A separator and a lithium ion battery comprising the same

Abstract

This invention provides a separator and a lithium-ion battery containing the separator, relating to the field of lithium-ion battery technology. The separator comprises a polymer, wherein the polymer monomers contain chlorine atoms, aromatic groups, amino groups, imine groups, acyl groups, and ester groups, which can improve the flexibility and structural stability of the polymer, while promoting lithium-ion conduction, and has broad application prospects.

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] As a crucial barrier between the positive and negative electrodes inside a lithium-ion battery, the separator's performance directly impacts the battery's safety and electrochemical performance. Current separator technology faces multiple challenges, urgently requiring breakthroughs in materials science and engineering.

[0003] Ion conduction and electrolyte retention are crucial for the electrochemical function of the separator. An ideal separator should possess high ionic conductivity and good electrolyte wettability to provide an efficient transport channel for lithium ions. Furthermore, the separator's toughness can resist the mechanical penetration of lithium dendrites during charging and discharging, preventing internal short circuits; it also exhibits superior resistance to thermal shrinkage.

[0004] However, no membrane with both excellent ion conductivity and toughness has been developed yet. 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 lithium-ion conductivity and the separator flexibility, while also taking into account the structural stability of the separator, 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, R1 is a substituted or unsubstituted aromatic group; R2 and R3 are each independently hydrogen and / or alkyl; R4 is a hydrocarbon group containing a chlorine atom substituent; and R5 is a hydrocarbon group.

[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 ion conduction capacity of the membrane and simultaneously optimize the toughness and structural stability of the membrane.

[0012] Formula (A).

[0013] Specifically, the polymer provided by this invention contains benzoyl groups and the structure shown in formula (A), which can provide certain steric hindrance and electronic effects, helping to maintain the structural stability of the membrane. The chlorine atom enhances the chemical stability of the polymer, and the hydroxyl group can interact with lithium ions in the electrolyte, promoting lithium ion conduction. The ester group improves the flexibility and processing performance of the polymer, making the membrane easier to prepare and apply. This invention preferably uses polymer monomers with the above-mentioned structure, wherein the chlorine-substituted methylene (Cl-CH2-) is separated from the ester group (-COO-CH3) by two carbon atoms, forming a polarity gradient (from strongly polar Cl to moderately polar ester group), ensuring both affinity with the electrolyte and avoiding excessive swelling; the aromatic group (phenyl) is directly connected to the structure of formula (A), enhancing structural rigidity through π-π conjugation, while simultaneously forming a "rigid-flexible balance" with the flexible segments of the ester group, giving the membrane both high toughness and puncture resistance.

[0014] Preferably, the aromatic group in R1 includes phenyl and / or naphthyl, and is preferably phenyl.

[0015] Preferably, R2 and R3 are each independently hydrogen. In this invention, R2 and R3 are preferably each independently hydrogen, without additional alkyl substituents. This reduces steric hindrance, making it easier for the polymer monomers to form regular chain structures during polymerization (narrower degree of polymerization distribution, PDI < 1.5). Simultaneously, the small size of hydrogen atoms avoids the inhibition of double bond (-CH=CH-) reactivity by alkyl groups, improving polymerization efficiency. Furthermore, hydrogen substitution makes molecular chain segments easier to rotate, enhancing polymer flexibility and better buffering the volume expansion of the silicon-based anode.

[0016] Preferably, R4 is an alkyl group with a chlorine atom substituent.

[0017] Preferably, the number of carbon atoms in R4 is 1 to 3, for example, it can be 1, 2 or 3.

[0018] Preferably, R4 is Cl-CH2-.

[0019] Preferably, R5 is an alkyl group.

[0020] Preferably, the number of carbon atoms in R5 is 1 to 3, for example, 1, 2, or 3, and preferably R5 is methyl. Preferably, the structural formula of the polymer monomer is shown in formula (2):

[0021] Equation (2).

[0022] Preferably, the weight-average molecular weight M of the polymer is... wThe range is 50,000 to 120,000 Da, for example, it can be 50,000 Da, 55,000 Da, 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, or 120,000 Da, etc.

[0023] 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.

[0024] Preferably, the preparation of the polymer includes: mixing polymer monomers, organic solvents and initiators, and carrying out a polymerization reaction to prepare the polymer.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] Preferably, the initiator accounts for 0.1 to 0.6 wt% of the total mass of the polymer monomers, for example, it may be 0.1 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.32 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, 0.55 wt%, or 0.6 wt%.

[0029] 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.

[0030] Preferably, the polymerization reaction temperature is 50~95℃, for example, it can be 50℃, 55℃, 60℃, 62℃, 65℃, 68℃, 70℃, 72℃, 75℃, 80℃, 85℃, or 90℃ or 95℃, etc.

[0031] Preferably, the polymerization reaction time is 10-30 hours, for example, 10 hours, 11 hours, 12 hours, 13 hours, 15 hours, 16 hours, 20 hours, 25 hours, 28 hours or 30 hours.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] Preferably, the membrane includes a functional membrane layer, and the polymer is located in the functional membrane layer. The functional membrane layer further includes alumina.

[0036] This invention preferably uses alumina in combination with the aforementioned polymer. Alumina (Al2O3) possesses high hardness and high-temperature resistance, which enhances the mechanical strength and thermal stability of the diaphragm. Its surface hydroxyl groups (-OH) can form hydrogen bonds with the (A) structure and ester groups (-COO-) in the polymer, improving interfacial bonding and promoting electrolyte adsorption and retention, ultimately resulting in superior ion conductivity, cycle stability, and safety performance of the diaphragm. Furthermore, the alumina is embedded in the polymer network, forming an organic-inorganic interpenetrating structure, reducing thermal shrinkage.

[0037] Preferably, the alumina has a particle size range of 20~60nm, for example, it can be 20nm, 25nm, 29nm, 34nm, 38nm, 43nm, 47nm, 48nm, 50nm, 55nm, 58nm or 60nm, etc.

[0038] 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.

[0039] Preferably, the mass ratio of alumina to polymer in the diaphragm is (15~25):(15~30), wherein the number of inorganic particles can be, for example, 15, 16, 18, 19, 20, 21, 22, 23, 24 or 25; and the number of polymers can be, for example, 15, 17, 19, 20, 22, 24, 25, 27, 29 or 30.

[0040] In this invention, the mass ratio of alumina to polymer is preferably controlled within the above-mentioned range. When the content of inorganic particles is too low, a continuous rigid support network cannot be formed, and the polymer chains are prone to sliding at high temperatures, leading to an increase in thermal shrinkage. At the same time, the mechanical strength of the coating is insufficient, making it difficult to resist lithium dendrite penetration, and the interfacial impedance increases too quickly during cycling. When the content of inorganic particles is too high, the particles are prone to agglomeration (agglomerate particle size > 1 μm), which disrupts the continuity of the polymer network and obstructs the lithium-ion transport channels. At the same time, the brittleness of the coating increases, making it prone to cracking during processing and reducing the yield.

[0041] Preferably, the functional film layer further includes a dispersant.

[0042] 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.

[0043] 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.

[0044] Preferably, the functional film layer further includes a wetting agent.

[0045] 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.

[0046] 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.

[0047] Preferably, the functional membrane layer further includes a membrane solvent and an adhesive.

[0048] Preferably, the film solvent includes water and isopropanol.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] Preferably, the first and second stirring are carried out in a planetary mixer or a high-speed disperser.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] Preferably, the coating comprises dotted coating.

[0064] 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.

[0065] Preferably, the dot coating is applied using ultrasonic dot spraying.

[0066] 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.

[0067] 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.

[0068] Preferably, the rewinding temperature is 60~100℃, for example, it can be 60℃, 65℃, 69℃, 74℃, 78℃, 83℃, 87℃, 92℃, 96℃ or 100℃, etc.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] Preferably, the air permeability of the base membrane is 70~120s / 100m, for example, it can be 70s / 100m, 76s / 100m, 82s / 100m, 87s / 100m, 93s / 100m, 98s / 100m, 104s / 100m, 109s / 100m, 115s / 100m or 120s / 100m, etc.

[0074] 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.

[0075] 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.

[0076] Preferably, the PI adhesive is DuPont Kapton® PI resin.

[0077] Preferably, the base film wetting agent includes DIGIC 270.

[0078] 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.

[0079] Preferably, the pore-forming agent of the base film includes polyethylene glycol.

[0080] Preferably, the thickness of the functional film layer is 1~4μm, for example, it can be 1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.8μm, 2.0μm, 2.2μm, 2.4μm, 2.5μm, 3.0μm, 3.2μm, 3.5μm, 3.8μm or 4μm, etc.

[0081] 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.

[0082] Preferably, the porosity of the diaphragm is 32-50%, for example, it can be 30%, 32%, 35%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 48% or 50%, etc.

[0083] In a second aspect, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the separator described in the first aspect.

[0084] 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.

[0085] Preferably, the ternary material is a high-nickel ternary material, wherein the nickel content in the high-nickel ternary material is 80~95wt%.

[0086] 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%.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] Preferably, the content of additives in the electrolyte is 0.5~1.0 wt%, for example, it can be 0.5 wt%, 0.52 wt%, 0.54 wt%, 0.58 wt%, 0.6 wt%, 0.67 wt%, 0.74 wt%, 0.8 wt%, 0.85 wt%, 0.9 wt%, 0.95 wt%, or 1.0 wt%.

[0093] Compared with the prior art, the present invention has at least the following beneficial effects:

[0094] The separator provided by the present invention is polymerized using polymer monomers containing chlorine atoms, aromatic groups, a structure of formula (A) and ester groups, which improves flexibility and structural stability, enhances the adsorption capacity of electrolyte, promotes lithium-ion conduction, and improves the overall performance of the battery. Detailed Implementation

[0095] 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.

[0096] Polymer A1

[0097] Polymer A1 is formed by the polymerization of polymer monomers, wherein the structural formula of the polymer monomers is shown in formula (2):

[0098] Equation (2);

[0099] The weight-average molecular weight M of the polymer w It is 80000Da.

[0100] The preparation methods of polymer A1 include:

[0101] A polymer monomer, an organic solvent (NMP and benzene in a volume ratio of 1:1), and an initiator (azobisisobutyronitrile) 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 (NMP and benzene) being 1:6.5. The polymer was prepared by polymerization at 55°C for 18 hours under an argon atmosphere. The polymer was then mixed with the precipitating solvent (acetone) at a mass ratio of 3.5:1 to precipitate the polymer. The precipitate was washed and dried to obtain polymer A1.

[0102] Polymer A2

[0103] 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 50000Da.

[0104] The preparation methods of polymer A2 include:

[0105] A polymer was prepared by mixing polymer monomers, an organic solvent (DMF and THF in a volume ratio of 1:1), and an initiator (benzoyl peroxide and azobisisobutyronitrile in a mass ratio of 1:1), with the initiator accounting for 0.6 wt% of the total mass of the polymer monomers and the mass ratio of polymer monomers to organic solvents (DMF and THF) being 1:5. The polymer was prepared by polymerization at 50°C for 11 hours under an argon atmosphere. The polymer was then mixed with the precipitating solvent (acetone) at a mass ratio of 5:1 to the polymerized material, resulting in a polymer precipitate. The polymer precipitate was washed and dried to obtain polymer A2.

[0106] Polymer A3

[0107] 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 120000Da.

[0108] The preparation methods of polymer A3 include:

[0109] A polymer monomer, an organic solvent (N-methylpyrrolidone), and an initiator (azobisisobutyronitrile) were mixed, with the initiator accounting for 0.1 wt% of the total mass of the polymer monomer. The mass ratio of polymer monomer to organic solvent (N-methylpyrrolidone) was 1:10. The polymer was prepared by polymerization at 95°C for 30 h under an argon atmosphere. The polymer was then mixed with the precipitating solvent (isopropanol) at a mass ratio of 3:1, resulting in polymer precipitation. The polymer precipitate was washed and dried to obtain polymer A3.

[0110] Polymer A4

[0111] 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 130,000 Da value, it is the same as polymer A1, and will not be described again here.

[0112] Polymer A5

[0113] 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 30000 Da value, it is the same as polymer A1, and will not be described again here.

[0114] Polymer D1

[0115] Polymer D1 is identical to polymer A1 except that the hydroxyl group is replaced with a methoxy group, i.e., the polymer monomer is methyl 3-(phenylamino)acrylate (CAS No. 4916-28-3), which will not be repeated here.

[0116] Polymer D2

[0117] Polymer D2 is identical to polymer A1 except that the polymer monomer is methyl 3-(2-chlorophenyl)-2-acrylate (CAS No. 42174-97-0), which will not be repeated here.

[0118] Polymer D3

[0119] Polymer D3 is identical to polymer A1 except that the polymer monomers include methyl 3-(2-chlorophenyl)-2-acrylate (CAS No. 42174-97-0) and methyl 3-(phenylamino)acrylate (CAS No. 4916-28-3) in a molar ratio of 1:1, and will not be described again here.

[0120] 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 50°C, with a dot-coating stretching speed difference of 5%, followed by rewinding at 80°C and a winding / unwinding tension of 28N. Then, the film was slit, with a winding / unwinding tension of 15N and a contact pressure of 12N, 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.

[0121] Example 1

[0122] 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 42%, and an air permeability of 85s / 100m; the thickness of the base membrane is 7μm; and the thickness of the functional membrane layer is 4μm.

[0123] The coating slurry for the functional film layer comprises: polymer A1, alumina with a particle size range of 20~45nm, water, wetting agent (sodium tripolyphosphate and sodium pyrophosphate in a mass ratio of 1:1), dispersant (sodium citrate), isopropanol and binder (hydroxypropyl methylcellulose) in a ratio of 25:20:50:0.05:0.3:1.5:3.

[0124] 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 1400 r / min, the revolution speed is 48 r / min, and the time is 55 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 18 r / min, and the time is 38 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.

[0125] The preparation method of the base film includes: mixing 350 parts by weight of PI adhesive (brand name DuPont Kapton® PI resin) with water (PI adhesive to water ratio of 350:65 g / mL) and sonicating for 68 min, then placing it in a ball mill jar and ball milling for 8 h at 32℃ and 650 rpm; then adding 2.5 parts of base film wetting agent (Digo 270) and 5 parts of base film dispersant (sodium dodecyl sulfate) to the ball mill jar, adjusting the ball milling speed to 600 rpm, and ball milling for 4 h, then adding 31.5 parts of base film pore-forming agent (polyethylene glycol, weight average molecular weight of 2000) and continuing ball milling for 2.5 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 113℃ on the production line, washing away the pore-forming agent by three hot water soaks to obtain the PI base film.

[0126] Example 2

[0127] 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 48.5% and an air permeability of 115s / 100m; the thickness of the base membrane is 6.5μm; and the thickness of the functional membrane layer is 2.5μm.

[0128] The coating slurry for the functional film layer comprises: polymer A2, alumina with a particle size range of 30~60nm, water, wetting agent (sodium hexametaphosphate), dispersant (sodium citrate), isopropanol and binder (polyvinyl alcohol, with a weight average molecular weight of 120000Da) = 15:25:66:0.02:0.1:4:7.

[0129] 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 3800 r / min, the revolution speed is 30 r / min, and the time is 50 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.

[0130] The preparation method of the base film includes: mixing 300 parts by weight of PI adhesive (brand name DuPont PI-2540) with water (PI adhesive to water ratio of 300:70 g / mL) and sonicating for 75 min, then placing it in a ball mill jar and ball milling for 9 h at 25℃ and 500 rpm; then adding 1 part of base film wetting agent (Digo 270) and 4.5 parts of base film dispersant (sodium dodecyl sulfate and triethylhexyl phosphate 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 3.5 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 120℃ on the production line, washing away the pore-forming agent by three hot water soaks to obtain the PI base film.

[0131] Example 3

[0132] 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 41.2%, and an air permeability of 72s / 100m; the thickness of the base membrane is 8μm; and the thickness of the functional membrane layer is 1.5μm.

[0133] The coating slurry for the functional film layer comprises: polymer A3, alumina with a particle size range of 35~55nm, water, wetting agent (sodium hexametaphosphate), dispersant (sodium silicate), isopropanol and binder (hydroxypropyl methylcellulose) = 25:15:45:0.03:0.15:2.8:6.8.

[0134] 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 1900 r / min, the revolution speed is 55 r / min, and the time is 55 min; then adding inorganic particles for a second stirring, wherein the rotation speed of the second stirring is 3500 r / min, the revolution speed is 15 r / min, and the time is 32 min; then adding isopropanol, binder, polymer and wetting agent, and then subjecting the mixture to vacuum oscillation to form the coating slurry for the functional film layer.

[0135] The preparation method of the base film includes: mixing 270 parts by weight of PI adhesive (brand name DuPont PI-2540) with water (PI adhesive to water ratio of 270:45 g / mL) and sonicating for 60 min, then placing it in a ball mill jar and ball milling for 6.5 h at 45 °C and 900 rpm; then adding 3 parts of base film wetting agent (Digo 270) and 6 parts of base film dispersant (triethylhexyl phosphate) to the ball mill jar, adjusting the ball milling speed to 550 rpm, and ball milling for 2.5 h, then adding 31 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 °C on the production line, washing away the pore-forming agent by three hot water soaks to obtain the PI base film.

[0136] Example 4

[0137] 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.

[0138] Example 5

[0139] 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.

[0140] Example 6

[0141] This embodiment provides a diaphragm, except that the mass fraction of alumina with a particle size range of 20~45nm is replaced with 28 parts, and the mass fraction of polymer A1 is adapted to be adjusted to 17 parts so that the mass ratio of inorganic particles to polymer A1 is 17:28. Otherwise, the diaphragm is the same as in Example 1, and will not be described again here.

[0142] Example 7

[0143] This embodiment provides a diaphragm, except that the mass fraction of alumina with a particle size range of 20~45nm 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 2, and will not be described again here.

[0144] Example 8

[0145] 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.

[0146] Example 9

[0147] This embodiment provides a diaphragm, which is the same as that in Embodiment 1 except that alumina is replaced with zirconium oxide, and will not be described again here.

[0148] Example 10

[0149] 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. The specific preparation method of comma coating includes injecting the coating slurry of 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 2.5 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, drying with hot air at 80℃ (drying time 12 min) removes the solvent (water and isopropanol) to form a uniform functional film layer; during the drying process, the tension is controlled at 10 N to avoid wrinkles in the base film.

[0150] Comparative Example 1

[0151] 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.

[0152] Comparative Example 2

[0153] 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.

[0154] Comparative Example 3

[0155] 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.

[0156] Electrical performance testing

[0157] 1. Preparation of lithium-ion batteries

[0158] (1) Preparation of positive electrode sheet

[0159] 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.

[0160] (2) Preparation of negative electrode sheet

[0161] Silicon-carbon anode material (48wt%), 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.

[0162] (3) Selection of electrolyte

[0163] 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, 0.7% DTD was added as an electrolyte additive; in Example 2, 1.0% TMSP was added as an electrolyte additive; and in Example 3, 0.5% LiPO2F2 was added as an electrolyte additive. All other steps were the same as in Example 1.

[0164] (4) Selection of separator membrane

[0165] The diaphragms of the above embodiments and comparative examples were selected.

[0166] (5) Preparation of lithium-ion batteries

[0167] 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.

[0168] 2. Performance Testing

[0169] 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.

[0170] (1) First Coulomb efficiency

[0171] 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.

[0172] 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%.

[0173] (2) Capacity retention rate after 1000 cycles at room temperature (1C / 2C)

[0174] 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.

[0175] 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.

[0176] (3) Room temperature 6C rate performance - constant current charge ratio

[0177] 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%.

[0178] (4) Capacity retention rate at room temperature 1C / 8C discharge

[0179] 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%.

[0180] (4) Thermal shrinkage rate of diaphragm at 150℃ / 30min

[0181] Refer to the standard test method (GB / T36363), specify the temperature (e.g., 150℃) and time (30min), measure the dimensional change of the diaphragm sample in the free state, and calculate the transverse (TD) and longitudinal (MD) thermal shrinkage rates.

[0182] High-temperature furnace: temperature control accuracy ±1℃, internal atmosphere is air or inert gas (such as N2, selected according to patent requirements).

[0183] Sample clamps: stainless steel frame or quartz glass plate, ensuring that the sample shrinks freely without restraint.

[0184] 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).

[0185] Sample preparation:

[0186] 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).

[0187] Test steps

[0188] Pretreatment: The sample was placed in an environment of 23±2℃ and 50±5%RH for 24 hours.

[0189] High-temperature treatment:

[0190] Place the sample flat on the fixture and put it into the center of a high-temperature furnace preheated to 150°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.

[0191] Size measurement:

[0192] 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.

[0193] Data calculation: heat shrinkage rate (%) = (L0-L1) / L0×100%; the transverse (TD) and longitudinal (MD) shrinkage rates need to be recorded separately.

[0194] (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).

[0195] (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.

[0196] (7) Method for testing the porosity of the diaphragm: Refer to GB / T21650.1-2008 "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion Porosimetry and Gas Adsorption Method - Part 1: Mercury Intrusion Porosimetry", specific steps: Sample preparation: Cut a 10mm×10mm diaphragm, dry it (80℃, 2h), weigh the mass m1, and measure the thickness d; Mercury intrusion test: Use a mercury intrusion porosimeter (such as Micromeritics AutoPore IV), pressure range 0~414MPa, record the mercury intrusion volume V; Calculation: Porosity P (%) = [V / (S×d-m1 / ρpolymer)]×100%, where S is the sample area, and ρpolymer is 1.1~1.2g / cm². 3 .

[0197] (8) Test method for the toughness of the diaphragm: According to GB / T1040.3-2006 standard, the universal testing machine is used for testing: cut a diaphragm sample of 15mm×100mm, clamp the sample with a spacing of 50mm, stretch the sample at a speed of 50mm / min, and record the elongation at break.

[0198] The test results of the above embodiments and comparative examples are shown in Table 1.

[0199] Table 1

[0200]

[0201] As can be seen from Table 1:

[0202] (1) As can be seen from the comprehensive examples 1 to 3, the diaphragm provided by the present invention has better toughness, and its elongation at break is preferably above 32%. It does not explode or catch fire when tested in the cell hot box at 150℃ for 30min, and there are no abnormalities in appearance. It also improves the thermal stability of the diaphragm, with the thermal shrinkage rate -TD at 180℃ / 30min being within 0.7% and the thermal shrinkage rate -MD at 180℃ / 30min being within 0.9%. It also improves the adsorption performance of electrolyte, with the porosity of the diaphragm being above 44%, the constant current charge ratio at room temperature 6C being above 81%, and the capacity retention rate at room temperature 1C / 2C for 1000 cycles being above 85%.

[0203] (2) In Comparative Example 1, polymer D1 was used, and the monomer was methyl 3-(phenylamino)acrylate (CAS4916-28-3), which does not contain chlorine atoms and has insufficient chemical stability; moreover, the hydroxyl group was replaced by the methoxy group, which lost the hydrogen bond with the electrolyte and the interfacial impedance increased.

[0204] In Comparative Example 2, the monomer is methyl 3-(2-chlorophenyl)-2-acrylate (CAS42174-97-0), which does not contain the (A) structure, exhibits poor wettability (contact angle >40°), insufficient structural rigidity (Tg <100℃), and a heat shrinkage rate >3% at 180℃.

[0205] Although two monomers were used in Comparative Example 3, the functional groups did not cooperate in distribution, and the cycle retention rate was still weaker than that of polymer A1.

[0206] The above demonstrates that the present invention uses a specific polymer as the membrane material, which can balance toughness and cycle performance, and has broad application prospects.

[0207] (3) As can be seen from Examples 1 and 6-8, in Example 6, there is too much alumina, and the excess Al2O3 agglomerates and occupies the polar sites of the (A) structure, weakening the hydrogen bonding with the electrolyte; resulting in the liquid absorption rate decreasing from 320% to 280%, the 180°C heat shrinkage rate (MD) increasing from 0.6% to 1.5%, the capacity retention rate after 1000 cycles at room temperature 1C / 2C decreasing from 86.5% to 79%, and the 6C constant current charge ratio decreasing from 82% to 75%; in Example 7, there is insufficient Al2O3, which cannot form an effective organic-inorganic network, and the polymer chain is easy to slide at high temperature, resulting in the 180°C heat shrinkage rate (TD) increasing from 0.8% to 1.3%, and the 8C discharge capacity retention rate decreasing from 79% to 74%. In Example 8, without the addition of alumina, the cell was still able to maintain a temperature of 150°C for 30 minutes without explosion or fire during the cell hot box test, but the toughness was reduced, the risk of lithium dendrite penetration increased, and the thermal stability was significantly reduced. This shows that by preferably controlling the content of alumina particles within a reasonable range, the present invention can further improve the performance of the separator.

[0208] (6) As can be seen from Examples 1 and 9, in Example 1, alumina was used as inorganic particles. Compared with the use of zirconium oxide as inorganic particles in Example 9, the hydrogen bonding between ZrO2 and ester groups in Example 9 was weak (the binding energy was 20% lower than that of Al2O3), and the coating adhesion decreased. The peel force decreased from 5 N / m in Example 1 to 3.5 N / m in Example 9, the interface impedance increased from 50 Ω in Example 1 to 65 Ω in Example 9, and the 6C charge ratio decreased from 82% to 77%.

[0209] The verification of synergistic effect with the electrolyte was performed using the diaphragms in Examples 1-3 and Comparative Examples 1-3. Except that 0.7 wt% DTD was not added to the electrolyte in Examples 1 and Comparative Examples 1-3, 1.0 wt% TMSP was not added to the electrolyte in Example 2, and 0.5% LiPO2F2 was not added to the electrolyte in Example 3, the rest of the test process was the same as above. The results are shown in Table 2.

[0210] Table 2

[0211]

[0212] As can be seen from Table 2, after adding electrolyte additives in Examples 1-3 of the present invention, the increase in capacity retention rate after 1000 cycles at room temperature 1C / 2C and the increase in constant current charge ratio at room temperature 6C compared to the absence of electrolyte additives are greater than the increase in the addition of electrolyte additives in Comparative Examples 1-3. 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.

[0213] 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 (2): Equation (2).

2. The diaphragm according to claim 1, characterized in that, The weight-average molecular weight M of the polymer w The range is 50,000 to 120,000 Da.

3. The diaphragm according to claim 1, characterized in that, The diaphragm includes a functional membrane layer, the polymer is located in the functional membrane layer, and the functional membrane layer further includes aluminum oxide.

4. The diaphragm according to claim 3, characterized in that, The alumina has a particle size range of 20~60nm.

5. The diaphragm according to claim 3, characterized in that, The mass ratio of alumina to polymer in the diaphragm is (15~25):(15~30).

6. The diaphragm according to claim 3, characterized in that, The functional membrane layer also includes a dispersant.

7. The diaphragm according to claim 6, characterized in that, The mass ratio of the dispersant to the polymer is (0.1~0.3):(15~30).

8. The diaphragm according to claim 3, characterized in that, The functional membrane layer also includes a wetting agent.

9. The diaphragm according to claim 8, characterized in that, The mass ratio of the wetting agent to the polymer is (0.02~0.08):(15~30).

10. The diaphragm according to claim 3, 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.

11. The diaphragm according to claim 10, characterized in that, The porosity of the base membrane is 40-50%.

12. The diaphragm according to claim 10, characterized in that, The air permeability of the base membrane is 70~120s / 100m.

13. The diaphragm according to claim 10, characterized in that, The thickness of the base film is 6~8μm.

14. The diaphragm according to claim 3, characterized in that, The thickness of the functional film is 1~4μm.

15. The diaphragm according to claim 1, characterized in that, The porosity of the diaphragm is 32-50%.

16. A lithium-ion battery, characterized in that, The lithium-ion battery includes the separator as described in any one of claims 1 to 15.

17. The lithium-ion battery according to claim 16, 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.

18. The lithium-ion battery according to claim 17, characterized in that, The ternary material is a high-nickel ternary material, and the nickel content in the high-nickel ternary material is 80~95wt%.

19. The lithium-ion battery according to claim 17, characterized in that, The silicon content in the silicon-carbon anode material is 45-55 wt%.

20. The lithium-ion battery according to claim 17, characterized in that, The silicon-carbon anode material has a particle size D50 of 4~10μm for silicon particles and / or carbon particles.

21. The lithium-ion battery according to claim 17, 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.

22. The lithium-ion battery according to claim 21, characterized in that, The content of additives in the electrolyte is 0.5~1.0wt%.

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