Modified lithium battery diaphragm material and preparation method thereof

Abstract

The invention provides application of a monomer containing unsaturated double bonds in a modified PP diaphragm. The monomer containing unsaturated double bonds has a structure as shown in a formula (I). The invention also provides a modified lithium battery diaphragm material and a preparation method thereof, the polymer coating containing the carboxyl functional group is deposited on the surface of the modified PP diaphragm, so that higher lithium ion transference number can be achieved, and the mechanical strength of the diaphragm can also be improved. According to the invention, the low-cost polar functional group-containing monomer is taken as a raw material and is combined with a vapor phase chemical deposition technology to obtain the modified PP diaphragm with good electrochemical performance, and when the material is taken as the lithium iron phosphate battery diaphragm, a lithium iron phosphate battery can stably circulate for 1000 circles, the reversible capacity is about 90mAh / g, and the capacity retention rate is about 85% under the condition of high multiplying power of 10C. The modification method provided by the invention is simple, low in cost, low in equipment investment and suitable for batch production. # imgabs0 #

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery separators, and relates to the application of monomers containing unsaturated double bonds in modified PP separators, a modified lithium battery separator and its preparation method, and applications, and particularly relates to a modified lithium battery separator material and its preparation method. Background Art

[0002] With the increasingly serious environmental problems, people expect that electric vehicles equipped with suitable storage systems can replace internal combustion engine vehicles to solve the global warming problem related to carbon dioxide. Compared with other rechargeable batteries, lithium-ion batteries have the characteristics of high energy density, excellent cycling performance, low self-discharge rate, etc., and have been widely used in the consumer electronics field. However, the growth of lithium dendrites and the formation of an unstable solid electrolyte interface (SEI) film affect the development of lithium batteries. Among them, lithium dendrites seriously affect the safety and cycling stability of lithium batteries. On the one hand, dendrites will pierce the separator, causing battery short circuit. On the other hand, dendrites will break off from the anode and form "dead lithium", resulting in a decrease in Coulomb efficiency (CE) and capacity. These problems have seriously hindered the large-scale and commercial development of rechargeable lithium batteries.

[0003] The separator is one of the most important components in a lithium-ion battery. During the entire charging and discharging process, the separator can separate the positive and negative electrodes to prevent internal short circuit of the battery; provide a channel for the migration of lithium ions on both sides of the separator; the separator of a lithium-ion battery is also an important component that determines the performance and safety of the battery. Polyolefin separators have been widely commercialized due to their excellent chemical stability, low cost, etc. However, currently commercially available polypropylene separators (PP), polyethylene separators (PE), and three-layer PP / PE / PP composite separators have many defects in practical applications, such as poor wettability, poor thermal stability, etc. The separator plays an important role in the industrial application of lithium-ion batteries, but there is still much room for improvement in terms of improving the safety, electrochemical performance, and lifespan of lithium-ion batteries. The above-mentioned properties of the separator can be improved by physical or chemical methods. In order to improve the transport performance of lithium ions, separators coated with nanoceramics or polymers have been proposed in the industry. However, these modified separators usually do not simultaneously have excellent ionic conductivity and a high lithium ion transference number because the coating will reduce the porosity of the separator and reduce the ionic conductivity. In addition, a thicker coating will result in a high resistance and reduce the power density of the lithium-ion battery.

[0004] Therefore, how to design a more suitable separator for lithium-ion batteries to solve the above problems existing in the existing lithium-ion battery separators has become one of the focuses widely concerned by many front-line scientific researchers in the field. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide the application of monomers containing unsaturated double bonds in modified PP diaphragms, a modified lithium battery diaphragm and its preparation method and application, especially a modified lithium battery diaphragm material. The present invention specifically designs monomers containing unsaturated double bonds with the structure of formula (I) to modify PP diaphragms. The modified PP diaphragms have excellent lithium ion transference numbers and mechanical strengths, and the affinity with electrolytes is judged by the surface contact angle between the modified PP diaphragms and commercial electrolytes. Moreover, the preparation method is simple and easy to implement, low in cost, mild in conditions, strong in controllability, good in stability, and more conducive to the popularization and application of industrial production.

[0006] The present invention provides the application of monomers containing unsaturated double bonds in modified PP diaphragms;

[0007] The monomers containing unsaturated double bonds have the structure shown in formula (I);

[0008]

[0009] Among them, R1 to R3 are each independently selected from C1 - C 50 alkyl groups, C1 - C 50 cycloalkyl groups, C2 - C 50 alkenyl groups, C2 - C 50 alkynyl groups, C6 - C 50 aryl groups, groups shown in formula (II) or (III);

[0010]

[0011] Among them, R4 to R7 are each independently selected from C1 - C 50 alkyl groups.

[0012] Preferably, the monomers containing unsaturated double bonds are specifically monomers containing polar functional groups;

[0013] The polar functional groups include carboxyl groups and / or amino groups;

[0014] The application is specifically the application of monomers containing unsaturated double bonds in improving the surface contact angle between PP diaphragms and electrolytes;

[0015] The modified PP diaphragms include modified lithium ion PP diaphragms.

[0016] Preferably, the monomers containing unsaturated double bonds have the structures shown in formula (IV), formula (V) or formula (VI);

[0017]

[0018] The modified PP separator is specifically a polymer coating formed by cross-linking monomers containing unsaturated double bonds on the PP separator;

[0019] The polymer coating is formed by in-situ cross-linking on the surface of the PP separator.

[0020] The present invention provides a modified lithium battery separator, comprising: a PP separator and a polymer coating formed by in-situ cross-linking on the surface of the PP separator;

[0021] The monomer of the polymer coating formed by in-situ cross-linking is a monomer containing an unsaturated double bond having the structure shown in formula (I);

[0022]

[0023] Wherein, R1 to R3 are each independently selected from C1 to C 50 alkyl groups, C1 to C 50 cycloalkyl groups, C2 to C 50 alkenyl groups, C2 to C 50 alkynyl groups, C6 to C 50 aryl groups, groups shown in formula (II) or (III);

[0024]

[0025] Wherein, R4 to R7 are each independently selected from C1 to C 50 alkyl groups.

[0026] Preferably, the thickness of the polymer coating is 1 to 500 nm;

[0027] There is an inter-crosslinked structure between the polymer coating and the PP separator;

[0028] The method for in-situ cross-linking to form the polymer coating includes the initiated chemical vapor deposition method.

[0029] The present invention provides a method for preparing a modified lithium battery separator, comprising the following steps:

[0030] 1) Place the PP separator in an iCVD reaction chamber equipped with a hot wire as a substrate, introduce the evaporated monomer gas, cross-linking agent gas and initiator gas into the vacuum reaction chamber, and perform chemical vapor deposition and initiate a polymerization reaction on the substrate to obtain a modified lithium battery separator;

[0031] The monomer is a monomer containing an unsaturated double bond having the structure shown in formula (I);

[0032]

[0033] Wherein, R1 to R3 are each independently selected from C1 to C 50alkyl groups of C1-C 50 cycloalkyl groups of C2-C 50 alkenyl groups of C2-C 50 alkynyl groups of C2-C 50 aryl groups, or groups represented by formula (II) or (III);

[0034]

[0035] wherein, R4 to R7 are each independently selected from C1-C 50 alkyl groups.

[0036] Preferably, the hot wire is specifically a hot wire array;

[0037] Before the gas is introduced into the vacuum reaction chamber, the vacuum pressure of the vacuum reaction chamber is 15-30 mTorr;

[0038] The evaporation temperature of the monomer gas is 30-80 °C;

[0039] The flow rate of the monomer gas is 2-5 sccm.

[0040] Preferably, the crosslinking agent includes one or more of 1,4-butanediol diacrylate, ethylene glycol dimethacrylate, ethylene glycol diacetate, and hexafluorobutyl acrylate;

[0041] The evaporation temperature of the crosslinking agent gas is 40-80 °C;

[0042] The flow rate of the crosslinking agent gas is 0.05-0.1 sccm;

[0043] The initiator includes one or more of di-tert-butyl peroxide, tributyl phosphate, and benzoyl peroxide;

[0044] The evaporation temperature of the initiator gas is 20-40 °C;

[0045] The flow rate of the initiator gas is 0.2-0.8 sccm.

[0046] Preferably, the initiator gas is decomposed after being pyrolyzed by the hot wire, and then deposited on the substrate to initiate a polymerization reaction;

[0047] The temperature of the hot wire is 200-250 °C;

[0048] After the gas is introduced into the vacuum reaction chamber, the pressure during the polymerization reaction in the vacuum reaction chamber is 200-300 mTorr.

[0049] The present invention also provides the application of the modified PP diaphragm in the application described in any one of the above technical solutions, the modified lithium battery diaphragm described in any one of the above technical solutions, or the modified lithium battery diaphragm prepared by the preparation method described in any one of the above technical solutions in lithium iron phosphate batteries.

[0050] The present invention provides the use of a monomer containing an unsaturated double bond in a modified PP diaphragm; the monomer containing an unsaturated double bond has a structure shown in formula (I). Compared with the prior art, the present invention specifically designs a monomer containing an unsaturated double bond with a specific structure and element composition, and uses it to modify the PP diaphragm to obtain a modified PP diaphragm. The coating on the surface of the modified PP diaphragm provided by the present invention retains the pores of the substrate and introduces a carboxyl functional group with a lone pair of electrons that can react with PF6 - Hydrogen bonds are formed between them to reduce the PF6 - The concentration of Li around the diaphragm is helpful to improve the rate performance. + The concentration will increase and the attraction between positive and negative charges will accelerate the Li + The flux is increased, and the cross-linked polymer coating also increases the mechanical strength of the diaphragm. The present invention deposits a polymer coating containing carboxyl functional groups on the surface of the PP diaphragm to have a higher lithium ion migration number, and the mechanical strength of the diaphragm can also be improved. The modified PP diaphragm has excellent lithium ion migration number and mechanical strength. In addition, the present invention can also judge the affinity with the electrolyte by the surface contact angle between the modified PP diaphragm and the commercial electrolyte.

[0051] The present invention provides a modification process for modifying the material of a lithium battery separator, using cheap polar functional group-containing monomers as raw materials, combined with vapor phase chemical deposition technology, to obtain a modified PP separator with good electrochemical properties. The modification method provided by the present invention is simple, low in cost, requires little equipment investment, and is more suitable for large-scale mass production.

[0052] The present invention also provides the application of modified lithium battery diaphragm materials. The diaphragm can be used as a lithium iron phosphate battery diaphragm to prevent lithium dendrites from piercing the diaphragm and affecting the battery cycle life, ensuring that the lithium iron phosphate battery will not be affected by the low mechanical strength and poor wettability of the PP diaphragm to a certain extent. Under high rate 10C conditions, the lithium iron phosphate battery can stably cycle 1000 times, the reversible capacity is about 90mAh / g, and the capacity is maintained at 85%. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 FT-IR image of the modified PP diaphragm prepared in Example 1 of the present invention;

[0054] Figure 2SEM diagram of the modified separator prepared in Example 1 of the present invention;

[0055] Figure 3 Charge-discharge cycle diagram of the lithium iron phosphate battery with the separator prepared in Example 1 of the present invention as the separator of the lithium iron phosphate battery at room temperature with a rate of 10C;

[0056] Figure 4 Rate performance diagram of the separator prepared in Example 1 of the present invention as the separator of the lithium iron phosphate battery;

[0057] Figure 5 Surface contact angle detection diagram of the modified PP separator prepared in the present invention and commercial electrolyte. Detailed implementation mode

[0058] To further understand the present invention, the preferred implementation modes of the present invention will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention rather than limiting the claims of the present invention.

[0059] For all raw materials of the present invention, there is no particular limitation on their sources, and they can be purchased on the market or prepared by conventional methods well-known to those skilled in the art.

[0060] For all raw materials of the present invention, there is no particular limitation on their purity. The present invention preferably uses analytical pure or the purity conventional in the field of lithium ion battery separator materials.

[0061] The present invention provides the application of monomers containing unsaturated double bonds in the modified PP separator.

[0062] The monomer containing unsaturated double bonds has the structure shown in formula (I).

[0063]

[0064] Among them, R1 to R3 are each independently selected from C1 to C 50 alkyl, C1 to C 50 cycloalkyl, C2 to C 50 alkenyl, C2 to C 50 alkynyl, C6 to C 50 aryl, the group shown in formula (II) or (III);

[0065]

[0066] Among them, R4 to R7 are each independently selected from C1 to C 50 alkyl.

[0067] In the present invention, the R1 to R3 are each independently selected from C1 to C 50alkyl group of C1-C 50 cycloalkyl group of C2-C 50 alkenyl group of C2-C 50 alkynyl group of C6-C 50 aryl group, group represented by formula (II) or (III), may be C 10 -C 40 alkyl group of C 10 -C 40 cycloalkyl group of C 10 -C 40 alkenyl group of C 10 -C 40 alkynyl group of C 10 -C 40 aryl group, group represented by formula (II) or (III), may be C 20 -C 30 alkyl group of C 20 -C 30 cycloalkyl group of C 20 -C 30 alkenyl group of C 20 -C 30 alkynyl group of C 20 -C 30 aryl group, group represented by formula (II) or (III).

[0068] In the present invention, R4-R7 are each independently selected from C1-C 50 alkyl group, may be C 10 -C 40 alkyl group, may be C 20 -C 30 alkyl group.

[0069] In the present invention, the monomer containing an unsaturated double bond is specifically preferably a monomer containing a polar functional group.

[0070] In the present invention, the polar functional group preferably includes a carboxyl group and / or an amino group, and more preferably a carboxyl group or an amino group.

[0071] In the present invention, the application is specifically preferably the application of the monomer containing an unsaturated double bond in improving the surface contact angle between the PP separator and the electrolyte.

[0072] In the present invention, the modified PP separator preferably includes a modified lithium-ion PP separator.

[0073] In the present invention, the monomer containing an unsaturated double bond preferably has a structure represented by formula (IV), formula (V) or formula (VI).

[0074]

[0075] In the present invention, the modified PP separator is specifically preferably a polymer coating formed by crosslinking a monomer containing an unsaturated double bond on the PP separator.

[0076] In the present invention, the polymer coating is preferably formed by in-situ crosslinking on the surface of the PP separator.

[0077] The present invention provides a modified lithium battery separator, comprising: a PP separator and a polymer coating formed by in-situ crosslinking on the surface of the PP separator.

[0078] In the present invention, the monomer of the polymer coating formed by in-situ crosslinking is preferably a monomer containing an unsaturated double bond having the structure shown in formula (I).

[0079]

[0080] Among them, R1 to R3 are each independently selected from alkyl groups of C1 to C 50 alkyl, cycloalkyl of C1 to C 50 cycloalkyl, alkenyl of C2 to C 50 alkenyl, alkynyl of C2 to C 50 alkynyl, aryl of C6 to C 50 aryl, or a group represented by formula (II) or (III);

[0081]

[0082] Among them, R4 to R7 are each independently selected from alkyl groups of C1 to C 50 alkyl.

[0083] Specifically, R1 to R3 are each independently preferably selected from alkyl groups of C1 to C 50 alkyl, cycloalkyl of C1 to C 50 cycloalkyl, alkenyl of C2 to C 50 alkenyl, alkynyl of C2 to C 50 alkynyl, aryl of C6 to C 50 aryl, or a group represented by formula (II) or (III), more preferably C 10 ~C 40 alkyl, C 10 ~C 40 cycloalkyl, C 10 ~C 40 alkenyl, C 10 ~C 40 alkynyl, C 10 ~C 40 aryl, or a group represented by formula (II) or (III), more preferably C 20 ~C 30 alkyl, C 20 ~C 30 cycloalkyl, C 20 ~C30 an alkenyl group having C 20 to C 30 an alkynyl group having C 20 to C 30 an aryl group having C, or a group represented by formula (II) or (III).

[0084] In the present invention, each of R4 to R7 is independently preferably selected from an alkyl group having C1 to C 50 preferably being an alkyl group having C 10 to C 40 preferably being an alkyl group having C 20 to C 30 an alkyl group having C.

[0085] In the present invention, the thickness of the polymer coating is preferably 1 to 500 nm, more preferably 10 to 400 nm, still more preferably 30 to 200 nm, and even more preferably 50 to 150 nm.

[0086] In the present invention, the polymer coating and the PP separator preferably have a crosslinked structure with each other.

[0087] In the present invention, the method for in-situ crosslinking to form the polymer coating preferably includes the initiated chemical vapor deposition method.

[0088] The present invention provides a method for preparing a modified lithium battery separator, comprising the following steps:

[0089] 1) Placing a PP separator in an iCVD reaction chamber equipped with a hot wire as a substrate, introducing the evaporated monomer gas, crosslinking agent gas, and initiator gas into the vacuum reaction chamber, and performing chemical vapor deposition on the substrate to initiate a polymerization reaction to obtain a modified lithium battery separator;

[0090] The monomer is a monomer containing an unsaturated double bond having the structure shown in formula (I);

[0091]

[0092] wherein, each of R1 to R3 is independently selected from an alkyl group having C1 to C 50 an alkyl group having C1 to C 50 a cycloalkyl group having C2 to C 50 an alkenyl group having C2 to C 50 an alkynyl group having C2 to C 50 an aryl group having C6 to C, or a group represented by formula (II) or (III);

[0093]

[0094] wherein, each of R4 to R7 is independently selected from an alkyl group having C1 to C 50 an alkyl group having C.

[0095] In the present invention, the hot wire is preferably a hot wire array.

[0096] In the present invention, before the gas is introduced into the vacuum reaction chamber, the vacuum pressure of the vacuum reaction chamber is preferably 15-30 mTorr, more preferably 18-27 mTorr, and even more preferably 21-24 mTorr.

[0097] In the present invention, the evaporation temperature of the monomer gas is preferably 30-80 °C, more preferably 40-70 °C, and even more preferably 50-60 °C.

[0098] In the present invention, the flow rate of the monomer gas is preferably 2-5 sccm, more preferably 2.5-4.5 sccm, and even more preferably 3-4 sccm.

[0099] In the present invention, the crosslinking agent preferably includes one or more of 1,4-butanediol diacrylate, ethylene glycol dimethacrylate, ethylene glycol diacetate, and hexafluorobutyl acrylate, and more preferably 1,4-butanediol diacrylate (BDDA), ethylene glycol dimethacrylate (EGDMA), ethylene glycol diacetate (EGDA), or hexafluorobutyl acrylate (HFBA).

[0100] In the present invention, the evaporation temperature of the crosslinking agent gas is preferably 40-80 °C, more preferably 45-75 °C, even more preferably 50-70 °C, and even more preferably 55-65 °C. Specifically, it can be 60 °C.

[0101] In the present invention, the flow rate of the crosslinking agent gas is preferably 0.05-0.1 sccm, more preferably 0.06-0.09 sccm, and even more preferably 0.07-0.08 sccm.

[0102] In the present invention, the initiator preferably includes one or more of di-tert-butyl peroxide, tributyl phosphate, and benzoyl peroxide, and more preferably di-tert-butyl peroxide, tributyl phosphate, or benzoyl peroxide. Specifically, it can be tributyl phosphate.

[0103] In the present invention, the evaporation temperature of the initiator gas is preferably 20-40 °C, more preferably 22-38 °C, even more preferably 25-35 °C, and even more preferably 27-33 °C. Specifically, it can be 30 °C.

[0104] In the present invention, the flow rate of the initiator gas is preferably 0.2-0.8 sccm, more preferably 0.3-0.7 sccm, and even more preferably 0.4-0.6 sccm.

[0105] In the present invention, the initiator gas is preferably decomposed by pyrolysis through the hot wire, and then deposited on the substrate to initiate a polymerization reaction.

[0106] In the present invention, the temperature of the hot wire is preferably 200 - 250 °C, more preferably 210 - 240 °C, and even more preferably 220 - 230 °C.

[0107] In the present invention, after the gas is introduced into the vacuum reaction chamber, the pressure during the polymerization reaction in the vacuum reaction chamber is preferably 200 - 300 mTorr, more preferably 220 - 280 mTorr, and even more preferably 240 - 260 mTorr.

[0108] The present invention provides the application of the modified PP separator in the application described in any one of the above technical solutions, the modified lithium battery separator described in any one of the above technical solutions, or the modified lithium battery separator prepared by the preparation method described in any one of the above technical solutions in a lithium iron phosphate battery.

[0109] In order to complete and refine the overall technical solution of the present invention, better ensure the structure and composition of the modified PP separator, and further improve the lithium ion transference number and mechanical strength of the modified PP separator, the application of the monomer containing an unsaturated double bond in the modified PP separator, a modified lithium battery separator material and its preparation method and application specifically may include the following content:

[0110] A material for a modified lithium battery separator and its modification process:

[0111] A material for a modified lithium battery separator specifically includes the following: screening the monomer of formula (I) containing an unsaturated double bond for modifying the PP separator.

[0112]

[0113] Among them, R1 - R3 are independently selected from alkyl groups of C1 - C 50 alkyl, cycloalkyl groups of C1 - C 50 alkenyl groups of C2 - C 50 alkynyl groups of C2 - C 50 aryl groups of C6 - C 50 or the groups shown in formula (II) and formula (II);

[0114]

[0115] From formula (I), the present invention screened monomers containing polar functional groups such as carboxyl and amino groups, and R4 - R7 are independently alkyl groups or other groups. Specifically, materials of formula (IV), formula (V), and formula (VI) are used to modify the PP separator.

[0116]

[0117]

[0118] The modification process of the material of the modified lithium battery separator provided by the present invention includes the following steps:

[0119] 1) The iCVD method is adopted, and the specific deposition process is as follows: The PP separator is placed into a customized iCVD reaction chamber equipped with an Ni80 / Cr20 filament (hot wire) array and the chamber is sealed, and the reaction chamber is evacuated to a vacuum environment of about 15 - 30 mTorr using a vacuum pump. During the deposition process, the precursor monomer, the crosslinking agent EGDA, and the initiator TBP are evaporated at 30 - 80 °C, 40 - 80 °C, and 30 - 60 °C respectively. A ball valve is used to control the introduction of the monomer and initiator vapors, and a needle valve is used to control the flow rate of the monomer and initiator vapors introduced;

[0120] 2) After the initiator TBP is introduced into the vacuum chamber, it will be cracked by the heated hot wire and rapidly decomposed into free radicals. Through thermocouple measurement, the temperature of the hot wire array is about 200 - 250 °C. A butterfly valve is used to adjust the pressure in the reaction chamber to keep it at 200 - 300 mTorr. Subsequently, the cooling circulating water is adjusted to control the substrate temperature to be maintained at about 25 - 35 °C. Due to the large temperature difference between the inside of the reaction chamber and the substrate, the generated free radicals, the monomer, and the crosslinking agent EGDA will be adsorbed on the separator together and a polymerization reaction will occur on its surface;

[0121] 3) The monomer flow rate is controlled at 2 - 5 sccm, the crosslinking agent flow rate is controlled at 0.05 - 0.1 sccm, and the initiator flow rate is controlled at 0.2 - 0.8 sccm. During the deposition process, an interference measurement system of a 633 nm He-Ne laser is used to monitor the coating thickness on the reference silicon wafer, and the thickness range is 50 - 150 nm.

[0122] Specifically, as the separator of the lithium iron phosphate battery, under the condition of a 10C rate, the lithium iron phosphate battery can stably cycle 1000 times, with a reversible capacity of about 90 mAh / g and a capacity retention rate of 85%.

[0123] The above content of the present invention provides the application of the monomer containing unsaturated double bonds in the modified PP separator, a modified lithium battery separator material and its preparation method, and application. The monomer containing unsaturated double bonds with a specific structure and element composition is specially designed by the present invention and is used to modify the PP separator to obtain the modified PP separator. The coating on the surface of the modified PP separator provided by the present invention, while retaining the pores of the substrate, introduces carboxyl functional groups with lone pair electrons, which can form hydrogen bond crosslinks with PF6 - to reduce the concentration of PF6 around the separator, which helps to improve the rate performance. At the same time, according to the principle of charge conservation, it can be known that the concentration of Li - around the separator will increase and through the mutual attraction between positive and negative charges, thereby accelerating Li + concentration will increase and through the mutual attraction between positive and negative charges, thereby accelerating Li+ The flux, and the crosslinked polymer coating also increases the mechanical strength of the separator. By depositing a polymer coating containing carboxyl functional groups on the surface of the PP separator, the present invention can have a higher lithium ion transference number, and the mechanical strength of the separator can also be improved. The modified PP separator has excellent lithium ion transference number and mechanical strength. Moreover, the present invention can also judge the affinity with the electrolyte by the surface contact angle between the modified PP separator and the commercial electrolyte.

[0124] The present invention provides a modification process of the material for the modified lithium battery separator. Using a cheap monomer containing polar functional groups as the raw material and combining with the gas phase chemical deposition technology, a modified PP separator with good electrochemical performance is obtained. The modification method provided by the present invention is simple, low in cost, and less in equipment investment, and is more suitable for large-scale batch production.

[0125] The present invention also provides the application of the modified lithium battery separator material. As the separator of the lithium iron phosphate battery, this separator can prevent lithium dendrites from piercing the separator and affecting the battery cycle life, ensuring that the lithium iron phosphate battery will not be affected by the low mechanical strength and poor wettability of the PP separator to a certain extent. Under the condition of a high rate of 10C, the lithium iron phosphate battery can stably cycle 1000 times, with a reversible capacity of about 90 mAh / g and a capacity retention of 85%.

[0126] To further illustrate the present invention, the following describes in detail the application of the monomer containing unsaturated double bonds in the modified PP separator, a modified lithium battery separator material and its preparation method, and the application provided by the present invention in combination with embodiments. However, it should be understood that these embodiments are implemented on the premise of the technical solution of the present invention, and the detailed implementation manners and specific operation processes are given. It is only to further illustrate the features and advantages of the present invention, rather than a limitation on the claims of the present invention. The protection scope of the present invention is not limited to the following embodiments.

[0127] In the examples, the monomer of formula (VI) is taken as an example in the present invention.

[0128] Example 1

[0129] A silicon wafer and the prepared PP film are used as substrates. During the deposition process, the precursors of the monomer, EGDA, and TBP are evaporated at 45 °C, 70 °C, and 35 °C respectively and introduced into the reactor. The flow rates of all precursors at different deposition stages are controlled by needle valves (Swagelok). The alloy wire array is heated to 250 °C to generate free radicals from the initiator (TBP) to initiate the polymerization reaction. The temperature of the sample stage is adjusted to 25 °C by the circulating water located on the back of the sample stage.

[0130] The modified PP separator prepared by the present invention is characterized and detected.

[0131] The thickness of the coating on the reference silicon wafer is monitored on-site by an interferometric measurement system, and a coating with a thickness of 50 nm is obtained according to the optical path difference calculation formula. After the deposition is completed, the ungrafted monomer branches are washed away with deionized water.

[0132] The obtained modified PP separator is subjected to Fourier transform infrared light (FT-IR) testing to detect the introduced functional groups ( Figure 1 ). See Figure 1 , Figure 1 for the FT-IR diagram of the modified PP separator prepared in Example 1 of the present invention.

[0133] The morphology of the material is observed by scanning electron microscopy (SEM), and the material maintains the maximum porosity ( Figure 2 ).

[0134] See Figure 2 , Figure 2 for the SEM diagram of the modified separator prepared in Example 1 of the present invention.

[0135] The prepared material is used as the separator of a lithium iron phosphate battery to improve the battery's electrochemical performance and cycling performance. Charge and discharge cycling are carried out under the condition of a rate of 10C. The lithium iron phosphate battery can stably cycle 1000 times, with a reversible capacity of about 90 mAh / g and a capacity retention of 85% ( Figure 3 ).

[0136] See Figure 3 , Figure 3 for the charge and discharge cycling diagram of the lithium iron phosphate battery with the separator prepared in Example 1 of the present invention as the separator under the condition of a rate of 10C at room temperature.

[0137] See Figure 4 , Figure 4 for the rate performance diagram of the separator prepared in Example 1 of the present invention as the separator of a lithium iron phosphate battery.

[0138] Under the same conditions of testing, the reversible capacity of the unmodified PP separator is only 80 mAh / g, which indicates that the modification method provided by the present invention helps to improve the rate performance.

[0139] Example 2

[0140] A silicon wafer and the prepared PP film are used as substrates. During the deposition process, the precursors of the monomer, EGDA, and TBP are evaporated and introduced into the reactor at 50 °C, 75 °C, and 40 °C respectively. The flow rates of all precursors at different deposition stages are controlled by needle valves (Swagelok). The alloy wire array is heated to 250 °C to generate free radicals from the initiator (TBP), thereby initiating the polymerization reaction. The temperature of the sample stage is adjusted to 25 °C by the circulating water located on the back of the sample stage.

[0141] The coating thickness on the reference silicon wafer is monitored on-site by an interferometric measurement system, and the coating thickness is obtained as 100 nm according to the optical path difference calculation formula.

[0142] The obtained modified PP separator is subjected to infrared spectroscopy analysis to detect the introduced functional groups; the morphology of the material is observed by scanning electron microscopy; the prepared material is used as a separator for lithium iron phosphate batteries, and the charge-discharge cycle performance of the lithium iron phosphate batteries is tested under the condition of 10C rate.

[0143] Example 3

[0144] Silicon wafers and the prepared PP films are used as substrates. During the deposition process, the precursors of the monomer, EGDA, and TBP are evaporated at 55 °C, 80 °C, and 45 °C respectively and introduced into the reactor. The flow rates of all precursors at different deposition stages are controlled by needle valves (Swagelok). The alloy wire array is heated to 250 °C to generate free radicals from the splitting initiator (TBP), thereby initiating the polymerization reaction. The tabletop temperature is adjusted to 25 °C by circulating water located on the back of the sample stage.

[0145] The coating thickness on the reference silicon wafer is monitored on-site by an interferometric measurement system, and a 150-nm coating is obtained according to the optical path difference calculation formula.

[0146] The obtained modified PP separator is subjected to infrared spectroscopy analysis to detect the introduced functional groups; the morphology of the material is observed by scanning electron microscopy; the prepared material is used as a separator for lithium iron phosphate batteries, and the charge-discharge cycle performance of the lithium iron phosphate batteries is tested under the condition of 10C rate.

[0147] The affinity with the electrolyte is judged by the surface contact angle between the modified PP separator and the commercial electrolyte, taking different cross-linking agents as examples. Among them, 1,4-butanediol diacrylate is BDDA, ethylene glycol dimethacrylate is EGDMA, ethylene glycol diacetate is EGDA, or hexafluorobutyl acrylate is HFBA. The commercial electrolyte is 1 M LiPF6 dissolved in EC:EMC:DMC (volume ratio 1:1:1).

[0148] See Figure 5 , Figure 5 This is the surface contact angle detection diagram of the modified PP separator prepared by the present invention and the commercial electrolyte.

[0149] The above has provided a detailed introduction to a modified lithium battery separator material and its preparation method according to the present invention. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention, including the best mode, and also enables any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention. The protection scope of the present invention patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to the literal description of the claims, or if they include equivalent structural elements that have no substantial difference from the literal description of the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. Application of monomers containing unsaturated double bonds in modified PP diaphragms; The monomer containing an unsaturated double bond has a structure shown in formula (I); in, R1 to R3 are each independently selected from C1 to C 50 Alkyl, C1~C 50 Cycloalkyl, C2~C 50 Alkenyl, C2~C 50 Alkynyl, C6~C 50 An aryl group, a group represented by formula (II) or (III); Wherein, R4 to R7 are each independently selected from C1 to C 50 of alkyl.

2. The use according to claim 1, characterized in that: The monomer containing an unsaturated double bond is specifically a monomer containing a polar functional group; The polar functional groups include carboxyl and / or amino groups; The application is specifically the application of a monomer containing an unsaturated double bond in improving the surface contact angle between a PP separator and an electrolyte; The modified PP separator includes a modified lithium ion PP separator.

3. The use according to claim 1, characterized in that: The monomer containing an unsaturated double bond has a structure as shown in formula (IV), formula (V) or formula (VI); The modified PP membrane is specifically a monomer containing unsaturated double bonds cross-linked on the PP membrane to form a polymer coating; The polymer coating is formed by in-situ cross-linking on the surface of the PP separator.

4. A modified lithium battery separator, characterized in that: include: A PP diaphragm and a polymer coating formed by in-situ cross-linking on the surface of the PP diaphragm; The monomer of the polymer coating formed by in-situ crosslinking is a monomer containing an unsaturated double bond having a structure shown in formula (I); Wherein, R1 to R3 are independently selected from C1 to C 50 Alkyl, C1~C 50 Cycloalkyl, C2~C 50 Alkenyl, C2~C 50 Alkynyl, C6~C 50 An aryl group, a group represented by formula (II) or (III); Wherein, R4 to R7 are independently selected from C1 to C 50 of alkyl.

5. The modified lithium battery separator according to claim 4, characterized in that: The thickness of the polymer coating is 1 to 500 nm; The polymer coating and the PP diaphragm have a cross-linked structure; The method for forming the polymer coating by in-situ cross-linking includes an initiated chemical vapor deposition method.

6. A method for preparing a modified lithium battery separator, characterized in that: The following steps are involved: 1) placing a PP separator in an iCVD reaction chamber equipped with a hot wire as a substrate, introducing evaporated monomer gas, crosslinker gas and initiator gas into the vacuum reaction chamber, performing chemical vapor deposition on the substrate and initiating a polymerization reaction to obtain a modified lithium battery separator; The monomer is a monomer containing an unsaturated double bond having a structure shown in formula (I); Wherein, R1 to R3 are independently selected from C1 to C 50 Alkyl, C1~C 50 Cycloalkyl, C2~C 50 Alkenyl, C2~C 50 Alkynyl, C6~C 50 An aryl group, a group represented by formula (II) or (III); Wherein, R4 to R7 are independently selected from C1 to C 50 of alkyl.

7. The preparation method according to claim 6, characterized in that: The hot wire is specifically a hot wire array; Before the gas is introduced into the vacuum reaction chamber, the vacuum pressure of the vacuum reaction chamber is 15-30 mTorr; The evaporation temperature of the monomer gas is 30 to 80°C; The flow rate of the monomer gas is 2-5 sccm.

8. The preparation method according to claim 6, characterized in that: The crosslinking agent includes one or more of 1,4-butanediol diacrylate, ethylene glycol dimethacrylate, ethylene glycol diacetate and hexafluorobutyl acrylate; The evaporation temperature of the crosslinking agent gas is 40 to 80°C; The flow rate of the cross-linking agent gas is 0.05 to 0.1 sccm; The initiator includes one or more of di-tert-butyl peroxide, tributyl phosphate and benzoyl peroxide; The evaporation temperature of the initiator gas is 20-40°C; The flow rate of the initiator gas is 0.2-0.8 sccm.

9. The preparation method according to claim 6, characterized in that: The initiator gas is decomposed after being cracked by the hot wire and then deposited on the substrate to initiate a polymerization reaction; The temperature of the hot wire is 200-250°C; After the gas is introduced into the vacuum reaction chamber, the pressure during the polymerization reaction in the vacuum reaction chamber is 200-300 mTorr.

10. Use of the modified PP diaphragm in the application described in any one of claims 1 to 3, the modified lithium battery diaphragm described in any one of claims 4 to 5, or the modified lithium battery diaphragm prepared by the preparation method described in any one of claims 6 to 9 in lithium iron phosphate batteries.

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