Battery diaphragm, preparation method thereof and battery

Abstract

The invention provides a battery diaphragm, a preparation method thereof and a battery. The battery diaphragm comprises a base membrane and a coating on at least one side surface of the base membrane, the coating comprises a polymer material; the polymer material contains substituted phenyl, aryl and acylamino; the substituted phenyl group is substituted by at least one electron withdrawing group. The battery diaphragm provided by the invention has electrolyte affinity, high thermal stability and excellent ionic conductivity, can resist oxygenolysis of an electrolyte under high voltage, prolongs the service life of the battery, is adaptive to a fast-charging battery under high voltage, and improves the electrochemical performance of the battery under high voltage.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and relates to a battery separator, a preparation method thereof and a battery. BACKGROUND

[0002] With the increasing demand for high energy density and fast charging of electric vehicles and energy storage systems, high-voltage positive electrode materials (such as high-nickel ternary and lithium-rich manganese-based materials) and fast charging technology have become a research hotspot. However, the traditional polyolefin separator (PE / PP) has the following limitations in the high-voltage fast charging system: 1) insufficient high-pressure resistance: electrolyte is easily oxidized and decomposed under high voltage (≥4.4V), and the traditional separator lacks the ability to inhibit the electrolyte side reaction, resulting in the accumulation of interface by-products and the attenuation of battery performance. 2) Poor thermal stability: local heat accumulation during fast charging can easily cause the separator to shrink (the melting point of PE is about 130℃), increasing the risk of short circuit; the mechanical strength of the existing ceramic-coated separator is still insufficient under high stress. 3) Low ionic conductivity: the porosity and pore size distribution of the traditional separator are not optimized for fast charging, and the lithium ion migration rate is limited, resulting in increased polarization and lithium precipitation problems.

[0003] Therefore, how to solve the above problems is currently urgent to explore. SUMMARY

[0004] In view of the deficiencies in the prior art, the purpose of the present application is to provide a battery separator, a preparation method thereof and a battery. The battery separator provided by the present application has electrolyte affinity, high thermal stability and excellent ionic conductivity, and can also resist the oxidation and decomposition of electrolyte under high voltage, improve the battery life, adapt to fast charging batteries under high voltage, and improve the electrochemical performance of the battery under high voltage.

[0005] To achieve the purpose of the present application, the following technical solutions are adopted:

[0006] In a first aspect, the present application provides a battery separator, which comprises a base film and a coating layer on at least one side surface of the base film; the coating layer comprises a polymer material; the polymer material has a substituted phenyl group, an aromatic group and an amide group; the substituted phenyl group is substituted with at least one electron-withdrawing group.

[0007] The following is a preferred technical solution of the present application, but not as a limitation of the technical solution provided by the present application. Through the following preferred technical solution, the technical purpose and beneficial effects of the present application can be better achieved and realized.

[0008] Preferably, the molar ratio of the substituted phenyl group, the aromatic group and the amide group is (0.8-1.2):(0.8-1.2):(0.8-1.2), preferably 1:1:1.

[0009] Preferably, the electron withdrawing group comprises any one of a nitro group, a cyano group, a trifluoromethyl group, a sulfonic acid group, or a halogen group.

[0010] Preferably, the electron withdrawing group is substituted at the meta position of the phenyl group.

[0011] Preferably, the aromatic group comprises a polycyclic aromatic hydrocarbon group comprising any one of a naphthyl group, an anthryl group, a phenanthryl group, or a pyrenyl group.

[0012] Preferably, the aromatic group is connected to the amide group via a linking group.

[0013] Preferably, the polymer material has a weight average molecular weight of 500,000 to 3,000,000.

[0014] Preferably, the polymer material comprises poly(E)-N-((R)-1-naphthalen-1-yl-ethyl)-3-(3-trifluoromethyl-phenyl)-acrylamide, the monomeric material of the polymer material comprises a carbon-carbon double bond containing material; the monomeric material of the polymer material comprises (E)-N-((R)-1-naphthalen-1-yl-ethyl)-3-(3-trifluoromethyl-phenyl)-acrylamide.

[0015] Preferably, the coating has a thickness of 1 μm to 6 μm.

[0016] Preferably, the battery separator has a total thickness of 7 μm to 18 μm.

[0017] Preferably, the battery separator has a porosity of 40% to 60%.

[0018] Preferably, the coating further comprises an inorganic oxide material.

[0019] Preferably, the polymer material and the inorganic oxide material have a mass ratio of (20 to 35):(5 to 18).

[0020] Preferably, the inorganic oxide material comprises a first inorganic oxide material and a second inorganic oxide material.

[0021] Preferably, the first inorganic oxide material comprises MgO and the second inorganic oxide material comprises mesoporous SiO2.

[0022] Preferably, the first inorganic oxide material and the second inorganic oxide material have a mass ratio of 4:1 to 1:4.

[0023] Preferably, the first inorganic oxide material has a median particle size D50 of 10 nm to 30 nm.

[0024] Preferably, the second inorganic oxide material has a median particle size D50 of 25 nm to 50 nm, a specific surface area of 200 m 2 / g to 300 m 2 / g, and a pore volume of 1.2 cm 3 / g to 1.5 cm 3 / g.

[0025] Preferably, the coating further comprises a binder.

[0026] In a second aspect, the present application provides a method for preparing the battery separator as described in the first aspect, the method comprising:

[0027] coating a coating slurry on at least one side surface of the base film to obtain the battery separator;

[0028] Preferably, the coating slurry further comprises an inorganic oxide material.

[0029] Preferably, the coating slurry further comprises an inorganic oxide material.

[0030] Preferably, the coating slurry further comprises an inorganic oxide material.

[0031] Preferably, the coating slurry further comprises an inorganic oxide material.

[0032] Preferably, the coating slurry further comprises an inorganic oxide material.

[0033] Preferably, the coating slurry further comprises an inorganic oxide material.

[0034] Preferably, the coating slurry further comprises an inorganic oxide material.

[0035] In a third aspect, the present application further provides a battery comprising the battery separator as described in the first aspect or prepared by the method as described in the second aspect.

[0036] Preferably, the battery comprises a lithium ion battery.

[0037] Preferably, the lithium ion battery comprises a positive electrode, a negative electrode, the battery separator as described in the first aspect or prepared by the method as described in the second aspect, and an electrolyte.

[0038] Preferably, the negative active material in the negative electrode comprises a silicon-based active material and / or a carbon-based active material, preferably a silicon-based active material.

[0039] Preferably, the electrolyte comprises an organic solvent and a main lithium salt.

[0040] Preferably, the organic solvent comprises a carbonate organic solvent.

[0041] Preferably, the electrolyte further comprises an electrolyte additive and / or an auxiliary lithium salt.

[0042] Compared with the prior art, the present application has the following beneficial effects:

[0043] In the battery separator of the present application, different from the conventional base film type separator and the ceramic separator with a pure ceramic coating in the prior art, a coating with a polymer material is adopted, which on the one hand cooperates with the base film, and on the other hand the various groups in the polymer material interact with each other, cooperate with each other, and jointly improve the performance of the battery separator; as a material in the coating, the polymer material can not only be used as a bonding material to realize good compounding of the coating and the base film, but also be used as a functional material, wherein the electron-withdrawing group in the substituted phenyl group can significantly improve the oxidation resistance of the polymer material, thereby improving the oxidation resistance of the battery separator, especially in a high-voltage battery system, which can resist the oxidative decomposition of the electrolyte and prolong the service life of the separator; the aromatic group not only enhances the thermal stability of the polymer, but also reduces the occurrence of side reactions through the steric hindrance effect, the synergistic effect of the rigid skeleton: and the aromatic group and the amide group can also form a rigid-flexible combined molecular structure, which can not only inhibit the shrinkage of the separator at high temperature and reduce the risk of thermal runaway, but also maintain the mechanical toughness of the coating and improve the puncture resistance, and the amide group has polarity, which can also improve the affinity of the separator to the electrolyte, reduce the interfacial impedance, and promote the uniform transmission of lithium ions. The battery separator in the present application can better adapt to the fast-charging type battery under high voltage, and improves the electrochemical performance of the battery under high voltage. DETAILED DESCRIPTION

[0044] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application, and should not be regarded as specific limitations on the present application.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the present application are intended to cover non-exclusive inclusion.

[0046] In the description of the present application, the technical terms "first", "second" and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly specified.

[0047] In one embodiment, the first aspect of the present application provides a battery separator, comprising a base film and a coating layer on at least one side surface of the base film; the coating layer comprises a polymer material; the polymer material has a substituted phenyl group, an aromatic group and an amide group; the substituted phenyl group is substituted by at least one electron-withdrawing group.

[0048] In the battery separator of the present application, it is different from the conventional base film separator and the ceramic separator with pure ceramic coating in the prior art; the coating layer with polymer material is used, on the one hand, the coating layer cooperates with the base film, and on the other hand, the various groups in the polymer material interact with each other and cooperate with each other to improve the performance of the battery separator; as the material in the coating layer, the polymer material can not only be used as a bonding material to realize good compounding of the coating layer and the base film, but also be used as a functional material, wherein the electron-withdrawing group in the substituted phenyl group can significantly improve the oxidation resistance of the polymer material, thereby improving the oxidation resistance of the battery separator, especially in the high-voltage battery system, which can resist the oxidative decomposition of the electrolyte and prolong the service life of the separator; the aromatic group not only enhances the thermal stability of the polymer, but also reduces the occurrence of side reactions through the steric hindrance effect, and the synergistic effect of the rigid skeleton: and the aromatic group can also form a rigid-flexible combined molecular structure with the amide group, which can not only inhibit the shrinkage of the separator at high temperature and reduce the risk of thermal runaway, but also maintain the mechanical toughness of the coating layer and improve the puncture resistance, and the amide group has polarity, which can also improve the affinity of the separator to the electrolyte, reduce the interfacial impedance and promote the uniform transmission of lithium ions. The battery separator in the present application can better adapt to the fast-charging battery under high voltage, and improve the electrochemical performance of the battery under high voltage.

[0049] In the present application, the substituted phenyl group, the electron-withdrawing group in the substituted phenyl group, the aromatic group and the amide group must exist simultaneously and cooperate synergistically, otherwise the absence of the electron-withdrawing group will cause a problem of a large impedance growth rate after 50 cycles at 4.5V (such as an impedance growth rate >200%).

[0050] The following is a preferred technical solution of the present application, but is not a limitation on the technical solutions provided by the present application. Through the following preferred technical solution, the technical purpose and beneficial effects of the present application can be better achieved and realized.

[0051] In some embodiments, the molar ratio of the substituted phenyl group, the aromatic group, and the amide group is (0.8-1.2):(0.8-1.2):(0.8-1.2), preferably 1:1:1, such as 0.8:1:1, 1:0.8:1, 1:1:0.8, 1:1:1, 1.2:1:1, 1:1.2:1, or 1:1:1.2, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0052] In the embodiments of the present application, by regulating the molar ratio of the substituted phenyl group, the aromatic group, and the amide group to a suitable ratio, a better conjugated system is obtained, avoiding the increase of coating brittleness or excessive π-π bond stacking caused by too many polar groups, and reducing the ion channel; the preferred ratio is 1:1:1, which can exert more excellent synergistic effect between the groups.

[0053] In some embodiments, the electron-withdrawing group includes any one of a nitro group, a cyano group, a trifluoromethyl group, a sulfonic acid group, or a halogen group.

[0054] In the present application, strong electron-withdrawing groups such as nitro group, cyano group, trifluoromethyl group, sulfonic acid group, or halogen group are further selected, which have more significant electron-withdrawing effect, thereby exerting more excellent antioxidant capacity, prolonging the life of the separator, and inhibiting the oxidative decomposition of the electrolyte under high voltage.

[0055] In some embodiments, the electron-withdrawing group substitutes the meta position of the phenyl group.

[0056] By substituting the meta position of the phenyl group in the polymer material with the electron-withdrawing group, not only the antioxidant capacity under high iron can be improved, but also the interference of the conjugation effect with the aromatic group can be reduced, the rigidity of the material can be improved, and a new conjugated system with the amide group can be formed; if substituted at the ortho position, the steric hindrance between the electron-withdrawing group and the aromatic group will increase, the conjugation effect will weaken, and the antioxidant capacity will decrease slightly.

[0057] In some embodiments, the aromatic group includes a polycyclic aromatic hydrocarbon group, and the polycyclic aromatic hydrocarbon group includes any one of a naphthyl group, an anthryl group, a phenanthryl group, or a pyrenyl group.

[0058] The large-volume polycyclic aromatic hydrocarbon group is selected for use in the polymer material, which can further reduce the occurrence of side reactions through strong steric hindrance effect, and can also act as a rigid skeleton to form a rigid-flexible molecular structure with the main chain structure of the amide group, which can inhibit the shrinkage of the separator under high temperature, ensure the mechanical toughness of the separator, and improve the puncture resistance of the separator.

[0059] In some embodiments, the aromatic group is connected to the amide group through a linking group.

[0060] In the present application, the aromatic group is not directly connected to the amide group, but is connected through a linking group, thereby forming a new steric hindrance effect, inhibiting excessive crystallization of the polymer material, and maintaining the flexibility of the coating.

[0061] Further, the present application does not make special limitations on the linking group, and the types of groups that do not affect the formation and play of the group are applicable, such as ethyl groups and the like.

[0062] In some embodiments, the weight average molecular weight of the polymer material is 50,000 to 300,000, such as 50,000, 80,000, 100,000, 130,000, 150,000, 180,000, 200,000, 230,000, 250,000, 280,000, or 300,000, etc., but not limited to the listed values, and other unlisted values within this range are also applicable.

[0063] Controlling the weight average molecular weight of the polymer material to be 50,000 to 300,000 can achieve a good balance between the film-forming property of the coating, the adhesion to the base film, and the mechanical strength, and better performance of the polymer material.

[0064] In some embodiments, the polymer material includes poly(E)-N-((R)-1-naphthalen-1-yl-ethyl)-3-(3-trifluoromethyl-phenyl)-acrylamide, and the monomer material of the polymer material includes a material containing a carbon-carbon double bond; the monomer material of the polymer material includes (E)-N-((R)-1-naphthalen-1-yl-ethyl)-3-(3-trifluoromethyl-phenyl)-acrylamide.

[0065] It should be noted that the specific polymerization process of the polymer material in the present application is a conventional technical solution, and any monomer material type and polymerization method known within any reasonable range of the art without deviating from the inventive concept of the present application is applicable in principle.

[0066] Exemplarily, the present application takes (E)-N-((R)-1-naphthalen-1-yl-ethyl)-3-(3-trifluoromethyl-phenyl)-acrylamide monomer material as an example to provide a polymerization method of poly(E)-N-((R)-1-naphthalen-1-yl-ethyl)-3-(3-trifluoromethyl-phenyl)-acrylamide:

[0067] Mixing (E)-N-((R)-1-naphthalen-1-yl-ethyl)-3-(3-trifluoromethyl-phenyl)-acrylamide (CAS No. 1095393-66-0), an initiator, and a solvent to perform a polymerization reaction to obtain the polymer material poly(E)-N-((R)-1-naphthalen-1-yl-ethyl)-3-(3-trifluoromethyl-phenyl)-acrylamide.

[0068] Optionally, the initiator comprises azobisisobutyronitrile (AIBN) and / or benzoyl peroxide (BPO).

[0069] Optionally, the solvent comprises any one or a combination of at least two of tetrahydrofuran (THF), toluene, N,N-dimethylformamide (DMF), or dichloromethane.

[0070] Optionally, the temperature of the polymerization reaction is 60-100°C, such as 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, or 100°C, etc., but not only limited to the listed values, other values not listed in the range are also applicable.

[0071] Optionally, in order to regulate the molecular weight distribution, a chain transfer agent such as a disulfide can be added to regulate the polymerization conditions.

[0072] The specific ratio of each raw material can be adaptively selected and adjusted by those skilled in the art according to actual needs.

[0073] In some embodiments, the thickness of the coating layer affects the uniform distribution of the coating layer and the total thickness of the battery separator. A suitable coating thickness is conducive to further improving the thermal stability and lithium ion transmission effect of the battery separator, and can also avoid the reduction of battery energy density and power density, affect the wetting effect of the electrolyte, and at the same time, an excessively thick coating layer will also cause an increase in internal resistance. Therefore, the thickness of the coating layer is preferably 1-6 μm, and the effect is more excellent, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or 6 μm, etc.

[0074] In some embodiments, the total thickness of the battery separator is 7-18 μm, such as 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, or 18 μm, etc., but not only limited to the listed values, other values not listed in the range are also applicable.

[0075] In some embodiments, the porosity of the battery separator is 40-60%, such as 40%, 45%, 50%, 55%, or 60%, etc., but not only limited to the listed values, other values not listed in the range are also applicable.

[0076] The total thickness of the battery separator is 7-18 μm and the porosity is 40-60%, which synergistically interact with each other and jointly have a positive effect on the performance of the separator.

[0077] In addition, it can be understood that the base film in the present application is a conventional technical solution, and any known conventional base film type is applicable in principle in the present application without deviating from the inventive concept of the present application.

[0078] For example, the base film includes a polyethylene (PE) base film, a polypropylene (PP) base film, a combined base film of PP and PE (such as a PP / PE base film or a PP / PE / PP base film, etc.).

[0079] Specifically, the thickness of the base film can be 6 μm to 12 μm, for example, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, or 12 μm, etc., but is not limited to the listed values, and other values not listed in this range are also applicable.

[0080] In some embodiments, the coating further includes an inorganic oxide material.

[0081] To further improve the performance of the coating, an inorganic oxide material can be added to the coating, which is dispersed in the polymer material to form a strong and tough organic-inorganic composite network, which on the one hand ensures the adhesion of the coating and the good performance of the polymer material, and on the other hand also has the effect of rigid support and thermal stability of the inorganic oxide material.

[0082] In some embodiments, the mass ratio of the polymer material to the inorganic oxide material is (20-35):(5-18), for example, 20:5, 20:10, 20:18, 25:5, 25:10, 25:18, 35:5, 35:10, or 35:18, etc., but is not limited to the listed values, and other values not listed in this range are also applicable.

[0083] In some embodiments, the inorganic oxide material includes a first inorganic oxide material and a second inorganic oxide material.

[0084] In some embodiments, the first inorganic oxide material includes MgO, and the second inorganic oxide material includes mesoporous SiO2.

[0085] The application can not only improve the mechanical strength and thermal stability of the separator by compounding the first inorganic oxide material and the second inorganic oxide material, but also can play a synergistic effect between different inorganic oxide materials. In particular, the MgO in the application is a nano material. Through the synergistic effect of the specific nano MgO and mesoporous SiO2, the MgO can also improve the puncture strength of the coating under the compounding of the polymer material, and has a strong ability to absorb HF in the electrolyte, neutralizes the acid quality of the electrolyte, while the mesoporous SiO2 can absorb the electrolyte on one hand to improve the electrolyte wettability of the separator, and on the other hand, it has a low dielectric constant, which can also reduce the interface polarization and improve the fast charging performance of the battery.

[0086] In some embodiments, the mass ratio of the first inorganic oxide material to the second inorganic oxide material is 4:1 to 1:4, for example, 4:1, 3:1, 2:1, 1:1, 1:2, 1:3 or 1:4, but not limited to the listed values, and other values not listed in the range are also applicable.

[0087] In the application, the mass ratio of the first inorganic oxide material to the second inorganic oxide material is controlled to be 4:1 to 1:4, the adsorption rate of HF in the electrolyte and the electrolyte retention are higher, and the ion conductivity is also improved, realizing the balance of corrosion resistance and ion transmission.

[0088] In some embodiments, the median particle size D50 of the first inorganic oxide material is 10 nm to 30 nm, for example, 10 nm, 15 nm, 20 nm, 25 nm or 30 nm, but not limited to the listed values, and other values not listed in the range are also applicable.

[0089] In some embodiments, the median particle size D50 of the second inorganic oxide material is 25 nm to 50 nm, for example, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm, but not limited to the listed values, and other values not listed in the range are also applicable.

[0090] By controlling the particle size of the first inorganic oxide material and the second inorganic oxide material, particles of different sizes can be matched to form more reasonable packing pores. The inorganic oxide material with a relatively large particle size serves as a skeleton, and the inorganic oxide material with a relatively small particle size is filled in the skeleton. Preferably, the median particle size D50 of the first inorganic oxide material is 10 nm to 30 nm and / or the median particle size D50 of the second inorganic oxide material is 25 nm to 50 nm, which can not only avoid blocking the pore structure of the battery separator due to the too large particle size of the particles, but also avoid excessive agglomeration of the particles, which can reduce the strength of the coating.

[0091] Preferably, the specific surface area of the second inorganic oxide material is 200 m 2 / g~300 m 2 / g, such as 200 m 2 / g, 210 m 2 / g, 220 m 2 / g, 230 m 2 / g, 240 m 2 / g, 250 m 2 / g, 260 m 2 / g, 270 m 2 / g, 280 m 2 / g, 290 m 2 / g or 300 m 2 / g, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0092] Preferably, the pore volume of the second inorganic oxide material is 1.2 cm 3 / g~1.5 cm 3 / g, such as 1.2 cm 3 / g, 1.3 cm 3 / g, 1.4 cm 3 / g or 1.5 cm 3 / g, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0093] The material with a higher specific surface area and a larger pore volume is selected as the second inorganic oxide material in the present application, which can further adsorb electrolyte and improve the liquid absorption rate.

[0094] In some embodiments, the coating further comprises a binder.

[0095] In order to further improve the binding effect of the coating and enhance the bonding strength between the coating and the base film, a binder can be additionally added.

[0096] In one embodiment, the second aspect of the present application provides a preparation method of the battery separator as described in the first aspect, and the preparation method comprises:

[0097] coating a coating slurry on at least one side surface of the base film to obtain the battery separator;

[0098] Preferably, the coating slurry comprises a polymer material and a solvent, the polymer material has a substituted phenyl group, an aromatic group and an amide group; and the substituted phenyl group is substituted by at least one electron-withdrawing group.

[0099] The coating structure can be obtained by simple coating, and the polymer material can also play a bonding effect, realizing good compounding of the coating and the base film.

[0100] In some embodiments, the coating slurry further comprises an inorganic oxide material.

[0101] In some embodiments, the coating slurry further comprises an auxiliary agent.

[0102] In some embodiments, the auxiliary agent comprises any one or a combination of at least two of a dispersant, a wetting agent and a binder.

[0103] In some embodiments, the mass ratio of the polymer material, the inorganic oxide material, the solvent and the auxiliary agent in the coating slurry is (20-35):(5-18):(42-72):(0.02-7), for example, 20:18:42:0.02, 35:18:72:0.08, 20:18:71:5, 35:18:42:7 or 25:15:60:4, etc., but not limited to the listed values, and other values not listed in the value range are also applicable.

[0104] In some embodiments, the mass ratio of the wetting agent, the dispersant and the binder is (0.02-0.08):(0.1-0.3):(2-6), for example, 0.02:0.1:2, 0.08:0.3:6, 0.08:0.3:6, 0.02:0.1:2 or 0.04:0.2:4, etc., but not limited to the listed values, and other values not listed in the value range are also applicable.

[0105] It can be understood that the specific types of the binder, the wetting agent, the dispersant and the solvent in the coating slurry of the present application are selected according to conventional techniques, and any substance suitable for the functional layer slurry of the diaphragm that can be known by a person skilled in the art within a reasonable range without departing from the inventive concept of the present application is applicable.

[0106] For example, the binder comprises at least one of carboxymethyl cellulose (CMC) / hydroxypropyl methyl cellulose (HPMC) or polyvinyl alcohol (PVA), etc.

[0107] For example, the wetting agent comprises at least one of sodium hexametaphosphate, sodium tripolyphosphate or sodium pyrophosphate, and the main function of the wetting agent is to reduce the surface tension and enhance the flowability of the slurry.

[0108] For example, the dispersant comprises at least one of silicate dispersant, sodium polyacrylate or sodium citrate.

[0109] For example, the solvent comprises water and isopropyl alcohol.

[0110] It is also necessary to point out that the preparation process of the coating slurry in the present application is not unique, and a suitable coating slurry system can be obtained.

[0111] Exemplarily, the present application provides a preparation process of a functional slurry:

[0112] The dispersant and water are first mixed, and then the inorganic oxide material is added for second mixing to obtain a second mixed solution; the remaining raw materials such as the polymer material, the binder and the additive are added to the second mixed solution for third mixing to obtain a functional layer slurry.

[0113] Optionally, all the mixing processes can be simultaneously subjected to ultrasonic treatment.

[0114] Optionally, the frequency of the ultrasonic treatment is 20KHz~50KHz, for example, 20KHz, 30KHz, 40KHz or 50KHz, etc.

[0115] In addition, the parameters in the mixing process can be adaptively selected and adjusted by those skilled in the art according to actual needs.

[0116] For example, the rotation speed in the mixing process can be independently 2000r / min~3100r / min, for example, 2000r / min, 2300r / min, 2500r / min, 2800r / min, 3000r / min or 3100r / min, etc., and the revolution speed can be independently 20r / min~40r / min, for example, 20r / min, 25r / min, 30r / min, 35r / min or 40r / min, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0117] In some embodiments, the coating method comprises microgravure printing coating.

[0118] In the present application, the microgravure printing coating method is preferably used for coating the coating slurry, which can further improve the thickness uniformity and better improve the cycle performance of the battery.

[0119] Specifically, those skilled in the art can adjust the specific operation process of the microgravure coating method according to the actual coating requirements to adapt to the coating effect of the coating slurry.

[0120] Optionally, in the microgravure printing method, the line number of the anilox roller is 150 lines / cm~200 lines / cm, for example, 150 lines / cm, 160 lines / cm, 170 lines / cm, 180 lines / cm, 190 lines / cm or 200 lines / cm, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0121] Optionally, in the microgravure printing method, the coating speed is 10 m / min to 29 m / min, for example, 12 m / min, 15 m / min, 18 m / min, 20 m / min, 23 m / min, 25 m / min, 28 m / min, or 29 m / min, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0122] Optionally, in the microgravure printing method, the printing gap is 0.1 mm to 0.3 mm, for example, 0.1 mm, 0.2 mm, or 0.3 mm, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0123] Optionally, in the microgravure printing method, the doctor blade angle is 45° to 65°, for example, 45°, 50°, 55°, 60°, or 65°, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0124] In some embodiments, after the coating, a drying process is performed.

[0125] After the slurry coating is completed, a drying process is inevitably required, and the drying temperature and time during the drying process are controlled to facilitate the rapid evaporation of the solvent on the coating surface and the absence of flow marks.

[0126] For example, the drying temperature is 40°C to 80°C, for example, 40°C, 50°C, 60°C, 70°C, or 80°C, etc., and the drying time is 1 min to 5 min, for example, 1 min, 2 min, 3 min, 4 min, or 5 min, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0127] In one embodiment, the third aspect of the present application further provides a battery comprising the battery separator according to the first aspect or the battery separator prepared by the preparation method according to the second aspect.

[0128] The battery separator in the present application is more suitable for high-voltage fast-charging battery structures, has excellent fast-charging performance, and the problem of oxidative decomposition of electrolyte under high voltage is also inhibited.

[0129] In some embodiments, the battery comprises a lithium ion battery.

[0130] In some embodiments, the lithium ion battery comprises a positive electrode, a negative electrode, a battery separator according to the first aspect or a battery separator prepared by the preparation method according to the second aspect, and an electrolyte.

[0131] In some embodiments, the negative active material in the negative electrode comprises a silicon-based active material and / or a carbon-based active material, preferably a silicon-based active material.

[0132] When the battery separator in the present application is used in combination with a negative electrode of a silicon-based active material system, the amide group in the battery separator can form a hydrogen bond structure with the hydroxyl group on the surface of the silicon-based negative active material, thereby improving the interaction between the battery separator and the negative electrode. At the same time, due to the excellent flexibility of the coating structure of the battery separator in the present application, the volume expansion of the negative electrode can be inhibited, thereby achieving buffering and protection of the expansion of the silicon-based negative electrode.

[0133] It can be understood that the silicon-based negative active material described in the present application is a conventional negative material of a silicon system, such as pure silicon material, silicon-carbon negative material, and silicon-oxygen negative material, and the source of the silicon-based negative active material can be prepared by a conventional technical solution or purchased directly by a commercial means.

[0134] In some embodiments, the positive active material in the positive electrode of the present application is a conventional technical solution. Without departing from the inventive concept of the present application, any known positive active material is applicable to the present application, for example, the positive active material comprises at least one of nickel-cobalt-manganese or nickel-cobalt-aluminum ternary positive material, lithium iron phosphate / lithium manganese iron phosphate positive material, lithium-rich manganese-based positive material, lithium nickel manganese oxide spinel positive material, cobalt-free nickel manganese positive material, or lithium cobalt oxide positive material.

[0135] In some embodiments, the electrolyte comprises an organic solvent and a main lithium salt.

[0136] In some embodiments, the organic solvent can include at least one of a carbonate compound, a carboxylate compound, an ether compound, a sulfone compound. As an example, the solvent can include, but is not limited to, at least one of ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone, sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE), methylsulfolane, dimethyl sulfoxide, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl ether, diethyl ether, nitromethane, N,N-dimethylformamide. The above-mentioned solvents can be used alone, or two or more of them can be used simultaneously.

[0137] In some embodiments, the main lithium includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6). The above-mentioned electrolyte salts can be used alone, or two or three or more of them can be used simultaneously.

[0138] In some embodiments, the organic solvent includes a carbonate-based organic solvent.

[0139] The amide group in the battery separator of the present application has good affinity for carbonate-based organic solvents, thereby reducing the interfacial impedance and promoting uniform transmission of lithium ions.

[0140] In some embodiments, the electrolyte further includes an electrolyte additive and / or an auxiliary lithium salt.

[0141] In some embodiments, the auxiliary lithium salt includes a lithium lithium salt of sulfonimide, and the mass percentage of the auxiliary lithium salt in the electrolyte is 1% to 3%, for example, 1%, 2% or 3%, etc., but is not limited to the listed values, and other values not listed in this range are also applicable.

[0142] The addition of lithium lithium salt of sulfonimide, such as lithium bis(fluorosulfonyl)imide LiFSI or lithium bis(trifluoromethanesulfonyl)imide LiTFSI, etc., further reduces the interfacial impedance of the battery, and cooperates with the modified separator.

[0143] In some embodiments, the electrolyte additive includes a phosphate ester additive and / or a low impedance additive, and the mass percentage of the electrolyte additive in the electrolyte is 0.1% to 1.5%, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5%, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0144] In the presence of the base electrolyte, the electrolyte additive, the phosphate ester additive and / or the low impedance additive can also be added, and the modified separator can also work together to further improve the rate performance of the battery.

[0145] Specifically, the phosphate ester additive includes but is not limited to tris(4-nitrophenyl) phosphate, and the low impedance additive includes but is not limited to lithium bis(oxalato)borate (LiBOB).

[0146] In some embodiments, the positive electrode can include a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector; and the negative electrode can include a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector.

[0147] In some embodiments, the shape of the positive electrode current collector and the negative electrode current collector can be a plate or a foil, and the embodiments of the present application are not limited thereto.

[0148] In some embodiments, the material of the positive electrode current collector and the negative electrode current collector is not particularly limited, and a material having electronic conductivity can be selected. For example, a simple substance or an alloy containing at least one element selected from C, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, and Al (e.g., stainless steel, etc.) can be used.

[0149] From the viewpoint of high conductivity, high stability in electrolyte, and good oxidation resistance, the C layer, Al foil, stainless steel foil, etc. in the positive electrode current collector are optional. The C layer, Cu foil, etc. in the negative electrode current collector are optional. From the viewpoint of further reducing production costs, the Al foil in the positive electrode current collector is more preferred, and the Cu foil in the negative electrode current collector is more preferred; further, those skilled in the art can make adaptive adjustment and selection according to the actual situation.

[0150] Example 1

[0151] This embodiment provides a battery separator, which includes a PP base film (thickness of 6 μm) and a coating layer (thickness of 3 μm) on both sides of the base film, and the porosity of the battery separator is 50%.

[0152] The coating comprises a polymer material with a weight average molecular weight of 150,000, a first inorganic oxide material MgO (D50 of 20 nm), and a second inorganic oxide material mesoporous SiO2 (D50 of 40 nm, specific surface area of 250 m 2 / g, pore volume of 1.5 cm 3 / g);

[0153] The polymer material is poly(E)-N-((R)-1-naphthalen-1-yl-ethyl)-3-(3-trifluoromethyl-phenyl)-acrylamide.

[0154] The mass ratio of MgO to mesoporous SiO2 is 1:1.

[0155] The preparation method of the battery separator is as follows:

[0156] (1) Preparation of coating slurry: first, the dispersant sodium polyacrylate and pure water are mixed by stirring at a self-rotation speed of 2500 r / min and a revolution speed of 30 r / min, then MgO powder and mesoporous SiO2 powder are added and continue to be stirred and mixed, and ultrasonic is performed at the same time to obtain a mixed solution; isopropanol, binder CMC, polymer material and wetting agent sodium pyrophosphate are added to the mixed solution and continue to be stirred and mixed, so that the mass ratio of the polymer material, all inorganic oxide materials, pure water, wetting agent, dispersant, isopropanol and binder is 25:15:50:0.06:0.3:3:4, and a coating slurry is obtained;

[0157] (2) The coating slurry is coated on both sides of the PP base film by using a double-sided micro-gravure coating method, and in the coating process, the line number of the anilox roll is 200 lines / cm, the coating speed is 20 m / min, the printing gap is 0.3 mm, and the doctor blade angle is 55°; after the coating is completed, drying treatment is performed at a drying temperature of 80°C to obtain the battery separator.

[0158] Example 2

[0159] The battery separator provided in this embodiment comprises a PP base film (thickness of 12 μm) and a coating (thickness of the coating is 1 μm) on both sides of the base film, and the porosity of the battery separator is 40%.

[0160] The coating comprises a polymer material with a weight average molecular weight of 50,000, MgO (D50 of 10 nm) and mesoporous SiO2 (D50 of 25 nm, specific surface area of 300 m 2 / g, pore volume of 1.2 cm 3 / g);

[0161] The polymer material is poly(E)-N-((R)-1-naphthalen-1-yl-ethyl)-3-(3-trifluoromethyl-phenyl)-acrylamide.

[0162] The mass ratio of MgO to mesoporous SiO2 is 4:1.

[0163] The preparation method of the battery separator is as follows:

[0164] (1) Preparation of coating slurry: first, the dispersing agent sodium polyacrylate is mixed with pure water at a self-rotation speed of 2100 r / min and a revolution speed of 40 r / min, then MgO powder and mesoporous SiO2 powder are added and continue to be stirred and mixed, and ultrasonic is performed at the same time to obtain a mixed solution; isopropanol, binder CMC, polymer material and wetting agent sodium pyrophosphate are added to the mixed solution and continue to be stirred and mixed, and the mass ratio of the polymer material, all inorganic oxide materials, pure water, wetting agent, dispersing agent, isopropanol and binder is 20:18:40:0.02:0.2:2:2, to obtain the coating slurry;

[0165] (2) The coating slurry is coated on both sides of the PP base film by using a double-sided micro-gravure coating method, and during the coating process, the line number of the anilox roller is 150 lines / cm, the coating speed is 29 m / min, the printing gap is 0.1 mm, and the doctor blade angle is 65°; after the coating is completed, drying treatment is performed at a drying temperature of 60°C to obtain the battery separator.

[0166] Example 3

[0167] The battery separator provided in this embodiment includes a PP base film (thickness of 8 μm) and a coating layer (thickness of 5 μm) on both sides of the base film, and the porosity of the battery separator is 60%.

[0168] The coating layer includes a polymer material with a weight average molecular weight of 300,000, MgO (D50 of 30 nm) and mesoporous SiO2 (D50 of 50 nm, specific surface area of 300 m 2 / g, pore volume of 1.3 cm 3 / g);

[0169] The polymer material is poly(E)-N-((R)-1-naphthalen-1-yl-ethyl)-3-(3-trifluoromethyl-phenyl)-acrylamide;

[0170] The mass ratio of MgO to mesoporous SiO2 is 1:4.

[0171] The preparation method of the battery separator is as follows:

[0172] (1) Preparation of coating slurry: first, the dispersant sodium polyacrylate and pure water are mixed by stirring at a self-rotation speed of 2500 r / min and a revolution speed of 30 r / min, then MgO powder and mesoporous SiO2 powder are added and continue to be stirred and mixed, and ultrasonic is performed at the same time to obtain a mixed solution; isopropyl alcohol, binder CMC, polymer material and wetting agent sodium pyrophosphate are added to the mixed solution and continue to be stirred and mixed, so as to ensure that the mass ratio of the polymer material, all inorganic oxide materials, pure water, wetting agent, dispersant, isopropyl alcohol and binder is 35:5:60:0.08:0.2:5:6, and the coating slurry is obtained;

[0173] (2) The coating slurry is coated on both sides of the PP base film by using a double-sided micro-gravure coating method, and in the coating process, the line number of the anilox roller is 200 lines / cm, the coating speed is 20 m / min, the printing gap is 0.3 mm, and the doctor blade angle is 55°; after the coating is completed, drying treatment is performed at a drying temperature of 80℃, and the battery separator is obtained.

[0174] Example 4

[0175] The difference between this embodiment and Example 1 is that the base film in this embodiment is a PE base film.

[0176] The remaining conditions are consistent with those of Example 1.

[0177] Example 5

[0178] The difference between this embodiment and Example 1 is that the thickness of the coating in this embodiment is 1 μm, the total thickness of the battery separator is 10 μm, and the porosity of the battery separator is 45%.

[0179] The remaining conditions are consistent with those of Example 1.

[0180] Example 6

[0181] The difference between this embodiment and Example 1 is that the thickness of the coating in this embodiment is 6 μm, the total thickness of the battery separator is 18 μm, and the porosity of the battery separator is 55%.

[0182] The remaining conditions are consistent with those of Example 1.

[0183] Example 7

[0184] The difference between this embodiment and Example 1 is that the weight average molecular weight of the polymer material in this embodiment is 50,000.

[0185] The remaining conditions are consistent with those of Example 1.

[0186] Example 8

[0187] The difference between this embodiment and embodiment 1 is that the weight average molecular weight of the polymer material in this embodiment is 300,000.

[0188] The rest of the conditions are consistent with embodiment 1.

[0189] Embodiment 9

[0190] The difference between this embodiment and embodiment 1 is that the mass ratio of MgO to mesoporous SiO2 in this embodiment is 4:1.

[0191] The rest of the conditions are consistent with embodiment 1.

[0192] Embodiment 10

[0193] The difference between this embodiment and embodiment 1 is that the mass ratio of MgO to mesoporous SiO2 in this embodiment is 1:4.

[0194] The rest of the conditions are consistent with embodiment 1.

[0195] Embodiment 11

[0196] The difference between this embodiment and embodiment 1 is that the thickness of the coating in this embodiment is 8 μm.

[0197] The rest of the conditions and parameters are consistent with embodiment 1.

[0198] Embodiment 12

[0199] The difference between this embodiment and embodiment 1 is that the trifluoromethyl group in the polymer material in this embodiment is located at the ortho position of the phenyl group, that is, the monomer material of the polymer material is (R)-N-(1-(naphthalen-1-yl)ethyl)-3-(2-(trifluoromethyl)phenyl)-propionamide (radical polymerization in acrylamide).

[0200] The rest of the conditions are consistent with embodiment 1.

[0201] Embodiment 13

[0202] The difference between this embodiment and embodiment 1 is that the weight average molecular weight of the polymer material in this embodiment is 10,000.

[0203] The rest of the conditions are consistent with embodiment 1.

[0204] Embodiment 14

[0205] The difference between this embodiment and embodiment 1 is that the weight average molecular weight of the polymer material in this embodiment is 350,000.

[0206] The rest of the conditions are consistent with embodiment 1.

[0207] Embodiment 15

[0208] The difference between this example and Example 1 is that the MgO and mesoporous SiO2 in this example have the same particle size, both being 30 nm.

[0209] The remaining conditions were the same as in Example 1.

[0210] Example 16

[0211] The difference between this example and Example 1 is that the first inorganic oxide material in this example is ZnO.

[0212] The remaining conditions were the same as in Example 1.

[0213] Example 17

[0214] The difference between this example and Example 1 is that the second inorganic oxide material in this example is mesoporous TiO2.

[0215] The remaining conditions were the same as in Example 1.

[0216] Example 18

[0217] The difference between this example and Example 1 is that the inorganic oxide material of the coating in this example does not contain a second inorganic oxide material.

[0218] The remaining conditions were the same as in Example 1.

[0219] Example 19

[0220] The difference between this example and Example 1 is that the inorganic oxide material of the coating in this example does not contain a first inorganic oxide material.

[0221] The remaining conditions were the same as in Example 1.

[0222] Example 20

[0223] The difference between this example and Example 1 is that the mass ratio of MgO to mesoporous SiO2 in this example is 5:1.

[0224] The remaining conditions were the same as in Example 1.

[0225] Example 21

[0226] The difference between this example and Example 1 is that the mass ratio of MgO to mesoporous SiO2 in this example is 1:5.

[0227] The remaining conditions were the same as in Example 1.

[0228] Comparative Example 1

[0229] The difference between this example and Example 1 is that the battery separator in this example is a pure base film structure and does not contain a coating.

[0230] Comparative Example 2

[0231] The difference between this comparative example and Example 1 is that the battery separator of this comparative example does not contain a polymeric material.

[0232] The remaining conditions are consistent with Example 1.

[0233] Comparative Example 3

[0234] The difference between this comparative example and Example 1 is that the polymeric material of this comparative example is polyacrylamide (CAS: 9003-05-8).

[0235] The remaining conditions are consistent with Example 1.

[0236] Comparative Example 4

[0237] The difference between this comparative example and Example 1 is that the polymeric material of this comparative example is poly(3-trifluoromethylstyrene), in which the monomer material is 3-(trifluoromethyl)styrene (CAS No.: 384-64-5).

[0238] The remaining conditions are consistent with Example 1.

[0239] Comparative Example 5

[0240] The difference between this comparative example and Example 1 is that the polymeric material of this comparative example is poly(1-vinylnaphthalene) (CAS No.: 29793-40-6).

[0241] The remaining conditions are consistent with Example 1.

[0242] Application Example 1

[0243] This application example provides a lithium ion battery, and the preparation method of the lithium ion battery is as follows:

[0244] (1) Preparation of the positive electrode sheet:

[0245] The ternary material NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O2) positive active material, the binder PVDF (polyvinylidene fluoride), the conductive agent SP (conductive carbon black Super-P), and the SWCNT (single-walled carbon nanotube) are mixed and stirred uniformly at a mass ratio of 96:2:1.9:0.1 to obtain a positive electrode slurry, and then the positive electrode slurry is coated on an aluminum foil through a coating process, and after a drying and cold pressing process, a positive electrode sheet is obtained.

[0246] (2) Preparation of the negative electrode sheet

[0247] The silicon-carbon negative electrode material, conductive agent SP (conductive carbon black Super-P), SWCNT (single-walled carbon nanotube), binder PAA (polyacrylic acid) and SBR are mixed and stirred uniformly at a mass ratio of 90:2:0.5:5:2.5 to obtain a negative electrode slurry, and the solid content is controlled at 30%. Then, the negative electrode slurry is coated on the copper foil current collector through a coating process, and the negative electrode sheet is obtained after vacuum drying and cold pressing.

[0248] (3) Selection of electrolyte

[0249] The organic solvents ethylene carbonate EC, propylene carbonate PC, dimethyl carbonate DMC, diethyl carbonate DEC and fluoroethylene carbonate are mixed at a mass ratio of 15:20:25:30:10, and then LiPF6 is added to make the concentration 1 mol / L, to obtain an electrolyte.

[0250] (4) Selection of separator

[0251] The battery separator provided in Example 1 is used as the separator;

[0252] (5) Preparation of lithium ion battery

[0253] The above positive electrode sheet, separator and negative electrode sheet are stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, and then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum packaging, standing, formation, shaping and other processes, a lithium ion battery is obtained.

[0254] Application Example 2-21 and Comparative Application Example 1-5

[0255] The difference between Application Example 2-21 and Comparative Application Example 1-5 and Application Example 1 is that the battery separator provided in Example 2-21 and Comparative Example 1-5 is used as the separator, respectively.

[0256] The remaining conditions are the same as those in Application Example 1.

[0257] Performance test

[0258] ①The heat shrinkage rate of the modified separator structure provided in the examples and comparative examples is tested according to the standard test method (GB / T36363). The size change of the separator sample in the free state is measured under the specified temperature (such as 150℃) and time (30min), and the transverse (TD) and longitudinal (MD) heat shrinkage rates are calculated. The test conditions are as follows:

[0259] 1) The modified separator sample is placed in an environment of 23±2℃ and humidity of 50±5%RH for 24 hours. After placing, the modified separator is cut away from the edge of 10mm, and a 100mm×100mm modified separator to be tested is obtained.

[0260] 2) The initial size of the modified separator was measured using an optical projector, and a cross line was drawn on the sample surface to record the initial length L0 (TD and MD, accurate to 0.1 mm) ;

[0261] 3) Then the modified separator to be tested after the initial size test in step 2) was fixed with a stainless steel frame clamp and placed in the center of a high-temperature furnace preheated to 150°C, ensuring that the sample did not contact the furnace wall; after constant temperature for 30 min, the clamp was quickly removed and cooled at room temperature for 10 min;

[0262] 4) The cross line length L1 of the sample after cooling was measured (TD and MD were measured respectively), and each sample was tested in triplicate, and the average value was taken. The thermal shrinkage rate in the transverse and longitudinal directions was calculated based on the initial size and the sample after cooling, and the calculation formula was: thermal shrinkage rate (%) = (L0-L1) / L0x100%, and the data results were recorded in Table 1.

[0263] The modified separator structure provided by the examples and comparative examples was subjected to puncture strength test, and the test conditions were as follows:

[0264] 1) The puncture clamp and blade were prepared before measurement;

[0265] 2) The blade was used to cut the modified separator to be tested, and the sample was a circular sample with a diameter of 100 mm. Notes: The modified separator should be defect-free and have no defects;

[0266] 3) After checking the cleanliness of the high-iron tensile testing machine, the puncture clamp was installed, and the first base film and the second base film were placed in the center of the clamp, and the upper cover was covered. Note: The sample must be placed flat without any wrinkles; the sample size should be larger than the puncture clamp, i.e. the sample is tightly pressed around the clamp;

[0267] 3) On the computer operation panel of the high-iron tensile testing machine, the test speed was set to 50 mm / min;

[0268] 4) Click "Start" to perform the puncture test in sequence, stop when the base film sample is pierced, and save the force-displacement curve; each group was tested in triplicate, and if the three force-displacement curves had good repeatability, the next sample was tested. Note: The unit of force F is N. The puncture resistance = force F / 9.8x103, unit: gf, the puncture resistance of the modified separator was obtained, and the data results were recorded in Table 1.

[0269] Table 1

[0270] 150°C / 30 min heat shrinkage rate-TD (%) 150°C / 30 min heat shrinkage rate-MD (%) Puncture resistance (gf) Example 1 0.2 0.5 2300 Example 2 0.3 0.6 2200 Example 3 0.4 0.7 2100 Example 4 0.3 0.5 2250 Example 5 0.5 0.8 2150 Example 6 0.6 0.9 2050 Example 7 0.4 0.7 2100 Example 8 0.5 0.8 2000 Example 9 0.3 0.6 2200 Example 10 0.4 0.7 2100 Example 11 0.9 1.0 2050 Example 12 0.8 1 2000 Example 13 1.0 1.2 1800 Example 14 0.9 1.1 1900 Example 15 0.7 0.9 2050 Example 16 1.2 1.5 1700 Example 17 1.1 1.4 1750 Example 18 1.5 1.8 1600 Example 19 1.3 1.6 1650 Example 21 1.4 1.7 1550 Example 21 1.6 1.9 1500 Comparative Example 1 10.2 12.3 950 Comparative Example 2 3.5 4.5 1100 Comparative Example 3 4.8 5.5 1150 Comparative Example 4 5.8 6.5 1200 Comparative Example 5 4.2 5.0 1300

[0271] ②Test on LAND battery test system of Wuhan Jinnuo Electronic Co., Ltd. at room temperature (25°C), and the specific test conditions are as follows:

[0272] a) Initial coulombic efficiency

[0273] At 25°C, the lithium ion battery is charged at 0.33C rate to 4.5V, and then discharged at 0.33C rate to 2.5V, and the initial coulombic efficiency of the lithium ion battery is calculated.

[0274] Initial coulombic efficiency (%) = lithium ion battery 0.33C initial discharge total capacity / lithium ion battery 0.33C initial charge total capacity x 100%.

[0275] b) Capacity retention rate at room temperature 1C / 2C for 1000 cycles

[0276] At 25°C, the lithium ion battery is charged at 1C rate to 4.5V, and then discharged at 2C rate to 2.5V, and the initial coulombic efficiency of the lithium ion battery is calculated.

[0277] Lithium ion battery capacity retention rate (%) after N cycles = (Nth cycle discharge capacity / initial discharge capacity) x 100%, N is the number of cycles of lithium ion battery.

[0278] c) Room temperature 6C rate performance - constant current charge ratio

[0279] At 25°C, the lithium ion battery is discharged at 1C rate to 2.5V, and then charged at 6C rate to 4.2V, and the initial coulombic efficiency of the lithium ion battery is calculated.

[0280] d) Room temperature 1C / 8C discharge capacity retention rate

[0281] The lithium-ion battery, after capacity gradation, was charged at 25℃ using a 1C rate with constant current and constant voltage to 4.2V, with a cutoff current of 0.05C; it was then allowed to stand for 10 minutes; next, the lithium-ion battery was discharged at a 1C rate with constant current to 2.5V, and its discharge capacity Q1C was recorded as the initial discharge capacity; then, the lithium-ion battery was charged at 25℃ using a 1C rate with constant current and constant voltage to 4.2V, with a cutoff current of 0.05C; it was allowed to stand for 10 minutes; then, the fully charged battery was discharged at an 8C rate with constant current to 2.5V, and its discharge capacity Q8C was recorded; the discharge capacity retention rate (%) of the lithium-ion battery at 1C / 8C rate was calculated as: discharge capacity Q8C at 8C rate / discharge capacity Q1C at 1C rate × 100%.

[0282] e) Oxidative decomposition of electrolyte:

[0283] Circulating gas generation test device:

[0284] Main equipment: Pressure-resistant sealed reactor (made of 316 stainless steel, volume 50mL, pressure ≥1MPa), with a battery fixing bracket inside the reactor (to prevent battery short circuit), and a high-precision pressure sensor (accuracy ±0.1kPa) and a gas sampling port (with valve) on the top of the reactor.

[0285] Auxiliary equipment: LAND battery testing system (voltage range 0~5V, current accuracy ±0.1mA), constant temperature water bath (temperature control accuracy ±0.5℃).

[0286] Initial state calibration:

[0287] The pretreated battery was placed in a pressure-resistant reactor, sealed, and then evacuated (vacuum degree ≤ -0.095MPa) for 30 minutes. The initial pressure (P0) and temperature (T0, 25℃) inside the reactor were recorded.

[0288] Inject an inert gas (such as high-purity Ar, 99.999%) into the vessel to standard atmospheric pressure (101.3 kPa), and calibrate the pressure sensor and volume scale (ensure that the effective volume V inside the vessel is known).

[0289] Circulating gas production test:

[0290] The cyclic regime was set as follows: In a 25℃ constant temperature water bath, the reactor was charged at a constant current and constant voltage of 1C to 4.5V (cutoff current 0.05C), and allowed to stand for 10 minutes; then discharged at a constant current of 2C to 2.5V, and allowed to stand for 10 minutes, constituting one cycle; the test was paused every 50 cycles, and the pressure inside the reactor (P) was recorded. n ) and temperature (T) n The gas production rate is calculated using the ideal gas law: gas production volume V n (Standard conditions, 0℃, 101.3kPa) = [(P n ×V) / (Tn [(P0 x V) / (T0 x R)] - [(P1 x V) / (T1 x R)] - [(P2 x V) / (T2 x R)] - [(P3 x V) / (T3 x R)] - [(P4 x V) / (T4 x R)] - [(P5 x V) / (T5 x R)] - [(P6 x V) / (T6 x R)] - [(P7 x V) / (T7 x R)] - [(P8 x V) / (T8 x R)] - [(P9 x V) / (T9 x R)] - [(P10 x V) / (T10 x R)] (wherein R is the gas constant, 8.314 kPa L / (mol K)).

[0291] f) Cell thermal runaway ARC test: Start ARC adiabatic thermal runaway test (test sample in the cavity from room temperature to 45±2ºC, after 90min, detect the change of battery temperature rise rate, if the temperature rise is more than 0.2ºC (i.e. SHR>0.02ºC / min) within 10min, it is considered that the self-heating reaction occurs inside the battery, and the adiabatic environment is maintained until the battery thermal runaway occurs; if the temperature rise is not more than 0.2ºC (i.e. SHR≤0.02ºC / min) within 10min, continue to the next step temperature rise test; 5ºC for each temperature step, repeat the steps at each step, the ARC test temperature range is 45℃~300℃, the self-heating starting temperature is T1 (the temperature rise rate SHR>0.02ºC / min), and the thermal runaway starting temperature is T2 (the temperature rise rate SHR>1ºC / min).

[0292] The battery performance test results are shown in Table 2.

[0293] Table 2

[0294] 0.33C initial efficiency (%) Ambient 1C / 2C cycle 1000 cycles capacity retention rate (%) Ambient 6C constant current charge ratio (%) Ambient 1C / 8C discharge capacity retention rate (%) Gas production (mL / g) 100 weeks Self-heat generation starting temperature T1 (°C) Thermal runaway starting temperature T2 (°C) Application Example 1 84.5 85.5 79.2 82.5 4.8 107.2 165.2 Application Example 2 83.8 84.2 78.5 81.2 5.2 106.8 164.5 Application Example 3 83.2 83.5 77.8 80.5 5.5 106.5 163.8 Application Example 4 84.2 85.0 78.8 82.0 5.0 107.0 165.0 Application Example 5 83.5 84.0 78.0 81.0 5.3 106.7 164.2 Application Example 6 82.8 83.0 77.2 80.0 5.8 106.2 163.5 Application Example 7 83.0 83.8 77.5 80.8 5.6 106.6 164.0 Application Example 8 82.5 82.5 76.8 79.8 6.0 106.0 163.2 Application Example 9 83.6 84.5 78.3 81.8 5.3 106.9 164.8 Application Example 10 83.3 83.8 77.9 80.9 5.7 106.4 163.9 Application Example 11 81.2 79.5 74.2 76.5 8.5 105.5 160.2 Application Example 12 82.0 81.0 75.5 78.2 7.2 105.8 161.5 Application Example 13 80.5 78.0 73.0 75.0 9.0 105.0 159.0 Application Example 14 81.0 78.8 73.8 75.8 8.2 105.2 159.8 Application Example 15 81.8 80.2 75.0 77.5 7.5 105.6 160.8 Application Example 16 80.0 77.2 72.5 74.2 9.5 104.8 158.5 Application Example 17 80.2 77.5 72.8 74.5 9.2 104.5 158.0 Application Example 18 79.5 76.0 71.2 73.0 10.5 104.0 157.0 Application Example 19 79.8 76.5 71.8 73.5 10.0 104.2 157.5 Application Example 20 78.5 75.0 70.5 72.0 11.0 103.8 156.5 Application Example 21 78.0 74.5 70.0 71.5 11.5 103.5 156.0 Comparative Application Example 1 77.8 63.4 67.9 65.2 22.0 98.5 140.2 Comparative Application Example 2 76.5 61.2 66.0 63.0 25.0 97.8 138.5 Comparative Application Example 3 75.2 59.0 64.5 61.5 28.0 97.0 137.0 Comparative Application Example 4 74.8 58.5 64.0 61.0 29.0 96.5 136.5 Comparative Application Example 5 75.5 59.5 65.0 62.0 27.0 97.2 137.5

[0295] From Tables 1-2, it can be seen that:

[0296] In Example 1, Example 5, Example 6 and Example 11, the thickness of the coating is relatively thick, which actually leads to the decrease of the shrinkage rate and puncture resistance of the battery separator, thereby affecting the electrochemical performance of the battery.

[0297] In Example 1 and Example 11, the electron-withdrawing group in the polymer material of the coating substitutes the non-metaposition of the aromatic group, which further strengthens the steric hindrance of the aromatic group, leads to the decrease of the performance of the material, affects the shrinkage rate and puncture resistance of the battery separator, and causes the decrease of the electrochemical performance of the battery.

[0298] In Example 1, Example 7, Example 8, Example 13 and Example 14, the polymer material is in a suitable range of molecular weight, the effect of the coating is more excellent, and the molecular weight is relatively too high or too low, which will obviously affect the shrinkage rate and puncture resistance of the battery separator, and cause the decrease of the electrochemical performance of the battery.

[0299] In Example 1 and Example 15, when the particle size of the inorganic oxide material in the coating is the same, the phenomenon of excessive particle agglomeration is easy to occur, which leads to the decrease of the coating strength.

[0300] In the coating of the battery separator in Embodiment 1, Embodiment 16, Embodiment 17, Embodiment 18 and Embodiment 18, when the inorganic oxide material is added, the strength of the coating, the liquid absorption effect is more excellent, and the interface polarization can be reduced, and the fast charging performance of the battery is further improved.

[0301] In the coating of the battery separator in Embodiment 1, Embodiment 9, Embodiment 10, Embodiment 20 and Embodiment 21, when the mass ratio of the two inorganic oxide materials in the coating is within the appropriate range, the shrinkage rate and the puncture resistance of the battery separator are obviously improved, and the electrochemical performance of the battery is also good.

[0302] In the coating of the battery separator in Embodiment 1, Embodiment 9, Embodiment 10, Embodiment 20 and Embodiment 21, when the mass ratio of the two inorganic oxide materials in the coating is within the appropriate range, the shrinkage rate and the puncture resistance of the battery separator are obviously improved, and the electrochemical performance of the battery is also good.

[0303] The above merely describes the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and those skilled in the art should understand that any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and all of them fall within the protection scope and disclosure scope of the present application.

Claims

1. A battery separator, characterized in that, The battery separator includes a base film and a coating on at least one surface of the base film; the coating includes a polymer material; the polymer material has substituted phenyl, aromatic and amide groups; the substituted phenyl groups are substituted by at least one electron-withdrawing group.

2. The battery separator according to claim 1, characterized in that, The molar ratio of the substituted phenyl, aromatic, and amide groups is (0.8~1.2):(0.8~1.2):(0.8~1.2), preferably 1:1:1; Preferably, the electron-withdrawing group includes any one of nitro, cyano, trifluoromethyl, sulfonic acid, or halogen groups; Preferably, the electron-withdrawing group substitutes for the meta position of the phenyl group; Preferably, the aromatic group comprises a polycyclic aromatic hydrocarbon group, which includes any one of naphthyl, anthraceneyl, phenanthryl or pyrene; Preferably, the aromatic group is linked to the amide group via a linking group; Preferably, the weight-average molecular weight of the polymer material is 50,000 to 300,000; Preferably, the polymer material comprises poly(E)-N-((R)-1-naphth-1-yl-ethyl)-3-(3-trifluoromethyl-phenyl)-acrylamide, and the monomer material of the polymer material comprises a material containing a carbon-carbon double bond; the monomer material of the polymer material comprises (E)-N-((R)-1-naphth-1-yl-ethyl)-3-(3-trifluoromethyl-phenyl)-acrylamide.

3. The battery separator according to claim 1 or 2, characterized in that, The thickness of the coating is 1μm to 6μm; Preferably, the total thickness of the battery separator is 7μm~18μm; Preferably, the porosity of the battery separator is 40% to 60%.

4. The battery separator according to claim 1 or 2, characterized in that, The coating also includes inorganic oxide materials; Preferably, the mass ratio of the polymer material to the inorganic oxide material is (20~35):(5~18). Preferably, the inorganic oxide material includes a first inorganic oxide material and a second inorganic oxide material; Preferably, the first inorganic oxide material comprises MgO, and the second inorganic oxide material comprises mesoporous SiO2; Preferably, the mass ratio of the first inorganic oxide material to the second inorganic oxide material is 4:1 to 1:4; Preferably, the median particle size D50 of the first inorganic oxide material is 10 nm to 30 nm; Preferably, the median particle size D50 of the second inorganic oxide material is 25 nm to 50 nm, and the specific surface area of ​​the second inorganic oxide material is 200 m². 2 / g~300m 2 / g, the pore volume of the second inorganic oxide material is 1.2cm³. 3 / g~1.5cm 3 / g.

5. The battery separator according to claim 1, characterized in that, The coating also includes an adhesive.

6. A method for preparing a battery separator as described in any one of claims 1-4, characterized in that, The preparation method includes: The battery separator is obtained by coating at least one surface of the base film with a coating slurry. The coating slurry comprises a polymer material and a solvent, wherein the polymer material has substituted phenyl, aromatic and amide groups; the substituted phenyl group is substituted by at least one electron-withdrawing group.

7. The preparation method according to claim 6, characterized in that, The coating slurry also includes inorganic oxide materials; Preferably, the coating slurry further includes additives; Preferably, the additives include any one or a combination of at least two of the following: dispersants, wetting agents, and binders; Preferably, in the coating slurry, the mass ratio of polymer material, inorganic oxide material, solvent and additive is (20~35):(5~18):(42~72):(0.02~7). Preferably, the mass ratio of the wetting agent, dispersant and binder is (0.02~0.08):(0.1~0.3):(2~6).

8. The preparation method according to claim 6 or 7, characterized in that, The coating method includes microgravure printing coating.

9. A battery, characterized in that, The battery includes the battery separator as described in any one of claims 1-5 or the battery separator prepared by the preparation method as described in any one of claims 6-8.

10. The battery according to claim 9, characterized in that, The battery includes a lithium-ion battery; Preferably, the lithium-ion battery includes a positive electrode, a negative electrode, a battery separator as described in any one of claims 1-5 or a battery separator prepared by the preparation method as described in any one of claims 6-8, and an electrolyte; Preferably, the negative electrode active material in the negative electrode includes silicon-based active material and / or carbon-based active material, and is preferably silicon-based active material; Preferably, the electrolyte comprises an organic solvent and a main lithium salt; Preferably, the organic solvent includes carbonate organic solvents; Preferably, the electrolyte further includes electrolyte additives and / or auxiliary lithium salts.