Separator, and electrochemical device and electronic device containing the same

Abstract

The present application discloses a diaphragm, and an electrochemical device and an electronic device comprising the same. The diaphragm comprises a porous substrate and a porous coating disposed on at least one side of the porous substrate, the porous coating comprises first filler particles, second microsphere particles and a binder, the second microsphere particles comprise a cavity and a shell covering the cavity, the shell comprises a plurality of pore structures, and the average thickness of the shell is 0.05 μm to 0.2 μm. The electrochemical device has both good cycle performance and thermal safety performance.

Description

Technical Field

[0001] The present application belongs to the field of electrochemical technology, and specifically relates to a diaphragm, and an electrochemical device and an electronic device containing the diaphragm. Background Art

[0002] As the demand for high energy density of lithium-ion batteries continues to increase, the compaction density of electrode plates continues to increase, and the thickness of the diaphragm continues to decrease, resulting in a reduction in the internal electrolyte storage space of lithium-ion batteries and a reduction in the amount of electrolyte retained. During the use of lithium-ion batteries, as the cycle of charge and discharge progresses, the amount of electrolyte retained gradually decreases, and purple spots and lithium precipitation are prone to occur at the interface of the electrode plates, and even lead to cycle diving. If the problem of reduced electrolyte retention is improved by increasing the amount of electrolyte injection, lithium-ion batteries, especially soft-pack lithium-ion batteries, are prone to swelling after packaging, which will also affect the use of lithium-ion batteries. Summary of the invention

[0003] The present application provides a diaphragm, and an electrochemical device and an electronic device comprising the diaphragm, wherein the electrochemical device has both good cycle performance and thermal safety performance.

[0004] In a first aspect, the present application provides a diaphragm comprising a porous substrate and a porous coating disposed on at least one side of the porous substrate, the porous coating comprising first filler particles, second microsphere particles and a binder, the second microsphere particles comprising a cavity and a shell covering the cavity, the shell comprising a plurality of pore structures, and the average thickness of the shell being 0.05 μm to 0.2 μm.

[0005] The porous coating of the diaphragm of the present application includes a second microsphere particle, the second microsphere particle is a hollow structure and the shell includes a plurality of pore structures, the pore structure connects the outside and the cavity, which can increase the porosity of the porous coating, so that the porous coating and the diaphragm have a lower ionic impedance; in addition, after injection, the electrolyte can enter the cavity through the pore structure of the shell, thereby increasing the electrolyte storage space of the porous coating, so that more electrolyte is stored in the diaphragm, and the swelling problem is improved; in addition, during the cyclic charge and discharge process of the electrochemical device, especially in the late cycle, the electrolyte stored in the cavity can also be released through the pore structure of the shell, thereby reducing the problem of interface purple spot lithium precipitation caused by electrolyte shortage, and improving the cycle performance of the electrochemical device using the diaphragm. The present application makes the average thickness of the shell from 0.05 μm to 0.2 μm, which can make the second microsphere particles easy to process and easy to coat on the diaphragm, and can provide more electrolyte storage space, improve the swelling problem and interface purple spot lithium precipitation problem. The porous coating of the separator of the present application also includes first filler particles, which can improve the heat resistance of the separator. Therefore, the separator provided by the embodiment of the present application has high heat resistance, good electrolyte wettability and good electrolyte retention, and is used in an electrochemical device to improve the problem of liquid swelling and the problem of purple spot lithium precipitation at the interface, so that the electrochemical device can have both good cycle performance and thermal safety performance.

[0006] In some embodiments, the average thickness of the shell is 0.05 μm to 0.1 μm. The shell meeting this range is more conducive to improving the problem of liquid swelling and the problem of purple spot lithium precipitation on the interface, and is more conducive to improving the cycle performance of the electrochemical device.

[0007] In some embodiments, the average particle size of the first filler particles is 0.2 μm to 2 μm, and can be 0.6 μm to 1 μm. This can make the electrochemical device have a higher energy density, and the porous coating have a higher packing density, thereby improving the heat resistance of the diaphragm and the thermal safety performance of the electrochemical device, and can also make the porous coating have more pores, thereby improving the ion transport characteristics of the diaphragm and the cycle performance of the electrochemical device.

[0008] In some embodiments, the average particle size of the second microsphere particles is 0.2 μm to 1 μm, and can be 0.6 μm to 1 μm. This can make the electrochemical device have a higher energy density, and the porous coating has a higher packing density, thereby improving the heat resistance of the diaphragm and the thermal safety performance of the electrochemical device, and can also make the porous coating have more pores, thereby improving the ion transport characteristics of the diaphragm and the cycle performance of the electrochemical device.

[0009] In some embodiments, the diameter of the cavity of the second microsphere particle is 0.1 μm to 0.9 μm, and can be 0.4 μm to 0.8 μm. This makes it easy to process the second microsphere particle and coat it on the diaphragm, and can provide more electrolyte storage space, improve the problem of electrolyte swelling and interface purple spot lithium precipitation, and improve the cycle performance of the electrochemical device.

[0010] In some embodiments, the ratio of the diameter of the cavity of the second microsphere particles to the average particle size of the second microsphere particles is 0.6: 1 to 0.9: 1, and can be 0.6: 1 to 0.88: 1. This makes it easy to process the second microsphere particles and coat them on the diaphragm, and can provide more electrolyte storage space, improve the problem of electrolyte swelling and interface purple spot lithium precipitation, and improve the cycle performance of the electrochemical device.

[0011] In some embodiments, the specific surface area of ​​the second microsphere particles is 5 m 2 / g to 30m 2 The second microsphere particles meeting the specific surface area range have a suitable area for contacting with the electrolyte, thereby improving the wettability of the electrolyte, improving the problem of liquid swelling and the problem of purple spot lithium precipitation at the interface, and improving the cycle performance of the electrochemical device.

[0012] In some embodiments, the average pore size of the pore structure of the shell is less than 20 nm. When the average pore size of the pore structure of the shell of the second microsphere particle meets the range of the present application, the liquid retention capacity and liquid storage effect of the second microsphere particle can be within a suitable range, thereby further improving the cycle performance of the electrochemical device.

[0013] In some embodiments, the average particle size of the first filler particles is greater than or equal to the average particle size of the second microsphere particles. By making the average particle size of the first filler particles greater than or equal to the average particle size of the second microsphere particles, the hollow structure of the second microsphere particles can be better maintained, and the risk of deformation of the second microsphere particles due to expansion and extrusion of the electrode sheet during the cyclic charge and discharge process of the electrochemical device can be reduced, so that the second microsphere particles can have good liquid retention and storage effects, which helps to further improve the cycle performance of the electrochemical device.

[0014] In some embodiments, the mass proportion of the first filler particles in the porous coating is 73% to 94%, the mass proportion of the second microsphere particles in the porous coating is 2% to 20%, and the mass proportion of the binder in the porous coating is 1% to 7%. By making the mass proportion of the first filler particles and the second microsphere particles within the above range, the separator can have high heat resistance, good electrolyte wettability and good electrolyte retention, which is conducive to improving the problem of liquid swelling and interface purple spot lithium precipitation, and is conducive to the electrochemical device having both good thermal safety performance and good cycle performance.

[0015] Optionally, the mass proportion of the first filler particles in the porous coating is 80% to 91%, the mass proportion of the second microsphere particles in the porous coating is 5% to 16%, and the mass proportion of the binder in the porous coating is 1% to 5%. The first filler particles and the second microsphere particles that meet this mass proportion are more conducive to the electrochemical device having both good thermal safety performance and good cycle performance.

[0016] In some embodiments, the ionic impedance of the porous coating of the separator is 0.001Ω to 0.15Ω. The porous coating of the separator has a small ionic impedance, good ion transport capacity, and good kinetic performance, which is beneficial to improving the cycle performance of the electrochemical device.

[0017] In some embodiments, the difference between the air permeability of the membrane and the air permeability of the porous substrate is greater than 0 and less than or equal to 20s / 100ml. The small difference between the air permeability of the membrane and the air permeability of the porous substrate indicates that the porous coating of the membrane has high air permeability.

[0018] In some embodiments, the thickness growth rate of the shell of the second microsphere particle after being immersed in the electrolyte at 60° C. for 24 hours is less than or equal to 80%. The second microsphere particle has a small swelling degree in the electrolyte and a high structural stability, which is conducive to improving the problem of liquid swelling and the problem of purple spot lithium precipitation at the interface, and improving the cycle performance of the electrochemical device.

[0019] In some embodiments, the shell of the second microsphere particle includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the second microsphere particle cavity, the first shell layer includes polystyrene, the second shell layer includes an acrylic polymer, and the first shell layer and the second shell layer are connected by a CC covalent bond. The first shell layer includes polystyrene, which can make the second microsphere particle have higher mechanical strength and better resistance to electrolyte swelling; the second shell layer includes an acrylic polymer, which is easy to form a pore structure, thereby reducing the ionic impedance of the diaphragm, improving the problem of liquid swelling and the problem of purple spot lithium precipitation at the interface, and improving the cycle performance of the electrochemical device.

[0020] In some embodiments, the acrylic polymer includes soft monomer structural units and hard monomer structural units, the soft monomer structural units include at least one of n-butyl acrylate structural units, n-pentyl acrylate structural units, isopentyl acrylate structural units, isooctyl acrylate structural units, 2-ethylhexyl acrylate structural units, 2-nonyl acrylate structural units, isononyl acrylate structural units, decyl acrylate structural units, undecyl acrylate structural units, lauryl acrylate structural units, tridecyl acrylate structural units, octadecyl acrylate structural units, decyl methacrylate structural units, undecyl methacrylate structural units, lauryl methacrylate structural units, tridecyl methacrylate structural units, and octadecyl methacrylate structural units, and the hard monomer structural units include at least one of methyl acrylate structural units, methyl methacrylate structural units, vinyl acetate structural units, acrylonitrile structural units, acrylamide structural units, and styrene structural units.

[0021] In some embodiments, the mass ratio of the soft monomer structural unit to the hard monomer structural unit is 40:60 to 20:80.

[0022] In some embodiments, the acrylic polymer also includes a multi-functional cross-linking structural unit, and the multi-functional cross-linking structural unit includes at least one of an ethylene glycol dimethacrylate structural unit, a polyethylene glycol dimethacrylate structural unit, a butylene glycol dimethacrylate structural unit, a hexanediol dimethacrylate structural unit, a polybutadiene dimethacrylate structural unit, a polyurethane dimethacrylate structural unit, a propoxylated glycerol trimethacrylate structural unit, and a divinylbenzene structural unit.

[0023] In some embodiments, the mass of the multi-functional cross-linking structural unit is 0.1% to 10% of the total mass of the soft monomer structural unit and the hard monomer structural unit.

[0024] In some embodiments, the acrylic polymer is composed of n-butyl acrylate structural units, methyl acrylate structural units, and ethylene glycol dimethacrylate structural units. In the acrylic polymer, the mass ratio of the n-butyl acrylate structural unit to the methyl acrylate structural unit is 40:60 to 20:80, and the mass of the ethylene glycol dimethacrylate structural unit is 0.5% to 10% of the total mass of the n-butyl acrylate structural unit and the methyl acrylate structural unit.

[0025] In some embodiments, the first filler particles are solid structures.

[0026] In some embodiments, the specific surface area of ​​the first filler particles is less than or equal to 20 m 2 / g. This is beneficial to improving the heat resistance of the diaphragm and the thermal safety performance of the electrochemical device.

[0027] In some embodiments, the glass transition temperature of the binder T g -40℃ to 15℃.

[0028] In some embodiments, the binder includes at least one of polymethacrylate binders, styrene-butadiene rubber, polyacrylic acid, and polyacrylate.

[0029] In some embodiments, the porous substrate has a thickness of 2 μm to 7 μm. A porous substrate having such a thickness is more conducive to improving the energy density of the electrochemical device.

[0030] In some embodiments, the thickness of the porous coating layer is 0.5 μm to 3 μm, which is more conducive to the electrochemical device having high energy density, good cycle performance and thermal safety performance.

[0031] In some embodiments, the total thickness of the separator is 2.5 μm to 10 μm.

[0032] In some embodiments, the bonding force between the porous substrate and the porous coating is 30 N / m to 100 N / m. The high bonding force between the porous substrate and the porous coating provides good stability of the separator, and the porous coating is not easy to fall off, which is more conducive to good cycle performance of the electrochemical device.

[0033] In some embodiments, the longitudinal heat shrinkage of the separator when heated at 130° C. for 1 hour is less than or equal to 5%.

[0034] In some embodiments, the transverse heat shrinkage of the separator when heated at 130° C. for 1 hour is less than or equal to 5%.

[0035] The thermal shrinkage of the diaphragm is small and its heat resistance is good, which is more conducive to the electrochemical device having good thermal safety performance.

[0036] In a second aspect, the present application provides an electrochemical device, comprising a positive electrode sheet, a negative electrode sheet, and the diaphragm of the first aspect of the present application, wherein the diaphragm is located between the positive electrode sheet and the negative electrode sheet.

[0037] In a third aspect, the present application provides an electronic device comprising the electrochemical device of the second aspect of the present application. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be clearly and completely described in conjunction with the embodiments below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. The relevant embodiments described herein are illustrative in nature 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 scheme provided by the present application and the embodiments given, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present application.

[0039] For simplicity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unspecified range.

[0040] In the description herein, unless otherwise specified, “above” and “below” include the number.

[0041] Unless otherwise specified, the terms used in this application have the commonly known meanings generally understood by those skilled in the art. Unless otherwise specified, the values ​​of the parameters mentioned in this application can be measured by 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 the parameters mentioned in this application is 25°C and the test pressure is standard atmospheric pressure.

[0042] 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.

[0043] The term "plurality" means more than two.

[0044] The diaphragm is an important component of an electrochemical device. It separates the positive and negative electrodes and prevents contact short circuits in the electrochemical device. The diaphragm can also close its pores at a certain temperature, blocking the transmission of lithium ions and the flow of current, preventing direct contact and short circuits between the positive and negative electrodes, thereby reducing problems such as combustion and explosion in the electrochemical device. At the same time, the diaphragm also needs to be able to absorb and retain a certain amount of electrolyte in its pore structure, forming an ion transmission channel, realizing lithium ion migration, and completing the electrochemical charge and discharge process.

[0045] As the thickness of the diaphragm continues to decrease, the electrolyte storage space it can provide decreases, and the electrolyte's liquid retention capacity becomes worse. During the use of the electrochemical device, purple spots and lithium precipitation are prone to occur at the electrode plate interface, and even cause the electrochemical device to experience a cycle dive.

[0046] At present, the diaphragm usually includes a porous substrate and a ceramic coating disposed on at least one side of the porous substrate. By increasing the porosity of the porous substrate, the electrolyte retention of the diaphragm can be improved. However, as the porosity of the porous substrate continues to increase, its structural strength deteriorates, the heat resistance of the diaphragm deteriorates, and the closed-cell characteristics of the diaphragm deteriorate, and it is unable to block the transmission of lithium ions and the flow of current when the electrochemical device is overheated, which may cause a direct contact short circuit between the positive and negative electrodes, which is not conducive to improving the thermal safety of the electrochemical device. Increasing the amount of electrolyte injection can easily lead to a liquid swelling problem after the electrochemical device is packaged, which will also affect the use of the electrochemical device.

[0047] Based on this, from the perspective of the diaphragm, the present application adjusts the composition of the porous coating of the diaphragm to enable the diaphragm to have high heat resistance, good electrolyte wettability and good electrolyte retention. When used in electrochemical devices, it can improve the problem of liquid swelling and the problem of purple lithium precipitation on the interface caused by electrolyte shortage, so that the electrochemical device can have both good cycle performance and thermal safety performance.

[0048] In a first aspect, an embodiment of the present application provides a diaphragm.

[0049] The diaphragm provided in the embodiment of the present application includes a porous substrate and a porous coating disposed on at least one side of the porous substrate, the porous coating includes first filler particles, second microsphere particles and a binder, the second microsphere particles include a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, and the average thickness of the shell is 0.05 μm to 0.2 μm. The first filler particles in the present application do not have a hollow structure.

[0050] The porous coating of the diaphragm of the present application includes a second microsphere particle, the second microsphere particle is a hollow structure and the shell includes a plurality of pore structures, the pore structure connects the outside and the cavity, which can increase the porosity of the porous coating, so that the porous coating and the diaphragm have a lower ionic impedance; in addition, after injection, the electrolyte can enter the cavity through the pore structure of the shell, thereby increasing the electrolyte storage space of the porous coating, so that more electrolyte is stored in the diaphragm, and the liquid swelling problem is improved; in addition, during the cyclic charge and discharge process of the electrochemical device, especially in the late cycle, the electrolyte stored in the cavity can also be released through the pore structure of the shell, thereby reducing the problem of interfacial purple spot lithium precipitation caused by electrolyte shortage and improving the cycle performance of the electrochemical device using the diaphragm.

[0051] The greater the thickness of the shell of the second microsphere particle, the smaller the electrolyte storage space that can be provided, and the smaller the improvement effect on the problem of liquid swelling and the problem of interface purple spot lithium precipitation; at the same time, the thickness of the shell of the second microsphere particle should not be too small. On the one hand, the difficulty of preparing the second microsphere particle increases and the production cost increases. On the other hand, the structural strength and processing performance of the second microsphere particle deteriorate, and the risk of shell deformation and rupture increases during the diaphragm preparation process, the electrochemical device assembly process, and the electrochemical device cycle charge and discharge process. After the shell is deformed, the liquid retention capacity and liquid storage effect of the second microsphere particle deteriorate or even lose, and the ionic impedance of the porous coating and the diaphragm will be increased after the shell is ruptured. The present application makes the average thickness of the shell 0.05μm to 0.2μm, which can make the second microsphere particle easy to process and easy to coat on the diaphragm, and can provide more electrolyte storage space, improve the problem of liquid swelling and the problem of interface purple spot lithium precipitation.

[0052] The porous coating layer of the separator of the present application further includes first filler particles, which can improve the heat resistance of the separator.

[0053] Therefore, the diaphragm provided in the embodiment of the present application has high heat resistance, good electrolyte wettability and good electrolyte liquid retention. When used in an electrochemical device, it can improve the problem of liquid swelling and the problem of purple spot lithium precipitation on the interface, thereby enabling the electrochemical device to have both good cycle performance and thermal safety performance.

[0054] The average thickness of the shell is 0.05μm to 0.2μm, for example, it can be 0.05μm, 0.055μm, 0.06μm, 0.065μm, 0.07μm, 0.075μm, 0.08μm, 0.085μm, 0.09μm, 0.095μm, 0.1μm, 0.11μm, 0.12μm, 0.13μm, 0.14μm, 0.15μm, 0.16μm, 0.17μm, 0.18μm, 0.19μm, 0.2μm, or a range consisting of any of the above numerical values.

[0055] Optionally, the average thickness of the shell can be 0.05μm to 0.18μm, 0.05μm to 0.15μm, 0.05μm to 0.12μm, 0.05μm to 0.1μm, 0.06μm to 0.18μm, 0.06μm to 0.15μm, 0.06μm to 0.12μm, 0.06μm to 0.1μm, 0.07μm to 0.18μm, 0.07μm to 0.15μm, 0.07μm to 0.12μm, 0.07μm to 0.1μm, 0.08μm to 0.18μm, 0.08μm to 0.15μm, 0.08μm to 0.12μm, 0.08μm to 0.1μm.

[0056] A shell that meets this range is more conducive to improving the liquid swelling problem and the purple spot lithium precipitation problem on the interface, and is more conducive to improving the cycle performance of the electrochemical device.

[0057] In some embodiments, the mass proportion of the first filler particles in the porous coating can be 73% to 94%, for example, it can be 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, or a range consisting of any of the above values.

[0058] In some embodiments, the mass proportion of the second microsphere particles in the porous coating can be 2% to 20%, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range consisting of any of the above values.

[0059] By making the mass ratio of the first filler particles and the second microsphere particles within the above range, it is beneficial to give full play to the high heat resistance of the first filler particles, and it is also beneficial to maintain the hollow structure of the second microsphere particles, so that the second microsphere particles can better play the role of storing and retaining the electrolyte. Therefore, by making the mass ratio of the first filler particles and the second microsphere particles within the above range, the separator can have high heat resistance, good electrolyte wettability and good electrolyte retention, which is beneficial to improve the problem of liquid swelling and interface purple spot lithium precipitation, and is beneficial for the electrochemical device to have both good thermal safety performance and good cycle performance.

[0060] Optionally, the mass proportion of the first filler particles in the porous coating layer may be 80% to 91%.

[0061] Optionally, the mass proportion of the second microsphere particles in the porous coating layer may be 5% to 16%.

[0062] The first filler particles and the second microsphere particles that meet this mass ratio are more conducive to the electrochemical device having both good thermal safety performance and good cycle performance.

[0063] In some embodiments, the binder may account for 1% to 7% by mass in the porous coating, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or any range thereof.

[0064] The binder is used to bind the first filler particles and the second microsphere particles to the porous substrate. By making the mass ratio of the binder in the porous coating within the above range, the first filler particles and the second microsphere particles can be firmly bonded to the porous substrate, reducing the problem of powder falling.

[0065] Optionally, the binder may account for 1% to 5% by mass in the porous coating layer.

[0066] In some embodiments, the first filler particles may be solid structures, which is beneficial to improving the heat resistance of the separator and the thermal safety performance of the electrochemical device.

[0067] In the present application, the first filler particles being a solid structure does not mean that the first filler particles are absolutely non-porous, and the first filler particles may also be a nearly solid structure.

[0068] In some embodiments, the specific surface area of ​​the first filler particles may be less than or equal to 20 m 2 / g. This is beneficial to improving the heat resistance of the diaphragm and the thermal safety performance of the electrochemical device.

[0069] Optionally, the specific surface area of ​​the first filler particles may be less than or equal to 15 m 2 / g, less than or equal to 10m 2 / g.

[0070] In some embodiments, the average particle size of the first filler particles can be 0.2μm to 2μm, for example, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2μm, or a range consisting of any of the above values.

[0071] If the average particle size of the first filler particles is too large (for example, greater than 2 μm), it is difficult to achieve a thin coating design of the porous coating, thereby affecting the energy density of the electrochemical device; if the average particle size of the first filler particles is too small (for example, less than 0.2 μm), it is easy to cause the first filler particles to accumulate and reduce the pores, affecting ion transmission, thereby affecting the cycle performance of the electrochemical device. By making the average particle size of the first filler particles 0.2 μm to 2 μm, the electrochemical device can have a higher energy density, and the porous coating can have a higher stacking density, thereby improving the heat resistance of the diaphragm and the thermal safety performance of the electrochemical device. The porous coating can also have more pores, thereby improving the ion transmission characteristics of the diaphragm and the cycle performance of the electrochemical device.

[0072] Optionally, the average particle size of the first filler particles can be 0.3μm to 1.8μm, 0.3μm to 1.6μm, 0.3μm to 1.4μm, 0.3μm to 1.2μm, 0.3μm to 1μm, 0.4μm to 1.8μm, 0.4μm to 1.6μm, 0.4μm to 1.4μm, 0.4μm to 1.2μm, 0.4μm to 1μm, 0.5μm to 1.8μm, 0.5μm to 1.6μm, 0.5μm to 1.4μm, 0.5μm to 1.2μm, 0.5μm to 1μm, 0.6μm to 1.8μm, 0.6μm to 1.6μm, 0.6μm to 1.4μm, 0.6μm to 1.2μm, 0.6μm to 1μm.

[0073] The first filler particles meeting this range are more conducive to improving the thermal safety performance and cycle performance of the electrochemical device.

[0074] In some embodiments, the first filler particles may include at least one of inorganic particles and organic particles. Alternatively, the first filler particles may include inorganic particles.

[0075] In some embodiments, the inorganic particles may include ceramic particles. As an example, the ceramic particles may include, but are not limited to, at least one of boehmite, aluminum oxide, zirconium oxide, titanium dioxide, magnesium oxide, silicon oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, yttrium oxide, mullite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium sulfate, silicon carbide, silicon nitride, boron nitride, and aluminum nitride.

[0076] In some embodiments, the organic particles may include at least one of melamine and dicyandiamide.

[0077] In some embodiments, the average particle size of the second microsphere particles may be 0.2 μm to 1 μm, for example, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, or any range thereof.

[0078] The average particle size of the second microsphere particles is too small (for example, less than 0.2 μm), which easily leads to a decrease in the accumulation pores of the second microsphere particles, affecting ion transmission, thereby affecting the cycle performance of the electrochemical device, and at the same time increasing the difficulty of preparing the second microsphere particles and increasing the production cost. By making the average particle size of the second microsphere particles 0.2 μm to 1 μm, the electrochemical device can have a higher energy density, and the porous coating can have a higher stacking density, thereby improving the heat resistance of the diaphragm and the thermal safety performance of the electrochemical device, and the porous coating can also have more pores, thereby improving the ion transmission characteristics of the diaphragm and the cycle performance of the electrochemical device.

[0079] Optionally, the average particle size of the second microsphere particles may be 0.3 μm to 1 μm, 0.4 μm to 1 μm, 0.5 μm to 1 μm, or 0.6 μm to 1 μm.

[0080] The second microsphere particles meeting this range are more conducive to improving the cycle performance of the electrochemical device.

[0081] In some embodiments, the diameter of the cavity of the second microsphere particle can be 0.1 μm to 0.9 μm, for example, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, or a range consisting of any of the above values.

[0082] The diameter of the cavity of the second microsphere particle is small, and the electrolyte storage space that can be provided is small, and the improvement effect on the liquid swelling problem and the interface purple spot lithium precipitation problem is small; at the same time, the diameter of the cavity of the second microsphere particle should not be too large, at this time the structural strength and processing performance of the second microsphere particle deteriorate, and the risk of shell deformation and rupture increases during the diaphragm preparation process, the electrochemical device assembly process, and the electrochemical device cyclic charge and discharge process. The present application makes the diameter of the cavity of the second microsphere particle 0.1μm to 0.9μm, which can make the second microsphere particle easy to process and easy to coat on the diaphragm, and can provide more electrolyte storage space, improve the liquid swelling problem and the interface purple spot lithium precipitation problem, and improve the cycle performance of the electrochemical device.

[0083] Optionally, the diameter of the cavity of the second microsphere particle may be 0.2 μm to 0.9 μm, 0.3 μm to 0.9 μm, 0.4 μm to 0.9 μm, 0.2 μm to 0.85 μm, 0.3 μm to 0.85 μm, 0.4 μm to 0.85 μm, 0.2 μm to 0.8 μm, 0.3 μm to 0.8 μm, 0.4 μm to 0.8 μm.

[0084] The second microsphere particles meeting this range are more conducive to improving the cycle performance of the electrochemical device.

[0085] In some embodiments, the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle can be 0.6:1 to 0.9:1, for example, 0.6:1, 0.62:1, 0.64:1, 0.66:1, 0.68:1, 0.7:1, 0.72:1, 0.74:1, 0.76:1, 0.78:1, 0.8:1, 0.82:1, 0.84:1, 0.86:1, 0.88:1, 0.9:1, or a range consisting of any of the above values.

[0086] The ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is small, and the electrolyte storage space that can be provided is small, and the improvement effect on the swelling problem and the interface purple spot lithium precipitation problem is small; at the same time, the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle should not be too large. On the one hand, the difficulty of preparing the second microsphere particle increases and the production cost increases. On the other hand, the structural strength and processing performance of the second microsphere particle deteriorate, and the risk of shell deformation and rupture increases during the diaphragm preparation process, the electrochemical device assembly process, and the electrochemical device cycle charge and discharge process. The present application makes the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle 0.6: 1 to 0.9: 1, which can not only make the second microsphere particle easy to process and easy to coat on the diaphragm, but also can provide more electrolyte storage space, improve the swelling problem and the interface purple spot lithium precipitation problem, and improve the cycle performance of the electrochemical device.

[0087] Optionally, the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle can be 0.6:1 to 0.9:1, 0.62:1 to 0.9:1, 0.64:1 to 0.9:1, 0.66:1 to 0.9:1, 0.6:1 to 0.88:1, 0.62:1 to 0.88:1, 0.64:1 to 0.88:1, 0.66:1 to 0.88:1, 0.6:1 to 0.84:1, 0.62:1 to 0.84:1, 0.64:1 to 0.84:1, 0.66:1 to 0.84:1, 0.6:1 to 0.8:1, 0.62:1 to 0.8:1, 0.64:1 to 0.8:1, 0.66:1 to 0.8:1.

[0088] The second microsphere particles meeting this range are more conducive to improving the cycle performance of the electrochemical device.

[0089] In some embodiments, the specific surface area of ​​the second microsphere particles can be 5m 2 / g to 30m 2 / g, for example, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g, 10m 2 / g, 11m 2 / g, 12m 2 / g, 13m 2 / g, 14m 2 / g, 15m 2 / g, 16m 2 / g, 17m 2 / g, 18m 2 / g, 19m 2 / g, 20m 2 / g, 21m 2 / g, 22m 2 / g, 23m 2 / g, 24m 2 / g, 25m 2 / g, 26m 2 / g, 27m 2 / g, 28m 2 / g, 29m 2 / g, 30m 2 / g, or any range consisting of the above values.

[0090] The second microsphere particles meeting the specific surface area range have a suitable area for contact with the electrolyte, thereby improving the wettability of the electrolyte, helping to improve the problem of liquid swelling and purple spot lithium precipitation on the interface, and helping to improve the cycle performance of the electrochemical device.

[0091] In some embodiments, the average pore size of the pore structure of the shell of the second microsphere particle may be less than 20 nm.

[0092] When the average pore size of the pore structure of the shell of the second microsphere particle meets the range of this application, the liquid retention capacity and liquid storage effect of the second microsphere particle can be within a suitable range, which is conducive to further improving the cycle performance of the electrochemical device. When the average pore size is too large, the liquid retention capacity and liquid storage effect of the second microsphere particle deteriorate, which is not conducive to better improving the problem of liquid swelling and interface purple spot lithium precipitation, and is not conducive to further improving the cycle performance of the electrochemical device.

[0093] In some embodiments, the thickness growth rate of the shell of the second microsphere particle after being immersed in the electrolyte at 60° C. for 24 hours may be less than or equal to 80%.

[0094] The second microsphere particles have a small degree of swelling in the electrolyte and a high structural stability, which is beneficial to improving the problem of liquid swelling and the problem of purple spot lithium precipitation on the interface, and improving the cycle performance of the electrochemical device.

[0095] The thickness growth rate of the shell of the second microsphere particle after being immersed in the electrolyte at 60°C for 24 hours can be tested as follows: disassemble the electrochemical device, take out a certain amount of free electrolyte, dry the diaphragm and test the average thickness of the shell of the second microsphere particle, recorded as H1, then soak the dried diaphragm in an electrolyte at 60°C, take it out after 24 hours, and test the average thickness of the shell of the second microsphere particle again, recorded as H2, and (H2-H1) / H1*100% represents the thickness growth rate of the shell of the second microsphere particle after being immersed in the electrolyte at 60°C for 24 hours.

[0096] In some embodiments, the shell of the second microsphere particle may include a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer may include polystyrene, the second shell layer may include an acrylic polymer, and the first shell layer and the second shell layer are connected by a CC covalent bond.

[0097] The first shell layer includes polystyrene, which can make the second microsphere particles have higher mechanical strength and better resistance to electrolyte swelling; the second shell layer includes acrylic polymer, which is easy to form a pore structure, thereby reducing the ionic impedance of the diaphragm, improving the liquid swelling problem and the interface purple spot lithium precipitation problem, and improving the cycle performance of the electrochemical device.

[0098] The second shell layer includes an acrylate polymer, which in some embodiments may include soft monomer structural units and hard monomer structural units.

[0099] Optionally, the soft monomer structural unit may include at least one of an n-butyl acrylate structural unit, an n-pentyl acrylate structural unit, an isopentyl acrylate structural unit, an isooctyl acrylate structural unit, a 2-ethylhexyl acrylate structural unit, a 2-nonyl acrylate structural unit, an isononyl acrylate structural unit, a decyl acrylate structural unit, an undecyl acrylate structural unit, a lauryl acrylate structural unit, a tridecyl acrylate structural unit, an octadecyl acrylate structural unit, a decyl methacrylate structural unit, an undecyl methacrylate structural unit, a lauryl methacrylate structural unit, a tridecyl methacrylate structural unit, and an octadecyl methacrylate structural unit.

[0100] Optionally, the hard monomer structural unit may include at least one of a methyl acrylate structural unit, a methyl methacrylate structural unit, a vinyl acetate structural unit, an acrylonitrile structural unit, an acrylamide structural unit, and a styrene structural unit.

[0101] Optionally, the mass ratio of the soft monomer structural unit to the hard monomer structural unit can be 40:60 to 20:80, for example, it can be 40:60, 39:61, 38:62, 37:63, 36:64, 35:65, 34:66, 33:67, 32:68, 31:69, 30:70, 29:71, 28:72, 27:73, 26:74, 25:75, 24:76, 23:77, 22:78, 21:79, 20:80, or a range consisting of any of the above numerical values.

[0102] Adjusting the mass ratio of the soft monomer structural unit to the hard monomer structural unit can make the second shell layer have both high mechanical strength and good resistance to electrolyte swelling, which is beneficial for the porous coating and the separator to have low ionic impedance.

[0103] In some embodiments, the acrylic polymer may further include a multi-functional cross-linking structural unit.

[0104] By making the acrylic polymer further include a multifunctional cross-linking structural unit, the mechanical strength and resistance to electrolyte swelling of the second shell layer can be improved, thereby improving the structural stability of the second microsphere particles and also facilitating the porous coating and the separator to have lower ionic impedance.

[0105] Optionally, the multifunctional cross-linking structural unit may include at least one of an ethylene glycol dimethacrylate structural unit, a polyethylene glycol dimethacrylate structural unit, a butylene glycol dimethacrylate structural unit, a hexanediol dimethacrylate structural unit, a polybutadiene dimethacrylate structural unit, a polyurethane dimethacrylate structural unit, a propoxylated glycerol trimethacrylate structural unit, and a divinylbenzene structural unit.

[0106] Optionally, the mass of the multi-functional cross-linked structural unit can be 0.1% to 10% of the total mass of the soft monomer structural unit and the hard monomer structural unit, for example, it can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any of the above values.

[0107] In some embodiments, the acrylic polymer may further include functional monomer structural units.

[0108] Optionally, the functional monomer structural unit may include at least one of an acrylic acid structural unit, a methacrylic acid structural unit, an itaconic acid structural unit, a hydroxyethyl acrylate structural unit, a hydroxypropyl acrylate structural unit, a hydroxybutyl acrylate structural unit, and a glycidyl acrylate structural unit.

[0109] By making the acrylic ester polymer further include a functional monomer structural unit, the functional monomer structural unit contains a lyophilic group, thereby improving the electrolyte wettability of the second shell layer and reducing the ionic resistance of the separator.

[0110] Optionally, the mass of the functional monomer structural unit can be 1% to 20% of the total mass of the soft monomer structural unit and the hard monomer structural unit, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range consisting of any of the above values.

[0111] In some embodiments, the acrylic polymer can be composed of n-butyl acrylate structural units, methyl acrylate structural units, and ethylene glycol dimethacrylate structural units. In the acrylic polymer, the mass ratio of the n-butyl acrylate structural unit to the methyl acrylate structural unit can be 40:60 to 20:80, and the mass of the ethylene glycol dimethacrylate structural unit can be 0.5% to 10% of the total mass of the n-butyl acrylate structural unit and the methyl acrylate structural unit.

[0112] In some embodiments, the preparation method of the second microsphere particles may include the following steps:

[0113] Through the seed polymerization method, a "nano seed" is polymerized to be used as a core, and the core includes an acrylic polymer;

[0114] Through interfacial polymerization, a coating layer is polymerized on the surface of the "nanoseed" to obtain latex particles with a core-shell structure, wherein the coating layer includes polystyrene;

[0115] The prepared core-shell structured emulsion particles are transferred to an acidic solution, an alkaline solution or an organic solvent, and the solvent penetrates through the coating layer to dissolve the core polymer material. During the dissolution process, the coating layer continues to expand, and the solvent penetrates the coating layer to form a through pore structure. The dissolved polymer material can be discharged through the pore structure to form a cavity of the second microsphere particle, and the remaining part (including the undissolved polymer material and the coating layer) serves as the shell of the second microsphere particle. The shell includes multiple pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity, the first shell layer includes polystyrene, the second shell layer includes an acrylic polymer, and the first shell layer and the second shell layer are connected by a CC covalent bond.

[0116] In some embodiments, the average particle size of the first filler particles may be greater than or equal to the average particle size of the second microsphere particles.

[0117] By making the average particle size of the first filler particles greater than or equal to the average particle size of the second microsphere particles, the hollow structure of the second microsphere particles can be better maintained, and the risk of deformation of the second microsphere particles due to expansion and extrusion of the electrode sheet during the cyclic charge and discharge process of the electrochemical device can be reduced, so that the second microsphere particles can have good liquid retention capacity and liquid storage effect, which helps to further improve the cycle performance of the electrochemical device.

[0118] In some embodiments, the glass transition temperature of the binder T g The temperature may be between -40°C and 15°C, for example, -40°C, -35°C, -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, or a range consisting of any of the above values.

[0119] In some embodiments, the binder may include, but is not limited to, at least one of polymethacrylate binders, styrene-butadiene rubber, polyacrylic acid, and polyacrylate.

[0120] In some embodiments, the porous coating may further include a wetting agent and / or a dispersant. The wetting agent and / or the dispersant may improve the consistency of the porous coating, thereby facilitating the reduction of the problem of purple lithium deposition at the interface.

[0121] The present application has no particular restrictions on the type and content of the dispersant and wetting agent, as long as the purpose of the present application can be achieved. Optionally, the dispersant may include but is not limited to at least one of sodium carboxymethyl cellulose, polyethylene glycol, polyvinyl pyrrolidone, polyvinyl alcohol compounds, and sodium dodecylbenzene sulfonate. Optionally, the wetting agent may include but is not limited to at least one of dimethyl siloxane, polyoxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, polyoxyethylene polyoxypropylene block copolymer, and polyether-modified trimethyl siloxane.

[0122] In some embodiments, the ionic resistance of the porous coating of the separator can be 0.001Ω to 0.15Ω, for example, 0.001Ω, 0.003Ω, 0.005Ω, 0.008Ω, 0.01Ω, 0.02Ω, 0.03Ω, 0.04Ω, 0.05Ω, 0.06Ω, 0.07Ω, 0.08Ω, 0.09Ω, 0.1Ω, 0.11Ω, 0.12Ω, 0.13Ω, 0.14Ω, 0.15Ω, or a range consisting of any of the above values.

[0123] The ionic impedance of the porous coating of the separator = the ionic impedance of the separator - the ionic impedance of the porous substrate.

[0124] The porous coating of the diaphragm has low ionic impedance, good ion transmission capacity and good kinetic performance, which is beneficial to improving the cycle performance of the electrochemical device.

[0125] In some embodiments, the difference between the air permeability of the membrane and the air permeability of the porous substrate may be greater than 0 and less than or equal to 20 s / 100 ml.

[0126] The difference between the air permeability of the membrane and the air permeability of the porous substrate (i.e., the air permeability of the membrane - the air permeability of the porous substrate) is small, indicating that the porous coating of the membrane has high air permeability.

[0127] Optionally, the difference between the air permeability of the membrane and the air permeability of the porous substrate may be greater than 0 and less than or equal to 18 s / 100 ml, greater than 0 and less than or equal to 15 s / 100 ml, greater than 0 and less than or equal to 12 s / 100 ml, greater than 0 and less than or equal to 10 s / 100 ml, greater than 0 and less than or equal to 9 s / 100 ml.

[0128] In some embodiments, the thickness of the porous substrate may be 2 μm to 7 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, or any range thereof. A porous substrate having such a thickness is more conducive to improving the energy density of the electrochemical device.

[0129] In some embodiments, the porosity of the porous substrate may be 20% to 50%, for example, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, or any range thereof. A porosity satisfying this range is more conducive to improving the cycle performance of the electrochemical device.

[0130] The porosity of a porous substrate can be tested by a true density tester. Place the porous substrate sample on the true density tester for testing to obtain the true volume of the porous substrate. Use a ruler to measure the length, width, and height of the sample, and calculate the apparent volume of the porous substrate. Porosity of porous substrate (%) = (apparent volume of porous substrate - true volume of porous substrate) / apparent volume of porous substrate × 100%.

[0131] The present application has no particular restrictions on the material of the porous substrate, as long as the purpose of the present application can be achieved. For example, the porous substrate can be a non-woven fabric, a film or a composite film with a porous structure, and the material of the porous 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.

[0132] The porous coating layer is disposed on at least one side of the porous substrate. For example, the porous coating layer may be disposed on one side of the porous substrate, or the porous coating layer may be disposed on both sides of the porous substrate.

[0133] In some embodiments, the thickness of the porous coating layer may be 0.5 μm to 3 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or any range thereof. The thickness of the porous coating layer refers to the thickness of the porous coating layer on one side of the porous substrate.

[0134] It is understandable that if the thickness of the porous coating is too low (e.g., less than 0.5 μm), the structural strength and heat resistance of the separator will decrease; if the thickness of the porous coating is too high (e.g., greater than 3 μm), the separator will become thicker as a whole, which is not conducive to improving the energy density of the electrochemical device. By making the thickness of the porous coating 0.5 μm to 3 μm, it is more conducive to the electrochemical device to have high energy density, good cycle performance and thermal safety performance.

[0135] In some embodiments, the total thickness of the membrane may be 2.5 μm to 10 μm, for example, 2.5 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range consisting of any of the above values.

[0136] In some embodiments, the bonding force between the porous substrate and the porous coating can be 30 N / m to 100 N / m, for example, 30 N / m, 40 N / m, 50 N / m, 60 N / m, 70 N / m, 80 N / m, 90 N / m, 100 N / m, or a range consisting of any of the above values.

[0137] The bonding force between the porous substrate and the porous coating can be tested by a 180° peeling test according to GB / T 2790-1995, with a peeling speed of 50 mm / min.

[0138] The bonding force between the porous substrate and the porous coating is high, the stability of the separator is good, and the porous coating is not easy to fall off, which is more conducive to the electrochemical device having good cycle performance.

[0139] In some embodiments, the longitudinal heat shrinkage of the membrane heated at 130° C. for 1 hour may be less than or equal to 5%. Optionally, the longitudinal heat shrinkage of the membrane heated at 130° C. for 1 hour may be less than or equal to 4.5%, less than or equal to 4%, less than or equal to 3.5%, or less than or equal to 3%.

[0140] In some embodiments, the transverse heat shrinkage of the membrane heated at 130° C. for 1 hour may be less than or equal to 5%. Optionally, the transverse heat shrinkage of the membrane heated at 130° C. for 1 hour may be less than or equal to 4.5%, less than or equal to 4%, less than or equal to 3.5%, or less than or equal to 3%.

[0141] The thermal shrinkage of the diaphragm is small and its heat resistance is good, which is more conducive to the electrochemical device having good thermal safety performance.

[0142] The preparation method of the diaphragm may include the following steps: providing a porous substrate; providing a porous coating slurry including first filler particles, second microsphere particles and a binder; coating the porous coating slurry on at least one side of the porous substrate, and obtaining the diaphragm after drying.

[0143] Optionally, the solvent in the slurry may include water.

[0144] The average particle size of each of the above particles (such as the first filler particles, the second microsphere particles, etc.) can be tested as follows: use a scanning electron microscope to refer to JY / T010-1996, obtain the SEM image of the diaphragm, arbitrarily select a test sample with a length × width of 50 mm × 100 mm on the diaphragm, randomly select multiple test areas (for example, 5) in the test sample, and read the particle size of each particle to be tested in each test area at a certain magnification (for example, more than 500 times); count the number and particle size values ​​of the particles to be tested in each test area, and take the arithmetic mean of the particle size of all particles to be tested in each test area as the average particle size of the particles to be tested. In order to ensure the accuracy of the test results, multiple test samples (for example, 10) can be taken for the above test, and the average value of each test sample is taken as the final test result. The testing instrument can be ZEISS Sigma300. It should be noted that when the particle to be tested is irregular in shape, the distance between the two farthest points on the particle to be tested is taken as the particle size of the particle to be tested.

[0145] The diameter of the cavity of the second microsphere particle refers to the straight-line distance passing through the center of the hollow cavity and extending to both ends of the hollow cavity, which can be measured by taking an average value at multiple (eg, more than 50) positions in the diaphragm section image.

[0146] The thickness of the shell of the second microsphere particle refers to the distance between the inner surface and the outer surface of the second microsphere particle. The distance between the inner surface and the outer surface of the second microsphere particle can be measured at multiple (for example, more than 50) positions in the diaphragm section image and then the average value is taken.

[0147] The specific surface area of ​​the above particles (such as the first filler particles, the second microsphere particles, etc.) can be obtained by referring to GB / T19587-2017 and using a specific surface area analyzer (such as TristarⅡ3020M) through nitrogen adsorption method.

[0148] Electrochemical Devices

[0149] In a second aspect, the present invention provides an electrochemical device, including any device in which an electrochemical reaction occurs to convert chemical energy into electrical energy, and its specific examples include all kinds of lithium primary batteries or lithium secondary batteries. In particular, lithium secondary batteries include lithium ion secondary batteries.

[0150] During the use of electrochemical devices, oxidation and reduction reactions of electrode active materials occur with charging and discharging. The negative electrode is an electrode that absorbs or lithiates lithium ions during charging and releases or delithiates lithium during discharging. The positive electrode is an electrode that releases or delithiates lithium ions during charging and absorbs or lithiates lithium during discharging.

[0151] In some embodiments, the electrochemical device may include a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, the separator is located between the positive electrode sheet and the negative electrode sheet, and the separator used in the electrochemical device is the separator of the first aspect of the embodiment of the present application. Therefore, the electrochemical device provided in the embodiment of the present application can have good cycle performance.

[0152] 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.

[0153] The electrochemical device also includes an outer package for packaging the electrode assembly and the electrolyte. In some embodiments, the outer package can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc., or a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as at least one of aluminum-plastic film, polypropylene, polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0154] The electrolyte may include an electrolyte salt and a solvent, wherein the electrolyte salt contains lithium ions. The types of the electrolyte salt and the solvent are not particularly limited and may be selected according to requirements.

[0155] In some embodiments, the electrolyte salt may include, but is not limited to, lithium hexafluorophosphate (LiPF 6 ), lithium perchlorate (LiClO 4 ), lithium tetrafluoroborate (LiBF 4 ) and lithium hexafluoroarsenate (LiAsF 6 At least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), and lithium dioxalatoborate (LiBOB). The above electrolyte salts may be used alone or in combination of two or more.

[0156] 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), vinylene carbonate (VC), 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 ( MP), ethyl propionate (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, N,N-dimethylformamide. The above solvents can be used alone or in combination of two or more.

[0157] The electrolyte can be prepared by conventional methods in the art. For example, the components such as the solvent and the electrolyte salt can be mixed uniformly to obtain the electrolyte. There is no particular restriction on the order of adding the materials. For example, the components such as the electrolyte salt can be added to the solvent and mixed uniformly to obtain the electrolyte.

[0158] The components and their contents in the electrolyte can be measured by conventional methods in the art, for example, by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), etc.

[0159] [Positive electrode]

[0160] The material, composition and manufacturing method of the positive electrode sheet may include any technology known in the prior art.

[0161] In some embodiments, the positive electrode sheet may include a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector.

[0162] In some embodiments, the positive electrode current collector may be in the shape of a plate or foil, which is not limited in the embodiments of the present application.

[0163] In some embodiments, the thickness of the positive electrode current collector may be 6 μm to 25 μm.

[0164] In some embodiments, the material of the positive electrode current collector is not particularly limited, and a material with electronic conductivity can be selected. For example, a single substance or alloy (such as stainless steel, etc.) containing at least one element of C, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, and Al can be used.

[0165] From the viewpoint of high conductivity, high stability in 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.

[0166] The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material may be selected from materials capable of absorbing and releasing lithium.

[0167] The specific type of positive electrode active material is not subject to specific restrictions and can be selected according to needs. As an example, the positive electrode active material may include but is not limited to lithium iron phosphate (LiFePO 4 )、Lithium manganese phosphate(LiMnPO 4 )、LiCoPO 4 ), ferric pyrophosphate (Li 2 FeP 2 O 7 ), lithium cobalt oxide (LiCoO 2 )、Spinel lithium manganese oxide(LiMn 2 O 4 ), spinel lithium nickel manganese oxide, layered lithium manganese oxide (LiMnO 2 ), lithium nickel oxide (LiNiO 2 ), lithium niobate (LiNbO 2 ), lithium ferrite (LiFeO 2 )、LiMgO 2 ), lithium calcium oxide (LiCaO 2 ), lithium copper oxide (LiCuO 2 )、LiZnO 2 ), lithium molybdate (LiMoO 2 ), lithium tantalate (LiTaO 2 ), lithium tungstate (LiWO 2 ), lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium-rich materials (such as lithium-rich nickel cobalt manganese oxide), manganese oxide (MnO 2 ), vanadium oxide, sulfur oxide, silicate oxide, and at least one of their modified compounds. These materials may be used alone or in combination of two or more.

[0168] Alternatively, the positive electrode active material may include lithium iron phosphate (LiFePO4 ), lithium cobaltate (LiCoO 2 ), lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, spinel type lithium nickel manganate, and at least one of their respective modified compounds.

[0169] As an example, the molecular formula of lithium nickel cobalt aluminum oxide can be LiNi x Co y Al 1-x-y O 2 , 0 < x < 1, 0 < y < 1, 0 < x + y < 1. For example, it can include but is not limited to LiNi 0.8 Co 0.15 Al 0.05 O 2 .

[0170] As an example, the molecular formula of lithium nickel cobalt manganese oxide can be LiNi x Co y Mn 1-x-y O 2 , 0 < x < 1, 0 < y < 1, 0 < x + y < 1. For example, it can include but is not limited to LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 、LiNi 0.5 Co 0.2 Mn 0.3 O 2 、LiNi 0.6 Co 0.2 Mn 0.2 O 2 、LiNi 0.8 Co 0.1 Mn 0.1 O 2 and at least one of them.

[0171] As an example, spinel type lithium nickel manganate can include but is not limited to LiNi 0.5 Mn 1.5 O 4 .

[0172] The modified compounds of the above-mentioned cathode active materials can be doping modification, surface coating modification, or simultaneous doping and coating modification of the cathode active materials.

[0173] In some embodiments, the porosity of the cathode active material layer can be 20% to 35%.

[0174] In some embodiments, the thickness of the cathode active material layer can be 15 μm to 150 μm, and the embodiments of the present application do not limit this. The thickness of the cathode active material layer refers to the thickness of the cathode active material layer on one side of the cathode current collector.

[0175] In some embodiments, the positive electrode active material layer may include a positive electrode conductive agent. 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 may be used alone or in combination of two or more.

[0176] In some embodiments, the positive electrode active material layer may include a positive electrode binder. The positive electrode binder 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).

[0177] The positive electrode sheet can be prepared according to conventional methods in the art. Usually, the positive electrode active material, positive electrode conductive agent, positive electrode binder, etc. are dispersed in a solvent to form a positive electrode slurry, and the positive electrode slurry is coated on the positive electrode collector, and 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.

[0178] The coating method may 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.

[0179] [Negative electrode]

[0180] The material, composition and manufacturing method of the negative electrode sheet may include any technology known in the prior art.

[0181] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector.

[0182] In some embodiments, the negative electrode current collector may be in a plate or foil shape, which is not limited in the embodiments of the present application.

[0183] In some embodiments, the thickness of the negative electrode current collector may be 4 μm to 25 μm.

[0184] In some embodiments, the material of the negative electrode current collector is not particularly limited, and a material with good electronic conductivity can be selected. For example, a single substance or alloy (such as stainless steel, etc.) containing at least one element of C, Cu, Ni, Fe, V, Nb, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, and Ag can be used. It can also be a composite material formed by plating different conductive substances on a conductive substance, for example, Cu can be plated on Fe.

[0185] 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.

[0186] The negative electrode active material layer includes a negative electrode active material, which may include at least one of a carbon material and a silicon-based material.

[0187] The mass content of the silicon-based material in the negative electrode active material may be 0% to 25%. A mass content of the silicon-based material of 0% indicates that the negative electrode active material does not contain the silicon-based material.

[0188] As an example, the carbon material may include natural graphite, artificial graphite, or a mixture thereof.

[0189] As an example, the silicon-based material may include at least one of elemental silicon, silicon oxide, a silicon-carbon composite material, and a silicon alloy.

[0190] In some embodiments, the porosity of the negative active material layer may be 25% to 45%.

[0191] In some embodiments, the thickness of the negative electrode active material layer may be 30 μm to 150 μm, which is not limited in the present embodiment. The thickness of the negative electrode active material layer refers to the thickness of the negative electrode active material layer located on one side of the negative electrode current collector.

[0192] In some embodiments, the negative electrode active material layer may include a negative electrode conductive agent. 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 may be used alone or in combination of two or more.

[0193] In some embodiments, the negative electrode active material layer may include a negative electrode binder. The negative electrode binder may include, butadiene styrene rubber (SBR), acrylonitrile multipolymer (e.g., LA-type water-based binder, optionally LA132, LA133), polyacrylic acid (PAA) and its salt, styrene acrylic resin, polyvinyl alcohol (PVA), and at least one of their respective derivatives. Derivatives generally refer to products derived from the substitution of hydrogen atoms or atomic groups in a polymer by other atoms or atomic groups.

[0194] In some embodiments, the negative electrode active material layer may further include a negative electrode dispersant, thereby improving the film-forming quality of the negative electrode active material layer. As an example, the negative electrode dispersant may include, but is not limited to, 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 by other atoms or atomic groups (such as amino groups, etc.).

[0195] The negative electrode sheet can be prepared according to conventional methods in the art. Usually, the negative electrode active material, negative electrode conductive agent, negative electrode binder, negative electrode dispersant, etc. are dispersed in a solvent to form a negative electrode slurry, and the negative electrode slurry is coated on the negative electrode current collector, and the negative electrode sheet is obtained through processes such as drying and compaction. The solvent may include but is not limited to at least one of water, ethanol, acetone, butanone, dimethylformamide, N-methylpyrrolidone, diethylformamide, dimethyl sulfoxide, and tetrahydrofuran.

[0196] The coating method may 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.

[0197] The negative electrode sheet provided in the embodiments of the present application does not exclude other additional functional layers in addition to the negative electrode active material layer. For example, in some embodiments, the negative electrode sheet may also include a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet may also include a protective layer covering the surface of the negative electrode active material layer.

[0198] Electronic Devices

[0199] In a third aspect, an embodiment of the present application further provides an electronic device, which includes the electrochemical device of the second aspect of the embodiment of the present application.

[0200] The electronic device provided in the embodiments of the present application is not particularly limited, and it can be used for 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-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, 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, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0201] Example

[0202] The following examples describe the disclosure of the present application in more detail, and these examples are only for illustrative purposes, as it is obvious to those skilled in the art that various modifications and variations can be made within the scope of the disclosure of the present application. Unless otherwise stated, all parts, percentages and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are commercially available.

[0203] Test Section

[0204] (1) Particle size test

[0205] The average particle size of the first filler particles and the second microsphere particles is tested as follows: use a scanning electron microscope to refer to JY / T010-1996, obtain the SEM image of the diaphragm, randomly select a test sample with a length × width of 50mm × 100mm on the diaphragm, randomly select 5 test areas in the test sample, and read the particle size of each particle in each test area at a certain magnification (for example, more than 500 times); count the number of particles and particle size values ​​in each test area, and take the arithmetic mean of the particle size of all particles in each test area as the average particle size of the particles. In order to ensure the accuracy of the test results, 10 test samples can be taken for the above test, and the average value of each test sample is taken as the final test result. The test instrument is ZEISS Sigma 300. It should be noted that when the particle is irregular in shape, the distance between the two farthest points on the particle is taken as the particle size of the particle.

[0206] The diameter of the cavity of the second microsphere particle refers to the straight-line distance passing through the center of the hollow cavity and extending to both ends of the hollow cavity, which can be measured by taking an average value after measuring 50 positions in the diaphragm section image.

[0207] The thickness of the shell of the second microsphere particle refers to the distance between the inner surface and the outer surface of the second microsphere particle, which can be measured by taking an average value of the distance between the inner surface and the outer surface of the second microsphere particle at 50 positions in the diaphragm section image.

[0208] (2) Ionic impedance test of porous coating of diaphragm

[0209] The test sample (such as a porous substrate or a separator) is combined with two electrode plates to form a symmetrical battery. The number of layers of the test sample in the symmetrical battery is stacked in a gradient design, and the number of layers of the test samples is set as follows: 2, 4, 6, 8, 10, and 12. The two electrode plates of the symmetrical battery are negative electrode plates that have not undergone charge and discharge cycles (i.e., fresh negative electrode plates prepared according to the method of Example 1).

[0210] The electrochemical workstation EIS (Electrochemical Impedance Spectroscopy) method was used to test the impedance values ​​of the test samples of the symmetrical battery with different test sample designs. Then, the gradient data value fitting was performed on the measured symmetrical battery ion impedance values ​​of the test sample designs with different test sample numbers. The ionic impedance of the single-layer test sample was calculated based on the fitting results in Ω. The test temperature was 25°C.

[0211] The ionic impedance of the porous coating = the ionic impedance of the separator - the ionic impedance of the porous substrate.

[0212] (3) Gas permeability test of porous substrates and diaphragms

[0213] Under the environment of temperature of 25℃ and humidity less than 80%, make the test sample (such as porous substrate or diaphragm) into 4cm×4cm area, use Air-permeability-tester, and test by Gurley test (100mL) mode to get the air permeability value in seconds, which means the time required for 100mL of air to pass through the test sample with 4cm×4cm area.

[0214] (4) Thermal shrinkage test of diaphragm

[0215] Cut the membrane into samples with a length of 70 mm in the MD direction and 50 mm in the TD direction. Fix the four corners of the sample on a piece of paper with tape. Then put the sample into a 130°C oven and bake it for 1 hour. After that, take out the sample and measure the length L of the membrane in the MD direction. 1 , TD direction length L 2 .

[0216] Thermal shrinkage of the diaphragm in MD direction = (70 - L 1) / 70 × 100%.

[0217] Thermal shrinkage of the diaphragm in TD direction = (50 - L 2 ) / 50 × 100%.

[0218] To ensure the accuracy of the above test results, 5 samples may be taken for testing in each embodiment and comparative example, and the average value is taken as the test result.

[0219] (5) Cycle performance test of lithium-ion secondary batteries

[0220] The lithium-ion secondary battery was placed at 25°C for 60 minutes, then charged at a constant current of 0.5C to a full charge voltage of 4.25V, and then continued to be charged at a constant voltage of 4.25V to a cut-off current of 0.02C. After being placed at 5 minutes, it was discharged at a constant current of 0.5C to 3.0V. This was a charge and discharge cycle, and the discharge capacity of the first cycle was recorded. The lithium-ion secondary battery was cycled 1000 times according to the above steps, and the discharge capacity after 1000 cycles was recorded.

[0221] The capacity retention rate of a lithium-ion secondary battery after 1,000 cycles = (discharge capacity after 1,000 cycles / discharge capacity in the first cycle) × 100%.

[0222] Example 1

[0223] (1) Preparation of diaphragm

[0224] The first filler particles, the second microsphere filler, and the polyacrylic acid binder were fully and evenly dispersed in deionized water at a solid content mass ratio of 91:5:4 to obtain a porous coating slurry; the porous coating slurry was evenly coated on both surfaces of a polyethylene porous substrate with a thickness of 5 μm, and then dried in an oven to obtain a separator. The thickness of the porous coating was 2 μm, and the thickness of the separator was 9 μm.

[0225] The first filler particles are boehmite, and the average particle size is 1 μm.

[0226] The second microsphere particle includes a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer is polystyrene, the second shell layer is n-butyl acrylate-methyl acrylate-ethylene glycol dimethacrylate copolymer, the mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5, and the first shell layer and the second shell layer are connected by a CC covalent bond. The diameter of the cavity is 0.6 μm, the average thickness of the shell is 0.1 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.75:1.

[0227] (2) Preparation of negative electrode sheet

[0228] Artificial graphite, acetylene black, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed at a solid content mass ratio of 96:1:1.5:1.5, and then deionized water was added as a solvent to prepare a slurry with a solid content of 70%, and stirred evenly. The slurry was evenly coated on one surface of a copper foil with a thickness of 8µm, and dried and cold pressed at 110°C to obtain a single-sided coated negative electrode sheet with a negative electrode active material layer thickness of 150μm. Then repeat the above steps on the other surface of the copper foil to obtain a double-sided coated negative electrode sheet. The negative electrode sheet was cut into a specification of 80mm×880mm and welded to the pole ear for standby use.

[0229] (3) Preparation of positive electrode

[0230] LiCoO 2 , acetylene black, and polyvinylidene fluoride (PVDF) are mixed at a solid content mass ratio of 94:3:3, and then N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75%, and stirred evenly. The slurry is evenly coated on one surface of an aluminum foil with a thickness of 12µm, and dried and cold pressed at 90°C to obtain a single-sided coated positive electrode sheet with a positive electrode active material layer thickness of 100μm. Then repeat the above steps on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. Cut the positive electrode sheet into a specification of 74mm×867mm and weld the pole ears for standby use.

[0231] (4) Preparation of electrolyte

[0232] 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 LiPF 6 and mix well to obtain an electrolyte. 6 The mass fraction is 8%.

[0233] (5) Preparation of lithium-ion secondary batteries

[0234] The positive electrode sheet, separator and negative electrode sheet prepared above are stacked and wound in order to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dehydrated at 80°C, injected with the prepared electrolyte, and subjected to vacuum packaging, standing, hot pressing, shaping and other processes to obtain a soft-pack lithium-ion secondary battery.

[0235] Example 2

[0236] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0237] The second microsphere particle includes a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer is polystyrene, the second shell layer is n-butyl acrylate-methyl acrylate-ethylene glycol dimethacrylate copolymer, the mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5, and the first shell layer and the second shell layer are connected by a CC covalent bond. The diameter of the cavity is 0.7 μm, the average thickness of the shell is 0.05 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.88:1.

[0238] Example 3

[0239] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0240] The second microsphere particle includes a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer is polystyrene, the second shell layer is n-butyl acrylate-methyl acrylate-ethylene glycol dimethacrylate copolymer, the mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5, and the first shell layer and the second shell layer are connected by a CC covalent bond. The diameter of the cavity is 0.64 μm, the average thickness of the shell is 0.08 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.8:1.

[0241] Example 4

[0242] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0243] The second microsphere particle includes a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer is polystyrene, the second shell layer is n-butyl acrylate-methyl acrylate-ethylene glycol dimethacrylate copolymer, the mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5, and the first shell layer and the second shell layer are connected by a CC covalent bond. The diameter of the cavity is 0.5 μm, the average thickness of the shell is 0.15 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.63:1.

[0244] Example 5

[0245] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0246] The second microsphere particle includes a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer is polystyrene, the second shell layer is n-butyl acrylate-methyl acrylate-ethylene glycol dimethacrylate copolymer, the mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5, and the first shell layer and the second shell layer are connected by a CC covalent bond. The diameter of the cavity is 0.4 μm, the average thickness of the shell is 0.2 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.5:1.

[0247] Example 6

[0248] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0249] The second microsphere particle includes a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer is polystyrene, the second shell layer is a copolymer of n-butyl acrylate-methyl acrylate-ethylene glycol dimethacrylate, the mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5, and the first shell layer and the second shell layer are connected by a CC covalent bond. The diameter of the cavity is 0.8 μm, the average thickness of the shell is 0.1 μm, the average particle size of the second microsphere particle is 1 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.8:1.

[0250] Example 7

[0251] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0252] The second microsphere particle includes a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer is polystyrene, the second shell layer is n-butyl acrylate-methyl acrylate-ethylene glycol dimethacrylate copolymer, the mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5, and the first shell layer and the second shell layer are connected by a CC covalent bond. The diameter of the cavity is 0.4 μm, the average thickness of the shell is 0.1 μm, the average particle size of the second microsphere particle is 0.6 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.67:1.

[0253] Example 8

[0254] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0255] The second microsphere particle includes a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer is polystyrene, the second shell layer is n-butyl acrylate-methyl acrylate-ethylene glycol dimethacrylate copolymer, the mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5, and the first shell layer and the second shell layer are connected by a CC covalent bond. The diameter of the cavity is 0.9 μm, the average thickness of the shell is 0.05 μm, the average particle size of the second microsphere particle is 1 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.9:1.

[0256] Example 9

[0257] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0258] The second microsphere particle includes a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer is polystyrene, the second shell layer is n-butyl acrylate-methyl acrylate-ethylene glycol dimethacrylate copolymer, the mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5, and the first shell layer and the second shell layer are connected by a CC covalent bond. The diameter of the cavity is 0.1 μm, the average thickness of the shell is 0.05 μm, the average particle size of the second microsphere particle is 0.2 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.5:1.

[0259] Comparative Example 1

[0260] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0261] (1) Preparation of diaphragm

[0262] Deionized water and boehmite particles are pre-dispersed, and then a polyacrylic acid binder is added and the mixture is stirred and mixed evenly. Then, a wetting agent, dimethylsiloxane, is added, stirred evenly, and degassed to obtain a porous coating slurry. The porous coating slurry is evenly coated on a polyethylene porous substrate with a thickness of 5 μm, and then dried in an oven to obtain a diaphragm.

[0263] The average particle size of boehmite is 1 μm. The solid content mass ratio of boehmite particles, binder, and wetting agent is 95:4:1. The thickness of the porous coating is 2 μm, and the thickness of the separator is 9 μm.

[0264] Comparative Example 2

[0265] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0266] The second microsphere particle includes a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer is polystyrene, the second shell layer is n-butyl acrylate-methyl acrylate-ethylene glycol dimethacrylate copolymer, the mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5, and the first shell layer and the second shell layer are connected by a CC covalent bond. The diameter of the cavity is 0.76 μm, the average thickness of the shell is 0.02 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.95:1.

[0267] Comparative Example 3

[0268] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0269] The second microsphere particle includes a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer is polystyrene, the second shell layer is n-butyl acrylate-methyl acrylate-ethylene glycol dimethacrylate copolymer, the mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 40:60:0.5, and the first shell layer and the second shell layer are connected by a CC covalent bond. The diameter of the cavity is 0.2 μm, the average thickness of the shell is 0.3 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.25:1.

[0270] Comparative Example 4

[0271] The preparation process of the lithium ion secondary battery is the same as that of Example 1, except that the porous coating layer of the separator does not contain the first filler particles.

[0272] Table 1

[0273]

[0274] It can be seen from the above test results that the porous coating of the diaphragm in the present application includes first filler particles and second microsphere particles, and the average thickness of the shell of the second microsphere particles is 0.05μm to 0.2μm. The diaphragm has high heat resistance, good electrolyte wettability and good electrolyte retention. The lithium-ion secondary battery using the diaphragm has good cycle performance.

[0275] The porous coating layer of the separator of Comparative Example 1 does not include the second microsphere particles, the separator has poor electrolyte wettability and electrolyte retention, and the cycle performance of the lithium ion secondary battery is poor.

[0276] The porous coating of the diaphragm of Comparative Example 2 includes first filler particles and second microsphere particles, but the average thickness of the shell of the second microsphere particles is less than 0.05 μm, and the heat resistance of the diaphragm is poor. At the same time, during the long-term cycle charge and discharge process of the lithium-ion secondary battery, the second microsphere particles are easily broken, resulting in poor long-cycle performance of the lithium-ion secondary battery.

[0277] The porous coating of the diaphragm of Comparative Example 3 includes first filler particles and second microsphere particles, but the average thickness of the shell of the second microsphere particles is greater than 0.2 μm, and the smaller the electrolyte storage space it can provide, the smaller the improvement effect on the liquid swelling problem and the interface purple spot lithium precipitation problem, which leads to poor cycle performance of the lithium-ion secondary battery.

[0278] The porous coating layer of the diaphragm of Comparative Example 4 does not include the first filler particles. When the porous coating layer does not contain the first filler particles boehmite, the heat resistance of the diaphragm will deteriorate, and the thermal safety performance of the lithium-ion secondary battery will deteriorate. At the same time, the mechanical strength of the diaphragm will also be reduced, and it is easy to deform during the cyclic charge and discharge process of the lithium-ion secondary battery, thereby causing the cycle performance of the lithium-ion secondary battery to deteriorate.

[0279] Example 1-1

[0280] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0281] The solid content mass ratio of the first filler particles, the second microsphere filler, and the polyacrylic acid binder is 73:20:7.

[0282] Example 1-2

[0283] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0284] The solid content mass ratio of the first filler particles, the second microsphere filler, and the polyacrylic acid binder is 80:16:4.

[0285] Examples 1-3

[0286] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0287] The solid content mass ratio of the first filler particles, the second microsphere filler, and the polyacrylic acid binder is 85:11:4.

[0288] Examples 1-4

[0289] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0290] The solid content mass ratio of the first filler particles, the second microsphere filler, and the polyacrylic acid binder is 94:2:4.

[0291] Table 2

[0292]

[0293] It can be seen from the above test results that further adjusting the content of the first filler particles, the second microsphere particles and the binder is beneficial for the separator to better combine high heat resistance, good electrolyte wettability and good electrolyte retention, which is beneficial to improving the cycle performance of lithium-ion secondary batteries.

[0294] Example 2-1

[0295] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0296] The first filler particles are boehmite, and the average particle size is 0.1 μm.

[0297] Example 2-2

[0298] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0299] The first filler particles are boehmite, and the average particle size is 2 μm.

[0300] Example 2-3

[0301] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0302] The first filler particles are boehmite, and the average particle size is 2.2 μm.

[0303] Table 3

[0304]

[0305] It can be seen from the above test results that further adjusting the average particle size of the first filler particles is beneficial for the separator to better combine high heat resistance, high air permeability and low ion impedance, which is beneficial to improving the cycle performance of lithium-ion secondary batteries.

[0306] Example 3-1

[0307] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0308] The second microsphere particle includes a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer is polystyrene, the second shell layer is n-butyl acrylate-methyl acrylate-ethylene glycol dimethacrylate copolymer, the mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 20:80:10, and the first shell layer and the second shell layer are connected by a CC covalent bond. The diameter of the cavity is 0.6 μm, the average thickness of the shell is 0.1 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.75:1.

[0309] Example 3-2

[0310] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0311] The second microsphere particle includes a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer is polystyrene, the second shell layer is a copolymer of n-butyl acrylate-methyl acrylate-ethylene glycol dimethacrylate, the mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 30:70:1, and the first shell layer and the second shell layer are connected by a CC covalent bond. The diameter of the cavity is 0.6 μm, the average thickness of the shell is 0.1 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.75:1.

[0312] Example 3-3

[0313] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0314] The second microsphere particle includes a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer is polystyrene, the second shell layer is n-butyl acrylate-methyl acrylate-ethylene glycol dimethacrylate copolymer, the mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 15:85:11, and the first shell layer and the second shell layer are connected by a CC covalent bond. The diameter of the cavity is 0.6 μm, the average thickness of the shell is 0.1 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.75:1.

[0315] Embodiment 3-4

[0316] The preparation process of the lithium ion secondary battery is the same as that of Example 1 except for the following differences.

[0317] The second microsphere particle includes a cavity and a shell covering the cavity, the shell includes a plurality of pore structures, the shell includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer is polystyrene, the second shell layer is n-butyl acrylate-methyl acrylate-ethylene glycol dimethacrylate copolymer, the mass ratio of n-butyl acrylate, methyl acrylate, and ethylene glycol dimethacrylate is 45:5:0.2, and the first shell layer and the second shell layer are connected by a CC covalent bond. The diameter of the cavity is 0.6 μm, the average thickness of the shell is 0.1 μm, the average particle size of the second microsphere particle is 0.8 μm, and the ratio of the diameter of the cavity of the second microsphere particle to the average particle size of the second microsphere particle is 0.75:1.

[0318] Table 4

[0319]

[0320] From the above test results, it can be seen that further adjusting the ratio of soft monomer structural units, hard monomer structural units and cross-linked structural units in the second shell layer of the second microsphere particles is beneficial for the separator to better combine high permeability and low ion impedance, which is beneficial to improving the cycle performance of lithium-ion secondary batteries.

[0321] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A membrane comprising a porous substrate and a porous coating disposed on at least one side of the porous substrate, characterized in that: The porous coating comprises first filler particles, second microsphere particles and a binder; The average particle size of the second microsphere particles is 0.2 μm to 1 μm; The first filler particles are solid structures; The second microsphere particle comprises a cavity and a shell covering the cavity, the shell comprises a plurality of pore structures, and the average thickness of the shell is 0.05 μm to 0.2 μm; The shell of the second microsphere particle includes a first shell layer and a second shell layer, the second shell layer is located between the first shell layer and the cavity of the second microsphere particle, the first shell layer includes polystyrene, the second shell layer includes an acrylic polymer, and the first shell layer and the second shell layer are connected by a CC covalent bond.

2. The diaphragm according to claim 1, characterized in that The average thickness of the shell is 0.05 μm to 0.1 μm.

3. The diaphragm according to claim 1, characterized in that The porous coating layer satisfies at least one of the following conditions (1) to (5): (1) The average particle size of the first filler particles is 0.2 μm to 2 μm; (2) The diameter of the cavity of the second microsphere particle is 0.1 μm to 0.9 μm; (3) the ratio of the diameter of the cavity of the second microsphere particle to the average particle diameter of the second microsphere particle is 0.6:1 to 0.9:1; (4) The specific surface area of ​​the second microsphere particles is 5m 2 / g to 30m 2 / g; (5) The average pore size of the pore structure of the shell is less than 20 nm.

4. The diaphragm according to claim 1, characterized in that The porous coating layer satisfies at least one of the following conditions (1) to (4): (1) The average particle size of the first filler particles is 0.6 μm to 1 μm; (2) The average particle size of the second microsphere particles is 0.6 μm to 1 μm; (3) The diameter of the cavity of the second microsphere particle is 0.4 μm to 0.8 μm; (4) The ratio of the diameter of the cavity of the second microsphere particles to the average particle size of the second microsphere particles is 0.6:1 to 0.88:

1.

5. The diaphragm according to claim 1, characterized in that The average particle size of the first filler particles is greater than or equal to the average particle size of the second microsphere particles.

6. The diaphragm according to claim 1, characterized in that The mass proportion of the first filler particles in the porous coating layer is 73% to 94%. The mass proportion of the second microsphere particles in the porous coating layer is 2% to 20%. The binder accounts for 1% to 7% by mass in the porous coating layer.

7. The diaphragm according to claim 6, characterized in that The mass proportion of the first filler particles in the porous coating layer is 80% to 91%. The mass proportion of the second microsphere particles in the porous coating layer is 5% to 16%. The binder accounts for 1% to 5% by weight of the porous coating.

8. The diaphragm according to claim 1, characterized in that The diaphragm satisfies at least one of the following conditions (1) to (2): (1) The ionic resistance of the porous coating of the separator is 0.001Ω to 0.15Ω; (2) The difference between the air permeability value of the diaphragm and the air permeability value of the porous substrate is greater than 0 and less than or equal to 20 s / 100 ml.

9. The diaphragm according to claim 1, characterized in that After the second microsphere particles are immersed in an electrolyte at 60° C. for 24 hours, the thickness growth rate of the shell is less than or equal to 80%.

10. The diaphragm according to claim 1, characterized in that The acrylic polymer comprises a soft monomer structural unit and a hard monomer structural unit. The soft monomer structural unit includes at least one of n-butyl acrylate structural unit, n-pentyl acrylate structural unit, isopentyl acrylate structural unit, isooctyl acrylate structural unit, 2-ethylhexyl acrylate structural unit, 2-nonyl acrylate structural unit, isononyl acrylate structural unit, decyl acrylate structural unit, undecyl acrylate structural unit, lauryl acrylate structural unit, tridecyl acrylate structural unit, octadecyl acrylate structural unit, decyl methacrylate structural unit, undecyl methacrylate structural unit, lauryl methacrylate structural unit, tridecyl methacrylate structural unit and octadecyl methacrylate structural unit. The hard monomer structural unit includes at least one of a methyl acrylate structural unit, a methyl methacrylate structural unit, a vinyl acetate structural unit, an acrylonitrile structural unit, an acrylamide structural unit, and a styrene structural unit.

11. The diaphragm according to claim 10, characterized in that The mass ratio of the soft monomer structural unit to the hard monomer structural unit is 40:60 to 20:

80.

12. The diaphragm according to claim 10, characterized in that The acrylic polymer also includes a multifunctional cross-linking structural unit. The multifunctional cross-linked structural unit includes at least one of an ethylene glycol dimethacrylate structural unit, a polyethylene glycol dimethacrylate structural unit, a butylene glycol dimethacrylate structural unit, a hexanediol dimethacrylate structural unit, a polybutadiene dimethacrylate structural unit, a polyurethane dimethacrylate structural unit, a propoxylated glycerol trimethacrylate structural unit, and a divinylbenzene structural unit; and / or, The mass of the multifunctional cross-linked structural unit is 0.1% to 10% of the total mass of the soft monomer structural unit and the hard monomer structural unit.

13. The diaphragm according to claim 12, characterized in that The acrylic polymer is composed of n-butyl acrylate structural units, methyl acrylate structural units, and ethylene glycol dimethacrylate structural units. In the acrylic polymer, the mass ratio of the n-butyl acrylate structural unit to the methyl acrylate structural unit is 40:60 to 20:80, and the mass of the ethylene glycol dimethacrylate structural unit is 0.5% to 10% of the total mass of the n-butyl acrylate structural unit and the methyl acrylate structural unit.

14. The diaphragm according to claim 1, characterized in that The diaphragm satisfies at least one of the following conditions (1) to (3): (1) The specific surface area of ​​the first filler particles is less than or equal to 20 m 2 / g; (2) Glass transition temperature of the binder T g -40℃ to 15℃; (3) The adhesive includes at least one of polymethacrylate adhesive, styrene-butadiene rubber, polyacrylic acid, and polyacrylate.

15. The diaphragm according to claim 1, characterized in that The diaphragm satisfies at least one of the following conditions (1) to (6): (1) The thickness of the porous substrate is 2 μm to 7 μm; (2) The thickness of the porous coating is 0.5 μm to 3 μm; (3) The total thickness of the diaphragm is 2.5 μm to 10 μm; (4) The bonding force between the porous substrate and the porous coating is 30 N / m to 100 N / m; (5) The longitudinal heat shrinkage of the diaphragm when heated at 130°C for 1 hour is less than or equal to 5%; (6) The transverse heat shrinkage of the diaphragm when heated at 130° C. for 1 hour is less than or equal to 5%.

16. An electrochemical device, characterized in that: It comprises a positive electrode sheet, a negative electrode sheet and a separator according to any one of claims 1 to 15, wherein the separator is located between the positive electrode sheet and the negative electrode sheet.

17. An electronic device, characterized in that: Comprising the electrochemical device according to claim 16.

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