Secondary battery and electronic device

Abstract

Provided in the present application are a secondary battery and an electronic device. The secondary battery comprises an electrode assembly of a wound structure, the electrode assembly comprising a positive electrode sheet, a negative electrode sheet, a first separator and a second separator, wherein at least part of the negative electrode sheet is located between the first separator and the second separator. In one winding turn of the electrode assembly, the first separator is farther from the winding center of the electrode assembly than the second separator. The first separator comprises a first base film, and the second separator comprises a second base film. The porosity n1 of the first base film is greater than the porosity n2 of the second base film, and the puncture resistance F2 of the second base film is greater than the puncture resistance F1 of the first base film, where 30％≤n1≤60％, and 300 gf≤F2≤650 gf. The secondary battery comprising the described structure achieves both high manufacturing yield and excellent kinetic performance.

Description

A secondary battery and electronic device

[0001] This application claims priority to Chinese Patent Application No. 202510360588.X, filed on March 25, 2025, entitled "A Secondary Battery and Electronic Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to a secondary battery and electronic device. Background Technology

[0003] With the widespread application of rechargeable batteries in various fields, people have higher and higher requirements for rechargeable batteries, and expect them to have more superior performance.

[0004] Secondary batteries typically use two identical separators. Due to the characteristics of the separators, it is impossible to simultaneously meet the requirements of high puncture resistance and high kinetic performance. Therefore, in some cases, secondary batteries cannot achieve both manufacturing efficiency and kinetic performance. Summary of the Invention

[0005] The purpose of this application is to provide a secondary battery and electronic device that balances manufacturing efficiency and kinetic performance.

[0006] It should be noted that while this application uses lithium-ion batteries as an example of secondary batteries to explain the invention, the secondary batteries in this application are not limited to lithium-ion batteries. The specific technical solution is as follows:

[0007] The first aspect of this application provides a secondary battery comprising a wound electrode assembly, the electrode assembly including a positive electrode, a negative electrode, a first separator, and a second separator, with at least a portion of the negative electrode located between the first separator and the second separator; the first separator includes a first base film, and the second separator includes a second base film, wherein the porosity n1 of the first base film is greater than the porosity n2 of the second base film, and the puncture resistance F2 of the second base film is greater than the puncture resistance F1 of the first base film, wherein 30% ≤ n1 ≤ 60%, and 300 gf ≤ F2 ≤ 650 gf. Therefore, using a first base film with higher porosity paired with a second base film with higher puncture resistance, and controlling the porosity of the first base film and the puncture resistance of the second base film within the aforementioned ranges, is beneficial for balancing the kinetic performance and manufacturing efficiency of the secondary battery.

[0008] In one embodiment of this application, the electrode assembly includes a flat region and a corner region. The negative electrode includes a negative current collector and a first negative electrode material layer and a second negative electrode material layer located on both sides of the thickness direction of the negative current collector. In the corner region, a first positive electrode corner segment is adjacent to a first negative electrode material layer corner segment. The first positive electrode corner segment is farther from the winding center of the electrode assembly than the first negative electrode material layer corner segment. A first separator is located between the first positive electrode corner segment and the first negative electrode material layer corner segment. By disposing the first separator, which includes a first base film, between the aforementioned first positive electrode corner segment and first negative electrode material layer corner segment, the higher porosity of the first base film results in a higher electrolyte retention capacity. This is beneficial for improving the problem of insufficient electrolyte in the corner region and also for the transport of active ions, thereby improving the interface problem and thus improving the lithium plating problem of the secondary battery, i.e., improving the kinetic performance.

[0009] In some embodiments of this application, 40% ≤ n1 ≤ 50%, and / or 400gf ≤ F2 ≤ 500gf. By controlling the porosity of the first base membrane and the puncture resistance of the second base membrane within the scope of this application, the first separator exhibits good wettability and liquid absorption / retention capabilities, which is beneficial for improving the wetting performance of the electrolyte, increasing the lithium-ion transport rate, further reducing the risk of lithium plating on the negative electrode, and further improving the kinetic performance of the secondary battery. Simultaneously, it is beneficial for improving the puncture resistance of the second separator, further improving the yield of the secondary battery's Hi-pot and K-value, thereby further improving the manufacturing yield of the secondary battery.

[0010] In one embodiment of this application, the first base film includes a first resin material with a weight-average molecular weight of 50W to 90W; the second base film includes a second resin material and a third resin material, the second resin material having a weight-average molecular weight of 50W to 90W, and the third resin material having a weight-average molecular weight of 100W to 200W. By adjusting the weight-average molecular weights of the first, second, and third resin materials within the range of this application, the obtained first base film has suitable puncture resistance and high porosity, which is beneficial for improving lithium-ion transport and reducing the risk of lithium plating on the negative electrode; the obtained second base film has high puncture resistance and suitable porosity, which is beneficial for improving lithium-ion transport, increasing the Hi-pot and K-value yield of the secondary battery, and further improving the manufacturing yield of the secondary battery while also taking into account kinetic performance.

[0011] In one embodiment of this application, based on the mass of the second base film, the mass percentage W1 of the second resin material is 70% to 90%, and the mass percentage W2 of the third resin material is 10% to 30%. By adjusting the mass percentages of the second and third resin materials within the scope of this application, the obtained second base film possesses both suitable porosity and high puncture resistance, thereby improving lithium-ion transport, reducing the risk of the separator being punctured by hard particles from the negative electrode, and improving the yield of the secondary battery's Hi-pot and K-value, thus further improving the manufacturing yield of the secondary battery while also considering its kinetic performance.

[0012] In one embodiment of this application, the first resin material, the second resin material, and the third resin material are each independently selected from at least one of polyethylene, polypropylene, polyimide, polyethyleneimine, or polyethylene terephthalate. When the first resin material, the second resin material, and the third resin material are selected from materials within the scope of this application, it is advantageous to obtain a first base film that balances high porosity and suitable puncture resistance, and a second base film that balances suitable porosity and high puncture resistance, thereby further improving the manufacturing yield of the secondary battery while also considering its kinetic performance.

[0013] In one embodiment of this application, a characteristic peak exists in the differential scanning calorimetry (DSC) spectrum of the first base film between 128°C and 134°C. The peak value of this characteristic peak in the DSC spectrum of the first base film corresponds to the melting temperature of the first resin material.

[0014] In one embodiment of this application, characteristic peaks are present in the differential scanning calorimetry (DSC) spectrum of the second base film at 128°C to 134°C and 136°C to 140°C. The DSC spectrum of the second base film shows a characteristic peak at 128°C to 134°C, the peak value of which corresponds to the melting temperature of the second resin material. The DSC spectrum also shows a characteristic peak at 136°C to 140°C, the peak value of which corresponds to the melting temperature of the third resin material.

[0015] In one embodiment of this application, 10% ≤ n2 ≤ 30%, 200gf ≤ F1 ≤ 300gf. By controlling the porosity of the second base film and the puncture resistance of the first base film within the scope of this application, the second base film possesses both high puncture resistance and suitable porosity and good ion transport performance. This helps reduce the risk of the separator being punctured by hard particles from the negative electrode, improving the Hi-pot and K-value yield of the secondary battery. The first base film, possessing both high porosity and suitable puncture resistance, helps improve lithium-ion transport, reduces the risk of lithium plating on the negative electrode, and also helps reduce the risk of the separator being punctured by hard particles from the negative electrode, improving the Hi-pot and K-value yield of the secondary battery. This further improves the kinetic performance of the secondary battery while maintaining manufacturing yield.

[0016] In one embodiment of this application, 15% ≤ n2 ≤ 30%. By adjusting the porosity of the second base membrane within the scope of this application, the second base membrane possesses both high puncture resistance and suitable porosity, which is beneficial for improving the wettability and liquid absorption and retention capacity of the second separator, improving the wetting performance of the electrolyte, improving lithium-ion transport, reducing the risk of lithium plating on the negative electrode, and further improving the manufacturing yield of the secondary battery while also taking into account its kinetic performance.

[0017] In one embodiment of this application, the thicknesses of the first base film and the second base film are each independently between 4 μm and 7 μm. Having the thicknesses of the first and second base films within this range also helps to balance the energy density of the secondary battery.

[0018] In one embodiment of this application, the first separator further includes a first ceramic layer, the porosity of the first separator being n3, where 40% ≤ n3 ≤ 70%. The presence of the first ceramic layer is beneficial for further improving the liquid absorption and retention capacity of the first separator, and further improving the kinetic performance of the secondary battery.

[0019] In one embodiment of this application, the coating weight CW1 of the first ceramic layer is 9 mg / 5000 mm². 2 Up to 15mg / 5000mm 2 The coating weight CW1 of the first ceramic layer is within the above range, and the first ceramic layer has a suitable thickness, which not only improves the dynamic performance of the secondary battery, but also helps to balance its energy density.

[0020] In one embodiment of this application, the first ceramic layer comprises first ceramic particles, which include at least one of alumina, boehmite, silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide. By selecting the above-mentioned types of first ceramic particles, it is beneficial to further improve the liquid absorption and retention capacity of the first separator, thereby improving the kinetic performance of the secondary battery.

[0021] In some embodiments of this application, the first negative electrode material layer includes a first negative electrode material, the second negative electrode material layer includes a second negative electrode material, and the first negative electrode material and / or the second negative electrode material includes silicon material. Simultaneously, the aforementioned first and second separators are used, with the first separator exhibiting good liquid absorption and retention properties, and the second separator possessing high puncture resistance, thereby facilitating a balance between the energy density, kinetic performance, and manufacturing yield of the secondary battery.

[0022] In one embodiment of this application, the silicon material includes at least one of elemental silicon, silicon carbide, silicon oxide, or silicon alloy. When the silicon material meets the above characteristics, it is beneficial to improve the energy density of the secondary battery.

[0023] A second aspect of this application provides an electronic device comprising the secondary battery described in the first aspect of this application.

[0024] The beneficial effects of this application are:

[0025] This application provides a secondary battery comprising a wound electrode assembly, the electrode assembly including a positive electrode, a negative electrode, a first separator, and a second separator, at least a portion of the negative electrode being located between the first separator and the second separator; in one winding of the electrode assembly, the first separator is farther from the winding center of the electrode assembly than the second separator; the first separator includes a first base film, the second separator includes a second base film, the porosity n1 of the first base film is greater than the porosity n2 of the second base film, and the puncture resistance F2 of the second base film is greater than the puncture resistance F1 of the first base film, wherein 30% ≤ n1 ≤ 60%, and 300gf ≤ F2 ≤ 650gf. By using a first base membrane with high porosity and a second base membrane with high puncture resistance, the porosity of the first base membrane is within the scope of this application. The first separator has good wettability and liquid absorption and retention capabilities, which is beneficial to improving the wetting performance of the electrolyte, increasing the lithium-ion transport rate, reducing the risk of lithium plating on the negative electrode, and improving the kinetic performance of the secondary battery. At the same time, the puncture resistance of the second base membrane is within the scope of this application, which can improve the puncture resistance of the second separator, reduce the risk of the separator being punctured by hard particles of the negative electrode, and improve the Hi-pot (high voltage resistance test value) and K-value (battery voltage drop per unit time) of the secondary battery, thereby taking into account both the manufacturing efficiency and kinetic performance of the secondary battery.

[0026] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0027] The accompanying drawings, which are provided to further illustrate this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0028] Figure 1 is a schematic diagram of the electrode assembly along its own thickness direction in one embodiment of this application;

[0029] Figure 2 is a magnified view of part A in Figure 1;

[0030] Figure 3 is a schematic diagram of the electrode assembly along its own thickness direction in another embodiment of this application;

[0031] Figure 4 is a magnified view of part B in Figure 3;

[0032] Figure 5 is a schematic cross-sectional view of the first diaphragm along its own thickness direction in one embodiment of this application;

[0033] Figure 6 is a cycle capacity retention curve of the lithium-ion batteries prepared in Examples 1-1 and Comparative Example 2 of this application;

[0034] Figure 7 is a graph showing the cycle expansion rate of the lithium-ion batteries prepared in Examples 1-1 and Comparative Example 2 of this application;

[0035] Figure 8 is a differential scanning calorimetry spectrum of the first base film in Embodiment 1-1 of this application;

[0036] Figure 9 is a differential scanning calorimetry spectrum of the second base film in Embodiment 1-1 of this application. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0038] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0039] This application provides a secondary battery including a wound electrode assembly. As shown in Figures 1 and 3, the electrode assembly 01 includes a positive electrode 10, a negative electrode 20, a first separator 30, and a second separator 40, with at least a portion of the negative electrode 20 located between the first separator 30 and the second separator 40. The first separator 30 includes a first base film, and the second separator 40 includes a second base film. The porosity n1 of the first base film is greater than the porosity n2 of the second base film, allowing the first base film to store more electrolyte, which is beneficial for improving the kinetic performance of the secondary battery. The puncture resistance F2 of the second base film is greater than the puncture resistance F1 of the first base film, improving the puncture resistance of the second base film and thus increasing the yield of the secondary battery's Hi-pot and K-value, which is beneficial for improving the manufacturing yield of the secondary battery.

[0040] In one embodiment of this application, 30% ≤ n1 ≤ 60%. For example, the porosity n1 of the first base film can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, or a range of any two of these values. When the porosity of the first base film is too small, for example, less than 30%, it will lead to poor electrolyte wetting, increased risk of lithium plating on the negative electrode, and poor kinetic performance of the secondary battery. When the porosity of the first base film is too large, for example, greater than 60%, it will lead to a decrease in the puncture resistance of the first base film and a decrease in manufacturing yield. Therefore, by controlling the porosity of the first base film within the scope of this application, the first separator has good wettability and liquid absorption and retention capabilities, which is beneficial to improving the electrolyte wetting performance, increasing the lithium ion transport rate, reducing the risk of lithium plating on the negative electrode, improving the kinetic performance of the secondary battery, and also ensuring manufacturing yield.

[0041] In one embodiment of this application, 300gf ≤ F2 ≤ 650gf. For example, the puncture resistance F2 of the second base film can be 300gf, 350gf, 400gf, 450gf, 500gf, 550gf, 600gf, 650gf, or a range of any two of these values. When the puncture resistance of the second base film is too low, for example, less than 300gf, the hard particles in the negative electrode material layer may puncture the separator, posing a safety risk and affecting the manufacturing yield of the secondary battery. When the puncture resistance of the second base film increases, the tendency for the separator to undergo physical short circuits during the preparation of the secondary battery will decrease. However, if the puncture resistance is too high, for example, greater than 650gf, it will affect the kinetic performance of the secondary battery, thereby affecting the degree of lithium plating. Therefore, by adjusting the puncture resistance of the second base membrane within the scope of this application, the puncture resistance of the second separator can be improved, thereby improving the manufacturing yield of the secondary battery, such as the Hi-pot yield and the K-value yield.

[0042] Therefore, using a first base membrane with higher porosity in combination with a second base membrane with higher puncture resistance, and controlling the porosity of the first base membrane and the puncture resistance of the second base membrane within the above range, is beneficial to balance the dynamic performance and manufacturing efficiency of the secondary battery.

[0043] In one embodiment of this application, as shown in Figures 1 to 4, the electrode assembly 01 includes a straight region 011 and a corner region 012, the positive electrode 10 includes a positive current collector 110 and a positive electrode material layer 120 disposed on two surfaces of the positive current collector 110, and the negative electrode 20 includes a negative current collector 210 and a first negative electrode material layer 220 and a second negative electrode material layer 230 located on both sides of the thickness direction of the negative current collector.

[0044] In some embodiments of this application, as shown in Figures 1 and 2, in the same negative electrode layer 20, the first negative electrode material layer 220 is farther away from the winding center of the electrode assembly 01 than the second negative electrode material layer 230. In the corner region 012 of the electrode assembly 01, a first positive electrode corner segment 101 is adjacent to a first negative electrode material layer corner segment 221. The first positive electrode corner segment 101 is farther away from the winding center of the electrode assembly 01 than the first negative electrode material layer corner segment 221. The first diaphragm 30 is located between the first positive electrode corner segment 101 and the first negative electrode material layer corner segment 221. The second diaphragm 40 is adjacent to the second negative electrode material layer 230. In a wound electrode assembly, a corner segment of a first positive electrode sheet is adjacent to a corner segment of a first negative electrode material layer but far from the winding center of the electrode assembly. In this case, the winding radius of the positive electrode material layer in the positive electrode sheet is larger than that of the first negative electrode material layer, resulting in a smaller positive-to-negative electrode ratio (Cell Balance, CB, the ratio of negative electrode capacity to positive electrode capacity per unit area). This easily leads to interface problems and lithium plating, thus requiring a sufficient electrolyte to transport active ions. Simultaneously, the corner region of the wound structure is prone to insufficient electrolyte or even electrolyte bridging, further exacerbating the interface problem. Therefore, this application addresses this by placing a first separator containing a first base film between the corner segments of the first positive electrode sheet and the first negative electrode material layer. The high porosity of the first base film results in higher electrolyte retention, which helps alleviate the problem of insufficient electrolyte in the corner region and also facilitates the transport of active ions, thereby improving the interface problem and ultimately improving the lithium plating issue in the secondary battery, i.e., improving kinetic performance. Furthermore, the addition of a second separator helps to balance the kinetic performance and manufacturing efficiency of the secondary battery. In this application, the straight area refers to the straight part of the electrode assembly, and the corner area refers to the curved part of the electrode assembly.

[0045] In some embodiments of this application, as shown in Figures 3 and 4, in the same negative electrode layer 20, the first negative electrode material layer 220 is farther away from the winding center of the electrode assembly 01 than the second negative electrode material layer 230. In the corner region 012 of the electrode assembly 01, a second positive electrode corner segment 102 is adjacent to a second negative electrode material layer corner segment 222. The second positive electrode corner segment 102 is closer to the winding center of the electrode assembly 01 than the second negative electrode material layer corner segment 222. The first separator 30 is located between the second positive electrode corner segment 102 and the second negative electrode material layer corner segment 222, and the second separator 40 is located between the first positive electrode corner segment 101 and the first negative electrode material layer corner segment 221.

[0046] In some embodiments of this application, 40% ≤ n1 ≤ 50%. For example, the porosity n1 of the first base membrane can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or a range of any two of these values. By adjusting the porosity of the first base membrane within the scope of this application, the first separator exhibits good wettability and liquid absorption and retention capabilities, which is beneficial for improving the wetting performance of the electrolyte, enhancing the lithium-ion transport rate, further reducing the risk of lithium plating on the negative electrode, and further improving the kinetic performance of the secondary battery.

[0047] In one embodiment of this application, the first base film includes a first resin material, the weight-average molecular weight of which is from 50W ("W" represents 10,000, 50W is 500,000, the same below) to 90W. For example, the weight-average molecular weight of the first resin material can be 50W, 55W, 60W, 65W, 70W, 75W, 80W, 85W, 90W, or any two of these values. By adjusting the weight-average molecular weight of the first resin material within the range of this application, the obtained first base film has suitable puncture resistance and high porosity, which is beneficial to improving lithium-ion transport, reducing the risk of lithium plating on the negative electrode, and further improving the kinetic performance of the secondary battery while also ensuring manufacturing yield.

[0048] In one embodiment of this application, the first resin material is selected from at least one of polyethylene, polypropylene, polyimide, polyethyleneimine, or polyethylene terephthalate. When the first resin material is selected from materials within the scope of this application, it is advantageous to obtain a first base film that balances high porosity and suitable puncture resistance, thereby further improving the kinetic performance of the secondary battery while maintaining manufacturing efficiency.

[0049] In one embodiment of this application, a characteristic peak exists in the differential scanning calorimetry (DSC) spectrum of the first base film between 128°C and 134°C. The peak value of this characteristic peak in the DSC spectrum of the first base film corresponds to the melting temperature of the first resin material. In this application, the peak value of the characteristic peak in the first base film is between 128°C and 134°C, i.e., characteristic peak A exists.

[0050] In one embodiment of this application, 200gf ≤ F1 ≤ 300gf. For example, the puncture resistance F1 of the first base film can be 200gf, 210gf, 220gf, 230gf, 240gf, 250gf, 260gf, 270gf, 280gf, 290gf, 300gf, or a range of any two of these values. By adjusting the puncture resistance of the first base film within the scope of this application, the first base film possesses both high porosity and suitable puncture resistance, which is beneficial for improving lithium-ion transport, reducing the risk of lithium plating on the negative electrode, and also reducing the risk of the separator being punctured by hard particles from the negative electrode. This improves the Hi-pot and K-value yield of the secondary battery, further improving the kinetic performance of the secondary battery while also ensuring manufacturing efficiency.

[0051] In one embodiment of this application, the thickness of the first base film is 4 μm to 7 μm. For example, the thickness of the first base film can be 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, or a range consisting of any two of these values. By adjusting the thickness of the first base film within the range of this application, the kinetic performance of the secondary battery can be further improved while also taking into account the energy density.

[0052] In one embodiment of this application, the first separator further includes a first ceramic layer, the porosity of which is n3, 40% ≤ n3 ≤ 70%. For example, the porosity of the first separator can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, or a range of any two of these values. The presence of the first ceramic layer helps to further improve the liquid absorption and retention capacity of the first separator, thereby enhancing the lithium-ion transport rate, reducing the risk of lithium plating on the negative electrode, and further improving the kinetic performance of the secondary battery.

[0053] In one embodiment of this application, the coating weight CW1 of the first ceramic layer is 9 mg / 5000 mm². 2 Up to 15mg / 5000mm 2 The coating weight (CW1) of the first ceramic layer can be 9 mg / 5000 mm. 2 10mg / 5000mm 2 11mg / 5000mm2 12mg / 5000mm 2 13mg / 5000mm 2 14mg / 5000mm 2 15mg / 5000mm 2 It can be a range consisting of any two of these values. By adjusting the coating weight CW1 of the first ceramic layer within the scope of this application, the first ceramic layer has a suitable thickness, which is beneficial to improving the kinetic performance of the secondary battery while also taking into account the energy density.

[0054] In one embodiment of this application, the first ceramic layer comprises first ceramic particles, which include at least one of alumina, boehmite, silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide. By selecting the above-mentioned types of first ceramic particles, it is beneficial to further improve the liquid absorption and retention capacity of the first separator, and further improve the kinetic performance of the secondary battery.

[0055] In one embodiment of this application, the first separator further includes a first adhesive layer disposed on both sides of the first base film, and a first ceramic layer disposed on one side of the first base film, with the first ceramic layer located between the first base film and the first adhesive layer. In some embodiments of this application, in the electrode assembly, the first ceramic layer is disposed facing the positive electrode, which is beneficial for further improving the problem of insufficient electrolyte in the corner area and also for the transport of active ions, thereby improving interface problems and thus improving the lithium plating problem of the secondary battery.

[0056] This application does not impose any particular limitation on the composition of the first adhesive layer, as long as it achieves the purpose of this application. For example, the first adhesive layer includes a first adhesive, which includes at least one selected from polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, or polyimide. This application does not impose any particular limitation on the thickness of the first adhesive layer, as long as it achieves the purpose of this application. For example, the thickness of the first adhesive layer can be from 1 μm to 5 μm.

[0057] In some embodiments of this application, as shown in FIG5, the first separator 30 includes a first base membrane 310, a first ceramic layer 330, and a first adhesive layer 320. The first ceramic layer 330 is disposed on the side of the first base membrane 310 near the positive electrode material layer 120. The first adhesive layer 320 is disposed on one surface of the first base membrane 310 away from the positive electrode material layer 120 and on one surface of the first ceramic layer 330 near the positive electrode material layer 120. The first ceramic layer 330 is located between the first base membrane 310 and the first adhesive layer 320. That is, the first separator 30 includes one first ceramic layer 330 and two first adhesive layers 320.

[0058] In some embodiments of this application, 400gf ≤ F2 ≤ 500gf. For example, the puncture resistance F2 of the second base film can be 400gf, 410gf, 420gf, 430gf, 440gf, 450gf, 460gf, 470gf, 480gf, 490gf, 500gf, or a range of any two of these values. By adjusting the puncture resistance of the second base film within the range of this application, it is beneficial to improve the puncture resistance of the second separator, further improve the yield of the secondary battery's Hi-pot and K-value, and thus further improve the manufacturing yield of the secondary battery.

[0059] In one embodiment of this application, the second base film includes a second resin material and a third resin material. The weight-average molecular weight of the second resin material is 50W to 90W, and the weight-average molecular weight of the third resin material is 100W to 200W. For example, the weight-average molecular weight of the second resin material can be 50W, 55W, 60W, 65W, 70W, 75W, 80W, 85W, 90W, or any combination of two of these values; the weight-average molecular weight of the third resin material can be 100W, 110W, 120W, 130W, 140W, 150W, 160W, 170W, 180W, 190W, 200W, or any combination of two of these values. By adjusting the weight-average molecular weights of the second and third resin materials within the range of this application, the obtained second base film has high puncture resistance and suitable porosity, which is beneficial for improving lithium-ion transport, increasing the Hi-pot and K-value yield of the secondary battery, and further improving the manufacturing yield of the secondary battery while also taking into account its kinetic performance.

[0060] In one embodiment of this application, based on the mass of the second base film, the mass percentage W1 of the second resin material is 70% to 90%, and the mass percentage W2 of the third resin material is 10% to 30%. For example, the mass percentage W1 of the second resin material can be 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, or any combination of two of these values; the mass percentage W2 of the third resin material can be 10%, 12%, 14%, 16%, 8%, 20%, 2%, 24%, 26%, 28%, 30%, or any combination of two of these values. By adjusting the mass percentages of the second and third resin materials within the scope of this application, the resulting second base film possesses both suitable porosity and high puncture resistance, thereby improving lithium-ion transport, reducing the risk of the separator being punctured by hard particles from the negative electrode, and improving the Hi-pot and K-value yield of the secondary battery, thus further improving the manufacturing yield of the secondary battery while also considering its kinetic performance.

[0061] In one embodiment of this application, the second resin material and the third resin material are each independently selected from at least one of polyethylene, polypropylene, polyimide, polyethyleneimine, or polyethylene terephthalate. When the second and third resin materials are selected from materials within the scope of this application, it is advantageous to obtain a second base film that balances suitable porosity and high puncture resistance, thereby further improving the manufacturing yield of the secondary battery while also considering its kinetic performance.

[0062] In one embodiment of this application, characteristic peaks are present in the differential scanning calorimetry (DSC) spectrum of the second base film at 128°C to 134°C and 136°C to 140°C. The DSC spectrum of the second base film also shows a characteristic peak at 128°C to 134°C, the peak value of which corresponds to the melting temperature of the second resin material. Furthermore, the DSC spectrum shows a characteristic peak at 136°C to 140°C, the peak value of which corresponds to the melting temperature of the third resin material. In this application, in the second base film, the peak values ​​of the characteristic peaks are between 128°C and 134°C, i.e., characteristic peak A is present; and the peak values ​​of the characteristic peaks are between 136°C and 140°C, i.e., characteristic peak B is present.

[0063] In one embodiment of this application, 10% ≤ n2 ≤ 30%. For example, the porosity n2 of the second base membrane can be 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, or a range of any two of these values. By adjusting the porosity of the second base membrane within the scope of this application, the second base membrane possesses both high puncture resistance and suitable porosity and good ion transport performance. This helps reduce the risk of the separator being punctured by hard particles from the negative electrode, improves the yield of the secondary battery's Hi-pot and K-value, and further improves the manufacturing yield of the secondary battery while also considering kinetic performance.

[0064] In one embodiment of this application, 15% ≤ n2 ≤ 30%. For example, the porosity n2 of the second base membrane can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or a range of any two of these values. By adjusting the porosity of the second base membrane within the scope of this application, the second base membrane possesses both high puncture resistance and suitable porosity, which is beneficial for improving the wettability and liquid absorption and retention capacity of the second separator, improving the electrolyte wetting performance, improving lithium-ion transport, reducing the risk of lithium plating on the negative electrode, and further improving the manufacturing yield of the secondary battery while also considering kinetic performance.

[0065] In one embodiment of this application, the thickness of the second base film is from 4 μm to 7 μm. For example, the thickness of the second base film can be 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, or a range of any two of these values. By adjusting the thickness of the second base film within the scope of this application, the manufacturing yield of the secondary battery can be further improved while maintaining energy density.

[0066] In some embodiments of this application, the second separator includes a second ceramic layer and a second adhesive layer. The second adhesive layer is disposed on both sides of the second base membrane, and the second ceramic layer is disposed on one side of the second base membrane, located between the second base membrane and the second adhesive layer. In some embodiments of this application, in the electrode assembly, the second ceramic coating is disposed facing the positive electrode, which is beneficial for further improving the problem of insufficient electrolyte in the corner region and also for the transport of active ions, thereby improving interface problems and thus improving the lithium plating problem of the secondary battery.

[0067] In one embodiment of this application, the second separator further includes a second ceramic layer, the porosity of which is n4, 20% ≤ n4 ≤ 40%. For example, the porosity of the second separator can be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, or a range of any two of these values. The provision of the second ceramic layer is beneficial for further improving the liquid absorption and retention capacity of the second separator, thereby improving lithium-ion transport performance, reducing the risk of lithium plating on the negative electrode, and further improving the kinetic performance of the secondary battery.

[0068] This application does not impose any particular limitation on the coating weight CW2 of the second ceramic layer, as long as the purpose of this application can be achieved. For example, the coating weight CW2 of the second ceramic layer is 9 mg / 5000 mm. 2 Up to 15mg / 5000mm 2 For example, the coating weight CW2 of the second ceramic layer can be 9 mg / 5000 mm. 2 9.5mg / 5000mm 2 10mg / 5000mm 2 10.5mg / 5000mm 2 11mg / 5000mm 2 11.5mg / 5000mm 2 12mg / 5000mm 2 12.5mg / 5000mm 2 13mg / 5000mm 2 13.5mg / 5000mm 2 14mg / 5000mm 2 14.5mg / 5000mm2 15mg / 5000mm 2 Or it can be a range consisting of any two of these values.

[0069] In one embodiment of this application, the second ceramic layer comprises second ceramic particles, which include at least one of alumina, boehmite, silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide. By selecting the above-mentioned types of second ceramic particles, the second ceramic layer exhibits good wettability and liquid absorption and retention capabilities, improves lithium-ion transport performance, reduces the risk of lithium plating on the negative electrode, and further improves the kinetic performance of the secondary battery.

[0070] This application does not impose any particular limitation on the composition of the second adhesive layer, as long as it achieves the purpose of this application. For example, the second adhesive layer includes a second adhesive, and the second adhesive includes at least one selected from polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, or polyimide. This application does not impose any particular limitation on the thickness of the second adhesive layer, as long as it achieves the purpose of this application. For example, the thickness of the second adhesive layer can be from 1 μm to 5 μm.

[0071] In some embodiments of this application, as shown in FIG5, the second diaphragm 40 can be understood in the same way as the first diaphragm 30, that is, the second diaphragm 40 includes a second ceramic layer 430 and two second adhesive layers 420.

[0072] The negative electrode material of secondary batteries contains silicon. Because silicon particles are relatively hard, they may puncture the separator, leading to poor yield in terms of Hi-pot and K-value, and a decrease in manufacturing yield. Furthermore, Si is a semiconductor with poor conductivity. Therefore, when using silicon-containing negative electrode sheets in secondary batteries, it is generally difficult to simultaneously achieve good energy density, kinetic performance, and manufacturing yield. Based on these problems, in some embodiments of this application, the first negative electrode material layer includes a first negative electrode material, which includes silicon. In some embodiments of this application, the second negative electrode material layer includes a second negative electrode material, which includes silicon. By combining the aforementioned first and second separators, the first separator has good liquid absorption and retention properties, and the second separator has high puncture resistance, thus helping to balance the energy density, kinetic performance, and manufacturing yield of the secondary battery.

[0073] In one embodiment of this application, the silicon material includes at least one of elemental silicon, silicon carbide, silicon oxide, or silicon alloy. When the silicon material meets the above characteristics, it is beneficial to improve the energy density of the secondary battery.

[0074] In this application, the features of the above-described embodiments can be combined arbitrarily.

[0075] This application does not impose any particular limitation on the preparation method of the first base film, as long as it can achieve the purpose of this application. For example, the preparation method of the first base film includes, but is not limited to, the following steps: (1) mixing additives and solvents in a mass ratio of (0.1 to 0.3):100 to obtain a mixed solution; (2) mixing the first resin material and the mixed solution in a mass ratio of (10:90) to (30:70) to obtain a first substrate by extrusion, casting, cooling, and casting; (3) stretching the first substrate longitudinally and transversely, and then extracting and drying it to obtain a first porous substrate; (4) stretching the first porous substrate a second time, heat-setting it, and winding it up to obtain the first base film. The solvent may include, but is not limited to, at least one of paraffin oil or dichloromethane; the additive may include, but is not limited to, at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF), or dimethyl sulfoxide (DMSO); the extractant used during extraction may include, but is not limited to, at least one of dichloromethane or n-hexane. The stretching ratios for longitudinal and transverse stretching may each be independently 6 to 8 times; the stretching ratio for secondary stretching may be 1 to 2 times; the extraction temperature may be 20°C to 30°C, and the extraction time may be 0.5 h to 1 h; the heat setting temperature may be 110°C to 135°C.

[0076] This application does not impose any particular limitation on the preparation method of the second base film, as long as it can achieve the purpose of this application. For example, the preparation method of the second base film includes, but is not limited to, the following steps: (1) mixing the second resin material and the third resin material uniformly according to the above W1 and W2 to obtain a mixed material; (2) mixing the additive and the solvent uniformly according to the mass ratio (0.1 to 0.3):100 to obtain a mixed solution; (3) mixing the mixed material and the mixed solution uniformly according to the mass ratio (10:90) to (30:70), and extruding, casting, cooling and casting to form a film to obtain a second substrate; (4) stretching the second substrate longitudinally and transversely, and obtaining a second porous substrate after extraction and drying; (5) stretching the second porous substrate a second time, heat-setting, and winding to obtain the second base film. The solvent may include, but is not limited to, at least one of paraffin oil or dichloromethane; the additives may include, but are not limited to, at least one of pentaerythritol ester [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF), or dimethyl sulfoxide (DMSO); the extractant used during extraction may include, but is not limited to, at least one of dichloromethane or n-hexane; the stretching ratios of longitudinal stretching and transverse stretching may each be independently 6 to 8 times; the stretching ratio of secondary stretching may be 1 to 2 times; the extraction temperature may be 20°C to 30°C, and the extraction time may be 0.5 h to 1 h; the heat setting temperature may be 110°C to 135°C.

[0077] In this application, the porosity n1 of the first base film can be controlled by adjusting the transverse stretching ratio, the longitudinal stretching ratio, the secondary stretching ratio, and the mass ratio of the solvent during the preparation process. For example, when other conditions remain unchanged, the porosity n1 of the first base film increases when the transverse stretching ratio of the first base film increases, and vice versa. When other conditions remain unchanged, the porosity n1 of the first base film increases when the longitudinal stretching ratio of the first base film increases, and vice versa. When other conditions remain unchanged, the porosity n1 of the first base film increases when the secondary stretching ratio of the first base film increases, and vice versa. When other conditions remain unchanged, the porosity n1 of the first base film increases when the mass ratio of the solvent during the preparation process increases, and vice versa.

[0078] In this application, the porosity n2 of the second base membrane can be adjusted in the same way as the porosity n1 of the first base membrane.

[0079] In this application, the puncture resistance F2 of the second base membrane can be controlled by adjusting the porosity of the second base membrane, the weight-average molecular weight of the second resin material, the mass percentage of the second resin material, the weight-average molecular weight of the third resin material, the mass percentage of the third resin material, and the thickness of the second base membrane. The method for controlling the porosity of the second base membrane is as described above. For example, when other conditions remain unchanged, if the porosity of the second base film increases, the puncture resistance F2 of the second base film decreases, and vice versa; when other conditions remain unchanged, if the mass percentage of the second resin material increases, the puncture resistance F2 of the second base film decreases, and vice versa; when other conditions remain unchanged, if the mass percentage of the third resin material increases, the puncture resistance F2 of the second base film increases, and vice versa; when other conditions remain unchanged, if the weight-average molecular weight of the second resin material increases, the puncture resistance F2 of the second base film increases, and vice versa; when other conditions remain unchanged, if the weight-average molecular weight of the third resin material increases, the puncture resistance F2 of the second base film increases, and vice versa; when other conditions remain unchanged, if the thickness of the second base film increases, the puncture resistance F2 of the second base film increases, and vice versa.

[0080] In this application, the puncture resistance F1 of the first base film can be adjusted in the same way as the puncture resistance F2 of the second base film.

[0081] In this application, the porosity n3 of the first diaphragm can be controlled by adjusting the porosity of the first base membrane and the coating quality of the first ceramic layer. The method for controlling the porosity of the first base membrane is as described above. For example, when other conditions remain constant, an increase in the porosity of the first base membrane leads to an increase in the porosity n3 of the first diaphragm, and vice versa; similarly, when the coating quality of the first ceramic layer increases, an increase in the porosity n3 of the first diaphragm leads to a decrease.

[0082] In this application, the porosity n4 of the second diaphragm can be adjusted in the same way as the porosity n3 of the first diaphragm.

[0083] In this application, the first, second, and third resin materials of different weight-average molecular weights and types can be purchased, and their weight-average molecular weights can be measured. The desired weight-average molecular weight can then be selected. Specific testing methods can be found in the relevant section on "Test Methods and Equipment".

[0084] In this application, the negative electrode sheet includes a negative current collector and a first negative electrode material layer and a second negative electrode material layer located on both sides of the negative current collector. The aforementioned "first negative electrode material layer and second negative electrode material layer located on both sides of the negative current collector" means that the first and second negative electrode material layers are respectively disposed on two surfaces of the negative current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the negative current collector or a partial surface area; this application has no particular limitation, as long as the purpose of this application is achieved.

[0085] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.

[0086] In some embodiments of this application, the first negative electrode material layer and the second negative electrode material layer may each independently include a negative electrode conductive agent and a negative electrode binder. This application does not particularly limit the types of negative electrode conductive agents and negative electrode binders, as long as they achieve the purpose of this application. For example, they may be at least one of a positive electrode conductive agent and a positive electrode binder. This application does not particularly limit the mass ratio of negative electrode material, negative electrode conductive agent, and negative electrode binder in the first and second negative electrode material layers. Those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved.

[0087] Optionally, the negative electrode sheet may further include a first negative electrode conductive layer, which is located between the negative electrode current collector and the first negative electrode material layer. This application does not particularly limit the composition of the first negative electrode conductive layer; it can be a conductive layer commonly used in the art. For example, the first negative electrode conductive layer includes a first negative electrode conductive layer conductive agent and a first negative electrode conductive layer binder. This application does not particularly limit the first negative electrode conductive layer conductive agent and the first negative electrode conductive layer binder; for example, they can be at least one of a positive electrode conductive agent and a positive electrode binder.

[0088] Optionally, the negative electrode sheet may further include a second negative electrode conductive layer, which is located between the negative electrode current collector and the second negative electrode material layer. This application does not impose any particular limitation on the composition of the second negative electrode conductive layer, and it can be a conductive layer commonly used in the art. For example, the second negative electrode conductive layer may include a second negative electrode conductive layer conductive agent and a second negative electrode conductive layer binder. This application does not impose any particular limitation on the second negative electrode conductive layer conductive agent and the second negative electrode conductive layer binder; for example, it can be at least one of a positive electrode conductive agent and a positive electrode binder.

[0089] This application does not impose any particular limitation on the thickness of the first negative electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the first negative electrode material layer is 30 μm to 120 μm.

[0090] This application does not impose any particular limitation on the thickness of the second negative electrode material layer, as long as it can achieve the purpose of this application. For example, the thickness of the second negative electrode material layer is 30 μm to 120 μm.

[0091] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the thickness of the negative electrode current collector can be from 4 μm to 20 μm.

[0092] In this application, the positive electrode includes a positive current collector and positive electrode material layers located on both sides of the positive current collector. The aforementioned "positive electrode material layers located on both sides of the positive current collector" means that the positive electrode material layers are disposed on two surfaces of the positive current collector along its thickness direction. It should be noted that the term "surface" here can refer to the entire surface area of ​​the positive current collector or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0093] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0094] The positive electrode material layer includes a positive electrode active material. This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include, but is not limited to, lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, or lithium manganese iron phosphate, at least one of these.

[0095] The positive electrode material layer may further include a positive electrode conductive agent and a positive electrode binder. This application does not impose any particular limitation on the types of positive electrode conductive agents and positive electrode binders, as long as they can achieve the purpose of this application. For example, the positive electrode conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. Conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0096] This application does not impose any particular restrictions on the positive electrode binder, as long as it can achieve the purpose of this application. For example, the positive electrode binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride.

[0097] This application does not impose any particular restrictions on the mass ratio of positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0098] This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector can be 5 μm to 20 μm, and the thickness of the positive electrode material layer can be 30 μm to 120 μm.

[0099] Optionally, the positive electrode may further include a positive conductive layer, which is located between the positive current collector and the positive electrode material layer. The composition of the positive conductive layer is not particularly limited and can be any conductive layer commonly used in the art. The positive conductive layer includes a positive conductive layer conductive agent and a positive conductive layer binder. This application does not particularly limit the positive conductive layer conductive agent and the positive conductive layer binder; for example, it can be at least one of the above-described positive conductive agents and positive conductive binders.

[0100] In this application, the secondary battery also includes an electrolyte, which includes lithium salts and non-aqueous solvents.

[0101] This application does not impose any particular limitation on lithium salts, as long as they achieve the purpose of this application. For example, lithium salts may include, but are not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylboron (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), tris(trifluoromethanesulfonyl)methyl lithium (LiC(SO2CF3)3), lithium hexafluorosilicate (LiSiF6), lithium bis(oxalateborate)borate (LiBOB), and lithium difluoroborate (LiF2OB). This application does not impose any particular limitation on the content of lithium salts in the electrolyte, as long as they achieve the purpose of this application.

[0102] This application does not impose any particular restrictions on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents.

[0103] The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. Other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved.

[0104] The secondary battery also includes a casing for housing a second separator, a positive electrode, a first separator, a negative electrode, and an electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0105] The fabrication process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the fabrication process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode, the first separator, the negative electrode, and the second separator in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. Alternatively, stacking the negative electrode, the second separator, the positive electrode, and the first separator in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0106] In some embodiments of this application, the secondary battery may include, but is not limited to, lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, or lithium-ion polymer secondary batteries. In some embodiments of this application, the secondary battery includes lithium-ion batteries.

[0107] A second aspect of this application provides an electronic device comprising the secondary battery described in the first aspect of this application.

[0108] This application does not specifically limit the type of electronic device; it can be any electronic device known in the prior art. In some embodiments of this application, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0109] Example

[0110] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0111] Test methods and equipment:

[0112] Sampling methods for the first and second septa:

[0113] The lithium-ion batteries in the tested examples and comparative examples were disassembled, and the first and second separators were removed. The separators were soaked in dimethyl carbonate (DMC) for 20 minutes to remove electrolyte residue. Then, the first and second separators were placed in an oven and dried at 60°C for 12 hours to obtain the first and second separator samples. Unless otherwise specified, the first and second separators were obtained using the above method in the following tests.

[0114] Sampling methods for the first and second base films:

[0115] The first and second septa obtained from the above sampling were placed in separate containers, N-methylpyrrolidone (NMP) was added, and the containers were placed in an ultrasonic instrument with heating function for ultrasonication at 45°C for 3 hours. Once the first and second septa became completely transparent, they were removed to obtain the first and second base films. Unless otherwise specified, the following tests will use the same method to obtain the first and second base films.

[0116] Porosity testing of the first base membrane, first diaphragm, second base membrane, and second diaphragm:

[0117] The gas displacement method was used for testing. Samples were prepared by punching the first base membrane, the first diaphragm, the second base membrane, and the second diaphragm using molds (those skilled in the art can select molds of common sizes and shapes in the field according to factors such as the size and shape of the test object and the requirements of the test equipment). The true volume V0 of the sample was measured using a true density meter. The apparent volume V of the sample can be calculated by measuring the area and thickness of the sample. The percentage of the sample pore volume to the total volume is (V-V0) / V×100%, which gives the porosity of the first base membrane, the first diaphragm, the second base membrane, and the second diaphragm.

[0118] Puncture resistance of the first base membrane and the second base membrane:

[0119] The mass applied to a given needle to puncture the first and second base films of the embodiment or comparative example is denoted as the puncture resistance strength.

[0120] The testing method is as follows:

[0121] 1. Prepare the puncture clamp and blade before measurement;

[0122] 2. Cut the first and second base films separately with a blade. The samples should be circular specimens with a diameter of 100 mm. Note: The first and second base films must be free of defects and flaws.

[0123] 3. After checking that the high-speed rail tensile testing machine is clean, install the puncture clamps, place the first and second base films in the center of the clamps respectively, and close the top cover. Note: The sample must be laid flat without any wrinkles; the sample size must be larger than the puncture clamps, that is, the sample must be tightly pressed against the clamps on all sides.

[0124] 4. On the computer control panel of the high-speed rail tensile testing machine, set the test speed to 50 mm / min;

[0125] 5. Click "Start" to perform puncture tests sequentially until the base film sample is punctured. Stop puncturing and save the force-displacement curve. Each group should be tested in parallel at least three times. If three force-displacement curves show good repeatability, proceed to test the next group of samples. Note: The unit of force F should be N. Puncture resistance = force F / 9.8 × 10 3 The unit is gf, which is used to obtain the puncture resistance of the first base film and the second base film, respectively.

[0126] Thickness testing of the first and second base films:

[0127] The first base film was argon-ion polished to obtain its cross-section. The morphology of the cross-section along the thickness direction of the first base film was observed and scanned electron microscopy (SEM) images were taken using a field emission scanning electron microscope (Philips XL-30). The thickness of the first base film was then measured using the SEM. By replacing the first base film with a second base film, the thickness of the second base film could be measured.

[0128] DSC spectrum analysis of the first and second base films:

[0129] The DSC spectrum of 8 mg of the first base film was measured using a differential scanning spectroscopy (ASTM D3418-15) at a heating rate of 10 °C / min, within a temperature range of 60 °C to 190 °C. The DSC spectrum of the first base film was then obtained by replacing the first base film with the second base film. In the obtained DSC spectrum, the characteristic peak corresponding to the peak value between 128 °C and 134 °C was designated as characteristic peak A, and the characteristic peak corresponding to the peak value between 136 °C and 140 °C was designated as characteristic peak B.

[0130] Based on the DSC spectrum of the second base film, the ratio of the peak area of ​​characteristic peak A to characteristic peak B is calculated. The peak area ratio is also the mass ratio of the second resin material and the third resin material. After conversion, the mass percentage content of the second resin material and the third resin material can be obtained.

[0131] Weight-average molecular weight tests of the first, second, and third resin materials:

[0132] 1) Sample preparation: Dissolve 5g of the first base film to be tested in 100g of 1,2,4-trichlorobenzene at 150℃ to prepare a 2wt% solution.

[0133] 2) Gel column selection: The smaller the pore size of the gel column and the slower the flow rate, the larger the molecular weight of the polymer that can be separated. By selecting a suitable gel column, the first resin material can pass through the gel column at an appropriate flow rate;

[0134] 3) Sample loading and elution: The prepared sample solution is injected into the ultra-high performance polymer chromatograph (APC, ACQUITY), and the solution is pumped through the gel column at a certain flow rate. At the same time, the gel column is eluted with an appropriate eluent to elute the separated polymers sequentially.

[0135] 4) Detection and recording: During the elution process, the concentration of the effluent is detected by a detector and the change in concentration over time is recorded.

[0136] 5) Data processing and analysis: The detected concentration data is imported into computer software, and the concentration data is converted into molecular weight and its distribution information based on the standard substance (polyethylene) as a reference, so as to obtain the weight-average molecular weight of the first resin material.

[0137] The first base membrane is replaced with the second base membrane. By selecting a suitable gel column, the second resin material and the third resin material are passed through the gel column at a suitable flow rate, thereby separating the second resin material and the third resin material. By repeating the above steps, the weight-average molecular weight of the second resin material and the third resin material can be obtained respectively.

[0138] Hi-pot Excellence Test:

[0139] Perform Hi-pot testing on lithium-ion batteries and calculate the pass rate.

[0140] The test method is as follows: The leakage current generated by the lithium-ion battery prepared in the examples or comparative examples under a test voltage of 100V output from a high-voltage tester is detected, and then the resistance value is calculated as: test voltage / leakage current.

[0141] The calculated resistance value is compared with the set judgment resistor. In this application, the preset value of the judgment resistor is 5mΩ.

[0142] If the detected resistance value is greater than or equal to the preset value of 5mΩ, the tested product is deemed to have passed the test (OK).

[0143] If the detected resistance value is less than the preset value of 5mΩ, the test voltage is cut off instantly and the product under test is judged to fail the test (NG).

[0144] Each set of examples or comparative examples uses 100 lithium-ion batteries for testing. The number of lithium-ion batteries that pass the test is X1, and the pass rate is X1 / 100×100%, which is also known as the Hi-pot success rate.

[0145] K-value excellence test:

[0146] The lithium-ion batteries prepared in the examples or comparative examples were charged at a constant current of 0.5C to a voltage of 3.95V. When the lithium-ion batteries stored 60% of their charge (60% SOC), their voltage was measured at 25±5℃ and recorded as the first voltage. After standing for 48 hours, their voltage was measured again and recorded as the second voltage. The voltage drop per unit time was recorded as K, where K = (first voltage - second voltage) / standing time.

[0147] A K value less than 0.006 mV / h is considered passing the K value test (OK).

[0148] A K value greater than or equal to 0.006 mV / h is considered a failure of the K value test (NG).

[0149] For each comparative example and each embodiment, 100 lithium-ion batteries were tested, and the pass rate of the K-value test for each group was recorded.

[0150] The number of lithium-ion batteries that passed the test was X2, and the pass rate was X2 / 100×100%, which is also the K-value excellence rate.

[0151] The degree of lithium deposition on the negative electrode after 1000 cycles:

[0152] The lithium-ion battery was placed in an environment of 25°C and charged at a constant current of 0.5C to a voltage of 4.5V. Then, it was charged at a constant voltage of 4.5V to a cutoff current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.5C to a voltage of 3.0V, allowed to stand for 5 minutes. This constitutes one charge-discharge cycle. Then, the same steps were repeated for 1000 charge-discharge cycles.

[0153] Then charge at a constant current of 0.5C to 4.5V, and then charge at a constant voltage of 4.5V to the cutoff current of 0.05C, and let stand for 5 minutes; then disassemble the lithium-ion battery and observe the lithium deposition on the negative electrode, the lithium deposition on the surface of the negative electrode opposite to the first separator, and the lithium deposition on the surface of the negative electrode opposite to the second separator.

[0154] For the surface of the negative electrode sheet opposite to the first separator, if there is no white lithium metal deposition, it is recorded as "no lithium deposition"; if there is white lithium metal deposition and the lithium deposition area percentage is greater than 0 and less than 5%, it is recorded as "slight lithium deposition"; if there is white lithium metal deposition and the lithium deposition area percentage is greater than or equal to 5% and less than or equal to 10%, it is recorded as "moderate lithium deposition"; if there is white lithium metal deposition and the lithium deposition area percentage is greater than 10%, it is recorded as "heavy lithium deposition". Here, the lithium deposition area percentage is the percentage of the lithium deposition area relative to the surface area of ​​the negative electrode material layer of the negative electrode sheet opposite the first separator.

[0155] Similarly, for the surface of the negative electrode opposite the second separator, if there is no white lithium metal deposition, it is recorded as "no lithium deposition"; if there is white lithium metal deposition and the lithium deposition area percentage is greater than 0 and less than 5%, it is recorded as "slight lithium deposition"; if there is white lithium metal deposition and the lithium deposition area percentage is greater than or equal to 5% and less than or equal to 10%, it is recorded as "moderate lithium deposition"; and if there is white lithium metal deposition and the lithium deposition area percentage is greater than 10%, it is recorded as "heavy lithium deposition". Here, the lithium deposition area percentage is the percentage of the lithium deposition area relative to the surface area of ​​the negative electrode material layer of the negative electrode opposite the second separator.

[0156] For the entire negative electrode sheet, if there is no white lithium metal deposition, it is recorded as "no lithium deposition"; if there is white lithium metal deposition and the lithium deposition area percentage is greater than 0 and less than 5%, it is recorded as "slight lithium deposition"; if there is white lithium metal deposition and the lithium deposition area percentage is greater than or equal to 5% and less than or equal to 10%, it is recorded as "moderate lithium deposition"; if there is white lithium metal deposition and the lithium deposition area percentage is greater than 10%, it is recorded as "heavy lithium deposition". The lithium deposition area percentage is the percentage of the lithium deposition area relative to the total area of ​​the negative electrode material layer on both surfaces of the negative electrode sheet.

[0157] The lithium plating test is used to characterize the kinetic performance of lithium-ion batteries. The less lithium plating, the better the kinetic performance, and vice versa.

[0158] Cyclic performance test:

[0159] At 25°C, the lithium-ion battery is charged at a constant current of 3C to 4.5V, then charged at a constant voltage of 0.05C, and finally discharged at 0.7C to 3.0V, completing one cycle, which is recorded as the first cycle. The discharge capacity of the first cycle is recorded. This process is repeated for 1500 cycles, and the discharge capacity after each cycle is recorded. At cycles 50, 100, 150, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, and 1400, the following charging and discharging steps are performed: constant current charging at 0.5C to 4.5V, then constant voltage charging to 0.02C, and finally discharging at 0.2C to 3.0V.

[0160] Cycle capacity retention (%) = (Discharge capacity after N cycles / Discharge capacity in the first cycle) × 100%. Where N is a positive integer from 1 to 1500.

[0161] During the cycling process, the thickness of the lithium-ion battery was measured using a pressure plate thickness gauge, and the initial thickness was recorded. Then, after 50, 100, 150, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, and 1500 cycles, the thickness of the lithium-ion battery after Q cycles was recorded.

[0162] Cyclic expansion rate (%) = {(thickness after Q cycles - thickness of the first cycle) / thickness of the first cycle} × 100%. Where Q is 50, 100, 150, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500.

[0163] Example 1-1

[0164] <Preparation of the first diaphragm>

[0165] (1) The additive pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] and the solvent paraffin oil were mixed evenly at a mass ratio of 0.2:100 to obtain a mixed solution;

[0166] (2) The first resin material polyethylene and the mixed solution are mixed evenly at a mass ratio of 20:80, added to the extruder system, extruded through a T-die, cast, cooled, and cast into a film to obtain the first substrate; wherein, the weight average molecular weight of the first resin material polyethylene is Mw1=70W;

[0167] (3) The first substrate was stretched longitudinally by 7 times and transversely by 7 times, extracted with dichloromethane at 25°C for 0.5 h, and dried to obtain the first porous substrate;

[0168] (4) The first porous substrate is stretched longitudinally by 1.5 times and transversely by 1.5 times, heat-set at 115°C, and wound up to obtain the first base film with a thickness of 5 μm.

[0169] (5) Inorganic boehmite particles with a Dv50 of 1 μm and polyacrylate were mixed at a mass ratio of 90:10 and dissolved in deionized water to form a first ceramic layer slurry with a solid content of 50%. The inorganic coating slurry was then uniformly coated onto a surface of the first base film using a microgravure coating method and dried to obtain the first ceramic layer. The coating weight CW1 of the first ceramic layer was 12 mg / 5000 mm². 2 The weight-average molecular weight of polyacrylate is Mw4 = 40W.

[0170] (6) The first adhesive, polyvinylidene fluoride (PVDF), has a weight-average molecular weight of 8.5 × 10⁻⁶. 6The mixture was added to a stirrer, and then deionized water was added and stirred to adjust the viscosity of the slurry to 3500 mPa·s and the solid content to 75 wt%, thus obtaining the first adhesive layer slurry. The first adhesive layer slurry was then uniformly coated onto the surface of the first ceramic layer away from the first base film using screen printing, and dried. The coating process was then repeated on the other surface of the first base film to obtain the first diaphragm. The single-layer coating thickness of the first adhesive layer was 2 μm.

[0171] <Preparation of the Second Diaphragm>

[0172] (1) The second resin material polyethylene and the third resin material polyethylene are mixed evenly to form a mixed material; wherein, the weight average molecular weight of the second resin material polyethylene is Mw2=70W, and the mass percentage of the second resin material is W1 is 80%; the weight average molecular weight of the third resin material polyethylene is Mw3=150W, and the mass percentage of the third resin material is W2 is 20%.

[0173] (2) The additive pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] and the solvent paraffin oil were mixed evenly at a mass ratio of 0.2:100 to obtain a mixed solution;

[0174] (3) Mix the mixed materials and mixed solution evenly at a mass ratio of 20:80, add them to the extruder system, extrude them through a T-die, cast them, cool them, and cast them into a film to obtain the second substrate.

[0175] (4) The second substrate was stretched longitudinally by 6 times and laterally by 6 times, extracted with dichloromethane at 25°C for 0.5 h, and dried to obtain the second porous substrate;

[0176] (5) The second porous substrate is stretched longitudinally by 1.5 times and transversely by 1.5 times, heat-set at 125°C, and wound up to obtain the second base film with a thickness of 5μm.

[0177] (6) Inorganic boehmite particles with a Dv50 of 1 μm and polyacrylate were mixed at a mass ratio of 90:10 and dissolved in deionized water to form a second ceramic layer slurry with a solid content of 50 wt%. The second ceramic layer slurry was then uniformly coated onto one surface of the second base film using a microgravure coating method and dried to obtain the second ceramic layer. The coating weight CW2 of the second ceramic layer was 12 mg / 5000 mm². 2 The weight-average molecular weight of polyacrylate is Mw5 = 40W.

[0178] (7) The second adhesive, PVDF, has a weight-average molecular weight of 8.5 × 10⁻⁶. 6Then, deionized water was added and stirred to adjust the viscosity of the slurry to 3500 mPa·s and the solid content to 75 wt%, thus obtaining the second adhesive layer slurry. The second adhesive layer slurry was then uniformly coated onto one surface of the second ceramic layer away from the second base film using screen printing, and subsequently dried in an oven. The coating process was repeated on the other surface of the second base film to obtain the second diaphragm. The single-layer coating thickness of the second adhesive layer was 2 μm.

[0179] <Preparation of Negative Electrode Sheets>

[0180] Artificial graphite, silicon carbide, acetylene black, styrene-butadiene rubber, and sodium carboxymethyl cellulose (NCM) were mixed in a mass ratio of 90:6:1:1.5:1.5. Deionized water was added as a solvent to prepare a slurry with a solid content of 70%. The mixture was stirred evenly in a vacuum mixer to obtain the first negative electrode slurry, which was also used as the second negative electrode slurry. The first negative electrode slurry was uniformly coated onto one surface of an 8 μm thick copper foil and dried at 110°C to obtain a negative electrode sheet with a first negative electrode material layer coating thickness of 50 μm. The second negative electrode slurry was coated onto the other surface of the copper foil used as the negative electrode current collector. After drying, the second negative electrode material layer on this surface was 50 μm thick, resulting in a negative electrode sheet with a total thickness of 108 μm. The coated negative electrode sheet was cold-pressed and then cut into 74 mm × 867 mm dimensions for later use. The compaction density of the first negative electrode material layer was 1.735 g / cm³. 3 The length is 720mm, and the compaction density of the second negative electrode material layer is 1.735g / cm³. 3 It has a length of 680 mm. The mass ratio of silicon to carbon in the silicon-carbon compound is 2:8.

[0181] <Preparation of the positive electrode>

[0182] Lithium cobalt oxide, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 94:3:3, and NMP was added as a solvent to prepare a slurry with a solid content of 75%. The mixture was then stirred evenly in a vacuum mixer to obtain the positive electrode slurry. The positive electrode slurry was uniformly coated onto one surface of a 12 μm thick aluminum foil and dried at 90°C to obtain a negative electrode sheet with a single-sided positive electrode material layer coating thickness of 55 μm. The positive electrode slurry was coated onto the other surface of the positive current collector aluminum foil, and after drying, the positive electrode material layer coating on this surface was also 55 μm thick, resulting in a positive electrode sheet with a total thickness of 122 μm. Cold pressing yielded a positive electrode sheet with a single-sided positive electrode material layer thickness of 122 μm. The coated positive electrode sheet was then cold-pressed, cut into 70 mm × 800 mm dimensions, and had tabs welded on for later use. The compaction density of the positive electrode material layer was 4.23 g / cm³. 3 .

[0183] <Preparation of Electrolyte>

[0184] Under conditions with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) were mixed in a mass ratio of 20:30:20:28:2. Lithium hexafluorophosphate (LiPF6) was then added to the non-aqueous organic solvents, dissolved, and mixed thoroughly to obtain the electrolyte. Based on the total mass of the electrolyte, the mass content of LiPF6 was 8%, with the remainder being the base solvent.

[0185] <Preparation of Lithium-ion Batteries>

[0186] The prepared positive electrode, first separator, negative electrode, and second separator are stacked in sequence and then wound to obtain an electrode assembly. Referring specifically to Figures 1 and 2, the corner segment of the first positive electrode is adjacent to the corner segment of the first negative electrode material layer, and the corner segment of the first positive electrode is further away from the winding center of the electrode assembly than the corner segment of the first negative electrode material layer. The first separator is located between the corner segment of the first positive electrode and the first negative electrode material layer, and the second separator is adjacent to the second negative electrode material layer. Furthermore, the first ceramic layer of the first separator faces the positive electrode, and the second ceramic layer of the second separator faces the positive electrode. In the same negative electrode layer, the first negative electrode material layer is further away from the winding center of the electrode assembly than the second negative electrode layer. This structure is denoted as Structure A. The electrode assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 80°C. A prepared electrolyte is injected, and the lithium-ion battery is obtained through vacuum sealing, settling, formation, and shaping processes.

[0187] Examples 1-2 to Examples 1-5

[0188] Except for adjusting the weight-average molecular weight of the first resin material according to Table 1, and adjusting the stretching ratio of the first base film in transverse stretching, longitudinal stretching, secondary transverse stretching, and secondary longitudinal stretching so that the porosity and puncture resistance of the first base film are as shown in Table 1, the rest is the same as in Example 1-1.

[0189] Examples 1-6 to Examples 1-9

[0190] Except for adjusting the mass percentage of the second and third resin materials according to Table 1, and adjusting the stretching ratio of the second base film in transverse stretching, longitudinal stretching, secondary transverse stretching, and secondary longitudinal stretching to make the puncture resistance and porosity of the second base film as shown in Table 1, the rest is the same as in Example 1-1.

[0191] Examples 1-10

[0192] Except for adjusting the <Preparation of Lithium-ion Batteries> according to the following steps, the rest is the same as in Example 1-1.

[0193] <Preparation of Lithium-ion Batteries>

[0194] The prepared positive electrode, second separator, negative electrode, and first separator are stacked in sequence and then wound to obtain an electrode assembly. Referring to Figures 3 and 4, the corner segment of the second positive electrode is adjacent to the corner segment of the second negative electrode material layer, and the corner segment of the second positive electrode is closer to the winding center of the electrode assembly than the corner segment of the second negative electrode material layer. The first separator is located between the corner segments of the second positive electrode and the second negative electrode material layer, and the second separator is located on the side of the positive electrode away from the first separator. Furthermore, the first ceramic layer of the first separator is close to the positive electrode, and the second ceramic layer of the second separator is close to the positive electrode. In the same layer of negative electrode, the first negative electrode material layer is farther from the winding center of the electrode assembly than the second negative electrode material layer. This structure is denoted as Structure B. The electrode assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 80°C. A prepared electrolyte is injected, and the lithium-ion battery is obtained through vacuum sealing, settling, formation, and shaping processes.

[0195] Examples 1-11 to Examples 1-17

[0196] Except for adjusting the relevant parameters according to Table 1, and adjusting the stretching ratio of the first base film in transverse stretching, longitudinal stretching, secondary transverse stretching, and secondary longitudinal stretching to make the porosity and puncture resistance of the first base film as shown in Table 1, the rest is the same as in Example 1-1.

[0197] Examples 2-1 to 2-13

[0198] Except for adjusting the relevant parameters according to Table 2, and adjusting the stretching ratio of the second base film in transverse stretching, longitudinal stretching, secondary transverse stretching, and secondary longitudinal stretching to make the porosity and puncture resistance of the second base film as shown in Table 2, the rest is the same as in Example 1-1.

[0199] Comparative Example 1

[0200] Except for replacing the second base film with the first base film, everything else is the same as in Example 1-1.

[0201] Comparative Example 2

[0202] Except for replacing the first base film with the second base film, the rest is the same as in Example 1-1.

[0203] Comparative Examples 3 to 4

[0204] Except for adjusting the weight-average molecular weight of the first resin material according to Table 1, and adjusting the stretching ratio of the first base film in transverse stretching, longitudinal stretching, secondary transverse stretching, and secondary longitudinal stretching to make the porosity and puncture resistance of the first base film as shown in Table 1, the rest is the same as in Example 1-1.

[0205] Comparative Example 5

[0206] Except for adjusting the weight-average molecular weight of the third resin material to 90W and adjusting the stretching ratio of the second base film in transverse stretching, longitudinal stretching, secondary transverse stretching, and secondary longitudinal stretching to make the porosity and puncture resistance of the second base film as shown in Table 1, the rest is the same as in Example 1-1.

[0207] Comparative Example 6

[0208] Except for adjusting the weight-average molecular weight of the third resin material to 206W and adjusting the stretching ratio of the second base film in transverse stretching, longitudinal stretching, secondary transverse stretching, and secondary longitudinal stretching to make the porosity and puncture resistance of the second base film as shown in Table 1, the rest is the same as in Example 1-1.

[0209] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1 and 2.

[0210] The porosity of the first base film and the puncture resistance of the second base film affect the kinetic performance and manufacturing yield of the secondary battery. As can be seen from Examples 1-1 to 1-17 and Comparative Examples 1 to 6, when the porosity of the first base film and the puncture resistance of the second base film are within the range of this application, the lithium-ion battery exhibits higher Hi-pot yield and K-value yield. After 1000 cycles, the degree of lithium plating on the negative electrode sheet, the surface of the negative electrode sheet opposite the first separator, and the surface of the negative electrode sheet opposite the second separator is lower, indicating that the lithium-ion battery prepared in this application can balance manufacturing yield and kinetic performance. As can be seen from Examples 1-1 to 1-5, the increased porosity of the first base film improves the degree of lithium deposition on the negative electrode and the surface of the negative electrode opposite to the first separator after 1000 cycles, indicating that the kinetic performance of the lithium-ion battery is improved. However, due to the increased porosity, the contact probability between the first base film and the negative electrode material layer increases, affecting the Hi-pot yield and K-value yield of the lithium-ion battery. Similarly, in Comparative Example 4, the porosity of the first base film is higher than the limit specified in this application, affecting the Hi-pot yield and K-value yield of the lithium-ion battery, indicating that the manufacturing yield of the lithium-ion battery is poor. In Comparative Example 6, the puncture resistance of the second base film is higher than the limit specified in this application, resulting in a higher degree of lithium deposition on the surface of the negative electrode and the surface of the negative electrode opposite to the second separator after 1000 cycles, indicating that the kinetic performance of the lithium-ion battery is affected.

[0211] The puncture resistance of the second base film is affected by the mass percentage content of the second resin material and the mass percentage content of the third resin material. As can be seen from Examples 1-1, 1-6 to 1-9, when the mass percentage content of the second resin material and the mass percentage content of the third resin material are within the range of this application, the puncture resistance of the second base film is within the range of this application.

[0212] As can be seen from Examples 1-1, 1-6 to 1-9, when the puncture resistance of the second base film increases, the manufacturing yield of the lithium-ion battery improves. Since the porosity of the first and second base films does not change, the degree of lithium deposition on the negative electrode sheet, the surface of the negative electrode sheet opposite to the first separator, and the surface of the negative electrode sheet opposite to the second separator does not change significantly after 1000 cycles, indicating that the kinetic performance of the lithium-ion battery is less affected. As can be seen from Examples 1-1, 1-12 to 1-13, when the puncture resistance of the first base film increases, the manufacturing yield of the lithium-ion battery improves. Since the porosity of the first and second base films does not change, the degree of lithium deposition on the negative electrode sheet, the surface of the negative electrode sheet opposite to the first separator, and the surface of the negative electrode sheet opposite to the second separator does not change significantly after 1000 cycles, indicating that the kinetic performance of the lithium-ion battery is less affected.

[0213] The structure of the electrode assembly affects the kinetic performance and manufacturing yield of the secondary battery. As seen in Examples 1-1 and 1-10, the first separator is located between the corner segment of the first positive electrode and the corner segment of the first negative electrode material layer. Compared to when the first separator is located between the corner segments of the second positive electrode and the second negative electrode material layer, the degree of lithium plating on the first negative electrode material layer is reduced, and the interface condition on one side of the first negative electrode material layer is optimized. This is because the corner segment of the first positive electrode is adjacent to a corner segment of the first negative electrode material layer and far from the winding center of the electrode assembly. In this case, the winding radius of the positive electrode material layer in the positive electrode is larger than that of the first negative electrode material layer, resulting in a smaller positive-to-negative electrode ratio (Cell Balance, CB, the ratio of negative electrode capacity per unit area to positive electrode capacity per unit area). This makes it easier for interface problems to occur, leading to lithium plating. Therefore, a sufficient amount of electrolyte is required to transport active ions. Simultaneously, the corner area of ​​the winding structure itself is prone to insufficient electrolyte or even electrolyte bridging, which further exacerbates the interface problems. Therefore, this application provides a first separator containing a first base film between the corner section of the first positive electrode and the corner section of the first negative electrode material layer. The first base film with higher porosity has a higher electrolyte retention capacity, which is beneficial to improving the problem of insufficient electrolyte in the corner area and also beneficial to the transport of active ions, thereby improving the interface problem and thus improving the lithium plating problem of the secondary battery, that is, improving the kinetic performance.

[0214] The material of the first base film affects the kinetic performance and manufacturing yield of the secondary battery. As can be seen from Examples 1-1 and 1-11, when the first resin material is within the scope of this application, the lithium-ion battery has a high Hi-pot yield and K-value yield, and after 1000 cycles, the degree of lithium plating on the negative electrode sheet, the surface of the negative electrode sheet opposite to the first separator, and the surface of the negative electrode sheet opposite to the second separator is low, indicating that the lithium-ion battery prepared in this application can balance manufacturing yield and kinetic performance.

[0215] The puncture resistance of the first base film is affected by the weight-average molecular weight of the first resin material. As can be seen from Examples 1-1, 1-12 to 1-13, when the weight-average molecular weight of the first resin material and the puncture resistance of the first base film are both within the range of this application, the lithium-ion battery exhibits high Hi-pot yield and K-value yield. After 1000 cycles, the degree of lithium plating on the negative electrode plate, the surface of the negative electrode plate opposite the first separator, and the surface of the negative electrode plate opposite the second separator is low, indicating that the lithium-ion battery prepared in this application can balance manufacturing yield and kinetic performance. When the weight-average molecular weight of the first resin material is higher than the range of this application, although the manufacturing yield and kinetic performance of the secondary battery are good, the excessively high weight-average molecular weight of the first resin material affects the pore-closing temperature and rupture temperature of the obtained first separator, thus affecting the thermal performance of the secondary battery.

[0216] The thickness of the first base film affects the kinetic performance and manufacturing yield of the secondary battery. As can be seen from Examples 1-1, 1-14 to 1-17, when the thickness of the first base film is within the range specified in this application, the lithium-ion battery exhibits higher Hi-pot yield and K-value yield. After 1000 cycles, the degree of lithium plating on the negative electrode sheet, the surface of the negative electrode sheet opposite the first separator, and the surface of the negative electrode sheet opposite the second separator is lower, indicating that the lithium-ion battery prepared in this application can balance manufacturing yield and kinetic performance. When the thickness of the first base film exceeds the range specified in this application, the kinetic performance of the prepared lithium-ion battery is affected; when the thickness of the first base film is below the range specified in this application, the manufacturing yield of the prepared lithium-ion battery is affected. The porosity of the first separator is affected by the porosity of the first base film. As can be seen from Examples 1-1 to 1-5, when the porosity of the first base film is within the range specified in this application, the porosity of the first separator is also within the range specified in this application.

[0217] As can be seen from Figures 6 and 7, the lithium-ion battery prepared in Example 1-1 has a lower cycle expansion rate and a higher cycle capacity retention rate than the lithium-ion battery prepared in Comparative Example 2 after 1500 cycles. This indicates that the lithium-ion battery prepared in the examples is beneficial to improving lithium-ion transport, that is, improving the kinetic performance of the secondary battery.

[0218] The presence of characteristic peak A in the DSC spectrum of the first base film is affected by the type and weight-average molecular weight of the first resin material. As can be seen from Examples 1-1 to 1-17, when the type and weight-average molecular weight of the first resin material are within the range of this application, the DSC spectrum of the prepared first base film always contains characteristic peak A. Specifically, as shown in Figure 8, the DSC spectrum of the first base film in Example 1-1 shows a characteristic peak between 128°C and 134°C, i.e., characteristic peak A is present.

[0219] The presence of characteristic peaks A and B in the DSC spectrum of the second base film is influenced by the types and weight-average molecular weights of the second and third resin materials. As can be seen from Examples 1-1 to 1-17, when the types and weight-average molecular weights of the second and third resin materials are within the range of this application, the DSC spectra of the prepared second base film all possess characteristic peaks A and B. Specifically, as shown in Figure 9, characteristic peaks, i.e., characteristic peaks A and B, are present in the DSC spectrum of the second base film at 128°C to 134°C and 136°C to 140°C.

[0220] The material of the second base film affects the kinetic performance and manufacturing yield of the secondary battery. As can be seen from Examples 1-1, 2-1, and 2-4, when the second and third resin materials are within the scope of this application, the lithium-ion battery exhibits higher Hi-pot yield and K-value yield. After 1000 cycles, the degree of lithium plating on the negative electrode sheet, the surface of the negative electrode sheet opposite to the first separator, and the surface of the negative electrode sheet opposite to the second separator is lower, indicating that the lithium-ion battery prepared in this application can balance manufacturing yield and kinetic performance.

[0221] The puncture resistance of the second base film is affected by the weight-average molecular weight of the second resin material and the weight-average molecular weight of the third resin material. As can be seen from Examples 1-1, 2-2 to 2-3, and 2-5 to 2-6, when the weight-average molecular weights of the second and third resin materials are within the range of this application, the puncture resistance of the second base film is also within the range of this application. When the weight-average molecular weights of the second and third resin materials are higher than the range of this application, although the manufacturing yield and kinetic performance of the secondary battery are better, the excessively high weight-average molecular weights of the second and third resin materials affect the pore-closing temperature and rupture temperature of the resulting second separator, thus affecting the thermal performance of the secondary battery.

[0222] The porosity of the second base film affects the kinetic performance and manufacturing yield of the secondary battery. As can be seen from Examples 1-1, 2-7 to 2-9, when the porosity of the second base film increases, the degree of lithium plating on the surface of the negative electrode and the negative electrode opposite to the second separator is improved after 1000 cycles, indicating that the kinetic performance of the lithium-ion battery is improved.

[0223] The thickness of the second base film affects the kinetic performance and manufacturing yield of the secondary battery. As can be seen from Examples 1-1, 2-10 to 2-13, when the thickness of the second base film is within the range specified in this application, the lithium-ion battery exhibits higher Hi-pot yield and K-value yield. After 1000 cycles, the degree of lithium plating on the negative electrode sheet, the surface of the negative electrode sheet opposite the first separator, and the surface of the negative electrode sheet opposite the second separator is lower, indicating that the lithium-ion battery prepared in this application can balance manufacturing yield and kinetic performance. When the thickness of the second base film exceeds the range specified in this application, the kinetic performance of the prepared lithium-ion battery is affected; when the thickness of the second base film is below the range specified in this application, the manufacturing yield of the prepared lithium-ion battery is affected.

[0224] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0225] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A secondary battery comprising a wound electrode assembly, the electrode assembly comprising a positive electrode, a negative electrode, a first separator, and a second separator, wherein at least a portion of the negative electrode is located between the first separator and the second separator; The first diaphragm includes a first base membrane, and the second diaphragm includes a second base membrane. The porosity n1 of the first base membrane is greater than the porosity n2 of the second base membrane, and the puncture resistance F2 of the second base membrane is greater than the puncture resistance F1 of the first base membrane. 30%≤n1≤60%, 300gf≤F2≤650gf.

2. The secondary battery according to claim 1, wherein, The electrode assembly includes a flat region and a corner region, and the negative electrode sheet includes a negative electrode current collector and a first negative electrode material layer and a second negative electrode material layer located on both sides of the thickness direction of the negative electrode current collector. In the corner region, a first positive electrode corner segment is adjacent to a first negative electrode material layer corner segment. The first positive electrode corner segment is farther away from the winding center of the electrode assembly than the first negative electrode material layer corner segment. The first separator is located between the first positive electrode corner segment and the first negative electrode material layer corner segment.

3. The secondary battery according to claim 1, wherein, 40% ≤ n1 ≤ 50%, and / or, 400gf ≤ F2 ≤ 500gf.

4. The secondary battery according to claim 1, wherein, The first base film includes a first resin material, wherein the weight-average molecular weight of the first resin material is 50W to 90W; The second base film comprises a second resin material and a third resin material, wherein the weight-average molecular weight of the second resin material is 50W to 90W, and the weight-average molecular weight of the third resin material is 100W to 200W.

5. The secondary battery according to claim 4, wherein, Based on the quality of the second base film, the mass percentage W1 of the second resin material is 70% to 90%, and the mass percentage W2 of the third resin material is 10% to 30%.

6. The secondary battery according to claim 4, wherein, The first resin material, the second resin material, and the third resin material are each independently selected from at least one of polyethylene, polypropylene, polyimide, polyethyleneimine, or polyethylene terephthalate.

7. The secondary battery according to any one of claims 1 to 6, wherein, In the differential scanning calorimetry spectrum of the first base film, a characteristic peak exists between 128°C and 134°C.

8. The secondary battery according to any one of claims 1 to 6, wherein, In the differential scanning calorimetry spectrum of the second base film, characteristic peaks exist at 128℃ to 134℃ and 136℃ to 140℃.

9. The secondary battery according to any one of claims 1 to 6, wherein, 10% ≤ n2 ≤ 30%, 200gf ≤ F1 ≤ 300gf.

10. The secondary battery according to claim 9, wherein, 15％≤n2≤30％。 11. The secondary battery according to any one of claims 1 to 6, wherein, The thickness of the first base film and the second base film are each independently between 4 μm and 7 μm.

12. The secondary battery according to any one of claims 1 to 6, wherein, The first diaphragm further includes a first ceramic layer, and the porosity of the first diaphragm is n3, 40% ≤ n3 ≤ 70%.

13. The secondary battery according to claim 12, wherein, The coating weight CW1 of the first ceramic layer is 9 mg / 5000 mm. 2 Up to 15mg / 5000mm 2 .

14. The secondary battery according to claim 12, wherein, The first ceramic layer includes first ceramic particles, which include at least one of alumina, boehmite, silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide.

15. The secondary battery according to claim 2, wherein, The first negative electrode material layer includes a first negative electrode material, the second negative electrode material layer includes a second negative electrode material, and the first negative electrode material and / or the second negative electrode material includes silicon material.

16. The secondary battery according to claim 15, wherein, The silicon material includes at least one of elemental silicon, silicon carbide, silicon oxide, or silicon alloy.

17. An electronic device comprising a secondary battery as claimed in any one of claims 1 to 16.

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