Positive pole piece of lithium ion battery, preparation method of positive pole piece and lithium ion battery

Abstract

The invention relates to a lithium ion battery positive pole piece and a preparation method thereof and a lithium ion battery, the preparation method of the positive pole piece comprises the following steps: immersing a lithium ion battery positive pole piece rough blank into an organic solution of a silane coupling agent, reacting, washing and drying to obtain a modified lithium ion battery positive pole piece rough blank; a COF layer is prepared on the surface of the positive electrode active material layer of the modified lithium ion battery positive electrode plate rough blank through a vapor phase epitaxial growth method, and a lithium ion battery positive electrode plate rough blank loaded with the COF layer is obtained; and then, carrying out gas-phase sulfonation modification on the COF layer-loaded lithium ion battery positive pole piece rough blank to obtain the lithium ion battery positive pole piece. The problems of transition metal dissolution, capacity fading, rate capability limitation and the like caused by positive electrode / electrolyte interface side reaction under high voltage (gt; 4.5 V) can be solved.

Description

Technical Field

[0001] The present invention relates to a positive electrode sheet for a lithium-ion battery, a preparation method thereof, and a lithium-ion battery, and particularly to a high-voltage lithium-ion battery positive electrode sheet based on a gas-phase epitaxial growth COF molecular sieve interface, a preparation method thereof, and a lithium-ion battery, belonging to the field of lithium-ion batteries. Background Art

[0002] In existing high-nickel ternary cathode materials (such as LiNi x Co y Mn 1-x-y O2, where 0 < x < 1, 0 < y < 1, and x + y < 1), there are interface failure problems under high-voltage conditions. With the increasing demand for energy density, high-nickel ternary cathode materials have become the mainstream choice due to their high specific capacity. However, during voltage cycling above 4.5 V, side reactions at the cathode / electrolyte interface can cause the dissolution of transition metal ions (such as Ni 2+ 、Co 3+ ), crystal structure deterioration, and capacity attenuation, severely restricting the cycle life and rate performance of the battery. As a quaternary cathode material, lithium nickel cobalt manganese aluminate (NCMA) suppresses the H2→H3 phase transition of high-nickel materials (such as Ni content ≥ 80%) through Al doping, reducing the probability of microcrack generation. Its typical composition is LiNi 0.89 Co 0.05 Mn[[ID=2**3]] 0.05 Al 0.01 O2, and the capacity retention rate can be increased by 12% compared to NCM811 after 100 cycles at 4.4V.

[0003] Currently, the surface modification technology of cathode materials mainly suppresses side reactions at the interface through a coating layer. For example, although a polymer coating (such as PVDF) can physically isolate the electrolyte, its pore size distribution is wide (usually > 5 nm), making it difficult to accurately screen out desolvated lithium ions (hydrated radius of about 0.38 nm) and multivalent metal ions (such as Ni 2+ with a hydrated radius of about 0.69 nm), and its mechanical stability is insufficient to effectively resist the volume expansion of the electrode under high voltage. On this basis, the developed inorganic coating materials (such as Al2O3, Li3PO4) can improve the interface stability, but will significantly increase the interface impedance (> 5**0 Ω·cm 2 ), resulting in a decline in rate performance (5C capacity is usually < 120 mAh / g), and the high-temperature sintering process (> 400°C) is likely to damage the structure of the cathode body.

[0004] In recent years, metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have been applied to cathode coating due to their adjustable pore characteristics. For example, Chinese Patent Application CN117229525A discloses a coating material for lithium-ion battery cathodes, its preparation method and application. Its Ni / Co-MOFs and COF hybridization technology requires the formation of a coating layer through liquid-phase synthesis combined with high-temperature sintering. However, this technology still has obvious limitations: solvent residues (such as DMF, DMSO) in the liquid-phase process are likely to block pores and reduce the lithium-ion transference number; the high-temperature sintering process may cause the collapse of the COF framework, resulting in deterioration of pore size uniformity; at the same time, this solution does not solve the core contradictions of high lithium-ion desolvation energy barrier and insufficient dynamic sieving of multivalent ions.

[0005] With the development of solid-state battery technology, there are problems of high interfacial impedance and lithium dendrite penetration at the cathode / solid electrolyte interface. The difference in thermal expansion coefficients (ΔCTE>5×10 -6 / K) between traditional solid electrolytes (such as LLZO, LATP) and high-nickel cathodes leads to interfacial delamination during cycling, and the rigid interface cannot inhibit lithium dendrite puncture. Existing solutions often use polymer buffer layers (such as PEO), but their ionic conductivity is low (<10 -4 S / cm) and the voltage window is narrow (<4.0V), making it difficult to match high-voltage cathodes.

[0006] Therefore, there is an urgent need to develop a cathode interface engineering technology with sub-nanometer pore size accuracy, high interfacial stability and industrial feasibility, which can achieve dynamic blocking of multivalent metal ions while ensuring efficient lithium-ion transmission, and avoid the risks of liquid-phase corrosion and high-temperature damage. Summary of the Invention

[0007] Aiming at the deficiencies of the existing technology, one of the purposes of the present invention is to provide a lithium-ion battery cathode plate with more excellent electrochemical performance (such as cycling performance) and its preparation method; the second purpose of the present invention is to provide a lithium-ion battery.

[0008] To solve the above technical problems, the technical solution of the present invention is as follows: A preparation method of a lithium-ion battery cathode plate, comprising the following steps: S1. Provide a rough blank of a lithium-ion battery cathode plate; Among them, the rough blank of the lithium-ion battery cathode plate includes a current collector and a cathode active material layer stacked in sequence; the cathode active material in the cathode active material layer includes lithium nickel cobalt manganate (its chemical formula can be selected as LiNi x Co y Mn 1-x-y O2, 0 < x < 1, 0 < y < 1, x + y < 1), lithium nickel cobalt aluminate (its chemical formula can be selected as LiNi x Coy Al z O2, where 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1), lithium nickel cobalt manganese aluminate (its chemical formula can be selected as LiNi x Co y Mn z Al w O2, where 0 < x < 1, 0 < y < 1, 0 < z < 1, 0 < w < 0.1, and x + y + z + w = 1); or one or more of them S2. Immerse the rough blank of the lithium-ion battery positive electrode sheet in an organic solution of a silane coupling agent. After the reaction, wash and dry to obtain a modified rough blank of the lithium-ion battery positive electrode sheet S3. Prepare a COF layer on the surface of the positive electrode active material layer of the modified rough blank of the lithium-ion battery positive electrode sheet by vapor phase epitaxial growth method (VPE) to obtain a rough blank of the lithium-ion battery positive electrode sheet loaded with the COF layer S4. Perform gas phase sulfonation modification on the rough blank of the lithium-ion battery positive electrode sheet loaded with the COF layer to obtain the lithium-ion battery positive electrode sheet

[0009] [[ID=zo]]Thus, first immerse the rough blank of the lithium-ion battery positive electrode sheet in an organic solution of a silane coupling agent to form amino anchoring sites on the surface of the positive electrode active material layer, activate the substrate, and lay a good foundation for the subsequent preparation of the COF layer on the positive electrode active material layer; Subsequently, prepare a COF layer (organic framework molecular sieve layer) on the surface of the positive electrode active material layer of the modified rough blank of the lithium-ion battery positive electrode sheet by vapor phase epitaxial growth method, and a COF layer with a tightly bound interface can be obtained on the surface of the positive electrode active material layer; Finally, through gas phase sulfonation modification, sulfonation modification is performed on the COF layer to obtain a lithium-ion battery positive electrode sheet with excellent electrochemical performance

[0010] Furthermore, in S1, the chemical formula of lithium nickel cobalt manganate is LiNi x Co y Mn 1-x-y O2, where 0.6 ≤ x < 1, 0 < y < 1, x + y < 1, preferably 0.6 ≤ x ≤ 0.9; the chemical formula of lithium nickel cobalt aluminate is LiNi x Co y Al z O2, where 0.6 ≤ x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1, preferably 0.6 ≤ x ≤ 0.9; the chemical formula of lithium nickel cobalt manganese aluminate is LiNi x Co y Mn z Al w O2, where 0.6 ≤ x < 1, 0 < y < 1, 0 < z < 1, 0 < w < 0.1, x + y + z + w = 1, preferably 0.6 ≤ x ≤ 0.9

[0011] Optionally, the lithium nickel cobalt manganese oxide is a common doped lithium nickel cobalt manganese oxide. Optionally, the lithium nickel cobalt aluminum oxide is a common doped lithium nickel cobalt aluminum oxide. Optionally, the lithium nickel cobalt manganese aluminum oxide is a common doped lithium nickel cobalt manganese aluminum oxide.

[0012] Optionally, the positive electrode active material is one or more of NCM811 and NCM622.

[0013] Furthermore, in S2, the concentration of the silane coupling agent in the organic solution is 1-10 vol%, further 2-8 vol%, and further 4-6 vol%; the silane coupling agent includes one or two of APTES and AEAPTMS; and the solvent in the organic solution includes one or more of toluene, xylene, and cyclohexane.

[0014] Furthermore, in S2, the lithium-ion battery positive electrode sheet blank is immersed in an organic solution of a silane coupling agent, and the reaction is carried out at 70-90°C for 1-3 hours under the condition of continuous introduction of an inert gas, followed by washing and drying to obtain a modified lithium-ion battery positive electrode sheet blank; preferably, the flow rate of the inert gas is controlled to be 5-30sccm, more preferably 10-25sccm, and even more preferably 15-20sccm, and the inert gas includes one or both of nitrogen and argon. Here, the continuous introduction of the inert gas can provide antioxidant protection, while removing the reaction by-products, promoting the condensation reaction to proceed fully, significantly enhancing the adhesion of the subsequently grown COF layer and inducing vertical orientation. Preferably, the reaction is carried out at 75-85°C for 1.5-2.5 hours.

[0015] In S2, a condensation reaction forms uniform amino anchoring sites on the surface of the cathode active material layer. XPS analysis reveals that the N 1s peak intensity increases to 2-5 times its initial value. The introduction of amino anchoring sites effectively enhances the adhesion of the subsequent in-situ generated COF layer, effectively reducing the possibility of COF layer delamination due to electrode volume expansion during high-voltage cycling.

[0016] Furthermore, in S3, when performing vapor phase epitaxial growth, the modified lithium ion battery positive electrode sheet blank is placed in a vacuum degree of ≤5×10 -2 In the reaction chamber of Pa, 40-60 cycles of deposition are carried out at 160-200°C to obtain a rough blank of a lithium-ion battery positive electrode sheet loaded with a COF layer; In each deposition cycle, the following steps are performed in sequence: first, nitrogen is used as a carrier gas to deliver an aldehyde monomer into the reaction chamber for 20-40 seconds (furthermore, 25-35 seconds) to achieve surface adsorption. Preferably, the gas delivery rate is controlled to be 5-15 sccm, more preferably 8-12 sccm; then, an inert gas is introduced into the reaction chamber for purging for 15-25 seconds (furthermore, 18-22 seconds) to completely remove reaction by-products. Preferably, the gas delivery rate is controlled to be 30-60 sccm, more preferably 40-50 sccm; finally, nitrogen is used as a carrier gas to deliver a diamine monomer into the reaction chamber for 30-50 seconds (furthermore, 35-45 seconds) to perform a condensation reaction to form a COF layer. Preferably, the gas delivery rate is controlled to be 5-15 sccm, more preferably 8-12 sccm; The aldehyde monomers include one or more of 1,3,5-triformylphloroglucinol, 2,4,6-triformyl-s-triazine, 2,5-dihydroxyterephthalaldehyde, 2,5-dimethoxyterephthalaldehyde, 2,5-dichloroterephthalaldehyde, and 2,3,5,6-tetrafluoro-p-benzaldehyde; the diamine monomers include one or more of p-phenylenediamine, benzidine, m-phenylenediamine, and o-phenylenediamine; and the inert gas is nitrogen and / or argon. The thickness of the COF layer grown in each deposition cycle is limited, but multiple cycles can precisely control the thickness of the COF layer. Therefore, controlling the appropriate reaction temperature helps suppress pore distortion caused by molecular thermal vibrations, resulting in more regular pores and ensuring the ultimate performance of the positive electrode. Vapor-phase epitaxial growth in a high vacuum environment helps reduce gas-phase collisions and ensure orderly pore growth. Inert gas purging effectively and promptly removes byproducts (such as H2O), preventing pore hydrolysis and collapse. Selecting the right monomers helps regulate the pore size of the COF layer, achieving the target pore size (e.g., 1.7-1.9 nm), and facilitates the coordinated optimization of pore size screening and ion selectivity.

[0017] Preferably, the single-cycle growth rate is monitored in real time during the deposition process by a quartz crystal microbalance (preferably 0.3-0.5 nm / cycle), and in-situ ellipsometer (QCM) is used to ensure film thickness uniformity (CV value <10%).

[0018] Optionally, in S3, the deposition is carried out at 170-190°C for 45-55 cycles, preferably, the deposition is carried out at 175-185°C for 48-52 cycles.

[0019] Furthermore, in S4, the lithium-ion battery positive electrode sheet blank loaded with the COF layer is placed in a sulfonating agent atmosphere for gas-phase sulfonation modification to obtain a lithium-ion battery positive electrode sheet; wherein the sulfonating agent is SO3 gas, chlorosulfonic acid vapor or SO3-dioxane complex, and the molar ratio of SO3 to dioxane in the SO3-dioxane complex is 1:1-3, and further 1:1.5-2.5.

[0020] Furthermore, the lithium-ion battery positive electrode sheet blank loaded with the COF layer is placed in a sulfonating agent atmosphere of 0.05-0.15 MPa (preferably 0.08-0.12 MPa) and subjected to vapor-phase sulfonation modification at 140-160° C. (preferably 145-155° C.) for 0.5-2 h (preferably 0.8-1.5 h, more preferably 0.9-1.2 h).

[0021] Based on the difference in diffusion-reaction kinetics, after gas-phase sulfonation modification, a gradient distribution structure of sulfonic acid groups is spontaneously formed in the COF layer (the density of sulfonic acid groups in the surface of the COF layer reaches 1.8-2.2 mmol / g, and the density of sulfonic acid groups in the bottom surface (i.e., the interface between the COF layer and the positive electrode active material layer) reaches 0.3-0.7 mmol / g), which can be specifically verified by TOF-SIMS or X-ray photoelectron spectroscopy.

[0022] Optionally, in S4, the pore size of the COF layer in the lithium-ion positive electrode sheet is 1.7-1.9 nm, further 1.75-1.85 nm, further 1.76-1.84 nm, further 1.77-1.82 nm, and further 1.78-1.8 nm.

[0023] Furthermore, the thickness of the COF layer is 14-24 nm, preferably 16-22 nm, and more preferably 18-20 nm.

[0024] Preferably, the pores of the COF layer are vertically connected to the surface of the positive electrode active material layer.

[0025] The present invention prepares a COF layer on the surface of the positive electrode active material layer through a vapor phase epitaxial growth method, which can achieve atomic-level in-situ precise film formation. Specifically, a COF molecular sieve layer with controllable thickness and vertically oriented pores is constructed on the surface of the positive electrode active material layer, which helps to achieve sub-nanometer scale ion screening. At the same time, the vapor phase epitaxial growth method can avoid solvent damage and avoid the pore blockage that may be caused by solvent residue in the liquid phase method. In addition, the substrate is activated before the COF layer is grown, which effectively improves the interface compatibility and allows the epitaxial growth to form a covalently bonded interface, which helps to suppress interface delamination under high voltage, ensure the normal performance of the electrode plate, and extend the service life of the battery.

[0026] By performing vapor-phase sulfonation modification on the COF layer to form a gradient sulfonic acid layer and regulating the effective pore size of the COF layer (1.8±0.1 nm), the synergistic effect of the two can help further improve ion selectivity, increase the lithium ion transfer number to above 0.85 (a significant improvement compared to the PVDF coating solution), and reduce the Ni² + The permeation rate is suppressed to below 5 ppm / cycle. Meanwhile, the COF layer's mechanical modulus of no less than 15 GPa effectively suppresses electrode expansion. Combined with the zero-solvent residue characteristic of the all-gas-phase process, the assembled liquid lithium-ion battery can maintain a capacity retention rate of ≥90% after 500 cycles at a high voltage of 4.5V. The constructed COF layer has a pore structure that perpendicularly connects to the positive electrode active material layer, significantly reducing the lithium-ion transport energy barrier. The 5C rate discharge capacity reaches over 160 mAh / g, and the 5C / 0.1C capacity ratio is ≥85%. Furthermore, the lithium-ion battery positive electrode sheet of the present invention is compatible with solid-state battery systems. The COF layer's mechanical modulus of 15-25 GPa is well matched to the stiffness of solid-state electrolytes (such as lithium lanthanum zirconate (LLZO)), reducing the interfacial impedance to 28 Ω·cm. 2 Below, the critical current density is increased to 2.0 mA / cm 2 , the capacity retention rate after 300 cycles at 4.5V is ≥89.5%. The present invention is suitable for solving the problems of transition metal dissolution, interfacial side reactions and rate performance attenuation under high voltage (≥4.5V) working conditions. In the present invention, the vapor deposition rate of S3 can reach 5 nm / min (10 times higher than that of the liquid phase method), the film thickness uniformity CV<8%, and no high-temperature sintering step is required, providing a positive electrode interface solution for high-voltage lithium-ion batteries with both high performance and industrial feasibility. In addition, after the present invention adopts the existing process to prepare the positive electrode sheet rough blank, the positive electrode sheet rough blank can be further processed. There is no need to change the existing positive electrode sheet production process. Only steps S2-4 need to be added, which can be more conveniently promoted and applied.

[0027] The present invention's high-voltage lithium-ion battery cathode, based on vapor-phase epitaxial growth of a COF molecular sieve interface and its preparation method, can address issues such as transition metal dissolution, capacity decay, and limited rate performance caused by side reactions at the cathode / electrolyte interface at high voltages (>4.5 V). Traditional polymer coatings (such as PVDF) struggle to balance ion screening and interface stability due to uncontrollable pore size and the tendency for electrode corrosion during liquid-phase modification. This invention, through innovative interface structure design and vapor-phase processing, achieves synergistic optimization of subnanometer-scale ion selective transport and interface strengthening.

[0028] The present invention is also applicable to the preparation of positive electrode sheets of doped positive electrode active materials such as lithium nickel cobalt manganese aluminum oxide (NCMA). The sulfonated COF layer is expected to synergistically improve the performance of the positive electrode sheet with the doped atoms.

[0029] Based on the same inventive concept, the present invention further provides: a positive electrode plate for a lithium-ion battery, which is prepared by the preparation method described above.

[0030] Based on the same inventive concept, the present invention further provides: a lithium-ion battery comprising the lithium-ion battery positive electrode sheet as described above.

[0031] The technical solution adopted by the present invention can be adapted to both liquid battery and solid-state battery systems.

[0032] When the cathode electrode of this invention is applied to a solid-state battery system, the solid electrolyte can be selected from a sulfide system (such as Li6PS5Cl), an oxide system (such as lithium lanthanum zirconate (LLZO)), or a polymer-ceramic composite electrolyte (such as a composite electrolyte of PVDF-HFP polymer and LLZTO). The COF layer has a mechanical modulus of approximately 15-25GPa and exhibits plastic deformation capability, which can buffer stress concentration at the rigid interface of the solid electrolyte (for example, the mechanical modulus of LLZO is approximately 150GPa). Combined with the gradient distribution of sulfonic acid groups within the COF layer, it creates a single-channel lithium ion transport pathway, effectively blocking lithium dendrite growth caused by electron leakage. Furthermore, after laminating the three-layer structure of the cathode electrode and solid-state electrolyte (positive electrode active material layer + COF layer + solid-state electrolyte), hot pressing at 80-120°C and 10-30 MPa can achieve interface integration.

[0033] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses vapor phase epitaxial growth and gradient sulfonation processes to construct a COF molecular sieve layer with precise pore size and mechanical stability at the interface of the positive electrode active material layer, achieving multiple technological breakthroughs: (1) Synergistic optimization of ion transport and screening performance. The sulfonic acid groups are distributed in a gradient within the COF layer, and the pore size of the COF layer is precisely controlled (1.8±0.1 nm), which increases the lithium ion migration number to above 0.85. At the same time, Ni 2+ The permeation of transition metal ions is suppressed to below 5 ppm / cycle.

[0034] (2) The high-voltage cycling stability is significantly improved. The mechanical modulus of the COF layer is not less than 15 GPa, which can effectively inhibit the expansion of the electrode (positive electrode active material layer). Combined with the zero solvent residue characteristics of the gas phase process, the capacity retention rate after 500 cycles at a high voltage of 4.5V is ≥90% (unmodified positive electrode ≤76%).

[0035] (3) A breakthrough has been achieved in rate performance. The vertically penetrating pore structure in the COF layer can significantly reduce the energy barrier for lithium ion transmission. The 5C rate discharge capacity can reach more than 160 mAh / g, and the retention rate of the 5C discharge capacity relative to the 0.1C discharge capacity is ≥85%.

[0036] (4) The advantages of industrial application are outstanding. The vapor phase epitaxy growth rate is increased to 5 nm / min (a significant increase compared to the liquid phase method), and the film thickness uniformity (CV <8%) and process stability are significantly improved. At the same time, the high-temperature sintering step can be avoided, which reduces the overall cost and fully adapts to the needs of large-scale production. In addition, the vapor phase epitaxy growth step and the vapor phase sulfonation modification step are both performed after the preparation of the cathode electrode rough blank. There is no need to adjust the existing preparation process of the cathode electrode rough blank, which is conducive to promotion and application.

[0037] (5) Compatibility with solid-state batteries: By matching the mechanical modulus of the COF layer of 15-25 GPa with the stiffness of the solid electrolyte, interfacial peeling can be effectively suppressed; the construction of gradient sulfonic acid channels can achieve single-ion conduction of lithium ions and block the growth of lithium dendrites caused by electron leakage; at the same time, the all-gas phase process avoids solvent contact, completely circumventing the risk of corrosion of the solid electrolyte by the liquid phase coating method, and also avoids adverse effects on the positive electrode active material layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the construction process of the COF molecular sieve interface structure of Example 1.

[0039] Figure 2 is the sulfonation process parameter-performance correlation diagram, where Figure 2 a is the relationship between surface sulfonic acid density and time; Figure 2 b is the relationship between Ni penetration and time; Figure 2 c is a graph showing the relationship between aperture change and time.

[0040] Figure 3 The figure is a comparison chart of the film thickness uniformity of Example 1, Comparative Example 1 and Comparative Example 7.

[0041] Figure 4 These are the cycle performance curves of Example 1, Example 5, Comparative Example 1, Comparative Example 3, and Comparative Example 7.

[0042] Figure 5 This is the rate performance curve of Example 1.

[0043] Figure 6 A bar chart comparing the number of lithium ion transferences.

[0044] Figure 7 Schematic diagram of the VPE deposition device.

[0045] Figure 8 The SEM comparison of the pole piece after cycling (wherein, Figure 8 a is the SEM of the positive electrode sheet after 500 cycles of Example 1, Figure 8 b is the SEM of the positive electrode sheet of Comparative Example 6 after 300 cycles).

[0046] Figure 9 Schematic diagram of the solid-state battery interface structure of Example 5.

[0047] Figure 10 This is the TEM image of the COF layer of Comparative Example 7. DETAILED DESCRIPTION

[0048] The present invention will be described in detail below with reference to the embodiments. It should be noted that the embodiments and features of the embodiments of the present invention can be combined with each other without conflict.

[0049] All examples and comparative examples adopt a unified method to prepare electrode sheets (NCM811 electrode sheets, NCA electrode sheets), and the specific process is as follows: First, the high voltage lithium-ion battery cathode material (from Xinxiang Tianli Lithium Energy, NCM811 model TLD806, chemical composition LiNi 0.8 Co0.1Mn 0.1 O2; NCA model is TLP910A, chemical composition LiNi 0.8 Co 0.15 Al 0.05 O2), conductive carbon black (Super P) and binder (PVDF) are mixed in a mass ratio of 96:2:2, and a solvent (N-methylpyrrolidone) is added. After 4 hours of vacuum ball milling, a homogeneous slurry with a solid content of 70wt% is formed; the slurry is then evenly coated on a 20 μm thick aluminum foil current collector (control surface density is 20 mg / cm²), and air-dried at 120°C for 2 hours to completely remove the solvent; finally, it is densified by roller pressing at a pressure of 10 MPa and cut into circular pole pieces with a diameter of 14 mm to ensure that the active material loading is precisely controlled at 4.5 mg / cm².

[0050] The performance testing and characterization instruments and methods used in the relevant embodiments and comparative examples are as follows: (1) Physical characterization: Film thickness uniformity: in-situ ellipsometer (Sentech SE850), CV value = standard deviation / mean × 100%.

[0051] Pore ​​size distribution: N2 adsorption-desorption (Micromeritics ASAP 2460), NLDFT model fitting.

[0052] Mechanical modulus test: A nanoindenter (Keysent G200) with a Berkovich probe was used, with a loading rate of 0.5 mN / s and a Poisson's ratio of 0.3.

[0053] Surface morphology: Scanning electron microscopy (SEM, Hitachi SU8010) combined with energy dispersive spectroscopy (EDS).

[0054] (2) Electrochemical test: Liquid battery assembly: negative electrode: lithium sheet; electrolyte: 1 M LiPF6 in EC / DMC (1:1 vol%); testing equipment: Blue Power CT3001A.

[0055] Solid-state battery assembly: anode: metallic lithium; solid-state electrolyte: Li6PS5Cl / LLZO; equipment: argon glove box (H2O <0.1 ppm).

[0056] Cycling performance: 4.5 V cutoff, 1C constant current charge and discharge, record the capacity retention rate for 500 times (liquid battery) or 300 times (solid-state battery); rate performance: 0.1C to 5C step discharge, calculate the 5C capacity retention rate.

[0057] Ion mobility shift number: Bruce-Vincent method (polarization voltage 10 mV).

[0058] Interfacial impedance: AC impedance spectroscopy (Chenhua CH760e electrochemical workstation), frequency 1 MHz~0.1 Hz, amplitude 10 mV.

[0059] Critical current density (CCD): step current method (0.2 mA / cm 2 Stepping, 10 min / step), voltage dip > 50% is considered failure.

[0060] Low temperature performance: After being placed in a -40℃ constant temperature box (Kejing MSK-TE906-150L) for 24 hours, 0.1C discharge test was performed.

[0061] Example 1 In this embodiment, the preparation process of the positive electrode sheet is as follows: (1) Substrate activation: The NCM811 electrode sheet was immersed in a 5 vol% APTES / toluene solution and reacted at 80°C for 2 hours under a continuous nitrogen flow of 15 sccm. The sheet was then rinsed three times with toluene and dried in a vacuum at 120°C to obtain a modified lithium-ion battery positive electrode sheet. XPS characterization showed that the N 1s peak intensity increased to 3.2 times the initial value, confirming the successful construction of amino anchor sites.

[0062] (2) Vapor phase epitaxial growth: at a vacuum of 5×10 -3 Pa, reaction chamber with a temperature of 180°C (see the schematic diagram for the specific structure Figure 7, keeping the positive electrode active material layer parallel to the horizontal plane and facing downward to enhance deposition efficiency and consistency), 50 cycles of deposition were performed on the surface of the positive electrode active material layer of the modified lithium-ion battery positive electrode blank to obtain a COF layer-loaded electrode sheet; wherein, each cycle sequentially performed the following steps: first, Tp (1,3,5-triformylphloroglucinol) monomer was delivered with 10 sccm nitrogen carrier gas and adsorbed for 30 seconds; then, it was switched to 50 sccm nitrogen purge for 20 seconds to remove by-products, and finally, Pa (p-phenylenediamine) was delivered with 10 sccm nitrogen carrier gas for 40 seconds of condensation reaction. The reaction process is shown in FIG. Figure 1 During this period, the single-cycle growth rate (0.4 nm / cycle) was monitored in real time by a quartz crystal microbalance, and the film thickness was measured by in-situ ellipsometer to be 21±1 nm (CV=6%).

[0063] (3) Vapor-phase sulfonation: The COF-loaded electrode was placed in a 0.1 MPa SO3 atmosphere and reacted at 150°C for 1 hour to obtain a lithium-ion battery positive electrode. X-ray photoelectron spectroscopy layer-by-layer etching (argon ion sputtering) showed that the sulfur (S 2p) element density decreased from 2.1 mmol / g on the surface of the lithium-ion battery positive electrode to 0.6 mmol / g on the substrate (positive electrode active material layer).

[0064] In this example, the TpPa-COF system was selected. Tp and Pa condensed to form a β-ketoenamine structure. The theoretical pore size of the β-ketoenamine structure is about 1.82 nm (which can be obtained through DFT calculation). Nitrogen adsorption and desorption tests showed that the specific surface area of ​​the obtained COF layer was 1680 m 2 / g, indicating that the pores in the COF layer have high permeability.

[0065] See also Figure 2 The pore size of the COF layer in Example 1 is about 1.78 nm. Based on Example 1, experiments were further conducted under other sulfonation time conditions (i.e., only the reaction time in step (3) was changed). It can be seen that controlling the appropriate reaction time is helpful to control the effective pore size of the COF layer and the density of the sulfonic acid groups on the surface of the COF layer, thereby reducing the Ni permeability.

[0066] Example 2 Example 1 was repeated, except that the APTES concentration in step (1) was adjusted to 2 vol%. XPS showed that the N 1s peak intensity only increased to 1.8 times the initial value.

[0067] Example 3 Example 1 was repeated, except that in step (2), the number of cycles was 40 (other steps were the same as in Example 1), and the film thickness was 16±2 nm (QCM data: 0.4 nm / cycle).

[0068] Example 4 Example 1 was repeated, except that in step (1), NCA electrode plates were used instead of NCM811 electrode plates, and the APTES concentration was 3 vol%. Other conditions were the same as in Example 1.

[0069] Example 5 First, the lithium-ion battery positive electrode prepared in Example 1 was used, and then the argyrodite-type sulfide solid electrolyte (Li6PS5Cl) powder was cold-pressed into an electrolyte layer with a thickness of 200 μm; Figure 9 After stacking the positive electrode active material layer, COF layer and electrolyte layer in sequence, they are hot pressed at 120°C and 20 MPa pressure for 10 minutes to achieve interface fusion; finally, a button-type solid-state battery is assembled with metallic lithium as the negative electrode to complete the full battery integration.

[0070] Comparative Example 1 Example 1 was repeated, except that step (1) was omitted and VPE deposition was performed directly (other steps were the same as in Example 1).

[0071] Comparative Example 2 Example 1 was repeated, except that in step (2), the number of cycles was 70 (other conditions were the same as in Example 1), and the film thickness was 28±3 nm (CV=15%).

[0072] Comparative Example 3 Example 1 was repeated, except that the gas phase sulfonation step (i.e., step (3)) was omitted.

[0073] Comparative Example 4 Example 1 was repeated, with the only difference being that the gas phase sulfonation step (i.e., step (3)) was replaced by liquid phase sulfonation, i.e., the electrode loaded with the COF layer was immersed in a dichloroethane solution of 1 M chlorosulfonic acid and reacted at 25°C for 1 hour (other conditions were the same as in Example 1).

[0074] Comparative Example 5 Example 1 was repeated, with the only difference being that in step (2), the nitrogen purge step was omitted (other steps were the same as in Example 1).

[0075] Comparative Example 6 Example 5 was repeated, with the only difference being that the positive electrode of the lithium-ion battery prepared in Example 1 was replaced by an NCM811 electrode (i.e., an electrode that was not substrate activated, not loaded with a COF layer, and not sulfonated). Other steps were the same as in Example 5.

[0076] See also Figure 8The positive electrode sheet of the present invention remained intact after 500 cycles, while the active material particles of the conventional NCM811 electrode sheet showed significant breakage after 300 cycles. This shows that the positive electrode sheet of the present invention exhibits higher structural stability during service.

[0077] Comparative Example 7 Example 1 was repeated, except that the aldehyde monomer was replaced by 2,6-naphthalenedicarbaldehyde (NDA) and the diamine monomer was replaced by 4,4'-diaminodiphenylmethane (DDM).

[0078] The results show that: The combination of NDA and DDM leads to significant pore structure collapse. Nitrogen adsorption and desorption tests show that the surface area of ​​the resulting COF layer is only 182 m 2 / g, compared with 1680 m 2 / g dropped by nearly an order of magnitude, and more than 85% of the effective pore size is less than 0.8 nm, which cannot meet the size requirements for lithium ion transmission. Figure 10 Combined with transmission electron microscopy (TEM) observations, it can be inferred that the naphthalene ring plane of NDA is excessively densely packed between layers due to the strong π-π stacking effect, resulting in irreversible collapse of the pore network.

[0079] Comparative Example 8 Example 1 was repeated, with the only difference being that in step (2), the temperature in the reaction chamber was controlled to be 150°C.

[0080] The lithium ion migration number dropped to 0.32, and the 5C rate discharge capacity of the resulting liquid battery was 63.6 mAh / g, which was significantly lower than that in Example 1. The possible reason was that the low temperature environment of 150°C resulted in insufficient monomer condensation reaction, and the β-ketoenamine structural defect rate in the COF skeleton was significantly increased compared with that in Example 1, thereby causing pore distortion and failing to form a COF molecular sieve layer with regular ion channels, resulting in performance degradation.

[0081] Comparative Example 9 Example 1 was repeated, except that in step (2), the temperature in the reaction chamber was controlled to be 200°C.

[0082] The results showed that the performance of the resulting lithium-ion battery cathode was significantly reduced. This was likely due to the high reaction temperature. The high temperature environment caused an abnormally high crosslink density, which accumulated stress within the COF layer, forming micron-sized cracks and making it difficult to obtain a structurally intact COF layer. During cycling, the electrolyte penetrated the cathode interface along these cracks, triggering side reactions such as transition metal dissolution. After 200 cycles, the direct current internal resistance (DCIR) increased significantly compared to Example 1.

[0083] See also Figure 3The COF layer of the electrode plate prepared by the method of the present invention has excellent film thickness uniformity, while when the substrate activation is not performed or the COF layer is prepared by using other monomers, the film thickness uniformity is poor.

[0084] See also Figure 4 The capacity retention rate of the liquid battery assembled with the positive electrode sheet of the lithium-ion battery prepared by the method of the present invention is as high as 92.5% after 500 cycles, and the capacity retention rate of the solid-state battery assembled therefrom is as high as 90% after 300 cycles. Figure 5 The liquid battery assembled with the lithium ion battery positive electrode sheet prepared by the method of the present invention has a high discharge capacity under the rate condition of 0.1~5C.

[0085] See also Figure 6 The lithium ion battery positive electrode sheet prepared by the method of the present invention has a higher lithium ion migration number.

[0086] The performance test results of various embodiments and comparative examples are shown in Table 1.

[0087]

[0088] Note: In Table 1, the capacity retention rate refers to the capacity retention rate after 500 cycles.

[0089] From the comparison of the data in Table 1, it can be seen that activating the substrate first and then performing vapor phase epitaxial growth can help obtain a COF layer with a smaller coefficient of variation and make the resulting positive electrode exhibit better electrochemical performance. The possible reasons are as follows: through substrate activation, the adhesion of the in-situ generated COF layer can be enhanced, and chemical anchoring sites can be constructed on the surface of the positive electrode active material layer to avoid the COF layer from peeling off due to electrode volume expansion during high voltage cycling, thereby improving the cycle performance; the anchored amino group regulates the epitaxial growth orientation, and the -NH2 group reacts with the COF monomer (aldehyde group of Tp) in a direction to induce the COF lattice to grow in a direction perpendicular to the positive electrode active material layer, ensuring vertical penetration of the pores; in addition, substrate activation is conducive to eliminating interface impedance, replacing the traditional physical coating method, forming a covalent bonding interface, and reducing Li + The transmission energy barrier helps to increase the ion migration number.

[0090] The chemical mechanism of step (1) in Example 1 is explained as follows: The -OH on the surface of the positive active material layer of the NCM811 electrode plate reacts with the ethoxy group of APTES to form a Si-OM bond, exposing the terminal -NH2, which then anchors the -NH2 on the surface of the positive active material layer to achieve substrate activation. The relevant reaction formula is as follows: Step 1 (hydrolysis): (EtO)3Si-(CH2)3-NH2+3H2O→(HO)3Si-(CH2)3-NH2+3EtOH; Step 2 (condensation): NCM811-OH+(HO)3Si-(CH2)3-NH2→NCM811-O-Si-(CH2)3-NH2+H2O.

[0091] As can be seen from the data in Table 1, the CV value of the positive electrode obtained by first activating the substrate and then performing vapor phase epitaxial growth is significantly lower. The possible reason is that the -NH2 anchored during substrate activation has a template effect: the Tp aldehyde group preferentially condenses with the anchoring site, inducing the COF lattice to grow vertically along the crystal plane, which helps to obtain a COF layer with more regular pores and more uniform film thickness. The chemical reaction formula that occurs during vapor phase epitaxial growth is as follows: Tp(-CHO)3+Pa(-NH2)2→TpPa-COF(-C=N-)+3H2O.

[0092] It can be seen from Example 1, Comparative Example 3 and Comparative Example 4 that the use of gas-phase sulfonation modification helps to more effectively improve the electrochemical properties such as cycle performance and reduce the permeability of transition metal ions such as nickel ions. The possible reason is that by introducing sulfonic acid groups into the pores of the COF layer, its ion selectivity can be precisely controlled, so that the positive electrode sheet preferentially adsorbs Li by electrostatic action. + and excludes polyvalent metal ions (Ni 2+ 、Co 3+ etc.), realizing the "ion screening" function; the use of gas-phase sulfonation modification method instead of the traditional liquid-phase method (such as the common chlorosulfonic acid solution) can eliminate the risk of solvent corrosion on the COF film and electrode substrate, avoid interfacial corrosion, and ensure the integrity and stability of the positive electrode active material layer, current collector, etc.; in addition, the introduction of sulfonic acid groups in the COF layer can enhance the compatibility of the COF layer with the electrolyte, inhibit side reactions under high voltage, improve interfacial stability, and thus improve the battery cycle life.

[0093] The present invention further explains the specific reaction mechanism and mechanism of action of the gas-phase sulfonation modification process in Example 1 as follows: (1) Chemical bonding process during gas-phase sulfonation modification "SO3 gas" → "penetrates the pores of the COF layer" → "reacts with the imine bond (-C=N-)" → "forms a sulfonamide group (-CN-SO3H)".

[0094] The reaction formula is as follows: COF-C=N+SO3→COF-CN-SO3H.

[0095] (2) Ion transport regulation mechanism Li+ Selective transport: the negatively charged pores of -SO3H attract Li + , while blocking Ni by size screening and electrostatic repulsion 2+ Equi-sized multivalent ions.

[0096] Desolvation promotion: sulfonic acid groups compete with EC solvent (the main component of the electrolyte) to coordinate Li + , weakening Li + -EC binding energy, reducing the desolvation energy barrier.

[0097] In Example 1, the sulfur (S 2p) element density decreases from 2.1 mmol / g on the surface of the lithium-ion battery positive electrode to 0.6 mmol / g on the substrate (positive electrode active material layer). A gradient-decreasing structure of sulfonic acid groups is constructed within the COF layer, which can simultaneously optimize interfacial ion transport kinetics and chemical stability: the sulfonic acid group density is higher near the solid electrolyte side, providing a fast lithium ion channel, while the sulfonic acid group density adjacent to the positive electrode active material layer is lower, helping to effectively inhibit oxidative corrosion of the sulfonic acid groups on the positive electrode material under high voltage. At the same time, the gradient change buffers the interfacial stress during the charge and discharge process. The present invention attempts to explain the relevant reasons as follows: (1) Diffusion-reaction competition model According to Fick's diffusion law, the concentration of gas in the pores of the COF layer decays exponentially with depth, causing the concentration of sulfonic acid groups in the surface COF layer to be greater than that in the bottom layer, forming a gradient sulfonic acid group structure.

[0098] (2) Synergistic effect of temperature field Substrate heat conduction effect: The thermal conductivity of the NCM811 electrode plate is greater than that of the COF layer, resulting in a lower substrate interface temperature and a higher COF surface temperature. The reaction rate constant obeys the Arrhenius equation, causing the gas sulfonation reaction on the COF surface to be more complete than that on the substrate, forming a gradient sulfonic acid group structure.

[0099] Ion migration number (t + )≥0.85, indicating that the pores in the COF layer of the obtained positive electrode are Li + The transmission of ions is highly selective (other ions are screened). The rate performance (5C) of the liquid batteries assembled with the positive electrode sheets of Examples 1-4 can reach above 152 mAh / g, indicating that the pore size of the COF layer of the obtained positive electrode sheet is suitable for the rapid desolvation of Li + transmission.

[0100] The performance test results of the solid-state batteries of Example 5 and Comparative Example 6 are shown in Table 2.

[0101]

[0102] As can be seen from Table 2, the solid-state battery assembled using the positive electrode sheet of the present invention has significantly better performance in terms of cycle performance, lithium ion migration number, interface impedance, CCD, low-temperature discharge capacity, etc. than the solid-state battery assembled using the traditional positive electrode sheet.

[0103] The Chinese and English comparison table of the professional terms involved in the present invention is shown in Table 3.

[0104]

[0105] The contents illustrated in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. After reading the present invention, various equivalent modifications of the present invention by those skilled in the art shall fall within the scope defined by the claims attached to this application.

Claims

1. A method for preparing a positive electrode sheet for a lithium-ion battery, characterized in that: The steps include: S1. Provide lithium-ion battery positive electrode sheet rough blank; The lithium-ion battery positive electrode sheet blank comprises a current collector and a positive electrode active material layer stacked in sequence; the positive electrode active material in the positive electrode active material layer comprises one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium nickel cobalt manganese aluminum oxide; S2, immersing the lithium ion battery positive electrode sheet blank in an organic solution of a silane coupling agent, and after reaction, washing and drying, to obtain a modified lithium ion battery positive electrode sheet blank; S3, preparing a COF layer on the surface of the positive electrode active material layer of the modified lithium ion battery positive electrode sheet rough blank by a vapor phase epitaxial growth method to obtain a lithium ion battery positive electrode sheet rough blank loaded with the COF layer; S4, performing vapor phase sulfonation modification on the rough lithium ion battery positive electrode sheet loaded with the COF layer to obtain a lithium ion battery positive electrode sheet.

2. The preparation method according to claim 1, characterized in that In S1, the chemical formula of lithium nickel cobalt manganese oxide is LiNi x Co y Mn 1-x-y O2, where 0.6 ≤ x < 1, 0 < y < 1, and x + y < 1; the chemical formula of lithium nickel cobalt aluminum oxide is LiNi x Co y Al z O2, where 0.6 ≤ x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1; the chemical formula of lithium nickel cobalt manganese aluminum oxide is LiNi x Co y Mn z Al w O2, where 0.6 ≤ x < 1, 0 < y < 1, 0 < z < 1, 0 < w < 0.1, and x + y + z + w = 1.

3. The preparation method according to claim 1, characterized in that In S2, the concentration of the silane coupling agent in the organic solution is 1-10 vol%, and the silane coupling agent includes one or two of APTES and AEAPTMS; the solvent in the organic solution includes one or more of toluene, xylene, and cyclohexane.

4. The preparation method according to claim 1, characterized in that In S2, the lithium-ion battery positive electrode sheet rough blank is immersed in an organic solution of a silane coupling agent, reacted at 70-90°C for 1-3 hours under the condition of continuous introduction of an inert gas, and then washed and dried to obtain a modified lithium-ion battery positive electrode sheet rough blank; wherein the flow rate of the inert gas is controlled to be 5-30 sccm, and the inert gas includes one or both of nitrogen and argon.

5. The preparation method according to claim 1, characterized in that In S3, when performing vapor phase epitaxial growth, the modified lithium ion battery positive electrode blank is placed in a vacuum of ≤5×10 -2 In the reaction chamber of Pa, 40-60 cycles of deposition are carried out at 160-200°C to obtain a rough blank of a lithium-ion battery positive electrode sheet loaded with a COF layer; In each deposition cycle, the following steps are performed in sequence: first, nitrogen is used as a carrier gas to deliver aldehyde monomers into the reaction chamber for 20-40 seconds; then, inert gas is introduced into the reaction chamber and purged for 15-25 seconds; finally, nitrogen is used as a carrier gas to deliver diamine monomers into the reaction chamber for 30-50 seconds; Among them, the aldehyde monomer includes one or more of 1,3,5-triformylphloroglucinol, 2,4,6-triformyl-s-triazine, 2,5-dihydroxyterephthalaldehyde, 2,5-dimethoxyterephthalaldehyde, 2,5-dichloroterephthalaldehyde, and 2,3,5,6-tetrafluoro-p-dibenzaldehyde; the diamine monomer includes one or more of p-phenylenediamine, benzidine, m-phenylenediamine, and o-phenylenediamine; and the inert gas is nitrogen and / or argon.

6. The preparation method according to any one of claims 1 to 5, characterized in that In S4, the lithium ion battery positive electrode sheet blank loaded with the COF layer is placed in a sulfonating agent atmosphere for gas-phase sulfonation modification to obtain a lithium ion battery positive electrode sheet; wherein the sulfonating agent is SO3 gas, chlorosulfonic acid vapor or SO3-dioxane complex, and the molar ratio of SO3 to dioxane in the SO3-dioxane complex is 1:1-3.

7. The preparation method according to claim 6, characterized in that The rough lithium-ion battery positive electrode sheet loaded with the COF layer is placed in a sulfonating agent atmosphere of 0.05-0.15 MPa and subjected to gas-phase sulfonation modification at 140-160° C. for 0.5-2 hours.

8. The preparation method according to claim 7, characterized in that The thickness of the COF layer is 14-24 nm.

9. A positive electrode plate for a lithium-ion battery, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

10. A lithium ion battery, characterized in that: The invention comprises the lithium-ion battery positive electrode sheet as claimed in claim 9.

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