Separator coating, composite separator comprising same, and secondary battery and preparation method therefor

Abstract

Provided in the present disclosure are a separator coating, a composite separator comprising same, and a secondary battery and a preparation method therefor. The separator coating comprises a first coating and a second coating provided on the surface of the first coating, the second coating being close to the positive electrode side. On the basis of the total mass of the materials of the first coating being 100%, the materials of the first coating include a ceramic material having a mass percentage of 70%-92%, an ion-conductive material having a mass percentage of 3%-24%, and an adhesive having a mass percentage of 3%-6%. The separator coating provided in the present disclosure can be transferred in situ to the surface of the positive electrode by means of the pressure during battery assembly, thereby improving the safety of the secondary battery.

Description

A separator coating, a composite separator comprising the same, a secondary battery, and a preparation method

[0001] Cross Reference to Related Applications

[0002] This application claims priority to the Chinese patent application No. 202410862041.5, filed on June 28, 2024, entitled "A separator coating, a composite separator comprising the same, a secondary battery, and a preparation method", the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure belongs to the technical field of battery materials, and specifically relates to a separator coating, a composite separator comprising the same, a secondary battery, and a preparation method. BACKGROUND

[0004] As one of the important components of lithium ion batteries, the separator not only affects the electrochemical performance of the secondary battery, but also is a key component to ensure the safety of the secondary battery. The performance of the separator at high temperature directly affects the thermal stability of the secondary battery, and therefore the separator material needs to maintain structural stability at high temperature to prevent battery failure caused by thermal runaway.

[0005] In recent years, commercialized separators usually adopt the structure of a base film plus a coating layer, and the selection and application of the coating material have a significant impact on the safety performance of the secondary battery, specifically including ceramic coatings, which are usually made of materials such as aluminum oxide (Al2O3), titanium oxide (TiO2), or zirconium oxide (ZrO2). Ceramic coatings have high melting points and good chemical stability, which can effectively improve the safety performance of the secondary battery. Among them, the ceramic coating mainly plays a role in supporting the framework, but since the base film of the ceramic separator is mostly a polyolefin base film, it has a large thermal shrinkage rate at high temperature, making it difficult for the ceramic coating to completely support the separator from deforming, thereby causing the positive and negative electrode materials to directly contact and short circuit, resulting in insufficient safety of the secondary battery.

[0006] Therefore, there is an urgent need in the art to develop a secondary battery with high safety to solve the above problems.

[0007] SUMMARY

[0008] In view of the deficiencies of the prior art, the purpose of the present disclosure is to provide a separator coating, a composite separator comprising the same, a secondary battery, and a preparation method. The separator coating provided by the present disclosure can be transferred in situ to the surface of the positive electrode through the pressure in the battery assembly process, thereby improving the safety of the secondary battery.

[0009] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0010] In a first aspect, the present disclosure provides a separator coating, the separator coating comprising a first coating layer and a second coating layer arranged on a surface of the first coating layer, the second coating layer being close to a positive electrode side;

[0011] The material of the first coating layer comprises, based on the total mass of the material of the first coating layer being 100%, 70%-92% of ceramic material, 3%-24% of ion-conducting material, and 3%-6% of adhesive.

[0012] It should be noted that the separator coating provided by the present disclosure is not conductive itself.

[0013] On the one hand, the separator coating provided by the present disclosure can be transferred to the positive electrode surface through the hot-pressing process in the battery preparation. Since the current collector of the positive electrode sheet is a metal material, the metal material does not substantially shrink after being heated at high temperature. Even if the base film of the separator shrinks after being heated, the separator coating can continue to play a role in isolating the positive and negative electrode materials under the support of the positive electrode sheet, thereby preventing short circuit in the battery. On the other hand, the separator coating has good heat conduction performance, which helps to evenly distribute the heat inside the battery, thereby reducing the risk of local overheating.

[0014] In addition, the separator coating is arranged on the positive electrode surface, which not only improves the safety of the battery, but also increases the electrolyte retention amount on the positive electrode side due to the pores between the particles of the separator coating, thereby helping to prolong the cycle life of the battery.

[0015] In the present disclosure, the mass percentage of the ceramic material is 70%-92%, for example, it can be 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92%, etc.

[0016] In the present disclosure, the mass percentage of the ion-conducting material is 3%-24%, for example, it can be 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 24%, etc.

[0017] In the present disclosure, the mass percentage of the adhesive is 3%-6%, for example, it can be 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, etc.

[0018] Further, the material of the first coating layer comprises, based on the total mass of the material of the first coating layer being 100%, 80%-90% of ceramic material, 3%-16% of ion-conducting material, and 4%-6% of adhesive.

[0019] Further, the ceramic material comprises any one or a combination of at least two of alumina, boehmite, magnesium hydroxide, barium sulfate, and silicon dioxide.

[0020] Further, the particle size of the ceramic material is 50-1000 nm, and further 200-600 nm, for example, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, etc.

[0021] Further, the ion-conducting material includes a combination of solid electrolyte material and organic material, so as to improve the ion conductivity of the separator and reduce the internal resistance of the battery.

[0022] Further, the solid electrolyte material includes lithium aluminum titanium phosphate (LATP) and / or lithium lanthanum zirconium oxide (LLZO).

[0023] Further, the organic material includes modified nanofiber.

[0024] Further, the modified nanofiber is formed by carboxylation treatment and grafting treatment of natural cellulose.

[0025] Further, the modified nanofiber is rod-shaped.

[0026] Further, the diameter of the modified nanofiber is 3-25 nm, for example, 3 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, 25 nm, etc., and the length is 50-600 nm, for example, 50 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, etc.

[0027] Further, the modified nanofiber includes lithium-modified nanofiber.

[0028] Further, the mass percentage of lithium in the modified nanofiber is 0.15%-0.8% based on the total mass of the modified nanofiber, and further 0.16%-0.3%, for example, 0.16%, 0.2%, 0.25%, 0.28%, 0.3%, 0.32%, 0.35%, 0.38%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc.

[0029] In the present disclosure, by regulating the mass percentage of lithium element in the modified nanofiber, the rod-shaped nanofiber and the solid-state electrolyte material are overlapped to form good ion conduction ability and heat-resistant support effect. If the mass percentage is too low, the ion conduction ability is weak, which cannot reduce the internal resistance, otherwise, the amount of nanofiber is small, which leads to large shrinkage of the diaphragm and affects the safety of the battery.

[0030] Further, the mass ratio of the solid-state electrolyte material and the organic material is (1-8):(1-2), for example, it can be 1:1, 1.2:1.3, 1.5:1.2, 1.8:1.4, 2:1.5, 2.2:1.6, 2.5:1.7, 2.8:1.8, 3:1.9, 3.2:2, 3.5:1, 3.8:1.2, 4:1.3, 4.2:1.4, 4.5:1.5, 5:1.6, 5.5:1.7, 6:1.8, 6.5:1.9, 7:2, 7.5:1.5, 8:1, etc.

[0031] In the present disclosure, by regulating the mass ratio of the solid-state electrolyte material and the organic material, the rod-shaped nanofiber and the solid-state electrolyte material are overlapped to form good ion conduction ability. If the mass ratio is too low, the organic material is easy to agglomerate, which affects the uniformity of the coating pore, otherwise, the bridging effect of the organic material between the particles is weak, which is not conducive to the further improvement of the ion conduction ability and safety performance.

[0032] Further, the adhesive includes a polyacrylamide compound.

[0033] Further, the glass transition temperature of the polyacrylamide compound is 80-210℃, for example, it can be 80℃, 90℃, 100℃, 120℃, 150℃, 180℃, 200℃, 210℃, etc.

[0034] Further, the total mass of the material of the first coating is 100%, and the material of the first coating further includes an auxiliary agent with a mass percentage of 0.4%-0.65%, for example, it can be 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, etc.

[0035] Further, the auxiliary agent includes a dispersing agent and a wetting agent.

[0036] In the present disclosure, the dispersing agent and the wetting agent can use commercially available products, for example, the dispersing agent can be a non-ionic dispersing agent, and the wetting agent can use a polyether compound, which is not limited in the present disclosure.

[0037] Further, the material of the first coating layer further comprises a dispersant with a mass percentage of 0.35%-0.55% and a wetting agent with a mass percentage of 0.05%-0.1%, based on the total mass of the material of the first coating layer being 100%.

[0038] In the present disclosure, the mass percentage of the dispersant is 0.35%-0.55%, for example, it can be 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, etc.

[0039] In the present disclosure, the mass percentage of the wetting agent is 0.05%-0.1%, for example, it can be 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, etc.

[0040] Further, the material of the second coating layer comprises a binding material.

[0041] Further, the binding material comprises polyvinylidene fluoride and / or polymethyl methacrylate.

[0042] Further, the particle size of the polyvinylidene fluoride is 100-300 nm, for example, it can be 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, etc.

[0043] Further, the glass transition temperature of the polyvinylidene fluoride is -50-145℃, for example, it can be -50℃, -45℃, -30℃, -20℃, -10℃, -5℃, 0℃, 10℃, 20℃, 30℃, 40℃, 45℃, 50℃, 60℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 145℃, etc.

[0044] Further, the particle size of the polymethyl methacrylate is 150-800 nm, for example, it can be 150 nm, 180 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, etc.

[0045] Further, the glass transition temperature of the polymethyl methacrylate is 40-120℃, for example, it can be 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 68℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, etc.

[0046] Further, the material of the second coating layer comprises a binding material with a mass percentage of 85%-95%, for example, it can be 85%, 88%, 90%, 92%, 95%, etc., based on the total mass of the material of the second coating layer being 100%.

[0047] Furthermore, based on the total mass of the material of the second coating being 100%, the material of the second coating also includes 5-10% other adhesives and 1.5%-5% other additives by mass percentage.

[0048] In this disclosure, the other adhesives are present in a mass percentage of 5%-10%, for example, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0049] In this disclosure, the mass percentage of other adjuvants is 1.5%-5%, for example, it can be 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or 5%.

[0050] Furthermore, the other additives include at least one of thickeners, dispersants, and wetting agents.

[0051] In this disclosure, the thickeners, dispersants and wetting agents mentioned above are all commercially available materials, and this disclosure does not impose any restrictions on them.

[0052] This disclosure provides an exemplary method for preparing the diaphragm coating, which includes the following steps:

[0053] The material of the first coating layer is prepared to obtain a first coating slurry, and the first coating slurry is applied to form a first coating layer;

[0054] The material for the second coating is prepared to obtain a second coating slurry. The second coating slurry is then applied to the surface of the first coating to form a second coating, with the second coating located near the positive electrode side.

[0055] In a second aspect, this disclosure provides a composite separator, the composite separator comprising a base membrane and a composite coating disposed on at least one side of the base membrane, the composite coating comprising a separator coating disposed on the positive electrode surface as described in the first aspect.

[0056] In this disclosure, the base film material exemplary includes at least one of polypropylene (PP), polyethylene (PE), polyimide (PI), and aramid.

[0057] In this disclosure, the thickness of the base film is 3-25 μm, for example, it can be 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, etc.

[0058] This disclosure provides an exemplary method for preparing the composite separator, which includes the following steps:

[0059] The material for the first coating layer is prepared to obtain the first coating slurry;

[0060] The material for the second coating is prepared to obtain the second coating slurry;

[0061] applying the first coating slurry on at least one side of the base film to obtain a composite separator after drying;

[0062] applying the second coating slurry on the surface of the first coating to obtain the composite separator after drying.

[0063] In the present disclosure, the amount of the coating is 0.15-8 g / m 2 , for example, 0.15 g / m 2 , 0.2 g / m 2 , 0.25 g / m 2 , 0.3 g / m 2 , 0.35 g / m 2 , 0.4 g / m 2 , 0.45 g / m 2 , 0.5 g / m 2 , 0.55 g / m 2 , 0.6 g / m 2 , 0.65 g / m 2 , 7 g / m 2 , 8 g / m 2 , etc.

[0064] In a third aspect, the present disclosure provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator comprises the composite separator according to the second aspect.

[0065] Further, the peeling strength between the first coating and the base film after the first coating is soaked in the electrolyte for 24 h is F1, and the F1 satisfies 10-30 N / m, for example, 10 N / m, 12 N / m, 15 N / m, 18 N / m, 20 N / m, 22 N / m, 25 N / m, 28 N / m, 30 N / m, etc.

[0066] Further, the peeling strength between the composite separator and the positive electrode sheet after the composite separator is soaked in the electrolyte for 24 h is F2, and the F2 satisfies 14-25 N / m, for example, 14 N / m, 18 N / m, 20 N / m, 22 N / m, 25 N / m, etc.

[0067] Further, the relationship between the F1 and the F2 satisfies F1 / F2>0.3, and more further satisfies 0.3<F1 / F2<2.5, for example, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.8, 2, 2.2, etc.

[0068] In the present disclosure, by regulating the relationship between F1 and F2, so that the composite coating of the separator can be transferred to the positive electrode surface in the finished battery after the heat pressing and pressurizing of the composite coating of the separator, if the ratio of F1 / F2 is too low, the separator coating is easy to fall off and powder during the battery assembly process, which is not conducive to the control of foreign matter on site, on the contrary, the separator coating is too firmly bonded with the base film, which is not conducive to the transfer of the composite coating in the battery.

[0069] In a fourth aspect, the present disclosure provides a method for preparing the secondary battery according to the third aspect, the method comprising the following steps:

[0070] The positive electrode sheet, the negative electrode sheet and the composite separator are subjected to heat pressing treatment, and the composite coating is transferred in situ to the surface of the positive electrode sheet by the pressure during the heat pressing treatment, and the secondary battery is obtained after injecting the electrolyte.

[0071] Further, the temperature of the heat pressing treatment is 85-95℃, for example, it can be 85℃, 88℃, 90℃, 92℃, 95℃, etc.; the pressure is 1.5-3Mpa, for example, it can be 1.5Mpa, 1.8Mpa, 2Mpa, 2.2Mpa, 2.5Mpa, 3Mpa, etc.; the time is 45-120s, for example, it can be 45s, 50s, 60s, 70s, 80s, 90s, 100s, 110s, 120s, etc. DETAILED DESCRIPTION

[0072] The technical solutions of the present disclosure will be further illustrated by specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present disclosure, and should not be regarded as specific limitations of the present disclosure.

[0073] Unless otherwise specified, the substances involved in the specific embodiments of the present disclosure are conventional materials in the art, which can be obtained by commercial purchase.

[0074] Embodiment 1

[0075] The present embodiment provides a separator coating arranged on the surface of the positive electrode, the separator coating comprising a first coating and a second coating arranged on the surface of the first coating, the second coating being close to the positive electrode side.

[0076] The material of the first coating layer comprises 82.54% of alumina (particle size of 400 nm), 13% of ion-conductive material, 4% of polyacrylamide adhesive (glass transition temperature of 145 DEG C), 0.4% of polyethylene glycol dispersant and 0.06% of polyether wetting agent (purchased from Tianjin Sepro Company, trade name E1206) in terms of total mass of the material of the first coating layer being 100%, wherein the ion-conductive material comprises a combination of lithium aluminum titanium phosphate (LATP) and lithium-modified nanofiber (lithium content of 0.195% in terms of total mass of the lithium-modified nanofiber being 100%) in a mass ratio of 4:1.5, the lithium-modified nanofiber is formed after carboxylation treatment and grafting treatment of natural cellulose, has a rod shape, a diameter of 10 nm and a length of 100 nm; the material of the second coating layer comprises 90% of polyvinylidene fluoride (particle size of 200 nm and glass transition temperature of -40 DEG C), 5% of acrylic emulsion adhesive, 2% of sodium carboxymethyl cellulose thickener and 3% of water-based aliphatic siloxane dispersant in terms of total mass of the material of the second coating layer being 100%.

[0077] The embodiment provides a composite diaphragm comprising the diaphragm coating and a preparation method thereof, the composite diaphragm comprising a polyethylene diaphragm with a thickness of 8 microns and the diaphragm coating arranged on both sides of the polyethylene diaphragm, and the preparation method comprises the following steps:

[0078] The material of the first coating layer is prepared to obtain a first coating layer slurry;

[0079] The material of the second coating layer is prepared to obtain a second coating layer slurry;

[0080] The first coating layer slurry is coated on both sides of the polyethylene diaphragm, and the coating amount is 7.8 g / m 2 , and a diaphragm comprising the first coating layer is obtained after drying;

[0081] The second coating layer slurry is coated on the surface of the first coating layer, and the coating amount is 1 g / m 2 , and a composite diaphragm is obtained after drying.

[0082] The embodiment also provides a lithium ion battery and a preparation method thereof, which comprises the following steps:

[0083] (1) Preparation of a positive electrode sheet: a positive electrode slurry is prepared by using a lithium iron phosphate material, and the positive electrode slurry is coated on a carbon-coated aluminum foil to obtain a positive electrode sheet, the mass content of the lithium iron phosphate material in the positive electrode active material layer is 96.5%, and the rest is polyvinylidene fluoride adhesive, Super P conductive agent and the like.

[0084] (2) Preparation of the negative electrode sheet: artificial graphite is used to configure negative electrode slurry, and the negative electrode slurry is coated on the copper foil to prepare the negative electrode sheet, the mass percentage of the artificial graphite material in the negative electrode active material layer is 95.5%, and the rest is butadiene-styrene latex adhesive, Super P conductive agent, etc.

[0085] (3) Preparation of the electrode group: the positive electrode sheet, the negative electrode sheet and the composite separator are subjected to hot pressing treatment in the form of a flat plate, the temperature of the hot pressing is 90°C, the surface pressure is 2 MPa, and the time is 80 s, the coating layer of the separator is transferred in situ to the surface of the positive electrode sheet through the pressure in the hot pressing treatment process, and then the electrode group after the hot pressing is subjected to short circuit test using a voltage of 50 V, wherein the peeling strength between the first coating layer and the polyethylene film after the first coating layer is soaked in the electrolyte for 24 h is 20 N / m; the peeling strength between the composite separator and the positive electrode sheet after the composite separator and the positive electrode sheet are soaked in the electrolyte for 24 h is 20 N / m.

[0086] (4) Packaging and liquid injection: the prepared electrode group is packaged in the form of a square shell, and then the electrolyte is injected.

[0087] (5) Pre-charging and formation: the battery cell is subjected to pre-charging and formation to prepare a lithium ion battery.

[0088] Example 2

[0089] The difference between this example and Example 1 is that, based on the total mass of the material of the first coating layer being 100%, the material of the first coating layer includes 80% of aluminum oxide (particle size of 200 nm), 15.5% of ion-conducting material, 4% of polyacrylamide adhesive (glass transition temperature of 110°C), 0.44% of polyethylene glycol dispersant and 0.06% of polyether wetting agent (purchased from Tianjin Sepro Company, model E1206), wherein the ion-conducting material includes a combination of lithium aluminum titanium phosphate (LATP) and lithium-modified nanofiber (based on the total mass of the lithium-modified nanofiber being 100%, the mass percentage of lithium element is 0.3%) at a mass ratio of 1:1, the lithium-modified nanofiber is formed after carboxylation treatment and grafting treatment of natural cellulose, and has a rod shape, a diameter of 5 nm and a length of 300 nm; based on the total mass of the material of the second coating layer being 100%, the material of the second coating layer includes 85% of polyvinylidene fluoride with a particle size of 150 nm and a glass transition temperature of -30°C, 10% of acrylic emulsion type adhesive, 2% of sodium carboxymethyl cellulose thickener and 3% of water-based aliphatic siloxane dispersant; the peeling strength between the first coating layer and the polyethylene film after the first coating layer is soaked in the electrolyte for 24 h is 12 N / m, the peeling strength between the composite separator and the positive electrode sheet after the composite separator and the positive electrode sheet are soaked in the electrolyte for 24 h is 15 N / m, and the others are the same as in Example 1.

[0090] Example 3

[0091] The difference between this embodiment and embodiment 1 is that the material of the first coating layer comprises 90% of alumina (particle size of 600 nm), 3.35% of ion-conductive material, 6% of polyacrylamide adhesive (glass transition temperature of 180°C), 0.55% of polyethylene glycol dispersant and 0.1% of polyether wetting agent (purchased from Tianjin Sepro Company, brand E1206) in terms of the total mass of the material of the first coating layer being 100%, wherein the ion-conductive material comprises a combination of lithium aluminum titanium phosphate (LATP) and lithium-modified nanofiber in a mass ratio of 8:1, the lithium-modified nanofiber is formed after carboxylation treatment and grafting treatment of natural cellulose, has a rod shape, a diameter of 20 nm and a length of 500 nm; the material of the second coating layer comprises 95% of polyvinylidene fluoride with a particle size of 250 nm and a glass transition temperature of -29°C and 5% of acrylic emulsion adhesive in terms of the total mass of the material of the second coating layer being 100%; the peeling strength between the first coating layer and the polyvinyl film after the first coating layer is soaked in electrolyte for 24 h is 30 N / m, the peeling strength between the composite diaphragm and the positive electrode sheet after the composite diaphragm is soaked in electrolyte for 24 h is 13 N / m, and the others are the same as in embodiment 1.

[0092] Embodiment 4

[0093] The difference between this embodiment and embodiment 1 is that the ion-conductive material comprises lithium aluminum titanium phosphate and lithium-modified nanofiber in a mass ratio of 0.5:4, and the others are the same as in embodiment 1.

[0094] Embodiment 5

[0095] The difference between this embodiment and embodiment 1 is that the ion-conductive material comprises lithium aluminum titanium phosphate and lithium-modified nanofiber in a mass ratio of 12:0.5, and the others are the same as in embodiment 1.

[0096] Embodiment 6

[0097] The difference between this embodiment and embodiment 1 is that the mass percentage of lithium element is 0.05% in terms of the total mass of the lithium-modified nanofiber being 100%, and the others are the same as in embodiment 1.

[0098] Embodiment 7

[0099] The difference between this embodiment and embodiment 1 is that the lithium-modified nanofiber is replaced by the same amount of unmodified nanofiber, and the others are the same as in embodiment 1.

[0100] Embodiment 8

[0101] The difference between this embodiment and embodiment 1 is that the lithium modified nanofiber is replaced by equal mass of lithium aluminum titanium phosphate, and the others are the same as embodiment 1.

[0102] Example 9

[0103] The difference between this embodiment and embodiment 1 is that the relationship between F1 and F2 satisfies: F1 / F2 = 0.1, and the others are the same as embodiment 1.

[0104] Comparative Example 1

[0105] The difference between this comparative example and embodiment 1 is that the first coating layer is not provided in the coating layer of the separator, and the others are the same as embodiment 1.

[0106] Comparative Example 2

[0107] The difference between this comparative example and embodiment 1 is that the second coating layer is not provided in the coating layer of the separator, and the others are the same as embodiment 1.

[0108] Comparative Example 3

[0109] The difference between this comparative example and embodiment 1 is that the material of the first coating layer includes 60% of aluminum oxide (particle size of 600 nm) and 35.54% of ion-conducting material by mass percentage, based on the total mass of the material of the first coating layer being 100%, and the others are the same as embodiment 1.

[0110] Comparative Example 4

[0111] The difference between this comparative example and embodiment 1 is that the ion-conducting material is replaced by equal content of aluminum oxide, and the others are the same as embodiment 1.

[0112] Test conditions

[0113] The lithium ion batteries provided in examples 1 to 9 and comparative examples 1 to 4 are subjected to the following performance tests, and the test methods are as follows:

[0114] (1) The prepared lithium ion battery is subjected to 200℃ hot box safety performance test: reference is made to the test method of GB 38031-2020 Safety requirements for power storage batteries for electric vehicles;

[0115] (2) Ion conductivity test: reference is made to the test method of GBT 36363-2018 Polyolefin separator for lithium ion batteries;

[0116] (3) Cycle performance: charging at 1 / 3C rate and discharging at 1C rate at 25℃, and the charging cut-off voltage is 3.65V.

[0117] The test results are shown in Table 1:

[0118] Table 1

[0119] As can be seen from Table 1, the thermal box safety pass rate of the battery cell assembled by the composite diaphragm satisfying the technical solution of the present disclosure is high, and the composition of the ion-conducting material in the first coating has a greater impact on the cycle performance of the battery, and appropriately increasing the amount thereof is beneficial to improving the capacity retention rate of the battery, and the modified nanofiber in the first coating has a certain influence on the safety and cycle performance of the battery.

[0120] As can be seen from Comparative Example 1 and Examples 4-5, by adjusting the mass ratio of lithium-modified nanofiber and lithium titanate aluminum phosphate, the nanofiber in a rod shape and the solid-state electrolyte material are lap jointed to form good ion-conducting ability and heat-resistant support.

[0121] As can be seen from Comparative Example 1 and Examples 6-7, if the nanofiber is not subjected to lithium modification treatment or the content of lithium element is too low, it has a certain influence on the ion conductivity of the composite diaphragm.

[0122] As can be seen from Comparative Example 1 and Example 8, adding lithium-modified nanofiber is beneficial to improving the safety of the battery.

[0123] As can be seen from Comparative Example 1 and Example 9, if the ratio of F1 / F2 is too low, the diaphragm coating is easy to fall off and powder in the battery assembly process, which is not conducive to the control of foreign matters on site.

[0124] As can be seen from Comparative Example 1 and Comparative Examples 1-2, setting a single coating cannot guarantee the heat resistance of the diaphragm and the safety of the battery.

[0125] As can be seen from Comparative Example 1 and Comparative Examples 3-4, the composition of the ion-conducting material in the first coating has an influence on the cycle performance and safety of the battery.

[0126] Compared with the prior art, the present disclosure has the following beneficial effects:

[0127] The present disclosure provides a diaphragm coating arranged on the surface of the positive electrode. On the one hand, the diaphragm coating provided by the present disclosure can be transferred to the surface of the positive electrode through the hot-pressing process in the battery preparation. Since the current collector of the positive electrode sheet is a metal material, the metal material does not substantially shrink after being heated at high temperature. Even if the diaphragm base film shrinks due to heating, the diaphragm coating can continue to play a role in isolating the positive and negative electrode materials under the support of the positive electrode sheet, preventing short circuit in the battery. On the other hand, the diaphragm coating has good heat conduction performance, which is helpful to the uniform distribution of heat in the battery, thereby reducing the risk of local overheating.

[0128] In addition, the present disclosure sets the separator coating on the positive electrode surface, which not only improves the safety of the battery, but also improves the electrolyte retention of the positive electrode side due to the pores between the separator coating particles, thereby helping to prolong the cycle life of the battery.

[0129] The applicant declares that the process of the present disclosure is illustrated by the above examples, but the present disclosure is not limited to the above process steps, that is, it does not mean that the present disclosure must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement of the present disclosure, equivalent replacement of the raw materials selected by the present disclosure, addition of auxiliary ingredients, selection of specific methods, etc. all fall within the protection scope and disclosure scope of the present disclosure. Industrial applicability

[0130] The separator coating of the present disclosure can be transferred in situ to the surface of the positive electrode by the pressure during the battery assembly process, thereby improving the safety of the secondary battery.

Claims

1. A separator coating, characterized by, The separator coating comprises a first coating layer and a second coating layer arranged on the surface of the first coating layer, and the second coating layer is close to the positive electrode side. The material of the first coating layer comprises, in terms of the total mass of the material of the first coating layer being 100%, 70%-92% of a ceramic material, 3%-24% of an ion-conducting material, and 3%-6% of a binder.

2. The separator coating according to claim 1, characterized in that, At least one of the following conditions is met: (1) the material of the first coating layer comprises, in terms of the total mass of the material of the first coating layer being 100%, 80%-90% of a ceramic material, 3%-16% of an ion-conducting material, and 4%-6% of a binder; (2) the ceramic material comprises any one or a combination of at least two of alumina, boehmite, magnesium hydroxide, barium sulfate, and silicon dioxide; (3) the particle size of the ceramic material is 50 nm-1000 nm; (4) the particle size of the ceramic material is 200 nm-600 nm.

3. The separator coating of claim 1, wherein, The ion-conducting material comprises a combination of a solid-state electrolyte material and an organic material.

4. The separator coating according to claim 3, characterized in that, The solid-state electrolyte material comprises lithium aluminum titanium phosphate and / or lithium lanthanum zirconium oxide.

5. The separator coating according to claim 3, wherein The organic material comprises modified nanofibers, and at least one of the following conditions is met: (1) the modified nanofibers are formed after carboxylation treatment and grafting treatment of natural cellulose; (2) the shape of the modified nanofibers is rod-shaped; (3) the diameter of the modified nanofibers is 3-25 nm, and the length is 50-600 nm; (4) the modified nanofibers comprise lithium-modified nanofibers; (5) in terms of the total mass of the modified nanofibers being 100%, the mass percentage of lithium in the modified nanofibers is 0.15%-0.8%; (6) in terms of the total mass of the modified nanofibers being 100%, the mass percentage of lithium in the modified nanofibers is 0.16%-0.3%.

6. The separator coating of claim 3, wherein, The mass ratio of the solid-state electrolyte material to the organic material is (1-8):(1-2).

7. The separator coating of claim 1, wherein, The binder comprises a polyacrylamide compound.

8. The separator coating according to claim 7, characterized in that, The glass transition temperature of the polyacrylamide compound is 80-210°C.

9. The separator coating according to any one of claims 1 to 8, characterized in that, In terms of the total mass of the material of the first coating layer being 100%, the material of the first coating layer further comprises 0.4%-0.65% of an auxiliary agent; and the auxiliary agent comprises a dispersant and a wetting agent.

10. The separator coating according to claim 9, characterized in that, In terms of the total mass of the material of the first coating layer being 100%, the material of the first coating layer further comprises 0.35%-0.55% of a dispersant and 0.05%-0.1% of a wetting agent.

11. The separator coating according to any one of claims 1 to 8, characterized in that, The material of the second coating layer comprises a binding material; and the binding material comprises polyvinylidene fluoride and / or polymethyl methacrylate.

12. The separator coating of claim 11, wherein, At least one of the following conditions is met: (1) the particle size of the polyvinylidene fluoride is 100-300 nm; (2) the glass transition temperature of the polyvinylidene fluoride is -50-145°C; (3) the particle size of the polymethyl methacrylate is 150-800 nm; (4) the glass transition temperature of the polymethyl methacrylate is 40-120℃.

13. The separator coating of claim 11, wherein, The material of the second coating layer comprises 85%-95% of the bonding material in terms of the total mass of the material of the second coating layer.

14. The separator coating of claim 11, wherein, The material of the second coating layer further comprises 5%-10% of other adhesives and 1.5%-5% of other additives in terms of the total mass of the material of the second coating layer; the other additives comprise at least one of thickening agent, dispersing agent and wetting agent.

15. A composite separator, characterized by, The composite separator comprises a base film and a composite coating layer arranged on at least one side of the base film, and the composite coating layer comprises the separator coating layer arranged on the surface of the positive electrode according to any one of claims 1-14.

16. A secondary battery characterized by comprising: The secondary battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, and the separator comprises the composite separator according to claim 15.

17. The secondary battery according to claim 16, characterized by At least one of the following conditions is met: (1) the peeling strength between the first coating layer and the base film after the first coating layer is soaked in the electrolyte for 24h is F1, and the F1 meets 10-30N / m; (2) the peeling strength between the composite separator and the positive electrode sheet after the composite separator and the positive electrode sheet are soaked in the electrolyte for 24h is F2, and the F2 meets 14-25N / m.

18. The secondary battery according to claim 17, characterized by The relationship between the F1 and the F2 meets F1 / F2>0.3; Alternatively, the relationship between the F1 and the F2 meets 0.3 19. A method of manufacturing the secondary battery according to claim 16, characterized by, The method comprises the following steps: The positive electrode sheet, the negative electrode sheet and the composite separator are subjected to hot-pressing treatment, the composite coating layer is transferred in situ to the surface of the positive electrode sheet through the pressure in the hot-pressing treatment process, and the secondary battery is obtained after the electrolyte is injected.

20. The method of claim 19, wherein, The temperature of the hot-pressing treatment is 85-95℃, the pressure is 1.5-3Mpa, and the time is 45-120s.

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