Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises an electrode assembly of a winding structure, the electrode assembly comprises a positive pole piece, a negative pole piece, a first diaphragm and a second diaphragm, and at least part of the negative pole piece is located between the first diaphragm and the second diaphragm; the first diaphragm comprises a first base diaphragm, the second diaphragm comprises a second base diaphragm, the puncture resistance F1 of the first base diaphragm is larger than the puncture resistance F2 of the second base diaphragm, the hole closing temperature T12 of the second base diaphragm is smaller than the hole closing temperature T11 of the first base diaphragm, the diaphragm breaking temperature T22 of the second base diaphragm is larger than the diaphragm breaking temperature T21 of the first base diaphragm, F1 is larger than or equal to 300 gf and smaller than or equal to 650 gf, T12 is smaller than or equal to 140 DEG C, and T22 is larger than or equal to 150 DEG C. According to the secondary battery provided by the invention, the manufacturing yield and the high-temperature hot box performance can be considered at the same time.

Description

Technical Field

[0001] The present application relates to the field of electrochemistry technology, and particularly to a secondary battery and an electronic device. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, have the advantages of high energy density, long cycle life, low self-discharge rate, environmental protection and no pollution, and have been widely used in the fields of aviation, aerospace, navigation, electric vehicles, etc. The performance of the separator in a lithium-ion battery determines the interface structure, internal resistance, etc. of the lithium-ion battery, and directly affects the capacity, cycle and safety performance of the lithium-ion battery. A separator with excellent performance plays an important role in improving the comprehensive performance of the lithium-ion battery. At present, the two separators in a secondary battery are usually the same separator, so it is difficult to balance various performances, for example, it is difficult to take into account both the manufacturing yield and the high-temperature hot box performance. Summary of the Invention

[0003] The purpose of the present application is to provide a secondary battery and an electronic device to take into account both the kinetic performance and the high-temperature hot box performance.

[0004] It should be noted that in the summary of the invention of the present application, a lithium-ion battery is used as an example of the secondary battery to explain the present application, but the secondary battery of the present application is not limited to the lithium-ion battery. The specific technical solutions are as follows:

[0005] The first aspect of the present application provides a secondary battery, which includes a wound electrode assembly. The electrode assembly includes a positive electrode tab, a negative electrode tab, a first separator and a second separator. At least part of the negative electrode tab is located between the first separator and the second separator; the first separator includes a first base film, the second separator includes a second base film, the puncture resistance F1 of the first base film is greater than the puncture resistance F2 of the second base film, the closure temperature T12 of the second base film is less than the closure temperature T11 of the first base film, and the film breakage temperature T22 of the second base film is greater than the film breakage temperature T21 of the first base film, where 300 gf ≤ F1 ≤ 650 gf, T12 ≤ 140 °C, T22 ≥ 150 °C. In some embodiments of the present application, 400 gf ≤ F1 ≤ 500 gf. In some embodiments of the present application, 120 °C ≤ T12 ≤ 140 °C. In some embodiments of the present application, 160 °C ≤ T22 ≤ 180 °C. Using the first base film with relatively high puncture strength and matching the second base film with relatively low closure temperature and relatively high film breakage temperature, and regulating the puncture resistance of the first base film and the closure temperature and film breakage temperature of the second base film within the above ranges is beneficial to taking into account both the manufacturing yield and the high-temperature hot box performance of the secondary battery.

[0006] In some embodiments of the present application, the electrode assembly includes a flat region and a corner region. In the corner region, a first positive electrode tab corner segment is adjacent to a second separator corner segment, and the first positive electrode tab corner segment is closer to the winding center of the electrode assembly than the second separator corner segment. A first positive electrode tab corner segment is adjacent to the corner segment of the first separator and is closer to the winding center. The winding radius of the corner segment of the first separator is slightly larger than that of the positive electrode tab corner segment, and heat can be effectively transferred, reducing the risk of thermal runaway of the secondary battery. At the same time, the first separator includes a second base film with a relatively low closed pore temperature and a relatively high film rupture temperature. When the secondary battery has a risk of thermal runaway at high temperature, the second separator can close the pores in time to hinder the transmission of active ions such as lithium ions, and the relatively high film rupture temperature is beneficial to reducing the short circuit between the positive and negative electrodes, further improving the high-temperature heat box performance of the secondary battery.

[0007] In some embodiments of the present application, the first base film includes a first resin material and a second resin material. The heat of fusion enthalpy H1 of the first resin material is 185 J / g to 195 J / g, and the melt flow rate MFR1 is 0.4 g / 10 min to 0.6 g / 10 min. The heat of fusion enthalpy H2 of the second resin material is 130 J / g to 180 J / g, and the melt flow rate MFR2 is 0.1 g / 10 min to 1.0 g / 10 min. The second base film includes a third resin material, a fourth resin material, and a fifth resin material. The heat of fusion enthalpy H3 of the third resin material is 140 J / g to 150 J / g, and the melt flow rate MFR3 is 6 g / 10 min to 14 g / 10 min. The heat of fusion enthalpy H4 of the fourth resin material is 185 J / g to 195 J / g, and the melt flow rate MFR4 is 0.4 g / 10 min to 0.6 g / 10 min. The heat of fusion enthalpy H5 of the fifth resin material is 130 J / g to 180 J / g, and the melt flow rate MFR5 is 0.1 g / 10 min to 100 g / 10 min. With the heat of fusion enthalpy and melt flow rate of the first resin material, the second resin material, the third resin material, the fourth resin material, and the fifth resin material within the above ranges, the obtained first base film and second base film have appropriate puncture resistance, closed pore temperature, and film rupture temperature. Thus, while improving the manufacturing yield, the first separator can also take into account the high-temperature heat box performance of the secondary battery, and the second separator is beneficial to improving the high-temperature heat box performance of the secondary battery.

[0008] In some embodiments of the present application, based on the mass of the first base film, the mass percentage content W1 of the first resin material is 70% to 90%, and the mass percentage content W2 of the second resin material is 10% to 30%. By adjusting the mass percentage contents of the first resin material and the second resin material within the scope of the present application, the obtained first base film has appropriate puncture resistance, closure temperature and film breakage temperature, so that while improving the manufacturing yield, the first separator can also take into account the high-temperature heat box performance of the secondary battery.

[0009] In some embodiments of the present application, the weight-average molecular weight of the first resin material is 50W to 90W, and the weight-average molecular weight of the second resin material is 100W to 200W. By regulating the weight-average molecular weights of the first resin material and the second resin material within the scope of the present application, the obtained first base film has appropriate puncture resistance, closure temperature and film breakage temperature, so that while improving the manufacturing yield, the first separator can also take into account the high-temperature heat box performance of the secondary battery.

[0010] In some embodiments of the present application, based on the mass of the second base film, the mass percentage content W3 of the third resin material is 5% to 15%, the mass percentage content W4 of the fourth resin material is 83% to 93%, and the mass percentage content W5 of the fifth resin material is 1% to 3%.

[0011] In some embodiments of the present application, the weight-average molecular weight of the third resin material is 20W to 40W, the weight-average molecular weight of the fourth resin material is 50W to 90W, and the weight-average molecular weight of the fifth resin material is 5W to 50W. When the mass percentage contents of the third resin material, the fourth resin material and the fifth resin material are within the above ranges, the obtained second base film has appropriate puncture resistance, closure temperature and film breakage temperature, so that the second separator is beneficial to improving the high-temperature heat box performance of the secondary battery and taking into account the manufacturing yield.

[0012] In some embodiments of the present application, the first resin material, the second resin material, the third resin material, the fourth resin material and the fifth resin material are each independently selected from at least one of polyethylene, polypropylene, polyimide, polyethyleneimine or polyethylene terephthalate. When the types of the first resin material, the second resin material, the third resin material, the fourth resin material and the fifth resin material are within the above ranges, the obtained first base film and second base film have appropriate puncture resistance, closure temperature and film breakage temperature, so that the first separator and the second separator are beneficial to improving the high-temperature heat box performance of the secondary battery and taking into account the manufacturing yield.

[0013] In some embodiments of the present application, the fifth resin material is different from the third resin material and the fourth resin material in type, which is beneficial to improving the high-temperature heat box performance of the secondary battery.

[0014] In some embodiments of the present application, in the differential scanning calorimetry test spectrum of the first base film, characteristic peaks exist at 128°C to 134°C and 136°C to 140°C.

[0015] In some embodiments of the present application, in the differential scanning calorimetry test spectrum of the second base film, characteristic peaks exist at 120°C to 126°C, 128°C to 134°C, and 150°C to 160°C.

[0016] In some embodiments of the present application, the secondary battery satisfies at least one of the following features:

[0017] (1) 200gf ≤ F2 ≤ 300gf;

[0018] (2) 145℃≤T11≤165℃;

[0019] (3)150℃≤T21≤180℃.

[0020] The secondary battery satisfies at least one of the above characteristics, which is beneficial for taking into account both the high-temperature hot box performance and the manufacturing efficiency of the secondary battery.

[0021] In some embodiments of the present application, the thickness of the first base film and the second base film are independently 4 μm to 7 μm. The thickness of the first base film and the second base film within the above range is also conducive to taking into account the energy density of the secondary battery.

[0022] In some embodiments of the present application, the negative electrode plate includes a negative electrode material layer, the negative electrode material layer includes a negative electrode material, and the negative electrode material includes a silicon material, which is beneficial for taking into account the energy density, high temperature hot box performance and manufacturing efficiency of the secondary battery.

[0023] In some embodiments of the present application, the silicon material includes at least one of silicon element, silicon carbon compound, silicon oxygen compound or silicon alloy, which is beneficial to take into account the energy density, high temperature hot box performance and manufacturing efficiency of the secondary battery.

[0024] A second aspect of the present application provides an electronic device, which includes the secondary battery in any one of the aforementioned embodiments.

[0025] Beneficial effects of this application:

[0026] The present application provides a secondary battery and an electronic device. The secondary battery includes a wound electrode assembly, and the electrode assembly includes a positive electrode tab, a negative electrode tab, a first separator, and a second separator. At least a part of the negative electrode tab is 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. The puncture resistance F1 of the first base film is greater than the puncture resistance F2 of the second base film. The closing temperature T12 of the second base film is less than the closing temperature T11 of the first base film. The breakdown temperature T22 of the second base film is greater than the breakdown temperature T21 of the first base film. Among them, 300 gf ≤ F1 ≤ 650 gf, T12 ≤ 140 °C, and T22 ≥ 150 °C. Using the first base film with relatively high puncture resistance and the second base film with relatively low closing temperature and relatively high breakdown temperature, and controlling the puncture resistance of the first base film and the closing temperature and breakdown temperature of the second base film within the above ranges is beneficial to taking into account the manufacturing yield and high-temperature hot box performance of the secondary battery.

[0027] Of course, it is not necessary for any product or method implementing the present application to achieve all the above advantages simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application, and those of ordinary skill in the art can also obtain other embodiments based on these drawings.

[0029] Figure 1 It is a schematic structural diagram of an electrode assembly in an implementation scheme of the present application;

[0030] Figure 2 It is Figure 1 a partial enlarged view of part A in

[0031] Figure 3 It is a schematic structural diagram of an electrode assembly in another implementation scheme of the present application;

[0032] Figure 4 It is Figure 3 a partial enlarged view of part B in

[0033] Figure 5 It is a differential scanning calorimetry test spectrum of the first base film in Example 1-1;

[0034] Figure 6 It is a differential scanning calorimetry test spectrum of the second base film in Example 1-1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] Next, in combination with the embodiments of the present application and the accompanying drawings, the technical solutions in the present application will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0036] It should be noted that in the specific implementation manners of the present application, a lithium-ion battery is taken as an example of a secondary battery to explain the present application. However, the secondary battery of the present application is not limited to lithium-ion batteries.

[0037] The first aspect of the present application provides a secondary battery, which includes a wound electrode assembly. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, a first separator, and a second separator. At least a part of the negative electrode sheet is located between the first separator and the second separator. The first separator includes a first base film, the second separator includes a second base film, the puncture resistance F1 of the first base film is greater than the puncture resistance F2 of the second base film, the closed pore temperature T12 of the second base film is less than the closed pore temperature T11 of the first base film, and the film break temperature T22 of the second base film is greater than the film break temperature T21 of the first base film.

[0038] In some embodiments of the present application, 300 gf ≤ F1 ≤ 650 gf. In some embodiments of the present application, 300 gf ≤ F1 ≤ 500 gf. For example, the puncture resistance F1 of the first base film can be 300 gf, 350 gf, 400 gf, 450 gf, 500 gf, 550 gf, 600 gf, 650 gf, or a range composed of any two of these values. When the puncture resistance of the first base film is too small, for example, less than 300 gf, the puncture resistance of the first base film is too low, and hard particles in the negative electrode material layer may pierce the separator, posing a safety risk and affecting the manufacturing yield of the secondary battery. When the puncture resistance of the first separator increases, the tendency of the separator to undergo physical short circuit during the preparation of the secondary battery will decrease. However, if the puncture resistance is too high, for example, greater than 650 gf, it will affect the closed pore performance of the separator, resulting in poor high-temperature hot box performance. Therefore, regulating the puncture resistance of the first base film within the scope of the present application can improve the puncture resistance of the first separator and take into account the closed pore performance, thereby improving the manufacturing yield of the secondary battery, such as the Hi-pot yield and the K-value yield, as well as the high-temperature hot box performance of the secondary battery.

[0039] In some embodiments of the present application, T12 ≤ 140 °C. In some embodiments of the present application, 120 °C ≤ T12 ≤ 140 °C. For example, the closed pore temperature T12 of the second base film can be 120 °C, 121 °C, 122 °C, 123 °C, 124 °C, 125 °C, 126 °C, 127 °C, 128 °C, 129 °C, 130 °C, 131 °C, 132 °C, 133 °C, 134 °C, 135 °C, 136 °C, 137 °C, 138 °C, 139 °C, 140 °C or a range composed of any two of these values. In some embodiments of the present application, T22 ≥ 150 °C. In some embodiments of the present application, 160 °C ≤ T22 ≤ 180 °C. For example, the film breaking temperature T22 of the second base film can be 150 °C, 151 °C, 152 °C, 153 °C, 154 °C, 155 °C, 156 °C, 157 °C, 158 °C, 159 °C, 160 °C, 161 °C, 162 °C, 163 °C, 164 °C, 165 °C, 166 °C, 167 °C, 168 °C, 169 °C, 170 °C, 171 °C, 172 °C, 173 °C, 174 °C, 175 °C, 176 °C, 177 °C, 178 °C, 179 °C, 180 °C or a range composed of any two of these values. When the closed pore temperature of the second base film is too low or the film breaking temperature is too high, for example, T12 is greater than 140 °C or T22 is less than 150 °C, when the secondary battery has a risk of thermal runaway at high temperature, the second base film cannot close the pores in time to hinder the transport of active ions, and it is also prone to breakage, causing a short circuit between the positive and negative electrodes, which will increase the generation of heat, increase the risk of thermal runaway, and affect the high-temperature heat box performance of the secondary battery. Therefore, by controlling the closed pore temperature and film breaking temperature of the second base film within the above ranges, it is beneficial to improve the high-temperature heat box performance of the secondary battery.

[0040] Therefore, using the first base film with relatively high puncture strength and the second base film with relatively low closed pore temperature and relatively high film breaking temperature, and controlling the puncture resistance of the first base film and the closed pore temperature and film breaking temperature of the second base film within the above ranges, is beneficial to balance the manufacturing yield and high-temperature heat box performance of the secondary battery.

[0041] In one embodiment of the present application, as Figures 1 to 4 shown, the electrode assembly 01 includes a flat region 011 and a corner region 012. The positive electrode sheet 10 includes a positive electrode current collector 110 and positive electrode material layers 120 provided on both surfaces of the positive electrode current collector 110. The negative electrode sheet 20 includes a negative electrode current collector 210 and negative electrode material layers 220 located on both sides in the thickness direction of the negative electrode current collector. The electrode assembly 01 further includes a first separator 30 and a second separator 40.

[0042] In some embodiments of the present application, as Figure 1 and Figure 2As shown, in the corner area 012 of the electrode assembly 01, when a first positive electrode tab corner segment 101 is adjacent to a second separator corner segment 401, the first positive electrode tab corner segment 101 is closer to the winding center of the electrode assembly 01 than the second separator corner segment 401. In the wound electrode assembly structure, the heat generation amount and heat generation rate of the positive electrode tab are greater than those of the negative electrode tab, and the generated heat diffuses outward. Therefore, in the corner area, when a first positive electrode tab corner segment is adjacent to the corner segment of the second separator and is closer to the winding center, the winding radius of the second separator corner segment will be slightly larger than that of the first positive electrode tab corner segment, so that the heat generated by the first positive electrode tab corner segment can be effectively transferred, reducing the risk of thermal runaway of the secondary battery and being beneficial to improving the high-temperature heat box performance of the secondary battery. At the same time, the second separator includes a second base film with a relatively low closed pore temperature and a relatively high film rupture temperature. When the secondary battery has a risk of thermal runaway at high temperature, the second separator can close the pores in time to hinder the transmission of active ions such as lithium ions, and the relatively high film rupture temperature is beneficial to reducing the short circuit between the positive and negative electrodes, further improving the high-temperature heat box performance of the secondary battery. In addition, the first separator includes a first base film with a relatively high puncture resistance, which matches the second separator, being beneficial to taking into account both the high-temperature heat box performance and the manufacturing yield of the secondary battery. In this application, the flat area refers to the flat part of the electrode assembly, and the corner area refers to the bent part of the electrode assembly.

[0043] In Figure 1 and Figure 2 In the electrode assembly 01 shown, in the corner area 012, the first separator 30 is located between the first positive electrode tab corner segment 101 and the negative electrode tab 20, and the first positive electrode tab corner segment 101, the first separator 30, and the negative electrode tab 20 are successively closer to the winding center.

[0044] In some embodiments of the present application, as Figure 3 and Figure 4 shown, in the corner area 012 of the electrode assembly 01, when a second positive electrode tab corner segment 102 is adjacent to a second separator corner segment 401, the second positive electrode tab corner segment 102 is farther from the winding center of the electrode assembly 01 than the second separator corner segment 401.

[0045] In Figure 3 and Figure 4 In the electrode assembly 01 shown, in the corner area 012, the first separator 30 is located between the second positive electrode tab corner segment 102 and the negative electrode tab 20, and the second positive electrode tab corner segment 102, the first separator 30, and the negative electrode tab 20 are successively farther from the winding center.

[0046] In some embodiments of the present application, the first base film comprises a first resin material and a second resin material. The heat of fusion enthalpy H1 of the first resin material is 185 J / g to 195 J / g, and the melt flow rate MFR1 is 0.4 g / 10 min to 0.6 g / 10 min. For example, the heat of fusion enthalpy H1 of the first resin material can be 185 J / g, 186 J / g, 187 J / g, 188 J / g, 189 J / g, 190 J / g, 191 J / g, 192 J / g, 193 J / g, 194 J / g, 195 J / g, or a range composed of any two of these values. For example, the melt flow rate MFR1 of the first resin material can be 0.4 g / 10 min, 0.42 g / 10 min, 0.45 g / 10 min, 0.48 g / 10 min, 0.5 g / 10 min, 0.52 g / 10 min, 0.55 g / 10 min, 0.58 g / 10 min, 0.6 g / 10 min, or a range composed of any two of these values. The heat of fusion enthalpy H2 of the second resin material is 130 J / g to 180 J / g, and the melt flow rate MFR2 is 0.1 g / 10 min to 1.0 g / 10 min. For example, the heat of fusion enthalpy H2 of the second resin material can be 130 J / g, 135 J / g, 140 J / g, 145 J / g, 150 J / g, 155 J / g, 160 J / g, 165 J / g, 170 J / g, 175 J / g, 180 J / g, or a range composed of any two of these values. For example, the melt flow rate MFR2 of the second resin material can be 0.1 g / 10 min, 0.2 g / 10 min, 0.3 g / 10 min, 0.4 g / 10 min, 0.5 g / 10 min, 0.6 g / 10 min, 0.7 g / 10 min, 0.8 g / 10 min, 0.9 g / 10 min, 1 g / 10 min, or a range composed of any two of these values. When the heat of fusion enthalpy and melt flow rate of the first resin material and the second resin material are within the above ranges, the obtained first base film has appropriate puncture resistance, closed-cell temperature, and film-breaking temperature. Thus, while improving the manufacturing yield, the first separator can also take into account the high-temperature hot-box performance of the secondary battery.

[0047] In some embodiments of the present application, based on the mass of the first base film, the mass percentage content W1 of the first resin material is 70% to 90%, and the mass percentage content W2 of the second resin material is 10% to 30%. For example, the mass percentage content W1 of the first resin material can be 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90% or a range composed of any two of these values; the mass percentage content W2 of the second resin material can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30% or a range composed of any two of these values. By adjusting the mass percentage contents of the first resin material and the second resin material within the scope of the present application, the obtained first base film has appropriate puncture resistance, closure temperature and film breaking temperature, so that while improving the manufacturing yield, the first separator can also take into account the high-temperature heat box performance of the secondary battery.

[0048] In some embodiments of the present application, the weight-average molecular weight of the first resin material is 50W (where "W" represents 10,000, 50W is 500,000, the same below) to 90W, and the weight-average molecular weight of the second resin material is 100W to 200W. For example, the weight-average molecular weight of the first resin material can be 50W, 55W, 60W, 65W, 70W, 75W, 80W, 85W, 90W or a range composed of any two of these values; the weight-average molecular weight of the second resin material is 100W, 110W, 120W, 130W, 140W, 150W, 160W, 170W, 180W, 190W, 200W or a range composed of any two of these values. By regulating the weight-average molecular weights of the first resin material and the second resin material within the scope of the present application, the obtained first base film has appropriate puncture resistance, closure temperature and film breaking temperature, so that while improving the manufacturing yield, the first separator can also take into account the high-temperature heat box performance of the secondary battery.

[0049] In some embodiments of the present application, the first resin material and the second resin material are each independently selected from at least one of polyethylene, polypropylene, polyimide, polyethyleneimine or polyethylene terephthalate. When the types of the first resin material and the second resin material are within the above range, the obtained first base film has appropriate puncture resistance, closure temperature and film breaking temperature, so that the first separator is beneficial to improving the manufacturing yield and taking into account the high-temperature heat box performance.

[0050] In some embodiments of the present application, 145°C ≤ T11 ≤ 165°C. For example, the closed-cell temperature T11 of the first base film can be 145°C, 147°C, 149°C, 150°C, 152°C, 154°C, 155°C, 157°C, 159°C, 160°C, 162°C, 164°C, 165°C, or a range formed by any two of these values. The closed-cell temperature of the first base film is within the above range, that is, the first base film has a relatively low closed-cell temperature, so that while improving the manufacturing yield, the first separator can also take into account the high-temperature hot box performance of the secondary battery.

[0051] In some embodiments of the present application, 150°C ≤ T21 ≤ 180°C. For example, the film-breaking temperature T21 of the first base film can be 150°C, 152°C, 155°C, 157°C, 160°C, 162°C, 165°C, 167°C, 170°C, 172°C, 175°C, 178°C, 180°C, or a range formed by any two of these values. That is, the first base film has a relatively high film-breaking temperature, so that while improving the manufacturing yield, the first separator can also take into account the high-temperature hot box performance of the secondary battery.

[0052] In some embodiments of the present application, in the differential scanning calorimetry test spectrum of the first base film, characteristic peaks exist at 128°C to 134°C and 136°C to 140°C. The peak value of the characteristic peak A between 128°C and 134°C corresponds to the melting temperature of the first resin material, and the peak value of the characteristic peak B between 136°C and 140°C corresponds to the melting temperature of the second resin material. In the present application, in the first base film, the peak value of the characteristic peak is between 128°C and 134°C, that is, the characteristic peak A exists; the peak value of the characteristic peak is between 136°C and 140°C, that is, the characteristic peak B exists.

[0053] In some embodiments of the present application, the thickness of the first base film is 4 μm to 7 μm. For example, the thickness h1 of the first base film can be 4 μm, 5 μm, 6 μm, 7 μm, or a range formed by any two of these values. When the thickness of the first base film is within the above range, it is also beneficial to take into account the energy density of the secondary battery.

[0054] In some embodiments of the present application, the first separator includes a first ceramic coating and a first adhesive layer. The first adhesive layer is disposed on both sides of the first base film, and the first ceramic coating is disposed on one side of the first base film. The first ceramic coating is located between the first base film and the first adhesive layer. In some embodiments of the present application, in the electrode assembly, the first ceramic coating faces the positive electrode tab, which is beneficial to improving the problem of insufficient electrolyte in the corner area, and is also beneficial to the transmission of active ions to improve the interface problem, and further improve the lithium plating problem of the secondary battery.

[0055] In some embodiments of the present application, the coating weight CW1 of the first ceramic coating is 9 mg / 5000 mm 2 to 15 mg / 5000 mm 2 For example, the coating weight CW1 of the first ceramic coating can be 9 mg / 5000 mm 2 、9.5 mg / 5000 mm 2 、10 mg / 5000 mm 2 、10.5 mg / 5000 mm 2 、11 mg / 5000 mm 2 、11.5 mg / 5000 mm 2 、12 mg / 5000 mm 2 、12.5 mg / 5000 mm 2 、13 mg / 5000 mm 2 、13.5 mg / 5000 mm 2 、14 mg / 5000 mm 2 、14.5 mg / 5000 mm 2 、15 mg / 5000 mm 2 or a range composed of any two of these values.

[0056] In some embodiments of the present application, the first ceramic coating includes first ceramic particles, and the first ceramic particles include at least one of alumina, boehmite, silica, magnesia, titania, stannic oxide, calcium oxide, zirconia, yttria, silicon carbide, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide.

[0057] The present application does not particularly limit the composition of the first adhesive layer, as long as the object of the present application can be achieved. Exemplarily, the first adhesive layer includes a first binder, and the first binder includes at least one of polyvinylidene fluoride, polyacrylonitrile, poly(ethylene oxide), or polyimide. The present application does not particularly limit the thickness of the first adhesive layer, as long as the object of the present application can be achieved. Exemplarily, the thickness of the first adhesive layer can be 1 μm to 5 μm.

[0058] In some embodiments of the present application, the second base film includes a third resin material, a fourth resin material, and a fifth resin material.

[0059] The heat of fusion H3 of the third resin material is from 140 J / g to 150 J / g, and the melt flow rate MFR3 is from 6 g / 10 min to 14 g / 10 min. For example, the heat of fusion H3 of the third resin material can be 140 J / g, 140 J / g, 142 J / g, 143 J / g, 144 J / g, 145 J / g, 146 J / g, 147 J / g, 148 J / g, 149 J / g, 150 J / g, or a range composed of any two of these values. For example, the melt flow rate MFR3 of the third resin material can be 6 g / 10 min, 7 g / 10 min, 8 g / 10 min, 9 g / 10 min, 10 g / 10 min, 11 g / 10 min, 12 g / 10 min, 13 g / 10 min, 14 g / 10 min, or a range composed of any two of these values. The heat of fusion H4 of the fourth resin material is from 185 J / g to 195 J / g, and the melt flow rate MFR4 is from 0.4 g / 10 min to 0.6 g / 10 min. For example, the heat of fusion H4 of the fourth resin material can be 185 J / g, 186 J / g, 187 J / g, 188 J / g, 189 J / g, 190 J / g, 191 J / g, 192 J / g, 193 J / g, 194 J / g, 195 J / g, or a range composed of any two of these values. For example, the melt flow rate MFR4 of the fourth resin material can be 0.4 g / 10 min, 0.42 g / 10 min, 0.45 g / 10 min, 0.48 g / 10 min, 0.5 g / 10 min, 0.52 g / 10 min, 0.55 g / 10 min, 0.58 g / 10 min, 0.6 g / 10 min, or a range composed of any two of these values. The heat of fusion H5 of the fifth resin material is from 130 J / g to 180 J / g, and the melt flow rate MFR5 is from 0.1 g / 10 min to 100 g / 10 min. For example, the heat of fusion H5 of the fifth resin material can be 130 J / g, 135 J / g, 140 J / g, 145 J / g, 150 J / g, 155 J / g, 160 J / g, 165 J / g, 170 J / g, 175 J / g, 180 J / g, or a range composed of any two of these values. For example, the melt flow rate MFR5 of the fifth resin material can be 0.1 g / 10 min, 1 g / 10 min, 5 g / 10 min, 10 g / 10 min, 20 g / 10 min, 30 g / 10 min, 40 g / 10 min, 50 g / 10 min, 60 g / 10 min, 70 g / 10 min, 80 g / 10 min, 90 g / 10 min, 100 g / 10 min, or a range composed of any two of these values.The melting enthalpy and melt index of the third resin material, the fourth resin material, and the fifth resin material are within the above ranges, and the obtained second base film has appropriate closed pore temperature and film breaking temperature, so that the second separator is beneficial to improving the high temperature heat box performance of the secondary battery.

[0060] In some embodiments of the present application, the weight average molecular weight M of the third resin material w3 is 20W to 40W. For example, the weight average molecular weight of the third resin material can be 20W, 22W, 25W, 27W, 29W, 30W, 32W, 35W, 37W, 39W, 40W, or a range composed of any two of these values. The weight average molecular weight M of the fourth resin material w4 is 50W to 90W. For example, the weight average molecular weight of the fourth resin material can be 50W, 55W, 60W, 65W, 70W, 75W, 80W, 85W, 90W, or a range composed of any two of these values. The weight average molecular weight of the fifth resin material is 5W to 50W. For example, the weight average molecular weight M of the fifth resin material w5 can be 5W, 10W, 15W, 20W, 25W, 30W, 35W, 40W, 45W, 50W, or a range composed of any two of these values. When the weight average molecular weights of the third resin material, the fourth resin material, and the fifth resin material are within the above ranges, the obtained second base film has appropriate puncture resistance, closed pore temperature, and film breaking temperature, so that the second separator is beneficial to improving the high temperature heat box performance of the secondary battery and taking into account the manufacturing yield.

[0061] In some embodiments of the present application, based on the mass of the second base film, the mass percentage content W3 of the third resin material is 5% to 15%, the mass percentage content W4 of the fourth resin material is 83% to 93%, and the mass percentage content W5 of the fifth resin material is 1% to 3%. For example, the mass percentage content W3 of the third resin material can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range composed of any two of these values. For example, the mass percentage content W4 of the fourth resin material can be 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, or a range composed of any two of these values. For example, the mass percentage content W5 of the fifth resin material can be 1%, 1.2%, 1.4%, 1.5%, 1.7%, 1.9%, 2%, 2.2%, 2.4%, 2.5%, 2.7%, 2.9%, 3%, or a range composed of any two of these values. When the mass percentage contents of the third resin material, the fourth resin material, and the fifth resin material are within the above ranges, the obtained second base film has appropriate puncture resistance, closed pore temperature, and film breaking temperature, so that the second separator is beneficial to improving the high temperature heat box performance of the secondary battery and taking into account the manufacturing yield.

[0062] In some embodiments of the present application, the third resin material, the fourth resin material, and the fifth resin material each independently include at least one of polyethylene, polypropylene, polyimide, polyethyleneimine, or polyethylene terephthalate. When the types of the third resin material, the fourth resin material, and the fifth resin material are within the above ranges, the obtained second base film has appropriate puncture resistance, closure temperature, and film rupture temperature, so that the first separator is beneficial to improving the high-temperature hot box performance of the secondary battery and taking into account the manufacturing yield.

[0063] In some embodiments of the present application, the fifth resin material is different from the third resin material and the fourth resin material in type. In some embodiments of the present application, the third resin material and the fourth resin material include polyethylene, and the fifth resin material includes polypropylene. The obtained second base film has a lower closure temperature and a higher film rupture temperature, which is beneficial to improving the high-temperature hot box performance of the secondary battery.

[0064] In some embodiments of the present application, in the differential scanning calorimetry test spectrum of the second base film, characteristic peaks exist at 120°C to 126°C, 128°C to 134°C, and 150°C to 160°C. The peak value of the characteristic peak C between 120°C and 126°C corresponds to the melting temperature of the third resin material, the peak value of the characteristic peak D between 128°C and 134°C corresponds to the melting temperature of the fourth resin material, and the peak value of the characteristic peak E between 150°C and 160°C corresponds to the melting temperature of the fifth resin material. In the present application, in the second base film, the peak value of the characteristic peak is between 120°C and 126°C, that is, the characteristic peak C exists; the peak value of the characteristic peak is between 128°C and 134°C, that is, the characteristic peak D exists; the peak value of the characteristic peak is between 150°C and 160°C, that is, the characteristic peak E exists.

[0065] In some embodiments of the present application, 200 gf ≤ F2 ≤ 300 gf. For example, the puncture resistance F2 of the second base film can be 200 gf, 210 gf, 220 gf, 230 gf, 240 gf, 250 gf, 260 gf, 270 gf, 280 gf, 290 gf, 300 gf, or a range composed of any two of these values. By controlling the puncture resistance of the second base film within the range of the present application, the second base film has a relatively appropriate puncture resistance while having a lower closure temperature and a higher film rupture temperature. While improving the lithium high-temperature hot box performance, it is beneficial to reduce the risk of the separator being punctured by hard particles of the negative electrode sheet, and improve the manufacturing yield of the secondary battery, such as the Hi-pot yield and the K-value yield.

[0066] In some embodiments of the present application, the thickness of the second base film is 4 μm to 7 μm. For example, the thickness h2 of the second base film can be 4 μm, 5 μm, 6 μm, 7 μm, or a range composed of any two of these values. When the thickness of the second base film is within the above range, it is also beneficial to take into account the energy density of the secondary battery.

[0067] In some embodiments of the present application, the second separator includes a second ceramic coating and a second adhesive layer. The second adhesive layer is disposed on both sides of the second base film, and the second ceramic coating is disposed on one side of the second base film, and the second ceramic coating is located between the second base film and the second adhesive layer. In some embodiments of the present application, in the electrode assembly, the second ceramic coating is disposed facing the positive electrode sheet, which is beneficial to further improve the problem of insufficient electrolyte in the corner area, and is also beneficial to the transmission of active ions to improve the interface problem, thereby improving the lithium deposition problem of the secondary battery.

[0068] The present application does not particularly limit the coating quality of the second ceramic coating, as long as the object of the present application can be achieved. Exemplarily, the coating weight CW2 of the second ceramic coating is 9 mg / 5000 mm 2 to 15 mg / 5000 mm 2 . For example, the coating weight CW2 of the second ceramic coating can be 9 mg / 5000 mm 2 , 9.5 mg / 5000 mm 2 , 10 mg / 5000 mm 2 , 10.5 mg / 5000 mm 2 , 11 mg / 5000 mm 2 , 11.5 mg / 5000 mm 2 , 12 mg / 5000 mm 2 , 12.5 mg / 5000 mm 2 , 13 mg / 5000 mm 2 , 13.5 mg / 5000 mm 2 , 14 mg / 5000 mm 2 , 14.5 mg / 5000 mm 2 , 15 mg / 5000 mm 2 or a range composed of any two of these values.

[0069] In some embodiments of the present application, the second ceramic coating includes second ceramic particles, and the second ceramic particles include at least one of alumina, boehmite, silica, magnesia, titania, stannic oxide, calcium oxide, zirconia, yttria, silicon carbide, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide.

[0070] The present application has no particular restrictions on the composition of the second bonding layer, as long as the purpose of the present application can be achieved. For example, the second bonding layer includes a second bonding agent, and the second bonding agent includes at least one of polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, or polyimide. The present application has no particular restrictions on the thickness of the second bonding layer, as long as the purpose of the present application can be achieved. For example, the thickness of the second bonding layer can be 1 μm to 5 μm.

[0071] At present, silicon materials have outstanding advantages in energy density compared with traditional carbon materials, but silicon material particles are hard and easy to puncture the diaphragm, affecting the manufacturing efficiency of secondary batteries, such as Hi-pot efficiency and K value efficiency. Therefore, the negative electrode containing silicon material is applied to secondary batteries, and it is usually difficult to take into account both energy density and manufacturing efficiency. Based on the above problems, in some embodiments of the present application, the negative electrode plate includes a negative electrode material layer, the negative electrode material layer includes a negative electrode material, and the negative electrode material includes a silicon material. In some embodiments of the present application, the negative electrode plate also includes a negative electrode current collector, and the negative electrode material layer is disposed on at least one surface of the negative electrode current collector. In some embodiments of the present application, the negative electrode material layer includes a first negative electrode material layer disposed on one surface of the negative electrode current collector, and a second negative electrode material layer disposed on another surface of the negative electrode current collector. In some embodiments of the present application, the first negative electrode material layer includes a first negative electrode material, and the first negative electrode material includes a silicon material. In some embodiments of the present application, the second negative electrode material layer includes a second negative electrode material, and the second negative electrode material includes a silicon material. At the same time, when used with the first diaphragm, the first diaphragm has a high puncture resistance, which is conducive to taking into account both the energy density and manufacturing efficiency of the secondary battery. In addition, when used with the second diaphragm, high-temperature hot box performance can also be taken into account.

[0072] In some embodiments of the present application, the silicon material includes at least one of silicon, silicon-carbon compound, silicon-oxygen compound or silicon alloy. Selecting the above silicon material is more conducive to obtaining a secondary battery with higher energy density.

[0073] In the present application, the features in the above-mentioned various embodiments can be combined arbitrarily.

[0074] The preparation method of the first base film of the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, the preparation method of the first base film includes but is not limited to the following steps: (1) Mix the first resin material and the second resin material evenly according to the above W1 and W2 to obtain a mixed material; (2) Mix the additive and the solvent evenly according to the mass ratio of (0.1 to 0.3):100 to obtain a mixed solution; (3) Mix the mixed material and the mixed solution evenly according to the mass ratio of (10:90) to (30:70), and form a film by extrusion, casting, and cooling to obtain a first base material; (4) Perform longitudinal stretching and transverse stretching on the first base material, and obtain a first porous base material after extraction and drying; (5) Perform secondary stretching on the first porous base material, perform heat setting, and wind up to obtain the first base film. Among them, the solvent may include but is not limited to at least one of paraffin oil or dichloromethane; the additive includes but is not limited to at least one of [β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester, 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 multiples of longitudinal stretching and transverse stretching may each independently be 6 to 8 times; the multiple of secondary stretching may be 1 to 2 times; the temperature of extraction may be 20°C to 30°C, and the time may be 0.5 h to 1 h; the temperature of heat setting may be 110°C to 135°C.

[0075] The present application has no particular limitation on the preparation method of the second base film, as long as the purpose of the present application can be achieved. For example, the preparation method of the second base film includes but is not limited to the following steps: (1) uniformly mixing a third resin material, a fourth resin material, and a fifth resin material according to the above W3, W4, and W5 to obtain a mixed material; (2) uniformly mixing an additive and a solvent in a mass ratio of (0.1 to 0.3):100 to obtain a mixed solution; (3) uniformly mixing the mixed material and the mixed solution in a mass ratio of (20:80) to (40:60), and extruding, casting, and cooling to form a film to obtain a second base material; (4) longitudinally stretching and transversely stretching the second base material, and obtaining a second porous base material after extraction and drying; (5) performing secondary stretching on the second porous base material, performing heat setting, and winding to obtain a second base film. Among them, the solvent may include but is not limited to at least one of paraffin oil or dichloromethane; the additive includes but is not limited to at least one of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF), or dimethyl sulfoxide (DMSO); the extraction agent used during extraction may include but is not limited to at least one of dichloromethane or n-hexane. The stretching multiples of longitudinal stretching and transverse stretching can be independently 6 to 8 times; the multiple of secondary stretching can be 1 to 2 times; the extraction temperature can be 20°C to 30°C, and the time can be 0.5 h to 1 h; the heat setting temperature can be 110°C to 135°C.

[0076] In the present application, the puncture resistance of the first base film varies with the melting enthalpy, melt index, weight average molecular weight, content, and type of the first resin material and the second resin material. The present application has no particular limitation on the regulation method of the puncture resistance of the first base film, as long as the purpose of the present application can be achieved. For example, when other conditions remain unchanged, as the weight average molecular weight of the first resin material and / or the second resin material increases, the puncture resistance increases, and vice versa. For another example, when other conditions remain unchanged, as the mass percentage content of the first resin material increases, the puncture resistance decreases, and vice versa; as the mass percentage content of the second resin material increases, the puncture resistance increases, and vice versa. In the present application, the puncture resistance and film breaking temperature of the second base film can be regulated in the same way as the puncture resistance of the first base film.

[0077] In this application, the closed-cell temperature and film-breaking temperature of the second base film vary with the melting enthalpy, melt index, weight-average molecular weight, content, and type of the third resin material, the fourth resin material, and the fifth resin material. For example, when other conditions remain unchanged and the weight-average molecular weight of the third resin material increases, the closed-cell temperature rises; conversely, the closed-cell temperature decreases. When the mass percentage content of the third resin material increases, the closed-cell temperature decreases; conversely, it rises. Another example is that when other conditions remain unchanged and the weight-average molecular weight of the fourth resin material increases, the closed-cell temperature and the film-breaking temperature are higher; conversely, the closed-cell temperature and the film-breaking temperature are lower. When the mass percentage content of the fourth resin material is higher, the closed-cell temperature is higher; conversely, it decreases. Still another example is that when other conditions remain unchanged and the weight-average molecular weight of the fifth resin material increases, the film-breaking temperature rises; conversely, it decreases. When the mass percentage content of the fifth resin material increases, the film-breaking temperature increases; conversely, it decreases. In this application, the closed-cell temperature and the film-breaking temperature of the first base film can be regulated in the same way as those of the second base film.

[0078] In this application, the first resin material, the second resin material, the third resin material, the fourth resin material, and the fifth resin material with different melting enthalpies, melt indexes, weight-average molecular weights, and types can be obtained by purchase. Their melting enthalpies, melt indexes, and weight-average molecular weights can be measured, and materials with the desired melting enthalpies, melt indexes, and weight-average molecular weights can be selected. Among them, the specific test methods can refer to the relevant content in the "Test Methods and Equipment" section.

[0079] This application places no particular restrictions on the negative electrode current collector, as long as the purpose of this application can be achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector. Exemplarily, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0080] In some embodiments of this application, the first negative electrode material layer and the second negative electrode material layer can also independently include a negative electrode conductive agent and a negative electrode binder. This application places no particular restrictions on the types of the negative electrode conductive agent and the negative electrode binder, as long as the purpose of this application can be achieved. For example, it can be at least one of a positive electrode conductive agent and a positive electrode binder. This application places no particular restrictions on the mass ratios of the negative electrode material, the negative electrode conductive agent, and the negative electrode binder in the first negative electrode material layer and the second negative electrode material layer. Those skilled in the art can select according to actual needs as long as the purpose of this application can be achieved.

[0081] 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. The present application has no particular limitation on the composition of the first negative electrode conductive layer, and it may be a commonly used conductive layer 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. The present application has no particular limitation on the first negative electrode conductive layer conductive agent and the first negative electrode conductive layer binder, and for example, it may be at least one of a positive electrode conductive agent and a positive electrode binder.

[0082] 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. The present application has no particular limitation on the composition of the second negative electrode conductive layer, and it may be a commonly used conductive layer in the art. For example, the second negative electrode conductive layer includes a second negative electrode conductive layer conductive agent and a second negative electrode conductive layer binder. The present application has no particular limitation on the second negative electrode conductive layer conductive agent and the second negative electrode conductive layer binder, and for example, it may be at least one of a positive electrode conductive agent and a positive electrode binder.

[0083] The present application has no particular limitation on the thickness of the first negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the first negative electrode material layer is 30 μm to 120 μm.

[0084] The present application has no particular limitation on the thickness of the second negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the second negative electrode material layer is 30 μm to 120 μm.

[0085] The present application has no particular limitation on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 20 μm.

[0086] In the present application, the positive electrode sheet includes a positive electrode current collector and positive electrode material layers located on both sides of the positive electrode current collector. The above "positive electrode material layers located on both sides of the positive electrode current collector" means that the positive electrode material layers are disposed on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here may be the entire area of the positive electrode current collector surface or a partial area of the positive electrode current collector surface. The present application has no particular limitation, as long as the purpose of the present application can be achieved.

[0087] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector), etc.

[0088] The positive electrode material layer includes a positive electrode active material. There is no particular limitation on the positive electrode active material in this application, as long as the object of this application can be achieved. For example, the positive electrode active material may include, but is not limited to, lithium nickel cobalt manganate (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate (LiCoO2), lithium manganate, or lithium manganese iron phosphate, etc., at least one of them.

[0089] The positive electrode material layer may further include a positive electrode conductive agent and a positive electrode binder. There is no particular limitation on the types of the positive electrode conductive agent and the positive electrode binder in this application, as long as the object of this application can be achieved. 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 fiber, flake graphite, graphene, metal material, or conductive polymer. The conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The above carbon nanotubes may include, but is not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above carbon fiber may include, but is not limited to, vapor-grown carbon fiber (VGCF) and / or nanofiber. The above metal material may include, but is not limited to, metal powder and / or metal fiber. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0090] There is no particular limitation on the positive electrode binder in this application, as long as the object of this application can be achieved. 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, polyamideimide, styrene-butadiene rubber, or polyvinylidene fluoride.

[0091] There is no particular limitation on the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode material layer in this application. Those skilled in the art can select according to actual needs, as long as the object of this application can be achieved.

[0092] There is no particular limitation on the thickness of the positive electrode current collector and the positive electrode material layer in this application, as long as the object of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the positive electrode material layer is 30 μm to 120 μm.

[0093] Optionally, the positive electrode sheet may further include a positive electrode conductive layer, which is located between the positive electrode current collector and the positive electrode material layer. The composition of the positive electrode conductive layer is not particularly limited and may be a commonly used conductive layer in the art. The positive electrode conductive layer includes a positive electrode conductive layer conductive agent and a positive electrode conductive layer binder. The present application places no particular restrictions on the positive electrode conductive layer conductive agent and the positive electrode conductive layer binder. For example, it may be at least one of the above-mentioned positive electrode conductive agents and the above-mentioned positive electrode binders.

[0094] In the present application, the secondary battery further includes an electrolyte, which includes a lithium salt and a non-aqueous solvent.

[0095] The present application places no particular restrictions on the lithium salt, as long as the object of the present application can be achieved. For example, the lithium salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylborate (LiB(C6H5)4), lithium methyl sulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium tris(trifluoromethylsulfonyl)methyl (LiC(SO2CF3)3), lithium hexafluorosilicate (LiSiF6), lithium bis(oxalato)borate (LiBOB), and lithium difluoroborate (LiF2OB). The present application places no particular restrictions on the content of the lithium salt in the electrolyte, as long as the object of the present application can be achieved.

[0096] The present application places no particular restrictions on the non-aqueous solvent, as long as the object of the present application can be achieved. For example, the non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds, carboxylate compounds, ether compounds, or other organic solvents.

[0097] The above-mentioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The above-mentioned 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 above-mentioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinylene ethylene carbonate (VEC). The fluorinated carbonate compounds may include, but are not limited to, at least one of fluorinated ethylene 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 trifluoromethyl ethylene carbonate. The above-mentioned carboxylate 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, decanolide, valerolactone, or caprolactone. The above-mentioned 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. The above-mentioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The present application does not particularly limit the content of the non-aqueous solvent in the electrolyte, as long as the object of the present application can be achieved.

[0098] The secondary battery further includes a housing for accommodating the second separator, the positive electrode sheet, the first separator, the negative electrode sheet, and the electrolyte, as well as other components known in the field of secondary batteries. The present application does not limit the above-mentioned other components. The present application does not particularly limit the housing, and it may be a housing well-known in the art, as long as the object of the present application can be achieved. For example, the housing may be a hard-shell housing or a flexible housing. The material of the hard-shell housing may be metal. The present application does not limit the type of metal, and a metal hard-shell housing known in the art may be used, as long as the object of the present application can be achieved. The flexible housing may be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0099] The preparation process of the secondary battery of the present application is well-known to those skilled in the art, and the present application has no special limitations. For example, the preparation process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode sheet, the first separator, the negative electrode sheet, and the second separator in sequence, and winding, folding, etc. as needed to obtain a wound structure electrode assembly, placing the electrode assembly into a housing, injecting an electrolyte into the housing and sealing it to obtain a secondary battery. Alternatively, stack the negative electrode sheet, the second separator, the positive electrode sheet, and the first separator in sequence, and wind, fold, etc. as needed to obtain a wound structure electrode assembly, place the electrode assembly into a housing, inject an electrolyte into the housing and seal it to obtain a secondary battery. In addition, an overcurrent protection element, a guide plate, etc. can be placed in the housing as needed to prevent the pressure inside the secondary battery from rising and overcharging / discharging.

[0100] In some embodiments of the present application, the secondary battery of the present application 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, etc. In some embodiments of the present application, the secondary battery includes a lithium ion battery.

[0101] The second aspect of the present application provides an electronic device, which includes the secondary battery described in the first aspect of the present application.

[0102] The present application does not particularly limit the type of the electronic device, and it can be any electronic device known in the prior art. In some embodiments of the present application, the electronic device may include, but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, portable cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries, and lithium ion capacitors, etc.

[0103] Examples

[0104] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0105] Testing method and equipment:

[0106] Sampling method for the first separator and the second separator:

[0107] Disassemble the lithium-ion batteries in the tested examples and comparative examples, take out the first separator and the second separator, soak them in dimethyl carbonate (DMC) for 20 min to remove the residual electrolyte, and then place the first separator and the second separator in an oven and dry them at 60 °C for 12 h to obtain the first separator sample and the second separator sample. Unless otherwise specified, the above method is used to obtain the first separator and the second separator for the following tests.

[0108] Sampling method for the first base film and the second base film:

[0109] Put the first separator and the second separator obtained by the above sampling into containers respectively, add N-methylpyrrolidone (NMP), place them in an ultrasonic instrument with a heating function for ultrasonic treatment, control the temperature at 45 °C, and perform ultrasonic treatment for 3 h. Take them out after the first separator and the second separator become completely transparent to obtain the first base film and the second base film. Unless otherwise specified, the above method is used to obtain the first base film and the second base film for the following tests.

[0110] Porosity test for the first base film, the first separator, the second base film, and the second separator:

[0111] The gas replacement method is used for testing. Samples are prepared by punching the first base film, the first separator, the second base film, and the second separator with a mold respectively (those skilled in the art can select common-sized and -shaped molds in the art 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 is measured by a true density tester, and the apparent volume V of the sample can be calculated by measuring the area and thickness of the sample. Then, the percentage of the pore volume of the sample in the total volume = (V - V0) / V × 100%, that is, the porosities of the first base film, the first separator, the second base film, and the second separator are obtained respectively.

[0112] Closed pore temperature and film rupture temperature of the first base film and the second base film:

[0113] The closed pore temperature and film rupture temperature of the sample are tested by the temperature rise internal resistance method. First, cut the sample into a fixed size of 5 cm × 5 cm, and the size of the base film sample is larger than the size of the fixture test area. Place the sample in a component composed of a ceramic and a stainless steel fixture, inject 10 mL of electrolyte, place the above fixture in an oven, set the oven temperature to 250 °C, and heat it at a certain rate of 15 °C / min. At the same time, monitor the resistance value and temperature of the fixture, and output the data of the fixture temperature and resistance value, oven temperature and time to obtain a temperature-resistance curve. Among them, the sample is the first base film or the second base film.

[0114] According to the temperature-resistance curve, the temperature at which the resistance value suddenly increases (reaches 1000 Ω) is the closed pore temperature of the separator; the maximum value of the resistance value is the highest resistance value of the separator.

[0115] On the basis of the above test of the diaphragm closing temperature, continue to increase the test time. When the resistance suddenly drops to the same value as the resistance at the closing temperature, the temperature at this time is the membrane-breaking temperature of the diaphragm.

[0116] Among them, the composition and preparation method of the electrolyte in the test are the same as those in Example 1-1.

[0117] Thickness test of the first base film and the second base film:

[0118] Perform argon ion polishing on the first base film to obtain the cross-section of the first base film. Observe the morphology of the cross-section of the first base film along the thickness direction through a field emission scanning electron microscope (Philips, XL-30 type) and take a scanning electron microscope photo. Measure the thickness of the first base film through the scanning electron microscope. Replace the first base film with the second base film to measure the thickness of the second base film.

[0119] DSC spectrum test of the first base film and the second base film:

[0120] Use a differential scanner (model: ASTM D3418-15) to test the DSC spectrum of 8 mg of the first base film. The heating rate is 10 °C / min, and the temperature range is 60 °C to 190 °C. Replace the first base film with the second base film to measure the DSC spectrum of the second base film. In the obtained DSC spectrum of the first base film, the characteristic peak corresponding to the peak value of 128 °C to 134 °C is recorded as characteristic peak A, and the characteristic peak corresponding to the peak value of 136 °C to 140 °C is recorded as characteristic peak B; in the obtained DSC spectrum of the second base film, the characteristic peak corresponding to the peak value of 120 °C to 126 °C is recorded as characteristic peak C, the characteristic peak corresponding to the peak value of 128 °C to 134 °C is recorded as characteristic peak D, and the characteristic peak corresponding to the peak value of 150 °C to 160 °C is recorded as characteristic peak E.

[0121] According to the DSC spectrum of the first base film, calculate the ratio of the peak areas of characteristic peak A and characteristic peak B. The peak area ratio is also the mass ratio of the first resin material to the second resin material. After conversion, obtain the mass percentage content of the first resin material and the second resin material. Similarly, according to the DSC spectrum of the second base film, calculate the ratio of the peak areas of characteristic peak C, characteristic peak D, and characteristic peak E, and then obtain the mass percentage content of the third resin material, the fourth resin material, and the fifth resin material.

[0122] Weight-average molecular weight test:

[0123] 1) Sample preparation: Dissolve 5 g of the first base film to be tested in 100 g of 1,2,4-trichlorobenzene at 150 °C to prepare a solution with a concentration of 2 wt%.

[0124] 2) Gel column selection: The smaller the pore size of the gel column, the slower the flow rate, and the larger the molecular weight of the polymer that can be separated. By selecting a suitable gel column, the first resin material and the second resin material can pass through the gel column at appropriate flow rates respectively, so that the first resin material and the second resin material can be separated.

[0125] 3) Sample loading and elution: Inject the prepared sample solution into a gel permeation chromatography (GPC) instrument, and pump the solution through the gel column at a certain flow rate. At the same time, elute the gel column with an appropriate eluent to elute the separated polymers in sequence.

[0126] 4) Detection and recording: During the elution process, detect the concentration of the effluent through a detector and record the change of concentration with time.

[0127] 5) Data processing and analysis: Import the detected concentration data into computer software, convert the concentration data into information on molecular weight and its distribution with a reference substance (polyethylene) as a reference, and obtain the weight-average molecular weights of the first resin material and the second resin material.

[0128] Replace the first base film with the second base film. Among them, by selecting a suitable gel column, the third resin material, the fourth resin material, and the fifth resin material can pass through the gel column at appropriate flow rates respectively, so that the third resin material, the fourth resin material, and the fifth resin material can be separated. Repeat the above steps to obtain the weight-average molecular weights of the third resin material, the fourth resin material, and the fifth resin material respectively.

[0129] Testing of melt index:

[0130] Use a melt flow rate tester to test the melt index of the material. Heat the instrument to 110 °C, place a standard die with a diameter of φ2.095 ± 0.005 mm, put the material into the barrel and compact it, keep it warm for 10 min, set the material cutting time to 60 s, apply a pressure of 2.16 kg to extrude the material, and calculate the melt index MFR of the material melt. MFR = mT / t, where t is the cutting time of 60 s, m is the mass of the material, and T is 600 s. The above materials can be the first resin material, the second resin material, the third resin material, or the fourth resin material.

[0131] Testing of melting enthalpy:

[0132] The melting enthalpy of the resin materials in each example and comparative example was measured using a differential scanning calorimeter. The sample material was placed in a crucible and heated from room temperature to 250 °C at a rate of 10 °C / min under a nitrogen atmosphere to obtain a differential scanning calorimetry curve (DSC curve). The melting enthalpy of the sample material was calculated based on the area enclosed by the melting peak in the DSC curve, and the peak temperature of the melting peak in the DSC curve was taken as the melting point of the sample material. The above numerical materials can be the first resin material, the second resin material, the third resin material, or the fourth resin material.

[0133] Melting enthalpy = integral area of the melting endothermic curve / mass.

[0134] High-temperature hot box performance test:

[0135] Under the condition of 25 °C, the lithium-ion battery charged at a constant current of 2C to 4.5V and then charged at a constant voltage of 4.5V until the current reached 0.02C was placed in a test chamber with circulating air convection, a temperature of 25 °C, and a humidity of 80%. After standing for 5 min, the test chamber was heated to 130 °C at a rate of 5 °C / min and maintained at 130 °C. After 1 h, the test was stopped, and it was checked whether the lithium-ion battery caught fire or exploded. Passing the test without catching fire or exploding. The passing rate of the hot box test at 130 °C = the number of lithium-ion batteries passing the hot box test at 130 °C / the total number of lithium-ion batteries tested in the hot box at 130 °C (5).

[0136] Under the condition of 25 °C, the lithium-ion battery charged at a constant current of 2C to 4.5V and then charged at a constant voltage of 4.5V until the current reached 0.02C was placed in a test chamber with circulating air convection, a temperature of 25 °C, and a humidity of 80%. After standing for 5 min, the test chamber was heated to 132 °C at a rate of 5 °C / min and maintained at 132 °C. After 1 h, the test was stopped, and it was checked whether the lithium-ion battery caught fire or exploded. The passing rate of the hot box test at 132 °C = the number of lithium-ion batteries passing the hot box test at 132 °C / the total number of lithium-ion batteries tested in the hot box at 132 °C (5).

[0137] Hi-pot excellent rate test:

[0138] The Hi-pot test of the lithium-ion battery was carried out, and the passing rate of the test was calculated.

[0139] The test method is as follows: The leakage current generated by the lithium-ion battery prepared in the example or comparative example under a test voltage of 100V output by the high-voltage machine was detected, and then the resistance value = test voltage / leakage current was calculated.

[0140] The calculated resistance value was compared with the set judgment resistance. In this application, the preset value of the judgment resistance is 5 mΩ.

[0141] If the detected resistance value is greater than or equal to the preset value of 5 mΩ, it is determined that the tested product passes the test (OK);

[0142] When the detected resistance value is less than the preset value of 5 mΩ, the test voltage is instantly cut off and the product under test is judged as not passing the test (NG).

[0143] For each group of examples or comparative examples, 100 lithium-ion batteries are tested. The number of lithium-ion batteries passing the test is X1, and the test passing rate is X1 / 100×100%, which is also the Hi-pot excellent rate.

[0144] K-value excellent rate test:

[0145] The lithium-ion batteries prepared in the examples or comparative examples are charged at a constant current of 0.5C until the voltage reaches 3.95V. When the lithium-ion batteries store 60% of the power (60% SOC), at 25±5°C, measure their voltage, which is recorded as the first voltage. After standing for 48 hours, measure the voltage again, which is recorded as the second voltage. The voltage drop per unit time is recorded as K, and K = (the first voltage - the second voltage) / standing time.

[0146] When the K value is less than 0.006 mV / h, it is judged as passing the K-value test (OK);

[0147] When the K value is greater than or equal to 0.006 mV / h, it is judged as not passing the K-value test (NG).

[0148] For each group of comparative examples and each group of examples, 100 lithium-ion batteries are tested, and the passing rate of the K-value test for each group is recorded. The number of lithium-ion batteries passing the test is X2, and the test passing rate is X2 / 100×100%, which is also the K-value excellent rate.

[0149] Example 1-1

[0150] <Preparation of the first separator>

[0151] (1) Mix the first resin material polyethylene and the second resin material polyethylene evenly to obtain a mixed material, where the mass percentage content W1 of the first resin material is 80%, and the mass ratio W2 of the second resin material is 20%; M w1 = 70W, H1 = 190 J / g, MFR1 = 0.5 g / 10 min; M w2 = 150W, H2 = 155 J / g, MFR2 = 0.5 g / 10 min;

[0152] (2) Mix the additive pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and the solvent paraffin oil evenly according to the mass ratio of 0.2:100 to obtain a mixed solution;

[0153] (3) Mix the mixed material and the mixed solution evenly according to the mass ratio of 20:80, add them to the extrusion machine system, extrude through a T-shaped die, and obtain the first substrate by casting, cooling, and film forming.

[0154] (4) The first substrate is longitudinally stretched by 7 times and transversely stretched by 7 times, extracted with dichloromethane at 25 °C for 0.5 h, and dried to obtain the first porous substrate;

[0155] (5) The first porous substrate is subjected to secondary longitudinal stretching by 1.5 times and secondary transverse stretching by 1.5 times, heat-set at 125 °C, and wound up to obtain the first base film. The thickness h1 of the first base film is 5 μm.

[0156] (6) The inorganic particle boehmite with a Dv50 of 1 μm and polyacrylate are mixed in a mass ratio of 90:10 and then dissolved in deionized water to form an inorganic coating slurry with a solid content of 50 wt%. Subsequently, the inorganic coating slurry is evenly coated on one surface of the first base film by microgravure coating and dried to obtain the first ceramic coating. Among them, the coating weight CW1 of the first ceramic coating is 12 mg / 5000 mm 2 . Among them, the weight-average molecular weight of polyacrylate is 40W.

[0157] (7) The first binder PVDF with a weight-average molecular weight of 8.5×10 6 , and then deionized water is added and stirred to adjust the viscosity of the slurry to 3500 mPa·s and the solid content to 75 wt% to obtain the first adhesive layer slurry; the first adhesive layer slurry is evenly coated on one surface of the first ceramic coating away from the first base film by screen printing and dried, and the above coating process is repeated on the other surface of the first base film to obtain the first separator. Among them, the single-layer coating thickness of the first adhesive layer is 2 μm.

[0158] <Preparation of the second separator>

[0159] (1) The third resin material polyethylene, the fourth resin material polyethylene, and the fifth resin material polypropylene are mixed evenly according to a mass ratio of 10:88:2 to obtain a mixed material; among them, M w3 = 30W, H3 = 145 J / g, MFR3 = 10 g / 10 min; M w4 = 70W, H4 = 190 J / g, MFR4 = 0.5 g / 10 min; M w5 = 28W, H5 = 185 J / g, MFR5 = 50 g / 10 min.

[0160] (2) The additive pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and the solvent paraffin oil are mixed evenly according to a mass ratio of 0.2:100 to obtain a mixed solution;

[0161] (3) Mix the mixed materials and the mixed solution evenly at a mass ratio of 20:80, add them to the extrusion system, extrude through a T-shaped die, and form a film by casting, cooling, and casting to obtain a second substrate;

[0162] (4) Stretch the second substrate 7 times longitudinally and 7 times transversely, extract it with dichloromethane at 25 °C for 0.5 h, and dry it to obtain a second porous substrate;

[0163] (5) Stretch the second porous substrate 2 times in the secondary stretching and 1.5 times in the secondary transverse stretching, perform heat setting at 125 °C, and wind it up to obtain a second base film. The thickness h2 of the second base film is 5 μm.

[0164] (6) Mix boehmite, an inorganic particle with a Dv50 of 1 μm, and polyacrylate (Mw = 400,000) at a mass ratio of 90:10, and then dissolve them in deionized water to form a first ceramic coating slurry with a solid content of 50 wt%. Subsequently, use the microgravure coating method to evenly coat the first ceramic coating slurry on one surface of the first base film, and dry it to obtain a second base film provided with a second ceramic coating. Among them, the coating weight CW2 of the second ceramic coating is 12 mg / 5000 mm 2 .

[0165] (7) The second binder PVDF has a weight average molecular weight of 8.5×10 6 ), then add deionized water and stir to adjust the viscosity of the slurry to 3500 mPa·s and the solid content to 75 wt% to obtain a second adhesive layer slurry; use the screen printing method to evenly coat the second adhesive layer slurry on one surface of the second ceramic coating away from the second base film, and then complete drying in an oven. Repeat the above coating process on the other surface of the second base film to obtain a second separator. Among them, the single-layer coating thickness of the second adhesive layer is 2 μm.

[0166] <Preparation of the negative electrode sheet>

[0167] Mix artificial graphite, silicon carbide compound, acetylene black, styrene-butadiene rubber and sodium carboxymethyl cellulose as the negative electrode active materials in a mass ratio of 90:6:1:1.5:1.5, then add deionized water as a solvent to formulate a slurry with a solid content of 70 wt%, and stir evenly with a vacuum mixer to obtain the first negative electrode slurry. At the same time, the first negative electrode slurry is also used as the second negative electrode slurry. Coat the first negative electrode slurry evenly on one surface of a copper foil with a thickness of 8 μm, and dry it at 110 °C to obtain a negative electrode sheet with a coating thickness of 50 μm for the first negative electrode material layer. The second negative electrode slurry is coated on the other surface of the negative electrode current collector copper foil. After drying, the coating thickness of the second negative electrode material layer on this surface is 50 μm, and then a negative electrode sheet with a total thickness of 108 μm is obtained. Cold press the coated negative electrode sheet, and then cut it into a size of 74 mm × 867 mm for standby. Among them, the tap density of the first negative electrode material layer is 1.735 g / cm 3 , with a length of 720 mm. The tap density of the second negative electrode material layer is 1.735 g / cm 3 , with a length of 680 mm. Among them, the mass ratio of silicon element to carbon element in the silicon carbide compound is 2:8.

[0168] <Preparation of the positive electrode sheet>

[0169] Mix lithium cobalt oxide, acetylene black, and PVDF as the positive electrode active materials in a mass ratio of 94:3:3, then add NMP as a solvent to formulate a slurry with a solid content of 75 wt%, and then stir evenly with a vacuum mixer to obtain the positive electrode slurry. Coat the positive electrode slurry evenly on one surface of an aluminum foil with a thickness of 12 μm, and dry it at 90 °C to obtain a negative electrode sheet with a coating thickness of 55 μm for the single-sided positive electrode material layer. The positive electrode slurry is coated on the other surface of the positive electrode current collector aluminum foil. After drying, the coating thickness of the positive electrode material layer on this surface is 55 μm, and then a positive electrode sheet with a total thickness of 122 μm is obtained. After cold pressing, a positive electrode sheet with a single-sided coating of a positive electrode material layer with a thickness of 122 μm is obtained. Cold press the coated positive electrode sheet, and then cut it into a size of 70 mm × 800 mm, weld the tabs, and set it aside. Among them, the tap density of the positive electrode material layer is 4.23 g / cm 3 .

[0170] <Preparation of the electrolyte>

[0171] In an environment with a water content of less than 10 ppm, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC), which are non-aqueous organic solvents, are mixed in a mass ratio of 20:30:20:28:2. Then, lithium hexafluorophosphate (LiPF6) is added to the non-aqueous organic solvent and dissolved and mixed evenly to obtain an electrolyte solution. Based on the total mass of the electrolyte solution, the mass content of LiPF6 is 8%, and the balance is non-aqueous organic solvent.

[0172] <Preparation of Lithium-Ion Battery>

[0173] Stack the positive electrode sheet, the first separator, the negative electrode sheet, and the second separator prepared above in sequence, and then wind them to obtain an electrode assembly. For details, refer to Figure 1 and Figure 2 , the corner section of the first positive electrode sheet is adjacent to the second separator, and the corner section of the first positive electrode sheet is closer to the winding center of the electrode assembly than the corner section of the second separator. The first separator is located between the corner section of the first positive electrode sheet and the negative electrode sheet, and the corner section of the first positive electrode sheet, the first separator, and the negative electrode sheet are successively closer to the winding center; and the first ceramic coating of the first separator faces the positive electrode sheet, and the second ceramic coating of the second separator faces the positive electrode sheet. This structure is denoted as Structure A. Place the electrode assembly into an aluminum-plastic film packaging bag, remove moisture at 80 °C, inject the prepared electrolyte solution, and obtain a secondary battery through processes such as vacuum packaging, standing, formation, and shaping.

[0174] Examples 1-2 to Examples 1-5

[0175] Except for adjusting the mass percentage content of the first resin material and the second resin material, and the stretching multiples of the first base film in transverse stretching, longitudinal stretching, secondary transverse stretching, and secondary longitudinal stretching according to Table 1, so that the tensile strength, closed pore temperature, and film breaking temperature of the first base film are as shown in Table 1, the rest are the same as Example 1-1.

[0176] Examples 1-6 to Examples 1-13, Example 19

[0177] Except for adjusting the types of the first resin material and / or the second resin material according to Table 1, and adjusting the stretching multiples of the first base film in transverse stretching, longitudinal stretching, secondary transverse stretching, and secondary longitudinal stretching, so that the tensile strength, closed pore temperature, and film breaking temperature of the first base film are as shown in Table 1, the rest are the same as Example 1-1.

[0178] Examples 1-14 to Examples 1-17

[0179] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as Example 1-1.

[0180] Example 1-18

[0181] Except for adjusting <the preparation of lithium-ion batteries> according to the following steps, the rest is the same as in Example 1-1.

[0182] <the preparation of lithium-ion batteries>

[0183] Stack the above-prepared positive electrode sheet, second separator, negative electrode sheet, and first separator in sequence, and then wind them to obtain an electrode assembly. Specifically, refer to Figure 3 and Figure 4 , the corner section of the second positive electrode sheet is adjacent to the second separator, and the corner section of the second positive electrode sheet is farther from the winding center of the electrode assembly than the corner section of the second separator. The first separator is located between the corner section of the second positive electrode sheet and the negative electrode sheet, and the corner section of the first positive electrode sheet, the first separator, and the negative electrode sheet are successively farther from the winding center; and the first ceramic coating of the first separator faces the positive electrode sheet, and the second ceramic coating of the second separator faces the positive electrode sheet. This structure is denoted as Structure B. Place the electrode assembly in an aluminum-plastic film packaging bag, remove moisture at 80 °C, inject the prepared electrolyte, and obtain a lithium-ion battery through processes such as vacuum packaging, standing, forming, and shaping.

[0184] Examples 2-1 to 2-12, Example 2-24

[0185] Except for adjusting the types of the third resin material, the fourth resin material, or the fifth resin material according to Table 2, and adjusting the stretching multiples of the second base film in transverse stretching, longitudinal stretching, secondary transverse stretching, and secondary longitudinal stretching so that the tensile strength, closed-hole temperature, and film-breaking temperature of the second base film are as shown in Table 2, the rest is the same as in Example 1-1.

[0186] Examples 2-13 to 2-23

[0187] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Example 1-1.

[0188] Comparative Examples 1-1 to 1-2

[0189] Except for adjusting the mass percentage contents of the first resin material and the second resin material according to Table 1, and the stretching multiples of the first base film in transverse stretching, longitudinal stretching, secondary transverse stretching, and secondary longitudinal stretching so that the tensile strength, closed-hole temperature, and film-breaking temperature of the first base film are as shown in Table 1, the rest is the same as in Example 1-1.

[0190] Comparative Example 1-3

[0191] Except for replacing the second base film with the first base film, the rest is the same as in Example 1-1.

[0192] Comparative Examples 2-1 to 2-2

[0193] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Example 1-1.

[0194] Comparative Example 2-3

[0195] Except for replacing the first base film with the second base film, the rest is the same as in Example 1-1.

[0196] The preparation parameters and performance tests of each example and comparative example are shown in Tables 1 to 2.

[0197]

[0198]

[0199]

[0200] It can be seen from Example 1-1 to Example 1-19, Example 2-1 to Example 2-24, Comparative Example 1-1 to Comparative Example 1-3, and Comparative Example 2-1 to Comparative Example 2-3 that when the puncture resistance strength F1 of the first base film in the lithium-ion battery is greater than the puncture resistance strength F2 of the second base film, the closed pore temperature T12 of the second base film is less than the closed pore temperature T11 of the first base film, the film breaking temperature T22 of the second base film is greater than the film breaking temperature T21 of the first base film, and F1, T12, and T22 are all within the scope of the present application at the same time, the obtained lithium-ion battery has a high passing rate in the hot box test at 130 °C and 132 °C, and the Hi-pot excellent rate and K value excellent rate are high, thereby indicating that the lithium-ion battery obtained in the present application can take into account the manufacturing excellent rate and high-temperature hot box performance. In Comparative Example 1-1 to Comparative Example 1-2, the puncture resistance strength of the first base film is not within the scope of the present application. In Comparative Example 1-3, the second base film is not used. For the obtained lithium-ion battery, although Comparative Example 1-1 and Comparative Example 1-2 have good high-temperature hot box performance, their manufacturing excellent rate is low; although Comparative Example 1-3 has a high manufacturing excellent rate, its high-temperature hot box performance is poor. In Comparative Example 2-1, the closed pore temperature of the second base film is not within the scope of the present application. In Comparative Example 2-2, the film breaking temperature of the second base film is not within the scope of the present application. In Comparative Example 1-3, the first base film is not used. For the obtained lithium-ion battery, although Comparative Example 2-1 and Comparative Example 2-2 have a high manufacturing excellent rate, their high-temperature hot box performance is poor; for Comparative Example 2-3, although it has good high-temperature hot box performance, its manufacturing excellent rate is low. It can be seen that the lithium-ion batteries in Comparative Example 1-1 to Comparative Example 1-3 and Comparative Example 2-1 to Comparative Example 2-3 are difficult to take into account the manufacturing excellent rate and high-temperature hot box performance.

[0201] The melting enthalpy, melt index and weight average molecular weight of the first resin material and the second resin material change in linkage. It can be seen from Examples 1-1, 1-6 to 1-13 that when the above parameters are within the scope of this application, the obtained lithium-ion battery has a high hot box test pass rate at 130°C and 132°C, and the Hi-pot excellence rate and K value excellence rate are high, which shows that the obtained lithium-ion battery can take into account both manufacturing excellence rate and high-temperature hot box performance. In Examples 1-1, 1-6 to 1-9, the weight average molecular weight and melting enthalpy of the first resin material in Example 1-9 are greater than those in Example 1-1, and the melt index is less than that in Example 1-1. The puncture resistance of the obtained first base film is also greater, and the closed-cell temperature and film rupture temperature are also more appropriate, so its high-temperature hot box performance and manufacturing excellence rate are better, but the porosity of the first base film is small, which affects the dynamic performance of the lithium-ion battery.

[0202] Whether the DSC spectrum of the first base film has characteristic peaks A and B is affected by the melting enthalpy, melt index and weight average molecular weight of the first resin material and the second resin material. It can be seen from Examples 1-1 to 1-19 that when the above parameters of the first resin material are within the range of this application, the DSC spectrum of the first base film has characteristic peaks A and B. Specifically, Figure 5 It can be seen that in the DSC spectrum of the first base film in Example 1-1, there are characteristic peaks at 128°C to 134°C and 136°C to 140°C, that is, there are characteristic peaks A and B.

[0203] From the examples 1-1, 1-14 to 1-17, it can be seen that when the thickness of the first base film is within the scope of the present application, the obtained lithium-ion battery has a high hot box test pass rate at 130°C and 132°C, and has a high Hi-pot rate and K value rate, which shows that the obtained lithium-ion battery can take into account both manufacturing rate and high-temperature hot box performance. The thickness of the first base film in Example 1-7 is much greater than that in Example 1-1, and the puncture resistance of the obtained first base film is also greater, and the closed-cell temperature and film rupture temperature are also more appropriate, so its high-temperature hot box performance and manufacturing rate are better, but the thickening of the first base film will increase the transmission path of lithium ions and thus affect the kinetic performance of the lithium-ion battery, and will also affect the energy density of the lithium-ion battery.

[0204] It can be seen from Examples 1-1 and 1-18 that the first positive electrode sheet corner segment is adjacent to the second diaphragm and the first positive electrode sheet corner segment is closer to the winding center of the electrode assembly than the second diaphragm corner segment, compared with the second positive electrode sheet corner segment being adjacent to the second diaphragm and the second positive electrode sheet corner segment being farther away from the winding center of the electrode assembly than the second diaphragm corner segment, the lithium-ion battery has a higher hot box test pass rate at 130°C and 132°C, which is more conducive to improving the high-temperature hot box performance of the lithium-ion battery.

[0205] The linked changes among the melt enthalpy, melt index and weight-average molecular weight of the third resin material, the fourth resin material and the fifth resin material will affect the closed-cell temperature and film-breaking temperature of the second base film, and further affect the high-temperature hot box performance of the lithium-ion battery. It can be seen from Examples 1-1, 2-1 to 2-12 that when the above parameters are within the scope of the present application, the obtained lithium-ion battery has a high passing rate in the hot box test at 130 °C and 132 °C, indicating that the obtained lithium-ion battery has good high-temperature hot box performance. In addition, the Hi-pot excellent rate and K-value excellent rate are relatively high, and the manufacturing excellent rate can be taken into account at the same time. In Examples 1-1, 2-9 to 2-12, the weight-average molecular weight and melt enthalpy of the fifth resin material in Example 2-12 are greater than those in Example 1-1, and the melt index is less than that in Example 1-1. The obtained closed-cell temperature and film-breaking temperature of the second base film are relatively appropriate, so its high-temperature hot box performance is better, but the porosity of the second base film is small, which affects the kinetic performance of the lithium-ion battery.

[0206] Whether there are characteristic peaks C, D, and E in the DSC spectrum of the second base film is affected by the melt enthalpy, melt index and weight-average molecular weight of the third resin material, the fourth resin material and the fifth resin material. It can be seen from Examples 2-1 to 2-25 that when the above parameters of the second resin material are within the scope of the present application, the DSC spectrum of the second base film has characteristic peaks C, D, and E. Specifically, from Figure 6 It can be seen that there are characteristic peaks in the DSC spectrum of the second base film in Example 1-1 at 120 °C to 126 °C, 128 °C to 134 °C, and 150 °C to 160 °C, that is, there are characteristic peaks C, D, and E.

[0207] The mass percentage contents of the third resin material, the fourth resin material and the fifth resin material will affect the closed-cell temperature and film-breaking temperature of the second base film, and further affect the high-temperature hot box performance of the lithium-ion battery. It can be seen from Examples 1-1, 2-13 to 2-19 that when the above parameters are within the scope of the present application, the obtained lithium-ion battery has a high passing rate in the hot box test at 130 °C and 132 °C, indicating that the obtained lithium-ion battery has good high-temperature hot box performance. In addition, the Hi-pot excellent rate and K-value excellent rate are relatively high, and the manufacturing excellent rate can be taken into account at the same time.

[0208] It can be seen from Examples 1-1, 2-20 to 2-23 that when the thickness of the second base film is within the scope of this application, the obtained lithium-ion battery has a high passing rate in the hot box test at 130 °C and 132 °C, and a high excellent rate of Hi-pot and K value, indicating that the obtained lithium-ion battery can balance the manufacturing excellent rate and high-temperature hot box performance. In Example 2-23, the thickness of the first base film is much larger than that in Example 1-1, and the obtained second base film has greater puncture resistance, and the closed pore temperature and film rupture temperature are also appropriate, so its high-temperature hot box performance and manufacturing excellent rate are better. However, the thickening of the second base film will increase the lithium-ion transmission path and thus affect the kinetic performance of the lithium-ion battery, and at the same time, it will also affect the energy density of the lithium-ion battery.

[0209] The foregoing are only the preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of this application shall be included within the scope of protection of this application.

Claims

1. A secondary battery comprising an electrode assembly of a wound structure, wherein the electrode assembly comprises a positive electrode sheet, a negative electrode sheet, a first separator and a second separator, and at least a portion of the negative electrode sheet is located between the first separator and the second separator; The first diaphragm includes a first base film, the second diaphragm includes a second base film, the puncture resistance F1 of the first base film is greater than the puncture resistance F2 of the second base film, the closed pore temperature T12 of the second base film is less than the closed pore temperature T11 of the first base film, and the rupture temperature T22 of the second base film is greater than the rupture temperature T21 of the first base film, wherein, 300gf≤F1≤650gf, T12≤140℃, T22≥150℃.

2. The secondary battery according to claim 1, wherein The electrode assembly includes a straight area and a corner area. In the corner area, a first positive electrode sheet corner segment is adjacent to a second diaphragm corner segment, and the first positive electrode sheet corner segment is closer to the winding center of the electrode assembly than the second diaphragm corner segment.

3. The secondary battery according to claim 1, which satisfies at least one of the following characteristics: (1) 400gf ≤ F1 ≤ 500gf; (2)120℃≤T12≤140℃； (3)160℃≤T22≤180℃。 4. The secondary battery according to claim 1, wherein The first base film includes a first resin material and a second resin material, wherein the first resin material has a melting enthalpy H1 of 185 J / g to 195 J / g and a melt index MFR1 of 0.4 g / 10 min to 0.6 g / 10 min, and the second resin material has a melting enthalpy H2 of 130 J / g to 180 J / g and a melt index MFR2 of 0.1 g / 10 min to 1.0 g / 10 min; The second base film includes a third resin material, a fourth resin material and a fifth resin material. The melting enthalpy H3 of the third resin material is 140 J / g to 150 J / g, and the melt index MFR3 is 6 g / 10min to 14 g / 10min. The melting enthalpy H4 of the fourth resin material is 185 J / g to 195 J / g, and the melt index MFR4 is 0.4 g / 10min to 0.6 g / 10min. The melting enthalpy H5 of the fifth resin material is 130 J / g to 180 J / g, and the melt index MFR5 is 0.1 g / 10min to 100 g / 10min.

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

6. The secondary battery according to claim 4, wherein The weight average molecular weight of the first resin material is 50W to 90W, and the weight average molecular weight of the second resin material is 100W to 200W.

7. The secondary battery according to claim 4, wherein Based on the mass of the second base film, the mass percentage W3 of the third resin material is 5% to 15%, the mass percentage W4 of the fourth resin material is 83% to 93%, and the mass percentage W5 of the fifth resin material is 1% to 3%.

8. The secondary battery according to claim 4, wherein The weight average molecular weight of the third resin material is 20W to 40W, the weight average molecular weight of the fourth resin material is 50W to 90W, and the weight average molecular weight of the fifth resin material is 5W to 50W.

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

10. The secondary battery according to claim 9, wherein The fifth resin material is different in type from the third resin material and the fourth resin material.

11. The secondary battery according to any one of claims 1 to 10, wherein In the differential scanning calorimetry test spectrum of the first base film, characteristic peaks exist at 128°C to 134°C and 136°C to 140°C.

12. The secondary battery according to any one of claims 1 to 10, wherein In the differential scanning calorimetry test spectrum of the second base film, characteristic peaks exist at 120°C to 126°C, 128°C to 134°C, and 150°C to 160°C.

13. The secondary battery according to any one of claims 1 to 10, which satisfies at least one of the following characteristics: (1) 200gf ≤ F2 ≤ 300gf; (2)145℃≤T11≤165℃； (3)150℃≤T21≤180℃。 14. The secondary battery according to any one of claims 1 to 10, wherein The thickness of the first base film and the second base film is each independently 4 μm to 7 μm.

15. The secondary battery according to any one of claims 1 to 10, wherein The negative electrode plate includes a negative electrode material layer, the negative electrode material layer includes a negative electrode material, and the negative electrode material includes a silicon material.

16. The secondary battery according to claim 15, wherein The silicon material includes at least one of silicon element, silicon carbon compound, silicon oxygen compound or silicon alloy. 17 . An electronic device comprising the secondary battery according to claim 1 .

Images