Composite separator and method for manufacturing the same

Abstract

The application discloses a composite diaphragm and a preparation method thereof. The composite diaphragm is provided with a functional coating of lithium titanium aluminum phosphate and lithium poly-2-acrylamide-2-methylpropane sulfonate, and the performance is significantly improved. Lithium titanium aluminum phosphate can spontaneously form a protective film in a low potential environment. The film can effectively block the penetration of lithium dendrites into the diaphragm, thereby greatly alleviating the problem of serious self-discharge of the diaphragm battery. The added lithium poly-2-acrylamide-2-methylpropane sulfonate and Li + show high binding energy. This characteristic not only promotes the Li + easily escapes from the constraint of the solvent sheath, but also significantly improves the ion conductivity of the diaphragm, effectively reduces the dissolution energy barrier, and ensures the high reversibility of the lithium deposition process. In addition, the addition of the binder makes the coating material closely connected, and the three complement each other, which not only significantly enhances the puncture resistance of the composite diaphragm, but also greatly optimizes the electrochemical performance of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to a composite separator and its preparation method. Background Technology

[0002] Lithium-ion batteries, as the most common type of commercially available rechargeable battery, are widely used in various electronic devices and power battery fields due to their excellent energy density, extremely low self-discharge rate, and superior cycle life. The core structure of this battery comprises four main components: the positive electrode, the negative electrode, the separator, and the electrolyte. Among these, the separator plays a crucial role, effectively isolating the positive and negative electrodes to prevent direct contact and also functioning as a ion transporter, making it a key component ensuring the safe and stable operation of the battery.

[0003] With the diversification of electronic products and the continuous expansion of power battery applications, the market has placed more stringent demands on the performance of lithium-ion batteries, which has indirectly spurred further improvements in the performance of separator materials. Traditionally, commercial separators are mainly made of polyolefin materials, such as polyethylene, polypropylene, or their composites. However, these materials are prone to dissolving at high temperatures, which may lead to internal short circuits in the battery and thus pose safety hazards.

[0004] To overcome the shortcomings of polyolefin separators under high-temperature conditions, the industry has attempted to improve them by uniformly coating one or both sides of the polyolefin separator with a ceramic layer. This ceramic-coated separator significantly enhances the high-temperature resistance of the separator and improves the overall safety of the battery. Nevertheless, current ceramic separators still have limitations in terms of puncture strength, meaning their ability to maintain structural integrity when punctured by a sharp object needs to be strengthened.

[0005] Given the aforementioned defects of current diaphragms, it is indeed necessary to provide a technical solution to address these problems. Summary of the Invention

[0006] The purpose of this invention is to provide a composite diaphragm that has high temperature resistance, high safety, and good puncture performance.

[0007] To achieve this objective, the present invention provides the following solution:

[0008] A composite diaphragm, comprising:

[0009] Base film;

[0010] A ceramic coating is disposed on at least one surface of the base film;

[0011] A functional coating comprising an adhesive, lithium aluminum titanium phosphate, and lithium poly-2-acrylamide-2-methylpropanesulfonate; disposed on one surface of the base film and / or the surface of the ceramic coating.

[0012] Preferably, the lithium poly-2-acrylamide-2-methylpropanesulfonate has a molecular weight of 20,000 to 40,000 and a degree of polymerization of 96 to 194.

[0013] Preferably, the mass ratio of the binder, the lithium titanium aluminum phosphate, and the lithium poly-2-acrylamide-2-methylpropanesulfonate is 0.1-10:20-80:0.5-15.

[0014] Preferably, the thickness ratio of the base film, the functional coating, and the ceramic coating is 4-5:1-3:1-2.

[0015] Preferably, the thickness of the base film is 4-5 μm, the thickness of the functional coating is 1-3 μm, and the thickness of the ceramic coating is 1-2 μm.

[0016] Preferably, the binder is at least one of polyvinylidene fluoride and polymethyl methacrylate; the chemical formula of lithium titanium aluminum phosphate is Li. (1+x) Al x Ti (2-x) X satisfies the relationship: 0.2≤X≤0.9. The particle size D50 of lithium titanium aluminum phosphate is 0.1μm-1.0μm, preferably 0.2μm-0.3μm.

[0017] This invention also provides a method for preparing a composite membrane, comprising the following steps:

[0018] Step 1: Dissolve ceramic particles and binder in a solvent, disperse them evenly to obtain a ceramic coating slurry, coat the ceramic coating slurry onto at least one surface of the base film, and dry to obtain a ceramic coating.

[0019] Step 2: Weigh 2-acrylamido-2-methylpropanesulfonic acid and azobisisobutyronitrile and add them to NMP. Heat and stir, add Li2CO3 powder, and continue heating and stirring to obtain solution A containing lithium poly-2-acrylamido-2-methylpropanesulfonate.

[0020] Step 3: Disperse the binder and lithium aluminum titanium phosphate in a solvent to obtain solution B; mix solution A with solution B in two batches to obtain the functional coating slurry;

[0021] Step 4: Apply the functional coating slurry to the other surface of the base membrane and / or the surface of the ceramic coating, and dry it to obtain the functional coating and the composite membrane.

[0022] Preferably, in steps one and three, the solvent is at least one selected from acetonitrile, chloroform, dichloroethane, dimethylformamide, N-methylpyrrolidone, and tetrahydrofuran.

[0023] Preferably, in step one, the adhesive includes at least one of polyethylene oxide, polyacrylic acid, and polyvinylidene fluoride.

[0024] Preferably, in step one, the ceramic particles are selected from AlO3 and boehmite.

[0025] Preferably, in step one, the adhesive accounts for 1 to 10 wt% of the ceramic coating slurry by mass; the ceramic particles account for 20 to 60 wt% of the ceramic coating slurry by mass; and the solvent accounts for 40 to 70 wt% of the ceramic coating slurry by mass.

[0026] Preferably, in step two, the mass ratio of 2-acrylamide-2-methylpropanesulfonic acid, azobisisobutyronitrile, and Li2CO3 powder is 60-80:1-5:20-30.

[0027] Preferably, in step two, the mass concentration of lithium poly-2-acrylamide-2-methylpropanesulfonate in solution A is 10% to 50%.

[0028] Preferably, in step three, the mass ratio of lithium titanium aluminum phosphate, the binder, and lithium poly-2-acrylamide-2-methylpropanesulfonate is 3-5:0.5-2:0.5-2.

[0029] Preferably, the solids content of the ceramic coating slurry and the functional coating slurry is 5% to 40%.

[0030] Preferably, in steps two and three, the stirring temperature is 25°C to 60°C.

[0031] The present invention also provides a secondary battery, comprising a separator, a negative electrode, an electrolyte, a battery casing, and a positive electrode, wherein the separator is the aforementioned composite separator.

[0032] Compared to existing technologies, the advantages of this invention are as follows: By applying a functional coating of lithium titanium aluminum phosphate and lithium poly-2-acrylamide-2-methylpropanesulfonate to the separator surface, this invention achieves a significant performance improvement. Specifically, lithium titanium aluminum phosphate can spontaneously form a protective film under low potential conditions. This film effectively prevents lithium dendrites from puncturing the separator, thereby greatly alleviating the problem of severe self-discharge in separator batteries. Simultaneously, the added lithium poly-2-acrylamide-2-methylpropanesulfonate and lithium... +It exhibits a high binding energy, a characteristic that not only promotes the growth of Li + Easily freed from the constraints of the solvent sheath, this significantly improves the ionic conductivity of the membrane and effectively reduces the desolvation barrier, ensuring a high degree of reversibility in the lithium deposition process. Furthermore, the addition of a binder ensures the coating materials are tightly bonded, forming a stable whole. These three factors work synergistically, not only significantly enhancing the puncture resistance of the composite membrane but also greatly optimizing the electrochemical performance of the lithium-ion battery. Attached Figure Description

[0033] Figure 1 The graph shows the test data of the capacitance retention rate of the lithium-ion batteries in Examples 1-8 and Comparative Examples 1-4 of this invention. Detailed Implementation

[0034] To make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] According to a first aspect of the present invention, a composite separator is provided, comprising:

[0036] Base film;

[0037] A ceramic coating is disposed on at least one surface of the base film;

[0038] Functional coatings, including binders, lithium aluminum titanium phosphate, and lithium poly-2-acrylamide-2-methylpropanesulfonate; disposed on one surface of a base film and / or the surface of a ceramic coating.

[0039] This invention achieves a significant performance improvement by incorporating lithium titanium aluminum phosphate and lithium poly-2-acrylamide-2-methylpropanesulfonate into the functional coating of the separator. Specifically, lithium titanium aluminum phosphate can spontaneously form a protective film under low potential conditions. This film effectively prevents lithium dendrites from puncturing the separator, thereby greatly alleviating the serious self-discharge problem of separator batteries. Simultaneously, the added lithium poly-2-acrylamide-2-methylpropanesulfonate and lithium... + It exhibits a high binding energy, a characteristic that not only promotes the growth of Li + Easily freed from the constraints of the solvent sheath, this significantly improves the ionic conductivity of the membrane and effectively reduces the desolvation barrier, ensuring a high degree of reversibility in the lithium deposition process. Furthermore, the addition of a binder ensures the coating materials are tightly bonded, forming a stable whole. These three factors work synergistically, not only significantly enhancing the puncture resistance of the composite membrane but also greatly optimizing the electrochemical performance of the lithium-ion battery.

[0040] In one embodiment of the present invention, the molecular weight of lithium poly-2-acrylamide-2-methylpropanesulfonate is 20,000 to 40,000, for example, 20,000, 25,000, 30,000, 35,000, or 40,000; the degree of polymerization is 96 to 194, for example, 96, 97, 98, 99, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, or 194. Lithium poly-2-acrylamide-2-methylpropanesulfonate with this molecular weight and degree of polymerization reacts with Li... + It exhibits a high binding energy, a characteristic that not only promotes the growth of Li + It easily breaks free from the constraints of the solvent sheath, significantly improves the ionic conductivity of the membrane, and effectively reduces the desolvation energy barrier, ensuring a high degree of reversibility in the lithium deposition process. Molecules exceeding this molecular weight or degree of polymerization cannot achieve the desired effect.

[0041] In one embodiment of the present invention, the mass ratio of the binder, lithium titanium aluminum phosphate, and lithium poly-2-acrylamide-2-methylpropanesulfonate is 0.1–10:20–80:0.5–15, for example, it can be 0.1:20:0.5, 0.1:30:0.5, 0.1:40:0.5, 0.1:50:0.5, 0.1:60:0.5, 0.1:70:0.5, 0.5:20:1, 1:20:0.5, etc. 2:20:0.5, 3:20:0.5, 4:20:0.5, 5:20:0.5, 6:20:0.5, 7:20:0.5, 8:20:0.5, 9:20:0.5, 10:20:0.5, 0.1:20:1, 2:20:2, 3:20:2, 4:20:2, 5:20:5, 6:20:5, 7:20:5, 8:20:8, 9:20:8, 10:20:9.

[0042] In one embodiment of the invention, the thickness ratio of the base film, functional coating, and ceramic coating is 4–5:1–3:1–2, for example, 4:1:1, 4.5:1:1, 5:1:1, 4:2:1, 4:3:1, or 4:1:2. The base film, as a support layer, provides good mechanical strength and stability due to its relatively thick thickness, helping to resist external pressure and impact. Although the functional coating and ceramic coating are relatively thin, their presence further enhances the overall mechanical properties, particularly exhibiting excellent performance in high-temperature resistance and puncture resistance.

[0043] In one embodiment of the present invention, the thickness of the base film is 4–5 μm, for example, 4 μm, 4.1 μm, 1.2 μm, 1.3 μm, 4.4 μm, 4.5 μm, 1.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, or 5 μm; the thickness of the functional coating is 1–3 μm, for example, 1 μm, 1.1 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 1.9 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 2.9 μm, or 3 μm; and the thickness of the ceramic coating is 1–2 μm, for example, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, or 2 μm.

[0044] In one embodiment of the present invention, the binder is at least one selected from polyvinylidene fluoride and polymethyl methacrylate; the chemical formula of lithium titanium aluminum phosphate is Li (1+x) Al x Ti (2-x) The value of X satisfies the relationship: 0.2 ≤ X ≤ 0.9, and can be, for example, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9, with 0.7 being preferred. The particle size D50 of lithium titanium aluminum phosphate is 0.1 μm-1.0 μm, preferably 0.2 μm-0.3 μm. For example, it can be 0.21 μm, 0.22 μm, 0.23 μm, 0.24 μm, 0.25 μm, 0.26 μm, 0.27 μm, 0.28 μm, 0.29 μm, or 0.3 μm. Lithium titanium aluminum phosphate with a particle size D50 in the range of 0.2 μm to 0.3 μm has a larger specific surface area, thereby increasing the contact area with the electrolyte, improving the utilization rate of active materials, and also helping to reduce battery polarization, especially during high-current charge and discharge. This helps maintain battery stability and extend battery life. In addition, lithium titanium aluminum phosphate can spontaneously form a protective film under low potential conditions. This film can effectively prevent lithium dendrites from puncturing the separator, thereby greatly alleviating the problem of severe self-discharge in separator batteries.

[0045] In a second aspect of the present invention, a method for preparing a composite separator is also provided, comprising the following steps:

[0046] Step 1: Dissolve ceramic particles and binder in solvent, disperse evenly to obtain ceramic coating slurry, coat the ceramic coating slurry onto at least one surface of the base film, and dry to obtain ceramic coating;

[0047] Step 2: Weigh 2-acrylamido-2-methylpropanesulfonic acid and azobisisobutyronitrile and add them to NMP. Heat and stir, add Li2CO3 powder, and continue heating and stirring to obtain solution A containing lithium poly-2-acrylamido-2-methylpropanesulfonate.

[0048] Step 3: Disperse the binder and lithium aluminum titanium phosphate in a solvent to obtain solution B; mix solution A with solution B in two batches to obtain the functional coating slurry;

[0049] Step 4: Apply the functional coating slurry to the other surface of the base membrane and / or the surface of the ceramic coating, dry it to obtain the functional coating, and obtain the composite membrane.

[0050] In one embodiment of the present invention, in steps one and three, the solvent is at least one selected from acetonitrile, chloroform, dichloroethane, dimethylformamide, N-methylpyrrolidone, and tetrahydrofuran.

[0051] In one embodiment of the present invention, in step one, the adhesive includes at least one of polyethylene oxide, polyacrylic acid, and polyvinylidene fluoride.

[0052] In one embodiment of the present invention, in step one, the ceramic particles are selected from AlO3 and boehmite.

[0053] In one embodiment of the present invention, in step one, the mass percentage of the binder in the ceramic coating slurry is 1-10 wt%, for example, it can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%; the mass percentage of the ceramic particles in the ceramic coating slurry is 20-60 wt%, for example, it can be 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, or 60 wt%; and the mass percentage of the solvent in the ceramic coating slurry is 40-70 wt%, for example, it can be 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, or 70 wt%.

[0054] In one embodiment of the present invention, in step two, the mass ratio of 2-acrylamide-2-methylpropanesulfonic acid, azobisisobutyronitrile, and Li₂CO₃ powder is 60–80:1–5:20–30. 2-Acrylamide-2-methylpropanesulfonic acid is a poly… Synthesis Poly-2-acrylamide-2-methylpropanesulfonic acid is the main material and accounts for a large proportion. Azobisisobutyronitrile (AIBN) is an azo-type free radical initiator, and its addition amount with AIBN is related to the proportion of initiators. Too much or too little initiator will affect the molecular weight and degree of polymerization of the generated polymer, which will affect the coating viscosity, mechanical strength, porosity, ionic conductivity, and other properties of the subsequently prepared separator. The content of Li2CO3 should not be too high, as too much lithium carbonate in the separator will have a negative impact on the battery's performance, safety, consistency, and production cost.

[0055] In one embodiment of the present invention, in step two, the mass concentration of lithium poly-2-acrylamide-2-methylpropanesulfonate in solution A is 10% to 50%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%. If the mass concentration of lithium poly-2-acrylamide-2-methylpropanesulfonate is too low, the amount of other substances added in subsequent steps will be too large; while if the concentration is too high, it will be detrimental to the smooth progress of the subsequent stirring process and the uniform dispersion of the material.

[0056] In one embodiment of the present invention, in step three, the mass ratio of lithium titanium aluminum phosphate, binder and lithium poly-2-acrylamide-2-methylpropanesulfonate is 3-5:0.5-2:0.5-2.

[0057] When the mass ratio of lithium titanium aluminum phosphate (LATP) is in the range of 3 to 5, it exhibits good ionic conductivity, mechanical stability, and thermal stability. However, adding too much or too little LATP will affect the ionic conductivity, mechanical stability, and thermal stability of the membrane. Excessive addition of LATP will also increase input costs. When the mass ratio of binder is in the range of 0.5 to 2, the slurry is stirred evenly, and the coating consistency is good. Adding too much or too little binder will affect the slurry viscosity, which will affect the uniformity of the slurry, the consistency of the coating, and mechanical properties. Similarly, adding too much or too little lithium poly-2-acrylamido-2-methylpropanesulfonate will affect the ionic conductivity and mechanical stability of the membrane.

[0058] In one embodiment of the present invention, the solid content of the ceramic coating slurry and the functional coating slurry is 5% to 40%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, or 40%. When the solid content is within this range, the stirring, coating, and drying efficiency of the slurry is relatively good, which can save time and energy and thus improve production efficiency. If the solid content is too low, there are fewer solid components in the slurry, and more slurry and a longer drying time may be required to achieve the required coating thickness, thereby increasing production costs and time. When the solid content is too high, the viscosity of the slurry is high, the fluidity of the slurry is poor, and it is difficult to form a uniform and continuous coating on the electrode, thereby affecting the performance and service life of the product.

[0059] In one embodiment of the present invention, in steps two and three, the stirring temperature is 25°C to 60°C, for example, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, or 60°C. Heating and stirring can accelerate the dissolution of the powder and make the slurry more uniformly dispersed.

[0060] The present invention also provides a secondary battery, comprising a separator, a negative electrode, an electrolyte, a battery casing, and a positive electrode, wherein the separator is the aforementioned composite separator.

[0061] The positive electrode includes a positive current collector and a positive active material layer coated on at least one surface of the positive current collector. The positive active material layer may be, but is not limited to, lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate oxide, and lithium iron phosphate. The positive current collector may be any material suitable for use as a positive current collector in lithium-ion batteries, such as aluminum foil, copper foil, nickel foil, stainless steel, or carbon materials.

[0062] The negative electrode includes a negative current collector and a negative active material layer coated on at least one surface of the negative current collector. The negative active material layer may be one or more of the following, including but not limited to graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium.

[0063] The graphite can be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; the tin-based material can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The negative electrode current collector is typically a structure or component that collects current. The negative electrode current collector can be any material suitable for use as a negative electrode current collector in a secondary battery, for example, it can be, but is not limited to, metal foil, and more specifically, it can be, but is not limited to, copper foil.

[0064] The secondary battery also includes an electrolyte, which comprises an organic solvent, an electrolyte lithium salt, and additives. The electrolyte lithium salt can be LiPF6 and / or LiBOB used in high-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, and LiPF6 used in low-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in overcharge-resistant electrolytes; or it can be at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent can be a cyclic carbonate, including PC and EC; it can also be a chain carbonate, including DFC, DMC, or EMC; or it can be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additives include, but are not limited to, at least one of film-forming additives, conductive additives, flame-retardant additives, overcharge-resistant additives, additives for controlling the H2O and HF content in the electrolyte, additives for improving low-temperature performance, and multifunctional additives.

[0065] The present invention will be further described below through specific embodiments.

[0066] Example 1

[0067] Preparation of composite membrane:

[0068] Step 1: Dissolve 30g of alumina and 2g of polyacrylic acid in 70mL of acetonitrile and disperse evenly to obtain a ceramic coating slurry. Coat the ceramic coating slurry onto one surface of the base film and dry to obtain a ceramic coating; the thickness of the ceramic coating is 1μm.

[0069] Step 2: Weigh 20g of 2-acrylamide-2-methylpropanesulfonic acid, 0.4g of azobisisobutyronitrile, and 7g of Li2CO3 powder according to a ratio of 73:1.5:25.5. Add the 2-acrylamide-2-methylpropanesulfonic acid and azobisisobutyronitrile to 80mL of NMP, heat and stir at 60℃, add the Li2CO3 powder, and continue heating and stirring at 60℃ to obtain solution A containing lithium poly-2-acrylamide-2-methylpropanesulfonate; wherein the mass concentration of lithium poly-2-acrylamide-2-methylpropanesulfonate in solution A is 23%.

[0070] Step 3: Disperse PVDF and lithium aluminum titanium phosphate in 300 mL of acetonitrile to obtain solution B; mix solution A with solution B in two batches to obtain functional coating slurry; wherein, the weight ratio of LATP, lithium poly-2-acrylamide-2-methylpropanesulfonate and PVDF is 4:1:1.

[0071] Step 4: Apply the functional coating slurry to the other surface of the base membrane, dry it to obtain the functional coating, and obtain the composite membrane.

[0072] Preparation of secondary batteries:

[0073] The negative electrode, positive electrode, and the aforementioned composite separator are interleaved and wound together, then encapsulated with an aluminum-plastic film to form a battery cell. This cell is then placed in a battery casing, electrolyte is added, and the casing is sealed to obtain a lithium-ion battery. The active material of the negative electrode is graphite; the active material of the positive electrode is the aforementioned composite positive electrode material.

[0074] Table 1 shows the data for Examples 1-10 and Comparative Examples 1-4. The rest are the same as in Example 1, and will not be repeated here.

[0075] Table 1

[0076]

[0077] Performance testing:

[0078] The composite diaphragms of Examples 1-10 and Comparative Examples 1-4 were subjected to diaphragm puncture performance tests, and the test results are shown in Table 2.

[0079] The cell self-discharge rate of the secondary batteries of Examples 1-10 and Comparative Examples 1-4 was tested, and the test results are shown in Table 2.

[0080] The electrochemical performance of the secondary batteries from Examples 1-8 and Comparative Examples 1-4 was tested, and the test results were obtained. Figure 1 .

[0081] Table 2

[0082] Group K value (mv / h) Diaphragm puncture performance (gf) Example 1 0.066 186 Example 2 0.0561 192 Implement column 3 0.0451 194 Example 4 0.035 196 Example 5 0.0391 201 Example 6 0.0219 231 Example 7 0.0391 203 Example 8 0.0201 250 Example 9 0.08 176 Example 10 0.075 180 Comparative Example 1 0.137 150 Comparative Example 2 0.129 156 Comparative Example 3 0.109 161 Comparative Example 4 0.09 169

[0083] As shown in Table 2, the test data of Examples 1-10 show that the puncture performance and K-value of the separator are superior to those of Comparative Examples 1-4. This indicates that the present invention achieves a significant performance improvement by adding lithium titanium aluminum phosphate and lithium poly-2-acrylamide-2-methylpropanesulfonate to the functional coating of the separator. Specifically, lithium titanium aluminum phosphate can spontaneously form a protective film under low potential conditions. This film can effectively block lithium dendrites from puncturing the separator, thereby greatly alleviating the problem of severe self-discharge in separator batteries. Simultaneously, the added lithium poly-2-acrylamide-2-methylpropanesulfonate and Li... + It exhibits a high binding energy, a characteristic that not only promotes the growth of Li + Easily freed from the constraints of the solvent sheath, this significantly improves the ionic conductivity of the membrane and effectively reduces the desolvation barrier, ensuring a high degree of reversibility in the lithium deposition process. Furthermore, the addition of a binder ensures the coating materials are tightly bonded, forming a stable whole. These three factors work synergistically, not only significantly enhancing the puncture resistance of the composite membrane but also greatly optimizing the electrochemical performance of the lithium-ion battery.

[0084] like Figure 1 The test data shown indicates that the capacitance retention rate of Examples 1-10 under 60°C and 28-day storage conditions is better than that of Comparative Examples 1-4. This demonstrates that by applying a functional coating to the separator, when the separator is used in a battery, the capacitance retention rate of the separator under 60°C and 28-day storage conditions can be improved.

[0085] In Examples 1-10, the K value range was ≤0.08, while in Comparative Examples 1-4, the K value range was >0.08. Under high-temperature conditions, the internal chemical reaction of the battery accelerated, and the self-discharge reaction was also enhanced. Poor K values ​​in Comparative Examples 1-4 indicate an abnormal self-discharge rate, which may lead to rapid capacity decay during high-temperature storage.

[0086] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A composite diaphragm, characterized in that, include: Base film; A ceramic coating is disposed on at least one surface of the base film; A functional coating comprising an adhesive, lithium aluminum titanium phosphate, and lithium poly-2-acrylamide-2-methylpropanesulfonate; disposed on one surface of the base film and / or the surface of the ceramic coating; The lithium poly-2-acrylamide-2-methylpropanesulfonate has a molecular weight of 20,000 to 40,000 and a degree of polymerization of 96 to 194; the mass ratio of the binder, the lithium titanium aluminum phosphate, and the lithium poly-2-acrylamide-2-methylpropanesulfonate is 0.1 to 10: 20 to 80: 0.5 to 15; the thickness ratio of the base film, the functional coating, and the ceramic coating is 4 to 5: 1 to 3: 1 to 2.

2. The composite diaphragm according to claim 1, characterized in that, The thickness of the base film is 4~5μm, the thickness of the functional coating is 1~3μm, and the thickness of the ceramic coating is 1~2μm.

3. The composite diaphragm according to claim 1, characterized in that, The chemical formula of the lithium titanium aluminum phosphate is Li (1+x) Al x Ti (2-x) X satisfies the relation: 0.2≤X≤0.

9.

4. A method for preparing the composite separator as described in any one of claims 1 to 3, characterized in that, Includes the following steps: Step 1: Dissolve ceramic particles and binder in a solvent, disperse them evenly to obtain a ceramic coating slurry, coat the ceramic coating slurry onto at least one surface of the base film, and dry to obtain a ceramic coating. Step 2: Weigh 2-acrylamido-2-methylpropanesulfonic acid and azobisisobutyronitrile and add them to NMP. Heat and stir, add Li2CO3 powder, and continue heating and stirring to obtain solution A containing lithium poly-2-acrylamido-2-methylpropanesulfonate. Step 3: Disperse the binder and lithium aluminum titanium phosphate in a solvent to obtain solution B; mix solution A with solution B in two batches to obtain the functional coating slurry; Step 4: Apply the functional coating slurry to the other surface of the base membrane and / or the surface of the ceramic coating, and dry it to obtain the functional coating and the composite membrane.

5. The method for preparing the composite diaphragm according to claim 4, characterized in that, In step two, the mass ratio of 2-acrylamide-2-methylpropanesulfonic acid, azobisisobutyronitrile, and Li2CO3 powder is 60~80:1~5:20~30.

6. The method for preparing the composite diaphragm according to claim 4, characterized in that, In step two, the mass concentration of lithium poly-2-acrylamide-2-methylpropanesulfonate in solution A is 10% to 50%.

7. The method for preparing the composite diaphragm according to claim 4, characterized in that, In step three, the mass ratio of lithium titanium aluminum phosphate, the binder and the lithium poly-2-acrylamide-2-methylpropanesulfonate is 3~5:0.5~2:0.5~2.

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