Composite separator and method of making and use thereof

Abstract

The application relates to the technical field of batteries, in particular to a composite diaphragm and a preparation method and application thereof, the composite diaphragm comprising a composite alumina layer, wherein the composite alumina layer comprises: an intermediate aluminum foil, the intermediate aluminum foil being provided with through holes; and a porous alumina layer, the porous alumina layer being arranged on at least one side of the intermediate aluminum foil. The composite diaphragm has better temperature resistance, high-temperature dimensional stability and heat conduction performance, and can improve the safety performance of a battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a composite diaphragm, a preparation method and application thereof, and more particularly to a composite diaphragm, a preparation method, a battery, a battery pack and an electric device. BACKGROUND

[0002] The diaphragm is a core component in a battery, and directly determines the safety of the battery. It is known that the safety risk of the battery mainly originates from the uncontrollability of the high energy density and the internal chemical reaction of the battery, and especially under certain conditions (such as short circuit, high temperature, etc.), heat runaway, fire, explosion and other serious consequences can be caused. Therefore, improving the temperature resistance, high-temperature dimensional stability and heat dissipation performance of the diaphragm is one of the key problems that need to be solved and the most important research direction at present. SUMMARY

[0003] The present application aims to at least solve one of the technical problems in the related art. To this end, the present application provides a composite diaphragm with good temperature resistance, high-temperature dimensional stability and heat dissipation performance, as well as a preparation method and application thereof.

[0004] In a first aspect, the present application provides a composite diaphragm. According to an embodiment of the present application, the composite diaphragm comprises a composite aluminum oxide layer, the composite aluminum oxide layer comprising: an intermediate aluminum foil, the intermediate aluminum foil having a through hole; and a porous aluminum oxide layer, the porous aluminum oxide layer being located on at least one side of the intermediate aluminum foil. In the composite diaphragm, the pores in the porous aluminum oxide layer and the through hole in the intermediate aluminum foil can form an active ion transmission channel, the porous aluminum oxide layer has heat conduction performance, and the structure is continuous, and there is basically no problem of powder falling off, and can play a role in supporting the framework. Even under high-temperature runaway, the porous aluminum oxide layer still maintains the role of the framework, has good heat resistance and high-temperature dimensional stability, and can effectively prevent short circuit. The intermediate aluminum foil can play a superior heat conduction ability, increase the heat conduction characteristics of the diaphragm, prolong the heat runaway time, and reduce the probability of battery heat runaway, thereby effectively improving the safety of the battery using the composite diaphragm.

[0005] According to an embodiment of the present application, the composite diaphragm further comprises: a polymer layer, the polymer layer being stacked with the composite aluminum oxide layer.

[0006] According to an embodiment of the present application, the material of the polymer layer comprises at least one of polyethylene, polypropylene, aramid, polyvinylidene fluoride, cellulose, polyethylene terephthalate, polyimide and non-woven fabric.

[0007] According to an embodiment of the present application, the polymer layer is located on one side of the composite aluminum oxide layer.

[0008] According to an embodiment of the present application, the polymer layer is located on opposite sides of the composite alumina layer.

[0009] According to an embodiment of the present application, the material of the polymer layer on one side of the composite alumina layer is polyethylene, and the material of the polymer layer on the other side of the composite alumina layer is polypropylene.

[0010] According to an embodiment of the present application, the composite alumina layer is located on opposite sides of the polymer layer.

[0011] According to an embodiment of the present application, the composite alumina layer comprises pores, the pores comprising large pores and small pores, the small pores being located in the porous alumina layer, and the large pores penetrating through the intermediate aluminum foil or penetrating through the porous alumina layer on one side of the intermediate aluminum foil and deep into the intermediate aluminum foil, the diameter φ1 of the large pores and the diameter φ2 of the small pores satisfying: φ2 < φ1.

[0012] According to an embodiment of the present application, the composite separator satisfies at least one of the following conditions:

[0013] The diameter φ1 of the large pores is 5 μm to 50 μm;

[0014] The diameter φ2 of the small pores is 20 nm to 5 μm;

[0015] The gap I1 between adjacent two large pores is 5 μm to 50 μm;

[0016] The gap I2 between adjacent two small pores is 30 nm to 1 μm;

[0017] The coverage L1 of the large pores is 5% to 50%;

[0018] The coverage L2 of the small pores is 5% to 60%;

[0019] The depth H1 of the large pores is the sum of the thickness of the intermediate aluminum foil and the porous alumina layer on one side or the thickness of the intermediate aluminum foil, in particular, H1 is 0.5 μm to 5 μm;

[0020] The depth H2 of the small pores is the thickness of the porous alumina layer on one side, in particular, H2 is 0.2 μm to 5 μm.

[0021] According to an embodiment of the present application, a functional material is arranged in the pores, the functional material comprising at least one of a solid-state electrolyte, a lithium supplementing material, an organic polymer, and a binder.

[0022] According to an embodiment of the present application, the functional material satisfies at least one of the following conditions:

[0023] The solid-state electrolyte comprises lithium titanium aluminum phosphate.

[0024] The lithium supplementing material comprises at least one of Li6CoO4, Li5FeO4, Li2C2O4, Li2NiO2;

[0025] The organic polymer comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polymethyl methacrylate;

[0026] The binder comprises a granular binder.

[0027] According to the embodiments of the present application, the composite diaphragm satisfies at least one of the following conditions:

[0028] The thickness of the composite diaphragm is 3 μm to 20 μm;

[0029] The thickness of the polymer layer is 2 μm to 22 μm;

[0030] The porosity of the polymer layer is 20% to 70%;

[0031] The thickness of the intermediate aluminum foil is 0.5 μm to 3 μm;

[0032] The thickness of the porous aluminum oxide layer is 0.3 μm to 2.5 μm.

[0033] In the second aspect, the present application provides a method for preparing the composite diaphragm described above. According to the embodiments of the present application, the method comprises: taking an aluminum foil as an anode, anodizing at least one side surface of the aluminum foil opposite to each other, forming an oxide layer on at least one side surface of the aluminum foil, and obtaining an anodization product; and performing pore-forming treatment on the surface of the anodization product, and obtaining a composite aluminum oxide layer. Specifically, by anodizing, a porous aluminum oxide layer with small pores can be formed on at least one side surface of the aluminum foil, and by further pore-forming treatment, large pores can be formed, and then by combining the large pores and the small pores, a transmission channel for active ions can be formed in the composite aluminum oxide layer, and meanwhile, part of the aluminum foil that has not been oxidized constitutes an intermediate aluminum foil. Therefore, the method is simple to operate, and the composite diaphragm obtained by the method has better temperature resistance and high-temperature dimensional stability, and the battery using the composite diaphragm has higher safety.

[0034] According to the embodiments of the present application, the anodizing satisfies at least one of the following conditions:

[0035] The electrolytic solution for the anodizing comprises at least one of oxalic acid, phosphoric acid, and sulfuric acid;

[0036] The cathode for the anodizing comprises a platinum electrode;

[0037] The current density for the anodizing is 1 A / dm 2 ~ 5 A / dm 2 ;

[0038] The temperature of the anodization is 0-60℃;

[0039] The time of the anodization is 10min-10h.

[0040] According to embodiments of the present application, the pore-forming treatment comprises at least one of chemical etching, focused ion beam etching and laser drilling.

[0041] According to embodiments of the present application, the pore-forming treatment satisfies at least one of the following conditions:

[0042] The ion beam current used in the focused ion beam etching is 1-50pA;

[0043] The residence time of the focused ion beam etching is 50-1000μs;

[0044] The laser frequency used in the laser drilling is 100-1000Hz;

[0045] The drilling speed of the laser drilling is 0.5-5m / min.

[0046] According to embodiments of the present application, the method further comprises depositing a functional material into the pores of the composite alumina layer.

[0047] According to embodiments of the present application, the deposition method comprises chemical vapor deposition.

[0048] According to embodiments of the present application, the method further comprises compounding the composite alumina layer and a polymer layer.

[0049] According to embodiments of the present application, the compounding comprises stacking the composite alumina layer and the polymer layer, and pressing the obtained stack to compound it.

[0050] In a third aspect, the present application provides a battery. According to embodiments of the present application, the battery comprises the composite separator as described above or prepared by the method as described above. The probability of short circuit and thermal runaway of the battery is significantly reduced, and the battery has higher safety.

[0051] In a fourth aspect, the present application provides a battery pack. According to embodiments of the present application, the battery pack comprises the composite separator as described above, prepared by the method as described above or the battery as described above. The battery pack has better safety performance.

[0052] In a fifth aspect, the present application provides a power consuming device. According to embodiments of the present application, the power consuming device comprises the composite separator as described above, the composite separator prepared by the method as described above, the battery as described above, or the battery pack as described above. The power consuming device has all the features and advantages of the battery as described above or the battery pack as described above, which will not be repeated here. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 is a structural schematic diagram of a composite separator according to an embodiment of the present application.

[0054] Figure 2 is a structural schematic diagram of a composite separator according to another embodiment of the present application.

[0055] Figure 3 is a structural schematic diagram of a composite separator according to another embodiment of the present application.

[0056] Figure 4 is a structural schematic diagram of a composite separator according to another embodiment of the present application.

[0057] Figure 5 is a structural schematic diagram of a composite separator according to another embodiment of the present application. DETAILED DESCRIPTION

[0058] Embodiments of the present application are described in detail below with reference to the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present application, and should not be understood as limiting the present application.

[0059] The present application is based on the discovery and realization of the inventors on the following facts and problems:

[0060] At present, in order to improve the high-temperature resistance and high-temperature dimensional stability of the separator, generally, inorganic ceramic materials are coated on both sides of the polymer separator to form a ceramic composite separator. Although the heat resistance of inorganic ceramic improves the high-temperature deformation resistance and high-temperature dimensional stability of the separator, since the ceramic layer is generally composed of ceramic particles, the ceramic particles are bonded by the adhesive, and problems such as powder falling off are prone to occur; at the same time, according to the energy density requirement, in order to reduce the thickness of the separator, single-sided ceramic is now widely used, but when the environmental humidity changes, the single-sided ceramic causes short circuit due to the problems of water absorption or water loss of the single-sided ceramic, in addition, the separator in the related art has poor thermal conductivity performance at high temperature, which cannot well guarantee the thermal safety. Based on the above problems, the inventors of the present application propose a composite separator with good high-temperature resistance, good high-temperature dimensional stability, and excellent thermal conductivity performance.

[0061] Therefore, in a first aspect, the present application provides a composite separator. According to embodiments of the present application, with reference to Figure 1The composite diaphragm comprises a composite aluminum oxide layer 10, which comprises: an intermediate aluminum foil 11 having a through hole; a porous aluminum oxide layer 12 located on at least one side of the intermediate aluminum foil 11, Figure 1 The intermediate aluminum foil is provided with the porous aluminum oxide layer 12 on both sides. In the composite diaphragm, the porous aluminum oxide layer has heat conduction performance and continuous structure, and basically does not have the problem of powder falling. The porous aluminum oxide layer can play a role of skeleton support, and even in the case of high temperature out of control, the porous aluminum oxide layer still maintains the skeleton function, has better heat resistance and high temperature dimensional stability, and can effectively prevent short circuit. The intermediate aluminum foil can play a superior heat conduction capacity, increase the heat conduction characteristics of the diaphragm, prolong the heat runaway time, and reduce the probability of battery heat runaway, thereby effectively improving the safety of the battery using the composite diaphragm.

[0062] According to the embodiments of the present application, the composite diaphragm further comprises: a polymer layer 20, which is arranged in a stack with the composite aluminum oxide layer 10. Thus, by arranging the polymer layer, when the temperature of the battery rises, the polymer layer can melt and close the pores to form a thermal block, preventing the battery from continuing to run out of control, thereby further improving the safety of the battery. Moreover, the polymer layer has better hydrophobic performance, so that the composite diaphragm itself has excellent hydrophobic efficiency.

[0063] According to the embodiments of the present application, the material of the polymer layer is not particularly limited, as long as it can meet the use requirements of the diaphragm. In some embodiments, the material of the polymer layer comprises at least one of polyethylene, polypropylene, aramid, polyvinylidene fluoride, cellulose, polyethylene terephthalate, polyimide, and non-woven fabric. Thus, the heat resistance is good, the pore closing temperature is high, and the material source is extensive and the cost is low.

[0064] According to the embodiments of the present application, the specific stacking mode of the polymer layer 20 and the composite aluminum oxide layer 10 is not particularly limited, and the number of the polymer layer 20 and the composite aluminum oxide layer 10 is also not particularly limited, which can be flexibly selected according to actual needs.

[0065] In some embodiments, referring to Figure 2 , the polymer layer 20 is located on one side of the composite aluminum oxide layer 10. Thus, by arranging the polymer layer, when the temperature of the battery rises, the polymer layer can melt and close the pores to form a thermal block, preventing the battery from continuing to run out of control, thereby further improving the safety of the battery. Moreover, the polymer layer has better hydrophobic performance, so that the composite diaphragm itself has excellent hydrophobic efficiency.

[0066] In some embodiments, referring to Figure 3polymer layer 20 is located on the opposite side of the composite aluminum oxide layer 10. In this way, the stress on both sides of the composite separator is uniform, which can effectively improve the problem of the crimping of the separator. At the same time, thermal interruption is formed to prevent the battery from continuing to run out of control, thereby further improving the effect of improving the safety of the battery, and the composite separator has excellent hydrophobic properties on both sides.

[0067] According to the embodiments of the present application, when the composite separator is provided with a polymer layer on both sides of the composite aluminum oxide layer, the material of the polymer layer on one side of the composite aluminum oxide layer is polyethylene, and the material of the polymer layer on the other side of the composite aluminum oxide layer is polypropylene. Specifically, in the battery, the potential and temperature of the positive electrode sheet are higher than those of the negative electrode sheet. By setting the composite separator to have polypropylene on one side and polyethylene on the other side, the polypropylene has more excellent oxidation resistance. Under the use conditions, the polypropylene separator is arranged towards the positive electrode sheet, which can effectively improve the problem of oxidation of the battery separator. The polyethylene on the other side provides better transverse tensile strength and improves the mechanical properties of the composite separator.

[0068] According to the embodiments of the present application, referring to Figure 4 , the composite aluminum oxide layer 10 is located on the opposite side of the polymer layer 20. In this way, the temperature resistance, high-temperature dimensional stability and thermal conductivity of the composite separator can be further improved, the effect of improving the crimping of the separator is further improved, and the safety performance of the battery using the composite separator can be further improved.

[0069] According to the embodiments of the present application, referring to Figure 5 , the composite aluminum oxide layer includes pores, the pores include large holes 101 and small holes 102, the small holes 102 are located in the porous aluminum oxide layer 12, and the large holes 101 penetrate through the intermediate aluminum foil or penetrate through the porous aluminum oxide layer 12 on one side of the intermediate aluminum foil and penetrate into the intermediate aluminum foil 11, and the diameter φ1 of the large hole and the diameter φ2 of the small hole satisfy: φ2 < φ1. In this way, by designing the small holes combined with the large holes, the straight-through holes can be avoided, the tortuosity of lithium ion transmission is increased, which is helpful to inhibit the growth of lithium dendrites and further improve the safety of the battery.

[0070] According to the embodiments of the present application, the diameter φ1 of the large hole is 5 μm to 50 μm, specifically, φ1 can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm or any range between any two of them. In this way, the diameter of the large hole is moderate, which is helpful to improve the uniformity of the large hole. If the diameter is too large, the uniformity is not good and may be locally concentrated. If the diameter is too small, the preparation difficulty is increased.

[0071] According to the embodiments of the present application, the diameter of the small hole is 20 nm to 5 μm; specifically, the diameter of the small hole can be 20 nm, 100 nm, 500 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any range between any two of them. In this way, the diameter of the small hole is moderate, which is conducive to improving the uniformity of the small hole. If the diameter is too large, the uniformity is poor, and the active ions may be concentrated locally. If the diameter is too small, the preparation difficulty is increased.

[0072] In this document, the diameter of the large hole and the small hole refers to the longest distance between any two points on the hole wall in the same horizontal plane, which can be detected by the SEM method.

[0073] According to the embodiments of the present application, the gap I1 between the two adjacent large holes is 5 μm to 50 μm; specifically, the gap I1 can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or any range between any two of them. In this way, the large hole has a suitable density, so that the composite alumina layer has a suitable porosity, which can ensure the transmission of active ions, and at the same time has a high tortuosity. If the gap is too large, the mechanical strength of the composite separator may be low. If the gap is too small, the active ion transmission impedance may be high.

[0074] According to the embodiments of the present application, the gap I2 between the two adjacent small holes is 30 nm to 1 μm; specifically, the gap I2 can be 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, or any range between any two of them. In this way, the small hole has a suitable density, so that the composite alumina layer has a suitable porosity, which can ensure the transmission of active ions, and at the same time has a high tortuosity. If the gap is too large, the mechanical strength of the composite separator may be low. If the gap is too small, the active ion transmission impedance may be high.

[0075] In this document, the gap between the two adjacent large holes and the gap between the two adjacent small holes refer to the distance between the geometric centers of the two adjacent holes, which can be detected by the SEM method.

[0076] According to embodiments of the present application, the coverage L1 of the large pores is 5% to 50%; specifically, L1 can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or a range between any two of them. Thus, the large pores have a suitable density, so that the composite aluminum oxide layer has a suitable porosity, which can ensure the transmission of active ions, while having a high tortuosity. If the coverage is too large, the mechanical strength of the composite separator can be low, and if the coverage is too small, the impedance of the transmission of active ions can be high.

[0077] According to embodiments of the present application, the coverage L2 of the small pores is 5% to 60%; specifically, L2 can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or a range between any two of them. Thus, the small pores have a suitable density, so that the composite aluminum oxide layer has a suitable porosity, which can ensure the transmission of active ions, while having a high tortuosity. If the coverage is too large, the mechanical strength of the composite separator can be low, and if the coverage is too small, the impedance of the transmission of active ions can be high.

[0078] Herein, the coverage of the large pores and the small pores refers to the proportion of the area of the pores to the entire base area (the surface of the porous aluminum oxide layer away from the center aluminum foil), which can be detected by the SEM method. It can be understood that the sum of the coverage of the large pores and the small pores is less than or equal to 100%.

[0079] According to embodiments of the present application, the depth H1 of the large pores is the sum of the thickness of the intermediate aluminum foil 11 and the single-layer porous aluminum oxide layer 12 or the thickness of the intermediate aluminum foil 11. That is, the large pores can form a through hole only through the intermediate aluminum foil, or can simultaneously penetrate the single-layer porous aluminum oxide layer and the intermediate aluminum foil. Thus, a transmission channel for active ions can be provided. In some embodiments, H1 can be specifically 0.5 μm to 5 μm, specifically, 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm or a range between any two of them. Thus, the active ions can pass through the composite separator smoothly, and have a high tortuosity, which has a low impedance and can effectively improve the problem of lithium dendrite.

[0080] According to embodiments of the present application, the depth H2 of the small holes is the thickness of the single side of the porous alumina layer 12. In this way, a transport channel for active ions can be provided. In some embodiments, H2 can be specifically 0.2 μm to 5 μm, specifically, 0.2 μm, 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, or any range between any two of them. In this way, the active ions can pass through the composite separator smoothly, and have a high tortuosity, both having a low impedance and effectively improving the lithium dendrite problem.

[0081] In this document, the depth of the large holes and the small holes refers to the size of the holes along the thickness direction (i.e. the stacking direction of the intermediate aluminum foil and the porous alumina layer), which can be detected by the SEM method.

[0082] According to embodiments of the present application, in order to further improve the performance of the composite separator, the pores of the porous alumina layer in the composite alumina layer can be further provided with a functional material, which includes at least one of a solid-state electrolyte, a lithium supplement material, an organic polymer, and a binder. In this way, the electrolyte wetting performance of the composite separator can be further improved, thereby improving the uneven distribution of the electrolyte and the problem of local lithium precipitation in the battery; it can also have a lithium supplement effect to reduce the capacity decay of the battery and prolong the cycle life of the battery; the organic polymer can melt when the temperature rises to the melting point of the organic polymer, the pores are sealed, thermal shutdown is achieved, and battery safety is provided; and the binder can penetrate into the pores to achieve the advantage of enhanced bonding force without increasing the thickness of the separator.

[0083] According to embodiments of the present application, the solid-state electrolyte includes lithium titanium aluminum phosphate. In this way, the effect of improving the electrolyte wetting performance of the composite separator is further improved, thereby further improving the uneven distribution of the electrolyte and the problem of local lithium precipitation in the battery.

[0084] According to embodiments of the present application, the lithium supplement material includes at least one of Li6CoO4, Li5FeO4, Li2C2O4, and Li2NiO2. In this way, the composite separator can also have a lithium supplement effect, reduce the loss of active ions in the battery, thereby reducing the capacity decay of the battery and prolonging the cycle life of the battery.

[0085] According to embodiments of the present application, the organic polymer includes at least one of polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), and polymethyl methacrylate (PMMA). In this way, when the temperature rises to the melting point of the organic polymer, the material melts, the pores are sealed, thermal shutdown is achieved, and battery safety is provided.

[0086] According to an embodiment of the present application, the binder comprises a granular binder. In this way, the advantages of enhanced bonding force without increasing the thickness of the separator can be achieved.

[0087] According to an embodiment of the present application, the thickness of the composite separator is 3-20 μm, specifically 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm or a range between any two of them. Within this thickness range, the mechanical properties meet the requirements while meeting the insulation performance, and the quality is lighter, which is beneficial to improving the overall performance of the battery.

[0088] According to an embodiment of the present application, the thickness of the polymer layer is 2-22 μm, specifically 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm or a range between any two of them. In this way, the composite separator has better toughness at low temperature, and can quickly melt and seal the pores at high temperature to achieve thermal shutdown and improve the safety of the battery.

[0089] According to an embodiment of the present application, the porosity of the polymer layer is 20-70%, specifically 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or a range between any two of them. In this way, the active ions can be smoothly transmitted through the composite separator, while having better mechanical properties. If the porosity is too small, the impedance of the active ion transmission may be high, and if the porosity is too large, the mechanical strength of the composite separator may be reduced, and the probability of short circuit may be increased.

[0090] According to an embodiment of the present application, the thickness of the intermediate aluminum foil is 0.5-3 μm, specifically 0.5 μm, 1 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3 μm or a range between any two of them. In this way, it has excellent thermal conductivity, which can further improve the safety of the battery.

[0091] According to an embodiment of the present application, the thickness of the porous aluminum oxide layer is 0.3-2.5 μm, specifically 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2.0 μm, 2.5 μm or a range between any two of them. In this way, it has better skeleton support, better temperature resistance and high-temperature dimensional stability, and the effect of improving the safety of the battery is further improved.

[0092] In a second aspect, the application provides a method for preparing the composite separator. According to an embodiment of the application, the method comprises: taking an aluminum foil as an anode, anodizing at least one side surface of the aluminum foil to form an oxide layer on the at least one side surface of the aluminum foil, and obtaining an anodization product; and performing a pore-forming treatment on the anodization product to obtain a composite aluminum oxide layer. Specifically, by anodization, a porous aluminum oxide layer with small pores can be formed on at least one side surface of the aluminum foil. Further, by pore-forming treatment, large pores can be formed. Then, by combining the large pores and the small pores, a transmission channel for active ions can be formed in the composite aluminum oxide layer, and part of the aluminum foil remains unoxidized to form an intermediate aluminum foil. Thus, the method is simple to operate, and the composite separator obtained has better temperature resistance and high-temperature dimensional stability, and the battery using the composite separator has higher safety.

[0093] It can be understood that the anodization treatment can be performed according to the following steps: taking an aluminum foil as an anode, additionally providing a cathode, placing the anode and the cathode in an electrolyte, and connecting a power source between the anode and the cathode. Under the action of the electric field, the aluminum foil as the anode undergoes an oxidation reaction to form a porous aluminum oxide layer.

[0094] According to an embodiment of the application, the electrolyte solution for anodization can comprise at least one of oxalic acid, phosphoric acid, and sulfuric acid. Thus, the electrolyte solution is conducive to forming a porous aluminum oxide layer with appropriate thickness, higher density, and higher mechanical strength.

[0095] According to an embodiment of the application, the cathode for anodization comprises a platinum electrode. Thus, the cathode has stable properties, does not substantially dissolve any metal ions, has uniform current distribution, is resistant to corrosion, has a long service life, and has a lower overpotential, and the anodization effect is better.

[0096] According to an embodiment of the application, the current density for anodization is 1 A / dm 2 to 5 A / dm 2 , specifically 1 A / dm 2 , 1.5 A / dm 2 , 2 A / dm 2 , 2.5 A / dm 2 , 3 A / dm 2 , 3.5 A / dm 2 , 4 A / dm 2 , 4.5 A / dm 2 , 5 A / dm 2 , or any range between any two of them. Within the above current density range, a porous aluminum oxide layer with appropriate thickness and higher mechanical strength can be generated at a faster speed.

[0097] According to an embodiment of the present application, the temperature of the anodization is 0-60°C, specifically 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, or a range between any two of them. Within the above temperature range, the film formation rate is faster, the tact time is shortened, and the cell voltage is lower, thereby reducing the energy consumption, while the current efficiency is high, which is conducive to obtaining suitable small holes.

[0098] According to an embodiment of the present application, the time of the anodization is 10 min-10 h, specifically 10 min, 30 min, 45 min, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, or a range between any two of them. Within the above time range, a porous aluminum oxide layer with a suitable thickness can be obtained, and the corrosion resistance, wear resistance, and insulation performance of the obtained porous aluminum oxide layer are effectively improved.

[0099] According to an embodiment of the present application, the pore-forming treatment includes at least one of chemical etching, focused ion beam etching, and laser drilling. In this way, a macropore with a suitable aperture and depth can be conveniently and quickly prepared, providing a better transmission channel for active ions.

[0100] According to an embodiment of the present application, the chemical etching can corrode the target substance by an acid solution or an alkali solution, so as to form a macropore structure in the composite aluminum oxide layer. The specific chemical etching solution can be selected according to the target macropore, which is not particularly limited in the present application.

[0101] According to an embodiment of the present application, the ion beam current used in the focused ion beam etching is 1-50 pA; specifically 1 pA, 5 pA, 10 pA, 15 pA, 20 pA, 25 pA, 30 pA, 35 pA, 40 pA, 45 pA, 50 pA, or a range between any two of them. Within the above current range, the material removal rate is higher, the processing efficiency is higher, and a macropore with a larger diameter and a greater depth can be formed at one time, while the processing precision is higher.

[0102] According to an embodiment of the present application, the residence time of the focused ion beam etching is 50-1000 μs; specifically 50 μs, 100 μs, 200 μs, 300 μs, 400 μs, 500 μs, 600 μs, 700 μs, 800 μs, 900 μs, 1000 μs, or a range between any two of them. Within the above time range, it is conducive to improving the etching precision and edge steepness, and reducing heat accumulation and ion damage, while the aspect ratio capability can be improved.

[0103] According to an embodiment of the present application, the laser frequency used in the laser drilling is 100 Hz to 1000 Hz, specifically 100 Hz, 200 Hz, 300 Hz, 400 Hz, 500 Hz, 600 Hz, 700 Hz, 800 Hz, 900 Hz, 1000 Hz, or any range between any two of them.

[0104] According to an embodiment of the present application, the drilling speed of the laser drilling is 0.5 m / min to 5 m / min, specifically 0.5 m / min, 1 m / min, 1.5 m / min, 2 m / min, 2.5 m / min, 3 m / min, 3.5 m / min, 4 m / min, 4.5 m / min, 5 m / min, or any range between any two of them. Within the above range, the processing efficiency is higher, the hole wall is smoother, the heat accumulation effect is lower, and the slag, edge collapse or carbonization phenomenon is less likely to occur, and it is beneficial to obtain a large hole with a high depth-diameter ratio.

[0105] According to an embodiment of the present application, the functional material can also be in the voids of the porous alumina layer, and therefore the method for preparing the composite diaphragm can further comprise: depositing a functional material into the pores of the composite alumina layer.

[0106] According to an embodiment of the present application, the deposition method comprises chemical vapor deposition. In this way, the functional material can be effectively deposited into the pores, and the method is mature.

[0107] According to an embodiment of the present application, the composite diaphragm can further comprise a polymer layer, and therefore the method for preparing the composite diaphragm can further comprise: compounding the composite alumina layer and the polymer layer.

[0108] According to an embodiment of the present application, the compounding comprises: stacking the composite alumina layer and the polymer layer, and pressing the obtained stacked product to make them compound. In this way, the composite alumina layer and the polymer layer can be compounded conveniently and quickly, and the bonding strength between them in the obtained composite diaphragm is higher.

[0109] Taking a composite diaphragm comprising a composite alumina layer and a polymer layer on both sides of the composite alumina layer as an example, the method for preparing the composite diaphragm according to the present application is described in detail, specifically as follows:

[0110] Using oxalic acid, phosphoric acid, sulfuric acid, etc. as the acidic electrolytic solution, aluminum foil as the anode, and platinum electrode as the cathode, the current density is 1 to 5 A / dm 2The aluminum foil is turned over and the above operation is repeated to obtain a double-sided aluminum oxide layer. The aluminum foil after anodic oxidation is subjected to pore forming treatment, wherein the ion beam current used in focused ion beam etching is 1-50 pA, the residence time is 50-1000 μs, the laser frequency used in laser drilling is 100-1000 Hz, the drilling speed is 0.5-5 m / min, the pore diameter can be 10 nm-100 μm, and the foil is turned over and the above pore forming treatment operation is repeated. The polyethylene separator, the porous aluminum oxide layer, and the polypropylene separator are stacked in a sandwich structure, and then are subjected to compounding under a pressure of 4.0 MPa to obtain the above three-layer composite high-safety composite separator.

[0111] In a third aspect, the present application provides a battery. According to embodiments of the present application, the battery comprises the above-mentioned composite separator or the composite separator prepared by the above-mentioned method. The probability of short circuit and thermal runaway of the battery is significantly reduced, and the battery has high safety.

[0112] According to embodiments of the present application, it can be understood that the specific type of the battery is not particularly limited, and can be a primary battery or a secondary battery; the shape of the battery can be a cylindrical battery, a square battery, or any other shaped battery, etc., and according to the classification by the outer packaging, the battery can be a hard-shell battery, a soft-pack battery, etc. In other embodiments, the battery can be a lithium ion battery, a sodium ion battery, etc.

[0113] Generally, the battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and the above-mentioned composite separator, wherein the positive electrode sheet, the negative electrode sheet, and the composite separator can be made into an electrode core by a winding or stacking process, and the electrode core and the electrolyte can be accommodated in an outer packaging. During the charging and discharging process of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly plays a role in preventing the short circuit of the positive electrode and the negative electrode, and at the same time can make the ions pass through.

[0114] The positive electrode sheet in the battery can comprise a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer is arranged on at least one surface of the positive electrode current collector.

[0115] In some embodiments, the positive electrode current collector can be a metal current collector or a composite current collector. For example, the metal current collector can include, but is not limited to, an aluminum foil current collector; the composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer (such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0116] In some embodiments, the positive electrode active material layer can include a positive electrode active material, a binder, and a conductive agent, and additives with specific functions and effects can also be added according to actual needs, such as thickening agents, sodium supplementing agents, film-forming additives, flame retardants, high / low temperature stabilizers, etc.

[0117] As an example, the positive electrode active material of the battery can include lithium nickel cobalt manganese oxide (including but not limited to NCM811, NCM613, NCM523, etc.), lithium cobaltate, lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, lithium nickel manganate, lithium-rich manganese-based material, or a positive electrode active material commonly used in the art.

[0118] As an example, the binder in the positive electrode active material layer can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester-based resin.

[0119] As an example, the conductive agent in the positive electrode active material layer can include at least one of super-conductive carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0120] In some embodiments, the negative electrode sheet can include a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector.

[0121] As an example, the negative electrode active material layer can include a negative electrode active material, a thickening agent, a conductive agent, and a binder, wherein the negative electrode current collector can be a metal foil, for example, the metal foil can be a copper foil.

[0122] According to embodiments of the present application, the negative electrode active material can include a carbon-based material, a silicon-based material, a tin-based material, etc.

[0123] According to embodiments of the present application, the binder in the negative material layer can include, but is not limited to, at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0124] According to embodiments of the present application, the conductive agent in the negative material layer can include, but is not limited to, at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0125] In a fourth aspect, the present application provides a battery pack. According to embodiments of the present application, the battery pack includes the composite separator as described above, the composite separator prepared by the method as described above, or the battery as described above. The battery pack has better safety performance.

[0126] It can be understood that the battery pack can be a battery module, a battery pack, or the like. Specifically, the specific structure of the battery module and the battery pack can refer to the conventional techniques in the art, which will not be described herein.

[0127] In a fifth aspect, the present application provides a power consuming device. According to embodiments of the present application, the power consuming device includes the composite separator as described above, the composite separator prepared by the method as described above, the battery as described above, or the battery pack as described above. The power consuming device has all the features and advantages of the battery as described above or the battery pack as described above, which will not be described herein.

[0128] According to embodiments of the present application, the specific type of the power consuming device is not particularly limited, and can be any device using a battery as a power source or an energy storage unit. As an example, the power consuming device includes, but is not limited to, an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), a mobile terminal (such as a mobile phone, a notebook computer, a game console, a wearable device, etc.), a drone, an aerospace device, a satellite, a ship, an energy storage system, and the like.

[0129] It can be understood that, in addition to the battery as described above, the power consuming device also includes necessary structures and components, which can refer to conventional techniques, for example, an electric vehicle, which can include a vehicle body, a chassis, tires, a navigation system, a radar system, a steering system, a braking system, a lubrication system, a cooling system, a driving system, and the like, which will not be described herein.

[0130] Embodiments of the present application will be described in detail below.

[0131] Embodiment 1

[0132] Anodization: 3.5-μm-thick aluminum foil was anodized and etched using a solution including 5 wt% oxalic acid, 2 wt% phosphoric acid, 1 wt% sulfuric acid, and the balance water as an acidic electrolytic solution, the aluminum foil as an anode, and a platinum electrode as a cathode at a current density of 3 A / dm2at 25°C for 1 h. The aluminum foil was flipped over and the above anodization was repeated to form a porous aluminum oxide layer having large pores, thereby obtaining an anodized product having an intermediate aluminum foil and a porous aluminum oxide layer on both surfaces of the intermediate aluminum foil. 2 2 Anodization: 3.5-μm-thick aluminum foil was anodized and etched using a solution including 5 wt% oxalic acid, 2 wt% phosphoric acid, 1 wt% sulfuric acid, and the balance water as an acidic electrolytic solution, the aluminum foil as an anode, and a platinum electrode as a cathode at a current density of 3 A / dm2at 25°C for 1 h. The aluminum foil was flipped over and the above anodization was repeated to form a porous aluminum oxide layer having large pores, thereby obtaining an anodized product having an intermediate aluminum foil and a porous aluminum oxide layer on both surfaces of the intermediate aluminum foil.

[0133] Pore formation: The anodized product was subjected to pore formation. The pore formation conditions can include focused ion beam etching followed by laser drilling, wherein the focused ion beam etching uses an ion beam current of 25 pA and a dwell time of 400 μs, and the laser drilling uses a laser frequency of 400 Hz and a drilling speed of 1 m / min. The foil was flipped over and the above pore formation was repeated to obtain a composite aluminum oxide layer.

[0134] A three-layer composite separator was obtained by drying after bonding and molding of a 3-μm-thick polyethylene having a porosity of 30%, the above composite aluminum oxide layer, and a 3-μm-thick polypropylene having a porosity of 30% at 25°C and 4 MPa.

[0135] In the porous aluminum oxide layer, the diameter φ1 of the large pores is 20 μm, the diameter φ2 of the small pores is 50 nm, the depth H1 of the large pores is 3 μm, the depth H2 of the small pores is 0.5 μm, the gap I1 between adjacent large pores is 20 μm, the gap I2 between adjacent small pores is 30 nm, the coverage L1 of the large pores is 19.63%, and the coverage L2 of the small pores is 30.68%.

[0136] Example 2

[0137] Anodization: 3.5-μm-thick aluminum foil was anodized and etched using a solution including 5 wt% oxalic acid, 2 wt% phosphoric acid, 1 wt% sulfuric acid, and the balance water as an acidic electrolytic solution, the aluminum foil as an anode, and a platinum electrode as a cathode at a current density of 3 A / dm2at 25°C for 1 h. The aluminum foil was flipped over and the above anodization was repeated to form a porous aluminum oxide layer having large pores, thereby obtaining an anodized product having an intermediate aluminum foil and a porous aluminum oxide layer on both surfaces of the intermediate aluminum foil.

[0138] ​Pore forming treatment: the anodization product is subjected to pore forming treatment, which can include: first, focused ion beam etching, and then laser punching, wherein the ion beam current used in the focused ion beam etching is 5 pA, and the residence time is 100 μs, and the laser punching uses a laser frequency of 200 Hz and a punching speed of 4 m / min. After the foil is turned over, the above punching operation is repeated to obtain a composite aluminum oxide layer.

[0139] The three-layer composite separator is obtained by drying after laminating and molding the polyethylene with a thickness of 3 μm and a porosity of 30%, the above-mentioned composite aluminum oxide layer, and the polypropylene with a thickness of 3 μm and a porosity of 30% at 25°C and 4 MPa.

[0140] In the porous aluminum oxide layer, the diameter φ1 of the large pores is 5 μm, the diameter φ2 of the small pores is 50 nm, the depth H1 of the large pores is 1 μm, the depth H2 of the small pores is 0.5 μm, the gap I1 between adjacent two large pores is 5 μm, the gap I2 between adjacent two small pores is 30 nm, the coverage L1 of the large pores is 19.63%, and the coverage L2 of the small pores is 30.68%.

[0141] Example 3

[0142] Anodization treatment: 5.5 μm aluminum foil is oxidized and etched, an acidic electrolytic solution including 5 wt% oxalic acid, 2 wt% phosphoric acid, 1 wt% sulfuric acid, and the balance water is used as the acid electrolytic solution, the aluminum foil is used as the anode, and a platinum electrode is used as the cathode, and the anodization treatment is performed at a current density of 3 A / dm 2 at 25°C for 1 h. After the aluminum foil is turned over, the above anodization operation is repeated to form a porous aluminum oxide layer with small pores, and an anodization product with an intermediate aluminum foil and a porous aluminum oxide layer on both sides of the intermediate aluminum foil is obtained.

[0143] Pore forming treatment: the anodization product is subjected to pore forming treatment, which can include: first, focused ion beam etching, and then laser punching, wherein the ion beam current used in the focused ion beam etching is 5 pA, and the residence time is 100 μs, and the laser punching uses a laser frequency of 200 Hz and a punching speed of 4 m / min. After the foil is turned over, the above punching operation is repeated to obtain a composite aluminum oxide layer.

[0144] The three-layer composite separator is obtained by drying after laminating and molding the polyethylene with a thickness of 3 μm and a porosity of 30%, the above-mentioned composite aluminum oxide layer, and the polypropylene with a thickness of 3 μm and a porosity of 30% at 25°C and 4 MPa.

[0145] In the porous alumina layer, the diameter of the macropores φ1 is 50 μm, the diameter of the micropores φ2 is 50 nm, the depth of the macropores H1 is 5 μm, the depth of the micropores H2 is 0.5 μm, the gap between two adjacent macropores I1 is 50 μm, the gap between two adjacent micropores I2 is 30 nm, the coverage of macropores L1 is 19.63%, and the coverage of micropores L2 is 30.68%.

[0146] Example 4

[0147] Anodizing treatment: A 3.5μm aluminum foil was oxidized and etched using an acidic electrolytic solution comprising 5wt% oxalic acid, 2wt% phosphoric acid, 1wt% sulfuric acid, and the remainder water. The aluminum foil served as the anode, and a platinum electrode as the cathode, at a current density of 2A / dm³. 2 The aluminum foil was anodized for 1 hour at 35°C. After flipping the aluminum foil, the above anodizing operation was repeated to form a porous alumina layer with small pores, resulting in an anodized product with an aluminum foil in the middle and porous alumina layers on both sides of the middle aluminum foil.

[0148] Hole-forming treatment: Hole-forming treatment is performed on the anodic oxide product. The conditions for hole-forming treatment may include: first, focused ion beam etching, followed by laser drilling. The focused ion beam etching uses an ion beam current of 25 pA and a residence time of 400 μs. The laser drilling uses a laser frequency of 400 Hz and a drilling speed of 1 m / min. After flipping the foil, the above drilling operation is repeated to obtain a composite alumina layer.

[0149] A three-layer composite membrane was obtained by bonding polyethylene with a thickness of 3μm and a porosity of 30%, the above-mentioned composite alumina layer, and polypropylene with a thickness of 3μm and a porosity of 30% at 25°C and 4MPa, followed by drying.

[0150] In the porous alumina layer, the diameter of the macropores φ1 is 20 μm, the diameter of the micropores φ2 is 20 nm, the depth of the macropores H1 is 3 μm, the depth of the micropores H2 is 0.5 μm, the gap between two adjacent macropores I1 is 20 μm, the gap between two adjacent micropores I2 is 20 nm, the coverage of macropores L1 is 19.63%, and the coverage of micropores L2 is 19.63%.

[0151] Example 5

[0152] Anodizing treatment: A 5.5μm aluminum foil was oxidized and etched using an acidic electrolytic solution comprising 5wt% oxalic acid, 2wt% phosphoric acid, 1wt% sulfuric acid, and the remainder water. The aluminum foil served as the anode, and a platinum electrode as the cathode, at a current density of 5A / dm³. 2, and the anodization treatment was performed for 3h at a temperature of 35℃. The aluminum foil was turned over, and the above-mentioned anodization operation was repeated to form a porous aluminum oxide layer having small pores, thereby obtaining an anodization product having an intermediate aluminum foil and a porous aluminum oxide layer on both surfaces of the intermediate aluminum foil.

[0153] Pore forming treatment: The anodization product was subjected to pore forming treatment, and the pore forming treatment conditions can include: first, focused ion beam etching, and then laser punching, wherein the ion beam current used in the focused ion beam etching is 25pA, the residence time is 400μs, the laser punching uses a laser frequency of 400Hz, and the punching speed is 1m / min. The foil was turned over, and the above-mentioned punching operation was repeated to obtain a composite aluminum oxide layer.

[0154] The three-layer composite separator was obtained by drying after laminating and molding polyethylene with a thickness of 3μm and a porosity of 30%, the above-mentioned composite aluminum oxide layer, and polypropylene with a thickness of 3μm and a porosity of 30% at 25℃ and 4MPa.

[0155] In the porous aluminum oxide layer, the diameter φ1 of the large pores is 20μm, the diameter φ2 of the small pores is 5μm, the depth H1 of the large pores is 3μm, the depth H2 of the small pores is 2.5μm, the gap I1 between adjacent two large pores is 20μm, the gap I2 between adjacent two small pores is 1μm, the coverage L1 of the large pores is 19.63%, and the coverage L2 of the small pores is 54.54%.

[0156] Example 6

[0157] Anodization treatment: 4μm aluminum foil was oxidized and etched, and a solution including 5wt% oxalic acid, 2wt% phosphoric acid, 1wt% sulfuric acid, and the balance water was used as an acidic electrolytic solution, the aluminum foil was used as an anode, and a platinum electrode was used as a cathode, and the anodization treatment was performed for 1h at a current density of 1A / dm 2 , and the anodization treatment was performed for 1h at a temperature of 45℃. The aluminum foil was turned over, and the above-mentioned anodization operation was repeated to form a porous aluminum oxide layer having small pores, thereby obtaining an anodization product having an intermediate aluminum foil and a porous aluminum oxide layer on both surfaces of the intermediate aluminum foil.

[0158] Pore forming treatment: The anodization product was subjected to pore forming treatment, and the pore forming treatment conditions can include: first, focused ion beam etching, and then laser punching, wherein the ion beam current used in the focused ion beam etching is 25pA, the residence time is 400μs, the laser punching uses a laser frequency of 400Hz, and the punching speed is 1m / min. The foil was turned over, and the above-mentioned punching operation was repeated to obtain a composite aluminum oxide layer.

[0159] 1% concentration of PVDF binder solution was transferred to both surfaces of the composite alumina layer by a gravure coating method, then a polypropylene separator with a thickness of 3 pm and a porosity of 30% was placed on one side, and a polyethylene separator with a thickness of 3 pm and a porosity of 30% was placed on the other side, and after being kept at 25°C and 0.3 MPa for 1 s, drying was performed to obtain a three-layer composite separator.

[0160] In the porous alumina layer, the diameter φ1 of the large pores is 20 pm, the diameter φ2 of the small pores is 70 pm, the depth H1 of the large pores is 3.5 pm, the depth H2 of the small pores is 0.5 pm, the gap I1 between adjacent two large pores is 20 pm, the gap I2 between adjacent two small pores is 25 pm, the coverage L1 of the large pores is 19.63%, and the coverage L2 of the small pores is 35%.

[0161] Example 7

[0162] Anodization treatment: 3.5 pm aluminum foil was oxidized and etched, an acidic electrolytic solution including 5 wt% oxalic acid, 2 wt% phosphoric acid, 1 wt% sulfuric acid, and the balance water was used, the aluminum foil was used as an anode, and a platinum electrode was used as a cathode, and anodization treatment was performed at a current density of 3 A / dm 2 at 25°C for 1 h. After the aluminum foil was turned over, the above anodization operation was repeated to form a porous alumina layer with small pores, and an anodization product with an intermediate aluminum foil and a porous alumina layer on both surfaces of the intermediate aluminum foil was obtained.

[0163] Pore forming treatment: the anodization product was subjected to pore forming treatment, which can include the following conditions: first, focused ion beam etching was performed, and then laser drilling was performed, wherein the ion beam current of the focused ion beam etching was 25 pA, and the residence time was 400 s, and the laser drilling used a laser frequency of 400 Hz and a drilling speed of 1 m / min. After the foil was turned over, the above drilling operation was repeated to obtain a composite alumina layer.

[0164] In the porous alumina layer, the diameter φ1 of the large pores is 20 pm, the diameter φ2 of the small pores is 50 nm, the depth H1 of the large pores is 3 pm, the depth H2 of the small pores is 0.5 pm, the gap I1 between adjacent two large pores is 20 pm, the gap I2 between adjacent two small pores is 30 nm, the coverage L1 of the large pores is 19.63%, and the coverage L2 of the small pores is 30.68%.

[0165] Example 8

[0166] Anodization treatment: 3.5 pm aluminum foil was oxidized and etched, an acidic electrolytic solution including 5 wt% oxalic acid, 2 wt% phosphoric acid, 1 wt% sulfuric acid, and the balance water was used, the aluminum foil was used as an anode, and a platinum electrode was used as a cathode, and anodization treatment was performed at a current density of 3 A / dm 2anodizing operation to form a porous alumina layer having large pores, to obtain an anodized product having an intermediate aluminum foil and a porous alumina layer on both surfaces of the intermediate aluminum foil.

[0167] Pore forming treatment: The anodized product is subjected to pore forming treatment, which can include focused ion beam etching followed by laser drilling, wherein the focused ion beam etching uses an ion beam current of 25 pA and a dwell time of 400 μs, and the laser drilling uses a laser frequency of 400 Hz and a drilling speed of 1 m / min. The foil is flipped over and the above drilling operation is repeated to obtain a composite alumina layer.

[0168] A 1% concentration of PVDF binder solution is transferred to one surface of the composite alumina layer using a gravure coating method, and then a polyethylene separator having a thickness of 3 μm and a porosity of 30% is placed on the adhesive side to form a composite separator, which is dried after being kept at 25°C and 0.3 MPa for 1 s.

[0169] In the porous alumina layer, the diameter φ1 of the large pores is 20 μm, the diameter φ2 of the small pores is 50 nm, the depth H1 of the large pores is 3 μm, the depth H2 of the small pores is 0.5 μm, the gap I1 between adjacent large pores is 20 μm, the gap I2 between adjacent small pores is 30 nm, the coverage L1 of the large pores is 19.63%, and the coverage L2 of the small pores is 30.68%.

[0170] Example 9

[0171] Anodizing treatment: A 3.5 μm aluminum foil is oxidized and etched using a solution including 5 wt% oxalic acid, 2 wt% phosphoric acid, 1 wt% sulfuric acid, and the balance water as an acidic electrolytic solution, the aluminum foil as an anode, and a platinum electrode as a cathode at a current density of 3 A / dm 2 anodizing operation to form a porous alumina layer having large pores, to obtain an anodized product having an intermediate aluminum foil and a porous alumina layer on both surfaces of the intermediate aluminum foil.

[0172] Pore forming treatment: The anodized product is subjected to pore forming treatment, which can include focused ion beam etching followed by laser drilling, wherein the focused ion beam etching uses an ion beam current of 25 pA and a dwell time of 400 μs, and the laser drilling uses a laser frequency of 400 Hz and a drilling speed of 1 m / min. The foil is flipped over and the above drilling operation is repeated to obtain a composite alumina layer.

[0173] 1% concentration of PVDF adhesive solution is transferred to both sides of the composite alumina layer by the method of gravure coating, and the two adhesive surfaces are respectively placed with polyethylene separators with a thickness of 3 μm and a porosity of 30%, and then dried after being combined and formed at 25°C and 0.3 MPa for 1 s to obtain a three-layer composite separator.

[0174] Example 10

[0175] The separator is prepared according to the preparation method of Example 1, and the difference between this example and Example 1 is that the focused ion beam etching residence time is 100 μs, and the single-sided surface of the aluminum foil is anodized for 6 h. The obtained composite separator is composed of a composite alumina layer, and only the single-sided surface of the middle aluminum foil has a porous alumina layer. The pore-forming treatment is performed from the side that has not been anodized, and the large holes formed only penetrate the middle aluminum foil.

[0176] In the porous alumina layer, the diameter φ1 of the large holes is 20 μm, the diameter φ2 of the small holes is 50 nm, the depth H1 of the large holes is 0.5 μm (i.e. the thickness of the middle aluminum foil), the depth H2 of the small holes is 3 μm, the gap I1 between adjacent two large holes is 20 μm, the gap I2 between adjacent two small holes is 30 nm, the coverage L1 of the large holes is 19.63%, and the coverage L2 of the small holes is 30.68%.

[0177] Example 11

[0178] The separator is prepared according to the preparation method of Example 1, and the difference between this example and Example 1 is that the focused ion beam etching residence time is 500 μs, and the anodization treatment is performed for 10 min.

[0179] In the porous alumina layer, the diameter φ1 of the large holes is 20 μm, the diameter φ2 of the small holes is 50 nm, the depth H1 of the large holes is 3.3 μm, the depth H2 of the small holes is 0.2 μm, the gap I1 between adjacent two large holes is 20 μm, the gap I2 between adjacent two small holes is 30 nm, the coverage L1 of the large holes is 19.63%, and the coverage L2 of the small holes is 30.68%.

[0180] Example 12

[0181] The separator is prepared according to the preparation method of Example 1, and the difference between this example and Example 1 is that the laser drilling uses a laser frequency of 400 Hz and a drilling speed of 0.25 m / min.

[0182] The diameter φ1 of the large holes in the porous alumina layer is 20 μm, the diameter φ2 of the small holes is 50 nm, the depth H1 of the large holes is 3.3 μm, the depth H2 of the small holes is 0.2 μm, the gap I1 between two adjacent large holes is 20 μm, the gap I2 between two adjacent small holes is 30 nm, the coverage L1 of the large holes is 5%, and the coverage L2 of the small holes is 30.68%.

[0183] Example 13

[0184] The separator is prepared according to the preparation method of Example 1, except that the laser frequency is 400 Hz and the punching speed is 2.5 m / min.

[0185] The diameter φ1 of the large holes in the porous alumina layer is 20 μm, the diameter φ2 of the small holes is 50 nm, the depth H1 of the large holes is 3.3 μm, the depth H2 of the small holes is 0.2 μm, the gap I1 between two adjacent large holes is 20 μm, the gap I2 between two adjacent small holes is 30 nm, the coverage L1 of the large holes is 50%, and the coverage L2 of the small holes is 30.68%.

[0186] Example 14

[0187] The separator is prepared according to the preparation method of Example 1, except that a solution comprising 0.5 wt% oxalic acid, 0.5 wt% phosphoric acid, 0.2 wt% sulfuric acid, and the balance water is used as the acidic electrolytic solution, and the anodization is performed at a current density of 1 A / dm 2 at a temperature of 25°C for 1 h.

[0188] The diameter φ1 of the large holes in the porous alumina layer is 20 μm, the diameter φ2 of the small holes is 50 nm, the depth H1 of the large holes is 3.3 μm, the depth H2 of the small holes is 0.2 μm, the gap I1 between two adjacent large holes is 20 μm, the gap I2 between two adjacent small holes is 30 nm, the coverage L1 of the large holes is 19.63%, and the coverage L2 of the small holes is 5%.

[0189] Example 15

[0190] The separator is prepared according to the preparation method of Example 1, except that a solution comprising 4 wt% oxalic acid, 4 wt% phosphoric acid, 2 wt% sulfuric acid, and the balance water is used as the acidic electrolytic solution, and the anodization is performed at a current density of 1 A / dm 2 at a temperature of 25°C for 1 h.

[0191] In the porous alumina layer, the diameter of the large pores is 20 μm, the diameter of the small pores is 50 nm, the depth of the large pores is 3.3 μm, the depth of the small pores is 0.2 μm, the gap between adjacent two large pores is 20 μm, the gap between adjacent two small pores is 30 nm, the coverage of the large pores is 19.63%, and the coverage of the small pores is 60%.

[0192] Example 16

[0193] The same as Example 1, except that the composite separator comprises a polyethylene film and a composite alumina layer located on the opposite sides of the polyethylene film.

[0194] Comparative Example 1

[0195] A two-layer composite separator was obtained by drying after laminating polyethylene with a thickness of 3 μm and a porosity of 30% and polypropylene with a thickness of 3 μm and a porosity of 30% at 25 °C and 4 MPa.

[0196] The alumina slurry formula: alumina: 55 parts by weight; water: 55 parts by weight; binder: butyl acrylate 10 parts by weight; CMC: 1 part by weight; polyether silicone: 2 parts by weight, coated on one side of the polyethylene separator by gravure, with a coating thickness of 3 μm, and the coated separator was obtained after drying.

[0197] Performance test:

[0198] 1. Heat shrinkage:

[0199] (1) Use a cutter to cut a square sample of 150 mm x 100 mm from the composite separator roll;

[0200] (2) Measure the horizontal and vertical dimensions of the composite separator using a projector and record the data;

[0201] (3) The composite separator sample after testing is flatly clamped in an A4 book;

[0202] (4) The A4 book clamping the composite separator sample is placed in an oven with a set time of 1 h and a temperature of 95 °C;

[0203] (5) After the baking time is over, the horizontal and vertical dimensions of the composite separator at the same position are measured using a projector;

[0204] (6) Record the data and calculate the heat shrinkage rate of the separator, heat shrinkage rate = (original width - width after baking) / original width.

[0205] 2. Heat puncture strength: tested by a puncture strength tester, the temperature is set to 80 °C, and the test method refers to GB / T36294-2018.

[0206] 3. Ionic conductivity: Refer to BG / T 36294-2018 to measure the ionic conductivity of the composite separator.

[0207] 4. Battery thermal runaway temperature:

[0208] Battery assembly:

[0209] 1) Preparation of positive electrode sheet

[0210] The positive electrode active material lithium iron phosphate, conductive agent conductive carbon black, binder PVDF, solvent NMP were mixed uniformly according to the mass ratio of 100:8:2.5:60, and the positive electrode slurry was obtained. The positive electrode slurry was coated on both sides of the positive electrode current collector aluminum foil, and then dried, rolled, and sheeted to obtain the positive electrode sheet.

[0211] 2) Preparation of negative electrode sheet

[0212] The negative electrode active material graphite, SBR, CMC, conductive graphite, NMP and H2O were mixed according to the mass ratio of 100:3:1.5:1:2:115, and the negative electrode slurry was obtained. The negative electrode slurry was coated on both sides of the negative electrode current collector copper foil, and then dried, rolled, and sheeted to obtain the negative electrode sheet.

[0213] 3) Preparation of electrolyte

[0214] Electrolyte (electrolyte composed of 13wt% LiPF6, 26wt% EC, 61wt% DEC)

[0215] 4) Preparation of lithium ion battery

[0216] The negative electrode sheet prepared above, the separator of each example or comparative example and the positive electrode sheet were placed in order, and then wound to obtain a battery cell. The battery cell was placed in an outer packaging foil, and then the battery was baked at 120°C for 10h, injected with electrolyte, and subjected to formation under a restraint pressure to obtain a lithium ion battery.

[0217] 5) Lithium battery test

[0218] Charging: at room temperature 25±5°C, charged to 3.8V at 1C for 5min, then charged to 3.8V at 0.2C, and then rested at room temperature for 1-2h. And take a photo;

[0219] Furnace heat conditions: first step: from room temperature to 60°C at 5°C / min, keep for 30min. Then continue to heat at 5°C / min, keep for 30min every 5 degrees Celsius. Until the battery thermal runaway.

[0220] 5. Composite separator crimping: Place the composite separator at 25℃ / 80% humidity for 2h, then place it at 25℃ / 50% humidity for 5min, lay the composite separator on a flat table, and test the height from the highest point of the crimped composite separator to the table.

[0221]

[0222]

[0223] According to the test results in Table 1, the composite aluminum oxide layer is used as the composite separator, the composite separator has better ion conductivity, small thermal shrinkage, strong thermal puncture strength, and improves the thermal runaway temperature of the battery, which can improve the safety performance of the battery.

[0224] In the description of the present application, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second" can be explicitly or implicitly included at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0225] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the skilled in the art can combine and combine the different embodiments or features of the embodiments or examples described in the present application without contradiction.

[0226] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A composite diaphragm, characterized in that, Includes a composite alumina layer, the composite alumina layer comprising: Intermediate aluminum foil, wherein the intermediate aluminum foil has through holes; A porous alumina layer, the porous alumina layer being located on at least one side of the intermediate aluminum foil; The composite alumina layer includes pores, which include macropores and micropores. The micropores are located in the porous alumina layer, and the macropores penetrate the intermediate aluminum foil. The diameter φ1 of the macropores and the diameter φ2 of the micropores satisfy: φ2 < φ1. The diameter φ1 of the large hole is 5μm~50μm; The diameter φ2 of the small hole is between 20 nm and 5 μm; The gap I1 between two adjacent large holes is 5μm~50μm; The gap I2 between two adjacent orifices is 30 nm to 1 μm; The coverage rate L1 of the large holes is 5%~50%; The coverage rate L2 of the small holes is 5%~60%; The depth H1 of the large hole is the sum of the thickness of the intermediate aluminum foil and the thickness of the porous alumina layer on one side, or the thickness of the intermediate aluminum foil; The depth H2 of the small hole is the thickness of the porous alumina layer on one side; The thickness of the composite diaphragm is 3μm~20μm; The thickness of the intermediate aluminum foil is 0.5μm~3μm; The thickness of the porous alumina layer is 0.3 μm to 2.5 μm.

2. The composite diaphragm according to claim 1, characterized in that, Also includes: A polymer layer is stacked with the composite alumina layer.

3. The composite diaphragm according to claim 2, characterized in that, The polymer layer is made of at least one of polyethylene, polypropylene, aramid, polyvinylidene fluoride, cellulose, polyethylene terephthalate, polyimide, and nonwoven fabric.

4. The composite diaphragm according to claim 2 or 3, characterized in that, The polymer layer is located on one side of the composite alumina layer.

5. The composite diaphragm according to claim 2 or 3, characterized in that, The polymer layer is located on opposite sides of the composite alumina layer.

6. The composite diaphragm according to claim 5, characterized in that, The polymer layer on one side of the composite alumina layer is made of polyethylene, and the polymer layer on the other side of the composite alumina layer is made of polypropylene.

7. The composite diaphragm according to claim 2 or 3, characterized in that, The composite alumina layer is located on opposite sides of the polymer layer.

8. The composite diaphragm according to claim 1, characterized in that, At least one of the following conditions must be met: H1 is 0.5μm~5μm; H2 ranges from 0.2 μm to 5 μm.

9. The composite diaphragm according to claim 1, characterized in that, The pores are provided with functional materials, which include at least one of solid electrolyte, lithium supplementation material, organic polymer and binder.

10. The composite diaphragm according to claim 9, characterized in that, The functional material satisfies at least one of the following conditions: The solid electrolyte includes lithium titanium aluminum phosphate; The lithium replenishment material includes at least one of Li6CoO4, Li5FeO4, Li2C2O4, and Li2NiO2; The organic polymer includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, and polymethyl methacrylate; The adhesive includes granular adhesives.

11. The composite diaphragm according to claim 2, characterized in that, At least one of the following conditions must be met: The thickness of the polymer layer is 2μm~22μm; The porosity of the polymer layer is 20% to 70%.

12. A method for preparing the composite diaphragm according to any one of claims 1 to 11, characterized in that, include: Using aluminum foil as the anode, at least one surface of the aluminum foil is anodized to form an oxide layer on at least one surface of the aluminum foil, thereby obtaining an anodized product; The anodic oxidation product is subjected to a pore-forming treatment to obtain a composite alumina layer.

13. The method according to claim 12, characterized in that, The anodizing process satisfies at least one of the following conditions: The electrolyte solution for anodic oxidation includes at least one of oxalic acid, phosphoric acid, and sulfuric acid; The cathode for the anodic oxidation includes a platinum electrode; The current density for the anodic oxidation is 1 A / dm³. 2 ~5A / dm 2 ; The anodizing temperature is 0℃~60℃; The anodizing time is 10 min to 10 h.

14. The method according to claim 12 or 13, characterized in that, The hole-forming process includes at least one of chemical etching, focused ion beam etching, and laser drilling.

15. The method according to claim 14, characterized in that, The pore-forming process satisfies at least one of the following conditions: The focused ion beam etching uses an ion beam current of 1pA to 50pA; The dwell time for the focused ion beam etching is 50 μs to 1000 μs; The laser frequency used in the laser drilling is 100Hz~1000Hz; The drilling speed of the laser drilling is 0.5m / min to 5m / min.

16. The method according to claim 12, characterized in that, Also includes: Functional materials are deposited into the pores of the composite alumina layer.

17. The method according to claim 16, characterized in that, The deposition method includes chemical vapor deposition.

18. The method according to claim 12, characterized in that, Also includes: The composite alumina layer and the polymer layer are combined.

19. The method according to claim 18, characterized in that, The composite includes: The composite alumina layer and the polymer layer are stacked together, and the resulting stacked product is pressurized to bond them together.

20. A battery, characterized in that, The composite membrane includes any one of claims 1 to 11 or a composite membrane prepared by any one of claims 12 to 19.

21. A battery pack, characterized in that, The composite separator includes any one of claims 1 to 11, the composite separator prepared by any one of claims 12 to 19, or the battery as described in claim 20.

22. An electrical appliance, characterized in that, The composite separator includes any one of claims 1 to 11, the composite separator prepared by any one of claims 12 to 19, the battery of claim 20, or the battery pack of claim 21.

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