Composite solid electrolyte diaphragm as well as preparation method and application thereof

Abstract

The invention relates to the technical field of battery materials, and discloses a composite solid electrolyte diaphragm as well as a preparation method and application thereof. The composite solid electrolyte diaphragm comprises a base membrane and a solid electrolyte coating arranged on at least one surface of the base membrane, the solid electrolyte coating comprises an electrolyte I and an electrolyte II; the electrolyte I is lithium titanium aluminum phosphate and lithium lanthanum zirconium tantalum oxide; and the electrolyte II is a compound of lithium bis (oxalate) borate and acetamide in a molar ratio of 1: (6.5-7.5). The composite solid electrolyte diaphragm provided by the invention can realize relatively high ionic conductivity, and when the composite solid electrolyte diaphragm is used in a lithium ion battery, the battery can have relatively low internal resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a composite solid electrolyte diaphragm and a preparation method and application thereof. Background Art

[0002] With the promotion of new energy vehicles and lithium-ion electric bicycles, the use of lithium-ion batteries has increased significantly. In recent years, solid-state batteries and solid-state electrolytes are expected to fundamentally solve the safety problems of lithium-ion batteries and have been widely studied. There may be a transition state in the transition from the traditional polyolefin separator plus liquid electrolyte to the final all-solid-state electrolyte. In this process, in addition to its basic insulating electron and conducting ion functions, the separator needs to continue to improve the safety of the battery and optimize the interface contact with the positive and negative electrode materials, thereby improving the battery's cyclability, power, high and low temperature performance and even energy density. In this regard, the researchers combined the existing separator technology with the cutting-edge research solid electrolyte materials to propose a solid electrolyte coating separator.

[0003] Patent CN110859053A discloses a composite lithium battery separator and its preparation method. The separator utilizes a fluorine-based or acrylic resin polymer, a high-molecular adhesive, and inorganic nanoparticles to form a coating layer on the surface of a base membrane. The inorganic nanoparticles are a mixture of conventional inorganic particles and inorganic particles with lithium ion conductivity. While the addition of inorganic particles with lithium ion conductivity to the coating layer improves the separator's ionic conductivity to a certain extent, the effect is limited, and the internal resistance of the battery increases when used in the battery. Summary of the Invention

[0004] To address the technical problem that existing solid-state electrolyte coating separators have low ionic conductivity, resulting in high internal resistance when used in batteries, the present invention provides a composite solid-state electrolyte separator, its preparation method, and its application. The composite solid-state electrolyte separator of the present invention achieves high ionic conductivity and, when used in lithium-ion batteries, reduces the internal resistance of the battery.

[0005] The specific technical solutions of the present invention are: In a first aspect, the present invention provides a composite solid electrolyte membrane, comprising a base membrane and a solid electrolyte coating provided on at least one surface of the base membrane; the solid electrolyte coating comprises electrolyte I and electrolyte II; the electrolyte I is lithium aluminum titanium phosphate (LATP) and lithium lanthanum zirconium tantalum oxide (LLZTO); the electrolyte II is a complex of lithium bis(oxalatoborate) (LiBOB) and acetamide in a molar ratio of 1:6.5-7.5.

[0006] Acetamide molecules have partially negatively charged O atoms and partially positively charged N atoms, resulting in a dipole property. When LiBOB complexes with acetamide, it undergoes Coulombic interactions with the partially negatively charged O atoms in acetamide, while the dioxalate borate ion interacts with the partially positively charged N atoms in acetamide. This interaction weakens the inherent hydrogen bonds between acetamide molecules and the interactions between Li and the dioxalate borate ion in the LiBOB lattice. While acetamide molecules rely on hydrogen bonds to form a relatively stable structure, and LiBOB possesses its own stable lattice structure, these interactions disrupt these structures, weakening the intermolecular and interionic forces. This allows the complex to overcome these forces and melt at lower temperatures, thereby lowering the melting point.

[0007] The present invention combines two specific materials, LiBOB and acetamide, in a specific molar ratio to achieve a suitable phase transition temperature (approximately 40-50°C) for electrolyte II. At this phase transition temperature, the following effects are achieved: when the battery is used at room temperature, electrolyte II exists as solid particles, due to the temperature being below the phase transition temperature, exhibiting excellent electrochemical and chemical stability. During the preparation of the solid electrolyte coating, the dispersion medium or solvent in the coating must be removed by drying. Because the drying temperature is above the phase transition temperature, electrolyte II transforms into a molten state with a certain degree of fluidity and viscosity. This ensures a more uniform distribution of the two solid electrolytes (electrolyte I and electrolyte II) on the surface of the base film and enhances interparticle adhesion, eliminating the need for additional binders during the coating process. Furthermore, during hot pressing of the separator into the battery, electrolyte II transforms into a molten state, filling the gap between the separator and the electrodes, thereby reducing the battery's internal resistance and facilitating battery charging and discharging.

[0008] On this basis, the present invention also adds LATP and LLZTO to the solid electrolyte coating. These, in combination with electrolyte II, can further improve the ionic conductivity of the separator and reduce the internal resistance of the battery. Specifically, LATP has a NASICON structure, and its three-dimensional framework provides a certain conduction path for lithium ions; LLZTO has a garnet-type structure and also has its own lithium ion conduction path. During the preparation of the solid electrolyte coating, electrolyte II transforms into a molten state during drying and can be filled between LATP and LLZTO, acting as a bridge at the junction of the two different structures. This allows lithium ions to migrate more smoothly between the different structures, forming a new conduction path that spans the different structures. This overcomes the limitations of single solid electrolyte conduction and enables the conduction channels of the two different structures, LATP and LLZTO, to better cooperate and give the separator higher ion conduction efficiency. In addition, the LiBOB in electrolyte II can form a boron- and lithium-rich interfacial film on the electrode surface. This film can cooperate with the interfacial layer formed by the specific electrolyte I of the present invention to jointly block side reactions between lithium metal and the electrolyte, thereby reducing the increase in interfacial resistance and lowering the internal resistance of the battery. Moreover, this composite interfacial layer can evenly distribute the deposition of lithium ions, avoiding the localized growth of lithium dendrites, thereby improving the cycle stability and safety of the battery.

[0009] Preferably, the mass ratio of lithium aluminum titanium phosphate to lithium lanthanum zirconium tantalum oxide is 1:0.6-1.5; the mass ratio of electrolyte I to electrolyte II is 1:0.3-1.2.

[0010] Under the above ratio, LATP, LLZTO and electrolyte II can better cooperate with each other, constructing a lithium ion conduction channel with higher ion conduction efficiency in the solid electrolyte layer. At the same time, the cooperation between the different interface layers formed by electrolyte I and electrolyte II on the electrode surface can be utilized to reduce the internal resistance of the battery.

[0011] Preferably, the solid electrolyte coating further comprises poly(hydroxyethyl methacrylate) gel, electrolyte I and electrolyte II are distributed in the poly(hydroxyethyl methacrylate) gel, and the mass ratio of poly(hydroxyethyl methacrylate) gel to electrolyte I is 1:18-28.

[0012] Poly(hydroxyethyl methacrylate) gel acts as a "molecular bridge," forming a "particle-polymer" co-continuous phase with the two solid electrolytes (electrolyte I and electrolyte II). Lithium ions can migrate simultaneously through the ceramic lattice channels and polymer chain segments, achieving complementary ion conduction pathways. Furthermore, poly(hydroxyethyl methacrylate) gel can form hydrogen bonds or coordination interactions with hydroxyl groups and oxygen ions on the surface of solid electrolyte particles through polar groups (such as hydroxyl groups), enhancing inter-particle adhesion and establishing a continuous ion conduction path.

[0013] Preferably, the base film is a polypropylene single-layer film, a polyethylene single-layer film, a polyolefin multi-layer co-extruded film or a cellulose film, with a porosity of 45-80% and a pore size of 80-800 nm.

[0014] In a second aspect, the present invention provides a method for preparing the composite solid electrolyte membrane, comprising the following steps: dispersing electrolyte I and electrolyte II into a dispersion medium, coating the mixture on the surface of a base membrane, and drying the mixture at 60-90°C to obtain a composite solid electrolyte membrane.

[0015] Preferably, the preparation method comprises the following steps: dispersing electrolyte I and electrolyte II into a dispersion medium, adding hydroxyethyl methacrylate (HEMA) and an initiator, coating the mixture on the surface of a base film, and then carrying out a polymerization reaction of hydroxyethyl methacrylate under the action of the initiator, and then drying the mixture at 60-90°C to obtain a composite solid electrolyte membrane.

[0016] Furthermore, the mass of the initiator is 1-1.5% of the mass of hydroxyethyl methacrylate.

[0017] Furthermore, the initiator is an ultraviolet light initiator; the polymerization reaction is carried out under ultraviolet light irradiation for 8 to 10 minutes.

[0018] Preferably, the preparation step of the electrolyte II comprises: mixing lithium bis(oxaloyl borate) and acetamide, heating to 40-50° C. and then cooling to obtain electrolyte II.

[0019] Furthermore, the preparation step of the electrolyte II includes: mixing lithium bis(oxaloyl borate) and acetamide at 20-30° C., heating to 40-50° C. and then cooling to 20-30° C. to obtain electrolyte II.

[0020] Preferably, the preparation step of the electrolyte I comprises: ball-milling lithium aluminum titanium phosphate and lithium lanthanum zirconium tantalum oxide to obtain electrolyte I; the ball-milling speed is 300-400 r / min, and the time is 1-2 h.

[0021] Preferably, in the process of dispersing electrolyte I and electrolyte II into the dispersion medium, a dispersant is also added, and the mass ratio of the dispersant to electrolyte I is 1:2~5; before coating on the base film surface, grinding is performed, and the grinding speed is 1000~4000r / min and the time is 1~4h.

[0022] Furthermore, the dispersant includes alkylphenol polyoxyethylene ether.

[0023] Alkylphenol polyoxyethylene ether is used as a dispersant. As a non-ionic surfactant, it can stabilize the slurry and is not easily destroyed by the electrolyte. It has good wettability to the electrolyte and can improve the energy density of the battery.

[0024] Preferably, the coating is performed by micro-concave roller coating, with a coating speed of 40-80 m / min and a pressure of 1-10 MPa.

[0025] Preferably, the drying time is 5 to 10 minutes.

[0026] In a third aspect, the present invention provides an application of the composite solid electrolyte membrane in a lithium-ion battery.

[0027] Compared with the prior art, the present invention has the following advantages: (1) The present invention uses LiBOB and acetamide in a certain molar ratio as electrolyte II. The phase change characteristics of electrolyte II can be utilized to fill the gap between the separator and the electrode during battery preparation, thereby reducing the internal resistance of the battery.

[0028] (2) The present invention adopts LATP, LLZTO and electrolyte II in combination. Electrolyte II forms a bridge between LATP and LLZTO with different structures and ion conduction channels, which can improve the ion conductivity of the diaphragm. At the same time, it can also utilize the different interface layers formed on the electrode surface to block the side reaction between lithium metal and electrolyte, thereby reducing the internal resistance of the battery and avoiding the local growth of lithium dendrites.

[0029] (3) In the present invention, poly(hydroxyethyl methacrylate) gel is added to the solid electrolyte coating to form a "particle-polymer" bicontinuous phase with electrolyte I and electrolyte II, which can further improve the ionic conductivity of the separator. DETAILED DESCRIPTION

[0030] The present invention will be further described below with reference to the embodiments.

[0031] First, the present invention relates to a composite solid electrolyte membrane, comprising a base membrane and a solid electrolyte coating provided on at least one surface of the base membrane; the solid electrolyte coating comprises an electrolyte I and an electrolyte II; the electrolyte I comprises lithium aluminum titanium phosphate (LATP) and lithium lanthanum zirconium tantalum oxide (LLZTO); and the electrolyte II comprises a complex of lithium bis(oxalatoborate) (LiBOB) and acetamide in a molar ratio of 1:6.5-7.5.

[0032] In some specific embodiments, the mass ratio of lithium aluminum titanium phosphate to lithium lanthanum zirconium tantalum oxide is 1:0.6-1.5; the mass ratio of electrolyte I to electrolyte II is 1:0.3-1.2.

[0033] In some specific embodiments, the solid electrolyte coating further comprises poly(hydroxyethyl methacrylate) gel, electrolyte I and electrolyte II are distributed in the poly(hydroxyethyl methacrylate) gel, and the mass ratio of poly(hydroxyethyl methacrylate) gel to electrolyte I is 1:18-28.

[0034] In some specific embodiments, the base film is a polypropylene single-layer film, a polyethylene single-layer film, a polyolefin multi-layer co-extruded film or a cellulose film, and has a porosity of 45-80% and a pore size of 80-800 nm.

[0035] Second, the present invention relates to a method for preparing the composite solid electrolyte membrane, comprising the following steps: dispersing electrolyte I and electrolyte II in a dispersion medium, coating the mixture on the surface of a base membrane, and drying the mixture at 60-90° C. to obtain the composite solid electrolyte membrane.

[0036] In some specific embodiments, the preparation method includes the following steps: dispersing electrolyte I and electrolyte II into a dispersion medium, adding hydroxyethyl methacrylate (HEMA) and an initiator, and then coating the mixture onto the surface of a base film. Then, polymerization of the HEMA is carried out under the action of the initiator, followed by drying at 60-90°C to produce a composite solid electrolyte separator. Optionally or preferably, the mass of the initiator is 1-1.5% of the mass of the HEMA; the initiator is a UV light initiator; and the polymerization reaction is carried out under UV light for 8-10 minutes.

[0037] In some specific embodiments, the preparation step of the electrolyte I includes: ball milling lithium aluminum titanium phosphate and lithium lanthanum zirconium tantalum oxide to obtain electrolyte I; the ball milling speed is 300~400r / min, and the time is 1~2h.

[0038] In some specific embodiments, the preparation step of the electrolyte II comprises: mixing lithium bis(oxaloyl borate) and acetamide, heating to 40-50°C, and then cooling to obtain electrolyte II. Optionally or preferably, during the preparation of electrolyte II, the temperature of mixing lithium bis(oxaloyl borate) and acetamide is 20-30°C, and the end point temperature of cooling is 20-30°C.

[0039] In some specific embodiments, a dispersant is added during the process of dispersing electrolyte I and electrolyte II into the dispersion medium, and the mass ratio of the dispersant to electrolyte I is 1:2 to 5. Optionally or preferably, the dispersant includes alkylphenol polyoxyethylene ether.

[0040] In some specific embodiments, grinding is performed before coating the surface of the base film, and the grinding speed is 1000-4000 r / min and the time is 1-4 hours.

[0041] In some specific embodiments, the coating is performed by micro-concave roller coating, with a coating speed of 40-80 m / min and a pressure of 1-10 MPa.

[0042] In some specific embodiments, the drying time is 5 to 10 minutes.

[0043] Third, the present invention relates to the application of the composite solid electrolyte membrane in lithium ion batteries.

[0044] The present invention is described below by way of specific examples. It should be understood that these examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit and scope of the inventive concept, any changes and advantages that can be imagined by those skilled in the art are included in the present invention, and the scope of protection of the present invention is defined by the appended claims and any equivalents thereof.

[0045] Example 1 The composite solid electrolyte membrane of this embodiment is prepared by the following steps: S1: Preparation of Electrolyte I LATP powder and LLZTO powder with a mass ratio of 1:1 were placed in a ball mill and ball milled at a speed of 350 r / min for 1.5 h to obtain electrolyte I.

[0046] S2: Preparation of Electrolyte II LiBOB and acetamide in a molar ratio of 1:7 were mixed uniformly at room temperature (25°C), heated to 45°C, and then slowly cooled to room temperature (25°C) to obtain electrolyte II.

[0047] S3: Initial preparation of slurry First, dissolve the alkylphenol polyoxyethylene ether in deionized water and stir evenly. Then gradually add electrolyte I and electrolyte II. Stir for 25 minutes to ensure that the components are initially dispersed evenly to obtain dispersion I. The mass ratio of electrolyte I, electrolyte II, alkylphenol polyoxyethylene ether and deionized water is 28:10:7:55.

[0048] S4: Introduction of polymer monomers and photoinitiators HEMA and benzoin dimethyl ether were added to dispersion I in amounts of 1% (by mass) and 0.1% (by mass), respectively, and the mixture was stirred uniformly to obtain dispersion II.

[0049] S5: Grinding The dispersion II was placed in a grinder for grinding at a speed of 2000 r / min for 2 h to obtain a uniform and fine slurry.

[0050] S6: Coating The slurry was coated on a base film (wet-process polyethylene monolayer film with a porosity of 62%, a pore size of 150 nm, and a thickness of 16 μm) by micro-concave roller coating. During the coating process, a certain pressure was applied to allow the slurry to enter the pores of the base film. The coating speed was 60 m / min and the pressure was 5 MPa to obtain a base film with slurry.

[0051] S7: Gelation The base film with the slurry was irradiated under 365 nm ultraviolet light for 10 minutes to induce a cross-linking polymerization reaction of HEMA to obtain a base film with a gel coating.

[0052] S8: Drying The base film with the gelled coating was placed in a drying oven and dried at 70° C. for 8 minutes to obtain a composite solid electrolyte membrane.

[0053] Example 2 The composite solid electrolyte membrane of this embodiment is prepared by the following steps: S1: Preparation of Electrolyte I LATP powder and LLZTO powder with a mass ratio of 1:0.6 were placed in a ball mill and ball milled at a speed of 350 r / min for 1.5 h to obtain electrolyte I.

[0054] S2: Preparation of Electrolyte II LiBOB and acetamide in a molar ratio of 1:7 were mixed uniformly at room temperature (25°C), heated to 45°C, and then slowly cooled to room temperature (25°C) to obtain electrolyte II.

[0055] S3: Initial preparation of slurry First, dissolve the alkylphenol polyoxyethylene ether in deionized water and stir evenly. Then gradually add electrolyte I and electrolyte II. Stir for 25 minutes to ensure that the components are initially dispersed evenly to obtain dispersion I. The mass ratio of electrolyte I, electrolyte II, alkylphenol polyoxyethylene ether and deionized water is 23:15:7:55.

[0056] S4: Introduction of polymer monomers and photoinitiators HEMA and benzoin dimethyl ether were added to dispersion I in amounts of 1% (by mass) and 0.1% (by mass), respectively, and the mixture was stirred uniformly to obtain dispersion II.

[0057] S5: Grinding The dispersion II was placed in a grinder for grinding at a speed of 2000 r / min for 2 h to obtain a uniform and fine slurry.

[0058] S6: Coating The slurry was coated on a base film (wet-process polyethylene monolayer film with a porosity of 62%, a pore size of 150 nm, and a thickness of 16 μm) by micro-concave roller coating. During the coating process, a certain pressure was applied to allow the slurry to enter the pores of the base film. The coating speed was 60 m / min and the pressure was 5 MPa to obtain a base film with slurry.

[0059] S7: Gelation The base film with the slurry was irradiated under 365 nm ultraviolet light for 10 minutes to induce a cross-linking polymerization reaction of HEMA to obtain a base film with a gel coating.

[0060] S8: Drying The base film with the gelled coating was placed in a drying oven and dried at 70° C. for 8 minutes to obtain a composite solid electrolyte membrane.

[0061] Example 3 The composite solid electrolyte membrane of this embodiment is prepared by the following steps: S1: Preparation of Electrolyte I LATP powder and LLZTO powder with a mass ratio of 1:1.5 were placed in a ball mill and ball milled at a speed of 350 r / min for 1.5 h to obtain electrolyte I.

[0062] S2: Preparation of Electrolyte II LiBOB and acetamide in a molar ratio of 1:7 were mixed uniformly at room temperature (25°C), heated to 45°C, and then slowly cooled to room temperature (25°C) to obtain electrolyte II.

[0063] S3: Initial preparation of slurry First, dissolve the alkylphenol polyoxyethylene ether in deionized water and stir evenly. Then gradually add electrolyte I and electrolyte II and continue stirring for 25 minutes to ensure that the components are initially dispersed evenly to obtain dispersion I. The mass ratio of electrolyte I, electrolyte II, alkylphenol polyoxyethylene ether and deionized water is 18:20:7:55.

[0064] S4: Introduction of polymer monomers and photoinitiators HEMA and benzoin dimethyl ether were added to dispersion I in amounts of 1% by mass and 0.1% by mass, respectively, and the mixture was stirred uniformly to obtain dispersion II.

[0065] S5: Grinding The dispersion II was placed in a grinder for grinding at a speed of 2000 r / min and a grinding time of 2 h to obtain a uniform and fine slurry.

[0066] S6: Coating The slurry was coated on a base film (wet-process polyethylene monolayer film with a porosity of 62%, a pore size of 150 nm, and a thickness of 16 μm) by micro-concave roller coating. During the coating process, a certain pressure was applied to allow the slurry to enter the pores of the base film. The coating speed was 60 m / min and the pressure was 5 MPa to obtain a base film with slurry.

[0067] S7: Gelation The base film with the slurry was irradiated under 365 nm ultraviolet light for 10 minutes to induce a cross-linking polymerization reaction of HEMA to obtain a base film with a gel coating.

[0068] S8: Drying The base film with the gelled coating was placed in a drying oven and dried at 70° C. for 8 minutes to obtain a composite solid electrolyte membrane.

[0069] Example 4 The only difference between this embodiment and embodiment 1 is that HEMA and dimethyl benzoate are not used to form a gel network in the solid electrolyte coating. Specifically, the composite solid electrolyte membrane of this embodiment is prepared by the following steps: S1: Preparation of electrolyte I: LATP powder and LLZTO powder with a mass ratio of 1:1 were placed in a ball mill and ball milled at a speed of 350 r / min for 1.5 h to uniformly mix them to obtain electrolyte I.

[0070] S2: Preparation of electrolyte II: LiBOB and acetamide in a molar ratio of 1:7 were mixed uniformly at room temperature (25°C), heated to 45°C, and then slowly cooled to room temperature (25°C) to obtain electrolyte II.

[0071] S3: Initial preparation of slurry: First, dissolve the alkylphenol polyoxyethylene ether in deionized water and stir evenly. Then gradually add electrolyte I and electrolyte II and continue stirring for 25 minutes to achieve a preliminary uniform dispersion of the components to obtain a dispersion. The mass ratio of electrolyte I, electrolyte II, alkylphenol polyoxyethylene ether, and deionized water is 28:10:7:55.

[0072] S4: Grinding treatment: The dispersion was placed in a grinder for grinding at a speed of 2000 r / min and a grinding time of 2 h to obtain a uniform and fine slurry.

[0073] S5: coating: The slurry was coated on a base film (wet-process polyethylene monolayer film with a porosity of 62%, a pore size of 150 nm, and a thickness of 16 μm) by micro-concave roller coating. During the coating process, a certain pressure was applied to allow the slurry to enter the pores of the base film. The coating speed was 60 m / min and the pressure was 5 MPa to obtain a base film with slurry.

[0074] S7: Drying: The base film with the slurry was placed in a drying oven and dried at 70° C. for 8 minutes to obtain a composite solid electrolyte membrane.

[0075] Example 5 The only difference between this embodiment and embodiment 1 is that the proportion of LLZTO in electrolyte I is reduced. Specifically, the composite solid electrolyte membrane of this embodiment is prepared by the following steps: S1: Preparation of Electrolyte I LATP powder and LLZTO powder with a mass ratio of 1:0.2 were placed in a ball mill and ball milled at a speed of 350 r / min for 1.5 h to obtain electrolyte I.

[0076] S2: Preparation of Electrolyte II LiBOB and acetamide in a molar ratio of 1:7 were mixed uniformly at room temperature (25°C), heated to 45°C, and then slowly cooled to room temperature (25°C) to obtain electrolyte II.

[0077] S3: Initial preparation of slurry First, dissolve the alkylphenol polyoxyethylene ether in deionized water and stir evenly. Then gradually add electrolyte I and electrolyte II. Stir for 25 minutes to ensure that the components are initially dispersed evenly to obtain dispersion I. The mass ratio of electrolyte I, electrolyte II, alkylphenol polyoxyethylene ether and deionized water is 28:10:7:55.

[0078] S4: Introduction of polymer monomers and photoinitiators HEMA and benzoin dimethyl ether were added to dispersion I in amounts of 1% by mass and 0.1% by mass, respectively, and the mixture was stirred uniformly to obtain dispersion II.

[0079] S5: Grinding The dispersion II was placed in a grinder for grinding at a speed of 2000 r / min and a grinding time of 2 h to obtain a uniform and fine slurry.

[0080] S6: Coating The slurry was coated on a base film (wet-process polyethylene monolayer film with a porosity of 62%, a pore size of 150 nm, and a thickness of 16 μm) by micro-concave roller coating. During the coating process, a certain pressure was applied to allow the slurry to enter the pores of the base film. The coating speed was 60 m / min and the pressure was 5 MPa to obtain a base film with slurry.

[0081] S7: Gelation The base film with the slurry was irradiated under 365 nm ultraviolet light for 10 minutes to induce a cross-linking polymerization reaction of HEMA to obtain a base film with a gel coating.

[0082] S8: Drying The base film with the gelled coating was placed in a drying oven and dried at 70° C. for 8 minutes to obtain a composite solid electrolyte membrane.

[0083] Example 6 The only difference between this embodiment and embodiment 1 is that the proportion of LLZTO in electrolyte I is increased. Specifically, the composite solid electrolyte membrane of this embodiment is prepared by the following steps: S1: Preparation of Electrolyte I LATP powder and LLZTO powder with a mass ratio of 3:7 were placed in a ball mill and ball milled at a speed of 350 r / min for 1.5 h to obtain electrolyte I.

[0084] S2: Preparation of Electrolyte II LiBOB and acetamide in a molar ratio of 1:7 were mixed uniformly at room temperature (25°C), heated to 45°C, and then slowly cooled to room temperature (25°C) to obtain electrolyte II.

[0085] S3: Initial preparation of slurry First, dissolve the alkylphenol polyoxyethylene ether in deionized water and stir evenly. Then gradually add electrolyte I and electrolyte II. Stir for 25 minutes to ensure that the components are initially dispersed evenly to obtain dispersion I. The mass ratio of electrolyte I, electrolyte II, alkylphenol polyoxyethylene ether and deionized water is 28:10:7:55.

[0086] S4: Introduction of polymer monomers and photoinitiators HEMA and benzoin dimethyl ether were added to dispersion I in amounts of 1% by mass and 0.1% by mass, respectively, and the mixture was stirred uniformly to obtain dispersion II.

[0087] S5: Grinding The dispersion II was placed in a grinder for grinding at a speed of 2000 r / min and a grinding time of 2 h to obtain a uniform and fine slurry.

[0088] S6: Coating The slurry was coated on a base film (wet-process polyethylene monolayer film with a porosity of 62%, a pore size of 150 nm, and a thickness of 16 μm) by micro-concave roller coating. During the coating process, a certain pressure was applied to allow the slurry to enter the pores of the base film. The coating speed was 60 m / min and the pressure was 5 MPa to obtain a base film with slurry.

[0089] S7: Gelation The base film with the slurry was irradiated under 365 nm ultraviolet light for 10 minutes to induce a cross-linking polymerization reaction of HEMA to obtain a base film with a gel coating.

[0090] S8: Drying The base film with the gelled coating was placed in a drying oven and dried at 70° C. for 8 minutes to obtain a composite solid electrolyte membrane.

[0091] Comparative Example 1 The only difference between this comparative example and Example 1 is that no electrolyte II is added to the solid electrolyte coating. Specifically, the composite solid electrolyte membrane of this comparative example is prepared by the following steps: S1: Preparation of Electrolyte I LATP powder and LLZTO powder with a mass ratio of 1:1 were placed in a ball mill and ball milled at a speed of 350 r / min for 1.5 h to uniformly mix them to obtain electrolyte I.

[0092] S2: Initial preparation of slurry Alkylphenol polyoxyethylene ether was first dissolved in deionized water and stirred evenly, then electrolyte I was gradually added and stirred for 25 minutes to allow the components to be preliminarily dispersed evenly to obtain dispersion I. The mass ratio of electrolyte I, alkylphenol polyoxyethylene ether, and deionized water was 38:7:55.

[0093] S3: Introduction of polymer monomers and photoinitiators HEMA and benzoin dimethyl ether were added to dispersion I in amounts of 1% by mass and 0.1% by mass, respectively, and the mixture was stirred uniformly to obtain dispersion II.

[0094] S4: Grinding The dispersion II was placed in a grinder for grinding at a speed of 2000 r / min and a grinding time of 2 h to obtain a uniform and fine slurry.

[0095] S5: coating The slurry was coated on a base film (wet-process polyethylene monolayer film with a porosity of 62%, a pore size of 150 nm, and a thickness of 16 μm) by micro-concave roller coating. During the coating process, a certain pressure was applied to allow the slurry to enter the pores of the base film. The coating speed was 60 m / min and the pressure was 5 MPa to obtain a base film with slurry.

[0096] S6: Gelation The base film with the slurry was irradiated under 365 nm ultraviolet light for 10 minutes to induce a cross-linking polymerization reaction of HEMA to obtain a base film with a gel coating.

[0097] S7: Dry The base film with the gelled coating was placed in a drying oven and dried at 70° C. for 8 minutes to obtain a composite solid electrolyte membrane.

[0098] Comparative Example 2 The only difference between this comparative example and Example 1 is that no electrolyte I is added to the solid electrolyte coating. Specifically, the composite solid electrolyte membrane of this comparative example is prepared by the following steps: S1: Preparation of Electrolyte II LiBOB and acetamide in a molar ratio of 1:7 were mixed uniformly at room temperature (25°C), heated to 45°C, and then slowly cooled to room temperature (25°C) to obtain electrolyte II.

[0099] S2: Initial preparation of slurry First, dissolve the alkylphenol polyoxyethylene ether in deionized water and stir evenly. Then gradually add electrolyte II and continue stirring for 25 minutes to ensure that all ingredients are initially dispersed evenly to obtain dispersion I. The mass ratio of electrolyte II, alkylphenol polyoxyethylene ether, and deionized water is 38:7:55.

[0100] S3: Introduction of polymer monomers and photoinitiators HEMA and benzoin dimethyl ether were added to dispersion I in amounts of 1% by mass and 0.1% by mass, respectively, and the mixture was stirred uniformly to obtain dispersion II.

[0101] S4: Grinding The dispersion II was placed in a grinder for grinding at a speed of 2000 r / min and a grinding time of 2 h to obtain a uniform and fine slurry.

[0102] S5: coating The slurry was coated on a base film (wet-process polyethylene monolayer film with a porosity of 62%, a pore size of 150 nm, and a thickness of 16 μm) by micro-concave roller coating. During the coating process, a certain pressure was applied to allow the slurry to enter the pores of the base film. The coating speed was 60 m / min and the pressure was 5 MPa to obtain a base film with slurry.

[0103] S6: Gelation The base film with the slurry was irradiated under 365 nm ultraviolet light for 10 minutes to induce a cross-linking polymerization reaction of HEMA to obtain a base film with a gel coating.

[0104] S7: Dry The base film with the gelled coating was placed in a drying oven and dried at 70° C. for 8 minutes to obtain a composite solid electrolyte membrane.

[0105] Comparative Example 3 The only difference between this comparative example and Example 1 is that LLZTO is not used in electrolyte I. Specifically, the composite solid electrolyte membrane of this comparative example is prepared by the following steps: S1: Preparation of Electrolyte I The LATP powder was placed in a ball mill and ball milled at a speed of 350 r / min for 1.5 h to obtain electrolyte I.

[0106] S2: Preparation of Electrolyte II LiBOB and acetamide in a molar ratio of 1:7 were mixed uniformly at room temperature (25°C), heated to 45°C, and then slowly cooled to room temperature (25°C) to obtain electrolyte II.

[0107] S3: Initial preparation of slurry First, dissolve the alkylphenol polyoxyethylene ether in deionized water and stir evenly. Then gradually add electrolyte I and electrolyte II. Stir for 25 minutes to ensure that the components are initially dispersed evenly to obtain dispersion I. The mass ratio of electrolyte I, electrolyte II, alkylphenol polyoxyethylene ether and deionized water is 28:10:7:55.

[0108] S4: Introduction of polymer monomers and photoinitiators HEMA and benzoin dimethyl ether were added to dispersion I in amounts of 1% (by mass) and 0.1% (by mass), respectively, and the mixture was stirred uniformly to obtain dispersion II.

[0109] S5: Grinding The dispersion II was placed in a grinder for grinding at a speed of 2000 r / min for 2 h to obtain a uniform and fine slurry.

[0110] S6: Coating The slurry was coated on a base film (wet-process polyethylene monolayer film with a porosity of 62%, a pore size of 150 nm, and a thickness of 16 μm) by micro-concave roller coating. During the coating process, a certain pressure was applied to allow the slurry to enter the pores of the base film. The coating speed was 60 m / min and the pressure was 5 MPa to obtain a base film with slurry.

[0111] S7: Gelation The base film with the slurry was irradiated under 365 nm ultraviolet light for 10 minutes to induce a cross-linking polymerization reaction of HEMA to obtain a base film with a gel coating.

[0112] S8: Drying The base film with the gelled coating was placed in a drying oven and dried at 70° C. for 8 minutes to obtain a composite solid electrolyte membrane.

[0113] Comparative Example 4 The only difference between this comparative example and Example 1 is that LATP is not used in electrolyte I. Specifically, the composite solid electrolyte membrane of this comparative example is prepared by the following steps: S1: Preparation of Electrolyte I The LLZTO powder was placed in a ball mill and ball milled at a speed of 350 r / min for 1.5 h to obtain electrolyte I.

[0114] S2: Preparation of Electrolyte II LiBOB and acetamide in a molar ratio of 1:7 were mixed uniformly at room temperature (25°C), heated to 45°C, and then slowly cooled to room temperature (25°C) to obtain electrolyte II.

[0115] S3: Initial preparation of slurry First, dissolve the alkylphenol polyoxyethylene ether in deionized water and stir evenly. Then gradually add electrolyte I and electrolyte II. Stir for 25 minutes to ensure that the components are initially dispersed evenly to obtain dispersion I. The mass ratio of electrolyte I, electrolyte II, alkylphenol polyoxyethylene ether and deionized water is 28:10:7:55.

[0116] S4: Introduction of polymer monomers and photoinitiators HEMA and benzoin dimethyl ether were added to dispersion I in amounts of 1% (by mass) and 0.1% (by mass), respectively, and the mixture was stirred uniformly to obtain dispersion II.

[0117] S5: Grinding The dispersion II was placed in a grinder for grinding at a speed of 2000 r / min for 2 h to obtain a uniform and fine slurry.

[0118] S6: Coating The slurry was coated on a base film (wet-process polyethylene monolayer film with a porosity of 62%, a pore size of 150 nm, and a thickness of 16 μm) by micro-concave roller coating. During the coating process, a certain pressure was applied to allow the slurry to enter the pores of the base film. The coating speed was 60 m / min and the pressure was 5 MPa to obtain a base film with slurry.

[0119] S7: Gelation The base film with the slurry was irradiated under 365 nm ultraviolet light for 10 minutes to induce a cross-linking polymerization reaction of HEMA to obtain a base film with a gel coating.

[0120] S8: Drying The base film with the gelled coating was placed in a drying oven and dried at 70° C. for 8 minutes to obtain a composite solid electrolyte membrane.

[0121] Comparative Example 5 The diaphragm of this comparative example is a wet-process polyethylene single-layer membrane, which has a porosity of 62%, a pore diameter of 150 nm, and a thickness of 16 μm.

[0122] Test Case The membranes prepared in each embodiment and comparative example were tested for air permeability and liquid absorption, and then the membranes were assembled into battery cells to test the internal resistance of the battery cells and the ionic conductivity of the membranes. The specific test methods are as follows: (1) Liquid absorption rate test: The liquid absorption rate of the solid electrolyte membrane is tested by weighing method.

[0123] (2) Air permeability test: Use an air permeability tester to test the air permeability of the solid electrolyte membrane.

[0124] (3) Internal resistance and ionic conductivity test: An electrochemical workstation is used to measure the internal resistance and ionic conductivity of the battery cell. The method for assembling the separator into a battery cell is as follows: the positive electrode sheet, separator and negative electrode sheet are stacked to form the basic structure of the battery cell, the stacked battery cell is placed in the battery shell, and the tabs are welded, and then hot pressed for 150 seconds at a temperature of 95°C and a pressure of 2MPa to shape the stacked battery cell.

[0125] The test results are shown in Table 1.

[0126] Table 1 Test results of diaphragm and battery cell performance

[0127] Analyzing the data in Table 1, we can see that: (1) Compared with Comparative Example 5, the ionic conductivity of Examples 1-6 is significantly improved, and the internal resistance of the battery cell is significantly reduced. This indicates that by applying the solid electrolyte coating of the present invention on the surface of the diaphragm base film, the ionic conductivity of the diaphragm can be effectively improved and the internal resistance of the battery can be reduced.

[0128] (2) Compared with Comparative Examples 1 and 2, Examples 1 to 3 have higher ionic conductivity and lower internal resistance of the battery cell. This shows that by using the specific electrolyte I and electrolyte II of the present invention in the solid electrolyte coating inside the diaphragm, the ionic conductivity of the diaphragm can be improved and the internal resistance of the battery can be reduced. The reason for this is that: in the process of making the diaphragm into a battery, the electrolyte II is transformed into a molten state during hot pressing, which can fill the gap between the diaphragm and the electrode, thereby reducing the internal resistance of the battery and facilitating battery charging and discharging; and, in the process of preparing the solid electrolyte coating, since the drying temperature is higher than the phase transition temperature of the electrolyte II, the electrolyte II can be transformed into a molten state with certain fluidity and viscosity, filling between LATP and LLZTO, and acting as a bridge at the junction of the two different structures of LATP and LLZTO. The ion transmission channel thus formed helps to improve the lithium ion conduction efficiency; in addition, the LiBOB in the electrolyte II can form a layer of boron and lithium-rich interface film on the electrode surface. This film can cooperate with the interface layer formed by the specific electrolyte I of the present invention to jointly block the side reaction between lithium metal and the electrolyte, thereby reducing the increase in interface resistance and reducing the internal resistance of the battery.

[0129] (3) Compared with Example 5, Example 6, Comparative Example 3 and Comparative Example 4, Examples 1 to 3 have higher ionic conductivity and lower internal resistance of the battery cell. This shows that by using a combination of LATP and LLZTO as electrolyte I, the ionic conductivity of the diaphragm can be improved and the internal resistance of the battery can be reduced, and the ratio between LATP and LLZTO will affect this effect. The reason for this is that: LATP has a NASICON structure, and its three-dimensional framework structure provides a certain conduction channel for lithium ions; LLZTO has a garnet structure and also has its own lithium ion conduction path; after the electrolyte II forms a bridge between LATP and LLZTO, the two different ion conduction channels can cooperate with each other to improve the lithium ion conduction efficiency.

[0130] (4) Compared with Example 4, Examples 1 to 3 have higher ionic conductivity and lower internal resistance of the battery. This shows that by adding poly(hydroxyethyl methacrylate) gel to the solid electrolyte coating, the ionic conductivity of the diaphragm can be improved and the internal resistance of the battery can be reduced. The reason for this is that poly(hydroxyethyl methacrylate) gel can act as a "molecular bridge" to form a "particle-polymer" bicontinuous phase with the two solid electrolytes (electrolyte I and electrolyte II). Lithium ions can simultaneously migrate through the ceramic lattice channels and polymer chain segments to achieve complementary ion conduction paths; in addition, poly(hydroxyethyl methacrylate) gel can also form hydrogen bonds or coordination effects with the hydroxyl groups and oxygen ions on the surface of the solid electrolyte particles through polar groups (such as hydroxyl groups), thereby enhancing the bonding between particles and constructing a continuous ion conduction path.

[0131] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this disclosure pertains. Unless otherwise specified, the raw materials and equipment used herein are conventional in the art and can be obtained from conventional commercial sources. The methods used herein are conventional in the art, unless otherwise specified.

[0132] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A composite solid electrolyte membrane, characterized in that: The invention comprises a base film and a solid electrolyte coating provided on at least one surface of the base film; the solid electrolyte coating comprises electrolyte I and electrolyte II; the electrolyte I is lithium aluminum titanium phosphate and lithium lanthanum zirconium tantalum oxide; the electrolyte II is a complex of lithium bis(oxalate borate) and acetamide in a molar ratio of 1:6.5-7.

5.

2. The composite solid electrolyte membrane according to claim 1, characterized in that The mass ratio of the lithium aluminum titanium phosphate and lithium lanthanum zirconium tantalum oxide is 1:0.6-1.5; the mass ratio of the electrolyte I and the electrolyte II is 1:0.3-1.

2.

3. The composite solid electrolyte membrane according to claim 1, characterized in that The solid electrolyte coating further comprises poly(hydroxyethyl methacrylate) gel, electrolyte I and electrolyte II are distributed in the poly(hydroxyethyl methacrylate) gel, and the mass ratio of poly(hydroxyethyl methacrylate) gel to electrolyte I is 1:18-28.

4. The composite solid electrolyte membrane according to claim 1, characterized in that The base film is a polypropylene single-layer film, a polyethylene single-layer film, a polyolefin multi-layer co-extruded film or a cellulose film, with a porosity of 45-80% and a pore diameter of 80-800 nm.

5. A method for preparing the composite solid electrolyte membrane according to any one of claims 1 to 4, characterized in that: The following steps are involved: The electrolyte I and the electrolyte II are dispersed in a dispersion medium, coated on the surface of the base film, and dried at 60-90° C. to obtain a composite solid electrolyte separator.

6. The preparation method according to claim 5, characterized in that The following steps are involved: Electrolyte I and electrolyte II are dispersed in a dispersion medium, and after adding hydroxyethyl methacrylate and an initiator, they are coated on the surface of the base film. Then, a polymerization reaction of hydroxyethyl methacrylate is carried out under the action of the initiator, and then the composite solid electrolyte membrane is obtained by drying at 60-90°C.

7. The preparation method according to claim 5 or 6, characterized in that: The preparation steps of the electrolyte II include: mixing lithium bis(oxalyl)borate and acetamide, heating to 40-50° C. and then cooling to obtain the electrolyte II.

8. The preparation method according to claim 5 or 6, characterized in that: The preparation steps of the electrolyte I include: ball milling and mixing lithium aluminum titanium phosphate and lithium lanthanum zirconium tantalum oxide to obtain electrolyte I; the ball milling rotation speed is 300-400 r / min, and the time is 1-2 hours.

9. The preparation method according to claim 5 or 6, characterized in that: In the process of dispersing electrolyte I and electrolyte II into the dispersion medium, a dispersant is also added, and the mass ratio of the dispersant to electrolyte I is 1:2~5; before being coated on the surface of the base film, grinding is performed, and the grinding speed is 1000~4000r / min and the time is 1~4h.

10. Use of the composite solid electrolyte membrane according to any one of claims 1 to 4 in a lithium ion battery.

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