A separator and a battery including the same

Abstract

The application provides a diaphragm and a battery comprising the diaphragm. By adding polymer microspheres with a melting point of 90-130 DEG C in the ceramic layer, the diaphragm realizes closed pores before 130 DEG C, insulates lithium ion shuttling between the positive and negative electrodes in the battery, and achieves the purpose of improving safety. Meanwhile, a heat-resistant polymer layer is coated on the surface of the ceramic layer, so that the diaphragm will not break at high temperature, the blocking effect of the diaphragm at high temperature is improved, the safety performance of the battery is improved, and further, a graphite containing surface-coated amorphous carbon is matched with the negative active material, so that the fast charging performance of the battery can be significantly improved, and the prepared battery can simultaneously consider the fast charging performance and the safety performance.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, specifically relating to a separator and a battery including the separator. Background Technology

[0002] In recent years, lithium-ion batteries have been widely used in smartphones, tablets, smart wearables, power tools, and electric vehicles. With the widespread use of lithium-ion batteries, consumers are increasingly demanding higher lifespans and better environmental performance, requiring them to offer both high-speed charging capabilities and excellent safety features.

[0003] Currently, lithium-ion batteries pose safety hazards during use. For example, when the battery temperature rises to a certain level, internal temperature runaway can easily lead to serious safety accidents, such as fires or even explosions. The main reasons for battery thermal runaway are twofold: firstly, the separator's heat resistance is insufficient, causing it to shrink or even rupture at high temperatures, thus failing to isolate the positive and negative electrodes; secondly, the separator's pore-closing temperature is too high, preventing it from closing before thermal runaway and thus failing to effectively block the ion channels inside the battery.

[0004] Given this situation, there is an urgent need to develop highly safe lithium-ion batteries. One approach is to coat the separator surface with a heat-resistant layer. However, this often only improves the separator's thermal shrinkage performance and cannot completely solve the battery's safety issues. Therefore, developing lithium-ion batteries that offer excellent fast-charging capabilities while maintaining high safety is currently the top priority. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of safety hazards in existing lithium-ion batteries during use, and the inability to balance fast charging capability and safety performance. This invention provides a separator and a battery including the separator, wherein the battery has excellent fast charging capability and high safety performance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A diaphragm includes a diaphragm substrate, a ceramic layer, a heat-resistant polymer layer, and an adhesive layer; the ceramic layer is disposed on at least one surface of the diaphragm substrate, the heat-resistant polymer layer is disposed on the surface of the ceramic layer, and the adhesive layer is disposed on the surface of the heat-resistant polymer layer.

[0008] The ceramic layer comprises ceramic powder, binder, and polymer microspheres; the heat-resistant polymer layer comprises a heat-resistant polymer; and the adhesive layer comprises an adhesive polymer.

[0009] According to an embodiment of the present invention, the pore-closing temperature of the diaphragm is 90°C to 130°C, for example, 90°C, 100°C, 110°C, 120°C, or 130°C. The pore-closing temperature refers to the temperature at which the micropores inside the diaphragm close.

[0010] According to an embodiment of the present invention, the membrane rupture temperature is greater than or equal to 230°C, for example, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, or 350°C. The membrane rupture temperature refers to the temperature at which the membrane ruptures (breaks) when the temperature rises further after the pores are closed, i.e., the temperature at which the membrane's appearance shows damage.

[0011] According to an embodiment of the present invention, the thickness of the ceramic layer is 1μm to 10μm, for example, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm.

[0012] According to an embodiment of the present invention, the ceramic powder is selected from at least one of alumina, boehmite, magnesium oxide, magnesium hydroxide, barium sulfate, barium titanate, zinc oxide, calcium oxide, silicon dioxide, silicon carbide, and nickel oxide.

[0013] According to an embodiment of the present invention, the adhesive is selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, polyacrylonitrile, poly(meth)acrylate, aramid resin, poly(meth)acrylic acid, styrene-butadiene rubber (SBR), polyvinyl alcohol, polyvinyl acetate, carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Na), and carboxyethyl cellulose.

[0014] According to an embodiment of the present invention, the polymer microspheres are made of at least one selected from polyethylene, polymethacrylic acid, polymethacrylate, polypropylene, and polyvinylidene fluoride.

[0015] According to an embodiment of the present invention, the polymer microspheres have a molecular weight of 50,000 to 500,000, a particle size distribution of 0.1 μm to 10 μm (e.g., 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm), and a melting point of 90℃ to 130℃ (e.g., 90℃, 100℃, 110℃, 120℃ or 130℃).

[0016] According to an embodiment of the present invention, in the ceramic layer, the mass percentage of ceramic powder is 50% to 80% (e.g., 50%, 55%, 60%, 65%, 70%, 75%, 80%), the mass percentage of binder is 5% to 40% (e.g., 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%), and the mass percentage of polymer microspheres is 10% to 45% (10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%).

[0017] According to an embodiment of the present invention, the thickness of the heat-resistant polymer layer is 1 μm to 10 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0018] According to an embodiment of the present invention, the heat-resistant polymer is selected from at least one of aramid, polyimide, polyurethane, chlorophosphazene polymer, boron nitrogen polymer, polysulfone, and polybenzimidazole.

[0019] According to an embodiment of the present invention, the thickness of the adhesive layer is 1μm to 10μm, for example, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm.

[0020] According to an embodiment of the present invention, the material of the coating polymer is selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, modified polyvinylidene fluoride-hexafluoropropylene and its copolymers, polyimide, polyacrylonitrile, polymethyl methacrylate, and polyacrylic acid.

[0021] According to embodiments of the present invention, the solvents used to prepare the ceramic layer, the heat-resistant polymer layer, and the adhesive layer are selected from at least one of acetone, tetrahydrofuran, dichloromethane, chloroform, dimethylformamide, N-methyl-2-pyrrolidone, cyclohexane, methanol, ethanol, isopropanol, and water.

[0022] The present invention also provides a battery comprising the above-described separator.

[0023] According to an embodiment of the present invention, the battery includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

[0024] According to an embodiment of the present invention, the battery is a high-safety lithium-ion battery with excellent fast-charging capability.

[0025] According to an embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer coated on one or both surfaces of the positive current collector, wherein the positive active material layer includes a positive active material, a conductive agent, and a binder.

[0026] According to an embodiment of the present invention, the positive electrode active material is selected from lithium cobalt oxide or lithium cobalt oxide doped with two or more elements selected from Al, Mg, Mn, Cr, Ti, and Zr, wherein the lithium cobalt oxide doped with two or more elements selected from Al, Mg, Mn, Cr, Ti, and Zr has the chemical formula Li. x Co 1-y1-y2-y3-y4 A y1 B y2 C y3 D y4 O2; 0.95≤x≤1.05, 0.01≤y1≤0.1, 0.01≤y2≤0.1, 0≤y3≤0.1, 0≤y4≤0.1, A, B, C, and D are selected from two or more elements among Al, Mg, Mn, Cr, Ti, and Zr.

[0027] According to an embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one or both surfaces of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder.

[0028] According to an embodiment of the present invention, the negative electrode active material is selected from at least one of graphite with amorphous carbon coated on its surface, a composite material of graphite with amorphous carbon coated on its surface and silicon oxide, and a composite material of graphite with amorphous carbon coated on its surface and nano-silicon.

[0029] In the composite material of graphite and silicon oxide with amorphous carbon coating, the content of silicon oxide is 1-15 wt%. In the composite material of graphite and nano-silicon with amorphous carbon coating, the content of nano-silicon is 1-15 wt%.

[0030] The beneficial effects of this invention are:

[0031] This invention provides a separator and a battery including the separator. By rationally designing the composition of the ceramic layer, heat-resistant polymer layer, and adhesive layer in the battery separator, the safety performance of the battery can be effectively improved. Furthermore, by combining a graphite containing amorphous carbon coated on its surface as the negative electrode active material, the fast-charging performance of the battery can be further enhanced. Specifically, by adding polymer microspheres with a melting point between 90℃ and 130℃ to the ceramic layer, the separator achieves pore closure before 130℃, isolating lithium-ion shuttle between the positive and negative electrodes inside the battery, thereby improving safety. Simultaneously, coating the surface of the ceramic layer with a heat-resistant polymer layer ensures that the separator will not rupture at high temperatures, improving the barrier effect of the separator at high temperatures and enhancing the safety performance of the battery. Further combining a graphite containing amorphous carbon coated on its surface as the negative electrode active material significantly improves the fast-charging performance of the battery, enabling the prepared battery to simultaneously achieve both fast-charging performance and safety performance. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0033] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0034] Comparative Examples 1-4 and Examples 1-9

[0035] The lithium-ion batteries of Comparative Examples 1-4 and Examples 1-9 were all prepared according to the following preparation method, with the only difference being the selection of the separator and the negative electrode. The specific differences are shown in Table 1.

[0036] (1) Preparation of positive electrode

[0037] The positive electrode active material LiCoO2, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black were mixed in a weight ratio of 97:1.0:2.0. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until a uniform and fluid positive electrode slurry was formed. The positive electrode slurry was uniformly coated onto an aluminum foil with a thickness of 10 μm. The coated aluminum foil was baked in an oven with five different temperature gradients, and then dried in an oven at 120°C for 8 hours. Finally, it was rolled and slit to obtain the desired positive electrode sheet.

[0038] (2) Preparation of negative electrode sheet

[0039] A slurry was prepared using a wet process, consisting of 96% artificial graphite anode material, 0.2% single-walled carbon nanotube (SWCNT) conductive agent, 1.0% conductive carbon black (SP) conductive agent, 1% sodium carboxymethyl cellulose (CMC) binder, and 1.8% styrene-butadiene rubber (SBR) binder. This slurry was coated onto the surface of the copper foil used as the anode current collector. The anode sheet was then dried (temperature: 85℃, time: 5h), rolled, and die-cut to obtain the anode sheet. Specifically, artificial graphite anode material 1 and artificial graphite 2 were selected. Artificial graphite 1 was commercially available and had no surface coating, while artificial graphite 2 was commercially available and had a layer of amorphous carbon coating on its surface, as detailed in Table 1.

[0040] (3) Preparation of non-aqueous electrolyte

[0041] In an argon-filled glove box (moisture content <10ppm, oxygen content <1ppm), ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP) were mixed uniformly in a mass ratio of 2:1.5:2. LiPF6 was slowly added to the mixed solution at 14wt.% based on the total mass of the non-aqueous electrolyte, and the mixture was stirred until homogeneous to obtain the non-aqueous electrolyte.

[0042] (4) Preparation of the diaphragm

[0043] The mixture of polymer microspheres, alumina, polymethacrylic acid, and water is denoted as solution T; the mixture of heat-resistant polymer and DMAc solvent is denoted as solution N; and the mixture of coating polymer and DMAc solution is denoted as solution P.

[0044] Solution T was coated onto both sides of a 5μm thick diaphragm substrate PE using a gravure roller coating method. After drying, a diaphragm with a 2μm thick ceramic layer on each side was obtained, denoted as diaphragm TP. Solution N was coated onto both sides of diaphragm TP using a gravure roller coating method. After drying, a diaphragm with a 2μm thick ceramic layer and a 2μm thick heat-resistant polymer layer on each side was obtained, denoted as diaphragm NP. Solution P was coated onto both sides of diaphragm NP using a gravure roller coating method. After drying, a diaphragm with a 2μm thick ceramic layer, a 2μm thick heat-resistant polymer layer, and a 1μm thick adhesive layer on each side was obtained.

[0045] The types of polymer microspheres, the proportion of polymer microspheres, the melting point of polymers, the types of heat-resistant polymers, and the types of adhesive polymers in the ceramic layer are detailed in Table 1.

[0046] (5) Preparation of lithium-ion batteries

[0047] The prepared positive electrode, separator, and negative electrode are wound together to obtain a bare battery without electrolyte filling. The bare battery is placed in an outer packaging foil, and the prepared electrolyte is injected into the dried bare battery. After vacuum sealing, standing, formation, shaping, and sorting, the desired lithium-ion battery is obtained.

[0048] The electrochemical performance of the batteries obtained in the comparative examples and embodiments above was tested, and the relevant explanations are as follows:

[0049] 1) 25℃ Cyclic Experiment: The batteries obtained in the above examples and comparative examples were placed in an environment of (25±2)℃ and left to stand for 2-3 hours. When the battery body reached (25±2)℃, the battery was charged at 3C constant current with a cutoff current of 0.05C. After the battery was fully charged, it was left to stand for 5 minutes, and then discharged at 3C constant current to the cutoff voltage of 3.0V. The highest discharge capacity of the first 3 cycles was recorded as the initial capacity Q. When the cycle reached 1000 times, the discharge capacity Q of the last cycle of the battery was recorded. The results are shown in Table 2.

[0050] The calculation formula used is as follows: Capacity retention rate (%) = Q1 / Q × 100%;

[0051] 2) 150℃ thermal shock test: The batteries obtained in the above examples and comparative examples were heated at an initial temperature of (25±3)℃ using convection or a circulating hot air chamber, with a temperature change rate of (5±2)℃ / min, and the temperature was increased to (150±2)℃. The test was ended after holding the temperature for 60 minutes, and the battery status results were recorded as shown in Table 2.

[0052] 3) Closed-pore test:

[0053] The diaphragms obtained in the above embodiments and comparative examples were baked at a certain temperature for 10 minutes. The air permeability of the diaphragms before and after baking was tested. When the air permeability increased by 10 times before and after baking, the diaphragm began to close its pores; when it increased by 100 times, the diaphragm was basically closed; and when it increased by 1000 times, the diaphragm was completely closed. The baking temperature corresponding to when the diaphragm was completely closed was recorded as the pore-closing temperature of the diaphragm.

[0054] 4) Membrane rupture test:

[0055] The diaphragms obtained in the above examples and comparative examples were subjected to TMA testing. The samples were cut into 4mm wide * 8mm long samples and tested under the conditions of heating rate of 5℃ / min and applied force of 0.01N. The temperature at which the diaphragm broke was recorded as the rupture temperature of the diaphragm.

[0056] Table 1 shows the composition of the batteries in Comparative Examples 1-4 and Examples 1-9.

[0057]

[0058] Table 2 shows the diaphragm performance test data results for Comparative Examples 1-4 and Examples 1-9.

[0059] project Closed-cell temperature / ℃ Film breaking temperature / ℃ Comparative Example 1 143.2 153.2 Comparative Example 2 142.7 152.9 Comparative Example 3 143.6 267.4 Comparative Example 4 120.6 153.4 Example 1 120.3 263.4 Example 2 123.8 260.5 Example 3 128.4 265.8 Example 4 124.3 243.5 Example 5 120.2 245.7 Example 6 124.7 240.8 Example 7 128.2 243.2 Example 8 124.5 246.5 Example 9 120.2 267.4

[0060] Table 3 shows the performance test results of the batteries in Comparative Examples 1-4 and Examples 1-9.

[0061]

[0062] Comparing Comparative Examples 1 and 2 reveals that the battery assembled using a conventional separator and artificial graphite 1 passes the furnace temperature test, but its fast-charging capability is significantly reduced. After 1000 cycles, the battery has no capacity left, indicating it cannot meet the 1000-cycle requirement. The battery assembled using a conventional separator and artificial graphite 2 shows a significantly improved fast-charging capability, achieving a capacity retention of 74.65% after 1000 cycles. However, its safety performance is drastically reduced, failing the furnace temperature test. This demonstrates that the introduction of a fast-charging negative electrode can degrade battery safety. Comparing Comparative Examples 2-4 with Example 1 shows that the battery of this application significantly improves safety performance while maintaining fast-charging capability, resulting in a battery that balances both safety and rate performance.

[0063] A comparison of Examples 1 through 8 revealed that by adjusting the composition of the ceramic layer, heat-resistant polymer layer, and adhesive layer of the separator within a reasonable range, a battery that balances battery safety and rate performance can be obtained. A comparison of Examples 1 and 9 showed that the battery obtained by assembling the separator of this application with artificial graphite 2 exhibits significantly improved safety performance while maintaining fast-charging capability. This indicates that the use of the separator of this application can avoid the adverse effects of fast-charging negative electrodes on battery safety performance.

[0064] In summary, as can be seen from the comparative examples and embodiments, the lithium-ion battery assembled with a separator of the present invention can effectively improve the fast-charging cycle life of the battery while taking into account the battery safety performance.

[0065] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A battery, characterized by, The battery comprises a separator, a positive electrode sheet, a negative electrode sheet, the separator arranged between the positive electrode sheet and the negative electrode sheet, and a non-aqueous electrolyte; The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer coated on one side or both sides of the negative electrode current collector, and the negative electrode active material layer comprises a negative electrode active material, a conductive agent and a binder; The negative electrode active material is selected from at least one of graphite coated with amorphous carbon on the surface, a composite of graphite coated with amorphous carbon on the surface and silicon oxide, and a composite of graphite coated with amorphous carbon on the surface and nano-silicon; The separator comprises a separator base material, a ceramic layer, a heat-resistant polymer layer and a glue coating layer; the ceramic layer is arranged on at least one side surface of the separator base material, the heat-resistant polymer layer is arranged on the surface of the ceramic layer, and the glue coating layer is arranged on the surface of the heat-resistant polymer layer; the ceramic layer comprises a ceramic powder, a binder and polymer microspheres; the heat-resistant polymer layer comprises a heat-resistant polymer; and the glue coating layer comprises a glue coating polymer; The material of the heat-resistant polymer is selected from at least one of aramid, polyimide, polyurethane, chlorinated phosphazene polymer, boron-nitrogen polymer, polysulfone and polybenzimidazole; and the molecular weight of the polymer microspheres is 50,000-500,000. The closed pore temperature of the separator is 90-130 ℃, and the membrane breaking temperature of the separator is greater than or equal to 230 ℃.

2. The battery of claim 1, wherein, The thickness of the ceramic layer is 1-10 μm.

3. The battery of claim 1, wherein, In the ceramic layer, the mass percentage of the ceramic powder is 50%-80%, the mass percentage of the binder is 5%-40%, and the mass percentage of the polymer microspheres is 10%-45%.

4. The battery of claim 1, wherein, The ceramic powder is selected from at least one of alumina, boehmite, magnesium oxide, magnesium hydroxide, barium sulfate, barium titanate, zinc oxide, calcium oxide, silicon dioxide, silicon carbide and nickel oxide. The material of the polymer microspheres is selected from at least one of polyethylene, polymethacrylic acid, polymethacrylate, polypropylene and polyvinylidene fluoride.

5. The battery of claim 1, wherein, The particle size distribution of the polymer microspheres is 0.1-10 μm, and the melting point of the polymer microspheres is 90-130 ℃.

6. The battery of claim 1, wherein, The thickness of the heat-resistant polymer layer is 1-10 μm.

7. The battery of claim 1, wherein, The thickness of the glue coating layer is 1-10 μm. The material of the glue coating polymer is selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene modification and a copolymer thereof, polyimide, polyacrylonitrile, polymethyl methacrylate and polyacrylic acid.

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