Self-repairing interface layer, modified positive electrode sheet, solid-state battery and preparation method

Abstract

The application relates to the technical field of batteries, in particular to a self-repairing interface layer, a modified positive plate, a solid-state battery and a preparation method. The self-repairing interface layer comprises a self-repairing polymer and functional fillers filled in the self-repairing polymer; the self-repairing polymer is a polymer containing reversible covalent bonds or supramolecular interactions; and the functional fillers are used for inducing the formation of stable CEI. The application provides a self-repairing high-voltage positive electrode interface stable structure resistant to high voltage, which is composed of a self-repairing polymer and interface stable functional fillers. The self-repairing polymer matrix contains a polymer with reversible covalent bonds or supramolecular interactions, a dynamic self-repairing polymer matrix provides a repair capacity, and the functional fillers provide high-voltage stability and ion conduction.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a self-healing interface layer, a modified positive electrode, a solid-state battery, and a method for its preparation. Background Technology

[0002] Solid-state batteries are considered an important direction for next-generation energy storage technology due to their high energy density and intrinsic safety, but their commercialization still faces many challenges. How to effectively regulate and stabilize the solid-state electrolyte interface is one of the key scientific issues driving the practical application of all-solid-state batteries. Poor cycle stability of the cathode in all-solid-state batteries is one of the key challenges restricting their commercialization, mainly due to the complexity of the solid-solid interface and the limitations of the materials themselves.

[0003] However, existing all-solid-state batteries suffer from a fatal interface problem: gaps exist in the physical contact between the electrodes and the electrolyte, resulting in poor interfacial contact and an interfacial impedance as high as 10. 3 Ω cm 2 The above significantly reduces ion conduction efficiency; during the charging and discharging process of lithium batteries, the volume change rate of electrode materials (such as ternary materials) can reach 4-8%, and the volume deformation damage causes microcracks at the interface; side reactions are aggravated, and the exposed fresh interface triggers side reactions such as electrolyte decomposition and element interdiffusion, forming a high-resistivity interface reaction layer. In existing solutions, interface modification methods (such as ALD coating) can only achieve initial interface optimization and can isolate the direct contact between the positive electrode active material and the electrolyte to a certain extent. However, they cannot cope with dynamic volume deformation during cycling and may hinder ion transport, leading to increased electrode interface impedance and decreased energy density. Flexible electrolyte design can buffer stress, but it lacks active repair capabilities and cannot solve the problem of interface cracks generated during cycling. The positive electrode side interface layer must not only be able to physically close cracks, but more importantly, it must form a chemical passivation interface to continuously resist oxidation corrosion and element interdiffusion under high voltage. Therefore, developing interface construction technology with dynamic repair capabilities has become the key to breaking through the bottleneck of practical application of all-solid-state batteries. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and defects of the prior art and to provide a self-healing interface layer, a modified positive electrode, a solid-state battery, and a preparation method thereof.

[0005] To achieve the above objectives, this application adopts the following solution: A self-healing interface layer includes a self-healing polymer and a functional filler filled within the self-healing polymer; the self-healing polymer is a polymer containing reversible covalent bonds or supramolecular interactions; the functional filler is used to induce the formation of a stable CEI.

[0006] The self-healing polymer includes at least one of the following: furan-maleimide-based Diels-Alder polymers, disulfide-containing polysulfide urethanes, disulfide-containing perfluoropolyethers (PFPEs), boronic acid ester polymers, or polyurethanes / polyureas based on multiple hydrogen bonds; preferably, disulfide-containing perfluoropolyethers (PFPEs).

[0007] The functional filler includes at least one of lithium-philic nanoparticle fluorinated compounds, lithium salts, or inorganic fast ion conductors; preferably, inorganic fast ion conductors.

[0008] The lithium-loving nanoparticles include at least one of ZnO, SiO2, or Al2O3; the fluorine-containing compound includes at least one of LiF or PVDF-HFP; the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium bis(fluorosulfonyl)imide (LiFSI); and the inorganic fast ion conductor includes at least one of LLZO or LGPS.

[0009] The functional filler has a mass content of 30-70 wt% in the self-healing polymer, preferably 50-60 wt%.

[0010] Preferably, the thickness of the self-healing interface layer is 8.7-10.2 nm; the room temperature ionic conductivity is 2.8 × 10⁻⁶. -6 S / cm-8.0×10 -5 S / cm.

[0011] The present invention also includes a modified positive electrode sheet, comprising a positive electrode sheet and the self-healing interface layer disposed on the surface of the positive electrode sheet.

[0012] The active material of the cathode includes at least one of layered transition metal oxides, lithium-rich manganese-based cathode materials, nickel-cobalt-manganese ternary cathode materials, and nickel-cobalt-aluminum ternary cathode materials.

[0013] The present invention also includes a method for preparing the modified positive electrode sheet, comprising the following steps: mixing a functional filler with a prepolymer liquid containing a self-healing polymer monomer to obtain a composite slurry; coating the composite slurry onto the surface of the positive electrode sheet and polymerizing it to obtain the modified positive electrode sheet.

[0014] The present invention also includes a solid-state battery comprising the modified positive electrode, electrolyte layer and negative electrode.

[0015] The present invention also includes a method for preparing the solid-state battery, comprising the following steps: assembling a molded solid-state battery in the order of positive electrode / self-healing interface layer / electrolyte layer / negative electrode; the battery assembly pressure is 20-100 MPa, preferably 20-50 MPa, and the pressure is maintained for 1-5 minutes, preferably 3 minutes; the assembled battery is left to stand at room temperature to allow the interface to fully contact.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a high-voltage resistant, self-healing, high-voltage cathode interface stabilization structure. The interface layer is composed of a self-healing polymer and an interface-stabilizing functional filler. The self-healing polymer matrix contains polymers with reversible covalent bonds or supramolecular interactions. The dynamic self-healing polymer matrix provides repair capabilities, while the functional filler provides high-voltage stability and ion conduction. The core of this invention lies in the in-situ composite of the self-healing polymer and the functional filler, allowing the self-healing polymer to be oriented and positioned on the surface of the functional filler, thus achieving a self-healing interface structure. This constructs a three-dimensional networked interface layer on the cathode surface that combines mechanical flexibility, electrochemical inertness, and dynamic repair capabilities. This interface layer can deform and rebound in real time with the cathode volume changes during charge-discharge cycles, and continuously heals microcracks through the reversible breakage / recombination of reversible covalent bonds, ensuring long-term cycle stability. Preferably, perfluoropolyether (PFPE) containing disulfide bonds is used as the self-healing polymer. PFPE exhibits excellent high-pressure and oxidation resistance. Its fluorocarbon backbone (CF bonds) possesses extremely high bond energy and very low electron cloud density, perfectly resisting the reactive oxygen species and strong oxidizing environment released from high-voltage cathodes (>4.5V). PFPE segments have an extremely low glass transition temperature (-105℃), are very flexible, and can adhere well to cathode particles and solid electrolyte particles, reducing interfacial impedance. Embedded disulfide bonds provide self-healing capabilities, effectively addressing volumetric strain and interfacial cracks caused by cathode particles, maintaining the physical integrity of the interface over the long term. This polymer matrix can act as a "carrier," uniformly dispersing the high-pressure stabilizing filler, thus providing additional lithium-ion conduction channels and physical barriers while simultaneously achieving self-healing.

[0017] The self-healing interface layer provided by this invention can reduce interfacial side reactions between the positive electrode active material and the sulfide electrolyte, alleviate the disruption of ion and electron pathways caused by volume changes in the positive electrode active material, block element interdiffusion between the electrode and the electrolyte, suppress the formation of a space charge layer, and improve the long-cycle stability of the battery. During the initial charging to high voltage, the high-voltage stabilizing filler (inorganic fast ion conductor) in the self-healing interface layer undergoes a controllable and slight interfacial reaction with the positive electrode surface, forming a "gradient passivation layer." During charging, the positive electrode particles expand and deform, causing microcracks inside the composite positive electrode. Part of the passivation layer ruptures, exposing a fresh high-voltage positive electrode surface. At this time, the heat generated by battery operation triggers dynamic polymer chain movement, polymer matrix flow, covering the cracks, dynamic bond recombination, and closing the gaps, thus "pulling" the high-voltage stabilizing filler particles back together, restoring the physical continuity of the passivation layer, and preventing cracks from expanding into side reaction channels. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0019] Example 1: A self-healing interface layer comprising a self-healing polymer and a functional filler filled within the self-healing polymer; the self-healing polymer is a polymer containing reversible covalent bonds or supramolecular interactions; the functional filler is used to induce the formation of a stable CEI. The self-healing polymer includes at least one of the following: furan-maleimide-based Diels-Alder polymers, disulfide-containing polyurethanes, disulfide-containing perfluoropolyethers (PFPEs), polymers containing borate ester bonds, or polyurethanes / polyureas based on multiple hydrogen bonds; preferably, disulfide-containing perfluoropolyethers (PFPEs). The functional filler includes at least one of the following: lithium-philic nanoparticle fluorinated compounds, lithium salts, or inorganic fast ion conductors; preferably, inorganic fast ion conductors. The lithium-loving nanoparticles include at least one of ZnO, SiO2, or Al2O3; the fluorine-containing compound includes at least one of LiF or PVDF-HFP; the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium bis(fluorosulfonyl)imide (LiFSI); and the inorganic fast ion conductor includes at least one of LLZO or LGPS.

[0020] This application uses perfluoropolyether PFPE containing disulfide bonds as the self-healing polymer and LLZO as the inorganic fast ion conductor as the functional filler for illustrative purposes.

[0021] 1. Preparation of the basic prepolymer solution: In a high-purity argon glove box, accurately weigh 10.00 g (5.0 mmol) of di-terminated alkenyl PFPE into a 50 mL glass bottle, and weigh 1.09 g (6.0 mmol) of dimercaptodiethyl disulfide and add it to the bottle. Add 0.11 g of photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone (1.0 wt% of the total mass of PFPE and disulfide). Place the mixture in a planetary centrifuge (Thinky) and stir at 2000 rpm for 5 minutes to obtain a clear, homogeneous, pale yellow viscous liquid, which is designated as the prepolymer solution and stored for later use.

[0022] 2. Preparation of composite slurry with 30% wt LLZO content: First, weigh 10g of prepolymer solution into a Thinky sample cup, weigh 4.29g of LLZO powder (30% wt LLZO refers to the mass percentage of LLZO filler in the total mass of the polymer matrix and LLZO filler. The mass of the "polymer matrix" is equal to the total mass of the olefin-terminated PFPE, dimercaptodiethyl disulfide, and photoinitiator added during preparation), and add it to the Thinky sample cup of prepolymer solution in 3 batches. After each batch, stir at 1500rpm for 3 minutes. Add 5% wt LiTFSI, with an added mass of 0.5g. Finally, add 3.0mL of hydrofluoroether (HFE) solvent (the amount of HFE is adjusted according to the solid content to ensure that the slurry viscosity is in the range of 500-1500cP). Stir at 2000rpm for 10 minutes to obtain a uniform milky white composite slurry.

[0023] 3. Preparation of the interface layer and modified positive electrode 1) Preparation of positive electrode sheet NCM811 positive electrode material, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 92:5:3, and a slurry was prepared using N-methylpyrrolidone as a solvent. The slurry was coated onto an aluminum foil current collector and dried under vacuum at 80°C for 12 hours to obtain the positive electrode sheet.

[0024] 2) Self-healing composite interface layer In an argon-filled glove box, the prepared composite slurry was coated onto the surface of the NCM811 positive electrode sheet using a scraper with a blade gap of 30 μm. After coating, the sheet was allowed to stand at room temperature for 10 minutes to allow the HFE-7200 solvent to evaporate, forming a touch-dry wet film. The electrode sheet was then transferred to a UV curing chamber (365 nm, 20 mW / cm²). 2 The electrode is irradiated for 120 seconds under a nitrogen atmosphere to form a self-healing composite interface layer with a thickness of approximately 8-10 μm. The cured electrode is then post-treated in a vacuum oven at 60℃ for 6 hours before use.

[0025] 4. Solid-state battery assembly and testing 1) In an argon glove box, weigh 200 mg of Li6PS5Cl powder, place it in a mold with a diameter of 10 mm, and press it under a pressure of 300 MPa for 5 minutes to obtain sulfide solid electrolyte tablets.

[0026] 2) Place the aforementioned positive electrode / self-healing interface layer in the mold, with the self-healing interface layer side close to the electrolyte sheet. Assemble the solid-state battery in the mold according to the sequence of "NCM811 positive electrode / self-healing interface layer / LPSC electrolyte sheet / lithium metal negative electrode". The battery assembly pressure is 20 MPa, held for 3 minutes. After assembly, allow the battery to stand at room temperature for 12 hours to allow sufficient interface contact before conducting electrochemical tests. Perform a 0.1C constant current charge-discharge test at 30℃ within a voltage window of 2.8-4.5V.

[0027] 3) Ionic conductivity testing: A stainless steel (SS) symmetrical cell structure (SS / interface layer / SS) was used. Electrochemical impedance spectroscopy was performed on an electrochemical workstation with a frequency range of 1MHz-1Hz, an amplitude of 10 mV, and a test temperature of 30℃. Ionic conductivity was calculated using the formula σ=d / (R·A), where d is the interface layer thickness, A is the effective area, and R is the bulk impedance.

[0028] Example 2: The LLZO content in step 2 of Example 1 was changed to 35%, the mass of LLZO was 5.38g, the mass of HFE was 3.5mL, and the other steps were the same as in Example 1.

[0029] Example 3: The LLZO content in step 2 of Example 1 was changed to 40%, the mass of LLZO was 6.67g, the mass of HFE was 4mL, and the other steps were the same as in Example 1.

[0030] Example 4: The LLZO content in step 2 of Example 1 was changed to 45%, the mass of LLZO was 8.18g, the mass of HFE was 4.5mL, and the other steps were the same as in Example 1.

[0031] Example 5: The LLZO content in step 2 of Example 1 was changed to 50%, the mass of LLZO was 10g, the mass of HFE was 5.0mL, and the other steps were the same as in Example 1.

[0032] Example 6: The LLZO content in step 2 of Example 1 was changed to 55%, the mass of LLZO was 12.22g, the mass of HFE was 5.5mL, and the other steps were the same as in Example 1.

[0033] Example 7: The LLZO content in step 2 of Example 1 was changed to 60%, the mass of LLZO was 15g, the mass of HFE was 6.0mL, and the other steps were the same as in Example 1.

[0034] Example 8: The LLZO content in step 2 of Example 1 was changed to 70%, the mass of LLZO was 23.33g, the mass of HFE was 8.0mL, and the other steps were the same as in Example 1.

[0035] Example 9: The assembly pressure during battery testing in step 4 of Example 1 was changed to 50 MPa, and the other steps were the same as in Example 1.

[0036] Example 10: The assembly pressure during battery testing in step 4 of Example 1 was changed to 100 MPa, and the other steps were the same as in Example 1.

[0037] Comparative Example 1: The LLZO content in step 2 of Example 1 was changed to 0%, the mass of LLZO was 0g, the mass of HFE was 2.0mL, and the other steps were the same as in Example 1.

[0038] Comparative Example 2: The LLZO content in step 2 of Example 1 was changed to 20%, the mass of LLZO was 2.5g, the mass of HFE was 2.5mL, and the other steps were the same as in Example 1.

[0039] Comparative Example 3: The positive electrode sheet prepared in Example 1 does not contain the PFPE self-healing interface layer, i.e., a rigid interface, and the other steps are the same as in Example 1.

[0040] Table 1. Room temperature ionic conductivity of interfacial layers with different LLZO contents

[0041] As shown in Table 1, as the LLZO content increases from 0 to 55 wt%, the interfacial ionic conductivity exhibits a three-order-of-magnitude jump (from 10 wt%). -9 S / cm increased to 7.5×10 -5 (S / cm). The critical inflection point occurs in the 40-50 wt% range, where conductivity decreases from 10... -6 S / cm level jumps to 10 -5 The conductivity is in the S / cm range, indicating that the interfacial network structure forms a continuous network within this range, and the conductivity gradually increases. The conductivity reaches its peak (8.6 × 10⁻⁶) at 55-60 wt%. -5 The conductivity (S / cm) may be due to the continuous extension and connection of interfacial transport paths, resulting in optimal interfacial network connectivity. When the content continues to increase to 70 wt%, the conductivity does not increase further, possibly due to filler agglomeration, polymer phase discontinuity leading to a slight decrease, and impaired self-healing function, causing a gradual decline in conductivity. This trend is highly consistent with the intrinsic non-lithium-conducting mechanism of the PFPE matrix, which relies entirely on interfacial conduction, confirming that the PFPE system requires ≥40 wt% filler to form an effective permeation network, with the optimal range being 50-60 wt%.

[0042] Table 2 Performance of all-solid-state batteries with different LLZO content interface layers

[0043] As shown in Table 2, the initial discharge specific capacity increases from 168.3 mAh / g to 193.8 mAh / g as the LLZO content increases from 0 to 55 wt%, reaching 80% of the theoretical capacity of NCM811. This indicates that the ion network structure constructed by the high-content filler significantly improves the interfacial lithium-ion flux. The LLZO content decreases slightly at 60 wt% (192.1 mAh / g) and further decreases to 185.7 mAh / g at 70 wt%, consistent with the trend of ionic conductivity. This suggests that when the content of functional filler reaches a certain level, agglomeration occurs, leading to discontinuity in the polymer phase and ion network structure, which hinders the conduction of lithium-ion pathways and reduces the discharge capacity.

[0044] Example 6 (55wt% LLZO) exhibited the best cycle life, with a capacity retention of 92.5% after 100 cycles at 0.2C and 85.3% after 300 cycles. In contrast, Comparative Example 1 (0% LLZO) had only 22.5% capacity retention after 300 cycles, and Comparative Example 2 (20wt% LLZO) had 35.8%. This result fully demonstrates the excellent protective effect of the PFPE composite interface layer with high LLZO content in 4.5V high-voltage sulfide all-solid-state batteries: the continuous LLZO interface network physically isolates the positive electrode from the sulfide electrolyte, suppressing the occurrence of side reactions; the disulfide bond dynamic repair function promptly closes microcracks generated during cycling; and PFPE has intrinsic high voltage resistance, so the interface layer itself will not undergo oxidative decomposition. When the filler content is too high (>60wt%), the cycling performance of Example 8 (70wt% LLZO) is significantly worse than that of Examples 6 and 7. The capacity retention rate is 79.4% after 100 cycles and drops to 62.1% after 300 cycles. This may be due to the excessive rigidity causing irreversible rupture of the interface layer when the cathode volume changes. Due to the excessive filler content, agglomeration occurs, resulting in uneven local impedance, insufficient polymer phase, discontinuous disulfide bond crosslinking network, and severely impaired self-repair function.

[0045] When the filler content is <30wt%, the interfacial layer ionic conductivity is less than 10. -6 The S / cm ratio is insufficient to meet battery performance requirements. When the filler content is >70wt%, the flexibility of the interface layer decreases significantly, the conformal contact with the electrode is destroyed, and the self-repair function of disulfide bonds is hindered. Considering the ionic conductivity and battery performance data, the optimal embodiment has an LLZO content of 55%.

[0046] Table 3 Performance of all-solid-state batteries under different assembly test pressures

[0047] As shown in Table 3, compared with the rigid interface layer in Comparative Example 3, the PFPE-based self-healing interface layer of this invention, due to its extremely low glass transition temperature (Tg = -105℃), can achieve sufficient solid-solid interface contact at a lower stacking pressure (20-50 MPa). Furthermore, the dynamic exchange mechanism of disulfide bonds enables the interface layer to repair microcracks caused by volume changes during cycling, thereby reducing dependence on continuously high external pressure. The first-cycle discharge capacity and cycling performance are optimal at a pressure of 20-50 MPa. Excessive pressure (-100 MPa) may lead to over-compression of the PFPE matrix and agglomeration of the LLZO filler, which adversely affects performance and interface integrity, resulting in a decrease in first-cycle discharge capacity and cycling performance. Therefore, the PFPE-based self-healing interface layer of this invention exhibits superior performance within the assembly test pressure range of 20-50 MPa.

[0048] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.

[0049] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A self-healing interface layer, characterized in that, It includes a self-healing polymer and a functional filler filled within the self-healing polymer; the self-healing polymer is a polymer containing reversible covalent bonds or supramolecular interactions; the functional filler is used to induce the formation of a stable CEI.

2. The self-healing interface layer according to claim 1, characterized in that, The self-healing polymer includes at least one of the following: furan-maleimide-based Diels-Alder polymers, disulfide-containing polysulfide urethanes, disulfide-containing perfluoropolyethers (PFPEs), boronic acid ester polymers, or polyurethanes / polyureas based on multiple hydrogen bonds; preferably, disulfide-containing perfluoropolyethers (PFPEs).

3. The self-healing interface layer according to claim 1, characterized in that, The functional filler includes at least one of lithium-philic nanoparticle fluorinated compounds, lithium salts, or inorganic fast ion conductors; preferably, inorganic fast ion conductors.

4. The self-healing interface layer according to claim 1 as described in claim 3, characterized in that, The lithium-loving nanoparticles include at least one of ZnO, SiO2, or Al2O3; the fluorine-containing compound includes at least one of LiF or PVDF-HFP; the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium bis(fluorosulfonyl)imide (LiFSI); and the inorganic fast ion conductor includes at least one of LLZO or LGPS.

5. The self-healing interface layer according to claim 1, characterized in that, The functional filler content in the self-healing polymer is 30-70 wt%; preferably 50-60 wt%; preferably, the thickness of the self-healing interface layer is 8.7-10.2 nm; and the room temperature ionic conductivity is 2.8 × 10⁻⁶. -6 S / cm-8.0×10 -5 S / cm.

6. A modified positive electrode, characterized in that, It includes a positive electrode sheet and a self-healing interface layer as described in any one of claims 1-5 disposed on the surface of the positive electrode sheet.

7. The modified positive electrode according to claim 6, characterized in that, The active material of the cathode includes at least one of layered transition metal oxides, lithium-rich manganese-based cathode materials, nickel-cobalt-manganese ternary cathode materials, and nickel-cobalt-aluminum ternary cathode materials.

8. A method for preparing the modified positive electrode sheet according to claim 6 or 7, characterized in that, The process includes the following steps: mixing a functional filler with a prepolymer liquid containing a self-healing polymer monomer to obtain a composite slurry; coating the composite slurry onto the surface of a positive electrode and polymerizing it to obtain a modified positive electrode.

9. A solid-state battery, characterized in that, It includes the modified positive electrode, electrolyte layer, and negative electrode as described in claim 6 or 7.

10. A method for preparing a solid-state battery according to claim 9, characterized in that, The process includes the following steps: assembling the mold solid-state battery in the order of positive electrode / self-healing interface layer / electrolyte layer / negative electrode; the battery assembly pressure is 20-100 MPa, preferably 20-50 MPa; holding the pressure for 1-5 minutes, preferably 3 minutes; and allowing the assembled battery to stand at room temperature to allow the interfaces to fully contact.

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