Multifunctional composite low-temperature diaphragm and preparation method thereof

Abstract

The multifunctional composite low-temperature diaphragm comprises a base film and a mixed coating layer, the mixed coating layer is formed on at least one side of the base film, and the mixed coating layer comprises an anti-dendritic crystal material and a solid electrolyte; or comprises a base film, a first coating layer and a second coating layer, the first coating layer comprises an anti-dendritic crystal material, and the second coating layer comprises a solid electrolyte; wherein the first coating is formed on one side of the base film, and the second coating is formed on the other side of the base film; or the first coating is formed on one side of the base film, and the second coating is formed on one side, opposite to the base film, of the first coating; or the second coating is formed on one side of the base film, and the first coating is formed on one side, opposite to the base film, of the second coating. According to the invention, the low-temperature discharge and the low-temperature cycle of the lithium battery are further improved through the synergistic effect between the dendritic crystal resistant material and the solid electrolyte. In addition, the invention also provides a preparation method of the multifunctional composite low-temperature diaphragm.

Description

Technical Field

[0001] The present invention relates to the technical field related to lithium ion batteries, and in particular to a multifunctional composite low-temperature diaphragm and a preparation method of the low-temperature diaphragm. Background Art

[0002] Lithium-ion batteries have been commercially used in many fields due to their high energy density, long life, low self-discharge rate, and fast charge and discharge capabilities, such as mobile phones, laptops, energy storage power stations, etc., especially in the field of electric vehicles, which has developed rapidly in recent years. However, the poor low-temperature performance of lithium-ion batteries limits their application in cold conditions, which is specifically manifested in the weakened discharge capacity at low temperatures and the poor cycle performance caused by the growth of lithium dendrites. Therefore, it is very urgent and necessary to improve the low-temperature performance of lithium batteries and expand their scope of use, which has market prospects.

[0003] At present, the improvement of low-temperature performance is mainly carried out from the material system of the battery cell, including optimization of the diaphragm coating, positive and negative electrode materials, electrolyte formulation, etc., to increase the lithium ion transmission rate at low temperatures, reduce lithium plating and the growth of lithium dendrites, and improve low-temperature performance.

[0004] In terms of the diaphragm, the lithium dendrite problem can be improved by adding a dendrite-suppressing metal compound coating, but it still cannot solve the problem of lithium battery's low-temperature discharge capacity attenuation, and cannot fully improve the low-temperature performance of lithium-ion batteries.

[0005] Based on this, developing a low-temperature diaphragm with improved low-temperature performance, improving the overall low-temperature performance of lithium batteries, and expanding the scope of use of lithium batteries are one of the directions that R&D personnel urgently need to break through. Summary of the invention

[0006] At present, the low-temperature performance of the diaphragm is improved only from a single performance point of view, and the low-temperature performance cannot be improved from multiple aspects as a whole. The present invention can reduce the interface impedance, increase the lithium ion transmission rate, and improve the low-temperature discharge capacity through the optimization of the multifunctional diaphragm coating, while also inhibiting the growth of lithium dendrites and improving the low-temperature cycle performance.

[0007] The present invention provides a multifunctional composite low-temperature diaphragm, comprising: a base film and a mixed coating, wherein the mixed coating is formed on at least one side of the base film, and the mixed coating contains an anti-dendrite material and a solid electrolyte.

[0008] Preferably, the anti-dendrite material includes one or more of tin oxide, stannous oxide, aluminum fluoride, strontium fluoride, and aluminum oxide.

[0009] Preferably, the solid electrolyte includes one or more of LLZO, LLZTO, LAGP, and LATP.

[0010] Preferably, the base film has a thickness of 5 μm to 20 μm, and the mixed coating has a thickness of 1 μm to 10 μm.

[0011] Preferably, the particle size D50 of the anti-dendrite material is 0.1 μm to 3 μm, and the particle size D50 of the solid electrolyte is 0.1 μm to 3 μm.

[0012] The present invention proposes a multifunctional composite low-temperature diaphragm, comprising: a base film, a first coating, and a second coating, wherein the first coating comprises an anti-dendrite material, and the second coating comprises a solid electrolyte; wherein the first coating is formed on one side of the base film, and the second coating is formed on the other side of the base film; or the first coating is formed on one side of the base film, and the second coating is formed on the side of the first coating opposite to the base film; or the second coating is formed on one side of the base film, and the first coating is formed on the side of the second coating opposite to the base film.

[0013] Preferably, the anti-dendrite material includes one or more of tin oxide, stannous oxide, aluminum fluoride, strontium fluoride, and aluminum oxide.

[0014] Preferably, the solid electrolyte includes one or more of LLZO, LLZTO, LAGP, and LATP.

[0015] Preferably, the base film has a thickness of 5 μm to 20 μm, the first coating layer has a thickness of 1 μm to 10 μm, and the second coating layer has a thickness of 1 μm to 10 μm.

[0016] Preferably, the particle size D50 of the anti-dendrite material is 0.1 μm to 3 μm, and the particle size D50 of the solid electrolyte is 0.1 μm to 3 μm.

[0017] The present invention proposes a method for preparing a multifunctional composite low-temperature diaphragm, comprising: providing a base film; providing a mixed slurry, the mixed slurry comprising an anti-dendrite material and a solid electrolyte; coating the mixed slurry on one side or both sides of the base film; and drying the mixed slurry to form a mixed coating.

[0018] The present invention proposes a method for preparing a multifunctional composite low-temperature diaphragm, comprising: providing a base film; providing a first slurry and a second slurry, wherein the first slurry contains an anti-dendrite material and the second slurry contains a solid electrolyte; applying the first slurry on one side of the base film and applying the second slurry on the other side of the base film; and drying the first slurry to form a first coating and drying the second slurry to form a second coating.

[0019] The present invention proposes a method for preparing a multifunctional composite low-temperature diaphragm, comprising: providing a base film; providing a first slurry and a second slurry, wherein the first slurry comprises an anti-dendrite material and the second slurry comprises a solid electrolyte; applying the first slurry to one side of the base film, and drying the first slurry to form a first coating; and applying the second slurry to a side of the first coating opposite to the base film, and drying the second slurry to form a second coating.

[0020] The present invention proposes a method for preparing a multifunctional composite low-temperature diaphragm, comprising: providing a base film; providing a first slurry and a second slurry, wherein the first slurry comprises an anti-dendrite material and the second slurry comprises a solid electrolyte; applying the second slurry to one side of the base film, and drying the second slurry to form a second coating; and applying the first slurry to the side of the second coating opposite to the base film, and drying the first slurry to form a first coating.

[0021] According to the present invention, two functional oxide materials are provided for coating the diaphragm; wherein the anti-dendrite material can react with lithium, reduce the growth of lithium dendrites, and improve the low-temperature cycle performance, while the solid electrolyte can reduce the interfacial impedance of the lithium battery at low temperatures, increase the lithium ion transfer rate, and improve the low-temperature discharge capability. Through the synergistic effect between the two functional oxide materials, the low-temperature discharge and low-temperature cycle of the lithium battery are further improved. In terms of testing, the anti-lithium dendrite function is evaluated through the design of a low N / P ratio battery, and the normal temperature cycle is greatly improved. In addition, the two functional oxide materials are adapted to the existing coating process to coat the diaphragm, and no major changes are required to the production line. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a cross-sectional schematic diagram showing a multifunctional composite low-temperature diaphragm according to a first embodiment of the present invention;

[0023] Figure 2 is a cross-sectional schematic diagram showing a multifunctional composite low-temperature diaphragm according to a second embodiment of the present invention;

[0024] Figure 3 is a cross-sectional schematic diagram showing a multifunctional composite low-temperature diaphragm according to a third embodiment of the present invention;

[0025] Figure 4 It is a cross-sectional schematic diagram showing a multifunctional composite low-temperature diaphragm according to a fourth embodiment of the present invention. DETAILED DESCRIPTION

[0026] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0027] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0028] Please refer to Figure 1 , which presents a multifunctional composite low-temperature diaphragm of the first embodiment of the present invention, comprising a base film (1) and a mixed coating (2), wherein the mixed coating (2) is formed on one side or both sides of the base film (1), and the mixed coating (2) comprises an anti-dendrite material and a solid electrolyte.

[0029] The base film (1) may be, but is not limited to, a polyolefin base film, preferably a polyethylene base film, a polypropylene base film or more. The thickness of the base film (1) may be, but is not limited to, 5 μm to 20 μm, preferably 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm. The thickness of the mixed coating (2) may be, but is not limited to, 1 μm to 10 μm, preferably 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm.

[0030] The anti-dendrite material may include, but is not limited to, one or more of tin oxide, stannous oxide, aluminum fluoride, strontium fluoride, and aluminum oxide, preferably one or more of tin oxide and aluminum oxide. Under the condition that the anti-dendrite material includes tin oxide and aluminum oxide, the mass ratio between tin oxide and aluminum oxide may be, but is not limited to, 1:(1 to 8), preferably 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, or 1:8. The particle size D50 of the anti-dendrite material may be, but is not limited to, 0.1 μm to 3 μm, preferably 0.1 μm, 0.25 μm, 0.5 μm, 0.75 μm, 1 μm, 1.25 μm, 1.5 μm, 1.75 μm, 2 μm, 2.25 μm, 2.5 μm, 2.75 μm, or 3 μm. Based on the total mass of the mixed coating (2), the anti-dendrite material may account for 15wt% to 61wt%, preferably 15wt%, 17wt%, 19wt%, 21wt%, 23wt%, 25wt%, 27wt%, 29wt%, 31wt%, 33wt%, 35wt%, 37wt%, 39wt%, 41wt%, 43wt%, 45wt%, 47wt%, 49wt%, 51wt%, 53wt%, 55wt%, 57wt%, 59wt%, or 61wt%.

[0031] The solid electrolyte may include but is not limited to one or more of LLZO, LLZTO, LAGP, and LATP. LLZO is lithium lanthanum zirconium oxide, which can be expressed as Li 7 La 3 Zr 2 O 12 LLZTO is lithium lanthanum zirconium tantalum oxide, which can be expressed as Li 6.75 La 3 Zr 1.75 Ta 0.25 O represents; LAGP is lithium aluminum germanium phosphate, which can be expressed as Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 Indicates; LATP is lithium aluminum titanium phosphate, which can be expressed as Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 The particle size D50 of the solid electrolyte may be, but is not limited to, 0.1 μm to 3 μm, preferably 0.1 μm, 0.25 μm, 0.5 μm, 0.75 μm, 1 μm, 1.25 μm, 1.5 μm, 1.75 μm, 2 μm, 2.25 μm, 2.5 μm, 2.75 μm, or 3 μm. Based on the total mass of the mixed coating (2), the solid electrolyte may account for 15wt% to 61wt%, preferably 15wt%, 17wt%, 19wt%, 21wt%, 23wt%, 25wt%, 27wt%, 29wt%, 31wt%, 33wt%, 35wt%, 37wt%, 39wt%, 41wt%, 43wt%, 45wt%, 47wt%, 49wt%, 51wt%, 53wt%, 55wt%, 57wt%, 59wt%, or 61wt%.

[0032] In order to make the anti-dendritic material and the solid electrolyte and other components uniformly dispersed in the mixed coating (2), the mixed coating (2) may further include a dispersant, which may include but is not limited to one or more of sodium polyacrylate, polyethylene oxide, polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, polyether silicone copolymer, polyoxyethylene alkanolamide, and polyacrylate ammonium salt, preferably including a first dispersant and a second dispersant, the first dispersant including sodium polyacrylate, and the second dispersant including sodium carboxymethyl cellulose. Based on the total mass of the mixed coating (2), the dispersant may account for 1wt% to 5wt%, preferably 1wt%, 2wt%, 3wt%, 4wt%, or 5wt%. Under the condition that the dispersant includes a first dispersant and a second dispersant, based on the total mass of the mixed coating (2), the first dispersant can account for 0.5wt% to 2.5wt%, preferably 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 2.5wt%; the second dispersant can account for 0.5wt% to 2.5wt%, preferably 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 2.5wt%.

[0033] In order to improve the hydrophilicity of the multifunctional composite low-temperature diaphragm, the mixed coating (2) may further include a wetting agent, which may include but is not limited to one or more of polyoxyethylene alkylphenol ethers, polyoxyethylene fatty alcohol ethers, and polyoxyethylene polyoxypropylene block copolymers. Based on the total mass of the mixed coating (2), the wetting agent may account for 0.05wt% to 0.2wt%, preferably 0.05wt%, 0.1wt%, 0.15wt%, or 0.2wt%.

[0034] In order to make the anti-dendritic material and the solid electrolyte and other components firmly bonded together in the mixed coating (2), or to improve the bonding performance between the base film (1) and the mixed coating (2), the mixed coating (2) may further include a binder, which may include but is not limited to one or more polymers obtained by copolymerization of acrylate, methacrylate, styrene-butadiene rubber or nitrile rubber with olefins or esters. Based on the total mass of the mixed coating (2), the binder may account for 6wt% to 20wt%, preferably 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, or 20wt%.

[0035] The following further illustrates the preparation method of the multifunctional composite low-temperature diaphragm of the present embodiment, but it should not be used as a technical solution to limit the multifunctional composite low-temperature diaphragm of the present embodiment; that is, the multifunctional composite low-temperature diaphragm of the present embodiment can be prepared by other preparation methods not mentioned.

[0036] First, a base film (1) is provided.

[0037] Next, a mixed slurry is provided, wherein the mixed slurry includes an anti-dendrite material and a solid electrolyte. The mixed slurry may further include one or more of a dispersant, a wetting agent, and a binder. Based on the total mass of the mixed slurry, the dispersant may account for 0.5wt% to 2.5wt%, preferably 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 2.5wt%; the wetting agent may account for 0.025wt% to 0.1wt%, preferably 0.025wt%, 0.05wt%, 0.075wt%, or 0.1wt%; the binder may account for 3wt% to 10wt%, preferably 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%. Under the condition that the dispersant includes a first dispersant and a second dispersant, based on the total mass of the mixed slurry, the first dispersant may account for 0.25wt% to 1.25wt%, preferably 0.25wt%, 0.05wt%, 0.75wt%, 1wt%, or 1.25wt%; the second dispersant may account for 0.25wt% to 1.25wt%, preferably 0.25wt%, 0.05wt%, 0.75wt%, 1wt%, or 1.25wt%. For example, the preparation of the mixed slurry may be as follows but not limited to: first add the first dispersant to the solvent (such as water), stir evenly, and then add the anti-dendrite material and the solid electrolyte; then, add the second dispersant after grinding, add the wetting agent and the binder, and stir evenly to obtain the mixed slurry. The mixed slurry may be but not limited to an aqueous slurry. The solid content of the mixed slurry may be, but not limited to, 30% to 60%, preferably 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, or 60%. The viscosity of the mixed slurry may be, but not limited to, 10mPa·s to 50mPa·s, preferably 10mPa·s, 15mPa·s, 20mPa·s, 25mPa·s, 30mPa·s, 35mPa·s, 40mPa·s, 45mPa·s, or 50mPa·s. The pH of the mixed slurry may be, but not limited to, 7 to 10, preferably 7, 7.5, 8, 8.5, 9, 9.5, or 10.

[0038] Then, the mixed slurry is coated on one or both sides of the base film (1).

[0039] Finally, the mixed slurry is dried to form a mixed coating (2).

[0040] Please refer to Figure 2, which presents a multifunctional composite low-temperature diaphragm of a second embodiment of the present invention, comprising a base film (1), a first coating (3) and a second coating (4), wherein the first coating (3) is formed on one side of the base film (1), and the second coating (4) is formed on the other side of the base film (1), and the first coating (3) comprises an anti-dendrite material, and the second coating (4) comprises a solid electrolyte.

[0041] The base film (1) may be, but is not limited to, a polyolefin base film, preferably a polyethylene base film, a polypropylene base film or more. The thickness of the base film (1) may be, but is not limited to, 5 μm to 20 μm, preferably 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm. The thickness of the first coating (3) may be, but is not limited to, 1 μm to 10 μm, preferably 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. The thickness of the second coating (4) may be, but is not limited to, 1 μm to 10 μm, preferably 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm.

[0042] The anti-dendrite material may include, but is not limited to, one or more of tin oxide, stannous oxide, aluminum fluoride, strontium fluoride, and aluminum oxide, preferably one or more of tin oxide and aluminum oxide. Under the condition that the anti-dendrite material includes tin oxide and aluminum oxide, the mass ratio between tin oxide and aluminum oxide may be, but is not limited to, 1:(1 to 8), preferably 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, or 1:8. The particle size D50 of the anti-dendrite material may be, but is not limited to, 0.1 μm to 3 μm, preferably 0.1 μm, 0.25 μm, 0.5 μm, 0.75 μm, 1 μm, 1.25 μm, 1.5 μm, 1.75 μm, 2 μm, 2.25 μm, 2.5 μm, 2.75 μm, or 3 μm. Based on the total mass of the first coating (3), the anti-dendrite material may account for 50wt% to 96wt%, preferably 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt%, 62wt%, 64wt%, 66wt%, 68wt%, 70wt%, 72wt%, 74wt%, 76wt%, 78wt%, 80wt%, 82wt%, 84wt%, 86wt%, 88wt%, 90wt%, 92wt%, 94wt%, or 96wt%.

[0043] The solid electrolyte may include but is not limited to one or more of LLZO, LLZTO, LAGP, and LATP. LLZO is lithium lanthanum zirconium oxide, which can be expressed as Li 7 La3 Zr 2 O 12 LLZTO is lithium lanthanum zirconium tantalum oxide, which can be expressed as Li 6.75 La 3 Zr 1.75 Ta 0.25 O represents; LAGP is lithium aluminum germanium phosphate, which can be expressed as Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 Indicates; LATP is lithium aluminum titanium phosphate, which can be expressed as Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 The particle size D50 of the solid electrolyte may be, but is not limited to, 0.1 μm to 3 μm, preferably 0.1 μm, 0.25 μm, 0.5 μm, 0.75 μm, 1 μm, 1.25 μm, 1.5 μm, 1.75 μm, 2 μm, 2.25 μm, 2.5 μm, 2.75 μm, or 3 μm. Based on the total mass of the second coating (4), the solid electrolyte may account for 50wt% to 96wt%, preferably 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt%, 62wt%, 64wt%, 66wt%, 68wt%, 70wt%, 72wt%, 74wt%, 76wt%, 78wt%, 80wt%, 82wt%, 84wt%, 86wt%, 88wt%, 90wt%, 92wt%, 94wt%, or 96wt%.

[0044] In order to make the anti-dendritic material and the solid electrolyte and other components uniformly dispersed in the first coating (3) and the second coating (4) respectively, the first coating (3) may further include a dispersant. The dispersant of the first coating (3) may include but is not limited to one or more of sodium polyacrylate, polyethylene oxide, polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, polyether silicone copolymer, polyoxyethylene alkanolamide, and polyacrylate ammonium salt, preferably including a first dispersant and a second dispersant. The first dispersant of the first coating (3) includes sodium polyacrylate, and the second dispersant of the first coating (3) includes sodium carboxymethyl cellulose; the second coating (4) may further include a dispersant. The dispersant of the second coating (4) may include but is not limited to one or more of sodium polyacrylate, polyethylene oxide, polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, polyether silicone copolymer, polyoxyethylene alkanolamide, and polyacrylate ammonium salt, preferably including a first dispersant and a second dispersant. The first dispersant of the second coating (4) includes sodium polyacrylate, and the second dispersant of the second coating (4) includes sodium carboxymethyl cellulose. Based on the total mass of the first coating (3), the dispersant of the first coating (3) may account for 1 wt% to 5 wt%, preferably 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%; based on the total mass of the second coating (4), the dispersant of the second coating (4) may account for 1 wt% to 5 wt%, preferably 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%. Under the condition that the dispersant of the first coating (3) includes the first dispersant and the second dispersant, based on the total mass of the first coating (3), the first dispersant of the first coating (3) may account for 0.5 wt% to 2.5 wt%, preferably 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, or 2.5 wt%; the second dispersant of the first coating (3) may account for 0.5 wt% to 2.5 wt%, preferably 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, or 2.5 wt%. Under the condition that the dispersant of the second coating (4) includes the first dispersant and the second dispersant, based on the total mass of the second coating (4), the first dispersant of the second coating (4) can account for 0.5wt% to 2.5wt%, preferably 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 2.5wt%; the second dispersant of the second coating (4) can account for 0.5wt% to 2.5wt%, preferably 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 2.5wt%.

[0045] In order to improve the hydrophilicity of the multifunctional composite low-temperature diaphragm, the first coating (3) may further include a wetting agent, and the wetting agent of the first coating (3) may include but is not limited to one or more of polyoxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, and polyoxyethylene polyoxypropylene block copolymer; the second coating (4) may further include a wetting agent, and the wetting agent of the second coating (4) may include but is not limited to one or more of polyoxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, and polyoxyethylene polyoxypropylene block copolymer. Based on the total mass of the first coating (3), the wetting agent of the first coating (3) may account for 0.05wt% to 0.2wt%, preferably 0.05wt%, 0.1wt%, 0.15wt%, or 0.2wt%; based on the total mass of the second coating (4), the wetting agent of the second coating (4) may account for 0.05wt% to 0.2wt%, preferably 0.05wt%, 0.1wt%, 0.15wt%, or 0.2wt%.

[0046] In order to ensure that the anti-dendrite material and the solid electrolyte and other components are firmly bonded together in the first coating (3) and the second coating (4), or to improve the bonding performance between the base film (1) and the first coating (3) and the second coating (4), the first coating (3) may further include a binder. The binder of the first coating (3) may include but is not limited to one or more polymers obtained by copolymerizing acrylates, methacrylates, styrene-butadiene rubber or nitrile rubber with olefins or esters; the second coating (4) may further include a binder. The binder of the second coating (4) may include but is not limited to one or more polymers obtained by copolymerizing acrylates, methacrylates, styrene-butadiene rubber or nitrile rubber with olefins or esters. Based on the total mass of the first coating (3), the binder of the first coating (3) may account for 6wt% to 20wt%, preferably 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, or 20wt%; based on the total mass of the second coating (4), the binder of the second coating (4) may account for 6wt% to 20wt%, preferably 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, or 20wt%.

[0047] The following further illustrates the preparation method of the multifunctional composite low-temperature diaphragm of the present embodiment, but it should not be used as a technical solution to limit the multifunctional composite low-temperature diaphragm of the present embodiment; that is, the multifunctional composite low-temperature diaphragm of the present embodiment can be prepared by other preparation methods not mentioned.

[0048] First, a base film (1) is provided.

[0049] Next, a first slurry and a second slurry are provided, wherein the first slurry comprises an anti-dendrite material, and the second slurry comprises a solid electrolyte. The first slurry may further comprise one or more of a dispersant, a wetting agent, and a binder of the first coating (3). Based on the total mass of the first slurry, the dispersant of the first coating (3) may account for 0.5wt% to 2.5wt%, preferably 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 2.5wt%; the wetting agent of the first coating (3) may account for 0.025wt% to 0.1wt%, preferably 0.025wt%, 0.05wt%, 0.075wt%, or 0.1wt%; the binder of the first coating (3) may account for 3wt% to 10wt%, preferably 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%. Under the condition that the dispersant of the first coating (3) includes the first dispersant and the second dispersant, based on the total mass of the first slurry, the first dispersant of the first coating (3) can account for 0.25wt% to 1.25wt%, preferably 0.25wt%, 0.05wt%, 0.75wt%, 1wt%, or 1.25wt%; the second dispersant of the first coating (3) can account for 0.25wt% to 1.25wt%, preferably 0.25wt%, 0.05wt%, 0.75wt%, 1wt%, or 1.25wt%. For example, the preparation of the first slurry can be as follows but not limited to: first add the first dispersant of the first coating (3) to the solvent (such as water), stir evenly and then add the anti-dendritic material; then, add the second dispersant of the first coating (3) after grinding, add the wetting agent and binder of the first coating (3), stir evenly to obtain the first slurry. The first slurry can be but not limited to a water-based slurry. The solid content of the first slurry may be, but not limited to, 30% to 60%, preferably 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, or 60%. The viscosity of the first slurry may be, but not limited to, 10mPa·s to 50mPa·s, preferably 10mPa·s, 15mPa·s, 20mPa·s, 25mPa·s, 30mPa·s, 35mPa·s, 40mPa·s, 45mPa·s, or 50mPa·s. The pH of the first slurry may be, but not limited to, 7 to 10, preferably 7, 7.5, 8, 8.5, 9, 9.5, or 10. The second slurry may further include one or more of a dispersant, a wetting agent, and a binder of the second coating (4).Based on the total mass of the second slurry, the dispersant of the second coating (4) may account for 0.5wt% to 2.5wt%, preferably 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 2.5wt%; the wetting agent of the second coating (4) may account for 0.025wt% to 0.1wt%, preferably 0.025wt%, 0.05wt%, 0.075wt%, or 0.1wt%; the binder of the second coating (4) may account for 3wt% to 10wt%, preferably 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%. Under the condition that the dispersant of the second coating (4) includes the first dispersant and the second dispersant, based on the total mass of the second slurry, the first dispersant of the second coating (4) can account for 0.25wt% to 1.25wt%, preferably 0.25wt%, 0.05wt%, 0.75wt%, 1wt%, or 1.25wt%; the second dispersant of the second coating (4) can account for 0.25wt% to 1.25wt%, preferably 0.25wt%, 0.05wt%, 0.75wt%, 1wt%, or 1.25wt%. For example, the preparation of the second slurry can be as follows but not limited to: first add the first dispersant of the second coating (4) to the solvent (such as water), stir evenly and then add the solid electrolyte; then, add the second dispersant of the second coating (4) after grinding, add the wetting agent and binder of the second coating (4), stir evenly to obtain the second slurry. The second slurry can be but not limited to an aqueous slurry. The solid content of the second slurry may be, but is not limited to, 30% to 60%, preferably 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, or 60%. The viscosity of the second slurry may be, but is not limited to, 10mPa·s to 50mPa·s, preferably 10mPa·s, 15mPa·s, 20mPa·s, 25mPa·s, 30mPa·s, 35mPa·s, 40mPa·s, 45mPa·s, or 50mPa·s. The pH of the second slurry may be, but is not limited to, 7 to 10, preferably 7, 7.5, 8, 8.5, 9, 9.5, or 10.

[0050] Then, the first slurry is applied on one side of the base film (1), and the second slurry is applied on the other side of the base film (1).

[0051] Finally, the first slurry is dried to form a first coating layer (3), and the second slurry is dried to form a second coating layer (4).

[0052] It should be noted that the symbol a represents "applying the first slurry to one side of the base film (1)", the symbol b represents "applying the second slurry to the other side of the base film (1)", the symbol c represents "drying the first slurry to form a first coating layer (3)", and the symbol d represents "drying the second slurry to form a second coating layer (4)". The order of the above four steps can be, but is not limited to, a→b→c→d, a→b→d→c, b→a→c→d, b→a→d→c, a→c→b→d, or b→d→a→c.

[0053] Please refer to Figure 3 , which presents a multifunctional composite low-temperature diaphragm of the third embodiment of the present invention, comprising a base film (1), a first coating (3) and a second coating (4), wherein the first coating (3) is formed on one side of the base film (1), and the second coating (4) is formed on the side of the first coating (3) opposite to the base film (1), and the first coating (3) comprises an anti-dendrite material, and the second coating (4) comprises a solid electrolyte.

[0054] The base film (1) may be, but is not limited to, a polyolefin base film, preferably a polyethylene base film, a polypropylene base film or more. The thickness of the base film (1) may be, but is not limited to, 5 μm to 20 μm, preferably 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm. The thickness of the first coating (3) may be, but is not limited to, 1 μm to 10 μm, preferably 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. The thickness of the second coating (4) may be, but is not limited to, 1 μm to 10 μm, preferably 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm.

[0055] The anti-dendrite material may include, but is not limited to, one or more of tin oxide, stannous oxide, aluminum fluoride, strontium fluoride, and aluminum oxide, preferably one or more of tin oxide and aluminum oxide. Under the condition that the anti-dendrite material includes tin oxide and aluminum oxide, the mass ratio between tin oxide and aluminum oxide may be, but is not limited to, 1:(1 to 8), preferably 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, or 1:8. The particle size D50 of the anti-dendrite material may be, but is not limited to, 0.1 μm to 3 μm, preferably 0.1 μm, 0.25 μm, 0.5 μm, 0.75 μm, 1 μm, 1.25 μm, 1.5 μm, 1.75 μm, 2 μm, 2.25 μm, 2.5 μm, 2.75 μm, or 3 μm. Based on the total mass of the first coating (3), the anti-dendrite material may account for 50wt% to 96wt%, preferably 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt%, 62wt%, 64wt%, 66wt%, 68wt%, 70wt%, 72wt%, 74wt%, 76wt%, 78wt%, 80wt%, 82wt%, 84wt%, 86wt%, 88wt%, 90wt%, 92wt%, 94wt%, or 96wt%.

[0056] The solid electrolyte may include but is not limited to one or more of LLZO, LLZTO, LAGP, and LATP. LLZO is lithium lanthanum zirconium oxide, which can be expressed as Li 7 La 3 Zr 2 O 12 LLZTO is lithium lanthanum zirconium tantalum oxide, which can be expressed as Li 6.75 La 3 Zr 1.75 Ta 0.25 O represents; LAGP is lithium aluminum germanium phosphate, which can be expressed as Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 Indicates; LATP is lithium aluminum titanium phosphate, which can be expressed as Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3The particle size D50 of the solid electrolyte may be, but is not limited to, 0.1 μm to 3 μm, preferably 0.1 μm, 0.25 μm, 0.5 μm, 0.75 μm, 1 μm, 1.25 μm, 1.5 μm, 1.75 μm, 2 μm, 2.25 μm, 2.5 μm, 2.75 μm, or 3 μm. Based on the total mass of the second coating (4), the solid electrolyte may account for 50wt% to 96wt%, preferably 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt%, 62wt%, 64wt%, 66wt%, 68wt%, 70wt%, 72wt%, 74wt%, 76wt%, 78wt%, 80wt%, 82wt%, 84wt%, 86wt%, 88wt%, 90wt%, 92wt%, 94wt%, or 96wt%.

[0057] In order to make the anti-dendritic material and the solid electrolyte and other components uniformly dispersed in the first coating (3) and the second coating (4) respectively, the first coating (3) may further include a dispersant. The dispersant of the first coating (3) may include but is not limited to one or more of sodium polyacrylate, polyethylene oxide, polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, polyether silicone copolymer, polyoxyethylene alkanolamide, and polyacrylate ammonium salt, preferably including a first dispersant and a second dispersant. The first dispersant of the first coating (3) includes sodium polyacrylate, and the second dispersant of the first coating (3) includes sodium carboxymethyl cellulose; the second coating (4) may further include a dispersant. The dispersant of the second coating (4) may include but is not limited to one or more of sodium polyacrylate, polyethylene oxide, polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, polyether silicone copolymer, polyoxyethylene alkanolamide, and polyacrylate ammonium salt, preferably including a first dispersant and a second dispersant. The first dispersant of the second coating (4) includes sodium polyacrylate, and the second dispersant of the second coating (4) includes sodium carboxymethyl cellulose. Based on the total mass of the first coating (3), the dispersant of the first coating (3) may account for 1 wt% to 5 wt%, preferably 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%; based on the total mass of the second coating (4), the dispersant of the second coating (4) may account for 1 wt% to 5 wt%, preferably 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%. Under the condition that the dispersant of the first coating (3) includes the first dispersant and the second dispersant, based on the total mass of the first coating (3), the first dispersant of the first coating (3) may account for 0.5 wt% to 2.5 wt%, preferably 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, or 2.5 wt%; the second dispersant of the first coating (3) may account for 0.5 wt% to 2.5 wt%, preferably 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, or 2.5 wt%. Under the condition that the dispersant of the second coating (4) includes the first dispersant and the second dispersant, based on the total mass of the second coating (4), the first dispersant of the second coating (4) can account for 0.5wt% to 2.5wt%, preferably 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 2.5wt%; the second dispersant of the second coating (4) can account for 0.5wt% to 2.5wt%, preferably 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 2.5wt%.

[0058] In order to improve the hydrophilicity of the multifunctional composite low-temperature diaphragm, the first coating (3) may further include a wetting agent, and the wetting agent of the first coating (3) may include but is not limited to one or more of polyoxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, and polyoxyethylene polyoxypropylene block copolymer; the second coating (4) may further include a wetting agent, and the wetting agent of the second coating (4) may include but is not limited to one or more of polyoxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, and polyoxyethylene polyoxypropylene block copolymer. Based on the total mass of the first coating (3), the wetting agent of the first coating (3) may account for 0.05wt% to 0.2wt%, preferably 0.05wt%, 0.1wt%, 0.15wt%, or 0.2wt%; based on the total mass of the second coating (4), the wetting agent of the second coating (4) may account for 0.05wt% to 0.2wt%, preferably 0.05wt%, 0.1wt%, 0.15wt%, or 0.2wt%.

[0059] In order to ensure that the anti-dendrite material and the solid electrolyte and other components are firmly bonded together in the first coating (3) and the second coating (4), or to improve the bonding performance between the base film (1) and the first coating (3) and between the first coating (3) and the second coating (4), the first coating (3) may further include a binder. The binder of the first coating (3) may include but is not limited to one or more polymers obtained by copolymerizing acrylates, methacrylates, styrene-butadiene rubber or nitrile rubber with olefins or esters; the second coating (4) may further include a binder. The binder of the second coating (4) may include but is not limited to one or more polymers obtained by copolymerizing acrylates, methacrylates, styrene-butadiene rubber or nitrile rubber with olefins or esters. Based on the total mass of the first coating (3), the binder of the first coating (3) may account for 6wt% to 20wt%, preferably 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, or 20wt%; based on the total mass of the second coating (4), the binder of the second coating (4) may account for 6wt% to 20wt%, preferably 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, or 20wt%.

[0060] The following further illustrates the preparation method of the multifunctional composite low-temperature diaphragm of the present embodiment, but it should not be used as a technical solution to limit the multifunctional composite low-temperature diaphragm of the present embodiment; that is, the multifunctional composite low-temperature diaphragm of the present embodiment can be prepared by other preparation methods not mentioned.

[0061] First, a base film (1) is provided.

[0062] Next, a first slurry and a second slurry are provided, wherein the first slurry comprises an anti-dendrite material, and the second slurry comprises a solid electrolyte. The first slurry may further comprise one or more of a dispersant, a wetting agent, and a binder of the first coating (3). Based on the total mass of the first slurry, the dispersant of the first coating (3) may account for 0.5wt% to 2.5wt%, preferably 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 2.5wt%; the wetting agent of the first coating (3) may account for 0.025wt% to 0.1wt%, preferably 0.025wt%, 0.05wt%, 0.075wt%, or 0.1wt%; the binder of the first coating (3) may account for 3wt% to 10wt%, preferably 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%. Under the condition that the dispersant of the first coating (3) includes the first dispersant and the second dispersant, based on the total mass of the first slurry, the first dispersant of the first coating (3) can account for 0.25wt% to 1.25wt%, preferably 0.25wt%, 0.05wt%, 0.75wt%, 1wt%, or 1.25wt%; the second dispersant of the first coating (3) can account for 0.25wt% to 1.25wt%, preferably 0.25wt%, 0.05wt%, 0.75wt%, 1wt%, or 1.25wt%. For example, the preparation of the first slurry can be as follows but not limited to: first add the first dispersant of the first coating (3) to the solvent (such as water), stir evenly and then add the anti-dendritic material; then, add the second dispersant of the first coating (3) after grinding, add the wetting agent and binder of the first coating (3), stir evenly to obtain the first slurry. The first slurry can be but not limited to a water-based slurry. The solid content of the first slurry may be, but not limited to, 30% to 60%, preferably 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, or 60%. The viscosity of the first slurry may be, but not limited to, 10mPa·s to 50mPa·s, preferably 10mPa·s, 15mPa·s, 20mPa·s, 25mPa·s, 30mPa·s, 35mPa·s, 40mPa·s, 45mPa·s, or 50mPa·s. The pH of the first slurry may be, but not limited to, 7 to 10, preferably 7, 7.5, 8, 8.5, 9, 9.5, or 10. The second slurry may further include one or more of a dispersant, a wetting agent, and a binder of the second coating (4).Based on the total mass of the second slurry, the dispersant of the second coating (4) may account for 0.5wt% to 2.5wt%, preferably 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 2.5wt%; the wetting agent of the second coating (4) may account for 0.025wt% to 0.1wt%, preferably 0.025wt%, 0.05wt%, 0.075wt%, or 0.1wt%; the binder of the second coating (4) may account for 3wt% to 10wt%, preferably 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%. Under the condition that the dispersant of the second coating (4) includes the first dispersant and the second dispersant, based on the total mass of the second slurry, the first dispersant of the second coating (4) can account for 0.25wt% to 1.25wt%, preferably 0.25wt%, 0.05wt%, 0.75wt%, 1wt%, or 1.25wt%; the second dispersant of the second coating (4) can account for 0.25wt% to 1.25wt%, preferably 0.25wt%, 0.05wt%, 0.75wt%, 1wt%, or 1.25wt%. For example, the preparation of the second slurry can be as follows but not limited to: first add the first dispersant of the second coating (4) to the solvent (such as water), stir evenly and then add the solid electrolyte; then, add the second dispersant of the second coating (4) after grinding, add the wetting agent and binder of the second coating (4), stir evenly to obtain the second slurry. The second slurry can be but not limited to an aqueous slurry. The solid content of the second slurry may be, but is not limited to, 30% to 60%, preferably 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, or 60%. The viscosity of the second slurry may be, but is not limited to, 10mPa·s to 50mPa·s, preferably 10mPa·s, 15mPa·s, 20mPa·s, 25mPa·s, 30mPa·s, 35mPa·s, 40mPa·s, 45mPa·s, or 50mPa·s. The pH of the second slurry may be, but is not limited to, 7 to 10, preferably 7, 7.5, 8, 8.5, 9, 9.5, or 10.

[0063] Then, the first slurry is applied to one side of the base film (1), and the first slurry is dried to form a first coating layer (3).

[0064] Finally, the second slurry is applied to the side of the first coating layer (3) opposite to the base film (1), and the second slurry is dried to form a second coating layer (4).

[0065] Please refer to Figure 4, which presents a multifunctional composite low-temperature diaphragm of the fourth embodiment of the present invention, comprising a base film (1), a first coating (3) and a second coating (4), wherein the second coating (4) is formed on one side of the base film (1), the first coating (3) is formed on the side of the second coating (4) opposite to the base film (1), and the first coating (3) comprises an anti-dendrite material, and the second coating (4) comprises a solid electrolyte.

[0066] The base film (1) may be, but is not limited to, a polyolefin base film, preferably a polyethylene base film, a polypropylene base film or more. The thickness of the base film (1) may be, but is not limited to, 5 μm to 20 μm, preferably 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm. The thickness of the first coating (3) may be, but is not limited to, 1 μm to 10 μm, preferably 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. The thickness of the second coating (4) may be, but is not limited to, 1 μm to 10 μm, preferably 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm.

[0067] The anti-dendrite material may include, but is not limited to, one or more of tin oxide, stannous oxide, aluminum fluoride, strontium fluoride, and aluminum oxide, preferably one or more of tin oxide and aluminum oxide. Under the condition that the anti-dendrite material includes tin oxide and aluminum oxide, the mass ratio between tin oxide and aluminum oxide may be, but is not limited to, 1:(1 to 8), preferably 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, or 1:8. The particle size D50 of the anti-dendrite material may be, but is not limited to, 0.1 μm to 3 μm, preferably 0.1 μm, 0.25 μm, 0.5 μm, 0.75 μm, 1 μm, 1.25 μm, 1.5 μm, 1.75 μm, 2 μm, 2.25 μm, 2.5 μm, 2.75 μm, or 3 μm. Based on the total mass of the first coating (3), the anti-dendrite material may account for 50wt% to 96wt%, preferably 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt%, 62wt%, 64wt%, 66wt%, 68wt%, 70wt%, 72wt%, 74wt%, 76wt%, 78wt%, 80wt%, 82wt%, 84wt%, 86wt%, 88wt%, 90wt%, 92wt%, 94wt%, or 96wt%.

[0068] The solid electrolyte may include but is not limited to one or more of LLZO, LLZTO, LAGP, and LATP. LLZO is lithium lanthanum zirconium oxide, which can be expressed as Li7 La 3 Zr 2 O 12 LLZTO is lithium lanthanum zirconium tantalum oxide, which can be expressed as Li 6.75 La 3 Zr 1.75 Ta 0.25 O represents; LAGP is lithium aluminum germanium phosphate, which can be expressed as Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 Indicates; LATP is lithium aluminum titanium phosphate, which can be expressed as Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 The particle size D50 of the solid electrolyte may be, but is not limited to, 0.1 μm to 3 μm, preferably 0.1 μm, 0.25 μm, 0.5 μm, 0.75 μm, 1 μm, 1.25 μm, 1.5 μm, 1.75 μm, 2 μm, 2.25 μm, 2.5 μm, 2.75 μm, or 3 μm. Based on the total mass of the second coating (4), the solid electrolyte may account for 50wt% to 96wt%, preferably 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt%, 62wt%, 64wt%, 66wt%, 68wt%, 70wt%, 72wt%, 74wt%, 76wt%, 78wt%, 80wt%, 82wt%, 84wt%, 86wt%, 88wt%, 90wt%, 92wt%, 94wt%, or 96wt%.

[0069] In order to make the anti-dendritic material and the solid electrolyte and other components uniformly dispersed in the first coating (3) and the second coating (4) respectively, the first coating (3) may further include a dispersant. The dispersant of the first coating (3) may include but is not limited to one or more of sodium polyacrylate, polyethylene oxide, polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, polyether silicone copolymer, polyoxyethylene alkanolamide, and polyacrylate ammonium salt, preferably including a first dispersant and a second dispersant. The first dispersant of the first coating (3) includes sodium polyacrylate, and the second dispersant of the first coating (3) includes sodium carboxymethyl cellulose; the second coating (4) may further include a dispersant. The dispersant of the second coating (4) may include but is not limited to one or more of sodium polyacrylate, polyethylene oxide, polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, polyether silicone copolymer, polyoxyethylene alkanolamide, and polyacrylate ammonium salt, preferably including a first dispersant and a second dispersant. The first dispersant of the second coating (4) includes sodium polyacrylate, and the second dispersant of the second coating (4) includes sodium carboxymethyl cellulose. Based on the total mass of the first coating (3), the dispersant of the first coating (3) may account for 1 wt% to 5 wt%, preferably 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%; based on the total mass of the second coating (4), the dispersant of the second coating (4) may account for 1 wt% to 5 wt%, preferably 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%. Under the condition that the dispersant of the first coating (3) includes the first dispersant and the second dispersant, based on the total mass of the first coating (3), the first dispersant of the first coating (3) may account for 0.5 wt% to 2.5 wt%, preferably 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, or 2.5 wt%; the second dispersant of the first coating (3) may account for 0.5 wt% to 2.5 wt%, preferably 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, or 2.5 wt%. Under the condition that the dispersant of the second coating (4) includes the first dispersant and the second dispersant, based on the total mass of the second coating (4), the first dispersant of the second coating (4) can account for 0.5wt% to 2.5wt%, preferably 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 2.5wt%; the second dispersant of the second coating (4) can account for 0.5wt% to 2.5wt%, preferably 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 2.5wt%.

[0070] In order to improve the hydrophilicity of the multifunctional composite low-temperature diaphragm, the first coating (3) may further include a wetting agent, and the wetting agent of the first coating (3) may include but is not limited to one or more of polyoxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, and polyoxyethylene polyoxypropylene block copolymer; the second coating (4) may further include a wetting agent, and the wetting agent of the second coating (4) may include but is not limited to one or more of polyoxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, and polyoxyethylene polyoxypropylene block copolymer. Based on the total mass of the first coating (3), the wetting agent of the first coating (3) may account for 0.05wt% to 0.2wt%, preferably 0.05wt%, 0.1wt%, 0.15wt%, or 0.2wt%; based on the total mass of the second coating (4), the wetting agent of the second coating (4) may account for 0.05wt% to 0.2wt%, preferably 0.05wt%, 0.1wt%, 0.15wt%, or 0.2wt%.

[0071] In order to ensure that the anti-dendrite material and the solid electrolyte and other components are firmly bonded together in the first coating (3) and the second coating (4), or to improve the bonding performance between the base film (1) and the second coating (4) and between the first coating (3) and the second coating (4), the first coating (3) may further include a binder. The binder of the first coating (3) may include but is not limited to one or more polymers obtained by copolymerizing acrylates, methacrylates, styrene-butadiene rubber or nitrile rubber with olefins or esters; the second coating (4) may further include a binder. The binder of the second coating (4) may include but is not limited to one or more polymers obtained by copolymerizing acrylates, methacrylates, styrene-butadiene rubber or nitrile rubber with olefins or esters. Based on the total mass of the first coating (3), the binder of the first coating (3) may account for 6wt% to 20wt%, preferably 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, or 20wt%; based on the total mass of the second coating (4), the binder of the second coating (4) may account for 6wt% to 20wt%, preferably 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, or 20wt%.

[0072] The following further illustrates the preparation method of the multifunctional composite low-temperature diaphragm of the present embodiment, but it should not be used as a technical solution to limit the multifunctional composite low-temperature diaphragm of the present embodiment; that is, the multifunctional composite low-temperature diaphragm of the present embodiment can be prepared by other preparation methods not mentioned.

[0073] First, a base film (1) is provided.

[0074] Next, a first slurry and a second slurry are provided, wherein the first slurry comprises an anti-dendrite material, and the second slurry comprises a solid electrolyte. The first slurry may further comprise one or more of a dispersant, a wetting agent, and a binder of the first coating (3). Based on the total mass of the first slurry, the dispersant of the first coating (3) may account for 0.5wt% to 2.5wt%, preferably 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 2.5wt%; the wetting agent of the first coating (3) may account for 0.025wt% to 0.1wt%, preferably 0.025wt%, 0.05wt%, 0.075wt%, or 0.1wt%; the binder of the first coating (3) may account for 3wt% to 10wt%, preferably 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%. Under the condition that the dispersant of the first coating (3) includes the first dispersant and the second dispersant, based on the total mass of the first slurry, the first dispersant of the first coating (3) can account for 0.25wt% to 1.25wt%, preferably 0.25wt%, 0.05wt%, 0.75wt%, 1wt%, or 1.25wt%; the second dispersant of the first coating (3) can account for 0.25wt% to 1.25wt%, preferably 0.25wt%, 0.05wt%, 0.75wt%, 1wt%, or 1.25wt%. For example, the preparation of the first slurry can be as follows but not limited to: first add the first dispersant of the first coating (3) to the solvent (such as water), stir evenly and then add the anti-dendritic material; then, add the second dispersant of the first coating (3) after grinding, add the wetting agent and binder of the first coating (3), stir evenly to obtain the first slurry. The first slurry can be but not limited to a water-based slurry. The solid content of the first slurry may be, but not limited to, 30% to 60%, preferably 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, or 60%. The viscosity of the first slurry may be, but not limited to, 10mPa·s to 50mPa·s, preferably 10mPa·s, 15mPa·s, 20mPa·s, 25mPa·s, 30mPa·s, 35mPa·s, 40mPa·s, 45mPa·s, or 50mPa·s. The pH of the first slurry may be, but not limited to, 7 to 10, preferably 7, 7.5, 8, 8.5, 9, 9.5, or 10. The second slurry may further include one or more of a dispersant, a wetting agent, and a binder of the second coating (4).Based on the total mass of the second slurry, the dispersant of the second coating (4) may account for 0.5wt% to 2.5wt%, preferably 0.5wt%, 1wt%, 1.5wt%, 2wt%, or 2.5wt%; the wetting agent of the second coating (4) may account for 0.025wt% to 0.1wt%, preferably 0.025wt%, 0.05wt%, 0.075wt%, or 0.1wt%; the binder of the second coating (4) may account for 3wt% to 10wt%, preferably 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%. Under the condition that the dispersant of the second coating (4) includes the first dispersant and the second dispersant, based on the total mass of the second slurry, the first dispersant of the second coating (4) can account for 0.25wt% to 1.25wt%, preferably 0.25wt%, 0.05wt%, 0.75wt%, 1wt%, or 1.25wt%; the second dispersant of the second coating (4) can account for 0.25wt% to 1.25wt%, preferably 0.25wt%, 0.05wt%, 0.75wt%, 1wt%, or 1.25wt%. For example, the preparation of the second slurry can be as follows but not limited to: first add the first dispersant of the second coating (4) to the solvent (such as water), stir evenly and then add the solid electrolyte; then, add the second dispersant of the second coating (4) after grinding, add the wetting agent and binder of the second coating (4), stir evenly to obtain the second slurry. The second slurry can be but not limited to an aqueous slurry. The solid content of the second slurry may be, but is not limited to, 30% to 60%, preferably 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, or 60%. The viscosity of the second slurry may be, but is not limited to, 10mPa·s to 50mPa·s, preferably 10mPa·s, 15mPa·s, 20mPa·s, 25mPa·s, 30mPa·s, 35mPa·s, 40mPa·s, 45mPa·s, or 50mPa·s. The pH of the second slurry may be, but is not limited to, 7 to 10, preferably 7, 7.5, 8, 8.5, 9, 9.5, or 10.

[0075] Then, the second slurry is applied to one side of the base film (1), and the second slurry is dried to form a second coating layer (4).

[0076] Finally, the first slurry is applied to the side of the second coating layer (4) opposite to the base film (1), and the first slurry is dried to form the first coating layer (3).

[0077] The present invention is illustrated by the following examples:

[0078] Example 1

[0079] In this embodiment, the base film has a thickness of 9 μm, and each coating layer has a thickness of 3 μm.

[0080] Add 1g of the first dispersant sodium polyacrylate to 100mL of deionized water, stir well, then add 17g of tin oxide and 68g of aluminum oxide. After grinding, add 1g of the second dispersant sodium carboxymethyl cellulose, add 12g of the glue polyacrylate and 0.1g of the wetting agent polyoxyethylene alkylphenol ether, stir well to obtain a slurry with a solid content of 40%, apply it to one side of the base film, and dry to obtain a diaphragm containing the first functional coating.

[0081] Add 1g of the first dispersant sodium polyacrylate to 100mL of deionized water, stir well, and then add 85g of LATP. After grinding, add 1g of the second dispersant sodium carboxymethyl cellulose, add 12g of the glue polyacrylate and 0.1g of the wetting agent polyoxyethylene alkylphenol ether, stir well to obtain a slurry with a solid content of 40%, apply it to the side of the first functional coating opposite to the base film, and dry it to obtain a diaphragm containing the first functional coating and the second functional coating (in order: base film, first functional coating, second functional coating).

[0082] Example 2

[0083] In this embodiment, the base film has a thickness of 9 μm, and each coating layer has a thickness of 3 μm.

[0084] Add 1g of the first dispersant sodium polyacrylate to 100mL of deionized water, stir evenly, and then add 85g of LATP. After grinding, add 1g of the second dispersant sodium carboxymethyl cellulose, add 12g of the glue polyacrylate and 0.1g of the wetting agent polyoxyethylene alkylphenol ether, stir evenly to obtain a slurry with a solid content of 40%, apply it to one side of the base film, and dry to obtain a diaphragm containing the second functional coating.

[0085] Add 1g of the first dispersant sodium polyacrylate to 100mL of deionized water, stir well, then add 17g of tin oxide and 68g of aluminum oxide. After grinding, add 1g of the second dispersant sodium carboxymethyl cellulose, add 12g of the glue polyacrylate and 0.1g of the wetting agent polyoxyethylene alkylphenol ether, stir well to obtain a slurry with a solid content of 40%, apply it to the side of the second functional coating opposite to the base film, and dry to obtain a diaphragm containing the first functional coating and the second functional coating (in order: base film, second functional coating, first functional coating).

[0086] Example 3

[0087] In this embodiment, the base film has a thickness of 9 μm, and each coating layer has a thickness of 3 μm.

[0088] Add 1g of the first dispersant sodium polyacrylate to 100mL of deionized water, stir evenly, then add 8.5g of tin oxide, 42g of LATP, and 34g of aluminum oxide. After grinding, add 1g of the second dispersant sodium carboxymethyl cellulose, 12g of the glue polyacrylate and 0.1g of the wetting agent polyoxyethylene alkylphenol ether, stir evenly to obtain a slurry with a solid content of 40%, apply it on the base film, and dry it to obtain a diaphragm containing a functional mixed coating (in order: base film, functional mixed coating).

[0089] Example 4

[0090] In this embodiment, the base film has a thickness of 9 μm, and each coating layer has a thickness of 3 μm.

[0091] Add 1g of the first dispersant sodium polyacrylate to 100mL of deionized water, stir well, then add 17g of tin oxide and 68g of aluminum oxide. After grinding, add 1g of the second dispersant sodium carboxymethyl cellulose, add 12g of the glue polyacrylate and 0.1g of the wetting agent polyoxyethylene alkylphenol ether, stir well to obtain a slurry with a solid content of 40%, apply it to one side of the base film, and dry to obtain a diaphragm containing the first functional coating.

[0092] Add 1g of the first dispersant sodium polyacrylate to 100mL of deionized water, stir well and then add 85g of LATP. After grinding, add 1g of the second dispersant sodium carboxymethyl cellulose, add 12g of the glue polyacrylate and 0.1g of the wetting agent polyoxyethylene alkylphenol ether, stir well to obtain a slurry with a solid content of 40%, apply it to the other side of the base film, and dry to obtain a diaphragm with the first functional coating and the second functional coating on both sides (in order: the second functional coating, the base film, the first functional coating).

[0093] Comparative Example 1

[0094] In this comparative example, the base film thickness is 9 μm, and the thickness of each coating layer is 3 μm.

[0095] Add 1g of the first dispersant sodium polyacrylate to 100mL of deionized water, stir evenly and then add 85g of aluminum oxide. After grinding, add 1g of the second dispersant sodium carboxymethyl cellulose, add 12g of the glue polyacrylate and 0.1g of the wetting agent polyoxyethylene alkylphenol ether, stir evenly to obtain a slurry with a solid content of 40%, apply it to one side of the base film, and dry to obtain a diaphragm containing an aluminum oxide coating (in order: base film, aluminum oxide coating).

[0096] Comparative Example 2

[0097] In this comparative example, the base film thickness is 9 μm, and the thickness of each coating layer is 3 μm.

[0098] Add 1g of the first dispersant sodium polyacrylate to 100mL of deionized water, stir evenly and then add 85g of LATP. After grinding, add 1g of the second dispersant sodium carboxymethyl cellulose, add 12g of the glue polyacrylate and 0.1g of the wetting agent polyoxyethylene alkylphenol ether, stir evenly to obtain a slurry with a solid content of 40%, apply it to one side of the base film, and dry to obtain a diaphragm containing a LATP coating (in order: base film, LATP coating).

[0099] Comparative Example 3

[0100] In this comparative example, the base film thickness is 9 μm, and the thickness of each coating layer is 3 μm.

[0101] Add 1g of the first dispersant sodium polyacrylate to 100mL of deionized water, stir evenly, then add 17g of tin oxide and 68g of aluminum oxide. After grinding, add 1g of the second dispersant sodium carboxymethyl cellulose, add 12g of the glue polyacrylate and 0.1g of the wetting agent polyoxyethylene alkylphenol ether, stir evenly to obtain a slurry with a solid content of 40%, apply it to one side of the base film, and dry to obtain a diaphragm containing a mixed coating of aluminum oxide and tin oxide (in order: base film, aluminum oxide and tin oxide mixed coating).

[0102] Comparative Example 4

[0103] In this comparative example, the thickness of the base film is 9 μm, and the base film is used as a separator.

[0104] Low-temperature discharge capacity retention rate: The fully charged battery cell was placed at -20℃ for 12h, discharged at 1C, with a cut-off voltage of 2.8V, and the capacity retention rate was recorded.

[0105] Low temperature cycle: The low temperature cycle is carried out in a cycle mode of -20℃ room temperature-low temperature-room temperature 1C / 1C for 10 cycles each, and the capacity retention rate is recorded after the cycle is completed.

[0106] Normal temperature cycle (low N / P): Take a specially designed low N / P (0.85) battery cell and cycle it at 0.5C / 1C at 25°C until the capacity retention rate reaches 80%, and record the number of cycles.

[0107] Table 1

[0108] Capacity retention rate Low temperature cycle Normal temperature cycle (low N / P) Example 1 58.1％ 75.2％ 750 weeks Example 2 58.4％ 74.8％ 732 weeks Example 3 54.2％ 74.3％ 725 weeks Example 4 58.5％ 75.6％ 763 weeks Comparative Example 1 46.7％ 64.7％ 32 weeks Comparative Example 2 57.5％ 65.3％ 35 weeks Comparative Example 3 46.2％ 74.1％ 720 weeks Comparative Example 4 45.3％ 52.5％ 20 weeks

[0109] First, from Table 1, by comparing Control Example 4 with other Control Examples and Examples 1 to 4, it can be seen that the capacity retention rate, low temperature cycle, and room temperature cycle can be improved through coating.

[0110] Secondly, from Table 1, by comparing Control Example 4 with Control Example 2, it can be seen that coating with solid electrolyte can increase the capacity retention rate by 12.2%, increase the low-temperature cycle by 12.8%, and increase the room-temperature cycle by 15 weeks.

[0111] Furthermore, from Table 1, by comparing the control example 4 with the control example 3, it can be seen that coating the anti-dendrite material can increase the capacity retention rate by 0.9%, increase the low temperature cycle by 21.6%, and increase the room temperature cycle by 700 cycles.

[0112] Finally, from Table 1, by comparing the control example 4 with the embodiment 1, it can be seen that by first coating the solid electrolyte and then coating the anti-dendrite material on the same side of the base film, the room temperature cycle can be increased by 730 weeks, which is greater than the expected 715 weeks; from Table 1, by comparing the control example 4 with the embodiment 3, it can be seen that by coating the mixture of the solid electrolyte and the anti-dendrite material, the capacity retention rate can be increased by 8.9%, which is greater than the expected 6.6%, the low temperature cycle can be increased by 21.8%, which is greater than the expected 17.2%, and the room temperature cycle can be increased by 705 weeks, which is greater than the expected 358 weeks; from Table 1, by comparing the control example 4 with the embodiment 4, it can be seen that by coating the solid electrolyte and the anti-dendrite material on different sides of the base film, the capacity retention rate can be increased by 13.2%, which is greater than the expected 13.1%, and the room temperature cycle can be increased by 743 weeks, which is greater than the expected 715 weeks. This can confirm that the present invention achieves a synergistic improvement in both low temperature discharge and low temperature cycle of lithium batteries through the synergistic effect between the anti-dendrite material and the solid electrolyte.

[0113] The above contents involving common knowledge are not described in detail, and those skilled in the art can understand them.

[0114] The above descriptions are only some specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention. The technical scope of the present invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A multifunctional composite low-temperature diaphragm, It is characterized in that include: A base film and a mixed coating are provided, wherein the mixed coating is formed on at least one side of the base film and comprises an anti-dendrite material and a solid electrolyte.

2. The multifunctional composite low-temperature diaphragm according to claim 1, It is characterized in that The anti-dendrite material includes one or more of tin oxide, stannous oxide, aluminum fluoride, strontium fluoride, and aluminum oxide.

3. The multifunctional composite low-temperature diaphragm according to claim 1, It is characterized in that The solid electrolyte includes one or more of LLZO, LLZTO, LAGP, and LATP.

4. The multifunctional composite low-temperature diaphragm according to claim 1, It is characterized in that The base film has a thickness of 5 μm to 20 μm, and the mixed coating has a thickness of 1 μm to 10 μm.

5. The multifunctional composite low-temperature diaphragm according to claim 1, It is characterized in that The particle size D50 of the anti-dendrite material is 0.1 μm to 3 μm, and the particle size D50 of the solid electrolyte is 0.1 μm to 3 μm.

6. A multifunctional composite low-temperature diaphragm, It is characterized in that include: A base film, a first coating layer, and a second coating layer, wherein the first coating layer comprises an anti-dendrite material and the second coating layer comprises a solid electrolyte; in, The first coating layer is formed on one side of the base film, and the second coating layer is formed on the other side of the base film; or The first coating layer is formed on one side of the base film, and the second coating layer is formed on a side of the first coating layer opposite to the base film; or The second coating layer is formed on one side of the base film, and the first coating layer is formed on a side of the second coating layer opposite to the base film.

7. The multifunctional composite low-temperature diaphragm according to claim 6, It is characterized in that The anti-dendrite material includes one or more of tin oxide, stannous oxide, aluminum fluoride, strontium fluoride, and aluminum oxide.

8. The multifunctional composite low-temperature diaphragm according to claim 6, It is characterized in that The solid electrolyte includes one or more of LLZO, LLZTO, LAGP, and LATP.

9. The multifunctional composite low-temperature diaphragm according to claim 6, It is characterized in that The base film has a thickness of 5 μm to 20 μm, the first coating layer has a thickness of 1 μm to 10 μm, and the second coating layer has a thickness of 1 μm to 10 μm.

10. The multifunctional composite low-temperature diaphragm according to claim 6, It is characterized in that The particle size D50 of the anti-dendrite material is 0.1 μm to 3 μm, and the particle size D50 of the solid electrolyte is 0.1 μm to 3 μm.

11. A method for preparing a multifunctional composite low-temperature diaphragm, It is characterized in that include: providing a base film; Providing a mixed slurry, wherein the mixed slurry comprises an anti-dendrite material and a solid electrolyte; Applying the mixed slurry on one side or both sides of the base film; as well as The mixed slurry is dried to form a mixed coating.

12. A method for preparing a multifunctional composite low-temperature diaphragm, It is characterized in that include: providing a base film; Providing a first slurry and a second slurry, wherein the first slurry contains an anti-dendrite material, and the second slurry contains a solid electrolyte; Applying the first slurry on one side of the base film, and applying the second slurry on the other side of the base film; as well as The first slurry is dried to form a first coating layer, and the second slurry is dried to form a second coating layer.

13. A method for preparing a multifunctional composite low-temperature diaphragm, It is characterized in that include: providing a base film; Providing a first slurry and a second slurry, wherein the first slurry contains an anti-dendrite material, and the second slurry contains a solid electrolyte; Applying the first slurry on one side of the base film, and drying the first slurry to form a first coating layer; as well as The second slurry is applied to a side of the first coating layer opposite to the base film, and the second slurry is dried to form a second coating layer.

14. A method for preparing a multifunctional composite low-temperature diaphragm, It is characterized in that include: providing a base film; Providing a first slurry and a second slurry, wherein the first slurry contains an anti-dendrite material, and the second slurry contains a solid electrolyte; Applying the second slurry on one side of the base film, and drying the second slurry to form a second coating layer; as well as The first slurry is applied to a side of the second coating layer opposite to the base film, and the first slurry is dried to form a first coating layer.

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