Battery, and electrochemical device and electronic device comprising same

Abstract

A battery, and an electrochemical device and electronic device comprising same. The battery comprises an electrode assembly and a packaging bag; the electrode assembly comprises electrode sheets and a separator; the separator comprises a porous base material; at least one surface of the porous base material is provided with a first coating; the first coating comprises a first polymer and a second polymer which have different melting points; and the battery satisfies 0.077≤(3.0-D2 / D1) / T≤0.118. The battery has good electrochemical performance, and the battery has a relatively wide hot box window and a relatively high hot box test passing rate.

Description

Battery, and electrochemical device and electronic device containing the same

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on August 11, 2023, with application number 202311017486.5 and invention name “Battery, and electrochemical device and electronic device containing the same”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the field of electrochemical technology, and specifically relates to a battery, and an electrochemical device and an electronic device containing the same. Background Art

[0003] Fast charging and high energy density are major trends in battery development. With the rapid increase in battery charge rate and energy density, the battery's hot box window is becoming increasingly narrow. Currently, improving the battery's hot box test pass rate often compromises the battery's electrochemical performance during normal use. Therefore, how to broaden the battery's hot box window and improve its hot box test pass rate without compromising its electrochemical performance during normal use has become a pressing technical challenge for those skilled in the art.

[0004] Summary of the Invention

[0005] The present application provides a battery, and an electrochemical device and an electronic device containing the same, which can enable the battery to have good electrochemical performance, and can also enable the battery to have a wider hot box window and a higher hot box test pass rate.

[0006] A first aspect of the present application provides a battery, comprising an electrode assembly and a packaging bag, wherein the electrode assembly comprises an electrode sheet and a separator.

[0007] The separator includes a porous substrate having a first coating disposed on at least one surface of the porous substrate. The first coating includes a first polymer and a second polymer having different melting points.

[0008] The battery satisfies 0.077≤(3.0-D2 / D1) / T≤0.118; D1 is the thickness of the battery obtained by testing after the battery is fully charged at 25°C, and the unit is mm; D2 is the thickness of the battery obtained by testing again after the fully charged battery is placed vertically in a hot box, heating from 25°C to 130°C at a rate of 5°C / min and standing for 60 minutes, and the battery temperature is dropped to 25°C, and the unit is mm; T is the adhesion between the first coating of the diaphragm and the electrode adjacent to the first coating, and the unit is N / m.

[0009] Batteries that meet 0.077≤(3.0-D2 / D1) / T≤0.118 can have a wider hot box window and a higher hot box test pass rate, while also having good electrochemical performance.

[0010] When the battery that meets 0.077≤(3.0-D2 / D1) / T≤0.118 is in the heat generation stage, the interface between the electrode and the diaphragm can be fully opened, so that the gas and heat at the interface can be transferred to the packaging bag in time, thereby reducing the heat accumulation at the interface, and then widening the battery's hot box window and improving the battery's hot box test pass rate.

[0011] Batteries that meet 0.077≤(3.0-D2 / D1) / T≤0.118 also have suitable interfacial adhesion under normal use conditions, thereby reducing the probability of deformation problems in the electrode assembly after the battery charge and discharge cycle, and further enabling the battery to have good electrochemical performance.

[0012] In any embodiment, the electrode sheets include a positive electrode sheet and a negative electrode sheet, and a first coating is provided on a surface of the porous substrate facing the positive electrode sheet.

[0013] In any embodiment, the battery satisfies 0.096≤(3.0-D2 / D1) / T≤0.110. By further adjusting (3.0-D2 / D1) / T within the above range, the battery can better achieve both good electrochemical performance and a high hot box test pass rate.

[0014] In any embodiment, T is 5.42 N / m to 10.23 N / m; and / or D2 / D1 is 2.12 to 2.42.

[0015] In any embodiment, T is 5.91 N / m to 7.91 N / m; and / or D2 / D1 is 2.21 to 2.38.

[0016] By adjusting the bonding force T between the first coating of the diaphragm and the electrode adjacent to the first coating within the above range, the battery can have appropriate interface bonding during normal use, thereby reducing the probability of deformation of the electrode assembly after the battery charge and discharge cycle, and thus the battery can have good electrochemical properties; by adjusting the bonding force T between the first coating of the diaphragm and the electrode adjacent to the first coating within the above range, it is also beneficial for the interface between the electrode and the diaphragm to be fully opened when the battery is in the heat generation stage, thereby allowing the gas and heat at the interface to be transferred to the packaging bag in a timely manner, thereby reducing the heat accumulation at the interface, and thus widening the battery's hot box window and improving the battery's hot box test pass rate.

[0017] When D2 / D1 is within the above range, it means that when the battery is in the heat generation stage, the interface between the electrode and the diaphragm can be fully opened, so that the gas and heat at the interface can be transferred to the packaging bag in time, thereby reducing the heat accumulation at the interface, and then widening the battery's hot box window and improving the battery's hot box test pass rate.

[0018] In any embodiment, the melting point of the first polymer is denoted as T m1 The melting point of the second polymer is recorded as T m2 , T m1 60℃ to 100℃, T m2 Greater than or equal to 130℃, and T m2 -T m1 By adjusting the melting point T of the first polymer m1 , the melting point T of the second polymer m2 and T m2 -T m1 Within the above range, the battery can have good electrochemical performance, and can also broaden the battery's hot box window and improve the battery's hot box test pass rate.

[0019] In any embodiment, T m1 70℃ to 90℃, T m2 is 135°C to 160°C, and T m2 -T m1 The temperature range is 50°C to 80°C. This can make the battery have better electrochemical performance, further broaden the battery's hot box window, and further improve the battery's hot box test pass rate.

[0020] In any embodiment, the volume distribution particle size Dv of the particles of the first polymer is (1) 50 and the volume distribution particle size Dv of the particles of the second polymer (2) 50 satisfies 0.50≤Dv (2) 50 / Dv (1) 50≤1.25, and the volume distribution particle size Dv of the particles of the first polymer (1) 90 and the volume distribution particle size Dv of the particles of the second polymer (2) 50 satisfies 2.0≤Dv (1) 90 / Dv (2) 50≤5.0.

[0021] In any embodiment, 0.60≤Dv (2) 50 / Dv (1) 50≤0.83, and 3.00≤Dv (1) 90 / Dv (2) 50≤4.17.

[0022] By adjusting Dv (2) 50 / Dv (1) 50 and Dv (1) 90 / Dv (2) 50 Within the above range, it is beneficial for the second polymer to be dispersed around the first polymer, improving the film-forming problem of the first polymer, and also beneficial for the first coating to have both suitable adhesion and air permeability, thereby enabling the battery to have good electrochemical performance and a higher hot box test pass rate.

[0023] In any embodiment, the volume distribution particle size Dv of the particles of the first polymer is (1) 50 is 0.8μm to 2.0μm.

[0024] In any embodiment, the volume distribution particle size Dv of the particles of the first polymer is (1) 90 is 2.0μm to 5.0μm.

[0025] By adjusting the volume distribution particle size Dv of the particles of the first polymer (1) 50 and / or Dv (1) When the thickness is within the above range, the first coating layer can have both suitable adhesion and air permeability, thereby enabling the battery to have good electrochemical performance and a high hot box test pass rate.

[0026] In any embodiment, the volume distribution particle size Dv of the particles of the second polymer is (2) 50 is 0.54μm to 1.5μm.

[0027] By adjusting the volume distribution particle size Dv of the second polymer particles (2) When the thickness is within the above range, the first coating layer can have both suitable adhesion and air permeability, thereby enabling the battery to have good electrochemical performance and a high hot box test pass rate.

[0028] In any embodiment, the weight content of the first polymer is recorded as m1, and the weight content of the second polymer is recorded as m2, both based on the total weight of the first coating, m1 is 50% to 86%, and m2 is 9% to 45%.

[0029] In any embodiment, m1 is 70% to 82%, and m2 is 13% to 25%.

[0030] By adjusting the weight content m1 of the first polymer and the weight content m2 of the second polymer within the above range, it is beneficial for the diaphragm and the electrode to have appropriate adhesion, and helps to fully open the interface between the electrode and the diaphragm when the battery is in the heat generation stage, so that the gas and heat at the interface can be transferred to the packaging bag in time, thereby reducing the heat accumulation at the interface, and then widening the hot box window of the battery and improving the pass rate of the hot box test of the battery; it can also make the first coating have both appropriate adhesion and air permeability, so that the battery can also have good electrochemical properties.

[0031] In any embodiment, the weight average molecular weight of the first polymer is denoted as M w1 The weight average molecular weight of the second polymer is recorded as M w2 , M w1 150,000 to 260,000, M w2 It is between 1.18 million and 2 million.

[0032] By adjusting M w1 and M w2 Within the above range, the battery can have better electrochemical performance, further broaden the battery's hot box window, and further improve the battery's hot box test pass rate.

[0033] In any embodiment, the first polymer comprises at least one of a homopolymer and a copolymer of at least one of ethylene, propylene, vinylidene fluoride, acrylic acid, acrylic ester, styrene, acrylonitrile, maleic anhydride, vinyl chloride, and allyl chloride.

[0034] In any embodiment, the second polymer includes at least one of a homopolymer and a copolymer of at least one monomer selected from the group consisting of vinylidene fluoride, hexafluoropropylene, propylene, vinyl chloride, styrene, butadiene, acrylate, and acrylic acid.

[0035] In any embodiment, a first coating is provided on one surface of the porous substrate, and a second coating is provided on another surface of the porous substrate. The second coating includes a third polymer, the third polymer including at least one of a homopolymer and a copolymer of at least one of butyl acrylate, octyl acrylate, isooctyl acrylate, styrene, and butadiene, and the melting point of the third polymer is 50°C to 70°C. This can reduce the probability of deformation of the electrode assembly after battery charge and discharge cycles, thereby also improving the battery's electrochemical performance.

[0036] In any embodiment, the coating weight of the first coating is 0.5 mg / 5000 mm 2 Up to 3mg / 5000mm 2 .

[0037] By adjusting the coating weight of the first coating layer within the above range, the first coating layer can have suitable adhesion, that is, the first coating layer has good adhesion when the battery is in normal use, and has lower adhesion when the battery is in the heat generation stage. This helps to fully open the interface between the electrode and the diaphragm when the battery is in the heat generation stage, so that the gas and heat at the interface can be transferred to the packaging bag in time, reducing heat accumulation at the interface, and thus widening the battery's hot box window and improving the battery's hot box test pass rate; it can also reduce the probability of deformation of the electrode assembly after the battery charge and discharge cycle, and thus can also make the battery have good electrochemical properties.

[0038] In any embodiment, the thickness of the first coating layer is 0.5 μm to 2.8 μm.

[0039] By adjusting the thickness of the first coating within the above range, the first coating can have suitable adhesion, that is, the first coating has good adhesion when the battery is in normal use, and has lower adhesion when the battery is in the heat generation stage. This helps to fully open the interface between the electrode and the diaphragm when the battery is in the heat generation stage, so that the gas and heat at the interface can be transferred to the packaging bag in time, reducing heat accumulation at the interface, and thus widening the battery's hot box window and improving the battery's hot box test pass rate; it can also reduce the probability of deformation of the electrode assembly after the battery charge and discharge cycle, and thus can also make the battery have good electrochemical properties.

[0040] In any embodiment, the battery is a pouch battery.

[0041] In any embodiment, the positive electrode plate includes a positive electrode active material, and the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, and their respective modified compounds, and the modification includes doping modification, surface coating modification, or simultaneous doping and coating modification.

[0042] In any embodiment, the negative electrode plate includes a negative electrode active material, the negative electrode active material includes at least one of graphite and a silicon-based material, and the weight content of the silicon-based material in the negative electrode active material is 0% to 25%.

[0043] A second aspect of the present application provides an electrochemical device, comprising the battery according to the first aspect of the present application.

[0044] A third aspect of the present application provides an electronic device comprising the battery according to the first aspect of the present application and / or the electrochemical device according to the second aspect of the present application. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as limiting the present application. Based on the technical solutions and embodiments provided in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present application.

[0046] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0047] In the description herein, unless otherwise specified, “above” and “below” include the number itself.

[0048] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application). Unless otherwise specified, the test temperature of each parameter mentioned in this application is 25°C and the test pressure is standard atmospheric pressure.

[0049] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0050] The term "plurality" means more than two.

[0051] The battery mentioned in the embodiments of the present application may include any device that undergoes an electrochemical reaction. In some embodiments, the battery may include a lithium-ion battery.

[0052] The battery's hot box failure process can be divided into three stages: heat generation, heat accumulation, and thermal runaway. Thermal runaway involves complex reactions, including the decomposition of the solid electrolyte interface (SEI), reactions between the cathode and the electrolyte, reactions between the anode and the electrolyte, and the decomposition of the electrolyte itself.

[0053] In the heat generation stage, the decomposition of the SEI film generates heat, which brings about the initial heat accumulation of the battery. The heat continues to accumulate until the battery reaches the heat accumulation stage. In the heat accumulation stage, the SEI film continues to decompose, causing the electrolyte to be continuously reduced, thereby leading to a reaction between the positive electrode and the electrolyte. In this stage, the battery will exhaust and may also produce a large amount of smoke. The continuous accumulation of heat will enter the thermal runaway stage. In the thermal runaway stage, the positive and negative electrodes react rapidly, causing the temperature to rise sharply, which may cause combustion or even cause the battery to explode.

[0054] Currently, strategies commonly used to broaden the battery's hot box window and improve the battery's hot box test pass rate include adjusting the electrolyte system composition and applying a low-adhesion coating to the separator surface. However, adjusting the electrolyte system composition can easily affect the battery's electrochemical performance during normal use; and applying a low-adhesion coating to the separator surface can easily reduce the battery's interfacial adhesion, which can easily lead to deformation of the electrode assembly after battery charge and discharge cycles, further affecting the battery's electrochemical performance during normal use, such as cycling performance.

[0055] The embodiments of the present application provide a battery that can have good electrochemical performance, a wider hot box window, and a higher hot box test pass rate.

[0056] The battery provided in the embodiment of the present application includes an electrode assembly and a packaging bag.

[0057] The electrode assembly includes an electrode sheet and a separator. The separator includes a porous substrate, at least one surface of the porous substrate is provided with a first coating, and the first coating includes a first polymer and a second polymer with different melting points.

[0058] The battery satisfies 0.077≤(3.0-D2 / D1) / T≤0.118; D1 is the thickness of the battery obtained by testing after the battery is fully charged at 25°C, and the unit is mm; D2 is the thickness of the battery obtained by testing again after the fully charged battery is placed vertically in a hot box, heating from 25°C to 130°C at a rate of 5°C / min and standing for 60 minutes, and the battery temperature is dropped to 25°C, and the unit is mm; T is the adhesion between the first coating of the diaphragm and the electrode adjacent to the first coating, and the unit is N / m.

[0059] The thickness direction of the battery is perpendicular to the main surface of the battery (ie, the surface with the largest battery area).

[0060] The thickness D1 of the battery can be tested as follows: at 25°C, let the battery stand for 5 minutes, charge at a constant current of 0.5C with a cut-off current of 0.025C. During the charging process, when the battery voltage reaches the charge limit voltage, switch to constant voltage charging until the charging current ≤ the cut-off current; then let the battery stand for 60 minutes and test the battery thickness, which is D1.

[0061] The adhesion force T between the first coating layer of the diaphragm and the electrode adjacent to the first coating layer can be tested according to the following steps: after the temperature of the battery after the hot box test is reduced to 25°C, the diaphragm and the electrode are disassembled and removed from the battery together, and then the adhesion force T between the first coating layer of the diaphragm and the electrode adjacent to the first coating layer is tested using the 180° peel test standard. The test standard can refer to GB / T 2790-1995. The testing instrument can be a tensile testing machine. After the test is completed, the ratio of the average value of the force in the plateau section of the peeling force curve to the width of the sample can be taken as the adhesion force T between the first coating layer of the diaphragm and the electrode adjacent to the first coating layer. The tensile rate (i.e., peeling rate) of the tensile testing machine is 50 mm / min. The test temperature is 25°C.

[0062] When conducting a 180° peel test, the separator and electrode can be removed from the battery and cut into 15mm×54.2mm strips for testing.

[0063] The melting point of the polymer is different, and its film-forming properties and adhesion are generally different. Generally, the film-forming properties of the polymer with low melting point are better and adhesion is also stronger. When it is used for the first coating of the diaphragm, the diaphragm is in the process of battery preparation (such as electrode assembly baking, hot pressing and forming processes) and the first coating in the process of normal use of the battery. The polymer softening and plugging risk is higher, which can affect the electrochemical performance of the battery. The first coating of the diaphragm provided in the embodiment of the present application includes the first polymer and the second polymer with different melting points, and by using a polymer combination with different film-forming properties and / or adhesion, the polymer with a high melting point can be dispersed around the polymer with a low melting point, thereby reducing the diaphragm in the process of battery preparation (such as electrode assembly baking, hot pressing and forming processes) and the first coating in the process of normal use of the battery. The first coating can also be made to have both suitable adhesion and air permeability.

[0064] The adhesion force T between the separator's first coating and the electrode adjacent to it reflects the bonding characteristics between the separator's first coating and the electrode adjacent to it during normal battery use. Increasing the adhesion force T between the separator's first coating and the electrode adjacent to it reduces the probability of electrode assembly deformation after battery charge and discharge cycles. However, this is not conducive to fully opening the electrode-diaphragm interface during the battery's heat generation phase, thereby hindering heat accumulation at the interface.

[0065] D2 / D1 can reflect the thickness change before and after the fully charged battery hot box test. When D2 / D1 is large, it means that when the battery is in the heat generation stage, the interface between the electrode and the diaphragm can be fully opened. However, when the battery is in normal use, the adhesion between the first coating of the diaphragm and the electrode adjacent to the first coating may be low, which increases the probability of deformation of the electrode assembly after the battery charge and discharge cycle and deteriorates the electrochemical performance of the battery. When D2 / D1 is small, it means that when the battery is in the heat generation stage, the interface between the electrode and the diaphragm cannot be opened or is not opened enough, which is not conducive to reducing heat accumulation at the interface.

[0066] Batteries that meet 0.077≤(3.0-D2 / D1) / T≤0.118 can have a wider hot box window and a higher hot box test pass rate, while also having good electrochemical performance.

[0067] When the battery that meets 0.077≤(3.0-D2 / D1) / T≤0.118 is in the heat generation stage, the interface between the electrode and the diaphragm can be fully opened, so that the gas and heat at the interface can be transferred to the packaging bag in time, thereby reducing the heat accumulation at the interface, and then widening the battery's hot box window and improving the battery's hot box test pass rate.

[0068] Batteries that meet 0.077≤(3.0-D2 / D1) / T≤0.118 also have suitable interfacial adhesion under normal use conditions, thereby reducing the probability of deformation problems in the electrode assembly after the battery charge and discharge cycle, and further enabling the battery to have good electrochemical performance.

[0069] For batteries that meet the (3.0-D2 / D1) / T requirement of less than 0.077, the adhesion force T between the first coating layer of the diaphragm and the electrode adjacent to the first coating layer is relatively large after the hot box test. When the battery is in the heat generation stage, the adhesion force between the first coating layer of the diaphragm and the electrode is relatively large, resulting in the electrode-diaphragm interface not opening or not opening to a sufficient degree. As a result, the gas and heat at the interface cannot be transferred to the packaging bag in a timely manner, and the heat at the interface continues to accumulate. Therefore, the hot box test pass rate of batteries that meet the (3.0-D2 / D1) / T requirement of less than 0.077 is relatively low. For batteries satisfying (3.0-D2 / D1) / T less than 0.077, the bonding force T between the first coating of the diaphragm and the electrode adjacent to the first coating is large after the hot box test. This also indicates that the design of the first coating of the diaphragm is unreasonable, the bonding property of the first polymer and / or the second polymer in the first coating is too strong, and the fluidity of the first polymer and / or the second polymer after softening by heat is strong. This will also lead to a high risk of pore plugging in the diaphragm during the battery preparation process (such as electrode assembly baking, hot pressing, etc.) and during normal use of the battery, which will affect the electrochemical performance of the battery.

[0070] For batteries that meet the requirement of (3.0-D2 / D1) / T greater than 0.118, the bonding force T between the first coating of the diaphragm and the electrode adjacent to the first coating is relatively small after the hot box test. This indicates that the interfacial bonding during normal use of the battery is poor, and the electrode assembly is prone to deformation after the battery charge and discharge cycle, which in turn affects the electrochemical performance of the battery during normal use. When the battery that meets the requirement of (3.0-D2 / D1) / T greater than 0.118 is in the heat generation stage, the interface between the electrode and the diaphragm may not open or may not open enough, so that the gas and heat at the interface cannot be transferred to the packaging bag in time, causing the heat at the interface to continue to accumulate. Therefore, the hot box test pass rate of batteries that meet the requirement of (3.0-D2 / D1) / T greater than 0.118 is still relatively low.

[0071] In some embodiments, the battery satisfies 0.088≤(3.0-D2 / D1) / T≤0.118, 0.090≤(3.0-D2 / D1) / T≤0.115, 0.092≤(3.0-D2 / D1) / T≤0.113, 0.094≤(3.0-D2 / D1) / T≤0.113, and 0.096≤(3.0-D2 / D1) / T≤0.110.

[0072] By further adjusting (3.0-D2 / D1) / T within the above range, the battery can better achieve both good electrochemical performance and a higher hot box test pass rate.

[0073] In some embodiments, the electrode sheets include a positive electrode sheet and a negative electrode sheet, and a first coating is provided on a surface of the porous substrate facing the positive electrode sheet.

[0074] In some embodiments, the bonding force T between the first coating layer of the diaphragm and the electrode piece adjacent to the first coating layer can be 5.42 N / m to 10.23 N / m, for example, 5.42 N / m, 5.56 N / m, 5.72 N / m, 5.91 N / m, 6.04 N / m, 6.16 N / m, 6.40 N / m, 6.58 N / m, 6.78 N / m, 6.92 N / m, 7.06 N / m, 7.20 N / m, 7.41 N / m, 7.56 N / m, 7.68 N / m, 7.80 N / m, 7.91 N / m, 8.10 N / m, 8.39 N / m, 8.68 N / m, 8.88 N / m, 9.10 N / m, 9.82 N / m, 10.11 N / m, 10.23 N / m, or a range consisting of any two of the foregoing values. Optionally, the adhesion force T between the first coating layer of the diaphragm and the pole piece adjacent to the first coating layer can be 5.91 N / m to 7.91 N / m.

[0075] By adjusting the bonding force T between the first coating of the diaphragm and the electrode adjacent to the first coating within the above range, the battery can have appropriate interface bonding during normal use, thereby reducing the probability of deformation of the electrode assembly after the battery charge and discharge cycle, and thus the battery can have good electrochemical properties; by adjusting the bonding force T between the first coating of the diaphragm and the electrode adjacent to the first coating within the above range, it is also beneficial for the interface between the electrode and the diaphragm to be fully opened when the battery is in the heat generation stage, thereby allowing the gas and heat at the interface to be transferred to the packaging bag in a timely manner, thereby reducing the heat accumulation at the interface, and thus widening the battery's hot box window and improving the battery's hot box test pass rate.

[0076] In some embodiments, D2 / D1 is 2.12 to 2.42, for example, 2.12, 2.15, 2.17, 2.20, 2.21, 2.23, 2.25, 2.27, 2.29, 2.31, 2.35, 2.38, 2.40, 2.42, or a range consisting of any two of the foregoing values. Alternatively, D2 / D1 can be 2.21 to 2.38.

[0077] When D2 / D1 is within the above range, it means that when the battery is in the heat generation stage, the interface between the electrode and the diaphragm can be fully opened, so that the gas and heat at the interface can be transferred to the packaging bag in time, thereby reducing the heat accumulation at the interface, and then widening the battery's hot box window and improving the battery's hot box test pass rate.

[0078] The above-mentioned parameters D2 / D1 and parameter T can be adjusted by adjusting parameters such as the melting point, volume distribution particle size, weight average molecular weight and weight content of the first polymer and the second polymer, as well as parameters such as the coating weight and thickness of the first coating layer.

[0079] In some embodiments, the melting point of the first polymer is denoted as T m1 , the melting point of the second polymer is recorded as T m2 , T m1 It can be from 60℃ to 100℃, T m2 Can be greater than or equal to 130℃, and T m2 -T m1 It can be from 40°C to 120°C.

[0080] The melting point T of the first polymer in the first coating layer m1When within the above range, the first coating layer can have good film-forming properties and suitable adhesion, that is, the first coating layer has good adhesion when the battery is in normal use, and has lower adhesion when the battery is in the heat generation stage, which is beneficial to reduce the probability of deformation of the electrode assembly after the battery charge and discharge cycle, thereby making the battery have good electrochemical properties, and can also fully open the interface between the electrode and the diaphragm when the battery is in the heat generation stage, and transfer the gas and heat at the interface to the packaging bag in time, reducing the heat accumulation at the interface, thereby widening the battery's hot box window and improving the battery's hot box test pass rate.

[0081] The melting point T of the second polymer in the first coating m2 When the amount is within the above range, the first coating layer can have appropriate gas permeability, thereby enabling the battery to have good electrochemical performance.

[0082] By adjusting T m2 -T m1 Within the above range, the second polymer can be dispersed around the first polymer, thereby reducing the risk of polymer softening and clogging in the first coating during the battery preparation process (such as electrode assembly baking, hot pressing, etc.) and normal use of the battery, thereby enabling the battery to have good electrochemical properties; it is also beneficial for the battery to be in the heat generation stage so that the interface between the electrode and the diaphragm is fully opened, and the gas and heat at the interface are transferred to the packaging bag in time, reducing heat accumulation at the interface, thereby widening the battery's hot box window and improving the battery's hot box test pass rate.

[0083] Therefore, by adjusting the melting point T of the first polymer m1 , the melting point T of the second polymer m2 and T m2 -T m1 Within the above range, the battery can have good electrochemical performance, and can also broaden the battery's hot box window and improve the battery's hot box test pass rate.

[0084] Melting point T of the first polymer m1 When the melting point T of the first polymer is too high, the first coating layer will have poor adhesion and film-forming properties under normal battery use, which will reduce the interfacial adhesion of the battery, and easily lead to deformation of the electrode assembly after the battery charge and discharge cycle, thereby affecting the electrochemical performance of the battery during normal use. m1When the first coating is large, when the battery is in the heat generation stage, the first polymer softens due to heat and increases the adhesion between the first coating of the diaphragm and the electrode, which is not conducive to the full opening of the interface between the electrode and the diaphragm, and the gas and heat at the interface cannot be transferred to the packaging bag in time, thereby causing the heat at the interface to continue to accumulate, and the battery's hot box test pass rate is low.

[0085] Melting point T of the first polymer m1 When the first polymer is relatively small, the fluidity of the first polymer after being softened by heat during the battery preparation process (such as baking of the electrode assembly, hot pressing, etc.) and normal use of the battery is relatively strong, which leads to a higher risk of diaphragm clogging, thereby affecting the electrochemical performance of the battery during normal use.

[0086] Melting point T of the second polymer m2 When the melting point T of the second polymer is small, the fluidity of the second polymer after being softened by heat during the battery preparation process (such as electrode assembly baking, hot pressing, etc.) and normal use of the battery is strong, which leads to a high risk of diaphragm pore blocking, thereby affecting the electrochemical performance of the battery during normal use; at the same time, the melting point T of the second polymer is large. m2 When the temperature is relatively small, when the battery is in the heat generation stage, the softening of the second polymer by heat will also increase the bonding force between the first coating of the diaphragm and the electrode adjacent to the first coating, which is not conducive to the full opening of the interface between the electrode and the diaphragm, and the gas and heat at the interface cannot be transferred to the packaging bag in time, thereby causing the heat at the interface to continue to accumulate, and the battery's hot box test pass rate is low.

[0087] T m2 -T m1 When the value is smaller, it is not conducive to the dispersion of the second polymer around the first polymer, thereby increasing the risk of clogging of the diaphragm during the battery preparation process (such as electrode assembly baking, hot pressing and other processes) and during normal use of the battery, which will affect the electrochemical performance of the battery during normal use; it is also not conducive to fully opening the interface between the electrode and the diaphragm when the battery is in the heat generation stage, so that the gas and heat at the interface cannot be transferred to the packaging bag in time, and the heat at the interface continues to accumulate, and the battery's hot box test pass rate is low.

[0088] In some embodiments, the melting point of the first polymer is denoted as T m1 , the melting point of the second polymer is recorded as T m2 , T m1 It can be from 70℃ to 90℃, T m2 can be from 135°C to 160°C, and T m2 -T m1 It can be 50°C to 80°C.

[0089] This can make the battery have better electrochemical performance, further widen the battery's hot box window, and further improve the battery's hot box test pass rate.

[0090] The present application does not particularly limit the method for adjusting the melting points of the first and second polymers, as long as the objectives of the present application can be achieved. For example, the melting points of the first and second polymers can be adjusted by adjusting one or more of the weight-average molecular weight, crystallinity, and the composition and ratio of the comonomers.

[0091] In some embodiments, the volume distribution particle size Dv of the particles of the first polymer is (1) 50 and the volume distribution particle size Dv of the particles of the second polymer (2) 50 satisfies 0.50≤Dv (2) 50 / Dv (1) 50≤1.25, for example, Dv (2) 50 / Dv (1) 50 can be 0.50, 0.60, 0.67, 0.75, 0.83, 0.90, 1.00, 1.10, 1.25, or a range consisting of any two of the above values. Optionally, 0.60≤Dv (2) 50 / Dv (1) 50≤0.83.

[0092] By adjusting Dv (2) 50 / Dv (1) 50 Within the above range, the film-forming problem of the first polymer can be improved, so that the first coating layer has both suitable adhesion and air permeability, thereby enabling the battery to have good electrochemical performance and a higher hot box test pass rate.

[0093] Dv (2) 50 / Dv (1) When 50 is larger, the adhesion of the first coating layer is poor under normal use of the battery, thereby reducing the interfacial adhesion of the battery, which can easily lead to deformation of the electrode assembly after the battery charge and discharge cycle, thereby affecting the electrochemical performance of the battery during normal use.

[0094] Dv (2) 50 / Dv (1) When Dv is too small, the first coating has a strong adhesive property when the battery is in the heat generation stage, which is not conducive to the full opening of the interface between the electrode and the diaphragm, and thus the gas and heat at the interface cannot be transferred to the packaging bag in time, thereby causing the heat at the interface to continue to accumulate, and the battery's hot box test pass rate is low; at the same time, Dv (2) 50 / Dv (1)When 50 is small, it is not conducive to the dispersion of the second polymer around the first polymer, thereby resulting in poor air permeability of the diaphragm and a high risk of clogging the diaphragm during the battery preparation process (such as electrode assembly baking, hot pressing, etc.) and normal use of the battery, which in turn affects the electrochemical performance of the battery.

[0095] In some embodiments, the volume distribution particle size Dv of the particles of the first polymer is (1) 90 and the volume distribution particle size Dv of the particles of the second polymer (2) 50 satisfies 2.0≤Dv (1) 90 / Dv (2) 50≤5.0, for example, Dv (1) 90 / Dv (2) 50 can be 2.0, 2.25, 2.50, 2.80, 3.00, 3.25, 3.50, 3.75, 4.0, 4.17, 5.0 or a range consisting of any two of the above values. Optionally, 3.00≤Dv (1) 90 / Dv (2) 50≤4.17.

[0096] By adjusting Dv (1) 90 / Dv (2) 50 Within the above range, the film-forming problem of the first polymer can be improved, so that the first coating layer has both suitable adhesion and air permeability, thereby enabling the battery to have good electrochemical performance and a higher hot box test pass rate.

[0097] Dv (1) 90 / Dv (2) When 50 is larger, the adhesion of the first coating layer is poor under normal use of the battery, thereby reducing the interfacial adhesion of the battery, which can easily lead to deformation of the electrode assembly after the battery charge and discharge cycle, thereby affecting the electrochemical performance of the battery during normal use.

[0098] Dv (1) 90 / Dv (2) When Dv is too small, the first coating has a strong adhesive property when the battery is in the heat generation stage, which is not conducive to the full opening of the interface between the electrode and the diaphragm, and thus the gas and heat at the interface cannot be transferred to the packaging bag in time, thereby causing the heat at the interface to continue to accumulate, and the battery's hot box test pass rate is low; at the same time, Dv (1) 90 / Dv (2) When 50 is large, it is not conducive to the dispersion of the second polymer around the first polymer, thereby resulting in poor air permeability of the diaphragm and a high risk of clogging the diaphragm during the battery preparation process (such as electrode assembly baking, hot pressing, etc.) and normal use of the battery, which in turn affects the electrochemical performance of the battery.

[0099] In some embodiments, the volume distribution particle size Dv of the particles of the first polymer is (1) 50 and the volume distribution particle size Dv of the particles of the second polymer (2) 50 satisfies 0.50≤Dv (2) 50 / Dv (1) 50≤1.25, and the volume distribution particle size Dv of the particles of the first polymer (1) 90 and the volume distribution particle size Dv of the particles of the second polymer (2) 50 satisfies 2.0≤Dv (1) 90 / Dv (2) 50≤6.0. Optionally, 0.60≤Dv (2) 50 / Dv (1) 50≤0.83 and 3.00≤Dv (1) 90 / Dv (2) 50≤4.17.

[0100] By adjusting Dv (2) 50 / Dv (1) 50 and Dv (1) 90 / Dv (2) 50 Within the above range, it is beneficial for the second polymer to be dispersed around the first polymer, improving the film-forming problem of the first polymer, and also beneficial for the first coating to have both suitable adhesion and air permeability, thereby enabling the battery to have good electrochemical performance and a higher hot box test pass rate.

[0101] In some embodiments, the volume distribution particle size Dv of the particles of the first polymer is (1) 50 may be 0.8 μm to 2.0 μm, optionally 1.0 μm to 2.0 μm, or 1.0 μm to 1.5 μm.

[0102] In some embodiments, the volume distribution particle size Dv of the particles of the first polymer is (1) 90 may be 2.0 μm to 5.0 μm.

[0103] By adjusting the volume distribution particle size Dv of the particles of the first polymer (1) 50 and / or Dv (1) When the thickness is within the above range, the first coating layer can have both suitable adhesion and air permeability, thereby enabling the battery to have good electrochemical performance and a high hot box test pass rate.

[0104] Volume distribution particle size Dv of the first polymer particles (1) 50 and / or Dv (1)When 90 is larger, the adhesion of the first coating layer is poor under normal use of the battery, thereby reducing the interfacial adhesion of the battery, which can easily lead to deformation of the electrode assembly after the battery charge and discharge cycle, thereby affecting the electrochemical performance of the battery during normal use.

[0105] Volume distribution particle size Dv of the first polymer particles (1) 50 and / or Dv (1) When the 90 is too small, the first coating has a strong adhesive property when the battery is in the heat generation stage, which is not conducive to the full opening of the interface between the electrode and the diaphragm, and thus the gas and heat at the interface cannot be transferred to the packaging bag in time, thereby causing the heat at the interface to continue to accumulate, and the battery's hot box test pass rate is low; at the same time, the volume distribution particle size Dv of the first polymer particles is (1) 50 and / or Dv (1) When 90 is smaller, the permeability of the diaphragm is poor and the risk of clogging the diaphragm during the battery preparation process (such as electrode assembly baking, hot pressing and other processes) and the normal use of the battery is still high, which will further affect the electrochemical performance of the battery.

[0106] In some embodiments, the volume distribution particle size Dv of the particles of the second polymer is (2) 50 may be 0.54 μm to 1.5 μm.

[0107] By adjusting the volume distribution particle size Dv of the second polymer particles (2) When the thickness is within the above range, the first coating layer can have both suitable adhesion and air permeability, thereby enabling the battery to have good electrochemical performance and a high hot box test pass rate.

[0108] Volume distribution particle size Dv of the second polymer particles (2) When 50 is larger, the adhesion of the first coating layer is poor under normal use of the battery, thereby reducing the interfacial adhesion of the battery, which can easily lead to deformation of the electrode assembly after the battery charge and discharge cycle, thereby affecting the electrochemical performance of the battery during normal use.

[0109] Volume distribution particle size Dv of the second polymer particles (2) When the value of 50 is too small, the adhesion of the first coating is too strong when the battery is in the heat generation stage, which is not conducive to the full opening of the interface between the electrode and the diaphragm, and the gas and heat at the interface cannot be transferred to the packaging bag in time, thereby causing the heat at the interface to continue to accumulate, and the pass rate of the hot box test of the battery is low; at the same time, the volume distribution particle size Dv of the second polymer particles is too large. (2) When 50 is small, the air permeability of the diaphragm is poor and the risk of clogging the diaphragm during the battery preparation process (such as electrode assembly baking, hot pressing and other processes) and the normal use of the battery is still high, which will further affect the electrochemical performance of the battery.

[0110] In some embodiments, the volume distribution particle size Dv of the particles of the first polymer is (1) 10 may be 0.1 μm to 0.7 μm.

[0111] By further adjusting the volume distribution particle size Dv of the particles of the first polymer (1) 10 Within the above range, the electrolyte transport capacity of the diaphragm can be further enhanced, and the cycle performance of the battery can be improved.

[0112] In some embodiments, the volume distribution particle size Dv of the particles of the second polymer is (2) 10 may be 0.1 μm to 0.5 μm.

[0113] In some embodiments, the volume distribution particle size Dv of the particles of the second polymer is (2) 90 may be 2.0 μm to 5.0 μm.

[0114] By further adjusting the volume distribution particle size Dv of the particles of the second polymer (2) 10 and / or Dv (2) 90 Within the above range, the electrolyte transport capacity of the diaphragm can be further enhanced, and the cycle performance of the battery can be improved.

[0115] Dv10 indicates the particle size at which 10% of the volume is accumulated, measured from the smallest particle size, in the volume-based particle size distribution of the material. Dv50 indicates the particle size at which 50% of the volume is accumulated, measured from the smallest particle size, in the volume-based particle size distribution of the material. Dv90 indicates the particle size at which 90% of the volume is accumulated, measured from the smallest particle size, in the volume-based particle size distribution of the material.

[0116] In some embodiments, the weight content of the first polymer is denoted as m1, and the weight content of the second polymer is denoted as m2, both based on the total weight of the first coating layer, where m1 can be 50% to 86% and m2 can be 9% to 45%. Alternatively, m1 can be 70% to 82% and m2 can be 13% to 25%.

[0117] By adjusting the weight content m1 of the first polymer and the weight content m2 of the second polymer within the above range, it is beneficial for the diaphragm and the electrode to have appropriate adhesion, and helps to fully open the interface between the electrode and the diaphragm when the battery is in the heat generation stage, so that the gas and heat at the interface can be transferred to the packaging bag in time, thereby reducing the heat accumulation at the interface, and then widening the hot box window of the battery and improving the pass rate of the hot box test of the battery; it can also make the first coating have both appropriate adhesion and air permeability, so that the battery can also have good electrochemical properties.

[0118] When the weight content m1 of the first polymer is small and the weight content m2 of the second polymer is large, the adhesion of the first coating under normal use of the battery is poor, thereby reducing the interfacial adhesion of the battery, which may easily lead to deformation of the electrode assembly after the battery charge and discharge cycle, thereby affecting the electrochemical performance of the battery during normal use.

[0119] When the weight content m1 of the first polymer is large and the weight content m2 of the second polymer is small, the first coating has strong adhesion when the battery is in the heat generation stage, which is not conducive to fully opening the interface between the electrode and the diaphragm when the battery is in the heat generation stage, so that the gas and heat at the interface cannot be transferred to the packaging bag in time, thereby causing the heat at the interface to continue to accumulate, and the battery's hot box test pass rate is low; at the same time, when the weight content m1 of the first polymer is large and the weight content m2 of the second polymer is small, it is not conducive to the second polymer being dispersed around the first polymer, thereby resulting in poor air permeability of the diaphragm and a high risk of clogging the diaphragm during the battery preparation process (such as electrode assembly baking, hot pressing, etc.) and during normal use of the battery, which will also affect the electrochemical performance of the battery.

[0120] In some embodiments, the weight average molecular weight of the first polymer is denoted as M w1 , M w1 It can be 50,000 to 500,000, for example, 50,000, 100,000, 150,000, 180,000, 200,000, 230,000, 260,000, 300,000, 350,000, 400,000, 450,000, 500,000, or a range consisting of any two of the above values. w1 It can be between 150,000 and 260,000.

[0121] By adjusting the weight average molecular weight M of the first polymer w1 Within the above range, the first coating can have suitable adhesion, and the battery can have suitable interface adhesion, which helps to fully open the interface between the electrode and the diaphragm when the battery is in the heat generation stage, so that the gas and heat at the interface can be transferred to the packaging bag in time, reducing the heat accumulation at the interface, and thus widening the battery's hot box window and improving the battery's hot box test pass rate; it can also reduce the probability of deformation of the electrode assembly after the battery charge and discharge cycle, and thus can also make the battery have good electrochemical properties.

[0122] The weight average molecular weight M of the first polymer w1 When it is low, the first polymer has strong fluidity after being softened by heat during the battery preparation process (such as baking of the electrode assembly, hot pressing, etc.) and normal use of the battery, which leads to a higher risk of diaphragm clogging, thereby affecting the electrochemical performance of the battery during normal use.

[0123] The weight average molecular weight M of the first polymer w1When the temperature is high, the first coating has poor adhesion under normal use of the battery, which will reduce the interfacial adhesion of the battery, and easily lead to deformation of the electrode assembly after the battery charge and discharge cycle, which will affect the electrochemical performance of the battery during normal use.

[0124] In some embodiments, the weight average molecular weight of the second polymer is denoted as M w2 , M w2 It can be 700,000 to 2.2 million, for example, 700,000, 800,000, 900,000, 1,000,000, 1,180,000, 1,340,000, 1,500,000, 1,810,000, 2,000,000, 2,200,000, or a range consisting of any two of the above values. w2 It can be between 1.18 million and 2 million.

[0125] By adjusting the weight average molecular weight M of the second polymer w2 Within the above range, the second polymer can be dispersed around the first polymer, thereby reducing the risk of pore plugging in the separator during battery preparation (such as electrode assembly baking, hot pressing and forming processes) and normal battery use, thereby enabling the battery to have good electrochemical performance; by adjusting the weight average molecular weight M of the second polymer w2 Within the above range, it is also beneficial for the diaphragm and the electrode to have appropriate adhesion, which helps to fully open the interface between the electrode and the diaphragm when the battery is in the heat generation stage, thereby timely transferring the gas and heat at the interface to the packaging bag, thereby reducing the heat accumulation at the interface, and further widening the battery's hot box window and improving the battery's hot box test pass rate.

[0126] The weight average molecular weight M of the second polymer w2 When the molecular weight of the second polymer is low, when the battery is in the heat generation stage, the softening of the second polymer by heat will also increase the bonding force between the first coating of the diaphragm and the electrode, which is not conducive to the full opening of the interface between the electrode and the diaphragm, and thus the gas and heat at the interface cannot be transferred to the packaging bag in time, thereby causing the heat at the interface to continue to accumulate, and the battery's hot box test pass rate is low; at the same time, the weight average molecular weight of the second polymer M w2 When the concentration is low, the second polymer has a strong fluidity after being softened by heat during the battery preparation process (such as baking of the electrode assembly, hot pressing, etc.) and normal use of the battery, which leads to a higher risk of the diaphragm being blocked by hot pressing, and further affects the electrochemical performance of the battery.

[0127] The weight average molecular weight M of the second polymer w2 When it is higher, the film-forming property of the second polymer is poor, and the adhesion of the first coating under normal use of the battery is poor, thereby reducing the interfacial adhesion of the battery, which can easily lead to deformation of the electrode assembly after the battery charge and discharge cycle, and further affect the electrochemical performance of the battery during normal use.

[0128] In some embodiments, M w1 It can be from RMB 150,000 to RMB 260,000, M w2 It can be between 1.18 million and 2 million.

[0129] By adjusting M w1 and M w2 Within the above range, the battery can have better electrochemical performance, further broaden the battery's hot box window, and further improve the battery's hot box test pass rate.

[0130] In some embodiments, 700,000 ≤ M w2 -M w1 ≤2.3 million, optionally, 980,000 ≤ M w2 -M w1 ≤1.61 million.

[0131] By adjusting M w2 -M w1 Within the above range, the second polymer is conducive to being dispersed around the first polymer, thereby reducing the risk of clogging of the diaphragm during the battery preparation process (such as electrode assembly baking, hot pressing and other processes) and during normal use of the battery. It can also make the first coating have both suitable adhesion and permeability, thereby making the battery have good electrochemical properties and a higher hot box test pass rate.

[0132] In some embodiments, the weight average molecular weight of the first polymer is denoted as M w1 The weight average molecular weight of the second polymer is recorded as M w2 , M w1 It can be from 50,000 to 500,000, M w2 It can be from RMB 700,000 to RMB 2.2 million, and RMB 700,000 ≤ M w2 -M w1 ≤2.3 million. Optionally, M w1 It can be from RMB 150,000 to RMB 260,000, M w2 It can be from 1.18 million to 2 million, and 980,000 ≤ M w2 -M w1 ≤1.61 million.

[0133] This can make the battery have better electrochemical performance, further widen the battery's hot box window, and further improve the battery's hot box test pass rate.

[0134] In some embodiments, the first polymer may include at least one of a homopolymer and a copolymer of at least one monomer selected from the group consisting of ethylene, propylene, vinylidene fluoride, acrylic acid, acrylic esters, styrene, acrylonitrile, maleic anhydride, vinyl chloride, and allyl chloride. The first polymer may include a homopolymer, a copolymer, or a blend of the two.

[0135] In some embodiments, the second polymer may include at least one of a homopolymer and a copolymer of at least one monomer selected from vinylidene fluoride, hexafluoropropylene, propylene, vinyl chloride, styrene, butadiene, acrylate, and acrylic acid. The second polymer may include a homopolymer, a copolymer, or a blend of the two.

[0136] In some embodiments, the coating weight of the first coating layer may be 0.5 mg / 5000 mm 2 Up to 3mg / 5000mm 2 , for example, it can be 0.5mg / 5000mm 2 , 0.8mg / 5000mm 2 , 1mg / 5000mm 2 , 1.5mg / 5000mm 2 , 2mg / 5000mm 2 , 2.5mg / 5000mm 2 、3mg / 5000mm 2 , or a range consisting of any two of the above values. Optionally, the coating weight of the first coating layer can be 0.5 mg / 5000 mm 2 Up to 1.5mg / 5000mm 2 .

[0137] By adjusting the coating weight of the first coating layer within the above range, the first coating layer can have suitable adhesion, that is, the first coating layer has good adhesion when the battery is in normal use, and has lower adhesion when the battery is in the heat generation stage. This helps to fully open the interface between the electrode and the diaphragm when the battery is in the heat generation stage, so that the gas and heat at the interface can be transferred to the packaging bag in time, reducing heat accumulation at the interface, and thus widening the battery's hot box window and improving the battery's hot box test pass rate; it can also reduce the probability of deformation of the electrode assembly after the battery charge and discharge cycle, and thus can also make the battery have good electrochemical properties.

[0138] When the coating weight of the first coating is low, the adhesion of the first coating under normal use of the battery is poor, thereby reducing the interfacial adhesion of the battery, which can easily lead to deformation of the electrode assembly after the battery charge and discharge cycle, thereby affecting the electrochemical performance of the battery during normal use.

[0139] When the coating weight of the first coating is high, the first coating has strong adhesion when the battery is in the heat generation stage, which is not conducive to the full opening of the interface between the electrode and the diaphragm, and thus the gas and heat at the interface cannot be transferred to the packaging bag in time, thereby causing the heat at the interface to continue to accumulate, and the battery's hot box test pass rate is low.

[0140] In some embodiments, the thickness of the first coating layer may be 0.5 μm to 2.8 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 2.8 μm, or a range consisting of any two of the above values. Alternatively, the thickness of the first coating layer may be 1 μm to 2 μm.

[0141] By adjusting the thickness of the first coating within the above range, the first coating can have suitable adhesion, that is, the first coating has good adhesion when the battery is in normal use, and has lower adhesion when the battery is in the heat generation stage. This helps to fully open the interface between the electrode and the diaphragm when the battery is in the heat generation stage, so that the gas and heat at the interface can be transferred to the packaging bag in time, reducing heat accumulation at the interface, and thus widening the battery's hot box window and improving the battery's hot box test pass rate; it can also reduce the probability of deformation of the electrode assembly after the battery charge and discharge cycle, and thus can also make the battery have good electrochemical properties.

[0142] When the thickness of the first coating is low, the adhesion of the first coating under normal use of the battery is poor, thereby reducing the interfacial adhesion of the battery, which can easily lead to deformation of the electrode assembly after the battery charge and discharge cycle, thereby affecting the electrochemical performance of the battery during normal use.

[0143] When the thickness of the first coating is high, the first coating has strong adhesion when the battery is in the heat generation stage, which is not conducive to the full opening of the interface between the electrode and the diaphragm, and thus the gas and heat at the interface cannot be transferred to the packaging bag in time, thereby causing the heat at the interface to continue to accumulate, and the battery's hot box test pass rate is low.

[0144] In some embodiments, the first coating layer may further include a thickener, a wetting agent, and the like. The present application does not particularly limit the thickener, and for example, it may be at least one of sodium carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, methyl hydroxyethyl cellulose, and ethyl hydroxyethyl cellulose. The present application does not particularly limit the wetting agent, and for example, it may be at least one of polyoxyethylene ether, dimethyl siloxane, sucrose ester, and sodium alkyl ether sulfate.

[0145] In some embodiments, a first coating is disposed on one surface of a porous substrate, and a second coating is disposed on another surface of the porous substrate. The second coating comprises a third polymer, and the third polymer may comprise at least one of a homopolymer and a copolymer of at least one of butyl acrylate, octyl acrylate, isooctyl acrylate, styrene, and butadiene. The third polymer may comprise a homopolymer, a copolymer, or a blend of the homopolymer and the copolymer.

[0146] This can reduce the probability of deformation of the electrode assembly after the battery charge and discharge cycle, and further enable the battery to have good electrochemical performance.

[0147] In some embodiments, the third polymer may have a melting point of 50°C to 70°C.

[0148] The thickness of the second coating layer is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, the thickness of the second coating layer can be 0.5 μm to 3 μm.

[0149] The present application has no particular limitation on the coating weight of the second coating layer, as long as the purpose of the present application can be achieved. For example, the coating weight of the second coating layer can be 0.5 mg / 5000 mm 2 Up to 3mg / 5000mm 2 .

[0150] In some embodiments, an inorganic coating layer may be provided between the porous substrate and the first coating layer. Providing the inorganic coating layer between the porous substrate and the first coating layer may also improve the thermal shrinkage, puncture resistance, and / or electrolyte transport properties of the separator.

[0151] In some embodiments, the inorganic coating may include a ceramic, which may include, but is not limited to, at least one of alumina, boehmite, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium hydroxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, and aluminum nitride.

[0152] In some embodiments, the inorganic coating may further include a binder. The present application does not particularly limit the type of the binder. For example, the binder may include at least one of polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose and potassium hydroxymethyl cellulose.

[0153] The thickness of the inorganic coating is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, the thickness of the inorganic coating can be 0.5 μm to 6 μm.

[0154] The present application has no particular limitation on the coating weight of the inorganic coating, as long as the purpose of the present application can be achieved. For example, the coating weight of the inorganic coating can be 3 mg / 5000 mm 2 Up to 20mg / 5000mm 2 .

[0155] The present application has no particular restrictions on the diaphragm substrate, as long as the purpose of the present application can be achieved. For example, the diaphragm substrate can be a non-woven fabric, a film or a composite film with a porous structure, and the material of the diaphragm substrate can include at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, polyamide, spandex and aramid. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0156] [Positive electrode]

[0157] The material, composition and manufacturing method of the positive electrode sheet may include any technology known in the prior art.

[0158] In some embodiments, the positive electrode sheet may include a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector.

[0159] In some embodiments, the positive electrode current collector may be in the shape of a plate or foil, which is not limited in this embodiment of the present application.

[0160] In some embodiments, the thickness of the positive electrode current collector may be 6 μm to 25 μm.

[0161] In some embodiments, the material of the positive electrode current collector is not particularly limited, and a material having electronic conductivity can be selected. For example, a single element or an alloy (e.g., stainless steel) containing at least one of C, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, and Al can be used.

[0162] From the viewpoint of high conductivity, high stability in the electrolyte and good oxidation resistance, C layer, Al foil, stainless steel foil, etc. are optional. From the viewpoint of further reducing production cost, Al foil is optional. Those skilled in the art can adjust according to actual conditions.

[0163] The positive electrode film layer includes a positive electrode active material. The positive electrode active material can be selected from materials that can absorb and release lithium. Alternatively, the positive electrode active material can include at least one of lithium cobalt oxide (LiCoO2), lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate (LiFePO4), and modified compounds thereof.

[0164] As an example, lithium nickel cobalt aluminum oxide may include but is not limited to LiNi 0.8 Co 0.15 Al 0.05 O2.

[0165] As an example, lithium nickel cobalt manganese oxide may include but is not limited to LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2、LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2、LiNi 0.8 Co 0.1 Mn 0.1 At least one of O2.

[0166] The modified compounds of the above-mentioned positive electrode active materials can be used to modify the positive electrode active materials by doping, surface coating, or both doping and coating.

[0167] In some embodiments, the positive electrode film layer may include a positive electrode conductive agent. The specific type of the positive electrode conductive agent is not subject to specific restrictions and can be selected according to demand. For example, the positive electrode conductive agent may include conductive carbon powder. As an example, the positive electrode conductive agent may include but is not limited to at least one of conductive carbon black, acetylene black (AB), Ketjen black (KB), graphite, carbon fiber, carbon tube, graphene, amorphous carbon, hard carbon, soft carbon, glassy carbon, carbon nanofiber, and carbon nanotube (CNT). These materials can be used alone or in combination of two or more.

[0168] In some embodiments, the positive electrode film layer may include a positive electrode adhesive. The specific type of the positive electrode adhesive is not subject to specific restrictions and can be selected according to demand. As an example, the positive electrode adhesive may include but is not limited to at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and polyvinyl alcohol (PVA).

[0169] In some embodiments, the thickness of the positive electrode film layer may be 15 μm to 150 μm, which is not limited in the present embodiment. The thickness of the positive electrode film layer refers to the thickness of the positive electrode film layer located on a single side of the positive electrode current collector.

[0170] The positive electrode sheet can be prepared according to conventional methods in the art. Typically, the positive electrode active material and optional positive electrode conductive agent, positive electrode binder, etc. are dispersed in a solvent to form a positive electrode slurry. The positive electrode slurry is then coated on the positive electrode current collector. The positive electrode sheet is obtained through processes such as drying and compaction. The solvent can be N-methylpyrrolidone (NMP), but the present application is not limited thereto.

[0171] The coating method can be a coating method known in the art, such as extrusion coating, gravure coating, micro-gravure coating, electrospraying, transfer coating, etc., which is not limited in the embodiments of the present application.

[0172] [Negative electrode]

[0173] The material, composition and manufacturing method of the negative electrode sheet may include any technology known in the prior art.

[0174] In some embodiments, the negative electrode plate may include a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.

[0175] In some embodiments, the negative electrode current collector may be in the shape of a plate or foil, which is not limited in the embodiments of the present application.

[0176] In some embodiments, the thickness of the negative electrode current collector may be 4 μm to 25 μm.

[0177] In some embodiments, the negative electrode current collector material is not particularly limited, and materials with good electronic conductivity can be selected. For example, a single element or alloy (such as stainless steel) containing at least one of C, Cu, Ni, Fe, V, Nb, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, and Ag can be used. Alternatively, a composite material can be formed by plating a conductive material with a different conductive material, such as Fe plated with Cu.

[0178] From the viewpoint of high conductivity, high stability in electrolyte and good oxidation resistance, Cu foil, Ni foil, stainless steel foil, etc. are optional. From the viewpoint of further reducing production cost, Cu foil and Ni foil are optional. Those skilled in the art can adjust according to actual conditions.

[0179] The negative electrode film layer includes a negative electrode active material, which may include at least one of graphite and silicon-based materials.

[0180] The weight content of the silicon-based material in the negative electrode active material may be 0% to 25%. A weight content of the silicon-based material of 0% indicates that the negative electrode active material does not contain the silicon-based material.

[0181] As an example, the graphite includes natural graphite, artificial graphite, or a mixture thereof.

[0182] As an example, the silicon-based material includes at least one of silicon, silicon oxide, silicon-carbon material, and silicon alloy.

[0183] In some embodiments, the negative electrode film layer may include a negative electrode conductive agent. The specific type of the negative electrode conductive agent is not subject to specific restrictions and can be selected according to demand. For example, the negative electrode conductive agent may include conductive carbon powder. As an example, the negative electrode conductive agent may include but is not limited to at least one of conductive carbon black, acetylene black (AB), Ketjen black (KB), graphite, carbon fiber, carbon tube, graphene, amorphous carbon, hard carbon, soft carbon, glassy carbon, carbon nanofiber, and carbon nanotube (CNT). These materials can be used alone or in combination of two or more.

[0184] In some embodiments, the negative electrode film layer may include a negative electrode binder. The specific type of the negative electrode binder is not subject to specific limitations and can be selected according to needs. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), acrylonitrile multipolymer (e.g., LA-type water-based binder, optionally LA132, LA133), polyacrylic acid (PAA) and its salts, styrene-acrylic resin, polyvinyl alcohol (PVA), and their respective derivatives. Derivatives generally refer to products derived from the replacement of hydrogen atoms or atomic groups in a polymer by other atoms or atomic groups.

[0185] In some embodiments, the negative electrode film layer may further include a negative electrode dispersant, thereby improving the film formation quality of the negative electrode film layer. As an example, the negative electrode dispersant may include at least one of sodium carboxymethyl cellulose (CMC) and its derivatives. Derivatives generally refer to products derived from the replacement of hydrogen atoms or atomic groups in a polymer with other atoms or atomic groups (e.g., amino groups).

[0186] In some embodiments, the thickness of the negative electrode film layer may be 30 μm to 150 μm, which is not limited in the present embodiment. The thickness of the negative electrode film layer refers to the thickness of the negative electrode film layer located on a single side of the negative electrode current collector.

[0187] The negative electrode sheet can be prepared according to conventional methods in the art. Typically, the negative electrode active material, metal salt, and optional negative electrode conductive agent, negative electrode binder, and negative electrode dispersant are dispersed in a solvent to form a negative electrode slurry. The negative electrode slurry is then coated onto the negative electrode current collector and subjected to drying, compaction, and other processes to produce the negative electrode sheet. The solvent can include at least one of water, ethanol, acetone, butanone, dimethylformamide, N-methylpyrrolidone, diethylformamide, dimethyl sulfoxide, and tetrahydrofuran, although this embodiment of the present application is not limited thereto.

[0188] The coating method can be a coating method known in the art, such as extrusion coating, gravure coating, micro-gravure coating, electrospraying, transfer coating, etc., which is not limited in the embodiments of the present application.

[0189] The negative electrode sheets provided in the embodiments of the present application do not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode sheet may further include a conductive primer layer (e.g., composed of a conductive agent and an adhesive) disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer; in some embodiments, the negative electrode sheet may further include a protective layer covering the surface of the negative electrode film layer.

[0190] [Electrolytes]

[0191] The battery also includes an electrolyte, which can be a solid electrolyte, a gel electrolyte, or a liquid electrolyte (also known as an electrolyte solution).

[0192] In some embodiments, the electrolyte may be an electrolyte solution that includes an electrolyte salt and a solvent, wherein the electrolyte salt contains lithium ions.

[0193] The types of electrolyte salt and solvent are not particularly limited and can be selected according to needs.

[0194] In some embodiments, the electrolyte salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), and lithium dioxalatoborate (LiBOB). One of the above electrolyte salts may be used alone, or two or more of them may be used simultaneously.

[0195] In some embodiments, the solvent may include at least one of a carbonate compound, a carboxylate compound, an ether compound, and a sulfone compound. As an example, the solvent may include, but is not limited to, ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MPC), propionic acid At least one of ethyl acetate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone, sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), diethyl sulfone (ESE), methyl sulfolane, dimethyl sulfoxide, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl ether, diethyl ether, nitromethane, and N,N-dimethylformamide. The above solvents may be used alone or in combination of two or more.

[0196] In some embodiments, the electrolyte may further contain additives, such as additives for improving various battery properties.

[0197] The electrolyte solution can be prepared according to conventional methods in the art. For example, the solvent, electrolyte salt, and optional other components can be uniformly mixed to obtain the electrolyte solution. The order of adding the materials is not particularly limited. For example, the electrolyte salt and optional other components can be added to the solvent and uniformly mixed to obtain the electrolyte solution.

[0198] The components and their contents in the electrolyte can be determined by conventional methods in the art, for example, by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), etc.

[0199] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly through a winding process or a lamination process.

[0200] In some embodiments, the battery may be a pouch cell.

[0201] In some embodiments, the outer packaging may be a soft bag, such as a bag-type soft bag. The material of the soft bag may be an aluminum-plastic film or plastic. As an example, the plastic may include at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0202] diaphragm

[0203] An embodiment of the present application also provides a diaphragm.

[0204] The separator includes a porous substrate. A first coating is provided on at least one surface of the porous substrate. The first coating includes a first polymer and a second polymer having different melting points.

[0205] In some embodiments, the melting point of the first polymer is denoted as T m1 , the melting point of the second polymer is recorded as T m2 , T m1 It can be from 60℃ to 100℃, T m2 Can be greater than or equal to 130℃, and T m2 -T m1 It can be from 40°C to 120°C.

[0206] By adjusting the melting point T of the first polymer m1 , the melting point T of the second polymer m2 and T m2 -T m1 Within the above range, the battery can have good electrochemical performance, and can also broaden the battery's hot box window and improve the battery's hot box test pass rate.

[0207] In some embodiments, the melting point of the first polymer is denoted as T m1 , the melting point of the second polymer is recorded as T m2 , T m1 It can be 70℃ to 90℃, T m2 can be from 135°C to 160°C, and T m2 -T m1 It can be 50°C to 80°C.

[0208] This can make the battery have better electrochemical performance, further widen the battery's hot box window, and further improve the battery's hot box test pass rate.

[0209] In some embodiments, the volume distribution particle size Dv of the particles of the first polymer is (1) 50 and the volume distribution particle size Dv of the particles of the second polymer (2) 50 satisfies 0.50≤Dv (2) 50 / Dv (1) 50≤1.25, for example, Dv (2) 50 / Dv (1) 50 can be 0.50, 0.60, 0.67, 0.75, 0.83, 0.90, 1.00, 1.10, 1.25, or a range consisting of any two of the above values. Optionally, 0.60≤Dv (2) 50 / Dv (1) 50≤0.83.

[0210] By adjusting Dv (2) 50 / Dv (1) 50 Within the above range, the film-forming problem of the first polymer can be improved, so that the first coating layer has both suitable adhesion and air permeability, thereby enabling the battery to have good electrochemical performance and a higher hot box test pass rate.

[0211] In some embodiments, the volume distribution particle size Dv of the particles of the first polymer is (1) 90 and the volume distribution particle size Dv of the particles of the second polymer (2) 50 satisfies 2.0≤Dv (1) 90 / Dv (2) 50≤5.0, for example, Dv (1) 90 / Dv (2) 50 can be 2.0, 2.25, 2.50, 2.80, 3.00, 3.25, 3.50, 3.75, 4.0, 4.17, 5.0 or a range consisting of any two of the above values. Optionally, 3.00≤Dv (1) 90 / Dv (2) 50≤4.17.

[0212] By adjusting Dv (1) 90 / Dv (2) 50 Within the above range, the film-forming problem of the first polymer can be improved, so that the first coating layer has both suitable adhesion and air permeability, thereby enabling the battery to have good electrochemical performance and a higher hot box test pass rate.

[0213] In some embodiments, the volume distribution particle size Dv of the particles of the first polymer is (1) 50 and the volume distribution particle size Dv of the particles of the second polymer (2) 50 satisfies 0.50≤Dv (2) 50 / Dv (1) 50≤1.25, and the volume distribution particle size Dv of the particles of the first polymer (1) 90 and the volume distribution particle size Dv of the particles of the second polymer (2) 50 satisfies 2.0≤Dv (1) 90 / Dv (2) 50≤6.0. Optionally, 0.60≤Dv (2) 50 / Dv (1) 50≤0.83 and 3.00≤Dv (1) 90 / Dv (2) 50≤4.17.

[0214] By adjusting Dv (2) 50 / Dv (1) 50 and Dv (1) 90 / Dv(2) 50 Within the above range, it is beneficial for the second polymer to be dispersed around the first polymer, improving the film-forming problem of the first polymer, and also beneficial for the first coating to have both suitable adhesion and air permeability, thereby enabling the battery to have good electrochemical performance and a higher hot box test pass rate.

[0215] In some embodiments, the volume distribution particle size Dv of the particles of the first polymer is (1) 50 may be 0.8 μm to 2.0 μm, optionally 1.0 μm to 2.0 μm, or 1.0 μm to 1.5 μm.

[0216] In some embodiments, the volume distribution particle size Dv of the particles of the first polymer is (1) 90 may be 2.0 μm to 5.0 μm.

[0217] By adjusting the volume distribution particle size Dv of the particles of the first polymer (1) 50 and / or Dv (1) When the thickness is within the above range, the first coating layer can have both suitable adhesion and air permeability, thereby enabling the battery to have good electrochemical performance and a high hot box test pass rate.

[0218] In some embodiments, the volume distribution particle size Dv of the particles of the second polymer is (2) 50 may be 0.54 μm to 1.5 μm.

[0219] By adjusting the volume distribution particle size Dv of the second polymer particles (2) When the thickness is within the above range, the first coating layer can have both suitable adhesion and air permeability, thereby enabling the battery to have good electrochemical performance and a high hot box test pass rate.

[0220] In some embodiments, the volume distribution particle size Dv of the particles of the first polymer is (1) 10 may be 0.1 μm to 0.7 μm.

[0221] By further adjusting the volume distribution particle size Dv of the particles of the first polymer (1) 10 Within the above range, the electrolyte transport capacity of the diaphragm can be further enhanced, and the cycle performance of the battery can be improved.

[0222] In some embodiments, the volume distribution particle size Dv of the particles of the second polymer is (2) 10 may be 0.1 μm to 0.5 μm.

[0223] In some embodiments, the volume distribution particle size Dv of the particles of the second polymer is (2) 90 may be 2.0 μm to 5.0 μm.

[0224] By further adjusting the volume distribution particle size Dv of the second polymer particles (2) 10 and / or Dv (2) 90 Within the above range, the electrolyte transport capacity of the diaphragm can be further enhanced, and the cycle performance of the battery can be improved.

[0225] In some embodiments, the weight content of the first polymer is denoted as m1, and the weight content of the second polymer is denoted as m2, both based on the total weight of the first coating layer, where m1 can be 50% to 86% and m2 can be 9% to 45%. Alternatively, m1 can be 70% to 82% and m2 can be 13% to 25%.

[0226] By adjusting the weight content m1 of the first polymer and the weight content m2 of the second polymer within the above range, it is beneficial for the diaphragm and the electrode to have appropriate adhesion, and helps to fully open the interface between the electrode and the diaphragm when the battery is in the heat generation stage, so that the gas and heat at the interface can be transferred to the packaging bag in time, thereby reducing the heat accumulation at the interface, and then widening the hot box window of the battery and improving the pass rate of the hot box test of the battery; it can also make the first coating have both appropriate adhesion and air permeability, so that the battery can also have good electrochemical properties.

[0227] In some embodiments, the weight average molecular weight of the first polymer is denoted as M w1 , M w1 It can be 50,000 to 500,000, for example, 50,000, 100,000, 150,000, 180,000, 200,000, 230,000, 260,000, 300,000, 350,000, 400,000, 450,000, 500,000, or a range consisting of any two of the above values. w1 It can be between 150,000 and 260,000.

[0228] By adjusting the weight average molecular weight M of the first polymer w1 Within the above range, the first coating can have suitable adhesion, and the battery can have suitable interface adhesion, which helps to fully open the interface between the electrode and the diaphragm when the battery is in the heat generation stage, so that the gas and heat at the interface can be transferred to the packaging bag in time, reducing the heat accumulation at the interface, and thus widening the battery's hot box window and improving the battery's hot box test pass rate; it can also reduce the probability of deformation of the electrode assembly after the battery charge and discharge cycle, and thus can also make the battery have good electrochemical properties.

[0229] In some embodiments, the weight average molecular weight of the second polymer is denoted as M w2 , M w2It can be 700,000 to 2.2 million, for example, 700,000, 800,000, 900,000, 1,000,000, 1,180,000, 1,340,000, 1,500,000, 1,810,000, 2,000,000, 2,200,000, or a range consisting of any two of the above values. w2 It can be between 1.18 million and 2 million.

[0230] By adjusting the weight average molecular weight M of the second polymer w2 Within the above range, the second polymer can be dispersed around the first polymer, thereby reducing the risk of pore plugging in the separator during battery preparation (such as electrode assembly baking, hot pressing and forming processes) and normal battery use, thereby enabling the battery to have good electrochemical performance; by adjusting the weight average molecular weight M of the second polymer w2 Within the above range, it is also beneficial for the diaphragm and the electrode to have appropriate adhesion, which helps to fully open the interface between the electrode and the diaphragm when the battery is in the heat generation stage, thereby timely transferring the gas and heat at the interface to the packaging bag, thereby reducing the heat accumulation at the interface, and further widening the battery's hot box window and improving the battery's hot box test pass rate.

[0231] In some embodiments, M w1 It can be from RMB 150,000 to RMB 260,000, M w2 It can be between 1.18 million and 2 million.

[0232] By adjusting M w1 and M w2 Within the above range, the battery can have better electrochemical performance, further broaden the battery's hot box window, and further improve the battery's hot box test pass rate.

[0233] In some embodiments, 700,000 ≤ M w2 -M w1 ≤2.3 million, optionally, 980,000 ≤ M w2 -M w1 ≤1.61 million.

[0234] By adjusting M w2 -M w1 Within the above range, the second polymer is conducive to being dispersed around the first polymer, thereby reducing the risk of clogging of the diaphragm during the battery preparation process (such as electrode assembly baking, hot pressing and other processes) and during normal use of the battery. It can also make the first coating have both suitable adhesion and permeability, thereby making the battery have good electrochemical properties and a higher hot box test pass rate.

[0235] In some embodiments, the weight average molecular weight of the first polymer is denoted as M w1 The weight average molecular weight of the second polymer is recorded as M w2 , Mw1 It can be from 50,000 to 500,000, M w2 It can be from RMB 700,000 to RMB 2.2 million, and RMB 700,000 ≤ M w2 -M w1 ≤2.3 million. Optionally, M w1 It can be from RMB 150,000 to RMB 260,000, M w2 It can be from 1.18 million to 2 million, and 980,000 ≤ M w2 -M w1 ≤1.61 million.

[0236] This can make the battery have better electrochemical performance, further widen the battery's hot box window, and further improve the battery's hot box test pass rate.

[0237] In some embodiments, the first polymer may include at least one of a homopolymer and a copolymer of at least one monomer selected from the group consisting of ethylene, propylene, vinylidene fluoride, acrylic acid, acrylic esters, styrene, acrylonitrile, maleic anhydride, vinyl chloride, and allyl chloride. The first polymer may include a homopolymer, a copolymer, or a blend of the two.

[0238] In some embodiments, the second polymer may include at least one of a homopolymer and a copolymer of at least one monomer selected from vinylidene fluoride, hexafluoropropylene, propylene, vinyl chloride, styrene, butadiene, acrylate, and acrylic acid. The second polymer may include a homopolymer, a copolymer, or a blend of the two.

[0239] In some embodiments, the coating weight of the first coating layer may be 0.5 mg / 5000 mm 2 Up to 3mg / 5000mm 2 , for example, it can be 0.5mg / 5000mm 2 , 0.8mg / 5000mm 2 , 1mg / 5000mm 2 , 1.5mg / 5000mm 2 , 2mg / 5000mm 2 , 2.5mg / 5000mm 2 、3mg / 5000mm 2 , or a range consisting of any two of the above values. Optionally, the coating weight of the first coating layer can be 0.5 mg / 5000 mm 2 Up to 1.5mg / 5000mm 2 .

[0240] By adjusting the coating weight of the first coating layer within the above range, the first coating layer can have suitable adhesion, that is, the first coating layer has good adhesion when the battery is in normal use, and has lower adhesion when the battery is in the heat generation stage. This helps to fully open the interface between the electrode and the diaphragm when the battery is in the heat generation stage, so that the gas and heat at the interface can be transferred to the packaging bag in time, reducing heat accumulation at the interface, and thus widening the battery's hot box window and improving the battery's hot box test pass rate; it can also reduce the probability of deformation of the electrode assembly after the battery charge and discharge cycle, and thus can also make the battery have good electrochemical properties.

[0241] In some embodiments, the thickness of the first coating layer may be 0.5 μm to 2.8 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 2.8 μm, or a range consisting of any two of the above values. Alternatively, the thickness of the first coating layer may be 1 μm to 2 μm.

[0242] By adjusting the thickness of the first coating within the above range, the first coating can have suitable adhesion, that is, the first coating has good adhesion when the battery is in normal use, and has lower adhesion when the battery is in the heat generation stage. This helps to fully open the interface between the electrode and the diaphragm when the battery is in the heat generation stage, so that the gas and heat at the interface can be transferred to the packaging bag in time, reducing heat accumulation at the interface, and thus widening the battery's hot box window and improving the battery's hot box test pass rate; it can also reduce the probability of deformation of the electrode assembly after the battery charge and discharge cycle, and thus can also make the battery have good electrochemical properties.

[0243] In some embodiments, the first coating layer may further include a thickener, a wetting agent, and the like. The present application does not particularly limit the thickener, and for example, it may be at least one of sodium carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, methyl hydroxyethyl cellulose, and ethyl hydroxyethyl cellulose. The present application does not particularly limit the wetting agent, and for example, it may be at least one of polyoxyethylene ether, dimethyl siloxane, sucrose ester, and sodium alkyl ether sulfate.

[0244] In some embodiments, a first coating is provided on the surface of the porous substrate facing the positive electrode sheet, thereby widening the hot box window of the battery and improving the hot box test pass rate of the battery.

[0245] In some embodiments, a first coating is provided on one surface of the porous substrate, and a second coating is provided on another surface of the porous substrate. Alternatively, the first coating is provided on the surface of the porous substrate facing the positive electrode sheet, and the second coating is provided on the surface of the porous substrate facing the negative electrode sheet.

[0246] The second coating layer includes a third polymer, which may include at least one of a homopolymer and a copolymer of at least one monomer selected from the group consisting of butyl acrylate, octyl acrylate, isooctyl acrylate, styrene, and butadiene. The third polymer may include a homopolymer, a copolymer, or a blend thereof.

[0247] This can reduce the probability of deformation of the electrode assembly after the battery charge and discharge cycle, and further enable the battery to have good electrochemical performance.

[0248] In some embodiments, the third polymer may have a melting point of 50°C to 70°C.

[0249] The thickness of the second coating layer is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, the thickness of the second coating layer can be 0.5 μm to 3 μm.

[0250] The present application has no particular limitation on the coating weight of the second coating layer, as long as the purpose of the present application can be achieved. For example, the coating weight of the second coating layer can be 0.5 mg / 5000 mm 2 Up to 3mg / 5000mm 2 .

[0251] In some embodiments, an inorganic coating layer may be provided between the porous substrate and the first coating layer. Providing the inorganic coating layer between the porous substrate and the first coating layer may also improve the thermal shrinkage, puncture resistance, and / or electrolyte transport properties of the separator.

[0252] In some embodiments, the inorganic coating may include a ceramic, which may include, but is not limited to, at least one of alumina, boehmite, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium hydroxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, and aluminum nitride.

[0253] In some embodiments, the inorganic coating may further include a binder. The present application does not particularly limit the type of the binder. For example, the binder may include at least one of polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose and potassium hydroxymethyl cellulose.

[0254] The thickness of the inorganic coating is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, the thickness of the inorganic coating can be 0.5 μm to 6 μm.

[0255] The present application has no particular limitation on the coating weight of the inorganic coating, as long as the purpose of the present application can be achieved. For example, the coating weight of the inorganic coating can be 3 mg / 5000 mm 2Up to 20mg / 5000mm 2 .

[0256] The present application has no particular restrictions on the diaphragm substrate, as long as the purpose of the present application can be achieved. For example, the diaphragm substrate can be a non-woven fabric, a film or a composite film with a porous structure, and the material of the diaphragm substrate can include at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, polyamide, spandex and aramid. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0257] The diaphragm can be prepared by the following method: uniformly stirring the first polymer, the second polymer and the solvent to obtain a first organic coating slurry; coating the first organic coating slurry on at least one surface of the porous substrate, and drying to obtain the diaphragm.

[0258] In some embodiments, the first coating slurry may further include a thickener, a wetting agent, and the like.

[0259] electrochemical devices

[0260] An embodiment of the present application further provides an electrochemical device, which includes the battery described in any of the aforementioned embodiments.

[0261] In one embodiment, the electrochemical device includes a housing, wherein a battery is disposed in the housing. The number of batteries may be multiple, and the multiple batteries are disposed in the housing.

[0262] In one embodiment, the electrochemical device may be a battery module or a battery pack.

[0263] electronic devices

[0264] An embodiment of the present application further provides an electronic device, which includes the battery and / or electrochemical device described in any of the aforementioned embodiments.

[0265] The electronic device of the present application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0266] Example

[0267] The following examples describe the present disclosure in more detail and are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further processing, and all instruments used in the examples are commercially available.

[0268] Test section

[0269] (1) Melting point test of the first polymer and the second polymer

[0270] The melting points of the first polymer and the second polymer are tested by differential scanning calorimetry (DSC). The sample mass may be 8 mg to 15 mg, the test temperature range is 25° C. to 400° C., and the heating rate is 10° C. / min.

[0271] (2) Test of weight average molecular weight of the first polymer and the second polymer

[0272] The weight average molecular weight of the first polymer and the weight average molecular weight of the second polymer were measured by gel permeation chromatography (GPC).

[0273] (3) Volume distribution particle size of the first polymer particles and the volume distribution particle size of the second polymer particles

[0274] The volume distribution particle size of the first polymer particles and the volume distribution particle size of the second polymer particles are measured according to GB / T 19077-2016. The testing equipment may be a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer manufactured by Malvern Instruments Ltd., UK.

[0275] (4) Hot box test

[0276] At 25°C, let the lithium-ion battery rest for 5 minutes, charge it to 4.5V at a constant current of 0.5C, then charge it to 0.025C at a constant voltage of 4.5V, let it rest for 60 minutes, and then perform a hot box test on the lithium-ion battery. Before the hot box test, check the appearance of the lithium-ion battery and take a photo. Attach the temperature sensor, place the lithium-ion battery vertically in the hot box, and heat it from 25°C to 130°C at a rate of 5°C / minute and keep it there for 60 minutes. If the lithium-ion battery does not catch fire or explode, it is considered to have passed the hot box test. The number of lithium-ion battery samples tested is 100, and the number of batteries that passed the hot box test is counted and the hot box test pass rate is calculated.

[0277] (5) Thickness test of lithium-ion batteries

[0278] At 25°C, the lithium-ion battery was allowed to stand for 5 minutes, charged to 4.5V at a constant current of 0.5C, and then charged to 0.025C at a constant voltage of 4.5V. After standing for 60 minutes, the thickness of the lithium-ion battery was tested and recorded as D1, which is the thickness before the hot box test.

[0279] The lithium-ion battery after the hot box test is taken out, and after the temperature of the lithium-ion battery drops to 25° C., the thickness of the lithium-ion battery is measured again and recorded as D2.

[0280] The thickness of the lithium-ion battery can be measured by a laser thickness gauge. To ensure the accuracy of the test results, five lithium-ion battery samples can be taken for testing in each embodiment and comparative example, and three points can be taken for each lithium-ion battery sample to obtain an average value.

[0281] (6) Adhesion test between the first coating of the diaphragm and the electrode adjacent to the first coating

[0282] The test standard can refer to GB / T 2790-1995.

[0283] The lithium-ion battery after the above-mentioned hot box test is taken out, and when the temperature of the lithium-ion battery drops to 25°C, the diaphragm and the pole piece are disassembled and taken out from the lithium-ion battery and cut into small strips of 15mm×54.2mm. Then, the 180° peel test standard is used to test the adhesion between the first coating of the diaphragm and the pole piece adjacent to the first coating and record it as T. The testing instrument is a universal tensile testing machine. After the test, the ratio of the average value of the force in the stable section of the peeling force curve to the width of the sample is taken as the adhesion T between the first coating of the diaphragm and the pole piece adjacent to the first coating. The tensile rate (i.e., peeling rate) of the tensile testing machine can be 50mm / min. To ensure the accuracy of the test results, 5 lithium-ion battery samples can be taken for testing in each embodiment and comparative example, and the average value is taken as the test result.

[0284] In the following examples and comparative examples, the adhesion force T tested in Examples 1-13 is the adhesion force between the first coating layer of the separator and the negative electrode plate, and the adhesion force T tested in other examples and comparative examples is the adhesion force between the first coating layer of the separator and the positive electrode plate.

[0285] (7) Cyclic performance test

[0286] The test temperature is 12℃.

[0287] After the lithium-ion battery rests for 5 minutes, charge it at a constant current of 2C to 4.45V, and then charge it at a constant voltage of 0.05C. After another 5 minutes of rest, discharge it at a constant current of 0.2C to 3.0V. Repeat this process three times (i.e., charge at 2C and discharge at 0.2C), and record the discharge capacity of the third cycle.

[0288] After the lithium-ion battery rests for 5 minutes, charge it at a constant current of 2C to 4.45V, and then charge it at a constant voltage of 0.05C. After resting for 5 minutes, discharge it at a constant current of 1C to 3.0V. Repeat this process 47 times (i.e., charge at 2C and discharge at 1C).

[0289] After the lithium-ion battery rests for 5 minutes, charge it at a constant current of 2C to 4.45V, then charge it at a constant voltage of 0.05C. After another 5 minutes of rest, discharge it at a constant current of 0.2C to 3.0V. Repeat this cycle 750 times (i.e., charge at 2C, discharge at 0.2C), for a total of 800 cycles. Record the discharge capacity at the 800th cycle.

[0290] The cycle capacity retention rate (%) of the lithium ion battery after 800 cycles = (discharge capacity at the 800th cycle / discharge capacity at the 3rd cycle) × 100%.

[0291] To ensure the accuracy of the test results, five lithium-ion battery samples were taken for testing in each embodiment and comparative example, and the average value was taken as the test result.

[0292] Example 1-1

[0293] (1) Preparation of diaphragm

[0294] Boehmite with a volume average particle size (Dv50) of 1 μm and a polyacrylate binder were dispersed in deionized water at a mass ratio of 90:10 to form an inorganic coating slurry with a solid content of 50%. The inorganic coating slurry was evenly coated onto one side of a 5 μm thick PE porous substrate using a micro-dimpled coating method. The inorganic coating was dried in an oven to obtain an inorganic coating with a thickness of 2 μm.

[0295] Add the polymer particles of the first polymer with propylene as the base monomer and the polymer particles of the second polymer with vinylidene fluoride as the base monomer shown in Table 1 to a blender and stir evenly; add sodium carboxymethyl cellulose to the blender and stir evenly; add dimethylsiloxane as the wetting agent to the blender, then add deionized water and stir, adjust the slurry viscosity to 40 mPa·s and the solid content to 5%, and obtain a first coating slurry. The first coating slurry is evenly coated on the inorganic coating and dried in an oven to obtain a first coating. The coating weight of the first coating slurry is 1 mg / 5000 mm 2 The thickness of the first coating layer is 1.5 μm. The mass ratio of the first polymer, the second polymer, sodium carboxymethyl cellulose, and dimethylsiloxane is 75:20:0.5:4.5. In Table 1, T m1 represents the melting point of the first polymer, T m2 represents the melting point of the second polymer. w1 represents the weight average molecular weight of the first polymer, M w2Denotes the weight average molecular weight of the second polymer. (1) 50 and Dv (1) 90 represents the volume distribution particle size of the particles of the first polymer, Dv (2) 50 represents the volume distribution particle size of the second polymer particles. m1 represents the weight content of the first polymer, and m2 represents the weight content of the second polymer, both based on the total weight of the first coating.

[0296] The third polymer, styrene-butyl acrylate-isooctyl acrylate copolymer, was added to a blender, followed by sodium carboxymethyl cellulose and stirred evenly. Dimethylsiloxane, a wetting agent, was added to the blender, followed by deionized water and stirred. The viscosity of the slurry was adjusted to 40 mPa·s and the solid content to 5%, thereby obtaining a second coating slurry. The second coating slurry was evenly coated on the other side of the PE porous substrate and dried in an oven to obtain a second coating. The coating weight of the second coating slurry was 1 mg / 5000 mm. 2 The thickness of the second coating layer was 1.5 μm. The mass ratio of the third polymer, sodium carboxymethyl cellulose, and dimethylsiloxane was 95:0.5:4.5.

[0297] (2) Preparation of negative electrode sheet

[0298] Artificial graphite, acetylene black, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed in a mass ratio of 96:1:1.5:1.5. Deionized water was then added as a solvent to create a slurry with a solids content of 70%, which was then stirred thoroughly. The slurry was evenly coated on one surface of an 8μm-thick copper foil. After drying at 110°C and cold pressing, a single-sided negative electrode sheet with a negative electrode film thickness of 150μm was obtained. The above steps were repeated on the other surface of the copper foil to obtain a double-sided negative electrode sheet. The negative electrode sheet was cut into a size of 74mm x 867mm and the tabs were welded before use.

[0299] (3) Preparation of positive electrode sheet

[0300] LiCoO2, acetylene black, and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 94:3:3. N-methylpyrrolidone (NMP) is then added as a solvent to form a slurry with a solid content of 75%, which is then stirred evenly. The slurry is evenly coated on one surface of a 12μm thick aluminum foil. After drying at 90°C and cold pressing, a single-sided coated positive electrode sheet with a positive electrode film thickness of 100μm is obtained. The above steps are then repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. The positive electrode sheet is cut into a specification of 74mm×867mm and the tabs are welded before use.

[0301] (4) Preparation of electrolyte

[0302] 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) were mixed in a mass ratio of 20:30:20:28:2, and then LiPF6 was added and mixed uniformly to obtain an electrolyte. The mass fraction of LiPF6 in the electrolyte was 8%.

[0303] (5) Preparation of lithium-ion batteries

[0304] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, the first coating of the separator is brought into contact with the positive electrode sheet, and then wound to form an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dehydrated at 80°C, and the prepared electrolyte is injected. After vacuum packaging, static standing, hot pressing, and shaping, a soft-pack lithium-ion battery is obtained.

[0305] Example 1-2 to Example 1-12

[0306] The preparation process is the same as that of Example 1-1, except that the melting point and weight-average molecular weight of the first polymer and / or the melting point and weight-average molecular weight of the second polymer are different in the preparation of the separator. Specific parameters are shown in Table 1.

[0307] Examples 1-13

[0308] Except that the first coating layer of the separator is in contact with the negative electrode plate when preparing the lithium-ion battery, the rest of the preparation process is the same as that of Example 1-1.

[0309] Examples 1-14

[0310] Except for the preparation process of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0311] (1) Preparation of diaphragm

[0312] Boehmite with a volume average particle size (Dv50) of 1 μm and a polyacrylate binder were dispersed in deionized water at a mass ratio of 90:10 to form an inorganic coating slurry with a solid content of 50%. The inorganic coating slurry was evenly coated on both surfaces of a 5 μm thick PE porous substrate using a micro-dimpled coating method. The inorganic coating was dried in an oven to obtain an inorganic coating with a thickness of 2 μm per side.

[0313] Add the polymer particles of the first polymer with propylene as the base monomer and the polymer particles of the second polymer with vinylidene fluoride as the base monomer shown in Table 1 into a blender and stir evenly; add sodium carboxymethyl cellulose into the blender and stir evenly; add dimethylsiloxane as the wetting agent into the blender, then add deionized water and stir, adjust the viscosity of the slurry to 40mPa·s and the solid content to 5%, and obtain the first coating slurry. The first coating slurry is evenly coated on the inorganic coating and dried in an oven to obtain the first coating. The coating weight of the first coating slurry (coating weight on one side) is 1mg / 5000mm 2 The thickness of the first coating layer (single-side thickness) is 1.5 μm. The mass ratio of the first polymer, the second polymer, sodium carboxymethyl cellulose, and dimethylsiloxane is 75:20:0.5:4.5. In Table 1, T m1 represents the melting point of the first polymer, T m2 represents the melting point of the second polymer. w1 represents the weight average molecular weight of the first polymer, M w2 Denotes the weight average molecular weight of the second polymer. (1) 50 and Dv (1) 90 represents the volume distribution particle size of the particles of the first polymer, Dv (2) 50 represents the volume distribution particle size of the second polymer particles. m1 represents the weight content of the first polymer, and m2 represents the weight content of the second polymer, both based on the total weight of the first coating.

[0314] Examples 1-15

[0315] The preparation process was the same as that of Example 1-1, except for the difference in melting point and weight-average molecular weight of the first polymer in the preparation of the separator. Specific parameters are shown in Table 1.

[0316] Comparative Example 1

[0317] Except for the preparation process of the diaphragm, the rest of the preparation process is the same as that of Example 1-1.

[0318] Boehmite with a volume average particle size (Dv50) of 1 μm and a polyacrylate binder were dispersed in deionized water at a mass ratio of 90:10 to form an inorganic coating slurry with a solid content of 50%. The inorganic coating slurry was evenly coated onto one side of a 5 μm thick PE porous substrate using a micro-dimpled coating method. The inorganic coating was dried in an oven to obtain an inorganic coating with a thickness of 2 μm.

[0319] Add the first polymer particles, which are based on propylene monomers, shown in Table 1, to a blender and stir evenly. Add sodium carboxymethyl cellulose to the blender and stir evenly. Add dimethylsiloxane, a wetting agent, to the blender, then add deionized water and stir. Adjust the slurry viscosity to 40 mPa·s and solid content to 5% to obtain a first coating slurry. Apply the first coating slurry evenly on the inorganic coating and dry in an oven to obtain a first coating. The coating weight of the first coating slurry is 1 mg / 5000 mm. 2 The thickness of the first coating layer is 1.5 μm. The mass ratio of the first polymer, sodium carboxymethyl cellulose, and dimethylsiloxane is 95:0.5:4.5.

[0320] The third polymer, styrene-butyl acrylate-isooctyl acrylate copolymer, was added to a blender, followed by sodium carboxymethyl cellulose and stirred evenly. Dimethylsiloxane, a wetting agent, was added to the blender, followed by deionized water and stirred. The viscosity of the slurry was adjusted to 40 mPa·s and the solid content to 5%, thereby obtaining a second coating slurry. The second coating slurry was evenly coated on the other side of the PE porous substrate and dried in an oven to obtain a second coating. The coating weight of the second coating slurry was 1 mg / 5000 mm. 2 The thickness of the second coating layer was 1.5 μm. The mass ratio of the third polymer, sodium carboxymethyl cellulose, and dimethylsiloxane was 95:0.5:4.5.

[0321] From the test results in Table 1, it can be seen that the battery that meets 0.077≤(3.0-D2 / D1) / T≤0.118 can have a higher hot box test pass rate and also have good electrochemical performance.

[0322] The battery prepared in Comparative Example 1 does not satisfy 0.077≤(3.0-D2 / D1) / T≤0.118, and the battery cannot have both a high hot box test pass rate and good electrochemical performance.

[0323] The first coating of the diaphragm prepared in Comparative Example 1 only uses the first polymer, which has a low melting point and has a strong fluidity after being softened by heat during the battery preparation process (such as baking of the electrode assembly, hot pressing, etc.) and during normal use of the battery, resulting in a higher risk of diaphragm clogging. Therefore, the electrochemical performance of the battery prepared in Comparative Example 1 is poor. At the same time, when the battery is in the heat generation stage, the interface between the electrode and the diaphragm of the battery prepared in Comparative Example 1 cannot be opened or the degree of opening is not enough, thereby failing to transfer the gas and heat at the interface to the packaging bag in time, thereby causing the heat at the interface to continue to accumulate. Therefore, the hot box test pass rate of the battery prepared in Comparative Example 1 is still relatively low.

[0324] It can also be seen from the test results of Examples 1-1 to 1-15 that by further adjusting the melting point T of the first polymerm1 , the melting point T of the second polymer m2 and the difference between the two, T m2 -T m1 range, which can further improve the overall performance of the battery.

[0325] Example 2-1 to Example 2-15

[0326] In Examples 2-1 to 2-13, except for the volume distribution particle size Dv of the first polymer in the preparation of the diaphragm, (1) 50 and Dv (1) 90, or the volume distribution particle size Dv of the second polymer (2) Except for the difference of 50, the rest of the preparation process is the same as that of Example 1-1. Specific parameters are shown in Table 2.

[0327] In Examples 2-14 and 2-15, except for the volume distribution particle size D of the second polymer in the preparation of the diaphragm, v(2) 50. Melting point T of the second polymer m2 Except for the above differences, the rest of the preparation process is the same as that of Example 2-3. Specific parameters are shown in Table 2.

[0328] Table 2

[0329] It can also be seen from the test results of Examples 1-1, 2-1 to 2-13 that by further adjusting the volume distribution particle size Dv of the particles of the first polymer (1) 50 and Dv (1) 90. Volume distribution particle size Dv of the second polymer particles (2) 50. Dv (2) 50 / Dv (1) 50. Dv (1) 90 / Dv (2) 50 or more can further improve the overall performance of the battery.

[0330] From the test results of Example 2-14 to Example 2-15, it can be seen that by further adjusting the difference T between the melting point of the second polymer and the melting point of the first polymer m2 -T m1 and the volume distribution particle size Dv of the particles of the first polymer and the second polymer (2) 50 / Dv (1) 50. Dv (1) 90 / Dv (2) 50, which can further improve the battery's hot box test pass rate and further improve the battery's cycle performance.

[0331] Example 3-1 to Example 3-7

[0332] The preparation process was the same as that of Example 1-1, except for the difference in the weight contents of the first polymer and the second polymer in the preparation of the separator. Specific parameters are shown in Table 3.

[0333] Table 3

[0334] It can also be seen from the test results of Examples 1-1 and 3-1 to 3-7 that the overall performance of the battery can be further improved by further adjusting the range of the weight content m1 of the first polymer and the weight content m2 of the second polymer in the first coating.

[0335] Example 4-1 to Example 4-6

[0336] Except for the coating weight of the first coating slurry and / or the thickness of the first coating layer in the preparation of the diaphragm, the rest of the preparation process is the same as that of Example 1-1. Specific parameters are shown in Table 4.

[0337] Table 4

[0338] It can also be seen from the test results of Example 1-1 and Example 4-1 to Example 4-6 that the overall performance of the battery can be further improved by further adjusting the coating weight and / or thickness of the first coating layer.

[0339] Example 5-1 to Example 5-5

[0340] The preparation process was the same as that of Example 1-1, except that the types, melting points, and weight-average molecular weights of the first and second polymers were different. Specific parameters are shown in Table 5.

[0341] Table 5

[0342] It can also be seen from the test results of Example 1-1, Example 5-1 to Example 5-5 that the different types of the first polymer and the second polymer have different effects on improving battery performance, but both can make the battery have a higher hot box test pass rate and good electrochemical performance.

[0343] In the above-described embodiments and comparative examples, the first polymer and the second polymer can be directly obtained commercially or obtained by polymerization according to methods known in the art. First polymers or second polymers having different volume particle size distributions can be obtained by grinding and screening resin particles obtained after the polymerization reaction or directly obtained commercially.

[0344] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present application, and such modifications or substitutions should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A battery, comprising an electrode assembly and a packaging bag, wherein the electrode assembly comprises an electrode sheet and a diaphragm, characterized in that: The separator comprises a porous substrate, a first coating is disposed on at least one surface of the porous substrate, and the first coating comprises a first polymer and a second polymer having different melting points; The battery satisfies 0.077≤(3.0-D2 / D1) / T≤0.118; D1 is the thickness of the battery obtained by testing after the battery is fully charged at 25°C, and the unit is mm; D2 is the thickness of the battery obtained by testing again after the fully charged battery is vertically placed in a hot box and heated from 25°C to 130°C at a rate of 5°C / min and left to stand for 60 minutes, and the battery temperature drops to 25°C, and the unit is mm; T is the adhesion between the first coating of the diaphragm and the electrode adjacent to the first coating, and the unit is N / m.

2. The battery according to claim 1, characterized in that The electrode sheets include a positive electrode sheet and a negative electrode sheet, and a first coating is disposed on a surface of the porous substrate facing the positive electrode sheet.

3. The battery according to claim 1, characterized in that The battery satisfies 0.096≤(3.0-D2 / D1) / T≤0.

110.

4. The battery according to any one of claims 1 to 3, characterized in that: T is 5.42 N / m to 10.23 N / m; and / or, D2 / D1 is 2.12 to 2.

42.

5. The battery according to claim 4, characterized in that T is 5.91 N / m to 7.91 N / m; and / or, D2 / D1 is 2.21 to 2.

38.

6. The battery according to any one of claims 1 to 3, characterized in that: The melting point of the first polymer is denoted as T m1 , the melting point of the second polymer is denoted as T m2 , T m1 60℃ to 100℃, T m2 Greater than or equal to 130°C, and T m2 -T m1 40℃ to 120℃.

7. The battery according to claim 6, characterized in that T m1 70℃ to 90℃, T m2 is 135°C to 160°C, and T m2 -T m1 50℃ to 80℃.

8. The battery according to any one of claims 1 to 3, characterized in that: The volume distribution particle size Dv of the particles of the first polymer (1) 50 and the volume distribution particle size Dv of the particles of the second polymer (2) 50Satisfies 0.50≤Dv (2) 50 / Dv (1) 50≤1.25, and the volume distribution particle size Dv of the particles of the first polymer (1) 90 and the volume distribution particle size Dv of the particles of the second polymer (2) 50Satisfies 2.0≤Dv (1) 90 / Dv (2) 50≤5.

0.

9. The battery according to claim 8, characterized in that 0.60 ≤ Dv (2) 50 / Dv (1) 50 ≤ 0.83 and 3.00 ≤ Dv (1) 90 / Dv (2) 50 ≤ 4.17 10. The battery according to any one of claims 1 to 3, characterized in that: The first coating satisfies at least one of the following conditions: (1) Volume distribution particle size Dv of the first polymer particles (1) 50: 0.8 μm to 2.0 μm; (2) Volume distribution particle size Dv of the first polymer particles (1) 90: 2.0 μm to 5.0 μm; (3) Volume distribution particle size Dv of the particles of the second polymer (2) 50 is 0.54μm to 1.5μm.

11. The battery according to any one of claims 1 to 3, characterized in that: The weight content of the first polymer is recorded as m1, and the weight content of the second polymer is recorded as m2, both based on the total weight of the first coating, m1 is 50% to 86%, and m2 is 9% to 45%.

12. The battery according to claim 11, characterized in that m1 is 70% to 82%, and m2 is 13% to 25%.

13. The battery according to any one of claims 1 to 3, characterized in that: The weight average molecular weight of the first polymer is denoted as M w1 The weight average molecular weight of the second polymer is recorded as M w2 , M w1 150,000 to 260,000, M w2 1.18 million to 2 million.

14. The battery according to any one of claims 1 to 3, characterized in that: The first polymer comprises at least one of a homopolymer and a copolymer of at least one monomer selected from the group consisting of ethylene, propylene, vinylidene fluoride, acrylic acid, acrylic ester, styrene, acrylonitrile, maleic anhydride, vinyl chloride, and allyl chloride; and / or, The second polymer includes at least one of a homopolymer and a copolymer of at least one monomer selected from the group consisting of vinylidene fluoride, hexafluoropropylene, propylene, vinyl chloride, styrene, butadiene, acrylate, and acrylic acid.

15. The battery according to any one of claims 1 to 3, characterized in that: A first coating is disposed on one surface of the porous substrate, and a second coating is disposed on the other surface of the porous substrate, wherein the second coating comprises a third polymer, wherein the third polymer comprises at least one of a homopolymer and a copolymer of at least one monomer selected from the group consisting of butyl acrylate, octyl acrylate, isooctyl acrylate, styrene, and butadiene, and wherein the melting point of the third polymer is between 50° C. and 70° C.

16. The battery according to any one of claims 1 to 3, characterized in that: The diaphragm satisfies at least one of the following conditions: (1) The coating weight of the first coating is 0.5 mg / 5000 mm 2 Up to 3mg / 5000mm 2 ; (2) The thickness of the first coating layer is 0.5 μm to 2.8 μm.

17. The battery according to claim 2, characterized in that The battery satisfies at least one of the following: (1) The battery is a soft pack battery; (2) The positive electrode plate includes a positive electrode active material, and the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, and their respective modified compounds, and the modification includes doping modification, surface coating modification, or doping and coating modification; (3) The negative electrode plate includes a negative electrode active material, the negative electrode active material includes at least one of graphite and a silicon-based material, and the weight content of the silicon-based material in the negative electrode active material is 0% to 25%.

18. An electrochemical device, characterized in that: Comprising a battery according to any one of claims 1 to 17.

19. An electronic device, characterized in that: Comprising the battery according to any one of claims 1 to 17 or the electrochemical device according to claim 18.

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