Solid-state electrolyte composite multilayer separator, method of making and use

Abstract

The application relates to the technical field of lithium ion battery separators, in particular to a solid electrolyte composite multilayer separator, a preparation method and application. The composite multilayer separator comprises an in-situ composite layer and lead-in layers arranged on both sides of the in-situ composite layer. The lead-in layer is a porous film formed by a polymer, and the in-situ composite layer is a porous structure formed by in-situ compounding of a solid electrolyte and a polymer. Since the solid electrolyte is introduced into the separator, the effect of promoting lithium ion transmission can be fully exerted, and the ion conductivity of the separator is improved. The composite structure of the in-situ composite layer and the lead-in layers arranged on both sides of the in-situ composite layer can also effectively ensure the porosity of the separator, and further improve the ion conductivity of the separator. Since the lead-in layer can play a covering and supporting role, the surface quality of the composite multilayer separator can be improved, thereby effectively improving the uniformity of the thickness or air permeability value of the separator, improving the overall toughness of the separator, and increasing the tensile strength, thereby improving the mechanical strength of the separator.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium ion battery separators, in particular to a solid electrolyte composite multilayer separator, a preparation method and application. BACKGROUND

[0002] The lithium ion battery separator can effectively separate the positive and negative electrodes, prevent short circuit and enable lithium ions to pass back and forth through the porous channel structure. The current lithium ion battery requires 3C or even higher rate, and research and analysis shows that the pore size structure and uniformity of the separator directly affect the lithium ion transmission and then affect the rate performance of the battery. At the same time, with the continuous improvement of the solidification degree of the battery, it is increasingly important to develop a separator with high ionic conductivity.

[0003] At present, the method for improving the ionic conductivity of the polyolefin separator is mainly achieved by coating a solid electrolyte coating. Such a method needs to introduce slurry preparation, coating and other processes, and the interface between the base film and the solid electrolyte coating is only a simple interface contact. After long cycle charging and discharging, local lithium dendrites are generated in the battery, which has a safety hazard of piercing the separator. SUMMARY

[0004] The application provides a solid electrolyte composite multilayer separator, a preparation method and application, which can effectively improve the mechanical strength and ionic conductivity of the separator and avoid the risk of short circuit and thermal runaway caused by piercing the separator.

[0005] The application provides a solid electrolyte composite multilayer separator, which comprises:

[0006] An in-situ composite layer, which is configured as a porous structure mainly formed by in-situ compounding of a solid electrolyte in a polymer a; and

[0007] Two lead-in layers, which are respectively arranged on the two sides of the in-situ composite layer; the lead-in layers are configured as porous membranes mainly formed by a polymer b.

[0008] In an optional embodiment, the polymer b comprises a polyolefin; the melt index of the polyolefin is 0.5 g / 10 min-2.0 g / 10 min.

[0009] In an optional embodiment, the polymer a comprises a polyolefin.

[0010] In an optional embodiment, the content of the polymer a in the in-situ composite layer is 90%-99.9% by mass percentage; the content of the solid electrolyte is 0.1%-10% by mass percentage.

[0011] In an optional embodiment, the solid electrolyte comprises an inorganic solid electrolyte.

[0012] Optionally, the solid-state electrolyte comprises at least one of an oxide solid-state electrolyte, a sulfide solid-state electrolyte, and a halide solid-state electrolyte.

[0013] Optionally, the solid-state electrolyte comprises at least one of lithium lanthanum gallate titanate, lithium phosphorous sulfide chloride, and lithium titanium aluminum phosphate.

[0014] Optionally, the solid-state electrolyte comprises Li 1.5 Al 0.5 Ti 1.5 (PO4)3.

[0015] In an optional embodiment, the D50 particle size of the solid-state electrolyte is 50 nm-200 nm.

[0016] In an optional embodiment, the solid-state electrolyte composite multilayer separator satisfies at least one of conditions (1)-(4):

[0017] (1) the introduction layer comprises a first introduction layer and a second introduction layer, the first introduction layer, the in-situ composite layer, and the second introduction layer are sequentially arranged; the mass ratio of the first introduction layer, the in-situ composite layer, and the second introduction layer is (0.4-1):1:(0.4-1);

[0018] (2) the thickness of the solid-state electrolyte composite multilayer separator is 4-20 μm; the thickness of the in-situ composite layer is 2-10 μm;

[0019] (3) the porosity of the solid-state electrolyte composite multilayer separator is 40%-70%;

[0020] (4) the air permeability value of the solid-state electrolyte composite multilayer separator is 50 s / 100 mL-200 s / 100 mL.

[0021] The present application provides a preparation method of a solid-state electrolyte composite multilayer separator, the solid-state electrolyte composite multilayer separator being as described above, and the steps comprising:

[0022] mixing the solid-state electrolyte and the polymer a according to a ratio, and melt mixing and granulating to form a granule A;

[0023] casting the polymer b for preparing the introduction layer and the granule A through a co-extrusion die head of a casting machine to form a three-layer structure cast sheet with an in-situ composite layer in the middle and introduction layers on both sides;

[0024] sequentially performing annealing treatment, low-temperature stretching, high-temperature stretching, and heat setting on the three-layer structure cast sheet to finally prepare the composite multilayer separator.

[0025] In an optional embodiment, the temperature for melt mixing and granulating the solid-state electrolyte and the polymer a does not exceed 230°C.

[0026] The casting temperature during co-extrusion of the granule A is 170℃-220℃; the casting temperature during co-extrusion of the introductory layer is 150℃-200℃.

[0027] The annealing temperature is 80℃-160℃; the low-temperature stretching temperature is 30℃-60℃ and the stretching ratio is 1.1-1.5; the high-temperature stretching temperature is 120℃-180℃ and the stretching ratio is 1.5-3.0.

[0028] This application provides a lithium-ion battery, including the composite multilayer separator as described above; or, including the composite multilayer separator prepared by the preparation method described above.

[0029] The solid electrolyte composite multilayer separator according to the above embodiments includes an in-situ composite layer and introductory layers disposed on both sides thereof. The introductory layer is a porous membrane formed by polymer b, and the in-situ composite layer is a porous structure formed by in-situ composite of solid electrolyte and polymer a. Introducing the solid electrolyte into the separator fully leverages its ability to promote lithium-ion transport, thereby improving the ionic conductivity of the separator. The composite structure of the in-situ composite layer and the introductory layers on both sides also effectively ensures the porosity of the separator, facilitating rapid lithium-ion conduction and further enhancing the ionic conductivity of the separator. Since the introductory layers are disposed on both sides of the in-situ composite layer, they provide coverage and support, improving the surface quality of the composite multilayer separator and effectively enhancing its uniformity, including thickness and permeability. This results in improved overall toughness and tensile strength of the separator, thus increasing its mechanical strength. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of a solid electrolyte composite multilayer membrane in one embodiment;

[0031] Figure 2 This is a morphology diagram of a solid electrolyte composite multilayer membrane in one embodiment.

[0032] Among them: 1. In-situ composite layer; 2. Introducing layer; 21. First introducing layer; 22. Second introducing layer. Detailed Implementation

[0033] The present application will now be described in further detail with reference to the accompanying drawings and specific embodiments. Similar elements in different embodiments are referred to by related similar element reference numerals. In the following embodiments, many details are described to facilitate a better understanding of the present application. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other elements, materials, or methods. In some cases, certain operations related to the present application are not shown or described in the specification. This is to avoid obscuring the core parts of the present application with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; they can fully understand the related operations based on the description in the specification and general technical knowledge in the art.

[0034] Furthermore, the features, operations, or characteristics described in the specification can be combined in any suitable manner to form various embodiments, and the operational steps involved in each embodiment can also be rearranged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the specification and drawings are only for clearly describing a particular embodiment and do not imply that they represent the necessary components and / or order.

[0035] The serial numbers assigned to components in this document, such as "first" and "second," are used only to distinguish the described objects and have no sequential or technical meaning. The terms "connection" and "linkage" used in this application, unless otherwise specified, include both direct and indirect connections (linkages).

[0036] Please see Figure 1 and Figure 2 This application provides a solid electrolyte composite multilayer membrane, comprising an in-situ composite layer 1 disposed in the middle layer and two inlet layers 2 disposed on both sides of the in-situ composite layer 1. Specifically, the inlet layers 2 include a first inlet layer 21 and a second inlet layer 22. The first inlet layer 21, the in-situ composite layer 1, and the second inlet layer 22 are sequentially arranged to form a three-layer composite structure. The in-situ composite layer 1 is constructed as a porous structure mainly formed by the in-situ composite of solid electrolyte in polymer A, and the inlet layers 2 are constructed as a porous membrane formed by polymer B. The morphology of this composite multilayer membrane is shown in the figure below. Figure 2 As shown. It is understandable that, in addition to the above-mentioned components, additives can be added to the in-situ composite layer 1 and the introduction layer 2 as needed. Typically, the mass percentage of the additives does not exceed 5%.

[0037] In the above three-layer structure, the two side introduction layers 2 are porous membranes formed by polymer b, meaning that introduction layers 2 are also porous structures and do not contain heterogeneous solid electrolytes; the middle layer is a porous structure formed by the combination of solid electrolyte and polymer a. Due to the combination of solid electrolyte and polymer a, the overall toughness of the in-situ composite layer 1 decreases, its brittleness increases, and its tensile strength decreases; after introducing introduction layers 2 on both sides, introduction layers 2 adhere to both sides of the in-situ composite layer 1 and play a supporting role, which can compensate for the decrease in the mechanical properties of the membrane caused by the introduction of solid electrolyte, thereby improving the overall toughness of the composite multilayer membrane and increasing its tensile strength, effectively improving the mechanical strength of the composite multilayer membrane.

[0038] Specifically, when organic polyolefins are composited with inorganic solid electrolytes through melt mixing, phase separation inevitably occurs, resulting in defects such as crystal points and pores on the membrane surface. By placing the in-situ composite layer 1 in the middle and the guide layer 2 on the outside, and using the guide layer 2 as a cover and support for the in-situ composite layer 1, the defects such as crystal points and pores on the surface of the in-situ composite layer 1 can be effectively covered, improving the surface quality of the composite multilayer membrane. This effectively improves its uniformity, including thickness and air permeability, thereby enhancing the overall mechanical strength.

[0039] It's important to further explain that during normal charging of a lithium-ion battery, lithium ions are extracted from the positive electrode and inserted into the negative electrode. However, due to insufficient space for lithium insertion in the negative electrode, high resistance to lithium ion insertion, and the rapid extraction of lithium ions from the positive electrode without an equal amount being inserted into the negative electrode, the lithium ions that cannot be inserted into the negative electrode can only gain electrons at the negative electrode and be reduced to form elemental lithium (lithium plating). Lithium plating leads to battery performance degradation, reduced cycle life, limited fast-charging capacity, and may even cause serious consequences such as combustion and explosion.

[0040] The composite multilayer (trilayer) battery separator of this application, acting as the separator directly facing lithium metal deposition, possesses sufficiently high mechanical strength to provide significant growth inhibition resistance in the early stages of lithium ion deposition. This suppresses further lithium ion deposition, preventing the formation of sharp lithium metal crystals that could pierce the separator, leading to short circuits and serious consequences, thus avoiding the risk of thermal runaway. By introducing a solid electrolyte in situ into polymer a, the lithium ion transport-promoting function of the solid electrolyte can be fully utilized, thereby improving the ionic conductivity of the prepared composite multilayer separator.

[0041] In some optional embodiments, the introduction layer 2 is configured as a porous membrane formed of polyolefin; the melt index of the polyolefin is 0.5 g / 10 min to 2.0 g / 10 min. The introduction layer 2 uses a polymer layer with a high melt index, which can form a continuous and stable support layer. This, combined with the in-situ composite layer 1 of the intermediate layer, can compensate for the reduction in the mechanical properties of the membrane caused by the introduction of the solid electrolyte. The in-situ composite layer 1 is configured as a porous structure mainly formed by the in-situ composite of the solid electrolyte in the polyolefin. That is, both polymer a and polymer b are polyolefins, which can improve the interfacial stability between the introduction layer 2 and the in-situ composite layer 1, resulting in a tightly bonded three-layer structure.

[0042] In some optional embodiments, the content of polymer a in the in-situ composite layer 1 is 90%-99.9% by mass percentage; the content of solid electrolyte is 0.1%-10%. Optionally, the content of solid electrolyte does not exceed 5%. For example, the content of solid electrolyte is 0.1%, 1%, 2%, 3%, 4%, or 5%, or any combination of the above values. Within this range, both ion transport efficiency and mechanical strength of the membrane can be effectively guaranteed.

[0043] In some optional embodiments, the solid electrolyte includes an inorganic solid electrolyte. Optionally, the solid electrolyte includes at least one of oxide solid electrolytes, sulfide solid electrolytes, and halide solid electrolytes. For example, the solid electrolyte includes at least three elements selected from lithium, sodium, tantalum, titanium, aluminum, zirconia, silicon, sulfur, oxygen, phosphorus, and nitrogen; optionally, the solid electrolyte includes lithium lanthanum zirconia tantalum oxide (LLZTO), lithium phosphorus sulfide chlorine (L6PS5Cl), and lithium titanium aluminum phosphate (Li... 1.5 Al 0.5 Ti 1.5 At least one of (PO4)3). Preferably, the solid electrolyte is a solid electrolyte raw material with a relatively high lithium content, namely Li. 1.5 Al 0.5 Ti 1.5 (PO4)3, in the solid-phase crystal structure formed by elements in solid electrolytes, can effectively conduct and transport lithium ions, constituting the basic structure of solid electrolytes; and some elements such as tantalum, titanium, and silicon can be introduced into the crystal as dopants, which can improve the interface performance between the solid electrolyte and the solid electrode, further promoting lithium ion transport and improving the ionic conductivity of the composite multilayer membrane. Meanwhile, lithium titanium aluminum phosphate (Li... 1.5 Al 0.5 Ti 1.5 (PO4)3) oxide solid electrolytes have strong air stability and advantages in large-scale application, and their cost is relatively controllable.

[0044] In some optional embodiments, the D50 particle size of the solid electrolyte is 50 nm to 200 nm. Optionally, the D50 particle size of the solid electrolyte is 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 150 nm, or 200 nm, or any combination of the above values. Within this range, ion transport efficiency can be effectively guaranteed while improving the mechanical strength of the membrane.

[0045] In some optional embodiments, the mass ratio of the first introductory layer 21, the in-situ composite layer 1, and the second introductory layer 22 is (0.4-1):1:(0.4-1). The first introductory layer 21 and the second introductory layer 22 can be made from raw materials with the same proportion, or they can be made with different proportions depending on the situation. For example, the mass ratio of the first introductory layer 21, the in-situ composite layer 1, and the second introductory layer 22 can be selected as 0.4:1:0.4, 0.4:1:1, 0.5:1:0.5, or 1:1:1, or any of the above values. To ensure the effect of this solid electrolyte composite multilayer membrane on promoting lithium-ion transport, the thickness of the first introductory layer 21 and the second introductory layer 22 on both sides usually does not exceed the thickness of the in-situ composite layer 1, and the mass percentage is proportional to the thickness, and its mass percentage can be close to the upper limit of 1:1:1. As the thickness of the in-situ composite layer 1 increases, the lithium-ion transport promotion effect becomes more obvious. A lower limit of 0.4 or above can effectively ensure the adhesion of the first and second introductory layers 21 and 22 on both sides to the in-situ composite layer 1, ensuring that the solid electrolyte composite multilayer membrane has a smooth overall appearance and excellent mechanical properties.

[0046] In some optional embodiments, the thickness of the solid electrolyte composite multilayer membrane is 4 μm-20 μm. For example, the thickness of the composite multilayer membrane can be 4 μm, 5 μm, 10 μm, 15 μm or 20 μm, or any combination of the above values.

[0047] In some optional embodiments, the porosity of the solid electrolyte composite multilayer membrane is 40%-70%. This effectively ensures ion transport, thereby guaranteeing battery cycle performance. For example, the porosity of the composite multilayer membrane can be 40%, 50%, 60%, or 70%, or any combination thereof.

[0048] In some optional embodiments, the gas permeability of the solid electrolyte composite multilayer membrane is 50s / 100mL-200s / 100mL.

[0049] This application also provides a method for preparing a solid electrolyte composite multilayer membrane, the steps of which include:

[0050] Solid electrolytes and polymers are mixed in a specific ratio and then melt-mixed and granulated to form granules A.

[0051] The raw materials and granules A used to prepare the introductory layer 2 are used to form a three-layer structure casting sheet with an in-situ composite layer 1 in the middle and introductory layers 2 on both sides through a co-extrusion die of a casting machine.

[0052] The three-layer structure casting was subjected to annealing, low-temperature stretching, high-temperature stretching and heat setting in sequence to finally prepare a composite multilayer diaphragm.

[0053] In some optional embodiments, the temperature during the melt mixing and granulation of the solid electrolyte and polymer a does not exceed 230°C, and the solid electrolyte and polymer a are melt-mixed and granulated in a twin-screw extruder with a screw speed of 100 rpm to 300 rpm.

[0054] In some optional embodiments, the casting temperature during co-extrusion of granule A is 170℃-220℃; the casting temperature during co-extrusion of the introducing layer 2 is 150℃-200℃; granule A is passed through the middle channel of the co-extrusion die of the casting machine, and polymer b is passed through the channels on both sides of the co-extrusion die to form a three-layer structure casting sheet. The middle layer of this three-layer structure is the in-situ composite layer 1, and the two outer layers are the introducing layers 2. The polymer b in the introducing layer 2 and the polymer a in the in-situ composite layer 1 can be made from the same raw material. The screw speed when granule A passes through the co-extrusion die of the casting machine is 50rpm-200rpm, and the screw speed when polymer b passes through the co-extrusion die is 30rpm-100rpm.

[0055] In some optional embodiments, the annealing temperature is 80℃-160℃; the low-temperature stretching temperature is 30℃-60℃ with a stretching ratio of 1.1-1.5; and the high-temperature stretching temperature is 120℃-180℃ with a stretching ratio of 1.5-3.0.

[0056] This application also provides a lithium-ion battery, including the above-mentioned solid electrolyte composite multilayer separator.

[0057] To illustrate the effects of this application, the following specific embodiments are also provided.

[0058] In the following examples / comparative examples, the raw materials polypropylene a and polypropylene b are the same, with a melt index of 1.2 g / 10 min.

[0059] Example 1

[0060] The membrane in this embodiment is a solid electrolyte composite multilayer membrane with a three-layer structure, consisting of a first induction layer 21, an in-situ composite layer 1, and a second induction layer 22. The in-situ composite layer 1 comprises 95% polypropylene a by mass and 5% Li by mass. 1.5 Al 0.5 Ti 1.5 (PO4)3 nanoparticles with a D50 particle size of 110 nm.

[0061] According to the above ratio, polypropylene a and Li 1.5 Al 0.5 Ti 1.5 (PO4)3 nanoparticles are co-extruded and granulated using a twin-screw extruder. The maximum temperature during co-melting and granulation is 230℃, and the extrusion speed is 200 rpm, yielding granule A. Granule A is then co-extruded through the middle channel of a three-layer die in a casting machine, while polypropylene b flows through the side channels of the three-layer die to form a three-layer structured casting sheet. The feed ratio of granule A to polypropylene b is 1:1:1, and the extrusion speed of the casting sheet is 27 m / min. After extrusion through the die, the casting sheet is bonded to a 45℃ cooling roller to obtain a B / A / B three-layer structured casting sheet.

[0062] The three-layer structured casting was annealed at 150℃, stretched 1.2 times at 50℃, and then stretched 2.0 times at 160℃ before being shaped to obtain a composite multilayer diaphragm. The stretching ratio was defined as the ratio of the length of the casting after stretching to the length before stretching.

[0063] Example 2

[0064] The membrane in this embodiment is a solid electrolyte composite multilayer membrane with a three-layer structure, consisting of a first induction layer 21, an in-situ composite layer 1, and a second induction layer 22. The in-situ composite layer 1 comprises 98% polypropylene a by mass and 2% Li by mass. 1.5 Al 0.5 Ti 1.5 (PO4)3 nanoparticles with a D50 particle size of 110 nm.

[0065] According to the above ratio, polypropylene A and Li... 1.5 Al 0.5 Ti 1.5 (PO4)3 nanoparticles are co-extruded and granulated using a twin-screw extruder. The maximum temperature during co-melting and granulation is 230℃, and the extrusion speed is 200 rpm, yielding granule A. Granule A is then co-extruded through the middle channel of a three-layer die in a casting machine, while polypropylene b flows through the side channels of the three-layer die to form a three-layer structured casting sheet. The feed ratio of granule A to polypropylene b is 1:1:1, and the extrusion speed of the casting sheet is 27 m / min. After extrusion through the die, the casting sheet is bonded to a 45℃ cooling roller to obtain a B / A / B three-layer structured casting sheet.

[0066] The three-layer structured casting was annealed at 150℃, stretched 1.2 times at 50℃, and then stretched 2.0 times at 160℃ before being shaped to obtain a composite multilayer diaphragm. The stretching ratio was defined as the ratio of the length of the casting after stretching to the length before stretching.

[0067] Example 3

[0068] The membrane in this embodiment is a solid electrolyte composite multilayer membrane with a three-layer structure, consisting of a first induction layer 21, an in-situ composite layer 1, and a second induction layer 22. The in-situ composite layer 1 comprises 95% polypropylene a by mass and 5% Li by mass. 1.5 Al 0.5 Ti 1.5 (PO4)3 nanoparticles with a D50 particle size of 110 nm.

[0069] According to the above ratio, polypropylene a and Li 1.5 Al 0.5 Ti 1.5 (PO4)3 nanoparticles are co-extruded and granulated using a twin-screw extruder. The maximum temperature during co-melting and granulation is 230℃, and the extrusion speed is 200 rpm, yielding granule A. Granule A is then co-extruded through the middle channel of a three-layer die in a casting machine, while polypropylene a flows through the side channels of the three-layer die to form a three-layer structured casting sheet. The feed ratio of granule A to polypropylene b is 0.5:1:0.5, and the extrusion speed of the casting sheet is 27 m / min. After extrusion through the die, the casting sheet is bonded to a 45℃ cooling roller to obtain a B / A / B three-layer structured casting sheet.

[0070] The three-layer structured casting was annealed at 150℃, stretched 1.2 times at 50℃, and then stretched 2.0 times at 160℃ before being shaped to obtain a composite multilayer diaphragm. The stretching ratio was defined as the ratio of the length of the casting after stretching to the length before stretching.

[0071] Example 4

[0072] The membrane in this embodiment is a solid electrolyte composite multilayer membrane with a three-layer structure, consisting of a first induction layer 21, an in-situ composite layer 1, and a second induction layer 22. The in-situ composite layer 1 comprises 98% polypropylene a by mass and 2% Li by mass. 1.5 Al 0.5 Ti 1.5 (PO4)3 nanoparticles with a D50 particle size of 110 nm.

[0073] According to the above ratio, polypropylene a and Li 1.5 Al 0.5 Ti 1.5(PO4)3 nanoparticles are co-extruded and granulated using a twin-screw extruder. The maximum temperature during co-melting and granulation is 230℃, and the extrusion speed is 200 rpm, yielding granule A. Granule A is then co-extruded through the middle channel of a three-layer die in a casting machine, while polypropylene b flows through the side channels of the three-layer die to form a three-layer structured casting sheet. The feed ratio of granule A to polypropylene b is 0.5:1:0.5, and the extrusion speed of the casting sheet is 27 m / min. After extrusion through the die, the casting sheet is bonded to a 45℃ cooling roller to obtain a B / A / B three-layer structured casting sheet.

[0074] The three-layer structured casting was annealed at 150℃, stretched 1.2 times at 50℃, and then stretched 2.0 times at 160℃ before being shaped to obtain a composite multilayer diaphragm. The stretching ratio was defined as the ratio of the length of the casting after stretching to the length before stretching.

[0075] Comparative Example 1

[0076] The diaphragm in this embodiment has a single-layer structure, which is the same as the in-situ composite layer 1 in Embodiment 1 above. It is composed of polymer a and solid electrolyte in-situ composite, including 95% polypropylene a by mass and 5% Li by mass. 1.5 Al 0.5 Ti 1.5 (PO4)3 nanoparticles with a D50 particle size of 110 nm.

[0077] According to the above ratio, polypropylene a and Li 1.5 Al 0.5 Ti 1.5 (PO4)3 nanoparticles are blended and granulated using a twin-screw extruder. The maximum temperature during blending and melt granulation is 230℃, and the extrusion speed is 200 rpm, yielding granule A. Granule A is then cast and extruded using a casting machine to form a single-layer structured sheet. The casting extrusion speed is 27 m / min, and the sheet is adhered to a 45℃ cooling roller after being extruded from the die, resulting in a single-layer structured sheet.

[0078] The above-mentioned single-layer structure casting was annealed at 150℃, stretched 1.2 times at 50℃, and then stretched 2.0 times at 160℃ before being shaped to obtain a composite multilayer diaphragm. The stretching ratio is defined as the ratio of the length of the casting after stretching to the length before stretching.

[0079] Comparative Example 2

[0080] The diaphragm in this embodiment has a single-layer structure, which is the same as the in-situ composite layer 1 in Embodiment 2 above. It is composed of a polymer and a solid electrolyte in situ composite, including 98% polypropylene a by mass and 2% Li by mass. 1.5 Al 0.5 Ti 1.5(PO4)3 nanoparticles with a D50 particle size of 110 nm.

[0081] According to the above ratio, polypropylene a and Li 1.5 Al 0.5 Ti 1.5 (PO4)3 nanoparticles are blended and granulated using a twin-screw extruder. The maximum temperature during blending and melt granulation is 230℃, and the extrusion speed is 200 rpm, yielding granule A. Granule A is then cast and extruded using a casting machine to form a single-layer structured sheet. The casting extrusion speed is 27 m / min, and the sheet is adhered to a 45℃ cooling roller after being extruded from the die, resulting in a single-layer structured sheet.

[0082] The above-mentioned single-layer structure casting was annealed at 150℃, stretched 1.2 times at 50℃, and then stretched 2.0 times at 160℃ before being shaped to obtain a composite multilayer diaphragm. The stretching ratio is defined as the ratio of the length of the casting after stretching to the length before stretching.

[0083] Comparative Example 3

[0084] The diaphragm in this embodiment is a composite multilayer diaphragm with a three-layer structure, all three layers of which are made of the material of the aforementioned introductory layer 2.

[0085] Polypropylene a is co-extruded using a three-layer die in a casting machine to form a three-layer structured sheet. The mass ratio of the three layers is 1:1:1, the extrusion speed of the cast sheet is 27 m / min, and the sheet is then bonded to a 45°C cooling roller after extrusion to obtain the three-layer structured sheet.

[0086] The three-layer structured casting was annealed at 150℃, stretched 1.2 times at 50℃, and then stretched 2.0 times at 160℃ before being shaped to obtain a composite multilayer diaphragm. The stretching ratio was defined as the ratio of the length of the casting after stretching to the length before stretching.

[0087] Comparative Example 4

[0088] The diaphragm in this embodiment is a composite multilayer diaphragm with a three-layer structure, all three layers of which are made of the material of the aforementioned introductory layer 2.

[0089] Polypropylene a is co-extruded using a three-layer die in a casting machine to form a three-layer structured sheet. The mass ratio of the three layers is 0.5:1:0.5, the extrusion speed of the cast sheet is 27 m / min, and the sheet is then bonded to a 45°C cooling roller after extrusion to obtain the three-layer structured sheet.

[0090] The three-layer structured casting was annealed at 150℃, stretched 1.2 times at 50℃, and then stretched 2.0 times at 160℃ before being shaped to obtain a composite multilayer diaphragm. The stretching ratio was defined as the ratio of the length of the casting after stretching to the length before stretching.

[0091] Comparative Example 5

[0092] The diaphragm in this embodiment has a single-layer structure, which is made of polypropylene a.

[0093] Polypropylene a is co-extruded into a single-layer structured sheet using a single-layer die in a casting machine. The extrusion speed of the cast sheet is 27 m / min, and after extrusion from the die, the sheet is bonded to a cooling roller at 45°C to obtain the single-layer structured sheet.

[0094] The above-mentioned single-layer structure casting was annealed at 150℃, stretched 1.2 times at 50℃, and then stretched 2.0 times at 160℃ before being shaped to obtain a composite multilayer diaphragm. The stretching ratio is defined as the ratio of the length of the casting after stretching to the length before stretching.

[0095] The membranes prepared in Examples 1 to 4, and Comparative Examples 1 to 5, were tested to determine their basic physicochemical properties, including thickness, air permeability, porosity, and puncture strength. At least 10 data points were collected for each test, and the average of these 10 data points was used as the final test result for comparison. Specifically:

[0096] Ionic conductivity is determined by the assembly of soft-pack batteries: 1 to 5 layers of separator are stacked, soft-pack batteries are assembled from stainless steel sheets, electrolyte is added and sealed, and the AC impedance is tested with an electrochemical workstation to determine the internal resistance of the soft-pack battery. The measured value is obtained by linear fitting.

[0097] The diaphragm thickness was measured using a Marl thickness gauge, with units in μm. The testing followed GB / T6672-2001 "Mechanical Measurement Method for Determination of Thickness of Plastic Films and Sheets".

[0098] The method for determining the porosity of the diaphragm is as follows: Cut a 10x10 cm film sample, weigh it using a balance (m1), and then calculate the porosity using the following formula: Porosity = 1 - m1 / (thickness * 0.00905). The test should refer to GB / T31729-2015 "Test Method for Unit Area Mass of Plastic Films".

[0099] The air permeability of the diaphragm was measured using an EG01-55-1MR air permeability meter and expressed as the time it takes for 100 mL of gas to pass through a fixed area diaphragm.

[0100] The puncture strength test of the diaphragm is performed by puncturing the sample with a flat-tipped needle of 1 mm diameter at a rate of 50 mm per minute. The force corresponding to the puncture of the membrane is the puncture strength, referring to GB / T 21302-2007 "General Rules for Composite Films and Bags for Packaging".

[0101] The specific test results are shown in Table 1 below.

[0102] Table 1

[0103]

[0104]

[0105] As can be seen from the table above, Examples 1 to 4 are all three-layer composite membranes consisting of a first introductory layer 21, an in-situ composite layer 1 (solid electrolyte and polymer composite), and a second introductory layer 22. The permeability of these membranes is less than 170s / 100mL, the porosity is higher than 40%, and the performance fluctuation range is small, indicating that the membrane has good uniformity.

[0106] As shown in the table above, the ionic conductivity of the membranes in Examples 1 to 4 all exceeded 2 mS / cm. In contrast, the membranes prepared in Comparative Examples 1 and 3 did not introduce a composite layer of solid electrolyte. As the membranes could not provide more lithium ion transport sites, their ionic conductivity was relatively low, all less than 2 mS / cm. This indicates that the introduction of a composite layer of solid electrolyte is beneficial to improving the ionic conductivity of the membrane.

[0107] In Comparative Examples 1 and 2, single-layer membranes were directly prepared using in-situ composite layers. Compared with those in Examples 1 to 4, the membranes prepared by these methods were thicker, had higher average air permeability, and some had punctures. The puncture strength of the membranes was also lower. This indicates that the three-layer composite structure of the first introductory layer 21, the in-situ composite layer 1 (solid electrolyte and polymer composite), and the second introductory layer 22 is beneficial to improving the mechanical strength of the membrane and reducing its thickness.

[0108] In Comparative Example 5, a single-layer membrane structure was prepared using polypropylene a, and its overall performance data was inferior to that of the membranes prepared in Examples 1 to 4. This indicates that the three-layer composite structure of the first introductory layer 21 - in-situ composite layer 1 (solid electrolyte and polymer composite) - second introductory layer 22 in this application is effective in solving the problem of local lithium dendrites forming inside the battery, which leads to membrane puncture, and can also improve the ionic conductivity of the membrane.

[0109] The above examples illustrate this application only to aid understanding and are not intended to limit its scope. Those skilled in the art to which this application pertains can make various simple deductions, modifications, or substitutions based on the ideas presented.

Claims

1. A solid electrolyte composite multilayer membrane, characterized in that, include: An in-situ composite layer is constructed as a porous structure primarily formed by the in-situ composite of a solid electrolyte in a polymer a, wherein the polymer a comprises a polyolefin, and the content of the polymer a in the in-situ composite layer is 90%-99.9% by mass; the content of the solid electrolyte is 0.1%-10%; the D50 particle size of the solid electrolyte is 50nm-200nm; and... The introductory layer comprises two layers, which are respectively disposed on both sides of the in-situ composite layer; the introductory layer is constructed as a porous membrane mainly formed of polymer b, wherein polymer b includes polyolefin; the melt index of the polyolefin is 0.5 g / 10 min to 2.0 g / 10 min; The preparation steps of the solid electrolyte composite multilayer membrane include: mixing the solid electrolyte and the polymer a according to the ratio, and melting and granulating them to form granules A; The polymer b used to prepare the introductory layer and the granules A are co-extruded through a casting machine to form a three-layer structure casting sheet with the in-situ composite layer in the middle and the introductory layer on both sides; the three-layer casting sheet is then subjected to annealing, low-temperature stretching, high-temperature stretching and heat setting in sequence to finally prepare the solid electrolyte composite multilayer diaphragm. The thickness of the solid electrolyte composite multilayer membrane is 4μm-20μm; the air permeability of the solid electrolyte composite multilayer membrane is 50s / 100mL-200s / 100mL.

2. The solid electrolyte composite multilayer membrane according to claim 1, characterized in that, The polymer b and the polymer a are constructed of the same polyolefin.

3. The solid electrolyte composite multilayer membrane according to claim 1 or 2, characterized in that, The import layer includes a first import layer and a second import layer, and the first import layer, the in-situ composite layer and the second import layer are arranged sequentially; the thickness of the first import layer and the second import layer does not exceed the thickness of the in-situ composite layer.

4. The solid electrolyte composite multilayer membrane according to claim 1, characterized in that, Both the introductory layer and the in-situ composite layer include additives, and the mass percentage of the additives is ≤5%.

5. The solid electrolyte composite multilayer membrane according to claim 1, characterized in that, The solid electrolyte includes inorganic solid electrolytes.

6. The solid electrolyte composite multilayer membrane according to claim 5, characterized in that, The solid electrolyte includes at least one of oxide solid electrolyte, sulfide solid electrolyte, and halide solid electrolyte.

7. The solid electrolyte composite multilayer membrane according to claim 5, characterized in that, The solid electrolyte includes at least one of lithium lanthanum zirconium tantalum oxide, lithium phosphorus sulfide chlorine, and lithium titanium aluminum phosphate.

8. The solid electrolyte composite multilayer membrane according to claim 1, characterized in that, The introductory layer includes a first introductory layer and a second introductory layer, wherein the first introductory layer, the in-situ composite layer and the second introductory layer are arranged sequentially; the mass ratio of the first introductory layer, the in-situ composite layer and the second introductory layer is (0.4-1):1:(0.4-1). And / or, the porosity of the solid electrolyte composite multilayer membrane is 40%-70%.

9. A method for preparing a solid electrolyte composite multilayer membrane, characterized in that, The solid electrolyte composite multilayer membrane is the solid electrolyte composite multilayer membrane as described in any one of claims 1-8, and the steps include: Solid electrolyte and polymer a are mixed in a certain proportion and then melt-mixed and granulated to form granules A; The polymer b used to prepare the introductory layer and the granules A are co-extruded through a casting machine to form a three-layer structure casting sheet with an in-situ composite layer in the middle and introductory layers on both sides; The three-layer structure casting was subjected to annealing, low-temperature stretching, high-temperature stretching and heat setting in sequence to finally prepare the composite multilayer diaphragm.

10. The method for preparing a solid electrolyte composite multilayer membrane according to claim 9, characterized in that, The temperature during the melt mixing and granulation of the solid electrolyte and polymer a shall not exceed 230°C; The casting temperature during co-extrusion of the granule A is 170℃-220℃; the casting temperature during co-extrusion of the introductory layer is 150℃-200℃. The annealing temperature is 80℃-160℃; the low-temperature stretching temperature is 30℃-60℃ and the stretching ratio is 1.1-1.5; the high-temperature stretching temperature is 120℃-180℃ and the stretching ratio is 1.5-3.

0.

11. A lithium-ion battery, characterized in that, Includes a solid electrolyte composite multilayer membrane as described in any one of claims 1-8; or includes a solid electrolyte composite multilayer membrane prepared by the preparation method described in claim 9 or 10.

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