A separator and a lithium ion battery comprising the same

Abstract

This invention provides a separator and a lithium-ion battery comprising the same, relating to the field of lithium-ion battery technology. The separator comprises a polymer, wherein the polymer monomers contain phenyl groups ortho-substituted with F and Cl, acrylonitrile, and benzene rings, which can improve the separator's adsorption capacity for electrolyte, improve the interfacial compatibility between the separator and the electrolyte, reduce the internal resistance of the battery, effectively suppress dendrite penetration, and improve the thermal stability of the separator.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more particularly to a separator and a lithium-ion battery comprising the separator. Background Technology

[0002] Insufficient thermal stability constitutes a major threat to battery safety. Traditional polyolefin-based separators (such as PP / PE) experience severe thermal shrinkage at high temperatures (typically >120°C), leading to direct contact between the positive and negative electrodes and triggering thermal runaway. Ordinary polypropylene separators have high shrinkage rates, while high-safety separators should achieve the smallest possible shrinkage. Furthermore, the thermal closure properties of separators (pore closure at high temperatures to block ion transport) and mechanical strength often conflict, making it difficult to simultaneously meet the requirements of high-temperature safety and room-temperature performance.

[0003] While rigid coatings (such as Al2O3 coatings) are puncture resistant, they lack flame retardancy. Flexible coatings (such as polyacrylic acid coatings) are easily torn by the expansion stress of silicon and are flammable at high temperatures, posing a high risk of thermal runaway.

[0004] Therefore, it is necessary to develop lithium-ion battery separators that have both high thermal stability and high mechanical strength. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a separator and a lithium-ion battery containing the separator, which can improve the thermal stability and mechanical strength of the separator and enhance the adsorption performance of electrolyte, and has broad application prospects.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a diaphragm comprising a polymer, wherein the polymer monomers of the polymer have the structural formula shown in formula (1):

[0008] Equation (1);

[0009] Wherein, one of R1 and R3 is a phenyl group containing F and Cl ortho-substituted phenyl groups; one of R1 and R3 is hydrogen, fluorine or chlorine; and R2 is a phenyl group substituted with F and / or Cl.

[0010] The diaphragm provided by this invention has the following special advantages:

[0011] The polymer of the present invention uses monomers as shown in formula (1) for polymerization, which can significantly improve the mechanical strength and flame retardant properties of the diaphragm.

[0012] The presence of chlorine and fluorine atoms in the polymer monomers of this invention enhances the chemical stability and flame retardant properties of the polymer. The acrylonitrile groups, with their strong polarity, improve the membrane's adsorption capacity for the electrolyte, enhance the interfacial compatibility between the membrane and the electrolyte, and reduce the battery's internal resistance. Simultaneously, the polymer's structure can inhibit lithium dendrite growth, improving battery safety and cycle life.

[0013] Specifically, this invention emphasizes the ortho-substitution of the benzene ring by fluorine and chlorine. The fluorine atom (strongly negative) induces the formation of a LiF-rich interface layer, inhibiting dendrite penetration. Simultaneously, the chlorine atom (steric hindrance) hinders the lateral growth of dendrites. These two elements work synergistically, with the ortho-chlorine and fluorine atoms forming a three-dimensional electronic barrier, forcing lithium ions to deposit uniformly within the coating pores, significantly improving the effect of inhibiting lithium dendrite growth. Furthermore, the polymer provided by this invention exhibits superior steric hindrance effect.

[0014] Preferably, one of R1 and R3 is hydrogen to maintain a planar configuration.

[0015] Preferably, R2 is an F-substituted phenyl group. In this invention, R2 is preferably an F-substituted phenyl group, which can enhance the polarity and chemical stability of the polymer. Moreover, the polar interaction between the fluorine atom and the carbonate solvent in the electrolyte is stronger, improving the affinity for the electrolyte. At the same time, the introduction of fluorine can reduce the flammability of the material, which has the advantage of further optimizing the flame retardant performance.

[0016] Preferably, the cis configuration of the polymerizable monomer accounts for >90%, for example, it can be 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%. The present invention preferably adopts the cis configuration. Compared with the trans configuration, the steric hindrance of the cis structure results in stronger intermolecular forces, leading to a more compact molecular chain packing and higher mechanical strength.

[0017] Preferably, the structural formula of the polymer monomer is shown in formula (2):

[0018] Equation (2).

[0019] The present invention preferably uses polymer monomers with the above-mentioned structure, wherein fluorine and chlorine are ortho-substituted on one benzene ring and meta-substituted on the other benzene ring, which has the steric hindrance and electronic effect of ortho-F / Cl to synergistically suppress lithium dendrites (the steric barrier formed by ortho-substitution is more significant), and meta-substitution can balance the advantages of molecular polarity and steric hindrance.

[0020] Preferably, the weight-average molecular weight M of the polymer is... wThe range is 60,000 to 130,000 Da, for example, it can be 60,000 Da, 65,000 Da, 70,000 Da, 75,000 Da, 80,000 Da, 85,000 Da, 90,000 Da, 100,000 Da, 110,000 Da, 120,000 Da, 125,000 Da, or 130,000 Da, etc.

[0021] The present invention preferably controls the weight-average molecular weight of the polymer within the above-mentioned range. If the molecular weight is too low, the film-forming properties and interfacial adhesion are insufficient, and the mechanical strength is insufficient. If the molecular weight is too high, the viscosity increases, the coating uniformity decreases, and the high molecular weight polymer has higher crystallinity, higher melting temperature but increased brittleness.

[0022] Preferably, the preparation of the polymer includes: mixing polymer monomers, organic solvents and initiators, and carrying out a polymerization reaction to prepare the polymer.

[0023] 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), wherein typical but non-limiting combinations are combinations of benzene and THF, benzene and NMP, NMP and THF, DMF and THF, and benzene and DMF.

[0024] Preferably, the mass ratio of the polymer monomer to the organic solvent is 1:5 to 1:10, for example, it can be 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:8.5, 1:9, 1:9.5 or 1:10, etc.

[0025] Preferably, the initiator comprises any one or a combination of at least two of azobisisobutyronitrile, azobisisoheptanenitrile, or benzoyl peroxide, wherein typical but non-limiting combinations are a combination of azobisisobutyronitrile and azobisisoheptanenitrile, a combination of benzoyl peroxide and azobisisoheptanenitrile, or a combination of azobisisobutyronitrile and benzoyl peroxide.

[0026] Preferably, the initiator accounts for 0.1 to 0.7 wt% of the total mass of the polymer monomers, for example, it can be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, 0.6 wt%, 0.65 wt%, or 0.7 wt%.

[0027] Preferably, the atmosphere for the polymerization reaction includes any one or a combination of at least two of argon, nitrogen, helium, or neon, wherein typical but non-limiting combinations are combinations of argon and nitrogen, helium and nitrogen, argon and helium, and neon and nitrogen.

[0028] Preferably, the polymerization reaction temperature is 75~120℃, for example, it can be 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃ or 120℃, etc.

[0029] Preferably, the polymerization reaction time is 18 to 48 hours, for example, it can be 18 hours, 20 hours, 25 hours, 28 hours, 29 hours, 30 hours, 31 hours, 32 hours, 35 hours, 38 hours, 40 hours, 42 hours, 45 hours or 48 hours.

[0030] Preferably, the preparation of the polymer further includes: mixing the material after the polymerization reaction with a precipitation solvent to precipitate a polymer, and washing and drying the polymer precipitate to obtain the polymer.

[0031] Preferably, the mass ratio of the material after polymerization to the precipitated solvent is (3~5):1, for example, it can be 3:1, 3.2:1, 3.5:1, 3.8:1, 3.9:1, 4:1, 4.2:1, 4.5:1, 4.8:1 or 5:1, etc.

[0032] Preferably, the precipitation solvent includes any one or a combination of at least two of propanol, isopropanol, or acetone, wherein typical but non-limiting combinations are a combination of propanol and isopropanol, a combination of acetone and isopropanol, or a combination of propanol and acetone.

[0033] Preferably, the membrane includes a functional membrane layer, and the polymer is located in the functional membrane layer. The functional membrane layer also includes inorganic particles.

[0034] Preferably, the inorganic particles are aluminum oxide.

[0035] This invention preferably uses alumina in combination with the aforementioned polymer. Alumina possesses high-temperature resistance (resisting structural collapse at high temperatures), high mechanical strength (enhancing the puncture resistance of the membrane), and polar adsorption capacity from its surface hydroxyl groups (-OH). These properties, combined with the polar F / Cl groups (such as ortho-F / Cl substituted benzene rings) and nitrile groups (-CN) in the polymer (forming hydrogen bonds between the polar groups and the hydroxyl groups on the alumina surface, strengthening interfacial bonding and preventing coating peeling), result in a membrane with superior thermal stability (high-temperature shrinkage resistance), mechanical strength (puncture resistance and resistance to silicon expansion), and electrolyte wettability (polar synergy enhances liquid absorption). Furthermore, the polymer "encapsulates" the alumina, forming a strong and tough organic-inorganic network. The polymer provides adhesion and stress buffering, while the alumina provides rigid support and a thermal barrier, synergistically resisting high-temperature thermal shrinkage and silicon expansion stress, resulting in a lower membrane thermal shrinkage rate.

[0036] Preferably, the alumina has a particle size range of 22~66nm, for example, it can be 22nm, 25nm, 29nm, 34nm, 38nm, 43nm, 47nm, 48nm, 50nm, 52nm, 55nm, 58nm, 60nm, 65nm or 66nm, etc.

[0037] The present invention preferably controls the particle size of alumina within a reasonable range, resulting in a more uniform coating and less tendency to agglomerate into micron-sized clumps.

[0038] Preferably, the mass ratio of inorganic particles to polymer in the diaphragm is (12~20):(15~30), wherein the number of inorganic particles can be, for example, 12, 13, 15, 16, 18, 19 or 20; and the number of polymers can be, for example, 15, 17, 19, 20, 22, 24, 25, 27, 29 or 30.

[0039] In this invention, the mass ratio of alumina to polymer is preferably controlled within the above-mentioned range. When the alumina content is too low, there are problems such as insufficient mechanical support (decreased puncture resistance of the diaphragm) and weakened high-temperature thermal barrier effect (increased thermal shrinkage rate). When the alumina content is too high, there are problems such as increased coating brittleness (decreased elongation at break), reduced porosity leading to insufficient electrolyte adsorption, and increased ion conduction resistance.

[0040] Preferably, the functional film layer further includes a dispersant.

[0041] Preferably, the dispersant comprises any one or a combination of at least two of silicates, sodium polyacrylate, or sodium citrate, wherein typical but non-limiting combinations are combinations of silicates and sodium polyacrylate, combinations of sodium citrate and sodium polyacrylate, and combinations of silicates and sodium citrate.

[0042] Preferably, the mass ratio of the dispersant to the polymer is (0.1~0.3):(15~30), wherein the number of parts of the dispersant can be, for example, 0.1, 0.13, 0.15, 0.17, 0.19, 0.22, 0.24, 0.26, 0.28 or 0.3, etc.; and the number of parts of the polymer can be, for example, 15, 17, 19, 20, 22, 24, 25, 27, 29 or 30, etc.

[0043] Preferably, the functional film layer further includes a wetting agent.

[0044] Preferably, the wetting agent comprises any one or a combination of at least two of sodium hexametaphosphate, sodium tripolyphosphate, or sodium pyrophosphate, wherein typical but non-limiting combinations are a combination of sodium hexametaphosphate and sodium tripolyphosphate, a combination of sodium pyrophosphate and sodium tripolyphosphate, or a combination of sodium hexametaphosphate and sodium pyrophosphate.

[0045] Preferably, the mass ratio of the wetting agent to the polymer is (0.02~0.08):(15~30), wherein the number of parts of the wetting agent can be, for example, 0.02, 0.027, 0.034, 0.04, 0.047, 0.054, 0.06, 0.067, 0.074 or 0.08, etc.; and the number of parts of the polymer can be, for example, 15, 17, 19, 20, 22, 24, 25, 27, 29 or 30, etc.

[0046] Preferably, the functional membrane layer further includes a membrane solvent and an adhesive.

[0047] Preferably, the film solvent includes water and isopropanol.

[0048] Preferably, the mass ratio of water, isopropanol, and polymer in the functional membrane layer is (40~66):(1~4):(15~30), wherein the number of parts of water can be, for example, 40, 43, 46, 49, 52, 55, 58, 61, 64, or 66; the number of parts of isopropanol can be, for example, 1, 1.4, 1.7, 2, 2.4, 2.7, 3, 3.4, 3.7, or 4; and the number of parts of polymer can be, for example, 15, 17, 19, 20, 22, 24, 25, 27, 29, or 30.

[0049] Preferably, the adhesive comprises any one or a combination of at least two of CMC (sodium carboxymethyl cellulose), hydroxypropyl methylcellulose (HPMC), or polyvinyl alcohol (PVA), wherein typical but non-limiting combinations are combinations of CMC and hydroxypropyl methylcellulose, combinations of polyvinyl alcohol and hydroxypropyl methylcellulose, and combinations of CMC and polyvinyl alcohol.

[0050] Preferably, the mass ratio of the adhesive to the polymer is (3~7):(15~30), wherein the number of parts of the adhesive can be, for example, 3, 3.5, 4, 4.5, 5, 5.2, 5.5, 5.8, 6, 6.2, 6.5, 6.8 or 7; and the number of parts of the polymer can be, for example, 15, 17, 19, 20, 22, 24, 25, 27, 29 or 30.

[0051] Preferably, the preparation method of the coating slurry of the functional film layer includes: mixing a dispersant and water for a first stirring, then adding inorganic particles for a second stirring, then adding isopropanol, binder, polymer and wetting agent, and then vacuum shaking to form the coating slurry of the functional film layer.

[0052] Preferably, the first and second stirring are carried out in a planetary mixer or a high-speed disperser.

[0053] Preferably, the rotation speed of the first stirrer is 1000~2000 r / min, for example, it can be 1000 r / min, 1100 r / min, 1200 r / min, 1300 r / min, 1400 r / min, 1500 r / min, 1600 r / min, 1700 r / min, 1880 r / min or 2000 r / min, etc.

[0054] Preferably, the revolution speed of the first stirrer is 40~60 r / min, for example, it can be 40 r / min, 43 r / min, 45 r / min, 47 r / min, 49 r / min, 52 r / min, 54 r / min, 56 r / min, 58 r / min or 60 r / min, etc.

[0055] Preferably, the first stirring time is 46 to 70 minutes, for example, it can be 46 minutes, 49 minutes, 52 minutes, 54 minutes, 57 minutes, 60 minutes, 62 minutes, 65 minutes, 68 minutes or 70 minutes.

[0056] Preferably, the rotation speed of the second stirrer is 3200~3800 r / min, for example, it can be 3200 r / min, 3250 r / min, 3300 r / min, 3400 r / min, 3460 r / min, 3500 r / min, 3600 r / min, 3650 r / min, 3700 r / min or 3800 r / min, etc.

[0057] Preferably, the revolution speed of the second stirrer is 10~30 r / min, for example, it can be 10 r / min, 13 r / min, 15 r / min, 17 r / min, 19 r / min, 22 r / min, 24 r / min, 26 r / min, 28 r / min or 30 r / min, etc.

[0058] Preferably, the second stirring time is 30 to 50 minutes, for example, it can be 30 minutes, 33 minutes, 35 minutes, 37 minutes, 39 minutes, 42 minutes, 44 minutes, 46 minutes, 48 ​​minutes or 50 minutes.

[0059] Preferably, the diaphragm includes a base membrane, and the functional membrane layer is disposed on the surface of the base membrane. The base membrane is made of PI (polyimide) film.

[0060] In this invention, the PI-based film has high temperature resistance (film breakage temperature up to 430℃), which can improve battery safety and increase the pass rate of needle penetration and hot box safety tests. The nitrogen-containing polar groups of PI form hydrogen bonds with the electrolyte solvent (ethylene carbonate EC or other solvents), which improves wettability and rate performance.

[0061] Those skilled in the art will understand that the preparation method of the diaphragm of the present invention includes coating, rewinding and slitting in sequence.

[0062] Preferably, the coating comprises dotted coating.

[0063] The present invention preferably employs dot-matrix coating, which has high air permeability and high porosity, thereby resulting in lower impedance, thus greatly improving the lithium-ion transport rate and improving the rate performance of the battery.

[0064] Preferably, the dot coating is applied using ultrasonic dot spraying.

[0065] Preferably, the temperature of the dotted coating is 40~90℃, for example, it can be 40℃, 46℃, 52℃, 57℃, 63℃, 68℃, 74℃, 79℃, 85℃ or 90℃, etc.

[0066] Preferably, the stretching speed difference of the dot-coating is 0.1% to 10%, for example, it can be 0.1%, 1.2%, 2.3%, 3.4%, 4.5%, 5.6%, 6.7%, 7.8%, 8.9% or 10%, etc.

[0067] Preferably, the rewinding temperature is 60~100℃, for example, it can be 60℃, 65℃, 69℃, 74℃, 78℃, 83℃, 87℃, 92℃, 96℃ or 100℃, etc.

[0068] Preferably, the winding and unwinding tension during the rewinding process is 0.1~50N, for example, it can be 0.1N, 5N, 10N, 15N, 20N, 25N, 30N, 38N, 40N or 50N, etc.

[0069] Preferably, the unwinding and rewinding tension of the slitting is 0.1~20N, for example, it can be 0.1N, 1N, 4N, 6N, 8N, 10N, 12N, 14N, 16N, 18N or 20N, etc.

[0070] Preferably, the contact pressure for the cutting is 0.01~16N, for example, it can be 0.01N, 1N, 3N, 5N, 6N, 8N, 10N, 11N, 13N, 15N or 16N, etc.

[0071] Preferably, the porosity of the base membrane is 40-50%, for example, it can be 40%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49% or 50%, etc.

[0072] Preferably, the air permeability of the base membrane is 70~120s / 100mL, for example, it can be 70s / 100mL, 76s / 100mL, 82s / 100mL, 87s / 100mL, 93s / 100mL, 98s / 100mL, 104s / 100mL, 109s / 100mL, 115s / 100mL or 120s / 100mL, etc.

[0073] Preferably, the thickness of the base film is 6~8μm, for example, it can be 6μm, 6.3μm, 6.5μm, 6.7μm, 6.9μm, 7.2μm, 7.4μm, 7.6μm, 7.8μm or 8μm, etc.

[0074] It is worth noting that the preparation method of the base film in this invention includes: mixing 250-350 parts of PI binder with water (the ratio of PI binder to water is 250-350:40-90 g / mL) and sonicating for 60-90 min, then placing it in a ball mill jar and ball milling for 6-9 h at a temperature of 25-45℃ and a speed of 500-900 rpm; then adding 1-3 parts of base film wetting agent and 3-6 parts of base film dispersant to the ball mill jar, adjusting the ball milling speed to 500-700 rpm, and ball milling for 2-5 h; then adding 31-35 parts of base film pore-forming agent and continuing ball milling for 2-4 h to obtain a base film slurry; using a casting coating machine to obtain the base film PI; after drying in a drying zone, the production line then passes through a hot water bath zone at a temperature of 100-120℃, and washes away the pore-forming agent by three hot water soaks to obtain the PI base film. The above parts are by weight.

[0075] Preferably, the PI-based film material is a homopolymer polyimide resin or a biphenyl polyimide resin.

[0076] Preferably, the base film wetting agent includes DIGIC 270.

[0077] Preferably, the base film dispersant comprises any one or a combination of at least two of triethylhexylphosphate, sodium lauryl sulfate, methylpentanol, cellulose derivatives, polyacrylamide, guru gum, or fatty acid polyethylene glycol esters, wherein typical but non-limiting combinations are the combination of triethylhexylphosphate and sodium lauryl sulfate, the combination of methylpentanol and sodium lauryl sulfate, the combination of triethylhexylphosphate and methylpentanol, the combination of cellulose derivatives and fatty acid polyethylene glycol esters, and the combination of guru gum and polyacrylamide.

[0078] Preferably, the pore-forming agent of the base film includes polyethylene glycol.

[0079] Preferably, the thickness of the functional film layer is 1~3μm, for example, it can be 1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.8μm, 2.0μm, 2.2μm, 2.4μm, 2.5μm or 3.0μm, etc.

[0080] It's worth noting that a thinner separator makes it more susceptible to puncture, while a thicker separator increases ion transport distance but reduces rate performance. High porosity reduces mechanical strength and leads to high-temperature shrinkage, while low porosity results in low electrolyte absorption and poor rate performance. An excessively thin functional coating can lead to uneven coverage, insufficient buffering / protection against silicon anode expansion, and limited improvement in thermal stability. An excessively thick functional coating increases the total separator thickness and internal resistance, reducing battery energy density and power density, and may result in excessively high permeability (Gurley value), affecting electrolyte wetting and ion transport, thus increasing costs.

[0081] Preferably, the porosity of the diaphragm is 32-45%, for example, it can be 32%, 33%, 34%, 35%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44% or 45%, etc.

[0082] In a second aspect, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the separator described in the first aspect.

[0083] Preferably, the lithium-ion battery includes a negative electrode, a positive electrode, and the separator. The positive electrode comprises a ternary material, and / or the negative electrode comprises a silicon-carbon negative electrode material.

[0084] Preferably, the ternary material is a high-nickel ternary material, wherein the nickel content in the high-nickel ternary material is 80~95wt%, for example, it can be 80wt%, 82wt%, 85wt%, 88wt%, 90wt%, 92wt%, 93wt%, 94wt%, or 95wt%, etc.

[0085] Preferably, the silicon content in the silicon-carbon anode material is 45-55 wt%, for example, it can be 45 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt%, 51 wt%, 52 wt%, 53 wt%, 54 wt%, or 55 wt%.

[0086] The separator of the present invention is preferably suitable for silicon content of 45-55 wt% in silicon-carbon anode materials, which can optimize the expansion problem and improve volumetric energy and rate performance.

[0087] Preferably, the particle size D50 of the silicon particles and / or carbon particles in the silicon-carbon anode material is 4~10μm, for example, it can be 4μm, 4.7μm, 5.4μm, 6μm, 6.7μm, 7.4μm, 8μm, 8.7μm, 9.4μm or 10μm, etc.

[0088] In this invention, the preferred silicon-carbon anode material has a particle size D50 of 4~10μm for silicon particles and / or carbon particles, which can improve rate performance and optimize dispersion.

[0089] Preferably, the lithium-ion battery further includes an electrolyte. The electrolyte includes additives, which include any one or a combination of at least two of ethylene sulfate (DTD), LiPO2F2, or tris(trimethylsilyl)phosphate (TMSP), wherein typical but non-limiting combinations are combinations of DTD and LiPO2F2, combinations of TMSP and LiPO2F2, and combinations of DTD and TMSP.

[0090] The present invention adds the above-mentioned additives to the electrolyte, which can further reduce the interfacial impedance and have a synergistic effect with the membrane.

[0091] Preferably, the content of additives in the electrolyte is 0.1~0.5wt%, for example, it can be 0.1wt%, 0.12wt%, 0.15wt%, 0.18wt%, 0.2wt%, 0.27wt%, 0.34wt%, 0.4wt%, 0.47wt%, or 0.5wt%, etc.

[0092] Compared with the prior art, the present invention has at least the following beneficial effects:

[0093] The separator provided by this invention is polymerized using polymer monomers containing phenyl, acrylonitrile and benzene rings with ortho-substituted F and Cl. This improves the separator's adsorption capacity for electrolyte, enhances the interfacial compatibility between the separator and the electrolyte, reduces the battery's internal resistance, effectively suppresses dendrite penetration, and improves the battery's overall performance, including thermal stability and cycle performance. Detailed Implementation

[0094] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0095] Polymer A1

[0096] Polymer A1 is formed by the polymerization of polymer monomers, wherein the structural formula of the polymer monomers is shown in formula (2):

[0097] Equation (2);

[0098] The weight-average molecular weight M of the polymer w It is 90000Da.

[0099] The preparation methods of polymer A1 include:

[0100] A polymer monomer, an organic solvent (THF), and an initiator (azobisisobutyronitrile and benzoyl peroxide in a mass ratio of 1:1.2) were mixed, with the initiator accounting for 0.55 wt% of the total mass of the polymer monomer and the polymer monomer to organic solvent (THF) mass ratio being 1:7. The polymer was prepared by polymerization at 102°C for 35 h under an argon atmosphere. The polymer was then mixed with the precipitating solvent (propanol and isopropanol in a volume ratio of 1:1) at a mass ratio of 4:1, resulting in polymer precipitation. The polymer precipitate was washed and dried to obtain polymer A1.

[0101] The infrared spectrum of polymer A1 in this invention is in the range of 2220-2240 cm⁻¹. - ¹The presence of a strong absorption peak indicates the presence of a -C≡N group, at 1230-1260 cm⁻¹. - ¹The presence of an absorption peak indicates the presence of CF stretching vibration; at 780-800 cm⁻¹ - ¹The presence of absorption peaks indicates the presence of C-Cl stretching vibrations; at 1590-1610 cm⁻¹ - ¹There is an absorption peak for the carbon-carbon double bond of the benzene ring.

[0102] In this invention, polymer A1 1 The HNMR spectrum is as follows: H of the ortho-F / Cl benzene ring: δ7.2-7.8ppm, this peak is a multiplet, 4H, F / Cl coupling splits into dd peaks; H of the cis-alkenyl group: δ6.5-6.8ppm (J=10-12Hz), the integration ratio is >90%, which proves that this configuration is cis configuration.

[0103] Polymer A2

[0104] Polymer A2 is formed by polymerization of monomers, wherein the monomers are the same as those in polymer A1, and the weight-average molecular weight M of the polymer is... w It is 65000Da.

[0105] The preparation methods of polymer A2 include:

[0106] Polymer monomers, organic solvents (THF and DMF in a volume ratio of 1:1.5), and initiator (azobisisobutyronitrile) are mixed, with the polymer monomers to organic solvent (THF) in a mass ratio of 1:10. The initiator accounts for 0.12 wt% of the total mass of the polymer monomers. The polymerization reaction is carried out in an argon atmosphere at 75°C for 18 h to prepare a polymer. The polymer after polymerization is mixed with the precipitation solvent (propanol and acetone in a volume ratio of 1:1) at a mass ratio of 5:1, and a polymer precipitate is formed. The polymer precipitate is washed and dried to obtain polymer A2.

[0107] Polymer A3

[0108] Polymer A3 is formed by polymerization of monomers, wherein the monomers are the same as those in polymer A1, and the weight-average molecular weight M of the polymer is... w It is 138000Da.

[0109] The preparation methods of polymer A3 include:

[0110] A polymer monomer, an organic solvent (DMF), and an initiator (benzoyl peroxide) were mixed, with the initiator accounting for 0.7 wt% of the total mass of the polymer monomer and the mass ratio of polymer monomer to organic solvent (THF) being 1:5. The polymer was prepared by polymerization at 120°C for 48 hours under an argon atmosphere. The polymer was then mixed with the precipitating solvent (isopropanol) at a mass ratio of 3:1 to precipitate the polymer. The precipitate was washed and dried to obtain polymer A3.

[0111] Polymer A4

[0112] In addition to adaptively adjusting the polymerization temperature and time in the preparation method, polymer A4 is prepared to achieve a polymer weight-average molecular weight M. w Except for the 135000 Da value, it is the same as polymer A1, and will not be described again here.

[0113] Polymer A5

[0114] In addition to adaptively adjusting the polymerization temperature and time in the preparation method, polymer A5 is prepared to achieve a polymer weight-average molecular weight M. w Except for the 55000 Da value, it is the same as polymer A1, and will not be described again here.

[0115] Polymer D1

[0116] Polymer D1 is identical to polymer A1 except that the hydroxyl group is replaced with a methoxy group, i.e., the polymer monomer is 4-fluorocinnamonitrile (CAS No. 24654-48-6), which will not be repeated here.

[0117] Polymer D2

[0118] Polymer D2 is identical to polymer A1 except that the polymer monomer is (E)-2,3-diphenylacrylonitrile (CAS No. 16610-80-3), and will not be described again here.

[0119] Polymer D3

[0120] Except for the polymer monomers (E)-2,3-diphenylacrylonitrile, 2-chloroacrylonitrile, and 4-fluorocinnamonitrile in a molar ratio of 1:1:1, polymer D3 is the same as polymer A1, and will not be described again here.

[0121] For ease of experimental comparison, the preparation methods of the diaphragms in the following embodiments and comparative examples all adopted the following steps: A coating slurry for the functional film layer was ultrasonically dot-coated onto the base film at 60°C, with a dot-coating stretching speed difference of 5%, followed by rewinding at 85°C and a winding / unwinding tension of 28N. Then, the film was slit, with a winding / unwinding tension of 12N and a contact pressure of 8N, to obtain the diaphragm. However, this does not mean that the diaphragm provided by this invention can only be prepared using the above process parameters; other process parameters are also applicable.

[0122] Example 1

[0123] This embodiment provides a diaphragm, which, by weight, includes a base membrane and a functional membrane layer disposed on the surface of the base membrane; the base membrane is made of PI base membrane with a porosity of 48.2% and an air permeability of 100s / 100mL; the thickness of the base membrane is 8μm; and the thickness of the functional membrane layer is 1.5μm.

[0124] The coating slurry for the functional film layer comprises: polymer A1, alumina with a particle size range of 30~50nm, water, wetting agent (sodium tripolyphosphate and sodium pyrophosphate in a mass ratio of 0.8:1), dispersant (sodium citrate), isopropanol and binder (hydroxypropyl methylcellulose) = 22:18:50:0.064:0.25:2.5:3.8.

[0125] The preparation method of the coating slurry for the functional film layer includes: mixing a dispersant and water for a first stirring, wherein the rotation speed of the first stirring is 1600 r / min, the revolution speed is 45 r / min, and the time is 60 min; then adding inorganic particles for a second stirring, wherein the rotation speed of the second stirring is 3400 r / min, the revolution speed is 25 r / min, and the time is 45 min; then adding isopropanol, binder, polymer and wetting agent, and subjecting the mixture to vacuum oscillation to form the coating slurry for the functional film layer.

[0126] The preparation method of the base film includes: mixing 290 parts by weight of PI adhesive (brand name: Kaneka Chemical Upilex-S resin) with water (PI adhesive to water ratio: 290:45 g / mL) and sonicating for 88 min, then placing it in a ball mill jar and ball milling for 6 h at 30℃ and 550 rpm; then adding 1.5 parts of base film wetting agent (Digo 270) and 6 parts of base film dispersant (polyacrylamide, weight average molecular weight of 8 million Da) to the ball mill jar, adjusting the ball milling speed to 700 rpm, and ball milling for 3.5 h, then adding 33.5 parts of base film pore-forming agent (polyethylene glycol, weight average molecular weight of 4000) and continuing ball milling for 3 h to obtain base film slurry, using a casting coating machine to obtain the base film PI, drying it in the drying zone, and then passing it through a hot water bath zone at 100℃ on the production line, washing away the pore-forming agent by three hot water immersions to obtain the PI base film.

[0127] Example 2

[0128] This embodiment provides a diaphragm, which, by weight, includes a base membrane and a functional membrane layer disposed on the surface of the base membrane; the base membrane is made of PI base membrane, has a porosity of 45.2%, and an air permeability of 110s / 100mL; the thickness of the base membrane is 6μm; and the thickness of the functional membrane layer is 3μm.

[0129] Example 3

[0130] This embodiment provides a diaphragm, which, by weight, includes a base membrane and a functional membrane layer disposed on the surface of the base membrane; the base membrane is made of PI base membrane with a porosity of 49.8% and an air permeability of 119s / 100mL; the thickness of the base membrane is 6.8μm; and the thickness of the functional membrane layer is 2.5μm.

[0131] The coating slurry for the functional film layer comprises: polymer A1, alumina with a particle size range of 35~66nm, water, wetting agent (sodium tripolyphosphate), dispersant (sodium citrate), isopropanol and binder (CMC) = 27:12:40:0.024:0.1:41:4.0.

[0132] The preparation method of the coating slurry for the functional film layer includes: mixing a dispersant and water for a first stirring, wherein the rotation speed of the first stirring is 1000 r / min, the revolution speed is 40 r / min, and the time is 70 min; then adding inorganic particles for a second stirring, wherein the rotation speed of the second stirring is 3200 r / min, the revolution speed is 28 r / min, and the time is 48 min; then adding isopropanol, binder, polymer and wetting agent, and subjecting the mixture to vacuum oscillation to form the coating slurry for the functional film layer.

[0133] The preparation method of the base film includes: mixing 250 parts by mass of PI resin (brand name Upilex-S) with water (PI adhesive to water ratio of 250:90 g / mL) and sonicating for 75 min, then placing it in a ball mill jar and ball milling for 8.5 h at 40℃ and 900 rpm; then adding 5.5 parts of base film wetting agent (Digo 270) and 5.8 parts of base film dispersant (sodium dodecyl sulfate and methyl pentanol in a mass ratio of 1:1) to the ball mill jar, adjusting the ball milling speed to 700 rpm, and ball milling for 5 h, then adding 35 parts of base film pore-forming agent (polyethylene glycol, weight average molecular weight of 4000) and continuing ball milling for 2 h to obtain base film slurry, using a casting coating machine to obtain the base film PI, drying it in the drying zone, and then passing it through a hot water bath zone at 100℃ on the production line, washing away the pore-forming agent by three hot water soaks to obtain the PI base film.

[0134] Example 4

[0135] This embodiment provides a diaphragm, which is the same as that in Example 1 except that it uses polymer A4, and will not be described again here.

[0136] Example 5

[0137] This embodiment provides a diaphragm, which is the same as that in Example 1 except that it uses polymer A5, and will not be described again here.

[0138] Example 6

[0139] This embodiment provides a diaphragm, except that the mass fraction of alumina with a particle size range of 30~50nm is replaced with 25 parts, and the mass fraction of polymer A1 is adapted to be adjusted to 15 parts so that the mass ratio of inorganic particles to polymer A1 is 15:25. Otherwise, the diaphragm is the same as in Example 1, and will not be described again here.

[0140] Example 7

[0141] This embodiment provides a diaphragm, except that the mass fraction of alumina with a particle size range of 30~50nm is replaced with 10 parts, and the mass fraction of polymer A1 is adapted to be adjusted to 30 parts so that the mass ratio of inorganic particles to polymer A1 is 30:10. Otherwise, the diaphragm is the same as in Example 1, and will not be described again here.

[0142] Example 8

[0143] This embodiment provides a diaphragm, which is the same as that in Embodiment 1 except that aluminum oxide is not added to the functional membrane layer, and will not be described again here.

[0144] Example 9

[0145] This embodiment provides a diaphragm, which is the same as that in Embodiment 1 except that aluminum oxide is replaced with silicon oxide, and will not be described again here.

[0146] Example 10

[0147] This embodiment provides a diaphragm, which is identical to that in Embodiment 1 except that ultrasonic dot coating is replaced with comma coating, and will not be repeated here. Specifically, the preparation method of comma coating includes injecting the coating slurry for the functional film layer into the hopper of a coating machine, adjusting the gap between the comma doctor blade and the base film surface (set to 2 μm to match the target thickness of the functional film layer), and continuously coating the slurry onto the base film surface at a coating speed of 20 m / min; after coating, it is dried with hot air at 70°C (drying time 10 min) to remove the solvent (water and isopropanol), forming a uniform functional film layer; during the drying process, the tension is controlled at 8 N to avoid wrinkles in the base film.

[0148] Comparative Example 1

[0149] This comparative example provides a diaphragm, which is the same as that in Example 1 except that it uses polymer D1, and will not be described again here.

[0150] Comparative Example 2

[0151] This comparative example provides a diaphragm, which is the same as that in Example 1 except that it uses polymer D2, and will not be described again here.

[0152] Comparative Example 3

[0153] This comparative example provides a diaphragm, which is the same as that in Example 1 except that it uses polymer D3, and will not be described again here.

[0154] Electrical performance testing

[0155] 1. Preparation of lithium-ion batteries

[0156] (1) Preparation of positive electrode sheet

[0157] The ternary material NCM811 (LiNi0.8Co0.1Mn0.1O2), the binder PVDF (polyvinylidene fluoride), the conductive agent 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.

[0158] (2) Preparation of negative electrode sheet

[0159] Silicon-carbon anode material (silicon content 50wt%), conductive agent SP (Super-P conductive carbon black), SWCNT (single-walled carbon nanotubes), binder PAA (polyacrylic acid) and SBR are mixed and stirred evenly in a mass ratio of 92:2:0.5:3:2.5 to obtain anode slurry. The solid content is controlled at 30wt%. Then, the anode slurry is coated onto a copper foil current collector through a coating process. After vacuum drying and cold pressing, the anode sheet is obtained.

[0160] (3) Selection of electrolyte

[0161] Electrolytes were prepared with a mass ratio of EC:PC:DMC:DEC:FEC of 15:20:25:30:10 and a LiPF6 concentration of 1.0 mol / L. In Example 1, 0.5% DTD was added as an electrolyte additive; in Example 2, 0.1% LiPO2F2 was added as an electrolyte additive; and in Example 3, 0.2% TMSP was added as an electrolyte additive. All other steps were the same as in Example 1.

[0162] (4) Selection of separator membrane

[0163] The diaphragms of the above embodiments and comparative examples were selected.

[0164] (5) Preparation of lithium-ion batteries

[0165] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then 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, a lithium-ion battery is obtained.

[0166] 2. Performance Testing

[0167] The rate performance of the battery was tested under lithium-ion battery testing conditions. The tests were conducted at room temperature (25℃) using the LAND battery testing system from Wuhan Jinno Electronics Co., Ltd., with the charge / discharge voltage limited to 2.5V~4.2V. The initial coulombic efficiency (first efficiency), cycle performance, and rate performance are shown in Table 1 below.

[0168] (1) First Coulomb efficiency

[0169] At 25°C, the lithium-ion battery was charged at a constant current and constant voltage of 0.33C to 4.2V, allowed to stand for 10 minutes, and then discharged at a constant current of 0.33C to 2.5V, allowed to stand for 10 minutes. The initial coulombic efficiency of the lithium-ion battery was calculated.

[0170] Initial coulombic efficiency (%) = Total capacity of lithium-ion battery during initial discharge at 0.33C / Total capacity of lithium-ion battery during initial charge at 0.33C × 100%.

[0171] (2) Capacity retention rate after 1000 cycles at room temperature (1C / 2C)

[0172] At 25°C, the lithium-ion battery was charged at a 1C rate with constant current and constant voltage to 4.2V, 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 2.5V 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.

[0173] 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.

[0174] (3) Room temperature 6C rate performance - constant current charge ratio

[0175] At 25℃, the lithium-ion battery was discharged at a 1C rate to 2.5V under constant current, allowed to stand for 10 minutes, and then charged at a 6C rate to 4.2V under constant current and constant voltage, with a cutoff current of 0.05C. After a 10-minute stand, the constant current charging capacity Q1 and the total constant current and constant voltage charging capacity Q2 were recorded. The constant current charge ratio at the 6C rate was calculated using 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%.

[0176] (4) Capacity retention rate at room temperature 1C / 8C discharge

[0177] The lithium-ion battery, after capacity gradation, was charged at 25℃ using a 1C rate with constant current and constant voltage to 4.2V, with a cutoff current of 0.05C; it was then allowed to stand for 10 minutes; next, the lithium-ion battery was discharged at a 1C rate with constant current to 2.5V, and its discharge capacity Q1C was recorded as the initial discharge capacity; then, the lithium-ion battery was charged at 25℃ using a 1C rate with constant current and constant voltage to 4.2V, with a cutoff current of 0.05C; it was allowed to stand for 10 minutes; then, the fully charged battery was discharged at an 8C rate with constant current to 2.5V, and its discharge capacity Q8C was recorded; the discharge capacity retention rate (%) of the lithium-ion battery at 1C / 8C rate was calculated as: discharge capacity Q8C at 8C rate / discharge capacity Q1C at 1C rate × 100%.

[0178] (4) Thermal shrinkage rate of diaphragm at 180℃ / 30min

[0179] Referring to the standard test method (GB / T36363), the dimensional changes of the diaphragm sample in the free state are measured at the specified temperature (e.g., 180℃) and time (30 min), and the transverse (TD) and longitudinal (MD) thermal shrinkage rates are calculated.

[0180] High-temperature furnace: temperature control accuracy ±1℃, internal atmosphere is air or inert gas (such as N2, selected according to patent requirements).

[0181] Sample clamps: stainless steel frame or quartz glass plate, ensuring that the sample shrinks freely without restraint.

[0182] A vernier caliper or optical projector with an accuracy of 0.02 mm (suitable for micron-level diaphragms); graph paper or laser rangefinder (for marking initial dimensions).

[0183] Sample preparation:

[0184] Cut size: 100mm × 100mm, 10mm away from the edge of the diaphragm. Marking: Draw a cross on the sample surface and record the initial length L0 in the transverse (TD) and longitudinal (MD) directions (accurate to 0.1mm).

[0185] Test steps

[0186] Pretreatment: The sample was placed in an environment of 23±2℃ and 50±5%RH for 24 hours.

[0187] High-temperature treatment:

[0188] 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.

[0189] Size measurement:

[0190] 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.

[0191] Data calculation: heat shrinkage rate (%) = (L0-L1) / L0×100%; the transverse (TD) and longitudinal (MD) shrinkage rates need to be recorded separately.

[0192] (5) 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, and after being left for 90 minutes, the change in the 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-heating reaction has occurred inside the battery. Maintain the adiabatic environment 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℃, and the steps are repeated on each step. The ARC test temperature range is 45℃~300℃. The self-heating 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-heating rate (SHR).

[0193] (6) 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. The cell is observed for 1 hour to see if an explosion or fire occurs.

[0194] (7) Method for testing the porosity of the diaphragm: The n-butanol displacement method is used: Weigh the mass m0 of the dried diaphragm sample and measure its volume V0. The unit can be cm. 3 Immerse the sample completely in n-butanol until no bubbles overflow. Remove it and quickly wipe away any residual liquid. Weigh the sample after immersion, m1 (in grams). Based on the density ρ of n-butanol (0.81 g / cm³),... 3 The porosity is calculated as [(m1-m0) / (ρ×V0)]×100%.

[0195] (8) Test method for mechanical strength of diaphragm: According to GB / T1040.3-2006 standard, a universal testing machine is used for testing: cut a 15mm×100mm diaphragm sample, clamp a distance of 50mm, stretch speed of 50mm / min, record the tensile strength (MPa) to characterize the mechanical strength.

[0196] The test results of the above embodiments and comparative examples are shown in Table 1.

[0197] Table 1

[0198]

[0199] As can be seen from Table 1:

[0200] (1) As can be seen from the comprehensive examples 1 to 3, the diaphragm provided by the present invention has superior tensile strength, preferably above 8.5 MPa. It does not explode or catch fire when tested in the cell hot box at 150℃ for 30 min. It also improves the thermal stability of the diaphragm. The thermal shrinkage rate -TD at 180℃ / 30 min is within 2.5%, and the thermal shrinkage rate -MD at 180℃ / 30 min is within 3.2%. It also improves the adsorption performance of electrolyte. The porosity of the diaphragm is above 43%, and the constant current filling ratio at room temperature 6C is above 80.2.

[0201] (2) In Comparative Example 1, polymer D1 was used, in which the monomer was 4-fluorocinnamonitrile. Due to the lack of Cl atoms, this monomer could not achieve the synergistic dendrite suppression effect of F / Cl (without the steric hindrance of Cl). Moreover, its polarity and flame retardant properties were weaker than those of the monomer of Formula (2) of this invention, which led to an increase in the interfacial impedance of the diaphragm and a decrease in thermal stability. During the cell hot box test at 150°C for 30 minutes, an explosion and fire occurred.

[0202] (3) In Comparative Example 2, (E)-2,3-diphenylacrylonitrile was used as a monomer. This monomer does not contain F and Cl, has low polarity (no strong electronegative atoms), poor adsorption capacity for electrolyte, and has no flame retardant and dendrite inhibition effect, which leads to shortened battery cycle life and deterioration of safety performance.

[0203] (4) In Comparative Example 3, the copolymer monomers have no adjacent F / Cl substitution structure, which cannot form a synergistic dendrite suppression effect. Furthermore, copolymerization leads to non-uniform molecular structure (disordered chain segment distribution), and significantly reduces interfacial properties (impedance increases by more than 20%) and mechanical strength.

[0204] (5) As can be seen from Examples 1 and 6-8, in Example 6, the coating becomes significantly more brittle due to the excessive amount of alumina particles, the porosity decreases, and the electrolyte wetting speed slows down; in Example 7, the alumina particle content is relatively low, resulting in insufficient inorganic thermal barrier effect, easy softening of polymer at high temperature, weakened mechanical support, and the puncture resistance of the diaphragm in Example 7 drops to 1.9N, while the puncture resistance of the diaphragm in Example 1 is 2.8N, and the thermal shrinkage rate in Example 7 increases significantly; in Example 8, without the addition of alumina, it can still maintain the cell hot box test at 150℃ for 30min without explosion or fire, but the mechanical strength is reduced, the risk of lithium dendrite penetration increases, and the thermal stability decreases significantly; thus, it is shown that the present invention can further improve the diaphragm performance by preferably controlling the alumina particle content within a reasonable range.

[0205] (6) As can be seen from Examples 1 and 9, in Example 1, aluminum oxide was used as inorganic particles. Compared with silicon oxide in Example 9, the density of hydroxyl (-OH) on the surface of silicon oxide in Example 9 was lower than that of aluminum oxide (about 60-70% of that of aluminum oxide). The hydrogen bonding with polar groups containing F / Cl and nitrile groups (-CN) in the polymer was weakened (interfacial bonding force decreased by 40-50%), which made the coating easy to delaminate from the base film. In addition, the hardness of silicon oxide (Mohs hardness 7) was lower than that of aluminum oxide, and the puncture resistance decreased.

[0206] The verification of synergistic effect with the electrolyte was performed using the diaphragms in Examples 1-3 and Comparative Examples 1-3. Except that 0.5 wt% DTD was not added to the electrolyte in Examples 1 and Comparative Examples 1-3, 0.1 wt% LiPO2F2 was not added to the electrolyte in Example 2, and 0.2% TMSP was not added to the electrolyte in Example 3, the rest of the test process was the same as described above, and the results are shown in Table 2.

[0207] Table 2

[0208]

[0209] As can be seen from Tables 1 and 2:

[0210] After adding electrolyte additives in Examples 1-3 of this invention, the increase in capacity retention rate and constant current charge ratio at room temperature 1C / 2C for 1000 cycles compared to those without electrolyte additives is greater than the increase in Comparative Examples 1-3 after adding electrolyte additives. This indicates that the present invention uses specific electrolyte additives in combination with the separator to further synergistically improve the cycle performance of lithium-ion batteries.

[0211] The present invention has been illustrated with the above embodiments to illustrate its detailed features, but the present invention is not limited to the above detailed features, that is, it does not mean that the present invention must rely on the above detailed features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the selected technical features, additions of auxiliary technical features, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A diaphragm, characterized in that, The membrane comprises a polymer, and the polymer monomer has the structural formula shown in formula (1): Equation (1); Wherein, one of R1 and R3 is a phenyl group containing ortho-substituted F and Cl; one of R1 and R3 is hydrogen, fluorine or chlorine; R2 is a phenyl group substituted with F and / or Cl.

2. The diaphragm according to claim 1, characterized in that, One of R1 and R3 is hydrogen.

3. The diaphragm according to claim 1, characterized in that, R2 is an F-substituted phenyl group.

4. The diaphragm according to claim 1, characterized in that, The cis configuration of the polymerized monomers is greater than 90%.

5. The diaphragm according to claim 1, characterized in that, The structural formula of the polymer monomer is shown in formula (2): Equation (2).

6. The diaphragm according to claim 1, characterized in that, The weight-average molecular weight M of the polymer w The range is 60,000 to 130,000 Da.

7. The diaphragm according to any one of claims 1 to 6, characterized in that, The membrane includes a functional membrane layer, and the polymer is located in the functional membrane layer; the functional membrane layer also includes inorganic particles, and the inorganic particles include alumina.

8. The diaphragm according to claim 7, characterized in that, The alumina has a particle size range of 22~66 nm.

9. The diaphragm according to claim 7, characterized in that, The mass ratio of alumina to polymer in the diaphragm is (12~20):(15~30).

10. The diaphragm according to claim 7, characterized in that, The functional membrane layer also includes a dispersant.

11. The diaphragm according to claim 10, characterized in that, The mass ratio of the dispersant to the polymer is (0.1~0.3):(15~30).

12. The diaphragm according to claim 10, characterized in that, The functional membrane layer also includes a wetting agent.

13. The diaphragm according to claim 12, characterized in that, The mass ratio of the wetting agent to the polymer is (0.02~0.08):(15~30).

14. The diaphragm according to claim 7, characterized in that, The diaphragm includes a base membrane, and the functional membrane layer is disposed on the surface of the base membrane; The base film is made of PI base film.

15. The diaphragm according to claim 14, characterized in that, The porosity of the base membrane is 40-50%.

16. The diaphragm according to claim 14, characterized in that, The air permeability of the base membrane is 70~120s / 100mL.

17. The diaphragm according to claim 14, characterized in that, The thickness of the base film is 6~8μm.

18. The diaphragm according to claim 14, characterized in that, The thickness of the functional film is 1~3μm.

19. The diaphragm according to any one of claims 1 to 6, characterized in that, The porosity of the diaphragm is 32-45%.

20. A lithium-ion battery, characterized in that, The lithium-ion battery includes the separator as described in any one of claims 1 to 19.

21. The lithium-ion battery according to claim 20, characterized in that, The lithium-ion battery includes a negative electrode, a positive electrode, and the separator; wherein the positive electrode includes a ternary material, and / or the negative electrode includes a silicon-carbon negative electrode material.

22. The lithium-ion battery according to claim 21, characterized in that, The lithium-ion battery further includes an electrolyte; wherein the electrolyte includes additives, and the additives include any one or a combination of at least two of DTD, LiPO2F2 or TMSP.

23. The lithium-ion battery according to claim 22, characterized in that, The content of additives in the electrolyte is 0.1~0.5wt%.

Images