A double-layer composite multifunctional CEI membrane structure and a preparation method thereof

Abstract

The application relates to the technical field of lithium batteries and discloses a double-layer composite multifunctional CEI film structure and a preparation method thereof, which comprises a composite inner layer film and an outer layer protective film which are sequentially arranged from bottom to top on the surface of a positive electrode; the composite inner layer film comprises LiF, Li2ZrO3 and LiNbO3; and the outer layer protective film is Li3PO4. The double-layer composite multifunctional CEI film of the application is closely attached to the surface of the positive electrode, can provide excellent lithium ion conductivity, chemical stability and transition metal shielding capacity, and has good corrosion resistance, solvent resistance and mechanical strength, can effectively prevent the electrolyte from corroding the positive electrode, and can slow down the influence of the change of the particle volume on the film layer; the inner layer and the outer layer are combined to realize multifunctional synergistic effect, optimize the interface stability of the high-voltage positive electrode material, improve the electrochemical performance and the mechanical performance, and effectively improve the interface stability and the cycle life of the high-voltage positive electrode.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and more specifically, to a double-layer composite multifunctional CEI film structure and its preparation method. Background Technology

[0002] With the continuous development of electrochemical energy storage technology, high-energy-density batteries have become the core direction of next-generation energy storage systems. Among them, high-voltage cathode materials have attracted widespread attention due to their high specific capacity and operating voltage performance. However, high-voltage cathodes face a series of complex problems under long-term operating conditions, including intensified interfacial side reactions, dissolution and migration of transition metal ions, and mechanical damage caused by particle volume changes. These problems can lead to rapid degradation of battery performance, significantly limiting their application potential.

[0003] Under high voltage conditions, the chemical reaction at the interface between the cathode material and the electrolyte becomes more intense. The deposition of unstable byproducts not only increases the interfacial impedance but also reduces the reversibility of the electrochemical reaction. Simultaneously, transition metal ions readily dissolve under high voltage and migrate to the electrolyte or anode surface, triggering complex side reactions. Furthermore, the high-voltage cathode undergoes significant volume expansion and contraction during charging and discharging, making its internal particle structure susceptible to mechanical stress, leading to particle cracking and damage to the electrochemical interface film (CEI). This particle damage, exposing fresh interfaces, further exacerbates electrolyte decomposition and the continued occurrence of side reactions, creating a vicious cycle.

[0004] To address these issues, researchers have proposed several interface modification strategies, including surface coating, in-situ film formation, and liquid-phase coating. These methods, by constructing a chemically stable interfacial film on the cathode surface, mitigate side reactions to some extent and extend battery cycle life. However, these strategies also have significant drawbacks. Surface coating, due to insufficient film uniformity and density, is prone to film damage during particle volume changes; while in-situ film formation can improve interfacial compatibility, the film formation process is difficult to control precisely, resulting in insufficient film functionality; liquid-phase coating technology, although improving film uniformity, typically exhibits low mechanical strength and struggles to provide comprehensive functional protection. These technologies primarily focus on improving the electrochemical stability of the interface, but pay insufficient attention to mechanical damage caused by particle volume changes and the need for multifunctional interfacial films, making it difficult to meet the stability requirements of high-voltage cathodes during long-term cycling.

[0005] In view of the above, this application is hereby submitted. Summary of the Invention

[0006] The existing technology has the problem that current interface modification strategies mainly focus on improving the electrochemical stability of the interface, which is difficult to meet the stability requirements of high-voltage cathodes in long-term cycling. This paper proposes a bilayer composite multifunctional CEI film structure and its preparation method. The inner layer is closely attached to the cathode surface, providing excellent lithium-ion conductivity, chemical stability and transition metal shielding ability. The outer layer has good corrosion resistance, solvent resistance and mechanical strength, which can effectively block the electrolyte from eroding the cathode and mitigate the impact of particle volume changes on the film layer. The combination of the functions of the inner and outer layers achieves a multifunctional synergistic effect, optimizes the interface stability of the high-voltage cathode material, and improves the electrochemical and mechanical properties, effectively improving the interface stability and cycle life of the high-voltage cathode.

[0007] This invention is achieved through the following technical solution:

[0008] In a first aspect, the present invention provides a double-layer composite multifunctional CEI membrane structure, comprising a composite inner membrane and an outer protective membrane constructed sequentially from bottom to top on the surface of the positive electrode;

[0009] The composite inner layer film includes LiF, Li2ZrO3 and LiNbO3;

[0010] The outer protective film is Li3PO4.

[0011] High-voltage cathode materials face multiple challenges in complex operating environments, including interfacial side reactions, mechanical failure caused by volume changes, decreased electrochemical stability, and increased interfacial impedance. These are precisely the problems that the bilayer CEI film material of this invention aims to solve. This invention, through its bilayer film design, fully integrates the performance characteristics of the inner and outer layers, achieving multiple layers of chemical, mechanical, and electrochemical protection at the interface.

[0012] The inner layer film of this invention is set on the positive electrode surface to directly respond to the interfacial reaction of the positive electrode surface, and uses three components, LiF, Li2ZrO3 and LiNbO3, as the inner layer material.

[0013] LiF possesses an extremely high band gap (8.72 eV) and a low formation energy (-3.19 eV / atom). The high band gap provides LiF with excellent electronic insulation under battery operating conditions, effectively preventing electron leakage and inhibiting electrolyte decomposition. Its low formation energy ensures the material's chemical stability, helping to prevent the dissolution of transition metal ions and thus stabilizing the interface between the cathode and the electrolyte. LiF's low Poisson's ratio (0.2) indicates that the material exhibits small lateral deformation under stress, enabling it to withstand significant stress and effectively alleviate the mechanical stress generated by volume changes in the cathode material during charging and discharging, maintaining the stability of the interface layer. Furthermore, LiF also possesses a high shear modulus (50 GPa), further enhancing its resistance to deformation and ensuring the mechanical support of the film layer.

[0014] Li₂ZrO₃ possesses a moderate band gap (3.73 eV) and a low formation energy (-3.038 eV / atom), giving it good chemical stability in the inner layer film. Despite its moderate band gap, the crystal structure of Li₂ZrO₃ provides excellent lithium-ion migration channels, contributing to improved ionic conductivity and enhanced electrochemical stability of the film, ensuring stable battery operation at high voltages. The combination of Li₂ZrO₃'s Poisson's ratio (0.27) and shear modulus (55 GPa) gives it stronger stress mitigation capabilities, effectively addressing the mechanical stress caused by volume changes in the cathode material during charging and discharging, thereby reducing interfacial stress and improving the overall stability of the film.

[0015] LiNbO3 has a band gap of 3.34 eV and possesses a high Poisson's ratio (0.29) and good elasticity, providing strong interfacial bonding in the inner layer film. The high Poisson's ratio of LiNbO3 allows it to effectively adapt to lateral expansion while elongating longitudinally under stress, thus improving its adaptability to interfacial structures and crack resistance. Furthermore, LiNbO3 exhibits excellent electrochemical stability, helping to maintain the integrity of the interfacial film during long-term cycling and ensuring the stability of the cathode-electrolyte interface under high-voltage operating environments.

[0016] The inner layer film of this invention utilizes LiF, Li2ZrO3 and LiNbO3. Under high operating voltage conditions, this interface film can effectively inhibit electrolyte decomposition and transition metal ion dissolution, enhance lithium-ion conductivity, and improve the electrochemical stability of the cathode material.

[0017] The outer layer of this invention is disposed outside the inner layer and is in direct contact with the electrolyte. Li3PO4 is used as the outer layer material. Li3PO4 has a high band gap (5.82 eV), significantly higher than Li2ZrO3 and LiNbO3, which means it has excellent electronic insulation properties, effectively preventing the flow of electrons and thus reducing electrolyte decomposition reactions and side reactions. Furthermore, Li3PO4 itself also has high chemical stability, effectively isolating the inner layer and cathode particles from electrolyte erosion, ensuring long-term interface stability.

[0018] The bilayer composite multifunctional CEI membrane of this invention has an inner layer that directly contacts the cathode particles. Utilizing the excellent mechanical properties and low formation energy of LiF, Li₂ZrO₃, and LiNbO₃, it provides a chemical barrier, electrochemical stability, and stress mitigation. The outer layer, Li₃PO₄, acts as a protective barrier, and its high band gap and excellent chemical stability further enhance the overall membrane's corrosion resistance, mechanical strength, and long-term stability. Through the synergistic effect of the inner and outer layers, the bilayer composite multifunctional CEI membrane effectively addresses the multiple challenges of high-voltage cathodes under complex operating environments, comprehensively optimizes the interfacial stability of high-voltage cathode materials, and simultaneously improves electrochemical and mechanical properties. This effectively enhances the interfacial stability of the high-voltage cathode, thereby improving the overall performance and operational stability of high-energy-density batteries and extending their cycle life.

[0019] In one specific embodiment, the composite ratio of LiF, Li2ZrO3 and LiNbO3 in the composite inner layer film is 1:0.5-1:0.5-1.

[0020] The proportions of the components in this invention have been creatively optimized to balance the advantages of each component. LiF provides excellent electrochemical stability and high electronic insulation, effectively preventing electrolyte decomposition and transition metal ion dissolution, while Li₂ZrO₃ and LiNbO₃ primarily enhance the membrane's corrosion resistance, mechanical strength, and thermal stability. This proportioning design ensures excellent membrane stability and a long service life under high-voltage conditions.

[0021] If the proportion of Li₂ZrO₃ is too high, the membrane will be too dense, potentially inhibiting lithium-ion migration and thus affecting the ionic conductivity of the electrolyte, reducing the battery's charge-discharge efficiency. Simultaneously, an excessively high proportion of LiNbO₃ may make the membrane too rigid, leading to cracks during charge-discharge processes, affecting membrane integrity and the battery's long-term stability. Conversely, if the proportions of Li₂ZrO₃ and LiNbO₃ are too low, the membrane's corrosion resistance and thermal stability will be insufficient, making it prone to deterioration or rupture under high voltage or high temperature environments, thus affecting battery performance and safety.

[0022] Therefore, the optimized ratio of 1:0.5-1:0.5-1 can improve battery performance while ensuring the overall stability and reliability of the membrane, and effectively improve the overall safety and lifespan of the battery.

[0023] In one specific embodiment, the thickness of the composite inner layer film is 30-50 nm, and the thickness of the outer protective film is 50-80 nm.

[0024] The composite inner layer membrane is primarily responsible for electrochemical reactions, providing ionic conductivity, and stabilizing the battery interface. Therefore, a thinner inner layer membrane helps reduce the battery's internal resistance, improve ionic conductivity, and maintain high electrochemical stability.

[0025] The main function of the outer protective film is to provide mechanical strength, prevent electrolyte decomposition, and prevent the dissolution of materials such as Co. Therefore, the thickness of the film needs to be moderate to ensure sufficient corrosion resistance and mechanical strength, while not affecting the overall performance of the battery.

[0026] Secondly, the present invention provides a method for preparing a bilayer composite multifunctional CEI membrane structure, comprising the following steps:

[0027] (1) A composite inner layer film is coated on the surface of the positive electrode using a fluidized bed method;

[0028] (2) An outer protective film is prepared on the prepared composite inner layer film by magnetron sputtering.

[0029] In a specific implementation, the specific method of step (1) is as follows:

[0030] LiF, Li2ZrO3 and LiNbO3 were mixed in proportion and added to a dispersion solvent to prepare a uniform suspension.

[0031] The suspension is introduced into a fluidized tank and sprayed onto the surface of the positive electrode material substrate to form a film layer;

[0032] The membrane layer is subjected to low-temperature annealing to obtain the composite inner layer membrane.

[0033] In one specific embodiment, the dispersing solvent is ethanol or water, and a surfactant is also added to the suspension.

[0034] In one specific embodiment, the surfactant is one of sodium dodecyl sulfate, polyvinyl alcohol, and the Tween series.

[0035] In one specific embodiment, the low-temperature annealing conditions are an annealing temperature of 200-300℃ and an annealing time of 1-2 hours.

[0036] In a specific implementation, step (2) is performed as follows:

[0037] The cathode material substrate with the prepared composite inner layer film was placed in a magnetron sputtering apparatus. The target material was set as Li3PO4. The sputtering process parameters were as follows: argon gas was used as the sputtering gas in the chamber, the pressure was 0.8-1.2 Pa, the sputtering power was 50-120 W, the substrate temperature was 100-150℃, and the sputtering time was 20-40 min. A Li3PO4 film layer was deposited on the coated composite inner layer film.

[0038] The Li3PO4 film was subjected to low-temperature annealing to obtain an outer protective film.

[0039] In one specific embodiment, the low-temperature annealing conditions for the Li3PO4 film are an annealing temperature of 200-300℃ and an annealing time of 1-2 hours.

[0040] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0041] 1. This invention provides a bilayer composite multifunctional CEI film structure and its preparation method. By combining the functions of the inner and outer layers, a multifunctional synergistic effect is achieved. This bilayer composite multifunctional CEI film can effectively solve the multiple challenges of high-voltage cathodes under complex working environments, comprehensively optimize the interfacial stability of high-voltage cathode materials, and simultaneously improve electrochemical and mechanical properties. This effectively enhances the interfacial stability of the high-voltage cathode, thereby improving the overall performance and operational stability of high-energy-density batteries and extending their cycle life.

[0042] 2. The present invention provides a double-layer composite multifunctional CEI film structure and its preparation method. The inner layer film is in direct contact with the positive electrode particles, combining the advantages of the three components LiF, Li2ZrO3 and LiNbO3, which can effectively inhibit electrolyte decomposition and transition metal ion dissolution, enhance lithium-ion conductivity, and improve the electrochemical stability of the positive electrode material.

[0043] 3. The present invention provides a double-layer composite multifunctional CEI membrane structure and its preparation method. The outer membrane directly contacts the electrolyte and uses Li3PO4 as the outer protective material, which has extremely high chemical stability and can effectively isolate the electrolyte from the erosion of the inner membrane and the positive electrode particles. Although its shear modulus of 44 GPa is slightly low, it has excellent corrosion resistance and mechanical strength. While providing sufficient mechanical support, it also has stronger structural durability and interfacial bonding, which helps to prevent the mechanical stress caused by the volume change of the positive electrode particles during cycling, thus preventing the inner membrane from being exposed to the electrolyte due to volume change. This effectively blocks the electrolyte from eroding the positive electrode and mitigates the impact of particle volume change on the membrane.

[0044] 4. The bilayer composite multifunctional CEI membrane structure and its preparation method provided in this embodiment of the invention, through reasonable selection of inner and outer membrane materials and preparation methods, can significantly improve the cycle life and working stability of high energy density batteries, providing strong support for the development of high-performance batteries. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 The double-layer composite multifunctional CEI membrane structure provided in the embodiments of the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0048] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known materials or methods have not been specifically described in order to avoid obscuring the invention.

[0049] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "an embodiment," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0050] High-voltage cathode materials face multiple challenges in complex operating environments, including interfacial side reactions, mechanical failure caused by volume changes, decreased electrochemical stability, and increased interfacial impedance. To address these issues:

[0051] Firstly, such as Figure 1 As shown, the present invention provides a double-layer composite multifunctional CEI membrane structure, comprising a composite inner layer membrane and an outer protective membrane constructed sequentially from bottom to top on the surface of the positive electrode;

[0052] The composite inner layer film includes LiF, Li2ZrO3 and LiNbO3;

[0053] The outer protective film is Li3PO4.

[0054] This invention fully combines the performance characteristics of the inner and outer layer materials through the design of a double-layer film, enabling multiple protections of the interface, including chemical, mechanical, and electrochemical properties.

[0055] One thing to note is that Figure 1 This is merely a schematic diagram of the double-layer composite membrane and does not represent the actual internal structure of the inner composite membrane. Figure 1 The purpose is simply to illustrate that the composite inner membrane contains three components.

[0056] The inner layer film of this invention is disposed on the positive electrode surface to directly address the interfacial reaction on the positive electrode surface. It uses a composite of three components: LiF, Li₂ZrO₃, and LiNbO₃ as the inner layer material. The properties of each component are shown in Table 1.

[0057] Table 1

[0058]

[0059] LiF possesses an extremely high band gap (8.72 eV) and a low formation energy (-3.19 eV / atom). The high band gap provides LiF with excellent electronic insulation under battery operating conditions, effectively preventing electron leakage and inhibiting electrolyte decomposition. Its low formation energy ensures the material's chemical stability, helping to prevent the dissolution of transition metal ions and thus stabilizing the interface between the cathode and the electrolyte. LiF's low Poisson's ratio (0.2) indicates that the material exhibits small lateral deformation under stress, enabling it to withstand significant stress and effectively alleviate the mechanical stress generated by volume changes in the cathode material during charging and discharging, maintaining the stability of the interface layer. Furthermore, LiF also possesses a high shear modulus (50 GPa), further enhancing its resistance to deformation and ensuring the mechanical support of the film layer.

[0060] Li₂ZrO₃ possesses a moderate band gap (3.73 eV) and a low formation energy (-3.038 eV / atom), giving it good chemical stability in the inner layer film. Despite its moderate band gap, the crystal structure of Li₂ZrO₃ provides excellent lithium-ion migration channels, contributing to improved ionic conductivity and enhanced electrochemical stability of the film, ensuring stable battery operation at high voltages. The combination of Li₂ZrO₃'s Poisson's ratio (0.27) and shear modulus (55 GPa) gives it stronger stress mitigation capabilities, effectively addressing the mechanical stress caused by volume changes in the cathode material during charging and discharging, thereby reducing interfacial stress and improving the overall stability of the film.

[0061] LiNbO3 has a band gap of 3.34 eV, and its high Poisson's ratio (0.29) and good elasticity provide strong interfacial bonding in the inner layer film. The high Poisson's ratio of LiNbO3 allows it to effectively adapt to lateral expansion while elongating longitudinally under stress, thus improving its adaptability to interfacial structures and crack resistance. Furthermore, LiNbO3 exhibits excellent electrochemical stability, which helps maintain the integrity of the interfacial film during long-term cycling, ensuring the stability of the cathode-electrolyte interface under high-voltage operating environments.

[0062] The inner layer film of this invention utilizes LiF, Li2ZrO3 and LiNbO3. Under high operating voltage conditions, this interface film can effectively inhibit electrolyte decomposition and transition metal ion dissolution, enhance lithium-ion conductivity, and improve the electrochemical stability of the cathode material.

[0063] The outer layer of this invention is disposed outside the inner layer and is in direct contact with the electrolyte. Li3PO4 is used as the outer layer material. Li3PO4 has a high band gap (5.82 eV), significantly higher than Li2ZrO3 and LiNbO3, which means it has excellent electronic insulation properties, effectively preventing the flow of electrons and thus reducing electrolyte decomposition reactions and side reactions. Furthermore, Li3PO4 itself also has high chemical stability, effectively isolating the inner layer and cathode particles from electrolyte erosion, ensuring long-term interface stability.

[0064] The bilayer composite multifunctional CEI membrane of this invention has an inner layer that directly contacts the cathode particles. Utilizing the excellent mechanical properties and low formation energy of LiF, Li₂ZrO₃, and LiNbO₃, it provides a chemical barrier, electrochemical stability, and stress mitigation. The outer layer, Li₃PO₄, acts as a protective barrier, and its high band gap and excellent chemical stability further enhance the overall membrane's corrosion resistance, mechanical strength, and long-term stability. Through the synergistic effect of the inner and outer layers, the bilayer composite multifunctional CEI membrane effectively addresses the multiple challenges of high-voltage cathodes under complex operating environments, comprehensively optimizes the interfacial stability of high-voltage cathode materials, and simultaneously improves electrochemical and mechanical properties. This effectively enhances the interfacial stability of the high-voltage cathode, thereby improving the overall performance and operational stability of high-energy-density batteries and extending their cycle life.

[0065] In one specific embodiment, the composite ratio of LiF, Li2ZrO3 and LiNbO3 in the composite inner layer film is 1:0.5-1:0.5-1.

[0066] The proportions of the components in this invention have been creatively optimized to balance the advantages of each component. LiF provides excellent electrochemical stability and high electronic insulation, effectively preventing electrolyte decomposition and transition metal ion dissolution, while Li₂ZrO₃ and LiNbO₃ primarily enhance the membrane's corrosion resistance, mechanical strength, and thermal stability. This proportioning design ensures excellent membrane stability and a long service life under high-voltage conditions.

[0067] If the proportion of Li₂ZrO₃ is too high, the membrane will be too dense, potentially inhibiting lithium-ion migration and thus affecting the ionic conductivity of the electrolyte, reducing the battery's charge-discharge efficiency. Simultaneously, an excessively high proportion of LiNbO₃ may make the membrane too rigid, leading to cracks during charge-discharge processes, affecting membrane integrity and the battery's long-term stability. Conversely, if the proportions of Li₂ZrO₃ and LiNbO₃ are too low, the membrane's corrosion resistance and thermal stability will be insufficient, making it prone to deterioration or rupture under high voltage or high temperature environments, thus affecting battery performance and safety.

[0068] Therefore, the optimized ratio of 1:0.5-1:0.5-1 can improve battery performance while ensuring the overall stability and reliability of the membrane, and effectively improve the overall safety and lifespan of the battery.

[0069] In one specific embodiment, the thickness of the composite inner layer film is 30-50 nm, and the thickness of the outer protective film is 50-80 nm.

[0070] The composite inner layer membrane is primarily responsible for electrochemical reactions, providing ionic conductivity, and stabilizing the battery interface. Therefore, a thinner inner layer membrane helps reduce the battery's internal resistance, improve ionic conductivity, and maintain high electrochemical stability.

[0071] The main function of the outer protective film is to provide mechanical strength, prevent electrolyte decomposition, and prevent the dissolution of materials such as Co. Therefore, the thickness of the film needs to be moderate to ensure sufficient corrosion resistance and mechanical strength, while not affecting the overall performance of the battery.

[0072] Secondly, the present invention provides a method for preparing a bilayer composite multifunctional CEI membrane structure, comprising the following steps:

[0073] (1) Select high voltage positive electrode material as substrate; First, clean the surface of the substrate to remove impurities, and ensure that the surface of the substrate is free of moisture and impurities through drying treatment to ensure uniformity and adhesion during film deposition.

[0074] (2) Mix LiF, Li2ZrO3 and LiNbO3 in a predetermined ratio to form a uniform suspension. The dispersant is either ethanol or deionized water. To ensure uniform dispersion of the powder, add an appropriate amount of surfactant (the surfactant is one of sodium dodecyl sulfate (SLS), polyvinyl alcohol (PVA) or Tween series) and use ultrasonic treatment to ensure uniform dispersion of the powder and avoid particle agglomeration.

[0075] (3) The prepared suspension is introduced into the fluidized tank and the airflow is controlled to spray the suspension onto the substrate surface. The airflow in the fluidized tank helps the particles to be evenly distributed on the substrate surface, forming a uniform inner film. By adjusting the airflow rate, spraying time and coating liquid concentration, the uniformity and density of the film layer are ensured. The particles are in a fluidized state under the action of airflow, which can achieve a good coating effect.

[0076] (4) After the spraying is completed, the inner layer film is subjected to low-temperature annealing treatment. The temperature range is 200-300℃ and the annealing time is 1-2 hours to optimize the crystal structure and interfacial bonding of the film layer, improve the conductivity and stability of the film layer, and obtain the composite inner layer film.

[0077] (5) After the composite inner layer film has been deposited and stabilized on the substrate surface, replace the target material in the magnetron sputtering equipment with Li3PO4 to ensure the cavity is clean and avoid cross-contamination; set the sputtering process parameters: use argon gas as sputtering gas in the cavity, adjust the pressure to 0.8-1.2Pa, the sputtering power to 50-120W, set the substrate temperature to 100-150℃, and the sputtering time to 20-40 minutes; the outer layer film will be uniformly deposited on the substrate surface coated with the composite inner layer film by magnetron sputtering technology.

[0078] (6) After sputtering, a low-temperature annealing treatment is performed. The annealing temperature range is 200-300℃, and the annealing time is 1-2 hours to obtain the outer protective film. Annealing treatment can improve the mechanical stability and corrosion resistance of the outer film, and enhance the bonding force between the outer film and the inner film, ensuring the overall stability and durability of the film layer.

[0079] Example 1

[0080] This invention provides a method for preparing a bilayer composite multifunctional CEI membrane structure, comprising the following steps:

[0081] (1) Inner membrane material ratio and preparation

[0082] LiF, Li₂ZrO₃, and LiNbO₃ were mixed in a ratio of 1:0.8:0.7, and the mixture was ball-milled for 4 hours to ensure uniform particle mixing. Ethanol was used as the dispersion medium, and 0.1% sodium dodecyl sulfate (SLS) was added. The mixture was then ultrasonically dispersed for 30 minutes to obtain a homogeneous suspension.

[0083] (2) Fluidized tank coating

[0084] High-voltage cathode material (LiCoO2) particles are placed in a fluidized bed to keep the particles uniformly suspended. The suspension is then uniformly sprayed into the fluidized bed using an aerosol spraying device at a spraying rate of 5 mL / min. After spraying, the temperature is raised to 100°C and maintained for 20 min for rapid drying.

[0085] (3) Post-processing

[0086] After coating, the cathode material particles are heated to 250°C for annealing for 1 hour to promote interfacial bonding of the inner membrane material and optimize the crystal structure of the cathode material.

[0087] (4) Preparation of outer layer film. After the inner layer film is prepared, the outer Li3PO4 film is deposited by magnetron sputtering. The sputtering conditions are argon pressure 0.9 Pa, power 80 W, substrate temperature 120 °C, sputtering time 30 min, and finally annealing at 250 °C for 1 h.

[0088] Example 2

[0089] This invention provides a method for preparing a bilayer composite multifunctional CEI membrane structure, comprising the following steps:

[0090] (1) Inner membrane material ratio and preparation

[0091] LiF, Li₂ZrO₃, and LiNbO₃ were mixed in a ratio of 1:0.6:0.6 to improve the conductivity of the film. The mixed powder was ball-milled for 4 hours to ensure uniform particle mixing. Ethanol was used as the dispersion medium to prepare the suspension, and 0.1% of the surfactant polyvinyl alcohol (PVA) was added. The suspension was ultrasonically dispersed for 30 minutes to obtain a uniform suspension.

[0092] (2) Fluidized tank coating

[0093] High-voltage cathode material (LiCoO2) particles were placed in a fluidized bed to keep the particles uniformly suspended. The suspension was then uniformly sprayed into the fluidized bed using an aerosol spraying device at a spraying rate of 8 mL / min. After spraying, the temperature was raised to 120°C and maintained for 15 min for rapid drying to optimize the deposition efficiency and uniformity of the inner layer film.

[0094] (3) Post-processing

[0095] After coating, the cathode material particles are heated to 250°C for annealing for 1 hour to promote interfacial bonding of the inner membrane material and optimize the crystal structure of the cathode material.

[0096] (4) Preparation of outer layer film. After the inner layer film is prepared, the outer Li3PO4 film is deposited by magnetron sputtering. The sputtering conditions are argon pressure 0.9 Pa, power 80 W, substrate temperature 120 °C, sputtering time 30 min, and finally annealing at 250 °C for 1 h.

[0097] Example 3

[0098] This invention provides a method for preparing a bilayer composite multifunctional CEI membrane structure, comprising the following steps:

[0099] (1) Inner membrane material ratio and preparation

[0100] LiF, Li₂ZrO₃, and LiNbO₃ were mixed in a 1:1:1 ratio to enhance the corrosion resistance and interfacial stability of the inner film. The mixed powder was ball-milled for 4 hours to ensure uniform particle mixing. A 3:2 mixture of ethanol and deionized water was used as the dispersion medium to improve powder dispersion and reduce solvent evaporation rate, thus optimizing the film formation process. 0.1% sodium dodecyl sulfate (SLS) was added as a surfactant, and a uniform suspension was obtained by ultrasonic dispersion for 30 minutes.

[0101] (2) Fluidized tank coating

[0102] High-voltage cathode material (LiCoO2) particles are placed in a fluidized bed to keep the particles uniformly suspended. The suspension is then uniformly sprayed into the fluidized bed using an aerosol spraying device at a spraying rate of 6 mL / min. After spraying, the temperature is raised to 90°C and maintained for 30 minutes for rapid drying to ensure that the film covers the surface of the cathode material particles more uniformly.

[0103] (3) Post-processing

[0104] After coating, the cathode material particles are heated to 250°C for annealing for 1 hour to promote interfacial bonding of the inner membrane material and optimize the crystal structure of the cathode material.

[0105] (4) Preparation of outer layer film. After the inner layer film is prepared, the outer Li3PO4 film is deposited by magnetron sputtering. The sputtering conditions are argon pressure 0.9 Pa, power 80 W, substrate temperature 120 °C, sputtering time 30 min, and finally annealing at 250 °C for 1 h.

[0106] Comparative Example 1

[0107] This comparative example provides a CEI membrane structure, which differs from Example 1 in that: only a suspension containing LiF is sprayed onto the surface of the positive electrode substrate to form an inner layer membrane, and then Li3PO4 is sprayed as an outer layer membrane.

[0108] Comparative Example 2

[0109] This comparative example provides a CEI film structure, which differs from Example 1 in that: only a mixed suspension of LiF, Li2ZrO3 and LiNbO3 is sprayed onto the surface of the positive electrode substrate to form a CEI film, and no outer film is sprayed.

[0110] Comparative Example 3

[0111] This comparative example provides a CEI film structure, which differs from Example 1 in that only the Li3PO4 suspension is sprayed onto the surface of the positive electrode substrate to form a CEI film, without an inner layer film.

[0112] Comparative Example 4

[0113] This comparative example provides a CEI film structure, which differs from Example 1 in that the ratio of LiF, Li₂ZrO₃, and LiNbO₃ is 1:2:2.

[0114] After the films of Examples 1-3 and Comparative Examples 1-4 were prepared, the films were comprehensively evaluated using various characterization methods to ensure that they met the actual requirements of high-voltage cathodes. Specifically, the annealed substrates were placed under an atomic force microscope (AFM), and the surface of the electrode coated with the CEI film was mechanically tested using the force-displacement curve measurement method. The Young's modulus of the film was further calculated to evaluate its mechanical strength. Subsequently, the prepared electrodes were assembled into coin cells, and a series of performance tests were conducted, including interfacial impedance, cycle stability, and rate performance, to comprehensively evaluate the performance of the film in practical applications. The test results are shown in Table 2 below.

[0115] Table 2

[0116]

[0117] As can be seen from the data in Table 2, although Comparative Example 1 prepared a bilayer membrane structure, the inner membrane was only coated with a single component, LiF. Therefore, its mechanical and electrochemical properties were lower than those of Example 1. Comparative Example 2 prepared the same inner membrane as Example 1, but did not have an outer membrane, so its mechanical and electrochemical properties were significantly lower. Compared with Example 1, Comparative Example 3 only had an outer membrane layer, so its mechanical and electrochemical properties were significantly lower than those of Example 1. The difference between Comparative Example 4 and Example 1 lies in the different proportions of the components in the inner membrane layer. The contents of Li2ZrO3 and LiNbO3 in Comparative Example 4 were much higher than those in Example 1, indicating that its mechanical and electrochemical properties were also reduced.

[0118] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A double-layer composite multifunctional CEI membrane structure, characterized in that, This includes a composite inner layer membrane and an outer protective membrane constructed sequentially from bottom to top on the surface of the positive electrode; The composite inner layer film includes LiF, Li2ZrO3 and LiNbO3; The outer protective film is Li3PO4; The composite molar ratio of LiF, Li2ZrO3 and LiNbO3 in the composite inner layer film is 1:0.5-1:0.5-1.

2. The double-layer composite multifunctional CEI membrane structure according to claim 1, characterized in that, The thickness of the composite inner layer film is 30~50 nm, and the thickness of the outer protective film is 50~80 nm.

3. The method for preparing a double-layer composite multifunctional CEI membrane structure as described in claim 1 or 2, characterized in that, Includes the following steps: (1) A composite inner layer film is coated on the positive electrode surface using a fluidized bed method; (2) The outer protective film is prepared on the prepared composite inner layer film by magnetron sputtering.

4. The method for preparing a double-layer composite multifunctional CEI membrane structure according to claim 3, characterized in that, The specific method for step (1) is as follows: LiF, Li2ZrO3 and LiNbO3 were mixed in proportion and added to a dispersion solvent to prepare a uniform suspension. The suspension is introduced into a fluidized tank and sprayed onto the surface of the positive electrode material substrate to form a film layer; The membrane layer is subjected to low-temperature annealing to obtain the composite inner layer membrane.

5. The method for preparing a double-layer composite multifunctional CEI membrane structure according to claim 4, characterized in that, The dispersing solvent is ethanol or water, and a surfactant is also added to the suspension.

6. The method for preparing a double-layer composite multifunctional CEI membrane structure according to claim 5, characterized in that, The surfactant is one of sodium dodecyl sulfate, polyvinyl alcohol, and the Tween series.

7. The method for preparing a double-layer composite multifunctional CEI membrane structure according to claim 4, characterized in that, The low-temperature annealing conditions are annealing temperature of 200-300℃ and annealing time of 1-2 hours.

8. The method for preparing a double-layer composite multifunctional CEI membrane structure according to claim 3, characterized in that, The specific method for step (2) is as follows: The cathode material substrate with the prepared composite inner layer film was placed in a magnetron sputtering apparatus. The target material was set as Li3PO4. The sputtering process parameters were as follows: argon gas was used as the sputtering gas in the chamber, the pressure was 0.8-1.2 Pa, the sputtering power was 50-120 W, the substrate temperature was 100-150℃, and the sputtering time was 20-40 min. A Li3PO4 film was deposited on the coated composite inner layer film. The Li3PO4 film was subjected to low-temperature annealing to obtain an outer protective film.

9. The method for preparing a double-layer composite multifunctional CEI membrane structure according to claim 8, characterized in that, The low-temperature annealing conditions for Li3PO4 films are: annealing temperature 200-300℃, annealing time 1-2h.

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