Composite solid electrolyte separator and preparation method and application thereof

Abstract

The application 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 film and a solid electrolyte coating layer arranged on at least one surface of the base film; the solid electrolyte coating layer comprises electrolyte I and electrolyte II; the electrolyte I is lithium aluminum titanium phosphate and lithium lanthanum zirconium tantalum oxide; and the electrolyte II is a composite of bimalonic acid lithium borate and acetamide with a molar ratio of 1:6.5-7.5. The composite solid electrolyte diaphragm can realize high ionic conductivity, and when used in a lithium ion battery, can enable the battery to have low internal resistance.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a composite solid electrolyte separator, its preparation method, and its application. Background Technology

[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 have been widely studied as they are expected to fundamentally solve the safety problems of lithium-ion batteries. The transition from traditional polyolefin separators with liquid electrolytes to the final all-solid-state electrolytes may involve a transitional phase. In this process, in addition to its basic functions of insulating electrons and conducting ions, the separator needs to further improve battery safety and optimize the interfacial contact with the positive and negative electrode materials, thereby improving the battery's cycle life, power, high and low temperature performance, and even energy density. Therefore, researchers have proposed solid-state electrolyte coated separators, combining existing separator technologies with cutting-edge research on solid-state electrolyte materials.

[0003] Patent CN110859053A discloses a composite lithium battery separator and its preparation method. It uses a fluorine-based or acrylic resin polymer, a polymeric 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. This patent, by adding inorganic particles with lithium-ion conductivity to the coating layer, can improve the ionic conductivity of the separator to some extent, but the effect is limited, and it results in a relatively high internal resistance when used in batteries. Summary of the Invention

[0004] To address the technical problem of low ionic conductivity in existing solid electrolyte coated separators, which leads to high internal resistance in batteries, this invention provides a composite solid electrolyte separator, its preparation method, and its application. The composite solid electrolyte separator of this invention achieves high ionic conductivity and, when used in lithium-ion batteries, enables the battery to have low internal resistance.

[0005] The specific technical solution of this invention is as follows:

[0006] In a first aspect, the present invention provides a composite solid electrolyte membrane, comprising a base membrane and a solid electrolyte coating disposed on at least one surface of the base membrane; the solid electrolyte coating comprises electrolyte I and electrolyte II; electrolyte I is lithium aluminum titanium phosphate (LATP) and lithium lanthanum zirconium tantalum oxide (LLZTO); electrolyte II is a composite of lithium dioxoborate (LiBOB) and acetamide in a molar ratio of 1:6.5~7.5.

[0007] In acetamide molecules, the O atoms are partially negatively charged, and the N atoms are partially positively charged, exhibiting dipole properties. When LiBOB is complexed with acetamide, it undergoes Coulomb interactions with the partially negatively charged O atoms in acetamide, while the diasoxaloborate ions interact with the partially positively charged N atoms in acetamide. These interactions weaken the original hydrogen bonds between acetamide molecules and the interactions between Li and diasoxaloborate ions in the LiBOB lattice. Originally, acetamide molecules rely on hydrogen bonds to form a relatively stable structure, and LiBOB also has its own stable lattice structure. The intervention of these interactions disrupts these structures, weakening the intermolecular and ionic forces. This allows the complex to overcome these forces and melt at a lower temperature, thus lowering the melting point.

[0008] This invention combines LiBOB and acetamide in a specific molar ratio, enabling electrolyte II to have a suitable phase transition temperature (approximately 40-50°C). At this phase transition temperature, the following effects can be achieved: When the battery is used at room temperature, because the temperature is below the phase transition temperature, electrolyte II exists in the form of solid particles, exhibiting good electrochemical and chemical stability. During the preparation of the solid electrolyte coating, the dispersion medium or solvent in the coating needs to be removed by drying. Since the drying temperature is higher than the phase transition temperature, electrolyte II can transform into a molten state with certain fluidity and viscosity, allowing the two solid electrolytes (electrolyte I and electrolyte II) to be more evenly distributed on the base film surface and increasing interparticle adhesion, eliminating the need for additional binders during the coating process. Furthermore, during the process of making the separator into a battery, electrolyte II transforms into a molten state during hot pressing, which can fill the gaps between the separator and the electrodes, thereby reducing the battery's internal resistance and facilitating battery charging and discharging.

[0009] Building upon this foundation, the present invention further incorporates LATP and LLZTO into the solid electrolyte coating. These, in conjunction with electrolyte II, further enhance the ionic conductivity of the separator and reduce the battery's internal resistance. Specifically, LATP possesses a NASICON structure, whose three-dimensional framework provides a conduction channel for lithium ions; LLZTO exhibits a garnet-type structure and also provides its own lithium-ion conduction pathway. During the preparation of the solid electrolyte coating, electrolyte II transforms into a molten state during drying, filling the space between LATP and LLZTO. It acts as a bridge at the interface between these two different structures, allowing lithium ions to migrate more smoothly between them, forming a novel conduction channel that transcends these structures. This overcomes the limitations of single-solid-electrolyte conduction, enabling the conduction channels of LATP and LLZTO to work more synergistically, resulting in higher ion conduction efficiency for the separator. Furthermore, LiBOB in electrolyte II can form a 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 this invention to jointly block the side reactions between lithium metal and electrolyte, thereby reducing the increase in interface resistance and lowering the battery internal resistance. Moreover, this composite interface layer can also uniformly distribute the deposition of lithium ions and avoid the local growth of lithium dendrites, thereby improving the cycle stability and safety of the battery.

[0010] Preferably, the mass ratio of lithium titanium aluminum phosphate to lithium lanthanum zirconium tantalum oxide is 1:0.6~1.5; and the mass ratio of electrolyte I to electrolyte II is 1:0.3~1.2.

[0011] With the above ratio, LATP, LLZTO and electrolyte II can better cooperate to build 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 reduce the internal resistance of the battery.

[0012] Preferably, the solid electrolyte coating further includes a poly(hydroxyethyl methacrylate) gel, wherein 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.

[0013] Poly(hydroxyethyl methacrylate) gel can act as a "molecular-level bridge," forming a "particle-polymer" bicontinuous phase with two solid electrolytes (electrolyte I and electrolyte II). Lithium ions can migrate simultaneously through ceramic lattice channels and polymer chain segments, achieving complementary ion conduction pathways. Furthermore, poly(hydroxyethyl methacrylate) gel can also enhance interparticle adhesion and construct continuous ion conduction pathways by forming hydrogen bonds or coordination interactions with hydroxyl and oxygen ions on the surface of solid electrolyte particles through polar groups (such as hydroxyl groups).

[0014] Preferably, the base membrane is a polypropylene monolayer membrane, a polyethylene monolayer membrane, a polyolefin multilayer co-extruded membrane, or a cellulose membrane, with a porosity of 45-80% and a pore size of 80-800 nm.

[0015] Secondly, the present invention provides a method for preparing the composite solid electrolyte membrane, comprising the following steps: dispersing electrolyte I and electrolyte II in a dispersion medium, coating them onto the surface of a base membrane, and drying them at 60~90°C to obtain the composite solid electrolyte membrane.

[0016] Preferably, the preparation method includes the following steps: dispersing electrolyte I and electrolyte II in a dispersion medium, adding hydroxyethyl methacrylate (HEMA) and an initiator, coating the substrate surface, then carrying out the polymerization reaction of hydroxyethyl methacrylate under the action of the initiator, and then drying at 60~90℃ to obtain a composite solid electrolyte membrane.

[0017] Furthermore, the mass of the initiator is 1 to 1.5% of the mass of hydroxyethyl methacrylate.

[0018] Furthermore, the initiator is an ultraviolet initiator; the polymerization reaction is carried out under ultraviolet light irradiation for 8-10 minutes.

[0019] Preferably, the preparation steps of electrolyte II include: mixing lithium dioxoborate and acetamide, heating to 40~50°C and then cooling to obtain electrolyte II.

[0020] Further, the preparation steps of electrolyte II include: mixing lithium dioxoborate and acetamide at 20~30°C, heating to 40~50°C and then cooling to 20~30°C to obtain electrolyte II.

[0021] Preferably, the preparation steps of electrolyte I include: ball milling lithium titanium aluminum 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.

[0022] Preferably, a dispersant is added during the process of dispersing electrolyte I and electrolyte II into the dispersion medium, wherein the mass ratio of the dispersant to electrolyte I is 1:2~5; and grinding is performed before coating onto the base film surface, wherein the grinding speed is 1000~4000 r / min and the grinding time is 1~4 h.

[0023] Furthermore, the dispersant includes alkylphenol polyoxyethylene ether.

[0024] Alkylphenol polyoxyethylene ether is used as a dispersant. As a nonionic 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.

[0025] Preferably, the coating is performed using a micro-grooving roller coating method, with a coating speed of 40~80m / min and a pressure of 1~10MPa.

[0026] Preferably, the drying time is 5 to 10 minutes.

[0027] Thirdly, the present invention provides the application of the composite solid electrolyte separator in lithium-ion batteries.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] (1) In this invention, LiBOB and acetamide are combined 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.

[0030] (2) The present invention uses LATP, LLZTO and electrolyte II in combination. Electrolyte II forms a bridge between LATP and LLZTO, which have different structures and ion conduction channels, which can improve the ionic conductivity of the membrane. At the same time, it can also use 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.

[0031] (3) In this 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 membrane. Detailed Implementation

[0032] The present invention will be further described below with reference to embodiments.

[0033] First, the present invention relates to a composite solid electrolyte membrane, comprising a base membrane and a solid electrolyte coating disposed on at least one surface of the base membrane; the solid electrolyte coating comprises electrolyte I and electrolyte II; electrolyte I is lithium aluminum titanium phosphate (LATP) and lithium lanthanum zirconium tantalum oxide (LLZTO); electrolyte II is a composite of lithium dioxoborate (LiBOB) and acetamide in a molar ratio of 1:6.5~7.5.

[0034] In some specific embodiments, the mass ratio of lithium titanium aluminum 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.

[0035] In some specific embodiments, the solid electrolyte coating further includes a poly(hydroxyethyl methacrylate) gel, wherein electrolyte I and electrolyte II are distributed in the poly(hydroxyethyl methacrylate) gel, and the mass ratio of the poly(hydroxyethyl methacrylate) gel to electrolyte I is 1:18~28.

[0036] In some specific embodiments, the base membrane is a polypropylene monolayer membrane, a polyethylene monolayer membrane, a polyolefin multilayer co-extruded membrane, or a cellulose membrane, with a porosity of 45-80% and a pore size of 80-800 nm.

[0037] 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 them onto the surface of a base membrane, and drying them at 60~90°C to obtain the composite solid electrolyte membrane.

[0038] In some specific embodiments, the preparation method includes the following steps: dispersing electrolyte I and electrolyte II in a dispersion medium, adding hydroxyethyl methacrylate (HEMA) and an initiator, coating the mixture onto the surface of a base membrane, then carrying out a polymerization reaction of hydroxyethyl methacrylate under the action of the initiator, and finally drying at 60-90°C to obtain a composite solid electrolyte membrane. Optionally or preferably: the mass of the initiator is 1-1.5% of the mass of hydroxyethyl methacrylate; the initiator is an ultraviolet (UV) photoinitiator; the polymerization reaction is carried out under UV irradiation for 8-10 minutes.

[0039] In some specific embodiments, the preparation steps of electrolyte I include: ball milling lithium titanium aluminum 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.

[0040] In some specific embodiments, the preparation steps of electrolyte II include: mixing lithium dioxoborate 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 at which lithium dioxoborate and acetamide are mixed is 20-30°C, and the final cooling temperature is 20-30°C.

[0041] In some specific embodiments, a dispersant is also added during the process of dispersing electrolyte I and electrolyte II into the dispersion medium, wherein the mass ratio of the dispersant to electrolyte I is 1:2 to 5. Optionally or preferably, the dispersant comprises alkylphenol polyoxyethylene ether.

[0042] In some specific embodiments, grinding is performed before coating onto the base film surface, wherein the grinding speed is 1000~4000 r / min and the time is 1~4 h.

[0043] In some specific embodiments, the coating is performed using a micro-grooving roller coating method, with a coating speed of 40~80m / min and a pressure of 1~10MPa.

[0044] In some specific embodiments, the drying time is 5 to 10 minutes.

[0045] Third, the present invention relates to the application of the composite solid electrolyte separator in lithium-ion batteries.

[0046] The present invention will now be described through specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Variations and advantages that can be conceived by those skilled in the art without departing from the spirit and scope of the inventive concept 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.

[0047] Example 1

[0048] The composite solid electrolyte membrane in this embodiment is prepared through the following steps:

[0049] S1: Preparation of electrolyte I

[0050] LATP powder and LLZTO powder in a mass ratio of 1:1 were placed in a ball mill and ball milled at 350 r / min for 1.5 h to mix them uniformly, thus obtaining electrolyte I.

[0051] S2: Preparation of Electrolyte II

[0052] LiBOB and acetamide in a molar ratio of 1:7 were mixed evenly at room temperature (25°C), heated to 45°C, and then slowly cooled to room temperature (25°C) to obtain electrolyte II.

[0053] S3: Initial preparation of slurry

[0054] First, dissolve alkylphenol polyoxyethylene ether in deionized water and stir until homogeneous. Then, gradually add electrolyte I and electrolyte II, and continue stirring for 25 minutes to allow the components to initially disperse evenly, thus obtaining dispersion I. The mass ratio of electrolyte I, electrolyte II, alkylphenol polyoxyethylene ether, and deionized water is 28:10:7:55.

[0055] S4: Introduction of polymer monomers and photoinitiators

[0056] HEMA and benzoin dimethyl ether were added to dispersion I, with the addition amounts of 1% (mass) and 0.1% (mass) respectively. The mixture was stirred until homogeneous to obtain dispersion II.

[0057] S5: Grinding process

[0058] Dispersion II was placed in a grinder for grinding at a speed of 2000 r / min for 2 hours to obtain a uniform and fine slurry.

[0059] S6: Coating

[0060] The slurry was coated onto 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) using a micro-grooving roller coating method. During the 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, resulting in a base film with the slurry.

[0061] S7: Gelation

[0062] The base film containing the slurry was irradiated under 365nm ultraviolet light for 10 minutes to induce cross-linking polymerization of HEMA, resulting in a base film with a gelled coating.

[0063] S8: Drying

[0064] The base membrane with the gelation coating was placed in a drying oven and dried at 70°C for 8 minutes to obtain a composite solid electrolyte membrane.

[0065] Example 2

[0066] The composite solid electrolyte membrane in this embodiment is prepared through the following steps:

[0067] S1: Preparation of electrolyte I

[0068] LATP powder and LLZTO powder in a mass ratio of 1:0.6 were placed in a ball mill and ball-milled at 350 r / min for 1.5 h to obtain electrolyte I.

[0069] S2: Preparation of Electrolyte II

[0070] LiBOB and acetamide in a molar ratio of 1:7 were mixed evenly 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

[0072] First, dissolve alkylphenol polyoxyethylene ether in deionized water and stir until homogeneous. Then, gradually add electrolyte I and electrolyte II, and continue stirring for 25 minutes to allow the components to initially disperse evenly, thus obtaining dispersion I. The mass ratio of electrolyte I, electrolyte II, alkylphenol polyoxyethylene ether, and deionized water is 23:15:7:55.

[0073] S4: Introduction of polymer monomers and photoinitiators

[0074] HEMA and benzoin dimethyl ether were added to dispersion I, with the addition amounts of 1% (mass) and 0.1% (mass) respectively. The mixture was stirred until homogeneous to obtain dispersion II.

[0075] S5: Grinding process

[0076] Dispersion II was placed in a grinder for grinding at a speed of 2000 r / min for 2 hours to obtain a uniform and fine slurry.

[0077] S6: Coating

[0078] The slurry was coated onto 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) using a micro-grooving roller coating method. During the 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, resulting in a base film with the slurry.

[0079] S7: Gelation

[0080] The base film containing the slurry was irradiated under 365nm ultraviolet light for 10 minutes to induce cross-linking polymerization of HEMA, resulting in a base film with a gelled coating.

[0081] S8: Drying

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

[0083] Example 3

[0084] The composite solid electrolyte membrane in this embodiment is prepared through the following steps:

[0085] S1: Preparation of electrolyte I

[0086] LATP powder and LLZTO powder in a mass ratio of 1:1.5 were placed in a ball mill and ball milled at 350 r / min for 1.5 h to mix them uniformly, thus obtaining electrolyte I.

[0087] S2: Preparation of Electrolyte II

[0088] LiBOB and acetamide in a molar ratio of 1:7 were mixed evenly at room temperature (25°C), heated to 45°C, and then slowly cooled to room temperature (25°C) to obtain electrolyte II.

[0089] S3: Initial preparation of slurry

[0090] First, dissolve alkylphenol polyoxyethylene ether in deionized water and stir until homogeneous. Then, gradually add electrolyte I and electrolyte II, and continue stirring for 25 minutes to allow the components to initially disperse evenly, thus obtaining dispersion I. The mass ratio of electrolyte I, electrolyte II, alkylphenol polyoxyethylene ether, and deionized water is 18:20:7:55.

[0091] S4: Introduction of polymer monomers and photoinitiators

[0092] HEMA and benzoin dimethyl ether were added to dispersion I, with the addition amounts of 1% (mass) and 0.1% (mass) respectively. The mixture was stirred until homogeneous to obtain dispersion II.

[0093] S5: Grinding process

[0094] Dispersion II was placed in a grinder for grinding at a speed of 2000 r / min for 2 hours to obtain a uniform and fine slurry.

[0095] S6: Coating

[0096] The slurry was coated onto 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) using a micro-grooving roller coating method. During the 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, resulting in a base film with the slurry.

[0097] S7: Gelation

[0098] The base film containing the slurry was irradiated under 365nm ultraviolet light for 10 minutes to induce cross-linking polymerization of HEMA, resulting in a base film with a gelled coating.

[0099] S8: Drying

[0100] The base membrane with the gelation coating was placed in a drying oven and dried at 70°C for 8 minutes to obtain a composite solid electrolyte membrane.

[0101] Example 4

[0102] The only difference between this embodiment and Example 1 is that HEMA and benzoin dimethyl ether were not used to form a gel network in the solid electrolyte coating. Specifically, the composite solid electrolyte membrane of this embodiment was prepared through the following steps:

[0103] S1: Preparation of electrolyte I:

[0104] LATP powder and LLZTO powder in a mass ratio of 1:1 were placed in a ball mill and ball milled at 350 r / min for 1.5 h to mix them uniformly, thus obtaining electrolyte I.

[0105] S2: Preparation of Electrolyte II:

[0106] LiBOB and acetamide in a molar ratio of 1:7 were mixed evenly 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:

[0108] First, alkylphenol polyoxyethylene ether was dissolved in deionized water and stirred until homogeneous. Then, electrolyte I and electrolyte II were gradually added, and stirring was continued for 25 minutes to allow the components to be initially and evenly dispersed, resulting in a dispersion. The mass ratio of electrolyte I, electrolyte II, alkylphenol polyoxyethylene ether, and deionized water was 28:10:7:55.

[0109] S4: Grinding process:

[0110] The dispersion was placed in a grinder for grinding at a speed of 2000 r / min for 2 hours to obtain a uniform and fine slurry.

[0111] S5: Coating:

[0112] The slurry was coated onto 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) using a micro-grooving roller coating method. During the 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, resulting in a base film with the slurry.

[0113] S7: Drying:

[0114] The base membrane containing the slurry was placed in a drying oven and dried at 70°C for 8 minutes to obtain a composite solid electrolyte membrane.

[0115] Example 5

[0116] 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 through the following steps:

[0117] S1: Preparation of electrolyte I

[0118] LATP powder and LLZTO powder in a mass ratio of 1:0.2 were placed in a ball mill and ball-milled at 350 r / min for 1.5 h to obtain electrolyte I.

[0119] S2: Preparation of Electrolyte II

[0120] LiBOB and acetamide in a molar ratio of 1:7 were mixed evenly at room temperature (25°C), heated to 45°C, and then slowly cooled to room temperature (25°C) to obtain electrolyte II.

[0121] S3: Initial preparation of slurry

[0122] First, dissolve alkylphenol polyoxyethylene ether in deionized water and stir until homogeneous. Then, gradually add electrolyte I and electrolyte II, and continue stirring for 25 minutes to allow the components to initially disperse evenly, thus obtaining dispersion I. The mass ratio of electrolyte I, electrolyte II, alkylphenol polyoxyethylene ether, and deionized water is 28:10:7:55.

[0123] S4: Introduction of polymer monomers and photoinitiators

[0124] HEMA and benzoin dimethyl ether were added to dispersion I, with the addition amounts of 1% (mass) and 0.1% (mass) respectively. The mixture was stirred until homogeneous to obtain dispersion II.

[0125] S5: Grinding process

[0126] Dispersion II was placed in a grinder for grinding at a speed of 2000 r / min for 2 hours to obtain a uniform and fine slurry.

[0127] S6: Coating

[0128] The slurry was coated onto 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) using a micro-grooving roller coating method. During the 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, resulting in a base film with the slurry.

[0129] S7: Gelation

[0130] The base film containing the slurry was irradiated under 365nm ultraviolet light for 10 minutes to induce cross-linking polymerization of HEMA, resulting in a base film with a gelled coating.

[0131] S8: Drying

[0132] The base membrane with the gelation coating was placed in a drying oven and dried at 70°C for 8 minutes to obtain a composite solid electrolyte membrane.

[0133] Example 6

[0134] 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 through the following steps:

[0135] S1: Preparation of electrolyte I

[0136] LATP powder and LLZTO powder in a mass ratio of 3:7 were placed in a ball mill and ball milled at 350 r / min for 1.5 h to mix them uniformly, thus obtaining electrolyte I.

[0137] S2: Preparation of Electrolyte II

[0138] LiBOB and acetamide in a molar ratio of 1:7 were mixed evenly at room temperature (25°C), heated to 45°C, and then slowly cooled to room temperature (25°C) to obtain electrolyte II.

[0139] S3: Initial preparation of slurry

[0140] First, dissolve alkylphenol polyoxyethylene ether in deionized water and stir until homogeneous. Then, gradually add electrolyte I and electrolyte II, and continue stirring for 25 minutes to allow the components to initially disperse evenly, thus obtaining dispersion I. The mass ratio of electrolyte I, electrolyte II, alkylphenol polyoxyethylene ether, and deionized water is 28:10:7:55.

[0141] S4: Introduction of polymer monomers and photoinitiators

[0142] HEMA and benzoin dimethyl ether were added to dispersion I, with the addition amounts of 1% (mass) and 0.1% (mass) respectively. The mixture was stirred until homogeneous to obtain dispersion II.

[0143] S5: Grinding process

[0144] Dispersion II was placed in a grinder for grinding at a speed of 2000 r / min for 2 hours to obtain a uniform and fine slurry.

[0145] S6: Coating

[0146] The slurry was coated onto 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) using a micro-grooving roller coating method. During the 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, resulting in a base film with the slurry.

[0147] S7: Gelation

[0148] The base film containing the slurry was irradiated under 365nm ultraviolet light for 10 minutes to induce cross-linking polymerization of HEMA, resulting in a base film with a gelled coating.

[0149] S8: Drying

[0150] The base membrane with the gelation coating was placed in a drying oven and dried at 70°C for 8 minutes to obtain a composite solid electrolyte membrane.

[0151] Comparative Example 1

[0152] The only difference between this comparative example and Example 1 is that electrolyte II was not added to the solid electrolyte coating. Specifically, the composite solid electrolyte membrane of this comparative example was prepared by the following steps:

[0153] S1: Preparation of electrolyte I

[0154] LATP powder and LLZTO powder in a mass ratio of 1:1 were placed in a ball mill and ball milled at 350 r / min for 1.5 h to mix them uniformly, thus obtaining electrolyte I.

[0155] S2: Initial preparation of slurry

[0156] First, dissolve alkylphenol polyoxyethylene ether in deionized water and stir until homogeneous. Then, gradually add electrolyte I and continue stirring for 25 minutes to allow the components to initially disperse evenly, obtaining dispersion I. The mass ratio of electrolyte I, alkylphenol polyoxyethylene ether, and deionized water is 38:7:55.

[0157] S3: Introduction of polymer monomers and photoinitiators

[0158] HEMA and benzoin dimethyl ether were added to dispersion I, with the addition amounts of 1% (mass) and 0.1% (mass) respectively. The mixture was stirred until homogeneous to obtain dispersion II.

[0159] S4: Grinding process

[0160] Dispersion II was placed in a grinder for grinding at a speed of 2000 r / min for 2 hours to obtain a uniform and fine slurry.

[0161] S5: Coating

[0162] The slurry was coated onto 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) using a micro-grooving roller coating method. During the 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, resulting in a base film with the slurry.

[0163] S6: Gelification

[0164] The base film containing the slurry was irradiated under 365nm ultraviolet light for 10 minutes to induce cross-linking polymerization of HEMA, resulting in a base film with a gelled coating.

[0165] S7: Drying

[0166] The base membrane with the gelation coating was placed in a drying oven and dried at 70°C for 8 minutes to obtain a composite solid electrolyte membrane.

[0167] Comparative Example 2

[0168] The only difference between this comparative example and Example 1 is that electrolyte I was not added to the solid electrolyte coating. Specifically, the composite solid electrolyte membrane of this comparative example was prepared by the following steps:

[0169] S1: Preparation of Electrolyte II

[0170] LiBOB and acetamide in a molar ratio of 1:7 were mixed evenly at room temperature (25°C), heated to 45°C, and then slowly cooled to room temperature (25°C) to obtain electrolyte II.

[0171] S2: Initial preparation of slurry

[0172] First, alkylphenol polyoxyethylene ether was dissolved in deionized water and stirred until homogeneous. Then, electrolyte II was gradually added, and stirring was continued for 25 minutes to allow the components to be initially and evenly dispersed, resulting in dispersion I. The mass ratio of electrolyte II, alkylphenol polyoxyethylene ether, and deionized water was 38:7:55.

[0173] S3: Introduction of polymer monomers and photoinitiators

[0174] HEMA and benzoin dimethyl ether were added to dispersion I, with the addition amounts of 1% (mass) and 0.1% (mass) respectively. The mixture was stirred until homogeneous to obtain dispersion II.

[0175] S4: Grinding process

[0176] Dispersion II was placed in a grinder for grinding at a speed of 2000 r / min for 2 hours to obtain a uniform and fine slurry.

[0177] S5: Coating

[0178] The slurry was coated onto 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) using a micro-grooving roller coating method. During the 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, resulting in a base film with the slurry.

[0179] S6: Gelification

[0180] The base film containing the slurry was irradiated under 365nm ultraviolet light for 10 minutes to induce cross-linking polymerization of HEMA, resulting in a base film with a gelled coating.

[0181] S7: Drying

[0182] The base membrane with the gelation coating was placed in a drying oven and dried at 70°C for 8 minutes to obtain a composite solid electrolyte membrane.

[0183] Comparative Example 3

[0184] The only difference between this comparative example and Example 1 is that LLZTO was not used in electrolyte I. Specifically, the composite solid electrolyte membrane of this comparative example was prepared by the following steps:

[0185] S1: Preparation of electrolyte I

[0186] LATP powder was placed in a ball mill and milled at 350 r / min for 1.5 h to obtain electrolyte I.

[0187] S2: Preparation of Electrolyte II

[0188] LiBOB and acetamide in a molar ratio of 1:7 were mixed evenly at room temperature (25°C), heated to 45°C, and then slowly cooled to room temperature (25°C) to obtain electrolyte II.

[0189] S3: Initial preparation of slurry

[0190] First, dissolve alkylphenol polyoxyethylene ether in deionized water and stir until homogeneous. Then, gradually add electrolyte I and electrolyte II, and continue stirring for 25 minutes to allow the components to initially disperse evenly, thus obtaining dispersion I. The mass ratio of electrolyte I, electrolyte II, alkylphenol polyoxyethylene ether, and deionized water is 28:10:7:55.

[0191] S4: Introduction of polymer monomers and photoinitiators

[0192] HEMA and benzoin dimethyl ether were added to dispersion I, with the addition amounts of 1% (mass) and 0.1% (mass) respectively. The mixture was stirred until homogeneous to obtain dispersion II.

[0193] S5: Grinding process

[0194] Dispersion II was placed in a grinder for grinding at a speed of 2000 r / min for 2 hours to obtain a uniform and fine slurry.

[0195] S6: Coating

[0196] The slurry was coated onto 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) using a micro-grooving roller coating method. During the 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, resulting in a base film with the slurry.

[0197] S7: Gelation

[0198] The base film containing the slurry was irradiated under 365nm ultraviolet light for 10 minutes to induce cross-linking polymerization of HEMA, resulting in a base film with a gelled coating.

[0199] S8: Drying

[0200] The base membrane with the gelation coating was placed in a drying oven and dried at 70°C for 8 minutes to obtain a composite solid electrolyte membrane.

[0201] Comparative Example 4

[0202] The only difference between this comparative example and Example 1 is that LATP was not used in electrolyte I. Specifically, the composite solid electrolyte membrane of this comparative example was prepared by the following steps:

[0203] S1: Preparation of electrolyte I

[0204] LLZTO powder was placed in a ball mill and ball-milled at 350 r / min for 1.5 h to obtain electrolyte I.

[0205] S2: Preparation of Electrolyte II

[0206] LiBOB and acetamide in a molar ratio of 1:7 were mixed evenly at room temperature (25°C), heated to 45°C, and then slowly cooled to room temperature (25°C) to obtain electrolyte II.

[0207] S3: Initial preparation of slurry

[0208] First, dissolve alkylphenol polyoxyethylene ether in deionized water and stir until homogeneous. Then, gradually add electrolyte I and electrolyte II, and continue stirring for 25 minutes to allow the components to initially disperse evenly, thus obtaining dispersion I. The mass ratio of electrolyte I, electrolyte II, alkylphenol polyoxyethylene ether, and deionized water is 28:10:7:55.

[0209] S4: Introduction of polymer monomers and photoinitiators

[0210] HEMA and benzoin dimethyl ether were added to dispersion I, with the addition amounts of 1% (mass) and 0.1% (mass) respectively. The mixture was stirred until homogeneous to obtain dispersion II.

[0211] S5: Grinding process

[0212] Dispersion II was placed in a grinder for grinding at a speed of 2000 r / min for 2 hours to obtain a uniform and fine slurry.

[0213] S6: Coating

[0214] The slurry was coated onto 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) using a micro-grooving roller coating method. During the 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, resulting in a base film with the slurry.

[0215] S7: Gelation

[0216] The base film containing the slurry was irradiated under 365nm ultraviolet light for 10 minutes to induce cross-linking polymerization of HEMA, resulting in a base film with a gelled coating.

[0217] S8: Drying

[0218] The base membrane with the gelation coating was placed in a drying oven and dried at 70°C for 8 minutes to obtain a composite solid electrolyte membrane.

[0219] Comparative Example 5

[0220] The diaphragm in this comparative example is a wet-process polyethylene monolayer membrane with a porosity of 62%, a pore size of 150 nm, and a thickness of 16 μm.

[0221] Test case

[0222] The membranes prepared in each embodiment and comparative example were tested for air permeability and liquid absorption rate. Then, the membranes were assembled into battery cells, and the internal resistance of the battery cells and the ionic conductivity of the membranes were tested. The specific test methods are as follows:

[0223] (1) Liquid absorption rate test: The liquid absorption rate of the solid electrolyte membrane was tested by weighing method.

[0224] (2) Air permeability test: The air permeability of the solid electrolyte membrane was tested using an air permeability tester.

[0225] (3) Internal resistance and ionic conductivity test: The internal resistance and ionic conductivity of the battery cell were measured using an electrochemical workstation.

[0226] The method for assembling the separator into a battery cell is as follows: the positive electrode, separator and negative electrode are stacked to form the basic structure of the battery cell. The stacked battery cell is placed into the battery case and the tabs are welded. Then, the stacked battery cell is hot-pressed for 150 seconds at a temperature of 95℃ and a pressure of 2MPa to shape the battery cell.

[0227] The test results are shown in Table 1.

[0228] Table 1. Test results of diaphragm and cell performance

[0229]

[0230] Analyzing the data in Table 1, we can see that:

[0231] (1) Compared with Comparative Example 5, the ionic conductivity of Examples 1-6 is significantly improved and the internal resistance of the cell is significantly reduced. This indicates that by applying the solid electrolyte coating of the present invention to the surface of the separator base film, the ionic conductivity of the separator can be effectively improved and the internal resistance of the battery can be reduced.

[0232] (2) Compared with Comparative Examples 1 and 2, Examples 1-3 have higher ionic conductivity and lower cell internal resistance. This indicates that by using the specific electrolytes I and II of this invention in the solid electrolyte coating within the separator, the ionic conductivity of the separator can be improved and the battery internal resistance can be reduced. The reasons are as follows: During the process of making the separator into a battery, electrolyte II transforms into a molten state during hot pressing, which can fill the gap between the separator and the electrode, thereby reducing the battery internal resistance and facilitating battery charging and discharging; and during the preparation of the solid electrolyte coating, since the drying temperature is higher than the phase transition temperature of electrolyte II, electrolyte II can transform into a molten state with certain fluidity and viscosity, filling between LATP and LLZTO, and acting as a bridge at the interface between the two different structures of LATP and LLZTO. The ion transport channel formed by this helps to improve the lithium ion conduction efficiency; in addition, LiBOB in electrolyte II can form a 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 this invention to jointly block the side reactions between lithium metal and electrolyte, thereby reducing the increase in interface resistance and reducing the battery internal resistance.

[0233] (3) Compared with Examples 5, 6, Comparative Examples 3 and 4, Examples 1-3 have higher ionic conductivity and lower cell internal resistance. This indicates that by using LATP and LLZTO as electrolyte I, the ionic conductivity of the separator can be improved and the battery internal resistance can be reduced, and the ratio of LATP to LLZTO affects 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-type structure and also has its own lithium ion conduction path; after electrolyte II forms a bridge between LATP and LLZTO, these two different ion conduction channels can cooperate with each other to improve lithium ion conduction efficiency.

[0234] (4) Compared with Example 4, Examples 1-3 have higher ionic conductivity and lower cell internal resistance. This indicates that by adding poly(hydroxyethyl methacrylate) gel to the solid electrolyte coating, the ionic conductivity of the separator 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-level bridge" to form a "particle-polymer" bicontinuous phase with the two solid electrolytes (electrolyte I and electrolyte II). Lithium ions can migrate simultaneously through ceramic lattice channels and polymer chain segments, achieving complementarity of ion conduction pathways. Furthermore, poly(hydroxyethyl methacrylate) gel can also form hydrogen bonds or coordination with hydroxyl and oxygen ions on the surface of solid electrolyte particles through polar groups (such as hydroxyl groups), enhancing interparticle adhesion and constructing a continuous ion conduction pathway.

[0235] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Unless otherwise specified, the raw materials and equipment used in this invention are conventional in the art and can be obtained through conventional commercial means; unless otherwise specified, the methods used in this invention are conventional methods in the art.

[0236] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for reducing the internal resistance of a lithium-ion battery, characterized in that, The internal resistance of a lithium-ion battery is reduced by adding electrolyte II to a solid electrolyte coating. The lithium-ion battery includes a composite solid electrolyte membrane. The composite solid electrolyte membrane includes a base membrane and a solid electrolyte coating disposed on at least one surface of the base membrane. The solid electrolyte coating includes electrolyte I and electrolyte II in a mass ratio of 1:0.3 to 1.

2. Electrolyte I is lithium aluminum titanium phosphate and lithium lanthanum zirconium tantalum oxide. Electrolyte II is a composite of lithium dioxoborate and acetamide in a molar ratio of 1:6.5 to 7.

5. The preparation steps of the composite solid electrolyte membrane include: dispersing electrolyte I and electrolyte II in a dispersion medium, coating them onto the surface of the base membrane, and drying them at 60~90℃.

2. The method according to claim 1, characterized in that, The mass ratio of lithium titanium aluminum phosphate to lithium lanthanum zirconium tantalum oxide is 1:0.6~1.

5.

3. The method according to claim 1, characterized in that, The solid electrolyte coating also includes poly(hydroxyethyl methacrylate) gel, with electrolyte I and electrolyte II 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 method according to claim 1, characterized in that, The base membrane is a polypropylene single-layer membrane, a polyethylene single-layer membrane, a polyolefin multilayer co-extruded membrane, or a cellulose membrane.

5. The method according to claim 1 or 4, characterized in that, The porosity of the base film is 45-80%, and the pore size is 80-800 nm.

6. The method according to claim 1, characterized in that, The preparation steps of the composite solid electrolyte membrane include: dispersing electrolyte I and electrolyte II in a dispersion medium, adding hydroxyethyl methacrylate and an initiator, coating the membrane onto the surface of a base membrane, then carrying out the polymerization reaction of hydroxyethyl methacrylate under the action of the initiator, and finally drying at 60~90℃ to obtain the composite solid electrolyte membrane.

7. The method according to claim 1 or 6, characterized in that, The preparation steps of electrolyte II include: mixing lithium dioxoborate and acetamide, heating to 40~50℃ and then cooling to obtain electrolyte II.

8. The method according to claim 1 or 6, characterized in that, The preparation steps of electrolyte I include: ball milling lithium titanium aluminum 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.

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

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