Flame-retardant PMMA (polymethyl methacrylate) binder as well as preparation method and application thereof

Abstract

The invention relates to the technical field of binders, in particular to a flame-retardant PMMA (polymethyl methacrylate) binder as well as a preparation method and application thereof, and the flame-retardant PMMA binder is prepared from the following raw materials in parts by weight: 40-50 parts of PMMA emulsion and 1-3 parts of modified ceramic powder. The flame-retardant PMMA binder prepared by the invention has good binding power, and can reduce the thermal shrinkage rate of a diaphragm when being used for the diaphragm, so that the safety of a battery is improved.

Description

Technical Field

[0001] The invention relates to the technical field of adhesives, and in particular to a flame retardant PMMA adhesive and a preparation method and application thereof. Background Art

[0002] Lithium-ion battery is a rechargeable battery that mainly relies on the movement of lithium ions between the positive electrode and the negative electrode to achieve the purpose of charging and discharging. It is widely used in many fields such as consumer electronics, electric vehicles, and energy storage systems. Lithium-ion batteries are composed of four main parts: positive electrode, negative electrode, electrolyte, and diaphragm. The diaphragm can isolate the positive and negative electrode materials and provide a channel for the migration of lithium ions. It is an important inner component of lithium-ion batteries. The performance of the diaphragm directly affects the internal resistance, cyclability, and safety of the battery. Polyolefin diaphragms have good chemical stability, excellent mechanical strength, and low prices and are widely used in lithium-ion batteries. However, their poor thermal stability and difficulty in wetting have greatly affected the performance of lithium-ion batteries, which can easily cause battery short circuits and lead to accidents such as combustion and explosion. In order to solve this problem, people in this field have tried to coat binders and ceramic particles on the diaphragm substrate to improve the heat resistance of the diaphragm to reduce the thermal shrinkage of the diaphragm, avoid short circuits in the battery, and improve safety.

[0003] Patent CN108949074A discloses a binder for lithium-ion battery diaphragm coating and a preparation method thereof. The binder for lithium-ion battery diaphragm coating comprises the following components by weight: acrylonitrile, acrylic acid, soft monomer, emulsifier, initiator, lithium salt, and ultrapure water. The application solves the problem that the lithium-ion battery diaphragm coating is not resistant to high temperature and has too high a moisture content, improves the conductivity of ions, and improves the safety performance of the battery. However, although the application improves the bonding performance of the binder, the addition of acrylonitrile may affect the swelling rate of the diaphragm and affect the cyclability of the battery.

[0004] Patent CN104140502B discloses a binder for lithium-ion battery separators, a preparation method, and a separator using the binder. The binder contains the following raw materials in parts by weight: 0.5-1 part of water-soluble polymer, 1-10 parts of flexible segment monomer, 1-10 parts of rigid segment monomer, 0.01-0.05 parts of initiator, and 1-10 parts of plasticizer. The binder for lithium-ion battery separators of the invention can improve the thermal stability and heat shrinkage resistance of the separator, so that the separator has good safety and overcharge resistance; at the same time, it is tightly bonded to inorganic substances, improves the wettability and liquid retention of the separator, and has excellent bonding force. However, the inorganic substances used in the invention are transition metal oxides, which are relatively expensive and have limited resources.

[0005] Therefore, there is an urgent need in the market for a binder that does not affect battery performance and whose raw materials are easily available. Summary of the invention

[0006] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a flame retardant PMMA adhesive having good bonding strength and simple preparation. When used in a diaphragm, it can reduce the thermal shrinkage rate of the diaphragm, thereby improving the safety and service life of the battery.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] The first aspect of the present invention provides a flame retardant PMMA adhesive, which comprises the following raw materials in parts by weight: 40-50 parts of PMMA emulsion and 1-3 parts of modified ceramic powder.

[0009] In some embodiments, the method for preparing PMMA comprises the following steps:

[0010] (1) adding polyvinyl pyrrolidone to an 80-90 wt% ethanol solution, stirring for 20-30 min, then adding a mixed solution of styrene, methyl methacrylate, N-methylacrylamide, and hydroxyethyl methacrylate, stirring at 500-600 r / min for 10-15 min at room temperature, then heating to 50-60° C., adding azobisisobutyronitrile, reacting for 1-2 h, cooling to room temperature, and emulsifying at 1500-2000 r / min for 1-3 min to obtain a core layer emulsion;

[0011] (2) Add 2-hydroxyethyl acrylate, modified 2-carboxyethyl acrylate, ethylene glycol dimethacrylate and epoxy resin to an 80-90 wt% ethanol solution, stir at 300-400 r / min for 20-30 min at room temperature to obtain a shell emulsion, then heat to 70-80° C., add sodium persulfate, and dropwise add the core emulsion obtained in step (1) while stirring. After the dropwise addition is completed, react for 10-12 hours to obtain a PMMA emulsion.

[0012] PVDF is a commonly used binder in the field of lithium batteries. Although it has excellent electrochemical and chemical stability, its own electronic and ionic conductivity is relatively weak. It needs to use N-methylpyrrolidine as a solvent. It has a high volatile temperature and is slightly polluting to the environment. The membrane prepared with this type of binder has poor toughness and is not easy to roll up. It is gradually replaced by more green and environmentally friendly PMMA-type binders, but conventional PMMA binders still have the disadvantages of insufficient support for the membrane and heat resistance, which makes the prepared battery safety low. The present invention prepares a PMMA emulsion containing core-shell PMMA microspheres by selecting specific monomers. The PMMA microspheres in the emulsion have uniform particle size and can be evenly arranged when coated on the membrane. It not only plays a good supporting role for the membrane, but also has good air permeability, avoiding the problem of conventional binders causing the membrane to have poor air permeability. The outer shell polymer has a strong binding force on the membrane, which increases the bonding of the binder.

[0013] Preferably, the particle size range of the PMMA microspheres in the PMMA emulsion is 1.3 μm≤D(10)≤1.5 μm, 2.3 μm≤D(50)≤2.5 μm, 3.6 μm≤D(90)≤4 μm, and 5.2 μm≤D(99)≤5.5 μm.

[0014] In some embodiments, the mass ratio of styrene, methyl methacrylate, N-methylacrylamide and hydroxyethyl methacrylate in step (1) is 1: (0.7-0.9): (0.3-0.5): (0.2-0.4).

[0015] The present invention limits the mass ratio of styrene, methyl methacrylate, N-methylacrylamide and hydroxyethyl methacrylate so that the formed core polymer microspheres have suitable mechanical strength and crosslinking degree, thereby alleviating the problem of diaphragm expansion caused by long-term battery circulation.

[0016] In some embodiments, the preparation method of the modified 2-carboxyethyl acrylate in step (2) comprises the following steps: adding 2-hydroxy-3-methoxy-5-vinylbenzoic acid, pentaerythritol phosphate and phosphoric acid to DMF, reacting at 70-80°C for 7-8h, then adding 2-carboxyethyl acrylate, reacting at 70-80°C for 7-8h, and rotary evaporating to obtain modified 2-carboxyethyl acrylate.

[0017] The invention reacts 2-hydroxy-3-methoxy-5-vinylbenzoic acid with pentaerythritol phosphate 2-carboxyethyl acrylate and then modifies the 2-carboxyethyl acrylate, grafts a heat-resistant benzene ring structure and a flame-retardant phosphate group on the 2-carboxyethyl acrylate, thereby avoiding the problem of uneven dispersion and poor compatibility of directly added flame retardants; at the same time, the modified 2-carboxyethyl acrylate has a plurality of double bonds, which, on the one hand, increases the crosslinking degree of the shell layer, and the prepared binder is more stable in the electrolyte; on the other hand, increases the interaction force with the diaphragm, and enhances the bonding force with the diaphragm; in addition, the modified 2-carboxyethyl acrylate increases a cage structure and an ether bond, thereby avoiding the problem of weakened lithium ion transmission performance caused by the diaphragm becoming thicker after being coated with the binder.

[0018] In some embodiments, the mass ratio of the 2-hydroxy-3-methoxy-5-vinylbenzoic acid, pentaerythritol phosphate and 2-carboxyethyl acrylate is (1-1.2):(0.1-0.3):1.

[0019] The invention limits the mass ratio of 2-hydroxy-3-methoxy-5-vinylbenzoic acid, pentaerythritol phosphate and 2-carboxyethyl acrylate so that 2-carboxyethyl acrylate can be fully grafted with 2-hydroxy-3-methoxy-5-vinylbenzoic acid and pentaerythritol phosphate, thereby increasing the flame retardancy and heat resistance of the adhesive.

[0020] In some embodiments, the mass ratio of 2-hydroxyethyl acrylate, modified 2-carboxyethyl acrylate and ethylene glycol dimethacrylate in step (2) is 1:(0.1-0.3):(0.5-0.7).

[0021] The present invention increases the heat resistance and flame retardancy of the shell layer by limiting the mass ratio of 2-hydroxyethyl acrylate, modified 2-carboxyethyl acrylate and ethylene glycol dimethacrylate without increasing the brittleness of the shell layer and deteriorating the adhesion with the diaphragm.

[0022] In some embodiments, the method for preparing the modified ceramic powder comprises the following steps: adding the ceramic powder and KH570 to ethanol, reacting at 70-80° C. for 5-6 hours, then adding polyethylene glycol monoallyl ether and azobisisobutyronitrile, and continuing the reaction for 1-2 hours to obtain the modified ceramic powder.

[0023] In order to improve the support of the binder to the diaphragm, it is usually necessary to add a certain amount of filler to the binder so that it has a certain degree of support for the diaphragm. However, most inorganic additives have poor dispersibility in the polymer system. The present invention improves the dispersibility of the ceramic powder in PMMA by modifying the ceramic powder with a silane coupling agent and then polymerizing it with polyethylene glycol monoallyl ether. This makes the obtained binder have strong support when used for the diaphragm and reduces the thermal shrinkage of the diaphragm. The possible reason is that the molecular weight of the modified ceramic powder is increased, the hydrogen bonding effect between molecules is weakened, and the agglomeration is reduced. At the same time, the addition of a certain number of ether bonds and hydroxyl groups not only increases the compatibility with PMMA, but also further improves the membrane's ability to transmit lithium ions.

[0024] In some embodiments, the mass ratio of the ceramic powder to polyethylene glycol monoallyl ether is (0.4-0.6):1.

[0025] The present invention limits the mass ratio of ceramic powder to polyethylene glycol monoallyl ether so that the ceramic powder has good dispersibility in PMMA and avoids the problem of reduced lithium ion transmission capacity due to reaction of some hydroxyl groups on the surface of the ceramic powder.

[0026] The second aspect of the present invention provides a method for preparing a flame retardant PMMA adhesive, comprising the following steps: adding modified ceramic powder to PMMA in 3-4 portions and stirring at 60-70° C. for 50-70 minutes to obtain the adhesive.

[0027] A third aspect of the present invention provides an application of a flame retardant PMMA binder in a lithium battery separator.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention selects specific monomers to prepare a binder obtained by compounding PMMA with a core-shell structure and a modified ceramic powder with a suitable particle size and uniform particle size. The binder not only has a good supporting effect on the diaphragm, but also has good air permeability, avoiding the problem of conventional binders causing the permeability of the diaphragm to deteriorate. The outer shell layer polymer has a strong bonding force to the diaphragm, thereby increasing the bonding properties of the binder.

[0030] 2. The present invention reacts 2-hydroxy-3-methoxy-5-vinylbenzoic acid with pentaerythritol phosphate 2-carboxyethyl acrylate and then modifies the 2-carboxyethyl acrylate. A benzene ring structure with heat resistance and a phosphate group with flame retardancy are grafted onto the 2-carboxyethyl acrylate, thereby avoiding the problem of uneven dispersion and poor compatibility of directly added flame retardants. Meanwhile, the modified 2-carboxyethyl acrylate has multiple double bonds, which, on the one hand, increases the crosslinking degree of the shell layer, and the prepared binder is more stable in the electrolyte. On the other hand, the interaction force with the diaphragm is increased, and the bonding force with the diaphragm is enhanced. In addition, the modified 2-carboxyethyl acrylate has a cage structure and an ether bond, thereby avoiding the problem of weakened lithium ion transmission performance caused by the diaphragm becoming thicker after being coated with the binder.

[0031] 3. The present invention improves the dispersibility of the ceramic powder in PMMA by modifying the ceramic powder with a silane coupling agent and then polymerizing it with polyethylene glycol monoallyl ether, so that the obtained adhesive has strong support when used for the diaphragm, thereby reducing the thermal shrinkage of the diaphragm. DETAILED DESCRIPTION

[0032] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following examples and comparative examples are only used to illustrate the present invention and are not intended to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0033] In order to facilitate those skilled in the art to implement the present invention, some raw materials and manufacturers of the embodiments and comparative examples are described as follows:

[0034] The compounds and related reagents used in the following examples and comparative examples can all be purchased from the market, among which polyvinyl pyrrolidone was purchased from Beijing Myrida Technology Co., Ltd., Mw=38000; polyethylene glycol monoallyl ether was purchased from Beijing Myrida Technology Co., Ltd., Mw=2400; ceramic powder was purchased from Lingshou County Shengfei Mineral Products Processing Plant, with a particle size of 2000 mesh; epoxy resin was purchased from Zhengzhou Wubaotong Trading Co., Ltd., with a brand name of CYDW-100.

[0035] Preparation Example 1

[0036] The preparation method of modified 2-carboxyethyl acrylate-1 comprises the following steps: adding 11 g of 2-hydroxy-3-methoxy-5-vinyl benzoic acid, 2 g of pentaerythritol phosphate and 5 ml of 75 wt% phosphoric acid into 100 ml of DMF, reacting at 75° C. for 7.5 h, adding 10 g of 2-carboxyethyl acrylate, reacting at 75° C. for 7.5 h, and rotary evaporating to obtain modified 2-carboxyethyl acrylate-1.

[0037] Preparation Example 2

[0038] The preparation method of modified 2-carboxyethyl acrylate-2 is the same as that of Preparation Example 1, except that the amount of 2-hydroxy-3-methoxy-5-vinylbenzoic acid added is 14 g.

[0039] Preparation Example 3

[0040] The preparation method of modified 2-carboxyethyl acrylate-3 is the same as that of Preparation Example 1, except that the amount of pentaerythritol phosphate added is 4 g.

[0041] Preparation Example 4

[0042] The preparation method of PMMA emulsion-1 comprises the following steps:

[0043] (1) Add 2 g of polyvinyl pyrrolidone to 100 ml of 85 wt% ethanol solution, stir for 25 min, then add a mixture of 20 g of styrene, 16 g of methyl methacrylate, 8 g of N-methylacrylamide, and 6 g of hydroxyethyl methacrylate, stir at 550 r / min for 15 min at room temperature, then heat to 55° C., add 0.1 g of azobisisobutyronitrile, react for 1.5 h, cool to room temperature, emulsify at 1800 r / min for 2 min, and obtain a core layer emulsion;

[0044] (2) 5 g of 2-hydroxyethyl acrylate, 1 g of modified 2-carboxyethyl acrylate, 3 g of ethylene glycol dimethacrylate and 0.3 g of epoxy resin were added to 30 ml of 85 wt% ethanol solution, and stirred at 350 r / min for 25 min at room temperature to obtain a shell emulsion. The temperature was then raised to 75° C., 0.01 g of sodium persulfate was added, and 150 g of the core emulsion obtained in step (1) was added dropwise while stirring at a dropping speed of 5 g / min. After the addition was completed, the reaction was allowed to proceed for 11 h to obtain PMMA emulsion-1. The particle sizes tested were: D(10)=1.412 μm, D(50)=2.379 μm, D(90)=3.932 μm, and D(99)=5.540 μm.

[0045] Preparation Example 5

[0046] The preparation method of PMMA emulsion-2, the specific implementation method is the same as that of Preparation Example 4, except that the amount of methyl methacrylate added is 12g, and the tested particle size is: D(10)=1.102μm, D(50)=2.413μm, D(90)=3.899μm, D(99)=5.327μm.

[0047] Preparation Example 6

[0048] The preparation method of PMMA emulsion-3, the specific implementation method is the same as that of Preparation Example 4, except that the added amount of N-methyl acrylamide is 4g, and the tested particle size is: D(10)=1.452μm, D(50)=2.138μm, D(90)=3.821μm, D(99)=5.492μm.

[0049] Preparation Example 7

[0050] The preparation method of PMMA emulsion-4, the specific implementation method is the same as that of Preparation Example 4, except that the added amount of hydroxyethyl methacrylate is 2g, and the tested particle size is: D(10)=1.232μm, D(50)=2.495μm, D(90)=3.671μm, D(99)=5.725μm.

[0051] Preparation Example 8

[0052] The preparation method of PMMA emulsion-5, the specific implementation method is the same as that of Preparation Example 4, the difference is that the modified 2-carboxyethyl acrylate-1 is replaced by modified 2-carboxyethyl acrylate-2 in equal amounts, and the tested particle sizes are: D(10)=1.401μm, D(50)=2.889μm, D(90)=4.786μm, D(99)=5.967μm.

[0053] Preparation Example 9

[0054] The preparation method of PMMA emulsion-6, the specific implementation method is the same as that of Preparation Example 4, the difference is that the modified 2-carboxyethyl acrylate-1 is replaced by modified 2-carboxyethyl acrylate-3 in equal amounts, and the tested particle sizes are: D(10)=1.401μm, D(50)=2.419μm, D(90)=3.906μm, D(99)=5.508μm.

[0055] Preparation Example 10

[0056] The preparation method of PMMA emulsion-7, the specific implementation method is the same as that of Preparation Example 4, the difference is that the added amount of modified 2-carboxyethyl acrylate-1 is 2g, and the tested particle size is: D(10)=1.482μm, D(50)=2.203μm, D(90)=3.771μm, D(99)=5.813μm.

[0057] Preparation Example 11

[0058] The preparation method of PMMA emulsion, the specific implementation method is the same as that of Preparation Example 4, except that the modified 2-carboxyethyl acrylate-1 is replaced by 2-carboxyethyl acrylate in an equal amount, and the tested particle size is: D(10)=1.3968μm; D(50)=2.413μm, D(90)=3.781μm, D(99)=5.501μm.

[0059] Preparation Example 12

[0060] The preparation method of modified ceramic powder-1 comprises the following steps: adding 10g ceramic powder and 5g KH570 into anhydrous ethanol, reacting at 75°C for 5.5h, then adding 5g polyethylene glycol monoallyl ether and 0.1g azobisisobutyronitrile, and continuing the reaction for 1.5h to obtain modified ceramic powder-1.

[0061] Preparation Example 13

[0062] The preparation method of modified ceramic powder-2 is the same as that of Preparation Example 12, except that the amount of polyethylene glycol monoallyl ether added is 8 g.

[0063] Example 1

[0064] A flame retardant PMMA adhesive comprises the following raw materials, measured in parts by weight: 1-45 parts of PMMA emulsion and 1-2 parts of modified ceramic powder.

[0065] The method for preparing the flame-retardant PMMA adhesive in this embodiment comprises the following steps: adding the modified ceramic powder-1 into the PMMA emulsion-1 in 4 portions and stirring at 65° C. for 60 minutes to obtain the flame-retardant PMMA adhesive.

[0066] Example 2

[0067] A flame retardant PMMA adhesive comprises the following raw materials, measured in parts by weight: 1-40 parts of PMMA emulsion and 1-1 parts of modified ceramic powder.

[0068] The method for preparing the flame-retardant PMMA adhesive in this embodiment comprises the following steps: adding the modified ceramic powder-1 into the PMMA emulsion-1 in 4 portions and stirring at 60° C. for 70 minutes to obtain the flame-retardant PMMA adhesive.

[0069] Example 3

[0070] A flame retardant PMMA adhesive comprises the following raw materials, measured in parts by weight: 150 parts of PMMA emulsion and 13 parts of modified ceramic powder.

[0071] The method for preparing the flame-retardant PMMA adhesive in this embodiment comprises the following steps: adding the modified ceramic powder-1 into the PMMA emulsion-1 in 4 portions and stirring at 65° C. for 50 minutes to obtain the flame-retardant PMMA adhesive.

[0072] Example 4

[0073] A flame retardant PMMA adhesive and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that an equal amount of PMMA emulsion-1 is replaced by PMMA emulsion-2.

[0074] Example 5

[0075] A flame retardant PMMA adhesive and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that an equal amount of PMMA emulsion-1 is replaced by PMMA emulsion-3.

[0076] Example 6

[0077] A flame retardant PMMA adhesive and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that an equal amount of PMMA emulsion-1 is replaced by PMMA emulsion-4.

[0078] Example 7

[0079] A flame retardant PMMA adhesive and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that an equal amount of PMMA emulsion-1 is replaced by PMMA emulsion-5.

[0080] Example 8

[0081] A flame retardant PMMA adhesive and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that an equal amount of PMMA emulsion-1 is replaced by PMMA emulsion-6.

[0082] Example 9

[0083] A flame retardant PMMA adhesive and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that an equal amount of PMMA emulsion-1 is replaced by PMMA emulsion-7.

[0084] Example 10

[0085] A flame retardant PMMA adhesive and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that an equal amount of modified ceramic powder-1 is replaced by modified ceramic powder-2.

[0086] Embodiment 11

[0087] A flame retardant PMMA adhesive and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that an equal amount of PMMA emulsion-1 is replaced by PMMA emulsion.

[0088] Comparative Example 1

[0089] A flame retardant PMMA adhesive and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that an equal amount of modified ceramic powder-1 is replaced by ceramic powder.

[0090] Performance Testing

[0091] A polypropylene microporous membrane with a thickness of 25 μm was corona pretreated at a machine speed of 30 m / min, a corona power of 500 w, and a corona voltage of 6 kV to obtain a base membrane. The adhesive prepared in each embodiment and comparative example was coated on the pretreated side of the base membrane by a coater with a coating thickness of 5 μm. The membrane was then dried at 80° C. for 7 h to obtain a diaphragm sample.

[0092] 1. Flame retardancy

[0093] The limiting oxygen index of the diaphragm sample was determined with reference to GB / T 2406.1-2008.

[0094] 2. Peel strength

[0095] Cut a sample with a width of 25 mm and a length of 180 mm along the mechanical direction (MD) of the diaphragm; adhere the adhesive side of the sample to the steel bar, lightly press the bonding surface, the effective bonding length is 60 mm, and test the peel strength with a universal testing machine at a tensile speed of 100 mm / min. Test three times in parallel and take the average value.

[0096] 3. Heat shrinkage

[0097] Cut the diaphragm sample into 120mm×120mm specimens, draw a 100mm×100mm midline along the center line of the opposite side; place the diaphragm at 150℃ for 2 hours, then place it at room temperature for 10 minutes, and measure the length L of the midline after heat shrinkage f and W f, calculate the mechanical direction (β MD ) and transverse (β TD ) shrinkage; test 3 times in parallel and take the average value. The calculation formula is as follows:

[0098] β MD =(1-L f / 100)×100%;

[0099] β TD =(1-W f / 100)×100%.

[0100] 4. Breathability

[0101] The air permeability of the membrane sample was tested using a Gurley tester, the test gas was air, and the gas volume was 100 ml.

[0102] The test results are shown in Table 1.

[0103] Table 1

[0104]

[0105] By comparing the experimental data of Examples 1-3 in Table 1, it can be seen that the diaphragm prepared by the PMMA binder has good flame retardancy, small heat shrinkage and high bonding strength; by comparing Examples 4, 5 and 6 with Example 1, it can be seen that the change in the ratio of styrene, methyl methacrylate, N-methylacrylamide and hydroxyethyl methacrylate leads to a change in the particle size of PMMA microspheres, and all the properties of the diaphragm are reduced; by comparing Examples 7 and 8 with Example 1, it can be seen that the change in the ratio of 2-hydroxy-3-methoxy-5-vinylbenzoic acid, pentaerythritol phosphate and 2-carboxyethyl acrylate leads to a decrease in the particle size of PMMA microspheres, and all the properties of the diaphragm are reduced. The uniformity of the particle size of PMMA microspheres decreases, and the air permeability of the diaphragm decreases. By comparing Example 9 with Example 1, it can be seen that the ratio of 2-hydroxyethyl acrylate, modified 2-carboxyethyl acrylate and ethylene glycol dimethacrylate changes, resulting in decreased air permeability and peel strength of the diaphragm. By comparing Example 10 with Example 1, it can be seen that the ratio of ceramic powder to polyethylene glycol monoallyl ether changes, and the peel strength of the adhesive decreases. By comparing Example 11, Comparative Example 1 and Example 1, it can be seen that when PMMA emulsion and ceramic powder are directly used, the performance of the diaphragm is reduced.

[0106] 5. Electrochemical performance

[0107] The separators prepared by the binders of Examples 1-3 and commercially available PP battery separators were used in lithium-ion batteries for testing. The electrode and electrolyte compositions of the 2032-type battery were as follows: positive electrode: LiCoO 2 , electrolyte: LiPF 6 / EC / DMC, negative electrode: graphite, charge / discharge rate is 0.5C / 0.5C, after 100 cycles, the battery specific capacity and capacity retention rate are tested.

[0108] The test results are shown in Table 2.

[0109] Table 2

[0110] Group Specific capacity mAh / g Capacity retention rate % Example 1 128 95 Example 2 125 94 Example 3 127 95 Commercially available PP battery separator 102 80

[0111] It can be seen from the data in Table 2 that when the separator prepared by the binder obtained in the present invention is used in a lithium ion battery, the battery can have good cycle performance and a long battery life.

[0112] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A flame retardant PMMA adhesive, characterized in that: The invention comprises the following raw materials in parts by weight: 40-50 parts of PMMA emulsion and 1-3 parts of modified ceramic powder.

2. The flame retardant PMMA adhesive according to claim 1, characterized in that: The preparation method of the PMMA emulsion comprises the following steps: (1) adding polyvinyl pyrrolidone to an 80-90 wt% ethanol solution, stirring for 20-30 min, then adding a mixed solution of styrene, methyl methacrylate, N-methylacrylamide, and hydroxyethyl methacrylate, stirring at 500-600 r / min for 10-15 min at room temperature, then heating to 50-60° C., adding azobisisobutyronitrile, reacting for 1-2 h, cooling to room temperature, and emulsifying at 1500-2000 r / min for 1-3 min to obtain a core layer emulsion; (2) Add 2-hydroxyethyl acrylate, modified 2-carboxyethyl acrylate, ethylene glycol dimethacrylate and epoxy resin to an 80-90 wt% ethanol solution, stir at 300-400 r / min for 20-30 min at room temperature to obtain a shell emulsion, then heat to 70-80° C., add sodium persulfate, and dropwise add the core emulsion obtained in step (1) while stirring. After the dropwise addition is completed, react for 10-12 hours to obtain a PMMA emulsion.

3. The flame retardant PMMA adhesive according to claim 2, characterized in that: The mass ratio of styrene, methyl methacrylate, N-methylacrylamide and hydroxyethyl methacrylate in step (1) is 1: (0.7-0.9): (0.3-0.5): (0.2-0.4).

4. The flame retardant PMMA adhesive according to claim 2, characterized in that: The preparation method of the modified 2-carboxyethyl acrylate described in step (2) comprises the following steps: adding 2-hydroxy-3-methoxy-5-vinylbenzoic acid, pentaerythritol phosphate and phosphoric acid to DMF, reacting at 70-80° C. for 7-8 hours, then adding 2-carboxyethyl acrylate, reacting at 70-80° C. for 7-8 hours, and rotary evaporating to obtain modified 2-carboxyethyl acrylate.

5. The flame retardant PMMA adhesive according to claim 4, characterized in that: The mass ratio of the 2-hydroxy-3-methoxy-5-vinylbenzoic acid, pentaerythritol phosphate and 2-carboxyethyl acrylate is (1-1.2):(0.1-0.3):

1.

6. The flame retardant PMMA adhesive according to claim 2, characterized in that: The mass ratio of 2-hydroxyethyl acrylate, modified 2-carboxyethyl acrylate and ethylene glycol dimethacrylate in step (2) is 1:(0.1-0.3):(0.5-0.7).

7. The flame retardant PMMA adhesive according to claim 1, characterized in that: The preparation method of the modified ceramic powder comprises the following steps: adding ceramic powder and KH570 into ethanol, reacting at 70-80° C. for 5-6 hours, then adding polyethylene glycol monoallyl ether and azobisisobutyronitrile, and continuing the reaction for 1-2 hours to obtain the modified ceramic powder.

8. The flame retardant PMMA adhesive according to claim 7, characterized in that: The mass ratio of the ceramic powder to polyethylene glycol monoallyl ether is (0.4-0.6):

1.

9. A method for preparing the flame-retardant PMMA adhesive according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: adding the modified ceramic powder into PMMA in 3-4 times and stirring at 60-70° C. for 50-70 minutes to obtain the product.

10. Use of the PMMA adhesive obtained by the preparation method of the flame-retardant PMMA adhesive according to any one of claims 1 to 8 or the flame-retardant PMMA adhesive according to claim 9 in lithium battery separators.

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