High-ionic-conductivity composite diaphragm and preparation method thereof

Abstract

The invention discloses a high-ionic-conductivity composite diaphragm and a preparation method thereof, and belongs to the field of lithium ion battery diaphragms. The composite diaphragm comprises a base membrane and an inorganic coating coated on one side or two sides of the base membrane, the inorganic coating comprises the following raw materials in parts by mass: 8-15 parts of modified Al2O3 nanorod coated LDO, 0.5-1 part of a dispersing agent, 0.3-0.6 part of a wetting agent, 2-4 parts of an adhesive and 100 parts of water; the surface of the modified Al2O3 nanorod (at) LDO is grafted with a poly (N-isopropylacrylamide) chain segment. The one-dimensional structure characteristic of the Al2O3 nanorod and the layered structure of the LDO can construct an efficient ion transmission channel and a liquid storage network, so that the ionic conductivity and the liquid retention property of the composite diaphragm are improved. And the poly (N-isopropylacrylamide) chain segment can help to form a dynamic nanorod cross-linked network, so that the liquid retention property is improved, the dynamic characteristic of the poly (N-isopropylacrylamide) chain segment is utilized to adapt to the temperature change in the circulation process, and the stability of the diaphragm is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery separators, and particularly to a high ionic conductivity composite separator and its preparation method. Background Technology

[0002] Compared to other types of batteries, lithium-ion batteries have advantages such as high energy density and low redox potential, making them an effective electrochemical energy storage device. The rapid development of lithium-ion batteries has driven the progress of the information age, greatly changing human life and production methods. Currently, lithium-ion batteries are widely used in portable electronic devices, mobile communications, automotive technology, smart grids, and other fields.

[0003] In lithium-ion batteries, the separator is one of the key components. Located between the two electrodes, the separator prevents physical contact between the electrodes, avoiding internal short circuits, and also contains the electrolyte, enabling rapid ion transport. The performance of the lithium-ion battery separator is extremely important for the cycle stability and rate performance, especially high-rate performance. Therefore, to optimize the performance of lithium-ion batteries, the performance of the separator must be comprehensively considered.

[0004] Polyolefin separators, with their good stability, reduced cost, and good mechanical strength, are widely used in lithium-ion batteries. While polyolefin separators offer many advantages in lithium-ion batteries, they also have several drawbacks. For example, the electrolytes currently used are primarily highly polar organic salt solutions, but polyolefin separators are non-polar polymers. This results in poor affinity between the microporous membrane surface and the polar electrolyte, leading to poor wetting of the membrane surface and pores by the electrolyte. This increases the battery's internal resistance, thus affecting its cycle performance and charge / discharge performance.

[0005] Meanwhile, the polarity difference also leads to poor compatibility between the separator and the polar electrolyte. Poor liquid retention further hinders the electrolyte from fully wetting the separator micropores, forming discontinuous ion transport channels, increasing interfacial impedance, and consequently reducing the ionic conductivity of the separator, thus affecting the electrochemical performance of the lithium-ion battery. Therefore, in order to improve the application performance of polyolefin separators in lithium-ion batteries and enhance battery safety, cycle performance, and high-rate performance, there is an urgent need to obtain a composite separator with high liquid retention and high ionic conductivity. Summary of the Invention

[0006] This invention provides a high ionic conductivity composite membrane and its preparation method, which can solve the problems of poor liquid retention and low ionic conductivity of polyolefin membranes in the prior art.

[0007] In a first aspect, the present invention provides a high ionic conductivity composite membrane, the composite membrane comprising a base membrane and an inorganic coating coated on one or both sides of the base membrane;

[0008] The inorganic coating comprises the following raw materials in parts by weight:

[0009] Modified Al2O3 nanorods@LDO, 8-15 parts;

[0010] Dispersant 0.5 to 1 part;

[0011] Wetting agent 0.3-0.6 parts;

[0012] 2-4 parts adhesive;

[0013] 100 parts water;

[0014] The surface of the modified Al2O3 nanorods@LDO is grafted with poly(N-isopropylacrylamide) segments.

[0015] Preferably, the base film includes any one of polyethylene base film, polypropylene base film, polyethylene / polypropylene double-layer co-extruded film, and polyethylene / polypropylene / polyethylene multilayer co-extruded film.

[0016] Preferably, the dispersant includes one or more combinations of sodium polyacrylate, polyvinyl alcohol, polyacrylamide, polyvinylpyrrolidone, and carboxyethyl cellulose.

[0017] Preferably, the wetting agent includes one or more combinations of sodium dodecylbenzenesulfonate, fatty alcohol polyoxyethylene ether, and sodium dodecyl sulfate.

[0018] Preferably, the adhesive includes an aqueous acrylic adhesive.

[0019] By adopting the above technical solution, in order to enhance the performance of polyolefin membranes, an inorganic coating is applied to the surface of the polyolefin membrane, which can improve mechanical strength and effectively block lithium dendrite penetration. The inorganic coating contains modified Al2O3 nanorods@LDO. On one hand, Al2O3 nanorods@LDO can construct efficient ion transport channels and liquid storage networks. The one-dimensional structure of Al2O3 nanorods can form vertically aligned nanochannels in the inorganic coating, significantly shortening the lithium ion migration path. Traditional alumina particles often result in high channel tortuosity due to particle stacking, thus increasing the lithium ion migration path. LDO (magnesium aluminum bimetallic oxide), on the other hand, has a layered structure and can provide liquid storage capacity through interlayer voids and surface hydroxyl groups. In-situ growth of LDO on the surface of Al2O3 nanorods can effectively increase the specific surface area of ​​inorganic particles, optimize the channel structure, and improve ionic conductivity.

[0020] On the other hand, Al2O3 nanorods@LDO contain a large number of polar groups, which can improve the wettability of the coating and enhance the affinity of the membrane to the electrolyte and the interfacial stability.

[0021] Furthermore, the Al2O3 nanorods@LDO were modified by grafting poly(N-isopropylacrylamide) segments onto their surface. The polar groups in poly(N-isopropylacrylamide) can form multiple hydrogen bonds, which can improve lithium-ion transport efficiency and anchor electrolyte molecules, thereby increasing the liquid absorption rate of the membrane.

[0022] Furthermore, the isopropyl amide groups contained in poly(N-isopropylacrylamide) have certain temperature-sensitive properties. Through hydrogen bonding and recombination, they can better adapt to temperature changes and prevent the stability from decreasing due to temperature rise during charging and discharging. Moreover, the molecular chains of poly(N-isopropylacrylamide) can connect adjacent Al2O3 nanorods@LDO through interchain entanglement to form a dynamic flexible cross-linked network, which effectively enhances the mechanical strength of the inorganic coating. During charging and discharging, internal stress can be released to prevent the coating from cracking during cycling and help extend the service life of the diaphragm.

[0023] Preferably, the raw materials for modified Al2O3 nanorods@LDO include Al2O3 nanorods@LDO, N-isopropylacrylamide, crosslinking agent and initiator in a mass ratio of 1:(0.3-0.5):(0.02-0.04):(0.01-0.02).

[0024] Preferably, the crosslinking agent includes one or a combination of two of N,N'-methylenebisacrylamide and ethylene glycol dimethacrylate; the initiator includes one or a combination of azobisisobutyronitrile, potassium persulfate, ammonium persulfate and benzoyl peroxide.

[0025] Preferably, the raw materials for Al2O3 nanorods@LDO include Al2O3 nanorods, soluble magnesium salts, and urea in a mass ratio of 1:(0.5-0.6):(0.2-0.3).

[0026] Preferably, Al2O3 nanorods are prepared according to the following method:

[0027] Soluble aluminum salt, urea and polyethylene glycol were mixed and added to water and stirred to dissolve. The mixture was then subjected to a hydrothermal reaction at 120–140 °C. After centrifugation, washing and filtration, the mixture was dried at 80–85 °C for 12–24 h. Finally, Al2O3 nanorods were obtained by grinding and high-temperature sintering.

[0028] More preferably, the soluble aluminum salt includes any one of aluminum nitrate nonahydrate, aluminum chloride, and aluminum sulfate.

[0029] More preferably, the mass ratio of soluble aluminum salt, urea and polyethylene glycol is 1:(0.9 to 1.05):(2.4 to 2.6).

[0030] More preferably, the Al2O3 nanorods have a length of 4–7 μm and a diameter of 200–300 nm.

[0031] More preferably, the high-temperature sintering temperature is 700–800°C.

[0032] Preferably, the soluble magnesium salt includes one or more combinations of magnesium chloride, magnesium nitrate hexahydrate, and magnesium sulfate heptahydrate.

[0033] Preferably, Al2O3 nanorods@LDO are prepared according to the following method:

[0034] Soluble magnesium salt and urea were mixed and dissolved in water, Al2O3 nanorods were added, and the mixture was soaked for 10-20 minutes. Then, it was transferred to a high-pressure reactor, the temperature was raised to 120-130℃, and the reaction was carried out for 6-8 hours. Finally, after washing, drying, grinding and calcining, Al2O3 nanorods@LDO were obtained.

[0035] Preferably, the modified Al2O3 nanorods@LDO are prepared according to the following method:

[0036] Al2O3 nanorods@LDO were dispersed in water, N-isopropylacrylamide and a crosslinking agent were added, and the mixture was stirred and dispersed at 60-65℃ for 2-3 hours. The temperature was then increased to 80-85℃, an initiator was added, and the mixture was stirred and reacted in an inert gas atmosphere for 3-4 hours. Finally, the modified Al2O3 nanorods@LDO were obtained by centrifugation and washing.

[0037] By adopting the above technical solution, Al2O3 nanorods have high aspect ratio and vertical alignment characteristics, which can form low-torsion high-speed ion transport channels in inorganic coatings, shorten the migration path of lithium ions, and thus improve the ionic conductivity of composite membranes.

[0038] Furthermore, magnesium-aluminum bilayer metal oxides were grown in situ on Al2O3 nanorods via hydrothermal method and high-temperature calcination. The hydroxyl groups on the surface of Al2O3 nanorods provided nucleation sites for their growth. On the one hand, the layered structure of LDO can improve the liquid retention of the membrane and reduce the formation of lithium dendrites. On the other hand, after LDO composite, the accumulation of Al2O3 nanorods can be effectively inhibited, preventing blockage of membrane pores and further improving the ion transport efficiency of the material, resulting in a highly safe lithium-ion composite membrane.

[0039] After grafting modification with poly(N-isopropylacrylamide), the aggregation of Al2O3 nanorods@LDO can be effectively prevented through electrostatic repulsion and steric hindrance, thereby improving the dispersibility of Al2O3 nanorods@LDO in the inorganic coating and ensuring uniform distribution in the inorganic coating, thus improving the ionic conductivity of the composite membrane.

[0040] Furthermore, through the hydrogen bonding of poly(N-isopropylacrylamide), a dynamic nanorod network can be formed in the inorganic coating. In addition to improving mechanical strength, this also enhances the liquid retention of the composite membrane. The thermosensitive properties of poly(N-isopropylacrylamide) drive network reconstruction, which can better adapt to temperature changes during cycling and improve the stability of the composite membrane. This results in a safe, highly stable composite membrane with high ionic conductivity and good liquid retention.

[0041] Preferably, a polydopamine layer is also coated between the base film and the inorganic coating.

[0042] Preferably, the thickness of the polydopamine is 1–3 μm; the thickness of the inorganic coating is 2–4 μm.

[0043] By employing the above technical solution, a polydopamine layer is coated between the base film and the inorganic coating of the composite separator. The polydopamine layer acts as a connecting bridge between the base film and the inorganic coating. The catechol groups in polydopamine exhibit good binding force with the polyolefin separator, and the amino groups can bond with the modified Al2O3 nanorods@LDO in the inorganic coating, thereby improving the peel strength between the inorganic coating and the base film. Simultaneously, the flexible long-chain structure of polydopamine can absorb the changing stress during charging and discharging, thus suppressing microcracks in the inorganic coating caused by internal stress, alleviating cyclic stress, and reducing the possibility of inorganic coating detachment. Furthermore, the polydopamine layer provides high-density grafting active sites for poly(N-isopropylacrylamide) segments, and the resulting network structure helps maintain the stability and integrity of the coating structure.

[0044] Furthermore, the addition of a polydopamine layer in the middle can effectively enhance lithium-ion transport efficiency. Its flexible segments can improve the toughness of the separator, thereby enhancing the puncture resistance of the composite separator, reducing the impact of lithium dendrite growth on the composite separator, and thus further improving the cycle performance and high-rate performance of the lithium battery.

[0045] Secondly, the present invention provides a method for preparing a composite membrane with high ionic conductivity, comprising the following process steps:

[0046] S1. Dissolve polydopamine in water, coat it on one or both sides of the base film, and dry it to form a polydopamine layer;

[0047] S2. Weigh the raw materials of the inorganic coating according to the corresponding mass parts, add the modified Al2O3 nanorods@LDO, dispersant, wetting agent and binder in water in sequence, and mix evenly to obtain inorganic slurry;

[0048] S3. Coat the polydopamine layer with an inorganic slurry, and after drying, a composite membrane with high ionic conductivity is obtained.

[0049] Preferably, the technical effect of the present invention can also be achieved by not coating a polydopamine layer between the base film and the inorganic coating of the high ionic conductivity composite membrane.

[0050] More preferably, the high ionic conductivity composite membrane without a polydopamine coating is prepared according to the following process steps:

[0051] S1. Weigh the raw materials of the inorganic coating according to the corresponding mass parts, add the modified Al2O3 nanorods@LDO, dispersant, wetting agent and binder in water in sequence, and mix evenly to obtain inorganic slurry;

[0052] S2. Coat one or both sides of the base membrane with an inorganic slurry, and after drying, a composite membrane with high ionic conductivity is obtained.

[0053] The beneficial effects of this invention are:

[0054] 1. The composite membrane of the present invention comprises a base membrane and an inorganic coating. Modified Al2O3 nanorods@LDO are added to the inorganic coating, which utilizes the one-dimensional structural characteristics of Al2O3 nanorods and the layered structure of LDO to construct efficient ion transport channels and a liquid storage network, thereby improving the ionic conductivity and liquid retention of the composite membrane. Furthermore, poly(N-isopropylacrylamide) segments are grafted onto the surface of the modified Al2O3 nanorods@LDO, which not only improves the dispersibility of Al2O3 nanorods@LDO in the inorganic coating but also forms a dynamic nanorod crosslinking network. While improving liquid retention, its dynamic characteristics allow it to adapt to temperature changes during cycling, thus enhancing the stability of the membrane.

[0055] 2. In the composite diaphragm of the present invention, a polydopamine layer can be added between the base film and the inorganic coating, which can effectively improve the interfacial bonding force between the inorganic coating and the base film, reduce the accumulation of internal stress, reduce the possibility of cracking or peeling of the inorganic coating, and also increase the mechanical properties of the composite diaphragm and improve the puncture resistance, so as to obtain a composite diaphragm with excellent electrical and mechanical properties. Detailed Implementation

[0056] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0057] Preparation Example

[0058] Preparation Example 1: A modified Al2O3 nanorod@LDO was prepared according to the following method:

[0059] Preparation of Al2O3 nanorods:

[0060] 10g of aluminum nitrate nonahydrate, 10g of urea and 26g of polyethylene glycol 2000 were mixed and added to 250mL of water and stirred to dissolve. The mixture was subjected to a hydrothermal reaction at 130℃. After centrifugation, washing and filtration, the mixture was dried at 80℃ for 24h. Finally, after grinding, the mixture was sintered at 700℃ to obtain Al2O3 nanorods.

[0061] Preparation of Al2O3 nanorods@LDO:

[0062] 6g of magnesium nitrate hexahydrate and 3g of urea were mixed and dissolved in 100mL of water. 10g of the Al2O3 nanorods obtained above were added and impregnated for 15min. Then, the mixture was transferred to a high-pressure reactor, the temperature was raised to 120℃, and the reaction was carried out for 8h. Finally, after washing, drying and grinding, Al2O3 nanorods@LDO were obtained by calcination at 450℃.

[0063] Preparation of modified Al2O3 nanorods@LDO:

[0064] 10g of the Al2O3 nanorods@LDO obtained above were dispersed in 250mL of water, 4g of N-isopropylacrylamide and 0.3g of N,N'-methylenebisacrylamide were added, and the mixture was stirred and dispersed at 60℃ for 3h. The temperature was then increased to 80℃, and 0.2g of azobisisobutyronitrile was added. The mixture was stirred and reacted in an argon atmosphere for 3h. Finally, the modified Al2O3 nanorods@LDO were obtained by centrifugation and washing.

[0065] Preparation Example 2, a modified Al2O3 nanorods@LDO, differs from Preparation Example 1 only in that, in the preparation process of Al2O3 nanorods@LDO, the amount of magnesium nitrate hexahydrate added is 5g and the amount of urea added is 2g.

[0066] Preparation Example 3: A modified Al2O3 nanorods@LDO, which differs from Preparation Example 1 only in that, during the preparation of the modified Al2O3 nanorods@LDO, the amount of N-isopropylacrylamide added is 3g, the amount of N,N'-methylenebisacrylamide added is 0.2g, and the amount of azobisisobutyronitrile added is 0.1g.

[0067] Preparation Example 4: A modified Al2O3 nanorods@LDO, which differs from Preparation Example 1 only in that, in the preparation process of the modified Al2O3 nanorods@LDO, the amount of N-isopropylacrylamide added is 5g and the amount of N,N'-methylenebisacrylamide added is 0.4g.

[0068] Preparation Example 5: A modified Al2O3 nanorods@LDO, which differs from Preparation Example 1 only in that the amount of N-isopropylacrylamide added in the preparation process of the modified Al2O3 nanorods@LDO is 1g.

[0069] Preparation Example 6: A modified Al2O3 nanorods@LDO, differing from Preparation Example 1 only in that the amount of N-isopropylacrylamide added during the preparation of the modified Al2O3 nanorods@LDO is 8g.

[0070] Preparation Example 7: A modified Al2O3 nanorod was prepared according to the following method:

[0071] Preparation of Al2O3 nanorods:

[0072] 10g of aluminum nitrate nonahydrate, 10g of urea and 26g of polyethylene glycol 2000 were mixed and added to 250mL of water and stirred to dissolve. The mixture was subjected to a hydrothermal reaction at 130℃. After centrifugation, washing and filtration, the mixture was dried at 80℃ for 24h. Finally, after grinding, the mixture was sintered at 700℃ to obtain Al2O3 nanorods.

[0073] Preparation of modified Al2O3 nanorods:

[0074] 10g of the Al2O3 nanorods obtained above were dispersed in 250mL of water, 4g of N-isopropylacrylamide and 0.3g of N,N'-methylenebisacrylamide were added, and the mixture was stirred and dispersed at 60℃ for 3h. The temperature was then increased to 80℃, and 0.2g of azobisisobutyronitrile was added. The mixture was stirred and reacted in an argon atmosphere for 3h. Finally, the modified Al2O3 nanorods were obtained by centrifugation and washing.

[0075] Preparation Example 8: A modified Al2O3@LDO was prepared according to the following method:

[0076] Preparation of Al2O3@LDO:

[0077] 6g of magnesium nitrate hexahydrate and 3g of urea were mixed and dissolved in 100mL of water. 10g of Al2O3 nanoparticles (particle size 20-30nm) were added and impregnated for 15min. Then the mixture was transferred to a high-pressure reactor, the temperature was raised to 120℃, and the reaction was carried out for 8h. Finally, after washing, drying and grinding, Al2O3@LDO was obtained by calcination at 450℃.

[0078] Preparation of modified Al2O3@LDO:

[0079] 10g of the Al2O3@LDO obtained above was dispersed in 250mL of water, 4g of N-isopropylacrylamide and 0.3g of N,N'-methylenebisacrylamide were added, and the mixture was stirred and dispersed at 60℃ for 3h. The temperature was then increased to 80℃, and 0.2g of azobisisobutyronitrile was added. The mixture was stirred and reacted in an argon atmosphere for 3h. Finally, the modified Al2O3@LDO was obtained by centrifugation and washing.

[0080] Preparation Example 9: An Al2O3 nanorod@LDO was prepared according to the following method:

[0081] Preparation of Al2O3 nanorods:

[0082] 10g of aluminum nitrate nonahydrate, 10g of urea and 26g of polyethylene glycol 2000 were mixed and added to 250mL of water and stirred to dissolve. The mixture was subjected to a hydrothermal reaction at 130℃. After centrifugation, washing and filtration, the mixture was dried at 80℃ for 24h. Finally, after grinding, the mixture was sintered at 700℃ to obtain Al2O3 nanorods.

[0083] Preparation of Al2O3 nanorods@LDO:

[0084] 6g of magnesium nitrate hexahydrate and 3g of urea were mixed and dissolved in 100mL of water. 10g of the Al2O3 nanorods obtained above were added and impregnated for 15min. Then, the mixture was transferred to a high-pressure reactor, the temperature was raised to 120℃, and the reaction was carried out for 8h. Finally, after washing, drying and grinding, Al2O3 nanorods@LDO were obtained by calcination at 450℃.

[0085] Example

[0086] Example 1: A composite membrane with high ionic conductivity was prepared according to the following method:

[0087] S1. Add 12 parts of the modified Al2O3 nanorods@LDO prepared in Preparation Example 1, 0.8 parts of polyacrylamide, 0.5 parts of sodium dodecylbenzenesulfonate and 3 parts of waterborne acrylate adhesive (solid content of 40 wt%) to 100 parts of water in sequence, and mix evenly to obtain an inorganic slurry.

[0088] S2. An inorganic slurry is coated on both sides of a polypropylene base membrane (10 μm thick) to form an inorganic coating with a thickness of 3 μm. After drying, a composite membrane with high ionic conductivity is obtained.

[0089] Examples 2 and 3 describe a high ionic conductivity composite membrane, differing from Example 1 only in the adjustment of the raw material ratio for the inorganic coating, as shown in Table 1.

[0090] Table 1. Raw material formulations for inorganic coatings in Examples 1-3

[0091] Example 1 Example 2 Example 3 <![CDATA[Modified Al2O3 nanorods@LDO / parts]]> 12 8 15 Polyacrylamide / part 0.8 0.5 1 Sodium dodecylbenzenesulfonate / part 0.5 0.6 0.3 Water-based acrylic adhesive / part 3 2 4 Water / part 100 100 100

[0092] In Examples 2 and 3, the modified Al2O3 nanorods@LDO prepared in Example 1 were used.

[0093] Example 4: A composite membrane with high ionic conductivity was prepared according to the following method:

[0094] S1. Add 12 parts of the modified Al2O3 nanorods@LDO prepared in Preparation Example 2, 0.8 parts of polyacrylamide, 0.5 parts of sodium dodecylbenzenesulfonate and 3 parts of waterborne acrylate adhesive (solid content of 40 wt%) to 100 parts of water in sequence, and mix evenly to obtain an inorganic slurry.

[0095] S2. An inorganic slurry is coated on one side of a polypropylene base membrane (10 μm thick) to form an inorganic coating with a thickness of 3 μm. After drying, a composite membrane with high ionic conductivity is obtained.

[0096] Example 5: A high ionic conductivity composite membrane, which differs from Example 1 only in that the modified Al2O3 nanorods@LDO prepared in Example 1 are replaced with an equal amount of modified Al2O3 nanorods@LDO prepared in Example 3.

[0097] Example 6: A high ionic conductivity composite membrane, differing from Example 1 only in that the modified Al2O3 nanorods@LDO prepared in Example 1 are replaced with an equal amount of modified Al2O3 nanorods@LDO prepared in Example 4.

[0098] Example 7: A high ionic conductivity composite membrane, differing from Example 1 only in that an equal amount of modified Al2O3 nanorods@LDO prepared in Example 5 is used instead of the modified Al2O3 nanorods@LDO prepared in Example 1.

[0099] Example 8, a high ionic conductivity composite membrane, differs from Example 1 only in that the modified Al2O3 nanorods@LDO prepared in Example 1 are replaced with an equal amount of modified Al2O3 nanorods@LDO prepared in Example 6.

[0100] Example 9: A composite membrane with high ionic conductivity was prepared according to the following method:

[0101] S1. Dissolve polydopamine in water and coat it on both sides of a polypropylene base film (10 μm thick). After drying, a polydopamine layer is formed with a thickness of 1 μm.

[0102] S2. Add 12 parts of the modified Al2O3 nanorods@LDO prepared in Preparation Example 1, 0.8 parts of polyacrylamide, 0.5 parts of sodium dodecylbenzenesulfonate and 3 parts of waterborne acrylate adhesive (solid content of 40 wt%) to 100 parts of water in sequence, and mix evenly to obtain an inorganic slurry.

[0103] S2. Coat the polydopamine layer with an inorganic slurry to form an inorganic coating with a thickness of 3 μm. After drying, a composite membrane with high ionic conductivity is obtained.

[0104] Comparative Example

[0105] Comparative Example 1, a composite membrane with high ionic conductivity, differs from Example 1 only in that the amount of modified Al2O3 nanorods@LDO added in Preparation Example 1 is 5 parts.

[0106] Comparative Example 2, a composite membrane with high ionic conductivity, differs from Example 1 only in that the amount of modified Al2O3 nanorods@LDO added in Preparation Example 1 is 20 parts.

[0107] Comparative Example 3, a composite membrane with high ionic conductivity, differs from Example 1 only in that the modified Al2O3 nanorods@LDO prepared in Example 1 are replaced with an equal amount of modified Al2O3 nanorods prepared in Example 7.

[0108] Comparative Example 4, a composite membrane with high ionic conductivity, differs from Example 1 only in that the modified Al2O3@LDO prepared in Example 1 is replaced with an equal amount of modified Al2O3@LDO prepared in Example 8.

[0109] Comparative Example 5, a composite membrane with high ionic conductivity, differs from Example 1 only in that an equal amount of Al2O3 nanorods@LDO prepared in Preparation Example 9 is used instead of the modified Al2O3 nanorods@LDO prepared in Preparation Example 1.

[0110] Performance testing

[0111] 1. Liquid retention test: The composite membranes obtained in the examples and comparative examples were prepared into samples with a size of 50mm×50mm. After drying for 24 hours, the mass of each sample was weighed as M0. The samples were immersed in a mixed solution of ethylene carbonate, dimethyl carbonate and diethyl carbonate with a volume ratio of 1:1:1. After soaking for 10 hours, the samples were removed and weighed immediately to obtain the mass of M1. After wiping off the excess liquid on the surface with filter paper, the mass of the sample was weighed as M2. The liquid absorption rate and liquid retention rate of the samples in the examples and comparative examples were calculated respectively.

[0112]

[0113] 2. Ionic conductivity test: The ionic conductivity of the composite membranes obtained in the examples and comparative examples was tested according to the relevant records in GB / T 36363-2018 "Polyolefin Films for Lithium-ion Batteries".

[0114] 3. Peel strength test: The composite membranes obtained in the examples and comparative examples are cut into strips of 25mm×200mm. The inorganic coating is adhered to the surface of 3M tape, and the test is carried out using a universal tensile testing machine at a speed of 50mm / min.

[0115] The results of the above experiments are shown in Table 2:

[0116] Table 2 Performance test results

[0117]

[0118] According to Table 2, in conjunction with Examples 1 and 9, it can be seen that the peel strength of Example 9 is increased compared to Example 1. The reason is that Example 9 adds a polydopamine layer between the base film and the inorganic coating. The polydopamine layer can use its polar groups as a connecting bridge between the base film and the inorganic coating, thereby improving the peel strength between the inorganic coating and the base film.

[0119] As can be seen from the comparison of Example 1 and Comparative Example 3, the performance of Comparative Example 3 is lower than that of Example 1. The reason is that the Al2O3 nanorods in Comparative Example 3 are not composite with LDO. On the one hand, the possibility of Al2O3 nanorods stacking increases, which will affect the ion transport efficiency. On the other hand, the lack of LDO layered structure regulation makes it impossible to build an efficient ion transport and liquid storage network, resulting in a decrease in liquid retention and ionic conductivity.

[0120] Combining Example 1 and Comparative Example 4, it can be seen that the ionic conductivity of Comparative Example 4 is lower than that of Example 1. The reason is that in Example 4, alumina nanoparticles were used to replace alumina nanorods. Compared with the one-dimensional structure of alumina nanorods, alumina nanoparticles have a higher curvature of the ion transport path, which increases the migration path of lithium ions and leads to a decrease in ionic conductivity.

[0121] Combining Example 1 and Comparative Example 5, it can be seen that the liquid retention and ionic conductivity of Comparative Example 5 decreased. This may be because the Al2O3 nanorods@LDO in Comparative Example 5 were not modified and lacked poly(N-isopropylacrylamide) segment grafting. This not only affects the dispersibility of the Al2O3 nanorods@LDO but also prevents the formation of a dynamic network, resulting in decreased liquid retention and stability.

[0122] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A composite membrane with high ionic conductivity, characterized in that, The composite membrane includes a base membrane and an inorganic coating applied to one or both sides of the base membrane; The inorganic coating comprises the following raw materials in parts by weight: Modified Al2O3 nanorods@LDO, 8-15 parts; Dispersant 0.5 to 1 part; Wetting agent 0.3-0.6 parts; 2-4 parts adhesive; 100 parts water; The modified Al2O3 nanorods@LDO have poly(N-isopropylacrylamide) segments grafted onto their surface.

2. The high ionic conductivity composite membrane according to claim 1, characterized in that, The modified Al2O3 nanorods@LDO are made from Al2O3 nanorods@LDO in a mass ratio of 1:(0.3-0.5):(0.02-0.04):(0.01-0.02), N-isopropylacrylamide, a crosslinking agent, and an initiator.

3. The high ionic conductivity composite membrane according to claim 2, characterized in that, The crosslinking agent includes one or a combination of two of N,N'-methylenebisacrylamide and ethylene glycol dimethacrylate; the initiator includes one or a combination of azobisisobutyronitrile, potassium persulfate, ammonium persulfate, and benzoyl peroxide.

4. The high ionic conductivity composite membrane according to claim 2, characterized in that, The raw materials for the Al2O3 nanorods@LDO include Al2O3 nanorods, soluble magnesium salts, and urea in a mass ratio of 1:(0.5-0.6):(0.2-0.3).

5. The high ionic conductivity composite membrane according to claim 4, characterized in that, The Al2O3 nanorods@LDO were prepared according to the following method: Soluble magnesium salt and urea were mixed and dissolved in water, Al2O3 nanorods were added, and the mixture was soaked for 10-20 minutes. Then, it was transferred to a high-pressure reactor, the temperature was raised to 120-130℃, and the reaction was carried out for 6-8 hours. Finally, after washing, drying, grinding and calcining, Al2O3 nanorods@LDO were obtained.

6. The high ionic conductivity composite membrane according to claim 2, characterized in that, The modified Al2O3 nanorods@LDO were prepared according to the following method: Al2O3 nanorods@LDO were dispersed in water, N-isopropylacrylamide and a crosslinking agent were added, and the mixture was stirred and dispersed at 60-65℃ for 2-3 hours. The temperature was then increased to 80-85℃, an initiator was added, and the mixture was stirred and reacted in an inert gas atmosphere for 3-4 hours. Finally, the modified Al2O3 nanorods@LDO were obtained by centrifugation and washing.

7. The high ionic conductivity composite membrane according to claim 1, characterized in that, The base film includes any one of polyethylene base film, polypropylene base film, polyethylene / polypropylene double-layer co-extruded film, and polyethylene / polypropylene / polyethylene multilayer co-extruded film.

8. The high ionic conductivity composite membrane according to claim 1, characterized in that, A polydopamine layer is also coated between the base film and the inorganic coating.

9. The high ionic conductivity composite membrane according to claim 8, characterized in that, The thickness of the polydopamine is 1–3 μm; the thickness of the inorganic coating is 2–4 μm.

10. A method for preparing a high ionic conductivity composite membrane according to any one of claims 1 to 9, characterized in that, The process includes the following steps: S1. Dissolve polydopamine in water, coat it on one or both sides of the base film, and dry it to form a polydopamine layer; S2. Weigh the raw materials of the inorganic coating according to the corresponding mass parts, add the modified Al2O3 nanorods@LDO, dispersant, wetting agent and binder in water in sequence, and mix evenly to obtain inorganic slurry; S3. Coat the polydopamine layer with an inorganic slurry, and after drying, a composite membrane with high ionic conductivity is obtained.

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