Fluorine-free oily coating material, preparation method and lithium ion battery coating diaphragm

Abstract

The invention discloses a non-fluorine oily coating material, a preparation method and a lithium ion battery coating diaphragm, the non-fluorine oily coating material is a linear acrylate copolymer with an active functional group structure, and can be dissolved in DMF (Dimethyl Formamide), DMAc (Dimethyl Ammonium Chloride) and NMP (N-Methyl Pyrrolidone) organic solvents; the linear acrylate copolymer is synthesized from the following monomer components in percentage by weight through solution polymerization under the action of an initiator: 30-70% of a hard monomer, 30-50% of a soft monomer and 5-10% of an active functional monomer, and the sum of the weight percentages of all the monomers is 100%; the addition amount of the initiator is 0.3-1% of the total monomer weight, and the total monomer mass concentration is controlled to be 10-50% during solution polymerization. The material is coated on the two sides of the diaphragm through an oily coating process, latent curing crosslinking is ingeniously utilized to solve the problems of excessive swelling and dissolution of PMMA, meanwhile, a polymer coating keeps good interface cohesiveness, PVDF-HFP can be replaced by a non-fluorine material, and the material is high in cost performance, environmentally friendly and capable of being widely applied and popularized.

Description

Technical Field

[0001] This invention relates to the field of lithium battery separator technology, and in particular to a non-fluorinated oil-based coating material and its preparation method, and a lithium-ion battery coated separator. Background Technology

[0002] In recent years, with the rapid development of the new energy field, lithium-ion batteries have stood out due to their superior performance and are widely used in electric vehicles, portable electronic devices, and energy storage systems. Compared with traditional rechargeable batteries, lithium-ion batteries have advantages such as high energy density, high operating voltage, and long cycle life. The separator, as one of the four main materials of lithium-ion batteries, can isolate the positive and negative electrodes to prevent short circuits, and its micro-nano pore structure provides an effective channel for lithium ions, allowing them to move back and forth between the positive and negative electrodes. Simultaneously, its porous structure also provides storage space for the electrolyte. As the future development of lithium batteries focuses on four main directions—long lifespan, fast charging, high safety, and low cost—demands for separators such as faster wetting and higher safety are also being placed on them.

[0003] Oil-based coating of lithium-ion battery separators is a crucial process for improving separator performance. Employing an oil-based phase separation and pore-forming process, an organic or inorganic / organic composite coating is applied to the base membrane surface, enhancing the separator's thermal stability, resistance to electrolyte corrosion, and compatibility with electrodes. Commonly used organic polymers in oil-based coatings include polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyimide (PI), and aramid fibers. Common inorganic fillers include alumina (Al2O3) and silica (SiO2), which are often combined with organic polymers to form composite coatings. Furthermore, dispersants, thickeners, and pore-forming agents are added to optimize coating dispersibility and coating effect, ensuring coating uniformity. Compared to existing water-based coated separators, oil-based coated separators are widely used in power and digital lithium-ion batteries, where safety and performance requirements are high.

[0004] However, existing oil-coated diaphragms often use PVDF-HFP polymers. PVDF-HFP not only possesses electrochemical stability but also imparts tackiness to the coating through swelling in the electrolyte solvent. However, with environmental requirements, especially in Europe and the United States, there are clear requirements for the defluorination of diaphragm coating materials, eliminating or reducing the use of fluorinated materials, thus limiting the application of PVDF-HF. On the other hand, polymers such as aramid and polyimide, due to their high material polarity or high cross-linking after thermosetting, exhibit excellent thermal stability but lack tackiness.

[0005] In addition, existing water-based coated separators using PMMA (polymethyl methacrylate) or modified polyacrylate copolymers have already replaced PVDF-HFP and are widely used. However, water-based coating also has certain limitations; the interfacial adhesion and stability cannot achieve the same effect as oil-based coatings, making it unsuitable for high-energy, ultra-thin battery systems. For example, the modified acrylate copolymers used in water-based separator coatings can dissolve. To avoid the dissolution of acrylate copolymers and the resulting degradation of battery performance, existing methods use structural crosslinking to solve problems such as dissolution, swelling, and pore blockage. The crosslinked PMMA or polyacrylate copolymers (such as patent CN114716696B) no longer possess organic solvent solubility and cannot be used in oil-based coating processes.

[0006] Therefore, it is necessary to seek an acrylate copolymer coating material that is soluble in organic solvents to be suitable for oil-based coating processes, can solve the problems of excessive swelling and dissolution of acrylate copolymers, and has interfacial adhesion. Summary of the Invention

[0007] In order to overcome the shortcomings of the prior art, one of the objectives of the present invention is to provide a non-fluorinated oil-based coating material.

[0008] The second objective of this invention is to provide a method for preparing a non-fluorinated oil-based coating material.

[0009] The third objective of this invention is to provide an oil-coated lithium-ion battery separator.

[0010] One of the objectives of this invention is achieved by the following technical solution: a non-fluorinated oil-based coating material, wherein the non-fluorinated oil-based coating material is a linear acrylate copolymer with an active functional group structure, which can be dissolved in DMF, DMAc, and NMP organic solvents;

[0011] The linear acrylate copolymer is synthesized by solution polymerization of the following monomer components in the presence of an initiator, according to the following weight percentages: 30-70% hard monomer, 30-50% soft monomer, and 5-10% active functional monomer, with the sum of the weight percentages of all the above monomers being 100%; the amount of initiator added is 0.3-1% of the total monomer weight, and the total monomer mass concentration is controlled at 10-50% during solution polymerization; existing synthesis methods include in-situ polymerization, emulsion polymerization, and solution polymerization, and the present invention preferably adopts solution polymerization.

[0012] The hard monomer is selected from one or more of styrene, methyl methacrylate, cyclohexyl methacrylate, α-methylstyrene, and acrylonitrile;

[0013] The soft monomer is selected from one or more of isooctyl acrylate, isooctyl methacrylate, butyl acrylate, butyl methacrylate, ethyl methacrylate, and ethyl acrylate.

[0014] The active functional monomer is selected from one or more of the following: hydroxyethyl acrylamide, diacetone acrylamide, glycidyl methacrylate, glycidyl acrylate, glycidyl ether acrylate, acrylic acid, methacrylic acid, and silane coupling agents with unsaturated double bonds; the silane coupling agent with unsaturated double bonds is selected from trimethoxysilane methacrylate, triethoxysilane methacrylate, and methacryloxypropyltrimethoxysilane.

[0015] The initiator is selected from one or a mixture of two or more of azobisisobutyronitrile and benzoyl peroxide;

[0016] The reaction solvent system used in solution polymerization is a pure alcohol or an alcohol-water system, and the alcohol is selected from methanol, ethanol or a mixture of the two.

[0017] Furthermore, the linear acrylate copolymer with active functional groups is synthesized by solution polymerization of the following monomer components in the presence of an initiator, in the following weight percentages: styrene 30%, methyl methacrylate 27%, isooctyl acrylate 25%, ethyl acrylate 5%, glycidyl methacrylate 10%, triethoxysilane methacrylate 2%, and hydroxyethyl acrylamide 1%; the initiator is azobisisobutyronitrile at 0.4% of the total monomer weight.

[0018] Alternatively, the linear acrylate copolymer with active functional groups may be synthesized by solution polymerization of the following monomer components in the presence of an initiator, in the following weight percentages: 60% methyl methacrylate, 30% butyl methacrylate, 2.5% acrylonitrile, 5% allyl glycidyl ether, 0.5% acrylic acid, and 2% diacetone acrylamide; wherein the initiator is 0.3% azobisisobutyronitrile by weight of the total monomers.

[0019] Alternatively, the linear acrylate copolymer with active functional groups may be synthesized by solution polymerization of the following monomer components in the presence of an initiator, in the following weight percentages: 45% styrene, 25% isooctyl acrylate, 10% acrylonitrile, 10% butyl acrylate, 2% methacrylic acid, 7% glycidyl methacrylate, and 1% methacryloyloxypropyltrimethoxysilane; wherein the initiator is 0.5% benzoyl peroxide by weight of the total monomers.

[0020] The second objective of this invention is achieved by the following technical solution: a method for preparing a non-fluorinated oil-based coating material, comprising the following steps:

[0021] (a) Material synthesis:

[0022] The hard monomer, soft monomer, and active functional monomer in the prescribed amounts are sequentially added to a reaction vessel and thoroughly mixed. A synthesis solvent is added to maintain the total monomer concentration at 10-50%. The initiator in the prescribed amount is added, and the mixture is stirred evenly at a speed of 200-600 r / min. The temperature is raised to 55-60℃, and the reaction solution is refluxed for 24 hours. The reaction solution changes from colorless and transparent to milky white, with a monomer conversion rate greater than 95%, yielding a semi-finished coating material dispersion. The solvent used is pure alcohol or an alcohol-water system, with the alcohol selected from methanol, ethanol, or a mixture of both.

[0023] (b) Powder drying:

[0024] The semi-finished coating material dispersion from step (a) is dried by low-temperature spray drying to obtain powder. The inlet air temperature of the atomizing dryer is controlled at 55-60℃, and the collection temperature is between 30-50℃. The organic solvent in the dispersion is recovered by the condensation system, and the dried powder is collected by the cyclone collection tower. The average particle size of the powder is controlled at 30-50μm, thus obtaining a linear acrylate copolymer with an active functional group structure. This linear acrylate copolymer with an active functional group structure can be dissolved in DMF, DMAc, and NMP organic solvents.

[0025] The third objective of this invention is achieved by the following technical solution: an oil-coated lithium-ion battery separator, prepared by the following method: (1) Slurry preparation:

[0026] A linear acrylate copolymer with active functional groups is added to a polar organic solvent and fully dissolved to obtain slurry A. A high-temperature resistant material is added to a polar organic solvent and fully dissolved to obtain slurry B. Slurry A and slurry B are mixed to obtain slurry C. A latent curing agent, deionized water and a pore-forming agent are added to slurry C and mixed evenly to obtain a non-fluorinated oil slurry for later use.

[0027] The ratio of the added high-temperature resistant material to the weight of the linear acrylate copolymer is 1:(1-3), the added amount of the latent curing agent is 1-5% of the weight of the linear acrylate copolymer, the added amount of deionized water is 4-10% of the weight of the linear acrylate copolymer, and the added amount of the pore-forming agent is 4-10% of the weight of the linear acrylate copolymer.

[0028] (2) Preparation of coated diaphragm:

[0029] The non-fluorinated oily slurry obtained in step (1) is coated on one or both sides of the diaphragm. The coating process can be carried out using a micro-concave roller, and the coating amount on each side is controlled at (1-3) ± 0.5 g / m. 2The coated separator is then placed in a solvent extraction tank, where a phase separation process is used to create pores. After drying and winding, a single-sided / double-sided oil-coated lithium-ion battery separator is obtained.

[0030] Further, in step (1), the linear acrylate copolymer with active functional groups is synthesized by solution polymerization of the following monomer components in the presence of an initiator, according to the following weight percentages: 30-70% hard monomer, 30-50% soft monomer, and 5-10% active functional monomer, with the sum of the weight percentages of all the above monomers being 100%; the amount of initiator added is 0.3-1% of the total monomer weight, and the total monomer mass concentration is controlled at 10-50% during solution polymerization;

[0031] The hard monomer is selected from one or more of styrene, methyl methacrylate, cyclohexyl methacrylate, α-methylstyrene, and acrylonitrile;

[0032] The soft monomer is selected from one or more of isooctyl acrylate, isooctyl methacrylate, butyl acrylate, butyl methacrylate, ethyl methacrylate, and ethyl acrylate.

[0033] The active functional monomer is selected from one or more of the following: hydroxyethyl acrylamide, diacetone acrylamide, glycidyl methacrylate, glycidyl acrylate, glycidyl ether acrylate, acrylic acid, methacrylic acid, and silane coupling agents with unsaturated double bonds; the silane coupling agent with unsaturated double bonds is selected from trimethoxysilane methacrylate, triethoxysilane methacrylate, and methacryloxypropyltrimethoxysilane.

[0034] The initiator is selected from one or a mixture of two or more of azobisisobutyronitrile and benzoyl peroxide;

[0035] The reaction solvent system used in solution polymerization is a pure alcohol or an alcohol-water system, and the alcohol is selected from methanol, ethanol or a mixture of the two.

[0036] Further, in step (1), the polar organic solvent is selected from DMF, DMAc, and NMP.

[0037] Further, in step (1), the high-temperature resistant material is selected from one or more of the following: aluminum oxide, boehmite, silicon dioxide, titanium dioxide inorganic particles with an average particle size of 100-500 nm, and high-temperature resistant resins: polyimide and aramid.

[0038] Further, in step (1), the latent curing agent is selected from one or a mixture of two or more of the following: an adduct of 2-methylimidazole and propylene oxide isooctyl ether (163 curing agent), an adduct of 2-methylimidazole and propylene oxide butyl ether (704 curing agent), and an adduct of 2-methylimidazole and 2-ethylhexyl glycidyl ether (705 curing agent).

[0039] Further, in step (1), the pore-forming agent is selected from PVP with a molecular weight of 1000-5000.

[0040] Further, in step (2), the membrane is selected from polyolefin membranes or ceramic membranes with a thickness of 5-16 μm and a porosity of 30-60%.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] This invention modifies acrylate copolymers to obtain linear acrylate copolymer modified coating materials with active functional groups that are soluble in a pair of organic solvents (DMF, DMAc, NMP). This material is applied to both sides of a membrane using an oil-based coating process. It cleverly utilizes latent curing crosslinking to solve the problems of excessive swelling and dissolution of PMMA. At the same time, the polymer coating maintains good interfacial adhesion. It can replace PVDF-HFP with non-fluorinated materials, offering high cost-effectiveness, environmental friendliness, and widespread application. Attached Figure Description

[0043] Figure 1 This is a production process diagram of a non-fluorinated oil-based coated lithium-ion battery separator according to a preferred embodiment of the present invention; Detailed Implementation

[0044] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0045] Example 1: Lithium-ion battery coated separator

[0046] like Figure 1 As shown, this embodiment illustrates the preparation of the oil-coated lithium-ion battery separator:

[0047] (1) Slurry preparation:

[0048] 100g of a non-fluorinated oil-based coating material (i.e., a linear acrylate copolymer with active functional groups) was added to 1000g of NMP organic solvent and dissolved completely to obtain slurry A; particle size D was... 50100g of alumina powder with a density of 300-400nm is added to 1000g of NMP organic solvent and dispersed thoroughly to obtain slurry B. 1100g of slurry A and 1100g of slurry B are mixed to obtain a homogeneous slurry C. 2% by weight of 704 curing agent (polymer weight) is added to the mixed slurry C, along with 4% by weight of deionized water and 4wt% by weight of PVP (weight average molecular weight 2000), and the mixture is homogeneous to obtain a non-fluorinated oil-based slurry for later use.

[0049] (2) Preparation of coated diaphragm:

[0050] The above non-fluorinated oil-based slurry is coated on both sides of a 9μm polyolefin membrane with a porosity of 42%. The coating process can be carried out using a micro-grooved roller, with the coating amount on each side controlled at 2.5±0.5g / m². 2 The coated separator is then placed in a solvent extraction tank, where it is pore-formed using a phase separation process, dried, and wound up to obtain the lithium-ion battery coated separator of Example 1.

[0051] The non-fluorinated oil-based coating material in step (1) of this embodiment includes the following synthetic monomer components by weight percentage:

[0052] 30% hard styrene monomer

[0053] methyl methacrylate (MMA) refers to methyl methacrylate hard monomers (27%).

[0054] Isooctyl acrylate soft monomer 25%

[0055] 5% ethyl acrylate soft monomer

[0056] Glycidyl methacrylate with 10% active functional monomers

[0057] Triethoxysilane methacrylate with 2% active functional monomer

[0058] Hydroxyethylacrylamide contains 1% active functional monomer.

[0059] The non-fluorinated oil-based coating material in this embodiment is prepared by the following method:

[0060] (a) Synthesis:

[0061] 30g styrene, 27g methyl methacrylate, 25g isooctyl acrylate, 5g ethyl acrylate, 10g glycidyl acrylate, 2g triethoxysilane methacrylate, and 1g hydroxyethyl acrylamide were added sequentially to a 1L reactor and mixed thoroughly. 400mL of ethanol was added as solvent, and 0.4g of azobisisobutyronitrile (AIBN) as initiator was added. The mixture was stirred at 300 rpm and heated to 60℃. It was then refluxed for 24 hours. The reaction solution changed from colorless and transparent to milky white, and the monomer conversion rate was greater than 95%. The dispersion was then cooled and set aside for later use.

[0062] (b) Powder drying:

[0063] The dispersion from step (a) is spray-dried at low temperature to obtain powder. The inlet air temperature for atomization drying is controlled at 55-60℃, and the collection temperature is between 30-50℃. The organic solvent ethanol in the dispersion will be recovered by the condensation system. The spray drying temperature should not be too high, as excessively high temperatures can easily cause the active functional groups to become inactive or to undergo self-crosslinking, resulting in the powder not being able to dissolve completely in the subsequent dissolution and slurry preparation process. The dried powder is collected by a cyclone collection tower, and the average particle size of the powder is controlled at 30-50μm to obtain the non-fluorinated oil-based coating material of Example 1.

[0064] Example 2: Lithium-ion battery coated separator

[0065] Preparation of the oil-coated lithium-ion battery separator in this embodiment:

[0066] (1) Slurry preparation:

[0067] 100g of a non-fluorinated oil-based coating material (i.e., a linear acrylate copolymer with active functional groups) was added to 1000g of DMAC organic solvent and dissolved thoroughly to obtain slurry A. 100g of a 10% solids content para-aramid slurry was added to 1000g of DMAC organic solvent and dispersed thoroughly to obtain slurry B. Slurry A and slurry B were mixed to obtain a homogeneous slurry C. 1% by weight of 705 curing agent, 4% by weight of deionized water, and 4 wt% by weight of PVP (weight-average molecular weight 3000) were added to the mixed slurry C and mixed uniformly to obtain a non-fluorinated oil-based slurry for later use.

[0068] (2) Preparation of coated diaphragm:

[0069] The above non-fluorinated oil-based slurry is coated on both sides of a 9μm polyolefin membrane with a porosity of 42%. The coating process can be carried out using a micro-grooved roller, with the coating amount on each side controlled at 1.5±0.5g / m². 2 The coated separator is then placed in a solvent extraction tank, where it is pore-formed using a phase separation process, dried, and wound up to obtain the lithium-ion battery coated separator of Example 2.

[0070] The non-fluorinated oil-based coating material in step (1) of this embodiment includes the following synthetic monomer components by weight percentage:

[0071] 60% methyl methacrylate hard monomer

[0072] 30% butyl methacrylate soft monomer

[0073] Acrylonitrile hard monomer 2.5%

[0074] Allyl glycidyl ether contains 5% active functional monomer.

[0075] Acrylic acid with active functional monomers 0.5%

[0076] Diacetone acrylamide contains 2% active functional monomers.

[0077] The non-fluorinated oil-based coating material in this embodiment is prepared by the following method:

[0078] (a) Synthesis:

[0079] 60g of methyl methacrylate, 30g of butyl methacrylate, 2.5g of acrylonitrile, 5g of allyl glycidyl ether, 0.5g of acrylic acid, and 2g of diacetone acrylamide were sequentially added to a 1L reactor and mixed thoroughly. Then, 400mL of a mixture of ethanol and water (ethanol accounting for 50% of the total solvent weight) was added, along with 0.3g of azobisisobutyronitrile (AIBN) initiator. The mixture was stirred until homogeneous at 300 rpm, heated to 55°C, and refluxed for 24 hours. The reaction solution changed from colorless and transparent to milky white, with a monomer conversion rate greater than 95%. The dispersion was then cooled and set aside for later use.

[0080] (b) Powder drying:

[0081] The dispersion from step (a) was spray-dried at low temperature to obtain powder. The inlet air temperature for atomization drying was controlled at 55-60℃, and the collection temperature was controlled at 30-50℃. Since the reaction solution contained a large amount of water, a large amount of drying gas at 30-40℃ was introduced during the drying process to ensure the powder was fully dried. The organic solvent ethanol in the dispersion was recovered by a condensation system. The spray drying temperature should not be too high, as excessively high temperatures can easily cause deactivation of active functional groups or self-crosslinking, resulting in the powder not being able to dissolve completely in the subsequent dissolution and slurry preparation process. The dried powder was collected in a cyclone collection tower, with an average particle size controlled at 30-50 μm, yielding the non-fluorinated oil-based coating material of Example 1.

[0082] Example 3: Lithium-ion battery coated separator

[0083] Preparation of the oil-coated lithium-ion battery separator in this embodiment:

[0084] (1) Slurry preparation:

[0085] 100g of a non-fluorinated oil-based coating material (i.e., a linear acrylate copolymer with active functional groups) was added to 1000g of DMF organic solvent and dissolved thoroughly to obtain slurry A. 100g of polyimide with a solid content of 10% was added to 1000g of NMP organic solvent and dispersed thoroughly to obtain slurry B. Slurry A and slurry B were mixed to obtain a homogeneous slurry C. 1% by weight of 705 curing agent, 4% by weight of deionized water, and 4 wt% by weight of PVP (weight-average molecular weight 1000) were added to the mixed slurry C and mixed uniformly to obtain a non-fluorinated oil-based slurry for later use.

[0086] (2) Preparation of coated diaphragm:

[0087] The above non-fluorinated oil-based slurry is coated on both sides of a 9μm polyolefin membrane with a porosity of 42%. The coating process can be carried out using a micro-grooved roller, with the coating amount on each side controlled at 1.5±0.5g / m². 2 The coated separator is then placed in a solvent extraction tank, where it is pore-formed using a phase separation process, dried, and wound up to obtain the lithium-ion battery coated separator of Example 1.

[0088] The non-fluorinated oil-based coating material in step (1) of this embodiment includes the following synthetic monomer components by weight percentage:

[0089] 45% Styrene hard monomer

[0090] Isooctyl acrylate soft monomer 25%

[0091] 10% acrylonitrile hard monomer

[0092] 10% butyl acrylate soft monomer

[0093] 2% methacrylic acid with active functional monomers

[0094] Glycidyl methacrylate with 7% active functional monomer

[0095] Methacryloxypropyltrimethoxysilane with active functional monomer 1%.

[0096] The non-fluorinated oil-based coating material in this embodiment is prepared by the following method:

[0097] (a) Synthesis:

[0098] 45g styrene, 25g isooctyl acrylate, 10g acrylonitrile, 10g butyl acrylate, 2g methacrylic acid, 7g glycidyl methacrylate, and 1g methacryloxypropyltrimethoxysilane were sequentially added to a 1L reactor and mixed thoroughly. Then, 400mL of methanol was added as solvent, along with 0.5g benzoyl peroxide as initiator. The mixture was stirred at 400 rpm and heated to 60℃, then refluxed for 24 hours. The reaction solution changed from colorless and transparent to milky white, with a monomer conversion rate greater than 95%. The dispersion was then cooled and set aside for later use.

[0099] (b) Powder drying:

[0100] The dispersion from step (a) is spray-dried at low temperature to obtain powder. The inlet air temperature for atomization drying is controlled at 55-60℃, and the collection temperature is controlled at 30-50℃. The organic solvent ethanol in the dispersion will be recovered by the condensation system. The spray drying temperature should not be too high, as excessively high temperatures can easily cause the active functional groups to become inactive or to undergo self-crosslinking, resulting in the powder not being able to dissolve completely in the subsequent dissolution and slurry preparation process. The dried powder is collected by a cyclone collection tower, and the average particle size of the powder is controlled at 30-50μm to obtain the non-fluorinated oil-based coating material of Example 1.

[0101] Comparative Example 1

[0102] Compared with Example 2, Comparative Example 1 differs in that: in (b) powder drying, the inlet air temperature for atomization drying is greater than 60°C, and is 70°C, while the other conditions and formulation are the same as in Example 1.

[0103] Comparative Example 2

[0104] Compared with Example 2, the difference of Comparative Example 2 is that: in step (1), no latent curing agent is added, and the remaining conditions and formulation are the same as in Example 1.

[0105] Comparative Example 3

[0106] Compared to Example 2, the coating slurry in Comparative Example 3 used a different polymer. Specifically, it was a 1:1 mass blend of commercially available PMMA (molecular weight of 200,000) and aramid (solid content of 10 wt%). The pore-forming agent consisted of 4 wt% water and 4 wt% PVP (molecular weight of 2000), and the amount of pore-forming agent added was a percentage of the total weight of the polymer in the slurry. No curing agent was added.

[0107] The above slurries were coated using the process method of Example 2, with other conditions as described in Example 2, to obtain the diaphragm of Comparative Example 3. The coating weight was 1.5 ± 0.5 g / m² per side. 2 .

[0108] Comparative Example 4

[0109] Compared to Example 2, the coating slurry in Comparative Example 4 used a different polymer, specifically PVDF-HFP (Arkema @LBG). The porogen consisted of 4 wt% water + 4 wt% PVP (molecular weight 2000), and the amount of porogen added was a percentage of the total weight of the polymer in the slurry. No curing agent was added.

[0110] The above slurries were coated using the process method of Example 2, with other conditions as described in Example 2, to obtain the diaphragm of Comparative Example 4. The coating weight was 1.5 ± 0.5 g / m² per side. 2 .

[0111] Comparative Example 5

[0112] Compared with Example 2, the polymer used in the coating slurry of Comparative Example 5 is different. Specifically, it is a cross-linked polyacrylate copolymer, that is, the cross-linked acrylate copolymer powder provided in Example 1 of Patent CN114716696B is used instead of the linear acrylate copolymer with active functional group structure in Example 2.

[0113] The above slurries were coated using the process method of Example 2, with other conditions as described in Example 2, to obtain the diaphragm of Comparative Example 5. The coating weight was 1.5 ± 0.5 g / m² per side. 2 .

[0114] Performance testing

[0115] 1. Peel force test

[0116] The coated separators obtained from Implementation Cases 1-3 and Comparative Cases 1-5 were respectively composited with the positive electrode ternary 622 and the negative electrode graphite electrode. The pressure composite conditions were 25℃, 5-6MPa, and 60s, respectively. The separators after being composited with the positive electrode were then subjected to a 180° peel test.

[0117] 2. Swelling degree and dissolution rate test

[0118] 1) Weigh 100g of the slurry from Examples 1-3 and Comparative Examples 1-5, place them in a 120°C oven, and bake for 24 hours to obtain dried gel blocks. Weigh 2-3g of each gel block and record it as w1(g). Immerse the gel blocks in an electrolyte with a molar ratio of propylene carbonate: ethylene carbonate: diethyl carbonate = 1:1:1. Set the electrolyte at 60°C and let it stand for 24 hours to allow the gel blocks to fully swell. Filter out the soaked samples, absorb the electrolyte on the sample surface with absorbent paper, weigh them accurately, and record them as w2(g). The swelling rate (%) = (w2-w1) / w1*100%.

[0119] 2) Weigh 2-3g of sample gel blocks, denoted as w3 (g), and immerse them in the electrolyte solution with a molar ratio of propylene carbonate: ethylene carbonate: diethyl carbonate = 1:1:1. Let them stand at 60℃ for 24 hours to allow the gel blocks to fully swell. Filter out the soaked sample, then wash it with ethanol to remove the adsorbed solvent inside the gel blocks. Bake at 100℃ for 12 hours to obtain a dry weight w4 (g). The dissolution rate (%) is calculated as (w3-w4) / w3*100%.

[0120] 3. Diaphragm Ratio and Cyclic Testing

[0121] The coated separators obtained from Examples 1-3 and Comparative Examples 1-5 were assembled into 3Ah 4.4V ternary 622 / graphite soft-pack batteries, and their rate performance and cycle performance were tested. The rate performance was 0.5C charge / 0.5C, 1C, 2C, 5C discharge, and the cycle performance was 1C / 1C charge / discharge.

[0122] Table 1 Performance test results for each instance

[0123]

[0124] In summary, the present invention uses a non-fluorinated oil-based membrane coating material synthesized by free radical polymerization. This material has a linear structure with active groups and can be dissolved by polar organic solvents. After the addition of a curing agent, the active groups can be fully cross-linked with the curing agent, thereby inhibiting the dissolution of the acrylate copolymer and controlling its swelling. In Examples 1-3, the dissolution rate is less than 2% and the swelling degree is less than 100%.

[0125] However, the spray drying temperature of Comparative Example 1 was too high, reaching 70°C. The active groups in the internal structure of the synthesized non-fluorine coating material had already undergone a certain degree of cross-linking due to the heat, which affected the subsequent powder dissolution and coating phase separation to form pores. The adhesion also decreased to a certain extent, and affected the battery performance of the separator to a certain extent.

[0126] In Comparative Example 2, because no latent curing agent was added to the coating, the coating film was not fully cured during the subsequent battery baking process. The coating swelled excessively, and a large amount of internal structural molecules dissolved out, which seriously affected the battery performance, especially the battery cycle performance.

[0127] Comparative Example 3 uses commercially available pure PMMA material. Due to its poor resistance to electrolytes, large swelling, and even dissolution by polar solvents in the electrolyte, the dissolved components will have a serious impact on battery cycle and rate. Therefore, pure PMMA material cannot directly replace PVDF for oily coating of separators.

[0128] Comparative Example 4 is an oily diaphragm with a commercial PVDF-HFP coating. Examples 1-3 have achieved performance levels comparable to those of PVDF-HFP coatings.

[0129] Comparative Example 5 uses a cross-linked waterborne acrylic copolymer coating material that cannot be dissolved during use and can only be dispersed in the slurry. Furthermore, the coating has low adhesion at the electrode interface and cannot achieve the effect of a soluble oil-based coating.

[0130] In summary, the non-fluorinated oily membrane coating material synthesized in this invention maintains the excellent electrode interface adhesion of acrylate copolymers. At the same time, its battery performance, cycle life, and rate capability are comparable to PVDF-HFP@LBG. Its excellent cost performance makes it an ideal non-fluorinated alternative material for oily membrane coatings.

[0131] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A non-fluorinated oil-based coating material, characterized in that, The non-fluorinated oil-based coating material is a linear acrylate copolymer with an active functional group structure, which can be dissolved in DMF, DMAc, and NMP organic solvents; The linear acrylate copolymer is synthesized by solution polymerization of the following monomer components in the presence of an initiator, according to the following weight percentages: 30-70% hard monomer, 30-50% soft monomer, and 5-10% active functional monomer, with the sum of the weight percentages of all the above monomers being 100%; the amount of initiator added is 0.3-1% of the total monomer weight, and the total monomer mass concentration is controlled at 10-50% during solution polymerization; The hard monomer is selected from one or more of styrene, methyl methacrylate, cyclohexyl methacrylate, α-methylstyrene, and acrylonitrile; The soft monomer is selected from one or more of isooctyl acrylate, isooctyl methacrylate, butyl acrylate, butyl methacrylate, ethyl methacrylate, and ethyl acrylate. The active functional monomer is selected from one or more of the following: hydroxyethyl acrylamide, diacetone acrylamide, glycidyl methacrylate, glycidyl acrylate, glycidyl ether acrylate, acrylic acid, methacrylic acid, and silane coupling agents with unsaturated double bonds; the silane coupling agent with unsaturated double bonds is selected from trimethoxysilane methacrylate, triethoxysilane methacrylate, and methacryloxypropyltrimethoxysilane. The initiator is selected from one or a mixture of two or more of azobisisobutyronitrile and benzoyl peroxide; The reaction solvent system used in solution polymerization is a pure alcohol or an alcohol-water system, and the alcohol is selected from methanol, ethanol or a mixture of the two.

2. The non-fluorinated oil-based coating material as described in claim 1, characterized in that, The linear acrylate copolymer with active functional groups is synthesized by solution polymerization of the following monomer components in the presence of an initiator, in the following weight percentages: styrene 30%, methyl methacrylate 27%, isooctyl acrylate 25%, ethyl acrylate 5%, glycidyl methacrylate 10%, triethoxysilane methacrylate 2%, and hydroxyethyl acrylamide 1%; the initiator is azobisisobutyronitrile (AIBN) at 0.4% of the total monomer weight. Alternatively, the linear acrylate copolymer with active functional groups may be synthesized by solution polymerization of the following monomer components in the presence of an initiator, in the following weight percentages: 60% methyl methacrylate, 30% butyl methacrylate, 2.5% acrylonitrile, 5% allyl glycidyl ether, 0.5% acrylic acid, and 2% diacetone acrylamide; wherein the initiator is 0.3% azobisisobutyronitrile by weight of the total monomers. Alternatively, the linear acrylate copolymer with active functional groups may be synthesized by solution polymerization of the following monomer components in the presence of an initiator, in the following weight percentages: 45% styrene, 25% isooctyl acrylate, 10% acrylonitrile, 10% butyl acrylate, 2% methacrylic acid, 7% glycidyl methacrylate, and 1% methacryloyloxypropyltrimethoxysilane; wherein the initiator is 0.5% benzoyl peroxide by weight of the total monomers.

3. A method for preparing a non-fluorinated oil-based coating material, characterized in that, Includes the following steps: (a) Material synthesis: The hard monomer, soft monomer, and active functional monomer in the prescribed amounts are sequentially added to a reaction vessel and thoroughly mixed. A synthesis solvent is added to maintain the total monomer concentration at 10-50%. The initiator in the prescribed amount is added, and the mixture is stirred evenly at a speed of 200-600 r / min. The temperature is raised to 55-60℃, and the reaction solution is refluxed for 24 hours. The reaction solution changes from colorless and transparent to milky white, with a monomer conversion rate greater than 95%, yielding a semi-finished coating material dispersion. The solvent used is pure alcohol or an alcohol-water system, with the alcohol selected from methanol, ethanol, or a mixture of both. (b) Powder drying: The semi-finished coating material dispersion from step (a) is dried by low-temperature spray drying to obtain powder. The inlet air temperature of the atomizing dryer is controlled at 55-60℃, and the collection temperature is between 30-50℃. The solvent in the dispersion is recovered by the condensation system, and the dried powder is collected by the cyclone collection tower. The average particle size of the powder is controlled at 30-50μm, thus obtaining a linear acrylate copolymer with an active functional group structure. This linear acrylate copolymer with an active functional group structure can be dissolved in DMF, DMAc, and NMP organic solvents.

4. An oil-coated lithium-ion battery separator, characterized in that, It is prepared by the following method: (1) Preparation of coating slurry: A linear acrylate copolymer with active functional groups is added to a polar organic solvent and fully dissolved to obtain slurry A. A high-temperature resistant material is added to a polar organic solvent and fully dissolved to obtain slurry B. Slurry A and slurry B are mixed to obtain slurry C. A latent curing agent, deionized water and a pore-forming agent are added to slurry C and mixed evenly to obtain a non-fluorinated oil slurry for later use. The ratio of the amount of the high-temperature resistant material to the weight of the linear acrylate copolymer is 1:(1-3), the amount of the latent curing agent is 1-5% of the weight of the linear acrylate copolymer, the amount of the deionized water is 4-10% of the weight of the linear acrylate copolymer, and the amount of the pore-forming agent is 4-10% of the weight of the linear acrylate copolymer. (2) Preparation of coated diaphragm: The non-fluorinated oily slurry obtained in step (1) is coated on one or both sides of the diaphragm. The coating process can be carried out using a micro-concave roller, and the coating amount on each side is controlled at (1-3) ± 0.5 g / m. 2 The coated separator is then placed in a solvent extraction tank, where a phase separation process is used to create pores. After drying and winding, a single-sided / double-sided oil-coated lithium-ion battery separator is obtained.

5. The oil-coated lithium-ion battery separator as described in claim 4, characterized in that, In step (1), the linear acrylate copolymer with active functional groups is synthesized by solution polymerization of the following monomer components in the presence of an initiator, according to the following weight percentages: 30-70% hard monomer, 30-50% soft monomer, and 5-10% active functional monomer, with the sum of the weight percentages of all the above monomers being 100%; the amount of initiator added is 0.3-1% of the total monomer weight, and the total monomer mass concentration is controlled at 10-50% during solution polymerization; The hard monomer is selected from one or more of styrene, methyl methacrylate, cyclohexyl methacrylate, α-methylstyrene, and acrylonitrile; The soft monomer is selected from one or more of isooctyl acrylate, isooctyl methacrylate, butyl acrylate, butyl methacrylate, ethyl methacrylate, and ethyl acrylate. The active functional monomer is selected from one or more of the following: hydroxyethyl acrylamide, diacetone acrylamide, glycidyl methacrylate, glycidyl acrylate, glycidyl ether acrylate, acrylic acid, methacrylic acid, and silane coupling agents with unsaturated double bonds; the silane coupling agent with unsaturated double bonds is selected from trimethoxysilane methacrylate, triethoxysilane methacrylate, and methacryloxypropyltrimethoxysilane. The initiator is selected from one or a mixture of two or more of azobisisobutyronitrile and benzoyl peroxide; The reaction solvent system used in solution polymerization is a pure alcohol or an alcohol-water system, and the alcohol is selected from methanol, ethanol or a mixture of the two.

6. The oil-coated lithium-ion battery separator as described in claim 4, characterized in that, In step (1), the polar organic solvent is selected from DMF, DMAc, and NMP.

7. The oil-coated lithium-ion battery separator as described in claim 4, characterized in that, In step (1), the high-temperature resistant material is selected from one or more of the following: aluminum oxide, boehmite, silicon dioxide, titanium dioxide inorganic particles with an average particle size of 100-500 nm, and high-temperature resistant resins: polyimide and aramid.

8. The oil-coated lithium-ion battery separator as described in claim 4, characterized in that, In step (1), the latent curing agent is selected from one or a mixture of two or more of the following: an adduct of 2-methylimidazole and propylene oxide isooctyl ether, an adduct of 2-methylimidazole and propylene oxide butyl ether, and an adduct of 2-methylimidazole and 2-ethylhexyl glycidyl ether.

9. The oil-coated lithium-ion battery separator as described in claim 4, characterized in that, In step (1), the pore-forming agent is selected from PVP with a molecular weight of 1000-5000.

10. The oil-coated lithium-ion battery separator as described in claim 4, characterized in that, In step (2), the membrane is selected from polyolefin membranes or ceramic membranes with a thickness of 5-16 μm and a porosity of 30-60%.

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