Diaphragm and preparation method thereof, energy storage device and electric equipment

Abstract

The invention provides a diaphragm and a preparation method thereof, an energy storage device and electric equipment. The diaphragm is applied to an energy storage device. The diaphragm is provided with a first part and a second part which are arranged in the width direction of the diaphragm, the first part has first porosity, the second part has second porosity smaller than the first porosity, and the first part is used for being closer to a tab of the energy storage device than the second part. The part with the first porosity is closer to the tab of the energy storage device, so that the liquid absorption speed and the liquid retention capacity of the diaphragm close to one end of the tab are improved, and the nonuniformity of ion concentration reduction at the upper part of the energy storage device is relieved; moreover, the electrolyte is timely supplemented for a pole piece dry area at the upper part of the energy storage device, so that the part with the second porosity is far away from a tab of the energy storage device, ion transmission of a diaphragm corresponding to the lower part of the energy storage device is slowed down, the overall dynamics of the upper part and the lower part of a battery cell of the energy storage device is balanced, and the problem of insufficient electrolyte at the upper part of the energy storage device after long-term operation is slowed down.

Description

Technical Field

[0001] This application belongs to the technical field of energy storage devices, and particularly relates to a separator and its preparation method, an energy storage device, and an electrical equipment. Background Art

[0002] After the energy storage device operates for a long time, the phenomenon of blocked ion transport in the upper part of the battery cell will occur inside the energy storage device, resulting in an increasing difference in ion transport speed between the upper and lower parts of the battery cell, causing inconsistent overall dynamics of the battery cell, and affecting the electrical performance of the energy storage device after long-term operation. Summary of the Invention

[0003] In view of this, in the first aspect of this application, a separator is provided, which is applied to an energy storage device. The separator has a first part and a second part arranged along its width direction. The first part has a first porosity, and the second part has a second porosity smaller than the first porosity. The first part is used to be closer to the tab of the energy storage device than the second part.

[0004] For the separator provided in the first aspect of this application, the part with the first porosity and the part with the second porosity are arranged along the width direction of the separator. This application makes the part with the first porosity closer to the tab of the energy storage device, which not only improves the liquid absorption speed and liquid retention capacity of the separator at the tab end, alleviates the unevenness of the decrease in ion concentration in the upper part of the energy storage device, but also timely replenishes the electrolyte for the dry area of the electrode plate in the upper part of the energy storage device, ensures that the active substances on the electrode plate can be re-wetted by the electrolyte and effectively participate in the charge and discharge reactions of the energy storage device, ensures smooth ion transport channels and sufficient electrochemical reaction active sites, reduces the internal resistance of the energy storage device and improves the cycle performance of the energy storage device. It also makes the part with the second porosity away from the tab of the energy storage device, which can slow down the ion transport of the separator corresponding to the lower part of the energy storage device, balance the overall dynamics of the upper and lower parts of the battery cell of the energy storage device, slow down the problem of insufficient electrolyte in the upper part of the energy storage device after long-term operation, and thus improve the electrical performance of the energy storage device.

[0005] Among them, the first porosity is 45% < P1 ≤ 70%, and the second porosity is 35% ≤ P2 < 40%.

[0006] Among them, the separator further includes a first transition part, which is connected between the first part and the second part, and the porosity of the first transition part gradually decreases along the direction from the first part to the second part.

[0007] Among them, the separator also has a third part located between the first part and the second part. The third part has a third porosity, the third porosity is smaller than the first porosity, and the third porosity is larger than the second porosity.

[0008] Among them, the third porosity is 40% ≤ P3 ≤ 45%.

[0009] Among them, along the width direction of the separator, the width ratio of the first part, the third part, and the second part is (0.05 - 0.1):(0.8 - 0.9):(0.05 - 0.1).

[0010] The second aspect of the present application provides a method for preparing a separator, and the preparation method includes:

[0011] Mixing materials: providing a substrate and a pore-forming agent, mixing the substrate and the pore-forming agent to obtain a mixed material, the mixed material includes a first mixed material and a second mixed material, the mass ratio of the pore-forming agent to the substrate in the first mixed material is a first pore-forming ratio, the mass ratio of the pore-forming agent to the substrate in the second mixed material is a second pore-forming ratio, and the second pore-forming ratio is less than the first pore-forming ratio;

[0012] Melting and extrusion: melting and extruding the first mixed material and the second mixed material respectively to obtain a first extruded sheet prepared from the first mixed material and a second extruded sheet prepared from the second mixed material;

[0013] Connection: connecting the first extruded sheet to the second extruded sheet;

[0014] Pore formation: removing the pore-forming agent in the first extruded sheet and the second extruded sheet, so that the first extruded sheet has a first porosity and the second extruded sheet has a second porosity less than the first porosity, to obtain a separator applied to an energy storage device.

[0015] The method for preparing a separator provided by the second aspect of the present application. By preparing mixed materials with different pore-forming ratios, melting and extruding the mixed materials respectively to obtain a first extruded sheet and a second extruded sheet, then connecting the first extruded sheet to the second extruded sheet, and removing the pore-forming agent in the extruded sheets, a separator with different porosities is obtained. It can also be understood that the separator has a part with a higher first porosity and a part with a lower second porosity.

[0016] When the separator is applied to an energy storage device, the part with the first porosity and the part with the second porosity are arranged along the width direction of the separator. The part of the separator with the first porosity is closer to the tab of the energy storage device, which not only improves the liquid absorption speed and liquid retention capacity of the separator at the end near the tab, alleviates the unevenness of the reduction of ion concentration in the upper part of the energy storage device, but also timely replenishes the electrolyte for the dry area of the electrode plate in the upper part of the energy storage device, ensures that the active substances on the electrode plate can be re-wetted by the electrolyte and effectively participate in the charge and discharge reactions of the energy storage device, ensures smooth ion transport channels and sufficient electrochemically reactive sites, reduces the internal resistance of the energy storage device and improves the cycle performance of the energy storage device. The part of the separator with the second porosity is far from the tab of the energy storage device to slow down the ion transport of the separator corresponding to the lower part of the energy storage device, balance the overall dynamics of the upper and lower parts of the battery core of the energy storage device, slow down the problem of insufficient electrolyte in the upper part of the energy storage device after long-term operation, and thus improve the electrical performance of the energy storage device.

[0017] Among them, in the steps of the melt extrusion and the connection, it includes:

[0018] Extrusion: Provide a first extrusion port for extruding the first mixture and a second extrusion port for extruding the second mixture. The first extrusion port and the second extrusion port are arranged adjacent to each other, and the extrusion direction of the first mixture is the same as the extrusion direction of the second mixture;

[0019] Melt connection: Make the first extrusion port extrude a first extruded sheet in a molten state; and make the second extrusion port extrude a second extruded sheet in a molten state; and connect the molten first extruded sheet to the molten second extruded sheet.

[0020] Among them, in the step of the melt connection:, it includes:

[0021] A first transition part is formed by mixing at the connection of the first extruded sheet and the second extruded sheet, and the first transition part is connected between the first extruded sheet and the second extruded sheet;

[0022] In the step of pore formation, it further includes:

[0023] Remove the pore-forming agent in the first transition part so that the porosity of the first transition part gradually decreases along the direction from the first extruded sheet to the second extruded sheet to obtain the separator.

[0024] Among them, in the step of mixing materials, it further includes:

[0025] The mixture further includes a third mixture. In the third mixture, the mass ratio of the pore-forming agent to the substrate is a third pore-forming ratio. The third pore-forming ratio is less than the first pore-forming ratio and greater than the second pore-forming ratio;

[0026] In the step of melt extrusion, it further includes:

[0027] Melting and extruding the third mixture to obtain a third extruded sheet prepared from the third mixture;

[0028] In the step of connection, it further includes:

[0029] Connecting the third extruded sheet between the first extruded sheet and the second extruded sheet;

[0030] In the step of pore formation, it further includes:

[0031] Removing the pore-forming agent in the third extruded sheet to make the third extruded sheet have a third porosity, where the third porosity is less than the first porosity and greater than the second porosity, to obtain the separator.

[0032] Wherein, the first pore-forming ratio is (80 - 85):(14 - 20), the third pore-forming ratio is (70 - 80):(20 - 30), and the second pore-forming ratio is (60 - 70):(30 - 40).

[0033] Wherein, the substrate includes at least one of ultra-high molecular weight polyethylene and high-density polyethylene. When the substrate includes ultra-high molecular weight polyethylene and high-density polyethylene, the mass ratio of ultra-high molecular weight polyethylene to high-density polyethylene is (0.5 - 1.5):(0.5 - 1.5).

[0034] The third aspect of the present application provides an energy storage device, which includes a tab, an electrolyte, a positive electrode plate, a negative electrode plate, and a separator as provided in the first aspect of the present application. The first part of the separator is closer to the tab than the second part of the separator.

[0035] The energy storage device provided in the third aspect of the present application, by using the separator provided in the first aspect of the present application, the part with the first porosity and the part with the second porosity are arranged along the width direction of the separator. The part of the separator with the first porosity is closer to the tab of the energy storage device, which not only improves the liquid absorption speed and liquid retention capacity of the separator at the end close to the tab, alleviates the unevenness of the reduction of ion concentration in the upper part of the energy storage device, but also timely replenishes the electrolyte for the dry area of the electrode sheet in the upper part of the energy storage device, ensures that the active substances on the electrode sheet can be re-wetted by the electrolyte and effectively participate in the charge and discharge reactions of the energy storage device, ensures smooth ion transport channels and sufficient electrochemically reactive sites, reduces the internal resistance of the energy storage device and improves the cycle performance of the energy storage device. The part of the separator with the second porosity is far from the tab of the energy storage device to slow down the ion transport of the separator corresponding to the lower part of the energy storage device, balance the overall dynamics of the upper and lower parts of the battery core of the energy storage device, slow down the problem of insufficient electrolyte in the upper part of the energy storage device after long-term operation, and thus improve the electrical performance of the energy storage device.

[0036] The fourth aspect of the present application provides an electrical device, which includes:

[0037] The device body; and

[0038] The energy storage device provided in the third aspect of the present application, and the energy storage device supplies power to the device body.

[0039] The electrical device provided in the fourth aspect of the present application, by using the energy storage device provided in the third aspect of the present application, the part of the separator with the first porosity and the part with the second porosity are arranged along the width direction of the separator. The separator makes the part with the first porosity closer to the tab of the energy storage device, which not only improves the liquid absorption speed and liquid retention capacity of the separator at the end close to the tab, alleviates the unevenness of the reduction of ion concentration in the upper part of the energy storage device, but also timely replenishes the electrolyte for the dry area of the electrode sheet in the upper part of the energy storage device, ensures that the active substances on the electrode sheet can be re-wetted by the electrolyte and effectively participate in the charge and discharge reactions of the energy storage device, ensures smooth ion transport channels and sufficient electrochemically reactive sites, reduces the internal resistance of the energy storage device and improves the cycle performance of the energy storage device. The part of the separator with the second porosity is far from the tab of the energy storage device to slow down the ion transport of the separator corresponding to the lower part of the energy storage device, balance the overall dynamics of the upper and lower parts of the battery core of the energy storage device, slow down the problem of insufficient electrolyte in the upper part of the energy storage device after long-term operation, and thus improve the electrical performance of the energy storage device. When the energy storage device supplies power to the device body, the energy storage device can provide a stable power source for the device body. Description of the Drawings

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will describe the drawings required to be used in the embodiments of the present application.

[0041] Figure 1 The process flow of the preparation method of the separator in an embodiment of the present application Figure 1 .

[0042] Figure 2 The structural schematic diagram of the separator in an embodiment of the present application Figure 1 .

[0043] Figure 3 The process flow of the preparation method of the separator in an embodiment of the present application Figure 2 .

[0044] Figure 4 The structural schematic diagram of the extruder in an embodiment of the present application.

[0045] Figure 5 The process flow of the preparation method of the separator in an embodiment of the present application Figure 3 .

[0046] Figure 6 The structural schematic diagram of the separator in an embodiment of the present application Figure 2 .

[0047] Figure 7 The process flow of the preparation method of the separator in an embodiment of the present application Figure 4 .

[0048] Figure 8 The structural schematic diagram of the separator in an embodiment of the present application Figure 3 .

[0049] Figure 9 The structural schematic diagram of the separator in an embodiment of the present application Figure 4 .

[0050] Figure 10 The structural schematic diagram of the separator in an embodiment of the present application Figure 5 .

[0051] Figure 11 The structural schematic diagram of the energy storage device in an embodiment of the present application.

[0052] Label description: separator - 1, first part - 11, second part - 12, third part - 13, first transition part - 141, second transition part - 142, third transition part - 143, extruder - 2, first extrusion port - 21, second extrusion port - 22, third extrusion port - 23, energy storage device - 3, tab - 31. Specific embodiments

[0053] The following are the preferred embodiments of the present application. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present application, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present application.

[0054] In the description of the present invention, it should be understood that the weight of the relevant components mentioned in the embodiments of the present invention not only can refer to the specific content of each component, but also can represent the proportional relationship of the weights between the components. Therefore, as long as the content of the relevant components in the embodiments of the present invention is enlarged or reduced in proportion, it is within the scope disclosed in the present invention. Specifically, the weight described in the embodiments of the present invention can be mass units well-known in the chemical industry such as μg, mg, g, kg, etc.

[0055] In addition, unless the context clearly uses otherwise, the singular form of a word should be understood to include the plural form of that word. The terms "comprising" or "having" are intended to specify the presence of a feature, quantity, step, operation, element, part, or a combination thereof, but are not used to exclude the presence or possible addition of one or more other features, quantities, steps, operations, elements, parts, or a combination thereof.

[0056] The energy storage device is composed of an electrolyte, a positive electrode plate, a negative electrode plate, and a separator. The battery cell is wound with a layer of separator and a layer of electrode plate. For example, the positive electrode plate, the separator, the negative electrode plate, and the separator are sequentially stacked and wound to form a battery cell. Among them, the separator plays a role in separating the positive and negative electrodes, preventing the positive and negative electrodes inside the battery from contacting and short-circuiting, and at the same time playing a role in transmitting ions. In the energy storage device, it is required that the separator simultaneously has a low resistance and a high conductivity, has a high permeability to ions, and the size of the separator porosity is directly related to the internal resistance of the energy storage device. The smaller the porosity, the higher the internal resistance, and the energy storage device cannot achieve high-current discharge.

[0057] The inventor has found through research that in the actual application of the energy storage device, especially for high-capacity batteries, such as square batteries or cylindrical batteries, after long-term operation, the phenomenon of blocked ion transmission in the upper part of the battery cell will occur inside the energy storage device. On the one hand, under the dual action of electrolyte consumption and gravity, the electrolyte consumption at different positions of the battery cell is different, and the problem of insufficient upper-layer electrolyte will occur. On the other hand, when the energy storage device undergoes charge and discharge reactions, due to the higher temperature near the tab, the charge and discharge reactions are faster, the electrolyte consumption is accelerated, and it is easier to form a dry area on the electrode plate. The existence of the dry area on the electrode plate will lead to a reduction in the effective active substances that the positive electrode plate and the negative electrode plate can participate in the charge and discharge reactions, a reduction in the ion transmission path between the positive electrode plate and the negative electrode plate, and an increase in the internal resistance, affecting the cycle performance of the energy storage device. Therefore, a dry area is easily formed in the upper part of the positive / negative electrode plate, and it is necessary to replenish the electrolyte in time to re-infiltrate the dry area on the electrode plate.

[0058] Generally speaking, in the upper part of the battery cell near the tab, after long-term operation, due to the reduction of the electrolyte volume and the formation of the dry area of the electrode sheet, the ion transport is hindered; while in the lower part of the battery cell, the electrolyte is sufficient and there is no dry area of the electrode sheet, and the ion transport is faster, which will cause the overall dynamics of the battery cell to be inconsistent and affect the electrical performance of the battery cell after long-term operation.

[0059] It should be noted that when the electrolyte is sufficient, the ion transport level is mainly determined by the kinetics of the positive and negative electrodes; when the electrolyte is consumed more, that is, when the electrolyte is insufficient, the problem of inconsistent transport between the upper and lower layers of the battery cell will occur.

[0060] Please refer to Figure 1 and Figure 2 , Figure 1 is the process flow of the preparation method of the separator in an embodiment of the present application Figure 1 . Figure 2 is the structural schematic diagram of the separator in an embodiment of the present application Figure 1 .

[0061] This embodiment provides a method for preparing a separator, and the preparation method includes:

[0062] S100, mixing: providing a substrate and a pore-forming agent, mixing the substrate and the pore-forming agent to obtain a mixed material, the mixed material includes a first mixed material and a second mixed material, in the first mixed material, the mass ratio of the pore-forming agent to the substrate is a first pore-forming ratio, and in the second mixed material, the mass ratio of the pore-forming agent to the substrate is a second pore-forming ratio, and the second pore-forming ratio is less than the first pore-forming ratio.

[0063] This embodiment provides a substrate, and the substrate can be polyethylene. In one embodiment, the substrate includes at least one of ultra-high molecular weight polyethylene and high density polyethylene. When the substrate includes ultra-high molecular weight polyethylene and high density polyethylene, the mass ratio of ultra-high molecular weight polyethylene to high density polyethylene is (0.5-1.5):(0.5-1.5).

[0064] Optionally, the molecular weight of the ultra-high molecular weight polyethylene is in (3-5)×10 6 ; the molecular weight of the high density polyethylene is (3-5)×10 5 .

[0065] Optionally, the mass ratio of ultra-high molecular weight polyethylene to high density polyethylene can be 0.5:0.5, or 0.5:1, or 0.5:1.5, or 1:0.5, or 1:1.5, or 1.5:0.5, or 1.5:1, etc. Preferably, the mass ratio of ultra-high molecular weight polyethylene to high density polyethylene is 1:1.

[0066] When the substrate includes ultra-high molecular weight polyethylene and high-density polyethylene, the ultra-high molecular weight polyethylene can provide better ductility, strength, toughness and manufacturability for the separator, and the high-density polyethylene can provide high crystallinity, relatively high strength and heat resistance. Therefore, by mixing ultra-high molecular weight polyethylene and high-density polyethylene, the processing performance of the separator can be improved, thereby reducing the preparation difficulty and improving the preparation efficiency.

[0067] This embodiment provides a pore-forming agent, and the pore-forming agent can be white oil. Optionally, the first pore-forming ratio is (80-85):(14-20), and the second pore-forming ratio is less than (80-85):(14-20). Further optionally, the second pore-forming ratio is (60-70):(30-40).

[0068] When the first pore-forming ratio is (80-85):(14-20) and the second pore-forming ratio is (60-70):(30-40), it not only provides a basis for obtaining a separator with a preset high porosity and a preset low porosity, timely replenishes the electrolyte for the dry area of the electrode sheet at the upper part of the energy storage device, and realizes the overall dynamics balance of the upper and lower parts of the energy storage device's battery cell, but also is beneficial to the stable operation of the separator in the energy storage device. If the first pore-forming ratio is too small or the second pore-forming ratio is too large, it will cause the separator to be unable to timely replenish the electrolyte for the dry area of the electrode sheet at the upper part of the energy storage device and unable to balance the overall dynamics of the upper and lower parts of the energy storage device's battery cell during long-term operation. If the first pore-forming ratio is too large or the second pore-forming ratio is too small, it will result in too large a high porosity of the separator or too small a low porosity of the separator, which is not conducive to the long-term stability of the separator in the energy storage device.

[0069] The first pore-forming ratio is (80-85):(14-20). In other words, the mass ratio of the pore-forming agent to the substrate in the first mixture is (80-85):(14-20).

[0070] Optionally, the mass ratio of the pore-forming agent to the substrate in the first mixture can be 80:14, or 80:17, or 80:20, or 82:14, or 82:17, or 82:20, or 85:14, or 85:17, or 85:20, etc.

[0071] The second pore-forming ratio is (60-70):(30-40). In other words, the mass ratio of the pore-forming agent to the substrate in the second mixture is (60-70):(30-40).

[0072] Optionally, the mass ratio of the pore-forming agent to the substrate in the second mixture can be 60:30, or 60:35, or 60:40, or 65:30, or 65:35, or 65:40, or 70:30, or 70:35, or 70:40, etc.

[0073] Optionally, in the step S100 of providing the substrate and the pore-forming agent, it further includes: providing an antioxidant, and mixing the substrate, the pore-forming agent, and the antioxidant to obtain a mixture.

[0074] Further optionally, the antioxidant includes phenolic antioxidants, phosphite antioxidants, and hindered phenolic antioxidants.

[0075] Further optionally, the mass ratio of the antioxidant in the mixture is 0.2%-2%.

[0076] S200, melt extrusion: melting and extruding the first mixture and the second mixture respectively to obtain a first extruded sheet prepared from the first mixture and a second extruded sheet prepared from the second mixture.

[0077] The first mixture is extruded from the first extrusion port, and the second mixture is extruded from the second extrusion port. By melting the first mixture and the second mixture respectively and extruding them through different extrusion ports, diaphragms with different porosities can be obtained subsequently, avoiding the problem that the porosities of the diaphragms produced subsequently are single due to the complete mixing of the first mixture and the second mixture during extrusion. It can also be understood that the first mixture and the second mixture are extruded from different flow channels in the extruder.

[0078] Wherein, the states of the obtained first extruded sheet and second extruded sheet can be either in a molten state or in a cooled and shaped state, and this embodiment does not limit this. And, the width direction of the extruded sheet is the same as the direction perpendicular to the extrusion direction of the mixture.

[0079] S300, connection: connecting the first extruded sheet to the second extruded sheet.

[0080] For example, the first extruded sheet is directly connected to the second extruded sheet. Another example is that the first extruded sheet is indirectly connected to the second extruded sheet through other extruded sheets.

[0081] For example, by making the whole of the first extruded sheet and the whole of the second extruded sheet in a molten state, the first extruded sheet and the second extruded sheet can be connected.

[0082] Another example is that by making the edges of the first extruded sheet and the edges of the second extruded sheet in a molten state, the edges of the first extruded sheet and the edges of the second extruded sheet can be connected.

[0083] The first extruded sheet and the second extruded sheet are connected to form an extruded sheet to be processed, and the first extruded sheet and the second extruded sheet are arranged along the width direction of the extruded sheet to be processed.

[0084] S400, pore formation: removing the pore-forming agent in the first extruded sheet and the second extruded sheet, so that the first extruded sheet has a first porosity and the second extruded sheet has a second porosity less than the first porosity, to obtain a separator for an energy storage device.

[0085] As Figure 2 shown, the separator 1 has a first portion 11 and a second portion 12 arranged along its width direction (as shown by direction D in Figure 2 ). The first portion 11 is obtained from the first extruded sheet, and the second portion 12 is obtained from the second extruded sheet. It should be noted that the shape of the pores in the separator of the present application is not limited. The pores can be circular, near-circular, square, polygonal, etc. The pores in the accompanying drawings provided in the present application are only for illustrative purposes.

[0086] Optionally, the first porosity is 45% < P1 ≤ 70%, and the second porosity is 35% ≤ P2 < 40%. Further optionally, the first porosity can be 47%, or 50%, or 53%, or 57%, or 60%, or 63%, or 67%, or 70, etc. The second porosity can be 35%, or 36%, or 37%, or 38%, or 39%, etc.

[0087] The method for preparing the separator provided in this embodiment. By preparing mixtures with different pore-forming ratios, and melting and extruding the mixtures respectively to obtain the first extruded sheet and the second extruded sheet, and then connecting the first extruded sheet to the second extruded sheet and removing the pore-forming agent in the extruded sheet, a separator with different porosities is obtained. It can also be understood that the separator has a part with a higher first porosity and a part with a lower second porosity.

[0088] When the separator is applied to an energy storage device, the part with the first porosity and the part with the second porosity are arranged along the width direction of the separator. The part of the separator with the first porosity is closer to the tab of the energy storage device, which not only improves the liquid absorption speed and liquid retention capacity of the separator near the tab end, alleviates the unevenness of the reduction of the ion concentration in the upper part of the energy storage device; but also timely replenishes the electrolyte for the dry area of the electrode plate in the upper part of the energy storage device, ensures that the active substances on the electrode plate can be re-infiltrated by the electrolyte and effectively participate in the charge and discharge reactions of the energy storage device, ensures smooth ion transmission channels and has enough electrochemically reactive sites, and reduces the internal resistance of the energy storage device and improves the cycle performance of the energy storage device.

[0089] The part of the separator with the second porosity is away from the tab of the energy storage device to slow down the ion transmission of the separator corresponding to the lower part of the energy storage device, balance the overall dynamics of the upper and lower parts of the energy storage device cell, slow down the problem of insufficient electrolyte in the upper part of the energy storage device after long-term operation, and thus improve the electrical performance of the energy storage device.

[0090] Optionally, after the step of obtaining the to-be-processed extruded sheet formed by connecting the first extruded sheet and the second extruded sheet, the method further includes: longitudinally stretching the to-be-processed extruded sheet, and then performing a first transverse stretching. Then, the pore-forming agent in the first extruded sheet and the second extruded sheet is removed. Then, after performing a second transverse stretching on the to-be-processed extruded sheet, it is then subjected to heat setting treatment to obtain a separator.

[0091] Among them, the longitudinal stretching can longitudinally roll the sheet-shaped extrusion material through a rolling press to stretch its length. The first transverse stretching can be heat-set. The second transverse stretching can eliminate the internal stress of the separator, improve the heat shrinkage performance of the separator, and perform heat setting.

[0092] Please refer to Figure 3 and Figure 4 , Figure 3 which is the process flow of the method for preparing a separator in an embodiment of the present application Figure 2 . Figure 4 which is the structural schematic diagram of an extruder in an embodiment of the present application. In one embodiment, in the step of melt extrusion and connection, it includes:

[0093] S210, extrusion: providing a first extrusion port for extruding the first mixture and a second extrusion port for extruding the second mixture, the first extrusion port and the second extrusion port are arranged adjacent to each other, and the extrusion direction of the first mixture is the same as the extrusion direction of the second mixture.

[0094] As Figure 4 shown, the extruder 2 includes a first extrusion port 21 and a second extrusion port 22. For example, there is a gap between the first extrusion port 21 and the second extrusion port 22. For another example, the first extrusion port 21 and the second extrusion port 22 are in contact with each other. The extrusion direction of the first mixture is the same as the extrusion direction of the second mixture, which can also be understood as that the opening directions of the first extrusion port 21 and the second extrusion port 22 are the same.

[0095] In this embodiment, by arranging the first extrusion port and the second extrusion port adjacent to each other and making the extrusion directions of the first mixture and the second mixture the same, the first extruded sheet extruded from the first extrusion port can quickly contact the second extruded sheet extruded from the second extrusion port, providing a basis for the subsequent connection of the first extruded sheet and the second extruded sheet.

[0096] S220, melt connection: making the first extrusion port extrude a first extruded sheet in a molten state; and, making the second extrusion port extrude a second extruded sheet in a molten state; and, connecting the first extruded sheet in the molten state to the second extruded sheet in the molten state.

[0097] In this embodiment, the first extruded sheet just extruded from the first extrusion port is in a molten state, and the second extruded sheet just extruded from the second extrusion port is in a molten state. Therefore, the first extruded sheet can quickly come into contact with the second extruded sheet and be connected together.

[0098] In this embodiment, by adjusting the position of the extrusion port, the extrusion direction of the mixture, and the state of the extruded sheet, the first mixture and the second mixture are quickly connected together while being extruded into the extruded sheet, thereby simplifying the preparation steps and improving the preparation efficiency.

[0099] Please refer to Figure 5 and Figure 6 , Figure 5 which is the process flow of the preparation method of the separator in an embodiment of the present application Figure 3 . Figure 6 which is the structural schematic diagram of the separator in an embodiment of the present application Figure 2 . In one embodiment, in the step of melt connection, it includes:

[0100] S221, a first transition part is formed by mixing at the connection part of the first extruded sheet and the second extruded sheet, and the first transition part is connected between the first extruded sheet and the second extruded sheet.

[0101] Since the first extruded sheet and the second extruded sheet are both in a molten state when connected, by adjusting the state when the first extruded sheet and the second extruded sheet are connected, part of the first extruded sheet and part of the second extruded sheet can be mixed with each other at the connection part of the first extruded sheet and the second extruded sheet to form a first transition part.

[0102] In the step of pore formation, it further includes:

[0103] S222, removing the pore-forming agent in the first transition part so that the porosity of the first transition part gradually decreases along the direction from the first extruded sheet to the second extruded sheet to obtain the separator.

[0104] As Figure 6 shown, in the first transition part 141, the porosity of the part close to the first extruded sheet is greater than the porosity of the part close to the second extruded sheet. In other words, the porosity of the part close to the first extruded sheet is greater than the porosity of the part far from the first extruded sheet. That is, the porosity of the first transition part 141 is a gradually changing gradient porosity.

[0105] In this embodiment, by regulating the connection state between the first extruded sheet and the second extruded sheet, a part of the first extruded sheet and a part of the second extruded sheet are mixed with each other to form a first transition part, so that there is no cliff-like porosity difference between the first extruded sheet and the second extruded sheet, but a first transition part with a gradually changing porosity is used for transition, thereby improving the stability of the separator. When the separator is applied to an energy storage device, it is more conducive to timely supplementing the electrolyte to the dry area of the electrode plate at the upper part of the energy storage device and balancing the overall dynamics of the upper and lower parts of the energy storage device, improving the electrical performance of the energy storage device and also improving the stability of the energy storage device.

[0106] Please refer to Figures 7 - 9 , Figure 7 which is the process flow of the preparation method of the separator in an embodiment of the present application Figure 4 . Figure 8 which is the structural schematic diagram of the separator in an embodiment of the present application Figure 3 . Figure 9 which is the structural schematic diagram of the separator in an embodiment of the present application Figure 4 .

[0107] In one embodiment, in the step of mixing the materials, it further includes:

[0108] S130, the mixed material further includes a third mixed material, in which the mass ratio of the pore-forming agent to the substrate in the third mixed material is a third pore-forming ratio, the third pore-forming ratio is less than the first pore-forming ratio, and the third pore-forming ratio is greater than the second pore-forming ratio.

[0109] Optionally, the third pore-forming ratio is (70 - 80):(20 - 30). In other words, the mass ratio of the pore-forming agent to the substrate in the third mixed material is (70 - 80):(20 - 30).

[0110] Optionally, the mass ratio of the pore-forming agent to the substrate in the third mixed material can be 70:20, or 70:25, or 70:30, or 75:20, or 75:25, or 75:30, or 80:20, or 80:25, or 80:30, etc.

[0111] Further optionally, the first pore-forming ratio is (80 - 85):(14 - 20), the third pore-forming ratio is (70 - 80):(20 - 30), and the second pore-forming ratio is (60 - 70):(30 - 40).

[0112] When the ratio of the third pore formation is (70 - 80) : (20 - 30), it not only provides a basis for obtaining a separator with a preset medium porosity, but also provides a transition between the first mixture part and the second mixture part. On the one hand, the part with the preset medium porosity is used to maintain the stability of the energy storage device throughout the operating cycle, thereby improving the electrical performance of the energy storage device. On the other hand, it prevents a cliff-like porosity difference from forming between the high-porosity part prepared from the first mixture and the low-porosity part prepared from the second mixture, thus improving the stability of the separator.

[0113] Optionally, in the first mixture, the ultra-high molecular weight polyethylene is 7 - 10 parts by weight; the high-density polyethylene is 7 - 10 parts by weight; the antioxidant is 0.2 - 1 part by weight; the white oil is 80 - 85 parts by weight.

[0114] In the third mixture, the ultra-high molecular weight polyethylene is 10 - 15 parts by weight; the high-density polyethylene is 10 - 15 parts by weight; the antioxidant is 0.2 - 1 part by weight; the white oil is 70 - 80 parts by weight.

[0115] In the second mixture, the ultra-high molecular weight polyethylene is 15 - 20 parts by weight; the high-density polyethylene is 15 - 20 parts by weight; the antioxidant is 0.2 - 1 part by weight; the white oil is 60 - 70 parts by weight.

[0116] In the step of melt extrusion, it further includes:

[0117] S230, melting and extruding the third mixture to obtain a third extruded sheet prepared from the third mixture.

[0118] As Figure 4 shown, the extruder 2 further includes a third extrusion port 23. The third mixture is extruded from the third extrusion port 23. Optionally, the first extrusion port 21, the third extrusion port 23, and the second extrusion port 22 are arranged in sequence. The extrusion directions of the first mixture, the third mixture, and the second mixture are all the same.

[0119] In the step of connection, it further includes:

[0120] S330, connecting the third extruded sheet between the first extruded sheet and the second extruded sheet.

[0121] One side of the third extruded sheet is connected to the first extruded sheet, and the other side is connected to the second extruded sheet. The first extruded sheet, the third extruded sheet, and the second extruded sheet are connected in sequence to form an extruded sheet to be processed, and the first extruded sheet, the third extruded sheet, and the second extruded sheet are arranged along the width direction of the extruded sheet to be processed.

[0122] In the step of pore formation, it further includes:

[0123] S430, remove the pore-forming agent in the third extruded sheet so that the third extruded sheet has a third porosity, where the third porosity is less than the first porosity and greater than the second porosity, thereby obtaining the separator 1.

[0124] As Figure 8 shown, the separator 1 has a first part 11, a third part 13, and a second part 12 arranged along its width direction (as shown by the direction D in Figure 8 ). The first part 11 is obtained from the first extruded sheet, the third part 13 is obtained from the third extruded sheet, and the second part 12 is obtained from the second extruded sheet.

[0125] Optionally, the third porosity is 40% ≤ P3 ≤ 45%. Further optionally, the third porosity can be 40%, or 41%, or 42%, or 43%, or 44%, etc. It should be noted that a porosity of 40% - 45% is the most favorable for the separator to exert the electrical performance of the energy storage device in the energy storage device.

[0126] In this embodiment, a third extruded sheet is provided between the first extruded sheet and the second extruded sheet, and the third porosity of the third extruded sheet is between the first porosity and the second porosity. It can also be understood that the separator has a part with a relatively high first porosity, a part with a medium third porosity, and a part with a relatively low second porosity.

[0127] When the separator is applied to an energy storage device, the part with the first porosity, the part with the third porosity, and the part with the second porosity are arranged along the width direction of the separator. The part with the first porosity and the part with the second porosity are used to timely supplement the electrolyte for the pole piece dry area at the upper part of the energy storage device and to balance the overall dynamics of the upper and lower parts of the energy storage device's battery core, alleviating the problem of insufficient electrolyte at the upper part of the energy storage device after long-term operation. At the same time, the part with the third porosity is used to maintain the stability of the energy storage device throughout the operation cycle, thereby improving the electrical performance of the energy storage device.

[0128] Please refer to Figure 10 , Figure 10 which is a schematic structure of the separator in an embodiment of the present application. Figure 5 . Optionally, a second transition part 142 is formed by mixing at the connection between the first extruded sheet and the third extruded sheet, and the second transition part 142 is connected between the first extruded sheet and the third extruded sheet. A third transition part 143 is formed by mixing at the connection between the third extruded sheet and the second extruded sheet, and the third transition part 143 is connected between the third extruded sheet and the second extruded sheet.

[0129] Remove the pore former in the second transition portion 142 and the third transition portion 143, so that the porosity of the second transition portion 142 gradually decreases along the direction from the first extruded sheet to the third extruded sheet, and the porosity of the third transition portion 143 gradually decreases along the direction from the third extruded sheet to the second extruded sheet, to obtain the separator 1.

[0130] Optionally, in the process of obtaining the first extruded sheet, the second extruded sheet, and the third extruded sheet, the extrusion pressure of the extruder on the third mixture is greater than the extrusion pressure of the extruder on the first mixture, and the extrusion pressure of the extruder on the third mixture is greater than the extrusion pressure of the extruder on the second mixture.

[0131] By regulating the extrusion pressure of the extruder on each mixture, so that when the first mixture, the third mixture, and the second mixture are just extruded into extruded sheets, the third extruded sheet can be quickly connected to the first extruded sheet and the third extruded sheet can be quickly connected to the second extruded sheet, thereby simplifying the preparation steps and improving the preparation efficiency.

[0132] Please refer to Figure 2 The present application also provides a separator 1, which is applied to an energy storage device. The separator 1 has a first portion 11 and a second portion 12 arranged along its width direction. The first portion 11 has a first porosity, and the second portion 12 has a second porosity smaller than the first porosity. The first portion 11 is closer to the tab of the energy storage device than the second portion 12.

[0133] Optionally, the thickness of the separator 1 is 7 μm - 20 μm. Further optionally, the thickness of the separator 1 can be 7 μm, or 10 μm, or 13 μm, or 15 μm, or 18 μm, or 20 μm.

[0134] When the thickness of the separator 1 is 7 μm - 20 μm, the separator 1 can have high liquid retention ability, structural strength, and insulation performance, and can also enable the energy storage device to have high energy density. If the thickness of the separator 1 is less than 7 μm, the separator 1 is too thin, which will reduce the liquid retention ability, structural strength, and insulation performance of the separator 1. If the thickness of the separator 1 is greater than 20 μm, the separator 1 is too thick, the resistance of the energy storage device increases, and the energy density of the energy storage device decreases.

[0135] The separator 1 provided in this embodiment can be obtained by the preparation method of the separator 1 provided in the present application. The first portion 11 of the separator 1 is obtained from the first extruded sheet, and the second portion 12 is obtained from the second extruded sheet.

[0136] The separator 1 provided in this embodiment has a portion with a first porosity and a portion with a second porosity arranged along the width direction of the separator 1. The portion of the separator 1 with the first porosity is closer to the tab of the energy storage device, which not only improves the liquid absorption speed and liquid retention capacity of the separator 1 at the end near the tab, alleviates the non-uniformity of the reduction of the ion concentration in the upper part of the energy storage device, but also timely replenishes the electrolyte for the dry area of the electrode plate in the upper part of the energy storage device, ensures that the active substances on the electrode plate can be re-wetted by the electrolyte and effectively participate in the charge and discharge reactions of the energy storage device, ensures smooth ion transport channels and sufficient electrochemically reactive sites, reduces the internal resistance of the energy storage device and improves the cycle performance of the energy storage device. The portion of the separator 1 with the second porosity is far from the tab of the energy storage device to slow down the ion transport of the separator 1 corresponding to the lower part of the energy storage device, balance the overall dynamics of the upper and lower parts of the energy storage device cell, slow down the problem of insufficient electrolyte in the upper part of the energy storage device after long-term operation, and thus improve the electrical performance of the energy storage device.

[0137] In one embodiment, the first porosity is 45% < P1 ≤ 70%, and the second porosity is 35% ≤ P2 < 40%.

[0138] Optionally, the first porosity is 45% < P1 ≤ 70%, and the second porosity is 35% ≤ P2 < 40%. Further optionally, the first porosity can be 47%, or 50%, or 53%, or 57%, or 60%, or 63%, or 67%, or 70, etc. The second porosity can be 35%, or 36%, or 37%, or 38%, or 39%, etc.

[0139] When the first porosity is 45% < P1 ≤ 70% and the second porosity is 35% ≤ P2 < 40%, it can not only timely replenish the electrolyte for the dry area of the electrode plate in the upper part of the energy storage device, achieve the balance of the overall dynamics of the upper and lower parts of the energy storage device cell, but also is beneficial to the stable operation of the separator 1 in the energy storage device. If the first porosity is too small or the second porosity is too large, it will cause the separator 1 to be unable to timely replenish the electrolyte for the dry area of the electrode plate in the upper part of the energy storage device and unable to balance the overall dynamics of the upper and lower parts of the energy storage device cell during long-term operation. If the first porosity is too large or the second porosity is too small, it will cause the high porosity of the separator 1 to be too large or the low porosity of the separator 1 to be too small, which is not conducive to the stability of the separator 1 during long-term operation in the energy storage device.

[0140] Please refer to Figure 6 , in one embodiment, the separator 1 further includes a first transition portion 141, the first transition portion 141 is connected between the first portion 11 and the second portion 12, and the porosity of the first transition portion 141 gradually decreases along the direction from the first portion 11 to the second portion 12.

[0141] In the first transition portion 141, the porosity near the first portion 11 is greater than the porosity near the second portion 12. In other words, the porosity near the first portion 11 is greater than the porosity far from the first portion 11. That is, the porosity of the first transition portion 141 is a gradually changing gradient porosity.

[0142] This embodiment enables no cliff-like porosity difference to be formed between the first portion 11 and the second portion 12, but rather a first transition portion 141 with a gradient porosity is used for transition, thereby improving the stability of the separator 1. When the separator 1 is applied to an energy storage device, it not only timely supplements the electrolyte to the dry area of the electrode sheet at the upper part of the energy storage device, but also is more conducive to balancing the overall dynamics of the upper and lower parts of the battery cell of the energy storage device, improving the electrical performance of the energy storage device, and also improving the stability of the energy storage device.

[0143] Please refer to Figure 8 and Figure 9 , in one embodiment, the separator 1 further has a third portion 13 located between the first portion 11 and the second portion 12. The third portion 13 has a third porosity, the third porosity is less than the first porosity, and the third porosity is greater than the second porosity.

[0144] The separator 1 provided by this embodiment can be obtained by the preparation method of the separator 1 provided by this application. The first portion 11 of the separator 1 is obtained from a first extruded sheet, the third portion 13 is obtained from a third extruded sheet, and the second portion 12 is obtained from a second extruded sheet.

[0145] In one embodiment, the third porosity is 40% ≤ P3 ≤ 45%.

[0146] Optionally, the third porosity is 40% ≤ P3 ≤ 45%. Further optionally, the third porosity can be 40%, or 41%, or 42%, or 43%, or 44%, etc. It should be noted that a porosity of 40% - 45% is the most conducive to the electrical performance of the separator 1 in the energy storage device.

[0147] When the separator 1 is applied to an energy storage device, the first portion 11 with the first porosity, the third portion 13 with the third porosity, and the second portion 12 with the second porosity are arranged along the width direction of the separator 1. The first portion 11 and the second portion 12 are used to timely supplement the electrolyte to the dry area of the electrode sheet at the upper part of the energy storage device and to balance the overall dynamics of the upper and lower parts of the battery cell of the energy storage device, slowing down the problem of insufficient electrolyte at the upper part of the energy storage device after long-term operation. At the same time, the third portion 13 is used to maintain the stability of the energy storage device during the entire operation cycle, thereby improving the electrical performance of the energy storage device.

[0148] Optionally, please refer to Figure 10, the separator 1 further includes a second transition portion 142 and a third transition portion 143. The second transition portion 142 is connected between the first portion 11 and the third portion 13, and the porosity of the second transition portion 142 gradually decreases in the direction from the first portion 11 to the third portion 13. The third transition portion 143 is connected between the third portion 13 and the second portion 12, and the porosity of the third transition portion 143 gradually decreases in the direction from the third portion 13 to the second portion 12.

[0149] Please refer to Figures 8 - 9 , in an embodiment, along the width direction of the separator 1, the width ratios of the first portion 11, the third portion 13, and the second portion 12 are (0.05 - 0.1):(0.8 - 0.9):(0.05 - 0.1).

[0150] Optionally, the width ratios of the first portion 11, the third portion 13, and the second portion 12 can be 0.05:0.8:0.05, or 0.05:0.85:0.05, or 0.05:0.9:0.05, or 0.05:0.8:0.08, or 0.05:0.8:0.1, or 0.08:0.8:0.05, or 0.1:0.8:0.05, etc.

[0151] Since the first portion 11 with high porosity and the second portion 12 with low porosity are mainly for timely supplementing electrolyte to the dry area of the electrode sheet at the upper part of the energy storage device and achieving the balance of the overall dynamics of the upper and lower parts of the battery cell, in terms of the width ratio of the separator 1, the widths of both the first portion 11 and the second portion 12 are smaller than that of the third portion 13. While timely supplementing electrolyte to the dry area of the electrode sheet at the upper part of the energy storage device and balancing the overall dynamics of the upper and lower parts of the battery cell, it can also reduce the manufacturing cost. And the third portion 13 with medium porosity is mainly for maintaining the stability of the battery cell of the energy storage device during the entire operation cycle. Therefore, in terms of the width ratio of the separator 1, the width of the third portion 13 is the largest to facilitate improving the stability of the energy storage device during the entire operation cycle.

[0152] Please refer to Figure 11 , Figure 11 is a schematic structural diagram of an energy storage device in an embodiment of the present application. The present application also provides an energy storage device 3, which includes a tab 31, an electrolyte, a positive electrode sheet, a negative electrode sheet, and the separator 1 provided as above in the present application. The first portion 11 of the separator 1 is closer to the tab 31 than the second portion 12 of the separator 1.

[0153] The number of energy storage devices 3 can be several. The several energy storage devices 3 are connected in series or in parallel with each other. The several energy storage devices 3 are supported and electrically connected by a separator (not shown in the figure). In this embodiment, "several" means two or more. An energy storage box can also be provided outside the energy storage device 3 for housing the energy storage device 3.

[0154] It can be understood that the energy storage device 3 can include, but is not limited to, single cells, battery modules, battery packs, battery systems, etc. When the energy storage device 3 is a single cell, the energy storage device 3 can be at least one of a cylindrical battery, a square battery, etc. The actual application form of the energy storage device 3 provided in the embodiments of the present application can be, but is not limited to, the listed products, and can also be other application forms. The embodiments of the present application do not strictly limit the application form of the energy storage device 3.

[0155] For the energy storage device 3 provided in this embodiment, by adopting the separator 1 provided above in the present application, the part with the first porosity and the part with the second porosity are arranged along the width direction of the separator 1. The separator 1 makes the part with the first porosity closer to the tab 31 of the energy storage device 3, only improving the liquid absorption speed and liquid retention capacity of the separator 1 at the end close to the tab 31, alleviating the non-uniformity of the reduction of the ion concentration in the upper part of the energy storage device 3; and timely replenishing the electrolyte for the dry area of the electrode plate in the upper part of the energy storage device 3, ensuring that the active substances on the electrode plate can be re-wetted by the electrolyte and effectively participate in the charge and discharge reaction of the energy storage device 3, ensuring a smooth ion transmission channel and having enough electrochemical reaction active sites, reducing the internal resistance of the energy storage device 3 and improving the cycle performance of the energy storage device 3. The part of the separator with the second porosity is far from the tab 31 of the energy storage device 3 to slow down the ion transmission of the separator 1 corresponding to the lower part of the energy storage device 3, balance the overall dynamics of the upper and lower parts of the battery core of the energy storage device 3, and slow down the problem of insufficient electrolyte in the upper part of the energy storage device 3 after long-term operation, thereby improving the electrical performance of the energy storage device 3.

[0156] The present application also provides an electrical device, which includes a device body and an energy storage device as provided above in the present application, and the energy storage device supplies power to the device body.

[0157] Optionally, the electrical device in the embodiments of the present application can be, but is not limited to, portable electronic devices such as mobile phones, tablet computers, laptop computers, desktop computers, smart toys, smart bracelets, smart watches, e-readers, game consoles, toys, etc.; it can also be large devices such as energy storage battery cabinets, battery cars, electric vehicles, ships, spacecraft, etc.

[0158] It can be understood that the electrical device described in this embodiment is only one form of the electrical device to which the energy storage device is applied, and should not be construed as a limitation on the electrical device provided in the present application, nor should it be construed as a limitation on the energy storage device provided in each embodiment of the present application.

[0159] The electrical equipment provided by this embodiment, by adopting the energy storage device provided above in this application, has a part with a first porosity and a part with a second porosity arranged along the width direction of the separator. The part of the separator with the first porosity is closer to the tab of the energy storage device, which only improves the liquid absorption speed and liquid retention capacity of the separator at the end close to the tab, alleviates the non-uniformity of the reduction of the ion concentration in the upper part of the energy storage device; moreover, it timely replenishes the electrolyte for the dry area of the electrode plate in the upper part of the energy storage device, ensures that the active substances on the electrode plate can be re-wetted by the electrolyte and effectively participate in the charge and discharge reactions of the energy storage device, ensures a smooth ion transmission channel and has enough electrochemically reactive sites, reduces the internal resistance of the energy storage device and improves the cycle performance of the energy storage device. The part of the separator with the second porosity is far from the tab of the energy storage device to slow down the ion transmission of the separator corresponding to the lower part of the energy storage device, balance the overall dynamics of the upper and lower parts of the energy storage device's battery core, slow down the problem of insufficient electrolyte in the upper part of the energy storage device after long-term operation, and thus improve the electrical performance of the energy storage device. When the energy storage device supplies power to the device body, the energy storage device can provide a stable power source for the device body.

[0160] To enable those skilled in the art to clearly understand the above-mentioned implementation details and operations of the present invention, the following examples are used to illustrate the above technical solutions.

[0161] After mixing ultra-high molecular weight polyethylene, high-density polyethylene, antioxidant and white oil with different ratios, the first mixture, the second mixture, and the third mixture are respectively obtained. After the first mixture, the second mixture, and the third mixture are extruded through the multi-channel of an extruder to obtain a molten extrusion sheet, and then after longitudinal stretching, a longitudinally stretched film is obtained.

[0162] The longitudinally stretched film obtained in the above step is subjected to the first transverse stretching, then the white oil in the film is extracted and removed, and after the second transverse stretching, it is further subjected to heat setting treatment to obtain a separator.

[0163] Among them, white oil (molecular weight 500), ultra-high molecular weight polyethylene resin (weight average molecular weight of 3,000,000), high-density polyethylene resin (weight average molecular weight of 500,000), and antioxidant are mixed evenly in a ratio of 8.0:0.95:0.95:0.1 to obtain the first mixture.

[0164] White oil (molecular weight 500), ultra-high molecular weight polyethylene resin (weight average molecular weight of 3,000,000), high-density polyethylene resin (weight average molecular weight of 500,000), and antioxidant are mixed evenly in a ratio of 7.5:1.19:1.19:0.12 to obtain the third mixture.

[0165] Mix white oil (molecular weight 500), ultra-high molecular weight polyethylene resin (weight average molecular weight 3,000,000), high density polyethylene resin (weight average molecular weight 500,000), and antioxidant 1010 evenly at a ratio of 6.8:1.5:1.5:0.2 to obtain a second mixture.

[0166] Detect the porosity of the first part, the third part, and the second part of the prepared separator, and take three sampling points for each part for detection respectively. The porosity detection results of the separator are shown in Table 1.

[0167] Table 1 Porosity detection results of the separator

[0168]

[0169] After the battery cell operates for a long time, the phenomenon of blocked ion transport in the upper part of the energy storage device will occur. By making the upper part of the separator have a high porosity (45%-70%) to match the upper battery cell, it not only improves the liquid absorption speed and liquid retention capacity of the separator near the tab end, alleviates the unevenness of the reduction of the ion concentration in the upper part of the energy storage device; but also timely replenishes the electrolyte to the dry area of the electrode plate in the upper part of the energy storage device, ensuring that the active substances on the electrode plate can be re-wetted by the electrolyte and effectively participate in the charge and discharge reactions of the energy storage device. And, by making the middle part of the separator have a middle porosity (40%-45%), the stability of ion transport during the long-term operation of the battery cell is ensured. Moreover, the electrolyte in the lower layer of the battery cell is sufficient and the ion transport is smooth. To match the transport capacity of the middle and upper parts of the battery cell and achieve consistent overall transport capacity of the battery cell. The lower part of the separator has a low porosity (35%-40%).

[0170] In order to obtain a separator with a gradient porosity in the width direction in this application, at the raw material ratio stage, different pore-forming ratios are designed, and at the same time, the flow channel of the extruder is changed from one to multiple flow channels. The extruded sheets obtained by extruding different mixtures are connected respectively, so as to obtain a separator with a gradient porosity.

[0171] The above has introduced in detail the content provided by the embodiments of this application. The principles and embodiments of this application have been elaborated and explained in this article. The above description is only used to help understand the method and its core idea of this application; at the same time, for those of ordinary skill in the art, according to the idea of this application, there will be changes in the specific embodiments and application scopes. In summary, the content of this specification should not be construed as a limitation to this application.

Claims

1. A separator, characterized in that, Applied to an energy storage device, the separator has a first part and a second part arranged along its width direction. The first part has a first porosity, and the second part has a second porosity smaller than the first porosity. The first part is configured to be closer to the tab of the energy storage device than the second part.

2. The diaphragm according to claim 1, wherein, The first porosity is 45% < P1 ≤ 70%, and the second porosity is 35% ≤ P2 < 40%.

3. The diaphragm according to claim 1, wherein The separator further includes a first transition part, which is connected between the first part and the second part. The porosity of the first transition part gradually decreases in the direction from the first part to the second part.

4. The diaphragm according to claim 1, wherein The separator also has a third part located between the first part and the second part. The third part has a third porosity, which is smaller than the first porosity and larger than the second porosity.

5. The diaphragm according to claim 4, wherein, The third porosity is 40% ≤ P3 ≤ 45%.

6. The diaphragm according to claim 4, wherein In the width direction of the separator, the width ratio of the first part, the third part, and the second part is (0.05 - 0.1) : (0.8 - 0.9) : (0.05 - 0.1).

7. A method for preparing a separator, characterized in that, The preparation method includes: Mixing materials: providing a substrate and a pore-forming agent, and mixing the substrate and the pore-forming agent to obtain a mixed material. The mixed material includes a first mixed material and a second mixed material. In the first mixed material, the mass ratio of the pore-forming agent to the substrate is a first pore-forming ratio, and in the second mixed material, the mass ratio of the pore-forming agent to the substrate is a second pore-forming ratio, and the second pore-forming ratio is smaller than the first pore-forming ratio; Melting and extrusion: melting and extruding the first mixed material and the second mixed material respectively to obtain a first extruded sheet prepared from the first mixed material and a second extruded sheet prepared from the second mixed material; Connection: connecting the first extruded sheet to the second extruded sheet; Pore formation: removing the pore-forming agent in the first extruded sheet and the second extruded sheet so that the first extruded sheet has a first porosity and the second extruded sheet has a second porosity smaller than the first porosity, thereby obtaining a separator applied to an energy storage device.

8. The preparation method according to claim 7, characterized in that, In the steps of melting and extrusion and connection, it includes: Extrusion: providing a first extrusion port for extruding the first mixed material and a second extrusion port for extruding the second mixed material. The first extrusion port and the second extrusion port are arranged adjacent to each other, and the extrusion direction of the first mixed material is the same as the extrusion direction of the second mixed material; Melting connection: making the first extrusion port extrude a first extruded sheet in a molten state; and making the second extrusion port extrude a second extruded sheet in a molten state; and connecting the first extruded sheet in the molten state to the second extruded sheet in the molten state.

9. The preparation method according to claim 8, characterized in that, In the step of melting connection, it includes: The connection part of the first extruded sheet and the second extruded sheet is mixed to form a first transition part, and the first transition part is connected between the first extruded sheet and the second extruded sheet; In the step of pore formation, it further includes: Remove the pore former in the first transition part, so that the porosity of the first transition part gradually decreases in the direction from the first extruded sheet to the second extruded sheet, and the separator is obtained.

10. The preparation method according to claim 7, characterized in that, In the step of mixing the materials, it further includes: The mixed material further includes a third mixed material. In the third mixed material, the mass ratio of the pore former to the substrate is a third pore-forming ratio. The third pore-forming ratio is less than the first pore-forming ratio and greater than the second pore-forming ratio. In the step of melt extrusion, it further includes: Melt and extrude the third mixed material to obtain a third extruded sheet prepared from the third mixed material. In the step of connection, it further includes: Connect the third extruded sheet between the first extruded sheet and the second extruded sheet. In the step of pore formation, it further includes: Remove the pore former in the third extruded sheet, so that the third extruded sheet has a third porosity. The third porosity is less than the first porosity and greater than the second porosity, and the separator is obtained.

11. The preparation method according to claim 10, characterized in that, The first pore-forming ratio is (80 - 85):(14 - 20), the third pore-forming ratio is (70 - 80):(20 - 30), and the second pore-forming ratio is (60 - 70):(30 - 40).

12. The preparation method according to claim 7, characterized in that, The substrate includes at least one of ultra-high molecular weight polyethylene and high-density polyethylene. When the substrate includes ultra-high molecular weight polyethylene and high-density polyethylene, the mass ratio of ultra-high molecular weight polyethylene to high-density polyethylene is (0.5 - 1.5):(0.5 - 1.5).

13. An energy storage device, characterized in that, The energy storage device includes a tab, an electrolyte, a positive electrode plate, a negative electrode plate, and the separator according to any one of claims 1 - 6. The first part of the separator is closer to the tab than the second part of the separator.

14. An electrical device, characterized in that, The electrical equipment includes: The equipment body; and The energy storage device according to claim 13, and the energy storage device supplies power to the equipment body.

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