A polymer-coated separator and its preparation method in lithium-ion batteries

Abstract

This invention provides a polymer-coated separator, its preparation method, and a lithium-ion battery. The polymer-coated separator includes a base film and a coating located on at least one side of the base film. The coating includes a polymer, and the monomers of the polymer include alkenyl groups, halogen substituents, thiourea groups, and carboxyl groups. The halogen substituents include bromine substituents and / or iodine substituents. The polymer-coated separator of this invention includes a coating containing a specific polymer. The monomers of the polymer contain halogen substituents, thiourea groups, and carboxyl groups, which enables the coating to improve the flame retardant properties of the separator, reduce the risk of battery combustion and explosion, enhance battery safety, promote lithium-ion conduction, improve the wettability of the separator and electrolyte, resolve the contradiction of traditional flame retardants reducing ionic conductivity, and improve the battery's safety performance, rate performance, and fast charging performance.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and relates to a polymer-coated separator, its preparation method, and lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries have become the mainstream development direction for rechargeable batteries due to their numerous advantages, including high efficiency, small size, light weight, long lifespan, and low maintenance costs. In recent years, high-energy-density lithium-ion batteries have developed rapidly, with their energy density reaching 300Wh / kg. Their applications have also expanded rapidly from traditional small-scale 3C electronics to large-scale power equipment such as new energy electric vehicles, energy storage, large drones, ships, and pure electric aircraft. However, with the continuous improvement of battery energy density and power density, battery spontaneous combustion and explosions have become increasingly frequent in recent years.

[0003] The core reason for battery spontaneous combustion and explosion lies in the fact that current lithium-ion battery separators are polyolefin microporous membranes based on polyethylene (PE) and polypropylene (PP), which lack sufficient heat resistance. They soften and deform above 100°C, making them prone to melting and rupture under conditions of overcharging, over-discharging, rapid charging and discharging, abuse, or high temperatures. This leads to internal short circuits within the battery, causing thermal runaway and resulting in fires and explosions. Traditional separators are particularly incompatible with high-energy-density fast-charging systems. Existing technologies utilize high-temperature resistant materials to prepare flame-retardant separators, thereby improving the safety performance of both the separator and the battery.

[0004] For example, CN104377329A discloses a novel heat-resistant and flame-retardant separator for lithium-ion batteries and its preparation method, which involves reacting melamine, formaldehyde, and other additives to form a copolymer, and then preparing a heat-resistant and flame-retardant nonwoven separator by electrospinning. Another example is CN102655228A, which discloses a high-temperature resistant polyimide battery separator and its preparation method, wherein the high-temperature resistant polyimide battery separator is prepared using a phase transition method. However, the existing preparation methods are cumbersome, have limited flame retardancy, and cannot simultaneously guarantee the ion conductivity of the separator.

[0005] Based on the above research, there is a need to provide a polymer-coated diaphragm that can resolve the contradiction of traditional flame retardants reducing ionic conductivity, while ensuring the flame retardant performance and ionic conductivity of the diaphragm. Summary of the Invention

[0006] The purpose of this invention is to provide a polymer-coated separator, its preparation method, and a lithium-ion battery. The polymer-coated separator includes a coating containing a specific polymer. The monomers of the polymer contain halogen substituents, thiourea groups, and carboxyl groups, which enables the coating to improve the flame retardant performance of the separator, reduce the risk of battery combustion and explosion, enhance battery safety, promote lithium-ion conduction, improve the wettability of the separator and electrolyte, resolve the contradiction of traditional flame retardants reducing ionic conductivity, and improve the battery's safety performance, rate performance, and fast charging performance.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a polymer-coated separator, the polymer-coated separator comprising a base membrane and a coating located on at least one side surface of the base membrane, the coating comprising a polymer, wherein the monomers of the polymer comprise alkenyl groups, halogen substituents, thiourea groups and carboxyl groups, the halogen substituents comprising bromine substituents and / or iodine substituents.

[0009] This invention provides a coating comprising a specific polymer on at least one side of a base membrane. The halogen substituents in the polymer monomers enhance the flame retardant properties of the separator, reducing the risk of battery combustion and explosion, and improving battery safety. The thiourea and carboxyl groups in the polymer monomers interact with lithium ions, promoting lithium ion conduction. Simultaneously, the carboxyl groups improve the wettability of the separator and electrolyte, enhancing overall battery performance. Furthermore, the flame retardant properties provided by the halogen substituents and the ionic conductivity provided by the thiourea groups work synergistically, resolving the contradiction of traditional flame retardants reducing ionic conductivity while ensuring both the flame retardant and ionic conductivity of the separator, thus improving battery safety, rate performance, and fast charging performance.

[0010] The halogen substituents described in this invention include bromine substituents and / or iodine substituents. Due to the high cost of iodine substituents, bromine substituents are preferred. Furthermore, bromine substituents cannot be replaced by chlorine or fluorine substituents. The principle by which bromine substituents improve the flame retardant performance of the membrane is as follows: C-Br has a low bond energy and can homolytically cleave to release bromine free radicals (Br·) at 150-300℃. These bromine free radicals can capture H· / HO· free radicals, resulting in the following reactions: Br· + H· → HBr (endothermic), HBr + HO· → Br· + H2O (cycle blocking), thereby achieving a flame retardant effect. In contrast, C-Cl has a high bond energy and requires a higher temperature to decompose, resulting in low flame retardant efficiency. CF has an even higher bond energy and is difficult to decompose for flame retardancy.

[0011] Preferably, the monomer of the polymer further includes a rigid group, which includes any one of substituted or unsubstituted phenyl, naphthyl, or biphenyl groups.

[0012] Preferably, the substituents in the rigid group include alkoxy groups (such as methoxy or ethoxy groups) or halogen groups (such as chlorine or fluorine groups).

[0013] Preferably, the rigid group includes a first rigid group and a second rigid group, wherein the first rigid group includes an alkoxy-substituted phenyl or an alkoxy-substituted naphthyl, and the second rigid group includes a halogen-substituted or unsubstituted phenyl or a halogen-substituted or unsubstituted biphenyl.

[0014] The rigid groups included in this invention can further improve the membrane performance. For example, alkoxy-substituted phenyl or alkoxy-substituted naphthyl groups give the polymer a certain rigidity and stability, which helps to maintain the membrane structure and improve the mechanical properties of the membrane. Halogen-substituted or unsubstituted phenyl or halogen-substituted or unsubstituted biphenyl groups can not only improve rigidity, but halogen substitution can further improve the polymer polarity and improve electrolyte wettability.

[0015] Preferably, the monomer of the polymer has the following general structural formula:

[0016] .

[0017] Wherein, R1 is selected from alkoxy-substituted phenyl or alkoxy-substituted naphthyl (wherein the alkoxy group may be methoxy or ethoxy), R2 is selected from halogen-substituted or unsubstituted phenyl or halogen-substituted or unsubstituted biphenyl (wherein the halogen may be chlorine or fluorine), and X is selected from Br or I.

[0018] Preferably, the monomers of the polymer include (4-(3-(3-(5-bromo-2-methoxyphenyl)acryloyl)thiourea)benzoic acid), CAS: 535936-56-2), (CAS: 530152-49-9) (CAS: 532978-58-8) or Any one or at least two of the following (CAS: 532432-36-3):

[0019] Preferably, the weight-average molecular weight of the polymer is 60,000 Da to 130,000 Da, for example, it can be 60,000 Da, 70,000 Da, 80,000 Da, 90,000 Da, 100,000 Da, 110,000 Da, 120,000 Da or 130,000 Da, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] When the weight-average molecular weight of the polymer described in this invention is low, it will lead to poor film-forming properties and interfacial adhesion of the coating, as well as insufficient mechanical strength. Conversely, if the molecular weight of the polymer is too high, it will increase the viscosity of the coating slurry, thereby reducing the uniformity of the coating and increasing the brittleness of the coating, ultimately adversely affecting the overall performance of the polymer-coated membrane.

[0021] Preferably, the thickness of the coating is 1μm to 3μm, for example, it can be 1μm, 1.5μm, 2μm, 2.5μm or 3μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] If the polymer coating in this invention is too thin, its coverage on the base film surface will be uneven, making it difficult to adequately buffer and protect the silicon anode from stress during expansion, and its effect on improving the thermal stability of the separator will also be limited. Conversely, if the polymer coating is too thick, it will not only increase the overall thickness and internal resistance of the separator but also reduce the energy density and power density of the battery. Furthermore, an excessively thick coating will negatively impact the wetting performance of the electrolyte and ion transport efficiency, while also increasing costs.

[0023] Preferably, the coating also includes inorganic oxides.

[0024] The coating of this invention also incorporates inorganic oxides, which interact with the polymer to construct an organic-inorganic composite network structure. The two work synergistically to effectively resist thermal shrinkage at high temperatures and the stress generated by the expansion of the silicon anode, thereby reducing the thermal shrinkage rate of the separator and significantly improving the overall performance of the polymer-coated separator.

[0025] Preferably, the inorganic oxide includes Sb2O3.

[0026] The inorganic oxide used in this invention to match the polymer is Sb2O3, which can synergistically improve the flame retardant efficiency with bromine.

[0027] Preferably, the particle size D50 of the inorganic oxide is 15nm~50nm, for example, it can be 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm or 50nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] If the particle size D50 of the inorganic oxides in this invention is too large, according to Stokes' law, their settling velocity in the coating slurry will be accelerated, leading to a thin upper layer and a thick lower layer in the coating slurry, ultimately resulting in an uneven coating distribution. Conversely, when the particle size of the inorganic oxides is too small, their specific surface area will increase significantly, making them prone to spontaneous aggregation into micron-sized agglomerates, thus affecting their uniform distribution in the coating.

[0029] Preferably, the mass ratio of the polymer to the inorganic oxide is (15~30):(10~23), for example, it can be 15:15, 20:10, 25:20, 30:23, 15:10, 15:23 or 30:10, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, the polymer coating further includes a first wetting agent, a first dispersant, and a binder.

[0031] Preferably, the mass ratio of polymer, inorganic oxide, first wetting agent, first dispersant and binder in the polymer coating is (15~30):(10~23):(0.02~0.08):(0.1~0.3):(3~7), for example, it can be 15:30:0.07:0.3:3, 20:15:0.04:0.15:4, 25:20:0.06:0.2:6 or 30:23:0.08:0.1:7, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0032] Preferably, the first wetting agent comprises any one or a combination of at least two of sodium hexametaphosphate, sodium tripolyphosphate, or sodium pyrophosphate.

[0033] Preferably, the first dispersant comprises any one or a combination of at least two of silicate compounds, sodium polyacrylate, or sodium citrate.

[0034] Preferably, the adhesive comprises any one or a combination of at least two of carboxymethyl cellulose, hydroxypropyl methyl cellulose, or polyvinyl alcohol.

[0035] Preferably, the porosity of the base membrane is 40% to 50%, for example, it can be 40%, 42.5%, 45%, 47.5% or 50%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the air permeability of the base membrane is 80s / 100mL to 100s / 100mL, for example, it can be 80s / 100mL, 85s / 100mL, 90s / 100mL, 95s / 100mL or 100s / 100mL, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the thickness of the base film is 7μm to 10μm, for example, it can be 7μm, 8μm, 9μm or 10μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the base film comprises a PI-based film (polyimide-based film).

[0039] In this invention, a polyimide (PI) base film is preferentially selected. This base film possesses high-temperature resistance, with a rupture temperature reaching up to 430°C, which significantly enhances battery safety performance and improves the pass rates of nail penetration and hot box tests. Furthermore, the PI base film contains polar nitrogen groups, which can form hydrogen bonds with solvents in the electrolyte (such as ethylene carbonate or other solvents), effectively improving the wettability of the polymer-coated separator and thus optimizing the battery's rate performance.

[0040] Preferably, the thickness of the polymer-coated membrane is 8μm to 13μm, for example, it can be 8μm, 9μm, 10μm, 11μm, 12μm or 13μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] If the polymer coating membrane in this invention is thin, its puncture resistance will be weakened and it will be easily punctured; while when the polymer coating membrane is thick, the ion transport path will be longer, which will lead to a reduction in rate performance.

[0042] Preferably, the porosity of the polymer-coated membrane is 32% to 45%, for example, it can be 32%, 36%, 38%, 40%, 42% or 45%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] When the porosity of the polymer-coated separator described in this invention is too high, its mechanical strength will be weakened and its shrinkage rate will increase under high temperature conditions; while if the porosity of the polymer-coated separator is too low, the absorption rate of the electrolyte will decrease, thereby deteriorating the rate performance of the battery.

[0044] In a second aspect, the present invention provides a method for preparing a polymer-coated separator as described in the first aspect, the method comprising the following steps:

[0045] The polymer-coated diaphragm is obtained by applying a coating slurry to at least one side surface of the base film;

[0046] The coating slurry includes a polymer, and the monomers of the polymer include alkenyl groups, halogen substituents, thiourea groups and carboxyl groups, wherein the halogen substituents include bromine substituents and / or iodine substituents.

[0047] Preferably, the method for preparing the polymer includes the following steps:

[0048] The polymer monomers, initiator, and organic solvent are mixed and reacted. After the reaction, the resulting solution is added to the precipitation solvent to obtain the polymer.

[0049] In the monomers of the polymer described in this invention, the polymerization group is an alkenyl group (a vinyl group attached to R1 in the general formula).

[0050] Preferably, the reaction temperature is 70℃~110℃, for example, 70℃, 80℃, 90℃, 100℃ or 110℃, and the time is 12h~30h, for example, 12h, 15h, 20h, 25h or 30h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] Preferably, the reaction is carried out under an inert gas protection environment, such as argon protection.

[0052] Preferably, the organic solvent includes any one or a combination of at least two of benzene, THF (tetrahydrofuran), NMP (N-methylpyrrolidone), or DMF (N,N-dimethylformamide).

[0053] Preferably, the initiator includes any one or a combination of at least two of azobisisobutyronitrile, azobisisoheptanenitrile, or benzoyl peroxide.

[0054] Preferably, the amount of initiator added is 0.2% to 0.8% of the monomer mass of the polymer, for example, it can be 0.2%, 0.4%, 0.6% or 0.8%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0055] Preferably, the precipitation solvent includes any one or a combination of at least two of propanol, isopropanol, or acetone.

[0056] Preferably, after the reaction, the resulting solution is added to the precipitation solvent, the polymer precipitates, and then the polymer is obtained after washing and drying.

[0057] Preferably, the coating slurry further includes inorganic oxides.

[0058] Preferably, the coating slurry further includes a first solvent (such as pure water), a first wetting agent, a first dispersant, a second solvent (such as isopropanol), and a binder.

[0059] Preferably, the mass ratio of the polymer, inorganic oxide, first solvent, first wetting agent, first dispersant, second solvent, and binder is (15~30):(10~23):(40~66):(0.02~0.08):(0.1~0.3):(1~4):(3~7), for example, it can be 15:23:40:0.02:0.3:1:7, 20:15:50:0.04:0.15:2:4, 25:20:60:0.06:0.2:3:6 or 30:10:66:0.08:0.1:4:3, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0060] Preferably, the preparation method of the coating slurry includes the following steps:

[0061] First, the first dispersant and the first solvent are mixed. Then, an inorganic oxide is added for a second mixing. Next, the second solvent, binder, polymer, and first wetting agent are added and mixed for a third mixing to obtain the coating slurry.

[0062] Preferably, ultrasound is performed simultaneously during the second mixing process.

[0063] Preferably, the rotation speed of the first mixture is 1000 r / min to 2000 r / min, for example, 1000 r / min, 1500 r / min or 2000 r / min, the revolution speed is 40 r / min to 60 r / min, for example, 40 r / min, 50 r / min or 60 r / min, and the stirring time is 46 min to 70 min, for example, 46 min, 50 min, 60 min or 70 min, but not limited to the listed values, other unlisted values ​​within the range are also applicable.

[0064] Preferably, the rotation speed of the second mixture is 3200 r / min to 3800 r / min, for example, 3200 r / min, 3300 r / min, 3600 r / min or 3800 r / min, the revolution speed is 10 r / min to 30 r / min, for example, 10 r / min, 20 r / min or 30 r / min, and the stirring time is 30 min to 50 min, for example, 30 min, 40 min or 50 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0065] Preferably, the third mixing method includes vacuum oscillation stirring blending.

[0066] Preferably, the coating method includes dot coating.

[0067] This invention employs a dot-coating process combined with a high-porosity base membrane, resulting in a polymer-coated separator with excellent air permeability and high porosity. This significantly reduces the membrane's impedance, thereby increasing the lithium-ion transport speed and ultimately improving the battery's rate performance.

[0068] Preferably, the coating process is followed by rewinding and slitting.

[0069] Preferably, the coating temperature is 40℃~90℃, for example, it can be 40℃, 50℃, 60℃, 70℃, 80℃ or 90℃, and the coating stretching speed difference is 0.1%~10%, for example, it can be 0.1%, 1%, 3%, 5%, 7%, 9% or 10%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0070] Preferably, the rewinding temperature is 60℃~110℃, for example, it can be 60℃, 80℃, 100℃ or 110℃, and the winding and unwinding tension is 0.1N~50N, for example, it can be 0.1N, 1N, 10N, 20N, 30N, 40N or 50N, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0071] Preferably, the unwinding and rewinding tension of the slitting is 0.1N~20N, for example, it can be 0.1N, 1N, 5N, 10N, 15N or 20N, and the contact pressure is 0.01N~16N, for example, it can be 0.01N, 0.1N, 1N, 5N, 10N or 16N, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0072] Preferably, the method for preparing the PI-based film includes the following steps:

[0073] A slurry is prepared by ball milling a PI emulsion, a second wetting agent (such as DIG 270), a second dispersant (such as any one or a combination of at least two of triethylhexyl phosphate, sodium dodecyl sulfate, methylpentanol, cellulose derivatives, polyacrylamide, glucon or fatty acid polyethylene glycol esters), and a pore-forming agent (such as polyethylene glycol). The PI-based film is then obtained by casting and coating.

[0074] Preferably, the method for preparing the PI-based film further includes the following steps:

[0075] The base film is obtained by mixing, casting, drying, and removing the pore-forming agent, along with the third solvent, second wetting agent, second dispersant, and pore-forming agent.

[0076] A preferred technical solution for the PI-based film includes the following steps:

[0077] Add 250-350g of PI (e.g., 250g, 300g, or 350g) and 40-90mL (e.g., 40mL, 60mL, 80mL, or 90mL) of NMP (N-methylpyrrolidone) to a beaker and sonicate for 60-90 minutes (e.g., 60min, 70min, 80min, or 90min). Then place the mixture in a ball mill jar and ball mill at 25-45℃ (e.g., 25℃, 35℃, or 45℃) and 500-900rpm (e.g., 500rpm, 600rpm, 700rpm, 800rpm, or 900rpm) for 6-9 hours (e.g., 6 hours, 7 hours, 8 hours, or 9 hours). Then add 1-3g of [unspecified ingredient] to the ball mill jar sequentially. Two wetting agents (e.g., 1g, 2g, or 3g) and 3-6g of a second dispersant (e.g., 3g, 4g, 5g, or 6g) are ball-milled at 500-700 rpm (e.g., 500 rpm, 600 rpm, or 700 rpm) for 2-5 hours (e.g., 2 hours, 3 hours, 4 hours, or 5 hours). Then, 31-35g of a pore-forming agent (e.g., 31g, 33g, or 35g) is added, and ball milling continues for 2-4 hours (e.g., 2 hours, 3 hours, or 4 hours) to obtain a slurry. After casting into a film using a casting coating machine, the film is dried in a drying zone and then passed through a hot water bath zone at 100-120°C (e.g., 100°C, 110°C, or 120°C) three times to remove the pore-forming agent, thus obtaining the base film.

[0078] Thirdly, the present invention provides a lithium-ion battery comprising a polymer-coated separator as described in the first aspect, or a polymer-coated separator prepared by the preparation method described in the second aspect.

[0079] Preferably, the negative electrode material of the lithium-ion battery includes silicon-carbon material.

[0080] Preferably, the silicon content in the silicon-carbon material is 45% to 55%, for example, it can be 45%, 50% or 55%, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0081] In the silicon-carbon material of this invention, if the silicon content is too high, the expansion will be large; if the silicon content is too low, the volumetric energy will be reduced and the rate performance will be poor.

[0082] Preferably, the particle size D50 of the silicon carbide material is 3μm to 7μm, for example, it can be 3μm, 4μm, 5μm, 6μm or 7μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0083] If the particle size D50 of the silicon-carbon material of this invention is too large, the rate performance will be reduced; if the particle size D50 is too small, the silicon-carbon material will be difficult to disperse.

[0084] Preferably, the electrolyte of the lithium-ion battery includes additives, which include any one or a combination of at least two of DTD (ethylene sulfate), LiPO2F2 (lithium difluorophosphate) or TMSP (tris(trimethylsilane)phosphate).

[0085] The present invention also adds additives to the electrolyte, which can further reduce the interfacial impedance with the composite membrane and play a synergistic role.

[0086] Preferably, the content of the additive in the electrolyte of the lithium-ion battery is 0.2wt% to 0.8wt%, for example, it can be 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt% or 0.8wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0087] Preferably, the electrolyte further includes a non-aqueous solvent and a lithium salt.

[0088] Preferably, the non-aqueous solvent includes EC (ethylene carbonate), PC (propylene carbonate), DMC (dimethyl carbonate), DEC (diethyl carbonate), and FEC (fluoroethylene carbonate).

[0089] Preferably, the concentration of lithium salt in the electrolyte is 0.9 mol / L to 1.3 mol / L, for example, it can be 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L or 1.3 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0090] Compared with the prior art, the present invention has the following beneficial effects:

[0091] This invention provides a coating comprising a specific polymer on at least one side of a base membrane. The halogen substituents in the polymer monomers enhance the flame retardant properties of the separator, reducing the risk of battery combustion and explosion, and improving battery safety. The thiourea and carboxyl groups in the polymer monomers interact with lithium ions, promoting lithium ion conduction. Simultaneously, the carboxyl groups improve the wettability of the separator and electrolyte, enhancing overall battery performance. Furthermore, the flame retardant properties provided by the halogen substituents and the ionic conductivity provided by the thiourea groups work synergistically, resolving the contradiction of traditional flame retardants reducing ionic conductivity while ensuring both the flame retardant and ionic conductivity of the separator, thus improving battery safety, rate performance, and fast charging performance. Detailed Implementation

[0092] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0093] Example 1

[0094] This embodiment provides a polymer-coated separator, which includes a PI base film and a coating on one side of the PI base film. The coating comprises a polymer, an inorganic oxide, a first wetting agent, a first dispersant, and a binder in a mass ratio of 25:18:0.05:0.2:5.5.

[0095] Wherein, the inorganic oxide is Sb₂O₃ with a particle size D50 of 35 nm, the first wetting agent is sodium hexametaphosphate, the first dispersant is sodium polyacrylate, the binder is carboxymethyl cellulose, and the monomer of the polymer is... ;

[0096] The polymer has a molecular weight of 90,000 Da, and the coating has a thickness of 2 μm;

[0097] The PI-based membrane has a porosity of 45%, an air permeability of 90 s / 100 mL, and a thickness of 8 μm.

[0098] The polymer-coated membrane has a thickness of 10 μm and a porosity of 41%.

[0099] The method for preparing the polymer-coated membrane includes the following steps:

[0100] (1) 310g of PI and 70mL of NMP were ultrasonicated in a beaker for 75min, and then placed in a ball milling jar and ball milled at 30℃ and 700rpm for 8h. Then, 2g of the second wetting agent and 5g of the second dispersant were added to the ball milling jar in sequence, and ball milled at 600rpm for 4h. Then, 33.5g of pore-forming agent was added and ball milled for another 3h to obtain a slurry. After casting and film formation by a casting coating machine, the film was dried in the drying zone and then passed through a hot water bath at 110℃. After three hot water immersions to remove the pore-forming agent, the PI-based film was obtained.

[0101] Wherein, the second wetting agent is TIG 270, the second dispersant is triethylhexylphosphoric acid, and the pore-forming agent is polyethylene glycol;

[0102] (2) Add the monomer of the polymer to DMF, and then add an initiator (specifically benzoyl peroxide). The amount of initiator added is 0.6% of the mass of the monomer of the polymer. Then heat at 90°C under argon protection for 25 hours to obtain a polymer solution. Add the polymer solution to propanol to obtain a polymer precipitate. Then wash and dry to obtain the polymer.

[0103] The first dispersant and water were mixed for 60 minutes at a rotation speed of 1600 r / min and a revolution speed of 52 r / min. Then, inorganic oxides were added and mixed for a second time at a rotation speed of 3400 r / min and a revolution speed of 22 r / min. During the second mixing process, ultrasonication was performed simultaneously. Then, isopropanol, binder, polymer and the first wetting agent were added and vacuum oscillation stirring was performed to obtain the coating slurry.

[0104] The mass ratio of the polymer, inorganic oxide, water, first wetting agent, first dispersant, isopropanol, and binder is 25:18:52:0.05:0.2:3:5.5.

[0105] (3) The coating slurry described in step (2) is applied to one side of the PI base film described in step (1) by dot coating at a temperature of 65°C and a stretching speed difference of 5%. Then, it is rewound at a temperature of 80°C and a winding tension of 30N. Finally, it is slit at a slitting winding tension of 11N and a contact pressure of 10N to obtain the polymer-coated diaphragm.

[0106] Example 2

[0107] This embodiment provides a polymer-coated separator, which includes a PI base film and a coating on one side of the PI base film. The coating comprises a polymer, an inorganic oxide, a first wetting agent, a first dispersant, and a binder in a mass ratio of 30:10:0.08:0.1:3.

[0108] Wherein, the inorganic oxide is Sb₂O₃ with a particle size D50 of 15 nm, the first wetting agent is sodium tripolyphosphate, the first dispersant is sodium citrate, the binder is hydroxypropyl methylcellulose, and the monomer of the polymer is... ;

[0109] The polymer has a molecular weight of 60,000 Da, and the coating thickness is 1 μm;

[0110] The PI-based membrane has a porosity of 50%, an air permeability of 100s / 100mL, and a thickness of 7μm.

[0111] The polymer-coated membrane has a thickness of 8 μm and a porosity of 45%.

[0112] The method for preparing the polymer-coated membrane includes the following steps:

[0113] (1) 250g of PI and 40mL of NMP were ultrasonicated in a beaker for 60min, and then placed in a ball milling jar and ball milled at 25℃ and 900rpm for 9h. Then, 3g of second wetting agent and 3g of second dispersant were added to the ball milling jar in sequence, and ball milled at 500rpm for 5h. Then, 35g of pore-forming agent was added and ball milled for 2h to obtain a slurry. After casting and film formation by a casting coating machine, the film was dried in the drying zone and then passed through a hot water bath at 120℃. After three hot water immersions to remove the pore-forming agent, the PI-based film was obtained.

[0114] Wherein, the second wetting agent is TIG 270, the second dispersant is sodium dodecyl sulfate, and the pore-forming agent is polyethylene glycol;

[0115] (2) Add the monomer of the polymer to DMF, and then add an initiator (specifically benzoyl peroxide). The amount of initiator added is 0.2% of the mass of the monomer of the polymer. Then heat at 70°C under argon protection and react for 12 hours to obtain a polymer solution. Add the polymer solution to acetone to obtain a polymer precipitate, and then wash and dry it to obtain the polymer.

[0116] The first dispersant and water were mixed for 70 minutes at a rotation speed of 2000 r / min and a revolution speed of 60 r / min. Then, inorganic oxides were added and mixed for a second time at a rotation speed of 3200 r / min and a revolution speed of 10 r / min. During the second mixing process, ultrasonication was performed simultaneously. Then, isopropanol, binder, polymer and the first wetting agent were added and vacuum oscillation stirring was performed to obtain the coating slurry.

[0117] The mass ratio of the polymer, inorganic oxide, water, first wetting agent, first dispersant, isopropanol, and binder is 30:10:40:0.08:0.1:4:3.

[0118] (3) The coating slurry described in step (2) is applied to one side of the PI base film described in step (1) by dot coating at a temperature of 90°C and a stretching speed difference of 2%. Then, it is rewound at a temperature of 110°C and a winding tension of 10N. Finally, it is slit at a slitting winding tension of 5N and a contact pressure of 2N to obtain the polymer-coated diaphragm.

[0119] Example 3

[0120] This embodiment provides a polymer-coated separator, which includes a PI base film and a coating on one side of the PI base film. The coating comprises a polymer, an inorganic oxide, a first wetting agent, a first dispersant, and a binder in a mass ratio of 15:23:0.02:0.3:7.

[0121] Wherein, the inorganic oxide is Sb₂O₃ with a particle size D50 of 50 nm, the first wetting agent is sodium pyrophosphate, the first dispersant is sodium polyacrylate, the binder is polyvinyl alcohol, and the monomer of the polymer is... ;

[0122] The polymer has a molecular weight of 130,000 Da, and the coating has a thickness of 3 μm;

[0123] The PI-based membrane has a porosity of 40%, an air permeability of 80 s / 100 mL, and a thickness of 10 μm.

[0124] The polymer-coated membrane has a thickness of 13 μm and a porosity of 32%.

[0125] The method for preparing the polymer-coated membrane includes the following steps:

[0126] (1) 350g of PI and 90mL of NMP were ultrasonicated in a beaker for 90min, and then placed in a ball milling jar and ball milled at 45℃ and 500rpm for 6h. Then, 1g of second wetting agent and 6g of second dispersant were added to the ball milling jar in sequence, and ball milled at 700rpm for 2h. Then, 31g of pore-forming agent was added and ball milled for another 4h to obtain a slurry. After casting and film formation by a casting coating machine, the film was dried in the drying zone and then passed through a 100℃ hot water bath zone. After three hot water immersions to remove the pore-forming agent, the PI-based film was obtained.

[0127] Wherein, the second wetting agent is TIG 270, the second dispersant is triethylhexylphosphoric acid, and the pore-forming agent is polyethylene glycol;

[0128] (2) Add the monomer of the polymer to DMF, and then add an initiator (specifically benzoyl peroxide). The amount of initiator added is 0.8% of the mass of the monomer of the polymer. Then heat at 110°C under argon protection and react for 30 h to obtain a polymer solution. Add the polymer solution to acetone to obtain a polymer precipitate, and then wash and dry it to obtain the polymer.

[0129] The first dispersant and water were mixed for 46 minutes at a rotation speed of 1000 r / min and a revolution speed of 40 r / min. Then, inorganic oxides were added and mixed for a second time at a rotation speed of 3800 r / min and a revolution speed of 30 r / min. During the second mixing process, ultrasonication was performed simultaneously. Then, isopropanol, binder, polymer and the first wetting agent were added and vacuum oscillation stirring was performed to obtain the coating slurry.

[0130] The mass ratio of the polymer, inorganic oxide, water, first wetting agent, first dispersant, isopropanol, and binder is 15:23:66:0.02:0.3:1:7.

[0131] (3) The coating slurry described in step (2) is applied to one side of the PI base film described in step (1) by dot coating at a temperature of 40°C and a stretching speed difference of 10%. Then, it is rewound at a temperature of 60°C and a winding tension of 50N. Finally, it is slit at a slitting winding tension of 20N and a contact pressure of 16N to obtain the polymer-coated diaphragm.

[0132] Example 4

[0133] This embodiment provides a polymer-coated separator, wherein the polymer-coated separator, except that the monomer of the polymer is... Except for the above, everything else is the same as in Example 1.

[0134] The preparation method of the polymer-coated diaphragm described in this embodiment is the same as that in Example 1, except that the monomer type changes during polymer preparation.

[0135] Example 5

[0136] This embodiment provides a polymer-coated separator, which is identical to that in Embodiment 1 except that the molecular weight of the polymer is 48000 Da.

[0137] The preparation method of the polymer-coated membrane is the same as that in Example 1, except for the change in reaction time during polymer preparation.

[0138] Example 6

[0139] This embodiment provides a polymer-coated separator, which is identical to that in Embodiment 1 except that the molecular weight of the polymer is 142000 Da.

[0140] The preparation method of the polymer-coated membrane is the same as that in Example 1, except for the change in reaction time during polymer preparation.

[0141] Example 7

[0142] This embodiment provides a polymer-coated diaphragm, which is the same as that in Embodiment 1 except that the thickness of the coating is 0.3 μm.

[0143] The preparation method of the polymer-coated diaphragm described in this embodiment is the same as that in Example 1, except for the change in coating thickness.

[0144] Example 8

[0145] This embodiment provides a polymer-coated diaphragm, which is the same as that in Embodiment 1 except that the thickness of the coating is 4.5 μm.

[0146] The preparation method of the polymer-coated diaphragm described in this embodiment is the same as that in Example 1, except for the change in coating thickness.

[0147] Example 9

[0148] This embodiment provides a polymer-coated separator, which is the same as that in Embodiment 1 except that the polymer coating does not contain Sb2O3.

[0149] The preparation method of the polymer-coated diaphragm described in this embodiment is the same as that in Example 1, except that Sb2O3 is not added to the coating slurry.

[0150] Comparative Example 1

[0151] This comparative example provides a diaphragm, which is the PI-based membrane from Example 1.

[0152] The preparation method of the diaphragm described in this comparative example is the same as the preparation method of the PI-based membrane in Example 1.

[0153] Comparative Example 2

[0154] This comparative example provides a polymer-coated separator, wherein the polymer-coated separator, except that the monomer of the polymer is... Except for (CAS: 5772-92-9), everything else is the same as in Example 1.

[0155] The preparation method of the polymer-coated membrane described in this comparative example is the same as that in Example 1, except that the monomer types are changed during polymer preparation.

[0156] Comparative Example 3

[0157] This comparative example provides a polymer-coated separator, wherein the polymer-coated separator, except that the monomer of the polymer is... Except for (CAS: 1180670-58-9), everything else is the same as in Example 1.

[0158] The preparation method of the polymer-coated membrane described in this comparative example is the same as that in Example 1, except that the monomer types are changed during polymer preparation.

[0159] Comparative Example 4

[0160] This comparative example provides a polymer-coated separator, wherein the polymer-coated separator, except that the monomer of the polymer is... Except for (CAS: 18257-89-1), everything else is the same as in Example 1.

[0161] The preparation method of the polymer-coated membrane described in this comparative example is the same as that in Example 1, except that the monomer types are changed during polymer preparation.

[0162] The separators obtained in the above embodiments and comparative examples are used to prepare lithium-ion batteries. The preparation method of lithium-ion batteries includes the following steps:

[0163] (1) Preparation of positive electrode sheet

[0164] The ternary material NCM811 (LiNi) 0.8 Co 0.1 Mn 0.1 O2, PVDF (polyvinylidene fluoride), SP (super-P conductive carbon black), and SWCNT (single-walled carbon nanotubes) were mixed and stirred evenly in a mass ratio of 94:3:2.9:0.1 to obtain a positive electrode slurry. The positive electrode slurry was then coated onto aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained.

[0165] (2) Preparation of negative electrode sheet

[0166] Silicon-carbon anode material (50% silicon, the remainder carbon), conductive agent SP (Super-P conductive carbon black), SWCNT (single-walled carbon nanotubes), PAA (polyacrylic acid), and SBR (styrene-butadiene rubber) are mixed and stirred evenly in a mass ratio of 92:2:0.5:3:2.5 to obtain a negative electrode slurry. The solid content is controlled at 30%. The negative electrode slurry is then coated onto a copper foil current collector through a coating process. After vacuum drying and cold pressing, a negative electrode sheet is obtained.

[0167] (3) Selection of electrolyte

[0168] The electrolyte consists of EC, PC, DMC, DEC and FEC in a volume ratio of 15:20:25:30:10, 1 mol / L LiPF6 and 0.5 wt% DTD.

[0169] (4) Preparation of lithium-ion batteries

[0170] The positive electrode sheet, the separator obtained in the above embodiments and comparative examples, and the negative electrode sheet are stacked in sequence, with the separator between the positive and negative electrode sheets to provide isolation, and the polymer coating side facing the negative electrode sheet. Then, the cells are wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained.

[0171] Performance testing

[0172] (1) Capacity retention rate after 1000 cycles at room temperature (1C / 2C)

[0173] At 25°C, the lithium-ion battery was charged at a 1C rate with constant current and constant voltage to 4.2 V, with a cutoff current of 0.05C. After resting for 10 minutes, the lithium-ion battery was discharged at a 2C rate with constant current to 2.5 V and then rested for 10 minutes. This constitutes one charge-discharge cycle. The lithium-ion battery was subjected to 1000 charge-discharge cycles using the above method. The capacity retention rate of the lithium-ion battery after 1000 charge-discharge cycles at 1C / 2C was calculated.

[0174] The capacity retention rate (%) of a lithium-ion battery after N cycles = (discharge capacity of the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

[0175] (2) Room temperature 6C rate performance - constant current charge ratio

[0176] At 25℃, the lithium-ion battery was discharged at a constant current rate of 1C to 2.5V, left to stand for 10 minutes, and then charged at a constant current and constant voltage rate of 6C to 4.2V with a cutoff current of 0.05C. After standing for 10 minutes, the constant current charging capacity Q1 and the total constant current and constant voltage charging capacity Q2 of the lithium-ion battery were recorded. The constant current charge ratio of the 6C rate charging was calculated according to the following formula: 6C rate charging constant current charge ratio = constant current charging capacity Q1 / total constant current and constant voltage charging capacity Q2 × 100%.

[0177] (3) Thermal shrinkage rate of diaphragm at 180°C / 30min

[0178] Referring to the standard test method (GB / T 36363), the dimensional changes of the diaphragm sample in the free state are measured at the specified temperature (180℃) and time (30min), and the transverse (TD) and longitudinal (MD) thermal shrinkage rates are calculated.

[0179] The high-temperature furnace used for testing heat shrinkage rate has a temperature control accuracy of ±1℃ and an internal inert gas atmosphere; the sample clamp is a stainless steel frame to ensure that the sample shrinks freely without constraint; the measuring tool is a vernier caliper with an accuracy of 0.02mm; and graph paper is used to mark the initial dimensions.

[0180] Sample preparation:

[0181] Cut to size: 100mm × 100mm, 10mm away from the edge of the diaphragm;

[0182] Marking: Draw a cross on the sample surface and record the initial length L0 in the transverse (TD) and longitudinal (MD) directions (accurate to 0.1 mm).

[0183] Test steps:

[0184] Pretreatment: The sample was placed in an environment of 23±2℃ and 50±5%RH for 24 hours.

[0185] High-temperature treatment:

[0186] Place the sample flat on the fixture and put it into the center of a high-temperature furnace preheated to 180°C, ensuring that the sample does not touch the furnace wall; after holding the temperature for 30 minutes, quickly remove the fixture and cool it at room temperature for 10 minutes.

[0187] Size measurement:

[0188] Measure the crosshair length L1 of the sample after cooling (measured separately in the TD and MD directions); test 3 parallel samples for each sample and take the average value.

[0189] Heat shrinkage rate (%) = (L0-L1) / L0×100%; record the transverse (TD) and longitudinal (MD) shrinkage rates respectively.

[0190] (4) Cell thermal runaway (ARC) test: Start the ARC adiabatic thermal runaway test. The test sample is heated from room temperature to 45±2℃ in the chamber. After resting for 90 minutes, the change in battery temperature rise rate is detected. If the temperature rise exceeds 0.2℃ within 10 minutes (i.e., SHR>0.02℃ / min), it is considered that a self-exothermic reaction has occurred inside the battery. The adiabatic environment is maintained until the battery thermal runaway occurs. If the temperature rise does not exceed 0.2℃ within 10 minutes (i.e., SHR≤0.02℃ / min), continue to the next step temperature rise test. Each temperature step is 5℃. Repeat the steps on each step. The ARC test temperature range is 45℃~300℃. The self-generated heat start temperature is T1 (temperature rise rate SHR>0.02℃ / min), and the thermal runaway start temperature is T2 (temperature rise rate SHR>1℃ / min). Wherein, SHR is the self-generated heat temperature rise rate.

[0191] (5) Cell heating chamber test 150℃ & 30min: After the single cell is fully charged (the lithium-ion battery after capacity division is charged at 25℃ at a 1C rate to 4.2V with constant current and constant voltage, and the cut-off current is 0.05C), it is placed in a temperature chamber and heated from room temperature to 150±2℃ at a rate of 5℃ / min. The temperature is maintained for 30min and then heating is stopped. Observe for 1h to see if an explosion or fire occurs.

[0192] The test results are shown in Table 1:

[0193] Table 1

[0194]

[0195] As can be seen from Table 1 above:

[0196] As shown in Example 1 and Comparative Example 1, the present invention, by setting a coating, can significantly improve and reduce the thermal shrinkage rate of the separator, improve the rate performance, fast charging performance, and safety performance of the battery, and reduce the thermal runaway temperature of the battery. As shown in Example 1 and Comparative Example 2, the polymer in the coating of the present invention contains bromine, which can play a flame retardant role, improve the safety performance of the battery, and reduce the battery runaway temperature. As shown in Example 1 and Comparative Examples 3-4, the thiourea group in the present invention can synergistically improve the safety and ion conductivity of the separator with bromine. Carboxyl and methoxy groups can promote electrolyte wetting and improve ion conductivity, while phenyl groups can improve the stability of the separator. When at least one functional group in the polymer of the present invention is missing, it will affect the overall performance of the separator and the battery. As shown in Example 1 and Examples 5-8, the weight-average molecular weight of the polymer and the thickness of the coating in the present invention will affect the performance of the coating, and thus affect the performance of the separator and the battery in many aspects. The comparison between Example 1 and Example 9 shows that adding inorganic oxides to the coating can optimize the performance of the separator and the battery in many aspects.

[0197] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A polymeric-coated separator, characterized in that, The polymer-coated membrane includes a base membrane and a coating located on at least one side of the base membrane. The coating includes a polymer, and the monomers of the polymer include alkenyl groups, halogen substituents, thiourea groups, and carboxyl groups. The halogen substituents include bromine substituents and / or iodine substituents. The monomers of the polymer also include rigid groups, which include a first rigid group and a second rigid group. The first rigid group includes an alkoxy-substituted phenyl or an alkoxy-substituted naphthyl group, and the second rigid group includes a halogen-substituted or unsubstituted phenyl or a halogen-substituted or unsubstituted biphenyl group. The weight-average molecular weight of the polymer is 60,000 Da to 130,000 Da; The thickness of the coating is 1μm to 3μm.

2. The polymeric-coated separator of claim 1, wherein, The substituents in the rigid group include alkoxy groups or halogens.

3. The polymeric-coated separator according to claim 1 or 2, characterized in that, The general structural formula of the monomer of the polymer is: ； Wherein, R1 is selected from alkoxy-substituted phenyl or alkoxy-substituted naphthyl, R2 is selected from halogen-substituted or unsubstituted phenyl or halogen-substituted or unsubstituted biphenyl, and X is selected from Br or I.

4. The polymer-coated separator according to claim 3, characterized in that, The monomers of the polymer include any one or a combination of at least two of , , or .

5. The polymeric-coated separator of claim 1, wherein, The coating also includes inorganic oxides.

6. The polymeric-coated separator of claim 5, wherein, The inorganic oxide includes Sb2O3.

7. The polymeric-coated separator of claim 5, wherein, The particle size D50 of the inorganic oxide is 15nm~50nm.

8. The polymeric-coated separator of claim 5, wherein, The mass ratio of the polymer to the inorganic oxide is (15~30):(10~23).

9. The polymeric-coated separator of claim 1, wherein, The porosity of the base membrane is 40%~50%.

10. The polymeric-coated separator of claim 1, wherein, The air permeability of the base membrane is 80s / 100mL~100s / 100mL.

11. The polymeric-coated separator of claim 1, wherein, The thickness of the base film is 7μm~10μm.

12. The polymeric-coated separator of claim 1, wherein, The base film includes a PI base film.

13. The polymeric-coated separator of claim 1, wherein, The thickness of the polymer-coated diaphragm is 8μm to 13μm.

14. The polymeric-coated separator of claim 1, wherein, The porosity of the polymer-coated membrane is 32%~45%.

15. A method of producing a polymeric-coated separator according to any one of claims 1 to 14, characterized in that, The preparation method includes the following steps: The coating slurry is applied to at least one side surface of the base film to obtain the polymer-coated separator; The coating slurry includes a polymer, and the monomers of the polymer include alkenyl groups, halogen substituents, thiourea groups and carboxyl groups, wherein the halogen substituents include bromine substituents and / or iodine substituents.

16. The method of claim 15, wherein, The coating slurry also includes inorganic oxides.

17. The preparation method according to claim 15, characterized in that, The coating slurry also includes a first solvent, a first wetting agent, a first dispersant, a second solvent, and a binder.

18. The method of claim 17, wherein, The mass ratio of the polymer, inorganic oxide, first solvent, first wetting agent, first dispersant, second solvent and binder is (15~30):(10~23):(40~66):(0.02~0.08):(0.1~0.3):(1~4):(3~7).

19. The method of claim 15, wherein, The coating method includes dot coating.

20. The method of claim 15, wherein, The coating process was followed by rewinding and slitting.

21. A lithium-ion battery, characterized in that, The lithium-ion battery includes a polymer-coated separator as described in any one of claims 1-14, or a polymer-coated separator prepared by the preparation method described in any one of claims 15-20.

22. The lithium-ion battery according to claim 21, characterized in that, The negative electrode material of the lithium-ion battery includes silicon-carbon material.

23. The lithium-ion battery according to claim 22, characterized in that, The silicon content in the silicon-carbon material is 45% to 55%.

24. The lithium-ion battery according to claim 22, characterized in that, The particle size D50 of the silicon-carbon material is 3μm~7μm.

25. The lithium-ion battery according to claim 21, characterized in that, The electrolyte of the lithium-ion battery includes additives, which include any one or a combination of at least two of DTD, LiPO2F2, or TMSP.

26. The lithium-ion battery according to claim 25, characterized in that, The content of the additive in the electrolyte of the lithium-ion battery is 0.2wt%~0.8wt%.

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