Separator, secondary battery, and electric device

Abstract

The present application relates to the technical field of batteries, and provides a separator, a secondary battery, and an electric device. In the separator provided by the present application, by sequentially providing a first coating and a second coating on the surface of a base membrane, controlling the Dv50 of first inorganic particles and the glass-transition temperature Tg of a first binder in the first coating within suitable ranges and selecting ceramic particles that are modified with an acrylic acid copolymer and have Dv50 within a suitable range as second inorganic particles in the second coating, the thermal stability and the electrolyte wetting rate of the separator can be significantly improved while the ion and electron transport rates of the separator are retained, thereby reducing the internal resistance of a secondary battery and improving the cycling performance and the rate capability of the secondary battery.

Description

A separator, secondary battery and electric device

[0001] The present application claims priority to the Chinese patent application No. 202410833080.2 filed on June 25, 2024, and entitled "A separator, secondary battery and electric device", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of battery, in particular to a separator, secondary battery and electric device. BACKGROUND

[0003] With the continuous development of new energy vehicle technology, people's performance requirements for vehicle secondary batteries are also getting higher and higher, among which the long cycle performance and high safety performance are the most prominent. Generally speaking, in order to meet the above requirements, the positive electrode, negative electrode and electrolyte are mainly considered, while there are few optimization design schemes for the separator. As one of the important components of the secondary battery, the performance of the separator directly affects the cycle and safety performance of the battery.

[0004] In particular, it is particularly noted that when the internal temperature of the battery reaches a certain time, the shrinkage of the separator in the TD direction is large, which leads to the short circuit of the positive and negative electrodes and the thermal runaway, and there is a safety risk. At the same time, in the later stage of the cycle, the free electrolyte in the shell is continuously reduced, and the thickness of the battery is continuously increased, which forces the free electrolyte to be weakly reabsorbed in the charging and discharging process, and then affects the wetting effect of the electrolyte in the separator and the electrode sheet, causing the adverse phenomena of local position appearing dark lines and lithium precipitation, leading to the cycle diving or thermal runaway of the battery. As can be seen, the heat resistance and wetting performance of the secondary battery separator are of great significance to the cycle and safety performance of the battery. SUMMARY

[0005] The purpose of the present application is to solve the problem of poor cycle performance and rate performance of the existing secondary battery, and to provide a separator with excellent thermal stability at high temperature and fast electrolyte wetting rate, a secondary battery with excellent cycle performance and rate performance and low internal resistance, and an electric device.

[0006] To achieve the above purpose, the first aspect of the present application provides a separator, comprising a base film, a first coating layer and a second coating layer, the first coating layer is arranged on at least one side of the base film, and the second coating layer is arranged on the surface of the first coating layer.

[0007] The first coating layer comprises first inorganic particles and a first binder; the Dv50 of the first inorganic particles is 0.1-0.5 μm, and the glass transition temperature Tg of the first binder is >100℃.

[0008] The second coating layer comprises second inorganic particles, the second inorganic particles are modified ceramic particles modified by acrylic copolymer, and the Dv50 of the second inorganic particles is 0.6-1.5 μm.

[0009] As an embodiment of the present application, the acrylic copolymer comprises at least one of carboxyl and cyano.

[0010] As an embodiment of the present application, at least one of the following is satisfied:

[0011] a. The thickness of the first coating layer is 0.5-4 μm;

[0012] b. The bulk density of the first coating layer is 1-4 g / cm 3 ;

[0013] c. The porosity of the first coating layer is 45-55%.

[0014] As an embodiment of the present application, at least one of the following is satisfied:

[0015] d. The thickness of the second coating layer is 1-4 μm;

[0016] e. The bulk density of the second coating layer is 1-3 g / cm 3 ;

[0017] f. The porosity of the second coating layer is ≥50%.

[0018] As an embodiment of the present application, the structural formula of the acrylic copolymer is shown in Formula I:

[0019] wherein R1-R5 are each independently selected from any one of hydrogen atom and C1-C6 alkyl.

[0020] As an embodiment of the present application, the swelling degree of the first binder immersed in electrolyte at 60 ℃ for 48 h is ≤50%.

[0021] As an embodiment of the present application, the second coating layer further comprises a second binder, and the swelling degree of the second binder immersed in electrolyte at 60 ℃ for 48 h is >50%.

[0022] As an embodiment of the present application, the first inorganic particles comprise at least one of aluminum trioxide, boehmite, silicon dioxide, montmorillonite, magnesium hydroxide, zirconium oxide and barium sulfate.

[0023] As an embodiment of the present application, the ceramic particles comprise at least one of aluminum trioxide, boehmite, silicon dioxide, montmorillonite, magnesium hydroxide, zirconium oxide and barium sulfate.

[0024] As an embodiment of the present application, the first binder and the second binder each independently comprise an organic binder or an inorganic binder.

[0025] As an embodiment of the present application, the first coating further comprises a first dispersant, and the second coating further comprises a second dispersant.

[0026] The first dispersant and the second dispersant each independently comprise at least one of sodium carboxymethyl cellulose, polyacrylamide, sodium polyacrylate, and polyvinyl carboxylic acid.

[0027] In a second aspect of the present application, a secondary battery is provided, comprising the separator of the present application.

[0028] In a third aspect of the present application, an electric device is provided, comprising the secondary battery of the present application.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] The separator provided by the present application can significantly improve the thermal stability of the separator and the impregnation rate of the electrolyte of the separator while maintaining the transmission rate of ions and electrons of the separator, thereby reducing the internal resistance of the secondary battery and improving the cycle performance and rate performance of the secondary battery, by sequentially arranging a first coating and a second coating on the surface of the base film, and controlling the Dv50 of the first inorganic particles in the first coating and the glass transition temperature Tg of the first binder within a suitable range, and simultaneously controlling the second inorganic particles in the second coating to comprise ceramic particles with acrylic polymer thereon. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a structural schematic diagram of the separator prepared in Example 1 of the present application: 1-base film, 2-first coating, 3-second coating;

[0032] Figure 2 is a structural schematic diagram of the separator prepared in Example 2 of the present application: 1-base film, 2-first coating, 3-second coating;

[0033] Figure 3 is a surface SEM image of the first coating prepared in Example 1 of the present application;

[0034] Figure 4 is a surface contact angle test schematic diagram of the first coating prepared in Example 1 of the present application;

[0035] Figure 5 is a surface SEM image of the second coating prepared in Example 1 of the present application;

[0036] Figure 6 is a surface contact angle test schematic diagram of the second coating prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0037] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts should fall within the scope of the present application.

[0038] In the present application, the technical features described in an open way include both the closed technical solutions consisting of the listed features and the open technical solutions containing the listed features.

[0039] In the present application, if no special description is made, the numerical range is regarded as continuous and includes the minimum value and the maximum value of the range and each value between the minimum value and the maximum value. Further, when the range refers to an integer, each integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or a property, the ranges can be combined. In other words, unless otherwise specified, all the ranges disclosed herein should be understood as including any and all sub-ranges falling within the range.

[0040] The reagents or instruments used in the present application are all conventional products that can be obtained from the market, if no manufacturer is specified.

[0041] In one embodiment of the present application, the present application provides a separator, which comprises a base film, a first coating layer and a second coating layer, the first coating layer is arranged on at least one side of the base film, and the second coating layer is arranged on the surface of the first coating layer.

[0042] The first coating layer comprises first inorganic particles and a first binder, the Dv50 of the first inorganic particles is 0.1-0.5 μm, and the glass transition temperature Tg of the first binder is greater than 100℃.

[0043] The second coating layer comprises second inorganic particles, the second inorganic particles comprise ceramic particles, the ceramic particles are coated with an acrylic copolymer, and the Dv50 of the second inorganic particles is 0.6-1.5 μm.

[0044] The inventors of the present application have found that the setting of the surface coating of the separator has a significant influence on the thermal stability of the separator and the wettability of the electrolyte, and also influences the conduction rate of ions or electrons, thereby affecting the cycle performance, rate performance and internal resistance of the secondary battery; when the provided separator is provided with a first coating layer and a second coating layer on the surface of the base film in sequence, and the Dv50 of the first inorganic particles in the first coating layer and the glass transition temperature Tg of the first binder are controlled within a suitable range, and the second inorganic particles in the second coating layer comprise ceramic particles and the ceramic particles have acrylic polymers thereon, the thermal stability of the separator and the wettability of the electrolyte to the separator can be significantly improved on the basis of ensuring excellent conduction rate of ions and electrons, thereby significantly improving the cycle performance and rate performance of the secondary battery and maintaining a low internal resistance of the secondary battery.

[0045] Specifically, when the Dv50 of the first inorganic particles in the first coating layer is within the range of 0.1-0.5 μm, the bulk density of the first coating layer can be improved, thereby improving the support ability of the separator when heated and maintaining the structural stability of the separator; when the glass transition temperature Tg of the first binder in the first coating layer is >100℃, the heat resistance of the separator can be further improved in combination with the selection of the Dv50 of the first inorganic particles within the range of 0.1-0.5 μm. The second inorganic particles in the second coating layer comprise ceramic particles and the ceramic particles have acrylic copolymers thereon, wherein the acrylic copolymers contain functional groups such as carboxyl and cyano groups, which have excellent liquid affinity and can improve the wettability of the electrolyte to the separator. In addition, the Dv50 of the second inorganic particles is 0.6-1.5 μm, and the design of larger particles can relatively reduce the bulk density and improve the porosity, thereby further improving the wettability of the electrolyte to the separator. In addition, the second coating layer is arranged on the surface of the first coating layer, which can better play the roles of the two, maintain high heat resistance, achieve high wettability of the electrolyte to the separator, and will not adversely affect the conduction rate of ions or electrons; and further achieve good cycle performance and rate performance of the secondary battery and a low internal resistance.

[0046] In an embodiment, the ceramic particles are modified by acrylic copolymers, and the acrylic copolymers include at least one of carboxyl and cyano groups.

[0047] It should be noted that the presence of acrylic copolymers on the ceramic particles and the presence of at least one of carboxyl and cyano groups in the acrylic copolymers can be determined by nuclear magnetic resonance spectroscopy and infrared spectroscopy.

[0048] Exemplarily, the Dv50 of the first inorganic particles can be any point value or any range value between any two point values in the range of 0.1-0.5 μm, such as 0.10 μm, 0.12 μm, 0.14 μm, 0.16 μm, 0.18 μm, 0.20 μm, 0.22 μm, 0.24 μm, 0.26 μm, 0.28 μm, 0.30 μm, 0.32 μm, 0.34 μm, 0.36 μm, 0.38 μm, 0.40 μm, 0.42 μm, 0.44 μm, 0.46 μm, 0.48 μm, 0.50 μm, etc.

[0049] In an embodiment, the Dv50 of the first inorganic particles is 0.3-0.4 μm, such as 0.31 μm, 0.33 μm, 0.35 μm, 0.37 μm, 0.39 μm, etc., or any range value between any two point values thereof. The inventors of the present application have found that when the Dv50 of the first inorganic particles in the first coating is further selected to be 0.3-0.4 μm, the heat-resistant stability of the obtained separator is more optimal, and the impedance thereof is smaller, and the conduction rate of ions and electrons is more optimal, so that when the obtained separator is applied to the preparation of a secondary battery, the internal resistance of the obtained secondary battery is lower, and the cycle performance and rate performance thereof are more optimal.

[0050] Exemplarily, the glass transition temperature Tg of the first binder can be any point value or any range value between any two point values in the range of greater than 100 ℃, such as 101 ℃, 110 ℃, 120 ℃, 130 ℃, 140 ℃, 150 ℃, 160 ℃, 170 ℃, 180 ℃, 190 ℃, 200 ℃, 210 ℃, 220 ℃, 230 ℃, 240 ℃, 250 ℃, 260 ℃, 270 ℃, 280 ℃, 290 ℃, 300 ℃, etc.

[0051] In an embodiment, the glass transition temperature Tg of the first binder is 160-200 ℃. For example, it can be 162 ℃, 164 ℃, 166 ℃, 168 ℃, 170 ℃, 172 ℃, 174 ℃, 176 ℃, 178 ℃, 180 ℃, 182 ℃, 184 ℃, 186 ℃, 188 ℃, 190 ℃, 192 ℃, 194 ℃, 196 ℃, 198 ℃, 200 ℃, etc., or any range value between any two point values thereof. The inventors of the present application have found that when the glass transition temperature Tg of the first binder is further selected to be 160-200 ℃, the comprehensive performance of the obtained secondary battery is more optimal.

[0052] For example, the Dv50 of the second inorganic particle can be any point value or any two point values ​​within the range of 0.6 to 1.5 μm, such as 0.60 μm, 0.65 μm, 0.70 μm, 0.75 μm, 0.80 μm, 0.85 μm, 0.90 μm, 0.95 μm, 1.00 μm, 1.05 μm, 1.10 μm, 1.15 μm, 1.20 μm, 1.25 μm, 1.30 μm, 1.35 μm, 1.40 μm, 1.45 μm, 1.45 μm, 1.50 μm, etc.

[0053] In one embodiment, the Dv50 of the second inorganic particles is 0.8–1.2 μm, for example, it can be 0.82 μm, 0.84 μm, 0.86 μm, 0.88 μm, 0.92 μm, 0.94 μm, 0.96 μm, 0.98 μm, 1.02 μm, 1.04 μm, 1.06 μm, 1.08 μm, 1.12 μm, 1.14 μm, 1.16 μm, 1.18 μm, or any two of these ranges. The inventors of this application have discovered that when the Dv50 of the second inorganic particles in the second coating is further selected to be 0.8–1.2 μm, the wettability of the electrolyte to the separator can be better improved, and the good impedance of the separator can be maintained, thereby achieving lower internal resistance and better cycle performance and rate performance of the secondary battery.

[0054] In one embodiment, the thickness of the first coating is 0.5 to 4 μm.

[0055] For example, the thickness of the first coating can be any point value or any two points within the range of 0.5 to 4 μm, such as 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4.0 μm, etc.

[0056] The inventors of this application have discovered that the choice of the thickness of the first coating affects the thermal stability of the separator and the ion and electron transport speed. When the thickness of the first coating is further selected to be 0.5 to 4 μm, the resulting secondary battery has lower internal resistance and better cycle performance and rate performance.

[0057] In one embodiment, the bulk density of the first coating is 1–4 g / cm³. 3 .

[0058] For example, the bulk density of the first coating may be 1 to 4 g / cm³. 3 The value at any point within the range, or the value between any two points, for example, 1.0 g / cm³. 3 1.2g / cm3 1.4 g / cm 3 1.6 g / cm 3 1.8 g / cm 3 2.0 g / cm 3 2.2 g / cm 3 2.4 g / cm 3 2.6 g / cm 3 2.8 g / cm 3 3.0 g / cm 3 3.2 g / cm 3 3.4 g / cm 3 3.6 g / cm 3 3.8 g / cm 3 4.0 g / cm 3 and the like.

[0059] In an embodiment, the bulk density of the first coating layer is 1.37-1.9 g / cm 3 .

[0060] The inventors of the present application have found that the bulk density of the first coating layer is influenced to some extent by the Dv50 value of the first inorganic particles and the type of the first inorganic particles, and when the Dv50 value and the type of the first inorganic particles are controlled to be within the ranges given in the present application, the bulk density of the obtained first coating layer is 1-4 g / cm 3 Within this range of bulk density, the stability of the separator under heat can be better improved, and thus the comprehensive performance of the secondary battery can be improved.

[0061] In an embodiment, the porosity of the first coating layer is 45-55%.

[0062] For example, the porosity of the first coating layer can be any point value or any range value within the range of 45-55%, such as 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, and the like.

[0063] The inventors of the present application have found that the porosity of the first coating layer not only influences the heat stability of the separator, but also influences the transmission of ions and electrons, and when the porosity of the first coating layer is further controlled to be 45-55%, the comprehensive performance of the obtained separator is better, the internal resistance of the obtained secondary battery is lower, and the cycle performance and rate performance are also more excellent.

[0064] In an embodiment, the thickness of the second coating layer is 1-4 μm.

[0065] Exemplarily, the thickness of the second coating layer can be any point value or any two-point range value in the range of 1-4 μm, such as 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4.0 μm, etc.

[0066] The inventors of the present application have found that the thickness of the second coating layer affects the impregnation of the electrolyte on the separator, and also affects the ion and electron transmission rate in application. When the thickness of the second coating layer is further controlled to be 1-4 μm, the obtained secondary battery has a lower internal resistance, and the cycle performance and rate performance are more excellent.

[0067] In an embodiment, the bulk density of the second coating layer is 1-3 g / cm 3 .

[0068] Exemplarily, the bulk density of the second coating layer can be any point value or any two-point range value in the range of 1-3 g / cm 3 , such as 1.0 g / cm 3 , 1.2 g / cm 3 , 1.4 g / cm 3 , 1.6 g / cm 3 , 1.8 g / cm 3 , 2.0 g / cm 3 , 2.2 g / cm 3 , 2.4 g / cm 3 , 2.6 g / cm 3 , 2.8 g / cm 3 , 3.0 g / cm 3 , etc.

[0069] In an embodiment, the bulk density of the second coating layer is 1.35-1.40 g / cm 3 .

[0070] The inventors of the present application have found that the bulk density of the second coating layer is affected to some extent by the Dv50 value of the second inorganic particles and the type of the second inorganic particles. When the Dv50 value and the type of the second inorganic particles are controlled to be within the ranges given in the present application, the bulk density of the obtained second coating layer is 1-3 g / cm 3 . Within this bulk density range, the impregnation of the electrolyte on the separator can be better improved, and thus the comprehensive performance of the secondary battery is improved.

[0071] In an embodiment, the bulk density of the first coating layer is greater than the bulk density of the second coating layer.

[0072] In an embodiment, the porosity of the second coating layer is ≥50%.

[0073] Illustratively, the porosity of the second coating layer can be any point value or any two-point range value within the range of ≥50%, such as 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, and the like.

[0074] In an embodiment, the porosity of the second coating layer is 50% to 70%.

[0075] The inventors of the present application have found that the porosity of the second coating layer not only affects the wettability of the electrolyte to the separator, but also affects the ion and electron transmission rate. When the porosity of the second coating layer is further controlled to be ≥50%, the comprehensive performance of the obtained separator is better, the internal resistance of the obtained secondary battery is lower, and the cycle performance and rate performance are also more excellent.

[0076] In an embodiment, the structural formula of the acrylic copolymer is shown as Formula I:

[0077] wherein R1 to R5 are each independently selected from any one of a hydrogen atom and a C1 to C6 alkyl group.

[0078] The inventors of the present application have found that the acrylic copolymer as described in the present application contains COO - and CN - , COO - and CN - have good lyophilicity, which can achieve good wettability of the electrolyte to the separator; at the same time, its structure can better promote the transmission of ions and electrons, thereby reducing the internal resistance of the secondary battery while improving the cycle performance and rate performance of the secondary battery.

[0079] In an embodiment, the weight average molecular weight of the acrylic copolymer is 300,000 to 2,000,000.

[0080] Illustratively, the weight average molecular weight of the acrylic copolymer can be any point value or any two-point range value between 300,000 and 2,000,000, such as 300,000, 500,000, 700,000, 900,000, 1,100,000, 1,300,000, 1,500,000, 1,700,000, 1,900,000, 2,000,000, and the like.

[0081] In an embodiment, the method for modifying the ceramic particles with the acrylic copolymer comprises the following steps:

[0082] S1, uniformly mixing ceramic particles, anhydrous ethanol, deionized water, ammonia water and methacrylic acid acryloxypropyl trimethoxysilane, and then performing ultrasonic reaction, centrifuging after the reaction is completed, collecting the solid and washing and drying to obtain a modified ceramic precursor;

[0083] S2, dispersing the modified ceramic precursor in deionized water, then adding an acrylic copolymer solution and an initiator, refluxing under an inert gas environment, filtering after the refluxing reaction, collecting the solid and washing, drying to obtain the modified ceramic particles modified by the acrylic copolymer.

[0084] In an embodiment, in step S1, the mass ratio of the ceramic particles, ammonia water and methylacrylic acid yloxypropyl trimethoxysilane is 1:(0.5-1):(0.5-1).

[0085] In an embodiment, in step S1, the temperature of the ultrasonic reaction is 25-45℃, and the time is 66-80h.

[0086] In an embodiment, in step S2, the mass ratio of the modified ceramic precursor, the acrylic copolymer solution and the initiator is 1:(1-2):(0.01-0.1).

[0087] In an embodiment, in step S2, the refluxing reaction time is 4-12h.

[0088] In an embodiment, the initiator includes at least one of potassium persulfate and azobis isobutyronitrile.

[0089] In an embodiment, as an embodiment of the present application, the swelling degree of the first binder immersed in the electrolyte at 60℃ for 48h is ≤50%.

[0090] It should be noted that the electrolyte is an electrolyte obtained by dissolving lithium hexafluorophosphate in a mixed solvent with a mass fraction ratio of EC:DMC:EMC of 1:2:1.

[0091] Illustratively, the swelling degree of the first binder immersed in the electrolyte at 60℃ for 48h can be any point value or any two-point range value within the range of ≤50%, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.

[0092] The inventors of the present application found that when the swelling degree of the first binder immersed in the electrolyte at 60℃ for 48h is limited within the range of ≤50%, it not only has good bonding performance, but also has excellent compatibility with other substances, thereby improving the uniformity and stability of the first coating, and further improving the comprehensive performance of the secondary battery.

[0093] In an embodiment, the second coating further includes a second binder, and the swelling degree of the second binder immersed in the electrolyte at 60℃ for 48h is >50%.

[0094] It should be noted that the electrolyte is an electrolyte obtained by dissolving lithium hexafluorophosphate in a mixed solvent with a mass fraction ratio of EC:DMC:EMC of 1:2:1.

[0095] Exemplarily, the swelling degree of the second binder soaked in the electrolyte at 60℃ for 48h can be any point value or any two-point range value in the range of >50%, such as 51%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, etc.

[0096] The inventors of the present application have found that when the swelling degree of the second binder soaked in the electrolyte at 60℃ for 48h is in the range given in the present application, the adhesion and uniform distribution of the second coating can be effectively balanced, thereby improving the overall performance of the secondary battery.

[0097] In an embodiment, the first inorganic particles include at least one of aluminum trioxide, boehmite, silicon dioxide, montmorillonite, magnesium hydroxide, zirconium oxide, and barium sulfate.

[0098] In an embodiment, the ceramic particles include at least one of aluminum trioxide, boehmite, silicon dioxide, montmorillonite, magnesium hydroxide, zirconium oxide, and barium sulfate.

[0099] In an embodiment, the first binder and the second binder each independently include an organic binder or an inorganic binder.

[0100] Exemplarily, the organic binder includes at least one of an acrylate-based binder, an acrylic-based binder, an acrylamide-based binder, an amide-based binder, and an acrylonitrile-based binder; and the inorganic binder includes at least one of a phosphate-based binder and a silicate-based binder.

[0101] In an embodiment, the first binder and the second binder each independently include at least one of polyacrylamide, polyacrylic acid, polyacrylonitrile, polyacrylate, phosphate, and silicate.

[0102] In an embodiment, the first coating further includes a first dispersant, and the second coating further includes a second dispersant.

[0103] The first dispersant and the second dispersant each independently include at least one of sodium carboxymethyl cellulose, polyacrylamide, sodium polyacrylate, and polyethylene carboxylic acid.

[0104] In an embodiment, the first coating further includes a first auxiliary agent, and the second coating further includes a second auxiliary agent.

[0105] The first and second auxiliary agents each independently include at least one of a polyacrylate, a polyether-modified polydimethylsiloxane, an organosiloxane copolymer, and an ammonium salt.

[0106] In an embodiment, the base film has a thickness of 2-20 μm. For example, it can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or any range between any two of these values.

[0107] In an embodiment, the base film has a pore size of 10-60 μm. For example, it can be 10 μm, 14 μm, 18 μm, 22 μm, 26 μm, 30 μm, 34 μm, 38 μm, 42 μm, 46 μm, 50 μm, 54 μm, 58 μm, 60 μm, or any range between any two of these values.

[0108] In an embodiment, the base film has an air permeability of <500 s / 100 mL. For example, it can be 498 s / 100 mL, 488 s / 100 mL, 478 s / 100 mL, 468 s / 100 mL, 458 s / 100 mL, 448 s / 100 mL, 438 s / 100 mL, 428 s / 100 mL, 418 s / 100 mL, 398 s / 100 mL, 358 s / 100 mL, 318 s / 100 mL, 288 s / 100 mL, 258 s / 100 mL, 208 s / 100 mL, 158 s / 100 mL, 108 s / 100 mL, 58 s / 100 mL, or any range between any two of these values.

[0109] In an embodiment, the base film has a porosity of 30-60%. For example, it can be 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, or any range between any two of these values.

[0110] In an embodiment, the base film includes at least one of a polyethylene film, a polypropylene film, a polyimide film, a polyethylene non-woven fabric, and a polyvinylidene fluoride film.

[0111] The inventors of the present application have found that when the parameters of the base film, such as thickness, pore size, air permeability, porosity, and material, are further selected to be within the above ranges, the performance of the resulting separator is more optimal, and when applied to the preparation of a secondary battery, the comprehensive performance of the resulting secondary battery is also more optimal.

[0112] In an embodiment, the method for preparing the separator includes the following steps:

[0113] S1, preparation of the first coating slurry: the first inorganic particles, the first binder, the first dispersant and the first auxiliary agent are mixed and stirred to obtain the first coating slurry;

[0114] S2, preparation of the second coating slurry: the second inorganic particles, the second binder, the second dispersant and the second auxiliary agent are mixed and stirred to obtain the second coating slurry;

[0115] S3, preparation of the separator: the first coating slurry is coated on at least one side of the base film, and then the second coating slurry is coated on the surface of the first coating after drying, and the separator is obtained.

[0116] In an embodiment, in step S1, the solid content of the first coating slurry is 20-60%, and the viscosity is 10-700 mPa.s.

[0117] In an embodiment, in step S2, the solid content of the second coating slurry is 20-60%, and the viscosity is 10-700 mPa.s.

[0118] In an embodiment, in step S3, the coating method includes micro-gravure coating.

[0119] In an embodiment of the present application, the present application provides a secondary battery, which comprises the separator described in the present application.

[0120] In an embodiment, the secondary battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator.

[0121] In an embodiment, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector; the positive electrode active material layer comprises a positive electrode active material. The present application does not limit the positive electrode active material, and any known positive electrode active material can be used.

[0122] In an embodiment, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; the negative electrode active material layer comprises a negative electrode active material. The present application does not limit the negative electrode active material, and any known negative electrode active material can be used.

[0123] In an embodiment, the electrolyte comprises an organic solvent, a lithium salt and an additive.

[0124] In an embodiment, the organic solvent comprises at least one of ethylene carbonate, propylene carbonate and diethyl carbonate; the lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate and lithium hexafluorophosphate arsenate; the additive comprises at least one of a film-forming additive, a conductive additive and a flame-retardant additive.

[0125] In an embodiment, the separator of the secondary battery is disposed between the positive electrode and the negative electrode.

[0126] In one embodiment of the present application, the present application provides an electric device, which comprises the secondary battery as described in the present application.

[0127] For example, the electric device can include a mobile device (e.g., a mobile phone, a notebook computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0128] Embodiment 1

[0129] The present application provides a separator and a secondary battery, and a preparation method of the secondary battery, which comprises the following steps:

[0130] (1) Preparation of the separator

[0131] S1, Preparation of the ceramic precursor: 50 g of ceramic particles (boehmite, Dv50 of 0.3 μm) were stirred in 2 L of anhydrous ethanol, and then 40 g of ammonia water and 40 g of methacrylic acid acryloxypropyl trimethoxysilane were sequentially added, stirred and ultrasonically treated for 72 h; after the ultrasonic treatment, centrifugation was performed, the solid was collected and washed with deionized water for 3 times, and then dried in a vacuum drying oven at 70°C to obtain the ceramic precursor;

[0132] S2, Preparation of the modified ceramic particles: 10 g of the ceramic precursor prepared in step S1 was stirred in 1 L of deionized water, and then 20 g of an acrylic acid copolymer solution (R1=CH3, R2=CH2CH3, R3=CH3, R4=(CH2)2CH3, R5=(CH2)3CH3, weight average molecular weight of 50,000) and 0.3 g of an initiator (potassium persulfate) were added, and refluxed for 8 h under the environment of nitrogen, and then filtered, the filter residue was collected and washed with deionized water for 3 times, and then dried in a vacuum drying oven at 70°C to obtain the modified ceramic particles;

[0133] S3, Preparation of the first coating slurry: the first inorganic particles (boehmite, Dv50=0.3 μm), the first binder (modified polyacrylamide polymer solution, glass transition temperature Tg of 180°C), the first dispersant (sodium carboxymethyl cellulose) and the first auxiliary agent (ammonium salt) were added into a stirring tank in a dry weight mass ratio of 95:1:3:1, and then stirred to obtain a first coating slurry with a solid content of 40% and a slurry viscosity of 180 mPa.s;

[0134] S4, Preparation of the second coating slurry: The modified ceramic particles (Dv50 = 0.3 pm), the second binder (polyacrylate), the second dispersant (sodium carboxymethyl cellulose) and the second additive (ammonium salt) were added into a stirring tank in a dry weight mass ratio of 93:1:5:1 and stirred thoroughly to obtain a second coating slurry with a solid content of 40% and a slurry viscosity of 95 mPa.s;

[0135] S5, Preparation of the separator: The first coating slurry prepared in S3 was coated onto one side of the base film (the base film material was PE, the thickness was 7 pm, the pore size was 40 nm, the air permeability was 150 s / 100 mL and the porosity was 36%) in a microgravure manner, and baked in an oven at 65°C for 20 s to obtain a first coating layer with a coating thickness of 2 pm, a bulk density of 1.48 g / cm3and a porosity of 50.83%; then the second coating slurry prepared in S4 was coated onto the surface of the first coating layer in a microgravure manner, and baked in an oven at 65°C for 20 s to obtain a second coating layer with a coating thickness of 2 pm, a bulk density of 1.37 g / cm3and a porosity of 54.43%; finally, the separator was obtained. 3 3

[0136] (2) Preparation of the secondary battery

[0137] S1, Preparation of the positive electrode sheet: The lithium iron phosphate, the conductive agent (conductive carbon black) and the binder (polyvinylidene fluoride polymer) were added into NMP solvent in a dry weight mass ratio of 97:1:2 and stirred thoroughly to form a positive electrode slurry with a solid content of 58% and a viscosity of 7000 mPa.s, then the positive electrode slurry was coated on an aluminum foil, dried, rolled, and cut to obtain the positive electrode sheet;

[0138] S2, Preparation of the negative electrode sheet: The graphite, the conductive agent (conductive carbon black), the dispersant (sodium carboxymethyl cellulose) and the binder (styrene butadiene rubber) were added into deionized water solvent in a dry weight mass ratio of 96:1:1:2 and stirred thoroughly to form a negative electrode slurry with a solid content of 53% and a viscosity of 3000 mPa.s, then the slurry was coated on a copper foil, dried, rolled, and cut to obtain the negative electrode sheet;

[0139] S3, Preparation of the electrolyte: Lithium hexafluorophosphate was dissolved in a mixed solvent with a mass fraction ratio of EC:DMC:EMC of 1:2:1 to obtain the electrolyte;

[0140] S4, Preparation of the secondary battery: The separator, the positive electrode sheet and the negative electrode sheet were wound to obtain a multi-tab cell, and then sequentially subjected to hot pressing (pressure 0.4 Mpa, time 8 s, hot pressing temperature 85°C), baking, liquid injection and formation to obtain the secondary battery.

[0141] Example 2

[0142] ​​The embodiment of the present application provides a diaphragm and a secondary battery, and the only difference between the preparation method of the secondary battery and the embodiment 1 is that in the S5 of the preparation of the diaphragm, the step S5 of the preparation of the diaphragm in the embodiment is:

[0143] The first coating slurry prepared in S3 is coated on two surfaces of the base film (the base film material is PE, the thickness is 7 microns, the pore size is 40 nm, the air permeability is 150 s / 100 mL, and the porosity is 36%) in a microgravure mode, and is baked in an oven at 65 DEG C for 20 s to obtain a first coating layer with a coating thickness of 2 microns, a bulk density of 1.48 g / cm 3 , and a porosity of 50.83%; then the second coating slurry prepared in S4 is coated on the surface of the first coating layer in a microgravure mode, and is baked in an oven at 65 DEG C for 20 s to obtain a second coating layer with a coating thickness of 2 microns, a bulk density of 1.37 g / cm 3 , and a porosity of 54.43%, and finally the diaphragm is obtained.

[0144] Embodiments 3-5

[0145] The embodiment of the present application provides a diaphragm and a secondary battery, and the only difference between the preparation method of the secondary battery and the embodiment 1 is that the Dv50 value of the first inorganic particles used is adjusted.

[0146] Embodiment 6

[0147] The embodiment of the present application provides a diaphragm and a secondary battery, and the only difference between the preparation method of the secondary battery and the embodiment 1 is that the first binder is a modified polyacrylamide high molecular water solution (Tg temperature is 160 DEG C).

[0148] Embodiment 7

[0149] The embodiment of the present application provides a diaphragm and a secondary battery, and the only difference between the preparation method of the secondary battery and the embodiment 1 is that the first binder is a modified polyacrylamide high molecular water solution (Tg temperature is 160 DEG C).

[0150] Embodiments 8-10

[0151] The embodiment of the present application provides a diaphragm and a secondary battery, and the only difference between the preparation method of the secondary battery and the embodiment 1 is that the Dv50 of the second inorganic particles is adjusted.

[0152] Embodiments 11-12

[0153] The embodiment of the present application provides a diaphragm and a secondary battery, and the only difference between the preparation method of the secondary battery and the embodiment 1 is that the thickness of the first coating layer is adjusted.

[0154] Embodiments 13-14

[0155] The present application provides a separator and a secondary battery, the only difference between the preparation method of the secondary battery and that of Example 1 is adjusting the thickness of the second coating.

[0156] Example 15

[0157] The present application provides a separator and a secondary battery, the only difference between the preparation method of the secondary battery and that of Example 1 is using aluminum oxide as the first inorganic particles.

[0158] Example 16

[0159] The present application provides a separator and a secondary battery, the only difference between the preparation method of the secondary battery and that of Example 1 is using zirconium oxide as the ceramic particles.

[0160] Comparative Examples 1-2

[0161] The present application provides a separator and a secondary battery, the only difference between the preparation method of the secondary battery and that of Example 1 is adjusting the Dv50 of the first inorganic particles.

[0162] Comparative Example 3

[0163] The present application provides a separator and a secondary battery, the only difference between the preparation method of the secondary battery and that of Example 1 is using polyacrylic acid emulsion (glass transition temperature is 100℃) as the first binder.

[0164] Comparative Examples 4-5

[0165] The present application provides a separator and a secondary battery, the only difference between the preparation method of the secondary battery and that of Example 1 is adjusting the Dv50 of the second inorganic particles.

[0166] Comparative Example 6

[0167] The present application provides a separator and a secondary battery, the only difference between the preparation method of the secondary battery and that of Example 1 is that the second inorganic particles in the second coating are unmodified ceramic particles.

[0168] Comparative Example 7

[0169] The present application provides a separator and a secondary battery, the only difference between the preparation method of the secondary battery and that of Example 1 is that in the preparation of the modified ceramic particles, polymethyl methacrylate is used instead of acrylic acid copolymer solution.

[0170] Comparative Example 8

[0171] The present application provides a separator and a secondary battery, the only difference between the preparation method of the secondary battery and that of Example 1 is that in the preparation of the modified ceramic particles, methyl acrylate monomer is used instead of acrylic acid copolymer solution.

[0172] Comparative Example 9

[0173] The application comparative example provides a separator and a secondary battery, and the only difference between the preparation method of the secondary battery and example 1 is that in the preparation of the separator, the step S5 of the preparation of the separator is:

[0174] The second coating slurry prepared in S4 is first coated on one side of the base film (the base film material is PE, the thickness is 7 μm, the pore size is 40Nm, the air permeability is 150 s / 100mL, and the porosity is 36%) in a microgravure mode, and is baked in an oven at 65°C for 20s to obtain a second coating layer with a coating thickness of 2 μm, a bulk density of 1.48 g / cm 3 , and a porosity of 50.83%; then the first coating slurry prepared in S3 is coated on the surface of the second coating layer in a microgravure mode, and is baked in an oven at 65°C for 20s to obtain a first coating layer with a coating thickness of 2 μm, a bulk density of 1.37 g / cm 3 , and a porosity of 54.43%, and finally a separator is obtained.

[0175] The parameters and performance data of the examples and comparative examples are shown in Tables 1-2, wherein the parameter tests in Tables 1-2 are as follows:

[0176] 1) Dv50 of the first inorganic particles and the second inorganic particles: tested by a laser particle size analyzer;

[0177] 2) Glass transition temperature of the first binder: tested by a DSC differential scanning calorimeter;

[0178] 3) Thickness of the first coating layer and the second coating layer: tested by a Malvern thickness meter;

[0179] 4) Bulk density of the first coating layer and the second coating layer: bulk density = area density / thickness, wherein the area density is tested by an electronic balance;

[0180] 5) Porosity of the first coating layer and the second coating layer: porosity = 1-(bulk density / true density of the material), wherein the true density of the material refers to the density of the first inorganic particles in the first coating layer and the ceramic particles in the second coating layer;

[0181] 6) Swelling degree of the first binder / second binder after being soaked in an electrolyte (the electrolyte is the electrolyte in step S3 of example 1) at 60°C for 48h: tested and calculated after weighing by an electronic balance;

[0182] 7) Contact angle of the separator: the solvent is an electrolyte (the electrolyte is the electrolyte in step S3 of example 1), the drop amount is 2 μL, the photographing time is 10s, and one photo is taken every 0.3s;

[0183] 8) Heat shrinkage of the separator: cut the separator into 100mm*100mm size separator, place it in the middle of two A4 papers, then place it in a 150℃ air oven for 1h, then measure the heat shrinkage of the separator in TD direction = (L0 before baking-L1 after baking) / L0 before baking*100%;

[0184] 9) DCR of the secondary battery: record the impedance of the lithium ion battery at 25℃ constant temperature box under 5C 10s discharge at 50% SOC state;

[0185] 10) Rate performance of the secondary battery: take the 1C charge-discharge capacity of the secondary battery as the benchmark, calculate the percentage of 3C discharge capacity to 1C charge-discharge capacity;

[0186] 11) Cycle performance of the secondary battery: count the cycle number of the lithium ion battery at 25℃ constant temperature box under equivalent 3.5C / 1C when the capacity retention rate is 80%;

[0187] Table 1

[0188] Table 2

[0189] As can be seen from Table 2, when the technical solution provided in the present application is adopted, the comprehensive performance of the secondary battery obtained is excellent, specifically, the internal resistance is low, below 0.76 mΩ, the rate performance is excellent, above 90.3%, and the cycle performance is excellent, above 3456 cycles.

[0190] As can be seen from Example 1 and Comparative Examples 1-2, when the Dv50 value of the first inorganic particles in the first coating layer is not within the range given in the present application, the rate performance and cycle performance of the secondary battery obtained both show a certain downward trend; as can be seen from Example 1 and Comparative Example 3, when the glass transition temperature of the first binder in the first coating layer is not within the range given in the present application, the rate performance and cycle performance of the secondary battery obtained both decrease significantly; as can be seen from Example 1 and Comparative Examples 4-5, when the Dv50 value of the second inorganic particles in the second coating layer is not within the range given in the present application, the rate performance and cycle performance of the secondary battery obtained also deteriorate significantly; as can be seen from Example 1 and Comparative Examples 6-8, whether the second inorganic particles in the second coating layer are not modified or are modified by other substances, the comprehensive performance of the secondary battery obtained all shows a significant downward trend; as can be seen from Example 1 and Comparative Example 9, the order of the first coating layer and the second coating layer in the separator also affects the comprehensive performance of the secondary battery.

[0191] In addition, a structure schematic diagram of the separator in Example 1 is shown in Figure 1, and a structure schematic diagram of the separator in Example 2 is shown in Figure 2; an SEM image of the first coating surface prepared in Example 1 is shown in Figure 3, and a contact angle test schematic diagram of the first coating surface is shown in Figure 4; an SEM image of the second coating surface prepared in Example 1 is shown in Figure 5, and a contact angle test schematic diagram of the second coating surface is shown in Figure 6.

[0192] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A diaphragm, wherein, It includes a base film, a first coating and a second coating, wherein the first coating is disposed on at least one side of the base film and the second coating is disposed on the surface of the first coating; The first coating comprises first inorganic particles and a first binder; the Dv50 of the first inorganic particles is 0.1 to 0.5 μm, and the glass transition temperature Tg of the first binder is >100℃; The second coating comprises second inorganic particles, which include ceramic particles with an acrylic copolymer on them, and the Dv50 of the second inorganic particles is 0.6 to 1.5 μm.

2. The diaphragm according to claim 1, wherein, The acrylic copolymer contains at least one of carboxyl and cyano groups.

3. The diaphragm according to claim 1, wherein, Satisfy at least one of the following: a. The thickness of the first coating is 0.5–4 μm; b. The bulk density of the first coating is 1-4 g / cm³. 3 ; c. The porosity of the first coating is 45-55%.

4. The diaphragm according to claim 1, wherein, Satisfy at least one of the following: d. The thickness of the second coating is 1–4 μm; e. The bulk density of the second coating is 1–3 g / cm³. 3 ; f. The porosity of the second coating is ≥50%.

5. The diaphragm according to claim 1, wherein, The structural formula of the acrylic copolymer is shown in Formula I: R1 to R5 are each independently selected from hydrogen atoms and C1 to C6 alkyl groups.

6. The diaphragm according to claim 1, wherein, The swelling degree of the first adhesive after soaking in an electrolyte at 60°C for 48 hours is ≤50%.

7. The diaphragm according to claim 1, wherein, The second coating also includes a second adhesive, which has a swelling degree of >50% after being immersed in an electrolyte at 60°C for 48 hours.

8. The diaphragm according to claim 7, wherein, The first inorganic particles include at least one of aluminum oxide, boehmite, silicon dioxide, montmorillonite, magnesium hydroxide, zirconium oxide, and barium sulfate; And / or, the ceramic particles include at least one of alumina, boehmite, silica, montmorillonite, magnesium hydroxide, zirconium oxide, and barium sulfate; And / or, the first adhesive and the second adhesive each independently include organic adhesives or inorganic adhesives.

9. The diaphragm according to claim 8, wherein, The organic adhesive includes at least one of acrylate adhesives, acrylic adhesives, acrylamide adhesives, amide adhesives, and acrylonitrile adhesives; the inorganic adhesive includes at least one of phosphate adhesives and silicate adhesives.

10. The diaphragm according to claim 8, wherein, The first adhesive and the second adhesive each independently include at least one of polyacrylamide, polyacrylic acid, polyacrylonitrile, polyacrylate, phosphate, and silicate.

11. The diaphragm according to claim 1, wherein, The first coating further includes a first dispersant, and the second coating further includes a second dispersant; The first dispersant and the second dispersant each independently include at least one of sodium carboxymethyl cellulose, polyacrylamide, sodium polyacrylate, and polyvinyl carboxylic acid.

12. The diaphragm according to claim 1, wherein, The first coating further includes a first additive, and the second coating further includes a second additive; The first and second additives each independently include at least one of polyacrylate, polyether-modified polydimethylsiloxane, organosiloxane copolymer, and ammonium salt.

13. The diaphragm according to claim 1, wherein, Satisfy at least one of the following: 1) The thickness of the base film is 2–20 μm; 2) The pore size of the base film is 10–60 μm; 3) The air permeability of the base membrane is <500s / 100mL; 4) The porosity of the base membrane is 30-60%; 5) The base film includes at least one of polyethylene film, polypropylene film, polyimide film, polyethylene nonwoven fabric, and polyvinylidene fluoride film.

14. A method for preparing a diaphragm, comprising the following steps: S1. Preparation of the first coating slurry: The first inorganic particles, the first binder, the first dispersant and the first additive are mixed and stirred to obtain the first coating slurry; S2. Preparation of the second coating slurry: The second inorganic particles, the second binder, the second dispersant, and the second additive are mixed and stirred to obtain the second coating slurry; S3. Preparation of the diaphragm: The first coating slurry is coated onto at least one side of the base membrane, dried, and then the second coating slurry is coated onto the surface of the first coating and dried to obtain the diaphragm.

15. The preparation method according to claim 14, wherein, In step S1, the solid content of the first coating slurry is 20-60%, and the viscosity is 10-700 mPa·s.

16. The preparation method according to claim 14, wherein, In step S2, the solid content of the second coating slurry is 20-60%, and the viscosity is 10-700 mPa·s.

17. The preparation method according to claim 14, wherein, In step S3, the coating method includes microgravure coating.

18. A secondary battery, wherein, This includes the diaphragm as described in any one of claims 1 to 13 or the diaphragm obtained by the preparation method described in any one of claims 14 to 17.

19. An electrical appliance, wherein, It includes the secondary battery as described in claim 18.

20. The electrical appliance according to claim 19, wherein, The electrical devices include mobile devices, electric vehicles, electric trains, ships and satellites, and energy storage systems.

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