A separator for semi-solid or solid-state batteries, its preparation method and applications

Abstract

The present invention relates to the field of battery separators, and discloses a separator for semi-solid or solid-state batteries, a preparation method thereof, and an application. The separator includes an upper surface layer, a middle layer, and a lower surface layer which are sequentially arranged from top to bottom; the raw materials of the middle layer include: high-density polyethylene with a weight-average molecular weight of 2×10 5 ~3×10 5 Da and a polydispersity coefficient of 12-20, and white oil with a flash point not higher than 80°C; the raw materials of the upper surface layer and the lower surface layer both include: high-density polyethylene with a weight-average molecular weight of 6×10 5 ~1×10 6 Da, and white oil with an initial boiling point higher than the separator forming temperature. The separator of the present invention has a larger pore size and a higher porosity, and can effectively accommodate more electrolytes when used in solid-state or semi-solid batteries.

Description

Technical Field

[0001] The present invention relates to the field of battery separators, and particularly to a separator for semi-solid or solid-state batteries, a preparation method thereof, and an application thereof. Background Art

[0002] Currently, the batteries widely used in the new energy industry are liquid lithium-ion batteries. Although liquid lithium batteries have high conductivity, they also have problems such as low energy density, electrolyte leakage, flammability and explosiveness, and the situation that lithium dendrites are likely to pierce the separator during charge and discharge, resulting in battery short circuit. Compared with liquid batteries, semi-solid or solid-state batteries use semi-solid or solid electrolytes, and only use less or no electrolyte, and have advantages such as high safety, wide electrochemical window and high energy density. Therefore, developing semi-solid or solid electrolytes is an important direction for promoting the development of new energy.

[0003] As an important component in the battery in addition to the positive electrode, negative electrode, and electrolyte, the battery separator plays a crucial role in the battery. The battery separator material is an insulating film containing a large number of microporous structures, and the main component is an insulating olefin polymer material. The separator has two main functions: one is to isolate the positive and negative electrodes of the battery to prevent direct contact and short circuit between the two poles, and at the same time, it needs to be as thin as possible under the premise of ensuring safety to reduce the distance between the two poles and lower the battery internal resistance; the other is to be able to store and retain sufficient electrolyte, and the microporous structure allows Li + to pass freely, realizing the rapid transmission of Li + between the positive and negative electrodes. Therefore, the performance of the battery separator such as heat resistance, wettability to the electrolyte, and adhesiveness to the electrode can directly affect the key performance of the lithium battery such as capacity, cycle performance, and charge and discharge current density.

[0004] With the development of semi-solid or solid-state batteries, new requirements are also put forward for the separator, such as high porosity and large pore size, which are beneficial to filling more electrolytes. When traditional separators are applied to semi-solid or solid-state batteries, due to their low porosity and small pore size, they cannot effectively accommodate more electrolytes. Summary of the Invention

[0005] In order to solve the above technical problems, that is, when the existing separator is used in semi-solid or solid-state batteries, the porosity is low and the pore size is small, resulting in the inability to effectively accommodate more electrolytes, the present invention provides a separator for semi-solid or solid-state batteries, a preparation method thereof, and an application thereof. The separator of the present invention has a larger pore size and a higher porosity, and can effectively accommodate more electrolytes when used in solid or semi-solid batteries.

[0006] The specific technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a separator for a semi-solid or solid-state battery, comprising an upper surface layer, an intermediate layer, and a lower surface layer sequentially arranged from top to bottom; the raw materials of the intermediate layer include: high-density polyethylene with a weight-average molecular weight of 2×10 5 ~3×10 5 Da and a polydispersity index of 12 - 20, and white oil with a flash point not higher than 80°C; the raw materials of the upper surface layer and the lower surface layer both include: high-density polyethylene with a weight-average molecular weight of 6×10 5 ~1×10 6 Da, and white oil with an initial boiling point higher than the separator forming temperature.

[0008] The present invention designs the separator into a three-layer structure and uses differentiated high-density polyethylene and white oil in the surface layers (upper surface layer and lower surface layer) and the intermediate layer. With the cooperation of these raw materials, the separator can have a larger pore size and a higher porosity, so that when the separator is used in a solid-state or semi-solid-state battery, it can effectively accommodate more electrolytes. Specifically, the cooperation effects between the raw materials in the three layers are as follows:

[0009] (1) White oil in the intermediate layer:

[0010] The white oil used in the intermediate layer has a lower flash point (not higher than 80°C) and is easy to volatilize. Therefore, during the process of making pores with white oil, there is no need to use an extraction method to remove the white oil, and pores can be formed by volatilization. Since the pore-forming method is a dynamic volatilization type rather than a static extraction type, a larger porosity and pore size can be obtained during the volatilization process.

[0011] (2) High-density polyethylene in the intermediate layer:

[0012] The high-density polyethylene used in the intermediate layer has a relatively large polydispersity index (12 - 20), that is, a wide molecular weight distribution range, and a relatively low weight-average molecular weight (M w =2×10 5 ~3×10 5 Da). This enables the intermediate layer to adopt a lower extrusion and processing temperature, which can reduce the volatilization loss of the white oil in the intermediate layer during the preparation and forming process of the separator, so that more white oil can volatilize during the drying process after the separator is formed, and thus play a better pore-forming role. At the same time, the relatively large polydispersity index and relatively low weight-average molecular weight of the high-density polyethylene in the intermediate layer can also make the intermediate layer easily expand in thickness as the white oil volatilizes, further increasing the porosity and pore size of the separator.

[0013] (3) White oil in the upper and lower surface layers:

[0014] The initial distillation point of the white oil used in the surface layer is higher than the molding temperature of the diaphragm (the molding of the three-layer diaphragm usually includes the process of three-layer co-extrusion, casting and stretching). It is not easy to volatilize during the preparation and molding of the diaphragm, and can slow down the volatilization of the white oil in the middle layer, thereby reducing the premature volatilization loss of the white oil in the middle layer; and, during the drying process after the diaphragm is formed, the white oil in the surface layer is driven to leave the diaphragm together with the volatilization of the white oil in the middle layer. Due to the lower volatilization rate of the white oil on the surface layer, the volatilization process of the white oil in the middle layer can be made more controllable. In this way, the diaphragm can form a larger pore size as a whole and have a higher porosity.

[0015] (4) High-density polyethylene in the upper and lower surface layers:

[0016] The high-density polyethylene used in the surface layer has a high weight average molecular weight (M w =6×10 5 ~1×10 6 Da), during the process of the white oil in the middle layer volatilizing and forming pores, the surface layer can support and restrict the middle layer, so that the thickness of the middle layer is more consistent after expansion.

[0017] Preferably, the raw materials of the intermediate layer include, by weight: 5 ~3×10 5 20 to 45 parts of high-density polyethylene with a Da and a polydispersity index of 12 to 20, 50 to 70 parts of white oil with a flash point not higher than 80°C, and 1 to 10 parts of an ion-conducting polymer.

[0018] Furthermore, the raw materials of the intermediate layer include, by weight: 5 ~3×10 5 20 to 45 parts of high-density polyethylene with a Da and a polydispersity index of 12 to 20, 50 to 70 parts of white oil with a flash point not higher than 80°C, and 5 to 10 parts of ion-conducting polymer.

[0019] In the middle layer, the ion-conducting polymer acts as a carrier for ion movement and has a high dielectric constant, which can reduce the dielectric impedance inside the battery and increase the transmission efficiency of lithium ions. Adding the ion-conducting polymer matrix to the separator can form a network that penetrates the inside of the separator and improve the ionic conductivity of the separator.

[0020] Preferably, the raw materials of the upper surface layer and the lower surface layer include, by weight: 5 ~1×10 6 30-50 parts of high-density polyethylene of Da, 50-70 parts of white oil with an initial boiling point higher than the diaphragm molding temperature.

[0021] Preferably, the melt index of the high-density polyethylene in the middle layer at 190 °C is 7-10 g / 10 min, and the melting point is not higher than 135 °C; the viscosity of the white oil in the middle layer at 40 °C is 1-5 mm 2 / s.

[0022] Preferably, the flash point of the white oil in the middle layer is 50-80 °C.

[0023] Preferably, the polydispersity coefficient of the high-density polyethylene in the upper surface layer and the lower surface layer is < 3, the melt index at 190 °C is 0.1-2 g / 10 min, and the melting point is not lower than 130 °C; the initial boiling point of the white oil in the upper surface layer and the lower surface layer is not lower than 220 °C, and the viscosity at 40 °C is 40-80 mm 2 / s.

[0024] Furthermore, the initial boiling point of the white oil in the upper surface layer and the lower surface layer is 220-280 °C.

[0025] Preferably, the ion-conducting polymer includes one or more of polyethylene oxide, polyacrylonitrile, polyvinyl alcohol, and polymethyl methacrylate.

[0026] Preferably, the thickness of the separator is 12-40 μm, and the thickness of the middle layer accounts for 40%-80% of the total thickness of the separator.

[0027] In a second aspect, the present invention provides a method for preparing the separator, the steps including: mixing the raw materials of the upper surface layer, the middle layer, and the lower surface layer respectively, then performing three-layer co-extrusion, casting, stretching, and then drying to volatilize the white oil.

[0028] Preferably, during the three-layer co-extrusion process, the extrusion temperature is 160-200 °C, and the die head temperature is 180-220 °C; the temperature of the casting is 50-80 °C; the drying temperature is 110-140 °C, and the time is 1-5 min; the stretching process includes: longitudinally stretching at 80-120 °C and transversely stretching at 100-130 °C.

[0029] In a third aspect, the present invention provides the application of the separator in a battery, and the battery is a solid-state battery or a semi-solid-state battery.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] The present invention designs the separator into a three-layer structure, and differential high-density polyethylene and white oil are adopted in the surface layer and the intermediate layer. Low-flash-point white oil and high-density polyethylene with a relatively large polydispersity coefficient and a relatively small molecular weight are used in the intermediate layer, and high-initial-boiling-point white oil and high-molecular-weight high-density polyethylene are used in the surface layer. This enables the separator to have larger pore sizes and higher porosities, so that when it is used in solid or semi-solid batteries, it can effectively accommodate more electrolytes. Detailed Embodiments

[0032] The present invention will be further described below in conjunction with embodiments.

[0033] A separator for a semi-solid or solid battery includes an upper surface layer, an intermediate layer, and a lower surface layer arranged in sequence from top to bottom; the raw materials of the intermediate layer include: high-density polyethylene with a weight-average molecular weight of 2×10 5 ~3×10 5 Da and a polydispersity coefficient of 12 to 20, and white oil with a flash point not higher than 80°C; the raw materials of the upper surface layer and the lower surface layer both include: high-density polyethylene with a weight-average molecular weight of 6×10 5 ~1×10 6 Da, and white oil with an initial boiling point higher than the separator forming temperature.

[0034] In some specific embodiments, the raw materials of the intermediate layer, by weight, include: 20 to 45 parts of high-density polyethylene with a weight-average molecular weight of 2×10 5 ~3×10 5 Da and a polydispersity coefficient of 12 to 20, 50 to 70 parts of white oil with a flash point not higher than 80°C, and 1 to 10 parts of an ion-conducting polymer. Optionally or preferably, the ion-conducting polymer includes one or more of polyethylene oxide, polyacrylonitrile, polyvinyl alcohol, and polymethyl methacrylate; the weight parts of the ion-conducting polymer are 5 to 10 parts.

[0035] In some specific embodiments, the raw materials of the upper surface layer and the lower surface layer, by weight, both include: 30 to 50 parts of high-density polyethylene with a weight-average molecular weight of 6×10 5 ~1×10 6 Da, and 50 to 70 parts of white oil with an initial boiling point higher than the separator forming temperature.

[0036] In some specific embodiments, the melt index of the high-density polyethylene in the intermediate layer at 190°C is 7 to 10 g / 10 min, and the melting point is not higher than 135°C; the viscosity of the white oil in the intermediate layer at 40°C is 1 to 5 mm 2 / s.

[0037] In some specific embodiments, the flash point of the white oil in the intermediate layer is 50 to 80°C.

[0038] In some specific embodiments, the polydispersity index of the high-density polyethylene in the upper surface layer and the lower surface layer is < 3, the melt index at 190 °C is 0.1 - 2 g / 10 min, and the melting point is not lower than 130 °C; the initial boiling point of the white oil in the upper surface layer and the lower surface layer is not lower than 220 °C, and the viscosity at 40 °C is 40 - 80 mm 2 / s. Optionally or preferably, the initial boiling point of the white oil in the upper surface layer and the lower surface layer is 220 - 280 °C.

[0039] In some specific embodiments, the thickness of the separator is 12 - 40 μm, and the thickness of the intermediate layer accounts for 40% - 80% of the total thickness of the separator.

[0040] A method for preparing the separator, the steps including: mixing the raw materials of the upper surface layer, the intermediate layer and the lower surface layer respectively, performing three-layer co-extrusion, stretching after casting, and then drying to volatilize the white oil.

[0041] In some specific embodiments, during the three-layer co-extrusion process, the extrusion temperature is 160 - 200 °C, and the die head temperature is 180 - 220 °C; the temperature of the cast film is 50 - 80 °C; the drying temperature is 110 - 140 °C, and the time is 1 - 5 min; the stretching process includes: performing longitudinal stretching at 80 - 120 °C and transverse stretching at 100 - 130 °C.

[0042] The application of the separator in a battery, where the battery is a solid-state battery or a semi-solid-state battery.

[0043] The present invention will be described below through specific examples. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. Without departing from the spirit and scope of the inventive concept, the changes and advantages that can be conceived by those skilled in the art are included in the present invention, and the scope of protection of the present invention is the appended claims and any equivalents thereof.

[0044] Example 1

[0045] This example prepares a separator for a semi-solid or solid-state battery according to the following steps:

[0046] S1: Preparation of surface layer materials

[0047] Weigh the following surface layer raw materials by weight: 30 parts of high-density polyethylene (M w =6×10 5 Da, the polydispersity index is 2, the melt index at 190 °C is 1 g / 10 min, and the melting point is 135 °C), 70 parts of white oil (the initial boiling point is 260 °C, and the viscosity at 40 °C is 60 mm 2 / s). After mixing all the surface layer raw materials in the mixing bin, they are put into the first twin-screw extruder.

[0048] S2: Intermediate layer preparation

[0049] Weigh the following intermediate layer raw materials by weight: 25 parts of high-density polyethylene (M w = 2.5×10 5 Da, polydispersity coefficient is 16, melt index at 190 °C is 8 g / 10 min, melting point is 130 °C), 70 parts of white oil (flash point is 60 °C, viscosity at 40 °C is 2 mm 2 / s), 5 parts of polyethylene oxide. After mixing all the intermediate layer raw materials in the mixing bin, they are put into the second twin-screw extruder.

[0050] S3: Diaphragm forming

[0051] Set the temperatures of the first and second twin-screw extruders to 180 °C. After melting and blending the raw materials therein, filter them. Use the material extruded from the first twin-screw extruder as the upper surface layer and the lower surface layer, and use the material extruded from the second twin-screw extruder as the intermediate layer. After in-mold compounding through a three-layer co-extrusion die head, extrude it, and set the die head temperature to 200 °C.

[0052] The melt extruded through the three-layer co-extrusion die head is cooled at a temperature of 70 °C to obtain a three-layer composite thick sheet at a traction speed of 30 m / min. Then, first longitudinally stretch the thick sheet at a temperature of 100 °C with a stretching ratio of 9.0, and then transversely stretch it at a temperature of 120 °C with a stretching ratio of 9.0 to obtain a stretched sheet.

[0053] S4: Drying and pore formation

[0054] Dry the stretched sheet at 130 °C for 5 min. After traction and thickness measurement, wind it up to obtain the diaphragm for semi-solid or solid-state batteries in this example. The thickness of the diaphragm in this example is 20 μm, where the thicknesses of the upper and lower surface layers are both 4 μm, and the thickness of the intermediate layer is 12 μm.

[0055] Example 2

[0056] This example prepares a diaphragm for semi-solid or solid-state batteries according to the following steps:

[0057] S1: Surface layer preparation

[0058] Weigh the following surface layer raw materials by weight: 50 parts of high-density polyethylene (M w = 6×10 5 Da, polydispersity coefficient is 2, melt index at 190 °C is 1 g / 10 min, melting point is 135 °C), 50 parts of white oil (initial boiling point is 260 °C, viscosity at 40 °C is 60 mm2 / s). After mixing all the surface layer raw materials in the mixing bin, they are put into the first twin-screw extruder.

[0059] S2: Intermediate layer preparation

[0060] Weigh the following intermediate layer raw materials by weight: 25 parts of high-density polyethylene (M w = 2.5×10 5 Da, the polydispersity coefficient is 16, the melt index at 190 °C is 8 g / 10 min, and the melting point is 130 °C), 70 parts of white oil (the flash point is 60 °C, and the viscosity at 40 °C is 2 mm 2 / s), 5 parts of polyethylene oxide. After mixing all the intermediate layer raw materials in the mixing bin, they are put into the second twin-screw extruder.

[0061] S3: Diaphragm forming

[0062] Set the temperatures of the first and second twin-screw extruders to 180 °C. After melting and blending the raw materials inside, filter them. Use the material extruded from the first twin-screw extruder as the upper surface layer and the lower surface layer, and use the material extruded from the second twin-screw extruder as the intermediate layer. After compounding in the three-layer coextrusion die head, extrude it, and set the die head temperature to 200 °C.

[0063] The melt extruded from the three-layer coextrusion die head is cooled at a temperature of 80 °C to obtain a three-layer composite thick sheet at a traction speed of 30 m / min. Then, first longitudinally stretch the thick sheet at a temperature of 100 °C with a stretching ratio of 9.0, and then transversely stretch it at a temperature of 120 °C with a stretching ratio of 9.0 to obtain a stretched sheet.

[0064] S4: Drying and pore formation

[0065] Dry the stretched sheet at 140 °C for 4 min. After traction and thickness measurement, wind it up to obtain the diaphragm for semi-solid or solid-state batteries in this embodiment. The thickness of the diaphragm in this embodiment is 20 μm, where the thicknesses of the upper and lower surface layers are both 4 μm, and the thickness of the intermediate layer is 12 μm.

[0066] Example 3

[0067] This embodiment prepares a diaphragm for semi-solid or solid-state batteries according to the following steps:

[0068] S1: Surface layer preparation

[0069] Weigh the following surface layer raw materials by weight: 30 parts of high-density polyethylene (M w = 6×10 5Da, the polydispersity index is 2, the melt index at 190 °C is 1 g / 10 min, and the melting point is 135 °C), 70 parts of white oil (the initial boiling point is 260 °C, and the viscosity at 40 °C is 60 mm 2 / s). After mixing all the surface layer raw materials in the mixing bin, they are put into the first twin-screw extruder.

[0070] S2: Intermediate layer preparation

[0071] Weigh the following intermediate layer raw materials by weight: 40 parts of high-density polyethylene (M w = 2.5×10 5 Da, the polydispersity index is 16, the melt index at 190 °C is 8 g / 10 min, and the melting point is 130 °C), 55 parts of white oil (the flash point is 60 °C, and the viscosity at 40 °C is 2 mm 2 / s), 5 parts of polyacrylonitrile. After mixing all the intermediate layer raw materials in the mixing bin, they are put into the second twin-screw extruder.

[0072] S3: Diaphragm forming

[0073] Set the temperatures of the first and second twin-screw extruders to 200 °C. After melting and blending the raw materials therein, filter them. Use the materials extruded from the first twin-screw extruder as the upper surface layer and the lower surface layer, and use the materials extruded from the second twin-screw extruder as the intermediate layer. After in-mold compounding through a three-layer co-extrusion die head, extrude, and set the die head temperature to 210 °C.

[0074] The melt extruded through the three-layer co-extrusion die head is cooled at a temperature of 70 °C to obtain a three-layer composite thick sheet at a drawing speed of 30 m / min. Then, the thick sheet is first longitudinally drawn at a temperature of 110 °C with a draw ratio of 9.0, and then transversely drawn at a temperature of 125 °C with a draw ratio of 9.0 to obtain a drawn sheet.

[0075] S4: Drying and pore formation

[0076] Dry the drawn sheet at 140 °C for 3 min. After traction and thickness measurement, wind it up to obtain the diaphragm for semi-solid or solid-state batteries in this example. The thickness of the diaphragm in this example is 20 μm, where the thicknesses of the upper and lower surface layers are both 4 μm, and the thickness of the intermediate layer is 12 μm.

[0077] Example 4

[0078] This example prepares a diaphragm for semi-solid or solid-state batteries according to the following steps:

[0079] S1: Surface layer preparation

[0080] Weigh the following surface layer raw materials by weight: 30 parts of high-density polyethylene (M w = 6×105 Da, the polydispersity index is 2, the melt index at 190 °C is 1 g / 10 min, and the melting point is 135 °C), 70 parts of white oil (the initial boiling point is 260 °C, and the viscosity at 40 °C is 60 mm 2 / s). After mixing all the surface layer raw materials in the mixing bin, they are put into the first twin-screw extruder.

[0081] S2: Intermediate layer preparation

[0082] Weigh the following intermediate layer raw materials by weight: 40 parts of high-density polyethylene (M w = 2.5×10 5 Da, the polydispersity index is 16, the melt index at 190 °C is 8 g / 10 min, and the melting point is 130 °C), 50 parts of white oil (the flash point is 60 °C, and the viscosity at 40 °C is 2 mm 2 / s), 10 parts of polyethylene oxide. After mixing all the intermediate layer raw materials in the mixing bin, they are put into the second twin-screw extruder.

[0083] S3: Diaphragm forming

[0084] Set the temperatures of the first and second twin-screw extruders to 200 °C. After melting and blending the raw materials therein, filter them. Use the material extruded from the first twin-screw extruder as the upper surface layer and the lower surface layer, and use the material extruded from the second twin-screw extruder as the intermediate layer. After in-mold compounding through a three-layer coextrusion die head, it is extruded, and the die head temperature is set to 210 °C.

[0085] The melt extruded through the three-layer coextrusion die head is cooled at a temperature of 70 °C to obtain a three-layer composite thick sheet at a traction speed of 30 m / min. Then, the thick sheet is first longitudinally stretched at a temperature of 110 °C with a stretching ratio of 9.0, and then transversely stretched at a temperature of 130 °C with a stretching ratio of 9.0 to obtain a stretched sheet.

[0086] S4: Drying and pore formation

[0087] Dry the stretched sheet at 120 °C for 5 min. After traction and thickness measurement, wind it up to obtain the diaphragm for semi-solid or solid-state batteries in this example. The thickness of the diaphragm in this example is 20 μm, where the thicknesses of the upper and lower surface layers are both 4 μm, and the thickness of the intermediate layer is 12 μm.

[0088] Example 5

[0089] This example prepares a diaphragm for semi-solid or solid-state batteries according to the following steps:

[0090] S1: Surface layer preparation

[0091] Weigh the following surface layer raw materials by weight: 30 parts of high-density polyethylene (Mw = 6×10 5 Da, the polydispersity index is 2, the melt index at 190 °C is 1 g / 10 min, and the melting point is 135 °C), 70 parts of white oil (the initial boiling point is 260 °C, and the viscosity at 40 °C is 60 mm 2 / s). After mixing all the surface layer raw materials in the mixing bin, they are put into the first twin-screw extruder.

[0092] S2: Intermediate layer preparation

[0093] Weigh the following intermediate layer raw materials by weight: 30 parts of high-density polyethylene (M w = 2.5×10 5 Da, the polydispersity index is 16, the melt index at 190 °C is 8 g / 10 min, and the melting point is 130 °C), 70 parts of white oil (the flash point is 60 °C, and the viscosity at 40 °C is 2 mm 2 / s). After mixing all the intermediate layer raw materials in the mixing bin, they are put into the second twin-screw extruder.

[0094] S3: Diaphragm forming

[0095] Set the temperatures of the first and second twin-screw extruders to 180 °C. After melting and blending the raw materials inside, filter them. Use the material extruded from the first twin-screw extruder as the upper surface layer and the lower surface layer, and use the material extruded from the second twin-screw extruder as the intermediate layer. After in-mold compounding through a three-layer co-extrusion die head, extrude it, and set the die head temperature to 200 °C.

[0096] The melt extruded through the three-layer co-extrusion die head is cooled at a temperature of 70 °C to obtain a three-layer composite thick sheet at a traction speed of 30 m / min. Then, first longitudinally stretch the thick sheet at a temperature of 100 °C with a stretching ratio of 9.0, and then transversely stretch it at a temperature of 120 °C with a stretching ratio of 9.0 to obtain a stretched sheet.

[0097] S4: Drying and pore formation

[0098] Dry the stretched sheet at 130 °C for 5 min. After traction and thickness measurement, wind it up to obtain the diaphragm for semi-solid or solid-state batteries in this example. The thickness of the diaphragm in this example is 20 μm, where the thicknesses of the upper and lower surface layers are both 4 μm, and the thickness of the intermediate layer is 12 μm.

[0099] Comparative Example 1

[0100] The difference between this comparative example and Example 1 is only that: the diaphragm in this comparative example only adopts the surface layer formula. Specifically, the diaphragm in this comparative example is prepared according to the following steps:

[0101] S1: Preparation of materials

[0102] Weigh the following raw materials by weight parts: 30 parts of high-density polyethylene (M w = 6×10 5 Da, with a polydispersity index of 2 and a melt index of 1 g / 10 min at 190 °C and a melting point of 135 °C), 70 parts of white oil (initial boiling point of 260 °C and a viscosity of 60 mm 2 / s at 40 °C). After mixing all the raw materials in the mixing bin, put them into the twin-screw extruder.

[0103] S2: Diaphragm forming

[0104] Set the temperature of the twin-screw extruder to 180 °C. After melting and blending the raw materials inside, filter them, and extrude them through the die head. The die head temperature is set to 200 °C.

[0105] The melt extruded through the die head is cooled at a temperature of 70 °C to obtain a thick sheet at a traction speed of 30 m / min. Then, the thick sheet is first longitudinally stretched at a temperature of 100 °C with a stretching ratio of 9.0, and then transversely stretched at a temperature of 120 °C with a stretching ratio of 9.0 to obtain a stretched sheet.

[0106] S3: Drying and pore formation

[0107] Dry the stretched sheet at 140 °C for 5 min. After traction and thickness measurement, wind it up to obtain the diaphragm for the semi-solid or solid-state battery of this comparative example. The thickness of the diaphragm in this comparative example is 20 μm.

[0108] Comparative Example 2

[0109] The difference between this comparative example and Example 1 is only that: the diaphragm in this comparative example only adopts the middle layer formula. Specifically, the diaphragm in this comparative example is prepared according to the following steps:

[0110] S1: Preparation of materials

[0111] Weigh the following raw materials by weight parts: 25 parts of high-density polyethylene (M w = 2.5×10 5 Da, with a polydispersity index of 16 and a melt index of 8 g / 10 min at 190 °C and a melting point of 130 °C), 70 parts of white oil (flash point of 60 °C and a viscosity of 2 mm 2 / s at 40 °C), 5 parts of polyethylene oxide. After mixing all the raw materials in the mixing bin, put them into the twin-screw extruder.

[0112] S2: Diaphragm forming

[0113] Set the temperature of the twin-screw extruder to 180 °C. After melting and blending the raw materials inside, filter them, and extrude them through the die head. The die head temperature is set to 200 °C.

[0114] The melt extruded through the die head is cooled at a temperature of 70 °C, and a thick sheet is obtained at a drawing speed of 30 m / min. Then, the thick sheet is first longitudinally drawn at a temperature of 100 °C with a draw ratio of 9.0, and then transversely drawn at a temperature of 120 °C with a draw ratio of 9.0 to obtain a drawn sheet.

[0115] S3: Drying for pore formation

[0116] The drawn sheet is dried at 130 °C for 4 min, and after being drawn and thickness measured, it is wound up to obtain the separator for semi-solid or solid-state battery of this comparative example. The thickness of the separator of this comparative example is 20 μm.

[0117] Comparative Example 3

[0118] The difference between this comparative example and Example 4 is only that: in this comparative example, in both the surface layer and the intermediate layer, the white oil in the surface layer of Example 4 is used, and the white oil is removed by extraction to achieve pore formation. Specifically, the separator is prepared according to the following steps:

[0119] S1: Preparation of surface layer materials

[0120] Weigh the following surface layer raw materials by weight: 30 parts of high-density polyethylene (M w = 6×10 5 Da, with a polydispersity coefficient of 2, a melt index of 1 g / 10 min at 190 °C, and a melting point of 135 °C), 70 parts of white oil (initial boiling point of 260 °C, viscosity at 40 °C of 60 mm 2 / s). After mixing all the surface layer raw materials in the mixing bin, they are put into the first twin-screw extruder.

[0121] S2: Preparation of intermediate layer materials

[0122] Weigh the following intermediate layer raw materials by weight: 40 parts of high-density polyethylene (M w = 2.5×10 5 Da, with a polydispersity coefficient of 16, a melt index of 8 g / 10 min at 190 °C, and a melting point of 130 °C), 50 parts of white oil (initial boiling point of 260 °C, viscosity at 40 °C of 60 mm 2 / s), 10 parts of polyethylene oxide. After mixing all the intermediate layer raw materials in the mixing bin, they are put into the second twin-screw extruder.

[0123] S3: Separator forming

[0124] Set the temperatures of the first and second twin-screw extruders to 200 °C. After melting and blending the raw materials therein, filter them. Use the materials extruded from the first twin-screw extruder as the upper and lower surfaces, and use the materials extruded from the second twin-screw extruder as the intermediate layer. After in-mold compounding through a three-layer coextrusion die head, extrude. Set the die head temperature to 210 °C.

[0125] The melt extruded through the three-layer coextrusion die head is cooled at a temperature of 70 °C to obtain a three-layer composite thick sheet at a traction speed of 30 m / min. Then, longitudinally stretch the thick sheet at a temperature of 110 °C with a stretching ratio of 9.0, and then transversely stretch it at a temperature of 130 °C with a stretching ratio of 9.0 to obtain a stretched sheet.

[0126] S4: Extraction for pore formation

[0127] Use dichloromethane as the extractant to extract the white oil in the stretched sheet. After traction and thickness measurement, wind it up to obtain the separator for semi-solid or solid-state batteries of this comparative example. The thickness of the separator in this comparative example is 20 μm, where the thicknesses of the upper and lower surfaces are both 4 μm, and the thickness of the intermediate layer is 12 μm.

[0128] Comparative Example 4

[0129] The difference between this comparative example and Example 4 is only that: in this comparative example, the white oil in the intermediate layer of Example 4 is used in both the surface layer and the intermediate layer. Specifically, the separator is prepared according to the following steps:

[0130] S1: Preparation of surface layer materials

[0131] Weigh the following surface layer raw materials by weight: 30 parts of high-density polyethylene (M w = 6×10 5 Da, polydispersity coefficient is 2, melt index at 190 °C is 1 g / 10 min, melting point is 135 °C), 70 parts of white oil (flash point is 60 °C, viscosity at 40 °C is 2 mm 2 / s). After mixing all the surface layer raw materials in the mixing bin, put them into the first twin-screw extruder.

[0132] S2: Preparation of intermediate layer materials

[0133] Weigh the following intermediate layer raw materials by weight: 40 parts of high-density polyethylene (M w = 2.5×10 5 Da, polydispersity coefficient is 16, melt index at 190 °C is 8 g / 10 min, melting point is 130 °C), 50 parts of white oil (flash point is 60 °C, viscosity at 40 °C is 2 mm 2 / s), 10 parts of ion-conducting polymer. After mixing all the intermediate layer raw materials in the mixing bin, put them into the second twin-screw extruder.

[0134] S3: Diaphragm forming

[0135] Set the temperatures of the first and second twin-screw extruders to 200 °C. After melting and blending the raw materials therein, filter them. Use the materials extruded from the first twin-screw extruder as the upper surface layer and the lower surface layer, and use the materials extruded from the second twin-screw extruder as the intermediate layer. After co-extrusion through a three-layer co-extrusion die head and in-die compounding, extrude, and set the die head temperature to 210 °C.

[0136] The melt extruded through the three-layer co-extrusion die head is cooled at a temperature of 70 °C to obtain a three-layer composite thick sheet at a draw speed of 30 m / min. Then, longitudinally stretch the thick sheet at a temperature of 110 °C with a draw ratio of 9.0, and then transversely stretch it at a temperature of 130 °C with a draw ratio of 9.0 to obtain a stretched sheet.

[0137] S4: Drying and pore formation

[0138] Dry the stretched sheet at 120 °C for 5 min. After traction and thickness measurement, wind it up to obtain the diaphragm for semi-solid or solid-state batteries in this comparative example. The thickness of the diaphragm in this comparative example is 20 μm, where the thicknesses of the upper and lower surface layers are both 4 μm, and the thickness of the intermediate layer is 12 μm.

[0139] Comparative Example 5

[0140] The difference between this comparative example and Example 4 is only that: in this comparative example, high-density polyethylene in the surface layer of Example 4 is used in both the surface layer and the intermediate layer. Specifically, the diaphragm is prepared in this comparative example according to the following steps:

[0141] S1: Preparation of surface layer materials

[0142] Weigh the following surface layer raw materials by weight: 30 parts of high-density polyethylene (M w = 6×10 5 Da, polydispersity index is 2, melt index at 190 °C is 1 g / 10 min, melting point is 135 °C), 70 parts of white oil (initial boiling point is 260 °C, viscosity at 40 °C is 60 mm 2 / s). After mixing all the surface layer raw materials in the mixing bin, put them into the first twin-screw extruder.

[0143] S2: Preparation of intermediate layer materials

[0144] Weigh the following intermediate layer raw materials by weight: 40 parts of high-density polyethylene (M w = 6×10 5 Da, polydispersity index is 2, melt index at 190 °C is 1 g / 10 min, melting point is 135 °C), 50 parts of white oil (flash point is 60 °C, viscosity at 40 °C is 2 mm2 ( / s), 10 parts of ion-conducting polymer. After mixing all the raw materials for the intermediate layer in the mixing bin, they are fed into the second twin-screw extruder.

[0145] S3: Diaphragm forming

[0146] Set the temperatures of the first and second twin-screw extruders to 200 °C. After melting and blending the raw materials therein, filter them. Use the materials extruded from the first twin-screw extruder as the upper and lower surfaces, and use the materials extruded from the second twin-screw extruder as the intermediate layer. After co-extrusion through a three-layer co-extrusion die head and in-die compounding, extrude. Set the die head temperature to 210 °C.

[0147] The melt extruded through the three-layer co-extrusion die head is cooled at a temperature of 70 °C to obtain a three-layer composite thick sheet at a traction speed of 30 m / min. Then, longitudinally stretch the thick sheet at a temperature of 110 °C with a stretching ratio of 9.0, and then transversely stretch it at a temperature of 130 °C with a stretching ratio of 9.0 to obtain a stretched sheet.

[0148] S4: Drying and pore formation

[0149] Dry the stretched sheet at 120 °C for 5 min. After traction and thickness measurement, wind it up to obtain the diaphragm for the semi-solid or solid-state battery of this comparative example. The thickness of the diaphragm of this comparative example is 17 μm, where the thicknesses of the upper and lower surfaces are both 4 μm, and the thickness of the intermediate layer is 9 μm.

[0150] Test example

[0151] Take the diaphragms prepared according to the methods in each example and comparative example, cut them into A4 size, and conduct performance tests. The test items and methods are as follows:

[0152] (1) Porosity:

[0153] Use an electronic balance to test the average density of the sample, and calculate the porosity of the sample according to the theoretical density. Test 3 samples and calculate their average value.

[0154] (2) Pore size:

[0155] Use a pore size analyzer to test the pore size of the sample. Test 3 samples and calculate their average value.

[0156] (3) Closing temperature:

[0157] Use a hot stage microscope to test the closing temperature of the sample, record the temperature when the diaphragm starts to melt. Test 5 samples and calculate their average value.

[0158] (4) Film-breaking temperature:

[0159] The hot stage microscope was used to test the film-breaking temperature of the samples, and the temperature at which the separator began to melt was recorded. Five samples were tested and their average value was calculated.

[0160] (5)Air permeability:

[0161] An air permeability tester was used to test the air permeability of the five-layer co-extruded microporous membrane. Five samples were tested and their average value was calculated.

[0162] (6)Liquid absorption rate:

[0163] The liquid absorption rate of the coated separator was tested by the weighing method. First, the mass was recorded after the separator was completely dried, and then the completely dried separator was immersed in the electrolyte for 24 h. After wiping the electrolyte on the surface, the weight of the separator was recorded again. The difference between the two recordings was the liquid absorption rate of the separator. Five samples were tested and their average value was calculated.

[0164] The test results of the separator performance are shown in Table 1.

[0165] Table 1 Test results of separator performance

[0166]

[0167] It can be seen from the test results of each example and comparative example shown in Table 1 that:

[0168] (1)Compared with Comparative Example 1 and Comparative Example 2, Example 1 has higher porosity, pore size and liquid absorption rate. It shows that by designing the separator into a three-layer structure and using different high-density polyethylene and white oil in the surface layer and the middle layer, the separator can have a larger pore size and porosity, and this characteristic enables the separator to accommodate more electrolytes when used in solid or semi-solid batteries.

[0169] (2)Compared with Comparative Example 3, Example 4 has higher porosity, pore size and liquid absorption rate. The reason is that the white oil used in the surface layer and the middle layer of Comparative Example 3 is difficult to volatilize and needs to be removed by extraction; Example 4 uses white oil that is easy to volatilize in the middle layer, and uses the volatilization of the white oil in the middle layer to drive the white oil in the surface layer away from the separator. Compared with the static extraction method, the dynamic volatilization method can obtain larger porosity and pore size.

[0170] (3) Compared with Comparative Example 4, Example 4 has a higher porosity, pore size, and liquid absorption rate. The reason is as follows: In Comparative Example 4, white oil that is easy to volatilize is used in both the surface layer and the intermediate layer. During the diaphragm forming process, a large amount of white oil will be volatilized and lost in advance, resulting in less white oil that can play a pore-forming role during the subsequent drying process after forming, and the volatilization rate of white oil during the drying process is too fast; in Example 4, white oil with a higher initial boiling point is used in the surface layer, which is not easy to volatilize during the diaphragm preparation and forming process. Therefore, it can slow down the volatilization of white oil in the intermediate layer, reduce the premature volatilization loss of white oil in the intermediate layer, and moreover, during the drying process after the diaphragm is formed, the white oil in the surface layer is driven to leave the diaphragm together during the volatilization of the white oil in the intermediate layer. Due to the lower volatilization rate of the white oil in the surface layer, the volatilization process of the white oil in the intermediate layer can be made more controllable.

[0171] (4) Compared with Comparative Example 5, Example 4 has a higher porosity, pore size, and liquid absorption rate. The reason is as follows: In Comparative Example 5, high-density polyethylene with a relatively large molecular weight and a narrow distribution range is used in both the surface layer and the intermediate layer, and the intermediate layer is not prone to thickness expansion as the white oil in it volatilizes; in Example 4, high-density polyethylene with a relatively small molecular weight and a wide distribution range is used in the intermediate layer. During the drying and pore-forming process, as the white oil volatilizes, the intermediate layer is prone to thickness expansion, further increasing the porosity and pore size of the diaphragm.

[0172] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the art to which the present disclosure belongs. The raw materials and equipment used in the present invention are conventional raw materials and equipment in the art and can be obtained from conventional commercial channels without special instructions; the methods used in the present invention are conventional methods in the art without special instructions.

[0173] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent transformations made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A semi-solid or solid battery separator, characterized in that: It includes an upper surface layer, an intermediate layer and a lower surface layer arranged in sequence from top to bottom; the raw materials of the intermediate layer include: a weight average molecular weight of 2×10 5 ~3×10 5 High-density polyethylene with a Da and a polydispersity index of 12 to 20, a flash point of 50 to 80°C and a viscosity of 1 to 5 mm at 40°C 2 / s white oil; the raw materials of the upper surface layer and the lower surface layer include: a weight average molecular weight of 6×10 5 ~1×10 6 Da high-density polyethylene, the initial boiling point is higher than the diaphragm molding temperature, the initial boiling point is not less than 220℃ and the viscosity is 40~80mm at 40℃ 2 / s of white oil.

2. The diaphragm according to claim 1, characterized in that The raw materials of the intermediate layer include, by weight: 5 ~3×10 5 20 to 45 parts of high-density polyethylene with a Da and a polydispersity index of 12 to 20, 50 to 70 parts of white oil with a flash point not higher than 80°C, and 1 to 10 parts of an ion-conducting polymer.

3. The diaphragm according to claim 1, characterized in that The raw materials of the upper surface layer and the lower surface layer are calculated by weight: 5 ~1×10 6 30-50 parts of high-density polyethylene of Da, 50-70 parts of white oil with an initial boiling point higher than the diaphragm molding temperature.

4. The diaphragm according to claim 1 or 2, characterized in that: The high-density polyethylene in the middle layer has a melt index of 7-10 g / 10 min at 190° C. and a melting point of no higher than 135° C.

5. The diaphragm according to claim 1 or 3, characterized in that: The polydispersity coefficient of the high-density polyethylene in the upper surface layer and the lower surface layer is less than 3, the melt index at 190° C. is 0.1-2 g / 10 min, and the melting point is not less than 130° C.

6. The diaphragm according to claim 2, characterized in that The ion-conducting polymer includes one or more of polyethylene oxide, polyacrylonitrile, polyvinyl alcohol and polymethyl methacrylate.

7. The diaphragm according to claim 1, characterized in that The thickness of the diaphragm is 12-40 μm, and the thickness of the middle layer accounts for 40%-80% of the total thickness of the diaphragm.

8. A method for preparing a diaphragm according to any one of claims 1 to 7, characterized in that the steps include: The raw materials of the upper surface layer, the middle layer and the lower surface layer are mixed separately, and then three layers are co-extruded, cast into sheets and stretched, and then dried to volatilize the white oil.

9. The preparation method according to claim 8, characterized in that: During the three-layer co-extrusion process, the extrusion temperature is 160-200°C, the die temperature is 180-220°C; the temperature of the cast sheet is 50-80°C; the drying temperature is 110-140°C, and the time is 1-5 minutes; the stretching process includes: longitudinal stretching at 80-120°C and transverse stretching at 100-130°C.

10. Use of the separator according to any one of claims 1 to 7 in a battery, characterized in that: The battery is a solid-state battery or a semi-solid-state battery.

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