Battery diaphragm with PE (Poly Ethylene) interlayer structure and manufacturing equipment

Abstract

A battery diaphragm with a PE interlayer structure comprises two PP outer layers and a PE inner layer, and a transparent densified PE interlayer structure or a densified interface of the PE inner layer is arranged between the PP outer layers and the PE inner layer; at least one PP outer layer is a transparent PP outer layer, and the thickness of the PP outer layer is smaller than that of the PE inner layer; the minimum value of the thickness of the battery diaphragm is reduced to 2 microns, and the maximum value of the thickness of the battery diaphragm is reduced to 12 microns. The transparent densified PE interlayer structure preparation line is extruded, stretched and relaxed to form a microporous transparent densified PE interlayer structure, and then the microporous transparent densified PE interlayer structure and the PE inner layer form a PE inner layer composite structure; the transparent densified PE interlayer structure preparation line comprises an upstream roller pair and a downstream roller pair, the rotation speed of the downstream roller pair is decreased relative to the upstream roller pair, so that the porosity of the PE interlayer structure is increased, and the PE intermittent pore interlayer structure is formed. The battery provided by the utility model is ultrathin, high in performance and long in service life.

Description

Technical Field

[0001] This utility model relates to battery separators with transparent dense PE interlayer structures or intermittent porous PE interlayer structures and their manufacturing equipment, which can provide ultra-thin / extremely thin, high-performance, and long-life batteries.

[0002] In the term "transparent and denser PE interlayer structure," "transparent" refers to a thickness of 0.05-0.25 micrometers, and "dense" refers to the interlayer structure density between the PP and PE layers, which, when stretched to a porosity of 28-49%, increases relative to HDPE raw materials, exceeding 0.941 g / cm³. 3 Even higher than 0.965 g / cm³ 3 .

[0003] The term "intermittent porosity PE interlayer structure" refers to the periodic variation in density of the interlayer structure between the PP and PE layers relative to HDPE raw materials, under stretched conditions with a porosity of 28-49%, where the PE density in certain sections exceeds 0.941 g / cm³. 3 Even higher than 0.965 g / cm³ 3 The adjacent section has a PE density of less than 0.965 g / cm³. 3 Even below 0.941 g / cm³ 3 .

[0004] The term "transparent PP layer" refers to a layer whose thickness has been reduced from more than 4 micrometers in the prior art to 0.25-2.0 micrometers, preferably about 0.5 and 1.5 micrometers, while still maintaining oxidation protection for the overall separator or PE layer structure. At the same time, the total ion transport rate and air transport rate can still be controlled or limited to ideal levels, allowing for high discharge rates, low ER and Gurley values. Background Technology

[0005] The battery industry is pursuing increasingly thinner battery separators. First, thinner separators allow for higher rate capacity, enabling higher current density across the separator and reducing separator resistance, which is crucial for electric vehicle acceleration and extended driving range. Second, thinner separators facilitate the manufacture of smaller batteries with equivalent power and extend battery life. Third, thinner separators allow for the customization of batteries for specific applications.

[0006] However, in the existing technology, in order to reduce the total thickness of the separator, every effort is made to reduce the thickness of the base layer and the thickness of each layer. This idea is constrained by the strength and permeability of the separator, which results in the total thickness of the battery separator being unable to break through the current minimum value. Utility Model Content

[0007] The purpose of this invention is to provide a battery separator with a PE interlayer structure and its manufacturing equipment, which can provide ultra-thin / extremely thin, high-performance, and long-life batteries.

[0008] Therefore, according to a first aspect of the present invention, a battery separator with a PE interlayer structure is provided, comprising two PP outer layers and one PE inner layer, wherein a transparent and dense PE interlayer structure or a denser interface of the PE inner layer is provided between the PP outer layers and the PE inner layer; at least one PP outer layer is a transparent PP outer layer, and the thickness of the PP outer layer is less than that of the PE inner layer; the minimum thickness of the battery separator is reduced to 2 μm, and the maximum thickness is reduced to 12 μm.

[0009] Preferably, at least one side of the PP layer is further provided with a ceramic coating, a PVDF coating, or a PVDF:HFP coating, and the maximum thickness of the coated battery separator is 25μm, 16μm, or 14μm.

[0010] Preferably, an epitaxial region or epitaxial layer for growing a sheet-like crystal structure is provided at the interface between PP and PE.

[0011] Preferably, each of the PP outer layers is 1μm to 4μm thick and the PE inner layer is 1μm to 4μm thick; each of the PP outer layers is 1μm to 3μm thick and the PE inner layer is 1μm to 3μm thick; each of the PP outer layers is 1μm to 4μm thick and the PE inner layer is 1μm to 2μm thick; each of the PP outer layers is 1μm to 2μm thick and the PE inner layer is 1μm to 6μm thick; each of the PP outer layers is 1μm to 2μm thick and the PE inner layer is 1μm to 5μm thick; each of the PP outer layers is 1μm to 2μm thick and the PE inner layer is 1μm to 4μm thick; each of the PP outer layers is 1μm to 2μm thick and the PE inner layer is 1μm to 3μm thick; each of the PP outer layers is 1μm to 2μm thick and at least one of the PE inner layers is 1μm to 2μm thick.

[0012] Preferably, the minimum thickness of the PE inner layer is 6μm, 5μm, 4μm, 3μm, 2μm, 1.5μm or 1μm.

[0013] Preferably, the maximum thickness of the battery separator is 12μm, 11μm, 10μm, 9μm, 8μm, 7μm, 6μm, 5μm, 4μm, 3μm or 2μm.

[0014] According to a second aspect of the present invention, a battery separator with a PE interlayer structure is provided, comprising two PP outer layers and one PE inner layer, wherein an intermittent PE porous interlayer structure is provided between the PP outer layers and the PE inner layer; at least one PP outer layer is a transparent PP outer layer, the thickness of the PP outer layer is less than that of the PE inner layer; the minimum thickness of the battery separator is reduced to 2 μm, and the maximum thickness is reduced to 12 μm.

[0015] According to a third aspect of this utility model, a manufacturing apparatus for a battery separator with a PE interlayer structure is provided, characterized in that the manufacturing apparatus comprises: two PP outer layer preparation lines, which undergo extrusion and stretching to form a microporous PP outer layer; a PE inner layer preparation line, which runs parallel to the PP outer layer preparation line, and undergoes extrusion and stretching to form a microporous PE inner layer; a transparent and dense PE interlayer structure preparation line, which runs parallel to the PP outer layer preparation line, and undergoes extrusion, stretching, and relaxation to form a microporous transparent and dense PE interlayer structure, and then forms a PE inner layer composite structure with the PE inner layer; and a laminator, which is located downstream of the PP outer layer preparation line, the PE inner layer preparation line, and the transparent and dense PE interlayer structure preparation line, and laminates the PP outer layer, the PE inner layer, and the transparent and dense PE interlayer structure together to form a battery separator with a transparent and dense PE interlayer structure.

[0016] Preferably, the transparent, denser PE interlayer structure forms the denser interface of the inner PE layer.

[0017] Preferably, the transparent and dense PE interlayer structure preparation line includes an upstream roller pair and a downstream roller pair. The rotation speed of the downstream roller pair decreases or increases relative to the upstream roller pair, causing the porosity of the PE interlayer structure to increase or decrease, forming an intermittent porous interlayer structure of PE.

[0018] According to a fourth aspect of the present invention, a battery separator having a PE interlayer structure is provided, which is directly obtained from the manufacturing equipment according to the present invention.

[0019] In the prior art, the industry has always believed that the shut-off characteristics of the partition depend on the total thickness of the PE layer. In contrast, according to the present invention, the PE density at the PE-PP interface is more important than the thickness of the PE layer itself.

[0020] In existing technologies, when preparing multilayer battery separators, each layer is first laminated together and then stretched to create micropores. This method obviously cannot produce the multilayer battery separator according to the present invention. Therefore, according to the preparation equipment of the present invention, at least one PE layer or PP layer is stretched individually to a transparent thickness and forms micropores before being laminated with other layers. During the formation of pores in the PE interlayer structure between PP and PE, the extrusion, tensile strain value, or active relaxation during stretching of the PE interlayer structure can be controlled to form a transparent, high-density PE layer, or to generate a PE layer with enhanced PE density at the PP and PE interface.

[0021] A typical three-layer battery separator uses a PP / PE / PP structure, rather than a PE / PP / PE configuration. This is because the inherently higher ion transport rate of the inner PE layer is limited by the lower transport rate of the outer PP layer, and the PP / PE / PP structure allows the battery separator to simultaneously provide oxidation protection and high-temperature shutdown functions, while also balancing a high Gurley value and ER. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structural principle of a battery separator manufacturing equipment with a PE interlayer structure according to the present invention.

[0023] Figure 2 A schematic diagram of a three-layer microporous membrane of PP / PE / PP with different pore sizes and its PP / PE interface is shown. In the figure, reference numerals 1, 2, and 3 represent PP layer, PE layer, and PP layer, respectively; reference numeral 12 represents the interface between PP layer 1 and PE layer 2, and reference numerals 2 and 3 represent the interface between PE layer 2 and PP layer 3, respectively.

[0024] Figure 3 This is a SEM micrograph of the surface of a 12μm PP / PE / PP three-layer microporous membrane at 20,000x magnification.

[0025] Figure 4 This is a cross-sectional SEM image of a 12μm PP / PE / PP three-layer microporous membrane at 4,400x magnification.

[0026] Figure 5A , Figure 5B , Figure 5C , Figure 5D , Figure 5E , Figure 5F , Figure 5G , Figure 5H , Figure 5I These are schematic diagrams of various configurations of single-layer and multi-layer PE and PP microporous membranes.

[0027] Figure 6This is a 7500x magnified SEM cross-sectional image of the PE inner layer of the PP / PE / PP three-layer microporous membrane, which has relatively large pores.

[0028] Figure 7 This is a cross-sectional SEM image of the PP / PE / PP three-layer microporous membrane with a relatively large pore size, taken at 8500x magnification.

[0029] Figure 8 This is a cross-sectional SEM image of an 8μm PP / PE / PP three-layer microporous membrane at 5000x magnification.

[0030] Figure 9 This is a cross-sectional micrograph of a 7μm PP / PE / PP three-layer microporous membrane, magnified 12000 times.

[0031] Figure 10 This is a cross-sectional micrograph of a 6μm PP / PE / PP three-layer microporous membrane, magnified 12000 times.

[0032] Figure 11 This is a cross-sectional micrograph of a 7μm PP / PE / PP three-layer microporous membrane, magnified 8500 times by SEM.

[0033] Figure 12 This is a cross-sectional micrograph of an 8μm PP / PE / PP three-layer microporous membrane, magnified 8500-8550 times.

[0034] Figure 13 This is a cross-sectional micrograph of an 8μm PP / PE / PP three-layer microporous membrane, magnified 8500-8550 times.

[0035] Figure 14 This is a cross-sectional micrograph of a 7-8μm PP / PE / PP three-layer microporous membrane, magnified 5000 times by SEM.

[0036] Figure 15 This is a SEM micrograph of a 9μm PE / PP / PE three-layer microporous membrane at 20,000x magnification.

[0037] Figure 16 This is a cross-sectional micrograph of a 9μm PE / PP / PE three-layer microporous membrane, magnified 8500 times by SEM.

[0038] Figure 17 This is a cross-sectional SEM image of an 8μm PE1 / PE2 / PE1 co-extruded three-layer microporous membrane at 7350x magnification.

[0039] Figure 18This is a graph showing the thermal turn-off relationship between resistance ER and temperature, illustrating two typical examples of thermal turn-off occurring in the film samples at approximately 130-132 °C, where the resistance ranges from approximately 8 ohms-cm. 2 Rising sharply to 10000 ohm-cm 2 From 130-175℃, ≥10000 ohm-cm 2 A persistently high level of resistance indicates 'complete' thermal shutdown.

[0040] Figure 19 This is a graph showing the thermal turn-off relationship between resistance ER and temperature, illustrating two instances of 'incomplete' thermal turn-off of the membrane sample at approximately 128°C, where the resistance ranges from approximately 10 ohms-cm. 2 It rose sharply to just above 1.0 × 10 2 ohm-cm 2 Subsequently, ER decreased. Detailed Implementation

[0041] like Figure 1 As shown, the battery separator with a PE interlayer structure PE' includes two PP outer layers PP1 and PP2 and a PE inner layer PE. A transparent and dense PE interlayer structure PE' or a denser interface PE' of the PE inner layer is provided between the PP outer layer and the PE inner layer.

[0042] like Figure 2 As shown, the battery separator with PE interlayer structures 12 and 23 includes two PP outer layers 1 and 3 and one PE inner layer 2. A transparent and dense PE interlayer structure 12 and 23 or a dense interface 12 and 23 of the PE inner layer is provided between the PP outer layer and the PE inner layer.

[0043] In various possible embodiments, a ceramic coating, a PVDF coating, or a PVDF:HFP coating is provided on at least one side of the PP layer, and the maximum thickness of the coated battery separator is 25μm, 16μm, or 14μm; an epitaxial region or epitaxial layer with a sheet-like crystal structure is provided at the interface between PP and PE.

[0044] Specifically, each of the PP outer layers is 1μm to 4μm thick and the PE inner layer is 1μm to 4μm thick; each of the PP outer layers is 1μm to 3μm thick and the PE inner layer is 1μm to 3μm thick; each of the PP outer layers is 1μm to 4μm thick and the PE inner layer is 1μm to 2μm thick; each of the PP outer layers is 1μm to 2μm thick and the PE inner layer is 1μm to 6μm thick; each of the PP outer layers is 1μm to 2μm thick and the PE inner layer is 1μm to 5μm thick; each of the PP outer layers is 1μm to 2μm thick and the PE inner layer is 1μm to 4μm thick; each of the PP outer layers is 1μm to 2μm thick and the PE inner layer is 1μm to 3μm thick; each of the PP outer layers is 1μm to 2μm thick and at least one of the PE inner layers is 1μm to 2μm thick.

[0045] In particular, the minimum thickness of the PE inner layer is 6μm, 5μm, 4μm, 3μm, 2μm, 1.5μm or 1μm.

[0046] In particular, the maximum thickness of the battery separator is 12μm, 11μm, 10μm, 9μm, 8μm, 7μm, 6μm, 5μm, 4μm, 3μm or 2μm.

[0047] like Figure 1 As shown, in one embodiment, the PE interlayer structure PE' can be an intermittent porous PE interlayer structure...HDHDHD....

[0048] like Figure 1 As shown, the equipment for manufacturing a battery separator with a PE interlayer structure includes:

[0049] Two PP outer layer preparation lines, which undergo extrusion and stretching to form microporous PP outer layers PP1 and PP2;

[0050] A PE inner layer preparation line, which runs parallel to the PP outer layer preparation line, undergoes extrusion and stretching to form a microporous PE inner layer;

[0051] A transparent, dense PE interlayer structure fabrication line has parallel PP outer layer fabrication lines. After extrusion, stretching, and relaxation to form a microporous, transparent, dense PE interlayer structure PE', it then forms a PE inner layer composite structure PE+PE' with the PE inner layer.

[0052] A laminator, located downstream of the PP outer layer preparation line, the PE inner layer preparation line, and the transparent dense PE interlayer structure preparation line, laminates the PP outer layer PP1, PP2, the PE inner layer PE, and the transparent dense PE interlayer structure PE' together to form a battery separator with a denser interface of either the transparent dense PE interlayer structure PE' or the PE inner layer.

[0053] In particular, the transparent densified PE interlayer structure PE' can serve as a densification interface for the inner layers of PE.

[0054] In particular, the transparent densified PE interlayer structure preparation line includes an upstream roller pair R1 and a downstream roller pair R2. The rotation speed of the downstream roller pair R2 decreases or increases relative to the upstream roller pair R1, causing the porosity and density of the PE interlayer structure PE' to increase or decrease, forming an intermittent porous interlayer structure of PE...HDHDHD...

[0055] In particular, the product directly produced by the manufacturing equipment of this utility model is the battery separator with PE interlayer structure according to this utility model.

[0056] According to this invention, the thickness of the multilayer microporous polyolefin membrane is ≤12μm, ≤11μm, ≤10μm, ≤9μm, ≤8μm, ≤7μm.

[0057] ≤6μm, ≤5μm, ≤4μm, ≤3μm, and even ≤2μm. That is, the total thickness of the battery separator is even smaller than the minimum value in the prior art.

[0058] According to this invention, the multilayer microporous polyolefin membrane has at least one shut-off polyethylene layer, the thickness of which is ≤6μm.

[0059] ≤5μm, ≤4μm, ≤3μm, ≤2μm, and even ≤1.5μm. That is, the thickness of the PE layer can be even smaller than the minimum value in the prior art.

[0060] According to this invention, the total thickness of the coated separator is ≤25μm, ≤20μm, ≤16μm, or even ≤14μm. That is, the total thickness of the coated battery separator can also be smaller than the minimum value in the prior art.

[0061] The battery separator according to this invention cannot be manufactured directly using known dry, wet, particle stretching, or β-nucleation precursor BOPP (biaxially oriented polypropylene) methods. Furthermore, there is no corresponding manufacturing equipment available in the prior art.

[0062] In the dry process (also known as the Celgard process), pore formation is caused by stretching a non-porous semi-crystalline extruded polymer precursor, without the use of solvents or fillers, and the resulting pore shapes are relatively regular.

[0063] In the wet process (also known as the phase inversion process, extraction process, or TIPS process), polymer raw materials are mixed with process oil (also known as plasticizer or plasticizer), this mixture is extruded, and then the process oil is removed to form pores (these films can be stretched before and after oil removal). In this process, both solvents and fillers are used, and the resulting pores are not only relatively regular but also relatively uniform in shape.

[0064] In the particle stretching process, particle fillers are introduced into the raw material. The cracks generated at the particle boundaries during stretching are used as pores. No solvent is used, but fillers are used. The resulting pore shapes are random, and the pore sizes are irregular and uneven.

[0065] Dry, wet, and particle stretching methods follow different process routes, have different mechanisms, and result in different product microstructures. Therefore, they cannot be used interchangeably. For example, if the inventiveness of a dry method invention is evaluated based on existing technical literature on particle stretching, practitioners in the field, based on existing technology and relevant background knowledge, would consider such an evaluation to be questionable.

[0066] According to this invention, a transparent PP layer, a transparent high-density PE interlayer structure, and / or an intermittent porous structure within the PE layer are provided, enabling the thickness of the microporous polymer battery separator to break through the thickness limit of the prior art, reducing it by approximately 2 to 12 micrometers, or even approximately 3 to 9 micrometers, while maintaining thermal shutdown functionality. The transparent PP layer, with a thickness of 1.0 to 2.0 micrometers, prevents oxidative degradation of the PE layer and acts as an ion transport rate limiting layer.

[0067] The extrusion equipment of this invention can precisely control the low mass flow of PP extrudate; before the PE layer and PP layer are laminated, the PE layer can be pre-calendered or subjected to other surface densification treatments; the temperature of the PE layer extrusion die is lower than that of the molten PE material; the friction coefficient of the inner surface of the PE layer extrusion die is increased, etc. The specific operation is well known to those skilled in the art and need not be elaborated.

[0068] The extruder, laminator, rollers, and roller speed controller of this invention can all be selected from standard products in the prior art.

[0069] This invention relates to a multilayer porous ultrathin separator, which can provide the ability to shut off, delay or prevent dendrite growth, delay or avoid internal short circuits caused by dendrite growth, and increase the cycle life of the battery.

[0070] According to this utility model, Tables 1 to 3 include data about Samples 1 to 10.

[0071] Table 1: Properties of Ultrathin Microporous Battery Separators

[0072]

[0073] Samples 1 to 4 are PP / PE / PP three-layer materials with excellent shut-off and a wide porosity range between 29% and 35%.

[0074] Samples 5 and 6 are PE materials with a more typical porosity range.

[0075] Table 2: Properties of PP / PE / PP 12μm three-layer microporous membranes with a 4μm PE inner layer.

[0076]

[0077] Table 3: Properties of ultrathin microporous membranes.

[0078] Sample 8: PP / PE / PP Sample 9: PP / PE / PP Sample 10: PP / PE / PP Thickness (μm) 9.4 9.05 9.75 JIS Gurley(s) 189 381 195 Puncture strength (g) 147 141 154 <![CDATA[Tensile stress in TD direction (kgf / cm 2 )]]> 161 199 188 Porosity (%) 48.56 42.57 43.35 MD shrinkage rate (%), 90℃ / 1 h <5 <5 5.00 Turn off Incomplete Incomplete Incomplete

[0079] Table 4: Possible Preferred Partition Properties

[0080] Example A Example B Example C Example D Thickness (μm) 9.5-12.0 6.5-9.5 5.5-6.5 3.5-5.5 Thickness range (μm) + / -2.0 + / -1.5 + / -1.0 + / -1.0 JIS Gurley(s) 150-450 100-400 100-400 75-150 Puncture strength (gr) 150-350 120-300 100-300 100-200 Porosity (%) 34-40 30-38 30-38 26-36 PE pore size (μm) <0.1 <0.1 <0.1 <0.1 PP pore size (μm) 0.020-0.050 0.020-0.050 0.020-0.050 0.020-0.050 MD shrinkage rate (%), 90°C / 1h <3 <3 <3 <3 MD shrinkage rate (%), 105C <10 <10 <10 <10 MD shrinkage rate (%), 120°C <20 <20 <20 <20 <![CDATA[TD Tension (kgf / cm 2 )]]> 130-300 130-300 130-300 100-250 MD elongation (%) 50-150 50-150 50-150 50-150 TD elongation (%) 75-300 50-250 50-250 50-250 <![CDATA[MD Tension (kgf / cm 2 )]]> 700-2500 700-1800 700-1800 500-1500 PP layer thickness (μm) 3.5-4.5 2.3-2.7 1.6-2.2 1.0-2.25 PE layer thickness (μm) 3.0-5.0 2.6-3.4 1.6-2.8 1.0-2.25 thermal shutdown yes yes yes yes

[0081] Examples of coating

[0082] A mixture of an aqueous polymer binder composed of a copolymer of sodium polyacrylate, acrylamide, and acrylonitrile and Degussa Al2O3 ceramic particles with an average particle size of <2 μm was used for coating. A 12μm microporous polyethylene (PE) membrane. The final coated membrane thickness is 16μm. It can be coated on one or both sides, with a total coating thickness of 4μm. The base membrane can be single-layer or multi-layer.

[0083] Comparative Examples

[0084] The non-woven separator 2 and the microporous multilayer separator 1 of this invention differ in terms of lithium dendrite growth and the resulting internal short circuits. A dual-electrode button cell was formed using graphite as the working electrode and lithium metal as the counter electrode material. Two different types of separators were used and studied. Separator 1 is a three-layer separator with a microporous structure (preferred), while separator 2 represents an independent non-woven structured separator (control).

[0085] Test 1 involved several charge and discharge cycles, with the cutoff voltage set at 5mV during charging or lithium insertion into the working electrode and at 2V during discharging or lithium extraction from the working electrode. 1mA / cm² was used during both charging and discharging in this test. 2 The current density.

[0086] A cell with separator 1 of this invention can be continuously cycled without voltage fluctuations during any charging or discharging step. A cell with a control non-woven separator 2 cannot be cycled in a similar manner to the cell with separator 1. Within 2 to 3 cycles, the cell with control separator 2 exhibits more voltage fluctuations, fails to reach the cutoff voltage, and eventually fails.

[0087] Separator 1 was removed from the cycled cell, and control separator 2 was removed from the cycled cell. Separator 1 did not show signs of lithium dendrite growth or internal short circuits related to Li dendrite growth. Separator 1 appeared transparent without any black spots or scorch marks. However, control separator 2 showed many black spots or scorch marks until control separator 2 clearly demonstrated internal short circuits caused by lithium dendrites.

[0088] Studies have shown that lithium dendrite growth and propagation, which are associated with battery performance and / or safety issues, are more likely to occur in non-woven, freestanding separators due to their key properties, including large pore size, high porosity, significantly lower twist, and / or lower Z-axis mechanical strength. These properties of non-woven, freestanding separators may accelerate lithium dendrite growth into the porous structure of this type of separator, and cause, allow, or promote negative issues, such as reduced cycle life of lithium-ion batteries. Dendrites require space or room to grow. Non-woven, freestanding separators provide this space or room.

[0089] According to this invention, the microporous membrane used as a battery separator has five basic properties with synergistic effects: torsion, porosity, pore size, pore size distribution, and mechanical strength. Each of these properties may have a significant impact on the performance of the separator and the battery.

[0090] According to this invention, separators with extremely high porosity, large pore size, low torsion, and poor mechanical strength, such as bare nonwoven spunbond separators, are prone to dendrite growth. Conversely, according to this invention, the multilayer microporous battery separator has an ideal balance of pore size, pore size distribution, porosity, torsion, and mechanical strength, which can suppress dendrite growth. The pores in the microporous separator provide an interconnected tortuous path network that restricts dendrite growth from the anode to the cathode. The higher the degree of winding of the porous network and the higher the separator torsion, the longer the cycle life of the Li-ion battery and the higher its safety.

[0091] To prevent cell failure, it is advantageous to have a microporous separator with high torsion between the electrodes. A separator with through-pores is defined as having a unit torsion. In battery separators that can suppress dendrite growth, a torsion value greater than 1, greater than 1.5, or even greater than 2 is required.

[0092] In this invention, in order to increase the total torsion of the diaphragm, such as Figure 2As shown, interfaces 12 and 23 are formed between layers 1, 2, and 3 of the multilayer separator. Interfaces are formed between adjacent polymer layers of the multilayer separator during lamination or co-extrusion. These interfaces formed at the bonding points between porous polymer layers have a microporous structure defined by their own pore size, porosity, thickness, and tortuosity. The number of different microporous polymer layers bonded together in the multilayer microporous separator determines the number of interfaces; multiple interfaces help improve the overall tortuosity of the battery separator and enhance its ability to inhibit dendrite growth.

[0093] In addition, the inclusion of an interlayer in the diaphragm to enhance tortuosity can prevent dendrite deposition and dendrite growth.

[0094] In one embodiment, the polypropylene (PP) and polyethylene (PE) multilayer laminated microporous membrane has an interlayer at the junction of the polypropylene and polyethylene layers, such as... Figure 2 As shown, the interface is formed during lamination and has a unique microstructure defined by its porosity, pore size and tortuosity, providing a region with an interconnected pore network of smaller pore size and higher tortuosity, thereby hindering, preventing or inhibiting lithium dendrite growth and lithium dendrite permeation through the multilayer membrane structure.

[0095] In another embodiment, the polypropylene and polyethylene multilayer separator manufactured by co-extrusion has a unique interlayer formed when the non-porous polypropylene and polyethylene layers of the separator leave the co-extrusion die. This interlayer is an epitaxial layer created at the interface between the polypropylene and polyethylene layers as the non-porous separator leaves the co-extrusion die. The formation of the epitaxial layer involves the growth of a lamellar crystalline structure as the multilayer non-porous separator (or separator precursor) leaves the die.

[0096] In other embodiments, the dry-manufactured monolayer microporous membrane has a microstructure suitable for preventing lithium dendrite growth.

[0097] In yet another embodiment, single-layer and multi-layer microporous membranes manufactured using a wet process have microstructures suitable for preventing lithium dendrite growth.

[0098] In another embodiment, the porous coating applied to the surface of the microporous battery separator has a microstructure of a twisted porous network that reduces or prevents dendrite growth. The porous coating can be one-sided or two-sided. The microporous battery separator coating is more conducive to reducing dendrite growth. Applying one or more coatings (such as polyvinylidene fluoride (PVdF) or PVDF-HFP copolymer) to one or both surfaces of the microporous membrane improves the adhesion between the membrane and the battery electrodes. The good adhesion between the coated separator and the electrodes improves the contact between them, resulting in smaller void spaces for lithium deposition and dendrite growth.

[0099] In another embodiment, the ceramic coating (such as a binder containing ceramic particles) applied to the surface of the microporous battery separator has a microstructure of a distorted porous network that can reduce or prevent dendrite growth. The porous coating can be unilateral or bilateral, which has a more beneficial effect on reducing dendrite growth.

[0100] Multilayer separators are used in materials such as Li-S, Li-LCO, Li-LMO, and SnLi. x SiLi x It performs well in many lithium metal-based rechargeable battery systems and non-rechargeable battery systems such as Li-MnO2 and Li-FeS2, and can be used in lithium / air battery systems.

[0101] Figure 2 Typical examples are shown. Two interfaces 12 and 23 exist in the PP / PE / PP three-layer separator. This type of separator has smaller PP pores in the outer layers 1 and 3 of the three-layer separator and larger PE pores in the inner layer 2 of the three-layer separator.

[0102] Regarding the manufacturing details of the diaphragm according to the present invention in the prior art, the following patent documents are incorporated herein by reference: US3,426,754; US3,588,764; US3,679,538; US3,801,404; US3,801,692; US3,843,761; US3,853,601; US4,138,459; US4,539,256; US4,726,989; US4,994,335; US6,057,060; and US6,132,654. Therefore, other details not mentioned in this invention are well known to those skilled in the art and need not be elaborated upon.

[0103] Typical test program

[0104] JISGurley value The Gurley value is defined as the Japanese Industrial Standard (JIS) Gurley value and is measured using an OHKEN permeability tester. JIS defines it as the time (in seconds) required for 100 cc of air to pass through a 1 square inch membrane under a constant pressure of 4.9 inches of water column.

[0105] thickness Thickness is measured in micrometers (μm) according to ASTM D374 using an Emveco Microgage 210-A precision micrometer.

[0106] PorosityPorosity is expressed as a percentage and is measured using ASTM D-2873 and defined as the percentage of void space in a microporous membrane.

[0107] Tension properties The machining direction (MD) and transverse direction (TD) tensile strength were measured using an Instron 4201 according to ASTM-882 procedure.

[0108] thermal shutdown Thermal shutdown is determined by measuring the resistance of the diaphragm while the temperature is increased linearly. See also Figure 18 The shut-off temperature is defined as the temperature at which the resistance (ER) increases a thousandfold. This thousandfold increase in resistance causes the battery separator to prevent heat dissipation within the battery. The increased resistance is due to the membrane melting, causing the pore structure to collapse.

[0109] Shrinkage Shrinkage was measured for 60 minutes at 90°C, 105°C, and 120°C using a modified ASTM D-2732-96 procedure.

[0110] Puncture strength Puncture strength is measured using an Instron 4442 model based on ASTM D3763. The unit of puncture strength is grams. It is measured across the width of the stretched product, and the average breakdown energy (puncture strength) is defined as the force required to break down the test specimen.

[0111] Pore ​​size Pore ​​size was measured using Aquapore data obtained from PMI (Porous Materials Inc.) and is expressed in micrometers (μm).

[0112] Interlaminar adhesion (measured by peel strength) can be lower than that of standard methods, preventing individual laminates from splitting (i.e., tearing) when peeled. The resistance to splitting is proportional to the thickness of the laminate. Therefore, if the laminates are stuck together (due to adhesion) and the adhesion is greater than the tear strength, the laminates cannot be separated (peeled) without splitting. For example, the adhesion of a laminate about 1 mil thick may be less than about 15 g / in, while for a 0.5 mil laminate, the adhesion may be less than about 8 g / in, and for a 0.33 mil laminate, it may be less than about 5 g / in. To reduce adhesion values, the annealing / stretching temperature of this method can be lower than that of standard methods. US61 / 609,586 and US61 / 680,550 are incorporated herein by reference in their entirety.

[0113] According to this invention, virtually all rechargeable lithium-ion batteries using carbon-based or lithium metal anode materials experience lithium dendrite growth, especially those using independent non-woven separators. During charging of a rechargeable lithium-ion battery with a carbon-based or lithium metal anode, lithium ions from the cathode are transported to the anode via the electrolyte medium through a microporous separator. During discharge, the opposite occurs, with ions from the anode moving to the cathode. Through continuous charge and discharge cycles, fine fibers or filaments of lithium metal (called lithium dendrites) form and grow on the anode surface. These dendrites accumulate from the anode surface and grow into the separator, establishing electron pathways that can lead to short circuits and battery malfunctions. Dendrite growth can cause thermal runaway, thereby compromising the safety of the lithium-ion battery and reducing the cycle life of the rechargeable lithium-ion battery.

[0114] Lithium dendrites growing from the anode surface and / or from the solid electrolyte interface (SEI) surface can cause battery performance and safety issues if they grow to and penetrate the separator, completely penetrating it to reach the other side. If lithium dendrites grow to form dendrite bridges connecting the positive and negative electrodes, the battery will short-circuit and fail to operate normally.

Claims

1. A battery separator with a PE interlayer structure, comprising two PP outer layers and one PE inner layer, characterized in that, A transparent, denser PE interlayer structure or a denser interface for the PE inner layer is provided between the outer PP layer and the inner PE layer. At least one PP outer layer is a transparent PP outer layer, and the thickness of the PP outer layer is less than that of the PE inner layer; The minimum thickness of the battery separator is reduced to 2 μm, while the maximum thickness is reduced to 12 μm.

2. The battery separator as described in claim 1, characterized in that, At least one side of the PP layer is further provided with a ceramic coating, a PVDF coating, or a PVDF:HFP coating, and the maximum thickness of the coated battery separator is 25μm, 16μm, or 14μm.

3. The battery separator as described in claim 1, characterized in that, At the interface between PP and PE, there is an epitaxial region or epitaxial layer for growing a sheet-like crystal structure.

4. The battery separator as described in claim 1, characterized in that, The outer PP layer of each of the aforementioned layers is 1 μm to 4 μm thick, and the inner PE layer of each layer is 1 μm to 4 μm thick. Each of the PP outer layers is 1μm to 3μm thick and the PE inner layer is 1μm to 3μm thick; Each of the PP outer layers is 1μm to 4μm thick and the PE inner layer is 1μm to 2μm thick; The outer PP layer of each of the above is 1 μm to 2 μm thick and the inner PE layer is 1 μm to 6 μm thick; The outer PP layer of each of the above is 1 μm to 2 μm thick and the inner PE layer is 1 μm to 5 μm thick; The outer PP layer of each PP layer is 1 μm to 2 μm thick and the inner PE layer is 1 μm to 4 μm thick; Each of the aforementioned PP outer layers is 1μm to 2μm thick and the aforementioned PE inner layer is 1μm to 3μm thick; or Each of the PP outer layers is 1 μm to 2 μm thick and at least one of the PE inner layers is 1 μm to 2 μm thick.

5. The battery separator as described in claim 1, characterized in that, The minimum thickness of the PE inner layer is 6μm, 5μm, 4μm, 3μm, 2μm, 1.5μm or 1μm.

6. The battery separator as described in claim 1, characterized in that, The maximum thickness of the battery separator is 12μm, 11μm, 10μm, 9μm, 8μm, 7μm, 6μm, 5μm, 4μm, 3μm or 2μm.

7. A battery separator with a PE interlayer structure, comprising two PP outer layers and one PE inner layer, characterized in that, An intermittent PE porous interlayer structure is provided between the PP outer layer and the PE inner layer; At least one PP outer layer is a transparent PP outer layer, and the thickness of the PP outer layer is less than that of the PE inner layer; The minimum thickness of the battery separator is reduced to 2 μm, and the maximum thickness is reduced to 12 μm.

8. A manufacturing apparatus for a battery separator having a PE interlayer structure, characterized in that, The manufacturing equipment includes: Two PP outer layer preparation lines, which go through extrusion and stretching to form a microporous PP outer layer; A PE inner layer preparation line, which runs parallel to the PP outer layer preparation line, undergoes extrusion and stretching to form a microporous PE inner layer; A transparent, dense PE interlayer structure fabrication line, with parallel PP outer layer fabrication lines, undergoes extrusion, stretching, and relaxation to form a microporous, transparent, dense PE interlayer structure, which is then combined with the PE inner layer to form a PE inner layer composite structure; and The laminator is located downstream of the PP outer layer preparation line, the PE inner layer preparation line, and the transparent dense PE interlayer structure preparation line. It laminates the PP outer layer, the PE inner layer, and the transparent dense PE interlayer structure together to form a battery separator with a transparent dense PE interlayer structure.

9. The manufacturing equipment as described in claim 8, characterized in that, The transparent, dense PE interlayer structure forms a denser interface within the PE inner layer.

10. The manufacturing equipment as described in claim 8, characterized in that, The transparent densified PE interlayer structure preparation line includes an upstream roller pair and a downstream roller pair. The rotation speed of the downstream roller pair decreases or increases relative to the upstream roller pair, causing the porosity of the PE interlayer structure to increase or decrease, forming an intermittent porous interlayer structure of PE.

11. A battery separator having a PE interlayer structure, characterized in that, The battery separator is obtained directly from the manufacturing equipment as described in claim 8.

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