer composite protective layer. However, these additives are gradually consumed during cycling, making it difficult to maintain SEI film stability in the later stages. Furthermore, the resulting film is brittle and prone to rigid fracture under conditions of large volume expansion, such as with silicon-based anodes. Artificially constructed protective layers are mostly static structures, making it difficult to adapt to the volumetric expansion and contraction of the anode. After long cycling, the protective layer itself is easily damaged, and there is a lack of active repair mechanisms to address the dynamic damage to the SEI film. Therefore, how to achieve in-situ repair of the SEI film after damage and maintain interfacial stability is a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0004] This invention provides a self-healing interface film for negative electrodes, its preparation method, and its application, in order to solve the problem that existing SEI films are difficult to maintain interface stability due to repeated damage during long-term cycling.

[0005] In a first aspect, the present invention provides a self-healing interface membrane for a negative electrode, comprising a cross-linked polymer containing dynamic disulfide bonds and a fluorosulfonyl imide salt ionic liquid dispersed in the cross-linked polymer containing dynamic disulfide bonds. When the SEI membrane is damaged due to negative electrode volume expansion or dendrite puncture, the dynamic disulfide bonds can achieve mechanical repair of the membrane structure through a sulfur-sulfide bond exchange reaction. Simultaneously, the lithium metal exposed at the damaged site triggers FSI in the ionic liquid. - Anions generate dense inorganic components such as LiF and Li3N in situ, which fill cracks and strengthen the repair area. The two repair mechanisms work together to maintain the long-term stability of the SEI film.

[0006] In one optional embodiment, the crosslinked polymer containing dynamic disulfide bonds includes a polyimide (PI-SS) and / or a polyurethane (PU-SS) containing dynamic disulfide bonds. The polyimide and polyurethane containing dynamic disulfide bonds can be prepared by conventional polymerization methods in the art. For example, a diamine monomer containing disulfide bonds can be polycondensed with a dianhydride monomer in a solvent, and the resulting product can be subjected to an imidization reaction to obtain a polyimide containing dynamic disulfide bonds; a diol monomer containing disulfide bonds can be polycondensed with a diisocyanate monomer to obtain a polyurethane containing dynamic disulfide bonds. Those skilled in the art will understand that the above preparation methods are merely illustrative and not intended to limit the invention. Other methods for obtaining polyimides or polyurethanes containing dynamic disulfide bonds are equally applicable and will not be elaborated further here.

[0007] In one alternative embodiment, the fluorosulfonyl imide salt ionic liquid comprises 1-vinyl-3-methylimidazolium difluorosulfonyl imide salt (VMI-FSI) and / or 1-ethyl-3-methylimidazolium difluorosulfonyl imide salt (EMIM-FSI).

[0008] In one optional embodiment, the mass ratio of the crosslinked polymer containing dynamic disulfide bonds to the fluorosulfonyl imide salt ionic liquid is (2~4):(4~6). For example, it can be 2:4, 2:5, 2:6, 3:4, 3:5, 3:6, 4:4, 4:5, or 4:6, as well as specific point values ​​between the above ratios. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific point values ​​included in the range.

[0009] Secondly, the present invention also provides a method for preparing a negative electrode self-healing interface film as described in the first aspect, comprising the following steps: A precursor dispersion was obtained by mixing a polymer containing dynamic disulfide bonds, polyethylene oxide, and a fluorosulfonyl imide salt ionic liquid in a solvent. The precursor dispersion is coated onto the surface of the negative electrode; In an inert atmosphere, ultraviolet light irradiation was used to perform in-situ crosslinking polymerization on the coated negative electrode surface, resulting in a self-healing interface film on the negative electrode surface.

[0010] In this method, polyethylene oxide undergoes cross-linking polymerization with alkenyl groups in an ionic liquid to form a three-dimensional network, fixing the polymer containing dynamic disulfide bonds as the backbone, while simultaneously incorporating FSI. - Anions are bound in a free state within the network, allowing for controlled release upon damage.

[0011] In one alternative embodiment, the polymer containing dynamic disulfide bonds comprises a polyimide containing dynamic disulfide bonds and / or a polyurethane containing dynamic disulfide bonds; the fluorosulfonyl imide salt ionic liquid comprises 1-vinyl-3-methylimidazolium difluorosulfonyl imide salt and / or 1-ethyl-3-methylimidazolium difluorosulfonyl imide salt; and the solvent comprises N-methylpyrrolidone.

[0012] In one optional embodiment, the mass ratio of the polymer containing dynamic disulfide bonds, polyethylene oxide, and fluorosulfonyl imide salt ionic liquid is (2~4):(1~3):(4~6). For example, the ratios can be 2:1:4, 2:1:5, 2:1:6, 2:2:4, 2:2:5, 2:2:6, 2:3:4, 2:3:5, 2:3:6, 3:1:4, 3:1:5, 3:1:6, 3:2:4, 3:2:5, 3:2:6, 3:3:4, 3:3:5, 3:3:6, 4:1:4, 4:1:5, 4:1:6, 4:2:4, 4:2:5, 4:2:6, 4:3:4, 4:3:5, or 4:3:6, as well as specific point values ​​between the above ratios. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0013] In one optional embodiment, the total mass ratio of the polymer containing dynamic disulfide bonds, polyethylene oxide, and fluorosulfonyl imide salt ionic liquid to the solvent is 1:(5~20). For example, it can be 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, or 1:20, as well as specific point values ​​between the above ratios. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific point values ​​included in the range.

[0014] In one optional embodiment, the mixing is carried out at 30°C to 90°C for 1 to 3 hours. For example, the temperature can be 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, or 90°C, and the time can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours, as well as specific point values ​​within each of the above temperature and time ranges. Due to space limitations and for the sake of brevity, this invention will not exhaustively list the specific point values ​​included in the ranges.

[0015] In one optional embodiment, the ultraviolet light has a wavelength of 300nm~400nm and a power of 30mW / cm². 2 ~100mW / cm 2 The irradiation time is 10-20 minutes; for example, the wavelength can be 300nm, 320nm, 340nm, 365nm, 380nm, or 400nm, and the power can be 30mW / cm².2 40mW / cm 2 50mW / cm 2 60mW / cm 2 70mW / cm 2 80mW / cm 2 90mW / cm 2 Or 100mW / cm 2 The time can be 10 min, 12 min, 15 min, 18 min, or 20 min, as well as specific point values ​​within each of the above wavelength, power, and time ranges. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the ranges. Preferably, the wavelength of the ultraviolet light is 365 nm, and the power is 50 mW / cm². 2 The irradiation time is 10-20 minutes.

[0016] In one optional embodiment, before coating the precursor dispersion onto the negative electrode surface, the negative electrode surface is further subjected to plasma cleaning. Preferably, the plasma cleaning power is 80W~120W, and the processing time is 3min~5min. For example, the power can be 80W, 90W, 100W, 110W, or 120W, and the time can be 3min, 4min, or 5min, as well as specific values ​​within the aforementioned power and time ranges. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific values ​​included in the ranges.

[0017] In one optional embodiment, the coating thickness is 5μm to 15μm. For example, it can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, or 15μm, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0018] In one alternative embodiment, the inert atmosphere includes, but is not limited to, nitrogen and / or argon.

[0019] Thirdly, the present invention also provides a negative electrode, wherein the surface of the negative electrode is coated with the negative electrode self-healing interface film described in the first aspect, or a negative electrode self-healing interface film prepared by the method for preparing the negative electrode self-healing interface film described in the second aspect.

[0020] In one alternative embodiment, the negative electrode is a graphite negative electrode, a silicon-carbon composite negative electrode, or a lithium metal negative electrode.

[0021] Fourthly, the present invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is the negative electrode described in the third aspect.

[0022] In one alternative implementation, the cathode is a LiCoO2 cathode, a LiFePO4 cathode, or an NCM ternary cathode.

[0023] In one optional embodiment, the electrolyte uses ethylene carbonate (EC) and dimethyl carbonate (DMC) as solvents, LiPF6 as lithium salt, and fluoroethylene carbonate (FEC) and lithium bis(oxalato)borate (LiBOB) as additives.

[0024] In one optional embodiment, the volume ratio of ethylene carbonate to dimethyl carbonate is 1:2; the concentration of LiPF6 is 1.0 mol / L to 1.2 mol / L, for example, 1.0 mol / L, 1.05 mol / L, 1.1 mol / L, 1.15 mol / L, or 1.2 mol / L, as well as specific values ​​between the above values. For space limitations and for the sake of brevity, this invention will not exhaustively list all the specific values ​​included in the range; the amount of fluoroethylene carbonate added is 2 wt% to 5 wt%, for example, 2 wt% or 2 wt%. The specific values ​​within the range of 5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, or 5wt%, and for the sake of brevity, are not exhaustively listed here. The amount of lithium bis(oxalate-borate) added is 0.5wt% to 1wt%, for example, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, or 1wt%, and for the sake of brevity, are not exhaustively listed here.

[0025] The technical solution of this invention has the following advantages: 1. The self-healing interface membrane for the negative electrode provided by this invention uses a cross-linked polymer containing dynamic disulfide bonds as a framework, and disperses a fluorosulfonyl imide salt ionic liquid within this framework. When the SEI membrane is damaged due to negative electrode volume expansion or dendrite puncture, the dynamic disulfide bonds can be rapidly reconstructed through a sulfur-sulfur bond exchange reaction at room temperature, achieving mechanical repair of the membrane structure and inhibiting crack propagation; simultaneously, the lithium metal exposed at the damaged site triggers the release of FSI from the fluorosulfonyl imide salt ionic liquid. - Anions generate dense inorganic components such as LiF and Li3N in situ, filling cracks and enhancing the interfacial stability of the repaired area. The two repair mechanisms work synergistically to maintain the structural integrity and interfacial stability of the SEI film during long-term cycling, thereby effectively inhibiting the consumption of active lithium and electrolyte decomposition, reducing interfacial impedance growth, and suppressing lithium dendrite formation.

[0026] 2. The preparation method of the present invention involves directly coating the precursor dispersion onto the negative electrode surface and performing in-situ photopolymerization. The process is simple, requires no modification to existing battery production lines, and can be widely adapted to various negative electrode systems such as graphite, silicon-carbon composite, or lithium metal, thus possessing good prospects for large-scale application.

[0027] 6. The lithium-ion battery using the negative electrode self-healing interface film described in this invention, combined with an optimized electrolyte system (using ethylene carbonate and dimethyl carbonate as solvents, LiPF6 as lithium salt, and fluoroethylene carbonate and lithium bis(oxalato)borate as additives), can form a composite structure of a self-healing functional layer and an inorganic SEI layer in situ during the first charge, further improving the repair efficiency and interface stability, and maintaining a high capacity retention rate under long-cycle and high and low temperature conditions. Detailed Implementation

[0028] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0029] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0030] Example 1 (1) Preparation of self-healing functional layer precursor: Polyimide (PI-SS) containing dynamic disulfide bonds, polyethylene oxide (PEO) and 1-vinyl-3-methylimidazolium bisfluorosulfonylimide salt (VMI-FSI) were mixed in a mass ratio of 3:2:5. N-methylpyrrolidone (NMP) solvent was added. The total mass ratio of polyimide containing dynamic disulfide bonds, polyethylene oxide and 1-vinyl-3-methylimidazolium bisfluorosulfonylimide salt to N-methylpyrrolidone was 1:10. The mixture was stirred at 60°C for 2 hours until a uniform dispersion was formed to obtain the precursor dispersion.

[0031] (2) Pretreatment of negative electrode surface: The graphite negative electrode is subjected to plasma cleaning with a power of 100W and a treatment time of 4 minutes.

[0032] (3) In-situ photopolymerization to construct a self-healing functional layer: The precursor dispersion prepared in step (1) is uniformly coated on the pretreated graphite anode surface in step (2) with a coating thickness of 10 μm. The anode is then irradiated with ultraviolet light under a nitrogen atmosphere with a wavelength of 365 nm and a power of 50 mW / cm². 2The irradiation time was 15 minutes to carry out in-situ crosslinking polymerization, and a self-healing interface film of the negative electrode was obtained on the surface of the graphite negative electrode.

[0033] Example 2 (1) Preparation of self-healing functional layer precursor: Polyurethane (PU-SS) containing dynamic disulfide bonds, polyethylene oxide (PEO) and 1-ethyl-3-methylimidazolium difluorosulfonyl imide salt (EMIM-FSI) were mixed in a mass ratio of 3:2:5. N-methylpyrrolidone (NMP) solvent was added. The total mass ratio of polyurethane containing dynamic disulfide bonds, polyethylene oxide and 1-ethyl-3-methylimidazolium difluorosulfonyl imide salt to N-methylpyrrolidone was 1:15. The mixture was stirred at 60°C for 2 hours until a uniform dispersion was formed to obtain the precursor dispersion.

[0034] (2) Pretreatment of negative electrode surface: The graphite negative electrode is subjected to plasma cleaning with a power of 100W and a treatment time of 4 minutes.

[0035] (3) In-situ photopolymerization to construct a self-healing functional layer: The precursor dispersion prepared in step (1) is uniformly coated on the pretreated graphite anode surface in step (2) with a coating thickness of 10 μm. The anode is then irradiated with ultraviolet light under a nitrogen atmosphere with a wavelength of 365 nm and a power of 50 mW / cm². 2 The irradiation time was 12 minutes to carry out in-situ crosslinking polymerization, and a self-healing interface film of the negative electrode was obtained on the surface of the graphite negative electrode.

[0036] Example 3 (1) Preparation of self-healing functional layer precursor: Polyimide (PI-SS) containing dynamic disulfide bonds, polyethylene oxide (PEO) and 1-ethyl-3-methylimidazolium bisfluorosulfonylimide salt (EMIM-FSI) were mixed in a mass ratio of 4:1:5. N-methylpyrrolidone (NMP) solvent was added. The total mass ratio of polyimide containing dynamic disulfide bonds, polyethylene oxide and 1-ethyl-3-methylimidazolium bisfluorosulfonylimide salt to N-methylpyrrolidone was 1:5. The mixture was stirred at 90°C for 1 hour until a uniform dispersion was formed to obtain the precursor dispersion.

[0037] (2) Pretreatment of negative electrode surface: The graphite negative electrode is subjected to plasma cleaning with a power of 100W and a treatment time of 4 minutes.

[0038] (3) In-situ photopolymerization to construct a self-healing functional layer: The precursor dispersion prepared in step (1) is uniformly coated on the pretreated graphite anode surface in step (2) with a coating thickness of 15 μm. The anode is then irradiated with ultraviolet light under an argon atmosphere with a wavelength of 365 nm and a power of 50 mW / cm². 2 The irradiation time was 20 minutes to carry out in-situ crosslinking polymerization, and a self-healing interface film of the negative electrode was obtained on the surface of the graphite negative electrode.

[0039] Example 4 (1) Preparation of self-healing functional layer precursor: Polyurethane (PU-SS) containing dynamic disulfide bonds, polyethylene oxide (PEO) and 1-vinyl-3-methylimidazolium difluorosulfonylimide salt (VMI-FSI) were mixed in a mass ratio of 2:3:5. N-methylpyrrolidone (NMP) solvent was added. The total mass ratio of polyurethane containing dynamic disulfide bonds, polyethylene oxide and 1-vinyl-3-methylimidazolium difluorosulfonylimide salt to N-methylpyrrolidone was 1:20. The mixture was stirred at 30°C for 3 hours until a uniform dispersion was formed to obtain the precursor dispersion.

[0040] (2) Pretreatment of negative electrode surface: The graphite negative electrode is subjected to plasma cleaning with a power of 100W and a treatment time of 4 minutes.

[0041] (3) In-situ photopolymerization to construct a self-healing functional layer: The precursor dispersion prepared in step (1) is uniformly coated on the pretreated graphite anode surface in step (2) with a coating thickness of 5 μm. The anode is then irradiated with ultraviolet light under a nitrogen atmosphere with a wavelength of 380 nm and a power of 80 mW / cm². 2 The irradiation time was 10 minutes to carry out in-situ crosslinking polymerization, and a self-healing interface film of the negative electrode was obtained on the surface of the graphite negative electrode.

[0042] Example 5 (1) Preparation of self-healing functional layer precursor: Polyimide (PI-SS) containing dynamic disulfide bonds, polyethylene oxide (PEO) and 1-vinyl-3-methylimidazolium bisfluorosulfonylimide salt (VMI-FSI) were mixed in a mass ratio of 2:2:4. N-methylpyrrolidone (NMP) solvent was added. The total mass ratio of polyimide containing dynamic disulfide bonds, polyethylene oxide and 1-vinyl-3-methylimidazolium bisfluorosulfonylimide salt to N-methylpyrrolidone was 1:8. The mixture was stirred at 50°C for 2.5 hours until a uniform dispersion was formed to obtain the precursor dispersion.

[0043] (2) Pretreatment of negative electrode surface: The graphite negative electrode is subjected to plasma cleaning with a power of 100W and a treatment time of 4 minutes.

[0044] (3) In-situ photopolymerization to construct a self-healing functional layer: The precursor dispersion prepared in step (1) is uniformly coated on the pretreated graphite anode surface in step (2) with a coating thickness of 12 μm. The anode is then irradiated with ultraviolet light under a nitrogen atmosphere with a wavelength of 365 nm and a power of 60 mW / cm². 2 The irradiation time was 15 minutes to carry out in-situ crosslinking polymerization, and a self-healing interface film of the negative electrode was obtained on the surface of the graphite negative electrode.

[0045] Example 6 (1) Preparation of self-healing functional layer precursor: Polyurethane (PU-SS) containing dynamic disulfide bonds, polyethylene oxide (PEO) and 1-ethyl-3-methylimidazolium difluorosulfonyl imide salt (EMIM-FSI) were mixed in a mass ratio of 4:1:6, and N-methylpyrrolidone (NMP) solvent was added. The total mass ratio of polyurethane containing dynamic disulfide bonds, polyethylene oxide and 1-ethyl-3-methylimidazolium difluorosulfonyl imide salt to N-methylpyrrolidone was 1:12. The mixture was stirred at 70°C for 1.5 hours until a uniform dispersion was formed to obtain the precursor dispersion.

[0046] (2) Pretreatment of negative electrode surface: The graphite negative electrode is subjected to plasma cleaning with a power of 100W and a treatment time of 4 minutes.

[0047] (3) In-situ photopolymerization to construct a self-healing functional layer: The precursor dispersion prepared in step (1) is uniformly coated on the pretreated graphite anode surface in step (2) with a coating thickness of 10 μm. The anode is then irradiated with ultraviolet light under a nitrogen atmosphere with a wavelength of 350 nm and a power of 70 mW / cm². 2 The irradiation time was 18 minutes to carry out in-situ crosslinking polymerization, and a self-healing interface film of the negative electrode was obtained on the surface of the graphite negative electrode.

[0048] Comparative Example 1 This comparative example provides a method for preparing a self-healing interface film for a negative electrode. The only difference between this method and Example 1 is that steps (1) and (3) are omitted. In other words, a bare graphite negative electrode without a precursor dispersion is used to directly assemble the battery. Other conditions are the same as in Example 1.

[0049] Comparative Example 2 This comparative example provides a method for preparing a negative electrode self-healing interface film. The only difference between this method and Example 1 is that polyimide (PI-SS) containing dynamic disulfide bonds is not added in step (1), and the other conditions are the same as in Example 1.

[0050] Comparative Example 3 This comparative example provides a method for preparing a negative electrode self-healing interface film. The only difference between this method and Example 1 is that 1-vinyl-3-methylimidazolium difluorosulfonylimide salt (VMI-FSI) is not added in step (1), and the other conditions are the same as in Example 1.

[0051] Comparative Example 4 This comparative example provides a method for preparing a negative electrode self-healing interface film. The only difference between this method and Example 1 is that in step (1), the polyimide (PI-SS) containing dynamic disulfide bonds is replaced with polyethylene glycol (i.e., polyethylene glycol borate) containing borate bonds. Other conditions are the same as in Example 1.

[0052] Comparative Example 5 This comparative example provides a method for preparing a self-healing interface film for a negative electrode. The only difference between this method and Example 1 is that in step (1), 1-vinyl-3-methylimidazolium difluorosulfonylimide salt (VMI-FSI) is replaced with an equimolar amount of lithium difluorosulfonylimide (LiFSI), while other conditions are the same as in Example 1.

[0053] Test Example 1 (a) Battery assembly Positive electrode: NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O2) is used as the positive electrode active material, mixed with conductive carbon black (SP) and polyvinylidene fluoride (PVDF) at a mass ratio of 97.5:1:1.5. N-methylpyrrolidone (NMP) is added as a solvent, and the solid content of the slurry is adjusted to 65wt%. After stirring until uniformly dispersed, it is coated onto the surface of a 12μm thick aluminum foil, dried, and rolled to a compaction density of 3.5g / cm³. 3 The positive electrode sheet is cut into 44mm×60mm pieces.

[0054] Negative electrode sheet: Graphite negative electrode sheets with a self-healing interface film attached to the surface, prepared in Examples 1-6 and Comparative Examples 1-5 (Comparative Example 1 is a bare graphite negative electrode sheet without the film attached). The preparation method of the graphite negative electrode sheet is as follows: Artificial graphite is used as the negative electrode active material, mixed with conductive carbon black (SP), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) at a mass ratio of 96:1:0.5:2.5. Deionized water is added as a solvent, and the solid content of the slurry is adjusted to 48wt%. After stirring until uniformly dispersed, it is coated onto the surface of an 8μm thick copper foil, dried, and rolled to a compaction density of 1.6 g / cm³. 3 The negative electrode sheet is cut into 44mm×62mm pieces.

[0055] Separator: 20μm thick polypropylene (PP) separator, cut to 48mm×66mm.

[0056] Electrolyte: Using ethylene carbonate (EC) and dimethyl carbonate (DMC) as solvents (volume ratio 1:2), add 1.0 mol / L LiPF6 lithium salt, and then add 3 wt% fluoroethylene carbonate (FEC) and 0.8 wt% lithium bis(oxalato)borate (LiBOB) as synergistic additives. After stirring evenly, remove water and oxygen to obtain the electrolyte.

[0057] Battery Assembly: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to form a cell. The cell is then placed in an aluminum-plastic film casing, and electrolyte is injected at a rate of 3.0 g / Ah. After sealing, it is left to stand at 45°C for 24 hours. Formation is then performed: the battery is charged at a constant current of 0.05C to 3.0V, then at a constant current of 0.1C to 3.5V, and finally at a constant current of 0.2C to 4.2V, followed by constant voltage charging until the current decays to 0.05C. After formation, the battery is aged at 60°C for 24 hours, and finally, capacity testing is performed (discharging at a constant current of 0.2C to 2.5V to measure the actual capacity) to obtain the lithium-ion battery.

[0058] (II) Performance Testing Methods (1) First-week coulombic efficiency test: Under 25℃ conditions, the assembled battery was charged at a constant current rate of 0.1C to 4.2V, then switched to constant voltage charging until the current decayed to 0.05C. After standing for 10 minutes, it was discharged at a constant current rate of 0.1C to 2.5V. The first charge capacity and the first discharge capacity were recorded, and the first-week coulombic efficiency was calculated using the following formula: First-week coulomb efficiency (%) = (first discharge capacity / first charge capacity) × 100%.

[0059] (2) Cycle capacity retention test: At 25°C, the assembled battery was charged at a constant current rate of 1C to 4.2V, then switched to constant voltage charging until the current decayed to 0.05C. After resting for 10 minutes, it was discharged at a constant current rate of 1C to 2.5V and rested for 10 minutes. This charging and discharging process was repeated 500 times. The first discharge capacity and the 500th discharge capacity were recorded. The 500-cycle capacity retention rate was calculated using the following formula: Capacity retention rate after 500 cycles (%) = (500th discharge capacity / 1st discharge capacity) × 100%.

[0060] (3) Interface impedance test: Electrochemical impedance spectroscopy (EIS) was used to test the interface impedance at 50% charge of the battery. The test frequency range was 0.01Hz to 100kHz and the AC amplitude was 10mV. After obtaining the Nyquist plot, the interface impedance value was obtained by fitting the equivalent circuit. The interface impedance values ​​before cycling (after formation and before capacity testing) and after 500 cycles were recorded respectively.

[0061] (III) Test Results The test results are shown in Table 1 below.

[0062] Table 1. Battery performance test results of Examples 1-6 and Comparative Examples 1-5

[0063] Based on the above test results, Example 1 exhibits the highest coulombic efficiency (94.6%) in the first week, the best capacity retention rate after 500 cycles (87.2%), and the smallest increase in interfacial impedance after cycling (from 48.5Ω to 76.3Ω). All examples demonstrate significantly better performance than the comparative examples. Comparative Example 1, lacking a self-healing membrane, shows the fastest capacity decay and a sharp increase in impedance, verifying the stabilizing effect of the self-healing SEI membrane on the negative electrode interface. Comparative Examples 2-3 lack either a dynamic disulfide bond framework or a fluorosulfonyl imide salt ionic liquid, while Comparative Examples 4-5 replace the disulfide bonds with borate ester bonds and the ionic liquid with LiFSI, respectively. Their cycle retention rates and impedance increases are significantly worse than the examples, proving that both the dynamic disulfide bond framework and the fluorosulfonyl imide salt ionic liquid are indispensable.

[0064] Test Example 2 (a) Battery assembly The graphite negative electrode with a self-healing interface film attached to the negative electrode was used as the fixed sample in Example 1. The positive electrode, separator and battery assembly methods were the same as in Test Example 1, except that the electrolyte formula was replaced according to Table 2 below, and the effect of electrolyte components on battery performance was investigated.

[0065] Table 2 Electrolyte Formulation

[0066] (II) Performance Testing Methods (1) First week Coulomb efficiency test: Test conditions are the same as in test example 1.

[0067] (2) 500-cycle capacity retention test: The test conditions are the same as those in test example 1.

[0068] (3) 60℃ High-Temperature Storage Capacity Recovery Rate Test: The battery was activated by charging and discharging three times at 25℃ at a 0.5C rate, then charged at 0.5C rate to 4.2V, and then switched to constant voltage charging until the current decayed to 0.05C. The initial discharge capacity was measured. The fully charged battery was stored in a 60℃ constant temperature chamber for 7 days, then removed and allowed to cool naturally to room temperature. It was then discharged at 25℃ at a 0.5C rate to 2.5V, and the remaining capacity was measured. The battery was then charged and discharged three more times at a 0.5C rate, and the recovered capacity was measured. The capacity recovery rate was calculated using the following formula: Capacity recovery rate (%) = (recovered capacity / initial discharge capacity) × 100%.

[0069] (III) Test Results The test results are shown in Table 3 below.

[0070] Table 3. Battery performance test results for different electrolyte formulations

[0071] Based on the test results above, formulation A exhibits the best first-week coulombic efficiency, cycle capacity retention, and high-temperature storage capacity recovery. Formulations B (lacking FEC) and C (lacking LiBOB) show significant performance degradation across all parameters, demonstrating the synergistic effect of FEC and LiBOB, and their indispensability. Replacing FEC with VC in formulation D and LiBOB with LiDFOB in formulation E both result in inferior performance compared to formulation A, indicating the irreplaceable nature of the selected FEC and LiBOB. Replacing DMC with EMC in formulation F slightly reduces performance, while replacing LiPF6 with LiTFSI in formulation G significantly worsens performance, highlighting the significant impact of solvent system and lithium salt selection on battery performance. In conclusion, formulation A is the optimal electrolyte formulation for this application.

[0072] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A self-healing interface membrane for a negative electrode, characterized in that, The negative electrode self-healing interface film includes a cross-linked polymer containing dynamic disulfide bonds and a fluorosulfonyl imide salt ionic liquid dispersed in the cross-linked polymer containing dynamic disulfide bonds.

2. The negative electrode self-healing interface film according to claim 1, characterized in that, The crosslinked polymers containing dynamic disulfide bonds include polyimides containing dynamic disulfide bonds and / or polyurethanes containing dynamic disulfide bonds.

3. The negative electrode self-healing interface film according to claim 1 or 2, characterized in that, The fluorosulfonyl imide salt ionic liquid includes 1-vinyl-3-methylimidazolium difluorosulfonyl imide salt and / or 1-ethyl-3-methylimidazolium difluorosulfonyl imide salt.

4. The negative electrode self-healing interface film according to claim 1 or 2, characterized in that, The mass ratio of the cross-linked polymer containing dynamic disulfide bonds to the fluorosulfonyl imide salt ionic liquid is (2~4):(4~6).

5. A method for preparing a negative electrode self-healing interface film as described in any one of claims 1 to 4, characterized in that, Includes the following steps: A precursor dispersion was obtained by mixing a polymer containing dynamic disulfide bonds, polyethylene oxide, and a fluorosulfonyl imide salt ionic liquid in a solvent. The precursor dispersion is coated onto the surface of the negative electrode; In an inert atmosphere, ultraviolet light irradiation was used to perform in-situ crosslinking polymerization on the coated negative electrode surface, resulting in a self-healing interface film on the negative electrode surface.

6. The preparation method according to claim 5, characterized in that, Before coating the precursor dispersion onto the negative electrode surface, the negative electrode surface is also subjected to plasma cleaning.

7. The preparation method according to claim 5, characterized in that, The coating thickness is 5μm~15μm.

8. A negative electrode, characterized in that, The negative electrode surface is coated with the negative electrode self-healing interface film according to any one of claims 1 to 4, or the negative electrode self-healing interface film is prepared by the preparation method of the negative electrode self-healing interface film according to any one of claims 5 to 7.

9. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is the negative electrode as described in claim 8.

10. The lithium-ion battery according to claim 9, characterized in that, The electrolyte uses ethylene carbonate and dimethyl carbonate as solvents, LiPF6 as lithium salt, and fluoroethylene carbonate and lithium bis(oxalato)borate as additives.

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