Diaphragm and battery

Abstract

The invention provides a diaphragm and a battery, the diaphragm comprises a base membrane and a coating arranged on at least one side of the base membrane, the coating comprises functional particles, the particle size of the functional particles is B [mu] m, the diaphragm is infiltrated in a solution for 3 min, and the infiltration area of the diaphragm is A < 2 >; a and B satisfy the following relation: 0.01 < = A * B < = 40. According to the diaphragm provided by the invention, the relationship between the particle size of the functional particles and the wettability parameter of the diaphragm is regulated and controlled, so that A * B is more than or equal to 0.01 and less than or equal to 40, and collaborative optimization among the affinity of the diaphragm to an electrolyte, the electrolyte retention capability and the water absorption control can be realized; therefore, the ion transmission efficiency and the cycle life of the battery under the high-rate charge-discharge condition can be improved.

Description

Technical Field

[0001] This invention relates to the field of batteries, and more particularly to a separator and a battery. Background Technology

[0002] With the increasing demands on battery performance from electric vehicles, energy storage systems, and consumer electronics, the separator, as a core component of lithium-ion batteries, must simultaneously meet the requirements of high heat resistance, excellent electrolyte affinity, stable mechanical strength, and good ion transport capability. In particular, under high-rate charge and discharge conditions (such as fast charging scenarios for power batteries), the separator needs to be rapidly wetted with electrolyte to ensure efficient ion transport, while avoiding cycle performance degradation due to insufficient electrolyte retention capacity. Summary of the Invention

[0003] Based on the above problems, the present invention provides a separator that achieves synergistic optimization of electrolyte affinity, liquid retention capacity and water absorption control by regulating the relationship between the particle size (B) of functional particles and the separator wetting performance parameter (A), which helps to improve the ion transport efficiency and cycle life of the battery under high-rate charge and discharge conditions.

[0004] The present invention also provides a preparation method that can prepare the above-mentioned battery, and the process is simple.

[0005] The present invention also provides a battery that, because it includes the above-described separator, has good rate capability and long cycle life.

[0006] In detail, in a first aspect, the present invention provides a diaphragm, comprising a base membrane and a coating disposed on at least one side of the base membrane, the coating comprising functional particles having a particle size of B μm, and the diaphragm being immersed in a solution for 3 min, the immersion area of ​​the diaphragm being A cm². 2 A and B satisfy the following relationship: 0.01≤A×B≤40.

[0007] In a second aspect, the present invention provides a method for preparing a diaphragm as described in the first aspect, comprising the following steps:

[0008] A coating comprising the functional particles is applied to at least one side of the base membrane, and after drying, a coating is formed to obtain the diaphragm.

[0009] Thirdly, the present invention provides a battery comprising the separator described in the first aspect.

[0010] The separator provided by this invention achieves synergistic optimization of electrolyte affinity, liquid retention capacity and water absorption control by adjusting the relationship between the particle size (B) of the functional particles and the separator wetting performance parameter (A) to satisfy: 0.01≤A×B≤40. This helps to improve the ion transport efficiency and cycle life of the battery under high-rate charge and discharge conditions. Attached Figure Description

[0011] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0012] Figure 1 This is a schematic diagram of a diaphragm according to a specific embodiment of the present invention.

[0013] In the figure, 1-coating, 2-base film. Detailed Implementation

[0014] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," and "right" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation or be constructed and operated in a specific orientation. Therefore, the terms describing positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0016] In this invention, the terms "first," "second," etc., are mainly used to distinguish different devices, elements, or components (the specific types and structures may be the same or different), and are not used to indicate or imply the relative importance and quantity of the indicated devices, elements, or components.

[0017] Currently, most batteries strive for higher fast-charging capabilities. It has been found that among the many factors restricting battery fast-charging capabilities, the separator, as the intermediate material between the positive and negative electrodes, is a crucial link for the transport of lithium ions between them. Further research has revealed that the separator's restriction on lithium-ion transport is mainly due to its poor affinity for the electrolyte. This results in poor electrolyte absorption, and since the electrolyte plays a major role in transporting lithium ions, a poor electrolyte absorption capacity of the separator will worsen the transport of lithium ions between the positive and negative electrodes, thus severely affecting the battery's fast-charging performance.

[0018] The wettable area of ​​the separator is used to indirectly reflect the wettability of the electrolyte to the separator. If the wettable area is insufficient, functional particles can be introduced into the coating of the separator while controlling the particle size of the functional particles, thereby improving the affinity of the coating to the electrolyte, improving the wettability of the separator to the electrolyte, and thus improving the fast charging performance of the battery. However, if the electrolyte is over-wetted, the excessively strong affinity and retention of liquid often lead to an increased tendency of the separator material to adsorb moisture from the environment. Trace amounts of moisture entering the battery system will react with the electrolyte to generate harmful substances such as HF, which corrode the electrode materials, deteriorate the solid electrolyte interphase (SEI) membrane, and impair the cycle stability and safety of the battery.

[0019] Therefore, there is an urgent need in this field for a new membrane design concept and method that can regulate and synergistically optimize the membrane's affinity for electrolyte, liquid retention capacity, and water absorption, thereby providing support for the development of high-performance lithium-ion batteries with both excellent rate performance and long cycle life.

[0020] Based on the above, the present invention provides the following technical solution:

[0021] In a first aspect, the present invention provides a diaphragm, see [link to diaphragm]. Figure 1 The membrane includes a base 2 and a coating 1 disposed on at least one side of the base membrane 2. The coating 1 includes functional particles with a particle size of B μm. The membrane is immersed in the solution for 3 min, and the immersion area of ​​the membrane is A cm². 2 A and B satisfy the following relationship: 0.01≤A×B≤40.

[0022] In this invention, by adjusting the relationship between the particle size (B) of the functional particles and the membrane wetting performance parameter (A) to satisfy 0.01≤A×B≤40, the electrolyte affinity, liquid retention capacity, and water absorption of the membrane can be synergistically optimized. The main reason for this is that research has found that the main factor restricting lithium-ion transport and affecting battery rate performance is the poor wetting ability of the membrane to the electrolyte. Since the electrolyte is the lithium-ion transport medium, the poor wetting ability of the membrane limits lithium-ion transport. The wetting area, or parameter A, is a quantitative expression of the apparent wetting behavior of the separator. Insufficient wetting area affects the transport of lithium ions between the positive electrode, separator, and negative electrode. By controlling the particle size of functional particles, or parameter B, the liquid absorption capacity of the separator can be improved, allowing the separator to store sufficient electrolyte, facilitating lithium ion transport and improving the battery rate performance. Therefore, based on the above, controlling B and A to be: 0.01≤A×B≤40 can optimize the electrolyte affinity, liquid retention capacity, and water absorption of the separator. If A×B is less than 0.01, it means the functional particles are too small or the wetting area is too small, resulting in insufficient wetting capacity of the separator and affecting the battery's fast-charging performance. If A×B is greater than 40, it corresponds to an excessively large proportion of functional particle size or wetting area, resulting in an excessively large coating. This leads to excessively large pore size and reduced pore tortuosity, which, while beneficial for rapid initial wetting, severely weakens capillary liquid holding capacity. The electrolyte is prone to loss or uneven distribution during cycling, leading to accelerated capacity decay in the later stages of battery cycling. Furthermore, excessively high A values ​​(e.g., high surface energy) are often accompanied by increased chemical polarity of the electrode material, which also exacerbates the adsorption and bonding of moisture, introducing moisture risk, increasing internal gas production in the battery, and deteriorating battery cycle performance.

[0023] In some embodiments, the above-mentioned test diaphragm wetted area is determined by cutting the diaphragm into a 10cm×20cm diaphragm sample; the volume of electrolyte in the wetted area of ​​the test diaphragm is at least sufficient to submerge the diaphragm.

[0024] In some embodiments, 10 μL of solution is taken with a pipette and dropped onto the surface of the diaphragm sample. After standing for 3 minutes, the size of the wetted area is measured, which is the wetted area of ​​the diaphragm.

[0025] It should be noted that the above solution includes a solvent and a lithium salt. The solvent includes ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a mass ratio of 1:1:1:. The lithium salt is lithium hexafluorophosphate, and the concentration of lithium hexafluorophosphate in the solution is 1 mol / L.

[0026] It should be noted that if the separator is inside the battery, the specific testing steps are as follows:

[0027] The battery was discharged at 0.33C to the lower limit voltage of 2.5V. The battery was disassembled, the separator was removed, and the separator was soaked in dimethyl carbonate (DMC) for 1 hour. The separator was then removed, dried, and set aside for later use. The wetting area was then tested according to the method described above.

[0028] The particle size of functional particles refers to the average particle size of functional particles. The testing methods include, but are not limited to: obtaining a microscopic magnified image of any cross section of the membrane using a scanning electron microscope (SEM), arbitrarily selecting at least 5 test areas, and using an X-ray energy dispersive spectroscopy (EDS) analyzer to select at least 20 functional particles in each test area, measuring their particle size, and calculating the average particle size of the functional particles in the 5 test areas to obtain the particle size (B) of the functional particles.

[0029] It should be noted that if the separator is inside the battery, the specific testing steps are as follows:

[0030] The battery was discharged at 0.33C to the lower limit voltage of 2.5V. The battery was disassembled, the separator was removed, and the separator was soaked in dimethyl carbonate (DMC) for 1 hour. The separator was then removed, dried, and set aside for later use. The wetting area was then tested according to the method described above.

[0031] By way of example and not limitation, A×B can be any value or a range of any two of the following: 0.01, 0.05, 1, 2, 4, 7, 10, 12, 14, 16, 17, 19, 20, 22, 25, 27, 30, 31, 32, 34, 37, 39, 40.

[0032] In order to further optimize the electrolyte affinity, liquid retention capacity and water absorption of the separator, thereby further improving the rate performance and long cycle life of the battery, in some specific embodiments, 0.5≤A×B≤15.

[0033] In some implementations, 0.15 ≤ A ≤ 20.

[0034] When A is within the above range, it can further ensure that the electrolyte wets the separator quickly and evenly, control the surface activity of the pores at a more suitable level, and thus further ensure the rate performance and long-cycle stability of the battery.

[0035] In order to further improve the wettability of the electrolyte to the separator, thereby further improving the rate capability and cycle performance of the battery, in some specific embodiments, 4≤A≤15.

[0036] In some embodiments, the wetting area A of the diaphragm can be adjusted by introducing a polymer into the functional particles, further adjusting the type of polymer, forming a shell by coating the polymer, adjusting the thickness of the shell, etc.; or by adjusting the type and content of the binder in the functional particle formulation.

[0037] By way of example and not limitation, A can be any value or a range of any two of the following: 0.15, 0.2, 1, 2, 4, 7, 10, 12, 14, 16, 17, 19, 20.

[0038] In some implementations, 0.05 ≤ B ≤ 2.5.

[0039] When B is within the above range, a more suitable microstructure of coating with pore size distribution and pore connectivity can be constructed, thereby effectively enhancing its capillary retention capacity while ensuring high-speed electrolyte wetting, and further ensuring the rate performance and long-cycle stability of the battery.

[0040] In order to ensure rapid electrolyte wetting while effectively enhancing its capillary retention capacity, thereby further guaranteeing the rate performance and long-cycle stability of the battery, in some specific implementations, 0.5≤B≤1.5.

[0041] In some embodiments, the particle size B of the functional particles can be adjusted by grinding process conditions, selecting different dispersants, and controlling the amount of dispersant. For example, zirconium beads (exemplarily, the size of the zirconium beads is 0.3μm-1.5μm) are added to the functional particle raw material components, and the mixture is sand-milled at a speed of 500rpm-800rpm for 30-50min.

[0042] By way of example and not limitation, B can be any value or a range of any two of the following: 0.05, 0.07, 0.09, 1, 1.2, 1.5, 1.7, 2, 2.5.

[0043] In some embodiments, the coating thickness is 1 μm-10 μm.

[0044] When the coating thickness is within the above range, it can further ensure that the coating provides sufficient thermal stability and mechanical protection while optimizing the ion transport path and controlling the overall porosity, thereby further improving the liquid retention capacity of the diaphragm without excessively increasing the internal resistance.

[0045] By way of example and not limitation, the thickness of the coating is any value or a range of any two of the following: 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm.

[0046] In some specific embodiments, the coating thickness is 2μm-5μm.

[0047] The coating thickness above can further ensure the density of the coating structure and effective protection of the base film, while minimizing ineffective pores and ion migration distance, thereby further balancing the relationship between the electrolyte distribution uniformity and interfacial impedance of the separator, and significantly improving the rate performance and long-cycle stability of the battery.

[0048] In some embodiments, the areal density of the diaphragm is 3 g / m³. 2 -10 g / m 2 .

[0049] When the areal density of the separator is within the above range, it can further optimize the pore volume and ion flux per unit area while ensuring the mechanical integrity and thermal stability of the separator. This effectively prevents internal short circuits and maintains sufficient liquid retention capacity, while avoiding the decrease in ion transport efficiency caused by mass overload, thereby further ensuring the rate performance and long-cycle stability of the battery.

[0050] By way of example and not limitation, the areal density of the membrane is 3 g / m³. 2 4 g / m 2 5 g / m 2 6 g / m 2 7 g / m 2 8 g / m 2 9 g / m 2 10 g / m 2 The range of any value in the range, or any combination of both.

[0051] By way of example, and not limitation, the method for testing the areal density of a diaphragm includes the following steps:

[0052] Take a sample of the diaphragm to be tested, cut it into 10cm × 10cm pieces, weigh them, and calculate the weight per square meter, which is the areal density, in g / m³. 2 .

[0053] It should be noted that if the separator is inside the battery, the specific testing steps are as follows:

[0054] The battery was discharged at 0.33C to the lower limit voltage of 2.5V. The battery was disassembled, the separator was removed, and the separator was soaked in dimethyl carbonate (DMC) for 1 hour. The separator was then removed, dried, and set aside for later use. The wetting area was then tested according to the method described above.

[0055] In some embodiments, the air permeability of the diaphragm is 50s / 100ml - 400s / 100ml.

[0056] When the permeability of the separator is within the above range, a balance can be further achieved between ion transport resistance and electrolyte retention, thereby further ensuring the rate performance and long-cycle stability of the battery.

[0057] By way of example and not limitation, the permeability of the diaphragm is any value or a range of any two of the following: 50 s / 100ml, 100 s / 100ml, 150 s / 100ml, 200 s / 100ml, 250 s / 100ml, 300 s / 100ml, 350 s / 100ml, 400 s / 100ml.

[0058] By way of example and not limitation, the method for testing the air permeability of a diaphragm includes the following steps:

[0059] The diaphragm's air permeability was tested using a Gurley air permeability meter. At 23°C and 50% relative humidity, the permeability was recorded as 6.45 cm for 100 mL of air at a constant pressure. 2 The time required for the membrane sample to be tested is expressed in seconds per 100 mL. Five points are tested for each sample and the average value is taken.

[0060] In some embodiments, the base film includes at least one of polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), cellulose, aramid, and polyimide (PI).

[0061] Among them, the above-mentioned membranes have a low dependence on functional particles, so they have a small impact on the wettability of the membrane, which helps to further improve the interfacial stability of the membrane.

[0062] To further ensure the safety of the diaphragm, in some embodiments, the base membrane includes polyethylene and / or polypropylene.

[0063] In some implementations, the thickness of the base film is 2 μm-16 μm.

[0064] The base film of this thickness possesses sufficient puncture resistance and dimensional stability, effectively preventing internal short circuits caused by separator damage during battery cycling. It also avoids prolonged lithium-ion transport paths or insufficient electrolyte wetting, further ensuring battery safety and cycle life under high-rate charge-discharge conditions. For example, the thickness of the base film is any value or a range of any combination of 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, and 16μm.

[0065] In some embodiments, the functional particle includes a core and a shell disposed on at least a portion of the surface of the core, the core comprising an inorganic ceramic material and the shell comprising a polymer material.

[0066] The core, consisting of inorganic ceramic materials, provides the necessary core thermal stability for the separator, while the outer shell, containing polymer materials, improves the wettability to the electrolyte. This allows the functional particles to balance heat resistance and good wettability, further ensuring the battery's safety and cycle performance.

[0067] In some implementations, based on the mass meter of functional particles, the mass percentage of the core is greater than or equal to 80 wt%.

[0068] When the mass percentage of the core is within the above range, it ensures that the core occupies the main mass fraction, maintaining the core thermal stability and mechanical strength of the coating as an inorganic barrier of the separator. At the same time, it controls the risk of thermal shrinkage of the coating within a low range, further ensuring the safety of the battery.

[0069] By way of example, and not limitation, the method for testing kernel quality percentage includes the following steps:

[0070] Weigh a certain mass of the dried diaphragm sample, denoted as m1, and place it in a pre-weighed crucible. In a temperature-controlled muffle furnace, ignite the sample. First, heat to approximately 500°C at a slow rate in air to fully decompose and carbonize the organic components (including the base membrane and outer shell). Then, continue heating to above 600°C (e.g., 800°C) and maintain this temperature for a sufficient time until all organic matter is completely ashed and the mass no longer changes. After cooling to room temperature in the furnace, accurately weigh the total mass of the crucible and residue, denoted as m2. The mass ratio of the core to the original diaphragm sample mass is the percentage of the residue mass after ignition, i.e., m2 / m1.

[0071] By way of example and not limitation, the mass percentage of the inorganic ceramic material is any value or a range of any two of the following: 80 wt%, 82 wt%, 85 wt%, 87 wt%, 90 wt%, 92 wt%, 94 wt%, 95 wt%, 98 wt%.

[0072] In some embodiments, the polymer material includes a polar functional group, which includes at least one selected from amide, amino, ammonium, carbonyl, aldehyde, ester, sulfonic acid, nitro, and cyano groups.

[0073] The above polar functional groups can form hydrogen bonds with the electrolyte, which can further improve the wetting rate and retention force of the membrane to the electrolyte, thereby optimizing parameter A and enhancing the interfacial transport efficiency of the lithium-ion solvation shell, and further improving the rate performance of the battery.

[0074] To further improve the affinity of the polymer material for the electrolyte, in some embodiments, the polymer material includes amino and / or sulfonic acid groups.

[0075] In some specific embodiments, the polymer material includes at least one of polyimide and aramid. These two polymer materials can more effectively suppress moisture penetration and electrolyte decomposition side reactions under high temperature and high humidity environments, thereby further improving the interfacial stability and thermal safety boundary of the diaphragm during long-term cycling.

[0076] In some embodiments, the inorganic ceramic material includes at least one of alumina, boehmite, silicon dioxide, and zirconium oxide.

[0077] The specific types of inorganic ceramic materials can be selected according to the different needs of the separator. For example, alumina and boehmite have high hardness, excellent thermal stability and good electrolyte affinity, which can further provide mechanical protection and thermal safety for the separator; silica has a higher specific surface area and surface modifiability, which is conducive to fine control of the separator's wetting behavior and electrolyte retention capacity; zirconium oxide has excellent chemical inertness and ionic conductivity, which is conducive to more effectively inhibiting the corrosion of trace amounts of acidic substances such as HF in the electrolyte, thereby slowing down the corrosion of electrode materials and separator substrate, and improving the chemical stability of the battery during long-term cycling.

[0078] In some specific embodiments, the inorganic ceramic material includes particles with a diameter of 0.04 μm to 1.5 μm. Exemplarily, it is any value or a range of any combination of 0.05 μm, 0.08 μm, 0.10 μm, 0.20 μm, 0.50 μm, 1.00 μm, and 1.50 μm.

[0079] To further ensure the wetting rate and retention force of the diaphragm on the electrolyte, in some specific embodiments, the thickness of the outer shell is 0.01 μm-1 μm. Exemplarily, the thickness of the outer shell is any value or a range of any combination of 0.01 μm, 0.02 μm, 0.05 μm, 0.08 μm, 0.10 μm, 0.20 μm, 0.50 μm, 0.80 μm, and 1.00 μm.

[0080] In a second aspect, the present invention provides a method for preparing a diaphragm as described in the first aspect, comprising the following steps:

[0081] A coating comprising functional particles is applied to at least one side of a base membrane, and after drying, a coating is formed to obtain a diaphragm.

[0082] The above preparation method involves placing a coating including functional particles on at least one side of a base film, specifically on at least one functional surface of the base film. The placement methods include, but are not limited to, spraying, slot coating, microgravure coating, dip coating, and transfer coating.

[0083] After drying, a coating is formed. The drying methods include, but are not limited to, hot air drying, infrared radiation drying, vacuum drying, and room temperature natural drying.

[0084] In some embodiments, before applying the coating comprising functional particles to at least one side of the base film, the method further includes the following steps:

[0085] Inorganic ceramics are modified with coupling agents to obtain coupling agent-modified inorganic ceramic materials;

[0086] A polymer material is coated onto at least a portion of the surface of a coupling agent-modified inorganic ceramic material to form a shell, thereby obtaining functional particles;

[0087] Functional particles, binders, and solvents are mixed to obtain a coating containing functional particles.

[0088] In some specific embodiments, the coupling agent includes, but is not limited to, at least one of the following: aminosilane coupling agents, epoxysilane coupling agents, phthalate coupling agents, sulfonic acid coupling agents, etc.

[0089] The adhesive includes, but is not limited to, at least one of the following: carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, sodium polyacrylate, etc.

[0090] The amount of binder can further ensure the wetting area of ​​the diaphragm. In some specific embodiments, the mass percentage of binder in the coating is 2%-8%; exemplary values ​​are any one of 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any combination of both.

[0091] In some specific embodiments, the solvent includes, but is not limited to, at least one of: deionized water, N-methylpyrrolidone (NMP), ethanol, etc.

[0092] In some embodiments, the coating including functional particles may further include dispersants, wetting agents, and defoamers, wherein the dispersants include, but are not limited to, at least one of: sodium salts of polyacrylate copolymers, ammonium salts of polyacrylate copolymers, and ammonium salts of alkanols containing acidic groups; the wetting agents include, but are not limited to, at least one of: fluorinated surfactants, silicone surfactants, acetylsyl glycol surfactants, and polyether-modified polysiloxanes; and the defoamers include, but are not limited to, at least one of: silicone defoamers, polyether defoamers, mineral oil-based defoamers, and non-silicone polymer defoamers.

[0093] In some embodiments, the mass ratio of functional particles, binder, and solvent is (30-50):(3-8):(40-70).

[0094] In other embodiments, the mass ratio of functional particles, binder, dispersant, wetting agent, and solvent is (30-50):(3-8):(0.1-2):(0.01-1):(40-70).

[0095] In some embodiments, the modification of inorganic ceramics with coupling agents includes the following steps:

[0096] 1) Place the inorganic ceramic in a sand mill and add zirconium beads with a diameter of 0.3-1.5μm. Grind at a speed of 500rpm-800rpm for 30-50min.

[0097] 2) Mix the coupling agent and solvent, adjust the pH of the mixture to 4-5, then add the inorganic ceramic ground in step 1), perform the first mixing treatment, keep it at 50℃-70℃, and obtain the coupling agent modified inorganic ceramic material after solid-liquid separation.

[0098] The above heat treatment at 50℃-70℃ can promote the full reaction between the coupling agent and the inorganic ceramic. For example, the -Si-OH of the coupling agent undergoes a condensation reaction with the -OH on the surface of Al2O3.

[0099] For example, the temperature of the heat preservation treatment is any value or a range of any two of the following: 50°C, 52°C, 55°C, 58°C, 60°C, 62°C, 65°C, 68°C, 70°C.

[0100] In some specific embodiments, when the coupling agent and solvent are mixed, the solvent includes ethanol and deionized water.

[0101] In some specific embodiments, the mass ratio of coupling agent, ethanol and water is (1-10):(30-80):(10-69).

[0102] In some specific embodiments, the mass ratio of inorganic ceramic to solvent is 30-100:1. Exemplarily, it is any ratio or a range of any two of the following: 30:1, 40:1, 45:1, 50:1, 55:1, 60:1, 65:1, 70:1, 75:1, 80:1, 85:1, 90:1, 95:1, 100:1.

[0103] In some specific embodiments, the first mixing process includes ultrasonic dispersion and magnetic stirring. Exemplarily, the magnetic stirring speed is 300 rpm-600 rpm, and the time is 1 h-2 h. Exemplarily, the magnetic stirring speed is any value or a range of any combination of 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, etc., and the time is any value or a range of any combination of 1.0 h, 1.2 h, 1.5 h, 1.8 h, 2.0 h, etc.

[0104] In some specific embodiments, solid-liquid separation includes a step of centrifugation at 8000-10000 rpm for 10-20 minutes.

[0105] In some specific embodiments, the solid-liquid separation process further includes washing and drying. The washing process uses ethanol as a detergent. The drying process includes vacuum drying, which is performed at a temperature of 70°C-80°C for 5-10 hours.

[0106] In some specific embodiments, when the polymer material includes polyimide, the polymer material coats at least a portion of the surface of the coupling agent-modified inorganic ceramic material to form a shell, including the following steps:

[0107] Under nitrogen protection, the polymer precursor is dispersed in a solvent, and then an inorganic ceramic material is added. After a second mixing treatment and an imidization treatment, a shell is formed.

[0108] In one specific embodiment, the polymer material precursor includes pyromellitic dianhydride (PMDA) and p-phenylenediamine (PPD).

[0109] Furthermore, the mass ratio of pyromellitic dianhydride to p-phenylenediamine is 0.9-1.1:1. Exemplarily, the mass ratio of pyromellitic dianhydride to p-phenylenediamine is any ratio or a range of any two of the following: 0.90:1, 0.92:1, 0.95:1, 0.98:1, 1.00:1, 1.02:1, 1.05:1, 1.08:1, 1.10:1.

[0110] Furthermore, dispersing the polymer precursor in a solvent includes stirring at room temperature to obtain a polyamic acid (PAA) solution; by way of example, and not limitation, the viscosity of the PAA solution is 200-2000 mPa·s.

[0111] Furthermore, the imidization process includes a first heat treatment at 200℃-250℃ for 1-2 hours, followed by a second heat treatment at 300℃-360℃ for 1-2 hours. The first heat treatment achieves pre-imidization of the PAA, while the second heat treatment completely imidizes the PAA to form a polyimide-containing shell.

[0112] In one specific embodiment, the secondary heat preservation includes a first heat preservation at 300℃-320℃ for 1 hour, and a second heat preservation at 340-360℃ for 0.5 hours.

[0113] In one specific embodiment, the second mixing process includes ultrasonic dispersion, magnetic stirring, and coating. For example, the ultrasonic dispersion process has a power of 400W-500W and a time of 30min-60min, the magnetic stirring process has a rotation speed of 200rpm-300rpm and a time of 2h-5h, and the coating process includes dropping the mixed system obtained by magnetic stirring into a mixed solvent to achieve PAA coating.

[0114] In one specific embodiment, the mixed solvent includes at least one of ethanol, water, toluene, n-hexane, diethyl ether, etc.

[0115] In one specific embodiment, after the second mixing treatment and before the imidization treatment, the process further includes: centrifugation to collect the precipitate and vacuum drying.

[0116] In some specific embodiments, when the polymer material includes aramid, the polymer material coats at least a portion of the surface of the coupling agent-modified inorganic ceramic material to form a shell, including the following steps:

[0117] The polymer material is dispersed in a solvent, and then an inorganic ceramic material is added for a third mixing process. Then, a mixed solvent is added to cause the polymer material to precipitate and coat the surface of the inorganic ceramic material, forming a shell.

[0118] In one specific embodiment, the polymer material includes meta-aramid resin (PMIA) and / or para-aramid (PPTA).

[0119] In one specific embodiment, the solvent includes N-methylpyrrolidone.

[0120] In one specific embodiment, the mass ratio of polymer material to solvent is 5-10:90-95, exemplarily any ratio or a range of any two of the following: 5:90, 5:92, 5:95, 7:90, 7:93, 7:95, 8:90, 8:92, 8:95, 10:90, 10:92, 10:95.

[0121] In one specific embodiment, the third mixing process includes: ultrasonic dispersion treatment and magnetic stirring treatment. For example, the ultrasonic dispersion treatment has a power of 400W-500W and a time of 30min-60min, and the magnetic stirring treatment has a rotation speed of 200rpm-300rpm and a time of 2h-5h.

[0122] In one specific embodiment, the mixed solvent is a mixture of ethanol and water in a mass ratio of 3-4:1-2, for example, a mixture of ethanol and water in a mass ratio of 4:1.

[0123] In one specific embodiment, the mixed solvent is added dropwise to cause the polymer material to precipitate and coat the surface of the inorganic ceramic material.

[0124] In one specific embodiment, after the polymer material is precipitated and coated on the surface of the inorganic ceramic material, the process further includes: centrifugation to collect the precipitate, drying, and holding at 100-120°C for 1-2 hours as a post-treatment step.

[0125] In one specific embodiment, the above drying includes a step of vacuum drying at 60°C for 4 hours.

[0126] In one specific embodiment, when the polymer material includes PMIA, the functional particles are prepared by the following process:

[0127] 1) Mix PMIA and solvent NMP at a ratio of 8:92 and stir at 80°C until completely dissolved to obtain a transparent and viscous PMIA solution; add the coupling agent-modified inorganic ceramic material to the PMIA solution for a third mixing treatment, specifically by ultrasonic dispersion for 30 min (500W power) and magnetic stirring for 2 h (200 rpm) to form a mixed solution of PMIA / inorganic ceramic material;

[0128] 2) Slowly drop the mixed solution of PMIA / inorganic ceramic material from step 1) into a large amount of mixed solvent. PMIA precipitates and coats the surface of the inorganic ceramic material. Collect the precipitate by centrifugation and dry it under vacuum at 60°C for 4 hours.

[0129] 3) The product from step 2) is kept at 100°C for 1 hour to remove residual solvent; PMIA-coated inorganic ceramic material, i.e., functional particles, is obtained.

[0130] Thirdly, the present invention provides a battery comprising the separator of the first aspect.

[0131] In some embodiments, the battery further includes a negative electrode and a positive electrode. The positive electrode includes a positive current collector and a positive electrode material layer located on at least one surface of the positive current collector. The positive electrode material layer includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material may be selected from one or more of lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based materials, lithium manganese iron phosphate, and their corresponding doped or coated modified materials. The conductive agent may be selected from at least one of carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, graphene, and conductive graphite. The binder may be selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, polyacrylic acid, and polyimide. The positive current collector may be a conventional positive current collector in the art, such as aluminum foil. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material, a conductive agent, a binder, and a dispersant. The negative electrode active material can be selected from one or more of graphite, hard carbon, soft carbon, silicon-based negative electrode, titanium-based material, nitride, tin compound, and lithium metal. The conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, metal powder, and graphene. The binder can be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate. The dispersant can be selected from at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, and sodium dodecyl sulfate. The negative electrode current collector can be a conventional negative electrode current collector in the art, such as copper foil.

[0132] Among them, lithium iron phosphate (LFP) is a positive electrode active material with an olivine-type crystal structure, which has the advantages of low cost and high safety. The general chemical formula of lithium iron phosphate can be LiFe. 1-x M x PO y Q z Where x≤0.1, 3.85≤y≤4, 0≤z≤0.05, and the doping element M includes, but is not limited to, one or more of Ti, V, Mg, Mn, Ni, Co, Cr, Cu, Bi, and Sb; the general chemical formula of nickel-cobalt ternary materials can be Li a Ni b Co c M 1d M 2e O f R gWherein, 0.75≤a≤1.2, 0<b<1, 0<c<1, 0<d<1, b+c+d=1, 0≤e≤0.2, 1≤f≤2.5, 0≤g≤1, f+g≤3, M1 includes but is not limited to Mn and / or Al, and M2 includes but is not limited to at least one of B, Zr, Ti, Si, Mo, La, Ce, Te, Nb, Ta, Si, Al, W, Sr, V, Y, Mg, Co, and Li.

[0133] In some embodiments, the battery is a lithium-ion battery, and its preparation steps include the following steps:

[0134] A bare cell is obtained by winding or stacking positive electrode sheets, negative electrode sheets, and separators in an orderly manner; the bare cell is placed in an outer packaging shell, dried, injected with electrolyte, and then packaged, left to stand, formed, and calibrated to obtain a lithium-ion battery.

[0135] The outer packaging shell includes aluminum-plastic film, metal shell, etc.; the metal shell specifically includes, but is not limited to, aluminum metal, aluminum alloy metal (aluminum-magnesium alloy, aluminum-manganese alloy, etc.); steel, stainless steel, nickel-plated steel, carbon steel, etc.; titanium metal, titanium alloy, etc.

[0136] In some specific embodiments, the preparation of the positive electrode sheet includes the following process: mixing positive electrode active material, conductive agent, binder and dispersant, adding solvent and continuing to mix to obtain positive electrode slurry, wherein the mass percentage of positive electrode active material: conductive agent: binder: dispersant is (90%-99%):(0.5%-5%):(0.5%-5%):(0%-2%); coating the positive electrode slurry on at least one surface of the positive electrode current collector, drying, rolling and slitting to obtain the positive electrode sheet.

[0137] In some specific embodiments, the preparation of the negative electrode sheet includes the following process: mixing negative electrode active material, conductive agent, binder and dispersant, adding solvent and continuing to mix to obtain negative electrode slurry, wherein the mass percentage of negative electrode active material: conductive agent: binder: dispersant is (90%-98%): (0%-5%): (1.5%-5%): (0.3%-1.5%), coating the negative electrode slurry on at least one surface of the negative electrode current collector, drying, rolling and slitting to obtain the negative electrode sheet.

[0138] Unless otherwise specified, all reagents involved in the embodiments of this invention are commercially available products and can be purchased through commercial channels.

[0139] To further understand the present invention, the technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0140] Example 1

[0141] This example provides a diaphragm, including a PE base film and a coating disposed on both sides of the base film, wherein the coating thickness is 1.8 μm, the base film thickness is 7 μm, the coating includes functional particles, the functional particles include an alumina ceramic core and a PI shell disposed on at least a portion of the surface of the alumina ceramic core, and other parameters are shown in Table 1.

[0142] Its preparation includes the following steps:

[0143] 1. Prepare a mixed solution by mixing aminosilane coupling agent, ethanol and deionized water in a mass ratio of 3:82:15. Add dilute acetic acid to adjust the pH of the mixed solution to 4-5. Stir magnetically at room temperature for 30 minutes. The mixed solution will change from transparent to slightly turbid.

[0144] 2. Alumina inorganic ceramic particles (average particle size 0.04-1.5 μm) were placed in a sand mill, and zirconium beads were added simultaneously. The particles were ground at 600 rpm for 40 min (zirconium bead diameter = 0.9 μm). The ground alumina inorganic ceramic particles were slowly added to the mixed solution obtained in step 1 (mass ratio of inorganic ceramic particles to mixed solution is 1:80). The mixture was ultrasonically dispersed for 20 min, and then magnetically stirred for 2 h (600 rpm) to ensure that the surface of the inorganic ceramic particles was in full contact with the coupling agent. The mixture was then transferred to a 50℃ constant temperature water bath and kept at that temperature for 2 h. After that, it was centrifuged at 8000 rpm for 10 min, and the solid was collected. The solid was washed three times with ethanol and then vacuum dried at 80℃ for 6 h to obtain the coupling agent modified inorganic ceramic material.

[0145] 3. Under nitrogen protection, pyromellitic dianhydride (PMDA) and p-phenylenediamine (PPD) were added sequentially to NMP at a mass ratio of 1:1 and stirred at room temperature for 4 hours to obtain a PAA solution with a viscosity of 500 mPa·s. The coupling agent-modified inorganic ceramic material was slowly added to the PAA solution, ultrasonically dispersed for 30 minutes (500 W power), and then magnetically stirred for 2 hours (200 rpm) to form a mixed solution of PAA and inorganic ceramic material.

[0146] 4. Slowly drop the PAA / inorganic ceramic material mixed solution from step 3 into a mixed solvent (the mixed solvent is a mixture of ethanol and water with a mass ratio of 4:1) with a mass of about 3-8 times that of the mixed solution. PAA will precipitate and coat the surface of the inorganic ceramic material. Collect the precipitate by centrifugation and dry it under vacuum at 60°C for 4 hours.

[0147] 5. The product from step 5 is heated at 100℃ for 1 hour to remove residual solvent; then it is pre-iminoized by heating at 200℃ for 1 hour; then it is fully iminoized by heating at 300℃ for 1 hour; and finally it is heated at 350℃ for 0.5 hours to obtain PI-coated inorganic ceramic material, i.e., functional particles.

[0148] 6. Mix functional particles, sodium polyacrylate binder, polyacrylic acid dispersant, and deionized water in a mass ratio of 35:3:0.2:61.75 to prepare a coating slurry; coat the slurry onto the base film using a micro-gravure roller to obtain a diaphragm.

[0149] Example 2

[0150] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0151] The preparation method differs from that in Example 1 in that, in addition to adjusting the parameters according to Table 1, the zirconium bead diameter is 1.1 μm in step 2, and then the beads are ground at 740 rpm for 40 min.

[0152] Example 3

[0153] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0154] The preparation method differs from that in Example 1 in that, in addition to adjusting the parameters according to Table 1, the zirconium bead diameter is 1.1 μm in step 2, and then the beads are ground at 700 rpm for 40 min.

[0155] Example 4

[0156] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0157] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zirconium bead diameter is 1.2 μm in step 2, and then the grinding process is carried out at a speed of 750 rpm for 45 min.

[0158] Example 5

[0159] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0160] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zirconium bead diameter is 0.8 μm in step 2, and then the grinding process is carried out at a speed of 600 rpm for 35 min.

[0161] Example 6

[0162] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0163] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zirconium bead diameter is 1.0 μm in step 2, and then the grinding process is carried out at a speed of 720 rpm for 40 min.

[0164] Example 7

[0165] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0166] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zirconium bead diameter is 1.3 μm in step 2, and then the grinding process is carried out at a speed of 770 rpm for 45 min.

[0167] Example 8

[0168] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0169] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zircon bead diameter is 0.3 μm in step 2, and then the grinding process is carried out at a speed of 500 rpm for 30 min.

[0170] Example 9

[0171] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0172] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zirconium bead diameter is 0.6 μm in step 2, and then the grinding process is carried out at a speed of 620 rpm for 35 min.

[0173] Example 10

[0174] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0175] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zirconium bead diameter is 1.2 μm in step 2, and then the grinding process is carried out at a speed of 740 rpm for 45 min.

[0176] Example 11

[0177] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0178] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zircon bead diameter is 0.7 μm in step 2, and then the grinding process is carried out at a speed of 640 rpm for 35 min.

[0179] Example 12

[0180] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0181] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zircon bead diameter is 1.4 μm in step 2, and then the grinding process is carried out at a speed of 820 rpm for 50 min.

[0182] Example 13

[0183] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0184] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zirconium bead diameter is 0.2 μm in step 2, and then the grinding process is carried out at a speed of 480 rpm for 25 min.

[0185] Example 14

[0186] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0187] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zircon bead diameter is 0.2 μm in step 2, and then the grinding process is carried out at a speed of 680 rpm for 40 min.

[0188] Example 15

[0189] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0190] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zircon bead diameter is 0.9 μm in step 2, and then the grinding process is carried out at a speed of 680 rpm for 40 min.

[0191] Example 16

[0192] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0193] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zirconium bead diameter is 1.3 μm in step 2, and then the grinding process is carried out at a speed of 770 rpm for 45 min.

[0194] Example 17

[0195] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0196] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zirconium bead diameter is 0.6 μm in step 2, and then the grinding process is carried out at a speed of 620 rpm for 35 min.

[0197] Example 18

[0198] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0199] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zircon bead diameter is 0.9 μm in step 2, and then the grinding process is carried out at a speed of 680 rpm for 40 min.

[0200] Comparative Example 1

[0201] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0202] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zirconium bead diameter is 0.5 μm in step 2, and then the grinding process is carried out at a speed of 610 rpm for 35 min.

[0203] Comparative Example 2

[0204] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0205] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zirconium bead diameter is 1.4 μm in step 2, and then the grinding process is carried out at a speed of 850 rpm for 50 min.

[0206] Comparative Example 3

[0207] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0208] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zirconium bead diameter is 0.2 μm in step 2, and then the grinding process is carried out at a speed of 450 rpm for 25 min.

[0209] Comparative Example 4

[0210] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0211] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zirconium bead diameter is 1.5 μm in step 2, and then the grinding process is carried out at 800 rpm for 50 min.

[0212] Comparative Example 5

[0213] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0214] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zirconium bead diameter is 0.5 μm in step 2, and then the grinding process is carried out at a speed of 610 rpm for 35 min.

[0215] Comparative Example 6

[0216] The diaphragm is basically the same as that in Example 1, except that the parameters in Table 1 are changed.

[0217] The preparation method differs from that of Example 1 only in that, in addition to adjusting the parameters according to Table 1, the zircon bead diameter is 1.4 μm in step 2, and then the grinding process is carried out at a speed of 820 rpm for 50 min.

[0218] Application Example 1

[0219] The separators of Examples 1-16 and Comparative Examples 1-4 above are used to assemble lithium iron phosphate lithium-ion batteries, including the following steps:

[0220] Preparation of the negative electrode sheet: Artificial graphite, conductive agent SP, and binder CMC are mixed and evenly dispersed in deionized water at a compound ratio of 97%:1.5%:1.5% to obtain a negative electrode slurry. This negative electrode slurry is then coated onto copper foil to obtain a double-sided coated electrode sheet. After rolling and cutting, the negative electrode sheet is obtained with an areal density of 200 g / m². 2 Compacted density 1.55 g / cm³ 3 ;

[0221] Preparation of the positive electrode: Lithium iron phosphate, PVDF binder, SP conductive agent, and CNT conductive agent are mixed and uniformly dispersed in NMP at a compound ratio of 96%:1.5%:1.5%:1% to obtain a positive electrode slurry; the positive electrode slurry is coated on aluminum foil to obtain a double-sided coated electrode; then rolled and cut to obtain a negative electrode with an areal density of 400 g / m³. 2 Compacted density 2.5 g / cm³ 3 .

[0222] Preparation of electrolyte: Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a mass ratio of 1:1:1: were mixed to obtain a solvent. Lithium hexafluorophosphate was added to the solvent to make its concentration 1 mol / L, thus obtaining the electrolyte.

[0223] Battery assembly: The positive electrode, negative electrode and separator are wound to obtain the bare cell. The bare cell is placed in an aluminum-plastic packaging shell, dried, injected with electrolyte, and then packaged, left to stand, formed and calibrated to obtain a lithium iron phosphate lithium-ion battery.

[0224] Application Example 2

[0225] The separators from Examples 17-19 and Comparative Examples 5-6 were used to assemble ternary lithium-ion batteries. The steps were basically the same as in Application Example 1, except that lithium iron phosphate was replaced with a ternary material (molecular formula: LiNi) when preparing the positive electrode. 0.6 Co 0.2 Mn 0.2 O2).

[0226] Test case

[0227] 1. Surface density: Take a sample of the diaphragm cut into 10cm×10cm size, weigh it, and calculate the weight per square meter, which is the surface density.

[0228] 2. Air permeability: The air permeability of the diaphragm was tested using a Gurley air permeability meter. Under conditions of 23℃ and 50% humidity, the air permeability of 100 mL of air at a fixed pressure was recorded as 6.45 cm. 2 The time required for the diaphragm sample is measured in seconds per 100 mL. Five points are tested for each sample, and the average value is taken.

[0229] If the separator has been assembled into the battery, it is necessary to remove the separator from the battery before testing its areal density and air permeability. The removal process includes: discharging the battery at 0.33C to the lower limit voltage of 2.5V, disassembling the battery, removing the separator, soaking the separator in dimethyl carbonate (DMC) solution for 1 hour, removing it and drying it, and then testing the wetting area according to the above method.

[0230] 3. Cycling and Rate Testing: For lithium-ion batteries with ternary cathode materials (Examples 17-19 and Comparative Examples 5-6), each lithium-ion battery was placed in a 25°C incubator and charged at 0.33C to the upper limit voltage of 4.25V, then charged at a constant voltage to the cutoff current of 0.05C; after resting for 30 minutes, it was discharged at 0.33C to the lower limit discharge voltage of 2.5V; the above operation was repeated 3 times, and the discharge capacity of the third cycle was taken as the fixed capacity of the lithium-ion battery; then the following tests were performed: At 25°C, the lithium-ion batteries prepared in the examples and comparative examples were cycled according to the following procedure:

[0231] 1) Discharge the lithium-ion battery after it has been capacitated to the lower limit voltage of 2.5V at 0.33C;

[0232] 2) Charge at a constant current rate of 1C to 3.65V, and then charge at a constant voltage until the current drops to 0.05C;

[0233] 3) Let it stand for 30 minutes;

[0234] 4) Discharge to 2.5V at a 1C rate;

[0235] 5) Let it stand for 30 minutes.

[0236] Perform cycle tests according to steps 2)-5) until the capacity of the lithium-ion battery is less than 80% of the initial capacity, and record the number of cycles.

[0237] For lithium-ion batteries with lithium iron phosphate as the cathode material (Examples 1-16 and Comparative Examples 1-4), each lithium-ion battery was placed in a 25°C incubator and charged at 0.33C to the upper limit voltage of 3.65V, then charged at a constant voltage to the cutoff current of 0.05C; after standing for 30 minutes, it was discharged at 0.33C to the lower limit voltage of 2.5V; the above operation was repeated 3 times, and the discharge capacity of the third cycle was taken as the battery's fixed capacity; then the following test was performed: at 25°C, the lithium-ion batteries prepared in the examples and comparative examples were cycled according to the following procedure:

[0238] 1) Discharge the battery after it has been capacitated to the lower limit voltage of 2.5V at 0.33C;

[0239] 2) Charge at a constant current rate of 1C to 3.65V, and then charge at a constant voltage until the current drops to 0.05C;

[0240] 3) Let it stand for 30 minutes;

[0241] 4) Discharge to 2.5V at a 1C rate;

[0242] 5) Let it stand for 30 minutes.

[0243] Perform cycle tests according to steps 2)-5) until the capacity of the lithium-ion battery is less than 80% of the initial capacity, and record the number of cycles.

[0244] Rate performance test: The lithium-ion batteries prepared in Examples 1-16 and Comparative Examples 1-4 were charged at 0.33C to the upper limit voltage of 3.65V, charged at constant voltage to the current of 0.05C, and then discharged at 2C to 2.5V. The 2C discharge capacity / constant capacity × 100% is the rate performance of the lithium-ion battery.

[0245] The lithium-ion batteries prepared in Examples 17-19 and Comparative Examples 5-6 were charged to the upper limit voltage of 4.25V at 0.33C, charged to the value current of 0.05C at constant voltage, and then discharged to 2.5V at 2C. The rate performance of the lithium-ion battery was calculated as 2C discharge capacity / constant capacity × 100%.

[0246] Table 1:

[0247]

[0248] As shown in Table 1, compared with Comparative Examples 1-6, the separators in Examples 1-18, by regulating the relationship between the particle size (B) of the functional particles and the separator wetting performance parameter (A), satisfy the condition: 0.01≤A×B≤40. This improves the ion transport efficiency and cycle life of the battery under high-rate charge and discharge conditions. Specifically, when the battery capacity is less than 80% of the initial capacity, its cycle count is greater than or equal to 942; and its rate performance is greater than or equal to 78.5%. Furthermore, if 0.5≤A×B≤15, the cycle performance and rate performance of the battery are even better. Specifically, when the battery capacity is less than 80% of the initial capacity, its cycle count is greater than or equal to 1296; and its rate performance is greater than or equal to 90.5%.

[0249] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A diaphragm, characterized in that, The membrane includes a base membrane and a coating disposed on at least one side of the base membrane. The coating comprises functional particles with a particle size of B μm. The membrane is immersed in a solution for 3 minutes, and the immersion area of ​​the membrane is A cm². 2 A and B satisfy the following relationship: 0.01≤A×B≤40.

2. The diaphragm according to claim 1, characterized in that, 0.15≤A≤20； And / or, 0.05≤B≤2.

5.

3. The diaphragm according to claim 1 or 2, characterized in that, The thickness of the coating is 1μm-10μm.

4. The diaphragm according to claim 1 or 2, characterized in that, The areal density of the diaphragm is 3 g / m³. 2 -10 g / m 2 ; And / or, the air permeability of the diaphragm is 50s / 100ml - 400s / 100ml.

5. The diaphragm according to claim 1 or 2, characterized in that, The base film includes at least one of polypropylene, polyethylene, polyethylene terephthalate, cellulose, aramid, and polyimide.

6. The diaphragm according to claim 5, characterized in that, The base film comprises polyethylene and / or polypropylene.

7. The diaphragm according to claim 1 or 2, characterized in that, The thickness of the base film is 2μm-16μm.

8. The diaphragm according to claim 1 or 2, characterized in that, The functional particle includes a core and a shell disposed on at least a portion of the surface of the core, the core comprising an inorganic ceramic material and the shell comprising a polymer material.

9. The diaphragm according to claim 8, characterized in that, The polymer material includes polar functional groups, which include at least one selected from amide, amino, ammonium, carbonyl, aldehyde, ester, sulfonic acid, nitro, and cyano groups.

10. The diaphragm according to claim 9, characterized in that, The polymer material includes amino and / or sulfonic acid groups.

11. The diaphragm according to claim 10, characterized in that, The polymer material includes at least one of polyimide and aramid; And / or, the inorganic ceramic material includes at least one of alumina, boehmite, silicon dioxide, and zirconium oxide.

12. The diaphragm according to claim 8, characterized in that, The thickness of the outer shell is 0.01μm-1μm.

13. A method for preparing a diaphragm as described in any one of claims 1-12, characterized in that, Includes the following steps: A coating comprising the functional particles is applied to at least one side of the base membrane, and after drying, a coating is formed to obtain the diaphragm.

14. The preparation method according to claim 13, characterized in that, Before applying the coating comprising the functional particles to at least one side of the base film, the method further includes the following steps: Inorganic ceramics were modified with coupling agents to obtain coupling agent-modified inorganic ceramic materials; The polymer material is coated onto at least a portion of the surface of the coupling agent-modified inorganic ceramic material to form a shell, thereby obtaining the functional particles; The functional particles, binder, and solvent are mixed to obtain the coating comprising the functional particles.

15. A battery, characterized in that, The membrane includes the membrane according to any one of claims 1-12 or the membrane prepared by the preparation method according to any one of claims 13-14.

16. The battery according to claim 15, characterized in that, It also includes a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte includes at least one solvent selected from ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, ethyl propionate, methyl propionate, and methyl methyl butyrate.

17. The battery according to claim 16, characterized in that, The positive electrode sheet includes a positive current collector and a positive electrode coating disposed on at least one side of the surface of the positive current collector, wherein the positive electrode coating includes at least one of lithium nickel cobalt manganese oxide and lithium iron phosphate.

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